Living and block polymerization of α-olefins using a Ni(II)-α-diimine catalyst containing OSiPh2tBu groups

A new siloxy-substituted α-diimine compound and its corresponding Ni(II) complex, {bis[N,N′-(4-tert-butyl-diphenylsiloxy-2,6-dimethylphenyl)imino]acenaphthene}dibromonickel (6), were successfully synthesized and the molecular structure of 6 characterized by X-ray crystallography. The precatalyst 6 activated by methylaluminoxane (MAO) or diethylaluminum chloride (DEAC) was tested in the polymerization of ethylene, showed to be highly active (e.g. 2.2×107 and 1.8×107 g polymer (mol Ni.h.bar)−1, respectively) and led to a branched polyethylene (ca. 35–55 branches/1000 C). The catalyst system 6/methylaluminoxane (MAO) catalyzes, at −11 °C, living polymerization of propylene, to a polypropylene showing a syndiotactic-rich microstructure (Pr=0.74). 1-Hexene was also successfully polymerized via a living process, both at −11 and +16 °C. The 13C NMR spectra of the poly(1-hexene)s obtained at room temperature show a microstructure almost exclusively composed by n-butyl and methyl branches, the latter being present in a much higher number. Diblock polypropylene-block-poly(1-hexene) and triblock poly(1-hexene)-block-poly(propylene-ran-1-hexene)-block-poly(1-hexene) copolymers have also been synthesized and characterized by GPC/SEC, DSC and NMR.