Polymerizations of substituted cyclopropanes. I. Radical polymerization of 1,1-disubstituted 2-vinylcyclopropanes

Diethyl 2-vinylcyclopropane-1,1-dicarboxylate (Ia), 2-vinylcyclopropane-1,1-dicarbonitrile (Ib), ethyl 1-cyano-2-vinylcyclopropanecarboxylate (Ic), and 1,1-diphenyl-2-vinylcyclopropane (Id) were radically homo- and copolymerized. Ia, Ib, and Ic polymerized cleanly in 1,5-type ring-opening fashion to yield polymers of high molecular weight. Id failed to homopolymerize but copolymerized with common monomers which included maleic anhydride. Infrared (IR) spectra indicated that the double bonds of the polymer chains were in trans form. All polymers were soluble in solvents and solution-cast films were clear and flexible, showing T_g values in the 25–40°C range. Model reactions of those monomers with benzenethiol also indicated predominant 1,5-addition reactions. From the results of our investigation it was concluded that the driving force for the facile radical 1,5-polymerization of Ia, Ib, and Ic was the stabilization of growing radicals by two substituents.