Biphenyltetracarboxylic Dianhydride Research Articles

Facile construction of a stable core-shell spherically magnetic polyimide covalent organic framework for efficient extraction of phenylurea herbicides

Efficient enrichment is crucial for the highly sensitive monitoring of phenylurea herbicides (PUHs) in various environmental waters. In this work, a stable core-shell spherically magnetic polyimide covalent organic framework (COF) was synthesized via a simple template-mediated precipitation polymerization method under mild conditions using tri(4-aminophenyl)amine (TAPA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) as the building units (denoted as Fe3O4@TAPA-BPDA). The Fe3O4@TAPA-BPDA exhibits remarkable adsorption performance for PUHs with an optimized adsorption time of only 10 min. The adsorption of PUHs by Fe3O4@TAPA-BPDA followed the pseudo-second-order kinetic model and the Langmuir model. Furthermore, hydrogen bonding, halogen bonding, hydrophobic interaction, electro donor-acceptor interaction and π-π interactions are identified as the dominant mechanisms contributing to excellent adsorption performance. It was demonstrated that halogen bonds play an important role in the adsorption of substances containing chlorine atoms. The Fe3O4@TAPA-BPDA is easy to operate and highly regenerable. A simple magnetic solid-phase extraction (MSPE) method based on the Fe3O4@TAPA-BPDA was then developed for the rapid extraction of five PUHs in real samples, coupled with high-performance liquid chromatography (HPLC) determination. The analytical method developed has a linear range of 0.5–50 ng/mL, and the limit of detection (LOD) ranges from 0.06 to 0.10 ng/mL. The method exhibits good accuracy with recoveries ranged from 74.5 % to 111.4 %. The analytical method was successfully applied to the highly sensitive detection of PUHs in environmental water samples, which highlighting the potential application of the Fe3O4@TAPA-BPDA in the sample pretreatment.

Polyimides with ultra-low coefficient of thermal expansion derived from diamine containing bisbenzimidazole and bisamide

To provide polyimide (PI) with high heat resistance and ultra-low coefficient of thermal expansion (CTE) for use in flexible display substrates, a novel diamine with bisbenzimidazole and bisamide groups, namely N,N'-(1H,1'H-[5,5'-bibenzo[d]imidazole]-2,2'-diyl)bis(4-aminobenzamide) (BZBA), was designed and successfully synthesized. Several poly(benzimidazole-amide-imide) (PBIAI) films were prepared by thermal imidization with 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 4,4'-oxydiphthalic anhydride (ODPA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), and 4,4'-(hexafluoroisopropylindene)-diphthalic anhydride (6FDA), respectively. Among them, BZBA-BPDA has a high glass transition temperatures ( Tg = 345 °C) while achieving an extremely low coefficients of thermal expansion (CTE = 1.9 ppm K−1), meeting the processing requirements of polymer flexible substrates in OLED devices. The effects of different dianhydrides on the performance of PBIAIs were compared, providing a meaningful reference for further adjusting the PI molecular structure to meet specific requirements for industrial polymer films.

Preparation and Properties of Low-Dielectric Polyimide Films Containing Tert-Butyl.

The design of high-performance polyimide (PI) films and understanding the relationship of the structure-dielectric property are of great significance in the field of the microelectronics industry, but are challenging. Herein, we describe the first work to construct a series of novel tert-butyl PI films (denoted as PI-1, PI-2, PI-3, and PI-4) based on a low-temperature polymerization strategy, which employed tetracarboxylic dianhydride (pyromellitic anhydride, 3,3',4,4'-biphenyl tetracarboxylic anhydride, 4,4'-diphenyl ether dianhydride, and 3,3',4,4'-benzophenone tetracarboxylic anhydride) and 4,4'-diamino-3,5-ditert butyl biphenyl ether as monomers. The results indicate that introducing tert-butyl branches in the main chain of PIs can enhance the free volume of the molecular chain and reduce the interaction between molecular chains of PI, resulting in a low dielectric constant. Particularly, the optimized PI-4 exhibits an excellent comprehensive performance with a high (5) wt% loss temperature (454 °C), tensile strength (117.40 MPa), and maximum hydrophobic angle (80.16°), and a low dielectric constant (2.90), which outperforms most of the results reported to date.

