Synthesis of polyamic acid derivatives via azolides

Abstract

The preparation of rigid, aromatic polyimides via derivatized poly(amic acids), e.g., alkyl esters, yields hydrolytically stable polyimide precursor solutions along with generally higher imidization temperatures as compared to poly(amic acids). This unique behavior has utility in various areas, including block copolyimides, polyimide blends, and photosensitive polyimide systems. Although derivatization of the polyimide precursor can be achieved directly in its polymeric form, i.e., conversion of the poly(amic acid) to the isoimide and reaction with either alcohols or amines, derivatization of the dianhydride monomer followed by activation of the remaining carboxylic acid groups to enable the monomer to enter a polymer forming reaction is preferred. One such activation scheme involves the formation of an azolide, which can then react with an amine hydrochloride to form the required amide linkage. Such azolides are readily prepared from commercially available materials and offer improved hydrolytic stability over acyl chloride derivatives. Additionally, since the derivatization reaction proceeds under relatively mild conditions, acid-sensitive functional groups can be tolerated. Experimental data on the preparation and the ability to form high molecular weight polyimide precusors, i.e., polyamic alkyl esters and polyamic dialkyl amides, for various azolides will be presented.