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The mechanism of decay of active centres in polymerization of trioxan in solution
THE MECHANISM OF DECAY OF ACTIVE CENTRES IN POLYMERIZATION OF TRIOXAN IN SOLUTION* Y~. N. SMm~Ov, V P VOLKOV,B A. ROZENBERG and N. S YENIKOLOPYAlq Institute of Chemmal Physms, U S.S R Academy of Scmnces
(Recewed 1 Febr~ary 1972) As a result of kinetic and sp~ctrophotometrm studms of the polymerizatmn of trmxan with B+A - salts as catalysts (where B + = P h s C +, CHACO+ or CH3OCH +, a n d A - ~ S b C I ~ or SbF~) it has been found t h a t t e r m l n a t m n of the growing chains revolves both physical and chemmal processes the ratm of the two being dependent on the structure of the active eentres and on the condltmns of polymerizatmn.
IT HAS been reported [1, 2] previously that when trioxane (TO) is polyInerized in benzene with trityl hexafluoroantimonate (THFA) as catalyst, as well with some other catalysts in other solvents [3], decay of active centres occurs, resulting in incomplete conversion of the monomer. Decay of active centres can occur b y a chemical process (such as chain termination on the solvent, impurities or the eounterion [4]) and also b y the physmal process of enclosure of the active centres within the mass of polymer [5], which must be a specific feature of heterogeneous polymerization/ Results that assist in solution of this problem are presented in the present paper. EXPERIMENTAL The TO was successively refluxed over then distilled from KOH, BaO a n d p o t a s s m m sodmm alloy. Methylene chloride and benzene were purffied b y the usual method and were then refluxed over a n d distilled from PiOb and Call2. 1,3-Dloxolane (DO) and methylal were redlstlllcd from sodmm and CaHz. n-Octane, whmh was used as a n internal standard, was refluxed over and redlstdled from p o t a s s m m - s o d m m alloy. Trltyl hexafluoroantlmonate was prepared from t n t y l fluoride and a n t n n o n y pentafluoride m trdiuorotrlchloroethane, m.p 209-210 ° (deeomp.), according to the hterature m.p. 211 ° [16]. T n t y l hexachloroantunonate (THCA) was obtained b y the method of reference [7] and methoxymethyl hexachloroantimonate (MMHCA) was prepared from chloromethyl * Vysokomol. soyed. A16: No. 2, 283-289, 1974. t The polymerization of t r m x a n m orgamc solvents m a heterogeneous process, with separation of crystalline polymer as a prempltate 327
328
Y ~ . N . SMZR~OV e~ al.
ether (CME) and SbC15 in heptane, m a high-vacuum apparatus. After the solvent and excess CME had been pumped off the catalyst was left m the form of a loose white powder. All the catalysts were made up as 0 1 M solutzons m mtrobenzene, whmh had been dlstdled i n v a c u o over P205 and then over BaO. The solution of MMHCA was stored at the temperature of dry me for up to 3 weeks and the other solutions were stored at room temperature Polymerization was earrmd out m a three.necked, glass reactor, fitted wzth,a heating jacket, a tap for removal of test samples, a stirrer and a fluoroplast seal. The solutmn of TO was transferred from a storage vessel to a measurmg cyhnder and then to the reactor. The other reactants were transferred by means of pipettes, m a countercurrent of carefully dined argon Before use the reactor ~ as washed at 50 ° with the TO solutmn. Test samples m the form of suspensmns were taken off into measuring cylinders contannng a solution of trmthylamme m benzene The polymer was then filtered off on a smtered glass filter, on whmh it was successively washed with methanol, water, acetone and ether, and finally drmd to constant weight ~n v a c u o at 40-60 °. The filtrate was analysed for TO by the GLC method, using an internal standard (condltmns of separatmn: KhL-4 chromatograph, column length 1.5 m, internal diameter 1 8 ram, packed with poly(ethylene glycol adlpate) on II~Z-600, temperature of separatmn 115°, flow rate 60 ml/mm). Ultrawolet spectra were recorded~m a CFD-2 instrument, using a cell of tlnekness 3 ram, whmh was filled rather in an argon contamer ("mozst condltmns") or under lugh vacuum ("dry condltmns"l. RESULTS AND DISCUSSION S t u d y of t h e d e p e n d e n c e of the m a x i m a l yield of p o l y m e r on t h e initial c a t a l y s t c o n c e n t r a t i o n in p o l y m e r i z a t i o n of TO in solution in benzene, c a t a l y s e d b y T H F A , has s h o w n [1] t h a t in these circumstances the active centres d e c a y according to the linear law Co--------(kt/kp) In (1--g~/~p)
(1)
where Co is the initial c a t a l y s t concentration, ~ t h e m a x i m a l degree of conversion of m o n o m e r , ge t h e equilibrium degree o f conversion of liquid m o n o m e r in t h e solid p o l y m e r (at 50 °, with [ T O ] = 2 . 1 mole/1, ae~--0"96), a n d k t a n d k, the r a t e c o n s t a n t s of c h a i n t e r m i n a t i o n a n d p r o p a g a t i o n respectively. A linear law of d e c a y is f o u n d also in c o p o l y m e r i z a t i o n of TO with DO (at a c o n c e n t r a t i o n o f t h e c o m o n o m e r of 0.1-0.2 mole/1.) in t h e presence of T H F A a n d T H C A (Figs. 1 a n d 2). Similar results were o b t a i n e d also in h o m o p o l y m e r i z a t i o n of TO in t h e presence of acetyl h e x a f l u o r o a n t i m o n a t e ( A H F A ) The linear n a t u r e of t h e d e c a y of active centres does n o t in itself indicate the actual m e c h a n i s m of d e c a y because it could be a t t r i b u t a b l e to b o t h chemical a n d physical processes. I t is obvious h o w e v e r t h a t increase in t h e p o l y m e r i z a tion t e m p e r a t u r e should bring a b o u t an increase in the rate of chemical processes associated with d e c a y of active eentres a n d a fall in t h e rate of a physical process. I t is seen from Fig. 3 t h a t t h e m a x i m a l yield of p o l y m e r increases as t h e t e m p e r a t u r e is increased. A n Arrhenius plot of t h e t e m p e r a t u r e dependence of t h e ratio o f t h e t e r m i n a t i o n a n d p r o p a g a t i o n rate constants, f o u n d f r o m
