Controlling the monomer sequence in hydroxy acid copolymers remains a significant challenge, yet it is essential for fine-tuning the properties of copolyesters. This study presents the regioselective ring-opening polymerization (ROP) of l-3-tert-butyl-6-methyl-1,4-dioxane-2,5-dione (l-tBMG), resulting in the synthesis of alternating polylactic acid-co-2-tert-butylglycolic acid copolymers. The process is facilitated by enantiomerically pure Schiff base aluminum catalysts featuring either a binaphthyl framework or a 2,2-dimethylpropylenediamine and 3,5-dichlorosalicylaldehyde framework. These catalysts promote regioselective ring-opening of the asymmetric cyclic diester specifically at the acyl-oxygen bond of the lactic acid moiety. The molecular chain structure of the resulting polymers was elucidated through heteronuclear multiple bond correlation spectroscopy, while chain regularity was assessed using ¹H NMR and quantitative ¹³C NMR (q-¹³C NMR). According to the ¹H NMR and q-¹³C NMR test results, the molecular chain regularity is about 0.93. Incorporation of 2-tert-butylglycolic acid units led to a glass transition temperature (T_g) of the random copolymer to 65 °C. Notably, the T_g of the isotactic polymer, synthesized via ROP catalyzed by the aforementioned catalysts, was further elevated to 70 °C.

中文翻译：

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不对称二酯的高区域选择性开环聚合


控制羟基酸共聚物中的单体序列仍然是一项重大挑战，但对于微调共聚酯的性能至关重要。本研究介绍了 l-3-叔丁基-6-甲基-1,4-二氧六环-2,5-二酮 （l-tBMG） 的区域选择性开环聚合 （ROP），从而合成交替的聚乳酸-co-2-叔丁基乙酸共聚物。该工艺由对映体纯的 Schiff 基铝催化剂实现，该催化剂具有联萘基框架或 2,2-二甲基丙烯二胺和 3,5-二氯水杨醛框架。这些催化剂促进不对称环二酯的区域选择性开环，特别是在乳酸部分的酰基-氧键处。通过异核多键相关波谱阐明所得聚合物的分子链结构，同时使用 ¹H NMR 和定量 ¹³C NMR （^q-13C NMR） 评估链规则性。根据 ¹H NMR 和 ^q-13C NMR 测试结果，分子链规则性约为 0.93。掺入 2-叔丁基乙醇酸单元导致无规共聚物的玻璃化转变温度 （T_g） 达到 65 °C。 值得注意的是，通过上述催化剂催化的 ROP 合成的等规聚合物的 T_g 进一步升高至 70 °C。