HIGH TENACITY AND HIGH MODULUS FIBERS FROM WHOLLY AROMATIC POLYIMIDES

Abstract

Poly (amic-acids) were synthesized from pyromellitic dianhydride (PMDA) and aromatic diamines, of which the resultant C-N bonds are coaxial and oppositely directed (rigid diamines), using Nmethylpyrrolidone as polymerization solvent. Random copolymers composed of rigid diamine, PMDA and 3, 3′, 4, 4′-diphenylethertetracarboxylic dianhydride (DTDA) were also synthesized. These poly (amic-acids) were partially imidized by adding an appropriate amount of acetic anhydride (15_??_30 mole% based on amic-acid unit) into their solutions and then wet-spun, since it was found that partially imidized polymer solutions gave more transparent and void-free coagulated fibers than poly (amic-acid) solutions as polymerized. These fibers were then chemically converted to polyimides by immersing them in an acetic anhydride-pyridine mixture and heat-drawn.Relatively lower crystalline polyimides such as polypyromellitimides of aromatic diamines bearing chlorine substituent on the nuclei or random copolyimides had better drawability and gave fibers having higher tensile strength than higher crystalline polymers. For example, poly [2, 2′-dichloro-4, 4′-biphenylene/p-phenylene (70/30) pyromellitimide] gave a fiber having tenacity (T) 16.3g/d, elongation (E) 2.0% and initial modulus (Mi) 960g/d. Another random copolymer composed of benzidine/PMDA/DTDA (100/40/60) yielded a fiber with the following tensile properties: T 19.7g/d, E 1.7% and Mi 1310g/d.