INTERRELATIONSHIPS IN THE SYNTHESIS OF HIGH-MOLECULAR POLYARYLATES IN THE ABSENCE OF SOLVENTS* V. 1~I. S A w , o r and L. B. SoxoT.ov ¥1adimir Scientific-Research I n s t i t u t e of Synthetic Resins
(Received 22 July 1965)
IT is well known that the high melting points of most polyarylates prevents preparation of these by polycondensation of acid chlorides with diols because the reaction mixture hardens soon after the onset of reaction, which cannot then be conducted in the melt without decomposition, and consequently polycondensation stops at a very early stage [1]. It is therefore of interest of synthesize these polymers at temperatures below their melting points in the absence of solvents, i.e. in the solid phase. The trend toward high melting, heat resistant polymers is producing increasing interest in solid-phase polycondensation. Studies in this field are not only of theoretical interest, the results can be applied to the production of condensation polymers. Polycondensation in the solid phase can obviously also be of definite value in the production of articles from high melting polymers by carrying out the reaction directly in the performed articles. The literature now contains reports on a fairly large number of polymers obtained by polycondensation in the solid phase and on studies of the interrelationships and specific features of this method of conducting the reaction [2-7]. In our work we set to study a number of the basic relationships in solid-phase polycondensa~ion, using the preparation of polyarylates from a dicarboxylic acid chloride and a. diol, in order to examine the possibility of producing these polymers with high molecular weights. The use of acid chlorides in polycondensation reactions is very widespread at the present time, but solid-phase polycondensation involving these has not been described. For this reason we felt that it would be advisable to publish some of our earlier (1960-1961) results. RESULTS AND DISCUSSION
We studied the relationships of solid-phase polycc,ndensation with low-molecular products of condensation of terephthalyl chloride with 2,2-bis-(4-hydroxyphenyl)propane (diphenylolpropane), which can be obtained by fusion of these reactants or by reaction in solution at an elevated temperature. * Vysokomol. soyed. _4,9: No. 7, 14i9-1423, 1967. 1587
1588
V. M. SAVINOVand L. B. SOKOLOV
Thus in our case polycondensation in the solid phase was, as it were, a second stage in the over-all process of production of a high-molecular polyester. The second method is worthy of consideration for the purpose of preserving the equimolar ratio of the reactants, which is best for production of the original lowmolecular polyesters, and this was the method we used (the solvent was chlorobenzene and the reaction temperature was the boiling point of the solvent). Terephthalyl'chloride was prepared from the acid and thionyl chloride and purified by recrystallization from n-octane; m.p. 80-81 °.
2 3 8O
.g
~0
f
20 ooi 20
r iO0
180 '
3 oT°c
1. Thermomechanlcal curves of low-molecular polyesters of different viscosity (load 3.4 kg]cm'). 1--[~]= 0.04, 2--[~]= 0.06, 3--[~]=0.12, 4--[~]=0.17, 5--[~]--0.22.
Fro.
Diphenylolpropane of m.p. 155-156 ° was obtained b y repeated recrystallization of the commercial product from 50% acetic acid. After evaporation of the solvent the product was dried i n vacuo and used for further polycondensation. The temperature interval of the subsequent condensation was chosen on the basis of results of thermomechanical study of the low-molecular polyesters (it was always below their softening points). As a rule for futher condensation we used polyesters with [t/]----0.18-0.22 (in tetrachloroethane--phenol at 20°), which according to the thermomechanical data (Fig. 1) have softening points above 300 °. Consequently we studied the effect of reaction temperature on molecular weight up to 300 °. The results are given in the Table, from which it is seen t h a t the viscosity increases steadily with increase in temperature. The Table also shows that there is no advantage in carrying out the reaction i n vavuo in comparison with an atmosphere of nitrogen. This is because removal of the liberated hydrogen chloride from the reaction zone is not an essential condition for increasing the degree of reaction, because it is irreversible. Therefore for our purpose solid-phase polycondensation can be carried out in any inert atmosphere. The subsequent use of vacuum in most experiments was merely for convenience.
