Description

MONOMER FOR PROTON- CONDUCTING POLYMER HAVING ACID GROUP IN SIDE CHAIN THEREOF, PROTON- CONDUCTING POLYMER PREPARED USING THE MONOMER, METHOD OF PREPARING THE PROTON- CONDUCTING POLYMER, ELECTROLYTE MEMBRANE COMPRISING THE PROTON- CONDUCTING POLYMER, AND MEMBRANE-ELECTRODE ASSEMBLY INCLUDING THE

ELECTROLYTE

Technical Field

[1] The present invention relates to a monomer for a proton-conducting polymer, a proton-conducting polymer prepared using the monomer, a method of preparing the proton-conducting polymer, an electrolyte membrane comprising the proton- conducting polymer, and a membrane-electrode assembly including the electrolyte membrane, and more particularly, to a monomer for a proton-conducting polymer, which is used to prepare an electrolyte membrane having excellent structural stability and excellent capability of inhibiting methanol crossover, a proton-conducting polymer prepared using the monomer, a method of preparing the proton-conducting polymer, an electrolyte membrane comprising the proton-conducting polymer, and a membrane- electrode assembly including the electrolyte membrane. Background Art

[2] Polymer electrolyte membrane fuel cells (PEMFCs) are a type of fuel cells which use a polymer membrane having proton exchange properties as an electrolyte, and are classified into various types, such as, solid polymer electrolyte fuel cells (SPEFCs), or proton exchange membrane fuel cells (PEMFCs). Compared with other types of fuel cells, polymer electrolyte membrane fuel cells (PEMFCs) have a low operating temperature of about 80 ⁰ C , high efficiency, high current density and power density, short start-up time, and quick response characteristics according to load changes. In particular, since PEMFCs use a polymer membrane as an electrolyte, there is no corrosion and no need for pH adjustment, and the polymer membrane is less sensitive to a change in the pressure of reactive gases. In addition, these fuel cells are advantageous due to their simple design, ease of manufacturing, and a wide range of

outputs, and thus can be applied to many fields, such as power sources for clean vehicles, on-site power generation, power sources for portable devices, and power sources for military devices.

[3] Such a fuel cell includes a stack which substantially generates electricity, the stack having a structure in which several to tens of unit cells, each having a membrane- electrode assembly (MEA) and separators (also referred to as 'bipolar plates'), are stacked. The MEA is composed of an anode (referred to also as a 'fuel electrode' or an 'oxidation electrode') and a cathode (referred to also as an 'air electrode' or a 'reduction electrode') that are separated by a proton conducting polymer electrolyte membrane.

[4] A principle of generating electricity in a fuel cell is as follows. A fuel is supplied to an anode as a fuel electrode, and absorbed in a catalyst at the anode, and the fuel is oxidized to produce protons and electrons. The electrons are transferred to a cathode as an oxidation electrode, via an external circuit, and the protons are transferred to the cathode through a polymer electrolyte membrane. An oxidant is supplied to the cathode, and the oxidant, protons, and electrons are reacted on a catalyst at the cathode to produce electricity along with water.

[5] Characteristics of proton exchange membranes are represented as ion exchange capacity (IEC) or equivalent weight (EW), and properties required for a proton exchange membrane used as an electrolyte membrane for a fuel cell are high proton conductivity and mechanical strength, low gas transmission, and transfer of water. The proton conductivity of the proton exchange membrane is rapidly decreased with dehydration, and thus resistance to dehydration is required. Electrolyte membranes require high resistance to oxidation and reduction reactions and hydrolysis that occur in the electrolyte membrane, good binding with cations, and homogeneity. Such properties should be maintained for a constant time period. In addition to satisfying all the conditions described above, there is a need to develop an inexpensive and environmentally-friendly preparation method in order to commercialize electrolyte membranes.

[6] A polyimide-based polymer electrolyte, a sulfonated polyimide (S-PI) membrane, is obtained by condensation of diamine having a sulfonic acid group and dianhydride. The obtained S-PI membrane has 3 times lower hydrogen gas transmission than that of Nafion 117 and cell performance similar to that of Nafion, whereas lifetime stability of the S-PI membrane is about 3000 hours. This is because chains are disconnected by hydrolysis, thereby decreasing mechanical strength.

