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UBC Theses and Dissertations

A nuclear magnetic resonance study of poly(ether ether ketone) and poly(polyphenylene sulfide) Clark, Jane N. 1986

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A NUCLEAR MAGNETIC RESONANCE STUDY OF POLY(ETHER ETHER KETONE) AND POLY(PHENYLENE SULFIDE) BY JANE N. CLARK B .Sc . ( E n g . ) , Q u e e n ' s U n i v e r s i t y a t K i n g s t o n , 1983 A THESIS SUBMITTED I N PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE I N THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF CHEMISTRY WE ACCEPT THIS THESIS AS CONFORMING J O THE REQUIRED STANDARD THE UNIVERSITY OF BRITISH COLUMBIA JUNE, 1986 © J . N . C l a r k , 1986 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date E-6 (3/81) i i ABSTRACT P o l y ( e t h e r e t h e r k e t o n e ) , PEEK, and p o l y ( p h e n y l e n e s u l f i d e ) , PPS, a r e b o t h p o l y m e r s o f c o m m e r c i a l i m p o r t a n c e on a c c o u n t o f t h e i r a p p l i c a -t i o n as m a t r i x m a t e r i a l s f o r c o m p o s i t e s . Amorphous and c r y s t a l l i n e f o r m s o f b o t h p l a s t i c s have b e e n s t u d i e d b y n u c l e a r m a g n e t i c r e s o n a n c e spec -t r o s c o p y : h i g h r e s o l u t i o n 1 3 C CP/MAS and w i d e - l i n e PMR. The h i g h r e s o l u t i o n s p e c t r a o f t h e p o l y m e r s were a s s i g n e d w i t h t h e a i d o f t h e d i p o l a r d e p h a s i n g t e c h n i q u e . The w i d t h o f t h e r e s o n a n c e l i n e s o f t h e CP/MAS s p e c t r a were seen t o be p r o p o r t i o n a l t o t h e c r y s t a l -U n i t y o f t h e s a m p l e , w i t h t h e f u l l y amorphous s p e c t r a b e i n g t h e w i d e s t . The v a r i a b l e - c o n t a c t - t i m e e x p e r i m e n t f o r PEEK i n d i c a t e d t h a t t h e op t imum c o n t a c t t i m e f o r t h e amorphous f o r m i s s h o r t e r t h a n t h a t o f t h e c r y s t a l -l i n e . V a r i a b l e t e m p e r a t u r e l i n e w i d t h and s p i n - l a t t i c e r e l a x a t i o n measurements were made o n b o t h t h e c r y s t a l l i n e and amorphous f o r m s o f t h e p o l y m e r s . The t e m p e r a t u r e r a n g e was a m b i e n t t o 440K. The p r o t o n s p e c t r a a p p e a r e d as a b r o a d l i n e w i t h a n a r r o w component s u p e r i m p o s e d . E x c e p t i n t h e case o f PPS above t h e T g , t h e b r o a d l i n e was b y f a r t h e more i n t e n s e . P a r t i a l l y r e l a x e d s p e c t r a b e l o w Tg i n d i c a t e d s e p a r a t e r e l a x a t i o n t i m e s f o r t h e two componen ts . L i n e w i d t h measurements were made on t h e b r o a d l i n e : a t a l l t e m p e r a t u r e s t h e c r y s t a l l i n e s p e c t r a were b r o a d e r t h a n t h e amorphous . The amorphous l i n e w i d t h s showed a b r u p t n a r r o w i n g a t t h e g l a s s t r a n s i t i o n t e m p e r a t u r e . A l l samples d i s p l a y e d maximum r e l a x a t i o n t i m e s i n t h e g l a s s t r a n s i t i o n r e g i o n . i i i D i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y was emp loyed t o complement t h e NMR d a t a . The m e l t i n g , g l a s s t r a n s i t i o n and c r y s t a l l i z a t i o n t e m p e r a t u r e s were measured b y DSC. An a t t e m p t was made t o c o r r e l a t e t h e r e s u l t s o f t h e s t u d y w i t h t h e m o r p h o l o g y and m o l e c u l a r m o t i o n a l b e h a v i o u r o f t h e two p o l y m e r s . i v TABLE OF CONTENTS Page ABSTRACT i i L I S T OF TABLES v i i i L I S T OF FIGURES i x ACKNOWLEDGEMENTS x i i 1. INTRODUCTION 1 1 . 1 G e n e r a l I n t r o d u c t i o n 1 1.2 The O r g a n i z a t i o n o f t h e T h e s i s 5 2. MATERIALS 6 2 . 1 H i s t o r y and S y n t h e s i s 6 2 . 1 . 1 P o l y ( e t h e r e t h e r k e t o n e ) 6 2 . 1 . 2 P o l y ( p h e n y l e n e s u l f i d e ) 8 2 . 2 M o r p h o l o g y and P r o p e r t i e s 9 2 . 2 . 1 P o l y ( e t h e r e t h e r k e t o n e ) 9 2 . 2 . 2 P o l y ( p h e n y l e n e s u l f i d e ) 20 2 . 3 The M a t e r i a l s Used i n T h i s Work 23 2 . 3 . 1 P o l y ( e t h e r e t h e r k e t o n e ) 23 2 . 3 . 2 P o l y ( p h e n y l e n e s u l f i d e ) 23 V 3. THERMAL ANALYSIS: DIFFERENTIAL SCANNING CALORIMETRY . . . 24 3 . 1 T h e r m a l A n a l y s i s T h e o r y 24 3 . 2 DSC Work b y O t h e r s PEEK and PPS 26 3 . 3 E x p e r i m e n t a l 26 3 . 4 R e s u l t s and D i s c u s s i o n 28 3 . 4 . 1 The G l a s s T r a n s i t i o n 31 3 . 4 . 2 C r y s t a l l i z a t i o n 33 3 . 4 . 3 M e l t i n g 35 3 . 5 Summary o f DSC Work 35 4 . HIGH RESOLUTION 1 3 C NMR STUDIES 37 4 . 1 I n t r o d u c t i o n t o CP/MAS NMR 37 4 . 2 S o l i d S t a t e 1 3 C NMR T h e o r y . 40 4 . 2 . 1 The E n e r g y I n t e r a c t i o n s 40 4 . 2 . 2 The CP/MAS E x p e r i m e n t 45 4 . 2 . 3 V a r i a t i o n s on t h e CP/MAS E x p e r i m e n t . . . 52 4 . 3 E x p e r i m e n t a l 54 4 . 3 . 1 R o t o r s 54 4 . 3 . 2 S e t - U p 55 4 . 3 . 3 P u l s e Programs 56 4 . 4 R e s u l t s and D i s c u s s i o n 56 4 . 4 . 1 P o l y ( p h e n y l e n e s u l f i d e ) 56 v i 4 . 4 . 2 P o l y ( e t h e r e t h e r k e t o n e ) 61 4 . 5 Summary and C o n c l u s i o n s o f CP/MAS Work 71 5. WIDE-LINE PROTON NMR STUDIES 73 5 . 1 I n t r o d u c t i o n t o S o l i d S t a t e P r o t o n NMR 73 5 . 2 S o l i d S t a t e P r o t o n NMR T h e o r y 75 5 . 2 . 1 L i n e - S h a p e s o f S o l i d S t a t e PMR S p e c t r a . . 75 5 . 2 . 2 R e l a x a t i o n 77 5 . 3 E x p e r i m e n t a l 86 5 . 4 R e s u l t s 87 5 . 4 . 1 L i n e - S h a p e R e s u l t s 87 5 . 4 . 2 S p i n - L a t t i c e R e s u l t s 93 5 . 5 D i s c u s s i o n 101 5 . 5 . 1 L i n e - S h a p e D i s c u s s i o n 101 5 . 5 . 2 S p i n - L a t t i c e R e l a x a t i o n D i s c u s s i o n . . . . 104 5 . 6 Summary and C o n c l u s i o n o f PMR Work 108 6. CONCLUSION 110 6 . 1 G e n e r a l Remarks 110 6 . 2 Summary 110 6 . 3 S u g g e s t i o n s f o r C o n t i n u a t i o n o f t h e S t u d y . . . . 113 V l l REFERENCES 1 1 5 8 . APPENDICES 1 2 0 v i i i L I S T OF TABLES Page T a b l e s 2 . 1 P h y s i c a l and M e c h a n i c a l P r o p e r t i e s o f PEEK R e s i n . . . 20 2 . 2 P h y s i c a l and M e c h a n i c a l P r o p e r t i e s o f PPS R e s i n . . . 22 3 . 1 DSC R e s u l t s f o r PEEK and PPS 30 4 . 1 The S p e c t r a l A s s i g n m e n t f o r PEEK 65 4 . 2 The S p e c t r a l L i n e w i d t h s f o r C r y s t a l l i n e and Amorphous PEEK 66 4 . 3 Opt imum C o n t a c t Time R e s u l t s f o r Amorphous and C r y s t a l l i n e PEEK 71 5 . 1 H a l f H e i g h t L i n e w i d t h s o f PMR S p e c t r a 87 5 . 2 Ti V a l u e s f o r PEEK and PPS 94 5 . 3 A c t i v a t i o n E n e r g i e s f r o m A r r h e n i u s P l o t s 98 5 . 4 S p i n - L a t t i c e R e l a x a t i o n Times f o r t h e I n d i v i d u a l Components o f PEEK 100 i x L I S T OF FIGURES Page F i g u r e s 2 . 1 P o l y c o n d e n s a t i o n r e a c t i o n o f a c i d c h l o r i d e s 6 2 . 2 R e a c t i o n o f b i s f l u o r o p h e n y l k e t o n e and t h e b i s p o t a s s i u m s a l t o f b i s - 4 - h y d r o x y p h e n y l k e t o n e . . . . 7 2 . 3 The p o l y m e r i z a t i o n r e a c t i o n o f p o l y ( p h e n y l e n e s u l f i d e ) 9 2 . 4 The r e p e a t i n g u n i t o f PEEK 10 2 . 5 The c o n f o r m a t i o n o f t h e c r y s t a l l i n e PEEK c h a i n . . . 10 2 . 6 S t a c k e d l a m e l l a e 12 2 . 7 L a m e l l a r g r o w t h 13 2 . 8 ( a ) Quenched s p h e r u l i t e s ( b ) F u l l y g rown s p h e r u l i t e s ^ 3 . 1 S e c t i o n a l v i e w o f DSC m e a s u r i n g c e l l 27 3 . 2 DSC scans o f amorphous and c r y s t a l l i n e PEEK 29 3 . 3 DSC scans o f amorphous and c r y s t a l l i n e PPS 30 3 . 4 S k e t c h o f a DSC g l a s s t r a n s i t i o n c u r v e 31 3 . 5 DSC g l a s s t r a n s i t i o n c u r v e f o r a n n e a l e d amorphous PEEK 32 3 . 6 DSC c r y s t a l l i z a t i o n e x o t h e r m f o r amorphous PEEK . . . 34 4 . 1 The i n t e r a c t i o n o f two d i p o l a r n u c l e i i n a m a g n e t i c f i e l d 42 4 . 2 The e f f e c t o f c h e m i c a l s h i f t a n i s o t r o p y i n t e r a c t i o n . 44 4 . 3 The c r o s s - p o l a r i z a t i o n e x p e r i m e n t 48 X 4 . 4 The t i m e a v e r a g e d r e s u l t o f a v e c t o r s p i n n i n g a b o u t an a x i s 51 4 . 5 The d i p o l a r d e p h a s i n g p u l s e sequence 53 4 . 6 The CP/MAS s p e c t r u m o f c r y s t a l l i n e PPS 57 4 . 7 The d i p o l a r dephased s p e c t r u m o f c r y s t a l l i n e PPS . . 58 4 . 8 The CP/MAS s p e c t r a o f PPS, v a r y i n g c r y s t a l l i n i t i e s . . 59 4 . 9 The CP/MAS s p e c t r u m o f c r y s t a l l i n e PEEK 62 4 . 1 0 The d i p o l a r dephased s p e c t r u m o f c r y s t a l l i n e PEEK . . 63 4 . 1 1 The CP/MAS s p e c t r a o f amorphous and c r y s t a l l i n e PEEK 66 4 . 1 2 The v a r i a b l e c o n t a c t t i m e s p e c t r a o f PEEK 67 4 . 1 3 V a r i a b l e c o n t a c t t i m e p l o t s f o r amorphous PEEK . . . 69 4 . 1 4 V a r i a b l e c o n t a c t t i m e p l o t s f o r a n o n - p r o t o n a t e d c a r b o n o f PEEK 70 5 . 1 The i n v e r s i o n r e c o v e r y T^ e x p e r i m e n t . 80 5 . 2 The s p i n - s p i n r e l a x a t i o n e f f e c t 82 5 . 3 T 2 , t h e F ID a t 1/e o f t h e o r i g i n a l v a l u e 83 5 . 4 The dependence o f r e l a x a t i o n t i m e s on t e m p e r a t u r e . . 84 5 . 5 The dependence o f t h e l o g o f r e l a x a t i o n t i m e s on i n v e r s e t e m p e r a t u r e 85 5 . 6 PMR s p e c t r a o f PEEK and PPS a t a m b i e n t t e m p e r a t u r e . . 88 5 . 7 L i n e w i d t h v s t e m p e r a t u r e f o r s p e c t r a o f c r y s t a l l i n e PEEK 89 5 . 8 L i n e w i d t h v s t e m p e r a t u r e f o r s p e c t r a o f amorphous PEEK 90 5 . 9 L i n e w i d t h v s t e m p e r a t u r e f o r s p e c t r a o f c r y s t a l l i n e PPS 90 5 . 1 0 L i n e w i d t h v s t e m p e r a t u r e f o r s p e c t r a o f amorphous PPS 91 x i 5 11 PMR s p e c t r a f o r PEEK and PPS a t h i g h t e m p e r a t u r e 92 5 12 A r r h e n i u s p l o t f o r c r y s t a l l i n e PEEK r e l a x a t i o n . . 95 5 13 A r r h e n i u s p l o t f o r amorphous PEEK r e l a x a t i o n . . . 95 5 14 A r r h e n i u s p l o t f o r c r y s t a l l i n e PPS r e l a x a t i o n . . . 96 5 15 A r r h e n i u s p l o t f o r amorphous PPS r e l a x a t i o n . . . 97 5 16 A p a r t i a l l y r e l a x e d s p e c t r u m o f c r y s t a l l i n e PPS . . 98 5 17 The T^ t e m p e r a t u r e p r o f i l e o f benzene . 106 x i i ACKNOWLEDGEMENTS S i n c e r e t h a n k s a r e e x p r e s s e d t o D r . F .G. H e r r i n g f o r h i s s u p p o r t and encou ragemen t d u r i n g my c o u r s e a t U . B . C . I am i n d e b t e d t o t h e p o s t d o c t o r a l f e l l o w s o f o u r r e s e a r c h g r o u p : D r . N.R. J a g a n n a t h a n f o r much h e l p and g u i d a n c e and t o D r . J . M . W i l l i s f o r many k i n d n e s s e s and a s s i s t a n c e i n t h e p r e p a r a t i o n o f t h i s manu-s c r i p t . S p e c i a l t h a n k s a r e due t o Mr . E . J . D e l i k a t n y and Mr . J . R e n d e l l f o r a l l t h e i r p a t i e n t and p r a c t i c a l h e l p . I w o u l d a l s o l i k e t o t h a n k D r . A . L . MacKay f o r s e v e r a l i n v a l u a b l e d i s c u s s i o n s . I am v e r y a p p r e c i a t i v e o f t h e w o r k o f t h e e l e c t r i c a l and m e c h a n i c a l s h o p s , i n p a r t i c u l a r I m e n t i o n Mr . K. S u k u l and Mr . E. M a t t e r . F i n a l l y , f i n a n c i a l s u p p o r t f r o m t h e N a t u r a l S c i e n c e and E n g i n e e r i n g R e s e a r c h C o u n c i l (NSERC), P o l y s a r L t d . and t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a i s g r a t e f u l l y a c k n o w l e d g e d . 1-1 . INTRODUCTION 1 . 1 GENERAL INTRODUCTION P o l y ( e t h e r e t h e r k e t o n e ) , (PEEK), and p o l y ( p h e n y l e n e s u l f i d e ) , (PPS) , a r e two s e m i - c r y s t a l l i n e t h e r m o p l a s t i c p o l y m e r s o f c o n s i d e r a b l e i n d u s t r i a l i n t e r e s t . These t h e r m o p l a s t i c s a r e r e p l a c i n g t h e r m o s e t t i n g r e s i n s as t h e m a t r i x m a t e r i a l s f o r h i g h - p e r f o r m a n c e c o m p o s i t e s . The i n t r o d u c t i o n o f t h e r m o p l a s t i c s f o r advanced c o m p o s i t e a p p l i c a t i o n s i s o f m a j o r i m p o r t a n c e t o t h e c o m p o s i t e i n d u s t r y . U n t i l r e c e n t y e a r s , t h e r m o -s e t t i n g r e s i n s , m a i n l y t h e e p o x i e s , were t h e e x c l u s i v e m a t r i c e s f o r f i b r e c o m p o s i t e s . However , as t h e a d v a n t a g e s o f c e r t a i n h i g h p e r f o r m a n c e t h e r m o p l a s t i c s become e v i d e n t and as s u i t a b l e f a b r i c a t i o n t e c h n i q u e s a r e d e v e l o p e d , t h e t h e r m o s e t m a r k e t i s b e i n g t h r e a t e n e d . Much o f t h e i m p e t u s f o r t h e r m o p l a s t i c c o m p o s i t e r e s e a r c h i s f r o m t h e m i l i t a r y a v i a t i o n i n d u s t r y w h i c h has l o n g b e e n a p i o n e e r i n t h e a p p l i c a t i o n and d e v e l o p -ment o f new c o m p o s i t e m a t e r i a l s . The s t i f f n e s s , s t r e n g t h and t o u g h n e s s p r o p e r t i e s o f s t r u c t u r a l c o m p o s i t e s v i e w i t h t h o s e o f t h e m e t a l a l l o y s and i n s t r e n g t h - t o - w e i g h t r a t i o , t h e c o m p o s i t e s f a r exceed t h e a l l o y s . The m a n u f a c t u r e r s o f t h e PEEK/ca rbon f i b r e (APC-1) b o a s t o f i t b e i n g 30% l i g h t e r t h a n a luminum ( 1 ) and h a v i n g a s t r e n g t h o f 1670 MN m " 2 ( 2 ) . S i g n i f i c a n t d i s a d v a n t a g e s o f t h e r m o s e t t i n g r e s i n m a t r i c e s c a n be overcome b y t h e r m o p l a s t i c s , e s p e c i a l l y i n t h e a r e a o f p r o c e s s i n g and a g i n g w i t h f a t i g u e . The rmose t p r o c e s s i n g i s messy and l a b o u r i n t e n s i v e , - 2 -r e q u i r i n g l a r g e vo lumes o f s o l v e n t and a u t o c l a v i n g w i t h l o n g and e l a b o r -a t e c u r e c y c l e s . Because t h e r m o s e t c u r i n g i n v o l v e s a c h e m i c a l r e a c t i o n b e t w e e n t h e r e s i n and c r o s s l i n k i n g a g e n t , t h e p r e p r e g s have l i m i t e d s h e l f l i v e s and o f t e n r e q u i r e r e f r i g e r a t e d s t o r a g e . T h e r e i s no c u r i n g p r o c e s s r e q u i r e d f o r a t h e r m o p l a s t i c , t h u s , a l t h o u g h h i g h t e m p e r a t u r e s and p r e s s u r e s a r e n e e d e d , t h e m o u l d c y c l e i s v e r y s h o r t and no s o l v e n t s a r e u s e d . The two m a j o r a r e a s o f f a i l u r e w i t h e p o x y / f i b r e c o m p o s i t e s i n a e r o -space a p p l i c a t i o n s a r e i n t e r l a m i n a r f r a c t u r e ( 3 ) and p o o r h o t / w e t c o m p r e s s i v e s t r e n g t h ( 4 ) . When f a t i g u e d , t h e r m o s e t c o m p o s i t e s t e n d t o become b r i t t l e and f a i l b y d e l a m i n a t i o n . V a r i o u s c o m p a r i s o n t e s t s show t h a t t h e r m o p l a s t i c c o m p o s i t e s w i t h s t a n d f a t i g u e f a r b e t t e r ; t h e y have s u p e r i o r c r a c k r e s i s t a n c e a n d , because t h e r e i s some p l a s t i c f l o w , f a i l -u r e i s n o t c a u s e d b y d e l a m i n a t i o n ( 3 , 5 - 7 ) . The t h e r m o p l a s t i c m a t r i c e s t e n d t o a b s o r b l e s s w a t e r t h a n t h e i r t h e r m o s e t c o u n t e r p a r t s ( 8 ) . I n a t e s t a g a i n s t a ' s t a t e - o f - t h e - a r t ' e p o x y / c a r b o n f i b r e c o m p o s i t e , t h e epoxy c o m p o s i t e a b s o r b e d o v e r t h r e e t i m e s as much w a t e r b y w e i g h t as t h e PEEK sample ( 9 ) . A t 120°C, t h e h u m i d i t y aged PEEK c o m p o s i t e was 15% s t r o n g e r , and a t 180°C, 75% s t r o n g e r ( 9 ) . One f u r t h e r a d v a n t a g e o f t h e t h e r m o p l a s t i c c o m p o s i t e s o v e r t h e t h e r m o s e t s i s t h a t t h e p l a s t i c s c a n be r e m e l t e d f o r r e p a i r and r e m o u l d i n g ( 1 0 , 1 1 ) ; i t i s e c o n o m i c a l l y a t t r a c -t i v e t o be a b l e t o r e u s e o f f - c u t s ( 1 ) . I n t h e p a s t , t h e r m o p l a s t i c s have f a i l e d as c o m p o s i t e m a t r i c e s because o f t h e d i f f i c u l t y i n f i n d i n g a p o l y m e r w h i c h h a d b o t h a d e q u a t e s t i f f n e s s a t h i g h t e m p e r a t u r e s and good c h e m i c a l r e s i s t a n c e . PEEK and PPS a r e r a r e i n e x h i b i t i n g b o t h p r o p e r t i e s . These two p o l y m e r s have t h e - 3 -h i g h e s t t h e r m a l s t a b i l i t i e s o f t o d a y ' s e n g i n e e r i n g p l a s t i c s , a p p r o x i -m a t e l y 50% above t h e c o m p e t i n g epoxy r e s i n s ( 1 2 ) . The o u t s t a n d i n g r e s i s -t a n c e o f PEEK and PPS t o a g g r e s s i v e c h e m i c a l e n v i r o n m e n t s ( 9 , 1 3 - 1 5 ) i s due t o t h e s e m i - c r y s t a l l i n e n a t u r e o f t h e p o l y m e r s . To d a t e , no amorphous t h e r m o p l a s t i c e v a l u a t e d has shown s a t i s f a c t o r y c h e m i c a l r e s i s -t a n c e ( 8 ) . J u s t as t h e t h e r m o s e t t i n g c o m p o s i t e s have h a d a s i g n i f i c a n t e f f e c t on t h e m e t a l i n d u s t r y , t h e t h e r m o p l a s t i c s a l s o have t h e p o t e n t i a l t o r e v o l u t i o n i z e t h e t h e r m o s e t c o m p o s i t e i n d u s t r y ( 9 ) . B e f o r e t h i s can h a p p e n , i t i s e s s e n t i a l t h a t t h e m e c h a n i c a l p r o p e r t i e s o f t h e t h e r m o -p l a s t i c s be f u l l y known i n o r d e r t o s e t r e l i a b l e c o n f i d e n c e l i m i t s f o r t h e p e r f o r m a n c e o f t h e m a t e r i a l . The b u l k o f t h e r e s e a r c h w h i c h has b e e n done a l r e a d y on PEEK and PPS has b e e n c o n c e r n e d w i t h t h e e v a l u a t i o n , o f v a r i o u s m e c h a n i c a l and p h y s i c a l p r o p e r t i e s o f t h e c o m p o s i t e s : t e n s i l e and f l e x u r e t e s t s , s t r e s s c r a c k i n g , s h e a r s t r e n g t h , and f a t i g u e as f u n c t i o n s o f t e m p e r a t u r e , e n v i r o n m e n t a l c o n d i t i o n s and t h e r m a l h i s t o r y ( 3 , 5 - 8 , 1 0 , 1 4 , 1 6 ) . R e s e a r c h on t h e p h y s i c a l p o l y m e r c h e m i s t r y o f t h e s e p l a s t i c s has f o c u s s e d on t h e m o r p h o l o g y and c r y s t a l s t r u c t u r e o f t h e n e a t r e s i n s . The good s o l v e n t r e s i s t a n c e o f t h e s e t h e r m o p l a s t i c s becomes a p r o b l e m when c h o o s i n g a n a l y t i c a l t e c h n i q u e s . C o n v e n t i o n a l p o l y m e r r e s e a r c h p r e -supposes t h a t t h e m a c r o m o l e c u l e may be s t u d i e d i n s o l u t i o n . T h i s , o f c o u r s e , i s n o t p o s s i b l e f o r PEEK and PPS, b o t h renowned f o r s o l v e n t r e s i s t a n c e . I n n e a r l y e v e r y c a s e , t h e a n a l y s i s o f t h e s e t h e r m o p l a s t i c s i s l i m i t e d t o t h e s o l i d s t a t e , t h e one e x c e p t i o n b e i n g a s t u d y o f PEEK d i s s o l v e d i n c o n c e n t r a t e d s u l f u r i c a c i d ( 1 7 ) . X - r a y d i f f r a c t i o n a n a l y s i s a p p e a r s t o be t h e p r o m i n e n t r e s e a r c h - 4 -t e c h n i q u e f o r t h e s e m a t e r i a l s ( 1 6 , 1 8 - 2 3 ) . I t has y i e l d e d t h e c r y s t a l s t r u c t u r e o f b o t h p o l y m e r s , as w e l l as p e r c e n t c r y s t a l l i n i t y e s t i m a t e s o f v a r i o u s p o l y m e r s a m p l e s . Some d i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y ( 8 , 2 4 - 2 6 ) , i n f r a r e d s p e c t r o s c o p y ( 1 6 , 2 7 ) and m e c h a n i c a l s p e c t r o s c o p y ( 2 8 , 2 9 ) r e s u l t s have a l s o b e e n p u b l i s h e d . N u c l e a r m a g n e t i c r e s o n a n c e (NMR) i s a l s o an a t t r a c t i v e t e c h n i q u e i n t h e s t u d y o f PEEK and PPS f o r , l i k e X - r a y d i f f r a c t i o n , t h e t e c h n i q u e has t h e v e r y i m p o r t a n t a d v a n t a g e t h a t t h e p o l y m e r sample n e e d n o t be d i s -s o l v e d i n t o s o l u t i o n f o r a n a l y s i s . NMR g i v e s i n s i g h t i n t o t h e s t r u c t u r e and t h e m o l e c u l a r m o t i o n o f i n t r a c t i b l e p o l y m e r s w h i c h c a n n o t be h a d b y any o t h e r m e t h o d . T h e r e has b e e n c o n s i d e r a b l e r e s e a r c h o f p o l y m e r sys tems u s i n g NMR ( 3 0 ) b u t t o d a t e t h e r e has b e e n l i t t l e s t u d y o f PEEK and PPS b y t h i s m e t h o d . Th ree r e p o r t s o f NMR w o r k on t h e s e t h e r m o -p l a s t i c s a r e f o u n d i n t h e c u r r e n t l i t e r a t u r e : ( i ) K a r a s z e t a l . ( 1 7 ) have done a s o l u b i l i t y s t u d y o f a p o l y ( e t h e r e t h e r k e t o n e ) i n s t r o n g a c i d s w h i c h i n c l u d e s a p r o t o n d e c o u p l e d l ^C s p e c t r u m o f t h e p o l y m e r d i s s o l v e d i n s u l f u r i c a c i d . The a n a l y -s i s o f t h i s s p e c t r u m i s i n p r e s s . ( i i ) W h i t a k e r and c o w o r k e r s ( 2 4 ) p u b l i s h e d a s o l i d s t a t e , h i g h -r e s o l u t i o n s p e c t r u m o f PEEK. ( i i i ) S c h l i c k and McGarvey ( 3 2 ) s t u d i e d t h e dynamics o f p o l y ( p h e n y l e n e s u l f i d e ) b y b r o a d - l i n e , p r o t o n m a g n e t i c r e s o n a n c e , d e t e r m i n i n g s p i n - l a t t i c e r e l a x a t i o n t i m e s and second moments as f u n c t i o n s o f t e m p e r a t u r e . The w o r k i n t h i s t h e s i s i s u n i q u e i n t h a t i t a n a l y z e s b r o a d - l i n e , and h i g h r e s o l u t i o n , s p e c t r a f o r b o t h c r y s t a l l i n e and amorphous - 5 -samples o f PEEK and PPS. 1.2 THE ORGANIZATION OF THE THESIS C h a p t e r 2 d i s c u s s e s t h e h i s t o r y , s y n t h e s i s and p r o p e r t i e s o f t h e two t h e r m o p l a s t i c s s t u d i e d . T h i s r e s e a r c h p r o j e c t a p p l i e d t h r e e d i s t i n c t t e c h n i q u e s t o t h e s t u d y o f PEEK and PPS: ( i ) t h e r m a l a n a l y s i s , ( i i ) h i g h r e s o l u t i o n , 1 3 C s o l i d s t a t e NMR, and ( i i i ) b r o a d - l i n e p r o t o n m a g n e t i c r e s o n a n c e . C h a p t e r 3 p r e s e n t s t h e t h e r m a l a n a l y s i s o f t h e m a t e r i a l s . C h a p t e r 4 f o c u s s e s on h i g h r e s o l u t i o n ^ 3 C s o l i d s t a t e s p e c t r o s c o p y and i t s a p p l i c a t i o n t o PEEK and PPS. C h a p t e r 5 d e a l s w i t h t h e use o f b r o a d - l i n e p r o t o n m a g n e t i c r e s o n a n c e t o examine t h e m o r p h o l o g y and m o l e c u l a r m o t i o n s o f t h e p l a s t i c s as f u n c t i o n s o f t e m p e r a t u r e . The s i x t h and f i n a l c h a p t e r s e r v e s t o summar ize t h e w o r k p r e s e n t e d i n t h e t h e s i s and makes s u g g e s t i o n s f o r t h e c o n t i n u a t i o n o f t h i s p r o j e c t . - 6 -2. MATERIALS 2.1 HISTORY AND SYNTHESIS 2.1.1 Poly(ether ether ketone) In the 1960's, researchers of three major plastics companies reported the synthesis of polyetherketones: (i) Bonner of du Pont, ( i i ) Goodman et a l . of ICI and ( i i i ) Farnham et a l . of Union Carbide (33). Bonner and Goodman performed a polycondensation of acid chlorides (Figure 2.1) and Farnham et a l . reacted bis-4-fluorophenyl ketone with the potassium salt of bis-1-hydroxyphenylketone in sulpholane (Figure 2.2). The principal problem in the synthesis was that of solvent, for, once formed, the polymer was insoluble in most organic solvents. As a result, a polymer of high molecular weight could not be obtained. This d i f f i c u l t y was later solved, in one case by using li q u i d HF as the solvent and in a another by carrying out the reaction in aryl sulfones at 280-340°C, just below the melting point of the polyetherketone (33). C ^ o ^ C ^ c o c i N — ' N — ' AICI3 in CH2CI2 at 20°C ~ ® - c o - ® - o - n Figure 2.1: Polycondensation reaction of acid chlorides. - 7 -F-@-CO-@-F + KO-@>-COH^OK ~230°C in sulpholane - - © - c o - 0 - 0 -n Figure 2.2: Reaction of bisfluorophenyl ketone and the bis potassium salt of bis-4-hydroxyphenyl ketone. Because o f i t s e x c e l l e n t c h e m i c a l and e n v i r o n m e n t a l r e s i s t a n c e , t h e i n i t i a l d e v e l o p m e n t o f c o m m e r c i a l PEEK was d i r e c t e d t o w a r d s w i r e c o a t i n g a p p l i c a t i o n s . I t was d u r i n g t h i s w o r k t h a t t h e g r e a t p o t e n t i a l o f PEEK f o r l i g h t w e i g h t s t r u c t u r a l c o m p o s i t e s was r e c o g n i z e d . I n 1981 I C I i n t r o d u c e d PEEK t o t h e m a r k e t u n d e r t h e t r a d e name o f V i c t r e x , a v a i l a b l e i n a v a r i e t y o f f o r m s . The n e a t t h e r m o p l a s t i c r e s i n i s s o l d as an amorphous f i l m and i n s e m i - c r y s t a l l i n e powder o r p e l l e t s . The PEEK com-p o s i t e s , APC-1 and APC-2 ( a r o m a t i c p o l y m e r c o m p o s i t e ) use c a r b o n f i b r e as r e i n f o r c e m e n t ; t h e y a r e o b t a i n e d as p r e p r e g t a p e and f i l a m e n t , and as c o n s o l i d a t e d s h e e t s . - 8 -2.1.2 Poly(phenylene su l f ide) P o l y ( p h e n y l e n e s u l f i d e ) s i g n i f i c a n t l y p r e d a t e s p o l y ( e t h e r e t h e r k e t o n e ) . I n f a c t , as e a r l y as 1888 t h e r e was a r e p o r t b y F r i e d e l and C r a f t s o f a c e r t a i n r e a c t i o n b y - p r o d u c t w h i c h i s now t h o u g h t t o be PPS ( 1 5 ) . I n 1898 G r e n v r e s s e r e c o r d e d f o r m a t i o n o f an i n s o l u b l e r e s i n b y t h e r e a c t i o n o f benzene w i t h s u l f u r i n t h e p r e s e n c e o f a lum inum c h l o r i d e ( 1 6 ) . T h e r e was no f u r t h e r p r o g r e s s u n t i l 1948 when M a c a l l u m i n London , O n t a r i o , p u b l i s h e d "A D r y S y n t h e s i s o f A r o m a t i c S u l f i d e s : P h e n y l e n e S u l f i d e R e s i n s " i n t h e J o u r n a l o f O r g a n i c C h e m i s t r y ( 3 1 ) . T h i s a u t h o r n o t e d t h e " s a t i s f a c t o r y " p h y s i c a l s t r e n g t h o f some o f t h e r e s i n s . The s y n t h e s i s p r o p o s e d b y M a c a l l u m , t h o u g h i n t e r e s t i n g , was o f no use i n d u s t r i a l l y because t h e r e a c t i o n c o u l d n o t be c o n t r o l l e d t o o b t a i n a c o n s i s t e n t p r o d u c t . I n 1967 Edmonds and H i l l p a t e n t e d , f o r t h e P h i l l i p s Company, a p o l y ( p h e n y l e n e s u l f i d e ) s y n t h e s i s p r o c e s s w h i c h r e a c t s p - d i c h l o r o b e n z e n e w i t h sod ium s u l f i d e i n a p o l a r o r g a n i c s o l v e n t . T h e r e i s a n u c l e o p h i l i c s u b s t i t u t i o n , w i t h NaCl f o r m e d as a b y - p r o d u c t . (See F i g u r e 2 . 