Synthesis, rheological behavior and swelling properties of copolymer hydrogels based on poly(n-isopropylacrylamide) with hydrophilic monomers

Abstract

In this study, hydrogels of poly(N-isopropylacrylamide-co-acrylamide) and poly(N-isopropylacrylamide-co-acrylic acid) having a thermoresponsive character were prepared by aqueous free-radical co-polymerization using the ammonium persulfate/N,N,N', N'-tetramethylethylenediamine (APS/TEMED) redox-pair initiator system in the presence of N,N'-methylenebisacrylamide (MBAAm) crosslinker. (NIPAAm-co-AAm) and (NIPAAm-co-AAc) hydrogels with different thermoresponsive properties were obtained by fixing the initial NIPAAm/AAm mole ratio and and (NIPAAm-co-AAc) mole ratio to 80/20 and changing the crosslinker concentration. The copolymers were characterized with infrared spectroscopy (IR) and differential scanning calorimetry (DSC) techniques. The swelling response of the copolymers networks as a function of time, temperature and swelling environment has been observed to be dependent on both structural aspects of the polymers and swelling environment. The swelling has been observed to be decrease with increase in MBAAm in the copolypolymers networks. Rheological behavior was studies in oscillatory module. All copolymers have a viscoelastic behaviour. We note that the elastic modulus G' increases with increasing hydrophilic monomers