Synthesis of Dye-Labeled Poly(vinyl acetate-co-ethylene) (EVA) Latex and Polymer Diffusion in their Latex Films

Abstract

We describe the synthesis of dye-labeled poly(vinyl acetate-co-ethylene) (EVA) latexes with the purpose of understanding the polymer diffusion behavior in their latex films. Polymer diffusion was followed with experiments based upon fluorescence resonance energy transfer (ET). Both the batch and semibatch emulsion polymerizations of vinyl acetate-ethylene (VAc-E) were examined. The ethylene content of these EVA samples was designed at ∼20 wt% (50 mol%). Under batch emulsion polymerization conditions, the reaction is characterized by a rapid monomer conversion and an increment of E content with reaction time. VAc-E batch emulsion polymerization in the presence of the donor dye 9-phenanthryl methyl methacrylate produced EVA with non-random dye distribution, which makes these samples unsuitable for ET experiments. The semibatch emulsion polymerization of VAc-E was carried out under VAc-starved feeding conditions. The resulting EVA was characterized by constant chemical composition throughout the feed. In addition, our data suggest the presence of two components, distinct in molar mass and degree of branching, in these EVA samples. More importantly, these VAc-E polymerizations in the presence of dyes [9-phenanthryl methyl acrylate as the donor and 2′-acryloxy-4′-methyl-4-(N,N-dimethylamino)-benzophenone as the acceptor] produced EVA with random dye incorporation, making these samples effective for ET experiments. Unlike the typical polymer diffusion behavior in latex films, characterized by small extents of polymer diffusion in newly dried latex followed by an increase of the extent of diffusion upon annealing, our ET experiments showed that polymer diffusion in these EVA latex films was complete by the time the films were dry. We attribute this striking difference to the low glass transition temperature (T g) of the EVA and to its low effective monomeric friction coefficient at the drying temperature.