Multiblock copolymers for moisture swing direct air capture

Abstract

Preparing a block copolymer comprising poly(diallyldimethylammonium) (PDADMAC) blocks and polysulfone (PSf) blocks includes contacting diallyldimethylammonium chloride (DADMAC) with an iniferter under ultraviolet (UV) radiation and heating to yield a PDADMAC oligomer, isolating the PDADMAC oligomer, contacting the PDADMAC oligomer with a hexafluorophosphate salt to yield a PDADMA(PF6) oligomer, isolating the PDADMA(PF6) oligomer, contacting the PDADMA(PF6) oligomer with a bis(fluoroaryl)sulfone and a bis-phenol in the presence of a base under dehydrating conditions to obtain a PSf-PDADMA(PF6) block copolymer, and isolating the PSf-PDADMA(PF6) block copolymer. Preparing a moisture-swing CO2 direct air capture and release membrane includes disposing a PSf-PDADMA(PF6) block copolymer on a substrate, delaminating the PSf-PDADMA(PF6) block copolymer from the substrate to yield a layer comprising the PSf-PDADMA(PF6) block copolymer, and ion-exchanging PF6 - with HO- in the layer to yield the membrane, wherein the membrane comprises a PSf-PDADMA(OH) block copolymer.

Description

MULTIBLOCK COPOLYMERS FOR MOISTURE SWING DIRECT AIR CAPTURECROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Patent Application No. 63 / 588,507 filed on October 6, 2023, which is incorporated herein by reference in its entirety.STATEMENT OF GOVERNMENT SUPPORT

[0002] This invention was made with government support under DE-AR0001103 awarded by the Department of Energy. The government has certain rights in the inventionTECHNICAL FIELD

[0003] This invention relates to block copolymers and to their use in moisture swing CO2 capture and release.BACKGROUND

[0004] The thermal, mechanical, and chemical stability of poly sulfones (PSf), particularly aromatic polysulfones, have led to their application in nanofiltration, energy storage, and biochemical separations. To produce polysulfones for specific applications, several copolymers and functionalized polysulfones have been developed. Properties including glass transition temperature, solubility, hydrophilicity, hydrophobicity, permittivity, and tensile strength of polysulfone materials have been modified through either copolymerization with an appropriate co-monomer or post-polymerization functionalization.SUMMARY

[0005] This disclosure describes the synthesis and characterization of stable, cationic multiblock polysulfones.

[0006] Embodiment l is a method of preparing a block copolymer comprising poly(diallyldimethylammonium) (PDADMAC) blocks and polysulfone (PSf) blocks, the method comprising: contacting diallyldimethylammonium chloride (DADMAC) with an iniferter under ultraviolet (UV) radiation and heating to yield a PDADMAC oligomer;isolating the PDADMAC oligomer; contacting the PDADMAC oligomer with a hexafluorophosphate salt to yield a PDADMA(PFe) oligomer; isolating the PDADMA(PFe) oligomer; contacting the PDADMA(PFe) oligomer with a bis(fluoroaryl)sulfone and a bis-phenol in the presence of a base under dehydrating conditions to obtain a PSf-PDADMA(PFe) block copolymer; and isolating the PSf-PDADMA(PFe) block copolymer.

[0007] Embodiment 2 is the method of Embodiment 1, wherein the iniferter is bis(4- fluoropheny 1 )di sul fi de .

[0008] Embodiment 3 is the method of Embodiment 1 or 2, wherein a molar ratio of DADMAC : iniferter is in a range of 5: 1 to 3500: 1.

[0009] Embodiment 4 is the method of any one of Embodiments 1-3, wherein a wavelength of the UV radiation is about 254 nm.

[0010] Embodiment 5 is the method of any one of Embodiments 1-4, wherein the heating comprises heating to a temperature in a range of about 50°C to about 70 °C.

[0011] Embodiment 6 is the method of any one of Embodiments 1-5, wherein isolating the PDADMAC oligomer comprises precipitating the PDADMAC oligomer from a first organic solvent to yield a precipitate and drying the precipitate under vacuum with heating.

[0012] Embodiment 7 is the method of Embodiment 6, further comprising dissolving the precipitate in a second organic solvent and re-precipitating the PDADMAC oligomer from the first organic solvent prior to drying the precipitate under vacuum with heating.

[0013] Embodiment 8 is the method of Embodiment 6 or 7, wherein the first organic solvent comprises acetone.

[0014] Embodiment 9 is the method of Embodiment 7, wherein the second organic solvent comprises methanol.

[0015] Embodiment 10 is the method of any one of Embodiments 1-9, wherein the PDADMAC oligomer is capped on one or both ends with a 4-fluorophenyl sulfide group.

[0016] Embodiment 11 is the method of any one of Embodiments 1-10, further comprising contacting the PDADMAC oligomer with an oxidizing agent.

