Metal ion sequestering particles were formed in a one-pot single step synthesis by azeotropically removing water while heating a reaction mixture containing a branched poly(ethylenimine), poly(acrylic acid), di-(2-picolylamine), a catalytic amount of N,N-duimethylformamide, toluene, and either glycine or a carboxy-terminated poly(N-isopropylacrylamide). No other catalyst was present. The branched and crosslinked particles formed using the poly(N-isopropylacrylamide) sequestered metal ion from water at ambient temperature and released the bound metal ion upon heating.