Synthesis of Polyampholyte Janus‐like Microgels by Coacervation of Reactive Precursors in Precipitation Polymerization

Abstract Controlling the distribution of ionizable groups of opposite charge in microgels is an extremely challenging task, which could open new pathways to design a new generation of stimuli‐responsive colloids. Herein, we report a straightforward approach for the synthesis of polyampholyte Janus‐like microgels, where ionizable groups of opposite charge are located on different sides of the colloidal network. This synthesis approach is based on the controlled self‐assembly of growing polyelectrolyte microgel precursors during the precipitation polymerization process. We confirmed the morphology of polyampholyte Janus‐like microgels and demonstrate that they are capable of responding quickly to changes in both pH and temperature in aqueous solutions.


Introduction
Microgels,w hich are defined as unique crosslinked macromolecular structures,f ill the gap between macromolecules and colloids.T hey exhibit interesting properties like stimuli-responsiveness,surface-activity,and adaptability. [1] Thep resence of charges in microgels makes them appealing for the development of drug-delivery carriers, [1a,2] emulsion stabilizers, [3] and functional coatings. [4] As pecial class of charged microgels are polyampholyte microgels that carry opposite charges at different pH. [5] Recently,p olyampholyte microgels with ar andom and core-shell distribution of charges were synthesized by miniemulsion and precipitation polymerization. [6] It has been shown that apart from their balance,t he distribution of charges in microgels strongly influences the uptake and release of charged molecules. [7] So far,nosuitable method has been reported to synthesize polyampholyte Janus-like microgels with oppositely charged faces.T he attempts to synthesize Janus microgels were focused mainly on post-modification methods,i ncluding masking techniques (surface adsorption/interface adsorption) [8] or phase separation in microfluidic droplets. [9] Dendukuri et al. reported the synthesis of Janus microgels by using am icrofluidic device.T wo non-miscible fluids (monomers) were mixed with ap hotoinitiator to generate biphasic droplets,f ollowed by UV-triggered crosslinking. [10] This method, however,c ould be applied only to al imited amount of monomers and cannot be used for the production of large quantities of Janus microgels.
Another approach to synthesize Janus colloids is the use of liquid-liquid interfaces for fixation and site-specific postmodification. H. Kawaguchi et al.,f or instance,p repared Janus microgels based on poly(N-isopropylacrylamide) (PNI-PA m) and acrylic acid (AAc). [11] Microgels were adsorbed at the toluene-water interface,a nd amino groups were introduced via acarbodiimide coupling reaction on the side of the particles which are in contact with water. However,s ince microgels show ad ifferent swelling extension to different solvents,i ti sd ifficult to predict the portion of the surface being functionalized.
Furthermore,m ost methods for the synthesis of Janus microgels only functionalize the particle surface,w hile the microgel interior is unaffected. Concerning possible applications as drug carriers,the presence of functional groups in the microgel interior is desired, as it offers several advantages, such as improved solubility of the drug, [12] protection against immunogenicity, [13] and degradability. [14] Furthermore,t he directed self-assembly of Janus colloids and multitude of their potential applications has raised high interest in the development of future advanced materials. [8a] With regard to this,t he investigation on Janus microgels will potentially promote the understanding of their properties and the development of new programmed materials. [8b, 15] Janus micro-gels show multiple functionalities and tunable interactions deriving from the polymeric motifs.T hey also allow responsive and adaptive interactions in bulk systems towards external stimuli and guest molecules that are needed for self-assembly. [16] In all, Janus microgels fulfill the concept of aw ell-defined, versatile,m ultifunctional, and responsive material, and are therefore of profound interest both for fundamental research as well as for application toward advanced materials.
Existing approaches to Janus colloids [16b,17] are limited to certain chemical functionalities and cannot be transferred directly to microgels.Also,such synthesis methods cannot be performed on al arge scale,p rohibiting the production of Janus microgels in large amounts.T he synthesis of Janus microgels by techniques that consider structure formation in aselective solvent or solvent mixtures like self-assembly, [15,18] or phase separation, [19] known for block-copolymer assemblies,have not been reported so far.
