Highly Active and Easily Accessible Catalysts for Vinyl Polymerization of Norbornene Obtained by Oxidative Addition of Salicylaldimine Ligands to Bis(1,5-cyclooctadiene)nickel(0) and Methylaluminoxane

Highly active, cheap, and easy to synthesize catalytic systems, obtained in situ by the oxidative addition of salicylaldimine ligands to bis(1,5-cyclooctadiene)nickel(0) and activated by methylaluminoxane (MAO), are now reported for the vinyl polymerization of norbornene. Their activity resulted mainly influenced by the nature of the substituents present both on the phenolate moiety and on the N-aryl ring as well as the content of free trimethylaluminum (TMA) present in the commercial MAO. In particular, the maximum activity, up to about 78,000 kg polynorbornene/mol Ni h, was ascertained when 3,5-dinitro-N-(2,6-diisopropylphenyl)salicylaldimine ligand was adopted in conjunction with Ni(cod)2 and TMA-depleted MAO. This remarkable performance, to the best of our knowledge, the highest never reported working in toluene instead of chlorinated aromatics, was reached adopting this more sustainable reaction medium. The influence of the main reaction parameters such as reaction time, temperature, monomer/Ni, and Al/Ni molar ratios on the catalytic performances and polymer characteristics was studied as well.