Highly spherical polyamide microparticles and methods for synthesizing the same

Abstract

The present invention is entitled "Highly Spherical Polyamide Microparticles and Synthesis Methods Related Thereto." A method for synthesizing polyamide microparticles may include: dehydrating and shearing a mixture comprising a matrix fluid, about 0.01 wt% to about 50 wt% of an emulsion stabilizer, based on the weight of the matrix fluid, about 13 wt% to about 75 wt% of a solvent, based on the weight of the matrix fluid, and about 20 wt% to about 90 wt% of a cyclic amide monomer, based on the weight of the matrix fluid, to produce an emulsion having a water content of about 1 wt% or less, based on the total weight of the emulsion; adding a deprotonating agent to the emulsion at a concentration of about 0.01 wt% to about 1 wt% based on the weight of the matrix fluid; and contacting the emulsion with a polymerization initiator under conditions effective to polymerize the cyclic amide monomer into a plurality of polyamide microparticles.

Description

Technical Field

[0001] The present disclosure relates to thermoplastic polyamide microparticles and methods for making such microparticles. Such microparticles, particularly highly spherical thermoplastic polyamide microparticles, can be used, among other things, as raw materials for additive manufacturing. Background Art

[0002] Three-dimensional (3D) printing (also known as additive manufacturing) is a rapidly growing field of technology. Although traditionally used for rapid prototyping activities, 3D printing is increasingly being used to prepare commercial and industrial objects that may have structural and mechanical tolerances that are significantly different from those required for rapid prototypes.

[0003] 3D printing operates by depositing either (a) small droplets or streams of molten or solidifiable material or (b) powder particles into precise deposition locations for subsequent consolidation into larger objects, which can have any number of complex shapes. Such deposition and consolidation processes are typically performed under computer control to provide layer-by-layer buildup of larger objects. In a specific example, the consolidation of powder particles can be performed in a 3D printing system using a laser to facilitate selective laser sintering (SLS). Incomplete interlayer fusion can create structural weaknesses, which can be problematic for printing objects with tight structural and mechanical tolerances.

[0004] Powder particles that can be used for 3D printing include thermoplastic polymers (including thermoplastic elastomers), metals and other solidifiable substances. Although a wide variety of thermoplastic polymers are known, relatively few have properties suitable for 3D printing, particularly when powder bed fusion (PBF) is used. Additive manufacturing methods using powder materials include PBF, selective laser sintering (SLS), selective heat sintering (SHM), selective laser melting (SLM), electron beam melting (EBM), binder jetting and multi-jet melting (MJF). In the SLS printing method, energy from a high-power laser causes the particles to fuse together. Typical thermoplastic polymers suitable for 3D printing include those with a well-defined melting point and a recrystallization point that is approximately 20°C to 50°C lower than the melting point. This difference allows more efficient coalescence between adjacent polymer layers, thereby promoting improved structural and mechanical integrity.

[0005] In order to achieve good printing performance using powder particles (particularly polymer powder particles), the powder particles need to maintain good flow properties in the solid state. Flow properties can be assessed, for example, by measuring the fraction of powder particles in the sample that can pass through a standard sieve of a specified size and / or measuring the angle of repose. A high fraction of sievable powder particles can indicate that the particles are present in the form of non-agglomerated, essentially separate particles, which can be a characteristic of ready-to-use powder flow. A lower value of the angle of repose can also be a characteristic of ready-to-use powder flow. A relatively narrow particle size distribution in the sample and the regularity of the particle shape can also help promote good powder flow properties.

[0006] Commercial powder particles are typically obtained through cryogenic grinding or precipitation processes, which can produce irregular particle shapes and wide particle size distributions. Irregular particle shapes can lead to poor powder flow properties during 3D printing. In addition, powder particles with irregular shapes (especially those obtained from current commercial processes) can lead to poor filling efficiency after deposition and consolidation, resulting in extensive formation of voids in the printed article due to the powder particles not being tightly packed together during deposition. Wide particle size distribution can similarly be problematic in this regard. Although poor powder flow properties can be addressed to a certain extent by dry mixing with fillers and flow aids, these techniques may have limited effectiveness for softer polymer materials (such as elastomers) due to particle aggregation. Summary of the Invention

[0007] The present disclosure relates to thermoplastic polyamide microparticles and methods for making such microparticles. Such microparticles, particularly highly spherical thermoplastic polyamide microparticles, can be used, among other things, as raw materials for additive manufacturing.

[0008] According to aspects described herein, a method for synthesizing polyamide microparticles is provided, the method comprising: dehydrating and shearing a mixture comprising a matrix fluid, from about 0.01 wt % to about 50 wt % of an emulsion stabilizer, based on the weight of the matrix fluid, from about 13 wt % to about 75 wt % of a solvent, based on the weight of the matrix fluid, and from about 20 wt % to about 90 wt % of a cyclic amide monomer, based on the weight of the matrix fluid, to produce an emulsion having a water content of about 1 wt % or less, based on the total weight of the emulsion; adding a deprotonating agent to the emulsion at a concentration of from about 0.01 wt % to about 1 wt % based on the weight of the matrix fluid; and contacting the emulsion with a polymerization initiator under conditions effective to polymerize the cyclic amide monomer into a plurality of polyamide microparticles.

[0009] According to aspects described herein, a method for synthesizing polyamide microparticles is provided, the method comprising: dehydrating and shearing a mixture comprising a matrix fluid, from about 0.01 wt % to about 50 wt % of an emulsion stabilizer, based on the weight of the matrix fluid, and from about 13 wt % to about 75 wt % of a solvent, based on the weight of the matrix fluid; while shearing, adding from about 20 wt % to about 90 wt % of a cyclic amide monomer, based on the weight of the matrix fluid, to the mixture to produce an emulsion; dehydrating the emulsion to a water content of about 1 wt % or less, based on the total weight of the emulsion, to produce a dehydrated emulsion; adding a deprotonating agent to the dehydrated emulsion at a concentration of from about 0.01 wt % to about 1 wt % based on the weight of the matrix fluid; and contacting the dehydrated emulsion with a polymerization initiator under conditions effective to polymerize the cyclic amide monomer into a plurality of polyamide microparticles. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The following drawings are included to illustrate certain aspects of the disclosure and should not be construed as exclusive embodiments. The disclosed subject matter is capable of considerable modification, alteration, combination, and equivalents in form and function, as will occur to those skilled in the art having the benefit of this disclosure.

[0011] Figure 1 is a flow chart of a non-limiting example method of the present disclosure.

[0012] Figure 2 FT-IR spectrum of the polyamide microparticles disclosed herein.

[0013] Figure 3 is a differential scanning calorimeter (DSC) trace of polyamide microparticles prepared according to the method of the present disclosure.

[0014] Figure 4A and Figure 4B are two scanning electron micrographs of polyamide microparticles prepared according to the method of the present disclosure. DETAILED DESCRIPTION

[0015] The present disclosure relates to thermoplastic polyamide microparticles and methods for making such microparticles. Such microparticles, particularly highly spherical thermoplastic polyamide microparticles, can be used, among other things, as raw materials for additive manufacturing.

[0016] More specifically, the thermoplastic polyamide microparticles described herein are produced by oil-in-oil melt emulsion ring-opening polymerization of cyclic amides in the presence of a deprotonating agent, resulting in highly spherical polyamide microparticles with good flowability.

[0017] Additionally, the emulsion stabilizers used in some of the synthetic methods described herein can advantageously associate with the outer surface of the polyamide microparticles.Such emulsion stabilizers can act as glidants, which further enhance the flowability of the polyamide microparticles described herein.

[0018] Definition and test methods

[0019] As used herein, the term "miscible" refers to a mixture of components that, when combined, form a single fluid phase.

[0020] As used herein, the term "thermoplastic" refers to a material that can reversibly soften and harden when heated and cooled.

[0021] As used herein, the term "oxide" refers to both metal oxides and non-metal oxides.For the purposes of this disclosure, silicon is considered a metal.

[0022] As used herein, the terms "associated," "associated," and grammatical variations thereof between an emulsion stabilizer and a surface refer to chemical bonding and / or physical adhesion of the emulsion stabilizer to the surface. Without being limited by theory, it is believed that the association between the polymers described herein and the emulsion stabilizers is primarily physical adhesion via hydrogen bonding and / or other mechanisms. However, chemical bonding may occur to some extent.

[0023] As used herein, the term "embedded" with respect to the surface of nanoparticles and polymer particles means that the nanoparticles extend at least partially into the surface such that the polymer contacts the nanoparticles to a greater extent than would be achieved if the nanoparticles were simply laid down on the surface of the polymer particle.

[0024] As used herein, D10, D50, D90, and diameter span are primarily used herein to describe particle size. As used herein, the term "D10" refers to the diameter at which 10% of a sample (on a volume basis, unless otherwise specified) consists of particles having a diameter less than the stated diameter value. As used herein, the term "D50" refers to the diameter at which 50% of a sample (on a volume basis, unless otherwise specified) consists of particles having a diameter less than the stated diameter value. As used herein, the term "D90" refers to the diameter at which 90% of a sample (on a volume basis, unless otherwise specified) consists of particles having a diameter less than the stated diameter value.

[0025] By using the Malvern MASTERSIZER TM Particle size was determined by light scattering techniques or analysis of optical digital micrographs using a 3000. Unless otherwise indicated, light scattering techniques were used to analyze particle size.

[0026] For light scattering techniques, the control sample is the product of the trade name Quality Audit Standards QAS4002 TM Glass microspheres with diameters ranging from 15 μm to 150 μm were purchased from Malvern Analytical Ltd. Unless otherwise specified, samples were analyzed as dry powders. TM The particles to be analyzed were dispersed in air and analyzed using the 3000. The particle size was determined from a plot of bulk density versus size using the instrument software.

