Phosphonic polymers

Higher pH chromate programs (pH 7.0 to 9.0), using chromate (3 to 15 ppm) with P04 (3 to 6 ppm) and/or Zn (0.5 to 2.5 ppm). Phosphonate/polymer support is required, the selection of which permits progressively lower chrome levels and higher cooling water pH. 

Ebdon, J. R Hunt, B. J., Joseph, P Konkel, C. S Price,D Pyrah, K Hull,T. R Milnes, G. J., Hill, S.B Lindsay, C. I., McCluskey, J., and Robinson, I., Thermal degradation and flame retardance in copolymers of methyl methacrylate with diethyl(methacryloyloxymethyl)phosphonate, Polym. Degrad. Stab., 2000, 70, 425 136. 

Phosphonates have also been prepared from alcohols and (Ar0)2P(=0)Cl, NEts and a TiCl4 catalyst. ° The reaction of (R0)2P(=0)H and aryl iodides with a Cul catalyst leads to aryl phosphonates. " Polymer-bound phosphonate esters have been used for olefination. Dienes are produced when allylic phosphonate esters react with aldehydes. 

Ajellal, N., Thomas, C.M., Carpentier, J.F., 2008. Controlled radical polymerization of conjugated 1,3-dienes with methyl 1,3-butadiene-l-phosphonate. Polymer 49 (20), 4344-4349. 

Phosphonated polymers have been proposed for fuel cells with the expectation of being thermally more stable and better retaining water than sulfonic groups [210, 211]. Phosphonated poly(phenylene oxide) [212], poly(4-phenoxy-benzoyl-l,4-phenylene) [213] and polysulfones [214, 215] have been reported. Phosphonated fluoromonomers were polymerized [164]. Characterization of phosphonated films in terms of their proton conductivity has been reported for some of the phosphonated polymers polyphosphazene [216], trifluoropolysty-rene [217], poly(4-phenoxybenzoyl-l,4-phenylene) [218]. Relatively low conductivity values were reported for most of the polymers prepared up to now. The values for polyphosphazene [216] and for perfluorocarbon polymers [219] were quite encouraging. Phosphonated poly(phenylene oxide) [211] was evaluated in fuel cell-tests. 

The phosphonate polymer was prepared via a neutral precursor polymer, which was soluble in organic solvents, enabling the material to be characterised by NMR and GPC. Sonogashira polymerisation of phosphonate monomer and 1,4-diethynylbenzene afforded neutral polymer in a 46% yield. Analysis of the neutral precursor polymer indicated Mw = 18.3 Kd and poly-dispersity 2,9. 

Finally, Chapter 13 by Jannasch and Bingol deals with proton conducting phosphonated polymers and membranes for fuel cells. Polymers functionalized with phosphonic acids enable both intrinsic and water-assisted proton conductivity and are thus attractive for use as electrolyte materials in electrochemical devices. 

The invention of Heath et al. relates to novel phosphonate allyl monomers, made from reaction of an unsaturated oxirane with amine- or hy-drojyl-functionalized phosphonic acids (Scheme 3.21). These monomers were copolymerized with other unsaturated species (acrylic acid, maleic acid, acrylamide, or monomer derivatives of sulfonic acid, etc), yielding phosphonate polymers or oligomers. Phosphorus-containing monomers were incorporated at a ratio of 0.1-30% and polymerized in aqueous media. The final polymers had a molecular weight of 800-30 000 g mol . With their phosphonic acids groups (free acid or salts forms), they are of particular use as oilfield scale inhibitors. 

Commercial anticorrosion phosphonated polymer compounds are generally formed from Sipomer or Phosmer monomers, which are phosphate-type (meth)actylates and can be readily polymerized via emulsion or solution. Polymers with some phosphonate functionality have long been established as excellent adhesives and anticorrosion compounds however, there has been very little investigation into the use of phosphonate-type methacrylates for the same purpose. 

Proton Conducting Phosphonated Polymers and Membranes for Fuel Cells... 

Similar to phosphoric acid, phosphonic acids are intrinsically proton conductive. However, phosphonic acids can he covalently attached to polymers in order to prevent leaching. Comparative studies of sulfonic acid, imidazole, and phosphonic acid functionalized model eompounds have indicated that phosphonie acids possess attractive features for applications in high-temperature PEMFCs. This has spawned extensive research in recent years to prepare and study phosphonated polymers as proton conductors under low humidity eonditions. ... 

