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

Abstract

A novel semi-aliphatic diamine with bulky cyclohexyl and ortho-substituted tertiary butyl groups (4,4'-(cyclohexylmethylene)bis(2-(tert-butyl)aniline), CHMBTBA) is synthesized via Mannich and rearrangement reactions of cyclohexanecarboxaldehyde and 2-tert-butylaniline. Afterward, several semi-aliphatic polyimides are prepared by the high-temperature one-pot polymerization of CHMBTBA with various aromatic dianhydrides respectively. The resulting PIs exhibit outstanding solubility in common organic solvents (i.e., trichloromethane, etc.) and are easily processed into light color or colorless transparent films (thickness: 25 ± 1 µm) by the blade coating of polymer solution. The transmittance of all resulting films is above 86% in the visible light region (400–760 nm). Their glass transition temperatures exceed 310 °C and reach even to 374 °C (by differential scanning calorimetry). They also display low water absorption (0.29–0.87%) and good mechanical properties (tensile strength: 50.9–87.7 MPa, Young's modulus: 2.0-2.5 GPa, elongation at break: 3.8–7.6%). Thus, they are promising potential candidates for flexible display substrates.