KR101766577B1 - Alkyl bisimidazolium-mediated crosslinked nion exchange membranes with comb-shaped structure - Google Patents

Abstract

The present invention not only improves conductivity by forming a self-aggregated anion exchange membrane having a complex structure by bonding a side chain polymer having a relatively long alkyl chain and a function of a cross-linking agent and an ion conductor to a main chain, To an alkylbisimidazolium-based cross-linkable anion exchange membrane having a comb structure having a comb structure, which is suitable for use in an alkaline exchange membrane fuel cell (AEMFC) as an anion exchange membrane having mechanical and dimensional stability.

Description

TECHNICAL FIELD [0001] The present invention relates to an alkylbenzimidazolium-based cross-linked anion exchange membrane having a complex structure,

The present invention relates to an alkylbisimidazolium-based crosslinked anion exchange membrane having a comb structure, and more particularly, to an anion exchange membrane having high conductivity and stability and having a comb structure suitable for use in an alkaline exchange membrane fuel cell (AEMFC) And an alkylbisimidazolium-based crosslinking type anion exchange membrane using alkylbisimidazole as an ionic conductor and a crosslinking agent.

At present, the anion-exchange membrane alkaline fuel cell (AEMFC) is growing in popularity because of its advantages over proton exchange membrane fuel cells (PEMFCs), which are well known and under development. AEMFC has the advantage of using a relatively low cost metal catalyst due to the fast reduction dynamics at the cathode, low corrosion, and high pH of the process conditions, without using a noble metal electrode catalyst.

Many polymers including hybrid composites comprising poly (ether sulfone), poly (ether ketone), polyimide, poly (phenylene oxide) and inorganic materials have been used as base polymers for anion exchange membranes (AEM). Hydroxide conducting groups such as quaternary ammonium salts, guanidinium salts, pyridazinium salts, moporininium salts and imidazolinium salts have been introduced into these base polymers and used. These base polymers have the advantage that they can be readily prepared and their properties can be easily changed, but their practical use in anion exchange membrane alkaline fuel cells (AEMFC) is limited due to their low stability under alkaline (high pH) conditions. In addition, it is difficult to develop anion exchange membrane (AEM) because it can not achieve high OH ^- ion conductivity due to low electrochemical migration of OH ^- ion compared to the mobility of H ⁺ in water. The most straightforward and direct method to maximize OH ^- ion conductivity in AEM is to increase the ion exchange capacity (IEC), defined as the milliequivalents (meq) of the conductive group per gram of polymer. However, a high ion exchange capacity (IEC) is accompanied by excessive water absorption which inevitably leads to a considerable swelling of the corresponding membrane, impairing the mechanical properties and causing the problem of decomposing the AEM, especially at high temperatures.

The stability of such a membrane can generally be increased by crosslinking the polymer, but crosslinking necessarily involves a decrease in the ionic conductivity of the polymer membrane. Therefore, development of a method that induces crosslinking but minimizes the reduction of conductivity is required.

Ion exchange membranes are generally made from copolymers having both hydrophilic units contributing to conductivity and hydrophobic units controlling the mechanical properties of the membrane. Ion clusters (hydration ions and surrounding water molecules) are typically distributed in the hydrophobic matrix, forming only small ion channels. However, introduction of a hydrophobic structure with an additional comb structure will allow the ion clusters to flocculate, thereby creating larger ion clusters, and interconnected, ionic coagulation structures with broad ion channels will improve OH ^- conductivity Thus, the present invention has been developed.

Korean Patent Publication No. 10-2014-0023152 Korean Patent Registration No. 10-1272661

SUMMARY OF THE INVENTION The present invention has been made to overcome the above problems, and it is an object of the present invention to provide an ion-conducting membrane which is superior in performance to a conventional AEM and has a low ion exchange capacity and high conductivity even at low moisture absorption, And an alkylbisimidazolium type crosslinked anion exchange membrane having a comb structure by using the same as a crosslinking agent.

These and other objects and advantages of the present invention will become apparent from the following description of a preferred embodiment.

The above object is achieved by an alkylbisimidazolium-based crosslinked anion exchange membrane having a comb structure having a comb-shaped structure prepared by combining a main chain, a cross-linking agent and a side chain polymer functioning as an ion conductor simultaneously .

Preferably, the main chain may be composed of at least one of poly (arylene sulfone), poly (arylene ketone), poly (imide), poly (amide) and poly (phenylene).

Preferably, the side chain polymer may be an alkyl bisimidazole.

Preferably, the alkyl group of the side chain polymer may have 4 to 10 carbon atoms.

Preferably, the main chain is composed of poly (arylene sulfone), and the side chain polymer is bisimidazole having 10 carbon atoms.

Preferably, the poly (arylene sulfone) may be prepared by polymerizing an OH-terminal oligomer and an F-terminal oligomer as poly (arylene ether sulfone).

Preferably, the OH-terminal oligomer and the F-terminal oligomer may have a degree of polymerization of 12.

Preferably, the thickness of the anion exchange membrane may be 40-50 mu m.

Preferably, the anion exchange membrane has an Ion Exchange Capacity (IEC) of 1.13 to 1.20 meg / g, which is calculated by the following equation (1)

(1)

IEC (meq / g) = ( V _{0 NaOH} C _NaOH - V _{X NaOH} C _NaOH ) / W _dry

Where V _{0 NaOH} and V _{x NaOH} are the volume of NaOH consumed in the titration and titration respectively, C _NaOH is the molar concentration of NaOH titrated with oxalic acid standard solution, and W _dry is the weight of the dried membrane.

Preferably, the anion exchange membrane has a hydroxide ion conductivity sigma of 0.012 S / cm or more at 20 占 폚 and not less than 0.060 S / cm at 80 占 폚, calculated by the following formula (2)

(2)

σ = 1 / RA

Here, 1 is the distance between the reference electrodes, A is the cross-sectional area of the film sample, and R is the resistance.

According to the present invention, a side chain polymer having a relatively long alkyl chain and simultaneously functioning as a crosslinking agent and an ion conductor is bonded to a main chain to form a self-coagulated anion exchange membrane having a comb structure, thereby improving conductivity, Thermal and mechanical stability, and dimensional stability.

However, the effects of the present invention are not limited to the above-mentioned effects, and other effects not mentioned can be clearly understood by those skilled in the art from the following description.

1 is a photograph of a bisimidazolium-based crosslinked PES membrane having three different alkyl chains according to Examples 1 to 3;
2 is a ¹ H-NMR spectrum (CDCl ₃ solvent) of (a) the OH-terminal oligomer (3) and (b) the F-terminal oligomer (4).
3 is a ¹ H-NMR spectrum (CDCl ₃ solvent) of the bromine-substituted form (2) of (a) PES block copolymer (5) and (b).
4 is a FT-IR spectrum of Br-PES (2), (b) BI-cPES-4, (c) BI-cPES-6 and ≪ / RTI > shows the FT-IR spectrum for the sample.
(BI-cPES-4), (b) Example 2 (BI-cPES-6), (c) Example 3 -cPES-10).
(BI-cPES-4), (b) Example 2 (BI-cPES-6), (c) Example 3 (BI-cPES-10).
FIG. 7 is a graph showing Arrhenius plots of the conductivity according to the temperature of the separator according to the embodiments at a relative humidity of 100%. FIG.
8 is a TGA temperature recording chart for the crosslinked BI-cPES separator of Examples and Comparative Examples.
9 is a graph showing the stress-strain curve for the crosslinked BI-cPES separator of the Examples in the dry state.
10 is a graph showing the conductivity of the crosslinked BI-cPES separator according to Examples after immersing in 2M NaOH at 60 ° C for 350 hours.
Fig. 11 is an FT-IR spectrum before and after immersing in 2M NaOH at 60 ° C for 350 hours. (A) before immersion in Example 1, (a ') after immersion in Example 1, (B ') shows the FT-IR spectrum after immersion in Example 2, (c) shows the FT-IR spectrum before immersion in Example 3, and (c') shows the FT-IR spectrum after immersion in Example 3.

Hereinafter, the present invention will be described in detail with reference to embodiments and drawings of the present invention. It will be apparent to those skilled in the art that these embodiments are provided by way of illustration only for the purpose of more particularly illustrating the present invention and that the scope of the present invention is not limited by these embodiments .

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control.

Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described herein.

In describing a given polymer, it is sometimes understood that the applicant refers to a polymer by the amount of monomers used to make the polymer or the monomers used to make the polymer. Such a description may not include the specific nomenclature used to describe the final polymer or may not include product-by-process terms, but any such reference to monomers and amounts is intended to encompass the use of the polymer Should be construed to mean that they include the amounts of these monomers (i.e., the copolymerized units of these monomers) or monomers, and the corresponding polymers and compositions thereof.

In describing and / or claiming the present invention, the term "copolymer" is used to refer to a polymer formed by copolymerization of two or more monomers. Such copolymers include binary copolymers, terpolymers, or higher order copolymers.

As a constituent element of the present invention, poly (arylene ether sulfone) may be referred to as poly (arylene sulfone) or poly (ether sulfone), and all means the same compound.

The alkylbisimidazolium-based crosslinked anion exchange membrane having a comb structure according to an aspect of the present invention is prepared by combining a main chain, a cross-linking agent, and a side chain polymer that simultaneously functions as an ion conductor, and comb- . In the present invention, a comb-shape means a polymer structure having a long side chain in the main chain.

In one embodiment, the backbone may comprise at least one of poly (arylene sulfone), poly (arylene ketone), poly (imide), poly (amide) and poly (phenylene).

Of these, the poly (arylene ether sulfone) series is of interest because of the introduction of long pendant hydrophobic side chains to the imidazolium cation to produce a comb-like hydroxyl-conducting polymer. It has been confirmed that AEM based on this combus shaped system causes ionic aggregation and successfully controls not only IEC but also the morphology of the polymer membrane. By forming large ion clusters, very high hydroxide conductivities appeared through a comb-shaped membrane with alkyl imidazolium functionality.

Cross-linking is also an effective method for stabilizing PEM or AEM with a particularly high ion exchange capacity for water swelling phenomena. These polymers cause very high levels of swelling when not crosslinked, resulting in unacceptable water uptake and large dimensional deformation, resulting in insufficient mechanical properties. In most cases, however, the introduction of crosslinking will inevitably lead to a reduction in ionic conductivity, and only a few reports are merely presenting crosslinked polymer membranes with high conductivity and dimensional / mechanical stability.

It is therefore an object of the present invention to combine the advantages of crosslinking properties and ionic flocculation properties of a comb polymer by the development of novel poly (arylene ether sulfone) having a pendant alkylbisimidazolium group as a crosslinking agent in polymer side chains. Crosslinking can provide a three-dimensional structure of a crosslinked polymer membrane with a pendant bisimidazolium group acting as both a crosslinking unit and an ionic conductor. The cross-linked comomorphic polymer membranes showed high conductivity even with excellent physico-chemical stability and even low ion exchange capacity.

