Synthesis and characterization of colorless polyimides derived from 4-(4-aminophenoxy)-2,6-dimethylaniline

Transparent polyimide films with ultra-low coefficient of thermal expansion

According to the application requirements of colorless transparent polyimide (CPI) film for low coefficient of thermal expansion (CTE) in the field of OLED display, the new aromatic dianhydride monomers with amide bond structure were synthesized, namely s-ABDA, i-ABDA, EADA. Furthermore, a series of CPI films were prepared by two-step method from the reaction of as-synthesized dianhydrides with 2.2′-bis (trifluoromethyl) −4.4′-diaminobiphenyl (TFMB) or trans-1.4′-cyclohexanediamine ( t-CHDA). Based on the analysis of performance results, the incorporation of amide group and biphenyl, benzene or ether bond into dianhydride monomer helped this new type of transparent polyimide film with excellent optical properties (T550 nm> 88%), great heat stability (CTE < 4.4 ppm/K; Tg > 314°C; Td5% > 478°C) and good mechanical strength (σ > 208 MPa). The film s-ABDA/TFMB showed ultra-low CTE value at 4.4 ppm/K, aligning with the maximum birefringence, indicating that the role of hydrogen bonding was of great benefit to the regulation of thermal expansion.

Highly Transparent Aromatic Polyamides from Unsymmetrical Diamine with Trifluoromethyl Groups

Soluble and transparent wholly aromatic polyamides (PAs) were synthesized from an unsymmetrical diamine monomer having trifluoromethyl (CF₃) groups, 4-(4′-aminophenoxy)-3,5-bis(trifluoromethyl)aniline. The monomer was polymerized with several dicarboxylic acid monomers via the Yamazaki–Higashi polycondensation method. All of the synthesized polyamides have an amorphous morphology, and they are soluble in many polar organic solvents at room temperature. Flexible and transparent films of the polyamides were prepared by solution casting and these polymer films show good optical transparencies with cut-off wavelengths of 337–367 nm and transparencies of 88%–90% at 550 nm. In addition, all the polymers were thermally stable over 400 °C and exhibited glass transition temperatures (T_g) higher than 300 °C. Unsymmetrically inserted trifluoromethyl groups on polyamides improves the solubility as well as the transparency of the polymers while maintaining good thermal properties. They also showed low refractive indices around 1.5333~1.5833 at 633 nm owing to the existence of low polarizable trifluoromethyl groups.

Super-heat resistant, transparent and low dielectric polyimides based on spirocyclic bisbenzoxazole diamines with Tg > 450°C

Maintaining ultra-high heat resistance and sufficient colorless transparency at the same time is a challenge for polymer materials because of conflicting design principles, but such materials are urgently needed for...

Terphenyl-based colorless and heat-resistant polyimides with a controlled molecular structure using methyl side groups

A methyl regulation strategy is proposed and verified to balance the optical and thermal properties of aromatic polyimides.

Colorless Polyimides Derived from an Alicyclic Tetracarboxylic Dianhydride, CpODA

An alicyclic tetracarboxylic dianhydride having cyclopentanone bis-spironorbornane structure (CpODA) was polycondensated with aromatic dianhydrides to form the corresponding poly(amic acid)s which possessed logarithmic viscosities in the range 1.47–0.54 dL/g. The poly(amic acid) was imidized by three methods: a chemical, a thermal, and a combined chemical and thermal process. In a thermal method, imidization temperature markedly influenced the film quality and molecular weight of the polyimide. When the poly(amic acid) was cured over the Tg of the corresponding polyimide, the flexible polyimide films were obtained and the molecular weights increased several times, which means that the post-polymerization took place. In spite of low-temperature cure below Tg flexible films with the imidization ratio of 100% were fabricated by a combined chemical and thermal imidization technique. The films possessed the decomposition temperatures in a range of 475–501 °C and Tgs over 330 °C. The high Tg results from a dipole–dipole interaction between the keto groups of the polymer chains as well as development of the rigid polyalicyclic unit. The polyimide films exhibited CTE between 17 and 57 ppm/K. All the films fabricated were entirely colorless and possessed the λcut-offs shorter than 337 nm. Notably, the films prepared by a chemical method exhibited outstanding optical properties.

