FLOW SYNTHESIS OF POLYMER NANOPARTICLES

CLAIM OF PRIORITY

[0001] This application claims the benefit of priority to U.S. Provisional Patent Application No. 62/854,074, filed May 29, 2019, the contents of which are hereby incorporated by reference herein.

TECHNICAL FIELD

[0002] This disclosure relates to polymer particles.

BACKGROUND

[0003] Polymeric nanoparticles (polymer NP or PNP) are solid particles having a size, for example, in the range of 10 nanometers (nm) to 1000 nm. More typically, the size of polymer nanoparticles is in the range of 10 nm to 100 nm. This size of less than 100 nm may facilitate penetration of the nanoparticles in applications. Also, the ratio of surface area to volume of nanoparticles may benefit applications that rely on reactions on the surface of particles. Polymer nanoparticles may have applications such as drug delivery systems, photonics, sensors, conducting materials, catalysts, agriculture, and pollution control. Polymer nanoparticles are typically prepared in a batch synthesis. The choice of the batch preparation technique may depend on factors such as particle size, particle size distribution, solvent types, and area of application.

SUMMARY

[0004] An aspect relates to a method of flow synthesis of polymer nanoparticles. The method includes feeding a mixture having a radical initiator to a continuous flow reactor having a channel, and heating the mixture in a preheating section of the continuous flow reactor. The method includes feeding monomer to the continuous flow reactor, and mixing the monomer with the mixture in a reaction section of the continuous flow reactor downstream of the preheating section. The method includes polymerizing the monomer in the presence of the radical initiator in the reaction section to form polymer nanoparticles, wherein the polymerizing of the monomer includes emulsion polymerization. The method includes discharging polymer nanoparticles from the continuous flow reactor.

[0005] Another aspect relates to a method of flow synthesis of polymer nanoparticles, including preheating a mixture having a radical initiator in a continuous flow reactor having a flow channel. The method includes polymerizing monomer having methacrylate units in presence of the initiator via an emulsion polymerization in the continuous flow reactor to form polymer nanoparticles that include polymer of the methacrylate units. The method includes discharging the polymer nanoparticles from the continuous flow reactor.

[0006] Yet another aspect relates to a method of flow synthesis of polymer nanoparticles. The method includes flowing a first mixture having a radical initiator and water to a continuous flow reactor having a flow channel for reactant flow. The method includes flowing monomer to the continuous flow reactor. The method includes forming in the continuous flow reactor a second mixture having the first mixture and the monomer. The method includes polymerizing, via emulsion polymerization, the monomer in the second mixture in the continuous flow reactor to form polymer nanoparticles.

[0007] Yet another aspect relates to a continuous flow reactor system having a continuous flow reactor having a flow channel. The continuous flow reactor system includes a first source to supply a mixture to a continuous flow reactor. The mixture includes a radical initiator and water. The continuous flow reactor system includes a second source to supply monomer to the continuous flow reactor. The continuous flow reactor has a mixing section to mix the monomer with the mixture to form a polymerization mixture for emulsion polymerization. The continuous flow reactor has a reaction section to polymerize the monomer in the polymerization mixture via emulsion polymerization to form polymer nanoparticles.

[0008] The details of one or more implementations are set forth in the accompanying drawings and the description to be presented. Other features and advantages will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF DRAWINGS

[0009] FIG. 1 is a diagram of a continuous flow reactor system for synthesizing polymer nanoparticles.

[0010] FIG. 2 is a perspective view of a laboratory configuration for a batch synthesis of polymer nanoparticles.

[0011] FIG. 3 is a simplified diagram of a module plate in the continuous flow reactor utilized in the Examples for the laboratory flow synthesis of polymeric nanoparticles.

[0012] FIG. 4 is a diagram of a channel in the module plates of the continuous flow reactor in the Examples for the flow synthesis.

[0013] FIG. 5 is a set-up diagram of the continuous flow reactor in the Examples for the flow synthesis.

[0014] FIG. 6 is a bar chart of particle size of the produced polymer nanoparticles in the Examples.

[0015] FIG. 7 is a bar chart of polydispersity index of the produced polymer nanoparticles in the Examples.

[0016] FIG. 8 is a plot of thermogravimetric analysis (TGA) curves for nanoparticles produced with the reaction condition A.

[0017] FIG. 9 is a plot of TGA curves for nanoparticles produced with the reaction condition C.

[0018] FIG. 10 is a block flow diagram of a method of flow synthesis of polymer nanoparticles.

DETAILED DESCRIPTION

[0019] Some aspects of the present disclosure are directed to synthesizing polymer nanoparticles utilizing a continuous flow reactor having a channel. Flow chemistry may be flow synthesis in a continuous flow reactor. Batch chemistry has traditionally been employed for polymerization of nanoparticles and microparticles due to the simplicity of batch synthesis. However, flow chemistry may provide advantages for reaction processes in the synthesis of polymer particles. Flow chemistry can give improvements in the synthesis, catalysis, reaction screening, scale-up, and quality control. Continuous flow reactors can achieve greater yields, faster production, and more uniform particle size or narrower particle size distribution than in batch production.

[0020] Batch synthesis has drawbacks for reactions that are sensitive to mixing and heating where heat transfer is an issue. Batch stirring or batch agitating forms gradients of temperature in the reaction solution. In reactions such as polymer syntheses, these temperature irregularities impact chain growth because the temperature gradients cause variability in the reaction speed among volume regions in the polymerization solution. This variability can be problematic in the laboratory or pilot plant and at industrial scale. Scale-up of batch reactions with the temperature gradients can increase irregularity in particle size distribution of the polymer. Thus, the quality of batch products may suffer where uniform particles or narrow particle size distribution (PSD) is desired.

[0021] In comparison to batch synthesis, flow synthesis may achieve more uniform heat distribution and more efficient heat transfer in polymerization reactions. In continuous flow reactors, the degree of mixing can be controlled by flow rates of the reactants. Increasing flow rates through the continuous flow reactor can achieve more uniform mixing of the reactants than in batch synthesis. The more uniform mixing may decrease the dispersity or polydispersity index (PDI) of the polymer nanoparticles. The reproducibility of conditions in flow synthesis facilitates consistent production of monodisperse materials.

[0022] Flow chemistry may improve the quality of syntheses by increasing the yield of reactions. This increase in yield may occur through the greater heat-transfer surface area to volume ratio in flow reactors (compared to batch reactors), increased mixing by increasing reactant flow rate, and better selectivity in some reactions. As for selectivity, flow implementation with a back pressure regulator (discussed later) may give better product selectivity than typical batch synthesis. This is because the flow reaction can be performed at increased pressure and therefore at temperatures greater than the atmospheric boiling point of the reagents. The back pressure regulator facilitates increase of the reaction pressure to allow for increase in

polymerization temperature. For some reactions, increased temperature kinetically favors the product over a byproduct and thus gives better selectivity. Flow syntheses with continuous flow reactors may facilitate a range of reaction pressures by employing back pressure regulators. Continuous flow reactors may provide ease of varying pressure via the back-pressure regulator.

[0023] Continuous flow reactors may provide ease of varying temperature via the greater heat-transfer area to volume ratio than in batch reactors while facilitating a greater production rate of product as compared to batch synthesis. In flow synthesis, the flow reactor may react multiple times (for example, ten times or 10X) the amount of material in the same time period as a corresponding-size batch process. Flow reactors give the capability to scale- up lab processes and produce kilograms of material in a few hours at pilot scale or commercial scale.

[0024] Nanomaterials have been primarily synthesized in batch mode in quantities less than one kilogram in the laboratory. Due to the inherently difficult reproducibility of size, distribution, and quality from batch to batch, there are challenges in scaling batch procedures up to the quantities of nanomaterials relevant for realization in industries such as the oil and gas industry. Conversely, present embodiments scale-up the synthesis of polymeric nanoparticles with flow synthesis via, for example, increasing the number of modules of a flow reactor. This technique for nanoparticle synthesis is demonstrated in the Examples presented later. The Examples show scale up of nanoparticle synthesis that yielded monodispersed polymer

nanoparticles at sub-50 nanometer (nm) particle size with only 10 weight percent of the amount of initiator used in a corresponding batch process. This continuous-flow nanoparticle synthesis was achieved at a faster rate than the batch synthesis. In application in the oil and gas industry, the synthesized polymer nanoparticles can be used as interwell or near-wellbore tracers and as tags for mud logging operations.