[0017] Embodiment 12 is the method of Embodiment 11, wherein the oxidizing agent is oxone.

[0018] Embodiment 13 is the method of any one of Embodiments 1-12, wherein the hexafluorophosphate salt is potassium hexafluorophosphate.

[0019] Embodiment 14 is the method of any one of Embodiments 1-13, wherein the bis(fluoroaryl)sulfone is bis(4-fluorophenyl)sulfone.

[0020] Embodiment 15 is the method of any one of Embodiments 1-14, wherein the bisphenol is 4,4'-(propane-2,2-diyl)diphenol.

[0021] Embodiment 16 is the method of any one of Embodiments 1-15, wherein the base is potassium carbonate.

[0022] Embodiment 17 is the method of any one of Embodiments 1-16, wherein the dehydrating conditions comprise collecting water by heated distillation at ambient pressure.

[0023] Embodiment 18 is the method of any one of Embodiments 1-17, wherein the mole% of DADMA(PF6) contacted with a bis(fluoroaryl)sulfone and a bis-phenol is from about 30% to about 70%.

[0024] Embodiment 19 is the method of preparing a moisture-swing CO2 direct air capture and release membrane, the method comprising: disposing a PSf-PDADMA(PF6) block copolymer on a substrate; delaminating the PSf-PDADMAfPFe) block copolymer from the substrate to yield a layer comprising the PSf-PDADMA(PFe) block copolymer; and ion-exchanging PFe’ with HO" in the layer to yield the membrane, wherein the membrane comprises a PSf-PDADMA(OH) block copolymer.

[0025] Embodiment 20 is the method of Embodiment 19, wherein disposing the PSf- PDADMA(PFe) block copolymer on the substrate comprises is evaporating a solution comprising the PSf-PDADMA(PFe) block copolymer and an organic solvent.

[0026] Embodiment 21 is the method of Embodiment 20, wherein the organic solvent is N,N-dimethylacetamide.

[0027] Embodiment 22 is the method of any one of Embodiments 19-21, wherein the delaminating comprises contacting the layer with water.

[0028] Embodiment 23 is the method of any one of Embodiments 19-22, wherein the ionexchanging comprises:ion-exchanging PFe’ with CF to yield a PSf-PDADMA(Cl) block copolymer; and ion-exchanging C1‘ with HO" to yield the PSf-PDADMA(OH) block copolymer.

[0029] Embodiment 24 is a moisture-swing CO2 direct air capture and release membrane comprising:PSf-PDADMA(OH) block copolymer, wherein the block copolymer comprises 15 mole% to 65 mole% of DADMA(OH).

[0030] A series of multiblock copolymers containing both diallyldimethylammonium blocks and polysulfone blocks were synthesized. Telechelic poly(diallyldimethylammonium hexafluorophosphate) (PDADMA(PFe)) oligomers were synthesized using bis(4- aminofluoro)disulfide as an iniferter molecule. The resultant fluorophenylsulfone-capped oligomers were then reacted in-situ with bis(4-fluorophenyl)sulfone and bisphenol A. The resultant multiblock copolymers were synthesized at high yield over a range of compositions, and films with good flexibility and strength were formed from most of the copolymer compositions. These copolymer materials are suitable for moisture-swing, direct-air CO2 capture.

[0031] The details of one or more embodiments of the subject matter of this disclosure are set forth in the accompanying drawings and the description. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.BRIEF DESCRIPTION OF DRAWINGS

[0032] FIG. 1 depicts an experimental setup used for moisture-swing CO2 direct air capture analysis.

[0033] FIG. 2 shows an exemplary 'H-NMR spectrum of bis(4-fluorophenyl)sulfone difunctionalized PDADMA(PFs) oligomer.

[0034] FIG. 3 shows a synthetic scheme for bis(4-fluorophenyl)sulfone functionalized PDADMA(PFe) oligomers and the in-situ synthesis of PSf-PDADMA(PFe) multiblock copolymers.

[0035] FIG. 4 shows an exemplary 'H-NMR spectrum of the 50 wt% PSf-PDADMA(PFe) block copolymer.

[0036] FIG. 5A shows TGA curves showing the decay temperatures of the PSf homopolymer and 50 wt% PSf-PDADMA(PFe). FIG. 5B shows DSC curves showing the Tgfor the PSf homopolymer and 50 wt% PSf-PDADMA(PFe).

[0037] FIG. 6 is a schematic showing moisture- swing CO2 uptake and release by PDADMA(OH) units.

[0038] FIGS. 7A-7C show changes in CO2 concentration (upper curves) and relative humidity (lower curves) for 20, 30, and 40 wt% PSf-PDADMA incorporation block copolymer films, respectively.

