Exploring Strategies for High Dielectric Constant and Low Loss Polymer Dielectrics

Polymer dielectrics having high dielectric constant, high temperature capability, and low loss are attractive for a broad range of applications such as film capacitors, gate dielectrics, artificial muscles, and electrocaloric cooling. Unfortunately, it is generally observed that higher polarization or dielectric constant tends to cause significantly enhanced dielectric loss. It is therefore highly desired that the fundamental physics of all types of polarization and loss mechanisms be thoroughly understood for dielectric polymers. In this Perspective, we intend to explore advantages and disadvantages for different types of polarization. Among a number of approaches, dipolar polarization is promising for high dielectric constant and low loss polymer dielectrics, if the dipolar relaxation peak can be pushed to above the gigahertz range. In particular, dipolar glass, paraelectric, and relaxor ferroelectric polymers are discussed for the dipolar polarization approach

Role of Methyl-2-nitrophenol Photolysis as a Potential Source of OH Radicals in the Polluted Atmosphere: Implications from Laboratory Investigation

Methyl-substituted 2-nitrophenols are important components of “brown carbon” from biomass burning. Photolysis is their major gas-phase degradation pathway. To determine the extent of light absorptions by 4-methyl-2-nitrophenol and 5-methyl-2-nitrophenol, we obtained their absorption cross sections in the 295–400 nm region by using cavity ring-down spectroscopy. Cross-section values for 4-methyl-2-nitrophenol were (1.01 ± 0.07) × 10^–18, (5.72 ± 0.39) × 10^–18, and (1.80 ± 0.17) × 10^–20 cm²/molecule at 295, 345, and 400 nm, where errors quoted represent 1σ measurement uncertainty. Cross-section values for 5-methyl-2-nitrophenol were (9.04 ± 0.77) × 10^–19, (5.89 ± 0.54) × 10^–18, and (2.81 ± 0.14) × 10^–20 cm²/molecule at 295, 345, and 400 nm. The HONO, NO₂, and OH formation channels following 308 and 351 nm photolysis of methyl-2-nitrophenols were investigated. The OH quantum yields at 308 and 351 nm were obtained as the ratio of the OH concentration generated in pump/probe laser overlap region to the photon density absorbed by methyl-substituted 2-nitrophenol in the same region; they were 0.066 ± 0.021 and 0.031 ± 0.017 for 4-methyl-2-nitrophenol and 0.078 ± 0.038 and 0.042 ± 0.015 for 5-methyl-2-nitrophenol, where uncertainties represent 1σ precision. The average HONO quantum yields at 308 and 351 nm were 0.26 ± 0.06 and 0.26 ± 0.03 for 4-methyl-2-nitrophenol and 0.37 ± 0.05 and 0.35 ± 0.06 for 5-methyl-2-nitrophenol. Estimated OH production rates from photolyzing 10 pptv of 4-methyl- and 5-methyl-2-nitrophenol are 2.3 × 10⁶ and 3.0 × 10⁶ molecules·cm^–3·s^–1 at 16.9° zenith angle

Table_1_Independent associations of serum calcium with or without albumin adjustment and serum phosphorus with nonalcoholic fatty liver disease: results from NHANES 1999-2018.doc

BackgroundThe associations of serum calcium and phosphorus with nonalcoholic fatty liver disease (NAFLD) remain unclear. In addition, there may be an effect of albumin correction on the association between serum calcium and NAFLD. We aimed to explore these relationships in the National Health and Nutrition Examination Survey (NHANES).MethodsEligible adult individuals from NHANES 1999-2018 were recruited for the study. We explored the associations of serum calcium, albumin-adjusted serum calcium, and serum phosphorus with NAFLD in multivariable-adjusted regression models. In addition, restricted cubic spline (RCS), stratified analysis, and multiple sensitivity analyses were used for further elaboration.ResultsThe study sample consisted of 20,900 participants, with an observed NAFLD prevalence of 44.65%. Fully adjusted models indicated that serum calcium was inversely associated with NAFLD (odds ratio [OR] and 95% confidence interval [CI] = 0.70 (0.62, 0.78), pConclusionSerum calcium and phosphorus were significantly associated with the development of NAFLD. These findings suggest the potential clinical significance of serum calcium/phosphorus and albumin levels in individuals at high risk for NAFLD. Our study supports the potential role of serum calcium/phosphorus homeostasis in the pathophysiology of NAFLD and could serve as NAFLD-related biomarkers.</p

