- Email: [email protected]
Studies in acyl peroxides—VI. Initiating effect of asymmetrical diacyl peroxides in the bulk polymerization of styrene
Studies in acyl peroxides
1791
culated for copolymers in dimethylformamide for the case of total macromolecule screening. (3) From the viscosity figures, it is concluded t h a t the macromolecules are coiled in solutions of high ionic strength. Translated by V. ALFORD REFERENCES 1. S. M. KOCHERGIN and V. P. BARABANOV, Vysokomol. soyed. 3: 1210, 1962 2. V. A. MYAGCHENKOV, Ye. V. KUZNETSOV, O. A. ISHAKOV and V. M. LUCHKINA, Vysokomol. soyed. 5: 724, 1963 3. N. A. IZMAILOV, Elektrokhimiya rastvorov. (Electrochemistry of Solutions.) Izd.-vo. KhGU, 1959 4. N. F. PROSIILYAKOVA, Dissertation, Fiz. khim. inst. im. A. Ya. Karpova, Moscow, 1958 5. A. KATCHALSKY and H. EISENBERG, J. Phys. Sci. 6: 145, 1951 6. T. de BOER and H. BAKER, Sinteza org. preparatov. (Synthesis of Organic Preparation.) Foreign Literature Publishing House, SB 6, 67, 1958; SB 8, 7, 1958 7. Yu. K. YUR'YEV, Praktich. raboty po organich, khim. (Practical Work in Organic Chemistry). Izd.-vo MGU 1961 8. J. BAXENDALE, S. BYWATER and M. EVANS, J. Polymer Sci. 1: 237, 1946 9. A. P. ALEKSANDROV, Dissertation, K KhTI, 1950 10. M. FUOSS and P. STRAUSS, J. Polymer Sci. 4: 96, 1949 11. M. FUOSS and G. CATHERS, J. Polymer Sci. 3: 602, 1958 12. I. P. SHUBTSOVA, T. S. DMITRIYEVA, V. B. SCHASTNEV and S. A. GLIKMAN, Vysokomol. soyed. 5: 135, 1963
STUDIES IN ACYL PEROXIDES--VI. INITIATING EFFECT OF ASYMMETRICAL DIACYL PEROXIDES IN THE BULK POLYMERIZATION OF STYRENE Yu. A. OLDEKOP and G. S. BYLINA V. I. Lenin Belorussian State University
(Received 19 October 1963) E A R L I E R r e p o r t s h a v e d e s c r i b e d a n e w m e t h o d of s y n t h e s i z i n g a s y m m e t r i c d i a c y l p e r o x i d e s , a n d p r o p e r t i e s o f a n u m b e r of n e w a s y m m e t r i c p e r o x i d e s of a r o m a t i c a l i p h a t i c a n d a l i p h a t i c series h a v e b e e n d e s c r i b e d [1]. I n t h i s w o r k we give t h e r e s u l t s of a s t u d y of t h e i n i t i a t i n g a c t i v i t y of s o m e of t h e e a r l i e r a n d a few n e w a s y m m e t r i c p e r o x i d e s of t h e a r o m a t i c - a l i p h a t i c series in t h e b u l k p o l y m e r i z a t i o n of s t y r e n e . * Vysokomol. soyed. 6: No. 9, 1617-1623, 1964.
1792
Yu. A. OLDEKOPand G. S. BYLINA
EXPERIMENTAL
Reagents. The styrene was dried with CaCI~ which had been vacuum distilled three times and kept at dry ice temperature. The monomer content 99.8-99.9%. All the peroxides used in this work were prepared by the method described in [1]: oxidation of the appropriate aldehyde in acetic anhydride or the anhydrides of other acids. Acetyl m-nitrobenzoyl peroxide was prepared by the Nef [2] method of nitrating acctylbenzoyl peroxide. The purity of the peroxides was determined by iodine titration [3]. They were all 98-100% pure. Experimental procedure. The polymerization was performed in the absence of atmospheric oxygen. The air dissolved was removed from the monomer by freezing and melting the solution of peroxide in monomer in a vacuum followed by purging with purified nitrogen. To remove the air completely, the freezing and melting operations had to be repeated 4-5 times. Dilatometers were filled in a vacuum, and when the system was completely filled with purified nitrogen, they were sealed. The dilatometers were appoximately 10 ml volume and the diameter of the capillary tube was about 1 ram. The final extent of polymerization was 15%. This was calculated from the reduction in the volume of the reaction system, assuming that at 100% polymerization of the styrene, the volume of the system would have fallen by 0.177 of its original [4]. The initial polymerization rate was determined graphically, and given in mole/1./sec. The polymerization rates were also found at 60, 70 and 80°. The temperature was kept constant within =]=0.05°. The peroxide concentration was 0.015 mole/1. in all the experiments. The styrene was bulk polymerized. Results. I n the w o r k b y Cooper [5] the initiating a c t i v i t y of a n u m b e r of diacyl peroxides were studied. F o r convenience in c o m p a r i n g our figures with published ones, a n d also because his m e t h o d was v e r y simple, we h a v e proceeded in the same w a y , using the e q u a t i o n k~----k t (R ~ - R~ )/ 2k~M2C,
