Methylene Dianiline Research Articles

Elaboration and investigation of formulated polymer composites as some potential anticorrosion coatings for brass surface in 3.5% NaCl solution: theoretical approaches

ABSTRACT Polymer composite derivatives [(TGEMM/MDA/0%, TGEMM/MDA/6%, TGP/MDA/0%, and TGP/MDA/6%)] were elaborated through using tetraglycidyl ether of methyl-α-D-mannopyranoside (TGEMM) and 2,3,4,5-tetraglycidyloxy pentanal (TGP) as matrices, methylene dianiline (MDA) as curing agent and glass system (1-x) (2Bi2O3 - B2O3) - x BaO (with x = 0% and 6%) as filler. Different composites prepared were investigated as some potential anticorrosive protection coatings for brass electrode in sodium chloride medium (3.5% NaCl). Polymer composite coatings were characterized using FTIR spectroscopy, SEM/EDS, EFM, PDP, and EIS techniques. The anticorrosive protection efficiencies increase with increasing charge incorporated in composites, in the following order: TGP/MDA/0% < TGEMM/MDA/0% < TGP/MDA/6% < TGEMM/MDA/6% and the later achieving a maximum of 90.67% (EFM), 95.45% (PDP), and 97.86% (EIS), respectively. SEM/EDS characterization suggests a smooth surface in the presence of composite derivatives, which is more significant in the presence of TGEMM/MDA/6%. DFT calculations and MD simulations confirm the data obtained by experimental study and offer insights into its structural properties.

Mechanical and Thermal Properties of Epoxy Resin upon Addition of Low-Viscosity Modifier.

Thermoset-based polymer composites containing functional fillers are promising materials for a variety of applications, such as in the aerospace and medical fields. However, the resin viscosity is often unsuitably high and thus impedes a successful filler dispersion in the matrix. This challenge can be overcome by incorporating suitable low-viscosity modifiers into the prepolymer. While modifiers can aptly influence the prepolymer rheology, they can also affect the prepolymer curing behavior and the mechanical and thermal properties of the resulting matrix material. Therefore, this study investigates the effects that a commercial-grade low-viscosity additive (butyl glycidyl ether) has on a common epoxy polymer system (diglycidyl ether of bisphenol-A epoxy with a methylene dianiline curative). The weight percentage of the modifier inside the epoxy was varied from 0 to 20%. The rheological properties and cure kinetics of the resulting materials were investigated. The prepolymer viscosity decreased by 97% with 20 wt% modifier content at room temperature. Upon curing, 20 wt% modifier addition reduced the exothermic peak temperature by 12% and prolonged the time to reach the peak by 60%. For cured material samples, physical and thermo-mechanical properties were characterized. A moderate reduction in glass transition temperature and an increase in elastic modulus was observed with 20 wt% modifier content (in the order of 10%). Based on these findings, the selected material system is seen as an expedient base for material design due to the ease of processing and material availability. The present study thus provides guidance to researchers developing polymer composites requiring reduced prepolymer viscosity for successful functional filler addition.

Screening of polyurethane-degrading microbes using a quenching fluorescence probe by microfluidic droplet sorting

Excessive use of polyurethane (PU) polymers has led contributed to serious environmental pollution. The plastic recycling technology using microorganisms and enzymes as catalysts offers a promising green and low-carbon approach for managing plastic waste. However, current methods for screening PU-degrading strains suffer from drawbacks such as being time-consuming and inefficient. Herein, we present a novel approach for screening PU-degrading microorganisms using a quenching fluorescent probe along with the fluorescence-activated droplet sorting (FADS). The FPAP could specifically recognize the 4,4′-methylenedianiline (MDA) derivates released from PU degradation, with fluorescence quenching as a response. Based on the approach, we successfully screen two PU-degrading strains (Burkholderia sp. W38 and Bacillus sp. C1). After 20 d of cultivation, strain W38 and C1 could degrade 41.58% and 31.45% of polyester-PU film, respectively. Additionally, three metabolites were identified during the degradation of PU monomer (2,4-toluene diamine, 2,4-TDA) and a proposed degradation pathway was established. Consequently, the fluorescence probe integrated with microfluidic droplet systems, demonstrates potential for the development of innovative PU-biocatalysts. Furthermore, the identification of the 2,4-TDA degradation pathway provides valuable insights that can propel advancements in the field of PU biodegradation.

