Synergetic Binary Organocatalyzed Ring Opening Polymerization for the Precision Synthesis of Polysiloxanes

Abstract

Abstract Organocatalytic ring opening polymerization (ROP) is a versatlie method for synthesizing well-defined polymers with controlled molecular weight, dispersity, and nonlinear macromolecular architectures. Despite spectacular advances in organocatalytic ROP, precision synthesis of polysiloxanes remains challenging due to the mismatch in polarity between highly polar initiators and nonpolar monomers and polymers and the difficulty in suppressing the formation of scrambling products via transetherification reactions during ROP of cyclic siloxanes. Here, we describe a binary organocatalytic ROP (BOROP) of hexamethylcyclotrisiloxane (D3) employing organic bases as catalysts and (thio)ureas as cocatalysts. The BOROP of D3 using triazabicyclodecene (TBD) and (thio)ureas generates polydimethylsiloxanes (PDMSs) with narrow dispersity (Mw/Mn < 1.1). Despite the similar basicity of TBD and 1,8-bis(tetramethylguanidino)naphthalene (TMGN), which is known as a proton sponge, a unitary organocatalytic system using TMGN was inactive for the ROP of D3. When TMGN was paired with acidic urea, the BOROP of D3 yielded PDMSs with narrow dispersity (Mw/Mn < 1.1). Data suggest that the synergetic use of TMGN and urea is in an unprecedented activation–deactivation equilibrium between dormant and propagating species. The benefits of the present BOROP system are demonstrated based on the formation of PDMS elastomers with more uniform network structures with highly stretchy and excellent mechanical properties.