[0027] Particle size measurements and diameter spans can also be determined by optical digital microscopy.Optical images were acquired using a Keyence VHX-2000 digital microscope and version 2.3.5.1 software for particle size analysis (system version 1.93).

[0028] As used herein, when referring to sieving, the hole / sieve size is described in terms of United States Standard Sieve (ASTM E11-17).

[0029] As used herein, the term "roundness" with respect to a particle refers to how close the particle is to a perfect sphere. To determine roundness, an optical microscopic image of the particle is taken. The perimeter (P) and area (A) of the particle in the plane of the microscopic image are calculated (e.g., using a SYSMEX FPIA 3000 particle shape and size analyzer, available from Malvern Instruments). The roundness of the particle is C EA / P, where C EA It is the circumference of a circle whose area is equal to the area of ​​the actual particle (A).

[0030] As used herein, the term "shear" refers to stirring or similar processes that cause mechanical agitation in a fluid.

[0031] As used herein, the term "aspect ratio" refers to the length divided by the width, wherein the length is greater than the width.

[0032] Unless otherwise indicated, the melting point of the polymers was determined by ASTM E794-06 (2018) with a 10°C / min ramp rate and cooling rate.

[0033] Unless otherwise indicated, the softening temperature or softening point of a polymer is determined by ASTM D6090-17.The softening temperature can be measured by using a cup and ball apparatus available from Mettler-Toledo using a 0.50 gram sample at a heating rate of 1°C / min.

[0034] The angle of repose is a measure of the flowability of a powder. Angle of repose measurements were determined using ASTM D6393-14 "Standard Test Method for Bulk Solids Characterized by Carr Indices" using a Hosokawa Micron Powder Characterization Tester PT-R.

[0035] Hausner ratio (Hausner ratio, H r ) is a measure of the flowability of the powder and is given by H r =ρ 振实 / ρ 堆积 Calculate, where ρ 堆积 is the bulk density according to ASTM D6393-14, and ρ 振实 is the tap density according to ASTM D6393-14.

[0036] Thermoplastic polyamide microparticles and preparation method thereof

[0037] The present disclosure relates to thermoplastic polyamide microparticles and methods for making such particles using oil-in-oil melt emulsion ring-opening polymerization.

[0038] Figure 1 1 is a flow chart of a non-limiting example method 100 of the present disclosure. A base fluid 102 and an emulsion stabilizer 104 are combined 106 to produce a mixture 108. Mixing and / or heating may be included during the combining 106 of the base fluid 102 and the emulsion stabilizer 104. The combining 106 of the base fluid 102 and the emulsion stabilizer 104 may be performed in any suitable mixing device.

[0039] Examples of the matrix fluid 102 include, but are not limited to, polysiloxane modified with fatty acids, polysiloxane modified with fatty alcohols, polysiloxane modified with polyoxyalkylenes, polydimethylsiloxane (PDMS), methylphenyl polysiloxane, alkyl-modified polydimethylsiloxane, alkyl-modified methylphenyl polysiloxane, amino-modified polydimethylsiloxane, amino-modified methylphenyl polysiloxane, fluorine-modified polydimethylsiloxane, fluorine-modified methylphenyl polysiloxane, polyether-modified polydimethylsiloxane, polyether-modified methylphenyl polysiloxane, silicone oil, fluorinated silicone oil, perfluorinated silicone oil, polyethylene glycol, paraffin, liquid petrolatum, vison oil, turtle oil, soybean oil, perhydrosqualene, sweet almond oil, calophyllum oil, and the like. oil), palm oil, parleam oil, grapeseed oil, sesame oil, corn oil, rapeseed oil, sunflower oil, cottonseed oil, almond oil, castor oil, avocado oil, jojoba oil, olive oil, cereal germ oil, esters of lanolin acid, esters of oleic acid, esters of lauric acid, esters of stearic acid, fatty acid esters, higher fatty acids and fatty alcohols, and the like, and any combination thereof.

[0040] The matrix fluid 102 can have a viscosity of about 50 cSt to about 500,000 cSt (or about 50 cSt to about 5,000 cSt, or about 1,000 cSt to about 60,000 cSt, or about 40,000 cSt to about 100,000 cSt, or about 75,000 cSt to about 150,000 cSt, or about 100,000 cSt to about 300,000 cSt, or about 250,000 cSt to about 500,000 cSt) at 25°C.

[0041] Emulsion stabilizers can include nanoparticles (eg, oxide nanoparticles, carbon black, polymer nanoparticles, and combinations thereof), surfactants, and the like, and any combination thereof.

[0042] Oxide nanoparticles can be metal oxide nanoparticles, non-metal oxide nanoparticles or their mixtures. Examples of oxide nanoparticles include, but are not limited to, silicon dioxide, titanium dioxide, zirconium oxide, aluminum oxide, iron oxide, copper oxide, tin oxide, boron oxide, cerium oxide, thallium oxide, tungsten oxide, etc. and any combination thereof. Mixed metal oxides and / or non-metal oxides such as aluminosilicates, borosilicates and aluminoborosilicates are also included in the term metal oxide. Oxide nanoparticles can be hydrophilic or hydrophobic, which may be natural to the particles or the result of surface treatment of the particles. For example, silicon dioxide nanoparticles with a hydrophobic surface treatment (such as dimethylsilyl, trimethylsilyl, etc.) can be used in the methods and compositions of the present invention. In addition, silicon dioxide with a functional surface treatment (such as methacrylate functionality) can be used in the methods and compositions of the present invention. Non-functionalized oxide nanoparticles may also be suitable for use.

[0043] Commercially available examples of silica nanoparticles include, but are not limited to, Silica®, available from Evonik. Particles (e.g. (with hydrophobic modified surface and 260±30m 2 / g BET surface area of ​​about 7nm average diameter silica nanoparticles), (with hydrophobic modified surface and 35±10m 2 / g BET surface area of ​​about 40nm average diameter silica nanoparticles), (with hydrophilic modified surface and 380±30m 2 / g of BET surface area of ​​silica nanoparticles)), etc., and any combination thereof.

[0044] Carbon black is another type of nanoparticle that can be present as an emulsion stabilizer in the compositions and methods disclosed herein. Various grades of carbon black are familiar to those of ordinary skill in the art, and any of these grades can be used herein. Other nanoparticles capable of absorbing infrared radiation can similarly be used.

[0045] Polymer nanoparticles are another type of nanoparticle that can be present as an emulsion stabilizer in the present disclosure. Suitable polymer nanoparticles can comprise one or more polymers that are thermosetting and / or cross-linked so that they do not melt when processed by melt emulsification according to the present disclosure. High molecular weight thermoplastic polymers with high melting points or decomposition points can similarly comprise suitable polymer nanoparticle emulsion stabilizers.

[0046] The nanoparticles can have an average diameter (volume-based D50) of about 1 nm to about 500 nm (or about 10 nm to about 150 nm, or about 25 nm to about 100 nm, or about 100 nm to about 250 nm, or about 250 nm to about 500 nm).

[0047] Nanoparticles can have a size of about 10 m 2 / g to about 500m 2 / g (or about 10m 2 / g to about 150m 2 / g, or about 25m 2 / g to about 100m 2 / g, or about 100m 2 / g to about 250m 2 / g, or about 250m 2 / g to about 500m 2 / g) of BET surface area.

[0048] Surfactants can be anionic, cationic, nonionic, or zwitterionic chemical substances. Examples of surfactants include, but are not limited to, sorbitan oleate, poly[dimethylsiloxane]-co-[3-(2-(2-hydroxyethoxy)ethoxy)propylmethylsiloxane], sulfates (e.g., sodium lauryl sulfate and sodium dodecylnaphthalene sulfate), sulfonates (e.g., sodium docusate (sodium 1,4-bis(2-ethylhexyloxy)-1,4-dioxobutane-2-sulfonate) and sodium dodecylbenzenesulfonate), dialkylbenzene alkyl sulfates, dialkylbenzene alkylsulfonates, acids (e.g., rosin acid available from Aldrich, NEOGEN R available from Daiichi Kogyo Seiyaku TM and NEOGEN SC TM ), alcohols (e.g., polyvinyl alcohol and dialkylphenoxypoly(ethyleneoxy)ethanol), acids (e.g., polyacrylic acid), ethers (e.g., polyoxyethylene cetyl ether, polyoxyethylene lauryl ether, polyoxyethylene octyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene oleyl ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene stearyl ether, polyoxyethylene nonylphenyl ether), methylcellulose, methylcellulose, ethylcellulose, propylcellulose, hydroxyethylcellulose, carboxymethylcellulose, ammonium (e.g., alkylbenzyldimethylammonium chloride, dialkylbenzylalkylammonium chloride, lauryltrimethylammonium chloride, alkylbenzylmethylammonium chloride, alkylbenzyldimethylammonium bromide, benzalkonium chloride), C12 trimethylammonium bromide, C15 trimethylammonium bromide, C17 trimethylammonium bromide, cetylpyridinium bromide, halide salts of quaternized polyoxyethylalkylamines, dodecylbenzyltriethylammonium chloride, etc., and any mixtures thereof. Commercially available examples of surfactants include, but are not limited to, CALFAX TMDB-45 (sodium dodecyl diphenyl ether disulfonate, available from Pilot Chemicals), SPAN TM 80 (sorbitan maleate nonionic surfactant), MERPOL TM Surfactants (available from Stepan Company), TERGITOL TM TMN-6 (water-soluble nonionic surfactant, available from DOW), TRITON TM X-100 (octylphenol ethoxylate, available from Sigma Aldrich), IGEPAL TM CA-360 (polyoxyethylene (9) nonylphenyl ether, available from Sigma Aldrich), BRIJ TM S10 (polyethylene glycol octadecyl ether, available from Sigma Aldrich), IGEPAL CA-210 TM (polyoxyethylene (2) isooctylphenyl ether, available from Sigma Aldrich), IGEPAL CA-520 TM (polyoxyethylene (5) isooctylphenyl ether, available from Sigma Aldrich), IGEPAL CA-720 TM (polyoxyethylene (12) isooctylphenyl ether, available from SigmaAldrich), IGEPAL CO-890 TM (polyoxyethylene (40) nonylphenyl ether, branched, available from Sigma Aldrich), IGEPAL CO-720 TM (polyoxyethylene (12) nonylphenyl ether, branched, available from Sigma Aldrich), IGEPAL CO-290 TM (alkylphenoxypoly(ethyleneoxy)ethanol, available from SigmaAldrich), IGEPAL CA-210 TM (polyoxyethylene (2) nonylphenyl ether, branched, available from Sigma Aldrich), ANTAROX 890 TM (dialkylphenoxypoly(ethyleneoxy)ethanol, available from Rhone-Poulenc), ANTAROX 897 TM (dialkylphenoxypoly(ethyleneoxy)ethanol, available from Rhone-Poulenc), etc., and any combination thereof. The selection of a particular surfactant or combination of surfactants, and the amount of each surfactant to be used, is within the ability of one skilled in the art.

