IMPROVING TENSILE MECHANICAL-PROPERTIES OF AROMATIC POLYIMIDES BY THERMAL IMIDIZATION AFTER COLD DRAWING OF POLY (AMIC ACIDS)

A new technique of thermal imidization after cold drawing of poly (amic acid) films is used to improve the tensile mechanical properties of various aromatic polyimide films. By this method PI (BDA/PPD) with linear, rigid main chains can be obtained as a high‐modulus and high‐strength material with Young's modulus of ca. 60 GPa and tensile strength of ca. 1.2 GPa. The enhancement of mechanical properties is favored by the rapid development of molecular order during imidization. The tensile properties of flexible polyimides such as PI (BDA/DDE) and PI (PMDA /DDE) are not significantly improved, because the orientation of cold‐drawn poly (amic acid) chains is easily relaxed at the temperature of imidization. Copyright © 1990 John Wiley & Sons, Inc.