Patent Publication Number: US-2023138382-A1

Title: Membranes and Their Uses

Description:
This invention relates to ion exchange membranes and to processes for their preparation and use. 
     Ion exchange membranes may be used in electrodialysis, reverse electrodialysis, electrolysis, diffusion dialysis and a number of other processes. Typically the transport of ions through the membranes occurs under the influence of a driving force such as an ion concentration gradient or, alternatively, an electrical potential gradient. 
     Ion exchange membranes are generally categorized as cation exchange membranes or anion exchange membranes, depending on their predominant charge. Cation exchange membranes comprise negatively charged groups that allow the passage of cations but reject anions, while anion exchange membranes comprise positively charged groups that allow the passage of anions but reject cations. 
     Ion exchange membranes may be produced by polymerizing curable monomers using an energy source, e.g. electron beam (EB) irradiation, ultraviolet (UV) irradiation or heat. Heat curing is a thermal polymerization process and is generally very slow. EB curing does not require initiators but instead requires expensive equipment. UV curing is a fast and efficient process that requires high power UV irradiation and a photoinitiator. 
     WO2017009602 (&#39;602) describes the preparation of ion exchange membranes from simple aliphatic monomers using thermal and Type I photoinitiators. 
     When the monomers used to make ion exchange membranes are all aliphatic and/or simple aromatic monomers (e.g. as in &#39;602) a UV curing step for forming the ion exchange membrane generally is quite effective. However when one or more of the monomers used to make an ion exchange membrane absorb significantly in the UV region (e.g. up to 380 nm or even higher) the absorption of UV light by the monomers can significantly interfere with the curing process. In such cases very high doses of UV light and/or high concentrations of photoinitiators are required to achieve the formation of sufficient number of radicals to accomplish the desired polymerization rate. The use of a high concentration of photoinitiators is undesirable for a number of reasons. For example, it is more expensive to use a high concentration of photoinitiators than a low concentration of photoinitiators. Membranes made from curing compositions containing a high concentration of photoinitiator(s) are often considered to be unsuitable for use in food and pharmaceutical applications due to potential toxicity fears and often require extra processing to reduce the chances of unacceptable levels of photoinitiator leaching-out from the membrane and into the food or pharmaceutical product. Furthermore, a high dose of UV light generates a lot of heat which requires cooling and increases the risk of burning the membrane or any support or carrier which is present during the curing process. Also high energy costs are involved. 
     Ion exchange membranes may also comprise a porous support in addition to an ionic polymer. The porous support provides mechanical strength and pores present within the support contain a polymer derived from curing a curable composition comprising ionic monomers. A problem with porous supports derived from aromatic compounds is that they can absorb the light intended for curing ionic monomers present in the curable composition. This problem means that many porous supports derived from aromatic compounds are unsuitable for the preparation of ion exchange membranes by curing with UV light. 
     In order to overcome the problem of porous supports derived from aromatic compounds absorbing the light needed to cure monomers, thermal curing methods have been used to prepare membranes comprising such supports. However thermal curing methods are generally slow. 
     In view of the foregoing, there is a need for a process for making ion exchange membranes from aromatic monomers which is quick and avoids the need for large amounts of photoinitiator. Furthermore, it is desirable for the ion exchange membrane to have good selectivity, low electrical resistance and high robustness. 
     According to a first aspect of the present invention there is provided an ion exchange membrane obtainable by curing a composition comprising:
     (a) a curable monomer comprising at least one anionic or cationic group;   (b) a photoinitiator which has an absorption maximum at a wavelength longer than 380 nm, when measured in one or more of the following solvents at a temperature of 23° C.: water, ethanol and toluene;   (c) at least one co-initiator; and
 
optionally (d) a curable monomer which is free from anionic and cationic groups; wherein at least one of the curable monomers present in the composition comprises an aromatic group.
   

     In this document (including its claims), the verb “comprise” and its conjugations is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. In addition, reference to an element by the indefinite article “a” or “an” does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article “a” or “an” thus usually mean “at least one”. The term ‘ion exchange membrane’ is often abbreviated herein to ‘membrane’. 
     The membranes of the present invention are preferably in the form of a sheet or hollow fibres. 
     Preferably component (b) is a Norrish Type II photoinitiator. 
     &#39;602 describes the use of thermal and Type I photoinitiators but not the use of the photoinitiators defined in component (b) of the present invention. 
     The ion exchange membrane is preferably, especially a cation exchange membrane (i.e. comprising anionic groups, also known as a CEM), an anion exchange membrane (i.e. comprising cationic groups, also known as an AEM) (depending on its predominant charge) or a bipolar membrane. As mentioned above, cation exchange membranes comprise negatively charged groups that allow the passage of cations but reject anions, while anion exchange membranes comprise positively charged groups that allow the passage of anions but reject cations. Bipolar membranes typically comprise a layer of cationic membrane adjacent to a layer of anionic membrane. 
     The preferred anionic group(s) which may be present in component (a) include acidic groups, for example a sulpho, carboxy and/or phosphato groups, especially sulpho groups. 
     Preferred cationic group(s) which may be present in component (a) include quaternary ammonium and phosphonium groups, especially quaternary ammonium groups. 
     Preferably component (a) is not polymeric, but monomeric or oligomeric. 
     Preferably component (a) has a molecular weight (MW) which satisfies the equation: 
       MW&lt;(3000+300 n ) 
     wherein:
         MW is the molecular weight of component (a); and   n has a value of 1, 2, 3 or 4 and is the number of ionic groups present in component (a).       

     In the above equation, for some embodiments MW is more preferably &lt;(250+250n), even more preferably &lt;(200+200n), especially &lt;(150+200n), wherein MW and n are as hereinbefore defined. 
     Component (a) preferably comprises an anionic group or a cationic group and one or more ethylenically unsaturated groups, e.g. polymerisable ethylenically unsaturated groups. Component (a) may comprise several different compounds. 
     Depending on the pH of the composition, the anionic or cationic groups present in component (a) may partially or wholly form a salt with a counter-ion, e.g. sodium, lithium, ammonium, potassium and/or pyridinium for anionic groups and chloride and/or bromide for cationic groups. 
     The preferred ethylenically unsaturated groups which may be present in component (a) and (d) (when present) are vinyl groups, e.g. in the form of (meth)acrylic, allylic or styrenic groups. The (meth)acrylic groups are preferably (meth)acrylate or (meth)acrylamide groups, more preferably acrylic groups, e.g. acrylate or acrylamide groups. 
     In one embodiment component (a) comprises a vinylaryl group, for example a vinylphenyl group, a vinylpyridyl group, a vinylimidazyl group, a vinylthiazinyl group, a vinyltriazinyl group, a vinylpyrryl group and/or a vinylpyrimidyl group. 
     The curable monomer comprising an ionic group is preferably component (a) but may also be component (d) or a further monomer present in the composition. Thus the invention is also applicable to ionic monomers not comprising an aromatic group. 
     Examples of curable monomers comprising at least one anionic group include acrylic acid, beta carboxy ethyl acrylate, maleic acid, maleic acid anhydride, vinyl sulphonic acid, phosphonomethylated acrylamide, (2-carboxyethyl)acrylamide, 2-(meth)acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, compounds according to formula M-1 to M-35 shown below, and mixtures comprising two or more thereof (in M-35, the letter M signifies 2 atoms selected from Na+ and Li+ and mixtures thereof): 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Preferred curable monomers comprising at least one cationic group comprise a quaternary ammonium group. Examples of such monomers include (3-acrylamidopropyl)trimethylammonium chloride, 3-methacrylamidopropyl trimethyl ammonium chloride, (ar-vinylbenzyl) trimethylammonium chloride, (2-(methacryloyloxy)ethyl)trimethylammonium chloride, [3-(methacryloylamino)propyl] trimethyl ammonium chloride, (2-acrylamido-2-methylpropyl) trimethylammonium chloride, 3-acrylamido-3-methylbutyl trimethyl ammonium chloride, acryloylamino-2-hydroxypropyl trimethyl ammonium chloride, N-(2-aminoethyl)acrylamide trimethyl ammonium chloride, quaternized vinylimidazole, compounds according to formula M-36 to M-42 shown below, compounds according to Formula (CL) and according to Formula (SM), and mixtures comprising two or more thereof. 
     
       
         
         
             
             
         
       
     
     In Formula (CL): 
     
         
         
           
             L1 represents an alkylene group or an alkenylene group; 
             R a , R b , R c , and R d  are each independently optionally substituted alkyl or optionally substituted aryl; or 
             R a  and R b , and/or R c  and R d  form a ring together with the N-L 1 -N group shown in Formula (CL); 
             n1 and n2 each independently have a value of from 1 to 10; and 
             X 1 — and X 2   −  each independently represent an organic or inorganic anion. 
           
