Patent Application
20220251120
Anion exchange membranes are useful in various electrochemical cells such as, for example, fuel cells, electrolyzers, batteries, and electrodialysis cells. Previous anion exchange membranes have been prepared from various copolymers having cationic, nitrogen-containing groups. These copolymers have been prepared, for example, by reacting styrene-co-4-vinylbenzyl chloride copolymers with various nitrogen-containing bases to provide corresponding quaternary ammonium groups. Typical membranes formed in this manner have inadequate mechanical strength for uses such as those described above. For example, the membranes often are brittle and have low tensile strength.
Toughening and improved elongation are desirable in anion exchange membranes used in carbon dioxide or water electrolysis, fuel cells, flow batteries, and similar electrochemical devices. The present disclosure provides ionic organosilanes suitable for inclusion in membrane polymers that may overcome the above-referenced deficiencies of anion exchange membranes.
Polymers are commonly toughened by adding an impact modifier such as a silicone which forms a low Tg second phase. However, in an electrochemical membrane, such an inert second phase occupies volume, does not contribute to conductivity, and thus decreases conductivity per unit volume relative to the same polymer without the additive. In addition, silicones may be chemically unstable even under mildly alkaline conditions.
Ionic organosilanes described in the present disclosure improve membrane elongation to break and toughness, with an unexpected combination of the benefits of carrying functionality that contributes to conductivity, and chemical stability under alkaline conditions.
In one aspect, the present disclosure provides a dihaloorganosilane represented by the formula:
wherein:
In another aspect, the present disclosure provides an ionic organosilane represented by the formula:
wherein:
In yet another, the present disclosure, the present disclosure provides a membrane composition comprising components:
In yet another aspect, the present disclosure provides a membrane comprising a membrane composition according to the present disclosure.
As used herein:
“monomer unit” refers to the largest constitutional unit contributed by a single monomer molecule to the structure of a polymer.
“phenylene” generically refers to a divalent benzene ring;
o-phenylene has the formula:
m-phenylene has the formula;
and
p-phenylene has the formula:
Features and advantages of the present disclosure will be further understood upon consideration of the detailed description as well as the appended claims.
The ionic organosilane can be synthesized from a precursor organosilane represented by the formula:
wherein each of the various groups is independently selected as previously defined.
Throughout this specification:
Each X independently represents Cl, Br, or I. Cl is typically preferred.
Each Ar1 independently represents a phenylene group optionally substituted by 1 to 4 alkyl groups selected from methyl or ethyl. The phenylene group may comprise o-, m-, or p-phenylene. p-Phenylene is typically preferred.
Each R1 independently represents an alkylene group (i.e., divalent) having from 2 to 18 carbon atoms, preferably 2 to 8 carbon atoms, more preferably 2 or 3 carbon atoms, and even more preferably 2 carbon atoms. Exemplary alkylene groups include ethylene, propylene, butylene, isobutylene, pentylene, hexylene, cyclohexylene, octylene, decylene, dodecylene, tetradecylene, hexadecylene, and octadecylene.
Each R2 independently represents methyl or ethyl, preferably methyl.
Each R4 independently represents an alkylene group (i.e., divalent) having from 2 to 18 carbon atoms, preferably 2 to 12 carbon atoms, more preferably 6 to 10 carbon atoms, and even more preferably 8 carbon atoms. Exemplary alkylene groups include ethylene, propylene, butylene, isobutylene, pentylene, hexylene, cyclohexylene, octylene, decylene, dodecylene, tetradecylene, hexadecylene, and octadecylene.
Each n is independently 0, 1, 2, 3, 4, or 5.
Precursor organosilanes can be made, for example, by a hydrosilation coupling of a dihydridocarbosilane with a halomethyl-substituted aralkene using a hydrosilylation catalyst (e.g., a Pt catalyst such as H2PtCl6 or Karstedt's catalyst) according to the reaction scheme below:
wherein Ar1, R1-R4, X, and n are as previously defined.
