Tertiary Silyloxonium Ions in the Ring-Opening Polymerization (ROP) of Cyclosiloxanes: Cationic ROP of Octamethyltetrasila-1,4-dioxane

Cationic ring-opening polymerization of octamethyltetrasila-1,4-dioxane (D-2(2)) initiated by strong protic acids leads to polymer which is the structural silicon analogue of polyoxyethylene. The study of the polymerization of D-2(2) using the new initiating system, R3SiH+Ph3C+ B(C6F5)(4)(-), indicates that tertiary silyloxonium ions participate in propagation. The polymerization shows kinetic features consistent with those observed for the process initiated by protic acids. The broad molecular weight distribution indicates that extensive transfer occurs in the polymerization system. Quantum mechanical calculations suggest the involvement of transient silylium ions in the chain transfer reactions.