Electron-withdrawing/donating effects of substituents on the preparation of phosphinated 4,4′-diaminodiphenylmethane for soluble, anti-oxidative, and high-Tg polyimides

In this work, we reveal a strategy to prepare a phosphinated 4,4'-diaminodiphenylmethane, 1,1-bis(4-aminophenyl)-1-(6-oxido-6H-dibenz < c, e <,2 > oxaphosphorin-6-yl)methane (3). During the preparation, it was found that the effect of the electron withdrawing/donating characteristic of substituents is crucial to the synthesis. A reaction mechanism including nucleophilic addition, reduction, and electrophilic substitution is proposed. Based on diamine (3), a series of polyimides (4a-4d) were prepared. Polyimides 4 are readily soluble in some organic solvents, and can be solution cast into flexible and foldable films. They show high T-g (310-390 degrees C), high moduli (3.34-4.63 GPa), moderate coefficient of thermal expansion (46-58 ppm degrees C-1), good anti-oxidative stability (T-d 5%: 480-537 degrees C (N-2); 456-504 degrees C (air)), and good flame retardancy (VTM V-0 rating).