[0049] The emulsion stabilizer can be included in the mixture 108 at a concentration of about 0.01 wt % to about 50 wt % (or about 0.01 wt % to about 10 wt %, or about 1 wt % to about 20 wt %, or about 10 wt % to about 30 wt %, or about 25 wt % to about 50 wt %) based on the weight of the matrix fluid 102.

[0050] The mixture 108 is then dehydrated 110 to remove most, if not all, of the water present, thereby forming a first dehydrated mixture 112. Dehydration 110 can be performed, for example, by heating the mixture 108 at a pressure (e.g., about 1 Pa to about 150 Pa, or about 1 Pa to about 10 Pa, or about 5 Pa to about 50 Pa, or about 25 Pa to about 100 Pa, or about 75 Pa to about 150 Pa) suitable for evaporating the water and at a temperature (e.g., about 100° C. or higher, about 100° C. to about 300° C., or about 150° C. or about 250° C.) suitable for evaporating the water and below the decomposition temperature of the matrix fluid 102 (preferably below the boiling point of the matrix fluid 102). The mixture 108 can also be subjected to shear conditions for mixing (e.g., stirring), for example, at a speed of about 200 RPM (revolutions per minute) to 300 RPM.

[0051] Solvent 114 is then added 113 to dehydrated mixture 112, forming mixture 116. Solvent 114 can be any solvent or solvent mixture that is miscible with matrix fluid 102 and has a boiling point of at least 150°C (or about 150°C to about 250°C, or about 165°C to about 200°C). Examples of solvents include, but are not limited to, decahydronaphthalene, bicyclohexane, phenylcyclohexane, butylcyclohexane, propylbenzene, butylbenzene, pentylbenzene, hexylbenzene, heptylbenzene, 1-phenyl-1-cyclohexene, 3-cyclohexen-1-ylbenzene, decane, dodecane, tridecane, tetradecane, pentadecane, heptadecane, hexadecane, propylcyclohexane, 4-phenyl-1-cyclohexene, 1-phenyloctane, octabenzonone, 1-phenylnonane, 1-phenyldecane, 1-phenylundecane, 1-phenyldodecane, 1-phenyltridecane, 1-phenyltetradecane, 1-phenylheptadecane, 1-phenyloctadecane, 1,4-dodecylbenzene, 1,4-bis(2-ethylhexyl)benzene, eicosane, triacontan, and the like, and any combination thereof. A non-limiting example of a commercially available solvent is DECALIN®. TM (Decalin, available from Sigma Aldrich.) Solvent 114 can be added 113 to dehydrated mixture 112 in a weight percentage (based on the weight of matrix fluid 102) of about 15 wt % to about 75 wt % (or about 15 wt % to 40 wt %, or about 30 wt % to 55 wt %, or about 50 wt % to 75 wt %).

[0052] The mixture 116 can then be dehydrated 117 to remove most, if not all, of the water present, thereby forming a second dehydrated mixture 118. Dehydration 117 can be performed, for example, by heating the mixture 116 at a pressure (e.g., from about 1 Pa to about 150 Pa, or from about 1 Pa to about 10 Pa, or from about 5 Pa to about 50 Pa, or from about 25 Pa to about 100 Pa, or from about 75 Pa to about 150 Pa) and a temperature (e.g., from about 100° C. or more, from about 100° C. to about 300° C., or from about 150° C., or from about 200° C.) suitable for evaporating a portion of the solvent (e.g., from about 10% to about 15% of the solvent).

[0053] Although the non-limiting example method 100 shows two dehydration steps, one skilled in the art will recognize that other methods may be used to achieve the second dehydrated mixture 118. Preferably, the second dehydrated mixture 118 comprises the matrix fluid 102, about 0.01 wt % to about 50 wt % (or about 0.01 wt % to about 10 wt %, 1 wt % to about 20 wt %, or about 10 wt % to about 30 wt %, or about 25 wt % to about 50 wt %) of the emulsion stabilizer 104, based on the weight of the matrix fluid 102, and about 13 wt % to about 75 wt % (or about 13 wt % to 40 wt %, or about 25 wt % to 55 wt %, or about 50 wt % to 75 wt %) of the solvent 114, based on the weight of the matrix fluid 102. Additionally, the second dehydrated mixture 118 preferably has a water content of about 1 wt % or less (or 0 wt % to about 1 wt %, or 0 wt % to about 0.1 wt %, or about 0.01 wt % to about 0.1 wt %) based on the total weight of the second dehydrated mixture 118.

[0054] Cyclic amide monomer 122 is then added 120 to second dehydrated mixture 118 to form emulsion 124. Preferably, during the addition 120 of cyclic amide monomer 122 to second dehydrated mixture 118, second dehydrated mixture 118 is sheared (preferably under high shear conditions) to facilitate the formation of emulsion 124.

[0055] Examples of cyclic amide monomers 122 include, but are not limited to, azetidinone, 2-azetidinone, 2-pyrrolidone, 2-piperidone, ε-caprolactam, 2-azaoctanone, 2-azanonanone, 2-azadecanone, 2-azaundecanone, 2-azacyclododecanone, laurolactam, and the like, and any combination thereof. Cyclic amide monomers 122 are preferably cyclic amide monomers suitable for preparing nylon 12, nylon 6, or copolymers thereof.

[0056] The cyclic amide monomers 122 may be present in a total of about 20 wt% to about 90 wt% (or about 20 wt% to 50 wt%, or about 30 wt% to 75 wt%, or about 50 wt% to 90 wt%) based on the weight of the matrix fluid 102.

[0057] The emulsion 124 is then dehydrated 126 at a pressure (e.g., from about 1 Pa to about 150 Pa, or from about 1 Pa to about 10 Pa, or from about 5 Pa to about 50 Pa, or from about 25 Pa to about 100 Pa, or from about 75 Pa to about 150 Pa) and a temperature (e.g., from about 100° C. or greater, from about 100° C. to about 300° C., or from about 150° C. to about 250° C.) sufficient to distill off most, if not all, of the water introduced by adding 120 the cyclic amide monomer 122 under high shear conditions, thereby producing a dehydrated emulsion 128. For example, the emulsion 124 can be stirred at a speed between about 550 RPM and 600 RPM and maintained at a temperature of about 130° C. to about 175° C. (or from about 140° C. to about 170° C., or from about 150° C. to about 160° C.).

[0058] While this non-limiting example method 100 shows several dehydration steps, one skilled in the art will recognize that other methods may be used to achieve the emulsion 124 . Preferably, the emulsion 124 comprises a base fluid 102, from about 0.01 wt% to about 50 wt% (or from about 0.01 wt% to about 10 wt%, or from about 1 wt% to about 20 wt%, or from about 10 wt% to about 30 wt%, or from about 25 wt% to about 50 wt%) of the emulsion stabilizer 104, based on the weight of the base fluid 102, from about 13 wt% to about 75 wt% (or from about 13 wt% to 40 wt%, or from about 25 wt% to 55 wt%, or from about 50 wt% to 75 wt%) of the solvent 114, and from about 20 wt% to about 90 wt% (or from about 20 wt% to 50 wt%, or from about 30 wt% to 75 wt%, or from about 50 wt% to 90 wt%) of the cyclic amide monomer 122, based on the weight of the base fluid 102. Additionally, the emulsion 124 preferably has a water content of about 1 wt % or less (or 0 wt % to about 1 wt %, or 0 wt % to about 0.1 wt %, or about 0.01 wt % to about 0.1 wt %) based on the total weight of the emulsion 124 .

[0059] A deprotonating agent 130 can then be added 132 to the dehydrated emulsion 128 under high shear and dehydration conditions. Without being limited by theory, it is believed that the deprotonating agent 130 deprotonates the cyclic amide monomer. For example, dodecane-12-lactam can be deprotonated with sodium hydroxide according to the following Scheme 1:

[0060]

[0061] Examples of deprotonating agents 130 include, but are not limited to, Group I and Group II metal hydroxides and hydrides (e.g., NaOH, NaH, KOH, LiH, LiOH), potassium methoxide, sodium methoxide, potassium ethoxide, sodium ethoxide, lithium ethoxide, potassium t-butoxide, sodium t-butoxide, lithium t-butoxide, sodium caprolactam (e.g., BRUGGOLEN® available from Brüggemann Chemical), and sodium hydride. TM C10 and ADDONYL available from RheinChemie TM CR CATALYZE AND ADDONYL TM Kat NL), ε-caprolactam magnesium bromide (e.g., NYRIM available from Brüggemann Chemicals TM C1), sodium dipropiolactam bis-(2-methoxyethoxy)-aluminate (e.g., DILACTAMATE available from Katchem TM ), etc., and any combination thereof. The deprotonating agent 130 can be added to the emulsion 124 at a concentration of about 0.01 wt % to about 1 wt % (or about 0.01 wt % to about 0.5 wt %, or about 0.05 wt % to about 0.5 wt %, or about 0.05 wt % to about 0.1 wt %, or about 0.1 wt % to about 0.5 wt %) based on the weight of the matrix fluid 102.

