Magnetorheological Elastomers Containing Ionic Liquids

Abstract

The term ionic liquid (IL) refers to a class of liquids that are composed solely of ions1. It is a synonym for molten salt. IL in a narrow sense often indicates room-temperature ionic liquid (RIL) that exists as a liquid at room temperature. Ionic liquids (ILs), which have been widely promoted as “green solvents”, are attracting much attention for applications in many fields of chemistry and industry due to their chemical stability, thermal stability, low vapour pressure and high ionic conductivity properties2. In recent years, ILs have been used in polymer science, mainly as polymerisation media in several types of polymerisation processes, including conventional free radical polymerisation3, living/controlling radical polymerisations (such as atom transfer radical polymerisations (ATRP), reversible addition-fragmentation transfer (RAFT))4, and ionic and coordination polymerisations5. When radical polymerizations are conducted in an IL, a significant increase of the kp/kt ratio is normally observed compared radical polymerizations conducted in other polar/coordinating solvents. As solvents for ATRP and RAFT, ILs facilitate the separation of the polymer from residual catalyst and reduce the extent of side-reactions. Applications of ILs as solvents for polymerisation processes have been reviewed by Kubisa6 and Shen and Deng7. However, application of ILs in polymer science are not limited to traditional polymerisation media. ILs have also been investigated as components of polymeric matrixes (such as polymer gels), as templates for porous polymers and as novel electrolytes for electrochemical polymerisations. This review focuses on recent developments and applications of ILs in the preparation of functional polymers. There is much current interest in ionic liquids. The much lower melting points of ionic liquids compared to those of inorganic salts can be partially attributed to the bulky cationic groups, i.e., the low charge density and incompatibility of the Coulombic attraction forces with steric hindrance. Ionic liquids have very low vapour pressures, although it was recently shown that they are distillable8. Therefore, they do not produce hazardous vapors (in contrast to many conventional organic solvents). Most ionic liquids have high ignition points, and they do not generate explosive air-vapour mixtures. They can act as solvents for chemical reactions, including catalytic reactions9. As a result of their interesting physical-chemical features ionic liquids have been extensively evaluated as environmentally friendly or “green” alternatives10 to conventional organic solvents for a broad range of organic synthetic applications. In addition, ionic liquids have