Shedding light on the poly(5‐ethylidene‐2‐norbornene) microstructural differences: Skeleton rearrangements during polymerization

Here, an attempt is made to study one of the less noticed aspects of the polymerization of 5‐ethylidene‐2‐norbornene (ENB) by nickel α‐diimine catalysts. Therefore, several (co)polymerization runs using MMAO‐activated binuclear catalyst (BNC) and mononuclear catalyst (MNC) were undertaken. Catalyst activities as high as 561.1 and 925.0 (kgpol mol−1Ni h−1) were observed for ENB polymerization by MNC and BNC, respectively. However, the utilization of comonomer (norbornene [NB]) led to a dramatic decline in the catalyst activities, reaching low levels of 69.4 and 144.4 (kgpol mol−1Ni h−1), respectively. Structural characterization (NMR and FTIR) corroborated the occurrence of ring opening via β‐C elimination and the subsequent β‐H elimination. Additionally, tandem transannular polymerization and ring‐opening metathesis polymerization of ENB were evidenced. The findings demonstrated that the transannular polymerization prevailed during the polymerization, albeit the MNC catalyst showed a higher contribution of ring opening via β‐C elimination. Importantly, comonomer (NB) was displayed to alter the governing polymerization mechanism. According to DMTA analysis, the structures of the monomer and catalyst were found to significantly influence the polymer damping behavior and microstructure heterogeneity. That is, the NB‐ENB copolymer obtained by MNC exhibited the lowest Tg value and highest tan δ along with the diminished microstructure heterogeneity. Binuclear and mononuclear nickel α‐diimine catalysts were used for the polymerization of ENB, Tandem cationic, addition, and ring‐opening metathesis polymerization mechanisms occurred based on monomers and catalysts that were used. Ring‐opening via β‐C elimination (VA/RO) and the subsequent β‐H elimination were evidenced.