Sonochemical production and activation of responsive polymer microspheres

This paper reports work aimed at extending previous studies of the sonochemical method for forming microspheres. It shows that a previously reported method for encapsulating and delivering hydrophilic species using a ‘double emulsion’ method can be used with chitosan or thiolated poly(methacrylic acid), PMAA _SH , based systems. One particular application involves targeted catalysis where gold nanoparticles are incorporated into chitosan microspheres and can be released to catalyse the borohydride reduction of 4-nitrophenol. Also reported is the use of ultrasound to ‘trigger’ the reduction reaction of 4-nitrophenol by rupturing nanoparticle-containing microspheres to release the catalyst. We also demonstrate that more sustainable and potentially lower environmental impact processes can be prepared by substituting commercial vegetable oil for the hydrocarbons used previously. We also report for the first time the use of responsive block copolymers to form microspheres. The copolymers consist of PMAA _SH blocks around a central, responsive block of poly(ethylene glycol), poly(4-vinylphenyl boronic acid) or poly(N-isopropylacrylamide) to give systems that potentially respond to pH, sugar concentrations or temperature.