Patent Description:
The present invention relates generally to methods and systems for desalinating water and compositions useful for desalinating water. More particularly, embodiments of the present invention provide sulfonated poly(arylene ether) polymers, methods of making such polymers, and methods and systems for using such polymers in desalination of water.

In one aspect, linear sulfonated poly(arylene ether)s are provided. Linear sulfonated polymers may be copolymers, such as polymers comprising two or more different monomer units. The polymers may be polymerized via chemical reaction between monomers. Linear sulfonated copolymers of this aspect may be formed from presulfonated monomers, meaning that one or more substituents of the monomers may be a sulfonate group (e.g., -SO<NUM>-, SO<NUM>Na, SO<NUM>K, etc.). In some cases, presulfonated and unsulfonated monomers are polymerized to form a copolymer. In other cases, the disclosure provides unsulfonated monomers are polymerized to form a copolymer, then sulfonate groups are added in a post-sulfonation reaction.

In a specific embodiment, a copolymer comprises the structure:
<CHM>
where each L<NUM> is independently
<CHM>
each L<NUM> is independently
<CHM>
each L<NUM> is independently a single bond,
<CHM>
one Y<NUM> is SO<NUM>Z and the other Y<NUM> is H, Z is a counterion (e.g., a metal ion), and each R is independently H, F, or CH<NUM>. Values for x are between <NUM> to <NUM>, and values for n are from <NUM> to <NUM>,<NUM>.

The disclosure provides in another aspect that a copolymer may comprise the structure:
<CHM>
where each L<NUM> is independently
<CHM>
each L<NUM> is independently
<CHM>
each L<NUM> is independently a single bond,
<CHM>
Y<NUM> is SO<NUM>Z or H, Z is a counterion (e.g., a metal ion), and each R is independently H, F, or CH<NUM>. Values for x may be from <NUM> to <NUM>, and values for n may be any suitable number for a polymer, such as from <NUM> to <NUM>,<NUM>, for example.

In some embodiments, a terminating group on one or both ends of a polymer may be included and the molecular weights may be controlled by adjusting the stoichiometries among the monomers and terminating agents by state of the art methods for synthesizing step-growth copolymers. The terminating groups may include or comprise an alkenyl group, a styrenic group, a fluorinated styrenic group, a carbonyl group, a carboxylate ester, an amino group, a phenol group, or other crosslinkable groups, which may be useful for permitting crosslinking between polymer chains, such as when exposed to a crosslinking agent. Optionally, a copolymer may comprise or further comprise one or more terminating groups A, each terminating group A independently selected from
<CHM>
<CHM>
tetrafluorostyrene, an aminophenol or a phenol. By subjecting a copolymer, or a blend of the copolymers with different molecular weights, containing one or more crosslinkable groups to a crosslinking agent, such as heat, light, a free radical initiator, an epoxy reagent, etc., a crosslinked network may be formed of any of the copolymers described herein. Low molecular weight crosslinkable monomers may also be added to these copolymers to make crosslinked networks from such mixtures.

An example crosslinkable oligomeric macromonomer of this aspect may have the structure:
<CHM>
where each L<NUM> is independently
<CHM>
each L<NUM> is independently
<CHM>
each L<NUM> is independently a single bond,
<CHM>
each Y<NUM> is independently H or SO<NUM>Z, Z is a counterion (e.g., Na+ or K+), each R is independently H, F, or CH<NUM>, each A is independently,
<CHM>
<CHM>
<CHM>.

The disclosure provides another crosslinkable oligomeric macromonomer prepared by post-sulfonation which may have the following structure
<CHM>
where each L<NUM> is independently
<CHM>
each L<NUM> is independently
<CHM>
or
<CHM>
each L<NUM> is independently a single bond,
<CHM>
each Y<NUM> is independently H or SO<NUM>Z, Z is a counterion (e.g., Na+ or K+), each R is independently H, F, or CH<NUM>, and each A is independently,
<CHM>
<CHM>
where Y<NUM> is SO<NUM>Z or H,
<CHM>
<CHM>.

Functional oligomeric macromonomers of the above aspects may optionally be crosslinked, such as after exposure to a crosslinking agent. Optionally, blends of functional oligomeric macromonomers with different crosslinkable terminating agents or with different molecular weights may be crosslinked together, or low molecular weight monomers or crosslinking agents may be added to the mixture.

Copolymers described herein may have any suitable molecular weight or length. The copolymers described herein are generally random copolymers in which a fractional amount (x or <NUM>-x) of a sulfonate containing structural unit ranges from about <NUM>% to about <NUM>%, which may optionally be referred to herein as the degree of sulfonation. Example fractional amounts of sulfonate containing structural units may include from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, or from <NUM>% to <NUM>%. It will be appreciated that the copolymer molecular weight or length and/or the fractional amounts of sulfonate containing structural units in a copolymer may dictate the copolymer's properties, which may in turn impact the suitability of the polymer for use in different applications. For example, the amount of sulfonation may correlate with the ion exchange capacity (IEC) of the copolymer. Optionally, the IEC may be expressed in units of milliequivalents per gram of dry polymer. Example IEC values for the copolymers described herein may range from about <NUM> to about <NUM>, such as from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>.

In another aspect, synthetic methods are described herein. In some embodiments, methods of making copolymers are described. An example method of making a copolymer comprises reacting HO-L<NUM>-OH with
<CHM>
optionally together with an aminophenol to endcap the copolymer and control the molecular weight, to generate a copolymer, where each L<NUM> is independently
<CHM>
L<NUM> is
<CHM>
L<NUM> is a single bond,
<CHM>
each R is independently H, F, or CH<NUM>, and X is a halogen. Optionally, a method of this aspect further comprises exposing the copolymer terminated with either a phenol or with an aromatic amine derived from reaction with an aminophenol to a crosslinking agent. Optionally, a method of this aspect further comprises reacting a copolymer having phenol endgroups with
<CHM>
or
<CHM>
or reacting a copolymer with phenol or aminophenol endgroups with an acryloyl halide (e.g., acryloyl chloride), a methacryloyl halide (e.g., methacryloyl chloride), isocyanatoethyl acrylate or isocyanatoethyl methacrylate to generate an end-functionalized copolymer. Optionally, the end-functionalized copolymer may be crosslinked by exposure to a crosslinking agent, such as heat, light, a free radical initiator, or an epoxy reagent.

The disclosure provides another method of making a copolymer comprises reacting HO-L<NUM>-OH with
<CHM>
optionally together with an aminophenol, to generate a copolymer, where each L<NUM> is independently
<CHM>
L<NUM> is
<CHM>
L<NUM> is a single bond,
<CHM>
each R is independently H, F, or CH<NUM>, and X is a halogen. The stoichiometry can be offset to generate controlled molecular weight macromonomers with phenol endgroups by state of the art methods for step-growth polymers, or aminophenol can be added in calculated amounts to generate controlled molecular weight copolymers with aromatic amine endgroups. Then those phenol or aromatic amine terminated macromonomers can be post-sulfonated to generate approximately one SO<NUM>Z group on each ring of L<NUM>, where Z is a counterion. Optionally, methods of this aspect further comprise reacting the phenol terminated copolymer or a sulfonated copolymer with
<CHM>
or a phenol or aminophenol terminated copolymer or sulfonated copolymer with an acryloyl halide, a methacryloyl halide, isocyanatoethyl acrylate, or isocyanatoethyl methacrylate to generate an end-functionalized copolymer or end-functionalized sulfonated copolymer. Optionally, methods of this aspect further comprise reacting the end-functionalized copolymer with a sulfonating reagent such as sulfuric acid to post-sulfonate the end-functionalized copolymer and generate an end-functionalized sulfonated copolymer. Optionally, methods of this aspect may include a crosslinking step, such as a step comprising initiating a crosslinking reaction by subjecting the end-functional phenol, aromatic amine from aminophenol, fluorostyrene, fluoroinated aromatic, acrylate, acrylamide, methacrylate, methacrylamide, or urea or urethane acrylate or methacrylate terminated copolymer to a crosslinking agent, such as heat, light, a free radical initiator or an epoxy reagent.

It will be appreciated that each of the aforementioned groups or structures in this summary section may be unsubstituted or substituted, meaning that any hydrogen atom may be replaced by another group as described below.

