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Topics in Current Chemistry (2018) 376:44
with 1.6-mm inner diameter. The results showed that the reaction rate in the tubular reactor was faster than that in batch, but the value of PDI was higher, which
might be attributed to the back mixing or axial distribution [144]. Cunningham et al.
reported the NMP mini-emulsion polymerization of styrene in a tubular reactor and
a batch reactor, and both of these operational modes showed stable particle latexes
and similar kinetics [145]. Zhu et al. performed the surfactant-free RAFT emulsion
polymerization of MMA in a stainless-steel tubular reactor, in which the RAFT
agent worked as emulsion stabilizer in the following reaction [146]. Furthermore, a
polymerization-induced self-assembly system was realized in a two-stage continuous tubular reactor [147]. Polyethylene glycol maleate (PEGMA) and MMA were
used as the monomers for the steric stabilizer block and core-forming block, and
the evolution of particle diameter during the flow process followed two modes. The
particle diameter either maintained constant or gradually increased, depending on
whether the mixer was a T-joint or a static mixer [148] (Fig. 12).
Boyer et al. reported the PET (photoinduced electron/energy transfer electron
transfer)-RAFT polymerization in a photoflow tubular microreactor for the production of polymer blends with specific molecular weight distributions and chemical
compositions at a flow rate from 10 to 433.3 μl/min. It was found that the injected
inert gas and the monomer solution formed the gas–liquid slug flow in the microreactor and thus increased the regularity of the polymer product. The gas–liquid twophase operation led to fluid profiles close to the plug flow behavior, even at very low
Reynolds numbers. In addition, the increased mixing in the liquid plugs during the
polymerization improved the homogeneity of the reaction mixture, and minimized
negative effects such as deviation from targeted molecular weights and long tailing
at high molecular weights [149].
4.7.3 Catalyzed Polymerization
The continuous-flow reactor is not only the sealed compartment through which the
reaction solution flows but also serves as the catalyst source required for the polymerization, which has already been demonstrated in the aforementioned ATRP heterogeneous polymerization [141, 142].
In other systems, Beers et al. reported the demonstration of a solid supported
enzyme-catalyzed polymerization in a continuous-flow mode (see Fig. 13). The
ring-opening polymerization of ε-caprolactone (CL) by using immobilized Candida Antarctica Lipase B (CALB) as a biocatalyst was conducted in the aluminum
microchannel reactor, inside which reactants were forced to be in contact with the
enzyme. Many active sites of the enzyme were available during the polymerization,
and the enzyme leaching was lower in the microreactor compared to the batch reactor. The apparent rate constant in the microreactor was 27 times larger than in the
batch reactor with the same amount of enzyme loading and the same temperature.
Moreover, higher end-group functionalization and higher molecular weights were
obtained in the microreactor [150].
Guo et al. established a PTFE tubular microreactor for enzymatic chemoselective ring open polymerization of ε-caprolactone and δ-valerolactone (VL). In this
continuous-flow processing, higher thiol fidelity, faster polymerization rates, and
175
Reprinted from the journal
Topics in Current Chemistry (2018) 376:44
with 1.6-mm inner diameter. The results showed that the reaction rate in the tubular reactor was faster than that in batch, but the value of PDI was higher, which
might be attributed to the back mixing or axial distribution [144]. Cunningham et al.
reported the NMP mini-emulsion polymerization of styrene in a tubular reactor and
a batch reactor, and both of these operational modes showed stable particle latexes
and similar kinetics [145]. Zhu et al. performed the surfactant-free RAFT emulsion
polymerization of MMA in a stainless-steel tubular reactor, in which the RAFT
agent worked as emulsion stabilizer in the following reaction [146]. Furthermore, a
polymerization-induced self-assembly system was realized in a two-stage continuous tubular reactor [147]. Polyethylene glycol maleate (PEGMA) and MMA were
used as the monomers for the steric stabilizer block and core-forming block, and
the evolution of particle diameter during the flow process followed two modes. The
particle diameter either maintained constant or gradually increased, depending on
whether the mixer was a T-joint or a static mixer [148] (Fig. 12).
Boyer et al. reported the PET (photoinduced electron/energy transfer electron
transfer)-RAFT polymerization in a photoflow tubular microreactor for the production of polymer blends with specific molecular weight distributions and chemical
compositions at a flow rate from 10 to 433.3 μl/min. It was found that the injected
inert gas and the monomer solution formed the gas–liquid slug flow in the microreactor and thus increased the regularity of the polymer product. The gas–liquid twophase operation led to fluid profiles close to the plug flow behavior, even at very low
Reynolds numbers. In addition, the increased mixing in the liquid plugs during the
polymerization improved the homogeneity of the reaction mixture, and minimized
negative effects such as deviation from targeted molecular weights and long tailing
at high molecular weights [149].
4.7.3 Catalyzed Polymerization
The continuous-flow reactor is not only the sealed compartment through which the
reaction solution flows but also serves as the catalyst source required for the polymerization, which has already been demonstrated in the aforementioned ATRP heterogeneous polymerization [141, 142].
In other systems, Beers et al. reported the demonstration of a solid supported
enzyme-catalyzed polymerization in a continuous-flow mode (see Fig. 13). The
ring-opening polymerization of ε-caprolactone (CL) by using immobilized Candida Antarctica Lipase B (CALB) as a biocatalyst was conducted in the aluminum
microchannel reactor, inside which reactants were forced to be in contact with the
enzyme. Many active sites of the enzyme were available during the polymerization,
and the enzyme leaching was lower in the microreactor compared to the batch reactor. The apparent rate constant in the microreactor was 27 times larger than in the
batch reactor with the same amount of enzyme loading and the same temperature.
Moreover, higher end-group functionalization and higher molecular weights were
obtained in the microreactor [150].
Guo et al. established a PTFE tubular microreactor for enzymatic chemoselective ring open polymerization of ε-caprolactone and δ-valerolactone (VL). In this
continuous-flow processing, higher thiol fidelity, faster polymerization rates, and
175
Reprinted from the journal