A Novel Process for Ultrasound‐Induced Radical Polymerization in CO2‐Expanded Fluids

Summary: A strong viscosity increase upon polymerization hinders cavitation and subsequent radical formation during an ultrasound‐induced bulk polymerization. In this work, ultrasound‐induced radical polymerizations of methyl methacrylate (MMA) have been performed in CO₂‐expanded MMA in order to reduce the viscosity of the reaction mixture. For this purpose, the phase behavior of CO₂/MMA systems has been determined. With temperature oscillation calorimetry, the influence of CO₂ on the viscosity and on the reaction kinetics of ultrasound‐induced polymerizations of MMA has been studied. In contrast to polymerizations in bulk, this technique shows that a low viscosity is maintained during polymerization reactions in CO₂‐expanded MMA. As a consequence, a constant or even increasing polymerization rate is observed when pressurized CO₂ is applied. Moreover, the ultrasound‐induced polymer scission in CO₂‐expanded MMA is demonstrated, which appears to be a highly controlled process. Finally, a preliminary sustainable process design is presented for the production of 10 kg/h pure PMMA (specialty product) in CO₂‐expanded MMA by ultrasound‐induced initiation.

Process flow diagram of the ultrasound‐induced polymerization of MMA in CO₂‐expanded MMA.