Bisphenol A-responsive microgel comprising hydrophilic poly(acrylamide) network

Stimuli-responsive microgels that exhibit rapid changes in size in response to external stimuli such as pH and temperature are of great interest for the development of smart sensors, drug delivery carriers, and separation materials. This paper describes the preparation of molecule-responsive microgels with molecular recognition sites comprising a hydrophilic network via inverse miniemulsion polymerization using a water-soluble emulsifier. The water-soluble emulsifier comprising hydrophilic poly(sulfobetaine) and hydrophilic/oleophilic poly[oligo(ethylene glycol)methacrylate-co-2-(2'-methoxyethoxy)ethyl methacrylate] blocks were synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization. The resulting block copolymer, PSB-POEG, stabilized the water-chloroform interface in a water-in-oil (W/O) emulsion. Water droplets in a W/O emulsion stabilized with PSB-POEG allowed the inverse miniemulsion polymerization of acrylamide (AAm), acryloyl-modified β-cyclodextrin (CD), and N,N'-methylenebisacrylamide to obtain CD-conjugated PAAm microgels with a diameter of approximately 150 nm. The resulting CD-PAAm microgels were stably dispersed in an aqueous medium by the addition of water, followed by evaporation of chloroform. The CD-PAAm microgels exhibited rapid shrinkage in response to bisphenol A (BPA) owing to the formation of CD-BPA-CD complexes acting as dynamic cross-links. The proposed method for preparing hydrophilic microgels by inverse miniemulsion polymerization using a water-soluble emulsifier allows the preparation of molecularly imprinted and bioconjugated microgels, providing a useful platform for designing rapidly responsive soft nanomaterials for molecular sensors, separation substrates, and drug delivery carriers.