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The protonic and aprotonic mechanism of polymerization initiated by potassium amine in Liquid ammonia
i2
A. I. SHATENSHTEINet al.
3. 4. 5. 6. 7. 8. 9.
I. Ya. PODDUBNYI, Khim. prom., No. 2, 4, 1958 G. NATTA, Makromol. Chem. 35: 94, 1960 C. S. MARVEL, et al., J. Org. Chem. 16: 838, 1951 A. I. YAKUBCHIK and B. I. TIKHOMIROV, Zh. obshch, khim. 30: 128, 1960 S. L. AGGARWAL and G. P. TILLEY, J. Polymer Sci. 18: 17, 1955 G. NATTA and P. CORRADINI, Suppl. Nuovo eimento 15: Ser. 10, 9, 1960 A. I. YAKUBCHIK, B. I. TIKHOMIROV and V. S. SULIMOV, Vestnik LGU, No. 22, 135, 1961 10. V. A. KARGIN and G. L. SLONIMSKII, Kratkie ocherki po fiziko-khimii polimerov. (Short Essays on the Physical Chemistry of Polymers.) p. 116, 1960 11. J. L. MATTHEWS, H. G. PEISER and R. B. RICHARDS, Acta crystallog. 2: 85, 1949 12. V. A. KARGIN, A. I. KITAIGORODSKI and G. L. SLONIMSKII, Kolloid. zh. 19: 131, 1957
THE PROTONIC AND APROTONIC MECHANISM OF POLYMERIZATION INITIATED BY POTASSIUM AMIDE IN LIQUID AMMONIA* A. I. SHATENSHTEIN, YE. A. YAKOVLEVA, YE. A. KOVRIZHNIK I ). N. MANOCHKINA and N. A. PRAVIKOVA L. Ya. Karpov
Physico-chemical
(Received 25 J a n u a r y
Institute
1961)
ANIONIC p o l y m e r i z a t i o n initiated b y a solution o f p o t a s s i u m amide in liquid a m m o n i a is one o f a n u m b e r of processes t h a t are a s s u m e d to proceed t h r o u g h a stage of c a r b a n i o n f o r m a t i o n . The c a r b a n i o n s m a y be f o r m e d b y the a d d i t i o n of a n N H : ion to a multiple b o n d or b y the transfer of a proton, i.e. b y a n aprotonic or a p r o t o n i c m e c h a n i s m . Sanderson a n d H a u s e r [1] a n d E v a n s , Higginson a n d W o o d i n g [2] showed t h a t the first o f these m e c h a n i s m s applies to the polymerization o f s t y r e n e b y p o t a s s i u m amide in liquid a m m o n i a . U n d e r these conditions a - m e t h y l s t y r e n e does n o t p o l y m e r i z e [1, 2]. I n c o n t r a s t to this s t a t e m e n t we h a v e p r e p a r e d a n d f r a c t i o n a t e d the p o l y m e r from ~-methylstyreue. The molecular weight, nitrogen c o n t e n t a n d b r o m i n e value f o u n d lead to the conclusion t h a t t h e p r o t o n i c m e c h a n i s m p r e d o m i n a t e s in the p o l y m e r i z a t i o n of a - m e t h y l s t y r e n e b y this initiating system. I n order to estimate the s t r e n g t h o f ~ - m e t h y l s t y r e n e as a h y d r o g e n acid we used the m e t h o d of isotope-exchange of h y d r o g e n [4] a n d applied it also to some diene h y d r o c a r b o n s which we also f o u n d to form low-molecular p o l y m e r s on p o l y m e r i z a t i o n with K N H 2 in liquid a m m o n i a . As far as we k n o w there is no i n f o r m a t i o n in the literature on the acid-base properties o f monomers. * Vysokomol. soyed. 4: No. 1, 42-51, 1962.
Protonic and aprotonic mechanism of polymerization
13
EXPERIMENTAL Preparations. S t y r e n e (ST) a n d c¢-methylstyrene (~-MST) a f t e r t h e u s u a l p u r i f i c a t i o n were distilled in vacuo, w i t h or w i t h o u t a c u r r e n t o f n i t r o g e n , a n d t h e m i d d l e f r a c t i o n was t a k e n . I n s o m e e x p e r i m e n t s t h e m o n o m e r s were a g a i n distilled f r o m m e t a l l i c s o d i u m . CommerciM b u t a d i e n e was d r i e d f o u r t i m e s o v e r solid p o t a s s i u m a m i d e . T h e o t h e r d i e n e h y d r o c a r b o n s were p r e s e n t e d t o u s b y B. A. K a z i n s k i i a n d I. V. G o s t i n s k a y a t o w h o m we e x p r e s s 20 20 o u r sincere g r a t i t u d e . I s o p r e n e : n B 1.4220, d~ 0.6810; 2 , 3 - d i m e t h y l b u t a d i e n e - l , 3 : b.p. 20 1.4393, d420 0-7266; h e x a d i e n e - 2 , 4 : b.p. 82-4°/760 m m , ~ o 1.4550, 68"3°/742 m m , ~1) d~°0.7216; 2 , 5 - d i m e t h y l h e x a d i e n e - 2 , 4 : b.p. 134"0°/734 r a m ; 7t~°o n 1-4772, d20 0.7619. E x p e r i m e n t a l method. T h e u s u a l l a b o r a t o r y a p p a r a t u s a n d e x p e r i m e n t a l t e c h n i q u e for w o r k i n g w i t h liquid a m m o n i a s o l u t i o n s were u s e d [5]. As a rule t h e m o n o m e r was a d m i t t e d t o t h e s y s t e m w i t h o u t t h e access o f air. I n o r d e r t o s t o p t h e p o l y m e r i z a t i o n a s m a l l q u a n t i t y o f w a t e r o r m e t h a n o l was a d d e d , a f t e r w h i c h t h e a m m o n i a was e v a p o r a t e d off. I n e x p e r i m e n t s o n t h e r a t e o f p o l y m e r i z a t i o n o f ~-MST a w e i g h e d q u a n t i t y o f t h e mon o m e r was sealed u n d e r h i g h v a c u u m in a s m a l l a m p o u l e a n d p l a c e d in t h e r e a c t i o n s y s t e m . A t t h e e n d o f t h e e x p e r i m e n t t h e a m m o n i a was r e m o v e d , a n a c c u r a t e l y k n o w n v o l u m e of" c h l o r o f o r m was a d d e d , a n a l i q u o t p a r t o f t h e s o l u t i o n was w i t h d r a w n b y m e a n s e t a p i p e t t e a n d t h e b r o m i n e v M u e w a s d e t e r m i n e d as d e s c r i b e d below. B e f o r e t h e i s o t o p e - e x c h a n g e e x p e r i m e n t s t h e d i e n e h y d r o - c a r b o n s were distilled in v ~ c u o a t a low t e m p e r a t u r e . T h e d e u t e r i u m - e x c h a n g e e x p e r i m e n t s were c a r r i e d o u t x~ith 0.1-0.2 g o f t h e m a t e r i a l a n d 5 - 6 m l o f t h e K N H ~ s o l u t i o n . A f t e r t h e r e a c t i o n m i x t u r e h a d b e e n k e p t in a t h e r m o s t a t for a set t i m e it was p o u r e d i n t o acidified w a t e r , t h e h y d r o c a r b o n x~as s e p a r a t e d a n d distilled o v e r a n h y d r o u s NiSOa a n d CaCI 2. T h e p r o d u c t was b u r n e d a n d t h e isotopic c o m p o s i t i o n o f t h e purified w a t e r w a s d e t e r m i n e d . W h e n t h e k i n e t i c s o f d e u t e r i u m e x c h a n g e w i t h g-MST were d e t e r m i n e d t h e p r o c e d u r e was t h e s a m e b u t 0.3 0-5 g o f m o n o m e r were t a k e n a n d b e f o r e c o m b u s t i o n t h e p r o d u c t was distilled it~ vaeuo over CuSO 4. All t h e p r o d u c t s a f t e r t h e isotope e x c h a n g e r e a c t i o n h a d r e f r a c t i v e indices close t o t h o s e of" t h e s t a r t i n g m a t e r i a l s . M. I. A r s h i n o v a a s s i s t e d in t h e d e u t e r i u m . e x c h a n g e experiments. Deter~ni*~atio~ of bromine value. A m o d i f i e d K a u f m a n m e t h o d [6J was u s e d fbr t h e d e t e r m i n a t i o n o f b r o m i n e values. T e s t s h a v e s h o w n t h a t p h e n y l e t h y l a m i n e a n d p o l y s t y r e n e e o n t a i n i n g n i t r o g e n do n o t r e a c t w i t h t h e r e a g e n t s u s e d in K a u f m a n ' s b r o m o m e t r i c t i t r a t i o n m e t h o d [6]. N u m e r o u s c o n t r o l a n a l y s e s o f ST a n d ~-MST a n d also o f m i x t u r e o f t h e m o n o m e r s a n d p o l y m e r s s h o w e d t h a t CCI4, CHC1 a a n d C6H6 c a n be u s e d as s o l v e n t s in plaee of' C H a O H . T h e b r o m i n e v a l u e is e x p r e s s e d as g Br2/100 g o f s u b s t a n c e . Determ[~¢ation of molecular weight. T h e m o l e c u l a r w e i g h t o f t h e p o l y m e r s was d e t e r m i n e d b y t h e ebullioscopie, cryoseopic a n d v i s c o m e t r i e m e t h o d s , a n d also b y e n d - g r o u p a n a l y s i s ( n i t r o g e n c o n t e n t ) . T h e ebullioscopie m e a s u r e m e n t s were e a r r i e d o u t b y P. P. A l i k l a n o v w i t h his o w n m o d i f i c a t i o n o f t h e R e y e b u l l i o m e t e r , w i t h a f i v e - j u n c t i o n t h e r m o e o u p l e . T h e o r d i n a r y a p p a r a t u s w i t h a B e e k m u n t h e r m o m e t e r was u s e d t b r t h e eryoseopie m e a s u r e m e n t s . T h e v i s c o s i t y o f t h e p o l y m e r s o l u t i o n s was m e a s u r e d in a n U b b e l o h d e v i s e o m e t e r . T h e i n t r i n s i c v i s c o s i t y [r/] was f o u n d f r o m t h e i n t e r c e p t o n t h e o r d i n a t e of' p l o t s o f Jlsp/e ~md log #r/c a g a i n s t t h e c o n c e n t r a t i o n o f t h e s o l u t i o n , c (g/100 ml). N i t r o g e n was d e t e r m i n e d by the semimicro Kjeldahl method. Fractionation of the polymers. T h e l o w - m o l e e u l g r ST a n d ~-MST p o l y m e r s were f r a e t i o n a t e d b y t h e m e t h o d o f F u e h s {7] w h i c h we m o d i f i e d b y r e p l a c i n g t h e fine a l u m i n i u m foil b y m e t a l (or glass) helices, u s e d f o r filling f r a e t i o n a t i n g c o l u m n s ( L e v y packing'). T h e use of' t h i s s u p p o r t c o n s i d e r a b l y s h o r t e n e d t h e t i m e o f t h e p r e l i m i n a r y w o r k o f p r e p a r a t i o n before e x t r a c t i o n w i t h t h e s o l v e n t - p r e e i p i t a n t m i x t u r e , a n d m a d e t h e process easier. T h e p a c k i n g , w i t h a t o t a l surface a r e a o f a b o u t 1000 c m 2, w a s t h o r o u g h l y w a s h e d w i t h b e n z e n e
14
A . I . SHATENSHTEIN et al.
