Probing Side Chain Dynamics of Branched Macromolecules by Pyrene Excimer Fluorescence
Bibliographic record
Abstract
Four different pyrene-labeled polymers were prepared by radical copolymerization of n -butyl methacrylate (BMA) and 1-pyrenemethyl methacrylate (PyEG 0 -MA), 1-pyrenemethoxyethyl methacrylate (PyEG 1 -MA), 1-pyrenemethoxyethoxyethyl methacrylate (PyEG 2 -MA), and 1-pyrenemethoxydiethoxyethyl methacrylate (PyEG 3 -MA) to yield PyEG 0 –PBMA, PyEG 1 –PBMA, PyEG 2 –PBMA, and PyEG 3 –PBMA, respectively. The only structural difference between the polymers was the length of the oligo(ethylene glycol) spacer separating the pyrene label from the main chain. Steady-state and time-resolved fluorescence were applied to investigate how the length of the spacer affected the photophysical properties of the pyrene-labeled polymers. Excimer formation between an excited-state and a ground-state pyrene was enhanced by a longer spacer which increased the probability of encounter between two pyrene labels. This conclusion was supported through the analysis of the fluorescence decays of the polymers according to the fluorescence blob model (FBM) which yielded the number ( N blob ) of monomers constituting the volume in the polymer coil probed by an excited pyrene and the rate constant of excimer formation, k blob, inside a blob. N blob increased more or less linearly with increasing spacer length reflecting a larger blob volume. k blob for PyEG 0 –PBMA was small due to steric hindrance while k blob took a larger but similar value within experimental error for all polymers labeled with pyrene derivatives having oligo(ethylene glycol) spacers. These experiments demonstrate that for a branched macromolecule the volume probed by the tip of a side chain and its dynamics can be characterized quantitatively by monitoring pyrene excimer fluorescence. They are expected to provide important dynamic and structural information about the numerous highly branched macromolecules that are currently under intense scientific scrutiny.
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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".