- Email: [email protected]
Synthesis of high-molecular weight liquid crystal polyesters based on a polycondensation mesogenic monomer
2882 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35.
A. Yu. BILIBIN et al.
S. TOMOTIKA, Proc. Roy. Soc. London A153: 302, 1936 A. ACRIVOS and T. S. LO, J. Fluid. Mech. 86: 641, 1978 J. M. RALLISON and A. ACRIVOS, J. Fluid Mech. 89f 191, 1978 M. GORDON, J. YERUSHALMI and R. SHINNER, Trans. Soc. Rheol. 17: 303, 1973 G. HESTRONI and S. HAVER, Rheol. Acta 9: 488, 1970 L. RAYLEIGH, Philos. Mag. 34: 145, 1892 C. Z. WEBER, Angew. Math. 11: 136, 1931 C. D. HAN, Multiphase Flow in Polymer Processing, pp. 228, 236, Acad. Press, N.Y., 1981 A. T. SERKOV and R. V. YEGOROVA, in: Teoriya formovaniya khimicheskikh volokon (Theory of Chemical Fibre Moulding). p. 21, Khimiya, Moscow, 1975 C. D. HAN and KAZUMORI FUNATSU, J. Rheol. 22: 113, 1978 N. HIRAI, J. Chem. Soc, Japan 75: 1019, 1954 S. P. PAPKOV, Khim. volokna, 3, 34, 1964 H. B. CHIN and C. D. HAN, J. Rheol. 24: 1, 1980 Yu. P. MIROSHNIKOV, M. K. PETROSIAN and V. N. KULEZNEV, Kolloidn. zh. 38: 279, 1976 Yu. P. MIROSHNIKOV, M. L. KAMINSKII and V. N. KULEZNEV, Kolloidn. zh. 41:1112, 1979 Yu. P. MIROSHNIKOV, A. M. GOL'MAN and V. N. KULEZNEV, Kolloidn. zh. 41: 1120, 1979 M. GOLDIN, J. YERUSHALMI, R. PREFFER and R. SHINNER, J. Fluid Mech. 38: 689, 1969
Polymer ScienceU.S.S.RVol. 26, No. 12, pp. 2882-2890, 1984 Printed in Poland
0032-3509/84 $10.00+ .00 © 1986PergamonPress Ltd.
SYNTHESIS OF HIGH-MOLECULAR WEIGHT LIQUID CRYSTAL POLYESTERS BASED ON A POLYCONDENSATION MESOGENIC MONOMER* A. Y u . BILIBIN, A. V. TEN'KOVTSEV, O. N. PIRANER a n d S. S. SKOROKHODOV High Molecular Compounds Institute, U.S.S.R. Academy of Sciences (Received 13 May 1983) This paper relates to the scheme proposed for the synthesis of high-molecular weight alkylene aromatic polyesters capable of forming liquid-crystal melts. This is the first time that the mesogenic dichloride, terephthaloyl-bis-(4-oxybenzoyl chloride) has been separated and characterized. Polyeondensation of this diacidchloride with various aliphatic and hydroxyaliphatic diols resulted in polymers with temperatures of transition to the liquid-crystal state in the interval from 40 to 360 °. The procedure and conditions of polycondensation were * Vysokomol. soyed. A26: No. 12, 2570-2576, 1984.
Synthesis of high-molecular weight liquid crystal polyesters
2883
selected, taking as an example the synthesisof a single polymer,polydecamethyleneterephthaloyl-bis-(4-oxybenzoate).Relationsbetween phase transition temperatures and MW have been investigated for this polymer. CURRENTLY tWO main trends are discernible in studies of the synthesis of thermotropic liquid-crystal polymers, whose mesomorphism is due to the main chain structures, viz, the synthesis of aromatic copolyesters, mainly consisting of 1,4-phenylene or 2,6naphthylene units, and the synthesis of thermotropic polymers whose main chains contain mesogenic groups similar to those used in the formation of low-molecular weight liquid crystals. Between the main chains there are rather long flexible sequences. Several groups of authors have synthesized thermotropic liquid-crystal polymers containing alternate rigid mesogenic groups and flexible sequences. Among the polymers that have been described are those that contain benzalazine [ 1], azo- and azoxy groups [2], azomethine [3] and terphenyl mesogenic groups [4]. However the interest of investigators has centred primarily on polymers containing ester type mesogenic groups. This is because of the scope envisaged for practical applications of thermotropic polyesters, as well as the hope that properties of the polymers could be compared with those of widely investigated low molecular liquid crystals containing ester bonds [5]. Widespread use of a mesogenic group in the form of an aromatic triad of 1,4phenylene units interconnected by ester bonds has recently become a feature of the synthesis of liquid-crystal polyesters. Polymers containing a combination of ether and ester bonds have been described by Luyen and Strzelecki [6]. Several series of thermotropic alkylene-aromatic poly(ether) esters containing aromatic triads have been described by Lenz and coworkers [7]. We have described the synthesis [8] of poly-l.4phenylene-bis-(4'-oxybenzoyl) alkanoates, and another paper of ours [9] contains data on orientation of the polymers in a magnetic field. In the case of the majority of the polymers described in the cited papers the intrinsic viscosity values do not exceed 0.5 dl/g (if the authors succeeded in selecting a solvent for the viscosity measurements). With such low viscosity values polyesters of this type are powdery products that have no film- or fibre-forming properties. This greatly narrows the scope of studies of these polymers and limits the amount of information that may be obtained in investigations. Our aim in the present investigation was to develop a simple and convenient method that may be used for the preparation of high-molecular weight alkylene-aromatic regular liquid-crystal polyesters in preparative amount so that various methods may be employed in studies of their molecular-weight characteristics, structure and properties. The present paper describes the synthesis of a series of thermotropic polyesters with an "inverted" (visa vis polymers described in [8]) system of ester bonds, namely polyalkyleneterephthaloyl-bis-(4-oxybenzoates) (PATOB) [10], having the general formula [
~CH-~
OC /2--'~' O
OC //-~---CO - J O
O
\\--CO--I O
The synthesis of polyesters of the type we selected, containing mesogenic triads,
