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Allyl Radical (allyl + radical)

Distribution by Scientific Domains

Polymers and Materials Science	60%

Selected Abstracts

CASSCF study into the mechanism for predissociation of the allyl radical

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2006
Milena Shahu
Abstract A theoretical study has been carried out on the allyl radical in its ground and first excited electronic states. Complete active space self-consistent field (CASSCF) calculations show the presence of a conical intersection between the ground and first excited electronic states (,400 cm,1 above the adiabatic excited state energy), reached by decreasing the CCC angle and twisting the CC bonds. The presence of this conical intersection provides a likely explanation for the very rapid predissociation in the excited electronic state. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]

ESR and FTIR studies on electron beam-irradiated low-density polyethylene blends

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007
Z. I. Ali
Abstract Low-density polyethylene (LDPE) composites modified with a resin based on ethylene/methacrylic acid copolymer (surlyn) and/or citric acid were electron beam-irradiated and investigated by electron spin resonance (ESR) at room temperature. ESR studies were carried out directly after irradiation and after various time intervals up to 72 h postirradiation. The irradiated samples showed the ESR spectrum of seven lines that was assigned to the formation of allyl radical. The nature and yield of the allyl radical of the different LDPE samples were analyzed as a function of time after irradiation. Also, the radical concentration, decay, decay rate, and kinetics of radical decay were evaluated. Fourier transform infrared (FTIR) analysis at a series of different temperatures upon cooling from room temperature to ,175°C and the reverse heating to +125°C was also carried out. The structural changes while cooling and heating of LDPE samples were investigated using FTIR spectrometry. The results showed that cooling of unirradiated LDPE samples to ,175°C results in a decrease of the intensities of IR bands. However, heating the samples from ,175°C up to +125°C led to a consequence increase in the intensities of the IR bands. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3461,3469, 2007 [source]

,-Irradiation of ultrahigh-molecular-weight polyethylene: Electron paramagnetic resonance and nuclear magnetic resonance spectroscopy and imaging studies of the mechanism of subsurface oxidation

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2004
Todd M. Alam
Abstract The shelf aging of irradiated ultrahigh-molecular-weight polyethylene (UHMWPE) causes subsurface oxidation, which leads to failure in UHMWPE orthopedic components, yet the mechanisms causing subsurface oxidation remain unclear. The shelf aging of ,-irradiated UHMWPE bars has been studied with electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) imaging and with microtoming and Fourier transform infrared microscopy. The bars initially contained only allyl radicals, and upon air exposure, a surface layer of peroxyl radicals formed through the reaction of allyl radicals with oxygen. Importantly, a band of low radical intensity just beneath the peroxyl layer became apparent. NMR imaging showed a zone of altered proton relaxation in this zone. With increasing time, surface peroxyl radicals persisted in comparison with the interior allyl radicals, although oxygen did not appear to penetrate any more deeply into the bar. The area of maximal oxidation and mechanical disruption, measured after 3 years, was at the interface between the zone of exterior peroxyl radicals and the zone of low radical intensity. We present a mechanism involving the intermediacy of sterically strained reactive dialkyl peroxides at this interface to explain subsurface oxidation. We also demonstrate that EPR and NMR imaging provides information that could potentially be used to identify subsurface oxidized UHMWPE components before failure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5929,5941, 2004 [source]