This invention provides a novel graft polymer that has excellent proton conductivity, is capable of regulating hydrogen permeability, methanol permeability, and the like, and can serve as a starting material for a polymer electrolyte membrane, which facilitates moisture balance control and efficient operation of a fuel cell. A polymer electrolyte membrane composed of such graft polymer is also provided. This graft polymer comprises a main chain comprising a hydroxyl group-containing polymer and a graft chain comprising a polymer containing a sulfonic acid group-containing monomer.
1. A crosslinked graft polymer comprising a main chain comprising polyvinyl alcohol (PVA) and a graft chain comprising a polymer containing a sulfonic acid group-containing monomer,
wherein the crosslinked graft polymer is obtained by a thermal treatment at 140° C. to 180° C., and
wherein the sulfonic acid group-containing monomer is selected from the group consisting of 2-acrylamido-2-methylpropane sulfonic acid, 2-(meth)acrylamido-2-methylpropane sulfonic acid, vinyl sulfonic acid, styrene sulfonic acid, α-methyl styrene sulfonic acid, 2-sulfoethyl methacrylate, and salts thereof.
2. The crosslinked graft polymer according to claim 1 , wherein the sulfonic acid group-containing monomer is 2-acrylamido-2-methylpropane sulfonic acid, 2-(meth)acrylamido-2-methylpropane sulfonic acid, or salts thereof.
3. The crosslinked graft polymer according to claim 1 , wherein the content of the sulfonic acid group-containing monomer is 1 to 90 mol % relative to the total amount of the graft polymer.
4. The crosslinked graft polymer according to claim 1 , wherein the content of the sulfonic acid group-containing monomer is 6 to 20 mol % relative to the total amount of the graft polymer.
5. The crosslinked graft polymer according to claim 1 , wherein the synthesized graft polymer is subjected to physical and/or chemical crosslinking.
6. The crosslinked graft polymer according to claim 5 , wherein the physical crosslinking is carried out via thermal treatment.
7. The crosslinked graft polymer according to claim 5 , wherein the chemical crosslinking is carried out with glutaraldehyde (GA).
8. A method for preparing a crosslinked graft polymer according to claim 1 comprising subjecting polyvinyl alcohol (PVA) to graft polymerization with a sulfonic acid group-containing monomer,
wherein the crosslinked graft polymer is obtained by a thermal treatment at 140° C. to 180° C., and
wherein the sulfonic acid group-containing monomer is selected from the group consisting of 2-acrylamido-2-methylpropane sulfonic acid, 2-(meth)acrylamido-2-methylpropane sulfonic acid, vinyl sulfonic acid, styrene sulfonic acid, α-methyl styrene sulfonic acid, 2-sulfoethyl methacrylate, and salts thereof.
9. The method for preparing the crosslinked graft polymer according to claim 8 , wherein the sulfonic acid group-containing monomer is 2-acrylamido-2-methylpropane sulfonic acid, 2-(meth)acrylamido-2-methylpropane sulfonic acid, or salts thereof.
10. The method for preparing the crosslinked graft polymer according to claim 8 , wherein a content of the sulfonic acid group-containing monomer is at least 2 mol % relative to the total amount of the graft polymer.
11. The method for preparing the crosslinked graft polymer according to claim 8 , wherein diammonium cerium nitrate (CAN) is used as a polymerization initiator.
12. A polymer electrolyte membrane comprising the crosslinked graft polymer according to claim 1 .
13. The polymer electrolyte membrane according to claim 12 , which is formed by casting the crosslinked graft polymer.
14. The polymer electrolyte membrane according to claim 12 , wherein the synthesized crosslinked graft polymer is subjected to physical and/or chemical crosslinking.
15. The polymer electrolyte membrane according to claim 14 , wherein the physical crosslinking is carried out via thermal treatment.
16. The polymer electrolyte membrane according to claim 14 , wherein the chemical crosslinking is carried out with glutaraldehyde (GA).
17. A method for preparing a polymer electrolyte membrane comprising a step of synthesizing the crosslinked graft polymers according to claim 8 and a step of casting the graft polymers.
18. The method for preparing the polymer electrolyte membrane according to claim 17 , which further comprises a step of subjecting the crosslinked graft polymer to physical and/or chemical crosslinking.
19. The method for preparing the polymer electrolyte membrane according to claim 18 , wherein physical crosslinking is carried out via thermal treatment.
20. The method for preparing the polymer electrolyte membrane according to claim 18 , wherein the chemical crosslinking is carried out with glutaraldehyde (GA).
21. The method for preparing the polymer electrolyte membrane according to claim 17 , wherein casting is carried out on a planar object.
22. The method for preparing the polymer electrolyte membrane according to claim 17 , wherein casting is carried out by allowing the crosslinked graft polymer to impregnate porous polymer.
23. The method for preparing the polymer electrolyte membrane according to claim 17 , which further comprises a step of insolubilizing the solution containing the crosslinked graft polymer with the use of an organic solvent.
24. The method for preparing the polymer electrolyte membrane according to claim 23 , wherein the organic solvent is acetone.
25. The method for preparing the polymer electrolyte membrane according to claim 17 , which further comprises a step of insolubilizing the solution containing the crosslinked graft polymer with the use of a salt.
26. A polymer electrolyte fuel cell comprising the polymer electrolyte membrane according to claim 12 .