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

ω-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.