固相二乙炴拓扑聚合及侧基效应的理论研究

用EHCO-ASED方法, 对固相二乙炔热聚合反应MDA→PBT→PDA及其侧基(R=Li、CH_3、F)效虚进行了研究。结果表明, 不同侧基的二乙炔体系的MDA—PBT—PDA变化中,在反应坐标0.86附近, 体系的能隙均达到近于零的极小值, 同时前线轨道对称性发生突变。上述变化使得此聚合反应成为热允许的。侧基的变化, 对该类反应的反应机理及活化能影响较小, 但对产物PDA的热力学稳定性的影响则较为显著。还用EHMO-ASED方法对此反应进行了计算。结果表明, 对不同侧基R, 当外推至体系重复单元数n→∞时, 都能得到与EHCO-ASED一致的结果。

Theoretical Investigation of the Topochemical Polymerization of Diacetylenes in Solid Phase and the Side-group Effect on the Reactions

The EHCO-ASED method has been used to investigate the reaction mechanism and the effect of side group (R) on it for the following thermal polymerization of diacetylenes in solid phase: MDA→PBT→PDA (R=Li, CH_3, F). The calculated results reveal that the energy gaps approximate to zero at the Reaction Coordinate 0.86 for all R, meanwhile, the symmetries of frontier orbitals change, so that the thermal polymerization goes smoothly. It is also found that all side groups affect the reaction mechanism and the activation energy of the polymerization very little but give a significant influence on the thermal stability of the products (PDA). All the correspoding reaction systems have been dealt with by using the EHMO-ASED method and taking different number of repeated units (n), and the variations of average unit energy (E_t) of PBT and PDA with the increasing n have been discussed.