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Two novel spiro-bis-benzimidazole-based diamines were synthesized and polymerized with commercial 4,4′-(hexafluoroisopropylidene)diphthalic anhydride dianhydride (6FDA) to produce two types of spiro-bis-benzimidazole-based polyimides (PIM-PBZIs). The resulting polymer membranes, PIM-PBZI-1 and PIM-PBZI-2, exhibited excellent thermal and mechanical properties, including glass transition temperature (T g) of 417 and 413 °C, 5 % thermal decomposition temperature (T d5%) above 500 °C, tensile strength of 72 and 74 MPa, and an elongation at break of 6.6 and 5.4 %. Additionally, these PIM-PBZIs were confirmed as novel microporous polymers with BET surface areas of 473–546 m2/g and pore sizes ranging from 4 to 9 Å. Furthermore, PIM-PBZI-1, modified with N -phenyl, demonstrated excellent organic solubility and gas separation performance, with CO 2 /CH 4 gas pair permeability selectivity exceeding the 1991 Robeson upper bound, providing an effective pathway for the development of high-performance gas separation membranes. [Display omitted] • Two novel spiro-bis-benzimidazole-based PIM-PBZIs were prepared. • The PIM-PBZIs exhibited high BET surface areas of 473–546 m2/g. • The PIM-PBZIs exhibited high thermal stability with T g values of 413–417 °C and T d5% above 500 °C. • The CO 2 /CH 4 separation properties of N -phenyl-modified PIM-PBZI-1 exceeded the 1991 Robeson upper bound. [ABSTRACT FROM AUTHOR]

Polyimide (PI) is considered one of the most promising candidate materials for the microelectronics and wireless communication industries. Nevertheless, the relatively high dielectric constant of PI has become a significant obstacle, constraining its utilization in the realm of microelectronics. Herein, novel PI nanocomposite films were fabricated by incorporating covalent organic frameworks (COFs) and their functionalized counterparts (COF@POSS and COF@DTF) through post-synthetic modification. Among all PI nanocomposites films, PI/COF@POSS nanocomposite film including 2 wt% COF@POSS achieved the lowest dielectric constant (2.41) and dielectric loss (0.0076). These values represented a reduction of 22.5 % and 24 % compared to pure PI, respectively. The decrease in dielectric constant is ascribed to the combined influence of the porous structure of COF and the augmentation in free volume fraction caused by the steric hindrance of POSS. Additionally, the tensile strength of the PI/COF@POSS and PI/COF@DTF nanocomposite films increased up to 121.1 MPa and 112.0 MPa, representing a 95 % and 80 % improvement over pure PI, respectively. Furthermore, the introduction of COFs functionalized with POSS and DTF significantly enhanced the hydrophobicity of PI nanocomposite films. The combination of porous organic nanofillers with surface functionalization offers a feasible route to create low-k PI nanocomposite films with improved mechanical properties and hydrophobicity. The PI nanocomposite films with functional covalent organic frameworks exhibited the decreased dielectric constant and dielectric loss with improved mechanical performance. [Display omitted] • The novel low dielectric PI films were obtained by adding functional COFs. • PI/COF@POSS films achieved the lowest dielectric constant of 2.41. • The maximum tensile strength of PI/COF@POSS films reaches 121.1 MPa. • The hydrophobicity of PI/COF@DTF films is greatly improved. [ABSTRACT FROM AUTHOR]

Polyimide (PI), as a high-performance polymer widely used in aerospace, optoelectronics, microelectronics, etc., the properties it focused on in different areas of application were diverse. However, most of the past machine learning studies in polyimide property prediction were focused only on the prediction of a single property. This study focused on four major categories of properties of polyimide, including thermal (Tg, T d5 , T d10 , and CTE), mechanical (Ts and TM), dielectric (ε), and optical (λ cutoff , T400, n av , and Δn), totaling eleven properties. PI data synthesized from previous studies were collected. MorGan fingerprints, improved MorGan fingerprints, RDkit and Mordred descriptors were selected as feature representations. Four ML models such as DNN, RF, XGBoost and BT were also built. Collectively, 176 machine learning models were trained for 11 predictions of properties. The performance and generalization ability of the models were confirmed by experimental validation, external validation and leave-one-out cross-validation. SHAP analysis was used to explain the optimal model for each property prediction from a physicochemical point of view and structural aspects, and three PIs with different structures were designed accordingly. Finally, a high-throughput virtual screening of nearly 7.6 million polyimides was performed based on the trained model. SA_scores was used to evaluate the ease of synthesis of each PI, and finally high-performance PIs with potential and easy to synthesize were selected for each field. This study could be expected to provide a guideline and a design framework for the application of PIs in various fields in the future. [Display omitted] • Eleven properties of polyimide were predicted, including thermal, mechanical, dielectric and optical properties. • MorGan fingerprints, improved MorGan fingerprints, RDkit and Mordred descriptors were selected as feature representations. • SHAP was used to interpret each optimal model from a physicochemical perspective and a substructural perspective. • Based on the interpretation of SHAP analysis, three polyimides with different structures were designed. • A high-throughput virtual screening of nearly 7.6 million polyimides was performed. [ABSTRACT FROM AUTHOR]

Black polyimides (BPIs) show increasing demand in the microelectronics and optoelectronics fields. However, the existing BPIs have drawbacks of poor masking ability, dimensional stability, thermal and electrical properties. 3,6-Bis(thiophen-2-yl)diketopyrrolopyrroles (TDPP) is a typical dye that possesses a high molar extinction coefficient. In the work, a new diamine (DPPTOMePDA) bearing TDPP connected with methoxyl-substituted benzene rings was synthesized. Based on such diamine and pyromellitic dianhydride (PMDA), a high-performance intrinsic BPI (DPPTOMePPI) was obtained. The resulting DPPTOMePPI exhibited a red-shifted and broadened absorption spectrum, thus achieving complete absorption of visible light and highly black color. Its cut-off wavelength (λ cut) was up to 734 nm, and the Commission International de l'Eclairage (CIE)-Lab coordinate L* decreased to 0.53. Furthermore, DPPTOMePPI exhibited excellent thermal and electrical performances with a low coefficient of thermal expansion (CTE). Density functional theory calculation was executed to analyze the underlying electron transitions of DPPTOMePPI. The results showed that the strong light absorption of DPPTOMePPI was primarily ascribed to the electronic transition of HOMO to LUMO+1 that occurred in the chromophores units. The flexible copper clad laminates (FCCLs) derived from DPPTOMePPI film showed high peel strength and resistance to solder heat. The work offers a theoretical guide for the construction of intrinsic black PI possessing complete visible absorption and low CTE. [Display omitted] • A diamine bearing TDPP grafted with methoxyl-substituted benzene ring was customized. • DPPTOMePPI bearing TDPP-based chromophore showed full visible-light absorption. • DPPTOMePPI maintained high electrical and thermal properties with a low CTE. • The coloration mechanism of DPPTOMePPI was revealed by theoretical calculation. • 2L-FCCL based on DPPTOMePPI showed high peel strength and solder heat resistance. [ABSTRACT FROM AUTHOR]

