Biphenyl Structures Research Articles

Synthesis and properties of modified polyimides containing multiple side methyl and biphenyl structures

With the rapid development of 5 G technology and microelectronics, there is an urgent demand to design and develop modified polyimide films with low dielectric constant as flexible matrix materials. In this work, a diamine containing multiple side methyl and biphenyl groups was synthesized by aromatic nucleophilicsubstitution reaction and oxidation-reduction reaction, respectively. Furthermore, this monomer was used to polymerize with four different commercially available dianhydrides (ODPA, BTDA, BPDA, and PMDA) to produce a class of polyimides (PI 3a∼3d). The structures of the diamine and its PIs are characterized, and the relationship between the structure and properties of the obtained PI films is investigated. These modified PIs are easy to cast into films and have low dielectric constants and water absorption. Their dielectric constants and dielectric losses are in the range of 2.66–2.91 and 0.00579–0.00677 at 1 MHz, respectively. Meanwhile, these PIs also maintains good thermal stability, with glass transition temperatures (T g) higher than 284 °C and 10% weight loss temperatures in the range of 496–505 °C at N2.

Effect of introducing oxygen into ethylene tar pitches on their carbonaceous products

Ethylene tar is a prospective precursor for preparing carbonaceous materials, which is regard-ed as a representative soft carbon material after carbonization. However, the introduction of oxygen can influence the morphology of the final carbonaceous materials. For the introduction of oxygen, dealkylation and dehydrogenation will be promoted and the molecules can be linked more effectively. For the subsequent carbonization, the biphenyl structures caused by the deoxygenation via the elimination of CO2, as well as the reserved aromatic ether bonds, can facilitate the strong cross-linking, which will restrain the movement of the carbon layers and the formation of the graphitic structures. After the graphitization treatment at 2800 oC, the oxidized pitch can lead to short-range ordered and long-range unordered structures, while the sample without oxidation can result in long-range ordered graphitic structures. It can be proved that a simple oxidation-carbonization treatment can transform ethylene tar into hard carbon structures.

Synthesis of C2 symmetric hydroxylated biphenyls by microwave-assisted oxidative coupling of natural phenols

Phenolic compounds, abundant in various plants, exhibit a range of biological properties such as anti-inflammatory, antiseptic, and antioxidant activities. C2-symmetric biphenyl structures, present in many pharmacologically active substances, serve as fundamental backbones in many natural products, highlighting the significance of these compounds. This study introduces innovative microwave-assisted oxidative coupling methods for the synthesis of C2 hydroxylated biphenyls starting from thirteen natural phenols, focusing on eco-friendliness and efficiency. This approach aims to minimize environmental impact while emphasizing safety and sustainability by employing microwaves in environmentally sustainable solvents like water. The proposed mechanisms for the oxidative coupling of phenols include various possible reaction pathways, encompassing both homo and hetero radical-radical couplings.

Ultrahigh Heat/Fire-Resistant, Mechanically Robust, and Closed-Loop Chemical Recyclable Polycarbonate Enabled by Facile Bond Dissociation Energy Modulation.

Plastics serve as an essential foundation in contemporary society. Nevertheless, meeting the rigorous performance demands in advanced applications and addressing their end-of-life disposal are two critical challenges that persist. Here, an innovative and facile method is introduced for the design and scalable production of polycarbonate, a key engineering plastic, simultaneously achieving high performance and closed-loop chemical recyclability. The bisphenol framework of polycarbonate is strategically adjusted from the low-bond-dissociation-energy bisphenol A to high-bond-dissociation-energy 4,4'-dihydroxydiphenyl, in combination with the incorporation of polysiloxane segments. As expected, the enhanced bond dissociation energy endows the polycarbonate with an extremely high glow-wire flammability index surpassing 1025°C, a 0.8mm UL-94V-0 rating, a high LOI value of 39.2%, and more than 50% reduction of heat and smoke release. Furthermore, the π-π stacking interactions within biphenyl structures resulted in a significant enhancement of mechanical strength by as more as 37.7%, and also played a positive role in achieving a lower dielectric constant. Significantly, the copolymer exhibited outstanding closed-loop chemical recyclability, allowing for facile depolymerization into bisphenol monomers and the repolymerized copolymer retains its high heat and fire resistance. This work provides a novel insight in the design of high-performance and closed-loop chemical recyclable polymeric materials.

