Vinylboron Monomers for Polymer Design via Side-Chain Replacement beyond Conventional Synthetic Limits

Organoboron compounds have long been recognized as versatile intermediates in organic synthesis owing to the unique transformability of the carbon–boron bond, and such chemistry has recently been exploited to address long-standing synthetic challenges in polymer science. In this perspective, we highlight vinylboron compounds in which a boron atom is directly attached to a vinyl group, as a new class of monomers for chain-growth polymerization. We discuss the characteristic polymerization behaviors of these monomers and the potential of main-chain-attached boron for side-chain replacement via postpolymerization transformations. Early studies on vinylboronic acid (without boron protection), certain vinyl boronates, and B-vinylborazine demonstrated the polymerizability of vinylboron compounds; however, undesired side reactions during polymerization were difficult to suppress due to the low stability of the boron pendants. More recent advances, including B-vinyl-1,2-azaborines, alkenylboronic acid pinacol esters, and anthranilamide-protected vinylboronic acids, established stable and highly polymerizable vinyl boron frameworks. The boron attaching to the polymer main chain enables not only side-chain replacement with other groups (mostly hydroxy group) but also the creation of advanced polymer functions based on the Lewis acidity of boron. Collectively, these developments demonstrate that vinylboron monomers can overcome long-standing limitations in chain-growth polymerization for polymer synthesis and open the door to the design of functional polymers.