Synthesis of Polyphosphazenes Bearing Geminal (Trimethylsilyl)methylene and Alkyl or Phenyl Side Groups

The ring-opening polymerization of a series of organosilylcyclophosphazenes of formula gem-N₃P₃Cl₄(CH₂SiMe₃)(R), where R = C₂H₅, i-C₃H₇, n-C₄H₉, t-C₄H₉, neo-C₅H₁₁, and C₆H₅, is described and is compared with the polymerization behavior of the non-silylated counterparts, gem-N₃P₃Cl₄(CH₃)(R). Polymerization is markedly favored by the presence of the organosilicon group. In the organosilyl derivatives, geminal t-C₄H₉or neo-C₆H₁₁cosubstituent groups retard polymerization compared to CH₃, C₂H₅, n-C₄H₉, or C₆H₅groups. The i-C₃H₇group has an intermediate effect. It is speculated that the t-C₄H₉, neo-C₆H₁₁, and i-c₃H₇groups give rise to polymerization-inhibiting side reactions. The polymers prepared by the polymerization of gem-N₃P₃Cl₄(CH₂SiMe₃)(R) were subjected to chlorine replacement reactions by treatment with sodium trifluoroethoxide. Reactions carried out in toluene solution allowed replacement of chlorine without concurrent attack on the organosilyl groups. In THF solvent, CH₂-Si bond cleavage occurred to replace the (trimethylsilyl)methylene units by methyl groups.