The success of metathesis chemistry techniques has sparked a tremendous interest in polymer and material chemistry. This contribution provides an overview of the state of the art in ring opening ...metathesis polymerisation (ROMP). It is intended to provide the reader with useful information on the interplay of initiators, monomers, and reaction conditions, thus aiding polymer chemists to utilise the ROMP toolbox. Prominent and illustrative examples from current research are given in the article.
The “ROMP toolbox”.
For the series of para-substituted triphenylamines, optimized geometries, HOMO and LUMO energy levels, ionization potentials Ip, reorganization energies for hole transport λ+, and frontier orbital ...contours have been calculated by means of ab initio computations. Relationships between them and the Hammett parameter are presented. According to calculations, electron releasing substituents increase the HOMO and LUMO energies of TPA, while electron withdrawing ones decrease it. This behavior is reflected in subsequent decreasing and increasing of ionization potentials of substituted TPAs. Calculations show that there exists also a strong substituent effect on the reorganization energy λ+, which is a dominating factor of hole mobility. It is concluded that proper tuning of the HOMO and LUMO levels (and, as a result, ionization potential, Ip) and reorganization energy λ+ (consequently, hole mobility) of the triphenylamine can be done by alteration of the TPA electronic structure by an appropriate substitution. It is demonstrated that the proper adjustment of the HOMO levels of HTM facilitates the reduction of an energy barrier at the interface of ITO/HTL and HTL/EL and ensure the high hole injection and hole transport rate. On the other hand, appropriate adjustment of the LUMO level prevents an electron leak from the EL into the HTM layer. Results of these calculations can be useful in the process of designing new HTM materials of desired properties (high efficiency, stability, and durability).
Aprotic alkali metal–oxygen batteries require reversible formation of metal superoxide or peroxide on cycling. Severe parasitic reactions cause poor rechargeability, efficiency, and cycle life and ...have been shown to be caused by singlet oxygen (1O2) that forms at all stages of cycling. However, its formation mechanism remains unclear. We show that disproportionation of superoxide, the product or intermediate on discharge and charge, to peroxide and oxygen is responsible for 1O2 formation. While the overall reaction is driven by the stability of peroxide and thus favored by stronger Lewis acidic cations such as Li+, the 1O2 fraction is enhanced by weak Lewis acids such as organic cations. Concurrently, the metal peroxide yield drops with increasing 1O2. The results explain a major parasitic pathway during cell cycling and the growing severity in K–, Na–, and Li–O2 cells based on the growing propensity for disproportionation. High capacities and rates with peroxides are now realized to require solution processes, which form peroxide or release O2via disproportionation. The results therefore establish the central dilemma that disproportionation is required for high capacity but also responsible for irreversible reactions. Highly reversible cell operation requires hence finding reaction routes that avoid disproportionation.
Poly(ether)s represent an important class of polymers and are typically formed by ring-opening polymerization, Williamson ether synthesis, or self-condensation of alcohols. The oxa-Michael reaction ...presents another method to form poly(ether)s with additional functional groups in the polymer backbone starting from di- or triols and electron deficient olefins such as acrylates, sulfones, or acrylamides. However, research on oxa-Michael polymerization is still limited. Herein, we outline the principles of the oxa-Michael polymerization and focus on the synthesis and preparation of poly(ether-sulfone)s, poly(ether-ester)s, poly(ether)s, and poly(ether-amide)s. Further, challenges as well as future perspectives of the oxa-Michael polymerization are discussed.
Graphical abstract
Inverse electron-demand Diels–Alder additions (iEDDA) between 1,2,4,5-tetrazines and suitable unsaturated dienophiles such as olefins, alkynes, or enol ethers provide facile access to pyridazines. ...Herein the use of cyclic enol ether derivatives for preparing pyridazines bearing 2-hydroxyethyl, 3-hyproxypropyl, and 3-oxopropyl substituents at the 4-position is disclosed and second order rate constants for the reactions with 2,3-dihydrofuran, 3,4-dihydro-2
H
-pyran, and 2-methoxy-3,4-dihydro-2
H
-pyran are presented.
Graphical abstract
Aprotic alkali metal-O
batteries face two major obstacles to their chemistry occurring efficiently, the insulating nature of the formed alkali superoxides/peroxides and parasitic reactions that are ...caused by the highly reactive singlet oxygen (
O
). Redox mediators are recognized to be key for improving rechargeability. However, it is unclear how they affect
O
formation, which hinders strategies for their improvement. Here we clarify the mechanism of mediated peroxide and superoxide oxidation and thus explain how redox mediators either enhance or suppress
O
formation. We show that charging commences with peroxide oxidation to a superoxide intermediate and that redox potentials above ~3.5 V versus Li/Li
drive
O
evolution from superoxide oxidation, while disproportionation always generates some
O
. We find that
O
suppression requires oxidation to be faster than the generation of
O
from disproportionation. Oxidation rates decrease with growing driving force following Marcus inverted-region behaviour, establishing a region of maximum rate.
Herein we propose an auto-tandem catalytic approach towards the preparation of poly(ester–ether)s from simple alkyl acrylates and diols. By combining oxa-Michael addition with transesterification the ...preparation of hydroxy functionalised acrylate monomers can be avoided.
Singlet oxygen (1O2) causes a major fraction of the parasitic chemistry during the cycling of non‐aqueous alkali metal‐O2 batteries and also contributes to interfacial reactivity of transition‐metal ...oxide intercalation compounds. We introduce DABCOnium, the mono alkylated form of 1,4‐diazabicyclo2.2.2octane (DABCO), as an efficient 1O2 quencher with an unusually high oxidative stability of ca. 4.2 V vs. Li/Li+. Previous quenchers are strongly Lewis basic amines with too low oxidative stability. DABCOnium is an ionic liquid, non‐volatile, highly soluble in the electrolyte, stable against superoxide and peroxide, and compatible with lithium metal. The electrochemical stability covers the required range for metal–O2 batteries and greatly reduces 1O2 related parasitic chemistry as demonstrated for the Li–O2 cell.
Serving quench: Singlet oxygen (1O2) formation deleteriously affects the cycling stability of many alkali cathodes, such as the Li–O2 cathode. An efficient and high‐voltage stable 1O2 quencher results in greatly reduced 1O2 related side reactions. Quenchers stable under high‐voltage are relevant to control 1O2 related interfacial reactivity and long‐term cyclability of many cathodes.
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