The Favorable Effects of Incorporating Bulky Rigid Moieties Into Polymethylsilane (<scp>PMS</scp>) on the Melt‐Spinnability of Its Derived Preceramic Polymer

ABSTRACT The wide applications of continuous silicon carbide fiber (SiC f ) are constrained by the high cost of its common raw material, polycarbosilane (PCS). Polymethylsilane(PMS) exhibits higher reactivity and a lower production cost than PCS. Nevertheless, the disadvantages of pyrophoric nature and thermoset properties in raw PMS necessitate improvements for practical applications. Herein, benzoxazine resin (VBR) with vinyl functional groups is utilized to modify PMS via hydrosilylation. After modification, a stable preceramic polymer with excellent processability is obtained. The ordered and symmetrical molecular architecture of the initial PMS is changed. This results in an increase of the molecular rigidity, which in turn constrains the alteration of molecular conformation and diminishes the tendency toward crystallization. The modified PMS exhibits a shear‐thinning behavior and thermoplastic properties upon heating, making it suitable for melt‐spinning. The molecular orientation of the newly formed network structure in the modified PMS is aligned with the shear force during melt‐spinning, facilitating the extrusion of green fibers and thereby imparting superior spinnability to the modified PMS. By optimizing the temperature of melt‐spinning to 210°C, we produce continuous SiC green fibers with lengths exceeding 10 km. This work presents a promising candidate for the economic preparation of SiC fiber.