Polyamic Alkyl Esters: Versatile Polyimide Precursors for Improved Dielectric Coatings

Abstract

The derivatization of the pendant acid moieties along the poly(amic acid) backbone in the form of alkyl ester groups provides a unique solution to the hydrolytic instability associated with the traditional polyimide precursors and offers additional benefits in the form of increased synthetic flexibility as well as a more desirable imidization behavior. These improvements are a direct result of eliminating the “monomer-polymer” equilibrium associated with poly(amic acids). In the absence of hydrolytic instability, it is now possible to utilize an aqueous work-up of the polyimide precursor. This presents an attractive synthetic pathway for well-defined, amine-terminated oligomers, which can then be formulated to yield low molecular weight, chain-extendable polyimide precursors. Furthermore, the higher imidization temperatures offered by the “amic alkyl ester” chemistry allows for more efficient chain extension prior to imidization. In the case of segmented copolyimides, the same features permit the extraction of the material with a suitable solvent to remove any homopolymer contamination as well as the development of a well-defined morphology. Alternatively, the lack of monomer randomization reactions offers the possibility to prepare polyimide blends, a very attractive and economical means of polymer modification. © 1992 IEEE