DENSITY PROFILE OF TERMINALLY ADSORBED POLYMERS

Specifically labeled terpolymers of 2-vinylpyridine, styrene, and deuterostyrene have been prepared by anionic polymerization. The deuterostyrene was deuterated in the methine position and placed either in the middle or at the end of the triblock terpolymer. The moderately low molecular weight polymers (ca. 20 000 g/mol, polydispersity ca. 1.4) were then adsorbed onto high surface area silica. The adsorption isotherm was measured from toluene solution to plateau at about 1.75 mg of polymer/m2 of silica. The environment of the styrene segments in the terpolymer attached to the silica surface and swollen with toluene was probed with 2H NMR. Comparison of 2H NMR spin–lattice relaxation time, T1, for the adsorbed polymer to that of the polymer in solution suggests that the local concentration of styrene segments near the middle of the polymer, i.e. next to the vinylpyridine segments, is about 0.11 g/mL. The concentration of segments located at the end of the polymer is estimated to be approximately 0.048 g/mL. These experiments suggest that the polymers are extended in a good solvent for styrene to about 4 times the styrene radius of gyration. The relaxation times (T1 and T2) of the surface-bound polymer were closer to each other than those for the homopolymer in solution, suggesting that the dynamics are rather different than in solution. © 1990, American Chemical Society. All rights reserved.