(1)
where ki is the p o l y m e r i z a t i o n initiation constant, k t is the chain breaking c o n s t a n t , R~ is t h e rate of initiated p o l y m e r i z a t i o n , R T is the rate of t h e r m a l p o l y m e r i z a t i o n k~ is the rate of chain growth, M t h e m o n o m e r c o n c e n t r a t i o n a n d C the initiator concentration. U p to 15 ~ conversion t h e m o n o m e r a n d initiator concentrations can be t a k e n as a c o n s t a n t , while the rate of t h e r m a l p o l y m e r i z a t i o n is low as c o m p a r e d with the initiated p o l y m e r i z a t i o n , a n d can be t a k e n as zero. E q u a t i o n (1) becomes
Ic =KR~,
(2)
where K = kJ2k~M~C. W e used e q u a t i o n (2) calculate the initiation c o n s t a n t of the p o l y m e r i z a t i o n reaction. Coopers w h e n he calculated the initiation constant, used the kt/k ~ values calculated b y B a m f o r d a n d D e w a r [6], a n d the result he got was K----440 mole -2 .1. ~ .see. B u t more reliable figures are n o w available for kt/]c~, a n d these were o b t a i n e d b y T o b o l s k y a n d Offenbach [7]. On t h e basis of these figures Walling [8] derived the following relation for k~/Ict: 1.7
×
e
(3)
Using e q u a t i o n (3), the/ct//c ~ values a t 60, 70 a n d 80 °, are 1300, 740 a n d 440 mole .1.-~. see respectively. W i t h a s t y r e n e c o n c e n t r a t i o n of 8.36 mole/1, a t 60 °,
Studies in aeyl peroxides
1793
8"28 mole/1, a t 70 ° a n d 8.20 mole/1, a t 80 °, a n d i n i t i a t o r c o n c e n t r a t i o n o f 0.015 mole/1, in all cases, t h e K v a l u e s o b t a i n e d a t 60, 70, a n d 80 ° are 620, 360 a n d 220 mole-2.12.sec r e s p e c t i v e l y . All t h e ]ci v a l u e s w e r e c a l c u l a t e d b y m e a n s o f e q u a t i o n (2). RESULTS AND DISCUSSION
T h e i n i t i a t i n g a c t i v i t y o f 21 d i a c y l p e r o x i d e s , 19 for t h e first t i m e h a s b e e n d e t e r m i n e d . T h e r e s u l t s are g i v e n in T a b l e 1, w h i c h s h o w s t h e p o l y m e r i z a t i o n r a t e a t 60, 70 a n d 80 ° , t h e a p p a r e n t a c t i v a t i o n energies o f t h e p o l y m e r i z a t i o n r e a c t i o n Ep, t h e i n i t i a t i o n c o n s t a n t /ci a t 60, 70 a n d 80 °, a n d t h e a p p a r e n t a c t i v a t i o n energies o f t h e i n i t i a t i o n r e a c t i o n E i. F o r c o m p a r i s o n we also s t u d i e d t h e init i a t i n g a c t i v i t y o f b e n z o y l p e r o x i d e (BP). I t is e v i d e n t f r o m t h e figures o b t a i n e d t h a t all t h e a s y m m e t r i c p e r o x i d e s o f t h e a l i p h a t i c series s t u d i e d h a v e h i g h e r i n i t i a t i n g a c t i v i t y t h a n B P . T h e o n l y e x c e p t i o n w a s a c e t y l - m - n i t r o b e n z o y l p e r o x i d e . C o n s i d e r a b l e influence on t h e i n i t i a t i n g a c t i v i t y o f t h e p e r o x i d e w a s e x e r t e d b y t h e v a r i o u s different c o n s t i t u e n t s in t h e b e n z e n e ring. S u b s t i t u e n t s in t h e ortho~position h a d t h e g r e a t e s t effect. I n this p o s i t i o n b o t h e l e c t r o n d o n o r a n d e l e c t r o n a c c e p t e r s u b s t i t u e n t s c a u s e d a TABLE 1. S T Y R E N E P O L Y M E R I Z A T I O N W I T H A S Y M M E T R I C A L D I A C Y L P E R O X I D E S
~ T.
g
Peroxides
Benzoyl Acetylbenzoyl Acetyl-o-chlorobenzoyl Acetyl-m-chlorobenzoyl Acetyl-p-chlorobenzoyl Acetyl-o-bromobenzoyl Acetyl-m-bromobenzoyl Acetyl-p-bromobenzoyl Acetyl-m-methylbenzoyl Acetyl-p-methylbenzoyl Acetyl-2,4,6-trimethylbenzoyl AcetyLo-methoxybenzoyl Acetyl-p-methoxybenzoyl Acetyl-o-acetoxybenzoyl Acetyl-p-phenylbenzoyl Acetyl-m-nitrobenzoyl Monochloroacetylbenzoyl Propionylbenzoyl Butylbenzoyl Isovalerylbenzoyl Acetylhexahydrobenzoyl
•$ ~
0.492 0'725 1'06 0.543 0.634 1.26 0.549 0-666 i 0'7331 0.766 2.95 1.59 0.930 f 0.742
1"28 1'77 2-71 1'34 1"47 3-10 1.24 1.66 1.92 1.94 7.32 4.01 2.41 1.91
i 0-733 1.89 i 0.276 0.85 0.802 1-97 i0.601 1.47 0-579 1.51 0-506 1.38 1.54 3.07
3.04 4.08 5.95 3.06 3.62 6.37 3-45 3-83 4-56 4.90 15.1 8.95 5.77 4-43 4-37 2-16 4.83 3.42 3.35 3-15
•
?