52884
A. Yu. BILIBIN et al.
may be carried out in at least two stages (as a minimum) with subsequent formation of "external" (relative to the mesogenic unit) and "internal" ester bond systems. In most cases preparation of the polymers described by us, containing aromatic triads took place with the formation of an external bond system in the first stage, and with the creation of the actual mesogenic unit in the second stage during the polycondensation process. With this order of stages the preparation of each polymer calls for the synthesis of a special monomer, which frequently involves a very laborius procedure [71. It would appear that na alternative method might well be recommended in regard to the creation of two ester bond systems in polymers containing triads. This would involve preparation of the mesogenic monomer in the first stage of the synthesis, and the preparation of a whole series of different mesomorphic polymers based on this monomer in the second stage. As regards the mesogenic monomers that could thus be used we prepared terephthaloyl-bis-(4-oxybenzoic) acid (TOBA)
HOC--,F-N--O--C--f-N._C_O_f-%,_COH II ~
0
El ~
0
II
0
~'x-=//
J
0
and its dichloride, viz. terephthaloyl-bis-(4-oxybenzoyl chloride) (TOBC) [10]
ClC__/7--~__O__C__~//-- \--C--O -- ~ - II ~ II ~ II -O O O
COl il O
For some years now these compounds have been widely used in our laboratory for the synthesis of various high-molecular weight liquid-crystal polyesters [11]. Quite recently, it was reported that Lenz and coworkers had attempted to synthesize this dichloride. However, those authors were unable to separate it from the reaction system or to characterize it. For this reason a product of indeterminate structure and composition was used by the cited authors [12] in the polycondensation. It is known that in polycondensation processes the quality of polymers and of initial monomers [ 131 plays a very influential role, which accounts for the extremely low-intrinsic viscosities of the products of polycondensation of the unpurified dichloride with diols (0.08-0.28 dl/g). In view of this some caution needs to be exercised in regard to data of the cited authors on the properties of these polycondensation products [12]. Using the method proposed by us TOBA is obtainable with a quantitative yield by interphase condensation of terephthaloyl chloride with 4-hydroxybenzoates. TOBA does not dissolve in the solvents tested, and does not melt at temperatures above 400 °. The dichloride may be prepared from TOBA by interaction with thionyl chloride or with phosphorus pentachloride. In an earlier investigation [ 10] we prepared a wide range of high-molecular weight thermotropic liquid-crystal polyesters by polycondensation of TOBC with various aliphatic and hydroxyaliphatic diols
Synthesis of high-molecular weight liquid crystal polyesters
2885
SOCI~ or PCl, HO--R--OH C I C _ . f - - ~ _ C C 1 HO--C.I-I,--COONa TOBC ~ ~. II ~ I1 -, TOBC 0 0 -.
0
0
0
0
Polymers of a similar type have been described by Lene and coworkers [2, 7]. Our data for many polymers differ greatly from those obtained by the cited authors, primarily as regards intrinsic viscosities of the polymers and also in respect to temperatures of phase transitions, and solubility. The reason for the discrepancies could, be that those authors [7, 12] were unable to separate initial products for the synthesis, or failed to select optimal conditions for the polycondensation. It is well known that good results in polycondensation processes largely depend on correct selection of the appropriate conditions [14]. Low temperature processes of synthesis of polymers in line with the proposed scheme present difficulties, because of poor solubility of the initial TOBC in solvents that might suitably be used for the synthesis, and, because of oligomers separating out of the reaction system in the early stages of the process. It is this factor that underlies cessation of chain propagation. Selection of the appropriate polycondensation procedures and optimal conditions was undertaken in our case, taking as an example the synthesis of polydecamethyleneterephthaloyl-bis-(4-oxybenzoate) (PDTOB) o
(CH,),o
0
0
0
0
This polymer is a most suitable study object, both for investigation of the polycondensation of TOBC with aliphatic diols, and for study of the principal properties of liquid-crystal high-molecular weight PATOBs. The interval (230-290 °) for its existence in the liquid-crystal state lies below its thermal degradation temperature. PDTOB is obtainable with maximal values of [q] (compared with other PATOB polymers) which may be as high as 3-0 dl/g in trifluoroacetic acid at 25 °. To synthesize PDTOB we tried various methods for the polycondensation. The results were evaluated on the basis of the intrinsic viscosity of the product in trifluoroacetic acid. The absence of acidolis of ester bonds at room temperature was proved by the fact that the viscosity of a solution of PDTOB in trifluoroacetic acid remained constant for a long time (Fig. 1). Table 1 gives the results of polycondensation of TOBC with 1,10-decanediol under various conditions, while in Tables 2 and 3 we have properties of the polymers obtained under comparable conditions, i.e. from the same batch of TOBC for each table. It is seen from the data in Table 1 that the best results are obtainable by high temperature acceptorless polycondensation in a high-boiling solvent together with an inert gas current. This method of polycondensation has been investigated in some detail by
2886
A. Yu'. BILIBINet
al.
V. V. K o r s h a k and coworkers [15]. A yield approximating 100~o is obtained for most of the polymers synthesized in this manner. F o r P D T O B we determined thermal properties in relation to MW. To do so we synthesized a series of P D T O B samples of different MWs, which was done by the introduction of reagents into the polycondensation in non-equimolar ratios. Figure 2 shows the intrinsic ~iscosity of P D T O B relative to the ratio of the reagents. Temperatures o f phase transitions were determined for all the samples by polarizing optical microscopy. The data obtained by this method are in good agreement with the data obtained by other methods (differential scanning calorimetry, IR-spectroscopy, X-ray analysis). Figure 3 shows the temperatures of phase transitions of P D T O B vs. values of [r/]. It is seen from photomicrographs of melts of these polymers (crossed polaroids to those o f low-molecular weight liquid crystals (Fig. 4a, b). A texture that is typical for thermotropic liquid-crystal polymers is formed at high values of [r/] (Fig. 4¢, d). At viscosity values above 0.7 dl/g the oriented texture of the melt (Fig. 4e, f ) remains visible for a long time (more than 10 min) on moving the cover glass. Under conditions developed in the synthesis of P D T O B (diphenyl oxide as a solvent, 200 °, inert gas current) we synthesized polymers with other aliphatic diols. For polymers TABLE 1.
