Abstract
Polyethylene terephthalate films, both unannealed and annealed, were drawn to various lengths. With increasing extension the transition temperature where the drawn samples begin to shrink on heating decreases for small elongation whereas it increases for large elongation. Such variation of the transition point with extension is similar to the density change of the sample; the point is considered to correspond to Tg. This correlation is well explained by assuming "iso-hole fraction" at Tg on the basis of the lattice theory.
Isotherms of recovery for the unannealed sample were closely superposable by horizontal shifts as in the case for the annealed one; the temperature dependence of logarithmic shift factor is in good accord with the Arrhenius equation rather than the WLF equation.
