Radical polymerization of alkenyl boronates and C–B bond transformation: polymer synthesis through side-chain replacement for overcoming synthetic limitations

Vinyl polymers are typically synthesized through the addition polymerization of corresponding vinyl compounds. However, the polymerization ability significantly depends on the substituent on the vinyl moiety, resulting in various synthetic limitations in the molecular structure of vinyl polymers. Given the increasing societal demand for enhanced properties and functions of polymer materials, innovative synthetic technologies are required for developing next-generation polymers through flexible molecular design. The author has made considerable efforts to overcome these limitations in polymer synthesis by employing alkenyl boronates as monomers for radical polymerization. The resulting polymers bear boron on the main chain, allowing the replacement of boron side chains with other elements through the cleavage of carbon–boron bonds in postpolymerization transformations. This strategy, based on “side-chain replacement,” has enabled the synthesis of various polymers that were previously inaccessible. The review highlights the author’s recent discovery of the radical (co)polymerization ability of alkenylboronic acid derivatives and C–B bond-cleaving side-chain replacement in polymer reaction. The polymerization ability is attributed to the vacant p-orbital of boron, which can stabilize chain-growth radical species. In copolymerization and controlled polymerization, the boron monomer behaves as a relatively electron-rich and conjugated monomer. The boron attached to the polymer main chain was replaceable with other elements, providing access to various polymers of which synthesis is not straightforward, such as poly(α-methyl vinyl alcohol), poly(vinyl alcohol-co-styrene), and poly(ethylene-co-acrylate).