Poly(ethylene-co-vinyl acetate-g-styrene) from macro-transfer agent: synthesis and use in polymer blend

A systematic study involving the free-radical graft polymerization of styrene in the presence of ethylene–vinyl acetate (EVA) copolymer functionalized with mercapto groups was investigated in terms of monomer, mercapto group and azo-bis-isobutyronitrile (AIBN) concentrations. The mercapto-modified EVA copolymer (EVALSH) acts as a macro-transfer agent, giving rise to graft copolymers with a relatively high grafting efficiency. High molecular weight of grafted chains and high grafting efficiency can be achieved by using low AIBN content and high amount of styrene. The amount of SH groups in the EVALSH backbone does not exert strong influence on the molecular weight of the grafted segments but increases the conversion of the monomer as graft. The addition of 5 wt.% of this copolymer in polystyrene/EVA (70:30 and 60:40 wt.%) blends resulted in better mechanical performance as compared to that of uncompatibilized blends. In addition, by employing scanning electron microscopy, it was possible to observe that the compatibilization decreased the size of the EVA phase, which became thinner and more elongated, contributing to the formation of a physical interpenetrating network.