Competitive polycondensation of model compound melamine-urea-formaldehyed (MUF) resin system by 13C NMR
Bibliographic record
Abstract
Melamine-urea-formaldehyde (MUF) resin is an excellent adhesive in the field of wood adhesives, however the competition mechanism is questionable which affects the structure control and performance optimization of the resin. In this study, the competitive resin synthesis polycondensation reaction of MUF system under alkaline condition was studied based on the model compound 1,3-dihydroxymethyl urea (UF2) and melamine (M) system, and the competitive reaction mechanism in the system was deduced by 13C NMR quantitative analysis. The results show that the energy barrier of hydroxymethylation of melamine is lower than that of urea, and the priority of hydroxymethylation is lower; the addition of melamine results in a large amount of hydrolysis of UF2, and the formed free formaldehyde, resulting in hydroxymethylation of melamine; there is obvious polycondensation reaction in UF2+M system, mainly from the relationship between hydroxymethylurea and melamine or hydroxymethylmelamine. The type I bridge bond structure of polycondensation mainly comes from the reaction of UF2 and M, which is difficult to form the type II bridge bond. At low molar ratio, the formation of bridge bond is superior to that of ether bond. With the increase of molar ratio, the formation of ether bond shows advantages, but there is obvious competition between them. There may be competitive presence of the UF self-condensation products, melamine-formaldehyde (MF) self-condensation products and MUF co-condensed products after the polycondensation reaction.
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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".