Scalable Miniemulsion Polymerization of Methyl Methacrylate (MMA) in Continuous Flow

Abstract

A scalable methodology to perform miniemulsion polymerizations is demonstrated for the polymerization of methyl methacrylate (MMA). Scalability of the miniemulsification was achieved by using a spinning disk reactor, which provides the required energy input to form a metastable emulsion, yielding miniemulsion droplets with an average size of 154 nm and a PDI of 0.17. Polymerization proceeds likewise in a scalable fashion, achieved by using agitated continuous flow reactors, which effectively prevent reactor fouling, a problem that typically limits emulsion polymerization in continuous flow. For the MMA miniemulsion process, synthesis of over 100g of polymer particles with well-defined particle distributions (the average polymer particle size, obtained after polymerization in the ATR reactor following emulsification using the SDR, was 170 nm with a PDI of 0.10) has been achieved, and operation of the designed reactor setup is stable over an entire workday. The space-time yield of the miniemulsion was found to be 53 g/Lh, significantly outperforming previous methods of miniemulsion polymerization.

Introduction

Emulsion polymerization is a widely used method for producing polymers that are used in adhesives, paints, paper additives, textiles, plastic composites, and construction materials. , Its popularity stems from several technical advantages: efficient heat removal during polymerization, low latex viscosity even at high polymer concentrations and molecular weights, and simple polymer recovery. Another key advantage is that emulsion polymerization typically allows faster reaction rates and the formation of polymers with higher molecular weights than other free-radical techniques. , Moreover, increasing environmental regulations targeting volatile organic compounds (VOCs) have accelerated the shift from solvent-based to waterborne coatings, further enhancing the relevance of this method. Miniemulsion polymerization has emerged as an attractive method for producing polymer nanoparticles in a 50–500 nm range, offering distinct benefits over conventional emulsion methods. − Although both processes are related, their mechanisms differ significantly, particularly in terms of particle nucleation. In conventional emulsions, polymerization and particle formation through homogeneous or micellar nucleation are accompanied by monomer exchange and a transfer of surface area from micelles to the growing polymer particles. This continuous redistribution alters the reaction dynamics and results in variable droplet sizes, making precise control over the particle dimensions challenging. Further, reaction kinetics are complex and difficult to control. In contrast, an ideal miniemulsion system maintains stability, as each monomer droplet formed serves directly as a precursor to a single polymer particle with a comparable surface area. This one-to-one correspondence reduces the radical competition during nucleation and enables the formation of polymer nanoparticles with precise, predetermined sizes. , Such nanoscale particles are widely utilized across diverse fields such as drug delivery, pharmaceuticals, medical imaging, cosmetics, food processing, and polymer production, owing to their unique ability to enable the synthesis of advanced materials like organic–inorganic hybrids and hollow nanoparticles, − while also serving as a versatile platform for implementing reversible deactivation radical polymerization (RDRP) techniques. − Miniemulsion polymerization is based on the formation of submicron monomer droplets that act as individual nanoreactors. , This concept was established by Schork and co-workers in the early 1990s through a comparison of methyl methacrylate polymerization in macroemulsions and miniemulsions, showing that when Ostwald ripening is suppressed by appropriate surfactant–costabilizer systems, polymerization occurs predominantly within preformed droplets. Their work provided early quantitative evidence that stable nanodroplets can be directly converted into polymer particles with well-defined and narrow size distributions, and that the resulting kinetics and latex properties differ fundamentally from those of conventional emulsion systems. The same group subsequently demonstrated continuous miniemulsion polymerization in a CSTR, revealing sustained steady-state operation and establishing a foundation for scalable reactor design. Later, the introduction of dodecyl mercaptan as a dual-function cosurfactant and chain-transfer agent showed that functional additives can be incorporated without compromising droplet stability while enabling molecular weight control. Collectively, these studies laid the groundwork for reactor design and process control strategies suited to miniemulsion processes. In practice, the required submicron droplets are typically produced using high shear methods such as ultrasonication, high-pressure homogenization, or static mixers. − While effective, their energy demands and limited scalability remain significant barriers to broader application; , moreover, scaling these high-energy emulsification methods often compromises droplet uniformity and process stability, underscoring the need for alternative strategies capable of achieving comparable droplet control under industrially scalable conditions. Several low-energy emulsification strategies , such as phase-inversion temperature, emulsion inversion point, and in situ surfactant generation ,, have been investigated for preparing miniemulsions. However, these methods still encounter challenges, particularly in maintaining control over the particle size. Recently, membrane emulsification has attracted attention as a promising low-energy alternative for generating the required monomer droplets with precise size control. − Nonetheless, this method also faces challenges, i.e., long reaction times and difficulties in scaling up. To the best of our knowledge, no strategies to truly intensify the miniemulsion process sufficiently have been reported to date. The above-mentioned advances to solve the energy input problem are still typically difficult to scale up, as they require complete reoptimization for different reactor volumes. This often leads to significant batch-to-batch variations in both the yield and droplet characteristics. Therefore, there is a pressing need to develop a sustainable, scalable approach for miniemulsion synthesis that ensures consistent droplet quality, facilitating the application of miniemulsion polymerization in a much broader application window that is not restricted to small amounts of materials.

