CHEMICAL-REACTIONS BETWEEN IMMISCIBLE POLYMERS IN THE MELT - TRANSESTERIFICATION OF POLY(ETHYLENE-CO-METHYL ACRYLATE) WITH MONO-HYDROXYLATED POLYSTYRENES

This article presents a unique example dealing with how chemical react ions between immiscible polymers in the melt behave differently than t hey would do in solution. Specifically, a model reaction was chosen: t he transesterification between poly(ethylene-co-methyl acrylate) (EMA) and polystyrene mono-hydroxylated at the chain end (PSOH). It was car ried out in the melt in a batch mixer. The overall rate of this reacti on has a similar dependence of temperature, composition of reactants, and the nature and concentration of catalyst as in solution. The react ivity of PSOH decreases drastically with increasing molecular weight, and it becomes very weak when the molecular weight exceeds 8000 g/mol. As opposed to a reaction in solution or in a homogeneous melt, mechan ical mixing increases the reaction rate since it generates interfacial area and reduces the diffusion length. The EMA-g-PS graft copolymer f ormed at the interfaces reduces the interfacial tension, and increases the miscibility of the reaction mixture. However, its occupation of t he interfaces reduces contact between the reactive moieties, thus decr easing the overall reactivity. More importantly and much to our surpri se, adding 1 to 2 wt% of an inert solvent increased greatly the overal l reaction rate. While an increased interfacial mixing and diffusion b y the presence of minor amounts of solvent are though to be the major factors contributing to the drastic increase in reactivity, numerous q uestions still remain. Nevertheless, this study clearly showed that as opposed to a reaction in solution, mechanical mixing and the presence of minor amounts of solvent are two additional and critical means to control chemical reactions between immiscible polymer melts. (C) 1995 John Wiley & Sons, Inc.