Poly Amic Acid Research Articles

Dynamic Non-Covalent Bonds Powering Enhanced Temporary Shape Retention Temperature and Mechanical Robustness in Shape Memory Polyurethane.

Shape memory polyurethane (SMPU) with excellent mechanical properties holds significant application value in engineering. However, achieving high strength and toughness typically relies on hydrogen bonding for energy dissipation, which limits the application of such PUs due to their deformation temperature being below room temperature. Here, we introduce a rigid long-chain polyamide acid with a rich aromatic structure as a chain extender, combined with metal coordination, to develop a shape memory polyurethane with a phase transition temperature of 50 °C and outstanding mechanical performance. The presence of rigid segments of polyamic acid (PAA) and -COOH not only increases the rigidity of the polyurethane chains but also promotes the formation of hydrogen bonds and π-π conjugation, leading to physical cross-linking points and significant microphase separation, resulting in superior mechanical properties for PU-PAA. The dynamic bonding characteristics impart self-healing and solvent recyclability to PU-PAA. The coordination interactions enhance the cross-linking points, enabling PU-PAA-Eu to exhibit excellent shape fixation and recovery rates, as well as fluorescence properties. Additionally, due to the presence of -COOH, PU-PAA demonstrates remarkable adhesion to various metals. This work provides a strategy toward the development of high performance SMPU and holds promising potential for applications such as anticounterfeit coatings.

One-pot aqueous-phase synthesis of polyimides from typical monomers

One-pot aqueous-phase synthesis of polyimides (PIs) offers great economic and environmental benefits and improves the hydrolytic stability of the precursor (polyamic acid) obviously. However, this method is only suitable for the polymerization of very limited dianhydride and diamine monomers up to now. In this study, the most commonly used dianhydrides and diamines for the preparation of commercially available PI products were selected for one-pot aqueous-phase synthesis of various polyamic acid salts (PAAS). The effects of the structure of monomers, the reaction temperature and the adding process of the organic base on the polymerization reaction were explored by rotational rheology, nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. The polymerization products obtained via the aqueous-phase route show high molecular weight when the reaction conditions have been optimized. Various PI films prepared by the thermal imidization of corresponding PAAS demonstrate good optical transparency, excellent thermal stability, and outstanding mechanical and electrical properties. This work proposes the reaction mechanism of PAAS via one-pot aqueous-phase route and utilizes this novel polymerization strategy to synthesize high-molecular-weight PIs from typical aromatic dianhydride and diamine monomers.

Superhydrophobic Electrospun PI/PTFE Membranes with Ultralow Dielectric Constants for High-Frequency Telecommunication.

High-frequency, high-power, and high-speed telecommunication in a complex environment promotes the development of dielectric materials toward a low dielectric constant, low dielectric loss, good thermal properties, and long-term reliability. Here, polyimide/polytetrafluoroethylene (PI/PTFE) nanofiber membranes with an inherent super hydrophobicity, excellent dielectric properties, good thermal stability, and enhanced tensile strength were prepared via a simple electrospinning strategy and an imidization reaction. The obtained PI/PTFE membranes demonstrate a superlow average dielectric constant of 1.22-1.27 and a dielectric loss of 0.032-0.048 in high frequency, together with an enhanced tensile strength, benefiting from the special nanofiber-bead structure formed in the composite membrane. The mixing of polyamic acid (PAA) and PTFE in the electrospinning solution endows the obtained PI/PTFE nanofiber membrane with a uniform distribution of PTFE and thus an inherent superhydrophobicity with a water contact angle of 156.1 and 159.2° for PI/PTFE-30% and PI/PTFE-40%, respectively. Besides, the hydrophobicity could be kept even after standing more than 10,000 water drops, and the thermal properties exhibited promising results with Tmax = 587 °C and Td5% = 423 °C, rendering these PI/PTFE membranes favorable alternatives for prospective telecommunication.

Cross-Linked Polyimide Aerogels with Excellent Thermal and Mechanical Properties.