INTRINSIC
Solvents
PDTOB
VISCOSITY OF
HCI acceptors
Benzyl benzoate o-Dichlorobenzene Tetraglyme Diphenylmethane Diphenyl oxide Tetrachloroethane
m
Pyridine Triethylamine Pyridine
THF Without a solvent
RELATIVE TO SYNTHESIS CONDITIONS
T°
Time, hr
[q], dl/g (CFsCOOH, 25°)
200 150 200 200 200 150 25 25 25 250
2'0 2"0 2"0 2"0 2'0 2'0 20"0 20"0 20"0 1"5
0"10 0'37 0'15 0"68 0"98 0"35 0"34 0"29 0'18 0'59*
* T h e p o l y m e r is slightly d i s c o l o u r e d .
TABLE 2. PROPERTIESOF THE POLYALKYLENETEREPHTHALOYL-BIS-(4-OXYBENZOATES) Aliphatic fragments
[t/l, dl/g (CFaCOOH, 25 °)
T°
T~o
-- (CH2)2 -(CH2)4 -- (CH2)s - (CH2)6 (CH2)6 - (CH2)t 0 -
Insoluble 0"40 0'71 0"75 1"20 3"00
360* 285 205 274 295 230
360* 320 355* 365* 290
-
-
] I
Solvents used for the synthesis 1-Chloronaphthalene
Diphenyl oxide
* D e t e r m i n a t i o n o f transition temperature is m a d e difficult by thermal degradation o f t h e sample. Note. Tlw-tvmpvraturv at which an isotropic l i q u i d is f o r m e d .
Synthesis of high-molecular weight liquid crystal polyesters
2887
TABLE 3. PROPERTIES OF THE POLY-(OXYALKYLENE)-TEREPHTHALOYL-BIS-(4-OXYBENZOATES)
-=O--(CH~--CHR--O),,~--C--C - / / ~ ,i ()
R
rn, v (diol)
-H -H -H -H - CH3 -CH3 - CH3 - CH3 - CH3 CH3 - CH3
~/
OC //---%--C0 !i ~ ', t)
CO l
~
(I
I',
|
0
Jn
[q], dl/g (CHCI3, 25 °)
Ta~
T~°'°
0'60* 0"88 0"47 0"45 0'63 0"48 0"44 0"40 0"39 0"45 0"45
200 175 100 90 110 110 80 65 45 35 30
350 225 130
2 (diethylene glycol) 3 (triethylene glycol) 6.8 (PEG-300) 8.6 (PEG-400) 2 (dipropylene glycol) 3.1 (PPG-200) 4.0 (PPG-250) 4.9 (PPG-300) * 5.7 (PPG-350) * 6.2 (PPG-375) t 7.0 (PPG-425)
-
/---~
185 195 160 130 85 60
* Viscosity measured in CFaCOOH. t Prepared from commercial PPG-200 and PPG-425, blended in definite properties.
with fewer than five methylene groups in a sequence we had to use a different solvent, since the polymers precipitated from diphenyl oxide in the early stages of the synthesis, even at temperatures above 200 °. 1-Chloronaphthalene was used as a solvent for the synthesis of these polymers. Table 2 gives the characteristics of the polyalkyleneterephthaloyl-bis-(4-oxybenzoates). It was shown in paper [8] that the incorporation of an oligoethylene oxide sequence instead of an oligomethylene one leads to a marked reduction in phase transition
17p !d,dl/~ 2 -
~ 1
2
~3 i
20
1
I
I
08 72 Time, hi, FIG. 1
I
96
I
I
0.8
I,.
1,
I
0.9TOBC:DIOL1.0 FiG. 2
FIG. 1. Time dependence of the reduced viscosity of solutions of PDTOB (1), PETP (2) and poly-1,4-phenylenesebacyl-bis-(4'-oxybenzoate (3) [8] in trifluoroacetic acid (c = 0"5 ~o, 25°). FIG, 2. Intrinsic viscosity of PDTOB vs. ratio of reagents in polycondensation of TOBC and 1,10-deeanediol (CF3COOH, 25°).
2888
A. Yu. BILIBIN e t al.
250
150~
~
,
0.5
,
,
1
'
~.o ~j, d/IE
FIG. 3. Plots of Tm (1) and Tl,o (2) for PDTOB vs. intrinsic viscosity in CF3COOH (25°).
FIG. 4. Photomicrographs of PDTOB samples with [t/] values of 0.23 (a); 0"28 (b); 0.36 (c); 0"47 (d); 0.74 (e) and 1-30 dl/g ( f ) at 160 (a), 195 (b), 215 (c), 220 (d) and 250 ° (e,f) (e and f - t h e cover glasses have been displaced). Viscosity measurements in CF3COOH; 25 °, × 250.