Herein, we present an easy and straightforward templatefree method for the synthesis of polyampholyte Janus-like microgels with oppositely charged sides.T his synthesis approach is based on the controlled electrostatically driven self-assembly and coacervation of growing oppositely charged microgel precursors during precipitation polymerization. The key feature of the developed synthesis method is the fast mixing of two reaction mixtures with separately growing polyelectrolyte microgels carrying opposite charges at as pecific reaction time (t* mix )a nd monomer conversion. We demonstrate that mixing two reaction mixtures at t mix < t* mix leads to the formation of microgels with arandom distribution of charges.C ontrary,m ixing two reaction mixtures at t mix > t* mix leads to the formation of am ixture of separate polyanionic and polycationic microgels (Scheme 1). Controlling the distribution of ionizable groups within polyampholyte Janus-like microgels enables the design of new efficient drug carriers,switchable emulsion stabilizers,and adaptive catalyst carriers.T he developed synthesis method opens new possibilities to synthesize microgels with complex internal architecture using an industrially relevant and up-scalable polymerization technique.

Results and Discussion
To evolve an ew synthesis approach for polyampholyte Janus-like microgels,w ed ecided to use N-isopropylacrylamide (NIPAm) as the main monomer along with itaconic acid (IA) and 1-vinylimidazole (VIm) as comonomers carrying ionizable groups of opposite charge. N,N'-methylenebis(acrylamide) (BIS) was used as the crosslinker and 2,2'-azobis [2methylpropionamidine] dihydrochloride (AMPA) as the initiator.NIPAm is probably the most widely used monomer for the synthesis of temperature-responsive microgels. [20] IA and VIm were used in our previous work for the synthesis of polyampholyte microgels with random [6a] and core-shell [20] distribution of charges (amounts of ingredients are listed in the Supporting Information, Tables S2 and S3), and therefore were applied in the present study to enable their comparison with the properties of polyampholyte Janus-like microgels.
Thesimplified design of the microgel synthesis developed in the present study is shown in Scheme 1. Thep recipitation polymerization of NIPAm-IA and NIPAm-VIm in water was initiated in two separated reaction vessels by the addition of the water-soluble radical initiator (AMPA) at ar eaction temperature of 70 8 8C(Supporting Information, Table S1). At certain reaction times,h ot solutions with growing microgel precursors were rapidly mixed in apre-heated reaction vessel, and the polymerization was continued at 70 8 8C. As shown in Scheme 1. Synthesis route for microgelsw ith various architectures and distributions of ionizable groups. When t mix < t* mix :microgels with arandom distributiono fionizable groups are obtained, when t mix = t* mix :J anus-likem icrogels are obtained, and when t mix > t* mix :separate microgels of opposite charges are obtained. t IA is the polymerization time of NIPAm-IA microgels, t VIm is the polymerization time of NIPAm-VIm microgels, t mix is the time at which NIPAm-IA and NIPAm-VIm microgels were mixed, t* mix is the time at which Janus-likem icrogels were observed,a nd t p is the polymerization time after mixing of the samples. Scheme 1, depending on the mixing time,p olyampholyte microgels with adifferent distribution of ionizable groups and architectures could be obtained. Thef ollowing parameters were varied to investigate their influence on the reaction process:1 )mixing time (t mix ), 2) polymerization time after mixing (t p ), 3) reaction temperature (before and after mixing), and 4) pH of reaction solutions.A ccordingly,w ef ound that ar eaction temperature of 70 8 8Cw as most suitable in terms of polymerization rates and microgel yield. Ap Ho f6 was found to be optimal to maintain the colloidal stability of formed microgels,t hus avoiding coagulate formation in the reactor.
In classical precipitation polymerization of NIPAm, the growing oligoradicals precipitate when they reach ac ritical chain length, forming microgel nuclei, which act as precursors for microgels. [21] It is believed that starting from this point, the formed microgel precursors grow in size by the precipitation/ crosslinking of newly formed polymer chains and reach the final size when all monomer is consumed. Based on these considerations,w ed ecided to explore the early stage of the microgel precursor growth to find as uitable route to microgels with complex architectures.
Thee ssential step was monitoring the precipitation copolymerization rate and microgel growth process for selected monomers.W eused reaction calorimetry to monitor the polymerization heat and calculate conversion-time dependencies for microgel synthesis.T urbidity measurements and in situ dynamic light scattering (DLS) were applied to follow the nucleation and growth of microgels throughout the precipitation polymerization.
