Precision Synthesis of Poly(Ionic Liquid)-Based Block Copolymers by Cobalt-Mediated Radical Polymerization and Preliminary Study of Their Self-Assembling Properties

A poly(ionic liquid)-based block copolymer (PIL BCP), namely, poly(vinyl acetate)-b-poly(N-vinyl-3-butylimidazolium bromide), PVAc-b-PVBuImBr, is synthesized by sequential cobalt-mediated radical polymerization (CMRP). A PVAc precursor is first prepared at 30 degrees C in bulk by CMRP of VAc, using bis(acetylacetonato)cobalt(II), Co(acac)(2), and a radical source (V-70). Growth of PVBuImBr from PVAc-Co(acac)(2) is accomplished by CMRP in DMF/MeOH (2:1, v/v). This PIL BCP self-assembles in the sub-micron size range into aggregated core-shell micelles in THF, whereas polymeric vesicles are observed in water, as evidenced by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Thin-solid sample cut from raw materials analyzed by TEM shows an ordered lamellar organization by temperature-dependent synchrotron small-angle X-ray scattering (SAXS). Anion exchange can be accomplished to achieve the corresponding PIL BCP with bis(trifluorosulfonyl)imide (Tf2N-) anions, which also gives rise to an ordered lamellar phase in bulk samples. A complete suppression of SAXS second-order reflection suggests that this compound has a symmetric volume fraction (f approximate to 0.5). SAXS characterization of both di- and triblock PIL BCP analogues previously reported also shows a lamellar phase of very similar behavior, with only an increase of the period by about 8% at 60 degrees C.