SynopsisThe kinetics and mechanism of the retarding action of phenol on the Vs+-thiourea initiated polymerization of methyl acrylate (MA) have been studied within the temperature range of 30-50°C. The effects of retarder (phenol), metal ion (V5'), monomer (MA), sulfuric acid, some organic solvents and inorganic salts on the percentage and rate of polymerization have been studied. The remarkable observation of the present study is the positive intercept obtained from the plot of [M]/R, vs. 1/[M]. This type of observation is significantly different from previous studies on retarded polymerization. The values of composite rate constants kok,/kik,kK have been calculated from plots of [M]/R, vs. 1/[M]. On the basis of experimental findings a reaction mechanism has been suggested, and a suitable rate expression has been proposed and explained.