In another aspect, water desalination membranes are described. An example desalination membrane may comprise any one or more of the copolymers described herein. Various different properties may be established in the desalination membrane by selection of suitable copolymers. For example, it may be desirable to employ copolymers with crosslinkable endgroups to permit crosslinking in the membrane, such as to provide or increase mechanical robustness in the membrane. Linear sulfonated poly(arylene ether sulfone)s are known to be relatively stable toward aqueous chlorine compounds commonly used as disinfectants in water treatment systems. To retain chlorine stability in the crosslinked networks, it may be desirable to employ copolymers with terminal groups or crosslinking agents that are also stable toward chlorine, e.g., fluorinated endgroups for crosslinking. Advantageously, membranes comprising the polymers and copolymers described herein may be useful for desalinating water including mixed valence salts (e.g., monovalent salts, such as those comprising Na+ and K+ with appropriate counterions, and polyvalent salts, such as those comprising Ca<NUM>+, Mg<NUM>+ with appropriate counterions, and any other ionic species). Prior sulfonated desalination membranes may exhibit poor performance for rejecting monovalent ions when divalent cations are present in a feed, but membranes comprising the polymers and copolymers described herein exhibit high rejection of monovalent ions despite the presence of divalent or polyvalent cations in a feed. For example, the water desalination membranes described herein may exhibit a rejection of aqueous monovalent ions of over <NUM>% in the presence of polyvalent cations. Optionally, the rejection may be greater than or about <NUM>%, greater than or about <NUM>%, greater than or about <NUM>%, greater than or about <NUM>%, greater than or about <NUM>%, greater than or about <NUM>%, greater than or about <NUM>%, greater than or about <NUM>%, greater than or about <NUM>%, greater than or about <NUM>%, greater than or about <NUM>%, or greater than or about <NUM>%.

In another aspect, methods of desalinating water utilizing the sulfonated poly(arylene ether) membranes of this invention are also described herein, such as with water including mixed salts and combinations of salts with mixed valencies.

A method of this aspect comprises exposing a first side of a sulfonated poly(arylene ether) water desalination membrane to an aqueous salt solution, the aqueous salt solution comprising a mixture of monovalent ions and polyvalent cations, wherein the water desalination membrane comprises a water desalination membrane that can reject at least <NUM>% of the monovalent salts even in the presence of multivalent salts; pressurizing the aqueous salt solution to drive a reverse osmosis process wherein water from the aqueous salt solution passes from the first side of the water desalination membrane through to a second side of the water desalination membrane and wherein at least <NUM>% of the monovalent ions are rejected from passing through the water desalination membrane in the presence of the polyvalent cations. Optionally, a concentration of the polyvalent cations is from <NUM> part per million to <NUM> parts per million. For example, a concentration of the polyvalent cations may be at least or about <NUM> parts per million, at least or about <NUM> parts per million, at least or about <NUM> parts per million, at least or about <NUM> parts per million or at least or about <NUM> parts per million. Optionally, a concentration of the monovalent cations is from <NUM> parts per million to <NUM>,<NUM> parts per million. For example, a concentration of the monovalent ions may be at least or about <NUM> parts per million, at least or about <NUM> parts per million, at least or about <NUM>,<NUM> parts per million, at least or about <NUM>,<NUM> parts per million, or at least or about <NUM>,<NUM> parts per million. Optionally, the water is saline water or seawater.

As noted above, the polymers and copolymers described herein may be stable in the presence of chlorine and chlorine compounds due to the excellent chemical stabilities of sulfonated and unsulfonated poly(arylene ether)s. Optionally, the aqueous salt solution includes a halide-based sterilization agent and the water desalination membrane remains substantially unoxidized by the halide-based sterilization agent.

These and other embodiments of the invention along with many of its advantages and features are described in more detail in conjunction with the text below and attached figures.

Embodiments of the present invention relate to water desalination membranes and methods of desalinating water. The water desalination membranes may employ poly(arylene ether)s, which may include one or more sulfonate groups at various points along the polymer chain, either directly attached to the chain or pendent to the polymer chain. In some embodiments, the polymers may be made from sulfonated monomers, and the resulting sulfonated polymers may be referred to herein as pre-sulfonated polymers. In some embodiments, the polymers may be made from non-sulfonated monomers but are subjected to a sulfonation process after polymerization, such as by exposing the polymers to sulfuric acid; the resulting sulfonated polymers may be referred to herein as post-sulfonated polymers. The sulfonated polymers described herein are useful for preventing transport of aqueous ionic species (e.g., NaCl) across a membrane made from the polymers while allowing water to pass.

The sulfonated polymers described herein provide numerous benefits. For example, the sulfonated polymers described herein exhibit good performance for rejecting monovalent ions in the presence of polyvalent cations. This is in contrast to data on separations of mixed salt feedwaters by reverse osmosis for previous sulfonated poly(arylene ether) membranes. See, e.g., <NPL>; <NPL>. ; and <NPL>. This aspect may be important for practical use in water desalination since polyvalent cations are always or almost always present in a source water feed used in desalination. Furthermore, embodiments of the present invention provide polymers that are stable in chlorinated waters. While it has been shown previously that sulfonated poly(arylene ether)s are resistant to degradation by aqueous chlorine compounds, this high chemical stability is a benefit relative to the interfacial polyamide desalination membranes that comprise most of the current desalination membrane market. Chlorine and chlorine-compounds are routinely used in water treatment to sterilize the water, but such sterilization agents may degrade some polymeric membranes. For desalination, de-chlorination processes may be used to remove chlorine compounds from water to be desalinated using a membrane. Advantageously, membranes made from the polymers described herein exhibit good stability in water containing chlorine disinfectants and so may allow for elimination or reduction of de-chlorination efforts prior to desalination.

The sulfonated polymers described herein may include monosulfonated polymers, which may refer to a single sulfonate group bonded to one of the copolymer units, or disulfonated polymers, which may refer to two sulfonate groups bonded to one of the copolymer units. In some cases, each of these configurations may find practical utility in semi-permeable membranes used for water desalination.

An example copolymer may comprise the structure:
<CHM>
where each L<NUM> is independently
<CHM>
each L<NUM> is independently
<CHM>
each L<NUM> is independently a single bond,
<CHM>
Z is a counterion (e.g., a metal ion), and each R is independently H, F, or CH<NUM>. Values for x may be from <NUM> to <NUM>, and values for n may be any suitable number for a polymer, such as from <NUM> to <NUM>,<NUM>, for example. In the case of monosulfonated polymers, one Y<NUM> is SO<NUM>Z and the other Y<NUM> is H. In the case of disulfonated polymers, the disclosure provides both Y<NUM> may be SO<NUM>Z. These polymers may optionally be crosslinked, such as after exposure to a crosslinking agent.

Another example copolymer, which may be monosulfonated or disulfonated may have the structure
<CHM>
where each L<NUM> is independently
<CHM>
each L<NUM> is independently
<CHM>
each L<NUM> is independently a single bond,
<CHM>
each Y<NUM> is independently H or SO<NUM>Z, Z is a counterion (e.g., Na+ or K+), each R is independently H, F, or CH<NUM>, each A is independently, a phenol or an aromatic amine derived from an aminophenol,
<CHM>
<CHM>
<CHM>
wherein X is a halogen.

The disclosure provides another example copolymer may comprise the structure:
<CHM>
where each L<NUM> is independently
<CHM>
wherein each L<NUM> is independently
<CHM>
wherein each L<NUM> is independently a single bond,
<CHM>
or
<CHM>
wherein Y<NUM> is SO<NUM>Z or H, wherein Z is a counterion, and wherein each R is independently H, F, or CH<NUM>. Such a copolymer may correspond to a post-sulfonated copolymer, for example.

Another example copolymer, which may correspond to a post-sulfonated copolymer, may have the structure
<CHM>
where each L<NUM> is independently
<CHM>
each L<NUM> is independently
<CHM>
or
<CHM>
each L<NUM> is independently a single bond,
<CHM>
each Y<NUM> is SO<NUM>Z or H, Z is a counterion (e.g., Na+ or K+), each R is independently H, F, or CH<NUM>, each A is independently,
<CHM>
<CHM>
<CHM>
a phenol, or an aromatic amine derived from an aminophenol, wherein X is a halogen.

In the above example copolymers, values for x may be from <NUM> to <NUM>, and values for n may be any suitable number for a polymer, such as from <NUM> to <NUM>,<NUM>, for example. Any of the aforementioned groups may have one or more hydrogen atoms optionally substituted by another group. These polymers may optionally be crosslinked, such as after exposure to a crosslinking agent.

In general the terms and phrases used herein have their art-recognized meaning, which can be found by reference to standard texts, journal references and contexts known to those skilled in the art. The following definitions are provided to clarify their specific use in the context of the invention.

"Linear polymer" is used to describe a polymer exhibiting an overall non-crosslinked configuration in its individual molecular form.

In an embodiment, disclosed compositions or compounds are isolated or purified. In an embodiment, an isolated or purified compound is at least partially isolated or purified as would be understood in the art.

The molecules disclosed herein contain one or more ionizable groups. Ionizable groups include groups from which a proton can be removed (e.g., -SO<NUM>H) or added (e.g., amines) and groups which can be quaternized (e.g., amines). All possible ionic forms of such molecules and salts thereof are intended to be included individually in the disclosure herein. With regard to salts of the compounds described herein, it will be appreciated that a wide variety of available counterions may be selected that are appropriate for salts of this invention for a given application. In specific applications, the selection of a given anion or cation for preparation of a salt can result in increased or decreased solubility of that salt.

As used herein, the terms "group" and "moiety" may refer to a functional group of a chemical compound. Groups of the disclosed compounds refer to an atom or a collection of atoms that are a part of the compound. Groups of the disclosed compounds may be attached to other atoms of the compound via one or more covalent bonds. Groups may also be characterized with respect to their valence state. The present disclosure includes groups characterized as monovalent, divalent, trivalent, etc. valence states. In embodiments, the term "substituent" may be used interchangeably with the terms "group" and "moiety.

