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Radical polymerization of benzyl methacrylate at high degrees of conversion
1030
L.G.
SUROVTSEV et a/.
REFERENCES 1. I. C. W. CHIEN a n d C. R. BOSS, J. Polymer Sci. 5, A I : 1683, 1967 2. A. P. GRIVA and Ye. T. DENISOVA, Kinetika i kataliz 17: 1465, 1976 3. N. V. ZOLOTOVA and Ye. T. DEI~ISOV, Vysokomol. soyed. B18: 605, 1976 (l~'ot trans. lated in Polymer Sci. U.S.S.R.) 4. Ye. L. SHANINA, V. A. ROGINSKII and V. B. MILLER, Vysokomol. soyed. AI8: 1160, 1976 (Translated in Polymer Sci. U.S.S.R. 18: 5, 1334, 1976) 5. V. A. ROGINSKII, V. Z. DUBINSKII, I. A. SHLYAPNIKOVA and V. B. MILLER, Europ. Polymer J. 13: 1050, 1977 6. V. A. ROGINSKII a n d V. B. MILLER, Dokl..~N SSSR 215: 1164, 1974 7. Ye. L. SH.ANINA, V. I. RUBTSOV, V. A. ROGINSKII and V. B. MILLER, Kinetika i kataliz 18: No. 6, 1977 8. Ye. T. DENISOV, V. V. KHARITONOV and V. V. FEDOROVA, Kinctika i kataliz 1 6 : 332, 1975 9. G. P. GLADYSHEV and V. F. TSEPALOV, Uspekhi khimii 44: 1830, 1975 10. A. P. GRIVA and Ye. T. DENISOV, J. Polymer Sci., Polymer Chem. Ed. 14: 1051, 1976 11. A. P. GRIVA a n d Ye. T. DENISOV, I n t e r n a t . J. Chem., Kinetics 5: 869, 1973 12. V. A. BELYAKOV, Ye. L. SHANINA, V. A. ROGINSKII a n d V. B. MILLER, Izv. AI~ SSSR, set. khim., 2685, 1975 13. B. A. GROMOV, V. B. MIIffJER, M. B. NEIMAN a n d Ya. A. SHLYAPNIKOV, I n t e r n a t . J. Appl. Radiation and Isotopes 13: 281, 1962 14. V. A. ROGINSgll a n d V. B. MrLLER, ]:)old. AN SSSR 218: 642, 1973 15. T. V. POKHOLOK, O. N. KARPUKHIN a n d V. Ya. SHLYAPINTOKH, J. Polymer SoL, Polymer Chem. Ed. 13: 525, 1975
Polymer Science U.S.S.R. Vol. 20, pp. 1030-1037.
0032-3950/7810401-1030107.5010
~) PergamonPress Ltd. 1979. Printed in Poland
RADICAL POLYMERIZATION OF BENZYL METHACRYLATE AT HIGH DEGREES OF CONVERSION* L. G. SUROVTSEV, M. A. BULATOV, S. S. SPASSKII
and K. A. CHARUSH~IKOV I n s t i t u t e of Chemistry, Urals Scientific Centre, U.S.S.R. Academy of Sciences
(Received 5 July 1977) A calorimetric study was made of radical polymerization of benzyl methacrylate at 30, 50 a n d 60 ° . I n t e r m i t t e n t illumination and results of the rate of initiation at various stages of conversion were used to determine kinetic parameters of poly-
* Vysokomol. soyed. A20: No. 4, 913-918, 1978.
Radical polymerization of benzyl methacrylate
1031
merization at degrees of 3, 15, 40, 50 and 80O/o. The variation of parameters with the extent of reaction is interpreted from the point of view of elementary stages of polymerization at advanced degrees. STUDIES of radical p o l y m e r i z a t i o n of b e n z y l m e t h a c r y l a t e (BMA) [1-4], n o w widely used in p r a c t i c e [5-8] are r e s t r i c t e d to i n v e s t i g a t i o n s of initial stages o f conversion. A s t u d y of regularities g o v e r n i n g p o l y m e r i z a t i o n b y t h e r a d i c a l m e c h a n i s m a t high degrees of conversion is n o t o n l y of theoretical, b u t also o f p r a c t i c a l interest. BMA was purified by three fold vacuum distillation, b.p. 89-90°/250 Pa, n~° 1-5142, d,*° 1.0420. AID and benzyl three times recrystallized from methanol were used as initiators, m.p. 102 and 95 ° respectively. 1,l-diphenyl-2-pycrylhydrazyl (DPPH), freshly oxidized and three times recrystallized from chloroform, m.p. 132° were the inhibitors. Polymerization was investigated thermometrically using a differential isothermal calorimeter [9]. The accuracy of measuring heat was 0.17% and the rate of heat liberation, 0.50%. Polymerization was carried out in hermetic cells with a fiuoroplastic fihn opening for UV lighting. Photo-initiation was carried out with the light of a very high pressure mercury arc quartz lamp pressure (SHP-120A), filtered with silicate glass 2 mm in thickness with light transmission of 365 n m - - 7 6 % and with 315 nm--19~o. The intensity of light I was regulated by a metal grid of varying density. Methods of measurement and calculation of kinetic parameters have been published previously [10]. The rate of initiation at high degrees of conversion were determined from the ratio
v~=vp/P,
(1)
where P is the instant~neous degree of polymerization calculated from the average degree of polymerization /5 and the degree of polymerization G from equation [11] P=
G dP"
(2)
I . . . . .
