Consideration of solvent effect on precipitation polymerization of poly(ether-ketone)s via Friedel-Craft acylation

Abstract

Precipitation polymerization of diphenyl ether and isophthaloyl chloride catalyzed by AlCl3 via Friedel-Crafts acylation was examined in various solvents to clarify the polymerization behavior. Polymerizations were carried out in three categorized solvents based on the solubility to both catalyst and polymer, which were cyclohexane (CH), 1,2-dichloroethane (DCE) and DCE containing 2 wt% nitrobenzene (2%-NB). In DCE which was widely used, the oligomers were precipitated as a form of the complex with AlCl3 at the early stage of polymerization. The precipitates of the oligomers were swollen by the solvent, in which any short-range regular structure did not exist. The further polymerization proceeded even in the precipitates with eliminating by-produced HCl, and high molecular weight poly(ether-ketone)s (PEK) were finally formed. Nevertheless the reaction in 2%-NB yielded the well-swollen precipitates, the high molecular weight PEK was not synthesized in the precipitates because the reaction was terminated by not only the inefficient elimination of HCl due to the higher solubility of HCl but also the deactivation of catalyst by coordination of NB to AlCl3. Although the precipitation occurred more readily in CH due to the lower solubility of oligomers, the polymer was not synthesized in the precipitates. The resulting precipitates comprised of the dimers were not swollen in this case, and thereby it was very difficult to react between dimers and eliminate HCI from the precipitates. The solvents having high miscibility to catalyst and the polymers, low solubility of HCl gas, and no basicity are necessary for making high molecular weight polymers via the precipitation polymerization.