Polymerization of and within self-organized mediasion polymerization is a reconstructive template synthe-sis w5 x. There hasrecently been considerable effort devoted to mechanistic

Current Opinion in Colloid and Interface Science 8(2003) 164–178

1359-0294/03/$ - see front matter� 2003 Elsevier Science Ltd. All rights reserved.doi:10.1016/S1359-0294Ž03.00018-9

Polymerization of and within self-organized media

Hans-Peter Hentze , Eric W. Kaler*1

Department of Chemical Engineering, University of Delaware, Newark, DE 19716, USA

Abstract

Self-organized surfactant solutions, such as microemulsions, vesicular solutions or dispersions, or lyotropic mesophases canserve as templates for the structure directed synthesis of organic polymers. Recent developments of templating within theseequilibrium nanostructured fluids are reviewed. Depending on the template structure and the reaction conditions, the outcomesmay be polyampholytes, amphiphiles, nanoparticles, hollow spheres, or mesoporous polymers. For each structure and morphology,the final product materials reflect a delicate balance between phase behavior and the reaction and mass transfer parameters thatset structure. Experimental and theoretical aspects of reaction kinetics and thermodynamics such as monomer partitioning, swellingbehavior and polymerization-induced phase separation are discussed.� 2003 Elsevier Science Ltd. All rights reserved.

Keywords: Microemulsions; Vesicles; Liquid crystals; Lyotropic mesophases; Polymerization; Nanoparticles; Nanocapsules; Mesoporousmaterials; Surfactant templating; Polymerizable surfactants; Hydrogels; Phase separation; Dissipative structures; Lipids; Block copolymers;Amphiphilic particles

1. Introduction

The synthesis of materials with submicron morphol-ogies is of increasing interest, and a goal of modernmaterials science is to control structure and the chemicaland physical properties of supramolecular materials ona nanoscopic scale. The use of self-organized surfactantsolutions as reaction templates or media is one of themost promising approaches towards the synthesis offunctional inorganic and organic nanomaterials, such asnanoparticles, hollow spheres, membranes or mesopo-rous bulk materialsw1,2 ,3–5 ,6x.● ●●

The general idea behind these templating approachesis to turn the fragile structure of a dynamic, self-organized molecular assembly into a mechanically andchemically stable supramolecular material. In the caseof so-called direct templating the morphology of thepolymeric product resembles the structure of the tem-plate. When polymerizable surfactants are used thisprocess is called ‘synergistic’ and the material obtainedis the cured template. On the other hand, a ‘transcriptive’synthesis results in a product that is a copy of the

*Corresponding author. Tel.:q1-302-831-3553; fax:q1-302-831-6751.

E-mail addresses: [email protected](E.W. Kaler),[email protected](H.-P. Hentze).

Tel.: q1-302-831-8919; fax:q1-302-831-1048.1

template structure, as results for example when monomerpolymerizes around the self-assembled template. Insome cases even when the template structure is notretained during polymerization the self-organized reac-tion medium can still direct polymer growth. In thisway new and typically hierarchically morphologies areformed, and these are interesting subjects for the studyof dissipative structure formation in self-organizedmedia. Such cases of indirect templating are called‘reconstructive’ synthesisw7 x.●●

The main developments of polymerization within self-organized media are summarized in a number of valua-ble review articlesw1,2 ,3–5 ,6x. This article will focus● ●●

only on recent trends and achievements in templatingwithin microemulsions, vesicles and lyotropic meso-phases. The templating of organic polymers within otherself-organized media, such as thermotropic liquid crys-tals w8x, block-copolymer bulk phasesw9x, colloidalcrystals w10x, or polyelectrolyte–surfactant complexesw11x, will not be considered in detail here.

2. Microemulsion polymerization

Microemulsions are thermodynamically stablemixtures of water, oil and surfactant that exhibit eithera discrete microdroplet or a bicontinuous sponge-likestructure. Most usually direct(oyw) or inverse(wyo)

165H.-P. Hentze, E.W. Kaler / Current Opinion in Colloid and Interface Science 8 (2003) 164–178

Fig. 1. Experimental and model rate vs. conversion profiles for thepolymerization of hexylmethacrylate in a microemulsion stabilized bythe surfactant DTAB(Reproduced fromw19x). The two curves are forinitiator concentrations of 0.045(top) and 0.015(bottom) wt.% rel-ative to the amount of monomer in the microemulsion. The solid linesare predictions of the Morgan modelw14x.

microemulsions are used for the synthesis of ultrasmallpolymer particles. These nanoparticles are typicallycharacterized by diameters between 5 and 100 nm, anarrow size distribution, and a small number of polymerchains per particlew12 x. Like in other heterophase●●

polymerization techniques, the presence of the continu-ous domain(water or oil) allows control of the poly-merization temperature and the final product is a highmolecular weight polymer dispersion with low viscosity.Because microemulsions are thermodynamically stable,unlike macro- or miniemulsions, the initial state of amicroemulsion before polymerization depends only oncomposition and temperature(at constant pressure), andthis allows intrinsic control and reproducibility of theproduct properties. Mechanistic studies show that inmicroemulsion polymerization usually only a very smallfraction (;1y1000) of the micelles are initiated andgrow into polymer particlesw13x. The main functions ofthe surfactant are isolation of monomer in confinednanodroplets, stabilization of the growing polymer par-ticles, and limitation of polymer growth by creating adynamic boundary the monomers must cross. The result-ing polymer beads are typically much larger than theoriginal microemulsion droplets. Therefore, microemul-sion polymerization is a reconstructive template synthe-sis w5 x.●●

There has recently been considerable effort devotedto mechanistic and kinetic investigations of microemul-sion polymerization from both experimental and theor-etical points of view. Compared to other self-organizedmedia, such as bicontinuous microemulsions or lyotropicmesophases, the discrete structure of direct and inversemicroemulsions simplifies study of the details of mon-omerypolymerysurfactant interactions and can help iso-late the importance of nucleation and monomer transportprocesses. These investigations provide a better generalunderstanding of complex polymerization mechanismsin self-organized media and enable the prediction ofreaction kinetics and molecular weight and particle sizedistributionsw14x.

In contrast to macroemulsion polymerization, thereaction kinetics of microemulsion polymerization ischaracterized by only two polymerization rate intervals;the interval of constant rate characteristic of emulsionpolymerization is missing(Fig. 1) w15x. Particles aregenerated continuously during the reaction by bothhomogeneous and micellar nucleation mechanisms. Asthe solubility of the monomer in the continuous domainincreases, homogeneous nucleation becomes moreimportantw16x. For microemulsion formulations contain-ing short-chain alcohols as cosurfactants(which can beavoided by proper study of phase behavior) the chainlength of the cosurfactant strongly affects the polymer-ization kinetics, apparently because of changes of thepolarity of the continuous domain and variation ofmonomer partitioningw17x.

In polymerization of a direct microemulsion, mono-mer partitioning between polymer particles and unini-tiated micelles via diffusion through the aqueous phasedetermines the concentration of monomer at the poly-merization loci. This partitioning plays an important rolein determining polymer particle formation and growthw13,14,18x. Small-angle neutron scattering(SANS)measurements of monomer partitioning between poly-mer particles and monomer-swollen micelles show thatthe monomer concentration profile in the polymer par-ticles over the course of polymerization depends stronglyon the properties of the starting microemulsion. In somecases nonlinear monomer partitioning, non-negligiblebimolecular termination and diffusion limitations topropagation have to be taken into account to achieve aproper description of the processw19x. Especially forinitial microemulsion compositions close to a phaseboundary, monomer partitioning can be significantlynonlinearw20x. Theoretical models that account for thesefactors can predict the observed molecular weight andparticle size distributionsw12 x.●●

Other mechanistic studies showed that the type ofemulsion employed(macro or micro) can strongly effecttermination reactions and, consequently, polymer prop-ertiesw21x. For example, in microemulsion polymeriza-tion of vinyl acetate(VA) chain transfer to monomer,not to polymer, is the main termination mechanism.Thus, the polymer has a lower degree of branching thandoes polyvinyl acetate produced by emulsion polymeri-zation, which terminates predominately by chain transferto polymer.

166 H.-P. Hentze, E.W. Kaler / Current Opinion in Colloid and Interface Science 8 (2003) 164–178

The kinetics of polymerizations in inverse systemshave also been studiedw22–24x. Owing to the interplaybetween transport phenomena, polymerization, and ini-tiation and nucleation rates, a complex evolution of theoverall polymerization rate was observed for the inversemicroemulsion polymerization of 2-methacryloyl oxy-ethyl trimethyl ammonium chloride(MADQUAT) w24x.When initiation by UV light in presence of azo-bis(isobutyronitrile) was used instead of metabisulfate ini-tiation, the more regular polymerization kinetics wereobserved and described by a mathematical modelw23x.

