BACKGROUND

[0001] Commercially, polyamides such as polyamide 6, can be synthesized by hydrolysis or by anionic ring opening polymerization. The hydrolytic polymerization process is more industrially viable, because it is easier to control and better adapted for large-scale operation. Anionically polymerized polyamides though have an improved crystallinity as compared to hydrolytically polymerized polyamides. For example, the crystallinity of anionically polymerized polyamide 6 is about 40%, which is significantly greater than the crystallinity of hydrolytic polyamide 6. It is believed that this increase in crystallinity is due to the fact that the anionically polymerized polyamide 6 can be synthesized at a temperature closer to its crystallization temperature, whereas hydrolytic polyamide 6 is synthesized above its melting point. Thus, anionically polymerized polyamide 6 exhibits a reduced water uptake, a better toughness, and improved impact resistance over hydrolytic polyamide 6.

[0002] A polyamide having an increased crystallinity is desired as such a polyamide could result in a polyamide composition with a reduced amount of water uptake.

BRIEF SUMMARY

[0003] Disclosed herein is a crystalline, porous polyamide composition and a method of making the same.

[0004] In an embodiment, a polyamide composition, comprises an anionically polymerized polyamide; wherein the polyamide composition has a crystallinity of greater than or equal to 45 wt% as determined by DSC; and a porosity of greater than or equal to 10 vol% as determined based on the density of the polyamide composition.

[0005] In another embodiment, a method of making any one or more of the preceding polyamide compositions comprises anionically polymerizing a monomer mixture comprising a cyclic lactam monomer, a solvent in which the cyclic lactam monomer is soluble, a catalyst, and an activator to form the anionically polymerized polyamide.

[0006] The above described and other features are exemplified by the following figures, detailed description, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Refer now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike.

[0008] FIG. 1 is a scanning electron microscopy image of the polyamide composition of Example 4;

[0009] FIG. 2 is a graphical illustration of the temperature with time of the polymerization of the polyamide of Example 1 ;

[0010] FIG. 3 is a graphical illustration of the temperature with time of the polymerization of the polyamide of Example 4;

[0011] FIG. 4 is a graphical illustration of the stress versus strain of Examples 1, 4, 7, and 8; and

[0012] FIG. 5 is a graphical illustration of the moisture update with time of the polyamide compositions of Examples 1 and 4.

DETAILED DESCRIPTION

[0013] In anionic polymerization conducted in the absence of solvent, an exotherm forms that increases the reaction temperature to a temperature greater than the crystallization temperature and any polymer polymerized at this increased temperature will be in the amorphous phase. As the reaction temperature decreases below the crystallization temperature, crystalline polyamide is formed. It was surprisingly discovered that an anionically polymerized polyamide (referred to herein as the polyamide composition) that was polymerized in the presence of a solvent resulted in a polyamide composition with an increased crystallinity as compared to a polyamide polymerized under the same conditions, but without the solvent. Due to the increased crystallinity, the polyamide composition can beneficially exhibit a reduced moisture uptake.

[0014] The process comprises anionically polymerizing a monomer mixture comprising a cyclic lactam monomer, a solvent in which the cyclic lactam monomer is soluble, a catalyst, and an activator to form the anionically polymerized polyamide. While not wishing to be bound by the theory of operation of the disclosure, it is thought that the presence of the solvent reduces or even eliminates the presence of an exotherm during polymerization. Specifically, it is believed that the solution comprising the cyclic lactam monomer having a boiling point that is generally greater than the crystallization and reaction temperatures and the solvent having a boiling point that is less than the crystallization and reaction temperatures results in a solution with a modified boiling point based on the rule of mixtures. As the solution boiling point is greater than that of the solvent boiling point, the solvent does not initially boil off during the polymerization and can be present to reduce the exotherm, ultimately resulting in the polymerization temperature being maintained below the crystallization temperature. Therefore, crystalline polyamide is formed throughout the polymerization reaction, resulting in a polyamide composition with increased crystallinity. As polymerization proceeds and the concentration of the monomer decreases, the boiling point of the solution also decreases and the solvent can begin to boil off under the right conditions. Any residual solvent present after the polymerization can be further evaporated.