Preparation of anisotropic polyimide aerogels for thermal protection with outstanding flexible resilience using the freeze-drying method.

Polyimide aerogels (PIAs) not only possess excellent thermodynamic properties but also have a high porosity structure, making them an exceptional protective and thermal insulation material, and further broadening their application scope in aerospace and other cutting-edge fields. In this work, a series of anisotropic polyimide aerogels (3,3',4,4'-biphenyltetracarboxylic dianhydride (S-BPDA), p-phenylenediamine (PDA), 4,4'-diaminodiphenyl ether (ODA)) with excellent properties were prepared. These PIAs were obtained by unidirectional freeze-drying and thermal amination of two different precursor solutions mixed in proportion. These PIAs possess an irregularly oval tubular structure, exhibiting pronounced anisotropy. (PIA-2 exhibits outstanding flexible resilience in the radial direction. It can still regain its original form after half an hour of compression by a universal testing machine, yet it cannot do so in the axial direction. The thermal diffusivity of PIA-5 in the radial direction at room temperature is as low as 0.067 mm2 s-1, and even at 200 °C, the thermal diffusivity is as low as 0.057 mm2 s-1. Meanwhile, the thermal diffusivity in the axial direction at room temperature is 0.11 mm2 s-1, surpassing the value of 0.106 mm2 s-1 of aerogels prepared from monomeric raw materials and dried under supercritical conditions). PIAs exhibit outstanding thermal stability (the axial strength and modulus retention of PIA-8 at 200 °C are as high as 52.63% and 44.82%), and its weight loss temperature of 5% is as high as 603 °C and it has a glass softening temperature of 387 °C. PIAs also demonstrate exceptional flame retardancy in imitation flame retardant experiments and exhibit outstanding thermal insulation performance when heated on a 150 °C heating plate for 10 minutes (the radial surface temperature of PIA-5 was only 49.9 °C). These anisotropic PIAs materials exhibit outstanding flexible resilience, and thermal protection performance, holding significant importance for their widespread adoption as thermal insulation materials in aerospace, high-precision electronic components, and other domains.

Synthesis and properties of modified thermoplastic polyimide films with good dielectric properties at high frequency and enhanced thermal stability via incorporation of rigid ester and biphenyl structural units

AbstractA series of ester‐ and fluoro‐containing thermoplastic polyimide (PI) films, PEsI‐1 ~ PEsI‐4 have been prepared by the two‐step thermal imidization procedure via the soluble poly(amic acid) (PEsAA) precursors from the copolymerization of four monomers, including the dianhydrides of bisphenol A dibenzoate‐3,3′,4,4′‐tetracarboxylic acid dianhydride (TMBPA) and 3,3′, 4,4′‐biphenyl tetracarboxylic acid dianhydride (BPDA) and the diamine monomers of 4‐aminophenyl‐4′‐ aminobenzoate (APAB) and 2,2′‐bis(trifluoromethyl)‐4,4′‐diamino biphenyl (TFMB) in the polar aprotic solvent of N‐methyl‐2‐pyrrolidinone (NMP). The PI films obtained from the high‐temperature dehydration of the PEsAA solutions exhibited the good thermal stabilities with the glass transition temperatures (Tg) over 269°C, the 5% weight loss temperatures (T5%) higher than 480°C, and the linear coefficients of thermal expansion (CTE) values in the range of 17.7 × 10−6/K–33.6 × 10−6/K in the temperature range of 50–250°C. Meanwhile, the PI films showed good thermoplasticity in the dynamic mechanical analysis (DMA) tests, in which the storage modulus of the PI films dropped sharply in the temperature range of glass transition of the polymers. At last, the PI films exhibited the good dielectric properties with the breakdown voltages (Vb) over 5200 V, the dielectric strength (Ds) higher than 210 V/μm, the dielectric constants (Dk) in the range of 3.26 ~ 3.32 at the frequency of 10 GHz, and the dielectric dissipation factors (Df) of 0.0038 ~ 0.0047. Compared with the commonly used PEsI‐ref film for high‐frequency flexible copper clad laminates (FCCL), the currently developed PI films exhibited the obviously increased Tg values, decreased CTE values, and comparable dielectric properties.

