Microreactor technology (MRT) has become a useful tool for polymer chemists in recent years. Microreactors feature significant advantages compared to classical batch reactors such as ideal heat dissipation, high operation stability and – as a consequence of the strictly isothermal conditions provided – relatively easy scale-up of reaction conditions from the milligram to kilogram scale or higher. Despite their small volumes, they are able to yield high amounts of materials due their continuous character. Facile upscaling is thus next to the ability to handle dangerous compounds with relative ease one of the main drivers for their fast introduction in academic laboratories and in industrial production.
On-line analysis of chemical processes provides real time data and thus allows for rapid kinetic screening and in consequence efficient optimization of chemical reactions. A combination of both – continuous flow processing and on-line monitoring – constitutes an ideal tool in any chemical synthesis. Off-line analysis slows down optimization procedures and prevent the full exploitation of the high-throughput potential of microreactor technology. The classical spectroscopic on-line analysis tools are in the context of polymerizations not sufficient to give a comprehensive overview on reaction progress. A technique such as electrospray ionization mass spectrometry (ESI-MS), which allows to match polymer endgroups (which is used as a measure for how controlled the reaction is), is here a very important addition.
In this perspective, the group of Tanja Junkers at Universiteit Hasselt now has realized an on-line ESI-MS/Microreactor coupling for fast and efficient screening and optimization of most prominently polymerizations but not limited to those. This on-line analysis method allows the continuous ‘nonstop’ analysis of the polymerization mixture inside the microreactor under any given set of reaction conditions. The setup can also be used for fundamental research or for continuous quality control of flow reactions in e.g. commercial product settings.
Online observation of high temperature RAFT polymerization via on-line ESI-MS/Microreactor gives a good example on the power of the technique. Not only is the reaction progress monitored in a wide range of conditions in minute amounts of time, also all occurring side products can be quantitatively scanned in quasi-continuous fashion, given access to a plethora of data not available by other techniques.