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Accelerated radiation polymerization of vinyl-divinyl comonomer systems Micko, Michal 1973

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ACCELERATED RADIATION POLYMERIZATION OF VINYL-DIVINYL COIvIONOMER' SYSTEMS  by MICHAEL M . MICKO BeChem ( E n q * )  C.Sc*  A  s  Slovak Technical B r a t i s l a v a , 1959  University,  Slovak Technical U n i v e r s i t y , B r a t i s l a v a , 1966  THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  i n t h e Department  Forestry  We  accept  t h i s t h e s i s as confirming  t o the required  standard»  THE  U N I V E R S I T Y OF B R I T I S H COLUMBIA April,  1973  In  presenting  this  thesis  an a d v a n c e d d e g r e e the L i b r a r y I  f u r t h e r agree  for  scholarly  by h i s of  shall  this  written  at  the U n i v e r s i t y  make  it  It  f i n a n c i a l gain  of  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, C a n a d a  requirements  B r i t i s h Columbia, for  Columbia  I agree  r e f e r e n c e and this  shall  that copying  not  or  for  that  study. thesis  by t h e Head o f my D e p a r t m e n t  is understood  permission.  Department  of  the  for extensive copying of  p u r p o s e s may be g r a n t e d  for  fulfilment of  freely available  that permission  representatives. thesis  in p a r t i a l  or  publication  be a l l o w e d w i t h o u t my  i  ABSTRACT  Gel-effect polymerization  (Ge) a c c e l e r a t i o n i n r a d i a t i o n  of methyl methacrylate  (MMA) - d i v i n y l monomer  (DVM) systems and p r o p e r t i e s of r e s u l t i n g polymer have been i n v e s t i g a t e d . v a r i a b l e molecular i . e . , ethylene  bridge  late  esters with  l e n g t h between the double bonds,  g l y c o l dimethacrylate  g l y c o l dimethacrylate dimethacrylate  Four methacrylate  products  (EGDMA), d i e t h y l e n e  (DEGDMA), t r i e t h y l e n e g l y c o l  (TrEGDMA) and t e t r a e t h y l e n e g l y c o l dimethacry- .  (TEGDMA), were used as DVM a c c e l e r a t o r s and c r o s s l i n k i n g  agents. The  course  of p o l y m e r i z a t i o n was f o l l o w e d by  temperature ( T ) - t i m e ( t ) p o l y m e r i z a t i o n exotherm c u r v e s . new technique  A  was developed t o determine the " G e l - E f f e c t  P o i n t " (GEP) and i n d i v i d u a l p o l y m e r i z a t i o n  parameters  a s s o c i a t e d w i t h g e l a t i o n i n c r o s s l i n k e d network, i . e . , polymerization rate c o e f f i c i e n t o v e r a l l curing rate ( l / t ^ ^ ) *  (PRC), c u r i n g time  (tii^),  and o v e r a l l a c c e l e r a t i o n  constant ( K ) . The  o v e r a l l c u r i n g r a t e was found t o be p r o p o r t i o n a l  t o the volume c o n c e n t r a t i o n of c r o s s l i n k i n g agent only up t o 15 t o 20% DVM i n the system.  Within t h i s concentration  interval  11  the o v e r a l l a c c e l e r a t i o n c o n s t a n t s  increased w i t h molecular  d i s t a n c e between DVM double bonds i n t h e f o l l o w i n g  order:  EGDMA (1.1 x I C T ) , DEGDMA (1.5 x 1 0 - 3 ) , TrEGDMA (1.8 x 1 0 ~ ) , 3  and  3  TEGDMA (2.4 x 1 0 ~  3  rnin"^ cone.""-*).  values, i . e . , concentration  i n reverse  order.  concentration  of d i v i n y l monomer r e q u i r e d t o  reduce t h e c u r i n g time t o one-half increased  Half-time  of t h a t f o r pure MMA,  Numerically,  half-time  concentra-  t i o n v a l u e s f o r TEGDMA, TrEGDMA, DEGDMA, and EGDMA were 3, 4, 5, and 7% r e s p e c t i v e l y . The allowed  calculated overall acceleration  p r e d i c t i o n and c a l c u l a t i o n of c u r i n g t i m e s for..,.  i n d i v i d u a l comonorner m i x t u r e s . p r e d i c t e d and e x p e r i m e n t a l l y error.  constant  The agreement between  measured v a l u e s was w i t h i n 5%  The d e r i v e d e m p i r i c a l e q u a t i o n  f o r p r e d i c t i o n of c u r i n g  time was a l s o a p p l i c a b l e t o t h e h e a t - c a t a l y s t  polymerization  system. A l l d i v i n y l monomers s t u d i e d were found t o be e f f i c i e n t c r o s s l i n k i n g a g e n t s and improved t h e thermomechanical and s t r e n g t h p r o p e r t i e s of the r e s u l t i n g c o p o l y m e r s .  The c o m p r e s s i o n  s t r e s s , s t r a i n and toughness e x h i b i t e d w e l l d e f i n e d maxima w i t h i n 5-lC/o o f d i v i n y l monomer i n t h e m i x t u r e . concentration  i n t e r v a l both  Within  maximal a c c e l e r a t i o n and s u p e r i o r  m e c h a n i c a l p r o p e r t i e s of copolymers were o b t a i n e d . numerical  value  this  o f copolymer c o n n e c t i o n  number (CN  The ) was found  t o be a u s e f u l s t r u c t u r a l parameter r e l a t i n g m e c h a n i c a l and t h e r m o m e c h a n i c a l p r o p e r t i e s w i t h copolymer c r o s s l i n k i n g d e n s i t y .  iii  TABLE OF CONTENTS PAGE i TABLE OF CONTENTS.. LIST OF  c e o  <>«»'«««  o  iii  r> f• o • * o » «•  vi  TABLES.....  viii  LIST OF FIGURES... LIST OF S Y M B O L S . . . . . . . . . . . . .  «• * * • • «• •  ACKNOWLEDGEMENTS...  «a • a 9 * • 0 0  o t> « • • # «•  2©0  L J ^ I I 2 J R . / \ T 0 Piiz  R IEV  11_ v •/»  0 « « «  » •  2.1 R a d i c a l Chain-Growth 2.1.1  Free r a d i c a l s ;  2.1.2  Radiation  © * o &»  * e © o  « •  t>  I  o * • 0 e  6 6  f o r m a t i o n and  p o l y m e r i z a t i o n of v i n y l  2.1.2.1 K i n e t i c  xiii  o » e  » ^ « » •  Polymerization...  xi  considerations........  7 9  polymerization  10  2.1.2.3 Bulk p o l y m e r i z a t i o n of MMA....  11  . 2.1.2.2 Overall rate  2.2 P o l y m e r i z a t i o n i n Gel-Phase  of  Media...........  13  A u t o a c c e l e r a t i o n ; experimental evidence f o r g e l - e f f e c t (Ge)...........  15  2.2.2 A c c e l e r a t i o n w i t h i n the c r o s s l i n k e d netv^ork; c o p o l y m e r i z a t i o n cf v i n y l d i v i n y l comonomer systems.............  22  2.2.2.1 O r o s s l i n k i n g and g e l a t i o n ; p r e d i c t i o n of g e l - e f f e c t (Ge).  23  2 . 2 . 2 . 2 I n f l u e n c e of d i v i n y l monomer molecular b r i d g e l e n g t h „.  28  2.2.1  PAGE 2.2.2.3 A c c e l e r a t e d p o l y m e r i z a t i o n i n f o r m i n g wood p o l y m e r c o m p o s i t e s ( i"/PC ) . . . . « « . . « . » . o o o . . o . . o . o . . .  3 l  3 « 0 M A T E R I A L S AND M E i H O D S . . . » . . « . • . . . . . . . . . . . . . . . . . . .  36  3 o 1 Mon 0 me r S e « o . « . . « o « o A 0 o # « o . o o e o t t . o « o . 0 . o « o o o . . 3.1.1  Methyl  3.1.2 D i v i n y l  m e t h a c r y l a t e . ••....«<»•••••...«.• •  36  m o n o m e r s . » . . . . o . . . . . . . . . . . . . . . «  36  3.1.3 C a l c u l a t i o n o f s t r u c t u r a l 3.1.4 P r e p a r a t i o n 3.2 R a d i a t i o n 3.2.1  parameters...  o f comonomer m i x t u r e s . . . . . .  Polymerization  D e f i n i t i o n and determination of polymerization parameters..............  40  3.3 P r o p e r t i e s  procedure.  o f Polymer  42  c  results  Products............  Thermomechanical  3.3.2 M e c h a n i c a l  n HT » r i  39 40  3.2.3 R e p r o d u c i b i l i t y o f e x p e r i m e n t a l  s  37  Technique...........  3.2.2 P o l y m e r i z a t i o n  3.3.1  36  43  »..  44  properties............  44  strength  properties...,.,...,  46  52  TOM  5.1 R a d i a t i o n P o l y m e r i z a t i o n o f t h e M-4A-TEGDMA C onion o (no IT S y s t G i i u * « 6 f ) « « 4 4 « < ( t i ) e * o « r } a a r } M « « « « « « 5.2 I n f l u e n c e o f M o l e c u l a r B r i d g e L e n g t h i n D i v l n y — Monomers* « o . . . . . . . » . . . . . . 4 . o . o o « . . o o . 5.3 P r e d i c t i o n a n d C a l c u l a t i o n o f C u r i n g 5.3.1  A p p l i c a t i o n of the derived p u b l i s h e d results..»•  Times...  61  equation t o  5.4 A n a l y s i s o f C r o s s l i n k e d P o l y m e r P r o d u c t Thermomechanical C u r v e s . . . . . . . . . . . . . . . 5.5 A n a l y s i s o f P o l y m e r P r o d u c t C o m p r e s s i o n S"LxGSo**o\,x*ciu. n u.xv©so # •» o « * * « « * * *>«*«0 © &  ^  * « * » « *  63 ,  r  1  0  70  0  V  6  tt  0 COwO.L< LIS IOl\fS  ftft««94a«0£te»«QG>00Q«*eo«9C.«««O0oe>»««»  7.0 RECOMMENDATIONS F O R F U R T H E R S T U D Y 3  o  0  Lj  X T H H.A. 1 LIR.E C 1 I E D «  « « M « « « 0 « * o i > « t ( i t o « e o t * t i o « * o » » «  PAGE 76  78 79  vi  L I S T OF TABLES  TABLE 2-1.  2-2.  PAGE  E f f e c t of c o n v e r s i o n tion characteristics  l e v e l on t h e p o l y m e r i z a of m e t h y l m e t h a c r y l a t e  ^  Some d a t a on p o l y m e r i z a t i o n o f d i m e t h a c r y l a t i c e s t e r s ( p h o t o i n i t i a t o r - b e n z o i n 0,2%) ( 8 ) . . . .  ^9  3-1»  Some p r o p e r t i e s o f m e t h y l m e t h a c r y l a t e (MMA) and d i v i n y l monomers (DVM) u s e d i n t h i s study-  90  3- 2.  C o n c e n t r a t i o n s and r e l a t i v e v i s c o s i t i e s o f d i f f e r e n t methyl methacrylate (Mr.'A)-divinyl monomer (DVM) m i x t u r e s , ..........  4 - I«  Polymerization•exotherm characteristics for t h e ' MMA-TEGDMA comonomer s y s t e m ( 6 7 , 6 9 ) . . . . . . .  92  C a l c u l a t e d p o l y m e r i z a t i o n parameters f o r t h e MMA--TEGDMA c omonomer s y s t e m (67,69) . . . . . . . . . . .  93  4-2. 4-3.  P o l y m e r i z a t i o n exotherm c h a r a c t e r i s t i c s f o r MMA-EGDMA, MMA-DEGDMA and MMA~ TrEGDMA -i  4-4.  4-5.  4-6.  4-7.  4-8.  QA.  c omon oine r sysuems » o . « « . . o . ?. ?. o . . . . . . . . C a l c u l a t e d p o l y m e r i z a t i o n p a r a m e t e r s f o r MMAEGDMA, MMA-DEGDMA and MMA-TrEGDMA comonomer  '•  D i f f e r e n c e s b e t w e e n measured and c a l c u l a t e d c u r i n g t i m e s f o r lower c o n c e n t r a t i o n s of d i v i n y l monomer (DVM) i n MMA-DVM s y s t e m s . . . . . . D i f f e r e n c e s between m e a s u r e d and c a l c u l a t e d c u r i n g times f o r lower c o n c e n t r a t i o n s of TEGDMA i n t h e s t y r e n e (S)-TEGDMA s y s t e m ( 7 0 ) . . D i f f e r e n c e s i n c a l c u l a t e d and p u b l i s h e d c u r i n g t i m e s f o r TBS.-di-and t r i - v i n y l comonomer s y s t e m s ( 5 3 ) . . . . i . . . . . . . . . . . . .  «  D i f f e r e n c e s i n c a l c u l a t e d and p u b l i s h e d c u r i n g times f o r h e a t - c a t a l y s t cured MMA-trimethylol p r o p a n e t r i r n e t h a c r y l a t e (TMPTMA) p o l y m e r i z a u X Oil  Sy S*t GHl  (  3 ) a t u p o :» i a 3 » a o « aQ4  +  o«oee*i<i6&*e4o  96  '  97  98  Vll  PAGE  4-9. 4-10.  R a d i a t i o n p o l y m e r i z a t i o n of TEGDMA a t d i f f e r e n t dose Thermomechanical p r o p e r t i e s of r a d i a t i o n c u r e d poly(MMA) and c r o s s l i n k e d MMA-DVM polymer prOdliCtS» e « o # » « o » * o a ( > O i » 4 o O ' j e c * « > j i ) i ) 8 i ) e * « » o O ( « 9 « o »  4-11.  M e c h a n i c a l p r o p e r t i e s o f r a d i a t i o n cured . poly(MMA) and c r o s s l i n k e d MMA-DVM polymer  4-12.  C a l c u l a t e d p a r a m e t e r s from c o m p r e s s i o n s t r e s s s t r a i n c u r v e s f o r r a d i a t i o n cured poly(MMA) and MMA-DVM polymer p r o d u c t s .  101  103  viii  L I S T ' O F FIGURES FIGURE  3-1.  3-2,  3-3.  PAGE  S o l u t i o n of a t y p i c a l p o l y m e r i z a t i o n exotherm curve i n c l u d i n a . d e r i v a t i o n of " G e l - E f f e c t P o i n t " (GEp)» "Cure" (MAX), and showing " A c t i v a t i o n " ( l ) and " A c c e l e r a t i o n " ( I I )  ^ •  T y p i c a l thermomechanical c u r v e s f o r thermop l a s t i c ( l ) , p a r t l y c r o s s l i n k e d (2) and f u l l y c r o s s l i n k e d ( 3 ) p o l y m e r p r o d u c t s ; and showing f o r (2) s o l u t i o n s f o r g l a s s t r a n s i t i o n temperature ( T g ) , thermal d i s t o r t i o n temperat u r e (TDT') and s l o p e ( s ) i n t h e t r a n s i t i o n  ^  P o l y m e r s t r e s s - s t r a i n c u r v e n o m e n c l a t u r e and t y p i c a l curves f o r d i f f e r e n t types of p l a s t i c s (90  - -  79)  1  4-1.  R e l a i. t i o n s h i p between t?,^x * volume c o n c e n i comonomer trat ion o — f TEGDMA — — — n t—h e "MMA-TEGDMA -- - ~ — — m i x t u r e (6 / , 6 9 ) . . . . . . . . . . . . . . . . . o . . . . . . . . . . . . .  4-2.  Polymerization rate c o e f f i c i e n t s i n " A c t i v a t i o n " (PRCi) and " A c c e l e r a t i o n " (PRCn) p e r i o d s a s f u n c t i o n s o f TEGDMA volume c o n c e n t r a t i o n i n t h e MMA-TEGDMA comonomer m i x t u r e (67 69)  a n c  4-3.  R e l a t i o n s h i p between o v e r a l l c u r i n g r a t e ( l / t s . - w ) and TEGDMA volume c o n c e n t r a t i o n i n t h e MMA-TEGD;- "iA comonomer m i x t u r e ( 6 7 . 6 9 ) . . . . . .  4-4.  Relationship (DVM)'volume  4-5.  4-6.  0 0  between t and d i v i n y l c o n c e n t r a t i o n i n MMA-DVM M  A  X  1 Q  8  monomer  R e l a t i o n s h i p between tQEP and d i v i n y l - m o n o m e r (DVM) volume c o n c e n t r a t i o n i n MMA-DVM corn0nornGx r n i x t i J X G S o * i » v t f » o * < > 4 o © L > » # « o < » # * e <?©«•<>*»* Polymerization rate c o e f f i c i e n t s i n " A c t i v a t i o n " ( P R C j ) and " A c c e l e r a t i o n " (PRCTJ) p e r i o d s a s f u n c t i o n s o f d i v i n y l monomer (DVM } volume c o n c e n t r a t i o n i n MMA-DVM comonomer  110  111  112  Ix  FIGURE  4-7,  R e l a t i o n s h i p b e t w e e n t ^ ^ and t p f o r d i f f e r e n t ' MMA-DVM comonomer s y s t e m s and t h e  4-8.  R e l a t i o n s h i p between o v e r a l l c u r i n g r a t e UAr/iAx) a n d DVM c o n c e n t r a t i o n i n MMA-DVM  4-9.  O v e r a l l a c c e l e r a t i o n c o n s t a n t (K) and i t s r e c i p r o c a l . (l/l<) a s f u n c t i o n s o f d i v i n y l monomer c o n n e c t i o n number (CNQYM* Table 3 - 1 ) . .  4-10.  G E  R e l a t i o n s h i p between o v e r a l l c u r i n g r a t e ( l / t j , / ^ ) a n d DVM c o n c e n t r a t i o n i n t - b u t y l s t y r e n e (TBS)-DVM m i x t u r e s , E v a l u a t i o n of o r i g i n a l heat c a t a l y s t data from ( 5 3 ) . . . oo a «  o  4-11.  Overall curing rate (lA^vO the r a d i a t i o n dose r a t e .  4-12.  Shape o f t h e r m o m e c h a n i c a l c u r v e s f o r MMAEGDMA p o l y m e r products.........................  4-13.  Shape o f t h e r m o m e c h a n i c a l c u r v e s f o r MMAi E G D i v i A polymex' produces.........................  4-14.  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 .) a s a f u n c t i o n o f c o p o l y m e r c o n n e c t i o n number ( C M ) f o r d i f f e r e n t MMA-DVM p o l y m e r p r o d u c t s  a  s  f u n c t i o n of  a  c  C 0  4-15.  T h e r m a l d e f o r m a t i o n d e g r e e (TDD) a n d t h e r m a l d i s t o r t i o n t e m p e r a t u r e (TDT) a s f u n c t i o n s o f c o p o l y m e r c o n n e c t i o n number ( C M ) f o r d i f f e r e n t MMA-DVM p o l y m e r p r o d u c t s . . . . . . . . . . . . . C 0  4-16.  L i n e a r thermomechanical deformation c o e f f i c i e n t (LTDC) a s a f u n c t i o n o f d i v i n y l monomer (DVM) v o l u m e c o n c e n t r a t i o n i n MMA-DVM p o l y m e r products.....  4-17.  L i n e a r thermomechanical deformation c o e f f i c i e n t (LTDC) a s a f u n c t i o n o f c o p o l y m e r c o n n e c t i o n number ( C N ) f o r d i f f e r e n t MMA-DVM p o l y m e r products. c o  4-18.  Shape o f c o m p r e s s i o n s t r e s s - s t r a i n c u r v e s f o r MMA-EGDMA p o l y m e r p r o d u c t s . . . . . . c . . . . .  X  FIGURE  4-19.  Shape o f c o m p r e s s i o n s t r e s s - s t r a i n f o r MMA-TEGDMA p o l y m e r p r o d u c t s . O O  curves 9  O  O  9  9  0  O  &  O  9  4-20,  Compression s t r e s s - s t r a i n parameters as f u n c t i o n s o f comonomer c o m p o s i t i o n . The MMAEGDMA comonomer s y s t e m . . . . . . . . . . . . . 0 0 0 0 0 * 0 0 0  4-21.  Compression s t r e s s - s t r a i n parameters as f u n c t i o n s o f comonomer c o m p o s i t i o n . The MMA DEGDMA comonomer s y s t e m . . . . . . . . . . Q G 4 O 0 0 O 0 O 0 O  4-22.  Compression s t r e s s - s t r a i n parameters as f u n c t i o n s o f comonomer c o m p o s i t i o n . Ihe MMA TrEGDMA comonomer s y s t e m . . . . . . , , , . O 0 0 O 0 0 Q 0 0  4-23.  Compression s t r e s s - s t r a i n parameters as f u n c t i o n s o f comonomer c o m p o s i t i o n . The MMA TEGDMA comonomer s y s t e m .  4-24.  Compression s t r e s s a t r u p t u r e as a f u n c t i o n c o p o l y m e r c o n n e c t i o n number ( C M ) f o r d i f f e r e n t MMA-DVM p o l y m e r p r o d u c t s C 0  4-25.  R e l a t i o n s h i p between a r e a u n d e r t h e c o m p r e s s i o n s t r e s s - s t r a i n c u r v e ( F ) and p l a s t i c d e f o r m a t i o n f o r d i f f e r e n t MMA-DVM p o l y m e r products, 0 O O * e « « O O 0 O 0 * O 9 « < ) « 0 » O O « « 0 » O O  xi  L I S T OF a A MA AN b BMA c CM CN d D dp DP DVB DVM DEGDMA E EGDMA f c o  r  Ge GEP h k K k k LTDC M MAX mf M/AA MW n OAC OCR 05 R P P PPC PRC PRC! PRC I I p  = = = —  = —  —  Number o f 2-way c o n n e c t e d atoms Allyl methacrylate Acrylonitrile Number of 3-way c o n n e c t e d atoms Butyl" methacrylate Number o f 4-way c o n n e c t e d atoms C o n n e c t i o n number C o p o l y m e r c o n n e c t i o n number S p e c i f i c g r a v i t y , g/cm3 R a d i a t i o n d o s e , Mrad D e p t h of p e n e t r a t i o n , mm Degree of p o l y m e r i z a t i o n D i v i n y l benzene D i v i n y l monomer Diethylene glycol dimethacrylate M o d u l u s o f e l a s t i c i t y , kg/cm^ Ethylene glycol dimethacrylate Monomer f u n c t i o n a l i t y A r e a under t h e s t r e s s - s t r a i n c u r v e , cmfGel-effect "Gel-Effect Point" P o l y m e r sample h e i g h t , mm S e n s i t i v i t y constant, mils/inch . O v e r a l l a c c e l e r a t i o n c o n s t a n t , min" . conc P.ropagation r a t e c o n s t a n t Termination rate constant L i n e a r t h e r m o m e c h a n i c a l d e f o r m a t i o n c o e f f i c i e n t , l/°C Monomer E x o t h e r m maximum, " C u r e " Mole f r a c t i o n Methyl methacrylate Molecular weight Number o f -G-CH2-CH2- u n i t s i n DVM O v e r a l l a c c e l e r a t i o n constant Overall curing rate Overall gelation rate Extent of oolycondensation r e a c t i o n , % • Dead p o l y m e r Paper polymer c o m p o s i t e s P o l y m e r i z a t i o n r a t e c o e f f i c i e n t , °C/min PPC i n " A c t i v a t i o n " p e r i o d , ° C / m i n PRC i n " A c c e l e r a t i o n " p e r i o d , ° C / m i n 0  —  = = =  t  poly(MMA) poiy(S)  SYMBOLS  = =  = =  Poly(methyl Polystyrene  methacrylate)  xii R* Ri RM* Rp s  = = = = =  S t T TBS TDD TDT TEGDiMA Tg  = = = = = = = =  Primary r a d i c a l Rate of i n i t i a t i o n Growing polymer r a d i c a l O v e r a l l r a t e of p o l y m e r i z a t i o n , /6/hr Slope of thermomechanical curve i n t r a n s i t i o n region Styrene Time, min Temperature, °C t - B u t y l styrene Thermal d e f o r m a t i o n degree, % Thermal d i s t o r t i o n temperature, °C Tetraethylene g l y c o l dimethacrylate G l a s s t r a n s i t i o n temperature, °C  tGEP ?GEP tr^AX TMAX TfvlPTA TMPTMA TrEGDMA VA VAD VC VPC VS WPC I II %xel  = " = = = = = = = = = = = =  Time t o onset GEP, min Temperature at GEP, °C Time t o reach exotherm maximum, min Temperature a t exotherm maximum, °C T r i m e t h y l o l propane t r i a c r y l a t e T r i m e t h y l o l propane t r i m e t h a c r y l a t e Triethylene g l y c o l dimethacrylate V i n y l acetate V i n y l adipate Vinyl chloride Veneer polymer composites V i n y l succinate Wood polymer composites "Activation" period "Acceleration" period Relative viscosity  xiii  ACKNOWLEDGEMENTS  I w i s h t o a c k n o w l e d g e c o n t r i b u t i o n s o f a l l my present  and p r e v i o u s  It  h a s b e e n my p r i v i l e g e  associated with Forestry  teachers.  Dr. L. Paszner,  and D r . J . W. W i l s o n ,  t o have b e e n  Research A s s o c i a t e , Professor,  I w i s h t o e x p r e s s my t h a n k s t o b o t h advice,  constructive criticism,  helpful  suggestions  of t h i s  dissertation.  years  i s deeply  during  closely  Faculty  of F o r e s t r y .  o f them f o r v a l u a b l e  thoughtful  c o n s i d e r a t i o n s and  t h e i n v e s t i g a t i o n s and p r e p a r a t i o n  Their  support  provided  over t h e past  appreciated.  I wish t o thank t h e U n i v e r s i t y of B r i t i s h f o r Graduate F e l l o w s h i p s : Fellowships Dr.  and o t h e r  N. C . F r a n z  final  stages  G„  the Faculty  financial  f o r support  of t h e s i s  Appreciation technical  staff;  thermomechanical  reporting.  support;  D r , R. V/. Wellwood and grant  during  preparation.  i s a l s o expressed  with  t o M i s s E . Budyk and  t o Mr, U. Rumma and  c o n s t r u c t i o n and c a l i b r a t i o n  of t h e  analyzer.  