New Insights into the Development of Ordered Structure in Poly(ethylene terephthalate). 1. Results from External Reflection Infrared Spectroscopy
Bibliographic record
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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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".