Thermoresponsive extraction of cadmium(II) ions by poly(TPEN-NIPA) gels. Effect of chain length and branched spacer structure on gel formation and extraction behavior

N,N,N',N'-(tetrakis-2-pyridylmethyl)ethylenediamine (TPEN) derivatives bearing a polymerizable double bond in the substituent structure of the pyridine ring were synthesized and subjected to copolymerization with N-isopropylacrylamide in the presence of azobisisobutyronitrile. The obtained poly(TPEN-NIPA) gels show thermoresponsive swelling/shrinking behaviors, and are used for the extraction of cadmium(II) (Cd(II)) ions from an aqueous solution to examine the relationship between gel characteristics and extraction performance. Polymer gels composed of TPEN derivatives bearing C3, C4, C10 and branched C3 spacer chains were synthesized, and the temperature-dependent Cd ion extraction behaviors of the gels were compared. The gels extracted Cd(II) ions efficiently from the aqueous solution in a swelling state at 5 degrees C, whereas little extraction was observed at 45 degrees C in the shrinking state. Poly(TPEN-NIPA) gel with branched C3 spacers (C3b) shows excellent thermoresponsive extraction performance. Polymer Journal (2011) 43, 630-634; doi:10.1038/pj.2011.38; published online 27 April 2011