Polymer superacid

Sulfonated styrene—divinylbensene cross-linked polymers have been appHed in many of the previously mentioned reactions and also in the acylation of thiophene with acetic anhydride and acetyl chloride (209). Resins of this type (Dowex 50, Amherljte IR-112, and Permutit Q) are particularly effective catalysts in the alkylation of phenols with olefins (such as propylene, isobutylene, diisobutylene), alkyl haUdes, and alcohols (210) (see Ion exchange). Superacids. 

Fluorinated polymers, especially polytetrafluoroethylene (PTFE) and copolymers of tetrafluoroethylene (TFE) with hexafluoropropylene (HFP) and perfluorinated alkyl vinyl ethers (PFAVE) as well as other fluorine-containing polymers are well known as materials with unique inertness. However, fluorinated polymers with functional groups are of much more interest because they combine the merits of pefluorinated materials and functional polymers (the terms functional monomer/ polymer will be used in this chapter to mean monomer/polymer containing functional groups, respectively). Such materials can be used, e.g., as ion exchange membranes for chlorine-alkali and fuel cells, gas separation membranes, solid polymeric superacid catalysts and polymeric reagents for various organic reactions, and chemical sensors. Of course, fully fluorinated materials are exceptionally inert, but at the same time are the most complicated to produce. 

Chemisorphon of the complexes [Cp MR2], [Cp MR3] or [MR4] (Cp = Cp, Cp M = Zr, Ti, Th R = Me, CH2 Bu, CH2TMS) onto superacidic sulfated zirconia (ZRS , where x refers to activation temperature) [81, 91] and sulfated y-alumina (AIS) [90] afforded active benzene hydrogenation catalysts and ethylene polymer-izahon catalysts. The most active catalyst system for the hydrogenation of benzene (arene Zr = 1.5 1, 25 °C, no solvent, 0.1 MPa H2) was [Cp ZrMe2] -ZRS400, which achieved a TOP of 970 h. The activity of this adsorbate catalyst rivals or exceeds those of the most active heterogeneous arene hydrogenahon catalysts known. The... 

Title Monomers Comprising Superacidic Groups, and Polymers Therefrom... 

Observations Polymer compositions containing superacidic functional groups were pre-... 

Friedel-Crafts aromatic substitution reactions have been widely explored in polymer chemistry [29,30] and generally proceed with Lewis acids such as AICI3 with elimination of hydrogen halides. In superacid solutions, however, the Friedel-Crafts reactions take place with dehydration from the oxygen of the carbonyl group and the proton of aromatics. The reactivity of the pro-tonated carbonyl group in the superacid can be further increased by the... 

The most important use of /3-sultones is for the preparation of fluorinated polymers such as Nafion 64. These solid acid catalysts containing perfluorinated sulfonic acid groups have been known for many years and the presence of the electron-withdrawing F atoms increases the acid strength of the terminal sulfonic acid groups, which become comparable to that of pure sulfuric acid. Prior to the last decade, Nafion had been in use as a superacid, a fuel cell electrolyte and as a membrane-ion separator <1996CHEC-II(1B)1083>. 

In a recent paper Saegusa and his co-workers (64) report that ethylene oxide is converted to dioxane in yields of up to 96% when the monomer is treated with a catalytic amount (generally 2—5 mol %) of a superacid such as trifluoromethanesul-fonic acid, or a derivative of a superacid such as ethylfluorosulfonate, in methylene chloride or nitromethane at temperatures between 10 and 40 °C. The authors propose that dioxane is formed by a simultaneous polymerization and degradation of the formed polymer. Propagation as well as degradation are assumed to occur via the ester species. 

Recently, various kinds of solid superacids have been developed. The first group is metal oxides and mixed oxides containing a small amount of sulfate ion, and those modified with platinum. The second group is metal oxides, mixed oxides, graphite, metal salts, etc. treated or combined with antimony fluoride or aluminum chloride. The third group is perfluorinated polymer sulfuric acid (Nafion-H). The fourth and fifth groups are H-ZSM-5 and a type of heteropolyacids, respectively. The last group is simply mixed oxides. 

Iodine readily reacts with polymers bound to coordination centres, yielding macromolecules containing iodide end groups. The C—I bond can react with silver salts of superacids yielding carbocations essentially in the sense of the last steps of eqn. (32). Doi et al. [251, 252] have used this reaction for the synthesis of the copolymer poly(propene)-Mocfc-poly(tetramethylene oxide) with blocks of syndiotactic polypropylene. 

The solvent and ion exchange sites in "Nafion" perfluori-nated membranes phase separate from the fluorocarbon matrix to form clusters (1-5). This ionic clustering will not only affect the mechanical properties of the polymer (JL), but should also have a direct effect on the transport properties across these membranes (2). In addition the exchange sites in the resin are strongly acidic and the polymer is extremely hydrophilic. Combined with the polymer s exceptional thermal and chemical stability, these properties make "Nafion" membranes particularly suitable for a variety of applications. These include applications as membrane separators in several electrochemical processes (6-9), as a superacid catalyst in organic syntheses (10-12), and as a membrane electrode (13). 

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