The inhibition effects of 2

2

6

6-tetramethyl-4-oxo-piperidine-l-oxyl (TMPO) on radical polymerization of methyl methacrylate

styrene and isoprene under the initiation of benzoyl perooxide or α

α'-azodiisobutyronitrile have been studied. The experimental results showed that the inhibition effect is predominant when the concentration of TMPO is approximately equal to 0.1% of that of monomers. This effect becomes more prominent when TMPO is incorporated with quinones

such as 1

4-ben-zoquinone

1

4-naphthoquinone

9

10-phenanthrenequinone and chloranil.