An electron spin resonance study of mechanical fracture of poly(methyl methacrylate)

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(-4) 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 similar to 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 < 1 min at room temperature. (C) 1997 John Wiley & Sons, Inc.