Synthesis of high-molecular weight liquid crystal polyesters
2889
temperatures of the polymers. Other authors have reported similar findings [4]. The fact that the T O B C used by us was highly pure made it possible to prepare two series of sufficiently high-molecular weight liquid-crystal polymers based on polyethylene glycols and polypropylene glycols. At the same time maximal values of [~/] for the polymers were determined by the purity and the functionality of the commercial glycols that were used for the synthesis. G o o d agreement between the TOBC equivalent and the calculated value was demonstrated by T O B C polycondensation with individual diols (Fig. 2). This meant that it could be used to determine the equivalents of diols of indeterminate composition. To do so T O B C was introduced into the polycondens a t i o n with a given diol in various ratios..The equivalent was determined for the diol being tested (Fig. 5) through the position of the m a x i m u m on the curve of [r/] for the polycondensation products vs. the ratio of the reagents. The data obtained for most of the diols tested in this way were in keeping with data provided by the manufacturers. Table 3 gives the characteristics of polymers prepared by polycondensation o f T O B C with polyethylene glycols and polypropylene glycols of different MWs. It can be seen that as the sequence lengthens temperatures of transitions in both series of polymers are uniformly reduced. When the sequence length amounts to ~ 2 0 atoms both series of polymers suffer less of the ability to go over into the liquid-crystal state. Various physical (including fibre-forming) properties of the polymers are now being investigated. r~] , rlllg -
I
I
1
185
790
195
0"5
I
I
1
200 205 210 275 m PP~-2OO(g) l mo/e TO BC
FIG. 5. Intrinsic viscosity [t/] of the polymer vs. weight fraction of PPG-200 introduced into the polycondensation per 1 mole TOBC. Intrinsic viscosity values were determined for the polymers, using an Ubbelohde viscometer Temperatures of phase transitions were determined and melts of the polymers were photographed (crossed polaroids) on a Boetius type heating stage (VEB Analytik, Dresden, East Germany) for determination of melting points. Diols and solvents were distilled before use in the synthesis. The polyethylene glycols (commercial grade) were obtained from Merk-Schuchardt, and the polypropylene glycols from Ferak-Berlin. Preparation of the terephthaloyl-bis-(4-oxybenzoic)acid. To a solution of 166 g of 4-hydroxybenzoic acid in 2-5 l. of a 0.4 N aqueous NaOH solution was added, whilst stirring rapidly (at room temperature) in the course of 10 rain a solution of 102 g of terephthaloyl chloride in 1 1. of carbon
2890
A. Yu. BILInIN et al.
tetrachloride, and 1 1. of a 1 N aqueous N a O H solution. Stirring was continued for a further 5 hr. A sediment separated out, and was filtered, dried, comminuted and transferred to a vessel where it was mixed for 1 hr with 1.5 1. of hydrochloric acid. The product was filtered, washed with water, and dried. Yield: 190 g (93~o). Found, %: C 65.41; H 3.61. C22Ht~Os. Calculated, ~o: C 65.03; H 3.47. The analysis of TOBA was carried out using a sample prepared by hydrolysis of TOBC. Preparation of the terephthaloyl-bis-(4-oxybenzoyl chloride). 20 g of TOBA were boiled with the reflux condenser in 300 ml of thionyl chloride. When the liberation of HCI ended and most of the sediment had dissolved the hot solution was filtered and cooled down to 0 °. The sediment that separated out was filtered, vacuum dried and recrystallized from chloroform. Yield 15.4 g (71 ~.), Tm=226 °. Found, ~o: C 59.87; H 2.61; CI 15.99. C22HtsO6C12. Calculated, ~ : C 59.61; H 2.73; CI 16.00. Preparation of polydecamethyleneterephthaloyl-bis-(4-oxybenzoate (typical polycondensation method). Into a 20 ml polycondensation test-tube were placed 0.887 g of TOBC, 0.348 g of 1,10-decanediol, and 5 ml of diphenyl oxide. The mixture was purged for 15 rain with dry argon at r o o m temperature, and then, while maintaining the gas current, was placed in a bath containing a high-temperature heat-transfer agent. The polycondensation was carried out for 2 hr at 200 °. On completion of the process the hot viscous solution was decanted into 50 ml of toluene. The polymer was filtered and vacuum dried. Yield 1.060 g (99~). Found, ~ : C 70.44; H 5.81. C32H32Os. Calculated, ~ : C 70-57; H 5.92. Using similar methods we prepared all the polymers described here. The results of elemental analysis of the polymers are in line with calculated values. The cJ'mpositions of polymers were verified by infrared spectroscopy.
Translated by R. J. A. HENDRY REFERENCES I. 2. 3. 4. 5. 6. 7. 8. 9.
10. 11.
12. 13. 14. 15.
A. ROVIELLO and A. STRIGU, Polymer Letters 13: 455, 1975 K. IIMURA, N. KOIDE, R. O H T A and M. TAKEDA, Makromolek. Chem. 182: 2563, 1981 D. G U I S O N and A. SKULIOS, Molec. Cryst. Liq. Cryst. Letters 49: 119, 1978 P. M E U R I S S E , C. NOEL, L. M O N N E R I E and B. FAYOLLE, Brit. Polymer J. 13: 55, 1981 M. J. S. D E W A R and R. M. RIDDLE, J. Amer. Chem. Soc. 97: 6658, 1975 D. L U Y E N and L. STRZELECKI, J. Europ. Polymer J. 16: 303, 1980 C. OBER, J. I. J I N and R. W. LENZ, Polymer J. 14: 9, 1982 A. Yu. BILIBON, A. A. SHEPELEVSKII, S. Ya. FRENKEL and S. S. SKOROKHODOV, Vysokomol. soyed. B22: 739, 1980 (Not translated in Polymer Sci. U.S.S.R.) A. I. GRIGORYEV, N. A. A N D R E Y E V A , A. Yu. BILIBIN, S. S. S K O R O K H O D O V and V. Ye. ESKIN, Vysokomol. soyed. B22:891 1980 (Not translated in Polymer Sci. U.S.S.R.) A. Yu. BILIBIN, T. Ye. SAVINOVA, A. A. SHEVELEVSKII and S. S. SKOROKHODOV, U.S.S.R. Pat. 792834, pub1. in Buyll. Izob., 12, 284, 1982 B. Z. VOLCHEK, N. S. K H O L M U R A D O V , A. V. PURKINA, A. Yu. BILIBIN and S. S. SKOROKHODOV, In: Abstracts of Reports at IV Internat. Conf. Socialist States on Liquid Crystals, vol. 2, p. 154, Tbilisi, 1981 G. GALLI, E. CHIELLINI, C. K. OBER and R. W. LENZ, Makromolek. Chem. 183: 2693, 1982 V. V. KORSHAK and S. V. VINOGRADOVA, Ravnovesnaya polikondensatsiya (The Equilibrium Polycondensation). p. 118, Nauka, Moscow, 1972 V. V. KORSHAK and S. V. VINOGRADOVA, Neravnovesnaya polikondensatsiya (The Nonequilibirium Polycondensaion). p. l I, Nauka, Moscow, 1972 V. V. KORSHAK and S. V. V1NOGRADOVA, Neravnovesnaya polikondensatsiya (The Nonequilibrium Polycondensation) p. 137, Nauka, Moscow, 1972