Synthesis and properties of poly(ester imide) copolymers from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride, 2,2′‐bis(trifluoromethyl)benzidine, and 4‐aminophenyl‐4′‐aminobenzoate

AbstractA series of poly(ester imide) (PEsI) copolymers were synthesized using 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (4,4′‐BPDA), 2,2′‐bis(trifluoromethyl)benzidine (TFMB), and 4‐aminophenyl‐4′‐aminobenzoate (APAB) as the monomers. Wide‐angle x‐ray diffraction results revealed that the average interchain distances of these polymers ranged from 4.6 to 5.7 Å, increasing with the increase of TFMB contents. PEsI‐0.3 and PEsI‐0.4 exhibited a glass transition temperature (Tg) of 445 and 455°C, respectively, while no distinctive Tg was observed for the PEsI copolymers when the APAB content was >50 mol%. The coefficients of thermal expansion (CTE) of these PEsI copolymers ranged from 3.8 to 24.2 ppm K−1, increasing with the increase of TFMB contents. The PEsI copolymers exhibited a modulus of 5.7–7.8 GPa, a tensile strength of 282–332 MPa, and an elongation‐at‐break of 10.2%–23.3%. Furthermore, these copolymers exhibited a dielectric constant of 2.53–2.76, and a low dissipation factor (Df) of 0.0026–0.0032 at 10 GHz in dry state. Because of their excellent combined properties, these PEsI copolymers are promising candidates as dielectric substrate materials for the applications in next generation flexible printed circuit boards operating at high frequencies.

Synthesis of novel biphenyl‐fused alicyclic tetracarboxylic dianhydride and its performance in thermostable and transparent colorless polyimides

AbstractBiphenyl fused alicyclic tetracarboxylic dianhydride, 6,6′,7,7′‐tetracarboxylic dianhydride‐5,5′,6,6′,7,7′,8,8′‐octahydro‐2,2′‐binaphthalene (OHBNDA) was successfully synthesized from biphenyltetracarboxylic dianhydride (BPDA) through hydrolysis, reduction, bromination, and Diels–Alder reaction. Three OHBNDA‐based polyimides (PIs) were synthesized by one‐step polycondensation at high temperature with 9,9‐bis(4‐aminophenyl)fluorene (BAFL), 2,2′‐bis(trifluoromethyl)‐4,4′‐diaminobiphenyl (TFMB), and 4,4′‐diamino‐2,2′‐dimethyl‐1,1′‐biphenyl (m‐TolDA) diamines, respectively. These PIs have moderate molecular weights and good solubility in polar organic solvents, such as N,N‐dimethylformamide, dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO). OHBNDA‐TFMB, OHBNDA‐m‐TolDA, and OHBNDA‐BAFL display glass transition temperatures (Tgs) of 309, 329, and 377°C from differential scanning calorimetry (DSC) curves, and the decomposition temperatures at 5% weight loss (Td5) of as high as 522, 507, and 548°C under nitrogen, respectively. Meanwhile, these PI films also show good optical transparency with the cut‐off wavelength <315 nm and the transmittance >75% at 400 nm. These results confirm that aryl‐fused alicyclic tetracarboxylic dianhydrides can afford transparent/colorless PIs with high thermal stability, especially the higher decomposition temperatures than the wholly alicyclic dianhydrides.

Novel rigid semi-alicyclic dianhydride with large side groups for high performance colorless polyimides (CPIs)

A new dianhydride 9,10-diphenyl-9,10-bis(trifluoromethyl)-9,10-dihydroanthracene-2,3,6,7-tetraacid dianhydride (6FDPDA) with rigid semi-alicyclic structure was reported. CPI materials were prepared by copolymerizing 6FDPDA with 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA) or 4,4’-(hexafluoroisopropene) diphthalic anhydride (6FDA) respectively, with 2,2′-bistrifluoromethyl benzidine (TFDB) as the diamine building blocks. Due to the ladder semi-alicyclic structure as well as –CF3 and phenyl large side groups, this new dianhydride exhibits two important advantages, the cut-off conjugated in the polymer backbone and suppressed intermolecular stacking. When 6FDA as the dianhydride comonomer, the obtained CPIs exhibits distinguished performance with transmission of 90 % at 550 nm, YI of 2.45, CTE of 16.5 ppm/K and Tg over 450 °C. These results demonstrated that 6FDPDA is an excellent building block to prepare the high performance CPIs in optoelectronic devices, for an example the substrates for flexible AMOLED display.

