Synthesis of polyethylene containing a terminal p-methylstyrene group: Metallocene-mediated ethylene polymerization with a consecutive chain transfer reaction to p-methylstyrene and hydrogen

This paper discusses a novel polymerization process for preparing polyethylene having a terminal p-methylstyrene (p-MS) group. The chemistry involves metallocene-mediated ethylene polymerization in the presence of p-MS and hydrogen. Apparently, the reaction mechanism, including the copolymerization and chain transfer reactions, can be controlled with a favorable combination of metallocene catalyst and hydrogen concentration. Under some specific reaction conditions, the Cp₂ZrCl₂/MAO catalyst selectively forms PE with a terminal p-MS terminal group (PE-t-p-MS) via a consecutive chain transfer reaction to p-MS and then hydrogen. The catalyst activity increases with the hydrogen concentration, and the polymer molecular weight is inversely proportional to the p-MS concentration. In contrast, [C₅Me₄(SiMe₂N^tBu)]TiCl₂/M AO initiates a copolymerization reaction between ethylene and p-MS, and hydrogen has little effect on the catalyst activity. The terminal p-MS unit at the PE chain end is a valuable reactive group that can be metalated to form a stable polymeric anion, which can be used to prepare functionalized PE polymers containing a polar terminal group or diblock copolymers.