Reactivity of stressed molecules: calculation of the effect of chain deformation on scission for macromolecules and middle macroradicals

Abstract

The effect of deformation ε of polyethylene molecule and radical on activation energy E a of the reaction of its monomolecular scission was calculated using MNDO and AM1 methods. Propane, octane, and decane molecules were used as models for PE chain. Reactions of molecule and radical scission were shown to be strongly accelerated by deformation, its activation energy, in contrast to previously studied reactions, being parabolic in chain deformation. The E a( ε) dependence for scission of molecules is shown to be linear only in the region of small (ε<3%) strains, for scission of macroradical such region is absent. Both semi-empirical methods give close results, but the AM1 method provides a better description for deformation of macroradicals. The proposed approach makes it possible to analytically describe calculated results, including the case of a reaction proceeding under the influence of constant force acting on a molecule. The possible cause for difference between the dependences of the local and integral rate constants on the load are considered.