Advanced Applications of Ionic Liquids in Polymer Science

During past few years, ionic liquids have kept attracting much attention as “green and designer” media for chemical reactions. Room-temperature ionic liquids have emerged as a potential replacement for organic solvents in catalytic processes on both laboratory and industrial scales (Holbrey & Seddon, 1999b). Literature reports on a wide range of reactions including advances in alkylation reactions (Earle et al., 1998), Diels-Alder cyclizations (Earle et al., 1999; Jaeger & Tucker, 1989), and the development of commercially competitive processes for dimerization, oligomerization, and polymerization of olefins (Abdul-Sada et al., 1995a; 1995b; Ambler et al., 1996; Chauvin et al., 1988; 1989). Effectively, Ionic liquids, among a unique set of chemical and physical properties (Chauvin, 1996; Chauvin & Mussmann 1995; Seddon, 1997), have no measurable vapor pressure, which lends them as ideal replacements for volatile, conventional organic solvents. The wide and readily accessible range of room-temperature ionic liquids with corresponding variations in physical properties, prepared by simple structural modifications to the cations (Gordon et al., 1998; Holbrey & Seddon, 1999a) or changes in anions (Bonhoˆte et al., 1996; Wilkes & Zaworotko, 1992), offers the opportunity to design an ionic liquid-solvent system optimized for particular processes. In other words, these ionic liquids can be considered as “designer solvents” (Freemantle, 1998). Applications of ionic liquids as solvents for polymerization processes have widely been reviewed in literature (Kubisa, 2004; Shen & Ding, 2004; Lua et al., 2009). Ionic liquids have been used in polymer science, mainly as polymerization media in several types of polymerization processes, including conventional free radical polymerization (Sarbu, & Matyjaszewski, 2001), living/controlling radical polymerizations (such as atomtransfer radical polymerizations (ATRP) (Ding et al., 2005; Shen & Ding., 2004; Biedron & Kubisa., 2001; Biedron & Kubisa., 2002; Biedron & Kubisa., 2003), reversible addition-ragmentation transfer (RAFT) (Perrier & Davis, 2002), as well as in ionic and coordination polymerizations (Chiefari et al., 1998; Vijayaraghavan & MacFarlane et al., 2004). When radical polymerizations are conducted in an ionic liquid, a significant increase of kp/kt ratio is normally observed in comparison to those carried out in other polar/coordinating solvents. As solvents for ATRP and RAFT, ionic liquids facilitate separation of the polymer from residual catalyst and reduce the extent of side-reactions.