Commercial organic Lewis-pair catalysts for efficient ring-opening polymerization of 1,2-butylene oxide

Abstract

Poly(1,2-butylene oxide) (PBO) with ethyl side chains exhibits enhanced hydrophobicity, lower glass transition temperatures, and more nonpolar characteristics compared to poly(propylene oxide) (PPO). However, the presence of large steric hindrance from side groups of 1,2-butylene oxide (BO) makes its ring-opening polymerization (ROP) inefficient. We report a metal-free Lewis pair catalytic system comprising triethylborane (Et₃B) and tetrabutylphosphonium bromide (TBPBr) that overcomes these limitations. This catalyst enables quantitative BO conversion under mild conditions (−20 °C), delivering high molecular weight PBO with a narrow polydispersity index (M_n = 37.2 kg mol⁻¹, Đ = 1.07) through controlled chain propagation. Notably, the exceptional active hydrogen tolerance of the system allows precise synthesis of low molecular weight PBO polyols (M_n = 1.4–3.5 kg mol⁻¹, Đ ≤ 1.05) using diols as initiators, with MALDI-TOF analysis confirming hydroxyl end-group fidelity. Furthermore, PBO polyols can be used directly in the synthesis of polyurethanes without the need for refining. We examined the influence of interactions between Lewis acids and Lewis bases on polymerization, and the results indicate that moderate interaction is critical for achieving optimal polymerization activity. This research demonstrates that a rational combination of a two-component Lewis pair catalyst offers a straightforward and practical approach for synthesizing polyethers with long side chains.