Exploring the essential features influencing the synthesis of methylenedianiline to support industrial processes

The most important intermediate of methylene diphenyl diisocyanate (MDI), the most widely and quantitatively produced isocyanate in the world, is methylenedianiline (MDA). MDA is industrially produced from the reaction of aniline and formaldehyde catalysed by inorganic acids, most commonly HCl. The reaction parameters used during the synthesis of MDA have a fundamental impact on the quality parameters of the resulting MDA product mixture, and thus on the properties of the final MDI product mixture as well. Although MDA is an important industrial intermediate, currently its synthesis at the industrial level is based on empirical rules, knowledge and rule of thumbs, the effects of production parameters and their magnitude on product properties are not known and not published in the literature. In this study, the correlations between the independent operating parameters and dependent product quality parameters characterizing the MDA mixture were explored by developing different regression models with the use of experimental laboratory synthesis data in order to support the industrial synthesis process with easily deployable models with satisfactorily high accuracy. After investigating the laboratory experiment data from a total of 46 individual laboratory experiments, it was found that with machine learning models almost all of the independent parameters can be described with satisfactory accuracy. The models presented in this work demonstrate that it is possible to develop models that can be used to adjust the ring distribution, isomer ratios and selectivity of the reaction with minimising by-product quantities according to market demands or to different objective functions by fine-tuning the production parameters., thus achieving an optimal product portfolio and operating cost for the industrial process as well.

Multi-technique characterization and thermal degradation study of epoxy modified resins designed for multifunctional applications

Tetraglycidyl methylene dianiline (TGMDA) was mixed with 1,4-Butanediol diglycidyl ether (BDE) (in a 4:1 mass ratio) and with a stoichiometric amount of the curing agent diaminodiphenyl sulfone which was solubilized at 120 °C for 20 min in the liquid mixture TGMDA + BDE. The so obtained unfilled epoxy resin matrix, denoted as ER, was blended with glycidyl polyhedral oligomeric silsesquioxane and carbon nanotubes in suitable proportions to obtain binary and ternary mixtures. Characterization of the formulated materials was performed using different experimental techniques, such as Dynamic mechanical analysis, Thermogravimetry (TG), Field emission scanning electron microscopy. Furthermore, the investigation of the flame behavior was carried out by the limiting oxygen index and mass loss calorimeter measurements. Direct current measurements and investigation by Tunneling atomic force microscopy of the conductive nanodomain map allowed the evaluation of the electrical properties of the developed nanofilled systems. The TG data related to thermal decomposition of ER and its binary and ternary mixtures were processed according to isoconversional kinetic analysis by assuming a non-Arrhenian behavior of the temperature function, and lifetime prediction was estimated at suitable relatively low temperatures and possible relation between the thermal stability and the presence of each component was discussed. This method of kinetic analysis paves the way for the possibility of evaluating in a more realistic way, on the basis of thermal stability, the potential application of structural resins with primary load functions in contact with hot areas of aeronautical aircraft engines.

One-Dimensional Covalent Organic Framework-Based Multilevel Memristors for Neuromorphic Computing.

Memristors are essential components of neuromorphic systems that mimic the synaptic plasticity observed in biological neurons. In this study, a novel approach employing one-dimensional covalent organic framework (1D COF) films was explored to enhance the performance of memristors. The unique structural and electronic properties of two 1D COF films (COF-4,4'-methylenedianiline (MDA) and COF-4,4'-oxydianiline (ODA)) offer advantages for multilevel resistive switching, which is a key feature in neuromorphic computing applications. By further introducing a TiO2 layer on the COF-ODA film, a built-in electric field between the COF-TiO2 interfaces could be generated, demonstrating the feasibility of utilizing COFs as a platform for constructing memristors with tunable resistive states. The 1D nanochannels of these COF structures contributed to the efficient modulation of electrical conductance, enabling precise control over synaptic weights in neuromorphic circuits. This study also investigated the potential of these COF-based memristors to achieve energy-efficient and high-density memory devices.

One‐Dimensional Covalent Organic Framework‐Based Multilevel Memristors for Neuromorphic Computing

AbstractMemristors are essential components of neuromorphic systems that mimic the synaptic plasticity observed in biological neurons. In this study, a novel approach employing one‐dimensional covalent organic framework (1D COF) films was explored to enhance the performance of memristors. The unique structural and electronic properties of two 1D COF films (COF‐4,4′‐methylenedianiline (MDA) and COF‐4,4′‐oxydianiline (ODA)) offer advantages for multilevel resistive switching, which is a key feature in neuromorphic computing applications. By further introducing a TiO2 layer on the COF‐ODA film, a built‐in electric field between the COF‐TiO2 interfaces could be generated, demonstrating the feasibility of utilizing COFs as a platform for constructing memristors with tunable resistive states. The 1D nanochannels of these COF structures contributed to the efficient modulation of electrical conductance, enabling precise control over synaptic weights in neuromorphic circuits. This study also investigated the potential of these COF‐based memristors to achieve energy‐efficient and high‐density memory devices.

Depolymerization of the polyester-polyurethane by amidase GatA250 and enhancing the production of 4,4'-methylenedianiline with cutinase LCC.

Polyurethane (PU) is a complex polymer synthesized from polyols and isocyanates. It contains urethane bonds that resist hydrolysis, which decreases the efficiency of biodegradation. In this study, we first expressed the amidase GatA250, and then, assessed the enzymatic characterization of GatA250 and its efficiency in degrading the polyester-PU. GatA250 degraded self-synthesized thermoplastic PU film and postconsumption foam with degradation efficiency of 8.17% and 4.29%, respectively. During the degradation, the film released 14.8µm 4,4'-methylenedianiline (MDA), but 1,4-butanediol (BDO) and adipic acid (AA) were not released. Our findings indicated that GatA250 only cleaved urethane bonds in PU, and the degradation efficiency was extremely low. Hence, we introduced the cutinase LCC, which possesses hydrolytic activity on the ester bonds in PU, and then used both enzymes simultaneously to degrade the polyester-PU. The combined system (LCC-GatA250) had higher degradation efficiency for the degradation of PU film (42.2%) and foam (13.94%). The combined system also showed a 1.80 time increase in the production of the monomer MDA, and a 1.23 and 3.62 times increase in the production of AA and BDO, respectively, compared to their production recorded after treatment with only GatA250 or LCC. This study provides valuable insights into PU pollution control and also proposes applicable solutions to manage PU wastes through bio-recycling.

Risk assessment-based verification of the CertiPURTM limit values for toluene diamine and methylene dianiline in flexible polyurethane foam.

Flexible polyurethane foams (PUF) are used in many consumer products. PUF may contain trace levels of aromatic diamine impurities that could represent a potential health risk. The risk associated with sleeping on a PUF mattress was evaluated. Toxicity benchmarks for sensitization and non-cancer endpoints were derived from the respective points-of-departure using standard assessment factors. For the cancer endpoints, toxicity benchmarks were derived from the 25th-percentile values of animal studies. Recently published emission and migration data allowed to link exposure with the CertiPURTM voluntary quality limits of ≤5mg.kg-1 for 2,4-toluene diamine and 4,4'-methylene dianiline in PUF. Using conservative exposure scenarios, lifetime-average daily internal doses from the combined inhalation and dermal exposures were calculated. Margins of safety for non-cancer and sensitization endpoints were >104. The theoretical excess cancer risk was ≤1.5 × 10-7. It is concluded that sleeping on a mattress that satisfies the CertiPUR limit value does not pose undue risk to consumers.

