Membrane forming polymers

Composite MIP membranes can also be obtained by incorporation of MIP particles into the membrane polymer matrix by mixing the particles in an appropriate solvent with the membrane-forming polymer that is then solidified by the phase inversion process. Membranes thus prepared were used for separation, with targets such as tetracycline [257], theophylline [255], methylphosphonic acid [258], bisphenol [259], indole derivatives [260], propanolol [261], luteolin [262] and norfloxacin... 

Semipermeable membrane-forming polymers for osmotic pumps... 

Additional semipermeable membrane—forming polymers are selected from the group consisting of acetaldehyde dimethyl cellulose acetate, cellulose acetate ethyl carbamate, cellulose dimethylamino acetate, semipermeable polyamides, semipermeable polyurethanes, or semipermeable sulfonated polystyrenes. Semipermeable cross-linked selectively permeable polymers formed by coprecipitation of a polyanion and a polycation also can be used for this purpose.22 23 Other polymer materials such as lightly cross-linked polystyrene derivatives, semipermeable cross-linked poly(sodium styrene sulfonate), and semipermeable poly (vinylbenzyltrimethyl ammonium chloride) may be considered.24,25... 

But of prime importance with regard to the final separation process is the nature of the membrane-forming polymer its hydrophihdty, charge density, polymer structure and molecular weight Typical polymers used in this phase-separation process are cellulose esters (most commonly CA), polyamides, poly(amide-hydra-zides), polyimides, (sulfonated) polysulfones, poly(phenylene oxide) and (sulfona-ted) poly(phthalazine ether sulfone ketone). 

Surface modification is a valuable tool for the design of appropriate membrane, as the interfacial characteristics required can rarely be achieved by bulk modification of the membrane-forming polymer without complications during membrane fabrication (He et al. 2009). Surface modification methods have been employed by the membrane manufacturers to produce hydrophilic, low-binding membranes (Peinemann and Nunes 2008) with improved membrane performances and properties (Pandey and Chauhan 2001 Robeson 1999). These methods include UV... 

An HEM is a membrane-form polymer electrolyte capable of conducting hydroxide anions (OH ), and an HEI is a binder-form polymer electrolyte capable of not only conducting hydroxide anions but also creating triple-phase boundary in the electrode catalyst layer. HEMs and HEIs are already used in hydroxide exchange membrane fuel cells (HEMFCs) and can also be used in many other electrochemical energy conservation and storage devices. 

Another version of the urea electrode (Figure 11.17) immobilizes the enzyme in a polymer membrane formed directly on the tip of a glass pH electrode. In this case, the electrode s response is... 

Ceramic, Metal, and Liquid Membranes. The discussion so far implies that membrane materials are organic polymers and, in fact, the vast majority of membranes used commercially are polymer based. However, interest in membranes formed from less conventional materials has increased. Ceramic membranes, a special class of microporous membranes, are being used in ultrafHtration and microfiltration appHcations, for which solvent resistance and thermal stabHity are required. Dense metal membranes, particularly palladium membranes, are being considered for the separation of hydrogen from gas mixtures, and supported or emulsified Hquid films are being developed for coupled and facHitated transport processes. 

Phase Inversion (Solution Precipitation). Phase inversion, also known as solution precipitation or polymer precipitation, is the most important asymmetric membrane preparation method. In this process, a clear polymer solution is precipitated into two phases a soHd polymer-rich phase that forms the matrix of the membrane, and a Hquid polymer-poor phase that forms the membrane pores. If precipitation is rapid, the pore-forming Hquid droplets tend to be small and the membranes formed are markedly asymmetric. If precipitation is slow, the pore-forming Hquid droplets tend to agglomerate while the casting solution is stiU fluid, so that the final pores are relatively large and the membrane stmcture is more symmetrical. Polymer precipitation from a solution can be achieved in several ways, such as cooling, solvent evaporation, precipitation by immersion in water, or imbibition of... 

Fig. 6. Proton-driven transport of alkali metal ions through a membrane formed from 12-crown-4 polymer (43 n = 1) (crown ether content of about 30%). M+], and (M+fc refer to metal ion concentrations at time - i and 0, respectively. (Cited from Ref.471)...

Membranes UF membranes consist primarily of polymeric structures (polyethersulfone, regenerated cellulose, polysulfone, polyamide, polyacrylonitrile, or various fluoropolymers) formed by immersion casting on a web or as a composite on a MF membrane. Hydrophobic polymers are surface-modified to render them hydrophilic and thereby reduce fouling, reduce product losses, and increase flux [Cabasso in Vltrafiltration Membranes and Applications, Cooper (ed.). Plenum Press, New York, 1980]. Some inorganic UF membranes (alumina, glass, zirconia) are available but only find use in corrosive applications due to their high cost. 

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. 

An ideal bioadhesive should be nontoxic, nonabsorbable, and nonirritating to the mucus membrane, form a strong noncovalent bond with the mucin-epithelial cell surfaces, allow easy incorporation of drug and should not offer hindrance to drug release, and should not decompose on storage or during the shelf-life of the dosage form. Some of the other desirable characteristics of the polymer have been discussed under bioadhesion. 

If the organic solution of diacid chloride is recast as a dispersed phase in an emulsion with the aqueous solution of diamine as the continuous phase, the polymer membrane forms around the dispersed phase droplets, effectively making polyamide shell capsules around the organic phase. Of course, the relative volumes could be reversed so that the aqueous phase was encapsulated if so desired. 

Still higher total conductivities are achievable in a special class of hydrogen-ion (proton)-conducting polymers. These polymers are particularly useful for fuel-cell and chlor-alkaU processing applications in which the efficient transfer of protons is critical. These polymers are of produced in membrane form and are therefore referred to as proton-exchange membranes (PEM). 

Some of the most useful polyphosphazenes are fluoroalkoxy derivatives and amorphous copolymers (11.27) that are practicable as flame-retardant, hydrocarbon solvent- and oil-resistant elastomers, which have found aerospace and automotive applications. Polymers such as the amorphous comb polymer poly[bis(methoxyethoxyethoxy)phosphazene] (11.28) weakly coordinate Li " ions and are of substantial interest as components of polymeric electrolytes in battery technology. Polyphosphazenes are also of interest as biomedical materials and bioinert, bioactive, membrane-forming and bioerodable materials and hydrogels have been prepared. 

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