Temperature‐responsive graft copolymers for immobilization of enzymes

A graft copolymer was prepared by coupling of poly(acrylic acid‐co‐acrylamide) (monomer ratio 1:8,5) with poly(N‐isopropylacrylamide) (PIPA) having an amino group at its end. The copolymer with the graft chains obtained [poly(AA‐co‐AAm)‐g‐PIPA] showed a temperature‐responsive phase transition at 34°C in water, and at 26°C in 1‐propanol/water (8:92 vol.‐%). Lipase from wheat germ was covalently bound to the graft copolymer using a water‐soluble carbodimide. The Arrhenius plots of the catalytic activity of the lipase immobilized to poly(AA‐co‐AAm)‐g‐PIPA had a bending point around 25 – 30°C in 1‐propanol/water (8:92 vol.‐%), which is consistent with the temperature‐responsiveness of the carrier polymer. As for lipase immobilized to the graft copolymer poly(AA)‐g‐PIPA, on the contrary, there was no bending point in the temperature dependence of the catalytic activity, probably due to electrostatic repulsion between acrylic acid residues, which perturbs the aggregation of PIPA side chains. The graft copolymer prepared here can be used as a component of temperature‐sensitive devices in various forms.