/5 dG The molecular weight of PBMA was found viscometrieally in benzene from the Mark-Kuhn equation, in which constants K and g for PBMA in benzene are 0.103× 104 and 0.82, respectively [ 12]. Constants of chain transfer through monomer molecules Cm were derived from the dependence of the inverse degree of polymerization 1//~ on the rate of polymerization vp at different initiator concentrations [13]. F i g u r e 1 shows s o m e kinetic c u r v e s of p o l y m e r i z a t i o n of BMA. I t is clearly seen t h a t t h e process of p o l y m e r i z a t i o n (gel effect) is accelerated. T h i s is a t y p i cal p a t t e r n w h i c h is o b s e r v e d e x p e r i m e n t a l l y in all cases o f p o l y m e r i z a t i o n o f BI~IA. A s t u d y of t h e effect,of i n i t i a t o r c o n c e n t r a t i o n on t h e r a t e of p o l y m e r i z a t i o n of B M A shows a s q u a r e r e l a t i o n b e t w e e n t h e m , w h i c h indicates t h e a p p l i c a b i l i t y t o t h i s s y s t e m o f a c o n v e n t i o n a l e q u a t i o n of radical p o l y m e r i z a t i o n of v i n y l c o m p o u n d s . E x p o n e n t I ' , d e r i v e d e x p e r i m e n t a l l y f r o m t h e d i a g r a m m a t i c relat i o n o f log vp-~f (log I ) is also 0 . 5 0 ± 0 . 0 1 , w h i c h is in s a t i s f a c t o r y a g r e e m e n t w i t h results p r e v i o u s l y o b t a i n e d [1], w h e r e n----0.51.
1032
L. G. S~ROV'rS,~V et a/.
A study of the effeet of initiator concentration on ~ of the polymer indicates that an increase in initiator concentration, or an increase of light intensity, i.e. an increase in the rate of initiation, the same way as an inereaze in temperature of polymerization (in initiation), displaces the maximum rate of polymerization to high degrees of conversion and reduces ~fW of the polymer formed. up't0 a, mole//. . sec
2 !
!
2
3
f. I0-~ sec
~"io. 1. ]{inetie curves of polymerization of BlVIA in bulk at 90 (1), 80 (2) and 70 ° (3); i n i t i a t o r - - A I D ; t--time.
Figures 2 and 3 show the linear dependence of 1]/5 on initiator concentration •and the rate of polymerization. The linearity of these relations proves the absence of chain transfer through molecules of the initiator in the concentration and temperature range examined. By extrapolation of the curve showing the linear relation of 1/P=f (vp)to Vp=0 the value of Cm may be found. As shown by Fig. 3, the c e n t a u r of chain transfer through BbfA molecules up to a temperature of lxl 0 P3
px rO'Z
8 J
I
/,./ 0
0.5 FIo. 2
1.0 lAID], %
5
I
I
I
0.,25
0"50
0"76
up. tO~,moldl sec
~ko. 3
F~a. 2. Relation between ~ and the concentration of AID at 60 (I), 70 (2), 80 (3) a n d 90° (d). }ho. 3. Relation between l i p and tho value ofvD in polymerization of BMA: 1--90, 2--80, -3--70, 4 - - 6 0 (initiator: AID), 5 - - 3 0 ° (photopolymerization: here a n d in Figs. 4-7 benzyl was used as sensitizer (0.05 molefl.).
Radical polymerization of benzyl methacrylato
1033
~}0° is negligibly low, which enables r a t i o (1) to be used t o d e t e r m i n e t h e r a t e o f i n i t i a t i o n a t high degrees o f conversion. T a b l e 1 shows results o f i n v e s t i g a t i n g p h o t o - i n i t i a t e d p o l y m e r i z a t i o n of B M A in b u l k a t 30, 50 a n d 60 ° a t different degrees o f conversion. T h e v a r i a b i l i t y of all k i n e t i c p a r a m e t e r s d u r i n g p o l y m e r i z a t i o n is o f m a i n significance. A sudden reTABLE 1. PHOTOPOLYM-ERIZATIO~N" OF BMA IN B U L K
(Sensitizer - benzyl, 0.05 mole/l.) T, °C
PX
v l x 10', 10-s mole/1., •see
30.0 50"0 60.0 30"0 50"0 60"0
13'5 25.3 31.2
I'19 1"10
G=3~0.5% 6.00 7.91 12.2 7.32 15.5 7.04
5"03 5"45 5"54
5"56 4.93 4'22
G = 15=t=3% 6.80 28.0 13.8 26-9 17-3 23-4
9.65 7.97 6-41
17"6 28'9 36'8
4-58 4.88 5.16
30"0 50"0 60-0
19"0 29"2 38'2
1-54
20"4 29'8 39"3
VpX 105, 10-'~kexl mole/l: [ R ' ] x l 0 " i k r x 0 -t, .see mole/1. ! 1./mole.see
5-95* 6.15 6-40
30'0 50'0 60-0
30.0 50"0 60.0
v, see
1'88 1.91 0.102 0.168 0.142
ke ~ X l0 t
1"31 2'90 4'01
2"52 3"10
6"41 7"53 10"l
4'82 10'2 14"7
7"57 13"5 14"5
G=30±3% 8.06 44.2 14.1 38.9 19.0 33"1
2-34 3"22 4"71
4'39 8'73 13'8
18"7 27-1 29'3
17"3 13.7 11.7
G=50±5% 2.94 26.7 5.40 25.7 7.30 22"3
2"15 2'85 3'84
3'72 7'10 ll'l
17'3 24"9 28"9
69.0 65.5 61.0
G = 8 0 - 57~ 0.208 7.03 0.503 11.0 0.560 8'66
2"06
2'48 3"84 5"43
12"0 26"2 28"7
1'33
95 115 129
1"38 1"89
1"38
