WO2010013861A1

WO2010013861A1 - Anion-exchange composite membrane containing styrene-based and vinylbenzene-based copolymer and method for preparing the same

Info

Publication number: WO2010013861A1
Application number: PCT/KR2008/005333
Authority: WO
Inventors: Jeong Hoon Kim; Soo Bok Lee; In Joon Park; Bong Jun Chang; Jong-Wook Ha; Min Chul Yoo; Jung Soo Lee; Jae Wan Park
Original assignee: Korea Reserach Institute Of Chemical Technology
Priority date: 2008-08-01
Filing date: 2008-09-10
Publication date: 2010-02-04
Also published as: KR100999048B1; KR20100013871A

Abstract

Provided are an anion-exchange composite membrane containing a styrene-based and vinylbenzene-based copolymer on a porous film, and a method for manufacturing the same. Specifically, provided is a an anion-exchange composite membrane containing a styrene-based and vinylbenzene-basedvinylbenzene-basedon a porous film, which is manufactured by performing polymerization through impregnation of the porous film with a polymerization solution containing a styrene-based monomer, a vinylbenzene-based monomer, a crosslinking agent and an initiator, and introducing ammonium ions. More specifically, provided are an anion-exchange composite membrane containing a styrene-based and vinylbenzene-based copolymer with excellent ion exchange capacity, mechanical properties, chemical resistance and processability, and a method for preparing the anion-exchange composite membrane.

Description

[DESCRIPTION]

[invention Title]

ANION-EXCHANGE COMPOSITE MEMBRANE CONTAINING STYRENE- BASED AND VINYLBENZENE-BASED COPOLYMER AND METHOD FOR PREPARING THE SAME

[Technical Field]

The present invention relates to an anion-exchange composite membrane containing a styrene-based and vinylbenzene-based copolymer on a porous film, and a method for preparing the anion-exchange composite membrane.

[Background Art]

An anion-exchange composite membrane using a polymer as an electrolyte, which is one kind of polymer membranes, is used in, for example, desalination, electrodialysis for fabrication of edible salt and purification, electrical desalination for producing pure water, and diffusion dialysis for recovering acid from acid waste. The anion- exchange membrane can selectively separate anions through electrostatic principle, and mainly employs a quaternary ammonium ion as an ion-exchange group commercially.

A paste method is a representative one of conventional methods for preparing such an anion-exchange membrane. In the paste method, a paste is prepared using a vinylbenzyl chloride-div±nylbenzene monomer and a plasticizer and powder of a copolymer thereof and a rubber; a support such as thin cloth is coated with the paste; and heat is applied to the thin cloth with the paste to thereby prepare the anion-exchange membrane. Such a paste method is excellent in mechanical properties. However, this paste method is disadvantageous in that fabrication process is too complicated, a membrane is brittle during dry process, fabrication cost is high, and chemical stability is deteriorated (Y. Mizutani, Structure of ion-exchange membranes, J. Membr. Sci. 49 (1990) 121) .

To solve theses disadvantages, researchers of Gwangju Institute of Science and Technology in Republic of Korea have invented a preparation method of polyethylene/poly (vinyl benzyl chloride) anion-exchange membrane (Korean Patent Registration No. 542,295), which includes absorbing a polymerization solution containing vinylbenzyl chloride, a swelling accelerating monomer, divinylbenzene and a photoinitiator to a nonporous low density polyethylene film internally; irradiating ultraviolet (UV) light to the resultant structure at room temperature to photopolymerize it; and introducing an amine group as an anion-exchange group through quaternary amination. This patent is advantageous in that it is possible to prepare an ion-exchange membrane through simple process in comparison with conventional paste methods. However, the content of a resin having ion- exchange capacity is limited due to the limitation in absorbability of the nonporous membrane, and it is difficult for UV light to permeate into the membrane. Therefore, this patented method is not available when the membrane gets thicker. Moreover, this method has a disadvantage that monomers are scattered into air during fabrication process. Thus, the present inventors have carried out researches to overcome the above problems, and resultingly, found out that a polyolefin film such as a polyethylene film and a polypropylene film could easily solve the above- described problems because it has a high molecular weight and a porous structure allowing inner parts to be communicated with each other. Then, a porous film was dipped into a polymerization solution where a styrene monomer inactive in amination, a vinylbenzene-based monomer active in amination, a crosslinking agent, an initiator were mixed together, thereby closing the inside of the porous film. Afterwards, thermal crosslinking polymerization was carried out, and quaternary ammonium ions were introduced. As a result, it is possible to prepare an anion-exchange membrane having low electrical resistance, excellent ion-exchange capacity, mechanical properties, chemical properties and processability . Further, the anion-exchange membrane of the present invention has such advantageous merits that the ion-exchange capacity and ion conductivity can be very easily controlled by adjusting the composition of the styrene-based monomer and the vinylbenzene-based monomer. In addition, by the use of porous supports with excellent mechanical strength and various thicknesses, it is possible to prepare the anion-exchange composite membrane of which conductivity and mechanical strength are superior to those of the ion-exchange membranes prepared by the conventional commercialized paste methods.

