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Polymerization of butadiene under the action of sodium organic initiators in slightly polar media
~PolFmerScience U.S.S.R. Vol. 24, ~o. 2, PP. 388-393, 1982
Printed in Poland
0032-3950/82/020888-06507.50/0
0 1988 PergamonPre~ I,kl.
POLYMERIZATION OF BUTADIENE UNDER THE ACTION OF SODIUM ORGANIC INITIATORS IN SLIGHTLY POLAR MEDIA* R . V. BASOVA, B. I . NAKIE~IA_~OVICH, E . V. K R I S T A L ' ~ I
and A. A. A~EsT-YAxuBOVIC~ L. Ya. K a r p o v Physico-chemical Research I n s t i t u t e
(Received 8 August 1980) A s t u d y has been made of the polymerization of bute~liene under the action of sodium organic derivatives in hydrocarbon media in the presence of 4,4-dimethyl1,3-dioxane (DMDO). I n benzene, ethyl benzene a n d eyclolmxane polymerization occurs quantitatively and a high molecular weight polymer is obtained; in the presence of toluene the M W and (in some cases) the polymer yields are lower as a result of metallation of the solvent. Buta~liene polymerization in mixtures of D1KDO and hydrocarbons is accompanied b y chain termination, a p p a r e n t l y as a result of abstraotion of a labile acetal hydrogen from DM_DO.
BUTADIE~E polymerization under the action of metallic sodium in the absence of solvent was first carried out almost 50 years ago; this was the first process used on a commercial scale in the production of synthetic rubber. Despite this, no fully adequate study has yet been made of butadiene polymerization under the action of sodium compounds in slightly polar media, i.e. in hydrocarbon solvents and mixtures of the latter with small amounts of electron donors. It is pointed out in [1-5] that incomplete conversion of monomer and low molecular weights of the resulting polymers are typical features of butadiene polymerization processes in the presence of sodium initiators in hydrocarbon media, and these findings attributed to instability of polybutadienylsodium under these conditions. For instance, according to [3] the maximum yield of polymer is 30% for butadiene polymerization in the presence of a dispersion of sodium in hexane a t 30°; in the case of polymerization in the presence of "butyl-sodium" (a mixture of butyl-sodium and sodium chloride) in llexane the polymer yield at 5° is 80%, and at 50 °, 45%. Our aim in the present instance was to investigate the main features of butadiene polymerization under the action of sodium initiators in hydrocarbon media and to study the polymerization in the presence of 4,4-dimethyl-l,3dioxane (DMDO) recently proposed [6] as a solvent for the anionic polymerization of butadiene. * Vysokomol. soyed. A$4: ~ o . 2, 357-360, 1982. 388
Polymerization of butadiene
389
Polymerization in a hydrocarbo~ medium was initiated with the aid of a solid sodiumanthracene prepared in ~ with subsequent evacuation of solvent under vacuum (Na-I) or by direct synthesis from sodium and anthracene in ethylbenzene at 110° by the method of [7] (NA.II); soluble 1,1-diphenylhexylsodium (DHI~ was also used as an initiator. The latter was prepared by reaction of 1,1-diphenylethylene (at room temperature) to products o f the reaction of sodium with butyl bromide ( D I ~ . ] ) or butyl chloride (DHI~'.I1) carried out in benzene at 6-10 ° in a vessel equipped with a stirrer with slow feeding of the alkyl halide from the gas phase (over 1.5-2 hr). Hydrocarbon solvents and monomer were purified b y normal procedure for anionic polymerization [8]; in the final stage the reagents were treated with dry ethyl lithium. Commercial DMDO (which, according to [9], may contain the following impurities: methyl alcohol, isoprene tort. butanol, unsaturated amylene alcohols, methyltetrahydropyran) was distilled (b.p. 133 ° [9]), held for 1 day over sodium wire and then in a vacuum apparatus was successively recondensed into ampoules Containing a metallic sodium mirror and a small amount of anthracene (until the blue ¢olouring of sodium-anthracene appeared), a potassium-sodium alloy, and a sodium mirror containing a small amount of ~-mcthylstyrene or naphthalene. When the solvent is sufficiently pure, the red colouring of sodium a-methylstyrene (or the green of sodium-naphthalene) appears almost immediately after warming the ampoule. DMDO was then stored under vacuum. The results of chromatographic analysis (column length 1 m, diameter 4 m, packing, 20% polyphenyl-methylsiloxane on Celite, 88 °, carrier-gas (nitrogen) rate 60 ml/min, flame-ionization detector) showed that the total amount of residual impurities after this treatment was N ~ 2~o. I t was however noted that volatile substances gradually accumulate in DMDO under prolonged storage ~n vacuo, and accordingly it was further treated with sodium containing a small amount of g-methylstyrene or naphthalene immediately before experiments. Molecular weights of the polymers were determined by viscometry, usizlg the formulae [y]-~ 9.01 × 10-5 M °'al [10] (for polybutadiene) and [~]= 1.04 × 10 -~ M °'~3 [111 (for PS).