In the preliminary experiments,w ep erformed three polymerization runs synthesizing NIPAm, NIPAm-IA, and NIPAm-VIm microgels under the same reaction conditions (monomer and initiator concentrations and reaction temperature). Thea ddition of the initiator to the pre-heated monomer solution set the start of the reaction. Thec alorimetric measurements of NIPAm and NIPAm-VIm (Supporting Information, Figure S1) indicate that the precipitation polymerization for all polymerization runs is completed after 40 min, reaching high monomer conversions (95-100 %). Remarkably,t he presence of comonomer VIm slows down the polymerization rate without strongly affecting the final monomer conversion, which was calculated based on the total polymerization heat. Unexpectedly,i tw as not possible to copolymerize NIPAm with IA in the calorimeter (though the reaction worked well in ad ouble-walled glass reactor), possibly due to as ide reaction between IA and the metal parts of the reaction calorimeter. However,E rbil et al. demonstrated that by using free radical polymerization in 1,4-dioxane,N IPAm units are considerably more reactive than IA units. [22] In situ time-dependent DLS measurements for three polymerization runs visualize the microgel nucleation and growth stages (Figure 1). Pure NIPAm microgels reach ah ydrodynamic radius R H of approximately 140 nm after 5min. NIPAm-VIm microgels need aslightly longer reaction time of approximately 8min to reach an R H of approximately 150 nm. NIPAm-IA microgels require the longest time (approximately 50 min) to reach their maximal size of approximately 110 nm. Thei nsitu DLS data of NIPAm-VIm correlate well with the calorimetric results presented in Figure S1 in the Supporting Information, showing that the presence of the comonomer VIm slows down microgel growth. An analogous statement can also be made for NIPAm-IA, due to the much longer polymerization time required to reach astable microgel size.This can be attributed to the increased hydrophilicity of oligoradicals containing VIm or IA monomer units and thus retarded precipitation onto the growing microgel nuclei. Another important conclusion from calorimetry and in situ DLS measurements is that the copolymerization processes of NIPAm with VIm and IA as well as the growth of microgels require different reaction times.B ased on these experimental data, we hypothesize that rapid mixing of growing microgel nuclei carrying opposite charge at aspecific reaction time may lead to the formation of polyampholyte Janus-like microgels. Consequently,w en arrowed down the most suitable mixing time between 0.5-5 min after the initiation of the polymerization, since both calorimetry and in situ DLS indicate that within this time frame,the microgel growth is fast.
Following this concept, we performed as eries of polymerizations,asshown in Scheme 1, where the polymerization mixtures from two separate reaction vessels were mixed at different times (0.5-5 min). In these experiments,o nly the mixing time (t mix )a nd the polymerization time (t p )a fter mixing were varied.
Fort he first set of experiments,t he synthesis of NIPAm-VIm microgels was initiated 2min after the initiation of NIPAm-IA microgel synthesis.A tt mix of 0.5, 1, 2, 3, 4, and 5min after initiation of NIPAm-VIm, 1mLofeach dispersion was taken from separate reactors,a nd both samples were mixed immediately under continuous stirring at 70 8 8C. The respective mixtures were then allowed to continue to react for t p = 1h at 70 8 8C. Depending on t mix ,c olorless (small t mix )o r milky (large t mix )d ispersions were obtained. All synthesized microgels were purified by dialysis and subjected to careful  at 70 8 8C). B) Zoom-in of (A) from 0to10min. Forall measurements, the particle growth during the polymerization process was fitted using the Boltzmann equation.
characterization with transmission electron microscopy (TEM). To verify the formation of Janus-like particles,t he samples were stained with uranyl acetate U(Ac) 3 first, given that U(Ac) 3 binds selectively to the carboxyl groups of IA.
TEM images for ab atch of samples prepared at t p = 1h are presented in Figure S2 in the Supporting Information. The images show that different t mix lead to the formation of microgels with different distributions of IA. Mixing after 3min results in some microgels with one side darker than the other, while the majority show microgels with ahomogeneous distribution (Supporting Information, Figure S2 B,C). This shows that IA and VIm groups are spatially separated in some cases,p roving the formation of Janus-like microgels.H owever,a so nly af ew Janus-like microgels could be detected during the TEM measurements,t he synthesis procedure needed to be optimized. One reasonable explanation for the observed paradox could be that if the polymerization time is too long, NIPAm monomer,w hich is in excess,b uilds up ashell around the "Janus-core" thus preventing the observation of Janus-like microgels through TEM.