A major drawback of conventional microemulsionpolymerization is the high surfactant to monomer ratiousually needed to form the initial microemulsion. Onestrategy to overcome this problem is to develop moreefficient surfactant systems, such as by varying counter-ion, the use of amphiphilic block copolymers as cosur-factants, or the synthesis of new surfactants that formmicroemulsions with improved solubilization properties.Gemini surfactants are an example of the latter approachw25x. Semi-empirical correlations such as cohesive ener-gy ratio and hydrophile–lipophile balance concepts, canbe used to optimize emulsion and microemulsion for-mulations. But even for these optimized formulationsthe amount of surfactants and monomer used in theinitial formulation are comparablew26 x.●

Surfactant can be used more efficiently in semi-continuous or fed polymerization processes. Because thepolymerization rates and conversions for microemulsionpolymerizations are high compared to those of othertechniques (e.g. solution polymerization), severalpolymerization cycles can be run in a short period oftime by stepwise addition of new monomer. After eachcycle most of the surfactant is available to form amicroemulsion again. One example is the semi-contin-uous microemulsion polymerization of VA, where laticeswith high polymer content(;30 wt.%) were obtainedat relatively low surfactant concentrations(;1 wt.%).Particle sizes and molecular weights were much smallerthan those obtained by macroemulsion polymerizationw27x.A mixture of surfactant and polymerizable surfactant

has been used for a fed microemulsion polymerizationof styrene. After nucleation within the initial micro-emulsion, additional monomer and polymerizable sur-factant is added by a continuous feed. This approachproduced latices with a particle diameter of approxi-mately 50–80 nm, a solids content up 17 wt.%, and apolymerysurfactant ratio of up to 15w28x. Hollow-fiberfeeding was used to polymerize not only styrene, butalso methyl methacrylate(MMA ) and butyl (meth-acrylate), with comparable efficienciesw29 x. In this●

case sodium dodecylsulfate and 1-pentanol were usedas stabilizers and a redox initiator system was employed.Inverse microemulsion polymerization is an attractive

approach to the synthesis of high-molecular-weight

water soluble polymers that can, for instance, be usedas flocculants. Recently, the semi-continuous polymeri-zation of inverse microemulsions was also reported. Inthis way polyampholyte latices based on N-isopropyl-acrylamide have been synthesized with low particlesizes(;70 nm) and high polymer contents(;20 wt.%)w30x. Continuous inverse microemulsion polymerizationcould be an attractive technique for large scale synthesis,as demonstrated by the polymerization of MADQUATin a continuous stirred tank reactorw31x.

Another major trend in microemulsion polymerizationis the fabrication of functionalized nanoparticles withcertain physical, chemical or biological properties. Via-ble approaches towards microlatex functionalization arecopolymerization, variation of polymerization tech-niques, polymer-analogue reactions, or surface modifi-cation by adsorption.As microemulsions enable the mixing of hydrophobic

and hydrophilic compounds in confined nanogeometries,they can be used for the copolymerization of hydropho-bic and hydrophilic monomers. This approach is aninteresting way to form polyampholytesw32x or amphi-philic polymers. Amphiphilic copolymers of styrene anda polymerizable surfactant were obtained byg-ray ini-tiated direct microemulsion polymerizationw33x. Thecopolymer composition was adjusted by partial substi-tution of the reactive surfactant with a non-reactivesurfactant. Cross-linking of this type of latex might bean interesting way to synthesize amphiphilic particles.Inverse microemulsions can also be used for copoly-merization of hydrophilic monomers and reactive sur-factantsw34x, as well as for the synthesis of multiblockionomers by polymerization of ionic and hydrophobicmonomersw35x. The lengths of the ionic blocks and theglass temperature of the polymer can be tuned byvariation of the monomer ratio.In addition to free-radical polymerization, which is

still the most established microemulsion polymerizationtechnique, oxidative, electrochemical, living or interfa-cial polymerizations can be carried out. Electricallyconducting polyaniline nanoparticles were synthesizedby oxidative polymerization within inverse microemul-sions w36,37x, as well as within direct anionic andnonionic micellesw38x. Electrically conducting polythio-phene was obtained from electrochemical polymeriza-tion of 3,4-ethylenedioxythiophene within directmicroemulsionsw39x. In these cases the main functionof the microemulsion is to increase the solubility of themonomer in the aqueous reaction medium. Controlledfree-radical polymerization has been used for the syn-thesis of fluorinated copolymersw40x. Due to the largepolymerization rate within the microemulsion, the livingprocess required only very small amounts of initiator. Acomplex kinetic model for this polymerization wasdeveloped and validated.


Fig. 2. Hollow polystyrene particles obtained from microemulsionpolymerization of core-shell particles and subsequent core etching.(Reproduced with permission fromw46 x.)●●

Functionalization by copolymerization was also usedfor the synthesis of metal-complexing nanoparticlesw41 x. A metal binding cyclam-monomer was co-poly-●

merized within an aqueous microemulsion of styrene(St) and divinylbenzene(DVB). The particles obtainedshowed high metal-binding selectivity and affinities, andwere soluble in aqueous and organic media. An exampleof biological functionalization of microlatices is theimmobilization of protease enzymes in a two-step pro-cedurew42x.

Particle morphologies more sophisticated than thetypical ‘solid and dense’ polymerization product canalso be fabricated using microemulsions. Core-shellnanoparticles have been obtained by a two-stage micro-emulsion polymerization beginning with a polystyreneseedw43x. Addition of butyl acrylate in a second stepyielded a core-shell poly(styrene)ypoly(butyl acrylate)morphology. The small particle size of the microemul-sion latex led to improved mechanical properties com-pared to similar products produced by emulsionpolymerization. Superparamagnetic nanoparticles with amagnetite core and a poly(methacrylic acid)-co-poly-(hydroxyethyl methacrylate) shell were synthesized in asingle inverse microemulsionw44x. The nanoparticleswere formed in a two-stage process and recovered bymagnetic separation. Insulin nanocapsules for drugdelivery purposes were obtained by interfacial poly-merization of ethyl 2-cyanoacrylate within a biodegrad-able microemulsionw45x. The resulting particles had adiameter of approximately 150 nm and exhibited acentral cavity surrounded by a single polymer wall.Hollow polymer particles can be made by etching

away the core of a core-shell particle. For example, afterthe synthesis of core-shell particles with a cross-linkedpolystyrene shell, the poly(methyl methacrylate) corewas dissolved with methylene chloridew46 x. The●●

diameter of the resulting hollow capsules could beadjusted between 15 and 30 nm by variation of thesurfactant to monomer ratio. The shell thickness wasapproximately 2–5 nm(Fig. 2). A more direct approachtowards hollow nanocapsules is the cross-linking poly-merization of styrene at the interface of isooctanemicrodropletsw47x.Applications of the different kinds of polymer nano-

particles synthesized in microemulsions range from pho-tographic processes to pharmaceuticalsw48x.Mesoporous polymeric materials can be obtained by

polymerization within the sponge-like bicontinuousmicroemulsions. In a few cases, e.g. when a macromon-omer is used as a polymerizable surfactant, the originaltemplate structure is retained and nanoporous polymernetworks are obtained. The compatibility of the polymernetwork with the microemulsion phase seems to beenhanced by the amphiphilic character and the slowdynamics of a reactive surfactantw49x. In many othercases the polymer morphologies obtained are structured

on a length scale much larger than the parental spongephase, and are the result of separation of the polymermatrix from the microemulsion phasew50,51x. Nonethe-less, because of their high porosity and the continuouspore structure these gels have interesting properties. Forthis reason most recent publications about bicontinuousmicroemulsion polymerization deal with applications ofthese porous bulk polymers as, for example, nanofiltra-tion membranesw52x.

Functionalization of bicontinuous polymer gels wasrealized by incorporation of electrolyte solutionsw53x,metal-ionsw54x or ruthenium(II) complexesw55x, result-ing in conducting composite electrolytes that couldbecome the basis for devices such as chemical sensors.Superparamagnetic bicontinuous composites wereobtained from biomimetic mineralization of magnetitewithin a bicontinuous polystyrene-co-poly(acrylic acid)gel w56x. Optically transparent PbS-polymer nanocom-posites synthesized within a bicontinuous microemulsionshowed large optical nonlinearity that was attributed toa surface-induced separation of delocalized charges andlocalized holesw57x. Potential applications for materialswith enhanced optical properties are optical computingor real-time holography.Interestingly, polymer nanoparticle dispersions with a

very narrow particle size distribution can be obtainedfrom polymerization in (and phase separation from)bicontinuous phasesw26 x. This process might be an●

interesting alternative to the unstable and turbid inverselatices prepared by classical inverse emulsion polymer-ization, as the microlatices produced by microemulsionpolymerization are remarkably stable. Compared to theresult of polymerization in microemulsions with a dis-crete microdroplet structure, the non-cross-linked poly-mers obtained by polymerization within the bicontinuousphase are characterized by a slightly lower molecular


weight w58x. Also, the final conversions for the copoly-merization of VA and 2-ethylhexyl acrylate were foundto depend strongly on the initial structure of the microe-mulsion w59x.

