WO2009089355A1 - Anion exchange membranes - Google Patents

Abstract

Alkaline anion exchange membranes are described. The synthesis of the polymers forming alkaline anion exchange membranes are described, including chloromethylation, quaternization, and alkalinization of polymers.

Description

ANION EXCHANGE MEMBRANES

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U. S. C. § 119(e) of U.S. Provisional Application Serial No. 61/020,582, filed January 11, 2008, the disclosure of which is hereby incorporated herein by reference.

TECHNICAL FIELD

The invention described herein pertains to membranes. In particular, the invention described herein pertains to anion exchange membranes. In addition, the invention described herein pertains to anion exchange membranes that may be used in fuel cells.

BACKGROUND

Fuel cells are electrochemical devices that convert chemical energy directly into electrical energy. Fuel cell research has become important because of the energy crisis. One of the key components of fuel cells is the electrolyte. The use of solid polymer electrolytes may represent an interesting path to pursue for these electrochemical devices (Varcoe, J. R., Slade, R. C. T., Fuel Cells 2005, 5, 187-200). Methanol/ethanol fuel cells and ethanol reformers, and the like are currently being developed as alternate sources of energy generation. Those fuel cells and reformers often include membranes that separate and prevent fuel crossover from the anode to cathode. Such membranes needed. In addition, such membranes that can minimize fuel crossover from the anode to cathode and/or have improved chemical and thermal stabilities are needed. Two types of solid polymer electrolytes exist in fuel cell research: proton exchange polymer membranes and anion exchange polymer membranes. The former is used for a proton exchange membrane fuel cell and the latter for an anion exchange membrane fuel cell. Much effort has been focused on proton exchange membrane (PEM) development (Blomen, L. J. M. J., Mugerwa, M. N., Fuel Cell Systems, Plenum Press: New York, NY, 1993). Although the PEMs exhibit excellent chemical, mechanical and thermal stability as well as high ionic conductivity, several significant disadvantages have been reported and may limit their further development when they are applied to fuel cells (Blomen, L. J. M. J., Mugerwa M. N., Fuel Cell Systems, Plenum Press: New York, NY, 1993). The reported disadvantages in the PEM-constructed fuel cells include slow electrode -kinetics, carbon monoxide poisoning of non-reusable expensive Pt and Pt-based electrocatalysts at low temperatures, high cost of membrane and high methanol permeability (Varcoe, J. R., Slade, R. C. T., Fuel Cells 2005, 5, 187-200). One approach to potentially improve on PEMs is through alkaline anion exchange membranes (AAEM). AAEMs may be designed to provide sufficient hydroxyl ions for ion exchange during electrochemical reactions in alkaline fuel cells. Alkaline fuel cells may have numerous advantages over proton exchange membrane fuel cells on both cathode kinetics and ohmic polarization. The inherently faster kinetics of the oxygen reduction reaction in an alkaline fuel cell may allow the use of non-noble and low-cost metal electrocatalysts such as silver and nickel. Furthermore, the anodic oxidation of methanol in alkaline media may be more feasible than that in acidic media.

Very few AAEMs have been evaluated for use as solid polymer electrolytes for alkaline fuel cells (Wan, Y., Creber, K. A. M., Peppley, B., Bui, V. T., J. Membr. ScL, 2006, 284, 331; Fang, J., Shen, P. K., J. Membr. ScL, 2006, 285, 317; Li, L., Wang, J., J. Membr. ScL, 2005, 262, 1; Yi, F., Yang, X., Li, Y., Polym. Adv. Technol, 1999, 10, 473;

Slade, R. C. T., Varcoe, J. R., Solid State Ionics, 2005, 176, 585; Kang, J.-J., Li, W.-Y., Lin, Y., Li, X.-P., Xiao, X.-R., Fang, S.-B., Polym. Adv. Technol., 2004, 75, 61). These membranes were constructed mainly from poly(sulfone-ether)s and polystyrenes because crosslinked polystyrenes have been widely used as building matrixes for cation and anion exchange resins (Elias, H. -G., Macromolecules: Volume 2: Industrial Polymers and

Syntheses, John Wiley & Sons Inc.: New York, NY, 2005). In addition, polysulfones are generally high-performance polymers that are thermally and chemically stable (Blinne, G., Knoll, M., Muller, D., Schlichting, K., Kunstoffe, 1985, 75, 29).

SUMMARY OF THE INVENTION

It has been discovered herein that polymers, including copolymers, block copolymers, graft polymers, and the like, that are formed from one or more optionally substituted bisphenol A monomers, and analogs and derivatives thereof, may be functionalized with cationic groups and subsequently used to prepare AAEMs. It has also been discovered that such polymers, including copolymers, block copolymers, graft polymers, and the like, that are formed from ethers of one or more optionally substituted bisphenol A monomers, and analogs and derivatives thereof, and one or more optionally substituted phthalate monomers, such as optionally substituted phthalimides, may be functionalized with cationic groups and subsequently used to prepare AAEMs. It has also been discovered that such polymers, including copolymers, block copolymers, graft polymers, and the like, that are formed from imides of one or more optionally substituted bisphenol A monomers, and analogs and derivatives thereof, and one or more optionally substituted phthalate monomers, may be functionalized with cationic groups and subsequently used to prepare AAEMs. It has also been discovered that such polymers, including copolymers, block copolymers, graft polymers, and the like, that are formed from amides of one or more optionally substituted bisphenol A monomers, and analogs and derivatives thereof, and one or more optionally substituted phthalate monomers, may be functionalized with cationic groups and subsequently used to prepare AAEMs. In addition, it has been discovered herein that such polymers may be cross-linked and subsequently used to prepare AAEMs.

In one embodiment, anion exchange membranes are described herein. In another embodiment, the anion exchange membranes include polymers or mixtures of polymers, where at least one of the polymers has a plurality of pendant cationic groups. It is appreciated that such cationic groups are capable of ionically bonding or coordinating an anion, and such cationic groups may be used as anion exchanging groups. In another embodiment, the polymers or mixture of polymers include a polymer, co-polymer, block copolymer, or graft polymer of one or more optionally substituted bisphenol A monomers, or an analog or derivative thereof.

In another embodiment, anion exchange polymers are described herein. In one aspect, the anion exchange polymer has a plurality of pendant cationic groups. It is appreciated that such cationic groups are capable of ionically bonding or coordinating an anion, and such cationic groups may be used as anion exchanging groups. In another aspect, the anion exchange polymer is a polymer, co-polymer, block copolymer, or graft polymer of bisphenol A, or an analog or derivative thereof.

In another embodiment, anion exchange membranes and anion exchange polymers are described herein where the polymer also includes residues of one or more optionally substituted phthalate monomers, including but not limited to phthalimide monomers, optionally substituted N-phenylphthalimide monomers, and the like. In one aspect, the polymers that include both the residues of one or more optionally substituted bisphenol A and phthalimide monomers include ethers of those two monomers in the polymer chain. In another aspect, the polymers that include both the residues of one or more optionally substituted bisphenol A and phthalimide monomers include amides of those two monomers in the polymer chain. In another aspect, the polymers that include both the residues of one or more optionally substituted bisphenol A and phthalimide monomers include imides of those two monomers in the polymer chain. In another aspect, the polymers that include both the residues of one or more optionally substituted bisphenol A and phthalimide monomers include both ethers and imides of those two monomers in the polymer chain. It is to be understood that in each of the foregoing embodiments, the polymers may also include the residues of other monomers, including but not limited to sulfone monomers, such as optionally substituted diarylsulfones, and the like. In another embodiment, anion exchange membranes and anion exchange polymers are described herein where the polymer also includes residues of one or more optionally substituted sulfone monomers, including but not limited to optionally substituted disarylsulfone monomers, and the like. In one aspect, the polymers that include both the residues of one or more optionally substituted bisphenol A and sulfone monomers include ethers of those two monomers in the polymer chain. In another aspect, the polymers that include both the residues of one or more optionally substituted bisphenol A and sulfone monomers include amides of those two monomers in the polymer chain. In another aspect, the polymers that include both the residues of one or more optionally substituted bisphenol A and sulfone monomers include both ethers and amides of those two monomers in the polymer chain. It is to be understood that in each of the foregoing embodiments, the polymers may also include the residues of other monomers, including but not limited to sulfone monomers, such as optionally substituted diarylsulfones, and the like.

In another embodiment, intermediates for preparing polymers that may be used to prepare AAEMs are described herein. In one embodiment, the intermediates are polymers, including copolymers, block copolymers, graft polymers, and the like, that are formed from one or more optionally substituted bisphenol A monomers, and analogs and derivatives thereof. In one variation, such intermediates are polymers that also include the residues of one or more optionally substituted phthalate monomers, including but not limited to phthalimide monomers, optionally substituted N-phenylphthalimide monomers, and the like.