Geometry-based cross-linking algorithm for modeling resorcinol resins through united-atom molecular dynamics simulations

The addition-condensation polymerization (ACP) of resorcinol with formaldehyde and the electrochemical polymerization (ECP) of resorcinol were desirable to improve the performances of resins. To achieve computational design, a new geometry-based cross-linking modeling algorithm for three-dimensional (3D) cross-linked network structures of resorcinol resins was developed for molecular dynamics (MD) simulations using a united-atom model. The ACP and ECP of resorcinol were successfully modeled using one algorithm by changing the parameters of the reaction rate constants of methylene, ether, and biphenyl bond formations. Furthermore, reaction judgment was performed under a reaction probability function comprising the Gaussian functions based on the interatomic distance of the reaction candidate atom pairs and interior angles regarding the spatial arrangement of two resorcinol rings. This geometry-based cross-linking algorithm successfully generated strainless 3D cross-linked network structures of the ACP and ECP resorcinol resins without the formation of highly bent unstable structures, such as U-shaped biphenyls. The MD simulation results indicated that the cross-linking of the ACP resin comprising methylene linkages proceeded with a network structure formation mechanism similar to that of phenolic resins, where the cross-linked network structure was determined at the gel point and the reactions after the gel point were to fix and freeze the network structure. For the ECP resins comprising ether and biphenyl linkages, the molar ratio of ether to biphenyl bonds affected the elastic property of the resins, and the incorporation of rigid biphenyl structures into ether-linkage networks increased the elastic modulus. Moreover, an increase in rigidity was observed as a decrease in the Poisson's ratio.

Reaction mechanism investigation of low Df epoxy-active ester film composites for 10 GHz high-frequency communications

The role of electronic-grade thin film composite materials in packaging circuits (integrated circuits) and printed circuit boards is critical. Developing epoxy-based thin film composite materials with low dielectric loss (Df) is a significant challenge, especially for that used in high frequency communication (eg. 10 GHz). Active esters, as excellent curing agents, do not form strongly polar hydroxyl groups upon reacting with epoxy resins, which offers significant advantages for low Df thin film composites. In this study, a low Df and high thermal resistance thin film composites was prepared by selecting epoxy resins with biphenyl structures and active esters with dicyclopentadiene groups. The introduction of rigid groups reduces the motility of the molecular chains, and its electron conjugation effect weakens the impact of an external electric field on the molecular dipole moment. The essence of low Df is explained by DFT calculations, in which the quenching effect of active esters on oxygen anions reduces the polarity of the molecular. Meanwhile, ensuring sufficient reaction at a sufficiently high temperature can reduce the number of residual free molecule fragments and ensure the integrity of the cross-link network. This work provides a new direction for the design of the next generation of high-performance low Df composites by deeply explaining the nature of active esters in reducing dielectric loss.

(Invited) Advanced Organic Electrode Materials for High-Performance and Sustainable Na-Ion Batteries

