FIELD

[0001] The present disclosure relates to cation exchange polymers, and water-based methods of making such polymers.

BACKGROUND

[0002] The following paragraph is not an admission that anything discussed therein is prior art or part of the knowledge of persons skilled in the art.

[0003] Ion-exchange membranes are used in electro-separation technologies, such as electrodialysis (ED), electrodialysis reversal (EDR) and electrodeionization (EDI). The ion- exchange membranes may be used to recover and enrich ions, or remove undesirable/toxic ions from waste water. Cation-exchange membranes may be prepared by polymerizing a monomer having an anionic functional group along with a crosslinker containing at least two polymerizable functionalities. An exemplary anionic functional group is sulfonate. The polymerization may be done in the presence of a stable reinforcing material, such as polypropylene, polyester, polyvinyl chloride, polyethylene, or another reinforcing material known in the art.

[0004] Cation-exchange membranes are also used in membrane capacitive deionization. Capacitive deionization (CD!) deionizes water through the electrosorption of ions. Application of an electrical potential difference over two porous carbon electrodes results in removal of anions through storage in the positively polarized electrode, and removal of cations through storage in the negatively polarized electrode. Membrane capacitive deionization includes an anion exchange membrane on the positively polarized electrode and a cation exchange membrane on the negatively polarized electrode.

INTRODUCTION

[0005] The following introduction is intended to introduce the reader to this specification but not to define any invention. One or more inventions may reside in a combination or sub-combination of the elements or method steps described below or in other parts of this document. The inventors do not waive or disclaim their rights to any invention or inventions disclosed in this specification merely by not describing such other invention or inventions in the claims. [0006] Since ionic monomers are charged, they are often water soluble. However, crosslinkers that are currently used for cation-exchange polymers are non-polar organic molecules, and are not sufficiently water soluble that they can be used to generate a homogenous solution with the ionic monomers in water. Without a homogeneous aqueous solution of crosslinkers and ionic monomers, it is difficult to generate a cation-exchange polymer. Mixtures of polar organic solvents or co-solvents may be used to prepare such a sufficiently homogeneous solution. However, using such solvents may be costly, toxic, require one or more downstream processes to treat the waste, or a combination thereof.

[0007] It is desirable to develop a method for generating a cation-exchange polymer where the reaction to form the polymer is performed in a water-based solution. One or more described embodiments attempt to address or ameliorate one or more shortcomings involved with producing a cation-exchange resin.

[0008] In one aspect, the present disclosure provides a method where an anionic monomer is polymerized in the presence of a crosslinker having a cationic functional group. The cationic crosslinker and the anionic monomer are dissolved in a water-based solution. Since polymerization of an anionic monomer with a cationic crosslinker results in a polymer having cationic functional groups, the authors of the present disclosure determined that the anionic monomer should be used in a sufficient amount to provide both the anionic charges necessary for cation exchange, and the anionic charges necessary to pair with and neutralize the cationic functional groups in the crosslinker. The anionic equivalency (e.g. meq/gram) of the polymer is determined by the molar excess of the anionic charges. The molar excess is determined based on the moles of anionic charges vs. the moles of cationic charges.

[0009] The cationic crosslinker and the anionic monomer may be selected so that they are sufficiently soluble in water that a sufficiently homogeneous solution may be made while substantially reducing or avoiding polar organic solvents. A water-soluble

polymerization catalyst may be used to help initiate the reaction.

[0010] Both the cationic crosslinker and the anionic monomer include mutually polymerizable functional groups. The crosslinker and the monomer may have functional groups that are polymerizable in a free-radical polymerization.

[0011] The cationic crosslinker may include a quaternary ammonium functional group, or a pyridinium-based functional group. The anonic monomer may include a sulfonate functional group, a phosphate functional group, or a carboxylate functional group. [0012] As noted above, the method includes polymerizing an anionic monomer in the presence of a cationic crosslinker. In some examples, the method includes first dissolving in the water-based solution the cationic crosslinker and at least one molar equivalent of the anionic monomer, thereby exchanging a non-polymerizabie counter-ion for the anionic monomer and forming a cation-based crosslinker paired with a polymerizable counter-ion. Additional anionic monomer is subsequently dissolved in the solution to form the mixture of the anionic monomer and the cationic crosslinker. The resulting mixture is then polymerized. The first portion of anionic monomer may be the same or different from the second portion of anionic monomer. For example, a cation-based crosslinker paired with chloride may be mixed in water with the hydrogen form of the anionic monomer to generate a mixture of chloride ions, hydronium ions, and the cation-based crosslinker paired with the anionic monomer. The resulting solution of the cationic crosslinker paired with the anionic monomer may then be mixed with additional anionic monomer and the resulting mixture polymerized.