[0025] FIG. 1 is a continuous flow reactor system 100 for synthesizing polymer nanoparticles. The system 100 polymerizes monomer into the polymer nanoparticles. The polymer nanoparticles may have an average or median particle size less than 200 nm, less than 100 nm, or less than 50 nm.

In some implementations, the polymer nanoparticles are monodisperse or near-monodisperse (for example, at least 90% monodisperse). Monodisperse (or uniform) polymer nanoparticles may mean the particle distribution is particles having approximately the same size or a size variation of less than 5% (or less than 10%). Monodisperse polymer nanoparticles may be polymer nanoparticles composed of molecules of approximately the same

mass. Monodisperse may mean a polydispersity index (PDI) less than 0.02. Near-monodisperse may mean a PDI of less than 0.08.

[0026] In implementations, the polymerization is an emulsion

polymerization. Emulsion polymerization may be a type of radical

polymerization that typically starts with an emulsion incorporating water, monomer, and surfactant. A type of emulsion polymerization is monomer-in- water emulsion, in which droplets of monomer are emulsified via surfactant in a continuous phase of water. Water-soluble polymers can also be utilized as an emulsifier or stabilizer. While an emulsion is formed (e.g., typically via a surfactant) for the polymerization, the polymerization may occur not in emulsion droplets but in formed colloid particles made of polymer chains. The surfactant may prevent coagulation of the colloid particles. The surfactant is generally present in the slurry of product polymer nanoparticles and water that discharge from the continuous flow reactor. An advantage of emulsion polymerization may that be high molecular weight polymers can be made at fast polymerization rates. In contrast, for bulk and solution free-radical polymerization, a tradeoff exists between molecular weight and polymerization rate.

[0027] In certain implementations, a surfactant is required to facilitate emulsion formation for the emulsion polymerization. Moreover, for

implementations, the polymerization is not a bulk radical polymerization.

Instead, with embodiments of the present polymerization, at least the major monomer (e.g., styrenic monomers or acrylic monomers) is not soluble in the solvent (water). Instead, the main monomer is dispersed in water to from an emulsion stabilized by a surfactant or by a water soluble comonomer. Further, the polymer nanoparticles formed are not soluble in the solvent (water).

Instead, the resulting polymer (e.g., copolymer) is dispersed (not dissolved) as nanoparticles in water forming a colloidal system. [0028] The monomer may be an acrylate monomer and the polymer nanoparticles are acrylate polymers. The monomer may be styrene or styrene-based (styrenic derivative) and the polymer nanoparticles are styrenic polymer such as polystyrene. In some embodiments, the operating conditions of the polymerization may include a pressure in a range of 0 pounds per square inch gauge (psig) to 260 psig and a polymerization temperature in a range of 120 °F to 250 °F.

[0029] In certain embodiments, the sequence of monomer addition includes a water-soluble minor monomer (comonomer) fed with the initiator in water to the continuous flow reactor. The water-soluble comonomer may be, for example, an acrylamide monomer. The reaction starts with the water-soluble comonomer. The major monomer (e.g., acrylate monomer or styrenic monomer) is fed to the continuous flow reactor to be mixed with the mixture of initiator, water, water-soluble comonomer in which reaction has already begun. Water-stable nanoparticles of copolymer are formed. This monomer addition sequence may be beneficial in resulting in more hydrophilic acrylamide on the surface of the copolymer nanoparticles. This monomer addition sequence may facilitate that the emulsion radical polymerization can be surfactant-free. The feeding of the water-soluble comonomer with the initiator and the downstream addition of the major monomer can give surfactant-free emulsion radical polymerization in some embodiments.

[0030] The continuous flow reactor system 100 includes a continuous flow reactor 102 having a flow channel(s) (fluid channel) for the reactant (monomer) in the reaction (polymerization). The flow channel may promote mixing of the reactants or mixture flowing through the channel. The geometry of the flow channel may promote mixing. The continuous flow reactor 102 may have one or more flow layers or paths adjacent the flow channel to route a heat transfer medium (fluid) for temperature control of the reaction.

[0031] The flow channel (flow passage) of the continuous flow reactor 102 for the monomer and the polymerization may have a width or hydraulic diameter greater than 1 millimeter (mm). In certain implementations, the channel is a microchannel having a width or hydraulic diameter less than 1 mm. In some embodiments, the continuous flow reactor 102 is a microreactor which may be labeled as a microstructured reactor, microchannel reactor, or microfluidic reactor. The size of the continuous flow reactor 102 and other equipment in the continuous flow reactor system 100 may depend on the production scale and the kinetics of the polymerization.

[0032] The continuous flow reactor 102 is a continuous operation as opposed to a batch operation. In some implementations, the continuous flow reactor 102 may be incorporated in a semi-batch reactor system. The overall system 100 associated with the continuous flow reactor 102 may have batch or semi-batch operations.

[0033] The flow passage through the interior of a flow channel for the reaction mixture may be labeled as the process side of the channel. This process side of the channel(s) is the passage through the channel in which the reaction (polymerization) mixture flows. In contrast, the flow layer or path adjacent to the flow channel that may route a heat transfer medium (fluid) for temperature control of the reaction can be labeled as the utility side of the flow channel. The reactor 102 or flow channel may have this utility side that is an external side or layer outside of the reaction flow channel (passage) and in which a heat transfer fluid flows.

[0034] The continuous flow reactor 102 or its flow channel (for example, microchannel) may have a heat transfer area per unit volume of the process side of at least 2500 square meters (m ² ) per cubic meter (m ³ ), at least 5000 m ² /m ³ , at least 7000 m ² /m ³ , or at least 10,000 m ² /m ³ . Continuous flow reactors 102 (including as microreactors) provide increased heat transfer as compared to batch reactors. The continuous flow reactor 102 may also generally provide increased heat transfer as compared to continuous reactors (not having a flow channel) such as tubular plug-flow reactors or continuous stirred-tank reactors (CSTR).

[0035] The continuous flow reactor 102 may have multiple modules each having a flow channel or flow microchannel. The modules may be arranged operationally (and physically) in series. For multiple modules in series, the channel in each module may be operationally coupled to give a flow channel for the reactor through the modules. The channel geometry can be different between the modules. With each module having a flow channel, the reactor 102 having multiple modules in series can be characterized as having multiple flow channels. However, because the flow channel in each module is coupled operationally in series, the reactor 102 having multiple modules in series is generally characterized as having a flow channel through the multiple modules.

[0036] Moreover, the continuous flow reactor 102 may be scalable in a sense of incorporating additional modules each having a flow channel to operationally couple to the flow channel through the existing modules. The continuous flow reactor 102 may include sensors, valves, and static mixers including as associated with the channel or microchannel. The modules of the flow channel may have various components including the sensors, valves, and static mixers in the channel and exterior to the channel. The number and size of the modules of the continuous flow reactor 102 may depend on the implementation scale of the continuous flow reactor system 100 for the specific reaction kinetics.

[0037] The continuous flow reactor system 100 may be laboratory scale that produces less than one kilogram per hour of polymer nanoparticles, such as less than 10 grams per hour of polymer nanoparticles. The continuous flow reactor system 100 may be pilot-plant scale or industrial scale that produces at least one kilogram per hour of polymer nanoparticles. A specified scale or production capacity of the continuous flow reactor 102 may be implemented, for example, by specifying the number of modules having a channel, the length and volume of the channel, the surface area of the channel, or by incorporating a batch tank after the flow reactor, or any combinations thereof. For the reactor 102 having modules of the channel(s), a specified scale of the continuous flow reactor 102 may be implemented, for example, via the number of modules, the length and volume of the channel per module, and the surface area of the channel per module. A module may have one channel. As discussed later, a module may have a flow-reactor plate having a channel.

