The Fraction of Bound Segments and the Chain Motion of Adsorbed Poly(methyl methacrylate) at the Solution-Solid Interface as Studied by Electron Spin Resonance

The configuration of poly(methyl methacrylate) adsorbed on silica from dilute solution (CCl4, benzene, and CHCl3) was studied from the point of view of the chain motion by a spin-labeling technique. The ESR spectrum of the adsorbed polymer was found to be composed of three portions, which had considerably different degrees of the motional freedom of the local chain segments. The rotational correlation times corresponding to the three portions were estimated by the line shape analysis and the rapid passage technique. These times were 1×10−9, 5×10−9, and longer than 10−6 s, and were attributed to the motions in the long loop, short loop, and train, respectively. The large fractions of the bound segments, obtained in all the cases of low surface coverage, showed highly flattened structures of the adsorbed chain molecules. In the adsorption from a poor solvent (CCl4), a strongly compressed structure with a large number of the short loops was found. The adsorbed layer thickness, indicated by the fraction of the segments in the three states, became much smaller with an increase in the solvent power and a decrease in the surface coverage.