Substituent effects of accelerator on nitroxide-mediated radical polymerization

The acceleration effect of various agents on the rate of styrene bulk polymerization in 2,2,6,6-tetramethylpiperidinyloxy (TEMPO) mediated polymerization was investigated, including dimethyl malonate (DMM), diethyl methyl malonate (DEMM), diethyl tert-butylmalonate (DEBM), diethyl diethylmalonate (DEDEM), 3-methyl-2,4-pentanedione (MPD), acetyl malononitrile (Ac-MN), and dimethyl malononitrile (DM-MN). Polymerization with the additive proceeded in a living manner, as indicated by keeping a low polydispersity and increasing the molecular weight with the reaction time and conversion. The structure of the styrene polymerization did not change in the presence of these additives. The monomer conversion efficiency was approximately 99% and maintained a relatively narrow polydispersity of 1.29 with the optimal [Ac-MN]/[TEMPO] molar ratios of 4 in 1.5 h. With the accelerator, dipole/dipole interactions led to a weakening of the C-ON bond and an acceleration of the reaction. There is a trend for a higher polymerization rate with more electron-withdrawing substituents.