基于Ziegler-Natta催化剂和ω-烯烃基甲基二氯硅烷共聚-水解化学制备长链支化高密度聚乙烯

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

由Ziegler-Natta催化剂所制备的高密度聚乙烯(HDPE)不含有长链支化结构,导致其加工应用性能受限.如何在Ziegler-Natta催化剂所制备的HDPE中引入长链支化结构,是烯烃聚合研究面临的长期挑战之一.本文报道通过ω-烯烃基甲基二氯硅烷共聚-水解化学,实现以Ziegler-Natta催化剂制备H型长链支化高密度聚乙烯(LCB-HDPE).以5-己烯基甲基二氯硅烷作为长链支化助剂,首先在Ziegerl-Natta催化剂催化的乙烯聚合中实现其与乙烯共聚,在聚乙烯分子链侧基上引入反应性二氯硅烷基团;聚合反应结束后对聚合物进行水处理,使近邻聚合物链上的二氯硅烷基团发生水解缩合反应,即制备H型LCB-HDPE.结果表明,Ziegler-Natta催化剂与ω-烯烃基甲基二氯硅烷共聚-水解化学的结合可实现LCB-HDPE的制备,长链支化密度可达0.15/1000C,而催化剂效率基本不受影响.所合成的LCB-HDPE的熔体流变学响应明显,随长链支化密度增加,熔体弹性增大,零切黏度提高,熔体强度和拉伸应变强化效应不断增强.同时,LCB-HDPE保持了高结晶性能,其熔点和结晶温度与线性聚乙烯相当,而结晶度有较大幅度提高.

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.ω-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 theω-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.