         
       
    
     In Formula (SM):
         R 1 , R 2 , and R 3  are each independently optionally substituted alkyl or optionally substituted aryl; or   R 1  and R 2 , or R 1 , R 2 , and R 3  form a ring together with the N atom shown in Formula (SM);   n3 has a value of from 1 to 10; and   X 3   −  represents an organic or inorganic anion.       

     Preferably the composition comprises 2 to 95 wt %, more preferably 20 to 95 wt %, especially 30 to 75 wt % of component (a). In some embodiments the composition preferably comprises 2 to 10 wt %, more preferably 2 to 6 wt %, e.g. 2 to 4 wt %, of component (a). 
     Component (a) optionally consists of one or more than one (e.g. 2 to 5) curable monomers, each having at least one anionic or cationic group. 
     Preferably component (a) has 1 to 5, more preferably 1 or 2 anionic or cationic group(s). 
     The photoinitiator is preferably a Norrish Type II photoinitiator. Typically Norrish Type II photoinitiators are compounds that upon irradiation with light of an appropriate wavelength and intensity reaches an excited (triplet) state, the energy of which is transferred to a co-initiator by abstracting an electron or hydrogen atom therefrom causing the co-initiator to form a reactive radical species. The reactivity of Norrish Type II photoinitiators (i.e. cure speed) can be assessed using a Mettler Toledo DSC822e Differential Scanning calorimeter (DSC) as described in the experimental section below. 
     The photoinitiator preferably has an absorption maximum (i.e. at least one) at a wavelength between 385 and 800 nm, more preferably between 400 and 800, e.g. between 430 nm and 800 nm, when measured at a temperature of 23° C. in one or more of the following solvents: water, ethanol and toluene. The absorption maxima are preferably measured using a 0.01 wt % concentration of the photoinitiator dissolved in the relevant solvent (i.e. water, ethanol or toluene) at 23° C., e.g. using a 1 mm path length (e.g. a quartz cuvette having an internal length through which light passes of 1 mm). One may measure the absorption maximum using, for example, a Varian Cary 100 conc. double beam UV/VIS spectrophotometer. 
     Most photoinitiators are soluble at a temperature of 23° C. in at least one of water, ethanol and toluene. However in the event that a photoinitiator is found that is not soluble in any of these, one or two drops of a better solvent may be added (e.g. dimethylsulphoxide) in order to achieve a complete solution. 
     Many suitable photoinitiators useful as component (b) comprise polar groups (e.g. amine groups, carbonyl groups, hydroxyl groups) and are soluble in ethanol. Photoinitiators that comprise ionic groups usually have good solubility in water. Photoinitiators that comprise fused aromatic rings generally have low or no solubility in water and ethanol and good solubility in toluene. For some photoinitiators a mixture of solvents may be preferred. Thus the absorption maximum of component (b) may be measured at 23° C. and generally one will choose a solvent selected from water, ethanol, toluene, and mixtures thereof in which component (b) is soluble. 
     The molar attenuation coefficient at the absorption maximum (i.e. longer than 380 nm) of the photoinitiator (b) is preferably at least 7,500 M −1  cm −1  (750 m 2  mol −1 ), more preferably at least 10,000 M −1  cm −1 . The molar attenuation coefficient may be measured using an UV-VIS spectrophotometer, e.g. a Cary™ 100 UV-visible spectrophotometer from Agilent Technologies. 
     Optionally component (b) has an absorption maximum at a wavelength of 380 nm or shorter, provided that it also has an absorption maximum at a wavelength longer than 380 nm (in each case when measured in one or more of the following solvents at a temperature of 23° C.: water, ethanol and toluene). 
     Preferably the composition is such that the ratio of the attenuation coefficient of the composition containing component (b) to the attenuation coefficient of the same composition but with component (b) omitted, when measured at the wavelength where component (b) has a maximum absorption (or at a wavelength where the irradiation source has significant emission), is more than 1, more preferably more than 1.5, especially more than 2. This ratio is an indication for the absorption capability of component (b) in the composition itself and thus forms a useful parameter defining the properties of a preferred photoinitiator for component (b). In the case that this ratio is equal to 1 the other components in the composition absorb much or all of the light intended to cause curing of the composition and this can render the photoinitiator ineffective. 
     Thus preferably the composition satisfies Equation 1: 
       ( A 1/ A 2)&gt;1.5   Equation 1
 
     wherein:
         A1 is the attenuation coefficient of the composition at wavelength X nm;   A2 is the attenuation coefficient at wavelength X nm of a composition identical to the composition except that component (b) is omitted; and   X nm is the wavelength of the absorption maximum of component (b);
 
wherein the attenuation coefficients are all measured at a temperature of 23° C.
       

