Long Chain Branched Isotactic Polypropylene

Abstract

Long chain branched isotactic polypropylene (LCB-PP) was synthesized using metallocene catalyst (rac-dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride activated by methylaluminoxane). The branching was in situ generated in a diluted polymerization condition using hexane or toluene as diluent. The polymers have a significant population of branched molecules as evidenced by multiangle laser light scattering analysis. More importantly, such a branching structure in isotactic polypropylene has been, for the first time, identified by 13C NMR spectroscopy. The 13C NMR resonance assignments of the branching structure are based on the model polymer characterization, stereo environment analysis, and chemical shift calculation. The unique stereo environment of the branching structure provides insight into the mechanism of LCB formation in such isotactic polypropylenes. The branching levels determined by 13C NMR are directionally consistent with that estimated from laser light scattering analysis.