-~
21.6 1'50 5.90 20.4 I 30.6 20.5 3.26 11.3 36.7 28.4 20.2 6.90 26.4 78.0 28.3 20.5 1"83 6.50 20.6 28.4 20.7 2.50 7.54 28.8 28.7 19-2 9-84 34.6 89.2 25.8 20.9 1-87 5.52 ~ 26-2 31.0 20.7 2.74 9.86 i 32.2 28.8 21.4 3"33 1 3 . 3 45-7 30.6 22.0 3.64 13-5 52.8 30.4 19.4 54.0 193.0 i502.0 26.2 20.4 15.7 57.7 !177.0 28-4 21.5 5.36 20.9! 73.2 30.4 21.1 3.41 13-1 43.2 29.7 21.1 3'33 12.9 i 42.0 29.7 24.2 0.47 2.63i 10.6 36.5 21.2 3.99 14-0 51.4 29.7 20-6 2.24 7.73 25.8 28.7 20-7 2.08 8.14 24.7 28.9 21-6 1.59 6.86 i 21.8 30.6 18-0 14'6 34-0 I -18.4
1794
Y u . A . OLDEKOP a n d G. S. BYLINA
big increase in the initiating activity of the peroxides. When both the orthopositions were substituted the initiating activity increased further (e.g. acetyl2,4, 6-trimethylbenzoyl peroxide). Substitution in the meta- and para-positions had on the whole much less influence t h a n substitution in the ortho-position. Besides this, unlike the orthoposition, the influence exerted here depends on the nature of the substituents. Electron acceptor substituents lower the initiation activity (this is manifest more strongly in the recta- t h a n in the para-position), while electron donor substituents on the other hand, increase the initiating activity. The figures obtained for the recta- and para-substituted acetylbenzoyl peroxide plot quite well into H a m m e t p - - a graphs (see Fig 1). The p value is--0.88. TABLE 2. INITIATION CONSTANTS OF SYI~IMETRICAL AND ASYMMETRICAL DIACYL
PEROXIDES AT 70°C
Peroxides kcetylbenzoyl keetyl-o-chlorobenzoyl kee~yl-m-chlorobenzoyl kcetyl p-chlorobenzoyl kcetyl-o-brornobenzoyl kcetyl-m-bromobenzoyl kcetyl-p-bromobenzoyl kcetyl-m-methylbenzoyl kcetyl-p-methylbenzoyl kcetyl-o-methoxybenzoyl tcetyl-p-methoxybenzoyl tcetyl-p-phenylbenzoyl ~eetyl-o-acetoxybenzoyl ~cetyl-m-nitrobenzoyl metylhexahydrobenzoyl 3utylbenzoyl
]c~.106,
/c~"106,
sec-1
SIN?-1
5.9 23.0 2.9 4.4 69.5 3.1 4.2 4.9 8.9 113 15"1 6'9 8'2 0"6 5'6 5"9
16"5 16'5 16"5 16"5 16"5 16"5 16"5 16"5 16'5 16"5 16"5 16'5 16"5 16'5 16.5 15-6
/C~'IO6, s e c - I
theoretical
experimente
11"2 19"7 11'2 12-7 43"0 9"8 10-4 10'7 12'7 64"7 15"8 11"7 12"4 8"5 36"2 11"7
11"3 26"4 6"5 7"5 34'6 5'5 9'9 i3.3 13.5 57.7 20-9 12.9 13.1 2.6 34-0 8.1
Comparing our results for asymmetrical diaeyl peroxides with those obtained by Cooper in [5] for diaroyl substituted peroxides, it is obvious t h a t the influence of the substituents is more or less the same in both cases. As in the case of the diaroyl symmetrical peroxides, so also with the meta- and para-substituted peroxides of acetyl benzoyl, the Hammer law is followed. According to Cooper, for the bulk polymerization of styrene with diaroyl symmetrical peroxides, and also according to Swain, Stockmayer and Clarke [9] for the breakdown of diaroyl peroxide in dioxane with 0.2 M 3,4-dichlorostyrene as initiated breakdown inhibitor p=--0-38. In our case p ~ - - 0 . 8 8 . This m a y be due to a difference in the nature of the peroxide used in the reaction. For instance, with Cooper [5], and ~wain, Stockmayer and Clarke [9] the peroxide bond was influenced by two
1795
Studies in aeyl peroxides
substituents, and in our case only one. Besides this, there is some ambiguity in the determination of the p value for the breakdown of diaxyl peroxides. Blomquist and Buselli for instance [10] got a p value of --0.5 to -- 1.0 for the breakdow~ of diacyl peroxide. +04 +0'2 ^ &~ 0
o ~ m-CH3
H ~
on-Br
-02
-04
-07 -04
I
0
I
+0'4
I
+08
FIG. 1. Initiation rate of styrene polymerization by substituted aeetylbenzoyl peroxides vs. the H a m m e r a-substitution groups.
The reaction of ortho-substituted acetylbenzoyl peroxide in the bulk polymerization of styrene suggests that steric factors gre very important in determining the initiating activity of peroxide. I f we compare the initiating activities of the ortho- and para-substituted peroxides, it can be seen that in the case of chlorine and bromine the value ]cior~ho/ki~o,-~3.5, while in the case of the methoxy groups it is 2.8, which means thgt the size of the substituent has very little effect upon the initiating activity of asymmetrical diacyl peroxides. This relation is much higher for symmetrical peroxides. For instance, for 2,2-dichlorobenzoyl peroxide and 4,4-dichlorobenzoyl peroxide it is 5-2, for 2,2-dibromobenzoyl and 4,4-dibromobenzoyl peroxide it is 16.3 [5]. It seems that the considerable influence of ortho~ubstituents upon the initiating activity in the case of symmetrical diacetyl peroxides is due to the presence of two three-dimensionally hindered radicals in the molecule of the symmetrical diacyl peroxide. From the figures obtained it can also be concluded t h a t the size of the substituent in the ortho-position is not of primary importance in determining the initiating activity of asymmetrical diacyl peroxides. With halide atom substitution at the ortho-position in symmetrical diacyl peroxides, Cooper [5] found that the size of the substituent did affect the initiating activity. The initiating activity of peroxides such as propionyl-, butryl- and isovalerylbenzoyl does fall, only slightly, in the following order: acetyl benzoyl>propionyl
1796
Yr. A. OLDEKOPand G. S. BYLINA
b e n z o y l > b u t y r y l benzoyl~isovalerylbenzoyl peroxide. This is consistent with the results obtained for symmetrical diacetyl peroxides of the aliphatic series; as the carbon chain grows the polymerization rate falls very slightly. The presence of chlorine in monochloroacetyl benzoyl peroxide causes an increase in the initiating activity of the peroxide. For most of the peroxides studied, polymerization proceeds at constant rate at a conversion of up to 15~o. The exception is aeetyl hexahydrobenzoyl peroxide at 60 and 70 ° (Fig. 2, curves 3 and 4). At lower temperatures (Fig. 2) lines I and 2) polymerization also proceeds at constant rates in the presence of this peroxide, although there is a definite point of deflexion on line 2 at 40 °.
