Morphology and Molecular Motion of Poly(ethylene terephthalate) in Polymer/Oligomer Gel

The structural heterogeneity and molecular motion in a thermoreversible gel consisting of poly(ethylene terephthalate) (PET) and a liquid ethylene glycol oligomer (PEG) was investigated by solid-state NMR and FT−Raman spectroscopies. PET was dissolved in PEG at elevated temperatures to form a concentrated solution (30 wt %), and the solution formed a gel rapidly on cooling. For the purpose of comparison, a PET/phenol binary system and PET crystallized by annealing methods were also investigated. The longest solid-state NMR relaxation times of 13C ( 13C T 1) in PET of PET/PEG gel among the samples indicated the slowest molecular motion and the highest rigidity PET chains. The structural heterogeneity of the PET/PEG gel investigated by H T 1 measurement and confirmed by FT−Raman spectroscopy indicated phase transition during gelation. The crystallinity of PET recovered from polymer/oligomer gels is near 70% as measured by wide-angle X-ray diffraction, which is about 20% higher than that for PET samples crystallized by solution crystallization and high-temperature annealing techniques.