As is customary and well known in the art, hydrogen atoms in chemical formulas disclosed herein are not always explicitly shown, for example, hydrogen atoms bonded to the carbon atoms of aliphatic, aromatic, alicyclic, carbocyclic and/or heterocyclic rings are not always explicitly shown in the formulas recited. The structures provided herein, for example in the context of the description of any specific formulas and structures recited, are intended to convey the chemical composition of disclosed compounds of methods and compositions. It will be appreciated that the structures provided do not indicate the specific positions of atoms and bond angles between atoms of these compounds. In the case of substituted groups, one or more hydrogen atoms may be replaced by any one or more of the other groups described herein.

The invention may be further understood by the following non-limiting examples.

Sulfonated poly(arylene ether) membranes for desalination of water can be prepared by direct polymerization using pre-sulfonated monomers or by synthesizing a non-sulfonated poly(arylene ether), then sulfonating the synthesized polymer, a process known as "post-sulfonation" since the sulfonation step is done after the polymer is synthesized. In the case of post-sulfonation, the sulfonate groups can be added to a linear copolymer, to a end functional macromonomer or to the crosslinked network. Firstly, pre-sulfonated monomers can be used to synthesize poly(arylene ether sulfone)s or poly(arylene ether ketone)s. This method has an advantage of enabling control over the degree of sulfonation by choosing the desired level of the sulfonated comonomer. It also produces a randomly sulfonated copolymer. Moreover, there is no reduction in molecular weight that might be caused by harsh reactants in a post-sulfonation process. Sulfonated monomers with either chlorine or fluorine reactive groups produce such structures. The analogous sulfonated aromatic ketone monomers are also included. For the case of a directly polymerized sulfonated poly(arylene ether ketone), <NUM>,<NUM>'-difluorobenzophenone would be used to replace <NUM>,<NUM>'-dichlorodiphenylsulfone as depicted in <FIG> or sulfonated <NUM>,<NUM>'-difluorobenzophenone can be incorporated.

The disclosure provides non-sulfonated poly(arylene ether)s can be synthesized, then selectively post- sulfonated only on aromatic rings that are not deactivated against electrophilic aromatic substitution post-sulfonation as shown in <FIG>. For such a method, the conditions of post-sulfonation can be carefully optimized to sulfonate only the non-deactivated rings (toward electrophilic aromatic sulfonation) and to avoid degradation of the molecular weight.

Membrane based desalination of water can be accomplished by reverse osmosis or by electrodialysis. In both processes, the separation membranes are non-porous and the separation process occurs by a solution-diffusion mechanism. Reverse osmosis utilizes saline feedwater pressurized against a membrane where the pressure must be at least sufficient to overcome the osmotic pressure (<FIG>). Membranes may be asymmetric or employ thin film composites with a sulfonated poly(arylene ether) atop a porous polymeric support. Effective reverse osmosis membranes must allow selective flux of water with high rejection of salt, and the separation layer must be thin (~<NUM>-<NUM>) to afford sufficiently high water flux. Current polyamide membranes (<FIG>) degrade in the presence of conventional chlorinated disinfectants, so the water must be pre-treated with chlorine, dechlorinated prior to passage through the membrane, then rechlorinated after desalination. Moreover, the nature of the interfacial polymerization atop the porous polymeric support that is used for the conventional polyamide thin film composite membranes leads to a rough surface relative to the sulfonated poly(arylene ether) membranes of the present invention (<FIG>). The rough surface contributes to fouling by salt and other impurities in the water during the desalination process. Fouling of interfacial polyamide thin film composites is a major deterrent to a desalination process.

Electrodialysis utilizes stacks of alternating anion exchange membranes (AEMs) and cation exchange membranes (CEMs) with compartments between the membranes for introduction of saline feedwater situated between an anode and a cathode. An electric current is applied that drives anions from the feedwater toward the positive electrode and cations toward the negative electrode (<FIG>). The CEMs are comprised of polyelectrolyte polymers that have fixed anions on their structure. The sulfonated poly(arylene ether)s of this invention similarly have fixed anions on their structures, so they may function as CEMs. They must selectively transport cations from the feedwater through the membranes and reject co-anions (e.g., transport sodium ions and reject chloride ions). Likewise, the AEMs contain fixed cations and those membranes must selectively transport anions and reject co-cations (e.g., transport chloride and reject sodium ions). The selectivity is driven by electrostatic Donnan exclusion of co-ions by the membrane fixed ions. Thus, the concentration of fixed ions on the membrane should be high. This means that the number of fixed ions per gram of dry polymer should be high and the amount of absorbed water should be kept relatively low. Ideally, electrodialysis membranes should be as thin as possible to minimize electrical resistance since more energy is required to run the desalination process as electrical resistance increases. Electrodialysis membranes may comprise crosslinked polyelectrolytes that are synthesized by free radical copolymerization. Common commercial monomers include chloromethylstyrene-divinylbenzene that can be post-aminated to make AEMs, sulfonated styrenedivinylbenzene to make CEMs, or alternative monomers as shown in <FIG>. The mechanical properties of commercial AEMs and CEMs are poor, so they must be reinforced with substantial amounts of hydrophobic polymers to be used in electrodialysis stacks. This increases areal electrical resistance in electrodialysis processes that require additional energy to operate and reduces effective membrane area, which increases capital costs. The sulfonated poly(arylene ether)s of the present invention have superior mechanical properties relative to conventional CEMs, and thus may not require as much support by hydrophobic polymers.

Structure-Property Relationships of Linear and Crosslinked Disulfonated Poly(arylene ether sulfone)s from Pre-disulfonated Sulfone Monomers. Linear directly polymerized sulfonated poly(arylene ether sulfone)s containing either biphenol or bisphenol A as the bisphenol monomer were made with systematically varied degrees of sulfonation by utilizing a pre-disulfonated monomer. In addition, controlled molecular weight oligomers with ~<NUM> and ~<NUM>,<NUM>/mole Mn were prepared with biphenol or bisphenol A as the bisphenol monomer that were terminated with m-aminophenol to yield aromatic primary amine endgroups. Those oligomers were reacted with a multifunctional epoxy reagent, tetraglycidyl bis(aminophenyl)methane (TGBAM), as shown in <FIG> to make crosslinked membranes. The amount of fixed sulfonate anions on these linear and crosslinked copolymers is expressed as the ion exchange capacity (IEC) in units of milliequivalents per gram of dry polymer. For a given IEC, the amount of water that can be absorbed (water uptake) decreases with network formation (Table <NUM>).

<CHM>
<CHM>
For example, the crosslinked entry number <NUM> in Table <NUM> (XLB50-<NUM> that was <NUM>% disulfonated with an oligomeric Mn of ~<NUM>,<NUM>/mole) has an IEC of <NUM> meq/g with a water uptake of <NUM>%, whereas the linear entry number <NUM> (BPS-<NUM> with <NUM>% of the comonomers disulfonated) has an IEC of <NUM> (slightly lower) and a water uptake of <NUM>% (significantly higher). Likewise, the crosslinked XLB60-<NUM> (<NUM>% disulfonated with a <NUM>,<NUM>/mole oligomer) has an IEC of <NUM> and a water uptake of only <NUM>% whereas the linear BPS-<NUM> with <NUM>% of the comonomer units disulfonated and an IEC of <NUM> (entry number <NUM> in Table <NUM>) has a much higher water uptake of <NUM>%. Thus, it is clear that network formation constrains the amount of water that is absorbed and thus, the fixed ion concentrations (moles of ions/Liter of absorbed water) are inherently higher for the networks relative to the analogous linear copolymers.

Water permeability increases and salt rejection decreases as the degree of disulfonation in the linear materials is increased (<FIG>). This may be directly related to the amount of absorbed water. A comparison of the same properties of analogous crosslinked materials, however, shows clearly that better retention of high salt rejection is achieved for the crosslinked materials vs. the linear membranes as water permeability increases (<FIG>). Again, this may be related to the lower amount of water absorption in the crosslinked networks relative to the linear materials. For example, the linear BPS-<NUM> with <NUM>% of the units disulfonated has a water uptake of <NUM>% and an IEC of <NUM> while crosslinked membranes with IECs of <NUM> (water uptake of <NUM>%) and <NUM> (water uptake of <NUM>%) have significantly better sodium chloride rejection. Sodium chloride permeability was measured by monitoring the conductivity of a receptor solution as the ions diffused through a series of crosslinked disulfonated poly(arylene ether sulfone) membranes. The diffusion cell is depicted in <FIG>. <FIG> and <FIG> illustrate the decrease in salt passage with decreased water uptake and the corresponding desirable decrease in salt passage as the fixed charge concentration in the membranes is increased, respectively. It is desirable to minimize the co-ion concentration in the membranes to achieve good salt rejection in reverse osmosis and good selectivity of counterion vs. co-ion transport through electrodialysis membranes. As the fixed charge concentration in the membrane is increased, the co-ion concentration in the membrane decreases. The Manning parameter, which characterizes the dimensionless fixed charge density, should be high to maintain selective low co-ion absorption and transport, and the Manning parameter decreases as the average distance between fixed charges on the membrane is increased. Methods to calculate the Manning parameter are set forth in <NPL>). Thus, as the degree of disulfonation is increased in these poly(arylene ether sulfone) membranes (i.e., the distance between fixed charge groups decreases), the Manning parameter increases and the co-ion sorption and transport decreases. However, the Manning parameter does not take into consideration differences in distribution of the fixed charge groups on the polymer backbone.

