PNIPAM Side Chains Research Articles

Linear viscoelasticity of thermoassociative chitosan-g-poly(N-isopropylacrylamide) copolymer

Chitosan-g-poly(N-isopropylacrylamide) (chitosan-g-PNIPAM) was synthesized and characterized rheologically in aqueous solutions. The copolymer solution exhibits a thermoassociative behavior in which its elastic response dramatically increases when temperature is above the critical temperature or the association temperature, T assoc. The copolymer at low concentration shows typical solution property. When the temperature is increased up to the critical temperature, the copolymer exhibits a gel-like characteristic due to the formation of physical cross-links between chitosan backbones through the self-aggregation of PNIPAM side chains. At high concentration, the system exhibits a weak elastic response due to the entanglement of the copolymer at 25°C. As temperature is raised above T assoc, the system shows a strong elastic behavior due to the formation of additional physical cross-links via the aggregation of PNIPAM side chains. Chitosan-g-PNIPAM offers an attractive associating behavior in aqueous solution at temperature close to the body temperature, thus providing potential applications in pharmaceutical and medical industries.

Thermally Induced Gelation of Poly(acrylamide) Grafted with Poly(N-isopropylacrylamide): A Small-Angle Neutron Scattering Study

Sieving matrixes of poly(acrylamide) grafted with poly(N-isopropylacrylamide) (PNIPAM) were developed in the framework of DNA sequencing by capillary electrophoresis. As a result of their thermodynamic properties, PNIPAM side chains self-aggregate above a critical temperature, leading to strong thermo-thickening effects in semidilute solutions. We report here a study of the transient network formation, carried out in D2O by small-angle neutron scattering on the basis of a large set of responsive copolymers tailored with PNIPAM grafts of different sizes (Mw = 10 000, 20 000, and 35 000 g/mol) and various graft densities (5, 7, 10, 14, and 18% w/w). For most of the aqueous solutions, a correlation peak is observed at finite scattering vectors when the temperature is increased above a critical value. The intensity of the scattering peak rises with the size of the PNIPAM stickers, the graft density, the concentration, and the temperature. Experimental data are fitted using a core−corona model, assuming that o...