Polymeric ionic liquids based on ether functionalized ammoniums and perfluorinated sulfonimides

A new family of polymeric ionic liquids (PILs) based on alkyl and alkyl ether substituted ammoniums and perfluorinated sulfonimides (i.e., bis(fluorosulfonyl)imide (FSI⁻), and bis(trifluoromethanesulfonyl)imide (TFSI⁻)) have been synthesized by polymerization of the corresponding ionic liquid monomers (ILMs). Their structures and compositions have been characterized by ¹H and ¹⁹F NMR, FTIR and viscosity-average molecular weight (M_v). The physicochemical properties of both the ILMs and the PILs have been studied in terms of thermal stability, phase transition, and ionic conductivity. All the prepared ILMs and PILs reveal excellent thermal stabilities to greater than 250 °C. The PILs containing alkyl ether side unit show significant decrease in glass transition temperature (T_g), the values of T_g of the alkyl ether based-PILs are all significantly lower by 10–77 °C in magnitude than those of the corresponding alkyl based ones. The ionic conductivity of alkyl ether based-PILs in the best case increases up to 4.0 × 10⁻⁶ S cm⁻¹ at 30 °C, and reaches 7.6 × 10⁻⁵ S cm⁻¹ at 60 °C, and outperform their ammonium counterparts with alkyl side chain that were synthesized as references.     

Novel chemically cross-linked solid state electrolyte for dye-sensitized solar cells

Poly(vinylpyridine-co-ethylene glycol methyl ether methacrylate) (P(VP-co-MEOMA)) and α,ω-diiodo poly(ethylene oxide-co-propylene oxide) (I[(EO)_0.8-co-(PO)_0.2]_yI) were synthesized and used as chemically cross-linked precursors of the electrolyte for dye-sensitized solar cells. Meanwhile, α-iodo poly(ethylene oxide-co-propylene oxide) methyl ether (CH₃O[(EO)_0.8-co-(PO)_0.2]_xI) was synthesized and added into the electrolyte as an internal plasticizer. Novel polymer electrolyte resulting from chemically cross-linked precursors was obtained by the quaterisation at 90 °C for 30 min. The characteristics for this kind of electrolyte were investigated by means of ionic conductivity, thermogravimetric and photocurrent-voltage. The ambient ionic conductivity was significantly enhanced to 2.3 × 10⁻⁴ S cm⁻¹ after introducing plasticizer, modified-ionic liquid. The weight loss of the solid state electrolyte at 200 °C was 1.8%, and its decomposition temperature was 287 °C. Solid state dye-sensitized solar cell based on chemically cross-linked electrolyte presented an overall conversion efficiency of 2.35% under AM1.5 irradiation (100 mW cm⁻²). The as-fabricated device maintained 88% of its initial performance at room temperature even without sealing for 30 days, showing a good stability.     

Ion transport properties of lithium ionic liquids and their ion gels

A new series of lithium ionic liquids were prepared by introducing of two electron-withdrawing trifluoroacetyl groups in borate salts containing two methoxy-oligo(ethylene oxide) groups in the structures. Successive substitution reactions of oligo-ethylene glycol monomethyl ether and trifluroacetic acid from LiBH₄ yielded the lithium salts, which were clear and colorless liquids at room temperature. The fundamental physicochemical properties, such as density, thermal property, viscosity, ionic conductivity, self-diffusion coefficients, and electrochemical stability, were measured. The lithium ionic liquids had self-dissociation ability and conducted ions even in the absence of organic solvents. New polymer electrolytes, named ‘ion gels’, were prepared by radical cross-linking reactions of a poly(ethylene oxide-co-propylene oxide)tri-acrylate macromonomer in the presence the lithium ionic liquid. An increase in the glass transition temperatures (T_g) of the ion gels was very small even with increasing lithium ionic liquid concentration, and the T_g's were lower than that of the ionic liquid itself. The ionic conductivity of the ion gels surpassed that of the lithium ionic liquid in the bulk at certain compositions.     

Study of the incorporation of protic ionic liquids into hydrophilic and hydrophobic rigid-rod elastomeric polymers

A series of polymers was synthesized that contain a rigid aromatic backbone connected through triazine linkages that are cross-linked by flexible diamine-terminated poly(ethylene oxide) oligomers. Polymers were made that contained both hydrophilic sulfonated aromatic and hydrophobic pyridinium triflate backbones. Thermal and mechanical properties of the resulting polymer films were studied, as well as uptake of water and protic ionic liquids. Ionic liquid uptake varied from 41 to 440%, depending upon the nature of the polymer. The ionic liquid-doped films were analyzed for proton conductivity at high temperatures (>150 °C) under non-humidified conditions. Conductivities as high as 5×10⁻² S/cm were observed at 150 °C.     