     Preferably (A1/A2)&gt;2. 
     In Equation 1 the attenuation coefficients are preferably measured at 23° C., e.g. using a 1 mm path length (e.g. using a quartz cuvette having an internal length through which light passes of 1 mm). 
     Component (b) preferably comprises a xanthene, flavin, curcumin, porphyrin, anthraquinone, phenoxazine, camphorquinone, phenazine, acridine, phenothiazine, xanthone, thioxanthone, thioxanthene, acridone, flavone, coumarin, fluorenone, quinoline, quinolone, naphtaquinone, quinolinone, arylmethane, azo, benzophenone, carotenoid, cyanine, phtalocyanine, dipyrrin, squarine, stilbene, styryl, triazine or anthocyanin-derived photoinitiator, in each case provided that it has an absorption maximum at a wavelength longer than 380 nm, when measured in one or more of the following solvents at a temperature of 23° C.: water, ethanol and toluene, or a mixture comprising two or more thereof (e.g. from 2 to 5 of such photoinitiators). More preferably component (b) comprises a xanthene, flavin, curcumin, porphyrin, anthraquinone, phenoxazine, phenazine, acridine, phenothiazine, thioxanthene, acridone, flavone, coumarin, fluorenone, quinoline, quinolone, naphtaquinone, quinolinone, arylmethane, azo, carotenoid, cyanine, phtalocyanine, dipyrrin, squarine, styryl, triazine or anthocyanin derived photoinitiator, in each case provided that it has an absorption maximum at a wavelength longer than 380 nm, when measured in one or more of the following solvents at a temperature of 23° C.: water, ethanol and toluene. 
     Examples of photoinitiators having the absorption maximum specified above include eosin Y, eosin Y disodium salt, fluorescein, uranine, erythrosine B, rose bengal, phloxine B, 4,5-dibromofluorescein, rhodamine B, riboflavin, flavin mononucleotide, acriflavin, curcumin, resazurin, safranin 0, phenosafranin, neutral red, acridine orange, acid blue 43, 1,4-diamino-anthraquinone, 1,4-dihydroxy-anthraquinone, bromaminic acid sodium salt, carminic acid, ethyl violet, patent blue V, methyl orange, naphtol yellow S, methylene blue, indigo carmine, (4-dimethylaminostyryl)methylpyridinium iodide, quinoline yellow, quinoline yellow WS, thionine acetate, beta-carotene, coumarin 6, coumarin 343, coumarin 153, zinc-protoporphyrin IX, zinc-tetraphenylporphyrin tetrasulfonic acid, zinc-phtalocyanine, cyanidin chloride, indomonocarbocyanine sodium, resorufin, nile red, pyronin Y, 9-fluorenone carboxylic acid, 3-butoxy-5,7-diiodo-6-fluorone, 3-hydroxy-2,4,5,7-tetraiodo-6-fluorone, 2-chlorothioxanthone and quercetin. Preferred photoinitiators include safranin-0, acridine orange, bromaminic acid sodium salt, ethyl violet, methyl orange, curcumin, riboflavin, flavin mononucleotide, methylene blue, zinc phthalocyanine, tetraphenylsulfonate porphyrin, quinolone yellow WS, eosin Y, eosin Y disodium salt, erythrosin B, rose bengal, rhodamine B, phloxine B and dibromofluorescein. 
     The photoinitiator used as component (b) preferably comprises a conjugated system having at least 10 (more preferably at least 12) delocalized (π) electrons. A conjugated system is a system of connected p-orbitals with delocalized electrons in molecules, generally having alternating single and multiple bonds. The conjugated system may be linear, cyclic (aromatic) or a combination of linear and cyclic (aromatic). Linear conjugated systems usually have a high attenuation coefficient but may have radical scavenging properties which are not desired. Therefore component (b) preferably comprises aromatic groups, optionally also including linear conjugated group(s). 
     The wavelength at which the photoinitiator has an absorption maximum and its attenuation coefficient are strongly influenced by functional groups present in the photoinitiator, especially if directly attached to an atom that forms a part of a conjugated system. Groups that have a positive effect on the attenuation coefficient are, for example, primary, secondary and tertiary amine groups, hydroxyl groups, ether groups, thioether groups, alkyl groups and carbonyl groups. The photoinitiator preferably comprises one or more of these groups. Halogens do not influence the absorption properties of the photoinitiator significantly but stabilize the exited state and thereby enhance the efficiency of the photoinitiator. Therefore the photoinitiator preferably comprises one or more halogen groups (e.g. chloro, iodo and/or bromo groups). 
     It is desirable for the composition to be in the form of a solution in which all components have good solubility. Thus where the composition comprises a polar solvent (e.g. water), the photoinitiator preferably comprises one or more charged groups as these enhance the solubility in polar solvents such as water. Suitable charged groups include sulfo and carboxyl groups in free acid or salt form and quaternary ammonium groups. 
     Preferably the photoinitiator is free from groups which have radical scavenging properties (e.g. nitro groups and thiol groups) as such groups may slow or inhibit curing. 
     Preferably the photoinitiator does not contain two or more hydroxyl groups attached to atoms which form a part of the conjugated system 
     Preferably the photoinitiator has at least two groups selected from chloro, bromo, iodo, primary, secondary or tertiary amino, alkyl, carbonyl, ether, thioether, carboxyl, sulfo and quaternary ammonium groups and is free from nitro, thiol and multiple hydroxyl groups. 
     In one embodiment the membrane according to the first aspect of the present invention is free from component (b) and degradation products thereof. In another embodiment the membrane according to the first aspect of the present invention comprises component (b) and/or degradation products thereof. 
     For membranes intended for use in food or pharmaceutical applications the photoinitiator(s) used as component (b) is or are preferably known to be harmless and/or are approved for food and/or pharmaceutical use (e.g. by the U.S. Food and Drug Administration (FDA)), e.g. erythrosin B, flavin mononucleotide, curcumin, riboflavin, tartrazine, quinolone yellow, azorubine, amaranth, ponceau 4R, allura red AC, patent blue V, indigo carmine, brilliant blue FCF, chlorophyll derivatives, copper complexes of chlorophyll or chlorophyllin derivatives, carotenoids, sunset yellow FCF, carminic acid, green S, xantophyll derivatives, brilliant black BN, or one or more thereof. Preferably component (b) is ‘edible’, i.e. is suitable for food and beverages, dietary supplements, drugs and cosmetics, and preferably has a visible colour, i.e. absorbs light in the wavelength range between 400 and 800 nm. 
     The preferred amount of component (b) present in the composition depends on a number of factors, including the absorption characteristics and molar attenuation coefficient of component (b), its solubility in the rest of the composition and also the degree of overlap between the absorption spectrum of component (b) and the emission spectrum of the radiation source. Preferably, however, the curable composition comprises 0.002 to 4 wt %, more preferably 0.005 to 2 wt %, especially 0.005 to 0.9 wt %, e.g. 0.02 wt %, 0.05 wt %, 0.1 wt %, 0.3 wt % or 0.6 wt % of component (b). 
     Preferably component (b) has a solubility in the rest of the composition of at least 0.05 wt %, more preferably at least 0.1 wt %. 
     If desired further initiator(s) may be included in the composition, in addition to component (b), e.g. one or more thermal initiators. 
     Component (b) typically absorbs light at a wavelength longer than 380 nm to generate an excited photoinitiator molecule which extracts an electron, a proton or both from the co-initiator (c) to generate a free radical. The free radical then causes components (a) and (d) (when present) to cure. Thus the co-initiator may be any chemical which can generate a free radical in reaction with component (b) when the latter is in an electronic exited state, e.g. when the composition is irradiated with light matching with the absorption spectrum of component (b) (having an absorption maximum at a wavelength longer than 380 nm). 
     Preferably component (c) comprises a tertiary amine, an acrylated amine, an onium salt (e.g. a salt of a iodonium, sulfonium, phosphonium or diazonium ion), a triazine derivative, an organohalogen compound, an ether group, a ketone, a thiol, a borate salt, a sulfide (e.g. thioether), a pyridinium salt, a ferrocenium salt, or two or more thereof. 
     Preferred co-initiators include triethylamine, triethanolamine, methyl diethanol amine, dimethylethanolamine, ethylenediamine-tetra(2-propanol), 1,4-dimethyl piperazine, n-phenyldiethanolamine, 4-(dimethylamino)benzaldehyde, 7-diethylamino-4-methylcoumarin, 2-(diethylamino)ethyl methacrylate, carbon tetrabromide, diphenyliodonium chloride, 2-ethylhexyl-4-dimethylaminobenzoate, 4-(dimethylamino) benzonitrile, ethyl-4-dimethylaminobenzoate, dimethylaminopropylacrylamide, dimethylaminoethyl methacrylate, diphenyliodonium nitrate, N-phenylglycine, 2,4,6-tris(trichloromethyl)-1,3,5-triazine, 2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine, hexaethylmelamine, hexamethylenetetramine, piperonyl alcohol, N,N-dimethyl-p-toluidine, L-arginine, and mixtures comprising two or more thereof. 
     Although component (c) may contribute to dissolving the components of the composition, e.g. triethanolamine, for the purpose of this specification component (c) is not regarded as a solvent. 
     Preferably the composition comprises 0.01 to 40 wt %, more preferably 0.05 to 20 wt %, even more preferably 0.1 to 5 wt %, of component (c). 
     Preferably the molar ratio of component (b):(c) present in the composition is larger than 1:1, more preferably larger than 1:2, especially larger than 1:5, more especially larger than 1:10. 
     Although generally not preferable, the curable composition may comprise a non-ionic monomer i.e. a monomer which is free from anionic and cationic groups, typically in low amounts for a specific purpose. Examples of component (d) include non-ionic monomers, e.g. hydroxyethylmethacrylate and methyl methacrylate, and non-ionic crosslinkers, e.g. as poly(ethylene glycol) diacrylate, bisphenol-A epoxy acrylate, bisphenol A ethoxylate diacrylate, tricyclodecane dimethanol diacrylate, neopentyl glycol ethoxylate diacrylate, propanediol ethoxylate diacrylate, butanediol ethoxylate diacrylate, hexanediol diacrylate, hexanediol ethoxylate diacrylate, poly(ethylene glycol-co-propylene glycol) diacrylate, poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) diacrylate, isophorone diacrylamide, divinylbenzene, N,N′-(1,2-dihydroxyethylene) bis-acrylamide, N,N-methylene-bis-acrylamide, N,N′-ethylenebis(acrylamide), bis(aminopropyl) methylamine diacrylamide, tricyclodecane dimethanol diacrylate, 1,4-diacryoyl piperazine, 1,4-bis(acryloyl)homopiperazine, glycerol ethoxylate triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane ethoxylate triacrylate, pentaerythrytol ethoxylate tetraacrylate, ditrimethylolpropane ethoxylate tetraacrylate, dipentaerythrytol ethoxylate hexaacrylate, 1,3,5-triacryloylhexahydro-1,3,5-triazine, 2,4,6-triallyloxy-1,3,5-triazine, and combinations comprising two or more thereof. 
     Preferably the composition comprises 0 to 50 wt % of component (d), more preferably 0 to 30 wt %. In one embodiment the composition is free from curable monomers which are free from anionic and cationic groups. 
     Optionally the composition further comprises, as component (e), one or more solvents. Component (e) may be any solvent which does not copolymerise with component (a) or (d) (when present) or act as a co-initiator. In an embodiment component (e) preferably comprises water and optionally an organic solvent, especially where some or all of the organic solvent is water-miscible. The water is useful for dissolving component (a) and the organic solvent is useful for dissolving other organic components of the composition. 
     Component (e) is useful for reducing the viscosity and/or surface tension of the composition, making the manufacturing process for the membrane easier in some respects, particularly when the membrane is required to be in the form of a sheet. 
     In one embodiment component (e) comprises at least 50 wt % water, more preferably at least 70 wt % water, relative to the total weight of component (e). In one embodiment component (e) comprises less than 30 wt % of organic solvent and any remaining solvent is water. In another embodiment the composition is free from organic solvents, providing environmental advantages due to the complete absence of (volatile) organic solvents. In a specific embodiment water is used as solvent, e.g. water having a pH below 7. 
     In another embodiment component (e) comprises one or more organic solvents to dissolve the components of the composition and is free from water. This is especially useful when components (a), (b), (c) and (d) (when present) have a low or no solubility in water. 
     Preferably, in some embodiments, the composition comprises 0 to 60 wt %, more preferably 4 to 50 wt %, most preferably 10 to 45 wt % of component (e). In other embodiments the composition comprises 35 to 95 wt %, preferably 60 to 90 wt % of component (e). 
     Preferred organic solvents which may be used as or in component (e) include C1-4 alcohols (e.g. mono ols such as methanol, ethanol and propan-2-ol); diols (e.g. 
     ethylene glycol and propylene glycol); triols (e.g. glycerol)); carbonates (e.g. ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, di-t-butyl dicarbonate and glycerin carbonate); dimethyl formamide; dimethylsulfoxide, acetone; N-methyl-2-pyrrolidinone; and mixtures comprising two or more of the foregoing. 
     The organic solvent is inert (i.e. not copolymerisable with component (a) or (d) (when present)). 
     Component (e) may comprise none, one or more than one organic solvent. 
     The curable composition may further comprise additives, for example a surfactant, pH regulator, viscosity modifier, structure modifier, stabilizer, polymerization inhibitor or two or more of the foregoing. 
     A surfactant or combination of surfactants may be included in the composition as, for example, a wetting agent or to adjust surface tension. Commercially available surfactants may be utilized, including radiation-curable surfactants. Surfactants suitable for use in the composition include non-ionic surfactants, ionic surfactants, amphoteric surfactants and combinations thereof. 
     Preferred surfactants are as described in WO 2007/018425, page 20, line 15 to page 22, line 6, which are incorporated herein by reference thereto. Fluorosurfactants are particularly preferred, especially Zonyl® FSN and Capstone® fluorosurfactants (produced by E.I. Du Pont). Also preferred are polysiloxane based surfactants, especially Surfynol™ from Air Products, Xiameter™ surfactants from DowCorning, TegoPren™ and TegoGlide™ surfactants from Evonik, Siltech™ and Silsurf™ surfactants from Siltech, and Maxx™ organosilicone surfactant from Sumitomo Chemical. 
     Preferably the composition comprises a polymerization inhibitor (e.g. in an amount of below 2 wt %). This is useful to prevent premature curing of the composition during, for example, storage. Suitable polymerization inhibitors include hydroquinone, hydroquinone mono methyl ether, 2,6-di-t-butyl-4-methylphenol, 4-t-butyl-catechol, phenothiazine, 4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy, free radical (4-oxo-TEMPO), 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy, free radical (4-hydroxy-TEMPO), 2,6-dinitro-sec-butylphenol, tris(N-nitroso-N-phenylhydroxylamine) aluminum salt, Omnistab™ IN 510, and mixtures comprising two or more thereof. 
     Thus in a preferred aspect of the present invention the composition comprises:
     (a) from 2 to 95 wt % of component (a);   (b) from 0.002 to 4 wt % of component (b), component (b) preferably being Norrish Type II photoinitiator which has an absorption maximum at a wavelength longer than 380 nm, when measured at a temperature of 23° C. in one or more of the following solvents: water, ethanol and toluene;   (c) from 0.01 to 40 wt % of component (c); and   (d) from 0 to 50 wt % of component (d).   