[7] Polysulfones are polymers in which phenyl rings are linked alternately by an ether

group and a sulfone (-SO ₂ -) group, and are commercially available as poly(arylether sulfone), polysulfone (PSU, Product name: Udel), and polyethersulfone (PES, Product name: Victrex). Even if a degree of sulfonation of sulfonated PSU (S-PSU) is about 30%, the polymer is dissolved in water, and thus a possibility of a use as a fuel cell is low. A sulfonated PES (S-PES) polymer membrane is very stable in water, but the membrane needs to have a high degree of sulfonation in order to increase ionic conductivity. However, the higher the degree of sulfonation, the weaker the mechanical strength of the electrolyte membrane. When the S-PES has a degree of sulfonation of 90% or greater, the conductivity of the S-PES is similar to that of Nafion. In this case, about 400% of swelling occurs, and thus mechanical strength is very low. To address the problem, if an activated sulfonic acid group is appropriately cross-linked thereto, the swelling can be reduced to about 50%. However, ionic conductivity is also decreased in this case.

[8] Polyetherketones are polymers in which phenyl groups are linked by ether and carbonyl groups. The most commonly-used polyetherketone is polyetheretherketone (PEEK) known as Victrex PEEK. Sulfonated polyarylene is well known as a commonly-used proton-conducting material.

[9] Such sulfonated polymers are obtained by polymerizing a general aromatic compound to prepare a polymer, and then reacting the resultant polymer with a sulfonating agent to introduce a sulfonic acid group. However, since a large amount of the sulfonating agent, such as concentrated sulfuric acid or funing sulfuric acid is used in the introduction of the sulfonic acid group, it is very dangerous when the sulfonated polymers are prepared, there is limitation on materials of a plant, and it may not be easy to control the amount and position of introduction of the sulfonic acid group to polymers.

Disclosure of Invention Technical Problem

[10] The present invention provides a monomer for preparing a proton-conducting polymer having an acid group in a side chain.

[11] The present invention also provides a proton-conducting polymer prepared using the monomer.

[12] The present invention also provides a method of preparing the proton-conducting polymer.

[13] The present invention also provides an electrolyte membrane comprising the proton- conducing polymer.

[14] The present invention also provides a membrane-electrode assembly including the electrolyte membrane comprising the proton-conducting polymer. Technical Solution

[15] According to an aspect of the present invention, there is provided a compound represented by Formula 1 below:

[16] <Formula 1>

CZ ₂ ) _q -A

[18] wherein R ₁ is each independently a C ₁ -C ₁₀ alkyl group, a C ₂ -C ₁₀ alkenyl group, or a phenyl group;

[19] p is an integer in the range of 0 to 4;

[20] B is halogen, hydroxyl, or amine;

[21] Y is a bivalent linker comprising at least one of C _! -C ₁₀ alkyl and C ₆ -C ₂₀ aryl;

[22] Z is hydrogen or fluorine;

[23] q is an integer in the range of 1 to 10; and

[24] A is an acid group that can have a proton, and is one selected from a sulfonic acid, sulfonate, a phosphoric acid, and sulfonyl(trifluoro methylsulfonyl). [25] A of Formula 1 may be a sulfonic acid or a sulfonate.

[26] Y of Formula 1 may be one selected from the groups represented by the following formulae: [27]

[28] According to another aspect of the present invention, there is provided a proton- conducting polymer comprising a repeating unit represented by Formula 2 below:

[29] <Formula 2>

[31] wherein R ₁ is each independently a Ci-Ci ₀ alkyl group, a C ₂ -Ci ₀ alkenyl group, or a phenyl group;

[32] p is an integer in the range of 0 to 4; [33] Y is a bivalent linker comprising at least one of C i-Ci ₀ alkyl and C ₆ -C ₂₀ aryl; [34] Z is hydrogen or fluorine; [35] q is an integer in the range of 1 to 10; [36] A is an acid group that can have a proton, and is one selected from a sulfonic acid, sulfonate, a phosphoric acid, and sulfonyl(trifluoro methylsulfonyl);

[37] m+n=l, 0<m<l, and 0<n<l; and [38] wherein the proton-conducting polymer has a nunber average molecular weight of about 5,000 to about 1,000,000.

