Modified Polyimide Films Research Articles

Synthesis and properties of modified polyimides containing multiple side methyl and biphenyl structures

With the rapid development of 5 G technology and microelectronics, there is an urgent demand to design and develop modified polyimide films with low dielectric constant as flexible matrix materials. In this work, a diamine containing multiple side methyl and biphenyl groups was synthesized by aromatic nucleophilicsubstitution reaction and oxidation-reduction reaction, respectively. Furthermore, this monomer was used to polymerize with four different commercially available dianhydrides (ODPA, BTDA, BPDA, and PMDA) to produce a class of polyimides (PI 3a∼3d). The structures of the diamine and its PIs are characterized, and the relationship between the structure and properties of the obtained PI films is investigated. These modified PIs are easy to cast into films and have low dielectric constants and water absorption. Their dielectric constants and dielectric losses are in the range of 2.66–2.91 and 0.00579–0.00677 at 1 MHz, respectively. Meanwhile, these PIs also maintains good thermal stability, with glass transition temperatures (T g) higher than 284 °C and 10% weight loss temperatures in the range of 496–505 °C at N2.

Fluorinated Al2O3/siloxane modified PI films towards vastly enhanced corona resistance performance

Polyimide (PI) films with excellent corona-resistant performance are vital in multitudinous electrical equipment. Here we employ a largely unexplored strategy to effectively restrain phase separation behavior of siloxane modified PI through chain extension copolymerization (PI-e-Si), thereby generating dense SiO2-like storage space under corona that shows powerful ability of encircling and restraining electron/ion, which restricts their direct and persistent attack for PI segment. Therefore, PI-e-Si film owns obviously longer corona-resistant lifetime (30.8 min) than that of pristine PI film (6.4 min) based on accelerated corona-aged test. Furthermore, fluorinated Al2O3 (F-Al2O3) with strong corona-resistant ability is applied to construct a solid barrier for dense SiO2-like storage space, which synergistically strengthens restraint effect for electron/ion, and it also optimizes heat-conducting and dielectric properties of PI film. Finally, fabricated composite film (PI-e-Si/F-Al2O3) further improves corona-resistant lifetime up to 66.8 min, superior to that of Kapton 100 CR film (a famous corona-resistant PI film).

Enhancing the Output Performance of a Triboelectric Nanogenerator Based on Modified Polyimide and Sandwich-Structured Nanocomposite Film

Recently, scientists have been facing major obstacles in terms of improving the performances of dielectric materials for triboelectric nanogenerators. The triboelectric nanogenerator (TENG) is one of the first green energy technologies that can convert random mechanical kinetic energy into electricity. The surface charge density of TENGs is a critical factor speeding up their commercialization, so it is important to explore unique methods to increase the surface charge density. The key to obtaining a high-performance TENG is the preparation of dielectric materials with good mechanical properties, thermal stability and output performance. To solve the problem of the low output performance of PI-based triboelectric nanogenerators, we modified PI films by introducing nanomaterials and designed a new type of sandwich-shaped nanocomposite film. Herein, we used polyimide (PI) with ideal mechanical properties, excellent heat resistance and flexibility as the dielectric material, prepared an A-B-A sandwich structure with PI in the outer layer and modified a copper calcium titanate/polyimide (CCTO/PI) storage layer in the middle to improve the output of a TENG electrode. The doping amount of the CCTO was tailored. The results showed that at 8 wt% CCTO content, the electrical output performance was the highest, and the open-circuit voltage of CCTO/PI was 42 V. In the TENG, the open-circuit voltage, short-circuit current and transfer charge of the prepared sandwich-structured film were increased by 607%, 629% and 672% compared to the TENG with the PI thin film, respectively. This study presents a novel strategy of optimizing dielectric materials for triboelectric nano-generators and has great potential for the future development of high output-performance TENGs.

Polyimide/crown ether composite film with low dielectric constant and low dielectric loss for high signal transmission.

