Advanced applications of ionic liquids in polymer science

doi:10.1016/j.progpolymsci.2008.12.001

Progress in Polymer Science

Volume 34, Issue 5, May 2009, Pages 431-448

https://doi.org/10.1016/j.progpolymsci.2008.12.001 Get rights and content

Abstract

Ionic liquids (ILs) are continuing as important media in which to effect various kinds of polymerizations, and it is particularly noteworthy that ionic polymerizations are being developed in IL solvents and that atom transfer radical polymerization (ATRP) catalysts are being attached to ILs to make them more easily recoverable in living polymerizations. In addition, the number of polymerizable ILs is steadily increasing, and ionic liquid polymers of polymerizable ionic liquid monomers have been produced as exotic polyelectrolytes. ILs are being used as plasticizers of various kinds of polymers and as key components in new classes of polymer gels. Polymers and inorganic substrates are being used to support ILs through covalent binding of the ILs, in which case the properties of the IL are modified to some extent, and polymer membranes and porous materials absorb ILs with concomitant changes in ionic conductivity and mobility. New applications of ILs include creating new classes of advanced materials, such as a new class of solvogels that are stimuli responsive and reversibly porate via pinned spinodal decomposition and the development of ILs derived from inorganic nanoparticle cores for use as new resin components for diverse materials and coatings applications.

Introduction

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 vapor pressure and high ionic conductivity properties. Over the last few years, ILs have been popularly used as solvents for organic synthesis, catalysis, and also been used as media for extraction processes [1], [2], [3], [4], [5], [6].

In recent years, ILs have been used in polymer science, mainly as polymerization media in several types of polymerization processes, including conventional free radical polymerization [7], living/controlling radical polymerizations (such as atom transfer radical polymerizations (ATRP) [8], [9], [10], [11], [12], [13], reversible addition-fragmentation transfer (RAFT)) [14], as well as in ionic and coordination polymerizations [15], [16]. When radical polymerizations are conducted in an IL, a significant increase of k_p/k_t ratio is normally observed in comparison to those carried out in other polar/coordinating solvents. As solvents for ATRP and RAFT, ILs facilitate separation of the polymer from residual catalyst and reduce the extent of side-reactions. Applications of ILs as solvents for polymerization processes have been reviewed by Kubisa [17] and Shen and Deng [10].

However, application of ILs in polymer science is not limited to traditional polymerization media. ILs are also investigated as components of the polymeric matrixes (such as polymer gels), as templates for porous polymers and as novel electrolytes for electrochemical polymerizations. This review focuses on recent developments and achievements of applications of ILs in the preparation of functional polymers.

Section snippets

Polymer gels based on ionic liquids

Ionic liquids have excellent ionic conductivity up to their decomposition temperature. This advantage enables them to play an important role in electrolyte matrixes. However, from the viewpoint of eliminating leakage, solid or quasi-solid ion-conductive electrolytes are generally preferred over fluidic materials. Therefore, it is desirable to convert IL-based electrolyte solutions into a solid or quasi-solid form. In recent years, the gelation of ILs by physical or chemical gelation has

From ionic liquids to porous polymer materials

Removal of ionic liquids from IL/polymer composites is a simple and convenient way to prepare porous polymers. Polymers with permanent porosity have been prepared by Winterton et al. through in situ polymerization in ionic liquid and subsequent removal of the ionic liquid from IL/polymer composites [85]. The produced polymers show pore sizes in the range of 290–570 nm.

Polyurea with exotic porous structures has been synthesized by the interfacial polymerization between hexane and a series of

Supported ILs

There are two important new application areas of supported ILs. In the first case, we have ionic liquid salts covalently linked to a polymer or to inorganic surfaces or particles, thereby supporting the organic salt. In such systems the character of the IL organic salt is changed to some extent, but many times the main features are retained. The second application area for supported ILs is where a polymeric membrane, porous matrix, particle, or bulk material absorbs an IL by solubilization or

Electrochemical polymerization in ILs

Ionic liquids are also ideal supporting electrolytes for the electrochemical generation of conjugated polymers because of their excellent oxidative and reductive stability, which allows access to potentials that cannot be provided in the smaller electrochemical windows of molecular solvent/electrolyte systems.

Naudin et al. reported the electrochemical oxidation of 3-(4-fluorophenyl) thiophene (FPT) in pure 1-ethyl-2,3-dimethylimidazolium bis((trifluoromethyl)sulfonyl) amide and

Ionic liquids as solvents for polymerization processes

The use of ionic liquids as solvents in polymerization instead of classical organic solvents offers not only some general advantages such as low volatility and nonflammability, but also markedly affect polymerization rate and degrees. In 2004, Kubisa [17] published an excellent review on the application of ionic liquids as solvents for polymerization processes. Since there is still a continuous increasing interest of polymerization processes in ionic liquid solvents, we provide a brief overview

Composites

A novel one-pot synthesis of conducting polymer-noble metal nanoparticle composites was developed by Pringle et al. [116], [118], based on their use of noble metals in IL solution as oxidizing agents. In this approach, gold or silver salts, such as gold chloride and silver nitrate, are solubilized in ILs, [EtMeIm][tf₂N], and the metal ions oxidatively polymerize monomers such as pyrrole and terthiophene, as described above. The composites obtained, as analyzed by TEM on samples supported on

Conclusions

The use of ionic liquids in polymer science has quickly advanced from use as solvents and has become focused on using ionic liquids as functional additives to polymer chains or to hybrid materials. This functionality may be due to the solubility of an IL monomer, the charge density of the resulting material, or due to the basic mobility of the IL, as in the case of hybrid materials.