With the increasing development of productivity, new materials that allow for the efficient use of energy are slowly becoming a sought-after goal, as well as a challenge that is currently being faced. For this reason, we have made aerogels as the target of our research and prepared different series (CLPI (1-5)) of cross-linked polyimide aerogels by mixing and cross-linking the heat-insulating cross-linking agent 1,3,5-tris(4-aminobenzylamino)benzene (TAB) with polyamic acid solution. We created a three-dimensional spatial organization by using vacuum freeze-drying and programmed high-temperature drying, then controlled the concentration of the polyamidate solution to investigate the concentration and TAB's influence on aerogel-related properties. Among them, the shrinkage is reduced from 40% in CLPI-1 to 28% in CLPI-5, and it also shows excellent mechanical characteristics, the highest compression strength (CLPI-5) reaches 0.81 MPa and specific modulus reaches 41.95 KN m/Kg. In addition, adding TAB improves the aerogel thermal resistance, T5 in N2 from PI-2 519 °C to CLPI-2 556 °C. The three-dimensional network-type structure of the aerogel shows an excellent thermal insulation effect, where the thermal conductivity can be as low as 24.4 mWm-1 K-1. Compared with some protective materials, cross-linked polyimide aerogel presents better flame-retardant properties, greatly improving the scope of its application in the industrial protection.

Fabrication of modified laser-induced graphene using activated carbon and polyamic acid coating for flexible and high-performance microsupercapacitors

In this study, we developed a method to combine polyamic acid (PAA) and activated carbon (AC), which were then coated on laser-induced graphene (LIG). The material was heated to facilitate the conversion of PAA–AC into polyimide (PI)–AC. Then, the resulting material was subjected to a second laser irradiation process to obtain AC–LIG composite materials. The resulting material features a robust and flexible electrode architecture with a high surface area, improved ion accessibility, and enhanced charge transfer kinetics. In tests conducted with a three-electrode setup, the AC–LIG configuration exhibited a considerably high specific capacitance, reaching 97.2 mF cm−2 at 0.2 mA cm−2, which is approximately fourteen times larger than that of pristine LIG (7.1 mF cm−2). When integrated into a flexible microsupercapacitor using a polyvinyl alcohol (PVA)–H2SO4 (sulfuric acid) gel-type electrolyte, AC–LIG exhibited a higher specific capacitance (68.4 mF cm−2 at 0.3 mA cm−2) than d-LIG (17.1 mF cm−2 at 0.3 mA cm−2). Furthermore, AC–LIG showed good Coulombic efficiency (98.5 %) and capacitance retention (90.0 %) after 10,000 cycles. These results highlight the potential of AC–LIG as a viable alternative for advanced supercapacitor (SC) applications, providing improved energy storage capacities and a reliable performance.

Enhanced High-Temperature performance of PEI dielectrics via deep trap energy levels and physically crosslinked effects

Dielectric capacitors are indispensable energy storage components in both civilian applications and industrial processes. Under elevated temperatures and intense electric fields, polymer dielectrics usually suffer from an inevitably increase in conductivity, leading to a significant reduction in breakdown strength, energy density and efficiency. This investigation aims to design an all-organic dielectric with enhanced high-temperature capacitive performance by introducing a small molecule P-xylene F (PF) into polyetherimide (PEI). Two mechanisms including the incorporation of deep trap energy levels via wide bandgap fillers and the electrostatic interactions by hydrogen bonding between the fillers and the polymer matrix are proposed to support the enhancement. The hydrogen bonding between PF and polyamic acid (PAA)chains induces the formation of physical cross-linking between PF and the negatively charged benzene rings in PEI after imidization. This influences benzene ring stacking within the polymer chains and enhances the film’s mechanical strength. Additionally, PF’s wider bandgap compared to PEI introduces deep trap energy levels, hindering carrier transport and reducing conductive losses at high temperatures. As results, the dielectric achieves an energy density (Ud) of 4.47 J/cm3 with an efficiency (η) above 90 % at 200 °C. Its excellent stability is also demonstrated with over 210,000 charge–discharge cycles at 200 °C. This study promotes the development of high-performance dielectrics at high temperature.

