Alkenylboronic Acid Derivatives as Monomers for Radical Polymerization Leading to Polymer Synthesis via Side-Chain Replacement and Development of Boron-Based Functions

Abstract

Vacant p-orbital of boron is often utilized for design of unique organic reactions based on its stabilization of adjacent carbon radical and Lewis acidity for interactions with internal or external base. In this study, these unique properties of boron were utilized to design vinyl monomers for chain-growth polymerization. The author unveiled that alkenylboronic acid derivatives, where boron is connected to a vinyl moiety, exhibit radical (co)polymerization ability due to the stabilization of chain-growth radical by the p-orbital on boron. The resulting polymers have boron atoms attached to the main chain, and the replacement of boron pendants with other elements in post-polymerization transformation step enabled the synthesis of novel polymers that are difficult to access by conventional methods [e.g., poly(α-methyl vinyl alcohol), branched poly(vinyl alcohol), and poly(ethylene-co-acrylate)]. Furthermore, boron on the main chain served not only as a replaceable side chain but also as a Lewis acidic moiety for developing novel polymer functions such as stimuli-responsive backbone degradation and side-chain cooperative polymer catalysts. The concept of boron-based monomer design thus opens new avenues in polymer chemistry and materials science.