Cation exchange materials prepared in aqueous media
View Patent ↗The application describes a method of preparing a polymer that includes: mixing in an aqueous solution comprising water and a water-soluble alcohol: a vinyl-based monomer having a sulfonic acid functional group, a bifunctional vinyl-based cross-linking agent, and a polymerization initiator, to form a reaction solution, where the monomer and the cross-linking agent are soluble in the reaction solution; and polymerizing the monomer and cross-linking agent to form the polymer. The application further describes a polymer that includes a polymer backbone comprising sulfonic acid functional groups; and crosslinks comprising alcohol functional groups.
1. A method of preparing a cation exchange membrane, the method comprising:
mixing in an aqueous solution comprising water and a water-soluble alcohol:
a vinyl-based monomer having a sulfonic acid functional group,
a divinyl cross-linking agent which is selected from the group consisting of glycerol dimethacrylate, ethyleneglycol dimethacrylate and poly(ethylene glycol) dimethacrylate, and
a thermally initializable polymerization initiator,
to form a reaction solution, wherein the monomer and the cross-linking agent are soluble in the reaction solution;
wherein the monomer and the cross-linking agent are mixed in a molar ratio ranging from 0.5:1 to 2.0:1 (monomer:cross-linking agent);
the polymerization initiator is added in a molar ratio ranging from 0.0025:1 to 0.02:1 (mols of polymerization initiator:total mols of monomer and cross-linking agent); and
the aqueous solution comprises water and the water-soluble alcohol in a weight ratio ranging from 1.0:1 to 3.0:1 (water:water-soluble alcohol);
placing the reaction solution on a backing cloth;
polymerizing the monomer and cross-linking agent to form a polymer sheet; and
converting the sulfonic acid group to a sulfonate functional group for forming the cation exchange membrane.
2. The method according to claim 1 , wherein the reaction solution comprises:
the vinyl based monomer having a sulfonic acid functional group and the cross-linking agent total between 50 and 80 wt % of the reaction solution; and
the aqueous solution and the thermally initializable polymerization initiator makes up the remaining wt % of the reaction solution.
3. The method according to claim 1 , wherein the vinyl-based monomer having a sulfonic acid functional group is 2-acrylamido-2-methylpropane sulfonic acid (AMPS), the cross-linking agent is glycerol dimethacrylate (GDMA), and the water-soluble alcohol is 1-propanol.
4. The method according to claim 1 , further comprising mixing the reaction solution under vacuum.
5. The method according to claim 1 , wherein the step of polymerizing occurs at a temperature between 60° C. and 90° C. for between 30 and 120 minutes.
6. The method according to claim 1 , wherein a saturated solution of sodium bicarbonate is used to convert the sulfonic acid groups to sulfonate functional groups.
7. The method according to claim 1 , wherein the backing cloth is selected from the group consisting of acrylic, polypropylene and polyester cloth.
8. The method according to claim 1 wherein the crosslinking agent is glycerol dimethacrylate (GDMA).
9. The method according to claim 1 , wherein the vinyl based monomer having a sulfonic acid functional group is 2-acrylamido-2-2-methylpropane sulfonic acid (AMPS), and the cross-linking agent is glycerol dimethacrylate (GDMA).