The cross-linked PES polymer membrane (BI-cPESs, 1) into which the bisimidazolium group is introduced has a nucleophilic substitution between the precursor polymer (bromobenzylated PES, BI-cPES) and the alkyl bisimidazole having three different alkyl chains The reaction can be carried out simply and efficiently. Although some polymer membranes based on a comb-like polymer have been reported, an example of a crosslinked comb-shaped polymer having an alkyl bis imidazolium cation is disclosed for the first time in the present invention. The effects of the alkyl chain on the bimidazolium group on the properties of the polymer as well as the corresponding anion exchange membrane have been extensively investigated.

In one embodiment, the side chain polymer may be composed of alkyl bisimidazole, and the alkyl group of the side chain polymer preferably has 4 to 10 carbon atoms, and most preferably 10 carbon atoms. When the number of carbon atoms is less than 4, the desired ion conductivity can not be achieved because OH ^- mobility can not be increased while maintaining proper ion exchange capacity (IEC) value. When the number of carbon atoms is more than 10, The ionic conductivity and the characteristics of the polymer membrane are reduced.

In one embodiment, the main chain is composed of poly (arylene sulfone) and the side chain polymer is comprised of bisimidazole having 10 carbon atoms. The poly (arylsulfone) can be prepared by polymerizing an OH-terminal oligomer and an F-terminal oligomer, and the degree of polymerization of each oligomer is preferably 12, but it is not limited thereto, Lt; / RTI >

In one embodiment, the thickness of the anion exchange membrane is preferably 40 to 50 mu m, and when it is more than 50 mu m, the decrease in ion conductivity due to the increase in the film thickness is accompanied.

In one embodiment, the ion exchange capacity (Ion Exchange Capacity, IEC) of the self-flocculating anion exchange membrane calculated by the following Equation 1 is 1.13 to 1.20 meg / g.

(1)

IEC (meq / g) = ( V _{0 NaOH} C _NaOH - V _{X NaOH} C _NaOH ) / W _dry

Where V _{0 NaOH} and V _{x NaOH} are the volume of NaOH consumed in the titration and titration respectively, C _NaOH is the molar concentration of NaOH titrated with oxalic acid standard solution, and W _dry is the weight of the dried membrane.

In one embodiment, the hydroxyl ion conductivity () of the self-flocculent anion exchange membrane calculated by the following formula (2) is 0.012 S / cm or more and 0.060 S / cm or more at 80 占 폚.

(2)

σ = 1 / RA

Here, 1 is the distance between the reference electrodes, A is the cross-sectional area of the film sample, and R is the resistance.

In this specification, alkyl bisimidazolium bridged poly (arylene ether sulfone) block copolymers having different C ₄ -C ₁₀ alkyl chains have been synthesized as novel anion exchange membranes. Also, the alkylbisimidazolium group used in the present specification is characterized in that it simultaneously functions not only as a crosslinking agent but also as an ion conductor capable of forming a comb structure. The bis-imidazolium-based crosslinked BI-cPES separator is superior to conventional AEM in performance and belongs to several crosslinked separators having high conductivity and excellent dimensional stability. Particularly, the separation membrane according to Example 3 (BI-cPES-10) of the present invention forms a self-aggregated structure by introducing a long pendent hydrophobic side chain, thereby forming a comb-structure. The bridged comb-structure system achieves high conductivity even at low IEC values and low moisture uptake. Also, the combination of the long chain of the comb structure with the crosslinking network indicates that the separator according to Example 3 (BI-cPES-10) of the present invention is a promising membrane as an electrode of an AEM fuel cell.

Hereinafter, the structure and effect of the present invention will be described in more detail with reference to examples and comparative examples. However, this embodiment is intended to explain the present invention more specifically, and the scope of the present invention is not limited to these embodiments.

First, the chemical substances used in this embodiment are as follows.

Bis- (4-fluorophenyl) -sulfone (FPS) was purchased from Aldrich. 2,2-bis (4-hydrophenyl) -hexafluoropropane (6-FBPA) was purchased from TCI. Potassium carbonate, FPS and 6-FBPA were dried for 24 hours under vacuum at 60 캜 before polymerization. Phenolphthalein (PP), 1,4-dibromobutane, 1,6-dibromohexane, 1,10-dibromodecane and 3,5-dimethylaniline (DMA) were purchased from Aldrich. The bisimidazole derivatives can be prepared by reacting imidazoles with the corresponding dibromoalkanes in the presence of NaH [M. Yang, K. Stappert and A.-V. Mudring, J. Mater. Chem . C , 2014, 2, 458-473. ≪ / RTI > 1-one was prepared by reacting 3,5-dimethylaniline (DMA) with phenolphthalein (PP) in the form of an acid. Lt; / RTI > Chen, X. Zhang, S. Zhang, T. Chen and Y. Wu, J. Appl. Polym. Sci ., 2007, 106, 2808-2816. Other chemicals were purchased from commercial companies and used as such without refining. Distilled water was used throughout this experiment.

[Preparation Example 1] Synthesis of OH-terminated oligomer (3) having a degree of polymerization of 12

1-one (7.2 g, 17.09 mmol), FPS (4.0 g, 15.73 mmol) and potassium carbonate ( 4.74 g, 34.35 mmol) was added to a mixture of DMAc (25 cm ³ ) and toluene (30 cm ³ ) in a 250 cm ³ round bottom two-necked flask equipped with a Dean-Stark apparatus and a nitrogen inlet . The reaction mixture was heated at 150 < 0 > C for 4 hours. Toluene was removed after azeotropic distillation. The temperature was then raised to 170 ° C and then stirred at that temperature for 16 hours under a nitrogen atmosphere. At the end of the reaction, a small amount of 2- (3,5-dimethylphenyl) -3,3-bis (4-hydroxyphenyl) isoindoline-1 was added in order to ensure end- -One. ≪ / RTI > After cooling the reaction mixture to room temperature and dissolved in DMF (15cm ^3), followed by 1: 1 was added to a mixture of ethanol and HCl (500cm ^3). The product was collected by filtration and washed several times with demineralized water. It was then dried in a vacuum at 80 캜 for at least 48 hours to give a hydroxy-terminated oligomer 3 (9.4 g, 83.0%) in white powder.