A. Yu. BILIBIN et al.
S. TOMOTIKA, Proc. Roy. Soc. London A153: 302, 1936 A. ACRIVOS and T. S. LO, J. Fluid. Mech. 86: 641, 1978 J. M. RALLISON and A. ACRIVOS, J. Fluid Mech. 89f 191, 1978 M. GORDON, J. YERUSHALMI and R. SHINNER, Trans. Soc. Rheol. 17: 303, 1973 G. HESTRONI and S. HAVER, Rheol. Acta 9: 488, 1970 L. RAYLEIGH, Philos. Mag. 34: 145, 1892 C. Z. WEBER, Angew. Math. 11: 136, 1931 C. D. HAN, Multiphase Flow in Polymer Processing, pp. 228, 236, Acad. Press, N.Y., 1981 A. T. SERKOV and R. V. YEGOROVA, in: Teoriya formovaniya khimicheskikh volokon (Theory of Chemical Fibre Moulding). p. 21, Khimiya, Moscow, 1975 C. D. HAN and KAZUMORI FUNATSU, J. Rheol. 22: 113, 1978 N. HIRAI, J. Chem. Soc, Japan 75: 1019, 1954 S. P. PAPKOV, Khim. volokna, 3, 34, 1964 H. B. CHIN and C. D. HAN, J. Rheol. 24: 1, 1980 Yu. P. MIROSHNIKOV, M. K. PETROSIAN and V. N. KULEZNEV, Kolloidn. zh. 38: 279, 1976 Yu. P. MIROSHNIKOV, M. L. KAMINSKII and V. N. KULEZNEV, Kolloidn. zh. 41:1112, 1979 Yu. P. MIROSHNIKOV, A. M. GOL'MAN and V. N. KULEZNEV, Kolloidn. zh. 41: 1120, 1979 M. GOLDIN, J. YERUSHALMI, R. PREFFER and R. SHINNER, J. Fluid Mech. 38: 689, 1969
Polymer ScienceU.S.S.RVol. 26, No. 12, pp. 2882-2890, 1984 Printed in Poland
0032-3509/84 $10.00+ .00 © 1986PergamonPress Ltd.
SYNTHESIS OF HIGH-MOLECULAR WEIGHT LIQUID CRYSTAL POLYESTERS BASED ON A POLYCONDENSATION MESOGENIC MONOMER* A. Y u . BILIBIN, A. V. TEN'KOVTSEV, O. N. PIRANER a n d S. S. SKOROKHODOV High Molecular Compounds Institute, U.S.S.R. Academy of Sciences (Received 13 May 1983) This paper relates to the scheme proposed for the synthesis of high-molecular weight alkylene aromatic polyesters capable of forming liquid-crystal melts. This is the first time that the mesogenic dichloride, terephthaloyl-bis-(4-oxybenzoyl chloride) has been separated and characterized. Polyeondensation of this diacidchloride with various aliphatic and hydroxyaliphatic diols resulted in polymers with temperatures of transition to the liquid-crystal state in the interval from 40 to 360 °. The procedure and conditions of polycondensation were * Vysokomol. soyed. A26: No. 12, 2570-2576, 1984.
Synthesis of high-molecular weight liquid crystal polyesters
2883
selected, taking as an example the synthesisof a single polymer,polydecamethyleneterephthaloyl-bis-(4-oxybenzoate).Relationsbetween phase transition temperatures and MW have been investigated for this polymer. CURRENTLY tWO main trends are discernible in studies of the synthesis of thermotropic liquid-crystal polymers, whose mesomorphism is due to the main chain structures, viz, the synthesis of aromatic copolyesters, mainly consisting of 1,4-phenylene or 2,6naphthylene units, and the synthesis of thermotropic polymers whose main chains contain mesogenic groups similar to those used in the formation of low-molecular weight liquid crystals. Between the main chains there are rather long flexible sequences. Several groups of authors have synthesized thermotropic liquid-crystal polymers containing alternate rigid mesogenic groups and flexible sequences. Among the polymers that have been described are those that contain benzalazine [ 1], azo- and azoxy groups [2], azomethine [3] and terphenyl mesogenic groups [4]. However the interest of investigators has centred primarily on polymers containing ester type mesogenic groups. This is because of the scope envisaged for practical applications of thermotropic polyesters, as well as the hope that properties of the polymers could be compared with those of widely investigated low molecular liquid crystals containing ester bonds [5]. Widespread use of a mesogenic group in the form of an aromatic triad of 1,4phenylene units interconnected by ester bonds has recently become a feature of the synthesis of liquid-crystal polyesters. Polymers containing a combination of ether and ester bonds have been described by Luyen and Strzelecki [6]. Several series of thermotropic alkylene-aromatic poly(ether) esters containing aromatic triads have been described by Lenz and coworkers [7]. We have described the synthesis [8] of poly-l.4phenylene-bis-(4'-oxybenzoyl) alkanoates, and another paper of ours [9] contains data on orientation of the polymers in a magnetic field. In the case of the majority of the polymers described in the cited papers the intrinsic viscosity values do not exceed 0.5 dl/g (if the authors succeeded in selecting a solvent for the viscosity measurements). With such low viscosity values polyesters of this type are powdery products that have no film- or fibre-forming properties. This greatly narrows the scope of studies of these polymers and limits the amount of information that may be obtained in investigations. Our aim in the present investigation was to develop a simple and convenient method that may be used for the preparation of high-molecular weight alkylene-aromatic regular liquid-crystal polyesters in preparative amount so that various methods may be employed in studies of their molecular-weight characteristics, structure and properties. The present paper describes the synthesis of a series of thermotropic polyesters with an "inverted" (visa vis polymers described in [8]) system of ester bonds, namely polyalkyleneterephthaloyl-bis-(4-oxybenzoates) (PATOB) [10], having the general formula [
~CH-~
OC /2--'~' O
OC //-~---CO - J O
O
\\--CO--I O
The synthesis of polyesters of the type we selected, containing mesogenic triads,
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may be carried out in at least two stages (as a minimum) with subsequent formation of "external" (relative to the mesogenic unit) and "internal" ester bond systems. In most cases preparation of the polymers described by us, containing aromatic triads took place with the formation of an external bond system in the first stage, and with the creation of the actual mesogenic unit in the second stage during the polycondensation process. With this order of stages the preparation of each polymer calls for the synthesis of a special monomer, which frequently involves a very laborius procedure [71. It would appear that na alternative method might well be recommended in regard to the creation of two ester bond systems in polymers containing triads. This would involve preparation of the mesogenic monomer in the first stage of the synthesis, and the preparation of a whole series of different mesomorphic polymers based on this monomer in the second stage. As regards the mesogenic monomers that could thus be used we prepared terephthaloyl-bis-(4-oxybenzoic) acid (TOBA)
