Membranes

1. A composite membrane comprising:

a. a porous support; and

b. a polymeric layer comprising dialkylsiloxane groups and a metal, the polymeric layer being present on the porous support;

c. a discriminating layer present on the polymeric layer; and

d. optionally a protective layer present on the discriminating layer

wherein the polymeric layer has a molar ratio of metal:silicon of at least 0.0005.

2. The membrane according to claim 1 , wherein the metal is derived from a metal complex.

3. The membrane according to claim 1 , wherein the metal is selected from any one of groups 4 and 5 of the periodic table.

4. The membrane according to claim 1 , wherein the metal is titanium, zirconium, hafnium, vanadium or niobium.

5. The membrane according to claim 1 , wherein the discriminating layer comprises a polyimide comprising trifluoromethyl groups.

6. The membrane according to claim 1 , wherein the average thickness of the discriminating layer is 20 nm to 2 μm and the polymeric layer has an average thickness of 25 to 1200 nm.

7. The membrane according to claim 1 , wherein the porous support has surface pores of average diameter 0.001 to 0.1 μm.

8. The composite membrane according to claim 1 which is a composite gas separation membrane.

9. A gas separation cartridge comprising a composite membrane according to claim 1 .

10. The composite membrane according to claim 1 wherein:

(a) the metal is derived from a metal complex;

(b) the metal is selected from any one of groups 4 and 5 of the periodic table;

(c) the discriminating layer comprises a polyimide comprising trifluoromethyl groups;

(d) average thickness of the discriminating layer is 20 nm to 2 μm; and

(e) the polymeric layer has an average thickness 25 to 1200 nm.

11. The composite membrane according to claim 10 which is a composite gas separation membrane.

12. The composite membrane according to claim 1 which is a composite gas separation membrane and has a pure water permeability at 20° C. of less than 6.10-8 m3/m2·s·kPa.

13. The composite membrane according to claim 10 which is a composite gas separation membrane and has a pure water permeability at 20° C. of less than 6.10-8 m3/m2·s·kPa.

14. A gas separation cartridge comprising a composite membrane according to claim 4 .

15. A gas separation cartridge comprising a composite membrane according to claim 6 .

16. A gas separation cartridge comprising a composite membrane according to claim 10 .

17. A process for preparing a composite membrane comprising the steps:

(i) applying to a porous support a radiation-curable composition comprising a polymerisable dialkylsiloxane and a metal;

(ii) irradiating the radiation-curable composition on the support, thereby forming a polymeric layer comprising dialkylsiloxane groups and a metal on the porous support;

(iii) forming a discriminating layer on the polymeric layer; and

(iv) optionally forming a protective layer on the discriminating layer;

wherein the polymeric layer has a molar ratio of metal:silicon of at least 0.0005.

18. The process according to claim 17 wherein the radiation-curable composition comprises a metal complex and a polymerisable poly(dialkylsiloxane).

19. The process according to claim 17 which further comprises the step of forming a protective layer on the discriminating layer (step (iv)).

20. The process according to claim 19 wherein:

(a) the metal is derived from a metal complex;

(b) the metal is selected from any one of groups 4 and 5 of the periodic table;

(c) the discriminating layer comprises a polyimide comprising trifluoromethyl groups;

(d) average thickness of the discriminating layer is 20 nm to 2 μm; and

(e) the polymeric layer has an average thickness 25 to 1200 nm.