[Disclosure] [Technical Problem] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an anion-exchange composite membrane containing a styrene- based and vinylbenzene-based copolymer with low electrical resistance and excellent ion exchange capacity, mechanical properties, chemical properties and processability, and a method for preparing the anion-exchange composite membrane.

Another object of the present invention is to provide an anion-exchange composite membrane containing a styrene- based and vinylbenzene-based copolymer, which is capable of easily controlling ion exchange capacity and ion conductivity by adjusting a composition of a styrene-based monomer and a vinylbenzene-based monomer, and a method for preparing the anion-exchange composite membrane.

[Technical Solution]

In order to accomplish the above object, the present invention provides an anion-exchange composite membrane containing a styrene-based and vinylbenzene-based copolymer, and a method for preparing the same, the method including: closing the inside of a porous film by dipping the porous film into a mixturet where a styrene-based monomer, a vinylbenzene-based monomer, a crosslinking agent, and an initiator are mixed; performing thermal crosslinking polymerization; and introducing quaternary ammonium ions.

[Advantageous Effects]

The present invention can provide an anion-exchange composite membrane with low electrical resistance and excellent ion exchange capacity, mechanical properties, chemical properties and processability . Also, the present invention can provide an anion-exchange composite membrane containing a styrene-based and vinylbenzene-based copolymer capable of easily adjusting ion exchange capacity and ion conductivity, and a method for preparing the same.

[Brief Description of the Drawings]

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

Figure 1 (a) is a scanning electron microscope (SEM) image (x 10,000) showing a surface of a support of a polyethylene (PE) film used in the present invention;

Figure 1 (b) is a SEM image (x 5,000) showing a section of the support of the PE film;

Figure 2 (a) is a SEM image (x 10,000) showing a surface of a composite membrane containing a PE/ammonium ionized styrene-based and vinylbenzene-based copolymer according to an embodiment 2 of the present invention;

Figure 2 (b) is a SEM image (x 5,000) showing a section of the composite membrane of Figure 2 (a) ;

Figure 3 (a) is a SEM image (x 10,000) showing a surface of a polypropylene (PP) film used in the present invention;

Figure 3 (b) is a SEM image (* 5,000) showing a section of the PP film; Figure 4 (a) is a SEM image (x 10,000) showing a surface of a composite membrane containing a PP/ammonium ionized styrene-based and vinylbenzene-based copolymer according to an embodiment 6 of the present invention; and Figure 4 (b) is a SEM image (x 5,000) showing a section of the composite membrane of Figure 4 (a) .

[Best Mode fop Carrying Out the Invention]

Hereinafter, the present invention will be described in detail. The present invention provides a quaternary ammonium group introduced anion-exchange composite membrane containing a crosslink type styrene-based and vibylbenzene- based copolymer on a porous film.

In the present invention, the styrene-based and vinylbenzene-based copolymer includes 20-80 wt . % of styrene-based monomer and 20-80 wt . % of vinylbenzene-based monomer, wherein the quaternary ammonium group is introduced into the vinylbenzene-based monomer of the copolymer. Well-known materials may be used for the styrene-based monomer. In addition, one of α-methylstyrene, styrene, vinylpyridine and trifluorostyrene may be used alone or a mixture thereof may be used for the styrene-based monomer, however, the present invention is not limited thereto. A styrene-based monomer, which is inactive in amination reaction, may be used. Using the styrene-based monomer inactive in amination reaction and adjusting the amount thereof make it possible to properly control the anion- exchange capacity of the anion-exchange composite membrane.

