Synthesis of Rigid-Flexible Polyetherketone–Based Copolymers

Abstract

Syntheses of symmetrical etherketone rigid blocks containing from four to ten aromatic rings were performed by a succession of Williamson synthesis steps, followed by deprotection by BBr3. Solubility decreased upon an increase in number of aromatic rings. Bis-(p-oxy-(p-hydroxyphenyl))benzophenone, a four-ring block, was soluble in the usual solvents (dichloromethane and chloroform), while 6 and 8-ring blocks were only soluble in dichloromethane to which trifluoroacetic acid was added. Rigid-flexible copolyetherketones with very short flexible segments were synthesized by reacting the 8-ring block with dibromo-terminated short alkane chains of 4 to 10 CH2 units in the presence of sodium hydride. Molar masses were estimated by MALDI-TOF, which was also used to verify the incorporation of the flexible spacers in a regular way. Copolymers are of moderate molecular weights (Mw values from 1240 to 2610 g mol−1), and of low polydispersity (from 1.02 to 1.17). Rigid blocks and rigid-flexible copolymers show high crystallinity and low solubility, in spite of the presence of the aliphatic spacers along the chain backbone, showing that incorporation of regularly spaced flexible segments does not decrease crystallization significantly. These flexible chains however decrease thermal stability of the copolymers.