Effect of simultaneously introduced bulky pendent group and amide unit on optical transparency and dimensional stability of polyimide film

Design and synthesis of fluorinated polyimides with low thermal expansion and enhanced dielectric properties

Modern microelectronics industries urgently require dielectric materials with low thermal expansion coefficients, low dielectric constants, and minimal dielectric loss. However, the design principles of materials with low dielectric constants and low thermal expansion are contradictory. In this study, a new diamine monomer containing a dibenzocyclooctadiene unit (DBCOD-NH2) was designed and synthesized, which was subsequently polymerized with high fluorine content 4,4'-hexafluoroisopr-opylidene diphthalic anhydride and 4,4'-diamino-2,2'-bis(trifleoromethyl)biphenyl to obtain a series of fluorinated polyimides (PIs). Due to the unique conformational transition of the eight-membered carbon ring, the resulting PI can reach a low averaging thermal expansion coefficient (CTE) of only 12.27 ppm/K over 5-150 ℃ with a size change rate of only 0.16 %. Surprisingly, the synergistic effect of DBCOD-NH2 with the other two monomers enhances the dielectric performance of the PIs. At an electric field frequency of 10 MHz, the dielectric constant (Dk) and the dielectric loss (Df) can be reduced to as low as 2.61 and 0.00194, respectively. The strategy used herein largely tackles the challenge of balancing low Dk with low CTE. Furthermore, these PI films also exhibit good thermal stability (with 5 wt% weight loss temperatures ranging from 453 to 537 ℃ in N2, and glass transition temperatures of 305-337 ℃) and robust mechanical properties (with a tensile modulus of 1.88-2.29 GPa and an elongation at break of 6.36-8.11 %). The combination of low thermal expansion and excellent dielectric properties renders these PIs highly promising for applications in the microelectronics and telecommunications industries.

High comprehensive properties of colorless transparent polyimide films derived from fluorine-containing and ether-containing dianhydride

Fluorinated colorless transparent polyimide (CPI) films are crucial for flexible displays and wearable devices, but their development is limited by high costs and relatively low mechanical properties. In this study, a series of colorless transparent polyimide films was synthesized by incorporating the cost-effective ether-containing diamine, 4,4'-isopropylidenediphenoxy bis(phthalic anhydride) (BPADA), into commercially available 4,4'-(hexafluoroisopropyl)diphthalic anhydride (6FDA) and 2,2'-bis(trifluoromethyl)benzidine (TFMB). The comprehensive properties of the films were systematically investigated using a combination of experimental and numerical methods, including molecular dynamics (MD) simulations and density functional theory (DFT). This study focuses on exploring the influence of varying dianhydride ratios on the aforementioned properties. The incorporation of BPADA in the dianhydride significantly enhances the mechanical properties and flexibility of the film. When the ratio of ether anhydride to fluorine anhydride is 4 : 6 (CPI-4), the tensile strength is 135.3 MPa, and the elongation at break is 8.3%, which is 109.6% and 118.45% higher than that of the original film without ether anhydride. This research provides valuable insights for the future application of new polyimide materials in flexible display devices.

Thermally Stable and Transparent Polyimide Derived from Side-Group-Regulated Spirobifluorene Unit for Substrate Application

Advancements in flexible electronic technology, especially the progress in foldable displays and under-display cameras (UDC), have created an urgent demand for high-performance colorless polyimide (CPI). However, current CPIs lack sufficient heat resistance for substrate applications. In this work, four kinds of rigid spirobifluorene diamines are designed, and the corresponding polyimides are prepared by their condensation with 5,5'-(perfluoropropane-2,2-diyl) bis(isobenzofuran-1,3-dione) (6FDA) or 9,9-bis(3,4-dicarboxyphenyl) fluorene dianhydride (BPAF). The rigid and conjugated spirobifluorene units endow the polyimides with higher glass transition temperature (Tg) ranging from 356 to 468 °C. Their optical properties are regulated by small side groups and spirobifluorene structure with a periodically twisted molecular conformation. Consequently, a series of CPIs with an average transmittance ranging from 75% to 88% and a yellowness index (YI) as low as 2.48 are obtained. Among these, 27SPFTFA-BPAF presents excellent comprehensive performance, with a Tg of 422 °C, a 5 wt.% loss temperature (Td5) of 562 °C, a YI of 3.53, and a tensile strength (δmax) of 140 MPa, respectively. The mechanism underlying the structure-property relationship is investigated by experimental comparison and theoretical calculation, and the proposed method provides a pathway for designing highly rigid conjugated CPIs with excellent thermal stability and transparency for photoelectric engineering.

Highly Stable Polyimide Composite Nanofiber Membranes with Spectrally Selective for Passive Daytime Radiative Cooling

Passive radiative cooling technology without electric consumption is an emerging sustainability technology that plays a key role in advancing sustainable development. However, most radiative cooling materials are vulnerable to outdoor contamination and thermal/UV exposure, which leads to decreased performance. Herein, we report a hierarchically structured polyimide/zinc oxide (PINF/ZnO) composite membrane that integrates sunlight reflectance of 91.4% in the main thermal effect of the solar spectrum (0.78-1.1 μm), the mid-infrared emissivity of 90.0% (8-13 μm), UV shielding performance, thermal resistance, and ideal hydrophobicity. The comprehensive performance enables the composite membrane to yield a temperature drop of ∼9.3 °C, compared to the air temperature, under the peak solar irradiance of ∼800 W m-2. In addition, the temperature drop of as-obtained composite membranes after heating at 200 °C for 6 h in a nitrogen/air atmosphere can be well maintained at ∼9.0 °C, demonstrating their ideal radiative cooling effect in a high-temperature environment. Additionally, the PINF/ZnO composite membrane shows excellent chemical durability after exposure to the outdoor environment. This work provides a new strategy to integrate chemical durability and thermal resistance with radiative cooling, presenting great potential for passive radiative cooling materials toward practical applications in harsh environments.

Fluorinated Polyimide/Allomelanin Nanocomposites for UV-Shielding Applications

A series of highly fluorinated polyimide/allomelanin nanoparticles (FPI/AMNPs) films were prepared with FPI as the matrix and AMNPs as the filler. Due to the formation of hydrogen bonds, significantly reinforced mechanical and UV-shielding properties are acquired. Stress-strain curves demonstrated a maximum tensile strength of 150.59 MPa and a fracture elongation of 1.40% (0.7 wt.% AMNPs), respectively, 1.78 and 1.56× that of pure FPI. The measurements of the UV-vis spectrum, photodegradation of curcumin and repeated running tests confirmed the splendid UV-shielding capabilities of FPI/AMNPs films. The enhancement mechanisms, such as synergistic UV absorption of the charge transfer complexes in FPI and AMNPs and photothermal conversion, were the reasons for its exceptional UV shielding. The excellent comprehensive properties above enable FPI/AMNPs nanocomposites to be potential candidates in the field of UV shielding.