FIBERS FROM A LOW DIELECTRIC-CONSTANT FLUORINATED POLYIMIDE - SOLUTION SPINNING AND MORPHOLOGY CONTROL

Control of the internal morphology of wet-spun fibers from a fluorinat ed polyimide has been achieved by varying the rate of polymer coagulat ion through adjustments in nonsolvent/ solvent miscibility and precipi tation strength of the coagulation bath. Filament internal morphologie s ranged from very porous or sponge-like to fully solid. Intermediate structures included fibers containing a spongy core with a nonporous s kin, sponge-like fibers containing large voids, and a relatively solid material containing randomly spaced small voids. The cross-sectional shape of the fiber is dependent upon the coagulation process as well a s the volume contraction of the initial extrudate. Drawn fibers (3X) r etained the original as-spun cross-sectional shape and also lost poros ity. Mechanical properties of poly(6FDA-4BDAF) fibers have an inverse relationship to filament porosity. Maximum modulus and break strength for drawn fibers is approximately 6 GPa and 200 MPa, respectively. As- spun mechanical properties were dependent upon the processing conditio ns and have moduli between 0.4-3.0 Cpa and break strengths of 10-160 M Pa. A dielectric constant of 2.50 for nonporous films was measured ove r a frequency range between 1.0 MHz to 1.8 GHz, showing little dispers ion. (C) 1997 John Wiley & Sons, Inc.