Last but not l e a s t , children Michelle  Columbia  of F o r e s t r y f o r R e s e a r c h  f r o m an NEC o p e r a t i n g  i n particular,  Bohnenkamp f o r h e l p  sacrifice  F a c u l t y of  I am g r a t e f u l t o my w i f e G i t k a and  and M a r t i n - M i k e f o r t h e i r  great  o v e r t h e many weekends d e v o t e d t o t h i s  p a t i e n c e and study  and I t s  1  INTRODUCTION  Wood i s a v a l u a b l e m a t e r i a l , used t r a d i t i o n a l l y i n i t s natural state.  Ease of f a b r i c a t i o n and f i n i s h i n g ,  pleasing  appearance, h i g h s t r e n g t h t o weight r a t i o and low c o s t are c h a r a c t e r i s t i c s c o n t r i b u t i n g t o i t s wide use. Numerous attempts have been made t o improve wood p r o p e r t i e s .  inherent  F i n i s h e s have been developed t o i n c r e a s e  r e s i s t a n c e t o weathering and mechanical a b r a s i o n , treatments have been developed t o improve d i m e n s i o n a l s t a b i l i t y  or t o  impart g r e a t e r r e s i s t a n c e t o decay, f i r e and b i o d e g r a d a t i o n . One treatment of c u r r e n t i n t e r e s t i s the combination of wood w i t h polymers t o form wood polymer composites (WPC). A means f o r producing WPC i n v o l v e s impregnation and i n si.tu p o l y m e r i z a t i o n of v i n y l monomers i n wood Among t e c h n i q u e s a v a i l a b l e f o r c u r i n g WPC, p o l y m e r i z a t i o n has-been much examined 82,84,85,90,93,99).  structures.  radiolytic  (4,5,30,31,49,54,55,56,  A f t e r a decade of e x t e n s i v e experimenta-  t i o n and development, WPC p r o d u c t s have begun t o appear i n the market  (30).  Monomers such as methyl m e t h a c r y l a t e (MMA)  and styrene (S) a r e e c o n o m i c a l l y  attractive.  A major r e s t r i c t i o n imposed by most monomers employed i n WPC manufacture has been long c u r i n g schedules, and  2  coxresponding h i g h dosages, r e q u i r e d t o complete polymerization.  The  requirement w i t h S,  only beyond reasonable economics, but the wood s u b s t r a t e .  radiolytic  as example, i s not  so l a r g e as t o degrade  Certainly, better radiation e f f i c i e n c y  has become a n e c e s s i t y t o f u r t h e r p r o c e s s development. Several  methods have been used t o  r a d i a t i o n polymerization wood m a t r i c e s .  accelerate  of v i n y l monomers i n c o r p o r a t e d  A d d i t i o n of low  molecular weight compounds,  p a r t i c u l a r l y carbon t e t r a c h l o r i d e ( C C 1 ) , was 4  a c c e l e r a t e the r a d i a t i o n c u r i n g (30,55,90,93).  found t o  of v a r i o u s v i n y l monomers  However, secondary e f f e c t s caused by  CC1 , 4  p a r t i c u l a r l y by i t s f u n c t i o n as a c h a i n - t r a n s f e r agent are  in  so disadvantageous t h a t i t i s not c o n s i d e r e d  (22),  for  t e c h n o l o g i c a l a p p l i c a t i o n s (30,82). I t has been known from the theory gelation  (38)  t h a t i n c o r p o r a t i o n of small amounts of  c r o s s l i n k i n g agents, c o n t a i n i n g two allows  formation  of t h r e e - d i m e n s i o n a l  e a r l y stages of p o l y m e r i z a t i o n comonomer system i n t o a g e l . done t o u t i l i z e the  Kent e_fc_ ad.  (55)  or more v i n y l  groups,  networks which,  r e a c t i o n s would t u r n  during  the  R e l a t i v e l y l i t t l e work has been  phenomena of g e l a t i o n t o  r a d i a t i o n polymerization. and  of monomer  So  accelerate  f a r only Raff ££. al..  (84)  have p a i d l i m i t e d a t t e n t i o n t o  a c c e l e r a t i o n i n v i n y l - d i v i n y l comonomer systems as r e l a t e d to r a d i a t i o n processing  of WPC.  Recently,  during  quite  3 advanced stages of t h i s work, Kenaga (53) Meyer (33)  and  Duran  and  attempted t o u t i l i z e t h i s method i n randomly  chosen h e a t - c a t a l y s t A systematic  systems. study of g e l a t i o n k i n e t i c s i n v i n y l -  d i v i n y l comonomer systems i s completely l a c k i n g . t h i s p o i n t no q u a n t i t a t i v e i n f o r m a t i o n  Up  to  has been a v a i l a b l e  on the f o l l o w i n g parameters: 1.  d i f f e r e n c e s i n curing rates before a f t e r the G e l - E f f e c t P o i n t  ii. iii. iv.  and  (GEP),  the temperature p r o f i l e during  polymerization,  e f f i c i e n c y of d i f f e r e n t c r o s s l i n k i n g agents, the  i n f l u e n c e of molecular bridge  length  between double bonds of d i v i n y l monomer on r e g u l a t i n g the p r o p a g a t i o n and r e a c t i o n s i n g e l l e d network, v.  and  the r e l a t i o n between o v e r a l l c u r i n g r a t e and  The  termination  (OCR)  composition of comonomer m i x t u r e s .  primary o b j e c t i v e of the present  study was  t e s t the h y p o t h e s i s t h a t r a d i a t i o n p o l y m e r i z a t i o n d i v i n y l comonomer systems may  be  a c c e l e r a t e d by  to  of v i n y l -  forming  g e l l e d three-dimensional  networks.  of these networks should  depend on d i v i n y l monomer  features,  l e n g t h between the double bonds.  such as b r i d g e  T h i s should  Further,characteristics  a l l o w p r e d i c t i o n s of the p o l y m e r i z a t i o n  (DVM)  course  4 and OCR by merely c o n s i d e r i n g the DVM chemical s t r u c t u r e . S i n c e the h y p o t h e s i s i n v o l v e s r e g u l a t i o n of i n d i v i d u a l elementary that  steps of p o l y m e r i z a t i o n r e a c t i o n s i t i s expected  such f i n d i n g s would be f u l l y a p p l i c a b l e t o a c c e l e r a t i o n  of h e a t - c a t a l y s t systems. F u r t h e r purposes of t h i s work were t o : i.  develop techniques which allow monitoring of r a d i a t i o n p o l y m e r i z a t i o n t o complete conversion, determination  of GEP and a s s o c i a t e d  parameters, ii.  i n v e s t i g a t e a c c e l e r a t i o n p o l y m e r i z a t i o n across wide ranges of comonomer c o n c e n t r a t i o n w i t h v a r i o u s systems, and  iii.  e l u c i d a t e p r o p e r t i e s of v a r i o u s polymer  products  a v a i l a b l e from the systems examined and attempt t o r e l a t e these t o monomer s t r u c t u r a l f e a t u r e s .  MMA  was s e l e c t e d as the b a s i c monomer f o r the study  because of i t s present u t i l i t y  i n WPC products and because  of wide l i t e r a t u r e a v a i l a b l e on such composites. reason was c o m p a t i b i l i t y of MMA  Another  w i t h a commercially  available  homologous DVM s e r i e s of g l y c o l d i m e t h a c r y l a t e e s t e r s . The DVM c r o s s l i n k i n g agents were ethylene dimethacrylate (DEGDMA),  (EGDMA), d i e t h y l e n e g l y c o l  glycol  dimethacrylate  t r i e t h y l e n e g l y c o l dimethacrylate  (TrEGDMA)  and  tetraethylene g l y c o l dimethacrylate  best  (TEGDMA).  To the  of the a u t h o r s knowledge no l i t e r a t u r e r e l a t e s  bridge  1  molecular  l e n g t h w i t h g e l a t i o n or a c c e l e r a t i o n i n v i n y l - d i v i n y l  comonomer systems. The 60Q . q  source of r a d i a t i o n w a s r  gamma r a y s from  I t was chosen on the b a s i s -of i t s a v a i l a b i l i t y ,  e f f e c t i v e n e s s i n i n i t i a t i o n of MMA penetrating  power, normally  wood composite  products.  polymerization  decaying proven  and i t s h i g h  r e q u i r e d f o r l a r g e s e c t i o n s of  6  2 . 0 LITERATURE REVIEW  2.1  R a d i c a l Chain-Growth P o l y m e r i z a t i o n  Polymers  of the type  macromolecules b u i l t number  containing  2.1.1  up by t h e l i n k i n g  of unsaturated  chain-growth  chemical  Free  liquid  i n reaction  either  species  radicals.  They c a n be  aggregates  radicals  of  unpaired either  different  are g e n e r a l l y considered  s p e c i e s because  of t h e i r  systems, p a r t i c u l a r l y  or gaseous r e a c t i o n  Production  Radical  by r e a c t i v e  c o n t a i n i n g one o r more  s p e c i e s or p o l y a t o m i c  t o be h i g h l y u n s t a b l e lifetime  t e r m e d monomers.  free radicals.  structure.  of a l a r g e  f o r m a t i o n and r e a c t i o n s  molecules  e l e c t r o n s a r e termed  study are  together  electrons, i . e . , free  radicals;  Organic  monoatomic  molecules  to this  polymerization i s initiated  unpaired  Free  important  very  short  i n homogeneous  media.  o f f r e e r a d i c a l s may be a c c o m p l i s h e d  by  o f two g e n e r a l r e a c t i o n s : i. ii.  homolytic  decomposition  of c o v a l e n t bonds, or  g e n e r a t i o n by an e l e c t r o n  Homolytic  decomposition  t r a n s f e r mechanism.  of c o v a l e n t bonds i n t o  two  7 or more r a d i c a l fragments may be a c c o m p l i s h e d by a b s o r p t i o n of energy i n almost any form; t h e r m a l , electrical,  s o n i c or m e c h a n i c a l .  electromagnetic,  A l l t h e s e energy forms  have been used f o r f r e e r a d i c a l p r o d u c t i o n r a d i c a l chain-growth polymerization For p r a c t i c a l a p p l i c a t i o n s t h e r m a l are t h e most i m p o r t a n t produced.  and i n i t i a t i o n of  (22,36,59,60,78,106). and e l e c t r o m a g n e t i c  energy  means by which f r e e r a d i c a l s a r e  The l a t t e r g e n e r a l l y i n c l u d e s e i t h e r o f two major  sources, u l t r a v i o l e t l i g h t or h i g h energy r a d i a t i o n .  These  are termed i o n i z i n g r a d i a t i o n . Free r a d i c a l s take p a r t i n a v a r i e t y of d e s t r u c t i v e chemical The  r e a c t i o n s , such as o x i d a t i o n and t h e r m a l  most i m p o r t a n t  degradation.  s y n t h e t i c type r e a c t i o n s i n v o l v i n g f r e e  radicals are: i. ii.  a d d i t i o n t o m u l t i p l e c o v a l e n t bonds, and r a d i c a l termination reactions.  Both r e a c t i o n s are c r u c i a l t o r a d i c a l chain-growth w i t h v i n y l monomers and w i l l be d i s c u s s e d s p e c i f i c problems of t h e p r e s e n t  2»lo2  polymerization  later i n relation to  study.  R a d i a t i o n p o l y m e r i z a t i o n of v i n y l monomers R a d i a t i o n induced p o l y m e r i z a t i o n of v i n y l monomers  i s a d i r e c t a p p l i c a t i o n of r a d i a t i o n c h e m i s t r y .  Such  s y n t h e s e s of h i g h polymers have been used f o r more t h a n t h r e e  8  decades and now producing  r e p r e s e n t w e l l e s t a b l i s h e d methods f o r  a v a r i e t y of polymers and c o p o l y m e r s .  Radiation  p o l y m e r i z a t i o n i s not j u s t a l a b o r a t o r y c u r i o s i t y , includes industrial applications. production  but  Its application to  of wood polymer c o m p o s i t e s (WPC), f o r example, i s  c u r r e n t l y p r a c t i c e d commercially  and  under f u r t h e r development  (30,55,56,90). I t i s known t h a t the i n i t i a t i o n  step i n r a d i c a l  c h a i n - g r o w t h p o l y m e r i z a t i o n r e a c t i o n s r e q u i r e s a p p l i c a t i o n of e x t e r n a l energy.  I n r a d i a t i o n p o l y m e r i z a t i o n t h i s energy i s  s u p p l i e d by i o n i z i n g r a d i a t i o n f r o m a source. growth r e a c t i o n i s s t a r t e d , however, the  Once the  chain-  polymerization  proceeds independent of the energy source a c c o r d i n g  to  conventional  polymeriza-  tion  k i n e t i c r u l e s derived f o r chain-growth  (22,36,42). Main f e a t u r e s of v i n y l monomer r a d i a t i o n p o l y m e r i z a t i o n  are b a s i c a l l y s i m i l a r t o those of c o n v e n t i o n a l free radical polymerization reactions.  The  chemical  r a d i a t i o n i s l i m i t e d t o the primary i n i t i a t i o n production  heat-catalyzed a c t i o n of  step l e a d i n g t o  of f r e e r a d i c a l s and t o a few p e c u l i a r secondary  e f f e c t s , such as d e g r a d a t i o n  and c r o s s l i n k i n g .  R a d i a t i o n p o l y m e r i z a t i o n mechanisms have been d e s c r i b e d by C h a p i r o i n an e x c e l l e n t monograph ( 2 2 ) , as w e l l as by o t h e r s (24,42,74).  In a l l these studies .  9 features  of r a d i a t i o n p o l y m e r i z a t i o n  k i n e t i c s are discussed.  I n a d d i t i o n , t h e p r e s e n t study r e q u i r e s  s p e c i a l emphasis on  a c c e l e r a t i o n v i a g e l - e f f e c t (Ge) phenomena i n h i g h l y and  crosslinked  2.1.2.1  viscous  structures.  Kinetic  considerations  K i n e t i c s of c h a i n - g r o w t h p o l y m e r i z a t i o n  i s based on  i n t e r p r e t a t i o n of e x p e r i m e n t a l r e s u l t s from f r e e r a d i c a l reactions.  A t l e a s t t h r e e t y p e s of r e a c t i o n s a r e d e s c r i b e d  (22) a s : i. ii.  i n i t i a t i o n , w h i c h produces f r e e r a d i c a l s , * p r o p a g a t i o n , w h i c h i n v o l v e s a sequence of i d e n t i c a l r e a c t i o n s r e p e a t e d many t i m e s , and  iii.  t e r m i n a t i o n , which stops the chain-growth reaction.  I t i s a l s o p o s s i b l e t h a t a s i n g l e f r e e r a d i c a l may i n i t i a t e formation  of more t h a n one polymer m o l e c u l e t h r o u g h  a r e a c t i o n i n which the a c t i v e s i t e , i . e . , f r e e r a d i c a l , i s t r a n s f e r r e d w i t h o u t l o s s of a c t i v i t y t o a n o t h e r m o l e c u l e i n the  system.  reaction.  T h i s t y p e of r e a c t i o n i s termed a c h a i n - t r a n s f e r F o r m a t i o n of macromoleculas c o n t a i n i n g thousands of  c o v a l e n t i y bonded monomer u n i t s i s an o v e r a l l r e s u l t of t h e above e l e m e n t a r y r e a c t i o n s .  .10  2.1.2.2  O v e r a l l r a t e of p o l y m e r i z a t i o n The o v e r a l l r a t e of v i n y l monomer p o l y m e r i z a t i o n ,  i . e . , t h e r a t e of monomer d i s a p p e a r a n c e i n t h e r e a c t i o n system, was d e s c r i b e d  (22,42) by t h e f o l l o w i n g k i n e t i c  Process: Initiation:  X  Propagation:  R° + M  Rates: 2 R  R^  <........... /2™l/ 0  > RM*  RMx + M — - > RM;  kp/RMV'/iV  +1  Termination:  RM° + RM' -> P  where:  any m o l e c u l e i n t h e system,  X  scheme:  k /RM*/  x + y  R*  = primary r a d i c a l ,  M  = monomer  2  t  ....../2-2/  ........./2-3/  ;  RM° = growing polymer c h a i n ^ P  = dead p o l y m e r , = r a t e of i n i t i a t i o n ,  kp  = r a t e constant  f o r propagation,  k^  = r a t e constant  f o r termination.  and  A f t e r m a t h e m a t i c a l t r e a t m e n t and steady s t a t e assumptions, t h e o v e r a l l polymerization rate ( p ) i s given as: R  -l/2  m  l/2 , .  This c l a s s i c a l equation polymerization  ,  .  i n d i c a t e s t h a t r a t e oi  i s p r o p o r t i o n a l t o t h e square r o o t of i n i t i a t i o n  11 1/2  rate.  The q u a n t i t y k /fc, P <*  , a constant value a t steady  state  c o n d i t i o n s , changes at h i g h e r c o n v e r s i o n degree and a c c e l e r a t e s the o v e r a l l r e a c t i o n r a t e .  As a second  consequence  an i n c r e a s e i n m o l e c u l a r weight (M.W), or degree of p o l y m e r i z a t i o n ( D P j j i s observed.  T h i s i s r e q u i r e d by t h e f o l l o w i n g  equation (22):  "''*•*  DP = k A f P t  M  /2-5/  With r e s p e c t t o a monomer of i n t e r e s t i n t h i s  study,  / 2  Ri  l / 2  «  x  (MMA), t h e p u b l i s h e d r e s u l t s on p o l y m e r i z a t i o n k i n e t i c s c o n f i r m / 2 - 4 / and /2-5/ MMA,  (22,59,106).  fully  Bulk p o l y m e r i z a t i o n of  e s p e c i a l l y t o the h i g h c o n v e r s i o n degree,  d e v i a t i o n s from these t h e o r e t i c a l p r e d i c t i o n s  exhibits (6,22,64,75,87,  89,103).  2.1.2.3  Bulk p o l y m e r i z a t i o n of MMA Much work has been done i n t h e area of MMA  polymerization.  radiation  The f r e e r a d i c a l mechanism f o r t h i s r e a c t i o n  was e s t a b l i s h e d by C h a p i r o ( 2 2 ) .  He deduced  the mechanism  from data which showed t h a t p o l y m e r i z a t i o n was i n h i b i t e d by a i r and benzoquinone. During process  i n i t i a l r e a c t i o n stages t h e p o l y m e r i z a t i o n  shows a c h a r a c t e r i s t i c  w i t h an a c t i v a t i o n energy  A r r h e n i u s temperature  of 4.9 kcal/mole  (3,22).  c o n s t a n t value of a c t i v a t i o n energy was observed  dependence, The  over wide  !2 temperature range ( -18 2.5  x 10^ r a d / h r , .  operated  r a t e of 3.7  5  be 3.85  °C) w i t h dose r a t e s 2.3  In a more r e c e n t work by Lipscomb  Weber (60), who x 10  °C t o 70  between -49  and  -19  °C and  rad/hr, the a c t i v a t i o n energy was  kcal/mole.  to  and  at a dose found t o  I t should be p o i n t e d out, however, t h a t  the f r e e z i n g p o i n t of MMA doubt as t o v a l i d i t y  i s -48;2  °C (86), which c a s t s  of the data a t -49  °C.  The r e a c t i o n c o n t r o l l e d r e g i o n i s dose r a t e dependent. Chapiro  (22) r e p o r t e d a dependence t o the 0.5  dose r a t e s ( l e s s than 5.4 the r e a c t i o n was  x 10^ r a d / h r ) .  power f o r low  Above 10^  s a i d t o be dose r a t e independent.  et a l . (3) r e p o r t e d dose r a t e dependence of 0.5 rad/hr.  Ballantine  up t o 2.0  x  10~*  In c o n t r a s t Lipscomb and Weber (60), working at  approximately 0.33  rad/hr  the  at both -49  same dose r a t e , r e p o r t e d a power f a c t o r of °C and  For MMA,  -19  °C.  as f o r other v i n y l monomers, the mechanism  of f r e e r a d i c a l p o l y m e r i z a t i o n changes d r a s t i c a l l y at h i g h c o n v e r s i o n degree. and  A s p e c i a l mechanism, which predominates  c o n t r o l s l a t e r stages of p o l y m e r i z a t i o n k i n e t i c s ,  been a t t r i b u t e d t o Ge. t o the present  study, Ge  has  Because of i t s p a r t i c u l a r  importance  phenomena are d i s c u s s e d  in detail in  a later section. Attempts t o d e f i n e o v e r a l l r e a c t i o n o r d e r s have been u n s u c c e s s f u l due  t o e f f e c t s a s s o c i a t e d w i t h Ge  phenomena.  13 N e v e r t h e l e s s , the MMA t o be of z e r o - o r d e r Rabinowitch  polymerization r e a c t i o n i s considered up t o about 20% c o n v e r s i o n  (12).  (83) d e r i v e d an e x p r e s s i o n r e l a t i n g r e d u c t i o n of  t h e t e r m i n a t i o n r a t e c o n s t a n t w i t h the r a t e of d i f f u s i o n f o r second order r e a c t i o n s *  Vaughan (104)  t r i e d t o c o r r e l a t e the e x p e r i m e n t a l u s i n g the R a b i n o w i t c h  equation.  and l a t e r R o b e r t s o n  data f o r MMA  The  and  (87)  styrene  r e s u l t , however,  was  unsatisfactory. A t t e m p t s t o q u a n t i f y p o l y m e r i z a t i o n r a t e s i n the r e g i o n have been hampered by two major f a c t o r s .  Ge  Firstly,  onset of Ge does not occur a t a s p e c i f i c c o n v e r s i o n .  the  Rather,  c o n v e r s i o n a t w h i c h Ge b e g i n s i s s t r o n g l y dependent upon temperature.  Secondly, experimental  measurements i n the  Ge  r e g i o n are i n h e r e n t l y d i f f i c u l t .  I s o t h e r m a l c o n d i t i o n s are  almost impossible t o maintain?and  a n a l y s i s of the p a r t l y •  p l a s t i c i z e d m a t e r i a l requires s p e c i a l experimental f o r r e c o v e r y and  techniques  s o l u t i o n of g e l s and i s o l a t i o n of the  u n c o n v e r t e d monomer.  2.2  P o l y m e r i z a t i o n i n Gel-Phase Media The  k i n e t i c scheme of f r e e r a d i c a l p o l y m e r i z a t i o n ,  d i s c u s s e d i n S e c t i o n 2.1.2.2, a p p l i e s o n l y t o the r e a c t i o n stage up t o a p p r o x i m a t e l y  initial  5 t o 10% c o n v e r s i o n .  If  r e a c t i o n s proceed t o h i g h e r c o n v e r s i o n degrees the m o b i l i t y of r e a c t i v e s p e c i e s i s reduced by a massive i n c r e a s e i n l o c a l  14 viscosity. This in  MMA  The r a t e  phenomenon m a n i f e s t s  bulk  polymerization  itself  of v i n y l  i s significantly i n Ge, commonly  reducedc observed  monomers, p a r t i c u l a r l y  with  (75,103)• The  of  of d i f f u s i o n  most i m p o r t a n t  the o v e r a l l  conversion reaction  system  level  h a s b e e n reached,,  radicals  i s suppressed  If viscosity  and t h e r e s i d u a l of s m a l l  Under a g i v e n  critical  of t h e  long range d i f f u s i o n of  reaction.  