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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Revolutionizing Methane Transformation with the Dual Production of Aromatics and Electricity in a Protonic Ceramic Electrocatalytic Membrane Reactor

Reducing the energy and carbon intensity of the conventional chemical processing industry can be achieved by electrochemically transforming natural gases into higher-value chemicals with higher efficiency and near-zero emissions. In this work, the direct conversion of methane to aromatics and electricity has been achieved in a protonic ceramic electrocatalytic membrane reactor through the integration of a proton-conducting membrane assembly and a trimetallic Pt–Cu/Mo/ZSM-5 catalyst for the nonoxidative methane dehydro-aromatization reaction. In this integrated system, a remarkable 15.6% single-pass methane conversion with an 11.4% benzene yield has been demonstrated, while a peak power density of 276 mW cm –2 is obtained at 700 °C. The enhanced 15.7% increase in conversion and 16.0% improvement in the yield are observed when compared with the thermochemical process, which is attributed to the shift of reaction equilibrium by the removal of hydrogen through the protonic membrane. Concurrently, the faster H2 removal at a higher electrical current gave rise to a higher methane conversion and benzene yield. Furthermore, the catalyst can be efficiently regenerated by eliminating carbon deposition. A stable cell potential is maintained for 45 h under a constant current load of 0.13 A cm –2 . Lastly, the dual production of aromatics and electricity in the electrocatalytic membrane reactor has been demonstrated to be an attractive approach for decarbonizing chemical processing.

aromatic compounds↗
DOE OSTI2021

Promoting Diels-Alder reactions to produce bio-BTX: Co-aromatization of textile waste and plastic waste over USY zeolite

Producing commodity aromatic hydrocarbons from textile waste is a promising approach to promote carbon neutrality and circular economy. Catalytic degradation of flax waste (FW) to generate furans and its subsequent Diels-Alder transformation to monocyclic aromatic hydrocarbons over USY zeolite were conducted. Experimental results indicated that USY catalyzed FW resulted in a 5.5-fold increase in furans production compared with the non-catalytic trial. The Si/Al molar ratio in USY played a determining role in furans formation, and a 5-fold increase was observed over USY with a Si/Al ratio of 5.3 as opposed to that with a Si/Al ratio of 11. Plastic waste, polyethylene (PE), co-fed with FW yielded 1.6 times higher aromatic hydrocarbons than polypropylene (PP). The selectivity to aromatic hydrocarbons reached 81.6% under 20% PE co-fed with 80% FW, in which benzene, toluene, and xylenes (BTX) were predominant products with the maximum selectivity of 68%. Furthermore, this study presents a cleaner approach for value-added resource recovery and sustainable management of textile and plastic waste.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Microbial assimilation of lignin-derived aromatic compounds and conversion to value-added products

Lignin is an abundant and sustainable source of aromatic compounds that can be converted to value-added products. However, lignin is underutilized, since depolymerization produces a complex mixture of aromatic compounds that is difficult to convert to a single product. Microbial conversion of mixed aromatic substrates provides a potential solution to this conversion challenge. Recent advances have expanded the range of lignin-derived aromatic substrates that can be assimilated and demonstrated efficient conversion via central metabolism to new potential products. Here, the development of additional non-model microbial hosts and genetic tools for these hosts have accelerated engineering efforts. However, yields with real depolymerized lignin are still low, and additional work will be required to achieve viable conversion processes.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Structure-Activity Relationships for Rates of Aromatic Amine Oxidation by Manganese Dioxide