In another embodiment, intermediates for preparing polymers that may be used to prepare AAEMs are described herein. In one embodiment, the intermediates are polymers, including copolymers, block copolymers, graft polymers, and the like, that are foraied from one or more optionally substituted bisphenol A monomers, and analogs and derivatives thereof, that include pendant chloroalkyl groups, such as chloro methyl groups. It is appreciated that the chloroalkyl groups may be attached to any position along the polymer chain. In one embodiment, the chloroalkyl groups are attached to the one or more optionally substituted bisphenol A monomer residues. It is to be understood that more than 1, such as 2 or 3 chloroalkyl groups may be attached to any selected optionally substituted bisphenol A monomer residues. It is also to be understood that selected optionally substituted bisphenol A monomer residues may not have any chloromethyl groups. Accordingly, the relative molar ratio of chloromethyl groups to optionally substituted bisphenol A monomer residues may be expressed as an average. In one variation, such intermediates are polymers that also include the residues of one or more optionally substituted phthalate monomers, including but not limited to phthalimide monomers, optionally substituted N-phenylphthalimide monomers, and the like.

In variations of each of the foregoing intermediates, the polymer includes the residues of other monomers, including but not limited to sulfone monomer residues, such as optionally substituted disarylsulfones, and the like.

In another embodiment, processes for preparing anion exchange membranes are described herein. The processes include one or more of the steps of (a) preparing a polymer comprising the residues of one or more optionally substituted bisphenol A monomers, it being understood that such polymers may include other monomer residues, including but not limited to one or more optionally substituted phthalate monomers, such as phthalimide monomers, optionally substituted N-phenylphthalimide monomers, and the like, and sulfone monomer residues, such as optionally substituted disarylsulfones, and the like; (b) chloroalkylating the polymer with a chloroalkylating agent; (c) optionally cross-linking the polymer with a cross-linking agent; (d) quaternizing the polymer with a quaternizing agent, and (e) alkalinizing the polymer with a base.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 : Effect of reaction temperature on the number of tethered chloromethyl groups: Time = 4.5h; CME = 2/1; Polymer cone. = 15%; ZnCl₂ = 5%. The number of chloromethyl groups was determined by ¹HNMR.

Figure 2: Effect of reaction time on the number of tethered chloromethyl groups: Temp. = 70 ⁰C; CME = 2/1; Polymer cone. = 15%; ZnCl₂ = 5%. Figure 3: Effect of polymer concentration on the number of tethered chloromethyl groups: Temp. = 70 ⁰C; Time = 4.5h; CME = 2/1; ZnCl₂ = 5%.

Figure 4: Effect of CME/polymer ratio on the number of tethered chloromethyl groups: Temp. = 70 ⁰C; Time = 4.5h; Polymer cone. = 15%; ZnCl₂ = 5%. Figure 5: Effect of amount of catalyst used on the number of tethered chloromethyl groups: Temp. = 70 ⁰C; Time = 4.5h; CME = 2/1; Polymer cone. = 15%.

Figure 6: TGA traces: poly(ether imide) and quaternized poly(ether imide).

Figure 7: Effect of the number of chloromethyl groups on ionic conductivity of the formed AAEM: The membranes were conditioned in 1 M KOH aqueous solution for 24 h prior to testing. The conductivity was measured at 24 ⁰C

Figure 8: Effect of KOH concentration on conductivity of AAEMs: The conductivity of the membrane was measured after being conditioned in 0.5 to 8.0 M KOH at room temperature for 24 h. The conductivity was measured at 24 ⁰C.

Figure 9: Conductivity of AAEMs with increasing temperature: The conductivity of the membrane was measured in de-ionized water as the temperature was raised to 95 ⁰C. The membrane was conditioned in 1.0 M KOH at room temperature for 24 h, followed by complete removal of free KOH prior to conductivity testing. The conductivity was measured at 24 ⁰C.

Figure 10: Conductivity of AAEM after treatment with KOH at elevated temperatures: The membrane was conditioned in 0.5 M, 1.0 M or 2.0 M KOH at elevated temperatures for 24 h followed by complete removal of free KOH prior to conductivity testing. The conductivity was measured at 24 ⁰C.

Figure 11: Water uptake of the membranes: original poly(ether- imide); chloromethylated poly(ether- imide); quaternized poly(ether-imide); and alkalized poly(ether- imide).

Figure 12: Conductivity of the AAEMs treated with TMEDA, followed by different tertiary amines: The conductivity was determined in de-ionized water at 24 ⁰C.

Figure 13: Effect of the thickness of the formed AAEM on conductivity: The conductivity was determined in de-ionized water at 24 ⁰C. Figure 14: Conductivity of AAEMs with increasing temperature: The conductivity of the membrane was measured in de-ionized water as temperature increased up to 95 ⁰C. The membrane was conditioned in 1.0 M KOH at room temperature for 24 h, followed by complete removal of free KOH prior to conductivity testing. The conductivity was measured in de-ionized water at 24 ⁰C.

Figure 15: Effect of KOH concentration on conductivity of AAEMs: The conductivity of the membrane was measured after the membrane was conditioned in 1.0 to 8.0 M KOH at room temperature for 24 h followed by complete removal of free KOH. The conductivity was measured in de-ionized water at 24 ⁰C.

DETAILED DESCRIPTION

In one embodiment, the membrane is prepared from a single anion exchange polymer. In another embodiment, the membrane is prepared from a mixture of anion exchange polymers. In another embodiment, the membrane also includes one or more additional polymeric components.

As used herein, the term "polymer" may include homopolymers, co-polymers, block copolymers, and/or graft polymers. In another embodiment, anion exchange membranes are described herein prepared from polymers comprising the residues of one or more optionally substituted bisphenol A monomers, or analogs or derivatives thereof, where a plurality of the residues of the bisphenol A monomers, or analogs or derivatives thereof, include one or more cationic groups. In another embodiment, anion exchange membranes are described herein prepared from polymers comprising the residues of one or more bisphenol A monomers, or analogs or derivatives thereof, and the residues of one or more phthalic acid monomers, where a plurality of the residues of the bisphenol A monomers, or analogs or derivatives thereof, include one or more cationic groups. In one variation, a portion of the bisphenol A monomers form ethers with a portion of the phthalic acid monomers. In another variation, a portion of the bisphenol A monomers form amides with a portion of the phthalic acid monomers. In another variation, a portion of the bisphenol A monomers form imides with a portion of the phthalic acid monomers. In another variation, a portion of the bisphenol A monomers form ethers with a portion of the phthalic acid monomers, and another portion of the bisphenol A monomers form imides with a portion of the phthalic acid monomers. In another embodiment, anion exchange membranes are described herein prepared from polymers comprising the residues of one or more bisphenol A monomers, or analogs or derivatives thereof, and the residues of one or more sulfone monomers, where a plurality of the residues of the bisphenol A monomers, or analogs or derivatives thereof, include one or more cationic groups. In one variation, a portion of the bisphenol A monomers form ethers with a portion of the sulfone monomers. In another variation, a portion of the bisphenol A monomers form amides with a portion of the sulfone monomers. In another variation, a portion of the bisphenol A monomers form ethers with a portion of the sulfone monomers, and another portion of the bisphenol A monomers form amides with a portion of the phthalic acid monomers.

In another embodiment, anion exchange membranes are described herein where the molar ratio of cationic groups to residues of bisphenol A monomers is in the range from about 1:1 to about 2.5:1, from about 1:1 to about 2:1; from about 1:1 to about 1.5:1; or from about 1.5:1 to about 2:1. In another embodiment, anion exchange membranes are described herein where the molar ratio of cationic groups to residues of bisphenol A monomers is about 1.5:1.

In another embodiment, anion exchange membranes are described herein where the cationic groups are ammonium groups. In one embodiment, the ammonium groups are selected from the group consisting of trimethylammoniumalkyl, triethylammoniumalkyl, dimethylethylammoniumalkyl, dimethylisopropylammoniumalkyl, dimethylaminoethyl- dimethylammoniumalkyl, alkyldimethylammonium-ethyl-dimethylammoniumalkyl, and combinations thereof. In another embodiment, a plurality of the cationic groups are trimethylammoniummethyl groups. In another embodiment, a plurality of the cationic groups are ethyldimethylammonium-ethyl-dimethylammoniumalkyl groups. In another embodiment, in each of the foregoing, a plurality of the anions are hydroxide ions.

