CHARACTERIZATION OF POLYIMIDES AND POLYAMIC ACIDS IN DILUTE SOLUTION.

Abstract

Dilute solution measurements on polyamic acids and polyimides provide an understanding of molecular structure which is not obtained by measurement of concentrated solution viscosity alone. Data obtained in amide solvents such as NMP, DMAc or DMF can be affected by trace impurities in the solvent, leading to polyelectrolyte effects. Measurement of both dilute solution viscosity and molecular weights by light scattering have shown that the cured polyimides retain essentially the same molecular weight and molecular conformation as their precursor polyamic acids, provided that the cure is extended to sufficiently high temperature. Samples which are cured chemically appear to require a high temperature post-bake to completely convert residual isoimide to the more stable imide.