Reactive Epoxy‐CTBN Rubber Blends: Reflection of Changed Curing Mechanism in Cure Shrinkage and Phase Separation Behaviour

During curing of epoxy resins shrinkage occurs, which is caused by the formation of polymeric and crosslinked structures. We analysed this shrinkage for a system consisting of diglycidyl ether of bisphenol‐A (DGEBA), diamino diphenyl sulfone (DDS) as hardener, and a reactive or a nonreactive rubber, with or without catalyst. The shrinkage and the phase separation behaviour strongly depend on the composition. The addition of reactive rubber and of the catalyst influences the curing mechanism and reduces the crosslinking density, which is reflected by lowered glass transition temperatures and reduced shrinkage. The reactive rubber is partially incorporated in the crosslinked epoxy phase and vice versa. In this way it is possible not only to modify the morphology‐related properties but also to control the degree of the unwanted shrinkage.