Exemplary dihydridocarbosilanes include 1,1,4,4,-tetramethyl-1,4-disilabutane, 1,1,4,4,-tetraethyl-1,4-disilabutane, 1,1-dimethyl-4,4-dimethyl-1,4-disilabutane, 1,1,6,6-tetramethyl-1,6-disilahexane, 1,1,8,8-tetramethyl-1,4-disilaoctane, 1,1,10,10-tetramethyl-1,10-disiladecane, 1,1,12,12-tetramethyl-1,12-disiladodecane, 1,1,16,16-tetramethyl-1,16-disilahexadecane, 1,1,18,18-tetramethyl-1,18-disilaoctadecane, 1,1,12,12,20,20-hexamethyl-1,12,20-trisilaeicosane. Dihydridocarbosilanes can be made by reduction of corresponding chlorocarbosilanes using lithium aluminum hydride, for example, according to conventional methods.
Suitable dihydridocarbosilanes and/or their dichlorinated precursor counterparts may be synthesized by known methods and/or obtained from a commercial supplier; for example, Gelest Inc., Morrisville, Pa.; ABCR, Karlsruhe, Germany; Alfa Aesar, Chennai, India; and TCI America, Portland, Oreg.
Exemplary halomethylphenylalkenes include p-chloromethylstyrene, p-bromomethylstyrene, p-iodomethylstyrene, m-chloromethylsytrene, o-chloromethylstyrene, p-allyl(chloromethyl)benzene, m-allyl(chloromethyl)benzene, o-allyl(chloromethyl)benzene, 4-chloromethyl-2-methylstyrene, 4-chloromethyl-3-methylstyrene, p-chloromethyl-2-propenylbenzene, and p-(chloromethyl)-1-buten-4-yl-benzene. Halomethylphenylalkenes can be obtained from commercial vendors such as, for example, Millipore-Sigma, Saint Louis, Mo., or TCI America, Portland, Oreg., and/or synthesized by known methods.
The dihaloorganosilane discussed above can be converted into the ionic organosilane by reaction with an appropriate imidazole. Typically, the reaction is carried out by combining the dihaloorganosilane and an imidazole in solvent with optional heating.
Suitable imidazoles include 1-allylimidazole, 1-allyl-2-methylimidazole, 1-allyl-4-methylimidazole, 1-allyl-5-methylimidazole, 1-allyl-2,4-dimethylimidazole, 1-allyl-2,5-dimethylimidazole, 1-allyl-4,5-dimethylimidazole, 1-allyl-2,4,5-trimethylimidazole, 1-methylimidazole, 1,2-dimethylimidazole, 1,4-dimethyllimidazole, 1,5-dimethylimidazole, 1,2,4-trimethylimidazole, 1,2,5-trimethylimidazole, 1,2,4,5-tetramethylimidazole, 1-ethylimidazole, 1-propylimidazole, 1-butylimidazole, 1-isobutylimidazole, 1-ethyl-2-methylimidazole, 1-ethyl-4-methylimidazole, 1-ethyl-5-methylimidazole, 1-ethyl-2,4-dimethylimidazole, 1-ethyl-2,5-dimethylimidazole, 1-ethyl-2,4,5-trimethylimidazole, 1-propyl-2-methylimidazole, 1-propyl-4-methylimidazole, 1-propyl-5-methylimidazole, 1-propyl-2,4-dimethylimidazole, 1-propyl-2,5-imethylimidazole, 1-propyl-2,4,5-trimethylimidazole, 1-butyl-2-methylimidazole, 1-butyl-4-methylimidazole, 1-butyl-5-methylimidazole, 1-butyl-2,4-dimethylimidazole, 1-butyl-2,5-imethylimidazole, and 1-butyl-2,4,5-trimethylimidazole. Suitable imidazoles can be obtained from commercial chemical suppliers such as, for example, Millipore Sigma and/or synthesized by conventional methods.
The membrane composition comprises components:
Component (a) may be prepared by reaction of a copolymer of styrene and p-chloromethylstyrene (or p-bromomethylstyrene) with an imidazole that is functionalized with appropriate groups R5 and R6, for example, in the same manner as in the case of the preparation of the ionic organosilane discussed above. Conversion of the chloromethyl groups may be partially or essentially complete.
p-Chloromethylstyrene and styrene are commercially available or can be synthesized by conventional methods and can be copolymerized in essentially any ratio using conventional free-radical polymerization techniques (e.g. using a thermal free-radical initiator such as a peroxide). Alternatively, many copolymers of styrene and p-chloromethylstyrene (also known as 4-vinylbenzyl chloride) are available from commercial chemical suppliers. The respective molar ratio of monomer unit (i) to monomer unit (ii) is 60:40 (i.e., 1.5 to 1) to 75:25, or 60:40 to 70:30, preferably 65:35 to 70:30.
