Well-Defined Shape-Memory Networks with High Elastic Energy Capacity

Abstract

Controlling network architecture and chain connectivity is critical to understanding elastic energy storage and improving performance of shape-memory polymers. Acrylate-terminated poly(caprolactones) were converted into thermoset networks by three different reactions: conventional free radical polymerization, radical-induced coupling with multifunctional thiols, and base-catalyzed Michael addition with multifunctional thiols. The highly efficient thiol–acrylate coupling reaction ensures that the molecular weight between cross-links is uniform, resulting in tougher, more elastic materials with a high degree of crystallinity and outstanding shape-memory properties. Elastomers can be cold drawn to achieve several hundred percent of strain, and upon heating, nearly complete shape recovery is observed. Shape fixity upon cold drawing is correlated to the degree of strain-induced crystallization which is influenced by the draw rate and stress treatment immediately following cold drawing. Slow unloading of samples drawn to 400% elongation indicates the material is capable of storing greater than 1.5 MJ/m3 of elastic energy.