[39] The repeating unit of Formula 2 may be represented by Formula 3 below: [40] <Formula 3>

[42] A in Formula 2 may be a sulfonic acid or a sulfonate. [43] Y in Formula 2 may be one selected from the groups represented by the following structures:

[44]

[45] According to another aspect of the present invention, there is provided a method of preparing the proton-conducting polymer according to claim 4, comprising etheri- fication of compounds represented by Formulae 4 through 6.

[46] <Formula 4>

₂ ) _q -A

[48] <Formula 5>

[50] <Formula 6>

[52] wherein X is chloro, bromo, iodine, or fluoro, and [53] R ₁ , A, Y, Z, p, and q are defined as above. [54] According to another aspect of the present invention, there is provided an electrolyte membrane comprising the proton-conducting polymer of Formula 2.

[55] The electrolyte membrane may further comprise at least one polymer selected from the group consisting of polyimide, polyetherketone, polysulfone, polyethersulfone, polyetherethersulfone, polybenzimidazole, polyphenylene oxide, poly- phenylenesulfide, polystyrene, polytrifluorostyrene sulfonic acid, polystyrene sulfonic acid, polyurethane, and a branched sulfonated poly(sulfone-ketone) copolymer.

[56] The electrolyte membrane may further comprise at least one inorganic compound selected from the group consisting of silicon oxide (SiO ₂ ), titaniun oxide (TiO ₂ ), an inorganic phosphate, a sulfonated silicon oxide (sulfonated SiO ₂ ), a sulfonated zirconium oxide (sufonated ZrO ₂ ), and a sulfonated zirconium phosphate (sulfonated ZrP).

[57] The electrolyte membrane may further comprise a porous support.

[58] According to another aspect of the present invention, there is provided a membrane- electrode assembly for a fuel cell comprising the electrolyte membrane. Advantageous Effects

[59] A polymer electrolyte membrane prepared using a proton-conducting polymer according to an embodiment of the present invention has excellent structural stability and low methanol crossover, and thus a fuel cell including the polymer electrolyte membrane can be prepared, wherein the fuel cell has excellent performance. Mode for Invention

[60] The present invention will now be described in greater detail.

[61] The present invention provides a proton-conducting polymer that has an acid group introduced into a side chain thereof, thereby having excellent proton conductivity and significantly low methanol permeability.

[62] In general, a proton-conducting polymer that can be used as a high temperature polymer electrolyte, such as polysulfone or polyketone, can be inexpensively prepared and has considerable stability under oxidation/reduction conditions at various ranges of temperature. In addition, in such polymer electrolyte, due to electron donor properties of an ether group, sulfonation of its main chain is easy, and once the sulfonation of the main chain occurs, the polymer electrolyte has appropriate proton conductivity. However, microphase separation into hydrophilic and hydrophobic regions of the polymer of which the main chain is sulfonated is decreased. This is because hydrophobic properties of the polymer are decreased due to the presence of an ether group in the main chain of the polymer and/or acidity of a sulfonyl group is decreased due to the ether group. In addition, the decrease in the microphase separation results in a decrease in ionic conductivity and methanol permeability.

[©] The proton-conducting polymer forms a flexible polymer chain by introducing an acid group to a side chain instead of a main chain, and has a structure in which mi- crophase separation between hydrophilic and hydrophobic regions can be effectively formed. To form such structure, the proton-conducting polymer has a repeating unit represented by Formula 2 below:

[64] <Formula 2>

[66] In Formula 2, benzene rings in a main chain may be respectively substituted with 0-4 R ₁ S where each R ₁ is the same as or different from each other, and may be a C _! -C ₁₀ alkyl group, a C ₂ -C ₁₀ alkenyl group, or a phenyl group. If p=0, that is, if the benzene ring is not substituted with R ₁ in Formula 2, the repeating unit of Formula 2 may be represented by Formula 3 below:

[67] <Formula 3>

[69] In Formula 2, Y constituting a portion of the side chain is a bivalent linker including C ₁ -C ₁₀ alkyl, C ₆ -C ₂₀ aryl, or both of them, and may be one selected from the groups represented by the following structures.