* The rate of initiation at low degreewas determinedby adding DPPH as inhibitor. d u c t i o n in t h e r a t e o f initiation w i t h t h e degree of p o l y m e r i z a t i o n is o b s e r v e d in e v e r y case. Since t h e r a t e of d e c o m p o s i t i o n o f t h e i n i t i a t o r r e m a i n e d c o n s t a n t , a c h a n g e in t h e r a t e of initiation is, e v i d e n t l y due t o a r e d u c t i o n in t h e efficiency o f i n i t i a t i o n in v i e w of t h e difficulty i n v o l v e d in t h e e m e r g e n c e of p r i m a r y radicals f r o m t h e "cell" caused b y diffusion. F i g u r e 4 shows t h e d e p e n d e n c e of a v e r a g e d e g r e e o f p o l y m e r i z a t i o n a n d t h e r a t e of initiation on t h e degree o f conversion. T a b l e 1 indicates t h a t t h e r a t e o f p o l y m e r i z a t i o n increases slowly in e v e r y ease w i t h t h e degree o f c o n v e r s i o n a n d passing t h r o u g h t h e m a x i m u m w i t h 8 0 - 4 0 % conversion, it s u d d e n l y decreases a n d t h e n g r a d u a l l y t e n d s to zero w i t h d e g r e e s o f conversion close to 100%. As a consequence o f t h e f o r m a t i o n of a p o l y -
L. G. Su~owrsEv et a/.
1034
mer product, the viscosity of the system increases with the degree of conversion. All process parameters change at the same time. The rate constant of chain rupture varies with an increase in viscosity, showing a marked reduction at the v e r y
Io9 ui+9 0"75 -
IogP f
2 #.27
0"25
#.Z3
-0"75
#.18
-0.75
#45 l/O
8o ¢,%
FzG. 4
FzG. 5
Fro. 4. Relation between log vi (1) and log P (2) and the degree of conversion G in photopolymerization of BMA at 30°. FIo. 5. Relation between vi (1), ko (2) and k¢ (3) and the degree of conversion in photo-polyrnerization of BMA at 30°. beginning of the process. This is due to considerable diffusion hindrances when macromolecular radicals encounter a monomer-polymer medium. Viscosity variation has a lower effect on monomer diffusion, therefore, the rate constant o f chain extension decreases less strongly than the rate constant of chain rupture (Fig. 5). A relatively higher reduction in the value of kr, compared with ke has the result that with an increase in polymer MW and therefore, the viscosity of t h e system, the value of ke/kr increases. A rapid drop in the rate constant of chain rupture has the result t h a t polymer radicals accumulate in the system ([1~']~ and the overall rate of polymerization increases in spite of a sudden reduction in the rate of initiation. l~igure 6 shows the dependence of Vp, JR'l, _P and ke/kr on the degree of polymerization. I t is significant that these relations which have maximum values with 30-40~/o degree of conversion i.e. in the range of the gel effect, are proportional. A reduction in the rate of chain rupture increases the life time of the free radical, which is particularly noticeable with high degrees of conversion. This is, apparently, due to a change in the mechanism of rupture in glassy systems,
Radical polymerization of benzyl methacryla~o
1035
transition from the diffusion kinetic region to relay radical transfer. With an increase in temperature, the viscosity of the system decreases, which increases constants of chain extension and rupture and the overall rate of polymerization. The life time v of the growing radical on increasing .temperature decreases in view of the higher rate of chain rupture. However, at these temperatures, t he same way as a t 30 ° the value of r shows a strong dependence on the degree of conversion (Fig. 7). T 88C
7O
50
<= /
,~1.~11
l_
"b;ol"1
~
I ~
"/.
\ \
qo
Fzo. 6
~'
so
,o-
80
G,%
o
#0
80 G,%'
FIo. 7
:Fro. 6. Relation between P (1), k,]kr (2) [R'] (3) and vp (4) and the degree of conversion of BMA at 30°. Fie. 7. Relation between the life time of a growing radical r and the degree of conversion in photepolymerization of BM_Aat 30 (1), 50 (2) and 60° (3). A sudden reduction in the rate of chain rupt ure increases the overall rate of t h e process and does not lower the effect on the degree of polymerization: t h e value of P increases with an increase of the degree of conversion. This increase in rate could continue until the monomer is completely used up, but a reduction in m o n o m e r concentration on t he one ha n d and the constant of t he rate of ex-
L. G. SUROVTSEV et a/.
1036
~ension, on the other, firstoffsetsthe gel effect and then completely stops the reaction. Activation energies of extension, rupture and polymerization on the whole (Table 2) confirm these relations.With an increase in the degree of polymerization (and therefore, the viscosity of the system), the energy of activation of chain rupture increases more rapidly than chain extension and therefore, the T A B L E 2. V A R I A T I O N OF A C T I V A T I O N E N E R G I E S E (J/MOLE) A N D P R E - E X P O NENTIAL F A C T O R S A (L./MOLE'SEC) W I T H T H E D E G R E E OF C O N V E R S I O N IN P H O T O P O L Y M E R I Z A T I O N OF BMA IN B U L K (Sensitizing agent - benzyl, 0.05 mole/l.)