In another embodiment, anion exchange membranes are described herein prepared from cross-linked polymers comprising the residues of one or more optionally substituted bisphenol A monomers, or analogs or derivatives thereof, where a plurality of the residues of the bisphenol A monomers, or analogs or derivatives thereof, include one or more cationic groups. In another embodiment, anion exchange membranes are described herein prepared from cross-linked polymers comprising the residues of one or more bisphenol A monomers, or analogs or derivatives thereof, and the residues of one or more phthalic acid monomers, where a plurality of the residues of the bisphenol A monomers, or analogs or derivatives thereof, include one or more cationic groups. In one variation, a portion of the bisphenol A monomers from ethers with a portion of the phthalic acid monomers. In another variation, a portion of the bisphenol A monomers from amides with a portion of the phthalic acid monomers. In another variation, a portion of the bisphenol A monomers from imides with a portion of the phthalic acid monomers. In another variation, a portion of the bisphenol A monomers from ethers with a portion of the phthalic acid monomers, and another portion of the bisphenol A monomers from imides with a portion of the phthalic acid monomers. In one aspect, the polymers are cross-linked with a polyamine. In one embodiment, the polyamine is a C₁-C₇ tetramethylalkylenediamine or pentamethyldialkylenetriamine, including but not limited to tetramethylethylenediamine, tetramethylpropylenediamine, pentamethyldiethylenediamine, and the like.

In another embodiment, anion exchange membranes are described herein prepared from cross-linked polymers comprising the residues of one or more bisphenol A monomers, or analogs or derivatives thereof, and the residues of one or more sulfone monomers, where a plurality of the residues of the bisphenol A monomers, or analogs or derivatives thereof, include one or more cationic groups. In one variation, a portion of the bisphenol A monomers from ethers with a portion of the sulfone monomers. In another variation, a portion of the bisphenol A monomers from amides with a portion of the sulfone monomers. In another variation, a portion of the bisphenol A monomers from ethers with a portion of the sulfone monomers, and another portion of the bisphenol A monomers from amides with a portion of the sulfone monomers. In one aspect, the polymers are cross-linked with a polyamine. In one embodiment, the polyamine is a C₁-C₇ tetramethylalkylenediamine or pentamethyldialkylenetriamine, including but not limited to tetramethylethylenediamine, tetramethylpropylenediamine, pentamethyldiethylenediamine, and the like.

Cross-linking may be performed after the chloroalkylation step or after the quaternization step. Generally, cross-linking may be performed after the chloroalkylation step. It has been observed herein that cross-linked polymers provide AAEMs with higher conductivities. Without being bound by theory, it has been discovered herein that when cross-linking is performed after the chloroalkylation, the quaternization may increase the overall number of quaternary groups that are placed in the polymer.

In another embodiment, anion exchange membranes are described herein having a conductivity of about 0.002 S/cm or greater in aqueous hydroxide, at a temperature of about 2O⁰C or greater, where the concentration of aqueous hydroxide is about 0.5 molar or greater, about 0.004 S/cm or greater, about 0.006 S/cm or greater, or about 0.007 S/cm or greater.

In another embodiment, anion exchange membranes are described herein that are stable to aqueous hydroxide at a concentration of about 2 molar or greater, or about 3 molar or greater. In another embodiment, anion exchange membranes are described herein that are stable to aqueous hydroxide at a concentration of about 0.5 molar or greater at a temperature of about 6O⁰C or greater, at a concentration of about 1 molar or greater at a temperature of about 6O⁰C or greater, at a concentration of about 1.5 molar or greater at a temperature of about 6O⁰C or greater, or at a concentration of about 2 molar or greater at a temperature of about 6O⁰C or greater. In another embodiment, anion exchange membranes are described herein that are stable to aqueous hydroxide at a concentration in the range from about 0.5 molar to about 1.5 molar at a temperature in the range of about 6O⁰C to about 8O⁰C, or at a concentration in the range from about 1 molar to about 1.5 molar at a temperature in the range of about 6O⁰C to about 8O⁰C.

In another embodiment, intermediates for preparing the anion exchange membranes described herein are described. In one embodiment, the intermediate is a polymer comprising the residues of one or more optionally substituted bisphenol A monomers, or analogs or derivatives thereof. In another embodiment, the intermediate is a polymer comprising the residues of one or more optionally substituted bisphenol A monomers, or analogs or derivatives thereof, where the one or more optionally substituted bisphenol A monomers include one or more chloroalkyl groups. In another embodiment, the intermediate is a polymer further comprising the residues of one or more optionally substituted phthalate monomers, or analogs or derivatives thereof. In one variation, a plurality of the bisphenol A monomers form ethers with a plurality of the phthalate monomers. In another variation, a plurality of the bisphenol A monomers form imides with a plurality of the phthalate monomers. In another variation, a plurality of the bisphenol A monomers form ethers with a plurality of the phthalate monomers, and another plurality of the bisphenol A monomers form imides with a plurality of the phthalate monomers. In another embodiment, processes for preparing the anion exchange membranes described herein are described. In one embodiment, the process comprises the step of reacting a polymer comprising the residues of one or more optionally substituted bisphenol A monomers, or analogs or derivatives thereof, with a chloroalkylating agent in the presence of a catalyst to form a chloroalkylated polymer. In another embodiment, the process comprises the step of reacting a polymer comprising the residues of one or more optionally substituted bisphenol A monomers, or analogs or derivatives thereof, and the residues of one or more optionally substituted phthalate monomers with a chloroalkylating agent in the presence of a catalyst to form a chloroalkylated polymer. In one variation, the bisphenol A monomers form a plurality of ethers with the phthalate monomers. In another variation, the bisphenol A monomers form a plurality of imides with the phthalate monomers. In another variation, the bisphenol A monomers form a plurality of ethers and imides with the phthalate monomers. In another embodiment, the chloroalkylating agent is bischloromethylether. In another embodiment, the ratio of the chloromethylating agent to the polymer is in the range of about 2:1 to about 8:1, about 3:1 to about 8:1; about 2:1 to about 6:1; about 3:1 to about 6: 1 ; about 2: 1 to about 5:1; about 3: 1 to about 5:1; about 2: 1 to about 4: 1 ; or about 3: 1 to about 4:1. In another embodiment, the processes described herein are performed at a temperature in the range of about 4O⁰C to about 100⁰C, or about 5O⁰C to about 8O⁰C, or about 6O⁰C to about 75⁰C. In another embodiment, the processes described herein are performed for a predetermined time in the range from about 1 h to about 24 h, or about 2.5 h to about 7.5 h, or about 3.5 h to about 4.5 h. In another embodiment, the processes described herein are performed at a concentration relative to the polymer in the range from about 15% to about 20% by weight.

In another embodiment, the process further comprises the step of reacting the chloroalkylated polymer with a quaternizing agent to form a quaternized polymer. In one embodiment, the quaternizing agent is a tertiary amine, such as a C₁-C₄ trialkylamine, where each alkyl group is independently selected. Illustrative tertiary amines include, but are not limited to, trimethylamine, triethylamine, dimethylethylamine, dimethylisopropylamine. In another embodiment, the quaternizing agent is a tertiary amine, such as a C₁-C₇ tetramethylalkylenediamine or pentamethyldialkylenetriamine, including but not limited to tetramethylethylenediamine, tetramethylpropylenediamine, pentamethyldiethylenediamine, and the like. In another embodiment, the process further comprises the step of reacting the quaternized polymer with hydroxide ion.

In another embodiment, the process further comprises the step of reacting the chloroalkylated polymer with a quaternizing agent to form a quaternized polymer with a diamine, such as a C₁-C₇ tetramethylalkylenediamine or pentamethyldialkylenetriamine, including but not limited to tetramethylethylenediamine, tetramethylpropylenediamine, pentamethyldiethylenediamine, and the like, and subsequently reacting the terminal dimethylamino groups with an alkylating agent, such as a C₁-C₄ alkylating agent. . It is appreciated that there may be advantages of using Alkaline Anion Exchange Membrane (AAEM) instead of proton-exchange membranes (PEM). Those advantages may be related to the kinetics of hydrogen or ethanol oxidation, where such kinetics are faster in an alkaline media. In addition, the catalysts that are included in such processes, including non-precious metal catalysts, transition metal macrocycles, and the like, are generally more stable in alkaline media, where they may easily decompose in a strong acid media.

It is also appreciated that the anion exchange membrane polymers may exhibit improved toughness, improved stability or resistance to different solvents, improved stability to high pH environments, and improved stability to environmental conditions and temperatures.

It is also appreciated that other characteristics of the membranes described herein may affect the aforementioned desirable properties or advantages, including but not limited to membrane preparation, thickness of membrane, conditions for quaternization, quantification of functional groups on the membrane, membrane preparation temperature, and factors affecting membrane ionic conductivity.

