Synthesis of Sulfonated Polyphosphazenes

24 Synthesis of sulfonated polyphosphazenes hy (a) direct suhstitution of PDCP with a protected sulfonic acid nucleophile and (h) postsulfonation using concentrated sulfuric acid. 

25 Direct synthesis of suifonated polyphosphazene using disodium salts of 2-hydroxyethanesulfonic acid and 2-(2-methoxyethoxy)ethanol. 

26 Sulfonation scheme used by Pintauro and co workers for sulfonation of various poly [(aryloxy)phosphazene]s [347-351]. 

Tang et al. [349] and Guo et al. [350] found that sulfonated poly[bis(3-methyl-phenoxy)phosphazene] (denoted as sPB3MPP) (Fig. 3.27b) offered an attractive combination of good proton conductivity, cross-linkability, and low methanol permeability, feamres especially important for direct methanol fuel cell membranes. UV-cross-linked membranes prepared from sPB3MPP with an lEC of 1.4 mmol/g exhibited a methanol diffusion coefficient on the order of 1.0 x 10 cm /s, which was 

27 Example structures of pol3fphosphazene sulfonic acids (a) sulfonated poly[(meth-ylphenoxy)(phenoxy)phosphazene], (b) sulfonated poly[bis(3-methylphenoxy)(phenoxy) phosphazene], (c) sulfonated poly[bis(phenoxy)phosphazene], and (d) sulfonated poly[bis (2-phenoxyethoxy)phosphazene]. 

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FIGURE 7.19 Direct synthesis of sulfonated polyphosphazene with disodium salt of 2-hydroxyethanesulfonic acid. (Reprinted with permission from Ganapathiappan, S., Chen, K., and Shriver, D.F., A new class of cation conductors Polyphosphazene sulfonates. Macromolecules, 21, 2299. Copyright 1988 American Chemical Society.)... 

FIGURE 7.20 Direct synthesis of sulfonated polyphosphazenes using the noncovalent protection method. (Reprinted with permission from Andrianov, A.K., Marin, A., Chen, J., Sargent, J., and Corbett, N., Novel route to sulfonated polyphosphazenes Single-step synthesis using noncovalent protection of sulfonic acid functionality. Macromolecules, 37, 4075. Copyright 2004 American Chemical Society.)... 

A. K. Rianov, a. Marin, ). Chen,. Sargent, N. Corbett, Novel Route to Sulfonated Polyphosphazenes Single-Step Synthesis Using Noncovalent ProtectionT of Sulfonic Acid Enmctional-ity. Macromolecules 37 (2004) 4075-4080. 

For a polyphosphazene to be used as the membrane material in a fuel cell, it must possess some kind of protogenic functionality, to allow the polymer to conduct protons. The most widely used protogenic group is the sulfonic acid moiety which can be incorporated into the macromolecular chain either at the polymer synthesis step (Fig. 4a) or later, during postsulfonation (Fig. 4b). While the postsulfonation reaction is generally easier to carry out, it is the direct synthesis of the functionahzed polyphosphazene that should give better control over the final material properties and minimize imwanted side... 

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