Dielectric properties of polyimide (PI) are constrained by its inherent molecular structure and inter-chain packing capacities. The compromised dielectric properties of PI, however, could be rescued by introducing trifluoromethyl and forming a host-guest inclusion complex with the introduction of crown ethers (CEs). Herein, we report PI/crown ether composite films as a communication substrate that could be applied under high frequency circumstances. In this work, three kinds of bisphenol A-containing diamine (2,2'-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(2-methyl-4-aminophenoxy)phenyl]propane, and 2,2-bis[4-(2-trifluoro methyl-4-aminophenoxy)phenyl]propane) are synthesized and polymerized with 4,4'-(hexafluoroisopropylidene)diphthalic anhydride to prepare low-dielectric PI films by means of thermal imidization. Crown ethers are introduced into the PI with different mass fractions to obtain three series of PI films. Following the combination of trifluoromethyl into the molecular chain of PI, high frequency dielectric loss of modified PI films can be effectively reduced. The properties of these materials (especially the dielectric properties) are thoroughly explored by crown ether addition. The results show that the crown ether addition process can offer crown ethers with increased free volume of PI matrix, thus allowing them to generate a special necklace-like supramolecular structure, which makes the crown ether disperse more uniformly in the PI matrix, resulting in improved dielectric properties. Importantly, the dielectric constant and dielectric loss of the composite films at high frequencies are remarkably reduced to 2.33 and 0.00337, respectively. Therefore, these composite films are expected to find extensive use as a 5G communication substrate at high frequencies in the future.

Flexible and quasi-isotropically thermoconductive polyimide films by guided assembly of boron nitride nanoplate/boron nitride flakes for microelectronic application

• A hierarchical “brick and plank” structure is fabricated by dopamine modified h -BN nanomaterials. • This special structure can be used to improve the performance of polyimide. • The modified PI films have quasi-isotropic thermal conductivity and high thermal stability. • The modified PI films have good flexibility and excellent electrical insulation. • The modified PI films show faster shape memory response time reducing 50 %. Currently, the application of polyimide (PI) based materials often demands mutual additional properties, such as high thermal conductivity, good flexibility, high thermal stability and low dielectric constant and loss, etc. . Herein, a well-aligned hierarchical “brick and plank” architecture by rational assembly of dopamine modified hexagonal boron nitride flakes and nanoparticles (PDA-BNF@BNNPs) which can effectively improve the thermal conductivity, thermal stability, electrical conductivity, dielectric properties and shape memory performance of pure PI. The alternating stacking of vertically arranged h -BNNPs and horizontally laid h -BNFs yield a quasi-isotropic thermal conductivity of PI films with a high through-plane thermal conductivity of 6.43 W/(mK) and an in-plane thermal conductivity of 11.85 W/(mK) because of the simultaneously vertical and horizontal phonon scattering enabled by the vertically arranged h -BNNPs and horizontally laid h -BNFs. Besides, this special structure also endues PI films high thermal stability of over 560 °C, prominent electrical resistance of over 1.40 × 10 -13 Ω•cm, and low dielectric loss of less than 0.02 in the high frequency. Moreover, the PDA-BNF@BNNP/PI films exhibit excellent flexibility and shape memory performance with faster recovery response time reduced over 50 % comparing with that of pure PI film. These outstanding properties combining with the facile and scalable fabrication process make PDA-BNF@BNNP/PI films are very promising in diverse electronic device applications, especially in flexible electronic devices or circuits requiring additionally high thermal conductivity and low dielectric loss.

High-Frequency Surface Insulation Strength with Nanoarchitectonics of Disiloxane Modified Polyimide Films.

High-frequency power transformers are conducive to the reliable grid connection of distributed energy sources. Polyimide is often used for the coating insulation of high-frequency power transformers. However, creeping discharge will cause insulation failure, therefore, it is necessary to use disiloxane for the purpose of modifying the molecular structure of polyimide. This paper not only introduces 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (GAPD) with a molar content of 1%, 2%, and 5% to polyimide, but also tests both the physical and chemical properties of the modified film and the high frequency creeping dielectric strength. The results show that after adding GAPD, the overall functional groups of the material do not change, at the same time the transfer complexation of intermolecular charge and the absorption of ultraviolet light increase. There is no phase separation of the material and the structure is more regular and ordered, moreover the crystallinity increases. The overall dielectric constant and the dielectric loss tangent value show different trends, which means that the former value increases, while the latter value decreases. In addition, the resistivity of the surface and the volume increase, which is the same as the glass transition temperature. The mechanical properties are excellent, and the strength of bulk breakdown is mounting. The insulation strength of the high frequency creeping surface has been improved, which will increase with larger contents of GAPD. Among them, the relative change of the creeping flashover voltage is not obvious, and the creeping discharge life of G5 is 4.77 times that of G0. Further analysis shows that the silicon-oxygen chain links of the modified film forms a uniformly dispersed Si-O-Si network in the matrix through chemical bonds and charge transfer complexation. Once the outer matrix is destroyed, it will produce dispersed flocculent inorganic particles which have the role of protecting the inner material and improving the performance of the material. Combined with the ultraviolet light energy absorption, the increase of deep traps, the reduction of dielectric loss, and the improvement of thermodynamic performance, can better improve the high-frequency creeping insulation strength of polyimide film and its potential application value.

