Cation-pool initiated

Figure 3. Microsystem for the "cation pool initiated polymerization of...

Yoshida and coworkers also developed a microreaction system for cation pool-initiated polymerization [62]. Significant control of the molecular weight distribution (Mw/Mn) was achieved when N-acyliminium ion-initiated polymerization of butyl vinyl ether was carried out in a microflow system (an IMM micromixer and a microtube reactor). Initiator and monomer were mixed using a micromixer, which was connected to a microtube reactor for the propagation step. The polymerization reaction was quenched by an amine in a second micromixer. The tighter molecular weight distribution (Mw/M = 1.14) in the microflow system compared with that of the batch system (Mw/M > 2) was attributed to the very rapid mixing and precise control of the polymerization temperature in the microflow system. 

Cation-pool Initiated Polymerization of Vinyl Ethers Using a Microflow System ... 

Scheme 9.9 Cation-pool initiated polymerization of vinyl ethers...

Nagaki A, Kawamura K, Suga S, Ando T, Sawamoto M, Yoshida J (2004) Cation pool-initiated controlled/living polymerization using microsystems. J Am Chem Soc 126(45) 14702-14703... 

The polymer end is living within the residence time of 0.5 s at —78°C, and can be effectively trapped by allyltrimethylsUane. Moreover, the cation pool -initiated... 

Therefore, as shown in the above example, the polymer end is really living within a residence time of 0.5 s at —78 °C in the cation pool-initiated polymerization using MCPT. 

The present cation pool-initiated polymerization using a microflow system can be applied to other vinyl ethers such as isobutyl vinyl ether (IBVE) and tert-butyl vinyl ether (TBVE) (Table 14.2). The corresponding macroscale batch polymerization results in much poorer molecular weight distribution control. 

Carbocationic Polymerization Using a Cation Pool" as an Initiator... 

Both the reaction of an initiator (In) with a monomer (M) and the reactions of propagating polymer (Pn) with a monomer (M) are very fast (Scheme 9.8). Therefore, we have to consider the possibility of disguised chemical selectivity, which is observed for Friedel-Crafts reactions of reactive aromatic compounds and a cation pool. If mixing is slow, the consecutive propagation reactions take place before all of the initiators react with monomers, even if the consecutive propagation reactions are slower than the initiation reaction. This is also an example of disguised... 

The requirement of extremely fast initiation can be met by the use of a highly reactive cation pool as an initiator, which we have already discussed in the previous chapters. In fact, the use of the less sterically demanding, highly reactive N-acyliminium ion shown in Scheme 9.9 is quite effective for polymerization of vinyl ethers. 

The example discussed in the previous sections illustrates the potential of microflow systems, in conjunction with a strong acid initiator, such as a cation pool, to effect cationic polymerization in a highly controlled manner without the deceleration inherent in the dynamic equilibrium... 

Fig. 5 Flow microreactor system for polymerization of vinyl ether initiated by Af-acyliminium ion (cation pool). Ml, M2 micromixers Rl, R2 microtube reactors...

Scheme 14.1 The formation of the cation pool and the initiation of the polymerization [13].

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