[0039] FIG. 8 shows CO2 uptake capacities observed for the 20, 30, and 40 wt% PSf- PDADMA incorporation block copolymer films.DETAILED DESCRIPTION

[0040] This disclosure describes multiblock copolymers containing diallyldimethylammonium blocks and polysulfone blocks that are formed into thin film membranes, which when rendered in hydroxide salt form, are used for moisture swing CO2 direct air capture.

[0041] The hydrophobic nature of poly sulfones make them prone to fouling during use in membrane purification applications. The functionalization of polysulfones with cationic groups through processes like grafting can reduce the affinity of the polymer surface for contaminants and therefore increases membrane performance. Cationic polysulfones may also serve as anion exchange membranes. While numerous cationic groups are available, quaternary ammonium groups are acceptable because of the variety of chemistries and stabilities that can be achieved.

[0042] When producing membranes with transport or conductivity properties, polymer morphology is a factor, and the presence of ion channels is known to influence membrane performance. Ion channels may be achieved through the introduction of blocks with different polarity from the rest of the polymer backbone, which can cause the polymer chains to align during membrane formation, leading to microphase separation. Multiblock copolymers containing a hydrophobic polysulfone block and cationic block can undergo microphase separation and thereby achieve high ionic conductivity. An additional benefit of multiblock copolymers is the ability to add comonomer without disrupting the structure of the poly sulfone backbone, thereby allowing for the charge content to be changed without eliminating thebeneficial thermal and mechanical properties of polysulfones. Polydiallydimethylammonium (PDADMAC) blocks have alkaline stability due at least in part to their cyclopolymerization, which makes the polymer suitable for applications where hydroxide ion concentration is high.DADMAC "PDADMAC"

[0043] The aforementioned properties of cationic poly sulfone polymers make them suitable for direct-air capture (DAC) of CO2. DAC of CO2 is of interest because reducing CO2 emissions may help address global climate change. Quaternary ammonium membranes with hydroxide counterions have an affinity for carbon dioxide due to the chemical equilibrium between carbonate, bicarbonate, and hydroxide ions (FIG. 6). When the cationic membrane is dry, CO2 is captured by reacting with hydroxide to form bicarbonate counterions. As humidity is increased, the high concentrations of water favor carbonate over bicarbonate counterions, and CO2 is released. The use of “moisture-swing” chemical absorption and desorption offers benefits over other DAC techniques because it relies on changes in relative humidity rather than the input of high levels of energy.

[0044] This disclosure describes stable, cationic multiblock copolymers derived from the condensation of difunctionalized ammonium oligomers, bis(4-fluorophenyl)sulfone monomers, and bisphenol monomers (see FIG. 3 and Example 1). The difunctionalized ammonium oligomers were made using an iniferter-based synthesis. Also disclosed herein are thin film membranes comprised of these block copolymers used for moisture-swing DAC of CO2.

[0045] Iniferters are a class of molecules that function as radical initiators as well as chain transfer agents and terminators. Disulfide molecules are one useful class of iniferters. Upon exposure to UV-irradiation, the sulfur-sulfur bond cleaves to produce two sulfide radicals, which initiate chain growth polymerization. When functionalized disulfide iniferters are employed in the polymerization of DADMAC, the result is PDADMAC oligomers functionalized on each end with groups resulting from the iniferter chemistry (see FIG. 3, top pane). A mechanism for termination in DADMAC polymerizations is recombination. Accordingly, in some cases the oligomers are difunctionalized as shown in FIG. 3. An additional benefit of iniferter-basedsyntheses is the ability to control the molecular weight of the oligomer by modulating the ratio of iniferter to monomer.

[0046] To produce oligomers suitable for the incorporation of poly sulfones, bis(4- fluorophenyl)disulfide was chosen as the iniferter. The fluorophenyl sulfide capped PDADMAC oligomers were characterized by quantitative1H-NMR spectroscopy by comparing the integration values of the peaks resulting from the methylene linkages of the DADMAC units to the integration values of the aromatic peaks resulting from the end-groups (FIG. 2). The iniferter to monomer ratio employed in the synthesis was 1 : 150 and the resulting oligomers were found to have 130 repeat units.

[0047] The PDADMAC oligomers required some modification before being used in a poly sulfone polymerization, specifically the sulfide end-groups of the oligomers were oxidized to sulfones. In some cases, this modification addresses the solubility issues caused by the hydrophilicity of the PDADMAC oligomers. Polysulfone syntheses typically require polar aprotic solvents, which are not suitable solvents for PDADMAC. Exchange of the chloride for other counterions can impact the solubility of both DADMAC and PDADMAC. Accordingly, in some cases, ion exchange from chloride to hexafluorophosphate produces oligomers with suitable solubility in polar aprotic solvents. The fluorophenyl sulfide capped PDADMA(PFe) oligomers disclosed herein are suitable for use in polysulfone synthesis procedures.

