Synthesis and characterization of shape memory poly (e-caprolactone) networks with programmable and reconfigurable shape-morphing behaviors

Poly(e-caprolactone) (PCL)-based semi-crystalline polymers are shape memory polymers that have been extensively used in various applications ranging from biological, soft robots and flexible electronic devices. Despite the large number of studies aiming at constructing the well-defined crosslinked polymer networks, detailed investigations in terms of structural factors that influence the thermal-mechanical and shape memory properties are still poorly understand and investigated. In this work, PCL crosslinked networks with different molecular weight of diacrylate PCL macromonoter (M-n) are prepared via base-catalyzed thiol-ene Michael addition. The results indicate that the melting temperature, the crystallization temperature and the crystallinity of the polymer networks exhibit an upward trend with increment of M-n. Besides that, the tensile strength and shape memory properties are also correlated with M-n. Controlled-strain DMA characterization on shape memory properties show that the cPCL-10000 network exhibits the most remarkable shape fixity and shape recovery ratio, indicative of lowering cross-linking density and chains mobility. In particular, permanent shape reconfiguration can also be achieved by triggering transesterification within the same polymer network, and a possible molecular mechanism responsible for the elasticity-based shape memory effect and plasticity-based permanent shape reconfigurability is proposed and combined to present the 2D-to-3D shape-morphing behaviors.