The membrane composition can be formed into a membrane by any suitable technique including, for example, solvent casting. For example, any membrane thickness up to about one millimeter may be made in this manner. Other methods and membrane thicknesses may also be used. Membranes according to the present disclosure may be useful, for example, as anion exchange membranes for electrolyzers, electrodialysis cells, fuel cells, and flow batteries.
In a first aspect, the present disclosure provides a dihaloorganosilane represented by the formula:
wherein X, Ar1, R1, R2, R3, R4 and n are as previously defined.
In a second embodiment, the present disclosure provides a dihaloorganosilane according to the first embodiment, wherein each R1 independently represents an alkylene group having 2 or 3 carbon atoms.
In a third embodiment, the present disclosure provides a dihaloorganosilane according to the first or second embodiment, wherein each R3 independently represents an alkylene group having from 2 to 4 carbon atoms.
In a fourth embodiment, the present disclosure provides a dihaloorganosilane according to any of the first to third embodiments, each R4 independently represents an alkylene group having from 6 to 10 carbon atoms.
In a fifth embodiment, the present disclosure provides a dihaloorganosilane according to any of the first to fourth embodiments, wherein n=0.
In a sixth embodiment, the present disclosure provides a dihaloorganosilane according to any of the first to fifth embodiments, wherein n=1.
In a seventh embodiment, the present disclosure provides an ionic organosilane represented by the formula:
In an eighth embodiment, the present disclosure provides an ionic organosilane according to the seventh embodiment, wherein each R1 independently represents an alkylene group having 2 or 3 carbon atoms.
In a ninth embodiment, the present disclosure provides an ionic organosilane according to the seventh or eighth embodiment, wherein each R3 independently represents an alkylene group having from 2 to 4 carbon atoms.
In a tenth embodiment, the present disclosure provides an ionic organosilane according to any of the seventh to ninth embodiments, wherein each R4 independently represents an alkylene group having from 6 to 10 carbon atoms.
In an eleventh embodiment, the present disclosure provides an ionic organosilane according to any of the seventh to tenth embodiments, wherein n=0.
In a twelfth embodiment, the present disclosure provides an ionic organosilane according to any of the seventh to tenth embodiments, wherein n=1.
In a thirteenth embodiment, the present disclosure provides a membrane composition comprising components:
In a fourteenth embodiment, the present disclosure provides a membrane composition according to the thirteenth embodiment, wherein each R1 independently represents an alkylene group having 2 or 3 carbon atoms.
In a fifteenth embodiment, the present disclosure provides a membrane composition according to the thirteenth or fourteenth embodiment, wherein each R3 independently represents an alkylene group having from 2 to 4 carbon atoms.
In a sixteenth embodiment, the present disclosure provides a membrane composition according to any of the thirteenth to fifteenth embodiments, wherein each R4 independently represents an alkylene group having from 6 to 10 carbon atoms.
In a seventeenth embodiment, the present disclosure provides a membrane composition according to any of the thirteenth to sixteenth embodiments, wherein n=0.
In an eighteenth embodiment, the present disclosure provides a membrane composition according to any of the thirteenth to sixteenth embodiments, wherein n=1.
In a nineteenth embodiment, the present disclosure provides a membrane composition according to any of the thirteenth to eighteenth embodiments, wherein R6 represents alkyl having from 1 to 4 carbon atoms.
In a twentieth embodiment, the present disclosure provides an ionic organosilane according to any of the thirteenth to nineteenth embodiments, wherein R6 represents allyl.
In a twenty-first embodiment, the present disclosure provides a membrane comprising a membrane composition according to any one of the thirteenth to twentieth embodiments.
Objects and advantages of this disclosure are further illustrated by the following non-limiting examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this disclosure.
Unless otherwise noted, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight. Table 1, below, reports materials used in the Examples.
Platinum divinyltetramethyldisiloxane complex (1 drop, 2.1-2.4 wt. % Pt in xylene) was added to a solution of 1,1,4,4-tetramethyl-1,4-disilabutane (4.40 g, 0.030 mol) and vinylbenzyl chloride (9.17 g, 0.060 mol) in toluene (60 mL). After an initial exotherm, the reaction mixture was stirred at room temperature for 3 days, and toluene was removed in vacuo to give the product shown above as a colorless oil.
