PREPARATION OF POLY(VINYL ACETATE-B-ACRYLONITRILE) BLOCK-COPOLYMER FROM LONG-LIVED VINYL-ACETATE MACRO-RADICALS BY PHOTOCHEMICAL METHOD

Long-lived Macro-radicals of Vinyl Acetate (VAc) were obtained by the irradiation of UV light on a solution of VAc in cyclohexane in the pre sence of Di-tert. butyl peroxide (DBPO) as photo-initiator and under n itrogen atmosphere for 96 hours at different temperatures. The PVAc ma croradicals were formed in the insoluble phase as trapped radicals. Th e presence of stable macro-radicals was confirmed by ESR spectroscopy. The stable PVAc macro-radicals were then allowed to react with Acrylo nitrile (AN) under N2 atmosphere at the desired temperature and for th e desired time period to get block copolymer. The block copolymer was purified by selective extraction and fractional precipitation techniqu es. The effects of various parameters such as first and second phase p olymerization lime and temperature; concentration of DBPO and monomer and solvent on the yield of block copolymer have been studied. The blo ck copolymers have been characterized by ESR, IR, NMR, DSC and TGA tec hniques.