Interrelationships in synthesis of high-molecular polyarylates
1589
Dp.PmCD~.~rc~. OF VISCOSITY OF POLYESTE~ O~ REAOTIOlq TEMPERATURE (Reaction time 180 rain) [t/] at 20 °
Reaction temperature, °C
in nitrogen
Initial polyester 200 220 250 280 290 300
in
vacuuIn
0.20 0.34 0.35 0.44 0.64 0.76 0.84
0"22 0"37 0"38 0"41 0-65 0"76 l~ot com,letely soluble
B e a r i n g in m i n d t h e f a c t t h a t our chosen r e a c t i o n t i m e (3 h r in t h e case g i v e n in t h e Table) is n o t t h e t i m e for c o m p l e t e r e a c t i o n (Fig. 2a) it m a y be considered t h a t p o l y c o n d e n s a t i o n in t h e solid p h a s e can p r o d u c e p o l y e s t e r s o f sufficiently a O8
o
'I 2
0.4
08
0
I
120
]
2zlO
I
360
i
420
Time, min O8
~
4
O.Z/
! °0200
I
r
I
220
200
2BO
J
280 T,°O
I
J
1
80 40 A, moZe%
0
40
f
B,mo% el 80
FIG. 2. Dependence of viscosity of the polyester: a - - o n reaction time: 1--in v~uo at 290 °, 2--in curren~ of nitrogen at 200°; b--on reaction temperature (reaction time 3 hr) for polyester with- 1 -- COC1 and 2-- COOH end groups; c -- on ratio of reactants (reaction time 3 hr): 1-- polyesters prepared in refluxing chlorobenzene (original, lowmolecular polyesters), 2-4--polyesters prepared from the corresponding low-molecular polyesters at 200 °, 250 ° and 300 ° respectively, 5--published data [8] for a polyester prepared in a high-boiling solvent; A -- excess acid chloride, B - - excess diphenylolpropane. h i g h m o l e c u l a r weight, s u i t a b l e for c o m m e r c i a l use, a n d t h a t b o t h t h e r e a c t i o n t e m p e r a t u r e a n d t i m e are quite s u i t a b l e for p r a c t i c a l e x p l o i t a t i o n o f t h i s process.
1590
V. ~I. SAwsov and L. B. So~:oLov
When considering the effect of temperature on molecular weight attention must be given to the fact that according to existing data [8] when this reaction (terephthalyl ct~oride-diphenylolpropane) is carried out in solution it goes in the desired direction at temperatures not above 220 °. The reduction in molecular weight that occurs, when the temperature is raised above 220 ° is associated with degradative processes. Our results indicate, however, that when the reaction is conducted in the solid phase this temperature limit is not found. The viscosity of the polymer increases steadily at least up to 300° . The increase in viscosity of our polymer is most probably due to linear polycondensation, i.e. to reaction between OH and COCI groups. It may be assumed the decreased contribution of degradative process in our case is associated with the lower mobility of the polyarylate chains in the solid phase in comparison with their mobility in solution. It is evident, however, that at sufficiently high temperatures (290-300 °) in addition to linear polyeondensation one cannot ignore other processes that can give rise to increase in viscosity, such as branching and crosslinking, which are indicated if only by the incomplete solubility of the products thus obtained. It should be possible to follow the linear polycondensation reaction by the decrease in the quantity of the two functional groups with increase in the molecular weight of the polymer. We were not able however, to make use of quantitative determination of these in order to prove predominance of linear polycondensation, because it is difficult to determine end groups in this case. We therefore studied the change in chlorine content simultaneously with the change in viscosity, and also the effect of replacing the acid chloride end groups in the low-molecular polyesters by carboxyl groups, on the rate of increase in viscosity. Determination of the chlorine content of the polymer cannot give a quantitative indication of the content of terminal COC1 groups, both because the error in determining small amounts of the latter is considerable and because the polymer can contain chlorine in the form of hydrogen chloride, liberated during the time of reaction and trapped in some way within the polymer. Nevertheless, a reduction in chlorine content with simultaneus increase in the viscosity of the polyester would indicate to some extent predominance of a reaction involving the COC1 groups, the most probable of which is reaction with the hydroxyl groups (linear polycondensation). Our results are presented in Fig. 3. The same conclusion can be drawn t~om the results shown in Fig. 2b. Replacement of COC1 by COOH groups (by hydrolysis) should have caused either change in the rate of some reactions or complete suppression of some of them, which in turn should affect the viscosity of the polymer. However we find approximately the same rate of increase in viscosity with temperature in the two cases. From these results it may thus be concluded that the
Interrelationships in synthesis of high-molecular polyarylates
1591
chemical reaction is probably not the rate determining factor in solid-phase polycondensation. The use of the highly reactive acid chlorides (instead of acids or esters) is however advantageous both in preparation of the initial, low-molecular polyesters and in the subsequent polycondensation, because of the irreversibility of the reaction.
