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-aminophenyI)-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-T-g values (310-384 degrees C), and moderate thermal properties (T-d 5 wt%, nitrogen: 461-477 degrees C; air, 456-474 degrees 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. (C) 2012 Elsevier Ltd. All rights reserved.