[70]

[71] The linker Y is linked to a linear (CZ ₂ ) _q by an ether bond. As such, the side chain may be further extended, whereby the proton-conducting polymer is more flexible and the microphase separation of the proton-conducing polymer may be increased more. In the formula (CZ ₂ ) _q , q controls the length of the side chain, allowing the proton- conducting polymer to have excellent physical properties, and may be an integer in the range of 1 to 10. Z is hydrogen or fluorine. To increase acidity of an acid group that can have a proton, Z may be fluorine.

[72] In Formula 2, A is an acid group that can have a proton independently, and is selected from sulfonate represented by -SO ₃ H (sulfonic acid) or SO ₃ M where M may be Na or K (sulfonate), a phosphoric acid represented by -OPO ₃ H, and sulfonyl(trifluoro methylsulfonyl). In this regard, A may be the sulfonic acid or sulfonate, because it has a very high acidity and a C-S bond has a strong resistance to oxidation conditions. When a hydrogen ion as a cation is attached to an anion of the sulfonic acid, it constitutes a hydrogen ion exchange membrane. In this regard, when water molecules exist together, the conductivity of the hydrogen ion is maintained higher. In the presence of water molecules, the sulfonic acid group attached to an electrolyte membrane is dissociated into the anion of the sulfonic acid and the hydrogen ion, whereby the hydrogen ion is transferred by concentration gradient or an electric field as in a hydrogen ion in a sulfuric acid electrolyte.

[73] In Formula 2, m and n may be appropriately selected to satisfy the conditions m+n=l, 0<m<l, and 0<n<l in order to allow the prepared proton-conducting polymer

to have desirable physical properties, and may be in the range of 0.1<m/(m+n)<10. [74] The proton-conducting polymer represented by Formula 2 may have a nunber average molecular weight of 5,000 to 1,000,000 in terms of mechanical strength and proton conductivity. [75] The proton-conducting polymer has a flexible polymer chain by introducing an acid group in its side chain, and the microphase separation of the proton-conducting polymer is also effective. An electrolyte membrane comprising the proton-conducting polymer has high proton conductivity and significantly low methanol permeability. [76] The proton-conducting polymer may be prepared using a compound represented by

Formula 1 below: [77] <Formula 1>

[79] wherein R ₁ is each independently a Ci-Ci ₀ alkyl group, a C ₂ -Ci ₀ alkenyl group, or a phenyl group;

[80] p is an integer in the range of 0 to 4;

[81] B is halogen, hydroxyl, or amine;

[82] Y is a bivalent linker including at least one of Ci-Ci ₀ alkyl and C ₆ -C ₂₀ aryl;

[83] Z is hydrogen or fluorine;

[84] q is an integer in the range of 1 to 10; and

[85] A is an acid group that can have a proton, and is one selected from a sulfonic acid, sulfonate, a phosphoric acid, and sulfonyl(trifluoro methylsulfonyl). [86] In the proton-conducting polymer prepared using the compound of Formula 1, the substituent B is linked to a main chain of the proton-conducting polymer and the acid group A that can have a proton is included in a side chain of the proton-conducting polymer. [87] The compound of Formula 1 may be a compound represented by Formula 4 below in terms of copolymerizability: [88] <Formula 4>

[89]

₂ ) _q -A

[90] In Formula 1, when B is halogen, such as fluoro, chloro, bromo, or iodine, the compound of Formula 1 is substituted with a hydroxyl group using a known method to prepare the compound of Formula 4.

[91] The proton-conducting polymer may be prepared by etherification represented by Reaction Scheme 1 below, but this method is only an exemplary embodiment for preparing the proton-conducting polymer and the preparation method is not limited thereto:

[92] <Reaction Scheme 1>

Z ₂ ) _q -A n Formula 4 Formula 5 Formula 6

Formula 2

[94] In Reaction Scheme 1, X in Formula 5 is an activated leaving group, and may be chloro, bromo, or iodine. R _u P, Y, Z, A, m, and n are the same as defined in Formula 2 above.

[95] First, compounds represented by Formulae 4, 5, and 6 above are added to an appropriate organic solvent in a ratio of m:m+n:n, to prepare a mixed solution. The organic solvent may be any solvent that can satisfactorily dissolve reactants and products, and in particular, may be dimethyl sulfoxide (DMSO), N,N'-dimethylacetamide (DMAc), or N^nethyl pyrrolidone (NMP). A hydrocarbon-

based solvent, such as toluene may be further added to the mixed solution, and the organic solvent and the hydrocarbon-based solvent may be mixed in a volume ratio of 3:1. In addition, an alkaline metal carbonate, such as, K ₂ CO ₃ or Na ₂ CO ₃ , as a catalyst may be added to the mixed solution.

