Cation radical chain cycloaddition polymerization: a fundamentally new polymerization mechanism

Cation radical chain cycloaddition polymerization, a fundamentally new addition polymerization method involving cation radical intermediates in each propagation step, is described and demonstrated. The cycloaddition reactions of appropriately constituted difunctional monomers, catalyzed by tris(4-bromophenyl)aminium hexachloroantimonate in dichloromethane solvent at 0 °C, is shown to afford polymers having average molecular weights of up to 150 000. Both cyclobutanation and Diels–Alder polymers were obtained in this way. The surprising efficiency of these polymerization reactions is believed to be the result of rapid intramolecular hole transfer from the site at which the hole is originally generated in the cycloaddition step to a reactive, terminal alkene moiety. Consequently, chain propagation is much more efficient than in the cycloadditions of corresponding monofunctional compounds, which necessarily involve intermolecular hole transfer.