Polyphosphazene-based membranes

Diffusion coefficients for methanol (concentration range 1.0-5.0 M) in ion-exchange membranes of UV-crosslinked sulfonated poly(bis-3-methoxyphenoxyphosphazene) (134) have been reported to be much smaller than those in Nafion perfluorosulfonic ion-exchange membranes. Application of polyphosphazene-based membranes in methanol-based fuel cells has been reported. ... 

The direct methanol fuel-cell performance of three polyphosphazene-based membrane systems is presented below. The first system deals with blends of PVDF with either sulfonated poly[(3-methylphenoxy)(4-ethylphenoxy)phos-phazene] (SP3MP4EPP) or sulfonated poly[(4-ethylphenoxy)(phenoxy)phos-phazene] (SP4EPPP), where the membranes were prepared by solution casting mixtures with subsequent crosslinking using electron-beam irradiation (60 MRad). The second membrane system was based on UV-photocrossHnked... 

The most well-studied polyphosphazene-based membrane materials for fuel cells are those bearing sulfonic acid groups. They have been synthesized by either a post-sulfonation approach or direct synthesis from the macromolecular precursor, PDCP. 

Carter, R. (2003). Sulfonated polyphosphazene based membranes for use in direct methanol fuel cells. Ph.D. Dissertation. Tulane University, New Orleans, LA. 

Guo, Q., Pintauro, P. N., Tang, H. and O Cormor, S. 1999. Sulfonated and cross-linked polyphosphazene-based proton-exchange membranes. Journal of Membrane Science 154 175-181. 

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. 

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]. 

Guo, Q. et al., Sulfonated and crosslinked polyphosphazene-based proton-exchange membranes, J. Membr. Sci., 154, 175, 1999. 

Q. Guo, P.N. PiNTAURO, H. Tang, S. O Connor, Sulfonated and crosslinked polyphosphazene-based proton-ex-change membranes. Journal of Membrane Science 154 (1999) 175. 

TE scaffolds made from polymers are available in different formats as already mentioned in Section 4.1. Polymeric scaffolds can be based on fibres, foams, membranes and 3D bulk materials, using simple linear polymers or crosslinking these, ending up with elastomeric or even thermoplastic structures. In general, the usage of polyphosphazenes should also allow the realisation of similar concepts. Nevertheless, in the literature only a relatively small number of examples are given for the fabrication of polyphosphazene-based scaffolds for TE [2-27]. 

Membranes with promising properties have been prepared from polyphosp-hazenes in combination with sulfonimide (polyphosphazene-based sulfonimide Chalkova et al., 2002) or with polyacrylonitrile (blended polyphosp-hazene/polyacrylonitrile Carter et al., 2002). Low methanol crossover was also seen with membranes prepared from poly(vinyl alcohol) that contained mordenite (a zeolite variety Libby et al., 2001). Various aspects of the work on composite membranes prepared from different polymers have been discussed in detail in a review by Savadogo (2004). 

Studies of methanol permeation through proton-conducting polyphosphazene membranes show that polyphosphazene-based proton-exchange membranes have low methanol permeability and good proton conductivity [15], These membranes have been tested in the DMFCs and have shown good performance. 

Jankowsky, S., Hiller, M.M., Wiemhoefer, H.D. 2014. Preparation and electrochemical performance of polyphosphazene based salt-in-polymer electrolyte membranes for lithium ion batteries. J. Power Sources 253 256-262. 

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. 

Preliminary results with membranes based on sulfonimide-substituted polyphosphazenes (226) show a good proton conductivity and moderate swelling in water, depending on the degree of cross-linking. ... 

Studies of membranes based on polyphosphazenes, bearing groups other that substituted phenoxy groups, have been continued, in particular to develop materials for specific apphcations. Ion-exchange membranes of cross-linked and non-crosslinked sulfonated [NP(OC6H4Me-3)2]n have been... 

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