[0048] Preparing a block copolymer comprising poly(diallyldimethylammonium) (PDADMAC) blocks and polysulfone (PSf) blocks includes contacting diallyldimethylammonium chloride (DADMAC) with an iniferter under ultraviolet (UV) radiation (e.g., about 254 nm) and heating (e.g., in a temperature in a range of about 50°C to about 70 °C) to yield a PDADMAC oligomer, isolating the PDADMAC oligomer, contacting the PDADMAC oligomer with a hexafluorophosphate salt (e.g., potassium hexafluorophosphate) to yield a PDADMA(PFe) oligomer, isolating the PDADMA(PFe) oligomer, contacting the PDADMA(PFe) oligomer with a bis(fluoroaryl)sulfone (e.g., bis(4-fluorophenyl)sulfone) and a bis-phenol (e.g., 4,4'-(propane-2,2-diyl)diphenol) in the presence of a base (e.g., potassium carbonate) under dehydrating conditions to obtain a PSf-PDADMA(PF6) block copolymer, and isolating the PSf-PDADMA(PFe) block copolymer.

[0049] In one example, the iniferter is bi s(4-fluorophenyl)di sulfide. A molar ratio of DADMAC: iniferter is typically in a range of 5:l to 3500: l. Isolating the PDADMAC oligomercan include precipitating the PDADMAC oligomer from a first organic solvent (e.g., acetone) to yield a precipitate and drying the precipitate under vacuum with heating. The precipitate can be dissolved in a second organic solvent (e.g., methanol) and re-precipitating the PDADMAC oligomer from the first organic solvent prior to drying the precipitate under vacuum with heating.

[0050] The PDADMAC oligomer is capped on one or both ends with a 4-fluorophenyl sulfide group. The PDADMAC oligomer can be contacted with an oxidizing agent (e.g., oxone). The dehydrating conditions can include collecting water by heated distillation at ambient pressure. The mole% of DADMA(PF6) contacted with a bis(fluoroaryl)sulfone and a bis-phenol is from about 30% to about 70%.

[0051] Preparing a moisture-swing CO2 direct air capture and release membrane includes disposing a PSf-PDADMA(PFe) block copolymer on a substrate, delaminating the PSf- PDADMA(PFe) block copolymer from the substrate to yield a layer comprising the PSf- PDADMA(PFe) block copolymer, and ion-exchanging PFe' with HO" in the layer to yield the membrane, wherein the membrane comprises a PSf-PDADMA(OH) block copolymer. Disposing the PSf-PDADMA(PFe) block copolymer on the substrate can include evaporating a solution comprising the PSf-PDADMA(PF6) block copolymer and an organic solvent (e.g., N,N- dimethylacetamide). The delaminating can include contacting the layer with water. The ionexchanging includes ion-exchanging PFe' with Cl' to yield a PSf-PDADMA(Cl) block copolymer, and ion-exchanging Cl' with HO' to yield the PSf-PDADMA(OH) block copolymer.

[0052] In one example, a moisture-swing CO2 direct air capture and release membrane includes PSf-PDADMA(OH) block copolymer, wherein the block copolymer includes 15 mole% to 65 mole% of DADMA(OH).

[0053] Copolymers were synthesized (see FIG. 3, bottom pane) at approximately 20, 30, 40, and 50 wt% incorporation of PDADMA(PFe) (see Example 1).

[0054] To produce polymer thin films, approximately 15 wt% polymer solutions in DMAc were passed through syringe filters onto glass slides to cover the slide entirely. The solvent was evaporated at 75 °C over approximately 30 minutes and the free-standing films were delaminated by submerging the slides in DI water. In some cases, the copolymer compositions formed standalone films, with varied properties depending on the amount of PDADMA(PFe) incorporation. While polysulfones produce films and membranes with good strength and flexibility, homo- PDADMA(PFe) forms brittle films that are not readily handled. The discrepancy in propertiesmanifested in copolymers containing higher amounts of PDADMA(PFe), specifically 50 wt%, were brittle and less flexible than those containing a greater amount of polysulfone.

