Preparation of High-melt-strength, High-impact-strength Polypropylene by α-Alkenylmethyldichlorosilane-mediated Heterophasic Copolymerization of Propylene

As one of the most important thermoplastic polymer materials, polypropylene (PP) is mainly flawed on mechanical properties by low impact strength (particularly at sub-zero temperatures) and on melt processibility by low melt strength, hindering greatly efforts that are aimed to expand its applications. It is thus of great scientific as well as practical importance to address these two issues simultaneously and to prepare both mechanical and processing-proof new PP materials. However, due to the long-standing challenge in propylene polymerization of long chain-branching, the past efforts succeeding in achieving increased impact strengths by heterophasic copolymerization incorporating elastomeric ethylene-propylene copolymer (EPR), have nonetheless failed to make progress in improving the processing side of properties. In this study, we introduce an alpha-alkenylmethyldichlorosilanemediated heterophasic copolymerization approach to address the problem. By introducing heterophasic copolymerization of propylene, alpha-alkenylmethyldichlorosilane can promote resultant PP/EPR heterophasic copolymers to be long chain-branched by an additional facile hydrolysis treatment. Phase-separated PP impact copolymers with long chain-branched structure were prepared by the rendered heterophasic copolymerization of propylene, which were confirmed by GPC, rheology, as well as morphology (SEM) measurements. The LCBed PP impact copolymers simultaneously possess high melt strength and strong strain-hardening effect in extensional rheology test and high impact resistance in mechanical properties test, providing a new platform for developing advanced PP materials with all-round application adaptability.