a n d e t h e r , a n d dried. A u n i f o r m l a y e r w a s p l a c e d o n t h e b o t t o m o f a c r y s t a l l i z i n g d i s h ( d i a m e t e r 15 cm) a n d 5 0 - 7 0 m l o f a b e n z e n e s o l u t i o n o f t h e p o l y m e r c o n t a i n i n g a b o u t 1.5 g o f t h e l a t t e r w a s p o u r e d o v e r it. T h e b e n z e n e was e v a p o r a t e d a n d t h e p a c k i n g w i t h its d e p o s i t e d l a y e r o f p o l y m e r was d r i e d t o c o n s t a n t w e i g h t a t 50 ° i n v a c u o . T h e p a c k i n g w a s t h e n t r a n s f e r r e d t o a t w o - n e c k e d , 500 m l flask w i t h g r o u n d - g l a s s caps. A s i n t e r e d glass filter was sealed i n t o o n e o f t h e n e c k s o f t h e flask. T h e flask was i m m e r s e d in a t h e r m o s t a t (20 °) a n d 1 0 0 m l o f a m i x t u r e o f b e n z e n e a n d m e t h a n o l (1 : 9 b y v o l u m e ) was a d d e d . E q u i l i b r i u m o f t h e d i s s o l v e d f r a c t i o n was a t t a i n e d a f t e r s h a k i n g for 10-15 m i n u t e s a n d t h e s o l u t i o n w a s filtered off t h r o u g h t h e glass filter. T h e e x t r a c t i o n w a s r e p e a t e d 10-15 t i m e s w i t h a s t e p w i s e i n c r e a s e i n t h e b e n z e n e c o n t e n t o f t h e m i x t u r e b y 5-10~o b y v o l m n e . T h e s o l v e n t w a s e v a p o r a t e d , t h e f r a c t i o n s were d r i e d t o c o n s t a n t w e i g h t i n v a c u o a n d dissolved i n a m e a s u r e d v o l m n e o f t o l u e n e . T h e v i s c o s i t y o f t h e s o l u t i o n s was m e a s u r e d in a s e m i m i c r o U b b e l o h d e viscometer. In order to test the reproducibility of the fractionation and to compare the original m e t h o d o f F u c h s w i t h o u r m o d i f i c a t i o n f o u r e x p e r i m e n t s were c a r r i e d o u t w i t h s a m p l e s o f p o l y s t y r e n e p r e p a r e d b y p o l y m e r i z a t i o n in a n a m m o n i a c a l s o l u t i o n o f K N H ~ . T h e p o l y m e r was dissolved in benzene, precipitated ten times with an equal volume of methanol and d r i e d i n v a c u o . T h e v i s c o s i t y o f s o l u t i o n s o f t h e p o l y m e r i n t o l u e n e a n d b e n z e n e a t 20 ° a n d 25 ° were f o u n d t o b e p r a c t i c a l l y t h e s a m e a t 0 " 0 9 3 i 0 " 0 0 3 . C o n s e q u e n t l y for t h e c a l c u l a t i o n o f m o l e c u l a r w e i g h t it is possible t o use ( w i t h i n t h e l i m i t s o f e x p e r i m e n t a l a c c u r a c y ) t h e f o m u l a e d e r i v e d for t h e s e t w o s o l v e n t s a t t h e t w o s t a t e d t e m p e r a t u r e s . A c c o r d i n g t o P e p p e r [8] for l o w - m o l e c u l a r , u n f r a c t i o n a t e d p o l y e s t y r e n e [~1]=2"27× 10 4 M0.72 (tool. wt. 4200),
(1)
a c c o r d i n g t o B a m f o r d a n d D e w a r [9] [ q ] = 4 . 4 0 × 10 -4 M °'~5 (tool. wt. 3700).
•2 lO0
i 10
• 2
AO
~e
•-PO
6
qo
u
20
2
5
/0
(2)
15
Z,O
[~/x:g
I n t e g r a l a n d differentia] m o ] e c u l a r w e i g h t d i s t r i b u t i o n curves: (i) f r a e t i o n a t e d p o l y m e r d e p o s i t e d o n a l u m i n i u m foil ( F u c h s m e t h o d ) , e x t r a c t i o n t i m e (t) 15 m i n u t e s ; (2) p o l y m e r d e p o s i t e d o n m e t a l helices, t = 15 m i n u t e s ; (3) p o l y m e r d e p o s i t e d o n glass helices, t ~ 1 0 m i n u t e s . A v e r y m u c h l o w e r figure is o b t a i n e d w i t h t h e f o r m u l a o f K e m p a n d P e t e r s [10], i n r e f e r e n c e [3] (tool. w t . 2600). T h e ebullioscopic m o l e c u l a r w e i g h t d e t e r m i n e d b y A l i k h a n o v was: 4600, 4000 4400, 4600, 4100, m e a n 4300.
Protonic and aprotonic mechanism of polymerization
15
The diagram shows the results of the fractionation of this polymer. The abscissa represents the values of ]t/l, the ordinate on the left the sum of the weights W of the successive fractions, expressed as a percentage of the weight of polymer taken, and on the right ((1W/d[tl])x 10-2. I t is seen that the original and modified Fuchs methods gave closely similar results. Curve B was obtained by graphical differentation of the integral curve A. This gives a graphical representation of the molecular weight distribution. Knowing the weights a n d intrinsic viscosities of the fractions we calculated (see I11]) the viscosity of' the solution of the unfractionated polsTmer. The calculated value) ([~/]--0.092) practically coincides with the value found experimentally in benzene and toluene at 20 ° and 25" ([q] =0.093~:0.003), thus confirming the reliability of the fractionation procedure and of the measurements carried out on the individual fractions. We also calculated by the method of Schulz [ l l ] the weight-average and numberaverage molecular weights of the polymer, using the results of the fractionation and applying firstly Pepper's equation [8] [~]--4.17 :< 10-4 M°'6°, (3) and secondly Rossi's equation [12] [ t / l - - 10.1 x 10 a M0.50
(4)
fbt' fractionated, low-molecular polystyrene. The results obtained were: ~iw=8000, M , = 4 9 0 0 [formula (3)]; i~W=8500, M,,=4300 [formula (4)]. The calculated values of M,, are close to the molecular weight obtained by Alikhanov by the ebullioscopic method.
RESULTS AND DISCUSSION
Styrene (ST) and a-methylstyrene (~-MST). E x p e r i m e n t s w e r e set u p t o c o m p a r e the polymerization of these monomers, initiated by KNH 2 in liquid ammonia. W h e n t h o r o u g h l y p u r i f i e d ST, p r e v i o u s l y t r e a t e d w i t h s o l i d K N H 2 a n d d i s t i l l e d i n h i g h v a c u u m , is m i x e d w i t h a 0 . 0 2 N s o l u t i o n o f K N H 2 a t 25 ° t h e p o l y m e r precipitates i m m e d i a t e l y in q u a n t i t a t i v e yield. F o r a period of 2-3 m i n u t e s the r e a c t i o n m i x t u r e r e m a i n s a l m o s t colourless, s u b s e q u e n t l y i t a c q u i r e s a p i n k a n d t h e n red eolour*, a-MST polymerizes m u c h more slowly a n d some t i m e elapses before the p o l y m e r begins to p r e c i p i t a t e from the red solution. I n e x p e r i m e n t s o n t h e p o l y m e r i z a t i o n o f ST, 1 m o l e o f m o n o m e r r e q u i r e d 25 m o l e s o f N H 3. T h e e x p e r i m e n t a l r e s u l t s a r e g i v e n i n T a b l e 1. * The appearance of a red colouration by the action of K N H 2 in a m m o n i a on polystyrene was observed in our laboratory by Ye. A. Izrailevich. Subsequently this phenomenon was studied in more detail by ¥e. N. Zyagintseva and Z. N. Ovehinnikova. Their experiments showed that the colour appears gradually and independently of the method of preparation of the polymer (by free-radical, cationic or anionic polymerization). A 0.02 N solution of the amide in equal volumes of liquid a m m o n i a and benzene was used to dissolve the polymer. The colouration also appeared when a polymer prepared by free-radical polymerization with benzoyl peroxide and repreeipitated several times in an atmosphere of nitrogen was dried by several treatments with liquid a m m o n i a in the absence of air, and air was also excluded (luring the course of the experiments. According to the findings of Ye. A. Rabinovich the solution absorbs light in the same region of wavelengths (~max 550-565 m~t) as the eoloured solution formed in the polymerization of ST by potassium amide in liquid a m m o n i a [ 13].
A. I. SIIATENStITELNet
16
al.
TABLE 1. POLYMERIZATIONOF STYRENE
TelTIperature
(~c)
~ 2 solution
(N)
1.0 0-1 0.05 0.02 0"02 0.02 0.02 0-02
25 25 25 25 50 25 --30 --50
Molar ratio ST:KNH~
(m)
1.4 15 30 80 80 80 80 80
Mol. wt. Molecular o f unrepreN weight [~]** Mol. wt. content cipitated (viscosity) (benzene, from N polyof content* 25 °) from from polymer styrene (g/100 ml) f o r m u l a f o r m u l a (M~) (%) (cryo(1) (2) scopic) 45O 75O 850 920 610 920
2.1
650
1.4 1.0 2.2 1.0 0.6
1000 1400 640 1400 2300 i
0.024 0-032 0.039 0.043 0.030 0.043 0.111 0.125
650 960 1000 1500 880 1500 5400 6400
560 750 820 1200 I 660 1200 4900 5900
* Assuming that the polymer ch:aincontains one NH.~group. ** Efflux time of solvent, 97'7 sec.
