Macromolecules, Vol.30, No.18, 5331-5338, 1997
Segmental Dynamics of Bulk and Adsorbed Poly(Methyl Acrylate)-D(3) by Deuterium NMR - Effect of Adsorbed Amount
Deuterium solid-state quadrupole-echo NMR techniques were used to probe the dynamics of bulk and silica-adsorbed methyl-labeled poly(methyl acrylate)-d(3) (PMA-d(3)). For bulk PMA-d(3), collapse of the H-2 NMR powder pattern indicated a sudden increase in segmental motion at about 50 degrees C. This temperature was 40 degrees C above the reported glass transition temperature (T-g) Of bulk PMA and was due to the higher frequencies to which the "NMR" T-g was sensitive. Surface samples with different adsorbed amounts exhibited different behavior at the silica-polymer-air interface and consisted of superpositions from different components. At lower temperatures, a mobile component not found in the bulk PMA-d(3) was observed while, at higher temperatures, a rigid component still existed. The mobile component was attributed to polymer segments near the polymer-air interface and the rigid component to segments nearer to the polymer-silica interface. As the adsorbed amount increased, the relative amounts of mobile components increased. The results were consistent with an interface graded in mobility with a broad distribution in the adsorbed layer. The mobilities were generally reduced at lower adsorbed amounts.
Keywords:NUCLEAR-MAGNETIC-RESONANCE;SOLID-LIQUID INTERFACE;POLYMER LAYERS;GOOD SOLVENT;THIN-FILMS;GLASS-TRANSITION;TEMPERATURE;THICKNESS;MOBILITY;FORCES