Network architecture and shape memory behavior of cold-worked epoxies

The shape memory behavior of polymers derives from a combination of their molecular architecture and thermomechanical history. In this study, several epoxies with various network architectures were prepared using mixtures of a diepoxide resin, a monoepoxide resin, and an aliphatic diamine hardener. A nonconventional cold-working programming, carried out below T-g, was employed to set the materials in a temporary configuration and allowed to fix considerable amounts of the applied strain. The shape memory behavior was evaluated through transient heating and isothermal recovery tests. All the resins are capable of complete recovery, which occurs as a sequence of an early process taking place below T-g and a major one close to T-g, which acted as the switching temperature (T-switch). The proximity of the deformation temperature to T-g influenced the amount of strain recovered within each process. It was shown that resins with different structures, although presenting similar T-switch, may have different recovery kinetics, and the roles of the network density and the chain stiffness on the recovery rate were evidenced.