~80
3
~4.0 1
80
/8O TiThe,m/n
24O
FIG. 2. Polymerization of styrene in the presence of acetylhexahidrobenzoyl at various temperatures: 1--25 °, 2--40 °, 3--60 °, 4--70 °. Comparing the initiating constants of asymmetric and symmetric diacyl peroxides at 70 °, we noted the following relation betweeu those of the asymmetric diacyl peroxide RCOOOCOR' of the araliphatic series and the corresponding symmetric peroxide RCOOOCOR and R'COOOCOR':
(4) where ]c~is the initiating constant of the asymmetric diacyl peroxide I~CO00COR': k~+ki are the initiating constants of the symmetric diaroyl and aliphatic peroxides respectively. For our calculation we used the initiating constants for symmetric peroxide taken from [5], b u t we made an appropriate conversion using K 360 mo1-2.1. 2. sec. The results are given in Table 2 where it can be seen that for the asymmetric diacyl peroxide the constants are in all cases intermediate between those for the corresponding symmetric diacyl peroxides. In a number of cases ki for the asymmetric diacyl peroxide can be quite accurately calculated from the corresponding constants of the symmetrical ones. The biggest difference between the theoretical and experimental values of the constants is observed for chloro- and bromo-substituted peroxide of acetyl benzoyl and acetyl-meta-nitrobenzoyl. B u t nevertheless, the figures obtained in this case can be used to find the initiating constant of the asymmetric peroxide from the corresponding ones for the symmetrical peroxides.
Studies in acyl peroxides
1797
The k~ figures obtained for the different peroxides are of definite interest, since they can be used find the rate of homolytie breakdown of the peroxides from the polymerization rates. It mnst be remembered in this case that k i is not exactly the same as k d, the rate constant of the breakdown of the peroxide. After calculating k i for a number of diacyl peroxides, Cooper identified k~ with/c a. B u t this only holds for f~- 1 where f is the efficiency of the initiator. B u t since the efficiency of diaeyl peroxide is less than unity [11], in practice it can only be possible from the polymerization rate to determine the value f . kd, and this can be used to find k d with accuracy only up to the coefficient f. On the basis, of the polymerization rates at different temperatures, we calculated the apparent activation energies of the bulk polymerization of styrene with different asymmetric peroxides. As a general rule it must be emphasized that within the range of experimental error the activation energy of the polymerization reaction is approximately 20 kcal/mole for all the peroxides, and this is in good agreement with the equation E z ½Ei ~-(Ep--½Et), where E is the activation energy of the polymerization reaction, E~ the activation energy of the initiation reaction (a value of the order of 30 keal/mole) and (Et--½Et)~-6.5 keal/mole [12], where Ep and E t are the activation energies of the growth and breaking of the chain. Acetylhexahydrobenzoyl peroxide has a polymerization activation energy of 18 kcal/mole, and low thermal stability. Acetyl-meta-nitrobenzyol peroxide has higher thermal stability. The activation energy of polymerization in the presence of B P (21-6 kcal/mole) is in good agreement with the published figure, 21.3 kcal/ mole [12]). From the initiation constants for the different temperatures, we calculated the apparent activation energies of initiation. As we can see from Table 1, for most of the peroxides the activation energy of initiation is between 28 and 30 kcal/mole. The more active initiators have lower figures. Acetyl-meta-nitrobenzoyl peroxide has high activation energy and is a poor initiator, not only due to its high stability, but also apparently, to the inhibiting effect of the NO 2 group. Iu view of the poor accuracy in finding the activation energy (8-10~), it is impossible to make any reliable conclusions regarding the influence of the substituents on this figure, since the difference in the activation energies is within the range of experimental error. The activation energy of the initiation reaction shows thut it is practically the same as that of the homolytie breakdown of the O - - O bond of diacyl peroxide. CONCLUSIONS
(1) A study has been made of the initiating activity of 21 substituted acetylbenzoyl peroxides in the bulk polymerization of styrene, 19 of them for the first time. (2) Except for aeetyl-m-nitrobenzoyl they are all more active initiators than benzoyl peroxide. (3) The substituents in the benzene ring in asymmetrical peroxides of the aromatic-aliphatie series have been found to have the same effect as in the ease
1798
R.M. LIVSHITSetal.
of diaroyl peroxides; meta- a n d p a r a - s u b s t i t u t e d a c e t y l b e n z o y l peroxides thus obey t h e H a m m e r law. (4) The initiating a c t i v i t y of a s y m m e t r i c a l diaeyl peroxides is i n t e r m e d i a t e b e t w e e n t h a t of t h e corresponding s y m m e t r i c a l diacyl peroxides. I n a n u m b e r o f cases t h e initiating c o n s t a n t of a s y m m e t r i c a l diacyl peroxides can be
Akad. l~auk BSSR, 8, 13, 1960; Zh. obshch, khim. 31: 2904, 1961; 33: 2771, 1963 2. I. U. NEF, Liebigs Ann. Chem. 298, 284, 1897 3. J. H. SKELLON and E. D. WILLS, Analyst 73: 78, 1948 4. N. NISHIMURA, Bull. Chem. Soe. Japan 34: 1158, 1961 5. W. COOPER, J. Chem. Soc. 3106, 1951 6. C. H. BAMFORD and M. $. S. DEWAR, Disc. Faraday Soc. 2: 313, 1947 7. A. V. TOBOLSKY and J. OFFENBACH, J. Polymer Sci. 16: 311, 1955 8. C. WALLING, Free radicals in solution, Izd. in. lit. 1960 9. C. G. SWAIN, W. H. STOCKMAYER and J. T. CLARKE, g. Amer. Chem. Soc. 78: 5426. 1950 10. A. T. BLOMQUIST and A. $. BUSELLI, g. Amer. Chem. Soc. 73: 3883, 1951 11. A. H. LOWELL and J. R. PRICE, g. Polymer Sci. 43: l, 1960 12. Kh. S. BAGDASARYAN, Teoriya radikalnoi polimerizatsii. (Theory of Radical Polymerization.) Izd. Akad. l~auk SSSR, 106, 1959
SYNTHESIS OF MODIFIED CELLULOSE GRAFT COPOLYMERS USING PENTAVALENT VANADIUMmHI. EFFECT OF THE INITIATING CONDITIONS ON DEGREE OF POLYMERIZATION AND THE NUMBER OF GRAFTED CHAINS*t l~. M. LIVSHITS, L. M. LEVITES a n d Z. A. ROGOVIN Moscow Textile Institute
(Received 22 October 1963) ONE of the methods of synthesizing graft copolymers, which is most promising from the practical point of view, is by redox systems in which the polymer plays * Vysokomol. soyed. 6: No. 9, 1624-1628, 1964. t 155th Report of the series "Study of the structure and properties of cellulose and its derivatives".
