Controlled Ring-Opening Polymerization of Hexamethylcyclotrisiloxane Catalyzed by Trisphosphazene Organobase to Well-Defined Poly(dimethylsiloxane)s

Precise synthesis of well-defined functional polysiloxanes on demand was challenging due to chain transfer and backbiting side reactions during ring-opening polymerization (ROP) of cyclosiloxane monomers. In this contribution, a trisphosphazene base (C3N3-Me-P3) with medium basicity and bulky molecular size was demonstrated as an effective organocatalyst to realize the controlled ROP of hexamethylcyclotrisiloxane (D3). Linear poly(dimethylsiloxane)s (PDMSs) with different end-groups were successfully synthesized by C3N3-Me-P3-catalyzed ROP and the subsequent end-capping of the propagating polysiloxanes using diverse organochlorosilanes. Molecular characterizations by GPC, 1H and 29Si NMR, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) verified the molecular weights (Mn = 3.7–16.5 kg/mol), narrow distributions (Đ ≤ 1.18), and well-defined structures of the resulting PDMSs. Moreover, kinetics investigations indicated that the ROP of D3 catalyzed by C3N3-Me-P3 proceeded in a fast and kinetically controlled manner. This work demonstrated an efficient strategy to make well-defined functional polysiloxane materials using phosphazene as an organocatalyst.