Polyimide aerogels with low thermal conductivity and high-temperature stable properties prepared by lyophilization for flexible thermal protection

Polyimide aerogel, presenting an outstanding new material for lightweight protective thermal insulation, has garnered significant attention in the aerospace field. Despite its potential, due to the high production cost of the supercritical drying method used for its preparation, its widespread application is limited. In this research, a series of lightweight polyimide aerogels (F-PIAs, 3,3',4,4'-biphenyl tetracarboxylic dianhydride (s-BPDA) and 4,4'-diaminodiphenyl ether (ODA)) with excellent thermal protection properties were prepared by lyophilization. The findings indicated that F-PIAs (Freeze-dried polyimide aerogels) exhibited comparable physical characteristics to S-PIAs (Supercritical-dried polyimide aerogels), while their preparation cost was even more economical. F-PIAs exhibits excellent flexible and compression behavior (compression strength up to 1.16 MPa, modulus up to 12.8 MPa), which provide a great structural basis for the production of molded thermal insulation protective materials. The average pore diameter of F-PIAs is in the range of 7∼11 nm. The nanoporous structure leads to the gas within the pores of the aerogel producing the Knudsen effect, thereby significantly enhancing the thermal insulation performance of the aerogel. The thermal conductivity of F-PIA-4 (Freeze-dried polyimide aerogels with a solid content of 4%) at room temperature is as low as 0.023 W·m−1·K−1, which is superior to the PIAs (0.043 W·m−1·K−1) prepared by lyophilization in literature. Its thermal diffusion coefficient changes from 0.108 mm2·s−1 to 0.18 mm2·s−1 in the temperature range of 27°C to 200°C, demonstrating good thermal insulation performance at high temperatures. Meanwhile, after heating on a 150°C flat plate for 11 min and 41 s, the surface temperature of F-PIA-4 was only 36.2°C, further verifying its excellent thermal insulation performance. The results of the TGA experiment on F-PIA-4 demonstrated the high-temperature stability of aerogel (Td5% is higher than 523°C, Td10% is higher than 566°C). The exceptional properties of F-PIAs hold significant practical reference value in helping to reduce the manufacturing cost of high-performance aerogel thermal insulation materials, thereby enabling their widespread application in aerospace, military, and civil field.

Insights into Entropy Change of β2 Relaxation in Retraction of Uniaxially Stretched Polyimide Films

AbstractStretching has been extensively applied for decades in the production of polyimide (PI) materials with improved mechanical, electrical, and thermal properties. Meanwhile, a detailed understanding of the molecular motions during stretching is still limited. Herein, the thermomechanical behaviors of uniaxially stretched PI films prepared from 3,3′,4,4′‐biphenyl tetracarboxylic dianhydride (BPDA) and 2,2′‐bis (trifluoromethyl) benzidine (TFDB) are studied, and the possible molecular motions responsible for the sub‐glass transition temperature (Tg) stretchability and retraction after stretching are systematically investigated. Based on X‐ray diffraction and dynamic mechanical analysis, it is revealed that both the sub‐Tg stretchability and retraction correlates with β2 relaxation, which originates from the highly cooperative molecular motions of conformational rotations involving segmented BPDA units. A thermodynamic model is established and applied for the analysis of the retraction behaviors of stretched BPDA‐TFDB PI films. It is found that the increase of entropy under stretching plays a significant role in most retraction cases. However, as the stretching temperature increases, the α relaxation‐correlated large‐scale molecular motions emerge. Such motions partially counterbalance the conformational rotations of BPDA segments, leading to an enhanced contribution of enthalpy decrease during the retraction of BPDA‐TFDB PI films.