3 ) S i x y e a r s l a t e r , i n 1973 P h i l l i p s began p r o d u c i n g PPS c o m m e r c i a l l y , u s i n g t h e t r a d e name o f " R y t o n " . The P h i l l i p s b r o c h u r e s p r o m o t e t h e p r o d u c t w i t h a s l o g a n : " R y t o n , t h e p l a s t i c t h a t t h i n k s i t ' s a m e t a l " . R y t o n i s made f o r two d i f f e r e n t m a r k e t s . The p r i m a r y m a r k e t i s t h a t o f t h e g e n e r a l m i d - p e r f o r m a n c e c o m p o s i t e s . PPS c o m p o s i t e s a r e r e p l a c i n g m e t a l s where a l i g h t e r , c h e a p e r o r more e n v i r o n m e n t a l l y r e s i s t a n t p a r t i s r e q u i r e d . The s e c o n d a r y m a r k e t i s i n e l e c t r i c a l m a t e r i a l s where t h e c o m b i n a t i o n o f good o v e r a l l i n s u l a t i v e p r o p e r t i e s , f l a m e r e s i s t a n c e and - 9 -CI CI S N a S N a solvent ; N a • CI CI CI CI n Figure 2.3: The polymerization reaction of poly(phenylene sulfide). thermal s t a b i l i t y make PPS a e x c e l l e n t choice f o r w i r e c o a t i n g s and e n c a p s u l a t i o n (15). PEEK i s a l s o used i n s i m i l i a r e l e c t r i c a l a p p l i c a -t i o n s . 2.2 MORPHOLOGY AND PROPERTIES 2.2.1 Poly(ether ether ketone) The r e p e a t i n g u n i t of p o l y ( e t h e r ether ketone) i s comprised of three a r y l groups j o i n e d by ether and ketone l i n k a g e s , w i t h an e t h e r - t o -ketone r a t i o o f 2:1. (See Figure 2.4). The commercial polymer i s reported as having weight average mole-c u l a r weights ranging from 2 . 0 x l 0 4 to 3 . 9 x l 0 4 g mol" 1 (17,34). - 10 -0 n F i g u r e 2 . 4 : The r e p e a t i n g u n i t o f p o l y ( e t h e r e t h e r k e t o n e ) Peek i s a s e m i - c r y s t a l l i n e p o l y m e r . The c r y s t a l s t r u c t u r e has b e e n d e t e r m i n e d b y X - r a y s c a t t e r i n g and i s p r e s e n t e d and d i s c u s s e d i n t h e l i t e r a t u r e ( 1 8 , 1 9 , 2 0 , 2 1 , 2 3 , 3 5 ) . The X - r a y d i f f r a c t i o n t e c h n i q u e a l s o y i e l d s an e s t i m a t e o f t h e p e r c e n t c r y s t a l l i n i t y o f t h e s a m p l e . The l a t t i c e s t r u c t u r e was f i r s t t h o u g h t t o be i d e n t i c a l t o t h a t o f p o l y ( p h e n y l e n e o x i d e ) , t h e e t h e r and k e t o n e g r o u p s b e i n g i n d i s t i n g u i s h -a b l e i n t h e l a t t i c e c e l l ( 1 8 ) . Subsequen t w o r k c o n f i r m e d t h e p r o p o s e d o r t h o r h o m b i c u n i t c e l l b u t m o d i f i e d t h e c e l l s t r u c t u r e t o a c c o u n t f o r t h e two t y p e s o f l i n k i n g g r o u p s p r e s e n t ( 2 0 ) . F i g u r e 2 . 5 shows t h e 124° i i i i '« 10.0 A *! F i g u r e 2 . 5 : The c o n f o r m a t i o n o f t h e c r y s t a l l i n e PEEK c h a i n . - 11 -c o n f o r m a t i o n o f t h e c r y s t a l l i z e d c h a i n . The a v e r a g e b o n d a n g l e f o r t h e k e t o n e and e t h e r l i n k s i s 1 2 4 ° , and t h e a r y l r i n g s l i k e l y show some o u t -o f - p l a n e t i l t i n g ( 2 0 , 3 6 ) . The c r y s t a l l i n i t y o f PEEK v a r i e s f r o m f u l l y amorphous t o a b o u t 40% c r y s t a l l i n e . C r y s t a l l i n i t y i s u s u a l l y a s s e s s e d b y w i d e - a n g l e X - r a y s c a t t e r i n g ; t h e a r e a o f t h e c r y s t a l l i n e peaks d i v i d e d b y t h e t o t a l a r e a i n t e g r a t e d u n d e r t h e d i f f r a c t o m e t e r s c a n y i e l d s t h e f r a c t i o n o f c r y s t a l -l i n e p h a s e . D e n s i t y and i n f r a r e d r e f l e c t i o n have b e e n u s e d t o s u p p o r t X - r a y d a t a ( 2 3 , 3 5 ) b u t on t h e i r own, appear i n s u f f i c i e n t f o r r e l i a b l e c r y s t a l l i n i t y e s t i m a t e s . A s e m i - c r y s t a l l i n e p o l y m e r has two d i s t i n c t p h a s e s : amorphous and c r y s t a l l i n e . The c h a i n s o f t h e amorphous phase a r e i n d i s o r d e r , c o i l e d i n a c o m p l e t e l y random f a s h i o n . R o d r i g u e z ( 3 7 ) h u m o r o u s l y b u t a p t l y com-p a r e s t h e amorphous p o l y m e r t o a b u c k e t f u l o f v e r y l o n g t h i n worms. The s t r e n g t h o f t h i s a n a l o g y l i e s n o t o n l y i n t h e random p o s i t i o n s o f t h e "worms" b u t a l s o i n t h e i r m o t i o n , f o r s e g m e n t a l B r o w n i a n m o t i o n i s an i m p o r t a n t c o n s i d e r a t i o n i n t h e e x p l a n a t i o n o f p o l y m e r p r o p e r t i e s . I n a d d i t i o n , i t i s an a p p r o p r i a t e p a r a l l e l t h a t j u s t as t h e f r e q u e n c y and d e g r e e o f m o t i o n i n t h e p o l y m e r i n c r e a s e s w i t h t e m p e r a t u r e , t h e s q u i r m -i n g o f t h e worms becomes more v i g o r o u s as t h e b u c k e t i s h e a t e d . The m o r p h o l o g y o f t h e c r y s t a l l i n e phase i s c o n s i d e r a b l y more d i f f i c u l t t o d e s c r i b e and i s a q u e s t i o n o f g r e a t e r u n c e r t a i n t y and d e b a t e . The d e f i n i t i o n o f c r y s t a l l i n e d i c t a t e s an o r d e r e d s t r u c t u r e . The c u r r e n t l y p o p u l a r t h e o r y i s t h e f o r m a t i o n o f l a m e l l a e o r p l a t e l e t s o f c r y s t a l l i n e m a t e r i a l . These l a m e l l a e a r e s t a c k e d , s e p a r a t e d b y amorphous r e g i o n s ; t h i s i s i l l u s t r a t e d b y t h e s i m p l e s c h e m a t i c d i a g r a m - 12 -of Figure 2.6. CRYSTALLINE Figure 2.6: Stacked lamellae showing crystalline and amorphous regions (38). I t i s now assumed that there i s c h a i n f o l d i n g i n the l a m e l l a e , although the evidence f o r t h i s i s not c o n c l u s i v e . The f o l d i n g i s not thought to be a b s o l u t e l y r e g u l a r : a molecule may leave a l a m e l l a and re-enter at a d i f f e r e n t l o c a t i o n or c o i l randomly i n the amorphous phase. The l a m e l l a r t h i c k n e s s depends upon the temperature at which c r y s t a l -l i z a t i o n occurs. B l u n d e l l and Osborn have estimated l a m e l l a r thicknesses of PEEK from small-angle X-ray s c a t t e r i n g data and show th a t the t h i c k -ness inc r e a s e s from 20 A to 59 A w i t h v a r i a t i o n of the c r y s t a l l i z a t i o n temperature from 200°C to 320°C (35). The l a m e l l a r formation begins at a n u c l e a t i o n s i t e and branches r a d i a l l y outward u n t i l the growing edge meets the boundary of another c r y s t a l l i z i n g r e g i o n or u n t i l the m a t e r i a l i s quenched. (See Figure 2.7.) These l a r g e r c r y s t a l l i n e s t r u c t u r e s are - 13 -c a l l e d s p h e r u l i t e s . They may be c i r c u l a r o r s p h e r i c a l [ F i g u r e 2 . 8 ( a ) ] , o r , i f one meets t h e o t h e r , p o l y g o n a l [ F i g u r e 2 . 8 ( b ) ) . The p o l y m e r c h a i n s a r e t a n g e n t i a l t o t h e g r o w t h d i r e c t i o n ; an a t t e m p t t o i l l u s t r a t e t h i s i s made i n F i g u r e 2 . 7 . a Figure 2 . 7 : (a) Lamellar growth, radially outward, (b) Growing f i b r i l t i p ( 3 9 ) . Figure 2 . 8 : (a) Quenched spherulites. (b) Boundaries formed where spherulites meet ( 3 9 ) . S p h e r u l i t e s o f t e n grow l a r g e enough t o be o b s e v e d b y o p t i c a l m i c r o -s c o p y . B l u n d e l l and Osborn i n a s t u d y o f PEEK m o r p h o l o g y ( 3 5 ) r e p o r t s p h e r u l i t e s o f r a d i i 13 t o 22 pm. The l a r g e r a r e f o u n d i n t h e samples - 14 -a n n e a l e d a t h i g h e r t e m p e r a t u r e s . These s p h e r u l i t e s , when v i e w e d b y p o l a r i z e d l i g h t , e x h i b i t t h e c h a r a c t e r i s t i c M a l t e s e c r o s s p a t t e r n . The t w i s t o f t h e r i b b o n - l i k e f i b r i l s as t h e y grow away f r o m t h e n u c l e u s causes a l t e r n a t e c o n s t r u c t i v e and d e s t r u c t i v e i n t e r f e r e n c e o f t h e t r a n s m i t t e d p o l a r i z e d l i g h t . PEEK s p h e r u l i t e s show a p o s i t i v e b i r e f r i n g e n c e ( 3 5 ) . The s e m i - c r y s t a l l i n e n a t u r e o f PEEK has s i g n i f i c a n t b e a r i n g on t h e p h y s i c a l and m e c h a n i c a l p r o p e r t i e s o f t h e m a t e r i a l . T a b l e 2 . 1 , (page 20) l i s t s t h e t h r e e i m p o r t a n t t e m p e r a t u r e t r a n s i t i o n s o f PEEK: g l a s s t r a n s i -t i o n , c r y s t a l l i z a t i o n and m e l t i n g p o i n t . Woodhams, i n a r e c e n t p a p e r on e n g i n e e r i n g r e s i n s ( 1 2 ) , r e p o r t s t h e U n d e r w r i t e r s L a b o r a t o r y T e m p e r a t u r e I n d e x f o r 19 c o m m e r c i a l p l a s t i c s . P o l y e t h e r e t h e r k e t o n e s a r e a t t h e t o p o f t h e l i s t , w i t h a UL r a t i n g o f 220°C. The m e l t i n g t e m p e r a t u r e o f PEEK i s e x t r a o r d i n a r i l y h i g h , 335°C. S t r o n g i n t e r c h a i n a t t r a c t i o n s , p o l a r i t y and Van d e r Waals f o r c e s a r e r e s p o n s i b l e f o r s u c h a h i g h v a l u e . The t h e r m a l s t a b i l i t y i s due t o t h e a r o m a t i c n a t u r e o f t h e p o l y m e r ; i n t h e r e p e a t i n g u n i t o f a r y l r i n g s j o i n e d b y e t h e r o r k e t o n e l i n k a g e s , t h e r i n g s p r o v i d e t h e n e c e s s a r y s t i f f n e s s t o m a i n t a i n r i g i d i t y i n t h e m a c r o m o l e c u l a r c h a i n . A second f a c t o r t o be c o n s i d e r e d i n t h e r m a l s t a b i l i t y i s t h a t t h e p o l y m e r n o t become d e g r a d e d b y c h a i n s c i s s o n o r a i r o x i d a t i o n a t t h e h i g h p r o c e s s i n g t e m p e r a t u r e s . PEEK has a r e l a t i v e l y n a r r o w p r o c e s s i n g r a n g e o f 360°C t o 400°C ( 4 0 ) . The g l a s s t r a n s i t i o n i n d i c a t e s t h e o n s e t o f f r e e r o t a t i o n i n t h e amorphous phase o f t h e p o l y m e r . Be low t h e g l a s s t r a n s i t i o n t e m p e r a t u r e ( T „ ) , t h e p o l y m e r c h a i n segments do n o t have s u f f i c i e n t e n e r g y t o move - 15 -p a s t e a c h o t h e r . A c e r t a i n amount o f e n e r g y i s needed t o c r e a t e a ' h o l e ' t o a l l o w f o r t h e r o t a t i o n o r d i f f u s i o n o f t h e p o l y m e r c h a i n . As t h e g l a s s t r a n s i t i o n t e m p e r a t u r e i s a p p r o a c h e d , t h e jumps o v e r t h e r o t a t i o n b a r r i e r become more f r e q u e n t . Because t h e s e m o l e c u l a r r o t a t i o n s a r e n o t i n s t a n t a n e o u s , a c e r t a i n p e r i o d o f t i m e must e l a p s e a f t e r an i n c r e m e n t i n t e m p e r a t u r e b e f o r e t h e new e q u i l i b r i u m i s r e a c h e d ; t h i s t i m e i s t h e n a t u r a l r e l a x a t i o n t i m e o f t h e m o l e c u l e . Above t h e g l a s s t r a n s i t i o n t e m p e r a t u r e t h e m o l e c u l a r c h a i n r o t a t i o n i s u n h i n d e r e d . Q u i t e d i f f e r e n t f r o m t h e m e l t i n g p o i n t , w h i c h i s a f i r s t o r d e r phase t r a n s i t i o n , t h e g l a s s t r a n s i t i o n i s a s e c o n d o r d e r t r a n s i t i o n c h a r a c t e r i z e d b y an a b r u p t change i n t h e s e c o n d d e r i v a t i v e o f t h e p r i m a r y t h e r m o d y n a m i c v a r i a b l e s . Fo r e x a m p l e , t h e p a r t i a l s e c o n d d e r i v a -t i v e o f t h e G ibbs f r e e e n e r g y w i t h r e s p e c t t o t e m p e r a t u r e shows t h a t h e a t c a p a c i t y e x h i b i t s an a b r u p t change a t t h e g l a s s t r a n s i t i o n t e m p e r a t u r e . I t i s i m p o r t a n t t o n o t e t h a t t h e g l a s s t r a n s i t i o n t e m p e r a t u r e i s d e p e n d e n t u p o n t h e o b s e r v a t i o n f r e q u e n c y u s e d i n t h e e x p e r i m e n t . A measurement made b y t h e r m a l a n a l y s i s i s a f u n c t i o n o f t h e h e a t i n g r a t e ; i n dynamic m e c h a n i c a l o r d i e l e c t r i c s p e c t r o s c o p y , i t i s t h e o s c i l l a t i o n p e r i o d w h i c h i s c r i t i c a l ( 4 1 ) . F o r e x a m p l e , i n dynamic m e c h a n i c a l spec -t r o s c o p y , a h i g h e r f r e q u e n c y o f t h e o s c i l l a t i o n s g i v e s a h i g h e r a p p a r e n t t r a n s i t i o n t e m p e r a t u r e because when p e r t u r b e d a t a f a s t e r r a t e t h e t a n g l e d p o l y m e r m o l e c u l e s have l e s s t i m e t o r e l a x . The m o l e c u l a r r e l a x -a t i o n t i m e d e c r e a s e s w i t h i n c r e a s i n g t e m p e r a t u r e . A t t h e g l a s s t r a n s i -t i o n t e m p e r a t u r e t h e m e c h a n i c a l l o s s ( o f t e n e x p r e s s e d as t h e r a t i o o f e n e r g y d i s s i p a t e d a g a i n s t t h e e n e r g y s t o r e d i n t h e s a m p l e , t a n 5) o f t h e - 16 -s t r e s s e d p o l y m e r i s a t t h e maximum ( 3 7 ) . T h i s i s e x p l a i n e d b y c o n s i d e r -i n g t h e e f f e c t o f t h e s t r e s s on t h e p o l y m e r s y s t e m : b e l o w t h e T g , t h e s t r e s s i s s t o r e d b y b o n d d i s t o r t i o n s and above t h e T g , b y u n c o i l i n g o f t h e c h a i n s . The g l a s s t r a n s i t i o n i s t h e u n i q u e p o i n t a t w h i c h t h e u n c o i l i n g o f t h e m o l e c u l e s i s h i n d e r e d b y t h e i n t e r m o l e c u l a r f o r c e s , m i n i m i z i n g t h e a b i l i t y o f t h e s y s t e m t o s t o r e e n e r g y . I n a somewhat a n a l o g o u s manner , t h e Tg measured b y NMR i s a f u n c t i o n o f t h e f r e q u e n c y o f t h e s p e c t r o m e t e r . The g l a s s t r a n s i t i o n a p p e a r s a t h i g h e r t e m p e r a -t u r e s i n a s t r o n g e r m a g n e t i c f i e l d ( 3 0 ) . The g l a s s t r a n s i t i o n t e m p e r a t u r e i s a u s e f u l p a r a m e t e r f o r t h e most p r a c t i c a l o f r e a s o n s ; i t i n d i c a t e s t h e t e m p e r a t u r e a t w h i c h t h e p o l y -m e r i c p r o p e r t i e s a r e a l t e r e d , where t h e m a t e r i a l changes f r o m t h e g l a s s y t o t h e r u b b e r y s t a t e . The s t i f f n e s s o f t h e PEEK c h a i n makes r o t a t i o n d i f f i c u l t and e x p l a i n s t h e h i g h Tg (144°C) o f t h e p o l y m e r . A p o l y m e r o f h i g h e r t r a n s i t i o n t e m p e r a t u r e may be made b y r e d u c i n g t h e p r o p o r t i o n o f e t h e r l i n k a g e s i n t h e c h a i n , t h e r e b y f u r t h e r i n c r e a s i n g t h e c h a i n s t i f f -n e s s . However , t h e r e s u l t i n g p o l y m e r i s l e s s f l e x i b l e . P r o v i s i o n a l p r o d u c t d a t a c l a i m s t h a t PEEK r e t a i n s 80% o f i t s s t r e n g t h e v e n t o 200°C, c o n s i d e r a b l y above t h e g l a s s t r a n s i t i o n t e m p e r a t u r e ( 2 ) ; t h i s i s on a c c o u n t o f t h e c r y s t a l l i n e phase w h i c h does n o t u n d e r g o a g l a s s t r a n s i -t i o n and a l s o because o f t h e f i b r e r e i n f o r c e m e n t i n t h e c o m p o s i t e . The re a r e many e m p i r i c a l r u l e s f o r t h e e s t i m a t i o n o f g l a s s t r a n s i t i o n t e m p e r a -t u r e s . One w h i c h h o l d s r e m a r k a b l y t r u e i n many cases i s t h e K e l v i n T g / T m r a t i o w h i c h i s a p p r o x i m a t e l y 2 / 3 f o r u n s y m m e t r i c a l p o l y m e r i c c h a i n s . For PEEK, t h i s r a t i o i s 0 . 6 9 . The t h i r d t e m p e r a t u r e t o be d i s c u s s e d i n t h e c h a r a c t e r i z a t i o n o f - 17 -s e m i - c r y s t a l l i n e p o l y m e r s i s t h e c r y s t a l l i z a t i o n t e m p e r a t u r e . T c . The mechanism and m o r p h o l o g y o f c r y s t a l l i z a t i o n have a l r e a d y b e e n d i s c u s s e d e a r l i e r i n t h i s s e c t i o n . The c r y s t a l l i z a t i o n t e m p e r a t u r e i s l o o s e l y d e f i n e d as t h a t t e m p e r a t u r e a t w h i c h t h e c r y s t a l l i z a t i o n r a t e i s m a x i -mum. T h e o r e t i c a l l y , t h e c r y s t a l l i z a t i o n t e m p e r a t u r e o f any s u b s t a n c e s h o u l d be t h e same as t h e m e l t i n g t e m p e r a t u r e ( T m ) f o r t h a t s u b s t a n c e ; t h i s i s t r u e f o r any s i m p l e o r g a n i c compound. I n p o l y m e r i c s y s t e m s , how-e v e r , c r y s t a l l i z a t i o n does n o t o c c u r u n t i l w e l l b e l o w t h e m e l t i n g p o i n t . T h i s s u p e r c o o l i n g i s n e c e s s a r y because t h e p o l y m e r c h a i n s have s u c h l o n g m o l e c u l a r r e l a x a t i o n t i m e s t h a t a l a r g e d r i v i n g f o r c e ( T m - T c ) i s r e q u i r e d t o i n d u c e c r y s t a l l i z a t i o n . Be low t h e c r y s t a l l i z a t i o n t e m p e r a -t u r e , t h e m o t i o n o f t h e m o l e c u l e s i s t o o s l u g g i s h t o a l l o w t h e c h a i n s t o o r i e n t i n a c r y s t a l c o n f o r m a t i o n . I n i n d u s t r y i t i s v e r y i m p o r t a n t t o know t h e c r y s t a l l i z a t i o n t e m p e r a t u r e o f t h e r m o p l a s t i c m a t r i c e s . Fo r e x a m p l e , i f a n amorphous m a t e r i a l i s r e q u i r e d , c a r e must be t a k e n n o t t o h e a t i t above t h e T c and c o n v e r s e l y , i f i t i s t h e c r y s t a l l i n e p l a s t i c w h i c h i s r e q u i r e d , t h e m o u l d e d amorphous p a r t may t h e n be a n n e a l e d i n o r d e r t o d e v e l o p t h e d e s i r e d c r y s t a l l i n i t y . One o f t h e u n i q u e a d v a n t a g e s o f t h e s e m i -c r y s t a l l i n e t h e r m o p l a s t i c s i s t h a t t h e end u s e r c a n t a i l o r t h e c r y s t a l -l i n e p r o p e r t i e s o f t h e f a b r i c a t e d i t e m t h r o u g h t h e s i m p l e p r o c e s s o f a n n e a l i n g . The d e n s i t i e s o f amorphous and c r y s t a l l i n e PEEK a r e r e p o r t e d as 1,265 k g m~ 3 and 1 ,400 k g m " 3 r e s p e c t i v e l y ( 1 8 ) . The amorphous sample has a s m a l l e r d e n s i t y because i t has a g r e a t e r f r e e v o l u m e . D e n s i t y measure -ments a r e somet imes u s e d t o e s t i m a t e t h e f r a c t i o n o f c r y s t a l l i n i t y o f a - 18 -s a m p l e . The c r y s t a l l i n e d e n s i t y must be c a l c u l a t e d f r o m t h e c r y s t a l s t r u c t u r e , d e t e r m i n e d b y X - r a y c r y s t a l l o g r a p h y ; t h e amorphous m a t e r i a l c a n be measured d i r e c t l y . T e n s i l e s t r e n g t h i s a w i d e l y q u o t e d p a r a m e t e r i n t h e assessment o f t h e m e c h a n i c a l p r o p e r t i e s o f p o l y m e r s , a l t h o u g h i n p r a c t i c a l a p p l i c a -t i o n s t h e f a b r i c a t e d i t e m a l m o s t n e v e r y i e l d s a t t h e t e n s i l e s t r e s s l i m i t . T h e r e a r e a l w a y s o t h e r f a c t o r s i n v o l v e d such as f a t i g u e , c r a c k -i n g , s t r e s s c o n c e n t r a t i o n s , and damaging e n v i r o n m e n t s w h i c h cause f a i l u r e b e f o r e t h e u l t i m a t e s t r e n g t h l i m i t i s r e a c h e d . I n a d d i t i o n , f o r f i b e r c o m p o s i t e m a t r i c e s l i k e PEEK, t h e f a i l u r e i s o f t e n c o n t i n g e n t on t h e f i b e r s t r e n g t h m o d u l u s . N e v e r t h e l e s s , t h e y i e l d s t r e s s i s a u s e f u l p a r a m e t e r because i t i s a r o u t i n e measurement w h i c h c o r r e l a t e s w e l l w i t h o t h e r modes o f f a i l u r e : i m p a c t , t e a r and f a t i g u e . Kemmish and Hay r e p o r t t h e y i e l d s t r e s s o f PEEK r e s i n as 59±1 MPa f o r t h e amorphous and 90±1 MPa f o r a 32% c r y s t a l l i n e sample ( 3 4 ) . The c r y s t a l l i n e phase o f t h e p o l y m e r t e n d s t o a c t as a r e i n f o r c e m e n t t o i m p r o v e t h e s t r e n g t h o f t h e m a t e r i a l . The e l o n g a t i o n o f t h e c r y s t a l l i n e sample i s s m a l l e r ( 3 8 ) . The e x t e n s i o n f i r s t o c c u r s i n t h e amorphous and t h e n t h e c r y s t a l l i n e r e g i o n s b e g i n t o b r e a k a p a r t . A l t h o u g h a t h i g h t e m p e r a t u r e s PEEK r e t a i n s most o f i t s s t i f f n e s s , t h e t e n s i l e s t r e n g t h does d r o p above T g ; i n a t e m p e r a t u r e i n c r e a s e o f 150°C t o 180°C, t h e s t r e n g t h d r o p s b y 64% ( 4 2 ) . F r a c t u r e t o u g h n e s s i s one o f t h e p a r t i c u l a r l y o u t s t a n d i n g f e a t u r e s o f PEEK ( 8 ) . Toughness i s a measure o f t h e e n e r g y a b s o r b e d on i m p a c t a t f a i l u r e and i s u s u a l l y e x p r e s s e d as e n e r g y p e r u n i t a r e a o f t h e c r a c k c r o s s s e c t i o n . PEEK c o m p o s i t e s a r e much t o u g h e r t h a n c o r r e s p o n d i n g epoxy c o m p o s i t e s due t o a d i f f e r e n t mode o f f a i l u r e . T a b l e 2 . 1 shows t h e - 19 -r e s u l t s o f t h e r e c e n t s t u d y o f Kemmich and Hay w h i c h emp loys t h e t h r e e p o i n t Charpy t e s t t o d e t e r m i n e t h e f r a c t u r e t o u g h n e s s o f PEEK samples o f v a r y i n g c r y s t a l l i n i t y . Unaged, amorphous PEEK i s many t i m e s t o u g h e r t h a n t h e c r y s t a l l i n e f o r m . The amorphous shows a d u c t i l e f a i l u r e mode w h i l e t h e c r y s t a l l i n e e x h i b i t s a b r i t t l e f a i l u r e . Fo r good t o u g h n e s s c h a r a c -t e r i s t i c s , c r y s t a l l i n i t y s h o u l d be k e p t l o w . U n f o r t u n a t e l y t h e r e i s a t r a d e - o f f because samples o f l o w c r y s t a l l i n i t y a r e most v u l n e r a b l e t o s o l v e n t a t t a c k . The i d e a l c r y s t a l l i n i t y depends upon t h e end use o f t h e p l a s t i c . S o l v e n t r e s i s t a n c e o f t h e c r y s t a l l i n e samples show PEEK t o be r e m a r k a b l y i m p e r v i o u s t o n e a r l y a l l a g g r e s s i v e e n v i r o n m e n t s . Humid a g i n g t e s t s a r e o f p r i m a r y i m p o r t a n c e : a f t e r 24 h r s a t 40% r e l a t i v e h u m i d i t y , a t room t e m p e r a t u r e , PEEK a b s o r b s 0.14% m o i s t u r e . E p o x i e s u n d e r s i m i l i a r c o n d i t i o n s show u p t a k e s o f 0.05% t o 0.2% ( 1 0 ) . Wate r a b s o r p t i o n i s q u i t e u n d e s i r a b l e because t h e w a t e r a c t s as a p l a s t i c i z e r , l o w e r i n g t h e Tg and r e d u c i n g t h e e l e v a t e d t e m p e r a t u r e p r o p e r t i e s o f t h e m a t e r i a l . O t h e r s o l v e n t t e s t s show no s i g n i f i c a n t e f f e c t i n t h e m e c h a n i c a l p r o p e r t i e s o f PEEK c o m p o s i t e s a f t e r i m m e r s i o n i n a w i d e v a r i e t y o f s o l v e n t s : G e n k l e n e , a c e t o n e , m e t h y l e t h y l k e t o n e , c y c l o h e x a n e and p a i n t -s t r i p p e r ( A r d o x 2526) . A f t e r one month o f i m m e r s i o n i n h y d r a u l i c f l u i d , k e r o s e n e , o r s y n t h e t i c l u b r i c a t i o n o i l , t h e c o m p o s i t e s t i l l r e t a i n e d 95% o f i t s o r i g i n a l s t r e n g t h ( 9 ) . T a b l e 2 . 