Abstract
The rotational isomeric state analysis of poly(ethylene terephthalate) (PET) was carried out by using parameters adjusted so as to reproduce the experimental results of 1H NMR and dipole moment measurements on ethylene glycol dibenzoate. The central OC-CO bond of the ethyleneglycol unit prefers to be in the gauche form at lower temperatures, suggesting that the PET chains should contain many kink conformations in the amorphous state. In the following part, the nematic conformation of the same C-C bond was studied by preparing a model compound which is capable of forming an enantiotropic nematic liquid crystalline (LC) phase. IR studies indicate that the trans fraction of the C-C bond increases from ∼15% in the isotropic liquid to ∼50% in the nematic LC state at the phase boundary. For this drastic change in the conformation at the transition, the C-C bond should be required to pay certain entropy penalty. These results are however compatible with the recent observations by SAXS and DPLS that the formation of nematic LC-like domains proceeds prior to the evolution of primary crystal nucleation during the cold-crystallization of PET. The PET chain is known to take the planar all-trans conformation in the crystalline state. Finally a possible mechanism leading to the nematic order in the amorphous PET is presented. Growth of the nematic LC-like domains in the amorphous phase may lead to a spinodal microphase separation, as suggested by Kaji et al.
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Abe, A., Furuya, H., Hiejima, T. et al. On the Stability of the Nematic Order Observed During the Cold-crystallization of PET. Polym J 40, 910–914 (2008). https://doi.org/10.1295/polymj.PJ2007204
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DOI: https://doi.org/10.1295/polymj.PJ2007204