DESALINATION OF POLYARYL ETHERS FROM A MELT POLYMERIZATION METHOD

Abstract

A method for desalinating a salt-containing polymer is provided. The salt-containing polymer contains a polyaryl ether and a salt. The method includes the steps of mechanically increasing the surface area of the salt-containing polymer to obtain a salt-containing polymer of increased surface area, and contacting the salt-containing polymer of increased surface area with an extractant to obtain a desalinated polymer containing the polyaryl ether, and a salt-containing extractant containing the extractant and the salt.

Claims

1. A method for desalinating a salt-containing polymer comprising a polyaryl ether and a salt, the method comprising a) mechanically increasing a surface area of the salt-containing polymer to obtain a salt-containing polymer of increased surface area, and b) contacting the salt-containing polymer of increased surface area with an extractant to obtain a desalinated polymer comprising the polyaryl ether, and a salt-containing extractant comprising the extractant and the salt, the surface area of the salt-containing polymer being mechanically increased in a) by foaming or drawing the salt-containing polymer.

2. The method according to claim 1, wherein the salt-containing polymer is prepared by a melt polymerization method.

3. The method according to claim 1, wherein the extractant in b) comprises water.

4. The method according to claim 1, wherein the desalinated polymer obtained in b) comprises not more than 150 ppm by weight of the salt, based on a total weight of the desalinated polymer.

5. The method according to claim 1, wherein b) is conducted at a temperature below a softening temperature of the polyaryl ether.

6. The method according to claim 1, wherein b) comprises: b1) contacting the salt-containing polymer of increased surface area obtained from a) with the extractant to obtain a pre-desalinated polymer comprising the polyaryl ether and residues of the salt, and a first salt-containing extractant comprising the extractant and a portion of the salt, and b2) contacting the pre-desalinated polymer obtained from b1) with the extractant to obtain the desalinated polymer comprising the polyaryl ether, and a second salt-containing extractant comprising the extractant and the residues of the salt.

7. The method according to claim 6, wherein b1) is conducted at a temperature of from 50 to 105° C.

8. The method according to claim 6, wherein b2) is conducted at a temperature of higher a 105° C. and lower than a softening temperature of the polyaryl ether.

9. The method according to claim 6, wherein b1) is conducted for a period of from 5 to 50 hours.

10. The method according to claim 6, wherein b2) is conducted for a period of from 10 to 90 hours.

11. The method according to claim 1, wherein the polyaryl ether is a polyaryl ether sulfone.

12. The method according to claim 1, wherein the salt comprises potassium chloride and/or sodium chloride.

13. (canceled)

Description

[0291] FIG. 1 shows the graph of the proportion of the salt (S), c [ppm], as a function of the duration of desalination, t [h], for comparative experiment C1 (circles) and comparative experiment C2 (rhombuses). It is clearly apparent that the proportion of salt (S) assumes a virtually constant value with time, which is in the region of 200 ppm or in the region of 400 ppm of salt (S) in the desalinated polymer (DP). The inventive proportion of salt (S) in the desalinated polymer (DP) of ≦150 ppm cannot be achieved by simply grinding the salt-containing polymer (SP) and then extracting the salt (S). FIG. 1 also shows that a lower proportion of salt (S) in the polymer is achieved more quickly when the salt-containing polymer (SP) has a greater particle size.

[0292] It becomes clear from the examples that it is possible by the method of the invention to obtain a smaller proportion of salt (S) in the desalinated polymer (DP) compared to the desalinated polymers (DP) where the surface area has not been increased mechanically prior to the desalination. Furthermore, the method of the invention gives a much quicker reduction in the proportion of salt (S) in the polymer. Moreover, significantly higher viscosity numbers are obtained for the polymers (DP) desalinated in accordance with the invention.