[0038] In the illustrated implementation, the continuous flow reactor 102 includes a preheater 104 and a reaction section 106. Both the preheater 104 and the reaction section 106 may include a channel(s) or modules having a channel. The channel may be a microchannel. The preheater 104 may be a preheater section as one or more modules of the channel integrated within the continuous flow reactor 102. In some implementations, the preheater 104 may be separate from and upstream of the continuous flow reactor 102. If so, the preheater 104 may be a shell-and-tube heat exchanger, a plate-and-frame heat exchanger, or a jacketed-conduit heat exchanger.

[0039] The continuous flow reactor 102 may include a designated mixing section, for example, downstream of the preheater 104 but upstream of the reaction section 106. The mixing section may be integrated within the continuous flow reactor 102. The mixing section may be a sub-section of the reaction section 106. The mixing section may have a flow channel (for example, microchannel) or a static mixer, or both. The mixing section as a module(s) of a channel may include a mixer (for example, static mixer) in or between modules. The flow channel in a mixing section may have a geometry to promote mixing. The flow channel in the reaction section 106 downstream of the mixing section may also have a geometry to promote mixing. If the upstream preheater 104 employs the flow channel (e.g., as at least one module of the flow channel), the flow channel in the preheater 104 may promote mixing of the contents (mixture) flowing through the preheater 104 and being preheated.

[0040] In certain implementations, the mixing section is a module (having a flow channel) disposed between the preheater 104 and the reaction section 106. In some embodiments, the mixing section (if employed) may be a mixer (for example, static mixer or turbine mixer) separate from the continuous flow reactor 102 and operationally disposed between the preheater 104 and the reaction section 106.

[0041] In operation for certain embodiments, monomer fed to the reactor 102 may mix with an aqueous solution in the mixing section. In some implementations, the monomer is fed directly to the mixing section of the reactor 102. The aqueous solution may include an initiator. The aqueous solution may include the initiator and a surfactant. The aqueous solution may include the initiator and a water-soluble comonomer. The aqueous solution having the initiator or a mixture of the initiator and the surfactant or

comonomer may be fed to the preheater 104 prior to entry of the aqueous solution into the mixing section. The reaction or polymerization may begin in the mixing section in some embodiments. If comonomer is present in the aqueous mixture, polymerization may begin in the upstream preheater 104.

[0042] The continuous flow reactor system 100 includes a monomer source 108 which provides monomer 1 10 for polymerization in the continuous flow reactor 102. In the illustrated embodiment, the monomer 1 10 is fed to the reaction section 106 downstream of the preheater 104. In certain

implementations, the monomer is fed to a mixing section which is an initial or first portion of the reaction section 106.

[0043] The monomer source 108 may include one or more vessels holding monomer 1 10. The vessel may be a container, cylinder, gas cylinder, storage vessel, or feed vessel. In lieu of (or in addition to) a vessel housing monomer, the monomer source 108 may receive monomer 1 10 from a pipeline, railcar, or truck. The monomer source 108 may include a motive device (for example, pump) to provide monomer 1 10 through a conduit to the continuous flow reactor 102. In one implementation, the monomer 1 10 is an acrylate monomer. In another implementation, the monomer 1 10 is a styrenic monomer. A styrenic monomer may be styrene or a derivative of styrene.

[0044] The monomer source 108 may include a control component to modulate flow rate of the monomer 1 10 fed to the continuous flow reactor 102. For example, the speed of a pump as a motive device may be manipulated to adjust flow rate of monomer 1 10 through the pump to the continuous flow reactor 102. In another implementation, a control valve may modulate flow rate of the monomer 1 10 to the continuous flow reactor 102. The control valve may be disposed on a conduit conveying the monomer 1 10. In a particular implementation, the control valve is disposed on a conduit at or near the motive device, for example, at the discharge of the motive device (e.g., pump).

[0045] The monomer source 108 may provide two or more monomers including for the same polymerization, such as with the polymerization in the continuous flow reactor 102 of two monomers into a copolymer. Thus, in the case of the monomer 110 including a first monomer and a second monomer, the monomer source 108 may be characterized as a first monomer source and a second monomer source. In certain implementations, the second monomer may be labeled as a comonomer. In some instances, the first monomer may be labeled as the major monomer or primary monomer. In operation, the first monomer and the second monomer (comonomer) may be fed separately (in different conduits) to the continuous flow reactor 102, for example, to an initial portion (for instance, mixing section) of the reaction section 106. For monomer 1 10 fed to the continuous flow reactor 102, the monomer source 108 may control the ratio (by weight or volume) of the second monomer to the first monomer. In one implementation, the first monomer is an acrylate monomer and the second monomer (comonomer) is styrene or a styrenic derivative monomer. In another implementation, the first monomer is an acrylamide monomer and the second monomer (comonomer) is a styrenic monomer. A styrenic monomer may be styrene or a monomer derivative of styrene.

Moreover, for particular embodiments, the second monomer or comonomer may be fed with initiator from the initiator source 1 12.

[0046] The continuous flow reactor system 100 includes an initiator source 1 12 that provides a stream 1 14 via a conduit to the continuous flow reactor 102. The stream 1 14 may be an initiator or a solution (for example, aqueous solution) having the initiator. The stream 1 14 may be a mixture having the initiator and water. The initiator may be a radical initiator. The amount of initiator in the mixture or aqueous solution may be, for example, in the range of 0.1 mole % (mol%) to 10 mol% of the total monomers fed to the reactor 102.

[0047] If a surfactant is employed in the polymerization in the reactor 102, the stream 1 14 may include the surfactant. Therefore, the stream 1 14 may include a mixture having the initiator and the surfactant. The mixture may also include water or other solvents (for example, alcohols). The concentration of the surfactant (if included) in the mixture or aqueous solution may be at least 0.2 weight percent (wt%). In some implementations, the surfactant is fed separately from the initiator to the preheater 104. Thus, in those

implementations, the initiator and surfactant may meet and mix in the preheater 104 and further mix, for example, in a mixing sub-section of the reaction section 106 downstream of the preheater 104.

[0048] In some embodiments, the second monomer (if utilized) may be provided from the initiator source 1 12. Thus, the stream 1 14 may include a mixture of initiator and a second monomer (comonomer). The stream 1 14 may include a mixture of initiator, comonomer, and water. The concentration of comonomer in the aqueous mixture may depend on the polymerization recipe or the type or grade of copolymer being produced in the reactor 102. An exemplary amount of comonomer in the aqueous mixture is in the range of 5 mol% to 50 mol% of the combination of the comonomer and the major monomer added downstream. The stream 1 14 may include a mixture having initiator, surfactant, and comonomer. The stream 1 14 may include a mixture having initiator, surfactant, water, and comonomer.

[0049] In implementations, the stream 1 14 includes a mixture having initiator with surfactant, comonomer, or water (or other solvent such as an alcohol), or any combinations thereof. The source 1 12 may receive or prepare the mixture for stream 1 14. The source 1 12 may include vessels, motive devices, and control components. In the illustrated implementation, the source 1 12 feeds the stream 1 14 to the process side of the preheater 104 of the continuous flow reactor 102.

[0050] In some implementations, the initiator is a salt of sulfate. In a particular implementation, the initiator is ammonium persulfate (APS). The initiator may be a chain transfer agent (CTA) or reversible addition- fragmentation chain transfer (RAFT) agent. Examples of RAFT agents include dithioesters and trithiocarbonates. RAFT agents may be thiocarbonylthio compounds such as dithioesters, dithiocarbamates, trithiocarbonates, and xanthates. The initiator as a water-soluble or water-miscible radical initiator may be, for example, potassium persulfate, hydrogen peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, benzoyl peroxide, 2, 2’-azobis(2- amidino-propane) dihydrochloride, succinic acid peroxide, 4,4’-azobis(4- cyanopentanoicacid), 4-cyano-pentanoic acid dithiobenzoate, or 2, 2’-azobis(2- amidino-propane) dihydrochloride.