HOC--,F-N--O--C--f-N._C_O_f-%,_COH II ~
0
El ~
0
II
0
~'x-=//
J
0
and its dichloride, viz. terephthaloyl-bis-(4-oxybenzoyl chloride) (TOBC) [10]
ClC__/7--~__O__C__~//-- \--C--O -- ~ - II ~ II ~ II -O O O
COl il O
For some years now these compounds have been widely used in our laboratory for the synthesis of various high-molecular weight liquid-crystal polyesters [11]. Quite recently, it was reported that Lenz and coworkers had attempted to synthesize this dichloride. However, those authors were unable to separate it from the reaction system or to characterize it. For this reason a product of indeterminate structure and composition was used by the cited authors [12] in the polycondensation. It is known that in polycondensation processes the quality of polymers and of initial monomers [ 131 plays a very influential role, which accounts for the extremely low-intrinsic viscosities of the products of polycondensation of the unpurified dichloride with diols (0.08-0.28 dl/g). In view of this some caution needs to be exercised in regard to data of the cited authors on the properties of these polycondensation products [12]. Using the method proposed by us TOBA is obtainable with a quantitative yield by interphase condensation of terephthaloyl chloride with 4-hydroxybenzoates. TOBA does not dissolve in the solvents tested, and does not melt at temperatures above 400 °. The dichloride may be prepared from TOBA by interaction with thionyl chloride or with phosphorus pentachloride. In an earlier investigation [ 10] we prepared a wide range of high-molecular weight thermotropic liquid-crystal polyesters by polycondensation of TOBC with various aliphatic and hydroxyaliphatic diols
Synthesis of high-molecular weight liquid crystal polyesters
2885
SOCI~ or PCl, HO--R--OH C I C _ . f - - ~ _ C C 1 HO--C.I-I,--COONa TOBC ~ ~. II ~ I1 -, TOBC 0 0 -.
0
0
0
0
Polymers of a similar type have been described by Lene and coworkers [2, 7]. Our data for many polymers differ greatly from those obtained by the cited authors, primarily as regards intrinsic viscosities of the polymers and also in respect to temperatures of phase transitions, and solubility. The reason for the discrepancies could, be that those authors [7, 12] were unable to separate initial products for the synthesis, or failed to select optimal conditions for the polycondensation. It is well known that good results in polycondensation processes largely depend on correct selection of the appropriate conditions [14]. Low temperature processes of synthesis of polymers in line with the proposed scheme present difficulties, because of poor solubility of the initial TOBC in solvents that might suitably be used for the synthesis, and, because of oligomers separating out of the reaction system in the early stages of the process. It is this factor that underlies cessation of chain propagation. Selection of the appropriate polycondensation procedures and optimal conditions was undertaken in our case, taking as an example the synthesis of polydecamethyleneterephthaloyl-bis-(4-oxybenzoate) (PDTOB) o
(CH,),o
0
0
0
0
This polymer is a most suitable study object, both for investigation of the polycondensation of TOBC with aliphatic diols, and for study of the principal properties of liquid-crystal high-molecular weight PATOBs. The interval (230-290 °) for its existence in the liquid-crystal state lies below its thermal degradation temperature. PDTOB is obtainable with maximal values of [q] (compared with other PATOB polymers) which may be as high as 3-0 dl/g in trifluoroacetic acid at 25 °. To synthesize PDTOB we tried various methods for the polycondensation. The results were evaluated on the basis of the intrinsic viscosity of the product in trifluoroacetic acid. The absence of acidolis of ester bonds at room temperature was proved by the fact that the viscosity of a solution of PDTOB in trifluoroacetic acid remained constant for a long time (Fig. 1). Table 1 gives the results of polycondensation of TOBC with 1,10-decanediol under various conditions, while in Tables 2 and 3 we have properties of the polymers obtained under comparable conditions, i.e. from the same batch of TOBC for each table. It is seen from the data in Table 1 that the best results are obtainable by high temperature acceptorless polycondensation in a high-boiling solvent together with an inert gas current. This method of polycondensation has been investigated in some detail by
2886
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V. V. K o r s h a k and coworkers [15]. A yield approximating 100~o is obtained for most of the polymers synthesized in this manner. F o r P D T O B we determined thermal properties in relation to MW. To do so we synthesized a series of P D T O B samples of different MWs, which was done by the introduction of reagents into the polycondensation in non-equimolar ratios. Figure 2 shows the intrinsic ~iscosity of P D T O B relative to the ratio of the reagents. Temperatures o f phase transitions were determined for all the samples by polarizing optical microscopy. The data obtained by this method are in good agreement with the data obtained by other methods (differential scanning calorimetry, IR-spectroscopy, X-ray analysis). Figure 3 shows the temperatures of phase transitions of P D T O B vs. values of [r/]. It is seen from photomicrographs of melts of these polymers (crossed polaroids to those o f low-molecular weight liquid crystals (Fig. 4a, b). A texture that is typical for thermotropic liquid-crystal polymers is formed at high values of [r/] (Fig. 4¢, d). At viscosity values above 0.7 dl/g the oriented texture of the melt (Fig. 4e, f ) remains visible for a long time (more than 10 min) on moving the cover glass. Under conditions developed in the synthesis of P D T O B (diphenyl oxide as a solvent, 200 °, inert gas current) we synthesized polymers with other aliphatic diols. For polymers TABLE 1.