Due to the rapid development of high frequency and high rate communication technology, polyimide (PI) films with ultra-low dielectric loss (D f) at high frequency, excellent thermal and mechanical properties are urgently needed. A series of PI films with ultra-low D f were prepared by introducing different mesogen units. Among them, one novel PI film with biphenyl liquid-crystal-like units (BAHQ-TFMB) achieve a recorded low D f of 0.00169 (10 GHz) which surpasses previous studies on pure PI bulk films. Importantly, the high degree of collinearity of the friction work (W f) and D f of PI films (Pearson's r = 0.992) was confirmed, which indicate that W f among PI macromolecules plays an important role in determining D f of PI films. To reveal underlying reason for reducing the W f and D f of PI films, the contribution of the degree of orientation and crystallinity of PI films with or without liquid-crystal-like structures were comparative studied. Through a two-dimensional orientation determinant, it is found that increasing the crystallinity of liquid-crystal-like PI films is the main contribution to reducing W f and corresponding D f of PI films while the orientation of PI films seems to have weak effect. Moreover, BAHQ-TFMB PI film exhibits excellent mechanical properties. The tensile strengths is 145.5 ± 12.0 MPa and Young's moduli is 4.76 ± 0.28 GPa. [Display omitted] • The PI film with biphenyl liquid-crystal-like units achieve a recorded low dielectric loss of 0.00169 (10 GHz). • The friction work (W f) among PI macromolecules plays an important role in determining D f of PI films. • Increasing the crystallinity of liquid-crystal-like PI films is the main contribution to reducing W f and D f of PI films. [ABSTRACT FROM AUTHOR]

We attempted to manufacture films in which fluorescent dye is dispersed using engineering plastic as a matrix which has high heat and chemical resistance as well as excellent mechanical performance. In this study, films containing highly dispersed perylene in colorless and transparent aromatic polyamide (PA) and polyimide (PI) were manufactured. The perylene-dispersed PA film emitted strong blue light with a maximum fluorescence at 457 nm. On the other hand, the perylene-dispersed PI film showed significant fluorescence quenching with its maximum fluorescence wavelength significantly red-shifted to 546 nm. The perylene-dispersed PI film treated with ethylene diamine at 80 °C showed strong blue fluorescence, and when the film was further heated at 200 °C, the fluorescence was quenched. These films are expected to be applied as back light unit or color conversion layer for OLED and Micro LED due to their excellent physical properties. [Display omitted] • Aromatic polyamide and polyimide films in which perylene was dispersed were prepared. • The polyamide film emitted strong blue light. • The polyimide film showed significantly quenched orange fluorescence. • When treated with ethylene diamine, the polyimide film emitted strong blue light. • When heated at a higher temperature, the fluorescence was quenched again. [ABSTRACT FROM AUTHOR]

This study selected three monomers, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BPDA), p -phenylenediamine (PDA), and 2-(4-amino-phenyl)-5-amino-benzimidazole (BIA), to prepare BPDA-PDA and BPDA-PDA-BIA (mole ratio PDA:BIA = 3:7) polyimide (PI) fibers through a two-step method and dry-jet wet-spinning process. The study investigated the effect of BIA monomer on the imidization process of polyamic acid (PAA) fibers and the mechanical properties of the final PI fibers. The evolution of fiber structure during the thermal imidization process was analyzed through TGA, TMA, DMA, FTIR and XRD. Kinetic analysis was made to provide the apparent activation energies, the reaction orders and the model functions of the imidization reaction. The research showed that the copolymerization of BIA introduced significant hydrogen bonding between the macromolecules. In the early stage of the imidization reaction, effect of hydrogen bonding was not significant. As imidization conversion increases, hydrogen bonding not only significantly hindered the imidization reaction but also hindered the formation of crystals inside PI fibers. The crystallization process had to be carried out at much higher temperatures. Mechanical properties of the fibers can be significantly improved as the BIA introduced into the polymer chains. [Display omitted] • The effect of BIA monomer on the imidization process of polyamic acid fibers was investigated through a comparative study. • The apparent activation energy and the model function of thermal imidization reaction was obtained through kinetic analysis. • The imidization reaction inside the fiber is a 1D to 3D process for the reaction order increases from 2 to higher values. [ABSTRACT FROM AUTHOR]

Due to the sensitive relations between aerogel physical, thermal, and mechanical properties, improving the polyimide aerogels performance requires understanding of their structure to properties relations, along with introducing a robust method to tailor aerogels properties to achieve the optimum performance. Given this background, this work extensively studies the structure to properties relations of pyromellitic dianhydride (PMDA) and biphenyl-tetracarboxylic acid dianhydride (BPDA) backbone polyimide aerogels at varying hybrid diamine fractions. Based on the results, combination of rigid and flexible diamine monomers at varying fractions successfully tailored the properties of the hybrid diamine polyimide aerogels. Also, physical, thermal, and mechanical properties of the two aerogel backbones presented a tendency to the hybrid diamine monomers fraction. However, the opposite trends of the two backbones suggested that, rather than the diamine or dianhydride monomers individually, their network structure and bonding nature would define the aerogel behavior. Furthermore, this work shows that the shrinkage and morphology are the two main parameters, those describe the aerogels properties. Therefore, tailoring these two parameters can provide aerogels with optimum performance. The fabricated aerogels presented wide range of properties with the maximum observed open cell content of 96.6% and compression modulus of 16.9 MPa along with the effective thermal conductivity and density as low as 32.5 mW/mK and 0.056 g/cm3, respectively. Image 1 • Study on structure to properties relations of hybrid diamine polyimide aerogels. • Tailoring hybrid polyimide aerogels properties by altering the diamine fraction. • Hybrid aerogels by combining a rigid and a flexible diamine monomer. • The shrinkage and morphology are the main parameters, defining aerogels properties. [ABSTRACT FROM AUTHOR]