In order to optimize the formation of Janus-like microgels, as econd set of experiments was developed similar to the procedure described above.H owever,t he polymerization time after mixing time was shortened to t p = 10 min at 70 8 8C after mixing,t op revent the formation of an extra shell ( Figure 2). Thep olymerization of the reaction mixture was stopped by rapid cooling and afterward purified by dialysis. All samples were first characterized by TEM, and the selected Janus-like microgels ( Figure 2E)w ere further characterized by using different analytical techniques.
Ther eduction of the polymerization time t p to 10 min resulted in the formation of Janus-like microgels at t mix between 2min and 4min ( Figure 2C-E). Similar to the set of reactions at t p = 1h(Supporting Information, Figure S2 A), microgels with ar andom distribution of charges were observed after 0.5 min and 1min mixing time (Figure 2A,B), since the mixing at this stage contains mostly unreacted monomers (Supporting Information, Figures S3 A, S4, S5, and S6). Starting from t mix = 2min, the formation of Janus-like microgels took place ( Figure 2C-E). These TEM images visualize the evolution of the Janus-like microgels,s tarting from the merging of two differently charged pre-microgels to reaching the colloidal stable state of the Janus-like microgels. Thec reation of stable Janus-like microgels can be explained by coacervation process driven by the electrostatic attraction of the ionizable groups and the crosslinking effect that holds two pre-microgels together (Supporting Information, Figure S3 B). As expected, at t mix > 4min, microgels containing either VIm or IA were formed. According to the images,the darker microgels,corresponding to NIPAM-IA microgels,are smaller than the NIPAM-VIm microgels ( Figure 2F), which is also supported by the results of in situ DLS ( Figure 1).
As super-resolved fluorescence microscopy (SFM) [23] method, dSTORM [24] has been proven to be very suitable for the imaging of microgels. [25] It was also used here to study the morphology of the Janus-like microgels in aqueous solution. Before measuring,Janus-like microgels were labeled with an egatively charged fluorescent dye sodium 5,5'-((perfluorocyclopent-1-ene-1,2-diyl)bis(2-ethyl-1,1-dioxidobenzo [b]thiophene-3,6-diyl))bis(2-methoxybenzenesulfonate) [26] that effectively attaches to the imidazole group at pH 4( Figure 3B). Figure 3A reveals the morphology of Janus-like microgels under acidic condition (pH 4), where protonation of imidazole groups take place,leading to amore prominent swelling of the NIPAm-VIm based side.T he SFM image in Figure 3B confirms the same statement. As predicted, under the same operation environment (pH 4, 20 8 8C) but in the aqueous state, the microgels show am ushroom-shaped structure where the labeled NIPAm-VIm side is more pronounced than the NIPAm-IA side which is in agreement with the TEM image ( Figure 3A).
Polyampholyte microgels based on NIPAm are both temperature-and pH-responsive. [27] Them icrogel size measurements as af unction of pH were performed with DLS to give abrief overview of how the microgels swell with various pH values (Supporting Information, Figure S7). Them icrogels are positively charged at pH < 5.5 and negatively charged at pH > 5.5. As ar esult, microgels are swollen both at lower pH 3(R H = 455 AE 7nm) and higher pH 10 (R H = 431 AE 8nm). This discrepancyb etween the two swollen states can be explained with the help of Figure 4A.T he TEM image reveals that the unstained (VIm) part is slightly larger than the stained (IA) part. Therefore,protonation of the imidazole ring leads to am ore prominent swelling. At the isoelectric point (pH 5.5), the microgels are in ac ollapsed state (R H = 418 AE 3nm) due to the compensation of charges.
