Radical ring-opening bicyclobutanes

Unlike other ring-opening polymerizations, most C-C single bond polymerizations have been carried out by free radical initiation, even though examples of cationic, anionic, and coordination polymerizations have been presented. The bicyclobutane monomers, such as bicyclobutane-1-carbonitrile (la X = CN), are as reactive in free radical polymerization as vinyl monomers ( ). 

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