In the anionic polymerization of methyl methacrylate (MMA) induced by imidazole (Im), an Im‐MMA adduct forms as an initiator adduct in methanol at 30°C in an argon atmosphere by the equimolar reaction of Im with theMMAmonomer. The additive effect of the adduct on the homopolymerization ofMMAin tetrahydrofuran at 30°C was investigated by dilatometry. The existence of the adduct increased the duration of the propagation step without shortening the formation step of the initiator adduct. The H‐D exchange reaction of the adduct was observed in D2O by1H NMR. Proton transfer of theMMAunit in the adduct was not observable until 45 h after initiation. The copolymerizability ofMMAwith acrylamide (AAm) induced by the Im catalyst in THF at 30°C was also investigated. It was found that the homo‐and copolymerizations proceeded at the same time. On the other hand, in theMMAhomopolymerization system, the addition of AAm monomer during the initial propagation step yielded copolymer of MMA and AAm for near equimolar concentration of the charged monomers.