Synthesis and Characterization of Thermotropic Liquid Crystalline Polyesters/Glass Fiber by <i>In Situ</i> Process

Abstract

Liquid crystalline polyesters containing central biphenylene moiety in the mesogenic unit with ester linkages to the different lengths of flexible spacers were synthesized using melt polycondensation reaction. Glass fiber, as a reinforce, was meltpolymerized with 4-acetoxybenzoic(ABA),4,4＇-diacetoxybiphenyl and terephthalic acid(TA) to make TLCPs with a good mechanical properties. All the obtained compounds were characterized by conventional spectroscopic methods. The thermal behavior of the polymers has been characterized using polarized optical microscopy and differential scanning calorimetry. The effect of monomer structure and mechanical properties has been investigated on the prepared polyesters and is also compared with that of the analogous polyester by other processing mode. Optical microscopy showed a highly threaded liquid crystalline texture to a high birefringent Schlierene texture characteristic of the nematic phase for all polyesters. DSC experiments were also found in accord with mesophase formation. The melting points of polymers having a central 4,4’-biphenyldicarboxylate residue have two broad endotherms. The glass transition temperature values of polyesters are not effect by the glass fiber. According to the SEM result showed that the composite had strong fiber-matrix adhesion. From the mechanical test result, it showed that TLCP are reinforced by rigid fiber further improvement of properties depending on fiber content, fiber fabric construction, fiber type. The mechanical properties of GF/TLCP had been improved greatly as the content of glass fiber was increased,but GF/TLCP mechanical properties do not improve remarkably as glass fiber content more than 30wt%.The effect of copolymerization with added glass fiber in synthesis process is compared with that of the anlogous homopolyesters by other processing mode. Our finding shows that the copolymers exhibit reduced technical process and maintained mechanical properties.