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ABSTRACT:The free radicals produced by ␥ irradiation in the polymer network are formed with ionizing radiation. The decay rates of radicals in the temperature range were used to estimate the diffusion coefficient of oxygen into polymeric spheres by an electron spin resonance (ESR) technique. The ESR results showed that the activation energy of the diffusion of oxygen into poly(methyl methacrylate) (PMMA) in the temperature range 10 -40°C is 29.6 kJ/mol. There are two activation energies of the diffusion of oxygen into poly(vinyl acetate) (PVAc) in the temperature range 25-50°C. The activation energies below and above 35°C, which is the glass transition temperature of PVAc, were found to be 16.8 and 82.5 kJ/mol, respectively.

In this article, initially, we designed a simple drilling apparatus to obtain the mechanoradicals of poly(methyl methacrylate) (PMMA). Using this apparatus, we prepared some PMMA samples at 77 K in vacuum. We observed some electron spin resonance (ESR) signal of these samples. It is found that the ESR spectrum of mechanically fractured PMMA strongly depends on the vacuum conditions. The spectrum observed from the mechanically fractured PMMA in 10 04 torr vacuum at 77 K coincides with the characteristic spectrum of the ''nine-line'' ESR spectrum of PMMA. Otherwise, because of the interaction between the polymer powders and air during the stage of preparing the sample, some of the mechanoradicals convert into the peroxy radicals. In this situation, spectrum is mainly nine-line and partially superposed with the spectrum of peroxy radicals. The peroxy line observed at low temperatures disappears rapidly from the mechanoradicals with increasing temperature. It vanishes completely at Ç 300 K and the spectrum turns into the nine-line spectrum of PMMA. Changes in the nine-line spectrum of mechanoradicals were investigated in the 100-350 K temperature interval. The line intensities were measured at each temperature. It was shown that the line intensities of both A and B do not change with time at constant temperature, and decrease with increasing temperature. The PMMA samples in vacuum were opened to air and the ESR spectrum was followed with time. It was observed that the nine-line spectrum converted into a line asymmetric spectrum in õ 1 min at room temperature.

In this study, initially, we tried to obtain the mechanoradicals of PMMA (poly(methyl methacrylate)). For this purpose, we designed a simple drilling apparatus. Using this apparatus, we prepared some PMMA samples at 77 K in vacuum. Later, by using an ESR (electron spin resonance spectrometer), we observed ESR signals for these samples at 77 K. This means that mechanoradicals have been successfully produced by mechanical fracture in PMMA using our drilling apparatus. Secondly, we tried to identify the radicals from these spectra through using theoretical analyses and, some computer simulations have been done by suggesting two different theoretical models for these ESR signals. Finally, by using experimental and theoretical data, we showed that our simple apparatus could be used to obtain mechanoradicals from polymers. Results were seen to be in very good agreement with the literature. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2195–2200, 1997

Electron spin resonance (ESR) spectroscopy has been used for the measurement of the diffusion coefficient of oxygen into polymeric spheres. It has been shown that there is an inverse dependency between the irradiation dose and the oxygen diffusion coefficient (D). The free-radical concentration (R 0 ) produced in the polymer depends on the dose of the g rays. In this study, we tried to find a relationship between the oxygen diffusion coefficient and the free-radical concentration produced in the polymer during the irradiation.