**2.2 ILs as monomers for chemical modification of HPPs**

In 2010, Li et al. reported that block co-PIs based on aromatic dianhydrides and diamines copolymerised with diamino IL monomers, specifically 1,3-di(3-aminopropyl) imidazolium bis[(trifluoromethyl)sulphonyl]imide ([DAPIM]-[Tf2N]) and 1,12-di[3-(3-aminopropyl)imidazolium]dodecane bis[(trifluoromethyl)sulphonyl] imide ([C12(DAPIM)2][Tf2N]2), as shown in **Figure 4**, were synthesised by the Boc protection method and using diverse compositions. These two ILs were first reacted with 2,2-bis(3,4-carboxylphenyl)hexafluoropropane dianhydride (6FDA) to produce 6FDA-IL oligomers as the IL component for block co-PIs. Later, the oligomers were reacted with 6FDA and *m*-phenylenediamine (MDA) at an oligomer concentration from 6.5 to 25.8 mol% to form block co-PIs. As the concentration of 6FDA-IL oligomer increased in the block co-PIs, the thermal degradation temperature and glass transition temperature of the produced co-PIs decreased, but their density increased. Compared to pure 6FDA-MDA, the gas permeability of the IL-based block co-PI decreased, but the ideal permeability selectivity for CO2/CH4 gas pair increased [52]. The co-PIs were mainly used in the separation of gases such as O2, N2, CH4 and CO2 [53, 54].

Later, a series of poly(arylene ether sulphone)s containing bulky imidazole groups (PSf-Im-x) based on a monomer 2,2′-bis-(2-ethyl-4-methylimidazole-1-ylmethyl)-biphenyl-4,4′-diol (EMIPO) were successfully synthesised. After the quaternisation by *n*-bromobutane, these polymers were evaluated as alkaline anion exchange membranes (AEMs) as shown in **Figure 5**. 2-Ethyl-3-butyl-4 methylimidazolium was introduced as the functional group in these polymers; the bulky groups present around the imidazolium ring reduced the access of OH<sup>−</sup> to imidazolium, thus increasing the alkaline stability of the membranes. The membrane showed an IEC value of 2.07 and ionic (OH<sup>−</sup>) conductivity of 0.014 S cm<sup>−</sup><sup>1</sup> at 30°C, in which 80% of the ionic conductivity was maintained even for the treatment in 1 M KOH at 60°C for 144 h [12].

#### **Figure 4.**

*Structures of monomers used in polyimide synthesis: (a) bis[(trifluoromethyl)sulphonyl]imide ([Tf2N]), (b) 2,2-bis(3,4-carboxylphenyl)hexafluoropropane dianhydride (6FDA), m-phenylenediamine (MDA), (c) 1,3-di(3-aminopropyl)imidazolium bis[(trifluoromethyl)sulphonyl] imide ([DAPIM] [Tf2N]), and (d) 1,12-di[3-(3-aminopropyl)imidazolium] dodecane bis[(trifluoromethyl)sulphonyl] imide ([C12(DAPIM)2][Tf2N]2).*

**107**

grease.

**Figure 5.**

*2.3.1 Membrane*

*Progress in Ionic Liquids as Reaction Media, Monomers and Additives in High-Performance…*

Recently, a new synthetic method was reported for the modification of PIs; the PIs were first transformed to their ionic forms via the subsequent *N*-alkylation and quaternisation of benzimidazole or quinuclidine moieties; then, an ion exchange reaction was carried out to prepare polymers bearing the bis(trifluoro-methylsulphonyl)imide anion. High-molecular-weight (Mn = 22,000–97,000) cationic polyelectrolytes with the degree of quaternisation as high as 96% were obtained under the optimal conditions. These new materials showed excellent mechanical and thermal properties, adjustable surface wettability, and improved gas transport properties [55]. Several recent articles reported that the incorporation of IL moieties into HPP by copolymerisation is a promising strategy to prepare novel copolymers of ILs with HPPs with improved properties. It is presumed that further related

The application of ILs for HPPs is not limited to their use as reaction media in polymerisations for preparing HPPs, and ILs are miscible with some HPPs and used as additives in the materials such as the components of polymer materials, plasticizers, and porogenic agents. By blending ILs with HPPs, the properties of the obtained mixtures can be considerably affected [56]. Thus, applications of ILs are being explored in the fields of membranes, microcapsules, electrolytes, NCs and

Supported IL materials have two main processes. First, ILs are covalently linked to polymers, inorganic surfaces or particles, thereby supporting the IL materials. In such systems, the properties of the ILs are modified to some extent, but generally,

*DOI: http://dx.doi.org/10.5772/intechopen.86472*

work will be reported in the future.

