Electron spin resonance study on plasma-induced surface radicals of poly(ethylene naphthalate)

We have undertaken Ar plasma irradiation on poly(ethylene naphthalate) (PEN) powder, and the radicals formed were studied by electron spin resonance (ESR). The room temperature ESR spectrum of plasma-irradiated PEN shows a five-line spectrum separated with nonbinomial intensity distribution, indicating that the spectrum is an outline of multicomponent spectra. The systematic computer simulation of the observed ESR spectra disclosed that the spectra consist of two types of radicals in structural term: the major radicals formed were assigned to dihydronaphthalenyl-type radicals generated by a nearly random addition of a hydrogen atom to the naphthalene ring, and immobilized dangling bond sites at the surface crosslinked moiety.