Continuous flow reactors have, over the last few years, emerged as efficient alternatives to traditional batch synthesis systems, offering precise control over temperature, pressure, residence time, and stoichiometry. , Their high surface-to-volume ratio ensures efficient heat transfer and safer handling of exothermic reactions, while controlled reagent addition enhances process safety. , Flow processes are easily scalable from laboratory to industrial production without extensive redesign, making the transition from research to industrial scale more efficient. , Continuous flow reactors have been widely employed for the synthesis of biphasic emulsions, various colloids and nanomaterials. In the context of miniemulsion polymerization, Nauman et al. demonstrated the use of membrane emulsification for batch synthesis of polymer nanoparticles, achieving submicron-sized particles for the first time with this method. However, as mentioned before, batch processes often face challenges such as poor product consistency, inefficient heat control, poor linear scalability, and long processing times. Transitioning from batch or semicontinuous to continuous reactors presents a promising strategy for process intensification in heterogeneous polymerizations. , So far, most studies have employed either continuous stirred-tank reactors (CSTRs) − or tubular plug flow reactors (PFRs), , initiated thermally or photochemically. Tubular reactors are often preferred for producing complex dispersed polymers through miniemulsion polymerization. However, when highly dispersed emulsions involving both organic and aqueous phases are processed in such reactors, blockages can easily form within the channels as a result of reactor fouling. As pointed out by Asua and co-workers, this issue arises when the monomer has a lower interfacial tension with the reactor wall than the aqueous phase does. Under these conditions, monomer molecules can spread along the reactor surface, where unwanted polymerization may then take place. Bistac and co-workers studied the causes of channel blockage in tubular reactors using butyl acrylate photoinitiated miniemulsion polymerization as a model. They found that while droplet size, flow rate, and emulsion stability had little effect, factors such as solids content, surfactant concentration, and reactor diameter played a major role in channel clogging. Photoinduced polymerizations have also been explored in batch, semibatch, and in tubular reactor setups. ,, However, scaling up polymerization in tubular flow reactors remains challenging, and CSTRs are often prone to fouling and clogging due to excessive solid deposition, although in some cases, this can be alleviated by using pulsed agitation. Thus, not only the continuous formation of miniemulsions but also the polymerization without fouling remains a significant challenge to date, and both problems need to be addressed concomitantly to realize a truly scalable miniemulsion system.

In this study, we report the successful continuous-flow miniemulsion synthesis and its subsequent stable polymerization under scalable conditions, addressing challenges that go beyond simply performing miniemulsion polymerization in a flow reactor. While continuous miniemulsion polymerization itself is relatively straightforward and has been demonstrated previously, the primary novelty of our work lies in the preparation of a stable, uniform miniemulsion at a significantly larger scale and in preventing fouling during continuous polymerization. Our work focuses on these aspects, enabling the reproducible production of polymer particles at scales and stabilities rarely reported in the literature, bridging the gap between laboratory-scale miniemulsion experiments and practically relevant, continuous manufacturing. To this end, the feasibility of continuous miniemulsification was investigated as a strategy to produce large quantities of miniemulsions with defined droplet sizes and narrow size distributions using methyl methacrylate (MMA) as a model monomer. The MMA miniemulsion is prepared using a commercially available spinning disk reactor (Synthetron) and then polymerized in a Coflore Agitated Tube Reactor (ATR), a pilot-scale flow reactor. After optimizing the process in both systems individually, we integrated them to demonstrate an end-to-end telescopic miniemulsion polymerization of PMMA nanoparticles.

