Ethylene/1-hexene copolymerization with TiCl4/MgCl2/AlCl3 catalyst in the presence of hydrogen

A TiCl4/AlCl3/MgCl2 (Cat-B) catalyst containing 5.2 wt.% Al was prepared by the reaction of TiCl4 with ethanol adduct of AlCl3/MgCl2 mixture. A TiCl4/MgCl2 catalyst (Cat-A) without doped AlCl3 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 AlEt3 was replaced by Al(i-Bu)3. Adding Ph2Si(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 AlCl3 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 AlCl3 in the catalyst resulted in slight decrease of product of reactivity ratios (r1r2) in both fraction A and fraction C.