The cation radical chain cycloaddition polymerization of N,3-bis (trans-1-propenyl) carbazole: The critical importance of intramolecular hole transfer in cation radical cycloaddition polymerization

The synthesis and polymerization of N,3-[bis (trans-1-propenyl)] carbazole (1) is reported. Using either the stable cation radical salt tris(4-bromoph enyl)aminium hexachloroantimonate (2(+.)) or anodic oxidation to initiate t he reaction, novel cycloaddition polymers are obtained in which the intermo nomer linkages are of the cyclobutane, and to some extent of the Diels-Alde r, type. A novel cation radical chain mechanism is proposed for the reactio n, and extensive support for this mechanism is presented. The greatly enhan ced reactivity of difunctional, as opposed to monofunctional, substrates in cation radical cycloadditions is dramatically highlighted by a comparison of the cycloaddition reactivity (rapid polymerization) of 1 versus N-propen ylcarbazole (inefficient cyclodimerization) under electrochemical oxidation conditions. The sharply enhanced reactivity of 1 is attributed to the avai lability of intramolecular hole transfer in the bifunctional but not the mo nofunctional case.