Strong low-density polymer aerogels have received intensive attention as thermal or sound insulator, filtration media and sensors, etc. However, dimensional instability has been regarded as one of issues that limits the wide application of polymer aerogels in a harsh temperature. In present work, polyimide aerogels were reinforced with attapulgite (AT) nanorods, one of natural fibrillar minerals, through the strong hydrogen-bonding interaction. In hybrid aerogels, AT nanorods act as the rigid skeleton that supporting the framework of aerogels. The resultant hybrid aerogels exhibit improved mechanical properties. At the 80% strain, the compressive stresses for the aerogels containing 10 wt% AT are 100% as high as those of the pure polyimide aerogels. Interestingly, modulus of hybrid aerogels increases as the density decreases. For example, the compression Young's and specific modulus increase by 100% and 105% for the hybrid ODA-based aerogel compared to the pristine sample, meanwhile, the density decreases by 10%. Furthermore, the AT nanorods show strong supporting effects in maintaining the structural integrity of aerogels, which produce a significant effect on reducing the shrinkage of hybrid aerogels at high temperatures and retaining their excellent thermal insulation performance. The detailed investigation reveals that the AT is an effective and low-cost additive for preparing high performance polymer nanocomposites aerogels with improved mechanical property and thermal dimensional stability. Image 1 • AT nanorods are used as reinforcing nanofiller for PI aerogels via H-bonding interaction. • Modulus of composite aerogels increases as the density decreases. • Improved mechanical properties of aerogels is due to AT supporting skeleton. • AT-reinforced aerogels exhibit an excellent thermal dimensional stability. [ABSTRACT FROM AUTHOR]

Abstract Six polyimides, containing pyridine and spirocyclic units, were successfully synthesized by chemical imidization. Structure-dependent properties such as thermal decomposition temperatures and gas permeabilities of the high-performance polymers were explicitly investigated. Results showed that all polyimide films exhibited good solubility in common organic solvents and non-polar solvents such as chloroform and tetrahydrofuran. The polymers exhibited good thermal stability, all demonstrating thermal decomposition temperatures (T d10%) over 496 °C in nitrogen. Important from a commercial viewpoint, the permeability coefficients of these for the acidic gas CO 2 showed an increase over other tested gases by virtue of the basic group pyridine (C–N linkages) in their structures. Graphical abstract Image 1 Highlights • Polyimides exhibited good solubility, which is easily to cast into film and apply in practice. • Polymers exhibited good thermal stability which maintain their structural integrity below 450 °C. • The permeability coefficients of CO 2 increased significantly by introduction of the pyridine groups. • Demonstrated the importance of introducing the rigidity to the chains for improving gas separation performance. [ABSTRACT FROM AUTHOR]

Abstract In this paper, photoacoustic spectroscopy (PAS) was presented to characterize the ion radiation-induced damage in the polyimide (PI). We demonstrated a mathematical model of monochromatic light excited photoacoustic (PA) pressure in ion radiation damaged PI. A dual-wavelength PA relative amplitude difference linear dependence on ion irradiation fluence was proposed to quantitatively determine the ion radiation damage in PI. The ion radiation-induced optical absorption modifications of PI films radiated by different fluence of ions were measured by means of wavelength-scanning (400 nm-800 nm) PAS and dual-wavelength (405 nm, 808 nm) laser PAS methods. The results indicated that the optical absorption of PI material was obviously enhanced with the increase of radiated ion fluence. The PA relative amplitude difference induced by laser at the wavelength of 405 nm and 808 nm showed approximate linear dependence on the radiation fluence of nitrogen ions, which was a good agreement with the theoretical model. PAS approaches have the merits of high specificity and sensitivity to the ion radiation-induced damage in PI material and provide a reliable tool to evaluate the damage quantitatively. Graphical abstract Image 10301 Highlights • Ion radiation damage in polyimide was characterized by photoacoustic spectroscopy. • Ion fluence was reliably accessed by dual-wavelength laser photoacoustic detection. • Photoacoustic signal has high specificity and sensitivity to ion radiation damage. [ABSTRACT FROM AUTHOR]

Polyimides (PIs) have been extensively developed as interlayer dielectrics in electronic package industry due to their excellent comprehensive properties. However, the insufficient adhesion between PI and copper wires usually led to delamination and thus compromising the reliability of applications. In this work, a diamine monomer (SPMNH 2) that contained pyrimidine side groups and ether bonds was synthesized, and a series of its copolyimides (SPI) were prepared by copolycondensation with 2-(4-aminophenyl)-1H-benzimidazol-5-amine (APBI) and pyromellitic dianhydride (PMDA). The incorporation of pyrimidine rings, along with the presence of benzimidazole rings promoted the adhesion between PI and copper (1.3805 N/3 mm of SPI-4). In addition, a desired coefficient of thermal expansion (15.28 ppm/K of SPI-4) close to that of copper was obtained, facilitating the adhesion of the interface during high-temperature processes. Moreover, SPI-4 exhibited exceptional mechanical (the elongation at break of 44.02% and tensile strength of 191.64 MPa) and thermal properties (T g = 363.70 °C, T 5% = 519.33 °C). Therefore, the high-performance SPI films showed great potential in advanced packaging. [Display omitted] • A new molecular design strategy was proposed in constructing PI with high adhesion to copper. • The synthesized SPI showed good adhesion with smooth copper and the failure mode was found to be cohesive failure. • The new polyimide exhibited excellent mechanical properties, and a CTE (15.28 ppm/K) close to that of copper. [ABSTRACT FROM AUTHOR]

Electronic crosstalk, signal propagation delay and loss on the redistribution layers (RDLs) have been increasingly serious along with the rapid development of wafer-level packing (WLP). Polyimide films with low dielectric permittivity (D k) and low dielectric loss (D f) at high frequency are in demand imminently as interlayer materials. In this work, a novel kind of intrinsic silane-containing polyimide was designed and prepared by the reactions of 1,3-Bis(3-aminopropyl)tetramethyldisiloxane (APDS) and 4,4′-Oxydianiline (ODA) with 2,2-Bis(3,4-anhydrodicarboxyphenyl) hexafluoropropane (6FDA). The chemical structure of polyimide was studied by FT-IR spectrum and NMR and their dielectric properties and other performances were systematically analyzed. Results showed that the lowest D k and D f of polyimide (6FDA/APDS) was 2.66 and 6 × 10−4 at 10 GHz. Furthermore, the dielectric permittivity and loss of silane-containing polyimide decreased with increasing the content of silane. The excellent dielectric properties were attributed to decreasing polarization and increasing the free volume of molecular chains when the silane was introduced into the molecular structure of polyimide. This work provided guidance for the intrinsic silane-containing polyimide with low dielectric properties. [Display omitted] • A novel kind of silane-containing polyimide was successfully prepared by means of polyamide ester. • The lowest dielectric constant and dielectric loss of silane-containing polyimide was 2.66 and 6 × 10−4 at 10 GHz. • The dielectric permittivity and loss of silane-containing polyimide decreased with increasing the content of silane. [ABSTRACT FROM AUTHOR]

