Segmental Dynamics of Interfacial Poly(methyl Acrylate)-d₃ in Composites by Deuterium NMR Spectroscopy

The interface in composite materials containing an ultrathin layer of poly(methyl acrylate)-d3 (PMA-d3) on silica was studied using deuterium NMR. PMA-d3 was deposited from solution at saturation coverage from toluene onto silica. The samples were dried and composite samples made by hot pressing the PMA-d3/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-d3 were studied at the air−polymer−silica and polymer−polymer−silica interfaces using deuterium solid-state quadrupole-echo NMR and the results compared to those for the bulk polymer. It was found that for samples at the air−polymer−silica interface, some of the polymer segments in the surface sample had segmental mobility higher than that of the corresponding bulk PMA-d3 sample at the same temperature. 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-d3, in the composite samples, decreased in mobility in the order of LMW−PMA \u3e HMW−PMA \u3e PS. The PS sample caused the greatest reduction in the PMA-d3 interfacial mobility. The order was consistent with the segmental mobilities of the polymers used for the overlayers. The lower the mobility of the polymer used for the overlayer, the more restricted were the polymer segments in the adsorbed PMA-d3 layer