In contrast to thiols in general, fl-aminomercaptans were found to have low chain transfer constants in the free radical polymerizations of acrylates. Transformation of the amines to their salts, or other modifications masking the basicity of the amines, produced dramatic improvements in their chain transfer capability. The chain transfer constants of typical primary, secondary and tertiary fl-aminomercaptans and their hydrochlorides were determined at 60 ° for MMA and in some cases also for styrene and ethyl acrylate. In the case of styrene, normal chain transfer behaviour was observed for the amines and their salts, suggesting that the retardation accompanying transfer is a special feature of the electron-deficient acrylate radicals. The observed trends in relative reactivities of the amines and their salts and complementary studies with other aminomercaptans led to the postulate that the decreased reactivity of the aminomercaptans towards the acrylate radicals may be due to perturbations from specific interaction between the non-bonding electrons on the amine and the electron-deficient attacking radical, through a six membered transition state which is sensitive to the steric crowding on the N-atom.