The Controlled Solvolysis of Ethylene−Vinyl Acetate Copolymers

Abstract

The basic “hydrolysis” of ethylene−vinyl acetate copolymers (EVA) leads to ethylene−vinyl alcohol copolymers (EVOH) or ethylene−vinyl acetate−vinyl alcohol terpolymers which can be used for their surface properties or for further chemical modification. The controlled basic solvolysis of EVA takes place via a complicated nonstoichiometric mechanism. The solvolysis by anhydrous methanol catalyzed by sodium methoxide has been investigated thoroughly. This reaction is capable of fully converting acetate groups; the solvolysis of an acetate group next to another acetate (in EVV triads) is faster than that for isolated vinyl acetate (EVE triads) and proceeds immediately to the neighboring acetate group. The rate constants of each elementary step have been determined with the help of numerical simulations of kinetics data. In particular, the forward rate constant, k+, of the SN2 attack of the methoxide ion on vinyl acetate strongly depends on solvent quality (methanol content), i.e., on polymer coil expansion. W...