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

Abstract

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 Tg (310–390°C), high moduli (3.34–4.63 GPa), moderate coefficient of thermal expansion (46–58 ppm °C−1), good anti-oxidative stability ( Td 5%: 480–537°C (N2); 456–504°C (air)), and good flame retardancy (VTM V-0 rating).