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Polymerization of α,α-dimethyl-β-propiolactone
POLYMERIZATION
OF a , a - D I M E T H Y L - p - P R O P I O L A C T O N E *
YU. N . S~.z)~I~ov, N. A. GLUKHOV a n d l~I. i~I. KOTON High Molecular Weight Compounds Institute, U.S.S.R. Academy of Sciences
(Received 27 November 1967)
I~ EARLIER investigations [1,2] we studied the polymerization of fl,fl-dimethylfl-propiolactone in the presence of basic and acid catalysts under various conditions. The experimental results showed that this monomer has weak polymerizing activity and yields a relatively low molecular weight polymer. As already noted in [3], comparative testing of the polymerization of g,~-bis-chloromethyl- and fl,fl-bis-chloromethyl-fl-propiolactones under identical conditions showed that the g-substituted lactone polymerizes much more readily and forms polymers with much better mechanical properties than the/if-substituted lactone. In view of this it was desired to consider the effect of change in the position of methyl substituents in the fl-lactone ring on the polymerizability and properties of the resulting product. A further aim in this investigation was to study some of the mechanisms of the polymerization of g,~-dimethyl-fl-propiolaetone (DPL). 0nly two reports have appeared regarding the polymerization of DPL [4, 5] and in these it is shown that this lactone polymerizes in the presence of certain acid catalysts to form a low molecular weight product; when alkaline catalysts are used polymers of higher molecular weight are obtained. In these experiments the basic and acid catalysts were triethylamine and hexafluorophenyldiazoniumphosphate respectively. EXPERIMENTAL
Synthesis of DPL. I ) P L m a y be obtained [4] b y alkaline hydrolysis of monochloropivolic acid, but with this method the p H of the medium must be exactly maintained during the reaction, and on separating the lactone there are big losses owing to hydrolysis of the product so that the yield of I ) P L does not exceed 15-23%. We assumed that I ) P L could be synthesized usig the lead salt of monochloropivolic acid b y the following reaction scheme: CH3 J S0~CI~ CHs--C--C00H --.------~ ]
CH, [ Pb(CiH60a)I CH3--C---C00H [
CH8
!
or Pb0
CH2C1
!
I
I
HIC---O * Vysokomol. soyed. A10: No. 10, 2359-2365, 1968. 2742
Polymerization of a,a-dimethyl-fl-propiolactone
2743
The t o t a l yield of lactone was increased to 95-98%. The obtained D P L was twice vacuumdistilled to constant up: the p u r i t y of the product was also varified chromatographically. The structure of the product lactone was confirmed b y olomontaxy analysis, a n d b y t h e results of molecular weight a n d infrared analysis. After purification the yield was 92-95% of theory, n ~ 1.4105, b.p. 46.5/°/8 m m (published d a t a [5] n~ 1.4086, 46°/9 ram). DPL was polymerized in ampoules in the presence of triothylamino and hexafluorophenyldiazoniumphosphate (PAP) in bulk, over t h e range 20 to 100 °. The procedure for purifying the catalysts and for the actual process of polymerization wore the same as those a d o p t e d in [1,2]. A t the end of the polymerization the ampoules were opened and the reactio~ products were t r e a t e d with petroleum ether; the eomminuted polymer was dried a~d then reprecipitated b y petroleum ether from a mixture of tetrachloroothane and phenol (1:1 b y volume), and was vacuum-dried after repeated washing with petroleum ether. To determine the mechanism of the polymerization of P D L kinetic measurements were carried out using the gravimetric method, the polymerization being conducted in a series of amp0ules under identical conditions for different periods of time; also b y means of dilatometry, with a mercury dilatometer and using the procedure described in [6]. The stage of initiation was studied b y means of a model reaction of D P L with triethylaxnine: to a solution of 0.01 mole of I ) P L in 10 ml of absolute ether were a d d e d dropwiso a solution of 0.01 mole of D P L in 10 ml of absolute ether for 10 min at 20 °. After the reaction h a d ended the mixture was left overnight, and the finely dispersed precipitate which separated was filtered and vacuum-dried. Yield 25%; it was difficult to determine the molt point owing to the hygroscopic nature of the product. The results of elementary analysis of the dried precipitate suggest t h a t the resulting substance is triethyl-a, a'-dimethylpropiobotaine of general