Novel radical addition chemistry, involving addition of CF3. radicals to octafluoro[2.2]paracyclophane (AF4), leads to formation of an unprecedented new class of dimeric CF3-substituted AF4 derivatives. These chemically stable, but highly sterically constrained compounds undergo a clean thermal homolytic retro process to form monomeric CF3-substituted radicals. These radicals can be trapped by atom-transfer,agents such as 1,4-cyclohexadiene or I-2, but in the absence of such agents, they undergo further homolysis to form trifluoromethyl radicals in a process that is amenable to their use as free-radical initiators, as was shown by a study of the polymerization of vinylidene fluoride.