The molecular weight of the polystyrene increases with decreasing temperature of polymerization and varies little even with large variations in K N H 2 concentration. This is in agreement with the data in the literature [3]. The absolute value of the molecular weight of polystyrene prepared with K N H 2 in ammonia is low. This is explained by the fact t h a t the polymer chain is soon terminated by ammonia. In fact, as was shown in reference [14], when the polymerization of styrene is initiated by solid K N H 2 in the absence of ammonia polymers with molecular weights of a few millions are obtained. I t was stated above t h a t a-MST polymerizes much more slowly t h a n ST. At 25 °, a K N H 2 concentration of 0.05 2( and m = 3 0 the degree of unsaturation (expressed as a percentage) of the material isolated from the reaction mixture varies as follows: Hours (~) Hours o~)
0 97 2 27
0 98 2 26
0 97 3 21
0"25 61 3 22
0"25 56 6 17
0"25 54 8 20
0"5 44 8 18
1 33 12 19
1 32 12 18
2 27 270 18
2 32
The residual unsaturation (~ 20%) is preserved even after l0 days and more. This can be explained by equilibrium between the polymerization reaction and the unsaturation of the polymer being formed. The low rate of polymerization of ~-MST enabled us to study the deuteration reaction in this process. In some experiments part of the monomer isolated after deuteration was oxidized with alkaline permanganate to benzoic acid which was isolated, sublimed and burned. The quantity of deuterium formed in the benzoic acid showed that in the benezene ring of a-MST the following fractions (in %) of the total number of hydrogen atoms are substituted by deuterium:
Protonie and aprotonie mechanism of polymerization
17
after 30 m i n u t e s - - 1 8 , 21, 18 (mean 19), after 60 m i n u t e s - - 2 5 , 22, 21 (mean 23). C o n s e q u e n t l y u n d e r these conditions the h y d r o g e n in the s u b s t i t u e n t g r o u p o f ~-MST undergoes e x c h a n g e p r e d o m i n a n t l y . Therefore for the calculation of the rate c o n s t a n t for the e x c h a n g e r e a c t i o n (by t h e first-order equation) we a s s u m e d t h a t there are five e x c h a n g e a b l e h y d r o g e n a t o m s in the ~-MST molecule. The e x p e r i m e n t a l conditions were: 25 °, K N H 2 c o n c e n t r a t i o n 0.02N, G - - t h e conc e n t r a t i o n of d e u t e r i u m in the a m m o n i a before the e x p e r i m e n t - - 4 . 2 4 a t o m s o/ /O (or 4.77 a t o m s ~o where m a r k e d with an asterisk), % is the c o n c e n t r a t i o n o f d e u t e r i u m in the w a t e r f r o m c o m b u s t i o n of the m o n o m e r after a n e x p e r i m e n t lasting r minutes, n the n u m b e r o f h y d r o g e n a t o m s e x c h a n g e d with d e u t e r i u m (calculated f r o m t h e coefficient o f d i s t r i b u t i o n o f d e u t e r i u m b e t w e e n C - - H a n d N - - H bonds, a = 0 . 9 2 ) a n d k t h e rate c o n s t a n t in sec 1. r cw ~ k × 1()~ r cw ~ k ~ 103
5 0"59 1"5 1"2 20* 1"75 4"0 1.2
5 0"60 1"5 1"2 30 1"69 4"3 1-1
10 0"95 2"4 1"1 30 l"72 4"4 1.2
10 1"05 2"7 ] "3 30 1"72 4"4 1-2
15 15 20 1"20 1"25 1"52 3"1 3"2 3"9 1"1 1"1 1"1 30* 1500 1"95 2"22 4"4 5"7 1-2 --
20
20*
1"47
1'62
3"8 1"2
3'7 1"1
The rate c o n s t a n t o f d e u t e r a t i o n in the side chain o f ~-MST m a i n t a i n s a c o n s t a n t value in e x p e r i m e n t s c o n t i n u e d for differen ~lengths of time. C o n s e q u e n t l y no i n e q u a l i t y in r e a c t i v i t y of the h y d r o g e n a t o m s could be observed. This can be a t t r i b u t e d to the f o r m a t i o n o f an ion of s t r u c t u r e I belowt
I n p r e l i m i n a r y e x p e r i m e n t s with fl-methylstyreue at the same t e m p e r a t u r e a n d a m u c h higher c o n c e n t r a t i o n o f the amide (CKNH:--I"5 12~) it was f o u n d t h a t in c o n t r a s t to a-MST o n l y two h y d r o g e n a t o m s u n d e r g o exchange. I t is k n o w n [15] t h a t in a n a m m o n i a c a l solution of p o t a s s i u m amide the following isomeric equilibrium exists, C 6 H s C H = C H - - C H a ( I I ) ~ C 6 H s C H 2 C H = C H 2 ( I I I ) , which suggests t h a t it is t h e t w o allylic h y d r o g e n a t o m s in I I I t h a t u n d e r g o exchange, f u r t h e r h y d r o g e n e x c h a n g e being hindered b y the n e g a t i v e charge of the c a r b a n i o n formed. t In a paper by M. Kolobielski and H. Pines (J. Amer. Chem. Soc. 79: 5820, 1959), which came to our notice after this paper had been sent for publication, a study was made of the chemical reactions occurring when ~-methylstyrene is heated with sodium. In their discussion of the mechanism of the reaction these authors also concluded that the earbanion I is probably formed.
18
A . I . SHATENSHTEIN et al.
The high value of the rate constant of the exchange reaction ( k = 1.2 × 10-a see -i) at a low concentration of K N H e (0.02 N) and a moderate t em perat ure (25 °) indicates a considerable mobility of the hydrogen atoms of the substituent group of ~-MST. The rate of deuteration in this group is greater t han t h a t in the CH a group of propylene [16] and is only slightly below the rate of deuteration in the CH a group of toluene [17]. The protonic mobility of the hydrogen atoms of the substituent group of a-methyl~tyrene is much higher t han the mobility of the hydrogen atoms of the aromatic nucleus. However, under suitable conditions the latter can be brought to light even in polystyrene. Ye. A. Izrailevich succeeded in introducing up to 60% of deuterium into finely dispersed polystyrene by prolonged t r e a t m e n t of the polymer (more t h a n 100 hours) with a 0.2 N solution of K N H 2 in liquid ammonia at 60 °. * We shall now consider the mechanism of initiation of the anionic polymerization of ST and ~-MST in ammoniacal solutions of K N H 2. The results presented in Table 1 show t h a t the molecular weight of the polystyrene calculated from the nitrogen content is close to the cryoscopic molecular weight. Consequently the polymerization of ST is initiated b y an aprotonic mechanism by the addition of an N H ~ ion to the double bond, in conformity with the results and conclusions of Higginson and Wooding [3]. The deuterium-exchange experiments disclosed a higher mobility of the hydrogen atoms of the substituent group of a-MST. This suggests t h a t it m a y polymerize b y a protonic mechanism. In order to test this idea we prepared polymers of ~-MST and ST under similar conditions. One hundred and fort y millilitres of a 0.02 N solution of K N H 2 was added to 6.5 g of a-MST and 300 ml of the same solution was added to 7.1 g of ST. The reaction mixtures were held at --15 ° for a sufficient length of time. The results of the fractionation of the solid polymers are summarized in Table 2. Both polymers were precipitated from benzene solution b y ten volumes of methanol. The filtrate after precipitation of the polystyrene was evaporated and the fraction of lowest molecular weight (fraction No. 1) was isolated from it. The intrinsic viscosity [r/] was measured for toluene solutions of the polymers at 25 ° and for some fractions of the poly-~-methylstyrene the relative viscosity of ground-molar solutions (~r) was determined for the calculation of molecular weight (M1) b y the Staudinger method [18]. The molecular weight, M2, of poly-~-MST was calculated from the formula of Brown and Mathieson [19] [r/]--3.5 × 10-5 M.
(5)
* It should be noted that in experiments carried out by V. M. Basmanova with ~methylstyrene that the isotopic exchange of hydrogen in the aromatic ring is more rapid with DBr than in the nucleus of toluene, i.e. ~-mcthylstyrene is a stronger base than toluene. This is of interest in connection with the discussion of certain problems of cationic polymerization where the monomer functions as a base.
P r o t o n i c an(][ a p r o t o n i c m e c h a n i s m o f p o l y m e r i z a t i o n
t9
TABLE 2. FRACTIO_NATION OF STYRENE AND ~-METHYLSTYRENE POLYMERS
i CHaOH
Fraction No.
C~H~ ! (vol. o ~ , ) (vol. o{~)
I .
.
.
I
Filtrate 10 20 25 30 35 45 50 55 60 70 100
90 80 75 70 65 55 50 45 40 30 0
] "
Poly-a-methylstyrene
[ q] = 0'042
.
D,Teight i (rag)
I
1 2 3 4 5 6 7 8 9 10 1l 12
! Polystyrene, I [ q] = 0"086
~,Yeight. ~
i [ q]
890 10 36 59 119 187 195 129 207 159 131 5
(mg)
[ q]
I
! q,.
3f I
.ll.
850 910 (990) (ll00)
800 850 910 1090 1140 1700
0-030 0"0365! 0-037 0"038 0-048 0"065 0-096 0-110 0"146 0"164
20 80 137 473 394 382 34 5 2 3 2
0.028 i 0-030 ~ 1.44 0.032 1.52 0-038 / 1.63 0"040 1-66 0"060
This magnitude m a y be increased because of the presence of a terminal group ill the polymers with which these authors worked [19]. Comparison of these molecular weights of the polymers of ~-MST and ST with those quoted in the literature for polymethylmethacrylate [20] and polymethacrylonitrile [21], prepared with K N H 2 in ammonia, shows t h a t the molecular weight of the polymer increases with increasing reactivity of the monomer in anionic polymerization: ~-MST < ST < methylmethacrylate < methacrylonitrile. Some of the fractions shown in Table 2 were studied in more detail. Values of [q] of 0.30 and 0.29 were obtained for polystyrene fraction No. 1 in two vise()meters. The following molecular weights were obtained by applying formulae for fractionated polystyrene: according to Pepper [18] (3) mol. wt. 1200; according to Bamford and Dewar [9] [~/] =2.92 x 10 4 M0.Gs (tool. wt. 1240) (6) according to Rossi and Bianchi [12] (4) tool. wt. S90, and according to Rossi et al. [22]
[q]=9.2 × 10-4 Mc5° (tool. wt. 1100)
(7)
The molecular weight determined by the ebullioscopic method (M~) was 750 and 770 (mean 760). The less accurate eryoscopic method gave values of M,: of 820 and 880 (mean 850). The nitrogen content was 1.45, 1.44, 1.40, 1.38 (mean 1.42°) whence Mx : 1000. Bromine value, 0-0.5. The following results were obtained for u-MST fractions: Fraction No. 4 5 6 7
Bromine calue 9.7 7.1 5.1
Nitrogen (°/o) 0.17; 0.14; 0.10;
0.17; 0.16 0.10
0.15
20
A.I. SHATENSHTEIN et
al.
In addition two samples of a-MST, prepared independently, were analysed: (1) a polymer of pasty consistency, [I;]=0.02, relative viscosity of a ground-molar solution t/r=l'28, ebullioscopic molecular weight 450, 450 (mean 450), molecular weight according to formula (5), 570, nitrogen content 0.33, 0.29 (mean 0.3% ), bromine value 12.2, 12.5; (2) a solid, white polymer (precipitated from a 1:10 mixture of benzene and methanol)* [t1]=0'033, molecular weight according to (5), 940, ebullioscopic molecular weight 1000, 940 (mean 970), nitrogen content 0.10, 0.14, 0-19, 0.15, 0.22 (mean 0-16%) :, bromine value 9.9, 9.6 (mean 9.8). Thus the ~-MST polymer contains approximately one tenth of the nitrogen in a polystyrene of similar molecular weight prepared under similar conditions. This fact in conjuetion with the unsaturati6n detected in poly-a-MST indicates t h a t in its formation an important part is played by the transfer of a proton from the monomer molecule. The following reactions are possible in the initation stage
+ Hf
/
C~H~
I
N H s- CH s- C-
C6H5/ CH2~
(I)
CH2
\ +NH_~
C6H5
I ) C--CH 2 + N H 3
(II)
CH~
The propagation stage is represented by the reactions
NH2CH2CI
+ [CH2=~
CH3 C~H~I
CHa. ~
[
"C6H5-1
C--CHill" + [ C H 2 = ~ CH2
--~ NHeCH2CI -- CHIC' CH 3 C~HsI
[----> cC- H - e2l C l ' -, !- I
CHa Jn
CH2
(Ia)
CH~ C6H~]_ I
{IIa)
CH 3
By reaction (IIa) the polymer chain retains the double bond and nitrogen is absent. The same result can be achieved if chain transfer to monomer occurs, accompanied by the release of a proton from the monomer molecule* * The weight of the solid polymer was 0.8 g and the weight of pasty polymer isolated from the filtrate was 3.0 g ([7] =0.021, n2D01"585). t This was brought to our attention by A. R. Gantmakher.