[0013] In other examples, the method includes dissolving in the water-based solution ail of the cationic crosslinker with all of the anionic monomer. This resulting mixture is then polymerized.

[0014] Cation-exchange polymers may be made by polymerizing the anionic monomer and the cationic crosslinker in a molar ratio from about 3.0 : 1 to about 1.8 : 1 (monomer : crosslinker). In monomers and crosslinker that each include only a single change, such ratios result in excess anionic changes of about 2 to about 0.8 moles. The chemical structures of the monomers and crosslinkers, and the amounts of the monomers and crosslinkers, may be selected so that the I EC of the resulting polymer is from about 1 to about 3 meq/g. Such molar ratios may generate a cation-exchange membrane with a desirable ion exchange capacity (IEC), permeability, selectivity, resistance, chemical stability, and mechanical stability. The water content of exemplary polymers may be from about 40% to about 60%. In particular examples, the water content may be from about 45% to about 55%. The resistance of exemplary polymers may be from about 140 Ocm to about 400 Dcm. The resistance of some specific polymers disclosed herein may be from about 320 Ocm to about 400 Dcm.

[0015] The present disclosure also provides a cation-exchange polymer that includes both cationic functional groups and anionic functional groups. The anionic functional groups are present in the polymer in sufficient density, and in sufficient excess of the cationic functional groups, that the polymer has an ion exchange capacity of at least 1.2 meq/g. In some examples, the anionic functional group and the cationic functional group are present in a molar ratio from about 3: 1 to 1.8: 1 , anionic charges to cationic charges. The anionic functional group may be derived from an anionic monomer having a molecular weight of less than 300 per anionic charge.

[0016] Without wishing to be bound by theory, the authors of the present disclosure expect that the ion exchange capacity may be increased by: reducing the molecular weight per charge, increasing the molar ratio of anionic charges to cationic charges, or both.

[0017] The cation-exchange polymer may be used to coat a carbon electrode, such as a non-faraday carbon electrode for use in an EDR stack. Such a coated carbon electrode may exhibit increased anti-fouling properties and/or increased scaling resistance.

DETAILED DESCRIPTION

[0018] The singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. The endpoints of all ranges reciting the same

characteristic are independently combinable and inclusive of the recited endpoint. All references are incorporated herein by reference.

[0019] The modifier "about" used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the tolerance ranges associated with measurement of the particular quantity).

[0020] "Optional" or "optionally" means that the subsequently described event, or circumstance may or may not occur, or that the subsequently identified material may or may not be present, and that the description includes instances where the event or circumstance occurs or where the material is present, and instances where the event or circumstance does not occur or the material is not present.

[0021] In the context of the present disclosure, a "water based solution" would be understood to refer to a reaction solution that is at least 50% water by weight. In some examples, the water-based solution is substantially only water. In some particular examples, the water-based solution is more than 80% water by weight, such as more than 90% water. In some further examples, the water-based solution is more than 95% water by weight. In other particular examples, the water-based solution is more than 99% water by weight. In some examples, the water-based solution does not include any additional solvents. The remaining portion of the water-based solution may be an organic solvent, such as N-methyl- 2-pyrrolidone, propylene glycol, dipropylene glycol, 1-propanol, isopropyl alcohol, or any other water-miscible organic solvent. It should be understood that the purity of the water- based solution is determined excluding the reaction materials, such as the crosslinker, monomer, catalyst, and salts associated with any of the reaction materials.

[0022] In the context of the present disclosure, it should be understood that discussion of a range of values, such as "at least 50%" or "from 70 to 90", is intended to include all of the ranges encompassed by the specifically disclosed range. For example, explicit disclosure of the range "at least 50%" is intended to also be a disclosure of the ranges: "50% to 60%", "70% to 100%", and "75% to 90%".

