Dialkyl iodomethylmalonates in the presence of tetrabutylammonium iodide initiate the polymerization of methyl methacrylate, but not of methyl acrylate or acrylonitrile. Typically, at 60 degrees C in 1,3-dimethyltetrahydro-2-1H-pyrimidone (DMPU) as the solvent, poly(methyl methacrylate (PMMA) is obtained in the number-average molecular weight range of 2000 to 8000, the molecular weight distribution being fairly narrow (ratio of weight- to number-average molecular weights <(M)over bar (W)>/<(M)over bar (n)> 1.2-1.3).