Copolymerization Of Ethylene And Propylene With MgCl₂-Supported Titanium/Vanadium Bimetallic Catalysts

Vanadium-based Ziegler-Natta catalysts are an important class of commocial commercial catalysts for the preparation of ethylene/propylene copolymer.Vanadium-based Ziegler-Natta catalysts are unique in their abilities to incorporate ethylene and propylene monomers in a random order.However,the low activity of vanadium catalyst limits its further application.Comparably,the traditional titanium-based Ziegler-Natta catalysts used in copolymerization of ethylene and propylene had a high catalytic activity while produced copolymers with block structures more often.Therefore,it is of great potential in combining the advantages of the two mentioned catalytic systems to invent a novel bimetallic catalyst.Very few publications were paid attention to the vanadium/titanium bimetallic Ziegler-Natta catalysts with a low cost but a high efficiency.The Performances of supported bimetallic catalyst systems for ethylene and propylene copolymerization were investigated . A novel MgCl₂-supported vanadium/titanium bimetallic Ziegler-Natta catalyst with di-i-butyl phthalate (DIBP) as internal donor (VCl₄/TiCl₄/MgCl₂/DIBP) was prepared by impregnation method.With AlEt₃ as a cocatalyst,effects of polymerization temperature,the molar ratio of alkylaluminum to vanadium and the ethylene/propylene molar ratio on the catalytic activity and product properties have been studied systematically.The products have been characterized by using gel permeation chromatography (GPC) differential scanning calorimeter (DSC) and ¹³C-NMR analysis to learn the performances of copolymers (obtained from different ethylene/propylene molar ratio in feed) containing the molecular weight and the molecular weight distribution,the crystalline and melting behaviors,the composition and microstructure.The copolymerization results obtained in atmospheric pressure indicated that the polymerization conditions have strong effects on activity and product properties.The catalyst activity is 125.4gpolymer/gcat·h when the optimal ethylene/propylene molar ratio is 44/56,Al/V molar ratio is 246 and temperature is 20℃.At the same time,a copolymer was obtained with the crystallinity of product in 5.7%.The ¹³C-NMR result indicates the ethylene/propylene copolymer has a random or short block structure.The GPC and DSC results show the products have a broad or bimodal molecular weight distribution with low crystallinity.