Ni(acac) 2 Mediated Vinyl Polymerization of Norbornene in the Presence of Bulky Salicylaldiminate Ligands: an Effective Strategy to Access Soluble Polynorbornenes

Late transition metals have long served as workhorses for vinyl polymerization of norbornene derivatives. Nevertheless, for such catalytic systems, insoluble polynorbornene (PNB) products are often produced which hampers their further detailed characterizations, such as molecular weights, polydispersities, stereoregularities, etc. In this work, we surprisingly found that for a traditional Ni(acac) 2 /MAO system that was previously reported to give insoluble PNBs, incorporation of highly bulk salicylaldiminate ligands could significantly improve the solubility of the PNBs in common organic solvents, which allowed for subsequent thorough detailed analysis of the polymer products. Moreover, it was also observed that high-temperature polymerization was beneficial for further improving the PNB’s solubilities due to the decreased molecular weights and stereoregularities. Different ligand skeletons and ligand equivalents were also investigated to give a comprehensive view of their influences on the polymers’ solubilities, and based on these results, a plausible mechanism that caused such a big difference was tentatively proposed.