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The use of perbenzoic acid for measuring the concentration of vinyl groups in emulsion polyisoprene Phillips, Norman E. 1950

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ft  Vo  f\*i  The Use of Perbenzoic A c i d For Measuring the C o n c e n t r a t i o n of V i n y l Groups i n Emulsion P o l y i s o p r e n e .  by NORMAN E. PHILLIPS.  A T h e s i s Submitted i n P a r t i a l F u l f i l m e n t of the Requirements f o r the Degree of MASTER OF ARTS i n the Department o f CHEMISTRY.  The U n i v e r s i t y of B r i t i s h Columbia September, 1950.  /  THE UNIVERSITY OF BRITISH COLUMBIA VANCOUVER. CANADA ISTRY  September 21,  1950.  To Whom I t May Concern: This i s  t o c e r t i f y that the t h e s i s  entitled  "The Use of Perbenzoic A c i d f o r Measuring the Concent r a t i o n of V i n y l Groups i n Emulsion P o l y i s o p r e n e " by N . E . P h i l l i p s measures up t o the r e q u i r e d of the M a s t e r ' s  thesis in this  standards  Department. lours truly.,  JGH-ew  ABSTRACT. •  The method, o f L e e , K o l t h o f f and M a i r s f o r c o r r e c t i n g the i o d i n e numbers o f polymers f o r s u b s t i t u t i o n ' by i o d i n e nionochloride  i s unsatis-  factory. An improved method of c a l c u l a t i n g t h e amount of v i n y l groups i n a polymer from i t s r a t e o f r e a c t i o n w i t h p e r b e n z o i c a c i d i s p r e s e n t e d and used t o compare t h r e e t y p e s o f e m u l s i o n with n a t u r a l rubber.  polyisoprene  ACKNOWLEDGMENT The w r i t e r wishes to acknowledge t h e guidance of Dr. R. H. C l a r k , under whose d i r e c t i o n t h i s r e s e a r c h has been conducted.  TABLE OF CONTENTS. I.  Introduction. S t r u c t u r e and p h y s i c a l p r o p e r t i e s o f p o l y m e r s . 1 Methods of measuring t h e amount o f 1-2 •• addition.  II.  III.  3  Improved method o f c a l c u l a t i o n f o r p e r b e n z o i c .acid t i t r a t i o n s .  13.  D e t e r m i n a t i o n of t o t a l u n s a t u r a t i o n .  16  Experimental. P r e p a r a t i o n o f polymer samples  24  Determination of t o t a l unsaturation.  26  Preparation of perbenzoic a c i d .  39  S t a b i l i t y of p e r b e n z o i c a c i d a t 0°C.  41  R e a c t i o n o f n a t u r a l rubber w i t h p e r b e n z o i c acid.  42  Reaction .of-synthetic polyisoprene w i t h perbenzoic acid.  44  Discussion of Results. D e t e r m i n a t i o n o f the p e r c e n t a g e o f v i n y l groups  52  Determination of t o t a l unsaturation  57  Bibliography.  5g  INTRODUCTION. STRUCTURE AND PHYSICAL PROPERTIES OF POLYMERS. The r e l a t i o n between the p h y s i c a l p r o p e r t i e s o f a polymer and i t s s t r u c t u r e i s n o t f u l l y understood but i t has o b v i o u s importance i n any e x p e r i m e n t a l work d e s i g n e d t o p r e p a r e polymers p o s s e s s i n g s p e c i a l q u a l i t i e s .  For  t h i s purpose i t i s n e c e s s a r y t o have methods o f d e t e r m i n i n g and comparing t h e s t r u c t u r e s o f d i f f e r e n t  polymers  and then t o r e l a t e the r e s u l t s of these s t u d i e s t o p r o p e r t i e s such as e l a s t i c i t y and d u r a b i l i t y .  E x p e r i m e n t a l work  of t h i s s o r t seems t o show t h a t t h e g r e a t e r t h e degree o f i n t r a m o l e c u l a r homogeneity t h e more d e s i r a b l e a r e t h e p r o p e r t i e s of t h e polymer i n g e n e r a l .  The new  low-temper-  a t u r e s y n t h e t i c r u b b e r s and p a r t i c u l a r l y n a t u r a l rubber a r e known t o have u n u s u a l l y h i g h degrees o f i n t r a m o l e c u l a r homog e n e i t y and s u p e r i o r p h y s i c a l p r o p e r t i e s . F a c t o r s which c o n t r i b u t e t o i n t r a m o l e c u l a r inhomogene i t y i n s y n t h e t i c polymers a r e : (a) I n copolymers t h e d i f f e r e n t monomer u n i t s may be r e g u l a r l y spaced or may o c c u r i n groups.  In a  copolymer o f b u t a d i e n e and s t y r e n e t h e s t y r e n e u n i t s a r e d i s t r i b u t e d a t random, and thus bute t o t h e degree of inhomogeneity.  contri-  (b) There i s u s u a l l y the p o s s i b i l i t y t h a t each monomer u n i t may  e n t e r t h e growing polymer m o l e c u l e i n more  than one way.  The way  i n which a monomer m o l e c u l e  i s i n c o r p o r a t e d i n t o the c h a i n depends on the p o i n t of a t t a c k of the f r e e r a d i c a l and the carbon atom of the monomer t o which the r a d i c a l i s t r a n s f e r r e d . In the case of i s o p r e n e t h e r e a r e t h r e e ways i n which each monomer m o l e c u l e c o u l d be CH —  joined.  3  C H _ - C  = C H -  CH  Ctrl—  1-4-a4«Uturn  3  __CH_C_ i  , ^ Addition  CH  (i  - CH - CHX~ I Cc)  3-H addition  I n the case o f 1-4 a d d i t i o n t h e double bond i n t h e c h a i n l e a d s to the e x i s t e n c e of c i s and t r a n s i s o m e r s .  I n a polymer made from, a s i n g l e monomer the degree o f i n t r a m o l e c u l a r homogeneity would be determined c o m p l e t e l y by the r e l a t i v e numbers of each of the d i f f e r e n t groups described, i n (b) and (c) and t h e i r o r d e r o f o c c u r r e n c e .  For  t h i s r e a s o n i t i s of i n t e r e s t t o be a b l e t o measure the amounts o f 1-2 and 1-4 a d d i t i o n i n a polymer. P o l y m e r i z a t i o n o f symmetr i c a l 1,3 d i e n e s by 3-4 a d d i t i o n would g i v e the sarae r e s u l t  as 1-2 a d d i t i o n but. i n t h e case o f u n s y m m e t r i c a l  dienes the  p o s s i b i l i t y o f t h r e e d i f f e r e n t groups must be c o n s i d e r e d . D e t e r m i n a t i o n o f the Amount o f 1-2 A d d i t i o n . In p a r t o f t h e d i s c u s s i o n t h a t f o l l o w s 1-2 and 1-4 a d d i t i o n i n p o l y i s o p r e n e w i l l be c o n s i d e r e d as examples. However, when i s o p r e n e i s p o l y m e r i z e d t h e p r o d u c t of 3-4 a d d i t i o n d i f f e r s from t h a t o f 1-2 a d d i t i o n and the problem of d e t e r m i n i n g the r e l a t i v e amounts o f each of the three, groups,  i f they a l l o c c u r r e d , would be more c o m p l i c a t e d .  Evidence w i l l be p r e s e n t e d i n t h e e x p e r i m e n t a l p a r t o f t h i s paper t o show t h a t o n l y one o f 1-2 or 3-4 a d d i t i o n o c c u r r e d i n s i g n i f i c a n t q u a n t i t i e s i n t h e polymers under investigation. Most of t h e methods used f o r measuring 1-2 a d d i t i o n i n polymers depend on t h e d i f f e r e n c e in. p r o p e r t i e s of t h e ethyl.enic bond l e f t i n t h e polymer by 1-2 and 1-4 a d d i t i o n . In  the case o f 1-4 a d d i t i o n the double bond i s w i t h i n t h e  c h a i n w h i l e both 1-2 and 3-4 a d d i t i o n r e s u l t s i n an e x t e r nal  double bond o r v i n y l group.  for  measuring 1-2 a d d i t i o n a r e :  The most i m p o r t a n t  methods  (a.) P o l y m e r i z a t i o n of E q u i m o l e c u l a r Q u a n t i t i e s of Monomer g  and M o d i f i e r . The p r i n c i p l e of t h i s method i s the use o f such a h i g h c o n c e n t r a t i o n o f m o d i f i e r t h a t a l a r g e p a r t o f the r e s u l t i n g p o l y m e r c o n s i s t s , of o n l y one monomer molecule  and one molecule  of modifier.  Equimolecular  q u a n t i t i e s of b u t a d i e n e and i n a persulfate catalyzed  b u t y l mercaptan were p o l y m e r i z e d  system, the r e s u l t i n g t h i o - @ t h e r s  were decomposed w i t h cyanogen c h l o r i d e , and b u t e n y l c h l o r i d e s was  fractionated.  arrangements the p o s i t i o n of the  the m i x t u r e of  I n the absence of r e -  c h l o r i n e atom injthe b u t e n y l  c h l o r i d e s shows the p o i n t of a t t a c k of the f r e e r a d i c a l and the. p o s i t i o n • of the double bond shews whether the was  1-2,  3-4  o r 1-4.  amount of 1-2,  1-4  addition  W h i l e t h i s method r e a l l y g i v e s and  3-4  the  a d d i t i o n injthe i n i t i a t i o n  re-  a c t i o n o n l y , the r e s u l t s p r o b a b l y g i v e some i n d i c a t i o n of the amounts i n the polymer and  i t has  d i s t i n g u i s h i n g between 1-2  3-4  and  the advantage of  a d d i t i o n even i n symmet-  r i c a l die.nes. (bj Ozone D e g r a d a t i o n .  The  i d e n t i f i c a t i o n and  quantitative  d e t e r m i n a t i o n of the p r o d u c t s of an ozone d e c o m p o s i t i o n of a polymer would determine c o m p l e t e l y the amounts of 1-2, and  1-4  a d d i t i o n . ; however the  a c i d s or t h e i r e s t e r s  complete s e p a r a t i o n  is difficult.  t h e r e should be one mole o f f o r m i c  A f t e r the  of  3-4 the  ozonolysis  a c i d f o r each mole  of v i n y l groups p r e s e n t but  the c o r r e c t time f o r  i s uncertain  the amount o f f o r m i c a c i d formed.  and  influences  I n a d d i t i o n t h e r e i s the added d i f f i c u l t y formic  ozonization  of s e p a r a t i n g  the  a c i d q u a n t i t a t i v e l y s i n c e i t forms a c o n s t a n t b o i l i n g  mixture with water.  Because o f t h e s e u n c e r t a i n t i e s i t has  been proposed t h a t the p e r c e n t a g e of v i n y l groups as by o z o n o l y s i s to as the  under c e r t a i n s p e c i f i e d c o n d i t i o n s  "ozone number" of the polymer and  be  found referred  used o n l y as  a  b a s i s of comparison f o r d i f f e r e n t polymers. The  ozone number cannot be c o n s i d e r e d as b e i n g a measure  o f the a c t u a l amount of 1-2  a d d i t i o n i n a polymer and  r e s u l t s are not u s u a l l y i n agreement w i t h . t h o s e  the  obtained  by  more r e l i a b l e methods. Perhaps the most important was  a p p l i c a t i o n of t h i s method  i t s o r i g i n a l use i n the d e t e r m i n a t i o n of the s t r u c t u r e  of n a t u r a l rubber.  H a r r i e s i s o l a t e d up t o 90$  of the  theo-  r e t i c a l amount of l e v u l i n i c a c i d and aldehyde from t h e o z o n i z e d rubber showing t h a t n a t u r a l r u b b e r was  largely  1-4  polyisoprene. CH - -  CH ~C  CH  3  =  X  CH  - CHJ-CHJ-  C  3  =  C  H-CH^-  i ~CH' -C a  x  H'0£-CH -CH -C  N  a  t ^ C - C H ^ -  a  o  o  (c) I n f r a - r e d A b s o r p t i o n S p e c t r a .  R e c e n t l y a l a r g e number  of experiments have been c a r r i e d out t o measure the amounts of 1-2  and  1-4  a d d i t i o n and  c i s - t r a n s i s o m e r i s m by  the i n f r a - r e d a b s o r p t i o n s p e c t r a of p o l y m e r s .  The  bands s t u d i e d are those due to the double bonds.  studying absorption The  diffi-  c u l t y w i t h t h i s method i s t h a t the i n s t r u m e n t s must be c a l i b r a t e d by u s i n g s i m p l e compounds w i t h a s t r u c t u r e s i m i l a r t o the s t r u c t u r a l u n i t s i n the polymer and assuming t h a t  the  remainder o f the polymer does not a f f e c t the a b s o r p t i o n band.  3 U s i n g t h i s method, Hart and Meyer have shown t h a t the tempe r a t u r e o f p o l y m e r i z a t i o n has no a p p r e c i a b l e e f f e c t on  the  amounts of 1-2  and  amounts of c i s and The  a d d i t i o n . , but does a f f e c t t h e  t r a n s isomers at the  amount of t r a n s 1-4  polymerization 1-4  1-4  a t -19°G  At h i g h e r  t u r e of c i s and t r a n s  e s s e n t i a l l y a l l of  temperatures t h e r e  the  i s a mix-  isomers.  I'd) P e r b e n z o i c A c i d T i t r a t i o n . an ethylene  i n t e r n a l double bonds  u n i t s i n c r e a s e s as the temperature of  decreases and  u n i t s are t r a n s .  relative  Perbenzoic acid reacts w i t h  t o f a r m t h e monobenzoyl e s t e r of t h e  correspond-  i n g 1,2. g l y c o l w h i c h t h e n s p l i t s o f f b e n z o i c a c i d , l e a v i n g the e p o x i d e . C  b  H  5  C 0  3  H  (  H-  f~  >  {  r—  C  6  H  5  C 0  V  - c I H O - C 2  I >  CD  (  +  C H COiH fe  s  I The  r e a c t i o n i s q u a n t i t a t i v e i n a s h o r t time f o r a g r e a t many  ethylenes  and. has been, used to measure the u n s a t u r a t L o n I n a  number of compounds.  