Results and Discussion

Scheme illustrates the overall approach, which involves the formation of an MMA miniemulsion using a spinning disk reactor (SDR), followed by its polymerization in the agitated tube reactor (ATR). Initially, efforts focused on producing MMA miniemulsion using the SDR, with optimization of the process achieved by varying parameters such as rotor-stator gap size and rotation speed (rpm). SDRs are ideal to achieve effective emulsification, as they provide very high shear forces, much beyond the level of conventional stirrers and mixers. These shear forces provide the energy required for breaking the thermodynamic barrier and reaching the kinetically stable miniemulsion regime. In conventional miniemulsification, the shear forces involved (ultrasound) typically generate heat, which can unintentionally trigger polymerization within the emulsion. Hence, often emulsification and polymerization are not distinct periods, but may occur partially simultaneously, ultimately leading to the formation of secondary structures and particle heterogeneities. To prevent any unintended polymerization during the emulsification step, the SDR was maintained at a low temperature. Additionally, its rotor-stator configuration generates not only high shear but also promotes efficient mass and heat transfer as the process fluid is confined to a micrometer-thick layer within the reactor, hence making cooling more effective than in conventional reactors.

1. Telescoped Continuous Flow Miniemulsion Polymerization of MMA through Emulsification in a Spinning Disk Reactor, Followed by Polymerization in an Agitated Tube Reactor.

Continuous Flow Miniemulsification Using a Spinning Disk Reactor

As a formulation for our work, we used the recipe described by Nauman et al. for membrane miniemulsification. The organic phase comprised methyl methacrylate (MMA), hexadecane (HD), and azoisobutyronitrile (AIBN), while the continuous phase consisted of water and sodium dodecyl sulfate (SDS); hexadecane plays a central role in stabilizing miniemulsions by suppressing Ostwald ripening. Its effectiveness arises from its extremely low solubility in the aqueous phase, which retards monomer diffusion between dropletsthe primary driving force for droplet coarsening. ,, The aqueous SDS solution (2.75 wt %, 5.83 mM) was introduced into the spinning disc reactor (SDR) from the top inlet, while the monomer mixture (comprising MMA (6 wt %), hexadecane (10 wt % relative to MMA), and AIBN (0.01 M)) was simultaneously fed from the side inlet (Figure ). Both the continuous and organic phase reagents were filtered before each experimental run to ensure smooth operation of the employed piston pumps. Within the SDR, the two streams rapidly mix to generate the miniemulsion, and samples were collected and diluted with water for subsequent particle size analysis.

1.

Schematic illustration of the previous membrane-based miniemulsification approach and our continuous flow strategy for generating miniemulsions using an SDR.

The reactor temperature was maintained at 15 °C. Under standard conditions (100 μm gap size and 1000 rpm), droplets of about 230 nm are consistently obtained, with a dispersity of close to 0.3 (determined via DLS). Both size and dispersity are well within range for a miniemulsion system, and particle sizes are in fact lower than what was observed for the membrane miniemulsification system. , Using the same formulation, we then explored the influence of various SDR parameters on the formed (mini)­emulsion, such as disc rotation speed (rpm) and interdisc gap size. Encouragingly, miniemulsion droplets were successfully obtained across interdisc spacings of 100–400 μm and rotational speeds ranging from 1000 to 3000 rpm (see Table ). Although particle size distributions did not show a consistent trend with changing the rotational speed or gap size, the emulsions exhibited impressively low polydispersity indices and droplet sizes between 154 and 320 nm. This is remarkable given that the residence time of the setup under these conditions is merely a few seconds. Optimal uniformity was obtained at a moderate interdisc spacing of 200 μm and a rotation speed of 2000 rpm, resulting in miniemulsion droplets with an average size of 154 nm and a PDI of 0.17 prior to polymerizationvalues that are widely regarded as optimal for a miniemulsion process. It should be hereby noted that the SDR allows us to produce already at this point very significant volumes of the emulsion, and almost one L (0.9 L) is easily prepared in an hour under the described conditions.