Physicochemical properties of new amide-based protic ionic liquids and their use as materials for anhydrous proton conductors

We prepared 3 protic ionic liquids based on trifluoromethanesulfonic acid and an amide, namely isobutyramide (ITSA), n-butyramide(NTSA), and benzamide(BTSA). All of the protic ionic liquids exhibit excellent thermal stability (above 200 °C). ITSA has the highest ionic conductivity, which is 32.6 mS/cm at 150 °C. ITSA was used to prepare anhydrous, conducting composite membranes based on polymers of polyvinylidene-fluoride (PVDF) to serve as intermediate temperature proton exchange membrane fuel cells. This type of composite membrane possesses good thermal stability, high ionic conductivity and good mechanical properties. Increasing the polymer content leads to the improvement of mechanical properties, but is accompanied by a reduction in ionic conductivity. We made efforts to eliminate the trade-off between strength and conductivity of the ITSA/PVDF composite membrane by adding polyamide imide, which resulted in a simultaneous increase in strength and conductivity. A conductivity of 7.5 mS/cm is achieved in a membrane containing 60 wt.% ITSA and 5 wt.% PAI in PVDF at 150 °C.     

New polymer electrolytes based on ether sulfate anions for lithium polymer batteries: Part I. Multifunctional ionomers: Conductivity and electrochemical stability

New lithium conducting ionomers based on commercial polyethers were synthesized by chemical modification in order to incorporate not only the anionic function on the polymer backbone but also polar aprotic and (or) protic groups improving both the salt dissociation and the anion-solvating ability of the multifunctional copolymers. The choice of environmentally friendly rather than perfluorinated anionic functions did not appear to compromise for the ionic conductivity. Lastly, the preliminary results on the use of an electrochemically stable and relatively cheap additive sparteine appear promising and could be generalized to a variety of polymer electrolytes for lithium batteries.     

Preparation and characterization of new anhydrous, conducting membranes based on composites of ionic liquid trifluoroacetic propylamine and polymers of sulfonated poly (ether ether) ketone or polyvinylidenefluoride

A novel ionic liquid of trifluoroacetic propylamine, i.e., [CH₃CH₂CH₂NH₃⁺] [CF₃COO⁻] (TFAPA), was synthesized from trifluoroacetic acid and propylamine. The ionic liquid of TFAPA was used to prepare anhydrous, conducting membranes based on polymers of sulfonated poly (ether ether) ketone (SPEEK) or polyvinylidenefluoride (PVDF). The ionic conductivity and mechanical strength of the composite membranes were investigated at elevated temperatures and under anhydrous conditions. Conductivity of 0.030 S/cm was achieved with TFAPA at 180 °C, and of 0.019 S/cm with a membrane containing 70% (wt) TFAPA in SPEEK with a sulfonation degree of 86% at 160 °C. Increasing either ionic liquid content or temperature reduced the mechanical strength of the composite membrane. Efforts were made to improve the strength of TFAPA/SPEEK composite membranes by cross-linking the SPEEK, which led to some strength enhancement at 110 °C and 130 °C.     

Fast proton conductor under anhydrous condition synthesized from 12-phosphotungstic acid and ionic liquid

In this study, we synthesized a molecular hybrid conductor electrolyte using PWA ([H₃PW₁₂O₄₀·nH₂O]) and [1-butyl-3-methylimidazole][bis-(fluoromethanesulfonyl) amide] ([BMIM][TFSI]) ionic liquid. The [BMIM][TFSI] ionic liquid can interact with the strongly acidic PWA. The hybrids were hydrophilic, and included some water molecules in the structure of the hybrids. The water molecules remained up to 80 °C, contributing to improve conductivity under an anhydrous N₂ atmosphere. The conductivity of PWA-[BMIM][TFSI] hybrid under anhydrous conditions increased from 10⁻⁴ S/cm to 0.04 S/cm at 60 °C. The conductivity of the hybrids at each temperature was higher than that of pure PWA and [BMIM][TFSI] under anhydrous condition. It can be due to the protonic carriers.     