Polymerxzation of trioxau m solution
329
equation (1), gives a complex curve (Fig. 1, curve 4). At 10--35 ° t h e c u r v e is approx4mately a straight line and the difference between the energies of activation for chain propagation and termination is 15 kcal/mole, b u t as the temperature is increased the Arrhenius curve bends and the difference in the aetivation energies gradually falls. c~
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FIG. 1. Kinetic curves of polymerization of TO xn benzene at 50°, catalysed by THFA (a) and THCA (5) at [TO]----2.1mole/L, [DO]=0.1 mole/h and G0× 10-3----0 2 (•); 0.15 (2); 0.1 (3); 0 05 (4}; 0.025 (5); 1 (6); 2 (7}; 3 (8} and 4 mole/1. (9). FIG. 2. Dependence of log (1--a~/~e) on co m homopolymerlzatlon of TO by THFA (1) and in copolymerxzatlon of TO with 0 1 mole/l, of DO by THFA (2} and THC/k (3). I t should be noted that in the presence of catalysts containing SbF~ as the counterion the dependence of the maximal yield on catalyst concentration fits equation (1) at both low and higher temperatures, i.e., the apparent kinetic law of decay of active centres does not alter in this interval of temperatures, although a change in the mechanism of the termination reaction could occur. The nature of the temperature dependence does in fact indicate a complex mechanism of decay of active centres and bearing in mind the fact that the energy of activation for chain growth in cationic polymerization of oxygen-containing ring compounds does not as a rule exceed 15 kcal/mole, one of the decay processes (the low temperature section of the curve) must have an activation energy that is either close to zero or is negative. From this it m a y be supposed that the relationship found in this range of temperatures is connected mainly with the physical aspect of the decay of active centres. I f this suggestion about the physical nature of deactivation is correct, factors causing increase in the segmental mobility of the polymer chains should bring about a decrease in the rate of decay of active centres, and hence should increase the maximal yield of polymer. It was in fact found that increase in the
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t e m p e r a t u r e of a p o l y m e r i z a t i o n m i x t u r e in which p o l y m e r i z a t i o n has s t o p p e d causes p o l y m e r i z a t i o n t o r e s t a r t * (Fig. 3). T h u s it m a y be concluded f r o m the above results t h a t physical effects p l a y t h e p r e d o m i n a n t role in t e r m i n a t i o n of growing chains a t low t e m p e r a t u r e s . T h e deviation f r o m linearity of t h e Arrhenins plot of t h e r a t e c o n s t a n t ratio a t high t e m p e r a t u r e s (Fig. 4, curve 1) is obviously due increase in the role o f
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FIO. 3. Ktuet,c curves of polymerization of TO m benzene by AHFA at 10° (•); 20° (2); 30° {3) and 50 ° (4); [TO]-----1mole/], and U0-----2× 10-' mole/]: a--temperature raised to 70°, b-- 0 2 mole/], of methylal added.
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Fxo. 4. Arrhemus plots of the ratio kp//~ m homopolymenzation of TO (1, 3) and m eopolymerization of TO with 0.2 mole/1, of DO (2) by A.T~I~A {A); THFA {B, G) and THCA (D). * A ~lml!ar effect is obtained when active compounds capable of producing an active centre m the liquid phase, by chum transfer, are added during the course of polymerL~ation.
331
Polymerlzatlon of tnoxan in solution
chemical processes in termination of the growing chains, namely decomposition of the ion pairs to molecular form and]or their hydrolysis b y water, which is usually present in the system at concentrations up to 2 × 10 -3 mole]l. The energy of activation for such processes is usually fairly high ( ~ 2 0 kcal/mole) [8, 9]. I t would be expected that a more basic comonomer (such as DO) would stabilize the active centres * against hydrolysis and decomposition of the ion pairs as a result of greater delocalization of the charge on the oxonium ions.
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FIc. 5. Kinetic curves of polyme~zatlon of TO m benzene by MMHCA at 7° (•); 15° (2); 25° (3) and 35° (4); ]TO]= 1 mole/L and c0=3× 10-3 molefl. I t was found in fact that in the presence of DO the relative rate of decay of active centres obeys the Arrhenius equation over a much wider range of temperatures (20-65 °) ~f than in homopolymerization (Fig. 4, curve 2). This means that in the presence of DO in this range of temperatures the active centres decay mainly b y a physical process and chemical conversion of these centres does not occur to a n y appreciable extent. Thus the well known rule that the reactivity (basicity) of monomers and the reactivity of the corresponding active centres affect the propagation reaction in the opposite w a y [10] can be extended to the reaction of deactivation of these centres, i.e., to the rate of hydrolysis and decomposition of the ion pairs. It follows from this, for example, that the rate of these reactions (the counterion being the same) should fall in the order of the monomers: T O ~ D O ~ T H F , and this is fully borne out b y experimental observation [I0, Ii]. The resistance of ion pairs to chemical change is dependent on the structure not only of the cation, but also of the counterion. To find the effect of the nature of the counterion on the stability of the active centres, .we studied the polymerization of T O under the influence of catalysts in which the counterion was SbCl~. In view of the fact that SbCl~ is more strongly * Use was made of the rule of adchtlmty of the reactlmty (baslmty) of the monomer and the reactivity of the corresponding propagating oentre [10]. t A smnlar stabilizing effect m obtained by addition of methy]al and other ohgoformals.