1791
culated for copolymers in dimethylformamide for the case of total macromolecule screening. (3) From the viscosity figures, it is concluded t h a t the macromolecules are coiled in solutions of high ionic strength. Translated by V. ALFORD REFERENCES 1. S. M. KOCHERGIN and V. P. BARABANOV, Vysokomol. soyed. 3: 1210, 1962 2. V. A. MYAGCHENKOV, Ye. V. KUZNETSOV, O. A. ISHAKOV and V. M. LUCHKINA, Vysokomol. soyed. 5: 724, 1963 3. N. A. IZMAILOV, Elektrokhimiya rastvorov. (Electrochemistry of Solutions.) Izd.-vo. KhGU, 1959 4. N. F. PROSIILYAKOVA, Dissertation, Fiz. khim. inst. im. A. Ya. Karpova, Moscow, 1958 5. A. KATCHALSKY and H. EISENBERG, J. Phys. Sci. 6: 145, 1951 6. T. de BOER and H. BAKER, Sinteza org. preparatov. (Synthesis of Organic Preparation.) Foreign Literature Publishing House, SB 6, 67, 1958; SB 8, 7, 1958 7. Yu. K. YUR'YEV, Praktich. raboty po organich, khim. (Practical Work in Organic Chemistry). Izd.-vo MGU 1961 8. J. BAXENDALE, S. BYWATER and M. EVANS, J. Polymer Sci. 1: 237, 1946 9. A. P. ALEKSANDROV, Dissertation, K KhTI, 1950 10. M. FUOSS and P. STRAUSS, J. Polymer Sci. 4: 96, 1949 11. M. FUOSS and G. CATHERS, J. Polymer Sci. 3: 602, 1958 12. I. P. SHUBTSOVA, T. S. DMITRIYEVA, V. B. SCHASTNEV and S. A. GLIKMAN, Vysokomol. soyed. 5: 135, 1963
STUDIES IN ACYL PEROXIDES--VI. INITIATING EFFECT OF ASYMMETRICAL DIACYL PEROXIDES IN THE BULK POLYMERIZATION OF STYRENE Yu. A. OLDEKOP and G. S. BYLINA V. I. Lenin Belorussian State University
(Received 19 October 1963) E A R L I E R r e p o r t s h a v e d e s c r i b e d a n e w m e t h o d of s y n t h e s i z i n g a s y m m e t r i c d i a c y l p e r o x i d e s , a n d p r o p e r t i e s o f a n u m b e r of n e w a s y m m e t r i c p e r o x i d e s of a r o m a t i c a l i p h a t i c a n d a l i p h a t i c series h a v e b e e n d e s c r i b e d [1]. I n t h i s w o r k we give t h e r e s u l t s of a s t u d y of t h e i n i t i a t i n g a c t i v i t y of s o m e of t h e e a r l i e r a n d a few n e w a s y m m e t r i c p e r o x i d e s of t h e a r o m a t i c - a l i p h a t i c series in t h e b u l k p o l y m e r i z a t i o n of s t y r e n e . * Vysokomol. soyed. 6: No. 9, 1617-1623, 1964.
1792
Yu. A. OLDEKOPand G. S. BYLINA
EXPERIMENTAL
Reagents. The styrene was dried with CaCI~ which had been vacuum distilled three times and kept at dry ice temperature. The monomer content 99.8-99.9%. All the peroxides used in this work were prepared by the method described in [1]: oxidation of the appropriate aldehyde in acetic anhydride or the anhydrides of other acids. Acetyl m-nitrobenzoyl peroxide was prepared by the Nef [2] method of nitrating acctylbenzoyl peroxide. The purity of the peroxides was determined by iodine titration [3]. They were all 98-100% pure. Experimental procedure. The polymerization was performed in the absence of atmospheric oxygen. The air dissolved was removed from the monomer by freezing and melting the solution of peroxide in monomer in a vacuum followed by purging with purified nitrogen. To remove the air completely, the freezing and melting operations had to be repeated 4-5 times. Dilatometers were filled in a vacuum, and when the system was completely filled with purified nitrogen, they were sealed. The dilatometers were appoximately 10 ml volume and the diameter of the capillary tube was about 1 ram. The final extent of polymerization was 15%. This was calculated from the reduction in the volume of the reaction system, assuming that at 100% polymerization of the styrene, the volume of the system would have fallen by 0.177 of its original [4]. The initial polymerization rate was determined graphically, and given in mole/1./sec. The polymerization rates were also found at 60, 70 and 80°. The temperature was kept constant within =]=0.05°. The peroxide concentration was 0.015 mole/1. in all the experiments. The styrene was bulk polymerized. Results. I n the w o r k b y Cooper [5] the initiating a c t i v i t y of a n u m b e r of diacyl peroxides were studied. F o r convenience in c o m p a r i n g our figures with published ones, a n d also because his m e t h o d was v e r y simple, we h a v e proceeded in the same w a y , using the e q u a t i o n k~----k t (R ~ - R~ )/ 2k~M2C,