Protonic and aprotonic mechanism of polymerization C~H5
21
C~H5 C6H5 C6H5 C6H5 C6H5 I I_ W [ r I NH2--CH2--Cw~ CH2--C + C H 2 - C ---~NH2--CHe--C~ CH2--CH+C CH~ I i I I [i CH a CH 3 CH 3 (?Ha CH a CH2 and s u b s e q u e n t l y according to e q u a t i o n (IIa). I t m u s t not be supposed t h a t in polymerizations t h a t are described b y schemes t h a t include the f o r m a t i o n of carbanions, t h a t the l a t t e r are always p r e s e n t ill reality'. I t is p r o b a b l e t h a t often, as has been f o u n d in ~)ther reactions betwee~l h y d r o c a r b o n s and bases [4], " a n i o n i z a t i o n " of the molecule occurs in t h e Vransition state. Diene hydrocarbons. I n a s t u d y o f d e u t e r a t i o n reactions carried out in our l a b o r a t o r y [23] it was observed t h a t when a solution of K N H 2 in a m n l o n i a is a d d e d to diene h y d r o c a r b o n s a colouration appears a n d the h y d r o c a r b o n polymerizes. These e x p e r i m e n t s h a v e now been r e p e a t e d with a larger n u m b e r of hydrocarbons. W h e n K N H 2 is a d d e d to a solution of b u t a d i e n e (~v) a yellow colour appears, which g r a d u a l l y changes to orange, red a n d t h e n violet, a n d a low-molecular p o l y m e r is deposited on the walls o f the vessel in the f o r m o f oily droplets. T h e m e t h y l - s u b s t i t u t e d h y d r o c a r b o n s m e n t i o n e d below b e c o m e coloured to different shades of red. The p o l y m e r deposits in the form o f droplets a n d the p o l y m e r izability decreases as the n u m b e r o f m e t h y l groups in the diene molecule increases. Usually even after several hours it is possible to isolate p a r t of t h e m o n o m e r unchanged, a n d t h u s isotope-exchange e x p e r i m e n t s can be made. In c o n t r a s t to the m e t h y l s u b s t i t u t e d dienes, at room t e m p e r a t u r e and CK~H.= 0 ' 0 2 N evet~ a f t e r 24 hours it is possible to e x c h a n g e o n l y one h y d r o g e n a t o m in IV. Yu. G. Dubinskii in our l a b o r a t o r y has shown t h a t the cryoscopic m o l e c u l a r weight of p o l y b u t a d i e n e , p r e p a r e d at 20-25 °, corresponds to a degree of polymerization of five or six (tool. wt. 265-310) a n d it remains c o n s t a n t o v e r a wide range o f K N H 2 concentrations (0.005 to 1.0 N) with a fixed m o l a r ratio of N H 3 to IV of 40:1. The p o l y m e r contains 5.2-5.5% of nitrogen. I f it is assumed t h a t b y the aprotonic initiation m e c h a n i s m the p o l y m e r molecule contains one a t o m of nitrogen the calculated molecular weight is 250-275, in good a g r e e m e n t with the figure o b t a i n e d b y direct m e a s u r e m e n t . The p o l y m e r i z a t i o n of I V was not r e p o r t e d i~t the previous papers [1, 2]. Ext)erimellts carried out w i t h the assistance of M. I. Arshinova on d e u t e r i u m (,x(~hange at 25 ° (CK~t~.-~0"05 N ) w i t h the m e t h y l - s u b s t i t u t e d dienes, showed from the n u m b e r a f atoms e x c h a n g e d t h a t the h y d r o g e n atoms of the CH 3 groups ;~ttached to a carbo~l a t o m of the double bonds t a k e p a r t in the e x c h a n g e reactio~ c()mparatively easily. 2-Methylbut(ldiene (isoprene) (V) c~)=5.01 a t o m s o~ D t l 2 n 6 rw 1.5l [.70 1.69 1.61 , 2,7 3.0 3.0 2.9 t r in hours.
A . I . SHATENSHTEINet al.
22
2,3-Dimethylbutadiene-l,3 (VI) c~o : 5 . 0 1 a t o m s °/o D cw ~
0.5
1
2
3
4
5
1.34 3-0
2.12 4.7
2.79 6.2
3.32 7"3
3.46 7.7
3.48 7.7
3 2.58 6.0
4 2.45 5.8
21 3.18 7"5
Hexadiene-2,4 ( V I I ) c ° = 4 - 7 1 a t o m s °/o D v cw n
0.25 2.13 5-0
0"5 2.24 5.7
1 2.40 5.7
2,5-Dimethylhexadiene-2,4 (VIII)c°--~4.71; 5.01 a t o m s °/o D m a r k e d *) r cw ~t
0.25 3"33 10"0
0"5 3"58 12"0
2* 3"89 12"1
3* 3"97 12"3
20 4"06 13"4
48 4"27 13"2
M e a s u r e m e n t s carried o u t a t the s a m e t e m p e r a t u r e b u t w i t h a lower c o n c e n t r a t i o n o f K N H 2 (0-02 N) s h o w e d t h a t c o m p o u n d s V, V I I a n d V I I I in 4 - 6 h o u r s e x c h a n g e 3, 6 a n d 12 h y d r o g e n a t o m s , in c o n f o r m i t y w i t h the n u m b e r of h y d r o gen a t o m s in t h e m e t h y l g r o u p s present. T h e r e m a i n i n g h y d r o g e n a t o m s , if t h e y e x c h a n g e a t all, do so m u c h m o r e slowly as was n o t e d in t h e case of b u t a diene. A s t u d y o f t h e p o l y m e r i z a t i o n of diene h y d r o c a r b o n s in liquid a m m o n i a a n d t h e p r o d u c t i o n o f m o r e detailed i n f o r m a t i o n on d e u t e r i u m e x c h a n g e will b e t h e s u b j e c t o f f u r t h e r investigations, f r o m which new i n f o r m a t i o n on t h e role o f p r o t o n i c a n d a p r o t o n i c m e c h a n i s m s in anionic p o l y m e r i z a t i o n s is e x p e c t e d . CONCLUSIONS
(1) I t is s h o w n t h a t a - m e t h y l s t y r e n e a n d a n u m b e r o f diene h y d r o c a r b o n s p o l y m e r i z e b y the action o f K N H 2 in liquid a m m o n i a to f o r m l o w - m o l e c u l a r p o l y m e r s . T h e low r a t e of p o l y m e r i z a t i o n enables the m e t h o d o f d e u t e r i u m e x c h a n g e w i t h a solution o f K N H 2 in d e u t e r a t e d liquid a m m o n i a to be used to e s t i m a t e t h e m o b i l i t y of the h y d r o g e n a t o m s of these m o n o m e r s . (2) T h e p o l y m e r i z a t i o n o f s t y r e n e a n d a - m e t h y l s t y r e n e in a m m o n i a solutions of K N H 2 has b e e n c o m p a r e d a n d a s t u d y has b e e n m a d e of t h e p r o p e r t i e s (molecu l a r weight, n i t r o g e n content, b r o m i n e value) o f t h e p o l y m e r s a n d t h e i r fractions. T h e conclusion is d r a w n t h a t in c o n t r a s t to t h e p o l y m e r i z a t i o n of s t y r e n e , which p o l y m e r i z e s b y a n a p r o t o n i c m e c h a n i s m , t h e m a i n role in t h e p o l y m e r i zation o f a - m e t h y l s t y r e n e is t a k e n b y processes a s s o c i a t e d w i t h t h e t r a n s f e r of a p r o t o n f r o m t h e m o n o m e r molecule. (3) Modifications h a v e b e e n m a d e in t h e m e t h o d of f r a c t i o n a t i o n of p o l y m e r s of low m o l e c u l a r w e i g h t b y e x t r a c t i o n . Tra~,slated by E. O. PHILLIPS REFERENCES
1. J. J. SANDERSON and C. R. HAUSER, J. Amer Chem. Soc. 71: 1595, 1949 2. M. G. EVANS, W. C. E. HIGGINSON and N. S. WOODING, Rec. tray. chim. 68: 1069, 1949
Disappearance of free radicals in irradiated polyvinylchloride
23
3. W. C. E. HIGGINSON and N. S. WOODING, J. Chem. Soc. 1952, 760 4. A. I. SHATENSHTEIN, Izotopnyi obmen i zameshchenie vodoroda v organicheskikh soyedinenyakh. (Isotope Exchange and the Substitution of Hydrogen in Organic Compounds.) Izd. Akad. N a u k SSSR, 1960 5. A. I. SHATENSHTEIN, Zh. fiz. khim. 15: 246, 1941 6. R. W. BARNE and I. B. JOHNSON, Anal. Chem. 28: 126, 195~ 7. O. FUCHS, Z. Electrochem. 60: 229, 1956 8. D. C. PEPPER, J. Polymer Sci. 7: 347, 1951 9. C. H. BAMFORD and M. J. S. DEWAR, Proc. Roy. Soc. 192: 310, 1948 10. A. R. KEMP and H. PETERS, Ind. Eng. Chem. 34: 1097, 1942 l l . G. V. SCHULTZ, Z, Electrochem. 60: 199, 1956 12. C. ROSSI and E. BIANCHI, J. P o l y m e r Sci. 41: 189, 1959 13. I. V. ASTAF'EV, Ye. A. RABINOVICH and A. I. SHATENSHTEIN, Vysokomol. soyed. 3: 555, 1961 14. A. I. SHATENSHTEIN, Ye. A. YAKOVLEVA and E. S. PETROV, Dokl. Akad. N a u k SSSR 136: 882, 1961 15. H. LEVY and H. C. COPE, J. Amer. Chem. Soc. 66: 1684, 1944 l(i. A. I. SHATENSHTEIN and L. N. VASIL'EVA, Dokl. Akad. Nauk SSSR 95: 115, 1954 17. A. I. SHATENSHTEIN and E. A. IZRAILEVICH, Zh. fiz. khim. 32: 2711. 1958 18. H. STAUDINGER and F. BRENSCH, Ber. 62: 442, 1929 19. C. P. BROWN and A. R. MATHIESON, J. Chem. Soc. 1958, 3445 20. W. E. GOODE, W. H. SNYDER and R. C. FETTES, J. Polymer Sci. 42: 366, 19~i0 21. C. G. OVERBERGER, H. YUKI and N. U R A K A W A , J. Polymer Sci. 45: 127, 1960 22. C. ROSSI, U. BIANCHI and E. BIANCHI, Makromol Chem. 41: 31, 1960 23. A. I. SHATENSHTEIN, L. N. VASIL'EVA and N. M. DYKHNO, Zh. fiz. khim. 2 8 : 1 9 3 1954
THE KINETICS OF THE DISAPPEARANCE OF FREE RADICALS IN IRRADIATED POLYVINYLCHLORIDE* Z. S. Y E G O R O V A , Y U . M. M A L I N S K I I , V. L. K A R P O V . A. ~]. K A L M A N S O N a n d L. A. B L Y U M E N F E L ' D L. Ya. K a r p o v Physico-chemieal Institute; Inst, itute of Chemical Physics, U.S.S.R. Academy of Sciences
(Received 30 ,la,nary 1961) W E HAVE s h o w n b y t h e e l e c t r o n spin r e s o n a n c e ( E S R ) m e t h o d t h a t w h e n polyv i n y l c h ] o r i d e (P VC ) is i r r a d i a t e d w i t h 7 - r a y s f r o m G°Co, f r e e r a d i c a l s a r e f o r m e d Ill]. A s a r e s u l t o f r e c o m b i n a t i o n a n d o x i d a t i o n t h e c o n c e n t r a t i o n o f p r i m a r y radicals decreases with time after irradiation. The rate of recombination and o × i d a t i o n i n c r e a s e s m a r k e d l y w i t h i n c r e a s e in t e m p e r a t u r e . * Vysokomol. soyed. 4: No. 1, 64 65, 1962.