     In an embodiment of this preferred aspect of the present invention the composition further comprises from 0 to 60 wt % of component (e), solvent. 
     Preferably the membrane is in the form of a sheet, for example the membrane (e.g. a composite ion exchange membrane) comprises a porous support. 
     Due to the presence of component (b) the porous support may optionally comprise aromatic groups. Thus the present invention has the advantage of providing a method for making composite membranes comprising a membrane and an aromatic porous support by a curing process involving light (e.g. UV or visible light curing) which is much faster than thermal curing processes. 
     As examples of porous supports there may be mentioned woven and non-woven synthetic fabrics and extruded films. Examples include wetlaid and drylaid non-woven material, spunbond and meltblown fabrics and nanofiber webs made from, e.g. polyethylene, polypropylene, polyacrylonitrile, polyvinyl chloride, polyphenylenesulfide, polyester, polyamide, polyaryletherketones such as polyether ether ketone and copolymers thereof. Porous supports may also be porous membranes, e.g. polysulfone, polyethersulfone, polyphenylenesulfone, polyphenylenesulfide, polyimide, polyethermide, polyamide, polyamideimide, polyacrylonitrile, polycarbonate, polyacrylate, cellulose acetate, polypropylene, poly(4-methyl 1-pentene), polyinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene and polychlorotrifluoroethylene membranes and derivatives thereof. 
     The porous support preferably has an average thickness of between 10 and 200 μm, more preferably between 20 and 150 μm. 
     Preferably the porous support has a porosity of 30 and 95%. The porosity of the support may be determined by a porometer, e.g. a Porolux™ 1000 from IB-FT GmbH, Germany. 
     The porous support, when present, is optionally a porous support which has been treated to modify its surface energy, e.g. to values above 45 mN/m, preferably above 55 mN/m. Suitable treatments include corona discharge treatment, plasma glow discharge treatment, flame treatment, ultraviolet light irradiation treatment, chemical treatment or the like, e.g. for the purpose of improving the wettability of and the adhesiveness of the membrane to the porous support. 
     Commercially available porous supports are available from a number of sources, e.g. from Freudenberg Filtration Technologies (Novatexx materials), Lydall Performance Materials, Celgard LLC, APorous Inc., SWM (Conwed Plastics, DelStar Technologies), Teijin, Hirose, Mitsubishi Paper Mills Ltd and Sefar AG. 
     Preferably the support is a polymeric support. 
     Aromatic porous supports include porous supports derived from one or more aromatic monomers, for example aromatic polyamide (aramid), (sulfonated) polyphenylenesulfone, poly(phenylene sulfide sulfone), aromatic polyesters (e.g. polyethyleneterephthalate (PET) or polybutyleneterephthalate (PBT)), aromatic polyether ether ketone, polyphenylenesulfide or a combination of two or more of the foregoing. In one embodiment the support strongly absorbs UV light (up to 380 nm). Absorption is regarded as strong as the support has less than 90% transmittance at a wavelength longer than 340 nm as measured in a UV spectrophotometer. 
     Examples of commercially available aromatic porous supports include Teijin, Hirose, Mitsubishi Paper Mills Ltd and Sefar AG. 
     The thickness of the membrane according to the first aspect of the present invention, including the porous support (when present), is preferably less than 250 μm, more preferably from 5 to 200 μm, most preferably from 10 to 150 μm, e.g. about 20, about 50, about 75 or about 100 μm. 
     Preferably the membrane has an ion exchange capacity of at least 0.1 meq/g, more preferably of at least 0.3 meq/g, especially more than 0.6 meq/g, more especially more than 1.0 meq/g, based on the total dry weight of the membrane (including the porous support when present). Ion exchange capacity may be measured by titration as described by Dlugolecki et al, J. of Membrane Science, 319 (2008) on page 217. 
     Preferably the membrane exhibits a swelling in water of less than 100%, more preferably less than 75%, most preferably less than 60%. The degree of swelling can be controlled by the amount of crosslinking agents, the amount of non-curable compounds and by selecting appropriate parameters in the curing step and further by the properties of the porous support (when present). Electrical resistance, permselectivity and swelling degree in water (aka water uptake) may be measured by the methods described by Dlugolecki et all, J. of Membrane Science, 319 (2008) on pages 217-218. 
     Typically the membrane is substantially non-porous, e.g. in swollen state not impregnatable by small molecules. The membrane preferably has pores all of which are smaller than the detection limit of a standard Scanning Electron Microscope (SEM). Thus using a Jeol JSM-6335F Field Emission SEM (applying an accelerating voltage of 2 kV, working distance 4 mm, aperture 4, sample coated with Pt with a thickness of 1.5 nm, magnification 100,000×, 3° tilted view) the average pore size is generally smaller than 2 nm, preferably smaller than 1 nm. 
     The membrane preferably has a low water permeability so that (hydrated) ions may pass through the membrane and (free) water molecules do not easily pass through the membrane. 
     Preferably the membrane&#39;s water permeability is lower than 1.10 −9  m 3 /m 2 ·s·kPa, more preferably lower than 1.10 −10  m 3 /m 2 ·s·kPa, most preferably lower than 5.10 −11  m 3 /m 2 ·s·kPa, especially lower than 3.10 −11  m 3 /m 2 ·s·kPa. 
     Preferably the membrane has a permselectivity for small cations (e.g. Na+) or anions (e.g. Cl − ) above 90%, more preferably above 95%. 
     Preferably the membrane has an electrical resistance less than 15 ohm·cm 2 , more preferably less than 10 ohm·cm 2 , most preferably less than 8 ohm·cm 2 . For certain applications a high electrical resistance may be acceptable especially when the permselectivity is very high, e.g. higher than 95%, and the water permeation very low, for example for processes that operate with low conductive streams such as systems used for producing ultrapure water and/or drinking water. 
     According to a second aspect of the present invention there is provided a process for preparing an ion exchange membrane comprising curing the composition defined in the first aspect of the present invention. 
     The process of the present invention may contain further steps if desired, for example the steps of applying the composition to a porous support prior to curing, washing and/or drying the cured composition (i.e. the membrane). 
     Optionally the process comprises the further step of washing out unreacted composition from the ion exchange membrane. 
     While in an embodiment it is possible to prepare a membrane according to the present invention on a batch basis using a stationary support, it is much preferred to prepare a membrane on a continuous basis using a moving support (especially a moving porous support). The porous support may be in the form of a roll which is unwound continuously, or in the form of a hollow fibre, or the porous support may rest on a carrier, e.g. a continuously driven belt (or a combination of these methods). Using such techniques the composition can be applied to a porous support on a continuous basis or it can be applied to a porous support on a large batch basis. 
     The curable composition may be applied to a porous support by any suitable method, for example by curtain coating, blade coating, air-knife coating, knife-over-roll coating, slide coating, nip roll coating, forward roll coating, reverse roll coating, micro-roll coating, dip coating, foulard coating, kiss coating, rod bar coating or spray coating. The curable composition typically forms a continuous film layer on the porous support or the carrier or the porous support may be impregnated with the composition. The coating of multiple layers can be done simultaneously or consecutively. When coating multiple layers, the curable compositions may be the same or different. 
     Thus the process step of applying the composition to a porous support may be performed more than once, either with or without curing being performed between each application of the composition. When the composition is applied to both sides of a porous support the resultant impregnated support may be symmetrical or asymmetrical. Thus the composition applied to one side of a porous support may be the same as or different to the composition applied to the other side of the porous support. 
     Thus in a preferred process, the composition is applied continuously to a moving support (preferably a porous support), preferably by means of a manufacturing unit comprising one or more composition application station(s), one or more irradiation source(s) for curing the composition, a membrane collecting station and a means for moving the porous support from the composition application station(s) to the irradiation source(s) and to the membrane collecting station. 
     The composition application station(s) may be located at an upstream position relative to the irradiation source(s) and the irradiation source(s) is/are located at an upstream position relative to the membrane collecting station. 
     In order to produce a sufficiently flowable composition for application by a high speed coating machine, it is preferred that the composition has a viscosity below 5000 mPa·s when measured at 23° C., more preferably from 1 to 1500 mPa·s when measured at 23° C. Most preferably the viscosity of the composition is from 2 to 500 mPa·s when measured at 23° C. 
     With suitable coating techniques, the composition may be applied to a moving porous support at a speed of over 1 m/min, e.g. 5 m/min, preferably over 10 m/min, more preferably over 15 m/min, e.g. more than 20 m/min, or even higher speeds, such as 30 m/min, or up to 40 m/min can be reached. 
     During curing components (a) and (d) (when present) typically polymerise to form the membrane. Preferably the curing occurs sufficiently rapidly to form a membrane within 30 seconds. If desired further curing may be applied subsequently to finish off, although generally this is not necessary. 
     Preferably curing of the composition begins within 3 minutes, more preferably within 60 seconds, after the composition has been applied to a support. 
     Preferably the curing is achieved by irradiating the composition for less than 30 seconds, more preferably less than 10 seconds, especially less than 3 seconds, more especially less than 2 seconds. In a continuous process the irradiation occurs continuously and the speed at which the composition moves through the beam of irradiation is mainly what determines the time period of curing. The exposure time is determined by the irradiation time by the concentrated beam; stray ‘light’ generally is too weak to have a significant effect. Preferably the curing uses white, blue or green light. Suitable wavelengths are longer than 380 nm, provided the wavelength of light matches with the absorbing wavelength of component (b). 
     Suitable sources of light having a wavelength in the range from 380 to 800 nm include light emitting diodes (e.g. white (450 nm &amp; broad peak at 550 nm that extends up to 750 nm), blue (450 nm), green (530 nm), yellow (590 nm), red (625 nm) or UV-V (385, 395, 405 or 420 nm); gas discharge lamps (mercury (430 &amp; 550 nm), gallium (400 &amp; 410 nm), indium (410 &amp; 450 nm), thallium (530 nm) or hydrogen (490 nm)); sulfur plasma lamps (broad peak in complete visible spectrum with maximum at 500 nm). Suitable light emitting diodes can be obtained from Cree, Osram, Hoenle and Chromasens. Gas discharge lamps can be obtained from Heraus, Hoenle and uv-technik meyer GmbH. Sulfur plasma lamps can be obtained from Plasma-international and PlasmaBright. Preferably the curing uses light from a light emitting diode (“LED”). 
     The energy output of the irradiation source used to cure the composition is preferably from 1 to 1000 W/cm, preferably from 2 to 500 W/cm but may be higher or lower as long as cure can be achieved. The exposure intensity is one of the parameters that can be used to control the extent of curing and thereby influences the final structure of the membrane. Preferably the exposure dose is at least 40 mJ/cm 2 , more preferably between 40 and 1500 mJ/cm 2 , most preferably between 70 and 900 mJ/cm 2 , as measured with a Power Puck II radiometer from Uvitron. A typical example of a light source for curing is a 420 nm monochromatic LED with an output of 25 W/cm as supplied by Hoenle. Alternatives are the 385 nm and the 405 nm LEDs from the same supplier. 
     To reach the desired exposure dose at high coating speeds, more than one irradiation source may be used, so that the composition is irradiated more than once. 
     According to a third aspect of the present invention there is provided use of an ion exchange membrane according to the first aspect of the present invention for treatment of an aqueous stream, for example for water softening, tartaric stabilization of wine, demineralization of whey, for purification of a liquid (e.g. water, a sugar syrup, fruit juice, organic solvents, mineral oils and a solution of metal ions), catalyzing chemical reactions, dehumidification, or for the generation of energy. 
     Although the membranes according to the present invention are primarily intended for use in water purification (e.g. by electrodeionisation or electrodialysis, including continuous electrodeionisation (CEDI) and electrodialysis reversal (EDR)), they may also be used for other purposes, e.g. capacitive deionisation used in e.g. flow through capacitors (FTC), Donnan or diffusion dialysis (DD) for e.g. fluoride removal or the recovery of acids, dehumidification, pervaporation for dehydration of organic solvents, fuel cells, redox flow batteries (RFB), electrolysis (EL) of water or for chlor-alkali production, and reverse electrodialysis (RED). 
     The membranes according to the present invention may also be used for other purposes, for example as protective coating (e.g. in printing, stereolithography and 3D printing) as a photocurable adhesive, in dental resins or for filtration purposes. 
     According to a fourth aspect of the present invention there is provided an electrodialysis or reverse electrodialysis unit, an electrodeionization module, a flow through capacitor, a diffusion dialysis apparatus, a membrane distillation module, an electrolyser, a redox flow battery or an acid-base flow battery, comprising one or more membranes according to the first aspect of the present invention. The electrodeionization module is preferably a continuous electrodeionization module. 
     Preferably the electrodialysis or reverse electrodialysis unit or the electrodeionization module or the flow through capacitor comprises at least one anode, at least one cathode and two or more membranes according to the first aspect of the present invention. 
     In a preferred embodiment the unit comprises at least 1, more preferably at least 5, e.g. 36, 64, 200, 600 or up to 1500, membrane pairs according to the first aspect of the present invention, the number of membranes being dependent on the application. The membrane may for instance be used in a plate-and-frame or stacked-disk configuration or in a spiral-wound design. 
     The present invention offers a number of advantages:
     (i) The use of component (b) having the specified absorption properties allows the components (a) and (d) to contain aromatic groups that absorb light in the wavelength range 200 to 380 nm. Thus not only aromatic monomers or oligomers can be used to make the ion exchange membranes of the present invention; also porous supports made from aromatic polymers can be used.   (ii) When component (b) is safely edible one may make membranes suitable for food and/or pharmaceutical uses.   (iii) When component (b) has a colour which is visible to the human eye, the resulting membranes are coloured: they absorb light in the wavelength range between 400 and 800 nm. By using a different component (b) for each membrane type (e.g. different membrane types such as anion exchange membrane, cation exchange membrane, monovalent anion exchange membrane, monovalent cation exchange membrane etc.), or the same component (b) in different amounts, each membrane type can be provided with a unique colour or depth of shade, thereby making it easier to assemble a stack of membranes and reducing the chances of making a stack in which the ion exchange membranes are in the wrong order.   (iv) The composition may be cured using visible light, e.g. LED light. Curing with visible light has many advantages compared to UV light (lower energy consumption, no harmful UV irradiation, no or much less useless IR irradiation and thus less heating of the product, no formation of ozone in the irradiation zone, a longer lifetime of the irradiation source and a higher spectral match that could reach 100% when monochromatic light is used). Thus LED light may be much more efficient than use of UV light.   (v) An ideal illumination source from a large number of possible sources can be selected for each photoinitiator system in order to maximize the spectral match between the emission spectrum of the light source and the absorption spectrum of the photoinitiator.   (vi) The curable composition may be handled under yellow or red light conditions, depending on the chosen photoinitiator.   (vii) Curing of the composition to form the membrane is inhibited less by the presence of oxygen than prior art processes which cure using Type I photoinitiators and UV light.   (viii) One may use lower amounts of photoinitiator than prior art processes due to the higher efficiency of the photoinitiator system.   

