Effect of copolymerization and semi-interpenetration with conducting polyanilines on the physicochemical properties of poly(N-isopropylacrylamide) based thermosensitive hydrogels

Thermosensitive hydrogels are made by radical homopolymerization of N-isopropylacrylamide (NIPAAM) or copolymerization of NIPAAM with 2-acrylamido-2-methyl-propane sulfonic acid (AMPS). The networks are semi-interpenetrated (s-IPN) with linear conducting polymers: polyaniline (PANI) or poly(N-methylaniline) (PNMANI). The semi-interpenetration affect slightly the phase transition temperature (measured by DSC) of the hydrogels, while water uptake capacity is strongly affected and depends on the relative hydrophobicity of the conducting polymer. Since polyanilines can be protonated in aqueous media, the swelling capacity of the s-IPN hydrogel depends strongly on pH unlike the unmodified hydrogel. The release of a model compound (tris(2,2′-bipyridine)ruthenium (II), image), driven by swelling or temperature, is also strongly affected both by the introduction of sulfonic groups, by copolymerization of NIPAAM with AMPS, semi-interpenetration and on the hydrophobicity of the conducting polymer. In that way, composite materials with quite different ion exchange behavior can be made by copolymerization and conducting polymer interpenetration.