碳纳米管CNT(5,5)内环氧乙烷的阴离子聚合机理

Anionic Polymerization Mechanism of Ethylene Oxide within CNT(5,5)

采用B3LYP/6-311++G**和ONIOM(B3LYP/6-311++G**:UFF)方法分别对环氧乙烷非受限状态以及在单壁碳纳米管CNT(5,5)内的阴离子聚合反应进行计算。结果表明,环氧乙烷与其亲核试剂(OH-)进攻产物形成的复合物进入CNT(5,5)碳纳米管内是一个放热过程,说明反应复合物进入CNT(5,5)形成包结物在能量上是有利的。由于碳纳米管的限制作用,环氧乙烷阴离子聚合的反应物、过渡态以及产物的结构与非受限状体下有所不同,在碳纳米管内的反应过程中分子构型会发生一定的扭转,以适应碳纳米管内的空间限制。与非受限状相比,环氧乙烷阴离子聚合反应的活化能垒增加了13.2 kcal/mol,表明碳纳米管CNT(5,5)对环氧乙烷阴离子聚合反应起到一定的抑制作用。

Anionic polymerization mechanism of ethylene oxide（EO） confined inside a single-walled carbon nanotube,CNT（5,5）,was calculated at the ONIOM（B3LYP/6-311＋＋G＊＊：UFF） level of theory.Meanwhile,the polymerization of EO in the isolated state was also calculated at the B3LYP/6-311＋＋G＊＊ method.We found that the encapsulation process was exothermic and favored in energy when the complex,which was formed by the EO and the EO/nucleophile（OH-） adduct,was entranced into CNT（5,5）.Due to the confinement of CNT（5,5）,the geometric parameters of reactant,transition state and product within nanotube were different from the corresponding parameters in the isolated state.During the reaction process of EO complex inside nanotube,rotation of the molecular configuration occurred for the EO complex in order to adapt to the inner space of nanotube.The energy calculation showed that the activation energy of the anionic polymerization within nanotube was 13.2 kcal/mol higher than the value in the case of the isolated state,which suggested that that the anionic polymerization of ethylene oxide was inhibited by the confinement in CNT（5,5）.