sets t o g l a s s , a l l polymeric  from d i f f u s i o n  i sacceleration  and o n l y l o c a l  segments e n s u r e s l i m i t e d  immobilized  o f Ge  p o l y m e r i z a t i o n r a t e , a s soon a s some  medium i s f u r t h e r i n c r e a s e d ,  polymeric polymer  consequence  m o b i l i t y of  Finally,  radicals  i f the  remain  r e a c t i o n , i f any, r e s u l t s  unreacted  monomer  only  molecules.  s e t of r e a c t i o n c o n d i t i o n s v a r i o u s  p o l y m e r i z a t i o n r e a c t i o n s may f a l l  into  any one o f t h r e e  cases  as: i.  both  propagation  controlled ii.  iii.  and t e r m i n a t i o n a r e  by r e a c t i o n r a t e ,  propagation  i s r e a c t i o n - c o n t r o l l e d and  termination  i s diffusion-controlled*  both  propagation  or  and t e r m i n a t i o n a r e  diffusion-controiled„  The  case  of d i f f u s i o n - c o n t r o l l e d  reaction-controlled  termination  propagation  i s a physical  and  impossibility,  15 s i n c e r e a c t i o n between two polymer r a d i c a l segments would be f a v o r e d  2.2.1  over r e a c t i o n between monomer and polymer r a d i c a l s .  Autoacceleration; experimental  evidence f o r g e l - e f f e c t  (Ge) B u l k p o l y m e r i z a t i o n of a number of v i n y l monomers, such as MMA  (6,13,62,75,87,89,103),  (15,64,65), b u t y l m e t h a c r y l a t e v i n y l acetate reactions.  (BMA) ( 1 4 ) , S (8,39,87) and  (VA) ( 5 9 ) , f o l l o w t h e p a t t e r n s o f a u t o c a t a l y t i c  The p o l y m e r i z a t i o n proceeds smoothly a t f i r s t  w i t h constant /2-4/.  m e t h y l a c r y l a t e (MA)  r a t e , a s e x p e c t e d f r o m steady s t a t e k i n e t i c s  A f t e r a c r i t i c a l conversion  i s attained the r e a c t i o n  r a t e suddenly i n c r e a s e s s e v e r a l t i m e s .  The r e a c t i o n a t t h i s  stage shows a d e f i n i t e a u t o a c c e l e r a t i o n c h a r a c t e r .  For S  p o l y m e r i z a t i o n , f o r example, t h e o v e r a l l a c c e l e r a t i o n f a c t o r i s 5.2 a t 38% and 16.9 a t 60% c o n v e r s i o n  (59).  Similarly for  MMA p o l y m e r i z a t i o n , t h e i n i t i a l p o l y m e r i z a t i o n r a t e of 3.5%/hr i n c r e a s e s t o 15.4%/hr a t 30% c o n v e r s i o n conversion  and 24.5%/hr a t 50%  (43) as shown i n T a b l e 2-1.  Simultaneously  with increase i n polymerization r a t e ,  s e v e r a l secondary e f f e c t s a r e evident..  These i n c l u d e  MW and c o n c o m i t a n t l o c a l t e m p e r a t u r e r i s e ( 2 2 , 3 6 ) . are e x p l a i n e d by t h e decreased t e r m i n a t i o n .  increased  These e f f e c t s  I t i s generally  a c c e p t e d t h a t r e d u c t i o n i n t h e r a t e of t e r m i n a t i o n i s caused by reduced m o b i l i t y of growing polymer c h a i n s i n t h e v i s c o u s medium.  16 Measurements of i n d i v i d u a l r a t e T a b l e 2-1  (43)., show t h a t the d e c r e a s e i n t e r m i n a t i o n r a t e  o c c u r s at f a i r l y  low c o n v e r s i o n ,  g e n e r a l l y between 10 t o  On the other hand, the p r o p a g a t i o n a f t e r 50 t o 60% c o n v e r s i o n , has  constants.  already g e l l e d .  r a t e i s enhanced o n l y  i . e . , a f t e r the r e a c t i o n  low a c t i v a t i o n e n e r g i e s  become d i f f u s i o n - c o n t r o l l e d .  He c o n c l u d e d t h a t are more l i k e l y  w h i l e a c t i v a t i o n energy f o r  i s * 5 t o 8 k c a l / m o l e (22,23,36).  c o n c l u s i o n was  reached by Vaughan (104) who  A  similar  calculated c r i t i c a l  v i s c o s i t i e s f o r elementary r e a c t i o n steps.  His  v i s c o s i t i e s f o r t e r m i n a t i o n and  were 2.0  10~* p o i s e , r e s p e c t i v e l y .  propagation  critical and 7,0  x  I t must be emphasized, however, t h a t  t h e v i s c o s i t y e f f e c t i s not due reactivities.  to  An average a c t i v a t i o n energy f o r  termination i s 0 t o 2 kcal/mole, propagation  mixture  T h i s i s i n accordance w i t h t h e o r e t i c a l  c o n c l u s i o n s drawn by R a b i n o w i t c h ( 8 3 ) . r e a c t i o n s having  30%,  t o changes i n r a d i c a l  I n s t e a d , i t a r i s e s from a p u r e l y p h y s i c a l e f f e c t  caused by the d i f f u s i o n b a r r i e r . Hayden and M e l v i l l e (43) s e v e r a l MMA  s t u d i e d v a r i a t i o n of  p o l y m e r i z a t i o n parameters w i t h c o n v e r s i o n , i n c l u d i n g  average l i f e t i m e of a k i n e t i c c h a i n and r a t e c o n s t a n t s both propagation  and t e r m i n a t i o n .  t e r m i n a t i o n rate constant  They p o i n t e d  out t h a t  the  d e c r e a s e d by about 1 0 0 , 0 0 0 - f o l d f r o m  t h e s t a r t of p o l y m e r i z a t i o n up t o 50% c o n v e r s i o n . conversion  for  The  e f f e c t of  on k i n e t i c v a r i a b l e s has been d i v i d e d i n t o t h r e e  d i s t i n c t stages  as*.  17 i.  Stage 1^  up t o 10% c o n v e r s i o n ,  ii.  Stage I I ,  iii.  Stage I I I  ?  between 10 t o 70% c o n v e r s i o n , and over 70% c o n v e r s i o n .  I n Stage I t h e r e a c t i o n m i x t u r e changes f r o m a mobile  l i q u i d t o a v i s c o u s s y r u p , but t h e r a t e of p o l y m e r i z a -  t i o n adheres t o steady s t a t e k i n e t i c s r e p r e s e n t e d by /2~4/. I n Stage I I t h e r e a c t i o n m i x t u r e changes from a v e r y viscous f l u i d t o a soft s o l i d .  Large i n c r e a s e s a r e o b t a i n e d  i n b o t h p o l y m e r i z a t i o n r a t e and l i f e t i m e of t h e k i n e t i c B o t h i n c r e a s e by a p p r o x i m a t e l y  chains.  ten fold.  In Stage I I I as c o n v e r s i o n nears c o m p l e t i o n , t i o n appears t o become a u n i m o l e c u l a r p r o c e s s  termina-  and even  p r o p a g a t i o n becomes d i f f u s i o n - c o n t r o l l e d as m o l e c u l e s are i m m o b i l i z e d i n t h e g e l - g l a s s y r e a c t i o n medium. Although  propagation  i n g e l i s hindered, the o v e r a l l  e f f e c t i s much s m a l l e r s i n c e kp v a l u e s are s m a l l e r t h a n k^ by a f a c t o r of 1 0  4  t o 10^ (Table 2 - l ) . T e r m i n a t i o n  involves the  r e a c t i o n of two l a r g e polymer segments /2-3/„ w h i l e i n propagation molecule  o n l y one l a r g e polymer r a d i c a l and a s m a l l monomer  a r e i n v o l v e d /2-2/.  High v i s c o s i t y a f f e c t s the  former much more than t h e l a t t e r . , l/2 kp/k^.  Therefore, the quantity ,  changes d u r i n g the p o l y m e r i z a t i o n p r o c e s s .  This  r e s u l t s , i n accordance w i t h /2-4/, i n an i n c r e a s e of t h e o v e r a l l polymerization rate with increasing conversion.  As a  second consequence, and  i n accordance w i t h /'2~b/,  i n m o l e c u l a r w e i g h t i s obtained..  an  increase  T h i s has been v e r i f i e d  e x p e r i m e n t a l l y a l s o f o r numerous v i n y l monomers (13,14,78). S o l v e n t s and c h a i n - t r a n s f e r agents, w h i c h d i r e c t l y reduce v i s c o s i t y and m o l e c u l a r  w e i g h t of polymer  d e l a y or even e l i m i n a t e the onset of 6e,  products,  As shown by  and Haborth ( 8 9 ) , a u t o a c c e l e r a t i o n i s c o m p l e t e l y when the r e a c t i o n system i s d i l u t e d w i t h 60% solvent.  eliminated  of an  inert  M o l e c u l a r weight of polymer formed i n d i f f e r e n t  s o l u t i o n s also decreases with i n c r e a s i n g d i l u t i o n . result  Schultz  of d e c r e a s e d k i n e t i c c h a i n l i f e t i m e due  c h a i n t e r m i n a t i o n (6,103).  I t was  This i s the  to bimolecular  f u r t h e r shown t h a t a d d i t i o n  of an i n e r t polymer, w h i c h i n c r e a s e s v i s c o s i t y of the r e a c t i o n media, brought about a premature appearance of Ge  (103).  Temperature changes of r e a c t i o n media were measured by  s e v e r a l i n v e s t i g a t o r s . I t was  noted t h a t a c c e l e r a t i o n i s  accompanied by c o n s i d e r a b l e o v e r h e a t i n g  of the system.  o r d e r t o a v o i d a d d i t i o n a l c o m p l i c a t i o n s , such as c r e a t e d non-isothermal  c o n d i t i o n s , S c h u l t z and H a r b o r t h  t h i n l a y e r s of MMA  onto a mercury s u r f a c e .  experiment c o n c l u s i v e l y demonstrated t h a t Ge  (89)  In by  polymerized  R e s u l t s of t h i s acceleration i s a  t r u l y k i n e t i c phenomenon. Temperature r i s e at t h e onset of Ge-'is much more pronounced w i t h MMA  t h a n w i t h S ( 3 ) , even at v e r y low  t i o n t e m p e r a t u r e s , e.g,,  -18  °C.  Difunctionai  polymeriza  methacrylates  19 and a c r y l a t e s , i r r a d i a t e d i n s o l i d s t a t e , showed remarkable t e m p e r a t u r e r i s e even at -90 °C r e a c t i o n t e m p e r a t u r e A d i r e c t consequence  (22).  of Ge i n p o l y m e r i z a t i o n under  c o n s t a n t r a t e of i n i t i a t i o n i s t h a t the c o n c e n t r a t i o n of growing polymer c h a i n s i n c r e a s e s w i t h t i m e  Thus the p o l y -  m e r i z a t i o n system does not f o l l o w s t a t i o n a r y k i n e t i c s due t o v i o l a t i o n of the steady s t a t e a s s u m p t i o n .  Overall polymeriza-  t i o n r a t e i s not p r o p o r t i o n a l t o the square r o o t of i n i t i a t i o n /2-4./c  Indeed, a marked d e p a r t u r e from c o n v e n t i o n a l  kinetics  i s observed and the r e a c t i o n o r d e r w i t h r e s p e c t t o i n i t i a t i o n r a t e r i s e s above t h e t h e o r e t i c a l 0.5 v a l u e .  A complete  t r e a t m e n t of Ge k i n e t i c s s h o u l d t a k e i n t o account b o t h the g r a d u a l d e c r e a s e of t e r m i n a t i o n r a t e and the c o n c o m i t a n t increase i n free r a d i c a l concentration. still  lacking  Such a t r e a t m e n t i s  (23).  R e d u c t i o n i n the t e r m i n a t i o n s t e p i n f r e e  radical  p o l y m e r i z a t i o n , and. c o n s e q u e n t l y premature onset of Ge, can be brought about by s e v e r a l p h y s i c a l methods.  A l l t h e s e methods  are based on the p r i n c i p l e t h a t t e r m i n a t i o n by the mutual r e a c t i o n of two polymer c h a i n s can be p r e v e n t e d by t h e growing polymer segments from each o t h e r .  isolating  I n many c a s e s ,  i s o l a t i o n of growing polymer fragments has been a c c o m p l i s h e d by " o c c l u s i o n " of the a c t i v e end groups w i t h i n d i s c r e t e polymer p a r t i c l e s .  T h i s phenomenon i s r e s p o n s i b l e f o r t h e  u n u s u a l r a t e b e h a v i o u r observed i n the f o l l o w i n g systems ( 5 9 ) :  20  i.  polymerization reactions i n i t i a t e d  i n gas  pha se, ii.  p o l y m e r i z a t i o n of a monomer i n a medium which i s non-solvent f o r the r e s u l t i n g termed p r e c i p i t a t i o n  iii. iv.  polymer,  polymerization,  emulsion polymerization, p o l y m e r i z a t i o n of c r y s t a l l i n e monomers i n the s o l i d systems, and  v.  p o l y m e r i z a t i o n w i t h i n c r o s s l i n k e d networks, such as v i n y l - d i v i n y l comonomer systems.  Systems i i ,  iii  and v are f a r the most important,  p a r t i c u l a r l y f o r p r a c t i c a l a p p l i c a t i o n s i n v o l v i n g WPC,  as w e l l  as paper polymer composites (PPC). If polymerization i s carried the r e s u l t i n g polymer i s chains  separate  precipitation.  out i n a medium i n which  i n s o l u b l e , the growing polymer  from the s o l u t i o n t o form a second phase by R e a c t i o n proceeds t h e r e a f t e r i n heterogeneous  medium and u s u a l l y shows a p e c u l i a r behaviour s i m i l a r i n many r e s p e c t s t o Ge. Systems which behave i n t h i s manner i n c l u d e : i.  pure monomers which do not d i s s o l v e t h e i r polymer, f o r example a c r y l o n i t r i l e  own  (AN) and  v i n y l c h l o r i d e (VC), ii.  monomer s o l u t i o n s immiscible w i t h  solvents  which are p r e c i p i t a n t s f o r the polymer, e.g., methanol-S, methanol-MMA. hexane-VA, and  21 iii.  comonomer m i x t u r e s w h i c h do not d i s s o l v e the r e s u l t i n g copolymer, as t h e AN-S comonomer system.  A c c e l e r a t i o n during  e a r l y r e a c t i o n , s t a g e s , a pheno-  menon i d e n t i c a l w i t h Ge, has been i n t e r p r e t e d a s impeded termination 22,75).  i n t h e presence of a polymer p r e c i p i t a n t (1,16,  Here r e l a t i v e c o n v e r s i o n r a t e i s a f u n c t i o n of  monomer/precipitant r a t i o .  Maximum a c c e l e r a t i o n i s observed  at p r e c i p i t a n t c o n t e n t s l i g h t l y below t h e p r e c i p i t a t i o n p o i n t where phase s e p a r a t i o n h i g h l y swollen  leads t o a viscous,  by monomer.  g e l - l i k e coagulate  The o v e r a l l p o l y m e r i z a t i o n  at t h i s p o i n t , r i s e s s h a r p l y  rate,  and t h e r e a c t i o n e x h i b i t s non-  steady s t a t e k i n e t i c s . P h y s i c a l s t a t e of t h e p r e c i p i t a t e d polymer and t h e e x t e n t of s w e l l i n g preparation reported  seem t o be v e r y i m p o r t a n t f a c t o r s i n  of g r a f t copolymers ( 2 l ) .  that a h i g h l y swollen  Thus., i t has been  substrate  i s n e c e s s a r y t o form  l a r g e amounts of g r a f t c o p o l y m e r s , e.g., i n c r e a s e d efficiency The  grafting  (21,49,57,96). alcohol-S  system has been used i n a p p l i e d  f o r r a d i a t i o n c u r e d WPC.  studie  S i a u et. al_. (90) compared g r a f t i n g  e f f i c i e n c y of S on r e d p i n e ( P i n u s r e s i n o s g A i t . ) , a s w e l l as on y e l l o w - p o p l a r  (Llriodencir.pn t u l i p i f e r a L. ).  Ramalingam  e t a l . (85) e v a l u a t e d e f f e c t s o f a t h r e e component system,  methanol-S-water, on g r a f t c o p o l y m e r i z a t i o n e f f i c i e n c y .  They  c o n c l u d e d t h a t , i n a d d i t i o n t o the observed a c c e l e r a t i o n e f f e c t s , t h i s system i n c r e a s e d g r a f t i n g e f f i c i e n c y .  This i s  i n accordance w i t h t h e o r e t i c a l c o n c l u s i o n s drawn from r a d i c a l l i f e t i m e s observed  2.2.2  i n v i s c o u s and s w o l l e n systems  (21,43).  A c c e l e r a t i o n w i t h i n the c r o s s l i n k e d network;  copoly-  m e r i z a t i o n of v i n y l - d i v i n y l comonomer systems I n many c o p o l y m e r i z a t i o n r e a c t i o n s d i v i n y l compounds are used as monomeric c o n s t i t u e n t s .  The  obvious reason f o r  i n c l u d i n g such compounds i s t o o b t a i n c r o s s l i n k s between l i n e a r macromolecuies.  This leads to three-dimensional  net-  works. When d i v i n y l monomers (DVM) comonomer system, o n l y one  are i n c o r p o r a t e d i n a  of the double bonds reacts//). The  o t h e r i s l e f t as a pendant v i n y l group. degree the pendant v i n y l group may  At higher conversion  be i n v o l v e d i n p r o p a g a t i o n  reactions.  A t such stage a r a t h e r abrupt t r a n s i t i o n i s  experienced  i n p a s s i n g from the l i q u i d t o g e l s t a t e .  If  s u f f i c i e n t p o l y f u n c t i o n a l c r o s s l i n k i n g agent i s used, a s i g n i f i c a n t d e p a r t u r e from l i n e a r i t y i n the o v e r a l l  polymeriza  t i o n r a t e can be a c h i e v e d d u r i n g e a r l y r e a c t i o n s t a g e s due a premature onset of Ge phenomena.  to  Increase i n p o l y m e r i z a t i o n  r a t e i s a d i r e c t consequence of r e d u c i n g the t e r m i n a t i o n r e a c t i o n s t e p by i s o l a t i n g the growing  polymer r a d i c a l  ments i n c r o s s l i n k e d t h r e e - d i m e n s i o n a l networks ( 5 9 ) ,  seg-  23 The f o r m a t i o n of such a n e t w o r k , r e s u l t i n g i n g e l a t i o n of t h e comonomer m i x t u r e , g e n e r a l l y t a k e s p l a c e over a v e r y narrow c o n v e r s i o n range and v a r i e s i n v e r s e l y w i t h b o t h t h e amount of c r o s s l i n k i n g agent and average DP (34,36,97,105). F l o r y (34) o u t l i n e d a g e n e r a l method f o r d e t e r m i n i n g and p r e d i c t i n g t h e e x t e n t of r e a c t i o n s i n which such a network i s p o s s i b l e and c a r r i e d out a d e t a i l e d c a l c u l a t i o n , f o r t h e case of p o l y c o n d e n s a t i o n r e a c t i o n s .  H i s c a l c u l a t i o n s were i n good  agreement w i t h e x p e r i m e n t a l r e s u l t s .  He i n d i c a t e d t h a t a  s i m i l a r method may be a p p l i e d t o a d d i t i o n p o l y m e r i z a t i o n , p a r t i c u l a r l y f o r v i n y l - d i v i n y l comonomer systems i n w h i c h a l l v i n y l groups have t h e same r e a c t i v i t y .  2.2.2.1  C r o s s l i n k i n g and g e l a t i o n ; p r e d i c t i o n of g e l - e f f e c t (Ge) According t o F l o r y ' s treatment  r e a c t i o n s , Ge i n monovinyl  on p o l y c o n d e n s a t i o n  and d i v i n y l comonomer m i x t u r e s i n  w h i c h a l l v i n y l groups have t h e same r e a c t i v i t y may be c a l c u l a t e d from t h e f u n c t i o n a l i t y e q u a t i o n ( 3 4 ) :  where: p = e x t e n t of r e a c t i o n f = average f u n c t i o n a l i t y DP = degree of p o l y m e r i z a t i o n  24 For a v e r y l a r g e DP, w h i c h i s always the case i n a d d i t i o n p o l y m e r i z a t i o n , /2-6/  reduces t o :  W i t h b i f u n c t i o n a l monomer m o l e c u l e s , of / 2 - 7 / , g e l a t i o n does not o c c u r .  as a consequence  With t r i -  and  tetra-  f u n c t i o n a l m o l e c u l e s g e l a t i o n o c c u r s at 66 and  50%  respectively.  r e s u l t s do  However, p r a c t i c a l e x p e r i m e n t a l  correlate with predicted values.  conversion,  L a r g e d e v i a t i o n s from  t h e o r e t i c a l v a l u e s were observed even f o r p o l y m e r i z a t i o n r e l a t e d monomers such as V A - v i n y l  d e v i a t i o n s , as p o i n t e d  succinate  (97,105).  or S - d i v i n y l benzene (DVB)  not  of  ( V S ) , MMA-EGDMA,  Explanation  of t h e s e  out by F l o r y (36) and W a l l i n g  (105),  l i e s m o s t l y i n two f a c t o r s : i.  a p p l i c a t i o n of the c o n d e n s a t i o n  polymerization  f u n c t i o n a l i t y equation t o chain-growth polym e r i z a t i o n systems, ii.  excessive  and  o c c u r r e n c e of i n t r a - m o l e c u l a r c r o s s -  l i n k i n g before  onset of Ge,  where wastage of  i n t e r - m o l e c u l a r c r o s s l i n k s i n t h i s manner i s n e g l e c t e d by • A l f r e y e i . a_l„  theory.  ( l ) c o n c l u d e d t h a t c r o s s l i n k i n g . and  subsequent g e l a t i o n depends on r e l a t i v e r e a c t i v i t i e s of double bonds i n DVM. treated mathematically  The  p o i n t at which Ge  two  o c c u r s has been  f o r s e v e r a l comonomer systems.  In a l l  25 i n s t a n c e s i t h a s b e e n assumed t h a t concentration, practical  since t h i s  type  i s the case encountered  i n most  applications. Generally,  to  DVM was p r e s e n t i n a low  t h r e e c a s e s were c o n s i d e r e d ( l ) a c c o r d i n g  of c r o s s l i n k i n g io  Case  I  agent,  as w e l l  as v i n y l  monomer  used:  c o p o l y m e r i z a t i o n of s y m m e t r i c a l  ?  with a v i n y l  DVM  monomer o f e q u a l  reactivity, ii.  Case  II,  c o p o l y m e r i z a t i o n o f a s y m m e t r i c a l DVM with a v i n y l  monomer o f  different  r e a c t i v i t y , and iii.  Case  III^  c o p o l y m e r i z a t i o n o f an u n s y m m e t r i c a l DVM w i t h v i n y l  monomer o f  different  reactivity. In Case and  I a l l d o u b l e b o n d s have t h e same  chemical structure. i. ii. iii.  of  such a system a r e :  MMA-EGDMAy VA-vinyl  a d i p a t e (VAD), and  S-DVB.  In C a s e  I I the r e a c t i v i t y  bonds i n DVM d i f f e r monomer.  Examples  reactivity  An example  Acceleration i n this  and s t r u c t u r e  of double  f r o m t h e d o u b l e bond c h a r a c t e r of t h i s  system  i n the v i n y l  i s S-EGDMA o r MMA-DV3.  s y s t e m was s t u d i e d  previously (70).  26 I n Case I I I t h e two double bonds i n d i e n e s d i f f e r e n t s t r u c t u r e s and r e a c t i v i t i e s . type i s MMA-allyl complicated  methacrylate  and i n e f f i c i e n t .  g e n e r a l l y lower  (AMA).  have  An example of t h i s T h i s system i s v e r y  A l l y l type double bends have  r e a c t i v i t y , t h e r e b y c r o s s l i n k i n g and Ge  occur  o n l y a f t e r c o n s i d e r a b l e c o n v e r s i o n has been a t t a i n e d . I n some c a s e s r e a c t i o n of one double bond i n t h e d i e n e r e s u l t s i n a marked r e d u c t i o n i n r e a c t i v i t y of t h e remaining i n Ge.  double bond.  