Initiator Activation and Active Chain End Stabilization Strategy via the Dual Hydrogen Bond for the Controlled Synthesis of Poly(fluorosiloxane)

Poly(fluorosiloxane) (PMTFPS) holds significant potential for applications in coatings, sealing materials, and sensors. A main barrier to high-precision PMTFPS, particularly PMTFPS with a narrow molecular weight distribution, is the severely backbiting side reactions during anionic ring-opening polymerization (AROP) of trimethyl trifluoropropyl cyclotrisiloxane (D3F) monomers. To address this issue, we developed a binary organocatalytic system based on sodium hexamethyldisilazane (NaHMDS) and indolecarbazole (ICZ). In this system, the sodium salt (NaICZ) generated during the reaction activates the initiator benzyl alcohol (BnOH), forming an initiating system that features dual hydrogen bonding and exhibits low nucleophilicity (with a nucleophilicity index of 4.05 eV). Mechanistic analysis demonstrated that introducing ICZ as a hydrogen bond donor increases the activation energy barrier of the chain initiation rate-determining step (ΔG = 13.23 kcal/mol) and enhances the stability of the active center (E = −18.80 kcal/mol), effectively suppressing backbiting reactions.