New Insights into the Development of Ordered Structure in Poly(ethylene terephthalate). 1. Results from External Reflection Infrared Spectroscopy

Abstract

Front-surface external reflection infrared spectroscopy was used to study a set of samples of poly(ethylene terephthalate) (PET) corresponding to various states of order: highly amorphous, drawn at 80 °C to different draw ratios, and thermally crystallized under different conditions. Kramers-Kronig transformation provided high-quality spectra that included an accurate representation of the most intense bands in the spectrum, which are generally saturated or distorted in transmission and internal reflection spectra. Factor analysis indicated the presence of three principal components in the spectra, and by taking linear combinations of the three principal factors, it was possible to generate three distinct physically meaningful basis spectra designated G, TC, and TX. The G spectrum corresponds to a gauche conformation of the ethylene glycol moiety, which is predominant in the amorphous state, while the other two correspond to a trans glycol conformation. The TC spectrum corresponds to the true crystalline state of PET, in which the carbonyl groups are coplanar with and in an all trans arrangement with respect to the benzene rings. The TX spectrum, on the other hand, corresponds to a less ordered trans structure in which the peaks associated with the terephthaloyl moiety of the molecule resemble those observed for the amorphous phase, where the carbonyl groups are either noncoplanar or cis and trans with respect to the benzene rings. However, the TX spectrum is a major contributor in the spectra of the drawn samples. This indicates that drawing at 80 °C produces a structure in which gauche conformers are converted into extended trans sequences, but the terephthaloyl conformation remains rather disordered. In other words, the development of order involves two processes that do not necessarily occur simultaneously. This provides new insight into the nature of the widely reported "intermediate" phase in PET and into the complex behavior of some of the trans peaks in the infrared spectrum. Detailed analysis of the basis spectra, including curve fitting, has also made it possible to suggest more precise assignments for some of the bands in the IR spectrum.

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“…Therefore, for PET the crystallization process slows down because the gauche to trans conversion is necessary for the crystal formation. [31,32] On the other hand, PE is characterized by a linear, long sequence of -(CH 2 )-units, that fit easily in folded crystals: thus, PE is reasonably the fastest crystallizing polymer in Figure 8. Therefore, considerations on chain flexibility and conformational characteristics must be considered in order to appreciate the influence of the chemical structure on the crystallization rate of macromolecules.…”

Influence of Plasma Treatments on the Hemocompatibility of PET and PET + TiO2 Films

“…In order to eliminate the artifacts of the ATR technique, like irreproducible optical contact between the sample and the internal reflection element, the absorbance values were normalized to the absorbance of the 1408 cm -1 band. The adsorption bands were fitted with Gauss functions, and the values of the integrated area were used to estimate sample crystallinity [20,21].…”

“…Generally, the polymer chains in PET are arranged in different domains, with a preferential orientation of ethylene glycol residue. Three different regions can be distinguished: a crystalline region, containing only trans conformers, an amorphous region, containing gauche conformers and a small number of trans conformers, and a mesophase region [20,24,25]. Figure 5 presents the FTIR spectrum in the 1320-1430 cm -1 region for untreated PET.…”

Proton-radiation resistance of poly(ethylene terephthalate)–nanodiamond–graphene nanoplatelet nanocomposites

“…Thus, by using FTIR it is possible to identify bands characteristic of the amorphous and crystalline phase. Furthermore IR conformational bands can be used to follow the PET crystallization process as well as to assess the presence of a crystal phase in starting samples [38]. The usual method to quantitatively compare the crystal fraction in films, which was used in this study, is to compare the integrated intensities of the trans -glycol conformation band at 1340 cm -1 (I1340) with the integrated intensity of a reference band that is unaffected by conformational changes of the monomeric unit.…”