Solid-state polymerization of a liquid crystalline copolyester derived from 2,6-naphthalene dicarboxylic acid, terephthalic acid, 4-acetoxybenzoic acid and hydroquinone diacetate

Solid-state polymerization (SSP) has been applied for the synthesis of a wholly aromatic thermotropic liquid crystalline polymer derived from 4-acetoxybenzoic acid, hydroquinone diacetate, 2,6-naphthalene dicarboxylic acid, and terephthalic acid. The influence of various operating parameters, such as reaction temperature, reaction time, nitrogen gas flow velocity, and particle size, on the solid-state polymerization has been studied, and the SSP products were characterized by polarized light microscope (PLM), differential scanning calorimeter (DSC) viscosity measurement, and nanoindentation test. It was found that the molar mass of the copolyester substantially increased during the SSP process, as shown by measurements of melting temperature and inherent viscosity of the product. The SSP reaction mechanism and rate are discussed with the changes of the operating parameters. Nanoindentation test shows the increase of hardness and modulus of the copolyesters, which is due to the increase of molar mass. A banded texture of the copolyesters with narrow bands was observed after SSP by using PLM.