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Kinetics of the polymerization of some acrylic monomers in thin layers in the presence of atmospheric oxygen
KINETICS OF THE POLYMERIZATION OF SOME ACRYLIC MONOMERS IN THIN LAYERS IN THE PRESENCE OF ATMOSPHERIC OXYGEN* YE. i~I. MOROZOVA,V. I. YELISEYEVA and M. A. KORSHUNOV Physical Chemistry Institute, U.S.S.R. A cad em y of Sciences
(Received 26 November 1968)
THE method of polymerizing monomers in thin layers in the presence of atmospheric oxygen is of great interest in regard to the production of coatings directly from monomers. This method may be economically advantageous through dispensing with the technological process of producing film-forming polymers or oligomers, and also the process of removing the solvent from them after they have been applied to the surface. In view of the difficulty of studying features of the polymerization of the usual low-boiling monomers under the conditions referred to above we specially selected monomers with a low vapour pressure, i. e. n-octyl methacrylate (OMA) and amino-substituted alkyl methacrylates; the latter were used because of the possibility of polymerization by autocatalytic redox-initiation in the presence of a peroxide. The thermometric method [1] is the one most suitable for studying the kinetics of polymerization to high conversions, and this method was used in this investigation. EXPERIMENTAL PROCEDURE AND RESULTS A dual compensating calorimeter was used to study the polymerization kinetics, and t h e procedure was t h e same as in [2]. The thickness of the layer of monomer in the polymerizing vessel, which was not hermetically sealed, was 0.5 mm. The experiments were conducted in t h e presence of benzoyl peroxide (BP) and the dinitrile of azoisobutyric acid (DAA), the a m o u n t introduced being 0.5 mol.%. B P was twice reprecipitated from chloroform with ethyl alcohol; D A A was twice recrystallized from methanol. OMA was double distilled in a current of nitrogen at 97 ° and 1 m m H g ; n~ 1.4360. fl-(N-piperidyl)ethyl methacrylate (PEMA) was double distilled in a current of nitrogen; b.p. 103.5°/3 m m , n~° 1-4695. The rate of polymerization in relation to temperature was studied over t h e range 30 to 80 ° with B P and D A A as initiators. I t was found t h a t with D A A as initiator t h e polymerization is measurable from t h e evolution of heat above 53 ° for PEMA, or above 65 ° for OMA. W i t h B P as initiator polymerization of P E M A was already observed at about 30 °, at which t e m p e r a t u r e OMA does n o t polymerize. * Vysokomol. soyod. A10: No. 10, 2354-2358, 1968. 2736
P o l y m e r i z a t i o n of s o m e acrylic m o n o m e r s in t h i n layers
2737
T h e relation of t h e degree of c o n v e r s i o n to t i m e in t h e p o l y m e r i z a t i o n of t h e m o n o m e r s in q u e s t i o n was c a l c u l a t e d b y m e a n s of t h e e x p e r i m e n t a l c u r v e s of h e a t e v o l u t i o n vs. t i m e obt a i n e d b y t h e m e t h o d described in [2J. I t is a p p a r e n t f r o m t h e kinetic curves shown in Fig. 1 t h a t t h e p o l y m e r i z a t i o n of t h e m e t h a c r y l a t e s u n d e r r e v i e w u n d e r t h e conditions a d o p t e d is c h a r a c t e r i z e d b y a m a r k e d increase in tho r a t e e v e n a t low conversions. W h e n D A A is used as t h e i n i t i a t o r t h e m a x i m u m r a t e of p o l y m e r i z a t i o n for b o t h m o n o m e r s increases w i t h a rise in t e m p e r a t u r e , while t h e t i m e n e e d e d to r e a c h this r a t e is reduced. T h e p o l y m e r i z a t i o n r a t e for PEM_A is several t i m e s higher t h a n t h a t for OI~IA a t similar
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FIG. 1. K i n e t i c curves of p o l y m e r i z a t i o n : a - - P E M A ~ - D A A : •--73"5, 2--64.5, 3 - - 6 2 . 7 , 4--55.5, 5 - - 5 3 ° ; b - - O M A ~ D A A : 1 - - 7 8 , 2 - - 7 6 . 5 , 3 - - 7 0 , 4--66°; c - - P E M A - ~ B P : 1--41-5, 2--31.5, 3 - - 5 5 , 4--69-5 °. K - - d e g r e e of conversion.
