Tuning the sugar-response of boronic acid block copolymers

A detailed study of the pH- and sugar-responsive behavior of poly(3-acrylamidophenylboronic acid pinacol ester)-b-poly(N,N-dimethylacrylamide) (PAPBAE-b-PDMA) block copolymers is presented. Reversible addition-fragmentation chain transfer (RAFT) polymerization of the pinacol ester of 3-acrylamidophenylboronic acid resulted in homopolymers with molecular weights between 12,000 and 37,000 g/mol. The resulting homopolymers were employed as macro-chain transfer agents during the polymerization of N,N-dimethylacrylamide (DMA). Successful chain extension and removal of the pinacol protecting groups to yield poly(3-acrylamidophenylboronic acid)-b-PDMA (PAPBA-b-PDMA) with free boronic acid moieties resulted in pH- and sugar-responsive block copolymers that were subsequently investigated for their behavior in aqueous solution. The PAPBA-b-PDMA block copolymers were capable of solution self-assembly due to the PAPBA block being water-insoluble below its pKa. The resulting aggregates were demonstrated to solubilize and release model hydrophobic compounds, as demonstrated by fluorescence studies. Dissociation of the aggregates was induced by raising the pH above the pKa of the boronic acid residues or by adding sugars capable of forming boronate esters. Aggregate size, dissociation kinetics, and the effect of various sugars were considered. The critical sugar concentration needed to induce aggregate dissociation was tuned by incorporation of hydrophilic DMA units within the PAPBA responsive segment to yield PDMA-b-poly(3-acrylamidophenylboronic acid-co-DMA) block copolymers. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012