Soluble and transparent polyimides with high Tgs from a new semi-aliphatic diamine with cyclohexyl and ortho-methyl groups

Herein a semi-aliphatic diamine 4,4′-(cyclohexylmethylene)bis(2-methylaniline) (CHMBMA) with a pendant cyclohexyl and two ortho-substituted methyl groups is synthesized from o-toluidine and cyclohexanecarbaldehyde by Mannich and rearrangement reactions. Then CHMBMA is polycondensed with five commercial aromatic dianhydrides by the high-temperature one-step method with the thermal imidization to produce a series of polyimides (PIs, PI-H(1–5)). The weight-averaged molecular weights ( M ws) of PI-H(1–5) are in the range from 9.08 × 104 to 27.48 × 104 g mol−1 with the polydispersity indices (PDI) from 3.29 to 6.13 by gel permeation chromatography (GPC) measurement. They are soluble in common organic solvents (such as THF, CHCl3 etc.) and can form transparent, tough films with light-color (Thickness: 20–26 μm) by the solution-casting method. The light transmittance of them is above 80% in the visible range from 400 to 760 nm. They exhibit excellent mechanical properties with tensile strength from 72.2 to 97.06 MPa and tensile modulus from 0.9 to 1.9 GPa. Furthermore, they also display low water absorption rates (<2.5%), good thermal stability (5% weight loss temperatures ( T 5%) in the range from 466 to 480°C under N2 atmosphere and high glass transition temperatures ( T gs ≥ 319°C). As comparison, we also synthesize these PIs (PI-L(1–5)) by the low-temperature two-step method with the chemical imidization. The M ws of PI-L(1–5) are lower than those of PI-H(1–5), but the film color of PI-L(1–5) is relatively lighter than the corresponding one of PI-H(1–5). In summary, the introduction of cyclohexyl and ortho-substituted methyl groups into the backbone can improve the solubility of PIs and the transparency of their corresponding films without reducing their T gs.

Reduced Coefficients of Linear Thermal Expansion of Colorless and Transparent Semi-Alicyclic Polyimide Films via Incorporation of Rigid-Rod Amide Moiety: Preparation and Properties

Semi-alicyclic colorless and transparent polyimide (CPI) films usually suffer from the high linear coefficients of thermal expansion (CTEs) due to the intrinsic thermo-sensitive alicyclic segments in the polymers. A series of semi-alicyclic CPI films containing rigid-rod amide moieties were successfully prepared in the current work in order to reduce the CTEs of the CPI films while maintaining their original optical transparency and solution-processability. For this purpose, two alicyclic dianhydrides, hydrogenated pyromellitic anhydride (HPMDA, I), and hydrogenated 3,3',4,4'-biphenyltetracarboxylic dianhydride (HBPDA, II) were polymerized with two amide-bridged aromatic diamines, 2-methyl-4,4'-diaminobenzanilide (MeDABA, a) and 2-chloro-4,4'-diaminobenzanilide (ClDABA, b) respectively to afford four CPI resins. The derived CPI resins were all soluble in polar aprotic solvents, including N-methyl-2-pyrrolidone (NMP) and N,N-dimethylacetamide (DMAc). Flexible and tough CPI films were successfully prepared by casing the PI solutions onto glass substrates followed by thermally cured at elevated temperatures from 80 °C to 250 °C. The MeDABA derived PI-I_a (HPMDA-MeDABA) and PI-II_a (HBPDA-MeDABA) exhibited superior optical transparency compared to those derived from ClDABA (PI-I_b and PI-II_b). PI-I_a and PI-II_a showed the optical transmittances of 82.3% and 85.8% at the wavelength of 400 nm with a thickness around 25 μm, respectively. Introduction of rigid-rod amide moiety endowed the HPMDA-PI films good thermal stability at elevated temperatures with the CTE values of 33.4 × 10^-6/K for PI-I_a and 27.7 × 10^-6/K for PI-I_b in the temperature range of 50-250 °C. Comparatively, the HBPDA-PI films exhibited much higher CTE values. In addition, the HPMDA-PI films exhibited good thermal stability with the 5% weight loss temperatures (T_5%) higher than 430 °C and glass transition temperatures (T_g) in the range of 349-351 °C.

