Molecular orientation and relaxation of poly(ethylene terephthalate) by polarization modulation infrared spectroscopy

Molecular orientation and relaxation of the trans and gauche conformers of poly(ethylene terephthalate), during and after an uniaxial deformation above the glass transition temperature, between 85 and 100 degreesC, were investigated using polarization modulation infrared linear dichroism. At all temperatures, it was found that the trans conformers orient much more that the gauche conformers whereas their relaxation rates are comparable. Gauche-trans conformational changes were observed during both stretching and relaxation. At temperatures of 93 degreesC or below, the relaxation was exponential with time, whereas above 93 degreesC, the initial decrease was followed by an increase of the orientation function due to crystallization. A reorientation of the gauche conformers, driven by the movement of the trans conformers, was also observed during crystallization.