The selective ring-opening homo-polymerization of CO2/butadiene-derived lactone monomers has emerged as an appealing approach for synthesizing chemically recyclable polyesters from CO2. Previous research has only concentrated on di-substituted six-membered lactones. In this study, a newly designed tri-substituted six-membered CO2/butadiene-derived lactone monomer, 3,3,6-triethyltetrahydro-2H-pyran-2-one (Et-HL), was polymerized successfully through selective ring-opening polymerization (ROP) using NaOMe, tBu-P4/BnOH, or tBu-P4. The tBu-P4/BnOH affords linear-poly(Et-HL) with typical living polymerization behaviors, while a maximum number-average molecular weight (Mn) of 1050 kg mol-1 and a dispersity (Đ) of 1.52 was achieved for cyclic-poly(Et-HL) using only tBu-P4. Catalytic methods were developed for monomer recycling of both linear- and cyclic-poly(Et-HL). Direct observation of key intermediates by Nuclear Magnetic Resonance (NMR) reveals the mechanistic differences between Et-HL and HL. A tail-to-head strain-releasing mechanism was proposed to rationalize the selective formation of cyclic polymers for both HL and Et-HL using only tBu-P4. In the case of linear polymers, HL and Et-HL share a similar mechanism involving initiator anion attacking the monomer ester bond. This work represents the first example for the ROP of six-membered lactones bearing more than 2 substituents, simultaneously offering fundamental understanding for the Thorpe-Ingold effect on the ROP of CO2/butadiene-derived six-membered lactones for the first time.

中文翻译：

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CO2/丁二烯衍生的三取代六元内酯的开环聚合


CO2/丁二烯衍生的内酯单体的选择性开环均聚已成为从 CO2 合成化学可回收聚酯的一种有吸引力的方法。以前的研究只集中在二取代的六元内酯上。在本研究中，使用 NaOMe、tBu-P4/BnOH 或 tBu-P4 通过选择性开环聚合 （ROP） 成功聚合了新设计的三取代六元 CO2/丁二烯衍生的内酯单体 3,3,6-三乙基四氢-2H-吡喃-2-酮 （Et-HL）。tBu-P4/BnOH 提供具有典型活性聚合行为的线性聚 （Et-HL），而仅使用 tBu-P4 的环状聚 （Et-HL） 的最大数均分子量 （Mn） 为 1050 kg mol-1，分散度 （Đ） 为 1.52。开发了用于线性和环状聚 （Et-HL） 单体回收的催化方法。通过核磁共振 （NMR） 直接观察关键中间体揭示了 Et-HL 和 HL 之间的机理差异。提出了一种尾对头的应变释放机制，以仅使用 tBu-P4 使 HL 和 Et-HL 的环状聚合物的选择性形成合理化。对于线性聚合物，HL 和 Et-HL 具有相似的机制，涉及引发剂阴离子攻击单体酯键。这项工作代表了带有 2 个以上取代基的六元内酯的 ROP 的第一个例子，同时首次为 Thorpe-Ingold 效应对 CO2/丁二烯衍生的六元内酯的 ROP 提供了基本理解。