The high frequency surface discharge behaviours of modified polyimide films: the effects of phenyl thioether in the backbone

High frequency surface discharge is one of the main causes of insulation failure in the high frequency power transformer. In order to extend the endurance lifetime and investigate the behaviours of surface discharge, a series of polyimide films containing phenyl thioether groups were prepared and tested in a self-built experimental platform with a high frequency voltage source. First, the surface discharge inception voltages on the films were tested under high frequency sinusoidal voltage. Then, with the application of continuous high frequency voltage, surface discharge tests were conducted to observe the entire evolution process of surface discharge including its initiation, self-sustaining, streamer and the ultimate flashover. Combining with the frequency-domain dielectric spectra and x-ray diffraction tests, effects of phenyl thioether content on the evolution process in each stage were analyzed. Experimental results and analyses indicate that the discharge inception voltage is opposite to the dielectric loss factor. The depth and distribution of traps caused by crystal and amorphous regions play the different role in various stages of surface discharge. The endurance lifetime of polyimide film containing 40% phenyl thioether was the longest and the effects of which were further discussed based on the discharge behaviour analysis. The paper demonstrates that molecular-structure modification is an effective method to improve the high frequency electrical performance of polyimide.

Influencing mechanism of phenyl thioether group in the main molecular chain on high frequency electrical properties of the modified polyimide films

Polyimides (PIs) and their nanocomposites may render quite high dielectric loss under high frequency (HF) electrical stresses, which will significantly affect the insulation properties and operating lifetime of the equipment when the composite materials are used in the high-voltage and large-capacity power electronics transformers (HFPTs). In this paper, the phenyl thioether groups of various molar ratios were introduced into the diamine residue as to prepare modified PI films via alternating copolymerization method. Frequency-domain dielectric spectrum and high frequency surface discharge were adopted to study the HF electrical properties. The results indicated that with the increase of the phenyl thioether content, the dielectric loss factor firstly decreased and thereafter rose up again, while the lowest arrived at 9.29 × 10–4 for a PI film incorporating 40% phenyl thioether content, which case also presented the longest endurance lifetime against surface discharge tests at 15 kHz. Based the UV–vis tests on the charge transfer complexation, further analysis verified that for the 40% molar content of phenyl thioether in the PI molecule, it was the weak charge transfer characteristics that resulted in the smallest stacking structure of the ordered molecular chain in the film, which led to the weakest lossy polarization under the HF alternating electric field and manifested the minimal dielectric loss factor accordingly. The proposed research presents a feasible technological approach to regulate HF electrical properties of the modified PI films.

Impact of the phenyl thioether contents on the high frequency dielectric loss characteristics of the modified polyimide films

With the combination of the phenyl thioether group into the molecular chain of polyimide, the high frequency dielectric loss of the modified polyimide film can be effectively reduced, which will avail this insulating material of application in high frequency electrical equipment. In the proposed study, polyimide films containing different proportions of phenyl thioether were prepared via alternating thermal imidization method and the impact of phenyl thioether contents on the high frequency dielectric loss characteristics investigated. Frequency-domain dielectric spectrum analysis indicated that the dielectric loss of the modified films decreased in the first instance and then roared again with increased phenyl thioether content, among which cases the lowest dielectric loss factor (tanδ = 0.000929 at 1 kHz) occurred in the film with phenyl thioether content of 40%. Both X-ray diffraction (XRD) and Ultraviolet-visible spectroscopy (UV–Vis) measurements, with reactive force field-based molecular dynamics simulation, were utilized to further elucidate the influencing mechanism of phenyl thioether content on dielectric loss characteristics. When the content of phenyl thioether was <40%, the charge transfer effect decreased with the increased phenyl thioether content, gradually reducing the degree of micro-crystallinity in the modified polyimide, and thereby increasing the dispersion of dipole moment that directly led to the reduced dielectric loss. When the phenyl thioether content is higher than 40%, the charge transfer effect reversed, which results in the PI film with increased crystalline region caused by the tighten molecular stacking and has the increased dielectric loss. Synthesis of the low-dielectric-loss polyimide films can be then optimized for high frequency applications.

