Properties and toughening of heat‐resistant thermosets based on unsaturated ester resins

Abstract We describe our investigations of the curing chemistry and properties of heat‐resistant thermosets comprised of unsaturated ester resins. We suggest a mechanism for the rearrangement of the cured matrix and volatile evolution during the curing process. We employed dielectric spectroscopy (DES) as a tool for monitoring the extent of cure, determining glass‐transition temperatures, and evaluating electrical properties of the resins. We compare and contrast results obtained by DES to results obtained by dynamic mechanical analysis (DMA). Fracture testing showed that improvements were made in the toughness of these materials by blending the uncured resin with impact modifiers such as hydrocarbon or silicone reactive rubber adducts or poly(arylene ether sulfone)‐based thermoplastic oligomers. We determined the effects of the thermoplastic toughening additive's molecular weight, concentration, and endgroup functionality on the phase separation, thermal stability, and fracture toughness of the blend. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 821–843, 2002