[0023] In the context of the present disclosure, "optionally functionalized alky!" should be understood to encompass a linear or branched Ci _-2 o alkyl; and "optionally functionalized aryl" should be understood to encompass a C ₅ . ₂ o aryl. An optional functionalization may be the replacement of one or more hydrogen atoms with any combination of: a halide, a heteroatom, an optionally functionalized alkyl, or an optionally functionalized aryl group. In particular examples, the "optionally functionalized alkyl" does not have more than 20 carbon atoms, including the carbon atoms in the optional functional groups. In particular examples, the "optionally functionalized aryl" does not have more than 20 carbon atoms, including the carbon atoms in the optional functional groups. The optional functionalization may be the replacement of one or more carbon atoms with a heteroatom. The optional functionalization may result in the alkyl or aryl group being a heteroalkyl or heteroaryl group. The optional functionalization of an alkyl or aryl group may include replacement of one or more hydrogen atoms, and the replacement of one or more carbon atoms.

[0024] An example of an optional functionalization of the alkyl or aryl group is the replacement of a carbon or hydrogen with, or the addition to the compound of, a non-charged functional group that increases the miscibiiity of the compound in water. An example of such a functionalization includes addition of an oxygen atom to result in: an ether bond, a hydroxyl group, or a heteroaryl compound. Another example of such a functionalization includes the addition of a nitrogen atom to result in a heteroaryl compound. The alkyl or aryl group may be functionalized with a plurality of functional groups. In view of the above, it should be understood that the term "optionally functionalized alkyl" in the context of a linking group includes, for example: -C ₆ H ₁₂ -; -C ₃ H ₆ (CHOH)C ₂ H4-: -C ₃ H ₆ -0-C ₃ H _e -; and cyclic alkyl

-C ₆ He(OH) ₂ -. Similarly, it should be understood that the term "optionally functionalized aryl" in the context of a linking group includes, for example: benzyl; 2-hydroxy benzyl; and 2- methylpyridine, where the two groups being linked are joined to the benzyl, 2-hydroxy benzyl, or 2-methylpyridine in place of hydrogen atoms.

[0025] In the context of the present disclosure, it should be understood that "anionic monomer" and "monomer having an anionic group" are equivalent, and both terms refer to both: (i) a monomer having a negative charge and a counter ion, such as 2-Acrylamido-2- methyl-1-propanesulfonate sodium salt, and (ii) a monomer having a neutral charge under one or more preparation conditions but a negative charge in the polymer under cation- exchange conditions, such as 2-Acrylamido-2-methyl-1 -propanesulfonic acid.

[0026] Generally, the present disclosure provides a method where a molar excess of an anionic monomer is polymerized in the presence of a crosslinker having a cationic functional group to generate a polymer having sufficient anionic charges per gram for cation exchange. The amount of anionic monomer is selected to be sufficient to neutralize the cationic functional groups in the crosslinker, and provide the anionic charges necessary for the polymer to act as a cation-exchange polymer. The anionic equivalency (e.g. meq/gram) of the polymer is determined by the molar excess of the anionic charges. The molar excess is determined based on the moles of anionic charges vs. the moles of cationic charges.

[0027] A cationic crosslinker suitable for a method according to the present disclosure includes at least one cationic functional group and at least two polymerizab!e functional groups. In particular examples, the cationic crosslinker includes only one cationic functional group.

[0028] An anionic monomer suitable for a method according to the present disclosure includes at least one anionic functional group and at least one polymerizable functional group.

[0029] The polymerizable functional groups are all polymerizable under the same reaction conditions. The polymerizable functional group may be an alkenyl-based functional group, such as a vinyl-based functional group, an acrylate-based functional group, a methacrylate-based functional group, an acrylamide-based functional group, or a

methacrylamide-based functional group. It should be understood that, in the context of the present disclosure, functional groups "based on" the noted chemical structures would include bonds to link the functional groups to the rest of the molecules. For example, a methacrylamide-based functional group refers at least to: The fuoeiionai groups "based on" the noted chemical structures may include optional functionalization of the base chemical structure. For example, the term "methacrylamide-based functional group"

also refers to compounds of formula: C ₂ -C ₁₂ alkyl is optionally functionalized.