3. Polymerization of vesicles

Vesicles are discrete spherical assemblies formed bylipids, surfactants, polymers or proteins. They consist ofclosed bilayer shells with an entrapped solvent core.Potential applications include drug-delivery systems,biosensors, and encapsulationw60,61 x.●●

Generally two broad classes of vesicles can be distin-guished, either uni- or multilamellar vesicles that formafter shearing and that are stable only kinetically, andequilibrium vesicles that form spontaneously and arestable with time. Most vesicular systems show a multi-lamellar, onion-like morphology with each vesicle beingformed by a number of bilayers. These so-called lipo-somes have typically diameters ranging from hundredsof nanometers up to several microns. By applying highshear such as by sonication or extrusion, multilamellarvesicles can often be transferred into kinetically stabi-lized unilamellar vesicles. In contrast, unilamellar equi-librium vesicles form spontaneously in some mixturesof anionic and cationic surfactants without any addition-al energy input. Their equilibrium size is typically inthe range of 50–100 nm and does not change with timeafter equilibration. Both kinds of vesicles can be usedas templates for the synthesis of polymer nanoparticlesor hollow nanocapsules.Three different approaches towards the templating of

vesicles are described in literature. One is the polymer-ization of standard monomers, i.e. styrene(St) or MMA,within the vesicle bilayers. More common is the use ofvesicle-forming polymerizable surfactants, such as lipidsor unsaturated amphiphilic block copolymers. In thethird case these two approaches are combined andmonomers and polymerizable surfactants are co-polymerized.The polymerization of hydrophobic standard mono-

mers within the bilayers of kinetically stabilized vesiclesof the surfactant dioctadecyldimethylammonium bro-mide (DODAB) was described in a series of papers.Because of phase separation of the polymer matrix fromthe bilayers the polymer did not resemble the vesiclestructure, and instead more complex vesicle-polymerhybrid morphologies were obtained(Fig. 3) w62x. Thenon-cross-linking polymerization of styrene producedthe so-called parachute architecture, which is character-ized by a single polystyrene bead that is attached to apure surfactant vesicle bilayer. Addition of cross-linkeror copolymerization of styrene and butyl methacrylatecould not prevent phase separation, but resulted insteadin the formation of multiple beads. In this case severalpolymer beads were attached to one vesicle bilayer to

give a ‘necklace’ morphology. The copolymerization ofstyrene with a small amount of polymerizable surfactantgave a ‘wrapped parachute’ or ‘matrioshka’ structure,wherein each parachute vesicle-polymer hybrid is encap-sulated in a unilamellar vesicle. Retention of the vesiclestructure was only achieved by the copolymerization ofstyrene with a vesicle-forming polymerizable surfactant,or by polymerization of cross-linker within prepolymer-ized vesicles of the same surfactantw63 x.●

The mechanism of the parachute morphology forma-tion was investigated by pulsed-laser polymerizationexperiments that provided simultaneously kinetic dataand thermodynamic information on the locus of poly-merizationw64 x. This study indicated that polymeriza-●

tion occurs in small polymer nuclei that separate fromthe bilayer, and this morphology was confirmed by adetailed SANS studyw65x. Characterization by micro-DSC, fluorescence studies, surfactant lysis and atomicforce microscopy revealed that the parachute morphol-ogy consists of a pure surfactant bilayer and an attachedand completely phase-separated polymer latex beadw66x.The presence of the polymer bead inside the vesiclebilayer strongly affects the dynamics and the electro-optic behavior of the vesiclesw67x.Direct templating without morphological changes and

by use of common monomers, such as styrene and DVB,was realized by the use of equilibrium vesiclesw68 x.●●

The catanionic templates formed by standard surfactantsare characterized by spontaneous assembly into unila-mellar vesicles. These vesicles can swell with monomer(DVB or DVBystyrene mixtures), and subsequent ther-mally initiated free-radical polymerization resulted inhollow polymer spheres with diameters approximately60 nm and shell thicknesses lower than 10 nm(Fig. 3)w69x. The nanoparticles are stable enough to withstanddialysis, vacuum drying and resuspension aided byadsorption of nonionic surfactant. Redispersable polye-lectrolyte nanocapsules were obtained by sulfonation ofthe polymer. The stability of these polymerizable vesi-cles results from the high cross-link density of poly-DVB, the compatibility of the aromatic surfactants andpolymer, and perhaps from the ability of the bilayer torearrange to accommodate the growing polymer. Analternative route to synthesis of polyelectrolyte hollowspheres is cross-linking UV-polymerization of acrylicacid esters within the bilayers of dioctadecyldimethylam-monium chloride followed by saponificationw70x. Theparticles obtained change size reversibly with changesin salt concentration or pH.The monomer isodecyl acrylate reacts differently

when polymerized within bilayers of fluorinated orhydrocarbon lipidw71 x. Polymerization in bilayers of●●

the non-fluorinated lipid resulted in phase separationand the formation of a parachute-like morphology. How-ever, polymerization within the fluorinated lipid bilayersyielded a homogeneous distribution of the polymer and


Fig. 3. Different polymer morphologies from vesicle templating: Hollow polymer spheres(top left) w68 x, parachutes(top right) w67x, necklaces●●

(bottom left) w62x, and matrioshka structures(bottom right) w17x. (Adapted with permission fromw62,67,68 x.)●●

retention of the vesicle structure. The lower molecularweight and the higher polymerization rates observed forthe reaction in the fluorinated bilayers suggested thatthe more confined and non-expandable character of thefluorinated bilayers plays a role in the synthesis.Biological functionalization of liposomes stabilized

by polymerization of hydrophobic methacrylate mono-mer was achieved by encapsulation of enzymes andincorporation of natural channel proteins into the bilayerw72 x. Lipid vesicles can also serve as templates for●

sequence-selective polycondensation of dipeptidesw73x.For most synergistic templating approaches polymer-

izable lipids are employed. One factor determining thesuccess of this approach is the final cross-linking density,which depends on the ratio of mono- to bifunctionallipids in the bilayer and on the site of the reactive groupw74x. Not surprisingly, when the reactive site is close tothe glycerol backbone the polymerization is substantiallymore efficient than when the group is in thev-positionon the hydrophobic chains. The type of initiation also

plays an important role in determining the final product.Photopolymerization of heterobifunctional lipids yieldedonly oligomers, while cross-linked vesicles wereobtained by redox initiation of the same systemw75x.Redox initiated polymerization of liposomes preparedfrom heterobifunctional lipids resulted in polymeric‘nanoballoons’ that were stable against freeze-dryingand rehydrationw76 x.●●

An acetylenic phosphocholine derivate was used forg-ray polymerization of vesicles prepared by extrusionw77x. The resulting hollow particles remained structurallyintact upon freeze-drying and subsequent redispersionin water.g-ray polymerization was also used to cross-link vesicles formed by a variety of dienoyl-functional-ized phosphocholinesw78x, and the resulting polymericvesicles resisted freeze-thaw damage.Ring-opening polymerization of lipids carrying dithio-

lane rings was performed for the encapsulation ofproteinsw79x and fluorescence markersw80x. The poly-merized vesicles were resistant to surfactant disruption


and thermal perturbation. Owing to the mild polymeri-zation conditions the activities of the encapsulatedenzymes were not affected, and antibody formation wastwo times more efficient than that for the non-polymer-ized drug delivery liposomes.Curvature modulation by addition of suitable cosur-

factants, e.g. polyhydroxylated telomers, was exploredfor the polymerization of hydrocarbon glycolipid surfac-tantsw81x. In this way disorganization of the bilayer andprecipitation were suppressed during polymerization.Polymerization of fluorocarbon derivatives of the sameglycolipids also led to successful synergistic templating,even without use of a cosurfactant.Another approach to synergistic template synthesis is

by the cross-linking of vesicle-forming amphiphilicblock copolymers. UV-polymerization of methacrylateendgroup-functionalized block copolymers yielded poly-mer nanocapsulesw82x. However, their stability was nothigh enough to withstand drying and redispersion with-out disruption, a condition probably reflecting a lowdegree of cross-linking with regard to monomer repeat-ing units. These vesicles were suitable for biologicalactivation by encapsulation of enzymes and incorpora-tion of channel proteins into the bilayerw83x. Free-radical cross-linking of giant-vesicle forming poly-(ethylene oxide)-b-polybutadiene block copolymersresulted in hollow capsules that were stable againstdrying, redispersion and lysis by addition of solventsw84 x. Rupture tensions and other physical properties●

were measured as a function of the cross-linking degreeusing micropipet aspiration methods.