[0051] The surfactant (if utilized) may be an anionic surfactant. In a particular embodiment, the surfactant is a sulfate in water. The sulfate may be, for example, sodium dodecyl sulfate (SDS). Surfactants as emulsifiers that may be employed include, for example, fatty acids, alkoxylates, sulfonates, and sulfates (for example, ether sulfates). A non-ionic surfactant may be utilized in combination with an anionic surfactant in the stream 1 14 mixture. The non-ionic surfactant may be, for example, phosphate esters, polyethylene oxide), poly(vinyl alcohol), or hydroxyethyl cellulose.

[0052] Surfactant-free emulsion polymerization may be performed with the flow reactor 102. In those implementations, surfactant is not fed to the reactor 102. In particular embodiments, a water-soluble monomer (for example, an acrylamide or acrylic acid) is utilized instead of a surfactant in the initiator mixture. In those embodiments, the stream 1 14 may include a mixture of initiator, the water-soluble monomer, and water. The solubility of the water- soluble monomer (comonomer) in water may be, for example, at a

concentration in the range of 0.01 kilogram per liter (Kg/L) to 5 Kg/L at a temperature in a range of 20 °C to 90 °C. The initiation of polymerization of the water-soluble monomer may start in the preheater 104 or preheating section of the flow reactor 102 to form short chains (for example, less than 50 carbons) of acrylamides. These short chains of acrylamides may then polymerize with the primary monomer (for example, styrenic monomer or acrylate monomer from the monomer source 108) in the reaction section 106 to form water-stable nanoparticles of copolymer (for example, styrenic- acrylamide copolymer). Both the water-soluble comonomer and surfactant may be included in the stream 1 14. The stream 1 14 may include a mixture of initiator, the water-soluble comonomer, surfactant, and water.

[0053] With or without the presence of surfactant, the polymer

nanoparticles may include polymer from acrylamide or acrylic acid. The polymer nanoparticles produced in (and discharged from) the continuous flow reactor 102 may be water-stable or generally water insoluble. The polymer nanoparticles may be partially soluble in water or soluble in water.

[0054] The continuous flow reactor system 100 includes a heat-transfer fluid system 1 16 that provides a heat-transfer fluid supply 1 18 via a conduit to the continuous flow reactor 102. The heat-transfer fluid supply 1 18 may circulate through the reactor 102 and discharge as heat-transfer fluid return 120 via a return conduit to the heat-transfer fluid system 1 16. The heat- transfer fluid system 1 16 may include a motive device (for example, centrifugal pump) to provide a motive force (for example, pump head) to circulate the heat-transfer fluid through the reactor 102, such as through the utility side of the reactor 102 or utility side of the channel(s) of the reactor 102. The heat- transfer fluid system 1 16 may include a heat exchanger (for example, a shell- and-tube heat exchanger or a plate-and-frame heat exchanger) to heat or cool the heat-transfer fluid return 120. The heat-transfer fluid system 1 16 may include control valves (for example, control valve 122) for the heat transfer fluid and sensors (for example, temperature sensor 124) for the heat transfer fluid.

[0055] The heat-transfer fluid supply 1 18 may flow from the heat-transfer fluid system 1 16 through the utility side (flow layers for heat transfer fluid) of the continuous flow reactor 102 channel. Thus, the heat transfer fluid supply 1 18 generally does not mix with the process fluids or slurry on the process side (interior flow passage of the channel) of the continuous flow reactor 102. The heat-transfer fluid supply 1 18 may include mineral oil, treated water (for example, demineralized water), cooling tower water, steam condensate, steam, or a glycol fluid.

[0056] The heat-transfer fluid supply 1 18 may flow through the utility side of the preheater 104 and the utility side (heat-transfer fluid layers) of the reaction section 106. The heat-transfer supply 1 18 may include parallel or serial flow through the preheater 104 and the reaction section 106. A flow sequence of the circulation can be the heat-transfer fluid supply 1 18 enters through the reaction section 106 and then flows through the preheater 104. Another sequence is the heat-transfer fluid 1 18 initially flows through the preheater 104 and then through the reaction section 106. In other implementations, a first stream of heat-transfer fluid supply 1 18 may be sent to the preheater 104 in parallel with a second stream of heat-transfer fluid supply 1 18 sent to the reaction section 106. Multiple streams of heat-transfer fluid supply 1 18 may be sent in parallel to the reaction section 106, such as to respective modules of the channel in the reaction section 106. The return 120 may include two or more return 120 streams that may merge into a single conduit or be received independently in separate respective conduits to the heat-transfer fluid system 1 16. [0057] The arrangement of the utility side of the reactor 102 channel may provide for cross-exchange of heat with the process side of the channel. The utility side may be a flow path or flow layer (in the reactor 102) adjacent to the channel for routing the heat-transfer fluid supply 1 18. The process side may be the interior volume of the channel in which the polymerization mixture flows. Heat may be transferred between the heat-transfer fluid supply 1 18 flowing through the utility side with the polymerization mixture flowing through the process side. The flow of the heat-transfer fluid supply 1 18 is typically countercurrent with flow on the process side but can be co-current flow.

[0058] As mentioned, the heat-transfer fluid system 1 16 receives the heat- transfer fluid return 120 via a conduit from the continuous flow reactor 102.

The flow rate of the heat-transfer fluid supply 1 18 through the utility side of the continuous flow reactor 102 may be controlled. In certain embodiments, the flow rate of the heat-transfer fluid supply 1 18 is controlled via a control valve 122 on the return 120 conduit. The flow rate of the heat-transfer fluid supply 1 18 may be manipulated by the control valve 122 to control the preheating temperature by the preheater 104 and the polymerization temperature in the reaction section 106. In other embodiments, the preheater 104 does not participate in the heat-transfer fluid system 1 16 circulation but instead receives a heat-transfer fluid other than the heat-transfer fluid supply 1 18.

[0059] The heat-transfer fluid system 1 16 may provide the heat-transfer fluid supply 1 18 at a specified temperature or temperature range. The temperature of the supply 1 18 may be measured by a temperature sensor 124. Additional temperature sensors to measure temperature of the heat transfer fluid supply 1 18 may be disposed in the continuous flow reactor 102. A temperature sensor may be disposed on the return 120 conduit.

[0060] The heat-transfer fluid supply 1 18 may be a heating medium for the preheater 104. The heat-transfer fluid supply 1 18 may be a heating medium for the reaction section 106 if the polymerization is endothermic or for maintenance of the reaction section 106. The heat-transfer fluid supply 1 18 may be a cooling medium for the reaction section 106 if the polymerization is exothermic or for mitigation of excessive temperature. [0061] The heat-transfer fluid system 1 16 may include two or more heat- transfer fluid systems. For instance, a first heat-transfer system 1 16 may supply a first heat-transfer fluid supply 1 18 as a heating medium to the preheater 104, and a second heat-transfer system 1 16 may supply a second heat-transfer fluid supply 1 18 as a cooling medium to the reaction section 106 (for example, if the polymerization is exothermic). Thus, the heat-transfer fluid supply 1 18 may include two or more supply 1 18 streams from two or more respective heat-transfer fluid systems 1 16. The return 120 may include two or more respective return 120 streams depending on the configuration and heating or cooling demands of the continuous flow reactor 102.

[0062] For the heat-transfer fluid supply 1 18 as a cooling medium, the heat- transfer fluid system 1 16 may cool the heat-transfer fluid return 120. The heat- transfer fluid system 1 16 may remove heat from the heat-transfer fluid return 120 that was acquired by the heat-transfer fluid supply 1 18 as a cooling medium in the continuous flow reactor 102. For the heat-transfer fluid supply 1 18 as a heating medium, the heat-transfer fluid system 1 16 may heat the heat-transfer fluid return 120. The heat-transfer fluid system 1 16 may add heat to the heat-transfer fluid return 120 to account for the heat loss by the heat-transfer fluid supply 1 18 as a heating medium in the continuous flow reactor 102.