G, ~o
E*× 10-s
E r × 10s
Ep ×10-a
3 15 30 50 80
30-6 31.0 31.8 34.8 23.0
11"3 14"7 17"6 19"3 2"1
24"9 23"4 23'0 25"1 20"9
A e× 10-7 23"9 9"6 14"0 8"5 0"02
A r × 1 0 -9 8"32 2.20 1"60 3"80 0"0015
activation energy of polymerization Ep somewhat decreases with the degree of conversion and has a minimum value in the range of 30%. A reduction in the energy barrier increases the rate of polymerization in this region. Table 2 also shows results of the variation of pre-exponential factors in Arrhenius equations for rate constants of chain extension and rupture. During photosensitized polymerization of BlYIA a sudden reduction occurs in the pre-exponenti'al factor of the constant of chain extension A e at the initial stages of polymerization (up to G~--15%). This is followed by a gradual increase in Ae and a repeated, even more sudden drop on transition of the system into the glassy state (G----80%). A similar pattern is observed on changing At. I t is known that the pre-exponent may be shown as two co-factors: a steric factor and a collision factor. The variation of pre-exponential factors observed is, apparently, due to the increase in the viscosity of the system during polymerization which results in a lower number of collisions and the possible ordering of the system with the polymer formed, which may increase the steric factor. The predominance of one or the other factor affects the reduction or increase of the pre~exponential factor (as well as the variations of corresponding constants ke and kr). In the final stage, when glass transition takes place in the system, the collision factor decreases considerably and the pre-exponent has very low values. Translated by E. SE~ERE
REFERENCES 1. K. YOKOTA, M. KANI and Y. ISHH, J . P o l y m er Sei. 6: A - I : 1325, 1968 2. A. S. BANK and M. A. ASKAROV, Uzb. khim zh. 8: 71, 1964 3. J. M A J E R , Chem. prumysl 8: 324, 1958
DTM in amorphous polymers
1037
4. I. DVORAK, Chem. prumysl 8: 287, 1958 5. T.D. MAKSUTOVA, Sb. Issledovaniya po uprugosti i plastichnosti (Elasticity a n d Plasticity Studies). Izd-vo LGU, 1963 6. V. A. BIYKOV, Sbornik rabot Mosk. lesotekhn, in-ta, 14, 1965 7. J. MAJER, Chem. prumysl. 7: 433, 1957 8. T. V. SHAMRAYEVSKAYA and S. N. SOKOLOV, K h i m i y a i khimich, tekhnologiya 9: 117, 1966 9. L. G. SUROVTSEV and M. A. BULATOV, Vysokomol. soyed. A14: 2106, 1972 (Translated in Polymer Sci. U.S.S.R. 14: 9, 2364, 1972) 10. L. G. SUROVTSEV, M. A. BULATOV, K. A. CHARUSt~TKOV a n d S. S. SPASSKII, Zh. fiz. khimii 46: 2684, 1972 11. G. P. GLADYSHEV, N. V. CHURBAKOVA and S. R. RAFIKOV, Izv. AN KazSSR, s e r . khimich., No. 2, 9, 1966 12. R. K. GRAHAM, J. Polymer Sci. 37: 441, 1959 13. F. R. MAYO, R. A. GREGG and M. S. MATHESON, J. Amer. Chem. Soc. 73: 169, 1951
Polymer Science U.S.S.R.Vol. 20, pp. 1037-1045. (~) Pergamon Press Ltd. 1979. Printed In Poland
0032-395017810401-1037507.$0/0.
EFFECT OF SLOW MOLECULAR MOTION ON DAMPING OF T R A N S V E R S E N U C L E A R MAGNETIZATION IN A M O R P H O U S POLYMERS*
V. D.
FEDOTOV,
V. l-~. CHERNOV and T. N. KHAZAXOVICH
S. M. Kirov Chemico-Technological Institute, K a z a n I n s t i t u t e of Chemical Physics, U.S.S.R. Academy of Sciences
(Received 5 J u l y 1977) The NMR pulse method was used to study the variation of the form of damping of transverse magnetization (DTM) in polybutadiene, polyisobutyleno and n a t u r a l rubber in the range of glass temperature of polymer up to 200 ° and in polyethyleneglycol at 75 °, according to molecular weight. To describe the relations derived a simple model was introduced, in which relaxation was caused by random local fields, these fields having two c o m p o n e n t s - - a rapid and a slow fluctuation component. I t is assumed furthermore, that fluctuations are Gaussian random Markoff processes. The ratios derived give a satisfactory description of all experimental curves of DTM.
DAMPnvo of transverse nuclear magnetization in polymers in the high elastic or
plastic states (at temperatures higher than the glass temperature or melting point) has been studied for many years, however, it is still not cle£r what infer* Vysokomol. soy~l. A20: :No. 4, 919-926, 1978.
