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Abstract Low‐strain cyclic olefin monomers, including five‐membered, six‐membered, eight‐membered, and macrocyclic rings, have been recently exploited for the synthesis of depolymerizable polyolefins via ring‐opening metathesis polymerization (ROMP). Such polyolefins can undergo ring‐closing metathesis depolymerization (RCMD) to regenerate their original monomers. Nevertheless, the depolymerization behavior of polyolefins prepared by ROMP of seven‐membered cyclic olefins, an important class of low‐strain rings, still remains unexplored. In this study, we demonstrate the chemical recycling of polyheptenamers to cycloheptene under standard RCMD conditions. Highly efficient depolymerization of polyheptenamer was enabled by Grubbs' second‐generation catalyst in toluene. It was observed that the monomer yields increased when the depolymerization temperature increased and the starting polymer concentration was reduced. A near‐quantitative monomer regeneration (>96%) was achieved within 1 h under dilute conditions (20 mM of olefins) at 60°C. Moreover, polyheptenamer exhibited a decomposition temperature above 430°C, highlighting its potential as a new class of thermally stable and chemically recyclable polymer materials.
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Sustainable synthesis of CO 2 -derived polycarbonates from d -xylose
Synthetic transformation of d -xylose into a four-membered cyclic ether allows for reactions with carbon dioxide (CO 2 ) leading to linear polycarbonates by either a one-step ring-opening copolymerisation (ROCOP) directly, or by sequential isolation of a preformed six-membered cyclic carbonate followed by ring-opening polymerisation (ROP).
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- PAR ID:
- 10341372
- Date Published:
- Journal Name:
- Polymer Chemistry
- Volume:
- 12
- Issue:
- 37
- ISSN:
- 1759-9954
- Page Range / eLocation ID:
- 5271 to 5278
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Cyclic ethers undergo H-abstraction reactions that yield carbon-centered radicals (Ṙ). The ether functional group introduces a competing set of reaction pathways: ring-opening and reaction with O2 to form peroxy radical adducts, ROȮ, which can result in stereoisomers. ROȮ derived from cyclic ethers can subsequently isomerize into hydroperoxy-substituted carbon-centered radicals, Q̇OOH, which can also undergo ring-opening reactions or pathways prototypical to alkyl oxidation. The balance of reactions that unfold from cyclic ether radicals depends intrinsically on the size of the ring and the structure of any substituents retained in the formation step. The present work examines unimolecular reactions of peroxy radicals from 2-ethyloxetane, a four-membered cyclic ether formed during n-pentane oxidation, and reveals stereoisomer-specific reaction pathways. Automated quantum chemical computations were conducted on constitutional and stereoisomers of ROȮ derived from O2-addition to 2-ethyloxetanyl radicals. Pressure-dependent rate calculations were conducted by solving the master equation from 300 – 1000 K and from 0.01 – 100 atm. Branching fractions were then calculated at 650 K and 825 K, the peak temperatures at which cyclic ethers form in alkane oxidation. Isomer-specific reaction pathways of anti-ROO and syn-ROO and resulting impact on radical production were evident. Q̇OOH ring-opening reactions were significant as were rates of bi-cyclic ether formation common in alkyl radical oxidation. Detailed prescription of rates and reaction mechanisms describing cyclic ether consumption mechanisms are important to enable accurate modeling of reactions of ephemeral Q̇OOH radicals because of the direct, isomer-specific formation pathways. In addition, detailed cyclic ether mechanisms are required to reduce mechanism truncation error. The results herein provide insight on connections between cyclic ethers and chain-reaction pathways yielding ȮH, HOȮ, and other radicals, in addition to pathways leading to performic acid (HOOC(=O)H), the decomposition of which via O–O scission results in an exothermic, chain-branching step.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D1PY00784J
