Diamine Research Articles

Manganese Catalyzed Oxidative Coupling of Aromatic Diamines and Alcohols with Aminoxyl Radicals in the Synthesis of Benzimidazoles

AbstractWe herein report a solvent‐free, oxidative coupling reaction of alcohols with aromatic diamines in air. 9‐Azabicyclo[3.3.1]nonan‐N‐oxyl (ABNO) in combination with a manganese(II) catalyst, serves to effectively promote the reaction, leading to the selective synthesis of 2‐substituted benzimidazoles and 1,2‐disubstituted benzimidazoles.

Design, synthesis and computational study of benzimidazole derivatives as potential anti-SARS-CoV-2 agents

As the human world has constantly been plagued by the COVID-19 pandemic since its emergence, researchers have been putting mountain-high efforts into designing new weapons to combat the virus. To join this battle against coronavirus, the present communication explores the synthesis of four benzimidazoles (1–4) from aromatic diamines utilizing two separate synthetic strategies. Afterwards, the synthesized four benzimidazole analogues along with sixteen previously synthesized benzimidazole analogues from our laboratory were subjected to in silico prediction of drug-likeness properties and ADMET (absorption, distribution, metabolism, excretion and toxicity) parameters. Additionally, all the compounds were computationally evaluated through molecular docking analysis against four vital target proteins of SARS-CoV-2 namely the main protease, the papain-like protease, the RNA-dependent RNA polymerase and the spike receptor binding domain to gain insight into the interaction pattern of the ligands with the binding site residues of the protein targets and thus to analyze the SARS-CoV-2 inhibitory proficiency of the synthesized derivatives. Among the studied ligands, compounds 1, 2, 13, 14, 15, 16 and 18 displayed excellent docking scores against two or more protein targets as compared to the established antiviral drugs Nirmatrelvir and Remdesivir. Based on the docking scores, the best four complexes (compound 18-Mpro, compound 2-PLpro, compound 1-RdRp and compound 2-spike-RBD) were subjected to molecular dynamic (MD) simulation to examine the stability of the complexes during the simulation period. This integrated molecular docking and MD simulation study suggested two compounds (1 and 18) that could be evolved as promising candidates for the design and discovery of new anti-SARS-CoV-2 agents.

Synthesis and characterization of fluorinated polyurethaneimide electro-optic waveguide material with novel structure

Abstract Structurally novel fluorinated polyurethaneimide (PUI) electro-optic polymer based on chromophore molecule b, diisocyanate MDI and anhydride BPAFDA was synthesized by stepwise polymerization of oligomer PUI with fluorinated aromatic diamines BATB and BATPP. Electro-optic (EO) PUI chain structure had the structure of polyimide and polyurethane chain segments, integrating the advantages of polyimide and polyurethane. The PUI possessed good film-forming property, a high glass transition temperature (T g = 193 °C) and good thermal stability (5 % weight loss temperature T d up to 320 °C). Y-Structured inverted ridge polymer optical waveguides were designed and fabricated using the PUI as the waveguide core material. The PUI had good optical performance with an EO coefficient (γ33) of 79 pm/V and 1.1 dB/cm optical propagation loss at a wavelength of 1550 nm. The results showed that the synthesized PUI met the performance requirements for the preparation of polymer optical waveguide devices and was suitable as a polymer electro-optic waveguide material.

Enhancing flame retardancy and optical functionality in multifunctional devices through advanced design of phosphorus‐containing copoly(imide‐oxadiazole)s

AbstractThe combination of flame retardance and optical functionality in phosphorus‐containing copoly(imide‐oxadiazole)s offers a remarkable opportunity for the development of advanced and multifunctional devices, including organic light‐emitting diodes, sensors, and photovoltaics. In this context, a series of phosphorus‐containing copoly(imide‐oxadiazole)s were synthesized through a polycondensation reaction. This involved an aromatic commercial dianhydride, 4,4′‐(4,4′‐isopropylidenediphenoxy)bis(phthalic anhydride), a diamine with phosphorus in the main and side chains, and various aromatic diamines with 1,3,4‐oxadiazole rings. To achieve this, a solution imidization method was employed, which effectively converted the poly(amic acid) intermediates into the corresponding polyimides with high efficiency. The chemical structure and thermal properties of the resulting polymers were investigated. All polymers exhibited high thermal stability. Moreover, the absorption bands observed in dichloromethane, N,N‐dimethylformamide, methanol, and N‐methyl‐2‐pyrrolidone exhibited weak intensities, appearing as shoulders, with maximum values around 270, 303, and 310 nm. In most solvents, the photoluminescence spectra of the polymers showed a single emission band. However, one of the polymers exhibited two emission bands due to pendant groups that disrupted the molecular structure. The fluorescence of these derivatives was influenced by the polarity and proticity of the solvents. Furthermore, they exhibited large Stokes shifts, indicating extended conjugation and the potential to maximize luminescence efficiency. Protonation and deprotonation of polyimides alter their optical properties. These findings provide insights for the design of materials with improved optical performance.

Preparation and Properties of Atomic-Oxygen Resistant Polyimide Films Based on Multi-Ring Fluoro-Containing Dianhydride and Phosphorus-Containing Diamine.

Colorless and transparent polyimide (CPI) films with good atomic oxygen (AO) resistance and high thermal endurance are highly required in low earth orbit (LEO) space exploration. Conventional CPI films based on fluoro-containing 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) have been widely used in space applications. However, the AO erosion yields and glass transition temperatures (Tg) of the 6FDA-based CPI films have to be modified in order to meet the severe serving environments. In the current work, novel CPI films based on a multi-ring fluoro-containing 9,9-bis(trifluoromethyl)xanthene-2,3,6,7-tetracarboxylicdianhydride (6FCDA) monomer were developed. In order to enhance the AO resistance of the derived CPI film, a phosphorus-containing aromatic diamine, 2,5-bis[(4-aminophenoxy)phenyl]diphenylphosphine oxide (BADPO) was used to polymerize with the dianhydride to create the organo-soluble resin. Then, two phosphorus-containing CPI films (PPI), including PPI-1 (6FDA-BADPO) and PPI-2 (6FCDA-BADPO) were prepared by thermally curing of the PPI solutions at elevated temperatures. The PPI films maintained good optical transparency with transmittance values over 80% at a wavelength of 450 nm. PPI-2 exhibited a Tg value of 311.0 °C by differential scanning calorimetry (DSC) measurement, which was 46.7 °C higher than that of the PPI-1 counterpart (Tg = 264.3 °C). In addition, the PPI-2 film showed a coefficient of linear thermal expansion (CTE) value of 41.7 × 10-6/K in the range of 50~250 °C, which was apparently lower than that of the PPI-1 sample (CTE = 49.2 × 10-6/K). Lastly, both of the two PPI films exhibited good AO resistance with the erosion yields (Ey) of 6.99 × 10-25 cm3/atom for PPI-1 and 7.23 × 10-25 cm3/atom for PPI-2 at an exposure flux of 5.0 × 1020 atoms/cm2. The Ey values of the current PPI films were obviously lower than that of the standard polyimide (PI) film based on pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA) (Ey = 3.0 × 10-24 cm3/atom).

Hollow CeO2 Nanospheres as Catalyst for the Conversion of Aromatic Diamines to Benzimidazoles

Hollow CeO₂ Nanospheres as Catalyst for the Conversion of Aromatic Diamines to Benzimidazoles

Aromatic amination of refined rice bran oil previously epoxidized with Novozym 435

Objective: To aromatically aminate refined rice bran oil (RBO), a by-product of the rice agro-industry,through a chemical-enzymatic epoxidation based on Novozym 435 and p-xylylenediamine insertion.Design/Methodology/Approach: Refined RBO was epoxidized with H2O2/Novozym 435. The resultingepoxidized rice bran oil (eRBO) was functionalized with the p-xylylenediamine aromatic diamine via epoxyring-opening (X-eRBO), using ZnCl2 as catalyst. Iodine value (IV), saponification value (SV), and oxiraneoxygen content (OOC) were determined to evaluate structural changes in oils. The RBO, the eRBO, and theX-eRBO were identified using FTIR, 1H, and 13C NMR.Results: The IV, the SV, and the OOC suggest that the synthesis of eRBO and X-eRBO were effective. Theincrease of molecular weight in eRBO point to the formation of 6 epoxy rings per original triglyceride. TheOOC value of X-eRBO was 22% lower than the OOC value of eRBO, implying that an effective aromaticamination was achieved. The FTIR, 1H and 13C NMR spectroscopy analysis confirmed the epoxidation andamination of the RBO.Study Limitations/Implications: X-eRBO may be a feasible precursor for value-added products, such ascrosslinked polymers or corrosion inhibitors.Findings/Conclusions: Refined rice bran oil was aromatically aminated after two stages under mild thermal conditions. This result was achieved with an epoxidation sequence with H2O2/Novozym 435, followed byfunctionalization with p-xylylenediamine.

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.

Synchronously enhancing thermal conductivity and dielectric properties in epoxy composites via incorporation of functionalized boron nitride.

Polymer-like dielectrics with superb thermal conductivity as well as high dielectric properties hold great promise for the modern electronic field. Nevertheless, integrating these properties into a single material simultaneously remains problematic due to their mutually limited physical connotations. In this study, we developed high-quality thermally conductive epoxy composites with excellent dielectric properties. This was achieved by incorporating surface-functionalized microscale hexagonal boron nitride (BN) along with N-[3-(Trimethoxysilyl)propyl]ethylene diamine (DN) and N-[3-(Trimethoxysilyl)propyl]aniline (PN). In the resulting epoxy composite, microscale BN serves as the primary building block for establishing the thermally conductive network, while silica particles act as bridges to regulate heat transfer and reduce interfacial phonon-scattering. The prepared composites were thoroughly examined across various filler contents (ranging from 10 to 80 wt%). Among them, the DNBN/epoxy composite exhibited higher thermal conductivity (in-plane: 47.03 W m-1 K-1) at 60 wt% filler content compared to BN/epoxy (39.40 W m-1 K-1) and PNBN/epoxy (33 W m-1 K-1) composites. These results highlight the usefulness of surface modification of BN in improving compatibility between fillers and epoxy, ultimately reducing composite viscosity. Furthermore, the DNBN/epoxy composite at 60 wt% demonstrated superb dielectric constant (∼6.15) without compromising on dissipation loss (∼0.06). The strategy adopted in this study offers significant insights into designing dielectric thermally conductive composites with superior performance outcomes.

Triazine‐based mesoporous organic polymers as palladium supports: physicochemical properties, porosity and catalytic performance in Suzuki coupling reaction

AbstractThis article reports the preparation of new mesoporous triazine‐based organic polymers and their characterization. The polymers were synthesized via a nucleophilic condensation reaction between cyanuric chloride and bisphenols or aromatic diamine linkers. As a result, two types of triazine‐based polymers were prepared: triazine‐ether and triazine‐amine polymers. The polymers reveal a mesoporous nature with surface area values ranging between 345 and 1275 m2 g−1 and mesopore volume between 0.273 and 1.03 cm3 g−1. These values were determined from argon gas isotherms at 87 K. The pore size distribution also confirmed the micro–mesoporosity, which reached up to 3.0 nm for all polymers. The triazine‐amine polymer shows good thermal oxidative stability up to 450 °C. Motivated by the mesopore size, the new polymers were also employed as palladium nanoparticle supports. The X‐ray diffraction technique indicated the successful incorporation of palladium nanoparticles, and Fourier transform infrared measurements proved that the framework of the polymers was retained after forming palladium supports. To ensure the catalytic reactivity of palladium nanoparticles, we employed one example as a catalyst in a Suzuki coupling reaction. The catalyst exhibited remarkable recyclability, maintaining catalytic efficiency through seven cycles, thereby enabling the use of palladium‐loaded triazine‐based polymeric catalysts in a variety of organic reactions in future. © 2023 Society of Industrial Chemistry.

AROMATIC POLYMER HAVING BOTH AZOBENZENE AND AZOMETHINE UNITS IN THE MAIN CHAIN AS AN EFFICIENT PHOTO-RESPONSIVE MATERIAL

Azobenzene and aromatic azomethine groups acting as versatile photoreversible optically switchable scaffolds attract much interest as efficient building blocks for the construction of light-responsive materials. The pronounced interest in light-sensitive polymers originates from their unique ability to become anisotropic after irradiation by polarized light. Despite the significant progress that has been made on the synthesis of either polyazobenzenes or polyazomethines, numerous challenges remain, and they have become the catalyst for the ongoing research. The polymer having both azobenzene and azomethine groups are fundamentally less developed. In this work, a strategy to the synthesis of the light-responsive polymer with azobenzene and azomethine units in the backbone is proposed. The polymer is prepared by condensation polymerization of octafluorobiphenylene-based bis-hydroxybenzaldehyde with aromatic meta-linked octafluorobiphenylene-based diamine. The structure of the polymer is characterized by Fourier transform infrared spectroscopy. The synthesized polymer can be solution-cast into flexible solid films with a tensile strength of 25 MPa. Furthermore, the polymer displays elevated glass transition temperatures (Tg), reaching 235 °C, and demonstrates an admirable thermal stability, retaining resilience at temperatures up to 390 °C. The polymer film underwent photoisomerization and exhibited changes in light-induced birefringence when exposed to 365 nm UV light and both polarized and unpolarized blue (405 nm) and green (532 nm) light. The ability to record optical information using polymer films in the form of diffraction gratings is demonstrated.