[0063] In operation, the continuous flow reactor 102 polymerizes monomer 108 into polymer nanoparticles and discharges the polymer nanoparticles 126, for example, through a discharge conduit. The stream discharged may be a slurry of the polymer nanoparticles 126 in water or in water and surfactant.

The slurry may include trace amounts of residual monomer and initiator. In some implementations, the polymer nanoparticles 126 produced are monodisperse or near-monodisperse (for example, PDI less than 0.08). At least 80% of the polymer nanoparticles 126 in the slurry may have the same particle size within a tolerance of 1 nm. The polymer nanoparticles 126 may be generally uniform as composed of molecules of the same or similar mass. The polymer nanoparticles 126 can be copolymer nanoparticles.

[0064] A modulating control valve 128 may be disposed on the discharge conduit to control or adjust flow rate of the slurry having the polymer nanoparticles 126 discharging from the continuous flow reactor 102. The control valve 128 may control or modulate pressure in the continuous flow reactor 102. The control valve 128 may facilitate maintaining a specified pressure on the process side of the channel(s) or microchannel(s). In some instances, the control valve 128 may be labeled as a backpressure regulator. The discharge may include a pressure sensor 130.

[0065] Additional pressure sensors may be disposed in the continuous flow reactor system 100 including on the utility side or process side of the reactor 102. One or more pressure sensors may be disposed along the reactor 102 on the channel and/or between modules of the channel. A pressure sensor may be disposed at the reactor 102 process inlet. The reactor system 100 may include other sensors, such as temperature sensors and flow sensors, disposed along the reactor 102.

[0066] The continuous flow reactor system 100 may include a control system 132. The control system 132 may include a processor and memory storing code (for example, instructions or logic) executed by the processor to facilitate control of the continuous flow reactor system 100. The processor may be one or more processors, and each processor may have one or more cores. The hardware processor(s) may include a microprocessor, a central processing unit (CPU), or a general-purpose graphics processing unit (GPU). The memory may include volatile memory (for example, cache and random access memory or RAM), nonvolatile memory (for example, hard drive, solid- state drive, and read-only memory or ROM), and firmware. The control system 132 may include a desktop computer, a console computer, multiple computing devices or nodes, a distributed control system (DCS), or a programmable logic controller (PLC). The control system 132 may include control components (for example, pumps or control valves) to modulate or maintain operating parameters of the reactor system 100. Operating parameters may include flow rate, pressure, and temperature on the utility side and process side of the reactor 102. The control system 132 may be operationally tied to pumps, control valves, and sensors in the reactor system 100. A user may input set points for operating parameters via the control system 132. [0067] The continuous flow reactor 102 having the flow channel (for example, reactant-flow channel) may be a microreactor. The flow channel(s) may be microchannel(s) having a width or hydraulic diameter less than 1 mm.

A scalable continuous flow reactor may be a microreactor. A continuous reactor without a channel or flow channel may be a tubular plug-flow reactor, a jacketed pipe reactor, a jacketed vessel reactor, a continuous stirred-tank reactor (CSTR), a loop reactor performing as a CSTR, or a fluidized-bed reactor. The continuous flow reactor having a channel(s) may provide for increased heat-transfer area as compared to these continuous reactors without a channel. The preheater 104 (if employed) may be a preheating section (for example, a channel) of the reactor 102, a shell-and-tube heat exchanger, a plate-and-frame heat exchanger, or a jacketed-conduit heat exchanger. The mixing section (if employed) may be a channel in the reactor 102, a static mixer, or a turbine mixer, or any combinations thereof.

[0068] An embodiment is a continuous flow reactor system having a continuous flow reactor with a channel such as a flow channel for reactant flow. The continuous flow reactor system includes a first source to supply a mixture to the continuous flow reactor. The mixture includes a radical initiator and water. The mixture may include a surfactant or a comonomer. The first source may have a mixer to combine the radical initiator, water, surfactant (if present), and comonomer (if present). In addition, the first source may have a control component to modulate flow rate of the mixture to the continuous flow reactor. The first source may have a motive device (for example, pump) to supply the mixture to the continuous flow reactor. In some implementations, a pump as a motive device is the control component in that speed of the pump may modulate flow rate of the mixture. The continuous flow reactor may have a preheater section to heat the mixture from the first source. If the continuous flow reactor has a preheater section, the first source may supply the mixture to the preheater section.

[0069] The continuous flow reactor system has a second source to supply monomer to the continuous flow reactor. The second source may have a control component to modulate flow rate of the monomer to the continuous flow reactor. The second source may have a motive device to supply the monomer to the continuous flow reactor. The monomer may include major monomer if a comonomer is supplied from the first source. The monomer may include the major monomer and the comonomer if the comonomer is not supplied from the first source. In particular implementations, the monomer source may supply comonomer to the first source. The continuous flow reactor has a mixing section to mix the monomer with the mixture from the first source to form a polymerization mixture. The continuous flow reactor has a reaction section to polymerize the monomer (including any comonomer present) in the polymerization mixture to form polymer nanoparticles.

[0070] The preheater section (if employed), the mixing section, and the reaction section may each include the flow channel. The mixing section may be an initial subsection of the reaction section. The flow channel may have a hydraulic diameter greater than 1 mm. In some implementations, a static mixer may be installed in the flow channel. The continuous flow reactor may be a microreactor. The channel may be a microchannel having a hydraulic diameter less than 1 mm. The flow channel may have a geometry (for example, heart-shaped, bends) or features (for example, grooves, slots, ridges, or baffles) to promote mixing or static mixing of the fluid or slurry flow through the channel.

[0071] The continuous flow reactor system may include a heat-transfer fluid system to circulate heat transfer fluid through a utility side of the reactor. The utility side may be for utility flow such as a heat-transfer fluid. Thus, the utility side may be labeled as heat transfer layers. The utility side or utility flow path may be adjacent the exterior of the channel. Thus, the utility side of the reactor may be characterized as a utility side of the channel.

Examples

[0072] FIG. 2 is a laboratory configuration 200 for a batch synthesis of polymer nanoparticles. In this experimental setup, the batch synthesis of the polymeric nanoparticles commenced with degassing a 60 milliliter (ml_) solution of 2.55 wt% sodium dodecyl sulfate (SDS) in water in a round bottom flask 202. At this concentration, the surfactant is greater than its critical micelle concentration (CMC). Gas was removed from the flask 202 via outlet tube 204. Next, 100 milligrams (mg) of the radical-initiator ammonium persulfate (APS) was added to the solution in the flask 202. The solution in the flask 202 was heated via a heating bath 206 for fifteen minutes (min) at 90 °C. The solution was stirred (maintained as a stirring solution) throughout the heating and subsequent polymerization. The solution was maintained at a temperature of 90 °C while 1 ml_ of monomer was added via syringe 208 dropwise into the solution of 2.55 wt % SDA in water and APS in the flask 202. Nitrogen was introduced through the inlet tube 210 to maintain a nitrogen pad in the flask 202.

[0073] In a first test, the monomer was butyl methacrylate (BMA). In a second test, the monomer was a styrene-butyl methacrylate mixture having a molar ratio 95:5 of styrene to BMA. These non-water soluble monomers reacted with the radical initiator (giving polymer initiation) while diffusing into the micelles to continue propagation. The reaction in the first test proceeded for one hour after monomer addition to complete polymerization of poly(butyl methacrylate) (PBMA) nanoparticles (NP). The reaction in the second test proceeded for one hour after monomer addition to complete polymerization of copolymer poly(styrene-co-butyl methacrylate) (PSBMA) NPs. These emulsion polymerizations allowed for nucleation sites to form resulting in nanoparticles of particle size in a range of 10 nm to 25 nm, as analyzed by dynamic light scattering (DLS).

[0074] FIG. 3 is a flow-reactor plate 300 as representative of the multiple flow-reactor plates (coupled in series) of the continuous flow reactor used in the Examples for the laboratory flow synthesis that gave polymeric

nanoparticles. Each flow-reactor plate 300 coupled in series may be labeled as a module having that respective flow-reactor plate 300.

