Polymerizations of substituted cyclopropanes. II. Anionic polymerization of 1,1-disubstituted 2-vinylcyclopropanes

Among the four 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), Ib and Ic polymerized well with sodium cyanide in N,N-dimethylformamide. Ib was most reactive and a polymer (IIb) from Ib exhibited an inherent viscosity of 1.05 dl/g (concentration of 1.0 g in 100 ml of 95% H₂SO₄). All experimental results indicated that the polymerization proceeded by ring opening and that the structure of the polymers had pendant vinyl groups. The polymer IIc from Ic was soluble in common solvents like acetone, but IIb was soluble only in 95% H₂SO₄. Reactions of those compounds with benzenethiolate ion in ethanol yielded addition products that supported the ring-opening polymerization of those monomers. In the postulated mechanism of polymerization cyanide ion attacks the carbon of a cyclopropane ring with electron-releasing vinyl group and the resulting anion is thereby stabilized by two electron-withdrawing substituents. The propagation takes place by the reaction of the anion with another monomer molecule.