Deamination of Polyols from the Glycolysis of Polyurethane.

Methylenedianiline (MDA) is a secondary, undesired, product of the glycolysis process of polyurethane (PU) scraps due to hydrolysis and pyrolysis side reactions. As an aromatic and carcinogen amine, MDA poses different problems in handling, transporting, and labelling recycled polyols derived from glycolysis, hindering the closure of PU recycling loop. Aiming to provide a solution to this issue, in this work different deaminating agents (DAs) were investigated with the purpose of analyzing their reactivity with MDA. A first part of the study was devoted to the analysis of MDA formation as a function of reaction time and catalyst concentration (potassium acetate) during glycolysis. It was observed that the amount of MDA increases almost linearly with the extent of PU depolymerization and catalyst content. Among the DAs analyzed 2-ethylhexyl glycidyl ether (2-EHGE), and acetic anhydride (Ac2 O) showed interesting performance, which allowed MDA content to be diminished below the limit for labelling prescription in 30 minutes. PU rigid foams were, therefore, synthesized from the corresponding recycled products and characterized in terms of thermal and mechanical performance. Ac2 O-deaminated polyols led to structurally unstable foams with poor compressive strength, while 2-EHGE-deaminated products allowed the production of foams with improved mechanical performance and unaltered thermal conductivity.

Toughened and reinforced the petroleum-based epoxy resin via thermotropic liquid crystal bio-based counterpart

Significant improvements in the fracture resistance of epoxy resins are highly desirable for various applications, but there is a “seesaw” between toughness and other properties. In this study, we incorporated a bio-based thermotropic liquid crystal epoxy precursor (THMT-EP) containing multi-aromatic s-triazine structure derived from vanillin into petroleum-based counterpart tetraglycidyl-4,4′-methylene dianiline (TGDDM) with 4,4-diaminodiphenyl sulfone (DDS) as a curing agent, and the cured co-blended resin system was able to immobilize the formed liquid crystal domains in a cross-linked network under optimal curing conditions. The blended system with THMT-EP added at 30 wt% exhibited the largest impact strength (31.1 kJ m−2), which was 90.8 % higher than pristine TGDDM/DDS epoxy resin. When THMT-EP was added at 50 wt%, the flexural modulus and strength of the blended system were as high as 4016 MPa and 171.5 MPa, respectively, which were 5.1 % and 48.5 % higher than those of the TGDDM/DDS system, and the resultant was able to pass the highest V-0 level of vertical combustion test. The above results show that it is feasible to improve the performance of petroleum-based epoxy resins with bio-based thermotropic liquid crystal counterpart.

Increased Endocrine Activity of Xenobiotic Chemicals as Mediated by Metabolic Activation.

The US Environmental Protection Agency (USEPA) is faced with long lists of chemicals that require hazard assessment. The present study is part of a larger effort to develop in vitro assays and quantitative structure-activity relationships applicable to untested chemicals on USEPA inventories through study of estrogen receptor (ER) binding and estrogen-mediated gene expression in fish. The present effort investigates metabolic activation of chemicals resulting in increased estrogenicity. Phenolphthalin (PLIN) was shown not to bind rainbow trout (Oncorhynchus mykiss) ER (rtER) in a competitive binding assay, but vitellogenin (Vtg) expression was induced in trout liver slices exposed to 10-4 and 10-3.7 M PLIN. Phenolphthalein (PLEIN), a metabolite of PLIN, was subsequently determined to be formed when slices were exposed to PLIN. It binds rtER with a relative binding affinity to 17β-estradiol of 0.020%. Slices exposed to PLEIN expressed Vtg messenger RNA (mRNA) at 10-4.3 , 10-4 , and 10-3.7 M, with no detectable PLIN present. Thus, Vtg expression noted in PLIN slice exposures was explained by metabolism to PLEIN in trout liver slices. A second model chemical, 4,4'-methylenedianiline (MDA), was not shown to bind rtER but did induce Vtg mRNA production in tissue slices at 10-4.3 , 10-4 , and 10-3.7 M in amounts nearly equal to reference estradiol induction, thus indicating metabolic activation of MDA. A series of experiments were performed to identify a potential metabolite responsible for the observed increase in activity. Potential metabolites hydroxylamine-MDA, nitroso-MDA, azo-MDA, and azoxy-MDA were not observed. However, acetylated MDA was observed and tested in both ER-binding and tissue slice Vtg induction assays. Environ Toxicol Chem 2023;42:2747-2757. © 2023 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Mucosal damage and γ-H2AX formation in the rat urinary bladder induced by aromatic amines with structures similar to o-toluidine and o-anisidine.

