Shape memory epoxy: Composition, structure, properties and shape memory performances

Due to the intrinsic properties of polymers, medical applications have been the primary targets for the development of shape memory polymers (SMPs) exhibiting softness at body temperature, biocompatibility, high deformability, good shape recovery (Rr) and good shape fixity (Rf). However, there is an increasing need for developing smart materials that would meet the drastically different requirements imposed by applications where, instead, high strength well above room temperature, durability, stability, and high thermo-mechanical endurance are necessary. Here, we present results obtained on a series of shape memory (SM) epoxies that appear promising base materials for such applications. The influence of molecular and structural design on their physical and SM properties were studied. The impact of various SM programming conditions (i.e., deformation load, recovery heating rate, number of cycles, and isothermal holding times in the hot and cold deformed shapes) was also investigated. The instantaneous SM behavior was found similar for all the networks with Rf and Rr values nearing 100% above 6 to 7% strain. The SM performances strongly depended on the strain-dependent thermal expansion/contraction of the materials during thermo-mechanical cycling. Networks with lower crosslink density, higher chain flexibility and/or mobility showed reduced SM performances, further diminished by more stringent thermo-mechanical cycling conditions.