X-ray Scattering Measurements Demonstrating In-Plane Anisotropy in Kapton Polyimide Films

X-ray scattering measurements were made on Kapton®1 films with thicknesses of 8, 25 and 50µm. These measurements indicate that the atomic scale structure is basically the same for the three Kapton films. However, the measurements reveal in-plane anisotropy of polymer chain alignment with preferred orientation parallel to an optical extinction direction. Anisotropy of x-ray scattering and therefore of polymer chain alignment within the polyimide film plane is greatest for the thinnest film, 8µm, and least for the thickest film, 50µm. The degree of anisotropy in tensile strength shows a similar dependence on film thickness. These appear to be the first x-ray scattering measurements demonstrating in-plane anisotropy for Kapton films. Furthermore, our measurements agree with previous measurements which have shown these polymer chains align in-plane rather than out-of-plane.