Japanese Chemists Have Synthesized Unique Polymers With an Unprecedented Structure

The development of polymer synthesis methods utilizing diazocarbonyl compounds as monomers.

For over 20 years, the Ihara research group at Ehime University has specialized in developing innovative methods for polymer synthesis using diazocarbonyl compounds as monomers.

They discovered that diazoacetate can be polymerized using a palladium (Pd)-based initiator to produce carbon–carbon (C–C) main-chain polymers, with each carbon atom in the backbone bonded to an alkoxycarbonyl (ester) group. Unlike traditional vinyl polymerization—where the polymer backbone is built from two-carbon units of vinyl monomers like ethylene and styrene—diazoacetate polymerization creates the C–C main chain from single-carbon units. This unique process, known as C1 polymerization, is a distinctive and significant feature of this synthesis method.

While the product of vinyl polymerization of alkyl acrylate has the substituent on every other main chain carbon atom, the product of C1 polymerization has the same substituent on every main chain carbon atom. The structural difference is expected to bring about unique physical properties and functionalities for the latter products. Credit: Eiji IharaThe products of C1 polymerization are expected to possess enhanced physical properties and functionalities. Following the first publication on this C1 polymerization project (E. Ihara, et al., Macromolecules, 36, 36 (2003)), intensive efforts have been devoted to this C1 polymerization by many groups around the world.

Enhanced Properties of C1 Polymers

A structure of the Pd-based initiators was devised leading to success in improving their activity for C1 polymerization. For example, it is now possible to prepare high molecular weight polymers (molecular weight > 50000), to control the stereo-structure (tacticity) of the C-C main chain, and to quantitatively incorporate a functional group at one end of the polymer chain.

In addition, utilizing the unique structures of the C1 polymers, success was made in preparing C1 polymers with enhanced acidity and much higher melting points, up to 130 °C, compared to their vinyl polymer counterparts with the same substituents. Also, it was found that the C1 polymers can be effectively degraded into low molecular weight compounds under mildly basic conditions, which is very important considering their potential as environmentally friendly polymeric materials.

Meanwhile, it was demonstrated that bis(diazocarbonyl) compounds bearing two diazocarbonyl groups in a molecule, can be used as a monomer for polycondensation, yielding a variety of new polymers with an unprecedented chemical structure. For the polycondensation, unique reactivities of diazocarbonyl groups were employed, such as O-H and N-H insertion and C=C bond formation. On the basis of this new polycondensation, it was possible to prepare polymers with facile degradability under mildly acidic conditions and electrochromic properties (reversible color change with the application of voltage in a film state). These results have stimulated research around the world in a similar project following the first publication on this polycondensation project (E. Ihara, et al., Macromolecules, 43, 4589 (2010)).

Reference: “Development of polymer syntheses using diazocarbonyl compounds as monomers” by Eiji Ihara, 10 October 2024, Polymer Journal.
DOI: 10.1038/s41428-024-00954-1

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