Black polyimide shows growing demand in optoelectronic apparatus instead of yellow transparent polyimide. However, the most used black polyimide filled with carbon black suffers from the deterioration of electrical and mechanical properties. In this work, a soluble intrinsically black polyimide (TPCPPPPI) with exceptional electrical and mechanical performances was designed and prepared by the polycondensation of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and a new diamine (TPCPPPDA), which bears tetraphenylcyclopentadienone (TPCP) linked with four benzene rings. Introduction of TPCP-based chromophore into PI molecular chain greatly red-shifted the absorption scope, thus achieving absorption of whole visible light. The resulted TPCPPPPI exhibited highly opaque and black color, with a cut-off wavelength (λ cut) up to 698 nm and CIE (Commission Internationale de l'Eclairage) color parameter L* low to 1.41. Simulation calculation suggested that the highly black color of TPCPPPPI was primarily ascribed to the electrons transitions from the highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) in the chromophore-bearing diamines, in which the charges chiefly migrated from the 2,5-position aryl groups to the middle cyclopentadienone. Meanwhile, TPCPPPPI exhibited exceptional solubility, mechanical and electric performance. The intrinsically black PI accompanying with exceptional performance and organosoluble feature has attractive potential application in optoelectronic field. [Display omitted] • A diamine bearing TPCP grafted with benzene rings was designed and synthesized. • A soluble intrinsic black PI was obtained by incorporation of TPCP-based chromophore. • The reason for the black color of PI was clarified by theoretical calculation. • The propeller-shaped TPCP moieties and –CF 3 groups improved the solubility of PI. • The black PI maintained high electrical, mechanical and thermal performances. [ABSTRACT FROM AUTHOR]

Abstract An oil-in-oil emulsion-templating method is used to fabricate polyimide aerogel foam materials. These materials contain micrometer size voids (macrovoids) in conjunction with inherently produced meso- and macropores in polyimide gels. Polyamic acid is first synthesized from diamines and dianhydrides and then chemically imidized to obtain a sol. An immiscible oil-type dispersed phase is introduced in the sol via emulsification and the sol is subsequently allowed to transition into a gel, thereby locking the dispersed phase droplets within the structure. The gel is subsequently dried under supercritical conditions to obtain aerogel foams. This paper evaluates the stability of the oil-in-oil emulsion used for templating with reference to the gel times of the continuous phase. Specifically, the effects of surfactant concentration on macrovoid size, mesopore size, and mechanical properties of the aerogel foams are investigated. In addition, water and oil absorption behavior of the aerogel foams are studied. Graphical abstract Image Highlights • Oil-in-oil emulsion templating produces aerogel foams from polyimides. • PEO-PPO-PEO block copolymer surfactant stabilizes oil-in-oil emulsions. • Surfactant reduces macrovoid size but increases polyimide strand size. • Surfactant organizes to produce higher contact angle and promotes oil absorption. [ABSTRACT FROM AUTHOR]

Abstract The photoconductive properties of seven types of fully aromatic polyimide (PI) films with a main chain triphenylamine structure were investigated by examining the wavelength dependence of photo-irradiation in the visible region under a direct current (DC) electric field. It was clarified that the out-of-plane photoconductivity of the PIs synthesized from seven types of dianhydrides and 4,4′-diamino-4″-methyltriphenylamine (DATPA) tends to increase as the intramolecular charge transfer (CT) interactions increase, which is essentially dominated by the electron accepting properties of the dianhydrides. In particular, the PIs derived from the pyromellitic dianhydrides substituted by two fluoro (−F) or one trifluoromethyl (−CF 3) substitutes with strong electron accepting properties (P2FDA/DATPA and P3FDA/DATPA) exhibited significantly enhanced photoconductivity with relatively strong optical absorbance in the visible region. Moreover, the P6FDA/DATPA PI prepared from pyromellitic dianhydrides and substituted by two bulky CF 3 substitutes exhibited intense optical absorbance but lower photoconductivity, owing to the enlarged interchain distance, as evaluated by the out-of-plane GI-WAXS pattern. This suggests that the charged carriers are preferentially transported along the interchain directions, and the photoconductivity of the PI films is significantly influenced, not only by the degree of intramolecular CT interactions, but also by the polymer aggregation structures facilitating the interchain charge transportation. Graphical abstract Image 1 Highlights • Photoconductive properties of seven types of polyimides (PIs) with a main chain triphenylamine structure were investigated. • PIs derived from fluorinated dianhydrides exhibited highly enhanced photoconductivity due to the strong CT interactions. • Not only the CT interactions, but also the aggregation structures of PI chains play a key role for the photoconductivity. [ABSTRACT FROM AUTHOR]

Abstract New generation spacecraft technology requires more and more deployable, light-weight, thin polymer films, in particular novel polyimide materials with high optical transparency, excellent foldability and superior flexibility. In this work, we develop a highly transparent, ultra-foldable, ultra-flexible and ultra-processable polyimide composite material by incorporating 5–8 wt% of ionic liquid 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide into colorless polyimide matrices. This 23-μm-thick polyimide composite film exhibits a high optical transmittance of 90.4% even at 450 nm wavelength and an incredibly low cutoff wavelength of 273 nm. It is an extremely strong and flexible material, with a tensile modulus of 844.6 MPa, a tensile strength of 48.2 MPa, a high elongation at break of 108.4%, and an extraordinary minimum bend radius of 1 μ m. It can be easily folded in half 4 times or twisted by 900° without any crack damages. Moreover, it has a low expense cost and good film processability for industrialization manufacturing. All of these superior performances render this ionic liquid/polyimide composite an ideal structural material for solar sails, solar arrays and thin-film photovoltaics, etc. Graphical abstract Image 1 Highlights • Ionic liquid/polyimide composites exhibit outstanding foldability, flexibility, processability and optical transparency. • This 23-μm-thick polyimide composite film exhibits a high optical transmittance of 90.4% even at 450 nm wavelength and an incredibly low cutoff wavelength of 273 nm. • This composite material has a super folding capability with a minimum bending radius of 1 μm, which is to our knowledge the lowest record for polymide materials. [ABSTRACT FROM AUTHOR]

Abstract Carboxyl group functionalization in honeycomb-patterned porous (HCP) films was obtained by breath figure process using polyimide (PI) which can react with KOH humidity at the polymer solution/aqueous alkali droplet interface to form carboxyl groups. PI containing CO-NR 2 imide ring group reacts with KOH for imide ring-cleavage reaction by interfacial reaction. In order to obtain pore-selective carboxyl group functionalized PI HCP films, we have suggested a new strategy introducing KOH humidity with time interval after using initial water humidity during breath figuring process. The carboxyl group functionalized pores can be applied to obtain ordered microarray of biological and inorganic materials, which have potential applications in biosensors, separations, medical biology, etc. Graphical abstract Image Highlights • A new strategy was developed for the pore selective carboxyl functionalization. • Polyimide reacts with KOH humidity to form carboxyl functionalized porous films. • Pore functionalization was enhanced by delayed introduction of KOH humidity. • Reactive carboxyl pores can be used as a template for further functionalization. • Silver functionalized porous polyimide films by ion-exchange self-metallization. [ABSTRACT FROM AUTHOR]