New energetic compounds are designed to minimize their potential environmental impacts, which includes their transformation and the fate and effects of their transformation products. The nitro groups of energetic compounds are readily reduced to amines, and the resulting aromatic amines are subject to oxidation and coupling reactions. Manganese dioxide (MnO 2 ) is a common environmental oxidant and model system for kinetic studies of aromatic amine oxidation. Here in this study, a training set of new and previously reported kinetic data for the oxidation of model and energetic-derived aromatic amines was assembled and subjected to correlation analysis against descriptor variables that ranged from general purpose [Hammett $\sigma$ constants ($\sigma^-$), pK a s of the amines, and energies of the highest occupied molecular orbital (E HOMO )] to specific for the likely rate-limiting step [one-electron oxidation potentials (E ox )]. The selection of calculated descriptors (pK a ), E HOMO , and E ox ) was based on validation with experimental data. All of the correlations gave satisfactory quantitative structure-activity relationships (QSARs), but they improved with the specificity of the descriptor. The scope of correlation analysis was extended beyond MnO 2 to include literature data on aromatic amine oxidation by other environmentally relevant oxidants (ozone, chlorine dioxide, and phosphate and carbonate radicals) by correlating relative rate constants (normalized to 4-chloroaniline) to E HOMO (calculated with a modest level of theory).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Capturing the Coverage Dependence of Aromatics’ Adsorption through Mean-Field Models

To capture the dominant interactions (surface-mediated and through-space steric) in catalytic hydrodeoxygenation systems, coverage-dependent mean-field models of aromatic adsorption are developed on Pt(111) and Ru(0001). We derive three key insights from this work: (1) we can universally apply mean-field models to capture the coverage-dependent behavior of oxygenated aromatics on transition metal surfaces, (2) we can deconvolute surface-mediated and throughspace steric interactions from the mean-field model, and (3) we can develop relatively accurate models that predict the adsorption energy of aromatics on transition metal surfaces for the full coverage range using the work function at lowest modeled coverage. In conclusion, our approach enables the rapid prediction of coverage-dependent behavior of oxygenated aromatics on transition metal surfaces, reducing the computational cost associated with these studies by an order of magnitude.

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

Water Dynamics of Superacid Aromatic Proton Exchange Membranes for Fuel Cell Applications

Proton exchange membranes (PEMs) with high conductivity are of critical importance for the development of fuel cells, electrolyzers, and other electrochemical technologies. In this research, poly(1,1,2,2-tetrafluoro-2-phenoxyethane-1-sulfonic acid) (PTPS) with an aromatic polymer main chain and a perfluorinated superacidic polymer side chain was synthesized. The water dynamics of PTPS were characterized across various length scales using a combination of Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) and compared with Nafion, a standard perfluorinated PEM, and sulfonated poly(ether sulfone) (SPES 40), an aromatic PEM without perfluorinated superacid side chains. The T 1 and T 2 relaxation times of water in the samples probed by NMR increase from SPES 40 to PTPS to Nafion, indicating that the local motion of the water molecules becomes faster. This trend corresponds well with the relative fraction of bulk-like water determined using FTIR. At larger length scales, the diffusion coefficient of water was characterized using pulsed-field gradient NMR (PFG-NMR). At a longer diffusion time (Δ = 100 ms), PTPS has a smaller diffusion coefficient compared with both Nafion and SPES 40, due to restricted diffusion, and this effect is also evident in the proton conductivity of the hydrated membranes. From this comparison, it is apparent that the aromatic backbone and side chain type greatly influence the water dynamics in PEMs at various length scales and the water dynamics significantly impact the bulk proton conductivity. These insights will lead to new designs for aromatic PEMs and help to identify bottlenecks in current materials.

25 ENERGY STORAGE↗
DOE OSTI2019

Selective Production of Aromatics by Catalytic Fast Pyrolysis of Furan with In Situ Dehydrogenation of Propane

Catalytic fast pyrolysis (CFP) of furan was studied with the co-feeding of propane over ZSM-5, CrOx/Al2O3, and mixed catalysts with both ZSM-5 and CrOx/Al2O3 to combine the dehydrogenation of propane and CFP of furan in the presence of in situ generated propylene. With 15 vol % propane co-feeding, a slight increase in aromatic yield was observed over ZSM-5 catalyst. These enhancement was further improved by using mixed catalysts consisting of CrOx/Al2O3 and ZSM-5 with different weight ratios. Over the best mixed catalyst with CrOx/Al2O3 to ZSM-5 weight ratio of 2, a nearly 2-fold increase in the aromatic yield was obtained. The toluene selectivity was also increased from 37% to 50%. The increase in aromatic yield is directly dependent on the propane to total flow volume ratio. Moreover, the coke formation within ZSM-5 was also reduced, leading to a slower catalyst deactivation. From mechanistic studies, a two-step cascade reaction pathway was observed over the bifunctional mixed catalysts. It was proposed that propane dehydrogenates to propylene over CrOx/Al2O3. The propylene then reacts with furan within ZSM-5 catalyst to selectively form aromatics. This work demonstrates a simple and economical strategy to further improve the CFP technique.

