Ion-exchange group bearing composite membranes

Composite membranes bearing ion-exchange groups suitable for use in membrane separation processes are produced by providing a porous substrate which is physically semipermeable by itself, applying a coating composition consisting essentially of a filmforming polymeric material to which ion-exchange groups are introduceable and a liquid medium onto the surface of said substrate, removing said liquid medium to provide an ultrathin membrane of said material having a thickness less than 10 microns, and treating said ultrathin membrane to provide said ion-exchange groups throughout said ultrathin membrane.

We claim:

1. A method for preparing a selectively permeable composite membrane having an ultrathin layer of ion exchange polymer film adhered to a polymeric microporous supporting substrate which is permeable to ions and molecules which pass through said ultrathin layer, which comprises:

a. coating said substrate with a composition consisting essentially of an inert diluent and a film-forming polymer which is substantially impermeable to said substrate and which contains at least on reactive site selected from the group consisting of benzene rings, double bonds, halogen atoms, hydroxyl groups or nitrile groups;

b. removing said inert diluent to form an ultrathin layer of said film-forming polymer having a dry thickness of less than 10 microns adhered to said substrate; and

c. converting said ultrathin layer into an ion exchange layer by chemically introducing ion exchange groups into said reactive sites.

2. A method according to claim 1, wherein said ion exchange groups are at least one member selected from the group consisting of sulfonyl, carboxyl, quaternary ammonium and tertiary amino groups.

3. A method according to claim 1, wherein said film-forming polymer is selected from the group consisting of a butadiene-styrene copolymer, a vinyl chloride-acrylonitrile copolymer and a polyvinyl alcohol.

4. A method according to claim 1, wherein said substrate comprises polyvinylchloride.

5. A method according to claim 4, wherein the film-forming polymer is a copolymer of butadiene and styrene.

6. A method according to claim 5, wherein said ion exchange groups are introduced by sulfonating benzene ring reactive sites in said ultrathin layer.

7. A method according to claim 6, further comprising reacting the resultant ion exchange layer with a mixture of epichlorohydrin and pyridine to introduce quaternary ammonium groups therein.

8. A method according to claim 4, wherein said film-forming polymer is a copolymer of vinyl chloride and acrylonitrile.

9. A method according to claim 8, wherein said ion exchange groups are introduced by substituting halogen atom reactive sites in said ultrathin layer with a tertiary amino group.

10. A method according to claim 8, wherein said ion exchange groups are introduced by hydrolyzing nitrile group reactive sites in said ultrathin layer.

11. A method according to claim 10, further comprising reacting the resultant ion exchange layer with ethylenediamine to introduce tertiary amino groups therein.

12. A selectively permeable composite membrane prepared according to the process of claim 1.

13. A selectively permeable composite membrane prepared according to the process of claim 2.

14. A selectively permeable composite membrane prepared according to the process of claim 3.

15. A selectively permeable composite membrane prepared according to the process of claim 4.

16. A selectively permeable composite membrane prepared according to the process of claim 6.

17. A selectively permeable composite membrane prepared according to the process of claim 7.

18. A selectively permeable composite membrane prepared according to the process of claim 10.

19. A selectively permeable composite membrane prepared according to the process of claim 11.