Low dielectric polyimide microsphere/polyimide composite films based on porous polyimide microsphere

AbstractA low dielectric polyimide/polyimide microsphere (PI/PM) composite film was constructed by thermal imidization of polyamic acid from pyromellitic dianhydride (PMDA) and 4,4′‐oxydianiline (ODA) in the presence of porous PM. The PM particles with particle size of about 2 μm were prepared via the solvothermal method using 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA) and ODA as monomers through thermal imidization. Due to the favorable compatibility between the porous PM and PI matrix, the mechanical properties, thermal stability, and dielectric properties of the obtained composite films were significantly improved. The PI/PM composite films had a tensile strength of 44.18–64.32 MPa, and the corresponding elongation at break of 6.21%–11.7%. Furthermore, the thermogravimetric temperatures of T5% were 538.9–563.7°C. The dielectric constants of the composite films at 1 MHz were 2.59–3.68, and the corresponding dielectric loss were only 0.0119–0.00405. Thus, the combination of excellent mechanical properties, high thermal stability, extremely low dielectric constant, and dielectric loss make the composite films ideal for deployment as high‐performance materials for 5G applications.Highlights Low dielectric polyimide composite film was prepared by thermal imidization of polyamic acid in the presence of porous polyimide microspheres. Porous polyimide microspheres were prepared by thermal using the imidization solvothermal method. Low dielectric polyimide composite film with good comprehensive properties.

Graphene nanoribbon hydrogel scaffold for highly conductive and robust polyimide nanocomposite

Although highly loaded graphitic nanocarbon materials effectively enhance the electrical, mechanical, and thermal properties of polymeric materials, their practical implementation has been hindered by severe aggregation issues. Here, we propose a method to achieve homogeneous nanocarbon-polyimide (PI) composites by integrating graphene oxide nanoribbons (GONRs) with polyamic acid ammonium (PAA) salt, a precursor of PI. Self-assembled scaffold structure of GONRs hydrogel enables the uniform integration and immobilization of PAA within the GONR scaffold, mitigating aggregation concerns. The resulting GONR/PAA hydrogel, formed through physical interactions, can be coated onto substrates via a shear stress-induced bar coating method due to its viscoelastic rheological properties. Subsequent heat treatment at 400 °C triggers the imidization reaction of PAA and the reduction of GONR, facilitating the formation of uniformly integrated GNR/PI nanocomposite coatings. Under optimized conditions, incorporating a high-loading GONR content in PAA (95 wt% of GONR and 5 wt% of PAA) yielded GNR/PI composites with excellent mechanical properties, exhibiting a hardness of 0.75 GPa and an elastic modulus of 8.3 GPa. Additionally, this GNR/PI composite displayed a good electrical conductivity of 3890 S/m, attributed to the electrical pathways formed by GNRs within the PI matrix.

Semiautomated experiment with a robotic system and data generation by foundation models for synthesis of polyamic acid particles

A semiautomated system for synthesizing polyamic acid particles using a custom liquid-handling device and a robotic arm is proposed in this study. Integration of cameras and a multimodal large language model facilitates continuous monitoring and documentation, enhancing objectivity in synthetic experiments and enabling future advancements in experimental research.

Elastic, strong polyimide/boron oxide composite aerogel with high thermal stability properties

Thermal insulation and energy saving materials play an important role in promoting the rational use of energy and realizing sustainable development. In this paper, reticulated crosslinked polyimide aerogels were made by depositing boron oxide particles formed by the introduction of boric acid transformation on the aerogel structure through an in situ thermal transformation process. The results show that the boric acid was homogeneously mixed with the precursor polyamic acid solution, leading to the uniform dispersion of boron oxide within the aerogel framework. Compared with pure polyimide aerogels, the composite aerogels dopped with boron oxide show excellent mechanical properties and thermal stability.

Photocurable comb polyamic acid for solvent-free direct ink writing with low dimensional shrinkage

Polyimides are high-performance organic polymers with excellent insulation, high-temperature resistance, and mechanical properties. However, their poor solubility makes it challenging to use them to prepare solvent-free high-performance photocurable polyimide inks with low dimensional shrinkage. In this study, photocurable comb polyamic acid resins were synthesized, and their solubility was examined based on density functional theory (DFT) calculations. Experiments showed that polyamic acid resins with specific topologies could be dissolved in photocurable monomers to prepare solvent-free photocured polyimide inks. A custom-made UV-assisted direct ink writing 3D printer was used to fabricate complex three-dimensional devices. Further heat treatment caused the polyamic acids to undergo dehydration and cyclization into rigid polyimide structures, and this process exhibited less than 6% dimensional shrinkage. The final material had a maximum storage modulus of 3.1 GPa (40 ℃) and a glass transition temperature of 204 ℃. The good comprehensive performance suggests great potential for aerospace applications.

