Method of making an anion exchange membrane
A method to manufacture an ion exchange membrane involves treatment of the membrane in a strong base to strengthen the membrane, decrease the membrane solubility, and create linkages that can be detected by analysis using two-dimensional nuclear magnetic resonance (NMR).
1. A process for making a crosslinked anion exchange membrane, comprising the steps of:
(a) providing a polymer membrane comprising a terpolymer of styrene, vinylbenzyl-R s and vinylbenzyl-R x , wherein R s is a positively charged cyclic amine group, wherein R x is at least one constituent selected from the group consisting of Cl, OH, and O—R z , wherein R z is selected from linear alkyls, branched alkyls, cyclic alkyls, heteroalkyls, aryls, heteroaryls, alkylaryls, and heteroalkylaryls, and wherein the total weight of the vinylbenzyl-R x groups is greater than 1% of the total weight of the polymer; and
(b) soaking the polymer membrane in a hydroxide-containing solution having a pH of at least 12 for at least 5 minutes.
2. The process of claim 1 , wherein step (b) comprises soaking the polymer membrane in a hydroxide-containing solution having a pH of at least 13 for at least 5 minutes.
3. The process of claim 2 , wherein step (b) comprises soaking the polymer membrane in a hydroxide-containing solution having a pH of at least 14 for at least 5 minutes.
4. The process of claim 1 , comprising the step of forming the polymer membrane by casting a polymer solution made from a solvent onto a polymeric film liner.
5. The process of claim 1 , wherein the total weight of the vinylbenzyl-R s groups in said polymer membrane is between 15% and 90% of the total weight of the polymer membrane.
6. The process of claim 1 , wherein said crosslinked ion exchange membrane has a thickness of from 10 to 300 micrometers.
7. The process of claim 1 , wherein the total weight of the vinylbenzyl-R x groups in said polymer membrane is between 0.3% and 25% of the total weight of the polymer membrane.
8. The process of claim 7 , wherein the total weight of the vinylbenzyl-R x groups in said polymer membrane is between 1% and 15% of the total weight of the membrane.
9. The process of claim 1 , wherein said positively charged cyclic amine group is an imidazolium or a pyridinium.
10. The process of claim 9 , wherein said positively charged cyclic amine group is an alkylpyridinium.
11. The process of claim 9 , wherein said positively charged cyclic amine group is tetramethylimidazolium.
12. The process of claim 1 , wherein said crosslinked anion exchange membrane is characterized by the presence of benzyl ether groups, as measured by 2D nuclear magnetic resonance spectroscopy.
13. The process of claim 12 , wherein the 2D proton/carbon-13 nuclear magnetic resonance spectroscopy measurements are performed on solid samples of said crosslinked anion exchange membrane that have been swollen by soaking the samples in dimethyl sulfoxide.
14. The process of claim 1 wherein a 2D H/C-13 HSQC nuclear magnetic resonance spectrum of crosslinked anion exchange membrane shows a correlation between peaks having a chemical shift of from δ3.3 to δ5.4 in the proton spectrum and from δ69 to δ76 in the carbon-13 spectrum.
15. The process of claim 14 wherein the 2D H/C-13 HSQC nuclear magnetic resonance spectrum of the crosslinked anion exchange membrane shows a correlation between peaks at δ4.4±1 in the proton spectrum and δ71±2 in the carbon-13 spectrum.
16. The process of claim 1 wherein a 2D H/C-13 HSQC nuclear magnetic resonance spectrum of the crosslinked anion exchange membrane shows a correlation between peaks at chemical shifts of δ4.4±1 in the proton spectrum and δ62±2 in the carbon-13 spectrum.
17. The process of claim 1 wherein a 2D H/C-13 HSQC nuclear magnetic resonance spectrum of the crosslinked anion exchange membrane shows a correlation between peaks at chemical shifts of δ3.2±1 in the proton spectrum and δ57±2 in the carbon-13 spectrum.
18. The process of claim 1 , wherein said crosslinked anion exchange membrane is insoluble in any solvent or solvent mixture selected from the group consisting of ethanol, dimethyl sulfoxide, and dimethyl formamide.
19. The process of claim 1 , wherein said crosslinked anion exchange membrane has a hydroxide ion conductivity of at least 40 mS/cm at 60° C. in 1 M KOH.
20. The process of claim 1 , wherein said crosslinked anion exchange membrane has a Young's Modulus of at least 15 MPa.