The o v e r a l l e f f e c t i s a marked  delay  An example of t h i s i s c o p o l y m e r i z a t i o n of v i n y l  monomers w i t h 1 , 3 - d i e n e s .  The 1,4 p o l y m e r i z a t i o n of diene  leads  t o r e s i d u a l 2,3 double bonds, w h i c h have lowered r e a c t i v i t y ( l ) . The most s t u d i e d d i e n e s and c h l o r o p r e n e  of t h i s t y p e a r e i s o p r e n e ,  (1,44,58,95).  Much e x p e r i m e n t a l  m a t e r i a l has been accumulated on  c o p o l y m e r i z a t i o n of s y m m e t r i c a l  DVM w i t h v i n y l monomer of  i d e n t i c a l double bond s t r u c t u r e (Case I ) . experimental  R e s u l t s d e r i v e d from  d a t a on g e l a t i o n were i n good agreement w i t h  predicted values range.  butadiene  ( l ) o n l y w i t h i n a l i m i t e d DVM c o n c e n t r a t i o n  There has been some c o n t r o v e r s y about t h e s e  discrepancies  (9V,105).  Storey  (97) s t u d i e d t h e a c c e l e r a t i o n e f f i c i e n c y of  DVB i n t h e S-DVB comonomer system u s i n g h e a t - c a t a l y s t .  He  found t h a t i n i t i a l p o l y m e r i z a t i o n r a t e v a r i e d l i n e a r l y w i t h  27 DVB c o n c e n t r a t i o n a t b o t h t e m p e r a t u r e s s t u d i e d (70 °C and 87 °C).  The MMA-EGDMA system was s t u d i e d by W a l l i n g  He a l s o examined t h e VA-VAD system.  (105),  I n a l l studies at higher  DVM c o n c e n t r a t i o n agreement between expected r e s u l t s and t h o s e o b t a i n e d was p o o r .  The d i s c r e p a n c y may have a r i s e n i n p a r t  f r o m i n t r a - m o l e c u l a r c h a i n c y c l i z a t i o n r e a c t i o n s (17,18,19,38, 40,41,61,92) w h i c h p r e v e n t DVM p a r t i c i p a t i o n i n i n t e r - m o l e c u l a r crosslinking.  W a l l i n g ( 1 0 5 ) , however, d i d n o t c o n s i d e r  t o be a major f a c t o r .  this  He i n t e r p r e t e d h i s r e s u l t s i n terms  associated with diffusion-controlled crosslinking reaction. According  t o h i s hypothesis, r a t e c o e f f i c i e n t of the c r o s s -  l i n k i n g process  d e c r e a s e s w i t h i n c r e a s i n g DVM c o n c e n t r a t i o n .  Simpson et. a l . (91) showed t h a t a c o n s i d e r a b l e f r a c t i o n of DVM i s used i n t h e i n t r a - m o l e c u l a r c y c l i z a t i o n reaction.  This r e s u l t e d i n delayed  high conversion degrees.  g e l a t i o n at comparatively  S u b s e q u e n t l y , Gordon and Roe (40)  examined a p p l i c a t i o n of t h e c l a s s i c a l g e l a t i o n t h e o r y t o t h e MMA-EGDMA comonomer system. was  They concluded  that t h i s  a p p l i c a b l e t o t h e i r r e s u l t s only i f f u r t h e r  were made f o r i n t e r n a l c y c l i z a t i o n .  Further,  theory  allowances  diffusion  c o n t r o l l e d c r o s s l i n k i n g , a s d e s c r i b e d by W a l l i n g ( 1 0 5 ) , was u n i m p o r t a n t u n t i l a f t e r Ge had been passed. L a t e r , H o l t and Simpson (48) e s t i m a t e d  the extent of  i n t e r - m o l e c u l a r c y c l i z a t i o n on a s e r i e s of d i a l l y l e s t e r s . A l l monomers s t u d i e d gave r i s e t o c h a i n c y c l i z a t i o n under  28 similar reaction conditions.  The tendency of monomers t o  c y c l i z e was found t o be c o n t r o l l e d by t h e m o l e c u l a r d i s t a n c e between double bonds i n t h e d i f u n c t i o n a l monomer.  T h i s has  not been c o n s i d e r e d as a s i g n i f i c a n t f a c t o r i n g e l a t i o n kinetics.  2.2.2.2  I n f l u e n c e of d i v i n y l monomer m o l e c u l a r b r i d g e l e n g t h I t may be t h e o r i z e d t h a t p o l y m e r i z a t i o n k i n e t i c s of  v i n y l - d i v i n y l comonomer systems and p r o p e r t i e s of t h e polymer p r o d u c t s from such systems a r e determined  not o n l y by t h e  n a t u r e of r e a c t i v e groups, b u t a l s o by t h e c h e m i c a l s t r u c t u r e and d i m e n s i o n  of t h e DVM m o l e c u l a r b r i d g e , i . e . , t h e m o l e c u l a r  fragment c o n n e c t i n g double bonds i n t h e DVM,  D i v i n y l monomers  h a v i n g c o n s i d e r a b l e m o l e c u l a r b r i d g e l e n g t h have h i g h e r viscosities.  T h i s may have an i n d i r e c t e f f e c t on d i f f u s i o n  p r o c e s s e s and p o l y m e r i z a t i o n k i n e t i c s , p a r t i c u l a r l y i n . connect i o n w i t h g e l a t i o n and a c c e l e r a t i o n v i a Ge. From e x p e r i m e n t a l d a t a c o l l e c t e d f o r o t h e r purposes i n (48,61) and f r o m o t h e r s t u d i e s (7,8,9,57,58,76,77) an i n f e r e n c e can be made as t o t h e importance d i s t a n c e between DVM double bonds. i.  of m o l e c u l a r  T h i s i s based on:  c o m p e t i t i o n between i n t e r - m o l e c u l a r and i n t r a - m o l e c u l a r p r o p a g a t i o n as r e l a t e d t o t h e ring size  3  i . e . , c y c l l z a t i o n versus cross-  l i n k i n g ; and  29 ii.  overall values  polymerization of i n d i v i d u a l  overall  The  kinetics,  rate constants,  polymerization  importance  polymerization  of i n t r a - m o l e c u l a r  crosslinked Extensive to  polymers with  work  d e t e r m i n e s whether  lar  appreciably Contrary as  of r i n g  s o l u b l e , non-  o r no r e s i d u a l  unsaturation.  (48,91,92) h a s h e l p e d  s t r u c t u r e w h i c h c a n be f o r m e d , polymerization  the formation  than those  to expectations,  o f 6-membered r i n g s i s  (59,78).  of l a r g e r s i z e  however, r i n g  structures  many a s 11 and 17 atoms have b e e n r e p o r t e d The  i n f l u e n c e of molecular  polymerization constants data  kinetics  has not been  are a v a i l a b l e .  or i n t r a -  i s t h e predominant r e a c t i o n f o r a p a r t i c u  As a r u l e , greater  was  monomers gave  inter-molecular  cyclization  monomer.  little  cyclization  (18,19) f o u n d t h a t  by S i m p s o n and c o - w o r k e r s  show t h a t t h e s i z e  molecular  of d i a l l y l  as well as  rate.  e m p h a s i z e d when B u t l e r and c o - w o r k e r radical  e.g., numerical  bridge  and n u m e r i c a l  containing  (17,33,48,61).  l e n g t h on  values  of i n d i v i d u a l  studied  systematically.  Recently,  however, S o v i e t  Only  limited  scientists  (7,8,9,57,53,76) have p u b l i s h e d c o m p r e h e n s i v e s t u d i e s on polymerization  kinetics  Berlin dimethacrylate  and p r o p e r t i e s  of such  (3) c a l c u l a t e d i n d i v i d u a l  polymers.  r a t e constants  e s t e r s of a l k y l e n e g l y c o l s h a v i n g  CHo i  CH where:  2  = C - COO - ( C H  x = 4, 6, 1 0 .  2  Ch" i ) - 00C - C = C H  of  the general  f ormula:  2  rate  30 The  initial  p o l y m e r i z a t i o n r a t e and p r o p a g a t i o n  r a t e c o n s t a n t s s h a r p l y i n c r e a s e d w i t h l e n g t h between bonds.  double  The a b s o l u t e kp v a l u e f o r MMA was 300 l / m o l e , sec and  i n c r e a s e d t o 600, 1,2.00, and 1,880 l / m o l e . sec f o r monomers w i t h x e q u a l t o 4,6, and 10 r e s p e c t i v e l y ( T a b l e 2-2).  A t lower and  average c o n v e r s i o n s , kp f o r t h e s e compounds exceeded kp f o r MMA by 5-10 t i m e s , a l t h o u g h t r u e MMA r a d i c a l r e a c t i v i t y and t h e double  bonds of m e t h a c r y l a t e e s t e r s do not depend on t h e n a t u r e  of g l y c o l or e s t e r r e s i d u e s ( 1 2 ) . From Table 2-2 i t i s e v i d e n t t h a t t h e i n i t i a l  poly-  m e r i z a t i o n r a t e f o r a l l o l i g o m e r s exceeds p o l y m e r i z a t i o n r a t e • for  MMA even a t 50% c o n v e r s i o n where v i s c o s i t y of t h e p o l y m e r i z a -  t i o n m i x t u r e i s much h i g h e r .  The r e a s o n f o r h i g h e r p o l y m e r i z a t i o n  r a t e i s o b v i o u s f r o m t h e n u m e r i c a l v a l u e of k ^ / k ^ ^ .  Simple  c a l c u l a t i o n of kp/k^.^^, from d a t a a t z e r o c o n v e r s i o n f o r e s t e r s w i t h x e q u a l t o 4, 6, and 10 g i v e s 67, 152 and 290 x 10"^, respectively.  A l l these values are s i g n i f i c a n t l y higher than the  maximum v a l u e found f o r MMA as demonstrated i n .Table 2-1 ( 4 3 ) . Similar increase i n i n i t i a l for  p o l y m e r i z a t i o n r a t e was p o i n t e d out  p o l y m e r i z a t i o n o f d i m e t h a c r y l a t e s and mixed a l l y l and  c a r b o x y a l l y l e s t e r s , such as (8) : R  where:  - 0 ~(CH -CH -0) _ ** 2 R  x  2  Rj_ i s : C H  ?  2  2  3  = C - COCH  R  I  3  i s : CH  2  = CH - C H  2  - COO  CH  2  = CH - C H  2  - 0 -  , or  31 The  increased r e a c t i v i t y with increase i n molecular  b r i d g e l e n g t h between double bonds was  attributed to multiple  e t h e r bonds w h i c h i n c r e a s e d f l e x i b i l i t y framework.  Because f l e x i b i l i t y  of the  three-dimensional  of t h e s e m o l e c u l e s f a v o u r s  t i g h t p a c k i n g , double bonds of a c r y l a t e groups are drawn t o g e t h e r and are arranged and  i n a "kinetically-favourable"  form "bundle a s s o c i a t e d swarms" s i m i l a r t o nematic forma-  tion i n l i q u i d crystals (8). polymerizable  The  t r a n s f o r m a t i o n from l i q u i d  e s t e r s to space-regular  c r y s t a l l i n e arrangements  i n d i c a t e s broad p o s s i b i l i t i e s of d i r e c t e d s y n t h e s i s r e g u l a t i o n of b o t h p o l y m e r i z a t i o n k i n e t i c s and t h e r e s u l t a n t polymer  2.2.2.3  and  p r o p e r t i e s of  products.  A c c e l e r a t e d p o l y m e r i z a t i o n i n f o r m i n g wood polymer composites  (WPC)  Much work has been p u b l i s h e d i n c o n n e c t i o n a p p l i c a t i o n of v i n y l monomers t o wood and p a p e r s . and heat c a t a l y s t t e c h n i q u e s  process  with Both r a d i a t i o n  of p o l y m e r i z a t i o n have been used  (4,5,30,31,33,49,53 - 56,82,84,85,90,93,96,101). c o n v e r t s wood i n t o WPC,  This  simple  a composite m a t e r i a l -with  improved p h y s i c a l p r o p e r t i e s such as h a r d n e s s , a b r a s i o n t a n c e and c o m p r e s s i o n s t r e n g t h . and a s s o c i a t e d wet MMA  pattern  Further, dimensional  s t r e n g t h p r o p e r t i e s are improved.  resis-  stability So f a r  and S have been the most w i d e l y used monomers f o r t h i s  purpose.  32 Problems w i t h i n s i t u r a d i a t i o n p o l y m e r i z a t i o n of v i n y l monomers r e l a t e t o r a d i a t i o n s e n s i t i v i t y of wood constituents, particularly c e l l u l o s e .  V i n y l monomers, such  as S r e q u i r e massive dosages (10 Mrad) f o r complete tion.  polymeriza-  The l a r g e dose requirements are necessary mainly because  of low G-value, 0.6 (22).  I t i"s a l s o expected t h a t monomers  a s s o c i a t e d w i t h wood components r e q u i r e more energy f o r polymerization  due t o i n f l u e n c e of wood components and oxygen  i n the wood s t r u c t u r e . I t i s known (22) t h a t c h l o r i n a t e d compounds, such as CCI4, The  accelerate r a d i a t i o n polymerization  method has been used f o r r e d u c i n g  production  of WPC  caused by C C I 4 ,  (30,55,82,93).  particularly  of v i n y l monomers.  dose requirements i n  However, secondary e f f e c t s  s i n c e i t f u n c t i o n s as a very  e f f i c i e n t c h a i n - t r a n s f e r agent (22,42,59), are disadvantageous and  l i m i t p r a c t i c a l value  of C C 1  4  a c c e l e r a t i o n technique  (30,82). A d d i t i o n of c r o s s l i n k i n g monomers, which c o n t a i n two or more v i n y l groups, t o common v i n y l monomers copolymerization  and formation  allows  of t h r e e - d i m e n s i o n a l  In a d d i t i o n t o improved WPC p h y s i c a l p r o p e r t i e s  networks.  (30,66) ,  c r o s s l i n k i n g agents q u i c k l y t u r n l i q u i d monomers, d e p o s i t e d i n the wood v o i d spaces, i n t o g e l s and thus: i. ii.  a c c e l e r a t e the p o l y m e r i z a t i o n  v i a Ge, and  e l i m i n a t e l a r g e monomer l o s s e s due t o evaporation.  33  So  f a r , only  accelerating systematic  ability  study  on  scant  a t t e n t i o n has  of d i f f e r e n t  been g i v e n t o  divinyl  gelation kinetics  monomer-s,  the  A  in vinyl-divinyl  comon-  omer s y s t e m s i s l a c k i n g .  Raff on r a d i a t i o n presence  e t a l . (84)  polymerization  of t h e  data  the  purpose  acceleration  (55)  of r a d i a t i o n  a d d i t i v e t o MMA,  at  2/o c o n c e n t r a t i o n was  Kenaga a  series  systems. t-butyl was  styrene  concentrations  small  not  very  shown t o be  and  wood and  caused  Based  more e f f e c t i v e  odor  other  weight,  a DVM  (EGDMA)  as w e l l  EGDMA was  vinyl-trivinyl  a g e n t s on (Tilda  on  accelerator.  amounts of d i e t h y l  conversion  examined  than  comonomer  polymerization  ameripana L )  of  at  t  90°C  e x o t h e r m method f o r evidence  provided  (TMPTA) was  Several DVB.  by  DVM his  selected  dimethacrylates The  latter  contain  benzene w h i c h remained t r a p p e d  problems.  as  heat-catalyst polymerization  time-temperature  most e f f e c t i v e  that  convincing.  i n basswood  t o 30%.  DVB  minor a c c e l e r a t i n g e f f e c t  t r i m e t h y l o l propane t r i a c r y l a t e  as the were  up  the  a d d i t i o n of  polymerization.  of c r o s s l i n k i n g  the  They f o u n d  increased  proposed  discussed  (TBS)  of 5%  given,  of v i n y l - d i v i n y l  Effect  effect  Unfortunately,  However, t h e  (53)  f o l l o w e d by  study  agent  of i n c r e a s i n g m o l e c u l a r  as  with  i n WPC,  dosage.  were n o t  K e n t et. al_. for  of S  crosslinking  degree f o r a p a r t i c u l a r comparative  i n v e s t i g a t e d the  in  34 In 1969 P a s z n e r (79) i n t r o d u c e d  and found TEGDMA t o  be a v e r y e f f e c t i v e c r o s s l i n k i n g agent and a c c e l e r a t o r f o r radiation polymerization  of MMA, and S.  Dose r e q u i r e m e n t s f o r  complete p o l y m e r i z a t i o n ,  as f o l l o w e d by t h e t i m e - t e m p e r a t u r e  exotherm method, were found t o be lower t h a n t h a t f o r an optimum m i x t u r e of S-AN.  Subsequently, the a c c e l e r a t i n g  a b i l i t y of TEGDMA was t e s t e d s y s t e m a t i c a l l y I n numerous other comonomer systems  (.11,25,26,52,67-71,79-81,98,99).  Recently,  Duran and Meyer (33) adopted a  systematic  approach f o r e v a l u a t i n g t h e a c c e l e r a t i n g a b i l i t y of t r i m e t h y l o / propane t r i m e t h a c r y l a t e composites. (3l)  (TMPTMA)  w i t h MMA i n basswood  U s i n g maxima of t i m e - t e m p e r a t u r e exotherm  curves  as i n d i c a t o r s of r e a c t i o n r a t e s showed t h a t time t o  exotherm  peak d e c r e a s e d r a p i d l y as percentage of c r o s s l i n k i n g  agent i n c r e a s e d  a c r o s s low c o n c e n t r a t i o n  a t t r i b u t e d the increase i n t i m e t o exotherm  l e v e l s (1-20%).  They  i n r e a c t i o n r a t e , i . e . , t h e decrease  peak, t o f o r m a t i o n  of a t h r e e - d i m e n s i o n a l  gel structure. I n our l a b o r a t o r i e s , a s r e p o r t e d  earlier  (68-70,79-81,  98) t i m e - t e m p e r a t u r e exotherm c u r v e s were used f o r q u a n t i t a t i v e c h a r a c t e r i z a t i o n of a c c e l e r a t i n g a b i l i t y of c r o s s l i n k i n g agents i n r a d i a t i o n p o l y m e r i z a t i o n systems.  of v i n y l - d i v i n y l comonomer  The most a t t r a c t i v e comonomer systems have been  a p p l i e d t o f a b r i c a t i o n of WPC, PPC and veneer polymer  composites  (VPC), as w e l l as proposed f o r t o u g h , h i g h l y r e s i s t a n t  surface  coatings  (25,26,52,79-81,98,99).  35 In  summary, much work h a s b e e n done t o c l a r i f y  acceleration Vinyl-divinyl studied  phenomena i n v i n y l comonomer  polymerization. only  but  i n v o l v e s many o t h e r  structure bridge  than that  accepted  on s t a t i s t i c a l  diffusion,  of d i v i n y l  treatment  of c r o s s l i n k p r o b a b i l i t i e s ,  f a c t o r s , such as i n t r a - m o l e c u l a r r e a c t i o n c o n d i t i o n s and  monomers.  As example, t h e  Much work r e m a i n s t o be done b e f o r e  vinyl-divinyl  comonomer  f o r condensation  l e n g t h b e t w e e n d o u b l e b o n d s may have  effects. in  of v i n y l - d i v i n y l  treat-  A c c e l e r a t i o n y_ia c r o s s l i n k i n g a g e n t s i s b a s e d  not  cyclization,  have n o t b e e n  I t i s clear that theoretical  polymerization  s y s t e m s i s more complex  homopolyrnerization.  s y s t e m s , however,  systematically.  ment o f Ge d u r i n g  monomer  Ge  systems.  chemical molecular  significant Ge i s u n d e r s t o o d  36  3.0 MATERIALS AND METHODS  Methods and some monomers used i n t h i s study were d e s c r i b e d i n d e t a i l e a r l i e r (67,69,79).  Only g e n e r a l monomer  c h a r a c t e r i s t i c s , b r i e f d e f i n i t i o n s of p o l y m e r i z a t i o n p a r a meters,  as w e l l  as thermomechanical  and p h y s i c a l - m e c h a n i c a l  t e s t s f o r polymer p r o d u c t s a r e r e p e a t e d below.  3.1  Monomers • Two k i n d s of monomers were used i n t h i s s t u d y .  v i n y l monomer was methyl m e t h a c r y l a t e commercially a v a i l a b l e  The  (MMA), w h i l e a  s e r i e s of g l y c o l d i m e t h a c r y l a t e s were  used as d i v i n y l monomers.  3.1.1  Methyl  methacrylate  Methyl m e t h a c r y l a t e was t h e b a s i c monomer used i n a l l experiments.  I t c o n t a i n e d a commercial  Inhibitor  hydroquinone) as s u p p l i e d by Eastman Co. t i o n was attempted  3.1.2  f o r these  (50 p.p.m.  No monomer p u r i f i c a -  experiments.  D i v i n y l monomers Four d i f f e r e n t d i v i n y l monomers (DVM) of t h e common  g l y c o l dimethacrylate structure,  w i t h various molecular chain  37 l e n g t h s between t e r m i n a l v i n y l double bonds, were s e l e c t e d . These comonomers served as c r o s s l i n k i n g agents a c c e l e r a t o r s f o r MMA by the g e n e r a l  The  polymerization.  A l l DVM  and are c h a r a c t e r i z e d  formula:  index "n" v a r i e d from 1 t o 4.  The  f o u r DVM  used i n t h i s  study were: i. ii. iii. iv.  Ethylene g l y c o l dimethacrylate  Diethylene glycol dimethacrylate Triethylene g l y c o l dimethacrylate  Pa.  (DEGDMA), (TrEGDMA),and  Tetraethylene g l y c o l dimethacrylate  P r o p e r t i e s of the MMA A l l DVM  (EGDMA),  and DVM  (TEGDMA).  used are g i v e n i n Table  3-1.  were purchased from Borden C h e m i c a l Co., P h i l a d e l p h i a ,  Higher homologs of the s e r i e s were not a v a i l a b l e at the  time.  3.1.3  C a l c u l a t i o n of s t r u c t u r a l parameters To t r a n s f e r f r o m monomer i n t o polymer, each carbon  atom i n the polymer c h a i n or i n the t h r e e - d i m e n s i o n a l must be connected t o at l e a s t two bonds.  L i n e a r one-dimensional  o t h e r atoms by  network  covalent  ( t h e r m o p l a s t i c ) macromolecules,  such as poly(MMA) f o r example, o n l y c o n t a i n 2-way connected c a r b o n atoms and t h u s have a c o n n e c t i o n number (CN)  equal t o  38  2,000.  Thermosettings c r o s s l i n k e d  c o n t a i n b o t h 2-vvay  polymers  or c o p o l y m e r s  and 3-way c o n n e c t e d c a r b o n atoms.  Their  CN i s between 2.000 and 3.000. Recently, Holliday and  demonstrated  analysis  predict  the usefulness  o f random p o l y m e r  structural  feature  physical  An structure  and c o w o r k e r  o f CN f o r s i m p l e  networks.  of polymers  properties  (45,46) p r o p o s e d topological  CM d e s c r i b e s  an a v e r a g e  and c a n be e x t e n d e d f u r t h e r t o  of polymer p r o d u c t s .  a v e r a g e CN c a n be c a l c u l a t e d  o f monomer r e p e a t i n g  from the chemical  units as:  2a + 3b + 4 c a  where:  + b  + c  a, b and c a r e , r e s p e c t i v e l y ,  connected  atoms i n t h e r e p e a t i n g  2-way, 3-way and 4-way  monomer u n i t s .  Calculated  v a l u e s f o r members o f t h e p r e s e n t s e r i e s a r e g i v e n  i n Table  3 Xo  The as copolymer average The  a v e r a g e CN c a n be e x t e n d e d  further  c o n n e c t i o n number (CN  CN  number o f n e t w o r k  numerical value of C N  comonomer m i x t u r e . CN  where:  CN,  co  V1MA  C 0  c o  p r o v i d e s an  i.e., crosslinking  depends on m o l a r  density.  