332
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nucleophl]ic than SbF~, it would be,expected that the part played by deactivation of active centres as a result of chemical change involving the counterion would be increased substantially. It is this that provides the explanation of the difference in the relative decay rate constants with SbF~ and SbGl~ as counterions, the smaller increase in the maximal yield of polymer with increase in temperature when the dioxolenium salt I~IM~CA is used as catalyst (Fig. 5) and the smaller difference between the energies of activation for propagation and termination when SbCI~ is used as the counterion (Fig. 4, curve 3). When TO was poly,7 I /
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mole/1, and v0----2×10 -3 mole/1.
merized in solution in benzene and in CHIC12, with M~HCA as catalyst, it was clearly demonstrated that chemical deactivation of the active centres occurs during the course of the reaction. The first stage in this process is the reversible reaction of decomposition of the active centre by reaction between the cation and eounterion, with formation of molecular compounds ~OCH+SbCI~ ~ ~OCH~CI-~SbC15
(2)
This is shown by the following facts. 1) The addition of easily hydrolysable organic halides such as acetyl chloride and CME brings about a substantial increase in the rate of polymerization of TO (Fig. 6). This effect occurs when the addition is made in the beginning or during the course of polymerization. 2) It is known [12, 13] that the SbCl~ anion in the free state and in the form of an ion pair gives an absorption band at ~max=272 nm. When polymerization of TO is eatalysed by hexachloroantimonates having stable organic cations (Et30 +, Ph3C+ and CHACO+) the intensity of the 272 n m band falls and new bands appear at shorter wavelengths (230-250 nm). When organic halides (CHsCOCI and CHaOCH~C1) are added to the polymerization solution, however, the intensity of absorption at ~max----272 nm again increases substantially. When PhaCC1 is added a band appears in the visible region of the spectrum (2max=412 nm), corresponding to absorption by the triphenylmethyl cation [14, 15].
Polymerization of trloxan in solution
333
As an alternative explanation of the above spectroscopic results chain transfer to R - - H a l ~ OCH~SbCI~Ph~CC1
(3)
~. ~ OCH2CI+Ph~C+SbCI~ m a y be suggested.
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7-Zme , r a i n
FIG. 7. I ~ n e t , c curves of polymerization of TO m CH,CI, a t 20 ° b y SbCls, without a d ditives (1); with addition of CME a t the b e ~ n n m g (2) and during the course of polymerization (3); [TO]-----2-3 mole]L; co=10 -8 mole/l.; [ H i O ] = 4 × 10 -8 mole/1, and [ C M E ] = 5 × 1 0 - ' mole/1.; a denotes tho point of addition of CME.
This reaction does not in fact occur however, as was shown b y addition of triphenylmethyl chloride and CME to the mother liquor obtained b y filtration of the polymerization solution. I t was found t h a t polymerization does n6t occur 17
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i
I-
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Z-%i _\
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I
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I
~'~
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I
~ ,nm
FIG. 8. Ultraviolet spectra of the products of reaction of SbC16 with methylal (1); TO (2) a n d CHsO(CHsOhCH, (8), and of the SbCI~-TO-CHIClfPhaCC1 (d) a n d TO-M~rRCA-CH,Cll systems (~) after 2 hr a t 30°; [SbCI~]=lX 10 -s mole/l, a n d [ H . O ] = 4 X 10 -s mole/L; 20 °.
•334
Yu. N. SMn~-~ove$ al.
in the mother liquor, but it begins again when alkyl halides are added. As has already been stated, the same effect is obtained when Mkyl halides are added to the polymerization system {Fig. 7). Thus the above experimental evidence shows t h a t in this polymerization system decomposition of the active centre to molecular forms occurs. Moreover it is Mso evident from these experiments t h a t the active centres are localized mainly in the solid phase, and the antimony pentachloride produced by decomposition of the active centre is reversibly converted to some less active compounds. The latter conclusion is based on the following facts. Antimony pentachloride is a fairly active catalyst of polymerization of TO but, as was shown above, there are practically no active propagating eentres in the liquid phase (filtration experiments) and the ultraviolet spectrum contains a band at )~max-~262 n m (Fig. 8). Addition of easily hydrolysable organic halides brings about polymerization in the system however, and the absorption band of the hexachloroantimonate ion again appears in the ultraviolet spectrum. Let us now examine possible further reactions of the products of decomposition of the active centre to molecular forms. I t is reasonable to ~assume t h a t the equilibrium decomposition reaction (2) moves in the direction of formation of molecular forms as a result of embedding of polymer chains with chloromethyl end groups in the solid phase. It is evident t h a t SbC15 becomes combined in complexes with all the electron donor molecules in the system {monomer, impurities) and this can initiate polymerization of TO by the following mechanisms * formation of a zwitterion [16] O~:)+CH.--O(CH.O).--SbC1, /-~O\
SbCI..O~
~/.
-~
~---O /
-SbClr(O--CH,)
+ /---O\
(4)
formation of an auto-complex [16, 17] m~t
2 S b C I ~ . O C : ) -* SbC1,O--(CH.O).--OCH+SbCI, -
(5)
a hydride transfer (or chlorination) reaction [18. 19] O C : ~ - { - 2 S b C 1 , -~ O~oO~CH+SbC1,--t-HCI-t-SbCI.
(6)
a reaction similar to (6) ff benzene is present [20] ~ - ~ - ~ 2SbC1, -. /~N~/C1 ~-H+SbCI, -~-SbC1. and the following reactions if water is present SbCls~-SHlO ~ H,O+SbC150H + 0
(7) (8)
• Snmlar reaotmns must also occur as a result of interaction of SbCI~ with the polymer.
