The authors detail herein the synthesis and controlled polymerization of a series of new permanently cationic ammonium exo-7-oxanorbornene derivatives via ROMP, with the first generation Grubbs' catalyst RuCl2(PCy3)(2)CHPh, in a novel solvent mixture composed of 1:1 vol/vol 2,2,2-trifluoroethanol (TFE)/methylene chloride. It is demonstrated that this cosolvent mixture is a convenient reaction medium facilitating the polymerization of hydrophilic substrates by hydrophobic initiators under homogeneous conditions. Homopolymerizations and copolymerizations proceed yielding materials with controlled molecular masses, and narrow molecular mass distributions. It is also demonstrated that this protocol is not limited to the use of TFE as a cosolvent and that additional halogenated alcohols, such as 2,2,2-trichloroethanol and 1,1,1,3,3,3-hexafluoroisopropanol are also effective cosolvents for the controlled polymerization of such cationic substrates. Finally, it is demonstrated that the TFE/methylene chloride mixture has no apparent detrimental effect on Grubbs' catalyst. (C) 2007 Wiley Periodicals, Inc.