Graft copolymers that exhibit temperature-induced phase transitions over a wide range of pH

Abstract

THERE are many potential applications of 'intelligent' aqueous polymer systems^1–8 in medicine, biotechnology, industry and in environmental problems^9–13. Many of these polymer systems undergo reversible phase transitions—for example, abrupt changes in volume—in response to external stimuli such as temperature, pH or the nature of the solvent. Most of the polymers studied previously are responsive to only one kind of stimulus. But for some applications, independent responsiveness to several factors, such as temperature and pH, may be required. Here we describe a polymer that undergoes marked solubility changes in water in response to temperature and/or pH changes. The polymer is prepared by grafting temperature-sensitive side chains onto a pH-sensitive backbone. We also find that block copolymers, in which the temperature- and pH-sensitive units alternate along the chain, show similar behaviour.