Crystalline and Liquid Crystalline Polyesters of Phenyl-Substituted 4,4‘-Biphenols. 5. Copolymers with 4,4‘-Oxybis(benzoic acid)

Abstract

Wholly aromatic, thermotropic copolyesters, derived from either 3-phenyl-4,4‘-biphenol (MPBP) or 3,3‘-diphenyl-4,4‘-biphenol (DPBP) with either terephthalic acid (TA) or 2,6-naphthalenedicarboxylic acid (NDA) and 50 mol % 4,4‘-oxybis(benzoic acid) (OBBA), were prepared by the melt polycondensation reaction, and their liquid crystalline properties were characterized by a number of experimental techniques. The solubility of these polyesters in common organic solvents had also been studied. They had lower fusion temperatures, Tf, than the Tm values of the copolyesters of 4,4‘-biphenol, TA, and 4-hydroxybenzoic acid. Their low Tf values were because of increased entropy of the respective monomers. Each of them exhibited a nematic phase above its Tf value that contained both the threaded and schlieren texture. The two copolyesters of MPBP and hand-drawn fibers therefrom showed a banded texture that could be preserved for a prolong period of time. Each of them showed a nematic-to-isotropic transition as determined by the polarizing light microscope studies. The copolyesters of MPBP had a much broader range of mesophase than those of DPBP. The two copolyesters of DPBP exhibited a biphase behavior at lower temperatures than those of the copolyesters of MPBP. Their random microstructures were confirmed with the WAXD studies of oriented fibers and the 13C-NMR spectroscopy, whenever possible. No development of crystallinity occurred in these copolyesters even on annealing. They had relatively high glass transition temperatures, Tg, in the range of 149−171 °C when compared with other liquid crystalline polyesters and good thermal stability, Td, in the range of 413−436 °C. Since they had no detectable crystallinity, the copolyesters of either MPBP or DPBP with TA and OBBA were soluble in common organic solvents, but those with NDA and OBBA were not soluble in these solvents.