Combined use of positron annihilation lifetime spectroscopy-an experimental
tool to investigate the intermolecular sub-nanometric spaces (free volume)
in polymers-and of specific volume data supply unique information on the o
ccupied volume in a semicrystalline polymer-poly(ethylene terephthalate)-,
in particular, on its thermal behavior. From our data an expansion coeffici
ent for the occupied volume alpha (o) = 2.9.10(-5) K-1 is obtained, when th
e dependence of ortho-positronium intensity on the temperature is taken int
o account. The free volume fraction at the glass transition temperature res
ults f = 0.04, in agreement with analogous estimates in other semicrystalli
ne polymers. (C) 2001 American Institute of Physics.