Poly Amic Acid Research Articles

Bridging solvent-free polyamic acid and epoxy resin by Si-O-C hyperbranched polymer for enhanced compatibility, toughness and self-lubrication performance

Despite the great application potential of epoxy resin (EP) modified with polyamic acid (PAA), the large amount of high-boiling-point non-protonic polar solvents used to promote their compatibility cannot be completely eliminated, which affects the fabrication and application of epoxy composites in practical engineering. Herein, PAA was prepared by solvent-free ball milling method, and then the primary amine hyperbranched polysiloxane (HSiNH2) was prepared by “one-pot” method as the “bridging structure” to improve the compatibility between PAA and EP. Compared to neat EP, the flexural, impact and tensile shear strength of the epoxy composite are increased by 22.2 %, 30.0 % and 23.2 %, while the average friction coefficient and volume wear rate are reduced by 26.5% and 20.6% under the contents of PAA and HSiNH2 are 1.50 wt% and 2.0 wt%, respectively. Moreover, the material exhibits excellent thermal properties. By comprehensively analyzing the structure and properties of the epoxy composite, it is mainly ascribed to the fact that HSiNH2 with a large number of reactive groups acted as a “bridging structure” to enhance the compatibility of PAA and EP, which results in the epoxy composite having excellent mechanical, tribological and thermal properties. This research also lays the theoretical foundation for the development of high-performance epoxy composites in aerospace.

Scalable synthesis of high-quality, reduced graphene oxide with a large C/O ratio and its dispersion in a chemically modified polyimide matrix for electromagnetic interference shielding applications.

High-purity reduced graphene oxide (RGO or rGO) with appreciable conductivity is a desired conductive filler for lightweight polymer composites used in coatings, electronics, catalysts, electromagnetic interference (EMI) shielding, and energy storage devices. However, the intrinsic conductivity and the uniform dispersion of RGO in relatively polar matrices are challenging, leading to poor overall conductivity and performance of the composite material. The reported study improved the RGO intrinsic conductivity by increasing its C/O ratio while also simultaneously enhancing its compatibility with the polyimide (PI) matrix through ester linkages for better dispersion. A two-step reduction method drastically increased the number of structural defects and carbon content in the resulting RGO, corresponding to a maximum ID/IG and C/O of 1.54 and ∼87, respectively. Moreover, the 2D nanosheets with limited hydroxyl (-OH) groups effectively interacted with anhydride-terminated polyamic acid (AT-PAA) through chemical linkages to make high-performance RGO/PI nanocomposites. Consequently, the polymer matrix composites possessed the highest direct current conductivity of 15.27 ± 0.61 S cm-1 for 20 wt% of the prepared RGO. Additionally, the composite material was highly stiff (3.945 GPa) yet flexible (easily bent through 180°), lightweight (∼0.34 g cm-3), and capable of forming thin films (162 ± 15 μm). Unlike most polymer matrix composites, it showcased one of its class's highest thermal stabilities (a weight loss of only 5% at 638 °C). Ultimately, the composite performed as an effective electromagnetic interference (EMI) shielding material in the X-Band (8 to 12 GHz), demonstrating outstanding shielding effectiveness (SE), shielding effectiveness per unit thickness (SEt), specific shielding effectiveness (SSE), and absolute shielding effectiveness (SSEt) of 46 dB, 2778 dB cm-2, 138 dB cm3 g-1, and 8358 dB cm2 g-1, respectively. As a consequence of this research, the high-purity RGO and its high-performance PI matrix nanocomposites are anticipated to find practical applications in conductive coatings and flexible substrates demanding high-temperature stability.

Electrochemical Monitoring of Super-Engineering Polymer Depolymerization: A Rapid and Simple Approach

