2-Hydroxyethyl methacrylate (HEMA) and styrene (S) have been copolymerized in a 3 mol.L-1 N,N'-dimethylformamide (DMF) solution using 2, 2'azobis (isobutyronitrile) (AIBN) as an initiator over a wide composition and conversion range. From low-conversion experiments and H-1-NMR analysis, the monomer reactivity ratios were determined according to the Mayo-Lewis terminal model. The comparison of the obtained results with those previously reported for copolymerization in bulk and in toluene reveals a relatively small but noticeable solvent effect that can be qualitatively explained by the bootstrap model. Cumulative copolymer composition as a function of conversion is satisfactorily described by the integrated Mayo-Lewis equation; overall copolymerization rate increases with increasing the HEMA/S ratio, and individual monomer conversion is closely related to the monomer molar fraction in the feed.