Synthesis and characterization of methacrylamide-acrylic acid-N-isopropylacrylamide polymeric hydrogel: degradation kinetics and rheological studies

Abstract

Methacrylamide-acrylic acid-N-isopropylacrylamide terpolymeric hydrogels have been prepared via free radical polymerization using diammonium-peroxo-disulphate initiator system and ethylene glycol-di-methacrylate as a cross-linker. The hydrogels were characterized by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, and differential scanning calorimetry. Molar mass was determined by viscometric method. Rheological profiling of the hydrogels was carried out by rheological measurements at various temperatures and methacrylamide contents in hydrogels. Thermogravimetric data were analyzed to assess the kinetic triplet by iso-conversional method. The values of apparent activation energy (E a) figured out from TG data were measured for each step by Kissinger–Akahira–Sunose method. On the findings of results, the decomposition reaction of terpolymeric hydrogels has been analyzed as a slow reaction, which is evident from the low-frequency factor values (A), i.e., 3 × 106, 2 × 1010, and 4 × 1015 s−1, respectively. The master plot method was used to predict the mechanism for degradation of MANIPAM-7. Flow curve and frequency sweep tests at different temperatures showed temperature dependency with shear rate indicating the pseudo-plastic nature of the synthesized samples. The rheological parameters were analyzed using various models. Out of these methods, the Ostwald, modified Bingham, and Herschel–Bulkley models were established to provide better fit to experimental data. Dynamic moduli measured as a function of angular frequency showed viscoelastic nature of all the samples. Frequency sweep studies indicated that storage (G′) and loss modulus (G″) showed an increase with increasing concentration of methacrylamide. Composition dependency of crossover frequency directed an increase in relaxation time with methacrylamide contents in the hydrogel.