INTRINSIC
Solvents
PDTOB
VISCOSITY OF
HCI acceptors
Benzyl benzoate o-Dichlorobenzene Tetraglyme Diphenylmethane Diphenyl oxide Tetrachloroethane
m
Pyridine Triethylamine Pyridine
THF Without a solvent
RELATIVE TO SYNTHESIS CONDITIONS
T°
Time, hr
[q], dl/g (CFsCOOH, 25°)
200 150 200 200 200 150 25 25 25 250
2'0 2"0 2"0 2"0 2'0 2'0 20"0 20"0 20"0 1"5
0"10 0'37 0'15 0"68 0"98 0"35 0"34 0"29 0'18 0'59*
* T h e p o l y m e r is slightly d i s c o l o u r e d .
TABLE 2. PROPERTIESOF THE POLYALKYLENETEREPHTHALOYL-BIS-(4-OXYBENZOATES) Aliphatic fragments
[t/l, dl/g (CFaCOOH, 25 °)
T°
T~o
-- (CH2)2 -(CH2)4 -- (CH2)s - (CH2)6 (CH2)6 - (CH2)t 0 -
Insoluble 0"40 0'71 0"75 1"20 3"00
360* 285 205 274 295 230
360* 320 355* 365* 290
-
-
] I
Solvents used for the synthesis 1-Chloronaphthalene
Diphenyl oxide
* D e t e r m i n a t i o n o f transition temperature is m a d e difficult by thermal degradation o f t h e sample. Note. Tlw-tvmpvraturv at which an isotropic l i q u i d is f o r m e d .
Synthesis of high-molecular weight liquid crystal polyesters
2887
TABLE 3. PROPERTIES OF THE POLY-(OXYALKYLENE)-TEREPHTHALOYL-BIS-(4-OXYBENZOATES)
-=O--(CH~--CHR--O),,~--C--C - / / ~ ,i ()
R
rn, v (diol)
-H -H -H -H - CH3 -CH3 - CH3 - CH3 - CH3 CH3 - CH3
~/
OC //---%--C0 !i ~ ', t)
CO l
~
(I
I',
|
0
Jn
[q], dl/g (CHCI3, 25 °)
Ta~
T~°'°
0'60* 0"88 0"47 0"45 0'63 0"48 0"44 0"40 0"39 0"45 0"45
200 175 100 90 110 110 80 65 45 35 30
350 225 130
2 (diethylene glycol) 3 (triethylene glycol) 6.8 (PEG-300) 8.6 (PEG-400) 2 (dipropylene glycol) 3.1 (PPG-200) 4.0 (PPG-250) 4.9 (PPG-300) * 5.7 (PPG-350) * 6.2 (PPG-375) t 7.0 (PPG-425)
-
/---~
185 195 160 130 85 60
* Viscosity measured in CFaCOOH. t Prepared from commercial PPG-200 and PPG-425, blended in definite properties.
with fewer than five methylene groups in a sequence we had to use a different solvent, since the polymers precipitated from diphenyl oxide in the early stages of the synthesis, even at temperatures above 200 °. 1-Chloronaphthalene was used as a solvent for the synthesis of these polymers. Table 2 gives the characteristics of the polyalkyleneterephthaloyl-bis-(4-oxybenzoates). It was shown in paper [8] that the incorporation of an oligoethylene oxide sequence instead of an oligomethylene one leads to a marked reduction in phase transition
17p !d,dl/~ 2 -
~ 1
2
~3 i
20
1
I
I
08 72 Time, hi, FIG. 1
I
96
I
I
0.8
I,.
1,
I
0.9TOBC:DIOL1.0 FiG. 2
FIG. 1. Time dependence of the reduced viscosity of solutions of PDTOB (1), PETP (2) and poly-1,4-phenylenesebacyl-bis-(4'-oxybenzoate (3) [8] in trifluoroacetic acid (c = 0"5 ~o, 25°). FIG, 2. Intrinsic viscosity of PDTOB vs. ratio of reagents in polycondensation of TOBC and 1,10-deeanediol (CF3COOH, 25°).
2888
A. Yu. BILIBIN e t al.
250
150~
~
,
0.5
,
,
1
'
~.o ~j, d/IE
FIG. 3. Plots of Tm (1) and Tl,o (2) for PDTOB vs. intrinsic viscosity in CF3COOH (25°).
FIG. 4. Photomicrographs of PDTOB samples with [t/] values of 0.23 (a); 0"28 (b); 0.36 (c); 0"47 (d); 0.74 (e) and 1-30 dl/g ( f ) at 160 (a), 195 (b), 215 (c), 220 (d) and 250 ° (e,f) (e and f - t h e cover glasses have been displaced). Viscosity measurements in CF3COOH; 25 °, × 250.
