Facile synthesis of histidine functional poly(N-isopropylacrylamide): Zwitterionic and temperature responsive materials

N-Isopropylacrylamide is copolymerised with aldehyde functional monomers to facilitate post polymer functionalisation with histidine via reductive amination. This strategy is successfully performed without the use of protecting groups with high yields, demonstrating the facile application of this synthetic strategy with high functional group tolerance. The resulting temperature responsive, histidine functionalised polymers are characterised and their responsive nature is explored. The functionalised polymers exhibit sharp Lower Critical Solution Temperatures (LCST) at histidine incorporations of up to 8%. Upon 12 and 23% incorporation, the LCST transition extends over a wider range of temperature, indicating that the LSCT is being counteracted by an increase in solubility from the histidine moieties which interact strongly with water. Dynamic Light Scattering data indicates responsive self-assembly.