In another embodiment, the anion exchange polymer is prepared from bisphenol A, or an analog or derivative thereof, such as a compound of the formulae:

Z-Ar-X-Ar-Z or Z-Ar-O-Ar-X-Ar-O-Ar-Z wherein Ar is an optionally substituted divalent or trivalent benzene; X is C(R)₂, C(O), SO₂, and the like, where R is alkyl, such as methyl, or haloalkyl, such as trifluoromethyl, and the like; and Z is OH, NH₂, CO₂H, and the like, or Z forms a fused anhydride. Illustratively, the anion exchange polymer is prepared from bisphenol A, or an analog or derivative thereof. Illustrative bisphenol A monomers include the following formulae:

In another embodiment, in each of the foregoing monomers, one or more of the aryl groups are optionally substituted at one or more aromatic carbons. Illustrative substituents include alkyl, such as C₁-C₄ alkyl, halo, such as fluoro, chloro, bromo, and iodo, alkoxy, such as C₁-C₄ alkoxy, haloalkyl, haloalkoxy, cyano, nitro, and the like.

In one illustrative aspect, the anion exchange polymer is prepared from a homopolymer of a single bisphenol A, or analog or derivative thereof. In another illustrative aspect, the anion exchange polymer is prepared from a copolymer of a plurality of bisphenol A, and analogs or derivatives thereof. In another illustrative aspect, the anion exchange polymer is prepared from a copolymer of one or more of bisphenol A, and analogs or derivatives thereof, and another monomer. In this latter aspect, illustrative other monomers include, but are not limited to compounds of the formulae:

In another embodiment, in each of the foregoing monomers, one or more of the aryl groups are optionally substituted at one or more aromatic carbons. Illustrative substituents include alkyl, such as C₁-C₄ alkyl, halo, such as fluoro, chloro, bromo, and iodo, alkoxy, such as C₁-C₄ alkoxy, haloalkyl, haloalkoxy, cyano, nitro, and the like.

It is to be understood that the anion exchange polymers described herein may be formed from a variety of monomers, the residues of which are linked to each other with a variety of functional groups, including, but are not limited to, amides, ethers, amines, imides, esters, ureas, urethanes, and the like.

In another illustrative embodiment, the polymers used to prepare the anion exchange polymers described herein are compounds of the following formulae, or include one or more fragments of the following formulae:

where n is an integer.

In another embodiment, in each of the foregoing polymers, one or more of the aryl groups are optionally substituted at one or more aromatic carbons. Illustrative substituents include alkyl, such as C₁-C₄ alkyl, halo, such as fluoro, chloro, bromo, and iodo, alkoxy, such as C₁-C₄ alkoxy, haloalkyl, haloalkoxy, cyano, nitro, and the like.

In another embodiment, in each of the foregoing polymers, one or more of the aryl groups, other than the aryl groups forming the bisphenol A divalent radical are optionally substituted at one or more aromatic carbons. Illustrative substituents include alkyl, such as C₁-C₄ alkyl, halo, such as fluoro, chloro, bromo, and iodo, alkoxy, such as C₁-C₄ alkoxy, haloalkyl, haloalkoxy, cyano, nitro, and the like.

In another illustrative embodiment, the anion exchange polymer is a compound of the following formulae, or includes one or more fragments of the following formulae:

where R an independently selected alkyl group in each instance, such as a C₁-C₄ alkyl group, including methyl, ethyl, isopropyl, butyl, and the like; and n is an integer. In another embodiment, R is methyl in each instance.

In another embodiment, in each of the foregoing anion exchange polymers, one or more of the aryl groups are optionally substituted at one or more aromatic carbons. Illustrative substituents include alkyl, such as C₁-C₄ alkyl, halo, such as fluoro, chloro, bromo, and iodo, alkoxy, such as C₁-C₄ alkoxy, haloalkyl, haloalkoxy, cyano, nitro, and the like.

In another embodiment, in each of the foregoing anion exchange polymers, one or more of the aryl groups, other than the aryl groups forming the bisphenol A divalent radical are optionally substituted at one or more aromatic carbons. Illustrative substituents include alkyl, such as C₁-C₄ alkyl, halo, such as fluoro, chloro, bromo, and iodo, alkoxy, such as C₁-C₄ alkoxy, haloalkyl, haloalkoxy, cyano, nitro, and the like.

In each of the foregoing embodiment, the integer n is illustratively that which corresponds to an average molecular weight of the corresponding polymer in the range from about 10 kD toa bout 80 kD, or in the range from about 20 kD to about 60 kD, or in the range from about 30 kD to about 50 kD.

In another embodiment, the anion exchange polymer described herein has a glass transition (T_G) temperature of at least about 100 ⁰C, about 150 ⁰C, or about 250 ⁰C. In another embodiment, the anion exchange membrane includes one or more additional polymer components that are also anion exchange polymers selected from polystyrenes, and the like. It is appreciated that not all polymeric components have similar levels of TQ. In an illustrative variation, a polymer with a low T_G can be mixed with another polymer with a high T_G to prepare the membranes described herein. It is also appreciated that polymers in which the aryl groups are substituted with hydrophilic substituents increase the water solubility of the membrane.

It is appreciated that in each of the embodiments described herein, some or all of one or more of the polymer components forming the anion exchange membrane may be present in various levels of crystallinity, including both amorphous and partially crystalline forms.

In another illustrative embodiment, the anion exchange polymers described herein may be prepared according to the following process:

In one aspect of the illustrative process, the first step for functionalization of polymer is chloroalkylation, such as chloromethylation. In another aspect, the solvents for chloroalkylation include chloroform, methylene chloride, dichloroethane, chloroethane, trichloroethane, hexane, petroleum ether, and the like. In another aspect, the catalysts for chloroalkylation include aluminum chloride, sulfuric acid, boron trifluride, zinc chloride, tin chloride, strontium chloride, and the like. In another aspect, the chloroalkylation agents include chloroacetyl chloride, chloropropionyl chloride, chloromethylether, chloroethylether, chlorobutylether, acetyl chloride, acetic anhydride, and the like.

Illustratively, the reaction temperature for chloroalkylation, such as chloromethylation, ranges from about 40 ⁰C to about 90 ⁰C, or alternatively from about 65 ⁰C to about 80 ⁰C. Also illustratively, the reaction time for chloroalkylation, such as chloromethylation, ranges from about 2 h to about 36 h, or alternatively from about 3 h to about 12 h.

In one aspect, the chloromethylation step is performed below a temperature above which the polymer will no longer be soluble, or above which the polymer will form a gel. In another aspect, the chloromethylation step is performed below a concentration above which the polymer will no longer be soluble, or above which the polymer will form a gel. In another aspect, the chloromethylation step is performed for a period of time above which the polymer will no longer be soluble, or above which the polymer will form a gel.

In another aspect of the illustrative process, the second step is to quaternize the chloroalkylated polymer. Illustratively, the quaternization agents include trimethylamine, triethylamine, tributylamine, triphenylamine, dimethylethylamine, dimethylisopropylamine, tetramethylethylenediamine, and the like. Also illustratively, the concentration of quaternization agent ranges from about 15% to about 70% by weight, or alternatively from about 25% to about 55% by weight. Also illustratively, the reaction temperature ranges from about 50⁰C to about 130 ⁰C, or alternatively from about 65⁰C to about 98 ⁰C. Also illustratively, the reaction time ranges from about 1 h to about 36 h, or alternatively from about 8 h to about 16 h.

In another aspect of the illustrative process, the third step is to alkalinize the quaternized polymer. Illustratively, the alkalization agents include sodium hydroxide, potassium hydroxide, lithium hydroxide, and the like. Also illustratively, the concentration of alkalization agent ranges from about 0.5 N to about 5 N, or alternatively from about 1 N to about 3 N. Also illustratively, the reaction temperature ranges from about 10⁰C to about 90 ⁰C, or alternatively from about 20⁰C to about 50 ⁰C. Also illustratively, the reaction time ranges from about 2 h to about 48 h, or alternatively from about 4 h to about 24 h.

In another embodiment, the membrane can be prepared before or after quaternization. In either case, the conditions for membrane preparation are disclosed herein. Illustratively, the solvents used for membrane preparation include chloroform, dichloroethane, chloroethane, trichloroethane, DMF, NMP, DMAc, DMSO, xylene, toluene, and the like. Also illustratively, the concentration of polymer in solvent ranges from about 0.5% to about 60% by weight, or alternatively from about 3% to about 25% by weight. Also illustratively, the reaction temperature ranges from about 70⁰C to about 350 ⁰C, or alternatively from about 120⁰C to about 250 ⁰C. Also illustratively, the reaction time ranges from about 3 h to about 48 h, or alternatively from about 4 h to about 24 h.