4. Polymerization within lyotropic mesophases

As is the case for other liquid crystals, lyotropicmesophases combine both the flow properties of liquidsand the long-range order of crystals. As they are ther-modynamically stable they form spontaneously, as domicroemulsions or equilibrium vesicles. They showlong-range order in one(lamellar phases), two (hexag-onal phases), or three(cubic phases) dimensions. Theirphase behavior at constant pressure depends not only ontemperature, as it is the case for thermotropic liquidcrystals, but also critically on solvent type and concen-tration. Their morphological complexity enables theirpotential use for templated synthesis not only of nano-particles, but also of bulk materials with isotropic oranisotropic morphologies.As is the case for polymerization within vesicle

bilayers, most studies deal with the synergistic templat-ing of lyotropic mesophases by polymerization of sur-factantsw85x. However, polymerization of monomers ina surfactant template has considerable advantages overpolymerization of amphiphilic monomers. Firstly,because the phase behavior of common surfactants isknown or relatively easily measured, it is easy to modify

known mixtures to produce the desired template. Sec-ondly, the effect of added monomers often can bepredicted and if necessary compensated for changingphase behavior parameters such as temperature. Finally,the cost of specially synthesized surfactants is such thatlarge scale applications will be dramatically restricted.For these reasons there are also numerous examples ofpolymerization of standard monomers within lyotropicmesophases with the aim of transcriptive synthesis forthe fabrication of a one-to-one copy of the template.Again, only in relatively few studies have a combinationof both polymerizable surfactant and monomer beenexplored.Phase separation is the common outcome when stan-

dard monomers are employed for polymerization withinlyotropic mesophasesw86x. Nonetheless, the resultingsolids typically have high porosities and surface areasand so still show very interesting properties. For exam-ple, hydrogels made this way respond quickly to changesin pH or ionic strength because of rapid ion transportwithin the porous polymerw87 x.●

As described above for the polymerization of styrenewithin the bilayers of DODAB vesicles, the polymeri-zation of styrene within a bicontinuous cubic phase ofthe same surfactant also produced macroscopic phaseseparationw88 x. Similar diffraction patterns before and●●

after polymerization were found by small-angle X-rayscattering, and the viscous nature of the cubic phasefirst suppressed the expulsion of the polymer. However,cooling and storage of the samples eventually causedmacroscopic phase separation into a polymer-rich and asurfactant-rich phase. The morphology of the polymerwas not investigated.Earlier studies showed that a liquid-crystalline reac-

tion medium can still direct polymer growth duringpolymerization-induced phase separation and will yieldhierarchical morphologies(Fig. 4a) w89x. A recent inves-tigation gave more insight into the mechanism of dissi-pative structure formation within self-organized mediaw90 x. The cross-linking polymerization of styrene with-●●

in inverse hexagonal sodium bis(2-ethylhexyl) sulfo-succinate(AOT) phases resulted in phase-separated, butnanostructured polymer gels(Fig. 4b). Polymer nano-particles with a diameter of approximately 100 nmformed, phase separated at an early stage of polymeri-zation, and then fused into polymer strands that madeup extended polymer sheets. The extension and defini-tion of these polymer layers depended strongly on thecross-linking degree and polymerization kinetics. Asuggested mechanism for the dissipative structure for-mation is based on the role of anisotropic viscositiesand transport properties within the single domains ofthe hexagonal template. Analogous morphologies werefound for colloidal ordering by thermally-induced phaseseparation of silicon oils within nematic liquid crystalsw91 x, and for the sol–gel synthesis of silica within●●


Fig. 5. Transmission electron micrograph of a polymerized dienyl sub-stituted lipid, cross-linked in a cubic mesophase; scale bars100 nm.(Adapted with permission fromw98x.)

Fig. 4. Polymer gels with hierarchical structures formed by polymerization-induced phase separation within lyotropic mesophasesw89,90 x.●●

inverse hexagonal AOT mesophasesw92x. Modeling ofthese highly non-equilibrium dynamic processes offersbetter understanding of dissipative structure formationof polymers within self-organized mediaw93,94x.

The surface topology of lyotropically templated poly-acrylamide hydrogels was studied by AFMw95x. Surfaceareas increased systematically with increasing surfactantconcentration. Another interesting effect of a confinedlyotropic reaction media is its influence on polymeriza-tion kineticsw96x. For the photopolymerization of acryl-amide within a nonionic cubic mesophase a tenfoldincrease in polymerization rate was observed comparedto solution polymerization at identical monomerconcentrations.Significant differences were found for the polymeri-

zation of monomers with different polarities withinlyotropic phases of the non-reactive surfactant dodecyl-trimethylammonium bromide(DTAB) w97x. Nonpolarmonomers partitioned to the oil-soluble domains whilepolar monomers segregated at the waterysurfactant inter-face. Owing to the higher local concentration, polym-erization rates of nonpolar monomers were higher in themicellar phase than in hexagonal or lamellar phases. Forpolar monomers the opposite behavior was observed,with the fastest polymerization occurring in the lamellarphase.The most common approach for synergistic templating

within lyotropic mesophases involves the use of poly-merizable surfactants. Although the final materials oftenshow no significant porosity after purification and dry-ing, in many cases the internal interfaces become acces-sible by swelling with polar or non-polar solvents. Evenin cases where the polymerization is not complete thereis often an increase in the stability of the phase totemperature change or solvent addition.The synergistic synthesis of nanostructured cubic

polymer gels was realized by copolymerization of dienyl

substituted lipidsw98x. No phase transitions or changesin dimensions were observed with temperature changesfor the polymerized sample. Furthermore, the polydo-main square lattice of the purified gel matrix could bevisualized by TEM(Fig. 5). In contrast, copolymeriza-tion of monoacylglycerol and 1,2-diacylglycerol in acubic lyotropic state did not result in a continuous gelstructure w99x. Linear polymer chains were obtainedinstead, and the cubic morphology was destroyed byaddition of organic solvent. Similar polymerizations inthe inverted hexagonal phase yield an increased stabilityof the lyotropic phase against temperature changesw100x.For the polymerization of amphiphilic phosphonium

dienes, 3,4,5-tris(v-acryloxyalkoxy)benzoate salts orstyrene ether-modified fatty acid, high conversions ofup to 90% were observedw101–104x. Homopolymeri-zation and copolymerization of the lyotropic phases withthe cross-linker DVB resulted in freestanding, mechan-ically stable films. X-ray diffraction and polarized lightmicroscopy showed the hexagonal order before and after


Fig. 6. Micrographs of cross-linked poly(butadiene)-b-poly(ethylene oxide) gels, templated in cubic(a), hexagonal(b), and lamellar(c) phases.(Reproduced with permission fromw114 x.)●

polymerization. The cross-linked polymer gels can beemployed for templated nanocomposite formation or asheterogeneous catalysisw105 x.●

Copolymers with amphiphilic properties were synthe-sized within lyotropic phases of oleic acidw106–108x.The polymeric surfactants obtained by copolymerizationof amphiphilic monomers within lamellar phases showedimproved surface activity and formed uni-molecularmicelles through coiling of the hydrophobic chainsw108x.Poly(oxyethylenes) with polymerizable, hydrophobic

endgroups were cross-linked within oriented lamellarphases of the ternary system C Eydecaneywaterw109x.12 5

Cross-linked and oriented polymer gels were obtainedthat retained their lamellar morphology after extractionof the template, and which showed one-dimensionalswelling by water.Complete or partial ‘locking in’ of the initial lyotropic

structure was realized by balancing mixing polymeriza-ble surfactants so that they retain the same preferredcurvature before and after cross-linkingw110,111x.

g-ray polymerization is an efficient strategy for thereaction of the polymerizable cationic low molecularweight surfactants (2-methacryloylethyl)dodecyldi-methylammonium bromide and(11-methacryloylunde-

cyl)trimethylammonium bromide in cubic andhexagonal binary phasesw112x. The nanostructured gelproducts retained their morphology during drying andreswelling with hydrophilic or hydrophobic solvents.Cholesteric morphologies of higher molecular weightcellulose derivates in water were also successfully cross-linked by g-ray polymerizationw113x. g-irradiation hasbeen employed for the synergistic templating of lyotrop-ic mesophases formed by poly(ethylene oxide)-b-poly-butadiene block copolymersw114 x. Cross-linking within●

lamellar, hexagonal and cubic mesophases resulted inmechanically and chemically stable, transparent polymergels (Fig. 6). The retention of order was proved bysmall-angle X-ray scattering, SANS and electron micros-copy. No significant porosity could be determined byBET because of the highly compact character of thedried polymer gels. The gel morphology was stableagainst temperature changes, extraction, drying andreswelling with polar or nonpolar solvents. Electronmicroscopy of ultramicrotomed samples provideddetailed views of lyotropic morphologies, defect struc-tures, morphologies of transition states, and the topolog-ical effects of concentration, block length ratio andmolecular weight of the block copolymer templatew115x.


