Heterocycle-Activated Aromatic Nucleophilic Substitution: Poly(aryl ether phenylquinoxalines). 2

Abstract

A synthetic approach for the preparation of poly(aryl ether phenylquinoxalines) has been developed wherein the generation of an aryl ether linkage is the polymer-forming reaction. Fluorines located on the para position of the benzene rings of various 2,3-diphenylquinoxaline heterocycles were found to be activated toward nucleophilic aromatic substitution. Model reactions demonstrated that these fluorine atoms on the phenyl groups of the diphenylquinoxaline were displaced by phenoxides in high yield, and the process was deemed suitable as a polymer-forming reaction. Thus, the pyrazine component of the phenylquinoxaline heterocycle has an activating effect on both the annulated benzo ring and the pendant phenyl groups, albeit to a lesser extent in the latter case. The extent of activation of the diphenylquinoxaline aryl fluorides was evaluated by both 1H NMR and 19F NMR spectroscopy. Appropriately substituted bis(fluorophenyl)-quinoxaline monomers were prepared and polymerized with bisphenols in high-boiling aprotic dipolar solvents containing potassium carbonate. High molecular weight polymers were obtained with glass transition temperatures ranging from 190 to 240 °C. Enhanced polymer solubility was achieved. © 1993, American Chemical Society. All rights reserved.