Aminated Thermoresponsive Microgels Prepared from the Hofmann Rearrangement of Amides without Side Reactions

Thermoresponsive microgels bearing primary amine groups were prepared by the Hofmann rearrangement of methacrylamide groups present in cross-linked NIPMAM (N-isopropylmethacrylamide) microgels. Most thermoresponsive microgels are based on NIPAM (N-isopropylacrylamide). By substituting NIPMAM for NIPAM, and methacrylamide for acrylamide, side reactions and the generation of carboxyl groups were prevented during the Hofmann reaction. The Hofmann rearrangement is sufficiently slow under our conditions (1 h for a 51% conversion) to permit fine control of the primary amine contents in the microgels. When starting with PNIPMAM microgels containing both methacrylamide and acrylic acid residues, we prepared a series of amphoteric microgels spanning a range of amine contents, all from a common parent microgel. Therefore, every microgel in the series had the same microstructure, cross-link density, and molecular weight.