ENERGETICS OF STRESS-RELAXATION OF GLASSY-POLYMERS AT HIGH-PRESSURE

Kinetic changes of relaxation of the shift stress of glassy poly(methyl methacrYlate) were studied when temperatures and pressures were changed in isobaric, isothermal, and isochoric conditions. In isochoric conditions the relaxation rate depends slightly on temperature. The volume of the polymer is the main parameter for the rate of stress relaxation. Isobaric and isochoric activation energies and activation volume of stress relaxation were determined. The results are shown to satisfy the thermodynamic relation of the activation parameters of the relaxation process. The dimensions of elementary kinetic unit of the stress relaxation process were estimated.