Polymerization in hydrocarbon media.
T a b l e 1 gives t h e results o f p o l y m e r i z a t i o n in t h e h y d r o c a r b o n m e d i a . I t w a s f o u n d . t h a t a benzene-soluble c o m p o u n d is o b t a i n a b l e b y a d d i t i o n o f 1,1-diphenylethylene to " b u t y l s o d i u m " ( t h o u g h a c c o r d i n g t o s p e c t r o p h o t o m e t r i c a n a l y s i s t h e s o l u b i l i t y ( 8 × 1 0 -4 mole/l.) is slight) a l t h o u g h t h e a n a l y s i s r e v e a l s t h a t chlorine is p r e s e n t in solution in t h e m o l a r r a t i o o f c h l o r i n e / a c t i v e sodium-----1 : 2 ( a p p a r e n t l y in t h e f o r m o f a c o m p l e x o f •aC1 w i t h Rl~a). A c c o r d i n g to t h e t a b u l a t e d d a t a p o l y m e r i z a t i o n in t h e presence of all t h e i n i t i a t o r s t a k e s p l a c e q u a n t i t a t i v e l y in benzene, e t h y l b e n z e n e a n d c y c l o h e x a n e , a n d h i g h p o l y m e r s are o b t a i n e d . T h u s p o l y b u t a d i e n y l s o d i u m a c t i v e centres in t h e s e solutions a p p e a r to be r e a s o n a b l y stable. T h e m o l e c u l a r w e i g h t is signif i c a n t l y lower in toluene, a n d in s o m e cases t h e r e is i n c o m p l e t e c o n v e r s i o n o f monomer. In butadiene polymerization under the action of sodium initiators s e c o n d a r y effects w e r e p r e v i o u s l y o b s e r v e d [12, 13] in t h e presence o f toluene. On e x a m i n i n g t h e results it is r e a d i l y seen t h a t t h e o b t a i n e d p o l y m e r s c o n t a i n s i g n i f i c a n t l y m o r e 1,2-units t h a n those p r e p a r e d u n d e r s i m i l a r conditions in t h e p r e s e n c e o f m e t a l l i c s o d i u m [14], w h e r e the c o n c e n t r a t i o n o f 1,2 u n i t s is 32-35~/o. Since a t l e a s t one o f t h e i n i t i a t o r s u s e d by us (NA-II) could n o t u n d e r t h e conditions a d o p t e d c o n t a i n a n y s o l v a t i n g i m p u r i t i e s of n o n - h y d r o c a r b o n
390
R . V . BAsovA e$ a/.
character, the larger number of 1,2-units is apparently attributable to the fact that in the presence of a metal mirror polymerization takes place at a significantly lower concentration of active centres compared with the case where organosodium initiators are used. This is supported b y the fact that in the case of polymerization in presence of the metal under conditions conducive to a higher concentration of growing chains (polymerization on a comminuted metal with vigorous stirring) the number of 1,2 units is increased to 7 0 ~ . Relations between polydiene structure and the initiator concentration are well known for lithium polymerization [14], b u t it should be noted t h a t so marked a difference in polymer structure with initiation b y the free metal or b y its compounds [14] was not observed for either lithium or potassium. Polymerization in the 1~resence of 4,4-dimethyl-l,3-dioxan (DMDO). The use of DMI)O as a solvent for anionic polymerization was described for the first time in [6], DMDO being a weak Lewis base. According to [15] t h e pKB value for this compound is 6.3 (for T H F , 5, for diethyl ether 5.2 and for 1,4-dioxan 5.9 [16]). According to the data in [17] the degree of diphenyl conversion to anion-radicals in the reaction with sodium (used as a measure of the solvating power of solvents relative to the sodium cation) is 1 4 ~ in 1,3-dioxan (42~/o in T H F , and 100% in dimethoxyethane). Likewise, according to our findings, only 2 0 ~ of the naphthalene is converted to anion-radicals in the reaction with sodium in DMDO (compared with almost 100% in T H F ) . T,~n~
~ ~
1. B v T ~ u ~ . ~ r s - P o ~ r m ~ i z A ~ o ~
Initiators
I
for con- [ centration, [I
Solvent
[
tion
~S~CE
Poly[ rner
%
Or O~O~O-SOD~M
I
n~_~ToRs
c~. 1,4
trana-
10 17 14 -20 12
25 19 29 -22 18
1,4
molefl. DHN-I* DHI~.IIt DHN-II NA-I NA-I NA.II
--
0.4 17 7
Toluene Benzene Benzene Cyelohexane Toluene Ethylbenzeno
22 5 mint 24 1 5 72
50 100 100 100 100 100
-1000 36 35
20 136 605 60 19 --
50 64 57 -58 70
* Solution of initiator and Freeil~ltate. t Turbulen~ reaction wl~h evolution of heat.
