PHASE-EQUILIBRIUM AND STRUCTURE OF THIN-F ILMS BASED ON POLY(METHYL METHACRYLATE) AND POLY(VINYL ACETATE)

The films based on PMMA-PVA blends with different compositions were st udied by means of light-scattering technique. Film thickness was varie d from 10 to 70 mum. In a temperature range of 393 - 403 K, the blends are characterized by the existence of binodal with a lower critical s olution temperature (LCST), above which phase separation via spinodal mechanism according to Cahn's criterion occurs. In a temperature range from 323 to 360 K, the polymer blends with different compositions are shown to experience some reversible structural transitions in a singl e-phase system. These transitions are associated with different rigidi ty and mobility of the cross-linking macromolecules as well as with a possible formation of anisotropic PMMA structures in PVA matrix. Varia tions in film thickness are accompanied by changes in the temperature of the above transition by 15 - 20 K and in LCST - only by 4 - 5 K.