One-step synthesis of well-defined block copolymer is of great fundamental and practical values. Here, an aromatic-aliphatic block copolyester is one-step synthesized from the mixture of phthalic anhydride (PA), cyclohexene oxide (CHO), and δ -valerolactone ( δ -VL) at room temperature in the presence of a metal-free Lewis pair catalyst consisting of triethylborane and excess phosphazene base. Alcohol-initiated ring-opening alternating copolymerization of PA and CHO occurs first and selectively because of the overwhelmingly higher activity of PA than CHO and δ -VL toward the reaction with base-activated hydroxy species. Only after full conversion of PA is reached can ring-opening polymerization of δ -VL occur from the terminus of the aromatic polyester so that a well-defined (AB) n C m type block copolyester is formed. The two polymerizations are both highly chemoselective without homopolymerization of CHO or extensive transesterification reactions. Owing to the sequence-selective and living characteristics of the terpolymerization, hepta- and undecablock copolyesters with controlled molar mass and low dispersity are obtained through addition of the three-component monomer mixture in batches. Applicability of the method to propylene oxide and ε -caprolactone is also examined.
Xianqiang Zeng,Chen Liu,Xue Wang,Yan Cao,Zheng Zheng,Peng He,Huiquan Li,Liguo Wang
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 (Mn = 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 (Mn = 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.
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