The relative reactivity of a polymerizable tertiary amine in free radical polymerization is analysed through the study of its copolymerization with methyl methacrylate initiated by benzoyl peroxide at low temperature. Copolymers of N,N-dimethylaminobenzyl methacrylate with methyl methacrylate were prepared in solution at low temperature (30 and 35 degrees C) by using the polymerizable acrylic amine/BPO redox system as initiator. The reactivity ratios were calculated according to the general copolymerization equation from composition data of copolymer samples determined by H-1 n.m.r. spectroscopy, and by using both linearization methods and the non-linear least square analysis of Tidwell and Mortimer. The values obtained indicated that this system approaches to the ideal behaviour. Wetting experiments were carried out at room temperature in air to determine the surface energy of the copolymers. It was found that the surface energy increased with the content of N,N-dimethylaminobenzyl methacrylate in the copolymer, the copolymers becoming more hydrophobic as the fraction of this monomer increased in the copolymer.