The mechanical properties and processability of polymers are strongly influenced by their molecular weight, underscoring the critical importance of controlling depolymerization during storage in polymer synthesis and application. However, conventional methods of determining molecular weight, including viscosity measurements, gel permeation chromatography (GPC), and nuclear magnetic resonance (NMR) spectroscopy, typically necessitate substantial quantities of polymer samples and protracted measurement times. Moreover, certain polymers may undergo continuous degradation post-polymerization, rendering depolymerization analysis via traditional means highly challenging. Hence, there is an imperative need to develop novel analysis techniques that overcome these limitations and facilitate comprehensive depolymerization characterization.To surmount these challenges, we have developed a novel electrochemical method utilizing cyclic voltammetry to facilitate polymer depolymerization measurement. For measuring degree of depolymerization, we used thermal depolymerization process. As the polymer's molecular weight diminishes because of thermal depolymerization, the solution viscosity decreases correspondingly, thereby enabling unimpeded redox species diffusion and a proportional increase in steady-state current. By constructing a calibration curve of current versus thermal depolymerization time for a polymer, we can swiftly and accurately determine its molecular weight tendency in solution. Our investigations indicate that this electrochemical technique is more efficient and cost-effective as it necessitates smaller sample volumes and shorter measurement times than conventional methods, and it exhibits excellent potential for analyzing and maintaining polymer properties across various industries.[1] Kim, J. W., Kim, S. J., Song, I. Y., Lee, W. E., Heo, K., Kim, S. Y., ... & Kim, B. K. (2022). Simple and rapid electrochemical monitoring for depolymerization of polyamic acid. Analytica Chimica Acta, 1233, 340489.

Covalent Introduction of Plasma-Treated carbon nanotubes into polyimide nanocomposites at Ultra-Low content

In this paper, the effect of plasma treatment on the structure of carbon nanotubes (CNTs) and the structure/properties of polyimide (PI) nanocomposites with CNTs at ultra-low content (0.001 wt% ∼ 0.004 wt%) were investigated. Plasma treatment of CNTs under the mixture-gas of N2 and CO2 resulted in introducing isocyanate group on the surface of CNTs. PI nanocomposites with non-treated CNTs (nCNTs) or plasma-treated CNTs (pCNTs) were synthesized by in-situ polymerization, where PI as well as polyamic acid (precursor of PI) was polymerized under the presence of fillers. The structural studies revealed that pCNTs were highly dispersed in the nanocomposites with the strong interfacial interaction of covalent bond at the interface between PI and pCNTs. As a result, the excellent reinforcement effect of CNTs was successfully exploited to the PI nanocomposites at ultra-low content. For example, the Young’s modulus, tensile strength and toughness increased by 83 %, 51 % and 41 % by the incorporation of only 0.001 wt% of pCNTs, while the nanocomposite with nCNTs showed brittle behavior caused by poor interfacial interaction. Here in, we show that the characteristics of polymer matrices can be drastically changed by the addition of ultra-low content of nanofillers where the surface chemistry is optimized.

Three-dimensional nitrogen and oxygen co-doped hierarchical porous carbons prepared from polyacrylonitrile/polyamic acid composite films for supercapacitors

Porous carbon materials are widely used in energy storage, adsorption, catalysis, and wastewater treatment. Polymer composite films of polyacrylonitrile (PAN) and polyamic acid (PAA) were firstly prepared by phase separation with modulation of coagulation bath composition. Using these composite films as precursors, nitrogen and oxygen co-doped porous carbon materials were successfully fabricated by preoxidation, carbonization, and subsequent NaOH activation. The porous carbons had a three-dimensional interconnected structure with a specific surface area of 450–737 m2 g−1. The pore volume was 0.245–0.508 m3 g−1 and the pore size mainly located between 1 and 5 nm. The activated porous carbon obtained from PAN/PAA coagulated at a DMSO to water ratio of 3 showed a high oxygen content of 28.0 wt% and nitrogen content of 3.3 wt%. The resultant porous carbon exhibited a good mass-specific capacitance of 407.7 F g−1 at a current density of 0.5 A g−1, an excellent rate capability (237.7 F g−1 at 20 A g−1) and cyclic stability. Using the material as the electrode, a coin-cell symmetric supercapacitor (CR2032) was assembled, which provided a specific capacitance of 156 F g−1 at 0.1 A g−1 and a maximum energy density of 10.9 Wh kg−1 at a power density of 50 W kg−1. The high number of heteroatoms as well as the textural properties could be beneficial for the improvement of electrochemical performance of the carbon-based supercapacitors.