[Preparation Example 2] Synthesis of F-terminal oligomer (4) having a degree of polymerization of 12

FPS (3.96 g, 15.60 mmol) and potassium carbonate (4.33 g, 31.35 mmol) were added to a 250 cm ³ round bottom equipped with a nitrogen inlet and a Dean-Stark apparatus 2 (two-necked) was added to the DMAc (25cm ³⁾ and toluene (30cm ³⁾ the mixture in the flask. The reaction mixture was heated at 150 < 0 > C for 4 hours and toluene was removed after azeotropic distillation. The temperature was then raised to 170 ° C and then stirred at this temperature for 16 hours under a nitrogen atmosphere. At the end of the reaction time, a small amount of FPS was added to ensure end-capping. The reaction mixture was cooled to room temperature, it was dissolved in DMF (10cm ^3), followed by addition of methanol (500cm ^3). The product was collected by filtration and the remaining inorganic material was removed by washing several times with demineralized water. This was repeated twice and the solids were dried under vacuum at 80 ° C for at least 48 hours. F-terminal oligomer 4 (7.8 g, 86.6%) in white powder was obtained.

[Preparation Example 3] Synthesis of poly (arylene ether sulfone) (PES) block copolymer (5)

The OH-terminal oligomer 3 (4.0 g, 0.49 mmol) and the F-terminal oligomer 4 (3.40 g, 0.49 mmol) were placed in a 250 cm ³ round bottom equipped with a Dean- Stark apparatus and a nitrogen inlet Was mixed with potassium carbonate (0.15 g, 1.04 mmol) in a two-necked flask. DMAc (350 cm ³ ) and toluene (30 cm ³ ) were added and the reaction mixture was heated at 150 ° C to essentially remove water by azeotropic distillation. After 4 hours, the toluene was removed and the temperature of the reaction mixture was raised to 170 占 폚. It was then stirred at this temperature for 18 hours under a nitrogen atmosphere. After this time, the mixture was cooled to room temperature and dissolved in DMF (20 cm ³ ). The reaction mixture was separated by precipitating in methanol (700 cm ³ ) and precipitating. The product (block copolymer) was washed several times with demineralized water to remove residual minerals. The resulting solid was dried at 80 캜 under vacuum for 48 hours to obtain a multi-block copolymer (5) (6.8 g, 91.8%) as a white bead.

[Production Example 4] Synthesis of bromine-substituted PES copolymer (Br-PES, 2)

In a 500 cm ³ two-necked flask equipped with a magnetic stirrer, a nitrogen inlet and a condenser, the block copolymer (5) (6.5 g, 0.43 mmol) was completely dissolved in 1,1,2,2-tetrachloroethane To dissolve. To avoid side reactions, a small amount of a brominating agent, N-bromosuccinimide (NBS, 3.03 g, 17.06 mmol) and an initiator, benzoyl peroxide (BPO) catalyst, was added. The reaction mixture was further heated at 85 [deg.] C for 8 hours. After cooling to room temperature, the solution was precipitated in methanol (750 cm ³ ) and the solid was collected by filtration. Finally, the solid was washed with water and dried in a vacuum at 80 ° C for at least 24 hours to give a bromine-substituted PES copolymer (2) (6.0 g, 82%) as a yellow solid.

[Preparation Example 5] Synthesis of bisimidazolium-based crosslinked PES (BI-cPES) separator (1)

A method of producing AEM in which quaternization and crosslinking are simultaneously performed is as follows. (0.41 mmol) of a bromine-substituted PES copolymer (Br-PES, 2) (4.0 g) dissolved in 8.0 cm ³ of dry DMF was added to the solution to prepare a homogeneous solution. Lt; / RTI > The solution was then filtered through a plug of cotton and the filtered solution was poured onto a glass plate and dried in an oven at 80 ° C for 12 hours. Next, the film was dried in an oven at 80 DEG C for 8 hours to evaporate the remaining solvent. The film thickness was adjusted using a doctor blade. The membrane was peeled off by immersion in demineralized water and the membrane produced to obtain an OH ^- form membrane was immersed in 1M NaOH in a sealed container at room temperature for 48 hours. Finally, the obtained membrane was immersed in demineralized water for 48 hours and then used to measure the physical properties.

[Examples 1 to 3]

Using the methods of Preparations 1 to 5, the Br-PES (2) according to Preparation Example 4 and the bisimidazole of three different alkyl chains, namely, bisimidazole having butyl, hexyl and decyl groups Bis-imidazolium-based crosslinked PES membranes (BI-cPESs, 1) according to Preparation Example 5 were prepared by reacting 2.0 equivalents of a polyisocyanate (BI-4, BI-6 and BI-10) . During the drying process, the reactive benzyl bromide group in polymer (2) reacts with a bisimidazole group having BI-4, BI-6 and BI-10 to form a bisimidazolium bridged PES membrane having three different alkyl chains (BI-cPESs). (BI-cPES-4), Example 2 (BI-cPES-6) and Example 3 (BI-cPES-10), respectively. Then, these separators were immersed in sodium hydroxide to prepare a bisimidazolium-based crosslinked separator (BI-cPESs), which is a transparent and flexible separator having a hydroxide counter anion. The thickness of the membrane was adjusted to 40 mm. The bisimidazolium group functions simultaneously as a crosslinking agent and an ionic conductor.

The properties of the crosslinked polymer membranes according to Examples 1 to 3 were measured through the following experimental examples and their characteristics were described below.

