METHOD FOR SULFONATING POLYMERS

Abstract

The present invention relates to a method of forming a sulfonated aromatic polymer, to the sulfonated aromatic polymer thus formed and to the method of using the sulfonated aromatic polymer in the manufacture of membranes.

Claims

1.-12. (canceled)

13. A method of forming a sulfonated aromatic polymer by reacting an aromatic polymer with at least one sulfonating agent in the presence of a solvent comprising sulfur dioxide, where the aromatic polymer is a polyarylene ether comprising building blocks of general formula (I) ##STR00007## where t and q are each independently 0, 1, 2 or 3, Q, T and Y are each independently a chemical bond or a group selected from the group consisting of O, S, SO.sub.2, SO, CO, NN and CR.sup.aR.sup.b, where R.sup.a and R.sup.b are each independently a hydrogen atom or a C.sub.1-C.sub.12 alkyl, C.sub.1-C.sub.12 alkoxy or C.sub.6-C.sub.18 aryl group, and Ar and Ar.sup.1 are each independently an arylene group having from 6 to 18 carbon atoms, wherein the at least one sulfonating agent is selected from the group consisting of sulfur trioxide, sulfuric acid, fuming sulfuric acid and polyalkylbenzenesulfonic acids, and wherein the solvent comprises not less than 80 wt % of sulfur dioxide, based on the total weight of the solvent.

14. The method according to claim 13 wherein the polyaryl ether is a polyarylene ether sulfone comprising building blocks of general formula (I) where at least one of Q, T and Y is SO.sub.2.

15. The method according to claim 13 wherein the aromatic polymer is selected from the group consisting of polysulfones (PSU), polyether sulfones (PESU), polyphenylene sulfones (PPSU) and copolymers thereof.

16. The method according to claim 13 wherein the at least one sulfonating agent is sulfur trioxide.

17. The method according to claim 13 wherein the weight ratio of the aromatic polymer to the solvent is in the range from 0.1:100 to 1:1.

18. The method according to claim 13 wherein the sulfur dioxide comprised in the solvent is in liquid form during the reaction.

19. The method according to claim 13 wherein the temperature during the reaction is in the range from 30 to +100 C. and/or the pressure during the reaction is in the range from 0.1 to 100 bar.

20. The method according to claim 13 wherein the method comprises the steps of: a) reacting the aromatic polymer with the at least one sulfonating agent in the presence of the solvent to obtain the sulfonated aromatic polymer dissolved in the solvent, separating the solvent from the sulfonated aromatic polymer to obtain the sulfonated aromatic polymer in solid form.

21. The method according to claim 20 wherein the step of separating off the solvent in step b) is effected by evaporation.

22. A sulfonated aromatic polymer obtained by the method according to claim 13.

23. The sulfonated aromatic polymer according to claim 22 wherein the sulfonated aromatic polymer has from 0.001 to 1 SO.sub.2X groups, where X is Cl or OZ, where Z is hydrogen or a cation equivalent, per aromatic ring.

24. A method comprising utilizing the sulfonated aromatic polymer according to claim 22 in the manufacture of membranes.

Description

EXAMPLES

Example 1

[0167] The aromatic polymer used was a random polyether sulfone-polyphenylene sulfone copolymer (PESU-PPSU copolymer) having a polyphenyl sulfone fraction of 10 mol %, based on the total amount-of-substance amount of the aromatic polymer. The viscosity number (VN) was measured to DIN ISO 1628-1 in a 1 wt % NMP solution at 25 C. The viscosity number of the copolymer was 52 ml/g.

[0168] The aromatic polymer was dissolved at 20 wt %, based on the combined weight of aromatic polymer and sulfur dioxide, in liquid sulfur dioxide at 15 C. and 1 bar (ambient pressure).

[0169] Then, 0.9 wt % of sulfur trioxide was admixed and the mixture was reacted at 15 C. for 5 hours. Then, the sulfur dioxide and also any sulfur trioxide still present were separated from the sulfonated aromatic polymer obtained by evaporating the sulfur dioxide and also any sulfur trioxide present at 65 C. and a pressure of 1 bar (ambient pressure) for 1 hour.

[0170] The viscosity number of the sulfonated aromatic polymer obtained was 53 ml/g. The degree of sulfonation (number of sulfonic acid groups per aromatic ring) of the copolymer was determined using H NMR spectroscopy and IR spectroscopy.

[0171] The H NMR spectroscopy measurements were carried out with an Agilent Technologies MR 400 DD2, 400 MHz, in dimethyl sulfoxide-d6, at 23 C. The degree of sulfonation was determined from the ratio of the aromatic protons adjacent to the sulfonic acid group (=8.13 ppm, singlet) relative to the protons ortho to the sulfone bridges (=8.03 ppm and =8.01 ppm, doublet). The sulfonated aromatic polymer was shown by H NMR spectroscopy to contain 0.015 sulfonic acid groups per aromatic ring.

[0172] The IR spectroscopy measurements were carried out using a Nicolet 6700 FTIR. The sulfonated aromatic polymer was dissolved in DMF dimethylformamide, applied as a film to KRS5 windows and vacuum dried at 160 C. After cooling down to room temperature (25 C.), the film was measured in transmission. The spectrum of the sulfonated aromatic polymer has a characteristic band at v=1023 cm.sup.1 for the SO.sub.3 group. The number of SO.sub.3H groups introduced can be identified from the ratio of the band area at v=1023 cm.sup.1 relative to the reference band at v=1012 cm.sup.1 after calibration. Calibration was performed using sulfonated aromatic polymers having a known degree of sulfonation (sulfonated aromatic polymers having a known degree of sulfonation were obtainable for example by synthesis of sulfonated aromatic polymers using monomers having a known degree of sulfonation). The sulfonated aromatic polymer was shown by IR spectroscopy to contain 0.021 sulfonic acid groups per aromatic ring.