[0015] It was found that the type and amount of solvent can have a dramatic effect on the resultant morphology of the polyamide composition. For example, depending on the amount of solvent initially present, the polyamide composition can have a closed pore structure, an open pore structure, both open pores and closed pores, or an aggregate pore structure if the initial solvent concentration is high. In some instances, a spherulitic morphology was observed to create the open pore structures and the aggregate pore structures. Here, it is believed that the spherulitic formation arises from a reduction of the exotherm that results not only in a reduction in the polymerization temperature, but also slows down the polymerization kinetics of the cyclic lactam monomer. As the cyclic lactam monomer polymerizes, the spherulitic crystalline domains grow, becoming interconnected and forming a porous network. As the spherulites grow, the polymer becomes increasingly immiscible in the solvent and spherulite growth is eventually inhibited. The resulting polyamide composition therefore has a hierarchical morphological structure comprising spherulitic structures having a lamella length scale of only a few micrometers or less, forming the overall spherulite having a length scale in the 10s of micrometers. For example, FIG. 1 is an SEM image of an example of a polyamide composition having a spherulite morphology with an open pore structure that can arise from the present polymerization. FIG.1 shows spherulites having an overall length scale on the order of 10s of micrometers comprising lamella having a length scale of only a few micrometers. This hierarchical morphology can result in one or both of a lotus leaf effect and an ultrahydrophobic surface.

[0016] The polyamide composition comprises an anionically polymerized polyamide. The anionically polymerized polyamide can have a weight average molecular weight of 2,000 to 100,000 Daltons (Da), or 5,000 to 50,000 Daltons as measured by gel permeation chromatography based on polystyrene standards. [0017] The polyamide composition can have a crystallinity of greater than or equal to 45 weight percent (wt%), or greater than or equal to 50 wt%, or 45 to 75 wt% as determined by differential scanning calorimetry (DSC). In determining the crystallinity using DSC, a polyamide composition having a size of 4.5 ± 0.1 milligram (mg) is sealed in a closed hermetic aluminum pan and heated at a heating rate of 10 degrees Celsius per minute (°C/min) over a temperature range of -20 to 250 degrees Celsius (°C). The weight percent crystallinity (X _c ) is then determined by dividing the change in enthalpy of the polyamide composition measure from the DSC scan (AH _m ) by the change in enthalpy of a 100 wt% crystalline sample of the same polyamide (AH _C ) as shown in Equation (I).

X ro/ ₀ ) = 0≡ x ₁₀ () (I)

c ^J AH _C '

[0018] The polyamide composition can have a porosity of greater than or equal to 10 volume percent (vol%), or 10 to 50 vol% as determined using a density method as defined by Equation (II).

Porosity = (l ^pbulk ) x 100% (II)

\ Ppolyamide/

In Equation (II), the bulk density pbuik is calculated by dividing the weight of the polyamide composition by the volume of polyamide composition and p _po iyamide is the density of the polyamide.

[0019] The polyamide composition can have a reduced water uptake as compared to a corresponding polyamide formed in the absence of a solvent. The polyamide composition can have a water uptake of less than or equal to 6 wt%, or less than or equal to 5 wt%, or 1 to 6 wt%. Without being bound by theory, it is noted that water vapor permeability of polymers depends on their phase morphology and the diffusion of water molecules can be facilitated by the free volume of an amorphous phase in polymers. However, the crystalline phase, being ordered and tightly packed, can hinder the diffusion of water molecules. Polyamide compositions though, in spite of being semicrystalline, can exhibit high moisture absorption due to the presence of hydrogen bonded amide groups. It was surprisingly discovered that by increasing the crystallinity of the polyamide compositions, a reduction in moisture uptake of greater than or equal to 40% was achieved, where final moisture uptake, Wf, can be determined by measuring the weight increase of an initially dry polyamide composition in a closed desiccator having a relative humidity of 65% and a temperature of 70 °C and using Equation (III).

Moisture uptake, W _f = ^χ 100% (III) In Equation (III), W, is the initial (dry) weight of the sample and Wf is the final weight of the sample measured at a time, t, once a final weight is achieved.

