Synthesis of poly(arylene)s copolymers containing pendant sulfonic acid groups bonded to naphthalene as proton exchange membrane materials
A new series of wholly aromatic poly(arylene ether ether ketone ketone)s containing pendant sulfonic acid groups (SPAEEKK) were conveniently prepared by potassium carbonate mediated nucleophilic polycondensation reactions of inexpensive commercially available monomers: 1,3-bis(4-fluorobenzoyl)benzene (BFBB), sodium 6,7-dihydroxy-2-naphthalenesulfonate (DHNS), and 4,4′-biphenol or hydroquinone in N-methyl-2-pyrrolidone (NMP) at 170° C. FT-IR and NMR were used to characterize the structures and the sulfonate or sulfonic acid contents (SC) of the polymers. Flexible membrane films were obtained by casting N,N-dimethylacetamide (DMAc) solutions of copolymers. Membrane films in acid form were then obtained by treating the sodium form membrane films in 2 N sulfuric acid at room temperature. Glass transition temperatures (T g s) and decomposition temperatures (T d s) of SPAEEKKs in both sodium and acid forms were determined. Water uptake and swelling ratio values increased with SCs and temperatures. The proton conductivities of acid form membrane films increased with SC value and temperature and reached 5.6×10 −2 S/cm at 100° C. for SPAEEKK-100.
1. A poly(arylene ether ether ketone ketone) copolymer containing sulfonic acid groups (SPAEEKK) of structural formula I, consisting of
wherein X is H or a cation,
Y is sulfur or oxygen,
B and D are
C is derived from either a bisphenol or bisthiol and is used to control the sulfonate content in the copolymer and is selected from:
wherein a,b,c,d represent mol fractions of the monomer present in the copolymer where each are independently from 0.1 to 1, and (a+c)=(b+d).
2. A co-polymer according to claim 1 , wherein X is H or an alkali metal counterion selected from the group consisting of Li + , Na + , K + , Rb + or Cs + , or an ammonium salt,
3. A co-polymer according to claim 2 , wherein C is selected from the group consisting of biphenyl, naphthyl, and hexafluoro-isopropylidene-bisphenyl.
4. A co-polymer according to claim 3 , wherein X is Na + .
5. A co-polymer according to claim 4 , wherein C is biphenyl.
6. A co-polymer according to claim 1 wherein the sulfur content (SC) of the co-polymer is 0.5 to 1.0.
7. A co-polymer according to claim 1 , in the form of a membrane.
8. A process for making a co-polymer of structural formula I as defined in claim 1 comprising reacting at elevated temperature in the presence of K 2 CO 3 , a compound resulting from polycondensation in the residue of a monomer
a sulfonated naphthalene diphenol monomer of structural formula II
wherein X is H or an alkali metal counterion selected from the group consisting of Li + , Na + , K + , Rb + or Cs + , or an ammonium salt,
and a compound resulting from polycondensation in the residue of a monomer of structural formula III
wherein Y is sulfur or oxygen, and
C is derived from either a bisphenol or bisthiol and is used to control the sulfonate content in the copolymer and is selected from:
wherein a,b,c,d represent mol fractions of the monomer present in the copolymer where each are independently from 0.1 to 1, and (a+c)=(b+d).
9. A process according to claim 8 , wherein the reaction is effected under inert gas atmosphere.
10. A process according to claim 9 , wherein an aprotic polar solvent and a drying agent are also present.
11. A process according to claim 10 , wherein the organic solvent is NMP, DMAc, DMF, or DMSO and the drying agent is toluene or xylene.
12. A process according to claim 11 , wherein C is selected from the group consisting of biphenyl, naphthyl, and hexafluoro-isopropylidene-bisphenyl.
13. A process according to claim 12 , wherein the reaction is effected in a heating step to 130-140° C. to de-hyd rate, and then increasing the temperature to 160-170° C. to complete the reaction.
14. A process according to claim 8 , wherein the sulfur content (SC) of the co-polymer is 0.5 to 1.0.
15. A process according to claim 14 , wherein X is Na.
16. A process according to claim 15 , wherein C is biphenyl.
17. A process according to claim 8 , including the additional step of casting the co-polymer in the form of a membrane.