Synthesis of Allyl-Terminated Syndiotactic Polypropylene:  Macromonomers for the Synthesis of Branched Polyolefins

Abstract

Low molecular weight syndiotactic polypropylene ( syndio- PP) with an olefin end group was synthesized using methylaluminoxane-activated bis(phenoxyimine)titanium dichloride ((PHI) 2 TiCl 2 ) 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) 2 TiCl 2 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.