[0075] The plate 300 includes a flow channel 302 for flow of reactant(s) and the polymerization mixture. The flow channel 302 may promote mixing. The plate 300 includes two heat-transfer fluid layers 304 adjacent the flow channel 302. The layers 304 are flow passages for heat transfer fluid that may be heating fluid or cooling fluid.

[0076] In the Examples, the continuous flow reactor is a Corning® G1 Advanced-Flow™ Reactor by Corning Inc. of Corning, New York, USA. Each module of the reactor has a single plate 300 and a support. The flow reactor has multiple modules in series. Thus, the flow reactor is composed of plates 300 in series. The plates 300 in the flow reactor include hybrid glass-silicon carbide (SiC) plates attached in series.

[0077] Design conditions for the flow reactor is a flow rate of 30 milliliters per minute (mL/min) to 200 mL/min through the channel 302, temperatures of - 60 °C to 200 °C, and pressures up to 18 bar gauge (barg) (261 psig). Each plate 300 is designed for mixing and heat transfer. Mixing is achieved via the flow channel 302. Temperature is controlled via the two heat-transfer fluid layers 304 that flow heat transfer fluid.

[0078] The flow channel 302 include a mixing channel or a static mixing channel (for example, heart-shaped static mixing channel). A separate static mixer was not installed in the channel 302 but instead the geometry (including features) of the channel 302 promoted mixing or static mixing.

[0079] The inside or interior of the channel 302 may be characterized or labeled as the process side of the channel 302 or the process side in the reactor. The two heat-transfer fluid layers 304 adjacent the channel 302 may be characterized or labeled as the utility side of the channel 302 or a utility side in the continuous flow reactor.

[0080] Each reactor module has a single plate 300. Each plate 300 includes a single flow channel 302 wrapped by heat-transfer fluid layers 304.

[0081] FIG. 4 are types of the flow channel 302 used in the respective module plates 300 of the Corning® G1 Advanced-Flow™ Reactor for the flow synthesis in the Examples in the laboratory. The heat-transfer fluid layers 304 (not shown) are on the exterior of the channel 302.

[0082] The flow channel 402 is for the Corning G1 R ^* H module plate. The flow channel 404 is for the Corning G1 SHF module plate. The flow channel 406 is for the Corning G1 SHH module plate. The flow channel for the Corning 1 G1 SHH33 module plate utilized in the reactor is not depicted. Each reactor module has a single plate having a single flow channel that couple in series to give the single flow channel of the reactor.

[0083] For the fluid reactant flow, the single channel 302 of each plate 300 may have one inlet or multiple inlets. The channel 302 flow path and geometry (for example, heart-shaped) provide for mixing or static mixing without installation of a distinct static mixer. The particular channel 302 may have interior grooves to promote mixing or static mixing. In other implementations, a continuous flow reactor has a static mixer installed inside a flow channel.

[0084] The Corning G1 SHH module plate channel 406 has an internal volume of 8.2 ml_ and a heart-shaped design that generates mixing. The Corning G1 R ^* H module plate channel 402 has an internal volume of 8.2 inl _¬ and the heart-shaped design. The inlet and outlet configuration of the channel 402 facilitates use of the G1 R ^* H module for preheating (or precooling) or to increased residence time. The Corning G1 SHF module plate channel 404 has an internal volume of 9.2 ml_ and a hybrid design of heart-shaped and non heart shaped. Finally, the Corning 1 G1 SHH33 module plate channel (not shown) has an internal volume of 8.2 ml_. The 1 G1 SHH33 module is from the Corning® Advanced-Flow™ G1 SiC Reactor. The silicon carbide-glass of the 1 G1 SHH33 module plate provides chemical durability for basic solutions.

[0085] FIG. 5 is the setup of reactor modules for the continuous flow reactor 500 (Corning® G1 Advanced-Flow™ Reactor) utilized in the laboratory flow synthesis in the Examples. Each overall rectangle in FIG. 5 is a module.

There is one plate per module. There is one flow channel per plate.

[0086] The continuous flow reactor 500 is composed of ten modules of plates in the following sequence: the G1 R ^* H module 504 plate, the G1 R ^* H module 506 plate, the G1 SHH module 508 plate, the G1 R ^* H module 510 plate, the G1 SHF module 512 plate, the 1 G1 SHH33 module 514 plate, the G1 R ^* H module 516 plate, the G1 R ^* H module 518 plate, the G1 R ^* H module 520 plate, and the 1 G1 SHH33 module 522 plate. In FIG. 5, the internal volume of the plate flow channel in the respective module is given for each module. This setup of the reactor 500 made up a total internal volume of 74.8 mL (bypass module 506 plate), which passed reactant fluid through the reactor 500 in 147 seconds (2.45 minutes) at a flow rate of 30.5 mL/min.

[0087] In the flow synthesis, a stream 502 maintained at ambient temperature after nitrogen (N2) purge was pumped into the module 504 at a rate of 30 mL/min. The stream 502 was heated in 504 module to 87 °C within 16.4 seconds (0.27 minute) prior to being pumped through the second module 506. The stream 502 was an SDS-water-initiator solution. [0088] The first two modules 504, 506 preheated the SDS-water-initiator solution that entered the module 504 as stream 502. The first module 504 preheated the SDS-water-initiator solution to 87 °C. The module 506 was primarily for passing through SDS-water-initiator solution. The module 508 was primarily for mixing SDS-water-initiator solution with the introduced monomer 524. The monomer 524 after N2 purge was pumped at a rate of 0.5 mL/min to the third module 508 where the monomer 524 met the preheated aqueous solution of SDS and the initiator. The reaction (polymerization) started in the third module 508 and proceeded through the flow reactor 500 for a total of 2.45 minutes of residence time in the reactor 500. The modules 510, 512, 514, 516, 518, 520, and 512 were primarily for reaction but with continued mixing.

[0089] The flow reactor 500 having the depicted setup did not have adequate internal volume to provide one hour of residence time to complete the polymerization. Therefore, the polymerization solution 526 discharged from the continuous flow reactor 500 was collected in a heated round-bottom flask. The polymerization solution 526 was stirred in the flask for one hour at 90 °C to complete formation of the polymer nanoparticles. If the flow reactor 300 has adequate internal volume to provide one hour of residence time, this emulsion polymerization can instead be performed completely in the continuous flow reactor 300.

[0090] The one-hour flask polymerization to complete the polymerization can be considered a batch operation combined with the upstream continuous operation of the flow reactor 300. However, the results in the Examples discussed later when referring to flow synthesis are for the combined synthesis of 2.45 minutes in the flow reactor plus the 1-hour batch synthesis in the flask. When the results in the Examples refer to batch synthesis or batch operation, the results are for only batch synthesis (FIG. 2) in the flask with no upstream flow synthesis.

[0091] The synthesis performed with the flow synthesis (initial flow synthesis followed by the batch synthesis to complete the polymerization) resulted in nanoparticles having a different size and PDI compared to the nanoparticles synthesized only in the batch process. The polymerizations were compared via a varied molar ratio of monomer to initiator, M:l, as shown in Table 1. The molar ratio of styrene to butyl methacrylate for the copolymer is 95:5. All reactions performed in the batch and flow syntheses were at the same constant SDS concentration (2.55 wt% in water). The data for the four flow-synthesis reactions A, B, C, and D are presented in Table 1. The amount of initiator in reactions C and D was one tenth of the amount of initiator used in reactions A and B.

Table 1 . Varied M:l conditions

[0092] Nanoparticle hydrodynamic size and polydispersity characterization were performed via DLS. Polymer yield was determined via thermogravimetric analysis (TGA) at a scan rate of 20 °C/min. Polydispersity index (PDI), dispersity index, heterogeneity index, or dispersity (D) can be a measure of the distribution of molecular mass in a given polymer sample. However, PDI (or D) of a colloidal system is the size distribution of the particles.

