Probing the Mechanism of the PCl<sub>5</sub>−Initiated Living Cationic Polymerization of the Phosphoranimine Cl<sub>3</sub>P═NSiMe<sub>3</sub> using Model Compound Chemistry
Bibliographic record
Abstract
New insight into the mechanism of the ambient temperature PCl5-initiated living cationic chain growth polycondensation of the N-silylphosphoranimine Cl3P=NSiMe3 (1) to give poly(dichlorophosphazene), [N=PCl2]n, has been provided by studies of model compound chemistry. Investigations of the reactivity of Cl- salts of the proposed cationic intermediates [Cl3P=N=PCl3]+ ([2]+) and [Cl3P=N-PCl2=N=PCl3]+ ([6]+) toward Ph3P=NSiMe3 (3a) provided evidence that under the usual polymerization conditions that involve a high monomer to initiator ratio, propagation occurs at both chain ends. However, analogous studies of near stoichiometric processes suggested that propagation is faster at one chain end, particularly when the chains are short. In addition, experiments involving [Ph3P=N=PPh3][PCl6] ([9][PCl6]) and the N-silylphosphoranimines R3P=NSiMe3 3a (R = Ph) and 3b (R = p-CF3C6H4), showed that the [PCl6]- anion, which is formed in the early stages of the polymerization and has hitherto been assumed to be an innocent spectator counteranion, is actually reactive under the reaction conditions and can initiate oligomerization and polymerization. Finally, the absence of reactions between phosphoranimines 3b or 1 with the Cl- salts of the cations [Ph3P=N-PCl2=N=PPh3]+ ([10a]+), [Ph3P=N-(PCl2=N)2=PPh3]+ ([5]+), and [Ph3P=N-(PCl2=N)3=PPh3]+ ([8]+) with P-Cl bonds located internally but not at the chain ends have shown that chain branching reactions are unlikely to be significant during the polymerization. These results identify key factors that complicate the living PCl5-initiated chain growth polycondensation of 1 and potentially lead to a loss of control over molecular weight and broaden the molecular weight distributions, but also indicate that the polymer formed is essentially linear rather than branched.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.002 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.002 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 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".