Direct Synthesis of Epoxy-Functionalized Polysiloxanes with Tunable Epoxy-Siloxane Contents via Phosphazene Base-Catalyzed Ring-Opening Polymerization

The synthesis of epoxy-functionalized polysiloxanes (E-PDMSs) via ring-opening copolymerization (ROCP) is challenging due to the significant reactivity disparity between octamethylcyclotetrasiloxane (D4) and 1,3,5,7-tetramethyl-1,3,5,7-tetrakis[3-(glycidyloxy)propyl]cyclotetrasiloxane (D4O) and their propensity for cross-linking. In this contribution, we report a facile and controlled synthesis of E-PDMS via cyclic trimeric phosphazene base (CTPB) catalyzed ROCP of D4 and D4O at 50 °C both in bulk and in THF solution. This method affords E-PDMSs with tunable epoxy-siloxane contents up to 20.4 mol % and high molecular weights up to 87.9 kg·mol–1. Moreover, a series of E-PDMSs with vinyl-siloxane and diphenyl-siloxane contents ranging from 0.5 to 10.9 mol % were synthesized via CTPB catalyzed ternary ROCP. The E-PDMS copolymer structures were verified by 1H NMR, MALDI-TOF MS, and GPC, with compositions closely matching theoretical values, demonstrating the high controllability and functional group tolerance of the CTPB catalyzed ROCP. DSC measurements confirmed that the incorporation of both epoxy-siloxane and diphenyl-siloxane units effectively suppressed the low-temperature crystallization while maintaining the glass transition temperatures (Tgs) below −100 °C. Moreover, lap shear tests revealed a high bonding strength of 2.76 MPa, demonstrating the potential of E-PDMSs as high-performance adhesives.