Porous Adsorbents Cross-Linked with Waste Polystyrene Foam and 3,3′,4,4′-Biphenyltetracarboxylic Acid Dianhydride for the Effective Removal and Enrichment of Cationic Dyes

Porous Adsorbents Cross-Linked with Waste Polystyrene Foam and 3,3′,4,4′-Biphenyltetracarboxylic Acid Dianhydride for the Effective Removal and Enrichment of Cationic Dyes

High performance imide oligomers and thermosets derived from 9,9-bis (3,4-dicarboxyphenyl)fluorene dianhydride

In this work, a new class of imide oligomers and thermosets with improved overall properties was developed by exploiting the steric effects of 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF). First, a model compound was prepared from BPAF and aniline. This model compound possessed a twisted architecture, with two dihedral angles between fluorene ring and phthalimide segments of around 75°. Then, an array of phenylethynyl-endcapped imide oligomers was synthesized from BPAF, 4-phenylethynyl phthalic anhydride (4-PEPA), and aromatic diamines (4,4′-oxydianiline (4,4′-ODA), 2,2′-bis(trifluoromethyl)benzidine (TFMB), m-phenylenediamine (m-PDA)). The BPAF-derived imide oligomers exhibited improved organic solvents solubility and higher melt viscosity compared to those based on 2,3,3′,4′-biphenyltetracarboxylic dianhydride (3,4′-BPDA), due to their bulky, twisted, and sterically hindered cardo architectures. The imide oligomers under pressure were converted into thermosets by the thermal crosslinking of phenylethynyl at 370 °C for 2 h. The BPAF-derived thermosets exhibited much higher glass transition temperature (Tg) (＞ 404 °C), 5% weight-loss temperature (T5%) (＞ 549 °C) in an air environment, and more excellent high-frequency dielectric properties from 30 to 45 GHz (dielectric constant as low as 2.85 and dielectric loss factor as low as 0.0037) while possessing comparable or even better mechanical properties relative to the 3,4′-BPDA-derived polymers. Therefore, these polymers based on BPAF may have potential applications as matrix resins for heat-resistant, structural and functional composites.

Investigating the structure–sensitivity relationship of photosensitive polyimide formulated by using a photobase generator

AbstractPhotosensitive polyimides (PSPIs) have been widely used in the buffer coating layer and insulation layer due to their excellent thermal and mechanical stability. In this work, a series of negative‐type PSPIs based on poly(amic acid) (PAA) and a photobase generator (PBG) have been developed. Two diamines of 4,4′‐oxydianiline (ODA), 3,3′‐diaminodiphenyl sulfone (SDA), and four dianhydrides of pyromellitic dianhydride (PMDA), 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), 4,4′‐oxydiphthalic anhydride (ODPA) and cyclobutene‐1,2,3,4‐tetracarboxylic dianhydride (CBDA) are copolymerized to PAA through polyaddition, and the PAA is further thermally imidized to polyimide (PI). Through scrutinizing the structure–sensitivity relationship of these PIs, we find that the rigidity and transparency of the PAA/PI backbone play an important role in the sensitivity and contrast of PSPI. Accordingly, PSPI (SDA‐ODPA), possessing high optical transparency and a low rigidity represented by the low glass transition point, is capable of providing good photosensitivity of 30 mJ/cm2, a high contrast of 2.46, and an excellent pattern resolution of 4 μm after optimizing the prebaking (100°C for 5 min), exposure dose (380 mJ/cm2), post‐exposure baking (130°C for 7 min), and development parameters. This work provides the concept of structural design for negative‐type PSPI in the microelectronic application.

