Polyimide Fibers Obtained by Spinning Lyotropic Solutions of Rigid‐Rod Aromatic Poly(amic ethyl ester)s

Abstract

Summary: Fibers were spun from a lyotropic solution of a high‐molecular‐weight (η = 5.89 g · dL−1), rigid‐rod, fully aromatic polyimide precursor polymer in a dry‐jet, wet‐spinning process in NMP. Acetone was identified as the coagulant of choice since fibers could be drawn extensively in this solvent, resulting in improved mechanical properties (tensile modulus: E = 17 GPa, strength at break: σbreak = 400 MPa, elongation at break: εbreak = 5.3%) and orientation, which was shown by WAXS patterns. SEM images showed a layered, skin‐core morphology without any visible fibrillation. Additional processing of these fibers by step‐wise hot‐drawing up to 400 °C under tension rendered oriented polyimide fibers with excellent mechanical properties. (E = 68 GPa, σbreak = 700 MPa, εbreak = 1%). An analysis of the WAXS diffraction patterns showed an improved orientation of the fibers in the axial and lateral directions; however, probably due to the CF3 side groups, the lateral distance was still too large for crystallization. SEM images of these imidized fibers showed, for the first time, a fibrillar morphology in addition to the typical, skin‐core, sheet‐like morphology.SEM image of the hot‐drawn fiber PI 4 (12). The image shows a skin‐core morphology which was delaminating into ribbons during preparation.magnified imageSEM image of the hot‐drawn fiber PI 4 (12). The image shows a skin‐core morphology which was delaminating into ribbons during preparation.

Introduction of fluorin into PBO polymer chains: Toward higher thermal stability and lower dielectric constant

“…The lower tensile strengths and tensile modulus of 6FPBO fibers should be owing to the relatively lower molecular weight and looser assembly structures of 6FPBO compared with PBO. However, mechanical properties of 6FPBO fibers were still higher than common ones, for instance, the tensile strengths and tensile modulus of 6FPBO-1% fibers are significantly higher than fluorinated polyimide material [25] . Figure 4 shows the dielectric constant spectra of the 6FPBO polymers.…”

Preparation and characterization of ternary copolyimide fibers via partly imidized method

“…They can be made into films, coatings, laminates and fibers. [1][2][3][4][5][6] In particular, the high-performance aromatic PI fibers are expected to have suitable properties for special uses. However, in comparison with the other high performance fibers, the mechanical properties of PI fibers are not so high, and far lower than their theoretical value.…”