The  usual, p r o c e d u r e i s t o a l l o w an  ex-  cess of p e r b e n z o i c a c i d t o r e a c t w i t h the compound b e i n g tested i n a chloroform  s o l u t i o n , add a s o l u t i o n o f potas,sium  i o d i d e in. d i l u t e a c i d , and t i t r a t e t h e l i b e r a t e d i o d i n e standard The  sodium t h i o s u l p h a t e s o l u t i o n . r a t e of t h e r e a c t i o n i s s t r o n g l y i n f l u e n c e d by  s u b s t i t u e n t s on the e t h y l e n e ;  negative  r a t e and p o s i t i v e groups i n c r e a s e i t . l e n e s t h a t are formed by 1-4 attached  with  the  groups d e c r e a s e the I n polymers the  ethy-  a d d i t i o n have more a l k y l groups  t o them t h a n those formed by 1-2  a d d i t i o n , and  t h e r e f o r e t h e y r e a c t raore r a p i d l y .  The d i f f e r e n c e I n r e a c t i v -  i t y of i n t e r n a l double bonds and v i n y l groups i s i l l u s t r a t e d by the r a t e c o n s t a n t s f o r the o x i d a t i o n of o l e i c and undecyl e n i e a c i d s which are 23 l.mT hr7" and 0.9.6 I . m 7 h r 7 1  L  1  1  respec-  tively. For a m i x t u r e o f compounds c o n t a i n i n g v i n y l groups and i n t e r n a l double bonds, the f r a c t i o n of t h e double bonds o x i d i z e d by perbenzoic. a c i d w i l l i n c r e a s e r a p i d l y u n t i l a l l t h e i n t e r n a l double' bonds have r e a c t e d , and then more s l o w l y w h i l e t h e v i n y l groups r e a c t .  D u r i n g the war, German s c i e n t i s t s made  use o f t h e d i f f e r e n t r a t e s of r e a c t i o n of i n t e r n a l and  exter-  n a l double bonds t o e s t i m a t e t h e p e r c e n t a g e of 1-2 a d d i t i o n i n IS  polymers.  They a l l o w e d a sample of t h e polymer t o r e a c t w i t h  an excess o f p e r b e n z o i c a c i d under s p e c i f i e d  conditions for 2  hours and then t i t r a t e d the r e m a i n i n g p e r b e n z o i c a c i d .  The  f r a c t i o n o f d o u b l e bonds o x i d i z e d i n t h i s t i m e was c a l l e d t h e " p e r a c i d v a l u e " of t h e polymer and was a measure o f t h e p e r c e n tage of i n t e r n a l double bonds.. value d i r e c t l y to  I n o r d e r t o r e l a t e the p e r a c i d  t h e p e r c e n t a g e of i n t e r n a l double bonds,  they c o n s t r u c t e d c a l i b r a t i o n curves from t h e e x p e r i m e n t a l p e r a c i d v a l u e s of known m i x t u r e s c o n t a i n i n g double bonds s i m i l a r t o those i n the p o l y m e r s . The n e c e s s i t y of assuming  t h a t the d o u b l e bonds i n a p o l y -  mer r e a c t a t the same r a t e - a s those i n a s i m p l e compound l i m i t s the u s e f u l n e s s of t h i s method and the r e s u l t s cannot be  con-  s i d e r e d as a c c u r a t e l y r e p r e s e n t i n g the p e r c e n t a g e o f v i n y l groups p r e s e n t .  K o l t h o f f and L e e ^ and l a t e r S a f f e r and Johnson, l a v e used m o d i f i c a t i o n s results.  of t h e method t h a t g i v e more a c c u r a t e  K o l t h o f f and Lee a l l o w e d  a s o l u t i o n t h a t was .02 M  i n double bonds and .03 H harper b e n z o i c a c i d t o r e a c t a t 0°C. A t regular- i n t e r v a l s o f t i m e t h e y withdrew a l i q u o t  portions  of t h e r e a c t i o n m i x t u r e and t i t r a t e d them i o d o m e t r i c a l l y for excess perbenzoic a c i d .  S a f f e r and. Johnson recommend  the use o f o n l y 25$ excess of p e r b e n z o i c a c i d a t 6°G but o t h e r w i s e t h e i r experimental,  procedure i s s i m i l a r .  Each of t h e methods proposed by K o l t h o f f and Lee f o r the  c a l c u l a t i o n o f t h e p e r c e n t a g e o f v i n y l groups depends  on an e x t r a p o l a t i o n o f a p l o t o f t h e c o n c e n t r a t i o n  o f double  bonds o x i d i z e d v e r s u s t i m e .  of i n t e r -  I f t h e concentrations  n a l and e x t e r n a l d o u b l e bonds i n a m i x t u r e a r e I and E r e s p e c t i v e l y , t h e p l o t of the c o n c e n t r a t i o n  o f d o u b l e bonds  o x i d i z e d v e r s u s t i m e f o r t h e m i x t u r e and f o r each of t h e two k i n d s  o f double bonds s e p a r a t e l y , would be;:something l i k e ,  the c u r v e s shown i n F i g u r e 1 . Double bonds  oxidized  E -  Figure (1) e x t e r n a l double bonds (2) i n t e r n a l double bonds  1  Time  (S) m i x t u r e o f i n t e r n a l and e x t e r n a l double bonds.  9.  K o l t h o f f and Lee p o i n t out t h a t s i n c e t h e e x t e r n a l double bonds r e a c t v e r y s l o w l y curves (1) and  (3) w i l l be  almost  s t r a i g h t l i n e s s e v e r a l hours a f t e r the r e a c t i o n has  started.  E x t r a p o l a t i o n of the curve r e p r e s e n t i n g t h e m i x t u r e back to time =• o should g i v e a p p r o x i m a t e l y the v a l u e of I and the p e r c e n t a g e  hence  of i n t e r n a l double bonds i f 1+ E, t h e t o t a l  c o n c e n t r a t i o n of double bonds, i s known.  S i n c e the c u r v e i s  e x p o n e n t i a l and not r e a l l y a s t r a i g h t l i n e the v a l u e of I o b t a i n e d i s not c e r t a i n and depends on t h e t i m e a t w h i c h tangent  the  t o the curve i s drawn.  A second more c o m p l i c a t e d method used by K o l t h o f f  and  Lee was t o c a l c u l a t e the r a t e constant f o r t h e r e a c t i o n b e t ween t h e e x t e r n a l double bonds and p e r b e n z o i c a c i d from t h e e x p e r i m e n t a l r a t e curve f o r the m i x t u r e , and t o use t h e c u l a t e d v a l u e o f k to c o n s t r u c t a c a l i b r a t i o n curve the p e r c e n t a g e  giving  of v i n y l groups p r e s e n t from the f r a c t i o n of  double bonds o x i d i z e d i n a c e r t a i n time under c e r t a i n ditions.  cal-  con-  I n o r d e r to c a l c u l a t e t h e r a t e c o n s t a n t k f o r t h e  e x t e r n a l double bonds i t i s n e c e s s a r y  to assume t h a t the  i n t e r n a l double bonds r e a c t a l m o s t i n s t a n t l y compared w i t h the e x t e r n a l double bonds.  I f P i s the c o n c e n t r a t i o n o f  p e r b e n z o i c a c i d i n i t i a l l y p r e s e n t the c o n c e n t r a t i o n p r e s e n t a f t e r the r e a c t i o n of the i n t e r n a l double bonds i s w i l l be P - I .  Actually  complete  t h e c e n c e n t r a t i o n of p e r b e n z o i c  acid  w i l l be reduced t o P-I o n l y a f t e r s e v e r a l hours, but i f , d u r i n g t h i s t i m e , v e r y few o f the e x t e r n a l double  bonds  have r e a c t e d , the e f f e c t , so f a r as the r e a c t i o n o f t h e  10.  e x t e r n a l double bonds i s concerned, w i l l be the same as i f the c o n c e n t r a t i o n stantly.  of p e r b e n z o i c a c i d was reduced to P-I i n -  Therefore, i t i s possible t o c a l c u l a t e the rate  c o n s t a n t f o r t h e r e a c t i o n o f t h e e x t e r n a l double bonds from, the second o r d e r r a t e e q u a t i o n u s i n g P-I f o r t h e c o n c e n t r a t i o n o f p e r b e n z o i c a c i d , and u s i n g t h e e x p e r i m e n t a l d a t a f o r the r a t e o f o x i d a t i o n of t h e m i x t u r e o f i n t e r n a l and e x t e r n a l double bonds.  (p-l)-E  (P-lXE-X)  I = i n i t i a l concentration  o f i n t e r n a l d o u b l e bonds.  E = i n i t i a l concentration  o f e x t e r n a l double bonds.  P = initial  of perbenzoic a c i d .  concentration  X = concentration  of e x t e r n a l double bonds o x i d i z e d a f t e r  time t . The  v a l u e s o f I and E i n j t h i s e q u a t i o n were o b t a i n e d  by  e x t r a p o l a t i n g t h e r a t e curve to t i m e - 0 and t h e v a l u e o f X was o b t a i n e d ' b y s u b t r a c t i n g I from t h e t o t a l of p e r b e n z o i c a c i d used.  concentration  K o l t h o f f and Lee argue t h a t a  s m a l l e r r o r in. the g r a p h i c a l a p p r o x i m a t i o n to I w i l l not appreciably  a f f e c t t h e c a l c u l a t e d value.of  k.  However,  i n some o f t h e i r c a l c u l a t i o n s t h e r e a r e d i f f e r e n c e s of over 50% i n t h e v a l u e s o f the r a t e c o n s t a n t s c a l c u l a t e d f o r the...saise polymer a t d i f f e r e n t t i m e s .  The e f f e c t on t h e v a l u e o f k  .of an e r r o r i n t h e v a l u e o f I would be most s e r i o u s f o r polymers t h a t had v e r y few v i n y l groups p r e s e n t .  11 The c a l i b r a t i o n curve was c o n s t r u c t e d t o g i v e t h e p e r centage o f i n t e r n a l d o u b l e bonds d i r e c t l y from t h e c o n c e n t r a t i o n o f double bonds o x i d i z e d i n a c e r t a i n t i m e .  The t i m e  f o r t h e c a l i b r a t i o n curve was chosen so t h a t the r e a c t i o n o f the i n t e r n a l double bonds was e s s e n t i a l l y complete b u t n o t a l l of the v i n y l groups had r e a c t e d . K o l t h o f f and Lee chose 4.5 h o u r s .  For polyisoprene,  The c a l c u l a t i o n s n e c e s s a r y  for t h e c a l i b r a t i o n curve were, i n a sense, t h e i n v e r s e o f t h o s e used i n c a l c u l a t i n g the r a t e c o n s t a n t . The same assumptions and the same e q u a t i o n were used.  Suppose, f o r example, that,  a sample o f p o l y i s o p r e n e c o n t a i n e d 50$ e x t e r n a l d o u b l e  bonds;  t h e n , I = .01, E = .01, P = .03,, t = 4.5, and t h e v a l u e o f k has a l r e a d y been c a l c u l a t e d .  T h e r e f o r e t h e o n l y unknown  q u a n t i t y i n e q u a t i o n (1) i s x, and i t may be c a l c u l a t e d . S i n c e i t was assumed t h a t a l l o f t h e i n t e r n a l bonds have r e a c t e d , the t o t a l c o n c e n t r a t i o n of double bonds t h a t would have been o x i d i z e d i n a polymer thaijhad 50$ e x t e r n a l d o u b l e  bonds,  i n ' 4 . 5 h o u r s , c o u l d be found by a d d i n g .01 t o t h e c a l c u l a t e d v a l u e o f x.  S i m i l a r c a l c u l a t i o n s were made f o r 10, 30, 30 and  40$ e x t e r n a l double bonds and the r e s u l t s were p l o t t e d i n a graph o f c o m p o s i t i o n of the polymer v e r s u s t h e f r a c t i o n o f double bonds o x i d i z e d i n 4.5 h o u r s .  U s i n g t h i s g r a p h i t was  o n l y n e c e s s a r y t o make one t i t r a t i o n at 4.5 hours t o determine the p e r c e n t a g e o f 1-2 a d d i t i o n i n a sample.  K o l t h o f f and Lee  made t h e n e c e s s a r y c a l c u l a t i o n s f o r c a l i b r a t i o n c u r v e s f o r s e v e r a l d i f f e r e n t types of polymers and where the d a t a i s a v a i l a b l e t h e i r r e s u l t s agree w i t h i n a few p e r c e n t . w i t h t h o s e  obtained The  by i n f r a - r e d a b s o r p t i o n  techniques.  obvious advantage o f u s i n g t h i s f o r m o f a c a l i b r a t i o n  curve i n roautine work i s t h a t i t a l l o w s t h e p e r c e n t a g e of 1-2 a d d i t i o n t o be c a l c u l a t e d from, a s i n g l e t i t r a t i o n i n s t e a d o f perhaps- t e n t h a t would be n e c e s s a r y f o r t h e g r a p h i c a l mation.  approxi-  I t should be n o t e d , however, t h a t r e s u l t s o b t a i n e d by  t h i s method a r e r e a l l y no more a c c u r a t e than the: g r a p h i c a l a p p r o x i m a t i o n t h a t was n e c e s s a r y t o c a l c u l a t e t h e r a t e  constant.  The w h o l e c a l c u l a t i o n r e a l l y amounts t o making a guess a t I from the. r a t e c u r v e , u s i n g t h i s v a l u e o f I t o c a l c u l a t e k and then, u s i n g  the c a l c u l a t e d v a l u e -of k to r e - c a l c u l a t e I f r o m  the same e q u a t i o n .  