Synthesis of allyl-terininated syndiotactic polypropylene: Macromonomers for the synthesis of branched polyolefins

Low molecular weight syndiotactic polypropylene (syndio-PP) with an olefin end group was synthesized using methylaluminoxane-activated bis(phenoxyimine)titanium dichloride ((PHI)(2)TiCl2) catalysts. Propylene enchainment occurs by a 2,1-insertion mechanism, and termination by beta-hydride elimination produces low molecular weight syndio-PP with allyl end groups. Several new (PHI)(2)TiCl2 complexes with various ligand modifications were found to display a wide range of activities (turnover frequency (TOF) = 3-1200 h(-1)) and syndiospecificities ([rrrr] = 0.46-0.93) for propylene polymerization. While the TOF increases with increasing reaction temperature and propylene concentration, the molecular weight of the resulting macromonomer shows little variation. This provides strong support for a chain-transfer mechanism involving one molecule of propylene. The allyl-terminated PPs reported herein can be used to synthesize branched polyolefins or other new polyolefin architectures.