1 3
Topics in Current Chemistry (2018) 376:44
they carried out the RAFT polymerization of acrylates, and the polymer samples were
directly used as macro-RAFT agents to sequentially copolymerize with butyl acrylate
for a second block, demonstrating that the whole polymerization could proceed in a
well-controlled manner with the use of microreactors. In order to prolong the time for
RAFT processes, continuous and looping processing can be applied. Zhu et al. conducted the RAFT polymerization of butyl acrylate in 50 wt% toluene, initiated with 2,
2′-azobisisobutyronitrile and mediated with 3-benzyltrithiocarbonyl propionic acid in
tube reactor operated in three modes (i.e., batch, continuous and looping processing)
[123]. The dynamic and steady state kinetics were analyzed and compared, confirming
that the polymerization in the microtube reactor exhibited good livingness and yielded
unimodal polymer products. It also demonstrated that the looping tube reactor combined with living radical polymerization technology represented a powerful tool to tailor polymers with multimodal molecular weight distributions, simply by adjusting the
residence time and recycle ratio.
4.6 NMP Processes
Ryu and coworkers investigated the polymerization of styrene, butyl acrylate, or
methyl methacrylate via NMP in microreactors [124]. The polymerization processes
that were carried out in the microreactors had higher conversions and the produced
polymers had lower PDI values in comparison with the conventional batch reactors.
Serra et al. conducted the NMP process of styrene or n-butyl acrylate at 140 °C in a
stainless-steel microreactor with an inner diameter of 900 μm [125]. In this microreactor system, a back pressure regulator was equipped to keep the system pressure
greater than 20 bar with the reaction mixture as a liquid phase. The polymerization
performance in the microreactor was investigated and compared with a conventional
batch reactor. For the polymerization of styrene, the polymer property difference
between the batch reactor and the microreactor could not be distinguished. However,
for the n-butyl acrylate polymerization, the PDI value of synthesized polymers was
decreased from 1.80 in the batch reactor to 1.44 in the microreactor.
4.6.1 Polycondensation
Polycondensation is a kind of step-growth polymerization in which monomer molecules typically containing two reactive end groups join together and generate small
molecules as byproducts such as water and methanol [10]. Linear polymers are produced from bifunctional monomers, i.e., compounds with two reactive end groups
[126]. Most polycondensation processes, such as the processes for production of
polyamide, polyurethane, and polyimide, are highly exothermic, which require an
efficient heat-removal ability for the reactor. Recently, the application of microreactors has been extended to polycondensation processes due to its excellent heat transfer performance.
Wang et al. designed a microstructured chemical system for the preparation of
poly(p-phenylene terephthalamide) (PPTA) by the polycondensation method including two steps, which consisted of the fast process for the generation of the reactive
169
Reprinted from the journal
Topics in Current Chemistry (2018) 376:44
they carried out the RAFT polymerization of acrylates, and the polymer samples were
directly used as macro-RAFT agents to sequentially copolymerize with butyl acrylate
for a second block, demonstrating that the whole polymerization could proceed in a
well-controlled manner with the use of microreactors. In order to prolong the time for
RAFT processes, continuous and looping processing can be applied. Zhu et al. conducted the RAFT polymerization of butyl acrylate in 50 wt% toluene, initiated with 2,
2′-azobisisobutyronitrile and mediated with 3-benzyltrithiocarbonyl propionic acid in
tube reactor operated in three modes (i.e., batch, continuous and looping processing)
[123]. The dynamic and steady state kinetics were analyzed and compared, confirming
that the polymerization in the microtube reactor exhibited good livingness and yielded
unimodal polymer products. It also demonstrated that the looping tube reactor combined with living radical polymerization technology represented a powerful tool to tailor polymers with multimodal molecular weight distributions, simply by adjusting the
residence time and recycle ratio.
4.6 NMP Processes
Ryu and coworkers investigated the polymerization of styrene, butyl acrylate, or
methyl methacrylate via NMP in microreactors [124]. The polymerization processes
that were carried out in the microreactors had higher conversions and the produced
polymers had lower PDI values in comparison with the conventional batch reactors.
Serra et al. conducted the NMP process of styrene or n-butyl acrylate at 140 °C in a
stainless-steel microreactor with an inner diameter of 900 μm [125]. In this microreactor system, a back pressure regulator was equipped to keep the system pressure
greater than 20 bar with the reaction mixture as a liquid phase. The polymerization
performance in the microreactor was investigated and compared with a conventional
batch reactor. For the polymerization of styrene, the polymer property difference
between the batch reactor and the microreactor could not be distinguished. However,
for the n-butyl acrylate polymerization, the PDI value of synthesized polymers was
decreased from 1.80 in the batch reactor to 1.44 in the microreactor.
4.6.1 Polycondensation
Polycondensation is a kind of step-growth polymerization in which monomer molecules typically containing two reactive end groups join together and generate small
molecules as byproducts such as water and methanol [10]. Linear polymers are produced from bifunctional monomers, i.e., compounds with two reactive end groups
[126]. Most polycondensation processes, such as the processes for production of
polyamide, polyurethane, and polyimide, are highly exothermic, which require an
efficient heat-removal ability for the reactor. Recently, the application of microreactors has been extended to polycondensation processes due to its excellent heat transfer performance.
Wang et al. designed a microstructured chemical system for the preparation of
poly(p-phenylene terephthalamide) (PPTA) by the polycondensation method including two steps, which consisted of the fast process for the generation of the reactive
169
Reprinted from the journal