Trans-1,4-stereospecific copolymerization of ethylene and isoprene catalyzed by MgCl2-supported Ziegler-Natta catalyst

摘要

Copolymerization of ethylene and isoprene (Ip) catalyzed by TiCl4/MgCl2-Al(i-C4H9)(3) catalyst was systematically studied. Homopolymer of ethylene and Ip were synthesized under the same conditions for making comparisons. Proton nuclear magnetic resonance was employed to characterize chain structure of the copolymer. Influences of Ip concentration, molar ratio of cocatalyst to Ti and reaction temperature on the copolymerization activity and copolymer chain structure were investigated. The copolymerization activity was evidently lowered by increasing Ip concentration, and the Ip content in copolymer was rather low under reaction conditions leading to higher activity. Insertions of Ip in polymer chain showed rather high regioselectivity for 1,4-connections (85%) and medium to high stereoselectivity for trans-1,4-isomer (70%) under typical conditions, but the regio and stereoselectivities tended to decrease with decrease in Ip concentration and increase in Al/Ti ratio. Melting temperature of the copolymer decreased with increase of Ip content, indicating incorporation of Ip units in most of the copolymer chains. This work has proved feasibility of introducing small amount of Ip units with high trans-1,4-stereoselectivity into ethylene/isoprene copolymer chains by catalyzed copolymerization with MgCl2-supported Ziegler-Natta catalysts. The copolymer is expected to be a promising candidate of easily degradable film or packaging materials. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2715-2722