Membrane chemically functionalized polymer

Figure 7.16 Design and synthesis of a chemically functional polymer membrane by an interfacial polycondensation reaction and multilayer flow inside a microchannel.

Fluorinated polymers, especially polytetrafluoroethylene (PTFE) and copolymers of tetrafluoroethylene (TFE) with hexafluoropropylene (HFP) and perfluorinated alkyl vinyl ethers (PFAVE) as well as other fluorine-containing polymers are well known as materials with unique inertness. However, fluorinated polymers with functional groups are of much more interest because they combine the merits of pefluorinated materials and functional polymers (the terms functional monomer/ polymer will be used in this chapter to mean monomer/polymer containing functional groups, respectively). Such materials can be used, e.g., as ion exchange membranes for chlorine-alkali and fuel cells, gas separation membranes, solid polymeric superacid catalysts and polymeric reagents for various organic reactions, and chemical sensors. Of course, fully fluorinated materials are exceptionally inert, but at the same time are the most complicated to produce. 

Polypropylene (PP) is a hydrophobic and chemically inert polymer which needs to be activated in order to be functional as a support for NA immobilization. Typically, PP membranes are aminated by exposure to an ammonia plasma generated by radiofrequency plasma discharge. Once aminated, the PP membranes can be reacted with derivatized ONDs using common coupling methods [56-58]. 

More recently cation-exchange membranes with good mechanical and chemical stability and well-controlled ion-exchange capacity are prepared by dissolving and casting a functionalized polymer such as sulfonated polysulfone, or sulfonated polyetheretherketone in an appropriate solvent, followed by casting the mixture into a film and then evaporation of the solvent [12]. 

N. L., Ramakrisna, S. (2006). Functionalized polymer nanofibre membranes for protection Irom chemical warfare stimulants. Nanotechnology 17 2947-53. 

The idea of using polymer-supported bilayers has been around for more than a decade (34), but it became practical for chemical and biological applications only more recently. Early versions have used relatively short tethers to link the membranes to the solid substrate and thereby increase their durability for practical applications (25, 35). Because these approaches do not increase the gap distance between substrate and membrane and therefore have not been used to reconstitute integral membrane proteins functionally, they will not be discussed here. 

Polymeric membranes are monolithic, continuously porous materials. Membranes can be produced from numerous organic polymers including polyalkanes (polyethylene and polypropylene) and their fluorinated derivatives [polyvinylidene fluoride and polytetrafluoroethylene (PTFE)]. Once formed, a membrane can be chemically functionalized by a number of methods including direct conversion of functional groups in the bulk polymer, coating of the surface with a preformed polymer, or graft copolymerization of reactive monomers onto the membrane surface. 

Second generation Membranes made of polymers, mainly derived from polyolefins or polyethersul-fone. They were introduced in 1975, with different chemical compositions and functional properties, such as PA and PS membranes. They are resistant to hydrolysis (cleavage of internal links of the polymer) and strong acids and bases and high temperature. However, they have a low resistance to mechanical compaction. These membranes are commonly used today. 

Surface-active agents can be embedded in a nanofiber membrane by chemical functionalization, by postspinning modification, by physical adsorption, or by nanoparticle polymer composites. 

E) F unctionalization of membranes - Membranes containing functional groups, which dominate their choice and use as reactive materials, are made by (a) polymerizing styrene-divinylbenzene in sheet-shaped molds followed by further chemical reactions for incorporation of the active species, (b) copolymerization of the functionalized monomer with divinylbenzene in thin film form, and (c) mechanically incorporating powdered functionalized polymer into a sheet of some other extrudable or moldable matrix [77-82]. 

Patents relating to the apphcation of radiation-grafted ion-exchange membranes in fuel cells have been granted to Scherer et al. [89] and to Stone and Stock [90, 91]. These patents mention the functionalization of base polymers with quaternary ammonium groups to yield alkaline polymers. The use of fluorine-substituted styrenic monomers is also claimed to improve membrane chemical stability when utilized in fuel cells (removal of undesired and reactive C-H bonds). 

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