Static scattering methods are well known for allowing the investigation of polymer structures in solution. [28] As discussed above,the uneven swelling of the different sides of the microgels is expected when changing the pH from 2, over 6to 9. We used static light scattering (SLS) to distinguish between the different global structures of the microgels.W eexpect the fuzzy sphere model, which is commonly used for microgels,to match the particle form factor of the microgels at its isoelectric point (pH % 6), where the swelling is homogenous. [29] Contrary,t he fuzzy sphere model is expected to fail when fitting the particle form factors at pH 2a nd pH 9. In these regimes,the microgels are most likely anisometric. Figure 4A shows the experimental data of the particle form factor for the three states of the microgel obtained via SLS.T he data were fitted using the software FitIt!,a nd the implemented fuzzy sphere model. [22] Forp H6only one fit is shown. Thef it not only matches the data but also shows physically reasonable characteristic parameters.A dditional data on these microgels for ab roader q-range,a sw ell as at high temperatures in their collapsed state are shown in Figures S13 and S14 in the Supporting Information. Thef it results in ar adius of R SLS = 334 AE 7nm, while DLS [30] gives R H = 419 AE 11 nm (Supporting Information, Figure S15). Since SLS is not sensitive to the dangling chains at the . C) Computers imulation snapshots of the symmetrical, Js, and asymmetrical, Ja, Janus-like microgels formed by (top row) the same size precursorm icrogels, C 16k (NIPAm-VIm) + A 16 (NIPAm-IA), and (bottom row) by the different size precursor microgels, C 16k (NIPAm-VIm) + A 8k (NIPAm-IA) (Supporting Information,T able S4). Snapshots represent the slices of 10s width of the equilibrated microgels through the center of mass of the microgel in the XZ plane. The main axis of the microgel coincides with the direction of the unit vector along the OZ axis and the center of coordinates match the center of mass of the microgel. NIPAm and VIm groups in the cationic precursor microgel,C ,are marked in green and yellow,respectively.NIPAm and IA groups in the anionic precursor microgel, A, are marked in violet and pink, respectively.Symbols I, II, III, IV,and Vdenote the cases of different ratios of ionized groups IA:Vim within the microgel (emulation of the system at different pH values): I À0%:10 %; II À2.5 %:7.5 %; III À5%:5 %; IV À7.5 %:2.5 %; V À10 %:0 %( Supporting Information,T able S4). The corresponding fit for pH 6i sbased on the fuzzy sphere model. The data for pH 2and pH 9cannot be fitted based on spherical models. B) The dependence of sphericity, " b, cylindricity, " c, and relative shape anisotropy, k 2 of the symmetrical, Js, (solid lines) and asymmetrical, Ja, (dash-dottedl ines) Janus-likem icrogels on the different ratio of ionized groups IA:VIm within the microgels:IÀ0%:10 %; II À2.5 %:7.5 %; III À5%:5 %; IV À7.5 %:2.5 %; V À10 %:0 %. microgels periphery,t he radius obtained via SLS is expected to be smaller than the hydrodynamic radius.AtpH6and T = 50 8 8C, the form factor can be fitted with the model of ahomogeneous sphere.
However,the scattering data at pH 2and pH 9cannot be fitted with form factor models for spherical objects.The fuzzy sphere form factor model does not describe the experimental data (Supporting Information, Figure S13), which clearly demonstrates that the microgels are non-spherical for pH values at which either one side is charged.
Further to the experimental results,the simulations of the equilibrium structure of the Janus-like microgels in symmetric and asymmetric cases have been performed ( Figure 3C,t op and bottom rows). In our designation, Janus-like microgel is considered to be symmetric (Js) or asymmetric (Ja) when it is formed by the cationic and anionic precursor microgels of the same or different sizes (Supporting Information, Table S4). Thequantities describing the shape and structure of the Js and Ja microgels were estimated for different pH values.S imulation on pH changes in the system was performed by avariation on the ratio of the ionized groups IA:VIm within the microgel (Supporting Information, Computer simulation (Model)). Theaverage eigenvalues " l x , " l y ,and " l z (Supporting Information, Eq. (5)) after division by R 2 g are plotted in Figure S9 in the Supporting Information. In all cases,m icrogels have an oblong shape,e longated in the direction of the major principal axis Z( Figure 3C). Thee igenvalues " l x and " l y " l z coincide with each other within the error,w hile " l z > " l x , " l y .T he average relative asphericities " b and the average relative acylindricities " c (Supporting Information, Eq. (12)), as well as the average relative anisotropy coefficients " k 2 (Supporting Information, Eq. (14)) are plotted in Figure 4B. It is evident that at extreme pH points,Iand V, where only cationogenic or anionogenic groups are ionized, microgels show very cylindrically symmetric shapes (" c % 0, " b around 0.5) and turn less cylindrical and more spherical (" c % 0, " b % 0:1) near the isoelectric point ( Figure 3C,III (top) and IV (bottom)). According to the measurements of gyration radius R g (Supporting Information, Eq. (6)) as afunction of pH, the microgel swells both at lower and higher pH values while it gradually shrinks when approaching the isoelectric point. The detailed examination of the swelling behavior based on the analysis of the distribution of beads within the microgel along the major principal axis,Z(Supporting Information, Figures S11 and S12) clearly indicates that at extreme pH points (I and V), the charged side of the Janus-like microgel swells more,c ompared to the uncharged side.T he reasons for this phenomenon are the electrostatic repulsion of similarly charged groups and the osmotic pressure of the counterion clouds.p Hc hanges towards the isoelectric point lead to the appearance of pairs of oppositely charged subchains within the relevant parts of the microgels having astrong tendency to form neutral complexes.D irecting attention at the peaks in Figure S11 (II-IV) in the Supporting Information, striking features become apparent:the complexation is accompanied by the collapse of the inner part of the Janus-like microgel, redistribution of the masses within the microgel, increasing the contact area of oppositely charged precursor microgels, interpenetration of the subchains belonging to the different precursor microgels and release of the counterions.Weexpect these changes to become more pronounced for the case of alow crosslinked gel.
