Segmental dynamics of interfacial poly(methyl acrylate)-d(3) in compositesby deuterium NMR spectroscopy

The interface in composite materials containing an ultrathin layer of poly( methyl acrylate)-d(3) (PMA-d(3)) on silica was studied using deuterium NMR. PMA-d(3) was deposited from solution at saturation coverage from toluene o nto silica. In samples were dried and composite samples made by hot pressin g the PMA-d(3)/silica samples with hydrogenated polystyrene (PS) and high ( HMW) and low (LMW) molecular weight hydrogenated poly(methyl acrylate) (PMA ) as the overlayer. The interfacial layers of PMA-d(3) were studied at the air-polymer-silica and polymer-polymer-silica interfaces using deuterium so lid-state quadrupole-echo NMR and the results compared to those for the bul k polymer. It was found that for samples at the air-polymer-silica interfac e, some of the polymer segments in the surface sample had segmental mobilit y higher than that of the corresponding bulk PMA-d(3) sample at the same te mperature. When overcoated with unlabeled polymer, the interfacial polymer at the polymer-polymer-silica interface showed reduced mobility due to the presence of the overlayer. The adsorbed PMA-d(3), in the composite samples, decreased in mobility in the order of LMW-PMA > HMW-PMA > PS. The PS sampl e caused the greatest reduction in the PMA-d(3) interfacial mobility. The o rder was consistent with the segmental mobilities of the polymers used for the overlayers. The lower the mobility of the polymer used for the overlaye r, the more restricted were the polymer segments in the adsorbed PMA-d(3) l ayer.