AbstractRadical polymerization and copolymerization behaviour of ethyl α‐(halomethyl)acrylates was examined. Among them the bromomethylacrylate did not yield a homopolymer nor a copolymer because of fast chain transfer to the monomer. The chloromethylacrylate (ECMA) polymerized slower to form a lower molecular weight polymer than the fluoromethylacrylate (EFMA). In the copolymerizations with styrene and methyl methacrylate, ECMA was less reactive than EFMA owing to the steric effect of the slightly larger chloromethyl group. The reactivity of EFMA in the copolymerization was enhanced by the polar and resonance effects of the α‐substituent, prevailing over the steric effect. Characterization of the polymers by NMR spectroscopy and thermogravimetric analysis revealed the existence of steric congestion caused by the halomethyl groups in both pol