Phenoxyethyl methacrylate (POEMA) and butyl methacrylate (BMA) were copolymerized by free-radical copolymerization using ,'-azobisisobutyronitrile (AIBN) in 2-butanone solution at 3331K. Copolymers were characterized by FTIR, 1H-NMR and 13C-NMR spectroscopic methods and by comparison of the spectra with the corresponding homopolymers. Thermogravimetric analysis of the copolymers was carried out in order to know their thermal stability. Copolymer composition was established by 1H-NMR analysis. Monomer reactivity ratios (MRR) were computed using the classical Fineman - Ross (FR) and Kelen - Tudos (KT) procedures. MRR were also estimated using a nonlinear computational fitting procedure, known as reactivity ratios error in variable model (RREVM). The mean sequence lengths of the copolymers were estimated and suggest that random copolymers were obtained.