L.G.
SUROVTSEV et a/.
REFERENCES 1. I. C. W. CHIEN a n d C. R. BOSS, J. Polymer Sci. 5, A I : 1683, 1967 2. A. P. GRIVA and Ye. T. DENISOVA, Kinetika i kataliz 17: 1465, 1976 3. N. V. ZOLOTOVA and Ye. T. DEI~ISOV, Vysokomol. soyed. B18: 605, 1976 (l~'ot trans. lated in Polymer Sci. U.S.S.R.) 4. Ye. L. SHANINA, V. A. ROGINSKII and V. B. MILLER, Vysokomol. soyed. AI8: 1160, 1976 (Translated in Polymer Sci. U.S.S.R. 18: 5, 1334, 1976) 5. V. A. ROGINSKII, V. Z. DUBINSKII, I. A. SHLYAPNIKOVA and V. B. MILLER, Europ. Polymer J. 13: 1050, 1977 6. V. A. ROGINSKII a n d V. B. MILLER, Dokl..~N SSSR 215: 1164, 1974 7. Ye. L. SH.ANINA, V. I. RUBTSOV, V. A. ROGINSKII and V. B. MILLER, Kinetika i kataliz 18: No. 6, 1977 8. Ye. T. DENISOV, V. V. KHARITONOV and V. V. FEDOROVA, Kinctika i kataliz 1 6 : 332, 1975 9. G. P. GLADYSHEV and V. F. TSEPALOV, Uspekhi khimii 44: 1830, 1975 10. A. P. GRIVA and Ye. T. DENISOV, J. Polymer Sci., Polymer Chem. Ed. 14: 1051, 1976 11. A. P. GRIVA a n d Ye. T. DENISOV, I n t e r n a t . J. Chem., Kinetics 5: 869, 1973 12. V. A. BELYAKOV, Ye. L. SHANINA, V. A. ROGINSKII a n d V. B. MILLER, Izv. AI~ SSSR, set. khim., 2685, 1975 13. B. A. GROMOV, V. B. MIIffJER, M. B. NEIMAN a n d Ya. A. SHLYAPNIKOV, I n t e r n a t . J. Appl. Radiation and Isotopes 13: 281, 1962 14. V. A. ROGINSgll a n d V. B. MrLLER, ]:)old. AN SSSR 218: 642, 1973 15. T. V. POKHOLOK, O. N. KARPUKHIN a n d V. Ya. SHLYAPINTOKH, J. Polymer SoL, Polymer Chem. Ed. 13: 525, 1975
Polymer Science U.S.S.R. Vol. 20, pp. 1030-1037.
0032-3950/7810401-1030107.5010
~) PergamonPress Ltd. 1979. Printed in Poland
RADICAL POLYMERIZATION OF BENZYL METHACRYLATE AT HIGH DEGREES OF CONVERSION* L. G. SUROVTSEV, M. A. BULATOV, S. S. SPASSKII
and K. A. CHARUSH~IKOV I n s t i t u t e of Chemistry, Urals Scientific Centre, U.S.S.R. Academy of Sciences
(Received 5 July 1977) A calorimetric study was made of radical polymerization of benzyl methacrylate at 30, 50 a n d 60 ° . I n t e r m i t t e n t illumination and results of the rate of initiation at various stages of conversion were used to determine kinetic parameters of poly-
* Vysokomol. soyed. A20: No. 4, 913-918, 1978.
Radical polymerization of benzyl methacrylate
1031
merization at degrees of 3, 15, 40, 50 and 80O/o. The variation of parameters with the extent of reaction is interpreted from the point of view of elementary stages of polymerization at advanced degrees. STUDIES of radical p o l y m e r i z a t i o n of b e n z y l m e t h a c r y l a t e (BMA) [1-4], n o w widely used in p r a c t i c e [5-8] are r e s t r i c t e d to i n v e s t i g a t i o n s of initial stages o f conversion. A s t u d y of regularities g o v e r n i n g p o l y m e r i z a t i o n b y t h e r a d i c a l m e c h a n i s m a t high degrees of conversion is n o t o n l y of theoretical, b u t also o f p r a c t i c a l interest. BMA was purified by three fold vacuum distillation, b.p. 89-90°/250 Pa, n~° 1-5142, d,*° 1.0420. AID and benzyl three times recrystallized from methanol were used as initiators, m.p. 102 and 95 ° respectively. 1,l-diphenyl-2-pycrylhydrazyl (DPPH), freshly oxidized and three times recrystallized from chloroform, m.p. 132° were the inhibitors. Polymerization was investigated thermometrically using a differential isothermal calorimeter [9]. The accuracy of measuring heat was 0.17% and the rate of heat liberation, 0.50%. Polymerization was carried out in hermetic cells with a fiuoroplastic fihn opening for UV lighting. Photo-initiation was carried out with the light of a very high pressure mercury arc quartz lamp pressure (SHP-120A), filtered with silicate glass 2 mm in thickness with light transmission of 365 n m - - 7 6 % and with 315 nm--19~o. The intensity of light I was regulated by a metal grid of varying density. Methods of measurement and calculation of kinetic parameters have been published previously [10]. The rate of initiation at high degrees of conversion were determined from the ratio
v~=vp/P,
(1)
where P is the instant~neous degree of polymerization calculated from the average degree of polymerization /5 and the degree of polymerization G from equation [11] P=
G dP"
(2)
I . . . . .
