Spiropyran-based supramolecular elastomers with tuneable mechanical properties and switchable dielectric permittivity†

Silicone elastomers are widely used in various applications, each demanding different properties and functionalities. To be used in such a broad spectrum, silicones with easily tunable or switchable properties are needed. We showed this is achievable with novel metallo-supramolecular polysiloxanes. Poly(dimethylsiloxane-co-3-aminopropylmethylsiloxane) was reacted with an epoxy-modified spiropyran (SP) in the presence of ZnCl₂ as a catalyst. We have found that the ZnCl₂ allows the formation of metallo-supramolecular polymers with tuneable mechanical propertiers. The influence of the amount of ZnCl₂ used on the thermal and mechanical properties of the synthesized materials was investigated by DSC, tensile test, and DMA. The ability of SP to act not only as a physical cross-linker, but also as a molecular switch was investigated by UV-Vis spectroscopy and dielectric permittivity measurements. It was found that depending on the amount of ZnCl₂ used, the dielectric permittivity can either increase or decrease after exposure to UV or visible light, respectively. Additionally, the developed materials can be reprocessed similarly to thermoplastic elastomers. Furthermore, their solubility can be manipulated from insoluble in practically any solvent to highly soluble by simply adding ZnCl₂.