Abstract :
[en] Temperature-responsive shape memory polymers (SMPs) have gained significant
attention for their use in various fields, including biomedical, aerospace, textiles, sensors, and actuators due to their low cost, easy processing, low density and large recoverable strains. In addition, improvement of their stiffness can be achieved by combining a shape memory polymer with various fillers leading to shape memory composites. Advantageously, the judicious selection of conductive or magnetic fillers also allows triggering the shape memory effect by internal resistive Joule heating or by the application of a magnetic field. Such remotely actuated SMPs are especially of interest for applications where the actuation by heating via increasing the temperature of the surrounding environment is not feasible, e.g., in implanted biomedical devices, or self-deployable aerospace structures. However, challenges remain, such as controlling fillers dispersion and interfacial strength, so as developing recyclable polymer materials and reprocessable networks in order to be part of an ecoresponsible and sustainable development fitting applications relevant for the future generation. The objective of this thesis is to design high-performance shape-memory composites
that can be reprocessed and/or recycled and internally actuated by Joule or magnetothermal effects. The strategy involves functionalizing the chain-ends of star-shaped poly-(ε- caprolactone) (PCL) by furan and maleimide moieties in order to reach a covalent adaptable network by the thermoreversible Diels-Alder addition. By adding fillers, i.e., multi-walled carbon nanotubes (MWCNTs) or Fe3O4 nanoparticles (NP) during blending, conductive or magnetic composite networks are obtained exhibiting a shape recovery actuated by Joule effect or magnetothermal effect. Semi-crystalline PCL was selected for its biocompatibility and remarkable mechanical and shape-memory properties. The impact of the diene nature (furan or anthracene) and of the type of filler on the shape memory performances of composite stripes has been deeply investigated. In addition, a solvent-free batch foaming process utilizing supercritical carbon dioxide
(scCO2) has been developed to produce recyclable shape-memory foams starting from the furan/maleimide PCL stars. Thanks to the thermal control of the PCL network density throughout the foaming process, foams with an unprecedented low density and exhibiting shape memory properties with high fixity and recovery ratios have been achieved. Additionally, these PCL shape memory foams are fully reprocessable. Application of these foams as self-deploying implant for vessel occlusion has been demonstrated in this work.