When the content of the styrene-based monomer exceeds

80% by weight, the ion exchange capacity is lowered due to the lack of the amount of ammonium ions during the amination. In contrast, when the content of the styrene- based monomer is less than 20% by weight, the amount of ammonium ions is too excessive to increase the water swellability of the membrane, thus leading to a decrease in membrane strength.

Well-known materials may be used for the vinylbenzene- based monomer. In addition, one of vinylbenzyl chloride, vinylbenzyl bromide, and vinylbenzyl iodide may be used alone or a mixture thereof may be used for the vinylbenzyl monomer, however, the present invention is not limited thereto. A vinylbenzene-based monomer, which is active in amination reaction, may be used. The vinylbenzene-based monomer active in amination reaction functions to give the anion-exchange capacity through amination reaction after being polymerized to the composite membrane according to the present invention. When the content of the vinylbenzene-based monomer is less than 20% by weight, the function of the anion-exchange composite membrane is degraded. On the contrary, when the content of the vinylbenzene-based monomer is more than 80% by weight, mechanical properties become poor.

The anion-exchange composite membrane of the present invention can easily control ion exchange capacity and ion conductivity by adjusting the composition of the styrene- based monomer and the vinylbenzene-based monomer. The porous film may employ a polyolefin film such as a polyethylene film and a polypropylene film. The porous polyolefin-based film is used as a support of the anion- exchange composite membrane in the present invention, thereby improving the mechanical strength of the anion- exchange composite membrane.

Furthermore, as expressed in following Scheme 1, the present invention provides a method of preparing an anion- exchange composite membrane. The method includes: impregnating a porous film with a polymerization solution containing a styrene-based monomer, a vinylbenzene-based monomer, a crosslinking agent and an initiator (step 1); polymerizing the porous film impregnated with the polymerization solution to prepare a styrene-based and vinylbenzene-based copolymer composite membrane (step 2); and introducing a quaternary ammonium as an anion exchange group by reacting a tertiary amine with the styrene-based and vinylbenzene-based copolymer composite membrane (step3)

<Scheme 1> p led

Hereinafter, the method for preparing the anion- exchange composite membrane of the present invention will be more fully described for each step. The step 1 according to the present invention is a step of impregnating a porous film 2 with a polymerization solution that includes a styrene-based monomer 3, a vinylbenzene-based monomer 4, a crosslinking agent 5 and an initiator . To begin with, the styrene-based monomer 3, the vinylbenzene-based monomer 4, the crosslinking agent 5 and the initiator are mixed to thereby prepare a polymerization solution. The polymerization solution may contain a monomer mixture, 5-20 parts by weight of the crosslinking agent based on 100 parts by weight of the monomer mixture, and 0.5-5 parts by weight of the initiator based on 100 parts by weight of the monomer mixture. Herein, the monomer mixture includes 20-80 wt . % of the styrene-based monomer and 20-80 wt . % of the vinylbenzene-based monomer.

Well-known materials may be used for the styrene-based monomer 3. Furthermore, one of α-methylstyrene, styrene, and trifluorostyrene may be used alone or a mixture thereof may be used for the styrene-based monomer 3, however, the present invention is not limited thereto. A styrene-based monomer, which is inactive in amination reaction, may be used. Well-known materials may be used for the vinylbenzene- based monomer 4. Furthermore, one of vinylbenzyl chloride, vinylbenzyl bromide, and vinylbenzyl iodide may be used alone or a mixture thereof may be used for the vinylbenzyl monomer 4, however, the present invention is not limited thereto. A vinylbenzene-based monomer, which is active in amination reaction, may be used.

