Copolymerization of olefin with carbon monoxide has received considerable interest from both academia and industry, and the introduction of polar carbonyl group renders the resultant polyketones with excellent mechanical strength, crystallinity, photodegradability, hydrophilicity, surface, and barrier properties. However, most of the reported polyketones are difficult to be processed because of limited solubility in common solvents and high melting temperature (T m ∼ 260 °C) resulting from the strictly alternative structure. Nonalternating copolymerization of ethylene with CO is a very promising method to circumvent the problem of processability of traditional perfectly alternating polyketone. In the contribution, the palladium coordinated diphosphazane monoxide substituted by strong electron-donating groups is discovered to be highly reactive for producing nonalternating polyketones, and up to 24.2% extra ethylene incorporation has lowered T m values to 147 and 165 °C and further improved thermal stability (T d ∼ 339 °C) of the resultant materials. Our data demonstrates that cationic palladium complexes can also exhibit excellent reactivity and an unprecedented nonalternating degree in this copolymerization.

Comprehensive SummaryThe introduction of carbonyl group with a high density in polyethylene backbone corresponds to polyketone materials, which features excellent mechanical strength, crystallinity, photodegradability, hydrophilicity, surface and barrier properties. Due to the extremely high binding affinity of carbon monoxide (CO) and kinetic preference for its subsequent insertion, the formation of nonalternating structure with extra ethylene insertion is exceptionally challenging, however, this nonalternating strategy is of significant importance for polymer modification in term of processing and solubility. Here, we have communicated our study on cationic palladium coordinated diphosphazane monoxide (PNPO) for the nonalternating copolymerization of ethylene with CO, the systematical investigation on the amine and phosphine oxide moieties in PNPO platform in term of electronic and steric modulation has been performed. It is discovered that the installation of aliphatic structure on amine moiety favors the improvement of catalyst activity and longevity, while the amino groups on phosphine oxide moiety promotes the nonalternating copolymerization. In particular, we have computationally investigated herein the aspects of the nonalternating degree by comparing with PNPO platform and 1,3‐bis(diphenylphosphanyl)propane ligands based palladium catalysts. These mechanistic studies can help to understand the catalyst structure and polyketone property relationships and shed light on future design of high‐performance copolymerization catalysts.

The bimetallic synergistic strategy has attracted interest and been frequently explored in late-transition-metal-catalyzed olefin (co)­polymerization. In this contribution, a series of bulky o-phenylene-bridged bimetallic α-diimine Ni­(II) and Pd­(II) catalysts were designed, synthesized, and investigated in ethylene polymerization and copolymerization with polar monomers. The molecular structures of bimetallic Pd­(II) complexes have been determined by X-ray diffraction. The bimetallic Ni­(II) catalysts exhibit excellent activity and generate high-molecular-weight polyethylene with lower branching density in comparison with the corresponding monometallic analogues. Moreover, the mechanical properties of the obtained polyethylene products could be adjusted in a wide range by the structures of the Ni­(II) catalysts and the polymerization conditions. In particular, polyethylene materials generated by Ni 2 -Me and Ni 2 - i Pr exhibited excellent mechanical properties and up to 86% strain recovery value (SR), comparable to the best reported recovery values of polyethylene thermoplastic elastomers. Furthermore, bimetallic α-diimine Pd­(II) catalysts are more efficient than the corresponding monometallic analogues in terms of polymerization activity, molecular weight, and branching density. In addition, these bimetallic Pd­(II) complexes are also tolerant of polar monomers in copolymerizations with ethylene.