[0055] Polymers of relatively high molecular weight are suitable for formation of thin films. Because step-growth polymerizations are dependent on stoichiometric balance, the ability to produce high molecular weight polymer indicates that the PDADMA(PFe) oligomers were both quantitatively functionalized and accurately characterized herein. Additionally, it was considered whether the inclusion of PDADMA(PFe) blocks influence the thermal stability of the block copolymers. Even at the highest incorporation of PDADMA(PFe), TGA showed no significant degradation of the copolymer until 283 °C (FIG. 5A). The 50 wt% copolymer was also characterized to have a Tgof 182 °C (FIG. 5B). The decomposition temperature and Tgof homopolymers of polysulfone synthesized under the same conditions (stoichiometry 0.95-1.05:1 4,4'-sulfonylbis(fluorobenzene): 4,4'-(propane-2,2-diyl)diphenol) was found to be 448 °C and 188 °C, respectively. In some cases, the PSf-PDADMA(PFe) copolymers can be processed by melt pressing above their Tginto thin films. In some cases, the PSf-PDADMA(PFe) copolymers can be prepared by solvent casting into thin films. In some cases, the properties of the solvent cast thin films are better than those made by melt pressing.Moisture-Swing, Direct-Air CO2 Uptake Testing

[0056] For the membranes to be used as CO2 capture materials, they were converted from PFe counterions to HO' (hydroxide) counterions (see Example 3).

[0057] The experimental setup measured CO2 concentration in the headspace of a closed loop system (FIG. 1). Changes in CO2 concentration were observed as a function of relative humidity (Figure 7A-7C), and each of the three tested films demonstrated some capacity for CO2 uptake. Furthermore, each of the three membranes showed the ability to be humidity cycled. As the relative humidity (bottom curve in FIGS. 7A-7C) was cycled it caused changes in the CO2 concentration (top curve in FIGS. 7A-7C), which corroborates the mechanism shown in FIG. 6. Specifically, as the relative humidity was increased, the headspace CO2 concentration increased, corresponding to a release of CChby the sample. Conversely, as the relative humidity was decreased, the CO2 concentration in the chamber decreased, which is attributed to the sorption of CO2 by the sample. The CO2 uptake values for the 20, 30, and 40 wt% PSf-PDADMA films were found to be 10, 25, and 48 pmol / g respectively (FIG. 8). The film containing a higher concentration of ammonium groups had an increased capacity for CO2 sorption. The increase inCO2 uptake corresponds to an increase in the theoretical ion exchange capacities of the copolymer materials, which were calculated to be 906 pmol / g for the 20 wt% copolymer, 1 ,350 pmol / g for the 30 wt% copolymer, and 1,950 pmol / g for the 40 wt% copolymer. The uptake profiles in FIG. 8 showed a short incubation period at the beginning of the uptake profile mirrored in the humidity profile; the water vapor concentration did not immediately reach the 8 ppt setting, and settled at higher relative humidity for approximately 30 min before reaching the set point. This caused the slower uptake profile at the beginning of the curve. From the incubation point on, the three samples reach the equilibrium loading after approximately the same time, suggesting comparable uptake kinetics.

[0058] Although the multiblock copolymer thin film membranes showed a capacity for both the uptake and release of CO2 as a function of relative humidity, the total concentrations absorbed were only a small percent of what would be expected based on theoretical ion exchange capacity (IEC). As shown in FIG. 6, the moisture swing requires two cations to stabilize the carbonate in the “Wet-Empty” state; therefore the maximum loading capacity for the moisture swing mechanism is half of the IEC. Although there may be many reasons for this, one factor is total hydroxide ion concentration. In this system, CO2 uptake requires the presence of hydroxide or bicarbonate counterions when the membrane is in the wet stage. The block copolymers were produced at relatively high cation concentrations. Their mechanical properties decrease with increasing incorporation of PDADMA(PFe), specifically the 50 wt% thin film was too brittle to be evaluated in the DAC experiment (Example 3).

[0059] In addition to the influence of ammonium concentration on CO2 affinity, the effectiveness of the ion exchange to hydroxide is also crucial for this application. Since PFc, does not react with CO2, residual PFe counterions can decrease the CO2 uptake capacity of the polymer membranes. After moisture-swing testing indicated a less-than-expected CO2 uptake for the multiblock copolymer thin film membranes, the effectiveness of the counterion exchange was examined. Upon FT-IR analysis of the ion exchanged membranes, it was determined that a large characteristic PFr, peak was still present.EXAMPLES

[0060] 4-fluorothiophenol (98%) was purchased from Aldrich and used as received. Diallyldimethylammonium chloride (DADMAC) was obtained from TCI America as anapproximately 60% aqueous solution and was used as received. Bis(4-fluorophenyl) sulfone (99%) and bisphenol A (BPA) (97%) were received from Aldrich, twice recrystallized from toluene, and dried under vacuum immediately before use. N,N-dimethylacetamide (DMAc) (99%) was purchased from Aldrich, distilled under reduced pressure, and stored under N2. Potassium hexafluorophosphate (KPFe) (98%) and potassium carbonate (K2CO3) (100%) were used as received from Aldrich. Deuterated dimethyl sulfoxide (DMSO-d6) (99.8%) was purchased from Cambridge Isotopes, Inc. Iodine crystals (USP grade) were used as received from Fischer. All other chemicals and solvents were obtained from commercial sources and used without further purification. A model number SCT-4 UV pen lamp (25 amps, 115 volts) was obtained from Ultra-Violet Products, Inc.