High-performance polyimides based on pyridine and xanthene pendant groups; synthesis, characterization, photoactivity, thermal, antibacterial, and Cr(VI) ion adsorption properties

A group of new polyimides (PIs) containing xanthene bulky groups and heterocyclic pyridine ring were synthesized by polycondensation reaction by using new symmetric and asymmetric diamines with available dianhydrides. The prepared diamines and PIs were characterized by Fourier transform infrared, elemental analysis, and proton nuclear magnetic resonance spectroscopy and carbon nuclear magnetic resonance spectroscopy. The PIs have desirable solubility in common aprotic solvents like dimethyl sulfoxide, N-methyl-2-pyrrolidone, dimethylacetamide, and pyridine as a less polar solvent. The PIs with inherent viscosities in the range of 0.51–0.72 dL/g were amorphous in nature, showed glass transition temperatures ( Tgs) of about 270–300°C, and 10% weight loss at temperatures 384–443°C. They showed fluorescence emission (quantum yield 7–12%) due to the presence of xanthene and pyridine groups in their structure. The prepared PIs showed tensile strength of 81–91 MPa with elongation at break of 19–23%. The antibacterial properties of the PIs against Gram negative and Gram positive bacteria and funguses were investigated. Also, a membrane of PI prepared by electrospinning method was used for the removal of different concentrations of Cr(VI) from aqueous solutions.

Effect of charge transfer and chain stacking on the optical and thermal properties of polyimides derived from sulfone and amide-containing dianhydride

To study the effect of charge transfer and chain stacking on the optical and thermal properties, a group of polyimides (PIs) were prepared from various diamines and dianhydrides containing sulfone, amide, and/or trifluoromethyl groups. Ultraviolet–visible spectroscopy, thermomechanical analysis, and thermogravimetric analysis were employed to study the properties of PIs. PIs containing sulfone and amide groups exhibited transmittance varying from 2.9% to 44.9% at 400 nm with good thermal stabilities of 5% weight loss in nitrogen at 455–466°C. The coefficient of thermal expansion values were 37.7–49.8 ppm/°C and glass transition temperatures were 261–299°C. The improved optical properties are owing to incorporation of amide group that decreases the electron-acceptability and sulfone group that distorts the chains, inhibiting the dense chain stacking. There is a trade-off relationship between the optical property and thermal property.

Highly Durable and Flexible Transparent Electrode for Flexible Optoelectronic Applications

A highly-durable, highly-flexible transparent electrode (FTE) is developed by applying a composite made of a thin metal grid and a doped conducting polymer onto a colorless polyimide-coated NOA63 substrate. The proposed FTE exhibits a transparency of 90.7% at 550 nm including the substrate and a sheet resistance of 30.3 Ω/sq and can withstand both moderately high-temperature annealing (∼180 °C) and acidic solution (70 °C, pH 0.3) processes without performance degradation. The fabricated FTE yielded good mechanical stability under 10 000 cycles of bending deformations at a bending radius less than 1 mm without degradation of electrical conductivity. The high durability of the proposed FTE allows for the fabrication of flexible energy harvesting devices requiring harsh conditions, such as highly flexible perovskite solar cells (FPSCs) with a steady-state power conversion efficiency (PCE) of 12.7%. Notably, 93% of the original PCE is maintained after 2000 bending cycles at an extremely small bending radius of 1.5 mm. The FPSCs installed on curved surfaces of commercial devices drive them under various environments. The applicability of the proposed FTE is further confirmed via the fabrication of a flexible perovskite light-emitting diode. The proposed FTE demonstrates great potential for applications in the field of flexible optoelectronic devices.