Poly(aryl ether) synthesis

Poly(aryl ethers) are an important class of commerical polymers and are a member of the family of materials referred to as engineering thermoplastics (1). Commercial examples include Amoco's poly(aryl ether sulfone) (Udel), ICI's poly(ether ether ketone) (PEEK), and General Electric's Ultem poly(ether imide). They display an attractive balance of properties such as relatively low cost, good processability, excellent chemical resistance, high thermal stability and good mechanical properties. Since the initial report of their synthesis by nucleophilic aromatic displacement polymerization of activated aryl dihalo compounds with bisphenolates (2), significant effort has been devoted towards these polymer systems (3). It is the purpose of this article to review many of the latest developments in the field of poly(aryl ether) synthesis, including mechanistic results, new activating groups and polymer structures, and alternative synthetic routes. The most commonly used synthetic route to poly(aryl ether)s involves generation of an ether linkage by nucleophilic aromatic substitution (SNAr) as the polymer-forming reaction (Scheme I). Early work focused primarily on sulfones and ketones as activating groups for the displacement of halides (2), and nitro groups (4). The role of heterocycles as activating groups was first reported for a 1,3,4-oxadiazole group (2a), and later for the nitro-displacement polymerization of bis(nitrophthalimides) to afford poly(ether imides) (4b). The nature of the activating group, leaving group, bisphenolate, and solvent all play an important role in the polymer forming reaction, the details of which will be discussed further in the following section.