Temperature induced phase transition of interpenetrating polymer networks composed of poly(vinyl alcohol) and copolymers of N-isopropylacrylamide with acrylamide or 2-acrylamido-2-methylpropyl-sulfonic acid

Interpenetrating polymer networks (IPNs) composed of poly(vinyl alcohol) (PVA) and poly(N-isopropylacrylamide-co-X) (PNIPAAm-co-X) were prepared by using a two-step method. Hydrophilicity of PNIPAAm chains was increased by adding acrylamide (AAm; hydrophilic neutral monomer) or 2-acrylamido-2-methylpropylsulfonic acid (AMPS; anionic charged monomer). The effect of the incorporation of chemically crosslinked PVA into the temperature induced phase transition as well as swelling behavior of the responsive hydrogels were studied. The volume phase transition (VPT) of IPNs was investigated by cloud point measurement and differential scanning calorimetry. Significant differences in volume phase transition enthalpies of PNIPAAm (ΔHVPT) and volume phase transition temperatures (TVPT) were found. The ΔHVPT decreases with increasing co-monomer concentration. In several cases the phase transition was not followed by macroscopic shrinking of IPNs. Thus this property is advantageous for several technical applications.