A series of copolymers of sodium 2-acrylamido-2-methylpropanesulfonate (NaAMPS) and 2-methacryloyloxyethyltrimethylammonium chloride (MADQUAT) prepared by microemulsion polymerization was characterized by means of several techniques. After dialysis, the samples self-neutralize with formation of monomer pairs in the copolymer. The molecular weights determined by light scattering are high (greater-than-or-equal-to 10(7)) and were found to be relatively unaffected by monomer feed ratios. The copolymer microstructure was calculated from the reactivity ratios and compared to that obtained for copolymers synthesized in aqueous solution. The microemulsion polymerization process yields copolymers more homogeneous in composition (r(A)r(B) congruent-to 1.6) than those obtained by polymerization in solution which have a strong tendency to alternation (r(A)r(B) congruent-to 0.05). These differences are discussed in terms of microenvironment and polymerization mechanisms.