[0062] The resulting emulsion 134 is then preferably exposed to an inert gas (e.g., a Group 18 gas or nitrogen or a mixture thereof) to bring the pressure to atmospheric pressure while avoiding water contamination. Although it is preferred to carry out the next step of the reaction at atmospheric pressure, these steps can be carried out at reduced or increased pressures relative to atmospheric pressure.

[0063] A polymerization initiator 136 is then added 138 to the emulsion 134 to form a mixture 140, which is processed 142 under sufficient temperature and shear conditions to maintain emulsion stability and avoid water contamination while promoting polymerization of the cyclic amide monomer.

[0064] Examples of polymerization initiators include, but are not limited to, diisocyanates (e.g., toluene diisocyanate (TDI) and methylene diphenyl diisocyanate (MDI)), N-acetyl-ε-caprolactam, diisocyanate derivatives, N-carbamoyl lactams, hexamethylene-1,6-dicarbamoyl caprolactam (e.g., BRUGGOLEN® available from Brüggemann Chemicals), and N-acetyl-ε-caprolactam. TM C20), polyisocyanates (e.g., ADDONYL TM ACTIVATE, ADDONYL TM8101、ADDONYL TM TT and ADDONYL TM P, and GRILONIT LA available from Ems Chemie), polycarbodiimide, N,N'-alkylenebisamide (e.g., N,N'-ethylene-bisstearamide), etc., and any combination thereof. Thus, a molten emulsion 144 containing droplets of polymerized cyclic amide monomer ("polyamide") is formed.

[0065] When describing the polymerization of cyclic monomers herein, individual cyclic monomers may be in either the deprotonated form or the protonated form, and both forms may be present simultaneously in a mixture.The term cyclic monomer is not to be construed as limited to a particular form or the relative concentration of each form.

[0066] Although Figure 1 The deprotonating agent 130 is added to the emulsion before the polymerization initiator 136, but the methods described herein may include (a) adding the deprotonating agent to the emulsion after the polymerization initiator, or (b) adding the deprotonating agent and the polymerization initiator to the emulsion simultaneously.

[0067] Generally, the temperature at which the molten emulsion 144 is processed 142 should be greater than the melting point or softening temperature of the polyamide being produced and less than the decomposition temperature of any component in the molten emulsion 144. For example, the temperature at which the molten emulsion 144 is processed 142 and formed can be from about 150°C to about 170°C (or from about 150°C to about 160°C, or from about 155°C to about 170°C, or from about 160°C to about 170°C) greater than the melting point or softening temperature of the polyamide being produced, provided that the temperature at which the molten emulsion 144 is processed 142 is less than the decomposition temperature of any component in the molten emulsion 144.

[0068] The shear rate of processing 142 and forming the molten emulsion 144 should be high enough to disperse the polyamide in the form of droplets. The droplets should include droplets having a diameter of about 1000 μm or less (or about 1 μm to about 1000 μm, or about 1 μm to about 50 μm, or about 10 μm to about 100 μm, or about 10 μm to about 250 μm, or about 50 μm to about 500 μm, or about 250 μm to about 750 μm, or about 500 μm to about 1000 μm). High shear conditions can include, for example, stirring the mixture 140 at a speed between about 575 RPM and 625 RPM.

[0069] The time for maintaining the temperature and shear rate for processing 142 and forming molten emulsion 144 can be from about 10 seconds to about 18 hours or longer (or from about 10 seconds to about 30 minutes, or from about 5 minutes to about 1 hour, or from about 15 minutes to about 2 hours, or from about 1 hour to about 6 hours, or from about 3 hours to about 18 hours). Without being limited by theory, it is believed that a steady state of droplet size will be reached, at which point processing 142 can be stopped. This time may also depend on, among other things, the temperature, shear rate, droplet composition, solvent 114 composition, and emulsion stabilizer 104 composition.

[0070] The mixing apparatus used in process 142 to produce molten emulsion 144 should be capable of maintaining molten emulsion 144 at a temperature greater than the melting point or softening temperature of the polyamide produced and applying a sufficient shear rate to maintain dispersion of polyamide droplets in molten emulsion 144. Examples of mixing apparatus used in process 142 to produce molten emulsion 144 include, but are not limited to, extruders (e.g., continuous extruders, batch extruders, etc.), stirred reactors, mixers, reactors with in-line homogenizer systems, and the like, and apparatus derived therefrom.

[0071] The molten emulsion 144 can then be cooled 148. Cooling 148 can range from slow (e.g., allowing the molten emulsion to cool under ambient conditions) to fast (e.g., quenching). For example, the cooling rate can range from about 10°C / hour to about 100°C / second to almost instantaneous when quenching (e.g., in dry ice) (or about 10°C / hour to about 60°C / hour, or about 0.5°C / minute to about 20°C / minute, or about 1°C / minute to about 5°C / minute, or about 10°C / minute to about 60°C / minute, or about 0.5°C / second to about 10°C / second, or about 10°C / second to about 100°C / second).

[0072] During cooling, little or no shear may be applied to the molten emulsion 144. In some cases, the shear applied during heating may also be applied during cooling.

[0073] The cooled mixture 150 resulting from cooling 148 the molten emulsion 144 contains solidified polyamide microparticles and other components (eg, solvent 110, excess emulsion stabilizer 104, matrix fluid 102, etc.) The polyamide microparticles may be dispersed or settled in the matrix fluid / solvent / emulsion stabilizer mixture.

[0074] The specific composition of the polyamide microparticles depends, among other things, on the cyclic amide monomer 122 added 120 to the second dehydrated mixture 118. Examples of polyamides that can be prepared by the methods disclosed herein include polyamide 12 (nylon 12) in embodiments where the cyclic amide comprises poly(dodecane-12-lactam) and polyamide 6 (nylon 6) in embodiments where the cyclic amide comprises poly(hexane-6-lactam). In the presence of poly(dodecane-12-lactam) and poly(hexane-6-lactam), a copolyamide 6 / 12 can be prepared.

[0075] Other polyamides that can be formed include poly(caprolactam) (nylon 46, polyamide 46, or PA46), polyhexamethylene adipamide (nylon 66, polyamide 66, or PA66), polypentamethylene adipamide (nylon 56, polyamide 56, or PA56), polyhexamethylene sebacamide (nylon 610, polyamide 610, or PA610), polyundecanamide (nylon 11, polyamide 11, or PA11), and polyhexamethylene terephthalamide (nylon 6T, polyamide 6T, or PA6T), nylon 10.10 (polyamide 10.10, or PA10.10). ), nylon 10.12 (polyamide 10.12 or PA10.12), nylon 10.14 (polyamide 10.14 or PA10.14), nylon 10.18 (polyamide 10.18 or PA10.18), nylon 6.10 (polyamide 6.10 or PA6.10), nylon 6.18 (polyamide 6.18 or PA6.18), nylon 6.12 (polyamide 6.12 or PA6.12), nylon 6.14 (polyamide 6.14 or PA6.14), semi-aromatic polyamides, and the like, and any combination thereof. Copolyamides may also be used. Examples of copolyamides include, but are not limited to, PA 11 / 10,10, PA 6 / 11, PA 6,6 / 6, PA 11 / 12, PA 10,10 / 10,12, PA 10,10 / 10,14, PA 11 / 10,36, PA 11 / 6,36, PA 10,10 / 10,36, etc. and any combination thereof. Examples of polyamides include, but are not limited to, polycaprolactam (nylon 6, polyamide 6, or PA6), poly(hexamethylene succinamide) (nylon 46, polyamide 46, or PA46), polyhexamethylene adipamide (nylon 66, polyamide 66, or PA66), polypentamethylene adipamide (nylon 56, polyamide 56, or PA56), polyhexamethylene sebacamide (nylon 610, polyamide 610, or PA610), polyundecanamide (nylon 11, polyamide 11, or PA11), polydodecamide (nylon 12, polyamide 12, or PA12), and polyhexamethylene terephthalamide (nylon 6T, polyamide 6T, or PA6T). Nylon 10.10 (polyamide 10.10 or PA10.10), nylon 10.12 (polyamide 10.12 or PA10.12), nylon 10.14 (polyamide 10.14 or PA10.14), nylon 10.18 (polyamide 10.18 or PA10.18), nylon 6.10 (polyamide 6.10 or PA6.10), nylon 6.18 (polyamide 6.18 or PA6.18), nylon 6.12 (polyamide 6.12 or PA6.12), nylon 6.14 (polyamide 6.14 or PA6.14), semi-aromatic polyamides, and the like, and any combination thereof. Copolyamides may also be used.Examples of copolyamides include, but are not limited to, PA 11 / 10,10, PA 6 / 11, PA 6,6 / 6, PA 11 / 12, PA 10,10 / 10,12, PA 10,10 / 10,14, PA 11 / 10,36, PA 11 / 6,36, PA 10,10 / 10,36, etc. and any combination thereof. Examples of polyamide elastomers include, but are not limited to, polyesteramides, polyetheresteramides, polycarbonate-esteramides, and polyether-block-amide elastomers.

[0076] The cooled mixture 150 can then be treated 156 to separate the polyamide microparticles 152 from the other components 154. Suitable treatments include, but are not limited to, washing, filtering, centrifuging, decanting, and the like, and any combination thereof. The solvent used to wash the polyamide microparticles 152 should generally be (a) miscible with the matrix fluid and the solvent and (b) non-reactive with the polyamide (e.g., non-swelling and non-dissolving). The choice of wash solvent will depend, among other things, on the composition of the matrix fluid and the composition of the polyamide microparticles 152. For example, the polyamide microparticles 152 can be washed with one or more of n-heptane, n-hexene, ethyl acetate, and methanol.

