Friedel-Crafts and related polymers

Polyphenylene is normally a brittle material (see also Chapter 21). In order to obtain useful polymers it is necessary to space the rings with ether, sulphide or methylene links to make the structure less brittle. It is also essential to be able to control the reactions so as to have available intermediates which can be processed by conventional means. 

One approach by Monsanto (described in the basic patent BP 1037111) is to prepare a modified polypenylene by reacting an aromatic sulphonyl halide such as benzene-1,3-disulphonyl dichloride with an aromatic compound having replaceable nuclear hydrogen (e.g. bisphenoxybenzene, sexiphenyl and diphenyl ether). This was discussed in Chapter 21. 

Alternative approaches using Friedel-Crafts catalysts were developed independently by Phillips and Harris at about the same time as the Monsanto developments. 

The Phillips approach involved the reaction of aryl halides with aromatic nuclei in the presence of Friedel-Crafts catalysts. Whilst many variations in the process existed three main cases were distinguishable. 

The resins are substantially more expensive than general purpose phenolic resins and are therefore special purpose resins which are of interest for the following reasons  

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Polymeric catalysts. A very useful modification of the catalyst is obtained by ligand exchange with a (polyallyl)triflamide, forming polymer-bound scandium triflamide bistriflate. The catalyst has been used in the combinatorial synthesis of a tetrahydroquinoline library from anilines, aldehydes, and alkenes. A related catalyst prepared from ScClj-bHjO and Nafion is effective in several useful synthetic reactions, including allylation, Diels-Alder reaction, and Friedel-Crafts acylation. ... 

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