ma501164u_si_001.pdf (8.02 MB)
Download file

Mesomorphism and Shape-Memory Behavior of Main-Chain Liquid-Crystalline Co-Elastomers: Modulation by the Chemical Composition

Download (8.02 MB)
journal contribution
posted on 12.08.2014, 00:00 by Alfonso Ramon García-Márquez, Benoît Heinrich, Nicolas Beyer, Daniel Guillon, Bertrand Donnio
The mesomorphic behavior, shape shifting, and shape-memory types of two homologous series of main-chain liquid-crystalline co-elastomers (MC-LCEs) with composition-tunable transition temperatures and mesophases structures are reported. The weakly cross-linked macromolecules were prepared in a one-step procedure by the versatile platinum-catalyzed hydrosilylation reaction between siloxane oligomers (linear spacers and netlike point molecules) and liquid-crystalline binary mixtures, composed of defined proportions of divinylic monomeric mesogens. First, the two sets of alternated, linear copolymers with disiloxane or trisiloxane chain extender, respectively, were investigated. They either exhibit both smectic C (SmC) and nematic (N) phases or a single SmC phase, the nature of which being dictated by the length of the inserted siloxane moieties, and the temperatures ranges regulated by the composition of the mesogenic mixture (mesogens ratio). As anticipated, the thermal behavior of the corresponding co-elastomers is not greatly affected by the weak reticulation (less than 5% w/w), whose transition temperatures (from the ambient to ca. 100 °C) and mesophases types (SmC and N) are quasi-replicated from the polymers and still majority governed by the intermingling of the constitutive components (mesogens ratios, siloxane, and comonomers). Moreover, these MC-LCEs exhibit two types of shape-memory behaviors, which are imposed selectively by the nature of the siloxane extender and which are understood in relation to the mesophases’ structures. The combination of small-angle X-ray scattering and thermoelastic experiments gives some fundamental insights into the relationships between molecular structures and macroscopic elastic properties in MC-LCEs in general, which should be beneficial for future designs of soft materials with desired shape-memory properties.