Influence of N-oxyls on the free radical autopolymerization of styrene

Abstract

SUMMARY: Through comparative studies on the controlled thermally initiated radical polymerization of styrene in the presence of N-oxyls, the effect of the type of the N-oxyls (2,2,6,6-tetramethylpiperidine-Noxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (OH-TEMPO), 4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl (oxo-TEMPO) and 4-acetamido-2,2,6,6-tetramethylpiperidine-N-oxyl (acetamido-TEMPO)), as well as the concentration of the N-oxyls (3 -20 mmol L -1 ) are discussed. The radical formation proceeds exclusively through the thermal initiation of styrene, i.e. without using any initiator. It is observed, that the thermal self-initiation of styrene increases the radical yield remarkably with the N-oxyls concentration, independent of the type of the N-oxyl. The concentration-dependent side reactions of substituted Noxyls are remarkably more pronounced than those of unsubstituted N-oxyl. This leads to the reduction of the overall rate of polymerization (v br ) as compared to TEMPO (v br = v br (thermal polymerization)) with respect to the concentration, but independent of the type of substituents.ZUSAMMENFASSUNG: Durch vergleichende Untersuchungen der kontrollierten thermisch initiierten radikalischen Polymerisation von Styrol in Gegenwart eines N-Oxyls wird der Einfluß der Art des N-Oxyls (2,2,6,6-Tetramethylpiperidin-N-oxyl (TEMPO), 4-Hydroxy-2,2,6,6-tetramethylpiperidin-N-oxyl (OH-TEMPO), 4-Oxo-2,2,6,6-tetramethylpiperidin-N-oxyl (Oxo-TEMPO), 4-Acetamido-2,2,6,6-tetramethylpiperidin-N-oxyl (Acetamido-TEMPO)) und der Konzentration des N-Oxyls (3 -20 mmol L -1 ) diskutiert. Die Radikalbildung erfolgt ausschließlich durch die thermische Initiierung von Styrol, also ohne Zusatz eines Initiators. Beobachtet wird eine wesentliche Erhöhung der Radikalausbeute der thermischen Selbstinitiierung von Styrol in Abhängigkeit von der Konzentration des N-Oxyls, unabhängig von der Art des N-Oxyls. Die konzentrationsabhängigen Nebenreaktionen substituierter N-Oxyle sind wesentlich ausgeprägter. Das führt zur Reduzierung der Bruttopolymerisationsgeschwindigkeit (v br ) im Vergleich zu TEMPO (v br = v br (thermische Polymerisation)) in Abhängigkeit von der Konzentration, aber unabhängig von der Art der Substituenten.

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Thermal self‐initiation of styrene in the presence of TEMPO radicals: Bulk and miniemulsion

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