Chen Changjuan, Jiang Jinxing, Mao Xiaoyang, Cong Yong, Cui Yaqin, Pan Xiaobo, Wu Jincai
State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province , Lanzhou University , Lanzhou 730000 , People's Republic of China.
College of Chemistry and Pharmaceutical Engineering , Huanghuai University , Zhumadian 463000 , People's Republic of China.
Inorg Chem. 2018 Mar 19;57(6):3158-3168. doi: 10.1021/acs.inorgchem.7b03184. Epub 2018 Mar 1.
Three potassium crown ether complexes supported with bulky amidinate ligands were synthesized for the ring-opening polymerization (ROP) of rac-lactide. The side polymerization reaction initiated directly by ligand anion was suppressed well in the presence of alcohol as our design, and the synthesis of linear polylactide with a molecular weight as high as 117.7 kg/mol was successful together with an isoselectivity value of P = 0.88 at -70 °C. In this system, lactide can be deprotonated by amidinate anion to give lactide enolate, which can initiate the ROP of lactide as a side reaction in the absence of alcohol; however, this side reaction can also be suppressed well in the presence of alcohol by a decrease in temperature. An interesting anti-Arrhenius-like behavior in the polymerization was discovered, which can be attributed to the fact that the active catalyst can be converted to a less active lactide enolate potassium complex at a high temperature.
合成了三种由庞大脒基配体支撑的钾冠醚配合物，用于外消旋丙交酯的开环聚合（ROP）。如我们所设计，在醇存在的情况下，由配体阴离子直接引发的副聚合反应得到了很好的抑制，成功合成了分子量高达117.7 kg/mol的线性聚丙交酯，在-70°C下的等规选择性值P = 0.88。在该体系中，丙交酯可被脒基阴离子去质子化生成丙交酯烯醇盐，在没有醇的情况下，丙交酯烯醇盐可作为副反应引发丙交酯的ROP；然而，在醇存在的情况下，通过降低温度也可以很好地抑制这种副反应。在聚合过程中发现了一种有趣的类似反阿累尼乌斯的行为，这可归因于活性催化剂在高温下可转化为活性较低的丙交酯烯醇盐钾配合物这一事实。
