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.

Ceric ammonium nitrate (CAN) in the presence of nitric acid has been used as efficient initiator for graft copolymerization of the ethyl acrylate onto cellulose at 35.0 +/- 0.1 degrees C. Graft copolymerization of ethyl acrylate onto cellulose has taken place through the radical initiation process. The graft yield and other grafting parameters have been evaluated by varying concentration of ethyl acrylate from 2.5 x 10(-1) to 15.0 x 10(-1) mol dm(-3) and ceric ammonium nitrate from 5.0 x 10(-3) to 25.0 x 10(-3) mol dm(-3) at constant concentration of the nitric acid (8.0 x 10(-2) mol dm(-3)). The rate of graft copolymerization has shown 1.5 order with respect to the concentration of the ceric ammonium nitrate. The graft copolymerization data obtained at different temperatures were used to calculate the energy of activation, which has been found to be 28.9 kJ mol(-1) within the temperature range from 20 to 50 degrees C. The effect of addition of cationic and anionic surfactants on graft copolymerization has also been studied. On the basis of the experimental observations, reaction steps have been proposed and a suitable rate expression for graft copolymerization has been derived.

ABSTRACT:The graft copolymerization of acrylamidemethylacrylate comonomers was carried out using ceric ammonium nitrate as initiator in the presence of nitric acid at 25 Ϯ 1°C. The effects of feed molarity, feed composition, reaction time, and temperature on graft yield (%G) and other grafting parameters were investigated. The determination of rate of ceric (IV) ions disappearance as a function of feed molarity and reaction time was useful in the determination of the rate of ceric (IV) ions consumption during graft copolymerization. The graft yield (%G) in the presence of acrylamide increases because of the synergistic effect of acrylamide comonomer. The composition of the grafted chains (F AAm ) varies on varying the feed composition and reaction temperature but is almost constant during feed molarity variation. The Mayo and Lewis method was used to determine the reactivity ratios of acrylamide (r 1 ) and methylacrylate (r 2 ), which are 0.65 and 1.07, respectively. The product of reactivity ratio (r 1 r 2 ) is less then unity; hence, an alternate arrangement of comonomer blocks in the grafted copolymer chain is proposed. The rate of graft copolymerization of comonomers onto cellulose is second power to the concentration of comonomers and square root to the concentration of ceric ammonium nitrate. Suitable reaction steps for graft copolymerization of comonomers onto cellulose are proposed.

ABSTRACT:The graft copolymerization of acrylamide (AAm) and ethylmethacrylate (EMA) monomers onto cellulose has been carried out using ceric ammonium nitrate (CAN) as initiator in presence of nitric acid at (25 Ϯ 1)°C and varying feed molarity from 7.5 ϫ 10 Ϫ2 mol dm Ϫ3 to 60.0 ϫ 10 Ϫ2 mol dm Ϫ3 at fixed feed composition (f AAm ϭ 0.6). The graft yield (%G Y ) has shown a linear increasing trend upto a feed molarity of 37.5 ϫ 10 Ϫ2 mol dm Ϫ3 . The composition of grafted copolymer chains was found to be constant (F AAm ϭ 0.56) during feed molarity variation but shown variations with feed composition (f AAm ) and reaction temperature. The grafting parameters have shown increasing trends up to 7.5 ϫ 10 Ϫ3 mol dm Ϫ3 concentration of ceric (IV) ions and decreased on further increasing the concentration of ceric (IV) ions beyond 7.5 ϫ 10 Ϫ3 mol dm Ϫ3 . The IR and elemental analysis data were used to determine the composition of grafted chains (F AAm ) and reactivity ratio of acrylamide (r 1 ) and ethylmethacrylate (r 2 ) comonomers. The reactivity ratio for acrylamide (r 1 ) and ethylmethacrylate (r 2 ) has been found to be 0.7 and 1.0 respectively, which suggested for an alternate arrangement of average sequence length of acrylamide (mM 1 ) and ethylmethacrylate (mM 2 ) in grafted chains. The rate of graft copolymerization of comonomers onto cellulose was found to be proportional to square concentration of comonomers and square root to the concentration of ceric (IV) ions. The energy of activation (⌬Ea) of graft copolymerization was found to be 9.57 kJ mol Ϫ1 within the temperature range of 20 -50°C. On the basis of experimental findings, suitable reaction steps have been proposed for graft copolymerization of selected comonomers.

Graft copolymerization of acrylamide (AAm) and ethyl acrylate (EA) onto cellulose has been carried out from their binary mixtures using ceric ammonium nitrate (CAN) as an initiator in the presence of nitric acid at 25 ± 1 °C. The extent of acrylamide grafting increased in the presence of the EA comonomer. The composition of the grafted chains (FAAm = 0.52) was found to be constant during the feed molarity variation from 7.5 × 10−2 to 60.0 × 10−2 mol L−1, whereas the composition of the grafted chains (FAAm) was found to be dependent on feed composition (fAAm) and reaction temperature. The effects of ceric(IV) ion concentration, reaction time and temperature on the grafting parameters have been studied. The grafting parameters showed an increasing trend up to 6.0 × 10−3 mol L−1 concentration of CAN at a feed molarity of 30.0 × 10−2 mol L−1 and showed a decreasing trend on further increasing the concentration of CAN (>6.0 × 10−3 mol L−1) at a constant concentration of nitric acid (5.0 × 10−2 mol L−1). The composition of the grafted chains (FAAm) was determined by IR spectroscopy and nitrogen content and the data obtained then used to determine the reactivity ratios of the acrylamide (r1) and ethyl acrylate (r2) comonomers by using a Mayo and Lewis plot. The reactivity ratios of acrylamide and ethyl acrylate were found to be r1 = 0.54 and r2 = 1.10, respectively, and hence the sequence lengths of acrylamide (m̄M1) and ethyl acrylate (m̄M2) in the grafted chains are arranged in an alternating form, as the product of the reactivity ratios of acrylamide and ethyl acrylate (r1 × r2) is less than unity. The rate of graft copolymerization of the comonomers onto cellulose was found to be dependant on the ‘squares’ of the concentrations of the comonomers and on the ‘square root’ of the concentration of ceric ammonium nitrate. The energy of activation (ΔEa) of graft copolymerzation was found to be 5.57 kJ mol−1 within the temperature range from 15 to 50 °C. On the basis of the results, suitable reaction steps have been proposed for the graft copolymerzation of acrylamide and ethyl acrylate comonomers from their mixtures. Copyright © 2005 Society of Chemical Industry