Pseudoliving free-radical polymerization mediated by macromolecular nitroxides based on nitrones

Benzoyl peroxide-initiated polymerization of styrene mediated by phenyl-tert-butylnitrone was studied by isothermal calorimetry, ESR, and gel permeation chromatography (GPC). At a high temperature (120°C), the reaction follows the mechanism of reversible inhibition of growing radicals by macromolecular nitroxides resulting from the trapping of primary growing radicals by the nitrone. The polymerization shows features typical of pseudoliving processes: after a short initial period, the reaction proceeds at a constant reduced rate, the M n of polystyrene (PS) increases with conversion, and the isolated PS further reinitiates the polymerization of styrene and butyl acrylate. In the latter case, a block copolymer appears, as demonstrated by a two-detector GPC and selective extraction. The constant of living-dormant-chain equilibrium and the rate constant for the trapping of growing radicals by the nitrone were calculated.