To develop membrane materials for gas separation, a series of semi-alicyclic polyimides was synthesized using one-step thermal solution imidization from an alicyclic dianhydride with non-planar twisted structure, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride (DOCDA). All synthesized polyimides exhibited amorphous structures and superior thermal stability, with high glass transition temperatures (242–288 °C) withstanding high operation temperature and pressure. They also showed excellent solubility in many polar organic solvents commonly used in the fabrication of gas separation membranes. The gas permeation properties of the polyimide membranes were measured for six representative gases (H 2 , CO 2 , O 2 , CO, N 2 , and CH 4 ). The gas permeabilities and selectivities of polyimide membranes were significantly influenced by the chemical structure of the diamines, which could be explained reasonably by the kinetic diameter of gases, the fractional free volumes, and d -spacing values of the polyimides. Two DOCDA-based polyimides showed very high selectivities for H 2 /CH 4 and CO 2 /CH 4 and slightly low permeabilities for H 2 and CO 2 , which performances were comparable to the commercial polyimide materials such as P84 ® and Matrimid ® used in gas separation field. [ABSTRACT FROM AUTHOR]

Novel polyimide nanocomposites with excellent mechanical and tribological properties were achieved using amine functionalized multi-walled carbon nanotubes (MWCNT-NH 2 ). MWCNT-NH 2 was successfully obtained through Friedel-Crafts acylation and nitroreduction. PI nanocomposites with different contents of MWCNT-NH 2 were prepared via in-situ polymerization. In contrast with the properties of pure PI or PI/MWCNT blends, the tribological properties, mechanical properties, and thermal performance of PI/MWCNT-NH 2 nanocomposites were evidently improved due to the homogeneous dispersion of MWCNT-NH 2 in PI matrix as well as the strong interfacial covalent bonds between MWCNT-NH 2 and the PI matrix. Notably, it was demonstrated that the PI/MWCNT-NH 2 nanocomposite adding with 0.7 wt% MWCNT-NH 2 exhibited the best tribological properties in consideration of the friction coefficient (0.310) and wear rate (2.234 × 10 −4 mm 3 /Nm) under dry sliding condition. Furthermore, the resulting PI/MWCNT-NH 2 nanocomposites possessed the combined excellent tribological and mechanical properties, evidencing their potential applications in the field of the friction materials and other high-performance areas. [ABSTRACT FROM AUTHOR]

Anisotropic linear and volumetric thermal expansion behaviors of four types of isomeric polyimides (PIs) were investigated based on thermal mechanical analyses and optical interferometric measurements. Among PI films of poly ( p -phenylene 3,3′,4,4′-diphenyldiimide) ( s BPDA/PPD) with different chain packing densities, a film with a higher refractive index exhibited a smaller coefficient of volumetric thermal expansion (CVE), indicating that a smaller amount of free volume leads to a smaller CVE even at much lower temperatures than the glass transition temperature ( T g ). The PI films containing quasi-linear s BPDA structures exhibited smaller CVEs than those containing bent 2,3′,3,4′-diphenyldiimide ( a BPDA) structures, whereas the PI films with bent m -phenylene (MPD) linkages exhibited smaller CVEs than those containing linear p -phenylene (PPD) linkages. It is noteworthy that s BPDA/MPD exhibited a significantly smaller CVE (113.7 ppm/K) than that of s BPDA/PPD despite its lower packing coefficient. This value could be the smallest CVE among solid polymers. Based on the dynamic mechanical analyses and the consideration of stereochemical structures with conformational energy calculations, the local molecular motions of PIs containing MPD are more restricted in the solid state than those with PPD even below their T g s because π -flip rotation at the m -phenylene linkage is sterically inhibited in the former, while that at the p -phenylene linkage is allowed in the latter. [ABSTRACT FROM AUTHOR]

A series of PIs (APIs) containing naturally occurring adenine moiety in polymer backbone has been prepared from adenine-containing diamine ( p -APA) and commercial dianhydrides by a two-step polymerization process. FTIR study confirmed the structures of APIs. The hydrogen-bonding interactions of APIs were studied by FTIR, in-situ FTIR and theoretical methods. The crystalline behavior of APIs were studied by XRD, and the results showed that the APIs have relatively high degree of crystalline. Birefringence and polarized ATR FTIR studies showed that the groups and chains in API films could be simultaneously self-arranged in the in-plane direction without any further stretching. Molecular simulation methods were introduced to study the relationship between self-arranged in-plane orientation and hydrogen-bonding interactions. Thermogravimetric analysis (TGA) showed that the 5% weight loss of APIs ( T 5 ) are in the range of 511–569 °C in nitrogen, and the char yields ( CR ) of APIs are in the range of 55–67% under nitrogen condition. Dynamic mechanical analysis showed that the glass-transition temperature ( T g ) are in the range of 315–400 °C. The mechanical properties were studied by universal strength tester, and the results showed that the tensile modulus of API films were in the range of 4.43–9.21 GPa, and the tensile strength of API films were in the range of 124.9–162.9 MPa. Thermal mechanical analysis showed that the in-plane CTE of APIs are in the range of −5.85–37.82 ppm/ ° C. [ABSTRACT FROM AUTHOR]

A hydroxyl-functionalized triptycene-based polyimide of intrinsic microporosity (TDA1-APAF) was converted to a polybenzoxazole (PBO) by heat treatment at 460 °C under nitrogen atmosphere. TDA1-APAF treated for 15 min (TR 460) resulted in a PBO conversion of 95% based on a theoretical weight loss of 11.7 wt% of the polyimide precursor. The BET surface area of the TR 460 (680 m 2 g −1 ) was significantly higher than that of the TDA1-APAF polyimide (260 m 2 g −1 ) as determined by nitrogen adsorption at −196 °C. Heating TDA1-APAF for 30 min (TRC 460) resulted in a weight loss of 13.5 wt%, indicating full conversion to PBO and partial main-chain degradation. The TR 460 membrane displayed excellent O 2 permeability of 311 Barrer coupled with an O 2 /N 2 selectivity of 5.4 and CO 2 permeability of 1328 Barrer with a CO 2 /CH 4 selectivity of 27. Interestingly, physical aging over 150 days resulted in enhanced O 2 /N 2 selectivity of 6.3 with an O 2 permeability of 185 Barrer. The novel triptycene-based TR 460 PBO outperformed all previously reported APAF-polyimide-based PBOs with gas permeation performance close to recently reported polymers located on the 2015 O 2 /N 2 upper bound. Based on this study, thermally-rearranged membranes from hydroxyl-functionalized triptycene-based polyimides are promising candidate membrane materials for air separation, specifically in applications where space and weight of membrane systems are of utmost importance such as nitrogen production for inert atmospheres in fuel lines and tanks on aircrafts and off-shore oil- or natural gas platforms. Mixed-gas permeation experiments also demonstrated good performance of the TR 460 membrane for natural gas sweetening with a CO 2 permeability of ∼1000 Barrer and CO 2 /CH 4 selectivity of 22 at a typical CO 2 wellhead partial pressure of 10 bar. [ABSTRACT FROM AUTHOR]