[0093] FIG. 6 is a bar chart 600 of particle size 602 (nm) of the produced polymer nanoparticles versus the M:l condition 604 listed in Table 1. The patterned bars are for the flow synthesis. The clear bars are for the batch synthesis. Thus, FIG. 6 is particle size comparison of PBMA and PSBMA nanoparticles synthesized in a flow reactor (patterned bars) versus in a batch flask (clear bars). Labels A, B, C, and D correspond to Table 1.

[0094] FIG. 7 is a bar chart 700 of polydispersity (PDI) 702 of the produced polymer nanoparticles versus the M:l condition 604 listed for A, B, C, and D in Table 1 . The patterned bars are for the flow synthesis. The clear bars are for the batch synthesis. Thus, FIG. 7 is polydispersity comparison of PBMA and PSBMA nanoparticles synthesized in a flow reactor (patterned bars) versus in a batch flask (clear bars). The PDI reported is for size distribution of particles. The calculation of PDI is: where d is the average hydrodynamic size of the particles and N is the number of particles for the summation.

[0095] The reaction conditions A and B performed in the flow reactor (plus the completion in the flask) resulted in PBMA and PSBMA particles, respectively, of 29 ± 0.23 nm in size and PDIs < 0.1 . The corresponding reactions (not in Table 1 ) performed only in the batch flask 202 formed particles of 10 nm to 25 nm in size and with PDIs > 0.2. See FIGS. 6 and 7. The larger particle size made in the flow reactor compared to batch flask synthesis stems from the difference in monomerinitiator loading. In the batch synthesis, the monomer is slowly added dropwise into the reaction mixture. This results in a changing M:l ratio throughout the monomer addition allowing for nucleation sites (and thus more particles) to form initially but with the particles being smaller size. In contrast for the flow synthesis, the monomer meets the initiator in the solution at a constant M:l ratio. The M:l ratio in the flow synthesis is greater than the M:l ratio initially in the batch flask synthesis but less than the final M:l ratio in the batch flask synthesis. Consequently, fewer but larger particles form in the flow synthesis than in the batch synthesis. Flow synthesis, however, may have an advantage of making particles of lower polydispersity than in the batch synthesis. In some cases, the flow synthesis may make monodisperse particles or near-monodisperse (for example, PDI less than 0.1 ) due to the mixing and heat transfer. See FIG. 7.

[0096] The reaction conditions C and D performed in the flow reactor resulted in particles of 18 ± 0.3 nm in size and PDIs > 0.2. The corresponding reactions (not in Table 1 ) performed in the batch synthesis formed particles of approximately 10 nm and comparable PDIs > 0.2. Overall, the size of the particles under these conditions in the flow and batch syntheses decreased due to the increase in initiator and the PDIs remained consistently 0.2. The mixing and heat transfer in the flow reactor did not decrease the PDIs at these reaction conditions. At this greater initiator loading, the number of nucleation sites may be the source of the overall greater PDIs. The flow synthesis resulted in different yields compared to the batch process, as discussed later with respect to FIGS. 8 and 9.

[0097] FIG. 8 is a plot 800 of TGA curves in weight percent 802 versus temperature 804 (°C) for the reaction condition A (Table 1 ). For both the batch synthesis and the flow synthesis at the polymerization reaction condition A, the produced slurry of nanoparticles in surfactant and water was subjected to TGA. In the TGA, the water evaporated at 100 °C. The water was about 96 weight % of the slurry. The TGA curves in FIG. 8 start after the water has been removed. The TGA curve 806 is for the flow synthesis. The TGA curve 808 is for the batch synthesis.

[0098] FIG. 9 is a plot 900 of TGA curves in weight percent 902 versus temperature 904 (°C) for the reaction condition C (Table 1 ). For both the batch synthesis and the flow synthesis at the polymerization reaction condition B, the produced slurry of nanoparticles in surfactant and water was subjected to TGA. In the TGA, the water evaporated at 100 °C. The water was about 96 weight % of the slurry. The TGA curves in FIG. 9 start after the water has been removed. The TGA curve 906 is for the batch synthesis. The TGA curve 908 is for the flow synthesis.

[0099] Thus, yields were determined using TGA. TGA showed that water evaporated at 100°C (not shown in FIG. 8 and FIG. 9) and that SDS then decomposed at 225°C. Finally, the polymeric NPs decomposed at 390°C. For the reaction condition A, the flow synthesis resulted in a 1.5 times greater yield than that of the batch synthesis (see FIG. 8). As mentioned previously, the mixing that is a product of a greater flow rate and the static-mixing channel in the Corning flow reactor warrants the increase in yield. Additionally, the TGA results illustrate that the flow reactor synthesized NPs have more equally- distributed molecular weight compared to that of the batch synthesis.

[0100] The TGA of the polymerization results show an additional small weight loss at about 390°C where nanoparticles of smaller molecular weight decomposed. For the reaction condition C, this additional weight loss was approximately 1.20 wt % (flow synthesis) and 1.40 wt % (batch synthesis).

[0101] For reaction condition C, TGA results as indicated in FIG. 9 revealed that the flow synthesis resulted in a similar yield and molecular weight distribution as the batch synthesis. As noted, the greater initiator

concentration increased the overall quantity of nucleation sites. As a result, the reaction conditions C and D yielded nanoparticles of greater PDI than in reaction conditions A and B. For the reaction condition C, the mixing and heat transfer in the flow reactor did not affect the PDI for the nanoparticle yield in remaining similar as with the batch synthesis.

[0102] The flow synthesis may hold an advantage in how fast

polymerizations are completed for scale-up synthesis in the laboratory. The batch polymerization involves longer reaction times (than flow polymerization) for making tens of grams of dispersed NPs. Scaling-up the batch process in a larger flask demands long reaction times (for example, greater than 10 hours) for making dispersed NPs because of the drop-wise addition of monomers (or addition of monomer using a syringe pump or similar motive device). Further, the mixing is typically less efficient in a larger flask. In comparison, the Corning continuous flow reactor can accomplish approximately a 27-gram NP synthesis within 1.5 hrs. (Table 2). The NP synthesis can be done

continuously using a flow reactor with about 1.8 liter (L) of internal volume. Table 2 gives a basis of the reaction conditions A and C.

Table 2. Parameters for scaling up NP synthesis (to 27 g of styrene) in the flow reactor.

[0103] For the Examples, the flow synthesis of PSBMA nanoparticles and PBMA nanoparticles made nanoparticles of equal or better (greater) polydispersity at shorter reaction times compared to a batch synthesis in a flask. The flow synthesis of monodispersed PBMA nanoparticles and monodispersed PSBMA nanoparticles was demonstrated in a Corning flow reactor with a usage of 74.6 ml of the 83 mL internal volume. The flow process may be beneficial for scaling up NP synthesis to tens or hundreds of grams in laboratory with desired particle size and particle size distribution. Analysis may consider synthesis in flow versus batch using other methacrylate and styrene-based monomers. Also considered may be the effect of flow rates, reaction temperatures, and different M:l ratios on the kinetics of the flow synthesis.

[0104] FIG. 10 is a method 1000 of flow synthesis of polymer nanoparticles in a flow reactor such as a continuous flow reactor having a flow channel. In certain embodiments, the continuous flow reactor is a microreactor. In some implementations, the flow channel is a flow microchannel having a hydraulic diameter of less than 1 mm.

[0105] At block 1002, the method may include feeding a surfactant (for example, an anionic surfactant) to the continuous flow reactor. However, in embodiments, a surfactant is not fed the continuous flow reactor. Instead, the polymerization in the continuous flow reactor may be a surfactant-free polymerization.

[0106] At block 1004, the method includes feeding an initiator to the continuous flow reactor. The initiator may be a radical initiator. The method may include feeding a mixture having the initiator to the continuous flow reactor. The mixture may include water. The mixture may include the surfactant if utilized. Instead of feeding a surfactant independently to the continuous flow reactor, the surfactant (if utilized) may be fed in the mixture with initiator to the continuous flow reactor. The mixture may include a water- soluble comonomer.