Synthesis and Characterization of Multicolor Luminescent and Thermally Stable Thioureas and Polythioamides.

Two new polythioamides were prepared through the polycondensation reaction between thiourea monomers and terephthaloyl dichloride, while the thiourea monomers were synthesized by the interaction of aromatic (4,4'-diaminophenylsulfone) or alicyclic (1,2-cyclohexanediamine) diamine with ammonium thiocyanate. The elemental composition of polythioamides was confirmed through CHN microanalysis. The structure and properties of thiourea monomers and polythioamides were determined through proton NMR, UV-Vis, FT-IR spectroscopy, fluorescence, TGA/DTA and SEM. The polythioamides indicated high thermal stabilities which were assessed from their Tmax (temperature indicating highest rate of weight loss) values (670 °C and 346 °C) observed in their DTG graphs. The thioureas and polythioamides were fluorescent and showed multicolor (violet, green, yellow, orange and red) emissions at different excitation wavelengths. All the synthesized compounds were also tested for their antifungal and antibacterial functions and showed antibacterial activity against Salmonella typhi, Bacillus subtilis and Staphylococcus aureus, and antifungal activity against Candida albicans.

Tailoring Three-Dimensional Cross-Linked Networks Based on Water-Soluble Polymeric Materials for Stable Silicon Anode.

For stable battery operation of silicon (Si)-based anodes, utilizing cross-linked three-dimensional (3D) network binders has emerged as an effective strategy to mitigate significant volume fluctuations of Si particles. In the design of cross-linked network binders, careful selection of appropriate cross-linking agents is crucial to maintaining a balance between the robustness and functionality of the network. Herein, we strategically design and optimize a 3D cross-linked network binder through a comprehensive analysis of cross-linking agents. The proposed network is composed of poly(vinyl alcohol) grafted poly(acrylic acid) (PVA-g-PAA, PVgA) and aromatic diamines. PVgA is chosen as the polymer backbone owing to its high flexibility and facile synthesis using an ecofriendly water solvent. Subsequently, an aromatic diamine is employed as a cross-linker to construct a robust amide network that features a resonance-stabilized high modulus and enhanced adhesion. Comparative investigations of three cross-linkers, 2,2'-bis(trifluoromethyl)benzidine, 3,3'-oxidianiline, and 4,4'-oxybis[3-(trifluoromethyl)aniline] (TFODA), highlight the roles of the trifluoromethyl group (-CF3) and the ether linkage. Consequently, PVgA cross-linked with TFODA (PVgA-TFODA), featuring both -CF3 and -O-, establishes a well-balanced 3D network characterized by heightened elasticity and improved binding forces. The optimized Si and SiOx/graphite composite electrodes with the PVgA-TFODA binder demonstrate impressive structural stability and stable cycling. This study offers a novel perspective on designing cross-linked network binders, showcasing the benefits of a multidimensional approach considering chemical and physical interactions.

Siloxane‐containing polyimide films with high heat resistance and low dielectric constant

AbstractA series of siloxane‐containing polyimide films (PIS) were prepared by copolymerising with rigid aromatic dianhydride, siloxane diamines and six different aromatic diamines. The effects of siloxane structures, fluorine and imide content, rigid or flexible segment on the heat resistance, moisture absorption, dielectric performance, mechanical and bonding properties were systematically studied. The results show that PIS films maintain good heat resistance with Tg between 292 and 420°C and 5% weight loss temperature higher than 500°C. The moisture absorption and dielectric constant can be significantly reduced due to the presence of siloxanes and fluorinated groups, with the absorption rate as low as 1.2% and dielectric constant of 2.85 at 1 MHz. When measured at 10 GHz, the dielectric constant ranges from 3.10 to 3.50, and dielectric loss varies from 0.0059 to 0.0098. The PIS‐6 film has the best comprehensive performance due to the low imide content, introduction of trifluoromethyl and ether bonds. The peeling strength of bonding PIS‐6 film with a copper foil can reach 9.2 N/cm. It is proven that siloxane‐containing PIS films with high heat resistance, low dielectric and outstanding adhesion are achieved, which can be applied for flexible integrated circuit boards, high‐frequency electronics and microelectronics fields.

