Synthesis,characterization and physiochemical investigation of chitosan-based multi-responsive Copolymeric hydrogels

This paper describes the synthesis and physicochemical characterization of Poly(N-isopropylacrylamide)-Chitosan-Poly(Acrylic acid) [PNIPAAm-CS-PAA] based polymeric microgels. Three different samples of multi-responsive (PNIPAAM-CS-PA) microgels were synthesized using various amounts of N N^?- Methylene bis-acrylamide (MBA) and Acrylic acid (AA) by free radical emulsion polymerization. The redox initiator Ammonium per sulfate (APS) was used to initiate the reactions while MBA was used as a crosslinking agent. The purified polymeric microgels were then characterized using UV-Visible spectroscopy, Fourier transform infrared spectroscopy (FT-IR), Laser light scattering (LLS), Ostwald viscometry, dynamic Rheology and swelling/de-swelling measurements. From the spectroscopic result it was observed that all the reactions have been completed and the resultant microgels were successfully synthesized. The influence of various parameters such as, chemical composition and some external stimuli like temperature and pH on the physicochemical behavior of polymeric microgels was investigated through visual stability test, laser light scattering, viscometry and rheological measurement. The LLS analysis was performed to deduce the size, in the terms of hydrodynamic radius (R_h), of the microgel samples in aqueous media at different pH and temperature. From LLS analysis the microgels were found to be stable at all pH values above the pKa values (4.2) of AA in temperature ranges from 20 °C to 50 °C. With rising in temperature and pH causes aggregation of particles and decrease in stability of microgels due to the decrease in hydrophobicity. From the Rheological measurements, various physiochemical properties such as, elasticity, viscosity, shear stress, storage modulus, loss modulus, phase angle and complex viscosity of the microgels were gathered. The Ostowald viscometry was used to measure the flow viscosity of microgels at different pH and temperatures. The present observations reflect that the prepared samples are multi-responsive and their physicochemical behavior can be tuned very easily by changing their composition and/or varying the external stimuli.