Selective surface modification of PVC films as revealed by confocal Raman microspectroscopy

The chemical modification of PVC films with sodium azide and 4-aminothiophe nol was investigated. Using mixtures of a good and a nonsolvent for PVC, re actions took place in a controlled way, and the films remained transparent and smooth. To obtain information about the surface selectivity of the reac tions, the degree of modification of the polymer across the film was determ ined by depth profiling carried out using confocal Raman microscopy. It is shown that the reaction with sodium azide always occurs homogeneously throu gh the film while in the case of aminothiophenol, conditions could be found that allowed the polymer film to be preferentially modified at the surface . The gradient of the degree of modification and the surface selectivity de pend on the relationship between the rate constants of the substitution rea ction and the diffusion process of the reactant. They are, therefore, funct ions of reaction time, temperature, and the proportion of solvent/nonsolven t used for the reaction. The measured depth profiles as a function of react ion time have been fitted to a solution of the second Fickian law and combi ned diffusion/reaction coefficients for the transport of the reactant have been calculated.