MD analysis on structure and property of thermosetting polyimides end-capped by phenylethynyl groups

Four phenylethynyl-containing thermosetting polyimide monomers, based on aromatic diamines with various molecular structure and 4-phenylethynylphthalic anhydride, were designed and synthesized to investigate their structure-properties relationships from a molecular dynamics perspective. The trifluoromethyl linkage in the diamine moiety of a polyimide gives the highest flexibility whereas the amide linkage imparts the lowest flexibility to the polymer chain. A more flexible polyimide has a lower melting temperature, lower cohesive energy density, lower mechanical properties, and larger the fraction free volume. Besides, intermolecular hydrogen bonding plays a critical role in the maintenance of physical properties. These simulated values show good agreement with experimental data. This project provided an important opportunity to advance the understanding of structure-property relationships of polyimides.

RhB-Embedded Mn-MOF with Cyclotriphosphazene Skeleton as Dual-Emission Sensor for Putrescine as well as Smart Fluorescent Response of Aromatic Diamines and Nitrophenol.

Luminescent metal-organic framework composites with multiple luminescence emissions have been efficient sensing platforms. Herein, a fluorescent sensor (RhB@1-0.4) with dual-emission fluorescence properties was prepared by introducing rhodamine B (RhB) into the framework of complex 1, [Mn2.5(HCPCP)(H2O)4]·(CH3CN)0.5 [HCPCP = hexa-(4-carboxyl-phenoxy)-cyclotriphosphazene and CH3CN = acetonitrile), which is a novel crystalline two-dimensional (2D) coordinated organic framework material. It is a highly desirable material, realizing a ratiometric fluorescence response to putrescine with a high signal-to-noise ratio, and the detection limit can be as low as 6.8 μM. In addition, RhB@1-0.4 exhibited a better fluorescent sensing performance for aromatic diamines and nitrophenols compared with that of complex 1. It is a potential functionalized MOF material for the application of multichannel fluorescence sensing.

Synthesis and characterization of semi‐alicyclic transparent polyimide films containing benzanilide and fluorene units with improved high‐temperature dimensional stability and low‐optical retardations

AbstractTwo solution‐processable semi‐alicyclic transparent polyimide (PI) films with improved high‐temperature dimensional stability and low‐optical retardations were prepared from the stereo‐isomeric alicyclic dianhydrides, 1S,2R,4S,5R‐hydrogenated pyromellitic dianhydride (ccHPMDA) and 1R,2S,4S,5R‐hydrogenated pyromellitic dianhydride (ctHPMDA) and an aromatic diamine, 9,9‐bis[4‐(4‐aminobenzamide)phenyl]fluorene (FDAADA), respectively. The alicyclic cyclohexane units in the dianhydride moiety endowed the derived PI‐1 (ccHPMDA‐FDAADA) and PI‐2 (ctHPMDA‐FDAADA) films good optical transparency, the rigid‐rod benzanilide units provided the PI films low coefficients of thermal expansion (CTE), and the fluorene units resulted in good solution processability and low‐optical retardations (Rth) for the PI films. The PI films exhibited the glass transition temperatures over 400°C and the CTE value of 33.2 × 10−6/K for PI‐1 and 29.0 × 10−6/K for PI‐2 in the temperature range of 50 ~ 250°C, respectively. In addition, the PI films showed good optical transparency in the ultraviolet–visible light region with the optical transmittances higher than 80% for PI‐1 film at the wavelength of 500 nm. The PI films exhibited the average refractive indices of 1.6505 for PI‐1 and 1.6485 for PI‐2 film, respectively. The birefringence values of the PI films were all lower than 0.01, resulting in the low‐optical anisotropies with the optical retardation (Rth) of 77 nm for PI‐1 film and 84 nm for PI‐2 film.

Modulating Charge Transfer Pathways to Enhance Photocatalytic Performance of the Metal-Organic Layer Nanosheet.