/5 dG The molecular weight of PBMA was found viscometrieally in benzene from the Mark-Kuhn equation, in which constants K and g for PBMA in benzene are 0.103× 104 and 0.82, respectively [ 12]. Constants of chain transfer through monomer molecules Cm were derived from the dependence of the inverse degree of polymerization 1//~ on the rate of polymerization vp at different initiator concentrations [13]. F i g u r e 1 shows s o m e kinetic c u r v e s of p o l y m e r i z a t i o n of BMA. I t is clearly seen t h a t t h e process of p o l y m e r i z a t i o n (gel effect) is accelerated. T h i s is a t y p i cal p a t t e r n w h i c h is o b s e r v e d e x p e r i m e n t a l l y in all cases o f p o l y m e r i z a t i o n o f BI~IA. A s t u d y of t h e effect,of i n i t i a t o r c o n c e n t r a t i o n on t h e r a t e of p o l y m e r i z a t i o n of B M A shows a s q u a r e r e l a t i o n b e t w e e n t h e m , w h i c h indicates t h e a p p l i c a b i l i t y t o t h i s s y s t e m o f a c o n v e n t i o n a l e q u a t i o n of radical p o l y m e r i z a t i o n of v i n y l c o m p o u n d s . E x p o n e n t I ' , d e r i v e d e x p e r i m e n t a l l y f r o m t h e d i a g r a m m a t i c relat i o n o f log vp-~f (log I ) is also 0 . 5 0 ± 0 . 0 1 , w h i c h is in s a t i s f a c t o r y a g r e e m e n t w i t h results p r e v i o u s l y o b t a i n e d [1], w h e r e n----0.51.
1032
L. G. S~ROV'rS,~V et a/.
A study of the effeet of initiator concentration on ~ of the polymer indicates that an increase in initiator concentration, or an increase of light intensity, i.e. an increase in the rate of initiation, the same way as an inereaze in temperature of polymerization (in initiation), displaces the maximum rate of polymerization to high degrees of conversion and reduces ~fW of the polymer formed. up't0 a, mole//. . sec
2 !
!
2
3
f. I0-~ sec
~"io. 1. ]{inetie curves of polymerization of BlVIA in bulk at 90 (1), 80 (2) and 70 ° (3); i n i t i a t o r - - A I D ; t--time.
Figures 2 and 3 show the linear dependence of 1]/5 on initiator concentration •and the rate of polymerization. The linearity of these relations proves the absence of chain transfer through molecules of the initiator in the concentration and temperature range examined. By extrapolation of the curve showing the linear relation of 1/P=f (vp)to Vp=0 the value of Cm may be found. As shown by Fig. 3, the c e n t a u r of chain transfer through BbfA molecules up to a temperature of lxl 0 P3
px rO'Z
8 J
I
/,./ 0
0.5 FIo. 2
1.0 lAID], %
5
I
I
I
0.,25
0"50
0"76
up. tO~,moldl sec
~ko. 3
F~a. 2. Relation between ~ and the concentration of AID at 60 (I), 70 (2), 80 (3) a n d 90° (d). }ho. 3. Relation between l i p and tho value ofvD in polymerization of BMA: 1--90, 2--80, -3--70, 4 - - 6 0 (initiator: AID), 5 - - 3 0 ° (photopolymerization: here a n d in Figs. 4-7 benzyl was used as sensitizer (0.05 molefl.).
Radical polymerization of benzyl methacrylato
1033
~}0° is negligibly low, which enables r a t i o (1) to be used t o d e t e r m i n e t h e r a t e o f i n i t i a t i o n a t high degrees o f conversion. T a b l e 1 shows results o f i n v e s t i g a t i n g p h o t o - i n i t i a t e d p o l y m e r i z a t i o n of B M A in b u l k a t 30, 50 a n d 60 ° a t different degrees o f conversion. T h e v a r i a b i l i t y of all k i n e t i c p a r a m e t e r s d u r i n g p o l y m e r i z a t i o n is o f m a i n significance. A sudden reTABLE 1. PHOTOPOLYM-ERIZATIO~N" OF BMA IN B U L K
(Sensitizer - benzyl, 0.05 mole/l.) T, °C
PX
v l x 10', 10-s mole/1., •see
30.0 50"0 60.0 30"0 50"0 60"0
13'5 25.3 31.2
I'19 1"10
G=3~0.5% 6.00 7.91 12.2 7.32 15.5 7.04
5"03 5"45 5"54
5"56 4.93 4'22
G = 15=t=3% 6.80 28.0 13.8 26-9 17-3 23-4
9.65 7.97 6-41
17"6 28'9 36'8
4-58 4.88 5.16
30"0 50"0 60-0
19"0 29"2 38'2
1-54
20"4 29'8 39"3
VpX 105, 10-'~kexl mole/l: [ R ' ] x l 0 " i k r x 0 -t, .see mole/1. ! 1./mole.see
5-95* 6.15 6-40
30'0 50'0 60-0
30.0 50"0 60.0
v, see
1'88 1.91 0.102 0.168 0.142
ke ~ X l0 t
1"31 2'90 4'01
2"52 3"10
6"41 7"53 10"l
4'82 10'2 14"7
7"57 13"5 14"5
G=30±3% 8.06 44.2 14.1 38.9 19.0 33"1
2-34 3"22 4"71
4'39 8'73 13'8
18"7 27-1 29'3
17"3 13.7 11.7
G=50±5% 2.94 26.7 5.40 25.7 7.30 22"3
2"15 2'85 3'84
3'72 7'10 ll'l
17'3 24"9 28"9
69.0 65.5 61.0
G = 8 0 - 57~ 0.208 7.03 0.503 11.0 0.560 8'66
2"06
2'48 3"84 5"43
12"0 26"2 28"7
1'33
95 115 129
1"38 1"89
1"38
