Depolymerization of Free-Radical Polymers with Spin Migrations.

The mechanism of depolymerization is one of the most essential issues in chemical engineering and materials science. In this work, we investigate the depolymerization reactions of three typical free-radical poly(alpha-methylstyrene) tetramers by using first-principles density functional theory. The calculated results show that these reactions all need to overcome the energy barriers in the range of 0.58 to 0.77 eV, and that breaking the C-C bond at the chain end leads to the dissociation of alpha-methylstyrene monomers from the polymers. Electronic-structure analysis indicates that the reactions occur easily at the CR3 unsaturated end, and that the frontier molecular orbitals that participate in the reactions are mainly localized at the unsaturated ends. Meanwhile, spin population analysis presents the unique net spin-transfer process in free-radical depolymerization reactions. We hope the current findings can contribute to understanding the free-radical depolymerization mechanism and help guide future experiments.