Electron paramagnetic resonance study of mechanically degraded poly(ethylene terephthalate) and nylon 6 fibers

Peroxide radical concentrations were measured from both PET and nylon 6 fibers mechanically stretched in air at room temperature and quickly quenched into liquid nitrogen. The radical concentrations depend on degree of stretching as well as conditions under which the fibers were made, i.e., morphology. Drawn fibers of PET and nylon 6 produced peroxide radical concentrations of the same order of magnitude at the breaking points. These results indicate that chain scissions occur both in PET and nylon 6 under mechanical stretching.     

Electron paramagnetic resonance of ultraviolet-irradiated polyolefins

If films of polyolefins are ultraviolet-irradiated at liquid nitrogen temperature, alkyl radicals which can be examined by EPR are produced. No EPR spectra are observed from polyolefins irradiated at room temperature in air. Ultraviolet irradiation of polyolefins containing small alkyl side chains generally produces radicals corresponding to the pendant group or methyl radicals if the side chains contain a methyl branch. For some polymers the radical species could not be identified with certainty. Stabilization studies indicate that an optimum concentration of ultraviolet stabilizer is necessary for maximum stabilization of polyolefins. Preliminary results of EPR studies of the ultraviolet irradiation of various polyolefins are given, and some possible radical species are discussed.     

Electron paramagnetic resonance for everybody--MICROspec-X--a new class of electron paramagnetic resonance spectrometer

The electron paramagnetic resonance spectroscopy is the only method for detecting free radicals. Free radicals have an increased importance in our daily life. A small transportable EPR spectrometer is presented for the popularisation of the EPR method. The technical construction and some applications are illustrated which show the usability of the spectrometer.     

Electron spin resonance study of radiation degradation of polytetrafluoroethylene

Electron spin resonance measurements were performed at different stages of radiation degradation of polytetrafluoroethylene. It was found that under radiation, peroxy radicals were transformed into chain-end fluorocarbon radicals, which in turn became into chain-side radicals. On the basis of these data, a scheme for the degradation mechanism is given.     

Electron paramagnetic resonance in various gadolinium complexes

Journal of Structural Chemistry -     

Electron paramagnetic resonance study of 3,4,5-trimethoxytetraphenyl porphyrinoxovanadium (IV) complex

3,4,5-Trimetoxytetraphenylporphyrinoxovanadium (IV) complex (3,4,5-TMVOTPP) was synthesized by a new one pot synthetic method. The complex was studied in the form of single crystal, powder (polycrystalline state), solution and frozen solution (glassy state) by electron paramagnetic resonance (EPR) between room temperature (RT) and liquid nitrogen temperature (LNT). Interestingly a well-resolved octet in the EPR spectrum at RT is observed in the pure paramagnetic state of the crystal. This observation is attributed to a greatly reduced dipolar interaction between paramagnetic vanadyl ions due to the large size of the molecule and the resultant stacking in the crystalline state. The line width of the EPR signals in single crystal at RT is approximately 3.3 mT which is more than the usual line width in diluted paramagnets ( approximately 1.5 mT) and is attributed to some kind of broadening effect akin to slow motion broadening. The line width in solvents is more than the crystal value but decreases appreciably at low temperatures. The decrease in line width at low temperature is attributed to the increase in spin-lattice-relaxation time and quenching of RT broadening motion. Only one octet is observed in the crystal EPR spectra which suggests only one formula unit per unit cell or a parallel/antiparallel ordering of V=O vectors in case the formula units per unit cell are more than one. This result needs verification by a detailed X-ray investigation. The crystalline field symmetry around the V(4+) metal ion is revealed to be axial by the observed angular dependence of the EPR spectrum and the powder EPR spectrum. No super hyperfine splitting of the hyperfine lines of the vanadyl ion is observed in solid state or diluted glass up to liquid nitrogen temperature. This suggests an expected weak in-plane pi-bonding with ligands. The spin Hamiltonian parameters for vanadyl ion in crystal, powder, diluted solutions and frozen glasses are evaluated and discussed.     

Electron paramagnetic resonance spectra of γ-irradiated polycaprolactam

The nature of the saturation is investigated for radicals trapped in a matrix of polycaprolactam. The radicals were generated with the help of a Co⁶⁰ source of -rays by irradiating evacuated samples consisting of fibers of kapron with two different structural modifications: stretched and unstretched. It is shown that, from its behavior, the broadening is intermediate between the homogeneous and inhomogeneous cases. A study was made of the effect of irradiating dosages in the interval from 1.5 Mrad to 200 Mrad on the form of the EPR spectra; as a result, it was established that with increasing dosage the form of the spectrum (quintet) is preserved, but the intensity of the middle component decreases. The saturation factor here is substantially decreased, but this effect manifests itself to different degrees for specimens of different structural modifications: in the case of the stretched fibers it is enormously stronger than in the case of the unstretched fibers. The study of saturation in the case of specimens of the two investigated modifications, subjected to identical irradiation dosages, has shown that the saturation factor is less for radicals trapped in the more ordered matrix (stretched kapron fibers). Some questions about the chemical nature of the radicals are also considered.