Synthesis of high-molecular weight liquid crystal polyesters
2889
temperatures of the polymers. Other authors have reported similar findings [4]. The fact that the T O B C used by us was highly pure made it possible to prepare two series of sufficiently high-molecular weight liquid-crystal polymers based on polyethylene glycols and polypropylene glycols. At the same time maximal values of [~/] for the polymers were determined by the purity and the functionality of the commercial glycols that were used for the synthesis. G o o d agreement between the TOBC equivalent and the calculated value was demonstrated by T O B C polycondensation with individual diols (Fig. 2). This meant that it could be used to determine the equivalents of diols of indeterminate composition. To do so T O B C was introduced into the polycondens a t i o n with a given diol in various ratios..The equivalent was determined for the diol being tested (Fig. 5) through the position of the m a x i m u m on the curve of [r/] for the polycondensation products vs. the ratio of the reagents. The data obtained for most of the diols tested in this way were in keeping with data provided by the manufacturers. Table 3 gives the characteristics of polymers prepared by polycondensation o f T O B C with polyethylene glycols and polypropylene glycols of different MWs. It can be seen that as the sequence lengthens temperatures of transitions in both series of polymers are uniformly reduced. When the sequence length amounts to ~ 2 0 atoms both series of polymers suffer less of the ability to go over into the liquid-crystal state. Various physical (including fibre-forming) properties of the polymers are now being investigated. r~] , rlllg -
I
I
1
185
790
195
0"5
I
I
1
200 205 210 275 m PP~-2OO(g) l mo/e TO BC
FIG. 5. Intrinsic viscosity [t/] of the polymer vs. weight fraction of PPG-200 introduced into the polycondensation per 1 mole TOBC. Intrinsic viscosity values were determined for the polymers, using an Ubbelohde viscometer Temperatures of phase transitions were determined and melts of the polymers were photographed (crossed polaroids) on a Boetius type heating stage (VEB Analytik, Dresden, East Germany) for determination of melting points. Diols and solvents were distilled before use in the synthesis. The polyethylene glycols (commercial grade) were obtained from Merk-Schuchardt, and the polypropylene glycols from Ferak-Berlin. Preparation of the terephthaloyl-bis-(4-oxybenzoic)acid. To a solution of 166 g of 4-hydroxybenzoic acid in 2-5 l. of a 0.4 N aqueous NaOH solution was added, whilst stirring rapidly (at room temperature) in the course of 10 rain a solution of 102 g of terephthaloyl chloride in 1 1. of carbon
2890
A. Yu. BILInIN et al.
tetrachloride, and 1 1. of a 1 N aqueous N a O H solution. Stirring was continued for a further 5 hr. A sediment separated out, and was filtered, dried, comminuted and transferred to a vessel where it was mixed for 1 hr with 1.5 1. of hydrochloric acid. The product was filtered, washed with water, and dried. Yield: 190 g (93~o). Found, %: C 65.41; H 3.61. C22Ht~Os. Calculated, ~o: C 65.03; H 3.47. The analysis of TOBA was carried out using a sample prepared by hydrolysis of TOBC. Preparation of the terephthaloyl-bis-(4-oxybenzoyl chloride). 20 g of TOBA were boiled with the reflux condenser in 300 ml of thionyl chloride. When the liberation of HCI ended and most of the sediment had dissolved the hot solution was filtered and cooled down to 0 °. The sediment that separated out was filtered, vacuum dried and recrystallized from chloroform. Yield 15.4 g (71 ~.), Tm=226 °. Found, ~o: C 59.87; H 2.61; CI 15.99. C22HtsO6C12. Calculated, ~ : C 59.61; H 2.73; CI 16.00. Preparation of polydecamethyleneterephthaloyl-bis-(4-oxybenzoate (typical polycondensation method). Into a 20 ml polycondensation test-tube were placed 0.887 g of TOBC, 0.348 g of 1,10-decanediol, and 5 ml of diphenyl oxide. The mixture was purged for 15 rain with dry argon at r o o m temperature, and then, while maintaining the gas current, was placed in a bath containing a high-temperature heat-transfer agent. The polycondensation was carried out for 2 hr at 200 °. On completion of the process the hot viscous solution was decanted into 50 ml of toluene. The polymer was filtered and vacuum dried. Yield 1.060 g (99~). Found, ~ : C 70.44; H 5.81. C32H32Os. Calculated, ~ : C 70-57; H 5.92. Using similar methods we prepared all the polymers described here. The results of elemental analysis of the polymers are in line with calculated values. The cJ'mpositions of polymers were verified by infrared spectroscopy.
Translated by R. J. A. HENDRY REFERENCES I. 2. 3. 4. 5. 6. 7. 8. 9.
10. 11.
12. 13. 14. 15.
A. ROVIELLO and A. STRIGU, Polymer Letters 13: 455, 1975 K. IIMURA, N. KOIDE, R. O H T A and M. TAKEDA, Makromolek. Chem. 182: 2563, 1981 D. G U I S O N and A. SKULIOS, Molec. Cryst. Liq. Cryst. Letters 49: 119, 1978 P. M E U R I S S E , C. NOEL, L. M O N N E R I E and B. FAYOLLE, Brit. Polymer J. 13: 55, 1981 M. J. S. D E W A R and R. M. RIDDLE, J. Amer. Chem. Soc. 97: 6658, 1975 D. L U Y E N and L. STRZELECKI, J. Europ. Polymer J. 16: 303, 1980 C. OBER, J. I. J I N and R. W. LENZ, Polymer J. 14: 9, 1982 A. Yu. BILIBON, A. A. SHEPELEVSKII, S. Ya. FRENKEL and S. S. SKOROKHODOV, Vysokomol. soyed. B22: 739, 1980 (Not translated in Polymer Sci. U.S.S.R.) A. I. GRIGORYEV, N. A. A N D R E Y E V A , A. Yu. BILIBIN, S. S. S K O R O K H O D O V and V. Ye. ESKIN, Vysokomol. soyed. B22:891 1980 (Not translated in Polymer Sci. U.S.S.R.) A. Yu. BILIBIN, T. Ye. SAVINOVA, A. A. SHEVELEVSKII and S. S. SKOROKHODOV, U.S.S.R. Pat. 792834, pub1. in Buyll. Izob., 12, 284, 1982 B. Z. VOLCHEK, N. S. K H O L M U R A D O V , A. V. PURKINA, A. Yu. BILIBIN and S. S. SKOROKHODOV, In: Abstracts of Reports at IV Internat. Conf. Socialist States on Liquid Crystals, vol. 2, p. 154, Tbilisi, 1981 G. GALLI, E. CHIELLINI, C. K. OBER and R. W. LENZ, Makromolek. Chem. 183: 2693, 1982 V. V. KORSHAK and S. V. VINOGRADOVA, Ravnovesnaya polikondensatsiya (The Equilibrium Polycondensation). p. 118, Nauka, Moscow, 1972 V. V. KORSHAK and S. V. VINOGRADOVA, Neravnovesnaya polikondensatsiya (The Nonequilibirium Polycondensaion). p. l I, Nauka, Moscow, 1972 V. V. KORSHAK and S. V. V1NOGRADOVA, Neravnovesnaya polikondensatsiya (The Nonequilibrium Polycondensation) p. 137, Nauka, Moscow, 1972