Free radical copolymerization of 2-hydroxyethyl methacrylate with butyl methacrylate using 3.0 mol l(-1) N,N'-dimethyl formamide, DMF, solution and 9.0 X 10(-3) mol l(-1) of 2,2' azobisisobutyronitrile, AIBN, as initiator, was carried out at 50 degrees C. Experiments performed in bulk have evidenced the possible solvent effect in the values of monomer reactivity ratios. Besides, the homopolymers glass transition temperature, T-g, the intra and intermolecular structure along with Johnston's equation have enabled describing the experimental variations of HEMA-BMA copolymers' T-g.