Design and synthesis of unsymmetric phosphinated diamines for high-Tg, transparent polyimides

Two phosphinated diamines, 1-(4-aminophenyl)-1-(3-t-butyl-4-aminophenyl) -1- (6-oxido-6H -dibenz <c,e> <1,2> oxaphosphorin-6-yl)ethane (1) and 1-(4-aminophenyl) -1-(3-methxoy-4-aminophenyl)-1-(6-oxido-6H -dibenz <c,e> <1,2> oxaphosphorin-6-yl)ethane (2), were prepared via a facile, one-pot reaction of DOPO, 4-aminoacetophenone and 2-tertbutylaniline or 2-anisidine in the presence of p-toluenesulfonic acid. Based on diamines (1–2), a series of unsymmetric polyimides (3–4) were prepared in NMP/xylene by high-temperature solution polymerization. Transparency polyimides 3–4 with flexibility, organo-solubility, high-Tg values (310–384 °C), and moderate thermal properties (Td 5 wt%, nitrogen: 461–477 °C; air, 456–474 °C) can be achieved. We found that the transparency of polyimide films is related with the orientation of the biphenylene phosphinate pendant, and the orientation is influenced by the bulkiness of the ortho-substituted substituent.