Flow-microreactor-system-controlled polymerization

Recently, it has been demonstrated that good control of molecular weight and molecular weight distribution can be attained by using microreactor systems without stabilizing the carbocationic intermediates. The concept of this new technology (flow-microreactor-system-controlled polymerization) is described in the following... 

An example of microreactor systems for block copolymerization is shown in Fig. 7. The first monomer IBVE is mixed with TfOH in the first micromixer (Ml). Introduction of the second monomer (NB VE or EVE) at the second micromixer M2 results in the formation of the polymer of higher molecular weight with narrow molecular weight distribution [128]. Block copolymerization can be carried out with any combination and with either order of monomer addition, as shown in Table 3, demonstrating that the present method serves as a flexible method for the synthesis of block copolymers. Therefore, flow-microreactor-system-controlled polymerization can serve as a powerful method for synthesis of structurally well-defined polymers and copolymers in industry. 

It is easily anticipated that flow microreactors can enjoy industrial applications by virtue of inherent advantages based on their microstructure and flow nature. Significant progress in flow-microreactor-system-controlled polymerization to obtain structurally well-defined polymers has already been made to meet the demands of the chemical industry. The lack of need for cryogenic conditions for anionic polymerizations may enable commercial production. Some pilot plants have already been built and tested to examine the feasibility and durability of polymerization in flow microreactors. For example, a microchemical pilot plant... 

Similarly, MF synthesis offers crucial benefits for living anionic polymerization [39b,46]. For example, for polymerization of alkyl methacrylates conducted in a flow microreactor system, control over molecular weight distribution was achieved under easily accessible conditions at temperatures of —28 °C (methyl methacrylate, Mw/Mn = 1.16), 0°C (butyl methacrylate, M /M = 1.24), and 24°C (t-butyl methacrylate, M /M = 1.12) [39b]. The molecular weight of the polymer increased with increasing monomer to initiator ratio. Furthermore, a subsequent reaction of a reactive polymer chain with alkyl methacrylate yielded a block copolymer with a narrow molecular weight distribution. 

Microreactors have also been used for ionic polymerization or polycondensation processes. Nagaki et al. [136] have synthesized polystyrene-poly(alkyl methacrylate) block copolymers by butyllithium initiated anionic polymerization in an integrated flow microreactor system. A high level of control of molecular weight was achieved at temperatures between -28 and +24 °C due to fast mixing, fast heat transfer, and residence time control. Santos and Metzger... 

Controlled/Living Cationic Polymerization of Vinyl Ethers Based on Cation Stabilization Using Flow Microreactor Systems [100]... 

Controlled/Living Anionic Polymerization of Styrenes in Polar Solvent Using Flow Microreactor Systems [145]... 

Therefore, it is important to control these steps. However, in conventional batch systems, control of polymerization is difhcult due to local concentration gradients. In contrast, flow microreactor systems enable such control (Fig. 32)... 

A silicon-glass-based flow microreactor system that is suitable for long periods of use has been developed and applied to the polymerization of amino acid NCAs [229]. The flow microreactor exhibits excellent controllability of the molecular weight distribution. Moreover, a single flow microreactor can produce 100 mg/min of copoly(Lys-Leu). This means that more than 200 g of copoly(Lys-Leu) acids can be produced in 2 months. 

In Chap. 8, we have learned that a flow microreactor system incorporating a micromixer is useful in controlling competitive consecutive reactions. The ultimate reaction system in which reactions occur in chains, or consecutively, is polymerization. This chapter describes how we can exploit the advantages of the flow microreactor system in controlling the molecular weight or molecular weight distribution in polymerization reactions, including cationic polymerizalion and anionic polymerization. 

Polymerization of vinyl ethers initiated by an A -acyUminium ion pool has demonstrated that the molecular weight and the molecular weight distribution can be controlled by using the flow microreactor system (Fig. 10.5) [4, 5]. An iV-acyh-minium ion generated and accumulated by the cation pool method was used as an initiator, which was mixed with a vinyl ether at high speed using a micromixer. The polymerization proceeded in a flow microreactor and was complete within a short residence time. An amine was then introduced using a micromixer to terminate the polymerization. Thus, this polymerization can be called flash polymerization. 

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