Polymerization of Ester-Functionalized Norbornenes Using Neutral Nickel Catalysts

Addition-type polynorbornenes have shown tremendous promise for a variety of applications; however, the direct polymerization of polar functionalized monomers is often challenging when using transition metal-based catalysts. This result is often ascribed to the oxophilic nature of many early transition metal species. Strategies to overcome this issue include the use of late transition metal catalysts, such as those containing Ni and Pd active sites, which generally exhibit greater monomer functional group tolerance. However, discrepancies in molecular weight and yield are still often encountered for the vinyl addition polymerization of polar vs nonpolar functionalized norbornene monomers. While researchers have studied these effects for Pd-based complexes, analogous studies using neutral, single-site nickel-based catalysts are absent from the literature. Herein, we show that polar functionalized norbornenes and a variety of polar additives readily coordinate LnNi(C6F5)2 type vinyl-addition polymerization catalysts and affect their polymerization behavior. These results suggest that simple trends in polynorbornene molecular weight are observed as a function of coordinating ligand (Ln) strength for the polymerization of nonpolar substituted norbornenes when using O-donor ligands of moderate coordination ability but do not fully explain why the polymerization of polar functionalized norbornenes routinely produce low molecular weight polymers in poor yields.