EXAMPLES The following examples describe illustrative embodiments of the invention. However, these examples are illustrative only, and should not be construed to limit the scope of the invention described herein. Modifications and variations as described herein are to be understood as falling within the scope of the invention. EXAMPLE: Materials: Poly(ether-imide), 1,2-dichloroethane, zinc chloride, chloromethyl ether, methanol, N,N-dimethylformamide, 45% trimethylamine aqueous solution, trimethylamine (TMA), triethylamine (TEA), dimethylethylamine (DMEA), dimethylisopropylamine (DMIPA), tetramethylethylenediamine (TMEDA), bromoethane (BE), potassium hydroxide, deuterated chloroform, and all other commercially available reagents and solvents were used as received from Fisher Scientific Inc. (Pittsburgh, PA) or other commercial vendors without further purification.

EXAMPLE: Illustrative Synthesis of Polyimides. A mixture of 12.3 g of 4,4' - (4,4'-isopropylidene-diphenyl-l,l'-diyldioxy)dianiline, 15.6 g of 4,4'-(4,4'-isopropylidene- diphenoxy)bis(phthalic anhydride), 12 ml pyridine, 60 ml of DMF, was heated with stirring at 150 ⁰C for 3 h. After water was collected with a Dean-Stark trap, the temperature was increased to 190-200 ⁰C and kept for another 2 h. The polymer was precipitated with methanol, followed by washing with distilled water. The obtained polymer was freeze-dried and stored before use. The yield was 99%. The inherent viscosity of polymer was determined at a concentration of 0.5 g/dl in DMAc at 30 ⁰C.

EXAMPLE: Illustrative Synthesis of Polyethers. To 13.7 g of bisphenol A in 40 ml DMF, 10.0 g sodium hydroxide aqueous solution (50 wt%) and 80 ml of toluene were added. The mixture was reacted at 160-180 ⁰C in the presence of N₂ with the help of Dean- stark trap to remove water. After all the water and toluene were removed, the temperature was cooled down to room temperature. Then 4-chlorophenyl sulfone, 17.23 g, in 40 ml DMF was added into the above solution. The mixture was allowed to react in DMF at 160-180 ⁰C under N₂ purging for 3 h before purification. The polymer was precipitated with methanol followed by washing with distilled water. The obtained polymer was freeze-dried or vacuum-dried at 80-90 ⁰C for 24 h. The inherent viscosity of the polymer was determined at a concentration of 0.5 g/dl in DMAc at 30 ⁰C.

EXAMPLE: Chloromethylation. To 2 g of polyimide or polyether in chloroform, 0.6 g zinc chloride and 1 ml of chloromethyl methyl ether was added. The reaction was kept at 60 ⁰C for 3 h before purification. The polymer was precipitated with methanol and dried in a vacuum oven. EXAMPLE: Membrane Formation. The above chloromethylated polymer was dissolved in DMF and heated at 150 ⁰C in a glass container for 5 h, followed by heating at 200 ⁰C for another 2 h. The membrane was detached from the glass container for further use. EXAMPLE: Quaternization. To the chloromethylated membrane, 30% trimethylamine was added. The reaction was run at 90 ⁰C overnight. After that, the membrane was washed with distilled water three times.

EXAMPLE: Alkalization. To the quaternized membrane, 1 N KOH was added. The reaction was run at room temperature overnight. After that, the membrane was washed with distilled water until the pH became neutral.

EXAMPLE: Characterization. The synthesized polymers were characterized using viscometry and differential scanning calorimetry (DSC). The functionalized polymers were characterized by Fourier transform-infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. FT-IR spectra were obtained on a FT-IR spectrometer

(Mattson Research Series FT/IR 1000, Madison, WI). ¹H-NMR spectra were obtained on an NMR spectrometer (Varian-Inova narrow-bore 500 MHz NMR, Varian, Inc., Palo Alto, CA) using deuterated methyl sulfoxide as a solvent. Viscosity was measured using a Ubbelohde viscometer. Relative viscosity was obtained from measured time for polymer solution divided by measured time for pure solvent when liquid passed through the capillary part of the viscometer. Inherent viscosity was obtained from the equation: Ln RV/c, where RV = relative viscosity and c = concentration of polymer solution. Glass-transition temperature was measured at 10 min/°C in the presence of nitrogen using a differential scanning calorimeter (Perkin Elmer). EXAMPLE: Viscosity and Glass-Transition Temperature of Synthesized

Polymers. The viscosity and glass-transition temperatures of illustrative synthesized polymers are displayed in Table 1. It is appreciated that, in general, viscosity values reflect molecular weight (MW) of polymers, and that inherent viscosity has been commonly used to indirectly characterize the MWs of polyimides and polyethers.

Table 1. Viscosity and Glass-transition Temperature of Illustrative Synthesized Polymers.

Polymer Relative Viscosity Inherent Viscosity Glass-transition

1 1.11 0.21 220.0

2 1.10 0.20 193.0

3 1.18 0.33 216.0

4 1.16 0.29 186.0

5 1.07 0.13 202.7

6 1.05 0.10 198.0

Viscosity was measured using a Ubbelohde viscometer. Relative viscosity was obtained from measured time for polymer solution divided by measured time for pure solvent when liquid passed through the capillary part of the viscometer. Inherent viscosity was obtained from the equation: Ln RV/c, where RV = relative viscosity and c = concentration of polymer solution. ³Glass-transition temperature was measured at 10 min/ 0C in the presence of nitrogen using a differential scanning calorimeter (Perkin Elmer). EXAMPLE. Synthesis of Chloromethylated Polyimides and Quaternized Polyimides. Following are illustrative chloromethylated polyimides and quaternized polyimides that were synthesized as described in the above EXAMPLES. The chemical structures of the resulting chloromethylated polyimides and the quaternized polyimides are shown in Scheme 1. The conversion to chloromethylated polyimides and quaternized polyimides was monitored by comparative IR spectroscopy and ¹H-NMR spectroscopy. Characteristic peaks in these spectra were indicative of the compounds that are shown.

Scheme 1

Chloromethylation of the poly(ether-imide): To a reactor charged with 15 ml 1,2-dichloroethane, 2.0 g poly(ether-imide) and 0.1 g zinc chloride, 1.3 ml chloromethyl ether was added dropwise with stirring at 70 ⁰C. The reaction was allowed to continue for 4.5 h. After that, the polymer was precipitated with methanol to remove the catalyst, excess chemicals and solvent, followed by washing with methanol and de-ionized water several times prior to drying. Quaternization of the poly(ether-imide): The purified chloromethylated polymer was dissolved in N,N-dimethylformamide, followed by pouring into a Petri dish. The polymer in the Petri dish was dried in an oven overnight at 70 ⁰C and then at 150 ⁰C for an additional two hours. The formed membrane was then treated overnight with 30% trimethylamine solution followed by washing with de-ionized water several times. The thickness of the formed membranes was in the range of 25-30 μm.

Alkalization of the poly(ether-imide): The quaternized membrane was soaked in a 1 M potassium hydroxide aqueous solution at room temperature for 24 h prior to testing. The alkalized membrane was then washed with de-ionized water several times and soaked in de-ionized water with numerous washings within 24 h prior to evaluation.

EXAMPLE: Characterization of Chloromethylated Polyimides and Quaternized Polyimides. ¹H-NMR was used for characterization of the poly(ether-imide), chloromethylated poly(ether-imide) and quaternized poly(ether-imide). The chemical shifts of the poly(ether-imide) were found as follows (ppm): a: 7.26-7.9 (multiple hydrogens on phenyl groups) and b: 1.72 (CH₃). The chemical shifts of the chloromethylated poly(ether- imide) were (ppm): a: 7.26-7.9 (multiple hydrogens on phenyl groups), b: 4.64 (CH₂Cl) and c: 1.72 (CH₃). The chemical shifts for the quaternized poly(ether-imide) were (ppm): a: 7.26- 7.9 (multiple hydrogens on phenyl groups), b: 2.70 (CH₃ linked to N) and c: 1.72 (CH₃ on Bisphenol A). The characteristic chemical shift at 4.64 confirmed the formation of the chloromethylated poly(ether-imide). The disappearance of the chemical shift at 4.64 and the appearance at 2.70 confirmed the formation of the quaternized poly(ether-imide).

EXAMPLE: Effect of Reaction Temperature on Chloromethylation. An important step in preparing AAEMs is chloromethylation, because the degree of chloromethylation may also determine how many conductive hydroxyl groups can be loaded onto the polymer chain, which in turn may determine the conductivity. It is appreciated that several parameters may affect the chloromethylation reaction and the number of tethered chloromethyl group on the polymer. It should also be appreciated that under certain conditions chloromethylation may cause gelation, leading to a lower yield of the chloromethylated polymer. Likewise, it should be appreciated that crosslinking often takes place rapidly during chloromethylation, such as for example, in chloromethylation of polystyrene resins, wherein an active aromatic ring on one polymer chain attacks the chloromethyl group on another polymer chain in a Friedel-Crafts alkylation fashion, resulting in inter-polymer or intra-polymer crosslinking or gel formation (Lenz, R. W., Organic Chemistry of High Polymers, Interscience Publishers: New York, NY, 1967).