Polymerization of trioxan m solution
335
The band with ;tmax----252 nm can according to Neumann [12, 13] be assigned to SbClaOH- from reactions (8) or (9), or to SbC15(N~ (reaction (4)). Furthermore the product of reaction (5), i.e., SbC140~ could also absorb in t h a t region. The antimony derivative SbC14OCH3 (modelling SbC14OCH 3~), prepared by the method of reference [21], does in fact absorb at ;Lmax-~252 nm. Therefore this band cannot be assigned unequivocally to any one of reactions (4)-(9), though reactions (6) and (7) obviously cannot be responsible for the appearance of this absorption band. In order to assess the role of water in reactions (8) and (9) a study was made of the ultraviolet spectra of the products of interaction of SbC15 with TO, DO and methylal under "moist" conditions ([H20]~_3× 10 -3 mole/1.) and with DO and methylal under " d r y " conditions ([H30] ~<5 × 10 -4 mole/1.). I t was found t h a t under moist conditions the band with ~max=252 nm appeared rapidly (Fig. 8, curves I and 2), whereas under dry conditions a band with ~max----235 n m appeared rapidly (similar to the spectrum obtained in reference
[22]). Note that a similar spectral pattern was found in the case of polymerization of DO in the presence of EtaO+SbCl~ [23]. Under dry conditions a band with ~max-----230n m rapidly appeared and under dry conditions one with 2max----255nm. The appearance of the band with ~max= 252 nm only in the presence of quantities of water commensurate with the catalyst concentration means t h a t it is produced by the SbC15 (OH)- eounterion. Thus the sharp fall in polymerization rate t h a t occurs under moist conditions (Fig. 7) and the corresponding appearance of a band with 2max at 252 n m can be explained by hydrolysis of SbCI* (reactions (8) and (9)) and formation of ionic species of low or no reactivity in polymerization, for example of the types + 0 +/H H--O~__O~;--CH2--O~H; HsO+SbClsOHThese species are in equilibrium with active polymerization centres, which when the concentration of water in the system is high are present in very low concentration however. The addition of easily ionizable organic halides causes a shift in the equilibrium in the direction of formation of ionic species that are active in polymerization (Fig. 7), for example + /---\0
/~0\
CH,OCHICI
Thus under moist conditions the main cause of chemical deactivation of the active centres is decomposition to molecular species and reaction of these with water. At the same time water inhibits reactions (6) and (7), which occur under dry conditions [23], beeanse water is an effective competitor of linear and cyclic acetals in reactions with SbCl 5. *
Transla~
by E . O. l ~ ] e s
* Hydrolysis of the cou~termn SbCl~itself occurs at a low rate at room temperature [13].
336
V . V . KOl~S~AIr et aZ.
REI:ERENCES 1. Yu. N. 8MIRNOV, V. P. VOLKOV, V. I. IRZHAK and N. S. YENIKOLOPYAN, Dokl. Akad. Nauk SSSR 190: 1403, 1970 2. Yu. N. 8MIRNOV, V. P. VOLKOV and N. S. YENIKOLOPYAN, Plast. massy, No. 2, 8, 1971 3. N. S. YENIKOLOPYAN and S. A. VOL'FSON, Khimiya i tekhnologlya poliformaldeg~da (Chemistry and Technology of Polyformaldchyde). p. 84, "Khimiya", 1968, 4. P. ONYON and K. TAYLOR, European Polymer J. 1: 133, 1965 5. L. LEECE and M. BAUMBER, Polymer 5: 380, 1964 6. J. OLAH, W. TOLGYESI and 8. KUHN, J. Amer. Chem. Soc. 85: 1328, 1963 7. W. PACIKA, Tetrahedron 22: 557, 1966 8. F. R. JONES and P. H. PLESCH, J. Chem. Soc., D 21: 1231, 1969 9. N. BONNER and W. GOISHI, J. Amer. Chem. Soc. 88: 85, 1961 10. B. A. ROZENBERG, Dissertation, 1965 11. E. L. BERMAN, Dissertation, 1971 12. H. NEUMANN, J. Amer. Chem. Soc. 76: 2611, 1954 13. S. WILI.I8 and H. NEUMANN, J. Amer. Chem. Soe. 91: 2924, 1969 14 E . F . OLFANIK, O. A. PLECHOVA, V. P. NOVOTORTSEV, V. P. VOLKOV, Ire. F. RAZ• VAD0VSRTI and N. S. YENIKOLOPYAN, Dokl. Akad. Nauk SSSR 199: 368, 1971 15. N. KALFOGLOU and M. SZWARC, J. Phys. Chem. 72: 2233, 1968 16. H. MEERWEIN, D. DEI.F8 and H. MORSCHEL, Angew. Chem. 72: 927, 1960 17. B. A. ROZENBERG, Yc. B. LYUDVIG, T. M. ZVEREVA, A. R. GANTM3tWHER and S. S. I~EI~VEDEV, Vysokomol. soyed. 7: 269, 1965 (Translated in Polymer Sei. U.S.S.R. 7: 2, 296, 1965) 18. S. SLOMKOWSKI and 8. PENCZEK, J. Chem. Soe., D 22: 1347, 1970 19. A. LEDWITH, Advan. Chem. Ser. 91: 317, 1969 20. P. KOVACIC and A. SPARKS, J. Org. Chem. 28: 972, 1963 21. A. MEUWSEN and H. 1KEGLING, Z. anorg, und allgem. Chem. 285: 262, 1956 22. P. KUBIS£ and 8. PENCZE~ Makromolek. Chem. 144: 169, 1971 23. Ye. B. LYUDVIG, Ye. L. BERMAN, Z. I. NYSENKO and V. A. PONOMARENKO, Vyso. komol, soyed. A18: 1375, 1971 (Translated in Polymer Sei. U.S.S.R. 18: 6, 1546, 1971)
ROTATIONAL ISOMERISM IN POLYARYLATES OBTAINEI} BY LOW TEMPERATURE POLYESTERIFICATION* V. V• KORS~AW, S. V. VINOGRADOVA, V. A. BAs~Ev, V. A. VASIL'~.v, A. A. ASKAVSKII,T. A. BABVSHKINA,G. L. SLONIMSKII, G. K. SEmi, ¥v. K. GODOVSKII a n d Y~,. S. OBOLO~KOVA Institute for Elemento-orgamc Compounds, U.S.S.R. Academy of Sciences
(Re~ived 14 ~ebruary 1972) I t has been found that, when low temperature polyesterificatlon is carried out, favourable condatlons are created for the rcalizatlon of block sequences of particular isomeric forms of the o, o'.disubstltuted blsphenol residue. The nature of the reac* Vysokomol. soyed. AI6: No. 2, 291-298, 1974.
(Recewed 1 Febr~ary 1972) As a result of kinetic and sp~ctrophotometrm studms of the polymerizatmn of trmxan with B+A - salts as catalysts (where B + = P h s C +, CHACO+ or CH3OCH +, a n d A - ~ S b C I ~ or SbF~) it has been found t h a t t e r m l n a t m n of the growing chains revolves both physical and chemmal processes the ratm of the two being dependent on the structure of the active eentres and on the condltmns of polymerizatmn.
