Solvent effects on TEMPO-mediated radical polymerizations: behaviour of 3-vinylpyridine in a protic solvent

Solvents can strongly influence the equilibrium between dormant and active species which is involved in 2,2,6,6-tetramethyl-1 -piperidinyloxy (TEMPO)- mediated radical polymerizations. At 110 degreesC, the overall polymerizati on rate of 3-vinylpyridine in pyridine was logically found lower than that in bulk, due to dilution. However, in ethylene-glycol, the opposite behavio ur was observed. According to infrared spectroscopy, this unexpected increa se in the overall polymerization rate was attributed to hydrogen bonding be tween ethylene-glycol and the pyridine rings, which weakens the C-O-N bond of the TEMPO-terminated polymers. Semi-empirical molecular orbital calculat ions were used to support the FTIR results and to calculate the decrease in the dissociation enthalpy of the polymer-nitroxide bond. (C) 2001 Elsevier Science Ltd. All rights reserved.