t e m p e r a t u r e s (Fig. la, c u r v e 2, a n d Fig. lb, c u r v e 4). A t t h e s a m e t i m e t h e p o l y m e r i z a t i o n of P E M A is c h a r a c t e r i z e d b y a shorter i n d u c t i o n p e r i o d a n d a higher degree of conversion. I n t h e case of P E M A w h e n B P is used as i n i t i a t o r t h e t e m p e r a t u r e d e p e n d e n c e of t h e r a t e of p o l y m e r i z a t i o n differs f r o m t h a t o b s e r v e d w i t h D A A as initiator. O v e r t h e t e m p e r a t u r e r a n g e 31.5 to 69"5 ° t h e p o l y m e r i z a t i o n is g r e a t e s t a t 41"5°; w i t h a rise in t e m p e r a t u r e t h e m a x i m u m r a t e is reduced, a n d this is p a r t i c u l a r l y m a r k e d at t e m p e r a t u r e s a b o v e 55 ° . T h e t h e r m a l effect of p o l y m e r i z a t i o n was d e t e r m i n e d b y i n t e g r a t i o n b y weighing of curves of h e a t e v o l u t i o n versus t i m e [3]. Since t h e r e a c t i o n was n o t c o n t i n u e d up to 1 0 0 ~ c o n v e r s i o n t h e h e a t effect to be d e t e r m i n e d was r e l a t e d to t h e a m o u n t of p o l y m e r formed.
Y~.. M. NIOROZOVAet a/.
2738
The degree of conversion was found b y means of the residual monomer using the polaxographic method [4]. The thermal effect for 100% conversion was calculated from the equation: Q - ~ Q~. - - 100 K where Q is the thermal effect of polymerization; K is the degree of conversion, %; Q~ is the heat evolution per mole of monomer for a particular degree of conversion. I t m a y be seen from Fig. 2 t h a t the thermal effect in the polymerization of PEMA increases from 13.5 to 20 keal/mole with a rise in temperature from 30 to 70 °.
(~,kcal/mole 20
o/40
10
I 40
I 50
r 60
7-;,oc
r 70
Fie. 2. Change in thermal effect with rise in the polymerization temperature of P E n DAA and B P as initiators: 1--DA.A; 2 - - B P .
with
The thermal effect for the polymerization of OMA at 66-78 ° varies within limits of 13.2 to 13.5 kcal/mole, which is in agreement with data published in [5, 6]. C 2
1
dK ._c-t
40 ~
a
-•T
40
2O
20
:~-, $8C-1
/ /
10 20 40 60 80 100 K,%
3 20 40 60
80
K, %
20 40 60 80 1£,0 K,%
FIG. 3. Polymerization rate vs. degree of conversion of monomer to polymer: a - - P E M A - k DAA: •--73.5, 2--64, 3--55.5°; b--OMA-FDAA: 1--31.5, 2--41.5, 3--55°; c--PEM_A-pPB; 1--31.5, 2--41-5, 3--55; 4--69.5 °. Figure 3 shows the dependence of the polymerization rate on the degree of conversion of monomer. According to these data, the highest rate of polymerization for both monomers with DAA as initiator is obtained at a definite degree of conversion, irrespective of tom-
Polymerization of some acrylic monomers in thin layers
2739
perature. I n the case of PEMA this conversion is around 24%, while for OM_Ait is about
17~ . In the polymerization of PEMA with BP the maximum rate in relation to temperature corresponds to different degrees of conversion corresponding to the highest conversion at lower temperatures. The overall activation energy for the polymerization of the monomers in question with different initiators was calculated by the graphic method (Fig. 4); for instance, the activation energy at 10 ~o conversion for PEMA+DAA is 23.4, and for PEMA+BP it is 8-35 kcal/mole; for OMA with DAA as initiator the activation energy was 26.1 kcal/mole. dK ln-d'c 3"6
2"8
\
2.0 t
0.0029
i
I
00031
00033 1/T
FIG. 4. In dK/dv vs. 1/T: 1--OMA+DAA; 2--PEMA+DAA; 3--PEMA+BP. DISCUSSION OF RESULTS