[0061] Final polymer compositions and structures were determined by 'H-NMR spectroscopy on a JEOL ECA-500 FT-NMR using DMSO-d6 as solvent. Thermogravimetric analysis (TGA) was carried out on a Seiko Instruments TG / DTA 320. Samples were heated under air to 100 °C at 40 °C per minute, held at 100 °C for 5 to 10 minutes, then heated to 800 °C at 10 °C per minute before being cooled to room temperature. All runs were performed in a platinum pan with an empty platinum pan as reference. Differential scanning calorimetry (DSC) was performed on a TA Instruments Q20 DSC to measure thermal transitions. Samples in hermetically sealed T-zero aluminum pans were heated from 0 °C to an appropriate maximum temperature between 230 °C and 300 °C at a rate of 10 °C per minute then cooled back down to 0 °C. Two cycles were completed and data from the second cycle was used to determine glass transition temperatures. All runs were completed under a 20 mL per min flow of N2 with an empty T-zero aluminum pan as reference.

[0062] The desired aromatic polysulfones were synthesized through condensation reaction between bis(4-fluorophenyl)sulfone and bisphenol A (FIG. 3). To produce multiblock copolymers, the appropriate stoichiometric amount of the small molecule difluoro monomer was replaced with the functionalized oligomer while maintaining a stoichiometric equivalence of phenol groups to fluorophenyl groups.

[0063] A 50 mL round bottom flask was charged with a stir bar, DI water (10 mL), and methanol (10 mL). The addition of 4-fluorothiophenol (2.41 g, 18.8 mmol) produced two distinct layers. The flask was lowered into an ice bath and solid iodine (2.38 g, 9.40 mmol) was added in small portions over approximately 20 minutes. Upon addition of the iodine, the solution becamecloudy and brown. After a period of rapid stirring, the brown color indicative of unreacted iodine dissipated, and a yellow-green oil formed. The oily bis(4-fluorophenyl)disulfide product was recovered by extraction (2.24 g, 93% yield).

[0064] The experimental concentration of the reported 60% DADMAC in water solution was determined by Mohr titration to be 70.3±0.2% DADMAC by weight. Therefore, a 2.5 M DADMAC solution in I LO / MeOH was prepared by diluting the DADMAC solution (14.38 g, 0.0625 mol) to 25 mL with methanol. The iniferter (bis(4-fluorophenyl)disulfide) and monomer concentrations were chosen to target oligomers of approximately 150 repeat units. Three 10 mL test tubes with stir bars were each charged with the 2.5 M DADMAC solution (8 mL, 20 mmol) followed by a 1 M bis(4-fluorophenyl)disulfide in methanol solution (0.13 mL, 0.13 mmol). All tubes were then septum sealed and sparged with N2 in ice for 30 minutes. They were then lowered into a 60 °C oil bath and allowed to temperature equilibrate for 10 min before being exposed to a 254 nm UV light for 48 hours. After 48 hours, the reaction tubes were removed from heat and UV and allowed to cool to room temperature before being opened to air. The clear, colorless solutions were poured slowly into stirring acetone to give a fine white precipitate. This was collected by vacuum filtration, dissolved in a small amount of methanol, reprecipitated in acetone, collected by vacuum filtration, and dried under vacuum at 60 °C overnight (5.19 g, 38% yield). The oligomers were calculated to have 130 repeat units by 'H-NMR spectroscopy by comparing the integration values of the peaks resulting from the methylene linkages (a) of the DADMAC units to the integration values of the aromatic peaks of the end-groups (e,f) as shown in FIG 2.

[0065] To oxidize the sulfide oligomer end groups to sulfones, the 5.19 g of functionalized oligomer was dissolved in approximately 25 mL of DI water in a 50 mL round bottom with stir bar. To this was added 0.0604 g KHSOs 0.5KHSO4 O.5K2SO4 (oxone) (1.97 mmol, approximately eight times end group concentration). The mixture was stirred until homogenous then placed in a 60 °C oil bath for 18 hours. This was cooled to room temperature and concentrated to a viscous solution by rotary evaporation, which was then poured into a saturated solution of potassium hexafluorophosphate (KPFe) to produce a white precipitate. The solid product was collected by vacuum filtration, washed with an excess of DI water, and dried under vacuum at 60 °C overnight to afford PDADMAfPF ,) oligomer (6.92 g, 87% yield). Full oxidation was confirmed by ’H-NMR. ’H-NMR (500 MHz, DMSO-d6, 5): 7.97 (d, 4H; Ar H),7.54 (d, 4H; Ar H), 5.37 (bs, 2H; CH2), 3.67 (bs, 4H; CH2), 3.13 (m, 6H; CH3), 2.47 (bs, 2H; CH), 1.13 (m, 4H; CH2).Example 1. Preparation of multiblock poly sulfones

