We determined the reactivity ratios of hydroxyethyl methacrylate (HEMA) and dimethylaminoethyl methacrylate (DMAEMA) during atom transfer radical copolymerization (ATRP) in isopropyl alcohol, tetrahydrofuran, acetonitrile, and dimethyl sulfoxide (DMSO). The reactivity ratios in DMSO are near unity (r(HEMA) = 1.08 and r(DMAEMA) = 1.12). While there was considerable deviation between the initial monomer composition and the average polymer composition during copolymerization in most solvents, copolymerization in DMSO resulted in random copolymers of poly(HEMA-co-DMAEMA) with average polymer compositions that were identical to the monomer feed compositions. Poly(HEMA-co-DMAEMA) copolymers with molar feed compositions of f(HEMA) = 0.25 and f(HEMA) = 0.50 were synthesized in DMSO by ATRP with uniform compositions along the polymer chain. These polymers achieve their target molecular weights and are near monodisperse (M-w/ M-n < 1.11). The glass transition temperatures of these copolymers increase with increasing HEMA content.