bio-inspired↗
DOE OSTI2019

Method to Regioselectively Iodine-Tag Free-Phenolic Aromatic End-Groups in Lignin for 1 H– 13 C-HSQC NMR Analysis

Phenolic end-groups on lignin molecules are vital sites for continued lignification, their influence over lignin molecular properties, their ability to enhance lignin degradation, and their potential for derivatization to produce lignin materials. Here we use iodination to regioselectively tag, and HSQC-NMR to monitor, guaiacyl phenolic aromatic end-groups in lignins. Using dimeric lignin models, iodination at the 5-position of the phenolic ring was shown to be clean, and almost quantitative. Additionally, the 6-position C/H correlation peak shifted downfield in both carbon and proton dimensions in HSQC spectra. As phenolic aromatic rings could be selectively iodinated, and as their C6/H6 aromatic signals appear in a clear region of HSQC NMR spectra (different from the original position), we would have a new method for tagging and analyzing such phenolic aromatic rings in lignins if the method could be applied to the polymer. The new tagging approach was therefore applied to a synthetic guaiacyl lignin polymer (DHP) and a milled wood lignin (MWL) isolated from Japanese cedar ( Cryptomeria japonica ). The derivatization proceeded directly in the NMR tube, without needing isolation or purification, from which HSQC-NMR revealed that the diagnostic C6/H6 correlations matched one from the dimeric model compound. This phenolic unit tagging method adds a useful method to the lignin structural analysis toolbox, helping to gain a better understanding of lignin’s phenolic end-units.

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

Manipulating Aromaticity to Redirect Topochemical Polymerization Pathways

Topochemical polymerization (TCP) represents an essential route to create regio- and stereoregular polymers through solid-state transformations. Herein, we present an innovative strategy for controlling topochemical polymerization pathways by tailoring the terminal group aromaticity in the para-azaquinodimethane (AQM) ring system. Substituting phenyl groups with less aromatic furyl units extends significant spin density delocalization across the conjugated core upon thermal activation, inducing significant diradicaloid characters at furyl positions and enabling unconventional reactivities in both solution and solid states. Thermal treatment in toluene yields a unique cyclophane dimer formed via furyl-methine C-C coupling, confirmed by X-ray crystallography, while solid-state reactions produce polymers formed via both intercolumnar furyl-methine coupling and intracolumnar methine-methine coupling. The spin-center-directed mechanism underlying these transformations is validated through theoretical modeling and isotopic labeling experiments. This study highlights the prowess of aromaticity modulation in functional pro-aromatic systems, which enables the synthesis of polymers with main chain structures that are otherwise difficult to access.

Zhang, Qingsong↗
DOE OSTI2023

Complex regulation in a Comamonas platform for diverse aromatic carbon metabolism

Critical to a sustainable energy future are microbial platforms that can process aromatic carbons from the largely untapped reservoir of lignin and plastic feedstocks. Comamonas species present promising bacterial candidates for such platforms because they can use a range of natural and xenobiotic aromatic compounds and often possess innate genetic constraints that avoid competition with sugars. However, the metabolic reactions of these species are underexplored, and the regulatory mechanisms are unknown. Here we identify multilevel regulation in the conversion of lignin-related natural aromatic compounds, 4-hydroxybenzoate and vanillate, and the plastics-related xenobiotic aromatic compound, terephthalate, in Comamonas testosteroni KF-1. Transcription-level regulation controls initial catabolism and cleavage, but metabolite-level thermodynamic regulation governs fluxes in central carbon metabolism. Quantitative 13 C mapping of tricarboxylic acid cycle and cataplerotic reactions elucidates key carbon routing not evident from enzyme abundance changes. This scheme of transcriptional activation coupled with metabolic fine-tuning challenges outcome predictions during metabolic manipulations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Role of ring-enlargement reactions in the formation of aromatic hydrocarbons

