Temperature dependence of polymer diffusion in poly(vinyl acetate-co-dibutyl maleate) latex films

Abstract

We describe polymer diffusion and its temperature dependence in poly(vinyl acetate-co-dibutyl maleate) [P(VAc-DBM)] latex films prepared from 4:1 w/w ratio of VAc:DBM. Two sets of polymers were investigated: one set containing 50% gel (high-M); the other set, with Mw ≈ 250000 (M250K), free of a measurable gel content. Despite their similar chemical compositions, as determined by 1H NMR, these two sets of samples exhibited different glass transition temperatures (Tg). Latex particles were labeled with 9-methacryloxymethylphenanthrene as the donor dye and 2′-acryloxy-4′-methyl-4-(N,N-dimethyl-amino)benzophenone as the acceptor. Polymer diffusion was monitored by nonradiative energy transfer (ET), and apparent diffusion coefficients (Dapp) were calculated from the ET data using a simple diffusion model. These values increased with temperature and were characterized by an apparent activation energy (Ea) of 37 ± 2 kcal/mol for the high-M polymer and 45 ± 2 kcal/mol for the M250K sample. Rheology measurements at different fixed temperatures were carried out to follow the response of the dynamic moduli (G′, G″) with respect to frequency (ω). A master curve based on the Williams-Landel-Ferry (WLF) equation could be constructed as a plot of shift factors vs 1/T, and shift factors for Dapp for both sets of polymers as well as for the G′, G″ values fell on the same curve. Thus, the difference in Ea values for the polymer diffusion can be ascribed to changes in the microscopic friction coefficient and the differences in Tg of the two sets of samples.