IT HAS been reported [1, 2] previously that when trioxane (TO) is polyInerized in benzene with trityl hexafluoroantimonate (THFA) as catalyst, as well with some other catalysts in other solvents [3], decay of active centres occurs, resulting in incomplete conversion of the monomer. Decay of active centres can occur b y a chemical process (such as chain termination on the solvent, impurities or the eounterion [4]) and also b y the physmal process of enclosure of the active centres within the mass of polymer [5], which must be a specific feature of heterogeneous polymerization/ Results that assist in solution of this problem are presented in the present paper. EXPERIMENTAL The TO was successively refluxed over then distilled from KOH, BaO a n d p o t a s s m m sodmm alloy. Methylene chloride and benzene were purffied b y the usual method and were then refluxed over a n d distilled from PiOb and Call2. 1,3-Dloxolane (DO) and methylal were redlstlllcd from sodmm and CaHz. n-Octane, whmh was used as a n internal standard, was refluxed over and redlstdled from p o t a s s m m - s o d m m alloy. Trltyl hexafluoroantlmonate was prepared from t n t y l fluoride and a n t n n o n y pentafluoride m trdiuorotrlchloroethane, m.p 209-210 ° (deeomp.), according to the hterature m.p. 211 ° [16]. T n t y l hexachloroantunonate (THCA) was obtained b y the method of reference [7] and methoxymethyl hexachloroantimonate (MMHCA) was prepared from chloromethyl * Vysokomol. soyed. A16: No. 2, 283-289, 1974. t The polymerization of t r m x a n m orgamc solvents m a heterogeneous process, with separation of crystalline polymer as a prempltate 327
328
Y ~ . N . SMZR~OV e~ al.
ether (CME) and SbC15 in heptane, m a high-vacuum apparatus. After the solvent and excess CME had been pumped off the catalyst was left m the form of a loose white powder. All the catalysts were made up as 0 1 M solutzons m mtrobenzene, whmh had been dlstdled i n v a c u o over P205 and then over BaO. The solution of MMHCA was stored at the temperature of dry me for up to 3 weeks and the other solutions were stored at room temperature Polymerization was earrmd out m a three.necked, glass reactor, fitted wzth,a heating jacket, a tap for removal of test samples, a stirrer and a fluoroplast seal. The solutmn of TO was transferred from a storage vessel to a measurmg cyhnder and then to the reactor. The other reactants were transferred by means of pipettes, m a countercurrent of carefully dined argon Before use the reactor ~ as washed at 50 ° with the TO solutmn. Test samples m the form of suspensmns were taken off into measuring cylinders contannng a solution of trmthylamme m benzene The polymer was then filtered off on a smtered glass filter, on whmh it was successively washed with methanol, water, acetone and ether, and finally drmd to constant weight ~n v a c u o at 40-60 °. The filtrate was analysed for TO by the GLC method, using an internal standard (condltmns of separatmn: KhL-4 chromatograph, column length 1.5 m, internal diameter 1 8 ram, packed with poly(ethylene glycol adlpate) on II~Z-600, temperature of separatmn 115°, flow rate 60 ml/mm). Ultrawolet spectra were recorded~m a CFD-2 instrument, using a cell of tlnekness 3 ram, whmh was filled rather in an argon contamer ("mozst condltmns") or under lugh vacuum ("dry condltmns"l. RESULTS AND DISCUSSION S t u d y of t h e d e p e n d e n c e of the m a x i m a l yield of p o l y m e r on t h e initial c a t a l y s t c o n c e n t r a t i o n in p o l y m e r i z a t i o n of TO in solution in benzene, c a t a l y s e d b y T H F A , has s h o w n [1] t h a t in these circumstances the active centres d e c a y according to the linear law Co--------(kt/kp) In (1--g~/~p)
(1)
where Co is the initial c a t a l y s t concentration, ~ t h e m a x i m a l degree of conversion of m o n o m e r , ge t h e equilibrium degree o f conversion of liquid m o n o m e r in t h e solid p o l y m e r (at 50 °, with [ T O ] = 2 . 1 mole/1, ae~--0"96), a n d k t a n d k, the r a t e c o n s t a n t s of c h a i n t e r m i n a t i o n a n d p r o p a g a t i o n respectively. A linear law of d e c a y is f o u n d also in c o p o l y m e r i z a t i o n of TO with DO (at a c o n c e n t r a t i o n o f t h e c o m o n o m e r of 0.1-0.2 mole/1.) in t h e presence of T H F A a n d T H C A (Figs. 1 a n d 2). Similar results were o b t a i n e d also in h o m o p o l y m e r i z a t i o n of TO in t h e presence of acetyl h e x a f l u o r o a n t i m o n a t e ( A H F A ) The linear n a t u r e of t h e d e c a y of active centres does n o t in itself indicate the actual m e c h a n i s m of d e c a y because it could be a t t r i b u t a b l e to b o t h chemical a n d physical processes. I t is obvious h o w e v e r t h a t increase in t h e p o l y m e r i z a tion t e m p e r a t u r e should bring a b o u t an increase in the rate of chemical processes associated with d e c a y of active eentres a n d a fall in t h e rate of a physical process. I t is seen from Fig. 3 t h a t t h e m a x i m a l yield of p o l y m e r increases as t h e t e m p e r a t u r e is increased. A n Arrhenius plot of t h e t e m p e r a t u r e dependence of t h e ratio o f t h e t e r m i n a t i o n a n d p r o p a g a t i o n rate constants, f o u n d f r o m
Polymerxzation of trioxau m solution
329
equation (1), gives a complex curve (Fig. 1, curve 4). At 10--35 ° t h e c u r v e is approx4mately a straight line and the difference between the energies of activation for chain propagation and termination is 15 kcal/mole, b u t as the temperature is increased the Arrhenius curve bends and the difference in the aetivation energies gradually falls. c~
05~ 02
a
/
= "--
"
=~
--
"
"-
/osE/-~.J~p)