1 p r e s e n t s a summary o f t h e p r o p e r t i e s o f p o l y ( e t h e r e t h e r k e t o n e ) . - 20 -Table 2.1: Physical and Mechanical Properties of PEEK Resin Chemical structure T m melting point Tg glass transition T c crystallization density: crystalline amorphous tensile strength^*) : crystalline amorphous -^©-o-@-o-®-c--340°C 144 °C 173°C 1,400 kg nT 3 1,265 kg m"3 90 MPa 59 MPa o. 613K 417K<d) 446K (18) (34) fracture toughness^: crystalline (30%) 3.0 kJ m"3 b r i t t l e failure amorphous 85 kJ m"^  ductile failure (3^) water absorption^ 0) 0.14% (10) (a) (b) (c) (d) strain rate 2 x 10"^ s, charpy test. 24 h, 40% humidity. Table 3.1 2.2.2 Poly(phenylene sulfide) Most of the theoretical aspects of the above section apply equally well to PPS as to PEEK. The structure of PPS is somewhat simpler than that of PEEK; the repeating unit consists of aryl groups linked by sulfur atoms. Light scattering studies indicate that the molecular weight of the virgin resin is moderate, about 17,000 g mol"* (15). How-ever, when the powdered resin is heated in air to temperatures ranging - 21 -f r o m 175 t o 280°C, a ' c u r i n g ' r e a c t i o n t a k e s p l a c e and t h r o u g h a c o m b i -n a t i o n o f o x i d a t i o n , c r o s s - l i n k i n g and c h a i n e x t e n s i o n , t h e m o l e c u l a r w e i g h t i s i n c r e a s e d . The c u r i n g phenomenon, t h o u g h n o t w e l l u n d e r s t o o d , i s c e r t a i n l y an a d v a n t a g e as i t p r o v i d e s a s i m p l e method o f c o n t r o l l i n g t h e m o l e c u l a r w e i g h t o f t h e p l a s t i c f o r s p e c i f i c a p p l i c a t i o n s . The maximum a t t a i n a b l e c r y s t a l l i n i t y o f PPS exceeds t h a t o f PEEK; i t i s a b o u t 65%, o b t a i n e d f o r t h e v i r g i n r e s i n . X - r a y d i f f r a c t i o n s t u d i e s show t h a t , l i k e PEEK, t h e u n i t c e l l i s o r t h o r h o m b i c , each c e l l c o n t a i n i n g f o u r - m o n o m e r i c u n i t s . The p l a n e s o f t h e p h e n y l e n e g r o u p s a r e a t r i g h t a n g l e s t o each o t h e r and t h e s u l f u r b o n d a n g l e i s 110° j u s t as i n a l i p h a t i c s u l f u r p o l y m e r s ( 2 2 ) . PPS has somewhat l o w e r t r a n s i t i o n t e m p e r a t u r e s t h a n PEEK; m e l t i n g o c c u r s a t a b o u t 2 8 2 " C ; t h e g l a s s t r a n s i t i o n a p p e a r s a t a p p r o x i m a t e l y 87°C; and a g a i n , t h e T g / T m r a t i o e q u a l s 2 / 3 . The c r y s t a l l i z a t i o n endo-t h e r m i s maximum a t 122°C and t h e amorphous p l a s t i c c r y s t a l l i z e s r e a d i l y above t h e g l a s s t r a n s i t i o n t e m p e r a t u r e . The m a t e r i a l d e n s i t y i s q u i t e s i m i l a r t o PEEK, t h e c r y s t a l l i n e i s a b o u t 8% more dense t h a n t h e amorphous . The t e n s i l e s t r e n g t h o f PPS i s a l i t t l e l e s s t h a n t h a t o f PEEK, 51 MPa f o r t h e a n n e a l e d , and 47 MPa f o r t h e u n a n n e a l e d s p e c i m e n ( 1 6 ) . T h i s i s o p p o s i t e t o t h e t r e n d n o r m a l l y o b s e r v e d i n s e m i - c r y s t a l l i n e p o l y m e r s . B r a d y ( 1 6 ) s u g g e s t s t h a t i n s t e a d o f h a v i n g a r e i n f o r c i n g e f f e c t as i n PEEK, t h e c r y s t a l l i n e r e g i o n s o f PPS i n t r o d u c e i n t e r f a c i a l s t r a i n i n t h e p o l y m e r n e t w o r k . The f r a c t u r e t o u g h n e s s f o r PPS r e s i n a l o n e i s n o t a v a i l a b l e . However , i n an i n t e r l a m i n a r f r a c t u r e t e s t o f c a r b o n f i b r e c o m p o s i t e s made w i t h PEEK, PPS, p o l y s u l f o n e and epoxy m a t r i c e s , t h e PPS - 22 -was only slightly less tough than the PEEK and far superior to both other plastics (4). PPS excels in resistance to moisture uptake. Water absorption after 24 hours at room temperature was less than 0.02% of the i n i t i a l weight (10), much less than any of the other matrix thermoplastics. The envi-ronmental resistance of PPS is an important se l l i n g feature; PPS has excellent applications for pumps, valves and regulators which are in contact with corrosive fluids. Tests show PPS undamaged by any solvent at room temperature, although, after extended exposure of 6 months or more at above Tg temperatures, some strong acids and organic solvents are capable of damaging PPS (43). Table 2.2 presents a summary of the properties of poly(phenylene sulfide). Table 2 . 2 : Physical and Mechanical Properties of PPS Resin Chemical structure T m melting point Tg glass transition T c crystallization density: crystalline amorphous tensile strength: annealed unannealed water absorption <0.02% (10) (24 h, ASTM D570) 282°C 555K 87°C 360K<a) 121°C 394K 1,430 kg m"3 1,320 kg m"3 <22> 47 MPa 51 MPa <16> <a> Table 3.1. - 23 -2 . 3 THE MATERIALS USED I N THIS WORK 2 . 3 . 1 P o l y ( e t h e r e t h e r k e t o n e ) Two f o r m s o f PEEK were s t u d i e d , amorphous and c r y s t a l l i n e . The m a t e r i a l u s e d as " c r y s t a l l i n e " was o b t a i n e d f r o m I C I A m e r i c a s , D e l a w a r e , v i a D r . Greg Luoma o f De fence R e s e a r c h E s t a b l i s h m e n t P a c i f i c (DREP). I t was i n t h e f o r m o f a l i g h t g r e y p o w d e r , w i t h a w i d e p a r t i c l e s i z e d i s t r i b u t i o n ( a p p r o x i m a t e l y 0 . 0 1 t o 1 mm d i a m e t e r ) . The powder was assumed t o be a b o u t 35% c r y s t a l l i n e ( 9 ) . The amorphous PEEK sample was p u r c h a s e d f r o m W e s t l a k e P l a s t i c s , P e n n s y l v a n i a , as a t r a n s l u s c e n t , amber , f l e x i b l e f i l m o f 3 m i l n o m i n a l t h i c k n e s s . T h i s f i l m was assumed f u l l y amorphous . Upon h e a t i n g above t h e g l a s s t r a n s i t i o n t e m p e r a t u r e , i t r e a d i l y c r y s t a l l i z e d , b e c o m i n g more b r i t t l e and t u r n i n g opaque b e i g e i n c o l o u r . 2 . 3 . 2 P o l y ( p h e n y l e n e s u l f i d e ) The c r y s t a l l i n e PPS was m a n u f a c t u r e d b y t h e P h i l l i p s P e t r o l e u m Company, a g a i n s u p p l i e d b y D r . Luoma as a v e r y f i n e , f l o u r y powder o f p a l e b e i g e c o l o u r . I t was a v i r g i n r e s i n i n t h e f o r m w h i c h i s i s o l a t e d d i r e c t l y f r o m t h e r e a c t i o n s o l v e n t ( 1 5 ) . The amorphous c o m p o s i t e m a t e r i a l was d o n a t e d b y A m e r i c a n Thermo-p l a s t i c s C o r p o r a t i o n , a s u b s i d i a r y o f P h i l l i p s P e t r o l e u m Company. The c o m p o s i t e was 40% g l a s s - f i l l e d , p r o c e s s e d i n t o i r r e g u l a r l y s h a p e d , b r o w n p e l l e t s h a v i n g an a v e r a g e d i a m e t e r o f a b o u t 3 mm. - 24 -I I I . THERMAL ANALYSIS: DIFFERENTIAL SCANNING CALORIMETRY 3 . 1 THERMAL ANALYSIS THEORY T h e r m a l a n a l y s i s h a s , as a g e n e r a l t e r m , come t o mean " t h e measure ment o f some m a t e r i a l r e s p o n s e t o a programmed change o f t e m p e r a t u r e " ( 4 4 ) . D i f f e r e n t i a l S c a n n i n g C a l o r i m e t r y (DSC) i s j u s t one me thod i n a l a r g e f a m i l y o f t h e r m a l a n a l y t i c a l t e c h n i q u e s . D e v e l o p e d i n t h e 1 9 6 0 s , DSC i s an o f f - s h o o t o f t h e much o l d e r D i f f e r e n t i a l T h e r m a l A n a l y s i s (DTA) t e c h n i q u e . DSC d i f f e r s f r o m DTA n o t so much i n t h e f i n a l i n f o r m a -t i o n g a i n e d b u t r a t h e r i n t h e p a r a m e t e r m e a s u r e d . DTA r e c o r d s t h e d i f -f e r e n c e i n t e m p e r a t u r e b e t w e e n a sample and a r e f e r e n c e m a t e r i a l when b o t h a r e h e a t e d a t a c o n s t a n t r a t e . On t h e o t h e r h a n d , DSC uses a s e r v o s y s t e m t o measure t h e q u a n t i t y o f h e a t w h i c h must be added t o t h e sampl t o m a i n t a i n i t a t t h e same t e m p e r a t u r e as t h e r e f e r e n c e . The most l a u -d a b l e a d v a n t a g e o f DSC o v e r DTA i s t h a t i n DSC t h e e n t h a l p y o f t r a n s i -t i o n s c a n be o b t a i n e d d i r e c t l y b y i n t e g r a t i o n o f t h e s c a n n i n g c u r v e s . DSC has now g e n e r a l l y r e p l a c e d t h e DTA m e t h o d , save p e r h a p s f o r some h i g h t e m p e r a t u r e a p p l i c a t i o n s . P o l y m e r c h e m i s t s were q u i c k t o r e c o g n i z e t h e v a l u e o f DSC t o p o l y m e r s c i e n c e . Fo r n e a r l y two d e c a d e s , DSC has b e e n e m p l o y e d t o d e t e r m ine g l a s s t r a n s i t i o n s , m e l t i n g p o i n t s , c r y s t a l l i z a t i o n k i n e t i c s , h e a t c a p a c i t i e s , t h e r m a l d e g r a d a t i o n , and m i s c i b i l i t i e s o f many, v a r i e d p o l y m e r s y s t e m s . The s i g n a l o b t a i n e d b y DSC i s p r o p o r t i o n a l t o t h e d i f f e r e n c e i n t h - 25 -h e a t c a p a c i t y o f t h e sample and t h e r e f e r e n c e c e l l . The g l a s s t r a n s i t i o n t e m p e r a t u r e i s marked b y a change i n t h e h e a t c a p a c i t y o f t h e m a t e r i a l and on t h e DSC s c a n t h i s a p p e a r s as a sudden e n d o t h e r m i c s h i f t i n t h e b a s e l i n e . As t h e p o l y m e r u n d e r g o e s t h e change f r o m a g l a s s t o a r u b b e r y s o l u t i o n , t h e i n t r o d u c t i o n o f r o t a t i o n a l f r e e d o m above Tg causes an i n c r e a s e i n t h e h e a t c a p a c i t y . The m e l t i n g t r a n s i t i o n i s i n d i c a t e d b y an e n d o t h e r m i c p e a k on t h e t h e DSC s c a n because t h e p o l y m e r r e q u i r e s a d d i t i o n a l l a t e n t h e a t f o r t h e change o f p h a s e . The m e l t i n g p o i n t ( T m ) i s t a k e n as t h e t e m p e r a t u r e a t w h i c h t h e t h e peak maximum o c c u r s . I t i s s i m p l e t o o b t a i n an e s t i m a t e o f t h e m e l t i n g e n t h a l p y b y i n t e g r a t i o n o f t h e e n d o t h e r m i c p e a k a r e a . T h i s i s p o s s i b l e because t h e o r d i n a t e o f t h e DSC c u r v e i s i n u n i t s o f p o w e r . I f t h e h e a t i n g r a t e o f t h e DSC c e l l i s c o n s t a n t , t h e u n i t s o f power a r e r e a d i l y c o n v e r t e d i n t o u n i t s o f e n e r g y - p e r - d e g r e e ( t h e u n i t s o f h e a t c a p a c i t y ) . The i n t e g r a t i o n o f t h e c u r v e w i t h r e s p e c t t o t e m p e r a t u r e y i e l d s a v a l u e i n u n i t s o f e n e r g y , t h a t i s , t h e e n t h a l p y o f t h e t r a n s i -t i o n . G e n e r a l l y i t i s e x p r e s s e d as J o u l e s p e r gram o f s a m p l e . I t I s w o r t h n o t i n g t h a t w h i l e t h e peak shape and p o s i t i o n a r e e f f e c t e d b y t h e s c a n n i n g r a t e , t h e i n t e g r a t e d v a l u e o f t h e peaks i s e s s e n t i a l l y i n d e p e n -d e n t o f t h e h e a t i n g r a t e . The c r y s t a l l i z a t i o n t e m p e r a t u r e and e n t h a l p y a r e a r r i v e d a t i n much t h e same way as f o r t h e m e l t i n g t r a n s i t i o n . A t t h e c r y s t a l l i z a t i o n t e m p e r a t u r e , t h e DSC s c a n i s e x o t h e r m i c because t h e amorphous p o l y m e r c o n v e r t s t o t h e more s t a b l e s e m i - c r y s t a l l i n e f o r m w h i c h has l o w e r e n t h a l p y . A g a i n , t h e c r y s t a l l i z a t i o n t e m p e r a t u r e i s t a k e n f r o m t h e peak maximum and an e s t i m a t e o f t h e c r y s t a l l i z a t i o n e n t h a l p y i s made b y - 26 -i n t e g r a t i o n o f t h e peak a r e a . 3 . 2 PREVIOUS DSC WORK ON PEEK AND PPS O t h e r w o r k e r s have u s e d D i f f e r e n t i a l S c a n n i n g C a l o r i m e t r y i n t h e s t u d y o f p o l y ( e t h e r e t h e r k e t o n e ) and p o l y ( p h e n y l e n e s u l f i d e ) . Kemmish and Hay ( 3 4 ) f o u n d h e a t c a p a c i t i e s o f t h e amorphous and c r y s t a l l i n e PEEK and t h e r e s p e c t i v e h e a t s o f c r y s t a l l i z a t i o n and f u s i o n . These a u t h o r s a l s o examined t h e e f f e c t o f p h y s i c a l a g i n g on t h e f o r m o f t h e g l a s s t r a n s i t i o n c u r v e . Yoda ( 2 5 ) emp loyed DSC a l o n g w i t h X - r a y d i f f r a c t i o n t o s t u d y t h e e f f e c t s o f r a d i a t i o n on amorphous PEEK. Lower m e l t i n g t e m p e r a t u r e s and p o o r e r c r y s t a l l i z a t i o n were f o u n d i n t h e samples w h i c h h a d b e e n g i v e n r a d i a t i o n doses o f 1000 t o 5000 Mrad i n a 2 MeV e l e c t r o n beam. The DSC t e c h n i q u e was u s e d b y I t o and P o r t e r ( 2 6 ) t o s t u d y t h e d r a w i n g t e m p e r a t u r e o f PPS: samples w h i c h were d rawn a t l o w t e m p e r a -t u r e s , b e l o w t h e g l a s s t r a n s i t i o n , were o b s e r v e d t o have s t r e s s - i n d u c e d c r y s t a l l i n i t y w h i l e t h e undrawn and h i g h t e m p e r a t u r e d rawn samples r e m a i n e d amorphous . 3 . 3 EXPERIMENTAL The t h e r m a l a n a l y s i s o f PEEK and PPS was p e r f o r m e d on t h e e q u i p m e n t o f D r . R.C. Thompson o f t h e D e p a r t m e n t o f C h e m i s t r y , U . B . C . T h i s e q u i p -- 27 -ment was c o m p r i s e d o f a M e t t l e r TC-10A p r o c e s s o r and a DSC-20 d i f f e r e n -t i a l s c a n n i n g c a l o r i m e t e r c e l l o f t h e same make. The d a t a was p l o t t e d as i t was c o l l e c t e d b y a Swiss M a t r i x p r i n t e r . The most r e c e n t s c a n was r e t a i n e d f o r t h e n u m e r i c a l e v a l u a t i o n o f t h e e v e n t s . The samples were e n c a p s u l a t e d i n a luminum p a n s . The sample w e i g h t s were known t o an a c c u -r a c y o f ± 0 . 0 2 mg, and v a r i e d f r o m a b o u t 8 t o 28 mg. An empty p a n was u s e d as t h e r e f e r e n c e s t a n d a r d . F i g u r e 3 . 1 shows a c r o s s - s e c t i o n a l d i a g r a m o f t h e c e l l . The p l a t i -num s e n s o r a t t h e l e f t measures t h e t e m p e r a t u r e o f t h e f u r n a c e w h i l e t h e s a m p l e pan r e f e r e n c e pan D C h e a t e r x 0 D C T P t s e n s o r A T s i g n a l p u r g e g a s in le t F i g u r e 3 . 1 : S e c t i o n a l v i e w o f DSC m e a s u r i n g c e l l . - 28 -t h e r m o p i l e l o c a t e d on t h e d i s k b e t w e e n t h e sample and r e f e r e n c e pans r e c o r d s t h e t e m p e r a t u r e g r a d i e n t and t r i g g e r s an a d j u s t m e n t o f t h e h e a t f l o w t o t h e s a m p l e . U n l e s s o t h e r w i s e s p e c i f i e d , t h e sample was h e a t e d a t a r a t e o f 10 K min"- '- f r o m 35°C t o a t l e a s t 50°C above t h e m e l t i n g p o i n t . The p l a t i n u m t h e r m a l s e n s o r was c a l i b r a t e d a g a i n s t t h e f u s i o n t e m p e r a t u r e s o f i n d i u m , l e a d and z i n c and t h e h e a t f l o w c a l i b r a t i o n was made u s i n g t h e h e a t o f f u s i o n o f an e x a c t l y known mass o f i n d i u m . I n a s e r i e s o f t e m p e r a t u r e c a l i b r a t i o n r u n s , t h e t e m p e r a t u r e o f t h e i n d i u m sample was c o n s i s t e n t t o w i t h i n ± 0 . 1 K. The s o f t w a r e p r o v i d e d b y t h e M e t t l e r TC-10A p r o c e s s o r was u s e d t o o b t a i n t h e T g , T c , and T m v a l u e s as w e l l as t h e c r y s t a l l i z a t i o n and m e l t i n g e n t h a l p i e s . 3 . 4 RESULTS AND DISCUSSION J . M . R i c h a r d s o n ( 4 5 ) w r i t e s : " E v e n r e l a t i v e l y c r u d e methods o f t h e r m a l a n a l y s i s , t y p i f i e d b y s c a l e l e s s o r d i n a t e s , have p r o v e d o f g r e a t v a l u e i n p o l y m e r c h a r a c t e r i z a t i o n ; t h e p r e s e n c e o r absence o f a peak i s o f t e n s u f f i c i e n t t o i n f e r w h a t s t r u c t u r e i s p r e s e n t and hence w h a t t h e u l t i m a t e p r o p e r t i e s w i l l b e . " I n t h i s w o r k no a t t e m p t was made t o do s e r i o u s q u a n t i t a t i v e t h e r m a l a n a l y s i s b y DSC. The p r i m a r y o b j e c t i v e s i n t h e use o f t h e r m a l a n a l y s i s were ( i ) t o e s t a b l i s h t h e p r i n c i p a l t r a n s i t i o n t e m p e r a t u r e s , - 29 -( i i ) t o d e t e r m i n e q u a l i t a t i v e l y i f t h e sample was c r y s t a l l i n e o r amorphous , and ( i i i ) t o d e t e c t t h e a n n e a l i n g o f t h e amorphous samples a f t e r r e m o v a l f r o m t h e v a r i a b l e t e m p e r a t u r e NMR p r o b e . The DSC a n a l y s i s p r o v i d e d i n s i g h t i n t o t h e n a t u r e o f t h e samples w h i c h were f u r t h e r s t u d i e d b y NMR. F i g u r e s 3 . 2 and 3 . 3 show DSC scans o f PEEK and PPS ( h e a t i n g r a t e 4 K . m i n " 1 ) . T a b l e 3 . 1 l i s t s t h e t r a n s i t i o n t e m p e r a t u r e s and e n t h a l p i e s f o r PEEK and PPS. The t a b u l a t e d number r e p r e s e n t s t h e a v e r a g e t a k e n o v e r 4 e x p e r i m e n t s . The t e m p e r a t u r e measurements were c o n s i s t e n t t o w i t h i n ± 0 . 5 ° C and t h e e n t h a l p y v a l u e s v a r i e d b y a b o u t 10%. I n some c a s e s , t h e t r a n s i t i o n t e m p e r a t u r e s d i f f e r f r o m t h o s e o f t h e l i t e r a t u r e . V a r i a t i o n s l i k e l y r e f l e c t v a r y i n g m o l e c u l a r w e i g h t s and t h e r m a l h i s t o r i e s o f t h e samples r a t h e r t h a n an a c t u a l e r r o r i n t h e m e a s u r e m e n t s . t - *40°C F i g u r e 3 . 2 : DSC scan o f PEEK ( a ) amorphous ( b ) c r y s t a l l i n e ( h e a t i n g r a t e 4 K m i n " 1 ) . - 30 -X- m °c A Figure 3.3: DSC scan of PPS (a) amorphous (b ) crystalline (heating rate 4 K min" 1). Table 3.1: DSC Results for PEEK and PPS. PEEK PPS T g [ ° C ] 143 5 87 2 T c r c ] 173 1 121 7 AH C [ J g "1 ] 22 9 25 4 T m [ ° C ] 340 3 282 0 A H m [ J g ' l ] 43 1 42 9 - 31 -3 . 4 . 1 The G l a s s T r a n s i t i o n T e m p e r a t u r e The f i r s t e v e n t , v i s i b l e o n l y i n t h e amorphous samples o f b o t h PEEK and PPS, i s t h e g l a s s t r a n s i t i o n . The t r a n s i t i o n t e m p e r a t u r e i s t a k e n as t h e p o i n t o f i n f l e c t i o n o f t h e c u r v e d d r o p i n h e a t c a p a c i t y ; a t t h i s p o i n t t h e t r a n s i t i o n i s 50% c o m p l e t e ( 4 6 ) F i g u r e 3 . 4 shows t h e s k e t c h o f a t y p i c a l Tg c u r v e and t h e p o i n t s c a l c u l a t e d b y t h e M e t t l e r p r o c e s s o r . T F i g u r e 3 . 4 : S k e t c h o f a DSC g l a s s t r a n s i t i o n c u r v e . Samples w h i c h were a n n e a l e d i n t h e Tg r e g i o n e x h i b i t t h e c h a r a c t e r -i s t i c e n d o t h e r m i c peak o b s e r v e d b y Kemmish and Hay ( 3 4 ) . F i g u r e 3 .5 p r e s e n t s t h e g l a s s t r a n s i t i o n o f an amorphous PEEK sample w h i c h h a d been h e l d a t 137°C i n t h e NMR p r o b e . The e n d o t h e r m i c peak i s q u i t e - 32 -p r o n o u n c e d . T h i s phenomenon i s common t o a g r e a t many amorphous t h e r m o -p l a s t i c s (47). The a n n e a l i n g a l l o w s f o r m a t i o n o f a l o w e r e n t h a l p y g l a s s , w h i c h t e n d s t o s u p e r h e a t , and t h e e n d o t h e r m i c peak above Tg r e p r e s e n t s t h e " c a t c h - u p " p e r i o d o f t h e g l a s s as i t r e t u r n s t o e q u i l i b r i u m . The h e i g h t o f t h e peak i s a f u n c t i o n o f a n n e a l i n g t i m e and t e m p e r a t u r e , w h i l e t h e maximum o f t h e peak g e n e r a l l y o c c u r s a t a t e m p e r a t u r e 15 t o 20°C b e l o w T „ . I I J F i g u r e 3 . 5 : DSC g l a s s t r a n s i t i o n c u r v e f o r amorphous PEEK a n n e a l e d a t 1 3 7 ° . - 33 -3 . 4 . 2 C r y s t a l l i z a t i o n The s e c o n d t h e r m a l e v e n t i s a l s o e x h i b i t e d o n l y i n t h e amorphous s a m p l e s ; i t i s t h e c r y s t a l l i z a t i o n e x o t h e r m . The a r e a o f t h e c r y s t a l -l i z a t i o n e x o t h e r m i s s m a l l e r f o r samples w h i c h have b e e n a n n e a l e d above T g . I n a sample o f maximum c r y s t a l l i n i t y , no e x o t h e r m i s s e e n . The mos t d i f f i c u l t p r o b l e m i n c a l c u l a t i n g t h e e n t h a l p y o f c r y s t a l -l i z a t i o n i s t h e d e t e r m i n a t i o n o f t h e c o r r e c t b a s e l i n e (44). I n t h i s w o r k , t h e b a s e l i n e was f o u n d b y t h e e x t r a p o l a t i o n o f t h e l i n e s o n e i t h e r s i d e o f t h e e v e n t , t h e l i n e s t h e n b e i n g c u r v e d t o meet b e n e a t h t h e peak maximum. T h i s p e a k i n t e g r a t i o n c a l c u l a t i o n was a v a i l a b l e as p a r t o f t h e M e t t l e r p r o c e s s i n g ( b a s e l i n e t y p e 8 ) . F i g u r e 3 . 6 shows an i l l u s t r a t i o n o f t h e b a s e l i n e c o n s t r u c t i o n . I m p l i c i t i n t h i s c h o i c e o f b a s e l i n e i s t h e a s s u m p t i o n t h a t a t t e m p e r a t u r e s b e l o w T c , t h e sample i s f u l l y amorphous and a t t e m p e r a t u r e s above T c , i t i s f u l l y c r y s t a l l i z e d . F o r t h e a c c u r a c y d e s i r e d i n t h i s w o r k , t h e a s s u m p t i o n i s a d e q u a t e . I n a c t u a l f a c t , t h e i n t e g r a t e d a r e a i s t h e e n t h a l p y d i f f e r e n c e b e t w e e n t h e amorphous p o l y m e r a t t h e o n s e t o f c r y s t a l l i z a t i o n a t t h e b e g i n n i n g o f t h e e n d o t h e r m , and t h e c o m p l e t e l y c r y s t a l l i z e d p o l y m e r , a t t h e end o f t h e e n d o t h e r m i c p e a k . T h u s , t o f i n d a t r u e c r y s t a l l i z a t i o n e n t h a l p y , t h e change i n e n t h a l p y due t o h e a t i n g o f t h e amorphous and c r y s t a l l i n e r e g i o n s d u r i n g t h e c r y s t a l l i z a t i o n must be s u b t r a c t e d : T2 T2 ^ c r y s t " [ H ( a m o r . , T x ) - H ( c r y s t . , T 2 ) ] - [ / x C p c d T + / ( l - x ) C p a d T ] T l T X ( 3 . 1 ) - 34 -F i g u r e 3.6: DSC c r y s t a l l i z a t i o n e x o t h e r m f o r amorphous PPS. T]_ t o T2 i s t h e r a n g e o f t h e c r y s t a l l i z a t i o n e n d o t h e r m , T c i s t h e pea t e m p e r a t u r e , C p c and C p a a r e t h e h e a t c a p a c i t i e s o f t h e amorphous r e g i o n s and x i s t h e c r y s t a l l i n e w e i g h t f r a c t i o n w h i c h i s a f u n c t i o n t e m p e r a t u r e . F o r t h e f u l l y amorphous PEEK s a m p l e , t h e i n t e g r a t i o n o f t h e e x o -t h e r m i s 23 J g " l w h i c h a g r e e s v e r y w e l l w i t h t h a t o f 22 J g " 1 - 35 -p r e v i o u s l y r e p o r t e d ( 3 4 ) . Because t h e amorphous PPS was o n l y a v a i l a b l e as a c o m p o s i t e , t h e A H C v a l u e , e x p r e s s e d i n J g "1 o f s a m p l e , was a d j u s t e d t o t h e w e i g h t f r a c t i o n o f PPS i n t h e g l a s s / P P S c o m p o s i t e . 3 . 4 . 3 M e l t i n g The f i n a l e v e n t , t h e m e l t i n g t r a n s i t i o n , i s e v i d e n t i n t h e c r y s t a l -l i n e and t h e ' a m o r p h o u s ' ( c r y s t a l l i z e d i n t h e c o u r s e o f t h e DSC s c a n ) p o l y m e r s . I n s i m p l e c r y s t a l l i n e m a t e r i a l s , a DSC s c a n r e c o r d s a m e l t i n g e n d o t h e r m as a s h a r p , d i s t i n c t i v e peak a t t h e m e l t i n g t e m p e r a t u r e . S i n c e p o l y m e r s a r e i m p e r f e c t s y s t e m s , any sample c o n t a i n s r e g i o n s w h i c h m e l t a t v a r i o u s t e m p e r a t u r e s and t h i s r a n g e o f m e l t i n g p o i n t s i s r e f l e c t e d i n t h e b r o a d n e s s o f t h e DSC c u r v e . The m e l t i n g o f PEEK i s d e t e c t e d f r o m 300°C t o 356°C, p e a k i n g a t 340°C. and f o r PPS, t h e r a n g e i s f r o m 265° t o 2 9 8 ° C , p e a k i n g a t 282°C. The i n t e g r a t i o n o f t h e s e m e l t i n g peaks y i e l d s a c r u d e e s t i m a t e o f t h e h e a t o f f u s i o n o f t h e p o l y m e r s . A g a i n , j u s t as i n t h e c r y s t a l l i z a t i o n e x o t h e r m c a l c u l a t i o n , t h e same t y p e o f e r r o r s due t o t h e b a s e l i n e a s s u m p t i o n s a r e made. 3 .5 SUMMARY OF DSC WORK DSC measurements o f p o l y ( e t h e r e t h e r k e t o n e ) and p o l y ( p h e n y l e n e s u l f i d e ) e s t a b l i s h e d v a l u e s o f g l a s s t r a n s i t i o n , c r y s t a l l i z a t i o n and - 36 -m e l t i n g p o i n t t e m p e r a t u r e s f o r t h e s e p a r t i c u l a r s a m p l e s . The v a l u e s were w i t h i n t h e r a n g e s f o u n d i n t h e l i t e r a t u r e . E s t i m a t e s o f t h e e n t h a l p i e s o f f u s i o n and o f c r y s t a l l i z a t i o n were a l s o made. The most i m p o r t a n t a s p e c t o f t h i s w o r k was t h a t i t p r o v i d e d a s i m p l e q u a l i t a t i v e way t o d e t e r m i n e t h e t h e r m a l h i s t o r y o f t h e p o l y m e r s a m p l e s : ( i ) Samples c r y s t a l l i z e d t o t h e f u l l e s t e x t e n t show no g l a s s t r a n s i -t i o n o r c r y s t a l l i z a t i o n e x o t h e r m . ( i i ) C o m p l e t e l y amorphous samples e x h i b i t b o t h t h e e v e n t s a b s e n t i n ( i ) . ( i i i ) Samples w h i c h have undergone a n n e a l i n g a t o r j u s t b e l o w t h e Tg show a s h a r p e n d o t h e r m i c s p i k e i m m e d i a t e l y a f t e r t h e g l a s s t r a n s i -t i o n . ( i v ) Samples w h i c h have b e e n a n n e a l e d a t h i g h e r t e m p e r a t u r e s have a r e d u c e d c r y s t a l l i z a t i o n e x o t h e r m . - 37 -4 . HIGH RESOLUTION 1 3 C NMR STUDIES 4 . 