[0020] A method of making the composition can comprise anionically polymerizing a monomer mixture comprising a cyclic lactam monomer and a solvent to form the anionically polymerized polyamide. The monomer mixture can further comprise a catalyst and an initiator. The solvent can be a solvent in which the cyclic lactam monomer is soluble. The polymerizing can comprise melt polymerizing at a temperature of greater than or equal to the melting temperature of the cyclic lactam monomer and below the melting point of the polymerizing polyamide. For example, the melt polymerizing can occur at a temperature of 25 to 70 °C, or 80 to 220 °C, or 100 to 200 °C, or 145 to 165 °C. For cyclic lactam monomers containing less than 6 carbon atoms in the lactam ring, the melt polymerizing can occur at a temperature of less than or equal to 190 °C. When the cyclic lactam monomer comprises ε-caprolactam, then the melt polymerizing can occur at a temperature of 100 to 220 °C, or 145 to 165 °C.

[0021] The cyclic lactam monomer can comprise greater than or equal to 3 carbon atoms, or 3 to 14, or 5 to 10 carbon atoms in the lactam ring. The cyclic lactam monomer can comprise β-propiolactam (also known as 2-azetidinone), γ-butyrolactam (also known as 2- pyrrolidone), δ-valerolactam (also known as 2-piperidine), ε-caprolactam, enantholactam, caprylolactam, laurolactam, β,β-dimethylpropiolactam, α,α-dimethylpropiolactam, amylolactam, or a combination comprising at least one of the foregoing. The cyclic lactam monomer can comprise an alkyl substituted cyclic lactam, an aryl substituted cyclic lactam, or a combination comprising at least one of the foregoing. The cyclic lactam monomer can comprise ε-caprolactam. The cyclic lactam monomer can comprise a combination comprising at least one of the foregoing cyclic lactam monomers.

[0022] The polymerizing occurs in the presence of a solvent and the cyclic lactam monomer can be soluble in the solvent. For example, the cyclic lactam monomer can be considered soluble in the solvent if greater than or equal to 100 mg of the cyclic lactam monomer can be dissolved in 1 milliliter (mL) of solvent at 23 °C. The solvent can comprise methyl tert-butyl ether, isopropyl ether, diphenyl ether, biphenyl, an alkanol (such as methanol, ethanol, 1-propanol, 2-propanol, n-butanol, isobutanol, and tert-butanol), a polyol (such as diethylene glycol and tetraethylene glycol), an aromatic hydrocarbon (such as benzene, toluene, xylene (such as meta-xylene, ortho-xylene, and para-xylene)), a carboxylate (such as a carboxylic acid having 1 to 8 carbon atoms), an alkyl- substituted lactam (such as N-methylpyrrolidone, N-methylcaprolactam, and N-ethylcaprolactam), or a combination comprising at least one of the foregoing. The solvent can comprise xylene, specifically, meta-xylene. The solvent can comprise n-nonane, a-pinene, n-decane, or a combination comprising at least one of the foregoing. The solvent can comprise a combination comprising at least one of the foregoing solvents.

[0023] The solvent can have a boiling point that is less than the polymerization temperature, or less than or equal to the polymerization temperature minus 5 °C. For example, the solvent can comprise m-xylene having a boiling point of 140 °C, the cyclic lactam monomer can comprise ε-caprolactam, and the polymerization temperature can be 150 °C. The solvent can have a boiling point that is greater than or equal to the polymerization temperature, or greater than or equal to the polymerization temperature plus 5 °C. Using a solvent having a boiling point that is greater than the polymerization temperature can result in the formation of closed pores in the resultant polyamide composition.

[0024] The monomer mixture can comprise 2 to 50 wt%, or 10 to 40 wt% of the solvent based on the total weight of the monomer mixture. If the monomer mixture comprises greater than 0 to 15 wt% of the solvent, then the polyamide composition can have a closed pore structure. If the monomer mixture comprises greater than 15 to 25 wt% of the solvent, then the polyamide composition can have a mixed pore structure comprising both open and closed pores. If the monomer mixture comprises greater than 25 to 35 wt% of the solvent, then the polyamide composition can have an open pore structure. If the monomer mixture comprises greater than 45 wt% of the solvent, then the polyamide composition can have an aggregate pore structure. A closed pore structure can refer to a polyamide composition, where the pores are not connected to each other. An open pore structure can refer to a polyamide composition having an interconnected pore structure. The open pore structure can allow for near complete or complete removal of the solvent from the polyamide composition (for example, 95 to 100 wt% of the initial solvent can be removed from the polyamide composition). A mixed pore structure can refer to a polyamide composition having both open and closed pores. The aggregate pore structure can refer to a polyamide composition having pores of multiple length scales, for example, on the micrometer length scale (such as 5 to 100 micrometers) as well as on the millimeter length scale (such as 0.2 to 2 millimeters).