Polyacrylonitrile In-Situ reinforced polyimide superhydrophobic porous fibers: A miraculous thermal insulation and flame-retardant material

In response to the demand for safety protective textiles suitable for extreme conditions such as intense heat and humidity, we have innovatively developed a novel approach using polyacrylonitrile (PAN) in-situ reinforced polyimide (PI) superhydrophobic porous fibers. We blended fluorinated polyamic acid (PAA) with PAN and prepared PI/pre-oxidized fiber (panof) porous fibers using a process that includes wet phase separation spinning and integrated synchronous imidization/pre-oxidation. Special emphasis was placed on the chemical mechanisms during the heat treatment stage of the preparation process. The uncapped PAA underwent imidization reactions and also facilitated PAN’s pre-oxidation, which notably enhanced the structural stability of the PI porous fibers. This novel enhancement mechanism effectively addresses the challenges of structural collapse and volume shrinkage encountered in the preparation of traditional PI porous fibers. In addition, our investigation into the impact of thermal imidization temperature on the structure of porous fibers led to the evaluation of PI/panof porous fibers. The PI/panof-320 porous fibers, produced by the combined enhancement effect of fluorinated PI and PAN, showcased exceptional features: superhydrophobicity (water contact angle = 168.9°), low density (0.078 g/cm3), reduced thermal conductivity (0.0251 W/(m·K)), high strength (22.18 MPa), outstanding flexibility (bend radius = 205 μm), and superior flame retardancy and insulation. The outstanding performance of these composite porous fibers paves the way for innovative, comfortable, and safe wearable devices in high heat and humidity environments, highlighting their extensive applicability and potential.

Janus structure design of polyimide composite foam for absorption-dominated EMI shielding and thermal insulation

In the present work, by virtue of the synergistic and independent effects of Janus structure, an asymmetric nickel-chain/multiwall carbon nanotube/polyimide (Ni/MWCNTs/PI) composite foam with absorption-dominated electromagnetic interference (EMI) shielding and thermal insulation performances was successfully fabricated through an ordered casting and directional freeze-drying strategy. Water-soluble polyamic acid (PAA) was chosen to match the oriented freeze-drying method to acquire oriented pores, and the thermal imidization process from PAA to PI exactly eliminated the interface of the multilayered structure. By controlling the electro-magnetic gradient and propagation path of the incident microwaves in the MWCNT/PI and Ni/PI layers, the PI composite foam exhibited an efficient EMI SE of 55.8 dB in the X-band with extremely low reflection characteristics (R = 0.22). The asymmetric conductive network also greatly preserved the thermal insulation properties of PI. The thermal conductivity (TC) of the Ni/MWCNT/PI composite foam was as low as 0.032 W/(m K). In addition, owing to the elimination of MWCNT/PI and Ni/PI interfaces during the thermal imidization process, the composite foam showed satisfactory compressive strength. The fabricated PI composite foam could provide reliable electromagnetic protection in complex applications and withstand high temperatures, which has great potential in cutting-edge applications such as advanced aircraft.

Synthesis of micro/nano multi-scale polyimide aerogels via confinement-controlled freeze-casting

The freeze-casting is widely utilized as a tool for regulating micro-scale pore structures in the fabrication of flexible polyimide (PI) aerogels for applications in adsorption, filtration, and fire-retardant. Herein, a confinement-controlled freeze-casting method is developed to fabricate PI aerogels with excellent thermal insulation properties by designing multi-scale structural adaptability. In a confinement-controlled system, the enhanced solid/solid and solid/liquid interface interactions in the solution dispersion system induce dendritic evolution of ice crystals. Under the directional freezing, grown dendritic ice crystals squeeze the loaded particles to form polyamic acid salt (PAAs) cryogels. Followed by template removal and thermal imidization, PI aerogels with a micro/nano-scale slit-like porous structure were obtained. The PI aerogels are characterized by ultra-low density (as low as 9.82 mg/cm3) and exceptional thermal insulation performance (25.0 mW/(m·K) at 25 °C).

