Influence of annealing on the spun fiber properties of thermotropic liquid crystalline polyesters with flexible units in a main chain

Abstract

Semiflexible thermotropic liquid crystalline (TLC) polyesters with a mesogenic unit of 4,4'-diphenoxy terephthalate and two flexible spacers of decamethylene and hexamethylene were synthesized changing the ratio of two aliphatic units in a main chain. Those random copolyesters had the following schematic molecular structures: [GRAPHICS] where each molecule had an x value of 0, 0.25, 0.5, 0.75 and 1. An as-spun fiber showed a better orientation and higher modulus with increase of draw ratio, An annealed fiber spun with low draw ratio exhibited an improvement of modulus and tensile strength while that with a high draw ratio showed the lower modulus and tensile strength after they were annealed. The decrease in modulus and tensile strength of the annealed fiber spun with a high draw ratio could be explained by the reason that the relaxation of the orientation during annealing.