Molecular network development and evolution of nanoscale morphology in an epoxy‐amine thermoset polymer

Epoxy‐amine thermoset polymers exhibit a complicated, highly crosslinked network structure. The connectivity of this network drives material parameters such as mechanical properties and solvent permeation. Understanding the molecular network architecture is also an important aspect of the developing realistic network topologies for use in molecular dynamic simulations. Here, the evolution of network connectivity in a typical crosslinked epoxy‐amine network (Epon 828/3‐aminophenyl sulfone) is monitored as a function of cure time. Special attention is paid to nanoscale variation in the crosslink density of the network. Submicron atomic force microscope images of sample fracture surfaces revealed three distinct types of crack tip propagation. Near‐infrared spectroscopy, rheological and thermal characterization were used to correlate each type of fracture propagation behavior to a different stage of network development. Monitoring changes in the nanoscale fracture behavior reveals information regarding changes in the network architecture during cure and provides insight into the final structure of the epoxy‐amine network.