I f the i n i t i a l "approximation to l i s in. e r r o r  a l l t h e c a l c u l a t e d v a l u e s o f k w i l l be i n e r r o r and hence t h e average v a l u e o f k used i n . c o n s t r u c t i n g t h e c a l i b r a t i o n c u r v e w i l l be i n e r r o r t o o .  The e r r o r made i n u s i n g ' t h e  calibration  curve w i l l t h e r e f o r e be j u s t about t h e same as the e r r o r made i n the g r a p h i c a l a p p r o x i m a t i o n .  K o l t h o f f and Lee s a y t h a t  an e r r o r o f 3$ i n t h e g r a p h i c a l estimation- o f I f o r a polymer t h a t has 40$ 1-2 a d d i t i o n w i l l produce a n e g l i g i b l e e r r o r i n k but by t h e same argument t h i s n e g l i g i b l e e r r o r i n k w i l l duce an e r r o r o f about 3$ i n r e s u l t s o b t a i n e d bration, curve.  As p o i n t e d  pro-  from the c a l i -  out by S a f f e r and Johnson, t h e  g r a p h i c a l e x t r a p o l a t i o n i s more a c c u r a t e for- polymers t h a t have o n l y 10$- 20$  of e x t e r n a l double bonds, b u t even s o , t h e  l i m i t s o f a c c u r a c y a r e about 1$. I t was f e l t  that there/should  measuring t h e amount o f  be a more exact method o f  1-2 a d d i t i o n s i n c e f r o m r e s u l t s  13 of o t h e r workers c e r t a i n f a c t o r s s u c h as temperature o f p o l y m e r i z a t i o n and f o r m a t i o n of  g e l appear t o have o n l y s m a l l  e f f e c t i f any on t h e amount o f 1-2 a d d i t i o n .  T h i s makes, an  a c c u r a c y of g r e a t e r than 1 p a r t i n 100 n e c e s s a r y f o r purposes of comparison.  The method to be d e s c r i b e d below has been  used to compare the amounts o f 1-2 a d d i t i o n i n d i f f e r e n t samples o f p o l y i s o p r e n e p r p p a r e d i n t h i s l a b o r a t o r y and i t appears to o f f e r some advantages. The e x a c t r a t e e q u a t i o n f o r t h e r e a c t i o n o f a polymer sample c o n t a i n i n g two k i n d s of double bonds w i t h p e r b e n z o i c a c i d would be t h a t f o r a m i x t u r e o f two r e a c t a n t s i n . competing reactions f o r a t h i r d reactant.  T h i s e q u a t i o n would  be t o o c o m p l i c a t e d to be u s e f u l and t h e r e f o r e an approximate treatment i s n e c e s s a r y .  The same assumptions t h a t K o l t h o f f  and Lee made i n u s i n g . t h e second o r d e r r a t e e q u a t i o n c a n be shown t o be j u s t i f i e d .  In;a s o l u t i o n t h a t i s .03 M i n p e r -  b e n z o i c a c i d and .02 M i n double bonds t h a t r e a c t w i t h a -1 -1 r a t e c o n s t a n t o f 100 l.m. h r . t h e double bonds would be.99$ o x i d i z e d i n 3.52 hours,but i f the r a t e c o n s t a n t was 0.5, o n l y 5.1$ would be o x i d i z e d i n t h e same t i m e .  I f the s o l -• -  u t i o n had been .02 M i n a m i x t u r e o f about 8 0 $ . i n t e r n a l , and 20% e x t e r n a l double bonds, t h e i n t e r n a l double bonds would be o x i d i z e d i n r o u g h l y t h e same t i m e .  The e x t e r n a l ,  double bonds would r e a c t more s l o w l y , b o t h because o f t h e i r lower c o n c e n t r a t i o n and because the c o n c e n t r a t i o n o f perbenz o i c a c i d would d e c r e a s e r a p i d l y as i t r e a c t e d w i t h the i n t e r n a l double bonds.  14. In polyisoprene, and  the r a t e c o n s t a n t s  f o r the i n t e r n a l  e x t e r n a l double bonds are o f t h e o r d e r o f 100 and 0.5  respectively.  Therefore i t i s a reasonable approximation  t o say t h a t d u r i n g the time i n xvhich the i n t e r n a l d o u b l e bonds a r e almost c o m p l e t e l y  o x i d i z e d , o n l y a few  of the e x t e r n a l bonds have r e a c t e d .  percent,  T h i s means t h a t t h e  second o r d e r r a t e equation w i t h P - I i n s t e a d of P f o r t h e concentration  of p e r b e n z o i c a c i d can be used f o r the  re-  a c t i o n s o f the e x t e r n a l double bonds. A c t u a l l y , the c o n c e n t r a t i o n  of p e r b e n z o i c a c i d  will  be reduced from P t o P-I o n l y a f t e r about f o u r h o u r s , but  i t i s s t i l l a good a p p r o x i m a t i o n and the e r r o r  i s small for large values k t  =  '  2.303 logr  P-I-E  involved  of t . E(P-I-X-)  .(P-I)(E-X)  For the l a r g e v a l u e s  o f t f o r w h i c h the  approximate  e q u a t i o n may be used, p r a c t i c a l l y a l l of the i n t e r n a l d o u b l e bonds w i l l have r e a c t e d and concentration  t h e v a l u e o f x,which i s t h e  o f e x t e r n a l double'bonds o x i d i z e d , can be  found by s u b t r a c t i n g 1 f r o m t h e t o t a l c o n c e n t r a t i o n o f double bonds o x i d i z e d .  I f R i s t h e f r a c t i o n o f double  bonds o x i d i z e d , and A i s the i n i t i a l t o t a l  concentration  of double bonds, then X = RA - I . A f t e r s u b s t i t u t i n g t h i s value second o r d e r r a t e e q u a t i o n ,  of X i n t o the approximate  t h e l o g a r i t h m i c term can be  s e p a r a t e d i n t o two p a r t s , one o f which depends o n l y on'  measurable  q u a n t i t i e s - and t h e second o n l y on t h e c o m p o s i t i o n  of t h e polymer. kt  -  P-T-E  2.303 lo# E ( P - I - R A ^  I)  ( P - I ) ( E - R A + I)  A =E - I (P-A)M =  2 . 3 0 3 \o  e  R-RA A - R A  +  2.3 03  log- A-1  P-I  S i n c e R i s measured e x p e r i m e n t a l l y and A i s known, . i t i s p o s s i b l e t o p l o t l o g (P-RA)/A(1-R) v e r s u s t , and t h e r e s u l t i n g curve should be a s t r a i g h t l i n e f o r the v a l u e s o f t f o r which t h e a p p r o x i m a t i o n s made i n d e r i v i n g t h e e q u a t i o n are v a l i d .  By e x t r a p o l a t i n g the s t r a i g h t p a r t o f t h e c u r v e  back to t=o t h e term l o g (A-I)/(P-I) can be read d i r e c t l y from the graph,and s i n c e A and P a r e knovm, the v a l u e o f I The percentage o f 1 - 2 a d d i t i o n i n the  c a n be c a l c u l a t e d .  polymer;, i s then 1 0 0 ( A - I ) / A .  For r o u t i n e work the v a l u e  of t h e r a t e c o n s t a n t can be measured from t h e s l o p e of the l i n e and used t o c o n s t r u c t a c a l i b r a t i o n curve as was done b y . K o l t h o f f and Lee.  log"  k  =  A-.I  P-ftA  P-I P-RA  2.303  P-A  A-RA A t  16 D e t e r m i n a t i o n o f T o t a l Unsaturate i o n . The method d e s c r i b e d above f o r d e t e r m i n i n g the amount of 1-2  a d d i t i o n i n a polymer depends on b e i n g a b l e to p r e p -  a r e a s o l u t i o n of the polymer c o n t a i n i n g a known c o n c e n t r a t i o n of double bonds.  T h i s means t h a t t h e r e must be  an  a c c u r a t e method of measuring the t o t a l unsaturati.bn,:of a polymer. I n polyisoprene. t h e r e s h o u l d be one double bond f o r each i s o p r e n e molecule  t h a t p o l y m e r i z e s , ho¥jever, the  results  of some -experimental d e t e r m i n a t i o n s i n d i c a t e t h a t the  unsatu-  r a t i o n i s not 100% of the t h e o r e t i c a l but something l e s s . The reasons f o r t h e low v a l u e of the u n s a t u r a t i o n are not known but c y c l i z a t i o n r e a c t i o n s a r e one of the  suggested  possibilities. Kemp and P e t e r s ^ e a r r i e d out a number of  experiments  designed t o adapt W i j ' s method f o r measuring u n s a t u r a t i o n i n s i m p l e compounds, t o polymers.  The r e a c t i o n betxveen  polymers s w o l l e n i n n o n - p o l a r s o l v e n t s and c h l o r i d e i n g l a c i a l a c e t i c a c i d was T h e i r f i n a l procedure  i o d i n e mono-  found u n s a t i s f a c t o r y .  was t o d i s s o l v e a sample i n p a r a -  d i c h l o r o b e n z e n e a t about 175°C and then add c h l o r o f o r m as the s o l u t i o n c o o l e d to prevent the s o l v e n t f r o m c r y s t a l l i z i n g . (They showed t h a t h e a t i n g the s o l u t i o n t o t h i s temperature  did  not a f f e c t t h e measured v a l u e of the u n s a t u r a t i o n . ) When t h e s o l u t i o n had c o o l e d t o room temperature monochloride  an excess of i o d i n e  d i s s o l v e d i n carbon t e t r a c h l o r i d e was  added  and the m i x t u r e a l l o w e d t o stand f o r 1 hour i n t h e dark.  The  u n r e a e t e d i o d i n e m o n o c h l o r i d e was determined by a d d i n g an aqueous s o l u t i o n of p o t a s s i u m i o d i d e and t i t r a t i n g the e r a t e d i o d i n e w i t h a s t a n d a r d s o l u t i o n of sodium  lib-  thiosulphate.  When t h i s procedure i s c a r e f u l l y s t a n d a r d i z e d , i t i s u s e f u l as a comparison o f the u n s a t u r a t i o n i n d i f f e r e n t samples of the same type o f polymer, but i t cannot be cons i d e r e d as g i v i n g an a c c u r a t e v a l u e o f the u n s a t u r a t i o n , or even a comparison between d i f f e r e n t t y p e s o f p o l y m e r s * I t ' s u s e f u l n e s s i s r e s t r i c t e d by the o c c u r r e n c e o f another r e a c t i o n which a l s o decreases the c o n c e n t r a t i o n of i o d i n e m o n o c h l o r i d e i n the r e a c t i o n m i x t u r e . I o d i n e m o n o c h l o r i d e adds to e t h y l e n e s atjrates w h i c h are markedly dependent on t h e c h a r a c t e r of t h e groups a t t a c h e d to t h e carbon atoms o f t h e double bond, but. i t a l s o undergoes R H + IC1  a s u b s t i t u t i o n r e a c t i o n w i t h hydrocarbons,. RC1  +HI  I f a time o f r e a c t i o n c o u l d be found d u r i n g which t h e a d d i t i o n r e a c t i o n was  complete, but t h e amount o f s u b s t i -  t u t i o n was n e g l i g i b l e , t h e u n s a t u r a t i o n c o u l d be found by t h i s method.  However, t h i s time would depend on the r a t e s ,  of s u b s t i t u t i o n and a d d i t i o n and f o r most polymers does not e x i s t , s i n c e the l a s t p a r t of t h e a d d i t i o n r e a c t i o n i s slow.  The o n l y way t o measure t h e u n s a t u r a t i o n a c c u r a t e l y  w i t h iodine monochloride i s t o c o r r e c t f o r s u b s t i t u t i o n .  M c l l h i n e y ' used a d e t e r m i n a t i o n , of the. amount of a c i d formed as a measure of t h e amount o f s u b s t i t u t i o n t h a t had t a k e n p l a c e . , S i n c e one mole of h y d r o h a l i c a c i d i s formed for  each mole o f i o d i n e mon.ochloride t h a t i s used i n the  s u b s t i t u t i o n r e a c t i o n , i t should  be p o s s i b l e t o f i n d the  number of moles of i o d i n e m o n o c h l o r i d e used f o r a d d i t i o n by s u b t r a c t i n g the number o f moles of a c i d formed.from the t o t a l number of moles of i o d i n e m o n o c h l o r i d e used. The polymer sample and i o d i n e m o n o c h l o r i d e were d i s s o l v e d i n o r g a n i c s o l v e n t s i n which the a d d i t i o n p r o d u c t would a l s o be s o l u b l e . The r e a c t i o n was c a r r i e d put i n a volumetric  f l a s k from which a c c u r a t e l y measured samples  were withdrawn f o r a n a l y s i s a t d i f f e r e n t i n t e r v a l s o f  time.  The samples of the r e a c t i o n m i x t u r e were added t o aqueous p o t a s s i u m i o d i d e and t i t r a t e d w i t h sodium The o r g a n i c  thiosulphate.  l a y e r was s e p a r a t e d and d i s c a r d e d , an excess o f  p o t a s s i u m i o d a t e was added t o t h e aqueous l a y e r , and the m i x t u r e was a g a i n t i t r a t e d w i t h sodium, t h i o s u l p h a t e . first  The  t i t r a t i o n g i v e s t h e amount o f i o d i n e m o n o c h l o r i d e  l e f t , and t h e second g i v e s t h e amount of a c i d , s i n c e t h e potassium, i o d a t e r e a c t s w i t h the a c i d and t h e excess o f p o t a s s i u m i o d i d e a l r e a d y p r e s e n t to form i o d i n e . KI0  3  * SKI  + GHC1  -»3I  2  +3H 0 -v 2  GKC1  Therejis a p r a c t i c a l d i f f i c u l t y a s s o c i a t e d w i t h the procedure.  