The relaxation of polyimid films after the axial tension has been investigated by measuring life-time of positrons and angular correlation of annihilation photons. The nonmonotonic change of mean life-time while relaxing the free film has been found. Two range of changes of positron-sensitive properties can be seen: "rapid" relaxation for 4-5 hours (characterized by reducing life-time of short-lived component) and "slow" relaxation (characterized by reducing the intensity of longlived component).The results of this investigation have been compared with those of measuring of sample density and dielectric losses. The possible explanations and the changes of mechanizms of relaxation with the conditions of deformation and "the rest" of polymers are analyzed.

The behavior of glassy polymers was studied with the aid of mechanical tests on the basis of free volume. Three types of experiments were carried out and interpreted using modern ideas about the structure of free volume. They were: 1. The study of changes in the total free volume occurring as a result of deformation (by measurement of density) 2. The study of micro voids and their changes on deformation using small angle X-ray scattering (SAXS) and positron annihilation 3. The study of mobile regions by the measurement of dielectric loss (using an original interpretation) during deformation. This allows several parts of the total free volume to be distinguished and investigated. A model for the free volume relaxation during deformation is proposed.