Bis(4-aminophenoxy)phenyl phosphonate (BAPP) was used in various ratios in combination with diethyltoluenediamine (DETDA) to investigate the effect of increasing phosphorous addition upon the thermal and mechanical properties of diglycidyl ether of bisphenol A (DGEBA) and tetra glycidyl dimethylenedianiline (TGDDM) based epoxy networks. Increasing, phosphorous content was shown to decrease the temperature of the initial onset of degradation, while the char yield at 540 degrees C increased in both the nitrogen and air atmosphere. At 700 degrees C. however, the char formation was shown to be dependent upon the atmosphere with an oxidative environment promoting further chain scission. while a non-oxidative environment promoted char formation through crosslinking reactions. Increasing phosphorous content was found to produce only modest decreases in the glass transition temperatures, while no significant deleterious effects upon the mechanical and physical properties such as flexural properties and CTE were observed. (c) 2006 Elsevier Ltd. All rights reserved.