Description of Various Embodiments. While the rejection of sodium chloride by the disulfonated linear and crosslinked poly(arylene ether) membranes from the pre-disulfonated sulfone monomers is good, when mixed salt feeds containing a monovalent and multivalent cation were tested, the presence of the multivalent cation severely compromised the otherwise good rejection of sodium chloride of some membranes. This is illustrated in <FIG> where the salt rejection of a linear disulfonated poly(arylene ether sulfone) with <NUM>% of the repeat units disulfonated was tested against feedwater containing mixtures of sodium chloride and calcium chloride. This is a major deterrent against the utility of such membranes since virtually all water to be desalinated contains significant amounts of multivalent salts in addition to monovalent salts. The reasons for this undesirable behavior with mixed salt feeds are not completely understood.

Several series of sulfonated poly(arylene ether sulfone)s with different chemical structures were prepared to identify membranes where the sodium chloride rejection is not significantly compromised by the presence of multivalent salts mixed with monovalent salts:.

These were compared against the disulfonated biphenol based membranes that utilized pre-disulfonated sulfone monomers (structure IV, BPS-XX above) as depicted in <FIG>. These included high molecular weight linear copolymers with somewhat different backbone structures, copolymers where the sulfonate anions were on adjacent rings on the sulfone unit versus those where the sulfonate anions were on adjacent rings on the biphenol unit, those where no two adjacent rings were sulfonated, and also sulfonated oligomeric copolymers that were later crosslinked. Unexpectedly, key features of some of these structures were identified that alleviated the problem of reduced monovalent salt rejection in the presence of multivalent salts. Results of sodium chloride rejection capacities in mixed sodium chloride/calcium chloride feeds are shown in Table <NUM>. The water permeability (L µm m-<NUM> h-<NUM> bar-<NUM> or cm<NUM> s-<NUM>), salt permeability (cm<NUM> s-<NUM>), salt rejection (%) and water/NaCl selectivity were determined at <NUM> using stainless steel crossflow cells. The pressure difference across the membrane (<NUM><NUM>) was <NUM> psi. The initial aqueous feed contained <NUM> ppm NaCl, and the feed solution was circulated past the samples at a continuous flow rate of <NUM> min-<NUM>. The feed pH was adjusted to a range between <NUM> and <NUM> using a <NUM>/L sodium bicarbonate solution. NaCl concentrations in the feed water and permeate were measured with an Oakton <NUM> digital conductivity meter.

Firstly, the only difference in chemical structure of the mBPS-XX copolymers (II) relative to the BPS-XX copolymers (IV) is that mBPS-XX (II) has sulfonate ions on isolated rings whereas BPS-XX (IV) has sulfonate ions in sets of two on adjacent sulfone rings. Both sets are random copolymers. The copolymers that have the sulfonate ions distributed along the chain in sets of two that were prepared from the pre-disulfonated monomer (structure IV) uptake significantly more water relative to those that have the sulfonate ions on the isolated rings that were prepared from the pre-monosulfonated monomer (structure II) (Table <NUM>).

A comparison of mBPS-<NUM> (II) and BPS-<NUM> (IV) with almost equal numbers of ions (i.e., equal IECs) shows that the copolymer with isolated ring sulfonates (II) only absorbs about half the amount of water relative to the disulfonated BPS copolymer (IV). This makes the fixed charge concentration of the mBPS-<NUM> (II) significantly higher than that for BPS-<NUM> (IV). The result is very little compromise in sodium chloride rejection in the presence of calcium salts with mBPS-<NUM> relative to significant compromise in BPS-<NUM>. The reason for the unexpected dramatic change in water absorption capacity with equivalent backbone structures and equivalent IECs is not understood. Secondly, comparison of entry <NUM> (SHQS-<NUM> (I)) with entry <NUM> (mBPS-<NUM> (II)) shows that these copolymers have equivalent water absorption with unequal numbers of ions (i.e., unequal IECs). This makes the fixed charge concentration of the mBPS-<NUM> higher than that for SHQS-<NUM> at equivalent amounts of water absorption and equivalent water permeabilities. The sodium chloride rejection in the presence of divalent calcium salts is good in both cases relative to the BPS copolymer but it is particularly outstanding for the case of mBPS-<NUM> with the higher fixed charge concentration. In hindsight, the lower polarity of the backbone chemical structure of mBPS-<NUM> relative to SHQS-<NUM> may contribute to the capacity to increase the ion concentration yet maintain lower water absorption. The sodium rejection versus the amount of calcium ions added to the sodium chloride feed is summarized in <FIG>. All of the copolymers in <FIG> except BPS-<NUM> have the sulfonates on isolated rings whereas BPS-<NUM> has sulfonates randomly distributed but in sets of two on adjacent rings. Thus, it is now recognized that sulfonated poly(arylene ether sulfone) membranes where the sulfonate anions are distributed randomly along the chain on isolated rings rather than distributed randomly but in sets of two adjacent rings next to a sulfone moiety have significantly improved monovalent salt rejection properties when exposed to mixed salt feedwaters. Surprisingly, structure II above, where the sulfonate ions are located on adjacent rings on biphenol units (rather than on sulfone units), also does not show significantly reduced monovalent salt rejection in the presence of CaCl<NUM>. Thus, the exact placement of the sulfonates on poly(arylene ether)s with respect to their capacity to retain high monovalent salt rejection in mixed salt feedwaters that also contain multivalent salts is surprising.

Example <NUM>. Synthesis of monosulfonated dichlorodiphenylsulfone monomer. <NUM>,<NUM>'-Dichlorodiphenylsulfone (<NUM> mmol, <NUM>) was introduced into a <NUM>-mL, round bottom flask equipped with a mechanical stirrer and condenser, and purged with nitrogen for <NUM> minutes. The nitrogen flow was stopped and fuming sulfuric acid (<NUM> mmol, <NUM>) was introduced to the reaction flask. The <NUM>,<NUM>'-dichlorodiphenylsulfone dissolved in the fuming sulfuric acid at room temperature. When dissolution was complete, the oil bath temperature was raised to <NUM>. The reaction was allowed to proceed for <NUM>-<NUM> hours. The reaction mixture was cooled to room temperature, then the reaction flask was placed in an ice bath. Over <NUM> minutes, a mixture of DI water (<NUM>) and ice (<NUM>) was slowly added to the reaction while stirring. After complete addition of the ice water, the reaction was heated to <NUM> and NaCl (<NUM>) was slowly added to precipitate the mixture. The mixture was filtered and the filtrate was returned to the reaction flask. DI water (<NUM>) was added to the flask to form a suspension that contained both insoluble and soluble products. The suspension was neutralized by slowly adding <NUM> aqueous NaOH solution. The neutralization was constantly checked with litmus paper. The suspension was re-precipitated by adding NaCl (<NUM>) at <NUM>. The precipitate was filtered and the solid filtrate was collected. The solid was dissolved in a DI water (<NUM>) and CHCl<NUM> (<NUM>) mixture and the aqueous layer was collected. <NUM>-Butanol (<NUM>) was added to the aqueous layer and the mixture was shaken and allowed to separate. The <NUM>-butanol layer was collected, dried over MgSO<NUM>, and filtered. After solvent evaporation via rotary evaporator, the product was collected with a yield of <NUM>%. The monosulfonated <NUM>,<NUM>'-dichlorodiphenylsulfone did not melt up to the limit of <NUM> of the melting point apparatus.

Synthesis of a linear sulfonated poly(arylene ether sulfone) by direct polymerization with isolated sulfonated rings. Aromatic nucleophilic substitution step copolymerization was used to synthesize a series of monosulfonated biphenol-based poly(arylene ether sulfone) (mBPS-XX) and disulfonated biphenol-based poly(arylene ether sulfone) (BPS-XX) copolymers. In this series "XX" represent the degree of monosulfonation and disulfonation in mBPS and BPS, respectively.

Example <NUM>. A mBPS-<NUM> with <NUM>% of the repeat units monosulfonated was synthesized as follows. Biphenol (<NUM> mmol, <NUM>), <NUM>,<NUM>'-dichlorodiphenylsulfone (<NUM> mmol, <NUM>), monosulfonated <NUM>,<NUM>'-dichlorodiphenylsulfone (<NUM> mmol, <NUM>), and DMAc (<NUM>) were charged into a <NUM>-mL three neck round bottom flask equipped with a mechanical stirrer, condenser, nitrogen inlet, and Dean-Stark trap filled with toluene. The mixture was stirred in an oil bath at <NUM> until the monomers completely dissolved. K<NUM>CO<NUM> (<NUM> mmol, <NUM>) and toluene (<NUM>) were added into the flask. The reaction was refluxed for <NUM> hours to azeotropically remove water from the system. Toluene was drained from the Dean-Stark trap, and the oil bath temperature was raised to <NUM> to remove residual toluene from the reaction. The reaction solution was stirred for <NUM> hours, then cooled to room temperature. After dilution of the solution with DMAc (<NUM>), it was filtered to remove the salt. The transparent solution was precipitated by addition into isopropanol (<NUM>) with vigorous stirring. The white fibers were filtered and then stirred in boiling DI water for <NUM> hours to remove any residual DMAc. The copolymer was filtered and dried at <NUM> under reduced pressure in a vacuum oven. Yield <NUM>% copolymer.

