Effect of Hydrogen on Copolymerization between Dichlorosilane-functionalized Nonconjugated alpha,omega-Diolefin and Propylene

Dichlorosilane functionalized nonconjugated alpha,omega-diolefin and propylene copolymers, prepared by heterogeneous Ziegler-Natta catalysts, have been newly found to trigger dehydration condensation reaction among/between polypropylene chains to form long-chain branched (LCB) structures in the presence of water. Hydrogen is often used as a chain transfer agent to regulate the molecular weight of the polymer in olefin polymerization. Therefore, whether or how hydrogen affects the insertion of the di(5-hexenyl)dichlorosilane in the polymerization of propylene is a topic worthy of study. Herein, the copolymerization of di(5-hexenyl) dichlorosilane and propylene has been investigated based on MgCl2/TiCl4 catalyst (9,9-bis(methoxymethyl)fluorine (BMMF), as internal electron donor) in bulk polymerization conditions. The polypropylene microstructure was analysed by changing hydrogen content while the amount of di(5-hexenyl)dichlorosilane was fixed. It was found that hydrogen significantly improved the activity of catalyst and reduced the molecular weight of polymer. The H-1-NMR results show that the pendant double bonds in the polypropylene chain decreased from 0.12 mol% to 0.05 mol%, illustrating that hydrogen inhibited the insertion of di(5-hexenyl)dichlorosilane in the polymerization. The higher the hydrogen content, the lower the insertion of di(5-hexenyl)dichlorosilane in the polypropylene chain, which corresponds to the decreasing density of long-branched chains in the polymer. Analysis of the insoluble portion of the polymer in the xylene showed that there is no gel in the presence of hydrogen. The creep test results exhibit that the value of M-b/M-w increases from 0.70 to 0.95, which quantitatively indicates that the long-chain branching density in the polymer decreases with the increasing hydrogen content. The long-branched chain density in polymer decreases with the increasing hydrogen content, which is also confirmed by the results of small amplitude oscillatory shear rheology test.