A latent crosslinkable PCL-based polyurethane: Synthesis, shape memory, and enzymatic degradation

Seeking a latent-crosslinkable, mechanically flexible, fully thermoplastic shape memory polymer, we have developed a simple but effective macromolecular design that includes pendent crosslinking sites via the chain extender of a polyurethane architecture bearing semicrystalline poly(epsilon-caprolactone) (PCL) soft segments. This new composition was used to prepare fibrous mats by electrospinning and films by solvent casting, each containing thermal initiators for chemical crosslinking. The one-step synthesis strategy proved successful, and the crosslinking sites within PCL segments resulted in two-way (reversible) shape memory: repeatable elongation (cooling) and contraction (heating) under constant tensile stress. Being fully characterized, the crosslinked fiber mats revealed promising one-way and two-way (reversible) shape memory phenomena, with lower storage moduli though, compared to uncrosslinked films. We observed for both fibrous mats and films that increasing the applied tensile stress led to greater crystallization-induced elongation upon cooling as well as smaller strain hysteresis, particularly for covalently crosslinked samples. Relevant to medical applications, the materials were observed to feature unique, two-stage enzymatic degradation that was sensitive to differences in crystallinity and microstructure among samples.