Na-ion batteries (NIBs) are promising alternatives to Li-ion batteries (LIBs) due to the low cost, abundance, and high sustainability of sodium resources. However, the high performance of inorganic electrode materials in LIBs does not extend to NIBs because of larger ion size of Na+ than Li+ and more complicated electrochemistry. Therefore, it is vital to search for high-performance electrode materials for NIBs. To this end, organic electrode materials (OEMs) with the advantages of high structural tunability and abundant structural diversity show great promise in developing high-performance NIBs. To achieve advanced OEMs for NIBs, a fundamental understanding of the structure–performance correlation is desired for rational structure design and performance optimization. Tailoring molecular structures of OEMs can enhance their performance in Na-ion batteries, however, the substitution rules and the consequent effect on the specific capacity and working potential remain elusive. Herein, we explored the electrochemical performances and reaction mechanisms of various carboxylate-based anode materials, including halogenated sodium carboxylates, N-doped sodium carboxylates, etc. By examining sodium carboxylates with different functional groups, selective N substitution, and extended conjugation structure, we exploited the correlation between structure and performance to establish substitution rules for high-capacity OEMs. Our results show that substitution position and types of functional groups are essential to create active centers for uptake/removal of Na+ and thermodynamically stabilize organic structures. Furthermore, rational host design and electrolytes modulation were performed to extend the cycle life. In addition to sodium carboxylate-based anode materials, we also designed and synthesized novel organic cathode materials based on azo and carbonyl groups for NIBs. The electrochemical performance of the organic cathode materials with an extended conjugated structure such as a naphthalene backbone structure is better than that with benzene and biphenyl structures due to faster kinetics and lower solubility in the electrolyte. It unravels the rational design principle of extending π-conjugation aromatic structures in redox-active polymers to enhance the electrochemical performance. To further optimize the organic cathodes, nitrogen-doped or single layer graphene is employed to increase the conductivity and mitigate the dissolution of organic materials in the electrolytes. The resulting organic cathodes deliver high specific capacity, long cycle life, and fast-charging capability. Post-cycling characterizations were employed to study the chemical structure and morphology evolution upon cycling, demonstrating that the active centers (azo and carbonyl groups) in the organic cathode materials can undergo reversible redox reactions with Na+ for sustainable NIBs. Our work provides a valuable guideline for the design principle of high-capacity and stable OEMs for sustainable energy storage.

Introducing Trifluoromethoxyarenes as Halide Surrogates in Mechanochemical Realizations of Ni‐catalyzed Cross‐coupling Reactions

AbstractSince the introduction of the TM‐catalyzed cross‐couplings their scope of starting materials has been growing systematically, allowing for more flexible design of synthetic routes with the coupling as a key step, particularly late‐stage modifications. Herein we present the use of trifluoromethoxyarenes as halide surrogates in Ni‐catalyzed couplings with arylboronic acids, potassium aryl trifluoroborates and aryl trialkoxysilanes, under mechanochemical conditions. In total, 22 biphenyl structures were obtained in good yields. Successful gram scale experiments confirm the usefulness of our protocol. The developed transformations’ mechanism was discussed in relation to the experimental and literature data and DFT calculations. The unusual reactivity of potassium benzoyltrifluoroborates was uncovered. 6 examples of resulting benzophenones were obtained in very good yields and the protocol was extended to gram scale. The described methods present a powerful tool when combined with the recent advances in organofluorine chemistry.

A fruitful century for the scalable synthesis and reactions of biphenyl derivatives: applications and biological aspects.

This review provides recent developments in the current status and latest synthetic methodologies of biphenyl derivatives. Furthermore, this review investigates detailed discussions of several metalated chemical reactions related to biphenyl scaffolds such as Wurtz-Fittig, Ullmann, Bennett-Turner, Negishi, Kumada, Stille, Suzuki-Miyaura, Friedel-Crafts, cyanation, amination, and various electrophilic substitution reactions supported by their mechanistic pathways. Furthermore, the preconditions required for the existence of axial chirality in biaryl compounds are discussed. Furthermore, atropisomerism as a type of axial chirality in biphenyl molecules is discussed. Additionally, this review covers a wide range of biological and medicinal applications of the synthesized compounds involving patented approaches in the last decade corresponding to investigating the crucial role of the biphenyl structures in APIs.

Sulfonyloxylation and Acetoxylation of Aryl C–H Proximal to a λ3-Iodanediyl Group on Biaryl Structures

λ3-Iodane-mediated proximal aryl C–H sulfonyloxylation and acetoxylation on 2-iodo-1,1′-biphenyl structures have been achieved. Intramolecular electron transfer between cationic I(III) and proximal 2-Ar groups in 2-arylphenyl-λ3-iodanes is a key step to generate the iodanyl radical intermediate with a radical cationic Ar moiety that undergoes the nucleophilic addition of acetate or sulfonate. Electron spin resonance experiments supported the proposed mechanism. A 2-benzyl-iodobenzene structure was also applicable to this reaction system.

Transformation of dissolved organic matter in landfill leachate during a membrane bioreactor treatment

In this study, a cutting-edge mass spectrometry (MS) technique, Orbitrap fusion MS with ultrahigh resolution, was used to analyze the molecular composition, chemical properties, formation mechanism, and environmental impact of refractory dissolved organic matter (rDOM) in leachate. The results showed that the bioavailable DOM (bDOM) and rDOM constituents varied substantially during the biological treatment of landfill leachate. Compared with bDOM, the rDOM in leachate had a higher degree of unsaturation, aromaticity, and oxidation, and a larger molecular weight, and contained more organic matter with benzene ring and biphenyl structures. Using high-throughput 16S rRNA sequencing, metagenomics, the Kendrick mass defect (KMD), and a mass difference network (MDiN), it was found that rDOM in leachate is generated through carboxylation (+COO), dehydro-oligomerization (-H2), and chain scission (-CH2) pathways due to the activity of microbes such as Patescibacteria, Chloroflexi, and Proteobacteria. Compared with Suwannee River fulvic acid (SRFA), the rDOM in leachate contained more organics with nitrogen, sulfur, benzene rings, and biphenyls. If the rDOM in leachate enters the environment it will affect the composition of the original organic matter, and its biogeochemical transformation and environmental fate will then need to be monitored and may require special attention.

Toughening and strengthening epoxy resins with a new bi-DOPO biphenyl reactive flame retardant

It is still challenging to simultaneously improve the strength and toughness of flame retardant epoxy resins. In this study, a new reactive flame retardant (DOPO-M) including bi-DOPO and biphenyl structures was successfully synthesized and applied as a co-curing agent. The introduction of DOPO-M accelerated the ring-opening reaction of epoxy resin. E51-DM-P composites exhibited improved transparency and retained good thermal resistance and thermal stability. Notably, the rigid biphenyl structure of DOPO-M and the in situ microphase separation effect created by DOPO-M-rich domains can both improve the tensile strength and toughness of composites by 28.6% and 24.4%, respectively. Meanwhile, the flame retardant property and fire safety of E51-DM-P composites have improved. With only 2.8 wt% DOPO-M (0.25 wt% of phosphorus), the E51-DM-P composites achieved UL-94 V-0 and a high LOI value of 30.2%. Furthermore, the peak heat release rate (PHRR) and total heat release (THR) of E51-DM-P0.5% decreased by 30.4% and 27.3%, respectively. All of these findings indicate that DOPO-M is a multifunctional and highly effective flame retardant that can be applied to manufacture epoxy resins with superior comprehensive properties.

Multimodal Imaging of Silicified Sorghum Leaves

AbstractThe plant cell wall is a complex composite material made of polysaccharides, polyphenols, proteins, and minerals. In this work, a multimodal imaging approach was taken, using Raman and Fourier‐transform infrared (FTIR) microspectroscopy along with fluorescence imaging, scanning electron microscopy (SEM), and elemental mapping by energy dispersive X‐ray spectroscopy (EDX). We characterized the chemical composition of sorghum leaf cross‐sections extracted from fresh tissue as well as after paraffin embedding. The complementary vibrational information of Raman and FTIR spectra related a silica deposition to a specific organic composition in the epidermis, specifically with respect to lignin. Moreover, the data enable in situ correlation of autofluorescence with a specific lignin structure. Our results showed that lignin 5–5’ linkages that produce biphenyl structures are important determinants of the cell wall fluorescence properties. The reported multimodal approach will help to clarify the process of biosilica formation and related questions regarding cell wall biochemistry.

Polybenzimidazole membranes derived from novel tetraamines containing 2,2′-disubstituted biphenyl structures for high temperature proton exchange membrane fuel cell application