A. I. SHATENSHTEINet al.
3. 4. 5. 6. 7. 8. 9.
I. Ya. PODDUBNYI, Khim. prom., No. 2, 4, 1958 G. NATTA, Makromol. Chem. 35: 94, 1960 C. S. MARVEL, et al., J. Org. Chem. 16: 838, 1951 A. I. YAKUBCHIK and B. I. TIKHOMIROV, Zh. obshch, khim. 30: 128, 1960 S. L. AGGARWAL and G. P. TILLEY, J. Polymer Sci. 18: 17, 1955 G. NATTA and P. CORRADINI, Suppl. Nuovo eimento 15: Ser. 10, 9, 1960 A. I. YAKUBCHIK, B. I. TIKHOMIROV and V. S. SULIMOV, Vestnik LGU, No. 22, 135, 1961 10. V. A. KARGIN and G. L. SLONIMSKII, Kratkie ocherki po fiziko-khimii polimerov. (Short Essays on the Physical Chemistry of Polymers.) p. 116, 1960 11. J. L. MATTHEWS, H. G. PEISER and R. B. RICHARDS, Acta crystallog. 2: 85, 1949 12. V. A. KARGIN, A. I. KITAIGORODSKI and G. L. SLONIMSKII, Kolloid. zh. 19: 131, 1957
THE PROTONIC AND APROTONIC MECHANISM OF POLYMERIZATION INITIATED BY POTASSIUM AMIDE IN LIQUID AMMONIA* A. I. SHATENSHTEIN, YE. A. YAKOVLEVA, YE. A. KOVRIZHNIK I ). N. MANOCHKINA and N. A. PRAVIKOVA L. Ya. Karpov
Physico-chemical
(Received 25 J a n u a r y
Institute
1961)
ANIONIC p o l y m e r i z a t i o n initiated b y a solution o f p o t a s s i u m amide in liquid a m m o n i a is one o f a n u m b e r of processes t h a t are a s s u m e d to proceed t h r o u g h a stage of c a r b a n i o n f o r m a t i o n . The c a r b a n i o n s m a y be f o r m e d b y the a d d i t i o n of a n N H : ion to a multiple b o n d or b y the transfer of a proton, i.e. b y a n aprotonic or a p r o t o n i c m e c h a n i s m . Sanderson a n d H a u s e r [1] a n d E v a n s , Higginson a n d W o o d i n g [2] showed t h a t the first o f these m e c h a n i s m s applies to the polymerization o f s t y r e n e b y p o t a s s i u m amide in liquid a m m o n i a . U n d e r these conditions a - m e t h y l s t y r e n e does n o t p o l y m e r i z e [1, 2]. I n c o n t r a s t to this s t a t e m e n t we h a v e p r e p a r e d a n d f r a c t i o n a t e d the p o l y m e r from ~-methylstyreue. The molecular weight, nitrogen c o n t e n t a n d b r o m i n e value f o u n d lead to the conclusion t h a t t h e p r o t o n i c m e c h a n i s m p r e d o m i n a t e s in the p o l y m e r i z a t i o n of a - m e t h y l s t y r e n e b y this initiating system. I n order to estimate the s t r e n g t h o f ~ - m e t h y l s t y r e n e as a h y d r o g e n acid we used the m e t h o d of isotope-exchange of h y d r o g e n [4] a n d applied it also to some diene h y d r o c a r b o n s which we also f o u n d to form low-molecular p o l y m e r s on p o l y m e r i z a t i o n with K N H 2 in liquid a m m o n i a . As far as we k n o w there is no i n f o r m a t i o n in the literature on the acid-base properties o f monomers. * Vysokomol. soyed. 4: No. 1, 42-51, 1962.
Protonic and aprotonic mechanism of polymerization
13
EXPERIMENTAL Preparations. S t y r e n e (ST) a n d c¢-methylstyrene (~-MST) a f t e r t h e u s u a l p u r i f i c a t i o n were distilled in vacuo, w i t h or w i t h o u t a c u r r e n t o f n i t r o g e n , a n d t h e m i d d l e f r a c t i o n was t a k e n . I n s o m e e x p e r i m e n t s t h e m o n o m e r s were a g a i n distilled f r o m m e t a l l i c s o d i u m . CommerciM b u t a d i e n e was d r i e d f o u r t i m e s o v e r solid p o t a s s i u m a m i d e . T h e o t h e r d i e n e h y d r o c a r b o n s were p r e s e n t e d t o u s b y B. A. K a z i n s k i i a n d I. V. G o s t i n s k a y a t o w h o m we e x p r e s s 20 20 o u r sincere g r a t i t u d e . I s o p r e n e : n B 1.4220, d~ 0.6810; 2 , 3 - d i m e t h y l b u t a d i e n e - l , 3 : b.p. 20 1.4393, d420 0-7266; h e x a d i e n e - 2 , 4 : b.p. 82-4°/760 m m , ~ o 1.4550, 68"3°/742 m m , ~1) d~°0.7216; 2 , 5 - d i m e t h y l h e x a d i e n e - 2 , 4 : b.p. 134"0°/734 r a m ; 7t~°o n 1-4772, d20 0.7619. E x p e r i m e n t a l method. T h e u s u a l l a b o r a t o r y a p p a r a t u s a n d e x p e r i m e n t a l t e c h n i q u e for w o r k i n g w i t h liquid a m m o n i a s o l u t i o n s were u s e d [5]. As a rule t h e m o n o m e r was a d m i t t e d t o t h e s y s t e m w i t h o u t t h e access o f air. I n o r d e r t o s t o p t h e p o l y m e r i z a t i o n a s m a l l q u a n t i t y o f w a t e r o r m e t h a n o l was a d d e d , a f t e r w h i c h t h e a m m o n i a was e v a p o r a t e d off. I n e x p e r i m e n t s o n t h e r a t e o f p o l y m e r i z a t i o n o f ~-MST a w e i g h e d q u a n t i t y o f t h e mon o m e r was sealed u n d e r h i g h v a c u u m in a s m a l l a m p o u l e a n d p l a c e d in t h e r e a c t i o n s y s t e m . A t t h e e n d o f t h e e x p e r i m e n t t h e a m m o n i a was r e m o v e d , a n a c c u r a t e l y k n o w n v o l u m e of" c h l o r o f o r m was a d d e d , a n a l i q u o t p a r t o f t h e s o l u t i o n was w i t h d r a w n b y m e a n s e t a p i p e t t e a n d t h e b r o m i n e v M u e w a s d e t e r m i n e d as d e s c r i b e d below. B e f o r e t h e i s o t o p e - e x c h a n g e e x p e r i m e n t s t h e d i e n e h y d r o - c a r b o n s were distilled in v ~ c u o a t a low t e m p e r a t u r e . T h e d e u t e r i u m - e x c h a n g e e x p e r i m e n t s were c a r r i e d o u t x~ith 0.1-0.2 g o f t h e m a t e r i a l a n d 5 - 6 m l o f t h e K N H ~ s o l u t i o n . A f t e r t h e r e a c t i o n m i x t u r e h a d b e e n k e p t in a t h e r m o s t a t for a set t i m e it was p o u r e d i n t o acidified w a t e r , t h e h y d r o c a r b o n x~as s e p a r a t e d a n d distilled o v e r a n h y d r o u s NiSOa a n d CaCI 2. T h e p r o d u c t was b u r n e d a n d t h e isotopic c o m p o s i t i o n o f t h e purified w a t e r w a s d e t e r m i n e d . W h e n t h e k i n e t i c s o f d e u t e r i u m e x c h a n g e w i t h g-MST were d e t e r m i n e d t h e p r o c e d u r e was t h e s a m e b u t 0.3 0-5 g o f m o n o m e r were t a k e n a n d b e f o r e c o m b u s t i o n t h e p r o d u c t was distilled it~ vaeuo over CuSO 4. All t h e p r o d u c t s a f t e r t h e isotope e x c h a n g e r e a c t i o n h a d r e f r a c t i v e indices close t o t h o s e of" t h e s t a r t i n g m a t e r i a l s . M. I. A r s h i n o v a a s s i s t e d in t h e d e u t e r i u m . e x c h a n g e experiments. Deter~ni*~atio~ of bromine value. A m o d i f i e d K a u f m a n m e t h o d [6J was u s e d fbr t h e d e t e r m i n a t i o n o f b r o m i n e values. T e s t s h a v e s h o w n t h a t p h e n y l e t h y l a m i n e a n d p o l y s t y r e n e e o n t a i n i n g n i t r o g e n do n o t r e a c t w i t h t h e r e a g e n t s u s e d in K a u f m a n ' s b r o m o m e t r i c t i t r a t i o n m e t h o d [6]. N u m e r o u s c o n t r o l a n a l y s e s o f ST a n d ~-MST a n d also o f m i x t u r e o f t h e m o n o m e r s a n d p o l y m e r s s h o w e d t h a t CCI4, CHC1 a a n d C6H6 c a n be u s e d as s o l v e n t s in plaee of' C H a O H . T h e b r o m i n e v a l u e is e x p r e s s e d as g Br2/100 g o f s u b s t a n c e . Determ[~¢ation of molecular weight. T h e m o l e c u l a r w e i g h t o f t h e p o l y m e r s was d e t e r m i n e d b y t h e ebullioscopie, cryoseopic a n d v i s c o m e t r i e m e t h o d s , a n d also b y e n d - g r o u p a n a l y s i s ( n i t r o g e n c o n t e n t ) . T h e ebullioscopie m e a s u r e m e n t s were e a r r i e d o u t b y P. P. A l i k l a n o v w i t h his o w n m o d i f i c a t i o n o f t h e R e y e b u l l i o m e t e r , w i t h a f i v e - j u n c t i o n t h e r m o e o u p l e . T h e o r d i n a r y a p p a r a t u s w i t h a B e e k m u n t h e r m o m e t e r was u s e d t b r t h e eryoseopie m e a s u r e m e n t s . T h e v i s c o s i t y o f t h e p o l y m e r s o l u t i o n s was m e a s u r e d in a n U b b e l o h d e v i s e o m e t e r . T h e i n t r i n s i c v i s c o s i t y [r/] was f o u n d f r o m t h e i n t e r c e p t o n t h e o r d i n a t e of' p l o t s o f Jlsp/e ~md log #r/c a g a i n s t t h e c o n c e n t r a t i o n o f t h e s o l u t i o n , c (g/100 ml). N i t r o g e n was d e t e r m i n e d by the semimicro Kjeldahl method. Fractionation of the polymers. T h e l o w - m o l e e u l g r ST a n d ~-MST p o l y m e r s were f r a e t i o n a t e d b y t h e m e t h o d o f F u e h s {7] w h i c h we m o d i f i e d b y r e p l a c i n g t h e fine a l u m i n i u m foil b y m e t a l (or glass) helices, u s e d f o r filling f r a e t i o n a t i n g c o l u m n s ( L e v y packing'). T h e use of' t h i s s u p p o r t c o n s i d e r a b l y s h o r t e n e d t h e t i m e o f t h e p r e l i m i n a r y w o r k o f p r e p a r a t i o n before e x t r a c t i o n w i t h t h e s o l v e n t - p r e e i p i t a n t m i x t u r e , a n d m a d e t h e process easier. T h e p a c k i n g , w i t h a t o t a l surface a r e a o f a b o u t 1000 c m 2, w a s t h o r o u g h l y w a s h e d w i t h b e n z e n e
14
A . I . SHATENSHTEIN et al.