Comparatty Example 2

[0173] The aromatic polymer used is the PESU-PPSU copolymer of Example 1.

[0174] The aromatic polymer is mixed 20 wt %, based on the combined weight of aromatic polymer and sulfolane, and at 25 C. and 1 bar (ambient pressure) with sulfolane and admixed with sulfur trioxide. The viscous mixture obtained is maintained at 25 C. and 1 bar (ambient pressure) for 5 hours.

[0175] After the sulfur trioxide and sulfolane have been removed, it is not a sulfonated aromatic polymer which is obtained, but only the originally employed aromatic polymer.

[0176] It is clearly seen that a sulfonation of the aromatic polymer in sulfolane with sulfur trioxide is not possible even at room temperature (25 C.).

Comparative Example 3

[0177] The aromatic polymer used is the PESU-PPSU copolymer of Example 1.

[0178] The aromatic polymer is dissolved at 20 wt %, based on the combined weight of aromatic polymer and sulfolane, in sulfolane at 85 C. and 1 bar (ambient pressure) and admixed with sulfur trioxide.

[0179] The solution obtained is highly viscous and but difficult to process, especially react.

[0180] When sulfolane instead of sulfur dioxide is used as solvent, solutions comprising higher concentrations of aromatic polymer cannot be reacted, since but very highly viscous solutions form even at high temperatures of, for example, 85 C.

Comparative Example 4

[0181] The aromatic polymer used is the PESU-PPSU copolymer of Example 1.

[0182] The aromatic polymer is dissolved at 8 wt %, based on the combined weight of aromatic polymer and sulfolane, in sulfolane at 90 C. and 1 bar (ambient pressure).

[0183] Then, sulfur trioxide is admixed and the mixture is reacted at 90 C. for 1 hour.

[0184] Removing the sulfolane and also any sulfur trioxide still present from the sulfonated aromatic polymer obtained in the reaction by evaporation of sulfolane and sulfur trioxide is but scarcely possible, since sulfolane has but a low volatility and the mixture obtained in the reaction decomposes at higher temperatures. When lower temperatures are used, the evaporation times become uneconomically long, resulting in incomplete removal of sulfolane. Removal is therefore effected by the reaction mixture obtained being first dissolved in N-methylpyrrolidone and then precipitated in ethanol. After filtration, the precipitate obtained is washed in a hot-water extraction at 90 C. for 20 h (hours) and vacuum dried at 150 C. for 15 h.

[0185] The residual sulfolane content of the sulfonated aromatic polymer is 0.7 wt % of sulfolane, based on the weight of the sulfonated aromatic polymer.

Comparative Example 5

[0186] The aromatic polymer used is the PESU-PPSU copolymer of Example 1.

[0187] The aromatic polymer is dissolved at 8 wt %, based on the combined weight of aromatic polymer and sulfuric acid, in concentrated sulfuric acid (98 wt % in water) at 50 C. The mixture is reacted at 80 C. and 1 bar (ambient pressure) for 5 hours.

[0188] The sulfonated aromatic polymer obtained after separation has a 20% lower molecular weight than the aromatic polymer used. This shows that some chain degradation takes place on sulfonating in sulfuric acid.

Comparative Example 6

[0189] The aromatic polymer used is the PESU-PPSU copolymer of Example 1.

[0190] The aromatic polymer is dissolved at 10 wt %, based on the combined weight of aromatic polymer and sulfolane, in sulfolane at 90 C. and 1 bar (ambient pressure).

[0191] Then, a stoichiometric amount of concentrated sulfuric acid (98 wt % in water) for a 20% degree of sulfonation of the aromatic polymer is admixed and the mixture obtained is reacted at 90 C. for 1 hour.

[0192] The product obtained is separated off by precipitation in ethanol. H NMR spectroscopy studies show that no sulfonated aromatic polymer is obtained. The H NMR spectrum obtained is that of the originally employed aromatic polymer.

Comparative Example 7

[0193] The aromatic polymer used is the PESU-PPSU copolymer of Example 1.

[0194] The aromatic polymer is dissolved at 10 wt %, based on the combined weight of aromatic polymer and sulfolane, in sulfolane at 90 C. and 1 bar (ambient pressure).

[0195] Then, a stoichiometric amount of concentrated sulfuric acid (98 wt % in water) for a 100% degree of sulfonation of the aromatic polymer is admixed and the mixture obtained is reacted at 90 C. for 1 hour.

[0196] The product obtained is separated off by precipitation in ethanol. H NMR spectroscopy studies show that no sulfonated aromatic polymer is obtained. The H NMR spectrum obtained is that of the originally employed aromatic polymer.

Comparative Example 8

[0197] The aromatic polymer used is the PESU-PPSU copolymer of Example 1.

[0198] The aromatic polymer is dissolved at 10 wt %, based on the combined weight of aromatic polymer and sulfolane, in sulfolane at 90 C. and 1 bar (ambient pressure).

[0199] Then, a 5-fold stoichiometric excess of concentrated sulfuric acid (98 wt % in water) for a 100% degree of sulfonation of the aromatic polymer is admixed and the mixture obtained is reacted at 90 C. for 1 hour.

[0200] The product obtained is separated off by precipitation in ethanol. H NMR spectroscopy studies show that no sulfonated aromatic polymer is obtained. The H NMR spectrum obtained is that of the originally employed aromatic polymer.

[0201] Comparative Examples 6, 7 and 8 show that the reactivity of concentrated sulfuric acid as a sulfonating agent in purely sulfolane as solvent is even at temperatures of 90 C. insufficient to sulfonate the aromatic polymer.