Macrocyclic oligomers of the aromatic polyetherketone "PK99": synthesis, fractionation, structural characterisation and ring-opening polymerisation

Cyclo-condensation of 4,4'-dihydroxybiphenyl with 1,3-bis(4-fluorobenzoyl)benzene under conditions of pseudo-high dilution affords a new series of macrocyclic ether-ketone oligomers. A number of these (the cyclic [2 + 2] dimer, [3 + 3] trimer, and [5 + 5] pentamer) have been isolated chromatographically as pure compounds. The odd-numbered macrocycles are readily-soluble, non-crystalline glasses, but the cyclic dimer is crystalline, high-melting (403 degrees C) and relatively insoluble. Its structure, determined by single-crystal X-ray methods, provides a new model for chain-folding within lamellar crystallites of aromatic polyketones. The [4 + 4] cyclic tetramer, although detectable by MALDI-TOF MS, appears to be so insoluble that it cannot be extracted from the product mixture. The amorphous cyclic trimer undergoes ring-opening polymerisation at 300 degrees C in the presence of a fluoride initiator, to give tough, semi-crystalline polymer.