     The present invention also provides the use of the membranes according to the first aspect of the present invention to prepare a membrane stack. An exemplary stack comprises alternate anionic membranes and cationic membranes and the anionic membranes each have the same colour or depth of shade as each other and a different colour and/or depth of shade than the cationic membranes. The anionic and cation membranes are preferably as defined in the first aspect of the present invention. Thus the invention provides a stack of ion exchange membrane comprising alternate anionic membranes and cationic membranes wherein the anionic membranes each have the same colour or depth of shade as each other and a different colour and/or depth of shade than the cationic membranes. When also monovalent selective membranes are used they can be given a different colour than the standard membranes by selecting a different component (b) or a different amount of component (b). Therefore the stack preferably comprises AEMs and CEMs obtained from the compositions as described above in relation to the first aspect of the present invention which comprise a sufficient amount of component (b) to provide a visible difference between the AEMs and the CEMs of the stack. Preferably the stack comprises AEMs and CEMs obtained from the compositions as described above in relation to the first aspect of the present invention which comprise at least 0.0005 wt %, more preferably at least 0.001 wt % and especially at least 0.01 wt %, of component (b). Preferably the stack comprises AEMs and CEMs obtained from the compositions as described above in relation to the first aspect of the present invention which comprise less than 4 wt %, more preferably less than 0.5 wt %, especially less than 0.2 wt %, of component (b). 
     As component (b) may remain in the membrane after curing, the present invention further provides an ion exchange membrane comprising at least 0.0005 wt %, more preferably at least 0.001 wt % and especially at least 0.01 wt %, of component (b). Preferably such ion exchange membranes less than 4 wt %, more preferably less than 0.5 wt %, especially less than 0.2 wt %, of component (b). Component (b) is as defined above in relation to the first aspect of the present invention. 
     Adding dyes or pigments to a prior art composition applying Type I photoinitiators is often not possible since these compounds interfere with the curing process due to their high absorption in the UV region. 
     The invention will now be illustrated with non-limiting Examples where all parts and percentages are by weight unless specified otherwise. 
     In the Examples the following properties were measured by the methods described below. 
     Materials 
       
