Process of making a composite membrane

Abstract

The present invention relates to methods of fabricating composite membranes wherein at least one of the components is initially provided in the form of a precursor. The composite material comprising the precursor is processed to transform the precursor and obtain a membrane having a desired property. Including a thermoplastic precursor to a desired component, which itself is less thermoplastic, permits separate pieces of the membrane to be joined by welding or other thermal processes relying on the meltability of the components to achieve a bond. The invention also encompasses fabricating a reinforced ion conducting membrane by melting and mixing a non ion-conducting precursor to an ion-conducting polymer with an essentially inert polymer. The composite material is then processed to transform the non ion-conducting polymer into the ion-conducting form. The mixing of the precursor and the inert polymer may also be achieved by co-precipitating a solution of the precursor and a suspension of the inert polymer; impregnating the precursor onto the walls of the pores of a porous, essentially inert polymer; filling the pores of a porous, essentially inert polymer with a solution of comprising a non ion-conducting precursor to an ion conducting precursor and evacuating the solvent to substantially fill the pores of a the porous, essentially inert polymer with the precursor; or melting the precursor, filling the pores of a porous essentially inert polymer with the melted precursor and cooling the precursor to form an essentially pore free composite membrane.

What is claimed is:  
     
         1 . A method of making a composite membrane, comprising: 
 (a) combining a first polymer component with a second polymer component; wherein the first polymer component is a non ion-conducting precursor to an ion-conducting polymer; and    (b) converting the first polymer component from the non ion-conducting precursor to the ion-conducting polymer.    
     
     
         2 . The process of  claim 1  wherein the combining of the components comprises melting and mixing the polymers.  
     
     
         3 . The process of  claim 2  wherein the second polymer component comprises a substantially inert polymer.  
     
     
         4 . The process of  claim 3  wherein the substantially inert polymer is selected from polytetrafluoroethylene (PTFE), perfluoroalkoxy derivative of PTFE (PFA), fluorinated ethylene-propylene copolymer (FEP), polyvinyl chloride, polyvinyl dichloride, polyvinyl fluoride (PVF), polystyrene, polytrifluorostyrene (TFS), polyether ketone, polyether sulfone, polyparaphenylene, and mixtures thereof.  
     
     
         5 . The process of  claim 1  wherein the ion conducting polymer component is selected from long side chain perfluorosulfonic acid, short side chain perfluorosulfonic acid, trifluorostyrene, partially derivatized trifluorostyrene, polystyrene, and mixtures or copolymers thereof.  
     
     
         6 . The process of  claim 1  wherein the first component comprises a polymer capable of being dissolved in a solvent and the second component comprises a polymer capable of forming a suspension.  
     
     
         7 . The process of  claim 6  wherein the step of combining the first and second polymer components comprises mixing a solution of the first component and a suspension of the second component, co-precipitating the first and second polymer components to form a gelatinous mass, and drying the gelatinous mass.  
     
     
         8 . The process of  claim 7  wherein the first polymer component is selected from long side chain perfluorosulfonylfluoride, short side chain perfluorosulfonylfluoride, trifluorostyrene, partially derivatized trifluorostyrene, polystyrene, poly-bis[{perfluoroalkyl)sulfonyl]imide and its derivatives, perfluoro-ethylene-1,2-bis-phosphonic acid derivatives, and mixtures thereof.  
     
     
         9 . The process of  claim 7  wherein the second polymer component is selected from polytetrafluoroethylene (PTFE), perfluoroalkoxy derivative of PTFE (PFA), fluorinated ethylene-propylene copolymer (FEP), polyvinyl chloride, polyvinyl dichloride, polyvinyl fluoride (PVF), polystyrene, polytrifluorostyrene (TFS), polyether ketone, polyether sulfone, polyparaphenylene, and mixtures thereof.  
     
     
         10 . The process of  claim 7  further comprising rolling the dried gelatinous mass into a sheet.  
     
     
         11 . The process of  claim 10  wherein the rolling is carried out at a temperature of about 150° C.  
     
     
         12 . The process of  claim 11  further comprising sintering the dried gelatinous mass at a temperature higher than 150° C.  
     