Two novel tetraamines, 4,4′,5,5′-tetraamino-2,2′-dimethylbiphenyl (5) and 4,4′,5,5′-tetraamino-2,2′-trifluoromethoxy)biphenyl (10), containing methyl and trifluoromethoxy groups on the 2 and 2′ positions of biphenyls, were synthesized. Polybenzimidazoles P1 and P2 were prepared by polymerizing these two monomers with 4,4′-oxybis(benzoic acid) (OBA) in Eaton's reagent, respectively. P1 and P2 with inherent viscosities of 3.2 and 2.9 dL g−1, measured in methanesulfonic acid at 35 °C and 0.2 g dL−1, had the decomposition temperatures at 5% weight loss of 413 and 516 °C, exhibiting outstanding thermal stability. With the bulky trifluoromethoxy group, P2 showed better solubility and can be dissolved in polar aprotic solvents such as DMF, NMP, and DMSO. P1 and P2 can be fabricated into tough and flexible membranes by solvent casting. Their membranes also showed excellent oxidative stability. The residual weights of P1 and P2 were 89.5% and 93.7%, respectively, after 216 h of Fenton test. When the membranes reached their equilibrium phosphoric acid uptakes of 204% and 142%, the tensile strengths of P1 and P2 were 24.4 and 17.0 MPa, and the proton conductivities were 4.7 × 10−2 and 1.17 × 10−2 S cm−1 at 160 °C, respectively. At the saturated doping levels, the peak power density of single cells based on P1 and P2 reached 907 and 656 mW cm−2, respectively, compared to 573 mW cm−2 of m-PBI at 160 °C. These results demonstrate that P1 and P2 were promising candidates for HT-PEMFC application.

Multi‐Functionalized Polymers as Organic Cathodes for Sustainable Sodium/Potassium‐Ion Batteries

AbstractIn this work, we designed and synthesized three novel polymeric cathode materials based on azo and carbonyl groups for Na‐ion and K‐ion batteries. The electrochemical performance of the polymer with a naphthalene backbone structure is better than that with benzene and biphenyl structures due to faster kinetics and lower solubility in the electrolyte. It unravels the rational design principle of extending π‐conjugation aromatic structures in redox‐active polymers to enhance the electrochemical performance. To further optimize the polymeric cathodes, the polymer with a naphthalene backbone structure is mixed with nitrogen‐doped graphene to increase the conductivity and mitigate the dissolution. The resulting cathodes deliver high specific capacity, long cycle life, and fast‐charging capability. Post‐cycling characterizations were employed to study the chemical structure and morphology evolution upon cycling, demonstrating that the active centers (azo and carbonyl groups) in the polymer can undergo reversible redox reactions with Na+/K+ for sustainable alkali‐ion batteries.

Effect on the thermal resistance and thermal decomposition properties of thermally cross-linkable polyimide films obtained from a reactive acetylene

Homopolyimides are prepared by 4,4′-(ethyne-1,2-diyl)diphthalic anhydride as dianhydride monomer and several diamine monomers. The copolyimides are prepared with 4,4′-oxydianiline as an amine monomer， 3,3′,4,4′-oxydiphthalic anhydride as an anhydride monomer with the addition of 4,4′-(ethyne-1,2-diyl)diphthalic anhydride as another anhydride monomer. The structure of polyimides is characterized by Fourier transform infrared spectroscopy and X-ray diffraction. Thermogravimetric analysis, thermomechanical analysis and thermo-oxidative degradation kinetics analysis are used to investigate the properties of polyimides. The homopolyimide show the best thermal stability in both nitrogen and air atmosphere by 4,4′-oxydianiline and 4,4′-(ethyne-1,2-diyl)diphthalic anhydride. The results also indicate that the thermally cross-linkable copolyimide films not only enhance the thermal stability behaviors of polyimide by controlling the addition of dianhydride, but also improve substantially the upper limit temperature of thermal aging by undergoing chemical cross-linking reaction of the diphenylethynylene structures and providing multifarious naphthalene ring groups and biphenyl structures. Diphenylacetylene crosslinking merging to the long-chain of polyimide is a useful conversion for enhancing the thermal stability and the thermal degradation stability of aromatic polymers.

Thermal and flame-retardant properties of intrinsic flame-retardant epoxy resin containing biphenyl structures and phosphorus

