The organometallic-mediated radical polymerization (OMRP) of N-vinyl-3-alkylimidazolium-type monomers, featuring the bis(trifluoromethylsulfonyl)imide counter-anion (Tf2N-) in the presence of Co(acac)(2) as controlling agent, is reported. Polymerizations of monomers with methyl, ethyl, and butyl substituents are fast, reaching high monomer conversion in ethyl acetate as solvent at 30 degrees C, and afford structurally well-defined hydrophobic poly(ionic liquid)s (PILs) of N-vinyl type. Block copolymer synthesis is also achieved by sequential OMRP of N-vinyl-3-alkyldazolium salts carrying different alkyl chains and different counteranions (Tf2N- or Br-). These block copolymerizations are carried out at 30 degrees C, either under homogeneous solution in methanol or in a biphasic medium consisting of a mixture of ethyl acetate and water. Unprecedented PIL-b-PIL block copolymers are thus prepared under these conditions. However, anion exchange occurs at the early stage of the growth of the second block. Finally, diblock copolymers generated in the biphasic medium can be readily coupled by addition of isoprene, forming all PIL-based and symmetrical ABA-type triblock copolymers in a one-pot process. Such a direct block copolymerization method, involving vinylimidazolium monomers bearing different alkyl chains, thus opens new opportunities in the precision synthesis of all PIL-based block copolymers of tunable properties.