Synthesis and characterization of multi-responsive poly (NIPAm-co-AAc) microgels

Two samples of multi-responsive copolymer microgels, poly(N-isopropylacrylamide-co-acrylic acid) [P(NIPAm-co-AAc)], were synthesized by emulsion polymerization using different amounts of emulsifier. The unreacted monomers and surfactant were removed from the microgels by dialysis. Dynamic Laser Light Scattering (DLS) was used to determine the diffusion coefficient and hydrodynamic radius (Rh) of the microgels at different pH values and temperatures. At pH 7 the microgel showed rapid response to temperature and underwent volume phase transition (VPT) as the temperature was raised. At lower temperature the microgels were in the hydrated or swollen state but beyond 38oC, the size was abruptly decreased. Under different conditions of pH and NaCl concentrations, variations in VPTT values were noticed. By increasing pH the VPTT was increased but the addition of salt had an inverse effect. The weight average molar mass (Mw) and radius of gyration (Rg) were measured by Static Laser Light Scattering (SLS). FTIR spectroscopy was used to confirm the chemical structures of microgels