[0030] The cationic and anionic functional groups are joined to their respective polymerizable functional groups by linkers, such as an optionally functionalized alkyl or optionally functionalized aryl group. The linker joining the cationic functional group to one of the polymerizable groups may be different from the linker joining the cationic functional group to the other polymerizable group.

[0031] In some examples, the cationic crosslinker has a chemical structure according to Formula (I): P -Z -N ⁺ (R )(R ₂ )~Z2~P ₂ where: P-i and P ₂ are each, independently, an alkenyl-based functional group; and Z ₂ are each, independently, an optionally

functionalized alkyl-based linker or an optionally functionalized aryl-based linker; and R-i and R ₂ are each, independently, an optionally functionalized alkyl group, such as methyl.

[0032] P ₁ and P ₂ may be independently, for example: a vinyl-based functional group, an acrylate-based functional group, a methacrylate-based functional group, an acrylamide- based functional group, or a methacrylamide-based functional group. Particular examples of P-i and P ₂ include:

the group

consisting of: optionally functionalized aryl, such as " ; and Ci. ₂ o alkyl optionally substituted with hydroxyl, such as ethyl, propyl, or 2-hydroxy propyl

[0034] In specific examples, the cationic crosslinker may be:

[0035] In other examples, the cationic crosslinker may be a compound as disclosed in U.S. Patent No. 5, 1 18,717 (incorporated herein by reference), such as a compound according to Formula (II):

Formula (II)

where R ₃ is an alkyloxy or an alkylimino group; and R is a benzyl or an alkyl group, and R ₅ and R ₆ are methyl or higher alkyl group (such as C ₂ -C ₄ alkyl). In specific examples, the cationic crosslinker may be:

[0036] In yet other examples, the cationic crosslinker be a compound as disclosed in

U.S. Patent No. 7,968,663 (incorporated herein by reference), such as a compound according to Formul

Formula (III)

where R ₇ is hydrogen or a C C ₂ alkyl group; R ₈ is -[CH ₂ ] _n -; Rg is -[CH ₂ -CH(OH)] ₂ -X;

R ₁₀ and Rn are each, independently, -[CH ₂ ] _m -CH ₃ ; W is oxygen or N-R ₁₂ where R ₁₂ is hydrogen or -[CH ₂ j _m -CH ₃ ; X is a bridging group or atom; m in each instance is an integer from 0 to 20; and n is an integer from 1 to 20. X may be a hydrocarbon group, an inorganic group or inorganic atom. X may be, for example: a Ci-C ₃₀ alkyl group, C ₁ -C ₃₀ alkyl ether group, C ₆ -C ₃₀ aromatic group, C ₆ -C ₃₀ aromatic ether group, or a siloxane. X may be, for example: a d-Ce alkyl group, Ci-C ₆ alkyl ether group, a C ₆ -C ₁₀ aromatic group, or a C ₆ -C ₁₀ aromatic ether group. X may be, for example: methyl, ethyl, propyl, butyl, isobutyl, phenyl, 1 ,2-cyclohexanedicarboxylate, bisphenol A, diethylene glycol, resorcinol,

cyciohexanedimethanol, poly(dimethylsiloxane), 2,6-tolylene diisocyanate, 1 ,3-butadiene or dicyclopentadiene.

[0037] In specific examples, the cationic crosslinker may be:

where x is an integer from 0 to 100.

[0038] Crosslinkers according to the present disclosure may be prepared by reacting, in water, a polymerizable tertiary amine with a polymerizable alkylating compound to result in a quaternary ammonium compound having two polymerizable functional groups. The polymerizable alkylating compound may include an epoxide and the alkylation may be performed under acidic conditions. The counter-ion of the produced cationic crossiinker may be exchanged though reaction with an anionic monomer. The resulting cationic crossiinker includes a cationic quaternary ammonium group linked to two polymerizable functional groups, and a counter-ion having a polymerizable functional group. The produced crossiinker may be mixed with additional anionic monomer, and a polymerizing initiator. A sufficient amount of anionic monomer may be added to result in a molar ratio from about 3:1 to about 1.8:1 (monomercrosslinker).

