Themodynamic properties of small alkyl and alkyl-peroxy radicals are Studied to model primary, secondary and tertiary radicals in non-fluorinated and perfluorinated polymers. Bond strengths, bond lengths, and total atomic charges from tile Mulliken population analysis are calculated using the B3LYP DFT method with spin-restricted orbitals. On this basis we find that the experimentally observed conversion of alkyl-peroxy to alkyl radicals is most likely by detachment of molecular oxygen or possibly by hydrogen but not by fluorine abstraction, although all of these reactions are predicted to be endothermic. Fluorine substitution leads to interesting charge polarization effects. (C) 2004 Elsevier B.V. All rights reserved.