A density functional theory study of the mechanisms of scandium-alkoxide initiated coordination–insertion ring-opening polymerization of cyclic esters
A density functional theory study of the mechanisms of scandium-alkoxide initiated coordination–insertion ring-opening polymerization of cyclic esters
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DOI：
10.1016/j.polymer.2009.06.006
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发表时间：
2009-07
期刊：
影响因子：
4.6
通讯作者：
Jun Ling;Jingguo Shen;T. Hogen-esch
中科院分区：
文献类型：
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作者：
Jun Ling;Jingguo Shen;T. Hogen-esch
用密度泛函理论研究了烷氧基钪引发的α-己内酯（CL）、三亚甲基碳酸酯（TMC）和（S，S）-丙交酯（LLA）开环聚合的配位插入机理.四个关键的建议中间体的几何形状和相应的能量进行了评估，发现这些结构一致。对应于单体加成的过渡态表示五配位钪，并且对于所有单体具有几乎相同的能量。因此，CL，TMC和LLA经历类似的过程，Sc-单体配位的能量相对较小的差异，但TMC的前过渡态络合物的能量比其他单体低得多。在所有情况下，中间体接近过渡态和过渡态本身的偶极矩均低于反应物的偶极矩，预测在低极性溶剂中反应速率更快，与实验结果一致。本研究可应用于钇等稀土配合物介导的开环聚合反应。
The generally accepted coordination–insertion mechanisms of scandium-alkoxide initiated ring-opening polymerizations of ɛ-caprolactone (CL), trimethylene carbonate (TMC) and (S,S)-lactide (LLA) were investigated using density functional theory calculations. The geometries and corresponding energies of four key proposed intermediates were evaluated and found consistent with these structures. The transition states corresponding to monomer addition indicate a penta-coordinate scandium and have nearly the same energies for all monomers. Thus CL, TMC and LLA undergo similar processes with relatively small differences in the energies of Sc-monomer coordination but the pre-transition state complex of TMC is much lower in energy than that of the other monomers. The dipole moments of the intermediates close to the transition states and the transition states themselves in all cases are lower than those of the reactants predicting faster reaction rates in low polarity solvents, consistent with experimental results. This study may be applicable to ring-opening polymerizations mediated by yttrium and other rare earth complexes.