Hydrophobic poly fiber

The electrochemical oxidation of phenols produces quinones that can be used as dienophiles for the Diels-Alder reaction. A typical example is shown in Scheme 14, where a lithium perchlorate/nitromethane system and an electrode coated with a PTFE [poly-(tetrafluoroethylene)] fiber, to create a hydrophobic reaction layer. 

Doherty [4] prepared water compatible hydrophobic polymers such as poly (acrylamide-co-t-octylacrylamide), (11), that were used as components in cellulosic fiber compositions. 

Gitsov et al 10) produced a nanoreactor fi om laccase and linear poly(ethylene oxide)-dendritic poly(benzyl ether) diblock copolymers. A notable feature of this system is the presence of hydrophobic dendritic pockets that increase the local concentration of water-insoluble organic compounds near the active site where they are oxidized. Li and Hsieh (77) employed a hydrogel fiber membrane, with a large surface area and improved organic solvent solubility in order to facilitate lipase reactions. He (72) grafted lipase onto silica particles, which permitted him to carry out synthesis of polyesters, polycarbonates, polyphosphates, and their copolymers at temperatures up to 150°C. 

Another way to obtain the desired dense-coagulated fiber structure is to add an ionic comonomer to the chain. Terada [269] has used mercury porosimetry to follow the change in the microvoid size distribution that occurs when comonomers of differing polarity and ionic structure are added to PAN. When hydrophobic comonomers such as methyl acrylate (MA) are used, the peak of the pore size distribution is shifted in the direction of increased size. However, ionic comonomers such as SSS or sodium allyl sulfonate (SAS) shift the peak in the direction of decreased size. With a three-component composition containing both the hydro-phobic and ionic comonomers, as in poly(AN-MA-SAS), the distribution has both characteristics. Examples of void size distributions are shown in Figure 12.27. The 5% MA comonomer has a fairly sharp peak near 850 A and the maximum size is extended to 200 A. Moreover, there is only a slight proportion of pores with small sizes present. 

Membrane contactors can be made out of flat sheet membranes, which have some commercial applications. However, the most common commercial membrane contactors are made from small-diameter microporous hollow-fiber (or capillary) membranes with fine pores that run from the inner surface to the outer surface of the hollow-fiber wall. The contactor resembles a tube-in-shell configuration with inlet-outlet ports for the shell side and tube side. These kinds of membranes are typically made of hydrophobic materials such as polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), poly(tetrafluoroethylene-co-perfluorovinylether) (PEA), or polyvinylidene fluoride (PVDE). The membrane in a contactor acts as a passive barrier and as a means of bringing two immiscible fluid phases, such as gas and liquid or an aqueous liquid and an organic liquid, into contact with each other... 

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