Preparation of Isotropic Branched LCP Films via a Dynamic Rotating Die: Relationship among Orientation, Mechanical Properties, and Microstructure

Liquid crystal polymer (LCP) is highly favored in the field of 5G due to its exceptional dielectric performance and low moisture absorption. However, the anisotropy of mechanical properties and poor processability significantly affect the service properties of LCP films. In this study, ADR 4468, a chain extender, was employed to enhance the viscoelasticity of the LCP through melt blending. Subsequently, a series of modified LCP films with low dielectric loss (less than 0.002 at 8.5 GHz) and varying degrees of orientation were obtained by blow molding with a rotating die. Results from polarized infrared spectroscopy, scanning electron microscopy, and dynamic mechanical analysis demonstrated that as the rotation speed increased, the film's orientation underwent a transition from anisotropy to isotropy and back to anisotropy, and the film prepared at a rotational speed of 10 rpm approached isotropy; an improvement in the elongation at break for both the longitudinal (a maximum increase of 450%) and transverse directions was observed. Additionally, the fracture behavior of the films was transitioned from brittle to ductile. By studying the morphology of the tensile fracture surface, the influence of the mechanism of orientation behavior on the mechanical properties of LCP films was elucidated. Furthermore, results from differential scanning calorimetry and X-ray diffraction indicated that the rotation speed also influenced the crystalline structure of the LCP films.