ESR studies of spin-labelled poly(vinyl acetate)
The work presented in this thesis involved spin-labelling poly(vinyl acetate), PVAc, in the polymer backbone and using the resulting polymers to study PVAc in solution, at the solid-liquid interface and to a small extent in the bulk state. Two methods were employed to synthesize PVAc labelled in the polymer backbone, I) a Keana type synthesis on vinyl acetate-carbon monoxide copolymers (PVAcI). II) direct copolymerization of vinyl acetate with 2,2,5,5-tetramethyl- pyrrolline-3-carboxyamide, (TMPC), with subsequent oxidation of the TMPC monomer units (PVAcII). PVAcI proved unsatisfactory because of a low label density and a high susceptibility to degradation. In contrast, PVAcII was more heavily labelled and was ideally suited for spin-label studies. The rotational correlation time tauR for the nitroxide label is readily obtained from the ESR spectrum of the labelled polymer in solution. Rotation of the label was found to be anisotropic, with rotation about the polymer backbone ocurring faster than rotation perpendicular to this direction. The different methods for accounting for the effects of inhomogeneous broadening were evaluated and in this study the additional broadening method was found to be the most appropriate. Analysis of the rotational correlation times showed that motion of the label can be subdivided into two different modes of motion, namely whole molecule tumbling and segmental reorientation. Segmental motion was shown to dominate the relaxation of a polymer of molecular weight 20000. The dynamics of these segmental processes were found to obey the high frictional limit of Kramers' theory for the diffusion of a particle over a barrier indicating the chain dynamics are controlled by the viscous drag of the solvent and intramolecular steric effects. Adsorption studies of PVAcII-1 showed that such labelled polymers can yield information on the conformation of PVAc adsorbed at a solid-liquid interface. Studies on several solvent/substrate systems showed that the solvent quality and the nature of the surface have significant effects on the conformation and degree of adsorption of the polymer. Finally, relaxation studies on bulk PVAcII showed that the label slightly perturbs the effective volume of a relaxing segment.