[0025] The monomer mixture can comprise a catalyst. The catalyst can comprise an iminium salt that can be prepared by reacting a base with a lactam such as the cyclic lactam monomer. For example, the cyclic lactam monomer to be polymerized can be used for the preparation of the catalyst; but the catalyst can likewise be prepared from a different lactam. The iminium salt can be prepared by reacting the lactam with a metal compound. The metal compound can comprise a metal, a basic derivative of the metal, or a combination comprising at least one of the foregoing. The metal can comprise an alkali metal (such as sodium and potassium), an alkaline earth metal (such as magnesium), aluminum, or a combination comprising at least one of the foregoing. The basic derivative of the metal can comprise a hydroxide, an alkoxide, a hydride, an aryl, an amide, an organic acid salt, or a combination comprising at least one of the foregoing. The basic derivative of the metal can comprise sodium hydroxide, potassium hydroxide, lithium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, lithium hydride, sodium hydride, sodium methylate, sodium ethylate, sodium phenolate, sodium beta-naphtholate, sodamide, sodium stearate, lithium aluminium hydride, aluminium propylate, or a combination comprising at least one of the foregoing. The catalyst can comprise sodium caprolactamate, such as CIO commercially available from BASF SE of Ludwigshafen, Germany.

[0026] The iminium salt can be prepared by adding the metal compound to the cyclic lactam monomer; or by first adding the metal compound to a portion of the cyclic lactam monomer and then adding the iminium salt to the remaining cyclic lactam monomer.

[0027] Little or no polymerization can occur during the preparation of the catalyst. The lactam can be as anhydrous as the metal compound. The catalyst can be present in an amount of 0.1 to 10 mole percent (mol%), or 0.1 to 5 mol% based on the total moles of the lactam and catalyst. The catalyst can be present in an amount of 1 to 6 wt% based on a total weight of the monomer, activator, and catalyst. The more catalyst added, the lower the molecular weight of the resultant polyamide. The time used for the preparation of the catalyst depends upon the properties of the compounds employed, the quantity added, and the temperature chosen, and can generally be from a few seconds to several hours (hrs). The iminium salt can be prepared by reacting the lactam with the metal compound by heating at a temperature of 25 to 220 °C.

[0028] The monomer mixture can comprise an activator (also referred to as a co- catalyst). The activator can comprise any compound that, in addition to the catalyst, brings about polymerization of the cyclic lactam monomer. The activator can comprise a carbodiimide (such as Ν,Ν'- diisopropyl carbodiimide, N,N'-di-(o-tolyl)-carbodiimide, Ν,Ν'- dicyclohexyl carbodiimide, 2,2',6,6'-tetraisopropyl diphenyl carbodiimide, or poly-(2,2- diisopropyl)-p-phenylene carbodiimide), a blocked or unblocked isocyanate (such as diphenyl methane diisocyanate, hexamethylene diisocyanate, toluol diisocyanate, isophorone diisocyanate, m-xylidene diisocyanate, p-xylidene diisocyanate, or phenyl isocyanate), an acylated lactam (such as an acetylated caprolactamate or laurin lactamate), oxazoline, a bisoxazoline (such as phenylene bisoxazoline), an oxazoline derivative, oxazolone, N- substituted 2-oxazolidone, a fatty alkyl oxazoline, a hydroxy-fatty alkyl oxazoline, an oxazoline produced with hydroxy acid (such as with ricinoleic acid), a lactam (such as bis-N- acyl lactam, N-acetyl caprolactam, Ν,Ν-terephthaloyl-bis-caprolactam, Ν,Ν'- sebacoyl-bis- caprolactam, or bifunctional hexamethylene- 1,6-dicarbamoylcaprolactam), or a combination comprising at least one of the foregoing. The activator can comprise bifunctional

hexamethylene- 1,6-dicarbamoylcaprolactam, such as C20 commercially available from BASF SE of Ludwigshafen, Germany. The activator can comprise a multifunctional activator (such as poly(hexamethylene diisocyanate, poly[(phenyl isocyanate)-co- formaldehyde], methyl isocyanate bound to polystyrene, 1-adamentyl isocyanate, or a combination comprising at least one of the foregoing. The activator can comprise a combination comprising at least one of the foregoing activators.

