Controlled Radical Polymerization of Vinyl Acetate Mediated by a Bis(imino)pyridine Vanadium Complex
Bibliographic record
Abstract
The mechanism of controlled radical polymerization of vinyl acetate using vanadium catalysts is investigated using a range of experimental and computational studies. Optimal control is achieved using the noninnocent bis(imino)pyridine ligand framework. [BIMPY]VCl 3, where BIMPY = 2,6-[(2,6- i Pr 2 C 6 H 3 )N═C(Me)] 2 (C 5 H 3 N)), is one of only a few transition metal systems capable of mediating the polymerization of vinyl acetate. Initiation using AIBN at 120 °C results in excellent control over poly(vinyl acetate) molecular weights and PDIs to give vanadium-terminated polymer chains which can be readily converted to both proton-terminated poly(vinyl acetate) or poly(vinyl alcohol). Irreversible halogen transfer from the parent [BIMPY]VCl 3 complex to a radical derived from AIBN generates the active species, [BIMPY]VCl 2 . This catalyst cannot use the halogen atom transfer equilibrium to control polymerization but can act as a persistent radical and trap the propagating polymer chains through an OMRP reversible termination process. Computational studies support this novel two-step reaction pathway and reveal that the poor control exerted over styrene versus the excellent control observed for vinyl acetate under these conditions is not only dependent on radical reactivity but also due to chelation of the carbonyl group of vinyl acetate to the vanadium center, making the trapping step more favorable. This correlates with an energy difference of just 4 kcal/mol between the reduced [BIMPY]VCl 2, and [BIMPY]VCl 2 R species for vinyl acetate compared to over 20 kcal/mol for styrene. This [BIMPY]VCl 3 system can be extended to other vinyl ester monomers, with good control over molecular weights and PDIs obtained for vinyl propionate, vinyl pivalate, and vinyl benzoate.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 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) | 0.042 | 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 teacher head, 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".