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 Na-AMPS 
                 is sodium salt of 2-acryloylamido-2- 
               
               
                   
                 methylpropanesulfonic acid from Sigma-Aldrich. 
               
               
                 DMAPAA-Q 
                 is 3-acrylamidopropyl-trimethylammonium chloride 
               
               
                   
                 from Kohjin. 
               
               
                 LiP 
                 is lithium p-styrenesulfonate, a monomer from Tosoh 
               
               
                   
                 Corp. 
               
               
                 VBTMAC 
                 is 4-vinylbenzyl trimethyl ammonium chloride from 
               
               
                   
                 Sigma-Aldrich 
               
               
                 TEOA 
                 is triethanolamine a co-initiator from Sigma-Aldrich. 
               
               
                 IO 
                 is diphenyliodonium chloride, a co-initiator from TCI 
               
               
                   
                 Co. 
               
               
                 Darocur ™ 1173 
                 is a Type I photoinitiator from BASF. 
               
               
                 2223-10 
                 is Viledon ® Novatexx 2223-10 (a non-woven, 
               
               
                   
                 polypropylene/polyethylene porous support from 
               
               
                   
                 Freudenberg Filtration Technologies and free from 
               
               
                   
                 aromatic groups). 
               
               
                 CL-3 
                 is N,N-(1,4-phenylenebis(methylene))bis(3-acrylamido 
               
               
                   
                 N,N-dimethylpropan-1-aminiurn) bromide, a 
               
               
                   
                 cationically charged crosslinking agent as 
               
               
                   
                 described in WO2013011273. 
               
               
                   
               
            
           
         
       
     
     Riboflavin, Resazurin, Rhodamine B, Quinoline Yellow WS, Neutral Red and Curcumin are Type II photoinitiators from TCI Co and have an absorption maximum at a wavelength longer than 380 nm, when measured in one or more of the following solvents at a temperature of 23° C.: water, ethanol and toluene. 
     Erythrosin B, Eosin Y disodium salt, Flavin mononucleotide, lumichrome, zinc phtalocyanine, rose Bengal, methylene blue, acridine, safranin-O, 1-amino-anthraquinone, carminic acid, thio michler&#39;s ketone, martius yellow, ethyl violet, camphorquinone, Quinaldine red and fluorescein sodium salt are Type II photoinitiators from Sigma-Aldrich and have an absorption maximum at a wavelength longer than 380 nm, when measured in one or more of the following solvents at a temperature of 23° C.: water, ethanol and toluene. 
     1,4-Anthraquinone, benzophenone, michler&#39;s ketone, anthraquinone-2-sulfonate, isopropylthioxanthone (ITX) are optically active reference molecules from Sigma-Aldrich that do not have an absorption maximum at a wavelength longer than 380 nm, when measured in one or more of the following solvents at a temperature of 23° C.: water, ethanol and toluene (i.e. used in Comparative Examples). 
     An overview of the properties of several photoinitiators is given in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Properties of photoinitiators 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                 Molar 
                 Number of 
                 Falls within 
               
               
                   
                 Abs. 
                   
                 attenuation 
                 conjugated 
                 definition of 
               
               
                   
                 max. 
                   
                 coefficient 
                 π 
                 component 
               
               
                 Photoinitiator 
                 (nm) 
                 Solvent 
                 (M −1 cm −1 ) 
                 electrons 
                 (b)? 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Erythrosin B 
                 530 
                 ethanol 
                 84500 
                 20 
                 Yes 
               
               
                 Eosin Y disodium salt 
                 525 
                 water 
                 112000 
                 20 
                 Yes 
               
               
                 Flavin mononucleotide 
                 445 
                 water 
                 12200 
                 12 
                 Yes 
               
               
                 Lumichrome 
                 392 
                 Water 
                 11000 
                 12 
                 Yes 
               
               
                 Zinc Phtalocyanine 
                 705 
                 toluene 
                 281800 
                 36 
                 Yes 
               
               
                 Rose Bengal 
                 560 
                 ethanol 
                 90400 
                 20 
                 Yes 
               
               
                 Methylene Blue 
                 654 
                 ethanol 
                 40700 
                 14 
                 Yes 
               
               
                 Acridine 
                 392 
                 ethanol 
                 13800 
                 14 
                 Yes 
               
               
                 Safranin-O 
                 519 
                 water 
                 101000 
                 20 
                 Yes 
               
               
                 1,4-Anthraquinone 
                 299 
                 ethanol 
                 9300 
                 16 
                 No 
               
               
                 1-Amino-anthraquinone 
                 460 
                 ethanol 
                 7000 
                 16 
                 Yes 
               
               
                 Carminic acid 
                 494 
                 water 
                 10000 
                 16 
                 Yes 
               
               
                 Benzophenone 
                 248 
                 ethanol 
                 19400 
                 14 
                 No 
               
               
                 Michler&#39;s ketone 
                 365 
                 ethanol 
                 39800 
                 14 
                 No 
               
               
                 Thio Michlers ketone 
                 460 
                 ethanol 
                 25000 
                 14 
                 Yes 
               
               
                 Anthraquinone 2-sulfonate 
                 292 
                 water 
                   
                 16 
                 No 
               
               
                 Martius yellow 
                 430 
                 ethanol 
                 8000 
                 10 
                 Yes 
               
               
                 Ethyl violet 
                 490 
                 water 
                 93500 
                 18 
                 Yes 
               
               
                 Riboflavin 
                 445 
                 ethanol 
                 13200 
                 12 
                 Yes 
               
               
                 Resazurin 
                 600 
                 Water 
                 20600 
                 14 
                 Yes 
               
               
                 Rhodamine B 
                 540 
                 Ethanol 
                 106000 
                 20 
                 Yes 
               
               
                 Neutral Red 
                 560 
                 Ethanol 
                 15500 
                 14 
                 Yes 
               
               
                 Quinaldine Red 
                 528 
                 Water 
                 108000 
                 18 
                 Yes 
               
               
                 Fluorescein sodium salt 
                 480 
                 water 
                 92300 
                 20 
                 Yes 
               
               
                 Quinoline yellow WS 
                 412 
                 Water 
                 22700 
                 20 
                 Yes 
               
               
                 Curcumin 
                 420 
                 Ethanol 
                 55000 
                 20 
                 Yes 
               
               
                 Darocur ™ 1173 
                 243 
                 ethanol 
                   
                 6 
                 No 
               
               
                 Isopropyl Thioxanthone 
                 365 
                 Toluene 
                 6500 
                 12 
                 No 
               
               
                 Camphorquinone 
                 460 
                 Ethanol 
                 50 
                 4 
                 Yes 
               
               
                   
               
            
           
         
       
     
     In Table 1 Abs. max. (nm) means absorption maximum in nm when measured in the solvent specified in the third column at a temperature of 23° C. 
     The absorption maxima quoted in Table 1 were measured using a Varian Cary 100 conc. double beam UV/Vis spectrophotometer. The measurements were carried out with a 0.01 wt % concentration of the photoinitiator in a solvent (pure water, ethanol or toluene) using a 1 mm path length quartz cuvette at 23° C. The absorption spectrum was measured from 800 to 200 nm. 
     The curing rate of compositions including the photoinitiators was tested in a Mettler Toledo DSC822e Differential Scanning calorimeter (DSC) equipped with a Sylvania ES50 V4 620LM DIM 865 36° SL lamp. 
    