Ring-enlargement reactions can provide a fast route towards the formation of six-membered single-ring or polycyclic aromatic hydrocarbons (PAHs). To investigate the participation of the cyclopentadienyl (C 5 H 5 ) radical in ring-enlargement reactions in high-temperature environments, a mass-spectrometric study was conducted. Experimental access to the C 5 H 5 high-temperature chemistry was provided by two counterflow diffusion flames. Cyclopentene was chosen as a primary fuel given the large amount of resonantly stabilized cyclopentadienyl radicals produced by its decomposition and its high tendency to form PAHs. In a second experiment, methane was added to the fuel stream to promote methyl addition pathways and to assess the importance of ring-enlargement reactions for PAH growth. The experimental dataset includes mole fraction profiles of small intermediate hydrocarbons and of several larger species featuring up to four condensed aromatic rings. Results show that, while the addition of methane enhances the production of methylcyclopentadiene and benzene, the concentration of larger polycyclic hydrocarbons is reduced. The increase of benzene is probably attributable to the interaction between the methyl and the cyclopentadienyl radicals. However, the formation of larger aromatics seems to be dominated only by the cyclopentadienyl driven molecular-growth routes which are hampered by the addition of methane. Furthermore, in addition to the experimental work, two chemical mechanisms were tested and newly calculated reaction rates for cyclopentadiene reactions were included. In an attempt to assess the impact of cyclopentadienyl ring-enlargement chemistry on the mechanisms’ predictivity, pathways to form benzene, toluene, and ethylbenzene were investigated. Results show that the updated mechanism provides an improved agreement between the computed and measured aromatics concentrations. Nevertheless, a detailed study of the single reaction steps leading to toluene, styrene, and ethylbenzene would be certainly beneficial.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Aromatic porous polymer network membranes for organic solvent nanofiltration under extreme conditions

Aromatic porous polymer networks (PPNs) are promising candidate materials for organic solvent nanofiltration (OSN) membranes, in which molecular-sieving selectivity, high permeability, and chemical/structural stability can be integrated. In this work, aromatic PPN membranes p-PPN, m-PPN and tri-PPN are fabricated by in situ aldol triple condensation cross-linking. These membranes demonstrate high stability, permeability and sharp selectivity in OSN, thanks to the aromatic nature of the backbone, high surface area (up to 1235 m 2 g -1 ), and narrowly distributed pore sizes. They possess a high organic solvent permeability so that a good permeance is achieved despite a thickness of over 100 μm. The molecular weight cut-off and molecular weight retention onset of these membranes are ~600 g mol -1 and 350 g mol -1 , respectively, making it possible to efficiently separate molecules from a complex mixture composed of compounds with only marginally different molecular weights. As a result of the highly stable nature of the aromatic backbones, these PPN membranes show retained structural integrity and OSN performance in the presence of either a strong acid or strong base for over 50 h. The extraordinary stability integrated with excellent permeability and selectivity renders these PPN membranes promising candidates for challenging OSN applications under extreme conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microwave spectra, molecular structure, and aromatic character of 4a,8a-azaboranaphthalene

The microwave spectra for seven unique isotopologues of 4a,8a-azaboranaphthalene [hereafter referred to as BN-naphthalene] were measured using a pulsed-beam Fourier transform microwave spectrometer. Spectra were obtained for the normal isotopologues with {sup 10}B, {sup 11}B, and all unique single {sup 13}C and the {sup 15}N isotopologue (with {sup 11}B), in natural abundance. The rotational, centrifugal distortion and quadrupole coupling constants determined for the {sup 11}B{sup 14}N isotopologue are A = 3042.712 75(43) MHz, B = 1202.706 57(35) MHz, C = 862.220 13(35) MHz, D{sub J} = 0.06(1) kHz, 1.5χ{sub aa} ({sup 14}N) = 2.5781(61) MHz, 0.25(χ{sub bb} − χ{sub cc}) ({sup 14}N) = − 0.1185(17) MHz, 1.5χ{sub aa} (11B) = − 3.9221(75) MHz, and 0.25(χ{sub bb} − χ{sub cc}) ({sup 11}B) = − 0.9069(24) MHz. The experimental inertial defect is Δ = − 0.159 amu Å{sup 2}, which is consistent with a planar structure for the molecule. The B—N bond length from the experimentally determined structure is 1.47 Å, which indicates π-bonding character between the B and N. The measured quadrupole coupling strengths provide important and useful information about the bonding, orbital occupancy, and aromatic character for this aromatic molecule. Extended Townes-Dailey analyses were used to determine the B and N electron sp{sup 2}-hybridized and p-orbital occupations. These results are compared with electron orbital occupations from the natural bond orbital option in theoretical calculations. From the analyses, it was determined that BN-naphthalene has aromatic character similar to that of other N-containing aromatics. The results are compared with similar results for B—N bonding in 1,2-dihydro-1,2-azaborine and BN-cyclohexene. Accurate and precise structural parameters were obtained from the microwave measurements on seven isotopologues and from high-level G09 calculations.

