Comparison of olefin polymerization behavior of sterically crowded tris(pyrazolyl)borate group 4 metal complexes

The ethylene polymerization and ethylene/α-olefin copolymerization behavior of the sterically crowded tris(pyrazolyl)borate group 4 metal complexes TpMs*TiCl3 (1, TpMs* = HB(3-mesitylpyrazolyl)2(5-mesitylpyrazolyl)−), {K[TpMs*TiCl3]}2 (2), TpMs*TiCl2(O-2,4,6-tBu3-Ph) (3), TpMs*ZrCl3 (4), TpMsZrCl3 (5, TpMs = HB(3-mesitylpyrazolyl)3−), and TpMs*HfCl3 (6) were studied with dried-MAO activation in toluene solution. These catalysts all produce very high molecular weight (Mv > 106) linear polyethylene. Zirconium catalyst 5 excels in productivity in ethylene homopolymerization and ethylene/1-hexene copolymerization, molecular weight, and hexene incorporation ability. Catalyst 5 produces moderately alternating ethylene/1-hexene copolymer (41 mol% hexene) with ultra-high molecular weight (Mw = 1.3 × 106), narrow molecular weight distribution (Mw/Mn = 2.2) and narrow composition distribution with high efficiency.

Graphical abstractThe olefin polymerization performance of sterically crowded group 4 (tris-pyrazolylborate)MX3/dried-MAO catalysts was investigated. Diverse behavior is observed for complexes with different metals, oxidation states and ligands. TpMsZrCl3 (5, TpMs = HB(3-mesitylpyrazolyl)3−) produces moderately alternating ethylene/1-hexene copolymer (41 mol% hexene) with ultra-high molecular weight (Mw = 1.3 × 106, Mw/Mn = 2.2), and uniform composition distribution with high efficiency at 80 °C in toluene.Figure optionsDownload full-size imageDownload as PowerPoint slide