Enhanced performance of densified laser-induced graphene supercapacitor electrodes in dimpled polyimide

We fabricate a densified laser-induced graphene (d-LIG) electrode derived from a dimpled polyimide (PI) sheet. The fabrication process involves placing a PI sheet on a Si wafer and generating dimples on the PI surface via laser irradiation at the PI/Si interface. d-LIG is fabricated using the duplicated laser-induced carbonization, during which regular LIG is infiltrated with polyamic acid (PAA) and then irradiated with a CO2 laser. Compared to pristine PI, the LIG based on the dimpled PI facilitates deeper penetration of the PAA solution into the interior of the LIG, resulting in an increased amount of d-LIG and high nitrogen doping. When tested in a three-electrode configuration, the d-LIG derived from the dimpled PI (or d-LIG-D) exhibits a high specific capacitance of 67 mF/cm2 at 0.2 mA/cm2, which is almost twice that of the d-LIG derived from pristine PI (or d-LIG-P) (28.9 mF/cm2). When fabricated into a flexible solid-state supercapacitor with polyvinyl alcohol-H2SO4 gel-type electrolyte, d-LIG-D exhibits a higher specific capacitance (19.5 mF/cm2 at 0.05 mA/cm2) than d-LIG-P (8.4 mF/cm2). Furthermore, it possesses good capacitance retention, Coulombic efficiency, and mechanical flexibility. These properties make d-LIG-D a promising candidate for advanced supercapacitor applications, offering enhanced energy storage capabilities and robust performance.

Polyimide/titanium dioxide self-cleaning nano-hybrid films with high photocatalytic properties

Self-cleaning films are considered an emerging paradigm of environmentally functional materials. Enhancing the photocatalytic activities of self-cleaning film is a viable strategy for improving its antifouling characteristics. In this work, a polyimide/titanium dioxide (TiO2) film (PI/TiO2) film was developed by casting a mixture of polyamic acid solution and TiO2 hydrosol with a subsequent thermal imidization. TiO2 with a concentration of 1, 3, and 5 ​wt% was successfully incorporated into the PI matrix and was equally distributed in nanometer size in the PI/TiO2 nano-hybrid films. The addition of TiO2 into the film significantly improved its catalytic performance as indicated by the photocatalytic degradation of methylene blue and resazurin solution, suggesting a good self-cleaning property for antifouling applications. In addition, the thermal and mechanical stability of the PI film were improved with the addition of TiO2. After eight cycles, the PI-TiO2 films also demonstrated excellent cycling stability. This study introduces a novel self-cleaning film family composed of PI/TiO2 nano-hybrid film and emphasizes the engineering potential of photocatalytic materials in the context of self-cleaning film.

Ultralight and superelastic multifunctional PI composite aerogels with a nanofibrous‐laminar synergistic structure for highly efficient electromagnetic wave absorption

AbstractHigh‐performance and lightweight electromagnetic wave‐absorbing materials with broad frequency bandwidths and strong absorption capabilities can effectively protect the human body from electromagnetic radiation hazards. However, manufacturing protective materials that are also flexible, comfortable, and permeable to air and moisture is challenging. In this study, a high‐performing aerogel material that absorbs electromagnetic waves was constructed using electrospinning and freeze‐drying processes. Ce3+‐doped Li0.35Zn0.3Fe2.35O4/silica (CLZFO/SiO2) inorganic magnetic nanofibers and polyamide imide/silicon carbide (PAI/SIC) organic nanofibers were used as the reinforcing phase in the aerogel. These nanofibers were uniformly dispersed in a mixed solution containing polyamic acid (PAA), graphene oxide (GO), and SIC nanoparticles. Subsequent freeze‐drying and thermal amidation produced a PAI/SIC and CLZFO/SiO2 nanofiber‐reinforced (PASI/CLS) polyimide (PI) composite aerogel, which had a nanofibrous‐laminar synergistic structure with a uniform filling of GO and SIC nanoparticles. The PASI/CLS aerogel exhibited efficient electromagnetic wave absorption with a minimum reflection loss (RLmin) of −49 dB at 5.4 GHz and an effective absorption bandwidth of 4.3 GHz. The excellent mechanical properties, thermal insulation performance, and superhydrophobicity of the aerogel ensure the long‐term stability of its microwave absorption capacity in complex and extreme environments.