Because of the unique conjugated heterocyclic structure and the presence of reactive groups, adenine which can be obtained from biomass may be an ideal bio-based alternative structure of petroleum-based aromatic/heterocyclic structures. In this paper, the adenine was introduced into mainchain of polyimide (API) for the first time to evaluate the feasibility of replacing petroleum-based aromatic/heterocyclic structures by adenine. Systematic studies showed that the API possesses outstanding solubility, thermal and mechanical properties (glass transition temperature ( T g ): 363 °C, weight residual of 95%: 513 °C (N 2 ); 506 °C (Air), tensile strength: 144 MPa). Systematic studies indicated that hydrogen-bonding interaction could be a significant cause of these unique thermal and mechanical properties. [ABSTRACT FROM AUTHOR]

An intrinsic high-barrier and thermally stable polyimide (2,7-CPPI) was prepared by the polymerization of pyromellitic dianhydride (PMDA) and novel diamine (2,7-CPDA), which consists of rigid planar carbazole moiety. The resulted 2,7-CPPI exhibits excellent barrier properties, with oxygen transmission rate and water vapor transmission rate low to 0.2 cm 3 m −2 ·day −1 and 0.1 g m −2 ·day −1 , respectively. Wide angle X-ray diffractograms (WAXD), positron annihilation lifetime spectroscopy (PALS) and molecular dynamics simulations reveal that the excellent barrier properties of 2,7-CPPI are mainly ascribed to the crystallinity, high chain rigidity and low free volume, which are resulted from the rigid planar structure and strong hydrogen bonding among molecular chains. Meanwhile, 2,7-CPPI also presents outstanding thermal stability and mechanical properties with a glass transition temperature of 437 °C, 5 wt % loss temperature of 556 °C under N 2 , coefficient of thermal expansion of 2.89 ppm/K and tensile strength of 143.8 MPa. The polyimide shows attractive potential applications in flexible electronics and high-grade packaging area, especially using as the substrates for top-emitting OLEDs display. [ABSTRACT FROM AUTHOR]

The thermal imidization process of 1,2,4,5-benzenetetracaboxylic (PMDA)/4,4’-diamnodiphenyl ether (4,4′-ODA) solutions in N -methyl-2-pyrrolidone (NMP) from polyimide (PI) precursor, poly (amic acid) (PAA), was systematically investigated through a series of characterization methods, such as Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). At the low-temperature drying stage, mechanical properties and T g of polymer films were increased as a result of solvent removal. TGA method was used to quantitatively monitor the evaporations of hydrogen-bonded solvents on PAA and of the dehydration during the imidization reaction that occurred above 150 °C. During the imidization stage, the interplay between the solvent evaporation and the imidization was the key factor that determined the enhancement of the mechanical properties and T g . The degree of imidization approached 94% when the temperature was increased to 250 °C. A “complete” imidization was achieved by annealing between 350 and 400 °C. The enhancement in the mechanical properties of final PI films may result from the increased T g and the crystallized structure formed during the annealing stage. [ABSTRACT FROM AUTHOR]

Polyimide (PI) is widely used as a mainstream antenna material for fourth-generation communication technology (4G) due to its excellent dielectric properties and mechanical properties. However, the relatively high dielectric constant and dielectric loss make traditional polyimide unable to meet the requirement of the fifth-generation communication technology. The molecular engineering strategy is an effective method to improve the dielectric properties and control the comprehensive performance of the polyimide. In this work, an m-phenylenediamine containing tetrafluorostyrol pendant group [(4-(2,3,5,6-tetrafluoro-4-vinylphenoxy) benzene-1,3-diamine (TFVPDM)] has been designed. On the one hand, the rigid m-phenylene and biphenyl structure in TFVPDM is beneficial for balancing the solubility and thermal properties of the TFVPDM-based polyimides. On the other hand, the tetrafluorostyrol pendant group can provide cross-linkable sites and help construct the hydrophobic network in the TFVPDM-based cross-linked fluorinated polyimides (CL-FPIs: CL-FPI-10; CL-FPI-20; CL-FPI-30), which can improve their dielectric properties and water resistance. The CL-FPIs films were obtained through polymerization of TFVPDM, 2,2′-bis(trifluoromethyl) benzidine (TFDB), and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), and subsequent cross-linking reaction. Among CL-FPIs, the CL-FPI-30 shows the best comprehensive performance including low dielectric constant (2.29 at room temperature and 2.03 at 200 °C), low dielectric loss (0.0051 at 1 MHz), high glass transition temperature (T g) (346.9 °C), low coefficient of thermal expansion (CTE) (44.1 ppm °C−1), low water absorption (0.128%) and good stability of dielectric constant in a humid environment. [Display omitted] • A series of cross-linked polyimides (CL-FPIs) were prepared by main-chain engineering and cross-linking reaction. • CL-FPIs have excellent dielectric properties and good water resistance. • CL-FPIs have outstanding thermal and mechanical performance. [ABSTRACT FROM AUTHOR]

Polyimide (PI) films have been extensively used in the field of microelectronic as insulating materials. With the rapid development of microelectronic devices towards miniaturization and large power, the development of low dielectric properties of PI materials has attracted more and more attention. In this study, the breath figure (BF) process was used to prepare single-layered and multi-layered microporous PI films, for obtaining the low dielectric properties. The BF porous structure of PI film was successfully constructed by two implementing strategies, i.e., solution casting for direct preparation of PI film and solvent treatment upon pre-shaped PI film for in-situ pore-formation. By changing solution concentration, environmental humidity and temperature, efficient manipulation of the pore morphology of the film both on the surface and in the bulk layer was achieved. Such multi-layered porous BF structure has been proved to significantly lower the dielectric constant of PI film, from 3.7 of non-porous film to 1.7 of porous film. In order to further expand the application range of BF microporous PI film, both ways of alkali treatment and thermal oxidation were taken for the cross-linking of the porous PI films, greatly improving the solvent resistance of the film. The original porous morphology was completely retained, ensuring that the low dielectric properties were not affected. This is the first report on the preparation of multi-layered microporous low dielectric PI films by BF process. Multi-layered microporous PI film with low dielectric constant was prepared by utilizing the breath figure process. [Display omitted] • Single-layered and multi-layered microporous structures were constructed in PI film via one-step procedure of BF method. • Dynamically tunable pore-formation was achieved both on the surface and in the bulk layer of the porous PI film. • The dielectric properties of the BF-structured PI film could be manipulated by controlling the pore-formation process. • Cross-linked low-k PI material was obtained with fine property of solvent resistance. [ABSTRACT FROM AUTHOR]