[Experimental Example 1: Compound analysis]

^One H-NMR spectrum

(400 MHz) device using d ₆ -DMSO or CDCI ₃ as a reference or internal deuterium lock.

FT-IR spectrum

And recorded on a Nicolet MAGNA 560-FTIR spectrometer.

Molar mass

Or by Gel Permeation Chromatography (GPC) using two mixed C columns of PL Gel 30 cm x 5 mu m at 30 [deg.] C operating in DFM, as determined by ¹ H NMR spectroscopy , And then adjusted for polystyrene ( M _n = 600-10 ⁶ g / mol) standard using a Knauer refractive index detector.

The x-ray diffraction pattern of the dried film

Using a Rigaku HR-XRD Smart Rap diffraction device, the scan speed was 0.1 ㅀ / min (0.1 ㅀ / min) within the range of 0 ㅀ to 1.5 2 using a Cu-Kα X-ray (λ = 1.54 Å) lost. The dried film was measured after standing at 80 캜 for 24 hours under vacuum.

Tapping mode Atomic Force Microscopy (AFM)

Tapping mode AFM was performed using a Bruker MultiMode device. Samples at room temperature were imaged using a silicon cantilever with an end radius exceeding 10 nm and a force constant of 40 N / m (NCHR, nanosensor, f = 300 kHz). And equilibrated to 50% relative humidity for 24 hours. The measurements were performed under the same conditions for each sample to maintain consistency.

Thermal Stability of Hydroxyform Membrane

The nitrogen flow was analyzed by thermogravimetric measurements on a Shimadzu TGA-2950 instrument at a heating rate of 10 ° C min ^-1 .

Tensile Properties

Measured with a bench top tensile tester on a Shimadzu EZ-TEST E2-L instrument at a crosshead speed of 50% relative humidity and 1 mm / min at 25 占 폚. The membrane has a thickness of 40 to 50 탆.

Engineering stress and Young's modulus (E)

The nominal stress was calculated from the initial cross-section of the specimen and the Young's modulus (elongation modulus) (E) was measured from the initial slope of the stress-strain curve. The membrane samples were cut into rectangular shapes of 80 mm x 8 mm (total) and 80 mm x 3 mm (test area).

[Experimental Example 2: Ion exchange capacity (IEC) measurement]

The ion exchange capacity (IEC) of the anion exchange membrane (AEM) is determined by the back titration method. 0.03 g of each of the membrane samples of Examples 1 to 3 and Comparative Example is equilibrated with 35 cm ³ of 0.01 M HCl solution for 48 hours and then reversed with 0.01 M NaOH standard solution with phenolphthalein as indicator. The experimental IEC value is calculated using the following equation (1).

(1)

IEC (meq / g) = ( V _{0 NaOH} C _{NaOH -} V _{X NaOH} C _NaOH ) / W _dry

Where V _{0 NaOH} and V _{x NaOH} are the volume of NaOH consumed in the titration and titration respectively, C _NaOH is the molar concentration of NaOH titrated with oxalic acid standard solution, and W _dry is the weight of the dried membrane. Three measurements were made for each sample, and the IEC was calculated by the average of the three measured values. The theoretical IEC was calculated as the product of the total molar mass of one block copolymer and the degree of functionalization.

[Experimental Example 3: Total water absorption (WU,%) measurement]

WU of the anion exchange membrane (AEM) is immersed in demineralized water for at least 24 hours, then wiped with filter paper and weighed immediately ( W _wet ), then dried under vacuum until a constant weight of the membrane ( W _dry ) is obtained. The water absorption of the membrane was calculated using the following equation (2), and the average value of the moisture absorption was measured three times.

(2)

WU (%) = [( W _wet - W _dry ) / W _dry ]

Where W _wet and W _dry are the weights of the wet film and the dry film, respectively.

[Experimental Example 4: Measurement of dimensional change]

The dimensional change of the film was evaluated by measuring the swelling ratio of the film irradiated by immersing the round-shaped film at room temperature and water at 80 ° C, respectively, and using the following equation (3) The change was calculated, and after three measurements, the average value was calculated.

(3)

Δ t (%) = [( t - t _dry ) / t _dry ] × 100

Where t _dry is the thickness of the dried film and t is the thickness of the film immersed in water for 24 hours. The dried membrane was prepared by allowing it to stand in a vacuum of 60 캜 for 24 hours before measurement.

[Experimental Example 5: OH ^- Conductivity Measurement]

Hydroxide ion conductivity (?) In the plane direction of each of the membranes of the examples 1 to 3 and the comparative example (size in the aqueous solution: 1 cm x 4 cm) is calculated using the following equation (4).

(4)

σ = 1 / RA

Here, 1 denotes the distance between the reference electrodes, A denotes the cross-sectional area of the film sample, and R denotes the resistance. The ohmic resistor (R) is a two-point probe alternating current using an electrode system connected to an impedance / gain-face analyzer (SI-1260) and an electrochemical interface (SI-1287) It is measured by impedance spectroscopy. Conductivity in aqueous solutions is measured in the temperature range of 20-80 ° C. To minimize the formation of unwanted carbonates, the cell is fully immersed in de-gassed de-gassed and the impedance spectrum is collected quickly. Conductivity values are measured at least three times in the same time interval and are averaged.

[Experimental Example 6: Evaluation of Chemical Stability]

The chemical stability of the membrane was evaluated by immersing the OH ^- form membrane in stirred 2M NaOH solution at 60 ° C for at least 500 hours to measure ionic conductivity, IEC and IR spectral changes. Before measurement, each membrane is washed two or three times with demineralized water and soaked in demineralized water for at least 48 hours at room temperature to remove free NaOH in the membrane. The ionic conductivity of each membrane is determined in 20 ° C deionized water.

