The ring-opening polymerization of l-lactide initiated by rare earth metal silylamido complexes [Ln(OSSO){N(SiHMe₂)₂}(THF)] (1−3:  Ln = Y, Lu; OSSO = 1, ω-dithiaalkanediyl-bridged bisphenolato) was studied. MALDI-TOF mass spectrometry and ¹H NMR spectroscopy suggested that the polymerization proceeded via a conventional coordination−insertion mechanism involving silylamide ligand as the initiating group and the cleavage of acyl−oxygen bond of the monomer. A two-stage linear relationship between ln([LA]₀/[LA]_t) and the polymerization time was observed for the yttrium complex [Y(pdtbp){N(SiHMe₂)₂}(THF)] (pdtbp = 1,5-dithiapentanediyl-bis{4,6-di-tert-butylphenolato}, 3). In both stages, the polymerization showed first-order kinetics for the monomer concentration. The first-order dependency of the initiator concentration was only observed when the monomer conversion to PLA was less than 50−60%. The aggregation of the active growing polymer chain into dimeric structure occurred in the second stage. In contrast, the in situ generated alkoxide initiator [Ln(OSSO){N(SiHMe₂)₂}(THF)]/ⁱPrOH showed a different behavior. When 3 was reacted with 2-propanol in 1:2 ratio, the in situ generated alkoxides initiated the living polymerization of l-lactide. Neither aggregation nor intramolecular transesterification was observed over the entire conversion range. Polylactides with controlled molecular parameters (M_n, end groups) and low polydispersities were formed as a result of fast alkoxide/alcohol exchange.

中文翻译：

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稀土金属甲硅烷基酰胺配合物聚合l-丙交酯的动力学和机理：酒精添加的影响

的开环聚合升由稀土金属silylamido配合物[LN（OSSO）{N（SiHMe发起丙交酯₂）₂ }（THF）]（1 - 3：LN = Y，路; OSSO = 1，ω-研究了二硫代链烷二基桥接的双酚。MALDI-TOF质谱和¹ H NMR光谱表明，聚合反应是通过常规的配位插入机理进行的，该机理包括甲硅烷基酰胺配体作为引发基团和单体的酰基-氧键裂解。对于钇配合物[Y（pdtbp）{N（SiHMe ₂）] ，观察到ln（[LA] ₀ / [LA] _t）与聚合时间之间的两阶段线性关系。₂ }（THF）]（pdtbp = 1,5-二硫杂戊二基-双{4,6-二叔丁基苯酚基}，3）。在两个阶段中，聚合反应均显示出单体浓度的一级动力学。仅当单体向PLA的转化率小于50-60％时，才观察到引发剂浓度的一阶依赖性。活性增长的聚合物链聚集成二聚体结构发生在第二阶段。相反，原位生成的醇盐引发剂[Ln（OSSO）{N（SiHMe ₂）₂ }（THF）] / ⁱPrOH表现出不同的行为。当3与2-丙醇以1∶2的比例反应时，原位生成的醇盐引发1-丙交酯的活性聚合。在整个转化范围内均未观察到聚集或分子内酯交换反应。通过快速的醇盐/醇交换，形成了具有受控分子参数（M _n，端基）和低多分散性的聚丙交酯。