Transition metal chlorides complexes with tetrahydrofuran [MtCl4(THF)2] used as precursors
of ethylene polymerization catalysts
Polimery 2002, No 2, 85
Three complexes of transition metal chlorides with tetrahydrofuran (THF), viz., [TiCl4(THF)2] (I), [ZrCl4(THF)2] (II), and [HfCl4(THF)2] (III), were prepared and studied as the precursors of titanium—magnesium catalysts to be used in low-pressure polymerization (0.5 MPa, 323 K) of ethylene using AlEt3 (most favorable), A1Et2C1, or Al(i-Bu)3 as cocatalysts. The activity of catalysts increases in the order [HfCl4(THF)2] < [ZrCl4(THF)2] < [TiCl4(THF)2]. Degree of crystallinity (C), density, buik density, M, MWD, and m.p. were determined for the resulting HDPE. Catalyst activity, found to obey the following ascending type (III) < (II) < (I), increased as the element electronegativity was raised and the partial charge on the transition metal atom in the precursor was diminished. The catalyst surface patterns visualized by a computer supported the experimental data. The uncomplexed, [MgCl2(THF)2]-supported tetrachlorides yielded catalysts less active than (I)—(III), but following the same general activity correlations.
Keywords: polymerization of ethylene, catalysts, transition metal chloride complexes with tetrahydrofuran, molecular modeling