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 kf,0 = 6.28 · 107 l2 · mol−2 · s and EA = 7.75 · 104 J · mol−1. The decomposition rate constants were determined from batch dead‐end polymerizations and found to be kd,0 = 4.73 · 107 l · mol−1 · s−1 and EA = 8.56 · 104 J · mol−1. magnified image

Thermally unstable polymers such as poly(methyl methacrylate) are degraded considerably during industrial processing. This degradation and its reduction to a minimum have been investigated in both lab and continuous pilot-scale experiments. A threestep degradation mechanism, starting at 180 C, was proved by Thermogravimetrical Analysis (TGA) and a kinetic approach to describe it was derived. The knowledge of this degradation behavior was then applied to a pilot-scale process with a production rate of 10 kg/h and the process yield loss during the devolatilization step was investigated. Using heat stabilizers, the overall process yield could be improved by 10 %, whereas the residual organic volatiles concentration (VOC) was drastically reduced to values below 1000 ppm. In order to preserve the molecular weight of the final product these stabilizers were added into the process, separately, at the end of the polymerization reaction but before the devolatilization step.

High-temperature polymerization has recently become of interest for industry because it yields higher reaction rates, and thus less reaction time, lower viscosity, and higher conversions. However, it also leads to new challenges for process engineering in regards to materials, reactor design, and, most of all, process modeling. Because practically all kinetic research in the field of polymerizations has been realized for rather low temperature ranges (mostly below the glass transition temperature), the correct modeling of a high-temperature polymerization requires the investigation of various parameters, such as thermal initiation effects, depropagation reactions, etc., and a careful adaptation of existing models for kinetics at significantly higher temperatures. The attention is focused on the modeling of the gel effect based on existing models available from the literature. Therefore, two different types of models, one semiempirical and one based on the free-volume theory, are examined for their applicability to high-temperature polymerization by comparison with the experimental results from differential scanning calorimetry batch polymerizations. Model fitting was realized using the software package PREDICI by CiT GmbH, Rastede, Germany.

Efficient stirring is needed to realize heat flow analysis with a thermally homogeneous medium. Because dispersion polymerization with supercritical fluids can be destabilized under stirring, a preliminary target has been to find a compromise between synthesis and basic reaction calorimetry requirements. This paper describes the use of poly (dimethylsiloxane) macromonomer with a molecular weight 5000 g/mol as stabilizer for the dispersion polymerization of methyl methacrylate in supercritical carbon dioxide. The effect of stirring speed and stabilizer concentration has been examined. This study has shown that poly (methyl methacrylate) can be produced at high yield and molecular weight using 10 wt% (respect to monomer) poly (dimethylsiloxane) macromonomer at stirring speeds up to 600 rpm. A polymerization enthalpy of −57.6±2 kJ/mol has been calculated being in good agreement with previously reported data. Thus, preliminary results for the heat balance using the newly developed high pressure reaction calorimeter for supercritical fluid applications have shown the important potential of reaction calorimetry to promote supercritical fluid technologies at industrial scale allowing for the determination of kinetics and thermodynamic and safety data, respectively.

Summary: The present paper deals with state‐of‐the‐art static devolatilization technology for polymer melts. Recent results obtained by CFD‐studies as well as by experimental testing at pilot scale are presented for the devolatilization of technical thermoplasts like polystyrene, poly (methyl methacrylate) and polycarbonate. It is shown that with the correct design of preheater and devolatilization chamber, volatiles like monomers and solvents can be efficiently removed from the polymer melt, both from the economical and technological point of view. As design criteria for the preheater, maldistribution and heat transfer efficiency are explained in detail.