Physicochemical and structural characteristics of hybrid nanocomposites based on branched polyimide with a low content of inorganic component

The series of organic-inorganic hybrid nanocomposites based on branched polyimide matrix and with different amounts of tetraethoxysilane (TEOS) (5, 20, and 50 wt.% of the initial polyamic acid mass) were synthesized and studied using nitroxyl paramagnetic probe, measuring dielectric permittivity, X-ray structural analysis and optical microscopy. It was shown that in some cases the introduction of inorganic component is accompanied by a decrease in the segmental mobility of polyimide matrix as a result of the partial immobilization of organic macrochains during the formation of inorganic microregions. In the presence of inorganic component, a weak dependence of the polymer permeability on the content of the organic component in the system is observed, also the specific density changes little with an increase in TEOS content. Extreme changes in the segmental mobility and dielectric permittivity of the branched matrix formed in the presence of 5 wt% TEOS were found compared to systems of other compositions. This can be caused to a large extent by structural changes in the system. At a low content of TEOS occurs significant «loosening» of organic matrix, a sharp decrease in the dielectric constant and a significant increase in the segmental mobility of the polyimide matrix. Small angle X-ray scattering diffractograms demonstrate drastic changes in polyimide composite heterogeneity in the presence of 5 wt.% TEOS content. According to the optical microscopy data, the introduction of TEOS into polyimide is accompanied by the formation of microaggregates of inorganic nanoparticles in the system, the number and average size of which depend on the SiO2 content and looks most homogeneous at a low TEOS content.

Effect of the molar mass of polyimide based on pyromellitic dianhydride and 4,4′‐oxydianiline on dielectric and mechanical properties of nonwoven oriented polyimide materials

AbstractThis work is dedicated to the development and investigation of the properties of low‐dielectric‐constant nonwoven materials obtained by electrospinning from a polyimide‐based polymer, PMDA‐ODA, which is composed of pyromellitic dianhydride (PMDA) and 4,4′‐oxydianiline (ODA). The influence of the molar mass of PMDA‐ODA on the structural, mechanical, and dielectric properties of the resulting samples has been investigated. The molar mass of the polyimide has been determined through light scattering and viscosity measurements of polyamic acid solutions. As the molar mass of PMDA‐ODA increases from 13.400 to 49.300 g/mol, the glass transition temperature of the produced nonwoven samples increases, and their tensile mechanical properties are improved. The dielectric constant of PMDA‐ODA nonwoven polyimide materials varies from 1.55 to 1.91 at a temperature of 30°C in a frequency range from 1 Hz to 1 MHz, depending on the molar mass of the polymer used.

Polyimide-assisted fabrication of highly oriented graphene-based all-carbon foams for increasing the thermal conductivity of polymer composites

Graphene and its derivatives are often preferentially oriented horizontally during processing because of their two-dimensional (2D) layer structure. As a result, thermal interface materials (TIMs) composed of a polymer matrix and graphene-derived fillers often have a high in-plane (IP) thermal conductivity (K), however, the low through-plane (TP) K makes them unsuitable for practical use. We report the development of high-quality polyimide/graphite nanosheets (PG) perpendicular to the plane using a directional freezing technique that increase the TP K of polymer-based composites. Graphene-derived nanosheets (GNs) were obtained by the crushing of scraps of highly thermally conductive graphene films. A water-soluble polyamic acid salt solution was used to disperse the hydrophobic GNs filler to achieve directional freezing. The polyimide, which facilitated the directional alignment of the GNs, was then graphitized. The introduction of the GNs increases the order and density of the PG, thus improving the strength and heat transfer performance of its polydimethylsiloxane (PDMS) composite. The obtained PG/PDMS composite (21.1% PG, mass fraction) has an impressive TP K of 14.56 W·m−1·K−1, 81 times that of pure PDMS. This simple polyimide-assisted 2D hydrophobic fillers alignment method provides ideas for the widespread fabrication of anisotropic TIMs and enables the reuse of scraps of graphene films.

