One-Pot Synthesis of Thermoresponsive PNIPAM Hydrogel Microcapsules Designed to Function in Apolar Media

Abstract

Poly(N-isopropylacrylamide) (PNIPAM) hydrogel microcapsules having a hydrophobic corona (MCs) were prepared by precipitation−polymerization performed in water-in-oil emulsion using polyethyleneoxide−polyisoprene block copolymer as macromolecular surfactant and a corona-forming compound. The resulting hydrogel MCs form stable dispersions even in highly apolar organic solvents, such as cyclohexane, but flocculate in water. An approach to load the MCs with water, based on addition of aqueous solutions to the dispersion of the MCs in THF followed by addition of apolar solvents to induce segregation of a water-rich phase, was developed. The water-filled hydrogel MCs show a well-pronounced swelling/deswelling transition triggered by temperature in an environment that contains only minute amounts of water. Encapsulating capabilities of the MCs were also demonstrated. The MCs can be envisaged for applications that require controlled dispersion and release of hydrophilic species in oils