[0029] The activator can be present in an amount of 0.1 to 5 mol% based on the total moles of the cyclic lactam monomer. The activator can be present in an amount of 1 to 4 wt% based on a total weight of the monomer, activator, and catalyst. A molar ratio of the catalyst to the activator can be 0.5 to 2, or 0.8 to 1.2. The activator can be added before, during, or after adding the catalyst. The activator can be dissolved in a portion of the cyclic lactam monomer and the dissolved activator can be added as an activator mixture. Likewise, the catalyst can be dissolved in a portion of the cyclic lactam monomer and the dissolved catalyst can be added as a catalyst mixture.

[0030] The polymerization can be performed in an inert environment. For example, an inert gas (such as nitrogen, argon, and a noble gas) can be introduced onto the surface of the reaction mixture during the polymerization to prevent oxidation.

[0031] The polymerization can comprise polymerizing the reaction mixture in a batch reactor. The polymerization can comprise mixing the solvent and the cyclic lactam monomer with one of the catalyst and the activator to form a monomer mixture, increasing the temperature of the monomer mixture to a polymerization temperature, and adding the other of the catalyst and the activator to initiate polymerization and form the polyamide composition. After polymerization, the polyamide composition can be dried, for example, by heating to remove any remaining solvent.

[0032] Alternatively, the polymerization can be performed via reaction injection molding. Reaction injection molding can be useful in rapidly preparing cast articles of varying size and shape directly from the cyclic lactam monomer. In particular, reaction injection molding can have advantages when used in the manufacture of large molded articles, because reaction injection molding or similar processes use high temperatures and high pressures for their operations. Therefore, simpler and lighter weight molds can be employed and faster cycles can often be obtained in the manufacture of large shaped articles. The reaction injection molding can comprise injecting a single mixture comprising the cyclic lactam monomer, the solvent, the catalyst, and the activator into a mold; two or more mixtures can be mixed just prior to the injection molding; or the two or more mixtures can be simultaneously added to the mold during the injection molding. For example, a first mixture comprising the cyclic lactam monomer, the solvent, and one of the catalyst and the activator can be mixed with a second mixture comprising the other of the catalyst and the activator just prior to the injection molding and the combined mixture can be injected into a mold to form the article.

[0033] After forming the polyamide composition, the polyamide composition can be ground up to form a high crystallinity powder. The high crystallinity powder can be used as an extrusion additive. For example, the high crystallinity powder can be added as an extrusion additive in order to reduce the viscosity of the polymer melt. If the extrusion time is greater than the time is would take for the polyamide crystals to melt and to reach their entanglement density, then the resultant extrudate could have improved properties.

[0034] The high crystallinity powder could also be used in three dimensional (3D) printing applications. Using the high crystallinity powder could be advantageous as the polymer segments in the crystalline regions of the high crystallinity powder are inherently disentangled and, upon melting, the polymer chains are also initially disentangled. Therefore, the initial viscosity of the melt will be low, but the driving force for the polymer chains to reach its equilibrium entanglement density will be high, which could ultimately result in a faster, sintering polymer. Furthermore, as the high crystallinity powder has a high fraction of crystallinity, upon melting, the high crystallinity powder will inherently expand during the melting, which can potentially reduce void formation during printing. [0035] The polyamide composition can further comprise a second polymer. For example, the second polymer can be present during the polymerization of the cyclic lactam monomer. The second polymer can be at least partially soluble in the cyclic lactam monomer. The second polymer can comprise a polyacetal, a polyolefin, a polyacrylic, a polycarbonate, a polystyrene, a polyester, a second polyamides, a polyamideimide, a polyarylate, a polyarylsulfone, a polyethersulfone, a polyphenylene sulfide, a polyvinyl chloride, a polysulfone, a polyimide, a polyetherimide, a polyfluoroethylene, a