A solution of sodium-~-methylstyrene (SMS) in DMDO, as in T H F [8], has an absorption peak in the electronic spectrum at 330 nm. However, the solution is less stable than in T H F - - a f t e r only 7 days the intensity of the main peak is significantly reduced, and disappears altogether in 10 days (the colour o f the solution changing from bright red to yellow).
Polymerization of butadiene
39I
Table 2 gives the results of polymerization experiments in DMI)0 and in DMI)O mixed with hydrocarbons. Butadiene polymerization in I)MI)0 (experiments 1, 3) and also styrene polymerization in a DlKD0-cyclohexane mixture (experiment 6) takes place turbulently with evolution of heat; the polymer yield is quantitative and the MW is close to the theoretical. The polybutadiene microstructure (75% 1,2-, 11~/o cis-l,4- and 14°/o trans-l,4-units) is close to t h a t of polymers formed in the presence of other sodium initiators (Table 1). However, the reaction stops after a rapid initial period (2-5 rain) in the case of butadiene polymerization in ])M_DO-toluene mixtures (experiments 2, 4), and in DMDO-cyclohexane mixtures it stops immediately after introduction of the monomer (experiment 5). To shed light on the cause of termination of the reaction the process was conducted in the presence of SMS synthesized in T H F medium. I n this case, as in previous experiments, the reaction stopped (experiment 7) in the h e p t a n e - I ) M D 0 system, whereas in the reference experiment [8] it proceeded aeoompanied b y heat evolution and have polymer with a yield of 100%. This means t h a t termination is due to growing chains reacting with I)MX)0; the reaction is probably the result of abstraction of labile aceta] atoms of hydrogen (in experiments 4, 5, 7 the molar ratio of DMI)0 : Na is 80-50, and so termination cannot be due to impurities introduced with I)MI)O, the impurities concentration being, as we said above, lower by one order t h a n the sodium concentration). In this connection it should be noted t h a t termination reactions with the participation of acetal hydrogen occur also in the anionic polymerization of a structurally similar monomer, 2-vinyl-l,3-dioxan [18]. T~
2. PO~.Ymm~ZA~ONV~V~ . ~
AC~ON or somvM n~r~ToRs ~N ~
~.s~.NeB
OF E L E C T R O N D O N O R S AT R O O M T E M P E R A T ~ B E
Initiator
~xperiment No.
1 2 3 4 5
Monomers
Initiators
Butadiene SN* . . . . ,, SMS . . . . . . . .
M
concentration, c × 10s, g-equiv./ /l. 7.4 7"1 13 13 13
Solvent
I)MI)O Toluene ~-DMDO (25%) DMI)O Toluene-~ DMDO (5%) Cyelohexane-~DMI)O
X I0 -s
Polymer, yield, Mm~r.! My % 100t 15 100t 13 0
50 -22 ---
47 -26 --
100t 0
50 --
44 --
100t 100t
-21
-32
--
(4%)
6 7
Styrene Butadiene
8 . . . . 9 . . . . * Sodium.naphtlu~ne.
,, ,,
9 16 16 2.3
Ditto Heptane %THF (10%) +DMDO (8%) Heptane +THF (10%) THF + DMI)O (10%)
? Turbulent reaction aceomlmnied by heat evolution.
392
R.V.
BAsovA e t a / .
According to the data cited above the stability of carbanions relative to DMDO increases along with the degree of branching of carbanions (butadiene < styrene <~-methylstyrene). I t is noteworthy t h a t the process steps only in weakly polar mixtures of DMT)O and hydrocarbons, whereas in ])M_DO itself (as well as in the polar system D]KDO-THF (experiment 9)) the polymerization occurs rapidly and quantitatively, although the concentration of the terminating agent is in this case increased. The reason for this behaviour apparently lies in the fact t h a t a change in the solvating power of the medium, and consequently in the polarity of the carbon--sodium bond in the active centre is nonuniform in its influence on rates of propagation and termination. Certainly, the propagation reaction normally increases significantly with increasing polarity of the medium [8]; one can also cite examples of metallation reactions in which the reaction rate de~ creases with increasing polarity of the bond [19] (these reactions are associated ~,ith proton transfer from a earbanion with a localized negative charge to a delocalized carbanion, as occurs in this case). Thus it appears t h a t as the solvat}ng power of the medium decreases on diluting DM])O with hydrocarbons the propagation]termination rate ratio is drastically reduced, and leads to the complete extinction of the process. Tra~,tslated by R. J. A. HE~DrtY REFERENCES
