Responsive Emulsions Stabilized by Amphiphilic Supramolecular Graft Copolymers Formed in Situ at the Oil–Water Interface

Amphiphilic supramolecular graft copolymers which can stabilize oil-in-water (o/w) emulsions and enable responsive demulsification were demonstrated in this study. Linear poly[(N,N-dimethylacrylmide)-stat-(3-acrylamidophenylboronic acid)] (PDMA-stat-PAPBA) copolymers with phenylboronic acid (PBA) groups and linear polystyrene homopolymers with cis-diol terminals (PS(OH)2) were synthesized by reversible addition–fragmentation chain transfer polymerization. By the homogenization of the biphasic mixtures of an alkaline water solution of PDMA-stat-PAPBA copolymer and a toluene solution of PS(OH)2 homopolymer, stable o/w emulsions could be generated, although neither PDMA-stat-PAPBA nor PS(OH)2 alone was able to stabilize the emulsion. It was verified that the dispersed oil droplets in the emulsions were stabilized by the amphiphilic PDMA-stat-PAPBA-g-PS supramolecular graft copolymers, which were formed in situ at the oil–water interface by the complexation between the lateral PBA groups of PDMA-stat-PAPBA and the diol terminals of PS(OH)2 during homogenization. These emulsions showed pH- and glucose-responsive demulsification because of the reversible B–O bonds between the PDMA-stat-PAPBA backbones and the PS side chains. The effects of polymer concentrations on emulsion formation were also investigated. The current study provides an alternative method for the facile preparation of responsive polymeric emulsifiers, which potentially may be extended to other polymer pairs containing PBA and cis-diol groups.