Preparation and Properties Magnetite/Polyimide Composites

To make the polyimide (PI) composite material having both heat resistance and magnetic permeability, Fe3O4/PI magnetic polyimide composite powder was synthesized by one-step solvothermal method. 4,4'-diaminodiphenyl ether (ODA) as monomers, ether anhydride polyamic acid (PAA) was designed and prepared by Fe3+ and polyimide precursor-polyamic acid triethylamine salt (PAAS) was reacted in a reactor, and the PI/Fe3O4 composite powders were synthesized under the condition of high temperature and high pressure. The obtained PI/Fe3O4 composite powders were analyzed by infrared spectroscopy, microscopic morphology and thermal properties. The morphology and structure of the samples were both characterized by scanning electron microscopy (SEM) and infrared spectroscopy (IR). The thermal properties of the composite microspheres were studied via thermogravimetric analysis (TGA) and the magnetic properties were determined by a vibrating sample magnetometer (VSM). The saturation magnetization decreases gradually, increasing the polyimide content, with a saturation magnetization of PI/Fe3O4 determined to be 20.29 emu/g.

A new dip-coating approach for plasticization-resistant polyimide hollow fiber membranes: In situ thermal imidization and cross-linking of polyamic acid

Polymeric hollow fiber membranes (HFMs) are in high demand for gas separation due to their superior processability and cost-effectiveness, despite exhibiting high vulnerability to plasticization. In this study, we present a new dip-coating technique for fabricating defect-free and plasticization-resistant polyimide HFMs on a cross-linked polyimide/polysilsesquioxane hollow fiber support. This is achieved through an in situ process involving thermal imidization and cross-linking of a polyamic acid (PAA) precursor solution. The use of a thermally stable cross-linked nanoporous hollow fiber support ensures the coating of various glassy PAA solutions prepared by different dianhydrides and diamine monomers without disturbing its internal pore structure. The resulting polyimide hollow fiber membranes enhanced CO2/CH4 separation performance compared to as-synthesized polyimide solution-coated counterpart. It is because in situ thermal imidization and cross-linking of PAA solutions induced the formation of more imine linkages, possibly generating larger free volume elements due to the disturbance of intersegmental chain packing while maintaining sufficient chain rigidity. Additionally, the membrane’s practical applicability was confirmed as the hollow fibers demonstrated resistance to plasticization when subjected to an equimolar CO2/CH4 mixed feed of approximately 50 bar. Our simple but versatile dip-coating approach allows for the formation of highly plasticization-resistant polyimide HFMs.

Analysis of the kinetics of soluble polyimide formation by the thermal imidization of polyamic acids in amide solvents with allowance for the side reaction of anhydride group hydrolysis

Analysis of the kinetics of soluble polyimide formation by the thermal imidization of polyamic acids in amide solvents with allowance for the side reaction of anhydride group hydrolysis

Influence of Molecular Weight on Thermal and Mechanical Properties of Carbon-Fiber-Reinforced Plastics Based on Thermoplastic Partially Crystalline Polyimide.

For the first time, a study of the influence of the molecular weight of the thermoplastic partially crystalline polyimide R-BAPB on the thermophysical and mechanical properties of carbon plastics was presented. The molecular weight of polyimide was determined using the method of light scattering and the study of the intrinsic viscosity of polyamic acid solutions. To obtain CFRPs, the uniform distribution of polyimide powder on continuous carbon fibers via electrostatic spraying and further hot calendering and pressing were applied. The study of the structure of the obtained carbon plastics via scanning electron microscopy has shown that the growth of the molecular weight of polyimide prevents the impregnation of carbon fiber with the introduced polyimide. Moreover, an increase in the molecular weight of polyimide leads to a rise in glass transition and thermal decomposition temperatures up to 590 °C, while the degree of crystallinity of CFRP falls. Nonetheless, raising the molecular weight from 22,000 to 70,000 g/mol of a binder polymer improves the interlayer fracture toughness G1C by more than five times.

Unidirectional Fracturing of Super Engineering Plastic Films

Polyamideimides and polyimides are prepared based on chemical imidization using aromatic diamine, diacid anhydride, and diacid chloride as monomers, with the precursor polyamic acid remaining in part, to produce mechanically unique films through convection drying. The resulting films are colorless and transparent and exhibit unidirectional fracture behavior. These films do not break when bent in the direction of the air contact surface but easily break when bent in the opposite direction. A cross‐sectional electron microscope image of the broken film shows that the film consists of a double layer. After examining both sides of the film through various spectroscopic and gel permeation chromatography analyses, it is found that the residual polyamic acid undergoes both hydrolytic and thermal decomposition, exclusively on the air contact surface. Later, the polymer film is laminated with two sheets of glass through UV curing of commercial acryl resin. Because of the unidirectional fracture characteristics of the film, the laminated glass does not completely break when subjected to bending toward the air contact surface but easily breaks (without fragments) in the opposite direction, indicating its potential application in safety glasses suitable for emergency escapes.