1. T. C. ~*HENG, A. F. HALASA and D. P. TATE, J. Polymer Sci. A-l, 9: No. 9, 2493, 1971 2. T. C. CHENG, A. F. ~ A and D. P. TATE, J. Polymer Sci., Polymer Chem. Ed. 11: No. 1, 253, 1973 3. T. C. CHENG and A. F. HALASA, J. Polymer Sci., Polymer Chem. Ed. 14: No. 3, 573, 1976 4. A. F. HALASA, T. C. CHENG and J. E. HALL, J. Polymer Sci., Polymer Chem. Ed. 17: No. 6, 1771, 1979 5. V. G. SHALGANOVA, V. I. RADUGINA, L. Ya. I Z R ~ H J T , N. M. SEMENOVA, S. I. NESTEROVA and L. B. POSTOVALOVA, Polibutadieny s razliehnym soderzhaniyem vinfl'nykh zvenyev (Polybutadienes with Different Concentrations of Vinyl Units). TsNTITENeftekhim., Moscow, 1978 6. U.S.S.R. Pat. 655706; Byull. izobr., No. 13, 1979 7. A. A. AREST-YAKUBOVICH, A. R. GANTM~I~HER and S. S. MEDVEDEV, Vysokoreel. soyed. 8: 7, 1003, 1961 (Translated in Polymer Sci. U.S.S.R. 3: 5, 788, 1962) 8. M. SHVARTS, Anionnaya polimerizatsiya (Anionic Polymerization). Mir, Moscow, 1971 9. S. K. 0GORODNIKOV, In: Sinteticheskii kauehuk (Synthetic Rubber). p. 696, A. V. Garmonova (Ed.), Khlmlya, Leningrad, 1976 10. J. N. ANDERSON, M. L. BARZAN and H. E. ADAMS, Rubber Chem. and Technol. 45: No. 5, 1270, 1972 11. L M. 6t. COWIE, D. J. WORSFOLD and S. BYWATER, Trans. Faraday See. 57: No. 4, 705, 1961 12. K. GEHRKE and R. SCHONE,Plaste und Kautsehuk 2all: No. 10, 726, 1976
Thermal and thermooxidative degradation of polyamidoimide films
308
13. A. PRONL {3. ¢ORNO, A. ROGGERIO, G. 8ANTI and A. GANDINI, Polymer 20: No. 1, 116, 1979 14. T. V. TALALAYEVA and K. A. KOCHES1TKOV, Metody elemontoorganich, khimiL Litii, natrii, kalii, rubidii, tsezii (Heteroorganic Chemistry Methods. Lithium, Sodium, Potassium, Rubidium, Cesium), 2: p. 917, Nauka, Moscow, 1971 15. F. N. LATYNOVA, T. F. A~KHUNOV,S. S. ZLOTSKII, E. Ire. 8ALOVA and D. L. RAKHMANKULOV, Zh. prikl, khimii 50: No. 1, 223, 1977 16. G.I. GORSHKOVA, Z. B. BARINOVA, V. T. ALEgSANYAN and V. A. PONOMARENKO, Izv. AN SSSR, Seriya khimich., No. 2, 312, 1968 17. A. I. 8HATEINSHTEIN, E. S. PETROV, M. I. BELOUSOVA, K. G. YANOVA and Ye. A. YAKOVLEVA, Dokl. Akad. Nauk SSSR 151: No. 2, 353, 1963 18. N. YAMASHITA, Y. NISHI and T. MAESHIMA, Polymer Latters 17: No. 8, 521 1979 19. A. A. SOLOVYANOV and I. P. BELETSKAYA, Uspekhi Kh~mii 47: No. 5, 819, 1978
Polymer Science U.S.S.R. Vol. 24, No. 2, pp. 293--400, 1982 P r i n t e d in Poland
0032.-3950/82/020393-08507.50/0
~
O 1983 P e r g a m o n P r e ~ L t d .
ESR ANALYSIS OF THE THERMAL AND THERMOOXIDATIVE DEGRADATION OF POLYAMIDOIMIDE FILMS* O. A. ImD~,VA, G. B. P~a~Is,~ V. V. Tt~Ezvov a n d D. YA. TOl~YGIN Chemical Physics Institute, U.S.S.R. Academy of Sciences
(Received 24 November 1980) The emergence of free radicals of polyconjugated systems (PCS) in the thermal and thermooxidative degradation of polyamidoimide films was observed in the temperature range 553-673°K. According to the ESR spectra these radicals are practicaUy identical in character. The rate of accumulation and the limit concentrations of these PCS radicals are significantly higher in the thermal oxidation as compared with thermal degradation processes. This is attributable to a difference in the rates of formation of isoimide rings and in their limit concentrations in these processes. In the case of thermal oxidation the kinetic curves of accumulation of PCS radicals are described by a model of kinetic nonequivalence of reactive centres in solidphase radical reactions. Effective rate constants and activation energies have been determined for the accumulation of PCS radicals during the thermal oxidation. T~ERMAL stability, g o o d b o n d s t r e n g t h to m e t a l s a n d good m e c h a n i c a l p r o p e r t i e s are characteristic o f p o l y a m i d o i m i d e coatings as is t h e use o f fine-particle fillers for these coatings [1]. A u t h o r s h a v e a c c o r d i n g l y s h o w n p a r t i c u l a r i n t e r e s t in t h e t h e r m a l a n d t h e r m o o x i d a t i v e d e g r a d a t i o n o f p o l y a m i d o i m i d e s (PAI). I t is reasonable t o assume t h a t the t h e r m a l a n d t h e r m o o x i d a t i v e d e g r a d a t i o n * Vysokomol. soyed. ALl4: No. 2, 301-366, 1982.
