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Results for “cycloalkenes”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Selectively Depolymerizable Polyurethanes from Unsaturated Polyols Cleavable by Olefin Metathesis

This communication describes a novel series of linear and crosslinked polyurethanes (PUs) and their selective depolymerization under mild conditions. Two unique polyols are synthesized bearing unsaturated units in a configuration designed to favor ring-closing metathesis (RCM) to five- and six-membered cycloalkenes. These polyols are co-polymerized with toluene diisocyanate to generate linear PUs and trifunctional hexamethylene- and diphenylmethane-based isocyanates to generate crosslinked PUs. The polyol design is such that the RCM reaction cleaves the backbone of the polymer chain. Upon exposure to dilute solutions of Grubbs’ catalyst under ambient conditions, the PUs are rapidly depolymerized to low molecular weight, soluble products bearing vinyl and cycloalkene functionalities. These functionalities enable further re-polymerization by traditional strategies for polymerization of double bonds. We anticipate that this general approach can be expanded to develop a range of chemically recyclable condensation polymers that are readily depolymerized by orthogonal metathesis chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Polymers depolymerizable by metathesis of a cleavable unit

Novel polymers are depolymerizable by metathesis of a cleavable unit. As an example, a series of linear and crosslinked polyurethanes were prepared that can be selectively depolymerized under mild conditions. Two unique polyols were synthesized bearing unsaturated units in a configuration designed to favor ring-closing metathesis to five- and six-membered cycloalkenes. These polyols were co-polymerized with toluene diisocyanate to generate linear polyurethanes and trifunctional hexamethylene- and diphenylmethane-based isocyanates to generate crosslinked polyurethanes. The polyol design is such that the ring-closing metathesis reaction cleaves the backbone of the polymer chain. Upon exposure to dilute solutions of Grubbs' catalyst under ambient conditions, the polyurethanes were rapidly depolymerized to low molecular weight, soluble products bearing vinyl and cycloalkene functionalities. These functionalities enabled further re-polymerization by traditional strategies for polymerization of double bonds. This general approach can be expanded to develop a range of chemically recyclable condensation polymers that are readily depolymerized by orthogonal metathesis chemistry.

Jones, Brad Howard↗
DOE OSTI2020

Vacuum-ultraviolet absorption cross-sections of functionalized cyclic hydrocarbons: Five-membered rings

Cross-sections were measured at 50 °C and 800 Torr using differential absorption spectroscopy in the vacuum-ultraviolet from 5.17 – 9.92 eV for a series of five-membered cyclic hydrocarbons: cyclopentane, cyclopentene, methylcyclopentane, tetrahydrofuran, furan, 2-methyltetrahydrofuran, 2,3-dihydro-5-methylfuran, tetrahydrofuran-3-one, 2-methyl-1,3-dioxolane, cyclopentanol, 2-hydroxytetrahydrofuran, cyclopentanone, 2-cyclopenten-1-one, 3-cyclopenten-1-one, 2-methylcyclopentan-1-one, 2-methylcyclopent-2-en-1-one, 1,2-epoxycyclopentane, 2,3-epoxycyclopentanone, and 3,4-epoxycyclopentanone. The majority of the species are functionalized and are directly related to chain-reactions relevant to combustion, such as substituted cyclic ethers and cycloalkenes. Uncertainty calculations were conducted as a function of photon energy to quantify errors associated with experimental repeatability, signal-to-noise ratio, and gas-phase concentration, yielding an upper limit of 5% in spectral regions where absorption is >2%. Here, the primary objective of the present work is to provide quantitative absorption cross-sections of species commonly produced in combustion reactions. Comparing qualitative differences among the five-membered cyclic species, in order to analyze the effect of functional groups on absorption, is a secondary objective. The majority of the spectra are reported for the first time and enable quantitative isomer-resolved speciation measurements in combustion chemistry.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2025

Toward Efficient Entropic Recycling by Mastering Ring–Chain Kinetics

Traditional chemical recycling approaches for condensation polymers suffer compounding energy losses and CO 2 emissions across multiple polymerization and depolymerization cycles. Entropic recycling can address these energy losses by entrapping free energy within the deconstruction products. Entropic recycling involves depolymerization to macrocyclic monomers, but such processes have not been feasible due to the high dilutions typically required to generate macrocyclic compounds. Here, we leverage selective catalysis to allow entropic recycling at concentrations 20–2000× higher than typical for macrocyclization reactions. We find that Ru-based olefin metathesis catalysts containing bulky iodine ligands significantly bias the ring–chain kinetic product distribution during ring-closing metathesis (RCM) toward the formation of oligomeric cycloalkenes. Further improvements in reaction concentration and macrocycle yield are obtained by using high catalyst loadings and by predisposing the alkene substrates to undergo favorable macrocyclization. These RCM optimizations translate effectively to cyclodepolymerization (CDP) of an olefin-containing polymer, with RCM and CDP affording similar macrocycle product distributions under identical reaction conditions. Macrocycle polymerization by entropy-driven ring-opening metathesis provides much higher molecular weight polymers than condensation polymerization of linear analogues, reducing the time to achieve high molecular weight from hours to minutes and enabling polymerization at room temperature. Finally, our findings re-emphasize the importance of energy consumption during a polymer’s lifecycle and provide a framework for the design of efficient entropic recycling systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Alkane Dehydrogenation and H/D Exchange by a Cationic Pincer-Ir(III) Hydride: Cooperative C–H Addition and β -H Elimination Modes Induce Anomalous Selectivity

We report that the cationic iridium complex ( iPr PCP)IrH + catalyzes the transfer-dehydrogenation of alkanes to give alkenes and hydrogen isotope exchange (HIE) of alkanes and arenes. Contrary to established selectivity trends found for C–H activation by transition metal complexes, strained cycloalkanes, including cyclopentane, cycloheptane, and cyclooctane, undergo C–H addition much more readily than n-alkanes, which in turn are much more reactive than cyclohexane. Aromatic C–H bonds also undergo H/D exchange much less rapidly than those of the strained cycloalkanes, but much more favorably than cyclohexane. The order of reactivity toward dehydrogenation correlates qualitatively with the reaction thermodynamics, but the magnitude is much greater than can be explained by thermodynamics. Accordingly, the cycloalkenes corresponding to the strained cycloalkanes undergo hydrogenation much more readily than cyclohexene, despite the less favorable thermodynamics of such hydrogenations. Here, computational (DFT) studies allow rationalization of the origin of reactivity and the unusual selectivity. Specifically, the initial C–H addition is strongly assisted by β-agostic interactions, which are particularly favorable for the strained cycloalkanes. Subsequent to α-C–H addition, the H atom of the β-agostic C–H bond is transferred directly to the hydride ligand of ( iPr PCP)IrH + to give a dihydrogen ligand.

02 PETROLEUM↗