Membranes-polyphosphazene

It has been demonstrated that a variety of different polyphosphazenes can be developed as biomaterials, membranes or hydrogels, bioactive polymers, and bioerodible polymers. As with most new areas of polymer chemistry and biomaterials science, molecular design forms the basis of most new advances, but the rate-controlling step is the testing and evaluation of the materials in both in vitro and in vivo environments. This is particularly true for polyphosphazenes where the availability of research quantities only has limited the... 

Allcock, H. R., Gebura, M., Kwon, S., and Neenan, T. X., Amphiphilic polyphosphazenes as membrane materials Influence of side group on radiation crosslinking, semipermeability, and surface morphology. Biomaterials. 19. 500, 1988. 

Wycisk, R. and Pintauro, P. N. 1996. Sulfonated polyphosphazene ion-exchange membranes. Journal of Membrane Science 119 155-160. 

Tang, H., Pintauro, P. N., Guo, Q. and O Connor, S. 1999. Polyphosphazene membranes. ni. Solid-state characterization and properties of sulfonated poly[bis(3-methylphenoxy)phosphazene]. Journal of Applied Polymer Science 71 387-399. 

Developmental carbon and zeolite membrar ies Inorganic membranes produced by anodic oxidation Polyphosphazene membranes... 

Polyphosphazene-based PEMs are potentially attractive materials for both hydrogen/air and direct methanol fuel cells because of their reported chemical and thermal stability and due to the ease of chemically attaching various side chains for ion exchange sites and polymer cross-linking onto the — P=N— polymer backbone. Polyphosphazenes were explored originally for use as elastomers and later as solvent-free solid polymer electrolytes in lithium batteries, and subsequently for proton exchange membranes. 

In another report polyphosphazene copolymers were synthesized from bis (2-methylphenoxy) phosphazene, which was sulfonated after polymerization. Polymers such as polyvinylidene fluoride, polyhexa-fluoropropylene, and polyacrylonitrile were used to produce a blended membrane system. Polymer blends, cross-linking, and other means of re-enforcement are... 

Allcock et al. also have investigated the use of phosphonated polyphosphazenes as potential membrane materials for use in direct methanol fuel cells (Figure A2) Membranes were found to have lEC values between 1.17 and 1.43 mequiv/g and proton conductivities between 10 and 10 S/cm. Methanol diffusion coefficients for these membranes were found to be at least 12 times lower than that for Nafion 117 and 6 times lower than that for a cross-linked sulfonated polyphosphazene membrane. 

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. 

Polyphosphazenes block copolymers containing sulfonimide side groups, (V), were prepared by Allcock et al. (4) and used in membrane blends in fuel cells. 

Passi, P., Zadro, A., Marsilio, E, Lora, S., Caliceti, P., and Veronese, F.M. (2000). Plain and drug loaded polyphosphazene membranes and microspheres in the treatment of rabbit bone defects. J. Materials Science-Materials Med., 11, 643-654. 

A number of liquid crystalline polyphosphazenes with mesogenic side groups have been prepared (48—50). Polymers with nonlinear optical activity have also been reported (51). Polyphosphazene membranes have been examined for gas, liquid, and metal ion separation, and for filtration (52—54). There is interest in phosphazene—organic copolymers, blends, and interpenetrating polymer networks (IPNs) (55—61) to take advantage of some of the special characteristics of phosphazenes such as flame retardance and low temperature flexibility. A large number of organic polymers with cydophosphazene substituents have been made (62). 

Membranes are thin polymeric films that may permit the faster diffusion of some molecules than of others. Thin films of polymers are widely used for the separation of gases and for liquid-phase separations (dialysis). Because of the ease of property tuning, polyphosphazenes are of great interest for these types of applications, although only a few examples have yet been investigated. 

Liquid-phase separations can be carried out with membranes produced from several different classes of polyphosphazenes. An example membrane prepared from [NP(NHC4H9)2] is shown in Figure 3.13. The polymer, [NP(OCH2CF3)2] , can be employed to concentrate alcohols, because the alcohol diffusion rate is much faster than that of water.156... 

Many polyphosphazenes form strong films and membranes when solutions are spread on a flat surface and the solvent is allowed to evaporate. Some of these films have special properties such as resistance to UV radiation, and are thus of interest as coatings for solar cells, aircraft, or space craft. The polymer [NP(OCH2CF3)2] and related mixed-substituent derivatives have been studied from this viewpoint.1... 

The use of synthetic polymers in medicine and biotechnology is a subject of wide interest. Polymers are used in replacement blood vessels, heart valves, blood pumps, dialysis membranes, intraocular lenses, tissue regeneration platforms, surgical sutures, and in a variety of targeted, controlled drug delivery devices. Poly(organosiloxanes) have been used for many years as inert prostheses and heart valves. Biomedical materials based on polyphosphazenes are being considered for nearly all the uses mentioned above. 

Hydrogels and amphiphilic membranes Poly(carbophosphazenes) and poly(thiophosphazenes) New condensation syntheses NLO and high refractive index polymers Microencapsulation of mammalian cells (PCPP) Polyphosphazene polymer blends and IPN s Borazine derivatives Poly(phosphazophosphazenes)... 

Veronese, F. M., Marsillo, F., et al. Polyphosphazene membranes and microspheres in periodontal diseases and implant surgery. Biomaterials 20(l) 91-98, 1999. 

Among the various materials are crosslinked PAN, polyphosphazenes, polyphe-nylenesulfide, polyetheretherketone, and various polymer blends [28-31]. Particularly interesting is the use of zeolites as filler in organic polymers, which aims at improving the performance of (silicone-based) membranes for separations in nonpolar solvents, by adding more cross-links to the membrane material [32, 33]. 

Figure 2 Properties in polyphosphazenes are determined hy (1) the backbone bonds that control the inherent flexibility of the polymer via their influence on bond torsional freedom, and also provide photo-and thermo-oxidative stahihty (2) the side groups control polymer solubility, reactivity, thermal stability, crystallinity, cross-linking, and (indirectly) polymer flexibility (3) free volume between the side groups affects polymer motion, solvent penetration, membrane behavior, and density (4) functional groups (usually introduced hy secondary reactions) affect soluhihty, biological behavior, proton conduction, cross-hnking, and many other properties...

Polyphosphazene has good chemical and thermal stability. Its polyphosphazene backbone is highly flexible. Various side chains can be introduced to this backbone readily. Cross-linking is needed in order to reduce the dimensional changes in the presence of methanol or water. The membranes have shown reasonable proton conductivity and low methanol crossover. However, an improvement in mechanical strength is needed for practical fuel cell applications. 

Wycisk, R., Lee, J.K., and Pintauro, P.N., Sulfonated polyphosphazene-polybenzimid-azole membranes for DMFCs, J. Electrochem. Soc., 152, A892, 2005. 

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