Due t o t h e s l i g h t s o l u b i l i t y of the h y d r o h a l i c  a c i d s i n n o n - p o l a r s o l v e n t s , t h e r e i s a c e r t a i n l o s s of  a c i d by v o l a t i l i z a t i o n unreliable.  and t h i s makes the r e s u l t s somewhat  I n a d d i t i o n t o t h i s , i t has been shown t h a t t h e r e  i s a s p l i t t i n g out r e a c t i o n w i t h t h e a d d i t i o n p r o d u c t , which forms more a c i d .  T h i s may be e i t h e r a c y c l i z a t i o n r e a c t i o n  to- form, a six-membered r i n g o r the s p l i t t i n g out of hydrogen and h a l o g e n from a d j a c e n t carbon atoms. K o l t h o f f , Lee and M a i r s have developed a procedure w h i c h e l i m i n a t e s both o f t h e s e d i f f i c u l t i e s .  The  procedure  i s based on a d e t e r m i n a t i o n of i o d i n e i n s t e a d of a c i d i n the reaction mixture.  The a c i d formed by b o t h the s p l i t t i n g  and s u b s t i t u t i o n r e a c t i o n s  out  i s p r o b a b l y h y d r i o d i e a c i d , and  would r e a c t i n s t a n t l y w i t h the excess i o d i n e p r e s e n t to f o r m h y d r o c h l o r i c  a c i d and i o d i n e .  monochloride The  procedure  of K o l t h o f f , Lee and M a i r s i s an attempt t o measure the amount of i o d i n e formed by the s u b s t i t u t i o n m e a c t i o n a l o n e i n o r d e r to c o r r e c t the v a l u e of the u n s a t u r a t i o n f o r s u b s t i tution. Most of t h e double bonds i n a polymer r e a c t w i t h  iodine  m o n o c h l o r i d e w i t h i n a fe?; minutes and the s p l i t t i n g out r e a c t i o n t a k e s about the same t i m e .  The  substitution reaction  i s much s l o w e r and the amount o f s u b s t i t u t i o n t h a t t a k e s p l a c e i n 10 or 15 minutes i s n e g l i g i b l e . . K o l t h o f f , Lee and M a i r s determined the amount o f i o d i n e and the t o t a l amount of i o d i n e and i o d i n e m o n o c h l o r i d e i n the r e a c t i o n m i x t u r e at d i f f e r e n t i n t e r v a l s of time,and i n a d d i t i o n , they determined t h e amount of i o d i n e and the t o t a l amount of i o d i n e and i o d i n e monochloride i n a blank.  so,.  Since p r a c t i c a l l y  a l l t h e i o d i n e t h a t i s formed from,  the s p l i t t i n g out r e a c t i o n i s formed i n the f i r s t few m i n u t e s , the amount o f i o d i n e formed by t h e s u b s t i t u t i o n r e a c t i o n a t any time can be found by s u b t r a c t i n g t h e c o n c e n t r a t i o n o f i o d i n e , a f t e r 10-15 minutes present at that time.  from t h e t o t a l amount of i o d i n e  The amount o f i o d i n e m o n o c h l o r i d e  used i n t h e a d d i t i o n r e a c t i o n can t h e n be found by s u b t r a c t i n g t h e amount of s u b s t i t u t i o n from the d e c r e a s e i n the t o t a l amount o f i o d i n e and i o d i n e m o n c h l o r i d e . The r e a c t i o n s i n v o l v e d a r e : (1) S u b s t i t u t i o n "RH + I C l - * ' R C 1 + H I + K 1 -» H C l  HI  4  I  z  " R f W I C l -* H C l  i  z  (2) S p l i t t i n g o u t • C H - C H * Cl I  ->  1  or:  - C i ell.  CH-  -t- H I w  I  I  \  i  '  1  \  I  '  *  -c-c-c-c-c-c1  Hi * l e i  1  H  I  ,  I  H i  z  +  HCI  The s p l i t t i n g out r e a c t i o n does not change t h e t o t a l i o d o m e t r i c t i t r e o f t h e s o l u t i o n , but t h e s u b s t i t u t i o n r e a c t i o n d e c r e a s e s i t by 1 mole.  A =  The decrease i n t h e t o t a l  iodometric t i t r e of the  sample any t i m e a f t e r 0.5 h o u r s .  T h i s i s found,  from t h e d i f f e r e n c e between the i o d o m e t r i c t i t r e s of t h e sample and t h e b l a n k . B =  C =  The amount o f i o d i n e i n t h e sample a f t e r 10 o r 15 minutes.  T h i s r e p r e s e n t s t h e amount formed by t h e  splitting  out r e a c t i o n .  The amount of i o d i n e i n t h e sample any time a f t e r about 0.5 h o u r s . The number o f moles o f i o d i n e m o n o c h l o r i d e t h a t have  been used by t h e s u b s t i t u t i o n r e a c t i o n a t any time i s C-B, and t h e number o f moles of i o d i n e m o n o c h l o r i d e used f o r a d d i t i o n i s A-(C-B).  The q u a n t i t y A-O+B s h o u l d be i n d e -  pendent o f time and s h o u l d r e p r e s e n t t h e c o r r e c t v a l u e o f the  unsaturation.  I t has been assumed t h a t , i f  the s p l i t t -  ing  out r e a c t i o n produces more double bonds, t h e y do n o t  r e a c t f u r t h e r w i t h i o d i n e m o n o c h l o r i d e because o f t h e i n d u c t i v e e f f e c t o f the. c h l o r i n e atom, on t h e double bond, and a l s o t h a t the a c i d formed i n t h e s u b s t i t u t i o n r e a c t i o n is hydriodic  acid.  T h i s p r o c e d u r e was used on a number o f polymers and i t was r e p o r t e d t h a t t h e v a l u e s o f t h e u n s a t u r a t i o n o b t a i n e d i*rere i n d e p e n d e n t proceed.  of the time t h e r e a c t i o n was a l l o w e d t o  T h e i r r e s u l t s f o r e m u l s i o n p o l y i s o p r e n e and  n a t u r a l rubber a r e :  22 N a t u r a l rubber  fo u n s a t u r a t i o n Time (hours)  Polyisoprene  fo u n s a t u r a t i o n The  experimental  1.0  4.2  97.8  96.7  96.5  0.1  1.2  4.0  96.5  96.8  96.8  0.17  Time (hours)  p r o c e d u r e used by K o l t h o f f , Lee and  M a i r s was t o d i s s o l v e the sample i n a m i x t u r e o f c h l o r o f o r m and  carbon d i s u l f i d e i n a v o l u m e t r i c  f l a s k and add a s o l u t i o n  of i o d i n e m o n o c h l o r i d e i n carbon t e t r a c h l o r i d e . iodometric  The t o t a l  t i t r e was determined by adding a measured volume  of t h e r e a c t i o n m i x t u r e t o aqueous p o t a s s i u m i o d i d e and t i t r a t i n g with  sodium t h i o s u l p h a t e .  The method used f o r the d e t e r m i n a t i o n a l o n e was. based on a p r o c e d u r e d e s c r i b e d  of t h e iodine  by Andrews f o r t h e  q u a n t i t a t i v e e s t i m a t i o n o f i o d i d e s and i o d i n e i n aqueous solutions.  Andrews showed t h a t e i t h e r c h l o r i n e  water o r  p o t a s s i u m i o d a t e would q u a n t i t a t i v e l y o x i d i z e a s o l u t i o n of i o d i d e i o n s o r f r e e i o d i n e t o i o d i n e m o n o c h l o r i d e , i f t h e r e was p r e s e n t a l a r g e excess o f h y d r o c h l o r i c a c i d .  K10  3  +21 + C & H C 1 - ^ 3 H O + 2  z  KC1+5IC1  I n a l l . t h e experiments d e s c r i b e d  by Andrews, t h e  i o d i n e was p r e s e n t i n an aqueous s o l u t i o n and o n l y a r e l a t i v e l y s m a l l amount o f an o r g a n i c indicator.  s o l v e n t was added as an  I n the p r o c e d u r e used by K o l t h o f f , Lee and  M a i r s , a 25 ml. sample o f the c h l o r o f o r m m i x t u r e t o be a n a l y z e d  earbon d i s u l f i d e  f o r i o d i n e i s p i p e t t e d i n t o 50 m i s .  6 N h y d r o c h l o r i c a c i d and t i t r a t e d w i t h .005 M p o t a s s i u m i o d a t e to the d i s a p p e a r a n c e of t h e v i o l e t c o l o r f r o m the organic•layer.  .  II. Experimental PREPARATION OF POLYMER SAMPLES. Experiments were c a r r i e d out u s i n g samples o f s y n t h e t i c p o l y i s o p r e n e p r e p a r e d by t h r e e d i f f e r e n t methods and a l s o on n a t u r a l r u b b e r .  The s y n t h e t i c l a t i c e s were  p r e p a r e d as f o l l o w s : A•  225 m i s . HgO 4.8 gms. R.R.G. soap  0.1 gms. F S 0 e  4  0.2 gms. d o d e c y l mereaptan 6  mis . 3$ H 0 2  2  .100 gms . I o s p r e n e The soap and water were heated t o g e t h e r t o t h e b o i l i n g p o i n t and t h e s o l i d f e r r o u s s u l p h a t e was added.  The soap  and f e r r o u s s u l p h a t e s o l u t i o n was l e f t open t o t h e a i r i n . a b o t t l e f o r 24 hours and t h e n the i s o p r e n e , d o d e c y l mercaptan and hydrogen p e r o x i d e were added.  The b o t t l e was  t i g h t l y s e a l e d and r o t a t e d end over end f o r 24 hours i n a constant temperature b a t h a t 45°C. B.  180 gms. K 0 2  100 gms. i s o p r e n e 4.2 gms. R.R.C. soap 0.1 gms. F e S 0  A  1.0 gms.  NA P 0 4  g  7  0.23  gms. MTM-4 (mixed t e r t i a r y  0.17  gms. cumene h y d r o p e r o x i d e  1.0  gms. g l u c o s e  The  sodium pyrophosphate  mercaptans)  and f e r r o u s s u l p h a t e were  d i s s o l v e d i n one 10 ml. p o r t i o n o f water and t h e g l u c o s e i n another.  Both of t h e s e s o l u t i o n s were added to a c o l d  s o l u t i o n o f the soap i n the remainder o f the w a t e r . isoprene,  The  cumene h y d r o p e r o x i d e , and MTM-4 were added and  the m i x t u r e was r o t a t e d i n a c l o s e d b o t t l e a t 45°C f o r 2.5 hours. C. 200 m i s . H 0. 2  100 gms. I s o p r e n e 4.5 gms . R. R. C. s.oap 0.8 gms. The  p-tolyldiazo,p  naphthyl thio-ether  i s o p r e n e and d i a z o t h i o - e t h e r were added.to  a solu-  t i o n of the soap i n water and the m i x t u r e was p i y m e r i z e d as. above f o r 16 h o u r s . With each, of t h e s y n t h e t i c polymers and a l s o w i t h t h e n a t u r a l rubber t h e polymer was p r e c i p i t a t e d from t h e l a t e x by the a d d i t i o n of i s o p r o p y l a l c o h o l .  The p r e c i p i t a t e d  sample was. washed s e v e r a l t i m e s uvith clean, i s o p r o p y l a l c o h o l and d r i e d under vacuum, a t room temperature, i n t h e dark, f o r about 36 hours..  F i v e gram samples o f t h e d r i e d  polymer were a l l o w e d t o stand, i n 400 ml. of benzene f o r about f o u r days and any u n d i s s o l v e d  s o l i d m a t e r i a l and g e l  were f i l t e r e d o f f . The polymer was r e p r e c i p i t a t e d by a d d i n g the benzene . s o l u t i o n s l o w l y t o about 5 times i t s volume of absolute ethanol, with vigorous s t i r r i n g . ted  The r e p r e c i p i t a -  sample was f i n e l y d i v i d e d and d r i e d under l e s s t h a n  3 m.m. p r e s s u r e f o r 36 hours a t room, t e m p e r a t u r e . A l l the samples t h a t were used e i t h e r f o r t h e d e t e r m i n a t i o n of i o d i n e numbers o r 1-2 a d d i t i o n were i m m e d i a t e l y weighed out and d i s s o l v e d i n the proper s o l v e n t .  I t was no-  t i c e d t h a t i f t h e samples were a l l o w e d t o stand b e f o r e use, even under vacuum, t i i e y underwent a change i n appearance and became more d i f f i c u l t t o d i s s o l v e .  F r e s h l y p r e p a r e d samples  u s u a l l y d i s s o l v e d i n a few hours,; whereas one t h a t had been s t a n d i n g f o r a week or so would t a k e s e v e r a l days... and p e r haps not d i s s o l v e c o m p l e t e l y even t h e n . DETERMINATION OF TOTAL UNSATURATION. The procedure o f K o l t h o f f , L e e and. M a l r was a t f i r s t thought t o o f f e r t h e best method of d e t e r m i n i n g the t o t a l unsaturation.  No d i f f i c u l t y was found i n measuring  amount of i o d i n e and i o d i n e monochloride procedure  the t o t a l  t o g e t h e r but. t h e  f o r d e t e r m i n i n g the i o d i n e a l o n e was found t o te  unsatisfactory. A number o f samples were p r e p a r e d as d e s c r i b e d above and d i s s o l v e d i n 50 m i s . of- c h l o r o f o r m and 140 m i s . o f carbon d i s u l f i d e i n a 250 ml. v o l u m e t r i c f l a s k . was  c o o l e d t o 0°C and 50 m i s . o f 0.11 M i o d i n e  The s o l u t i o n monochloride  i n c h l o r o f o r m were added and t h e f l a s k was f i l l e d t o t h e  mark w i t h c h l o r o f o r m .  T w e n t y - f i v e ml. samples were p i p e t t e d  i n t o 50 m l . p o r t i o n s of h y d r o c h l o r i c a c i d and  titrated  with  .005 M potassium, i o d a t e . The  r e s u l t s obtained  i n t h i s way  of i o d i n e p r e s e n t were i n c o n s i s t e n t .  