In a s t u d y of the polymerization of high-boiling alkyl methacrylates and amino-substituted alkyl methaerylates in thin layers in the presence of atmospheric oxygen it was shown t h a t under suitable conditions the process m a y be carried out to a high conversion with practically no loss of monomers. A comparative s t u d y of the polymerization of both monomers, i, e. OMA and PEMA, in the presence of a peroxide initiator (BP) and an azo-eompound (DAA) revealed the specific nature of the polymerization of amino-substituted alkyl methacrylates under these conditions. The activation energy for the polymerization of both monomers with DAA as initiator determined by the authors under conditions allowing free access to oxygen is higher t h a n the activation energy determined by other authors for similar monomers in the absence of atmospheric oxygen. For instance, in [7] the authors give the activation energy for the polymerization of N-diethylaminoethyl methaerylate, N-dimethylaminoethyl methaerylate and methyl methacrylate as being respectively 19.4, 19.7 and 19.5 keal/mole, while in our experiments for the polymerization of PEMA and OMA we obtained activation energies of 23.4 and 26.1 keM/mole respectively. On comparing the polymerization of both monomers under the conditions adopted by the present authors it is apparent t h a t in the presence of DAA PEMA polymerizes at a higher rate and with slightly lower activation energy t h a n OMA.
2740
YE. M. Mo~ozovA et
al.
The rise observed in the total activation energy for both monomers m a y be attributed to increase in the activation energy of initiation with the inhibiting action of atmospheric oxygen, and the slightly lower activation energy for PEMA compared with OMA m a y be attributed to the formation of an initiating redoxsystem. This system m a y result from the interaction of an amine with an ester bond [8] or with a peroxide radical formed under the conditions adopted, according to data in [9]. These assumptions are further supported by the difference in the change in the polymerization rate relative to the degree of conversion for PEMA and OMA. Benzoyl peroxide used to initiate the polymerization of PEMA results in a high reaction rate, lower activation energy and a shorter induction period. In the case under consideration the reduced initiating efficiency found with a rise in temperature above 55 ° is characteristic, and m a y possibly be due to the rapid depletion of the peroxide in the system. The special efficiency of the peroxide initiator in the polymerization of the amino-substituted alkyl methacrylate is apparently due to the formation of an initiating redox-system between the amino-containing monomer and the peroxide. The formation of initiating systems from peroxides and nonmonomeric amines was studied in [10-12], and the interaction of BP with amino-substituted methacrylates is referred to in [7], where the authors apparently found no initiating effect. Acording to [10-12] when a B P - t e r t i a r y amine system is used to initiate polymerization there is a redox reaction between the two components accompanied by the formation of radicals capable of initiating the polymerization. The thermal effect of polymerization for OMA determined over the range 6678 °, or 31-45 ° in the case of PEMA varies within limits of 13.5 kcal/mole, which corresponds to the energy of the double bond of methacrylic esters. With a rise in temperature to 70 ° the thermal effect of PEMA polymerization with both initiators is increased to 20 kcal/mole. This m a y be due to the additional evolution of heat resulting from oxidation of the amino-containing monomer; the process under consideration in the presence of atmospheric oxygen takes place more rapidly at elevated temperatures than at low ones. The authors wish to thank M. F. Margaritovaya and V. E. Lazaryanets for their interest in the experiments and for useful advice given during discussion of the results obtained in the investigation. CONCLUSIONS
(1) The kinetics of the polymerization of fl-(N-piperidyl)ethyl methacrylate and n-octyl methacrylate have been investigated with benzoyl peroxide and the dinitrile of azoisobutyric acid as initiators, the process being conducted in thin layers in the presence of atmospheric oxygen. I t has been shown t h a t these monomers m a y be polymerized with inappreciable losses up to high conversions under mild polymerization conditions.
