Helical polymer/Fe3O4 NPs constructing optically active, magnetic core/shell microspheres: preparation by emulsion polymerization and recycling application in enantioselective crystallization

Hybrid materials combining chirality and magneticity are stimulating much interest in diverse research areas. This article reports the preparation of a new type of optically active, magnetic Fe3O4NP@polyacetylene core/ shell microspheres (Fe3O4@PA MPs) consisting of magnetic Fe3O4 NPs as the core and helical polyacetylene as the shell. The Fe3O4@PA MPs integrate two significant concepts, "macromolecular helicity-derived chirality" and "magneticity" in one single microsphere entity. The composite MPs were prepared by emulsion polymerization approach and characterized by TEM, XRD, FT-IR, VSM, TGA, circular dichroism and UV-vis absorption spectroscopy techniques. They simultaneously showed fascinating optical activity and considerable magneticity. The MPs were further used as a chiral additive to induce enantioselective crystallization of racemic threonine. L-Threonine was preferentially induced to form rectangular-shaped crystals with an enantiomeric excess up to 90% (after enantioselective crystallization twice). The microspheres can be recycled conveniently with the assistance of an external magnetic field, demonstrating the MPs' significant potential applications in chiral fields.