[0066] Four feed ratios were designed to target a range of PDADMA(PFe) incorporation by weight percent (Table 1). For all the synthesized block copolymers, the PDADMA(PFe) oligomers with an average of 130 repeat units were used. A representative procedure is as follows: A two neck, 15 mb round bottom flask with stir bar was connected to a pre-filled Dean- Stark trap, water cooled condenser, and N2inlet. The flask was charged with BPA (0.4566 g, 2.000 mmol), K2CO3(0.42 g, 3.00 mmol), toluene (2 mL), and DMAc (5 mL) and lowered into a 150 °C oil bath for 3 hours to remove water to the Dean-Stark trap. After 3 hours, the solution was cooled to room temperature and bis(4-fluorophenyl)sulfone (0.5056 g, 1.989 mmol) and PDADMA(PFe) (0.4000 g, 0.01135 mmol end groups) were added in quick succession. The Dean-Stark trap was removed, and the solution was brought to reflux for 24 hours under N2. The viscous, cloudy, tan solution was cooled to room temperature, opened to air, and poured slowly into stirring methanol. The fibrous, white precipitate was isolated by vacuum filtration and washed with methanol. The dried product was then transferred to a 100 mL round bottom flask with approximately 70 mL of DI water and boiled overnight to remove residual salt. The polymer was again isolated by vacuum filtration, washed with DI water and methanol, and dried under vacuum at 60 °C overnight (1.17 g, 92%).Table 1. Composition of the monomer feed, copolymer product, and yield for all multiblock copolymerizations.

[0067] The relative incorporation of DADMA(PF6) in each block copolymer was determined by1H-NMR spectroscopy by integration of the peaks from the methylene linkages of the DADMAfPFs) repeat units compared to the integration of the aromatic peaks resulting from the sulfone repeat units (FIG. 4). Each of the four trials targeted copolymers having approximately 20, 30, 40, and 50 wt% PDADMA(PFe) (Table 1), and there was good agreement between the monomer feed ratios and copolymer composition.Example 2. Preparation of block copolymer films

[0068] Each block copolymer (0.21 g) was dissolved in 1.4 mL of DMAc and placed on a shaker overnight to dissolve fully. The viscous, slight cloudy solutions were passed through 1.5 pm syringe filters onto glass microscope slides. The solution was spread until the full slide surface was covered and the solvent was evaporated at approximately 75 °C over 30 minutes. The films were delaminated by submerging them in DI water to obtain free-standing films. Example 3. Moisture-swing CO2 sorption / desorption experiments

[0069] For the membranes to be used as CO2 capture materials, they were converted from PFe counterions to HO' (hydroxide) counterions. To ion exchange the films, they were first converted to the chloride form and then to the hydroxide form. To accomplish this, the cast films were submerged in saturated potassium chloride solutions and refluxed for 96 hours. The films were then washed with DI water and patted dry with a Kim Wipe before being transferred to a saturated potassium hydroxide solution for an additional 48 hours. Because the 50 wt% PSf- PDADMA (PFe) film was more brittle than the other compositions, it broke into a few large pieces during the refluxing step and thus lacked the continuous surface area required for testing. Accordingly, the 20, 30, and 40 wt% copolymers, considered to be converted to the hydroxide salt form, were evaluated for CO2 uptake.

[0070] To perform the moisture-swing testing, the polymer films were dried, weighed, and tested in a system, such as system 100 depicted in FIG. 1. System 100 includes computer 102, infrared gas analysis (IRGA) unit 104, blower 106, sample chamber 108, and humidity controller 110. Polymer film 112 is placed in the sample chamber 108. Polymer film 112 can be, for example, a moisture-swing CO2 direct air capture and release membrane. The humidity level was changed by cycling the closed system air through a humidity controller. For each experiment, the humidity was cycled between 8 ppt (30% relative humidity at 22 °C) and 25 ppt (95% relative humidity at 22 °C). The CO2 and H2O (humidity) concentration were measured in real time by aLi-Cor model Li-840A infrared gas analyzer (IRGA) in parts per million (ppm) and parts per thousand (ppt), respectively. The volume of the closed system was 145 mL, and the humidity was adjusted by cycling the closed system air through a humidity controller by a pump. The humidity controller was equipped with a 1 mL water bath and copper tubing that controls the dew point of the circulating air. For membranes demonstrating moisture-sensitive CO2 uptake and release, the dry membranes should have a high affinity for CO2 that is then released when relative humidity is high (FIG. 6). The change in CO2 concentration as a function of relative humidity in shown in FIGS. 7A-7C, and the CO2 uptake capacities observed for the 20, 30, and 40 wt% copolymer films is shown in FIG. 8.