    
     PREPARATION OF MEMBRANE EXAMPLES 1 TO 34 AND COMPARATIVE MEMBRANE EXAMPLES CEX1 TO CEX4 
     The compositions described in Table 2 below were prepared by dissolving the ingredients specified in pure water (the water makes up the amount to 100 wt %). In the final column of Table 2 “A” means an anionic exchange membrane (CEM) and “C” means a cationic exchange membrane (AEM). 
     In Table 2 “Time (sec.)” means the time in seconds required for the composition to become 90% cured. The point at which the composition was 90% cured was determined by the DSC method described above. 
     Procedure: 20 mg of each composition under test was placed in a DSC pan at 25° C. and irradiated for 10 minutes from 1 cm distance using a Sylvania ES50 V4 620LM DIM 865 36° SL lamp. The curing was followed by measuring the heat of the reaction formed against a reference DSC pan containing 20 mg of the same photoinitiator as that used in the composition under test in the same solvent. The composition under test was deemed to be acceptable if the cure time in seconds (i.e. the time in seconds required for the composition to become 90% cured) was less than 300 seconds. Preferably, the cure time was lower than 150 seconds. Results are given in Table 2. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Preparation of Membranes 
               
            
           
           
               
               
               
               
            
               
                   
                 Composition 
                 Cure 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Component 
                 Photointiator 
                 Component 
                 Time 
                 Type of 
               
               
                 Example 
                 (a) (wt %) 
                 (wt %) 
                 (c) (wt %) 
                 (sec.) 
                 membrane 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 CEX1 
                 DMAPAA-Q 
                 Anthraquinone 2- 
                 TEOA (1.0) 
                 &gt;600 
                 C 
               
               
                   
                 (50) 
                 sulfonate (0.25) 
               
               
                   
                   
                 (Comparative) 
               
               
                 CEX2 
                 Na-AMPS 
                 Michlers&#39; ketone (0.10) 
                 TEOA + IO 
                 &gt;600 
                 A 
               
               
                   
                 (50) 
                 (Comparative) 
                 (1.0 + 0.1) 
               
               
                 CEX3 
                 LiP (50) 
                 Darocur ™ 1173 (0.50) 
                 — 
                 &gt;600 
                 A 
               
               
                   
                   
                 (Comparative) 
               
               
                 CEX4 
                 VBTMAC (50) 
                 Anthraquinone 2- 
                 TEOA + IO 
                 &gt;600 
                 C 
               
               
                   
                   
                 sulfonate (0.50) 
                 (1.0 + 0.1) 
               
               
                   
                   
                 (Comparative) 
               
               
                 1 
                 LiP (50) 
                 Methylene Blue (0.20) 
                 TEOA + IO 
                 120 
                 A 
               
               
                   
                   
                   
                 (4.0 + 0.2) 
               
               
                 2 
                 LiP (50) 
                 Rose Bengal (0.20) 
                 TEOA + IO 
                 100 
                 A 
               
               
                   
                   
                   
                 (3.0 + 0.2) 
               
               
                 3 
                 LiP (50) 
                 Flavin mononucleotide 
                 TEOA + IO 
                 150 
                 A 
               
               
                   
                   
                 (0.50) 
                 (4.0 + 0.2) 
               
               
                 4 
                 LiP (50) 
                 Fluorescein sodium 
                 TEOA + IO 
                 80 
                 A 
               
               
                   
                   
                 salt (0.20) 
                 (4.0 + 0.5) 
               
               
                 5 
                 LiP (50) 
                 Eosin Y disodium salt 
                 TEOA + IO 
                 100 
                 A 
               
               
                   
                   
                 (0.20) 
                 (4.0 + 0.2) 
               
               
                 6 
                 LiP (50) 
                 Eosin Y disodium salt 
                 TEOA + IO 
                 150 
                 A 
               
               
                   
                   
                 (0.05) 
                 (4.0 + 0.2) 
               
               
                 7 
                 LiP (50) 
                 Eosin Y disodium salt 
                 TEOA + IO 
                 150 
                 A 
               
               
                   
                   
                 (0.50) 
                 (4.0 + 0.2) 
               
               
                 8 
                 LiP (50) 
                 Eosin Y disodium salt 
                 TEOA + IO 
                 250 
                 A 
               
               
                   
                   
                 (1.0) 
                 (4.0 + 0.2) 
               
               
                 9 
                 VBTMAC (50) 
                 Methylene Blue (0.20) 
                 TEOA + IO 
                 120 
                 C 
               
               
                   
                   
                   
                 (4.0 + 0.2) 
               
               
                 10 
                 VBTMAC (50) 
                 Rose Bengal (0.20) 
                 TEOA + IO 
                 100 
                 C 
               
               
                   
                   
                   
                 (3.0 + 0.2) 
               
               
                 11 
                 VBTMAC (50) 
                 Flavin mononucleotide 
                 TEOA + IO 
                 100 
                 C 
               
               
                   
                   
                 (0.50) 
                 (4.0 + 0.2) 
               
               
                 12 
                 VBTMAC (50) 
                 Fluorescein sodium 
                 TEOA + IO 
                 70 
                 C 
               
               
                   
                   
                 salt (0.20) 
                 (4.0 + 0.5) 
               
               
                 13 
                 VBTMAC (50) 
                 Eosin Y disodium salt 
                 TEOA + IO 
                 80 
                 C 
               
               
                   
                   
                 (0.20) 
                 (4.0 + 0.2) 
               
               
                 14 
                 VBTMAC (50) 
                 Eosin Y disodium salt 
                 TEOA + IO 
                 120 
                 C 
               
               
                   
                   
                 (0.05) 
                 (4.0 + 0.2) 
               
               
                 15 
                 VBTMAC (50) 
                 Eosin Y disodium salt 
                 TEOA + IO 
                 120 
                 C 
               
               
                   
                   
                 (0.50) 
                 (4.0 + 0.2) 
               
               
                 16 
                 VBTMAC (50) 
                 Eosin Y disodium salt 
                 TEOA + IO 
                 200 
                 C 
               
               
                   
                   
                 (1.0) 
                 (4.0 + 0.2) 
               
               
                 17 
                 DMAPAA-Q 
                 Methylene Blue (0.20) 
                 TEOA + IO 
                 90 
                 C 
               
               
                   
                 (50) 
                   
                 (1.0 + 0.1) 
               
               
                 18 
                 DMAPAA-Q 
                 Rose Bengal (0.20) 
                 TEOA (1.0) 
                 70 
                 C 
               
               
                   
                 (50) 
               
               
                 19 
                 DMAPAA-Q 
                 Flavin mononucleotide 
                 TEOA (1.0) 
                 60 
                 C 
               
               
                   
                 (50) 
                 (0.20) 
               
               
                 20 
                 DMAPAA-Q 
                 Fluorescein sodium 
                 TEOA (0.5) 
                 80 
                 C 
               
               
                   
                 (50) 
                 salt (0.20) 
               
               
                 21 
                 DMAPAA-Q 
                 Eosin Y disodium salt 
                 TEOA + IO 
                 40 
                 C 
               
               
                   
                 (50) 
                 (0.20) 
                 (1.0 + 0.1) 
               
               
                 22 
                 DMAPAA-Q 
                 Curcumin (0.20) 
                 TEOA + IO 
                 120 
                 C 
               
               
                   
                 (50) 
                   
                 (1.0 + 0.1) 
               
               
                 23 
                 DMAPAA-Q 
                 Lumichrome (0.20) 
                 TEOA + IO 
                 250 
                 C 
               
               
                   
                 (50) 
                   
                 (1.0 + 0.1) 
               
               
                 24 
                 Na-AMPS 
                 Methylene Blue (0.20) 
                 TEOA + IO 
                 90 
                 A 
               
               
                   
                 (50) 
                   
                 (1.0 + 0.1) 
               