The disclosure provides Example <NUM>. Synthesis of a linear sulfonated poly(arylene ether sulfone) with isolated sulfonated rings by post-sulfonation. Aromatic nucleophilic substitution step copolymerization was used to synthesize a series of hydroquinone-based poly(arylene ether sulfone) copolymers (HQS xx). HQS-<NUM> with <NUM>% of the repeat units containing hydroquinone was synthesized as follows. Hydroquinone (<NUM> mmol, <NUM>), <NUM>,<NUM>'-dichlorodiphenylsulfone (<NUM> mmol, <NUM>), bisphenol sulfone (<NUM> mmol, <NUM>) and sulfolane (<NUM>) were charged into a <NUM>-mL three neck round bottom flask equipped with a mechanical stirrer, condenser, nitrogen inlet, and Dean-Stark trap filled with toluene. The mixture was stirred and heated in an oil bath at <NUM> until the monomers dissolved. K<NUM>CO<NUM> (<NUM> mmol, <NUM>) and toluene (<NUM>) were added into the flask. The reaction was refluxed for <NUM> hours to azeotropically remove water from the system. Toluene was drained from the Dean-Stark trap, and the oil bath temperature was raised to <NUM> to remove residual toluene from the reaction. The reaction solution was stirred for <NUM> hours at <NUM>. The reaction mixture was hot filtered to remove salts and precipitated in DI water. The polymer was stirred in boiling DI water for <NUM> hours to remove any residual solvent. The polymer was filtered and dried at <NUM> under reduced pressure in a vacuum oven. For sulfonation, <NUM> of the dry polymer was dissolved in <NUM> of concentrated sulfuric acid in a three neck round bottom flask equipped with a nitrogen inlet and thermometer, overhead stirrer, and a condenser. An oil bath was used to maintain the temperature at <NUM>. The reaction was stirred vigorously to promote rapid dissolution. After maintaining the reaction temperature for <NUM> hours, the solution was precipitated into ice cold water, and rinsed thoroughly to remove residual acid. The polymers were stirred in <NUM> NaCl overnight, dried at <NUM> for <NUM> hours at atmospheric pressure, then dried for <NUM> hours under vacuum at <NUM>.

Example <NUM>. Oligomer Synthesis with the Pre-monosulfonated Monomer. The reaction scheme for the synthesis is shown in <FIG>. The molecular weights may be controlled by adjusting the stoichiometry of the monomers and terminating reagents according to methods well known for step-growth polymerizations. The following procedure is for a <NUM>,<NUM>/mole oligomer terminated with crosslinkable tetrafluorostyrene endgroups. <NUM>,<NUM>'-Dichlorodiphenylsulfone (<NUM> mmol, <NUM>), monosulfonated-<NUM>,<NUM>'dichlorodiphenylsulfone (<NUM> mmol, <NUM>), <NUM>,<NUM>'-biphenol (<NUM> mmol, <NUM>), potassium carbonate (<NUM> mmol, <NUM>), dimethylacetamide (<NUM>), and toluene (<NUM>) were added to a <NUM>-mL three neck round bottom flask equipped with a mechanical stirrer, Dean-Stark trap, condenser, and nitrogen inlet. The reaction vessel was immersed in an oil bath and heated to <NUM> to azeotropically dry the mixture for <NUM> hours. The toluene was drained from the Dean-Stark trap and the oil bath temperature was increased to <NUM> for <NUM> hours. The reaction was allowed to cool to room temperature, then pentafluorostyrene (<NUM> mmol, <NUM>) was added to the reaction vessel, and the mixture was heated to <NUM> for <NUM> hours. The reaction was diluted with dimethylacetamide (<NUM>) and allowed to cool to room temperature. The reaction mixture was precipitated into stirring isopropyl alcohol (<NUM>), resulting in a white polymer. The polymer was filtered and added to stirring deionized water (<NUM>) at room temperature overnight to remove salts and residual DMAc. The polymer was isolated and dried in vacuo at <NUM> for <NUM> hours to obtain an <NUM>% yield.

Example <NUM>. Crosslinking a thin film of the ~<NUM>, <NUM>/mole oligomer described above by free radical polymerization. The oligomer (<NUM>) was dissolved in <NUM> of dimethylacetamide. AIBN (<NUM>) was dissolved in the mixture. A clean glass plate was placed in an oven that was continuously purged with nitrogen, the plate was levelled, then heated to <NUM>. The polymer solution in DMAc was poured onto the plate and a doctor's blade with a gap of ~<NUM> microns was utilized to spread the solution across the plate. The <NUM> temperature was maintained for <NUM> minutes, then the film was immersed in deionized water to delaminate the film from the glass plate. The film was boiled in deionized water for <NUM> hours to remove residual dimethylacetamide, then dried under vacuum at <NUM> for <NUM> hours. Thermogravimetric analysis showed that <<NUM>% of dimethylacetamide/water remained. The film was submerged in dimethylacetamide for <NUM> hours at room temperature to extract the sol fraction. The mixture was vacuum filtered, and the gel fraction was dried for <NUM> hours at <NUM> under vacuum. Thermogravimetric analysis showed ~5wt% dimethylacetamide remaining. The gel fraction was <NUM> wt %.

Another example reacted a mixture of the <NUM>,<NUM>/mole tetrafluorostyrene terminated oligomer with a <NUM>/mole tetrafluorostyrene terminated oligomer. The oligomer mixture (<NUM>) contained the <NUM>,<NUM>/mole oligomer (<NUM>) and the <NUM>/mole oligomer (<NUM>) and <NUM> of AIBN dissolved in <NUM> of dimethylacetamide. The mixture was cured under nitrogen at <NUM> for <NUM> minutes. The gel fraction after exhaustive extraction with dimethylacetamide was <NUM>%.

Another example reacted a mixture of the <NUM>,<NUM>/mole tetrafluorostyrene terminated oligomer with a <NUM>/mole tetrafluorostyrene terminated oligomer with divinylbenzene as a low molecular weight reactant. The oligomer mixture (<NUM>) contained the <NUM>,<NUM>/mole oligomer (<NUM>) and the <NUM>/mole oligomer (<NUM>). Divinylbenzene (<NUM>) and <NUM> of AIBN were dissolved in <NUM> of dimethylacetamide. The mixture was cured under nitrogen at <NUM> for <NUM> minutes. The gel fraction after exhaustive extraction with dimethylacetamide was <NUM>%.

Alternatively, the ~<NUM>,<NUM>/mole tetrafluorostyrene-functional oligomer described above was cured with light. The oligomer (<NUM>) and <NUM> of <NUM>,<NUM>,<NUM>-trimethylbenzoyl-diphenylphosphine oxide (TPO) were dissolved in <NUM> of dimethylacetamide plus <NUM> of diethylene glycol. The solution was cast on a glass plate and cured at <NUM> with <NUM> light for <NUM> seconds. The gel fraction of the film was <NUM>% after exhaustive extraction with dimethylacetamide.

Blends of different molecular weight oligomers with functional endgroups can be cured by free radical polymerization either thermally or photochemically. For example, a blend of a minor amount of a <NUM>,<NUM>/mole tetrafluorostyrene terminated oligomer can be mixed with a major amount of a <NUM>,<NUM>/mole tetrafluorostyrene terminated oligomer and cured in a similar manner to that designated above in example <NUM>. Moreover, small amounts of low molecular weight monomers, e.g., ~<NUM>-<NUM> weight percent of divinylbenzene, may also be co-cured with such mixtures.

The disclosure provides controlled post-sulfonation of linear non-sulfonated poly(arylene ether sulfone)s, some that contained hydroquinone comonomers and some that contained biphenol, have also been achieved. The hydroquinone (or biphenol) rings in the copolymers should be the only rings that are activated for electrophilic aromatic sulfonation. By using mild sulfonation conditions, those activated rings can be quantitatively monosulfonated (for hydroquinone) or disulfonated (for biphenol) without sulfonating any of the other positions on the backbone.

The inventors have further discovered and the disclosure provides that controlled molecular weight end-functional oligomers can be prepared, then selectively post-sulfonated only on positions that are activated for electrophilic aromatic substitution. This inventive aspect has the advantage over other membranes in that no monosulfonated or disulfonated monomers are required. The method affords a means to prepare crosslinked sulfonated polysulfone networks without the need to synthesize pre-formed sulfonated monomers. By forming random copolymeric oligomers by step-growth polymerization, the method allows for controlling both the level of sulfonation and also the distribution of sulfonate anions along the oligomer backbones. These networks provide a means for improving the fixed charge concentration without the necessity of synthesizing and purifying new monomers.