[0071] Although this disclosure contains many specific embodiment details, these should not be construed as limitations on the scope of the subject matter or on the scope of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in this disclosure in the context of separate embodiments can also be implemented, in combination, in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments, separately, or in any suitable sub-combination. Moreover, although previously described features may be described as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

[0072] Particular embodiments of the subject matter have been described. Other embodiments, alterations, and permutations of the described embodiments are within the scope of the following claims as will be apparent to those skilled in the art. While operations are depicted in the drawings or claims in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed (some operations may be considered optional), to achieve desirable results.

[0073] Accordingly, the previously described example embodiments do not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure.

Claims

WHAT IS CLAIMED IS:

1. A method of preparing a block copolymer comprising poly(diallyldimethylammonium) (PDADMAC) blocks and polysulfone (PSf) blocks, the method comprising: contacting diallyldimethylammonium chloride (DADMAC) with an iniferter under ultraviolet (UV) radiation and heating to yield a PDADMAC oligomer; isolating the PDADMAC oligomer; contacting the PDADMAC oligomer with a hexafluorophosphate salt to yield a PDADMA(PFe) oligomer; isolating the PDADMA(PFfi) oligomer; contacting the PDADMA(PFe) oligomer with a bis(fluoroaryl)sulfone and a bis-phenol in the presence of a base under dehydrating conditions to obtain a PSf-PDADMA(PFe) block copolymer; and isolating the PSf-PDADMA(PF6) block copolymer.

2. The method of claim 1, wherein the iniferter is bis(4-fluorophenyl)disulfide.

3. The method of claim 1, wherein a molar ratio of DADMAC: iniferter is in a range of 5:1 to 3500: 1.

4. The method of claim 1, wherein a wavelength of the UV radiation is about 254 nm.

5. The method of claim 1, wherein the heating comprises heating to a temperature in a range of about 50°C to about 70 °C.

6. The method of claim 1, wherein isolating the PDADMAC oligomer comprises precipitating the PDADMAC oligomer from a first organic solvent to yield a precipitate and drying the precipitate under vacuum with heating.

7. The method of claim 6, further comprising dissolving the precipitate in a second organic solvent and re-precipitating the PDADMAC oligomer from the first organic solvent prior to drying the precipitate under vacuum with heating.

8. The method of claim 6, wherein the first organic solvent comprises acetone.

9. The method of claim 7, wherein the second organic solvent comprises methanol.

10. The method of claim 1, wherein the PDADMAC oligomer is capped on one or both ends with a 4-fluorophenyl sulfide group.

11. The method of claim 1, further comprising contacting the PDADMAC oligomer with an oxidizing agent.

12. The method of claim 1, wherein the oxidizing agent is oxone.

13. The method of claim 1, wherein the hexafluorophosphate salt is potassium hexafluorophosphate.

14. The method of claim 1, wherein the bis(fluoroaryl)sulfone is bis(4-fluorophenyl)sulfone.

15. The method of claim 1, wherein the bis-phenol is 4,4'-(propane-2,2-diyl)diphenol.

16. The method of claim 1, wherein the base is potassium carbonate.

17. The method of claim 1, wherein the dehydrating conditions comprise collecting water by heated distillation at ambient pressure.

18. The method of claim 1, wherein the mole% of DADMA(PF6) contacted with a bis(fluoroaryl)sulfone and a bis-phenol is from about 30% to about 70%.

19. A method of preparing a moisture-swing CO2 direct air capture and release membrane, the method comprising: disposing a PSf-PDADMA(PFe) block copolymer on a substrate; delaminating the PSf-PDADMAfPFe) block copolymer from the substrate to yield a layer comprising the PSf-PDADMA(PFe) block copolymer; and ion-exchanging Pf<>' with HO' in the layer to yield the membrane, wherein the membrane comprises a PSf-PDADMA(OH) block copolymer.

20. The method of claim 19, wherein disposing the PSf-PDADMA(PFe) block copolymer on the substrate comprises is evaporating a solution comprising the PSf-PDADMA(PFs) block copolymer and an organic solvent.

21. The method of claim 20, wherein the organic solvent is N,N-dimethylacetamide.

22. The method of claim 19, wherein the delaminating comprises contacting the layer with water.

23. The method of claim 19, wherein the ion-exchanging comprises: ion-exchanging PFe'with Cl' to yield a PSf-PDADMA(Cl) block copolymer; and ion-exchanging Cl' with HO' to yield the PSf-PDADMA(OH) block copolymer.

24. A moisture- swing CO2 direct air capture and release membrane comprising: PSf-PDADMA(OH) block copolymer, wherein the block copolymer comprises 15 mole% to 65 mole% of DADMA(OH).

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