Diglycidyl ether of bisphenol A (DGEBA) was cured with gamma-butyrolactone (gamma-BL) with ytterbium triflate as a catalyst. The curing was studied with differential scanning calorimetry, Fourier transform infrared (FTIR), and thermomechanical analysis. FTIR studies confirmed that four elemental reactions took place during the curing process: the formation of a spiroorthoester (SOE) by the reaction of DGEBA with gamma-BL, the homopolymerization of SOE, the homopolymerization of DGEBA, and the copolymerization of SOE and DGEBA. Moderate proportions of gamma-BL produced materials with higher glass-transition temperatures, and the curing occurred with lower shrinkage after gelation because of the polymerization of SOE, with near-zero shrinkage during the final stages of the curing. (C) 2003 Wiley Periodicals, Inc.