Effect of chemical composition on properties of pH-responsive poly(acrylamide-co-acrylic acid) microgels prepared by inverse microemulsion polymerization

In this research, a series of pH-responsive microgels based on acrylamide (AM), acrylic acid (AA) as the main monomers, and N,N′-methylenebisacrylamide as a divinyl cross-linking agent, have been prepared by inverse microemulsion polymerization. The effect of chemical composition of poly(acrylamide-co-acrylic acid) (P(AM-co-AA)) on hydrodynamic diameters, morphology, swelling ratios and pH-responsive behaviour and thermal properties of microgels were discussed. With an increase of the mole percentages of AA in the feed ratio, the microgels have higher swelling ratios. The TEM photographs show that the spherical morphology of the microgels are regular relatively. Comparing with PAM microgels, number-average diameters of P(AM-co-AA) microgels were larger because of the presence of AA chain segment in the polymer chain. Turbidities of microgels determined through UV–vis spectrophotometer indicate that the microgels exhibit favourable pH-responsive behaviour, and responsive pH value is related to the dissociation constant of AA. Moreover, thermal stable properties of microgels were confirmed by differential scanning calorimeter. It was observed that an increase in the mole percentages of AA in the feed ratio provided lower glass transition temperature and thermal decomposition temperature of pH-responsive microgels.