[0039] An anionic monomer that may be used in a method according to the present disclosure may have chemical structure according to Formula (IV):

Formula (IV)

wherein

P ₃ is an alkenyl-based functional group;

Q is -SO ₃ ^" , -OPO ₃ ^" , or -COO ^" ; and

Z ₃ is an optionally functionalized alkyl-based linker, or an optionally functionalized aryl-based linker.

[0040] P ₃ may be, for example: a vinyl-based functional group, an acrylate-based functional group, a methacrylate-based functional group, an acrylamide-based functional group, or a methacrylamide-based functional group. Particular examples of P ₃ include:

[0041] Z ₃ may be, for e particular examples, Z ₃ is

[0042] The anionic monomer, absent any counter-ion, may have a molecular weight of less than 300 per anionic charge. Specific examples of an anionic monomer which may be used in a method of the present disclosure include: 2-Acrylamido-2-methyl-1 - propanesulfonate (AMPS), 4-vinylbenzenesulfonate, 2-sulfoethylmethacrylate, 3-sulfopropyl acrylate, 3-sulfopropyl methacrylate, and salts thereof.

[0043] Polymerizing initiators that may be used in methods according to the present disclosure include water-soluble azo-based initiators, such as 2,2'-Azobis[2-(2-imidazolin-2- yl)propane]dihydrochloride ("VA-044") and 2,2'-Azobis(2-methylpropionamidine) dihydrochloride ("V-50").

[0044] The mixture of cationic crosslinker, anionic monomer, and initiator may be cast on a backing and cured to initiate polymerization. The backing may be, for example, reinforcing material, such as a fabric, a felt, a microporous support (for example a micro- or ultra-filtration material), or a woven or nonwoven cloth. The backing may be made, for example, of polypropylene, polyester, polyacrylonitrile, polyvinyl chloride or polyamide. The thickness of the resulting membrane may be from about 0.1 mm to about 0.77 mm. The curing may include exposure of the reaction mixture to an elevated temperature, such as about 50 X to about 120 °C, and/or to a UV light. In particular methods, the curing includes increasing the temperature from room temperature to about 120 °C using multiple heating tables.

[0045] The non-polymerizable counter-ion of the cationic crosslinker may be the conjugate base of a strong acid, such as an acid having a pKa less than 1. Examples of such non-polymerizable counter-ions include CI ^" , CH ₃ -S0 ₃ ^" , N0 ₃ ^" , HS0 ^" , and citrate.

Examples - Summary

[0046] Specific examples are discussed in greater detail below. Table 1 is a summary of the reagents and amounts used in the discussed examples. GMA = glycidyl methacrylate; DMAPMA = /V-[3-(dimethylamino)propyl]methacrylamide; DMAEMA = 2-(dimethylamino)ethyl methacrylate; VBC = 4-vinylbenzyl chloride; AMPS = 2-acrylamido-2-methyl-1 - propanesulfonic acid; and SSS = sodium 4-viny!benzenesulfonate. "AMPS 1 " and "SSS 1 " refer to the AMPS and SSS compounds used as counter ions to the quaternary ammonium. "AMPS 2" and "SSS 2" refer to the AMPS and SSS compounds used as the source of excess anionic charges. In all of the examples, the total amount of anionic monomer present in a polymerization mixture is the sum of AMPS 1 and AMPS2, or of SSS1 and SSS2.

a e

Example 1

[0047] Water (50 g) was added to a flask. DMAPMA (10.2 g) was added to the water with stirring. Hydrochloric acid (3.3 g of 33% HCI) was slowly added, maintaining the temperature below 60 °C using a water bath. GMA (8.53 g) was added to the solution and the temperature of the water bath was raised to about 55 °C. The reaction was allowed to stir for about 1 hour, resulting in a crosslinker having a quaternary amine group of the following structure:

[0048] AMPS (12.5 g) was added to the solution, resulting in a crosslinker according to the present disclosure. This AMPS is identified as "AMPS 1 " in Table 1. Additional AMPS (18.8 g) was added and allowed to dissolve. This additional AMPS is identified as "AMPS 2" in Table 1.

[0049] The resulting mixture was allowed to cool to room temperature. VA-044 (1 g) was added as a polymerizing initiator. The mixture was cast on a backing to result in a membrane having thickness of about 0.6 mm, and cured in an oven at 80-90 °C.

