A new phosphorus-containing aromatic diamine, 1,4-bis(4-aminophenoxy)2-(6-oxido-6H-dibenz[c,e] [1,2]oxaphosphorm-6-yl) phenylene (3) was synthesized by the nucleophilic aromatic substitution of 2-(6-oxido-6H-dibenz[c,e][1,2]oxaphosphorin-6-yl)-1,4-dihydroxy phenylene (1) with 4-fluoronitrobenzene, followed by catalytic hydrogenation. Light color, flexible, and creasable polyimides with high molecular weight, high glass transition, high thermal stability, improved organosolubility, and good oxygen plasma resistance were synthesized from the condensation of (3) with various aromatic dianhydrides in N,N-dimethylacetamide, followed by thermal imidization. The number-average molecular weights of polyimides are in the range of 7.0-8.3 X 10(4) g/mol, and the weight-average molecular weights are in the range of 12.5-16.5 X 10(4) g/mol. The T(g)s of these polyimides range from 230 to 304 degrees C by differential scanning calorimetry and from 228 to 305 degrees C by DMA. These polyimides are tough and flexible, with tensile strength at around 100 MPa. The degradation temperatures (T-d 5%) and char yields at 800 degrees C in nitrogen range from 544 to 597 degrees C and 59-65 wt %, respectively. Polyimides 5c and 5e, derived from OPDA and 6FDA, respectively, with the cutoff wavelength of 347 and 342 mu m, respectively, show very light color. These polyimides also exhibit good oxygen plasma resistance. (c) 2007 Wiley Periodicals, Inc.