Synthetic strategies for highly transparent and colorless polyimide film

L, Ortiz PA. Novel Co-Polyamides Containing Pendant Phenyl/Pyridinyl Groups with Potential Application in Water Desalination Processes

This study explores the development and evaluation of a novel series of aromatic co-polyamides featuring diverse pendant groups, including phenyl and pyridinyl derivatives, designed for water desalination membrane applications. These co-polyamides, synthesized with a combination of hexafluoroisopropyl, oxyether, phenyl, and amide groups, exhibited excellent solubility in polar aprotic solvents, thermal stability exceeding 350 °C, and the ability to form robust, flexible films. Membranes prepared via phase inversion demonstrated variable water permeability and NaCl rejection rates, significantly influenced by the pendant group chemistry. Notably, pyridinyl-substituted membranes achieved water fluxes up to 17.7 L m-2 h-1 and a NaCl rejection of 37.3%, while phenyl-substituted variants provided insights into the interplay of hydrophobicity and porosity. These findings highlight the critical role of pendant group functionality in tailoring membrane performance, offering a foundation for further structural modifications to enhance efficiency in water treatment technologies.

Preparation and Characterization of a Novel Self-Healing Transparent Polyimide Film Based on Dynamic Disulfide Bonds

Self-healing optically transparent polyimides have potential applications in optoelectronic device fabrication. In this study, for the first time, we successfully prepared a novel self-healing polyimide film containing reversible disulfide bonds through chemical imidization by introducing cystamine as a self-healing functional monomer into the molecular structure of conventional polyimides. The incorporation of cystamine enabled the films to maintain high transmittance (>87%) and tensile strength (>99 MPa). Meanwhile, tensile tests showed that the prepared film with a cystamine content of 50% achieved an excellent self-healing efficiency of up to 91.8%. Stress relaxation tests further revealed that disulfide bonds were rapidly cleaved upon thermal stimulation and the network topology was rearranged to complete the self-healing process. These results suggest that the dynamic covalent polymer network made of aliphatic disulfide bonds presents a new strategy for the development of optically transparent polyimides with excellent self-healing properties.

From Molecular Design to Practical Applications: Strategies for Enhancing the Optical and Thermal Performance of Polyimide Films

Polyimide (PI) films are well recognized for their outstanding chemical resistance, radiation resistance, thermal properties, and mechanical strength, rendering them highly valuable in advanced fields such as aerospace, sophisticated electronic components, and semiconductors. However, improving their optical transparency while maintaining excellent thermal properties remains a significant challenge. This review systematically checks over recent advancements in enhancing the optical and thermal performance of PI films, focusing on various strategies through molecular design. These strategies include optimizing the main chain, side chain, non-coplanar structures, and endcap groups. Rigid and flexible structural characteristics in the proper combination can contribute to the balance thermal stability and optical transparency. Introducing fluorinated substituents and bulky side groups significantly reduces the formation of charge transfer complexes, enhancing both transparency and thermal properties. Non-coplanar structures, such as spiro and cardo configurations, further improve the optical properties while maintaining thermal stability. Future research trends include nanoparticle doping, intrinsic microporous PI polymers, photosensitive polyimides, machine learning-assisted molecular design, and metal coating techniques, which are expected to further enhance the comprehensive optical and thermal performance of PI films and expand their applications in flexible displays, solar cells, and high-performance electronic devices. Overall, systematic molecular design and optimization have significantly improved the optical and thermal performance of PI films, showing broad application prospects. This review aims to provide researchers with valuable references, stimulate more innovative research and applications, and promote the deep integration of PI films into modern technology and industry.

