Study on the inverse emulsion copolymerization of microgels based on acrylamide/2-acrylamido-2-methylpropane sulfonic acid

Abstract

Inverse emulsion copolymerization of acrylamide and AMPS was conducted, and the effects of cross-linker concentration, initiator type, and reaction temperature on particle size distribution, equilibrium swelling and thermal properties were studied. Fourier transform infrared spectrophotometry (FTIR) and differential scanning calorimetry (DSC) results were used to confirm the copolymerization of the monomers. In this study, relatively high amounts of AMPS comonomer were used successfully to synthesize AAm/AMPS based microgels. Thermal properties were determined using thermogravimetric analysis (TGA) and it was found that degradation threshold shifted to higher temperatures with increasing cross-linking. There was a good agreement between the DSC and TGA thermograms depicting the different stages of microgel degradation including the departure of amide and sulphonic acid groups. Dynamic light scattering (DLS) demonstrated that higher cross-link densities resulted in the formation of smaller particles with narrower distribution and lower swelling capacity. The results of scanning electron microscopy (SEM) showed that the more hydrophobicity of the initiator led to the decrease in particle size and swelling capability. Swelling ratio reached its maximum value at about 50 °C. Interestingly, mean particle size had a close relation with equilibrium swelling as samples with lower mean particle diameters exhibited lower swelling capacities.