[0077] The solvent and other remaining components can be removed from the polyamide microparticles 152 by drying using an appropriate method such as air drying, heat drying, reduced pressure drying, freeze drying, or a mixture thereof. Heating can preferably be performed at a temperature below the glass transition point of the thermoplastic polymer (e.g., about 50° C. to about 150° C.).

[0078] The polyamide microparticles 152, after being separated from the other components 154, may optionally be further classified 157 (or filtered by size) to produce purified polyamide microparticles 158. For example, to narrow the particle size distribution (or reduce the diameter span), the polyamide microparticles 152 may be passed through a sieve having a pore size of about 10 μm to about 250 μm (or about 10 μm to about 100 μm, or about 50 μm to about 200 μm, or about 150 μm to about 250 μm).

[0079] In another exemplary purification technique, the polyamide microparticles 152 can be washed with water to remove at least some of the emulsion stabilizer (e.g., surfactant). In yet another exemplary purification technique, the polyamide microparticles 152 can be blended with additives to achieve the desired end product. Examples of such additives include flow aids (e.g., silica nanoparticles, carbon black, or PTFE particles), other polymer particles, fillers, and the like, as well as any combination thereof.

[0080] In some cases, the emulsion stabilizer used to prepare the polyamide microparticles 152 may be undesirable in downstream applications. Thus, yet another example purification technique may include at least substantially removing the emulsion stabilizer from the polyamide microparticles 152 (eg, by washing and / or pyrolysis).

[0081] In some cases, emulsion stabilizers may act as glidants (eg, silica nanoparticles, carbon black, or PTFE particles).

[0082] The polyamide microparticles 152 and / or purified polyamide microparticles 158 (referred to as particles 152 / 158) can be characterized by composition, physical structure, and the like.

[0083] The polyamide may be present in the microparticles 152 / 158 in an amount of about 90% to about 99.5% by weight (or about 90% to about 95% by weight, or about 92% to about 97% by weight, or about 95% to about 99.5% by weight) of the polyamide microparticles 152 / 158.

[0084] As described above, the emulsion stabilizer is located at the interface between the polyamide droplets and the surrounding liquid mixture. Thus, when the mixture is cooled, the emulsion stabilizer remains at or near the interface. Thus, the polyamide microparticles 152 / 158 can include the emulsion stabilizer associated with the outer surface of the particles 152 / 158, such as (a) dispersed as a coating on the outer surface of the particles 152 / 158 and / or (b) embedded in the outer portion (e.g., the outer 1% by volume) of the particles 152 / 158.

[0085] The coating can be substantially uniformly disposed over the outer surface. As used herein with respect to a coating, the term "substantially uniform" refers to a uniform coating thickness across the surface locations (particularly across the outer surface) covered by the coating composition (e.g., emulsion stabilizer). The emulsion stabilizer 104 can form a coating that covers at least 5% (or about 5% to about 100%, or about 5% to about 25%, or about 20% to about 50%, or about 40% to about 70%, or about 50% to about 80%, or about 60% to about 90%, or about 70% to about 100%) of the surface area of ​​the polyamide microparticles 152 / 158. When purified to at least substantially remove the emulsion stabilizer, the emulsion stabilizer 104 can be present in the polyamide microparticles 158 at less than 25% (or 0% to about 25%, or about 0.1% to about 5%, or about 0.1% to about 1%, or about 1% to about 5%, or about 1% to about 10%, or about 5% to about 15%, or about 10% to about 25%) of the surface area of ​​the polyamide microparticles 158. The coverage of the emulsion stabilizer 104 on the outer surface of the polyamide microparticles 152 / 158 can be determined using image analysis of SEM micrographs. The emulsion stabilizer 104 can form a coating that covers at least 5% (or about 5% to about 100%, or about 5% to about 25%, or about 20% to about 50%, or about 40% to about 70%, or about 50% to about 80%, or about 60% to about 90%, or about 70% to about 100%) of the surface area of ​​the polyamide microparticles 152 / 158. When purified to at least substantially remove the emulsion stabilizer, the emulsion stabilizer 104 may be present in the particles 128 at less than 25% (or 0% to about 25%, or about 0.1% to about 5%, or about 0.1% to about 1%, or about 1% to about 5%, or about 1% to about 10%, or about 5% to about 15%, or about 10% to about 25%) of the surface area of ​​the particles 128. Image analysis of SEM micrographs can be used to determine the coverage of the emulsion stabilizer 104 on the outer surface of the polyamide microparticles 152 / 158.

[0086] Furthermore, if voids are formed within the polyamide microparticles, the emulsion stabilizer 104 may be located at the interface between the voids and the polyamide microparticles. The voids typically do not contain polyamide microparticles. Instead, the voids may contain, for example, a solvent (e.g., solvent 114, a wash solvent), air, or be voided. Particles 152 / 158 may comprise about 5% or less (or about 0.001% to about 5% by weight, or about 0.001% to about 0.1% by weight, or about 0.01% to about 0.5% by weight, or about 0.1% to about 2% by weight, or about 1% to about 5% by weight) of particles 138 / 144.

[0087] The emulsion stabilizer 104 may be present in the microparticles 152 / 158 at about 10% or less by weight (or about 0.01% to about 10% by weight, or about 0.01% to about 1% by weight, or about 0.5% to about 5% by weight, or about 3% to about 7% by weight, or about 5% to about 10% by weight). When purified to at least substantially remove the emulsion stabilizer, the emulsion stabilizer 104 may be present in the microparticles 156 at less than 0.01% by weight (or 0% to about 0.01% by weight, or 0% to 0.001% by weight).

[0088] Polyamide microparticles 152 / 158 may have a D10 of about 0.5 μm to about 125 μm, a D50 of about 1 μm to about 200 μm, and a D90 of about 70 μm to about 300 μm, wherein D10 < D50 < D90. Microparticles 138 / 144 may also have a diameter span of about 0.2 to about 10 (or about 0.2 to about 0.5, or about 0.4 to about 0.8, or about 0.5 to about 1.0, or about 1 to about 3, or about 2 to about 5, or about 5 to about 10). Without limitation, a diameter span value of 1.0 or greater is considered wide, and a diameter span value of 0.75 or less is considered narrow.

[0089] The polyamide microparticles 152 / 158 may have a roundness of about 0.8 or greater (or about 0.8 to about 1, or about 0.80 to about 0.95, or about 0.90 to about 1.0, or about 0.93 to about 0.99, or about 0.95 to about 0.99, or about 0.97 to about 0.99, or about 0.98 to about 1.0).

[0090] The particles 152 / 158 may have an angle of repose of about 22° to about 50° (or about 22° to about 30°, or about 25° to about 35°, or about 30° to about 40°, or about 35° to about 45°, or about 40° to about 50°).

[0091] The particles 152 / 158 can have a Hausner ratio of about 1.0 to about 1.5 (or about 1.0 to about 1.2, or about 1.1 to about 1.3, or about 1.2 to about 1.35, or about 1.3 to about 1.5).

[0092] The particles 152 / 158 may have a mass of about 0.3 g / cm 3 to about 0.8g / cm 3 (or about 0.3g / cm 3 to about 0.6g / cm 3 , or about 0.4g / cm 3 to about 0.7g / cm 3 , or about 0.5g / cm 3 to about 0.6g / cm 3, or about 0.5g / cm 3 to about 0.8g / cm 3 ) of the bulk density.

[0093] Depending on the temperature and shear rate of processing 142, as well as the composition and relative concentrations of the components, different shapes of the structures comprising the polyamide particles 152 / 158 have been observed. Typically, the polyamide particles 152 / 158 comprise substantially spherical particles (having a roundness of approximately 0.90 or greater). However, other structures have been observed in the polyamide particles 152 / 158, including discs and elongated structures. Thus, the polyamide particles 152 / 158 may include one or more of the following: (a) substantially spherical particles having a roundness of 0.90 or greater, (b) disc structures having an aspect ratio of approximately 2 to approximately 10, and (c) elongated structures having an aspect ratio of 10 or greater. Each of the (a), (b), and (c) structures has an emulsion stabilizer dispersed on the outer surface of the (a), (b), and (c) structures and / or embedded in the exterior of the (a), (b), and (c) structures. At least some of the (a), (b), and (c) structures may be agglomerated. For example, (c) elongated structures may be laid on the surface of (a) substantially spherical particles.

[0094] Applications of thermoplastic polyamide microparticles

[0095] The polyamide microparticles described herein can be used in 3D printing processes, particularly those employing selective laser sintering to facilitate particle consolidation. The polyamide microparticles disclosed herein can exhibit properties superior to polymer particles having irregular shapes or wider particle distributions, such as those commercially available. In a non-limiting example, the polyamide microparticles disclosed herein can consolidate at lower laser powers and provide reduced void formation in 3D printed articles.

[0096] The 3D printing process of the present disclosure may include depositing the polyamide microparticles of the present disclosure onto a surface in a specified shape, and once deposited, heating at least a portion of the polyamide microparticles to promote consolidation and form a consolidated body (article), wherein the consolidated body has a void percentage of approximately 1% or less after consolidation. For example, the heating and consolidation of the polyamide microparticles may be performed in a 3D printing device using a laser, such that the heating and consolidation are performed by selective laser sintering.

[0097] Any polyamide microparticles disclosed herein can be formulated into a composition suitable for 3D printing. The choice of composition can be based on various factors, such as, but not limited to, the laser power used for selective laser sintering, the type of article to be prepared, and the intended use conditions of the article.

[0098] Examples of items that can be 3D printed using the polyamide microparticles of the present disclosure include, but are not limited to, containers (e.g., for food, beverages, cosmetics, personal care compositions, pharmaceuticals, etc.), shoe soles, toys, furniture parts and decorative household items, plastic gears, screws, nuts, bolts, cable ties, automotive parts, medical supplies, prostheses, orthopedic implants, aviation / aircraft related parts, preparation of artifacts to assist learning in education, 3D anatomical models to assist surgery, robots, biomedical devices (orthotics), household appliances, dental, electronic devices, sporting goods, etc.