Kinetic studies were also performed for the synergistictemplating of lyotropic mesophasesw116x. Due to thediffusional limitations of the propagating chains, thepolymerization kinetics depended strongly on the liquidcrystalline morphology. For the polymerization of aquarternized dimethylaminoethyl methacrylate withinlyotropic phases formed by mixtures with DTAB, thepolymerization rate decreased as the phase morphologychanged from lamellar to bicontinuous cubic to hexag-onal. Morphological studies of the polymer productsafter purification were not performed.For the polymerization of a semifluorinated alkyl

methacrylic acid an increase of the polymerization ratewith the degree of order of the lyotropic mesophase wasreportedw117x. The maximum conversion for theg-raypolymerization of allyldimethyldodecylammonium bro-mide within lamellar phases was restricted to 35% withinhexagonal and cubic mesophases, while it was 100% inmicellesw118x. The difference was explained by differ-ences in molecular mobility favoring terminationreactions.

5. Templating within self-organized media—somegeneral considerations

Templating within organized solutions is a much morecomplex process than suggested by the simple pictureof ‘casting’ a surfactant assembly. A polymerizationreaction within a highly dynamic self-organized mediumprogresses in a continuously changing physico-chemicalenvironment. As the monomer phase is substituted by apolymer phase, changes of the polarity of the dispersionmedium and the partitioning of each compound occur.Many monomers show some degree of surface activityand consequently segregate at the assembly’s interface.Therefore, polymerization can cause phase transitionsby driving changes in the interface curvature. Moresevere effects arise due to the loss of entropy or chemicalincompatibility of the polymer with the surfactant, andthis commonly drives phase separation and concomitantdisruption of the initial structure. In these cases thesurfactant phase still coexists with the demixed polymerphase, so there are usually no significant changes ofoptical textures or diffractograms recorded before andafter polymerization. For this reason the existence of aliquid crystalline or microemulsion phase after polym-erization, as verified for example by small-angle scat-tering, cannot be the lone determinant of whether or notdirect templating occurred. Only characterization of thepurified polymer matrix can provide evidence about theactual polymer morphologies formed. Of course, theprocess of extraction of the template may itself causemorphological changes, but a viable templating reactionshould produce materials capable of withstanding suchenvironmental changes.

Given the dilemma that phase separation induced bypolymerization is always the enemy of direct synergisticor transcriptive templating using a complex fluid, twostrategies can be developed for the synthesis of orderedsupramolecular materials. One is to suppress phaseseparation by adjusting thermodynamic and kinetic par-ameters, either in the original formulation or, perhaps,by changing conditions as the reaction proceeds. To dothis, and to realize true one-to-one templating, severalapproaches are described above. They are:(i) kineticstabilization by the use of surfactants with slowerexchange dynamics(e.g. amphiphilic block copoly-mers), (ii) polymerization within templates with longrearrangement times(e.g. hexagonal and cubic phases),(iii ) thermodynamic adjustment of the surfactantymon-omerypolymer mixture(e.g. by matching the molecularstructure to induce some attractive interaction and bythis compatibility, as was done for DVB polymerizationin equilibrium vesicles), (iv) cross-linking of the poly-mer matrix to ‘compensate’ for the entropy loss causedby producing the polymer matrix in a confined nano-geometry(e.g. monomers with a high number of reactiveentities per molecule can be fully cross-linked at lowconversions, or small multifunctional monomers such asDVB that intrinsically form cross-linked networks).Another strategy for the synthesis of ordered materi-

als, not yet fully developed, is to make use of the highsensitivity of the interaction between polymer gel chem-istry and surfactant mesophase chemistry. When aimingat the reconstructive templating of polymers with evenmore complex morphologies, this sensitivity can be usedas a powerful tool for the synthesis of new hierarchicalpolymer structures. One example is the colloidal order-ing of polymer gels by polymerization-induced phaseseparation within inverse hexagonal phasesw90x. Mod-ern theory will provide new insights and a betterunderstanding of dissipative structure formation withinthese highly dynamic, non-equilibrium processes.

6. Conclusions

Thermodynamically stable self-organized media, suchas microemulsions, vesicles and lyotropic mesophasesdisplay highly ordered structures on a nanometer scale.Because of their lack of mechanical stability and theirsensitivity to environmental changes they are unsuitablefor material applications. Templated synthesis of poly-mers within these phases is therefore employed to obtainordered, nanostructured materials for potential applica-tions including separations, catalysis, drug delivery,nanocomposite synthesis and as biomimetic materials.Polymerization of organic monomers within surfactant

solutions provides materials that usually cannot beobtained by conventional bulk or solution polymeriza-tion. Most strategies of polymer templating aim at thefabrication of one-to-one copies of the surfactant assem-


blies. In this way sometimes nanoparticles, hollow cap-sules, or mesoporous bulk polymers can be obtained.The success of true one-to-one templating dependsstrongly on balancing thermodynamic and kinetic para-meters, e.g. monomer partitioning and diffusion,exchange dynamics and template rigidity, the use ofcross-linkers and the compatibility of surfactant, mono-mer and polymer. By adjusting these parameters, sepa-ration into polymer-rich and surfactant-rich phases canbe suppressed and the initial template structure pre-served. A better understanding of the interplay of theseparameters will allow and improve systematicalapproaches towards the design of nanostructuredpolymers.In other approaches, polymerization-induced phase

separation within self-organized media is employed forthe colloidal ordering of hierarchically structured poly-mers. The supramolecular morphologies obtained byreconstructive templating usually show order on lengthscales from nano- to micrometer. In future this excitingfield of research, where modern theory and polymer gelchemistry meet, will gain more attention and providedeeper insight into dissipative structure formation withinnon-equilibrium systems.

Acknowledgments

The authors want to thank Srinivasa Raghavan, CarlosCo, and Craig McKelvey for their assistance and manyinteresting discussions. HPH is grateful for receiving anOtto-Hahn fellowship from the Max-Planck Society.This work was supported by the National ScienceFoundation, CTS 9814399.

References and recommended reading

● of special interest●● of outstanding interest

w1x Meier W. Nanostructure synthesis using surfactants andcopolymers. Curr Opin Colloid Interf Sci 1999;4:6–14.

w2x●

Hentze H-P, Antonietti M. Template synthesis of porousorganic polymers. Curr Opin Solid State Mater Sci2001;5:343–53.

This review is an overview of templating in microemulsions,vesicles, and lyotropic phases, as well as in colloid crystals,molecules, micelles, amphiphilic block copolymer bulk phases,and polyelectrolyte–surfactant complexes.w3x Miller SA, Ding JH, Gin DL. Nanostructured materials based

on polymerizable amphiphiles. Curr Opin Colloid Interf Sci1999;4:338–47.

w4x Mueller A, O’Brien DF. Supramolecular materials via polym-erization of mesophases of hydrated amphiphiles. Chem Rev2002;102:727–57.

w5x●●

Paul EJ, Prud’homme RK. Material synthesis by polymeri-zation in surfactant mesophases. In: Texter J, editor. InReactions and synthesis in surfactant systems. Marcel Dek-ker; 2001. 525–535. Surfactant science series, vol. 100.

A comprehensive review article about templating organic poly-mers within microemulsions, vesicles and lyotropic mesophases.

The different approaches towards direct templating are criticallydiscussed. A model towards a solution for the templatingbreakthrough is presented on basis of thermodynamic and kineticconsiderations.

w6x Hentze H-P, Antonietti M. Porous polymers and resins forbiotechnological and biomedical applications. Rev Mol Bio-technol 2002;90:27–53.

w7x●●

Mann S, Burkett SL, Davis SA, et al. Sol–gel synthesis oforganized matter. Chem Mater 1997;9:2300–10.

