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A 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. [ABSTRACT FROM AUTHOR]

The proposed paper presents the design of a leaky‐wave antenna inspired by holographic metasurfaces employing thin film. Leveraging the holographic principle, this metasurface showcases its transformative capacity by converting an omnidirectionally radiating monopole into a highly directional antenna emitting leaky waves. The holographic metasurface is constructed using a thin film of polyimide (PI) (Df = 0.008; Dk = 3.5), measuring 50 μm in thickness. The antenna structure comprises multiple layers, commencing with the top PI layer, succeeded by a 40 μm thick adhesive layer (Df = 0.004; Dk = 6). Subsequent layer includes the Rogers RT/duroid 5880 substrate (Df = 0.0009; Dk = 2.20), grounded at the bottom and has a thickness of 1.6 mm. The meticulously tailored design of the proposed antenna ensures optimal performance at 15 GHz, facilitating directional radiation and precise beam steering at 10 degrees (ϴ = 10°). This innovative design, incorporating the holographic metasurface on thin film, significantly enhances the antenna's performance, increasing gain from 1.5 dBi to 13.8 dBi. [ABSTRACT FROM AUTHOR]

Mechanical damage to the surface of polyimide during manufacture and utilization may act as critical determinants of the properties and longevity of the material. In order to address this issue, this study prepared thermoplastic polyimide (TPI) films through the copolymerization of isocyanate and acid anhydride, which possesses superior self‐healing ability after being mechanical damaged. Moreover, polyimide films still retain its exceptional tensile strength (>90 MPa) with Young's modulus (E) (>3 GPa), high thermal stability (glass transition temperature (Tg) >220°C), and excellent insulation performance (breakdown strength (Eb) >180 kV/mm) after self‐healing. Introducing cross‐linked structures and flexible groups into the thermoplastic resin matrix appropriately not only imparts self‐healing capabilities to the material but also retains its excellent mechanical properties. The combination of straightforward copolymerization and distinctive self‐healing prowess renders it an appropriate strategy for confronting self‐healing challenges. [ABSTRACT FROM AUTHOR]

Polymer materials with a low dielectric constant and low dielectric loss have the potential to be applied to high-frequency signal transmissions, such as mobile phone antennas and millimeter wave radars. Two types of diamines, 4,4′-diamino-p-tetraphenyl (DPT) and crown ether diamine (CED), were prepared for ternary copolymerization with BPDA in this study. Cross-links with molecular chains were formed, increasing molecular chain distance by utilizing rings of CED. The MPI films exhibit a good thermal performance with the increase in CED addition, with Tg > 380 °C and CTE from −4 × 10−6 K−1 to 5 × 10−6 K−1. The Young's modulus can reach 8.6 GPa, and the tensile strength is above 200 MPa when 5% and 7% CED are introduced. These MPI films exhibit good mechanical performances. The dielectric constant of PI−10% film can go as low as 3.17. Meanwhile, the relationship between dielectric properties and molecular structure has been demonstrated by Molecular Simulation (MS). PI molecules are separated by low dielectric groups, resulting in a decrease in the dielectric constant. [ABSTRACT FROM AUTHOR]

In order to meet the requirements of highly integrated and miniaturized electronic components, there is an urgent need for low dielectric materials with high mechanical properties and optical transparency in the field of microelectronics. In this study, a series of novel polyimide films (FPI) containing fluorenyl were prepared, and the effects of the fluorenyl content on the thermal, mechanical, and dielectric properties of the copolymerized films were investigated and discussed. The results demonstrate a significant decrease in the dielectric constant of the FPI films following the introduction of fluorenyl into polyimide (PI) chain segment. The FPI films also exhibited high mechanical properties, including tensile strengths between 92 and 106 MPa and elongation at break in the range of 8.4%–13.0%. Additionally, the introduction of the noncoplanar fluorenyl considerably improved the optical transparency and solubility of the FPI film. It is noteworthy that the FPI‐3 has the best dielectric properties, with a low dielectric constant of 2.61 at 10 MHz and shows low water absorption (0.49%). The results show that we have prepared a novel low dielectric PI material film with excellent mechanical properties and optical transparency by introducing fluorenyl into the PI chain segment. These FPI films with satisfactory properties may be good candidates for dielectric materials for electronic components. [ABSTRACT FROM AUTHOR]

In order to prepare polymer dielectric materials with high energy storage density, a series of polyimide (PI) based Janus composite films were prepared by metal–organic frameworks (MOFs) material (UiO‐66) with high dielectric constant (ɛr) and boron nitride nanosheets (BNNSs) with high breakdown strength (Eb). As reported, the UiO‐66 can significantly improve the ɛr of the composites. The ɛr of 20 wt% UiO‐66/PI film is 10.51 at 103 Hz, which is 3.1 times that of pure PI film (3.39 at 103 Hz). However, the Eb of 20 wt% UiO‐66/PI is only 58 MV m−1, which is only 16.51% of pure PI (352 MV m−1). The sharp decline in Eb reduces the energy storage capacity of the composites. To solve this problem, first, BNNSs with an average diameter of 2 μm and a thickness of 1.36 nm (about 4–5 layer) were obtained by hydrothermal reflux stripping. BNNSs/PI//UiO‐66/PI Janus composite films with double‐layer structure were prepared by directly casting BNNSs/PI on the surface of UiO‐66/PI. For 0.3 wt% BNNSs/PI//10 wt% UiO‐66/PI, the calculated energy storage density (Ue) is 5.75 J cm−3 at 140 MV m−1, which is 3.57 times that of pure PI film (1.61 J cm−3 at 140 MV m−1). Meanwhile, the charge discharge efficiency is 82.55% (at 140 MV m−1). Highlights: BNNSs prepared by hydrothermal reflux stripping have fewer layers.BNNSs/PI composites improve the Eb of UiO‐66/PI composites by Janus structure.The Ue of BP‐0.3//UP‐10 composites with Janus structure was 5.75 J cm−3. [ABSTRACT FROM AUTHOR]

