Bis(β-ketoimino)nickel(II) Complexes for Random Copolymerization of Norbornene and Methyl 5-Norbornene-2-carboxylate with Controlled Ester Group Incorporation

Abstract

A series of bis(β-ketoimino)nickel(II) complexes with p-substituted N-phenyl groups, Ni[CH 3 C(O)CHC(NPhR)-CH 3 ] 2 (Ni1: R = −OCH 3 ; Ni2: R = −CH 3 ; Ni3: R = −CF 3 ), were synthesized, and their general coordination geometry was elucidated by single-crystal X-ray diffraction analysis of Ni3. These complexes were paired with tris(pentafluorophenyl)borane (B(C 6 F 5 ) 3 ) to catalyze the vinyl addition copolymerization of norbornene (NB) and methyl 5-norbornene-2-carboxylate (NBE). All the catalyst systems exhibited high catalytic activities (>10 5 g polymer mol Ni −1 h −1 ) at NBE feed contents of up to 50 mol %, resulting in the production of copolymers with high molecular weights (M w = 135−355 kg mol −1 , Đ = 1.78−2.12). In addition, the content of polar ester groups was precisely controlled by the feed ratio of the monomers. For Ni3, two monomer reactivity ratios were found to be close to unity (Fineman−Ross method: r NB = 0.951, r NBE = 0.903; Kelen−Tudos method: r NB = 1.15, r NBE = 0.978). Since the copolymerization behaviors were revealed to be independent of the electronegativity of p-substituent, all the catalyst systems of Ni1−Ni3/B(C 6 F 5 ) 3 were considered to serve the random copolymerization of NB and NBE. The resulting poly(norbornene-random-methyl 5-norbornene-2-carboxylate)s exhibited the dielectric and surface properties well tunable by compositional modulation.

Palladium(II)-Catalyzed Synthesis of a Vinyl-Addition Ultrahigh-Molecular-Weight Polynorbornene Copolymer with an Entanglement Network for Enhanced Fracture Resistance

“…Second, β-hydride elimination by a C 3 –H bond is sterically restricted by cis insertion, the predominant mode of incorporating NB and its substituted derivatives. − This mode induces noncoplanarity between the C 2 –metal bond and C 3 –H bond, creating steric hindrance to β-agostic interaction and ultimately prohibiting the formation of an intramolecular four-center transition state . Palladium(II)- and nickel(II)-based catalyst systems are predominantly employed for the vinyl-addition polymerization of NB and its substituted derivatives. ,,,,− 5-Alkyl-2-norbornenes (AlkylNBs) are promising counter monomers for (quasi)living copolymerization with NB owing to the excellent chemical inertness of alkyl substituents. Consequently, the combination of NB and AlkylNBs has potential merit for expanding the molecular weight limit.…”

High-Refractive-Index Cross-Linked Cyclic Olefin Polymers with Excellent Transparency via Thiol–Ene Click Reaction

“…High refractive index optical polymers are important materials and have witnessed increasing attention over recent years. − Cyclic olefin polymer (COP) is one of the predominant materials in optical encapsulants, biomedical applications, optical devices, and the semiconductor industry − due to these advantages, such as high optical transmittance, high thermal stability, low optical dispersion, low birefringence, and low dielectric constant. − However, due to the nature of pure hydrocarbon structure, the greatest shortcoming of commercial COP is the low refractive index ( n = 1.52–1.54), which is significantly lower than those (1.70 and higher) in sulfur-containing and aromatic group-containing poly­(phenylene thioether), poly­(thioester) and poly­(thioether sulfone). , Thus, how to enhance the refractive index of COP for broader applications is meaningful and challenging.…”