A novel consecutive chain transfer reaction to p-methylstyrene and hydrogen during metallocene-mediated olefin polymerization

This paper describes the first example of consecutive chain transfer reaction, first to p-methylstyrene (or styrene) and then to hydrogen, during metallocene-catalyzed propylene polymerization by rac-Me₂Si[2-Me-4-Ph(Ind)]₂ZrCl₂/MAO complex. The PP molecular weight is inversely proportional to the molar ratio of [p-methylstyrene]/[propylene] and [styrene]/[propylene] with the chain transfer constants of k_tr/k_p = 1/6.36 and 1/7.5, respectively. Although hydrogen does not influence the polymer molecular weight, it greatly affects the catalyst activity. Each PP chain formed contains a terminal p-methylstyrene (or styrene) unit. The terminal p-MS unit can be metalated to form a stable polymeric anion for living anionic polymerization to prepare new PP diblock copolymers, such as PP-b-PS, which are very difficult to prepare by other methods. The overall process resembles a transformation reaction from metallocene to living anionic polymerization.