A continuous-flow microreactor was used to synthetize II–VI semiconductor quantum dots (CdSe). In order to improve the size distribution of the nanoparticles, the synthesis was carried out in a two-step procedure. A seed solution was obtained in a separate nucleation step, followed by a controllable growth step. Quantum dots that are synthesized with the two-step method show a much narrower size distribution in comparison to those obtained in a conventional batch synthesis.
Heat pipes used for cooling of microstructured reactors are a new approach for sustainable processing also in the lab-scale within a temperature range from ambient to more than 180 °C. The main advantage of heat pipe cooling is the dynamic behavior, i.e., the cooling rate depends on the heat released. Heat pipes can also suppress thermal runaways due to their extremely short response times on momentary temperature rises. As an example, the highly exothermal synthesis of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate from the respective reactants 1-ethyl-imidazole and methyltrifluoromethanesulfonate was investigated. By transferring the protocol to continuous-flow conditions in the microscale and by applying cooling with heat pipes, an out-of-control processing can be avoided.
Hyperbranched polymers have been synthesized in a microreactor for the first time, employing the known ring-opening multibranching polymerization of glycidol. Microreactors are well-known to be beneficial for highly exothermic reactions because of their capability to enhance mass and heat transfer due to short diffusion pathways and large interfacial areas per volume. The characteristics of the microstructured reaction system were utilized to engineer a continuous flow process for the preparation of well-defined hyperbranched polyglycerols with molecular weights up to 1,000 g/mol. Increased flow rates, as well as the use of highly polar solvents, led to the partial formation of very narrowly distributed (Mw/Mn = 1.05–1.15) high molecular weight fractions (Mn up to 150,000 g/mol). NMR- and MALDI-ToF spectra confirmed incorporation of the multifunctional initiator core into the hyperbranched polymer structure.