Printed in Poland
0032-3950/82/020888-06507.50/0
0 1988 PergamonPre~ I,kl.
POLYMERIZATION OF BUTADIENE UNDER THE ACTION OF SODIUM ORGANIC INITIATORS IN SLIGHTLY POLAR MEDIA* R . V. BASOVA, B. I . NAKIE~IA_~OVICH, E . V. K R I S T A L ' ~ I
and A. A. A~EsT-YAxuBOVIC~ L. Ya. K a r p o v Physico-chemical Research I n s t i t u t e
(Received 8 August 1980) A s t u d y has been made of the polymerization of bute~liene under the action of sodium organic derivatives in hydrocarbon media in the presence of 4,4-dimethyl1,3-dioxane (DMDO). I n benzene, ethyl benzene a n d eyclolmxane polymerization occurs quantitatively and a high molecular weight polymer is obtained; in the presence of toluene the M W and (in some cases) the polymer yields are lower as a result of metallation of the solvent. Buta~liene polymerization in mixtures of D1KDO and hydrocarbons is accompanied b y chain termination, a p p a r e n t l y as a result of abstraotion of a labile acetal hydrogen from DM_DO.
BUTADIE~E polymerization under the action of metallic sodium in the absence of solvent was first carried out almost 50 years ago; this was the first process used on a commercial scale in the production of synthetic rubber. Despite this, no fully adequate study has yet been made of butadiene polymerization under the action of sodium compounds in slightly polar media, i.e. in hydrocarbon solvents and mixtures of the latter with small amounts of electron donors. It is pointed out in [1-5] that incomplete conversion of monomer and low molecular weights of the resulting polymers are typical features of butadiene polymerization processes in the presence of sodium initiators in hydrocarbon media, and these findings attributed to instability of polybutadienylsodium under these conditions. For instance, according to [3] the maximum yield of polymer is 30% for butadiene polymerization in the presence of a dispersion of sodium in hexane a t 30°; in the case of polymerization in the presence of "butyl-sodium" (a mixture of butyl-sodium and sodium chloride) in llexane the polymer yield at 5° is 80%, and at 50 °, 45%. Our aim in the present instance was to investigate the main features of butadiene polymerization under the action of sodium initiators in hydrocarbon media and to study the polymerization in the presence of 4,4-dimethyl-l,3dioxane (DMDO) recently proposed [6] as a solvent for the anionic polymerization of butadiene. * Vysokomol. soyed. A$4: ~ o . 2, 357-360, 1982. 388
Polymerization of butadiene
389
Polymerization in a hydrocarbo~ medium was initiated with the aid of a solid sodiumanthracene prepared in ~ with subsequent evacuation of solvent under vacuum (Na-I) or by direct synthesis from sodium and anthracene in ethylbenzene at 110° by the method of [7] (NA.II); soluble 1,1-diphenylhexylsodium (DHI~ was also used as an initiator. The latter was prepared by reaction of 1,1-diphenylethylene (at room temperature) to products o f the reaction of sodium with butyl bromide ( D I ~ . ] ) or butyl chloride (DHI~'.I1) carried out in benzene at 6-10 ° in a vessel equipped with a stirrer with slow feeding of the alkyl halide from the gas phase (over 1.5-2 hr). Hydrocarbon solvents and monomer were purified b y normal procedure for anionic polymerization [8]; in the final stage the reagents were treated with dry ethyl lithium. Commercial DMDO (which, according to [9], may contain the following impurities: methyl alcohol, isoprene tort. butanol, unsaturated amylene alcohols, methyltetrahydropyran) was distilled (b.p. 133 ° [9]), held for 1 day over sodium wire and then in a vacuum apparatus was successively recondensed into ampoules Containing a metallic sodium mirror and a small amount of anthracene (until the blue ¢olouring of sodium-anthracene appeared), a potassium-sodium alloy, and a sodium mirror containing a small amount of ~-mcthylstyrene or naphthalene. When the solvent is sufficiently pure, the red colouring of sodium a-methylstyrene (or the green of sodium-naphthalene) appears almost immediately after warming the ampoule. DMDO was then stored under vacuum. The results of chromatographic analysis (column length 1 m, diameter 4 m, packing, 20% polyphenyl-methylsiloxane on Celite, 88 °, carrier-gas (nitrogen) rate 60 ml/min, flame-ionization detector) showed that the total amount of residual impurities after this treatment was N ~ 2~o. I t was however noted that volatile substances gradually accumulate in DMDO under prolonged storage ~n vacuo, and accordingly it was further treated with sodium containing a small amount of g-methylstyrene or naphthalene immediately before experiments. Molecular weights of the polymers were determined by viscometry, usizlg the formulae [y]-~ 9.01 × 10-5 M °'al [10] (for polybutadiene) and [~]= 1.04 × 10 -~ M °'~3 [111 (for PS).
Polymerization in hydrocarbon media.