     
         13 . The process of  claim 10  wherein the rolling is carried out at a temperature of about 300° C.  
     
     
         14 . The process of  claim 13  further comprising sintering the dried gelatinous mass at a temperature higher than 300° C.  
     
     
         15 . The process of  claim 7  further comprising pressing the dried gelatinous mass into a sheet.  
     
     
         16 . The process of  claim 1  wherein the first polymer component comprises a soluble polymer and the second polymer component comprises a porous matrix.  
     
     
         17 . The process of  claim 16  wherein the step of combining the first and second polymer components comprises forming a solution of the first polymer component, filling the pores of the porous matrix with the solution; removing the solvent from the pores of the matrix to form an essentially pore-free composite material.  
     
     
         18 . The process of  claim 16  wherein the porous matrix comprises an organic polymer.  
     
     
         19 . The process of  claim 16  wherein the matrix polymer is selected from polytetrafluoroethylene (PTFE), perfluoroalkoxy derivative of PTFE (PFA), fluorinated ethylene-propylene copolymer (FEP), polyvinyl chloride, polyvinyl dichloride, polyvinyl fluoride (PVF), polystyrene, polytrifluorostyrene (TFS), polyether ketone, polyether sulfone, polyparaphenylene, and mixtures thereof.  
     
     
         20 . The process of  claim 16  wherein the porous matrix comprises an inorganic material.  
     
     
         21 . The process of  claim 20  wherein the inorganic material is selected from fiber glass, fibrous quartz, rock wool, fibrous alumina, other fibrous silicates or alumino-silicates, and mixtures thereof.  
     
     
         22 . The process of  claim 16  wherein the soluble polymer is selected from long side chain perfluorosulfonylfluoride, short side chain perfluorosulfonylfluoride, trifluorostyrene, partially derivatized trifluorostyrene, and polystyrene.  
     
     
         23 . The process of  claim 1  wherein the second polymer component comprises a porous polymer matrix, and wherein the step of combining the first and second polymer components comprises melting the first polymer component, filling the pores of the porous matrix with the first polymer component, and cooling the polymer to form an essentially pore-free composite material.  
     
     
         24 . The process of  claim 23  wherein the second polymer component comprises an inorganic material.  
     
     
         25 . The process of  claim 24  wherein the inorganic material is selected from fiber glass, fibrous quartz, rock wool, fibrous alumina, other fibrous silicates or alumino-silicates, and mixtures thereof.  
     
     
         26 . The process of  claim 1  wherein the composite membrane comprises regions essentially made of the first polymer component and regions essentially made of the second polymer component.  
     
     
         27 . The process of  claim 26  wherein the regions essentially made of the first polymer component form an ion-conducting path capable of transporting ions through the membrane.  
     
     
         28 . The process of  claim 27  wherein the ion-conducting path comprises a hydrophilic path.  
     
     
         29 . A method of making a composite membrane, comprising: 
 (a) initiating a living chain co-polymerization of a first monomer and a second monomer, wherein the first monomer is a non-derivatizable monomer and the second monomer is a non ion-conducting precursor to an ion-conducting monomer;    (b) propagating the polymerization to form a co-polymer chain having at least one region essentially comprised of non-derivatizable monomers and at least one region essentially comprised of precursor monomers;    (c) fabricating a membrane from the co-polymer chain; and    (d) transforming at least a portion of the non ion-conducting precursor monomers into ion-conducting monomers.    
     
     
         30 . The process of  claim 29  wherein the number of non-derivatizable monomers in the co-polymer chain is greater than the number of precursor monomers in the co-polymer chain.  
     
     
         31 . The process of  claim 29  wherein the number of non-derivatizable monomers in the co-polymer chain is lower than the number of precursor monomers in the co-polymer chain.  
     
     
         32 . The process of  claim 29  wherein the regions comprising precursor monomers or ion-conducting monomers obtained by transforming precursor monomers form an ion-conducting path capable of transporting ions through the composite membrane.  
     
     
         33 . The process of  claim 32  wherein the ion-conducting path comprises a hydrophilic path.