Although aromatic amines are widely used as raw materials for dyes, some, such as o-toluidine and o-anisidine, have shown concerning results regarding carcinogenicity in the urinary bladder. We have recently developed a short-term detection method for bladder carcinogens using immunohistochemistry for γ-H2AX, a DNA damage marker. Here, using this method, we evaluated aromatic amines with structures similar to o-toluidine and o-anisidine for bladder mucosal damage and potential carcinogenicity. In total, 17 aromatic amines were orally administered to male F344 rats for 28days, and histopathological examination and γ-H2AX immunostaining of the urinary bladder were performed. Histopathological analysis revealed that seven aromatic amines, including 4-chloro-o-toluidine (4-CT), o-aminoazotoluene, 2-aminobenzyl alcohol (ABA), o-acetotoluidine (o-AT), 3,3'-dimethoxybenzidine, 4-aminoazobenzene (AAB), and 4,4'-methylenedianiline (MDA), induced various bladder lesions, such as hemorrhage, necrosis, and urothelial hyperplasia. The morphological characteristics of mucosal damage induced by these substances were divided into two major types: those resembling o-toluidine and those resembling o-anisidine. Six of these aromatic amines, excluding MDA, also caused significant increases in γ-H2AX formation in the bladder urothelium. Interestingly, 4-CT did not cause mucosal damage or γ-H2AX formation at the lower dose applied in previous carcinogenicity studies. These results showed for the first time that o-AT and ABA, metabolites of o-toluidine, as well as AAB caused damage to the bladder mucosa and suggested that they may be bladder carcinogens. In addition, 4-CT, which was thought to be a noncarcinogen, was found to exhibit bladder toxicity upon exposure to high doses, indicating that this compound may contribute to bladder carcinogenesis.

Model-Assisted Interpretation of 4,4'-Methylene Dianiline Adsorption on Soils at Micromolar Concentrations.

Adsorption kinetics and isotherms were determined for 4,4'-methylene dianiline (MDA) on five diverse soils at nominal concentrations of 0.01-1.0 mg L-1 (nominal soil loading 0.1-40 μg gs -1 ). The data were used to model the adsorption process based on the two-step mechanism that is characteristic of the adsorption of aromatic amines, consisting of a physical equilibrium between the aqueous phase and the soil organic matter and a chemical reaction between the adsorbed MDA and reactive sites in the soil organic matter. Generic parameters were determined that enabled application of the model to other soils, which was checked against previously published data for MDA adsorption. At the low concentrations evaluated, the adsorption process took place almost exclusively in the organic matter without the need to account for a separate ion exchange process with the soil mineral fraction. Physical adsorption was found to be mainly dependent on the protonation state of MDA and increased with decreasing pH of the soils. Because of the chemical reaction taking place, adsorption equilibrium constants (organic-carbon partition coefficient [KOC ]) normalized to the organic carbon content in the soil gradually increased with time; and it was demonstrated that, at steady-state conditions, values of log KOC > 3.5 can be expected for most any soil at conservatively estimated potential environmental MDA concentrations. Environ Toxicol Chem 2023;42:2580-2588. © 2023 SETAC.