This article presents the variety of concepts employed for struc-turing inorganic matter by general principals of biomimeticsynthesis. The nomenclature used in the present review is basedon the paradigms of Mann et al., as there are many analogsbetween templating inorganic and organic materials by self-organization.w8x Dierking I. Polymer-network-stabilized liquid crystals. Adv

Mater 2000;12:167–81.w9x Lipic PM, Bates FS, Hillmyer MA. Nanostructures thermo-

sets from self-assembled amphiphilic block copolymer epoxyresin mixtures. J Am Chem Soc 1998;120:8963–70.

w10x Velev OD, Lenhoff AM. Colloidal crystals as templates forporous materials. Curr Opin Colloid Interf Sci 2000;5:56–63.

w11x Faul C, Antonietti M, Sanderson R, Hentze H-P. Directedpolymerization in mesophases of polyelectrolyte–surfactantcomplexes. Langmuir 2001;17:2031–5.

w12x●●

Co CC, Cotts P, Burauer S, de Vries R, Kaler EW. Microe-mulsion polymerization. 3. Molecular weight and particlesize distributions. Macromolecules 2001;34:3245–54.

Molecular weight and particle size distribution were measured bya combination of analytical techniques for the microemulsionpolymerization ofn-butyl methacrylate,tert-butyl methacrylate,n-hexyl methacrylate, and styrene. The data support the predictionof an analytical model derived from monomer partitioning andkinetic studies, which is described in accompanying papers(13,20).w13x Co CC, Kaler EW. Particle size and monomer partitioning

in microemulsion polymerization. 2. Online small angleneutron scattering studies. Macromolecules 1998;31:3203–10.

w14x Morgan JD, Kaler EW. Particle size and monomer partition-ing in microemulsion polymerization. 1. Calculation of theparticle size distribution. Macromolecules 1998;31:3197–202.

w15x Girard N, Tadros TF, Bailey AI. Kinetics of polymerizationof styrene-in-water microemulsions. Colloid Polym Sci1999;277:997–1000.

w16x Mendizabal E, Flores J, Puig JE, Katime I, Lopez-Serrano F,Alvarez J. On the modeling of microemulsion polymeriza-tion. Experimental validation. Macromol Chem Phys2000;201:1259–65.

w17x Chern C-J, Wu L-J. Kinetics of microemulsion polymeriza-tion of styrene with short-chain alcohols as cosurfactant. JPolym Sci A: Polym Chem 2001;39:898–912.

w18x Sanghvi PG, Pokhriyal NK, Devi S. Effect of partitioning ofmonomer on the reactivities of monomers in microemulsion.J Appl Polym Sci 2002;84:1832–7.

w19x de Vries R, Co CC, Kaler EW. Microemulsion polymeriza-tion. 2. Influence of monomer partitioning, termination, anddiffusion limitations on polymerization kinetics. Macromol-ecules 2001;34:3233–44.

w20x Co CC, de Vries R, Kaler EW. Microemulsion polymeriza-tion. 1. Small-angle neutron scattering study of monomerpartitioning. Macromolecules 2001;34:3224–32.


w21x Lopez RG, Trvino ME, Peralta RD, et al. A kinetic descrip-tion of the free radical polymerization of vinyl acetate incationic microemulsions. Macromolecules 2000;33:2848–54.

w22x Barton J, Juranicova V. Polymerization of acrylamide instyrene containing inverse microemulsions: polymerizationkinetics and polymer product composition studies. Polym Int2000;49:1483–91.

w23x Saenz de Buruaga A, de la Cal JC, Asua JM. Modelinginverse microemulsion polymerization. J Polym Sci A:Polym Chem 1999;37:2167–78.

w24x Saenz de Buruaga A, de la Cal JC, Asua JM. Inversemicroemulsion polymerization of MADQUAT initiated withsodium metabisulfate. Polymer 2000;41:1269–76.

w25x Dreja M, Pyckhout-Hintzen W, Mays H, Tieke B. Cationicgemini surfactants with oligo(oxyethylene) spacer groupsand their use in the polymerization of styrene in ternarymicroemulsion. Langmuir 1999;15:391–9.

w26x●

Candau F, Pabon M, Anquetil J-Y. Polymerizable microe-mulsions: some criteria to achieve an optimal formulation.Colloids Surface A: Physicochemical Eng Aspects1999;153:47–59.

The semi-empirical energy concepts CER and HLB were success-fully employed for optimization of microemulsion formulations.Dispersions with high loads of nanoparticles with narrow sizedistribution were obtained by bicontinuous microemulsionpolymerization.w27x Sosa N, Peralta RD, Lopez RG, et al. A comparison of the

characteristics of poly(vinyl acetate) latex with high solidcontent made by emulsion and semi-continuous microemul-sion polymerization. Polymer 2001;42:6923–8.

w28x Xu XJ, Siow KS, Wong MK, Gan LM. Microemulsionpolymerization of styrene using a polymerizable nonionicsurfactant and a cationic surfactant. Colloid Polym Sci2001;279:879–86.

w29x●

Xu XJ, Siow KS, Wong MK, Gan LM. Microemulsionpolymerization via hollow-fiber feeding of monomer. Lang-muir 2001;17:4519–24.

Continuous feeding through hollow fibers is an efficient way toproduce microlatex. The polymer to surfactant weight ratio can beas high as 15:1.w30x Braun O, Selb J, Candau F. Synthesis in microemulsion and

characterization of stimuli-responsive polyelectrolytes andpolyampholytes based onN-isopropylacrylamide. Polymer2001;42:8499–510.

w31x Saenz de Buruaga A, de la Cal JC, Asua JM. Continuousinverse microemulsion polymerization. J Appl Polym Sci1999;72:1341–8.

w32x Candau F, Braun O, Essler F, Stahler K, Selb J. Polymeri-¨zation in nanostructured media: applications to the synthesisof associative polymers. Macromol Symp 2002;179:13–25.

w33x Pyrasch M, Tieke B. Copolymerization of styrene and reac-tive surfactants in a microemulsion: control of copolymercomposition by addition of nonreactive surfactant. ColloidPolym Sci 2000;278:375–9.

w34x Moumen N, Pileni MP, Mackay RA. Polymerization ofmethacrylate in a wyo microemulsion stabilized by a meth-acrylate surfactant. Colloids Surface A: Physicochemical EngAspects 1999;151:409–17.

w35x Essler F, Candau F. Synthesis of multiblock ionomers bycopolymerization in inverse microemulsions. Colloid PolymSci 2001;279:405–12.

w36x Yan F, Xue G. Synthesis and characterization of electricallyconducting polyaniline in water–oil microemulsion. J MaterChem 1999;9:3035–9.

w37x Xia H, Wang Q. Synthesis and characterization of conductivepolyaniline nanoparticles. J Nanoparticle Res 2001;3:401–11.

w38x Kim BJ, Oh SG, Han MG, Im SS. Preparation of polyanilinenanoparticles in micellar solutions as polymerization medi-um. Langmuir 2000;16:5841–5.

w39x Tasakova V, Winkels S, Schultze JW. Anodic polymerizationof 3,4-ethylenedioxythiophene from aqueous microemul-sions. Electrochim Acta 2000;46:759–68.

w40x Apostolo M, Arcella V, Storti G, Morbidelli M. Free radicalcontrolled polymerization of fluorinated copolymers pro-duced in microemulsion. Macromolecules 2002;35:6154–66.

w41x●

Amigoni-Gerbier S, Larpent C. Synthesis and properties ofselective metal-complexing nanoparticles. Macromolecules1999;32:9071–3.

Selective metal-binding microlatices were fabricated by copoly-merization of styrene and divinylbenzene with a cyclam monomer.The nanoparticles formed showed high selectivity for bindingcupric ions. The subsequent hybrid particles have potential asprecursors in nanocomposite synthesis.w42x Moustafa AB, Kahil T, Faizalla A. Preparation of porous

polymeric structures for enzyme immobilization. J ApplPolym Sci 2000;76:594–601.

w43x Aguiar A, Gonzales-Villegas S, Rabelero M, Mendizabal E,Puig JE. Core-shell polymer with improved mechanicalproperties prepared by microemulsion polymerization. Mac-romolecules 1999;32:6767–71.

w44x Dresco PA, Zaitsev VS, Gambino RJ, Chu B. Preparationand properties of magnetite and polymer magnetite nanopar-ticles. Langmuir 1999;15:1945–51.

w45x Watnasirichaikul S, Davies NM, Rades T, Tucker IG. Pre-paration of biodegradable insulin nanocapsules from biocom-patible microemulsions. Pharm Res 2000;17:684–9.

w46x●●

Jang J, Ha H. Fabrication of hollow polystyrene nanospheresin microemulsion polymerization using triblock copolymers.Langmuir 2002;18:5613–8.

