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

Abstract

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. Fully implemented impact copolymerization of propylene preparing impact polypropylene copolymers was engaged with LCB agent 5-hexenylmethyldichlorosilane, which prompted formation of multifold H-shape LCB structures in the copolymers. The multifold LCB structures in turn induced profound improvement on multiple fronts of the copolymer properties. • ω -Alkenylmethyldichlorosilane is used as a LCB agent in impact copolymerization of propylene. • The new IPC polymers contain multifold H-type LCB structures. • The LCB structures induced significant improvement in properties of IPC on many fronts.