Cross-Linking Control of PDMS Rubber at High Temperatures Using TEMPO Nitroxide
Bibliographic record
Abstract
A novel composition using 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) and dicumyl peroxide (DCP) for scorch delay and control of the final network topology of polydimethylvinylmethylsiloxane (vinyl-PDMS) at high temperatures has been proposed. The evolution of linear viscoelasticity during cross-linking reaction was carried out on parallel plate geometry rheometer. The rubber was cross-linked with different ratios of [TEMPO]/[DCP] in order to control scorch time, which is defined as the time during which the PDMS rubber can be worked at a given temperature before cross-linking begins (i.e., the time at which the complex shear modulus suddenly increases). We showed that scorch delay increases according to the amount of TEMPO acting as an inhibitor. Nuclear magnetic resonance spectroscopy ( 1 H NMR) has been used to investigate the effect of TEMPO. This study reveals that the delayed action is the result of a TEMPO-grafted polymer action formed by reaction between TEMPO and polymer radicals. Furthermore, polymeric radicals are rapidly trapped by a grafting reaction before they are able to form cross-links. The cross-linking density (ν) and the number of junctions (μ) have been obtained from the phenomenological network model of Langley and Dossin and Graessley. In addition, a differential scanning calorimeter (DSC) was used to characterize the cross-linking reaction. Specific heat data show two exothermic reactions. These reactions may be associated on one hand to the decomposition of DCP and TEMPO grafting in vinyl-PDMS and on the other hand to the C−C covalent bonds creation. The DSC results indicate that the variation of scorch time with the [TEMPO]/[DCP] ratio is in reasonable agreement with those obtained from rheological measurements. Finally, an original method based on DSC experiments was derived to estimate the density of chemical junctions in PDMS networks. This method is based on the balance between the enthalpy of created cross-linked bonds and the standard enthalpy for one covalent carbon−carbon bond. Interestingly, predicted numbers of chemical junctions are in close agreement with those calculated using viscoelastic data.
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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".