Controlled Ring‐Opening Polymerization of 1,2‐Butylene Oxide Catalyzed by Cyclic Trimeric Phosphazene Base for the Synthesis of <scp>PBO</scp> Lubricating Oils

ABSTRACT Poly(1,2‐butylene oxide) (PBO), synthesized through the ring‐opening polymerization (ROP) of 1,2‐butylene oxide (BO), exhibits significant potential as polyether lubricating oil due to its exceptional lubricating properties and excellent miscibility with base oils. However, the metal‐free controlled ROP of BO remains a considerable challenge due to the sterically hindered substituent and relatively lower reactivity of BO. In this study, the effective ROP of BO with a metal‐free cyclic trimeric phosphazene base (CTPB) is reported. The CTPB catalyst exhibits precise control and high activity (turnover frequency (TOF) of up to 3333 h −1 ) in the ROP process, as demonstrated by kinetic investigations, 1 H NMR and SEC spectra, as well as MALDI‐TOF‐MS analysis. A diverse range of hydroxyl and carboxylic acid initiators can efficiently initiate the ROP of BO, providing well‐defined PBOs with controlled molecular weights ( M n = 7.1–20.8 kDa), narrow molecular weight distributions ( Đ ≤ 1.07) and high end‐group fidelities. Furthermore, PBOs demonstrate superior lubricating properties, characterized by a viscosity index as high as 285. This study introduces an efficient method for synthesizing well‐defined PBOs, which hold significant potential for industrial production of high‐performance lubricating oils.