One-pot synthesis of sequence-controlled multiblock copolymers via intramolecular Lewis pair mediated switchable polymerization of epoxide/isocyanate mixtures

The precise incorporation of monomers into polymer chains to create sequence-controlled polymers remains one of the key challenges in modern polymer chemistry. Notably, the alternating, periodic, or block copolymers consisting of two monomers represent the simplest form of sequence-controlled block copolymers. One attractive strategy in preparing sequence-controlled block copolymers is to link two different polymerization cycles, which involves ring-opening polymerization (ROP) and ring-opening copolymerization (ROCOP) due to the large library of cyclic monomers and comonomers. In this work, we report for the first time that switchable polymerization from propylene oxide (PO) and p-tosyl isocyanate (TSI) mixtures in solution using intramolecular phosphonium borane Lewis pair (PBB-Br) as a catalyst. This system can efficiently toggle between the ROCOP of PO/TSI and ROP of PO under mild conditions, enabling the one-pot synthesis of multiblock copolymers with up to 33 segments through nine sequential monomer mixture additions. Physical properties of the copolymers are analyzed, and DFT calculations reveal that biased activation of TSI provides a pathway to mediate the ROCOP of TSI and PO over the ROP of PO. This approach shows strong potential for synthesizing sequentially and architecturally complex polymers with precise monomer sequence control, enabling advanced material design.