(1)
where ki is the p o l y m e r i z a t i o n initiation constant, k t is the chain breaking c o n s t a n t , R~ is t h e rate of initiated p o l y m e r i z a t i o n , R T is the rate of t h e r m a l p o l y m e r i z a t i o n k~ is the rate of chain growth, M t h e m o n o m e r c o n c e n t r a t i o n a n d C the initiator concentration. U p to 15 ~ conversion t h e m o n o m e r a n d initiator concentrations can be t a k e n as a c o n s t a n t , while the rate of t h e r m a l p o l y m e r i z a t i o n is low as c o m p a r e d with the initiated p o l y m e r i z a t i o n , a n d can be t a k e n as zero. E q u a t i o n (1) becomes
Ic =KR~,
(2)
where K = kJ2k~M~C. W e used e q u a t i o n (2) calculate the initiation c o n s t a n t of the p o l y m e r i z a t i o n reaction. Coopers w h e n he calculated the initiation constant, used the kt/k ~ values calculated b y B a m f o r d a n d D e w a r [6], a n d the result he got was K----440 mole -2 .1. ~ .see. B u t more reliable figures are n o w available for kt/]c~, a n d these were o b t a i n e d b y T o b o l s k y a n d Offenbach [7]. On t h e basis of these figures Walling [8] derived the following relation for k~/Ict: 1.7
×
e
(3)
Using e q u a t i o n (3), the/ct//c ~ values a t 60, 70 a n d 80 °, are 1300, 740 a n d 440 mole .1.-~. see respectively. W i t h a s t y r e n e c o n c e n t r a t i o n of 8.36 mole/1, a t 60 °,
Studies in aeyl peroxides
1793
8"28 mole/1, a t 70 ° a n d 8.20 mole/1, a t 80 °, a n d i n i t i a t o r c o n c e n t r a t i o n o f 0.015 mole/1, in all cases, t h e K v a l u e s o b t a i n e d a t 60, 70, a n d 80 ° are 620, 360 a n d 220 mole-2.12.sec r e s p e c t i v e l y . All t h e ]ci v a l u e s w e r e c a l c u l a t e d b y m e a n s o f e q u a t i o n (2). RESULTS AND DISCUSSION
T h e i n i t i a t i n g a c t i v i t y o f 21 d i a c y l p e r o x i d e s , 19 for t h e first t i m e h a s b e e n d e t e r m i n e d . T h e r e s u l t s are g i v e n in T a b l e 1, w h i c h s h o w s t h e p o l y m e r i z a t i o n r a t e a t 60, 70 a n d 80 ° , t h e a p p a r e n t a c t i v a t i o n energies o f t h e p o l y m e r i z a t i o n r e a c t i o n Ep, t h e i n i t i a t i o n c o n s t a n t /ci a t 60, 70 a n d 80 °, a n d t h e a p p a r e n t a c t i v a t i o n energies o f t h e i n i t i a t i o n r e a c t i o n E i. F o r c o m p a r i s o n we also s t u d i e d t h e init i a t i n g a c t i v i t y o f b e n z o y l p e r o x i d e (BP). I t is e v i d e n t f r o m t h e figures o b t a i n e d t h a t all t h e a s y m m e t r i c p e r o x i d e s o f t h e a l i p h a t i c series s t u d i e d h a v e h i g h e r i n i t i a t i n g a c t i v i t y t h a n B P . T h e o n l y e x c e p t i o n w a s a c e t y l - m - n i t r o b e n z o y l p e r o x i d e . C o n s i d e r a b l e influence on t h e i n i t i a t i n g a c t i v i t y o f t h e p e r o x i d e w a s e x e r t e d b y t h e v a r i o u s different c o n s t i t u e n t s in t h e b e n z e n e ring. S u b s t i t u e n t s in t h e ortho~position h a d t h e g r e a t e s t effect. I n this p o s i t i o n b o t h e l e c t r o n d o n o r a n d e l e c t r o n a c c e p t e r s u b s t i t u e n t s c a u s e d a TABLE 1. S T Y R E N E P O L Y M E R I Z A T I O N W I T H A S Y M M E T R I C A L D I A C Y L P E R O X I D E S
~ T.
g
Peroxides
Benzoyl Acetylbenzoyl Acetyl-o-chlorobenzoyl Acetyl-m-chlorobenzoyl Acetyl-p-chlorobenzoyl Acetyl-o-bromobenzoyl Acetyl-m-bromobenzoyl Acetyl-p-bromobenzoyl Acetyl-m-methylbenzoyl Acetyl-p-methylbenzoyl Acetyl-2,4,6-trimethylbenzoyl AcetyLo-methoxybenzoyl Acetyl-p-methoxybenzoyl Acetyl-o-acetoxybenzoyl Acetyl-p-phenylbenzoyl Acetyl-m-nitrobenzoyl Monochloroacetylbenzoyl Propionylbenzoyl Butylbenzoyl Isovalerylbenzoyl Acetylhexahydrobenzoyl
•$ ~
0.492 0'725 1'06 0.543 0.634 1.26 0.549 0-666 i 0'7331 0.766 2.95 1.59 0.930 f 0.742
1"28 1'77 2-71 1'34 1"47 3-10 1.24 1.66 1.92 1.94 7.32 4.01 2.41 1.91
i 0-733 1.89 i 0.276 0.85 0.802 1-97 i0.601 1.47 0-579 1.51 0-506 1.38 1.54 3.07
3.04 4.08 5.95 3.06 3.62 6.37 3-45 3-83 4-56 4.90 15.1 8.95 5.77 4-43 4-37 2-16 4.83 3.42 3.35 3-15
•
?