Incorporation of Aramids into Polybenzimidazoles to Achieve Ultra-High Thermoresistance and Toughening Effects

Polybenzimidazoles (PBIs) are recognized for their remarkable thermal stability due to their unique molecular structure, which is characterized by aromaticity and rigidity. Despite their remarkable thermal attributes, their tensile properties limit their application. To improve the mechanical performance of PBIs, we made a vital modification to their molecular backbone to improve their structural flexibility. Non-π-conjugated components were introduced into PBIs by grafting meta-polyamide (MA) and para-polyamide (PA) onto PBI backbones to form the copolymers PBI-co-MA and PBI-co-PA. The results indicated that the cooperation between MA and PA significantly enhanced mechanical strain and overall toughness. Furthermore, the appropriate incorporation of aromatic polyamide components (20 mol% for MA and 15% for PA) improved thermal degradation temperatures by more than 30 °C. By investigating the copolymerization of PBIs with MA and PA, we unraveled the intricate relationships between composition, molecular structure, and material performance. These findings advance copolymer design strategies and deepen the understanding of polymer materials, offering tailored solutions that address thermal and mechanical demands across applications.

Preparation of MoS2@PDA-Modified Polyimide Films with High Mechanical Performance and Improved Electrical Insulation

Polyimide (PI) has been widely used in cable insulation, thermal insulation, wind power protection, and other fields due to its high chemical stability and excellent electrical insulation and mechanical properties. In this research, a modified PI composite film (MoS2@PDA/PI) was obtained by using polydopamine (PDA)-coated molybdenum disulfide (MoS2) as a filler. The low interlayer friction characteristics and high elastic modulus of MoS2 provide a theoretical basis for enhancing the flexible mechanical properties of the PI matrix. The formation of a cross-linking structure between a large number of active sites on the surface of the PDA and the PI molecular chain can effectively enhance the breakdown field strength of the film. Consequently, the tensile strength of the final sample MoS2@PDA/PI film increased by 44.7% in comparison with pure PI film, and the breakdown voltage strength reached 1.23 times that of the original film. It can be seen that the strategy of utilizing two-dimensional (2D) MoS2@PDA nanosheets filled with PI provides a new modification idea to enhance the mechanical and electrical insulation properties of PI films.

Colorless Polyimides Derived from 5,5'-bis(2,3-norbornanedicarboxylic anhydride): Strategies to Reduce the Linear Coefficients of Thermal Expansion and Improve the Film Toughness

In this paper, novel colorless polyimides (PIs) derived from 5,5'-bis(2,3-norbornanedicarboxylic anhydride) (BNBDA) were presented. The results of single-crystal X-ray structural analysis using a BNBDA-based model compound suggested that it had a unique steric structure with high structural linearity. Therefore, BNBDA is expected to afford new colorless PI films with an extremely high glass transition temperature (Tg) and a low linear coefficient of thermal expansion (CTE) when combined with aromatic diamines with rigid and linear structures (typically, 2,2'-bis(trifluoromethyl)benzidine (TFMB)). However, the polyaddition of BNBDA and TFMB did not form a PI precursor with a sufficiently high molecular weight; consequently, the formation of a flexible, free-standing PI film via the two-step process was inhibited because of its brittleness. One-pot polycondensation was also unsuccessful in this system because of precipitation during the reaction, probably owing to the poor solubility of the initially yielded BNBDA/TFMB imide oligomers. The combinations of (1) the structural modification of the BNBDA/TFMB system, (2) the application of a modified one-pot process, in which the conditions of the temperature-rising profile, solvents, azeotropic agent, catalysts, and reactor were refined, and (3) the optimization of the film preparation conditions overcame the trade-off between low CTE and high film toughness and afforded unprecedented PI films with well-balanced properties, simultaneously achieving excellent optical transparency, extremely high Tg, sufficiently high thermal stability, low CTE, high toughness, relatively low water uptake, and excellent solution processability.