a n d e t h e r , a n d dried. A u n i f o r m l a y e r w a s p l a c e d o n t h e b o t t o m o f a c r y s t a l l i z i n g d i s h ( d i a m e t e r 15 cm) a n d 5 0 - 7 0 m l o f a b e n z e n e s o l u t i o n o f t h e p o l y m e r c o n t a i n i n g a b o u t 1.5 g o f t h e l a t t e r w a s p o u r e d o v e r it. T h e b e n z e n e was e v a p o r a t e d a n d t h e p a c k i n g w i t h its d e p o s i t e d l a y e r o f p o l y m e r was d r i e d t o c o n s t a n t w e i g h t a t 50 ° i n v a c u o . T h e p a c k i n g w a s t h e n t r a n s f e r r e d t o a t w o - n e c k e d , 500 m l flask w i t h g r o u n d - g l a s s caps. A s i n t e r e d glass filter was sealed i n t o o n e o f t h e n e c k s o f t h e flask. T h e flask was i m m e r s e d in a t h e r m o s t a t (20 °) a n d 1 0 0 m l o f a m i x t u r e o f b e n z e n e a n d m e t h a n o l (1 : 9 b y v o l u m e ) was a d d e d . E q u i l i b r i u m o f t h e d i s s o l v e d f r a c t i o n was a t t a i n e d a f t e r s h a k i n g for 10-15 m i n u t e s a n d t h e s o l u t i o n w a s filtered off t h r o u g h t h e glass filter. T h e e x t r a c t i o n w a s r e p e a t e d 10-15 t i m e s w i t h a s t e p w i s e i n c r e a s e i n t h e b e n z e n e c o n t e n t o f t h e m i x t u r e b y 5-10~o b y v o l m n e . T h e s o l v e n t w a s e v a p o r a t e d , t h e f r a c t i o n s were d r i e d t o c o n s t a n t w e i g h t i n v a c u o a n d dissolved i n a m e a s u r e d v o l m n e o f t o l u e n e . T h e v i s c o s i t y o f t h e s o l u t i o n s was m e a s u r e d in a s e m i m i c r o U b b e l o h d e viscometer. In order to test the reproducibility of the fractionation and to compare the original m e t h o d o f F u c h s w i t h o u r m o d i f i c a t i o n f o u r e x p e r i m e n t s were c a r r i e d o u t w i t h s a m p l e s o f p o l y s t y r e n e p r e p a r e d b y p o l y m e r i z a t i o n in a n a m m o n i a c a l s o l u t i o n o f K N H ~ . T h e p o l y m e r was dissolved in benzene, precipitated ten times with an equal volume of methanol and d r i e d i n v a c u o . T h e v i s c o s i t y o f s o l u t i o n s o f t h e p o l y m e r i n t o l u e n e a n d b e n z e n e a t 20 ° a n d 25 ° were f o u n d t o b e p r a c t i c a l l y t h e s a m e a t 0 " 0 9 3 i 0 " 0 0 3 . C o n s e q u e n t l y for t h e c a l c u l a t i o n o f m o l e c u l a r w e i g h t it is possible t o use ( w i t h i n t h e l i m i t s o f e x p e r i m e n t a l a c c u r a c y ) t h e f o m u l a e d e r i v e d for t h e s e t w o s o l v e n t s a t t h e t w o s t a t e d t e m p e r a t u r e s . A c c o r d i n g t o P e p p e r [8] for l o w - m o l e c u l a r , u n f r a c t i o n a t e d p o l y e s t y r e n e [~1]=2"27× 10 4 M0.72 (tool. wt. 4200),
(1)
a c c o r d i n g t o B a m f o r d a n d D e w a r [9] [ q ] = 4 . 4 0 × 10 -4 M °'~5 (tool. wt. 3700).
•2 lO0
i 10
• 2
AO
~e
•-PO
6
qo
u
20
2
5
/0
(2)
15
Z,O
[~/x:g
I n t e g r a l a n d differentia] m o ] e c u l a r w e i g h t d i s t r i b u t i o n curves: (i) f r a e t i o n a t e d p o l y m e r d e p o s i t e d o n a l u m i n i u m foil ( F u c h s m e t h o d ) , e x t r a c t i o n t i m e (t) 15 m i n u t e s ; (2) p o l y m e r d e p o s i t e d o n m e t a l helices, t = 15 m i n u t e s ; (3) p o l y m e r d e p o s i t e d o n glass helices, t ~ 1 0 m i n u t e s . A v e r y m u c h l o w e r figure is o b t a i n e d w i t h t h e f o r m u l a o f K e m p a n d P e t e r s [10], i n r e f e r e n c e [3] (tool. w t . 2600). T h e ebullioscopic m o l e c u l a r w e i g h t d e t e r m i n e d b y A l i k h a n o v was: 4600, 4000 4400, 4600, 4100, m e a n 4300.
Protonic and aprotonic mechanism of polymerization
15
The diagram shows the results of the fractionation of this polymer. The abscissa represents the values of ]t/l, the ordinate on the left the sum of the weights W of the successive fractions, expressed as a percentage of the weight of polymer taken, and on the right ((1W/d[tl])x 10-2. I t is seen that the original and modified Fuchs methods gave closely similar results. Curve B was obtained by graphical differentation of the integral curve A. This gives a graphical representation of the molecular weight distribution. Knowing the weights a n d intrinsic viscosities of the fractions we calculated (see I11]) the viscosity of' the solution of the unfractionated polsTmer. The calculated value) ([~/]--0.092) practically coincides with the value found experimentally in benzene and toluene at 20 ° and 25" ([q] =0.093~:0.003), thus confirming the reliability of the fractionation procedure and of the measurements carried out on the individual fractions. We also calculated by the method of Schulz [ l l ] the weight-average and numberaverage molecular weights of the polymer, using the results of the fractionation and applying firstly Pepper's equation [8] [~]--4.17 :< 10-4 M°'6°, (3) and secondly Rossi's equation [12] [ t / l - - 10.1 x 10 a M0.50
(4)
fbt' fractionated, low-molecular polystyrene. The results obtained were: ~iw=8000, M , = 4 9 0 0 [formula (3)]; i~W=8500, M,,=4300 [formula (4)]. The calculated values of M,, are close to the molecular weight obtained by Alikhanov by the ebullioscopic method.
RESULTS AND DISCUSSION
Styrene (ST) and a-methylstyrene (~-MST). E x p e r i m e n t s w e r e set u p t o c o m p a r e the polymerization of these monomers, initiated by KNH 2 in liquid ammonia. W h e n t h o r o u g h l y p u r i f i e d ST, p r e v i o u s l y t r e a t e d w i t h s o l i d K N H 2 a n d d i s t i l l e d i n h i g h v a c u u m , is m i x e d w i t h a 0 . 0 2 N s o l u t i o n o f K N H 2 a t 25 ° t h e p o l y m e r precipitates i m m e d i a t e l y in q u a n t i t a t i v e yield. F o r a period of 2-3 m i n u t e s the r e a c t i o n m i x t u r e r e m a i n s a l m o s t colourless, s u b s e q u e n t l y i t a c q u i r e s a p i n k a n d t h e n red eolour*, a-MST polymerizes m u c h more slowly a n d some t i m e elapses before the p o l y m e r begins to p r e c i p i t a t e from the red solution. I n e x p e r i m e n t s o n t h e p o l y m e r i z a t i o n o f ST, 1 m o l e o f m o n o m e r r e q u i r e d 25 m o l e s o f N H 3. T h e e x p e r i m e n t a l r e s u l t s a r e g i v e n i n T a b l e 1. * The appearance of a red colouration by the action of K N H 2 in a m m o n i a on polystyrene was observed in our laboratory by Ye. A. Izrailevich. Subsequently this phenomenon was studied in more detail by ¥e. N. Zyagintseva and Z. N. Ovehinnikova. Their experiments showed that the colour appears gradually and independently of the method of preparation of the polymer (by free-radical, cationic or anionic polymerization). A 0.02 N solution of the amide in equal volumes of liquid a m m o n i a and benzene was used to dissolve the polymer. The colouration also appeared when a polymer prepared by free-radical polymerization with benzoyl peroxide and repreeipitated several times in an atmosphere of nitrogen was dried by several treatments with liquid a m m o n i a in the absence of air, and air was also excluded (luring the course of the experiments. According to the findings of Ye. A. Rabinovich the solution absorbs light in the same region of wavelengths (~max 550-565 m~t) as the eoloured solution formed in the polymerization of ST by potassium amide in liquid a m m o n i a [ 13].
A. I. SIIATENStITELNet
16
al.
TABLE 1. POLYMERIZATIONOF STYRENE
TelTIperature
(~c)
~ 2 solution
(N)
1.0 0-1 0.05 0.02 0"02 0.02 0.02 0-02
25 25 25 25 50 25 --30 --50
Molar ratio ST:KNH~
(m)
1.4 15 30 80 80 80 80 80
Mol. wt. Molecular o f unrepreN weight [~]** Mol. wt. content cipitated (viscosity) (benzene, from N polyof content* 25 °) from from polymer styrene (g/100 ml) f o r m u l a f o r m u l a (M~) (%) (cryo(1) (2) scopic) 45O 75O 850 920 610 920
2.1
650
1.4 1.0 2.2 1.0 0.6
1000 1400 640 1400 2300 i
0.024 0-032 0.039 0.043 0.030 0.043 0.111 0.125
650 960 1000 1500 880 1500 5400 6400
560 750 820 1200 I 660 1200 4900 5900
* Assuming that the polymer ch:aincontains one NH.~group. ** Efflux time of solvent, 97'7 sec.
