SYNTHESIS OF WELL-DEFINED POLYPROPYLENE-GRAFT-POLYSTYRENE AND RELATIONSHIP BETWEEN STRUCTURE AND THE ABILITY TO COMPATIBILIZE THE POLYMERIC BLENDS

ABSTRACT: A new method to prepare polypropylene-graft-polystyrene copolymers with tailored structure has been developed. The ability of a series of copolymers with variable structure to compatibilize the polypropylene-polystyrene blends was evaluated through microscopic observation of the morphology of the blends. The synthesis is a two-step process, the first one being the preparation, in the presence of ansa-zirconocene-based catalyst, of the backbones formed by i-PP sequences spaced by p-methylstyreneethylene units. In the second step, the methyl groups in the aromatic rings are reacted with sec-butyllithium, and the resulting metalated polymers allowed to add the styrene to initiate the side polystyrene chains growth. This synthesis turns out versatile both in the first step because by changing monomers feed ratio, backbones with different number of the sites of growth of the grafts and with different length of the polypropylene sequences can be obtained, and in the last step because, by tuning styrene concentration and reaction time, the side chains length can be regulated. The PP-g-PS copolymers with PP sequences varying in the range of 24-98 units, with number of the side chains from 2 to 14 and with PS side chains length from 0.33 102 to 6.9 102 units, were obtained and afterward tested as compatibilizers in the PP/PS blends. The morphologies of the blends, analyzed and compared by scanning electron microscopy, suggest that the compatibility of PP/PS blends is improved with increasing either the PP sequences length or the PS side chains length or the number of the side chains in the PP-g-PS copolymer.