Rhodium-Catalyzed Hetero-(5 + 2) Cycloaddition of Vinylaziridines and Alkynes: A Theoretical View of the Mechanism and Chirality Transfer

A newly reported density functional theory method, M11-L, was performed to study the mechanism and chirality transfer for the intramolecular formal hetero-(5 + 2) cycloaddition of vinylaziridines with alkynes. Both (<i>E</i>)- and (<i>Z</i>)-olefinic substrates were considered in the density functional theory calculations. The computational results suggested a metallahydropyridine pathway for the generation of azepines, which involves aziridine cleavage, 2π insertion of the alkyne group into the Rh–C bond, and reductive elimination from a rhodium­(III) cation. The chirality transfer process for the (<i>E</i>)-alkene substrate is shown to occur on the <i>re</i> face of the alkene, whereas the (<i>Z</i>)-alkene cycloaddition chirality transfer occurs on the <i>si</i> face. The high enantioselectivity in this type of reaction is attributed to the greater ring strain in the <i>trans</i> allylic rhodium complex

Synthesis and Characterization of Azadipyrromethene-<i>alt</i>-<i>p</i>‑Phenylene Ethynylene Conjugated Polymers and Their Chelates

Several n-type conjugated polymers incorporating azadipyromethene (aza-DIPY) dyes in the main chain were synthesized by Sonogashira coupling of bisiodo­(tetraphenylazadipyrromethene)­s with 1,4-bis­((2-ethylhexyl)­oxy)-2,5-diethynylbenzene. Using branched alkoxy groups on the diethynylbenzene comonomer resulted in polymers with higher molecular weight and higher solubility in organic solvents than our previous report with dodecylalkoxy groups. The physical properties of these polymers were further tuned by coordination of the aza-DIPY moiety with BF₂, Cu­(I)­PEt₃, or Ag­(I)­PEt₃ via a postpolymerization reaction. Coordination with the electron-deficient BF₂ resulted in improved solubility in organic solvents, higher electron affinity (∼4.5 eV), lower LUMO energy levels (<−5.6 eV), and lower optical bandgaps (<1.34 eV) than the unchelated precursor. Coordination with the electron-rich Cu­(I) and Ag­(I) metals resulted in higher optical bandgaps (1.5 eV) and higher HOMO (−5.3 eV) and LUMO (−4.0 eV) energy levels. X-ray diffraction of the polymers in the solid state showed a lamellar spacing that varied with the solubilizing groups

Bimetallic Octahedral Ruthenium–Nickel Carbido Cluster Complexes. Synthesis and Structural Characterization

The reaction of Ru₅­(CO)₁₅­(μ₅-C) with Ni­(COD)₂ in acetonitrile at 80 °C affords the bimetallic octahedral ruthenium–nickel cluster complex Ru₅Ni­(NCMe)­(CO)₁₅­(μ₆-C), <b>3</b>. The acetonitrile ligand in <b>3</b> can be replaced by CO and NH₃ to yield Ru₅Ni­(CO)₁₆­(μ₆-C), <b>4</b>, and Ru₅Ni­(NH₃)­(CO)₁₅­(μ₆-C), <b>5</b>, respectively. Photolysis of compound <b>3</b> in benzene and toluene solvent yielded the η⁶-coordinated benzene and toluene Ru₅Ni carbido cluster complexes Ru₅Ni­(CO)₁₃­(η⁶-C₆H₆)­(μ₆-C), <b>6</b>, and Ru₅Ni­(CO)₁₃­(η⁶-C₇H₈)­(μ₆-C), <b>7</b>, respectively. All five new compounds were structurally characterized by single-crystal X-ray diffraction analyses