[0050] The resulting membrane has a water content of about 50% and an IEC of about 1.8 meq/g.

Example 2

[0051] Water (20.4 g) was added to a flask. DMAPMA (5.1 g) was added to the water with stirring. Hydrochloric acid (3.3 g of 33% HCI) was slowly added, maintaining the temperature below 60 °C using a water bath. GMA (4.3 g) was added to the solution and the temperature of the water bath was raised to about 55 °C. The reaction was allowed to stir for about 1 hour, resulting in a crosslinker having a quaternary amine group of the following structure:

[0052] AMPS (6.3 g) was added to the solution, resulting in a crosslinker according to the present disclosure. This AMPS is identified as "AMPS 1" in Table 1. Additional AMPS (7.1 g) was added and allowed to dissolve. This additional AMPS is identified as "AMPS 2" in Table 1.

[0053] The resulting mixture was allowed to cool to room temperature. VA-044 (1 g) was added as a polymerizing initiator. The mixture was cast on a backing to result in a membrane having thickness of about 0.6 mm, and cured in an oven at 80-90 °C. [0054] The resulting membrane has a water content of about 50% and an I EC of about 1.5 meq/g.

Example 3

[0055] Water (18.2 g) was added to a flask. DMAPMA (5.1 g) was added to the water with stirring. Methanesulfonic acid (2.8 g) was slowly added, maintaining the temperature below 60 °C using a water bath. GMA (4.3 g) was added to the solution and the temperature of the water bath was raised to about 55 °C. The reaction was allowed to stir for about 1 hour, resulting in a crosslinker having a quaternary amine group of the following structure:

[0056] AMPS (6.3 g) was added to the solution, resulting in a crosslinker according to the present disclosure. This AMPS is identified as "AMPS 1 " in Table 1. Additional AMPS (5.3 g) was added and allowed to dissolve. This additional AMPS is identified as "AMPS 2" in Table 1.

[0057] The resulting mixture was allowed to cool to room temperature. VA-044 (1 g) was added as a polymerizing initiator. The mixture was cast on a backing to result in a membrane having thickness of about 0.6 mm, and cured in an oven at 80-90 °C.

[0058] The resulting membrane has a water content of about 50% and an IEC of about 1.2 meq/g.

Example 4

[0059] Water (18.2 g) was added to a flask. DMAPMA (5.1 g) was added to the water with stirring. Methanesulfonic acid (2.8 g) was slowly added, maintaining the temperature below 60 °C using a water bath. GMA (4.3 g) was added to the solution and the temperature of the water bath was raised to about 55 °C. The reaction was allowed to stir for about 1 hour, resulting in a crosslinker having a quaternary amine group of the following structure:

[0060] AMPS (6.3 g) was added to the solution, resulting in a crosslinker according to the present disclosure. This AMPS is identified as "AMPS 1 " in Table 1. Additional AMPS (5.3 g) was added and allowed to dissolve. This additional AMPS is identified as "AMPS 2" in Table 1. Sodium bicarbonate (4.7 g) was added to convert the AMPS 2 to its sodium form.

[0061] The resulting mixture was allowed to cool to room temperature. V-50 (1 g) was added as a polymerizing initiator. The mixture was cast on a backing to result in a membrane having thickness of about 0.6 mm, and cured in an oven at 80-90 °C.

[0062] The resulting membrane has a water content of about 50% and an IEC of about 1.2 meq/g.

Example 5

[0063] . Water (18.2 g) was added to a flask. DMAPMA (5.1 g) was added to the water with stirring. Methanesulfonic acid (2.8 g) was slowly added, maintaining the temperature below 60 °C using a water bath. GMA (4.3 g) was added to the solution and the temperature of the water bath was raised to about 55 °C. The reaction was allowed to stir for about 1 hour, resulting in a rosslinker having a quaternary amine group of the following structure:

[0064] AMPS (6.3 g) was added to the solution, resulting in a crosslinker according to the present disclosure. This AMPS is identified as "AMPS 1 " in Table 1. Additional AMPS

(5.3 g) was added and allowed to dissolve. This additional AMPS is identified as "AMPS 2" in Table 1. Sodium hydroxide (2.2 g) was added to convert the AMPS 2 to its sodium form.

