Influence of N-oxyls on the free radical autopolymerization of styrene

Through comparative studies on the controlled thermally initiated radical p olymerization of styrene in the presence of N-oxyls, the effect of the type of the N-oxyls (2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), 4-hydroxy-2, 2,6,6-tetramethylpiperidine- (OH-TEMPO), 4-oxo-2,2,6,6-tetramethylpiperidin e-N-oxyl (oxo-TEMPO) and 4-acetamido-2,2,6, 6-tetramethylpiperidine-N-oxyl (acetamido-TEMPO)), as well as the concentration of the N-oxyls (3-20 mmol L-1) are discussed. The radical formation proceeds exclusively through the thermal initiation of styrene, i.e. without using any initiator. It is obse rved, that the thermal self-initiation of styrene increases the radical yie ld remarkably with the N-oxyls concentration, independent of the type of th e N-oxyl. The concentration-dependent side reactions of substituted N-oxyls are remarkably more pronounced than those of unsubstituted N-oxyl. This le ads to the reduction of the overall rate of polymerization ((Vbr)) as compa red to TEMPO ((vbr) = (Vbr) (thermal polymerization)) with respect to the c oncentration, but independent of the type of substituents.