-~
21.6 1'50 5.90 20.4 I 30.6 20.5 3.26 11.3 36.7 28.4 20.2 6.90 26.4 78.0 28.3 20.5 1"83 6.50 20.6 28.4 20.7 2.50 7.54 28.8 28.7 19-2 9-84 34.6 89.2 25.8 20.9 1-87 5.52 ~ 26-2 31.0 20.7 2.74 9.86 i 32.2 28.8 21.4 3"33 1 3 . 3 45-7 30.6 22.0 3.64 13-5 52.8 30.4 19.4 54.0 193.0 i502.0 26.2 20.4 15.7 57.7 !177.0 28-4 21.5 5.36 20.9! 73.2 30.4 21.1 3.41 13-1 43.2 29.7 21.1 3'33 12.9 i 42.0 29.7 24.2 0.47 2.63i 10.6 36.5 21.2 3.99 14-0 51.4 29.7 20-6 2.24 7.73 25.8 28.7 20-7 2.08 8.14 24.7 28.9 21-6 1.59 6.86 i 21.8 30.6 18-0 14'6 34-0 I -18.4
1794
Y u . A . OLDEKOP a n d G. S. BYLINA
big increase in the initiating activity of the peroxides. When both the orthopositions were substituted the initiating activity increased further (e.g. acetyl2,4, 6-trimethylbenzoyl peroxide). Substitution in the meta- and para-positions had on the whole much less influence t h a n substitution in the ortho-position. Besides this, unlike the orthoposition, the influence exerted here depends on the nature of the substituents. Electron acceptor substituents lower the initiation activity (this is manifest more strongly in the recta- t h a n in the para-position), while electron donor substituents on the other hand, increase the initiating activity. The figures obtained for the recta- and para-substituted acetylbenzoyl peroxide plot quite well into H a m m e t p - - a graphs (see Fig 1). The p value is--0.88. TABLE 2. INITIATION CONSTANTS OF SYI~IMETRICAL AND ASYMMETRICAL DIACYL
PEROXIDES AT 70°C
Peroxides kcetylbenzoyl keetyl-o-chlorobenzoyl kee~yl-m-chlorobenzoyl kcetyl p-chlorobenzoyl kcetyl-o-brornobenzoyl kcetyl-m-bromobenzoyl kcetyl-p-bromobenzoyl kcetyl-m-methylbenzoyl kcetyl-p-methylbenzoyl kcetyl-o-methoxybenzoyl tcetyl-p-methoxybenzoyl tcetyl-p-phenylbenzoyl ~eetyl-o-acetoxybenzoyl ~cetyl-m-nitrobenzoyl metylhexahydrobenzoyl 3utylbenzoyl
]c~.106,
/c~"106,
sec-1
SIN?-1
5.9 23.0 2.9 4.4 69.5 3.1 4.2 4.9 8.9 113 15"1 6'9 8'2 0"6 5'6 5"9
16"5 16'5 16"5 16"5 16"5 16"5 16"5 16"5 16'5 16"5 16"5 16'5 16"5 16'5 16.5 15-6
/C~'IO6, s e c - I
theoretical
experimente
11"2 19"7 11'2 12-7 43"0 9"8 10-4 10'7 12'7 64"7 15"8 11"7 12"4 8"5 36"2 11"7
11"3 26"4 6"5 7"5 34'6 5'5 9'9 i3.3 13.5 57.7 20-9 12.9 13.1 2.6 34-0 8.1
Comparing our results for asymmetrical diaeyl peroxides with those obtained by Cooper in [5] for diaroyl substituted peroxides, it is obvious t h a t the influence of the substituents is more or less the same in both cases. As in the case of the diaroyl symmetrical peroxides, so also with the meta- and para-substituted peroxides of acetyl benzoyl, the Hammer law is followed. According to Cooper, for the bulk polymerization of styrene with diaroyl symmetrical peroxides, and also according to Swain, Stockmayer and Clarke [9] for the breakdown of diaroyl peroxide in dioxane with 0.2 M 3,4-dichlorostyrene as initiated breakdown inhibitor p=--0-38. In our case p ~ - - 0 . 8 8 . This m a y be due to a difference in the nature of the peroxide used in the reaction. For instance, with Cooper [5], and ~wain, Stockmayer and Clarke [9] the peroxide bond was influenced by two
1795
Studies in aeyl peroxides
substituents, and in our case only one. Besides this, there is some ambiguity in the determination of the p value for the breakdown of diaxyl peroxides. Blomquist and Buselli for instance [10] got a p value of --0.5 to -- 1.0 for the breakdow~ of diacyl peroxide. +04 +0'2 ^ &~ 0
o ~ m-CH3
H ~
on-Br
-02
-04
-07 -04
I
0
I
+0'4
I
+08
FIG. 1. Initiation rate of styrene polymerization by substituted aeetylbenzoyl peroxides vs. the H a m m e r a-substitution groups.
The reaction of ortho-substituted acetylbenzoyl peroxide in the bulk polymerization of styrene suggests that steric factors gre very important in determining the initiating activity of peroxide. I f we compare the initiating activities of the ortho- and para-substituted peroxides, it can be seen that in the case of chlorine and bromine the value ]cior~ho/ki~o,-~3.5, while in the case of the methoxy groups it is 2.8, which means thgt the size of the substituent has very little effect upon the initiating activity of asymmetrical diacyl peroxides. This relation is much higher for symmetrical peroxides. For instance, for 2,2-dichlorobenzoyl peroxide and 4,4-dichlorobenzoyl peroxide it is 5-2, for 2,2-dibromobenzoyl and 4,4-dibromobenzoyl peroxide it is 16.3 [5]. It seems that the considerable influence of ortho~ubstituents upon the initiating activity in the case of symmetrical diacetyl peroxides is due to the presence of two three-dimensionally hindered radicals in the molecule of the symmetrical diacyl peroxide. From the figures obtained it can also be concluded t h a t the size of the substituent in the ortho-position is not of primary importance in determining the initiating activity of asymmetrical diacyl peroxides. With halide atom substitution at the ortho-position in symmetrical diacyl peroxides, Cooper [5] found that the size of the substituent did affect the initiating activity. The initiating activity of peroxides such as propionyl-, butryl- and isovalerylbenzoyl does fall, only slightly, in the following order: acetyl benzoyl>propionyl
1796
Yr. A. OLDEKOPand G. S. BYLINA
b e n z o y l > b u t y r y l benzoyl~isovalerylbenzoyl peroxide. This is consistent with the results obtained for symmetrical diacetyl peroxides of the aliphatic series; as the carbon chain grows the polymerization rate falls very slightly. The presence of chlorine in monochloroacetyl benzoyl peroxide causes an increase in the initiating activity of the peroxide. For most of the peroxides studied, polymerization proceeds at constant rate at a conversion of up to 15~o. The exception is aeetyl hexahydrobenzoyl peroxide at 60 and 70 ° (Fig. 2, curves 3 and 4). At lower temperatures (Fig. 2) lines I and 2) polymerization also proceeds at constant rates in the presence of this peroxide, although there is a definite point of deflexion on line 2 at 40 °.
