BEHAVIOR OF ETHYLENE HOMOPOLYMERIZATION AND ETHYLENE-1-BUTENE COPOLYMERIZATION WITH SIO2/MGCL2 BISUPPORTED TITANIUM CATALYST

Ethylene homopolymerization and ethylene-1-butene copolymerization with the SiO2/MgCl2 bisupported catalysts were investigated in detail. It was found that in the presence of bisupported catalysts, the polymerization temperature and time affect not only the molecular weight, but also the polydispersity M(w)BAR/M(n)BAR. The kinetics curves of ethylene homopolymerization were decay type, but acceleration-type kinetics curves of ethylene 1-butene copolymerization were obtained with the same catalysts. When AlEt2Cl was used as a co-catalyst the activity was very low, but there was a pronounced increase in activity when a mixture of AlEt3/AlEt2Cl was used as co-catalyst, and at an optimum AlEt3/AlEt2Cl ratio the activity was even higher than when only AlEt3 was used. The molecular weight (MW) and molecular weight distribution (MWD) of polyethylene (PE) with the (SiO2/MgCl2)/TiCl4-AlEt3 system were similar to those for the MgCl2/TiCl4-AlEt3 system, which indicates that the two catalyst systems have a similar active component. Under the same polymerization conditions, the activity for ethylene-1-butene copolymerization was much higher than that for ethylene homopolymerization. When the Mg content of the bisupported catalysts and the mole concentration of 1-butene co-monomer in the feed were increased, the activity of copolymerization and the content of 1-butene units in the copolymer increased, while the melting point, crystallinity and density of the polymer decreased. Results of C-13 NMR and DSC analysis of the polymer show that the 1-butene units in the copolymer principally form isolated ethyl branches, and the polymer is nearly a random copolymer. Ethylene/1-butene copolymer with ultra low density can be obtained with these bisupported catalysts.