Processability‐enhanced aromatic thermotropic liquid crystalline copolyesters via the introduction of the unsymmetrical units

Abstract

A series of ternary thermotropic liquid crystalline copolyesters was synthesized through a simple one-pot melt condensation based on 4-hydroxybenzoic acid (HBA), 6-hydroxy-2-naphthoic acid (HNA) and 4-hydroxy-2-naphthoic acid (4-HNA). The structures were modified via the introduction of the asymmetric 4-HNA unit. High glass transition temperature values (>80 C) and relatively low melting temperature values (<265 C) were achieved with 4-HNA molar fraction of over 0.5%, and the copolymer exhibited 5% degradation temperatures of 442-453 C and the char yields of 35.80%-36.74% at 800 C. This indicated that the introduction of asymmetric 4-HNA blocks into the backbone provides a "torsion axis" to regulate the dense stacking between different main-chains, which was crucial for the mobility of polyester during thermal processes. Moreover, crystallinity decreased with the increase of 4-HNA content. The incorporation of 4-HNA also endowed the obtained copolyester fiber with a skin-core structure and microfiber morphology. Due to the excellent temperature resistance and fibrous morphology of P-HBA/HNA/4-HNA. This work provided a novel strategy to synthesize aromatic thermotropic liquid crystalline copolyesters, which can be promising candidates for processing additives or reinforcing materials with improved processing properties, and potential application in processing, personal protection, and other extreme temperature environments.

Effects of Para‐ or Meta‐Aromatic Amide Units on the Microstructure, Thermal, Mechanical, Rheological, and Dielectric Properties of Thermotropic Liquid Crystalline Poly(ester amide)s

“…After the discovery of high‐performance lyotropic liquid crystalline polymers through poly( p ‐phenylene terephthalamide) (Kevlar) and poly( p ‐benzamide), thermotropic liquid aromatic polyesters (TLCPs) have also attracted great attention from industry and academia because of their high thermal stability, high strength/modulus, good chemical resistance, dimensional stability, and easy melt‐processibility. [ 1–10 ] TLCPs form partially ordered and anisotropic liquid crystals even above their melting transition temperatures due to rigid rod‐shaped structural units called mesogenic units. [ 6,11–16 ] Accordingly, TLCPs are applied to super‐engineering thermoplastics, technical fibers, composite materials for automobile parts, etc.…”