1 INTRODUCTION TO CP/MAS NMR The a p p l i c a t i o n o f h i g h r e s o l u t i o n n u c l e a r m a g n e t i c r e s o n a n c e t o t h e s t u d y o f p l a s t i c s began i n t h e l a t e 1 9 5 0 ' s . S o l u t i o n NMR s t u d i e s o f s m a l l m o l e c u l e s were w e l l underway when p o l y m e r c h e m i s t s f i r s t began t o c h a r a c t e r i z e m a c r o m o l e c u l e s b y NMR s p e c t r o s c o p y ; t h e r e s u l t s were s u r -p r i s i n g l y s u c c e s s f u l . However , h i g h r e s o l u t i o n , p o l y m e r s t u d i e s were l i m i t e d t o s o l u t i o n s ( p o l y m e r m e l t s o r p o l y m e r s d i s s o l v e d i n o r g a n i c s o l v e n t s ) u n t i l 1975 when S c h a e f e r and S t e j s k a l ( 4 8 ) made t h e d r a m a t i c b r e a k t h r o u g h t o h i g h r e s o l u t i o n , 1 3 C NMR s p e c t r o s c o p y o f s o l i d s , t h e CP/MAS e x p e r i m e n t . The new e x p e r i m e n t r e q u i r e d p r o t o n d e c o u p l i n g , p r o t o n - c a r b o n c r o s s - p o l a r i z a t i o n , and a t e c h n i q u e dubbed " m a g i c a n g l e s p i n n i n g " . The s p e c t r a were a m a z i n g ; t h e s i g n a l s o f t h e i n d i v i d u a l c a r b o n t y p e s , w h i c h h a d h i t h e r t o b e e n l o s t i n m a s s i v e d i p o l a r and a n i s o -t r o p i c s h i f t b r o a d e n i n g , were now c l e a r l y d i s t i n g u i s h a b l e . The samples f i r s t s t u d i e d b y S c h a e f e r and S t e j s k a l were p o l y ( m e t h y l m e t h a c r y l a t e ) and s o l i d p o l y s t y r e n e . P o l y m e r s were t h e p r i m a r y samples u s e d i n t h e p i o n e e r i n g o f t h e h i g h r e s o l u t i o n t e c h n i q u e . D u r i n g t h e l a s t t e n y e a r s , t h e CP/MAS e x p e r i m e n t has been a p p l i e d t o a w i d e r a n g e o f s o l i d m a t e r i a l : p o l y m e r s o f many t y p e s , wood , c e l l u l o s e , l i g n i n , c o a l s , s o i l s , z e o l i t e s , o r g a n o - m e t a l l i c complexes and v a r i o u s b i o l o g i c a l s y s -t e m s . S y n t h e t i c p o l y m e r s have c o n t i n u e d t o be among t h e most p o p u l a r m a t e r i a l s f o r NMR s t u d i e s . No d o u b t t h e c o n t i n u e d i n t e r e s t i n and a p p l i -- 38 -c a t i o n o f NMR i s due t o t h e i n h e r e n t s u i t a b i l i t y o f t h e i r m a c r o m o l e c u l a r n a t u r e , t h e i r immense c o m m e r c i a l i m p o r t a n c e and t h e numerous t y p e s w h i c h a r e w i d e l y a v a i l a b l e . Many e x t e n s i o n s and m o d i f i c a t i o n s have b e e n made t o t h e o r i g i n a l p r o c e d u r e p r e s e n t e d b y S c h a e f e r and S t e j s k a l : v a r i a b l e c o n t a c t t i m e , s i d e b a n d s u p p r e s s i o n , r e l a x a t i o n t i m e measurement , ' o f f - a n g l e ' , s l o w s p i n n i n g , d o u b l e r e s o n a n c e and 2D e x p e r i m e n t s . A l l o f t h e s e employ t h e CP/MAS t e c h n i q u e , now a r o u t i n e method on many i n s t r u m e n t s . The f i r s t t h r e e o f t h e above e x p e r i m e n t s were u s e d i n t h i s w o r k and w i l l be d i s -c u s s e d s u b s e q u e n t l y i n t h e c h a p t e r . H i g h r e s o l u t i o n , s o l i d s t a t e , 1 3 C NMR i s a v e r y a t t r a c t i v e me thod f o r p o l y m e r s t u d y . I t p r o v i d e s i n f o r m a t i o n a b o u t t h e c h e m i c a l s t r u c t u r e , t h e m o r p h o l o g y and t h e m o l e c u l a r m o t i o n o f t h e s a m p l e , a n d , i n s p e c i a l c a s e s , t h e t a c t i c i t y o f t h e p o l y m e r can a l s o be i n f e r r e d f r o m CP/MAS s p e c t r a ( 4 9 ) . S p e c t r a o f s o l u b l e p o l y m e r s a r e g e n e r a l l y o b t a i n e d i n t h e s o l u t i o n s t a t e b e f o r e c o l l e c t i o n o f a h i g h r e s o l u t i o n s o l i d s p e c t r u m and i t i s u s u a l t h a t t h e c h e m i c a l s h i f t s f o u n d i n s o l u t i o n s p e c t r a a r e q u i t e s i m i l a r t o t h o s e o f t h e s o l i d . D i f f e r e n c e s , when o b s e r v e d , c a n be i n f o r m a t i v e . Fo r e x a m p l e , s o l i d s t a t e e f f e c t s i n a c r y s t a l l i n e m a t e r i a l may cause t h e s p l i t t i n g o f a s i g n a l w h i c h i s f o u n d as a s i n g l e t i n s o l u -t i o n ; atoms e q u i v a l e n t i n s o l u t i o n c a n occupy d i f f e r e n t s i t e s i n t h e l a t t i c e and t h u s e x p e r i e n c e d i f f e r e n t e l e c t r o n i c e n v i r o n m e n t s . L i n e -s h a p e , r e l a x a t i o n and c r o s s - p o l a r i z a t i o n i n v e s t i g a t i o n s o f t h e p o l y m e r s g i v e i n s i g h t i n t o t h e m o r p h o l o g y and t h e m o t i o n a l f r e q u e n c i e s w h i c h o c c u r i n t h e p o l y m e r s y s t e m . The u l t i m a t e g o a l o f t h e s e s t u d i e s i s t o - 39 -c o r r e l a t e t h e m o l e c u l a r dynamics o f t h e m a t e r i a l w i t h i t s m e c h a n i c a l p r o p e r t i e s . T h u s , f o r e x a m p l e , S e f c i k e t a l . ( 5 0 ) have s u g g e s t e d t h a t t h e s h i f t f r o m d u c t i l e t o b r i t t l e i m p a c t f a i l u r e o f p o l y ( e t h y l e n e t e r e p h t h a l a t e ) c a u s e d b y a n n e a l i n g , i s r e l a t e d t o t h e d i s a p p e a r a n c e o f m o l e c u l a r m o t i o n i n t h e m i d - k i l o h e r t z f r e q u e n c y r a n g e . A s e c o n d a r e a o f p o l y m e r s where s o l i d s t a t e NMR y i e l d s u n i q u e and h e l p f u l r e s u l t s , i s t h a t o f p o l y m e r i c b l e n d s . The n a t u r e o f b l e n d c o m p a t i b i l i t y i s one o f c o n s i d e r a b l e i n t e r e s t and i s a l s o o f i n d u s t r i a l c o n c e r n . The u n d e r s t a n d i n g o f p o l y m e r m i s c i b i l i t y w i l l l e a d t o more e f f e c t i v e d e s i g n o f new b l e n d s . I n g e n e r a l , t h e d e g r e e o f b l e n d c o m p a t i -b i l i t y may be a d i f f i c u l t p a r a m e t e r t o d e t e r m i n e as t h e r e s u l t s a p p e a r t o be somewhat d e p e n d e n t upon w h i c h i n v e s t i g a t i v e t e c h n i q u e i s e m p l o y e d . T h e r e a r e two c l a s s i f i c a t i o n s o f b l e n d c o m p a t i b i l i t y : t h e p o l y m e r m i x -t u r e may e x h i b i t ( i ) c o m p l e t e h o m o g e n e i t y o r i t may show ( i i ) p a r t i a l c o m p a t i b i l i t y ( s m a l l r e g i o n s o f one p o l y m e r t y p e a r e f o u n d d i s p e r s e d i n t h e s e c o n d , w i t h m i x i n g o n l y a t t h e r e g i o n b o u n d a r i e s ) . S c h a e f e r e t a l . ( 5 1 ) u s e d t h e CP/MAS t e c h n i q u e s t o s t u d y b l e n d s o f p o l y s t y r e n e and p o l y ( p h e n y l e n e o x i d e ) . By c r o s s - p o l a r i z a t i o n , t h e T ^ s ( r o t a t i n g f rame r e l a x a t i o n t i m e s ) o f t h e p r o t o n s a t t a c h e d t o c a r b o n atoms were m e a s u r e d . Because o f s p i n d i f f u s i o n , t h e p r o t o n T i ^ s a r e v e r y d e p e n d e n t upon t h e i m m e d i a t e m a g n e t i c e n v i r o n m e n t ( w i t h i n a range o f a b o u t 1 n m ) . The p r o -t o n T^pS measured f o r p o l y s t y r e n e were f o u n d t o be q u i t e d i f f e r e n t f r o m t h o s e measured f o r p o l y ( p h e n y l e n e - o x i d e ) . However , t h e p r o t o n T i ^ s o b t a i n e d f o r b l e n d s o f t h e s e two p o l y m e r s c o r r e s p o n d e d t o t h e a v e r a g e d v a l u e s o f t h e i n d i v i d u a l p o l y m e r s . T h e r e f o r e , t h i s ag reemen t i n d i c a t e d an e x t e n s i v e , i f n o t a b s o l u t e l y c o m p l e t e , m i x i n g b e t w e e n t h e two c h a i n s . - 40 -S o l i d s t a t e NMR i s o f p a r t i c u l a r a d v a n t a g e i n t h e s t u d y o f i n t r a c t i b l e p o l y m e r s such as PEEK, PPS o r p o l y i m i d e s , and a l s o f o r t h e r m o s e t t i n g n e t w o r k p o l y m e r s , t h e c u r e d r e s i n s . The e a r l y CP/MAS w o r k o f Gar roway ( 5 2 , 5 3 ) on DGEBA epoxy r e s i n s i s w o r t h y o f n o t e . G e n e r a l l y , t h e s t u d y o f t h e s e m a t e r i a l s i s s e v e r e l y c u r t a i l e d b y t h e f a c t t h a t t h e y a r e i n s o l u b l e , and t h e r e f o r e s o l i d s t a t e CP/MAS NMR i s h i g h l y v a l u e d f o r i t s a b i l i t y t o d e t e r m i n e t h e s t r u c t u r e o f t h e s e m a c r o m o l e c u l e s , as w e l l as p r o v i d i n g i n f o r m a t i o n a b o u t t h e m o r p h o l o g y and m o t i o n o f t h e s y s t e m s . 4.2 SOLID STATE 1 3 C NMR THEORY 4.2.1 The E n e r g y I n t e r a c t i o n s The e n e r g y l e v e l s o f an a t o m i c n u c l e u s o f s p i n 1/2 p l a c e d i n a mag-n e t i c f i e l d a r e d e t e r m i n e d b y a s e r i e s o f i n t e r a c t i o n s : ( i ) t h e Zeeman i n t e r a c t i o n o f t h e m a g n e t i c n u c l e u s w i t h t h e m a g n e t i c f i e l d ( Z ) . ( i i ) t h e I n t e r a c t i o n o f t h e n u c l e a r d i p o l e w i t h t h e d i p o l e s o f any s u r r o u n d i n g m a g n e t i c n u c l e i ( D ) . ( i i i ) t h e i n t e r a c t i o n due t o t h e c h e m i c a l s h i f t a n i s o t r o p y (CSA) , and ( i v ) t h e s c a l a r c o u p l i n g i n t e r a c t i o n ( S C ) . The s p i n H a m i l t o n i a n f o r such a s y s t e m c o u l d t h e n be e x p r e s s e d as f o l l o w s : - 4 1 -H - H Z + H D + H C S + H S C (4.1) 4 . 2 . 1 a The Zeeman I n t e r a c t i o n The Zeeman i n t e r a c t i o n i s t h e p r i n c i p a l one o f t h e above i n t e r a c -t i o n s . G e n e r a l l y , i t has t h e g r e a t e s t m a g n i t u d e , a s t r e n g t h i n t h e o r d e r o f 10^ t o 10^ Hz. I t i s t h e Zeeman i n t e r a c t i o n w h i c h causes t h e e n e r g y o f a m a g n e t i c n u c l e u s ( o f s p i n 1 /2 ) i n a m a g n e t i c f i e l d t o s p l i t i n t o two d i s t i n c t l e v e l s . The d i f f e r e n c e b e t w e e n t h e s e e n e r g y l e v e l s i s 7hH, where 7 i s t h e g y r o m a g n e t i c r a t i o , h i s P l a n c k ' s c o n s t a n t and H i s t h e m a g n e t i c f i e l d s t r e n g t h . The m a g n i t u d e o f t h i s i n t e r a c t i o n i s l i n e a r w i t h t h e f i e l d s t r e n g t h ; as t h e f i e l d i n c r e a s e s so does t h e e n e r g y s e p a -r a t i o n . T h u s , t h e p o p u l a t i o n d i f f e r e n c e a l s o i n c r e a s e s b e t w e e n t h e two l e v e l s . Fo r t h i s r e a s o n a h i g h e r m a g n e t i c f i e l d u s u a l l y r e s u l t s i n a s p e c t r u m o f i m p r o v e d s i g n a l - t o - n o i s e r a t i o . 4 . 2 . 1 b The N u c l e a r D i p o l e I n t e r a c t i o n The d i p o l a r i n t e r a c t i o n a r i s e s when a m a g n e t i c n u c l e u s i s i n t h e p r e s e n c e o f o t h e r n u c l e i w h i c h a l s o have n o n - z e r o s p i n . A m a g n e t i c n u c l e u s , as a d i p o l e , has i t s own l o c a l f i e l d and t h i s f i e l d c o n t r i b u t e s ( e i t h e r p o s t i v e l y o r n e g a t i v e l y ) t o t h e n e t f i e l d e x p e r i e n c e d b y t h e n e i g h b o u r i n g d i p o l e s . The m a g n i t u d e o f t h i s c o n t r i b u t i o n depends upon t h e a n g l e (8) b e t w e e n t h e p r i n c i p a l m a g n e t i c f i e l d , H, and t h e i n t e r -- 42 -d i p o l e v e c t o r , and i s i n v e r s e l y p r o p o r t i o n a l t o t h e cube o f t h e d i s t a n c e 3 j b e t w e e n t h e d i p o l e s ( r j ^ ) • T h u s , t h e c o n t r i b u t i o n ( B z ) o f d i p o l e j t o t h e f i e l d o f d i p o l e k may be w r i t t e n a s : j B z - < 1 - 3 c o sz 0 > ( 4 . 2 ) r 3 k j where fiz i s t h e m a g n e t i c moment and t h e a n g u l a r b r a c k e t s d e n o t e t h e a v e r a g e o v e r m o l e c u l a r m o t i o n . F i g u r e 4 . 1 g i v e s a v e c t o r s c h e m a t i c o f t h i s i n t e r a c t i o n . The f i g u r e shows o n l y one s u c h i n t e r a c t i o n , b u t f o r t h e c o m p l e t e i n t e r a c t i o n , t h e e f f e c t o f a l l t h e d i p o l e s w h i c h s u r r o u n d k must be i n c l u d e d . F i g u r e 4 . 1 : The i n t e r a c t i o n o f two d i p o l a r n u c l e i , j , k i n t h e p r e s e n c e o f a s t r o n g m a g n e t i c f i e l d , B Q . - 43 -I n a r e a l i s t i c c a s e , d i p o l e k w o u l d be o f a 1 3 C n u c l e u s and j , o f a 1 3 p r o t o n . •L- ,C n u c l e i a r e s u f f i c i e n t l y d i l u t e i n n a t u r a l abundance t h a t i n t h e case o f t h e ^ 3 C n u c l e i , t h e 1 3 C d i p o l e i n t e r a c t i o n c a n be i g n o r e d . O n l y t h e C-H d i p o l e i n t e r a c t i o n needs t o be c o n s i d e r e d . The m a g n i t u d e o f t h i s i n t e r a c t i o n c a n be as l a r g e as 10-* Hz ( 4 9 ) . Because each 1 3 C atom i n a s o l i d sample i s i n a u n i q u e m a g n e t i c e n v i r o n m e n t , d e f i n e d b y t h e p o s i t i o n s o f t h e s u r r o u n d i n g p r o t o n d i p o l e s , each e x p e r i e n c e s a s l i g h t l y d i f f e r e n t m a g n e t i c f i e l d and c o r r e s p o n d i n g l y r e s p o n d s t o a d i f f e r e n t r e s o n a n c e f r e q u e n c y . The f i n a l e f f e c t i s t o b r o a d e n g r e a t l y t h e ^ 3 C r e s o n a n c e s i g n a l i n t h e s o l i d . 4 . 2 . 1 c The C h e m i c a l S h i f t A n i s o t r o p y I n t e r a c t i o n The CSA i s due t o t h e s h i e l d i n g o f t h e n u c l e i f r o m t h e e x t e r n a l m a g n e t i c f i e l d b y t h e s u r r o u n d i n g e l e c t r o n s . T h i s i n t e r a c t i o n i s v e r y d e p e n d e n t u p o n t h e c h e m i c a l e n v i r o n m e n t o f t h e n u c l e i and t h e m o l e c u l a r s t r u c t u r e , p a r t i c u l a r l y upon t h e atoms bonded t o t h e o b s e r v e d a t o m . Fo r t h i s r e a s o n , t h e c h e m i c a l s h i f t i s e x c e e d i n g l y u s e f u l as a ' c h e m i c a l d i a g n o s t i c ' t e c h n i q u e . C h e m i c a l s h i f t s a r e c e r t a i n l y a k e y p o i n t i n h i g h r e s o l u t i o n s o l u t i o n s p e c t r o s c o p y . I n s o l i d s t a t e s p e c t r o s c o p y h o w e v e r , t h e c h e m i c a l s h i f t i n t r o d u c e s a p r o b l e m o f l i n e b r o a d e n i n g . I n t h e l i q -u i d s t a t e t h e r a p i d t u m b l i n g o f m o l e c u l e s a v e r a g e s a l l t h e d i r e c t i o n a l dependence o f t h e c h e m i c a l s h i f t b u t i n t h e s o l i d s t a t e t h e e f f e c t o f t h e c h e m i c a l s h i f t a n i s o t r o p y becomes a p p a r e n t . The a r r a n g e m e n t o f t h e e l e c t r o n s a b o u t a n u c l e u s i s n e v e r s p h e r i c a l - 44 -s i n c e i t depends upon t h e n a t u r e and p o s i t i o n o f t h e m o l e c u l a r bonds i n w h i c h t h e e l e c t r o n d i s t r i b u t i o n i s h i g h l y d i r e c t i o n a l . C o n s i d e r , f o r e x a m p l e , t h e e l e c t r o n i c a l l y h i g h l y d i r e c t i o n a l c a r b o n y l b o n d , as shown i n F i g u r e 4 . 2 . The i n t e r a c t i o n o f t h e e l e c t r o n s w i t h t h e n u c l e u s v a r i e s c=o JL Hi O II _ A _ H-F i g u r e 4 . 2 : ( a ) The two e x t r e m e o r i e n t a t i o n s o f t h e bond r e l a t i v e t o t h e a p p l i e d m a g n e t i c f i e l d . ( b ) The c h e m i c a l s h i f t a n i s o t r o p y p a t t e r n a r i s i n g f r o m t h e random d i s t r i b u t i o n s o f o r i e n t a t i o n s i n a p o l y c r y s t a l -l i n e s a m p l e . ( c ) t h e s o l u t i o n s p e c t r u m s h o w i n g an i s o t r o p i c s i g n a l ( 4 9 ) . m a r k e d l y w i t h t h e a n g l e o f t h e b o n d , r e l a t i v e t o t h e p r i n c i p a l f i e l d . The r e s o n a n c e f r e q u e n c y i s a f u n c t i o n o f t h e bond o r i e n t a t i o n w i t h r e s -p e c t t o t h e p r i n c i p a l f i e l d . The o r i e n t a t i o n o f t h e b o n d d e t e r m i n e s t h e s h i e l d i n g f a c t o r a so t h a t t h e r e s o n a n c e c o n d i t i o n o f t h e n u c l e u s i s : " j - r / 2 J B 0 ( l - a j ) (4 -3 ) - 45 -where B Q i s t h e p r i n c i p a l m a g n e t i c f i e l d and trj i s t h e component o f mag-n e t i c s h i e l d i n g w h i c h i s a l i g n e d a l o n g t h e f i e l d d i r e c t i o n . The c h e m i c a l s h i f t v a l u e 6 i s e x p r e s s e d as t h e d i f f e r e n c e i n ppm b e t w e e n »>j and t h e r e s o n a n c e f r e q u e n c y o f some s t a n d a r d m a t e r i a l ( u s u a l l y TMS): " j " "TMS , S = — - x 1 0 6 ( 4 . 4 ) "TMS The v a l u e o f 6 i s l i n e a r l y p r o p o r t i o n a l t o t h e s t r e n g t h o f t h e p r i n -c i p a l m a g n e t i c f i e l d . The s h i f t a n i s o t r o p i e s t y p i c a l l y e x p e r i e n c e d b y 1 3 C atoms i n n e u t r a l s o l i d s i s o f t h e o r d e r o f 200 ppm ( 5 4 ) . 4 . 2 . I d The S c a l a r C o u p l i n g I n t e r a c t i o n The s c a l a r o r s p i n - s p i n c o u p l i n g i n t e r a c t i o n b e t w e e n n u c l e i i s c o n s i d e r a b l y s m a l l e r t h a n t h e o t h e r i n t e r a c t i o n s o f e q u a t i o n 4 . 1 . I t may be n e g l e c t e d i n t h i s t r e a t m e n t o f s o l i d s t a t e NMR. 4 . 2 . 2 The CP/MAS E x p e r i m e n t The a i m o f t h e h i g h r e s o l u t i o n , NMR s p e c t r o s c o p i s t w o r k i n g i n t h e s o l i d s t a t e i s t o m i m i c t h e random m o t i o n s w h i c h a r e c h a r a c t e r i s t i c o f t h e l i q u i d s t a t e . I n l i q u i d s , t h e s e i s o t r o p i c m o t i o n s s e r v e v e r y w e l l t o a v e r a g e o u t t h e d i p o l e - d i p o l e i n t e r a c t i o n s and t h e c h e m i c a l s h i f t - 46 -a n i s o t r o p y w h i c h , i n t h e s o l i d s t a t e , a r e t h e s o u r c e o f e x t r e m e l i n e b r o a d e n i n g . T h e r e a r e e s s e n t i a l l y t h r e e components o f t h e CP/MAS e x p e r i m e n t : ( i ) c r o s s - p o l a r i z a t i o n w h i c h a l l e v i a t e s t h e p r o b l e m s o f t h e weak s i g n a l f r o m t h e d i l u t e 1 3 C n u c l e i and a l s o t h e l o n g r e l a x a t i o n t i m e o f t h e c a r b o n n u c l e i , and ( i i ) h i g h power d e c o u p l i n g and ( i i i ) mag ic a n g l e s p i n n i n g , b o t h o f w h i c h r e d u c e t h e l i n e b r o a d e n i n g i n t e r a c t i o n s . 4 . 2 . 2 a C r o s s - P o l a r i z a t i o n The n a t u r a l abundance o f t h e 1 3 C n u c l e u s i s 1 . 1 1 % , one h u n d r e d t h t h a t o f t h e p r o t o n . Such a l o w abundance i s a g r e a t a d v a n t a g e because i t a s s u r e s two 1 3 C n u c l e i a r e r a r e l y i n so c l o s e a p r o x i m i t y as t o e x h i b i t any h o m o n u c l e a r d i p o l e e f f e c t . However , t h e n a t u r a l abundance i s a l s o a d i s a d v a n t a g e because i t l e a d s t o a v e r y l o w s e n s i t i v i t y f o r c a r b o n NMR. The 1 3 C n u c l e u s has o t h e r d rawbacks v i s a v i s t h e p r o t o n 6 f r o m t h e p o i n t o f v i e w o f NMR. The f i r s t i s t h e m a g n e t i c moment. The m a g n e t i z a -t i o n i s l i n e a r l y d e p e n d e n t on t h e moment and s i n c e t h e m a g n e t i c moment o f t h e J--'C n u c l e u s i s a q u a r t e r o f t h e p r o t o n moment, t h e s e n s i t i v i t y of c a r b o n NMR r e l a t i v e t o p r o t o n s p e c t r o s c o p y i s f u r t h e r r e d u c e d . The s e c -ond i s t h a t t h e s p i n - l a t t i c e r e l a x a t i o n r a t e o f t h e 1 3 C n u c l e u s i s c o n -s i d e r a b l y s l o w e r t h a n t h e p r o t o n r e l a x a t i o n . Fo r c a r b o n , t h e T^ ( s p i n -l a t t i c e r e l a x a t i o n t i m e ) i s t y p i c a l l y b e t w e e n 10 and 100 t i m e s l o n g e r t h a n f o r a p r o t o n i n t h e same m o l e c u l e (55). A l o n g r e l a x a t i o n t i m e i s i n e f f i c i e n t f o r c o l l e c t i o n o f s p e c t r a because i t n e c e s s i t a t e s t h e use of - 47 -l o n g r e c o v e r y t i m e s b e t w e e n p u l s e s e q u e n c e s . A l l t h e s e d i f f i c u l t i e s a r e e l i m i n a t e d b y c r o s s - p o l a r i z a t i o n . The essence o f t h e c r o s s - p o l a r i z a t i o n e x p e r i m e n t i s t h e t r a n s f e r o f m a g n e t i -z a t i o n f r o m t h e a b u n d a n t p r o t o n s p i n s y s t e m t o t h e l e s s a b u n d a n t c a r b o n s y s t e m . Fo r t h e t r a n s f e r t o o c c u r , t h e e n e r g i e s o f t h e two s p i n sys tems must be t h e same. T h i s i s a c h i e v e d b y m a t c h i n g t h e e n e r g i e s o f t h e ^ 3 C and t h e 1-H n u c l e i , l o c k i n g t h e s p i n s t o each o t h e r i n t h e x ' , y ' r e f e r -ence p l a n e . T h i s m a t c h i n g i s r e f e r r e d t o as t h e Har tmann-Hahn c o n d i t i o n ( 5 6 ) and m a t h e m a t i c a l l y , i t i s s i m p l y s t a t e d : H - 7 H ( 4 . 5 ) L H  lH 1 3 C 1 3 C where 7 and 7 a r e t h e r e s p e c t i v e g y r o m a g n e t i c r a t i o s and H and X H 1 3 C -^H H r e p r e s e n t t h e a p p r o p r i a t e l o c k i n g f i e l d a l o n g t h e y ' a x i s . S i n c e 1 3 C 7 / 7 - 4 / 1 , one may r e a d i l y see t h a t t h e l o c k i n g f i e l d o f t h e c a r -X H 1 3 C bons mus t be 4 t i m e s t h a t o f t h e h y d r o g e n l o c k i n g f i e l d . I n t h i s m a t c h e d c o n d i t i o n , t h e e n e r g y r e q u i r e d f o r t h e p r o t o n s p i n - f l i p i s i d e n t i c a l t o 1 3 t h a t f o r a C s p i n - f l i p . The d i l u t e s y s t e m a d o p t s t h e more f a v o u r a b l e s p i n d i s t r i b u t i o n o f t h e p r o t o n s , b u t t h e much l a r g e r p r o t o n s y s t e m i s l i t t l e a f f e c t e d b y t h e c a r b o n s y s t e m . F i g u r e 4 . 3 i l l u s t r a t e s t h e p r o c e d u r e f o r t h e c r o s s - p o l a r i z a t i o n e x p e r i m e n t : ( a ) shows t h e i n i t i a l p r o t o n m a g n e t i z a t i o n a l i g n e d a l o n g H 0 , t h e p r i n c i p a l m a g n e t i c f i e l d b e f o r e t h e a p p l i c a t i o n o f a 90° p u l s e a l o n g t h e x ' d i r e c t i o n w h i c h t i p s t h e m a g n e t i z a t i o n t o t h e y ' a x i s , ( b ) and ( c ) - 48 -a b e d Figure 4 . 3 : The cross-polarization experiment, showing the behaviour of the and 1 3C magnetization vectors and the corresponding pulse sequence ( 5 7 ) . (a) i n i t i a l proton magnetization along Z. (b) application of the spin locking pulse. (c) increase in 1 3C magnetization. (d) acquire 1 3C FID. (e) recycle time. - 49 -show t h e a p p l i c a t i o n o f t h e Har tmann-Hahn m a t c h e d " r . f . p u l s e t o l o c k t h e p r o t o n and c a r b o n m a g n e t i z a t i o n a l o n g t h e y ' a x i s . D u r i n g t h i s t i m e , when t h e s p i n sys tems a r e l o c k e d , t h e a m p l i t u d e o f t h e c a r b o n m a g n e t i z a -t i o n b u i l d s up b y s p i n e n e r g y t r a n s f e r f r o m t h e p r o t o n s , f r o m ( b ) t o ( c ) . A f t e r t h e ^ 3 C m a g n e t i z a t i o n has r e a c h e d i t s a p p r o x i m a t e maximum, t h e c a r b o n s p i n l o c k i n g p u l s e i s removed , ( d ) , t o a l l o w a c q u i s i t i o n o f t h e decay o f t h e c a r b o n m a g n e t i z a t i o n . The d e l a y t i m e , ( e ) , d u r i n g w h i c h no p u l s e s a r e a p p l i e d t o e i t h e r s p i n s y s t e m , p e r m i t s r e l a x a t i o n o f t h e s p i n s t o t h e i r e q u i l i b r i u m v a l u e s b e f o r e r e p e t i t i o n o f t h e s e q u e n c e . The d u r a t i o n o f t h e c a r b o n s p i n l o c k i n g p u l s e i s c a l l e d t h e c o n t a c t t i m e , and t h e op t imum l e n g t h o f t h e c o n t a c t t i m e depends u p o n t h e r a t e o f t h e t r a n s f e r o f t h e m a g n e t i z a t i o n f r o m t h e p r o t o n t o t h e c a r b o n s p i n s y s t e m s . 4 . 2 . 2 b D i p o l a r D e c o u p l i n g The d i p o l e - d i p o l e i n t e r a c t i o n i s a m a j o r b r o a d e n i n g f a c t o r o f s o l i d s t a t e NMR. I n t h e e x p e r i m e n t , i t i s t h e h e t e r o n u c l e a r d i p o l e i n t e r -a c t i o n b e t w e e n t h e p r o t o n and t h e 1 3 C d i p o l e s w h i c h causes t h e b r o a d e n -i n g . D i p o l a r d e c o u p l i n g i s s u c c e s s f u l l y emp loyed t o e l i m i n a t e t h i s t y p e o f b r o a d e n i n g . A s t r o n g d e c o u p l i n g f i e l d i s a p p l i e d a t t h e f r e q u e n c y o f t h e p r o t o n r e s o n a n c e , c a u s i n g t r a n s i t i o n s b e t w e e n t h e p r o t o n s p i n s t a t e s . The i n d u c e d s p i n f l i p p i n g i s s u f f i c i e n t l y r a p i d t h a t t h e d i p o l e i s a v e r a g e d t o z e r o and t h e r e i s no e n e r g y i n t e r a c t i o n w i t h t h e d i p o l e . - 50 -4 . 2 . 2 c M a g i c A n g l e S p i n n i n g Mag ic a n g l e sample s p i n n i n g removes t h e l i n e b r o a d e n i n g due t o t h e c h e m i c a l s h i f t a n i s o t r o p y as w e l l as r e s i d u a l d i p o l e c o u p l i n g . R e c a l l t h a t t h e CSA depends on t h e c h e m i c a l s h i e l d i n g f a c t o r , ozz, i n t h e d i r e c t i o n o f t h e p r i n c i p a l m a g n e t i c f i e l d , B Q . T h i s s h i e l d i n g c a n be r e l a t e d t o s h i e l d i n g a l o n g t h e p r i n c i p a l axes o f t h e m o l e c u l e b y : 3 °zz " I a i c o s 2  e± ( 4 . 6 ) i - 1 where i s t h e n u c l e a r s h i e l d i n g when B Q p o i n t s a l o n g t h e i t h a x i s , and 6^ i s t h e a n g l e b e t w e e n B Q and t h e a x i s . Fo r e x a m p l e , i n a m o l e c u l e w i t h a x i a l s y m m e t r y , l e t er^ = a 2 •* o± and a3 - a ; azz c a n be e x p r e s s e d a s : azz — c o s2 ^ + aj_ s i n 2 ^ ( 4 . 7 ) where # i s t h e a n g l e b e t w e e n B Q and a ( | . CT2Z c a n a l s o be w r i t t e n as t h e sum o f a n i s o t r o p i c and an a n i s o t r o p i c component : a z z = <a> + aa ( 4 . 8 ) where a i s t h e i s o t r o p i c s h i e l d i n g , t h e same as i s o b s e r v e d i n t h e l i q -u i d s p e c t r a , and a a i s t h e a n i s o t r o p i c p a r t w h i c h may be e x p r e s s e d a s : a 3 - 1/3 (a - aL) ( 3 c o s2 ^ - 1) ( 4 . 9 ) - 51 -T h i s e x p r e s s i o n i n d i c a t e s t h e dependence o f t h e a n i s o t r o p i c s h i f t on t h e t e r m ( 3 c o s 2 # - l ) . T h u s , i f t h i s t e r m were s e t t o z e r o , t h a t i s i f <j> were 5 4 . 7 ° , t h e a n i s o t r o p i c c o n t r i b u t i o n t o t h e CSA w o u l d d i s a p p e a r . R a p i d r o t a t i o n o f t h e sample a b o u t an a x i s o f 5 4 . 7 ° ( t h e mag ic a n g l e ) e f f e c -t i v e l y a v e r a g e s e v e r y a n g l e <j> t o 5 4 . 7 ° . F i g u r e 4 . 4 h e l p s t o i l l u s t r a t e t h i s c o n c e p t . F i g u r e 4 . 4 : The t i m e a v e r a g e d r e s u l t o f a v e c t o r AB s p i n n i n g a b o u t a x i s R (55). T h u s , t h e c h e m i c a l s h i f t o b s e r v e d i s ' m a g i c a l l y ' r e d u c e d t o o n l y t h e i s o t r o p i c s h i f t and t h e s o l i d s t a t e s p e c t r u m t h e n r e s e m b l e s a s o l u -t i o n s p e c t r u m . Fo r c o m p l e t e r e m o v a l o f t h e a n i s o t r o p i c CSA, t h e s p i n n i n g r a t e usr mus t e x c e e d t h e w i d t h o f t h e CSA powder p a t t e r n . Such s p i n n i n g r a t e s a r e o f t e n n o t p r a c t i c a l l y p o s s i b l e . However , r a t e s o f l e s s t h a n z R Y X - 52 -h a l f t h a t v a l u e w o r k q u i t e w e l l t o n a r r o w t h e l i n e w i d t h s , t h o u g h ' s p i n -n i n g s i d e b a n d ' s i g n a l s f l a n k t h e p r i n c i p a l s i g n a l a t f r e q u e n c y s e p a r a -t i o n s o f ^ s r . 4 . 2 . 3 V a r i a t i o n s on t h e CP/MAS E x p e r i m e n t A h o s t o f NMR e x p e r i m e n t s have b e e n d e v i s e d w h i c h a r e b a s e d upon t h e CP/MAS t e c h n i q u e . Two emp loyed i n t h i s w o r k a r e d i p o l a r d e p h a s i n g and v a r i a b l e c o n t a c t t i m e . 4 . 2 . 3 a D i p o l a r D e p h a s i n g The p r o c e d u r e o f d i p o l a r d e p h a s i n g was d e v e l o p e d b y O p e l l a and F r e y i n 1979 ( 5 9 ) ; t h e p u r p o s e o f t h e e x p e r i m e n t i s t h e d i s t i n c t i o n o f t h e p r o t o n a t e d c a r b o n s i g n a l s f r o m t h e n o n - p r o t o n a t e d . The p u l s e sequence d i f f e r s f r o m t h a t o f t h e c o n v e n t i o n a l CP/MAS e x p e r i m e n t i n one r e s p e c t , a d e l a y w i t h o u t p r o t o n d e c o u p l i n g i s i n t r o d u c e d i m m e d i a t e l y b e f o r e t h e s p e c t r a l a c q u i s i t i o n ( F i g u r e 4 . 