The properties of the alkylbisimidazolium-based crosslinked anion exchange membrane having a comb structure according to an embodiment of the present invention will be described based on the values measured by the above-described experimental examples.

Synthesis of bromine-substituted PES copolymer (Br-PES, 2) (precursor polymer) of poly (arylene ether sulfone) (PES) block copolymer (5)

Phenolphthalein (PP) was reacted with 3,5-dimethylaniline (DMA) to prepare a carbodiimide biphenol monomer having dibenzyl functional groups (S1 in Scheme 1 below). This cationic monomer separates the reactive benzylic site from which the ionic conductor is to be introduced from the polymer backbone and provides two reactive sites for the bisimidazolium group. As in Scheme 2, the OH-terminal oligomer (3) and the F-terminal oligomer (4) were each polymerized at a degree of polymerization of 12, as described in AHN Rao, H.-J. Kim, S. Nam and T.-H. Kim, Polymer , 2013, 54, 6918-6928. These macromonomers were polymerized to prepare a poly (arylene ether sulfone) (PES) block copolymer (5) having a multi-block structure with a high molecular weight ( M _n > 124 kDa).

The chemical structure of the PES block copolymer (5) was specified by ¹ H NMR spectrum (FIG. 3) with reference to the spectrum of the two starting oligomers (3 and 4) (FIG. 2).

The bromination of ArCH ₃ (1.5 equivalents of NBS) was carried out in tetrachloroethane of polymer (5) to produce bromobenzylated PES (Br-PES, 2). The comparative spectroscopic method of ¹ H NMR of polymers (5 and 2) showed that the degree of bromination in polymer (2) was 74% (FIG. 3). This is the result measured from the integral ratio of bromobenzyl protons (H ₂₆ ) of the polymer (5) to the benzyl protons (H ₂₀ ) of the polymer (2) (FIG.

(Scheme 1)

(Scheme 2)

Formation of bisimidazolium-based crosslinked separator (BI-cPESs, 1) having a comb structure

The crosslinked type separator is not soluble in organic solvents such as DMF, NMP, DMAc and DMSO, and it can be seen that a crosslinked network is successfully formed by using such properties. The gel fraction, an indirect measure of crosslink density, was very high (92%) in all three crosslinked BI-cPES-10, BI-cPES-6 and BI-cPES-4 membranes (see Table 1).

The structure of the crosslinked separator was further confirmed by comparing the FT-IR spectra of the Br-PES (2) and the crosslinked BI-cPES separator (1) (FIG. 4). The peak at 653 cm ^-1 corresponding to the C-Br stretching vibration of Br-PES (2) disappeared, and a characteristic peak at 1590 cm ^-1 and 758 cm ^-1 appears, which is due to the vibration mode of the imidazolium cation , Indicating a successful binding of the imidazolium group.

[Table 1] Solubility and gel fraction of Br-PES (2) and crosslinked BI-cPES membrane (1)

(BI-cPESs, 1) having a comb structure in the form of a bisimidazolium-based crosslinked separator

Morphological analysis of bisimidazolium type crosslinked membranes (1) was performed by Atomic Force Microscopy (AFM) and X-ray small angular scattering (SAXS). Tapping mode AFM images showed that phase separation occurred between hydrophilic and hydrophobic blocks in all three bridging BI-cPES-10, BI-cPES-6 and BI-cPES-4 membranes. However, phase separation occurred significantly in BI-cPES-10 membranes with long alkyl chains compared to BI-cPES-4 and BI-cPES-6 membranes. The AFM images of BI-cPES-10 had wider hydrophobic channels while the AFM images of BI-cPES-4 and BI-cPES-6 showed narrower channels (Figure 5 and Table 2)

[Table 2] SAXS and AFM data of crosslinked BI-cPES separator

The SAXS result is plotted as a function of the scattering vector q , plotted in FIG. 6 (see FIG. 6). A clear ionomeric peak for BI-cPES-6 and BI-cPES-10 (Examples 2 and 3) with a relatively long alkyl chain at 0.02 A- ¹ was observed in the SAXS profile, . Conversely, much broader peaks at higher q values represent BI-cPES-4 (Example 1) with very short alkyl chains, which means that phase separation in this polymer is less clear. D values which are interdomain spacings are much larger in Example 2 (BI-cPES-6) and Example 3 (BI-cPES-10) than in Example 1 (BI-cPES-4) (See Table 2). Although the comb structure of BI-cPES-6 is less clear, the comb structure of these crosslinked polymers (BI-cPES-6 and BI-cPES-10) appears to be due to their large d value. The d value of the AEM disclosed in other documents is much smaller than the above polymers and corresponds to 17 nm, which is the value obtained in BI-cPES-4 (Example 1).

SAXS and AFM analysis is believed to result in phase separation between hydrophilic and hydrophobic aggregates to form ion clusters promoted by long alkyl chains between the bisulphite crosslinkers. As can be seen below, the self-agglomerated form of a comb-shaped BI-cPES structure with a long alkyl chain (ie BI-cPES-10) has a strong influence on conductivity and dimensional stability. Also, SAXS and AFM analysis show that the ionic conductive pathway is more interconnected as the length of the alkyl chain between two imidazole crosslinkers increases. Therefore, the larger the ionic conductivity, the higher expected bis-imidazolium-bridged PES separator (BI-cPES-10> BI-cPES-6> BI-cPES-4) with longer alkyl chains.

