Abstract
A series of thermotropic liquid crystalline(LC) copolysters form $\rho$-acetoxybenzoic acid(HBA), poly(ethylene terephthalate)(PET), terephthalic acid(TPA) and 2,6-diacetoxy naphthalene(2,6-DHN) were prepared by melt polymerization. In order to investigate the effect of polymer composition on properties, monomer compositions of HBA and PET were varied while the composition of TPA as well as 2, 6-DHN was kept constant. High molecular weight copolyesters were prepared by the acidolysis of PET with carboxylic acids, and polycondensation between the acetate and carboxyl groups. The monomer compositions were varied to determine the limits of composition that give high mechanical performance and melt processibility. LC-copolyesters with an inherent viscosity in the range of 0.7 to 1.0 were obtained. The glass transition temperature, degradation temperature and density for the LC-copolyesters increased with increasing mesogenic unit content. The co-plyester chain structure was not completely random. Scanning electron micrographs obtained from etching of the sample revealed a heterogeneous structure consisting of a PET-rich phase and mesogenic units phase. Highly anisotropic melts observed on a hot stage of a polarizing microscope indicated the presence of a nematic mesophase. The thermotropic liquid crystalline copolyesters exhibited a well developed and highly oriented fibrillar structure upon extrusion from Brabender. The PET units lowered the melting and/or stick temperature, and PET content between 10 and 20 mole % was found to be the critical level to achieve their temperature in the range of 30$0^{\circ}C$ or lower. The copolyesters containing 5 to 10 mole %PET unit exhibited the highest mechanical properties and thermal transition temperature, with melting point near 29$0^{\circ}C$ and processing temperature below 33$0^{\circ}C$.
