Synthesis of Allyl-Terminated 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)2TiCl2) catalysts. Propylene enchainment occurs by a 2,1-insertion mechanism, and termination by β-hydride elimination produces low molecular weight syndio-PP with allyl end groups. Several new (PHI)2TiCl2 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.