ELECTRON-SPIN-RESONANCE STUDY ON PLASMA-INDUCED SURFACE RADICALS OF ETHYLENE-TETRAFLUOROETHYLENE COPOLYMER

We have undertaken Ar plasma irradiation on ethylene-tetrafluoroethylene (1:1) alternating copolymer (ETFE) powder, and the radicals formed were studied by electron spin resonance (ESR). The room temperature ESR spectrum of plasma-irradiated ETFE shows a six-line spectrum (sextet) similar to that of polyethylene (PE), due to a small difference in hyperfine splitting constant between beta-H and beta-F atom. Thus, the major radical formed was assigned to the midchain alkyl radical generated by hydrogen elimination. The ESR spectral parameters for a representative sextet deduced from the simulated spectra are as follows: g=2.0029, N-alpha=2.19 mT (1H), H-beta=2.88 mT (2H), and F-beta=2.80 mT (2F). It was also found that the sextet spectrum gradually turned toward a broad single-line spectrum as the plasma duration increased indicating the successive formation of dangling bond sites (DBS) due to the occurrence of cross-linked surface reaction.