T a b l e 1 gives t h e results o f p o l y m e r i z a t i o n in t h e h y d r o c a r b o n m e d i a . I t w a s f o u n d . t h a t a benzene-soluble c o m p o u n d is o b t a i n a b l e b y a d d i t i o n o f 1,1-diphenylethylene to " b u t y l s o d i u m " ( t h o u g h a c c o r d i n g t o s p e c t r o p h o t o m e t r i c a n a l y s i s t h e s o l u b i l i t y ( 8 × 1 0 -4 mole/l.) is slight) a l t h o u g h t h e a n a l y s i s r e v e a l s t h a t chlorine is p r e s e n t in solution in t h e m o l a r r a t i o o f c h l o r i n e / a c t i v e sodium-----1 : 2 ( a p p a r e n t l y in t h e f o r m o f a c o m p l e x o f •aC1 w i t h Rl~a). A c c o r d i n g to t h e t a b u l a t e d d a t a p o l y m e r i z a t i o n in t h e presence of all t h e i n i t i a t o r s t a k e s p l a c e q u a n t i t a t i v e l y in benzene, e t h y l b e n z e n e a n d c y c l o h e x a n e , a n d h i g h p o l y m e r s are o b t a i n e d . T h u s p o l y b u t a d i e n y l s o d i u m a c t i v e centres in t h e s e solutions a p p e a r to be r e a s o n a b l y stable. T h e m o l e c u l a r w e i g h t is signif i c a n t l y lower in toluene, a n d in s o m e cases t h e r e is i n c o m p l e t e c o n v e r s i o n o f monomer. In butadiene polymerization under the action of sodium initiators s e c o n d a r y effects w e r e p r e v i o u s l y o b s e r v e d [12, 13] in t h e presence o f toluene. On e x a m i n i n g t h e results it is r e a d i l y seen t h a t t h e o b t a i n e d p o l y m e r s c o n t a i n s i g n i f i c a n t l y m o r e 1,2-units t h a n those p r e p a r e d u n d e r s i m i l a r conditions in t h e p r e s e n c e o f m e t a l l i c s o d i u m [14], w h e r e the c o n c e n t r a t i o n o f 1,2 u n i t s is 32-35~/o. Since a t l e a s t one o f t h e i n i t i a t o r s u s e d by us (NA-II) could n o t u n d e r t h e conditions a d o p t e d c o n t a i n a n y s o l v a t i n g i m p u r i t i e s of n o n - h y d r o c a r b o n
390
R . V . BAsovA e$ a/.
character, the larger number of 1,2-units is apparently attributable to the fact that in the presence of a metal mirror polymerization takes place at a significantly lower concentration of active centres compared with the case where organosodium initiators are used. This is supported b y the fact that in the case of polymerization in presence of the metal under conditions conducive to a higher concentration of growing chains (polymerization on a comminuted metal with vigorous stirring) the number of 1,2 units is increased to 7 0 ~ . Relations between polydiene structure and the initiator concentration are well known for lithium polymerization [14], b u t it should be noted t h a t so marked a difference in polymer structure with initiation b y the free metal or b y its compounds [14] was not observed for either lithium or potassium. Polymerization in the 1~resence of 4,4-dimethyl-l,3-dioxan (DMDO). The use of DMI)O as a solvent for anionic polymerization was described for the first time in [6], DMDO being a weak Lewis base. According to [15] t h e pKB value for this compound is 6.3 (for T H F , 5, for diethyl ether 5.2 and for 1,4-dioxan 5.9 [16]). According to the data in [17] the degree of diphenyl conversion to anion-radicals in the reaction with sodium (used as a measure of the solvating power of solvents relative to the sodium cation) is 1 4 ~ in 1,3-dioxan (42~/o in T H F , and 100% in dimethoxyethane). Likewise, according to our findings, only 2 0 ~ of the naphthalene is converted to anion-radicals in the reaction with sodium in DMDO (compared with almost 100% in T H F ) . T,~n~
~ ~
1. B v T ~ u ~ . ~ r s - P o ~ r m ~ i z A ~ o ~
Initiators
I
for con- [ centration, [I
Solvent
[
tion
~S~CE
Poly[ rner
%
Or O~O~O-SOD~M
I
n~_~ToRs
c~. 1,4
trana-
10 17 14 -20 12
25 19 29 -22 18
1,4
molefl. DHN-I* DHI~.IIt DHN-II NA-I NA-I NA.II
--
0.4 17 7
Toluene Benzene Benzene Cyelohexane Toluene Ethylbenzeno
22 5 mint 24 1 5 72
50 100 100 100 100 100
-1000 36 35
20 136 605 60 19 --
50 64 57 -58 70
* Solution of initiator and Freeil~ltate. t Turbulen~ reaction wl~h evolution of heat.
A solution of sodium-~-methylstyrene (SMS) in DMDO, as in T H F [8], has an absorption peak in the electronic spectrum at 330 nm. However, the solution is less stable than in T H F - - a f t e r only 7 days the intensity of the main peak is significantly reduced, and disappears altogether in 10 days (the colour o f the solution changing from bright red to yellow).