Thermally induced chemical evolution in polyimide films investigated by X‐ray photoelectron spectroscopy

Thermally modified polyimide films based on 1,4‐Phenylene diamine (p‐PDA) and 3,3′,4,4′ – Benzophenone tetracarboxylic dianhydride (BTDA) were prepared and their chemical structure transformation after thermal treatment at 350 °C–500 °C was investigated. X‐ray diffraction results revealed an increase in the polymer chain order for all treated PI samples as a consequence of the thermal treatment and chain interaction. TGA analysis showed that the heat treatment promoted different thermal degradation profiles. Electron spin resonance evidenced a large population of free radicals as a result of homogeneous bond cleavage when the thermal treatment was performed at 500 °C. X‐ray photoelectron spectroscopy analysis indicated that the chemical structure transformation not only occurs on the outer surface but also in the sub‐surface layer. These results show that controlled fast thermal treatment can produce materials with specific characteristics and may serve as a general strategy for changing both structural and chemical properties of the polymers. POLYM. ENG. SCI., 58:943–951, 2018. © 2017 Society of Plastics Engineers

Discharge Breakdown Characteristics With Fluorinated Polyimide Films in High-Temperature Superconducting Cable Insulation

The application of high-temperature superconducting cable now has been in the process of being implemented in power system. Polyimide (PI) film has been used as insulation in the high-temperature superconducting cable systems with the advantage of good performance in low temperature, excellent mechanical properties, and dielectric properties. However, due to the organic properties of PI films, it can be aged even brake down in the service of HTS cable. It is found that partial discharge in HTS cable can lead to insulation material degradation and finally breakdown. Our recent researches have shown that fluorination can influence the surface charge behaviors thus influence the PD characteristics of modified PI films. In this paper, PI films were fluorinated in laboratory, the relationship between the fluorination time and discharge characteristics of the films were researched. The surface topography of direct-fluorinated samples were obverted by using an Atomic force acoustic microscope. It can be found from the experiment results that the discharge times and quantity both showed decreasing tendency with the fluorination time increasing. The discharge breakdown voltage shows increasing tendency with the fluorination time from zero minutes to forty-five minutes, and then shows decreasing tendency.

The influence of moisture on charge relaxation in modified polyimide films

The influence of moisture on charge relaxation in modified polyimide films

The influence of moisture on charge relaxation in modified polyimide films

The charge relaxation processes in the films based on polyimide and polytetrafluoroethylene (the latter serves as a coating) have been studied. The coating effect on the charge relaxation processes in the films under high humidity conditions was revealed. The obtained experimental data was analyzed in the context of the present-day knowledge of the charge relaxation mechanism. The complex spectra of the thermally stimulated depolarization currents (TSDC) were resolved into individual components described by the first-order kinetics equations using computer simulation. The TSDC activation energies were calculated and interpreted in terms of the mechanism of release of charge carriers. It was shown that the polytetrafluoroethylene coats on film surfaces lead to an essential increase in the electret state stability at elevated temperature and high humidity.

Potentiometric Control of Metal Concentration for Chelation Kinetics of Modified Polyimide Films

Interaction of modified polyimide films with agrentium nitrate solutions of various concentrations was studied. Sorption of Ag ions by films is divided into three steps: formation of Ag ion layer on the border of film surface; diffusion inside the films; and final saturation of film by Ag ions. The data are confirmed by calculation of weight of the sorbed Ag ions onto the films with various thicknesses. Electrochemical Ag loading of PI films includes two parallel reactions: film dissolution accompanied by chelation.

Immobilization of alpha‐amylase on aminated polyimide membrane: Preparation, characterization, and properties

α‐amylase was covalently immobilized on functionalized polyimide (PI) membranes via glutaraldehyde (GA) activation. 3,3′,4,4′‐Benzophenonetetracarboxylic acid dianhydride (BTDA) and 4,4′‐oxydianline (4,4′‐ODA) based polyimide membranes were obtained via thermal imidization. Free amine groups on the surface of the polyimide membranes were generated by the amination reaction of polyimides with hexamethylenediamine (HMDA). Surface‐aminated membranes were subjected to enzyme immobilization after GA activation. Immobilization efficiency and enzyme activity of α‐amylase was examined at various pH (3.0–8.0) and temperature (15–80°C). The storage stability and reusability of immobilized α‐amylase were investigated. Immobilization yield was found as 359.53 mg per gram of modified polyimide films. Enzyme assays demonstrated that the immobilized enzyme exhibited better thermo stability than the free one. The storage stability and reusability improved by the immobilization on this enzyme support. Free enzyme lost its activity completely within 15 days. On the other hand, the immobilized enzyme retained 79.98% of its activity after 30 days. These results confirmed that α‐amylase was successfully immobilized and gained more stable character compared to the free enzyme.