Highly efficient dye-sensitized solar cells: A comparative study with two different system of solvent-free binary room-temperature ionic liquid-based electrolytes

In this work, novel redox electrolytes based on poly (ethylene oxide) (PEO) were prepared using binary ionic liquid 1-methyl-3-propylimidazolium iodide (MPII) with 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI) or 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄) to reduce the high viscosity of MPII. The addition of low viscosity ionic liquids is to overcome the low mass transportation of redox mediator faced by the single ionic liquid. Therefore, different ratios of ionic liquids were added, and their effect on the electrical properties of the ionic liquid-based gel polymer electrolytes (GPE) was observed. It was confirmed that all the system dominant by ions rather than electron. The binary ionic liquid system containing 37.5 wt.% of BMIMBF₄ showed the highest ionic conductivity of 24.2 mS cm⁻¹. Fourier-transform infrared and X-ray diffraction studies confirmed that complexation occurred between all materials. The combination of two alkyl side chain length has enhanced the efficiency of the DSSC with short-circuit current density (J_SC) of 26.81 mA cm⁻¹, open-circuit voltage (V_OC) of 0.67 V, fill factor of 44.5% and photovoltaic conversion efficiency (η) of 7.8%. This work has provided valuable insight for further stability of binary ionic liquid-based GPE compared to single ionic liquid electrolytes.     

Highly ion conductive flexible films composed of network polymers based on polymerizable ionic liquids

Ionic liquid-type polymer brushes having different hydrocarbon (HC) chain lengths between polymerizable group and imidazolium ring were synthesized. When the carbon number of HC chain was 6, the ionic liquid-type polymer brush exhibited the highest ionic conductivity of 1.37×10⁻⁴ S cm⁻¹ at 30 °C, reflecting low T_g of −60 °C. Moreover, for the first time, we succeeded in obtaining transparent and flexible films without considerable decrease in the ionic conductivity as compared with that of corresponding monomers by using suitable cross-linkers. The most ion conductive (1.1×10⁻⁴ S cm⁻¹ at 30 °C) film was obtained when tetra(ethylene glycol)diacrylate was used 0.5 mol% to ionic liquid monomer as the cross-linker. This film is one of excellent conductive films among single-ion conductive materials.     

Ternary polymer electrolytes with 1-methylimidazole based ionic liquids and aprotic solvents

New polymer gel electrolytes containing ionic liquids were developed for modern chemical power sources—supercapacitors and lithium-ion batteries. Ternary systems polymer-ionic liquid-aprotic solvent as well as materials containing also lithium salts (LiClO₄ or LiPF₆) were prepared by direct, thermally initiated polymerisation. Poly(2-ethoxyethyl methacrylate) PEOEMA was combined with various ionic liquids based on 1-methylimidazole. Only 1-butyl-3-methylimidazolium hexafluorophosphate BMIPF₆ formed a homogenous and slightly translucent polymer electrolyte, where aprotic solvents—propylene carbonate and ethylene carbonates were used as plasticisers. Materials were studied using the electrochemical and thermogravimetric methods and exhibit high ionic conductivity up to 0.94 mS cm⁻¹ at 25 °C together with high electrochemical stability: the accessible potential window on the glassy carbon was found ca. 4.3 V. Prepared non-volatile materials are long-term and thermally stable up to 150 °C.     

Anhydrous proton-conducting glass membranes doped with ionic liquid for intermediate-temperature fuel cells

Proton-conducting glass membranes based on SiO₂ monoliths and a protic ionic liquid (diethylmethylammonium trifluoromethanesulfonate, [dema][TfO]) as the anhydrous proton conductor were studied. The [dema][TfO]/SiO₂ hybrid glass membranes were prepared via a sol–gel process. The stability and ionic conductivity of the glass membrane were investigated. The [dema][TfO]/SiO₂ hybrid glass monoliths exhibit very high anhydrous ionic conductivities that exceed 10^?2 S cm^?1 at 120–220 °C.     