*Synthetic routes of PSf-Im-x and PSf-ImmOm-x.*

**2.3 ILs as additives for physical processing of HPPs**

*Progress in Ionic Liquids as Reaction Media, Monomers and Additives in High-Performance… DOI: http://dx.doi.org/10.5772/intechopen.86472*

**Figure 5.**

*Solvents, Ionic Liquids and Solvent Effects*

**2.2 ILs as monomers for chemical modification of HPPs**

MW irradiation [51].

as O2, N2, CH4 and CO2 [53, 54].

ment in 1 M KOH at 60°C for 144 h [12].

condensing agent under MW irradiation. The obtained PAIs had inherent viscosities in the range 0.32–0.49 dL/g; they were amorphous polymers with nanostructures in which the nanosized particles are in the range from 66 to 78 nm [50]. Soluble, thermally stable PAIs modified with siloxane linkages with a reduced dielectric constant were synthesised via the isocyanate method in TBAB, tetrabutyl-phosphonium bromide (TBPB), and 1-buthyl-3-methyl imidazolium chloride ([bmim][Cl]) under

In 2010, Li et al. reported that block co-PIs based on aromatic dianhydrides and diamines copolymerised with diamino IL monomers, specifically 1,3-di(3-aminopropyl) imidazolium bis[(trifluoromethyl)sulphonyl]imide ([DAPIM]-[Tf2N]) and 1,12-di[3-(3-aminopropyl)imidazolium]dodecane bis[(trifluoromethyl)sulphonyl] imide ([C12(DAPIM)2][Tf2N]2), as shown in **Figure 4**, were synthesised by the Boc protection method and using diverse compositions. These two ILs were first reacted with 2,2-bis(3,4-carboxylphenyl)hexafluoropropane dianhydride (6FDA) to produce 6FDA-IL oligomers as the IL component for block co-PIs. Later, the oligomers were reacted with 6FDA and *m*-phenylenediamine (MDA) at an oligomer concentration from 6.5 to 25.8 mol% to form block co-PIs. As the concentration of 6FDA-IL oligomer increased in the block co-PIs, the thermal degradation temperature and glass transition temperature of the produced co-PIs decreased, but their density increased. Compared to pure 6FDA-MDA, the gas permeability of the IL-based block co-PI decreased, but the ideal permeability selectivity for CO2/CH4 gas pair increased [52]. The co-PIs were mainly used in the separation of gases such

Later, a series of poly(arylene ether sulphone)s containing bulky imidazole groups (PSf-Im-x) based on a monomer 2,2′-bis-(2-ethyl-4-methylimidazole-1-ylmethyl)-biphenyl-4,4′-diol (EMIPO) were successfully synthesised. After the quaternisation by *n*-bromobutane, these polymers were evaluated as alkaline anion exchange membranes (AEMs) as shown in **Figure 5**. 2-Ethyl-3-butyl-4 methylimidazolium was introduced as the functional group in these polymers; the bulky groups present around the imidazolium ring reduced the access of OH<sup>−</sup> to imidazolium, thus increasing the alkaline stability of the membranes. The membrane showed an IEC value of 2.07 and ionic (OH<sup>−</sup>) conductivity of 0.014 S cm<sup>−</sup><sup>1</sup>

30°C, in which 80% of the ionic conductivity was maintained even for the treat-

*Structures of monomers used in polyimide synthesis: (a) bis[(trifluoromethyl)sulphonyl]imide* 

*([Tf2N]), (b) 2,2-bis(3,4-carboxylphenyl)hexafluoropropane dianhydride (6FDA), m-phenylenediamine (MDA), (c) 1,3-di(3-aminopropyl)imidazolium bis[(trifluoromethyl)sulphonyl] imide ([DAPIM] [Tf2N]), and (d) 1,12-di[3-(3-aminopropyl)imidazolium] dodecane bis[(trifluoromethyl)sulphonyl]* 

at

**106**

**Figure 4.**

*imide ([C12(DAPIM)2][Tf2N]2).*

*Synthetic routes of PSf-Im-x and PSf-ImmOm-x.*

Recently, a new synthetic method was reported for the modification of PIs; the PIs were first transformed to their ionic forms via the subsequent *N*-alkylation and quaternisation of benzimidazole or quinuclidine moieties; then, an ion exchange reaction was carried out to prepare polymers bearing the bis(trifluoro-methylsulphonyl)imide anion. High-molecular-weight (Mn = 22,000–97,000) cationic polyelectrolytes with the degree of quaternisation as high as 96% were obtained under the optimal conditions. These new materials showed excellent mechanical and thermal properties, adjustable surface wettability, and improved gas transport properties [55]. Several recent articles reported that the incorporation of IL moieties into HPP by copolymerisation is a promising strategy to prepare novel copolymers of ILs with HPPs with improved properties. It is presumed that further related work will be reported in the future.
