AbstractAnionic copolymerization of β‐cyanopropionaldehyde (M1) with methyl isocyanate (MeI, M2) was studied with use of benzophenone–dilithium complex as initiator at −78°C. The values of monomer reactivity ratio were determined to ber1= 8.3 ± 0.3 andr2= 0.01 ± 0.01. The structure of resulting copolymer was investigated by means of NMR analysis. The MeI unit is presumed to enter the copolymer chain through its C