1034 Macromolecules 1983, 16, 1034-1036 Liquid-Crystalline Polymers. 12. Polyesters with either Alternating or Random Orientation of Mesogenic Units Christopher Ober and Robert W. Lenz* Materials Research Laboratory, Chemical Engineering Department, University zyx of Massachusetts, Amherst, Massachusetts 01003 Giancarlo Galli and Emo Chiellini Istituto Chimica Organica Industriale, Uniuersitd di Pisa, zyxwv 56100 Pisa, Italy. Received August 19, 1982 ABSTRACT: A new synthetic route was used to prepare polymers containing either random or alternating sequences of the mesogenic dyad -O-CO-C6H4-0-CO-C6H4-co-o-. The polymer with random head-tail orientations of the oxybenzoate units in the dyad was thermotropic, but the liquid-crystal phase existed over a much narrower temperature range when compared to that for the polymer with related triad mesogenic units. Surprisingly, the compositionally identical polymer with an exactly alternating head-tail arrangement of mesogenic units in successive dyads did not form a mesophase. Hence, the randomness of mesogenic group orientations in the main chain can be very important in determining mesophase formation and properties. Introduction Main-chain thermotropic polymers generally contain mesogenic units consisting of structures with two or more aromatic or cycloaliphatic rings, and these units may or may not be connected by flexible spacers.'B2 Both the molecular structure of the components and the manner in which they are assembled can have a great effect on the thermal properties of these polymers, as demonstrated by Blumstein and co-workers using azoxy mesogenic group^.^ In fact, changes of type and even of direction of their connecting bonds alter the geometry and the polarizability of the mesogenic units and ultimately the liquid-crystal properties. Most synthetic routes result in polymers with a well- defined arrangement of the mesogenic units in the main hai in,^-^ but an outstanding exception to this is the series of thermotropic copolyesters, obtained by melt-phase transesterification, containing several different types of mesogens with a terephthaloyl unit and one or more p- oxybenzoyl units.&* Recently we reportedg on the syn- thesis of new liquid-crystalline polymers containing regu- larly "alternating" head-to-tail, tail-to-head aromatic ester dyads with one terephthaloyl, T, and one p-oxybenzoyl, 0, unit, structure I in Figure 1. As a part of these studies, polymers were also prepared that contained the aromatic dyad oriented along the polymer chain in a "random" fashion, structure I1 in Figure 1. These polymers can be considered to be random co- polymers of head-to-tail and tail-to-head ester units as indicated in Figure 1. Decamethylenediol and triethylene glycol were chosen as flexible spacers, which were known to be able to yield, under appropriate conditions, smec- tic-like polyester~.~J~ As a comparison a polymer sample containing decamethylenediol and the mesogneic dyad with an "alternating" orientation was obtained by the procedure previously r e p ~ r t e d . ~ Experimental Section Benzyl 4-(Carbobenzoxy)phenyl Terephthalate (5). Reflux of 12.3 g (0.048 mol) of 2 in 40 mL (0.37 mol) of SOCl, was w r i e d out for 1 h in the presence of a catalytic amount of DMF. The SOClz was removed, and the white crystalline acid choloride (3) was ready for use. To a solution of 15 g (66 mmol) of 4 in 200 mL of dry pyridine was added 15.5 g (48 mmol) of 3. The mixture was heated at 60 "C for 4 h, stirred at ambient temperature for 2 days, and poured into 600 mL of 2 N HCl. The precipitate zyxwvutsr (5) was filtered, dried, and crystallized in 95% ethanol: yield 65%; mp 98-100 "C; IR (KBr) 3060 (weak), 1740,1720,1710,1605,1500,1450,1410,1380, 0024-9297/83/2216-1034$01.50/0 1370,1260,1205,1160,1105,1065,1015,760, 730,715,695 cm-'; 'H NMR (CDC13) 6 8.40-8.05 (m, 3, terephthalate and 2,6-oxy- benzoate), 7.65-720 (m, 6, aromatic benzyl and 3,5-oxybenzoate), 5.39 and 5.37 (2 zyxwv s, 2, CH2). Anal. Calcd for C2&06: C, 74.7; H, 4.7. Found: C, 74.4; H, 4.8. 4-Carboxyphenyl Hydrogen Terephthalate (6). Benzyl- blocked diacid 5 (10 g (0.021 mol)) was dissolved in 150 mL of CF3COOH, 5 mL of a 33% solution of HBr in CH3COOH was added, and the mixture was allowed to stir for 4 h. A precipitate formed after about 15 min, and stirring became more difficult. The reaction was stopped by addition of acetone, and the product was filtered, washed with acetone, dried under vacuum, and then crystallized from a 5:l CH3COOH/water mixture:l0 yield 79% ; dec. >310 "C; IR (KBr) 2900 (very broad), 1745,1690,1500,1425, 1270,1205,1165,1070,1020,760,720 cm-'; 'H NMR (Me2SO-d6) d 8.45-7.90 (m, 3, terephthalate and 2,6-oxybenzoate), 7.36 (d, 1, 3,5-oxybenzoate). Anal. Calcd for C16H1006: C, 62.9; H, 3.6. Found: C, 63.2; H, 3.9. Polymer Preparation and Characterization. Preparation of the diacid chlorides and soltuion polymerization were carried out according to earlier procedures? Viscosity measurements were performed in 1,2-dichloroethane solution at 25 "C by using a Desreux-Bischoff dilution viscometer. Calorimetric analyses were carried out on a Perkin-Elmer DSC-2 apparatus at a heating and cooling rate of 10 "C/min. Indium standards were used for temperature calibration. Thermal-optical analysis (TOA) mea- surements were made with an American Optical Microstar po- larizing microscope, suitably equipped with a Mettler FP5 pro- grammable heating stage and a photometer. Results and Discussion The synthetic route leading to the mono(4-carboxy- phenyl) ester of terephthalic acid (6), a mesogenic structure capable of yielding thermotropic polyesters, is outlined in Scheme I. It is of interest to note that in this reaction sequence, neither 6 nor any of the intermediates have liquid-crystalline properties. Polymers with randomly oriented mesogenic groups were prepared in 1,2-dichloroethane solution at 60 zy "C by re- acting the diacid 6, after quantitative in situ conversion to the diacid chloride, with the appropiate diol. The polymeric products were obtained in good yields and were characterized by low molecular weights, as suggested by the values of the intrinsic viscosity, but precise values of molecular weight are not known. The IR and NMR spectra exhibit the expected signals of both reacted mo- nomeric units to substantiate the formation of aryl alkyl polyesters. In the present case the mesogenic dyads, OT and TO, are "randomly" oriented in the polymer chain, while in the earlier system constitutional regularity was provided by 0 1983 American Chemical Society