formula (C2Hs)s+.NCH,(CHa)2COO, CI1H23NO2. Found, ~ C 65.70; H 11.51; N 7.02; O 15.77, Calculated, ~ C 65.81; H 11.46; N 6.88; O 15.85. The I R spectra show bands characteristic of COO groups in the region of 1740 cm -~ and of pentavalent nitrogen in the region 2400-2700 em -~. However on reerystallization of the obtained compound from absolute alcohol a product is separated (yield 79.5°/o) with m.p. 186.5°; elementary analysis of ~his product and the I R spectra show almost complete absence of nitrogen, indicating t h a t a p p a r e n t l y no betaine is formed in the reaction of D P L with (C2Hs)aN, b u t only an unstable product which changes into a polyether. Similar experiments were carried out at 40, 60 a n d 80 ° to determine how the lactone in question reacted with triethylamine; it was found t h a t with a rise in the reaction t e m p e r a t u r e the yield polyester increased to 42.3; 68.7 and 95.4O/o repectively. DISCUSSION OF RESULTS
Polymerization of P D P in the presence of triethylamine. T o d e t e r m i n e t h e m e c h a n isms of the polymerization of DPL a number of experiments was carried out w i t h a c o n s t a n t m o n o m e r c o n c e n t r a t i o n (m0----10 m o l e / l . ) v a r y i n g s e p a r a t e l y t h e i n i t i a l c o n c e n t r a t i o n o f c a t a l y s t (no) a n d t h e p o l y m e r i z a t i o n t e m p e r a t u r e . T h e r e s u l t s o f t h e s e e x p e r i m e n t s a r e p r e s e n t e d in t h e f o r m o f k i n e t i c c u r v e s c a l c u l a t e d i n t h e c o o r d i n a t e s d e g r e e o f p o l y m e r i z a t i o n x - - c o n v e n t i o n a l t i m e (p, u s i n g t h e k n o w n m e t h o d [7] ( F i g . l a , b a n d c). T h e c u r v e s i n q u e s t i o n s h o w 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 d e p e n d s b o t h o n n o a n d also o n t h e r e a c t i o n t e m p e r a ture; moreover, a rise in both these factors increases the rate of polymer formation. The shape of the kinetic curves also changes with a rise in the polymerization
2744
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l~Io. 1. :Polymerization of D P L in the presence of (C2Hs)sN. I)ogreo of polymerization (~) vs. conventional time (@) (for m 0 = 10 and the following values of no (mole/L). 1--0.2~ 2--0.1, 8--0.026, 4--0.009; 5--0.005; 6--0.001; a - - a t 20 °, b - - a t 60 °, c ~ a t n0=0"0009 and temperatures: 1--80°; 2--60°; 3--40°; 4 - - 2 0 ° .
Polymerization of a,a-dimethyl-fl-propiolactone
2745
temperature. For instance at 20 ° (Fig. la) there is a rectilinear rise in x with ~0 over a wide range of n o for all values of x, which is usually characteristic of a stepwise mechanism of polymerization in which the constants of initiation (kl) and propagation (k2) are equal. However, with a rise in the reaction temperature the reaction proved to be stationary only during the second period of polymerization, and moreover this section was reduced with increase in n o (Fig. lb, inflexions), and also with reduction in temperature.
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Polymerization temperature 60°, determined for x=0.3.
The results obtained by experiment cannot be explained from the standpoint of a "stepwise" continuous process for the following reasons: dx (1) where /Q_~k2, ~ = F ( n 0 ) should be a linear function of n o over the whole range of n o values, whereas the experimental curve appears to show saturation (Fig. 2); 2) the experimentally observed differences in the rate of polymerization where n0=const and m 0 = c o n s t indicates t h a t the process is accelerated towards the end of the polymerization; this acceleration depends both on the initial concentration of catalyst n o (Fig. lb) and on the temperature of polymerization (Fig. lc); 3) the apparent value of the propagation constant k [8] determined for sections of the kinetic curve x=F(~0) before and after the inflexion changes from 265 to 7.8 1..mole -1 hr -1 for the first section, and from 466 to 10 1..mole-l.hr -1 for the second section, with n o changing from 1 × 10 -4 to 2 × 10 -~' mole/1.; 4) the experimental molecular weights of the resulting polymers depend in a complex w a y on the catalyst concentration no, the degree of polymerization x, and on the polymerization temperature. At 20 ° the experimental molecular weights are a lot higher t h a n the calculated values even for low values of n o
Yu. N. S~zAwovet ed.
