defined self-assembling block copolymers containing polybor-oxole as a saccharide-responsive polymeric domain have not yetbeen synthesized.We report here the first synthesis of the boroxole-containingstyrenic monomer 1 and its controlled radical polymerizationvia the reversible addition−fragmentation and chain transfer(RAFT) method. Synthesized poly(styreneboroxole) (PBOx)showed binding to monosaccharides in phosphate buffer atneutral pH (pH 7.4), which was quantitatively studied usingWang’s competitive binding assay.19By virtue of a controlledradical polymerization of 1, we synthesized a series of sugar-responsive block copolymers that self-assembled to formpolymersomes in water. We demonstrated that the polymer-somes of these block copolymers could encapsulate water-soluble cargo molecules such as insulin, which could then bereleased from the polymersomes only in response to thepresence of monosaccharides in aqueous solution underphysiological pH conditions (Figure 1).Styreneboroxole 1 was synthesized from 3-bromo-4-(bromomethyl)benzonitrile in seven steps in a moderate yield(Scheme 1).15,20During the synthesis, the protecting group forbenzyl alcohol was switched from a tert-butyldimethylsilyl(TBDMS) group to a methoxymethyl (MOM) group because