Recent Trends on Transparent Colorless Polyimides with Balanced Thermal and Optical Properties: Design and Synthesis

Abstract

Recently, colorless and transparent plastic substrates with high glass transition temperature and suitable thermo‐mechanical properties are in high demand in optoelectronic device industries, due to their various optical applications. Colorless polyimides (CPIs) exhibit both high thermo‐mechanical stability as well as high transparency that are suitable for optoelectronic applications. The most recent (2010–2018) developments on CPIs, in terms of design and synthesis of new monomers and their effects on the thermo‐optical properties of the obtained CPIs, are reviewed in this article.

Superhydrophobic and Low‐k Polyimide Film with Porous Interior Structure and Hierarchical Surface Morphology

“…Polyimide (PI) is a well‐known engineering plastic that possesses excellent thermal stability, high chemical resistance, good mechanical properties as well as a low dielectric constant (low‐ k ) . Therefore, they have become an excellent candidate for microelectronics applications, such as interlayer dielectrics and flexible circuitry carriers .…”

“…As shown in the FTIR spectra in Figure 1, the PAA materials were confirmed by the characteristic peaks at 1720, 1660, and Polyimide (PI) is a well-known engineering plastic that possesses excellent thermal stability, high chemical resistance, good mechanical properties as well as a low dielectric constant (low-k). [1][2][3][4][5] Therefore, they have become an excellent candidate for microelectronics applications, such as interlayer dielectrics and flexible circuitry carriers. [6] On the other hand, conventional PIs with dielectric constants of ≈3.2-3.9 are inadequate for the requirements of ultralow-k (k < 2.0) materials in microelectronic and insulating applications.…”

“…The color of the casted "wet films" changed slowly from transparent to turbid light yellow. Finally, the hierarchical surface and porous structure formed after all the solvent and non-solvent had evaporated out completely (5), resulting in the final PI film. In the entire process, humid air exposure leads to the slow transfer of water from the vapor phase into the "wet film" and induces phase separation.…”

Optically Transparent and Thermal‐Stable Polyimide Films Derived from a Semi‐Aliphatic Diamine: Synthesis and Properties

“…However, the drawbacks of deep color and poor processability of conventional aromatic PIs seriously limited their applications in modern optoelectronic field, especially in flexible electronic and display technology. Generally, the present of intramolecular and intermolecular charge transfer complexes (CTC) are considered to cause the deep color of PIs, and the rigid backbones lead to the insolubility and infusibility of PIs 4. In addition, the processing temperature on flexible polymer substrates was usually over 300 °C in the fabrication of thin‐film‐transistors used in flexible active matrix organic light emitting display devices 5.…”

“…Generally, the present of intramolecular and intermolecular charge transfer complexes (CTC) are considered to cause the deep color of PIs, and the rigid backbones lead to the insolubility and infusibility of PIs. [4] In addition, the processing temperature on flexible polymer substrates was usually over 300 °C in the fabrication of thin-film-transistors used in flexible active matrix organic light emitting display devices. [5] A lot of efforts have been launched to develop highperformance colorless poly imides with superior heat-resistance (glass transition temperature (T g ) > 300 °C), suitable coefficient of thermal expansion (CTE < 50 ppm °C −1 ) and good processability.…”