Phase-transfer catalysis polymerizations

A method for the polymerization of polysulfones in nondipolar aprotic solvents has been developed and reported (9,10). The method reUes on phase-transfer catalysis. Polysulfone is made in chlorobenzene as solvent with (2.2.2)cryptand as catalyst (9). Less reactive crown ethers require dichlorobenzene as solvent (10). High molecular weight polyphenylsulfone can also be made by this route in dichlorobenzene however, only low molecular weight PES is achievable by this method. Cross-linked polystyrene-bound (2.2.2)cryptand is found to be effective in these polymerizations which allow simple recovery and reuse of the catalyst. 

Typical systems. A considerable number of immobilized polyether systems have been synthesized both for phase transfer catalysis as just discussed and for use in a number of analytical applications. Such immobilized systems are generally synthesized by either copolymerization of suitably functionalized macrocycles in the presence of cross-linking agents or by appending functionalized macrocycles to existing polymeric substrates. Structures (184)-(186) give examples of different... 

Water is a unique solvent because of its high polarity and ability to form a network of H-bonds. It is immiscible with many organic solvents and is therefore a suitable solvent for use in biphasic reactions in which catalysts are made preferentially soluble in the aqueous phase. Phase transfer catalysis allows the use of aqueous reagents with substrates that have low solubility in water. That water is abundant and totally non-toxic make it the perfect clean solvent, provided that solubility issues can be overcome, and it is in use as a solvent on an industrial scale for polymerization, hydroformylation, and a range of organic chemistry involving PTC. These applications are discussed further in Chapters 7-11. 

Polymeric phosphonium salt-bound carboxylate, benzenesulphinate and phenoxide anions have been used in nucleophilic substitution reactions for the synthesis of carboxylic acid esters, sulphones and C/O alkylation of phenols from alkyl halides. The polymeric reagent seems to increase the nucleophilicity of the anions376 and the yields are higher than those for corresponding polymer phase-transfer catalysis (reaction 273). 

Ditelluracyclohexane 77 was obtained in low yield (11%) by coupling 1,4-diiodobutane with Na2Te2 in DMF [88JOM(338)9]. When the phase-transfer catalysis technique was applied and the reaction was carried out in H20-benzene the yield of 77 was slightly increased to 15%. Along with 77, the polymeric compound [(CH2)4Te] was formed in a substantial amount. 

Peroxidic initiators, like dibenzoyl peroxide, are too reactive with phenolic and aminic moieties and can be applied only exceptionally [50], Inorganic peroxides, like potassium persulfate, were used for emulsion polymerization of functionalized monomers [51]. Phase transfer catalysis may be also applied using persulfate initiation. To circumvent problems with the peroxide initiation, 4,4 -azobis(4-cyanovaleric acid), a water soluble initiator, was successfully used [48]. 

The preparation of mono- and diadducts 5 and 6, respectively, of dibromocarbene with cyclo-hexa-1,4-diene is described. The synthesis of the diadduct encounters difficulties in its isolation, due to the formation of an emulsion and polymeric products. Such problems occur occasionally if an alkene is allowed to react with bromoform under phase-transfer catalysis conditions. 

Examples of phase transfer catalysis include hydrolysis, condensation, oxidation, and polymerization ". There are many industrial applications. 

Cheng, T. C., Anionic Polymerization IX. A Review of the Use of Crown Ether as a Modifier in the Anionic Polymerization and Copolymeiization of Diene, Crown Ethers and Phase Transfer Catalysis in Polymer Science, L. J. Mathias and C. E. Carraher, Jr., eds., Plenum Press, New York, p. 155 (1984). 

Tagle, L. H, F. R. Diaz, and R. Fuenzalida, Polymerization hy Phase Transfer Catalysis. 18. Polycarbonates and Polythiocarbonates from Chlorinated Diphenols, J. M. S.-Pure Appl. Chem, A31, 283 (1994). 

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