Platinum divinyltetramethyldisiloxane complex (1 drop, 2.1-2.4 wt. % Pt in xylene) was added to a solution of 1,1,4,4-tetramethyl-1,4-disilabutane (8.80 g, 0.060 mol), 1,7-octadiene (3.30 g, 0.0.03 mol) and vinylbenzyl chloride (9.17 g, 0.060 mol) in toluene (40 mL). After an initial exotherm, the reaction mixture was stirred at room temperature for 3 days, and toluene was removed in vacuo to give the unpurified product as a viscous liquid.
A 250-mL 3-necked round bottom flask equipped with magnetic stirring, heating mantle, thermocouple, and inlet for nitrogen blanketing was charged with 10 g styrene/vinylbenzyl chloride copolymer (S/VBC, composition 63.1 mol % styrene, 36.9 mol % VBC, Mn=55-60 kg/mole, polydispersity 1.3), a mixture of tetramethylimidazole (3.27 g, 26.3 mmol), organosilane OS1 (0.15 g, 0.664 mmol benzyl chloride, 1.1 wt. % of total solids) to a total of 0.85 equiv. base to 1 equiv. benzyl chloride (contributed by copolymer and carbosilane), and 1-methoxy-2-propanol (26.8 g). The mixture was stirred at 70° C. for 48 hr, resulting in a pale yellow solution.
A 250-mL 3-necked round bottom flask equipped with magnetic stirring, heating mantle, thermocouple, and inlet for nitrogen blanketing was charged with 10 g styrene/vinylbenzyl chloride copolymer (S/VBC, composition 63.1 mol % styrene, 36.9 mol % VBC, Mn=55-60 kg/mole, polydispersity 1.3), a mixture of tetramethylimidazole (3.33 g, 26.8 mmol), organosilane OS1 (0.29 g, 1.288 mmol benzyl chloride, 2.1 wt. % of total solids) to a total of 0.85 equiv. base to 1 equiv. benzyl chloride (contributed by copolymer and carbosilane), and 1-methoxy-2-propanol (26.8 g). The mixture was stirred at 70° C. for 48 hr, resulting in a pale yellow solution.
A 250-mL 3-necked round bottom flask equipped with magnetic stirring, heating mantle, thermocouple, and inlet for nitrogen blanketing was charged with 10 g styrene/vinylbenzyl chloride copolymer (S/VBC, composition 63.1 mol % styrene, 36.9 mol % VBC, Mn=55-60 kg/mole, polydispersity 1.3), a mixture of tetramethylimidazole (3.24 g, 26.1 mmol), organosilane OS2 (0.15 g, 0.424 mmol benzyl chloride, 1.1 wt. % of total solids) to a total of 0.85 equiv. base to 1 equiv. benzyl chloride (contributed by copolymer and carbosilane), and 1-methoxy-2-propanol (26.8 g). The mixture was stirred at 70° C. for 48 hr, resulting in a pale yellow solution.
A 250-mL 3-necked round bottom flask equipped with magnetic stirring, heating mantle, thermocouple, and inlet for nitrogen blanketing was charged with 10 g styrene/vinylbenzyl chloride copolymer (S/VBC, composition 63.1 mol % styrene, 36.9 mol % VBC, Mn=55-60 kg/mole, polydispersity 1.3), tetramethylimidazole (3.19 g, 25.7 mmol) to a total of 0.85 equiv. base to 1 equiv. benzyl chloride (contributed by copolymer only), and 1-methoxy-2-propanol (26.8 g). The mixture was stirred at 70° C. for 48 hr, resulting in a pale yellow solution.
A 250-mL 3-necked round bottom flask equipped with magnetic stirring, heating mantle, thermocouple, and inlet for nitrogen blanketing was charged with 10 g styrene/vinylbenzyl chloride copolymer (S/VBC, composition 63.1 mol % styrene, 36.9 mol % VBC, Mn=55-60 kg/mole, polydispersity 1.3), a mixture of tetramethylimidazole (3.33 g, 26.8 mmol), control organosilane 1,1,4,4-tetramethyl-1,4-disilabutane (0.15 g, 1.1 wt. % of total solids, no benzyl chloride functionality) to a total of 0.88 equiv. base to 1 equiv. benzyl chloride (contributed by copolymer only), and 1-methoxy-2-propanol (26.8 g). The mixture was stirred at 70° C. for 48 hr, resulting in a pale yellow solution.
