polymer chemistry in microfluidic reaction system

Micro and Nanosystems, 2009, 1, 193-204 193

1876-4029/09 $55.00+.00 © 2009 Bentham Science Publishers Ltd.

Polymer Chemistry in Microfluidic Reaction System

Masaya Miyazaki*,1,2

, Hiroshi Yamaguchi1, Takeshi Honda

#,1, Maria Portia P. Briones-Nagata

1,

Kenichi Yamashita1 and Hideaki Maeda

1,2,3

1Nanotechnology Research Institute, National Institute of Advanced Industrial Science and Technology, Saga, Japan

2Department of Molecular and Material Science, Interdisciplinary Graduate School of Engineering Sciences, Kyushu

University, Fukuoka, Japan

3CREST, Japan Science and Technology Agency, Saitama, Japan

Abstract: Polymer synthesis requires strict control of reaction conditions such as temperature, reaction time, and mixing of reagents. Microfluidic reaction systems enable efficient mixing and rapid heat exchange. Moreover, laminar stream in a microfluidic channel enables control of the resulting shape of a molecule.

This article reviews the use of microfluidic technology in the field of polymer chemistry. First, conformational aspects of polymers in microfluid are summarized. Next, the techniques for linear and branched polymer synthesis are described. We also describe the potential use of microreaction system for polymer particle and membrane synthesis. A description of how it would be possible to use this technology to prepare larger quantities of polymer compounds is also given.

INTRODUCTION

Reactions involved in chemical polymerization should be highly controlled because reaction condition determines polymer properties such as average molecular weight, mo-lecular weight distribution, and size and shape of particle. These features strongly affect the functions of resulting polymer materials. When using polymers of less well known functions, the molecular weight or size and shape should be carefully selected, and the molecular weight or size distribu-tion should be controlled as narrow as possible to know much about the properties of polymers. Such requirements could be satisfied by utilizing microfluidic systems. Micro-fluidic reaction systems have several distinctive features [1]. One of the unique features of microfluidic system is the abil-ity to control molecular weight distribution and simple con-trol of average molecular weight of linear polymers. In addi-tion, microfluidic systems enable efficient emulsification with strictly controlled size and shape. Present-day investiga-tions on polymer materials are directed towards the devel-opment of novel functional substances with controlled shape by using high-throughput and combinatorial synthesis meth-ods. The microdevices developed for this purpose should be simple, controllable, and capable of continuous combinato-rial synthesis process with high-throughput screening system for polymer material libraries. Moreover, there is a require-ment for accelerated multi-parameter optimization of reac-tion conditions for polymer synthesis. In this review, efforts towards the development of microreactors for linear and branched polymer synthesis and preparation of simple and complicated polymer particle are summarized.

*Address correspondence to this author at the Nanotechnology Research

Institute, National Institute of Advanced Industrial Science and Technology,

807-1 Shuku, Tosu, Saga 841-0052, Japan; Tel: +81(942)81-4059; Fax:

+81(942)81-3627; E-mail: [email protected] #Present Address: Department of Pharmacology, Yamaguchi University

Graduate School of Medicine, Yamaguchi, Japan.

BASIC ASPECT OF MICROFLUIDIC SYSTEMS FOR POLYMER CHEMISTRY

Enhanced Mixing in Microchannel

To control polymerization reactions, mixing is important

to obtain homogeneous reaction mixture solutions. Stirring

in classical reactors, such as round-bottom flasks and larger

batch reactors, is limited by non-homogeneities in the flow

fields created by the stirring bar or impeller, respectively.

The shear forces that cause the convection by stirring bar are

significantly dampened away from the stirrer, and the major-

ity of the round-bottom flask or reactor experiences little or

no mixing. The idle portions of a reaction environment allow

time for unproductive chemistry to take place because of

local concentration gradients. If unproductive chemistry is

not an issue, longer reaction times may be used to drive reac-

tions to completion, decreasing efficiency. Rapid mixing

results in faster reaction times and thus cleaner chemistry,

although rapid mixing is difficult to achieve in a classic reac-tor for the reasons outlined previously.