[96] The reaction may be performed at a reaction temperature in the range of 100 to 200

⁰ C for 30 minutes to 48 hours in order for the proton-conducting polymer to have a molecular weight in appropriate ranges. The reaction may be performed such that after stirring is performed at 140-150 ⁰ C for 3 to 5 hours, water in the azeotropic distillate is removed using a dean-stark trap, and after all of the water is removed, the reaction mixture is continuously stirred at 170-190 ⁰ C for 6 to 24 hours. During the reaction, water may be removed by adding toluene to the reaction mixture by using an addition funnel, if necessary.

[97] Hereinafter, a proton-conducting polymer electrolyte membrane according to an embodiment of the present invention will be described.

[98] The proton-conducting polymer electrolyte membrane may be prepared by dissolving the proton-conducting polymer described above in an organic solvent to prepare an electrolyte membrane forming composition, and then using a general method, such as a solvent casting method or hot pressing method, to form a proton-conducting polymer electrolyte membrane having a desired thickness. The thickness of the proton- conducting polymer electrolyte membrane may be in the range of about 5 to about 200 μ m. The organic solvent may be a general organic solvent, and in particular, may be the same as the organic solvent used in preparing the proton-conducting polymer described above. The proton-conducting polymer electrolyte membrane cast is dried to remove the solvent therefrom, thereby obtaining a film-type proton-conducting polymer electrolyte membrane. In this regard, the drying process is performed by slowly raising the temperature from room temperature up to 80 ⁰ C , drying for 24 hours at 80 ⁰ C , and then further drying at 110 ⁰ C for 24 hours.

[99] Alternatively, the proton-conducting polymer electrolyte membrane may be prepared by mixing, with an organic solvent, the proton-conducting polymer described above and at least one polymer selected from polyimide, polyetherketone, polysulfone, poly- ethersulfone, polye there thersulf one, polybenzimidazole, polyphenylene oxide, poly- phenylenesulfide, polystyrene, polytrifluorostyrene sulfonic acid, polystyrene sulfonic acid, polyurethane, and branched sulfonated poly(sulfone-ketone) copolymer to prepare a polymer blend composition, and then applying the polymer blend composition to a substrate. In the preparation of the polymer blend composition, the

amount of the proton-conducting polymer may be in the range of about 1 to about 99 parts by weight based on 100 parts by weight of the total weight of the polymer blend composition.

[100] The branched sulfonated poly(sulfone-ketone) copolymer refers to a sulfonated poly- sulfoneketone copolymer including an aromatic sulfone repeating unit, an aromatic ketone repeating unit, and a branch unit, as disclosed in Korean Patent No. 2005-0112185 filed by the present applicant, and the disclosure of which is incorporated herein in its entirety by reference.

[101] In addition, the proton-conducting polymer electrolyte membrane may further include an inorganic compound, in addition to the proton-conducting polymer. The inorganic compound may be an inorganic metal oxide, such as silicon oxide (SiO ₂ ) or titanium oxide (TiO ₂ ); an inorganic phosphate, such as zirconium phosphate (Zr(HPO ₄ ) 2 ^• nH ₂ 0) or phosphotungstic acid (H ₃ PW ₁₂ O ₄ ^• nH ₂ 0); or a sulfonic acid group- substituted inorganic compound, such as a sulfonated silicon oxide (sulfonated SiO ₂ ), a sulfonated zirconiun oxide (sufonated ZrO ₂ ), or a sulfonated zirconiun phosphate (sulfonated ZrP).

[102] In particular, the sulfonic acid group-substituted inorganic compound introduces an acid group, and thus the conductivity of the proton-conducting polymer electrolyte membrane is increased. The inorganic compound to which a sulfonic acid is introduced may be prepared such that ammonia water is dropped on a precursor such as a metal chloride to prepare a colloidal solution of a metal hydride, the colloidal solution thereof is washed and dried, and then a sulfuric acid is added to the resulting particles and the resultant is calcinated at 600 ⁰ C.