Catalytic upcycling of waste bisphenols via tandem amination-ammonolysis to high value diamines

Hydrogenated methylene dianiline (H12MDA) is a valuable precursor for thermoplastic polyurethane. Traditionally, H12MDA is obtained by hydrogenation of methylene dianiline (MDA). However, the route from aniline to MDA produces large acidic waste streams linked to the nitration of benzene and the HCl-catalyzed reaction with formaldehyde, as well as a poor selectivity for the 4,4′-isomer in the condensation reaction with formaldehyde. Herein, we report a green and efficient amination process for synthesis of H12MDA starting from (waste) bisphenols. Palladium on moderately acidic catalyst supports (carbon, Al2O3, ZrO2) provided excellent yields of H12MDA (>97%) in short reaction times (3 h) at 200 °C, with limited addition of H2 and NH3. It was found that the reaction partially proceeds via a secondary amine intermediate. A high dispersion of palladium is essential to achieve high yields of the desired H12MDA. Finally, the use of polycarbonate as an alternative feedstock for H12MDA was demonstrated via a tandem ammonolysis-amination process.

Development of new polymer composites formulated by glass as a potential protective coating for 3D printed H13 steel in acidic medium: DFT, MC and MD computational

This paper highlights the anticorrosion protection potential of new EPT/MDA, EPT/MDA/0.04 and EPT/MDA/0.08 cured epoxy polymer composite coatings to protect 3D printed H13 steel surface in 1 M HCl medium. These polymer composite coatings were obtained through a condensation reaction between 2,4,6-tris(4-(2-(4-(2-methoxy oxiran) phenyl) propan-2-yl)phenoxy)-1,3,5-triazine (EPT) and methylene dianiline (MDA) as crosslinking agent. Varying percentages (0.04 and 0.08) of glass oxide were added as charge. Characterization of these coatings was performed using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), electrochemical measurements (PDP and EIS) and contact angle (CA). The corrosion currents density showed a significant decrease in the presence of different polymer composite coatings. The anticorrosion protection was shown to increases with increasing charge of oxide glass in composite, achieving a maximum of 93% in protection efficiency for EPT/MDA/0.08. A morphology analysis by SEM indicated a smooth surface in presence of polymer composites, even more significantly with EPT/MDA/0.08. Furthermore, FTIR data confirm the retention of EPT/MDA, EPT/MDA/0.04 and EPT/MDA/0.08 on the H13 steel surface. DFT calculation provided insights on the nature and active centers of the corrosion inhibitory efficiency of the polymer composite coatings assessed. MC and MD simulation showed that the investigated polymer composites have the maximum inhibition efficiencies at nitrogen and oxygen heteroatoms.

Rapid and selective removal of aromatic diamines from the polyurethane bio-hydrolysate by β-cyclodextrin appended hyper-cross-linked porous polymers

During the degradation and recycling process of polyurethane (PU) through biotechnology, it is essential to remove toxic and hazardous aromatic diamines (4,4′-methylene dianiline (MDA), 2,4-toluene diamine (TDA)) selectively and rapidly before the biorefinery of residues in the PU hydrolysate. In this study, β-cyclodextrin (β-CD) appended hyper-cross-linked polymers (HCPs) with high porosity were constructed via the Friedel-Crafts alkylation reaction. In particular, with partial hydroxyl groups on β-CD units, the hydrophilicity of HCP-BCDOH was drastically improved, contributing to fast adsorption equilibrium for TDA (1 min) and MDA (15 min). Besides, the isothermal experiments demonstrate high maximum theoretical adsorption capacities of HCP-BCDOH upon MDA (2.27 mmol·g−1) and TDA (1.53 mmol·g−1). Moreover, spectral analysis and thermodynamic experiments revealed the adsorption mechanism of aromatic diamines by HCP-BCDOH, which is mainly controlled by weak interactions, involving “host–guest” interaction, hydrophobic interaction, and π-π stacking. These interactions endow HCP-BCDOH with high selectivity and removal efficiencies towards MDA and TDA. Owing to the exceptional adsorption properties and high reusability of HCP-BCDOH, it may offer a promising and efficient adsorbent for the removal of aromatic amines from the PU bio-hydrolysate.

