Frontal polymerization synthesis and characterization of temperature- and pH-sensitive hydrogels

The temperature- and pH-sensitive hydrogels, poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AAc)), were synthesized via frontal polymerization (FP). The reaction components have been varied in order to find their influences on frontal parameters and copolymer features. The results showed that front velocity and front temperature were dependent on the initiator concentration, reactant dilution, and NIPMA/AAc molar ratio. In addition, the morphology and sensitive behavior of the FP hydrogels were mainly affected by monomers’ ratio. Namely, the pore size, swelling abilities, LCST, and response kinetics of copolymer hydrogels obviously increased with the increasing acrylic acid concentration; however, they slightly changed with varying of amounts of initiator and solvent. Finally, in comparison with the hydrogels prepared by conventional batch polymerization, the ones synthesized by frontal polymerization exhibited more homogeneous chain composition and improved microstructure and response ability.