Solvent Effects on the Preparation of Novel Amorphous Poly(aryl ether benzil)s

Abstract

A synthetic approach for the preparation of amorphous poly(aryl ether benzil)s has been developed wherein the generation of the aryl ether linkage is the polymer-forming reaction. Fluoride atoms located at the para-position of the benzil moiety were found to be very activated toward nucleophilic aromatic substitution. Facile displacement occurred at these positions since the benzil moiety can accept the negative charge developed in the transition state through a Meisenheimer complex intermediate, analogous to a conventional activating group (i.e., benzophenone). Two synthetic approaches were surveyed to determine the most efficient manner to prepare high molecular weight polymer. The conventional potassium carbonate/dipolar aprotic solvent route was the most effective, but only if dimethyl sulfoxide (DMSO) or sulfolane was used as the solvent. Polymer chain cleavage after initial molecular weight buildup occurred if Nmethylpyrrolidinone (NMP) or 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU) was employed. The silylated bisphenol route in NMP containing a catalytic amount of cesium fluoride afforded high molecular weight polymers; however, long reaction times were required. The Tg's of the polymers ranged from 157 to 242 °C depending on the bisphenol utilized, and the thermal stability was comparable to that of other poly(aryl ether)s in air, with decomposition temperatures in the 500 °C range. All of the polymers prepared in DMSO or sulfolane were formed into tough flexible films by solution or melt processing. © 1994, American Chemical Society. All rights reserved.