The crosslinking agent 5 functions to determine a swelling degree and a crosslinking degree of the membrane finally. Although the crosslinking agent to be used in the present invention is not specifically limited, divinylbenzene is generally used in the present invention. The content of the crosslinking agent 5 is 5-20 parts by weight based on 100 parts by weight of the monomer mixture. When the content of the crosslinking agent is less than 5 parts by weight, the crosslinking agent is deficient. When the content of the crosslinking agent is more than 20 parts by weight, the crosslinking degree is too high, causing the brittleness of the membrane to be increased. The initiator to be used in the present invention is not specifically limited. In particular, N, N ' -azo-bis- isobutyronitrile (AIBN) , benzoyl peroxide (BPO) , cumyl peroxide, lauroyl peroxide, and so forth may be used as the initiator. The content of the initiator is in the range of 0.5-5 parts by weight based on 100 parts by weight of the monomer mixture. Preferably, the content of the initiator is in the range of 1-2 parts by weight. When the content of the initiator is less than 0.5 parts by weight, crosslinking is not sufficiently carried out. In contrast, when the content of the initiator is more than 5 parts by weight, the content of the initiator itself is too excessive, leading to deterioration in properties.

Thereafter, the porous film 2 is impregnated with the polymerization solution prepared by mixing the above- described ingredients for 30 minutes to 24 hours, thereby forming a pore-filled film 6. The porous film 2 applicable to the present invention has a soluble selectivity with respect to an organic solvent, and has excellent chemical resistance and oxidation resistance. For example, a polyolefin-based film such as a polyethylene film and a polypropylene film may be used for the porous film 2. A crosslink type vinylbenzene-based ion-exchange membrane manufactured by the conventional paste method is susceptible to be broken due to an increase in brittleness. For this reason, if the vinylbenzene-based ion-exchange membrane is used for thinning or a composite membrane, there is a problem in that the mechanical stability is deteriorated. In the present invention, however, pores of the porous film are filled with the polymerization solution by impregnating the porous film with the polymerization solution containing the styrene- based monomer 3 and the vinylbenzene-based monomer 4, and plasticized while network structures of each pore are processed. This makes it possible to prepare an ion- exchange membrane with uniformity and excellent mechanical strength and chemical resistance in comparison with conventional membranes .

The step 2 according to the present invention is a step of preparing a styrene-based and vinylbenzene-based copolymer membrane 7 by polymerizing the porous film impregnated with the polymerization solution of the step 1.

The porous film impregnated with the polymerization solution in the step 1 is polymerized to manufacture the styrene-based and vinylbenzene-based copolymer membrane

The polymerization reaction in the step 2 is performed for 30 minutes to 24 hours such that the monomer and the initiator are sufficiently absorbed on the porous film to reach an equilibrium state. Preferably, the porous film is left in a monomer solution for about 1 hour to about 12 hours at room temperature, then a membrane, on which a reaction solution is absorbed, is positioned on a rectangular glass plate, and thereafter another glass plate covers it. Afterwards, the polymerization is performed for 1 hour to 24 hours at a temperature ranging from 50 ^°C to 100 ^°C , thereby forming the styrene-based and vinylbenzene- based copolymer membrane 7. After completion of the polymerization, to remove unreacted monomers remaining on the membrane, the styrene-based and vinylbenzene-based copolymer membrane 7 is dipped into an organic solvent such as tetrahydrofuran, dichloroethane, acetone, and toluene, and then washed several times in the organic solution.

The step 3 according to the present invention is a step of introducing a quaternary ammonium as an anion exchange group by reacting tertiary amine with the styrene- based and vinylbenzene-based copolymer membrane 7, thereby manufacturing an anion-exchange composite membrane 1.

In the step 3, the tertiary amine reacts with the styrene-based and vinylbenzene-based copolymer membrane 7 to thereby introduce quaternary ammonium as the anion exchange group. In the present invention, trimethylamine, triethyamine, diphenylethylamine, diethylphenylamine, or the like is used as the tertiary amine. In this case, the amine itself or the amine diluted with ultrapure water or an organic solvent such as acetone and tetrahydrofuran is made to react with the styrene-based and vinylbenzene-based copolymer membrane 7. The concentration is not limited in the reaction, but it is preferable that the concentration is 1% or more by weight. The crosslinked membrane is dipped into the prepared amine or amine solution for 1 hour to 36 hours, preferably 10-24 hours, at room temperature. After completion of the reaction, the composite membrane is washed several times at room temperature (25 "C) in ultrapure water or organic solvent so as to remove unreacted amine remaining on the composite membrane. Thereafter, the composite membrane is again dipped into ultrapure water or organic solution for one night, and then washed several times again, thereby preparing the anion-exchange composite membrane 1 to which the quaternary ammonium is introduced. Since the porous film, the styrene-based monomer, and the vinylbenzene-based monomer are used together in the above-described process, it is possible to prepare the anion-exchange composite membrane with excellent mechanical properties, high ion conductivity, low electrical resistance, and good processability .