On the other hand, continuously flowing microreactors

allow rapid and homogeneous mixing because of their small

dimensions. Microreactors can achieve complete mixing in

microseconds, whereas classical reactors mix on the times-

cale of seconds. Microreactors achieve this rapid mixing

using a variety of strategies. The multilamellar approach in

which layers of fluids ranging in thickness from 50 to 200

μm are sandwiched together, have been widely applied. The

commercially-available systems, such as IMM mixers, the

small dimensions allow rapid diffusional mixing to occur in

as little as 100μs [2]. Such rapid mixing occurs because

these lamellar systems achieve surface-to-volume ratios of

up to 30,000 m2 m

-3, in contrast to laboratory beakers and

batch reactors, which typically have surface-to-volume ratios

of 100 and 4 m2 m

-3, respectively. These surface-to-volume

ratios impact thermal and mass transport. Several micromix-ers have been used for much type of chemical reactions [3].

194 Micro and Nanosystems, 2009 Vol. 1, No. 3 Miyazaki et al.

Efficient Thermal Exchange

Heating and cooling is an important variable for chemical reactions. Batch reactors often provide broad temperature profiles that can allow access to multiple pathways when only one pathway is desired. The precise thermal manage-ment available in a microreactor enables efficient, high-temperature reactions, such as the conversion of methane to methanol, fine control over the reaction selectivity, and the ability to perform otherwise explosive chemistry. Polymer syntheses have been recognized as an exothermic reaction which can cause explosions. A microreactor can enable highly exothermic polymerizations safely and with a degree of control that limits side reactions such as premature chain termination or chain transfer.

Conformational Aspects of Polymers in Laminar Flow System

Laminar flow system provides conformational restriction for the polymers. The interface between liquids flowing laminarly has some unique attributes. Fluid behavior within a microchannel forms a laminar flow, and the fluids did not

mix convectively; rather, the individual streams flowed side by side, mixing only by diffusion at the interface. The lami-nar flow within microchannel creates an extensional flow field in which large macromolecules can be aligned. If two fluids flowing past each other are moving at different rates, a shear force develops at the interface that can align structures. For instance, we showed that DNA can be elongated and aligned to the direction of flow. We reported that direct ob-servation method for macromolecules, such as long-strand DNA, in microchannel flow (Fig. 1) as well as a simple method for stretching DNA strands by microfluidics [4]. Stretching and orientation of DNA molecules by control of flow within a microchannel was observed by optical micros-copy. This DNA stretching is explained by coil–stretch tran-sition of polymer molecules [5]. We thought such elongation of macromolecules might be useful for creating chemical reactions with macromolecules, because steric hindrance by tanglar polymer molecule is minimized. We demonstrate this hypothesis by accomplishment of efficient hybridization of long-strand DNA by low affinity short PNA molecules [6]. Photoaffinity labeling very weak binder reacts with target sequence within DNA molecule efficiently. We also demon-strated that the shift in thermal stability of DNA duplex and

Fig. (1). Long-strand DNA structure in microchannel. DNA molecules are at non-flow state (A), flowing at 5 ml min-1 (B), and 10ml min-1.

(D) Fluorescence intensity distribution map single DNA chain (encircled in panel (C)) and its expected form. This figure was reproduced

with permission from ref. [6].

Polymer Chemistry in Microfluidic Reaction System Micro and Nanosystems, 2009 Vol. 1, No. 3 195

its thermodynamics spectroscopically, caused by stretching and orientation of DNA strands in a microchannel laminar flow [7,8]. The enthalpy-entropy compensation was influ-enced by both DNA strand length and flow speed, and the penalties of enthalpy were 2-12% greater than the benefits of entropy. Such conformational and thermodynamic features of laminar flow system are applicable for direct chemical substitution of other macromolecules.