Synthesis and Characterization of Organo-Soluble Polyimides Based on Polycondensation Chemistry of Fluorene-Containing Dianhydride and Amide-Bridged Diamines with Good Optical Transparency and Glass Transition Temperatures over 400 °C

Polymeric optical films with light colors, good optical transparency and high thermal resistance have gained increasing attention in advanced optoelectronic areas in recent years. However, it is somewhat inter-conflicting for achieving the good optical properties to the conventional thermal resistant polymers, such as the standard aromatic polyimide (PI) films, which are well known for the excellent combined properties and also the deep colors. In this work, a series of wholly aromatic PI films were prepared via the polycondensation chemistry of one fluorene-containing dianhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (FDAn) and several aromatic diamines with amide linkages in the main chain, including 9,9-bis [4-(4-aminobenzamide)phenyl]fluorene (FDAADA), 2,2'-bis(trifluoromethyl)-4,4'-bis[4-(4-aminobenzamide)] biphenyl (ABTFMB), and 2,2'-bis(trifluoromethyl)-4,4'-bis[4-(4-amino-3-methyl)benzamide] biphenyl (MABTFMB). The derived FLPI-1 (FDAn-FDAADA), FLPI-2 (FDAn-ABTFMB) and FLPI-3 (FDAn-MABTFMB) resins showed good solubility in the polar aprotic solvents, such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc) and dimethyl sulfoxide (DMSO). The solution-processing FDAn-PI films exhibited good optical transmittance over 80.0% at a wavelength of 500 nm (T500), yellow indices (b*) in the range of 1.01-5.20, and haze values lower than 1.0%. In addition, the FDAn-PI films showed low optical retardance with optical retardation (Rth) values in the range of 31.7-390.6 nm. At the same time, the FDAn-PI films exhibited extremely high glass transition temperatures (Tg) over 420 °C according to dynamic mechanical analysis (DMA) tests. The FDAn-PI films showed good dimensional stability at elevated temperatures with linear coefficients of thermal expansion (CTE) in the range of (31.8-45.8) × 10-6/K.

Dielectrics for Two-Dimensional Transition-Metal Dichalcogenide Applications

Despite over a decade of intense research efforts, the full potential of two-dimensional transition-metal dichalcogenides continues to be limited by major challenges. The lack of compatible and scalable dielectric materials and integration techniques restrict device performances and their commercial applications. Conventional dielectric integration techniques for bulk semiconductors are difficult to adapt for atomically thin two-dimensional materials. This review provides a brief introduction into various common and emerging dielectric synthesis and integration techniques and discusses their applicability for 2D transition metal dichalcogenides. Dielectric integration for various applications is reviewed in subsequent sections including nanoelectronics, optoelectronics, flexible electronics, valleytronics, biosensing, quantum information processing, and quantum sensing. For each application, we introduce basic device working principles, discuss the specific dielectric requirements, review current progress, present key challenges, and offer insights into future prospects and opportunities.

Polyimide Layers with High Refractivity and Surface Wettability Adapted for Lowering Optical Losses in Solar Cells

The performance of photovoltaics with superstrate configuration is limited by the rigidity and low refractivity of a classical glass cover. In this work, two polyimides (PIs) and two copolyimides combined in the main chain cycloaliphatic moieties, aromatic sequences, chalcogen atoms, and having/lacking fluorine atoms, are proposed as shielding covers for solar cells. The samples containing small cycloaliphatic moieties displayed high transmittance above 80% at 550 nm. The refractive index values under changeable wavelengths and temperatures were shown to influence the magnitude of the reflection losses. At the sample interface with the transparent electrode, optical losses were reduced (~0.26%) in comparison to the classical glass (~0.97%). The samples with the best optical features were further subjected to a surface treatment to render the self-cleaning ability. For this, a new approach was used residing in irradiation with the diffuse coplanar surface barrier discharge (DCSBD), followed by spraying with a commercial substance. Scanning electron microscopy and atomic force microscopy scans show that the surface characteristics were changed after surface treatment, as indicated by the variations in root mean square roughness, surface area ratio, and surface bearing index values. The proposed PI covers diminish the optical losses caused by total internal reflection and soiling, owing to their adapted refractivity and superhydrophobic surfaces (contact angles > 150°), and open up new perspectives for modern photovoltaic technologies.