The present invention will be more fully described according to following embodiments, however, the present invention is not limited to those embodiments .

[Mode for Invention]

Preparation of anion-exchange composite membrane of the present invention using polyethylene film Embodiment 1

Vinylbenzyl chloride, styrene and divinylbenzene were mixed at a ratio of 70 : 20 : 10 by weight, and a polymerization solution containing 2 parts by weight of benzoyl peroxide (BPO) as an initiator was prepared based on 100 parts by weight of the mixture. About 50 μm-thick porous polyethylene (PE) film was dipped into toluene for one hour and then pulled out. Thereafter, the porous polyethylene (PE) film was again dipped into the polymerization solution, and was left remaining for 10 hours . The porous polyethylene (PE) film impregnated with the polymerization solution was placed on a rectangular glass plate, and the resultant was then covered with another glass plate. Afterwards, the resultant structure was sealed with a tape to prevent the loss of the polymerization solution. When the polymerization is completed, the membrane was separated from the glass plate, and was dipped into tetrahydrofuran for 12 hours at room temperature. The membrane was took out from the tetrahydrofuran, and again dipped into the tetrahydrofuran, thus removing unreacted monomers several times.

The composite membrane prepared through the polymerization reaction was dipped into solution mixture where 25 wt . % of trimethylamine aqueous solution and acetone are mixed at a ratio of 1 to 3, and then aminated for 24 hours at room temperature. After completion of the amination, to remove unreacted trimethylamine remaining on the composite membrane that has undergone the reaction, the membrane was washed several times with ultrapure water at room temperature (25 ^°C ) , and dipped into ultrapure water for one night and then washed several times, thereby preparing an anion-exchange membrane to which quaternary ammonium (-N⁺(CH₃)) is introduced. Through the above- described process, the anion-exchange composite membrane of which a total thickness is about 70 [M was prepared, which contains the styrene-based and vinylbenzene-based copolymer where polyethylene and ammonium are ionized. Properties were measured according to a following property measurement method, of which results are shown in Table 1.

Embodiments 2 through 5

Embodiments 2 through 5 were performed in the same manner as the embodiment 1 except for the content of each ingredient shown in Table 1. Properties were measured according to the following property measurement method, of which results are shown in Table 1.

Comparative example 1

The comparative example 1 was carried out in the same manner as the embodiment 1 except that 90 wt . % of vinylbenzyl chloride and 10 wt . % of divinylbenzene were used in preparation of a polymerization solution instead of using styrene . Properties were measured according to a following measurement method, of which results are shown in Table 1.

Comparative example 2

Properties were measured according to a following property measurement method by using a commercial membrane (about 40 μm thick, AMX, ASTOM corporation in Japan) , which is purchasable on the market and prepared through a conventional paste method. The measurement results are shown in Table 1.

Property measurement method

1) Water content: An anion-exchange membrane is dipped into ultrapure water for 24 hours or more to sufficiently swell the membrane. Thereafter, moisture on the membrane surface is carefully dried down and then an increased weight Wi (g) is then measured. The resultant membrane is dried in a vacuum oven for 24 hours at 120 ^°C , and then a dry weight W₂ (g) is measured. The water content (%) is calculated as following Equation:

Water content (%) = [(W₁ - W₂) /W₂] *100 2) Measurement of ion-exchange capacity: The dry weight of the anion-exchange membrane is measured, and then the membrane is dipped in 1. OM NaCl solution. Afterwards, the membrane is dipped in 0.5M Na₂COa solution, and 1-3 droplets of potassium dichromate (5%) are dripped into this solution such that Cl- ions are titrated until reddish brown precipitations of AgNO₃ are produced. Thereafter, the ion-exchange capacity (IEC, unit: meq/g) is calculated through following Equation using the amount (ml) of the consumed AgNO₃. Ion-exchange capacity (IEC, unit: meq/g) = (VxC) /W_y 8 005333

where W_y represents the weight of the dried membrane, V represents the consumed the amount of the consumed AgNθ₃, and C represents the concentration of AgNO₃ solution used in titration.

