Nature of infrared radiation accompanying the mechanical fracture of poly(methyl methacrylate)

The spectrum of infrared radiation accompanying the mechanical fracture of poly(methyl methacrylate) is shown to consist of two components: a continuous Planck component (the thermal one) and a line component in the form of three separate lines. It is suggested that the lines of the line component should be regarded as a fragment of the spectral series that emerges due to radiative deactivation of three adjacent vibrationally excited levels of the macromolecule. Two processes can contribute to the line component: chemiluminescence and phase radiation. Chemiluminescence may be due to the exothermal reaction of methyl methacrylate polymerization on the cooling fracture surface when its temperature falls below 197degreesC, which is the ceiling temperature for poly(methyl methacrylate). Phase radiation may be due to orientational crystallization of syndiotactic PMMA blocks in the layer of the oriented polymer adjacent to the fracture surface. Orientational crystallization must be accompanied by generation of the upper harmonics of phase radiation. Experimentally recorded spectral lines at wavelengths of 8.28, 6.2, and 4.96 mum are found to correspond to the third, fourth, and fifth harmonics, respectively. The energy of the first harmonic (4.816 kJ/mol) coincides with the average energy (4.812 kJ/mol) of hole formation (termination) calculated by Wunderlich according to the experimental value of the heat capacity jump DeltaC(p)(T-g) for poly(methyl methacrylate). The temperature of the freshly formed fracture surface in the range of its lifetimes 5-100 mus remains invariable and equal to 113-140degreesC.