EFFECT OF ACETATE DISTRIBUTION ON SURFACE SEGREGATION IN POLY(VINYL ALCOHOL-CO-VINYL ACETATE) COPOLYMER FILMS

The level of acetate-group surface segregation in poly(vinyl alcohol-c o-vinyl acetate) (PVA-PVAc) films was found to depend markedly on the functional group distribution along the backbone (blockiness). PVA-PVA c polymers with both random and blocky distributions were prepared at levels between 2 and 12 mol % acetate and cast into films from aqueous solution. Films from polymers with blocky distributions showed signif icantly higher levels of acetate at the surface than in the bulk, whil e polymers with random distributions of acetate functionality exhibite d little or no surface segregation. The level of acetate surface segre gation was determined by both X-ray photoelectron spectroscopy (XPS) a nd time-of-flight secondary ion mass spectroscopy (ToF-SIMS). Blocky P VA-PVAc films containing 4 mol % were seen to have approximately 40 mo l % PVAc at the outermost surface by XPS at low take-off angle. Bulk a cetate levels and acetate group distributions were determined by NMR. Variations in the weight average molecular weight (M(W)) between 40k a nd 155k, modifying the casting solvent, or annealing the films above T -g did not effect the level of surface segregation, suggesting that th e segregation is not simply a kinetic phenomenon.