The construction of photoresponsive polymer particles with supramolecular helicity from achiral monomers by helix-sense-selective polymerization†
The induction of supramolecular chirality from achiral azobenzene-containing polymers has been widely investigated in solution and in the film state. However, the construction of micron-sized optically active azobenzene-containing polymer particles (Azo-OAPPs) with supramolecular chirality in heterogeneous systems has not yet been demonstrated. Here, Azo-OAPPs were successfully prepared from achiral Azo-containing monomers for the first time by helix-sense-selective dispersion polymerization (HSSDP), also known as asymmetric helix-chirogenic polymerization. The trans-Azo units in the polymer side chains constituting the OAPPs adopt supramolecular helical structures with preferential screw sense, and thus the OAPPs have remarkable chiral properties. The Azo-OAPPs in an ethanol dispersion were characterized by CD and UV-vis spectroscopy, and this demonstrated the successful transfer of chirality from the chiral octanol molecules to the polymer particles during HSSDP. In addition, the supramolecular chirality of the Azo-OAPPs could be easily controlled by adjusting the volume of chiral solvent, polymerization time and UV light irradiation time. The morphologies and sizes of the Azo-OAPPs were investigated by TEM and DLS studies. Moreover, a supramolecular helical system in which covalent bonds were introduced into the Azo-OAPPs using a divinylbenzene (DVB) crosslinker was also investigated. Interestingly, the chirality of the crosslinked Azo-OAPPs demonstrated improved UV-resistance compared with the non-crosslinked counterparts. The present study develops a novel strategy for preparing Azo-OAPPs with supramolecular chirality from an achiral source, which is expected to find potential applications in chiroptical materials.