Although polyimide films have a low dielectric constant, with the advent of the 5G era, the dielectric properties of the material are required to be further improved. Therein, we prepared controlled hollow mesoporous SiO2 nanomicrospheres by the hard template method to make mesoporous low dielectric polyimide films. The composite membrane exhibits better thermal stability, mechanical properties, and hydrophobicity compared to the pure membrane. Hollow mesoporous SiO2 dispersed in polyimide can reduce the inhomogeneity of charge distribution between molecules and reduce the interaction between polar chemical bonds and aromatic rings, thus improving the dielectric properties of the whole film. The minimum dielectric constant of the composite films was 2.80 when the hollow mesoporous SiO2 was added at 1.0%. These results fully indicate that the addition of hollow mesoporous SiO2 is beneficial to the multifaceted performance of the polyimide films. Highlights: Preparation of hollow mesoporous SiO2 microspheres by using different polystyrene microsphere solutions and TEOS ratios.Synthesis of composite films with different contents of hollow mesoporous SiO2 as functional fillers.The effect of hollow mesoporous SiO2 content on the mechanical properties and thermal stability of PI composite films was investigated.Addition of hollow mesoporous SiO2 reduces the dielectric constant of polyimide composite films. [ABSTRACT FROM AUTHOR]

A 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. [ABSTRACT FROM AUTHOR]

Polyimide belongs to the class of high performance polymers containing imide functionalities in the backbone. Polyimide has wide ranging properties of optical transparency, heat stability, mechanical strength, dimensional stability, thermal conductivity, dielectric properties, etc. Fullerene is a zero dimensional hollow symmetrical nanocarbon, frequently employed as nanofiller in the polymers. Fullerene has been reinforced in the polyimide films to further augment the exclusive features and performance. This state-of-the-art review basically emphases the fundamentals, structure, properties, and applications of polyimide films, especially the films reinforced with fullerene nanofiller. The polyimide/fullerene nanocomposite films have been prepared using facile routes such as solution casting, spin casting, in situ method, and other film forming methods. Fullerene nanofiller has been filled in numerous designed polyimides. Number of experimental and theoretical studies have been performed on the high performance polymer/fullerene nanocomposite films. The structural diversity of the polymer/fullerene nanocomposite films and inimitable characteristics have led to significant applications in the optoelectronic devices, photodetectors, and sensors. [ABSTRACT FROM AUTHOR]

Polyimide (PI) is widely used in the communication field benefited from its low dielectric properties and good electrical insulating properties, however, its low thermal conductivity simultaneously limits its application in electronic packaging. Delayed heat dissipation can exacerbate the thermal stress generated by device operation to damage electronic structures, thereby affecting work efficiency. As a result, it is necessary to improve the thermal conductivity of polyimide and maintain excellent dielectric performance. Here, we demonstrate the polyimide (BPDA‐ODA) composites with ordered structure are prepared by filling commercial polyimides with aramid nanofibers connection nitrides greatly improve thermal conductivity and maintain the low dielectric loss. When the filling amount of SBN@CN is 30 wt%, the thermal conductivity increases to 1.162 W/mK, which is 8 times higher than that of pure PI (0.0147 W/mK). Moreover, thermal stability and mechanical properties are maintained, realizing that the dielectric constant is about 3.81 and the dielectric loss is as low as 0.0034 at 100 MHz, which endows a new insight for the application of polyimide in electronic packaging. [ABSTRACT FROM AUTHOR]

The rapid development of communication networks (5G and 6G) that rely on high-speed devices requiring fast and high-quality intra- and inter-terminal signal transmission media has led to a steady increase in the need for high-performance, low-dielectric-constant (Dk) (<2.5) materials. Consequently, low-dielectric polymeric materials, particularly polyimides (PIs), are very attractive materials that are capable of meeting the requirements of high-performance terminal devices that transmit broadband high-frequency signals. However, such a PI needs to be properly designed with appropriate properties, including a low Dk, low dielectric loss (Df), and low water absorptivity. PI materials are broadly used in various fields owing to their superior property/processibility combinations. This review summarizes the structural designs of PIs with low Dk and Df values, low water-absorbing capacity, and high optical transparency intended for communication applications. Furthermore, we characterize structure–property relationships for various PI types and finally propose structural modifications required to obtain useful values of the abovementioned parameters. [ABSTRACT FROM AUTHOR]

Firstly, the BaTiO3 nanoparticles were coated with a layer of paraffin, forming a core shell structure. Then, as‐prepared paraffin@BaTiO3 nanofillers were directly blended with polyimide (PI) prepolymer to fabricate paraffin@BaTiO3/PI composite films. The microstructure, thermal, and dielectric properties were investigated in detail. The surface‐modified paraffin@BaTiO3 nanoparticles exhibited a typical core shell structure with uniform and complete coverage. The char yield of the composite film with 10 wt% paraffin@BaTiO3 increased from 56.40% to 70.73%. It is obvious that the paraffin@BaTiO3 nanofillers have a positive effect on ablative performance of the composite film. Compared with pure PI, the εr of paraffin@BaTiO3/PI composites with 40% mass fraction increased from 3.41 to 9.35 (1 kHz). The tanδ of paraffin@BaTiO3/PI composites was just 0.0065 (1 kHz) when the filler loading was 40 wt%. Temperature dependency of the permittivity of the composites reveals a zero‐temperature‐coefficient from 80°C to 180°C. [ABSTRACT FROM AUTHOR]

In the present study, amine groups were first modified to diamond and silver nanoparticles using APTMS to improve their homogeneous dispersion and compatibility in polyamic acid. Flexible polyimide nanocomposite films were successfully prepared by adding modified nanodiamond and silver nanoparticles to 4,4′-(1,3-phenylenedioxy) dianiline and benzophenone-3,3′,4,4′-tetracarboxylic dianhydrides with different proportions. The effects of added amine-modified nanoparticles on dielectric constant and thermal stability were investigated. With SEM analysis, nanoparticles were homogeneously distributed on the polyimide surface and the presence of Si atom resulting from APTMS modification is clearly seen with the SEM-EDAX results. Considering the thermal resistance, the maximum decomposition temperature of the nano particle-free PI film was found to be 501 °C, while the thermal decomposition temperatures of the PI nanocomposite film that contains 1% m-Ag and the PI film that contains 5% m-ND, 502 °C and 505 °C, respectively. Also, it was seen that the dielectric constants of the prepared nanocomposite films that contain m-Ag NP decrease with increasing m-Ag NP ratio, and the dielectric constants of the films that contain m-ND increase with increasing m-ND ratio. [ABSTRACT FROM AUTHOR]

