Polymer, uses as membrane

This article focuses on the commercial, ethylene-based ionomers and includes information on industrial uses and manufacture. The fluorinated polymers used as membranes are frequently included in ionomer reviews. Owing to the high concentration of polar groups, these polymers are generally not melt processible and are specially designed for specific membrane uses (see Fluorine compounds, organic—perfluoroalkane sulfonic acids Membrane technology). 

As a rule, permeability in glassy polymers (e.g. cellulose) is lower than in rubbery polymers (e.g. polydimethylsiloxane, PDMS) on the other hand, selectivity is dictated by the molecular dimensions of the permeating species [167]. The polymers used as membranes in analytical pervaporation are similar to those employed for gas separation and possess a dense, non-porous macroscopic structure. The difference between the two lies in the transport mechanism and arises mainly from a large affinity difference between the permeating molecules and the polymer membrane. 

Polybenzimidazole - the polymer used as membrane in the fuel cell is intermixed with neat phosphoric acid... 

The main aim for FCC gasoline desulfurization is to remove thiophenic sulfur compounds. Membranes made from polar polymers with solubility parameter close to thiophenic sulfur are used for desulfurization of gasolines by PV It is evident that solubility parameter of primary sulfur components of gasolines, that is, thiophenic sulfur components, is 19-21 (J/cm )", while for other hydrocarbons, these values are 14-15 (J/cm )". This difference can be exploited for separation by PV. Solubility parameter values of most of the polymers used as membrane material lie in the range of 21-26 (J/cm )". Thus, membranes made from these polymers afford good selectivity for thiophenic sulfur. Apart from various homopolymers, chemically and physically modified polymers have also been used for per-vaporative desulfurization. Some of these modifications include using different types and amounts of cross-linkers, blending two polymers, and copolymerization. Composite and treated ionic membranes have also been tried for this separation. Polymer membranes tried for this separation include PDMS/PAN, PDMS/PEI, PDMS/PES, PDMS/ ceramic, polyetherimine (PI)/polyester, PEG/PES, and PU/PTEE. ... 

R.F. Savinell, M.H. Litt (Case Western University) Proton conducting polymers used as membranes. US Patent 5525436, )un 11, 1996. 

Figure II - 26. Some hydrophobic polymers used as membrane material for micro-filcntion.

The polymers used as membrane materials can be classified as either natural or synthetic. The vast majority of membranes today are made from synthetic polymers however, polysaccharides and rubbers are significant examples of natural membrane materials. A membrane s barrier properties and other significant characteristics are determined by its macromolecular structure. Key factors include the chemical structure of a polymer s chain segments, its chain length (molar mass) and chain flexibility, as well as intra-and inter-molecular interactions. ... 

One of the extensively used synthetic polymers used as a support for immobilization of biocatalysts is polyacrylamide (PAAm) [287,288], The major advantage is that it can be polymerized either chemically or by using radiation. Advantages of y-ray polymerization against chemical polymerization is that the polymerization can be carried out even under frozen conditions thus allowing the matrix to be molded to any form such as beads or membranes [289-291], However one of the major drawbacks of this polymer especially in a membranous form is its brittleness. 

A wide range of polymers has been used as membrane materials including polyacrylonitrile [216, 221-224], polysulfone [219, 225], nylon [218] and dextran... 

Membrane design and fabrication requires more optimization than the synthesis of the right type of polymer. For example, those phosphazene polymers that contained the highest ratios of methylamino groups were too brittle to be used as membranes (because of the high glass-transition temperatures) and too soluble in aqueous media. However, the polymers could be made insoluble in water by radiation cross-linking as shown in reaction (54). 

Hydrophobic polymers also play an important role in pharmacy. When these materials are used as membranes, containers or tubing material, their surfaces may come into contact... 

Most membranes used as supports in Hquid membrane technologies are polymeric in nature, although inorganic membranes have also become available. While many polymers have been examined for use as membrane materials, only a few are widely used. Detailed description of polymeric membranes can be found in reviews [100-106]. 

Lafferty, S.V., Evaluation of Properties of Polymers Used as Controlled Release Membranes, Ph.D. thesis, School of Pharmacy, University of London, 1992. 

In contrast to the LCP results just presented, in glassy polymers used as gas separation membranes, free volume influences diffusion coefficients much more than solubility coefficients. Figure 6 provides an example of this effect. In this figure, the solubility, diffusivity, and permeability of methane in a series of glassy, aromatic, amorphous poly(isophthalamides) [PIPAs] are presented as a function of the fractional free volume in the polymer matrix. (More complete descriptions of the transport properties of this family of materials are available elsewhere (59, 40)). The fractional free volume is manipulated systematically in this family of glassy polymers by synthesizing polymers with different substituent and backbone elements as shown in... 

Although metallic and ceramic materials are used as membranes, polymeric materials account for the vast majority of commercial products. Polymer selection depends on a number of factors including intrinsic transport properties, mechanical properties, thermal stability, chemical stability (e.g., chemical resistance and biocompatibility), membrane manufacturability, cost, and patentability. The two most common types of polymers are glassy engineering thermoplastics and rubbery polysiloxanes. 

The inventors caU this polymer class polymers of intrinsic microporosity (PIMs) , because their porosity arises as a consequence of the molecular structure and is not generated solely through processing. The PIMs can exhibit analogous behavior to that of conventional materials, but, in addition, may be processed into convenient forms for use as membranes [291]. The gas-permeation properties of membranes formed from PIM-1 were investigated at the GKSS... 

For strategy (1), there are only a few examples yet, such as embedding MIP particles in a film, e.g., with a polymer used as glue [4], or creating a flat three-dimensional arrangement of MIP particles, e.g., as a filter cake on a membrane or immobilized between two films, membranes, or frits [5]. Until now this route yielded mainly thick MIP films with low integrity and homogeneity, and thus with poorly defined shape. 

Membranes can be prepared from both ceramic and polymeric materials. Ceramic materials have several advantages over polymeric materials, such as higher chemical and thermal stability. However, the market share of polymeric membranes is far greater than ceramic membranes as the polymeric materials are easier to process and less expensive. A handful of technical polymers are currently used as membrane materials for 95% of all practical applications [2]. Polymeric materials that are used to prepare separation membranes are mostly organic compounds. A number of different techniques are available to prepare synthetic membranes. 

Also, chiral hehcal polymers are used as membranes, electrodes, and for nonlinear optical applications (13JMC2797). 

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