Polymerization of some acrylic monomers in thin layers
2741
(2) T h e t h e r m a l effect o f t h e p o l y m e r i z a t i o n of n - o c t y l m e t h a c r y l a t e a n d fl-(N-piperidyl)ethyl m e t h a e r y l a t e a t low t e m p e r a t u r e s is ~ 1 3 . 5 k c a l / m o l e w h i c h agrees w i t h p u b l i s h e d d a t a for m e t h a c r y l i c esters. H o w e v e r , in t h e case of fl-(N-piperidyl)ethyl m e t h a e r y l a t e a rise in t e m p e r a t u r e is a c c o m p a n i e d b y a greater t h e r m a l effect, w h i c h is due to o x i d a t i v e processes t a k i n g place a t t h e s a m e time. (3) T h e overall a c t i v a t i o n e n e r g y o f p o l y m e r i z a t i o n for t h e m o n o m e r s in question w i t h t h e dinitrile o f a z o i s o b u t y r i c acid as initiator is slightly higher t h a n t h e a c t i v a t i o n e n e r g y d e t e r m i n e d b y o t h e r a u t h o r s u n d e r oxygen-fi'ee conditions, which is a p p a r e n t l y due to a rise in t h e e n e r g y of initiation caused b y the inhibiting a c t i o n o f oxygen. (4) fl-(N-piperidyl)ethyl m e t h a c r y l a t e p o l y m e r i z e s in t h e presence of b e n z o y l p e r o x i d e w i t h a lower a c t i v a t i o n energy: this is a t t r i b u t e d to the f o r m a t i o n of a n initiating r e d o x - s y s t e m b e t w e e n b e n z o y l p e r o x i d e a n d t h e a m i n o - c o n t a i n i n g monoIner. Translated by R. J. A. HENDRY REFERENCES
1. G. V. KOROLEV, B. V. PAVLOV and A. A. BERLIN, Vysokomol. soyed, l: 1396, 1959 (Not translated in Poiymer Sei. U.S.S.R.) 2. Ye. M. MOROZOVA, A. S. MOROZOV and V. I. Y E L I S E Y E V A , Zh. fiz. k h i m i i 42:
297, 1968 3. E. KALVE and A. PRAT, Microcalorimetry. (In Russian) Foreign Lit. Pub. House, 1963 4. V. D. BEZUGLYI, Polyarografiya v khimii i tekhnologii polimerov (Polarography in Polymer Chemistry and Technology). p. 58, publ. by Univ. of Kharkov, 1964 5. R. M. JOCHI, Makromolek. Chem. 66: 114, 1966 6. L. TONG and W. KENYON, J. Amer. Chem. Soe. 67: 1279, 1945 7. E. I. ABLYAKIMOV, Thesis, 1967 8. S. D. YEVSTRATOVA, K. F. MARGARITOVA and S. S. MEDVEDEV, Vysokomol. soyed. 5: 1574, 1963 (Translated in Polymer Sci. U.S.S.R. 5: 4, 681, 1964) 9. W. KERN, Makromolek. Chem. 2: 48, 1948 10. M. F. MARGARITOVA and I. Yu. MUSABEKOVA, Vysokomol. soyed. 3: 530, 1961 (Translated in Polymer Sci. U.S.S.R. 3: 4, 552, 1962) 11. S. D. STAVROVA, G. V. PEREGUDOV and M. F. MARGARITOVA, I)okl. AN SSSR, 157: 636, 1964 12. S. N. TRUBITSYNA, M. F. MARGARITOVA and S. S. MEDEVDEV, Vysokomol. soyed. 7: 1973, 1965 (Translated in Polymer Sci. U.S.S.R. 7: 11, 2165, 1965)
(Received 26 November 1968)
THE method of polymerizing monomers in thin layers in the presence of atmospheric oxygen is of great interest in regard to the production of coatings directly from monomers. This method may be economically advantageous through dispensing with the technological process of producing film-forming polymers or oligomers, and also the process of removing the solvent from them after they have been applied to the surface. In view of the difficulty of studying features of the polymerization of the usual low-boiling monomers under the conditions referred to above we specially selected monomers with a low vapour pressure, i. e. n-octyl methacrylate (OMA) and amino-substituted alkyl methacrylates; the latter were used because of the possibility of polymerization by autocatalytic redox-initiation in the presence of a peroxide. The thermometric method [1] is the one most suitable for studying the kinetics of polymerization to high conversions, and this method was used in this investigation. EXPERIMENTAL PROCEDURE AND RESULTS A dual compensating calorimeter was used to study the polymerization kinetics, and t h e procedure was t h e same as in [2]. The thickness of the layer of monomer in the polymerizing vessel, which was not hermetically sealed, was 0.5 mm. The experiments were conducted in t h e presence of benzoyl peroxide (BP) and the dinitrile of azoisobutyric acid (DAA), the a m o u n t introduced being 0.5 mol.