3) Sheet resistance of membrane: The sheet resistance of the anion-exchange membrane is calculated through following Equation using an impedance and a phase angle measured by an LCZ meter in 0.5M NaCl aqueous solution.

Sheet resistance of membrane (Ω cuf) = membrane area x cosΘ x [Z] where Z represents an impedance, and Θ represents a phase angle.

4) Tensile strength (kgf/cilf): The tensile strength of the anion-exchange membrane is measured according to ASTM

(D-638) . [Table l]

As shown in Table 1, compared to the comparative example 1 where vinylbenzyl chloride is used alone, it can be appreciated that the anion-exchange composite membranes of the embodiments 1 through 5 using styrene in preparation of the polymerization solution have no great difference in sheet resistance of a membrane and an ion exchange capacity associated with the function of the anion-exchange membrane. However, the anion-exchange composite membranes of the embodiments 1 through 5 exhibit lower water content and higher tensile strength than the anion-exchange composite membrane of the comparative example 1. From theses results, it can be understood that the anion- exchange composite membranes of the embodiments 1 through 5 are suitable for mass production because the brittleness of each anion-exchange composite membrane of the embodiments 1 through 5 is significantly reduced and mechanical strength is enhanced in comparison with the comparative example 1.

In consideration of the respective thicknesses, it can be appreciated that the anion-exchange composite membranes (70 μm-thick) of the embodiments 1 through 5 are superior in tensile strength to the commercial membrane (AMX, about 140 μm-thick) . Further, it can be appreciated that the anion-exchange composite membranes of the embodiments 1 through 5 have much lower sheet resistance than the commercial membrane, i.e., AMX, of the comparative example 2. Figure 1 is a scanning electron microscope (SEM) image of a polyethylene (PE) film used in the embodiments 1 through 5. Specifically, Figure 1 (a) is a SEM image (x 10,000) of a surface of the polyethylene film, and Figure 1 (b) is a SEM image (*5,000) of a section of the polyethylene film. Figure 2 is a SEM image of a composite membrane of the embodiment 2 containing a PE/ammonium ionized styrene-based and vinylbenzene-based copolymer. Particularly, Figure 2 (a) is a SEM image

(^χl0,000) of a surface of the composite membrane, and Figure 2 (b) is a SEM image (^χ5,000) of a section of the composite membrane. From the SEM images, it can be appreciated that whole the porous film is completely filled with a resin, and a phase separation and a pinhole are not observed.

Preparation^' of anion-exchange composite membrane of the present invention using a polypropylene film Embodiments 6 through 10 A polymerization solution was prepared by mixing ingredients of composition shown in following Table 2, and abut 70 jwn-thick porous polypropylene film was dipped into the polymerization for 5 hours. Thereafter, the embodiments 6 through 10 were performed in the same manner as the embodiment 1 except for polymerization reaction, and properties were . measured according to the property measurement method, of which results are shown in Table 2 below .

Comparative example 3 The comparative example 3 was performed in the same manner as the embodiment 6 except that 90 wt . % of vinylbenzyl chloride and 10 wt . % of divinylbenzene were used in preparation of a polymerization solution instead of using styrene . Properties were measured according to a following measurement method, of which results were shown in Table 2.

Comparative example 4

Properties were measured according to a following property measurement method by using a commercial membrane

(AMX, ASTOM corporation in Japan) , which is purchasable on the market and prepared through a conventional paste method. The measurement results are shown in Table 2.