Hierarchical LTL Zeolite as an Efficient and Sustainable Solid Acid Catalyst for Replacing HCl in the Production of Polyurethane Intermediates.

In many industrially important reactions, caustic mineral acid catalysts have been successfully replaced with green solid acids such as zeolites. In this context, extensive efforts have been devoted to replacing HCl to produce methylenedianiline (MDA), a key intermediate in polyurethane production. Unfortunately, limited success has been achieved thus far due to low activity, selectivity towards the desired 4,4'-MDA, and rapid catalyst deactivation. Here we report that meso-/microporous hierarchical LTL zeolite exhibits unprecedentedly high activity, selectivity, and stability. The one-dimensional cage-like micropores of LTL promote the bimolecular reaction between two para-aminobenzylaniline intermediates to selectively produce 4,4'-MDA and inhibit the formation of undesired isomers and heavy oligomers. Meanwhile, the secondary mesopores alleviate mass transfer limitations, resulting in a 7.8-fold higher MDA formation rate compared to solely microporous LTL zeolite. Due to suppressed oligomer formation and fast mass transfer, the catalyst exhibits inappreciable deactivation in an industrially relevant continuous flow reactor.

Hierarchical LTL Zeolite as an Efficient and Sustainable Solid Acid Catalyst for Replacing HCl in the Production of Polyurethane Intermediates

AbstractIn many industrially important reactions, caustic mineral acid catalysts have been successfully replaced with green solid acids such as zeolites. In this context, extensive efforts have been devoted to replacing HCl to produce methylenedianiline (MDA), a key intermediate in polyurethane production. Unfortunately, limited success has been achieved thus far due to low activity, selectivity towards the desired 4,4′‐MDA, and rapid catalyst deactivation. Here we report that meso‐/microporous hierarchical LTL zeolite exhibits unprecedentedly high activity, selectivity, and stability. The one‐dimensional cage‐like micropores of LTL promote the bimolecular reaction between two para‐aminobenzylaniline intermediates to selectively produce 4,4′‐MDA and inhibit the formation of undesired isomers and heavy oligomers. Meanwhile, the secondary mesopores alleviate mass transfer limitations, resulting in a 7.8‐fold higher MDA formation rate compared to solely microporous LTL zeolite. Due to suppressed oligomer formation and fast mass transfer, the catalyst exhibits inappreciable deactivation in an industrially relevant continuous flow reactor.

Synthesis and Characterization of Flexible Meta‐Aramid Modified with 4,4′‐Methylenedianiline

AbstractMeta‐aramids (poly(m‐phenylene isophthalamide), PMIA) have excellent flame, heat resistance, and electrical insulation. However, the rigid molecular backbone of PMIA and the strong hydrogen bonding force between its molecular chains make it poorly flexible, soluble, and processed. In this study, a series of modified PMIA containing methylene groups on the main chain (APMIA‐n, where n is the molar fraction of 4,4′‐methylenedianiline (MDA) in m‐phenylenediamine, and n = 0, 5, 10, 15, 20) is synthesized by introducing different ratios of MDA into PMIA by copolymerization. APMIA‐n films are prepared by the solution casting method. The results show some improvement in the solubility of APMIA‐n in polar organic solvents such as N,N‐dimethylformamide and dimethyl sulfoxide. With the increase of the molar fraction of MDA, the tensile modulus of obtained APMIA‐n films decrease from 4.62 to 2.98 GPa, indicating that the flexibility of the films is evidently increased. APMIA‐n films are self‐extinguishing which suggests that the addition of MDA during copolymerization has a slight influence on the flame resistance of the synthesized PMIA. Moreover, APMIA‐n films containing MDA components exhibit good optical transparency, which may expand the application of PMIA in more fields such as packaging and screen display.