[0107] The mixture generally includes initiator and water. The mixture may further include surfactant or water-soluble comonomer.

[0108] At block 1006, the method includes heating the mixture (block 1004) having the initiator in a preheater or preheating section of the continuous flow reactor. The preheater or preheating section may be a flow channel or flow channels. The heating may be by circulating heat transfer fluid on a utility side (for example, flow layers) of the preheater or of the continuous flow reactor.

[0109] At block 1008, the method includes feeding monomer to the continuous flow reactor. The method may include mixing the monomer with the mixture (having the initiator) in a mixing section of the continuous flow reactor to form the polymerization mixture. In certain embodiments, the mixing section receives the mixture (having the initiator) from the preheater or preheater section. In some implementations, more than one monomer may be fed to the continuous flow reactor.

[0110] In certain implementations, the monomer is a vinyl monomer (for example, an acrylate monomer) and the polymer nanoparticles produced are a vinyl polymer (for example, an acrylate polymer). In some embodiments, the monomer includes a first vinyl monomer (for example, an acrylate monomer) and a second vinyl monomer (for example, styrene or a styrenic monomer generally). In those embodiments, the polymer nanoparticles may be a copolymer. The method may include controlling a weight ratio (or mole ratio) of a first vinyl monomer (for example, an acrylate monomer) to the second vinyl monomer (for example, styrene) to reduce agglomeration of the polymer nanoparticles. Moreover, as indicated, the second monomer (comonomer) may be fed in the mixture having the initiator to the reactor.

[0111] At block 1010, the method includes polymerizing the monomer in presence of the initiator in the continuous flow reactor to form the polymer nanoparticles. The method may include forming the polymer nanoparticles from a polymerization mixture in a process side of the flow channel(s). The polymerization mixture includes the monomer and the initiator. The

polymerizing of the monomer(s) may be an emulsion polymerization. The polymer nanoparticles may have a particle size less than 50 nm. The polymer nanoparticles may be monodisperse or near-monodisperse having a PDI less than 0.1 or less than 0.05.

[0112] At block 1012, the method includes circulating heat transfer fluid through a utility side of the flow channel to control temperature of the polymerization mixture. In one embodiment, the heat transfer fluid is oil such as mineral oil. The continuous flow reactor may have a heat transfer area per unit volume of the process side (inside volume of the flow channel) of at least 5000 m ² /m ³ . The utility side may a utility side of the continuous flow reactor. The utility side may be flow passages or flow layers in the continuous flow reactor adjacent the flow channel.

[0113] At block 1014, the method includes discharging polymer

nanoparticles from the continuous flow reactor. The discharging of the polymer nanoparticles may involve discharging a slurry from the continuous flow reactor. The slurry may include the polymer nanoparticles and water (and surfactant if utilized in the polymerization). The slurry may also include any residual (unreacted) monomer.

[0114] An embodiment is a method of flow synthesis of polymer

nanoparticles. The method includes feeding a mixture having a radical initiator to a continuous flow reactor having a flow channel. The mixture may include water. The mixture may include a surfactant (for example, anionic surfactant) in certain implementations. The surfactant (if present and utilized) may be fed separate from the mixture to the continuous flow reactor or in the mixture having the initiator to the continuous flow reactor. In a particular

implementation, the mixture (having the initiator) includes a water-soluble comonomer, and where the polymer nanoparticles are a copolymer of a monomer and the water-soluble comonomer. The mixture includes the initiator and may include water, a surfactant, or a water-soluble monomer, or any combinations thereof. The method includes heating the mixture in a preheating section of the continuous flow reactor. The preheating section may include an upstream portion of the flow channel for flow of the mixture. The method includes feeding monomer to the continuous flow reactor. The method includes mixing the monomer with the mixture in a reaction section of the continuous flow reactor downstream of the preheating section. The method includes polymerizing the monomer in presence of the radical initiator in the reaction section to form polymer nanoparticles, wherein polymerizing the monomer includes emulsion polymerization. The method includes discharging the polymer nanoparticles from the continuous flow reactor. The discharging of the polymer nanoparticles may involve discharging a slurry having the polymer nanoparticles in at least water from the continuous flow reactor. The polymer nanoparticles may be monodispersed polymer nanoparticles. In certain implementations, the continuous flow reactor is a microreactor. The flow channel of the continuous flow reactor may have a hydraulic diameter less than 1 mm.

[0115] The flow channel may run through the reaction section for mixing the monomer with the mixture (having the initiator) and for the emulsion polymerization of the monomer into the polymer nanoparticles. The mixing may include mixing the monomer with the mixture in an initial subsection (for example, a mixing section) of the reaction section. The feeding of the monomer may involve feeding a first monomer and a second monomer (for example, comonomer). The polymer nanoparticles may be a copolymer of the first monomer and the second monomer. The method may include

polymerizing the monomer(s) in presence of the radical initiator via the emulsion polymerization in the continuous flow reactor to form the polymer nanoparticles, wherein the polymer nanoparticles have a particle size less than 100 nanometers (nm). The method may include forming the polymer nanoparticles from a polymerization mixture in the flow channel. The polymerization mixture has at least the monomer and the radical initiator. The polymerization mixture may include the surfactant to facilitate formation of the emulsion and the emulsion polymerization. The monomer may include a vinyl monomer (for example, an acrylate monomer), and where the polymer nanoparticles include a vinyl polymer (for example, an acrylate polymer). The monomer may include a first vinyl monomer (for example, an acrylate monomer) and a second vinyl monomer (for example, a styrenic monomer). The vinyl polymer may be a copolymer of the acrylate polymer and the styrenic monomer. The method may include controlling a weight or mole ratio of the styrenic monomer to the acrylate monomer to reduce agglomeration of the polymer nanoparticles. The method may include circulating a heat transfer fluid through a flow layer in the continuous flow reactor. The flow layer is adjacent the flow channel. The method may include circulating heat transfer fluid through a utility side of the continuous flow reactor to control temperature of the polymerization mixture in the flow channel (including in the reaction section and in the preheating section in implementations). The continuous flow reactor (for example, microreactor) may have a heat transfer area per unit volume of the flow channel of at least 5000 m ² /m ³ .

[0116] Another embodiment is a method of flow synthesis of polymer nanoparticles, including preheating a mixture having a radical initiator in a continuous flow reactor having a flow channel. In some implementations, the flow channel has a width less than 1 millimeter (mm). The mixture may include water and a surfactant (for example, a sulfate). The method includes polymerizing monomer methacrylate units in presence of the initiator by an emulsion polymerization in the continuous flow reactor to form polymer nanoparticles including polymer of the methacrylate units. The method includes discharging the polymer nanoparticles from the continuous flow reactor. The monomer having the methacrylate units may be butyl

methacrylate (BMA), and where the polymer of the methacrylate units is poly(butyl methacrylate) (PBMA). The monomer may be a monomer mixture of styrene and BMA, and where the polymer of the methacrylate units is the copolymer poly(styrene-co-butyl methacrylate) (PSBMA).

[0117] Yet another embodiment includes a method of flow synthesis of polymer nanoparticles, including flowing a first mixture having a radical initiator and water to a continuous flow reactor having a flow channel(s) for reactant flow. In some implementations, the first mixture includes a surfactant. The method may include preheating the first mixture in the continuous flow reactor. The method includes flowing monomer to the continuous flow reactor and forming in the continuous flow reactor a second mixture having the first mixture and the monomer. The forming of the second mixture may involve mixing the monomer with the first mixture in the continuous flow reactor. The method includes polymerizing, via emulsion polymerization, the monomer in the second mixture in the continuous flow reactor to form polymer nanoparticles. The flow channel(s) may be a microchannel having a hydraulic diameter less than 1 mm. The continuous flow reactor may be a microreactor. The method may include discharging a slurry from the continuous flow reactor. The slurry may include at least the polymer nanoparticles, water, and residual monomer. The discharged slurry may include the surfactant if employed in the

polymerization.

[0118] A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure.