3-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl (4-oxo-TEMPO)- and 4-acetamido-2,2,6,6-tetramethylpiperidine-N-oxyl (4-acetamido-TEMPO)-controlled free radical polymerization of styrene

The controlled free radical polymerization of styrene initiated with benzoy l peroxide (BPO) in the presence of 4-oxo-2,2,6,6-tetramethylpiperidine-N-o xyl (4-oxo-TEMPO) as well as 4-acetamido-2,2,6,6-tetramethylpiperidine-N-ox yl (4-acetamido-TEMPO) at 135 degrees C was studied. The obtained results w ere compared with those of the 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) controlled free radical polymerization of styrene. Up to a nitroxide/BPO m olar ratio of 1.5:1, the conversions in the 4-oxo-TEMPO/BPO-system are high er than the conversions in the other systems. The conversion in the 4-aceta mido-TEMPO/BPO-system is lower than that in the 4-oxo-TEMPO/BPO-system, but higher than the conversion in the TEMPO/BPO-system under the same reaction conditions. The shortest induction periods were observed in the 4-oxo-TEMP O/BPO-system, while the longest induction periods were observed in the TEMP O/BPO-system. Except in the lower region of nitroxide/BPO molar ratio (1:1) , the number-average molecular weight ((M) over bar n) increases linearly w ith conversion in all systems. Interestingly, the growth of the molecular w eight (M,) is independent of the nitroxide/BPO molar ratio in the 4-oxo-TEM PO-controlled free radical polymerization of styrene, while M, in the 4-ace tamido-TEMPO/BPO- and the TEMPO/BPO-system decreases with increasing nitrox ide/BPO molar ratio. The polydispersities ((M) over bar(w)/(M) over bar(n)) of the obtained polymers are below 1.4 except those of low nitroxide/BPO m olar ratios, which indicates a controlled polymerization process.