In order to improve chloromethylation without gelation or with less gelation, the effect of reaction temperature on the number of resulting tethered chloromethyl groups was studied, using ¹H-NMR as a monitoring tool. The number of chloromethyl groups was obtained by integration of the peaks exhibited in the NMR spectra by the chloromethyl and phenyl groups. The results are displayed in Figure 1, which shows that, in general, raising the reaction temperature results in a greater degree of chloromethylation of the polymer backbone. However, it may appear that above about 70 ⁰C the number of tethered chloromethyl groups does not increase further.

EXAMPLE: Effect of Reaction Time on Chloromethylation. The effect of reaction time on chloromethylation was studied using ¹H-NMR as a monitoring tool. The results are displayed in Figure 2, which may indicate that the longer the reaction time, the greater the degree of chloromethylation of the polymer backbone. However, too long a reaction time may generally result in formation of increased amounts of gel (e.g., see Table 2).

EXAMPLE: Effect of Polymer Concentration on Chloromethylation. The effect of polymer concentration on chloromethylation was studied using ¹H-NMR as a monitoring tool. The results are shown in Figure 3. In general, it was observed that the higher the polymer concentration, the greater the number of tethered chloromethyl groups.

However, above a concentration of about 20%, it appears that greater amounts of gel begin to form (Table 2).

EXAMPLE: Effect on Chloromethylation of the Ratio of Chloromethylether (CME) to Polymer. The effect of CME/Polymer ration on chloromethylation was studied using ¹H-NMR as a monitoring tool. As seen in Figure 4, it appears that increasing the ratio of CME to polymer may be important in increasing the number of resultant tethered chloromethyl groups. However, there may also be an increase in gel formation (see Table X).

EXAMPLE: Effect of Catalyst Concentration. Catalyst concentration may have an important effect on reaction rate (Bartholomew C. H., Fundamentals of Industrial Catalytic Processes, 2nd ed., Wiley: Hoboken, NJ. 2006). The effect of catalyst concentration on chloromethylation was studied using ¹H-NMR as a monitoring tool. The data in Figure 5 may indicate that increasing the catalyst oncentration may increase the number of tethered chloromethyl groups. The catalyst may also shorten the reaction time (see Table 2).

EXAMPLE: Effect of Reaction Scale. The chloromethylation process described herein was performed at three different scales, 2g, 4g, and 6g of polyimide, and monitored using ¹H-NMR, which showed no discernible variation in yield.

EXAMPLE: Effect of Various Parameters on Chloromethylation and Gelation. Table 2 displays the chloromethylation data obtained upon studying various reaction parameters.

TABLE 2. Effects of the Various Parameters Affecting Chloromethylation.

Temp. Time CME/polymer Polymer cone. Catalyst added Gelation¹ Tethered

(⁰C) (h) (wt/wt) (wt) (wt) CH₂Cl²

23 4.5 2/1 15% 5% No 0

50 4.5 2/1 15% 5% No 0.08

60 4.5 2/1 15% 5% No 0.39

70 4.5 2/1 15% 5% No 0.55

85 4.5 2/1 15% 5% No 0.56

70 1 2/1 15% 5% No 0.19

70 3 2/1 15% 5% No 0.38

70 8 2/1 15% 5% No 0.73

70 16 2/1 15% 5% No 0.82

70 24 2/1 15% 5% 10% 1.00

70 4.5 1/1 15% 5% No 0.25

70 4.5 4/1 15% 5% No 0.89

70 4.5 6/1 15% 5% 22% 1.35

70 4.5 8/1 15% 5% 78% 1.52

70 4.5 2/1 10% 5% No 0.12

70 4.5 2/1 20% 5% No 0.74

70 4.5 2/1 25% 5% 30% 0.83

70 4.5 2/1 15% 10% No 0.80

70 4.5 2/1 15% 15% 16% 1.05

Gelation was determined by weighing. The number of chloromethyl groups was determined by HNMR. EXAMPLE: Synthesis and Preparation of Alkaline Anion Exchange Membranes. The alkaline anion exchange membrane, poly(bisphenol-A-co-4-nitrophthalic anhydride-co-l,3-phenylenediamine), was synthesized and prepared as described in the above EXAMPLES. The resulting membrane was strong and transparent. The thickness of the membrane was approximately 8-10 μm. .

EXAMPLE: Thermal Decomposition. The thermal decomposition history of both poly(ether-imide) and quaternized poly(ether-imide) membranes was determined on a thermo gravimetric analyzer (Perkin Elmer TGA 7, Shelton, CT) at a heating rate of 10 °C/min under nitrogen flow.

Figure 6 shows the TGA weight-loss curves for the poly(ether-imide) and quaternized poly(ether-imide). For the poly(ether-imide), the weight loss is observed between 400 and 550 ⁰C. This loss was approximately 55%, which may suggest that the polymer was very stable and only partially degraded at such a high temperature. For the quaternized poly(ether-imide), two significant weight-loss transition traces were noticed: (1) a weight loss between 140 and 270 ⁰C, which, without being bound by theory, may be attributable to the removal of the quaternary ammonium groups (Fang, J., Shen, P. K., J. Membr. Sci., 2006, 285, 317); and (2) a weight loss above 325 ⁰C, which, without being bound by theory, may be attributable to a partial degradation of poly(ether-imide). Both weight-loss curves may indicate that this poly(ether-imide) is a very thermally stable polymer.

EXAMPLE: Ionic Conductivity Measurements. The OH^" ionic conductivity of the formed membranes was measured using AC impedance spectroscopy with a Solartron 1250 frequency response analyzer interfaced with a 1287 potentiostat/galvanostat. The measurement was conducted in the galvanostatic mode over frequencies ranging from 0.1 Hz to 60 KHz with a galvanostatically controlled AC current of 5 mA. A standard four-probe conductivity cell (BekkTech LLC, Loveland, CO) was used to assemble the membrane test sample. The area resistance of the membrane was determined in de-ionized water at 24 ⁰C. Ionic conductivity, σ (S/cm), was calculated according to the equation: σ = 1 / (RTW), where 1 = the length of the membrane between two potential sensing platinum wires (cm), R = the membrane resistance (Ω), T = the thickness of the membrane (cm) and W = the width of the membrane (cm) (Park, J.-S., Park, G.-G., Park, S.-H., Yoon, Y.-G., Kim, C-S.,; Lee, W.-Y., Macromol Symp. 2007, 249/250, 174-182). To test the conductivity of the functionalized poly(ether-imide), several polymers with different numbers of tethered functional groups per unit were selected. After being converted to tertiary amines that can carry hydroxyl ions, the conductivity of the formed membrane was measured. Figure 7 shows the effect of the number of the tethered chloromethyl group on ionic conductivities of the illustrative AAEMs. It is generally known that ionic conductivity is proportional to the number of ions that can be exchanged or transported through the membrane under an electrical potential. The ions for conductivity may actually be hydroxyl anions (OH^"). Thus, the more chloromethyl groups tethered onto the poly(ether-imide), the more OH^" anions would be available, and the higher the expected ionic conductivity. As may be construed from Figure 7, it seems that increasing the number of tethered chloromethyl groups may lead to increased ionic conductivity. Thus, conductivity ranged from 9.21 x 10^~4 to 4.20 x 10^"3 corresponding to the number of tethered chloromethyl groups per unit of poly(ether-imide) from 0.25 to 1.45.

EXAMPLE: Ionic Conductivity of AAEM. Figure 8 shows the effects of alkaline concentration on the ionic conductivity of the formed AAEM at room temperature. To examine the chemical stability of the formed AAEM to different concentrations of KOH, the membrane was conditioned in KOH from 0.5 to 8.0 M for 24 h. After the free KOH was completely removed, the conductivity of the membrane was measured. There was almost no change in conductivity for all the membranes treated with different concentrations of KOH solutions. The conductivity ranged from 2.28 to 2.55 x 10^"3 S/cm. The result may indicate that the membrane is quite stable at room temperature even when treated with a KOH concentration up to 8.0 M.