[0065] The resulting mixture was allowed to cool to room temperature. V-50 (1 g) was added as a polymerizing initiator. The mixture was cast on a backing to result in a membrane having thickness of about 0.6 mm, and cured in an oven at 80-90 °C. [0066] The resulting membrane has a water content of about 50% and an IEC of about 1.2 meq/g.

Example 6

[0067] Water (23.1 g) was added to a flask. DMAEMA (4.71 g) was added to the water with stirring. Methanesulfonic acid (2.6 g) was slowly added, maintaining the temperature below 60 °C using a water bath. GMA (4.3 g) was added to the solution and the temperature of the water bath was raised to about 55 °C. The reaction was allowed to stir for about 1 hour, resulting in a crosslinker having a quaternary amine group of the following structure:

[0068] AMPS (6.3 g) was added to the solution, resulting in a crosslinker according to the present disclosure. This AMPS is identified as "AMPS 1 " in Table 1. Additional AMPS (9.4 g) was added and allowed to dissolve. This additional AMPS is identified as "AMPS 2" in Table 1.

[0069] The resulting mixture was allowed to cool to room temperature. VA-044 (1 g) was added as a polymerizing initiator. The mixture was cast on a backing to result in a membrane having thickness of about 0.6 mm, and cured in an oven at 80-90 °C.

[0070] The resulting membrane has a water content of about 50% and an IEC of about 1 .8 meq/g.

Example 7

[0071] Water (20.6 g) was added to a flask. DMAEMA (4.71 g) was added to the water with stirring. Methanesulfonic acid (2.6 g) was slowly added, maintaining the temperature below 60 °C using a water bath. GMA (4.3 g) was added to the solution and the temperature of the water bath was raised to about 55 °C. The reaction was allowed to stir for about 1 hour, resulting in a crosslinker having a quaternary amine group of the following structure:

[0072] AMPS (6.3 g) was added to the solution, resulting in a crosslinker according to the present disclosure. This AMPS is identified as "AMPS 1" in Table 1. Additional AMPS (6.9 g) was added and allowed to dissolve. This additional AMPS is identified as "AMPS 2" in Table 1.

[0073] The resulting mixture was allowed to cool to room temperature. VA-044 (1 g) was added as a polymerizing initiator. The mixture was cast on a backing to result in a membrane having thickness of about 0.6 mm, and cured in an oven at 80-90 °C.

[0074] The resulting membrane has a water content of about 50% and an I EC of about 1.5 meq/g.

Example 8

[0075] Water (52.4 g) was added to a flask. DMAPMA (8.6 g) was added to the water with stirring. Hydrochloric acid (6.6 g of 33% HCI) was slowly added, maintaining the temperature below 60 °C using a water bath. GMA (8.6 g) was added to the solution and the temperature of the water bath was raised to about 55 °C. The reaction was allowed to stir for about 1 hour, resulting in a crosslinker having a quaternary amine group of the following structure:

[0076] SSS (12.6 g) was added to the solution, resulting in a crosslinker according to the present disclosure. This SSS is identified as "SSS 1" in Table 1. Additional SSS (10.4 g) was added and allowed to dissolve. This additional SSS is identified as "SSS 2" in Table 1.

[0077] The resulting mixture was allowed to cool to room temperature. V-50 (1 g) was added as a polymerizing initiator. The mixture was cast on a backing to result in a membrane having thickness of about 0.6 mm, and cured in an oven at 80-90 °C. [0078] The resulting membrane has a water content of about 55% and an IEC of about 1.2 meq/g.

Example 9

[0079] Water (52.4 g) was added to a flask. DMAPMA (10.2 g) was added to the water with stirring. Hydrochloric acid (6.6 g of 33% HCI) was slowly added, maintaining the temperature below 60 °C using a water bath. GMA (8.6 g) was added to the solution and the temperature of the water bath was raised to about 55 °C. The reaction was allowed to stir for about 1 hour, resulting in a crosslinker having a quaternary amine group of the following structure:

[0080] SSS (12.6 g) was added to the solution, resulting in a crosslinker according to the present disclosure. This SSS is identified as "SSS 1 " in Table 1 . Additional SSS (10.4 g) was added and allowed to dissolve. This additional SSS is identified as "SSS 2" in Table 1 .

