A B S T R A C T Thermal effects which accompany the polymer fracture process have been investigated by means of calorimetric measurements and by inertialess detection of IR radiation. The data obtained are considered in the framework of energy characteristics of elementary scissions of overstressed macromolecules. It is concluded that the elastic energy released after macromolecular scission contributes substantially to the observed exothermic effects. Heat evolution due to molecular disruptions can lead to local acceleration of the destructive process in stressed polymers.

A B S T R A C T Direct physical methods were used for studying molecular fracture in stressed polymers. The macromolecular ruptures were detected by electron paramagnetic resonance, infrared spectroscopy, and mass spectrometry. Nucleation of incipient submicrocracks was registered by small-angle X-ray scattering and light scattering. All methods were used to study fracture kinetics at different stresses and temperatures. The thermal fluctuation nature of microruptures is verified and the activation energy for the elementary events of polymeric fracture is estimated. This energy coincides with the activation energy for macrorupture evaluated in the study of the lifetime of polymers. Chain chemical reactions of stresses macromolecules disruption are proved to take part in formation of incipient cracks. The main features of the micromeehanics of polymer fracture are listed.

It is well known that during the mechanical degradation of polymers there takes place scission of molecular chains and the formation of macroradicals. It is of considerable interest to study the electron paramagnetic resonance (EPR) spectra of the macroradicals produced by milling, and to compare them with the spectra of the macroradicals formed in the process of polymerization, and also during the irradiation of polymers by gamma rays and neutrons. We may endeavor to compare the amount of macroradicals formed with the extent of mechanical destruction (for instance with the area of the new interface which is formed). In addition, as was found by experience, the macroradicals formed by mechanical scission are good models for the investigation of reactivity since practically all of them are in the newly formed surface layers and are therefore very accessible to various chemical influences. They enter easily into reaction with various agents present in the medium since in this process diffusion from the surface is found in practice not to be a predominating factor. In the present communication we give the first EPR results obtained on mechanically degraded polymers.

No abstract