Figure 9 shows the effect of temperature on the ionic conductivity of the formed AAEM. To examine the effect of temperature, the membrane was treated with 1.0 M KOH at room temperature for 24 h. It was then washed with de-ionized water numerous times and soaked in de-ionized water for 24 h. After complete removal of the free KOH, the conductivity of the membrane was measured at elevated temperatures. The conductivity increased from 25 to 40 ⁰C followed by almost no change in the conductivity up to 95 ⁰C. The conductivity values ranged from 2.28 to 3.51 x 10^"3 S/cm. In general, conductivity increases with increasing temperature for ionic conductive materials (Fang, J., Shen, P. K., Quaternized poly(phthalazinon ether sulfone ketone) membrane for anion exchange membrane fuel cells, J. Membr. Sci., 2006, 285, 317-322). However, the membrane herein appears to have increased its conductivity from 25 to 40 ⁰C and then remained constant. Figure 10 shows the conductivity of the AAEM after treatment with different concentrations of KOH at elevated temperatures for 24 h. This was done to test the tolerance of the membrane to base treatments at elevated temperatures. Three concentrations (0.5 M, 1.0 M, and 2.0 M) of KOH were applied. After the AAEMs were soaked in 0.5 M, 1.0 M or 2.0 M at different temperatures, the conductivities of the specimens were measured at room temperature. The conductivity values from the tested membranes ranged from 2.05 to 3.20 x 10^"3 S/cm. No significant change was found between different concentrations of KOH at 25 ⁰C. There was a slight decrease in conductivity at 40 ⁰C when the concentration of KOH was increased. No differences in conductivity were found between the membranes treated with 0.5 and 1.0 M KOH at 60 ⁰C or 80 ⁰C. The AAEMs soaked in either 0.5 M or 1.0 M KOH at 80 ⁰C showed the highest conductivities (3.12 and 3.20 x 10^"3 S/cm). However, the membranes treated with 2.0 M KOH at 60 ⁰C and 80 ⁰C, as well as all the membranes treated with 0.5 M, 1.0 M, and 2.0 M at 100 ⁰C, were found to have deteriorated or degraded. Thus, the conductivity of these membranes could not be measured. The results may suggest that these membranes may not tolerate the KOH treatment at 100 ⁰C, but may tolerate 1.0 M KOH at 80 ⁰C.

EXAMPLE: Water Uptake of Polymers. Water uptake of the membranes was determined using a moisture analyzer (OmniMark 2, Sartorius Mechatronics, Tempe, AZ). The membrane sample was briefly soaked in de-ionized water for 24 hours, and then the surface water was carefully wiped off with paper. The sample was then placed in the moisture analyzer. Water uptake was calculated based on the following formula: water uptake = (Ww - Wd)AVd x 100, where Ww = weight of wet membrane and Wd = weight of dried membrane. Figure 11 shows the water uptake data of the poly(ether-imide) (PBNAPDA), chloromethylated poly(ether-imide) (PI-CH₂Cl), quaternized poly(ether-imide) (PI-TMA), and alkalized poly(ether-imide) (PI-OH). The alkalized poly(ether-imide) appears to have the greatest water uptake (43.1%), followed by the quaternized polymer (7.82%), chloromethylated polymer (3.43%), and poly(ether-imide) (0.58%). Without being bound by theory, this difference in water uptake may be attributed to the nature of the functional group that the different polymers carry. EXAMPLE: Ion Exchange Capacity Determination. The ion exchange capacity (IEC) of the membrane was determined following the procedures described elsewhere (Hwang, G. -J., Ohya, H., Preparation of anion-exchange membrane based on block copolymers: Part 1. Amination of the chloromethylated copolymers., J. Membr. Sci., 1998, 140, 195-203). The quaternized polymer membrane was soaked in 1 M potassium hydroxide solution for 24 hours to replace the Cl^" with an OH^". Afterward, the membrane was washed and soaked in de-ionized water for another 24 hours to remove the attached alkali. The membrane was then equilibrated with 50 ml of 0.01 M HCl aqueous solution for 24 hours, followed by back titration using an automated titrator (SMTitrino 702, Westbury, NY) for determination of IEC. The dry weight (Wa) of the sample was then measured using the moisture analyzer. The IEC of the anion-exchange membrane was calculated based on the formula: IEC = (M₀ - M_t)/Wd, where M₀ = moles of HCl added originally and M_t = moles of HCl or equivalent to the moles of potassium hydroxide consumed during back titration. Table 3 shows the IEC values of both quaternized and alkalized poly(ether-imide), in addition to water uptake and conductivity values. Table 3. WS, IEC, and ionic conductivity of the tested membranes

_{Λ Λ ^} . , WS (%, by „„ , _{I Λ} Ionic Conductivity x 10³

Material . ' / IEC (meq/g) ,„ . . ^} weight) ^ ^b (S/cm)

Quaternized poly(ether-imide) 7.82 0.186 0.57

Alkalized poly(ether-imide) 43.1 0.983 2.28-3.51

EXAMPLE: Polymers Quaternized with Amines Other Than Trimethylamine. In this study, three approaches were used to quaternize the chloromethylated polymer. The ionic conductivity test was used as an evaluation tool. The first approach was to quaternize the pre-formed membrane via TMA, as described earlier. The second approach was to use a difunctional crosslinker, TMEDA, to quaternize the chloromethylated polymer when the polymer was still in solution. As a result, a cross-linked polymer network was initially formed. Following that, the unreacted CH₂Cl groups were further quaternized by a mono- or di-tertiary amine in order to convert as many of the CH₂Cl groups as possible to quaternized groups. The ionic conductivity resulting from the second approach was significantly higher with the values ranging from 6.5 to 9.8 x 10^"3 S/cm, even at CH₂Cl = 1.2, which is almost twice ionic conductivity resulting from the first approach. Five tertiary amines were studied for quaternization. The ionic conductivity of these five tertiary amines (see Figure 12) was in the decreasing order: TMA > DMEA > DMIPA > TMEDA > TEA. Without being bound by theory, a comparison of the structures of the tertiary amines with the conductivity results, may show that steric hindrance determines the ease of quaternization. The smaller methyl group made the quaternization the easiest, which allows the membrane quaternized with TMA to have the highest conductivity. In contrast, TEA had the lowest conductivity and TMEDA had the second lowest. The third approach was to cross-link the polymer and then quaternize the cross-linked membrane via BE. This approach was designed to further quaternize the one-end dimethylamino group pendent on the polymer after the membrane was quaternized with difunctional TMEDA. This approach led to significantly increased the ionic conductivity as well. As shown in the Figure, TMED A/BE exhibited a conductivity value of 9.83 x 10^~3 S/cm at CH₂Cl = 1.2. This value was also higher than that for the membrane simply treated with TMA without cross-linking in Approach 1. The data may suggest that the second and third approaches may provide higher conductivity of the AAEM than the first approach.

EXAMPLE: Effect of Thickness, Temperature and KOH Concentration on Conductivity of the Formed Membrane. Membrane thickness is important to the performance of the AAEM. Generally, a thinner membrane may provide lower resistance across the membrane, whereas a thicker membrane may exhibit better mechanical stability. To determine the effect of thickness on conductivity, the ionic conductivities of membranes with thicknesses of approximately 33, 67, 110 and 160 μm we measured. The results shown in Figure 13 may indicate that there are no differences in ionic conductivities between membranes of different thicknesses, which may mean that both quaternization and alkalization occur uniformly throughout the membrane.

EXAMPLE: Comparison of the Effect of Temperature on Ionic Conductivity of Membranes Prepared via Approach 1 and Approach 2. Figure 14 shows the effect of temperature on the ionic conductivity of the membranes prepared via approach 1 (pre-formed membrane treated with TMA) and approach 2 (polymer cross-linked with TMEDA and then treated with TMA). The quaternized membranes were treated with 1.0 M KOH at room temperature for 24 h, followed by washing with de-ionized water numerous times and soaking in de-ionized water for 24 h. After complete removal of the free KOH, the conductivity of the membranes was measured at elevated temperatures. The measured conductivity for both membranes showed an increase with increasing temperatures. The conductivity for the membrane quaternized via Approach 1 increased from 25 to 40 °C followed by almost no change in the conductivity up to 95 °C, with values ranging from 2.28 to 3.51 x 10^"3 S/cm. The conductivity for the membrane quaternized via Approach 2 showed a continuous increase from 25 to 95 °C, with values ranging from 7.83 x 10^~3 to 1.53 x 10^~2 S/cm. Improvement in conductivity appears to have been achieved when the membrane was cross-linked with TMEDA and post-quaternized during the gel-formation stage. Without being bound by theory, a possible explanation may be that in approach 1, TMA treatment takes place after the membrane is formed, and thus only the surface or at least not the whole membrane is quaternized; in contrast, in approach 2, treatment with TMEDA/TMA takes place during the gel formation stage, which allows a thorough quaternization throughout the membrane.

