Abstract: The transesterification reaction of acetates and etherification reaction during the polycondensation reaction of p-acetoxybenzoic acid (Ac-PHB)and poly(ethylene terephthalate)were studied by analyzing the reaction mixture sampled after different reaction time by ¹H NMRspectra and [η] determination.Just in the beginning of the polycondensation reaction the PETchains degraded vigorously with the formation of acetoxy ethylene end groups of about 25% (molar ratio)of total ethylene content.Both the acetoxy ethylene and acetoxy phenylene end groups were reactive toward the polycondensation reaction.Using PETof low molecular weight or bis-hydroxyethylene terephthalate as the original material, the copolyester of high molecular weight could be prepared.However, it's T_f and HDTwere lower, and the solubility was higher than those as PETof high molecular weight was used.These poor properties of copolyester were explained by the high content of ethylene groups and the formation of ether bonds, among which the semi-aromatic ether content is much higher than the aliphatic one.Both the two ether bonds could react with carboxy end groups to propagate the chains under vacuum reaction condition .

Key words: Liquid crystalline copolyester, Poly(4-oxybenzoate-co-ethylene terephthalate), Acetate transesterification reaction