Self-associating copolymers of methacrylic acid (MAA) with poly(ethylene glycol)monomethacrylate (PEGMA) were prepared by free radical copolymerization of MAA with PEGMA using dispersion polymerization in D2O, or solution polymerization in a 50/50 ethanol-D2O mixture. These copolymers have been studied as components of reversible hydrogels(1) and in medical applications.(2) in order to understand the relationship between the copolymer structure and its performance, it is important to determine the sequence distribution of the copolymer. The copolymer architecture is determined by the reactivity ratios and integrated instantaneous feed compositions. The reactivity ratios were determined using the first-order Markov method(3) by running a series of reactions at various initial monomer ratios and determining the monomer incorporation into the copolymer as a function of time, via H-1 nuclear magnetic resonance. The reactivity ratios for dispersion copolymerizations of MAA with PEGMA in water were determined to be r(1) = 1.03 and r(2) = 1.02, whereas solution copolymerization in 50/50 EtOH-H2O gave reactivity ratios of r(1) = 2.0 and r(2) = 3.6. These results show that the reactivity ratios and copolymer architecture are influenced by the solvent system.