1. Effect of Gap Size and rpm on the Droplet Size in SDR Miniemulsification.

gap size (μm)	rpm	droplet size (nm)	PDI
100	1000	234	0.27
	2000	251	0.30
	3000	301	0.28
200	1000	218	0.20
	2000	154	0.17
	3000	183	0.21
300	1000	241	0.31
	2000	298	0.28
	3000	320	0.28
400	1000	234	0.29
	2000	215	0.31
	3000	314	0.27

Continuous Flow Miniemulsion Polymerization Using Agitated Flow Reactors

At this point, however, it would be possible that the system is emulsified yet does not constitute a miniemulsion system. A key differentiator between mini- and classical emulsions is that the initiator is present in the droplet phase in miniemulsion. Further, the number of particles remains constant during the process, and also, the particle size ideally does not significantly change during the polymerization. Since an oil-soluble initiator was used, the first prerequisite was fulfilled, yet it still needed to be established if particles remain intact during the polymerization (hence not allowing for homonucleation and migration of monomer between micelles, as would be the case in a classical emulsion). Thus, the (mini)­emulsions obtained from the SDR were first subjected to classical thermal batch polymerization at 70 °C for 24 h. Indeed, under these conditions, a monomer conversion of 89% is reached. Starting from the optimized SDR conditions (154 nm, PDI = 0.17), after polymerization, an average size of 140 nm and a PDI of 0.11 is observed, closely matching the precursor emulsion droplet size. This nicely underpins that the emulsion that is formed in the SDR is indeed equivalent to a miniemulsion and follows the same polymerization characteristics.

The next step was to translate the batch miniemulsion polymerization to a continuous-flow process. As mentioned above, polymerizing emulsions in continuous flow is challenging due to reactor fouling, and often reactions, even though successful for short runtimes, cannot be carried out for significant amounts of time. Further, while tubular reactors are often used in laboratory settings, they are not easily linearly scaled and are therefore not fully suitable for high-throughput or large-scale production. To address this, we opted to use a commercially available pilot-scale agitated tube reactor (Coflore Agitated Tube Reactor). The ATR is capable of handling solid slurries and suspensions as well as gas–liquid and solid–liquid–gas processes − and enables kilo-scale production with relative ease. , More importantly, the ATR, as its name suggests, provides continuous agitation, preventing the deposition of colloids at the reactor wall and thus reactor fouling. The reactor is hence ideal to scale up an emulsion polymerization process.

Prior to scaling of the miniemulsion, first preliminary experiments on a smaller scale were conducted to explore the flow polymerization. To this aim, the obtained miniemulsion from the SDR was continuously pumped through an agitated cell reactor (ACR) at 85 °C with varying residence times (RT) of 15, 20, 30, and 45 min. The ACR consists of a series of continuous stirred-tank reactors on a small scale, which, as the ATR, allows the colloids to remain in motion, providing a stable operation of the flow. With ACR, we monitored the evolution of particle distributions and monomer conversion over time. At shorter residence times, the particle size distributions were relatively broad, exhibiting bimodality in the DLS-obtained distribution (Figure A), and the monomer conversion remained relatively low (11% at 15 min, 33% at 20 min, and 58% at 30 min), with the resulting particle morphology appearing suboptimal (see Supporting Information). However, when moving to a residence time of 45 min, monomodal particle size distribution along with enhanced monomer conversion (67%) and well-defined particle morphology (see Figure B) were obtained. Most pleasingly, the particles obtained under these optimal conditions match the size distribution of the miniemulsion, again underpinning the mechanistic observation made earlier. The bimodal particle size distribution observed at short residence times in Figure A likely arises from secondary nucleation or the formation of minor particle populations during the initial stages of polymerization. These early-formed particles exist at relatively low concentrations and low conversion, which explains why they can no longer be detected at longer residence times. As the reaction proceeds, the primary particle population grows, ultimately resulting in a uniform, monomodal distribution in the final product, as confirmed by both DLS and SEM measurements.

2.

(A) Number-average size distribution plot for monomer droplet (synthesized using SDR) and polymer particle synthesized using ACR at various RT (15, 20, 30, 45 min). (B) Scanning electron microscopy (SEM) image of the final polymer particle obtained after 45 min RT in the ACR.