The disclosure provides that historically, the post-sulfonation route led to uncontrolled sequences of sulfonic acid groups along the chains unless special compositions were utilized. Most previous work on post-sulfonation of polysulfones utilized rather harsh conditions because the rings to be sulfonated included both activated and deactivated rings toward the electrophilic aromatic sulfonation reaction. Hence, post-sulfonation as an approach for sulfonating poly(arylene ether sulfone)s was abandoned due to poor control over the extent of sulfonation, inability to control the microstructure of the sulfonated units, and decrease in molecular weight due to chain scission during sulfonation. These post sulfonated polysulfone membranes were found to be resistant to degradation by chlorine but showed relatively low salt rejections relative to the stateof-the-art interfacial polyamides. Alternatively, controlled post-sulfonation of poly(arylene ether sulfone)s that contained hydroquinone or biphenol units may be performed. The sulfonation reaction may proceed only at the hydroquinone (or biphenol) because all of the other rings were deactivated toward electrophilic aromatic sulfonation by the electron withdrawing sulfone groups. In the current example, the reaction kinetics and measurements of molecular weight of a polysulfone containing hydroquinone were studied to optimize the sulfonation process with a minimal level of chain scission. This information was used for developing a series of post-sulfonated polymers with varying structures to determine their relationships among structures and properties.

The disclosure provides description of various embodiments - Synthesis and characterization of controlled molecular weight oligomers that are made by post-sulfonation with crosslinkable endgroups. A systematic series of oligomers with a range of hydroquinone content was synthesized by varying the ratio of bisphenol sulfone and hydroquinone monomers. The polymerization takes place via the carbonate method in which K<NUM>CO<NUM> deprotonates the phenol monomers to form an anionic nucleophile. The nucleophile attacks the electronegative carbon attached to the halogen, with release of the halogen. Only a slight excess of K<NUM>CO<NUM> was utilized to avoid any hydrolysis of the halogen functional monomer, thus in turn, preventing unwanted endgroups.

The disclosure provides that a reaction using post-sulfonation to generate controlled molecular weight aminophenol-terminated oligomers by post-sulfonation is provided. The first step is synthesis of the non-sulfonated oligomer, the second step is post-sulfonation, the third step is regeneration of the amine endgroups and conversion of the pendent sulfonic acid groups to salts. In the second step, only the hydroquinone units become sulfonated because all of the other rings are selected to be deactivated toward the electrophilic aromatic sulfonation reaction, so that they do not react under the mild conditions used for the post-sulfonation. The hydroquinone sulfonations are quantitative, thus allowing control over the degree of sulfonation by controlling how much hydroquinone is charged into the reaction, even though an excess of sulfuric acid is used in the post-sulfonation reaction. Rose showed (<CIT>) selective sulfonation of the hydroquinone but he did not discuss any method for forming controlled molecular weight oligomers so that they could be functionalized with amine endgroups or with other types of functional endgroups. So the Rose patent does not disclose crosslinking reactions or crosslinked polymers. The copolymer moieties derived from the bisphenol sulfone do not post-sulfonate but the moieties derived from the hydroquinone do. There are other bisphenols that could potentially be used with the bisphenol sulfone as alternatives for the hydroquinone (listed below). An example utilizing biphenol instead of hydroquinone is provided herein. During post-sulfonation, it sulfonates with approximately one ion on each ring (the use of biphenol is not included in Rose's <NUM> patent).

The disclosure provides that the below structures show other bisphenols that are useful for post-sulfonation in addition to hydroquinone, where each R can independently be H or CH<NUM>:
<CHM>.

The disclosure provides Example <NUM>. Synthesis of amine terminated hydroquinone polysulfone oligomers for subsequent post-sulfonation and crosslinking. A reaction to prepare a <NUM>,<NUM>/mole Mn, amine-terminated oligomer with <NUM> mole % of the bisphenol moieties being hydroquinone is provided. It is recognized that other molecular weights may be synthesized by adjusting the stoichiometry of the reactants. Hydroquinone (<NUM>, <NUM> mmol), bisphenol sulfone (<NUM>, <NUM> mmol), and m-aminophenol (<NUM>, <NUM> mmol) were dissolved in <NUM> of sulfolane in a <NUM>-neck round bottom flask equipped with a nitrogen inlet, overhead stirrer, and condenser with a Dean Stark trap. Toluene (<NUM>) and K<NUM>CO<NUM> (<NUM>, <NUM> mmol) were added and the reaction was refluxed at <NUM>-<NUM> to azeotropically remove any water. After <NUM> hours, the toluene was removed from the Dean Stark trap. <NUM>,<NUM>'-Dichlorodiphenylsulfone (<NUM>, <NUM> mmol) was added into the reaction and the reaction temperature was raised to <NUM>-<NUM>. After <NUM> hours, the mixture was allowed to cool to ~<NUM> and then diluted with <NUM> of N,N-dimethylacetamide. The solution was filtered hot to remove salts and subsequently precipitated in isopropanol. The polymer was boiled in water with <NUM> changes of water to remove trace amounts of sulfolane and then dried at <NUM> for <NUM> hours, followed by <NUM> hours under vacuum at <NUM>. The reaction had a yield of <NUM>%.

The disclosure provides Example <NUM>. Synthesis of amine terminated, biphenol polysulfone oligomers for subsequent post-sulfonation and crosslinking. A reaction to prepare a <NUM>,<NUM>/mole Mn, amine-terminated oligomer with <NUM> mole % of the bisphenol moieties being biphenol is provided. Biphenol (<NUM>, <NUM> moles), bisphenol sulfone (<NUM>, <NUM> moles), and m-aminophenol (<NUM>, <NUM> moles) were dissolved in <NUM> of sulfolane in a <NUM>-neck round bottom flask equipped with a nitrogen inlet, overhead stirrer, and condenser with a Dean Stark trap. The reaction temperature was controlled with a temperature controller connected to a thermocouple in a salt bath. Toluene (<NUM>) and K<NUM>CO<NUM> (<NUM>, <NUM> moles) were added and the reaction was refluxed at <NUM>-<NUM> to azeotropically remove any water. After ~<NUM> hours, the toluene was removed from the Dean Stark trap. <NUM>,<NUM>'-dichlorodiphenylsulfone (<NUM>, <NUM> moles) was added into the reaction flask and the temperature was raised to <NUM>-<NUM>. After <NUM> hours, the mixture was allowed to cool to ~<NUM> and then diluted with <NUM> of N,N-dimethylactamide. The mixture was hot-filtered, then kept above the melting point of sulfolane (<NUM>) while it was precipitated in isopropanol to remove traces of solvents. The polymer was boiled in water with <NUM> changes of water to remove trace amounts of sulfolane and then dried at <NUM> for <NUM> hours, followed by <NUM> hours under vacuum at <NUM>.

The disclosure provides Example <NUM>. Post sulfonation of amine-terminated, hydroquinone polysulfone oligomers. A dry <NUM>,<NUM>/mole Mn hydroquinone polysulfone oligomer (<NUM>) was dissolved in <NUM> of concentrated sulfuric acid in a <NUM>-neck round bottom flask equipped with a nitrogen inlet and thermometer, overhead stirrer, and a condenser. An oil bath was used to maintain a reaction temperature of <NUM>. After <NUM> hours of reaction, the solution was precipitated into ice-cold water, then rinsed with water to remove excess acid until litmus paper showed no traces of acid in the filtrate. The sulfonated polysulfone oligomer with ammonium endgroups was converted to the salt form and the ammonium endgroups were converted to amines by stirring in <NUM> aq. NaOH for <NUM> hours. The amine terminated sulfonated hydroquinone polysulfone oligomer was filtered and dried at <NUM> for <NUM> hours at atmospheric pressure, then for <NUM> hours under vacuum at <NUM>. Proton NMR showed that the hydroquinone units had been sulfonated. A water insoluble product was obtained and no degradation of the oligomer was observed. The sulfonic acid groups were only substituted on the activated hydroquinone for electrophilic aromatic substitution due to the mild reaction conditions.

The disclosure provides that <FIG> provides a <NUM>H NMR spectrum of a <NUM>-<NUM>-HQS oligomer showing quantitative terminal endgroup functionality. The fraction of hydroquinonecontaining units were confirmed from the <NUM>H NMR spectra (<FIG>). The integral corresponding to the amine peaks (I) was standardized at <NUM> and integration of the cluster of peaks from the protons adjacent to the sulfone groups was subtracted from the integrals of the cluster of peaks B, B<NUM>, and C, to yield the number of protons on the hydroquinone units. Hence, by determining the number of hydroquinone and the bisphenol sulfone units, molecular weights of the oligomers were calculated.

