Abstract
Summary: Several researches have dealt with the thermal initiation of methyl methacrylate (MMA) in the past. Some of them already discussed the presence of peroxide containing species that are formed from dissolved oxygen and the monomer itself as main reason for this initiation. However, a more detailed investigation as well as a kinetic description of this phenomenon is still due in literature. In this paper, the formation and decomposition of methyl methacrylate peroxides are described. MMA that has been in contact with air forms macromolecular peroxides at temperatures below 100 °C from physically dissolved oxygen. These peroxides have molecular weights of approximately 3 000–5 000 g · mol^−1^, depending on the temperature during formation. Above this temperature, these peroxides decompose quickly and initiate the radical polymerization. Depending on the reaction conditions, monomer conversions from 15 to 30% are obtained. In combination with additional initiators, the MMA peroxides provoke an acceleration of the reaction rate and can also lead to bimodal molecular weight distributions. An analytical method based on UV‐spectrophotometry was developed for the quantification of the peroxide content in the monomer. The kinetic rate constants for the formation were determined in batch experiments with purified, air‐saturated monomer to be k~f,0~ = 6.28 · 10^7^ l^2^ · mol^−2^ · s and E~A~ = 7.75 · 10^4^ J · mol^−1^. The decomposition rate constants were determined from batch dead‐end polymerizations and found to be k~d,0~ = 4.73 · 10^7^ l · mol^−1^ · s^−1^ and E~A~ = 8.56 · 10^4^ J · mol^−1^.
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