After optimization of the polymerization residence time in the ACR, the process was scaled up using the ATR system for subsequent polymerization experiments. Scaling of the experiment introduces the problem that even though the miniemulsion obtained from the SDR is stable in its size distribution, sedimentation can still occur when solutions are held for significant amounts of time. At the same time, a reservoir of the emulsion is required to be placed between the SDR and the ATR, as flow rates are vastly different, and a direct coupling of the reactors is neither feasible nor practical. To prevent issues in the experimental design, the collected miniemulsion was continuously recirculated through the SDR (see Scheme and detailed experimental procedures are provided in the SI). This approach ensures homogeneity, maintains droplet integrity, and enhances reproducibility in the polymerization process, which is essential for achieving consistent polymer particle size and overall product quality. The miniemulsion droplet size was monitored during recirculation, and no significant change or droplet ripening was observed, indicating a stable, uniform, and robust miniemulsion (Figure A). From this recirculated reservoir, the ATR was then fed for polymerization at a flow rate, according to a 45 min residence time. The reservoir itself was sealed during operation to avoid oxygen contamination. As we did before with the ACR, the ATR setup operated at 85 °C, achieving a somewhat lower monomer conversion of approximately 45%, yet resulting in PMMA particles with a uniform, monomodal size distribution and well-defined morphology (see Figure (B,C)) that closely matches the obtained emulsion. The looping configuration used here arises solely from the mismatch between the flow-rate windows of the SDR and the ATR and is not intrinsic to the process concept. Here, recirculation allowed us to decouple the individual flow rates to test their influence on the overall process individually. In an industrial setting, volumes of the SDR and the ATR reactors would be adjusted to allow for a single flow rate. Commercially available spinning disc reactor, such as the Flowid SpinPro R-10, capable of producing emulsions with precise droplet-size control at feed flow rates up to at least 600 Lh^–1. This would enable direct one-pass coupling of the SDR with a continuous ATR without the need for recirculation.

3.

(A) Particle size distributions obtained during recirculation of the miniemulsion in the SDR, (B) comparison of the emulsion size distribution before and after polymerization, and (C) particle morphology obtained after polymerization at 85 °C. (D) Stability tests for extended runtime of the combined SDR-ATR setup showing obtained particle size and monomer conversion, with the corresponding particle size distributions (E), and polymer morphology obtained after polymerization at 110 °C (F).

While this result was pleasing, the conversion was deemed to be on the low end. To improve this, polymerization was subsequently carried out at an elevated temperature of 110 °C, bringing the final conversion (gravimetrically determined) to about 75%. It is very likely that higher conversions could be achieved by extending the residence time. We did not further optimize this parameter, as a conversion of 75% was sufficient to demonstrate stable continuous operation over prolonged periods without a loss of performance or reactor blockage. Importantly, batch miniemulsion polymerizations using the same formulation consistently reached much higher final conversions (up to ∼89% after 24 h), confirming that the chemistry itself readily supports greater extents of polymerization. Any residual monomer can be removed downstream by evaporation, which is a standard practice in emulsion polymerization processes. Approaches to further increase conversion, including operation at longer residence times, are currently under investigation and constitute part of our ongoing and future research directions. The elevated temperature had no detrimental effect on the particle distribution and morphology (see Figure (E,F)) again confirming the miniemulsion nature of the polymerization process. The slightly more “packed” appearance observed in Figure F is most likely an artifact introduced during SEM sample preparation, particularly during solvent evaporation and drying on the stub, which can promote capillary-driven particle rearrangement. Importantly, the corresponding DLS measurements show no meaningful difference in particle size or dispersity between these samples, indicating that the apparent change in packing is not associated with a real morphological difference. Importantly, we checked for the consistency of the reaction to see if fouling would occur when the reactor keeps running. Hence, the integrated reactor system was operated continuously for a total runtime of 7 h and 30 min. No significant fouling was observed. To further assess reproducibility and consistency, samples were withdrawn at regular intervals, one every 45 min throughout the reaction, and analyzed for particle size, morphological consistency, and conversion (see Figure D). Within reasonable variation limits, the particle size remained constant, as did the monomer conversion. With the setup described here, the productivity of the process was 18.6 g/h, hence easily allowing for the production of more than 100g of polymer particles in a single day. While the SDR and the ATR are commercially used equipment, they nonetheless fit a classical laboratory scale, and hence this productivity is deemed very advantageous, and considering the typical limitations in volume handling, very good for laboratory-scale synthesis. The space-time yield (STY) of the reaction is 53 g/Lh. For comparison, the membrane batch miniemulsion polymerization produced a throughput of 0.021 g/h and an according STY of 0.84 g/Lh, while the continuous flow tubular reactor-based miniemulsion photopolymerization achieved a throughput of 2.96 g/h (no STY is given for this example since the reactor would not be able to operate for extended periods).