The hydrolytic stability of polyimide films (PI) in a 0.9% sodium chloride solution in the temperature range of existing biological objects was studied. The kinetic parameters of hydrolysis of PI films were calculated. It was established that the hydrolysis rate constant of an adamantane-containing film was significantly lower than that of an industrial Kapton film. The dielectric constant after hydrolysis was determined. It was shown that the dielectric properties of the adamantane-containing polymer remained unchanged under the hydrolysis conditions. [ABSTRACT FROM AUTHOR]

Materials with outstanding mechanical properties and excellent dielectric properties are increasingly favored in the microelectronics industry. The application of polyimide (PI) in the field of microelectronics is limited because of the fact that PI with excellent mechanical properties does not have special features in the dielectric properties. In this work, PI composite films with high dielectric properties and excellent mechanical properties are fabricated by in-situ reduction of fluorinated graphene (FG) in polyamide acid (PAA) composites. The dielectric permittivity of pure PI is 3.47 and the maximum energy storage density is 0.664 J/cm3 at 100 Hz, while the dielectric permittivity of the PI composite films reaches 235.74 under the same conditions, a 68-times increase compared to the pure PI, and the maximum energy storage density is 5.651, a 9-times increase compared to the pure PI films. This method not only solves the problem of the aggregation of the filler particles in the PI matrix and maintains the intrinsic excellent mechanical properties of the PI, but also significantly improves the dielectric properties of the PI. [ABSTRACT FROM AUTHOR]

The burgeoning realms of artificial intelligence, the Internet of Things and 5G communication, have engendered a consistent increase in the demand for interlayer insulation materials featuring a reduced dielectric constant, thereby enhancing the signal transmission speed as large-scale integrated circuits progressively turn towards miniaturization and high integration. Polyimide has received tremendous attention as interlayer insulating material owing to the inherent advantages including excellent thermal and chemical stability, and mechanical strength. Thus far, endeavors aimed at diminishing the dielectric constant to low (<2.5) or even ultralow (≤2.2) levels of polyimide have attracted extensive interest. Herein, starting from a brief overview of the design principles of low dielectric materials, the latest research progress in the designation of intrinsic low dielectric polyimides, including fluorinated polyimides, polyimides with rigid and bulky structures, and other intrinsic low dielectric polyimides, has been thoroughly reviewed. Furthermore, the dielectric properties, water absorption capacity, and mechanical and thermal performances of different polyimides are elucidated. Finally, the key issues and challenges faced in the advancement of intrinsic low dielectric polyimides are elaborated, and the outlooks of the design of the materials are furtherly outlined. The primary objective of this paper is to acquire comprehensive and profound insights into intrinsic low dielectric polyimides, offering solid theoretical foundations and empirical references to guide future development of next-generation polyimides endowed with exceptional dielectric properties. [Display omitted] • Reducing molecular polarizability and number of polarized molecules decrease ε. • Fluorination and rigid and bulky groups modification are used to prepare low- k PI. • Dielectric constant and water absorption capacity correlate with fluorine content. [ABSTRACT FROM AUTHOR]

Novel fluorine-containing polyimides were synthesized through copolymerization by using 2,3,3′,4′-biphenyltetracarboxylic dianhydride (α-BPDA) and 4,4′-(4,4′-isopropydenediphenox-y) bis-(phthalic anhydride) (BPADA) as dianhydrides and 4,4′-oxydianiline (ODA) and 2,2 - Bis [4-(4-aminophenoxy)phenyl]-hexafluoropropanane (HFBAPP) as diamines. Noncoplanar structure, flexible ether bond, and trifluoromethyl give the polyimide good thermoplastic, solubility, and heat resistance. The glass transition temperatures of polyimide films are 232.5°C∼262.2°C, the 5% weight loss temperatures are 521.5°C∼531.0°C, and the residual mass is more than 50% as heating to 800°C. With the increase of HFBAPP content in diamine, the dielectric constant of the material decreases from 3.21 to 2.78, and the dielectric loss decreases from 0.00962 to 0.00687 at 1 MHz, which greatly improves the dielectric properties of the material. [ABSTRACT FROM AUTHOR]

The dimensional and property stability after heating is considered to be one of the most important properties for low‐dielectric‐constant materials. Herein, porous structure contained composite PI film with porous PI structure on the surface of a flat PI film was prepared through the simple and low‐cost microemulsion method. The introduction of porous coating can significantly improve the dielectric and water resistance properties of PI film, while maintaining its good mechanical properties. More importantly, the porous structures were well preserved after heating, but with the remove of surfactant layer on the inner surface of the pores, leading to lower dielectric constants with 1.06%–3.50% of reduction and lower dielectric losses less than 0.015 with the maintenance of good water resistance and mechanical properties. Excellent durability of the low dielectric constants and low dielectric losses upon high humidity were also shown for the heated composite PI film. In addition, the morphology and properties of the composite PI film both before and after heating could be controlled through varying the fabrication conditions. These results provide valuable information for the construction of the thermally stable low‐dielectric‐constant material. [ABSTRACT FROM AUTHOR]

A novel method of patterning high precision copper conductive micropatterns on flexible polymer substrate (polyimide) is developed. We utilized the coordination effect between palladium salts and pyridine structures to fix the palladium chloride (PdCl2) on the surface of polymer film while the 2,6-dimethylpyridine structures formed in the specific areas under ultraviolet light guaranteed the resolution of final patterns. Simultaneous thermal reduction of PdCl2 on the surface can be achieved in the process of thermal cyclization of the polymer substrate. As a consequence, the obtained polyimide (PI) film can be patterned with conductive copper micropatterns directly by electroless plating. In particular, we accomplished the deposition of high precision copper pattern with a minimum line width of 50 µm and minimum line spacing of 20 µm on PI thin films (thickness ∼10 µm) by electroless plating. The prepared conductive copper micropatterns exhibit a low resistivity of 1.78 µΩ·cm the same as the pure block copper. And the relationship between the structures of the polymer chains and the physical properties of polymer substrates, such as the dimensional stability, mechanical and dielectric properties were also discussed in detail. This simple and novel method of patterning metal on the polymer surface does not need to achieve the catalytic metal adhesion required for electroless plating at the cost of destroying the substrate surface and avoiding the introduction of unstable interlayers. This patterning method is compatible with the current roll-to-roll production process and can be used to develop high-performance micro-integrated circuits. [ABSTRACT FROM AUTHOR]