2 il
"- 5
"--
.og 0 5
....~
,
02
Y 07
x~
r 0
~ 50
t t [0,2 150 ~ ' m e , rain
FIG. 1
1 200
0
I0
20 YO G " fO~ mo/e//..
FIG. 2
FIG. 1. Kinetic curves of polymerization of TO xn benzene at 50°, catalysed by THFA (a) and THCA (5) at [TO]----2.1mole/L, [DO]=0.1 mole/h and G0× 10-3----0 2 (•); 0.15 (2); 0.1 (3); 0 05 (4}; 0.025 (5); 1 (6); 2 (7}; 3 (8} and 4 mole/1. (9). FIG. 2. Dependence of log (1--a~/~e) on co m homopolymerlzatlon of TO by THFA (1) and in copolymerxzatlon of TO with 0 1 mole/l, of DO by THFA (2} and THC/k (3). I t should be noted that in the presence of catalysts containing SbF~ as the counterion the dependence of the maximal yield on catalyst concentration fits equation (1) at both low and higher temperatures, i.e., the apparent kinetic law of decay of active centres does not alter in this interval of temperatures, although a change in the mechanism of the termination reaction could occur. The nature of the temperature dependence does in fact indicate a complex mechanism of decay of active centres and bearing in mind the fact that the energy of activation for chain growth in cationic polymerization of oxygen-containing ring compounds does not as a rule exceed 15 kcal/mole, one of the decay processes (the low temperature section of the curve) must have an activation energy that is either close to zero or is negative. From this it m a y be supposed that the relationship found in this range of temperatures is connected mainly with the physical aspect of the decay of active centres. I f this suggestion about the physical nature of deactivation is correct, factors causing increase in the segmental mobility of the polymer chains should bring about a decrease in the rate of decay of active centres, and hence should increase the maximal yield of polymer. It was in fact found that increase in the
Yu.
330
N. SMm~OV
e$ a/.
t e m p e r a t u r e of a p o l y m e r i z a t i o n m i x t u r e in which p o l y m e r i z a t i o n has s t o p p e d causes p o l y m e r i z a t i o n t o r e s t a r t * (Fig. 3). T h u s it m a y be concluded f r o m the above results t h a t physical effects p l a y t h e p r e d o m i n a n t role in t e r m i n a t i o n of growing chains a t low t e m p e r a t u r e s . T h e deviation f r o m linearity of t h e Arrhenins plot of t h e r a t e c o n s t a n t ratio a t high t e m p e r a t u r e s (Fig. 4, curve 1) is obviously due increase in the role o f
0"9
b'-" . . . . . . .
0 0"5
~
-
-
Cl
0"1 I
0
I
50
I
100 /50 T/me, m/n
I
1
200
ZSO
FIO. 3. Ktuet,c curves of polymerization of TO m benzene by AHFA at 10° (•); 20° (2); 30° {3) and 50 ° (4); [TO]-----1mole/], and U0-----2× 10-' mole/]: a--temperature raised to 70°, b-- 0 2 mole/], of methylal added.
7"q
0"8
O'Z t
J'0
I
I
3"q
i
io3/r
]
J'8
Fxo. 4. Arrhemus plots of the ratio kp//~ m homopolymenzation of TO (1, 3) and m eopolymerization of TO with 0.2 mole/1, of DO (2) by A.T~I~A {A); THFA {B, G) and THCA (D). * A ~lml!ar effect is obtained when active compounds capable of producing an active centre m the liquid phase, by chum transfer, are added during the course of polymerL~ation.
331
Polymerlzatlon of tnoxan in solution
chemical processes in termination of the growing chains, namely decomposition of the ion pairs to molecular form and]or their hydrolysis b y water, which is usually present in the system at concentrations up to 2 × 10 -3 mole]l. The energy of activation for such processes is usually fairly high ( ~ 2 0 kcal/mole) [8, 9]. I t would be expected that a more basic comonomer (such as DO) would stabilize the active centres * against hydrolysis and decomposition of the ion pairs as a result of greater delocalization of the charge on the oxonium ions.
0,#'
/
OJ 0"3 0
I
I
JO
fO0
i
150 T/me, rn[n
I
I
ZOO
250
FIc. 5. Kinetic curves of polyme~zatlon of TO m benzene by MMHCA at 7° (•); 15° (2); 25° (3) and 35° (4); ]TO]= 1 mole/L and c0=3× 10-3 molefl. I t was found in fact that in the presence of DO the relative rate of decay of active centres obeys the Arrhenius equation over a much wider range of temperatures (20-65 °) ~f than in homopolymerization (Fig. 4, curve 2). This means that in the presence of DO in this range of temperatures the active centres decay mainly b y a physical process and chemical conversion of these centres does not occur to a n y appreciable extent. Thus the well known rule that the reactivity (basicity) of monomers and the reactivity of the corresponding active centres affect the propagation reaction in the opposite w a y [10] can be extended to the reaction of deactivation of these centres, i.e., to the rate of hydrolysis and decomposition of the ion pairs. It follows from this, for example, that the rate of these reactions (the counterion being the same) should fall in the order of the monomers: T O ~ D O ~ T H F , and this is fully borne out b y experimental observation [I0, Ii]. The resistance of ion pairs to chemical change is dependent on the structure not only of the cation, but also of the counterion. To find the effect of the nature of the counterion on the stability of the active centres, .we studied the polymerization of T O under the influence of catalysts in which the counterion was SbCl~. In view of the fact that SbCl~ is more strongly * Use was made of the rule of adchtlmty of the reactlmty (baslmty) of the monomer and the reactivity of the corresponding propagating oentre [10]. t A smnlar stabilizing effect m obtained by addition of methy]al and other ohgoformals.
332
Y~. N. SuTawov e~ at.
nucleophl]ic than SbF~, it would be,expected that the part played by deactivation of active centres as a result of chemical change involving the counterion would be increased substantially. It is this that provides the explanation of the difference in the relative decay rate constants with SbF~ and SbGl~ as counterions, the smaller increase in the maximal yield of polymer with increase in temperature when the dioxolenium salt I~IM~CA is used as catalyst (Fig. 5) and the smaller difference between the energies of activation for propagation and termination when SbCI~ is used as the counterion (Fig. 4, curve 3). When TO was poly,7 I /
0-5
O
0
Z
g.h'
O , m
o I
I
!
