The In-situ Copolymerization Of Ethylene To Prepare Branched Polyethylene

This thesis was composed in three parts: (1) the performance of the catalysts for the oligomerization and polymerization of ethylene; (2) the comonomer effect of the in-situ copolymerization of ethylene by the bis(imino)-pyridyl iron complexes and metallocenes; (3) the in-situ copolymerization of ethylene by cobalt-based catalysts and metallocenes.In part 1, the oligomerization of ethylene was investigated by the iron-based catalyst 1, 2, 3 and 4. The molar ratio of aluminoxane, MAO as co-catalyst, to the iron-based catalyst and the reaction temperature had some influence on the activity and the distribution of the oligomers. The effects of the concentration, the molar ratio of MAO to the metallocene C3 or C4 and the polymerization temperature on the polymerization activity were also investigated individually. And the copolymerization activities of the combination of the two catalysts were compared to the polymerization activity of the metallocene under the same experiment conditions. The positive comonomer effect was observed.In part 2, several catalytic systems were used to prepare long-branched polyethylene. The comonomer effect was investigated systematically in these catalytic systems. The structure of the metallocene had an important influence on the maximum activity of the comonomer effect. With the decreasing in the "bite-angle" of the metallocene, the maximum activities of the systems also decreased. The structure of the iron-based catalyst had some influence on the optimum value of n(Fe)/n(Zr). With the increase of the polymerization temperature from 40℃ to 80℃, the optimum values of n(Fe)/n(Zr) in these catalytic systems were shifted to some degree. The long-branched polyethylenes made from these catalytic systems had the characteristics of low melt point, low density, narrow distribution of molecular weight.In part 3, the in-situ copolymerization of ethylene was investigated by the combinations of the cobalt-based catalyst and the metallocene to prepare short-branched polyethylene. The major oligomers catalyzed by the cobalt-based catalyst 5, 6 and 7 werel-butene, and the minor were 1-hexene. The comonomer effects were also observed. Under the same reaction conditions the positive comonomer effects were obtained in some catalytic systems and the negative comonomer effects were got in other catalytic systems. The densities, melting points and crystallinities of the copolymers were decreased compared to those of polyethylene under the same experiment conditions.In conclusion, the properties of the polymers can be controlled to some extent by simply adjusting the ratio of the catalysts (n(Fe)/n(Zr)) in the in-situ copolymerization of ethylene.