In this work, a high‐performance composite film polyimide (PI)/boron nitride nanosheets (BNNS) + aramid nanofibers (ANFs) was prepared by in‐situ polymerization. Modified two‐dimensional (2D) BNNS were prepared by urea‐assisted ball milling to exfoliate and NH2 functionalize hexagonal boron nitride(h‐BN) in one step. One‐dimensional (1D) ANFs prepared by deprotonation method and 2D BNNS were simultaneously incorporated into PI and used as effective reinforcement nanofillers. This novel PI/BNNS + ANFs composite film has excellent thermal stability and mechanical properties. Compared with pure PI, the glass transition temperature (Tg) increased by approximately 18°C, and the coefficient of thermal expansion (CTE) decreased by 11.45%. Remarkably, the tensile strength and elongation at break of PI/BNNS + ANFs‐1 wt% composite film increased by 18.6% and 133.4%, respectively. The improvement of thermal stability and mechanical properties were ascribed to the uniform dispersion of BNNS + ANFs and the interfacial interaction between BNNS + ANFs and PI matrix. Furthermore, the PI/BNNS + ANFs composite films show good dielectric properties and optical transparency. These excellent comprehensive properties of the PI/BNNS + ANFs composite films make it a good candidate for the flexible substrate. [ABSTRACT FROM AUTHOR]

Laser-induced Graphene (LIG) electrodes on flexible substrates have attracted significant research interest, making them an excellent alternative to conventional fabrication of transducers on rigid planar substrates. In this study, four individual capacitor-like triangular LIG electrodes were fabricated on polyimide (PI) film with micron gap (MG) spacing of 30, 66, 125 and 180 µm, to study the relationship between gap spacing and capacitance. A novel N, N-carbonyldiimidazole-copper (CDI-Cu) hybrid nanoflower (NF) was synthesised via one-pot biomineralization and deposited at the triangular junction of acid-base treated LIG-MG for the immobilization of neutravidin. The gap spacing and structure of the LIG-MG were analysed using high-resolution microscopes, revealing a porous nanofiber-like graphene structure. X-ray Photoelectron Spectroscopy (XPS) of acid-base treated PI film proved carboxyl group formation. A decrease in capacitance was observed with an increasing gap spacing in a non-faradaic environment. The capacitance of CDI-Cu NF following neutravidin modification for 30, 66, 125 and 180 µm spacings were 1.77E-07, 1.36E-07, 4.73E-08, 4.84E-08 F, respectively, suggesting excellent biomolecular modification sensitivity of the LIG-MG with 30 µm spacing. A comparative analysis of dielectric performance for different gap-spaced devices revealed that a 30 µm spacing would be optimal for bio-capturing because of the close confinement of biomolecules for smaller gapped areas. [Display omitted] • A new LSG MG was developed via a one-step CO2 laser irradiation method. • The CDI-Cu NF was developed and applied for the immobilization of neutravidin. • The dielectric properties were closely studied in a non-faradaic environment. • LIG MG 30 µm spacing possess highest sensitivity for bio capturing. • Optimal for bio-capturing with a close confinement on smaller gapped areas. [ABSTRACT FROM AUTHOR]

With the rise of 5G communication technology and the development of microelectronics industry, establishing a balance between dielectric constant (D k) and coefficient of thermal expansion (CTE) becomes significant for polyimide. Herein, a series of poly(amide-imide) (PAI) films were fabricated by using pyrophthalic dianhydride, 4,4′-diaminodiphenyl ether and 4,4′-diaminobenzanilide containing an amide structure as constitutional units; and then 1,3,5-tris(4-aminophenoxy)benzene (TAPOB) as the crosslinker was introduced to form the crosslinked structure within PAI films. The results indicated that well-designed crosslinked network could effectively balance the relationship between dimensional stability and the dielectric properties of PAI films. With the addition of just 0.1 mmol TAPOB, the D k of corresponding PAI films decreased to 3.37 (at 105 Hz), compared with unmodified PAI films. Furthermore, the CTE of such PAI film revealed a 50.6 % reduction, revealing the superior dimensional stability. This work provides a novel strategy to design high-performance polyimide films for a practical application in flexible printed circuit board. [Display omitted] • A series of micro-crosslinked PAI films were synthesized by a two-step method. • Film's dielectric properties and dimensional stability were controlled by micro-crosslinked and amide structures. • Micro-crosslinked PAI films with suitable D k and low CTE were obtained. [ABSTRACT FROM AUTHOR]

Polyimide aerogels are high-performance polymer materials, but they have been restricted by costly drying and low mechanical strength in practical applications. Here, we report a family of porous polyimide (PI) aerogel films prepared through a partial pre-imidization process under ambient pressure drying and freeze-drying. The effect of pre-imidization degree (pre-ID) on the mechanical and dielectric properties of porous films was investigated in detail. The Fourier transform infrared spectra show that the partial pre-imidization process made the molecular chain with coexisted amide acid and imide rings. The porous structure of film was successfully controlled by adjusting the pre-ID, which was confirmed by pore size distributions. These aerogel films with nanoporous structures exhibit better mechanical properties (e.g., 10.61 MPa at 0.433 g cm−3 at room temperature) and lower dielectric constant (minimum of 1.414 at 106 Hz) over the entire bulk density range (0.398–0.5 g cm−3). Their morphology, pore characteristics, and properties were similar, whether by ambient pressure drying or freeze-drying. Moreover, this work will provide a new perspective on the fabrication of porous PI aerogel film via ambient pressure drying with efficient processability. [ABSTRACT FROM AUTHOR]

In this study, KMnO4 was applied as an etchant to partially decompose the silica microspheres into mesoporous structures. 1H,1H,2H,2H-perfluorodecyltriethoxysilane was grafted onto the surface of the hollow silica. A fluorinated silica/polyimide hybrid material was prepared. Meanwhile, the influence of fluorinated silica on the dielectric property and moisture absorption property of the hybrid material was discussed. It is found that the fluorinated silica can lower the dielectric constant and hygroscopicity of the hybrid film. The fluorinated silica is characterized by strong hydrophobicity, good dispersibility, and good thermal stability. Even at a very low filling level of only 2 wt%, the dielectric constant of the polyimide hybrid is significantly reduced to 2.61 without sacrificing thermal stability. The water absorption rate of the polyimide hybrid film is reduced from approximately 3.1% to 2.1 wt%. Moreover, this provides a new idea for reducing the dielectric and water absorption properties of materials. [ABSTRACT FROM AUTHOR]