SYNTHESIS OF LINEAR POLYMERS IN MICRO-FLUIDIC REACTOR

Microreaction systems involve microreaction apparatuses that enable high controllability of chemical reactions. Such controllability results from efficient heat transfer, mass transport, and/or larger surface/interface area. Recent studies have shown the potential benefits of using microfluidic reac-tors for various chemical reactions [9]. Reactions using mi-cromixing devices give better results than batchwise reac-tions. This is because micromixer enables rapid mixing and therefore, yields excellent controllability of rapid reactions.

Application of microreaction technology for linear poly-mer syntheses has been initially performed by several re-searchers, but the field is still in its infancy. Most of the work utilized a combination of micromixing and reaction parts.

Radical Polymerization

The most popular polymerization method is radical po-lymerization in which the reactive center of a polymer chain consists of a radical. The polymerization reaction is initiated by free-radical initiators, which generate radicals by thermal decomposition, photoimitiation, or redox initiation. Applica-tion of microreaction systems for radical polymerizations has been widely reported. Wu et al. performed radical polymeri-zation by using a chip-type microreactor (Fig. 2) [10]. The system is composed of a microstirrer mixer connected to a microchannel reaction part. The molecular mass of the polymer produced is governed by the flow rate or polymeri-zation time. The monomer conversion agrees well with the bulk reaction kinetics reported in literature. The reactor is convenient and inexpensive to manufacture, with a versatile design that can be reconfigured and prototyped in less than a day. Radical polymerization technique was also applied for

block copolymerization of poly(ethylene oxide-block-2-hydroxypropyl methacrylate) [11]. A series of well-controlled polymerizations was carried out at different pumping rates or reaction times with a constant ratio of monomer to initiator. The stoichiometry of the reactants was also adjusted by varying relative flow rates to change the reactant concentrations. Another example of radical polym-erization in a microreactor was described by Iwasaki et al. who reported a microreactor consisting of commercially available micromixers (T-shape, 500 μm i.d.) connected with capillary tubes (i.d. 500 μm) (Fig. 3) [12]. Thermal decom-position of 2,2-azobis(isobutylronitrile) (AIBN) was exam-ined first and subsequent polymerization of butyl acrylate (BA), benzyl methacrylates (BMA), methyl methacrylate (MMA), vinyl benzoate (VBz), and styrene (St) were per-formed. The microreactor was quite effective in controlling the molecular weight distribution for highly exothermic reac-tions (BA, BMA, and MMA) but not so effective for less thermic polymerizations (VBz and St).

Fig. (2). Microfluidic chip device used for radical polymerization.

This figure was reproduced with permission from ref. [10].

Rosenfeld et al. also reported radical copolymerization

using nitroxide initiator [13]. They performed synthesis of poly(n-butyl acrylate)-block-poly(styrene) copolymers in two serial continuous microtube reactors. The main advan-tage of interdigital micromixers is their ability to achieve an efficient and intimate mixing between a viscous (first block) and a liquid (comonomer) fluid due to the small film thick-nesses of the lamellae. In all experiments, the microtube re-actors coupled with a multilamination micromixer gave the narrowest molecular weight distributions. They concluded that the control of the copolymerization reaction was im-proved in their system.

Fig. (3). Microcapillary reactor system for polymerization. This figure was reproduced with permission from ref. [12].


Cationic Polymerization

Controlling cationic polymerization, which uses Br nstead acid or Lewis acid as the initiator of polymeriza-tion, was performed in a microreaction system consisting of two micromixers connected by microcapillaries (Fig. 4) [14]. A method that used irreversible generation and accumulation of highly reactive cations in the absence of nucleophile was applied for polymerization. The molecular weight distribu-tion was controlled by extremely fast micromixing, and the resulting polymer could be used for the follow-up reaction.

