Fast Passage Dispersion Signals In Inhomogeneously Broadened Electron Spin Resonance Spectra - Application To Measurement Of Spin-Lattice Relaxation Times Of Free Radicals Derived From Esters And Salts Of Poly(Methacrylic Acid)

The shape of the first derivative of the dispersion mode of an inhomogeneously broadened electron spin resonance spectrum changes markedly on saturation. This behavior provides a convenient and rapid technique for estimating the spin latice relaxation time of the paramagnetic species involved. The technique is described together with the relevant theory. Values for the relaxation times of free radicals derived from poly(methyl methacrylate) and from poly(sodium methacrylate) have been obtained by this method and are found to be in good agreement with those obtained by the progressive saturation technique. A series of salts of polymethacrylic acid have been γ-irradiated, and the spin lattice relaxation times of the resulting trapped radicals were determined at 77 and 299°K. For a given polymer the relaxation times show little variation with temperature. This is attributed to a broad distribution of correlation times.