Abstract:

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.

Key words: Solid-state topochemical polymerization, Diacetylenes, Polydiacetylenes, EHMO-ASED, EHCO-ASED