EXAMPLE: Comparison of Effects of Alkaline Concentration on Ionic Conductivity of AAEMs Treated with TMA Alone and TMEDA/TMA. Figure 15 shows the effect of alkaline concentration on the ionic conductivity of both AAEMs treated with TMA alone and TMEDA/TMA at room temperature. To determine the chemical stability of the formed AAEM toward different concentrations of KOH, the membranes were conditioned individually in KOH from 1.0 to 8.0 M for 24 h. After the free KOH was completely removed, the conductivity of each membrane was measured. There was hardly any change in conductivity for the membranes treated with different concentrations of KOH solutions. The measured conductivity ranged from 2.28 to 2.55 x 10^"3 S/cm for the TMA-treated membrane and from 7.13 to 9.5 x 10^"3 S/cm for the TMEDA/TMA-treated membrane. These results may indicate that the membrane is quite stable at room temperature even when treated with a KOH concentration up to 8.0 M.

Claims

WHAT IS CLAIMED IS:

1. An anion exchange membrane comprising a polymer comprising the residues of one or more optionally substituted bisphenol A monomers, where a plurality of the residues of the optionally substituted bisphenol A monomers include one or more cationic groups.

2. The membrane of claim 1 wherein the polymer further comprises the residues of one or more optionally substituted phthalate monomers.

3. The membrane of claim 2 wherein a plurality of the residues of the one or more optionally substituted bisphenol A monomer and a plurality of the residues of the one or more optionally substituted phthalate monomer form ethers.

4. The membrane of claim 2 wherein a plurality of the residues of the one or more optionally substituted bisphenol A monomer and a plurality of the residues of the one or more optionally substituted phthalate monomer form imides.

5. The membrane of claim 2 wherein a plurality of the residues of the one or more optionally substituted bisphenol A monomer and a plurality of the residues of the one or more optionally substituted phthalate monomer form ethers and imides.

6. The membrane of claim 1 wherein the molar ratio of cationic groups to residues of bisphenol A monomers is in the range from about 1:1 to about 2.5:1.

7. The membrane of claim 1 wherein the molar ratio of cationic groups to residues of bisphenol A monomers is in the range from about 1 : 1 to about 2: 1.

8. The membrane of claim 1 wherein the molar ratio of cationic groups to residues of bisphenol A monomers is in the range from about 1:1 to about 1.5:1.

9. The membrane of claim 1 wherein the molar ratio of cationic groups to residues of bisphenol A monomers is in the range from about 1.5:1 to about 2:1.

10. The membrane of claim 1 wherein the molar ratio of cationic groups to residues of bisphenol A monomers is about 1.5:1.

11. The membrane of any one of claim 1 to 10 wherein the cationic groups are ammonium groups.

12. The membrane of claim 10 wherein a plurality of the ammonium groups are selected from the group consisting of trimethylammoniumalkyl, triethylammoniumalkyl, dimethylethylammoniumalkyl, dimethylisopropylammoniumalkyl, dimethylaminoethyl-dimethylammoniumalkyl, alkyldimethylammonium-ethyl- dimethylammoniumalkyl, and combinations thereof.

13. The membrane of claim 12 wherein a plurality of the cationic groups are trimethylammoniummethyl groups.

14. The membrane of claim 12 wherein a plurality of the cationic groups are ethyldimethylammonium-ethyl-dimethylammoniumalkyl groups.

15. The membrane of any one of claims 1 to 10 further comprising one or more anions, where a plurality of the anions are hydroxide ions.

16. The membrane of any one of claims 1 to 10 wherein the polymer is crosslinked with a polyamine.

17. The membrane of claim 16 wherein the polyamine is a tetramethylalkylenediamine .

18. The membrane of claim 16 wherein the membrane has a conductivity of about 0.002 S/cm or greater in aqueous hydroxide, at a temperature of about 2O⁰C or greater, where the concentration of aqueous hydroxide is about 0.5 molar or greater.

19. The membrane of claim 16 wherein the membrane has a conductivity of about 0.004 S/cm or greater.

20. The membrane of claim 16 wherein the membrane has a conductivity of about 0.006 S/cm or greater.

21. The membrane of claim 16 wherein the membrane has a conductivity of about 0.007 S/cm or greater.

22. The membrane of any one of claims 1 to 10 wherein the membrane is stable to aqueous hydroxide at a concentration of about 2 molar or greater.

23. The membrane of any one of claims 1 to 10 wherein the membrane is stable to aqueous hydroxide at a concentration of about 3 molar or greater.

24. The membrane of any one of claims 1 to 10 wherein the membrane is stable to aqueous hydroxide at a concentration of about 0.5 molar or greater at a temperature of about 6O⁰C or greater.

25. The membrane of any one of claims 1 to 10 wherein the membrane is stable to aqueous hydroxide at a concentration of about 1 molar or greater at a temperature of about 6O⁰C or greater.

26. The membrane of any one of claims 1 to 10 wherein the membrane is stable to aqueous hydroxide at a concentration of about 1.5 molar or greater at a temperature of about 6O⁰C or greater.

27. The membrane of any one of claims 1 to 10 wherein the membrane is stable to aqueous hydroxide at a concentration of about 2 molar or greater at a temperature of about 6O⁰C or greater.

28. The membrane of any one of claims 1 to 10 wherein the membrane is stable to aqueous hydroxide at a concentration in the range from about 0.5 molar to about 1.5 molar at a temperature in the range of about 6O⁰C to about 8O⁰C.

29. The membrane of any one of claims 1 to 10 wherein the membrane is stable to aqueous hydroxide at a concentration in the range from about 1 molar to about 1.5 molar at a temperature in the range of about 6O⁰C to about 8O⁰C.

30. An intermediate for preparing the anion exchange membrane of any one of claims 1-10 , where the intermediate is a polymer comprising the residues of one or more optionally substituted bisphenol A monomers.

31. The intermediate of claim 30 wherein the one or more optionally substituted bisphenol A monomers include one or more chloroalkyl groups.

32. The intermediate of any one of claims 1-10 wherein the polymer further comprises the residues of one or more optionally substituted phthalate monomers.

33. The intermediate of claim 32 where a plurality of the bisphenol A monomers form ethers with a plurality of the phthalate monomers, a plurality of the bisphenol A monomers form imides with a plurality of the phthalate monomers, or a plurality of the bisphenol A monomers form ethers and imides with a plurality of the phthalate monomers.

34. A process for preparing the anion exchange membrane of any one of claims 1-10 , the process comprising the step of reacting a polymer comprising the residues of one or more optionally substituted bisphenol A monomers, with a chloroalkylating agent in the presence of a catalyst to form a chloroalkylated polymer.

35. The process of claim 34 wherein the polymer further comprises the residues of one or more optionally substituted phthalate monomers.

36. The process of claim 35 where a plurality of the bisphenol A monomers form ethers with a plurality of the phthalate monomers; a plurality of the bisphenol A monomers form imides with a plurality of the phthalate monomers; or a first plurality of the bisphenol A monomers form ethers with a first plurality of the phthalate monomers, and a second plurality of the bisphenol A monomers form imides with a second plurality of the phthalate monomers.

37. The process of claim 36 wherein the chloroalkylating agent is bischloromethylether.

38. The process of any one of claims 34-37 wherein the ratio of the chloromethylating agent to the polymer is in the range of about 2:1 to about 8:1.

39. The process of any one of claims 34-37 wherein the ratio of the chloromethylating agent to the polymer is in the range of about 3:1 to about 8:1.

40. The process of any one of claims 34-37 wherein the ratio of the chloromethylating agent to the polymer is in the range of about 2:1 to about 6:1.

41. The process of any one of claims 34-37 wherein the ratio of the chloromethylating agent to the polymer is in the range of about 3:1 to about 6:1.

42. The process of any one of claims 34-37 wherein the ratio of the chloromethylating agent to the polymer is in the range of about 2: 1 to about 5:1.

43. The process of any one of claims 34-37 wherein the ratio of the chloromethylating agent to the polymer is in the range of about 3:1 to about 5:1.

44. The process of any one of claims 34-37 wherein the ratio of the chloromethylating agent to the polymer is in the range of about 2:1 to about 4:1.

45. The process of any one of claims 34-37 wherein the ratio of the chloromethylating agent to the polymer is in the range of about 3:1 to about 4:1.

46. The process of any one of claims 34-37 further comprising the step of reacting the chloroalkylated polymer with a quaternizing agent to form a quaternized polymer.

47. The process of claim 46 wherein the quaternizing agent is a tertiary amine.

48. The process of claim 47 wherein the tertiary amine is selected from the group consisting of trimethylamine, triethylamine, dimethylethylamine, dimethylisopropylamine, and tetramethylethylenediamine.

49. The process of claim 46 wherein the quaternizing agent is a diamine.

50. The process of claim 49 wherein the diamine is selected from the group consisting of tetramethylethylenediamine, tetramethylpropylenediamine, and pentamethyldiethylenediamine .

51. The process of claim 50 further comprising the step of alkylating the quaternized polymer with a C₁-C₄ alkylating agent.

52. The process of any one of claims 34-37 further comprising the step of reacting the quaternized polymer with hydroxide ion.