5 ) . The r e s u l t i s t h a t t h e p r o t o n a t e d c a r b o n s i g n a l s a r e s u r p r e s s e d . As p r e v i o u s l y s t a t e d , t h e d i p o l a r i n t e r a c t i o n i s i n v e r s e l y d e p e n d e n t upon 1 / r 3 , d u r i n g t h e d e l a y w i t h o u t d e c o u p l i n g . The s t r o n g d i p o l e - d i p o l e e f f e c t on c a r b o n s bonded t o t h e p r o t o n s causes r a p i d d e p h a s i n g o f t h e c a r b o n m a g n e t i z a t i o n . The e f f e c t i s much weaker on t h e n o n - p r o t o n a t e d c a r b o n s , where t h e c a r b o n and h y d r o g e n n u c l e i a r e s u f f i c i e n t l y f a r - 53 -90° PULSE I F i g u r e 4 . 5 : The d i p o l a r d e p h a s i n g p u l s e sequence s h o v i n g t h e d e l a y b e f o r e a c q u i s i t i o n . a p a r t , because t h e q u a t e r n a r y c a r b o n s e x p e r i e n c e v e r y l i t t l e d e p h a s i n g b y d i p o l a r i n t e r a c t i o n s . I n a d d i t i o n t o i n t e r n u c l e a r d i s t a n c e , d i p o l a r i n t e r a c t i o n i s r e d u c e d b y m o l e c u l a r m o t i o n . I t i s f o r t h i s r e a s o n t h a t s i g n a l s f r o m t h e c a r b o n s o f m e t h y l g r o u p s p r o n e t o r o t a t i o n , w i l l o f t e n a p p e a r i n t h e d i p o l a r dephased s p e c t r u m . 4 . 2 . 3 c The V a r i a b l e C o n t a c t Time E x p e r i m e n t The v a r i a b l e c o n t a c t t i m e e x p e r i m e n t i s s i m i l i a r t o t h e d i p o l a r - 54 -d e p h a s i n g e x p e r i m e n t i n t h a t i t p r o v i d e s i n f o r m a t i o n a b o u t t h e p r o t o n a -t i o n and i m m e d i a t e e n v i r o n m e n t o f t h e c a r b o n n u c l e i . I n t h e c r o s s -p o l a r i z a t i o n t e c h n i q u e , t h e r a t e o f 1 3 C m a g n e t i z a t i o n i s d e p e n d e n t on t h e s p i n - l a t t i c e r e l a x a t i o n t i m e i n t h e r o t a t i n g f r a m e ( T ^ ^ ) o f t h e p r o t o n s . The e x p e r i m e n t a l p r o c e d u r e i n v o l v e s c o l l e c t i n g a s e r i e s o f CP/MAS s p e c t r a , each w i t h a d i f f e r e n t c o n t a c t t i m e . From t h e s e s p e c t r a , p l o t s o f i n t e n s i t y v e r s u s c o n t a c t t i m e a r e o b t a i n e d , one p l o t f o r each t y p e o f c a r b o n a tom i n t h e m o l e c u l e . 4 . 3 EXPERIMENTAL The h i g h r e s o l u t i o n CP/MAS e x p e r i m e n t s were c a r r i e d o u t u s i n g a B r u k e r CXP 200 MHz p u l s e d F o u r i e r t r a n s f o r m s p e c t r o m e t e r , e q u i p p e d w i t h t h e a p p r o p r i a t e l y t u n e d p r o b e c a p a b l e o f mag ic a n g l e sample r o t a t i o n . The o p e r a t i n g f r e q u e n c i e s were 200 MHz f o r p r o t o n r e s o n a n c e and 5 0 . 3 MHz f o r 1 3 C n u c l e i . The c o n v e n t i o n a l CP/MAS s p e c t r a were o b t a i n e d u s i n g t h e r o u t i n e p u l s e sequence r e p o r t e d i n t h e l i t e r a t u r e ( 5 4 ) . (The p u l s e sequence i s a l s o shown i n F i g u r e 4 . 3 and A p p e n d i x I . ) 4 . 3 . 1 R o t o r s The r o t o r s u s e d i n t h i s w o r k were t h e Beams-Andrew t y p e made o f D e l r i n o r o f b o r o n n i t r i d e . The s t r o n g r e s o n a n c e s i g n a l o f D e l r i n , - 55 -p o l y ( o x y m e t h y l e n e ) , a t 8 8 . 9 ppm f r o m TMS was u s e d as t h e r e f e r e n c e s i g -n a l f o r t h e CP/MAS w o r k . The b o r o n n i t r i d e r o t o r has t h e a e s t h e t i c a d v a n t a g e o f h a v i n g no c a r b o n s i g n a l . The powdered c r y s t a l l i n e samples o f PPS and PEEK were p a c k e d f i r m l y i n t o t h e r o t o r s . The PEEK f i l m was punched i n t o d i s k s o f t h e same d iame-t e r as t h e i n s i d e o f t h e r o t o r s , and a s t a c k o f s u c h d i s k s was made t o f i l l t h e r o t o r . The s m a l l amorphous PPS p e l l e t s were p a c k e d c l o s e l y i n t o t h e r o t o r and KBr u s e d t o f i l l i n t h e gaps b e t w e e n t h e p e l l e t s . 4.3.2 S e t - u p A l l t h e s p e c t r a were o b t a i n e d w i t h t h e B r u k e r s o f t w a r e CXPNMR programme. L i q u i d benzene was u s e d f o r t h e i n i t i a l s p e c t r o m e t e r s e t - u p and t u n i n g o f t h e c a r b o n and p r o t o n t r a n s m i t t e r s . Magnet s h i m m i n g was a c c o m p l i s h e d b y m a x i m i z i n g t h e o f f - r e s o n a n c e f r e e i n d u c t i o n decay o f t h e benzene p r o t o n s u n t i l t h e F o u r i e r t r a n s f o r m o f t h e F ID y i e l d e d a l i n e -w i d t h o f a b o u t 3 0 - 4 0 Hz a t h a l f h e i g h t . The 180" p r o t o n p u l s e l e n g t h was e s t a b l i s h e d b y a d j u s t i n g t h e p r o t o n g a i n o f t h e t r a n s m i t t e r u n t i l t h e F ID a p p e a r e d l e v e l w i t h t h e b a s e l i n e . The 90° p u l s e l e n g t h was t h e n assumed t o be h a l f t h e v a l u e o f t h e 180° p u l s e l e n g t h . The 9 0 " p u l s e l e n g t h f o r t h e s e e x p e r i m e n t s was 6 . The c o r r e c t s e t t i n g f o r t h e Har tmann-Hahn c o n d i t i o n was a c h i e v e d u s i n g a sample o f adamantane. E x t e r n a l f i e l d s o f 40G f o r t h e and 10G f o r t h e p r o t o n s were r e q u i r e d f o r s p i n - l o c k i n g . The mag ic a n g l e a d j u s t m e n t was made u s i n g p o w d e r e d K B r , f o l l o w i n g - 56 -t h e m e t h o d o f F r y e and M a c i e l ( 6 0 ) . 4 . 3 . 3 P u l s e p r o g r a m s A p p e n d i x I c o n t a i n s t h e p u l s e p r o g r a m s and g i v e s t h e p u l s e l e n g t h s and d e l a y t i m e s f o r each t y p e o f e x p e r i m e n t as p e r f o r m e d : ( i ) t h e c o n -v e n t i o n a l CP/MAS e x p e r i m e n t , ( i i ) t h e d i p o l a r d e p h a s i n g and ( i i i ) t h e v a r i a b l e c o n t a c t t i m e e x p e r i m e n t s . A l l programmes u s e d phase a l t e r n a t i o n t o e l i m i n a t e b a s e l i n e and i n t e n s i t y a r t i f a c t s . The number o f t r a n s i e n t s a c c u m u l a t e d v a r i e d w i t h t h e d e s i r e d s i g -n a l - t o - n o i s e r a t i o and t h e e x p e r i m e n t a l c o n d i t i o n s . The f r e e i n d u c t i o n decays ( F I D s ) were c o l l e c t e d i n b l o c k s o f s i z e 2K. The F ID was z e r o f i l l e d t o 32K and t h e b a s e l i n e c o r r e c t and e x p o n e n t i a l m u l t i p l i c a t i o n r o u t i n e s were a p p l i e d . F o u r i e r t r a n s f o r m a t i o n o f t h e F ID t o t h e f r e q u e n c y doma in was t h e n p e r f o r m e d . The r e s u l t i n g s p e c t r u m was t h e n p h a s e d w i t h b o t h z e r o and f i r s t o r d e r p h a s i n g . 4 . 4 RESULTS AND DISCUSSION 4 . 4 . 1 P o l y ( p h e n y l e n e s u l f i d e ) The s p e c t r u m o f p o l y ( p h e n y l e n e s u l f i d e ) , shown i n F i g u r e 4 . 6 , i s q u i t e s t r a i g h t f o r w a r d . PPS c o n t a i n s o n l y two m a g n e t i c a l l y d i s t i n c t i v e c a r b o n a t o m s , t h e d e c o u p l e d s p e c t r u m shows o n l y two p e a k s , a t 1 2 9 . 1 ppm - 57 -and a t 1 3 1 . 5 ppm. The s p e c t r u m I s t h e s i m p l e , c o n v e n t i o n a l CP/MAS s p e c t r u m o f c r y s t a l l i n e PPS. The s p i n n i n g s i d e b a n d s were u s e d t o measure t h e s p i n n i n g r a t e o f 3 . 0 kHz . The a s s i g n m e n t o f t h e two s p e c t r a l peaks was made w i t h t h e a i d o f a d i p o l a r d e p h a s i n g e x p e r i m e n t . F i g u r e 4 . 7 ( a ) shows t h e n o r m a l CP/MAS s p e c t r u m o f c r y s t a l l i n e PPS and t h e s p e c t r u m i n 4 . 7 ( b ) , w i t h d i p o l a r d e p h a s i n g . B e f o r e d a t a a c q u i s t i o n , a d e l a y o f 40 (is was i n t r o d u c e d , w i t h o u t s p i n - l o c k i n g . D u r i n g t h i s d e p h a s i n g t i m e when t h e d e c o u p l e r i s t u r n e d o f f , t h e r e l a x a t i o n o f t h e p r o t o n a t e d c a r b o n s o c c u r s . The s i g n a l o f t h e s e c a r b o n s i s seen t o be s i g n i f i c a n t l y a t t e n u a t e d i n t h e dephased s p e c t r u m , w h i l e , t h e q u a t e r n a r y c a r b o n s w h i c h have no e f f i c i e n t r e l a x -a t i o n p a t h w a y s , show e s s e n t i a l l y no d e c r e a s e o f i n t e n s i t y . T h i s i n d i -c a t e s c o n c l u s i v e l y t h a t t h e peak a t 1 3 1 . 5 ppm i s due t o t h e q u a t e r n a r y c a r b o n s o f PPS and t h a t t h e peak a t 1 2 9 . 1 ppm i s c o r r e c t l y a s s i g n e d t o t h e p r o t o n a t e d c a r b o n s . -A F i g u r e 4 . 6 : S o l i d s t a t e CP/MAS s p e c t r u m o f c r y s t a l l i n e PPS s h o w i n g s p i n n i n g s i d e b a n d s ( * ) . - 58 -1 2 F i g u r e 4 . 7 : ( a ) The r e p e a t i n g u n i t o f PPS. ( b ) The c o n v e n t i o n a l CP/MAS s p e c t r u m o f c r y s t a l l i n e PPS. ( c ) The d i p o l a r dephased s p e c t r u m o f c r y s t a l l i n e PPS ( d e l a y - 40 / i s ) . F i g u r e 4 . 8 ( a ) shows t h e h i g h r e s o l u t i o n s p e c t r u m o f t h e amorphous PPS c o m p o s i t e . I t i s c o n s i d e r a b l y b r o a d e r t h a n t h e s p e c t r u m o f c r y s t a l -l i n e PPS. A l i n e w i d t h c o m p a r i s o n was made b y m e a s u r i n g t h e w i d t h s o f t h r e e PPS g l a s s c o m p o s i t e samples ( F i g u r e 4 . 8 a , b , c ) and t h e c r y s t a l l i n e powder ( F i g u r e 4 . 8 d ) . The f i r s t sample ( a ) , assumed t o be f u l l y amor-p h o u s , showed a l i n e w i d t h o f 15 ppm. Sample ( c ) was a n n e a l e d above t h e T c and e x h i b i t e d no c r y s t a l l i z a t i o n e x o t h e r m i n a DSC s c a n ; t h e s p e c t r a l w i d t h o f t h i s sample was 8 . 9 ppm. The two d i s t i n c t c r y s t a l l i n e peaks a r e c l e a r l y s e e n . The s e c o n d f o r m ( b ) was o f i n t e r m e d i a t e c r y s t a l l i n i t y , p r e p a r e d b y a n n e a l i n g j u s t above t h e g l a s s t r a n s i t i o n t e m p e r a t u r e f o r a l i m i t e d t i m e . The A H C o f t h i s sample was 4 . 7 J / g , w h i c h i s s l i g h t l y l e s s - 59 -t h a n h a l f o f t h e c y s t a l l i z a t i o n e x o t h e r m o f t h e f u l l y amorphous PPS. The l i n e w i d t h o f t h i s t h i r d sample was f o u n d t o be 1 1 . 4 ppm t h e a p p r o x i m a t e a v e r a g e o f t h e w i d t h s o f t h e o t h e r two f o r m s . The PPS v i r g i n r e s i n ( d ) has t h e h i g h e s t c r y s t a l l i n i t y , i n t h e s p e c t r u m o f t h i s powdered sample t h e two peak w i d t h s were d i s t i n g u i s h i b l e a t h a l f h e i g h t : 1 .45 ppm f o r t h e l i n e a t 1 3 1 . 5 ppm and 2 . 3 3 ppm f o r t h e l i n e a t 1 2 9 . 1 ppm. C l e a r l y , l i n e w i d t h i s a f u n c t i o n o f c r y s t a l l i n i t y . F i g u r e 4 . 8 : S o l i d s t a t e CP/MAS s p e c t r a o f PPS: ( a ) amorphous ( b ) and ( c ) i n t e r m e d i a t e c r y s t a l l i n t i e s ( d ) f u l l y c r y s t a l l i n e p o w d e r . A t f i r s t g l a n c e , t h i s p a t t e r n o f l i n e w i d t h a p p e a r s c o n t r a r y t o w h a t i s e x p e c t e d . The amorphous sample i s c a p a b l e o f g r e a t e r m o l e c u l a r - 60 -m o t i o n and t h u s t h e a rgumen t o f Veeman e t a l . ( 6 1 ) , f r o m r e s e a r c h on p o l y ( o x y m e t h y l e n e ) , m i g h t be c o n v i n c i n g l y made: " T h e n i t seems a n a t u r a l a s s u m p t i o n t h a t t h e n a r r o w l i n e . . . i s due t o t h e amorphous m a t e r i a l and t h a t t h e b r o a d s t r u c t u r e i s a c h e m i c a l s h i f t a n i s o t r o p y b r o a d e n e d l i n e f r o m t h e c r y s t a l l i n e r e g i o n s i n t h e s a m p l e . The re i s so much m o t i o n i n t h e amorphous m a t e r i a l t h a t t h e c h e m i c a l s h i f t a n i s o t r o p y i s l a r g e l y , b u t n o t c o m p l e t e l y , a v e r a g e d o u t . " However s u b s e q u e n t w o r k on s e m i - c r y s t a l l i n e p o l y m e r s , f o r e x a m p l e , t h e s t u d y o f p o l y ( e t h y l e n e t e r e p h t h a l a t e ) b y S c h a e f e r e t a l . ( 5 0 ) and t h e s t u d y o f Bunn e t a l . ( 6 2 ) o n p o l y p r o p y l e n e , i n d i c a t e t h a t i t i s t h e amorphous p o l y m e r w h i c h e x h i b i t s t h e w i d e s t l i n e s . Two f a c t o r s may be r e s p o n s i b l e f o r b r o a d e n e d l i n e s . The most p r e v a l e n t i s h e t e r o g e n e o u s b r o a d e n i n g due t o t h e d i s t r i b u t i o n o f i s o t r o p i c c h e m i c a l s h i f t s i n t h e s a m p l e . I n t h e amorphous PPS t h e r e i s a much g r e a t e r r a n g e o f p o s i t i o n s a v a i l a b l e t o t h e c a r b o n atoms because t h e m o r p h o l o g y i s l e s s o r d e r e d t h a n i n t h e c r y s t a l l i n e s a m p l e . Homogeneous b r o a d e n i n g may a l s o be a f a c t o r . I t comes a b o u t when t h e m o l e c u l a r m o t i o n s o f t h e p o l y m e r " a r e d e s c r i b e d b y a n e f f e c t i v e a u t o c o r r e l a t i o n f r e q u e n c y c o m p a r a b l e t o t h e d e c o u p l i n g f i e l d " ( 5 0 ) . I n a d d i t i o n t o t h e l i n e w i d t h , t h e l i n e - s h a p e o f t h e s e PPS s p e c t r a i s a l s o i n f o r m a t i v e . The l i n e - s h a p e s s u g g e s t a s u p e r p o s i t i o n o f t h e b r o a d amorphous s i g n a l on t h e n a r r o w d o u b l e t o f t h e c r y s t a l l i n e compo-n e n t . T h i s t h e o r y i s s u p p o r t e d b y t h e f i n d i n g o f s i m i l i a r f e a t u r e s i n o t h e r p o l y m e r s y s t e m s , n o t a b l y t h e w o r k o f D e c h t e r ( 6 3 ) on p o l y e t h y l e n e o x i d e and t h e w o r k o f F y f e e t a l . ( 6 4 ) on p o l y e t h y l e n e . C o n t a c t t i m e , as w e l l as sample c r y s t a l l i n i t y , p l a y s a r o l e i n t h e - 61 -r e l a t i v e a p p e a r a n c e o f t h e two components i n t h e s p e c t r a . S i n c e t h e amorphous n u c l e i have f a s t e r r o t a t i o n f rame r e l a x a t i o n r a t e s , s p e c t r a o b t a i n e d u s i n g s h o r t e r c o n t a c t t i m e s w i l l d i s p l a y g r e a t e r amorphous n a t u r e . Because o f t h i s , t h e p e r c e n t c r y s t a l l i n i t y o f t h e sample can n o t be o b t a i n e d b y s i m p l e d e t e r m i n a t i o n o f t h e p r o p o r t i o n s o f t h e two compo-n e n t s i n t h e s p e c t r u m . A c o m p l e t e u n d e r s t a n d i n g o f T ^ b e h a v i o u r o f t h e s y s t e m i s n e c e s s a r y i n o r d e r t o make r e l i a b l e e s t i m a t e s o f t h e d e g r e e o f c r y s t a l l i n i t y . 4 . 4 . 2 P o l y ( e t h e r e t h e r k e t o n e ) The h i g h r e s o l u t i o n ^ 3 C s p e c t r u m o f PEEK i s c o n s i d e r a b l y more com-p l e x t h a n t h a t o f PPS. The r e p e a t i n g u n i t o f PEEK h a s s e v e n m a g n e t i c a l l y i n e q u i v a l e n t c a r b o n a t o m s , as shown i n F i g u r e 4 . 9 ( a ) . The consequence o f t h i s l a r g e r r e p e a t i n g u n i t i s t h a t t h e a s s i g n m e n t o f t h e s p e c t r u m was a f a r g r e a t e r c h a l l e n g e f o r PEEK t h a n f o r PPS. I n f a c t , t h e a s s i g n m e n t made i n t h i s w o r k d i f f e r s f r o m t h a t w h i c h was p r e v i o u s l y r e p o r t e d i n t h e l i t e r a t u r e ( 2 4 ) . F i g u r e 4 . 9 ( b ) shows t h e c o n v e n t i o n a l h i g h r e s o l u t i o n , CP/MAS s p e c -t r u m o f c r y s t a l l i n e PEEK powder . The f i n a l a s s i g n m e n t o f t h e peaks i s a l s o marked i n t h e f i g u r e . I n o r d e r t o make t h i s a s s i g n m e n t two f u r t h e r t y p e s o f s p e c t r a were c o l l e c t e d : t h e d i p o l a r dephased s p e c t r u m and a s e t o f s p e c t r a h a v i n g v a r i e d c o n t a c t t i m e s . The v a r i a b l e c o n t a c t t i m e s p e c t r a s e r v e d t o c o n -f i r m t h e r e s u l t s o f t h e d i p o l a r d e p h a s i n g e x p e r i m e n t . - 62 -4 3 o - < u v - o ^ ( n > - c — o n i—| i i— i — r— |— i— i— i— i— |— r 250 200 150 i | i i i i | i i 100 50 - j — r - i — 0 PPM Figure 4 . 9 : (a) The repeating unit of PEEK. (b) The solid state CP/MAS spectrum of crystalline PEEK. (* denotes the signal due to delrin). C o m p a r i s o n o f t h e dephased s p e c t r u m w i t h t h e c o n v e n t i o n a l one i n d i -c a t e s a r e d u c t i o n i n t h e peak a t 1 3 2 . 2 ppm and t h e d i s a p p e a r a n c e o f t h e peak a t 1 1 9 . 0 ppm. (See F i g u r e 4 . 1 0 . ) These peaks were a s s i g n e d t o t h e p r o t o n a t e d c a r b o n s : C - 3 , C-4 and C-7 . The i n t e n s i t y o f t h e l i n e a t 1 3 2 . 2 ppm was n o t removed b u t r e d u c e d b y a b o u t h a l f , i n d i c a t i n g t h a t a n o n -p r o t o n a t e d c a r b o n a l s o c o n t r i b u t e s t o t h e s i g n a l . - 63 -I ~i—i—|—i i i i | i i i i—|—i—i i i | i i i i j i i i i • [ — i i i 250 200 150 100 50 0 PPM F i g u r e 4 . 1 0 : ( a ) The c o n v e n t i o n a l CP/MAS s p e c t r u m o f c r y s t a l l i n e PEEK. ( b ) The d i p o l a r dephased s p e c t r u m o f PEEK ( d e l a y - 40 p s ) . ( * d e n o t e s t h e s i g n a l due t o d e l r i n ) . S i n c e t h e r e a r e s e v e n d i s t i n c t c a r b o n atoms i n t h e m o l e c u l e b u t o n l y f i v e l i n e s i n t h e s p e c t r u m , two o f t h e l i n e s l i k e l y r e p r e s e n t o v e r -l a p p e d c a r b o n r e s o n a n c e s . Fo r e x a m p l e , t h e i n t e n s i t y and w i d t h o f t h e l i n e a t 1 1 9 . 0 ppm s u g g e s t s c o n t r i b u t i o n s f r o m two t y p e s o f c a r b o n a t o m s , b o t h p r o t o n a t e d . T h i s l i n e i s a s c r i b e d t o C-4 and C - 7 , t h e two p r o t o -n a t e d c a r b o n s w h i c h a r e i n t h e most s i m i l a r e n v i r o n m e n t s . Perhaps C-4 i s s h i f t e d s l i g h t l y t o l o w e r f i e l d because i t i s c l o s e r t o t h e c a r b o n y l . - 64 -C-3 i s t h e p r o t o n a t e d c a r b o n n e a r e s t t o t h e c a r b o n y l and i s t h u s a s s i g n e d t o t h e s i g n a l a t 1 3 2 . 2 ppm. Of t h e n o n - p r o t o n a t e d c a r b o n s , t h e a s s i g n m e n t o f t h e c a r b o n y l a tom t o t h e r e s o n a n c e a t l o w e s t f i e l d ( 1 9 2 . 8 ppm) i s t h e most s t r a i g h t f o r -w a r d . The c a r b o n y l e x p e r i e n c e s t h e g r e a t e s t d e s h i e l d i n g o f any o f t h e c a r b o n atoms i n t h e m o l e c u l e . I t i s a l s o t h e s i g n a l o f l e a s t i n t e n s i t y . T h e r e i s b u t one c a r b o n y l a tom p e r r e p e a t i n g u n i t o f PEEK, w h i l e t h e r e a r e two o f each o t h e r m a g n e t i c a l l y d i f f e r e n t n u c l e i . T h i s a s s i g n m e n t i s s u p p o r t e d b y t h e CP/MAS s p e c t r a o f mode l compounds, p - a l k o x y b e n o z i c a c i d s . The c a r b o n y l s i g n a l o f p - b u t o x y b e n z o i c a c i d a p p e a r s a t 1 7 3 . 6 ppm and i s t h e l o w e s t f i e l d r e s o n a n c e i n t h e a l k o x y b e n z o i c a c i d s p e c t r u m ( 6 5 ) . The mode l compounds a r e a l s o o f h e l p i n t h e a s s i g n m e n t o f t h e r e m a i n i n g c a r b o n s : C - 2 , C-5 and C-6 t o t h e l i n e s a t 1 3 2 . 2 ppm, 1 5 0 . 8 ppm and 1 5 9 . 3 ppm. C-5 and C-6 a r e a t t a c h e d t o t h e e t h e r l i n k and t h u s a r e e x p e c t e d t o r e s o n a t e a t h i g h e r f r e q u e n c y t h a n C - 2 . T h u s , t h e C-2 r e s o -nance i s a s c r i b e d t o t h e s i g n a l a t 1 3 2 . 2 ppm. A g a i n , t h i s a s s i g n m e n t a g r e e s w i t h t h e p a r a l l e l a s s i g n m e n t o f t h e p - a l k o x y b e n z o i c a c i d s p e c t r a ( 6 5 ) . F i n a l l y , b y n o t i n g t h a t t h e c a r b o n C-6 i s i n a r i n g f l a n k e d b y two e t h e r l i n k s and t h e C-5 i s i n t h e r i n g a t t a c h e d t o one e t h e r and t o t h e c a r b o n y l , t h e C-6 r e s o n a n c e i s a s s i g n e d t o t h e l o w e r f i e l d s i g n a l a t 1 5 9 . 3 ppm and C-5 , t o t h e 1 5 0 . 8 ppm s i g n a l . The above a s s i g n m e n t o f t h e CP/MAS s p e c t r u m o f PEEK does n o t ag ree w i t h t h a t made b y W h i t a k e r e t a l . ( 2 4 ) . N e v e r t h e l e s s , t h e peak p o s i -t i o n s o f t h e p u b l i s h e d s p e c t r u m a r e t h e same as i n t h i s w o r k . The f i r s t d i f f e r i n g a s s u m p t i o n i s i n t h e number o f m a g n e t i c a l l y i n e q u i v a l e n t c a r -- 65 -b o n s ; W h i t a k e r e t a l . assume t h a t t h e r e a r e o n l y f i v e , t h a t C-6 and C-7 a r e i d e n t i c a l t o C-5 and C - 4 . T a b l e 4 . 1 d i s p l a y s t h e two a s s i g n m e n t s . V a r i a b l e c o n t a c t t i m e e x p e r i m e n t s were u s e d b y w h i t a k e r e t a l . t o d i s -t i n g u i s h p r o t o n a t e d and n o n - p r o t o n a t e d c a r b o n a t o m s , b u t t h e s e s p e c t r a were n o t p u b l i s h e d . Table 4.1: Spectral Assignmment for PEEK: Comparison of Present Vork with Whitaker et a l . ( 2 4 ) (ppm relative to TMS). L i n e P o s i t i o n A s s i g n m e n t L i n e P o s i t i o n 3 A s s i g n m e n t * (ppm) (ppm) 1 9 2 . 8 1 1 9 3 . 5 1 1 5 9 . 3 6 1 6 0 . 0 5 , 6 1 5 0 . 8 5 1 5 1 . 0 2 1 3 2 . 2 2 , 3 1 3 3 . 0 4 , 7 1 1 9 . 0 4 , 7 1 1 8 . 5 3 f r o m r e f e r e n c e 2 4 . J u s t as t h e s p e c t r u m o f amorphous PPS i s w i d e r t h a n t h e c r y s t a l -l i n e , so t h e amorphous PEEK s p e c t r u m i s w i d e r t h a n t h e c r y s t a l l i n e . F i g u r e 4 . 1 1 shows s p e c t r a o f t h e amorphous and c r y s t a l l i n e PEEK samples w h i c h were o b t a i n e d u n d e r t h e same c o n d i t i o n s . The d i f f e r e n c e i n w i d t h s i s n o t as p r o n o u n c e d f o r PEEK as f o r PPS. T h i s i s n o t s u r p r i s i n g because t h e f r a c t i o n a l c r y s t a l l i n i t y o f PEEK i s l e s s t h a n t h a t o f PPS (40% v e r -- 66 -sus 65%) . T a b l e 4 . 2 l i s t s t h e h a l f h e i g h t w i d t h s f o r t h e c r y s t a l l i n e and amorphous s p e c t r a . F i g u r e 4 . 1 1 : ( a ) The s o l i d s t a t e CP/MAS s p e c t r u m o f amorphous PEEK. ( b ) The s o l i d s t a t e CP/MAS s p e c t r u m o f c r y s t a l l i n e PEEK. T a b l e 4 . 2 : S p e c t r a l l i n e w i d t h s f o r c r y s t a l l i n e and amorphous PEEK L i n e P o s i t i o n (ppm) A s s i g n m e n t C r y s t a l l i n e L i n e w i d t h (ppm) Amorphous L i n e w i d t h (ppm) 1 9 2 . 8 1 21 39 1 5 9 . 3 6 20 45 1 5 0 . 8 5 20 66 1 3 2 . 2 2 , 3 26 53 1 1 9 . 0 4 , 7 26 103 Figure 4.12: Variable contact time CP/MAS spectra of crystalline PEEK. (* denotes the signal due to delrin). - 68 -I n t h e v a r i a b l e c o n t a c t t i m e e x p e r i m e n t , t h e p r o t o n a t e d c a r b o n n u c l e i a p p e a r w i t h g r e a t e r i n t e n s i t y a t s h o r t e r c o n t a c t t i m e s because c r o s s - p o l a r i z a t i o n o f p r o t o n a t e d c a r b o n s i s more e f f e c t i v e . F i g u r e 4 . 1 2 p r e s e n t s a s e l e c t i o n o f s p e c t r a f r o m a v a r i a b l e c o n t a c t t i m e e x p e r i m e n t on c r y s t a l l i n e PEEK. Even a t as s h o r t a c o n t a c t t i m e as 0 . 0 1 ms, t h e p r o t o n a t e d s i g n a l s a r e a p p a r e n t . The q u a t e r n a r y c a r b o n s r e q u i r e l o n g e r c o n t a c t t i m e s i n o r d e r t o d e v e l o p maximum m a g n e t i z a t i o n and t h e c a r b o n y l r e q u i r e s t h e l o n g e s t c o n t a c t t i m e o f a l l . T h i s e x p e r i m e n t s e r v e d t o c o n f i r m t h e s p e c t r a l a s s i g n m e n t and t o a s c e r t a i n t h a t 1 ms was a s u i t -a b l e c o n t a c t t i m e f o r t h e o t h e r CP/MAS e x p e r i m e n t s p e r f o r m e d . The op t imum c o n t a c t t i m e i s d e p e n d e n t upon t h e o p e r a t i n g c o n d i t i o n s o f t h e s p e c t r o m e t e r , p a r t i c u l a r l y on t h e Har tmann-Hahn m a t c h i n g o f t h e p r o t o n and c a r b o n f i e l d s . I n o r d e r t o make f a i r a c o m p a r i s o n b e t w e e n t h e c o n t a c t t i m e r e s u l t s o f t h e c r y s t a l l i n e and amorphous f o r m s o f PEEK t h e e x p e r i m e n t s were d u p l i c a t e d and p a r t i c u l a r l y i n t h e s e c o n d s e t , a t t e n -t i o n was p a i d t o m a i n t a i n i n g i d e n t i c a l a c q u i s i t i o n c o n d i t i o n s . L o g - l o g p l o t s o f t h e r e l a t i v e peak i n t e n s i t y a g a i n s t t h e c o n t a c t t i m e f o r t h e s i n g l e q u a t e r n a r y c a r b o n s , C-5 and C-6 and f o r t h e comb ined s i g n a l o f t h e p r o t o n a t e d c a r b o n s C-3 and C-4 a r e g i v e n i n A p p e n d i x I I . Due t o a n o v e r l a p w i t h a s p i n n i n g s i d e b a n d t h e c a r b o n y l s i g n a l c o u l d n o t be m e a s u r e d . However , f r o m t h e s p e c t r a o f F i g u r e 4 . 1 2 , i t i s c o n c l u d e d t h a t t h e op t imum c o n t a c t t i m e o f t h e c a r b o n y l exceeds t h a t o f t h e q u a t -e r n a r y c a r b o n s . The s c a t t e r o f t h e d a t a p o i n t s i s due t o two m a i n f a c t o r s : ( i ) t h e l o n g e x p e r i m e n t a l t i m e o f t w e n t y h o u r s , d u r i n g w h i c h t h e Har tmann-Hahn c o n d i t i o n does n o t r e m a i n c o n s t a n t and ( i i ) t h e d i f f i c u l t y i n o b t a i n i n g - 69 -a good baseline i n the noisy spectra from which to measure the peak heights (the number of scans was limited by the length of the exper-iment) . The data points were f i t a r b i t r a r i l y to a quintic polynomial. The contact time profiles for two signals of the amorphous PEEK sample are plotted in Figure 4.13. The C-3 and C-4 protonated carbon z LU r— Z . LU O -3.0 -2.0 -1.0 0.0 1.0 LN OF CONTACT TIME [ L N MSEC] Figure 4.13: Variable contact time plots for amorphous PEEK: ID C-3, C-4 protonated carbons. A C-6 non-protonated carbon. magnetization i s seen to reach maximum intensity quickly relative to the quaternary carbon, C-6. A similiar trend is noted in the spectra of the crystalline sample. Figure 4.14 compares the contact time plots of the C-5 carbon in the crystalline and amorphous samples. The C-5 signal of the crystalline has the longer optimum contact time. - 70 -0.5 -3.0 -2.0 -1.0 0.0 1.0 LN" OF CONTACT TIME [ L N MSEC] Figure 4.14: Variable contact time plots for C-5, non-protonated carbon of PEEK: A amorphous Q crystalline The results of these experiments indicate that the optimum contact time of protonated carbons is less than that of non-protonated and that the amorphous form has a slightly shorter optimum contact time than the crystalline. Table 4 .3 summarizes these findings. Again, these results are somewhat contrary to expectation since the dipolar interactions which promote efficient cross-polarization are l i k e l y to be stronger in the crystalline material because the crystal-line PEEK is both more r i g i d and more dense than the amorphous. However, as previously mentioned with respect to PPS, the cross-polarization - 71 -T a b l e 4 . 