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Noncovalently functionalized boron nitride nanotubes and polymer nanocomposites with water-soluble poly (amic acid) salt

In this study, polyamic acid salt-BNNTs (PAS-BNNTs) were prepared by noncovalently functionalizing water-soluble PAS with improved dispersion stability in organic solvents, and high compatibility with polyimide (PI) nanocomposites. We show that BNNTs functionalized with PAS have enhanced mechanical properties that are influenced by various loadings of PAS-BNNT/PI films through in situ polymerization. Compared with the pure PI film, the tensile strength and tensile modulus increased by about 20% and 37%, respectively. The proposed system also improved the coefficient of thermal expansion (CTE) from 52.6 to 45.7 ppm/oC. The enhanced mechanical properties of the PI nanocomposite were due to the interfacial bond strength enhanced by the reinforcing effect of PAS-BNNTs. Our study demonstrates the potential of PAS-BNNTs for preparing BNNT/PI nanocomposites with various structures.

Storage Stability of 6FDA-DMB Polyamic Acid Solution Detected by Gel Permeation Chromatography Coupled with Multiple Detectors

Polyamic acid (PAA) is the precursor of polyimide (PI), and its solution's properties have a direct influence on the final performances of PI resins, films, or fibers. The viscosity loss of a PAA solution over time is notorious. A stability evaluation and revelation of the degradation mechanism of PAA in a solution based on variations of molecular parameters other than viscosity with storage time is necessary. In this study, a PAA solution was prepared through the polycondensation of 4,4'-(hexafluoroisopropene) diphthalic anhydride (6FDA) and 4,4'-diamino-2,2'-dimethylbiphenyl (DMB) in DMAc. The stability of a PAA solution stored at different temperatures (-18, -12, 4, and 25 °C) and different concentrations (12 wt% and 0.15 wt%) was systematically investigated by measuring the molecular parameters, including Mw, Mn, Mw/Mn, Rg, and [η], using gel permeation chromatography coupled with multiple detectors (GPC-RI-MALLS-VIS) in a mobile phase 0.02 M LiBr/0.20 M HAc/DMF. The stability of PAA in a concentrated solution decreased, as shown by the reduction ratio of Mw from 0%, 7.2%, and 34.7% to 83.8% and that of Mn from 0%, 4.7%, and 30.0% to 82.4% with an increase of temperature from -18, -12, and 4 to 25 °C, respectively, after storage for 139 days. The hydrolysis of PAA in a concentrated solution was accelerated at high temperatures. Notably, at 25 °C, the diluted solution was much less stable than the concentrated one and exhibited an almost linear degradation rate within 10 h. The Mw and Mn decreased rapidly by 52.8% and 48.7%, respectively, within 10 h. Such faster degradation was caused by a greater water ratio and less entanglement of chains in the diluted solution. The degradation of (6FDA-DMB) PAA in this study did not follow the chain length equilibration mechanism reported in literature, given that both Mw and Mn declined simultaneously during storage.

A Fluorinated Polyimide Based Nano Silver Paste with High Thermal Resistance and Outstanding Thixotropic Performance.

Because of high conductivity, acceptable cost and good screen-printing process performance, silver pastes have been extensively used for making flexible electronics. However, there are few reported articles focusing on high heat resistance solidified silver pastes and their rheological properties. In this paper, a fluorinated polyamic acids (FPAA) is synthesized by polymerization of the 4,4'-(hexafluoroisopropylidene) diphthalic anhydride and 3,4'-diaminodiphenylether as monomers in the diethylene glycol monobutyl. The nano silver pastes are prepared by mixing the obtained FPAA resin with nano silver powder. The agglomerated particles caused by nano silver powder are divided and the dispersion of nano silver pastes are improved by three-roll grinding process with low roll gaps. The obtained nano silver pastes possess excellent thermal resistance with 5% weight loss temperature higher than 500 °C. The volume resistivity of cured nano silver paste achieves 4.52 × 10-7 Ω·m, when the silver content is 83% and the curing temperature is 300 °C. Additionally, the nano silver pastes have high thixotropic performance, which contributes to fabricate the fine pattern with high resolution. Finally, the conductive pattern with high resolution is prepared by printing silver nano pastes onto PI (Kapton-H) film. The excellent comprehensive properties, including good electrical conductivity, outstanding heat resistance and high thixotropy, make it a potential application in flexible electronics manufacturing, especially in high-temperature fields.

