Summary: Structures of polyethylene, poly(propylene) and polystyrene macroradicals have been studied by means of the B3LYP/6‐31G** method. The polystyrene tertiary alkyl radical has been found to be less active as having spin density partially delocalized on the aromatic ring neighboring to the radical site. Considering the main chain bond orders, the following radicals have been found to be susceptible to main chain scission: the sec‐ and tert‐oxyl poly(propylene) ones, the sec‐ and tert‐oxyl polystyrene ones as well as the tertiary alkyl polystyrene one. The energy levels of the last frontier molecular orbitals in the polyolefin macroradicals have been found to be split up and moved—up and down for HOMOs and LUMOs, respectively. The alkyl macroradicals have single occupied molecular orbital with increased energy. In the oxyl and peroxyl radicals the spin density comes from two or three last orbitals that are spread over a broad molecular region and no single occupied molecular orbital (SOMO) may be identified.
