SEGMENTAL DYNAMICS OF BULK AND ADSORBED POLY(METHYL ACRYLATE)-D(3) BYDEUTERIUM NMR - EFFECT OF ADSORBED AMOUNT

Deuterium solid-state quadrupole-echo NMR techniques were used to prob e 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 abou t 50 degrees C. This temperature was 40 degrees C above the reported g lass transition temperature (T-g) Of bulk PMA and was due to the highe r frequencies to which the ''NMR'' T-g was sensitive. Surface samples with different adsorbed amounts exhibited different behavior at the si lica-polymer-air interface and consisted of superpositions from differ ent 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 polym er segments near the polymer-air interface and the rigid component to segments nearer to the polymer-silica interface. As the adsorbed amoun t increased, the relative amounts of mobile components increased. The results were consistent with an interface graded in mobility with a br oad distribution in the adsorbed layer. The mobilities were generally reduced at lower adsorbed amounts.