Polystyrene hollow spheres were synthesized by removing the coreof core-shell polymer particles obtained from microemulsionpolymerization.w47x Jang J, Lee K. Facile fabrication of hollow polystyrene

nanocapsules by microemulsion polymerization. ChemComm 2002;1098–9.

w48x Texter J. Precipitation and condensation of organic particles.J Disper Sci Technol 2001;22:499–527.

w49x Liu J, Gan LM, Chew CH, Teo WK, Gan LH. Nanostructuredpolymeric materials from microemulsion polymerizationusing poly(ethylene oxide) macromonomer. Langmuir1997;13:6421–6.

w50x Burban JH, He MT, Cussler EL. Organic microporous mate-rials made by bicontinuous microemulsion polymerization.AIChE 1995;41:907–14.

w51x Antonietti M, Hentze H-P. Synthesis of sponge-like polymerdispersions via polymerization of bicontinuous microemul-sions. Colloid Polym Sci 1996;274:696–702.

w52x Liu J, Teo WK, Chew CH, Gan LM. Nanofiltration mem-branes prepared by direct microemulsion copolymerizationusing poly(ethylene oxide) macromonomer as a polymeriz-able surfactant. J Appl Polym Sci 2000;77:2785–94.

w53x Xu W, Siow KS, Gao Z, Lee SY, Chow PY, Gan LM.Microporous polymeric composite electrolytes from microe-mulsion polymerization. Langmuir 1999;15:4812–9.

w54x Chow PY, Chew CH, Ong CL, Wang J, Xu G, Gan LM.Ion-containing membranes from microemulsion polymeriza-tion. Langmuir 1999;15:3202–5.


w55x Moy HY, Chow PY, Yu WL, Wong KMC, Yam VWW, GanLM. Ruthenium(II) complexes in polymerised bicontinuousmicroemulsions. Chem Comm 2002;982–3.

w56x Breulmann M, Colfen H, Hentze H-P, Antonietti M, Mann¨S, Walsh D. Elastic magnets: template-controlled minerali-zation of iron oxide colloids in a sponge-like gel matrix.Adv Mater 1998;10:237–41.

w57x Liu B, Li H, Chew CH, et al. PbS-polymer nanocompositewith third-order nonlinear optical response in femtosecondregime. Mater Lett 2001;51:461–9.

w58x Hao J. Microemulsion polymerization of acrylamide andstyrene: effect of the structure of reaction media. J PolymSci A: Polym Chem 2001;39:3320–34.

w59x Donescu D, Vasilescu M, Fusulan L, Petcu C. Microemul-sions of a vinyl acetatey2-ethylhexyl acrylate monomermixture. Langmuir 1999;15:27–31.

w60x Zasadzinski JA, Kisak E, Evans C. Complex vesicle-basedstructures. Curr Opin Colloid Interf Sci 2001;6:85–90.

w61x●●

Hubert DHW, Jung M, German AL. Vesicle templating. AdvMater 2000;12:1291–4.

A brief overview of the polymerization of and within vesiclebilayers, followed by a general discussions of parameters control-ling the evolution of morphologies during the templating process.w62x Jung M, Hubert DHW, Bomans PHH, Frederik P, van Herk

AM, German AL. A topology map for novel vesicle-polymerhybrid architectures. Adv Mater 2000;12:210–3.

w63x●

Jung M, den Ouden I, Montoya-Goni A, et al. Polymerizationin polymerizable vesicle bilayer membranes. Langmuir2000;16:4185–95.

A comparison of different polymerization techniques within vesiclebilayers. A combination of pre-cross-linking polymerizable surfac-tants and subsequent polymerization of monomers within thebilayer yielded in hollow spheres that resembled the original vesiclestructure.w64x

●Jung M, van Casteren I, Monteiro M, van Herk AM, GermanAL. Pulsed-laser polymerization in compartimentalized liq-uids. 1. Polymerization in vesicles. Macromolecules2000;33:3620–9.

Pulsed-laser polymerization was employed for the mechanisticinvestigation of the formation of parachute morphologies by polym-erization-induced phase separation.w65x Jung M, Robinson BH, Steytler DC, German AL, Heenan

RK. Polymerization of styrene in DODAB vesicles: a small-angle neutron scattering study. Langmuir 2002;18:2873–9.

w66x Jung M, Hubert DHW, van Veldhoven E, Frederik P,van Herk AM, German AL. Vesicle-polymer hybrid architec-tures: a full account of the parachute architecture. Langmuir2000;16:3165–74.

w67x Hubert DHW, Cirkel PA, Jung M, Koper GJM, Meuldijk J,German AL. Electrooptic behavior and structure of novelpolymer-vesicle hybrids. Langmuir 1999;15:8849–55.

w68x●●

McKelvey CA, Kaler EW, Zasadzinski JA, Coldren B, JungHT. Templating hollow polymeric spheres from catanionicequilibrium vesicles: synthesis and characterization. Lang-muir 2000;16:8285–90.

Hollow nanospheres with diameters of about 60 nm and shellthicknesses of less than 10 nm were obtained by polymerizationwithin the bilayers of two different equilibrium vesicle systems.The hollow particles were characterized in detail by light scattering,small-angle neutron scattering and cryo-TEM.w69x McKelvey CA, Kaler EW. Characterization of nanostructured

hollow polymer spheres with small-angle neutron scattering(SANS). J Colloid Interf Sci 2002;245:68–74.

w70x Sauer M, Meier W. Responsive nanocapsules. Chem Comm2001;55–6.

w71x●●

Krafft MP, Schieldknecht L, Marie P, et al. Fluorinatedvesicles allow intrabilayer polymerization of a hydrophobicmonomer, yielding polymerized microcapsules. Langmuir2001;2872–7.

Intact polymer nanocapsules were synthesized from the bilayers offluorinated vesicles. Disruption of the initial bilayer was found forthe templating within non-fluorinated vesicles. The differencesbetween the two templates are discussed with regard to the differentbilayer microstructures and properties.w72x

●Graff A, Winterhalter M, Meier W. Nanoreactors frompolymer-stabilized liposomes. Langmuir 2001;17:919–23.

Nano-bioreactors were formed by encapsulation of enzymes andincorporation of channel-forming proteins into the bilayer ofpolymerized vesicles.w73x Blocher M, Liu D, Walde P, Luisi PL. Liposome-assisted

selective polycondensation ofa-amino acids and peptides.Macromolecules 1999;32:7332–4.

w74x Liu S, O’Brien DF. Cross-linking polymerization in two-dimensional assemblies: effect of the reactive group site.Macromolecules 1999;32:5519–24.

w75x Liu SL, Sisson TM, O’Brien DF. Synthesis and polymeriza-tion of heterobifunctional amphiphiles to cross-link supra-molecular assemblies. Macromolecules 2001;34:465–73.

w76x●●

Liu S, O’Brien DF. Stable polymeric nanoballoons: lyophil-ization and rehydration of cross-linked liposomes. J AmChem Soc 2002;124:6037–42.

Unilamellar vesicles with diameters about 100 nm were success-fully polymerized by cross-linking of polymerizable lipids. Thenanocontainers obtained were stable against lysis by addition ofTriton X-100. Surface modification was achieved by polymeradsorption.w77x Stanish I, Singh A. Highly stable vesicles composed of a

new chain-terminus acetylenic photopolymeric phospholipid.Chem Phys Lipids 2001;112:99–108.

w78x Akama K, Yano Y, Tokuyama S, Hosoi F, Omichi H.g-rayirradiation of liposomes of polymerizable phopholipids con-taining octadeca-2,4-dienoyl groups and characterization ofthe irradiated liposomes. J Mater Chem 2000;10:1047–59.

w79x Jeong JM, Chung YC, Hwang JH. Enhanced adjuvanticproperty of polymerized liposome as compared to a phos-pholipid liposome. J Biotechnol 2002;94:255–63.

w80x Chung MH, Chung YC. Polymerized ion pair amphiphilethat shows remarkable enhancement in encapsulation effi-ciency and very slow release of fluorescent markers. ColloidsSurface B: Biointerf 2002;24:111–21.

w81x Walthier M, Polidori A, Ruiz K, Fabiano AS, Pucci B.Stabilization of polymerized vesicular systems: an applica-tion of the dynamic molecular shape concept. Chem PhysLipids 2002;115:17–37.

w82x Nardin C, Hirt T, Leukel J, Meier W. Polymerized ABAtriblock copolymer vesicles. Langmuir 2000;16:1035–41.

w83x Nardin C, Widmer J, Winterhalter M, Meier W. Amphiphilicblock copolymer nanocontainers as bioreactors. Eur Phys JE 2001;4:403–10.

w84x●

Discher BM, Bermudez H, Hammer DA, Discher DE, WonYY, Bates FS. Cross-linked polymersome membranes: vesi-cles with broadly adjustable properties. J Phys Chem B2002;106:2848–54.