2746
(Fig. 3a); with a rise in the polymerization temperature with low values of no the molecular weights are equal (Fig. 3b) at certain degrees of conversion, while in a number of cases the experimental molecular weights obtained with a rise in
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All the results given here show that the mechanism of DPL polymerization is Inore complex than the normal stepwise process: it is probably of a type similar to the "coordination" mechanism [9] which includes two interchanging processes in the course of polymerization. With a rise in the temperature of polymerization this transition begins earlier, probably on account of the thermodynamic stability or instability of the polymer chain which is growing in accordance with the first process. This temperature dependence was also observed during the model reaction of equimolecular amounts Of monomer and triethylamine, where it was shown t h a t during a single period of time the amount of the resulting adduct, and then of the polyester also, increases with a rise in the reaction temperature. Assuming as in ~[1] that it is not triethylamine itself that initiates the polymerization but the product of its interaction with the lactone, it then becomes understandable, in the light of the model reaction described above, why the molecular weight of the polymer is reduced with a rise in the polymerization temperature, since this rise in temperature increases the amount of the resulting adduct and hence the number of active centres on which the polymerization m a y proceed. In order to study process connected with the change in molecular weight at high degrees of conversion, and to consider the complete mechanism of polymerization in all its complexity, a further series of experiments will have to be carried Gut on a future occasion. All the polymers synthesized in the presence of triethyl-
Polymerization of a,a.dimethyl-fl-propiolactone
2747
amine are solid crystalline products (except the oligomers with MW below 1000) soluble only in hot phenol or in a mixture of tetrachloroethane and phenol (1 : 1 b y vol.); moreover the solubility decreases gradually with increase in the molecular weight of the products. The highest molecular weight with a degree of polymerization of ~ 1 ( ~ 80,000) was found with the polymer obtained at 20 ° and with n o mol.w~. ~fO"a 50
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FIG. 4. Change in molecular weight of DPL polymer with degree of polymerization when no -----0.005 molefl, mo~ 10 (mole/L); catalyst (C~H6)sN at temperatures: 1--20, 2--40, 3--60, 4--80 °. Solid line calculated for a "stepwise" mechanism. ~--0.009 mole/1. In view of these findings one would expect to obtain a polymer with still higher molecular weight b y reducing no, b u t in this case the polymerization is greatly retarded, and the time required to produce a polymer with high yield and with MW above 100,000-200,000 will be very long. The results of I R analysis and end group determination (mainly for the oligomers) showed that the synthesized polymer has a complex polyether structure. Thermographic measurements showed that the D P L polymer melts at 240260 ° (or MW>20,000). Thermal degradation with marked loss of weight begins at 310-325 °, and is accompanied b y a strong endothermic effect; the maximum rate of degradation was observed at 400 ° with a heating rate of 12°/min. On calculating the order of the degradation reaction over the range of 10-92% loss
Y~. N. SAZAWOVeta/.
2748
in weight (n----1.02) we m a y conclude that the decomposition takes place as a single-stage process with an activation energy of 32.7 kcal/mole. Polymerization in the presence of P A P . Whereas in the presence of the basic catalyst (triethylamine) the polymerization of DPL proceeds fairly readily and yields polymers of high molecular weight, we find that the nature of the process changes when an acid catalyst is used. Figure 5 shows that the polymerization of the lactone in the presence of P A P takes place more slowly than with (C2Hs)3N; the degree of conversion does not exceed 45.5%, and at relatively high values of no the S-shaped nature of the kinetic curves shows t h a t there is a long induction X