Much simpler polymerization technique using CF3SO3H initiation was also performed in microfluidic format [15]. Two micro heat exchangers were connected to a micromixer followed by reactor part to form microreaction system. Using this system the monomer solution and CF3SO3H solution were loaded separately. Polymerizations of several diisopro-pylbenzenes in microreactor yielded narrower molecular weight distribution.

Anionic Polymerization

Not only the cationic polymerization, but living anionic polymerization was also performed in a microfluidic format.

Wurn applied micromixing technique using IMM’s multi-lamination micromixer for living anionic polymerization of stylene [16]. They performed homo- and diblock copolymer synthesis of stylene, which requires “break-seal” and “high-vacuum” reaction techniques. By microfluidic system, they did not require such special technique, and yielded complete end-functionalized polymers at the range of MW=500-70000 with Mw/Mn=1.09-1.25.

Another example was reported by Iida et al. using chip-type microreactor with active mixing (Fig. 5) [17]. They designed flow channel structure at 2D, and examined its ef-fect. They concluded passive mixing arise from designated channel improved the reaction conditions.

Polycondensation

The benefit of microreaction system is not limited to cationic, anionic or radical polymerization. Amino acid po-lymerization, a kind of polycondansation, was performed in microfluidic format [18,19]. Polymerization reaction of -amino acid N-carboxyanhydride (NCA: Scheme 1) in mi-croreactor tethering miultilamination micromixer (Fig. 6) yielded better molecular weight distribution than that of macroscale reaction product. Also, the average molecular

Fig. (4). Microreaction system used for cationic polymerization. This figure was reproduced with permission from ref. [14].

Fig. (5). Schematic of living anionic polymerization using a microfluidic reactor. This figure was reproduced with permission from ref. [17].


Scheme 1.

Fig. (6). Microreaction system used for polycondensation of amino acids. This figure was reproduced with permission from ref. [18].

weight could be controlled by changing the flow rates. Not only simple polymerization, copolymerization of two differ-ent NCA performed in this microreaction system yielded narrower molecular weight distributions.

We also examined effect of microfluidic reaction system for peptide polymerization reaction [20]. Model peptide polymers of elastin and collagen were synthesized in micro-

fluidic reactor tethering chaotic micromixer. DMSO solu-tions of peptide monomers [H-Pro-Hyp(Bzl)-Gly-OH for collagen and H-Gly-Val-Gly-Val-Pro-OH for elastin] and condensation reagent DPPA (diphenylphosphoryl azide) were loaded from different inlet of chaotic micromixer chip (Fig. 7). Resulting polymer was higher molecular weight than conventional synthesis in flask with narrower molecular weight distribution.

Fig. (7). The microreaction system used for peptide polymer synthesis. (a) The chaotic micromixer chip; (b) Total setup. This figure was

reproduced with permission from ref. [20].


Syntheisi of Branched Polymer

Synthesis of dendric molecule was also performed. Chang et al. synthesized ethylenediamine-cored poly(amido-amine) (PAMAM) dendrimer (Scheme 2) using interdigital micromixer (Fig. 8) [21]. By using this method, synthesis of generation 2 through generation 5 PAMAM dendrimer was confirmed by microchip capillary zone electrophoresis. Fur-thermore, the synthesized polyamide dendron was deposited onto functionalized glass surface through the formation of amide bond using a facile coupling procedure via a microre-actor. The dendron deposition process involved two major steps: functionalization of the native glass surface using 3-aminopropyl triethoxysilane, and coupling of the synthesized polyamide dendron with an aminosilanised surface. Com-pared with the conventional synthesis method, the microre-actor provides better yield, selectivity, and considerably faster synthesis rate. Nanostructured polyamide G1 dendron thin films could be deposited using an impinging flux from this microreactor in minutes.

