Synthesis and characterization of long chain branched isotactic polypropylene via metallocene catalyst and T-reagent

Long chain branched isotactic polypropylenes (LCBPP) prepared via the combination of rac-Me₂-Si(2-Me-4-Ph-Ind)ZrCl₂/MAO catalyst and a p-(3-butenyl)styrene (T-reagent) were characterized to investigate their synthesis, structure, solution properties, and melt properties. The T-reagent, in the presence of hydrogen, simultaneously served as a comonomer and chain transfer agent, resulting in a LCBPP with high molecular weight, desirable branch point density, and relatively well-defined molecular structure. Additionally, the metallocene catalyst remained highly reactive. To understand the structure-property relationships, a series of LCBPPs were prepared with similar weight-average molecular weights of about 250 000 g/mol and different branch densities ranging from 0 (linear iPP) to 3.3 branch points per 10000 carbons. ¹H NMR and SEC equipped with triple detectors revealed structural information. Melt properties were examined by small-amplitude dynamic oscillatory shear and extensional flow measurements. LCBPPs of similar molecular weights displayed a systematic increase in zero-shear viscosity and Arrhenius flow activation energy as branch density increased. LCBPPs with high branch point density displayed thermorheologically complex behavior. Strain hardening was observed in extensional flow of LCBPPs.