An intrinsic flame-retardant epoxy resin was synthesized by introducing biphenyl structures and phosphorous into epoxy resin. The biphenyl structures could increase the glass transition temperature by more than 10 °C, as well thermal stability as indicated by the elevation in char yield. They could also enhance mechanical properties as reflected by the increments of 86.4% and 176.5% in tensile strength and breaking elongation, respectively, and offset the negative effects of phosphorus-containing structures. The introduction of elemental phosphorus could improve the flame-retardant properties of epoxy resin. The resulting epoxy resin presented a high limiting oxygen index of 32.4% and a V-0 rating in the UL-94 test. Moreover, it exhibited better flame-retardant parameters than pure epoxy resin in the cone calorimeter test. It could be decomposed to generate PO∙ and PO2∙ radicals to quench active free radicals, reduce toxic and smoke gas generation, and form a dense and stable char layer. It could simultaneously achieve gas and condensed phase flame retardancy. The presence of the biphenyl structure and phosphorus element in the epoxy resin system improved the thermal, mechanical, and flame-retardant properties of epoxy resin simultaneously. This work offered a facile method for preparing intrinsic phosphorus-containing flame-retardant epoxy resin without sacrificing thermal and mechanical properties.

Synthesis, Structures, and Properties of Highly Strained Cyclophenylene–Ethynylenes with Axial and Helical Chirality

AbstractSingle and double cyclophenylene–ethynylenes (CPEs) with axial and helical chirality have been synthesized by the Sonogashira cross‐coupling of di‐ and tetraethynyl biphenyls with a U‐shaped prearomatic diiodoparaphenylene followed by reductive aromatization. X‐ray crystallographic analyses and DFT calculations revealed that the CPEs possess highly twisted bent structures. Bend angles on the edge of the paraphenylene units were close to the value of [5]cycloparaphenylene (CPP)—the smallest CPP to date. The double and single CPEs possessed stable chirality despite flexible biphenyl structures because of the high strain in the diethynyl–paraphenylene moiety. In both the single and double CPEs, orbital interactions along the biphenyl axis were observed by DFT calculations in LUMO and LUMO+2 of the single CPE and LUMO+1 of the double CPE, which likely cause lowering of these orbital energies. Concerning chiroptical properties: boosting of the gabs value was observed in the biphenyl‐based double CPE, as well as the binaphthyl‐based single CPE, compared to the biphenyl‐based single CPE.

Synthesis, Structures, and Properties of Highly Strained Cyclophenylene-Ethynylenes with Axial and Helical Chirality.

Single and double cyclophenylene-ethynylenes (CPEs) with axial and helical chirality have been synthesized by the Sonogashira cross-coupling of di- and tetraethynyl biphenyls with a U-shaped prearomatic diiodoparaphenylene followed by reductive aromatization. X-ray crystallographic analyses and DFT calculations revealed that the CPEs possess highly twisted bent structures. Bend angles on the edge of the paraphenylene units were close to the value of [5]cycloparaphenylene (CPP)-the smallest CPP to date. The double and single CPEs possessed stable chirality despite flexible biphenyl structures because of the high strain in the diethynyl-paraphenylene moiety. In both the single and double CPEs, orbital interactions along the biphenyl axis were observed by DFT calculations in LUMO and LUMO+2 of the single CPE and LUMO+1 of the double CPE, which likely cause lowering of these orbital energies. Concerning chiroptical properties: boosting of the gabs value was observed in the biphenyl-based double CPE, as well as the binaphthyl-based single CPE, compared to the biphenyl-based single CPE.

Mechanism of Li storage on graphene nanoflakes: Density functional theory study

The efficiency of metal storage in carbon materials directly affects battery performance. Therefore, elucidating the storage mechanism is important for developing high-efficiency and new storage materials. In this study, interatomic interactions between Li species (Li atoms and Li+ ions) and graphene nanoflakes (GRs) have been investigated using the density functional theory method to elucidate the mechanism of Li storage on GRs. Moreover, single, double, and triple Li species were examined. For single Li systems (n = 1), the binding energy and diffusion barrier of Li on GRs were investigated, while the interatomic interactions and packing structures of Li species on GRs were investigated for double and triple Li systems (n = 2 and 3, respectively). The diffusion barriers for Li+ and Li for n = 1 were calculated to be 5.90 and 6.84 kcal/mol, respectively. For n = 2, the diffusion was strongly affected by the counter Li species and was attributed to the repulsive interactions. For n = 2, the close packing configurations of Li species on the surface of the GRs consisted of biphenyl structures where Li species were located inside the benzene rings of the biphenyl-like site of GRs. For n = 3, three Li species were bound to the triphenylene sites (two biphenyl-like sites). The electronic states of the Li species stored on GRs were discussed using the theoretical results.