The disclosure provides that <FIG> provides a <NUM>H NMR of <NUM>-<NUM>-SHQS. Quantitative monosulfonation of the hydroquinone rings in the oligomers was confirmed by <NUM>H NMR as shown in <FIG>. Due to the presence of water and the hydrophilicity, broad peaks were observed. However, appearance of the peak C' was observed simultaneously with a disappearance or reduction in C peaks. Correlation <NUM>H NMR spectroscopy (<FIG>) confirmed that the C' peak corresponded to the proton next to the sulfonic acid group since it did not correlate to any other proton. <FIG> provides COSY NMR data of <NUM>-<NUM>-SHQS confirming sulfonation only on the hydroquinone units.

The disclosure provides End group analysis of the oligomers by fluorine derivatization. The amine terminated oligomers with amine and any residual phenolic end groups were reacted with trifluoroacetic anhydride to produce the respective trifluoroacetate derivatives. The reaction for the derivatization of a <NUM>,<NUM>/mole, amine-terminated oligomer with <NUM> mole % of the bisphenol moieties being hydroquinone (<NUM>-HQS-<NUM>) is provided. <NUM>-HQS-<NUM> oligomer (<NUM>, <NUM> mmol), with amine end groups and possibly unreacted hydroxyl end groups, was dissolved in <NUM> of CHCl<NUM> in a <NUM>-mL flask and trifluoroacetic anhydride (<NUM>, <NUM> mmol) was added. The reaction mixture was held at <NUM> for <NUM> hours. DI water (<NUM>) was added to the reaction mixture to hydrolyze the remaining anhydride, and the mixture was stirred at room temperature for <NUM> hours. The organic phase was analyzed by <NUM>F NMR.

The disclosure provides that <FIG> provides an overview of the synthesis of controlled molecular weight random oligomers by nucleophilic aromatic substitution. X= <NUM>, <NUM>, <NUM>, <NUM>. <FIG> provides an overview of the fluorine derivatization of the oligomers to check for unreacted monomers and completion of the reaction.

The disclosure provides that to confirm the absence of undesirable residual phenol or chlorine end groups after the reaction, the oligomer was derivatized with trifluoroacetic anhydride as shown in <FIG>. The anhydride reacts with the amine end groups forming a derivative that resonates at ~ -<NUM> ppm in the <NUM>F NMR spectrum (<FIG>). The anhydride also reacts with any unreacted end groups of Bis-S or hydroquinone, resonating downfield from the amine. An aliquot taken at <NUM> hours showed that there was one equivalent of phenol from Bis-S for very five equivalents of amine. However, an aliquot taken at <NUM> hours showed successful completion of the reaction. <FIG> provides <NUM>F NMR spectra of the oligomers showing unreacted hydroxyl end groups and amine groups of the oligomer-aliquot at <NUM> of the reaction and <FIG> provides <NUM>F NMR spectra of only amine end groups of the oligomer-aliquot at <NUM> of the reaction.

The disclosure provides that <FIG> provides light scattering SEC curves of <NUM>-<NUM>-SHQS and <NUM>-<NUM>-HQS to confirm the molecular weights. <FIG> displays symmetric light scattering curves. The elution times of the sulfonated oligomers were lower than their non-sulfonated counterparts (<FIG>). The molecular weights and percentages of hydroquinone units are shown in Table <NUM>.

The disclosure provides Example <NUM>. Post-sulfonation of an amine-terminated biphenol polysulfone oligomer. Post-sulfonation of an amine-terminated biphenol polysulfone oligomer was conducted in the same manner as an amine-terminated hydroquinone polysulfone oligomer described in example <NUM>. One sulfonate on each biphenol ring resulted.

The disclosure provides Example <NUM>. Crosslinking of amine-terminated, post-sulfonated, hydroquinone polysulfone oligomers with epoxy reagents. Film casting involved crosslinking of the post-sulfonated telechelic oligomers with the crosslinking agent TGBAM utilizing triphenylphosphine as a catalyst. The crosslinking reaction was conducted above the Tgs of the oligomers, which were suppressed by the solvent (DMAc). The IECs of the crosslinked networks were lower than the precursor oligomers due to incorporation of the hydrophobic TGBAM. The fixed charge concentration was calculated as the ratio of IEC to water uptake. High gel fractions (~<NUM>%) were observed for all of the networks.

The disclosure provides that a crosslinking reaction for a <NUM>,<NUM>/mole oligomer is provided. A <NUM>,<NUM>/mole Mn, amine-terminated, post-sulfonated hydroquinone polysulfone oligomer (<NUM> mmol, <NUM>), tetraglycidyl bis(p-aminophenyl)methane (<NUM> mmol, <NUM>) and triphenylphosphine (<NUM> × <NUM>-<NUM> mmol, <NUM>) were dissolved in <NUM> of N,N-dimethylacetamide. The solution was syringe-filtered through a <NUM> polytetrafluoroethylene filter. The solution was cast on a circular Teflon mold with flat edges and a diameter of <NUM>. The mold was placed on a levelled surface in an oven at <NUM>. The temperature was ramped from <NUM> to <NUM> over <NUM> hours and the film was cured at <NUM> for <NUM> hours. The epoxy-cured network was detached from the Teflon mold by immersion in deionized water and dried.

A summary of IECs, water uptakes and gel fractions is provided in Table <NUM>. Crosslinked membranes were dried at <NUM> under vacuum overnight. After drying, <NUM>-<NUM> of the sample was placed in a <NUM>-mL scintillation vial filled with DMAc and stirred at <NUM> for ~<NUM> hours. The remaining solid was filtered, transferred to a weighed vial, dried at <NUM> under vacuum for ~<NUM> hours, and then weighed. Three measurements were taken for each film and gel fractions were calculated by Equation <NUM>. <MAT> The water uptakes of the crosslinked membranes were determined gravimetrically. First, the membranes in their sodium salt form were dried at <NUM> under vacuum for <NUM> hours and weighed. These membranes were soaked in water at room temperature for <NUM> hours. Wet membranes were removed from the liquid water, blotted dry to remove surface droplets, and quickly weighed. The water uptake of the membranes was calculated according to Equation <NUM>, where massdry and masswet refer to the masses of the dry and the wet membranes, respectively.

Hydrated Tensile properties. Absorbed water stretches the polymer network, and the stretching is resisted by elastic retractive forces. Hence, the tensile properties of the networks depend upon the water uptake. The yield strengths and moduli dropped upon increase in water uptake, but the hydrated networks remained in the glassy regime. <FIG> provides a graph of modulus vs water uptake for fully hydrated membranes; <FIG> provides a plot of yield strength vs water uptake for fully hydrated membranes. <FIG> provides a schematic illustration of crosslinking of post-sulfonated amine terminated oligomers.

The disclosure provides that networks prepared with ~<NUM>,<NUM> and ~<NUM>,<NUM>/mole oligomers show different trends with respect to ultimate strains in their fully hydrated states. <FIG> provides stress strain curves of fully hydrated membranes with a <NUM>-XX-SHQS series, and <FIG> provides stress strain curves of fully hydrated membranes with a <NUM>-XX-SHQS series. The <NUM>,<NUM>/mole series networks were restricted to ~<NUM>% ultimate strains. This could be attributed to hydrostatic forces becoming much greater than the elastic forces of the polymer network as the networks absorbed more water. The <NUM>,<NUM>/mole oligomer networks had higher water uptakes than the <NUM>/mole counterparts, likely attributable in part to the lower amount of hydrophobic crosslinking reagent used to crosslink the <NUM>,<NUM>/mole oligomer. The crosslinking agent not only decreased the hydrophilicity of the system due to inherent hydrophobicity but it also reduced the flexibility of the <NUM>/mole networks to a greater extent than the networks prepared with the <NUM>,<NUM>/mole oligomers. This made the networks with the <NUM>/mole oligomers more brittle than those containing the <NUM>,<NUM>/mole prepolymers. Hence, networks that contained the <NUM>,<NUM>/mole prepolymers were more flexible due to the higher chain length between crosslinks.

The disclosure provides Example <NUM>. Reaction of amine-terminated, post-sulfonated polysulfone oligomers with endgroups for subsequent free radical crosslinking, then crossinking the oligomers with light. Amine-terminated, post-sulfonated polysulfone oligomers can be reacted with acrylate and methacrylate reagents to produce acrylate, methacrylate, acrylamide or methacrylamide endgroups. These functional oligomers can then be crosslinked thermally or with light by free radical polymerization. It is recognized that alternative functional endgroups and/or alternative crosslinking reagents could be used in a similar manner to produce crosslinked membranes wherein a controlled molecular weight oligomer, or blends of different molecular weight oligomers, are utilized as macromonomers. Examples of alternative functional endgroups are phenol, maleimide, nadimide, acrylate, methacrylate, acrylamide, methacrylamide, ethynyl, phenylethynyl, styrene, tetrafluorostyrene and others. Alternative crosslinking reagents are amines, azides, halogenated benzylic monomers and comonomers including molecules with double bonds that are reactive by free radical polymerization. <CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>.

The disclosure provides that functionalization of an amine-terminated, post-sulfonated hydroquinone polysulfone oligomer with acryloyl chloride to produce a post-sulfonated oligomer crosslinkable by free radical polymerization.