[0099] Other applications of the polyamide microparticles of the present disclosure may include, but are not limited to, use as fillers in paints and powder coatings, inkjet materials, and electrophotographic toners, etc. In some cases, the polyamide microparticles may have other preferred properties, such as diameter and span, that may be useful in such other applications.

[0100] Terms

[0101] Item 1. A method for synthesizing polyamide microparticles, the method comprising: dehydrating and shearing a mixture comprising a matrix fluid, an emulsion stabilizer, a solvent, and a cyclic amide monomer to produce an emulsion, the emulsion having a water content of about 1 weight percent or less based on the total weight of the emulsion; adding a deprotonating agent to the emulsion at a concentration of about 0.01 weight percent to about 1 weight percent based on the weight of the matrix fluid; adding a polymerization initiator to the emulsion; and polymerizing the cyclic amide monomer into a plurality of polyamide microparticles.

[0102] Clause 2. The method of Clause 1, wherein the emulsion stabilizer is from about 0.01 wt % to about 50 wt % based on the weight of the base fluid.

[0103] Clause 3. The method of any preceding clause, wherein the solvent is from about 13 wt% to about 75 wt% based on the weight of the matrix fluid.

[0104] Clause 4. The method of any preceding clause, wherein the cyclic amide monomer is from about 20 wt% to about 90 wt% based on the weight of the matrix fluid.

[0105] Clause 5. The method of Clause 1 or Clause 2 or Clause 3 or Clause 4, wherein the deprotonating agent is added before the polymerization initiator is added.

[0106] Clause 6. The method of Clause 1 or Clause 2 or Clause 3 or Clause 4, wherein the deprotonating agent is added after the polymerization initiator is added.

[0107] Clause 7. The method according to Clause 1 or Clause 2 or Clause 3 or Clause 4, wherein the adding of the deprotonating agent is carried out simultaneously with the adding of the polymerization initiator.

[0108] Clause 8. The method according to any preceding clause, wherein the cyclic amide monomer is selected from azetidinone, 2-azetidinone, 2-pyrrolidone, 2-piperidone, ε-caprolactam, 2-azaoctanone, 2-azanonanone, 2-azadecanone, 2-azaundecanone, 2-azadodecanone, laurolactam, and any combination thereof.

[0109] Item 9. A method according to any preceding item, wherein the polyamide of the polyamide microparticles is selected from the group consisting of polycaprolactam, poly(hexamethylene succinamide), polyhexamethylene adipamide, polypentamethylene adipamide, polyhexamethylene sebacamide, polyundecanamide, polydodecamide, polyhexamethylene terephthalamide, nylon 10.10, nylon 10.12, nylon 10.14, nylon 10.18, nylon 6.10, nylon 6.18, nylon 6.12, nylon 6.14, and any copolyamides thereof.

[0110] Clause 10. The method according to any preceding clause, wherein the matrix fluid comprises one selected from the group consisting of: polysiloxane modified with fatty acid, polysiloxane modified with fatty alcohol, polysiloxane modified with polyoxyalkylene, polydimethylsiloxane (PDMS), methylphenyl polysiloxane, alkyl-modified polydimethylsiloxane, alkyl-modified methylphenyl polysiloxane, amino-modified polydimethylsiloxane, amino-modified methylphenyl polysiloxane, fluorine-modified polydimethylsiloxane, fluorine-modified methylphenyl polysiloxane, polyether-modified polydimethylsiloxane, Silicone, polyether-modified methylphenyl polysiloxane, silicone oil, fluorinated silicone oil, perfluorinated silicone oil, polyethylene glycol, paraffin, liquid petrolatum, mink oil, turtle oil, soybean oil, perhydrosqualene, sweet almond oil, crabapple oil, palm oil, parleam oil, grape seed oil, sesame oil, corn oil, rapeseed oil, sunflower oil, cottonseed oil, almond oil, castor oil, avocado oil, jojoba oil, olive oil, corn germ oil, esters of lanolin acid, esters of oleic acid, esters of lauric acid, esters of stearic acid, fatty acid esters, higher fatty acids and fatty alcohols, and any combination thereof.

[0111] Clause 11. The method of any preceding clause, wherein the emulsion stabilizer comprises nanoparticles and / or surfactants.

[0112] Clause 12. The method of Clause 11, wherein the nanoparticles comprise oxide nanoparticles, carbon black, and / or polymer nanoparticles.

[0113] Clause 13. The method of Clause 11 or Clause 12, wherein the nanoparticles are associated with the outer surface of the polyamide microparticles.

[0114] Clause 14. The method of Clause 11 or Clause 12 or Clause 13, wherein at least a portion of the nanoparticles are embedded in the outer surface of the polyamide microparticles.

[0115] Clause 15. The method of clause 11 or clause 12 or clause 13 or clause 14, wherein the surfactant comprises one selected from the group consisting of sorbitan oleate, poly[dimethylsiloxane]-co-[3-(2-(2-hydroxyethoxy)ethoxy)propylmethylsiloxane], sulfates, sulfonates, dialkylbenzene alkyl sulfates, dialkylbenzene alkyl sulfonates, acids, alcohols, acids, ethers, methylcellulose, ethylcellulose, propylcellulose, hydroxyethylcellulose, carboxymethylcellulose, ammonium (e.g., alkylbenzyldimethylammonium chloride, dialkylbenzenealkylammonium chloride, lauryltrimethylammonium chloride, alkylbenzylmethylammonium chloride, alkylbenzyldimethylammonium bromide, benzalkonium chloride), C12 trimethylammonium bromide, C15 trimethylammonium bromide, C17 trimethylammonium bromide, cetylpyridinium bromide, halide salts of quaternized polyoxyethylalkylamines, dodecylbenzyltriethylammonium chloride, and any mixtures thereof.

[0116] Clause 16. The method of any preceding clause, wherein the solvent has a boiling point greater than about 150°C.

[0117] Clause 17. The method according to any preceding clause e, wherein the solvent comprises one selected from the group consisting of decahydronaphthalene, bicyclohexane, phenylcyclohexane, butylcyclohexane, propylbenzene, butylbenzene, pentylbenzene, hexylbenzene, heptylbenzene, 1-phenyl-1-cyclohexene, 3-cyclohexen-1-ylbenzene, decane, dodecane, tridecane, tetradecane, pentadecane, heptadecane, hexadecane, propylcyclohexane, 4-phenyl-1-cyclohexene, 1-phenyloctane, octabenzone, 1-phenylnonane, 1-phenyldecane, 1-phenylundecane, 1-phenyldodecane, 1-phenyltridecane, 1-phenyltetradecane, 1-phenylheptadecane, 1-phenyloctadecane, 1,4-docosylbenzene, 1,4-bis(2-ethylhexyl)benzene, eicosane, triacontan, and any combination thereof.

[0118] Clause 18. The method of any preceding clause, wherein the dehydrating is performed by heating the mixture to a temperature of about 100°C to about 300°C at a pressure of about 1 Pa to about 150 Pa.

[0119] Clause 19. The method of any preceding clause, wherein the dehydration is performed such that about 10% to about 15% of the solvent is distilled off during the dehydration.

[0120] Clause 20. The method of any preceding clause, wherein the polymerization initiator comprises one selected from the group consisting of toluene diisocyanate (TDI), methylene diphenyl diisocyanate (MDI), and any combination thereof.

[0121] Clause 21. The method of any preceding clause, wherein the deprotonating agent comprises Group I and Group II metal hydroxides, Group I and Group II metal hydrides, potassium methoxide, sodium methoxide, potassium ethoxide, sodium ethoxide, lithium ethoxide, potassium tert-butoxide, sodium tert-butoxide, lithium tert-butoxide, sodium caprolactam, ε-caprolactam magnesium bromide, sodium dipropiolactam bis-(2-methoxyethoxy)aluminate, and any combination thereof.

[0122] Clause 22. The method of any preceding clause, further comprising: washing the polyamide microparticles.

[0123] Clause 23. The method according to Clause 22, wherein the washing is performed with n-heptane, n-hexane, ethyl acetate, methanol, or any combination thereof.

[0124] Clause 24. The method of any preceding clause, wherein the polyamide microparticles have a D10 of about 0.5 μm to about 125 μm, a D50 of about 1 μm to about 200 μm, and a D90 of about 70 μm to about 300 μm, wherein D10 < D50 < D90.

[0125] Clause 25. The method of any preceding clause, wherein the polyamide microparticles have a diameter span of about 0.2 to about 10.

[0126] Clause 26. The method of any preceding clause, wherein the polyamide microparticles have a roundness of about 0.8 or greater.

[0127] Clause 27. The method of any preceding clause, wherein the polyamide microparticles have an angle of repose of about 22° to about 50°.

[0128] Clause 28. The method of any preceding clause, wherein the polyamide microparticles have a Hausner ratio of about 1.0 to about 1.5.

[0129] Clause 23. The method of any preceding clause, wherein the polyamide microparticles have a g / cm 3 to about 0.8g / cm 3 The bulk density.

[0130] Item 24. A method for synthesizing polyamide microparticles, the method comprising: dehydrating and shearing a mixture comprising a matrix fluid, about 0.01 wt% to about 50 wt% of an emulsion stabilizer, based on the weight of the matrix fluid, and about 13 wt% to about 75 wt% of a solvent, based on the weight of the matrix fluid; while shearing, adding about 20 wt% to about 90 wt% of a cyclic amide monomer, based on the weight of the matrix fluid, to the mixture to produce an emulsion; dehydrating the emulsion to a water content of about 1 wt% or less, based on the total weight of the emulsion, to produce a dehydrated emulsion; adding a deprotonating agent to the dehydrated emulsion at a concentration of about 0.01 wt% to about 1 wt% based on the weight of the matrix fluid; and contacting the dehydrated emulsion with a polymerization initiator under conditions effective to polymerize the cyclic amide monomer into a plurality of polyamide microparticles. One or more of Items 5-23 may also be combined with Item 24.

