Group transfer polymerization of polar conjugated monomers using pinacolborane and thiourea anions

Abstract Group transfer polymerization (GTP) plays a crucial role in polymerizing (methyl) acrylate. The utilization of cheap and easily synthesized thiourea anion (TUA) combined with pinacolborane (HBpin) undergoes controlled GTPs of methyl methacrylate (MMA), methacrylate (MA), and α‐methylenebutyrolactone (MBL) at ambient temperature. The mechanistic study reveals that the TUA′‐1 having ‐NEt 2 moiety works out as a cocatalyst to assist HBpin undergoes the 1,4‐hydroboration reaction with α, β‐unsaturated acrylates to in situ generate a boron enolate (boryl ketene acetal [BKA]). Different from typical GTP, in which silyl ketene acetal (SKA) is used as an initiator, this work shows that BKA could act as an initiator with the assistance of the cocatalyst TUA′‐1 to generate the polymer. The chain end groups of the obtained polymer are characterized by MALDI‐TOF‐MS, indicating one of the chain ends features a hydride from the HBpin and another chain end has a linear or back‐biting cyclic structure. Moreover, the polymerization process is strongly supported by density functional theory (DFT) calculations. The application of BKA expands the research area of GTP reactions. The tunable and structural properties of TUA/hydroboranes significantly broaden the types of initiators in the GTP and pave a new methodology to achieve functional polymers.