Luminescent N-isopropylacrylamide–surfmer copolymer hydrogels prepared upon electrostatic self-assembly of 1-pyrenesulfonate

The preparation of luminescent hydrogels based on the electrostatic self-assembly of 1-pyrenesulfonate (PyS) anions in a positively charged N-isopropylacrylamide (NiPAAm)/surfmer copolymer gel is described. The hydrogels were prepared from a micellar aqueous solution of 11-acryloyloxyundecyltrimethylammonium bromide and NiPAAm upon 60Co-gamma irradiation. For assembly of PyS, the gel was shrunken at 50 °C and re-swollen at 20 °C in an aqueous solution of sodium 1-pyrenesulfonate. Re-swelling was accompanied by electrostatic assembly of PyS anions within the gel. Subsequently, the excess non-bound PyS ions were removed by repeatedly swelling and shrinking the gel in pure water at 20 °C and 50 °C, respectively. Incorporation of PyS ions in the hydrogel was studied using UV/Vis spectroscopy and energy dispersive x-ray (EDX) measurements. The amount of electrostatically adsorbed PyS was found to be proportional to the amount of copolymerized surfmer. EDX studies indicated that 20% of the bromide counterions were replaced for PyS. The PyS counterions could be released again if the functionalized hydrogel was immersed in acidified water. At a pH of 1, an almost complete release of PyS was found after 250 h. The preparation method can be used to introduce a variety of functional properties in thermoresponsive charged copolymer gels.