Low-cost and processable polyimides with ultrahigh thermal/chemical stability is urgently demanded in microelectronic and aeronautics/astronautics industries. In this work, crystalline polyimides containing reactive cyano groups were synthesized from readily available monomers by facile one-step solution polycondensation method. The obtained polyimides are soluble at room temperature in the common solvents, and can be easily made into transparent polymer films. After curing, the resultant products become completely insoluble in any solvents, exhibiting excellent chemical stability. The glass transition temperature (T g) and 5% thermal decomposition temperature (T 5) for the cured polyimides are as high as 462 °C and 570 °C, respectively. The ultrahigh T g and T 5 together with good solubility are superior to most polyimides already reported in the literature. Moreover, the polyimide films are quite tough with the tensile strengths of 94–118 MPa, Young's moduli of 2.3–2.7 GPa and elongations at break of 5.3%–8.6%. The combination of facile synthesis method, solution-proccesability, excellent thermal/chemical resistance and mechanical property endows the polymers with promising applications in polymer films and composite materials. [Display omitted] • Crystalline cyano-containing polyimides are synthesized via a facile method. • The polyimides are self-crosslinkable and soluble at room temperature. • The cured products possess ultrahigh glass transition temperature up to 462 °C. • The 5% weight-loss temperature of the polyimides reaches 570 °C. • The water uptake measured in the boiling water for 24 h is as low as 1.39%. [ABSTRACT FROM AUTHOR]

Effective and reversible iodine adsorption is among the most important means to solve nuclear pollution. Herein, a novel electron-rich hypercrosslinked polymer (HCP) was obtained via a simple photocycloaddition of the cinnamoyl-containing polyimide precursor. The resulting polymer showed a high specific surface area of 531 m2 g−1 and high thermal stability. Taking advantage of the high porosity, high electron-rich heteroatoms contents and π-electron conjugated backbone, the material exhibits excellent iodine capture performance, including ultrahigh iodine vapor capture (528 wt%) and iodine removal efficiency from aqueous solution. The capture behavior is consistent with the pseudo-second-order model and the spectral results indicate that the captured iodine existed in the form of polyiodide anions. Furthermore, the HCP maintained 90.76% of the uptake capacity after four cycles. This study provides a new proposal for the preparation of functional HCP as an efficient iodine absorbent to solve environmental issues. [Display omitted] • Novel electron-rich hypercrosslinked polymer (HCP) was obtained via a simple photocycloaddition of polyimide precursor. • The resulting polymer showed a high specific surface area of 531 m2 g−1 and high thermal stability. • It exhibits excellent iodine capture performance (528 wt%) and iodine removal efficiency in aqueous solution (83.5%). • The HCP maintained 90.76% of the uptake capacity after four cycles. [ABSTRACT FROM AUTHOR]

In this study, two series of polyimides (PI) were synthesized from one step solution polycondensation of two diamines containing sulphonyl group with aromatic and aliphatic dianhydrides. These PIs showed good organosolubility and were casted into films with high transparency of T 500 >86%, and cutoff wavelength in the range of 295–370 nm. Optical birefringence (0.0020–0.0127) of these PIs was lower than that of traditional aromatic PI. PI films demonstrated out-of-plane retardation (R th) in the range of 42–279 nm, indicating low optical anisotropy of these films. All PIs also exhibited high thermal stability with glass transition temperatures ranging from 200 to 339 °C. PI- 1c derived from bis[4-(3-aminophenoxy)phenyl] sulfone (m -BAPS) and 4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA) showed the lowest birefringence and good transparency. [Display omitted] • Synthesis of two series of transparent PI films with low birefringence and retardation. • Role investigation of ether and SO 2 groups of two diamines on polymer film properties. • PI- 1c with T 500 of 87% showed the lowest birefringence of 0.0020 and R th of 42 nm. [ABSTRACT FROM AUTHOR]

Polydimethylsiloxane (PDMS)-graft copolyimides were synthesized by polycondensation of 3,5-bis(4-aminophenoxy)benzyloxypropyl-terminated PDMS macromonomer with 4,4’-hexafluoroisopropylidene diphthalic anhydride (6FDA) followed by chemical imidization to investigate the effects of PDMS segment length of copolyimides on the membrane characteristics, the gas permeability and the pervaporation performance. The copolyimide membranes, which were prepared by solvent-casting method from the chloroform solutions, became insoluble in any solvents after the thermal treatment over 150 °C in vacuo . It was confirmed from TEM observation of these membranes that the phase separation of flexible PDMS domains and hard polyimide backbones. The gas permeability coefficients of copolyimide membranes were increased as the PDMS segment length increased, but decreased after thermal treatment at 200 °C. It would be due to the chain scission and the rearrangement of PDMS segments in the side chain to become a cross-linked structure, which make the membranes insoluble. From the results of pervaporation of dilute aqueous solutions of organics, it was found that the copolyimide membranes exhibited the excellent permselectivity toward several organics, such as ethanol, acetone, benzene, chloroform and dichloromethane with a high and stable permeation. Furthermore, it was confirmed that the removal of dichloromethane from its saturated aqueous solution was efficiently achieved by the pervaporation. [ABSTRACT FROM AUTHOR]

We investigate the adhesion behavior between polyimide and silica glass using molecular dynamics simulations, which is important for improving the manufacturing process of flexible displays. Various polyimides are simulated to understand the complex adhesion mechanisms that occur at the interface with inorganic glass. Through the pulling process implemented within the framework of steered molecular dynamics using reactive force-field, we calculate properties such as potential of mean force, pulling distance, and pulling force, which govern the adhesion behavior at the polymer-glass interface. It is found that a polyimide with a lower coefficient of thermal expansion requires a greater force but a shorter pulling distance to completely detach it from the silica surface. The change in the chain conformation during the pulling process reveals that polyimide chains near the interface dominate the molecular response due to their stronger adhesion to the glass surface. The decomposed energy terms from the interatomic potential indicate that the contribution from bonds and coulombic energy play the most significant role in the deformation of the system. Finally, failure mode analysis demonstrates that adhesive failure is the dominant mechanism regardless of the type of polyimide. [ABSTRACT FROM AUTHOR]

