ABSTRACT
Nearly all polymers formed by plasma contain large amounts of free radicals detectable by electron spin resonance (ESR), and there is no doubt that polymer formation proceeds with free radicals. However, the presence of a large number of free radicals in deposition is in contradiction with the conventional free-radical polymerization mechanism (i.e., polymers formed by conventional free-radical addition-polymerization do not contain sizable free radicals, because the recombination of two growing molecules with a free radical at the growing chain-end is the termination process of free-radical polymerization). Furthermore, organic molecules that are not monomers of free-radical polymerization (e.g., saturated vinyl monomers) form polymers just as easily as corresponding vinyl monomers in the luminous gas phase (plasma). In plasma polymerization, reactive species with free radicals are created by the electron-impact dissociation of molecules, and many gases used in plasma polymerization (e.g., methane, benzene, etc.) do not have functional groups for free-radical addition-polymerization. In other words, the evidence that plasma-polymerized polymers contain large amounts of free radicals is proof that free-radical plasma polymerization is not conventional chain growth free-radical polymerization.