1,2,3-Triazolium-based poly(acrylate ionic liquid)s

Nitroxide-mediated radical polymerization of a tailor-made acrylate carrying a 1,2,3-triazole group with an undecanoyl spacer affords a well-defined (M_n = 7860 g mol⁻¹ and D = 1.39) neutral polyacrylate precursor. A series of 1,2,3-triazolium-based poly(ionic liquid)s (TPILs) is then obtained by straightforward quaternization of the 1,2,3-triazole groups with methyl iodide and subsequent anion metathesis reactions. Among the prepared materials, TPIL with bis(trifluoromethane)sulfonimide anion exhibits low glass transition temperature (T_g = −40 °C), high thermal stability (T_d10 = 325 °C) and anhydrous ionic conductivity of 4 × 10⁻⁶ S cm⁻¹ at 30 °C, as measured by differential scanning calorimetry, thermogravimetric analysis and broadband dielectric spectroscopy, respectively.     

α,ω-Difunctional oligo(oxyethylene)-based crosslinked resins as solid-liquid phase transfer catalysts

Crosslinked resins were prepared from α,ω-diglydicyl and α,ω-dimethacryloyl oligo(ethylene oxide)s by anionic polymerization with triethylenediamine/n-pentanol initiating system or by free-radical polymerization, respectively. Their activity as solid-liquid phase transfer catalysts was proved in the reaction of 1-bromobutane with potassium phenoxide, and compared with the activity of similar resins synthesized from α,ω-diglycidyl oligo(ethylene oxide)s and triethylenetetramine (TETA). The catalytic activity of dimethacryloyl resins was higher than that of diglycidyl resins for oligomer chains longer than 6–7 oxyethylene units, whereas the opposite was true for resins of shorter chain lengths. These differences were explained by an unlike graft content of the resins in the former case, and by a different ability to complex the potassium cation into the meshes of the resin lattice, in the latter. In order to improve the catalytic activity of the resins two methods were developed consisting in the increase of the number of grafts either by decreasing the ratio of TETA/epoxy end groups used to the crosslinking of diglycidyl oligomers or by adding 2-mercaptoethanol as a transfer agent to the free-radical crosslinking process of dimethacryloyl oligo(ethylene oxide)s.     

Synthesis and Aggregation Behavior of Trisiloxane Ionic Liquids in Aqueous Solution

Trisiloxane ionic liquids with polyether groups (Si₃pyCl-EO₃) were synthesized via thiol-ene reaction between 1-methyl-1-[bis(vinyldimethylsiloxy)methyl]silylpropylpyrrolidinium chloride (Vi-Si₃pyCl) and tri(ethylene glycol) methyl ether thiol. The aggregation behavior of the trisiloxane ionic liquids, Si₃pyCl-EO₃ and Vi-Si₃pyCl, in aqueous solution was investigated using surface tension, electrical conductivity, dynamic light scattering, and transmission electron microscopy. The structures of trisiloxane ionic liquids can obviously influence their aggregation behavior. Vi-Si₃pyCl has excellent surface activity (22.3 mN m⁻¹). However, Si₃pyCl-EO₃ can only reduce the surface tension of water to 33.5 mN m⁻¹. In comparison with Vi-Si₃PyCl, Si₃PyCl-EO₃ has a bulkier hydrophobic group and a higher Α_min value (127.8 Ų) caused by the introduction of the tri(ethylene glycol) methyl ether groups by thiol-ene reaction. The micellization of Vi-Si₃PyCl is entropy driven, while the aggregation process of Si₃PyCl-EO₃ in aqueous solution is enthalpy driven.     

Electrosynthesis of β-methylpentadecanedioic acid dimethyl ester

β-Methylpentadecanedioic acid dimethyl ester ( I ) was synthesized electrochemically by Kolbe reaction using β-methylglutaric acid monomethyl ester ( II ) and α,ω-dodecanedioic acid monomethyl ester (III) as starting materials in MeOH solution. Electrolysis was carried out ofr about 4–5 h, when solution pH ≥ 7, followed by extraction with petroleum ether and distillation to obtain a colourless oily product ( I ) The minimum production cost occurred when the mole ration of II to III was 1:1·38 and unreacted III could be recovered. The product synthesized ( I ) completely met the requirement of artificially synthesized musk.     

Exceptionally effective H2S absorption and conversion into thiols in novel superbase protic ionic liquids

We demonstrate an effective strategy for capture and conversion of H₂S in novel superbase protic ionic liquids (SPILs). It is found that the synthesized SPILs with the multiple active sites exhibit the unprecedented H₂S uptake via chemical absorption (up to 1.81 mol mol⁻¹ at 298.2 K and 1 bar). More importantly, H₂S molecule is activated by these SPILs during the absorption process, so that the activated H₂S can be converted further into high value-added thiols in situ with excellent yields under mild conditions (303.2 K and 1 bar) without any solvents and metallic catalysts. Since H₂S-saturated SPILs can be regenerated by chemical conversion of absorbed H₂S into thiols, thereby eliminating the higher input of energy consumption during the process of H₂S stripping. This SPIL-mediated scheme provides an alternative approach for the capture and chemical conversion of H₂S.     

