Fully aromatic thermotropic liquid crystalline polyesters of substituted 4,4′‐biphenols. IV. Homopolyesters with terephthalic acid and copolyesters with terephthalic acid and 4‐hydroxybenzoic acid

A series of fully aromatic thermotropic polyesters based on mono‐, di‐, and tetra‐substituted biphenols was prepared by the melt polycondensation method and examined for their thermotropic behavior by a variety of experimental techniques. The homopolyesters obtained from substituted biphenols containing either one phenyl or two phenyl groups as substituent(s) and TA formed nematic melts, but the homopolymers of the substituted biphenols containing either four sec‐butyl groups or two tert‐butyl groups with TA had melting transitions, Tm, above 400°C. Thus, it was not possible to determine whether they formed nematic melts. On copolymerization with 30 mol % HBA most of the resulting copolyesters had much lower Tm values, compared to those of respective homopolyesters, and the copolymers of the biphenol monomer containing the tert‐butyl groups formed a nematic melt at an observable temperature. However, the copolymer of the biphenol with sec‐butyl groups still had a Tm above 400°C.