Polymeric membranes chemical properties

Solvent polymeric membranes, conventionally prepared from a polymer that is highly plasticized with lipophilic organic esters or ethers, are the scope of the present chapter. Such membranes commonly contain various constituents such as an ionophore (or ion carrier), a highly selective complexing agent, and ionic additives (ion exchangers and lipophilic salts). The variety and chemical versatility of the available membrane components allow one to tune the membrane properties, ensuring the desired analytical characteristics. 

The preceding structural characteristics dictate the state of polymer (rubbery vs. glassy vs. semicrystalline) which will strongly affect mechanical strength, thermal stability, chemical resistance and transport properties [6]. In most polymeric membranes, the polymer is in an amorphous state. However, some polymers, especially those with flexible chains of regular chemical structure (e.g., polyethylene/PE/, polypropylene/PP/or poly(vinylidene fluoride)/PVDF/), tend to form crystalline... 

PEFCs are defined as a special class of fuel cells owing to the polymeric nature of the electrolyte. This electrolyte confers on the PEFC unique properties of a pseudo-solid-state device (only deionized water needs to be managed), operating at relatively low temperatures. The properties of the polymeric membrane are, therefore, the key for achieving high cell performance and long-term stability. Chemical structures of a variety of membrane materials that have been used in PEFCs, or developed and tested for PEFCs, are shown in Table 1. 

In contrast to the polymeric materials for RO and NF membranes, for which the macromolecular structures have much to do with their permeation properties such as salt rejection characteristics, the choice of membrane material for UF does not depend on the material s influence on the permeation properties. Membrane permeation properties are largely governed by the pore sizes and the pore size distributions of UF membranes. Rather, the thermal, chemical, mechanical, and biological stability is considered of greater importance. 

The function of the polymeric membrane electrolyte is to permit the transfer of protons produced in anodic semi-reaction (3.11) from anode to cathode, where they react with reduced oxygen to give water. This process is of course essential for fuel cell operation, as it allows the electric circuit to be closed inside the cell. On the other hand, the membrane must also hinder the mixing between fuel and oxidant, and exhibit chemical and mechanical properties compatible with operative conditions of the fuel cell (temperature, pressures, and humidity). 

The complex of physical-chemical properties enable to hold out the unsaturated halogen containing block-copolysulfonarilats as warm-, thermo- and fire-proof constructive and membranous materials. The accessibility of the feedstock for receiving monomers on the basis of chloral, and also the manufacturability acceptor-catalytic polycondensation mekes it possible to refer the new halogen containing unsaturated block-copolysulfonarilats to industrialy-perspective polymeric materials. 

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