Two flame-retardant epoxy curing agents, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-yl-tris(4-hydroxyphenyl)met hane (1) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-yl-(4-aminophenyl)-bis(4-hydroxyphenyl)methane (2), were prepared by a facile, economic, one-pot procedure. The structures of the curing agents were confirmed by IR, high-resolution mass, 1-D, and 2-D NMR spectra. A reaction mechanism was proposed for the preparation, and the effect of electron withdrawing/donating effects on the stabilization of the carbocation was discussed. (1-2) served as curing agents for diglycidyl ether of bisphenol A (DGEBA), dicyclopentadiene epoxy (HP-7200), and cresol novolac epoxy (CNE). Properties such as glass transition temperature, coefficient of thermal expansion, thermal decomposition temperature, and flame retardancy of the resulting epoxy thermosets were evaluated. The resulting epoxy thermosets show high T-g low thermal expansion, moderate thermostability, and excellent flame retardancy. The bulky biphenylene phosphinate pendant makes polymer chains difficult to rotate, explaining the high T, and low thermal expansion characteristic. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7898-7912, 2008