0.,2
oL
2O0
0.0
,
2~0
2 280 T,°g
,0.2
~G. 3. Temperature dependence of viscosity (1) and chlorine content (2) of the reac. tion products (reaction time 3 hr). As a result of this we were able to prepare polyesters with [ff] up to 1.0 comparatively easily. Equilibrium polyesterification (acid(ester)-diol) in the solid phase nsally gives less satisfactory results. For example, in reference [4], which describes the preparation of polyethyleneterephthalate in the solid phase, samples of the polyester with ~/sp (0.5% solution) of only about 0.1 (0.06-0.11) were obtained. It was of great interest to study the effect of the ratio of the reactants (diphenylolpropane and acid chloride) on molecular weight (viscosity) in preparation of the polyester in the solid phase. The results can provide information on side reactions. From the results shown in Fig. 2c it is seen, for example, that at sufficiently high temperatures (300 °) there is a marked increase in the viscosity of polyesters prepared at a high excess of one of the reactants. This increase in viscosity can scarcely be attributed entirely to linear polycondensation. Thus when high-molecular polyesters are prepared from products with a low degree of polycondensation at temperatures below their softening points, linear polycondensation occurs,complicated to some extent by side reactions. In the case studied by us these reactions occur to a significant extent only at temperatures in the region of 300 °, hence it is possible to obtain soluble highmolecular products at temperatures lower than this. The authors express their gratitude to G. A. Kuznetsova and L. N. Fomenko for making the thermomechanical measurements. CONCLUSIONS
(1) It is shown that when low-molecular products of reaction between terephthalyl chloride and 2,2-bis-(4-hydroxyphenyl) propane are heated below their melting points high-molecular polyesters are obtained.
1592
A.A. KAOH~T and YE. F. MERTVICHENKO
(2) The effect of temperature, reaction time, vacuum and the nature of t he end groups on the molecular weight (viscosity) of the polymer has been studied. (3) I t is shown t h a t at high temperatures linear polycondensation is complicated b y a n u m b e r of side reactions. Translated by E. O. P]~IL~PS REFERENCES
I. V. V. KORSHAK and S. V. VINOGRADOVA, Uspekhi khimii 30: 421, 1961 2. G. KI.ARE, Khimiya i tekhnologiya poliamidnykh volokon (The Chemistry and Techno. logy of Polyamide Fibres). p. 90, Gizlegprom., 1956 3. H. LUDEWIG, Germ. Dem. Rep. Pat. No. 9346; Chem. Abs. 52: 5883, 1958 4. A. I. KORETSKAYA, G. I. KUDRYAVTSEV and A. A. KONKIN, Vysokomol. soyed. 6: 434, 1964 (Translated in Polymer Sci. U.S.S.R. 6: 3, 481, 1966) 5. A. I. KORETSKAYA, G. I. KUDRYAVTSEV and A. A. KONKIN, VysokomoL soyed. 7: 980, 1965 (Translated in Polymer Sci. U.S.S.R. 7: 5, 1003, 1965) 6. B. A. BAGRAMYANTS, A. K. BONETSKAYA, N. S. YENIKOLOPYAN and S. M. SKURATOV, Sb. Geterotsepnye vysokomolekulyamye soyedineniya (Collected papers. Heterochain Macromolecular Compounds). p. 160, Izd. '~Nauka", 1964 7. A. V. VOLOI(HINA and G. I. KUDRYAVTSEV, Dokl. Akad. Nauk SSSR 127: 1221, 1959 8. V. V. KORSHAK, S. V. VINOGRADOVA, P. M. VALETSlgll and Yu. V. MIRONOV, Vysokomol. soyed. 3: 66, 1961 (Not translated in Polymer Sci. U.S.S.R.)
THE EFFECT OF THE PERMEABILITY OF CAPRON FIBRE ON THE KINETICS OF VAPOUR-PHASE GRAFT POLYMERIZATION OF ACRYLONITRILE AND ACRYLIC ACID* A. A. K~0HA~ and YE. F. I~ERTVICHENKO Institute of the Chemistry of Macromoleeular Compounds, Ukr. S.S.R. ~tcademy of Sciences
(Recelved 23 May 1966) DETERMINATION of the role of absorption and diffusion is of great importance in elucidation of the mechanism and kinetics of vapour-phase, post-polymerization of vinyl monomers on various materials. U n f o r t u n a t e l y there are as y e t few d ata in the literature for determining the conditions whereby diffusion of t he monomers to the macroradicals of t he substrate becomes t he controlling factor in graft polymerization. I n reference [1], in a st udy of t he vapour-phase graft polymerization of acrylonitrile on Capron fibre no account was t aken of the *Vysokomol. soyed. AP: No. 7. 1424-1428, 1967.