Stable Free Radical Polymerization Process: Kinetic and Mechanistic Study of the Thermal Decomposition of MB-TMP Monitored by NMR and ESR Spectroscopy

A detailed experimental investigation was conducted to study the thermal decomposition of the nitroxide adduct N-(1‘-methylbenzyloxy)-2,2,6,6-tetramethylpiperidine (MB-TMP) at elevated temperatures using 1H NMR and ESR spectroscopy. At 125 °C, the concentration of TEMPO was followed by ESR spectroscopy, while 1H NMR spectroscopy was employed to monitor MB-TMP and the various byproducts of MB-TMP decomposition: styrene, N-hydroxylamine of TEMPO, acetophenone, and sec-phenethyl alcohol. A mechanism was developed to describe the formation of these various products. When oxygen is present in the system, even in trace amounts, the inhibiting effect of aerial oxygen via autoxidation preferentially competes with the reversible capping of 1-phenylethyl radical by TEMPO, which produced acetophenone and sec-phenethyl alcohol.