Poly(propylene-g-styrene) graft copolymers with well-defined microstructure by metallocene catalyzed copolymerization of propylene with allyl-terminated polystyrene macromonomers

摘要

The synthesis of well-defined poly(propylene-g-styrene) (PP-g-PS) graft copolymers was investigated by metallocene catalyzed copolymerization of propylene and allyl-terminated polystyrene macromonomer (PS-allyl) obtained via quasiliving atom transfer radical polymerization (ATRP) and subsequent carbocationic allylation. It was found that the structural parameters of PP-g-PS can be controlled in a broad range by the variation of reaction conditions. At low conversion the number of polystyrene side chains per 1000 propylene units is proportional to the feed concentration of the PS-allyl macromonomer, while the length of polypropylene backbone decreases with increasing feed concentration. The number-average molecular weight (M-n) of PS-allyl determines the side chain length, but it also affects the side chain density and backbone length. Both decrease with increasing M-n of the macromonomer. At constant pressure, by ensuring the constant concentration ratio of propylene to PS-allyl, the PP backbone length can be varied by alteration of temperature while the side chain density remains nearly uniform. This semicombinatorial library of structural parameters vs reaction conditions affords designed synthesis of PP-g-PS graft copolymers with predetermined structure, that is, with desired length of the PS side chains, grafting density, and length of the PP backbone.