INTERPRETATION OF THE TRANS FRACTION AND FINE STRUCTURE OF MELT-QUENCHED POLY (ETHYLENE TEREPHTHALATE)

In a preceding paper we determined the absolute trans fraction of CH2-CH2 bonds in melt-quenched poly (ethylene terephthalate) (PET) by means of infrared spectroscopy. The obtained fraction was an unexpectedly small value, 0.2, which is inconsistent with the probability of trans conformers, 0.3, averaged over all internal bonds of the unperturbed chain. From this fact and density consideration, we suggested that each chain in melt-quenched PET does not possess the random coil conformation but the folded chain conformation containing specially preferable conformers. In order to obtain the reasonable local conformation for the sequence CO-O-CH2-CH2-O-CO, we calculated the intramolecular potential energy. From this and a consideration of the intermolecular chain packing, the trans fraction of the ethylene glycol moiety and the fine structure of melt-quenched PET were discussed. In conclusion we suggest that the fine structure of meltquenched PET is very close to that in the crystals and is characterized as such that the crystallographic requirement between parallel folded chains is not satisfied owing to the irregular foldings.