copolymers can be also synthesized by sequential introduction of styrene and two
different alkyl methacrylates in a similar manner (styrene–t-BuMA–MMA triblock
copolymer, M n ¼ 8,800, M w /M n ¼ 1.23; styrene–t-BuMA–butyl methacrylate
triblock copolymer, M n ¼ 9,000, M w /M n ¼ 1.35).
1.4 Radical Polymerization
1.4.1 Free-Radical Polymerization Using Flow Microreactor Systems
Free-radical polymerization is an important process for the industrial synthesis
of macromolecules because free radicals are compatible with a wide variety of
functional groups that do not survive in ionic and metal-catalyzed polymerizations
[164]. Because free-radical polymerization is usually highly exothermic, a precise
temperature control is essential for performing free-radical polymerization in a
highly controlled manner. Therefore, the polymerization in a conventional batch
macroreactor often suffers from a low level of molecular weight distribution control
because of inefficient heat removal and the lack of homogeneity of the reaction
temperature. Therefore, the controllability of the reaction temperature is a major
concern in free-radical polymerization from the viewpoint of industrial applications.
As a matter of fact, heat removal capacity is often a limiting factor in polymerizations
in batch macroreactors. Therefore, the advantage of flow microreactors for radical
polymerization is obvious because they enable fast heat transfer.
Iwasaki and Yoshida reported the free-radical polymerization of various
monomers using flow microreactor systems. Polymerization of butyl acrylate
(BA) gives a polymer of much smaller M w /M n than that obtained with a batch
macroreactor because of a much higher heat-removal efficiency in the flow
microreactor (Fig. 20) [165]. For the polymerization of benzyl methacrylate
(nBMA) and MMA, the effect of the flow microreactor on molecular weight
distribution control is smaller than for BA. For the polymerization of vinyl benzoate
(VBz) and styrene, no appreciable effect is observed. The tendency indicates that
the flow microreactor is quite effective for highly exothermic polymerization such
as that of BA, but not so effective for less exothermic polymerizations. Similar
results on the polymerization of styrene have been reported by Leveson et al. [166].
Moreover, a microchemical pilot plant for radical polymerization of MMA has been
built by numbering-up (i.e., scaling up by parallel operation of a number of units)
eight microtube reactors (vide infra) [167].
The effects of mixing in radical polymerization of MMA are interesting [168].
The use of a 5 mm static mixer leads to fouling in the reactor. In contrast, the use of
an interdigital multilamination micromixer with 36 lamellae of 25 mm thickness
results in a reduction in fouling. This numbering-up approach enables production of
2,000 tons per year without the fouling problem [169].
Controlled Polymerization in Flow Microreactor Systems
21
different alkyl methacrylates in a similar manner (styrene–t-BuMA–MMA triblock
copolymer, M n ¼ 8,800, M w /M n ¼ 1.23; styrene–t-BuMA–butyl methacrylate
triblock copolymer, M n ¼ 9,000, M w /M n ¼ 1.35).
1.4 Radical Polymerization
1.4.1 Free-Radical Polymerization Using Flow Microreactor Systems
Free-radical polymerization is an important process for the industrial synthesis
of macromolecules because free radicals are compatible with a wide variety of
functional groups that do not survive in ionic and metal-catalyzed polymerizations
[164]. Because free-radical polymerization is usually highly exothermic, a precise
temperature control is essential for performing free-radical polymerization in a
highly controlled manner. Therefore, the polymerization in a conventional batch
macroreactor often suffers from a low level of molecular weight distribution control
because of inefficient heat removal and the lack of homogeneity of the reaction
temperature. Therefore, the controllability of the reaction temperature is a major
concern in free-radical polymerization from the viewpoint of industrial applications.
As a matter of fact, heat removal capacity is often a limiting factor in polymerizations
in batch macroreactors. Therefore, the advantage of flow microreactors for radical
polymerization is obvious because they enable fast heat transfer.
Iwasaki and Yoshida reported the free-radical polymerization of various
monomers using flow microreactor systems. Polymerization of butyl acrylate
(BA) gives a polymer of much smaller M w /M n than that obtained with a batch
macroreactor because of a much higher heat-removal efficiency in the flow
microreactor (Fig. 20) [165]. For the polymerization of benzyl methacrylate
(nBMA) and MMA, the effect of the flow microreactor on molecular weight
distribution control is smaller than for BA. For the polymerization of vinyl benzoate
(VBz) and styrene, no appreciable effect is observed. The tendency indicates that
the flow microreactor is quite effective for highly exothermic polymerization such
as that of BA, but not so effective for less exothermic polymerizations. Similar
results on the polymerization of styrene have been reported by Leveson et al. [166].
Moreover, a microchemical pilot plant for radical polymerization of MMA has been
built by numbering-up (i.e., scaling up by parallel operation of a number of units)
eight microtube reactors (vide infra) [167].
The effects of mixing in radical polymerization of MMA are interesting [168].
The use of a 5 mm static mixer leads to fouling in the reactor. In contrast, the use of
an interdigital multilamination micromixer with 36 lamellae of 25 mm thickness
results in a reduction in fouling. This numbering-up approach enables production of
2,000 tons per year without the fouling problem [169].
Controlled Polymerization in Flow Microreactor Systems
21