%. B P was twice reprecipitated from chloroform with ethyl alcohol; D A A was twice recrystallized from methanol. OMA was double distilled in a current of nitrogen at 97 ° and 1 m m H g ; n~ 1.4360. fl-(N-piperidyl)ethyl methacrylate (PEMA) was double distilled in a current of nitrogen; b.p. 103.5°/3 m m , n~° 1-4695. The rate of polymerization in relation to temperature was studied over t h e range 30 to 80 ° with B P and D A A as initiators. I t was found t h a t with D A A as initiator t h e polymerization is measurable from t h e evolution of heat above 53 ° for PEMA, or above 65 ° for OMA. W i t h B P as initiator polymerization of P E M A was already observed at about 30 °, at which t e m p e r a t u r e OMA does n o t polymerize. * Vysokomol. soyod. A10: No. 10, 2354-2358, 1968. 2736
P o l y m e r i z a t i o n of s o m e acrylic m o n o m e r s in t h i n layers
2737
T h e relation of t h e degree of c o n v e r s i o n to t i m e in t h e p o l y m e r i z a t i o n of t h e m o n o m e r s in q u e s t i o n was c a l c u l a t e d b y m e a n s of t h e e x p e r i m e n t a l c u r v e s of h e a t e v o l u t i o n vs. t i m e obt a i n e d b y t h e m e t h o d described in [2J. I t is a p p a r e n t f r o m t h e kinetic curves shown in Fig. 1 t h a t t h e p o l y m e r i z a t i o n of t h e m e t h a c r y l a t e s u n d e r r e v i e w u n d e r t h e conditions a d o p t e d is c h a r a c t e r i z e d b y a m a r k e d increase in tho r a t e e v e n a t low conversions. W h e n D A A is used as t h e i n i t i a t o r t h e m a x i m u m r a t e of p o l y m e r i z a t i o n for b o t h m o n o m e r s increases w i t h a rise in t e m p e r a t u r e , while t h e t i m e n e e d e d to r e a c h this r a t e is reduced. T h e p o l y m e r i z a t i o n r a t e for PEM_A is several t i m e s higher t h a n t h a t for OI~IA a t similar
b
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FIG. 1. K i n e t i c curves of p o l y m e r i z a t i o n : a - - P E M A ~ - D A A : •--73"5, 2--64.5, 3 - - 6 2 . 7 , 4--55.5, 5 - - 5 3 ° ; b - - O M A ~ D A A : 1 - - 7 8 , 2 - - 7 6 . 5 , 3 - - 7 0 , 4--66°; c - - P E M A - ~ B P : 1--41-5, 2--31.5, 3 - - 5 5 , 4--69-5 °. K - - d e g r e e of conversion.
t e m p e r a t u r e s (Fig. la, c u r v e 2, a n d Fig. lb, c u r v e 4). A t t h e s a m e t i m e t h e p o l y m e r i z a t i o n of P E M A is c h a r a c t e r i z e d b y a shorter i n d u c t i o n p e r i o d a n d a higher degree of conversion. I n t h e case of P E M A w h e n B P is used as i n i t i a t o r t h e t e m p e r a t u r e d e p e n d e n c e of t h e r a t e of p o l y m e r i z a t i o n differs f r o m t h a t o b s e r v e d w i t h D A A as initiator. O v e r t h e t e m p e r a t u r e r a n g e 31.5 to 69"5 ° t h e p o l y m e r i z a t i o n is g r e a t e s t a t 41"5°; w i t h a rise in t e m p e r a t u r e t h e m a x i m u m r a t e is reduced, a n d this is p a r t i c u l a r l y m a r k e d at t e m p e r a t u r e s a b o v e 55 ° . T h e t h e r m a l effect of p o l y m e r i z a t i o n was d e t e r m i n e d b y i n t e g r a t i o n b y weighing of curves of h e a t e v o l u t i o n versus t i m e [3]. Since t h e r e a c t i o n was n o t c o n t i n u e d up to 1 0 0 ~ c o n v e r s i o n t h e h e a t effect to be d e t e r m i n e d was r e l a t e d to t h e a m o u n t of p o l y m e r formed.
