Organic synthesis in microflow systems has attracted increasing interest in the past decades. Recently this novel technology has been exploited for polymer chemistry and several polymerization techniques have been transformed from conventional systems to microfluidic devices.1 The micro structured reactors (inner dimensions: 10-100 micrometers) provide a high specific surface area with superior heat exchange properties and highly efficient mixing, which is due to special designed reactor geometry. The continuous flow enables the control of stoichiometry, temperature and reaction time during ongoing reactions.2 By the use of various mixing geometries specialized reactor setups can be designed for a variety of polymerization techniques.3
Figure 1: 4 way jet mixing device (left) and HPIMM (right)4
The living anionic polymerization of styrene based monomers to homo- and diblock copolymers in continuous flow reduces the reaction time and experimental effort compared to classical batch methods ("break-seal" and "high vacuum" techniques).5 We successfully transferred the carbanionic polymerization of 2-vinyl pyridine from a common batch system to a micro structured reactor setup. Thereby we avoided the usually needed addition of salts and additionally no cooling was needed. In combination with the safer setup compared to batch systems the use of microreactors is a step to greener and more controlled processes.6 Also the functionalization of living carbanionic polymers with epoxide derivatives are of particular interest to obtain single hydroxyl or multiple orthogonal functionalities at the terminal position.7 A newly developed continuous polymerization-termination sequence enabled quantitative functionalization of living carbanions by utilizing different acetal-protected functional epoxides as termination reagents. Subsequent acidic-hydrolysis leads to multihydroxyl end functional polystyrenes.8
Figure 2: Schematic reactor setup for (co)polymerization and end-functionalization of "living" carbanions
References
| [1] | "Microstructured Reactors for Polymer Synthesis: A Renaissance of Continuous Flow Processes for Tailor-Made Macromolecules?" D. Wilms, J. Klos, H. Frey, Macromol. Chem. Phys. 2008, 209, 343–356. DOI: 10.1002/macp.200700588. |
| [2] | In cooperation with the research group of Professor Holger Löwe |
| [3] | "Microflow Technology in Polymer Synthesis" C. Tonhauser, A. Natalello, H. Löwe, H. Frey, Macromolecules 2012, 45, 9551–9570. DOI: 10.1021/ma301671x. |
| [4] | Institut für Mikrotechnik Mainz GmbH, Carl-Zeiss-Strasse 18-20, 55129 Mainz |
| [5] | "Carbanions on Tap – Living Anionic Polymerization in a Microstructured Reactor" F. Wurm, D. Wilms, J. Klos, H. Löwe, H. Frey, Macromol. Chem. Phys. 2008, 209, 1106–1114. DOI: 10.1002/macp.200700613. |
| [6] | "Living Anionic Polymerization in Continuous Flow: Facilitated Synthesis of High-Molecular Weight Poly(2-vinylpyridine) and Polystyrene" A. Natalello, J. Morsbach, A. Friedel, A. Alkan, C. Tonhauser, A. H. E. Müller, H. Frey, Org. Process Res. Dev. 2014, 18, 1408–1412. DOI: 10.1021/op500149t. |
| [7] | "A road less traveled to functional polymers: Epoxide termination in living carbanionic polymer synthesis" C. Tonhauser, H. Frey, Macromol. Rapid Commun. 2010, 31, 1938–1947. DOI: 10.1002/marc.201000353. |
| [8] | "Multihydroxyl-Functional Polystyrenes in Continuous Flow" C. Tonhauser, D. Wilms, F. Wurm, E. B. Nicoletti, M. Maskos, H. Löwe, H. Frey, Macromolecules 2010, 43, 5582–5588. DOI: 10.1021/ma902849r. |