Numerical Simulation

Not only efforts on synthesis of linear or branched poly-mer molecules have been achieved, but theoretical studies were also performed. Serra et al. conducted numerical simu-lation of free radical polymerization in microfluidic devices [22,23]. Three microfluidic devices were modeled; two in-terdigital multilamination micromixers respectively with a large and short focusing section, and a simple T-junction followed by a microtube reactor together considered as a bilamination micromixer with a large focusing section. The simulations showed that in spite of the heat released by the polymerization reaction, the thermal transfer in such micro-fluidic devices was high enough to ensure isothermal condi-

tions. Moreover, for low radial Peclet number, microfluidic devices with a large focusing section could achieve better control over the polymerization than a laboratory scale reac-tor as the polydispersity index obtained was very close to the theoretical limiting value. They concluded that the reactive medium cannot be fully homogenized by the diffusion trans-port before leaving the system resulting in a high polydisper-sity index and a loss in the control of polymerization as the characteristic dimension of the microfluidic device increases, i.e. for high radial Peclet number.

SYNTHESIS OF POLYMER PARTICLES

Synthesis of Simple Polymer Particle

There is an increasing demand for polymer particles by the industry particular for painting formulation and drug de-livery applications. Microfluidic reaction system provides superior controllability of fluid because the flow forms sim-ple laminar streams. Thus, efforts have been exerted to polymer particle synthesis using mucrofluidics because of its unique capacity to generate microdroplets with very narrow size distributions. Nishisako et al. used simple T-junction microchip (Fig. 9a) for synthesizing monodisperse particles of diameters 30-120μm by changing flow rates [24]. Result-ing products have a coefficient variation below 2%.

Flow-focusing geometry [25] was applied for generation of monodisperse particles. Polymerization of tripropylengly-col diacrylate was performed in microfluidic flow focusing device (Fig. 10) [26]. Resulting particles have diameters from 20 to 1000 μm. This technique was also applied for preparation of alginate particle [27]. The flow-focusing approach was further extended to eliminate effect of surface on droplet formation. Axisymmetric or coaxial systems

Scheme 2. This scheme was reproduced with permission of [21].


Fig. (8). Microreaction system used for dendrimer synthesis. A schematic diagram of the experimental setup (A) and interdigital micromixer

(B) were shown. This figure was reproduced with permission from ref. [21].

Fig. (9). Schematic representation of channel rayout used for droplet formation: (a) T-shaped and (b) Y-shaped channel with two coflowing

channels. This figure was reproduced with permission from ref. [24].


Fig. (10). A representation of the flow-focusing geometry used in

microfluidic droplet formation. This figure was reproduced with

permission from ref. [26].

(Fig. 11), which prevent one phase from touching the walls of the device, enables formation of droplet of reaction mix-ture and therefore produce polymer particles [28]. Depend-ing on the parameters of the system, a liquid jet can trans-form from a thin finger of fluid to droplets. The process that breaks the stream into droplets is called a Rayleigh–Plateau instability, and it arises when the jet becomes unstable to perturbations longer than its circumference and breaks up into droplets to minimize the surface area.

Fig. (11). An axisymettrical flow focusing microchannel (left) and

uits cross-sectional view of a channel with droplet (right). This

figure was reproduced with permission from ref. [28].

Simple microfluidic device, which consists from PVC tube and syringe, was used for polymer particle synthesis (Fig. 12) [29]. In this system, the disperse phase is entirely surrounded by continuous flow phase, which was only formed by axysymettric device. Interfacial polymerization was performed in this device. Similar system was prepared by assembling microcapillary. Serra et al. used sheath-flow microfluidic device for particle synthesis [30]. Photopolym-erization using MMA, GMA, and DIMAEG was performed in this system.

Fig. (12). Photographic image of microfluidic device consisting of

needle and PVC tube. This figure was reproduced with permission

from ref. [29].

