Mechanical property changes produced by the thermal cyclization of poly (acid) amides

Abstract Thermal imidization is accompanied by a non-uniform change of the mechanical properties. We show here that this phenomenon is typical of all the aromatic polyimides and is due to additional reactions which reduce or increase the molecular weight. Confirmation was obtained for the soluble polyimide by a direct comparison of the molecular weight with the mechanical strength parameters. An important part is also played by the physical processes which are associated with a structural rearrangement during thermal cyclization.