Controlling the Nanoparticle Size Using SDS

After the flow miniemulsion process was defined and successfully tested as described above, we then tested whether the system also allows for the typical variation that is expected for a miniemulsion with respect to particle size selection. As discussed initially, changing the SDR parameters only exhibited a limited influence on the overall particle size, hinting that the obtained size distribution is thermodynamically controlled. Thus, the particle size should be primarily determined by the surfactant concentration used in the formulation. To examine the influence of surfactant concentration on the final particle size, a series of experiments were conducted using SDS concentrations of 0.6, 2, 6, 8, and 16 mM while maintaining all other operating parameters of the SDR and ATR constant. The selected concentrations encompass values both below and above the critical micelle concentration (CMC) of SDS, which is 8.2 mM. Unsurprisingly, we found that increasing the SDS concentration from 0.6 to 16 mM resulted in a decrease in the final particle size, ranging from approximately 504 to 102 nm. At SDS concentrations below 6 mM, the resulting nanoparticles were further nonuniform and exhibited bimodal particle size distributions. In contrast, increasing the SDS concentration beyond this point sufficiently stabilized the nanodroplets, resulting in the formation of uniform and stable miniemulsions (Figure S8). This behavior is not uncommon for miniemulsions and can be attributed to insufficient surface coverage by surfactant molecules at low surfactant concentrations. Under such conditions, the system increasingly resembles a conventional emulsion polymerization regime, leading to a departure from true miniemulsion behavior and, consequently, diminished control over the particle size. Because the final polymer particles are essentially one-to-one replicas of the precursor miniemulsion droplets, improved surface coverage during emulsification results in polymer particles with similar stability characteristics. This trend is expected as a certain degree of miniemulsion degradation through Ostwald ripening and coalescence is unavoidable. However, the extent of such instabilities was notably lower at higher surfactant concentrations, as anticipated.

To investigate the effect of SDS concentration on polymerization conversion, gravimetric analysis was performed across a range of surfactant levels to calculate the polymer conversion. The results show that increasing the SDS concentration generally accelerates the polymerization due to the enhanced compartmentalization in miniemulsions: higher SDS levels produce smaller nanodroplets, which facilitate faster reaction rates. At low SDS concentrations, the conversions were limited (0.6 mM: 25%; 2 mM: 39%), while moderate levels significantly improved conversion (6 mM: 73%; 8 mM: 68%). However, at very high SDS concentrations (16 mM), although the polymerization proceeds rapidly, excessive reaction rates increase the likelihood of radical–radical coupling, which ultimately restricts further growth. As a result, the highest SDS concentration yielded only 63% conversion, indicating that additional SDS does not lead to a higher polymerization efficiency.

Conclusion

Miniemulsion polymerization, despite its unique potential in applications, has to date been resistant to effective scaling of the process, and polymerizations have been typically restrained to low volumes. This limitation is given because miniemulsions by definition are metastable and require significant energy input in order to form efficiently. In here, we demonstrated that a spinning disk reactor is capable of producing (mini)­emulsions very effectively for the monomer MMA, a classically used monomer in miniemulsion. The throughput of the emulsification is very high, allowing us to easily produce the emulsions at scale. A further challenge in scalable (mini)­emulsion polymerization is that continuous flow reactors, which are typically used for scaling industrially, are prone to reactor fouling when colloidal systems are present. We could overcome this issue by using an agitated cell and tube reactor and demonstrating that the combination of the spinning disc reactor and the agitated reactor allowed for miniemulsion polymerization at very significant outputs. It is noteworthy to say that the reactor setup used here is useable in the footprint of a regular laboratory and does not require any specific infrastructure. While we believe that further scaling to larger volumes should be possible, the production of more than 100g of polymer particles per day with consistent and well-defined features is already a very significant advance. Exploring higher solid content formulations, particularly for industrial latex applications, and their effect on droplet stability and fouling in the SDR–ATR setup is an important aspect and forms part of our ongoing and future investigations. We expect that with this method being available, several bottlenecks in miniemulsion polymerization can be lifted, opening pathways to more complex particles with encapsulated payloads or more complicated core–shell morphologies in the future.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacsau.5c01613.

• Basic experimental setup, general experimental details, procedures, SEM images, and size-distribution plots (PDF)

CRediT: Gayathri Dev Ammini data curation, formal analysis, investigation, methodology, validation, visualization, writing - original draft; Nagaraj Nayak investigation, methodology; Anil Kumar funding acquisition, project administration, supervision, writing - review & editing; Tanja Junkers conceptualization, funding acquisition, project administration, supervision, writing - review & editing.

The authors declare no competing financial interest.

Published as part of JACS Au special issue “Continuous Flow Chemistry”.