Topics in Current Chemistry (2018) 376:44
1 3
showed that the polymerization carried out in droplets proceeded under nearly isothermal conditions, hence achieving narrow molecular weight distributions, benefiting from efficient heat removal by the continuous aqueous phase [131]. Moreover,
they applied a microfluidic platform to establish a continuous and rapid process for
the preparation of phosphine-functionalized polystyrene microcapsules through the
suspension polymerization. In situ and continuous droplet formation and polymerization in the microchannels allowed the particle sizes of the microcapsules to be
accurately controlled in the range of 320–420 μm with about 4-min residence time.
The microcapsules could effectively immobilize Pd(PPh 3 ) 4 catalysts, and showed
superior catalytic activity than homogeneous Pd catalysts, possessing great potential
application on fixed-bed reactors [132].
Controllable synthesis of micro-sized polymer particles bearing features such as
nonspherical shapes and spatially segregated chemical properties becomes increasingly important. Fundamental studies such as self-assembly and rheological behavior of polymer particles are being carried out, which are driven by relevant applications related to medical diagnostics and photonic devices. Chu et al. demonstrated
a versatile method to prepare hole-shell poly (N-isopropylacrylamide) microparticles in coaxial capillary microreactors, and the control over the hole-shell structures
was realized by manipulating the adhesion-energy-dependent configuration of the
W/O/W double emulsions for the free radical polymerization, as shown in Fig. 10
[133].
Based on a single-step method of continuous microfluidic technology, Nie et al.
synthesized highly monodispersed spherical polymer capsules, with each having a
controllable number of droplets. A planar microfluidic flow-focusing device was
fabricated to obtain a coaxial jet of silicon oil and monomer tripropyleneglycol diacrylate (TPGDA) or ethyleneglycol dimethacrylate (EGDMA) in the continuous
aqueous phase. Controllable rupture of the coaxial liquid thread resulted in the production of highly uniform droplets with various morphologies, which were subsequently photopolymerized in this microfluidic reactor to produce spherical polymer
capsules or granules with different shapes [134]. Latterly, they achieved the synthesis of amphiphilic Janus particles and three-phase particles in microfluidic devices,
having distinct interfaces between the constituent phases. Furthermore, the structure and size distribution of microbeads can be precisely controlled [135]. Luo et al.
described a method for the controllable preparation of monodispersed polyacrylamide (PAM) hydrogel microspheres in microchannels. With n-octane as the continuous phase, droplets containing monomers, cross-linkers, and initiators are continuously produced in a coaxial microfluidic device, which had uniform size in the range
of 400–600 μm with the coefficient of diameter variation below 4%. The influences
of various reaction temperatures and monomer solution compositions on the skeletal
structure and absorptive capacity of PAM in deionized water were also investigated
[136]. Then, a series of core–shell poly (acrylamide-co-sodium acrylate) hydrogel
beads were prepared in this microfluidic device by the one-step inverse suspension
polymerization, which had potential use in optical, sensor and other fields [137]
(Fig. 11).
172
Reprinted from the journal
1 3
showed that the polymerization carried out in droplets proceeded under nearly isothermal conditions, hence achieving narrow molecular weight distributions, benefiting from efficient heat removal by the continuous aqueous phase [131]. Moreover,
they applied a microfluidic platform to establish a continuous and rapid process for
the preparation of phosphine-functionalized polystyrene microcapsules through the
suspension polymerization. In situ and continuous droplet formation and polymerization in the microchannels allowed the particle sizes of the microcapsules to be
accurately controlled in the range of 320–420 μm with about 4-min residence time.
The microcapsules could effectively immobilize Pd(PPh 3 ) 4 catalysts, and showed
superior catalytic activity than homogeneous Pd catalysts, possessing great potential
application on fixed-bed reactors [132].
Controllable synthesis of micro-sized polymer particles bearing features such as
nonspherical shapes and spatially segregated chemical properties becomes increasingly important. Fundamental studies such as self-assembly and rheological behavior of polymer particles are being carried out, which are driven by relevant applications related to medical diagnostics and photonic devices. Chu et al. demonstrated
a versatile method to prepare hole-shell poly (N-isopropylacrylamide) microparticles in coaxial capillary microreactors, and the control over the hole-shell structures
was realized by manipulating the adhesion-energy-dependent configuration of the
W/O/W double emulsions for the free radical polymerization, as shown in Fig. 10
[133].
Based on a single-step method of continuous microfluidic technology, Nie et al.
synthesized highly monodispersed spherical polymer capsules, with each having a
controllable number of droplets. A planar microfluidic flow-focusing device was
fabricated to obtain a coaxial jet of silicon oil and monomer tripropyleneglycol diacrylate (TPGDA) or ethyleneglycol dimethacrylate (EGDMA) in the continuous
aqueous phase. Controllable rupture of the coaxial liquid thread resulted in the production of highly uniform droplets with various morphologies, which were subsequently photopolymerized in this microfluidic reactor to produce spherical polymer
capsules or granules with different shapes [134]. Latterly, they achieved the synthesis of amphiphilic Janus particles and three-phase particles in microfluidic devices,
having distinct interfaces between the constituent phases. Furthermore, the structure and size distribution of microbeads can be precisely controlled [135]. Luo et al.
described a method for the controllable preparation of monodispersed polyacrylamide (PAM) hydrogel microspheres in microchannels. With n-octane as the continuous phase, droplets containing monomers, cross-linkers, and initiators are continuously produced in a coaxial microfluidic device, which had uniform size in the range
of 400–600 μm with the coefficient of diameter variation below 4%. The influences
of various reaction temperatures and monomer solution compositions on the skeletal
structure and absorptive capacity of PAM in deionized water were also investigated
[136]. Then, a series of core–shell poly (acrylamide-co-sodium acrylate) hydrogel
beads were prepared in this microfluidic device by the one-step inverse suspension
polymerization, which had potential use in optical, sensor and other fields [137]
(Fig. 11).
172
Reprinted from the journal