Vinyl alcohol, polymeric, membranes

In the suspension polymerization of PVC, droplets of monomer 30—150 p.m in diameter are dispersed in water by agitation. A thin membrane is formed at the water—monomer interface by dispersants such as poly(vinyl alcohol) or methyl cellulose. This membrane, isolated by dissolving the PVC in tetrahydrofuran and measured at 0.01—0.02-p.m thick, has been found to be a graft copolymer of polyvinyl chloride and poly(vinyl alcohol) (4,5). Early in the polymerization, particles of PVC deposit onto the membrane from both the monomer and the water sides, forming a skin 0.5—5-p.m thick that can be observed on grains sectioned after polymerization (4,6). Primary particles, 1 p.m in diameter, deposit onto the membrane from the monomer side (Pig. 1), whereas water-phase polymer, 0.1 p.m in diameter, deposits onto the skin from the water side of the membrane (Pig. 2) (4). These domain-sized water-phase particles may be one source of the observed domain stmcture (7). 

Polymeric pH indicators, phenolphthalein-formaldehyde (PPF) and o-cresolphthalein-formaldehyde (CPF) were synthesized with phenolphthalein and o-cresolphthalein reacted by formaldehyde under alkaline conditions, respectively. They can be immobilized in hydrolyzed cellulose diacetate membranes (HCDA) mainly due to macromolecular entrapment, and can be covalently bound to poly(vinyl alcohol) (PVA) via the considerable newly produced hydroxylmethyl groups [168,169], Phenol red (phenolsulfonphthalein) and its derivatives are commonly used for pH determination. 

The purple membrane is harvested semiindustrially from halobacteria mutants which are bred in fermenters. The BR is then embedded into a polymeric matrix of poly(vinyl alcohol) or polyacrylamide. The BR films manufactured in this way are used for different applications, preferably in holography, for example, as a reversible transient data storage system for optical information processing (159). Another example is real-time interferometry by using the property of BR films to integrate over time (160). BR has been proposed also as a two-photon memory material because of its unusually large two-photon cross section. 

Johnson et al. reported adhesion studies of some polymeric matrix membrane by using PVC, Urushi and copolymer (vinylchloride/vinyl alcohol copolymer matrix membrane with treatment of tetrachlorosilane) by using an ultrasonic bath (10). They also reported the use of Urushi gives improved adhesion lasting over 5 hours and that in some cases the membrane lasted for over 20 hours. The stability of the Urushi matrix ISFETs was discussed in detail elsewhere (6). 

Zou, J. and Ho, W.S.W. C02-selective polymeric membranes containing amines in crosslinked poly(vinyl alcohol). Journal of Membrane Science, 2006, 286, 310. 

Impregnation and polymerization of vinyl monomers in polymeric films. Vinyl monomers swell some kinds of polymer films styrene and divinylbenzenes swell poly(vinyl chloride) films substantially. After a polymer film such as poly(vinyl chloride) or polyethylene has been swollen in a vinyl monomer mixture containing a radical initiator, the film is covered with another film that does not swell with the vinyl monomers, e.g. cellulose film, poly(vinyl alcohol) film, and heated to polymerize the monomers in the film. Ion exchange groups are introduced into the resulting precursor membrane, for example by sulfonation, chloromethylation... 

Reports are also available on CO2 selective membrane reactors for WGS reaction. Zou et al. [40] first time synthesized polymeric C02-selective membrane by incorporating fixed and mobile carriers in cross-linked poly vinyl alcohol. Micro-porous Teflon was used as support. They used Cu0/Zn0/Al203 catalyst for low temperature WGS reaction. They investigated the effect of water content on the CO2 selectivity and CO2/H2 selectivity. As the water concentration in the sweep gas increased, both CO2 permeability and CO2/H2 selectivity increased significantly. Figure 6.18 shows the influence of temperature on CO2 permeability and CO2/H2 selectivity. Both CO2 permeability and CO2/ H2 selectivity decrease with increasing reactimi temperature. After the catalyst activation, the synthesis gas feed containing 1% CO, 17% CO2, 45% H2 and 37% N2 was pumped into the membrane reactor. They are able to achieve almost 100% CO conversion. They also developed a one-dimensional non-isothermal model to simulate the simultaneous reaction and transport process and verified the model experimentally under an isothermal condition. 

Zhang et al. [39] studied composite NT membranes prepared by interfadal polymerization of piperazine and trimesoyl chloride and coated with poly(vinyl alcohol) (PVA). ATM showed that the coating was effective in membrane surface smoothing. Even though no data was shown, they argue that the increase in hydrophilicity and smoothness of the membrane surface may lead to reduction of surface fouling based on the previous findings [8]. 

In the search for PEMs with lower alcohol permeability than Nafion and other perfuorinated membranes, without degradation of the proton conductivity, a number of new polymeric membranes were synthetized and characterized, such as sulfonated polyimides, poly(arylene ether)s, polysulfones, poly(vinyl alcohol), polystyrenes, and acid-doped polybenzimidazoles. A comprehensive discussion of the properties of these alternative membranes is given in Chap. 6, along with those of Nafion and Nafion composites. 

Lee, Y.M. and J.H. Kim, Controlled release of insulin through crosslinked poly(vinyl alcohol)/chitosan blend membrane. Proceedings of. CS Division of Polymeric Matetials Science and Engineering, 70 (1994), 322-323. 

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