A 250-mL 3-necked round bottom flask equipped with magnetic stirring, heating mantle, thermocouple, and inlet for nitrogen blanketing was charged with 10 g styrene/vinylbenzyl chloride copolymer (S/VBC, composition 63.1 mol % styrene, 36.9 mol % VBC, Mn=55-60 kg/mole, polydispersity 1.3), a mixture of tetramethylimidazole (3.33 g, 26.8 mmol), control organosilane, 1,4,4-tetramethyl-1,4-disilabutane (0.29 g, 2.1 wt. % of total solids, no benzyl chloride functionality) to a total of 0.88 equiv. base to 1 equiv. benzyl chloride (contributed by copolymer only), and 1-methoxy-2-propanol (26.8 g). The mixture was stirred at 70° C. for 48 hr, resulting in a pale yellow solution.
Membrane polymers composed of dimethylimidazole (E4, CE4) and N-allylimidazole (E5, CE5) were synthesized in respective procedures analogous to those described for tetramethylimidazole (E1 and CE1).
Membranes (reported in Table 2) were prepared by coating 30-33 weight percent solids ionomer solutions on to a release liner with a polyethylene terephthalate backing coated with an acrylic-based release layer as described in U.S. Pat. No. 7,816,477 (Suwa et al.). Membranes were coated using a BYK BYKO-drive automatic applicator (Gardco) at a speed setting of 1 inch/sec (2.54 cm/sec) and with a notch bar applicator having a 10 mil (0.01 inch, 0.254 mm) gap, and then dried in a forced air oven at 80° C. for 30 minutes. Measured dry coating thicknesses were in the range of 45-52 microns.
The tensile stress-strain behavior of wet membranes was examined at a constant strain rate of 2 mm/second. Samples were removed from the release liner and soaked in aqueous 1M KOH solution for 24 hours at room temperature, thoroughly washed with deionized water, cut into 1.00 cm×4.00 cm strips, and tested in a fully hydrated state using a TA XTPlus Texture Analyzer (Texture Technologies, Hamilton, Mass.). Four strips were cut and tensile tested for each membrane. The mean value from the four replicates is reported in Table 3. Dimensions of the membranes (x, y, z) were measured before and after the alkali soak in order to calculate swelling values.
The results show that loadings of 1 wt. % ionomeric organosilane OS1 are optimal to increase elongation at break and toughness for TMIM, DMIM and allyl IM membrane polymers (E1, E4, E5) relative to membrane polymers of comparable ION EXCHANGE CAPACITY (IEC) that do not carry carbosilane (CE1, CE4, CE5). The results also show that a loading of 1 wt. % ionomeric organosilane OS2 increases elongation at break and toughness for a TMIM membrane polymer (E3) relative to a membrane polymer of comparable ION EXCHANGE CAPACITY (IEC) that does not carry carbosilane (CE1). A 2 wt. % loading of ionomeric organosilane OS1 does not confer the same benefit at comparable IEC (E2), nor does a non-ionomeric control carbosilane at comparable IEC and wt. % loading (CE2, CE3).
Ionic conductivity was measured using a 4-probe BekkTech BT-110 conductivity clamp (Scribner Associates, Inc., Southern Pines, N.C.) and a VMP3 Multi-channel potentiostat (Bio-Logic Science Instruments, Seyssinet-Pariset, France). A dry membrane sample in the chloride form (1.40 cm×4.00 cm) was assembled under two platinum wires, and the clamp was immersed into 18 megaohms deionized water for 2 hours before measurement to hydrate and swell the membrane. A current-voltage curve was recorded by applying a linear voltage sweep from an open circuit voltage (OCV) to 0.3 V first, then to −0.3 V, and finally back to OCV at 10 mV/second scan rate. Ionic conductivity was calculated from the slope of the resulting current-voltage curve using the measured dry membrane size and thickness, and an ionic conductivity clamp constant of 0.425 cm.
The preceding description, given in order to enable one of ordinary skill in the art to practice the claimed disclosure, is not to be construed as limiting the scope of the disclosure, which is defined by the claims and all equivalents thereto.
This invention was made with Government support under Cooperative Agreement DE-AR0000950 awarded by the U.S. Department of Energy. The U.S. Government may have certain rights in this invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2020/055547 | 6/12/2020 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62862327 | Jun 2019 | US |
