聚乙二醇老化机理的分子模拟

Molecular Simulation Study on the Aging Mechanism of Polyethylene Glycol

为研究聚乙二醇(PEG)粘合剂的老化机理,基于密度泛函理论(DFT)的B3LYP方法和小曲率隧道效应校正的正则变分过渡态理论(CVT/SCT),对PEG单分子以及NO_2分子存在下PEG分子老化反应类型进行了分子模拟与计算。结果表明,PEG单分子反应条件下存在C—O断键反应和H原子转移反应两种降解断裂。C(2)—O(2)化学键断裂的键离解能较O(1)—C(1)、C(1)—C(2)化学键小,为PEG单分子断键反应的引发点。H原子转移反应为与C(1)相连的H原子逐渐向O(2)转移的过程,反应所需吸收热量为29.19kJ·mol-1。NO_2分子参与下,PEG分子存在降解断裂反应、硝化反应和环化反应三种老化模式,且所需的活化能均小于PEG单分子老化反应。聚合度为2、4、6、8、10的PEG分子各老化反应所需的键离解能或活化能变化范围小于3kJ·mol-1,证明聚合度对反应影响不大。在20~60℃贮存温度下,NO_2分子参与下的降解断裂反应和环化反应速率常数为H原子转移反应的103~1028倍。得到了NO_2分子存在下PEG分子的基本老化规律,认为NO_2分子参与下的PEG硝化反应、环化反应和降解断裂反应为主要老化模式,H原子转移反应为次老化模式,而C—O断键反应发生最为困难。

To study the detailed aging mechanisms of polyethylene glycol（PEG）adhesive,based on the B3 LYP method of density functional theory（DFT）and canonical variational transition state theory combined with a small-curvature tunneling correction（CVT/SCT）,the molecular simulation and calculation for the aging reaction type of PEG molecule in the presencee of PEG unimolecule and NO2 molecule were carried out.Results show that there are two kinds of degradation breaking of C—O bond breaking reaction and hydrogen atom transfer reaction under the PEG unimolecular reaction condition.The bond dissociation energy of C（2）—O（2）bond is smaller than those of the chemical bonds O（1）—C（1）and C（1）—C（2）,the C（2）—O（2）breaking is the trigger point of the cleavage reaction of PEG unimolecular.The hydrogen atom transfer reaction is the process of gradual transfer of hydrogen atom connected to C（1）to O（2）atom and the amount of heat absorbed by the reaction is 29.19 kJ·mol-1.Under the participation of NO2 molecule,there are three kinds of aging reaction modes,namely the degradation breaking reactions of PEG molecule,nitration reaction and cyclization reaction,the activation energies required is less than that of the aging reactions of PEG unimolecular.The change range of bond dissociation energies and activation energies required by aging reactions of PEG molecule with the polymerization degree of 2,4,6,8 and10 are less than3 kJ·mol-1,indicating that the polymerization degree has little effect on the reaction.At the storage temperature of 20-60 ℃,the rate constants of degradation breaking reactions and cyclization reaction under the participation of NO2 molecule are 103-1028 times as much as that of hydrogen atom transfer reaction.The basic aging rule of PEG molecule in the presence of NO2 molecule is obtained,considering that the cleavage reaction,nitration reaction and cyclization reaction for PEG under the participation of NO2 molecule are the main aging modes,the hydrogen transfer reaction of PEG unimolecular are the secondary aging mode,while the occurrence of the C—O bond breaking reaction is the most difficult.