Synthesis of Star Isotactic Polypropylene via Styryldichlorosilane/Hydrogen Consecutive Chain Transfer Reaction

This paper elucidates the consecutive chain transfer reaction, initially to (p-vinylphenyl) methyl dichlorosilane (or (p-vinylbenzyl) methyl dichlorosilane), followed by hydrogen, during metallocene-catalyzed propylene polymerization by an isospecific metallocene catalyst (i.e., rac-dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride, I)/ activated with methylaluminoxane (MAO), rendering a catalytic access styryldichlorosilane capped isotactic polypropylenes (iPP). The PP molecular weight is inversely related to the molar ratio of [(p-vinylphenyl) methyl dichlorosilane]/[propylene] and [(p-vinylbenzyl) methyl dichlorosilane]/[propylene]. Every polypropylene chain formed presents a terminal (p-vinylphenyl) methyl dichlorosilane (or (p-vinylbenzyl) methyl dichlorosilane) unit. Hydrogen enhances the concentration of the starting arm polymer for the subsequent synthesis of the star polymer by increasing the incorporation of the chain terminal group. In order to create star polymers with isotactic polypropylene(iPP) as the arm and a siloxane cross-linking structure as the core, the terminal dichlorosilane iPP unit can work up (with water) to create cyclic siloxane oligomer interlinkages between iPP chains.