* The rate of initiation at low degreewas determinedby adding DPPH as inhibitor. d u c t i o n in t h e r a t e o f initiation w i t h t h e degree of p o l y m e r i z a t i o n is o b s e r v e d in e v e r y case. Since t h e r a t e of d e c o m p o s i t i o n o f t h e i n i t i a t o r r e m a i n e d c o n s t a n t , a c h a n g e in t h e r a t e of initiation is, e v i d e n t l y due t o a r e d u c t i o n in t h e efficiency o f i n i t i a t i o n in v i e w of t h e difficulty i n v o l v e d in t h e e m e r g e n c e of p r i m a r y radicals f r o m t h e "cell" caused b y diffusion. F i g u r e 4 shows t h e d e p e n d e n c e of a v e r a g e d e g r e e o f p o l y m e r i z a t i o n a n d t h e r a t e of initiation on t h e degree o f conversion. T a b l e 1 indicates t h a t t h e r a t e o f p o l y m e r i z a t i o n increases slowly in e v e r y ease w i t h t h e degree o f c o n v e r s i o n a n d passing t h r o u g h t h e m a x i m u m w i t h 8 0 - 4 0 % conversion, it s u d d e n l y decreases a n d t h e n g r a d u a l l y t e n d s to zero w i t h d e g r e e s o f conversion close to 100%. As a consequence o f t h e f o r m a t i o n of a p o l y -
L. G. Su~owrsEv et a/.
1034
mer product, the viscosity of the system increases with the degree of conversion. All process parameters change at the same time. The rate constant of chain rupture varies with an increase in viscosity, showing a marked reduction at the v e r y
Io9 ui+9 0"75 -
IogP f
2 #.27
0"25
#.Z3
-0"75
#.18
-0.75
#45 l/O
8o ¢,%
FzG. 4
FzG. 5
Fro. 4. Relation between log vi (1) and log P (2) and the degree of conversion G in photopolymerization of BMA at 30°. FIo. 5. Relation between vi (1), ko (2) and k¢ (3) and the degree of conversion in photo-polyrnerization of BMA at 30°. beginning of the process. This is due to considerable diffusion hindrances when macromolecular radicals encounter a monomer-polymer medium. Viscosity variation has a lower effect on monomer diffusion, therefore, the rate constant o f chain extension decreases less strongly than the rate constant of chain rupture (Fig. 5). A relatively higher reduction in the value of kr, compared with ke has the result that with an increase in polymer MW and therefore, the viscosity of t h e system, the value of ke/kr increases. A rapid drop in the rate constant of chain rupture has the result t h a t polymer radicals accumulate in the system ([1~']~ and the overall rate of polymerization increases in spite of a sudden reduction in the rate of initiation. l~igure 6 shows the dependence of Vp, JR'l, _P and ke/kr on the degree of polymerization. I t is significant that these relations which have maximum values with 30-40~/o degree of conversion i.e. in the range of the gel effect, are proportional. A reduction in the rate of chain rupture increases the life time of the free radical, which is particularly noticeable with high degrees of conversion. This is, apparently, due to a change in the mechanism of rupture in glassy systems,
Radical polymerization of benzyl methacryla~o
1035
transition from the diffusion kinetic region to relay radical transfer. With an increase in temperature, the viscosity of the system decreases, which increases constants of chain extension and rupture and the overall rate of polymerization. The life time v of the growing radical on increasing .temperature decreases in view of the higher rate of chain rupture. However, at these temperatures, t he same way as a t 30 ° the value of r shows a strong dependence on the degree of conversion (Fig. 7). T 88C
7O
50
<= /
,~1.~11
l_
"b;ol"1
~
I ~
"/.
\ \
qo
Fzo. 6
~'
so
,o-
80
G,%
o
#0
80 G,%'
FIo. 7
:Fro. 6. Relation between P (1), k,]kr (2) [R'] (3) and vp (4) and the degree of conversion of BMA at 30°. Fie. 7. Relation between the life time of a growing radical r and the degree of conversion in photepolymerization of BM_Aat 30 (1), 50 (2) and 60° (3). A sudden reduction in the rate of chain rupt ure increases the overall rate of t h e process and does not lower the effect on the degree of polymerization: t h e value of P increases with an increase of the degree of conversion. This increase in rate could continue until the monomer is completely used up, but a reduction in m o n o m e r concentration on t he one ha n d and the constant of t he rate of ex-
L. G. SUROVTSEV et a/.
1036
~ension, on the other, firstoffsetsthe gel effect and then completely stops the reaction. Activation energies of extension, rupture and polymerization on the whole (Table 2) confirm these relations.With an increase in the degree of polymerization (and therefore, the viscosity of the system), the energy of activation of chain rupture increases more rapidly than chain extension and therefore, the T A B L E 2. V A R I A T I O N OF A C T I V A T I O N E N E R G I E S E (J/MOLE) A N D P R E - E X P O NENTIAL F A C T O R S A (L./MOLE'SEC) W I T H T H E D E G R E E OF C O N V E R S I O N IN P H O T O P O L Y M E R I Z A T I O N OF BMA IN B U L K (Sensitizing agent - benzyl, 0.05 mole/l.)