f o r the  concentration  Instead, of i n c r e a s i n g  at a f a i r l y u n i f o r m r a t e as might be e x p e c t e d , t h e a p p a r e n t concentration  of iodine increased  from one t i t r a t i o n t o the n e x t . the r a t e of s h a k i n g  e r r a t i c a l l y and even d e c r e a s e d F i n a l l y i t was  of the sample d u r i n g the  seemed to cause t h e u n u s u a l r e s u l t s . shaken r a p i d l y a p p a r e n t l y  noticed  that  titration  Samples t h a t were  took l e s s potassium iodate than  samples t h a t were shaken l e s s r a p i d l y . I t seemed p r o b a b l e t h a t t h e p o t a s s i u m i o d a t e was  being  reduced by something o t h e r t h a n i o d i n e p r e s e n t i n the aqueous phase, i f t h e r e was  no i o d i n e t h e r e , but r e a c t e d f i r s t  whatever i o d i n e was  p r e s e n t i n t h e aqueous phase.  shaking  t r a n s f e r r e d to the. aqueous l a y e r and  so d e c r e a s e  the amount of potassium, i o d a t e used up by the o t h e r  bed  Vigorous  o f t h e m i x t u r e would i n c r e a s e the r a t e at w h i c h  i o d i n e was  agent.  with  reducing  I n o r d e r to t e s t t h i s t h e o r y the experiments d e s c r i -  below were carried out. A sample of i o d i n e w e i g h i n g a p p r o x i m a t e l y 0.5  d i s s o l v e d i n 300 mis. chloroform.  of carbon d i s u l f i d e and  gms.  200 m i s .  of  Twenty ml. p o r t i o n s of t h i s s o l u t i o n were  p i p e t t e d i n t o 50 ml. p o r t i o n s o f 6 M h y d r o c h l o r i c a c i d t i t r a t e d with  was  .-005 M p o t a s s i u m i o d a t e .  and  B o t h i o d i n e mono-  28. c h l o r i d e and i o d i n e impart a y e l l o w i s h brown c o l o r t o aqueous s o l u t i o n s but i o d i n e c o l o r s the o r g a n i c l a y e r v i o l e t an3Iodine monochloride  makes i t a v e r y p a l e y e l l o w .  T h e r e f o r e , at, t h e  end p o i n t , the o r g a n i c l a y e r should change from v i o l e t t o colorless or pale yellow. throughout  The aqueous l a y e r i s l i g h t . : y e l l o w  the t i t r a t i o n .  An attempt was made t o t i t r a t e f o u r o f t h e samples w h i l e they were b e i n g given" almost the same amount of shaki n g and w h i l e t h e p o t a s s i u m i o d a t e was r u n i n a t t h e same rate.  F o r t h i s purpose a m i c r o - b u r e t t e w i t h v e r y f i n e t i p  was used, w i t h t h e s t o p c o c k f u l l y opened so t h a t t h e r a t e o f a d d i t i o n of i o d a t e depended o n l y on the s i z e o f t h e t i p , and s h o u l d be t h e same i n each t i t r a t i o n .  The samples were  shaken by hand as f a s t as was c o n v e n i e n t and a t r o u g h l y t h e same s t e a d y r a t e .  The f o u r volumes of p o t a s s i u m  used were 7.85,7.82, 7.82 and 7.83 m l .  iodate  Three other 20 m l .  samples t h a t were shaken a t a more moderate r a t e d u r i n g t h e i r t i t r a t i o n r e q u i r e d 8;>01, 8.02 and 8.07 m i s . t o r e a c h an end p o i n t , - w h i l e another sample t h a t was shaken even more s l o w l y t o o k 8.48 m l . When 7.80 m l . o f p o t a s s i u m i o date was r u n i n w i t h o u t s h a k i n g , f o l l o w e d by a v i g o r o u s s h a k i n g o f t h e m i x t u r e , the o r g a n i c l a y e r was s t i l l , b r i g h t l y c o l o r e d , and i i t t o o k more t h a n 3 m l . e x t r a , w i t h v i g o r o u s s h a k i n g , t o make i t c o l o r l e s s . In another experiment, weighing  a sample o f r e s u b l i m e d i o d i n e  .360 gms. was d i s s o l v e d i n 300 m i s . of c a r b o n  d i s u l f i d e and 200 m i s . o f c h l o r o f o r m .  I f none o f t h e i o d i n e  was l o s t by v o l a t i l i z a t i o n - t h e r e s u l t i n g s o l u t i o n would be .00283 M i n i o d i n e .  Three 25 m l . p o r t i o n s were p i p e t t e d i n t o  50 m i s . of water and', t i t r a t e d w i t h phate.  .05013 N. sodium t h i o s u l -  The volumes o f sodium t bio s u l p h a t e :  required i n the  t h r e e t i t r a t i o n s were 2.55, 2.55 and 2.58 m i s .  On the b a s i s  of t h e s e t i t r a t i o n s t h e m o l a r i t y of t h e i o d i n e s o l u t i o n was o n l y .00257, but t h i s low r e s u l t i s t o be expected because o f the v o l a t i l i t y o f the i o d i n e .  Three more 25 m l . p o r t i o n s o f  t h e i o d i n e s o l u t i o n were p i p e t t e d i n t o 50 m l . o f 6 13 h y d r o c h l o r i c a c i d and t i t r a t e d w i t h .004=95 EE p o t a s s i u m i o d a t e t o t h e d i s a p p e a r n a c e of t h e v i o l e t c o l o r from t h e o r g a n i c l a y e r . The  samples were shaken v i g o r o u s l y t h r o u g h o u t t h e t i t r a t i o n ,  and  the p o t a s s i u m i o d a t e was added a t a p p r o x i m a t e l y the same  r a t e i n each ease.  The t h r e e volumes r e q u i r e d were 9.88,  9.82 and 9.92 m i s . U s i n g 9.87 as an average, t h e apparent m o l a r i t y o f t h e i o d i n e s o l u t i o n i s .00396. I t appeared t h a t i f t h e s o l u t i o n s were shaken,at t h e same s t e a d y r a t e d u r i n g the a d d i t i o n of t h e p o t a s s i u m iodate-; t h e apparent . c o n c e n t r a t i o n s  of i o d i n e found i n s u c c e s s i v e  t i o n s were r e a s o n a b l y p r e c i s e , but were not a c c u r a t e . the experiment d e s c r i b e d  In  above, i n w h i c h t h e m o l a r i t y o f an  i o d i n e s o l u t i o n was determined both by t i t r a t i o n . w i t h t h i o s u l p h a t e and w i t h p o t a s s i u m i o d a t e , t h e v a l u e concentration  titra-  of iodine,obtained  i s 54$ h i g h e r t h a n that o b t a i n e d  sodium  f o r the  with the iodate t i t r a t i o n , with the thiosulphate  titra-  tioiu  The  v a l u e o b t a i n e d w i t h the. t h i o s u l p h a t e t i t r a t i o n i s  i n reasonable  agreement w i t h t h a t c a l c u l a t e d from the weight-  of the sample of i o d i n e , s i n c e i t i s a l i t t l e l o w e r ,  but  t h a t c a l c u l a t e d from the i o d a t e t i t r a t i o n i s c o n s i d e r a b l y h i g h e r than the weight of the sample would i n d i c a t e , and t h e r e f o r e i t cannot be c o r r e c t . I n o r d e r t o t e s t f o r the p o s s i b i l i t y  of o x i d a t i o n of  the h y d r o c h l o r i c a c i d i t s e l f , 10 ml. p o r t i o n s o f a  standard  s o l u t i o n of p o t a s s i u m i o d a t e were p i p e t t e d i n t o 50 m l . 6N h y d r o c h l o r i c a c i d and a l l o w e d to stand f o r v a r i o u s of t i m e . a c i d was  A t the end  of the chosen t i m e , the  n e u t r a l i z e d w i t h sodium h y d r o x i d e ,  room t e m p e r a t u r e .  of lengths.,  hydrochloric and  cooled  to  To t e s t f o r t h e amount of o x i d i z i n g  agent l e f t i n the s o l u t i o n , 3 ml. of 2N s u l p h u r i c a c i d  and  10 ml. of 10$ p o t a s s i u m i o d i d e s o l u t i o n were added and  the  l i b e r a t e d i o d i n e was sulphate. was  added.  t i t r a t e d w i t h standard  Near the end p o i n t 2 m l . o f lf  0  sodium t h i o -  starch solution  The m o l a r i t y of the p o t a s s i u m i o d a t e  was  .00495 and  t h a t of the sodium t h i o s u l p h a t e was  .05013 M  Therefore,  i f none of the o x i d i z i n g agent had been used  the t h i o s u l p h a t e t i t r a t i o n should have taken 5.93 The  r e s u l t s are shov/n i n t a b l e  1.  ml.'  up  TABLE 1 Test f o r O x i d a t i o n o f H y d r o c h l o r i c  Acid  Volume o f NAgSgQ  Time  3  <?o o f K I 0  left  3  0.5 m i n .  5.55  93.7  5.0 m i n .  5.31  89.6  10.0 min.  5.12  86.3  15.0 min.  4.95  83.5  T h i s sho?/s t h a t i t i s t h e o x i d a t i o n o f t h e h y d r o c h l o r i c a c i d by p o t a s s i u m i o d a t e t h a t i n t e r f e r e s w i t h t.he r e a c t i o n . S i n c e e e r i e ammonium s u l p h a t e w i l l o x i d i z e i o d i n e t o i i o d i n e monochloride i n 6 N. h y d r o c h l o r i c a c i d , but w i l l not o x i d i z e the h y d r o c h l o r i c a c i d i t s e l f , i t was t r i e d i n p l a c e o f t h e potassium iodate. A .02055 N s o l u t i o n o f e e r i e ammonium- s u l p h a t e p r e p a r e d and s t a n d a r d i z e d  against arsenious  was  anhydride.  A n o t h e r s o l u t i o n of i o d i n e i n 60$ carbon d i s u l f i d e and 40$ chloroform  was made up and t i t r a t e d w i t h s t a n d a r d  thiosulphate,as  sodium  b e f o r e , t o determine i t s o a n c e n t r a t i o n .  T w e n t y - f i v e . m l . p o r t i o n s o f the i o d i n e s o l u t i o n were p i p e t t e d i n t o 50 m l . volumes o f 6N. h y d r o c h l o r i c a c i d and t i t r a t e d with the standard  e e r i e ammonium s u l p h a t e .  The o r g a n i c  l a y e r undergoes a g r a d u a l t r a n s i t i o n from v i o l e t , t h r o u g h red and orange to y e l l o w .  A t what should  have been the end  32. point  t h e o r g a n i c l a y e r was s t i l l  d i s t i n c t l y orange and a t  no time was t h e r e a sharp, c o l o r change.  The t i t r a t i o n s , were  r e p e a t e d u s i n g 2 drops o f f e r r o i n as an i n d i c a t o r ; but the and p o i n t was s t i l l not d i s t i n c t , the e q u i v a l e n c e  A t what was a p p r o x i m a t e l y  p o i n t the aqueous l a y e r t u r n e d a p a l e  i s h b l u e c o l o r , but t h e change was n e i t h e r d i s t i n c t  green-  nor per-  manen t . A second change i n t h e p r o c e d u r e t h a t was M e d , i n t h e hope t h a t I t might g i v e a c o r r e c t v a l u e of i o d i n e p r e s e n t ,  f o r the concentration  was t h e s u b s t i t u t i o n o f a m i x t u r e of 25  ml. o f e t h a n o l and 25 m l . of• 12 N h y d r o c h l o r i c a c i d f o r t h e 50 m l . of 6H h y d r o c h l o r i c a c i d .  I t was thought t h a t t h e  e t h a n o l might i n c r e a s e t h e s o l u b i l i t y , and t h e r e f o r e t h e conc e n t r a t i o n , o f t h e i o d i n e i n t h e aqueous phase, so that t h e i o d i n e would be. o x i d i z e d i n s t e a d o f t h e h y d r o c h l o r i c a c i d . T w e n t y - f i v e m l . samples o f a .00334 M s o l u t i o n of i o d i n e i n carbon, d i s u l f i d e and c h l o r o f o r m  were added t o 50  m l . of 6N h y d r o c h l o r i c a c i d and t i t r a t e d w i t h assium i o d a t e .  .00495 M. p o t -  Two samples t o o k 11.38 and 11.54 m l .  Two  o t h e r samples t h a t were t i t r a t e d i n t h e m i x t u r e of e t h a n o l aid  12N h y d r o c h l o r i c a c i d t o o k 11.00 and 11.14 m l . o f the  same p o t a s s i u m i o d a t e .  I n the f i r s t case t h e average c a l c u -  l a t e d m o l a r i t y i s .00455 and i n t h e seoond i t is: .00438. The  use of the e t h a n o l seems t o make a small.improvement,  but the r e s u l t i s s t i l l The  f a r from c o r r e c t .  method o f Kemp and P e t e r s f o r d e t e r m i n i n g  unsatura-  t i o n w i t h o u t any c o r r e c t i o n f o r s u b s t i t u t i o n , was  tried in  the hope t h a t i t might be used t o compare the u n s a t u r a t i o n i n t h e d i f f e r e n t t y p e s o f polymers used i n the a n a l y s i s f o r 1-2 a d d i t i o n .  I t d i d not seem l i k e l y t h a t the d i f f e r e n t ,  t y p e s of p o l y i s o p r e n e i n samples A, B and C would have v e r y d i f f e r e n t r a t e s of a d d i t i o n o r s u b s t i t u t i o n , soi t h a t i f the v a l u e of the u n s a t u r a t i o n was found t o be independent o f the time o f the r e a c t i o n f o r even a short t i m e i t c o u l d be used. Samples o f p o l y i s o p r e n e w e i g h i n g .227 gms. w i t h 113.5 gms.  were h e a t e d  of p a r a d l c h l o r o b e n z e n e to 150°C. i n a 250 ml  v o l u m e t r i c f l a s k u n t i l the sample d i s s o l v e d .  