Double michael addition reactions of the nazarov reagent with 2-cyano-2-cycloalkenones: An alternative approach to cis-fused bicyclic systems

[[abstract]]A highly stereoselective annulation reaction of 2-cyano-2-cycloalkenones with the Nazarov reagent catalyzed by 1,8-diaza-bicyclo[5.4.0]undec-7-ene (DBU), leading to densely functionalized bicyclic systems, is developed

Synthesis of 1‑Cyanoalkynes and Their Ruthenium(II)-Catalyzed Cycloaddition with Organic Azides to Afford 4‑Cyano-1,2,3-triazoles

A new method to convert terminal alkynes under relatively mild conditions to 1-cyanoalkynes using in situ formed cyanogen is described. 1-Cyanoalkynes have a higher reactivity than terminal alkynes in the ruthenium­(II)-catalyzed regiospecific azide–alkyne cycloaddition to afford 4-cyano-1,2,3-triazoles. A mechanistic proposal different from the one that terminal alkynes adopt under the same reaction conditions is proposed. This work provides a new and convenient two-step sequence to prepare 4-cyano-1,2,3-triazoles from terminal alkynes and organic azides

Synthesis of 1‑Cyanoalkynes and Their Ruthenium(II)-Catalyzed Cycloaddition with Organic Azides to Afford 4‑Cyano-1,2,3-triazoles

A new method to convert terminal alkynes under relatively mild conditions to 1-cyanoalkynes using in situ formed cyanogen is described. 1-Cyanoalkynes have a higher reactivity than terminal alkynes in the ruthenium­(II)-catalyzed regiospecific azide–alkyne cycloaddition to afford 4-cyano-1,2,3-triazoles. A mechanistic proposal different from the one that terminal alkynes adopt under the same reaction conditions is proposed. This work provides a new and convenient two-step sequence to prepare 4-cyano-1,2,3-triazoles from terminal alkynes and organic azides

Understanding the Paraelectric Double Hysteresis Loop Behavior in Mesomorphic Even-Numbered Nylons at High Temperatures

Novel ferroelectric properties, such as slim double and single hysteresis loop (DHL and SHL) behaviors, are attractive for high energy density and low loss dielectric applications. In this study, temperature-dependent ferroelectric behavior was studied for mesomorphic even-numbered nylons (i.e., nylon-12 and nylon-6) using electric displacement–electric field (<i>D</i>–<i>E</i>) loop measurements. Upon raising the temperature from room temperature to 100 °C, the <i>D</i>–<i>E</i> loops became increasingly narrower, finally leading to slim DHLs with significantly enhanced apparent dielectric constants (i.e., ∼30 and ∼60) and small remanent polarizations (i.e., 3.5 and 8.2 mC/m²) for quenched and stretched nylon-12 and nylon-6, respectively. Combining wide-angle X-ray diffraction and infrared studies, changes in the mesophases and orientation of hydrogen-bonded amide groups after electric poling were used to unravel the structure–ferroelectric property relationship for the even-numbered nylons. At 100 °C, the quenched and stretched nylon-12 and nylon-6 films exhibited a paraelectric mesophase with twisted chain conformation and disordered hydrogen bonds. Upon high field poling (>100 MV/m), transient nanodomains could be generated with additional twists in the main chain. The observed DHL behavior was attributed to the electric-field-induced reversible transitions between the paraelectric (less twisted chains) and ferroelectric (more twisted chains) states in the mesomorphic crystals of even-numbered nylons. The knowledge gained from this study can inspire potential applications of <i>n</i>-nylons for electric energy storage, e.g., high temperature and high energy density multilayer polymer film capacitors