[0131] Clause 25. A method for synthesizing polyamide microparticles, the method comprising: dehydrating and shearing a mixture comprising a matrix fluid, about 0.01 wt% to about 50 wt% of an emulsion stabilizer, based on the weight of the matrix fluid, and about 13 wt% to about 75 wt% of a solvent, based on the weight of the matrix fluid, wherein the emulsion stabilizer comprises nanoparticles; while shearing, adding about 20 wt% to about 90 wt% of a cyclic amide monomer, based on the weight of the matrix fluid, to the mixture to produce an emulsion; dehydrating the emulsion to a water content of about 1 wt% or less, based on the total weight of the emulsion, to produce a dehydrated emulsion; adding a deprotonating agent to the dehydrated emulsion at a concentration of about 0.01 wt% to about 1 wt% based on the weight of the matrix fluid; and contacting the dehydrated emulsion with a polymerization initiator under conditions effective to polymerize the cyclic amide monomer into a plurality of polyamide microparticles, wherein the nanoparticles are associated with outer surfaces of the polyamide microparticles. One or more of clauses 5-11 and 14-23 may also be combined with clause 25. The emulsion stabilizer may further comprise a surfactant (eg, the surfactant described in Item 15).

[0132] In order to facilitate a better understanding of the embodiments of the present invention, the following examples of preferred or representative embodiments are given. The following examples should in no way be construed as limiting or defining the scope of the present invention.

[0133] Example

[0134] Example 1. By combining PDMS and polyoxyethylene (9) nonylphenyl ether (IGEPAL TM CS-360) and vacuum drying the combined mixture to prepare polyamide microparticles containing nylon 12 ("Ny12"). Decalin (DECALIN TM), and the combined mixture was dried under vacuum. Laurolactam ("LL") was added under vacuum, followed by a deprotonating agent to deprotonate a portion of the laurolactam. The vacuum was broken and replaced with a slow flow of inert gas. The reaction mixture was stirred while several aliquots of AROP (aromatic ring-opening polymerization) initiator were gradually added (at 30 minute intervals). The reaction mixture was cooled, and the spherical Ny12 microparticles were washed sequentially with n-hexane, ethyl acetate, and methanol. The Ny12 microparticles were dried in an oven at 80°C overnight. Table 1 lists various non-limiting exemplary reaction conditions suitable for preparing the polyamide microparticles of the present disclosure.

[0135] Table 1

[0136]

[0137] The chemical structure of the obtained polyamide microparticles was confirmed by FTIR spectroscopy. An exemplary FTIR spectrum is shown in Figure 2 In. Appeared at 1636cm -1 and 3264cm -1 The excellent carbonyl and amide NH stretching absorption peaks at 400 nm confirm the polyamide.

[0138] As discussed in this disclosure, residual PDMS oil may be present in the polyamide microparticles. Silicon measurements by inductively coupled plasma (ICP) were used to determine the PDMS oil remaining after the washing procedure. Based on the ICP results, 762 ppm of silicon remained in the Ny12 microparticle sample, which can represent a rough estimate of the silicone oil contained in the sample. Calculations showed that 2.0 g of silicone oil was present in 1000 g of the polymer sample, which may be on the surface of the microparticles or trapped within them.

[0139] Samples of polyamide microparticles were also analyzed by differential scanning calorimetry (DSC). A typical DSC scan of Ny12 was obtained at Figure 3 Shown in.

[0140] Example 2. PDMS (16.0 g, 30,000 centistokes, available from Clearco Product Inc, USA) and 4.0 g IGEPAL TM CO-630 (nonionic emulsifier; polyoxyethylene (9) nonylphenyl ether available from Sigma-Aldrich) was mixed in the reactor. The reactor was vacuum sealed while stirring at 170°C and 250 RPM for one hour. Then, 8.0 g of DECALIN was added. TMThe mixture was vacuum dried at the same RPM for another hour or more. The temperature was maintained at 143°C to 145°C. The temperature setting point was adjusted to distill off 10% to 15% of the DECALIN depending on the reaction scale and reactor size. TM . Then, 11.24 grams of laurolactam were added and vacuum dried at 155°C and 550-600 RPM stirring for 45 minutes. Finally, 0.05 grams of sodium hydroxide were added and vacuum dried for 15 minutes under the same temperature / stirring conditions. The vacuum was then broken and a slow stream of nitrogen was introduced while the system reached 160°C with steady stirring at 600 RPM. By adding TDI as an activator, the oil-in-oil molten emulsion system was ready to initiate AROP. 200 μL of TDI was divided into 4 equal parts and 4 equal parts were slowly added (about 2 minutes) with a time interval of 30 minutes between each part and vigorously stirred at 600 RPM. After the last aliquot of TDI was added, the system was kept at 160°C for 3 hours and then discharged onto an aluminum plate containing dry ice for rapid cooling. Washing was performed with n-hexane (three times), ethyl acetate and methanol (three times) to remove PDMS, impurities and unreacted monomers. The resulting material was an off-white powder, which was dried at 80°C overnight.

[0141] Figure 4A and Figure 4B are two scanning electron micrographs of polyamide microparticles prepared in Example 2.

[0142] Example 3. PDMS (16.0 g, 30,000 centistokes, available from Clearco Product Inc, USA) and 4.0 g IGEPAL TM CO-630 (nonionic emulsifier; polyoxyethylene (9) nonylphenyl ether available from Sigma-Aldrich) was mixed in the reactor. The reactor was vacuum sealed while stirring at 170°C and 250 RPM for one hour. Then, 8.0 g of DECALIN was added. TM The mixture is then vacuum dried at the same RPM for another hour or more. The temperature is maintained at 143°C to 145°C due to solvent reflux. The temperature set point must be adjusted to distill off 10% to 15% of the DECALIN depending on the scale of the reaction and the size of the reactor. TM. Then, 11.19 grams of laurolactam was added and vacuum dried at 155°C and 550-600 RPM stirring for 45 minutes. Finally, 0.08 grams of sodium hydroxide was added and vacuum drying was continued for 15 minutes under the same temperature / stirring conditions. The vacuum was then broken and a slow stream of nitrogen was introduced while the system reached 160°C with steady stirring at 600 RPM. By adding TDI as an activator, the oil-in-oil molten emulsion system was ready to initiate AROP. 200 μL of TDI was divided into 4 equal parts and 4 equal parts were slowly added (about 2 minutes) with a time interval of 30 minutes between each part and vigorously stirred at 600 RPM. After the last aliquot of TDI was added, the system was kept at 160°C for 3 hours and then discharged onto an aluminum plate containing dry ice for rapid cooling. Washing was carried out with n-hexane (three times), ethyl acetate and methanol (three times) to remove PDMS, impurities and unreacted monomers. The resulting material was an off-white powder, which was dried at 80°C overnight.

[0143] Example 4. PDMS (33.9 g, 10,000 centistokes, available from Clearco Product Inc, USA) and 4.23 g IGEPAL TM CO-630 (nonionic emulsifier; polyoxyethylene (9) nonylphenyl ether available from Sigma-Aldrich) was mixed in the reactor. The reactor was vacuum sealed while stirring at 250 RPM for one hour at 170°C. Then, 12.08 g of DECALIN was added. TM The mixture is then vacuum dried at the same RPM for another hour or more. The temperature is maintained at 143°C to 145°C due to solvent reflux. The temperature set point must be adjusted to distill off 10% to 15% of the DECALIN depending on the scale of the reaction and the size of the reactor. TM . Then, 12.88 grams of laurolactam were added and vacuum dried at 155°C and 550-600RPM stirring for 45 minutes. Finally, 0.06 grams of sodium hydroxide were added and vacuum dried for 15 minutes under the same temperature / stirring conditions. The vacuum was then broken and a slow stream of nitrogen was introduced while the system reached 160°C with steady stirring at 600RPM. By adding TDI as an activator, the oil-in-oil molten emulsion system was ready to initiate AROP. 250 μL of TDI was divided into 5 equal parts and 4 equal parts were slowly added (about 2 minutes) with a time interval of 30 minutes between each part and vigorously stirred at 600RPM. After the last aliquot of TDI was added, the system was kept at 160°C for 3 hours and then discharged onto an aluminum plate containing dry ice for rapid cooling. Washed with n-hexane (three times), ethyl acetate and methanol (three times) to remove PDMS, impurities and unreacted monomers. The resulting off-white powder was dried overnight at 80°C.

[0144] Example 5. PDMS (20.6 g, 10,000 centistokes, available from Clearco Product Inc, USA) and 0.6 g IGEPAL TM CO-630 (nonionic emulsifier; polyoxyethylene (9) nonylphenyl ether available from Sigma-Aldrich) was mixed in the reactor. The reactor was vacuum sealed while stirring at 250 RPM for one hour at 170°C. Then, 10.3 g of DECALIN was added. TM The mixture is then vacuum dried at the same RPM for another hour or more. The temperature is maintained at 143°C to 145°C due to solvent reflux. The temperature set point must be adjusted to distill off 10% to 15% of the DECALIN depending on the scale of the reaction and the size of the reactor. TM . Then, 11.0 grams of laurolactam was added and vacuum dried at 155°C and 550-600RPM stirring for 45 minutes. Finally, 0.07 grams of sodium hydroxide was added and vacuum dried for 15 minutes under the same temperature / stirring conditions. The vacuum was then broken and a slow stream of nitrogen was introduced while the system reached 160°C with steady stirring at 600RPM. By adding TDI as an activator, the oil-in-oil molten emulsion system was ready to initiate AROP. 25 μL of TDI was divided into 5 equal parts and 4 equal parts were slowly added (about 2 minutes) with a time interval of 30 minutes between each part and vigorously stirred at 600RPM. After the last aliquot of TDI was added, the system was kept at 160°C for 3 hours and then discharged onto an aluminum plate containing dry ice for rapid cooling. Washed with n-hexane (three times), ethyl acetate and methanol (three times) to remove PDMS, impurities and unreacted monomers. The resulting off-white powder was dried overnight at 80°C.

