Onset of forming ordering in uniaxially stretched poly(ethylene terephthalate) films due to π-π Interaction clarified by the fluorescence technique

Abstract

The initial stage of a cold crystallization process for uniaxially stretched poly(ethylene terephthalate) (PET) was examined in detail by means of fluorescence spectroscopy and wide-angle X-ray diffraction measurements. The cold crystallization of PET annealed at around Tg, which occurred by way of mesomorphic ordering, was investigated with respect to the π-π interactions between the main-chain phenylene groups of PET by measuring the polarized fluorescence intensities and the distribution of the ground-state dimer (GD) of PET. The mesomorphic ordering was found to be induced by GDs acting as nucleation centers; these GDs seemed to progressively assume a smectic form upon annealing at temperatures around Tg. Moreover, the flat plane in the smectic form was suggested as the cause of the unique tilted orientation observed in triclinic PET crystals. © 2013 American Chemical Society.