Synthesis of Complicated Polymer Particle

Application of microfluidic system for polymer particle synthesis is further examined for complicated polymer parti-

cle synthesis. Nisisako et al. formed monodisperse double emulsions using a tandem Y-junction arrangement (Fig. 9b) [24]. Nie et al. reported a novel approach to continuous and scalable production of core-shell droplets and polymer cap-sules in microfluidic devices [31]. They used laminar flow of three immiscible liquids: aqueous SDS, monomer, and sili-con oil in a microfluidic system. The described method is also useful for the synthesis of polymer particles with non-spherical shapes (Fig. 13). They used capillary instability-driven break-up of a liquid jet formed by two immiscible fluids. Precise control of emulsification of each liquid al-lowed production of highly monodispersed core-shell drop-lets with a predetermined diameter of cores and thickness of shells. They also achieved control over the number of cores per droplet and the location of cores in the droplet. The authors carried out fast throughput photopolymerization of the monomeric shells and obtained polymer particles with various shapes and morphologies, including spheres, trun-cated spheres, hemispheres, and single and multicore cap-sules. Photolithography was also applied for the synthesis of polymer particles. Dendukuri et al. reported a one-phase method using T-junction microchannel to create solid disk and plug-shaped particles (Fig. 14) [32]. Snap-off at the junction yielded plugs containing Norland optical adhesive (NOA) 60, a photopolymerizable resin. When an ultraviolet (UV) beam was shone on the plug in the narrow channel, a plug structure was captured, but if the plug was allowed to expand laterally and then polymerized, a disk was formed. Because of the small dimensions of the plugs and disks, the photopolymerization occurred in less than 1 s, using only 3 J cm

-2 of energy. They also developed an evolutionally ad-

vanced microfluidic system by combining the advantages of microscope projection photolithography and microfluidics to continuously form morphologically complex or multifunc-tional particles down to the colloidal length scale (Fig. 15) [33]. Exploiting the inhibition of free-radical polymerization of diacrylate monomers near PDMS surfaces, they were able to repeatedly pattern and flow rows of particles in less than 0.1 s, affording a throughput of near 100 particles per second using the simplest of device designs. Polymerization was also carried out across laminar, co-flowing streams to gener-ate Janus particles, which is a chemically biphasic particles. They synthesized Janus polymer by using co-flowing lami-nar streams of monomer, one of which contained a rho-damine-labeled crosslinker, and forming particles across this interface. The relative proportions of Janus particle could be easily tuned. They also developed stop-flow lithography sys-tem for high throughput preparation of polymer particles [34], and UV light reflector system for significant improve-ment of UV polymerization conditions [35]. These new high-throughput techniques offer unprecedented control over par-ticle size, shape and anisotropy.

PREPARATION OF POLYMER MEMBRANE

WITHIN MICROCHANNEL

The interface between fluids formed in laminar stream offers the opportunity to perform polymerization at the inter-face at which the two fluids meet. Fig. (16) is an early exam-ple from the Whitesides laboratory in which a polymer was deposited at the interface between two fluids to create a per-meable membrane in situ [36]. Most microreactors are


Fig. (13). (a-e) Scanning electron microscopy images of polymer microbeads obtained by polymerizing TPGDA in droplets obtained in re-

gimes A, B, C, D, respectively, after removing a SO core. (Inset) Cross section of the core-shell particle. (f) Cross section of a polyTPGDA

particle with three cores obtained by polymerizing core-shell droplets with three cores. The particle is embedded in epoxy glue. Scale bar is

40μm. This figure was reproduced with permission from ref. [31].

Fig. (14). Microchannel geometry used to create plugs and disks: (a) schematic of channel with plug and disk creation zonesmarked; (b) po-

lymerized plugs in the 200μm section of the channel, 38 μm height; and (c) polymerized disks in the 200 μm sectionof the channel, 16 μm

height. This figure was reproduced with permission from ref. [32].


