AbstractEthyl α‐acetoacetoxymethylacrylate (1) was prepared by reaction of diketene and ethyl α‐hydroxymethylacrylate which was obtained from the reaction of triethyl phosphonoacetate and an aqueous solution of formaldehyde.1contains 27% of the enol tautomer. The polymerization of1in benzene initiated with dimethyl 2,2′‐azoisobutyrate (2) was investigated kinetically. The overall activation energy of polymerization was determined to be 84,8 kJ/mol. The polymerization rate (Rp) at 50°C is expressed byRp=k[2]0,5[1]1,1. From an electron spin resonance study, the polymerization system was revealed to involve persistent propagating poly(1) radicals. The rate constants of propagation and termination were estimated to bekp= 300 andkt= 1,0 · 1061 · mol−· s−at 60°C, respectively, using the polymer radical concentration and assuming stationary state conditions. Copolymerization of1(M1) and styrene (M2) was examined at 50°C, and the following copolymerization parameters were obtained;r1= 0,28,r2= 0,22,Q1