Polyolefin structural control using phenoxy-imine ligated group 4 transition metal complex catalysts

Abstract

This paper describes the structural control of polyolefins achieved by using group 4 transition metal complex catalysts featuring a pair of phenoxy-imine chelate ligands (named FI catalysts). FI catalysts can produce very low to ultrahigh molecular weight polymers. For example, a Zr-FI catalyst bearing a cycloalkyl group on the imine-nitrogen with methylaluminoxane (MAO) activation is capable of selectively forming vinyl-terminated low molecular weight polyethylenes (Mw < 5000) whereas a Zr-FI catalyst with a triethylsilyl group ortho to the phenoxyoxygen can generate ethylene/propylene amorphous copolymers with ultra-high molecular weights (Mw > 10 000 000) when treated with iBu3Al/Ph3CB(C6F5)4. In addition, a Ti-FI catalyst, possessing an o-phenoxytrimethylsilyl group, with MAO can form highly syndiotactic polypropylenes ([rrrr] = 84%, Tm = 140°C) via a chainend control mechanism. Conversely, upon activation with iBu3Al/Ph3CB(C6F5)4, a Hf-FI catalyst with a tert-butyl group ortho to the phenoxy-oxygen is able to produce high molecular weight isotactic polypropylenes ([mm] = 69%, Tm = 124°C, Mw = 412 000) via a site control mechanism. Therefore, FI catalysts have shown the ability to create various polyolefin architectures by simple variation of the central metal, the ligand structure and the co-catalyst.