Synthesis of transition‐metal‐ion‐selective poly(N‐isopropylacrylamide) hydrogels by the incorporation of an Aza crown ether

A functionalized cyclam was synthesized by the attachment of a polymerizable acryloyl group to one of the four nitrogens on the cyclam molecule. The polymerization of the functionalized cyclam was performed with N ‐isopropylacrylamide and N , N ′‐methylene bisacrylamide, and the gels obtained were studied in the presence of different transition‐metal‐ion solutions. There was a drastic difference in the phase‐transition temperature ( T c ) of the poly( N ‐isopropylacrylamide) (PNIPAAm)/cyclam gel in comparison with the pure PNIPAAm gel. For the described system, a T c shift of 15 °C was obtained. The presence of functionalized cyclam increased the hydrophilicity and T c of the aforementioned polymer gels in deionized water (at pH 6) because of the presence of protonated amino moieties. The PNIPAAm/cyclam gels showed a dependence of the swelling behavior on pH. T c of the pure PNIPAAm gel was weakly influenced by the presence of any transition‐metal ions, such as Cu 2+ , Ni 2+ , Zn 2+ , and Mn 2+ . The addition of Cu 2+ or Ni 2+ to the PNIPAAm/cyclam gel reduced T c of the polymer gel, and a shift of approximately 12 °C was observed.