Temperature-Responsive Cellulose by Ceric(IV) Ion-Initiated Graft Copolymerization of N-Isopropylacrylamide

Abstract

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.

A versatile characterization of poly(N-isopropylacrylamide-co-N,N'-methylene-bis-acrylamide) hydrogels for composition, mechanical strength, and rheology

“…It should be noted that in the 2 nd series of experiments Soxhlet extraction was used to purify the gels despite the temperature of purification being higher than the phase transition temperature. Gupta et al [23] have also used Soxhlet extraction for removing ungrafted PNIPAAm homopolymer from grafted cellulose. It was expected that impurities become entrapped at higher cross-link ratio in the gel during Soxhlet purification, due to the high cross-link density, and collapsed structure of the gels during extraction.…”

Polysaccharide‐Containing Block Copolymers: Synthesis, Properties and Applications of an Emerging Family of Glycoconjugates

“…Following one of these two chemical pathways, polyesters such as polylactide or poly(e-caprolactone) have been grafted onto cellulose, [13] dextran, [14] alginate, [15] chitosan [16] and hyaluronan [17] resulting in amphiphilic copolymer structures. Vinyl monomers such as styrene, [18][19][20] methyl methacrylate, [21,22] vinyl acetate [23] and N-isopropylacrylamide [24] also have been polymerized along polysaccharide chains through conventional free radical methods [21,24] or more recently by living/controlled polymerization methods. [18][19][20]22,23] The reverse approach, namely the grafting of polysaccharide chains onto synthetic polymer backbone has been reported as well.…”

Stimuli‐Responsive Hydrogels Based on Polysaccharides Incorporated with Thermo‐Responsive Polymers as Novel Biomaterials

“…Gupta et al studied the activation energy for graft copolymerization of NIPAAm onto cellulose by using CAN. [58] They found that the grafting was increased below LCST of PNIPAAm, and obtained a low energy of activation (18.0 kJ Á mol À1 ) within the temperature range of 10-35 8C. The NIPAAm-g-cellulose has shown significant improvement in its properties such as thermal stability, water absorbency, and degree of swelling.…”