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FIG. 5. Degree of polymerization x vs. time (v) in the polymerization of DPL in the presence of PAP at 100° and with no (mole/1.): 1--0.075; 2--0.008 and 3--0.001. period in the first stage of the reaction, and that during the final stage reactions inhibiting the polymerization take place. I t is noteworthy that on reaching a certain limit (3000-4000) the molecular weights remain constant despite increase in the time of polymerization, and do not change over a wide range of changes in no (1-75 × 10 -3 mole/1.). All these findings and experimental data show t h a t the effect of changing to acid catalysts is detrimental both in regard to the polymerization process itself, and also with respect to the properties of the resulting polymers. This is also apparent from the thermal characteristics of the polymer obtained in the presence of P A P (m.p. 170-185 °, degradation temperature 200°). I t has already beenpointed out [3, 9, 10] that a similar difference in the effect of acid and basic catalysts was found in the polymerization of ~,~-bis-chloromethyl-#-propiolactone, and this is apparently connected with the position of the substituent in the fl-lactone ring. On comparing the results of our experiments with those obtained in [1, 2, 111 it m a y be seen that the introduction of the substituents in question into the ~-position in the fl-lactone ring increases the polymerizing activity of the latter in the ease of basic catalysts, and reduces it when acid catalysts are used, while at the same time the introduction of the same substituents into the #-position has the reverse effect. This tendency m a y be complicated by the nature of substitu-
Polymerization of a,a.dimethyl-fl-propiolaetene
2749
ents and the properties of the catalysts, b u t it now appears possible by appropriate calculations to predict t he possible effect of introducing different substituents into the ~- or fl-position of the fl-propiolactone ring, with some degree of approximation. CONCLUSIONS (1) a,~-Dimethyl-fl-propiolactone (DPL) has been produced with ~ 9 0 % yield by the pyrolysis of the lead salt of a-chloropivolic acid under a high vacuum. (2) A D P L polymer has been synthesized in the presence of (C2H5)3N with molecular weight up to 80,000, possessing thermal stability up to 300 °. (3) A D P L polymer has been synthesized in the presence of hexafluorophenyldiazoniumphosphate. (4) I t has been found by kinetic studies of the polymerization of D P L in the presence o f (C2Hs)zN t h a t this process cannot be described from the standpoint of a "stepwise" mechanism of polymerization. (5) The difference in the polymerization of substituted lactones has been elucidated in relation to the position of the substituents and the nature of the catalyst. TransloJexl by R. J. A. I-LE~rD~y
REFERENCES
1. Yu. N. SAZANOV, N. A. GLUKHOV and M. M. KOTON, Vysokomol. soyed. B I 0 : 8 1968 (Not translated in Polymer Sci. U.S.S.R.) 2. Yu. N. SAZANOV, N. A. GLUKHOV and M. M. KOTON, Vysokomol. soyed. B10: 501, 1968 (Not translated in Polymer Sei. U.S.S.R.) 3. Yu. N. SAZANOV, M. M. KOTON, N. A. GLI.1]KHOVand T. D. D'YACHENKO, Report at XV Conf. on High Melee. Weight Compounds, Moscow, 1965 4. R. THIEBOUT, N. FISCHER, Y. ETIANNE and J. COSTE, Industr. Plast. Modern 2: 1, 1962 5. Y. YAMASHITA, Y. ISCHIKAWA and T. TSUDA, J. Chem. Soc. Japan, Industr. Chem. Sect. 67: 252, 1964 6. V. V. KORSHAK, Osnovy khimii vysokomolekulyarnykh soyedinenii (Principles of the Chemistry of High Molecular Weight Compounds). p. 347, Izd. AN SSSR, 1953 7. A. A. KOROTKOV and A. F. PODOL'SKH~ Vysokomol. soyed. 8: 332, 1966 (Translated in Polymer Sci. U.S.S.R. 8: 2, 363, 1966) 8. A. A. KOROTKOV and A. F. PODOLSKII, J. Polymer Sci. B3: 901, 1965 9. A. A. KOROTKOV and A. F. PODOLSKII, Vysokomol. soyed. 8: 1952, 1966 (Translated in Polymer Sei. U.S.S.R. 8: 11, 2157, 1966) 10. T. D. D'YACHENKO, N. A. GLUKHOV, M. M. KOTON and Yu. N. SAZANOV, Geterotsepnye vysokomolekularnye soyedineniya (Heterochain High Molecular Weight Compounds). p. 236, Izd. "l~auka", 1964 11. Yu. N. SAZANOV, N. A. GLUKHOV and M. M. KOTON, Vysokomol. soyed. A10: 1122, 1968 (Translated in Polymer Sci. U.S.S.R. 10: 5, 1968)
OF a , a - D I M E T H Y L - p - P R O P I O L A C T O N E *
YU. N . S~.z)~I~ov, N. A. GLUKHOV a n d l~I. i~I. KOTON High Molecular Weight Compounds Institute, U.S.S.R. Academy of Sciences
(Received 27 November 1967)
