AbstractThermoplastic polycarbosilane precursors for silicon carbide were prepared in high yield through potassium metal dechlorinations of mixtures of vinylic or chloromethyl (ClCH2—) methylchlorosilanes with other methylchlorosilanes in tetrahydrofuran solvent. Monomer mixtures are selected to maximize formation of backbone silicon‐carbon bonds and to maximize backbone branching at silicon, while retaining high synthetic yield and tractability and high yield of silicon carbide composition on pyrolysis. These precursor polymers are nonhazardous, relatively inert, i.e., stable to air and moisture, and have been spun to fiber form for ultimate conversion to silicon carbide fib