The polymerization of norbornenes and dienes has been investigated using a variety of (π-allyl)nickel initiators. There is great interest in the polymerization of norbornene because polynorbornene possesses good mechanical strength, high chemical resistance, optical transparency, low birefringence, high glass transition temperatures, low dielectric constant, and large refractive indices, which lead to its high utility in industry. Metal-catalyzed vinyl addition polymerization of norbornene is of interest in order to produce saturated polymers with high molecular weights. Here we report the vinyl addition polymerization of norbornene using cationic (π-allyl)nickel complexes containing bulky dialkylbiaryl phosphine ligands, without a cocatalyst. Although complexes possessing dialkylbiaryl phosphines have been evaluated in a number of catalytic applications, they have not been previously evaluated in polymerization reactions. Figure 1 depicts a library of catalysts produced by the O’Connor group. Different substituents, attached to phosphorus and the lower aryl ring, were evaluated to determine the influence the electronics and sterics at the nickel center play on polymerization activity. Polynorbornene was obtained in 26-98% yield, where the lowest yields were observed when utilizing initiators without substituents on the lower aryl ring of the biaryl phosphine ligand (1, 5), while the highest yields were obtained when using initiators bearing electron donating methoxy substituents on the lower aryl ring of the biaryl phosphine ligand (3). Complexes possessing ditertbutylbiaryl phosphine ligands exhibited higher yields, when compared to dicyclohexylbiaryl phosphine analogs (6 vs. 8). The average Mw was 9900 and the average PDI was 2.2 for the polynorbornene, supporting the polymerization is not living.

Norbornene polymerization initiated by cationic (π-allyl)nickell(II) complexes containing dialkylbiaryl phosphine ligands

251st National Meeting (2016)

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