Graphene oxide produced by Tour's method (GO) and GO functionalized with 4-4′ oxydianiline (ODAGO) are incorporated at 0.01 to 0.10 weight percent (wt%) into a polyimide (PI) made from 3,3′-benzophenonetetracarboxylic dianhydride (BTDA) and 4-4′ oxydianiline (ODA). The performance properties of these two systems GO-PI and ODAGO-PI at extremely low GO concentrations are compared. ODAGO-PI nanocomposite's performance properties are comparable to previous results citing concentrations 10 times higher and displayed significantly greater improvement than unfunctionalized GO-PI films. The 0.01 wt% ODAGO-PI film demonstrated a factor of ten decrease in water vapor permeability. The 0.10 wt% ODAGO-PI film displayed the maximum increase of 82% in Young's modulus. The water vapor permeability results were fit to the Nielsen law. We found that the model yielded unphysically large aspect ratios for the 0.01 wt% ODAGO-PI, 100 times larger than the AFM-measured value. For the GO-PI, we observe less enhancement of the barrier properties. The large aspect ratio indicates tortuosity effects alone cannot explain the enhanced barrier properties. We propose that the improved barrier properties are also due to a stabilizing effect of the flakes on the polymer matrix, where reduced mobility of the PI chain reduces diffusion through the polymer matrix. ATR-FTIR, WAXS, Raman and T g results support this view. [ABSTRACT FROM AUTHOR]

The elastic properties of a fully aromatic polyimide were measured for the first time by Brillouin scattering in a high-pressure diamond anvil cell. Its isothermal compressibility and pressure dependence of mechanical moduli (K s , E, and G) were studied and determined up to 6.4 GPa. Further, piezochromic behavior of the polyimide film was observed and studied in detail by spectroscopic analysis. Pressure-induced red shift of the absorption edge and a hysteretic phenomenon were found, due to an enhancement of the van der Waals interaction upon decreasing the interchain distances and partially collapsing the free volume under extreme pressure. A comprehensive study of elastic properties and piezochromism behavior of polyimide film under high pressure will provide useful information for developing pressure sensitive coatings, pressure sensors, pressure resistance parts and components. [ABSTRACT FROM AUTHOR]

The polyimide (PI)/polyacrylonitrile (PAN) blend fibers were successfully prepared through a wet-spinning method, derived from the blend of poly (amic acid) (PAA) and PAN precursors in dimethyl sulfoxide (DMSO) solvent. Herein, the effects of thermal treated time and PAN weight ratios on the structures and properties of the PI/PAN blend fibers were systematically explored. The increased thermal treated time favored the imidization of PAA and cyclization of PAN. As a consequence, the optimum mechanical properties of the PI/PAN blend fibers were obtained at a thermal treated time of 10 min with the tensile strength of 1.15 GPa and initial modulus of 50.87 GPa. On the other hand, the combination of PI and PAN facilitated the imidization process of PAA and the formation of ladder structures of PAN, while the optimum mechanical performances were achieved when the PAN weight ratio was 23 wt%. In addition, the PI and PAN macromolecules exhibited good compatibility in the blend fibers with the glass transition temperature around 300 °C. [ABSTRACT FROM AUTHOR]

A new method to characterize local conformations of aromatic imide compounds and polyimides was established via Fourier transform infrared (IR) spectroscopy at low frequencies (far-IR) and density functional theory (DFT) calculations. The far-IR spectrum of an imide model compound ( s BPDA/An) was well reproduced by the DFT calculations in the 650–100 cm −1 range by considering local molecular conformations and the effects of neighboring molecules. The conformations of 3,3′,4,4’-biphenyltetracarboxylic ( s BPDA) type polyimide films were subsequently analyzed using their far-IR spectra compared with the calculated spectra of s BPDA/An. The dihedral angle between biphenyldiimide moieties ( ϕ ) tends to be coplanar in the highly ordered region, whereas that between phthalimide and phenylene ( ω ) tends to be more twisted. Conformation dependent far-IR is a facile and versatile tool to estimate local conformations of aromatic polymers. [ABSTRACT FROM AUTHOR]

Thermal oxidative crosslinking results in the generation of oxygen bridges among polymer chains and helps regulate the membrane microstructure. Simultaneously, any strategy to increase the crosslinking sites of polyimide (PI) can improve the crosslinking efficiency and allow precise control of the pore structure of membranes. Phenolphthalein-based PIs are potentially suitable precursors for thermal oxidative crosslinking of membranes, since thermal treatment will result in the degradation of lactone ring leading to the generation of a pair of phenyl crosslinking sites. In this work, three phenolphthalein-based diamines with different structures were designed and synthesized. The three diamines were subsequently reacted with 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) to prepare phenolphthalein-based PIs. The original membranes were post-treated by thermal oxidation crosslinking at 400 °C and 425 °C, respectively; the lactone ring underwent decomposition, and the imide ring opened at the same time, resulting in the generation of multiple crosslinking sites and correspondingly improving the crosslinking efficiency. The effect of the side groups (−CH 3 , –CF 3 or unsubstituted) of phenolphthalein-based diamine and thermal treatment temperatures on the gas separation performance of phenolphthalein-based PI membranes were investigated. Wide-angle X-ray diffractometry (WAXD) and wide-angle X-ray scattering (WAXS) analysis demonstrated that the π-π stacking distance were improved. BTDA-FPP-425 had a CO 2 /CH 4 selectivity of 37.68. This thermal degradation along with thermal oxidative crosslinking strategy provides a promising approach for fabrication of CO 2 /CH 4 separation membrane. [Display omitted] • Phenolphthalein-based polyimide is a suitable precursor for thermal crosslinking. • BTDA-based polyimide has low cost and good mechanical properties. • The lactone ring and the imide ring open, generating multiple crosslinking sites. • Thermal degradation and oxidative crosslinking improved the π-π stacking values. • A strategy for making CO 2 /CH 4 separation membrane with anti-plastic was achieved. [ABSTRACT FROM AUTHOR]

A novel series membranes based on non-linear all-aromatic polyimides (PIs) was investigated with the aim to understand how the PI backbone geometry and local electrostatics govern gas transport and the ability to separate CO 2 /CH 4 mixtures. Non-linear 3-ring aromatic diamines, with exocyclic bond angles varying between 120 and 134°, enable the design of high Tg (>276 °C) PIs. A polar 1,3,4-oxadiazole diamine (ODD) (μ = 3D) monomer and a non-polar m -terphenyl diamine (TPD) reference monomer were synthesized and coupled with 3 dianhydrides, i.e. ODPA, ODDA, and 6FDA. In 6FDA-based membranes CO 2 permeabilities (P CO2) are the highest of the series. The 6FDA-ODD membrane shows excellent membrane performance with high P CO2 values at all feed pressures. Up to 12 bar (6 bar CO 2) none of the membranes reached their plasticization pressure. The non-linear backbone geometry promotes CO 2 permeability, whereas the presence of an electrostatic dipole moment associated with the 1,3,4-oxadiazole heterocycle governs CO 2 /CH 4 separation selectivity. [Display omitted] • The role of Polyimide (PI) backbone and polarity in gas separation performance. • Amorphous high T g PIs with polar & non-polar moieties. • Incorporation of polar 1,3,4-oxadiazole group in PI yields high CO 2 /CH 4 selectivity. • Backbone geometry of PI governs CO 2 permeability. [ABSTRACT FROM AUTHOR]