Synthesis of Polypropylene-co-p-methylstyrene Copolymers by Metallocene and Ziegler-Natta Catalysts

摘要

This paper discusses the copolymerization reaction of prokpylene and p-methylstyrene (p-MS) via four of the best-known isospecific catalysts, including two homogeneous metallocene catalysts, namely, {SiMe_2[2-Me-4-Ph(Ind)]_2}ZrCl_2 and Et(Ind)_2ZrCl_2, and two heterogeneous Ziegler-Natta catlysts, namely, MgCl_2/TiCl_4/electron donor (ED)/AlEt_3 and TiCl_3. AA/Et_2AlCl. By comparing the experimental results, metallocene catalysts show no advantage over Ziegler-Natta catalysts. The combination of steric jamming during the consective insertion of 2-2,1-inserted p-MS and 1,2-inserted propylene (k_21 reaction) and the lack of p-MS homopolymerization (k_22 reaction) in the metallocene coordination mechanism mechanism drastically reduces catalyst activity and polymer molecular weight. On the other hand, the Ziegler-Natta heterogeneous catalystproceeding with 1,2-specific insertion manner for both monomers shows no retardation because of the p-MS comonomer. Specifically, the supported MgCl_2/TiCl_4/ED/AlEt_3 catalyst,which contains an internal ED, produces copolymers with high molecular weight, high melting point, and no p-MS homopolymer.