No abstract

Shape-memory polymers (SMPs) are a class of stimuli-responsive materials that have attracted tremendous attention in various applications, especially in the medical field. While most SMPs are thermally actuated, relating to a change of thermal transition (e.g., melting temperature), SMPs that can be actuated upon exposure to light are emerging. Recently, there has been new interest into multiple stimuli-responsive SMPs in order to cover the range of applications for these smart materials. In this work, poly­(ester-urethane)­s (PURs) made of heating-responsive poly­(ε-caprolactone) (PCL) segments of various degrees of crystallinity and photoresponsive N,N-bis­(2-hydroxyethyl) cinnamide (BHECA) monomer were successfully prepared using reactive extrusion technology to design dual-stimuli-responsive SMPs (DSRSMP). In order to tune the SMP properties (temperature or light), the crystallinity of the PCL segment was finely adjusted by the copolymerization of ε-caprolactone with para-dioxanone in bulk at 160 °C using tin­(II) octoate. The resulting polyester segments were then coupled with BHECA using n-octyl diisocyanate at 130 °C. The SMP properties of resulting PURs were correlated with DSC and DMTA measurements. Further addition of di- and tetracinnamate PCL segments into these SMPs was also studied in order to enhance the photoactuated SMP properties.

Cellulose nanocrystal (CNC)-reinforced poly(lactic acid) (PLA) nanocomposites were prepared by twin-screw extrusion followed by injection-molding using a masterbatch approach. Noncovalent modification of CNCs was performed with two different poly( l -lactide) (PLLA)-based surfactants to improve the filler/matrix compatibility. They both have a PLLA block that is expected to improve the compatibility with the PLA matrix and differ by the polar head. It consists of either a poly(ethylene glycol) (PEG) block (PEG- b -PLLA) or an imidazolium group (Im-PLLA), that is able to interact with the surface of the CNCs. The morphological, structural, thermal, rheological, and mechanical properties of the nanocomposites were investigated. The different modes of interaction of the polar head of the surfactant lead to different properties. However, the global decrease in the molecular weight of PLA, induced by the short PLLA blocks from the surfactants and the possible degradation during melt processing, results in a plasticization effect and impacts the crystallization of the matrix.

A novel poly(vinyl alcohol) hybrid hydrogel based on metal–ligand interactions and hydrogen bonding was fabricated, possessing highly-stretchable and self-healing properties.

In this work, the synthesis and characterization of triple-shape and twoway shape-memory effect of novel poly(ester-urethane)s (PURs) made of a poly(ε-caprolactone) (PCL) and poly(ω-pentadecalactone) (PPDL) segments and N,N-bis(2-hydroxyethyl)cinnamide (BHECA) monomer by reactive extrusion (REx) is reported. PCL and PPDL are chosen as semicrystalline segments because of their inherent ability to undergo tensile elongation upon cooling, as prerequisite for the two-way shape-memory effect. BHECA is used as the "cross-linker" due to its ability to participate in reversible [2+2] cycloaddition reaction and to mainly maintain the crystalline features of semicrystalline precursors within these PURs. This novel simple strategy is considered extremely versatile and adaptive because of the possibility to vary crystallizable segments and coupling agents, thus paving the way to the design of a multitude of triple (or more) shape-memory polymers with two-way behavior. Feasibility with PURs containing PCL, PPDL, and BHECA is demonstrated by adjusting the shape-memory behavior (one and two-way effects), and studying the structure-property relationships of the resulting PURs by DSC, DMTA, and 2D wide angle X-ray scattering analyses while varying the weight composition of the two semicrystalline segments.