Ion Exchange Capacity (IEC) and Hydroxide Conductivity

The ion exchange capacity (IEC), measured in meq / g, is an important parameter that determines the performance of AEM and provides information on the ionic conductivity site density in the membrane. The IEC of bis-imidazolium-based crosslinked BI-cPES membranes was measured using an acid-base titration method and ranged from 1.13 to 1.20 meq / g (see Table 3). The IEC value decreased due to the enhanced hydrophobicity due to the longer alkyl chain length of the bisimidazolium cation. Example 3 (BI-cPES-10) showed the lowest IEC value (1.13 meq / g).

[Table 3] IEC, Conductivity, Apparent Activation Energy ( E _a ) of BI-cPES Membrane

Hydroxide conductivities of BI-cPES membranes (BI-cPESs) were measured in water at 20-80 캜 (see Table 3). Example 3 (BI-cPES-10) with the longest alkyl chain exhibited a high conductivity of 0.027 S / cm at 20 DEG C with an IEC of 1.13 meg / g. This conductivity is much higher than the value measured in conventional AEM membranes (AEMs) and higher than the highest IEC measured for crosslinked AEMs. Unlike in most crosslinked systems where crosslinking occurs through a hydrophobic network that dilutes conductive groups, the crosslinked polymers described herein are bound by a bisimidazolium group that also acts as an ionic conductor. Therefore, crosslinking did not reduce the membrane conductivity.

The interconnected nanotube channel formed by the phase separation between hydrophilic and hydrophobic aggregates with a comb structure has further improved conductivity in long alkyl chain crosslinked membranes even at low IEC values. As can be seen from both SAXS and AFM, BI-cPES-10 formed the largest ion channel and showed that this membrane had the highest conductivity.

In addition, the conductivity of the crosslinked BI-cPES separator showed the Arrhenius type behavior with high temperature dependency (FIG. 7 and Table 3). All three crosslinked BI-cPES membranes exhibited a conductivity of greater than 0.06 S / cm at 80 ° C, which is greater than the conductivity of a typical AEM with similar IECs. The apparent activation energy (ΔE _a ) of the hydroxylation conduction estimated from the slope of the Arrhenius plot was calculated from the activation energy (17.1 kJ / mol) of Example 3 (BI-cPES-10) (23.8 kJ / mol) of Example 1 (BI-cPES-4) and the activation energy (21.8 kJ / mol) of BI-cPES-6. These results indicate that the percolation threshold of the ion channel to which the hydroxide ion can be delivered is achieved in a polymer (BI-cPES-10) having a complex structure with long alkyl chains self-aggregating to form a conductive channel . The conductivity difference between BI-cPES-4 and BI-cPES-6 at all measured temperatures is actually less than the conductivity difference between BI-cPES-6 and BI-cPES-10 (Table 3).

Water Absorption and Dimensional Stability

In most of the anion exchange membranes (AEM), the water absorption by the membrane is closely related to the hydroxide conductance because the water molecule acts as a transmitter for anion transport. However, excessive water absorption causes severe swelling, which makes the separator mechanically very weak to apply the anion exchange membrane. The water absorption of the crosslinked BI-cPES membranes was measured at temperatures of 20 ° C and 80 ° C (see Table 4). As expected, cross-linking efficiently inhibited swelling and even at 80 ° C the water uptake of all crosslinked BI-cPES membranes was very small (<12%). This indicates that the membrane is flexible even in water at high temperatures. The least water uptake was confirmed in BI-cPES-10, which forms a self-aggregating structure that interferes with water absorption.

In the field of fuel cells, water absorption (WU) and conductivity ( σ ) are particularly important. A bismimidazolium-based crosslinked BI-cPES-10 membrane (Example 3) of the comb structure having an extremely low conductivity with very low moisture absorption provides an ideal membrane in the AEMFC field.

Examining the dimensional stability of the crosslinked BI-cPES membranes, all crosslinked BI-cPES membranes showed very low swelling as expected (see Table 4). Increasing the alkyl chain length of the bisimidazolium cation The swelling phenomenon could be reduced. The least swelling occurred in the BI-cPES-10 membrane (Example 3) due to the combined effect of the crosslinked three-dimensional network and the self-aggregated structure formed by the comb-shaped polymer.

[Table 4] Moisture Absorption and Dimensional Stability of Crosslinked BI-cPES Membrane

Thermal Stability and Mechanical Stability

The thermal stability of the crosslinked BI-cPES membranes in the hydroxide form was investigated by TGA (see FIG. 8). The initial weight loss of the membrane of less than 3% corresponds to the evaporation of the solvent of hydrated water and balance. Step weight loss for all three crosslinked membranes. The first weight loss between 340 and 450 ° C corresponds to the loss of the imidazolium group. The second stage of weight loss from 470 ° C corresponds to the degradation of the polymer side chain and backbone. The bis-imidazolium-based crosslinked BI-cPES membranes showed higher thermal stability than conventional crosslinked quaternary ammonium or quaternary guanidinium cations. The high thermal stability is a desirable property for AEM fuel cells to reduce the thermodynamic voltage loss caused by the pH value difference of the separator. These results indicate that the introduction of alkyl bisimidazole as a crosslinking agent enhances thermal stability and maintains high rigidity of the polymer backbone.

Mechanical properties are essential parameters for fabricating AEMFC membrane electrode assemblies. The mechanical properties of the crosslinked BI-cPES membranes were measured at 50% relative humidity (see Table 5 and Figure 9). The bis-imidazolium-based crosslinked BI-cPES membranes exhibited high Young's modulus in the range of 2.1 - 3.9 GPa. The Young's modulus increases with the alkyl chain length between the two imidazolium groups. (BI-cPES-6) of Example 2 (BI-cPES-6) and 2.1 GPa of Example 1 (BI-cPES-4) at 3.9 GPa in BI-cPES-10 Respectively. This shows enhanced mechanical properties due to the self-aggregating structure in the polymer separator (BI-cPES-10) having a cross-linked comb structure.