Y~.. M. NIOROZOVAet a/.
2738
The degree of conversion was found b y means of the residual monomer using the polaxographic method [4]. The thermal effect for 100% conversion was calculated from the equation: Q - ~ Q~. - - 100 K where Q is the thermal effect of polymerization; K is the degree of conversion, %; Q~ is the heat evolution per mole of monomer for a particular degree of conversion. I t m a y be seen from Fig. 2 t h a t the thermal effect in the polymerization of PEMA increases from 13.5 to 20 keal/mole with a rise in temperature from 30 to 70 °.
(~,kcal/mole 20
o/40
10
I 40
I 50
r 60
7-;,oc
r 70
Fie. 2. Change in thermal effect with rise in the polymerization temperature of P E n DAA and B P as initiators: 1--DA.A; 2 - - B P .
with
The thermal effect for the polymerization of OMA at 66-78 ° varies within limits of 13.2 to 13.5 kcal/mole, which is in agreement with data published in [5, 6]. C 2
1
dK ._c-t
40 ~
a
-•T
40
2O
20
:~-, $8C-1
/ /
10 20 40 60 80 100 K,%
3 20 40 60
80
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20 40 60 80 1£,0 K,%
FIG. 3. Polymerization rate vs. degree of conversion of monomer to polymer: a - - P E M A - k DAA: •--73.5, 2--64, 3--55.5°; b--OMA-FDAA: 1--31.5, 2--41.5, 3--55°; c--PEM_A-pPB; 1--31.5, 2--41-5, 3--55; 4--69.5 °. Figure 3 shows the dependence of the polymerization rate on the degree of conversion of monomer. According to these data, the highest rate of polymerization for both monomers with DAA as initiator is obtained at a definite degree of conversion, irrespective of tom-
Polymerization of some acrylic monomers in thin layers
2739
perature. I n the case of PEMA this conversion is around 24%, while for OM_Ait is about
17~ . In the polymerization of PEMA with BP the maximum rate in relation to temperature corresponds to different degrees of conversion corresponding to the highest conversion at lower temperatures. The overall activation energy for the polymerization of the monomers in question with different initiators was calculated by the graphic method (Fig. 4); for instance, the activation energy at 10 ~o conversion for PEMA+DAA is 23.4, and for PEMA+BP it is 8-35 kcal/mole; for OMA with DAA as initiator the activation energy was 26.1 kcal/mole. dK ln-d'c 3"6
2"8
\
2.0 t
0.0029
i
I
00031
00033 1/T
FIG. 4. In dK/dv vs. 1/T: 1--OMA+DAA; 2--PEMA+DAA; 3--PEMA+BP. DISCUSSION OF RESULTS
In a s t u d y of the polymerization of high-boiling alkyl methacrylates and amino-substituted alkyl methaerylates in thin layers in the presence of atmospheric oxygen it was shown t h a t under suitable conditions the process m a y be carried out to a high conversion with practically no loss of monomers. A comparative s t u d y of the polymerization of both monomers, i, e. OMA and PEMA, in the presence of a peroxide initiator (BP) and an azo-eompound (DAA) revealed the specific nature of the polymerization of amino-substituted alkyl methacrylates under these conditions. The activation energy for the polymerization of both monomers with DAA as initiator determined by the authors under conditions allowing free access to oxygen is higher t h a n the activation energy determined by other authors for similar monomers in the absence of atmospheric oxygen. For instance, in [7] the authors give the activation energy for the polymerization of N-diethylaminoethyl methaerylate, N-dimethylaminoethyl methaerylate and methyl methacrylate as being respectively 19.4, 19.7 and 19.5 keal/mole, while in our experiments for the polymerization of PEMA and OMA we obtained activation energies of 23.4 and 26.1 keM/mole respectively. On comparing the polymerization of both monomers under the conditions adopted by the present authors it is apparent t h a t in the presence of DAA PEMA polymerizes at a higher rate and with slightly lower activation energy t h a n OMA.
2740
YE. M. Mo~ozovA et
al.