c o m p o s i t i o n of t h e  I t i s calculated as:  (CN^^AX  and C N  bonds,  )«.  t o copolymers  D V M  nif^^)  +  (C^DVN * ^DVM^ ••••••• «/3-2/ m  a r e c o n n e c t i o n numbers f o r MMA  and DVM.  39  ^MMA  m  anc  * ^DVM m  a  r  e  rn  °l  f r a c t i o n s of MMA and DVM i n  e  t h e comonomer system,  respectively.  I n c a l c u l a t i n g an average CN  only those connections are  c o n s i d e r e d which form p a r t of polymer network.  Thus, s i d e  s u b s t i t u e n t s such as CH^- or CH^OOC- i n poly(MMA), f o r example, were e x c l u d e d .  3.1,4  P r e p a r a t i o n of comonomer m i x t u r e s M i x t u r e s o f MMA and r e s p e c t i v e DVM were prepared on a  volume/volume b a s i s i n l o t s of 50 ml t o m i n i m i z e e r r o r due t o m i x i n g . polymerization.  experimental  These were s t o r e d a t -10 °C p r i o r t o  Volume c o n c e n t r a t i o n s , as w e l l as mole r a t i o s  are g i v e n i n T a b l e 3-2. R e l a t i v e v i s c o s i t i e s ( £ i ) of t h e pure monomer and xe  comonomer m i x t u r e s were measured w i t h a Ubbelohde l /  a  viscosi-  meter (K = 0.05394) a t 25 °C and c a l c u l a t e d a s : t  mixture  .  tMMA where:  ^mixture  a n c i  ^MMA  a  r  e  e f f l u x t i m e s f o r t h e comonomer  m i x t u r e and MMA, r e s p e c t i v e l y ,  R e l a t i v e v i s c o s i t i e s f o r pure  monomers a r e g i v e n i n Table 3-1 and f o r t h e comonomer m i x t u r e s i n Table 3-2.  40  3,2  Radiation  Polymerization  Technique  Although r a d i a t i o n induced well  established technique,  given  to polymerization  production for  of WPC.  reason  has  a t t e n t i o n has  been l a c k  and methods  polymers,  Difficulties  degree  a  been  of p r o p e r  o f monomers t o  radiation field.  k i n e t i c s to high  i s now  as r e l a t e d t o Ge  transformation  e s p e c i a l l y w i t h i n the polymerization  scant  kinetics  One  f o l l o w i n g the  only  polymerization  in  of c o n v e r s i o n  studying  are  well  documented.  Davies radiation Britt.)  et  a l . . (31)  polymerization  and  previously  red  pine  described  i n yellow  In h i s  From the  shape of t i m e - t e m p e r a t u r e  related  polymerization  study  during  stages  peak t e m p e r a t u r e . study. tion  3.2.1  The  Ge  obtained,  and  s u c h as  ( T ) , °C  exothermic  and  these  of  for  at  this  polymeriza-  (67,69,70).  of p o l y m e r i z a t i o n  versus  were  conversion  adopted  determination  previously  heat  kinetically  complete  was  of  automatically.  were d e r i v e d  shown i n F i g , 3-1,  following polymerization  a method  exotherms,  determination  temperature  MMA  polymerization  recorded  same t e c h n i q u e  p a r a m e t e r s have b e e n g i v e n  Definition  the  phenomena and  D e t a i l e d d e s c r i p t i o n s and  The  the  was  of p o l y m e r i z a t i o n  to i n h i b i t i o n ,  of  b i r c h (Betula alleghaniensis  f o r heat-catalyst bulk  released  important  kinetics  (P,i,nu,$, r e s i n p s a A i t . ) by  monomers ( 5 , 8 8 ) .  vinyl  s t u d i e d the  time  (t),.min  were a n a l y s e d  characteristics:  to  parameters  records provide  41 Initial  i. ii.  condition  of t h e system  "Gel-Effect Point" solution  (T35, t ) ; 0  (GEP) b y g e o m e t r i c  ( F i g . 3-1) a s t h e e x o t h e r m  i n t e r s e c t i o n by t h e p e r p e n d i c u l a r common p o i n t and (T iii.  late G E  p,  t  obtained  curve G E  curve  through the  by e x t r a p o l a t i n g  stages,  and w i t h  early  components  p);  " C u r e " a t t h e e x o t h e r m maximum (MAX) w i t h  (T^^x, ^^/J^)  components iv.  "Activation" ( i )period  I  as time  interval to  r e a c h GEP and c a l c u l a t e d a s ( t £ p  - t ) , and  G  v.  "Acceleration"  (II) period  as time  interval  b e t w e e n GEP and t h e e x o t h e r m maximum, and calculated (t^^ ~ "^GEP^ * As for  time  shown a l s o i n F i g . 3-1, d o s e  ( t ) , thereby describing  at t h e s i n g l e dose r a t e  To  examined  compare r e l a t i v e  "Activation"  i n the present  rates  Polymerization "Activation" GEP -  T  T  requirements study.  of p o l y m e r i z a t i o n i n (II) periods,  the following  c o e f f i c i e n t s (PRC) were c a l c u l a t e d :  i.  PRC  the i r r a d i a t i o n  ( I ) and " A c c e l e r a t i o n "  polymerization  (D) may be s u b s t i t u t e d  «  -  T  rate  coefficient  (PRCj) p e r i o d a s :  : 36 0 0 0 0 0 0 0  ~  f o r the  t  o  « i £ O o « * o 0 0 « « . 0  0O0«o«a  /3-4/  42  ii.  Polymerization  rate coefficient  (PRGn)  "Acceleration"  T P R C  II ~ t  The numerically due  ratio  curing  -  T GEP  MAX  -  ^EP  of t h e s e  e x p r e s s e s the  t o t h e Ge  (l/tjY^)  MAX  period  the  as:  .  coefficients,  increase  for  PRCjj/PRCj,  i n polymerization  rate  phenomena.  Reciprocal  of t i m e needed t o a t t a i n  i s used  a measure f o r c h a r a c t e r i z i n g t h e  rate  ,  as  e x o t h e r m maximum overall  (OCR):  1 OCR.  —  — —  0 4 0 0 O 0 0 0 0 0 O 3 9 0 O 9  ^* 6  /  uMAX By (l/t^pp),  analogy, r e c i p r o c a l of the  r e f e r s t o the  c h a r a c t e r i z e s the Ge  overall  efficiency  gelation rate  of the  (OGR)  GEP and  c r o s s l i n k i n g agent t o  onset  phenomena.  3.2.2  Polymerization For  procedure  determination  of p o l y m e r i z a t i o n  of monomer or comonomer m i x t u r e a  time t o r e a c h  small  glass v i a l ,  w h i c h was  p a r a m e t e r s 5 ml  ( v o l u m e / v o l u m e ) were p l a c e d  then flushed with  nitrogen  and  in  43 sealed.  Radiation  polymerization  220  dose r a t e  a t 0,82 M r a d / h r , a s d e t e r m i n e d b y F r i c k e  with  dosimetry  (27).  attenuators  was done i n a G a m m a c e l l  I n two e x p e r i m e n t s , r a d i a t i o n d o s e  were used t o e v a l u a t e  rate  i n f l u e n c e o f d o s e r a t e on  OCR.  Comonomer m i x t u r e s were f i r s t a m b i e n t Gammacell styrofoam  chamber t e m p e r a t u r e  seat which p r o v i d e d  reproducible  Use  In each case,  an i c e - w a t e r  tested  above.  operators, with  ii.  "tQEP tji^  =  results p a r a m e t e r s , as  exotherms by t h r e e  standard  (ll),  e x p e r i m e n t s , done a s d e s c r i b e d deviation values  (50): i.  polymerization  t h e MMA-TEGDIvA comonomer s y s t e m  on s i x t e e n i d e n t i c a l  The f o l l o w i n g  (67,71).  c o m p a r i s o n s may be  of p o l y m e r i z a t i o n  from r a d i a t i o n p o l y m e r i z a t i o n  independent  junction.  studied,  R e p r o d u c i b i l i t y of experimental  derived  stripchart  reference  i n detail  e v o l u t i o n and t h a t  Reproducibility  was  t o a time based  i n v o l v e s assumptions that  made b e t w e e n t h e s y s t e m s  exotherm  copper-constantan  has been d e s c r i b e d  r e l a t e s t o heat  3.2.3  by i n s e r t  s i g n a l s sent  technique  o f t h e method  rate  set i n a  p o s i t i o n i n t h e chamber.  c a l i b r a t e d against  similar  (36 ° C ) , t h e n i n s u l a t i o n and  thermocouples, with  A  t othe  thermal  t e m p e r a t u r e s were f o l l o w e d  recorder  conditioned  17.5 - 1.5 rnin, :  = 23.2 - 1.7 min,  were c a l c u l a t e d  44  3.3  iii.  T  iv.  T  G  E  - 63.0 t 2,5  P  = 143.0 t 7.8  mx  P r o p e r t i e s of Polymer  Properties the  b a s i s of t h e i r  behaviours.  compression  3.3,1  ° . C  Products  of p o l y m e r p r o d u c t s were e v a l u a t e d thermomechanical  The i n d i v i d u a l  unconventional  °C, and  and m e c h a n i c a l  characteristics,  thermomechanical curves,  stress-strain  curves  strength  determined  a s w e l l as  are described  below.  Thermomechanical p r o p e r t i e s  y^ere o b t a i n e d b y a s i m p l e deformation Polymer  rod  e x t e n s i o n was  and h e a t e d high)  coupled  variable  o i l was  used  specimens  (67,69,80).  were r e s t e d on a t u b e  with  2  cm  2  position  i n cross-section.  transducer.  a s h e a t i n g medium,  mode.  and  The  High-temperature  The o i l  f o l l o w e d by an i n s e r t  S i g n a l s generated  of the t r a n s d u c e r  support  a probe l e a d i n g i n t o the core  differential  (12 t o 15 °C/min),  products  constructed f o r recording  r e g u l a t e d t o i n c r e a s e t h e sample t e m p e r a t u r e  thermocouple.  X-Y  (3 mm  device  l o a d e d v i a a r o d 3.2 x 10"*  silicone  rate  of l o a d e d  samples  of a l i n e a r  was  from  standard  T h e r m o m e c h a n i c a l p r o p e r t i e s of t h e p o l y m e r  were  on  temperature  at constant  copper-constantan  by c h a n g e s i n t e m p e r a t u r e  p r o b e were  and  fed t o a recorder i n the  45 Glass distortion in  temperature  F i g , 3-2,  constant range,  temperature  In a d d i t i o n ,  characteristic  of c r o s s l i n k e d  polymer  demonstrated  rubbery  state  polymers,  was  d e f o r m a t i o n degree  h e r e , TDD v a r i e s  crosslinked  as  t h e magnitude of r e l a t i v e l y  thermomechanical  calculated  (Tg) and t h e r m a l  (TDT) were d e t e r m i n e d  deformation a c r o s s the broad  calculate  fully  transition  temperature used t o  (TDD),  As  from 0 t o 1 f o r t h e r m o p l a s t i c t o  products.  N u m e r i c a l v a l u e s of TDD  were c a l c u l a t e d a s :  h TDD  where:  h dp The  (LTDC) was  =  ... »•..!•  j  i  i  dp  ., • . I.,. . . i  .,  «4  O *  O •  = sample h e i g h t ,  mm,  = depth  penetration,  linear  of p r o b e  •  •  «  »  9  O  •  9  O  9  fl  O O  «  »/3*'7/  and  thermomechanical  calculated  .1  mm.  deformation  according t o Holsworth  coefficient  (47) a s :  k x s h  where:  k  = the s e n s i t i v i t y  (mils/inch  of r e c o r d e r  chart  paper), s  = slope  of t h e r m a l d e f o r m a t i o n c u r v e i n the  transition h  = sample  region  height.  ( F i g , 3 - 2 ) , and  46  3.3.2  Mechanical  strength  Stress-strain determined Testing  testing  characteristics  on a 5 0 0 0 kg c a p a c i t y S  Instrument.  standard  properties  I t was  INSTRON M o d e l TM-L  e q u i p p e d w i t h a CCM  p o t e n t i o m e t r i c - t y p e graph recorder c o n d i t i o n s were used  i. ii. iii.  recorder full  chart  scale  a t 0.1  speed  load  compression  (5l).  Universal cell  The  following  cm/min,  a t 1*0 cm/min, and  test  s p e c i m e n s were  manufactured  P o l y m e r i z a t i o n s were done  w i t h 10 ml of monomer o r comonomer  mixture.  The sample  according  t o ASTM S t a n d a r d D 695-68T f o r d e t e r m i n a t i o n o f  compressive  sectional  l e n g t h t o d i a m e t e r r a t i o ivas 2:1,  properties  Test  specimen  of r i g i d  ii. iii, iv.  on a m e t a l  d i a m e t e r ~- 1.0 height =2,0 radius  plastics (2).  dimensions w i t h uniform c i r c u l a r  a r e a , as m a c h i n e d i,  Fig.  3-3  (20,72).  were as f o l l o w s :  cm,  o f g y r a t i o n = 0.25, and  slenderness r a t i o =  polymers,  lathe,  cross-  cm,  8.0  V a r i o u s t y p e s of s t r e s s - s t r a i n different  and  a t 5,000 k g .  as c y l i n d e r s f r o m c u r e d p o l y m e r s . a separate experiment  load  were  f o r a l l samples:  c r o s s - h e a d speed  Standard  in  i n compression  curves, obtained with  and s t a n d a r d n o m e n c l a t u r e  a r e shown i n  47  4,0 RESULTS  Radiation  polymerization  s y s t e m was i n v e s t i g a t e d o v e r 0:100, these  Results  as d e r i v e d  are  summarized  for  some o f t h e s e  relation in  i n Tables  between OCR  MMA-TEGDMA  polymerization  are given  (l/t^v,)  exotherm  i n F i g , 4-1 and 4-2, The concentration  i s p l o t t e d i n F i g . 4-3.  t h e MMA-TEGDMA  comonomer  system  d e m o n s t r a t e d t h a t most a c c e l e r a t i o n was o b t a i n e d narrow c o n c e n t r a t i o n range, e s p e c i a l l y concentration. proportional agent. placed  reason  for in  MMA  Tables  e m p h a s i s i n f u r t h e r e x p e r i m e n t s was  Accordingly,  with t h e other  OCR. wa.s n o t  of the c r o s s l i n k i n g  on s t u d y i n g DVM c o n c e n t r a t i o n s  comonomer m i x t u r e s .  within a  b e t w e e n 2.5 t o 1 0 % DVM  TEG DMA c o n c e n t r a t i o n s  t o volume c o n c e n t r a t i o n  For this only  At higher  curves,  Graphical interpretations  and TEG DMA. volume  comonomer m i x t u r e s  Results with  parameters of  from p o l y m e r i z a t i o n  4-1 and 4-2,  results  comonomer  t h e c o n c e n t r a t i o n r a n g e 100:0 t o  for individual  mixtures,  o f t h e MMA-TEGDMA  three  4-3 and 4-4.  polymerization  crosslinking  Graphical  up t o 3 0 % i n characteristics  a g e n t s a r e summarized  interpretation  o f tMAX  a n c  *  t(3£p, a s f u n c t i o n s o f DVM c o n c e n t r a t i o n  i n these  g i v e n F i g . 4-4 and 4-5,  rate coefficients i n  "Activation" function  Polymerization  (PRCj) and " A c c e l e r a t i o n " (PRCjj)  systems, i s  periods  o f DVM c o n c e n t r a t i o n a r e p l o t t e d i n F i g , 4-6.  as a  48 i n F i g . 4-7  Illustrations and  time r e q u i r e d  studied,  The  work  M  concentration  A  Linear  V  c o m p a r i s o n , OCR v a l u e s  from  (33)  p r o p o r t i o n a l l y w i t h DVM  systems a r e g i v e n  i nFig.  4-8.  as c a l c u l a t e d f r o m r e s u l t s o f  proportionality  i n F i g . 4-8  slopes  represent  the overall  (K) f o r i n d i v i d u a l DVM.  r e l a t e d t o DVM c o n n e c t i o n  number  constants  These a r e  (CNj^y^) a s seen i n  4-9.  Fig.  The  linear  concentration times  allows  r e l a t i o n s h i p between OCR and DVM c a l c u l a t i o n and p r e d i c t i o n o f c u r i n g  ( t ^ x ) f ° MMA-DVM m i x t u r e s . r  measured low  f o r t h e four, s y s t e m s  are included.  a c c e l e r a t i o n constant inversely  ^  S-TEGDMA s y s t e m as t a k e n  increased  The ( l / t ^ A x / ^ ' \ o n c ^ calculated  V  r e l a t i o n s h i p s between OCR and DVM  for the four  D u r a n and Meyer  the  j  (70).  OCR ( l / t ) MAX  concentration.  r e l a t i o n s h i p between t  t o o n s e t Ge ( t ^ p p )  i n c l u d i n g r e s u l t s with  from e a r l i e r  For  show t h e  and p r e d i c t e d  DVM c o n c e n t r a t i o n s  curing  Differences  between  times f o r the four  a r e summarized  i n Table  systems a t  4-5.  c a l c u l a t i o n s f o r t h e 5-TEGDMA comonomer s y s t e m a r e Table  4-6  as taken from e a r l i e r  The  rather  experimentally  work  Similar given i n  (70).  good agreement between p r e d i c t e d and  measured  systems of t h e p r e s e n t  curing  times f o r d i f f e r e n t  and p r e v i o u s  (70)  studies  comonomer suggested  49 further  application  catalyst  results.  new t e c h n i q u e t o p u b l i s h e d  Such d a t a f r o m q u i t e  ( 5 3 ) a r e examined crosslinking  of t h i s  i n T a b l e 4-7.  agent  dissimilar  heat-  experiments  F u r t h e r , OCR a s a f u n c t i o n o f  c o n c e n t r a t i o n f o r these data i s demonstrated  i n F i g . 4-10.  D i f f e r e n c e s between h e a t - c a t a l y s t published  by D u r a n  method a r e g i v e n constant two  curing  problem  reaction  radiation  be  over wide range  curing  and t h e a s s o c i a t e d  density  using a  peak  exotherm  dose r a t e , as  i n F i g . 4-11.  used  c u r v e s * o b t a i n e d by a  a r e r e p r o d u c e d f o r MMA-EGDMA  i n F i g . 4-12 and 4-13,  parameters  that,  The OCR v a r i e d  of r a d i a t i o n  Shapes of thermomechanical  systems  rapidly  method, p o l y m e r i z a t i o n r a t e c a n  w i t h t h e square root  simple device  from  method").  increases very  c a n be c o n s i d e r a b l y r e d u c e d .  demonstrated  only  temperatures are v i r t u a l l y  T a b l e 4-9 d e m o n s t r a t e s  controlled  linearly  acceleration  (the "two-point  and peak t e m p e r a t u r e  up t o 180-190 °C ( 5 3 ) .  temperature  b y t h e new  encountered with the h e a t - c a t a l y s t  process i s that  uncontrollable  The o v e r a l l  times  t i m e s were c a l c u l a t e d  chosen experiments  One  altered  ( 3 3 ) and c a l c u l a t e d  i n T a b l e 4-8.  and p r e d i c t e d  randomly  curing  and Meyer  curing  respectively.  s u c h a s T , TDD and TDT, a s w e l l g  as r e p r e s e n t e d by copolymer  and MMA-TEGDMA Thermomechanical  as c r o s s l i n k i n g  c o n n e c t i o n numbers  (CN  C 0  ),  50 axe  given  and  TDD r e l a t e  of t h e s e CN  C 0  ,  i n Table  4-10 f o r t h e f o u r  m o b i l i t y of heated  systems s t u d i e d .  polymer  parameters with c r o s s l i n k i n g  i srepresented  i n F i g . 4-14 and 4-15.  The e x p o n e n t i a l r e l a t i o n s h i p  concentration F i g . 4-16.  f o r t h e two e x t r e m e  The r e l a t i o n s h i p  systems i s g i v e n  MMA-EGDMA  For  comparison  rate i n the t r a n s i t i o n  between LTDC- and DVM  systems i s i l l u s t r a t e d i n  b e t w e e n LTDC and CN  for the four  i n F i g . 4-17.  Compression the  Variation  d e n s i t y , c a l c u l a t e d as  LTDC c h a r a c t e r i z e s d e f o r m a t i o n region.  segments.  T , TDT  stress-strain  curves  f o r products  comonomer s y s t e m a r e s i m u l a t e d similar  curves  from  i n F i g . 4-18,  f o r t h e MMA-TEGDMA  system are  shown i n F i g , 4-19.  Numerical  v a l u e s f o r some  physical-mechanical  parameters of t h e polymer p r o d u c t s , stress-strain summarized stress  tests  for the four  i n Table  at rupture,  compression  concentraion, t o 4-23,  CN  c o  The stress-strain  slope  strain  at rupture  a s an e s t i m a t e  compression and a r e a  o f t o u g h n e s s , and  a r e shown f o r t h e v a r i o u s s y s t e m s i n F i g . 4-20  Compression  f o r the four  curve  compression  systems examined, a r e  4-11. R e l a t i o n s h i p s b e t w e e n  under t h e s t r e s s - s t r a i n DVM  as d e r i v e d from  stress a t rupture,  as a f u n c t i o n of  systems examined, i s g i v e n of the i n i t i a l  curves  represents  straight  the e l a s t i c  i n F i g , 4-24.  line  p o r t i o n of  modulus ( E ) ,  Numerical  v a l u e s o f E,  stress-strain are  curve  summarized  deformation  (F) f o r the  i n T a b l e 4-12.  and  stress-strain  plastic  toughness  curve  deformation different Correlation  as e s t i m a t e d by  i s demonstrated  and  area  polymer between area  in Fig.  under  products plastic  under  4-25.  the  52  5.0 DISCUSSION  Some e a r l y r e s u l t s polymerization improved  on a c c e l e r a t e d r a d i a t i o n  o f MMA-TEGDMA  curing  comonomer m i x t u r e s  t i m e s and s t r e n g t h  (79)  showed  p r o p e r t i e s of the r e s u l t i n g  polymer  products.  These p r e l i m i n a r y  further  systematic  s t u d i e s on r a d i a t i o n p o l y m e r i z a t i o n o f  vinyl-divinyl and  comonomer  S-TEGDMA comonomer  concentration briefly tions  ranges  summarized  systems.  of the mixtures  as f o l l o w s ,  5.1 R a d i a t i o n P o l y m e r i z a t i o n  vol  at different  mixtures) from polymerization  values  obtained  Tables  4-1 and 4-2.  illustrated decrease  from bulk  These  as the i n i t i a l  full  results,  observa-  was d e v e l o p e d .  System  p a r a m e t e r s f o r t h e MMA-TEGDMA comonomer c o m p o s i t i o n s exotherm c u r v e s .  polymerizations  over a wide c o n c e n t r a t i o n  (vol/  These  a r e summarized i n  The a c c e l e r a t i n g a b i l i t y  o f TEGDMA i s  r a n g e by a h y p e r b o l i c  i n t ^ ^ a s shown i n F i g . 4-1, Pronounced  as  over  o f t h e MMA-TEGDMA Comonomer  polymerization  s y s t e m were d e r i v e d  i n detail  (67,69,70),  served  study  encouraged  S u b s e q u e n t l y , t h e MMA-TEGDMA  s y s t e m s were s t u d i e d  on w h i c h t h e p r e s e n t  Radiation  experiments  a c c e l e r a t i o n accompanying  measured by t ^ ^  concentration  1  S  interval  primarily restricted ,  Additions  TEGDMA a d d i t i o n  t o a narrow  o f TEGDMA up t o 10% a r e o f  53 particular  interest;  effective. decreased  amounts i n e x c e s s  F o r example, a d d i t i o n of 1 0 % TEGDMA t o MMA t ^ ^ ^  r  o  m  H  7  m i n  f °  »  TEGDMA a d d i t i o n s i n f l u e n c e d t comonomer c o m p o s i t i o n , mixture 15  over  min.  x  p u r e MMA,  only moderately.  j V 1 A X  with  higher  a g e n t were l e s s  assumed t h a t  at high concentrations  as a d i f f u s i o n b a r r i e r  monomer t o a c t i v e r a d i c a l  "Activation"  as  t j ^ x "t only a  sensitive.  It i s  the c r o s s l i n k i n g  t r a n s l o c a t i o n of  sites.  