Positron annihilation study of the free volume changes in thermally treated polymers based on acrylate oligomers

Positron annihilation lifetime spectroscopy has been applied to the study of free volume properties in polymers based on the acrylate oligomers. The measurements have been made on samples heated to a temperature of 483 K. A differential scanning calorimeter was used for the study of the thermal properties. The longest lifetime, obtained via three-component analyses of the spectra, was associated with the pick-off annihilation of ortho-positronium trapped in the free volume. After the thermal treatment, changes in the ortho-positronium lifetimes and the relative intensity of the longest component were observed. These results are discussed on the basis of a free volume model.