New and effective approaches to the synthesis of 1,3-bis(diphenylsilyl)-2,2,4,4-tetraphenylcyclodisilazane-containing polydimethylsiloxanes (P1 and P2) were developed. P1 was obtained by polycondensation of cyclodisilazane lithium salt and chloroterminated polydimethylsiloxane. P2 was produced by hydrosilylation of vinyl-terminated cyclodisilazane and hydrogen-terminated polydimethylsiloxane. The polycondensation completed quickly at room temperature, while the hydrosilylation was facile and did not require cumbersome air-sensitive operations. P1 and P2 were characterized by Fourier transform infrared, nuclear magnetic resonance, gel permeation chromatography, differential scanning calorimetry, thermogravimetric analysis (TGA), and isothermal gravimetric analysis (IGA). TGA revealed the outstanding thermal properties of P1 and P2 with 5% weight loss temperatures (Td5) higher than 450 degrees C. IGA proved their better thermal stability at 450 degrees C for 800 min, compared to polydimethyldiphenylsiloxane. Dynamic mechanical analysis showed that silicone rubbers made from cyclodisilazane-containing polydimethylsiloxanes could have a maximum tan value as high as 1.13 and had good prospects for damping material applications. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013