quantitatively  of TEGDMA a s r e l a t e d  t o Ge  by PRC a s d e t e r m i n e d i n  t h e onset  vary with  o f GEP, r e s p e c t i v e l y .  composition  i'.e.,  Both  o f t h e comonomer  mixture  shown i n F i g . 4-2. Up  very  tion  t o 2 0 % TEGDMA  rapidly  crosslinked  a d d i t i o n both  due t o r e d u c e d media  (43).  termination  Further  coefficients i n viscous  increase  increased  and p a r t l y  i n TEGDMA  concentra-  a f f e c t e d not only the r a t e of t e r m i n a t i o n , but a l s o  influenced  the propagation  stabilized  within the intermediate  (20-50%).  I n h i g h l y c r o s s l i n k e d systems, i . e . , over  c h a i n growth p r o p a g a t i o n the  agent  ( P R C j ) and " A c c e l e r a t i o n " ( P R C T J ) p e r i o d s ,  and a f t e r  coefficients  efficient  c o n c e n t r a t i o n of  limiting  accelerating ability  may be e x p r e s s e d  before  radiation  Further  The 50:50  t h e most  t h e whole c o n c e n t r a t i o n range w i t h  crosslinking  The  t o 31 m i n .  however, r e p r e s e n t e d  Comonomer m i x t u r e s  functions  of 10% a r e l e s s  rate.  B o t h PRCj and PRCJ-J- became range  becomes f u l l y  r e a c t i o n s y s t e m was i m m o b i l i z e d  o f TEGDMA  concentration 5 0 % TEGDMA,  diffusion-controlled;  and c o n s e q u e n t l y  less  54 radiation  sensitive.  The dose r e q u i r e d  t o obtain  c o p o l y m e r w i t h t h e 50:50 m i x t u r e was 0.2 Mrad S u c h a comonomer c o m p o s i t i o n sensitive  than pure  The /3-6/.  MMA.  ( F i g . 4-3),  ^^MAX^  i t i s evident  OCR d e v i a t e d  OCR  diffusion  was p o s s i b l e  falling  within  empirical  ( m i x t u r e ) = l/tMAX(MMA)  where:  +  crosslinked  K  t i m e s of other  /DVM/  vol - concentration  K  =  o v e r a l l a c c e l e r a t i o n constant  equation  o f TEGDMA, and  times w i t h i n  i t i s possible  curing  region.  The p r o p o r t i o n a l i t y c o n s t a n t ability  mixtures  (OAC),  a s i n F i g . 4-3.  required  accelerating  networks.  ........,/5-l/  =  Using t h i s  At higher  equation:  /DVM/  slope  I t s value  linearly.  TEGDMA  t h e p r o p o r t i o n a l i t y range  t o predict the curing  t o the following  f o r lower  p o s s i b l y due t o a  b a r r i e r s e t i n t h e more h i g h l y  concentrations  according  that  from p r o p o r t i o n a l i t y  a c c e l e r a t i n g e f f i c i e n c y decreased,  l/t^Ax  characterizes  (up t o 10%) OCR i n c r e a s e d  TEGDMA c o n c e n t r a t i o n s  it  (Table 4-2).  From t h e r e l a t i o n s h i p b e t w e e n OCR and TEGDMA  concentrations  For  solid  i s 7.7 t i m e s more r a d i a t i o n  r e c i p r o c a l of t ^ ^  concentration  as  a  to predict  t h e most i m p o r t a n t  concentration  (K) c h a r a c t e r i z e s  overall  o f a p a r t i c u l a r DVM o r c r o s s l i n k i n g a g e n t .  f o r t h e MMA-TEGDMA  system  (0 t o 10% TEGDMA) a s  55 c a l c u l a t e d from t h e l i n e a r p o r t i o n of F i g . 4-3 i s 1.1 x 1 0 ~  J  . -1.cone -1. rain Deviation  of OCR from the p r o p o r t i o n a l i t y l i n e  10 t o 20% TEGDMA c o n c e n t r a t i o n agreement w i t h r e s u l t s , L a z a r (100).  polymeric c h a i n s , crosslinked  i n t e r v a l ( F i g . 4-3) i s i n good  derived  They s t u d i e d as w e l l  within  from ESR s t u d i e s by Szocz and  decay and segmental m o b i l i t y of as monomer molecules  within  p o l y g l y c o l methacrylate network.  For comonomer mixtures having higher d e n s i t i e s of c r o s s l i n k i n g , i . e . , a t higher TEGDMA  concentrations,  a c c e l e r a t i o n a c c o r d i n g t o Ge has t o be c o n s i d e r e d as the o v e r a l l effect  of two c o n c u r r e n t f a c t o r s : i.  DVM a c c e l e r a t i o n r e s u l t i n g from decreased termination  i n the p a r t l y crosslinked  network,  and ii.  DVM r e t a r d a t i o n  r e s u l t i n g from d i f f u s i o n  b a r r i e r s and consequent d i f f u s i o n - c o n t r o l l e d propagation i n h i g h l y crosslinked Gradual i n c r e a s e s  of TEGDMA up t o 10% c r e a t e s  reaction conditions  i n which i predominates over  A d d i t i o n a l increase  i n DVM c o n c e n t r a t i o n  11 c a u s i n g d e v i a t i o n ( F i g . 4-3).  networks.  ii.  increasingly  of OCR from the p r o p o r t i o n a l i t y  enlarges line  56 5.2 I n f l u e n c e  of M o l e c u l a r  Bridge Length i n D i v i n y l  Monomers  C r o s s l i n k i n g d e n s i t y of g e l l e d MMA-DVM network depends on: i.  frequency i.e.,  ii.  of c r o s s l i n k s on the polymer backbone  poly(MMA), and  molecular  b r i d g e l e n g t h between DVM double  bonds. It  seemed reasonable  DVM molecular ability  t o assume t h a t v a r i a t i o n i n  b r i d g e l e n g t h would i n f l u e n c e the DVM a c c e l e r a t i n g  and a f f e c t the delay or premature onset  of GEP.  This  h y p o t h e s i s was t e s t e d w i t h a s e r i e s of d i m e t h a c r y l a t e  esters  s e l e c t e d t o a c t as c r o s s l i n k i n g agents.  abilities  of EGDMA, DEGDMA and TrEGDMA  Accelerating  are g i v e n i n Tables 4-3 and 4-4,  w h i l e g r a p h i c a l i n t e r p r e t a t i o n s of these r e s u l t s are i l l u s t r a t e d i n F i g . 4-4 and 4-5. Changes i n the a c c e l e r a t i n g a b i l i t y MMA-DVM systems s t u d i e d , as shown by t^AX ^ t h a t a c c e l e r a t i n g a b i l i t y changed a c c o r d i n g bridge length. di  With i n c r e a s i n g b r i d g e  c o n c e n t r a t i o n range s t u d i e d .  length.  F  I  9 »  4  ~ » indicate 4  t o DVM molecular .mono- (EGDMA), glycol  over t h e whole  A c c e l e r a t i o n by DVM i n MMA-DVM  mixtures i s thus shown t o be d i r e c t l y bridge  n  length  (DEGDMA), t r i - (TrEGDMA) t o t e t r a e t h y l e n e  d i m e t h a c r y l a t e (TEGDMA) \ t j ^ decreased  of the d i f f e r e n t  r e l a t e d t o DVM molecular  57  For  examples  f r o m 83 m i n ' f o r comonomer  min,  MMA-EGDMA  system.  MMA-TrEGDMA  i . e . , DVM  for half-time  decreasing  DVM m o l e c u l a r  iii. iv.  systems  concentrations  E G D M A  MMA-TrEDGMA  A%,  MMA-TEGDMA  3%.  t o reduce t ^  A  Y  concentrations  of h a l f - t i m e study  replaced  of t h a t  bridge  length.  (Fig. 4-4):  concentrations  f o r t h e two  (MMA-EGDMA and MMA-TEGDMA)  that  i n t h e MMA-EGDMA  The p r o p a g a t i o n  shows  a s much DVM was r e q u i r e d  f o r p u r e MMA.  H i g h e r EGDMA  system i n c r e a s e d c r o s s l i n k i n g . barriersi n  r e a c t i o n i s assumed t o become  a t an e a r l i e r  t h a n i n t h e MMA-TEGDMA  Such  and  TEGDMA, t w i c e  t o one-half  diffusion-controlled  pure  concentrations  o f t h e g e l l e d network, c r e a t i n g d i f f u s i o n  system.  for  }  5%,  of t h i s  by e v a l u a t i o n  1%  MMA-DEGDMA  Comparison  t h a t when  s y s t e m s t u d i e s were  ' M M A - E G D M A  ii.  the  values,  values  for the four  i .  density  f o r MMA-DEGDMA and  t o reduce the c u r i n g time t o one-half  increased with  extreme  values  S i m i l a r r e s u l t s were o b t a i n e d  concentration  Extrapolated  values  decreased  i V l A X  s y s t e m s , a t t h e same c o n c e n t r a t i o n , were 77 and 72  of h a l f - t i m e  MMA.  t  t o 60 rain f o r t h e MMA-TEGDMA  Numerical  respectively.  required  a t 2*5% DVM c o n c e n t r a t i o n  system.  r e a c t i o n stage  Consequently,  for  MMA-EGDMA  t^AX i n c r e a s e s  progressively.  Differences  I n c r o s s l i n k i n g d e n s i t i e s i n t h e s e two  s y s t e m s c a n be d e m o n s t r a t e d by t h e a v e r a g e  segment  molecular  58 weight between two c r o s s l i n k s on the poly(MMA) backbone. F o r example, mixtures of 93:7 MMA-EGDMA and 97:3 MMA-TEGDMA represent  comonomers of i d e n t i c a l c u r i n g times,  h a l f of t h a t needed t o cure MMA.  e q u a l l i n g one-  However, the c r o s s l i n k  frequency i s c o n s i d e r a b l y h i g h e r  i n 93:7 MMA-EGDMA system i n  p r o p o r t i o n t o d i f f e r e n c e s i n DVM- c o n c e n t r a t i o n and r e s p e c t i v e CNj3YM» two  The estimated  average segment molecular  weights between  c r o s s l i n k s , assuming random d i s t r i b u t i o n of DVM i n the  system, i s n e a r l y 10,000 f o r t h e 97:3 MMA-TEGDMA system, but i n the 93:7 MMA-EGDMA  system only. 1,600-3,400 (based on MMA/DVM  mole r a t i o s g i v e n i n Table molecular longer  bridge  higher  l e n g t h of the  segmental m o b i l i t y and  i n the MMA-TEGDMA mixtures due t o the  f l e x i b l e C - 0 - C linkages branching  In a d d i t i o n the  between double bonds, which i s f o u r times  i n TEGDMA, assures  flexibility  3-2).  of the molecular  d i f f u s i o n b a r r i e r and,  (lO). bridge  A d d i t i o n a l s u b s t i t u e n t s or i n c r e a s e s the  consequently, t ^ x »  from lower a c c e l e r a t i n g a b i l i t y  numerous  effective  This i s also  evident  of the t r i f u n c t i o n a l c r o s s l i n k -  i n g agent used by Duran and Meyer (33), as demonstrated i n F i g . 4-4.  Formation of r i n g  s t r u c t u r e s a r i s i n g from i n t e r n a l  c y c l i z a t i o n may a l s o i n f l u e n c e c u r i n g times. EGDMA as an example, f o r m a t i o n i s theoretically possible:  Considering  of the f o l l o w i n g r i n g  structure  59  CH  (CH )C  2  q  CO 0  CO -  CH. 2  -  l  -  CH, 2  0  V CH  (CH )C 0  CO  CO  0  An  additional  results the  -  CH 2  ethylene  membered r i n g s  The  internal  linkage  s i z e by t h r e e  otherwise  formation.  The o v e r a l l  most f a v o u r a b l e  and TEGDMA,  surrounding  diffusion barriers.  constitutes  curing  0  i n t h e DVM m o l e c u l a r  of t h e r i n g  w h i c h would  a loss  participate result  time.  bridge  members.  Thus,  active  size.  of r i n g  bonding  and g e l  i s d e l a y e d GEP  o f 6-membered  rings i s  formation  T h i s would e x p l a i n t h e i n t h e sequence  TEGDMA t o EGDMA, i . e . , 23 t o 41 m i n a t 1 0 % DVM ( F i g . 4-5 and T a b l e s 4-1 and 4 - 3 ) .  sites  In addition, the  of both e f f e c t s  o f GEP f o r DVM s t u d i e d  f o r m a t i o n of such i n t e r n a l  radical  i n crosslinking  Formation  ring  respectively.  of i n t e r m o l e c u l a r  (59,78) and p o s s i b i l i t y  decreases with increasing i n onset  unit  structures,  as a d d i t i o n a l  delay  -  0  f o r DEGDMA, TrEGDMA  ring  increased  CH 2  o f EGDMA e n l a r g e s t o 1 1 - , 14-, and 17-  function  and  -  glycol  i n enlargement  8-membered r i n g  -  2  from  concentration  Once GEP h a s b e e n  l i n k s becomes p r o g r e s s i v e l y  passed, less  60  important links  as t h e  fades.  structure  d i s t i n c t i o n between i n t e r n a l  Consequently, P R C J J i s independent  of DVM  ( F i g , 4-6)  t o t Q g p r e g a r d l e s s of DVM Similar  polymerization  The has  formation  been proposed  predicted proposed  and  t-,,^ i s d i r e c t l y  molecular  bridge  as  time  s y s t e m s has  on  polymer  c o p o l y m e r s may  molecular  i s not ring  products.  provide  the  proportional (Fig, 4-7),  polymerizations  f o r poor c o r r e l a t i o n  internal  the  accelerated  s t r u c t u r e s i n DVM  been v e r i f i e d  However, t h e r e  of  S-TEGDMA comonomer s y s t e m ( 7 0 ) ,  inter-intra  supporting  crosslinked  of r i n g  a reason  alternating  (17,18,40).  of t h e  external  length  actual gelation (38,40,48,91).  polymerization  this  and  c o n c l u s i o n s were drawn f r o m r e s u l t s  radiation  and  between  Subsequently,  propagation  f o r a number  for of  enough d i r e c t  evidence  structures in  studied  Further  necessary  structural  evidence  DVM at  analyses  t o b a c k up  these  of  these  contentions.  The  r e l a t i o n s h i p between P R C j and  concentrations  i s i n d i c a t e d i n F i g . 4-6,  increased with  i n c r e a s i n g amount  mixture Absolute  over  the  c o n c e n t r a t i o n range  PRCJJ_ v a l u e s  at the  from PRCj v a l u e s ,  accelerating  effects  i n the  i n the  studied  as e x p e c t e d  system  a c c e l e r a t i o n by represented  B o t h , P R C j and  (up  to 30%  f r o m two  and  PRCJJ  DVM).  differed separate  studied:  increased v i s c o s i t y  by P R C j ,  DVM  comonomer  same c o n c e n t r a t i o n l e v e l  considerably  i.  of DVM  P R C J J at v a r i o u s  as  61 ii.  a c c e l e r a t i o n b y Ge a s r e p r e s e n t e d  Numerical  values of P R C J J  magnitude h i g h e r t h a n is  those  are at l e a s t  onset  observed  o f G E P r e p o r t e d by B a r t h a l e m y  (4).  t o be i n d e p e n d e n t  o f DVM s t r u c t u r e ,  initial  o f t h e comonomer m i x t u r e s ,  5.3  viscosity  Prediction  and C a l c u l a t i o n  In p r e v i o u s  while  of C u r i n g  This  b e f o r e and  PRCJJ  was f o u n d  PRCj i n c r e a s e d w i t h given i n Table 3-2.  Times  s t u d i e s (67,69) an e m p i r i c a l method was  suggested  for predicting  comonomer  system.  valid  one o r d e r o f  o f P R C j ( T a b l e s 4 - 2 and 4 - 4 ) .  i n a good a g r e e m e n t w i t h r a t e c o n s t a n t s  after  by PRCjr.  curing times  (t^^) f°  r  "the MMA-TEGDMA  The e m p i r i c a l e q u a t i o n / 5 - l / was f o u n d  t o be  f o r TEGDMA c o n c e n t r a t i o n up t o '\Q% i n t h e MMA-TEGDMA  comonomer m i x t u r e . derived  Application  of / 5 - l / t o the present  f o r t h e MMA-DVM s e r i e s ,  of p r e v i o u s data w i t h r e s u l t s  Mathematical  allows integration  of the present  treatment  of data  g i v e s t h e f o l l o w i n g OAC, a s c a l c u l a t e d  .  ^MMA-EGDMA  i a  *  1  "  _  1 1  •  ^MMA-DEGDMA  i i i . l v  *  ~  ^MMA-TrEGDMA = MMA-TEGDMA  K  =  L  -1  X  i n T a b l e s 4 - 1 and 4 - 3 from  • cone 1  linear  '-3  o  5  X  1  ,  8  x  2,4  -1  0  r-  l  1  1  x  0  0  and c o m p a r i s o n  study.  b e t w e e n OAC and DVM c o n c e n t r a t i o n i n F i g . 4 - 8 : mm  data  3  10"  3  relationships  62 Numerical values  o f OAC f o r t h e d i f f e r e n t  systems demonstrate t h a t a c c e l e r a t i n g a b i l i t y DVM m o l e c u l a r OAC  values  estimate  length.  are i n v e r s e l y After  ( C N Q Y ^ K  related  calculation  MMA~DVM  =  5  ,  2 X  i n F i g . 4-9  t o DVM c o n n e c t i o n  o f CN  C N  increases with  , using / 3 - l / ,  number one c a n  equation:  DVM  -  10.55 ....... ./5-2/  CN ,,, i s c o n n e c t i o n  number  linear  g i v e n by /5-2/ i s i l l u s t r a t e d  nw  The  As i l l u s t r a t e d  OAC f r o m t h e f o l l o w i n g  1//K  where:  bridge  MMA-DVM  relationship  o f r e s p e c t i v e DVM.  i n F i g , 4-9.  Relative expressed in  of  : DEGDMA  i s i n good  dimethacrylate  Increase  effective  (EGDMA), i n c r e a s e d a s :  : TrEGDMA  Correlation length  o f t h e DVM s t u d i e d ,  a s OAC r a t i o s w i t h r e s p e c t t o t h e l e a s t  the series  EGDMA  accelerating ability  : TEGDMA = 1.0 : 1.36 : 1.64 :  o f OAC w i t h  agreement w i t h e s t e r s having  i nabsolute values  t h e DVM m o l e c u l a r recent data  bridge  on p o l y m e r i z a t i o n  v a r i a b l e bridge  of p r o p a g a t i o n  distances (8).  constants  (k ) w i t h  P molecular  bridge  l e n g t h i s demonstrated  2.18  i n T a b l e 2-2.  63 From c a l c u l a t e d it  i s possible to predict  exotherm c u r v e s . /5-l/g  from  Table 4 - 5  and  f o r the  MMA-TEGDMA (70)  for  (67,69),  later  i n Table 4 - 6 .  first  of t h e  d e r i v e d f o r the  The  equation  can  of t h e  four  curing  (53)  by  and  r e c e n t l y D u r a n and  monomers ( 5 3 )  of r e s u l t s  trifunctional  Meyer  from  the  The  from  data  values  ( 5 3 ) ; were p l o t t e d  agents.  applied to average  the  error  was  expected  of Eq. / 5 - l /  used  the  agents and  i n wood. authors  study,  results  accelerating  (33)  B o t h MMA  present  (33)  crosslinking  were p o l y m e r i z e d  applicability  Numerical data  The  t o evaluate the  h e a t - c a t a l y s t systems.  to test  times  be  system  systems s t u d i e d  s i m i l a r i t i e s b e t w e e n t h e c o n c l u s i o n s of t h e s e  interest  S-TEGDMA  derived equation to published  of v a r i o u s d i - and  implications  results  a p p l i e d t o the  p o l y m e r i z a t i o n exotherm technique  styrene-type  These  4-r5).  Kenaga  polymerized  calculated  (tjy^)  comonomer s y s t e m s .  c u r i n g times  Application  ability  systems  of maxima on p o l y m e r i z a t i o n  systems s t u d i e d .  of v i n y l - d i v i n y l  5.7% (Table  comonomer  measured e x p e r i m e n t a l l y , a r e g i v e n i n  four  system  predicting  5,3.1  occurrence  u s e f u l n e s s of / 5 - l / ,  as r e c o r d e d  a variety  of i n d i v i d u a l  D i f f e r e n c e s i n c u r i n g times those  demonstrate the  t  OAC  i t was  Due  to  and  the  of  to prediction  of  published. of OAC,  calculated  from  a g a i n s t c o n c e n t r a t i o n of linear  relationships  systems are g i v e n i n F i g . 4 - 1 0 .  The  Kenaga s 1  crosslinking  f o r these  f o l l o w i n g OAC  comonomer  v a l u e s were  64 calculated  f o r these  2.6  x  10~  3,6  x  1 0  TBS-TMPTMA  ii.  K  T B S - T r EGDMA  iii.  K  TBS-EGDMA  4.0  x  10~  K  TBS-TEGDMA  4,8  x  lO"  individual  =  s y s t e m s used  be t h e l i m i t e d  by Kenaga  (53),  di-functional calculated  curing  times  to /5-l/.  calculated  out over t h e  experiments  within  TMPTMA,  those  T h i s suggests  that  reaction.  OAC f r o m d a t a  of Kenaga  for individual Differences  ( 5 3 ) were used t o  comonomer  i n curing  of d i f f e r e n c e s  initiating  system  used.  mixtures  times  and p u b l i s h e d v a l u e s a r e summarized  regardless  5%.  for this  However, OAC f o r a l l t h r e e  agreement was f o u n d b e t w e e n a c t u a l  than t  between OAC o f  a g e n t s were h i g h e r t h a n  for the propagation  according  4  on t h e m o l e c u l a r b r i d g e f u n c t i o n s a s a d i f f u s i o n  Calculated predict  4  carried  (only four  for the t r i - f u n c t i o n a l  substitution barrier  crosslinking  4  The r e a s o n  number o f e x p e r i m e n t s  0-30% c o n c e n t r a t i o n i n t e r v a l ) .  -1  -4  s m a l l d i f f e r e n c e s were f o u n d  r a t h e r wide c o n c e n t r a t i o n r a n g e  Good  cone,  K  Only  the  min"""*" i.  iv.  may  systems:  ( t ^ ^ ) between  i n T a b l e 4-7.  and p r e d i c t e d  values,  i n p o l y m e r i z a t i o n c o n d i t i o n s and The a v e r a g e  error  o f t ^ ^ - was l e s s  65  Only predict  OAC.  mixtures  two e x p e r i m e n t s Expected  curing times  for different  w i t h i n c o n c e n t r a t i o n range covered  experiments "two-point published  by t h e two  method" was t e s t e d b y u s i n g e x p e r i m e n t a l by D u r a n and Meyer  i.  (33),  3  time,  MMA:TMPTMA =  t,,.., = 108.3 min; MAX  comonomer c o m p o s i t i o n , curing  Based  time,  on t h e s e  v  two e x p e r i m e n t s ,  t h e c a l c u l a t e d OAC  nT  c u r i n g times  o f v a r i o u s MMA-TMPTMA  D i f f e r e n c e s between c a l c u l a t e d summarized  i n T a b l e 4-8.  By  integrating  and  t j y ^ = 60.8 m i n .  3  predicting  ) was used  and p u b l i s h e d v a l u e s  Agreement  ability  (33.) a r e  a g a i n , was q u i t e  experimental  results  and c u r i n g t i m e s  for  compositions.  from  already p u b l i s h e d , i t i s demonstrated  acceleration  93:2;  MMA:TMPTMA = 91:9;  (K„,„ ,. ,,, = 1.03 x 10""" m i n " c o n e . " MMA-TMPTMA T  data  The f o l l o w i n g tv/o e x p e r i -  comonomer c o m p o s i t i o n ,  ii.  This  chosen:  curing  with data  comonomer  with t h e a i d of / 5 ~ l A  c a n be c a l c u l a t e d  ments were r a n d o m l y  value  have t o be r u n i n o r d e r t o  good.  this  work  that  for different  comonomer  s y s t e m s , r e g a r d l e s s o f t h e p o l y m e r i z a t i o n c o n d i t i o n s , c a n be estimated  w i t h i n t h e most d e s i r a b l e p r a c t i c a l  r e g i o n by / 5 - l / w i t h comparison DVM  level  of confidence.  o f t h e r e s p e c t i v e OAC v a l u e s  s t u d i e d were more e f f e c t i v e  trifunctional Fig.  a high  TMPTMA.  4-4 and 4-8,  concentration From  i t i s apparent  direct that a l l  a c c e l e r a t o r s than the  T h i s i.s g r a p h i c a l l y  illustrated i n  66  A further agents i s that process.  (33) w h i c h  a v o i d e d by  source  radiation  be  l o w e r i n g OCR  that  dose  OCR  more g r a d u a l l y  agents i s t h e i r  )  i n j u r i o u s t o WPC.  