Abstract: Siloxane compounds were treated with the compounds containing internal donors, such as aromatic ester, phosphate, or 1,3-diether compounds, and the resulting intermediates were further reacted with TiCl₄ to form the modified Ziegler-Natta catalysts for ethylene/1-hexene(E-H) copolymerization. Using the modified Ziegler-Natta catalysts, the effect of the internal donors and the molar ratio of alcohol to magnesium on the catalyst performance was investigated by the orthogonal experiments. The synthetic method of the catalysts was also optimized by choosing the proper way to mix the internal donors. The branch degree, sequence structure, molecular weight, and molecular weight distribution of the copolymer products were determined by Fourier transform infrared spectroscopy(FTIR), carbon-13 nuclear magnetic resonance(¹³C NMR) spectrometry and gel permeation chromatography(GPC). Under the optimum conditions, the catalytic system with tetraethyl orthosilicate and 2,2-dimethoxypropane as the internal donors exhibited the best performance with an activity of 926.74 g copolymer/(g Cat·h^-1). The branch degree, 1-hexene content, and molecular weight distribution of the resulting copolymers reached up to 40 branches/1000C, 5.99% and 5.8, respectively.

Key words: Ziegler-Natta catalyst, Internal donor, Lewis base, Ethylene-olefin copolymerization, Copolymer structure