Molecular Design of Phosphonated Polymers for Proton Conducting Membranes... 

Table 13.1 Proton conductivity of selected phosphonated polymers and PEMs.

Phosphonated polymers with fluorinated backbones have been obtained by reacting fluorinated poly(atylene ether)s with a H-phosphonate diester in the presence of Pd(PPh3)4 (Scheme 13.3d). Using fluorinated aromatic polymers as the backbone can be expected to improve the dimensional stability of the membranes compared to aromatic polymers with hydrocarbon backbones because of the increased hydrophobicity induced by the presence of the fluorocarbon. The phosphonated polymers with fluorinated aromatic backbones reached a conductivity of 6 mS cm at 95% RH at 80 °C and 2.6 mS cm in water at room temperature, which was below that of Nafion 117. 

Roualdes and co-workers have prepared phosphonated polymers by synthesizing fluorinated polymers via radical polymerization of fluorinated al-kenes such as chlorotrifluoroethylene and vinyl ethers such as 2-chloroethyl vinyl ether, followed by phosphonation via the Arbuzov reaction. The resulting polymers depicted in Scheme 13.3c had a phosphonic acid content ranging from 18 to 47 mol%. The level of conductivity was found to be in the range 0.02-20 mS cm, which was comparable with Nafion 115 at about 50 mS cm at 25 °C and 95% RH. 

B. Lafitte and P. Jannasch, On the prospects for phosphonated polymers as proton-exchange fuel cell membranes, in Advances in Fuel Cells, ed. T. S. Zhao, K. D. Kreuer, and T. Van Nguyen, Elsevier, Oxford, 2007, vol. 1, p. 119. 

Lafitte B and Jannasch P (2007), On the prospects for phosphonated polymers as proton-exchange fuel cell membranes , Fuel Cells, 1,119-185. 

The success of widening the operating temperature for water-based proton conduction system has so far not been matched in the field of intrinsically dry proton conductors. Although interesting developments were reported in the field of polymers having tethered imidazole groups [31-34], these and other approaches based on phosphonated polymers, either in their pure form or as acid-base copolymers or blends, show conductivity values, which are at least an order of magnitude too low [34—36]. 

In the following, those publications dealing with synthesis and characterization of intermediate-T blend membranes from PBI basic polymers and sulfonated or phosphonated polymers utilized as acidic macromolecular cross-linkers in the blends are discussed. In Fig. 4.4, those polybenzimidazoles along... 

Apart from sulfonated polymers, it could recently be shown that phosphonated polymers can also be used advantageously as macromolecular ionical cross-linkers for PBI blend membranes poly(tetrafluorostyrene-4-phosphonic acid) (PWN2010, Sll, Fig. 4.5) was synthesized via nucleophilic aromatic... 

The phosphonated polymer was then mixed with PBIOO (B4, Fig. 4.4) in a molar relation imidazole/P03H2 groups = 3/7... 

In [74], completely phosphoric acid-free inter-mediate-T membranes and MEAs from 1/1 (mole imidazole/mole PO3H2) blend membranes of the PBI B5 (Fig. 4.4) and the phosphonated polymer polyvinyl phosphonic acid (PVPA) S12 (Fig. 4.5) were presented and compared to PA-doped membranes and MEAs. In the MEAs, a Pt electrocatalyst was deposited onto multiwaUed carbon nanotubes (MWNT) which have previously been coated with B5. This technique has previously been used for the preparation of electrocatalysts for anion-exchange membrane fuel cells [75]. In the final step, the MWNTs were coated with a layer of S12. It turned out that these membranes and MEAs possessed much higher durabilities than membranes and MEAs which have been doped with PA, therefore opening leeway for long-lasting intermediate-T fuel cell membranes without the PA leaching problems which are always present in PA-doped intermediate-T membranes and MEAs [76]. 

Sll, Fig. 4.5) are depicted along with B2. Again, all TGAs indicate excellent and similar thermal stabilities of all membranes up to 300 °C. Therefore, it can be concluded that both sulfonated and phosphonated polymers can be selected as acidic cross-linkers for polybenzimidazole membranes. 

The use of a phosphonated polymer as ionical cross-linker AND proton conductor both in the membrane and the electrodes of intermediate-T MEAs opens perspectives for highly durable intermediate-T fuel cell membranes without PA leaching problems which are always present in PA-doped intermediate-T membranes and MEAs. 

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