ELECTRON-SPIN-RESONANCE STUDY OF THE SPECIAL FEATURES OF PLASMA-INDUCED RADICALS AND THEIR CORRESPONDING PEROXY-RADICALS IN POLYTETRAFLUOROETHYLENE

Plasma-induced polytetrafluoroethylene (PTFE) radicals were first studied by electron spin resonance (ESR). The room temperature ESR spectrum of plasma-irradiated powdered PTFE consists of three kinds of spectral components: double quintet (3.2 and 8.7 mT) as a major spectrum, a triplet (1.4 mT) with broad lateral peaks due to hyperfine anisotropy, and smeared-out broad line. The double quintet and triplet were assigned to the mid-chain radical, -CF2-CF-CF2-, and the end-chain radical, -CF2CF2, respectively. The smeared-out broad line, thought to be an intermediate level of conversion to a broad single line, was assigned to an immobilized dangling-bond site at the cross-linked portion. It has also been shown that the effect of plasma irradiation on radical formation of PTFE was much smaller than on hydrocarbon polymers due to the much larger dissociation energy of the C-F bond over that of the C-H bond (e.g. PTFE; k = 4.3 x 10(12) spin cm-2 min-1, polyethylene (PE); k = 1.9 x 10(14) spin cm-2 min-1 for initial rate of radical formation at 40 W). When the plasma-irradiated PTFE was exposed to air, peroxy radicals were rapidly formed. They were markedly stable for a long period of time at room temperature due to the absence of hydrogens in PTFE which could undergo chain termination reactions through the hydroperoxide. It was difficult to isolate completely each of the component radicals formed because of the presence of durable dangling-bond sites. Thus, in view of the fact that the ESR spectra of the gamma-irradiated PTFE are superficially similar to that of plasma-irradiated PTFE, we suggest that the study of molecular motion by use of a peroxy radical probe in PTFE should take into account the effect of the cross-linkings.