Data  c e a s e due  and  at  55  and 49.4  network.  In a d d i t i o n , polymer  min,  r a t e s the  temperature lower.  crosslinking barriers.  i s readily  F o r example, "tjvsAX  i s essentially  t h e same  C o n v e r s i o n degree  at these  however, d e c r e a s e d f r o m 8 5 . 6 % t o 82.3%  trifunctional  crosslinking  agents form  p r o d u c t s w i t h lower a b r a s i o n r e s i s t a n c e  was  reported  f o r WPC  5.4  Analysis  of C r o s s l i n k e d  of  o f monomer d i f f u s i o n i n  T h i s problem  respectively.  energy  and F i g . 4-11  i s considerably  20% TMPTiMA i n t h e s y s t e m  concentrations,  as t h e  square r o o t  to lack  to  could  w i t h the  d e m o n s t r a t e d w i t h t h e MvlA-TMPTMA s y s t e m . 15  i s used  h i g h tendency t o develop d i f f u s i o n  crosslinked  at  polymerization  This  i n T a b l e 4-9  linearly  T^^  crosslinking  increased very rapidly  At lower dose and  the  d i s a d v a n t a g e of t r i f u n c t i o n a l  P o l y m e r i z a t i o n may highly  A X  i f radiation  varies  rate.  Another  the  may  (T^  for polymerization.  demonstrate  rises  t h e y e v o l v e more h e a t d u r i n g  Peak t e m p e r a t u r e  180-190 °C be  disadvantage of t r i f u n c t i o n a l  (33).  brittle  (63).  This  by Kenaga ( 5 3 ) .  Polymer  Product  Thermomechanical  Curves  Thermomechanical p r o d u c t s depend  primarily  properties  of c r o s s l i n k e d  upon t h e t i g h t n e s s  of t h e  polymer network  67 structure,  i . e . , crosslinking  concentration functioned  of c r o s s l i n k i n g  as e f f i c i e n t  and t h e r m o p l a s t i c  linked  products.  demonstrated  It  different  values, CN  here  a g e n t s and t r a n s f o r m e d  and p a r t l y  or p a r t l y  cross-  crosslinked  thermomechanical  but v a r i e d  <^  polymer  c u r v e s as  DVM  studied  with molecular bridge  length.  of i n d i v i d u a l  t o t h e sequence:  TrEGDMA  i s demonstrated  copolymer  fully  efficiency  according  TEGDMA This  A l l DVM s t u d i e d  i n F i g . 3-2.  not i d e n t i c a l increased  agent.  poly(MMA) t o f u l l y  Linear,  Crosslinking was  c a u s e d by a g i v e n  crosslinking  linear  products exhibit  density  by shape  p r o d u c t s formed  <f  DEGDMA  <^  EGDMA  of thermomechanical  curves for  f r o m t h e two DVM h a v i n g extreme CN  i . e . , EGDMA w i t h CN 2.200 ( F i g . 4-12) and TEGDMA.with  2.105 ( F i g . 4 - 1 3 ) . Comparison  additions  of e i t h e r  o f F i g . 4-12 and 4-13 shows t h a t DVM t o MMA  poly(MMA) t o a c r o s s l i n k e d network  strength  efficiency  rapidly  thermoset  changed  plastic  at higher temperatures,  o f EGDMA was, however,  Differences  DVM c a n be d e m o n s t r a t e d mechanical parameters  by c o m p a r i s o n  the linear  with  increased  Transformation  significantly  i n crosslinking  small  efficiency  higher.  f o r t h e s e two  of r e s p e c t i v e  a s o b t a i n e d a t t h e same DVM  thermo-  concentration  68 level,  as  shown i n T a b l e  system, f o r example, The  T  , TDD  °C„  To  o b t a i n the  concentration 4-10  and  has  F i g . 4-12  systems  studied,  increased  i.  Tg mobility  Table  DVM  4-10,  i s an  of v a n  assess  the  T ,  TDT  Q  .  der  As  202  °C.  TDT  TEGDMA, i t s 30%  (Table  t o the  f o r the overall  four observation  thermomechanical  TDD,  and  parameter which i s r e l a t e d t o segments  At  c o p o l y m e r CN)  (72,73).  As  expected,  m o b i l i t y cf polymer  the  the  s e g m e n t a l m o b i l i t y and  Stabilization  effects  and  molecular  i t i s possible  bridge  length  o f Tg  as:  to  four  same c r o s s l i n k i n g d e n s i t y  s h o r t e r DVM  higher  T  at higher  i n t e r p r e t e d by  as r e l a t e d t o T_  i n F i g . 4-14,  chains  segments •  c r o s s l i n k e d network i n the  studied.  be  with  to approximately  and  c o n t r i b u t i o n o f DVM  can  ° C , . T D D 52%  influenced  illustrated  systems  ( F i g . 4-14)  and  MMA-TEGDMA  W a a l ' s f o r c e s between p o l y m e r  MMA-DVM  lower  77%  LTDC.  important  m o b i l i t y of t h e  by  113  MMA-EGDMA  ways:  overall  expressed  T^  leads  c a r b o n - c a r b o n bonds r e d u c e d T  °C,  TEGDMA i n t h e  concentration  • decreased  increased  were 127  of t h e r m o m e c h a n i c a l d a t a  of m a c r o m o l e c u l a r  replacement  to  lower;  EGDMA i n t h e  4-13).  increased  ii.  and  TDT  increased  and  p a r a m e t e r s i n two  by  and  10%  same p a r a m e t e r v a l u e s  t o be  Analysis  that  At  same p a r a m e t e r s f o r 10%  s y s t e m were c o n s i d e r a b l y 165  4-10,  bridge  length  (as  gave  ( F i q . 4-14).  crosslinking densities  overlapping  of two  independent  69  i.  crosslinking  ii.  The  effect,  copolymerization  and  effect.  crosslinking  effect  a l w a y s i n c r e a s e s T^,whereas t h e  copolymerization  effect  decreases  additive CN  C 0  ,  (61).  The c r o s s l i n k i n g  At higher  crosslinking effect.  DVM  effect  temperature  Both e f f e c t s are  effect  prevails  at lower  c o n c e n t r a t i o n t h e c o n t r i b u t i o n of t h e i s balanced  The o v e r a l l  Resistance  T .  result  by t h e c o p o l y m e r i z a t i o n  is T  of i n d i v i d u a l  deformation  (rig.  stabilization  polymer p r o d u c t s  c a n be e x p r e s s e d  by TDD,  4-14).  t o high  while  strength  o f t h e c r o s s l i n k e d n e t w o r k i s p r o p o r t i o n a l t o TDT  values.  As d e m o n s t r a t e d  (Fig,  4-15),  copolymer the  both  parameters  connection  molecular  number  bridge  interval.  crosslinking This  rapidly  Further  densities  i s an i m p o r t a n t  c o i n c i d e s with both properties (compare  studied  (TDD and TDT) a r e dependent..on (  C  N  C  0  K  r e g a r d l e s s of t h e s i z e of agent  used.  w i t h i n t h e n a r r o w DVM  a d d i t i o n o f DVM changed  t o induce  TDD and TDT o n l y  optimal  of polymer  products  a t low DVM  higher moderately.  concentrations  and 4 - 1 0 ) .  The  thermomechanical deformation  transition  concentra-  a c c e l e r a t i o n and t h e r m o m e c h a n i c a l  Tables 4-3  linear  Both  o b s e r v a t i o n and s u g g e s t i v e l y t h e e f f e c t  (LTDC) c h a r a c t e r i z e s b e h a v i o u r the  stystems  of the c r o s s l i n k i n g  parameters Increased tion  f o r the four  region.  of heated  polymer  LTDC r e p r e s e n t s t h e r a t e  coefficient products  within  of polymer  70  deformation rubbery in  associated  state.  until  equalling  i sconstant  t h e polymer  across a broad  temperature  l o s e s coherence a t temperatures  i s t o t h e advantage  of t h e p r e s e n t  w i t h DVM c o n c e n t r a t i o n  the  semi-logarithmic  advantage  T h i s i s demonstrated  i n F i g . 4-16,  by copolymer  exponentially  (MMA-EGDMA and MMA-TEGDMA)  b e t w e e n LTDC and p o l y m e r  as r e p r e s e n t e d used t o g r e a t  plot  polymer  LTDC d e c r e a s e d  i n t h e system.  t h e two s y s t e m e x t r e m e s  relationship  of c r o s s l i n k e d  study t h a t  for  behaviour  polymer p r o d u c t s  TDT ( F i g . 3-2, 4-12 and 4 - 1 3 ) .  It products  from p l a s t i c t o  D e f o r m a t i o n of c r o s s l i n k e d  the rubbery region  interval  with the t r a n s i t i o n  connection  i n predicting  o f complex c r o s s l i n k e d  using  Further, the  crosslinking number  density  ( C N ) c a n be C 0  thermomechanical  polymer  products derived  f r o m comonomer m i x t u r e s .  5.5  Analysis  of Polymer  Compression  Product Compression  stress-strain  Stress-Strain  Curves  c u r v e s were f o u n d t o  follow patterns represented  by c u r v e s i l l u s t r a t e d  i n F i g . 3-3.  These  i n properties ranging  from  show a w i d e v a r i a t i o n  elastic,  semi-rigid,  hard, tough t o b r i t t l e  materials  In g e n e r a l ,  soft  ( F i g . 3-3a) e x h i b i t  and weak p o l y m e r s  low modulus o f e l a s t i c i t y  ( E ) , low y i e l d  deformation at rupture.  Hard  h i g h E , no w e l l - d e f i n e d  yield  rupture  ( F i g . 3-3b).  Soft  and b r i t t l e point  point  (20,72).  and m o d e r a t e  materials  show  and l o w d e f o r m a t i o n a t  and t o u g h p l a s t i c s  ( F i g . 3 - 3 c ) show  71  low  E and y i e l d  point but high  Hard  and s t r o n g  high  E and y i e l d  hard  and t o u g h m a t e r i a l s  deformation  plastics  deformation  ( F i g . 3-3d),  point but only  and r u p t u r e  Typical  and r u p t u r e  on t h e o t h e r  ( F i g . 3-3e) show E, y i e l d  compression  are reproduced  and MMA-TEGDMA),  hard  t o those  and m o d e r a t e l y t o u g h  homopolyrners o f p u r e EGDMA exhibited polymers  behaviour  of p o l y ( S )  Highly  compression  stress-strain  of h a r d  w i t h i n t h e most a t t r a c t i v e  interest  curves  of MMA-DVM comonomer m i x t u r e s .  ( F i g . 4-19)  t o study  as o b t a i n e d  f o r t h e wide  E x p e r i m e n t s were  concentration  shapes of  interval,  range  concentrated i . e . , up t o  A s shown i n  4-1 and 4-3 and F i g . 4-4, t h i s r e g i o n was o f p a r t i c u l a r  interest  because  of s i g n i f i c a n t l y  within  this  volume  concentration  concentration  As EGDMA  crosslinked  and b r i t t l e  DVM i n t h e r e s p e c t i v e c.omonomer s y s t e m s .  Tables  i . e . , i t was  ( F i g . 3-3b).  I t was o f p a r t i c u l a r  10%  stress-strain  ( F i g . 4-18) and TEGDMA  characteristic  range  i n F i g . 4-18 and  (20,70);  ( F i g . 3-3d).  f o r t h e two  concentration  poly(MMA) e x h i b i t e d c o m p r e s s i o n  similar  point,  s t r e s s - s t r a i n curves  (MMA-EGDMA  properties  Finally,  s t r e s s a l l t o be h i g h .  over t h e f u l l  Linear  hand, e x h i b i t  moderate d e f o r m a t i o n *  e x t r e m e DVM s y s t e m s s t u d i e d  4-19.  stress.  interval  curing.  OCR  was p r o p o r t i o n a l t o DVM  (Fig. 4-8).  demonstrated  o r TEGDMA t o MMA  compression  accelerated  i n F i g . 4-18 and 4-19, a d d i t i o n o f  caused  stress-strain  change i n shape  curves  according  of polymer  t o amount  o f DVM  added.  72 They changed f r o m and  tough-types  response  hard  and b r i t t l e - t y p e s  ( F i g . 3-3e).  indicate  improvement  ( F i g . 3-3b) t o h a r d  These changes i n s t r e s s - s t r a i n i n mechanical  p r o p e r t i e s as  follows: i.  rupture  stress,  plastic  under t h e s t r e s s - s t r a i n increased MMA.  ii.  from  MMA  data  change i n s l o p e o f t h e i n i t i a l occurred.  of i n d i v i d u a l  compression  points at  c o n c e n t r a t i o n , and  no s i g n i f i c a n t  MMA-DVM s y s t e m s  much  addition to  of w e l l - d e f i n e d y i e l d  Hookean p o r t i o n  derived  stress-strain  s t u d i e d a r e summarized  mechanical curves  parameters,  f o r the four  i n T a b l e s 4-11 and  4-12.  Graphical interpretation  strain  a t r u p t u r e and a r e a u n d e r t h e s t r e s s - s t r a i n  a function studied,  By and  of compression  o f comonomer c o m p o s i t i o n  are given  s t r e s s and  f o r the four  c u r v e , as  systems  i n F i g . 4-20 t h r o u g h 4-23.  comparison  4-12 t h e f o l l o w i n g  i.  and a r e a  f,  higher  Numerical  c u r v e were  w i t h 2.5 t o 10% DVM  development  iii.  deformation  of the r e s u l t s  compiled  i n T a b l e s 4-11  o b s e r v a t i o n s c a n be made:  compression  s t r e s s - s t r a i n p r o p e r t i e s of  poly(MMA) w i t h r e s p e c t t o r u p t u r e , y i e l d and toughness of ii.  parameters  were h i g h e r t h a n  those  any DVM homopolymers s t u d i e d ;  p r o p e r t i e s of products  from  comonomer  mixtures  are  not a d d i t i v e  not  contribute  their iiia  strength  under  s t r e s s and s t r a i n ,  maxima  exhibited  strength  well-defined  p r o p e r t i e s f o r t h e system*  s t u d i e d were r e s t r i c t e d concentration  v.  for all  ( F i g . 4-20 t h r o u g h 4 - 2 3 ) ;  superior  in  as w e l l as  s t r e s s - s t r a i n curves,  systems s t u d i e d ,  iv.  i n proportion t o  presence;  compression area  i . e . , t h e components do  s  region,  t o t h e narrow .  within  5 t o 1 0 % DVM  t h e s y s t e m ; and  the concentration strength  interval  showing  p r o p e r t i e s broadened w i t h  DVM m o l e c u l a r  bridge  length,  superior increasing  i . e . , i n the  s e q u e n c e f r o m EGDMA t o TEGDMA.  Individual details.  Consider,  MMA-DVM  EGDMA the be  curves  system ( F i g . 4-20).  estimated  3-2),  that  units  They 'MMA-  system  n e a r 1 0 % TEGDMA c o n c e n t r a t i o n .  I t can.  MMA/DVM mole r a t i o s , i . e . ,  and 24,4 f o r t h e MMA-TEGDMA.system  copolymers with  possess approximately  i n the  However, i n t h e MMA-TEGDMA  from the r e s p e c t i v e  f o r t h e MMA-EGDMA  (Table  i n specific  ( F i g . 4-20 t h r o u g h 4 - 2 3 ) .  a t a p p r o x i m a t e l y 5% EGDMA c o n c e n t r a t i o n  maxima were l o c a t e d  34.3  only  a s an e x a m p l e , l o c a t i o n of t h e maxima on  properties/composition appeared  systems d i f f e r e d  superior  strength  properties  one c r o s s l i n k f o r e v e r y 25 t o 35 monomer  on t h e poly(MMA) b a c k b o n e .  Considering  t h e MW  o f MMA t o  74 be  e q u a l t o 100, a number a v e r a g e  molecular weight  t o 3,500 i s o b t a i n e d f o r poly(MMA) successive with  junctions.  These  averages d e r i v e d  copolymers  o f 2,500  segments b e t w e e n two  v a l u e s a r e i n v e r y good  f o r crosslinked  ( 7 3 ) , as c a l c u l a t e d  from  agreement  r u b b e r s and t h e r m o s e t  swelling  equilibria  measurements.  From t h e l i m i t e d crosslinks, studied,  c a n be r e l a t e d  Fig. CN  C 0  suggested that  used.  Compression  irrespective  tells  Physical are  density  i s a useful  networks,  i t does  length  systems parameters ).  CM  C 0  of  included i n  as demonstrated i n  i s strongly  related to  of c r o s s l i n k i n g  of polymer  structural  MvV between  networks  agent  as  parameter.  Although  aspects of the  quantitatively  characterize  t o b o t h m e c h a n i c a l and t h e r m o m e c h a n i c a l d e f o r m a t i o n s .  and t h e r m o m e c h a n i c a l  assumed t o be f u n c t i o n s  described  studied,  of t h e b r i d g e  (CN  from /3-2/,are  n o t h i n g about t h e c o n f i g u r a t i o n a l  crosslinked resistance  strength  stress at rupture,  systems  The c r o s s l i n k i n g  e x p r e s s e d by CN CN  compression  as c a l c u l a t e d  4-24 f o r a l l f o u r ,  comonomer  t o comonomer c o n n e c t i o n number  copolymers,  T a b l e 4-11.  i n segmental  e s t i m a t e d f o r t h e two extreme  i t was  individual  differences  properties  of polymer  of c r o s s l i n k i n g  density  products as  by CM co Observation  o f maxima a t l o w D V M ' c o n c e n t r a t i o n s  ( F i g . 4-20 t h r o u g h 4-23) d e m o n s t r a t e s that  strength properties  of s o l i d  an i m p o r t a n t  crosslinked  discovery;  polymer  products  vary with  concentration  manner as  strength  elstomers  (28,29,32,35,3?,63,94,102).  applications, is  the  of c r o s s l i n k i n g  a n a r r o w DVM  most a t t r a c t i v e .  For  concentration  Within  this  compression capable also  range a l s o r a p i d l y  of c o n s i d e r a b l e  that failure  t r e m e n d o u s sound  In toughness, still in  spite  of t h e  standardized  plastic  plastic  From t h e  deformation  compression the  four  linear  comonomer  storage  resulting before  similar system  t o r e l e a s e of t h e  and  considerable and  i s indicative  curve  and  under  energy  independent  are was  with  stored.  of  small  4 - 1 9 ) , i t was  the  It  polymer  are stresses  deformation  in  assumed  of t o u g h n e s s .  plastic  with  copolymers  importance  observation that  c o n c l u s i o n was  (70).  area  copolymers occurred  s y s t e m s s t u d i e d i n F i g . 4-25.  A  thermo-  failure.  r e l a t i o n s h i p between t h e  stress-strain  c o p o l y m e r s seems t o be length.  The  ( F i g . 4-18  both  I n t r o d u c t i o n of DVM  significance  range produced  d e m o n s t r a t e d by  (up t o . 10%)  procedures f o r i t s evaluation  tough polymer p r o d u c t s that  interval  increased the  of t h e s e  e f f e c t s due  l a c k i n g (72).  the  energy  and  practical  s u p e r i o r m e c h a n i c a l and  s t r e s s - s t r a i n curve.  observed  same  c o n c e n t r a t i o n range  m e c h a n i c a l p r o p e r t i e s were o b t a i n e d . within this  i n the  p r o p e r t i e s of c r o s s l i n k e d r u b b e r s  maximum a c c e l e r a t i o n and  MMA  agent  This i s  area, u n d e r  deformation  T o u g h n e s s of  the  for'  these  of DVM  molecular  bridge  reported  f o r the  S-TEGDMA  76  6.0 CONCLUSIONS  lo  Acceleration  vinyl-divinyl linked  length.  agents,  i n particular to their  The o v e r a l l c u r i n g  proportional  rate  t o volume c o n c e n t r a t i o n  DVM c o n n e c t i o n  number  1/K  increases EGDMA  =  of t h e  molecular  bridge  of d i v i n y l  t o be monomer  (DVM).  (K) i s i n v e r s e l y r e l a t e d t o  (CNgy^) a s :  5,2 x C N  The r e l a t i v e  -  D V M  : TrEGDMA  10,55  acceleration ability  w i t h DVM m o l e c u l a r b r i d g e  : DEGDMA  structure  (OCR) was f o u n d  o v e r a l l a c c e l e r a t i o n constant  2.  of  comonomer s y s t e m s v i a . g e l - e f f e c t (Ge) i n c r o s s -  n e t w o r k s was r e l a t e d t o t h e c h e m i c a l  crosslinking  The  i n radiation polymerization  : TEGDMA  concentration  values  length =  o f DVM  studied  i n the order:  1.00: 1 3 6 : 1,64 : 0  The  half-time  f o r EGDMA, DEGDMA,  and  TEGDMA were a p p r o x i m a t e l y 7, 5, 4, and 3%  2.18.  TrEGDMA  (vol/vol),  respectively.  3. obtained mixtures. and  Substantial  with  decrease  time  up t o 10% DVM i n t h e r e s p e c t i v e  Within  this  concentration  thermomechanical p r o p e r t i e s 4.  i n curing  Tfie e m p i r i c a l  interval  ( t ^ ^ ) was  comonomer superior  o f c o p o l y m e r s were a l s o  mechanical observed.  equation f o r c a l c u l a t i n g the o v e r a l l  77  acceleration derived  and  extension to catalyst  constant applied  and  t o the  published  s y s t e m s was  for  systems  and  the  6. the  most  a well  Its  i n heat-  applicable.  r e s u l t s was  was  Agreement  withini5/o  error  number  (CN  ) was  s t r u c t u r a l parameter f o r and  correlates  introduced crosslinked  quantitatively  thermomechanical p r o p e r t i e s  with  copolymer  densities.  The  MMA-TEGDMA  s u i t a b l e and  balanced  p a r a m e t e r s and composite  and  times  observed.  It characterizes  mechanical  crosslinking  a useful  curing  acceleration fully  Copolymer c o n n e c t i o n  f o u n d t o be  copolymers.  on  published  of  systems s t u d i e d .  f o u n d t o be  and  b.  four  results  between p r e d i c t e d a l l copolymer  prediction  comonomer s y s t e m was  economically a t t r a c t i v e .  compromise  of  improved  copolymer p r o p e r t i e s ,  products.  found to It  be  represents  polymerization  suitable  for  wood-polymer  78  7.0 RECOMMENDATIONS FOR FURTHER STUDY  Based results  on t h e o r e t i c a l  of t h e p r e s e n t  deserving  of f u r t h e r  i.  c o n s i d e r a t i o n s and e x p e r i m e n t a l  study the f o l l o w i n g  a r e recommended a s  research:  extend  a c c e l e r a t e d p o l y m e r i z a t i o n t o t h e MMA-  methyl  acrylate  system  t o examine  i n f l u e n c e of  - C H 3 g r o u p s on Ge a c c e l e r a t i o n ; ii.  extend  the present  MMA-DVM  systems t o h i g h e r  h o m o l o g o u s members  (hexa-,  deca-, e t c . ,  polyethylene effects  o f Ge o n s e t  controlled iii.  examine  d i m e t h a c r y l a t e ) t o examine and d e l a y e d  o f polymer  f o r possible  ring  formation;  move f r o m b u l k c o p o l y m e r i z a t i o n t o a c c e l e r a t e d  study the e f f e c t MMA-DVM in  system,  the presence  resistance vi.  products t o c o l l e c t  internal  p o l y m e r i z a t i o n w i t h i n wood v.  diffusion-  propagation;  structure  evidence iv.  glycol  further  of a t h i r d  component  i n the  f o r example t o i n c r e a s e OCR o f oxygen a n d / o r t o i m p a r t  fire  properties (68);  extend  utilization  as p r e s e n t l y proposed of veneer  structures;  polymer  of exothermic  f o r one-step  overlaid  plywoods  heat  production (52,81).  79  8.0 LITERATURE C I T E D  1.  