               
                 25 
                 Na-AMPS 
                 Rose Bengal (0.20) 
                 TEOA + IO 
                 40 
                 A 
               
               
                   
                 (50) 
                   
                 (1.0 + 0.1) 
               
               
                 26 
                 Na-AMPS 
                 Flavin mononucleotide 
                 TEOA + IO 
                 60 
                 A 
               
               
                   
                 (50) 
                 (0.20) 
                 (1.0 + 0.1) 
               
               
                 27 
                 Na-AMPS 
                 Fluorescein sodium 
                 TEOA + IO 
                 60 
                 A 
               
               
                   
                 (50) 
                 salt (0.20) 
                 (0.5 + 0.1) 
               
               
                 28 
                 Na-AMPS 
                 Eosin Y disodium salt 
                 TEOA (1.0) 
                 100 
                 A 
               
               
                   
                 (50) 
                 (0.20) 
               
               
                 29 
                 Na-AMPS 
                 Quinoline yellow WS 
                 TEOA (1.0) 
                 120 
                 A 
               
               
                   
                 (50) 
                 (0.20) 
               
               
                 30 
                 DMAPAA-Q 
                 Erythrosin B (0.025) 
                 TEOA + IO 
                 60 
                 A 
               
               
                   
                 (15) + CL-3 
                   
                 (0.5 + 0.25) 
               
               
                   
                 (45) 
               
               
                 31 
                 DMAPAA-Q 
                 Erythrosin B (0.1) 
                 TEOA + IO 
                 40 
                 A 
               
               
                   
                 (15) + CL-3 
                   
                 (0.5 + 0.25) 
               
               
                   
                 (45) 
               
               
                 32 
                 DMAPAA-Q 
                 Erythrosin B (0.5) 
                 TEOA + IO 
                 60 
                 A 
               
               
                   
                 (15) + CL-3 
                   
                 (0.5 + 0.25) 
               
               
                   
                 (45) 
               
               
                 33 
                 DMAPAA-Q 
                 Flavin mononucleotide 
                 TEOA + IO 
                 60 
                 A 
               
               
                   
                 (15) + CL-3 
                 (0.1) 
                 (0.5 + 0.25) 
               
               
                   
                 (45) 
               
               
                 34 
                 DMAPAA-Q 
                 Flavin mononucleotide 
                 TEOA + IO 
                 80 
                 A 
               
               
                   
                 (15) + CL-3 
                 (0.5) 
                 (0.5 + 0.25) 
               
               
                   
                 (45) 
               
               
                   
               
            
           
         
       
     
     For a few examples from Table 2 the attenuation coefficients of the compositions were determined with and without photoinitiator. A ratio (A1/A2)&gt;1.5 is preferred. The results are shown in Table 3 below.
     A1 is the attenuation coefficient of the composition at wavelength X nm;   A2 is the attenuation coefficient at wavelength X nm of a composition identical to the composition except that component (b) is omitted; and   X nm is the wavelength of the absorption maximum of component (b).   

     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 A1/A2 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 Component 
                 Photoinitiator 
                   
                   
                 Wavelength 
                   
               
               
                 Example 
                 (a) (wt %) 
                 (wt %) 
                 A1 (/cm) 
                 A2 (/cm) 
                 X (nm) 
                 A1/A2 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 CEX3 
                 LiP (50) 
                 Darocur ™ 
                 42850 
                 42500 
                 240 
                 1.01 
               
               
                   
                   
                 1173 (0.50) 
                   
                   
                   
                   
               
               
                 4 
                 LiP (50) 
                 Fluorescein 
                 491 
                 2 
                 480 
                 246 
               
               
                   
                   
                 sodium salt 
                   
                   
                   
                   
               
               
                   
                   
                 (0.20) 
                   
                   
                   
                   
               
               
                 21 
                 DMAPAA-Q 
                 Eosin Y 
                 325 
                 0.01 
                 525 
                 32500 
               
               
                   
                 (50) 
                 disodium salt 
                   
                   
                   
                   
               
               
                   
                   
                 (0.20) 
                   
                   
                   
                   
               
               
                 29 
                 Na-AMPS 
                 Quinoline 
                 95 
                 0.1 
                 412 
                 950 
               
               
                   
                 (50) 
                 yellow WS 
                   
                   
                   
                   
               
               
                   
                   
                 (0.20) 
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     Anion exchange membranes (AEMs) were prepared using the compositions described in Table 4. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                 Ex. 30 
                 Ex. 31 
                 Ex. 32 
                 Ex. 33 
                 Ex. 34 
               
               
                 Component (type) 
                 (wt %) 
                 (wt %) 
                 (wt %) 
                 (wt %) 
                 (wt %) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 DMAPAA-Q (a) 
                 15.0 
                 15.0 
                 15.0 
                 15.0 
                 15.0 
               
               
                 CL-3 (a) 
                 45.0 
                 45.0 
                 45.0 
                 45.0 
                 45.0 
               
               
                 Erythrosin B (b) 
                 0.025 
                 0.1 
                 0.5 
               
               
                 Flavin 
                   
                   
                   
                 0.1 
                 0.5 
               
               
                 mononucleotide (b) 
               
               
                 IO (c) 
                 0.25 
                 0.25 
                 0.25 
                 0.25 
                 0.25 
               
               
                 TEOA (c) 
                 0.5 
                 0.5 
                 0.5 
                 0.5 
                 0.5 
               
               
                 Water (e) 
                 39.225 
                 39.15 
                 38.75 
                 39.15 
                 38.75 
               
               
                   
               
            
           
         
       
     
     The compositions described in Table 4 were applied to a PET sheet using a 100 μm Meyer bar. A porous support (2223-10) was placed in the layer of composition and any excess composition was scraped-off. The composition present in the porous support was then cured by placing it on a conveyer belt set at 5 m/min, equipped with a Heraeus F450 microwave-powered UV-curing system with a medium-pressure mercury bulb (240 W/cm, 100%) to give the AEMs. 
     The presence of photoinitiator in the membrane may be determined visibly, photospectrometrically or analytically. 
     The amounts of photoinitiator were determined analytically by extraction (in duplo). The analysis was performed by cutting 10×10 cm pieces of the AEMs into small rectangles that were placed in a 20 ml glass container to which 5 ml of pure water was added. The glass containers were capped and packed in aluminum foil to protect them from light. The glass containers were shaken at 125 RPM on the rotary shaker for 24 hours. Thereafter, the content of the glass containers were filtered through a 0.45 μm cellulose filter and transferred to a HPLC 
     Analysis Method HPLC 
     Instrument: Waters ACQUITY arc HPLC 
     Detector: 2998 ACQ-PDA 
     Column: TKSgelODA-100V HPLC column (4.6×150, 5 μm)
 
Maximum pressure: 450 [bar]
 
     Column Temperature: 40 [° C.] 
     Sample Temperature: 5 [° C.] 
     Absorbance, resolution: 254, 270, 280, 440, 540, 485 (4.8) [nm] 
     254 nm=identification Riboflavin monophosphate 
     485 nm=identification of erythrosine B 
     Injection volume: 100 [microliter]
 
Run Time: 24 [min]
 
Next inj. Delay: 0 [min]
 
Installed sample loop: 250 [microliter]
 
Solvents: A: acetonitrile+0.1% trifluoroacetic acid
         B: pure water+0.1% trifluoroacetic acid       

     Gradient: 
     
       
         
           
               
               
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Time [min] 
                 Flow [ml/min] 
                 A [%] 
                 B [%] 
               
               
                   
                   
               
               
                   
                 Initial 
                 0.5 
                 5 
                 95 
               
               
                   
                 1 
                 0.5 
                 5 
                 95 
               
               
                   
                 3 
                 0.5 
                 40 
                 60 
               
               
                   
                 5 
                 0.5 
                 40 
                 60 
               
               
                   
                 6 
                 0.5 
                 80 
                 20 
               
               
                   
                 7 
                 0.5 
                 80 
                 20 
               
               
                   
                 8 
                 0.5 
                 100 
                 0 
               
               
                   
                 11 
                 0.5 
                 100 
                 0 
               
               
                   
                 20 
                 0.5 
                 100 
                 0 
               
               
                   
                 20.1 
                 0.5 
                 5 
                 95 
               
               
                   
                 24 
                 0.5 
                 5 
                 95 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Ex. 30 
                 Ex. 31 
                 Ex. 32 
                 Ex. 33 
                 Ex. 34 
               
               
                 Extracted amounts 
                 (wt %) 
                 (wt %) 
                 (wt %) 
                 (wt %) 
                 (wt %) 
               
               
                   
               
               
                 Erythrosin B (b) 
                 0.002 
                 0.012 
                 0.050 
               
               
                 Flavin 
                   
                   
                   
                 0.020 
                 0.080 
               
               
                 mononucleotide (b)