Abstract
The free volume hole and its distribution in polyoxymethylene have been studied over the temperature range (5–90
°C) by positron annihilation lifetime spectroscopy. At a certain temperature (20
°C) the variation of ortho-positronium lifetime shows a distinct increase in its slope. The hole volume shows a small linear increase with temperature below glass transition temperatue and a steeper increase above it. A linear relation between ln(
σT
0.5) and 1/
V
h was observed and the critical hole volume was estimated.