Synthesis of Polyurethane Thermoplastic Elastomer via Phosphonium Borane Lewis Pair Mediated Sequential Homopolymerization of Epoxides and Copolymerization of Epoxides and p-Tosyl Isocyanate

Ring-opening copolymerization (ROCOP) of epoxides with isocyanates provides an alternate pathway for the synthesis of polyurethane (PU) featuring different tertiary carbamate linkages, thereby offering new possibilities for material properties and applications. Herein, we present the controlled ROCOP of propylene oxide (PO) and p-tosyl isocyanate (TSI) using PBB-Br as a highly efficient organocatalyst under mild conditions. Density functional theory (DFT) calculations revealed that the selective TSI activation changes the reaction pathway from PO homopolymerization to copolymerization of PO and TSI. Taking advantage of PBB-Br serving as a switchable catalyst between ROP of PO and ROCOP of PO and TSI, it facilitates us to first synthesize well-defined PPO soft block using chain transfer agent. Subsequently facile one-pot tandem feeding of PO and TSI mixture allows us to realize the preparation of varied molecular weights and PU/PPO ratios of PU-b-PPO-b-PU triblock polymers for the first time. The mechanical properties of the prepared triblock polymers are carefully measured and behave as good elastomers.