Impact polypropylene copolymers containing multifold H-shape long-chain-branching structures: Synthesis and properties

omega-Alkenylmethyldichlorosilane as a proven in-situ long-chain-branching agent particularly effective with olefin polymerization by Ziegler-Natta catalysts was seamlessly fit into fully implemented impact copolymerization of propylene exercised by polymerization, steam-treatment of afforded polymer granules, and twin-screw extrusion in a row to deliver, for the first time, long-chain-branched impact polypropylene copolymers (LCB-IPCs). Multifold H-type LCB structures were revealed with the LCB-IPCs, including two homologous structures based on polypropylene (PP -H-PP) and ethylene-propylene copolymer (EPC-H-EPC) individually, and a heterologous structure mixed of PP and ethylene-propylene copolymer (PP-H-EPC). Though all in minute amount, the LCB structures induced significant improvement in IPCs on many fronts. On melt properties, LCB-IPCs gained the unprecedented strain hardening property in extensional flow. On phase morphology, the LCB structures helped reduce the dispersion dimension of ethylene-propylene copolymer and the tendency of grain coarsening in post-preparation processing. On melt crystallization, the LCB structures enhanced the crystallization in an all-round way by prompting self-nucleation. On mechanical properties, by reinforcing the PP matrix and strengthening the interface to facilitate stress transfer between PP and EP copolymer, the LCB structures enabled an all-out promotion of mechanical properties with simultaneous reinforcement on stiffness and toughness.

Automated summary

The use of omega-alkenylmethyldichlorosilane as a long-chain-branching agent in the fully implemented impact copolymerization of propylene has shown significant improvements in IPCs. The introduction of LCB structures has led to advancements in melt properties, phase morphology, melt crystallization, and mechanical properties of the copolymer, resulting in enhanced stiffness and toughness.