Poly(glyceryl glycerol): A multi-functional hydrophilic polymer for labeling with boronic acids

The synthesis of poly(glyceryl glycerol) (PGG), a polymer featuring a polyethylene oxide backbone and 1,2-diol groups in every repeating unit, is presented. PGG was prepared by monomer-activated ring-opening polymerization of (dl-1,2-isopropylidene glyceryl) glycidyl ether, introducing a functional azido- or bromo-head group to each chain. The 1,2-diol groups, which were released by acidic deprotection, readily reacted with boronic acid derivatives, enabling the attachment of functional moieties under mild aqueous conditions. PGG was conjugated to poly(l-lactide) (PLLA) via azide-alkyne cycloaddition and the resulting copolymer assembled into nanoparticles of 70 nm diameter in aqueous solution. Labeling of the PGG-PLLA particles was achieved by simple mixing with a boronic acid-functional fluorophore. The labeling efficiency was determined by fluorescence spectroscopy to be 85.5% for boronic acid-functional rhodamine B compared with 0.2% for plain rhodamine B. The strong interaction of PGG with boronic acids is ascribed to its polyol structure. This study demonstrates the usefulness and versatility of PGG as a hydrophilic polymer for possible biomedical applications. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 1822-1830