Magnetokinetic changes intervened in the radical polymerization of methyl acrylate in a continuous external magnetic field of 0.22 T was evidenced. The use of a matrix of polymerization, respectively, poly(ethylene glycol), was correlated with the obtained kinetic data. The occurring-magnetokinetic changes were justified by the radical pair mechanism, Deltag, which corresponds to the benzoyl peroxide decomposition into a magnetic field. The intervened magnetokinetic modifications during the reactions are correlated with the reaction conditions. The influence of the magnetic field is confirmed by the molecular weights of the obtained polymers, values interpreted from the viewpoint of the reaction conditions. (C) 2004 Wiley Periodicals, Inc.