60
/00
!
Time
I
150 ~rain
ZOO
FzG. 6. Kmehc curves of polymerization of TO m benzene at 20° by MMHCA, with [ C M E ] × 1 0 - ~ = 0 (•); 2 ( 2 ) a n d 5 mole/l. (3); [TO]=I
mole/1, and v0----2×10 -3 mole/1.
merized in solution in benzene and in CHIC12, with M~HCA as catalyst, it was clearly demonstrated that chemical deactivation of the active centres occurs during the course of the reaction. The first stage in this process is the reversible reaction of decomposition of the active centre by reaction between the cation and eounterion, with formation of molecular compounds ~OCH+SbCI~ ~ ~OCH~CI-~SbC15
(2)
This is shown by the following facts. 1) The addition of easily hydrolysable organic halides such as acetyl chloride and CME brings about a substantial increase in the rate of polymerization of TO (Fig. 6). This effect occurs when the addition is made in the beginning or during the course of polymerization. 2) It is known [12, 13] that the SbCl~ anion in the free state and in the form of an ion pair gives an absorption band at ~max=272 nm. When polymerization of TO is eatalysed by hexachloroantimonates having stable organic cations (Et30 +, Ph3C+ and CHACO+) the intensity of the 272 n m band falls and new bands appear at shorter wavelengths (230-250 nm). When organic halides (CHsCOCI and CHaOCH~C1) are added to the polymerization solution, however, the intensity of absorption at ~max----272 nm again increases substantially. When PhaCC1 is added a band appears in the visible region of the spectrum (2max=412 nm), corresponding to absorption by the triphenylmethyl cation [14, 15].
Polymerization of trloxan in solution
333
As an alternative explanation of the above spectroscopic results chain transfer to R - - H a l ~ OCH~SbCI~Ph~CC1
(3)
~. ~ OCH2CI+Ph~C+SbCI~ m a y be suggested.
05 0 f
o/
0
I
5O
I f~O
lO0
I 2O0
7-Zme , r a i n
FIG. 7. I ~ n e t , c curves of polymerization of TO m CH,CI, a t 20 ° b y SbCls, without a d ditives (1); with addition of CME a t the b e ~ n n m g (2) and during the course of polymerization (3); [TO]-----2-3 mole]L; co=10 -8 mole/l.; [ H i O ] = 4 × 10 -8 mole/1, and [ C M E ] = 5 × 1 0 - ' mole/1.; a denotes tho point of addition of CME.
This reaction does not in fact occur however, as was shown b y addition of triphenylmethyl chloride and CME to the mother liquor obtained b y filtration of the polymerization solution. I t was found t h a t polymerization does n6t occur 17
'f
/ \\~. 4
i
I-
2ZO
Z-%i _\
I
I
Z60
I
~'~
JO0
I
~ ,nm
FIG. 8. Ultraviolet spectra of the products of reaction of SbC16 with methylal (1); TO (2) a n d CHsO(CHsOhCH, (8), and of the SbCI~-TO-CHIClfPhaCC1 (d) a n d TO-M~rRCA-CH,Cll systems (~) after 2 hr a t 30°; [SbCI~]=lX 10 -s mole/l, a n d [ H . O ] = 4 X 10 -s mole/L; 20 °.
•334
Yu. N. SMn~-~ove$ al.
in the mother liquor, but it begins again when alkyl halides are added. As has already been stated, the same effect is obtained when Mkyl halides are added to the polymerization system {Fig. 7). Thus the above experimental evidence shows t h a t in this polymerization system decomposition of the active centre to molecular forms occurs. Moreover it is Mso evident from these experiments t h a t the active centres are localized mainly in the solid phase, and the antimony pentachloride produced by decomposition of the active centre is reversibly converted to some less active compounds. The latter conclusion is based on the following facts. Antimony pentachloride is a fairly active catalyst of polymerization of TO but, as was shown above, there are practically no active propagating eentres in the liquid phase (filtration experiments) and the ultraviolet spectrum contains a band at )~max-~262 n m (Fig. 8). Addition of easily hydrolysable organic halides brings about polymerization in the system however, and the absorption band of the hexachloroantimonate ion again appears in the ultraviolet spectrum. Let us now examine possible further reactions of the products of decomposition of the active centre to molecular forms. I t is reasonable to ~assume t h a t the equilibrium decomposition reaction (2) moves in the direction of formation of molecular forms as a result of embedding of polymer chains with chloromethyl end groups in the solid phase. It is evident t h a t SbC15 becomes combined in complexes with all the electron donor molecules in the system {monomer, impurities) and this can initiate polymerization of TO by the following mechanisms * formation of a zwitterion [16] O~:)+CH.--O(CH.O).--SbC1, /-~O\
SbCI..O~
~/.
-~
~---O /
-SbClr(O--CH,)
+ /---O\
(4)
formation of an auto-complex [16, 17] m~t
2 S b C I ~ . O C : ) -* SbC1,O--(CH.O).--OCH+SbCI, -
(5)
a hydride transfer (or chlorination) reaction [18. 19] O C : ~ - { - 2 S b C 1 , -~ O~oO~CH+SbC1,--t-HCI-t-SbCI.
(6)
a reaction similar to (6) ff benzene is present [20] ~ - ~ - ~ 2SbC1, -. /~N~/C1 ~-H+SbCI, -~-SbC1. and the following reactions if water is present SbCls~-SHlO ~ H,O+SbC150H + 0
(7) (8)
• Snmlar reaotmns must also occur as a result of interaction of SbCI~ with the polymer.
