Liquid-crystalline polyimides .28. Thermoplastic elastomers with smectic hard phase based on 3,5:3',5'-biphenyltetracarboximides

Two series of copoly(ether-imide)s were prepared by polycondensation of 3,5:3',5'-biphenyltetracarboxylic anhydride (BTCA) and mixtures of 4,4'-(nonamethylenedioxy)-dianiline and polytetrahydrofuran (polyTHF) containing two amino end groups. Two samples of polyTHF were used, one sample with a number-average molecular weight (M) over bar(a) = 750 and another sample with (M) over bar(n), around 2100. All polycondensations were conducted in the form of a ''one-pot procedure'' in refluxing m-cresol. The mole ratio of poly-THF and 4,4'-(nonamethylenedioxy)dianiline was varied, so that the length of the hard segments varied. Wide-angle X-ray scattering (WAXS) powder patterns proved that at least the hard phase of those poly(ether-imide)s with relatively long hard segments possesses a smectic-crystalline layered structure analogous to that of the homopolymer derived from BTCA and 4,4'-(nonamethylenedioxy)dianiline. Only one polyimide showed highly elastic behavior.