New End-Group Functionalization Technique Developed for Polymer Synthesis

A research team led by H. Shimomoto and E. Ihara at Ehime University has developed a new palladium (Pd)-based initiator system that enables the preparation of polymers with carbon-carbon main chains bearing three functional groups. This development is expected to contribute to advances in polymer chemistry and enable the development of new functional polymer types.

Vinyl polymerization (polymerization of vinyl compounds) is an important method used to prepare sp³ carbon-based main-chain polymers, including commercial plastics. In this method, the polymer backbone consists of two-carbon units derived from the vinyl groups of monomers. In contrast, polymerization of diazo compounds results in a polymer backbone composed of one-carbon units, yielding sp³ carbon-based main-chain polymers. In this C1 polymerization system, diazoacetates are suitable monomers and form polymers bearing an alkoxycarbonyl group (ester) at each carbon atom in the main chain [poly(alkoxycarbonylmethylene)s].

In this study, the research team succeeded in developing a new initiator system for the polymerization of diazoacetates. More specifically, it was demonstrated that newly prepared Pd(0) complexes bearing N-arylmaleimide as a ligand are effective in the polymerization of diazoacetates when used together with a borate such as NaBPh₄, and enable the polymers to be obtained in high yield. In particular, it was shown that the initiation, chain growth (propagation), and termination stages of the polymerization all proceed in a highly regular and controlled manner.

The most notable characteristic of the [Pd(N-arylmaleimide)/NaBPh₄] initiator system developed by the team is the near-quantitative (approximately 100%) incorporation of the N-arylmaleimide molecule initially coordinated to the Pd center into the α-chain end of the resulting polymer. In this way, the research team will be able to introduce a wide variety of functional groups to the α-chain end of poly(alkoxycarbonylmethylene)s by using N-substituted maleimides bearing (protected) functional groups. These new findings are expected to expand the scope of diazoacetate polymerization, which is gaining increasing importance in the preparation of sp³ carbon-based main-chain polymers, and to increase its application potential.

Academic Reference
Polymerization of Diazoacetates Initiated by the Pd(N-arylmaleimide)/ NaBPh4 System: Maleimide Insertion into a Pd–C Bond Preceding to Initiation Leading to Efficient α-Chain-End Functionalization of Poly(alkoxycarbonylmethylene)s Hiroaki Shimomoto,* Hinano Hayashi, Kyoka Aramasu, Tomomichi Itoh, and Eiji Ihara

Macromolecules, 2022, 55, 5985–5996

DOI: 10.1021/acs.macromol.2c00508

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