Thet hermo-and pH-sensitivity of polyampholyte Januslike microgels and its difference from the polyampholyte microgels with random and core-shell distribution of ionizable groups are discussed in this section. Figure 5A shows the temperature-responsive behavior of all three polyampholyte microgels at pH 6, where the polyampholyte microgels should exhibit both positive and negative charges,leading to charge compensation. This is shown by the electrophoretic mobility in Figure 5B.T he swelling of polyampholyte microgels is influenced by two factors,I )the physical crosslinking within the opposite charged groups/subchains,a nd II) the counterions in the microgel network. [6b,31] Polyampholyte microgels with ar andom distribution of ionizable groups exhibit weak temperature responsiveness due to the efficient charge compensation, leading to more physical crosslinking and fewer counterions within the network. Interestingly,polyampholyte microgels with the same amounts of monomers but different distributions of VIm and IA groups behave completely differently upon temperature change.
Polyampholyte microgels with core-shell distribution of ionizable groups exhibit less temperature dependencya nd less swelling at lower temperatures compared to polyampholyte Janus-like microgels.A tp H6,t he oppositely charged groups are distributed in different compartments of the microgel. According to the type of microgels,the contact area (A)b etween the opposite charges is different (A core-shell > A Janus-like ). Therefore,less physical crosslinking of the different ionizable groups and more counterions are present in the Janus-like polyampholyte microgels,r esulting in am ore pronounced collapse when turning to ah igher temperature. Another interesting observation is the shift of the volume phase transition temperature (VPTT,t he temperature when the microgels turn from ah ighly swollen state to ac ollapsed state). While pure NIPAm microgels exhibit aV PTT at around 32 8 8C, the Janus-like polyampholyte microgels show one at 35.9 8 8C. This effect can be attributed to the presence of the spatially separated hydrophilic monomer units (VIm and IA) in the microgels. [6b] Furthermore,the sharp temperatureinduced transition in the case of Janus-like polyampholyte microgels can be explained by the reduction of the charge interference and absence of the "corset" effect reported for core-shell polyampholyte microgels. [31] Conclusion In conclusion, we demonstrated asimple,and straightforward method for the synthesis of Janus-like polyampholyte microgels.Our synthesis approach is based on the controlled coacervation and phase separation of growing polyelectrolyte microgel precursors during the precipitation polymerization process.C alorimetric studies,a swell as in situ time-dependent DLS measurements,were employed to identify the ideal mixing time (t mix )o ft wo growing polyelectrolyte microgel populations.TEM and SFM images of polyampholyte microgels revealed that they have aJ anus-like distribution of ionizable groups.T he synthesized polyampholyte Janus-like microgels are both temperature-and pH-sensitive.T he pHsensitivity enables particles to be swollen at low and high pH while being collapsed at the isoelectric point.
Thes ynthesized polyampholyte Janus-like microgels are unique colloids with ab road range of useful applications. They could potentially be used as novel drug carriers for simultaneous delivery and controlled, on-demand release of different drugs.Polyampholyte Janus-like microgels can act as compartmentalized catalyst carriers for the combination of enzymes and organocatalysts or metal complexes in tandem reactions.