Transition metal chlorides complexes with tetrahydrofuran [MtCl4(THF)2] used as precursors of ethylene polymerization catalysts

Abstract

Three complexes of transition metal chlorides with tetrahydrofuran (THF), viz., [TiCl 4 (THF) 2 ] (I), [ZrCl 4 (THF) 2 ] (II), and [HfCl 4 (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 AlEt 3 (most favorable), AlEt 2 Cl, or Al(i-Bu) 3 as cocatalysts. The activity of catalysts increases in the order [HfCl 4 (THF) 2 ] < [ZrCl 4 (THF) 2 ] < [TiCl 4 (THF) 2 ]. Degree of crystallinity (C), density, bulk 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, [MgCl 2 (THF)) 2 ]-supported tetrachlorides yielded catalysts less active than (I)-(III), but following the same general activity correlations.