4-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

摘要

The controlled free radical polymerization of styrene initiated with benzoyl peroxide (BPO) in the presence of 4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl (4-oxo-TEMPO) as well as 4-acetamido-2,2,6,6-tetramethylpiperidine-N-oxyl (4-acetamido-TEMPO) at 135deg C was studied. The obtained results were compared with those of the 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) controlled free radical polymerization of styrene. Up to a nitroxide /BPO molar ratio of 1.5 is to 1, the conversions in the 4-oxo-TEMPO/BPO-system are higher than the conversions in the other systems. The conversion in the 4-acetamido-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-TEMPO/BPO-system, while the longest induction periods were observed in the TEMPO/BPO-system. Except in the lower region of nitroxide/BPO molar ratio (1 is to 1), the number-average molecular weight (M-bar_n) increases linearly with conversion in all systems. Interestingly, the growth of the molecular weight (M-bar_n) is independent of the nitroxide/BPO molar ratio in the 4-oxo-TEMPO-controlled free radical polymerization of styrene, while M-bar_n in the 4-acetamido-TEMPO/BPO- and the TEMPO/BPO-system decreases with increasing nitroxide/BPO molar ratio. The polydispersities (M-bar_w/M-bar_n) of the obtained polymers are below 1.4 except those of low nitroxide/BPO molar ratios, which indicates a controlled polymerization process.