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E f f e c t o f c o n v e r s i o n l e v e l on p o l y m e r i z a t i o n c h a r a c t e r i s t i c s of methyl m e t h a c r y l a t e (MMA) at  Conversion, /o  •  22.50C  (43).  FL P' l  /O/ %/hz  k  k  p  x 10~  t  5  (k /k p  0  3.5  384  442  5.78  10  2.7  234  273  4.58  20  6.0  267  72.6  8.81  30  15.4  303  14.2  25*60  40  23.4  368  8.93  33.90  50  24.5  258  4.03  40o60  60  20.0  74  0.498  33.20  70  13.1  16  0.0564  21.30  80  2.8  1  0.0076  3.95  I t  ^ )xl0 2  2  Table  N  2-2.  Some d a t a on p o l y m e r i z a t i o n of d i m e t h a c r y l a t i c ( p h o t o i n i t i a t o r - b e n z o i n 0*2%) (.8).  The compound  M.  Symbol  I 2  Methylmcthacrylale MMA Dimctlmcryiaic of butyk'iicKlycoi 3 Dinielhaciyiate of biaylciicsjlyci.il MU 4 Dinictliitcrylalc of butylcneglycol MB 5 Diriicthacrylafehe.xamcihylciu'ijlycol MO r> Diiv.eiliacrylatelicxanicihylcncglycol MG 7 Dimelliacrylalehexamclliylcncylycol MG 8 Diir.ctlucrylatedeeamciliylcncglycol MD 9 Dimethacrylalcdocainclhylciicglycol M D 10. Dimcthacrylatcdccamcthylcncglycol M D 11 D i m c 111 a c r y 1 a 1 c (bisdicthylencglycol) plithalolc MGPh 12 Dimethacrylate (bisdiclliylcncylycol) plithalolc) MGI'h 13 DiiiK-lbaciylatc (/;;> diclhylcncglycol) plithalote MGPh Notes:  100  Viscosity c.p.  50  esters  W _ 10 M (sec- )  The degree of transformation (%)  The temperature of polymerization  50  25  0-2  _  5  K,  1. mole" ' s e c  - 1  1. mole"' sec  1  226  40  0  25 '  3-8  600  8.10  226  —  30  25  40  112  2-3.10  226  —  5  25  33-0  17  83.10*  244  4-9  0  25  13-0  1200  6-2.10  5  244  —'  5  25  7-0  245  3-7.10  4  244  —  30  25  4-0  26  1 -3.10  J  300  7-7  0  25  160  1880  • 4-2.10  s  300  —  5  25  24-0  1400  300  —  30  25  29-0  S40  2-5.10  4  566  51-0  0  30-6  20-0  2470  4-8.10  5  566  —  5  30-6  24-0  2300  2-7.10  5  566  —  30  30-6  54-0  1750  3-2.10*  .  (I) l o r M M A at a 0 per cent K 300 I. m o l e " ' sec" (T 25°). (2) The kinetics of polymerization of MB, M G , M D , M G F were studied by methods of precision dilatomctry and thermometry. 1  n  s  4  1 -5.10  CO vO  s  90 Table  3-1.  Some p r o p e r t i e s o f m e t h y l m e t h a c r y l a t e (MM) and d i v i n y l monomers (DVM) used I n t h i s s t u d y *  Name, ( a b r „ )  n  Mw  formula  Methyl (MMAJ C H 0 5 9 2  —  100  0.940  2.000  1,0  (EGDMA)  1  198  1,045  2.200  4,2  2  242  1.062  2,150  6.9  3  286  1,090  2.125  10.5  4  330  1.140  2.105  23.4  10 14°4 H  Diethylene  glycol  dimethacrylate, 12 18°  (DEGDMA)  H  5  Trmethylene  glycol  dimethacrylate,(TrEGDMA) 14 22°6 H  Tetraethylene  glycol  dimethacrylate, C  25°C  glycol  dimethacrylate,  C  grel  methacrylate,  Ethylene  C  CM  g/cm  s  C  d,  16 26°7 H  (TEGDMA)  91  Table  3-2.  C o n c e n t r a t i o n s and r e l a t i v e v i s c o s i t i e s o f d i f f e r e n t m e t h y l m e t h a c r y l a t e ( M M A ) - d i v i n y l monomer (DVM) mixtures.  DVM f r a c t i o n i n DVM  EGDMA  DEGDMA  T r EGDMA  TEGDMA  Mole  r a t i os  comonomer m i x t u r e  DVM/MMAxlO  MMA/DVM  25° C  volume  mole  0.025  0.013  0.14  70.5  1.04  0.050  0.028  1.08,  0.059  0.29 0.63  34.3  0,100  15.9  1,14  0.150  0.087  1.00  10.0  1.24  0.200  0.123  1.40  7,1  1.33  0,300  0.194  2.40  4.2  .1.41  0.025  0.012  0.13  83.5  1,05  0,050  0.024  0,25  40,5  1.11  0.100 0.150  0.049 0.077  0.52 0.83  19.2 12,0  1,18 1,27  ,0.200  0.104  1,16  8.6  1,34  0.300  0.167  2.00  5.0  1.55  0.025  0.011  0.12  85.4  1.08  0.050  0.020  0.21  47.0  1.20  0.100  0.043  0.45  22.2  1.28  0.150  0.065  0,69  14.4  1,42  0.200  0.092  1.01  9.9  1 o 53  0.300  0.144  1,69  5.9  1.83  0.025  0.009  0.09  102.0  1.14  0.050  0.019  0.19  57.8  1,29  0.100  0.039  0.41  24.4  1.48  0.800  0.138  1.88  5.3  ' 2.54  92  Table 4-1.  P o l y m e r i z a t i o n exotherm c h a r a c t e r i s t i c s f o r t h e MMA-TEGDMA comonomer s y s t e m (67,69).  Comonomer composition, vol. %  MMA  100  Gel-Effect Point (GEP)  TEGDMA  0  ^GEP,  T  GEP,  MAX  H'AX,  T  MAX,  min  °C  min  °C  106  62  117  120  97.5  2.5  52  69  60  159  95  5  30  60  45  160  90  10  23  57  31  167  70  30  14  54  20  165  50  50  10  53  15  157  30  70  13  57  18  149  0  100  16  61  22  130  93  4-2.  Table  C a l c u l a t e d polymerization parameters f o r t h e MMA-TEGDMA comonomer s y s t e m ( 6 7 , 6 9 ) .  Comonomer  Exotherm  peak  Polymerization PRC Rate V C o e f f i c i e n t (PRC)., T T  X  Composition,  v  parameters  ol %  MMA  °C/min  TEGDMA  Dose, Mrad  £T,  °c  P  R  C  I  PRC  X I  0  1.50  84  0.24  5.2  95,5  2.5  0.81  123  0.64  5.0  95  5  0.61  124  0.80  6.7  8.4  90  10  0.42  131  0.91  13.8  15.2  70  30  0.27  129  1.28  18.3  14.3  50  50  0.20  121  lo64  20.0  12.7  30  70  0.24  111  1.60  16.7  9.8  0  100  0.30  94  1.56  11.5  7.3  100  21.6 '  7.9  94 T a b l e 4-3.  DVM  P o l y m e r i z a t i o n exotherm c h a r a c t e r i s t i c s f o r MMA-EGDMA, -MMA-DEGDMA and MMA-TrEGDMA comonomer s y s t e m s .  Comonomer composition, vol %  MMA  97.5  EGDMA  DEGDMA  TrEGDMA  DVM  Gel-Effect Point (GEP)  t  „ GEP, min  T GEP, OC  MAX  t  MAX, min  T  MAX, °C  2.5  69  68  83  149  95  5  55  156  10  41  62 57  66  90  50  171  85  15  34  57  41  174  80  20  30  56  37  176  70  30  25  59  31 .  176  0  100  21  52  37  114  97.5  2.5  64  66  77  95  5  50  64  61  156 164  90  10  28  59  39  176  85  15  25  58  33  178  80  20  23  56  176  70  3D  21  60  29 27  179  0  100  18  56  30  • 128  97.5  2.5  59  68  72  154  95  5  44  64  54  160  90  10  27  57  36  174  85  15  22  56  29  174  30  20  20  56  27  134  70  30  18  56  24  175  0  100  18  57  28  127  95 Table 4 - 4 . C a l c u l a t e d p o l y m e r i z a t i o n parameters f o r MMA-EGDMA, MMA-DEGDMA a n d MMA-TrEGDMA comonomer s y s t e m s .  DVM  Comonomer composition, vol %  MMA  EGDMA  TrEGDMA  peak P o l y m e r i z a t i o n PRC Rate parameters Coeff Icient(PRC), p R  0 C / r rn m  Dose, Mrad  AT, °C  PRCj  PRC  / C  II  97.5  2.5  0.91  113  0,46  5.8  1o 9  95  5  0.73  120  0.47  8,5  18,1  90  10  85  15  0.55 0.45  .135 138  0.51 0.62  12.6 16.7  24.8 26,9  80  20  0,39  140  0o66  17.1  25.8  70  30  0.34  140  0.92  19.5  2JL 2  0  100  0.39  78  0.76  3.9  5.1  0.85  120  0,53'  6.9  13.0  0,56 0.80  9.1 11.7  16.2 14.7  97.5  DEGDMA  DVM  Exotherm  2.5  Q  95 90  5 10  0,67 0,43  128 140  85  15  0.36  142  0,88  17,2  X9< > !D  80 •  20  0,32  140  0,90  15,0  16.6  70  30  0.30  143  1.10  19.8  18.0  0  100  0.33  92  1.11  6,0  5.4  6.6  12.2 J. 3«5 16.9  97.5 95 90  2.5 5 10  0.79 0.59  118 124  0.54 0.64  0,39  133  0.77  9.6 13.0  85 80  15 20  0.32 0.30  138 146  0,91 1,00  16.9 18.0  18*5 18.0  30 100  0,26 0.3.1  139 91  1.20 1.16  19,0 7,0  15.8 6.0  70.. 0  96  T a b l e 4-5.  DVM  D i f f e r e n c e s between measured and c a l c u l a t e d c u r i n g t i m e s f o r l o w e r c o n c e n t r a t i o n s of d i v i n y l monomer (DVM) i n MMA-DVM s y s t e m s *  Comonomer composition, 0/ vol  MMA  ,97.5 EGDMA  95  DVM'  DEGDMA  TrEGDMA  TEGDMA  Difference  mm  0/  calculated  measured  2.5  88  83  +5  +6.0  5  70  66  +4  + 6.1  49  50  -I  -2.0  38  41  -3  -7.3  90 85  t MAX,  15  min  97.5  2,5  81  77  +4  +4.9  95  5  62  61  +1  + 1,6  90  10  42  39  +3  +7.1  85  15  31  33  -2  -6,5  97.5  2.5  76  72  +4  + 5.5  95  5  56  54  +2  +3.7  90  10  37  36  +1  + 2,8  85  15  27  29  -2  -6.9  97.5  2.5  68  60  +8  • 13 o 5  95  5  48  45  +3  +6,7  90  10  30  31  -1  -3.3  time  f o r the four  'An a v e r a g e e r r o r f o r p r e d i c t i n g c u r i n g systems s t u d i e d .  97  T a b l e 4-6,  D i f f e r e n c e s between measured and c a l c u l a t e d c u r i n g times f o r lower c o n c e n t r a t i o n s of TEGDMA i n t h e s t y r e n e (S)-TEGDMA s y s t e m ( 7 0 ) ,  Comonomer composition, vol %  S  TEGDMA  Difference min  calculated  measured  min  %  95  5  887  822  ,+ 55  +6.5  90  10  445  462  -17  -3.8  80  20  222  228  -6  -2.6  80  20  222  222  0  0.0  70  30  148  135  +13  +9.6  60  40  110  97  + 13  +13.2  50  50  69  87  -18  -20.6  98 T a b l e 4-7,  D i f f e r e n c e s i n c a l c u l a t e d and p u b l i s h e d curing t i m e s f o r TBS - d i - and t r i - v i n y l comonomer systems ( 5 3 ) .  Crosslinking• monomer  type  0/  '°  TEGDMA •  TMPTMA  .Difference  measured  calculated  min  /°  52  53  +1  +1.9  10  46  48  +2  +4.3  20  40  40  0  30  34  35  +1  36  36  0  0  10  34  34  0  0  20  30  30  0  0  30  27  27  0  0  5  40  41  +1 .  +2.5  10  35  37  +2  + 5.7  20  34  32  -2  -5,9  30  27  28  +1  + 3.7  5  50  49  -1  -2.1  10  48  46  -2  -4.2  20  40  42  +2  +5,0  30  37  37  0  5 TrEGDMA  t  min  5 EGDMA  • MAX,•  0 +3,1  0  99 T a b l e 4-8.  D i f f e r e n c e s i n c a l c u l a t e d and published.curing t i m e s f o r h e a t - c a t a l y s t c u r e d MMA - t r i r n e t h y l o l ' propane-trimethacrylate (TMPTMA) p o l y m e r i z a t i o n system (33).  t  /o  Differences  MAX, min  TMPTMA,  calculated  •mea s u r e d  • min  ,°/ yo  1  123,0  123.4  -0.4  -0 3  2*  108.3  108.3  0.0  0.0  5  81 o 5  81.3  + 0.2  + 0.3  7  69.8  72.5  -2.7  -3,7  9*  60.8  60.8  0.0  0.0  51.3  55«5  -4.2  -7,6  12  *  o  V a l u e s used f o r c a l c u l a t i o n of o v e r a l l a c c e l e r a t i o n c o n s t a n t by " t w o - p o i n t method,"  100 T a b l e 4-9.  R a d i a t i o n p o l y m e r i z a t i o n o f TEGDMA a t d i f f e r e n t dose r a t e s .  Dose  rate  MAX l/t  xlO MAX  r ad/sec  (r ad/sec)  l/2  t  T  MAX,  "MAX,  mm  °C  220  14.8  22  130  4.55  202  14.1  31  107  3.22  156  12.5  89  88  1.12  101  Table  4-10.  Thermomechanical p r o p e r t i e s of r a d i a t i o n cured p o l y (MMA) and c r o s s l i n k e d MMA-DVM p o l y m e r products.  Comonomer Composition, vol  %  EGDMA  DEGDMA  TrEGDMA  TEGDMA  4  CM  Monomer  MMA  LTDCxiO ,  CO  1/°C  T  TDD,  °c  0/  TDT,  0 C  /o  MMA  DVM  100  0  2.000  551  108  0  125  97.5  2.5  2.003  388  115  49  175  95  5  2.006  302  123  60  198  90  10  2.012  125  127  77  202  70  30  2,039  15  130  92  214  50  50  2.072  4  130  94  250*  97.5  2.5  2.002  437  114  41  158  95  5  2.004  350  115  46  164  90  10  2.007  263  119  61  175  70  30  2.025  82  122  82  200  50  50  2.048  21  125  87  198  97.5  2.5  2.001  476  111  25  155  95  5  2.003  375  113  50  165  90  10  2.005  275  116  63  180  70  30  2,018  102  119  83 •  195  50  50  2.036  57  122  92  207  95  5  2.002  425  110  37  90  10  2.004  326  113  52  165  85  15  2.007  275  115.  61  185  70  30  2.014  126  117  81  203  50  50  2.029  63  117  88  197  Over 250 ° C , maximum f o r e q u i p m e n t  .  160  102  T a b l e 4-11.  Mechanical p o l y (MMA) p r o d u c t s.  p r o p e r t i e s of r a d i a t i o n and c r o s s l i n k e d MMA-DVM  Comonomer composition, vol.  %  YIELD  0  0  DVM  STRESS, STRAIN, STRESS, STRAIN, •kg/cm  MMA  EGDMA  DEGDMA  TrEGDMA  TEGDMA  100  RUPTURE  CN  Monomer MMA  cured polymer  2  %  kg/cm  2  %  0  2.000  1,080  6,0  2,100  50.5  97,5 95 90 • 80 50 40 20 0  2.5 5 10 20 50 60 80 100  2,003 2.006 2.012 2.024 2,072 2.092 2.138 2.200  1,080 1,060 1 080 1,020 955 — —  7,0 6.7 7.0 6.0 5.0 — —  4,450 4,770 3,950 2,550 1,530 1,330 1,210 895  62.2 67.5 55.0 38.5 20.0 17.5 12,5 5.5  97,5 95 90 70 50 20 0  2.5 5 10 30 50 80 100  2.002 2.004 2.007 2.025 . 2.048 2,099 2,150  1,150 1,050 1,050 1,050 1,020 895 —  7.5 7,0 7.0 6.5 6.0 5.5 — -  3,915 4,680 3,950 2,770 1,910 1,400 825  60,5 65.5 54.0 42.5 27.0 15.0 5.5  97,5 95 90 70 60 50 30 0  2.5 5 10 30 40 50 70 100  2.001 2,003 2.005 2.018 2.026 2.036 2.061 2.125  1,020. 1,050 1,020 1,000 960 950 950 —  7,0 7.5 7.6 7.0 6,5 6.0 5.5 — -  3,630 4,650 4,580 3,120 2,510 2,230 1,520 1,250  63.0 66.0 62,5 48.0 44.5 36.0 20,0 11.5  95.5 9590 70 50 40 20 • .0  2.5 5 10 30 50 60 80 100  2.001 2., 002 2,004 2,014 2.029 2,037 2.062 2,105  925 955 1,080 1,050 955 860 765 510  6.0 6.5 7.0 7.0 7.0 6,0 5.0 2.5  4,710 5,100 5,030 3,890 2,450 2,250 1,520 .1,660  67.0 68.5 67.0 59.5 47,0 41.0 2.7.0 26.5  9  103  T a b l e 4-12.  Monorner  C a l c u l a t e d parameters from compression s t r a i n curves f o r r a d i a t i o n cured poly and MMA-DVM p o l y m e r p r o d u c t s .  Comonomer composition, vol, % , MMA  MMA  100  97.5 95 90 EGDMA  so  '50 40 20 0  97.5 95 90  DEGDMA  TrEGDMA  TEGDMA  70  •  E, kg/cm^xlO  DVM  stress(MMA)  Plastic Deforma_3 tion,  F  %  cm'  0  19.0  44.5  32.3  2.5 5 10  20.0 19.0 19.0  55.0 61.0 48.0  49.5 55.7 45.8  50 60  18.5  15.0  20  19,0  32.5  27.8  SO  18.0 16.5  —— ——  11.1 6.8 6.1 1.0  2.5 5 10  19.0 19.5 19.0  53.0 58.5 44.0  50.9 56.6 48.1  21.0 9.5 ——  17.1 7.3 1.5  100  30  18.0  18.0  36.0  30.4  50 20 0  50 80 100  18.0 17,0 17.0  97.5 95 90 70 60 50 30 0  2,5 5 10 30 40 50 70 100  18.0 19.5 20.0 17.0 16.5 17.0 17.0 17.0  56.0 58.5 55,0 41.0 38,0 30.0 14,5  47.5 56,5 54.1 34.8 26,6 23.3 10.9 7.7  97.5 95 90  2,5 5 10  18.5 18.5 20,0  61.0 62.0 60,0  55.6 59.5 57.5  70  30  19.5  50 40 20 0  50 60 80 100  17,0 16.0 15.0 15.0  52.5  40.0 35,0 22.0 24.0  49.4  34.8 25.3 1.4,5 13,9  104  Figure  3-1.  S o l u t i o n of a t y p i c a l p o l y m e r i z a t i o n exotherm c u r v e i n c l u d i n g d e r i v a t i o n of " G e l - E f f e c t P o i n t " ( G E P ) , " C u r e " (MAX), and showing " A c t i v a t i o n " ( I ) and " A c c e l e r a t i o n " ( I I ) p e r i o d s ( 6 7 , 6 9 , 7 1 ) .  t  t  0  t GEP  Time  D  (t)» min  D  D  0  GEP Dose  MAX  ( D ) , Mrad  MAX  105 Figure  3-2.  T y p i c a l thermomechanical curves f o r thermoplastic ( I ) , p a r t l y c r o s s l i n k e d ( 2 ) and f u l l y c r o s s l i n k e d ( 3 ) p o l y m e r p r o d u c t s ; and showing f o r ( 2 } solutions f o r g l a s s t r a n s i t i o n temperature (Tg), thermal d i s t o r t i o n t e m p e r a t u r e (TDT) and s l o p e ( s ) i n t h e t r a n s i t i o n region (67 69). 9  c o  Temperature  ( T ) , °C  106 F i g u r e 3-3.  Polymer s t r e s s - s t r a i n curve nomenclature and t y p i c a l curves f o r d i f f e r e n t types of p l a s t i c s (20,72).  S_train a t rupture_  s t r e s s at rupture  Plastic  Deformation  strain  s o f t and weak  r  /1 hard s t r o nand g  y  hard and brittle  / hard and  s o f t and  tough  tough  107  Figure  4-1.  R e l a t i o n s h i p between "^MAX and volume concentrat i o n o f TEGDMA i n t h e MMA-TEGDMA comonomer mixture (67,69).  108  Figure  4-2.  Polymerization rate coefficients i n"Activation" ( P R C j ) and " A c c e l e r a t i o n " ( P R C J J ) p e r i o d s a s f u n c t i o n s o f TEGDMA volume c o n c e n t r a t i o n i n t h e MMA-TEGDMA comonomer m i x t u r e ( 6 7 , 6 9 ) .  0  20  40  60  80  TEGDMA, v o l .  100 %  109  Figure  4-3.  R e l a t i o n s h i p between o v e r a l l c u r i n g r a t e (l/tj^) and TEGDMA volume c o n c e n t r a t i o n i n t h e MMATEGDMA comonomer m i x t u r e ( 6 7 , 6 9 ) ,  60  50 c  •H  e  o  <  40  30  20  10  0 0  10  20  30  40  50  TEGDMA, v o l . %  110  Figure  4-4.  R e l a t i o n s h i p between MAX and d i v i n y l monomer (DVM) volume c o n c e n t r a t i o n i n MMA-DVM comonomer m i x t u r e s . t  0  10  20  30  DVM,  vol.%  Ill  112 F i g u r e 4-6.  Polymerization rate c o e f f i c i e n t s i n "Activation" (PRCj) and " A c c e l e r a t i o n " (PRG__) p e r i o d s as f u n c t i o n s of d i v i n y l monomer (DVM) volume c o n c e n t r a t i o n i n MMA-DVM comonomer m i x t u r e s .  O  MMA  - EGDMA  X  A  MMA  - DEGDMA  . Q  MMA MMA  - TrEGDMA - TEGDMA  DVM, v o l .  %  113 F i g u r e 4-7.  R e l a t i o n s h i p between WMX MMA-DVM comonomer s y s t e m s  and ''GEP f o r d i f f e r e n t and t h e S- TEGDMA s y s t e m .  70.  60  50  40  30  20  10  0 0  10  20  30  40 ^GEP,  50 min  114  Figure  4-8.  R e l a t i o n s h i p between o v e r a l l c u r i n g r a t e - ( l / t w A ^ ) and DVM c o n c e n t r a t i o n i n MMA-DVM m i x t u r e s . 1  0  O  MMA  - EGDMA  A  MMA  - DEGDMA  *  MMA  - TrEGDMA  5  .  H  MMA  - TEGDMA  ©  MMA  - TMPTMA ( 3 3 )  A  MMA  10  15 DVM, v o l . %  115  Figure 4 - 9 .  O v e r a l l a c c e l e r a t i o n constant (K) and i t s r e c i p r o c a l ( l / K ) as f u n c t i o n s of d i v i n y l monomer c o n n e c t i o n number (CNr,.,,,, Table 3 - l ) . UVM O MMA-EGDMA  X MMA-TrEGDMA  A MMA-DEGDMA  IS MMA-TEGDMA  2.100  2.150  2.200 CN  DVM  116 F i g u r e 4-10.  R e l a t i o n s h i p between o v e r a l l c u r i n g r a t e ( l / t ^ y ) and DVM c o n c e n t r a t i o n i n t - b u t y l styrene (TBS/-DVM m i x t u r e s . E v a l u a t i o n of o r i g i n a l h e a t - c a t a l y s t data from ( 5 3 ) .  B  A X  0  TBS-EGDMA TBS-TrEGDMA TBS-TEGDMA TBS-TMPTMA  40  c  •H  E  CO O  30  20  10  0 20  30  C r o s s l i n k i n g agent, %  117  Figure  4-11,  O v e r a l l c u r i n g r a t e ( l / t ^ ) o f TEGDMA as f u n c t i o n of r a d i a t i o n d o s e ' r a t e .  a  Figure 4-12.  Shape of thermomechanical c u r v e s f o r MMA-EGDMA polymer p r o d u c t s . Numbers i n d i c a t e p e r cent of EGDMA i n comonomer mixture and copolymer c o n n e c t i o n number ( C N ) .  100  75  co  c o  •H  +>  3  50  m o  M-i cu  Q  25  RO• 50  100  150  0070 ^ 0 : | 2.POO, 200  T e m p e r a t u r e , °C  F i g u r e 4-13.  Shape of thermomechanical c u r v e s f o r MMA-TEGDMA polymer p r o d u c t s . Numbers i n d i c a t e per cent of TEGDMA i n comonomer mixture and copolymer c o n n e c t i o n number ( C N ) C 0  0  50  100  150 Temperature  200 °C  F i g u r e 4-14.  G l a s s t r a n s i t i o n temperature (T ) as a f u n c t i o n of copolymer c o n n e c t i o n number ( C N ) f o r d i f f e r e n t Mf'M-DVM p o l y m e r products. C 0  F i g u r e 4-15.  T h e r m a l d e f o r m a t i o n d e g r e e (TDD) and t h e r m a l d i s t o r t i o n t e m p e r a t u r e (TDT) as f u n c t i o n s o f c o p o l y m e r c o n n e c t i o n number ( C N ) f o r d i f f e r e n t MMA-DVM p o l y m e r products* c o  122  F i g u r e 4-16,  0  L i n e a r thermomechanical deformation c o e f f i c i e n t (LTDC). as a f u n c t i o n of d i v i n y l monomer (DVM) c o n c e n t r a t i o n i n MMA-DVM p o l y m e r p r o d u c t s .  10  20  30  40  50 DVM,  vol, %  F i g u r e 4-17.  2.000  L i n e a r t h e r m o m e c h a n i c a l d e f o r m a t i o n c o e f f i c i e n t tLJ/DC) a s a f u n c t i o n o f c o p o l y m e r c o n n e c t i o n number (CN ) for. d i f f e r e n t MMA-DVM p o l y m e r p r o d u c t s .  2.010  2.020 CN co  2.030  2.040  124  F i g u r e 4-18.  Shape of c o m p r e s s i o n s t r e s s - s t r a i n c u r v e s f o r MMA-EGDMA p o l y m e r p r o d u c t s . R a t e o f s t r a i n 0.1 cm/min.  125  F i g u r e 4-19.  Shape of c o m p r e s s i o n s t r e s s - s t r a i n c u r v e s f o r MMA-TEGDMA p o l y m e r p r o d u c t s . R a t e o f s t r a i n 0.1 cm/min.  126 F i g u r e 4-20.  Compression s t r e s s - s t r a i n parameters as f u n c t i o n s of comonomer c o m p o s i t i o n . The MMA-EGDMA comonomer system. (Rate of s t r a i n 0.1 cm/min.) 0 Compression s t r e s s a t r u p t u r e , kg/cm xl0~2 •Jf Compression s t r a i n a t r u p t u r e , % A Area under s t r e s s - s t r a i n c u r v e , F, cm . 2  2  EGDMA MMA concentration, v o l . %  127 Figure 4-21.  Compression s t r e s s - s t r a i n parameters as f u n c t i o n s of comonomer c o m p o s i t i o n . The MMA-DEGDMA comonomer system. (Rate of s t r a i n 0.1 cm/min.) 0 Compression s t r e s s at r u p t u r e , kg/cm^xl0~2 •X* Compression s t r a i n at r u p t u r e , % A Area under the s t r e s s - s t r a i n curve F , cm^.  T  x  DEGDMA MMA  0 100  20 80  40 60  60 40  80 20  concentration, v o l . %  100 0  128 Figure 4-22.  TrEGDMA 0 MMA 100  Compression s t r e s s - s t r a i n parameters as f u n c t i o n s of comonomer c o m p o s i t i o n . The MMA-TrEGDMA comonomer system. (Rate of s t r a i n 0.1 cm/min). © Compression s t r e s s at r u p t u r e , kg/cm2xl0~ •ft Compression s t r a i n at r u p t u r e , % A Area under the s t r e s s - s t r a i n curve F , cm^  20 80  40 60  60 40  80 20  100 0  concentration, v o l . %  129 F i g u r e 4-23.  Compression s t r e s s - s t r a i n parameters as f u n c t i o n s of comonomer c o m p o s i t i o n . The MMA-TEGDMA comonomer system. (Rate of s t r a i n 0.1 cm/min.) © Compression s t r e s s a t r u p t u r e , kg/cm xl0""2 •ft Compression s t r a i n at r u p t u r e , % A Area under the s t r e s s - s t r a i n curve F cm 2  2  f  TEGDMA MMA  0 100  20 80  40 60  60 40  80 20  concentration, v o l . %  100 0  oer  131 F i g u r e 4-25,  0  R e l a t i o n s h i p between a r e a under t h e c o m p r e s s i o n s t r e s s - s t r a i n c u r v e ( F ) and p l a s t i c d e f o r m a t i o n f o r d i f f e r e n t MMA-DVM p o l y m e r p r o d u c t s ,  15  30  45 Plastic  60 deformation,  %  

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