[103] The inorganic compound is dispersed in an organic solvent to prepare a dispersion, and then the dispersion is mixed with a proton-conducting polymer dissolved in an organic solvent. The amount of the inorganic compound may be in the range of about 1 to about 99 parts by weight based on 100 parts by weight of the proton-conducting polymer. Next, the resultant composition may be cast on a glass plate using the same method as described above to prepare an organic-inorganic complex electrolyte membrane comprising the proton-conducting polymer and the inorganic compound.

[104] The inorganic compound is dispersed in an organic solvent to prepare a dispersion, and then the dispersion is mixed with a proton-conducting polymer dissolved in an organic solvent. The amount of the inorganic compound may be in the range of about 1 to about 99 parts by weight based on 100 parts by weight of the proton-conducting polymer. Next, the resultant composition may be cast on a glass plate using the same

method as described above to prepare an organic-inorganic complex electrolyte membrane comprising the proton-conducting polymer and the inorganic compound.

[105] In addition, the proton-conducting polymer electrolyte membrane may comprise the proton-conducting polymer and a porous support having a nano-sized particle size. The porous support may include at least one selected from the group consisting of silica, alunina, zirconia, zeolite, and titaniun oxide, and the particle size of the porous support is in the range of about 0.1 to about 300 nm. The proton-conducting polymer electrolyte membrane comprising the porous support may be prepared using an electrolyte membrane forming composition prepared by dissolving a proton- conducting polymer in an organic solvent to form a mixed solution, and then dispersing a porous support in the mixed solution.

[106] A membrane-electrode assembly according to an embodiment of the present invention may be prepared by interposing the proton-conducting polymer electrolyte membrane between a cathode and an anode using a general method.

[107] The present invention will now be described in greater detail with reference to the following examples. The following examples are for illustrative purposes and are not intended to limit the scope of the invention.

[108] Example

[109] <Synthesis Example>

[110] First, Compound 4 is synthesized through Reaction Scheme 2.

[I l l] <Reaction Scheme 2>

[113] ( 1 ) Synthesis of Compound 1

[114] 3 equivalent weight of dimethoxybenzene was dissolved in 250 ml of THF, and then

3.3 equivalent weight of n-butyllithiun was slowly added to the nixed solution using an addition funnel. Then, 1 equivalent weight of 4-bromo-(4'-hydroxyphenyl)benzene was slowly added to the reaction solution through the addition funnel. After the reaction solution was cooled to room temperature, the reaction was terminated with 300 ml of IM hydrochloric acid and the organic product was extracted using di- ethylether. Then, the organic layer containing the organic product was washed several times using a NaCl solution, and then moisture was removed therefrom using magnesiun sulfate. Then, the resultant product was separated using a colunn chromatography (yield: 82%) to obtain Compound 1.

[115] NMR and mass analysis results of the separated product are as follows.

[116] IH NMR: 7.45-6.79 (rnJ lH), 3.81(s,3H), 3.77(s,3H)

[117] Mass: 306(M+, 100), 291(28), 276(21), 260(16)

[118] (2) Synthesis of Compound 2

[119] The prepared Compound 1 (1 equivalent weight) and NaH (1.2 equivalent weight) were dissolved in 100 ml of dimethylsulfoxide and the mixture was reacted at room temperature for 1 hour. Then, 2 equivalent weight of dibromotetrafluoroethane was added to the resultant reaction solution and the resultant was further reacted for 4 hours. The reaction was terminated with a saturated NaCl solution, and then an organic compound was extracted using dimethylether. Then, the resultant product was separated by column chromatography (yield: 89%) to obtain Compound 2.

[120] IH NMR: 7.5-6.83 (m, 1 IH), 3.78 (s,3H), 3.74(s,3H)

[121] 19F NMR: -θ8.47(t, J= 4Hz, 2F), -86.30(t, J=4Hz, 2F)

[122] (3) Synthesis of Compound 3

[123] BBr ₃ was slowly added dropwise to a solution in which the obtained Compound 2 (1 equivalent weight) was dissolved in chloroform and the mixture was reacted at room temperature for 4 hours. Then, distilled water was added to the reaction mixture to terminate the reaction. An organic layer was collected from the resultant and a solvent was removed therefrom to obtain Compound 3.