The molecular weight of the polystyrene increases with decreasing temperature of polymerization and varies little even with large variations in K N H 2 concentration. This is in agreement with the data in the literature [3]. The absolute value of the molecular weight of polystyrene prepared with K N H 2 in ammonia is low. This is explained by the fact t h a t the polymer chain is soon terminated by ammonia. In fact, as was shown in reference [14], when the polymerization of styrene is initiated by solid K N H 2 in the absence of ammonia polymers with molecular weights of a few millions are obtained. I t was stated above t h a t a-MST polymerizes much more slowly t h a n ST. At 25 °, a K N H 2 concentration of 0.05 2( and m = 3 0 the degree of unsaturation (expressed as a percentage) of the material isolated from the reaction mixture varies as follows: Hours (~) Hours o~)
0 97 2 27
0 98 2 26
0 97 3 21
0"25 61 3 22
0"25 56 6 17
0"25 54 8 20
0"5 44 8 18
1 33 12 19
1 32 12 18
2 27 270 18
2 32
The residual unsaturation (~ 20%) is preserved even after l0 days and more. This can be explained by equilibrium between the polymerization reaction and the unsaturation of the polymer being formed. The low rate of polymerization of ~-MST enabled us to study the deuteration reaction in this process. In some experiments part of the monomer isolated after deuteration was oxidized with alkaline permanganate to benzoic acid which was isolated, sublimed and burned. The quantity of deuterium formed in the benzoic acid showed that in the benezene ring of a-MST the following fractions (in %) of the total number of hydrogen atoms are substituted by deuterium:
Protonie and aprotonie mechanism of polymerization
17
after 30 m i n u t e s - - 1 8 , 21, 18 (mean 19), after 60 m i n u t e s - - 2 5 , 22, 21 (mean 23). C o n s e q u e n t l y u n d e r these conditions the h y d r o g e n in the s u b s t i t u e n t g r o u p o f ~-MST undergoes e x c h a n g e p r e d o m i n a n t l y . Therefore for the calculation of the rate c o n s t a n t for the e x c h a n g e r e a c t i o n (by t h e first-order equation) we a s s u m e d t h a t there are five e x c h a n g e a b l e h y d r o g e n a t o m s in the ~-MST molecule. The e x p e r i m e n t a l conditions were: 25 °, K N H 2 c o n c e n t r a t i o n 0.02N, G - - t h e conc e n t r a t i o n of d e u t e r i u m in the a m m o n i a before the e x p e r i m e n t - - 4 . 2 4 a t o m s o/ /O (or 4.77 a t o m s ~o where m a r k e d with an asterisk), % is the c o n c e n t r a t i o n o f d e u t e r i u m in the w a t e r f r o m c o m b u s t i o n of the m o n o m e r after a n e x p e r i m e n t lasting r minutes, n the n u m b e r o f h y d r o g e n a t o m s e x c h a n g e d with d e u t e r i u m (calculated f r o m t h e coefficient o f d i s t r i b u t i o n o f d e u t e r i u m b e t w e e n C - - H a n d N - - H bonds, a = 0 . 9 2 ) a n d k t h e rate c o n s t a n t in sec 1. r cw ~ k × 1()~ r cw ~ k ~ 103
5 0"59 1"5 1"2 20* 1"75 4"0 1.2
5 0"60 1"5 1"2 30 1"69 4"3 1-1
10 0"95 2"4 1"1 30 l"72 4"4 1.2
10 1"05 2"7 ] "3 30 1"72 4"4 1-2
15 15 20 1"20 1"25 1"52 3"1 3"2 3"9 1"1 1"1 1"1 30* 1500 1"95 2"22 4"4 5"7 1-2 --
20
20*
1"47
1'62
3"8 1"2
3'7 1"1
The rate c o n s t a n t o f d e u t e r a t i o n in the side chain o f ~-MST m a i n t a i n s a c o n s t a n t value in e x p e r i m e n t s c o n t i n u e d for differen ~lengths of time. C o n s e q u e n t l y no i n e q u a l i t y in r e a c t i v i t y of the h y d r o g e n a t o m s could be observed. This can be a t t r i b u t e d to the f o r m a t i o n o f an ion of s t r u c t u r e I belowt
I n p r e l i m i n a r y e x p e r i m e n t s with fl-methylstyreue at the same t e m p e r a t u r e a n d a m u c h higher c o n c e n t r a t i o n o f the amide (CKNH:--I"5 12~) it was f o u n d t h a t in c o n t r a s t to a-MST o n l y two h y d r o g e n a t o m s u n d e r g o exchange. I t is k n o w n [15] t h a t in a n a m m o n i a c a l solution of p o t a s s i u m amide the following isomeric equilibrium exists, C 6 H s C H = C H - - C H a ( I I ) ~ C 6 H s C H 2 C H = C H 2 ( I I I ) , which suggests t h a t it is t h e t w o allylic h y d r o g e n a t o m s in I I I t h a t u n d e r g o exchange, f u r t h e r h y d r o g e n e x c h a n g e being hindered b y the n e g a t i v e charge of the c a r b a n i o n formed. t In a paper by M. Kolobielski and H. Pines (J. Amer. Chem. Soc. 79: 5820, 1959), which came to our notice after this paper had been sent for publication, a study was made of the chemical reactions occurring when ~-methylstyrene is heated with sodium. In their discussion of the mechanism of the reaction these authors also concluded that the earbanion I is probably formed.
18
A . I . SHATENSHTEIN et al.
The high value of the rate constant of the exchange reaction ( k = 1.2 × 10-a see -i) at a low concentration of K N H e (0.02 N) and a moderate t em perat ure (25 °) indicates a considerable mobility of the hydrogen atoms of the substituent group of ~-MST. The rate of deuteration in this group is greater t han t h a t in the CH a group of propylene [16] and is only slightly below the rate of deuteration in the CH a group of toluene [17]. The protonic mobility of the hydrogen atoms of the substituent group of a-methyl~tyrene is much higher t han the mobility of the hydrogen atoms of the aromatic nucleus. However, under suitable conditions the latter can be brought to light even in polystyrene. Ye. A. Izrailevich succeeded in introducing up to 60% of deuterium into finely dispersed polystyrene by prolonged t r e a t m e n t of the polymer (more t h a n 100 hours) with a 0.2 N solution of K N H 2 in liquid ammonia at 60 °. * We shall now consider the mechanism of initiation of the anionic polymerization of ST and ~-MST in ammoniacal solutions of K N H 2. The results presented in Table 1 show t h a t the molecular weight of the polystyrene calculated from the nitrogen content is close to the cryoscopic molecular weight. Consequently the polymerization of ST is initiated b y an aprotonic mechanism by the addition of an N H ~ ion to the double bond, in conformity with the results and conclusions of Higginson and Wooding [3]. The deuterium-exchange experiments disclosed a higher mobility of the hydrogen atoms of the substituent group of a-MST. This suggests t h a t it m a y polymerize b y a protonic mechanism. In order to test this idea we prepared polymers of ~-MST and ST under similar conditions. One hundred and fort y millilitres of a 0.02 N solution of K N H 2 was added to 6.5 g of a-MST and 300 ml of the same solution was added to 7.1 g of ST. The reaction mixtures were held at --15 ° for a sufficient length of time. The results of the fractionation of the solid polymers are summarized in Table 2. Both polymers were precipitated from benzene solution b y ten volumes of methanol. The filtrate after precipitation of the polystyrene was evaporated and the fraction of lowest molecular weight (fraction No. 1) was isolated from it. The intrinsic viscosity [r/] was measured for toluene solutions of the polymers at 25 ° and for some fractions of the poly-~-methylstyrene the relative viscosity of ground-molar solutions (~r) was determined for the calculation of molecular weight (M1) b y the Staudinger method [18]. The molecular weight, M2, of poly-~-MST was calculated from the formula of Brown and Mathieson [19] [r/]--3.5 × 10-5 M.
(5)
* It should be noted that in experiments carried out by V. M. Basmanova with ~methylstyrene that the isotopic exchange of hydrogen in the aromatic ring is more rapid with DBr than in the nucleus of toluene, i.e. ~-mcthylstyrene is a stronger base than toluene. This is of interest in connection with the discussion of certain problems of cationic polymerization where the monomer functions as a base.
P r o t o n i c an(][ a p r o t o n i c m e c h a n i s m o f p o l y m e r i z a t i o n
t9
TABLE 2. FRACTIO_NATION OF STYRENE AND ~-METHYLSTYRENE POLYMERS
i CHaOH
Fraction No.
C~H~ ! (vol. o ~ , ) (vol. o{~)
I .
.
.
I
Filtrate 10 20 25 30 35 45 50 55 60 70 100
90 80 75 70 65 55 50 45 40 30 0
] "
Poly-a-methylstyrene
[ q] = 0'042
.
D,Teight i (rag)
I
1 2 3 4 5 6 7 8 9 10 1l 12
! Polystyrene, I [ q] = 0"086
~,Yeight. ~
i [ q]
890 10 36 59 119 187 195 129 207 159 131 5
(mg)
[ q]
I
! q,.
3f I
.ll.
850 910 (990) (ll00)
800 850 910 1090 1140 1700
0-030 0"0365! 0-037 0"038 0-048 0"065 0-096 0-110 0"146 0"164
20 80 137 473 394 382 34 5 2 3 2
0.028 i 0-030 ~ 1.44 0.032 1.52 0-038 / 1.63 0"040 1-66 0"060
This magnitude m a y be increased because of the presence of a terminal group ill the polymers with which these authors worked [19]. Comparison of these molecular weights of the polymers of ~-MST and ST with those quoted in the literature for polymethylmethacrylate [20] and polymethacrylonitrile [21], prepared with K N H 2 in ammonia, shows t h a t the molecular weight of the polymer increases with increasing reactivity of the monomer in anionic polymerization: ~-MST < ST < methylmethacrylate < methacrylonitrile. Some of the fractions shown in Table 2 were studied in more detail. Values of [q] of 0.30 and 0.29 were obtained for polystyrene fraction No. 1 in two vise()meters. The following molecular weights were obtained by applying formulae for fractionated polystyrene: according to Pepper [18] (3) mol. wt. 1200; according to Bamford and Dewar [9] [~/] =2.92 x 10 4 M0.Gs (tool. wt. 1240) (6) according to Rossi and Bianchi [12] (4) tool. wt. S90, and according to Rossi et al. [22]
[q]=9.2 × 10-4 Mc5° (tool. wt. 1100)
(7)
The molecular weight determined by the ebullioscopic method (M~) was 750 and 770 (mean 760). The less accurate eryoscopic method gave values of M,: of 820 and 880 (mean 850). The nitrogen content was 1.45, 1.44, 1.40, 1.38 (mean 1.42°) whence Mx : 1000. Bromine value, 0-0.5. The following results were obtained for u-MST fractions: Fraction No. 4 5 6 7
Bromine calue 9.7 7.1 5.1
Nitrogen (°/o) 0.17; 0.14; 0.10;
0.17; 0.16 0.10
0.15
20
A.I. SHATENSHTEIN et
al.
In addition two samples of a-MST, prepared independently, were analysed: (1) a polymer of pasty consistency, [I;]=0.02, relative viscosity of a ground-molar solution t/r=l'28, ebullioscopic molecular weight 450, 450 (mean 450), molecular weight according to formula (5), 570, nitrogen content 0.33, 0.29 (mean 0.3% ), bromine value 12.2, 12.5; (2) a solid, white polymer (precipitated from a 1:10 mixture of benzene and methanol)* [t1]=0'033, molecular weight according to (5), 940, ebullioscopic molecular weight 1000, 940 (mean 970), nitrogen content 0.10, 0.14, 0-19, 0.15, 0.22 (mean 0-16%) :, bromine value 9.9, 9.6 (mean 9.8). Thus the ~-MST polymer contains approximately one tenth of the nitrogen in a polystyrene of similar molecular weight prepared under similar conditions. This fact in conjuetion with the unsaturati6n detected in poly-a-MST indicates t h a t in its formation an important part is played by the transfer of a proton from the monomer molecule. The following reactions are possible in the initation stage
+ Hf
/
C~H~
I
N H s- CH s- C-
C6H5/ CH2~
(I)
CH2
\ +NH_~
C6H5
I ) C--CH 2 + N H 3
(II)
CH~
The propagation stage is represented by the reactions
NH2CH2CI
+ [CH2=~
CH3 C~H~I
CHa. ~
[
"C6H5-1
C--CHill" + [ C H 2 = ~ CH2
--~ NHeCH2CI -- CHIC' CH 3 C~HsI
[----> cC- H - e2l C l ' -, !- I
CHa Jn
CH2
(Ia)
CH~ C6H~]_ I
{IIa)
CH 3
By reaction (IIa) the polymer chain retains the double bond and nitrogen is absent. The same result can be achieved if chain transfer to monomer occurs, accompanied by the release of a proton from the monomer molecule* * The weight of the solid polymer was 0.8 g and the weight of pasty polymer isolated from the filtrate was 3.0 g ([7] =0.021, n2D01"585). t This was brought to our attention by A. R. Gantmakher.
