Temperature-responsive cellulose by ceric(IV) ion-initiated graft copolymerization of N-isopropylacrylamide.

Temperature-responsive cellulose has been obtained by graft copolymerization of N-isopropylacrylamide (NIPAAm) monomer using ceric ammonium nitrate (CAN) as initiator at 25.0 +/- 0.1 degrees C in acidic medium. Kinetic and grafting parameters were evaluated at different concentrations of NIPAAm ranging from 1.25 x 10(-3) to 12.5 x 10(-3) mol dm(-3) and varying concentrations of CAN from 1.5 x 10(-3) to 9.0 x 10(-3) mol dm(-3) at constant concentration of nitric acid (2.5 x 10(-2) mol dm(-3)). The graft copolymerization of NIPAAm onto cellulose has shown a significant increasing trend below lower critical solution temperature (LCST) of poly(N-isopropylacrylamide) (PNIPAAm) and shown low energy of activation (18.0 kJ mol(-1)) for graft copolymerization within the temperature range of 10-35 degrees C as determined with Arrhenius plot. The PNIPAAm-grafted cellulose has shown improved thermal stability and shown temperature-dependent degree of swelling. Variation in degree of swelling of PNIPAAm-grafted cellulose as a function of temperature has been used to determine LCST of PNIPAAm-grafted cellulose. The contact angle (theta) has shown variation on increasing the graft yield and temperature. On the basis of experimental observations, the reaction steps for graft copolymerization have been proposed and a rate expression has been derived.