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

Dissociation of gas-phase anisole induced by low-energy electron interactions: understanding patterns of aromatic bond cleavage

Abstract In view of elucidating the fragmentation patterns of aromatic systems induced by low-energy electron interactions, dissociative electron attachment (DEA) to gas-phase anisole was performed. Anionic fragments resulting from this DEA process were detected by a quadrupole mass spectrometer, and ion yields of those fragments as a function of incident electron energy were rendered. Our study showed the formation of CH 3 − , HCC − , and OCH 3 − fragments, suggesting that various dissociation channels proceed out of DEA to anisole. We employed density functional theory to compute thermodynamic threshold energies for each potential dissociation channel. Those theoretical calculations supported the prediction that the CH 3 − and OCH 3 − fragments form via mechanisms of single-bond cleavage; the HCC − fragments may form through two-, three-, or four-body dissociation channels that entail hydrogen transfers and the cleavage of multiple aromatic bonds. The experimental resonance energies that form the CH 3 − , HCC − , and OCH 3 − fragments were 6.0 eV, 5.8 and 9.7 eV, and 9.8 eV, respectively. Given the classification of anisole as a monosubstituted aromatic species, our results explain generalizable patterns of electron-mediated dissociation in aromatic systems.

Finley, Jacob (ORCID:0009000606963352)↗
DOE OSTI2016

Structural Biology of Aromatic Amino Acid Biosynthesis in Plants: The Prephenate Branch Point

Plants are chemists that have spent the last 425 million years evolving unique secondary metabolites to communicate with their surroundings, defend themselves against pathogens, insects, and herbivores, and grow and develop. Many secondary metabolites are biosynthesized from the aromatic amino acids tryptophan, tyrosine, and phenylalanine, and the shikimate and aromatic amino acid biosynthetic pathways link primary and specialized metabolism. Prephenate aminotransferase (PAT) is a key enzyme in aromatic amino acid biosynthesis because its product, arogenate, is the immediate precursor for both tyrosine and phenylalanine. Interestingly, the enzyme has a dual role in metabolism and can also function as a classical aspartate aminotransferase. AtPAT is pyridoxal 5′‐phosphate‐dependent (PLP) enzyme belonging to the AAT‐like aspartate aminotransferase domain and follows a ping‐pong bi‐bi reaction mechanism through Schiff‐base formation to a catalytic K306 in the active site. Each subunit of the AtPAT dimer consists of a large domain and a small domain that belong to the α‐β class of protein fold. Despite the structural similarities to aspartate aminotransferases, the molecular basis of prephenate binding specificity remains elusive. To gain an understanding of the enzyme's chemistry and substrate selectivity, a 2.5 Å x‐ray structure of PAT from the model plant Arabidopsis thaliana (thale cress) was solved in complex with the PLP. To our knowledge, this is the first structure of a bona fide prephenate aminotransferase. Amino acid sequence comparisons of all known functional PATs shows that T84 and K169 are highly conserved; however, some enzymes annotated as PAT display sequence variations at these positions. Biochemical analysis of T84V, K169V, and T84V/K169V PAT reveals that the double mutant gained tyrosine aminotransferase activity and was able to convert 4‐hydroxyphenylpyruvate to tyrosine. T84 is on the opposite side of the active site pocket, while the amine backbone of K169 hydrogen bonds to PLP. We hypothesize that Thr84 and Lys169 are important for substrate recognition in the active site and will use these mutants in future crystallographic experiments. Overall, our structural studies will assist in understanding the role of this bi‐functional enzyme in the context of aromatic amino acid biosynthesis in plants. Support or Funding Information This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE‐1143954. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. Results shown in this report are derived from work performed at Argonne National Laboratory, Structural Biology Center at the Advanced Photon Source. Argonne is operated by UChicago Argonne, LLC, for the U.S. Department of Energy, Office of Biological and Environmental Research under contract DE‐AC02‐06CH11357.

