Dynamics of Bulk and Adsorbed Poly(Vinyl Acetate)
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We have recently completed a series of experiments on methyl-labeled poly(vinyl acetate)-d3, (PVAc-d3)1 and poly(methyl acrylate)-d3 (PMA-d3).234 the systems have been studied as a function of the adsorbed amount, molecular weight, and presence of a protonated overlayer. Using deuterium line shape analysis, we have found that around the glass transition temperature, the adsorbed polymers show the presence of a motional gradient. Polymer segments near the silica-polymer interface have less mobility than the bulk polymer and those near the polymer-air interface are more mobile than those of the bulk polymer. A schematic representation of the motional gradient is shown in Figure 1. In the present work, we report the results of 2-dimensional deuterium NMR exchange (2dX) experiments on PVAc-d3 in bulk and adsorbed on silica. The results of these experiments can be used to identify the dynamics of the adsorbed polymer so that the nature of the motional gradient can be identified. We find that the dynamics of the adsorbed polymer around the glass transition can be described by a bimodal distribution of reorientation times.