Polyimide Orientation Layers Prepared from Lyotropic Aromatic Poly(Amic Ethyl Ester)s

Abstract

The synthesis and characterization of liquid‐crystalline precursor polymer solutions[1] for polyimides permit for the first time the preparation of bulk‐ and surface‐oriented polyimide thin films from the nematic lyotropic state by shear. A special shearing technique was developed and optimized to orient viscous solutions into thin films with thicknesses below 100 nm. The films produced were thermally imidized and characterized by polarized light microscopy, as well as polarized FTIR and UV‐vis spectroscopy before and after imidization. The dichroic ratios (DRs) before imidization were determined as 5 by FTIR, and 4.5 by UV‐vis spectroscopies. After imidization the DRs increased to 14 and 7, respectively. The shear‐oriented layers possess a surface profile in the form of striations, which was characterized by mechanical surface scanning and atomic force microscopy (AFM). The profile height was determined in the nanometer range in contrast to the profile distance in the micrometer range, thus the latter is a magnitude larger than the film thickness. To quantify and compare the orientation potential of the obtained orientation layers, cells with a liquid‐crystalline host and a dichroic azo dye as guest were prepared. Interesting for this class of rod‐like polyimides is that layers, which were cast from low concentration isotropic solutions and rubbed, exhibited an almost doubled DR of 15 compared to analogously prepared alignment layers based on commercial flexible polyimide systems (DR = 8).

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

“…The mechanical data for fiber (11) are comparable to the data of fiber (9); this implies that the fiber under tension at 350 8C did not achieve a sufficient degree of orientation. Much better mechanical performance was then achieved by drawing fiber (11) at 400 8C.…”

“…This is completely different for the diffraction pattern of fiber (12), which shows three distinct reflections in this direction. The meridional layer lines are basically identical in number and intensity to what was recorded for fiber (11).…”

“…Fiber (10), which was first drawn at 150 8C and then at 250 8C, still shows only two, broad, meridional arcs which indicates poor orientation in the fiber axis direction, accompanied by the lack of any sharp equatorial reflex. In contrast, for fiber (11), which was drawn at 350 8C, more meridional layer lines are visible, indicating a better alignment in the direction of the fiber axis, but the equatorial reflections are still weak and diffuse. This is completely different for the diffraction pattern of fiber (12), which shows three distinct reflections in this direction.…”

“…In view of commercialized high modulus fibers with excellent performance, such as M5, Zylon, or others (see entries [8][9][10][11][12], the aim of this work was not to attempt to produce yet another high modulus PI fiber. In the course of our studies of order in lyotropic PAEs, [11][12][13] where the orientation in a two-dimensional thin film was investigated, we now want to examine the development of orientation in an elongated, fibrillar geometry.…”

“…In the course of our studies of order in lyotropic PAEs, [11][12][13] where the orientation in a two-dimensional thin film was investigated, we now want to examine the development of orientation in an elongated, fibrillar geometry. This was realized by dry-jet, wet-fiber-spinning of lyotropic solutions at a high solid content of 40 wt.-% in N-methylpyrrolidone (NMP) without the addition of any salts.…”