[124] IH NMR: 7.61-6.74 (m, 1 IH)

[125] 19F NMR: -68.51(S, J= 2F), -86.32(S, J=2F)

[126] Mass: 458(M+2, 100), 456(M+, 100), 256(18), 231(43), 202(40), 189(25), 176(19), 165(37), 131(27), 82(33)

[127] (4) Synthesis of Compound 4

[128] The obtained Compound 3 (1 eg.), Na ₂ S ₂ O ₄ (4 eg.), and NaHCO ₃ (1 eg.) were dissolved in a mixed solvent of dimethylsulfoxide (DMSO) and distilled water, and

then the nixed solution was reacted at 80 ⁰ C for 3 hours, and the reaction solution was cooled to room temperature. Then, an organic layer was extracted using ethylacetate. After removal of a solvent, the reaction mixture was dissolved in distilled water, hydrogen peroxide was added to the resultant and the reaction solution was further reacted for 2 hours. NaCl was added to the resultant reaction solution and then a precipitate was filtered to obtain Compound 4.

[129] 19F-NMR: -80(S, 2F), -116.06(S, 2F) [130] <Preparation of polymer for polymer electrolyte membrane> [131] A method of preparing a polymer using the obtained Compound 4 in Examples 1 through 4 below will now be described.

[132] <Reaction Scheme 3>

[134] Example 1 : Synthesis of polymer [135] Compound 4 (0.01 M), bis(4-chlorophenyl)sulfone (0.05 M), and 4,4'-dihydroxybiphenyl (0.04 M) were dissolved in N^nethylpyrrolidone (NMP), and then potassiun carbonate (K ₂ CO ₃ , 0.35 M) and an appropriate amount of toluene were added to the resultant mixed solution. The temperature of a reactor for reacting the mixed solution was increased to 130 ⁰ C , and the mixed solution was reacted for 4 hours under toluene reflux conditions. Then, the toluene was removed and the resultant was further reacted at 180 ⁰ C for 18 hours to complete the synthesis of a polymer. The polymer was purified by isopropyl alcohol precipitation.

[136] Example 2: Synthesis of polymer

[137] Compound 4 (0.015 M), bis(4-chlorophenyl)sulfone (0.05 M), and

4,4'-dihydroxybiphenyl (0.035 M) were dissolved in Nmethylpyrrolidone (NMP), and then potassiun carbonate (K ₂ CO ₃ , 0.35 M) and an appropriate amount of toluene were added to the resultant mixed solution. The temperature of a reactor for reacting the mixed solution was increased to 130 ⁰ C , the mixed solution was reacted for 4 hours under toluene reflux conditions. Then, the toluene was removed and the resultant was further reacted at 180 ⁰ C for 18 hours to complete the synthesis of a polymer. The polymer was purified by isopropyl alcohol precipitation.

[138] Example 3: Synthesis of polymer

[139] Compound 4 (0.02 M), bis(4-chlorophenyl)sulfone (0.05 M), and

4,4'-dihydroxybiphenyl (0.03 M) were dissolved in N^nethylpyrrolidone (NMP), and then potassiun carbonate (K ₂ CO ₃ , 0.35 M) and an appropriate amount of toluene were added to the resultant mixed solution. The temperature of a reactor for reacting the mixed solution was increased to 130 ⁰ C , and the mixed solution was reacted for 4 hours under toluene reflux conditions. Then, the toluene was removed and the resultant was further reacted at 180 ⁰ C for 18 hours to complete the synthesis of a polymer. The polymer was purified by isopropyl alcohol precipitation.

[140] Example 4: Synthesis of polymer

[141] Compound 4 (0.025 M), bis(4-chlorophenyl)sulfone (0.05 M), and

4,4'-dihydroxybiphenyl (0.025 M) were dissolved in N^nethylpyrrolidone (NMP), and then potassiun carbonate (K ₂ CO ₃ , 0.35 M) and an appropriate amount of toluene were added to the resultant mixed solution. The temperature of a reactor for reacting the mixed solution was increased to 130 ⁰ C , and the mixed solution was reacted for 4 hours under toluene reflux conditions. Then, the toluene was removed and the resultant was further reacted at 180 ⁰ C for 18 hours to complete the synthesis of a polymer. The polymer was purified by isopropyl alcohol precipitation.

