Free Radical Polymerization in Room Temperature Ionic Liquids

The methodology of conventional free radical polymerization was employed throughout our research to study polymerization behavior in three RTILs (room temperature ionic liquids): 1-butyl-3-methylimidazolium hexafluoroposphate ([BMIM]PF₆), (tetrabutylammonium dioctyl) sulfosuccinate (Terrasail) and (1-isopropyl-3-methylimidazolium) methanesulfonate (Marisail).

Sequential addition free radical polymerization in RTILs emerged as a new route to obtain polystyrene - poly(methyl methacrylate) block copolymers. We applied the same strategy to the block copolymerization of other two systems: the monomer pair of styrene-vinyl acetate in Terrasail, and the monomer pair of styrene-acrylic acid in [BMIM]PF₆. While styrene-vinyl acetate block copolymers with a composition of 50% (VAc mol%) were obtained, the polymerization of styrene-acrylic acid only yielded polymers with mainly styrene units. Therefore, sequential addition free radical polymerization in RTILs is not effective on all polymerization systems (eg. Styrene-acrylic acid/[BMIM]PF₆).

Our study on free radical homopolymerization of 2-hydroxyethyl methacrylate (HEMA) in RTILs showed that the positive effects of employing RTILs as reaction medium could be extended from polymerization of alkyl methacrylates to that of functional methacrylates. All of the reactions exhibited very high polymerization rates, and the resulting products possessed higher molecular weight than those polymers obtained using methanol as solvent.

Copolymerizations of the monomer pairs styrene/vinyl acetate, styrene/acrylic acid, styrene/HEMA (2-hydroxyethyl methacrylate) were carried out in RTILs via conventional free radical polymerization. However, our results failed to show any dramatic effects of RTILs on the free radical copolymerization, although RTILs are believed to be able to enhance the rates of propagation while depressing the rates of termination in homopolymerizations.