Very interesting initial applications for the incorporation of IL monomers into polymers have been published, but

Acknowledgments

This work was supported in part by U.S. Army Tank-Automotive and Armaments Command Cooperative Agreement No. DAAD19-03-2-0013, by U.S. Army Research Laboratory Contract W911QX-06-C-0102, and by AFOSR Grant No. FA9550-08-1-0431. F. Yan and J. Lu acknowledge the financial support provided by Natural Science Foundation of China (Nos. 20774063, 20874071, 20571054), the Program for New Century Excellent Talents in University (Grant NCET-07-0593), and Fok Ying Tung Education Foundation (No. 114022).

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Advanced applications of ionic liquids in polymer science

Abstract

Introduction

Section snippets

Polymer gels based on ionic liquids

From ionic liquids to porous polymer materials

Supported ILs

Electrochemical polymerization in ILs

Ionic liquids as solvents for polymerization processes

Composites

Conclusions

Acknowledgments

Prog Polym Sci

Prog Polym Sci

J Electroanal Chem

Solid State Ionics

Electrochim Acta

Eur Polym J

Electrochim Acta

Electrochim Acta

Polymer

Polymer

Polymer

Polymer

Room-temperature ionic liquids. Solvents for synthesis and catalysis

Chem Rev

Ionic liquid (molten salt) phase organometallic catalysis

Chem Rev

Catalysis in ionic liquids

Chem Rev

Biocatalysis in ionic liquids

Chem Rev

Ionic liquids—New “solutions” for transition metal catalysis

Angew Chem Int Ed

Ionic liquids: industrial applications for green chemistry

Synthesis of block copolymers of styrene and methyl methacrylate by conventional free radical polymerization in room temperature ionic liquids

Macromolecules

ATRP of methyl methacrylate in the presence of ionic liquids with ferrous and cuprous anions

Macromol Chem Phys

Ionic liquid catalyst for biphasic atom transfer radical polymerization of methyl methacrylate

Macromolecules

Ionic liquids as reaction media for polymerization processes: atom transfer radical polymerization (ATRP) of acrylates in ionic liquids

Polym Int

Atom transfer radical polymerization of acrylates in an ionic liquid: synthesis of block copolymers

J Polym Sci Part A Polym Chem

Atom-transfer radical polymerization of acrylates in an ionic liquid

Macromol Rap Commun

First report of reversible addition-fragmentation chain transfer (RAFT) polymerization in room temperature ionic liquids

Chem Commun

Living free-radical polymerization by reversible addition-fragmentation chain transfer: the RAFT process

Macromolecules

Living cationic polymerization of styrene in an ionic liquid

Chem Commun

Spontaneous self-assembly of glycolipid bilayer membranes in sugar-philic ionic liquids and formation of ionogels

Langmuir

Gelation of ionic liquids with a low molecular-weight gelator showing Tgel above 100 °C

Chem Lett

Quasi-solid-state dye-sensitized solar cells using room temperature molten salts and a low molecular weight gelator

Chem Commun

Specialist gelator for ionic liquids

Langmuir

Gelation of ionic liquid-based electrolytes with silica nanoparticles for quasi-solid-state dye-sensitized solar cells

J Am Chem Soc

High-temperature and long-term stable solid-state electrolyte for dye-sensitized solar cells by self-assembly

Chem Mater

A thermostable and long-term-stable ionic-liquid-based gel electrolyte for efficient dye-sensitized solar cells

Chem Phys Chem

Molecular ordering of organic molten salts triggered by single-walled carbon nanotubes

Science

Ionic liquids for soft functional materials with carbon nanotubes

Chem Eur J

Electrochemical functionalization of single-walled carbon nanotubes in large quantities at a room-temperature ionic liquid supported three-dimensional network electrode

Langmuir

Rational functionalization of carbon nanotube/ionic liquid bucky gel with dual tailor-made electrocatalysts for four-electron reduction of oxygen

J Phys Chem C

Macromolecules in ionic liquids: progress, challenges, and opportunities

Macromolecules

Upper critical solution temperature behavior of poly(N-isopropylacrylamide) in an ionic liquid and preparation of thermo-sensitive nonvolatile gels

Chem Lett

Lower critical solution temperature behavior of linear polymers in ionic liquids and the corresponding volume phase transition of polymer gels

Gelation of ionic liquids with a low molecular-weight gelator showing T_gel above 100 °C