Radical copolymerization of N-phenylmaleimide (PhMI) with 2-hydroxyethyl methacrylate (HEMA) and ethyl methacrylate (EMA) was studied. Synthesis of copolymers was carried out in p-dioxane at 65degreesC with 2,2'-azobisisobutyronitrile as the initiator. Copolymer compositions were calculated by the elemental analysis and H-1 NMR spectroscopy methods. Monomer reactivity ratios for the studied monomer pairs were determined using Kelen-Tudos and non-linear regression methods. PhMI monomer was found to have substantially different copolymerization constants in the radical copolymerization of the two monomer systems. Poly(PhMI-co-HEMA) possessed higher values of intrinsic viscosity and higher thermal stability, as well as showing specific melting endo-peaks in the DSC curves. These observations were explained by the effect of H-bonding between hydroxyl and imide groups with the formation of complexed macromolecular structures. (C) 2003 Society of Chemical Industry.