Ethylene/1-hexene copolymerization with TiCl 4/MgCl 2/AlCl 3 catalyst in the presence of hydrogen

Abstract

A TiCl 4/AlCl 3/MgCl 2 (Cat-B) catalyst containing 5.2 wt.% Al was prepared by the reaction of TiCl 4 with ethanol adduct of AlCl 3/MgCl 2 mixture. A TiCl 4/MgCl 2 catalyst (Cat-A) without doped AlCl 3 was also prepared by the same method. Ethylene-1-hexene copolymerization catalyzed by Cat-B in the presence of hydrogen showed slightly higher efficiency and higher 1-hexene incorporation than Cat-A. Comonomer incorporation was markedly increased when the cocatalyst AlEt 3 was replaced by Al( i-Bu) 3. Adding Ph 2Si(OMe) 2 as external donor in the catalyst system caused decrease in polymerization activity and 1-hexene incorporation. Each copolymer sample was fractionated into three fractions: n-heptane insoluble fraction (fraction A), n-heptane soluble and n-hexane insoluble fraction (fraction B) and n-hexane soluble fraction (fraction C). In most cases the amount of intermediate fraction (fraction B) was smaller than the other fractions and did not increase as the total 1-hexene content increase, indicating the presence of two classes of copolymer fractions with greatly different comonomer content and clear bimodality of the copolymer composition distribution. Doping AlCl 3 in the catalyst, changing cocatalyst and adding external donor mainly changed the weight ratio of fraction A to fraction C, but exerted little influences on their composition. According to the sequence distribution data of the fractions, doping AlCl 3 in the catalyst resulted in slight decrease of product of reactivity ratios ( r 1 r 2) in both fraction A and fraction C.