Holland, Cynthia K.↗
DOE OSTI2025

Thermal and photoinduced chemistry of the aromatic Criegee intermediate, benzaldehyde oxide: Implications for indoor air quality

Essential oils contain a complex mixture of volatile organic compounds, ranging from terpenes to aromatics. When released into the indoor air environment or into the atmosphere, they may undergo oxidation to generate complex reactive intermediates that affect indoor air quality. Cinnamaldehyde is one such aromatic molecule that is abundant in essential oils. When released into the indoor air environment, it may undergo oxidation to form a carbonyl oxide (Criegee intermediate) with an aromatic substituent: benzaldehyde oxide. In this manuscript, we present a high-level quantum chemical study that shows that, unlike smaller atmospherically relevant Criegee intermediates, benzaldehyde oxide is expected to undergo solar photolysis on timescales that are competitive with its ground state unimolecular and bimolecular chemistry. We show that aromatic substitution leads to a drastic bathochromic shift in the spectroscopically relevant excited states, revealing that photolysis in the indoor or outdoor environment should not be neglected when modeling the climate and air quality implications of Criegee intermediates with extended conjugation. Here, we predict a range of products that may be important for forming lower volatility compounds via tropospherically relevant photochemistry. To motivate future experimental validation of our results, we propose a viable synthetic procedure of the relevant precursor for generating and stabilizing benzaldehyde oxide.

atmospheric photochemistry↗
NASA NTRS1986

The high-temperature oxidation of aromatic hydrocarbons

Chemical mechanisms of the atmospheric pressure, high-temperature (875-1500 K) gas-phase oxidation of benzene, toluene, ethylbenzene, and propylbenzene are described and discussed. Oxidation trends evident from turbulent flow reactor experiments serve as the basis for the mechanisms of the oxidation of benzene and alkylated aromatics. The potential effects of very high temperatures and pressures on the chemistry of oxidation of aromatics are described. The oxidation of benzene and phenyl radical has been found to proceed in a stepwise C6-C5-C4 sequence. Species profiles obtained from flow-reactor experiments suggest that the oxidation of benzene and phenyl radical follows the generalized route via phenoxy, cyclopentadienyl and butadienyl radical. The oxidation of the C4 species branches into multiple pathways that yield copious amounts of ethylene and acetylene. Certain major trends are evident: the alkylated aromatics on initial attack either form styrene, benzyl radical or benzene. The styrene reacts further to produce a benzyl radical or benzene. The oxidation of an alkylated aromatic hydrocarbon appears eventually to reduce to the oxidation of either phenyl radical or benzene.

Brezinsky, K.↗
NASA NTRS1995

Polybenzimidazoles via aromatic nucleophilic displacement

Novel molecular weight controlled and endcapped polybenzimidazoles (PBI) are prepared by the aromatic nucleophilic displacement reaction of di(hydroxyphenyl benzimidazole) monomers with activated aromatic dihalides or activated aromatic dinitro compounds. The PBI are endcapped with mono(hydroxyphenyl) benzimidazoles. The polymerizations are carried out in polar aprotic solvents such as N-methyl-2-pyrrolidinone or N,N-dimethylacetamide using alkali metal bases such as potassium carbonate at elevated temperatures under nitrogen. Mono(hydroxyphenyl) benzimidazoles are synthesizedby reacting phenyl-4-hydroxybenzoate with aromatic (o-diamine)s in diphenylsulfone. Molecular weight controlled and endcapped PBI of new chemical structures are prepared that exhibit a favorable combination of physical and mechanical properties.

Connell, John W.↗