A detailed study of elasticity and mechanical membrane propertiesof polymerized giant vesicles. Measurements were performed usingmicropipet aspiration.w85x O’Brien DF, Armitage B, Benedicto A, et al. Polymerization

of preformed self-organized assemblies. Acc Chem Res1998;31:861–8.

w86x Antonietti M, Caruso RA, Hentze H-P, Goltner CG. Hydro-¨philic gels with new superstructures and their hybrids by


nanocasting technologies. Macromol Symp 2000;152:163–72.

w87x●

Zhao B, Moore JS. Fast pH- and ionic strength-responsivehydrogels in microchannels. Langmuir 2001;17:4758–63.

A comparison of physical properties of templated and non-tem-plated, pH- and electrolyte-sensitive hydrogels. Much fasterresponse times were found for the templated material, due toimproved transport properties.w88x●●

Jung M, German AL, Fischer HR. Polymerisation in lyotrop-ic liquid-crystalline phases of dioctodecyldimethylammon-ium bromide. Colloid Polym Sci 2001;279:105–13.

A detailed X-ray study of morphological changes during and afterpolymerization of styrene within lyotropic mesophases. The resultsare discussed with regard to earlier studies of polymerization incubic phases and templating of vesicles.w89x Antonietti M, Goltner C, Hentze HP. Polymer gels with a¨

micron-sized, layer-like architecture by polymerization inlyotropic cocogem phases. Langmuir 1998;14:2670–6.

w90x●●

Hentze H-P, Kaler EW. Morphosynthesis of nanostructuredpolymer gels by polymerization within reverse hexagonalmesophases. Chem Mater 2002;15:708–13.

Ordered polymer gels were formed by polymerization-inducedphase-separation within a lyotropic liquid crystal. The observedcolloidal ordering is directed by the anisotropic viscosity andtransport properties of the reaction medium, and by the force fieldsinduced by interaction of the polymer matrix with the template.w91x●●

Loudet JC, Barois P, Poulin P. Colloidal ordering from phaseseparation in a liquid-crystalline continuous phase. Nature2000;407:611–3.

This paper demonstrates the colloidal ordering of silicone oildroplets by thermally-induced phase separation from a thermotropicliquid crystal. The formation of the highly ordered morphologies(regular strands of oil droplets) was explained by modern theoryof polymer interactions with liquid crystals.w92x Liu L, Li S, Simmons B, et al. Nanostructured materials

synthesis in a mixed surfactant mesophase. J Disper SciTechnol 2002;23:441–52.

w93x Lee JC. Polymerization-induced phase separation. Phys RevE 1999;60:1930–5.

w94x Motoyama M, Nakazawa H, Ohta T, et al. Phase separationof liquid crystal–polymer mixtures. Comp Theor Polym Sci2000;10:287–97.

w95x Chakrapani M, Winkle DHV, Patterson BC, Rill RL. Acry-lamide polymerized in the presence of surfactants: surfaceanalysis using atomic force microscopy. Langmuir2002;18:6449–52.

w96x Lester CL, Smith SM, Guymon CA. Acceleration of polya-crylamide photopolymerization using lyotropic liquid crys-tals. Macromolecules 2001;34:8587–9.

w97x Lester CL, Colson CD, Guymon CA. Photopolymerizationkinetics and structure development of templated lyotropicliquid crystalline systems. Macromolecules 2001;34:4430–8.

w98x Lee YS, Yang JZ, Sisson TM, et al. Polymerization ofnonlamellar lipid assemblies. J Am Chem Soc1995;117:5573–8.

w99x Srisiri W, Benedicto A, O’Brien DF, et al. Stabilization of abicontinuous cubic phase from polymerizable monoacylgly-cerol and diacylglycerol. Langmuir 1998;14:1921–6.

w100x Srisiri W, Sisson TM, Obrien DF, McGrath KM, Han YQ,Gruner SM. Polymerization of the inverted hexagonal phase.J Am Chem Soc 1997;119:4866–73.

w101x Pindzola BA, Hoag BP, Gin DL. Polymerization of a phos-phonium diene amphiphile in the regular hexagonal phasewith retention of mesostructure. J Am Chem Soc2001;123:4617–8.

w102x Deng H, Gin DL, Smith RC. Polymerizable lyotropic liquidcrystals containing transition-metal and lanthanide ions:architectural control and introduction of new properties intonanostructured polymers. J Am Chem Soc 1998;120:3522–3.

w103x Resel R, Leising G, Markart P, Kriechbaum M, Smith R,Gin D. Structural properties of polymerised lyotropic liquidcrystals phases of 3,4,5-tris(omega-acryloxyalkoxy)benzoatesalts. Macromol Chem Phys 2000;201:1128–33.

w104x Reppy MA, Gray DH, Pindzola BA, Smithers JL, Gin DL.A new family of polymerizable lyotropic liquid crystals:control of feature size in cross-linked inverted hexagonalassemblies via monomer structure. J Am Chem Soc2001;123:363–71.

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Gin DL, Gu W, Pindzola BA, Zhou WJ. Polymerizedlyotropic liquid crystal assemblies for materials applications.Acc Chem Res 2001;34:973–80.This article presents an overview of the work of the Gingroup. The examples described mainly demonstrate thesynergistic templating of inverse hexagonal phases. A num-ber of potential applications of ordered nanocomposite gelsare discussed.

w106x Fu Q, Friberg SE, Zhang Z, Aikens PA. Polymeric surfactantsbased on oleic acid IV. Lamellar liquid crystal polymerizationof sodium oleateyoleic acidyaliphatic dieneywater system. JDisper Sci Technol 2000;21:1007–21.

w107x Kayali I, Li F, Zhang Z, Sandburg JD, Friberg SE. Polymericsurfactants based on oleic acids III. Copolymerization ofsodium acrylamidostearate and oleic acid in a lamellar liquidcrystal. J Disper Sci Technol 1999;20:1789–807.

w108x Li F, Zhang Z, Friberg SE, Aikens PA. Polymeric surfactantsbased on oleic acid. II. Copolymerization of sodium acrylam-idostearate and 10-undecen-1-ol in a lamellar liquid crystal.J Polym Sci A: Polym Chem 1999;37:2863–72.

w109x Meier W. Polymer networks with lamellar structure. Macro-molecules 1998;31:2212–7.

w110x Eastoe J, Summers M, Heenan RK. Control over phasecurvature using mixtures of polymerizable surfactants. ChemMater 2000;12:3533.

w111x Summers M, Eastoe J, Davis S, et al. Polymerization ofcationic surfactant phases. Langmuir 2001;17:5388–97.

w112x Pawlowski D, Haibel A, Tieke B.g-ray polymerization ofcationic surfactant methacrylates in lyotropic mesophases.Berichte der Bunsen-Gesellschaft-Phys Chem Chem Phys1998;102:1865–9.

w113x Hohn W, Tieke B.g-ray polymerization of lyotropic solutionsof cellulose derivatives under retention of the macroscopicorder. Macromol Chem Phys 1997;198:703–15.

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Hentze HP, Kramer E, Berton B, Forster S, Antonietti M,Dreja M. Lyotropic mesophases of poly(ethylene oxide)-b-poly(butadiene) diblock copolymers and their cross-linkingto generate ordered gels. Macromolecules 1999;32:5803–9.

Highly ordered polymer gels with lamellar, hexagonal, or cubicorder were obtained by cross-linking of a reactive block copol-ymer in the lyotropic state. The order was retained throughdrying, heating, and addition of polar and nonpolar solvents.Extensive characterization was performed by X-ray scattering,microscopy and electron microscopy. A detailed analysis of theblock copolymer structures, disclinations and transition stateswas presented in a following paperw115x.

w115x Forster S, Berton B, Hentze H-P, Kramer E, Antonietti M,¨ ¨Lindner P. Lyotropic phase morphologies of amphiphilicblock copolymers. Macromolecules 2001;34:4610–23.


w116x Lester CL, Guymon CA. Ordering effects on the photopo-lymerization of a lyotropic liquid crystal. Polymer2002;43:3707–15.

w117x Lester CL, Guymon CA. Phase behavior and polymerizationkinetics of a semifluorinated lyotropic liquid crystal. Mac-romolecules 2000;33:5448–54.

w118x Rodriguez JL, Soltero JFA, Puig JE, Schulz PC, Espinoza-Martinez ML, Pieroni O. Polymerization of aqueous liquid-crystalline allyldimethyldodecylammonium bromide. ColloidPolym Sci 1999;277:1215–9.

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Polymerization of and within self-organized mediasion polymerization is a reconstructive template synthe-sis w5 x. There hasrecently been considerable effort devoted to mechanistic