Polymerization of trioxan m solution
335
The band with ;tmax----252 nm can according to Neumann [12, 13] be assigned to SbClaOH- from reactions (8) or (9), or to SbC15(N~ (reaction (4)). Furthermore the product of reaction (5), i.e., SbC140~ could also absorb in t h a t region. The antimony derivative SbC14OCH3 (modelling SbC14OCH 3~), prepared by the method of reference [21], does in fact absorb at ;Lmax-~252 nm. Therefore this band cannot be assigned unequivocally to any one of reactions (4)-(9), though reactions (6) and (7) obviously cannot be responsible for the appearance of this absorption band. In order to assess the role of water in reactions (8) and (9) a study was made of the ultraviolet spectra of the products of interaction of SbC15 with TO, DO and methylal under "moist" conditions ([H20]~_3× 10 -3 mole/1.) and with DO and methylal under " d r y " conditions ([H30] ~<5 × 10 -4 mole/1.). I t was found t h a t under moist conditions the band with ~max=252 nm appeared rapidly (Fig. 8, curves I and 2), whereas under dry conditions a band with ~max----235 n m appeared rapidly (similar to the spectrum obtained in reference
[22]). Note that a similar spectral pattern was found in the case of polymerization of DO in the presence of EtaO+SbCl~ [23]. Under dry conditions a band with ~max-----230n m rapidly appeared and under dry conditions one with 2max----255nm. The appearance of the band with ~max= 252 nm only in the presence of quantities of water commensurate with the catalyst concentration means t h a t it is produced by the SbC15 (OH)- eounterion. Thus the sharp fall in polymerization rate t h a t occurs under moist conditions (Fig. 7) and the corresponding appearance of a band with 2max at 252 n m can be explained by hydrolysis of SbCI* (reactions (8) and (9)) and formation of ionic species of low or no reactivity in polymerization, for example of the types + 0 +/H H--O~__O~;--CH2--O~H; HsO+SbClsOHThese species are in equilibrium with active polymerization centres, which when the concentration of water in the system is high are present in very low concentration however. The addition of easily ionizable organic halides causes a shift in the equilibrium in the direction of formation of ionic species that are active in polymerization (Fig. 7), for example + /---\0
/~0\
CH,OCHICI
Thus under moist conditions the main cause of chemical deactivation of the active centres is decomposition to molecular species and reaction of these with water. At the same time water inhibits reactions (6) and (7), which occur under dry conditions [23], beeanse water is an effective competitor of linear and cyclic acetals in reactions with SbCl 5. *
Transla~
by E . O. l ~ ] e s
* Hydrolysis of the cou~termn SbCl~itself occurs at a low rate at room temperature [13].
336
V . V . KOl~S~AIr et aZ.
REI:ERENCES 1. Yu. N. 8MIRNOV, V. P. VOLKOV, V. I. IRZHAK and N. S. YENIKOLOPYAN, Dokl. Akad. Nauk SSSR 190: 1403, 1970 2. Yu. N. 8MIRNOV, V. P. VOLKOV and N. S. YENIKOLOPYAN, Plast. massy, No. 2, 8, 1971 3. N. S. YENIKOLOPYAN and S. A. VOL'FSON, Khimiya i tekhnologlya poliformaldeg~da (Chemistry and Technology of Polyformaldchyde). p. 84, "Khimiya", 1968, 4. P. ONYON and K. TAYLOR, European Polymer J. 1: 133, 1965 5. L. LEECE and M. BAUMBER, Polymer 5: 380, 1964 6. J. OLAH, W. TOLGYESI and 8. KUHN, J. Amer. Chem. Soc. 85: 1328, 1963 7. W. PACIKA, Tetrahedron 22: 557, 1966 8. F. R. JONES and P. H. PLESCH, J. Chem. Soc., D 21: 1231, 1969 9. N. BONNER and W. GOISHI, J. Amer. Chem. Soc. 88: 85, 1961 10. B. A. ROZENBERG, Dissertation, 1965 11. E. L. BERMAN, Dissertation, 1971 12. H. NEUMANN, J. Amer. Chem. Soc. 76: 2611, 1954 13. S. WILI.I8 and H. NEUMANN, J. Amer. Chem. Soe. 91: 2924, 1969 14 E . F . OLFANIK, O. A. PLECHOVA, V. P. NOVOTORTSEV, V. P. VOLKOV, Ire. F. RAZ• VAD0VSRTI and N. S. YENIKOLOPYAN, Dokl. Akad. Nauk SSSR 199: 368, 1971 15. N. KALFOGLOU and M. SZWARC, J. Phys. Chem. 72: 2233, 1968 16. H. MEERWEIN, D. DEI.F8 and H. MORSCHEL, Angew. Chem. 72: 927, 1960 17. B. A. ROZENBERG, Yc. B. LYUDVIG, T. M. ZVEREVA, A. R. GANTM3tWHER and S. S. I~EI~VEDEV, Vysokomol. soyed. 7: 269, 1965 (Translated in Polymer Sei. U.S.S.R. 7: 2, 296, 1965) 18. S. SLOMKOWSKI and 8. PENCZEK, J. Chem. Soe., D 22: 1347, 1970 19. A. LEDWITH, Advan. Chem. Ser. 91: 317, 1969 20. P. KOVACIC and A. SPARKS, J. Org. Chem. 28: 972, 1963 21. A. MEUWSEN and H. 1KEGLING, Z. anorg, und allgem. Chem. 285: 262, 1956 22. P. KUBIS£ and 8. PENCZE~ Makromolek. Chem. 144: 169, 1971 23. Ye. B. LYUDVIG, Ye. L. BERMAN, Z. I. NYSENKO and V. A. PONOMARENKO, Vyso. komol, soyed. A18: 1375, 1971 (Translated in Polymer Sei. U.S.S.R. 18: 6, 1546, 1971)
ROTATIONAL ISOMERISM IN POLYARYLATES OBTAINEI} BY LOW TEMPERATURE POLYESTERIFICATION* V. V• KORS~AW, S. V. VINOGRADOVA, V. A. BAs~Ev, V. A. VASIL'~.v, A. A. ASKAVSKII,T. A. BABVSHKINA,G. L. SLONIMSKII, G. K. SEmi, ¥v. K. GODOVSKII a n d Y~,. S. OBOLO~KOVA Institute for Elemento-orgamc Compounds, U.S.S.R. Academy of Sciences
(Re~ived 14 ~ebruary 1972) I t has been found that, when low temperature polyesterificatlon is carried out, favourable condatlons are created for the rcalizatlon of block sequences of particular isomeric forms of the o, o'.disubstltuted blsphenol residue. The nature of the reac* Vysokomol. soyed. AI6: No. 2, 291-298, 1974.