In this article, the polyimide (PI) composite films with synergistically improving thermal conductivity were prepared by adding a few graphene nanoplatelets (GNP) and various hexagonal boron nitride (h-BN) contents into the PI matrix. The thermal conductivity of PI composite film with 1 wt% GNP and 30 wt% h-BN content was 1.21 W(m·k)−1, which was higher than that of the PI composite film with 30 wt% h-BN content (0.45 W(m·k)−1), the synergistic efficiency of GNP under various h-BN content (10 wt%, 20 wt%, and 30 wt%) were 1.70, 2.71, and 3.09, respectively. And it was found that the increased h-BN content can suppress the dielectric properties caused by GNP in the matrix. The dielectric permittivity and dielectric loss tangent of 1 wt% GNP/PI composite film were 10.69, 0.661 at 103 Hz, respectively, and that of the 30 wt% h-BN + GNP/PI composite film were 4.29 and 0.1367, respectively. Moreover, the mechanical properties of the PI composite film were suitable for practical applications. And the heat resistance index and the residual rate at 700°C of PI composite film increased to 326.8°C, 74.43%, respectively, and these of PI film were 292.6°C and 59.26%. Thus, it may provide a reference value for applying the filler hybridization/PI film in the electronic packaging materials. [ABSTRACT FROM AUTHOR]

The preparation of polyimide (PI)/nanocomposite films and their thickness are a complex process with some ambiguous variables that are involved in the synthesis process. Therefore, it is crucial to understand those variables and reveal the chemistry behind them. Several methods have been probed until an optimal synthesis process was found. A detailed synthesis process optimization is described in this article to understand all variables, which can influence the molecular weight of polyamic acide (PAA) solution, the thickness of films, and nanoparticles dispersion. The spin coating technique was used to control the thickness of single and multilayer PI/nanocomposite films, which reveals that the thickness of the casted PI film depends on several factors, such as the viscosity, molecular weight of the PAA solution, and the spin speed of spin coater. Factors, which can influence the molecular weight of PAA solution, are discussed in detail. After completing the synthesis process, the single and multilayer PI nanocomposite films are characterized experimentally. The results reveal that using a thin layer of nanocomposite on PI film in the form of a multilayer structure improves the nanoparticles dispersion and thereafter its dielectric properties. [ABSTRACT FROM AUTHOR]

In this study, silver–polydopamine–hexagonal boron nitride (h-BN@Ag) particles were prepared using mussel chemistry and reducibility of catechol. The modified method was simple and eco-friendly. In addition, we prepared h-BN@Ag/polyimide (PI) composite films via in situ polymerization, the scraper method, and thermal imidization. Owing to the good dispersion of the h-BN@Ag filler particles in the PI matrix and the bridging role of the Ag nanoparticles, the thermal conductivities of the h-BN@Ag/PI composite films were higher than that of the pure PI film. The thermal conductivity of the h-BN@Ag/PI film with the filler content of 10 wt% was 0.382 W (m·K)−1, which was 108% higher than that of pure PI films (0.184 W (m·K) −1). Furthermore, the composite films presented extremely low dielectric permittivity and loss tangent. Moreover, the heat resistance index of the composite films (304.6°C) was higher than that of pure PI (294.3°C). Thus, h-BN@Ag/PI composite films could be promising electronic packaging materials. [ABSTRACT FROM AUTHOR]

A necklace‐like supramolecular structure is constructed from 18‐crown ether‐6 (18CE6) as the host molecule and fluorinated polyimide (FPI) as the guest molecule to enhance the mechanical properties as well as to further lower the dielectric constant of FPI. The introduction of 18CE6 simultaneously enhances the stiffness and toughness of FPI films. In particular, the elongation at break is increased by over 200%. Furthermore, the dielectric constant of FPI films with 40 mol% 18CE6 is decreased to 2.74 from 3.15 of pure FPI, which is attributed to the enlarged free volume by the necklace‐like supramolecular structure of 18CE6/FPI. Accordingly, the glass transition temperature of 18CE6/FPI films is slightly reduced to 305 °C, which is still high enough during the soldering process for the preparation of flexible copper clad laminate. In addition, the water absorption of FPI films is gradually decreased to 0.52% as the loading of 18CE6 raises to 40 mol%, representing the excellent moisture resistance of 18CE6/FPI films. [ABSTRACT FROM AUTHOR]

Polyimides (PIs) and their composites hold promise as low-cost alternatives to conventional ceramic-based dielectrics. Nevertheless, they are far unsatisfactory for practice applications, mainly resulting from the low interfacial compatibility between PI matrices and inorganic fillers. Herein, black phosphorous (BP) nanoflakes/PI composite films with outstanding dielectric and mechanical properties were fabricated via an in situ polymerization pathway. Owing to the hydrophilic surface of BP nanoflakes resulting from slight oxidation during fabrication, the robust noncovalent interaction between BP and PI can be formed, leading to good interfacial compatibility between the two domains and thus well dispersion of BP in PI. Even with a low BP content of 2 wt%, the composite can reach a high-permittivity value of 8.6 at 102 Hz and a low dielectric loss value of 0.02. Moreover, the BP/PI composite films inherited the good mechanical performance of PI matrix due to homogeneous dispersion and low loading of BP. [ABSTRACT FROM AUTHOR]