[142] <Preparation of polymer electrolyte membrane>

[143] Hereinafter, a method of preparing a polymer electrolyte membrane will be described.

[144] Examples 5-8: Preparation of polymer electrolyte membrane

[145] 1 g of each of the polymers prepared in Examples 1 through 4 was dissolved in N- methylpyrrolidone (NMP), and then the resultant mixed solution was cast on a glass plate. Then, the resultant was heated at 6O ⁰ C for 3 hours and dried in a vacuum at 12O ⁰ Cf or 24 hours. As a result, polymer electrolyte membranes having sulfonation

degrees different from each other were obtained.

[146] Example 9: Preparation of polymer blend electrolyte membrane

[147] 1 g of the polymer prepared in Example 4 and 0.3 g of sulfonated polyethereth- erketone were dissolved in 10 ml of N^nethylpyrrolidone, and then the resultant mixed solution was cast on a glass plate. Then, the resultant was heated at 60 ⁰ C for 3 hours and dried in a vacuum at 120 ⁰ C for 24 hours to obtain a polymer blend electrolyte membrane.

[148] Example 10: Preparation of organic-inorganic complex electrolyte membrane

[149] 1 g of the polymer prepared in Example 4 and 0.05 g of silicon oxide were dissolved in 10 ml of N^nethylpyrrolidone, and then the resultant mixed solution was cast on a glass plate. Then, the resultant was heated at 6O ⁰ C for 3 hours and dried in a vacuun at 120°Cfor 24 hours to obtain an organic-inorganic complex electrolyte membrane.

[150] Comparative Example 1 : Preparation of polymer electrolyte membrane

[151] A polymer electrolyte membrane was prepared in the same manner as in Example 5, except that Nafion 115 was used instead of the polymer of Example 1.

[152] <Evaluation of polymer electrolyte membrane>

[153] (1) Proton conductivity

[154] Each of the polymer electrolyte membranes prepared in Examples 5 through 10 and Comparative Example 1 was interposed between electrodes each having an area of 2.54 cm ² , and then an initial resistance of each polymer electrolyte membrane was measured at 30 ⁰ C using a potentiometer. The proton conductivity of the polymer electrolyte membranes was measured using Equation 1 below. The obtained proton conductivities are shown in Table 1.

[155] Proton Conductivity (S/αn) = (electrolyte membrane thickness (cm) / area (cm ² )) x initial resistance value (1/ohm) Equation 1.

[156] (2) Methanol Permeability

[157] Methanol permeating cells were prepared, and each of the polymer electrolyte membranes prepared in Examples 5 through 10 and Comparative Example 1 was interposed between the methanol permeating cells, and the assemblies were fixed to each other using an epoxy adhesive. 15 ml of a IM aqueous methanol solution was added to one of the cells, and 15 ml of distilled water was added to the other thereof. Then, 10 id of the resultant solution was collected from the cell including the distilled water once every 10 minutes, and 10 id of distilled water was added to the collected solution to maintain the volume thereof constant. The methanol concentration of the collected sample was measured by gas chromatography. A change in methanol concentration

according to time was measured to produce a graph, and the methanol permeability of each polymer electrolyte membrane was measured from a slope of the graph by using Equation 2 below. The results are shown in Table 1 below.

[158] Methanol Permeability (an ² /S) = [slope (ppm/s) x solution volune (an ³ ) x electrolyte membrane thickness (an)] / [electrolyte membrane area (cm ² ) x methanol concentration (ppm)] Equation 2.

[159] In Equation 2, the solution volume, electrolyte membrane area and methanol concentration were respectively maintained constant at 15αn ³ , 7.06αn ² , and 1M=32OOO ppm.

[160] <Table 1> [161] [Table 1] [Table ]

[162] Referring to Table 1, the polymer electrolyte membranes of Examples 5 through 10 maintain appropriate proton conductivity, and have much lower methanol permeability than that of the polymer electrolyte membrane of Comparative Example 1. That is, the polymer electrolyte membrane according to an embodiment of the present invention includes an acid group in a side chain thereof, thereby having structural stability due to effective microphase separation, resulting in a reduction in methanol permeability.

[163] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the

following claims.