3 : Opt imum C o n t a c t Time R e s u l t s f o r Amorphous and C r y s t a l l i n e PEEK. C r y s t a l l i n e Amorphous N u c l e u s o p t . c o n t a c t t i m e o p t . c o n t a c t t i m e [msec] [msec] C - 3 , C-4 1.3 0 . 8 C-5 2 . 3 1.5 C-6 1.7 1.6 r a t e s a r e d e p e n d e n t upon t h e s p i n - l a t t i c e r e l a x a t i o n t i m e s o f t h e p r o t o n s i n t h e r o t a t i n g f r a m e . The i n c r e a s e d m o l e c u l a r m o t i o n i n t h e amorphous m a t e r i a l may cause a s h o r t e r T-^p v a l u e and t h u s be r e s p o n s i b l e f o r t h e d e c r e a s e d ^ 3 C s i g n a l a t l o n g e r c o n t a c t t i m e s ( 6 3 ) . 4 . 5 SUMMARY AND CONCLUSION OF CP/MAS WORK The h i g h r e s o l u t i o n liC s p e c t r a f o r PEEK and PPS i n c r y s t a l l i n e and amorphous f o r m s have b e e n o b t a i n e d . The a s s i g n m e n t o f t h e s p e c t r u m o f each p o l y m e r was made w i t h t h e a i d o f t h e d i p o l a r d e p h a s i n g t e c h n i q u e , PEEK h a v i n g t h e more c o m p l i c a t e d a s s i g n m e n t o f t h e t w o . A c o m p a r i s o n o f t h e c r y s t a l l i n e and amorphous s p e c t r a shows t h a t i n b o t h cases t h e l a t t e r i s c o n s i d e r a b l y b r o a d e n e d ; a b r o a d e n i n g o f t h e amorphous l i n e I s g e n e r a l l y o b s e r v e d f o r s e m i - c r y s t a l l i n e p o l y m e r s . The s p e c t r a o f PPS h a v i n g i n t e r m e d i a t e c r y s t a l l i n i t i e s s u g g e s t t h e - 72 -s u p e r p o s i t i o n of amorphous and c r y s t a l l i n e l i ne-shapes. This i n d i c a t e s t h a t f u r t h e r s t u d i e s of v a r y i n g c r y s t a l l i n i t i e s employing s p e c t r a l sub-t r a c t i o n and l i n e c o n v o l u t i o n would be i n f o r m a t i v e . A l s o , v a r i o u s pulse sequence techniques may be used to i n d i c a t e the separate components: ( i ) Dechter (63) showed t h a t , i n polyethylene oxide, s p e c t r a o f long r e l a x -a t i o n times are p r i n c i p a l l y of c r y s t a l l i n e c h a r a c t e r , ( i i ) H a r r i s and coworkers (66) i n d i c a t e d t h a t a pre-contact time had a s i m i l i a r e f f e c t i n p o lyethylene t e r e p h t h a l a t e and ( i i i ) Fyfe e t a l . (64) used a n/2-r-n/2 sequence f o r polyethylene which, a t short r , y i e l d e d s p e c t r a of predominantly amorphous line-shape. The v a r i a b l e contact time experiments on PEEK i n d i c a t e d stronger d i p o l a r couplings f o r the protonated than f o r the non-protonated car-bons . The s h o r t e r optimum contact time f o r the amorphous PEEK i s exp l a i n e d as being due to the f a s t e r r o t a t i n g frame r e l a x a t i o n r a t h e r than to stronger d i p o l a r i n t e r a c t i o n s . A f u l l Tip r e l a x a t i o n study i s a p r e r e q u i s i t e f o r the i n t e r p r e t a t i o n of other CP/MAS experiments. R e l a x a t i o n s t u d i e s of 1 3 C n u c l e i and v a r i -able temperature CP/MAS may a l s o y i e l d i n f o r m a t i v e r e s u l t s . - 73 -5 . WIDE-LINE PROTON NMR STUDIES 5 . 1 INTRODUCTION TO SOLID STATE PROTON NMR One o f t h e e a r l i e s t s t u d i e s o f s e m i - c r y s t a l l i n e p o l y m e r s b y w i d e -l i n e p r o t o n NMR was made b y Pake and W i l s o n i n 1953 ( 6 7 ) . T h e i r w o r k was an a t t e m p t t o e s t a b l i s h c r y s t a l l i n i t i e s o f p o l y e t h y l e n e and p o l y -t e t r a f l u o r o e t h y l e n e ( T e f l o n ) b y means o f NMR l i n e - s h a p e a n a l y s i s . U n f o r -t u n a t e l y , t h o u g h t h e i r p r i n c i p l e was c o r r e c t , t h e a n a l y s i s was s i m p l y t o o a r b i t r a r y and t h e r e s u l t s d i d n o t c o r r e l a t e w i t h t h e c r y s t a l l i n i t y d e t e r m i n a t i o n s b y o t h e r m e t h o d s . However , Pake and W i l s o n were p i o n e e r s ; t h e y were t h e f i r s t t o u n d e r t a k e a p r o b l e m o f g r e a t m a g n i t u d e w h i c h has n o t y e t b e e n r e s o l v e d . S i n c e t h e 1 9 5 0 ' s many o t h e r r e s e a r c h e r s have u s e d w i d e - l i n e NMR i n t h e s t u d y o f s e m i - c r y s t a l l i n e t h e r m o p l a s t i c s . The p o l y m e r s s t u d i e d have p r i m a r i l y b e e n c o n f i n e d t o t h o s e o f m a j o r c o m m e r c i a l i m p o r t a n c e , i n p a r t i c u l a r , p o l y e t h y l e n e ( 6 8 - 7 4 ) and p o l y p r o -p y l e n e ( 6 2 , 6 8 , 7 5 - 7 8 ) . I n t h e c u r r e n t l i t e r a t u r e , t h e r e has b e e n no r e p o r t o f ^H NMR o f p o l y ( e t h e r e t h e r k e t o n e ) , and b u t one o f p o l y ( p h e n y l e n e s u l f i d e ) ( 3 2 ) . The g o a l s o f w i d e - l i n e p r o t o n NMR s t u d i e s o f m a c r o m o l e c u l e s a r e ( i ) t o complement t h e f i n d i n g s f r o m o t h e r t e c h n i q u e s s u c h as d i e l e c t r i c o r m e c h a n i c a l s p e c t r o s c o p i e s o r ( i i ) t o g a i n e x c l u s i v e i n f o r m a t i o n w h i c h i s n o t o b t a i n a b l e e x c e p t b y NMR. The re a r e e s s e n t i a l l y t h r e e a p p r o a c h e s t o t h e use o f s o l i d s t a t e p r o t o n NMR s t u d i e s : ( i ) r e l a x a t i o n measuremen ts , (T]_, T ^ _ , and T 2 ) , ( i i ) second moment o r l i n e w i d t h s t u d i e s and ( i i i ) - 74 -l i n e - s h a p e a n a l y s i s . These e x p e r i m e n t s a r e most u s e f u l i f t h e y a r e p e r -f o r m e d as f u n c t i o n s o f t e m p e r a t u r e o r sample p r e p a r a t i o n . The r e s u l t s o t h e t h r e e t y p e s o f e x p e r i m e n t s a r e v e r y much i n t e r c o n n e c t e d . The most i m p o r t a n t f u n c t i o n s o f s o l i d s t a t e PMR a r e t o g i v e i n s i g h t i n t o t h e p o l y m e r m o r p h o l o g y and t o d e t e r m i n e t h e n a t u r e o f t h e m o t i o n s o f t h e m a c r o m o l e c u l a r c h a i n s . I n some s e m i - c r y s t a l l i n e p o l y m e r s , l i n e - s h a p e a n a l y s i s has s e p a r -a t e d t h e s p e c t r a i n t o t w o , t h r e e o r more c o m p o n e n t s . C o r r e l a t i o n o f t h e r e l a t i v e i n t e n s i t i e s o f t h e components has y i e l d e d an e s t i m a t e o f p o l y m e r c r y s t a l l i n i t y ( 6 7 , 6 9 , 7 1 , 7 2 ) . One o f t h e most n o t a b l e s u c c e s s e s i s t h e w o r k o f Bergmann on p o l y e t h y l e n e ( 7 2 ) . The s p e c t r a l l i n e s a r e p r e s e n t e d as t h e sum o f a b r o a d , G a u s s i a n l i n e ; a n a r r o w , L o r e n t z i a n l i n e ; and a m e d i u m - w i d t h , G a u s s - L o r e n t z p r o d u c t l i n e . The b r o a d l i n e r e p r e s e n t s t h e c r y s t a l l i n e r e g i o n s and t h e o t h e r two c u r v e s i n d i c a t e t h p r e s e n c e o f two t y p e s o f amorphous p h a s e . P rob lems w i t h t h i s a n a l y s i s i n c l u d e t h e a r b i t r a r y n a t u r e o f t h e d e c o n v o l u t i o n p r o c e s s and t h e v a r i a t i o n o f t h e l i n e - s h a p e w i t h t e m p e r a t u r e . R e l a x a t i o n s t u d i e s and s e c o n d moment measurements r e f l e c t t h e m o l e c u l a r m o t i o n s i n t h e p o l y m e r . The t y p e o f e x p e r i m e n t and t h e mag-n e t i c f i e l d s t r e n g t h d e t e r m i n e t h e f r e q u e n c y o f t h e d e t e c t e d m o t i o n s . R e l a x a t i o n s t u d i e s c a n y i e l d a c t i v a t i o n e n e r g i e s f o r m o l e c u l a r m o t i o n s a n d , when c o m b i n e d w i t h i n f o r m a t i o n f r o m o t h e r t e c h n i q u e s , t h e e x a c t o r i g i n o f t h e m o t i o n s c a n o c c a s i o n a l l y be s u r m i s e d ( 3 2 ) . I n s e m i -c r y s t a l l i n e p o l y m e r s , r e l a x a t i o n t i m e s t u d i e s may p r o v i d e i n f o r m a t i o n a b o u t t h e s p a t i a l i n h o m o g e n e i t y o f t h e p o l y m e r . F o r e x a m p l e , t h e d e t e c -t i o n o f two o r more T i ^ t i m e s b u t o n l y one T^ t i m e i n d i c a t e s s p i n - 75 -d i f f u s i o n i n t h e s y s t e m ; t h e p r e s e n c e o f t h i s phenomenon c a n be u s e d t o e s t i m a t e t h e s i z e o f t h e d i f f e r e n t c r y s t a l l i n e and amorphous r e g i o n s ( 6 8 , 7 4 ) . 5 . 2 SOLID STATE PROTON NMR THEORY 5 . 2 . 1 L i n e - S h a p e s o f S o l i d S t a t e PMR S p e c t r a The s p i n H a m i l t o n i a n f o r a p r o t o n i n a s t r o n g m a g n e t i c f i e l d i s t h a t e x p r e s s e d i n e q u a t i o n 4 . 1 . L i k e t h e 1 3 C n u c l e u s , t h e p r o t o n has a n u c l e a r s p i n o f 1 / 2 , b u t u n l i k e t h e n u c l e u s , t h e ^H n u c l e u s i s 100% a b u n d a n t and has a l a r g e g y r o m a g n e t i c r a t i o . The h o m o n u c l e a r d i p o l a r i n t e r a c t i o n i s t h e d o m i n a n t t e r m i n t h e e q u a t i o n , so much s o , t h a t t h e s u b s e q u e n t t e r m s i n t h e e q u a t i o n may be n e g l e c t e d . The s t r o n g d i p o l a r i n t e r a c t i o n s o f t h e a b u n d a n t h y d r o g e n n u c l e i g i v e r i s e t o l o c a l f i e l d s w h i c h s u p p l e m e n t H Q . I n t h e s o l i d s t a t e , t h e m a g n i t u d e o f t h e s e l o c a l f i e l d s v a r y w i t h t h e p o s i t i o n o f t h e n u c l e i and t h i s v a r i a t i o n p r o d u c e s t h e b r o a d l i n e s w h i c h a r e c h a r a c t e r i s t i c o f t h e s o l i d s t a t e p r o t o n spec -t r o s c o p y . A l t h o u g h t h e d i p o l a r i n t e r a c t i o n I s d i r e c t i o n a l l y d e p e n d e n t i n samples w h i c h a r e n o t o r i e n t e d a n d / o r w h i c h c o n t a i n a number o f i n e q u i v a l e n t p r o t o n s , t h e d i p o l a r i n t e r a c t i o n g e n e r a l l y p r o d u c e s a G a u s s i a n d i s t r i b u t i o n o f r e s o n a n c e f r e q u e n c i e s . The i n t e r a c t i o n o f two m a g n e t i c moments (/*]_, 1 * 2 ) *- s g i v e n b y t h e h o m o n u c l e a r d i p o l e - d i p o l e c o u p l i n g e x p r e s s i o n ( 7 9 ) : - 76 -w 1 2 ~ r " 5 [ r 2 / * l ' A * 2 " 3 ( M l - r i 2 ) ( A * 2 * r 1 2 > ] < 5 - 1 ) where r ^ 2 i - s t n e i n t e r d i p o l e d i s t a n c e . E q u a t i o n 5 . 1 c a n a l s o be c o n s i d e r e d more s i m p l y a s : W12 = - / i 2 - H 1 2 ( 5 . 2 ) where H ^ 2 i s t h e f i e l d p r o d u c e d b y s p i n 1 a t s p i n 2 . The w i d t h o f t h e G a u s s i a n l i n e i s d e p e n d e n t upon t h e s t r e n g t h o f t h e d i p o l a r i n t e r a c -t i o n s . The two c o n v e n t i o n a l ways o f c o n v e y i n g t h e b r o a d n e s s o f t h e l i n e a r e b y l i n e w i d t h measurements and b y second moment c a l c u l a t i o n s . The l i n e w i d t h i s s i m p l y t h e w i d t h o f t h e s p e c t r a l l i n e a t h a l f h e i g h t , u s u a l l y g i v e n i n u n i t s o f f r e q u e n c y o r o f m a g n e t i c f i e l d . The s e c o n d moment, S 2 , i s c a l c u l a t e d b y : r° 7 J ( W - W Q ) ^ ( w ) d « -CO S 2 - ( 5 . 3 ) f° f ( w ) d » -00 where f ( w ) i s t h e f u n c t i o n o f t h e l i n e s h a p e and w D i s t h e a n g u l a r La rmor f r e q u e n c y o f t h e n u c l e i i n t h e e x t e r n a l m a g n e t i c f i e l d . A l t e r n a t i v e l y , t h e s e c o n d moment may be d e t e r m i n e d f r o m t h e FID w h i c h may be e x p r e s s e d a s : f ( t ) - M o ( l - S 2 t2 / 2 ! + S 4 t4 / 4 ! - S 6 t6 / 6 ! + . . . ) ( 5 . 4 ) - 77 -where S 2 , S 4 , and Sg a r e t h e s e c o n d , f o u r t h and s i x t h moments o f t h e l i n e . The h a l f h e i g h t l i n e w i d t h , < A H > i y 2 a r K * t h e s e c o n d moment, S 2 , f o r a p u r e l y G a u s s i a n l i n e a r e r e l a t e d b y t h e e x p r e s s i o n : < A H > 1 / 2 - 2 s 2 < 2 l o 8 2 ) 1 / 2 ( 5 - 5 ) One f a c t o r w h i c h d e t e r m i n e s t h e w i d t h o f t h e l i n e i s t h e i n t e r -d i p o l a r d i s t a n c e . A n o t h e r f a c t o r i s m o l e c u l a r m o t i o n . I n a s o l i d , t h e d i p o l a r c o u p l i n g i n t e r a c t i o n i s s t r o n g e s t when t h e l a t t i c e i s r i g i d . T h i s g e n e r a l l y o c c u r s a t v e r y l o w t e m p e r a t u r e s when t h e m o t i o n s have b e e n " f r o z e n o u t " . I n t h i s s i t u a t i o n , ( S 2 ) l / 2 r c » l , where r c i s t h e c o r r e l a t i o n t i m e w h i c h c h a r a c t e r i z e s t h e a v e r a g e t i m e f o r a t o m i c r e a r -rangemen t a b o u t a g i v e n n u c l e u s . C o n v e r s e l y , a t h i g h t e m p e r a t u r e s , t h e p r e s e n c e o f random i s o t r o p i c m o t i o n causes c o m p l e t e a v e r a g i n g o f t h e d i p o l e - d i p o l e c o u p l i n g and s p e c t r a l l i n e s e x h i b i t e x t r e m e n a r r o w i n g . H e r e , ( S 2 ) 1 / 2 , c « l and t h e c o r r e l a t i o n t i m e i s v e r y s h o r t . T h e r e i s , h o w e v e r , an i n t e r m e d i a t e r e g i o n i n w h i c h ( S 2 ) I n t h i s c a s e , t h e s p e c t r a l l i n e r e t a i n s much o f i t s G a u s s i a n c h a r a c t e r b u t i s somewhat n a r r o w e d due t o t h e w e a k e n i n g o f t h e d i p o l a r i n t e r a c t i o n b y m o t i o n i n t h e l a t t i c e . The e x t e n t o f t h e n a r r o w i n g g i v e s i n s i g h t i n t o t h e deg ree o f m o l e c u l a r m o t i o n w i t h i n t h e p o l y m e r . 5 . 2 . 2 R e l a x a t i o n T h e r e a r e t h r e e t y p e s o f r e l a x a t i o n t i m e s r e f e r r e d t o i n t h i s w o r k : - 78 -( i ) s p i n - l a t t i c e r e l a x a t i o n , T]_, ( i i ) s p i n - s p i n r e l a x a t i o n , T 2 , and ( i i i ) s p i n - l a t t i c e r e l a x a t i o n i n t h e r o t a t i n g f r a m e , T i ^ . S p i n - l a t t i c e r e l a x a t i o n , w h i c h i s most p e r t i n e n t t o t h i s s t u d y , i s d i s c u s s e d i n some d e t a i l b e l o w . The o t h e r two a r e more b r i e f l y d e f i n e d . 5 . 2 . 2 a S p i n - L a t t i c e R e l a x a t i o n A n u c l e u s o f s p i n 1/2 p l a c e d i n a m a g n e t i c f i e l d has two p o s s i b l e e n e r g y s t a t e s : a l i g n m e n t o f t h e s p i n w i t h o r a g a i n s t t h e f i e l d . I f t h e r e a r e many n u c l e i , a B o l t z m a n p o p u l a t i o n d i s t r i b u t i o n becomes a p p a r e n t . The r a t i o o f t h e number o f h i g h e r e n e r g y s p i n s t o l o w e r e n e r g y s p i n s i s p r o p o r t i o n a l t o e x p ( - A E / k T ) , where AE i s t h e e n e r g y d i f f e r e n c e b e t w e e n t h e s p i n s t a t e s , k , t h e B o l t z m a n c o n s t a n t and T , t h e t e m p e r a t u r e . The n e t m a g n i t u d e o f t h e m a g n e t i z a t i o n i n d u c e d w i t h i n t h e sample i s due t o t h e p o p u l a t i o n d i f f e r e n c e and t o t h e number o f s p i n s i n t h e s a m p l e . A t t h e i n s t a n t a sample i s p l a c e d i n t o a m a g n e t i c f i e l d , t h e s p i n p o p u l a -t i o n s a r e e v e n , t h e same number o f s p i n s a r e i n t h e h i g h e r e n e r g y l e v e l as a r e i n t h e l o w e r . However , a f t e r some t i m e , t h e s p i n p o p u l a t i o n s a d j u s t and t h e e q u i l i b r i u m B o l t z m a n d i s t r i b u t i o n o f s p i n s t a t e s f o r t h e p a r t i c u l a r f i e l d s t r e n g t h and t e m p e r a t u r e i s a c h i e v e d . The r e a s o n t h a t t h e r e a d j u s t m e n t o f t h e s p i n p o p u l a t i o n i s n o t i m m e d i a t e i s e x p l a i n e d by t h e phenomenon o f s p i n - l a t t i c e r e l a x a t i o n . I n o r d e r f o r a n u c l e u s i n t h e h i g h e r s p i n s t a t e t o ' r e l a x ' t o t h e l o w e r s t a t e , i t mus t g i v e up a quantum o f e n e r g y , AE, t o t h e s u r r o u n d -i n g s , c a l l e d t h e l a t t i c e . T h i s e n e r g y t r a n s f e r p r o c e s s r e q u i r e s s t i m u -- 79 -l a t e d e m i s s i o n , t h a t i s , t h e r e must be some r e l a x a t i o n mechanism a t t h e L a r m o r f r e q u e n c y w h i c h c a n a b s o r b t h e AE o f e n e r g y . The r a t e a t w h i c h t h e s y s t e m r e a d j u s t s t o e q u i l i b r i u m m a g n e t i z a t i o n i s a measure o f t h e a v a i l a b l i t y o f r e l a x a t i o n mechanisms a t t h e Larmor f r e q u e n c y . I n o r d e r t o be a s u i t a b l e r e l a x a t i o n mechanism f o r a s p i n 1/2 n u c l e u s , t h e f i e l d mus t be a t i m e - v a r y i n g , m a g n e t i c one and i t s f r e q u e n c y must c o r r e s p o n d t o t h e Larmor f r e q u e n c y o f t h e n u c l e u s . Such f l u c t u a t i n g f i e l d s a r i s e p r i m a r i l y f r o m t h e v a r i o u s m o t i o n s i n t h e s o l i d w h i c h cause f l u c t u a t i o n s o f t h e d i p o l a r i n t e r a c t i o n s . The f i e l d f l u c t u -a t i o n s f r o m an u n p a i r e d e l e c t r o n , ( s u c h as f o u n d i n p a r a m a g n e t i c O 2 ) , i s a p a r t i c u l a r l y e f f e c t i v e r e l a x a t i o n mechan ism. The s p i n l a t t i c e r e l a x a t i o n t i m e i s d e f i n e d as d M z ( M z - M D ) d t T l (5.6) where M z i s t h e n e t m a g n e t i z a t i o n o f t h e r e l a x i n g s p i n s y s t e m a t t i m e t , and M 0 i s t h e m a g n e t i z a t i o n a t l a r g e r , ( e q u i l i b r i u m ) . T h u s , i n a r e l a x -i n g s p i n s y s t e m , a t a t i m e T]_, t h e m a g n e t i z a t i o n has r e c o v e r e d t o 1/e o f t h e e q u i l i b r i u m m a g n e t i z a t i o n . T h e r e a r e a number o f d i f f e r e n t t e c h n i q u e s u s e d f o r m e a s u r i n g T^ . One o f t h e mos t s t r a i g h t f o r w a r d o f t h e s e i s t h e i n v e r s i o n r e c o v e r y m e t h o d w h i c h employs a 1 8 0 ° - T - 9 0 ° p u l s e s e q u e n c e . The 180° p u l s e i n v e r t s t h e m a g n e t i z a t i o n a l o n g t h e z a x i s . D u r i n g t h e w a i t i n g t i m e r , t h e m a g n e t i z a t i o n p a r t i a l l y r e c o v e r s , and t h e f i n a l p u l s e o f 90° t i p s t h e m a g n e t i z a t i o n i n t o t h e x y p l a n e t o a l l o w f o r i t s d e t e c t i o n . The r e c y c l e - 80 -t i m e b e t w e e n sequences i s t y p i c a l l y 5 t i m e s t h e s p i n - l a t t i c e r e l a x a t i o n t i m e . F i g u r e 5 . 1 shows a s c h e m a t i c r e p r e s e n t a t i o n o f t h e e x p e r i m e n t . The F i g u r e 5 . 1 : ( a ) A s c h e m a t i c r e p r e s e n t a t i o n o f t h e i n v e r s i o n r e c o v e r y sequence f o r s p i n - l a t t i c e r e l a x a t i o n t i m e measurements ( T 3 > T 2 > r x ) . ( b ) The c o r r e s p o n d i n g s p e c t r a . m a g n e t i z a t o n i s r e l a t e d t o t h e T^ v a l u e as shown i n e q u a t i o n 5 . 7 : M ( r ) - 1 - 2exp ( - r / T i ) ( 5 . 7 ) M 0 - 81 -where M ( r ) i s t h e m a g n e t i z a t i o n a t t i m e r . T h u s , a p l o t o f l n [ 1 - M ( r ) / M o ] a g a i n s t r g i v e s a l i n e o f s l o p e 1/Tj_. S p i n d i f f u s i o n i s an i m p o r t a n t phenomenon i n t h e c o n s i d e r a t i o n o f r e l a x a t i o n t i m e s i n two component s y s t e m s . A two component s y s t e m n a t u r a l l y has two s p i n - l a t t i c e r e l a x a t i o n t i m e s . However , i t i s o f t e n t h e case t h a t o n l y one i s o b s e r v e d . T h e r e a r e two p o s s i b l e r e a s o n s f o r t h i s phenomenon. The f i r s t i s t r i v i a l , t h a t i s , t h e T^s a r e c o i n c i d e n -t a l l y t h e same. The s e c o n d i s t h e p r e s e n c e o f s p i n d i f f u s i o n . D u r i n g t h e T^ r e l a x a t i o n , s p i n e n e r g y r e m a i n s i n t h e s p i n s y s t e m f o r a f i n i t e p e r i o d o f t i m e . W i t h i n t h i s p e r i o d , s p i n - l a t t i c e e n e r g y c a n p r o p a g a t e b e t w e e n n u c l e i b y a s e r i e s o f " f l i p - f l o p " e n e r g y - c o n s e r v i n g t r a n s i t i o n s . ( I n a s e n s e , t h i s p r o c e s s i s more a n a l o g o u s t o t h e r m a l c o n d u c t i o n t h a n t o m a t e r i a l d i f f u s i o n . ) U s u a l l y , s t r o n g d i p o l e - d i p o l e c o u p l i n g s m a i n t a i n t h e c o m m u n i c a t i o n b e t w e e n t h e s p i n s . The f i n a l r e s u l t o f t h e e n e r g y p r o p a g a t i o n i s t h a t a l l s p i n s r e l a x a t t h e same r a t e . 5 . 2 . 2 b S p i n - S p i n R e l a x a t i o n S p i n - s p i n r e l a x a t i o n i s t h e p r i m a r y f a c t o r i n t h e decay o f t h e p r e c e s s i n g m a g n e t i z a t i o n i n t h e x y p l a n e ( F i g u r e 5 . 2 ) . D i r e c t i n t e r a c -t i o n s b e t w e e n t h e n u c l e a r s p i n s p r o m o t e r e l a x a t i o n w i t h o u t l o s s o f e n e r g y t o t h e l a t t i c e s y s t e m . The a c t u a l decay o f t h e m a g n e t i z a t i o n i n * t h e x y p l a n e ( T 2 ) depends upon t h r e e f a c t o r s ( 8 0 ) : ( i ) t h e s p i n - l a t t i c e r e l a x a t i o n t i m e , ( i i ) t h e s p i n - s p i n r e l a x a t i o n and ( i i i ) t h e m a g n e t i c f i e l d i n h o m o g e n i e t y , 7 A H Q . - 82 -VT 2 * - l/2TX + VT 2 + 7AH0 (5.8) I n t h e s o l i d s t a t e , T ^ » T 2 . As a r e s u l t , g i v e n a f a i r l y homoge-* neous m a g n e t i c f i e l d , i t i s i s t h e case t h a t 1 / T 2 « 1 / T 2 . T h u s , T 2 r e p r e s e n t s t h e t i m e a t w h i c h t h e f r e e i n d u c t i o n decay i s 1/e o f i t s t, t, t, F i g u r e 5 . 2 : A s c h e m a t i c r e p r e s e n t a t i o n o f t h e s p i n - s p i n r e l a x a t i o n e f f e c t ( t 3 > t 2 > t 1 ) . maximum v a l u e ( F i g u r e 5.3). An a l t e r n a t e c o n v e n t i o n f o r any c u r v e t y p e i s t o s e t T 2 as t h e t i m e a t w h i c h t h e m a g n e t i z a t i o n decay i s 1/e o f t h e maximum. I t i s n e c e s s a r y t o n o t e t h a t because t h e T 2 d e t e r m i n e s t h e l i n e w i d t h o f t h e s p e c t r u m i n t h e f r e q u e n c y d o m a i n , s p i n - s p i n r e l a x a t i o n and s e c o n d moment d a t a p r o v i d e s i m i l a r i n f o r m a t i o n . - 83 -— T2 — F i g u r e 5 . 3 : T 2 , s p i n - s p i n r e l a x a t i o n t i m e , i s t h e t i m e r e q u i r e d f o r t h e F I D t o decay t o 1/e o f t h e o r i g i n a l v a l u e . 5 . 2 . 2 c S p i n - L a t t i c e R e l a x a t i o n i n t h e R o t a t i n g Frame The s p i n - l a t t i c e r e l a x a t i o n i n t h e r o t a t i n g f r a m e e x p e r i m e n t i s e s s e n t i a l l y t h e same as t h e n o r m a l T^ e x p e r i m e n t . The l a t t e r measurement y i e l d s i n f o r m a t i o n on t h e r e l a x a t i o n mechanisms o f t h e La rmor f r e q u e n c y o f t h e H D f i e l d , t y p i c a l l y o f t h e o r d e r o f MHz. The f o r m e r r e s p o n d s t o m o t i o n a t much s l o w e r f r e q u e n c i e s , o f t h e o r d e r o f k H z . The r o t a t i n g f r a m e r e l a x a t i o n t i m e , T i p , i s t h e c h a r a c t e r i s t i c decay t i m e o f t h e s p i n m a g n e t i z a t i o n w h i c h i s l o c k e d t o a r a d i o f r e q u e n c y f i e l d i n t h e r o t a t i n g x y p l a n e . 5 . 2 . 2 d The Dependence o f R e l a x a t i o n on T e m p e r a t u r e F i g u r e 5 . 4 s k e t c h e s t h e dependence o f T]_, T l p and T 2 on t e m p e r a t u r e f o r a t h e o r e t i c a l p o l y m e r h a v i n g two t r a n s i t i o n s . T^ and T j - show m in ima - 84 -a t t h a t t e m p e r a t u r e a t w h i c h w r c - l , (w i s t h e r e s o n a n c e f r e q u e n c y o f t h e n u c l e i i n t h e f i e l d H Q o r H]^ and rc i s t h e c o r r e l a t i o n t i m e ) . The t e m p e r a t u r e o f t h e minimum r e l a x a t i o n t i m e i s t h u s a f u n c t i o n o f f i e l d s t r e n g t h . H i g h e r f i e l d s show m i n i m a a t h i g h e r t e m p e r a t u r e s . T F i g u r e 5.4: The t h e o r e t i c a l dependence o f Tj_, T j . and T£ o n t e m p e r a t u r e ( 3 0 ) . The t r a n s i t i o n t e m p e r a t u r e s o f T 2 t e n d t o be a p p r o x i m a t e l y t h e same as t h o s e o f T ^ and b o t h r e s p o n d t o m o t i o n s i n t h e r a n g e o f 10 t o 100 kHz ( 3 0 ) . The b e h a v i o u r o f T 2 , w i t h r e s p e c t t o t e m p e r a t u r e , i s i n d i c a -t i v e o f d e c r e a s e d s p e c t r a l l i n e w i d t h due t o i n c r e a s e d m o t i o n w i t h t e m p e r a t u r e . An e s t i m a t e o f t h e a c t i v a t i o n e n e r g y may be o b t a i n e d b y p l o t t i n g t h e r e l a x a t i o n d a t a as t h e l o g o f r e l a x a t i o n t i m e a g a i n s t t h e i n v e r s e o f t e m p e r a t u r e , as s k e t c h e d i n F i g u r e 5 . 5 ( f o r a s i n g l e t r a n s i t i o n ) . Assum-i n g t h a t t h e c o r r e l a t i o n t i m e may be e x p r e s s e d as an A r r h e n i u s p r o c e s s : - 85 -r c - r Q exp (AE/RT) ' ( 5 . 9 ) t h e n t h e s l o p e o f t h e l i n e a r p o r t i o n s o f t h e p l o t i n F i g u r e 5 . 5 a r e -AE/R and AE/R r e s p e c t i v e l y . F i g u r e 5.5: The t h e o r e t i c a l dependence o f l o g T ^ , T ^ w and T 2 on I n v e r s e t e m p e r a t u r e ( 8 0 ) . - 86 -5 . 