Synthesis of Long-chain-branched High-density Polyethylene with Ziegler-Natta Catalyst and ω-Alkenylmethyldichlorosilane Copolymerization-Hydrolysis Chemistry

High density polyethylene (HDPE) prepared by Ziegler-Natta catalyst does not contain long chain branching structure, which results in limits in its processing and applications. How to introduce long chain branching structure into HDPE prepared by Ziegler-Natta catalyst is one of the long-term challenges in olefin polymerization research. This study discusses a new synthesis of long-chain-branched high-density polyethylene (LCB-HDPE) based on Ziegler-Natta catalysis. omega-Alkenylmethyldichlorosilane was used as LCB reagent, which is introduced into ethylene polymerization to generate PE chains containing pendant reactive dichlorosilane groups by ethylene/5-hexenylmethyldichlorosilane copolymerization. Followed by treating the polymer powders with water, the neigboring polymer chains-grafted dichlorosilane groups are hydrolyzed and H-type LCB structure is formed by hydrolytic condensation. The results indicate that the combination of Ziegler-Natta catalysts and the omega-alkenylmethyldichlorosilane copolymerization-hydrolysis chemistry resulted in successful preparation of LCB-HDPE with LCB density up to 0.15/1000C and hardly affected catalyst activity. The LCB-HDPEs have significant rheological properties responses. Their melt elasticity, zero-shear viscosity, melt strenght and strain-hardening effect all increase/intensify with the increase of LCB densities. Meanwhile, the LCB-HDPEs maintain high crystallization properties. With melting temperatures and crystallization temperatures being largely equivalent to those of linear PE, their crystallinities increased to a noticeable degree. It is expected that the new LCB-HDPEs with simultaneously high crystallinity and high melt strength will have good applications in the fields where the melt strength is highly required.

Automated summary

This study successfully introduces long-chain branching structure into HDPE by a new synthesis method, preparing LCB-HDPE with significant rheological properties responses and high crystallinity. The LCB-HDPE maintains high crystallinity while having high melt strength, showing great potential for wide applications.