Synthesis of amphiphilic macrocyclic graft copolymer consisting of a poly(ethylene oxide) ring and multi-poly(?-caprolactone) lateral chains

A series of amphiphilic macrocyclic graft copolymers composed of a hydrophilic poly(ethylene oxide) as ring and hydrophobic poly(?-caprolactone) as lateral chains with different grafting lengths and densities of side chains were prepared by a combination of anionic ring-opening polymerization and coordination-insertion ring-opening polymerization. The anionic ring-opening copolymerization of ethylene oxide (EO) and ethoxyethyl glycidyl ether (EEGE) was carried out first using triethylene glycol and diphenylmethyl potassium (DPMK) as co-initiators, and a linear α,ω-dihydroxyl poly(ethylene oxide) with pendant protected hydroxymethyls (l-poly(EO-co-EEGE)) was obtained. The monomer reactivity ratios of these compounds are r_1(EO) = 1.20 ± 0.01 and r_2(EEGE) = 0.76 ± 0.02, respectively. Then the ring closure of l-poly(EO-co-EEGE) was achieved via an ether linkage by reaction with tosyl chloride (TsCl) in the presence of solid KOH. The crude cyclized product containing the linear chain-extended polymer was hydrolyzed in acidic conditions first and then purified by treating with α-CD. The pure cyclic copolymer of EO and glycidol (Gly) with multipendant hydroxymethyls [c-poly(EO-co-Gly)] as the macroinitiator was used further to initiate the ring-opening polymerization of ?-caprolactone (CL), and a series of amphiphilic macrocyclic graft copolymers c-PEO-g-PCL were obtained. The final products and intermediates were characterized by GPC, NMR and MALDI-TOF in detail.     

One-step synthesis of α-p-vinylphenylalkyl-ω-hydroxy poly(ethylene oxide) macromonomers by anionic polymerization initiated from p-vinylphenylalkanols

ω-(p-Vinylphenyl)alkanols, including methanol, ethanol, propanol, pentanol, and hexanol, have been partially alkoxidated with potassium naphthalene to initiate anionic polymerization of ethylene oxide (EO) in order to directly prepare the corresponding α-p-vinylphenylalkyl-ω-hydroxy poly(ethylene oxide) (PEO) macromonomers. p-Vinylphenylmethanol, i.e. p-vinylbenzyl alcohol (VBA) afforded the expected well-defined macromonomer via living polymerization mechanism and the kinetics have been examined as a function of extent of potassium-alkoxidation. Other alcohols such as p-vinylphenylpropanol (VPP), -pentanol (VPPT), and -hexanol (VPH) were also successful to afford the corresponding PEO macromonomers, while p-vinylphenylethanol (VPE) alkoxide polymerized EO to give p-divinylbenzene and poly(ethylene glycol) without p-vinylphenylethoxy end group, which were supposed to form by a very facile intramolecular chain transfer of the activated oligomeric alkoxide chain end to abstract a benzylic proton of the initiating fragment.     

Aprotic ionic liquids as electrolyte components in protonic membranes

In this paper we describe the preparation and the properties of a series of aprotic ionic liquid-based, proton-conducting membranes. The ionic liquids (ILs) 1,2-dimethyl-3-n-propylimidazolium bis(trifluoromethanesulfonyl)imide and the 3-methyl-1-n-propylpyridinium bis(trifluoromethanesulfonyl)imide are used as the casting solvents of PVdF gel-type membranes; the proton conductivity is achieved by the addition of a superacid component, namely, trifluoromethanesulfonic acid (HTf) or N,N-bis(trifluoromethanesulfonyl)imide (HTFSI). The polymer electrolytes showed good thermal and electrochemical properties in the temperature range of interest for PEMFC applications. The strong coordination between the ILs and the HTFSI, which have the same anion, improves the thermal stability of this kind of membrane, but lowers the chemical properties and the conductivity, due to an increase in viscosity. HTf-added samples have an ionic conductivity of 2 × 10⁻² S cm⁻¹ at 100 °C, showing the best overall properties and making these membranes of interest applications in fuel cells.