Mechanism and kinetics of transesterification in poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalene dicarboxylate) polymer blends

Abstract

In a previous work [L. Alexandrova, A. Cabrera, M.A. Hernández, M.J. Cruz, M.J.M. Abadie, O. Manero, D. Likhatchev, Polymer 43 (2002) 5397. [1]], a model compounds study on the kinetics of a transesterification reaction in poly(ethylene terphthalate)–poly(ethylene naphthalene 2,6-dicarboxylate), PET–PEN blends, resulting from melt processing, was simulated using model compounds of ethylene dibenzoate (BEB) and ethylene dinaphthoate (NEN). A first-order kinetics was established under pseudo first-order conditions for both reactants, and thus the overall transesterification reaction was second-order reversible. Direct ester–ester exchange was deduced as a prevailing mechanism for the transesterification reaction under the conditions studied.In this work, the actual PET–PEN system was melt processed by mixing the polymers below the critical reaction temperature in a twin-screw extruder. Thereafter, the reaction was induced by temperature in open glass ampoules. A second order reversible kinetics was measured, in agreement with the kinetics established in the previous model compounds study. The equilibrium constant value corresponds to a forward rate constant which is four times larger than the reverse rate constant. The activation thermodynamic parameters confirmed the direct ester–ester exchange mechanism for the reaction.