I~ EARLIER investigations [1,2] we studied the polymerization of fl,fl-dimethylfl-propiolactone in the presence of basic and acid catalysts under various conditions. The experimental results showed that this monomer has weak polymerizing activity and yields a relatively low molecular weight polymer. As already noted in [3], comparative testing of the polymerization of g,~-bis-chloromethyl- and fl,fl-bis-chloromethyl-fl-propiolactones under identical conditions showed that the g-substituted lactone polymerizes much more readily and forms polymers with much better mechanical properties than the/if-substituted lactone. In view of this it was desired to consider the effect of change in the position of methyl substituents in the fl-lactone ring on the polymerizability and properties of the resulting product. A further aim in this investigation was to study some of the mechanisms of the polymerization of g,~-dimethyl-fl-propiolaetone (DPL). 0nly two reports have appeared regarding the polymerization of DPL [4, 5] and in these it is shown that this lactone polymerizes in the presence of certain acid catalysts to form a low molecular weight product; when alkaline catalysts are used polymers of higher molecular weight are obtained. In these experiments the basic and acid catalysts were triethylamine and hexafluorophenyldiazoniumphosphate respectively. EXPERIMENTAL
Synthesis of DPL. I ) P L m a y be obtained [4] b y alkaline hydrolysis of monochloropivolic acid, but with this method the p H of the medium must be exactly maintained during the reaction, and on separating the lactone there are big losses owing to hydrolysis of the product so that the yield of I ) P L does not exceed 15-23%. We assumed that I ) P L could be synthesized usig the lead salt of monochloropivolic acid b y the following reaction scheme: CH3 J S0~CI~ CHs--C--C00H --.------~ ]
CH, [ Pb(CiH60a)I CH3--C---C00H [
CH8
!
or Pb0
CH2C1
!
I
I
HIC---O * Vysokomol. soyed. A10: No. 10, 2359-2365, 1968. 2742
Polymerization of a,a-dimethyl-fl-propiolactone
2743
The t o t a l yield of lactone was increased to 95-98%. The obtained D P L was twice vacuumdistilled to constant up: the p u r i t y of the product was also varified chromatographically. The structure of the product lactone was confirmed b y olomontaxy analysis, a n d b y t h e results of molecular weight a n d infrared analysis. After purification the yield was 92-95% of theory, n ~ 1.4105, b.p. 46.5/°/8 m m (published d a t a [5] n~ 1.4086, 46°/9 ram). DPL was polymerized in ampoules in the presence of triothylamino and hexafluorophenyldiazoniumphosphate (PAP) in bulk, over t h e range 20 to 100 °. The procedure for purifying the catalysts and for the actual process of polymerization wore the same as those a d o p t e d in [1,2]. A t the end of the polymerization the ampoules were opened and the reactio~ products were t r e a t e d with petroleum ether; the eomminuted polymer was dried a~d then reprecipitated b y petroleum ether from a mixture of tetrachloroothane and phenol (1:1 b y volume), and was vacuum-dried after repeated washing with petroleum ether. To determine the mechanism of the polymerization of P D L kinetic measurements were carried out using the gravimetric method, the polymerization being conducted in a series of amp0ules under identical conditions for different periods of time; also b y means of dilatometry, with a mercury dilatometer and using the procedure described in [6]. The stage of initiation was studied b y means of a model reaction of D P L with triethylaxnine: to a solution of 0.01 mole of I ) P L in 10 ml of absolute ether were a d d e d dropwiso a solution of 0.01 mole of D P L in 10 ml of absolute ether for 10 min at 20 °. After the reaction h a d ended the mixture was left overnight, and the finely dispersed precipitate which separated was filtered and vacuum-dried. Yield 25%; it was difficult to determine the molt point owing to the hygroscopic nature of the product. The results of elementary analysis of the dried precipitate suggest t h a t the resulting substance is triethyl-a, a'-dimethylpropiobotaine of general formula (C2Hs)s+.NCH,(CHa)2COO, CI1H23NO2. Found, ~ C 65.70; H 11.51; N 7.02; O 15.77, Calculated, ~ C 65.81; H 11.46; N 6.88; O 15.85. The I R spectra show bands characteristic of COO groups in the region of 1740 cm -~ and of pentavalent nitrogen in the region 2400-2700 em -~. However on reerystallization of the obtained compound from absolute alcohol a product is separated (yield 79.5°/o) with m.p. 186.5°; elementary analysis of ~his product and the I R spectra show almost complete absence of nitrogen, indicating t h a t a p p a r e n t l y no betaine is formed in the reaction of D P L with (C2Hs)aN, b u t only an unstable product which changes into a polyether. Similar experiments were carried out at 40, 60 a n d 80 ° to determine how the lactone in question reacted with triethylamine; it was found t h a t with a rise in the reaction t e m p e r a t u r e the yield polyester increased to 42.3; 68.7 and 95.4O/o repectively. DISCUSSION OF RESULTS
Polymerization of P D P in the presence of triethylamine. T o d e t e r m i n e t h e m e c h a n isms of the polymerization of DPL a number of experiments was carried out w i t h a c o n s t a n t m o n o m e r c o n c e n t r a t i o n (m0----10 m o l e / l . ) v a r y i n g s e p a r a t e l y t h e i n i t i a l c o n c e n t r a t i o n o f c a t a l y s t (no) a n d t h e p o l y m e r i z a t i o n t e m p e r a t u r e . T h e r e s u l t s o f t h e s e e x p e r i m e n t s a r e p r e s e n t e d in t h e f o r m o f k i n e t i c c u r v e s c a l c u l a t e d i n t h e c o o r d i n a t e s d e g r e e o f p o l y m e r i z a t i o n x - - c o n v e n t i o n a l t i m e (p, u s i n g t h e k n o w n m e t h o d [7] ( F i g . l a , b a n d c). T h e c u r v e s i n q u e s t i o n s h o w 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 d e p e n d s b o t h o n n o a n d also o n t h e r e a c t i o n t e m p e r a ture; moreover, a rise in both these factors increases the rate of polymer formation. The shape of the kinetic curves also changes with a rise in the polymerization
2744
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I// / / / i i 111 / // ~1
~ I
I~ ~
1 11
T
t.1..-. ! ~ !11~ --~
50
100
fo , mole.1-1, hr,
150
l~Io. 1. :Polymerization of D P L in the presence of (C2Hs)sN. I)ogreo of polymerization (~) vs. conventional time (@) (for m 0 = 10 and the following values of no (mole/L). 1--0.2~ 2--0.1, 8--0.026, 4--0.009; 5--0.005; 6--0.001; a - - a t 20 °, b - - a t 60 °, c ~ a t n0=0"0009 and temperatures: 1--80°; 2--60°; 3--40°; 4 - - 2 0 ° .
Polymerization of a,a-dimethyl-fl-propiolactone
2745
temperature. For instance at 20 ° (Fig. la) there is a rectilinear rise in x with ~0 over a wide range of n o for all values of x, which is usually characteristic of a stepwise mechanism of polymerization in which the constants of initiation (kl) and propagation (k2) are equal. However, with a rise in the reaction temperature the reaction proved to be stationary only during the second period of polymerization, and moreover this section was reduced with increase in n o (Fig. lb, inflexions), and also with reduction in temperature.
dx/dv,%.hp-1
10/ 5
_--i
I
0.005
0"01
FIG. 2. Relative rate of polymerization
i
I
0.015 0"02 no, mole/L
-~ of DPL vs. n o in the presence of (C2Hs)sN.
Polymerization temperature 60°, determined for x=0.3.
The results obtained by experiment cannot be explained from the standpoint of a "stepwise" continuous process for the following reasons: dx (1) where /Q_~k2, ~ = F ( n 0 ) should be a linear function of n o over the whole range of n o values, whereas the experimental curve appears to show saturation (Fig. 2); 2) the experimentally observed differences in the rate of polymerization where n0=const and m 0 = c o n s t indicates t h a t the process is accelerated towards the end of the polymerization; this acceleration depends both on the initial concentration of catalyst n o (Fig. lb) and on the temperature of polymerization (Fig. lc); 3) the apparent value of the propagation constant k [8] determined for sections of the kinetic curve x=F(~0) before and after the inflexion changes from 265 to 7.8 1..mole -1 hr -1 for the first section, and from 466 to 10 1..mole-l.hr -1 for the second section, with n o changing from 1 × 10 -4 to 2 × 10 -~' mole/1.; 4) the experimental molecular weights of the resulting polymers depend in a complex w a y on the catalyst concentration no, the degree of polymerization x, and on the polymerization temperature. At 20 ° the experimental molecular weights are a lot higher t h a n the calculated values even for low values of n o
Yu. N. S~zAwovet ed.