Phase change materials encapsulated in a novel hybrid carbon skeleton for high-efficiency solar-thermal conversion and energy storage

Phase change materials (PCMs) with high energy density and stationary transition temperature are now considered promising solar energy storage mediums. However, their intrinsic poor light absorption, thermal conductivity and stability severely impede their potential applications. In this study, a novel carbonized hybrid aerogel (CHA) structure was firstly constructed by incorporating MXene and carbon nanofibers (CNFs) into a continuous phase polyamic acid salt (PAAS) aqueous solution, followed by directional freezing, vacuum drying, imidization, and carbonization processes. Finally, the composite PCMs (CPCMs) were fabricated by vacuum impregnation of PCMs into the CHAs. The CPCM, of which CHA consists of 20 wt% MXene and 10 wt% CNF@PDA, demonstrates high solar-thermal conversion efficiency (>91 %), improved thermal conductivity of 0.40 W·m−1·K−1, great thermal stability (enthalpy loss < 0.19 % after 100 cycling tests with no obvious leakage). The introduction of MXene and CNFs endows PCM with broader light absorption spectrum range. The skeleton matrix embedded with bonded MXene sheets and CNFs provides more thermal pathways, light absorption sites and carrying capacity, improves the thermal conductivity, solar-thermal conversion property and stability of PCM. In addition, CPCM also exhibits outstanding EMI SE (95 dB). The multifunctional and high-performance CPCMs shows potential to realize the effective capture and utilization of solar energy. This work provides a new strategy to construct stable and multifunctional hybrid carbon skeleton for high-efficiency solar-thermal conversion and energy storage.

Hydrophobic PI/SiO2 composites with excellent dielectric property and thermal stability via simple modification

Polyimide (PI) has been extensively used in 5G microelectronics however the relatively high dielectric constant (∼3.5) and moisture adsorption have greatly limit its practical applications in high-frequency region. Here hydrophobic PI/SiO2 composite films with low dielectric constant and excellent thermal stability were synthesized by dispersing methyl modified hollow silica nanospheres (MHS) into polyamic acid solution prior to imidization treatment. Comparing with unmodified hollow silica nanospheres (HS), the MHS obtained through methyl modification can disperse uniformly in the PI matrix. Thus, the relaxation and orientation polarization of the PI chains as well as their electron migration are suppressed, resulting in a significant decrease in dielectric constant. The PI/MHS-10% film exhibits a stable low dielectric constant (1.9–2.3) in the high-frequency range (8.2 GHz–12.4 GHz), meanwhile maintains a high breakdown voltage (192 kV/mm), mechanical properties (64 MPa) and an excellent thermal stability (Td5% = 546.5 °C; Tmax = 589.0 °C). Moreover. PI/MHS demonstrates much lower linear expansion coefficient of 25.0 ppm/K that better matches the substrate. The surface contact angle of PI/MHS increases from 73° to 110° and the water absorption rate decreases from 3.1% to 1.6%, effectively avoiding the moisture adsorption. This work provides a simple method to prepare high-performance composite films for 5G practical applications.

Superspreading-Based Fabrication of Thermostable Nanoporous Polyimide Membranes for High Safety Separators of Lithium-Ion Batteries.

The development of thermally stable separators is a promising approach to address the safety issues of lithium-ion batteries (LIBs) owing to the serious shrinkage of commercial polyolefin separators at elevated temperatures. However, achieving controlled nanopores with a uniform size distribution in thermostable polymeric separators and high electrochemical performance is still a great challenge. In this study, nanoporous polyimide (PI) membranes with excellent thermal stability as high-safety separators is developed for LIBs using a superspreading strategy. The superspreading of polyamic acid solutions enables the generation of thin and uniform liquid layers, facilitating the formation of thin PI membranes with controllable and uniform nanopores with narrow size distribution ranging from 121±5nm to 86±6nm. Such nanoporous PI membranes display excellent structural stability at elevated temperatures up to 300°C for at least 1h. LIBs assembled with nanoporous PI membranes as separators show high specific capacity and Coulombic efficiency and can work normally after transient treatment at a high temperature (150°C for 20min) and high ambient temperature, indicating their promising application as high-safety separators for rechargeable batteries.