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聚合物降解在原子层次上的理论研究是相关于高分子材料反应调控的重要课题.运用引入色散修正的密度泛函紧束缚理论(DFTB-D)方法,对两端不饱和与一端不饱和(C-端不饱和,CH2-端不饱和)共3种典型顺次连接的聚-?-甲基苯乙烯(PAMS)片段的降解过程进行了原子层次动力学模拟研究.结果显示,PAMS在500~600 K的温度环境下,降解都对应于解聚过程,并且单体单元逐一脱落主要发生在链的未饱和端部.进一步的3种片段的电子结构分析均显示,占据在最高占据分子轨道(HOMO)和最低非占据分子轨道(LUMO)的电子主要局域在未饱和一端,这与势能面预测的结论是相符的.此外,动力学模拟的结果也指出,适当的增加温度,能够让解聚反应加快进行.进一步基于DFTB-D方法的C—C键断裂过程的弛豫扫描也清晰地显示,从能量角度,解聚发生在不饱和端也更为容易.此外,自旋布居分析体现了这是与PAMS的电子自旋极化结构紧密相关的.我们希望,当前的理论研究能够对理解聚合物降解机理起到基本的参考作用.
The theoretical study of polymer degradation at the atomic level is an important issue related to the regulation of polymer materials reaction.Using the DFTB-D method which introduces dispersion correction, At the atomic level, the kinetics of degradation of three typical sequential poly (4-methylstyrene) (PAMS) fragments was investigated by using the atomic force microscopy ~ 600 K, the degradation is corresponding to the depolymerization process, and the monomer units fall off one by one mainly at the unsaturated end of the chain.Analysis of the electronic structure of three further fragments showed that the highest occupied molecular orbital (HOMO) and the lowest occupied molecular orbital (LUMO) at the unsaturated end, which is in agreement with the prediction of the potential energy surface.Furthermore, the results of the kinetic modeling also indicate that the appropriate increase in temperature allows The depolymerization reaction is accelerated further.The relaxation scan of the C-C bond cleavage process based on the DFTB-D method also clearly shows that it is easier to depolymerize at the unsaturated end from the energy point of view.In addition, Analysis shows that this is with The electron spin-polarized structure of PAMS is closely related, and we hope that current theoretical research can provide a basic reference for understanding the mechanism of polymer degradation.