Theoretical Study of the Copolymerization of Ethylene and Propylene by a Heterogeneous Ziegler−Natta Catalyst
Bibliographic record
Abstract
The copolymerization of ethylene and propylene by a heterogeneous Ti/MgCl 2 Ziegler−Natta catalyst is studied with density functional theory calculations. One particular model of an active site, the so-called “TiCl 3 -based slope site”, is looked at in detail. The influence of the previous monomer insertion is allowed for by examining sites where the growing polymer chain is modeled by a methyl, propyl, isobutyl, and 2-butyl group. Propylene is found to form a more stable π-complex with the active site than ethylene. Propylene is also found to have a lower barrier to insertion into the Ti−C bond than ethylene in most instances and to prefer to insert in a 1−2 orientation rather than a 2−1 orientation. The relative height of the insertion barriers of ethylene and propylene is in contradiction to experimentally observed copolymer compositions. Increasing steric bulk of the polymer chain disfavors propylene insertion relative to ethylene insertion and 1−2 propylene insertion relative to 2−1 insertion. Some of the insertion reactions examined are shown to be significantly stereoselective due to the interaction of propylene and the growing polymer chain. Despite these stereoselective reactions, the active site modeled here will not produce tactic polymer except under some special circumstances which are outlined.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".