Radical ring-opening polymerization of 1,1-dicyano-2-vinylcyclopropane 1 was performed in benzonitrile to find the corresponding homopolymer 2 soluble in organic solvents was successfully obtained while that in other solvents gave crosslinked and thus insoluble homopolymer. In addition, 1 underwent radical copolymerization with 1-cyano-1-ester-2-vinylcyclopropanes 3 and 4 to afford the corresponding copolymers 7 and 8. By increasing the content of the 1-derived unit in the resulting copolymers, the solubility of the copolymers in organic solvents became lower and the residual weights at 600 degrees C and their glass transition temperatures became higher. (c) 2019 Wiley Periodicals, Inc.