The disclosure provides that a procedure for synthesizing an ~<NUM>,<NUM>/mole Mn, amine-terminated, post-sulfonated hydroquinone polysulfone oligomer with <NUM>% of the repeat units sulfonated is provided. The oligomer (<NUM>, <NUM> × <NUM>-<NUM> equivalents of amine) was dissolved in a mixture of <NUM> of N,N-dimethylacetamide and <NUM> of toluene in a <NUM>-neck, round bottom flask equipped with a Dean Stark trap topped with a condenser and a nitrogen inlet. The mixture was azeotroped in an oil bath set at <NUM> to remove any water for <NUM> hours. It was cooled to <NUM> in an ice bath, then dry triethylamine (<NUM>, <NUM> × <NUM>-<NUM> moles) was added, then acryloyl chloride (<NUM>, <NUM> × <NUM>-<NUM> moles) was added by syringe. It was stirred at <NUM> for <NUM> hours, then precipitated in isopropanol, washed with isopropanol for <NUM> hours, filtered and dried under vacuum at <NUM> for <NUM> hours, then stored in the dark in a refrigerator. Proton NMR showed the quantitative appearance of acrylamide endgroups. The oligomer (<NUM>) and <NUM> of <NUM>,<NUM>,<NUM>-trimethylbenzoyl-diphenylphosphine oxide (TPO) were dissolved in <NUM> of dimethylacetamide plus <NUM> of diethylene glycol. The solution was cast on a glass plate and cured with <NUM>-nm light at <NUM> for <NUM> minutes. The cast membrane had a gel fraction of <NUM>% after exhaustive extraction with dimethylacetamide.

The disclosure provides Example <NUM>. Post-sulfonation of phenol terminated oligomers, then functionalization of terminal groups for free radical polymerization. Post-sulfonated oligomers can also be prepared with phenol endgroups by offsetting the stoichiometry according to known methods to control molecular weight, then further functionalized so that they can be crosslinked by free radical polymerization using either heat or light in conjunction with an initiator. The procedure involves synthesizing the oligomer containing bisphenol sulfone together with a bisphenol that can be selectively sulfonated under mild conditions, post-sulfonating the oligomer, then further reacting the phenol terminated sulfonated oligomer with pentafluorostyrene, acryloyl chloride or isocyanatoethyl acrylate, methacryloyl chloride or isocyanatoethyl methacrylate to form crosslinkable endgroups. These can be further reacted in the presence of either thermal, or UV initiators with light, to produce crosslinked networks. The networks with tetrafluorostyrene endgroups would be expected to be particularly chlorine stable.

Salt Permeability. The salt permeabilities of the polymer networks were measured under a concentration gradient where the upstream salt concentration was kept constant for all measurements. The salt permeabilities are plotted against water uptake and fixed charge concentration (<FIG>). It was observed that with a decrease in water content in the networks, the salt permeability decreased for all of the networks (<FIG>). However, this trend depended upon the block length of the prepolymers. The <NUM>,<NUM>/mole oligomers contain an average of just ~<NUM> repeat units which is on the threshold of entanglement length and this may make both their hydrated mechanical properties and their transport properties more sensitive toward even small changes in water uptake or fixed charge concentration. However, the <NUM>,<NUM>/mole blocks are likely more entangled and this may explain why their mechanical and transport properties were less sensitive to changes in water uptake or fixed charge concentration than the networks with the <NUM>/mole oligomers.

The observed trend of salt permeability vs. fixed charge concentration can be explained on the basis of Donnan equilibria. The higher the fixed charge concentration, the greater the co-ion (i.e., Cl-) rejection of these membranes, and the lower the salt permeability. Hence, it was observed that the salt permeability plummeted with increase in fixed charge concentration (<FIG>).

Electrodialysis (ED) requires a high selectivity of counterions vs. co-ions and a high counterion permeability. Counterion permeability increases with increases in water content as water offers a medium of flow to the ions. However, this water uptake should be optimized, as an increase in water uptake causes a decrease in fixed charge concentration, especially in the case of linear ion exchange polymeric membranes. Low co-ion permeability, which manifests itself as low salt permeability, is not only a necessity in ED but also in other desalination processes, such as RO and forward osmosis, which utilize ion exchange membranes and where a high salt rejection is desirable. To optimize the water uptake and the fixed charge concentration, the membranes of this invention were crosslinked. The salt permeability was somewhat mitigated by crosslinking. The <NUM>-<NUM>-SHQS displays these optimal properties, not only in terms of water uptake and salt permeability, but also in the hydrated mechanical properties. It displayed a hydrated modulus of ~<NUM> MPa. The cured membranes imbibed higher amounts of water with increasing degrees of sulfonation but they remained in the glassy state even when fully hydrated. The yield stresses of the fully hydrated, crosslinked networks ranged from approximately <NUM>-<NUM> MPa.

Structure and molecular weights of the functional oligomers. The non-sulfonated and sulfonated oligomers were characterized by quantitative <NUM>H NMR to calculate the molecular weights and degrees of sulfonation (<FIG> and <FIG>). Completion of the reaction was confirmed by the absence of peaks of undesired end groups in the spectra. The spectra were normalized using the peaks from the amine end groups.

The A, A1 signals overlapped and resonated at <NUM> to <NUM> ppm. The I peaks from the amine end groups resonated at <NUM> ppm. The C protons of the hydroquinone resonated at <NUM> ppm. After sulfonation, the C protons shifted downfield to <NUM> ppm due to the electron withdrawing nature of the sulfonic acid groups that deshielded the protons. The amine end groups were acidified during the sulfonation at <NUM> for <NUM> hours, shifting the peaks downfield. Thus, the sulfonated oligomers were stirred in a solution of <NUM>. 1N NaOH to recover the amine end groups. <FIG> and <FIG> provide <NUM>H NMR of an oligomer with a target molecular weight of ~<NUM>/mol and <NUM>% hydroquinone containing repeat units before sulfonation (<FIG>) and after sulfonation (<FIG>).

The degree of sulfonation was calculated from the spectra of the sulfonated oligomers, and the ion exchange capacities were calculated using the degrees of sulfonation (Equation <NUM>). In equation <NUM>, DS is the degree of sulfonation, MWSRU is the molecular weight of the sulfonated repeat unit in the Na+ form, MWNSRU is the molecular weight of the non-sulfonated repeat unit.

COSY NMR experiments were performed to confirm the structure of the post sulfonated oligomers (<FIG>). The C' proton correlated only with itself and did not show a three-bond correlation with any other proton. There were no other uncorrelated protons. Thus there were no secondary sites of sulfonation and all the hydroquinone moieties were strategically sulfonated by post-sulfonation. <FIG> provides COSY-NMR of a sulfonated oligomer with a target molecular weight of ~<NUM>/mol and <NUM>% hydroquinone containing repeat units (<NUM>-SHQS-<NUM>).

Membrane properties. The maximum absorption of water increases with IEC (<FIG>, Table <NUM>). <FIG> provides a plot showing fixed charge concentrations of the linear and the crosslinked (~<NUM>/mole) membranes as a function of their ion exchange capacities. The IECs of the crosslinked membranes were calculated from the IECs of the oligomers measured by <NUM>H NMR, by taking into account the addition of the non-ionic crosslinking agent (Equation <NUM>). The water uptakes of crosslinked membranes have been reported to be constrained due to reduced swelling and free volume. This is evident for the systems discussed in this example in <FIG> where, for a given IEC, the water uptakes of the epoxy networks prepared from the <NUM>/mole oligomers are less than the linear counterparts.

The fixed charge concentration of the membranes, <MAT>, is defined as the concentration of fixed ions on the polymer per unit of sorbed water (Equation <NUM> where ρw is assumed to be <NUM>/cc). <MAT> Increasing the membrane fixed charge concentration increases the Donnan potential, which should lead to better co-ion and salt rejection. Thus, increasing the fixed charge groups in the polymer matrix can increase the fixed charge concentration. However, increasing the IEC also increases the water uptake of the membranes which acts to reduce the fixed charge concentration. <FIG> provides a plot showing water uptake of the linear and the crosslinked membranes (~<NUM>/mole) as a function of their ion exchange capacities. <FIG> shows the fixed charge concentrations of the linear and crosslinked SHQS membranes with respect to IEC. It is clear that the crosslinked membranes have higher fixed charge concentrations than the linear counterparts. Thus, it is hypothesized that these crosslinked membranes will also show improved salt rejection. The effect of crosslinking on constraining the membranes made from the <NUM>,<NUM>/mole oligomers was not as prominent, likely due to their lower crosslink densities. It should also be noted that all of the SHQS membranes had higher fixed charge concentrations than those of some commercial GE Electrodialysis membranes.

Claim 1:
A copolymer comprising the structure:
<CHM>
wherein each L<NUM> is independently
<CHM>
wherein each L<NUM> is independently
<CHM>
wherein each L<NUM> is independently a single bond,
<CHM>
or
<CHM>
wherein one Y<NUM> is SO<NUM>Z and the other Y<NUM> is H, wherein Z is a counterion, wherein each R is independently H, F, or CH<NUM>; and wherein the value of x is between <NUM> and <NUM>, and the value for n is <NUM> to <NUM>,<NUM>.