Fig. (15). Scanning electron microscope images of particles. Microparticles formed using a 20 objective (except d, which was formed using

a 40 objective) were washed before being observed using SEM. The scale bar in all of the figures is 10 μm. a-c, Flat polygonal structures

that were formed in a 20-μm-high channel. d, A colloidal cuboid that was formed in a 9.6-μm-high channel. e,f, High-aspect-ratio structures

with different cross-sections that were formed in a 38-μm-high channel. g-i, Curved particles that were all formed in a 20-μm-high channel.

The inset in the figure shows the transparency mask feature that was used to make the corresponding particle. This figure was reproduced

with permission from ref. [33].

Fig. (16). Optical micrograph of a polymeric structure deposited on glass at the laminar ßow interface of 0.005% aqueous solutions of

poly(sodium 4-styrenesulfonate) and hexadimethrine bromide. This figure was reproduced with permission from ref. [36].

designed so that the interface of the two fluids contacts the ceiling and floor of the channels, and when an interfacial polymerization occurs, the polymer adheres to the walls.

Application of this technique was performed by several groups. Moore’s group used this technique to visualize inter-face of two immiscible solutions [37]. They synthesized ny-lon membrane to illuminate interface structure. Another ap-plication was reported by Kitamori’s group [38]. They ap-plied this technique for preparation of enzyme-immobilized

membrane. First they prepared nylon membrane at the inter-face, then enzyme was immobilized on this membrane to form chemicofunctionalized nylon membrane. They per-formed peroxidase assay using this membrane.

Formation of membranes on microchannel surface was also demonstrated. Honda et al. reported that cross-linking of enzymes using paraformaldehyde and gluaraldehyde yielded membrane structure on microchannel surface (Fig. 17) [39]. They also expand this approach to acidic enzymes which was


difficult to cross-link because they have no or just few amino group on surface, by adding poly-Lysine as co-cross-linking agent [40]. These techniques were used for preparation of enzyme microreactors [41].

Overall, organic membrane formation was developed but membranes themselves were mainly used for functionaliza-tion of microchannel device itself.

CONCLUSION AND FUTURE OUTLOOK

Microreactors will represent an indispensable tool for synthesizing polymers with controlled properties. Microreac-tion in microfluidic systems will find its way in the shift from conventional batchwise reaction to microreaction strat-egy. In future, microfluidic devices will find broad applica-tions particularly in linear polymer production aimed to ob-tain polymers of desired average molecular weight with nar-rower molecular weight distribution. In addition, the pros-pect of making novel polymer particles with unique shapes can be realized by microreaction system via control of spe-cific device geometry and flow parameters. The process of rapid prototyping and the emergence of simple, homemade devices that take only minutes or hours to construct have enabled many groups to explore this exciting field. More and more applications of microfluidic reaction systems for poly-mer synthesis are required to develop a generally-applicable microreactor for polymerization reaction. In addition to sim-ple reactions, an aspect of polymer synthesis that may offer great research opportunity is synthesis of novel particles with unique shapes, and thus, development of microscope projec-tion photolithography will be necessary. In addition, theo-retical studies such as numerical simulations are also re-quired to obtain a generally-applicable microreactor. Match-ing of experimental achievements and theoretical studies may accelerate development of microreactor for polymeriza-tion reaction.

Not only the microreactor provide efficient reaction ap-paratus for production of polymer materials, but also polym-erization in situ technique might become a strong tool for functionalization of inside microchannel. Multifunctionaliza-tion of microfluidic chip become the mainstream for the de-velopment of analytical microfluidic chip. Technical devel-opment for selective functionalization/polymerization at the

specific site within microchannel enables development of multifunctional microfluidic chemical chips.

Overall, the research process of polymer chemistry in microfluid is still under development, and this field is in its initial stage. This field has a big room for research and de-velopment.

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Received: October 07, 2009 Revised: October 23, 2009 Accepted: October 25, 2009

polymer chemistry in microfluidic reaction system

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