Electron paramagnetic rosonance studies of thermally produced radicals in phenylacetylene

EPR observations of the thermal polymerization of phenylacetylene suggest a phenyl-substituted polyenyl π-electron radical as an intermediate. Failure to observe radical production and polymerization for phenylpropyne under similar conditions indicates that the C-H bond is the reactive site in phenylacetylene. INDO MO calculations based on such an intermediate predict EPR hyperfine couplings in general agreement with those found experimentally and imply that the polymerization mechanism at the initiation step is head-tail-tail-head.