Colorless polyimide copolymers derived from isomeric biphenyltetracarboxylic dianhydrides and 2,2′-bis(trifluoromethyl)benzidine

Colorless polyimide (CPI) copolymers were synthesized by one-step or two-step methods, using 2,2′-bis(trifluoromethyl)benzidine (TFMB), 2,2′,3,3′-biphenyltetracarboxylic dianhydride (3,3′-BPDA), and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (4,4′-BPDA) as the monomers. These polymers exhibited a d-spacing value of 5.7–6.7 Å, and their d-spacing values increased while the intensity of π-π stacking interactions decreased with the increase of 3,3′-BPDA/TFMB contents. The solubility of the copolymers were gradually enhanced as the increase of 3,3′-BPDA/TFMB contents. Their coefficients of thermal expansion and glass transition temperatures increased with 3,3′-BPDA/TFMB contents, ranging from 15 to 68 ppm K−1 and 300 to 359 °C, respectively. These polymers exhibited excellent optical transparency (λ0 < 390 nm, T450 > 83.2%, and b* < 4). CPI-4 and CPI-5 with 40 mol% and 20 mol% of 3,3′-BPDA/TFMB contents exhibited well-balanced solution processability and physical properties. The CPI copolymers can be potentially used in optical and optoelectronic fields owing to their desirable overall properties.

High glass transition temperature and ultra‐low thermal expansion coefficient polyimide films containing rigid pyridine and bisbenzoxazole units

AbstractPolyimide (PI) films with extremely high heat‐resisting and dimensional stability are ideal substrate materials for flexible organic light‐emitting diodes. In this study, three diamines containing rigid bisbenzoxazole structures, 2,2′‐p‐phenylenebis(5‐aminobenzoxazole) (phDBOA), 2,2′‐m‐pyridylenebis(5‐aminobenzoxazole), and 2,2′‐p‐pyridylenebis(5‐aminobenzoxazole) (p‐PDBOA), were polymerized with 3,3′,4,4′‐biphenyl tetracarboxylic dianhydride and pyromellitic dianhydride (PMDA) separately with traditional two‐step approach to prepare a set of PI films. Introduction of bisbenzoxazole improves stiffness of molecular chain, whereas that of pyridine increases in‐plane orientation and molecular chain tend to be densely stacked. Among prepared films, PI‐6 (PMDA/p‐PDBOA) shows the most excellent mechanical properties, with an ultra‐high glass transition temperature of &gt;450°C, an ultra‐low thermal expansion coefficient of &lt;5 ppm K−1 (50–450°C), a tensile strength of 259 MPa, and a modulus of 8.3 GPa. Given these excellent properties, PI‐6 could be applied in flexible display.

Isomeric Aromatic Polyimides Containing Biphenyl Moieties for Gas Separation Applications

An optimized synthesis of the monomer 2,2'3,3'-biphenyltetracarboxylic dianhydride, iBPDA, was performed to obtain high molecular weight polymers. This monomer has a contorted structure that produces a non-linear shape, hindering the packing of the polymer chain. Aromatic polyimides of high molecular weight were obtained by reaction with the commercial diamine 2,2-bis(4-aminophenyl) hexafluoropropane, 6FpDA, which is a very common monomer in gas separation applications. This diamine has hexafluoroisopropylidine groups which introduce rigidity in the chains, hindering efficient packing. The thermal treatment of the polymers processed as dense membranes had two targets: on the one hand, to achieve the complete elimination of the solvent used, which could remain occluded in the polymeric matrix, and on the other hand to ensure the complete cycloimidization of the polymer. A thermal treatment exceeding the glass transition temperature was performed to ensure the maximum degree of imidization at 350 °C. The good mechanical properties of these materials allow for their use in high-pressure gas purification applications. Moreover, models of the polymers exhibited an Arrhenius-like behavior characteristic of secondary relaxations, normally associated with local motions of the molecular chain. The gas productivity of these membranes was high.

Synthesis and memory properties of a series of novel asymmetric soluble polyimides

Abstract Two asymmetric diamines [1,1′-biphenyl]-4-yl(3,5-diaminophenyl) methanone (BPDAM) and (3,5-diaminophenyl)(4′-(naphthalen-1-yl)-[1,1′-biphenyl]-4-yl) methanone(DANPBPM) were synthesized by Suzuki coupling reaction from (4-bromophenyl)(3,5-diaminophenyl) methanone (BDAM) and corresponding arylboronic acid. A series of polyimides exhibiting organic solubility were prepared from 2,2′,3,3′-biphenyl tetracarboxylic dianhydride(BPDA) and these above three new diamines via a two-stage process. The obtained polymers showed outstanding organic solubility and high thermal stability. And studies have shown that the storage device with a sandwich type configuration of Al/polyimide/ITO was prepared by the traditional liquid spin coating technology, which showed the storage capacity of flash memory type. All the polyimide-based devices showed bistable conductivity switching and nonvolatile memory behavior that had long preservation period and high ON/OFF electric current, the rate of which was 104.