Polymerization of butadiene
39I
Table 2 gives the results of polymerization experiments in DMI)0 and in DMI)O mixed with hydrocarbons. Butadiene polymerization in I)MI)0 (experiments 1, 3) and also styrene polymerization in a DlKD0-cyclohexane mixture (experiment 6) takes place turbulently with evolution of heat; the polymer yield is quantitative and the MW is close to the theoretical. The polybutadiene microstructure (75% 1,2-, 11~/o cis-l,4- and 14°/o trans-l,4-units) is close to t h a t of polymers formed in the presence of other sodium initiators (Table 1). However, the reaction stops after a rapid initial period (2-5 rain) in the case of butadiene polymerization in ])M_DO-toluene mixtures (experiments 2, 4), and in DMDO-cyclohexane mixtures it stops immediately after introduction of the monomer (experiment 5). To shed light on the cause of termination of the reaction the process was conducted in the presence of SMS synthesized in T H F medium. I n this case, as in previous experiments, the reaction stopped (experiment 7) in the h e p t a n e - I ) M D 0 system, whereas in the reference experiment [8] it proceeded aeoompanied b y heat evolution and have polymer with a yield of 100%. This means t h a t termination is due to growing chains reacting with I)MX)0; the reaction is probably the result of abstraction of labile aceta] atoms of hydrogen (in experiments 4, 5, 7 the molar ratio of DMI)0 : Na is 80-50, and so termination cannot be due to impurities introduced with I)MI)O, the impurities concentration being, as we said above, lower by one order t h a n the sodium concentration). In this connection it should be noted t h a t termination reactions with the participation of acetal hydrogen occur also in the anionic polymerization of a structurally similar monomer, 2-vinyl-l,3-dioxan [18]. T~
2. PO~.Ymm~ZA~ONV~V~ . ~
AC~ON or somvM n~r~ToRs ~N ~
~.s~.NeB
OF E L E C T R O N D O N O R S AT R O O M T E M P E R A T ~ B E
Initiator
~xperiment No.
1 2 3 4 5
Monomers
Initiators
Butadiene SN* . . . . ,, SMS . . . . . . . .
M
concentration, c × 10s, g-equiv./ /l. 7.4 7"1 13 13 13
Solvent
I)MI)O Toluene ~-DMDO (25%) DMI)O Toluene-~ DMDO (5%) Cyelohexane-~DMI)O
X I0 -s
Polymer, yield, Mm~r.! My % 100t 15 100t 13 0
50 -22 ---
47 -26 --
100t 0
50 --
44 --
100t 100t
-21
-32
--
(4%)
6 7
Styrene Butadiene
8 . . . . 9 . . . . * Sodium.naphtlu~ne.
,, ,,
9 16 16 2.3
Ditto Heptane %THF (10%) +DMDO (8%) Heptane +THF (10%) THF + DMI)O (10%)
? Turbulent reaction aceomlmnied by heat evolution.
392
R.V.
BAsovA e t a / .
According to the data cited above the stability of carbanions relative to DMDO increases along with the degree of branching of carbanions (butadiene < styrene <~-methylstyrene). I t is noteworthy t h a t the process steps only in weakly polar mixtures of DMT)O and hydrocarbons, whereas in ])M_DO itself (as well as in the polar system D]KDO-THF (experiment 9)) the polymerization occurs rapidly and quantitatively, although the concentration of the terminating agent is in this case increased. The reason for this behaviour apparently lies in the fact t h a t a change in the solvating power of the medium, and consequently in the polarity of the carbon--sodium bond in the active centre is nonuniform in its influence on rates of propagation and termination. Certainly, the propagation reaction normally increases significantly with increasing polarity of the medium [8]; one can also cite examples of metallation reactions in which the reaction rate de~ creases with increasing polarity of the bond [19] (these reactions are associated ~,ith proton transfer from a earbanion with a localized negative charge to a delocalized carbanion, as occurs in this case). Thus it appears t h a t as the solvat}ng power of the medium decreases on diluting DM])O with hydrocarbons the propagation]termination rate ratio is drastically reduced, and leads to the complete extinction of the process. Tra~,tslated by R. J. A. HE~DrtY REFERENCES
