THE MODEL OF VOLUME DEFORMATIONS FOR RELA XATION PROCESSES IN POLYMERS UNDER TEMPERATURE-CHANGES

Within general framework of the previously developed model for activat ion of elementary relaxation process proceeding via fluctuation of lin ear elastic volume deformation (dilation or contraction) of the consti tuent small parts of the system (activation elements), we analyzed tem perature dependence of free energy of activation DELTAF(a) above the g lass temperature. Two regions are distinguished on the temperature dep endence of DELTAF(a), separated by the temperature T. Above T* the pr ocess is activated at constant volume of activation element and relati ve shares of dilation and contraction in net DELTAF(a) are equal and w eakly dependent on temperature. Below T the volume of activation elem ent grows in activation and the relative share of dilation grows with decreasing temperature, while the share of contraction deformation dim inishes and becomes negligible at glass temperature. The volume of act ivation element is determined by the limit of linear elasticity for vo lume compression at T and is on the order of 10(-2) m3/mol. The model well fits the experimental data on temperature dependence of DELTAF(a ) for alpha-relaxation in polypropylene glycol.