3 EXPERIMENTAL The b r o a d - l i n e NMR measurements were made w i t h a B r u k e r CXP h i g h power F o u r i e r - t r a n s f o r m s p e c t r o m e t e r o p e r a t i n g a t 200 MHz f o r p r o t o n s . The B r u k e r s o f t w a r e programme, DISCXP was u s e d . D a t a was c o l l e c t e d i n a b l o c k s i z e o f 2K, t h e sweep w i d t h was 5 0 0 , 0 0 0 Hz, and t y p i c a l l y 16 t o 32 t r a n s i e n t s were a v e r a g e d . The s p e c t r o m e t e r c o n d i t i o n s were s e t such t h a t t h e s i g n a l was r e c e i v e d on o r v e r y c l o s e t o r e s o n a n c e , and p h a s e d so as t o m i n i m i z e t h e s i g n a l i n t h e i m a g i n a r y c h a n n e l . The T^ measurements emp loyed an i n v e r s i o n r e c o v e r y p u l s e sequence ( 1 8 0 - T - 9 0 ) . The r e c y c l e t i m e exceeded f i v e t i m e s Tj_, and s p e c t r a f o r a t l e a s t 10 w e l l - s p a c e d d e l a y t i m e s were o b t a i n e d p e r s a m p l e , w i t h two o r more d e l a y t i m e s e q u a l t o t h e r e c y c l e t i m e . The t e m p e r a t u r e r a n g e e x t e n d e d f r o m a m b i e n t t o 440K. An a i r f l o w d e v i c e c o n t r o l l e d t h e t e m p e r a t u r e t o an a c c u r a c y o f ± 0 . 5 ° C , w i t h a t h e r m a l g r a d i e n t a c r o s s t h e sample o f ±1°C ( m a n u f a c t u r e r ' s s p e c i f i c a -t i o n s ) . D a t a was t r a n s f e r r e d f r o m t h e B r u k e r s y s t e m t o a N i c o l e t N I C - 1 2 8 0 d a t a s t a t i o n f o r p l o t t i n g and p r o c e s s i n g . Because t h e r e c e i v e r r e c o v e r y t i m e o f t h e s p e c t r o m e t e r was =*8;us I t was n e c e s s a r y t o d e l e t e t h e f i r s t t h r e e p o i n t s o f t h e F ID b e f o r e a p p l i c a t i o n o f t h e b a s e l i n e c o r r e c t and F o u r i e r t r a n s f o r m a t i o n r o u t i n e s . The samples were p a c k e d i n 10 mm g l a s s t u b e s . The amorphous f i l m was c u t i n t o s m a l l ( l x l m m ) p i e c e s and p a c k e d so as t o e n s u r e random o r i e n t a t i o n . - 87 -5 . 4 RESULTS 5 . 4 . 1 L i n e - S h a p e R e s u l t s W i t h one e x c e p t i o n , t h e f u l l y r e l a x e d s p e c t r a ( t h o s e h a v i n g T > 5 T I ) , f r o m t h e r e l a x a t i o n t i m e e x p e r i m e n t s were u s e d f o r t h e l i n e - s h a p e s t u d y . The e x c e p t i o n was t h e case o f one s e t o f c r y s t a l l i n e PPS d a t a , ( s e r i e s 2 ) , where a s i m p l e J T / 2 p u l s e was u s e d t o o b t a i n t h e F I D . S p e c t r a were o b t a i n e d f o r amorphous and c r y s t a l l i n e samples o f PPS and PEEK f r o m a m b i e n t t e m p e r a t u r e t o 430K. A t a m b i e n t t e m p e r a t u r e , a l l s p e c t r a a p p e a r e d as b r o a d G a u s s i a n l i n e s w i t h a s m a l l n a r r o w component a t t h e a p p r o x i m a t e c e n t r e o f t h e G a u s s i a n l i n e . These s p e c t r a a r e shown i n F i g u r e 5 . 6 . The h a l f - h e i g h t l i n e w i d t h s ( i n kHz) f o r t h e f o u r p o l y m e r samples a t a m b i e n t t e m p e r a t u r e a r e p r e s e n t e d i n T a b l e 5 . 1 . I n b o t h p o l y m e r s , t h e l i n e s o f t h e c r y s t a l -l i n e m a t e r i a l a r e b r o a d e r t h a n t h o s e o f t h e amorphous . A t a l l t e m p e r a -t u r e s b e l o w t h e T g , t h e c r y s t a l l i n e s p e c t r a show b r o a d e r l i n e s t h a n t h e amorphous . T a b l e 5 . 1 : H a l f H e i g h t L i n e w i d t h s [ k H z ] f o r PEEK and PPS PMR S p e c t r a a t A m b i e n t T e m p e r a t u r e . C r y s t a l l i n e Amorphous PEEK 2 8 . 8 2 7 . 0 PPS 2 9 . 4 2 5 . 0 - 88 -Figure 5 . 6 : PMR spectra of (a) crystalline PEEK; (b) amorphous PEEK; (c) crystalline PPS; (d) amorphous PPS; a l l at ambient temperature. - 89 -The s p e c t r a l l i n e w i d t h i s i n v e r s e l y p r o p o r t i o n a l t o t e m p e r a t u r e . F o r a l l s a m p l e s , t h e l i n e s n a r r o w p r o g r e s s i v e l y as t h e t e m p e r a t u r e i n c r e a s e s ; F i g u r e s 5 . 7 t o 5 . 1 0 show p l o t s o f t h e w i d t h o f t h e b r o a d l i n e a g a i n s t t e m p e r a t u r e . (The two s e r i e s i n d i c a t e measurements made a t d i f f e r e n t t i m e s w i t h s l i g h t l y v a r i e d s p e c t r o m e t r i c c o n d i t i o n s . ) Be low T g , t h e l i n e w i d t h d e c r e a s e s a p p r o x i m a t e l y l i n e a r l y w i t h t e m p e r a t u r e . Above T g , t h e l i n e w i d t h s o f t h e c r y s t a l l i n e p o l y m e r s show a g r e a t e r r a t e o f d e c r e a s e w i t h t e m p e r a t u r e . Amorphous PEEK shows a n a b r u p t d r o p i n l i n e w i d t h b e t w e e n 420K and 430K. The l i n e w i d t h o f t h e amorphous PPS a l s o shows a s h a r p d e c r e a s e i n t h e r e g i o n 360K t o 370K, f o l l o w e d i m m e d i a t e l y b y an i n c r e a s e i n l i n e w i d t h . PEEK a t a m b i e n t t e m p e r a t u r e s p r e s e n t s a s p e c t r u m o f a b r o a d Gaus-s i a n l i n e w i t h a s m a l l n a r r o w component , l e s s t h a n 6% o f t h e t o t a l 30.0 • • • • • • • IS A • a lS.OL 290.0 320.0 350.0 380.0 TEMPERATURE CK3 410.0 440.0 F i g u r e 5.7: L i n e w i d t h v e r s u s t e m p e r a t u r e f o r •'-H s p e c t r a o f c r y s t a l l i n e PEEK ( i n d u p l i c a t e ) . - 90 -30.0 25.0 20.0 15.0 • A • A A <t • • • 290.0 320.0 350.0 380.0 TEMPERATURE CK3 410.0 440.0 Figure 5.8: Linewidth versus temperature for spectra of amorphous PEEK (in duplicate). 30.0 290.0 320.0 350.0 380.0 410.0 TEMPERATURE CK3 440.0 Figure 5.9: Linewidth versus temperature for spectra of crystalline PPS (in duplicate). - 91 -3 0 . 0 r*j a: 2 5 . 0 IU 2 0 . 0 15 .0 2 9 0 . 0 • • • 1$ • • a 3 2 0 . 0 3 5 0 . 0 3 8 0 . 0 4 1 0 . 0 4 4 0 . 0 TEMPERATURE CK] F i g u r e 5.10 L i n e w i d t h v e r s u s t e m p e r a t u r e f o r s p e c t r a o f amorphous PPS ( i n d u p l i c a t e ) . i n t e n s i t y . As t h e t e m p e r a t u r e r i s e s , t h e b r o a d l i n e becomes l e s s b r o a d and t h e n a r r o w l i n e i n c r e a s e s i n i n t e n s i t y t o a b o u t 10% o f t h e t o t a l . The amorphous PEEK f o l l o w s e s s e n t i a l l y t h e same p a t t e r n , t h o u g h , t h e G a u s s i a n l i n e i s n o t as w i d e and t h e n a r r o w component i s more i n t e n s e a t a l l t e m p e r a t u r e s . The e f f e c t o f t e m p e r a t u r e on t h e l i n e - s h a p e o f PPS s p e c t r a i s much more p r o n o u n c e d t h a n f o r PEEK. The s p e c t r a c o l l e c t e d b e l o w Tg a r e q u i t e s i m i l a r t o t h o s e o f PEEK, a l t h o u g h , t h e n a r r o w component i n t h e c r y s t a l -l i n e p o l y m e r i s more i n t e n s e t h a n i n t h e amorphous . The n a r r o w component i n c r e a s e s w i t h t e m p e r a t u r e ; t h i s i s e s p e c i a l l y marked above T g . A t h i g h t e m p e r a t u r e s ( 4 2 0 K ) , t h e n a r r o w component d o m i n a t e s t h e s p e c t r u m . F i g u r e 5.11 shows t h e h i g h t e m p e r a t u r e s p e c t r a o f t h e f o u r s a m p l e s . - 92 --i—r 40000 20000 r 20000 -40000 Hz • I ' • ' I 1 ' 1 I 40000 20000 0 Figure 5.11: PMR spectra of (a) crystalline PEEK (b) amorphous PEEK (c) crystalline PPS (d) amorphous PPS [(a-c) at 430K, (d) at 420K]. - 93 -5.4.2 S p i n - L a t t i c e R e l a x a t i o n R e s u l t s V a r i a b l e t e m p e r a t u r e s p i n - l a t t i c e r e l a x a t i o n t i m e s t u d i e s were made f o r amorphous and c r y s t a l l i n e p o l y ( e t h e r e t h e r k e t o n e ) and p o l y -( p h e n y l e n e s u l f i d e ) as d e s c r i b e d p r e v i o u s l y i n t h e e x p e r i m e n t a l s e c t i o n , 5 . 3 . The T^ v a l u e s o f t h e b u l k sample were o b t a i n e d f r o m t h e m a g n i t u d e o f t h e f i r s t good d a t a p o i n t o f t h e F I D ; t y p i c a l l y t h i s was t h e p o i n t a t 9/is f r o m t h e c e n t r e o f t h e 90 p u l s e . A p r o g r a m , T 1 3 I R , p a r t o f t h e N i c o l e t 1280 NMR p r o c e s s i n g s o f t w a r e ( 8 1 ) , was u s e d t o c a l c u l a t e t h e T^ v a l u e s . T 1 3 I R i s b a s e d on t h e t h r e e p a r a m e t e r f i t e q u a t i o n d e v e l o p e d b y L e v y and P e a t ( 8 2 ) f o r T^ c a l c u l a t i o n s : M z - M Q ( l - { l - k [ l - e x p ( - A T / T 1 ) ] } e x p ( - r / T 1 ) ) ( 5 . 1 0 ) T where M 2 i s t h e m a g n e t i z a t i o n a f t e r t h e d e l a y t i m e r , M Q i s t h e m a g n e t i -z a t i o n a t v e r y l o n g r , k i s a measure o f i m p e r f e c t i o n s i n t h e r . f . p u l s e ( t h e o r e t i c a l l y k ~ l ) , and AT i s t h e d a t a a c q u i s i t i o n t i m e . The t h r e e p a r a m e t e r s i n t h e f i t a r e M Q , k , and Tj_. The a d v a n t a g e o f t h i s f i t t i n g me thod i s t h a t i t accomodates f o r a l e s s t h a n p e r f e c t i n v e r s i o n o f t h e m a g n e t i z a t i o n . E r r o r s i n r e l a x a t i o n t i m e s a r e t y p i c a l l y i n t h e o r d e r o f 10% ( 8 2 ) . The a m b i e n t t e m p e r a t u r e T^ measurements were c o n s i s t e n t ; t h e y a r e p r e s e n t e d i n T a b l e 5 . 2 . These t i m e s a r e t h e a v e r a g e o f a t l e a s t two measurements made on d i f f e r e n t o c c a s i o n s and on d i f f e r e n t s a m p l e s . The - 94 -v a r i a t i o n b e t w e e n t h e a v e r a g e d v a l u e s was l e s s t h a n 4%. The r e l a x a t i o n t i m e s f o r t h e p o l y ( e t h e r e t h e r k e t o n e ) a r e s h o r t e r t h a n f o r t h e p o l y ( p h e n y l e n e s u l f i d e ) . The c r y s t a l l i n e f o r m o f PEEK has a l o n g e r T^ t h a n t h e amorphous . The o p p o s i t e i s t r u e o f t h e PPS, w i t h t h e amorphous PPS d i s p l a y i n g t h e l o n g e r T ^ . T a b l e 5 .2: T^ V a l u e s ( i n s e c o n d s ) f o r Samples o f PEEK and PPS a t A m b i e n t T e m p e r a t u r e . PEEK PPS c r y s t a l l i n e 1.35 1.67 amorphous 0 . 9 8 1 .84 T h e r e i s some s c a t t e r i n t h e d a t a p o i n t s o f t h e v a r i a b l e t e m p e r a -t u r e e x p e r i m e n t s , t h e T^ v a l u e s were n o t a l w a y s r e p r o d u c i b l e b u t a p p e a r e d t o depend upon t h e p a r t i c u l a r sample and t h e s p e c t r o m e t r i c c o n -d i t i o n s o f t h e d a y . Fo r t h i s r e a s o n , as f o r t h e l i n e w i d t h d a t a , measure -ments made c o n s e c u t i v e l y a r e i n d i c a t e d as b e i n g p a r t o f one s e r i e s . However , i t i s n o t e d t h a t t h e t r e n d s o f t h e T^ b e h a v i o u r w i t h t e m p e r a -t u r e g e n e r a l l y a r e r e p r o d u c i b l e . F i g u r e s 5 . 1 2 t o 5 . 1 5 p r e s e n t t h e c o m p l e t e r e l a x a t i o n s t u d y r e s u l t s , p l o t t e d as t h e l o g a r i t h m o f t h e r e l a x a t i o n t i m e a g a i n s t t h e i n v e r s e o f t h e t e m p e r a t u r e . The g e n e r a l f o r m o f a l l t h e p l o t s i s t h e same: t h e T^ i n c r e a s e s w i t h t e m p e r a t u r e , r e a c h -i n g a maximum v a l u e a t a p p r o x i m a t e l y Tg and t h e n d e c l i n i n g a t h i g h e r t e m p e r a t u r e s . - 95 -1.5 1.0 u LU cn _ _ i-. 0.5 O . O h -0.5 • 6 • • • • • • • 1 1 i i 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 1000/TCK] Figure 5.12: Log relaxation time versus inverse temperature for crystalline PEEK. 1.5 l . O r -u LU •_. 0.5r-0.0 -0.5 • A • • • • 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 1000/TCK] Figure 5.13: Log relaxation time versus inverse temperature for amorphous PEEK. - 96 -u LU to - 0 . 5 Figure 5.14: Log relaxation time versus Inverse temperature for crystalline PPS (in duplicate). u LU to Figure 5.15: Log relaxation time versus inverse temperature for amorphous PPS (in duplicate). - 97 -The amorphous m a t e r i a l s show some d i s c o n t i n u i t y a t h i g h e r t e m p e r a -t u r e s . T h i s i s because o f t h e o n s e t o f c r y s t a l l i z a t i o n above T g . The sample b e g a n t o c r y s t a l l i z e d u r i n g t h e c o u r s e o f t h e T^ measuremen ts . T h u s , t h e amorphous d a t a i s o n l y o f r e a l s i g n i f i c a n c e b e l o w t h e g l a s s t r a n s i t i o n t e m p e r a t u r e , and i n r e c o g n i z i n g t h e g l a s s t r a n s i t i o n t e m p e r a -t u r e i t s e l f . The amorphous PEEK i n d i c a t e s a t r a n s i t i o n i n t h e r e g i o n o f 410K ± 7K (137°C) and t h e T^ o f PPS e x p e r i e n c e s an a b r u p t d e c r e a s e a t 370K ± 7K ( 9 7 ° C ) . The T^ b e h a v i o u r o f t h e c r y s t a l l i n e samples i s more c o n t i n u o u s . The maximum Ti^ f o r t h e PEEK sample i s a b o u t 4 . 2 s a t 410 t o 420K ( 1 3 7 - 1 4 7 ° C ) and f o r t h e c r y s t a l l i n e PPS, 2 . 8 s a t 360 t o 370K ( 8 7 - 9 7 ° C ) . T h r o u g h o u t t h e t e m p e r a t u r e r a n g e , t h e r e l a x a t i o n t i m e o f t h e c r y s t a l l i n e PEEK i s g r e a t e r t h a n t h a t o f t h e amorphous f o r m . C o n v e r s e l y , T]_ v a l u e s o f PPS a r e a p p r o x i m a t e l y t h e same f o r b o t h t h e amorphous and t h e c r y s t a l l i n e s a m p l e s . The l n ( T i ) v s 1/T p l o t s a r e l i n e a r i n t h e l o w t e m p e r a t u r e r e g i o n . A c t i v a t i o n e n e r g y e s t i m a t e s o b t a i n e d f r o m t h e s l o p e s o f t h e l i n e s a r e p r e s e n t e d i n T a b l e 5 . 3 . The a c t i v a t i o n e n e r g y o f t h e c r y s t a l l i n e PPS i s g r e a t e r t h a n t h a t o f t h e amorphous . The a c t i v a t i o n e n e r g y o f t h e two PEEK m o r p h o l o g i e s a r e t h e same, and s i g n i f i c a n t l y l a r g e r t h a n t h e PPS e n e r g i e s . The T^ v a l u e s d i s c u s s e d above r e f e r t o t h e a v e r a g e T^ o v e r t h e w h o l e s a m p l e . I n some cases h o w e v e r , t h e samples e x h i b i t e d two d i s t i n c t s p i n - l a t t i c e r e l a x a t i o n s . These were more c l e a r l y seen i n t h e f r e q u e n c y t r a n s f o r m e d s p e c t r a t h a n i n t h e F I D s . A g r a p h i c i l l u s t r a t i o n i s g i v e n i n F i g u r e 5 . 1 6 . T h i s shows t h e p a r t i a l l y r e l a x e d s p e c t r u m o f c r y s t a l l i n e - 98 -T a b l e 5 . 3 : A c t i v a t i o n , E n e r g i e s E x p r e s s e d I n k J m o l ' 1 , O b t a i n e d f r o m t h e Low T e m p e r a t u r e P o r t i o n o f t h e I n v s P l o t s . R e g r e s s i o n E r r o r I n B r a c k e t s . PEEK PPS c r y s t a l l i n e 1 3 . 3 (±6%) 8 . 6 (±4%) amorphous 1 3 . 3 (±2%) 4 . 9 (±7%) p o l y ( p h e n y l e n e s u l f i d e ) a f t e r a 1 8 0 - r - 9 0 s e q u e n c e , w i t h r b e i n g 0 . 6 s ; t h e s p e c t r u m was c o l l e c t e d a t a m b i e n t t e m p e r a t u r e . B o t h t h e b r o a d and n a r r o w components a r e p r e s e n t . The r e m a r k a b l e f e a t u r e i s t h a t t h e m a g n e t i z a t i o n s o f t h e two components a r e o f o p p o s i t e s i g n , i n d i c a t i n g t h a t t h e b r o a d component , w h i c h has a n e g a t i v e m a g n e t i z a t i o n a t r - 0 . 6 s , has t h e l o n g e r r e l a x a t i o n t i m e . •0000 40000 20000 0 -20000 -40000 -40000 Hz F i g u r e 5 . 1 6 : A p a r t i a l l y r e l a x e d s p e c t r u m o f c r y s t a l l i n e PPS. - 99 -Two d i s t i n c t r e l a x a t i o n s a r e f o u n d i n t h e amorphous and t h e c r y s -t a l l i n e f o r m s o f PEEK a t a l l t e m p e r a t u r e s . I n PPS, o n l y t h e c r y s t a l l i n e sample shows two components o f d i f f e r i n g T]_. M o r e o v e r t h i s i s t r u e o n l y a t t e m p e r a t u r e s b e l o w T g . A t T g , t h e n a r r o w component becomes more i n t e n s e and t h e two components show t h e same r e l a x a t i o n r a t e . I t i s d i f f i c u l t t o measure t h e i n d i v i d u a l r e l a x a t i o n s . N o r m a l l y , two s e p a r a t e T^s may be e x t r a c t e d f r o m an a n a l y s i s o f t h e m a g n e t i z a t i o n M ( r ) v e r s u s r p l o t . I f , h o w e v e r , t h e two T^ v a l u e s d i f f e r b y a f a c t o r o f 2 , t h e y a r e u n r e s o l v a b l e ( 8 3 ) . I n t h i s c a s e , n o t o n l y a r e t h e T^s t o o c l o s e i n v a l u e b u t a l s o t h e p r o p o r t i o n o f t h e b r o a d component i s so much g r e a t e r t h a n t h a t o f t h e n a r r o w component t h a t i t c o m p l e t e l y d o m i n a t e s t h e F I D . I n t h i s w o r k , e s t i m a t e s o f t h e two T^s were o b t a i n e d f o r t h e two PEEK sample t y p e s b y d i r e c t measurement o f t h e component h e i g h t s i n t h e f r e q u e n c y s p e c t r a . The c u r v e s c o u l d be s e t q u i t e c o n f i d e n t l y b y e y e . The s p e c t r a u s e d f o r t h e s e measurements were p a r t o f t h o s e f i r s t c o l l e c t e d i n t h e p r o j e c t . The sweep w i d t h was 1 2 5 , 0 0 0 Hz , s m a l l e r t h a n t h e w i d t h o f 5 0 0 , 0 0 0 Hz u s e d f o r t h e b u l k o f t h e w o r k . I n mos t r e s p e c t s , t h e n a r r o w e r sweep w i d t h was a d i s a d v a n t a g e b e c a u s e , i n i n c r e a s i n g t h e d w e l l t i m e t o 8 (is, t h e e a r l i e s t p o r t i o n o f t h e F ID was l o s t and t h e component o f s h o r t T^ was more p o o r l y r e s o l v e d . S t i l l , t h e t r a n s f o r m e d s p e c t r a show h i g h e r r e s o l u t i o n o f t h e n a r r o w component due t o t h e s m a l l e r sweep w i d t h and t h e r e l a t i v e i n t e n s i t y o f t h e b r o a d p o r t i o n i s r e d u c e d because o f t h e l o s s o f t h e e a r l y p o i n t s i n t h e F I D . The two f a c t o r s c o m b i n e d made p o s s i b l e a r e a s o n a b l e e s t i m a t e o f t h e i n d i v i d u a l component i n t e n s i t i e s . The r e s u l t s a r e p r e s e n t e d i n T a b l e 5 . 4 . The v a l u e s f o r t h e b r o a d component a g r e e w e l l w i t h t h e T^ v a l u e s o b t a i n e d - 100 -f o r t h e b u l k sample f r o m an e a r l y p o i n t o f t h e F I D . I n a l l cases t h e n a r r o w component r e l a x e d more q u i c k l y t h a n t h e b r o a d . S p i n - l a t t i c e r e l a x a t i o n i s s e n s i t i v e t o t h e p r e s e n c e o f pa ramag-n e t i c o x y g e n , and i n p o l y m e r s t u d i e s , t h i s i s o f p a r t i c u l a r c o n c e r n a t s u b - a m b i e n t t e m p e r a t u r e s ( 8 4 ) . I n o r d e r t o a s c e r t a i n t h e m a g n i t u d e o f t h e e f f e c t w i t h r e s p e c t t o t h i s w o r k , t h e r e l a x a t i o n t i m e s o f an open T a b l e 5 .4 : S p i n - L a t t i c e R e l a x a t i o n T imes f o r t h e I n d i v i d u a l Components o f PEEK, Room T e m p e r a t u r e , T]_ E x p r e s s e d i n Seconds . b r o a d n a r r o w  amorphous 0 . 9 4 ± 0 . 0 3 0 . 6 6 ± 0 . 0 1 c r y s t a l l i n e 1.43 ± 0 . 0 1 1.32 ± 0 . 1 sample and o f a n e v a c u a t e d sample were d e t e r m i n e d u n d e r t h e same c o n d i -t i o n s . The T^ o f t h e e v a c u a t e d sample was 1.85 s and t h e open sample h a d a T^ o f 1 .64 s , (11% l o w e r ) . I t was d e c i d e d t h a t t h e d i s c r e p a n c y b e t w e e n t h e t w o , g i v e n t h e i n h e r e n t i n a c c u r a c y o f t h e T^ measuremen ts , d i d n o t w a r r a n t r e p e a t i n g t h e w o r k w i t h e v a c u a t e d s a m p l e s . The t r e n d s and g e n e r a l b e h a v i o u r o f t h e r e l a x a t i o n r e m a i n s u n a f f e c t e d . I t may be n o t e d t h a t t h e use o f b o t h e v a c u a t e d and open samples i s f o u n d i n t h e l i t e r a t u r e . - 101 -5 . 5 DISCUSSION 5 . 5 . 1 L i n e - S h a p e D i s c u s s i o n The d u a l i t y o f t h e p r o t o n s p e c t r a o f t h e s e two p o l y m e r s a r i s e s f r o m t h e p r e s e n c e o f two t y p e s o f m o l e c u l a r m o t i o n s . The b r o a d component o f t h e s i g n a l I s due t o t h e p r o t o n s w h i c h a r e h e l d r i g i d i n t h e l a t t i c e and t h e n a r r o w componen t , f r o m t h o s e w h i c h e x p e r i e n c e m o t i o n a l n a r r o w i n g . P o l y ( e t h e r e t h e r k e t o n e ) and p o l y ( p h e n y l e n e s u l f i d e ) a r e p r e s e n t e d as two somewhat d i f f e r e n t cases w i t h r e s p e c t t o l i n e - s h a p e . 5 . 5 . l a PEEK Be low T g , t h e n a r r o w component o f PEEK t e n d s t o be s l i g h t l y more i n t e n s e i n t h e s p e c t r a o f t h e amorphous f o r m t h a n o f t h e c r y s t a l l i n e . The r e a s o n u n d e r s t o o d f o r t h i s i s t h a t t h e r e d u c e d d e n s i t y o f t h e amorphous m a t e r i a l a l l o w s g r e a t e r m o b i l i t y o f c h a i n segments t h a n i s p o s s i b l e i n t h e c r y s t a l l i n e f o r m . The e f f e c t o f a d d i t i o n a l m o b i l i t y i n t h e amorphous sample i s a l s o seen i n t h e b r o a d component w h i c h i s l e s s w i d e i n t h e amorphous t h a n i n t h e c r y s t a l l i n e . L i n e w i d t h i s mos t s e n s i t i v e t o m o t i o n s i n t h e 5x10^ t o 3 . 3 x l 0 6 Hz r a n g e ( 8 4 ) . As t h e t e m p e r a t u r e i n c r e a s e s , t h e G a u s s i a n - t y p e l i n e c o n t i n u e s t o n a r r o w g r a d u a l l y due t o t h e p r o g r e s s i v e i n c r e a s e i n t h e r m a l m o t i o n s . The a b r u p t n a r r o w i n g o f t h e amorphous l i n e a t t h e g l a s s t r a n s i t i o n i s - 102 -e x p l a i n e d b y t h e o n s e t o f c o - o p e r a t i v e m o t i o n s o f l a r g e segments o f t h e m a c r o m o l e c u l a r c h a i n s . U n f o r t u n a t e l y , t h e e x p e r i m e n t a l l i m i t s on t h e t e m p e r a t u r e were such t h a t t h e maximum t e m p e r a t u r e o b t a i n a b l e was o n l y 20K above T g j t h e e f f e c t o f t e m p e r a t u r e s f u r t h e r above t h e Tg were n o t o b s e r v e d . 5 .5 . l b PPS Be low T g , i t i s t h e c r y s t a l l i n e f o r m o f PPS w h i c h d i s p l a y s a more p r o m i n e n t n a r r o w component . T h i s i s c o n t r a r y t o w h a t i s o b s e r v e d f o r t h e PEEK s p e c t r a and a l s o c o n t r a r y t o e x p e c t a t i o n . I t i s s u g g e s t e d t h a t t h e d i f f e r e n t m o l e c u l a r w e i g h t s b e t w e e n t h e amorphous and t h e c r y s t a l l i n e f o r m s i s r e s p o n s i b l e f o r t h i s d i s c r e p a n c y : t h e c r y s t a l l i n e powder i s an u n c u r e d r e s i n a n d , a l t h o u g h i t d i s p l a y s h i g h e r c r y s t a l l i n i t y , i t i s o f l o w e r m o l e c u l a r w e i g h t and i s a l s o l i k e l y t o c o n t a i n a s m a l l p r o p o r t i o n o f o l i g o m e r . Because c h a i n ends a r e t h e most m o b i l e p o r t i o n o f t h e m a c r o m o l e c u l e , t h e p o l y m e r o f l o w e r m o l e c u l a r w e i g h t , d e s p i t e i t s c r y s t a l l i n i t y , has t h e g r e a t e r p r o p o r t i o n o f m o b i l e p r o t o n s . The d i f f e r e n c e i n l i n e w i d t h b e t w e e n t h e c r y s t a l l i n e and amorphous s p e c t r a o f PPS i s g r e a t e r t h a n t h e d i f f e r e n c e b e t w e e n t h e two f o r m s o f PEEK. T h i s may be e x p l a i n e d i n t e r m s o f c r y s t a l l i n i t y s i n c e t h e deg ree o f PPS c r y s t a l l i n i t y i s h i g h e r t h a n t h a t o f PEEK; t h e g r e a t e r d i f f e r e n c e b e t w e e n t h e c r y s t a l l i n e and amorphous l i n e w i d t h i s n o t u n e x p e c t e d . J u s t as f o r PEEK, i n s p e c t r a o f t h e amorphous PPS, t h e b r o a d l i n e n a r r o w s s i g n i f i c a n t l y i n t h e g l a s s t r a n s i t i o n r e g i o n . The e q u i v a l e n t l y - 103 -a b r u p t i n c r e a s e i n l i n e w i d t h above t h e Tg i s due t o t h e c r y s t a l l i z a t i o n o f t h e amorphous m a t e r i a l . S e r i e s o f s p e c t r a measured f o r amorphous samples a t a t e m p e r a t u r e above Tg show an i n c r e a s e i n l i n e w i d t h w i t h t i m e . DSC scans o f t h e s e a n n e a l e d samples c o n f i r m p a r t i a l c r y s t a l l i n i t y . The h i g h t e m p e r a t u r e l i n e s h a p e o f PPS i s m a r k e d l y u n l i k e t h a t o f PEEK. Above T g , t h e r e i s an o n s e t o f much i n c r e a s e d m o t i o n . The i n t e n -s i t y o f t h e n a r r o w l i n e i n c r e a s e s a t t h e expense o f t h e b r o a d one because t h e c h a i n segments w h i c h were n e a r l y i m m o b i l e b e l o w Tg a p p r o a c h l i q u i d - l i k e m o t i o n s above T E . 5 . 5 . I c Second Moments Second moment c a l c u l a t i o n s a r e o f t e n made i n s t e a d o f l i n e w i d t h m e a s u r e m e n t s . S i n c e t h e G a u s s i a n l i n e w i d t h i s p r o p o r t i o n a l t o t h e s q u a r e r o o t o f t h e s e c o n d moment, t h e two methods y i e l d s i m i l a r r e s u l t s ( 3 2 ) . I n t h i s w o r k , two a t t e m p t s were made t o o b t a i n t h e s e c o n d moments v a l u e s o f t h e PEEK and PPS s p e c t r a . B o t h a p p r o a c h e s r e q u i r e d t h a t t h e v a l u e s o f t h e e a r l y p o i n t s o f t h e F ID l o s t i n t h e r e c e i v e r dead t i m e be r e c o v e r e d . Fo r t h e r e a l p o i n t s t h i s was a c h i e v e d b y f i t t i n g t h e p o i n t s t o a n e v e n p o l y n o m i a l ( w h i c h t y p i c a l l y c o n v e r g e d a f t e r a b o u t 5 t e r m s ) . The i m a g i n a r y p o i n t s were e x t r a p o l a t e d l i n e a r l y t o z e r o a t t h e o r i g i n . I t s h o u l d be p o s s i b l e t o c a l c u l a t e t h e second moment d i r e c t l y f r o m t h e c o n s t a n t o f t h e s q u a r e d t e r m o f t h e even p o l y n o m i a l . The d i f f i c u l t y e n c o u n t e r e d w i t h t h i s a p p r o a c h was t h a t t h e F IDs c o u l d n o t be e x p r e s s e d as a r e a l p a r t a l o n e . The d a t a c o u l d n o t be phased so as t o s e t t h e - 104 -s i g n a l i n t h e i m a g i n a r y c h a n n e l t o z e r o . (The r e a s o n f o r t h i s f a i l u r e was due t o t h e s l i g h t assymmet ry o f t h e l i n e s h a p e s . ) The s e c o n d a p p p r o a c h was t o use an i n t e g r a t i o n p r o g r a m t o c a l c u l a t e t h e s e c o n d moment f r o m t h e F o u r i e r t r a n s f o r m . U n f o r t u n a t e l y , t h e b a s e -l i n e s o f t h e s p e c t r a d i s p l a y e d some t i l t and t h e s e c o n d moment i s e x c e e d i n g l y s e n s i t i v e t o t h e s i g n a l c o n t r i b u t i o n f r o m t h e w i n g s t h e s i g n a l a t f r e q u e n c i e s f a r t h e s t away f r o m t h e c e n t r e f r e q u e n c y ( 7 9 ) . The u n e v e n b a s e l i n e s c a u s e d e x c e s s i v e s c a t t e r i n t h e moment c a l c u l a t i o n s and t h i s me thod was a l s o abandoned . The a t t r a c t i v e f e a t u r e a b o u t s e c o n d moments o b t a i n e d e x p e r i m e n t a l l y i s t h a t t h e y may be compared t o v a l u e s c a l c u l a t e d t h e o r e t i c a l l y f o r t h e r i g i d l a t t i c e . The c r y s t a l l i n e s t r u c t u r e o f t h e r i g i d l a t t i c e must be known. The d i f f e r e n c e b e t w e e n t h e two v a l u e s c a n p r o v i d e as e s t i m a t e o f t h e e x t e n t o f m o t i o n a l n a r r o w i n g w h i c h t a k e s p l a c e . 