2746
(Fig. 3a); with a rise in the polymerization temperature with low values of no the molecular weights are equal (Fig. 3b) at certain degrees of conversion, while in a number of cases the experimental molecular weights obtained with a rise in
Pe/Zc 3
+'.~
x
+~z+--+2_ i
I
I
]
0"25
0"5
0"75
1"0 X
0
- L ~ L 5 -°4 I
I
[
025
0"5
075
I
1"0 X
FIG. 3. Ratio of experimental (Pc) and calculated (Pc) coefficients of polymerization vs. x (for values of no see Fig. 1): a - - a t 20, b - - a t 60 °. the temperature of polymerization at the end of the process are even lower than t h e calculated values (Fig. 4).
All the results given here show that the mechanism of DPL polymerization is Inore complex than the normal stepwise process: it is probably of a type similar to the "coordination" mechanism [9] which includes two interchanging processes in the course of polymerization. With a rise in the temperature of polymerization this transition begins earlier, probably on account of the thermodynamic stability or instability of the polymer chain which is growing in accordance with the first process. This temperature dependence was also observed during the model reaction of equimolecular amounts Of monomer and triethylamine, where it was shown t h a t during a single period of time the amount of the resulting adduct, and then of the polyester also, increases with a rise in the reaction temperature. Assuming as in ~[1] that it is not triethylamine itself that initiates the polymerization but the product of its interaction with the lactone, it then becomes understandable, in the light of the model reaction described above, why the molecular weight of the polymer is reduced with a rise in the polymerization temperature, since this rise in temperature increases the amount of the resulting adduct and hence the number of active centres on which the polymerization m a y proceed. In order to study process connected with the change in molecular weight at high degrees of conversion, and to consider the complete mechanism of polymerization in all its complexity, a further series of experiments will have to be carried Gut on a future occasion. All the polymers synthesized in the presence of triethyl-
Polymerization of a,a.dimethyl-fl-propiolactone
2747
amine are solid crystalline products (except the oligomers with MW below 1000) soluble only in hot phenol or in a mixture of tetrachloroethane and phenol (1 : 1 b y vol.); moreover the solubility decreases gradually with increase in the molecular weight of the products. The highest molecular weight with a degree of polymerization of ~ 1 ( ~ 80,000) was found with the polymer obtained at 20 ° and with n o mol.w~. ~fO"a 50
! ~0 / /o 30
/
/ A
f
f
i . . --e--
,/ / //
sg
//
,.-,,' /.e-/ ×
0.ZS
0'5
LT.TJ
f.~7 X
FIG. 4. Change in molecular weight of DPL polymer with degree of polymerization when no -----0.005 molefl, mo~ 10 (mole/L); catalyst (C~H6)sN at temperatures: 1--20, 2--40, 3--60, 4--80 °. Solid line calculated for a "stepwise" mechanism. ~--0.009 mole/1. In view of these findings one would expect to obtain a polymer with still higher molecular weight b y reducing no, b u t in this case the polymerization is greatly retarded, and the time required to produce a polymer with high yield and with MW above 100,000-200,000 will be very long. The results of I R analysis and end group determination (mainly for the oligomers) showed that the synthesized polymer has a complex polyether structure. Thermographic measurements showed that the D P L polymer melts at 240260 ° (or MW>20,000). Thermal degradation with marked loss of weight begins at 310-325 °, and is accompanied b y a strong endothermic effect; the maximum rate of degradation was observed at 400 ° with a heating rate of 12°/min. On calculating the order of the degradation reaction over the range of 10-92% loss
Y~. N. SAZAWOVeta/.