Protonic and aprotonic mechanism of polymerization C~H5
21
C~H5 C6H5 C6H5 C6H5 C6H5 I I_ W [ r I NH2--CH2--Cw~ CH2--C + C H 2 - C ---~NH2--CHe--C~ CH2--CH+C CH~ I i I I [i CH a CH 3 CH 3 (?Ha CH a CH2 and s u b s e q u e n t l y according to e q u a t i o n (IIa). I t m u s t not be supposed t h a t in polymerizations t h a t are described b y schemes t h a t include the f o r m a t i o n of carbanions, t h a t the l a t t e r are always p r e s e n t ill reality'. I t is p r o b a b l e t h a t often, as has been f o u n d in ~)ther reactions betwee~l h y d r o c a r b o n s and bases [4], " a n i o n i z a t i o n " of the molecule occurs in t h e Vransition state. Diene hydrocarbons. I n a s t u d y o f d e u t e r a t i o n reactions carried out in our l a b o r a t o r y [23] it was observed t h a t when a solution of K N H 2 in a m n l o n i a is a d d e d to diene h y d r o c a r b o n s a colouration appears a n d the h y d r o c a r b o n polymerizes. These e x p e r i m e n t s h a v e now been r e p e a t e d with a larger n u m b e r of hydrocarbons. W h e n K N H 2 is a d d e d to a solution of b u t a d i e n e (~v) a yellow colour appears, which g r a d u a l l y changes to orange, red a n d t h e n violet, a n d a low-molecular p o l y m e r is deposited on the walls o f the vessel in the f o r m o f oily droplets. T h e m e t h y l - s u b s t i t u t e d h y d r o c a r b o n s m e n t i o n e d below b e c o m e coloured to different shades of red. The p o l y m e r deposits in the form o f droplets a n d the p o l y m e r izability decreases as the n u m b e r o f m e t h y l groups in the diene molecule increases. Usually even after several hours it is possible to isolate p a r t of t h e m o n o m e r unchanged, a n d t h u s isotope-exchange e x p e r i m e n t s can be made. In c o n t r a s t to the m e t h y l s u b s t i t u t e d dienes, at room t e m p e r a t u r e and CK~H.= 0 ' 0 2 N evet~ a f t e r 24 hours it is possible to e x c h a n g e o n l y one h y d r o g e n a t o m in IV. Yu. G. Dubinskii in our l a b o r a t o r y has shown t h a t the cryoscopic m o l e c u l a r weight of p o l y b u t a d i e n e , p r e p a r e d at 20-25 °, corresponds to a degree of polymerization of five or six (tool. wt. 265-310) a n d it remains c o n s t a n t o v e r a wide range o f K N H 2 concentrations (0.005 to 1.0 N) with a fixed m o l a r ratio of N H 3 to IV of 40:1. The p o l y m e r contains 5.2-5.5% of nitrogen. I f it is assumed t h a t b y the aprotonic initiation m e c h a n i s m the p o l y m e r molecule contains one a t o m of nitrogen the calculated molecular weight is 250-275, in good a g r e e m e n t with the figure o b t a i n e d b y direct m e a s u r e m e n t . The p o l y m e r i z a t i o n of I V was not r e p o r t e d i~t the previous papers [1, 2]. Ext)erimellts carried out w i t h the assistance of M. I. Arshinova on d e u t e r i u m (,x(~hange at 25 ° (CK~t~.-~0"05 N ) w i t h the m e t h y l - s u b s t i t u t e d dienes, showed from the n u m b e r a f atoms e x c h a n g e d t h a t the h y d r o g e n atoms of the CH 3 groups ;~ttached to a carbo~l a t o m of the double bonds t a k e p a r t in the e x c h a n g e reactio~ c()mparatively easily. 2-Methylbut(ldiene (isoprene) (V) c~)=5.01 a t o m s o~ D t l 2 n 6 rw 1.5l [.70 1.69 1.61 , 2,7 3.0 3.0 2.9 t r in hours.
A . I . SHATENSHTEINet al.
22
2,3-Dimethylbutadiene-l,3 (VI) c~o : 5 . 0 1 a t o m s °/o D cw ~
0.5
1
2
3
4
5
1.34 3-0
2.12 4.7
2.79 6.2
3.32 7"3
3.46 7.7
3.48 7.7
3 2.58 6.0
4 2.45 5.8
21 3.18 7"5
Hexadiene-2,4 ( V I I ) c ° = 4 - 7 1 a t o m s °/o D v cw n
0.25 2.13 5-0
0"5 2.24 5.7
1 2.40 5.7
2,5-Dimethylhexadiene-2,4 (VIII)c°--~4.71; 5.01 a t o m s °/o D m a r k e d *) r cw ~t
0.25 3"33 10"0
0"5 3"58 12"0
2* 3"89 12"1
3* 3"97 12"3
20 4"06 13"4
48 4"27 13"2
M e a s u r e m e n t s carried o u t a t the s a m e t e m p e r a t u r e b u t w i t h a lower c o n c e n t r a t i o n o f K N H 2 (0-02 N) s h o w e d t h a t c o m p o u n d s V, V I I a n d V I I I in 4 - 6 h o u r s e x c h a n g e 3, 6 a n d 12 h y d r o g e n a t o m s , in c o n f o r m i t y w i t h the n u m b e r of h y d r o gen a t o m s in t h e m e t h y l g r o u p s present. T h e r e m a i n i n g h y d r o g e n a t o m s , if t h e y e x c h a n g e a t all, do so m u c h m o r e slowly as was n o t e d in t h e case of b u t a diene. A s t u d y o f t h e p o l y m e r i z a t i o n of diene h y d r o c a r b o n s in liquid a m m o n i a a n d t h e p r o d u c t i o n o f m o r e detailed i n f o r m a t i o n on d e u t e r i u m e x c h a n g e will b e t h e s u b j e c t o f f u r t h e r investigations, f r o m which new i n f o r m a t i o n on t h e role o f p r o t o n i c a n d a p r o t o n i c m e c h a n i s m s in anionic p o l y m e r i z a t i o n s is e x p e c t e d . CONCLUSIONS
(1) I t is s h o w n t h a t a - m e t h y l s t y r e n e a n d a n u m b e r o f diene h y d r o c a r b o n s p o l y m e r i z e b y the action o f K N H 2 in liquid a m m o n i a to f o r m l o w - m o l e c u l a r p o l y m e r s . T h e low r a t e of p o l y m e r i z a t i o n enables the m e t h o d o f d e u t e r i u m e x c h a n g e w i t h a solution o f K N H 2 in d e u t e r a t e d liquid a m m o n i a to be used to e s t i m a t e t h e m o b i l i t y of the h y d r o g e n a t o m s of these m o n o m e r s . (2) T h e p o l y m e r i z a t i o n o f s t y r e n e a n d a - m e t h y l s t y r e n e in a m m o n i a solutions of K N H 2 has b e e n c o m p a r e d a n d a s t u d y has b e e n m a d e of t h e p r o p e r t i e s (molecu l a r weight, n i t r o g e n content, b r o m i n e value) o f t h e p o l y m e r s a n d t h e i r fractions. T h e conclusion is d r a w n t h a t in c o n t r a s t to t h e p o l y m e r i z a t i o n of s t y r e n e , which p o l y m e r i z e s b y a n a p r o t o n i c m e c h a n i s m , t h e m a i n role in t h e p o l y m e r i zation o f a - m e t h y l s t y r e n e is t a k e n b y processes a s s o c i a t e d w i t h t h e t r a n s f e r of a p r o t o n f r o m t h e m o n o m e r molecule. (3) Modifications h a v e b e e n m a d e in t h e m e t h o d of f r a c t i o n a t i o n of p o l y m e r s of low m o l e c u l a r w e i g h t b y e x t r a c t i o n . Tra~,slated by E. O. PHILLIPS REFERENCES
1. J. J. SANDERSON and C. R. HAUSER, J. Amer Chem. Soc. 71: 1595, 1949 2. M. G. EVANS, W. C. E. HIGGINSON and N. S. WOODING, Rec. tray. chim. 68: 1069, 1949
Disappearance of free radicals in irradiated polyvinylchloride
23
3. W. C. E. HIGGINSON and N. S. WOODING, J. Chem. Soc. 1952, 760 4. A. I. SHATENSHTEIN, Izotopnyi obmen i zameshchenie vodoroda v organicheskikh soyedinenyakh. (Isotope Exchange and the Substitution of Hydrogen in Organic Compounds.) Izd. Akad. N a u k SSSR, 1960 5. A. I. SHATENSHTEIN, Zh. fiz. khim. 15: 246, 1941 6. R. W. BARNE and I. B. JOHNSON, Anal. Chem. 28: 126, 195~ 7. O. FUCHS, Z. Electrochem. 60: 229, 1956 8. D. C. PEPPER, J. Polymer Sci. 7: 347, 1951 9. C. H. BAMFORD and M. J. S. DEWAR, Proc. Roy. Soc. 192: 310, 1948 10. A. R. KEMP and H. PETERS, Ind. Eng. Chem. 34: 1097, 1942 l l . G. V. SCHULTZ, Z, Electrochem. 60: 199, 1956 12. C. ROSSI and E. BIANCHI, J. P o l y m e r Sci. 41: 189, 1959 13. I. V. ASTAF'EV, Ye. A. RABINOVICH and A. I. SHATENSHTEIN, Vysokomol. soyed. 3: 555, 1961 14. A. I. SHATENSHTEIN, Ye. A. YAKOVLEVA and E. S. PETROV, Dokl. Akad. N a u k SSSR 136: 882, 1961 15. H. LEVY and H. C. COPE, J. Amer. Chem. Soc. 66: 1684, 1944 l(i. A. I. SHATENSHTEIN and L. N. VASIL'EVA, Dokl. Akad. Nauk SSSR 95: 115, 1954 17. A. I. SHATENSHTEIN and E. A. IZRAILEVICH, Zh. fiz. khim. 32: 2711. 1958 18. H. STAUDINGER and F. BRENSCH, Ber. 62: 442, 1929 19. C. P. BROWN and A. R. MATHIESON, J. Chem. Soc. 1958, 3445 20. W. E. GOODE, W. H. SNYDER and R. C. FETTES, J. Polymer Sci. 42: 366, 19~i0 21. C. G. OVERBERGER, H. YUKI and N. U R A K A W A , J. Polymer Sci. 45: 127, 1960 22. C. ROSSI, U. BIANCHI and E. BIANCHI, Makromol Chem. 41: 31, 1960 23. A. I. SHATENSHTEIN, L. N. VASIL'EVA and N. M. DYKHNO, Zh. fiz. khim. 2 8 : 1 9 3 1954
THE KINETICS OF THE DISAPPEARANCE OF FREE RADICALS IN IRRADIATED POLYVINYLCHLORIDE* Z. S. Y E G O R O V A , Y U . M. M A L I N S K I I , V. L. K A R P O V . A. ~]. K A L M A N S O N a n d L. A. B L Y U M E N F E L ' D L. Ya. K a r p o v Physico-chemieal Institute; Inst, itute of Chemical Physics, U.S.S.R. Academy of Sciences
(Received 30 ,la,nary 1961) W E HAVE s h o w n b y t h e e l e c t r o n spin r e s o n a n c e ( E S R ) m e t h o d t h a t w h e n polyv i n y l c h ] o r i d e (P VC ) is i r r a d i a t e d w i t h 7 - r a y s f r o m G°Co, f r e e r a d i c a l s a r e f o r m e d Ill]. A s a r e s u l t o f r e c o m b i n a t i o n a n d o x i d a t i o n t h e c o n c e n t r a t i o n o f p r i m a r y radicals decreases with time after irradiation. The rate of recombination and o × i d a t i o n i n c r e a s e s m a r k e d l y w i t h i n c r e a s e in t e m p e r a t u r e . * Vysokomol. soyed. 4: No. 1, 64 65, 1962.