• Offer a holistic understanding of the erosion mechanisms and rational design principles from both theoretical and experimental perspectives. • Present a comprehensive evaluation of strategies employed to enhance polyimide's resistance against atomic oxygen. • Emphasize the significance of theoretical calculations in understanding the underlying principles and mechanisms of AO-resistant polyimide materials. Atomic oxygen (AO), as the primary component in the low Earth orbit (LEO), poses significant hazards to polymer materials. Polyimide, due to its excellent dielectric properties, mechanical strength, thermal stability, and radiation resistance, has become an ideal space polymer material widely used in LEO applications, which is prone to erosion caused by AO. To address this issue, various strategies have been employed to enhance PI's resistance against AO. Previous reviews on AO-resistant PI have primarily concentrated on experimental preparation methods, with relatively little emphasis on theoretical calculations and erosion mechanism. This review summarizes the research progress of both experiments and theoretical calculations on AO-resistant PI materials, with a specific focus on elucidating the rationale behind material design. Firstly, we introduce commonly used commercial PI films in the aerospace field. Secondly, we review experimental methods aimed at improving PI's ability to resist atomic oxygen, including protective coatings, blending and intrinsic modification approaches. Furthermore, our focus extends towards theoretical calculations of AO-resistant PI films, analyzing the underlying principles and mechanisms governing PI's capability to withstand atomic oxygen erosion. Finally, we present an extensive evaluation of different methods to enhance PI's resistance against AO and provide valuable suggestions and prospects for future developments in AO-resistant PI materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • The transparent, flexible, semi-aliphatic CPI films were elaborately prepared. • CPI-55 film has excellent thermal stability and high transparency. • The outstanding dielectric and mechanical properties are given to CPI-55 film. • CPI-55 film has an excellent prospect for application in the display technology. A set of colorless polyimide (CPI) films with norbornene-aliphatic ring structures has here been prepared through polycondensation reactions by using cyclopentanone bis-spironorbornane tetracarboxylic dianhydride (CpODA), 4,4′-(hexafluoroisopropyl)diphthalic anhydride (6FDA) and 4,4′-diaminodiphenyl ether (ODA) monomers as raw materials. The transmissivities, dielectric properties and thermal stabilities of CPI films are optimized by adjusting the CpODA-to-6FDA molar ratios. Compared with the aromatic and aliphatic PI films, the thermal stabilities and transmissivities of CPI films are well balanced. Moreover, the CPI films possessed low dielectric constants and low dielectric losses. The thermal expansion coefficients, temperatures at a 5% weight loss and glass-transition temperatures are maintained at 31–41 ppm K−1, 461–484 °C and 348–362 °C, respectively. In addition, the transmittances (86–89%), dielectric constants (2.15–2.47) and dielectric losses (<0.023) are all prominent. In short, the CPI films have been shown to have a high potential for use in the display technology. [ABSTRACT FROM AUTHOR]

The simultaneous improvement of dielectric, mechanical and water resistance properties of dielectric materials is extremely important for their practical use, but rarely been realized. Here, the comprehensive properties of polyimide (PI) film were enhanced through the construction of sandwich-type porous film using the microemulsion method. Due to the introduction of porous structure on both sides of PI film, apparent decreases were observed in dielectric constant (16.50%) and water absorption (82.7%), accompanied by increases in tensile strength (5.14%) and tensile modulus (41.17%), compared to flat PI film. Furthermore, excellent durability of low dielectric constant of the sandwich-type porous film under moist environment was demonstrated since 1.76% of increase was found upon exposing to 75% R.H. for 32 h. This provides a novel method to optimize the comprehensive properties of dielectric materials and also displays underlying insight for the development of functional materials in electronic and electric areas. [ABSTRACT FROM AUTHOR]

In this study, a series of [3-(2-aminoethyl)amino]propyl-heptaisobutyl substituted polyhedral oligomeric silsesquioxane (AHIP) containing polyimide (PI) nanocomposites were successfully prepared. Structural, thermal and electrical properties of the polyimide nanocomposites were studied. The properties of AHIP containing polyimides were compared with those of the neat polyimide films. The surface morphology of the prepared AHIP containing polyimides were determined by using Scanning Electron Microscopy (SEM). The hydrophilic/hydrophobic nature of AHIP/polyimide composites were analyzed by measuring their water contact angles. It was found that the addition of AHIP into the polyimide slightly increased the contact angle values. The incorporation of 5% AHIP to the PI matrix decreased the dielectric constant value of pure PI from 8.6 to 11.7, respectively. Furthermore he dielectric permittivity was changed from 8.6 (neat polyimide) to 5.5 (PI3). [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]

[Display omitted] • A flexible ion-exchange technology is used to construct a nano-Al 2 O 3 coating on the surface of pristine PI at hundreds of nanometers depth. • The surface insulation properties of modified PIs were improved under HF electric stress. • The high-frequency surface insulation improvement mechanism brought by nano-Al 2 O 3 coating was further revealed. • The introduction of the nano-Al 2 O 3 coating promotes surface charge dissipation of the modified PI. Polyimide (PI) films used for inter-turn insulation of power electronic transformer (PET) are prone to premature insulation failure. Using ion-exchange technology to modify the surface of PI films effectively improves its high-frequency (HF) insulation strength. In this paper, the HF discharge characteristics of PI films were studied coated a nano-Al 2 O 3 layer. The experimental results illustrate that the introduction of nano-Al 2 O 3 coating can effectively improve the HF surface insulation strength of modified PIs, in which the maximum discharge lifetime is increased to 5.6 times of the pristine PI, and the creeping flashover voltage raised from the initial 6.34 kV to 11.98 kV, an increase of 88.96%. The enhanced mechanism of HF insulation performance of modified PIs is as follows: On the one hand, formed the functional nano-Al 2 O 3 coating improves the thermal management ability and the inorganic–organic phase structure of the modified PIs, which is effective in reducing the temperature rise of materials. On the other hand, the introduction of the nano-Al 2 O 3 coating increases the density of the shallow trap, increasing the surface conductivity of modified PIs, and hindering the development of HF surface discharge. This paper offers a prospective strategy for polyimide dielectrics with superior HF insulation performance. [ABSTRACT FROM AUTHOR]

Three polyimides (PI-p, PI-t, and PI-n) containing a 2,6-di(4-aminophenyl) pyridine body and different pendant groups are reported in this study. The resulting polyimide films exhibit excellent dielectric properties, with a dielectric constant of 2.91–2.62@10GHz and a dielectric loss in the range of 0.00939–0.00808@10GHz. Through computer simulation, the dielectric constant and dielectric loss of the polyimides are found to decrease with increasing pendant group volume. Moreover, the resulting strong and flexible polyimide films exhibit excellent thermal stability, with decomposition temperatures (at a 5% weight loss) in the range of 532.3–552 °C and glass-transition temperatures in the range of 343.7–376.4 °C. TGA/FTIR/MS experiments indicate that the thermal stability of the resin containing the methyl phenyl group is worse due to the degradation of the methyl group at low temperatures. In addition, the three polyimides also show excellent solubility and transparency. These superior properties indicate that the PI series is an ideal candidate material for future 5G communications. [Display omitted] • Polyimide resins containing 2, 6-bis (4-aminophenyl) pyridine bodies and different volume side groups are synthesized. • Computer simulation further proves that the D k and tanδ of PIs decrease with the increase of pendant group volume. • In addition to excellent dielectric properties (D k : 2.91–2.62 @10 GHz, tanδ: 9.39 × 10−3∼8.08 × 10−3 @10 GHz), the PI resin also showed high thermal stability [T d5 (N 2): 532.3–552 °C, T g : 376.4–343.7 °C], high transparency and excellent solubility. [ABSTRACT FROM AUTHOR]