Direct ink writing of polyimide/bacterial cellulose composite aerogel for thermal insulation

Polyimide (PI) aerogels are well known for their high porosity, low density, thermal insulation and outstanding mechanical strength, thus expected to be applied in aerospace vehicle, intelligent driving and batteries. However, currently most PI aerogels are fabricated through traditional molding process, seriously restricted their practical applications. Although some researches on 3D printing of PI aerogels have been reported, there are some critical restrictions in present work such as complex support structures, low porosity and high thermal conductivity resulting from high solid content in printed ink. Herein, we choose bacterial cellulose (BC) with high aspect ratio as rheological modifier to construct water-based polyamic acid (PAA)/BC ink with low solid content but high yield stress enough for direct ink writing (DIW). Due to the good printability and formability of PAA/BC ink, the PI/BC aerogel with various macrostructures can be easily printed. Owing to the orientation from printing, the obtained printed PI/BC aerogel shows lower shrinkage, lower thermal conductivity and enhanced mechanical properties compared with molded PI/BC aerogels. Such printed PI/BC aerogel is potentially to be applied as thermal insulators for designated products with specific complex structure in fields of buildings and petrochemical engineering.

Combination of multiple active sites in N, O co‐doped defective carbon materials for high performance aqueous supercapacitors

AbstractSupercapacitors have been used in a broad range of fields including electronics, transportation, and energies. Electrode materials with high capacitance and good rate performance are crucial for the future development and application of supercapacitors. Herein, we prepared N, O co‐doped defective carbon blocks (NO‐DCBs) with abundant active sites through carbonization and ball‐milling of polyimide. The as‐obtained NO‐DCBs exhibit high atomic content of N and O inherited from polyamic acid (PAA) precursor, as well as large amounts of intrinsic defects introduced by ball‐milling. Benefiting from the synergy of pseudocapacitance and electrical double‐layer capacitance provided by heteroatoms and intrinsic defects respectively, the NO‐DCBs assembled symmetric aqueous capacitor shows high capacitance of 329 F g−1 at 0.1 A g−1, good rate performance of 48% capacitance retention at 50 A g−1, and superb cycling stability. This work promotes the deep understanding of the synergy effect of functional groups and intrinsic defects for capacitive energy storage, and broadens the avenue for structural design of active sites in carbon materials.

Long-term atomic oxygen resistant polyimide films containing carborane nanocage structure in the main chains

High-temperature durable polymer films with long-term atomic oxygen (AO) resistant capabilities are highly desired for the development of spacecraft with long-servicing lifetimes in low earth orbit (LEO). The relatively poor AO resistance of conventional polyimide (Kapton® H) film severely limited its applications in LEO spacecraft. In this work, carborane nanocage rich in boron element was introduced into polyimide molecular chain to prolong the atomic oxygen resistance life of polyimide film. A series of carborane-containing polyimide (CBPI) nanocomposite films with ultrahigh AO resistance have been prepared by casting precursor polyamic acid (PAA) solution on a glass plate, followed by thermal imidization at several elevated temperatures. The AO exposure experiments were tested in a ground-based AO effects simulation facility in our laboratory with the filament discharge and bound of magnetic field. Incorporation of carborane nanocage structure apparently improved the thermal stability and AO resistance of the PI nanocomposite films. The CBPI-50 film exhibited the lowest AO average erosion yield (Es) of 2.3 × 10−25 cm3·atom−1 under AO exposure with a fluence of 3.33 × 1020 atoms·cm−2, which is more than one order of magnitude lower than the reference Kapton® H film. The protective mechanism of CBPI nanocomposite films during AO exposure was proposed.