Facile and Efficient Preparation of Phosphinate-Functionalized Aromatic Diamines and Their High-Tg Polyimides

Two novel phosphorus-functionalized aromatic diamines, 1,1-bis(4-aminophenyl)-1-(6-oxido-6H-dibenz < c,e > < 1,2 > oxaphosphorin-6-yl)ethane (1) and bis(4-aminophenyl)-(6-oxido-6H-dibenz < c,e > < 1,2 > oxaphosphorin-6-yl)phenylmethane (2), were prepared from 9,10-dihydro-oxa-10-phosphaphenanthrene-10-oxide, 4-aminoacetophenone, or 4-aminobenzophenone in excess aniline using p-toluenesulfonic acid monohydrate as catalyst by an efficient, one-pot procedure. The effect of electron withdrawing/donating groups on the stabilization of the resulting carbocation seems critical for the success of the process and was discussed in detail. Based on diamines (1-2), a series of new polyimides, (5a-5d) and (6a-6d), were prepared, respectively. Polyimides (5a-5d) are flexible and creasable. In contrast, polyimides (6a-6d) are brittle because of the structure rigidity, according to the analysis based on the NMR temperature-dependent spectra of (2). Polyimides 5 displaying high T-g (318-392 degrees C), high moduli (3.39-4.49 GPa), low coefficient of thermal expansion (42-50 ppm/degrees C), and moderate thermal stability (T-d 5 wt % at 426-439 degrees C), are excellent high-T-g and flame-retardant materials. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2486-2499, 2009