KINETICS OF MELT TRANSESTERIFICATION OF DIMETHYL TEREPHTHALATE WITH BIS(2-HYDROXYETHYL) TEREPHTHALATE IN THE SYNTHESIS OF POLY(ETHYLENE-TEREPHTHALATE)

The kinetics of melt transesterification of dimethyl terephthalate (DMT) with bis(2-hydroxyethyl) terephthalate (BHET) has been studied at 160-190-degrees-C with zinc acetate as a catalyst. It was observed that both transesterification and polycondensation occur simultaneously when large amounts of BHET are present. The effects of catalyst concentration on the transesterification, polycondensation, and ester interchange reactions have been analyzed, and a new procedure is proposed to quantify the effect of catalyst concentration on the effective rate constants. It was also found that the reactivity of hydroxyl end groups in BHET and higher oligomers is about half that in ethylene glycol. A molecular species model developed for the melt transesterification process was found to give excellent agreement with experimental data.