[0081] The resulting mixture was allowed to cool to room temperature. VA-044 (1 g) was added as a polymerizing initiator. The mixture was cast on a backing to result in a membrane having thickness of about 0.6 mm, and cured in an oven at 80-90 °C.

[0082] The resulting membrane has a water content of about 55% and an IEC of about 1.2 meq/g.

Example 10

[0083] Water (46.7 g) and A/-methyl-2-pyrrolidone (NMP) (5.7 g) were added to a flask. DMAPMA (10.2 g) was added to the water and NMP solution with stirring. Hydrochloric acid (6.6 g of 33% HCI) was slowly added, maintaining the temperature below 60 °C using a water bath. GMA (8.6 g) was added to the solution and the temperature of the water bath was raised to about 55 °C. The reaction was allowed to stir for about 1 hour, resulting in a crosslinker having a quaternary amine group of the following structure:

[0084] SSS (12.6 g) was added to the solution, resulting in a crosslinker according to the present disclosure. This SSS is identified as "SSS 1 " in Table 1. Additional SSS (10.4 g) was added and allowed to dissolve. This additional SSS is identified as "SSS 2" in Table 1 .

[0085] The resulting mixture was allowed to cool to room temperature. V-50 (1 g) was added as a polymerizing initiator. The mixture was cast on a backing to result in a membrane having thickness of about 0.6 mm, and cured in an oven at 80-90 °C.

[0086] The resulting membrane has a water content of about 55% and an SEC of about 1.2 meq/g.

[0087] The NMP was added to the water to increase the stability of the mixture.

Example 11

[0088] Water (57 g) was added to a flask. DMAEMA (9.3 g) was added to the water with stirring. ethanesuifonic acid (5.6 g) was slowly added, maintaining the temperature below 60 °C using a water bath. GMA (8.4 g) was added to the solution and the temperature of the water bath was raised to about 55 °C. The reaction was allowed to stir for about 1 hour, resulting in a crosslinker having a quaternary amine group of the following structure:

[0089] SSS (12.2 g) was added to the solution, resulting in a crosslinker according to the present disclosure. This SSS is identified as "SSS 1 " in Table 1. Additional SSS (10.4 g) was added and allowed to dissolve. This additional SSS is identified as "SSS 2" in Table 1.

[0090] The resulting mixture was allowed to cool to room temperature. V-50 (1 g) was added as a polymerizing initiator. The mixture was cast on a backing to result in a membrane having thickness of about 0.6 mm, and cured in an oven at 80-90 °C.

[0091] The resulting membrane has a water content of about 55% and an IEC of about 1.2 meq/g. Example s

[0092] Water (45 g) was added to a flask. DMAPMA (10.4 g) was added to the water with stirring. The temperature was raised to 40-42 °C, and VBC (9.3 g) was added dropwise to the solution. The temperature of the reaction was maintained below 45 °C. The reaction resulted in a crosslinker having a quaternary amine group of the following structure:

[0093] The reaction was cooled to room temperature, and AMPS (12.6 g) was added to the solution, resulting in a crosslinker according to the present disclosure. This AMPS is identified as "AMPS in Table 1. Additional AMPS (22.8 g) was added and allowed to dissolve. This additional AMPS is identified as "AMPS 2" in Table 1.

[0094] The resulting mixture was allowed to cool to room temperature. VA-044 (1 g) was added as a polymerizing initiator. The mixture was cast on a backing to result in a membrane having thickness of about 0.6 mm, and cured in an oven at 80-90 °C.

[0095] The resulting membrane has a water content of about 45% and an I EC of about 2 meq/g.

[0096] In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the examples. However, it will be apparent to one skilled in the art that these specific details are not required. Accordingly, what has been described is merely illustrative of the application of the described examples and numerous modifications and variations are possible in light of the above teachings.

[0097] Since the above description provides examples, it will be appreciated that modifications and variations can be effected to the particular examples by those of skill in the art. Accordingly, the scope of the claims should not be limited by the particular examples set forth herein, but should be construed in a manner consistent with the specification as a whole.