5 . 5 . 2 S p i n - L a t t i c e R e l a x a t i o n D i s c u s s i o n P r e v i o u s w o r k on o t h e r m a c r o m o l e c u l a r sys tems i n d i c a t e s t h a t t h e c r y s t a l l i n e m o r p h o l o g y g e n e r a l l y e x h i b i t s a l o n g e r r e l a x a t i o n t i m e t h a n t h e amorphous f o r m o f t h e same p o l y m e r ( 7 5 ) . C e r t a i n l y , t h i s p a t t e r n o f l o n g e r c r y s t a l l i n e r e l a x a t i o n was e s t a b l i s h e d f o r t h e PEEK s a m p l e . The amorphous m a t e r i a l r e l a x e s more q u i c k l y because o f t h e i n c r e a s e d m o t i o n o f t h e p o l y m e r c h a i n s r e l a t i v e t o t h e more r i g i d c r y s t a l l i n e s t r u c t u r e ; m o l e c u l a r m o t i o n i s c o n s t r a i n e d b y t h e c r y s t a l l i t e s . The m o l e c u l a r e x p l a n a t i o n f o r t h e T^ b e h a v i o u r o f PPS i s l e s s - 105 -c l e a r . T h i s a u t h o r s u g g e s t s t h a t because t h e c r y s t a l l i n e powder i s u n c u r e d , t h e a v e r a g e m o l e c u l a r w e i g h t i s l e s s t h a n t h e m o l e c u l a r w e i g h t o f t h e amorphous , R-4 p o l y m e r . The v i r g i n r e s i n a l s o c o n t a i n s a p r o p o r -t i o n o f l o w m o l e c u l a r w e i g h t m o l e c u l e s w h i c h a r e r e s p o n s i b l e f o r t h e n a r r o w s p i k e p r e s e n t i n t h e c r y s t a l l i n e PPS s p e c t r u m , e v e n a t l o w t e m p e r a t u r e s . R e l a x a t i o n r a t e s o f PPS, amorphous and c r y s t a l l i n e , a r e a p p r o x i m a t e l y t h e same because o f t h e e x t r a m o b i l i t y o f t h e s h o r t e r c h a i n l e n g t h s p r e s e n t i n t h e l a t t e r w h i c h p r o m o t e s p i n - l a t t i c e r e l a x a -t i o n . I n samples o f c r y s t a l l i n e and amorphous PPS o f i d e n t i c a l MJJ and M,,, t h e c r y s t a l l i n e w o u l d be l i k e l y t o e x h i b i t a l o n g e r T^ r e l a x a t i o n . The l n ( T ! ) v s 1/T p l o t s o f F i g u r e s 5 . 1 2 t o 5 . 1 5 d i f f e r f r o m t h e p l o t f o r a ' t h e o r e t i c a l p o l y m e r ' i n F i g u r e 5 . 5 . The l a t t e r p l o t s u g g e s t s t h a t t h e T^ v a l u e s h o u l d be s h o r t e s t a t t h e g l a s s t r a n s i t i o n t e m p e r a -t u r e . However , i n t h i s w o r k , t h e T^ a p p e a r s as a maximum a t T g . T h i s d i s c r e p a n c y i s e x p l a i n e d b y t h e v e r y h i g h f i e l d a t w h i c h t h i s w o r k was d o n e . The T^ minimum i n d i c a t e s t h e t e m p e r a t u r e a t w h i c h W T c = « 1 . F o r t h e 200 MHz f i e l d , t h e c o r r e l a t i o n t i m e a t w h i c h T^ i s m i n i m a l w o u l d be a p p r o x i m a t e l y 5 x l 0 " ^ s ; such a f a s t m o t i o n w o u l d o n l y be p r o m i n a n t a t c o n s i d e r a b l y h i g h e r t e m p e r a t u r e s . The maximum o f t h e l n ( T ^ ) v s 1/T p l o t seen h e r e , c o r r e s p o n d s t o a maximum T^ b e t w e e n two t r a n s i t i o n s (shown i n F i g u r e 5 . 4 ) . V e r y s i m i l i a r l i n e - s h a p e s have b e e n o b s e r v e d i n o t h e r s y s t e m s , f o r e x a m p l e , i n t h e l o w t e m p e r a t u r e T^ p r o f i l e o f benzene ( 8 5 ) shown i n F i g u r e 5 . 1 7 . The d o m i n a n t m o t i o n s a t Tg have c o r r e l a t i o n t i m e s o f t h e o r d e r o f 1 0 " ^ t o l O ' - ' s , and t h e T^ maxima a t t h i s t e m p e r a t u r e i n d i c a t e t h e r e l a t i v e p a u c i t y o f t h e h i g h f r e q u e n c y m o t i o n s . A c t i v a t i o n e n e r g i e s o b t a i n e d f r o m T^ p l o t s a r e t y p i c a l l y l e s s t h a n - 106 -F i g u r e 5 . 1 7 : The T^ t e m p e r a t u r e p r o f i l e o f benzene ( 8 5 ) . t h e a c t i v a t i o n e n e r g i e s d e t e r m i n e d b y o t h e r methods ( 3 0 ) . N e v e r t h e l e s s , NMR e s t i m a t e s a r e u s e f u l i n t h a t t h e y may be compared w i t h each o t h e r and w i t h e n e r g i e s o f o t h e r p o l y m e r s c a l c u l a t e d b y s i m i l a r t e c h n i q u e s . The l i k e a c t i v a t i o n e n e r g i e s o f PEEK, amorphous and c r y s t a l l i n e , may r e f l e c t a f i x e d e n e r g y b a r r i e r f o r r o t a t i o n , r e g a r d l e s s o f t h e p o l y m e r m o r p h o l o g y . A l s o , i t mus t be remembered t h a t t h e PEEK c r y s t a l -l i n e sample i t s e l f c o n t a i n s a h i g h d e g r e e o f amorphous m a t e r i a l . The r e l i a b l i t y o f t h e PPS a c t i v a t i o n e n e r g i e s i s somewhat s u s p e c t s i n c e t h e s l o p e o f t h e a c t i v a t i o n l i n e was t a k e n f r o m p o i n t s a p p r o a c h i n g t h e maximum T^ v a l u e . However , t h e d i f f e r e n c e b e t w e e n t h e two morpho-l o g i c a l samp les c l e a r l y s u g g e s t s f r e e r m o l e c u l a r m o t i o n i n t h e l e s s d e n s e , more d i s o r d e r e d , amorphous p h a s e . The a c t i v a t i o n e n e r g y o f t h e c r y s t a l l i n e PPS compares n o t u n f a v o u r -a b l y w i t h t h a t f o u n d b y o t h e r w o r k e r s . S c h l i c k and McGarvey ( 3 2 ) i n t h e i r s t u d y o f c r y s t a l l i n e PPS, a l s o b y PMR, f o u n d a c t i v a t i o n e n e r g i e s - 107 -b y two m e t h o d s . The T^ t e c h n i q u e y i e l d e d a s i n g l e a c t i v a t i o n e n e r g y o f 1 1 . 8 k J m o l " 1 and t h e l i n e - w i d t h a n a l y s i s gave two r e l a x a t i o n p r o c e s s e s o f 6 . 2 and 1 3 . 7 k J m o l " 1 . T h i s m o t i o n was a s s i g n e d t o t h e p h e n y l e n e r o t a t i o n a b o u t t h e S-S b o n d . O t h e r e s t i m a t e s o f a c t i v a t i o n e n e r g i e s f o r p h e n y l e n e g r o u p r o t a -t i o n s have b e e n made, b u t n o t f o r PPS o r PEEK. A l l a r e c o n s i d e r a b l y l a r g e r . Gar roway e t a l . ( 8 6 , 8 7 ) r e p o r t e d an a c t i v a t i o n e n e r g y o f 60 k J m o l " 1 f o r t h e p h e n y l r i n g m o t i o n i n t h e DGEBA epoxy p o l y m e r s . T h e o r e t i -c a l c a l c u l a t i o n s o f p h e n y l g r o u p r o t a t i o n s i n p o l y s t y r e n e made b y T o n e l l i ( 8 8 ) , and H a g e l l and Beck ( 8 9 ) gave a c t i v a t i o n e n e r g i e s as l a r g e as 40 t o 80 k J m o l " 1 . The p r e s e n c e o f d i s t i n c t s p i n - l a t t i c e r e l a x a t i o n t i m e s , o b s e r v e d f o r t h r e e o u t o f t h e f o u r p o l y m e r samples s t u d i e d , i s an i n t e r e s t i n g phenomenon. Two T^s a r e f o u n d f o r t h e c r y s t a l l i n e p o l y ( p h e n y l e n e s u l f i d e ) and f o r b o t h f o r m s o f p o l y ( e t h e r e t h e r k e t o n e ) . The o r i g i n s o f t h e n a r r o w PPS component a r e o f l e s s i m p o r t as i t i s t h o u g h t t o be due t o i s o l a t e d m o l e c u l e s o f l o w m o l e c u l a r w e i g h t w h i c h have i n c r e a s e d m o b i l i t y . Fo r a l l o f t h e PPS samples above T g , s p i n d i f f u s i o n was p r e d o m i n a n t , b o t h t h e n a r r o w and t h e b r o a d components e x p e r i e n c e t h e same r e l a x a t i o n . T h i s b e h a v i o u r i n d i c a t e s t h a t t h e two m o r p h o l o g i c a l phases a r e i n such c l o s e p r o x i m i t y t h a t s t r o n g d i p o l e i n t e r a c t i o n s a l l o w f o r s p i n e n e r g y t o be t r a n s p o r t e d b e t w e e n t h e s p i n s y s t e m s . The maximum d i s t a n c e f o r T^ s p i n d i f f u s i o n i s s e v e r a l t e n s o f n a n o m e t e r s . On t h e o t h e r h a n d , PEEK a t a l l t e m p e r a t u r e s and i n b o t h f o r m s d i s -p l a y s two T^ v a l u e s , t h u s s u g g e s t i n g t h e absence o f s p i n d i f f u s i o n a n d , - 108 -t h e r e f o r e , l a r g e (>10 nm) s e p a r a t e domains o f t h e two p h a s e s . Of c o u r s e , p a r t i a l s p i n d i f f u s i o n may be p r e s e n t b u t t h e e f f e c t o f t h i s w o u l d be d i f f i c u l t t o d e t e r m i n e . The m a j o r i t y o f s p i n r e l a x a t i o n s t u d i e s f o u n d s p i n d i f f u s i o n p r e s e n t ( 3 2 , 6 8 , 7 7 ) i n s e m i - c r y s t a l l i n e p o l y m e r s , and i t i s p r i m a r i l y i n b l e n d s o r m i x t u r e s ( 7 4 , 9 0 ) t h a t s e p a r a t e T^s a r e n o t i c e d . However , Tanaka ( 7 5 ) does r e p o r t on s e p a r a t e T^s o f h i g h l y c r y s t a l l i n e (>60%) samples o f i s o t a c t i c p o l y p r o p y l e n e . 5.6 SUMMARY AND CONCLUSION OF PMR WORK P r o t o n b r o a d - l i n e and s p i n - l a t t i c e r e l a x a t i o n measurements have b e e n made f o r amorphous and c r y s t a l l i n e samples o f p o l y ( p h e n y l e n e s u l -f i d e ) and p o l y ( e t h e r e t h e r k e t o n e ) , a t t e m p e r a t u r e s f r o m a m b i e n t t o 430K. The l i n e - s h a p e s o f a l l samples i n d i c a t e t h e p r e s e n c e o f r i g i d p r o -t o n s ( b r o a d l i n e ) and m o b i l e p r o t o n s ( n a r r o w l i n e ) . E x c e p t f o r s p e c t r a o f PPS a t h i g h t e m p e r a t u r e s , t h e b r o a d l i n e i s d o m i n a n t . The l i n e w i d t h d e c r e a s e s w i t h i n c r e a s i n g t e m p e r a t u r e a n d , i n t h e r e g i o n o f t h e g l a s s t r a n s i t i o n , t h e l i n e w i d t h d e c r e a s e s a b r u p t l y . A l s o , a t t h e T g , t h e s p i n -l a t t i c e r e l a x a t i o n t i m e s a r e l o n g e r t h a n a t any o t h e r t e m p e r a t u r e . From t h e r e l a x a t i o n d a t a , e s t i m a t e s o f a c t i v a t i o n e n e r g i e s were o b t a i n e d . P a r t i a l l y r e l a x e d s p e c t r a i n d i c a t e s e p a r a t e r e l a x a t i o n t i m e s f o r t h e b r o a d and n a r r o w components b e l o w t h e T g . Second moment v a l u e s were n o t c a l c u l a t e d b u t c o u l d be a t a l a t e r d a t e . T h i s w o u l d r e q u i r e t h e use o f a p u l s e p r o g r a m w h i c h w o u l d y i e l d s p e c t r a w i t h e v e n b a s e l i n e s . The r e c e i v e r c h a n n e l s h o u l d be t r i g g e r e d - 109 -b e f o r e t h e f i n a l p u l s e i n o r d e r t o e s t a b l i s h a good b a s e l i n e b e f o r e t h e F ID and phase a l t e r n a t i o n s h o u l d be e m p l o y e d . The e a r l y p o i n t s l o s t s h o u l d be e x t r a p o l a t e d b y t h e method d e s c r i b e d i n 5 . 5 . 1 ( c ) and t h e f i n a l v a l u e o f t h e second moment c a l c u l a t e d b y i n t e g r a t i o n o f t h e s p e c t r a i n t h e f r e q u e n c y d o m a i n . The v a l u e s c a l c u l a t e d f o r t h e s e c o n d moments c o u l d t h e n be compared w i t h v a l u e s o b t a i n e d f r o m t h e c r y s t a l s t r u c t u r e c a l c u l a t i o n s . T h i s p r o t o n NMR s t u d y , o f two s e m i - c r y s t a l l i n e p o l y m e r s , b r i n g s t o l i g h t some c o n t r a s t s b e t w e e n amorphous and c r y s t a l l i n e p o l y m e r s and b e t w e e n PEEK and PPS. The NMR l i n e s h a p e s and t h e dependence o f l i n e s h a p e o n t e m p e r a t u r e show t h e n a i v e t y o f a s s i g n i n g t h e n a r r o w l i n e t o t h e amorphous phase and t h e b r o a d t o t h e c r y s t a l l i n e . The amorphous p r o t o n s a r e n e a r l y as b r o a d as t h e c r y s t a l l i n e and t h e p r o p o r t i o n s v a r y w i t h t e m p e r a t u r e . Above T g , t h e o n s e t o f m o b i l i t y , seen as t h e i n c r e a s e o f t h e n a r r o w l i n e , i s as p r o m i n e n t i n t h e c r y s t a l l i n e as i n t h e amorphous s a m p l e . Compared t o PPS, t h e l i n e s h a p e o f PEEK shows r e l a t i v e l y l i t t l e f r e e m o t i o n above t h e g l a s s t r a n s i t i o n . I t i s l i k e l y t h a t t h e l a c k o f m o t i o n i s c l o s e l y r e l a t e d t o t h e r e m a r k a b l e a b i l i t y o f PEEK t o m a i n t a i n s t r e n g t h and s t i f f n e s s p r o p e r t i e s above T g . The a c t i v a t i o n e n e r g i e s f r o m r e l a x a t i o n d a t a s u g g e s t h i g h e r m o t i o n a l a c t i v a t i o n e n e r g i e s f o r PEEK t h a n f o r PPS; t h i s i s n o t e d i n l i g h t o f t h e s u p e r i o r s t r e n g t h o f PEEK. The p r e s e n c e o f two d i s t i n c t r e l a x a t i o n t i m e s i n t h e s i n g l e p o l y m e r l e a d s t o t h e i n f e r e n c e o f l a r g e r i g i d r e g i o n s ( o f s e v e r a l t e n s o f n a n o m e t e r s ) i n t h e p o l y m e r w h i c h may have a r e i n f o r c i n g e f f e c t , a g a i n c o n t r i b u t i n g t o t h e s t r e n g t h o f t h e m a t e r i a l ( 3 7 ) . - 110 -6. CONCLUSION 6 . 1 GENERAL REMARKS I n coming y e a r s , t h e h i g h p e r f o r m a n c e t h e r m o p l a s t i c s w i l l c o n t i n u e t o t a k e a g r e a t e r s h a r e o f t h e c o m p o s i t e m a t r i x m a r k e t . Improvemen ts i n t h e f a b r i c a t i o n t e c h n i q u e s and an i n c r e a s i n g a v a i l a b i l i t y o f t h e t h e r m o -p l a s t i c p o l y m e r s make t h e s w i t c h f r o m t h e t h e r m o s e t t i n g epoxy r e s i n s more a t t r a c t i v e t o i n d u s t r y . O t h e r t h e r m o p l a s t i c s , newer t o t h e compos-i t e m a r k e t t h a n PPS and PEEK a r e a l s o c o m p e t i n g w e l l . The r e s e a r c h i n t h i s f i e l d has a b r i g h t f u t u r e as w o r k e r s a r e e n c o u r a g e d b y t h e c o m m e r c i a l d e v e l o p m e n t s . T h e r e i s s t i l l much t o be l e a r n e d , e s p e c i a l l y i n t h e a r e a o f c o r r e l a t i n g t h e m a c r o s c o p i c and m i c r o s c o p i c p r o p e r t i e s o f p o l y m e r s . S o l i d s t a t e NMR i s one o f t h e most p r o m i s i n g t e c h n i q u e s f o r t h e s t u d y o f t h e m i c r o s c o p i c n a t u r e o f m a c r o -m o l e c u l e s : i t c a n p r o v i d e i n f o r m a t i o n a b o u t b o t h t h e m o l e c u l a r s t r u c t u r e and t h e m o l e c u l a r m o t i o n o f t h e p o l y m e r . 6 . 2 SUMMARY The p u r p o s e o f t h i s p a r t i c u l a r s t u d y was t o use NMR t o i n v e s t i g a t e two t h e r m o p l a s t i c p o l y m e r s , p o l y ( e t h e r e t h e r k e t o n e ) and p o l y ( p h e n y l e n e s u l f i d e ) . A l t h o u g h b o t h PEEK and PPS have v e r y good c h a r a c t e r i s t i c s f o r use - I l l -as f i b r e c o m p o s i t e m a t r i c e s , i n mos t c a s e s , PEEK d i s p l a y s s u p e r i o r p r o p -e r t i e s . T h i s i s f i r s t a p p a r e n t i n t h e t r a n s i t i o n t e m p e r a t u r e s measured b y DSC. The g l a s s t r a n s i t i o n , c r y s t a l l i z a t i o n and m e l t i n g t e m p e r a t u r e s o f PEEK a r e a l l a t l e a s t 50°C h i g h e r t h a n t h o s e o f PPS. The more comp lex s t r u c t u r e o f PEEK became a p p a r e n t i n t h e h i g h r e s o l u t i o n CP/MAS s p e c t r a . The s e v e n i n e q u i v a l e n t c a r b o n s o f PEEK were a s s i g n e d t o t h e f i v e l i n e s o f t h e s p e c t r u m . The a i d o f d i p o l a r dephas -i n g and r e f e r e n c e t o mode l compounds was r e q u i r e d . The PPS s p e c t r a l a s s i g n m e n t was s t r a i g h t f o r w a r d : two i n e q u i v a l e n t c a r b o n t y p e s ( p r o t o -n a t e d and n o n - p r o t o n a t e d ) were e a s i l y d i s t i n g u i s h e d b y t h e d i p o l a r d e p h a s i n g e x p e r i m e n t . A l t h o u g h t h e CP/MAS s p e c t r a o f b o t h p o l y m e r s a r e b r o a d e r t h a n t h e i r c r y s t a l l i n e c o u n t e r p a r t s , t h e d i f f e r e n c e i n l i n e w i d t h s b e t w e e n t h e amor-phous and c r y s t a l l i n e i s more marked i n t h e PPS s p e c t r u m . T h i s r e f l e c t s t h e g r e a t e r d e g r e e o f c r y s t a l l i n i t y o f PPS. The h i g h r e s o l u t i o n s p e c t r a o f samples o f v a r i o u s c r y s t a l l i n i t i e s s u g g e s t a s u p e r p o s i t i o n o f c r y s -t a l l i n e and amorphous l i n e s . V a r i a b l e - c o n t a c t - t i m e measurements f o r t h e CP/MAS e x p e r i m e n t s were n o t made on PPS. Those f o r PEEK i n d i c a t e t h a t t h e op t imum c o n t a c t t i m e s f o r p r o t o n a t e d c a r b o n s a r e s h o r t e r t h a n f o r n o n - p r o t o n a t e d c a r b o n s . I t i s t h o u g h t t h a t t h e s h o r t e r op t imum c o n t a c t t i m e s f o r t h e amorphous m a t e r i a l r e f l e c t t h e s h o r t e r T^p o f t h e s p i n - l o c k e d p r o t o n m a g n e t i z a t i o n and g r e a t e r m o l e c u l a r m o t i o n i n t h e amorphous m a t e r i a l . The PMR w i d e - l i n e s p e c t r o s c o p y a l l o w e d t h e p o l y m e r s t o be s t u d i e d as f u n c t i o n s o f t e m p e r a t u r e . A r r h e n i u s p l o t s o f r e l a x a t i o n measure -ments y i e l d e d a c t i v a t i o n e n e r g y e s t i m a t e s w h i c h were i n k e e p i n g w i t h t h e - 112 -p r o p e r t i e s o f t h e p o l y m e r s . The e n e r g y b a r r i e r f o r PEEK m o t i o n was l a r g e r (PEEK has h i g h e r s t r e n g t h and s t i f f n e s s and a h i g h e r g l a s s t r a n -s i t i o n t e m p e r a t u r e ) . The a c t i v a t i o n e n e r g y o f amorphous PPS was l o w e r t h a n f o r c r y s t a l l i n e PPS, s u g g e s t i n g a g a i n a l a r g e d i f f e r e n c e b e t w e e n t h e m o r p h o l o g i e s o f t h e two f o r m s . I t was i n t e r e s t i n g t o o b s e r v e t h e b e h a v i o u r o f t h e m a t e r i a l s i n t h e g l a s s t r a n s i t i o n r e g i o n . I n a l l cases t h e s p i n - l a t t i c e r e l a x a t i o n t i m e s were l o n g e s t a t t h e g l a s s t r a n s i t i o n t e m p e r a t u r e . I t i s u n c e r t a i n why t h e r e l a x a t i o n mechanism s h o u l d be most u n e f f e c t i v e a t t h a t t e m p e r a t u r e . Pe rhaps t h e phenomenon i s p a r a l l e l t o t h e m a x i m i z a t i o n o f t a n 6 a t t h e Tg w h i c h i s seen i n m e c h a n i c a l s p e c t r o s c o p y . The l i n e w i d t h a l s o shows d i s t i n c t i v e b e h a v i o u r a t t h e Tg as t h e o n s e t o f c o o p e r a t i v e m a i n c h a i n m o t i o n causes t h e n a r r o w i n g o f t h e s p e c t r a l w i d t h . S i m i l a r m o t i o n a l n a r r o w i n g i s r e s p o n s i b l e f o r amorphous s p e c t r a , b e i n g n a r r o w e r t h a n t h e c r y s t a l l i n e s p e c t r a a t a l l t e m p e r a -t u r e s . J u s t as i n t h e CP/MAS s p e c t r a , t h e a m o r p h o u s / c r y s t a l l i n e d i f f e r -ence i n l i n e w i d t h i s l a r g e r f o r PEEK t h a n f o r PPS. The l i n e s h a p e o f s p e c t r a measured above t h e Tg s u g g e s t t h a t t h e r e i s c o n s i d e r a b l y more m o l e c u l a r m o t i o n i n t h e PPS l a t t i c e t h a n i n t h e PEEK l a t t i c e . T h i s c o r r e l a t e s w i t h t h e o b s e r v a t i o n t h a t PEEK r e t a i n s a r e m a r k a b l e p r o p o r -t i o n o f i t s s t r e n g t h p r o p e r t i e s even a t t e m p e r a t u r e s above t h e g l a s s t r a n s i t i o n p o i n t . - 113 -6 . 3 SUGGESTIONS FOR THE CONTINUATION OF THE STUDY T h i s s t u d y o f t h e r m o p l a s t i c s b y NMR i s b y no means c o m p l e t e . The re a r e a v a r i e t y o f o t h e r e x p e r i m e n t s w h i c h r e m a i n t o be d o n e . ( i ) S p i n - l a t t i c e r e l a x a t i o n t i m e s i n t h e r o t a t i n g f r a m e w o u l d be w e l l w o r t h m e a s u r i n g . The r e s u l t s c o u l d be compared t o t h e l i n e w i d t h w o r k , as t h e two methods r e s p o n d t o m o t i o n s o f a p p r o x i m a t e l y t h e same f r e q u e n c y . A k n o w l e d g e o f t h e T-^p r e l a x a t i o n i s a l s o i m p o r -t a n t i n t h e i n t e r p r e t a t i o n o f t h e 1 3 C c o n t a c t t i m e s . ( i i ) Second moment measurements compared t o t h e c a l c u l a t e d r i g i d -l a t t i c e s e c o n d moments may g i v e i n s i g h t i n t o t h e m o t i o n a l n a r r o w -i n g w h i c h t a k e s p l a c e . ( i i i ) Low t e m p e r a t u r e s t u d i e s o f r e l a x a t i o n and s e c o n d moments c o u l d a l s o be u s e f u l . A c t i v a t i o n e n e r g y c a l c u l a t i o n s f r o m s e c o n d moment d a t a r e q u i r e s t h e l i m i t i n g v a l u e o f t h e l i n e w i d t h a t l o w t e m p e r a -t u r e s ( 3 2 ) . ( i v ) The c a p a c i t y t o do v a r i a b l e t e m p e r a t u r e CP/MAS, i n t h i s l a b o r a -t o r y , i s e x p e c t e d i n t h e n e a r f u t u r e . The h i g h r e s o l u t i o n s p e c t r a a t above Tg t e m p e r a t u r e s c o u l d p r o v e i n t e r e s t i n g . ( v ) L i n e s h a p e d e c o n v o l u t i o n and s p e c t r a l s u b t r a c t i o n c o u l d be done . I t may be p o s s i b l e t o e s t i m a t e t h e r e l a t i v e p r o p o r t i o n s o f t h e v a r i o u s c o m p o n e n t s . A m a j o r a c h i e v e m e n t w o u l d be a c o r r e l a t i o n o f NMR d a t a t o t h e f r a c t i o n a l c r y s t a l l i n i t y v a l u e s f o u n d b y X - r a y s p e c t r o s c o p y . L o o k i n g f a r t h e r a f i e l d , PEEK and PPS a r e o n l y two o f a g r o w i n g num-b e r o f h i g h p e r f o r m a n c e t h e r m o p l a s t i c s . S i m i l a r NMR s t u d i e s c o u l d be - 114 -made f o r t h e c o m p e t i n g p o l y i m i d e s : t h e K - p o l y m e r made b y Dupont and ULTEM b y G e n e r a l E l e c t r i c P l a s t i c s . The g o a l w o u l d be t o e s t a b l i s h a c l e a r p a t t e r n o f t h e NMR f i n d i n g s f o r t h e s e n o v e l t h e r m o p l a s t i c s . - 115 -REFERENCES 1 . " A r o m a t i c Po lymer C o m p o s i t e " , T e c h n i c a l L i t e r a t u r e ( I C I p i c , Welwyn Garden C i t y ) ( 1 9 8 2 ) . 2 . " ' V i c t r e x ' PEEK/carbon f i b r e " , T e c h n i c a l L i t e r a t u r e ( I C I p i c , Welwyn Garden C i t y ) PD3 ( 1 9 8 2 ) . 3 . B i s h o p , S . M . , C u r t i s , P . T . , and D o r e y , G . , R o y a l A i r c r a f t E s t a b -l i s h m e n t T e c h n i c a l R e p o r t 84061 ( 1 9 8 4 ) . 4 . Ma, C . C . M . , O ' C o n n o r , J . E . , and L o u , A . Y . , SAMPE Q u a r t e r l y , J u l y 12 ( 1 9 8 4 ) . 5 . B i t t e n c e , J . C . , M a t e r i a l s E n g i n e e r i n g , June 55 ( 1 9 8 4 ) . 6 . H a r t n e s s , J . T . , u n p u b l i s h e d r e s u l t s . 7 . D o n a l d s o n , S . L . , Compos i tes 1 6 , 103 ( 1 9 8 5 ) . 8 . H a r t n e s s , J . T . , SAMPE Q u a r t e r l y , 33 ( 1 9 8 3 ) . 9 . C o g s w e l l , F . N . and H o p p r i c h , M . , Compos i tes 1 4 , 251 ( 1 9 8 3 ) . 1 0 . Muzzy , J . D . and K a y s , A . O . , Po lymer Compos i tes 5, 169 ( 1 9 8 4 ) . 1 1 . " ' V i c t r e x ' PEEK A r o m a t i c P o l y m e r " , T e c h n i c a l L i t e r a t u r e ( I C I p i c , Welwyn Garden C i t y ) PD4 ( 1 9 8 2 ) . 1 2 . Woodhams, R . T . , P o l y m . Eng. S c i . 2 5 , 562 ( 1 9 8 5 ) . 1 3 . " ' V i c t r e x ' PEEK/carbon f i b r e " , T e c h n i c a l L i t e r a t u r e ( I C I p i c , Welwyn Garden C i t y ) PD5 ( 1 9 8 2 ) . 1 4 . H a r t n e s s , J . T . , 2 5 t h N a t i o n a l SAMPE Symposium, 376 ( 1 9 8 0 ) . 1 5 . B r a d y , D . 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NMR - 1280 M a n u a l , N i c o l e t M a g n e t i c s C o r p o r a t i o n , F reemont CA, p . 100 ( 1 9 8 2 ) . 8 2 . L e v y , G.C. and P e a t , I . R . , J . Magn. Reson . 1 8 , 500 ( 1 9 7 5 ) . 8 3 . T r a p p e n i e r s , N . J . , G e r r i t s m a , C . J . , and O o s t i n g , P . H . , P h y s i c a 3 0 , 997 ( 1 9 6 4 ) . 8 4 . M c B r i e r t y , V . J . , Po lymer 1 5 , 503 ( 1 9 7 4 ) . 8 5 . v a n S t e e n w i n k e l , R . , Z . N a t u r f o r s c h 2 4 a , 1526 ( 1 9 6 9 ) . 8 6 . R e s i n g , H.A. , G a r r o w a y , A . N . , Weber, D . C , F e r r a r i s , J . , and S l o t -f e l d t - E l l i n g s e n , D . , Pure amd A p p l . Chem. 5 4 , 595 ( 1 9 8 2 ) . 8 7 . G a r r o w a y , A . N . , R i t c h e y , W . M . , and M o n i z , W . B . , M a c r o m o l e c u l e s 15 , 1051 ( 1 9 8 2 ) . 8 8 . T o n e l l i , A . , M a c r o m o l e c u l e s 6 , 682 ( 1 9 7 3 ) . 8 9 . H a g e l l , P . C and Beck , L . , M a c r o m o l e c u l e s 1 0 , 213 ( 1 9 7 7 ) . 9 0 . L i n d , A . C , P o l y m . P r e p r . 2 1 , 241 ( 1 9 8 0 ) . - 120 -APPENDIX I CP/MAS PULSE PROGRAMS - 121 -PULSE PROGRAM FOR VARIABLE CONTACT TIME EXPERIMENT A D C B 0 1 +V 1 A +X +Y +W 2 B +Y +W 3 3 1 1 +W -W 4 1 B 6 5 0 F 6 0 7 1 E 1 -V 8 1 +X +Y +W 9 B +Y +W A 2 +W -W B 0 F D l = 6 . 0 x 1CT 6 DA - v a r i a b l e DB - 2 . 6 x 1 0 ' 5 D3 - 2 . 6 x 1 0 - 2 DO - 4 . 0 Fo r t h e c o n v e n t i o n a l CP/MAS p r o g r a m DA i s r e p l a c e d b y D2 and i s 1 ms i n l e n g t h . - 122 -PULSE PROGRAM FOR DIPOLAR DEPHASING EXPERIMENT A D C B 0 1 +V 1 2 +W 2 B +X +Y 3 3 1 1 +W -W 4 1 B 6 5 0 F 6 0 7 1 E 1 -V 8 1 +X +Y 9 B +Y +W A 2 +W -W B 0 F D I - 6 . 0 x 1 0 " 6 D3 - 2 . 5 x 1 0 ' 2 DA - 5 . 0 X 1 0 " 3 DO = 4 . 0 DB - 4 . 0 x 1 0 -- 123 -APPENDIX I I VARIABLE CONTACT TIME PLOTS FOR PEEK - 124 -o.s -1.5l I i I i -3.0 -2.0 -1.0 0.0 1.0 2.0 L N OF CONTACT T I M E CLN M S E C ] VRRIABLE CONTACT TIME FOR CRYSTALLINE PEEK 0.5 - l . s l i i i i I -3.0 -2.0 -1.0 0.0 1.0 2.0 LN OF CONTRCT T I M E [ L N M S E C ] VARIABLE CONTACT TIME FOR CRYSTALLINE PEEK - 125 -o.s -2, o - i . u ***** L N OF CONTACT T I M E CLN M S E C ] VARIABLE CONTACT TIME FOR AMORPHOUS FEEK 

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