1. T. C. ~*HENG, A. F. HALASA and D. P. TATE, J. Polymer Sci. A-l, 9: No. 9, 2493, 1971 2. T. C. CHENG, A. F. ~ A and D. P. TATE, J. Polymer Sci., Polymer Chem. Ed. 11: No. 1, 253, 1973 3. T. C. CHENG and A. F. HALASA, J. Polymer Sci., Polymer Chem. Ed. 14: No. 3, 573, 1976 4. A. F. HALASA, T. C. CHENG and J. E. HALL, J. Polymer Sci., Polymer Chem. Ed. 17: No. 6, 1771, 1979 5. V. G. SHALGANOVA, V. I. RADUGINA, L. Ya. I Z R ~ H J T , N. M. SEMENOVA, S. I. NESTEROVA and L. B. POSTOVALOVA, Polibutadieny s razliehnym soderzhaniyem vinfl'nykh zvenyev (Polybutadienes with Different Concentrations of Vinyl Units). TsNTITENeftekhim., Moscow, 1978 6. U.S.S.R. Pat. 655706; Byull. izobr., No. 13, 1979 7. A. A. AREST-YAKUBOVICH, A. R. GANTM~I~HER and S. S. MEDVEDEV, Vysokoreel. soyed. 8: 7, 1003, 1961 (Translated in Polymer Sci. U.S.S.R. 3: 5, 788, 1962) 8. M. SHVARTS, Anionnaya polimerizatsiya (Anionic Polymerization). Mir, Moscow, 1971 9. S. K. 0GORODNIKOV, In: Sinteticheskii kauehuk (Synthetic Rubber). p. 696, A. V. Garmonova (Ed.), Khlmlya, Leningrad, 1976 10. J. N. ANDERSON, M. L. BARZAN and H. E. ADAMS, Rubber Chem. and Technol. 45: No. 5, 1270, 1972 11. L M. 6t. COWIE, D. J. WORSFOLD and S. BYWATER, Trans. Faraday See. 57: No. 4, 705, 1961 12. K. GEHRKE and R. SCHONE,Plaste und Kautsehuk 2all: No. 10, 726, 1976
Thermal and thermooxidative degradation of polyamidoimide films
308
13. A. PRONL {3. ¢ORNO, A. ROGGERIO, G. 8ANTI and A. GANDINI, Polymer 20: No. 1, 116, 1979 14. T. V. TALALAYEVA and K. A. KOCHES1TKOV, Metody elemontoorganich, khimiL Litii, natrii, kalii, rubidii, tsezii (Heteroorganic Chemistry Methods. Lithium, Sodium, Potassium, Rubidium, Cesium), 2: p. 917, Nauka, Moscow, 1971 15. F. N. LATYNOVA, T. F. A~KHUNOV,S. S. ZLOTSKII, E. Ire. 8ALOVA and D. L. RAKHMANKULOV, Zh. prikl, khimii 50: No. 1, 223, 1977 16. G.I. GORSHKOVA, Z. B. BARINOVA, V. T. ALEgSANYAN and V. A. PONOMARENKO, Izv. AN SSSR, Seriya khimich., No. 2, 312, 1968 17. A. I. 8HATEINSHTEIN, E. S. PETROV, M. I. BELOUSOVA, K. G. YANOVA and Ye. A. YAKOVLEVA, Dokl. Akad. Nauk SSSR 151: No. 2, 353, 1963 18. N. YAMASHITA, Y. NISHI and T. MAESHIMA, Polymer Latters 17: No. 8, 521 1979 19. A. A. SOLOVYANOV and I. P. BELETSKAYA, Uspekhi Kh~mii 47: No. 5, 819, 1978
Polymer Science U.S.S.R. Vol. 24, No. 2, pp. 293--400, 1982 P r i n t e d in Poland
0032.-3950/82/020393-08507.50/0
~
O 1983 P e r g a m o n P r e ~ L t d .
ESR ANALYSIS OF THE THERMAL AND THERMOOXIDATIVE DEGRADATION OF POLYAMIDOIMIDE FILMS* O. A. ImD~,VA, G. B. P~a~Is,~ V. V. Tt~Ezvov a n d D. YA. TOl~YGIN Chemical Physics Institute, U.S.S.R. Academy of Sciences
(Received 24 November 1980) The emergence of free radicals of polyconjugated systems (PCS) in the thermal and thermooxidative degradation of polyamidoimide films was observed in the temperature range 553-673°K. According to the ESR spectra these radicals are practicaUy identical in character. The rate of accumulation and the limit concentrations of these PCS radicals are significantly higher in the thermal oxidation as compared with thermal degradation processes. This is attributable to a difference in the rates of formation of isoimide rings and in their limit concentrations in these processes. In the case of thermal oxidation the kinetic curves of accumulation of PCS radicals are described by a model of kinetic nonequivalence of reactive centres in solidphase radical reactions. Effective rate constants and activation energies have been determined for the accumulation of PCS radicals during the thermal oxidation. T~ERMAL stability, g o o d b o n d s t r e n g t h to m e t a l s a n d good m e c h a n i c a l p r o p e r t i e s are characteristic o f p o l y a m i d o i m i d e coatings as is t h e use o f fine-particle fillers for these coatings [1]. A u t h o r s h a v e a c c o r d i n g l y s h o w n p a r t i c u l a r i n t e r e s t in t h e t h e r m a l a n d t h e r m o o x i d a t i v e d e g r a d a t i o n o f p o l y a m i d o i m i d e s (PAI). I t is reasonable t o assume t h a t the t h e r m a l a n d t h e r m o o x i d a t i v e d e g r a d a t i o n * Vysokomol. soyed. ALl4: No. 2, 301-366, 1982.