Model problems in depolymerization kinetics of chain oligomers: 2. Random chain scission

Abstract

Kinetic equations related to the model of random chain scission (RCS) in the initial oligomer and intermediates (radicals and biradicals) have been solved, and the time dependence of concentrations, the average chain length, and its variance have been found. Despite of the difference in the sequence of formation between the intermediates (sequential reduction of chain length in the model of successive detachment of terminal monomer units and the preferential buildup of short chains in the RCS model), the changes in the average chain length in the two models are similar; i.e., they coincide with an appropriate change of the time scale. In the absence of bimolecular recombination, both the models are ergodic and nonmixing, a property that is due to the equidistant nature of the eigenvalue spectrum. Recombination leads to mixing and transition to equilibrium depolymerization. The change of the mode is determined by the ratio between the bond rupture, recombination, and evaporation rates.