[0145] All documents described herein are incorporated herein by reference for the purposes of all jurisdictions permitting such practice, including any priority documents and / or testing procedures, as long as they do not conflict with this document. As will be apparent from the foregoing general description and specific embodiments, although the forms of the present disclosure have been shown and described, various modifications may be made without departing from the spirit and scope of the present disclosure. Therefore, the present disclosure is not intended to be limited thereby. For example, the compositions described herein may not contain any component or composition not explicitly described or disclosed herein. Any method may lack any step not described or disclosed herein. Similarly, the term "comprising" is considered to be synonymous with the term "including". Whenever a method, composition, element, or group of elements is preceded by the transition phrase "comprising", it should be understood that we also contemplate the same composition or group of elements with the transition phrases "essentially consisting of," "consisting of," "selected from," or "is" before the description of the composition, element, or multiple elements, and vice versa.

[0146] Unless otherwise indicated, all numerals expressing the quantity of ingredients, characteristics (such as molecular weight), reaction conditions, etc. used in this specification and the related claims should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise indicated to the contrary, the numerical parameters listed in the following specification and the appended claims are approximate values, which may vary depending on the desired properties sought to be obtained by the embodiments of the present invention. At a minimum, and without attempting to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be interpreted in light of the number of reported significant digits and by applying conventional rounding methods.

[0147] Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range are specifically disclosed. In particular, each value range disclosed herein (in the form of "about a to about b," or equivalently, "about a to b," or equivalently, "about a b") should be understood to set forth each value and range encompassed within the broader value range. In addition, the terms in the claims have their ordinary, common meaning unless otherwise explicitly and clearly defined by the patentee. In addition, the indefinite articles "a" or "an" as used in the claims are defined herein to mean that there is one or more than one of the element it introduces.

[0148] One or more exemplary embodiments are presented herein. For the sake of clarity, all features of physical implementation are not described or shown in this application. It should be understood that in the development of the physical implementation of the present disclosure, many specific decisions must be made to achieve the developer's goal, such as meeting system-related constraints, business-related constraints, government-related constraints and other constraints, which vary and change over time due to implementation. Although the effort made by the developer may be time-consuming, such effort will be a routine task for those of ordinary skill in the art who benefit from the present disclosure.

[0149] Therefore, the present disclosure is well adapted to attain the ends and advantages mentioned, as well as those inherent therein. The particular embodiments disclosed above are exemplary only, as the present disclosure may be modified and practiced in different but equivalent manners apparent to one of ordinary skill in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design shown herein, except as described in the claims below. Therefore, it is apparent that the particular exemplary embodiments disclosed above may be altered, combined or modified, and all such variations are considered to be within the scope and spirit of the present disclosure. The embodiments illustratively disclosed herein may suitably be implemented in the absence of any element not specifically disclosed herein and / or any optional element disclosed herein.

Claims

1. A method for synthesizing polyamide microparticles, the method comprising: dehydrating and shearing a mixture comprising a base fluid, an emulsion stabilizer, a solvent, and a cyclic amide monomer to produce an emulsion having a water content of 1 wt % or less based on the total weight of the emulsion; adding a deprotonating agent to the emulsion at a concentration of 0.01 wt % to 1 wt % based on the weight of the matrix fluid; adding a polymerization initiator to the emulsion; as well as polymerizing the cyclic amide monomer to form a plurality of polyamide microparticles, wherein the polyamide microparticles have a roundness of 0.8 or greater.

2. The method of claim 1, wherein the emulsion stabilizer is present in an amount of 0.01 wt% to 50 wt% based on the weight of the base fluid.

3. The method of claim 1, wherein the solvent is present in an amount of 13 wt% to 75 wt% based on the weight of the matrix fluid.

4. The method of claim 1, wherein the cyclic amide monomer is present in an amount of 20 wt% to 90 wt% based on the weight of the base fluid. The method according to claim 1 , wherein the deprotonating agent is added before the polymerization initiator is added. The method according to claim 1 , wherein the deprotonating agent is added after the polymerization initiator is added. The method according to claim 1 , wherein the adding of the deprotonating agent is performed simultaneously with the adding of the polymerization initiator.

8. The method of claim 1, wherein the cyclic amide monomer is selected from the group consisting of 2-azetidinone, 2-pyrrolidone, 2-piperidone, ε-caprolactam, 2-azacyclooctanone, 2-azacyclononanone, 2-azacyclodecanone, 2-azacycloundecanone, 2-azacyclododecanone, laurolactam, and any combination thereof.

9. The method of claim 1 , wherein the polyamide of the polyamide microparticles is selected from the group consisting of polycaprolactam, poly(hexamethylene succinamide), polyhexamethylene adipamide, polypentamethylene adipamide, polyundecanamide, polydodecamide, polyhexamethylene terephthalamide, nylon 10.10, nylon 10.12, nylon 10.14, nylon 10.18, nylon 6.10, nylon 6.18, nylon 6.12, nylon 6.14, and any copolyamides thereof.

10. The method according to claim 1, wherein the matrix fluid comprises one selected from the group consisting of polysiloxane modified with fatty acid, polysiloxane modified with fatty alcohol, polysiloxane modified with polyoxyalkylene, polydimethylsiloxane (PDMS), methylphenyl polysiloxane, alkyl-modified polydimethylsiloxane, alkyl-modified methylphenyl polysiloxane, amino-modified polydimethylsiloxane, amino-modified methylphenyl polysiloxane, fluorine-modified polydimethylsiloxane, fluorine-modified methylphenyl polysiloxane, polyether-modified polydimethylsiloxane, [0014] The present invention also includes but is not limited to silicone oils, fluorosilicone oils, polyols, paraffins, liquid petrolatum, mink oil, turtle oil, soybean oil, perhydrosqualene, sweet almond oil, crabapple oil, palm oil, parleam oil, grape seed oil, sesame oil, corn oil, rapeseed oil, sunflower oil, cottonseed oil, almond oil, castor oil, avocado oil, jojoba oil, olive oil, corn germ oil, esters of lanolin acid, esters of oleic acid, esters of lauric acid, esters of stearic acid, fatty acid esters, higher fatty acids and fatty alcohols, and any combination thereof.

11. The method of claim 1, wherein the solvent has a boiling point greater than 150°C.

12. The method of claim 1, wherein the dehydration is performed such that 10% to 15% of the solvent is distilled off during the dehydration.

13. The method of claim 1, wherein the polymerization initiator comprises one selected from the group consisting of toluene diisocyanate (TDI), methylene diphenyl diisocyanate (MDI), and any combination thereof.

14. The method of claim 1, wherein the deprotonating agent comprises Group I and Group II metal hydroxides, Group I and Group II metal hydrides, potassium methoxide, sodium methoxide, potassium ethoxide, sodium ethoxide, lithium ethoxide, potassium tert-butoxide, sodium tert-butoxide, lithium tert-butoxide, sodium caprolactam, ε-caprolactam magnesium bromide, sodium dipropiolactam bis-(2-methoxyethoxy)aluminate, and any combination thereof.

15. The method according to claim 1, further comprising: The polyamide microparticles are washed.

16. The method of claim 1, wherein the polyamide microparticles have a D10 of 0.5 μm to 125 μm, a D50 of 1 μm to 200 μm, and a D90 of 70 μm to 300 μm, wherein D10 <D50<D90。 17. The method of claim 1, wherein the polyamide microparticles have a diameter span of 0.2 to 10.

18. A method for synthesizing polyamide microparticles, the method comprising: dehydrating and shearing a mixture comprising a base fluid, an emulsion stabilizer present in an amount of 0.01 wt % to 50 wt % based on the weight of the base fluid, and a solvent present in an amount of 13 wt % to 75 wt % based on the weight of the base fluid; while shearing, adding a cyclic amide monomer present in an amount of 20% to 90% by weight based on the weight of the base fluid to the mixture to produce an emulsion; dehydrating the emulsion to a water content of 1 wt % or less based on the total weight of the emulsion to produce a dehydrated emulsion; adding a deprotonating agent to the dehydrated emulsion at a concentration of 0.01 wt % to 1 wt % based on the weight of the matrix fluid; as well as contacting the dehydrated emulsion with a polymerization initiator under conditions effective to polymerize the cyclic amide monomer into a plurality of polyamide microparticles, wherein the polyamide microparticles have a roundness of 0.8 or greater.

19. A method for synthesizing polyamide microparticles, the method comprising: dehydrating and shearing a mixture comprising a matrix fluid, an emulsion stabilizer present in an amount of 0.01 wt % to 50 wt % based on the weight of the matrix fluid, and a solvent present in an amount of 13 wt % to 75 wt % based on the weight of the matrix fluid, wherein the emulsion stabilizer comprises nanoparticles; while shearing, adding a cyclic amide monomer present in an amount of 20% to 90% by weight based on the weight of the base fluid to the mixture to produce an emulsion; dehydrating the emulsion to a water content of 1 wt % or less based on the total weight of the emulsion to produce a dehydrated emulsion; adding a deprotonating agent to the dehydrated emulsion at a concentration of 0.01 wt % to 1 wt % based on the weight of the matrix fluid; as well as contacting the dewatered emulsion with a polymerization initiator under conditions effective to polymerize the cyclic amide monomer into a plurality of polyamide microparticles, wherein the nanoparticles are associated with outer surfaces of the polyamide microparticles, wherein the polyamide microparticles have a roundness of 0.8 or greater.

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