ω-Alkenylmethyldichlorosilane-assisted propylene polymerization with Ziegler-Natta catalyst to long chain-branched polypropylene

Abstract

Long chain-branched polypropylene (LCB-PP) with high melt strength characteristics has long been a class of high-end PP materials modified from their linear prototypes. Recent advances in catalyst technology has enabled direct synthesis of LCB-PP using metallocene/non-metallocene catalysts via, among others, non-conjugated α,ω-diolefin/propylene copolymerization. However, for Ziegler-Natta catalysts (MgCl2/TiCl4 catalysts) which dominate commercial PP production, chemistries for LCB-PP synthesis are still rare. To resolve the dilemma, this paper reports a new LCB-PP synthetic chemistry based on Ziegler-Natta catalyst technology. The new chemistry uses ω-alkenylmethyldichlorosilane as an LCB reagent to help with propylene polymerization, where it leverages its two distinct functionalities of α-olefin and alkylmethyldichlorosilane in main polymerization (with Ziegler-Natta catalyst) and during polymer workup (with water) to construct dialkylsiloxane oligomer interlinkages between PP chains, thus synthesizing H-shape LCB-PP. By completely ditching macromonomer copolymerization as being essential for LCB structure formation, the new chemistry is greatly reduced of steric barrier and suits Ziegler-Natta catalysts. Gelation can be prevented by containing the addition dosage of ω-alkenylmethyldichlorosilane. The synthesized LCB-PP samples exhibit strong LCB characteristics in rheology test. LCB densities are controlled by ω-alkenylmethyldichlorosilane incorporation rates in main propylene polymerization. Of different ω-alkenylmethyldichlorosilane derivatives, one that is more reactive for copolymerization with propylene is more efficient for LCB-PP synthesis. For the three synthesized ω-alkenylmethyldichlorosilanes their efficiencies for LCB-PP synthesis follow the order of 5-hexenylmethyldichlorosilane > 7-octenylmethyldichlorosilane > 3-butenylmethyldichlorosilane.