|Abstract||The Neilson group in the past has studied the thermal condensation reactions of N-silylphosphoranimines to yield polymeric and cyclic phosphazenes. It was found that different side groups on phosphorus can dramatically change the physical and chemical properties of the phosphazenes. Many of the alkyl/arylphosphazenes that were obtained by the Neilson method had two alkyl/aryl groups on phosphorus; however, no investigations have been carried out for mixed substituent phosphines (e.g., 1¿3 ) and phosphoranimines ( 4¿8 ).* In our investigations, mixed substituent N-silylphosphoranimines with two possible leaving groups on phosphorus, have been studied. Reactions were carried out by two condensation methods: (1) sealed ampule thermolysis and (2) dynamic vacuum thermolysis. In the sealed ampule thermolysis of compounds 5 and 6 it is very difficult to obtain a single product because of the constant presence of bromine and/or Me 3 SiBr. However, the utilization of a dynamic vacuum removes Me 3 SiBr during the reaction that affords cyclic alkylphosphazene trimers 9 and 10 in moderate yields. Thermolysis reactions with the remaining compounds 4 , 7 , and 8 are not successful, affording few phosphazene products in low yields.* Previous studies of reactions of CH 3 CH 2 OH with N-silylphosphoranimines were found to yield (alkyl/aryl)cyclophosphazene trimers. By the same method, cyclic phosphazenes can be obtained in good yields at lower temperatures.* Many of the isolated phosphazenes are cyclic trimers, however, two new polymers have also been obtained. All of the new compounds have been characterized by NMR, GUMS, and elemental analysis (EA). The molecular structure of a new cyclic phosphazene trimer has been determined by a single-crystal X-ray diffraction study. Please refer to dissertation for diagrams.