Poly phenylene Ether s

To this type of reaction belongs the synthesis of poly(phenylene ether)s from substituted phenols, for example, poly(2,6-dimethylphenylene ether), PPE, from 2,6-dimethylphenol in the presence of pyridine and copper(I) chloride  

The phenol must be relatively easily oxidizable substituents that raise the oxidation potential lead to an inhibition of the dehydrogenation reaction (2,6-dichlorophenol gives only a low-molecular-weight polymer and 2,6-dinitro-phenol does not react at all). 

The substituents in the 2- and 6-positions must not exceed a certain geometrical size. Otherwise, instead of regular -0-C- coupling leading to the po-ly(phenylene ether)s, there is simply a -C-C- coupling of the monomers to form diphenylquinones. This reaction is favored by higher temperatures. The pale-yellow coloration of poly(-2,6-dimethyl-l,4-phenylene ether) may be caused by the presence of quinones. 

Suitable catalysts are copper(I) salts [e.g., Cu(I) chloride, bromide, and sulfate] in combination with amines to form oxidation sensitive phenolates. The amine/copper salt ratio must be made as large as possible, to minimize the formation of diphenylquinone and to give a high molecular weight. 

Safety precautions Before this experiment is carried out. Sect. 2.2.5 must be read as well as the material safety data sheets (MSDS) for all chemicals and products used. 

Poly(2,6-dimethylphenylene ether) can be prepared by dehydrogenation of 2,6-dimethylphenol with oxygen in the presence of copper(l) chloride/pyridine as catalyst at room temperature. It is known that the mechanism involves a stepwise reaction, probably proceeding via a copper phenolate complex that is then dehydrogenated. 

Poly(2,6-dimethylphenylene ether) is amorphous and has a glass transition temperature of about 170°C. It is soluble in chlorinated hydrocarbons such as chloroform, carbon tetrachloride, as well as tetrachloroethane, and also in nitrobenzene and toluene. It is mainly used as a homogeneous blend with polystyrene (see Sect. 5.5). 

Around 1956, the oxidative coupling of 2,6 substituted phenols to yield high molecular products was discovered. Poly(phenylene ether) (PPE), also addressed as poly(phenylene oxide), was commercialized in 1964 by General Electric and AKZO, and eventually by several other companies. Remarkably, the oxidative coupling of phenols plays a role in certain biological reactions, e.g., in the formation of lignin or melamine.  

6- Dimethylphenol is also addressed as 2,6-xylenol. T)q)ical industrial processes for preparing 2,6-dimethylphenol involve the reaction of phenol and methanol in the presence of a metal oxide catalyst. The major byproduct of this reaction is 2,4,6-trimethylphenol. 2,4,6-Trimethylphenol is then dealkylated into 2,6-dimethylphenol. The process can run via  

For the selective alkylation to the -position of phenol, with methanol, catalysts based on ammonium metavanadate NH4VO3 and ferric nitrate Fe(N03)3 X 9H2O have been suggested. In this process a raw product of 2,6-dimethylphenol of 64% yield is recovered. Phenol and o-cresol are recycled in this process, as starting materials. 

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The incorporation of SO2 groups into the main chain of poly(phenylene ether)s leads to poly(phenylene ether sulfone)s. The preferential synthetic routes are ... 

Bromo-4, 4 -dlhydroxytrl phenyl methane Figure 4.1 Monomers Used for Poly(phenylene ether)s... 

Figure 4.1 Monomers used for poly(phenylene ether)s.

Poly(phenylene ether) s with pendant perfluoroalkyl sulfonic acids with an ion exchange capacity of 1.17-1.83 equivalents/g have been synthesized by an aromatic nucleophilic substitution reaction of a perfluo-romonomer, such as decafluorobiphenyl or hexafluo-robenzene with 2,5-bis(4 -iodophenyl)hydroquinone, followed by a Ullman coupling reaction with potassium 1,1,2,2-tetrafluoro-2-(l, 1,2,2-tetrafluoro-2-iodoethoxy)ethanesulfonate [100]. 

Poly(phenylene ether)s with sulfonic acid groups via long alkyl side chains have been prepared [101]. 

From these monomers, poly(phenylene ether)s can be formed by the aromatic nucleophilic substitution polycondensation with dihydroxy-monomers in the presence of potassium carbonate. 

Nakabayashi K, Higashihara T, Ueda M. Polymer electrolyte membranes based on poly-(phenylene ether)s with pendant perfluoroalkyl sulfonic acids. Macromolecules 2011 44(6) 1603-9. 

Ueda and co-workers [183] synthesized poly-(phenylene ether)s with pendant perfluoroal-kyl sulfonic acid groups with lEC values of 1.17-1.83 mEq./g by nucleophilic polycondensahon reachon of a perhuoromonomer such as decafluo-robiphenyl or hexahuorobenzene with 2,5-bisip-iodophenyl)hydroquinone, followed by the Ullmann coupling reaction with potassium 1,1,2,2-tetrafluoro... 

Scheme 2.50 Structures of poly(phenylene ether)s with pendant perfluoroalkyl sulfonic acid groups. Taken from Ref. [183],...

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