[The effect of physical aging on the structural behavior of amorphous poly(vinylpyrrolidone) polymers].

The purpose of the present study was to examine the physical ageing of amorphous polymers commonly applied in the pharmaceutical technology. Powder samples of polyvinylpyrrolidone were stored under different storage conditions (relative humidity, temperature). Positron annihilation lifetime spectroscopy (PALS) was applied for the analysis of the free volume changes of polymer samples as a function of the storage conditions. By the means of calculations on simplified model molecules it was determined that polymer chains and water molecules are able to form a hydrogen bound "network" under certain humidity conditions. Along with the ageing process the chemical changes of the examined polymers are interrelated in a dynamic and complex manner which can be tracked by the combination of SEM, ab initio calculations and positron lifetime measurements.