The thermal stability of polydiorganosiloxanes (PDOS) was studied in the presence or absence of silicon-nitrogen compounds (S-N) and/or Ph2Si(OH)z

water in nitrogen. It was found that in the presence of certain S-N the weight loss of PDOS decrease from 18% to 1.5% and the residual molecular weight of PDOS increases from 5.4×105 before heating to 6.7×105 at 350℃ for 24 hr. On the contrary

the residual molecular weight decreases from 5.4±105 to 1.7±105 when in the absence of S-N. Experimental results show that the weight loss of PDOS increases from 18% to 65% in the presence of certain Ph2Si(OH)2 or water at 350℃ for 24hr.

however

the weight can be decreased to 2-3% when the Ph2Si(OH)2 or water is added simu-ltaneously with the S-N to the PDOS. This means that the S-N can prevent siloxane chain degrdation caused by SiOH groups or water at high temperature. The S-N may play a role that removes SiOH groups and water in improving thermal stability of PDOS. This gives a simple method to obtain polyorganosiloxanes. resistant to temperature of 350℃.