[Table 5] UTM data of crosslinked BI-cPES membrane

Chemical stability

In addition to the excellent thermal, mechanical and dimensional stability, the long-term tolerance of the crosslinked BI-cPES membranes in alkaline solutions was investigated by comparing the IEC with the conductivity before and after immersing the membrane in 2M NaOH at 60 ° C for 350 hours 10). Conductivity changes were measured every 20 hours at 20 ° C. Both of the crosslinked BI-cPES membranes according to Examples 1 to 3 exhibited a slight decrease in their initial conductivity after heat treatment in the basic state. After 200 hours, a slight change in IEC and conductivity was observed, but no significant change in conductivity was observed until 200 hours (see FIG. 10 and Table 6). The alkali stability of such crosslinked BI-cPES membranes is much higher than typical AEM. Because a typical AEM is generally unstable in a concentrated basic solution at the same temperature as in this experiment.

Table 6 Conductivity and IEC of crosslinked BI-cPES membranes before and after immersing in 2M NaOH at 60 ° C for 350 hours

Further, by comparing the IR spectra before and after exposure to the heat treatment under the basic conditions in order to investigate the decomposition of the bisimidazolium group and the polymer main chain, the crosslinked BI-cPES separator (BI-cPES-4, BI-cPEs-6 and BI-cPES-10) were structurally analyzed. As can be seen in Fig. 11, no significant change in these membranes was observed in the IR spectrum. The characteristic peaks at 1590 cm ^-1 and 758 cm ^-1 corresponding to the imidazolium groups and the characteristic peaks at 1319 and 1151 cm ^-1 corresponding to the sulfonic polymer backbone remained the same. Therefore, it can be seen that the structural integrity of the crosslinked BI-cPES separator is maintained under harsh alkaline conditions, which means excellent chemical stability.

In this specification, alkyl bisimidazolium bridged poly (arylene ether sulfone) block copolymers having different C ₄ -C ₁₀ alkyl chains have been synthesized as novel anion exchange membranes. Also, the alkylbisimidazolium group used in the present specification is characterized in that it simultaneously functions as an ionic conductor as well as a crosslinking agent for the first time. The bis-imidazolium-based crosslinked BI-cPES separator is superior to conventional AEM in performance and belongs to several crosslinked separators having high conductivity and excellent dimensional stability. Particularly, the separation membrane according to Example 3 (BI-cPES-10) of the present invention formed a self-aggregated structure by introducing a long pendant hydrophobic side chain, and thus it was found that the separation membrane was composed of a comb-structure. The bridged comb-structure system achieved high conductivity even at low IEC values and low moisture uptake. Also, the combination of the long chain of the comb structure with the crosslinking network indicates that the separator according to Example 3 (BI-cPES-10) of the present invention is a promising membrane as an electrode of an AEM fuel cell.

It is to be understood that the present invention is not limited to the above embodiments and various changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention.

Claims (10)

An alkylbisimidazolium-based crosslinked anion exchange membrane having a comb structure, which is produced by combining a main chain and a side chain polymer which simultaneously functions as a crosslinking agent and an ion conductor, and has a comb-shape structure. The method according to claim 1,
Characterized in that the main chain consists of at least one of poly (arylene sulfone), poly (arylene ketone), poly (imide), poly (amide) Zolium type crosslinked anion exchange membrane. The method according to claim 1,
Wherein the side chain polymer is an alkylbisimidazole. 2. The alkylbisimidazolium-based crosslinking type anion exchange membrane according to claim 1, wherein the side chain polymer is an alkylbisimidazole. The method of claim 3,
The alkylbisimidazolium-based crosslinking type anion exchange membrane having a comb structure, wherein the alkyl group of the side chain polymer has 4 to 10 carbon atoms. 5. The method of claim 4,
Wherein the main chain is composed of poly (arylene sulfone), and the side chain polymer is composed of bisimidazole having 10 carbon atoms. 6. The method of claim 5,
Wherein the poly (arylene sulfone) is produced by polymerizing an OH-terminal oligomer and an F-terminal oligomer as poly (arylene ether sulfone), wherein the poly (arylene sulfone) is a poly (arylene ether sulfone). The method according to claim 6,
Wherein the OH-terminal oligomer and the F-terminal oligomer have a degree of polymerization of 12, and the alkylbisimidazolium-based crosslinking type anion exchange membrane having a comb structure. The method according to claim 1,
Wherein the anion exchange membrane has a thickness of 40 to 50 占 퐉. The alkylbisimidazolium-based cross-linkable anion exchange membrane having a comb structure. 9. The method according to any one of claims 1 to 8,
The anion exchange membrane has an Ion Exchange Capacity (IEC) of 1.13 to 1.20 meg / g, which is calculated by the following Equation 1,
(1)
IEC (meq / g) = ( V _{0 NaOH} C _NaOH - V _{X NaOH} C _NaOH ) / W _dry
Where V _{0 NaOH} and V _{x NaOH} are the volumes of NaOH consumed in the titration and titration respectively, C _NaOH is the molar concentration of NaOH titrated with oxalic acid standard solution, and W _dry is the weight of the dried membrane An alkylbisimidazolium-based cross-linkable anion exchange membrane having a comb structure. 9. The method according to any one of claims 1 to 8,
The anion exchange membrane preferably has a hydroxide ion conductivity (sigma) of 0.012 S / cm or more at 20 占 폚 and not less than 0.060 S / cm at 80 占 폚,
(2)
σ = 1 / RA
Here, l is the distance between the reference electrodes, A is the cross-sectional area of the film sample, and R is a resistance. The alkylbisimidazolium-based crosslinking type anion exchange membrane having a comb structure.

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