~80
3
~4.0 1
80
/8O TiThe,m/n
24O
FIG. 2. Polymerization of styrene in the presence of acetylhexahidrobenzoyl at various temperatures: 1--25 °, 2--40 °, 3--60 °, 4--70 °. Comparing the initiating constants of asymmetric and symmetric diacyl peroxides at 70 °, we noted the following relation betweeu those of the asymmetric diacyl peroxide RCOOOCOR' of the araliphatic series and the corresponding symmetric peroxide RCOOOCOR and R'COOOCOR':
(4) where ]c~is the initiating constant of the asymmetric diacyl peroxide I~CO00COR': k~+ki are the initiating constants of the symmetric diaroyl and aliphatic peroxides respectively. For our calculation we used the initiating constants for symmetric peroxide taken from [5], b u t we made an appropriate conversion using K 360 mo1-2.1. 2. sec. The results are given in Table 2 where it can be seen that for the asymmetric diacyl peroxide the constants are in all cases intermediate between those for the corresponding symmetric diacyl peroxides. In a number of cases ki for the asymmetric diacyl peroxide can be quite accurately calculated from the corresponding constants of the symmetrical ones. The biggest difference between the theoretical and experimental values of the constants is observed for chloro- and bromo-substituted peroxide of acetyl benzoyl and acetyl-meta-nitrobenzoyl. B u t nevertheless, the figures obtained in this case can be used to find the initiating constant of the asymmetric peroxide from the corresponding ones for the symmetrical peroxides.
Studies in acyl peroxides
1797
The k~ figures obtained for the different peroxides are of definite interest, since they can be used find the rate of homolytie breakdown of the peroxides from the polymerization rates. It mnst be remembered in this case that k i is not exactly the same as k d, the rate constant of the breakdown of the peroxide. After calculating k i for a number of diacyl peroxides, Cooper identified k~ with/c a. B u t this only holds for f~- 1 where f is the efficiency of the initiator. B u t since the efficiency of diaeyl peroxide is less than unity [11], in practice it can only be possible from the polymerization rate to determine the value f . kd, and this can be used to find k d with accuracy only up to the coefficient f. On the basis, of the polymerization rates at different temperatures, we calculated the apparent activation energies of the bulk polymerization of styrene with different asymmetric peroxides. As a general rule it must be emphasized that within the range of experimental error the activation energy of the polymerization reaction is approximately 20 kcal/mole for all the peroxides, and this is in good agreement with the equation E z ½Ei ~-(Ep--½Et), where E is the activation energy of the polymerization reaction, E~ the activation energy of the initiation reaction (a value of the order of 30 keal/mole) and (Et--½Et)~-6.5 keal/mole [12], where Ep and E t are the activation energies of the growth and breaking of the chain. Acetylhexahydrobenzoyl peroxide has a polymerization activation energy of 18 kcal/mole, and low thermal stability. Acetyl-meta-nitrobenzyol peroxide has higher thermal stability. The activation energy of polymerization in the presence of B P (21-6 kcal/mole) is in good agreement with the published figure, 21.3 kcal/ mole [12]). From the initiation constants for the different temperatures, we calculated the apparent activation energies of initiation. As we can see from Table 1, for most of the peroxides the activation energy of initiation is between 28 and 30 kcal/mole. The more active initiators have lower figures. Acetyl-meta-nitrobenzoyl peroxide has high activation energy and is a poor initiator, not only due to its high stability, but also apparently, to the inhibiting effect of the NO 2 group. Iu view of the poor accuracy in finding the activation energy (8-10~), it is impossible to make any reliable conclusions regarding the influence of the substituents on this figure, since the difference in the activation energies is within the range of experimental error. The activation energy of the initiation reaction shows thut it is practically the same as that of the homolytie breakdown of the O - - O bond of diacyl peroxide. CONCLUSIONS
(1) A study has been made of the initiating activity of 21 substituted acetylbenzoyl peroxides in the bulk polymerization of styrene, 19 of them for the first time. (2) Except for aeetyl-m-nitrobenzoyl they are all more active initiators than benzoyl peroxide. (3) The substituents in the benzene ring in asymmetrical peroxides of the aromatic-aliphatie series have been found to have the same effect as in the ease
1798
R.M. LIVSHITSetal.
of diaroyl peroxides; meta- a n d p a r a - s u b s t i t u t e d a c e t y l b e n z o y l peroxides thus obey t h e H a m m e r law. (4) The initiating a c t i v i t y of a s y m m e t r i c a l diaeyl peroxides is i n t e r m e d i a t e b e t w e e n t h a t of t h e corresponding s y m m e t r i c a l diacyl peroxides. I n a n u m b e r o f cases t h e initiating c o n s t a n t of a s y m m e t r i c a l diacyl peroxides can be
Akad. l~auk BSSR, 8, 13, 1960; Zh. obshch, khim. 31: 2904, 1961; 33: 2771, 1963 2. I. U. NEF, Liebigs Ann. Chem. 298, 284, 1897 3. J. H. SKELLON and E. D. WILLS, Analyst 73: 78, 1948 4. N. NISHIMURA, Bull. Chem. Soe. Japan 34: 1158, 1961 5. W. COOPER, J. Chem. Soc. 3106, 1951 6. C. H. BAMFORD and M. $. S. DEWAR, Disc. Faraday Soc. 2: 313, 1947 7. A. V. TOBOLSKY and J. OFFENBACH, J. Polymer Sci. 16: 311, 1955 8. C. WALLING, Free radicals in solution, Izd. in. lit. 1960 9. C. G. SWAIN, W. H. STOCKMAYER and J. T. CLARKE, g. Amer. Chem. Soc. 78: 5426. 1950 10. A. T. BLOMQUIST and A. $. BUSELLI, g. Amer. Chem. Soc. 73: 3883, 1951 11. A. H. LOWELL and J. R. PRICE, g. Polymer Sci. 43: l, 1960 12. Kh. S. BAGDASARYAN, Teoriya radikalnoi polimerizatsii. (Theory of Radical Polymerization.) Izd. Akad. l~auk SSSR, 106, 1959
SYNTHESIS OF MODIFIED CELLULOSE GRAFT COPOLYMERS USING PENTAVALENT VANADIUMmHI. EFFECT OF THE INITIATING CONDITIONS ON DEGREE OF POLYMERIZATION AND THE NUMBER OF GRAFTED CHAINS*t l~. M. LIVSHITS, L. M. LEVITES a n d Z. A. ROGOVIN Moscow Textile Institute
(Received 22 October 1963) ONE of the methods of synthesizing graft copolymers, which is most promising from the practical point of view, is by redox systems in which the polymer plays * Vysokomol. soyed. 6: No. 9, 1624-1628, 1964. t 155th Report of the series "Study of the structure and properties of cellulose and its derivatives".