Two-dimensional metal-organic layer (MOL) nanosheets, as nonhomogeneous catalysts, show better optical activity in the field of photocatalysis due to their unique structural advantages. Current research focuses on how to modify the structure of 2D nanosheets by means of crystal engineering to modulate the intralayer electron transfer pathway and systematically investigate the impacts of size effect and electron transfer pathway on the energy utilization efficiency of crystalline materials. In the present work, a triple lophine-derived ligand was designed and prepared, which exhibits a large π-conjugation system and multiple D-A (D: donor, A: acceptor) electron transfer pathways. 2D MOL constructed with Cd ions can be exfoliated by physical sonication to obtain double-walled 2D MOL nanosheets. Compared with the bulk crystalline material, the 2D nanosheets exhibit better photovoltaic properties. Benefiting from the excellent structural advantages, 2D MOL nanosheets could be used as photocatalysts for a variety of aerobic oxidation reactions under mild conditions (10 W white LED, room temperature), such as the trifluoromethylation of coumarins, the synthesis of benzimidazole derivatives from aromatic diamines and aromatic aldehydes, and the preparation of 2,4,6-triarylpyridine derivatives, all with high conversion rates and selectivity (yield typically greater than 88%). The related results illustrate that the introduction of the photoactive triple-lophine unit into 2D MOL nanosheets can effectively modulate the electron transport mode and enhance energy utilization, which provides a new research idea for the development of nonhomogeneous photocatalysts aimed at the applications of visible light-driven organic conversion.

Structure and Spectroscopic Studies of Bis Azo Compounds with S/SO2 Bridges and Containing Cyclic-1,3-Dicarbonyl Groups

A series of new bis azo dyes were synthesized starting from aromatic diamine with S/SO2 bridges and cyclic-1,3-dicarbonyl groups; contain active methylene group, namely; 3,3-dimethyl-1,5-cyclohexadione (dimedone), 1,3-cyclohexadione and 2,2-dimethyl-1,3-dioxane-4,6-dione to give 1-6. Whether the reaction is complete and the purity of the compounds were checked with TLC. The structure of the newly synthezed compounds was investigated by using, FT-IR, 1HNMR, LC–MS/MS and UV–Visible spectrophotometric methods, CH3OH was used in the LC-MS/MS experiments, and the molecular masses of the compounds were seen as M and M+1 protonated in the spectrum. In the UV-Vis spectra of these compounds, the solvent effect by using different solvents and also the acid-base effect by adding HCl or KOH to the medium were investigated. The tautomeric equilibrium forms (enol-imine O-H….N, keto-amine O….H-N forms) of the compounds were investigated according to the electronic spectrum recorded in chloroform, dimethylformamide (DMF), acetic acid, and methanol solvents. The results of the UV-visible and 1H-NMR spectra indicated that the compounds in chloroform, dimethylformamide (DMF), acetic acid and methanol were found in the hydrazo tautomer (keto-amine O….H-N forms) of the proposed tautomeric forms.

Colorless Polyimides Derived from 5,5'-bis(2,3-norbornanedicarboxylic anhydride): Strategies to Reduce the Linear Coefficients of Thermal Expansion and Improve the Film Toughness.

In this paper, novel colorless polyimides (PIs) derived from 5,5'-bis(2,3-norbornanedicarboxylic anhydride) (BNBDA) were presented. The results of single-crystal X-ray structural analysis using a BNBDA-based model compound suggested that it had a unique steric structure with high structural linearity. Therefore, BNBDA is expected to afford new colorless PI films with an extremely high glass transition temperature (Tg) and a low linear coefficient of thermal expansion (CTE) when combined with aromatic diamines with rigid and linear structures (typically, 2,2'-bis(trifluoromethyl)benzidine (TFMB)). However, the polyaddition of BNBDA and TFMB did not form a PI precursor with a sufficiently high molecular weight; consequently, the formation of a flexible, free-standing PI film via the two-step process was inhibited because of its brittleness. One-pot polycondensation was also unsuccessful in this system because of precipitation during the reaction, probably owing to the poor solubility of the initially yielded BNBDA/TFMB imide oligomers. The combinations of (1) the structural modification of the BNBDA/TFMB system, (2) the application of a modified one-pot process, in which the conditions of the temperature-rising profile, solvents, azeotropic agent, catalysts, and reactor were refined, and (3) the optimization of the film preparation conditions overcame the trade-off between low CTE and high film toughness and afforded unprecedented PI films with well-balanced properties, simultaneously achieving excellent optical transparency, extremely high Tg, sufficiently high thermal stability, low CTE, high toughness, relatively low water uptake, and excellent solution processability.