Abstract
<jats:p>The precipitation copolymerization method is a useful technique for preparing functional microgels incorporating a variety of functional groups. However, experimentally quantifying the heterogeneous distribution of functional groups formed within the microgels in an aqueous dispersion—the state in which the microgels exert their functions— is still challenging. In this study, microgels prepared by copolymerization with charged comonomers with different reactivity ratios were used as a model system. By applying surface property analysis based on interfacial electrokinetic phenomena to microgels aliquoted during polymerization, the distribution of charged groups within the microgels in the swollen state was evaluated. The charged-group gradient formed within the microgels during precipitation polymerization was successfully quantified using the surface properties obtained by electrokinetic analysis. Furthermore, the experimentally obtained charged-group distribution corresponded well with the composition drift predicted by radical copolymerization theory based on the Mayo–Lewis equation. In addition, a similar correlation between the experimental results and the predictions from radical copolymerization theory was also observed for copolymer systems in which two types of charged monomers were introduced simultaneously, demonstrating that this analytical method is applicable to more complex copolymer systems as well. These results indicate that analysis based on interfacial electrokinetic phenomena is an effective method for experimentally evaluating the distribution of functional groups formed within swollen microgels and for verifying the mechanisms underlying their formation. The findings obtained in this study contribute to the development of guidelines for designing the internal structures of functional microgels.</jats:p>