Polymeric precursors for silicon carbonitrides are prepared by three synthetic routes starting with ammonolysis of dichloromethylsilane (CH3SiHCl2). Two methods for raising pyrolysis yield are investigated. One method is to enhance the degree of crosslinking by copolymerizing with trichlorosilane (siHCl(3)) consecutively. The other is to leach out less soluble macromolecules in the polymer precursor by organic solvents. A 92% pyrolysis yield can be reached through combining these two methods. Those precursors with higher yields are characterized with weight losses and heat events during pyrolysis shifting towards higher temperatures.