ABSTRACT: Polyimide (PI) films used in aerospace and rail applications are degraded by thermal, chemical, and electric power under the effect of insulation aging. To prevent these types of degradation, we prepared nanocomposite films of PI and layered double hydroxide (LDH) modified with the potassium perfluorooctane sulfonate (FS) by an in situ method. On the whole, the glass‐transition temperature, dielectric constant (ɛ′), and corona‐resistance lifetime of the nanocomposite films increased over those of the pure PI film, but the temperature at 10 wt % weight loss, breakdown strength, and volume resistance decreased correspondingly as a whole. The PI matrix was protected by the inorganic material of LDH–FS with a high ɛ′ from corona corrosion. Furthermore, the heat and chemical interactions of the composite films improved the corona‐resistance lifetime, despite the decrease in the breakdown strength; this should result in promising applications for insulation parts of variable‐frequency motors. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46528. [ABSTRACT FROM AUTHOR]

Abstract: A honeycomb‐patterned porous film was conveniently prepared by means of the microemulsion method and then used as an effective coating for improving the dielectric properties and water resistance of polyimide (PI) film while maintaining its mechanical properties. The dielectric properties could be regulated by tuning the structure of the porous film through controlling its formation conditions. When suitable conditions were used, the prepared composite PI film exhibited a significant reduction of 28.3 % in its dielectric constant and 9.48–54.99 % in dielectric loss accompanied by an extremely low water uptake of 0.62 % relative to the 2.47 % of flat PI film. The composite PI film also displayed excellent durability under moist conditions, as the dielectric constant was still below 2.4 after exposure to 75 % relative humidity for more than 12 h. This provides a novel method to improve and control the dielectric properties of materials. It also suggests that this film is a suitable candidate for coating dielectric materials in high‐humidity environments. [ABSTRACT FROM AUTHOR]

ABSTRACT: A series of novel ultralow dielectric porous polyimide (PI) films containing adamantane groups was prepared via the thermolysis of polyethylene glycol (PEG) oligomers mixed into PI matrix. Scanning electron microscopy results indicated that the porous PI films showed closed pores with an average diameter of 120 ± 10 nm. Good thermal properties with 5% weight loss temperature of 499 °C in air atmosphere and glass transition temperature in excess of 310 °C were shown for porous PI films. Notably, the ultralow dielectric constant of porous PI films with 1.85 at 1 MHz was obtained and revealed via broadband dielectric spectroscopy. The effects of the chemical structure of the PI matrix and PEG content on the decomposition behavior of PEG and the performance of porous films were investigated. Wide‐angle X‐ray diffraction results indicated that the PI matrix with large d‐spacing generated weaker interactions between the PEG and PI backbone than those of PI matrix with small d‐spacing. As a result, the PEG for the PI matrix with large d‐spacing was completely decomposed. As indicated by the broadband dielectric spectroscopy results, lower dielectric porous PI films were prepared when the PEG contents in the PI matrix increased from 0 to 20 wt %. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 549–559 [ABSTRACT FROM AUTHOR]

Graphene nanoribbon (GNR) was introduced into in the polyimide (PI) composite films. The effects on dielectric and mechanical properties of PI/GNR composites were investigated. Results show that the dielectric and mechanical properties of the composite films are significantly enhanced compared to pure PI. This can attribute the excellent dispersion of and the strong interfacial interaction between GNR and the PI matrix. Tensile strength of PI/GNR composite films shows a first increasing and then decreasing trend with increased GNR content. With 0.1 wt% loading, the tensile strength is increased from 120.1 MPa to 166.7 MPa, and the dielectric constant of PI/GNR composite film is decreased from 3.6 to 3.1 compared to pure PI, respectively. The success of this preparation is believed to afford new avenue for the development of high strength polyimide based composites. [ABSTRACT FROM AUTHOR]

Polyimide (PI)/silicon dioxide (SiO 2 ) films have been fabricated by in-situ polymerization method. The average diameter of the SiO 2 nanoparticles is determined to be about 7 nm, which are modified by surface treatment to create surface charges (e-SiO 2 ). Their microstructures are investigated using small angle X-ray scattering (SAXS) technique, Raman Spectroscopy and Scanning Electron Microscopy (SEM). The morphology of the composite films shows better and more uniform dispersion of the e-SiO 2 nanoparticles in PI matrix than SiO 2 nanoparticles due to the coulomb repulsion among surface charged nanoparticles. Our study shows that the resulted uniform dispersion of e-SiO 2 in PI has direct impact on the dielectric constant, dielectric loss, corona aging time and thermal stability of PI/e-SiO 2 composite films and our studied result is presented. The corona aging time of a PI/e-SiO 2 composite film with 20 wt% doping is increased to 128 h, which is forty times more than that of a pure PI film (3 h). In addition, the thermal stability and tensile strength of composite films are also enhanced. [ABSTRACT FROM AUTHOR]

All-organic polyimide (PI)/poly(vinylidene fluoride) (PVDF) composite materials with high dielectric constant and low dielectric loss were fabricated via solution blending. The dielectric, mechanical, and thermal properties of the PI/PVDF composite films were studied. Results indicated that the dielectric properties of the composites were highly reinforced through the introduction of PVDF, and the composites exhibited excellent thermal stability. When the mass fraction of PVDF was adjusted to 30 wt%, the specimen demonstrated excellent thermal properties, superior mechanical properties, high dielectric constant (5.7, 1 kHz), and low dielectric loss (0.009, 1 kHz). Moreover, the dependence of the dielectric constant and dielectric loss on frequency was investigated. The composite presented stable dielectric constant and dielectric loss that were less than 0.04 within the testing frequency range of 100 Hz-10 MHz. This study demonstrated that the PI/PVDF composites were potential dielectric materials in the field of electronics. [ABSTRACT FROM AUTHOR]

