Preparation of Janus Particles Composed of Hydrophobic and Hydrophilic Polymers

Composite particles were prepared by the seeded polymerization of an ionic liquid monomer ([2-(methacryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)amide) ([MTMA][TFSAD in the presence of poly(methyl methacrylate) (PMMA) particles. The obtained particles have a core-shell morphology: PMMA core and P([MTMA][TFSA]) shell. To change the composite particle morphology from core-shell to Janus, we used the solvent-absorbing/releasing method with methyl isobutyl ketone, which is a suitable solvent for PMMA and P([MTMA]-[TFSA]) with nonionic surfactants (polyoxyethylene nonylphenyl ether, Emulgen 950) and Li[TFSA]. Based on the ultrathin cross-section observations, we found the core-shell PMMA/P([MTMA][TFSA]) composite particle morphology changed to a Janus structure. Moreover, anion exchange occurred in the obtained Janus particles. When using LiBr, we obtained PMMA hemisphere particles because of the changes in the PIL hemisphere polarity via anion exchange and dissolution in water. On the contrary, the use of poly(sodium styrenesulfonate) maintained the Janus structure because of ionic cross-linking and the changes in the PIL hemisphere to hydrophilic properties, which became swollen with medium water.