Enough c a r b o n  d i s u l f i d e was added t o keep the s o l v e n t from c r y s t a l l i z i n g and when the m i x t u r e was c o o l 50 m l . of 0.11 M i o d i n e monoc h l o r i d e i n carbon t e t r a c h l o r i d e was added and the f l a s k f i l l e d to the mark w i t h carbon d i s u l f i d e . were c a r r i e d out a t 25°C.  The  reactions  Twenty m l . samples were t i t r a t e d  f o r i o d i n e m o n o c h l o r i d e a t d i f f e r e n t i n t e r v a l s of time u s i n g .05013 N sodium t h i o s u l p h a t e . .•The r e s u l t s acre shown i n T a b l e s  A b l a n k t o o k 17.05  2-5.  V = volume o f sodium t h i o s u l p h a t e used f o r back % u n s a t u r a t i o n - (17.05-V)  .05015(68.11) .227  = .94-0 (17.05-V)  ml.  5 T  titration.  34. TABLE 2 R e a c t i o n o f N a t u r a l Rubber w i t h Iodine Monochloride  Time (hrs.)  V  17.05-V  fo U n s a t u r a t i o n  0.33  6.77  10.28  96.5  0,67  6.70  10.35  97.2  1.16  6.67  10.38  97.5  2.00  6.56  10.49  98.6  3.75  6.37  10.68  100.3  5.25  6.15  10.90  102.5  6.83  5.97  11.08;  104.0  18.00  5.60  11.45  107.5  29.00  5.34  11.71  110.0  TABLE 3 R e a c t i o n of Sample A with  Time(hrs.)  V  Iodine. Monochloride.  17.05-V  fo U n s a t u r a t i o n  0.5  6.90  10.15  95.3  1.0  6.83  10.22  96.0 ,  2.0  6.60  10.45  98.2  4.0  6.20  10.85  102.0  10.0  5.66  11.39  107.0  24.0  5.40  11.65  109.5  35. TABLE 4 R e a c t i o n o f Sample B with Iodine  17.05-V  T i k e (hrs  Monochloride.  %  Unsaturation  0.5  6.86  10.19  95.7  1.0  6.80  10.25  96.4  2.0  6.57  10.48  98.6  5.0  6.18  10.87  102.2  9.5  5.62  11.43  107.7  24.0  5.35  11.70  - 110.0  TABLE 5 R e a c t i o n o f Sample C with  Time ( h r s . )  Iodine Monochloride  v  17.05V  0.75  7.03  10.02  94.2  1.50  6.89  10.16  95.5  3.25  6.55  10.50  98.7  5.00  6.34  10.71  .100.7  5.83  11.17  105.0  5.47  11.58  108.9  12.00 24.25  :  %  Unsaturation  S i n c e there was no reason f o r choosing the v a l u e o f the u n s a t u r a t i o n a t any a r b i t r a r y time as being these r e s u l t s could not be used.  correct,  36. One o t h e r method was t r i e d f o r the d e t e r m i n a t i o n o f t h e t o t a l u n s a t u r a t i o n . T h i s was the use o f p e r b e n z o i c a c i d a t 25°C.  I t was thought t h a t i f l a r g e excesses of p e r b e n z o i c ,  a c i d Yiexe a l l o w e d t o r e a c t w i t h the polymer a t 25°C, t h e r e a c t i o n might be complete i n a s h o r t enough time t o be usef u l f o r measuring t h e t o t a l u n s a t u r a t i o n . Samples of polymer A weighing  .6811 gms. were d i s s o l v e d i n chloroform, i n 500 m l .  volumetric f l a s k s .  The r e q u i r e d amount of p e r b e n z o i c a c i d  i n benzene was added and t h e f l a s k was h e l d a t a of 25°C.  Samples were withdrawn  temperature  a t d i f f e r e n t i n t e r v a l s of  time and a n a l y z e d i o d o m e t r i c a l l y f o r u n r e a c t e d p e r b e n z o i c acid. To measure t h e s t a b i l i t y o f t h e p e r b e n z o i c a c i d  solu-  t i o n s a t t h i s temperature, b l a n k s were p r e p a r e d and a n a l y z e d at p e r i o d s up t o 75 hours.  The r e s u l t s / o f t h e t i t r a t i o n s on  the b l a n k s , a r e shown in. Table  6.  TABLE 6 D e c o m p o s i t i o n o f .01, .02 and .05 M P e r b e n z o i c Acid, a t 25°C  Time ( h r s . )  Concentration of Perbenzoic A c i d .  0.0 h r s .  .01000  .02000  .03000  2.0  .01000  .01996  .02995  4.0  .01000  .01996  .02995  8.0  .01000  .01996  .02995  12.0  .01000  .01996  .02990  25.0  .00998  .01990  .02985  48.0  .00999  .01984  .02981  72.0  .00997  .01978  .02970  37, Tables  7 and 8 show the r a t e s o f o x i d a t i o n of a s o l u t i o n  .02 M i n sample A by 50 and 100$ e x c e s s e s of p e r b e n z o i c  acid  at 25°C. TABLE 7 R e a c t i o n o f Sample A w i t h 100$ excess P e r b e n z o i c  Time (hrs..)  A c i d a t 35°G  f Double Bonds O x i d i z e d 0  95.6  2  96.1 10  96.4  24  96.8  50  97.4  75  98.4  TABLE 8 R e a c t i o n o f Sample A w i t h 50$ Excess P e r b e n z o i c  Time ( h r s . ) 3  93.8  8  94.3.  13  '94.5  24  95.2  48. '  ' fo Double Bonds O x i d i z e d  72  '  96.4 97.7  A c i d at 25°C  38. From the above t a b l e s i t can be seen t h a t even w i t h 100$ excess of p e r b e n z o i c  a c i d a t 25°C. the r e a c t i o n w i t h the e x -  t e r n a l double bonds i s much too slow t o be o f p r a c t i c a l use i n a quantitative determination. DETERMINATION OF THE AMOUNT OF 1-3 ADDITION. S i n c e i t seems t o be i m p o s s i b l e t o o b t a i n a r e l i a b l e  value  f o r the p e r c e n t a g e u n s a t u r d t i o n of. a polymer, i t was d e c i d e d t o assume 100$ u n s a t u r a t i o n . f o r t h e purpose.-- of d e t e r m i n i n g the amount o f 1-3 a d d i t i o n .  This approximation  is. p r o b a b l y  not more than one or two p e r c e n t , out and i s s i m i l a r t o one made by S a f f e r and Johnson. The and Lee.  experimental!, p r o c e d u r e f o l l o w e d was t h a t o f K o l t h o f f The r e a c t i o n was . c a r r i e d out i n a v o l u m e t r i c  flask  i n an i c e h a t h w h i c h was k e p t r a p i d l y s t i r r e d t o ensure t h a t a l l the water was a t 0°C. The c o n c e n t r a t i o n s o f double bonds and. p e r b e n z o i c  a c i d were .02 and .03 M r e s p e c t i v e l y ' .  The  polymer samples were d i s s o l v e d i n c h l o r o f o r m and c o o l e d t o 0°G.  The amount o f p e r b e n z o i c  a c i d i n benzene•necessary t o .  make the f i n a l volume .03M was added a l o n g w i t h enough benzene to ndce the s o l v e n t 10$ benzene, and then the f l a s k was f i l l e d to the mark w i t h c o l d c h l o r o f o r m .  The e x t r a benzene was  added so t h a t i n each r e a c t i o n m i x t u r e the s o l v e n t would be the same.  A l l the c h l o r o f o r m used as a s o l v e n t had been  washed t h r e e times w i t h h a l f i t s volume o f water, and d r i e d over anhydrous sodium s u l p h a t e .  39. P r e p a r a t i o n o f P e r b e n z o i c Acid:.. The method o f Braun' w i t h a few m o d i f i c a t i o n s , ?ras used. Sodium m e t h y l a t e , p r e p a r e d by the a d d i t i o n of 5.2 sodium'to 100 m i s . of a b s o l u t e m e t h a n o l , was w i t h 50 gms. The  gms.  of  allowed to r e a c t  of b e n z o y l p e r o x i d e i n 200 mis. of c h l o r o f o r m . ;  b e n z o y l p s r o x i d e was  added a t such a r a t e t h a t the tem-  p e r a t u r e of the r e a c t i o n m i x t u r e s t a y e d at about -5°C. the a d d i t i o n of the b e n z o y l p e r o x i d e was t u r e was  complete,  the m i x -  t r a n s f e r r e d to. a s e p a r a t o r y f u n n e l w i t h 500 m l . of  . chopped i c e and water and the c h l o r o f o r m l a y e r was The aqueous l a y e r was  discarded..  washed t h r e e times w i t h 100 m l . p o r t i o n s ;  of c h l o r o f o r m to remove the m e t h y l benzoate and t h e n w i t h 225 m l . of IN s u l f u r i c a c i d . a c i d was  When  The p r e c i p i t a t e d  acidifiedperbenzoic  e x t r a c t e d w i t h t h r e e 100 m l . p o r t i o n s o f benzene and  d r i e d over anhydrous sodium s u l p h a t e . p e r b e n z o i c a c i d was  The  s t o c k s o l u t i o n , of  s t o r e d i n a r e f r i g e r a t o r a t jus.t above  the f r e e z i n g p o i n t of the m i x t u r e . The  benzene s o l u t i o n was  i n t o a f l a s k c o n t a i n i n g 1 gm.  s t a n d a r d i z e d by p i p e t t i n g 5 m l . of p o t a s s i u m i o d i d e and 50  mis.  of 0.4N. a c e t i c a c i d and t i t r a t i n g the l i b e r a t e d i o d i n e w i t h s t a n d a r d sodium t h i o s u l p h a t e .  The amount o f stock, s o l u t i o n  n e c e s s a r y to make the r e a c t i o n m i x t u r e a b u r e t t e w i t h no grease on the  .03M  was measured from,  stopcock.  T i t r a t i o n of Samples. The  r e a c t i o n m i x t u r e was  analyzed f o r perbenzoic  a t d i f f e r e n t i n t e r v a l s o f time up t o about 50 hours.  acid Twenty  m l . samples were withdrawn f r o m the v o l u m e t r i c f l a s k w i t h a  p i p e t t e and  placed  in50 ml. o f 0.4  i n a s o l u t i o n o f 1 gm.  N acetic acid.  t i t r a t e d w i t h N/20  The  of p o t a s s i u m i o d i d e  i o d i n e formed was  sodium t h i o s u l p h a t e .  Ten  ml.  then  burettes  graduated i n f i f t i e t h s were used. The  a d d i t i o n of 2 mis. of a 1$ s o l u t i o n of s t a r c h near  the end p o i n t made the c o l o r change much more d i s t i n c t ,  and  the r e s u l t s more r e p r o d u c i b l e , but the s t a r e h s o l u t i o n decomposed so r a p i d l y t h a t a f t e r a few hours i t di anged t h e p o i n t by s e v e r a l hundredths of a ml.  A s t a r c h s o l u t i o n made  by d i s s o l v i n g 1 gm.  of s t a r c h i n 200  served with  of s a l i c y l i c a c i d was  ,0.5 gm.  better r e s u l t s .  end  ml. of water and  pre-  found t o g i v e much  To t e s t t h e p r e c i s i o n o f the t i t r a t i o n . : f o u r  samples of a r e a c t i o n m i x t u r e were . - t i t r a t e d .'-using the a r y s t a r c h s o l u t i o n and  f o u r more were t i t r a t e d u s i n g  preserved starch s o l u t i o n .  The  ordinary  s t a r c h , and 8.78Q, 8.780, 8.785 and 8.780 w i t h the  were r e p r o d u c i b l e  T h i s showed t h a t t h e  t o w i t h i n one  the  volumes of sodium t h i o s u l p h a t  used were 8.785, 8.780, 8.775 and 8.780 w i t h t h e  containing s a l i c y l i c acid.  ordin-  starch  titrations  one-hundredth of a m l .  and  t h a t the s a l i c y l i c a c i d d i d not i n t e r f e r e . When no i n d i c a t o r was  used,different  samples of the same  r e a c t i o n m i x t u r e sometimes t o o k amounts of sodium t h i o s u l phate d i f f e r i n g by 2 or 3 one-hundredths of a  ml.  O c c a s i o n a l l y , d u r i n g a t i t r a t i o n , a t h i c k e m u l s i o n formed and at t h e end p o i n t t h e r e were d r o p l e t s of s o l v e n t i n g u n r e a c t e d i o d i n e suspended i n i t .  The  formation  e m u l s i o n c o u l d be p r e v e n t e d by the a d d i t i o n of 10-15  containof  the  ml.  of  a l c o h o l and even,-after i t had s t a r t e d t o form, t h e a d d i t i o n of a l c o h o l removed i t .  However, w i t h a l c o h o l present,. t h e  c o l o r a t t h e end p o i n t changed from l i g h t b r o w n i s h y e l l o w to c o l o r l e s s and was not n e a r l y so sharp as when none was present. form  F o r t h i s reason, whenever an emulsion, s t a r t e d t o  the, sample was d i s c a r d e d and a new one t i t r a t e d w i t h -  out so' much shaking,-, r a t h e r than j u s t a d d i n g a l c o h o l . Decomposition o f P e r b e n z o i c A c i d a t 0°G. S o l u t i o n s t h a t were made up i n the same way as t h e r e a c t i o n m i x t u r e except t h a t they c o n t a i n e d no polymer and had- d i f f e r e n t c o n c e n t r a t i o n s o f p e r b e n z o i c a c i d , were kept at 0°G and a n a l y z e d f o r p e r b e n z o i c a c i d a t p e r i o d s o f t i m e up t o 100 h o u r s .  T w e n t y - f i v e m l . samples were withdrawn  and t i t r a t e d i o d o m e t r i c a l l y as d e s c r i b e d above, u s i n g .05066. N. sodium t h i o s u l p h a t e .  The r e s u l t s f o r s o l u t i o n s  t h a t were .01, .02 and .03 M i n p e r b e n z o i c a c i d a r e t a b u l a t e d i n Table 9. From t h e - r e s u l t s i n Table 9 i t was concluded t h a t no c o r r e c t i o n f o r t h e d e c o m p o s i t i o n o f p e r b e n z o i c a c i d at 0°C was n e c e s s a r y .  42. TABLE 9 D e c o m p o s i t i o n of P e r b e n z o i c A c i d a t 0°G  Time  Volume o f N A S 0 g  g  3  used t o T i t r a t e t h e B l a n k  .01 M  .02 M  " .