Indium Catalysts for Ring Opening Polymerization: Exploring the Importance of Catalyst Aggregation
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Bibliographic record
Abstract
Inexorably, the environmental persistence and damage caused by polyolefins have become major drawbacks to their continued long-term use. Global shifts in thinking from fossil-fuel to renewable biobased resources have urged researchers to focus their attention on substituting fossil-fuel based polymers with renewable and biodegradable alternatives on an industrial scale. The recent development of biodegradable polyesters from ring opening polymerization (ROP) of bioderived cyclic ester monomers has emerged as a promising new avenue toward this goal. Ever increasing numbers of metal-based initiators have been reported in the literature for the controlled ROP of cyclic esters, in particular for the polymerization of lactide to produce poly(lactic acid) (PLA). PLA has several material weaknesses, which hinder its use as a replacement for commodity plastics. Despite many advances in developing highly active and controlled catalysts for lactide polymerization, no single catalyst system has emerged to replace industrially used catalysts and provide access to PLA materials with improved properties. We reported the first example of indium(III) for the ring opening polymerization of lactide. Since then, indium(III) has emerged as a useful Lewis acid in initiators for the controlled polymerization of lactide and other cyclic esters. In particular, we have developed a large family of chiral dinuclear indium complexes bearing tridentate diaminophenolate ligands and tetradentate salen and salan ligands. Complexes within our tridentate ligand family are highly active initiators for the moderately isoselective living and immortal polymerization of rac-lactide, as well as other cyclic esters. We have shown that subtle steric effects influence aggregation in these systems, with polymerization typically proceeding through a dinuclear propagating species. In addition, profound effects on polymerization activities have been observed for central tertiary versus secondary amine donors in these and other related systems. In contrast, our well-controlled and highly active chiral indium salen systems are more isoselective than the tridentate analogues and polymerize lactide via a mononuclear propagating species. Again, we have noticed that subtle steric and electronic changes to the ligand can influence both polymerization activity and stereoselectivity via aggregation phenomena. Recently, we have reported a promising new chiral indium catalyst supported by a tetradentate salan ligand. This catalyst is remarkably water and air stable and can be activated by linear and branched alcohols to provide controlled access to multiblock copolymers in air. This catalyst represents an important step forward toward generating new, commercially relevant catalysts for ROP of cyclic esters to produce novel biodegradable polymers, and highlights the unique value of indium-based catalysts in the field.
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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 | 0.003 | 0.002 |
| 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 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.002 | 0.001 |
| 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 it