Polymerization Processes in Ionic Liquids. Cationic Polymerization of Styrene Malgorzata Bas´ko, Tadeusz Biedron´, Przemyslaw Kubisa * Summary: There is an increasing interest in using ionic liquids as solvents for polymerization processes. Most published data deals with controlled radical polymer- ization. It has been shown that ionic liquids offer several advantages for conducting Atom Transfer Radical Polymerization (ATRP), such as good solubility of catalyst and improved k p /k t ratio. Ionic liquids are highly polar therefore they seem to be suitable solvents for conducting also ionic polymerization processes. In our preliminary communication we reported on cationic polymerization of styrene initiated by R- Cl/TiCl 4 system in ionic liquid. To clarify the mechanism of this process, racemization of optically active 1-phenylethyl choride (initiator and the model of dormant species) was studied and it was shown that in ionic liquid racemization proceeds even in the absence of coinitiator (TiCl 4 ). Because racemization proceeds through ionization of C–Cl bond, this explains the cationic polymerization of styrene initiated by R-Cl alone (in the absence of coinitiator). Chain transfer, however, cannot be eliminated, therefore polymerization is not controlled. Keywords: cationic polymerization; ionic liquids; polystyrene Introduction Ionic liquids, organic salts that are liquid at ambient temperatures, have received much attention in many areas of chemistry due to their properties which make them attractive alternative to traditional solvents. [1] Due to such properties as negligible vapor pressure, ability to dissolve several inorganic and organometallic compounds as well as ther- mal and chemical stability, ionic liquids are used as solvents in organic synthesis. In recent years ionic liquids have been used also as solvents for polymer synthesis and there are several reviews that discuss the progress in this field. [2–5] Most papers describing the application of ionic liquids for polymer synthesis deals with controlled radical polymerization pro- cesses, mainly Atom Transfer Radical Poly- merization (ATRP). ATRP requires the presence of catalyst (most frequently cop- per salts) and ability of ionic liquids to dissolve catalyst offers significant advan- tage, although interesting kinetic effects (increasing of the ratio of rate constant of propagation to the rate constant of termi- nation [6] ) have also been observed for ATRP in ionic liquids. One of the properties of ionic liquids is their high polarity therefore they seem to be suitable solvents for conducting also ionic polymerizations. There is, however, very little research activity concerning application of ionic liquids as solvents for polymeriza- tions proceeding by ionic mechanism. High polarity of ionic liquids should especially affect the course of those ionic polymerization processes that involve equi- librium between active and dormant spe- cies. Ionization should be favored in more polar solvents, as it was shown for example for the cationic polymerization of tetrahy- drofuran initiated by triflic acid in organic Macromol. Symp. 2006, 240, 107–113 DOI: 10.1002/masy.200650814 107 Center of Molecular and Macromolecular Studies, Pol- ish Academy of Sciences, Sienkiewicza 112, 90-363 Lo ´ dz ´, Poland Fax: (þ48) 42 681 96 08 E-mail: pkubisa@bilbo.cbmm.lodz.pl ß 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim