PEN films of different morphologies have been studied by polarised infrared spectroscopy. These different structures have been obtained by thermally treating biaxially stretched PEN films. Calculations of orientation factors from the 767 and 1138 cm(-1) bands which are characteristic of naphthalene ring vibrations predominantly in the amorphous phase show that the amorphous phase is significantly disoriented when annealed at, a temperature of 260degreesC despite the increasing crystallinity.