Extractable Free Polymer Chains Enhance Actuation Performance of Crystallizable Poly(ε-caprolactone) Networks and Enable Self-Healing

Abstract

Abstract:Crosslinking of thermoplastics is a versatile method to create crystallizable polymer networks, which are of high interest for shape-memory actuators. Here, crosslinked poly(ε-caprolactone) thermosets (cPCLs) were prepared from linear starting material, whereby the amount of extractable polymer was varied. Fractions of 5-60 wt % of non-crosslinked polymer chains, which freely interpenetrate the crosslinked network, were achieved leading to differences in the resulting phase of the bulk material. This can be described as "sponge-like" with open or closed compartments depending on the amount of interpenetrating polymer. The crosslinking density and the average network chain length remained in a similar range for all network structures, while the theoretical accessible volume for reptation of the free polymer content is affected. This feature could influence or introduce new functions into the material created by thermomechanical treatment. The effect of interpenetrating PCL in cPCLs on the reversible actuation was analyzed by cyclic, uniaxial tensile tests. Here, high reversible strains of up to ∆ε = 24% showed the enhanced actuation performance of networks with a non-crosslinked PCL content of 30 wt % resulting from the crystal formation in the phase of the non-crosslinked PCL and co-crystallization with network structures. Additional functionalities are reprogrammability and self-healing capabilities for networks with high contents of extractable polymer enabling reusability and providing durable actuator materials.

Controlling Actuation Performance in Physically Cross-Linked Polylactone Blends Using Polylactide Stereocomplexation

“…Advances in multiblock copolymer chemistry have made the introduction of multiple functional chemical entities into one macromolecule possible. The potential shape-memory behavior of poly­(ε-caprolactone) (PCL) has been widely demonstrated, where the polymer’s broad melting transition can be used to provide both skeleton and actuator domains. , Here, the PCL crystallite population can be bisected by the selection of a suitable actuation temperature, with the more thermally stable fraction providing a rigid backbone, while the less thermally stable fraction drives the actuation. The second requirement of our material is the provision of specific anchoring points for the formation of physical netpoints.…”

Multifunctionality in Polymer Networks by Dynamic of Coordination Bonds

“…[1,[12][13][14] The resilience of covalently bonded structure and pliability of non-covalently crosslinked polymers can be combined by designing polymer networks with reversible interactions (e.g., host-guest interaction or dynamic covalent bonds), providing the system with self-healing, contact assembly capabilities or shape-memory capabilities. [12,13,[19][20][21][22] Here we aim at a material exhibiting a range of physical functions in form of chemically and mechanically induced fluorescence emission (FE) intensity changes, shape forming, self-healing capability, and modular fabrication by contact assembly. Our concept for such a multifunctional material is a rhodium-phosphine coordination polymer network (Rh-PCPN) (Figure 1a).…”

Multifunctionality in Polymer Networks by Dynamic of Coordination Bonds

“…[ 1,12–14 ] The resilience of covalently bonded structure and pliability of non‐covalently crosslinked polymers can be combined by designing polymer networks with reversible interactions (e.g., host–guest interaction or dynamic covalent bonds), providing the system with self‐healing, contact assembly capabilities or shape‐memory capabilities. [ 12,13,19–22 ]…”