Organo-soluble phosphinated polyimides from asymmetric diamines

Two new asymmetric diamines (1–2) were prepared via a facile, one-pot procedure. Based on diamine (1–2), a series of asymmetric polyimides (3–4) were prepared in NMP/xylene by high-temperature solution polymerization. The resulting polyimides are readily soluble in some organic solvents, and can be solution casted into flexible and creasable films. An intramolecular charge complex mechanism was proposed to the structure–optical transparency relationship. Polyimides 3–4 display high-Tg (319–401 °C), high moduli (2.40–7.20 GPa), moderate coefficient of thermal expansion (38–53 ppm/°C), and excellent flame retardancy. These results show that the introduction of the asymmetric structure is an effective way to improve organo-solubility while maintaining thermal properties. Because of these properties, polyimides 3–4 can be considered as excellent high-Tg and flame-retardant materials for microelectronic applications.