Ultra-high Tg and ultra-low CTE polyimide films based on tunable interchain crosslinking

A novel interchain crosslinking system was designed to improve the thermal performance of PI films. A diamine containing Cl atom (Cl-DAXBA) was prepared and polycondensed with pyromellitic dianhydride and 3,3′,4,4′-biphenyl tetracarboxylic dianhydride, respectively. Two series of PI films (PM and BP) were prepared under different curing temperatures in the range of 320–380 °C. The crosslinking of free radicals produced by Cl-DAXBA decomposition occurred between the molecular chains, and the crosslinking degree increased with raising the curing temperature. The network structure formed by crosslinking effectively inhibited the movement of molecular chains and promoted their close packing. The glass transition temperature (Tg) of PM films increased from 378 °C to >450 °C, and the coefficient of thermal expansion (CTE) decreased from 66.3 ppm·K−1 to 4.9 ppm·K−1. The Tg of BP films increased from 349 °C to >450 °C, and the CTE decreased from 50.4 ppm·K−1 to 17.7 ppm·K−1. Definitely, the tunable interchain crosslinking provides an effective strategy to improve both Tg and CTE simultaneously.

Mechanically Strong and Thermally Stable Chemical Cross-Linked Polyimide Aerogels for Thermal Insulator.

High-performance thermal insulating materials are highly desirable in several fields, especially for thermal insulation of buildings to reduce energy consumption. Owing to the remarkable thermal stability, high porosity, low density, and outstanding mechanical features, polyimide (PI) aerogels have attracted great attention. In this work, chemical cross-linked PI (CCPI) aerogels were fabricated via freeze-drying and thermal imidization, which possess outstanding mechanical properties, good thermal stability, and excellent thermal insulation characteristics. The chemically cross-linked structure can effectively inhibit shrinkage, while retaining the structural integrity, resulting in the lower density and lower shrinkage of the materials. In this paper, completely imidized and highly cross-linked polyimide aerogels were synthesized by using p-phenylenediamine (PDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), and the cross-linker 2,3,6,7,14,15-hexaaminotriptycene (HMT). The CCPI aerogels with excellent properties, such as covalently cross-linked chemical structure, low density (0.069 g/cm3), low volume shrinkage (10%), high decomposition temperature (Td5% = 587 °C), and low thermal conductivity (25 mW m-1K-1) are in high demand in the field of thermal insulation. This work furnishes a new method for the development of polymer-based thermal insulation materials for various prospective applications.

Shape memory polyimides and composites with tunable chain stiffness and ultrahigh transition temperature range

Shape memory polymer has shape morphing capabilities upon external stimuli, including thermal-, electro-, magnetic-, photo-, and so on. Among them, shape memory polyimide (SMPI) has excellent thermal stability, creep resistance, radiation resistance, and good mechanical properties, which can be applied in various fields. In this paper, 5-amino-2-(4-aminophenyl) benzimidazole, 2-(4-aminophenyl) benzoxazol-5-amine, and 3,3′,4,4′-biphenyltetracarboxylic dianhydride are utilized to synthesize two semi-trapezoidal aromatic heterocyclic SMPIs with tunable chain stiffness, including imidazole-based shape memory polyimide (M-SMPI) and oxazole-based shape memory polyimide (E-SMPI). Because of asymmetric imidazole groups, M-SMPI has the highest SMPI transition temperature in the world, at 416 ℃. Additionally, the M-SMPI/CF composite also has the highest SMPIC (shape memory polyimide composite) transition temperature, at 399 ℃. Thus, M-SMPI and M-SMPI/CF composites can be used as smart materials in deformable flexible electrodes, high temperature aerospace devices and deployable structures.