Acylium Cations in the Synthesis of Poly arylether Ketone s

ACYLIUM CATIONS IN THE SYNTHESIS OF POLY(ARYLETHER KETONE)S 

Acyl cations are involved as propagating species in the synthesis of poly-(ether ketone)s. Poly (ether ketone)s are a class of thermoplastic crystalline polymers that have many desirable properties that make them useful as high-performance engineering materials [153,154]. The poly(ether ke-tone)s with the most useful properties are actually para-linked poly(aryl-ether ketone)s (PAEKs). They have excellent chemical resistance to oxidation and hydrolysis, high thermal stability, and many useful mechanical properties. Unlike some other materials with similar properties they are readily melt processable using conventional equipment. In addition, their mechanical properties are not affected deleteriously by most solvents. These polymers are usually crystalline. PAEKs contain arene groups joined by ether and carbonyl linkages. For example, two commercial poly-(ether ketone)s are PEK and PEEK (Fig. 36). 

Two general methods, electrophilic and nucleophilic, predominate the synthesis PAEKs [153,154]. The nucleophilic route to PAEKs was used in the polymerization of various combinations of bis-electrophiles 

The first report of a totally aromatic PAEK [156] [Eq. (48)] and the first report of PEK [157] [Eq. (49)] involved electrophilic reactions. However, low molecular weight polymers were obtained due to their crystallization from the reaction mixture. 

PEK was also prepared in polyphosphoric acid [Eq. (50)] [158]. The protonation of the carbonyl groups helped to maintain solubility. 

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