Segmental dynamics in bulk and adsorbed poly(methyl acrylate)-d(3) by deuterium NMR

Deuterium solid-state quadrupole-echo NMR techniques were used to probe the dynamics of bulk and silica-adsorbed poly(methyl acrylate)-d{dollar}sb3{dollar} (PMA-d{dollar}sb3{dollar}). The effects of surface coverage, molecular weight and overlayer materials on the dynamics were investigated. Bulk PMA-d{dollar}sb3{dollar} with high molecular weight showed a collapse in the {dollar}sp2{dollar}H NMR powder pattern corresponding to a sudden increase in motional rate at about 50{dollar}spcirc{dollar}C (nmr T{dollar}sb{lcub}rm g{rcub}{dollar}), 40{dollar}spcirc{dollar}C above the reported glass transition temperature.; Surface samples were prepared by adsorption of PMA-d{dollar}sb3{dollar} onto silica. The NMR spectra were collected from surface species at the surface-air interface. The spectra consisted of different components. Some of the adsorbed material had an enhanced mobility attributed to segments near the air interface. The adsorbed PMA-d{dollar}sb3{dollar} was more rigid as the surface coverage decreased. The effect of molecular weight was also studied. Bulk PMA-d{dollar}sb3{dollar} with lower molecular weight was more mobile. Contrastly, the adsorbed PMA-d{dollar}sb3{dollar} with higher molecular weight was more mobile.; Composite samples were prepared by hot pressing a surface sample with hydrogenated polystyrene and PMA of different molecular weights as the overlayer. The composite samples were studied in the interfacial layer of PMA-d{dollar}sb3{dollar} between the silica and overlayer. No material in any composite sample had enhanced mobility and the lower the mobility of the overlayer, the more restricted the adsorbed PMA-d{dollar}sb3{dollar} layer was.