• Properties of two types of CPI films under the photo-oxidation are investigated. • The yellowness index, thermal stability and mechanical properties are degraded. • The microstructure evolution of CPI films under the photo-oxidation are studied. • The content of the C O with the depth under the photo-oxidation is studied. • The relationship between properties and the microstructure has been revealed. Colorless transparent polyimide (CPI) films with high thermal stability, superior mechanical and dielectric properties are widely used in optoelectronic devices, in which the properties are degraded in service. In this work, the degradation in properties and molecular mechanisms of the CPI-L film with the trifluoromethyl group and CPI-T film with the alicyclic group under photo-oxidation are revealed. It is found that for CPI-L and CPI-T films after 168 h photo-oxidation, the mechanical properties and thermal stability are decreased, especially the yellowness index is increased by 740% and 530%, respectively. Consequently, the degradation of the CPI-L film is more severe than the CPI-T film after photo-oxidation. This is because that the transmission at 365 nm of CPI-L and CPI-T films before photo-oxidation is 51% and 64%, respectively. After photo-oxidation, the ether bond, imide ring and phenyl of both CPI films are broken, and the rearrangement of C N in the CPI-L film is observed. And eroded voids and/or microcracks caused by off-gassing appear at 120 h and 72 h, respectively. Furthermore, possible molecular mechanisms of CPI films during photo-oxidation are proposed, and the relationship between molecular mechanisms and properties degradation is elucidated. Moreover, the content of the C O is decreased with the increased depth of CPI-L and CPI-T films, indicating the enrichment of the C O on the surface. It is mainly because free radicals generated during photo-oxidation can combine with the atmospheric O 2. [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]

[Display omitted] • The organic filler fluoroelastomers were introduced into polyimide, which realized controllable preparation of ultra-low permittivity (ε = 1.21) all-organic polyimide composite films for the first time. • The FEM/PI composite films exhibited excellent thermal stability, outstanding mechanical properties and high hydrophobicity. • The preparation process of FEM/PI composite films is simple and the developed films presented excellent practical application potential. Dielectric materials with low permittivity are urgently needed in the field of microelectronics due to the development of integration and miniaturization of integrated circuits. In this work, a series of all-organic polyimide (PI) films with ultra-low-permittivity and high hydrophobicity were successfully synthesized by introducing a kind of fluoroelastomer (FEM). And the significant permittivity reduction phenomenon was discussed through molecular dynamics simulations and practical tests. It was assumed that the hydrogen bond significantly inhibited the dipolar polarization of the FEM/PI composite system, which played an important role in determining the dielectric properties of FEM/PI composite films. At a low filler content of 7 wt%, FEM/PI composites exhibited the optimum permittivity (ε) of 1.21 at 106 Hz, which was the lowest permittivity of the PI films, while a low water absorption of 0.44 % and high thermal stability with a 10 % decomposition temperature (T d 10 %) of 548 °C were also observed. This simple and effective strategy of fabricating ultra-low-permittivity PI film is a potential way to realize commercial process. [ABSTRACT FROM AUTHOR]

• Two fluorinated polyimide films crosslinked by TAPP or TAPc were prepared. • The PI/TAPP and PI/TAPc films showed higher dielectric constant than neat PI. • The PI/TAPP and PI/TAPc exhibited smaller charge decay than neat PI in LS-TENGs. • The PI/TAPP and PI/TAPc showed higher friction coefficient stability than neat PI. In order to improve the charge retention, anti-decay ability and durability of traditional triboelectric materials in lateral sliding-mode triboelectric nanogenerators (LS-TENGs), two fluorinated polyimide films crosslinked by porphyrin tetra-amino phenyl porphyrin (TAPP) and tetra-amine phthalocyanine (TAPc) were synthesized, and their contact angles, dielectric properties, output performances and tribological properties were studied in detail. The results showed that the polyimide films crosslinked by TAPP (PI/TAPP) and TAPc (PI/TAPc) with lower surface energies had higher dielectric constants compared with neat PI and Kapton. In addition, TAPP and TAPc not only improved the electrical output with a small decay of charge density, but also reduced the wear of PI films during the whole triboelectrification process, which is attributed to the high permittivity and the crosslinked effect of PI with TAPP or TAPc. Thus, PI films with TAPP and TAPc hold great promise for dielectric research and LS-TENG applications. [ABSTRACT FROM AUTHOR]

The preparation of high-dielectric-constant (κ) materials is important in the field of electronics. However, how to effectively use the function of fillers to enhance κ is still a challenge. In this study, anisotropic graphene (GNS)-iron oxide (Fe3O4)/polyimide (PI) nanocomposite films with oriented GNSs were prepared by the in situ polymerization of 4,40-oxydianiline and pyromellitic anhydride in the presence of GNS-Fe3O4. Films of the precursors were fabricated, and this was followed by stepwise imidization under a magnetic field at a higher temperature to orient the magnetic sheets. The orientation of GNS-Fe3O4 and the relationships of the GNS-Fe3O4 content and measurement frequency with the dielectric properties of the GNS-Fe3O4/PI films were studied in detail. The dielectric property differences of the GNS-Fe3O4/PIs with GNS-Fe3O4 parallel or perpendicular to the film surface were not obvious, when the content of GNS-Fe3O4 was lower than 5 wt %. However, at the percolation threshold, the κ values of GNS-Fe3O4/ PI films with horizontal GNS-Fe3O4 were much higher than those of the other two kinds of films at 103 Hz; this was derived from the contribution of more effective microcapcitors parallel to the film surface. So, making the GNS-Fe3O4 parallel to the film surface greatly enhanced κ of GNS-Fe3O4. However, switching the charges on the large lateral surface of the parallel GNSs with the electric field also caused a higher dielectric loss and the frequency dependence of κ and the dielectric loss at low frequency. [ABSTRACT FROM AUTHOR]

BaTiO 3 nanowires/polyimide (BT-NWs/PI) and BaTiO 3 nanoparticles/polyimide (BT-NPs/PI) composites with low volume (≤10vol%) fraction of ceramic fillers were successfully prepared by in-situ dispersive polymerization. The BT-NWs were synthesized by a simple one-step hydrothermal method. The microstructure, dielectric properties, and energy storage density of the composites were studied. It was found that the two types of fillers were dispersed homogeneously in the PI matrix. Compared with BT-NPs/PI composites, the dielectric constant of composites filled by BT-NWs was larger at the same concentration. Stronger interfacial polarization mainly determined the dielectric properties that we observed on BT-NWs/PI composites. Furthermore, the energy storage density of the composites was significantly enhanced by BT-NWs, and energy storage density of 1.06 J/cm 3 was obtained under an electric field of 2200 kV/cm with the BT-NWs content of 2 vol%, which was 37% larger than that of the pure PI. The results indicate that the introduced wire-like ceramic fillers contribute to the enhancement of the dielectric properties and energy storage density of the composites. [ABSTRACT FROM AUTHOR]