Polymerization of cyclic monomers .2. Synthesis and radical polymerization of vinylcyclopropanes

New 1,1-disubstituted 2-vinylcyclopropanes were synthesized by reaction of the corresponding malonyl diesters with trans-1,4-dibromo-2-butene and of sodium hydride. The structure of the 2-vinylcyclopropanes could be confirmed by elemental analysis, IR, H-1 NMR and C-13 NMR spectroscopy. Radical polymerization of the 2-vinylcyclopropanes in bulk with 2,2'-azoisobutyronitrile (AIBN) and di-tert-butyl peroxide (DtBPO), respectively, gives transparent polymers. In case of the liquid monomers, the polymerization is accompanied by negative volume changes. Spectroscopic investigations show that 2-vinylcyclopropanes primarily undergo opening of the cyclopropane ring forming an 1,5-addition polymer.