A thorough study of the polymerization behavior of 4-fluoro-4 '-hydroxytriphenyl-phosphine oxide, 2, under nucleophilic aromatic substitution reactions has been carried out. The synthesis of 2 was achieved in excellent yields by the reaction of bis(4-fluorophenyl)phenylphosphine oxide, 1, with one equivalent of potassium hydroxide in DMSO/water. The structure and purity of 2 were confirmed via H-1, C-13, and P-31 NMR spectroscopy along with elemental analysis. Polymerization reactions of 2 in NMP or DMSO at 180 degrees C provided the corresponding linear poly(arylene ether phosphine oxide)s, PAEPOs, with number average molecular weights, M-n, ranging from 11,700 to 36,500 Da. All of the polymer samples were completely soluble in chloroform, tetrahydrofuran, DMSO, NMP, and DMAc. The polymerization reactions were accompanied by a competing intramolecular process that resulted in the formation of cyclic oligomeric species that were removed via a final precipitation from methanol. Analysis using 31P NMR spectroscopy and size exclusion chromatography (SEC) confirmed that the majority of the lower molecular weight cyclic species were removed via this process. The polymer samples formed tough films when chloroform solutions were slowly evaporated on a glass slide. The PAEPO samples prepared in this study exhibited excellent thermal stability with T-d (5%) values between 503 and 542 in air while the glass transition temperatures ranged from 223 to 237 degrees C. (c) 2006 Wiley Periodicals, Inc.