[Table 2] 008/005333

As shown in Table 2, compared to the comparative example 3 where vinylbenzyl chloride is used alone, it can be appreciated that the anion-exchange composite membranes of the embodiments 6 through 10 have no great difference in sheet resistance of a membrane and an ion exchange capacity associated with the function of the anion-exchange membrane. However, the anion-exchange composite membranes of the embodiments 1 through 5 exhibit lower water content and higher tensile strength than the anion-exchange composite membrane of the comparative example 3. From theses results, it can be understood that the anion- exchange composite membranes of the embodiments 6 through 10 are suitable for mass production because the brittleness of each anion-exchange composite membrane of the embodiments 6 through 10 is significantly reduced and mechanical strength is enhanced in comparison with the comparative example 3. In consideration of the respective thicknesses, it can be appreciated that the anion-exchange composite membranes

(70 μm-thick) of the embodiments 6 through 10 are superior in tensile strength to the commercial membrane (AMX, about

140 μm-thick) . Further, it can be understood that the anion-exchange composite membranes of the embodiments 6 through 10 have much lower sheet resistance than the commercial membrane, i.e., AMX, of the comparative example 4.

Figure 3 is a SEM image of a polypropylene (PP) film used in the embodiments 6 through 10. Specifically, Figure 3 (a) is a SEM image (x 10,000) of a surface of the polypropylene film, and Figure 3 (b) is a SEM image (*5,000) of a section of the polypropylene film. Figure 4 is a SEM image of a composite membrane of the embodiment containing a PP/ammonium ionized styrene-based and vinylbenzene-based copolymer. Particularly, Figure 4 (a) is a SEM image (^χl0,000) of a surface of the composite membrane, and Figure 4 (b) is a SEM image (^χ5,000) of a section of the composite membrane. From the SEM images, it can be appreciated that whole the porous film is completely filled with a resin, and a phase separation and a pinhole are not observed.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

[CLAIMS] [Claim l]

An anion-exchange composite membrane containing a styrene-based and vinylbenzene-based copolymer on a porous film, wherein the copolymer comprises 20-80 wt . % of styrene-based monomer and 20-80 wt . % of vinylbenzene-based monomer, and a quaternary ammonium group is introduced into the vinylbenzene-based monomer of the copolymer.

[Claim 2]

The anion-exchange composite membrane as set forth in claim 1, wherein the styrene-based monomer is a mixture having at least one selected from the group consisting of α-methylstyrene, styrene, and trifluorostyrene .

[Claim 3]

The anion-exchange composite membrane as set forth in claim 1, wherein the vinylbenzene-based monomer is a mixture having at least one selected from the group consisting of vinylbenzyl chloride, vinylbenzyl bromide, and vinylbenzyl iodide.

[Claim 4] The anion-exchange composite membrane as set forth in claim 1, wherein the porous film is selected from the group consisting of a polyethylene film and a polypropylene film.

[Claim 5]

A method for preparing an anion-exchange composite membrane, the method comprising: as expressed in following Scheme 1, impregnating a porous film with a polymerization solution including a styrene monomer, a vinylbenzyl monomer, a crosslinking agent and an initiator; polymerizing the impregnated porous film to prepare a styrene-based and vinylbenzene-based copolymer composite membrane; and introducing a quaternary ammonium as an anion exchange group by reacting tertiary amine with the styrene-based and vinylbenzene-based copolymer composite membrane <Scheme 1>

led

[Claim 6]

The method as set forth in claim 5, wherein the polymerization solution comprises a monomer mixture, 5-20 parts by weight of crosslinking agent based on 100 parts by weight of the monomer mixture, and 0.5-5 parts by weight of initiator based on 100 parts by weight of the monomer mixture, the monomer mixture comprising 20-80 wt . % of styrene- based monomer and 20-80 wt . % of vinylbenzene-based monomer.

[Claim 7]

The method as set forth in claim 5, wherein the styrene-based monomer is a mixture having at least one selected from the group consisting of α-methylstyrene, styrene, and trifluorostyrene.

[Claim 8]

The method as set forth in claim 5, wherein the vinylbenzene-based monomer is a mixture having at least one selected from the group consisting of vinylbenzyl chloride, vinylbenzyl bromide, and vinylbenzyl iodide.

[Claim 9]

The method as set forth in claim 5, wherein the porous film is selected from the group consisting of a polyethylene film and a polypropylene film.

[Claim 10]

The method as set forth in claim 5, wherein the polymerizing of the impregnated porous film is performed for 1 hour to 24 hours at a temperature ranging from 50 ^°C to 100 "C

[Claim 11]

The method as set forth in claim 5, wherein the tertiary amine is selected from the group consisting of trimethylamine, triethyamine, diphenylethylamine, and diethylphenylamine .