Preparation of Anisotropic Trimeric Poly(Ionic Liquid) Microspheres via Microwave-Assisted Dual-Crosslinked Seed Emulsion Polymerization

A microwave-assisted dual-crosslinked seed emulsion polymerization method is reported to prepare anisotropic trimeric poly(ionic liquid) (PIL) microspheres. First, ethylene glycol dimethacrylate (EGDMA)-crosslinked PIL (CPIL) seed microspheres are prepared. Then, the CPIL microspheres are swollen with ionic liquid (IL) emulsion containing divinylbenzene (DVB) and polymerized to form dual-crosslinked PIL (D-CPIL) microspheres under microwave irradiation. Finally, the D-CPIL microspheres are swollen with IL monomer emulsion to form trimeric morphology and polymerized to obtain trimeric PIL microspheres under microwave irradiation. The formation process of trimeric PIL microspheres is tracked using an optical microscope and their morphology is observed using scanning electron microscopy. Different from the repeat-swelling seed emulsion polymerization that needs dumbbell-like seed microspheres having gradient crosslinking or gradient surface wettability, this method depends on multiple local contraction forces in D-CPIL microspheres containing lowly crosslinked core and highlycrosslinked shell during swelling to form trimeric PIL microspheres. It is found that microwave polymerization is important because it can well retain trimeric morphology compared to conventional heating polymerization in oil or water baths. The morphology of trimeric PIL microspheres can be adjusted by changing the type and amount of crosslinkers, monomer/seed microsphere ratio, initiator dosage, temperature, etc.