-03 M •  0.00  9.89  19.78  29.65  2.50  9.88  19.78  29.64  6.50  9.88  19.79  29.64  .20.50  9.87  19.78  29.65  28.00  9.88  19.78  29.65  40.00  9.88  19.79  29.65  70.00  9.88  19.79  29.64  100.00  9.88  19.79  29.65  R e s u l t s of T i t r a t i o n s f o r Natural; Rubber. For purposes o f comparing d i f f e r e n t samples o f s y n t h e t i c p o l y i s o p r e n e w i t h n a t u r a l r u b b e r , a d e t e r m i n a t i o n o f the amount of 1-2 a d d i t i o n i n n a t u r a l r u b b e r was made.  The sample  of rubber was p r e p a r e d from the. l a t e x i n t h e way d e s c r i b e d p r e viously.  Assuming 100$ U n s a t u r a t i o n , t h e weight o f r u b b e r  n e c e s s a r y t o mfeke 500 m l . of a s o l u t i o n .021'! i n double bonds i s . 0 2 ( 6 8 . l l ) / 2 o r .6811 gms.  S i n c e the double bonds r e a c t e d  c o m p l e t e l y i n a r e l a t i v e l y s h o r t time and t h e n no more p e r b e n z o i c a c i d was used up, i t was concluded t h a t no e x t e r n a l double bonds were p r e s e n t .  I f this i s so, the r e a c t i o n should  be a s i m p l e second o r d e r r e a c t i o n obeying the u s u a l e q u a t i o n .  43,  k U  1 P-A  In  ^- > P tA-X) A  X  3C=RA I  1.  P-A.  P-RA P ( i - R )  R = f r a c t i o n o f d o u b l e bonds o x i d i z e d X  = c o n c e n t r a t i o n of p e r b e n z o i c  a c i d used up  P  = initial  concentration o f perbenzoic  A  •= i n i t i a l  c o n c e n t r a t i o n of, double bonds-  acid  Twenty m l . samples were t i t r a t e d w i t h .05066 N sodium thiosulphate.  The r e s u l t s o f the t i t r a t i o n s a r e shown i n  Table 10, and i n f i g u r e 2, l o g (P-RA)/P(1-R) i s p l o t t e d against V  time.  = volume of sodium t h i o s u l p h a t e used f o r t h e back t i t r a t i o n ,  TABLE 10 R e a c t i o n of N a t u r a l Rubber w i t h P e r b e n z o i c  Time  V  R  Acid  P-RA. log P(l-RJ  k .  1.25 .hr.  9.52 m l . 0 .8974  0.5927  109,0 l . m ^ f t r T  2.08  8.56  s0 .0882  0.9366  103.7  3.42  8.10  0 .9873  1.430  96.3  4.25  7.98  0.9948  1.811  98.0  15.00  7.90  1.000  23.42  7,. 89  1,001  27.25  7.89  1.001  39.00  7.89  1.001  47.00  7.89  1.001  1  As a sample c a l c u l a t i o n , t h a t f o r t h e t i t r a t i o n a t 1.25 h r . w i l l be done."  S i n c e the sodium t h i o s u l p h a t e used was  .05066 M., a 20 m l . sample of. .03 M p e r b e n z o i c a c i d would be e q u i v a l e n t t o 20 (.03)2/.05066 o r 23.69 m l . o f sodium t h i o sulphate.  The amount o f t h i o s u l p h a t e t h a t was used was  t h e r e f o r e 23.69-7 and the f r a c t i o n of the d o u b l e bonds o x i d i z e d was  (23.69- 9,52)/15.79 o r .8974, s i n c e 20 m4. of .02M  double bonds .would be e q u i v a l e n t t o 15.79 m l . of. sodium thiosulphate.  The r a t e c o n s t a n t k was found by s u b s t i t u t i n g  this  v a l u e o f H i n t o k ,= £_i2°3 1ry> P-RA \  A  O  : 0 3 - . o i 7 Q g  G  =  .03(.iozt)  .OI(I.ZS)  [o9  1^."'  The, v a l u e o f k was a l s o c a l c u l a t e d from f i g u r e 2 from, t h e r e l a t i o n between k and t h e s l o p e o f ' t h e l i n e .  <  P-RA k  =  2  '  3  °  P('r-H>  A  3  P-A s  2.303 .01  £>t  2  4.t7  s  .l.Tn". k r . ' 1  R e s u l t s of T i t r a t i o n s f o r • S y n t h e t i c P o l y i s o p r e n e ; Two samples :of .polymer A and one each o f B and G were  :  a n a l y z e d i n t h e same way d e s c r i b e d above f o r n a t u r a l r u b b e r . For  each t y p e o f polymer a p l o t of l o g  was made and  used t o c a l c u l a t e the r a t e c o n s t a n t f o r t h e e x t e r n a l d o u b l e bonds and t h e p e r c e n t a g e o f 1-2 a d d i t i o n . The r a t e c o n s t a n t f o r t h e r e a c t i o n o f the i n t e r n a l double bonds, k ,was c a l c u l a t e d f r o m d a t a o b t a i n e d d u r i n g 1  the  f i r s t t h r e e hours o f t h e r e a c t i o n .  The r e a c t i o n o f  the  e x t e r n a l double bonds i n t h i s time was n e g l e c t e d and, u s i n g  the  simple second order r a t e e q u a t i o n j l w a s c a l c u l a t e d s e p a r -  a t e l y f o r each sample of the r e a c t i o n mixture t i t r a t e d .  The  form of the second order r a t e equation used i s : v  *i  -  i  ~  m  (P-I)t  HP-*)  p  ( I  _ ) X  X = the c o n c e n t r a t i o n o f i n t e r n a l double bonds o x i d i z e d . Since t h i s equation i s used o n l y f o r p e r i o d s of time d u r i n g which a n e g l i g i b l e amount o f e x t e r n a l double bonds have r e a c t e d t h i s may of  be taken as equal to the t o t a l  double bonds o x i d i z e d , i . e . , X ~  A = total i n i t i a l  concentration  HA,  c o n c e n t r a t i o n of double bonds.  R = f r a c t i o n of double bonds o x i d i z e d . I = initial  c o n c e n t r a t i o n o f i n t e r n a l double bonds.  This q u a n t i t y i s o b t a i n e d d i r e c t l y from the graph of  log  t^k A(l-R)*  The data f o r the t i t r a t i o n s and c a l c u l a t i o n s of the amount of.1-2 a d d i t i o n f o r the two  samples  of polymer A  ( c a t a l y z e d by bydrogen p e r o x i d e and f e r r o u s s u l p h a t e ) are t a b u l a t e d i n t a b l e s 11 and 12 and the data f o r the c a l c u l a t i o n of the r a t e constant f o r the i n t e r n a l double bonds for  both samples  i s combined  i n t a b l e 13.  I n a l l the f o l l o w -  ing  t a b l e s Y i s - t h e volume of .05066 N sodium t h i o s u l p h a t e .  used i n the t i t r a t i o n of a twenty ml. sample of the r e a c t i o n mixture.  46. TABLE 11. R e a c t i o n of Polymer A (sample 1) with P e r b e n z o i c A c i d .  t  (hrs.)  Y  R  RA  Log. -=^A-RA P  0.25  14.22  .5997  .01199  0.75  12.51  .8069  .01614  1.33  10.39  .8423  .01685  2.75  9 .83  .8780  .01756  4.83  9.66  .8885  .01777  .7391  5.42  9.65  .8891  .01778  .7411  7.00  9.61  .8917  .01783  .7496  8.50  9.59  .8930  .01786  .7538  10.00  9 .57  .8942  .01788  .7580  12.08  9.57  .8942  .01788  .7580  21.25  9.46  .9012  .01802  .7827  24.83  9.44  .9025  .01805  .7874  26.00  9.42  .9037  .01807  .7920  31.00  9.36  .9075  .01815  .8066  47.42  9.22  .9165  .01733  .8443  A  TABLE 12. R e a c t i o n o f Polymer A (sample 2) w i t h P e r b e n z o i c A c i d .  log, P-RA A-RA  RA  V  R  0.50  11.94  .7442  .01488  1.58  10.22  .8531  .01706  3.42  9.73  .8842  .01768  .7259  4.75  9.64  .8898.  .01780  .7432  6.83  9.62  .8910  .01782  .7472  12.16  9.56  .8949  .01790  .7602  14.00  9.55  .8955  .01791  .7622  21.25  9.45  .9018  .01804  .7846  26.00  9.41  .9044  .01809  .7944  34.00  9.36  .9075  .01815  .8066  50.00  9.20  .9178  .01836  .8500  t (hrs.)  The v a l u e s o f t h e term l o g £ z M . A-RA  f o r samples 1 and 2  o f polymer A a r e p l o t t e d t o g e t h e r i n f i g u r e 3.  The s t r a i g h t  l i n e c u t s t h e a x i s r e p r e s e n t i n g t=o a t .733 and t h e v a l u e o f I , t h e i n i t i a l c o n c e n t r a t i o n o f d o u b l e bonds, i s c a l c u l a t e d from t h i s i n t e r c e p t . A-I l o g P-RA log p_j A-RA t- o =  £zl A-I  = a n t i l o g .733  T 1  - .733  -  5.41 A-P 5.41-1  =  0  1  •  = ? U  5.41  7 1  /  /  Therefore the percentage  of the double bonds that a r e  formed by 1-4 a d d i t i o n i s 100 »  0 1 7 7  =88.5 and the p e r c e n t -  .08 age of v i n y l groups is- 11.5. The  value of the r a t e constant f o r the r e a c t i o n o f the  e x t e r n a l double  bonds with perbenzoic a c i d i s found from the  slope of the l i n e through the r e l a t i o n log P-A  ^ t -1  m  2.505  .100  .01'  43.0  =  -1  0.535 l.m. h r .  TABLE 15.. Data f o r C a l c u l a t i o n of k j f o r Polymer A.  t  Cnrs.J  PA  l  n  pTi^Riy^  k^l.m^hrT ) 1  0.25  .01199  .62  202  0C50  .01488  1.15  187  0.75  .01614  1.66  180  1.33  .01685  2.21  135  1.58 *  .01706  2.48  128  2.75  .01756  3.96  117'  The  two v a l u e s of t marked w i t h an a s t e r i s k i n t a b l e 13  are f o r sample 2 and the remainder a r e f o r sample 1. that the apparent  The f a c t  value of the r a t e constant v a r i e s w i t h  w i l l be d i s c u s s e d i n the next  section.  time  The e x p e r i m e n t a l d a t a f o r t h e r e a c t i o n o f polymers B and C with perbenzoic a c i d i s tabulated the v a l u e s o f l o g " A-RA P  pectively.  R A  i n t a b l e s 14 and 16 an.d  a r e p l o t t e d i n f i g u r e s 4 and 5 r e s -  T a b l e s 15 and 17 c o n t a i n t h e d a t a f o r t h e c a l c u l a  t i o n of t h e r a t e c o n s t a n t s f o r t h e i n t e r n a l d o u b l e bonds i n polymers B and C r e s p e c t i v e l y . TABLE 14. Reaction.of.  t  (hrs.)  r  Polymer B w i t h P e r b e n z o i c A c i d .  V  R  RA  log &  A-RA  0.92  11.41  .7774  .01555  1.83  10.51  .8347  .01669  3.17  10.26  .8505  .01701  4.08  10.18,  .8556  .01711  .6497  14.68  9.99  .8676  .01735  .6792  23.08  9.88,  .8746  .01749  .6980  27.08  9.86  .8759  .01752  .7015  38.67  9.79  .8803  .01761  .7140  47.00  9.71  .8854  .01771  .7293  From f i g u r e 4 the  i n t e r c e p t of t h e l i n e i s  .659 and by  means of a c a l c u l a t i o n s i m i l a r t o t h a t done f o r polymer A the p e r c e n t a g e o f v i n y l groups i s found t o be 14.0. From the s l o p e o f t h e l i n e t h e r a t e c o n s t a n t f o r t h e o x i d a t i o n of t h e e x t e r n a l double bonds i s .337 l.mT^-hrT  1  TABLE 15. Data f o r C a l c u l a t i o n o f k  t  (hrs.)  AR  T  f o r Polymer B.  in ^P-^) P(I-RA)  .92  .01555  1.61  1.83  .01669  2.71  3.17  .01701  3.67  k 1  (l.mT^-hrl ) 1  T  137.0 '  116.0 90.4  TABLE 16. R e a c t i o n of Polymer C w i t h Perbenzoic  t  (hrs.)  V  R  RA  Acid.  log  £=£L A-RA  1.08  10.68  .8239  .01648  2.00  9.97  .8689  .01738  3225  9.66  .8885  .01777  4.17  9.60  .8,923  .01785  .7515  14.83  9.42  .9037  .01807  .7919  23.42  9.33  .9095  .01819  .8146  27.17  9.29  .9120  .01824  .8249  38.83  9.20  .9178  .01836  .8502  47.08  9.14  .9214  .01843  .8669  51; From f i g u r e 5 the amount o f 1-8 a d d i t i o n i n polymer C i s 10.5$ and the r a t e constant f o r the r e a c t i o n of the ex-1 -1 t e r n a l double bonds w i t h perbenzoic acid, i s .530 l.m. h r . TABLE 17. Data f o r C a l c u l a t i o n of k j f o r Polymer C.  t  (hrsi  -1 k j ( l . m . hr7  AR  1.08  .01648  1.74  133  2.00  .01738  2.67  110  3.25  .01777  4.05  102  I I I . DISCUSSION. OF RESULTS. D e t e r m i n a t i o n o f t h e P e r c e n t a g e o f V i n y l Groups. I n o r d e r t h a t t h e method o f c a l c u l a t i o n be u s e f u l , i t i s n e c e s s a r y t h a t each t i t r a t i o n have an e r r o r o f n o t more than 1/100 o f a m l . S i n c e s u c c e s s i v e of' l o g few  A-RA  p o i n t s on t h e graphs  versus time depend on d i f f e r e n c e s o f o n l y a  one-hundredths of a m l . an e r r o r o f more than 1/100 m l .  i n many o f the t i t r a t i o n s would make i t i m p o s s i b l e the s t r a i g h t l i n e a c c u r a t e l y .  to draw  I t was shown i n t h e ' e x p e r i -  mental p a r t t h a t , u s i n g a b u r e t t e graduated i n f i f t i e t h s and  a s t a b i l i z e d starch s o l u t i o n f o r i n d i c a t o r , the pre-  c i s i o n o f t h e t i t r a t i o n was about 1/100 ml.- S i n c e a s i m i l a r t i t r a t i o n f o r i o d i n e i n aqueous s o l u t i o n s i s a c c u r a t e t o a t l e a s t 1 p a r t i n 1000 these t i t r a t i o n s p r o b a b l y have t h e r e quired  accuracy.  Figures  3, 4 and 5 i n d i c a t e t h a t t h e e x t r a p o l a t i o n o f  the l i n e cannot be i n e r r o r by more t h a n about .005 and p r o b a b l y t h e e r r o r i s l e s s . An e r r o r o f .005 i n t h e measured v a l u e o f l o g £—i would make an e r r o r I n t h e c a l c u l a t e d p e r A-I c e n t . o f v i n y l groups o f about 2 p a r t s i n 1000. Suppose, p_  T  f o r example, t h a t l o g - — was between .700 and .705, t h e n the p e r c e n t , o f v i n y l groups would be between 87.6 and 87.8. Probably the inaccuracy  i n the c a l c u l a t e d percentage of  v i n y l groups due t o e r r o r s i n t h e t i t r a t i o n s and e r r o r s i n the e x t r a p o l a t i o n i s not more than 0.1  o r 0.2 p e r c e n t .  