Synthesis and Rheological Characterization of Star-Shaped and Linear Poly(hydroxybutyrate)
Bibliographic record
Abstract
Indium and zinc complexes, [(NNO tBu )InCl] 2 (μ-Cl)(μ-OTHMB) ( 2 ) and (NN i O tBu )Zn(CH 2 CH 3 ) ( 3 ), were used to produce monodispersed three- and six-armed star-shaped PHBs using tris(hydroxymethyl)benzene (THMB) and dipentaerythritol as the chain transfer agents. Reactions catalyzed by complex 2 were highly controlled, with THMB:catalyst ratios of up to 590:1, resulting in star-shaped PHBs with predictable molecular weights ( M n = 1.25–219 kDa) and narrow dispersities ( Đ = 1.02–1.08). The zinc-based catalyst, 3, was less controlled than the indium analogue but nevertheless generated moderately syndiotactic PHBs with maximum M n values of ∼100 kDa. Importantly, 3 allowed the formation of previously unknown 6-armed star PHBs, allowing us to compare the effects of the different PHB architectures on the rheological behavior of the materials. High molecular weight linear and star polymers were characterized using solution and melt viscoelastic studies. Zero-shear viscosity of linear PHBs exhibited a power law relationship with the span molecular weight; however, it scaled exponentially for star polymers with slightly higher values for the 6-armed star PHBs. This was attributed to the moderately syndiotactic microstructure of these polymers. The absence of a district arm retraction relaxation in the dynamic master curves, and overshoot in the transient viscosity for the 6-armed star PHBs, are due to the lower entanglement density and slightly broader molecular weight distribution of these polymers.
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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) | 0.000 | 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) | 0.000 | 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".