Ion-exchange membranes structured in the thickness and process for manufacturing these membranes

Abstract

Monolayer ion-exchange membrane structured in the thickness comprising ion-exchange sites covalently bonded to a support polymer, the membrane comprising two surface zones located on either side of a mid-zone, each surface zone having a thickness of not more than 15% of the total thickness of the membrane, in which the surface zones have a mean ion-exchange site density D surface calculated on the thickness of the surface zones of at least D total .

1 - 6 . (canceled) 
     
     
         7 . A process for producing a radiochemically grafted membrane in which a membrane is irradiated and is successively placed in contact with at least two different grafting compositions, each comprising at least one monomer to be grafted. 
     
     
         8 . The process according to  claim 7 , in which at least one grafting composition subsequently placed in contact with the membrane comprises a barrier monomer absent from at least one composition previously placed in contact. 
     
     
         9 . The process according to  claim 7 , in which the grafting compositions are in liquid form and the placing in contact is performed by immersing the membrane in at least two different baths. 
     
     
         10 . The process according to  claim 7 , in which at least two grafting compositions have different contents of polymerization additives. 
     
     
         11 . The process according to  claim 10 , in which at least one grafting composition previously placed in contact with the membrane has a content of at least one polymerization additive less than that of at least one composition subsequently placed in contact, the polymerization additive being a chain-transfer agent and/or an inhibitor and/or a curing agent. 
     
     
         12 . (canceled) 
     
     
         13 . A fuel cell comprising an ion-exchange membrane made in accordance with the process of  claim 7 . 
     
     
         14 . The process of  claim 7  in which the radiochemically grafted membrane formed by the irradiating and contacting comprises ion-exchange sites covalently bonded to a support polymer, wherein the radiochemically grafted membrane has a mean ion-exchange site density D total  of at least 2.5 meq/cm 3  calculated on the total thickness of the radiochemically grafted membrane, and
 wherein the membrane comprises two surface zones located on either side of a mid-zone, each surface zone having a thickness of not more than 5% of the total thickness of the radiochemically grafted membrane, in which the surface zones have a mean ion-exchange site density D surface  calculated on the thickness of the surface zones of at least 1.05×D total . 
 
     
     
         15 . The process according to  claim 14 , wherein the mean ion-exchange site density D surface  is at least 1.10×D total . 
     
     
         16 . The process according to  claim 14 , wherein the D total  of the radiochemically grafted membrane is at least 3 meq/cm 3 . 
     
     
         17 . The process according to  claim 7 , wherein the D surface  of the radiochemically grafted membrane is at least 1.15×D total . 
     
     
         18 . The process according to  claim 14 , wherein the ion-exchange sites comprise at least one group selected from the group consisting of a carboxyl group, a sulfonate group and the trimethyl amine group. 
     
     
         19 . The process according to  claim 14 , wherein the support polymer is at least one polymer selected from the group consisting of a fluorinated polymer, a polyolefin, an aromatic polymer and a polyamide. 
     
     
         20 . The process according to  claim 14 , wherein each surface zone has a thickness of not more than 2% of the total thickness of the radiochemically grafted membrane. 
     
     
         21 . The process according to  claim 14 , wherein the D surface  is from 1.05×D total  to 1.2×D total . 
     
     
         22 . The process according to  claim 14 , wherein the ion-exchange sites are sulfonic groups. 
     
     
         23 . The process according to  claim 14 , wherein the radiochemically grafted membrane has an exchange capacity measured according to AFNORNFX45-25 (Dec. 19, 1995) are from 1.6 meq/g to 2.19 meq/g. 
     
     
         24 . The process according to  claim 14 , wherein the radiochemically grafted membrane has no surface quaternary amine sites. 
     
     
         25 . A process for producing a radiochemically grafted membrane structured in thickness, comprising:
 irradiating a first membrane, and   successively placing the irradiated first membrane in contact with at least two different grafting compositions, wherein each grafting composition comprises at least one monomer to be grafted.