The rise observed in the total activation energy for both monomers m a y be attributed to increase in the activation energy of initiation with the inhibiting action of atmospheric oxygen, and the slightly lower activation energy for PEMA compared with OMA m a y be attributed to the formation of an initiating redoxsystem. This system m a y result from the interaction of an amine with an ester bond [8] or with a peroxide radical formed under the conditions adopted, according to data in [9]. These assumptions are further supported by the difference in the change in the polymerization rate relative to the degree of conversion for PEMA and OMA. Benzoyl peroxide used to initiate the polymerization of PEMA results in a high reaction rate, lower activation energy and a shorter induction period. In the case under consideration the reduced initiating efficiency found with a rise in temperature above 55 ° is characteristic, and m a y possibly be due to the rapid depletion of the peroxide in the system. The special efficiency of the peroxide initiator in the polymerization of the amino-substituted alkyl methacrylate is apparently due to the formation of an initiating redox-system between the amino-containing monomer and the peroxide. The formation of initiating systems from peroxides and nonmonomeric amines was studied in [10-12], and the interaction of BP with amino-substituted methacrylates is referred to in [7], where the authors apparently found no initiating effect. Acording to [10-12] when a B P - t e r t i a r y amine system is used to initiate polymerization there is a redox reaction between the two components accompanied by the formation of radicals capable of initiating the polymerization. The thermal effect of polymerization for OMA determined over the range 6678 °, or 31-45 ° in the case of PEMA varies within limits of 13.5 kcal/mole, which corresponds to the energy of the double bond of methacrylic esters. With a rise in temperature to 70 ° the thermal effect of PEMA polymerization with both initiators is increased to 20 kcal/mole. This m a y be due to the additional evolution of heat resulting from oxidation of the amino-containing monomer; the process under consideration in the presence of atmospheric oxygen takes place more rapidly at elevated temperatures than at low ones. The authors wish to thank M. F. Margaritovaya and V. E. Lazaryanets for their interest in the experiments and for useful advice given during discussion of the results obtained in the investigation. CONCLUSIONS
(1) The kinetics of the polymerization of fl-(N-piperidyl)ethyl methacrylate and n-octyl methacrylate have been investigated with benzoyl peroxide and the dinitrile of azoisobutyric acid as initiators, the process being conducted in thin layers in the presence of atmospheric oxygen. I t has been shown t h a t these monomers m a y be polymerized with inappreciable losses up to high conversions under mild polymerization conditions.
Polymerization of some acrylic monomers in thin layers
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(2) T h e t h e r m a l effect o f t h e p o l y m e r i z a t i o n of n - o c t y l m e t h a c r y l a t e a n d fl-(N-piperidyl)ethyl m e t h a e r y l a t e a t low t e m p e r a t u r e s is ~ 1 3 . 5 k c a l / m o l e w h i c h agrees w i t h p u b l i s h e d d a t a for m e t h a c r y l i c esters. H o w e v e r , in t h e case of fl-(N-piperidyl)ethyl m e t h a e r y l a t e a rise in t e m p e r a t u r e is a c c o m p a n i e d b y a greater t h e r m a l effect, w h i c h is due to o x i d a t i v e processes t a k i n g place a t t h e s a m e time. (3) T h e overall a c t i v a t i o n e n e r g y o f p o l y m e r i z a t i o n for t h e m o n o m e r s in question w i t h t h e dinitrile o f a z o i s o b u t y r i c acid as initiator is slightly higher t h a n t h e a c t i v a t i o n e n e r g y d e t e r m i n e d b y o t h e r a u t h o r s u n d e r oxygen-fi'ee conditions, which is a p p a r e n t l y due to a rise in t h e e n e r g y of initiation caused b y the inhibiting a c t i o n o f oxygen. (4) fl-(N-piperidyl)ethyl m e t h a c r y l a t e p o l y m e r i z e s in t h e presence of b e n z o y l p e r o x i d e w i t h a lower a c t i v a t i o n energy: this is a t t r i b u t e d to the f o r m a t i o n of a n initiating r e d o x - s y s t e m b e t w e e n b e n z o y l p e r o x i d e a n d t h e a m i n o - c o n t a i n i n g monoIner. Translated by R. J. A. HENDRY REFERENCES
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