Calorimetric studies on a series of anhydride-cured epoxy resins, in which the epoxy oligomer is a mixture of diglycidyl ether of bisphenol-A (DGEBA) and diglycidyl ether of poly(propylene glycol) (DGEPPG) in different mole ratios, were carried out. DGEPPG is a flexible epoxy oligomer that was used to tune glass transition temperature for the fully reacted epoxy resin. Conversion versus time curves for the systems with different DGEBA/DGEPPG mole ratios (not including the neat DGEPPG system) were found to overlap with each other in mass-controlled reaction regime, indicating similar reactivities of epoxy groups in both epoxy oligomers. Onset of diffusion-controlled reaction regime for different systems was estimated by fitting the conversion versus time data using a phenomenological kinetic equation, as well as from direct comparison of the conversion versus time curves. For the systems (i.e., 0, 10, and 30% DGEPPG) that vitrify during reaction, the crossover from mass-controlled to diffusion-controlled reaction occurs close to the onset of the vitrification, where T-g is about 25-30 K below the reaction temperature. For the system (i.e., 50% DGEPPG system) that does not vitrify during the reaction, such crossover still occurs when the T-g of the mixture reaches a value about 25 K below the reaction temperature. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2155-2165, 2008