I n the method o f c a l c u l a t i o n used by K o l t h o f f and  Lee  an e r r o r i n t h e g r a p h i c a l a p p r o x i m a t i o n t o I , from the r a t e curve, w i l l cause a s i m i l a r e r r o r i n each c a l c u l a t e d v a l u e of the r a t e c o n s t a n t remove the e r r o r .  and  averaging  As was  o f k does not  shown i n the I n t r o d u c t i o n ,  method can be no more a c c u r a t e mation.  the v a l u e s  than the g r a p h i c a l  approxi-  T h i s would maan a p o s s i b l e e r r o r of about 1$ f o r  polymers t h a t had v e r y s m a l l amounts o f v i n y l groups c o n s i d e r a b l y more f o r polymers t h a t had The  this  30 or  and  40$..  p r i n c i p a l advantages of the method o f c a l c u l a t i o n  used above a r e :  ('1) no approximate e s t i m a t e  r a t e curve i s u s e d j and  of I from t h e  (2) the graph tends t o c a n c e l  the  e r r o r s t h a t o c c u r f o r each s i n g l e p o i n t . There i s an e r r o r due mers are 100$. u n s a t u r a t e d  to the a s s u m p t i o n t h a t t h e  poly-  but s i n c e t h e r e seems to be  no  s a t i s f a c t o r y method of measuring the t o t a l u n s a t u r a t i o n t h i s ' cannot be a v o i d e d .  I n s i m i l a r p o l y m e r s , such as t h e  samples o f emulsion, p o l y i s o p r e n e  compared above, the  three values  of the u n s a t u r a t i o n would not l i k e l y d i f f e r by much and e r r o r due  the  t o t h i s would appear i n the r e s u l t s f o r each polymer  t o the same e x t e n t .  In the sample of n a t u r a l r u b b e r used  t h e r e were no v i n y l groups and measured w i t h p e r b e n z o i c a c i d . from these t i t r a t i o n s was  100$  so the u n s a t u r a t i o n The  unsaturation  could  be  calculated  w i t h i n the l i m i t s / o f e x p e r i -  mental e r r o r . The  assumption- t h a t p r a c t i c a l l y a l l the i n t e r n a l double  bonds r e a c t b e f o r e  an a p p r e c i a b l e  amount of e x t e r n a l double  bonds i s o x i d i z e d was p a r t i a l l y j u s t i f i e d t h e o r e t i c a l l y i n the I n t r o d u c t i o n and i s f u r t h e r s u p p o r t e d by t h e f a c t t h a t most of t h e p o i n t s i n f i g u r e s 3 - 5  f a l l as close t o a  s t r a i g h t l i n e as would be e x p e c t e d , i n v i e w of t h e e x p e r i m e n t al  errors. I n f i g u r e 4, t h e p l o t o f l o g (P-RA)/(A-RA.} f o r polymer  B, t h e p o i n t s a r e not q u i t e as c l o s e t o a s t r a i g h t l i n e as they are; i n f i g u r e s 5 and 5.  The s l o p e s o f the l i n e s i n .  f i g u r e s 3 and 5 and, t h e r e f o r e , the r a t e c o n s t a n t s  f o r the  e x t e r n a l double bonds i n polymers A and C, a r e almost t h e same but they a r e about 60$ g r e a t e r than t h o s e i n f i g u r e 4 and polymer B..  These f a c t s suggest t h e p o s s i b i l i t y  that  t h e r e a r e two k i n d s of e x t e r n a l double bonds i n polymer B. I f a l i n e i s drawn as c l o s e as p o s s i b l e t o t h e f o u r p o i n t s i n f i g u r e 4 a t 4.08, 14.68, 23.08 and 27.08 h o u r s , its  s l o p e would be p r a c t i c a l l y t h e same as t h a t o f f i g u r e s  3 and 5 but t h e p o i n t s f o r l o n g e r t i m e s w o u l d f a l l a b l y below t h e l i n e . contained  consider-  This, would be expected i f polymer B  the same k i n d of e x t e r n a l double bonds as polymers  A and C, and i n a d d i t i o n , a n o t h e r s l o w e r r e a c t i n g k i n d .  The  presence o f t h e s l o w e r r e a c t i n g double bonds would cause t h e apparent d e c r e a s e i n t h e r a t e constant, w i t h The  time.  f a c t t h a t the p o i n t s i n f i g u r e s 3 and 5 a r e so  c l o s e to a s t r a i g h t l i n e s u p p o r t s the assumption t h a t  only  one k i n d o f e x t e r n a l double bond i s p r e s e n t i n polymers A and  C, and the s i m i l a r i t y i n t h e s l o p e s of t h e two l i n e s  shows t h a t i t i s . t h e same k i n d i n each polymer.  There a r e  55. o n l y two k i n d s o f v i n y l groups p o s s i b l e ; those r e s u l t i n g f r o m 1-2 a d d i t i o n , and t h o s e r e s u l t i n g from 3-4 a d d i t i o n .  The  v i n y l groups t h a t a r e formed by 3-4 a d d i t i o n have a m e t h y l group a t t a c h e d to them t h a t i s not p r e s e n t on t h o s e formed by 1-2 a d d i t i o n and t h e r e f o r e the 3-4 u n i t s would r e a c t f a s t e r with perbenzoic acid.  I f t h e r e a r e two k i n d s of  e x t e r n a l double bonds p r e s e n t i n polymer B t h e f a s t e r r e a c t i n g of the two must be the same as t h o s e i n polymers A and G and they must be t h o s e formed by 3-4  addition.  The c a t a l y s t system used f o r the p o l y m e r i z a t i o n has a s m a l l e f f e c t on t h e amount of v i n y l groups. Catalyst F S0 -H 0 e  4  2  % of V i n y l Groups: 11.5  g  Cumene H y d r o p e r o x i d e  14.0  Diazo t h i o - e t h e r  10.5  The p o s s i b i l i t y t h a t the polymer p r e p a r e d u s i n g cumene h y d r o p e r o x i d e has b o t h 1-2 and 3-4 u n i t s w h i l e the o t h e r s c o n t a i n o n l y one o f the two i s t h e most s i g n i f i c a n t ence between the d i f f e r e n t c a t a l y s t s .  differ-  Polymer B a l s o  differs  markedly from A and C i n t h e speed o f t h e p o l y m e r i z a t i o n and i n the p e r c e n t a g e o f v i n y l g r o u p s . The v a l u e s of the r a t e c o n s t a n t s f o r the r e a c t i o n of the i n t e r n a l double bonds shown i n t a b l e s 13, 15 and 17 are about the same f o r each polymer and show a s t e a d y decrease w i t h time.  There are two p o s s i b l e e x p l a n a t i o n s  f o r t h i s decrease. (1) The f o r m a t i o n of t h e epoxide on t h e f i r s t i n t e r n a l , double bonds t o r e a c t decreases the r a t e of the r e a c t i o n o f t h e . r e m a i n i n g i n t e r n a l double bonds.  I t i s known t h a t  nega-  t i v e groups c l o s e t o the e t h y l e n e slow down t h e r a t e of a d d i t i o n o f p e r b e n z o i c a c i d but the epoxide would be a t l e a s t 3 carbon atoms awety from any u n r e a c t e d e t h y l e n e s and the e f f e c t ¥/ould not l i k e l y be as g r e a t as i s o b s e r v e d w i t h samples A, B & C. (2). There may be two k i n d s of i n t e r n a l double  bondspresent  that r e a c t w i t h perbenzoic a c i d at d i f f e r e n t  rates.  S i n c e o n l y 1-4 a d d i t i o n l e a d s t o i n t e r n a l double bonds, the two k i n d s would have t o be t h o s e due t o c i s 1-4 and t r a n s 1-4  addition.  N a t u r a l rubber i s known t o be almost c o m p l e t e l y c i s 1-4 polyisoprene.  From f i g u r e 2 the r a t e c o n s t a n t f o r the r e a c t i o n  of the double bonds w i t h p e r b e n z o i c a c i d i s 98.6 1 .mT hr7 and 1  1  i n n a t u r a l r u b b e r the s m a l l d e c r e a s e w i t h time i s not n e a r l y as g r e a t as t h a t observed w i t h the s y n t h e t i c p o l y m e r s .  The  observed r a t e c o n s t a n t f o r n a t u r a l r u b b e r i s w i t h i n . 10$ o f 100 l.m.^hrT  1  f o r t h e complete r e a c t i o n , but f o r the s y n t h e t i c  polymers the r a t e c o n s t a n t d e c r e a s e s from about 200 1.m.hr. -1 -1 at t h e s t a r t of the r e a c t i o n t o about 100 l.m. h r .  after 3  hours. P r o b a b l y the s m a l l d e c r e a s e of the r a t e c o n s t a n t f o r n a t u r a l rubber i s due t o t h e i n d u c t i v e e f f e c t o f t h e epoxide groups and the l a r g e r decrease i n t h e s y n t h e t i c polymers i s  1  57. due  p a r t l y t o t h i s but l a r g e l y to the p r e s e n c e of c i s and  t r a n s isomers i n the 1-4  addition units.  Determination of T o t a l  Unsaturation.  P e r b e n z o i c a c i d cannot be used to measure the t o t a l  un-  s a t u r a t i o n i n a polymer c o n t a i n i n g v i n y l groups because of t h e i r slow r a t e of r e a c t i o n .  From t a b l e 10 i t can be seen  t h a t the r e a c t i o n of n a t u r a l r u b b e r w i t h p e r b e n z o i c a c i d i s q u a n t i t a t i v e i n a s h o r t time but t h i s i s o n l y because n a t u r a l r u b b e r c o n t a i n s no v i n y l groups.  The  amount of u n r e a c t e d p e r b e n z o i c a c i d d i d not  fact that  the  change a p p r e c -  i a b l y between 15 and 47' hours shows t h a t t h e r e a r e no  inter-  f e r i n g s i d e r e a c t i o n s such as o c c u r w i t h i o d i n e m o n o c h l o r i d e . Tables 2 - 5  i l l u s t r a t e the f a c t t h a t i o d i n e mono-  c h l o r i d e cannot.be used t o measure the u n s a t u r a t i o n  accur-  a t e l y unless, t h e r e i s a method of c o r r e c t i n g f o r s u b s t i t u t i o n and  s p l i t t i n g out o f h y d r o h a l i c a c i d .  The  method of,  Lee, K o l t h o f f and M a i r s f o r making t h e s e c o r r e c t i o n s  may  l e a d to r e p r o d u c i b l e r e s u l t s i f the t i t r a t i o n s are c a r r i e d out under e x a c t l y s i m i l a r c o n d i t i o n s described  but the  experiments  i n P a r t I I show t h a t the r e s u l t s o b t a i n e d  are  not  r e a l l y s a t i s f a c t o r y s i n c e p a r t of the p o t a s s i u m i o d a t e i s reduced by h y d r o c h l o r i c a c i d i n s t e a d of by i o d i n e . .  The  decrease w i t h time I n the amount of o x i d i z i n g agent p r e s e n t i n a m i x t u r e of p o t a s s i u m i o d a t e and h y d r o c h l o r i c a c i d recorded i n t a b l e 1 i s ' n o t great d i f f e r e n c e iijrthe c o n c e n t r a t i o n  enough t o account f o r the  of i o d i n e found by  iodate  and t h i o s u l p h a t e solutions,  t i t r a t i o n s o f the carbon d i s u l f i d e - c h l o r o f o r m  However, d u r i n g t h e t i t r a t i o n s  s u l f ide-chloroform  of t h e carbon d i -  s o l u t i o n s o f i o d i n e , t h e m i x t u r e s were  shaken and t h i s might cause a g r e a t e r l o s s , b y  volatilization,  of c h l o r i n e w h i c h would o t h e r w i s e o x i d i z e the i o d i n e and make the net r e a c t i o n t h e same as i f t h e p o t a s s i u m i o d a t e the i o d i n e i n the f i r s t p l a c e .  oxidized  I t does seem, however, t h a t  i f a b e t t e r method f o r d e t e r m i n i n g the amount o f i o d i n e i n the r e a c t i o n m i x t u r e could be found t h e method o f L e e , K o l t h o f f and M a i r s would g i v e t h e c o r r e c t  unsaturation.  59  BIBLIOGRAPHYBraun, G.,  Organic S y n t h e s e s , C o l l . V o l . 1  F i e l d , J . E . , Woodford, D.E., and Genham, S. D., J . App. Phys. 17., 386 (1946) H a r t , E-  J . and Meyer, A. W., J . Am. Chem. S o c . 71_, 1980 (1949)  H i l l , R., L e w i s , J.R., and Siiaonsen, J . L . , Trans. Faraday Soc.  35, 1067, 1079 (1939)  Kemp, A. R., and P e t e r s , H., I n d . Eng. Chem. 15, 453 (1943) K o l t h o f f , I . IS., and L e e , T.S., J ".Polymer S c i . 2, 206 (1947) Lee,  T.S., K o l t h o f f , I.M., and M a i r s , M.A.,. J . Polymer S c i . 3, 66 (1948)  L o n g f i e l d , J . , B l a d e s , H. , and S i v e r t z , G., P r i v a t e communic a t i o n t o t h e O f f i c e o f Rubber Reserve. M c l l h i n e y , P.C., J". Am. Chem. "Soc. 21, 1084 (1899) Pummerer, R., Rubber Chem. Tech. &, 39 (1935) Rabjohn, N.., B r y a n , C. E., I n s k e e p , G.E., J o h n s t o n H., and Lawson, J.K., J.Am.Chem. S o c . 69,314 (1947) S a f f e r , A., and Johnson, B.L., Ind. Eng. Chem. 40, 538 (1948) W e i d l e i n , E.R., J . Chem.Eng .News 24, 771 (1946)  

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