The study of polyimide modified by Ni plasma and its adhesion to Cu films

Polyimide (PI) is an excellent functional material, which possesses desirable properties of high temperature resistance, good mechanical strength and so on; but it is hard to serve as a substrate deposited with metal films due to the inferior adhesion force between PI and metal films; surface modification method is one of the best ways to solve this technique problem. In this paper, surface of PI film was treated by home-made MEVVA and FCVA systems to improve the adhesion strength to metal coatings; specimens were pretreated by three different fluences of Ni ion plasma. PI deposited with a tie layer was analyzed by XRD to examine the as-deposited Cu films structure; the morphology of specimens were investigated by scanning electron microscopy (SEM), characteristic absorption peaks of modified PI films were depicted by Fourier Transform Infrared spectrum (FTIR). The simulation of PI films implanted with Ni ions with different fluences was also carried out by TRIDYN codes; the depth profile of Ni atoms distribution was obtained.

Adhesion Properties and Structure of Ion-Beam Modified Polyimide Films

Polyimide (PI) surface modification was carried out by an ion beam treatment to improve the adhesion between the polyimide film and copper. The PI film surface was treated with an ion-beam source at ion doses ranging from 1.96 × 1013 to 2.38 × 1013 ions/cm2 using a mixture of nitrogen (N2) and hydrogen (H2). Contact angle measurement, atomic force microscopy and X-ray photoelectron spectroscopy, respectively revealed an increase in the surface roughness, a decrease in contact angle, and the formation of oxygen complexes and functional groups on the treated PI surfaces. Adhesion between the copper and PI film treated with the beam was superior to that of the untreated PI film. The 90° peel test revealed the highest peel strength of 7.8 N/cm.

Ink-jet printing of Cu conductive ink on flexible substrate modified by oxygen plasma treatment

We conducted ink-jet printing of copper (Cu) conductive ink on polyimide (PI) film to form Cu conductive patterns and determine the correlation between Cu ink based on Cu complex and flexible substrate. First, the oxygen plasma treatment was performed to modify the surface property of the PI film, and contact angles were measured to confirm the change of its surface property. Thus, we confirmed the decrease of contact angles and optimized plasma treatment parameters. Then Cu conductive lines were formed on unmodified and modified PI films using ink-jet printing, and the printed lines were reduced and sintered by thermal treatment in hydrogen (H 2) atmosphere at 200 °C. The formed Cu conductive lines were analyzed by an optical microscope (OM), a field emission scanning electron microscope (FE-SEM), an X-ray diffractometer (XRD), a non-contact 3D Profiler, and a four-point probe to confirm the shape, microstructure, crystal structure of conductive lines, and electrical conductivity. The continuous lines having pure Cu phase and well-sintered microstructure were successfully formed on PI substrate modified by oxygen plasma treatment and the correlation between Cu ink and substrate surface property was determined.

Antibacterial surfaces through dopamine functionalization and silver nanoparticle immobilization

Immobilization of silver nanoparticles on the dopamine functionalized polyimide (PI) films was carried out by photo-induced silver ion-reduction under atmosphere conditions. The dopamine has been successfully deposited on the PI surface in mild aqueous environments. The effects of pH, dopamine concentration and reaction time on the dopamine polymerization were investigated. The water contact angles of the poly(dopamine) functionalized PI films reduced remarkably in comparison with that of the pristine PI film. The chemical composition and structure of the UV-induced deposited-silver on the modified PI films were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The topography of the modified PI films was investigated by scanning electron microscope (SEM). The deposited poly(dopamine) layer acted as binding sites for the silver ions. The silver-plated PI films showed good antibacterial activity due to that biofilm formation was inhibited on the polymeric surfaces in contact with bacteria.

A facile method for preparing highly conductive and reflective surface-silvered polyimide films

A novel method was developed for the preparation of reflective and electrically conductive surface-silvered polyimide (PI) films. The polyimide films were functionalized with poly(dopamine), simply by dipping the PI films into aqueous dopamine solution and mildly stirring at room temperature. Electroless plating of silver was readily carried out on the poly(dopamine) deposited PI (PI-DOPA) surface. The surface compositions of the modified PI films were studied by X-ray photoelectron spectroscopy (XPS). XPS results show that the PI-DOPA surfaces were successfully deposited with ploy(dopamine) and were ready for electroless deposition of silver. The poly(dopamine) layer was used not only as the chemi-sorption sites for silver particles during the electroless plating of silver, but also as an adhesion promotion layer for the electrolessly deposited silver. The as-prepared silvered PI films show high conductivity and reflectivity, with a surface resistance of 1.5 Ω and a reflectivity of 95%, respectively.