G, ~o
E*× 10-s
E r × 10s
Ep ×10-a
3 15 30 50 80
30-6 31.0 31.8 34.8 23.0
11"3 14"7 17"6 19"3 2"1
24"9 23"4 23'0 25"1 20"9
A e× 10-7 23"9 9"6 14"0 8"5 0"02
A r × 1 0 -9 8"32 2.20 1"60 3"80 0"0015
activation energy of polymerization Ep somewhat decreases with the degree of conversion and has a minimum value in the range of 30%. A reduction in the energy barrier increases the rate of polymerization in this region. Table 2 also shows results of the variation of pre-exponential factors in Arrhenius equations for rate constants of chain extension and rupture. During photosensitized polymerization of BlYIA a sudden reduction occurs in the pre-exponenti'al factor of the constant of chain extension A e at the initial stages of polymerization (up to G~--15%). This is followed by a gradual increase in Ae and a repeated, even more sudden drop on transition of the system into the glassy state (G----80%). A similar pattern is observed on changing At. I t is known that the pre-exponent may be shown as two co-factors: a steric factor and a collision factor. The variation of pre-exponential factors observed is, apparently, due to the increase in the viscosity of the system during polymerization which results in a lower number of collisions and the possible ordering of the system with the polymer formed, which may increase the steric factor. The predominance of one or the other factor affects the reduction or increase of the pre~exponential factor (as well as the variations of corresponding constants ke and kr). In the final stage, when glass transition takes place in the system, the collision factor decreases considerably and the pre-exponent has very low values. Translated by E. SE~ERE
REFERENCES 1. K. YOKOTA, M. KANI and Y. ISHH, J . P o l y m er Sei. 6: A - I : 1325, 1968 2. A. S. BANK and M. A. ASKAROV, Uzb. khim zh. 8: 71, 1964 3. J. M A J E R , Chem. prumysl 8: 324, 1958
DTM in amorphous polymers
1037
4. I. DVORAK, Chem. prumysl 8: 287, 1958 5. T.D. MAKSUTOVA, Sb. Issledovaniya po uprugosti i plastichnosti (Elasticity a n d Plasticity Studies). Izd-vo LGU, 1963 6. V. A. BIYKOV, Sbornik rabot Mosk. lesotekhn, in-ta, 14, 1965 7. J. MAJER, Chem. prumysl. 7: 433, 1957 8. T. V. SHAMRAYEVSKAYA and S. N. SOKOLOV, K h i m i y a i khimich, tekhnologiya 9: 117, 1966 9. L. G. SUROVTSEV and M. A. BULATOV, Vysokomol. soyed. A14: 2106, 1972 (Translated in Polymer Sci. U.S.S.R. 14: 9, 2364, 1972) 10. L. G. SUROVTSEV, M. A. BULATOV, K. A. CHARUSt~TKOV a n d S. S. SPASSKII, Zh. fiz. khimii 46: 2684, 1972 11. G. P. GLADYSHEV, N. V. CHURBAKOVA and S. R. RAFIKOV, Izv. AN KazSSR, s e r . khimich., No. 2, 9, 1966 12. R. K. GRAHAM, J. Polymer Sci. 37: 441, 1959 13. F. R. MAYO, R. A. GREGG and M. S. MATHESON, J. Amer. Chem. Soc. 73: 169, 1951
Polymer Science U.S.S.R.Vol. 20, pp. 1037-1045. (~) Pergamon Press Ltd. 1979. Printed In Poland
0032-395017810401-1037507.$0/0.
EFFECT OF SLOW MOLECULAR MOTION ON DAMPING OF T R A N S V E R S E N U C L E A R MAGNETIZATION IN A M O R P H O U S POLYMERS*
V. D.
FEDOTOV,
V. l-~. CHERNOV and T. N. KHAZAXOVICH
S. M. Kirov Chemico-Technological Institute, K a z a n I n s t i t u t e of Chemical Physics, U.S.S.R. Academy of Sciences
(Received 5 J u l y 1977) The NMR pulse method was used to study the variation of the form of damping of transverse magnetization (DTM) in polybutadiene, polyisobutyleno and n a t u r a l rubber in the range of glass temperature of polymer up to 200 ° and in polyethyleneglycol at 75 °, according to molecular weight. To describe the relations derived a simple model was introduced, in which relaxation was caused by random local fields, these fields having two c o m p o n e n t s - - a rapid and a slow fluctuation component. I t is assumed furthermore, that fluctuations are Gaussian random Markoff processes. The ratios derived give a satisfactory description of all experimental curves of DTM.
DAMPnvo of transverse nuclear magnetization in polymers in the high elastic or
plastic states (at temperatures higher than the glass temperature or melting point) has been studied for many years, however, it is still not cle£r what infer* Vysokomol. soy~l. A20: :No. 4, 919-926, 1978.