2748
in weight (n----1.02) we m a y conclude that the decomposition takes place as a single-stage process with an activation energy of 32.7 kcal/mole. Polymerization in the presence of P A P . Whereas in the presence of the basic catalyst (triethylamine) the polymerization of DPL proceeds fairly readily and yields polymers of high molecular weight, we find that the nature of the process changes when an acid catalyst is used. Figure 5 shows that the polymerization of the lactone in the presence of P A P takes place more slowly than with (C2Hs)3N; the degree of conversion does not exceed 45.5%, and at relatively high values of no the S-shaped nature of the kinetic curves shows t h a t there is a long induction X
I
E~
2
J.3
8 0.! o
I
2q
9#
7~
g~
/20
tqu
Time, hp
FIG. 5. Degree of polymerization x vs. time (v) in the polymerization of DPL in the presence of PAP at 100° and with no (mole/1.): 1--0.075; 2--0.008 and 3--0.001. period in the first stage of the reaction, and that during the final stage reactions inhibiting the polymerization take place. I t is noteworthy that on reaching a certain limit (3000-4000) the molecular weights remain constant despite increase in the time of polymerization, and do not change over a wide range of changes in no (1-75 × 10 -3 mole/1.). All these findings and experimental data show t h a t the effect of changing to acid catalysts is detrimental both in regard to the polymerization process itself, and also with respect to the properties of the resulting polymers. This is also apparent from the thermal characteristics of the polymer obtained in the presence of P A P (m.p. 170-185 °, degradation temperature 200°). I t has already beenpointed out [3, 9, 10] that a similar difference in the effect of acid and basic catalysts was found in the polymerization of ~,~-bis-chloromethyl-#-propiolactone, and this is apparently connected with the position of the substituent in the fl-lactone ring. On comparing the results of our experiments with those obtained in [1, 2, 111 it m a y be seen that the introduction of the substituents in question into the ~-position in the fl-lactone ring increases the polymerizing activity of the latter in the ease of basic catalysts, and reduces it when acid catalysts are used, while at the same time the introduction of the same substituents into the #-position has the reverse effect. This tendency m a y be complicated by the nature of substitu-
Polymerization of a,a.dimethyl-fl-propiolaetene
2749
ents and the properties of the catalysts, b u t it now appears possible by appropriate calculations to predict t he possible effect of introducing different substituents into the ~- or fl-position of the fl-propiolactone ring, with some degree of approximation. CONCLUSIONS (1) a,~-Dimethyl-fl-propiolactone (DPL) has been produced with ~ 9 0 % yield by the pyrolysis of the lead salt of a-chloropivolic acid under a high vacuum. (2) A D P L polymer has been synthesized in the presence of (C2H5)3N with molecular weight up to 80,000, possessing thermal stability up to 300 °. (3) A D P L polymer has been synthesized in the presence of hexafluorophenyldiazoniumphosphate. (4) I t has been found by kinetic studies of the polymerization of D P L in the presence o f (C2Hs)zN t h a t this process cannot be described from the standpoint of a "stepwise" mechanism of polymerization. (5) The difference in the polymerization of substituted lactones has been elucidated in relation to the position of the substituents and the nature of the catalyst. TransloJexl by R. J. A. I-LE~rD~y
REFERENCES
1. Yu. N. SAZANOV, N. A. GLUKHOV and M. M. KOTON, Vysokomol. soyed. B I 0 : 8 1968 (Not translated in Polymer Sci. U.S.S.R.) 2. Yu. N. SAZANOV, N. A. GLUKHOV and M. M. KOTON, Vysokomol. soyed. B10: 501, 1968 (Not translated in Polymer Sei. U.S.S.R.) 3. Yu. N. SAZANOV, M. M. KOTON, N. A. GLI.1]KHOVand T. D. D'YACHENKO, Report at XV Conf. on High Melee. Weight Compounds, Moscow, 1965 4. R. THIEBOUT, N. FISCHER, Y. ETIANNE and J. COSTE, Industr. Plast. Modern 2: 1, 1962 5. Y. YAMASHITA, Y. ISCHIKAWA and T. TSUDA, J. Chem. Soc. Japan, Industr. Chem. Sect. 67: 252, 1964 6. V. V. KORSHAK, Osnovy khimii vysokomolekulyarnykh soyedinenii (Principles of the Chemistry of High Molecular Weight Compounds). p. 347, Izd. AN SSSR, 1953 7. A. A. KOROTKOV and A. F. PODOL'SKH~ Vysokomol. soyed. 8: 332, 1966 (Translated in Polymer Sci. U.S.S.R. 8: 2, 363, 1966) 8. A. A. KOROTKOV and A. F. PODOLSKII, J. Polymer Sci. B3: 901, 1965 9. A. A. KOROTKOV and A. F. PODOLSKII, Vysokomol. soyed. 8: 1952, 1966 (Translated in Polymer Sei. U.S.S.R. 8: 11, 2157, 1966) 10. T. D. D'YACHENKO, N. A. GLUKHOV, M. M. KOTON and Yu. N. SAZANOV, Geterotsepnye vysokomolekularnye soyedineniya (Heterochain High Molecular Weight Compounds). p. 236, Izd. "l~auka", 1964 11. Yu. N. SAZANOV, N. A. GLUKHOV and M. M. KOTON, Vysokomol. soyed. A10: 1122, 1968 (Translated in Polymer Sci. U.S.S.R. 10: 5, 1968)