or a low molecular weight linear pnc oligomer they are usually a mixture of both cyclics and linears use of a stoichiometric excess of ammonium chloride favors formation of more cyclics whereas use of excess phosphorus pentachloride favors more linears either the linear or cyclic pnc oligomers can be used or mixtures can be used to make the substituted organo oligomers which are then cured by introduction of siloxane cross links the pnc oligomer is recovered by conventional means such as by distillation the crude pnc oligomer solution can be initially filtered and water washed prior to distillation to remove solids and unreacted water soluble salts such as ammonium chloride the pnc oligomer is then dissolved in a solvent such as tetrahydrofuran dimethoxyethane dioxane cyclohexane toluene and the like and is reacted with a solution or slurry of a sodium alkoxide or aryloxide in an inert solvent of the desired substituent group if both olefinic and non olefinic groups are used for substitution they can be reacted as a mixture with the pnc oligomer or they can be reacted in sequence in a sequential operation the sodium alkoxide or aryloxide which contains the olefinically unsaturated group is preferably reacted first for example if phosphazene is being prepared containing phenoxide 4 ethylphenoxide and 2 allylphenoxide groups an ether solution of sodium 2 allylphenoxide can be initially added to the pnc oligomer solution in an amount to supply the desired level of olefinic groups in the case where the pnc oligomer is mainly cyclic trimer this would be about 2 6 moles of sodium 2 allylphenoxide per mole.