polyetherketone, a poly(ether ether ketone), a poly(ether ketone ketone), a polybenzoxazole, a polyphthalide, a polyacetal, a poly anhydride, a polyvinyl ether, a polyvinyl thioether, a polyvinyl alcohol, a polyvinyl ketone, a polyvinyl halide, a polyvinyl nitrile, a polyvinyl ester, a polysulfonate, a polysulfide, a polythioester, a polysulfone, a polysulfonamide, a polyurea, a polyphosphazene, a polysilazane, or a combination comprising at least one of the foregoing. The second polymer can comprise a polystyrene, a polyphenylene oxide, a poly(ether ether sulfone), a poly( ether imide), a polysiloxane, or a combination comprising at least one of the foregoing. The polyamide composition can comprise a copolymerized siloxane that is polymerized simultaneously with the polyamide. For example, the copolymerized siloxane can be derived from octaphenylcyclotetrasiloxane.

[0036] The polyamide composition can comprise an additive. The additive can comprise a filler, an antioxidant, a blowing agent, a plasticizer, a colorant, or a combination comprising at least one of the foregoing. The additive can comprise eicosane, triacontane, a paraffin wax, or a combination comprising at least one of the foregoing.

[0037] An article can comprise the polyamide composition. The article can be a filter.

[0038] The following examples are provided to illustrate the polyamide composition and the method of making the same. The examples are merely illustrative and are not intended to limit the polyamide composition made in accordance with the disclosure to the materials, conditions, or process parameters set forth therein.

Examples

[0039] In the examples, the following test methods were used.

[0040] Different scanning calorimeter (DCS) was performed using a TA DSC Q200 to characterize the thermal transitions and crystallinity of polyamide compositions. The polyamide compositions had a size of 4.5 ± 0.1 mg and were tested at a heating rate of 10 °C/min over a temperature range of -20 to 250 °C. The samples were sealed in a closed hermetic aluminum pan prior to testing. The crystallinity of polyamide compositions was calculated using Equation (I). In Equation (I), Δ¾ for 100% crystalline polyamide 6 is 188 Joules per gram (J/g).

[0041] Wide angle x-ray scattering (WAXS) was performed to determine the crystallinity of the polyamide compositions. Samples for WAXS were prepared by cutting discs of with a diamond saw. Quantitative WAXS was performed using a Ganesha SAXS- lab system using Cu K-alpha radiation (0.154 nanometers (nm)) and 0.9 mm - 0.9 mm apertures (using scatterless slits). The detector to sample distance was about 100 millimeters. Measurements are transmission corrected to give absolute scattering intensity. The crystallinity of samples was calculated using background subtraction method.

[0042] The porosity of the polyamide compositions was determined using a density method as defined by Equation (II).

[0043] Compression testing on the polyamide compositions was carried out using a mechanical testing machine (Instron) on samples having a dimension of 15x 15 millimeters (mm) at a speed of 2 millimeters per minute (mm/min) at room temperature (about 23 °C).

Examples 1-6: Effect of the solvent on the formation of polyamide 6

[0044] In Example 1, anionic polymerization of ε-caprolactam was carried out in a 20 mL glass vial under atmospheric pressure. The monomer mixture, comprising ε-caprolactam and the C20 activator, was melt mixed at a temperature of 150 °C under constant stirring. The polymerization was initiated upon addition of the CIO catalyst, where the monomer mixture comprised 94 wt% of the ε-caprolactam, 2 wt% of the C20 activator, 4 wt% of the CIO catalyst; all based on the total weight of the monomer mixture.

[0045] In Examples 2-6, anionic polymerization of ε-caprolactam was carried out in accordance with Example 1, except that an amount of m-xylene was added to the monomer mixture. In Examples 2-6, the same amounts of the ε-caprolactam, the C20 activator, and the CIO catalyst as used in Example 1 were used and an amount of m-xylene was added such that the resultant monomer mixture comprised a wt% m-xylene based on the total weight of the monomer mixture as shown in Table 1.

[0046] The morphology of the polyamide compositions of Examples 1-6 was studied using scanning electron microscopy (SEM) and the morphology type is shown in Table 1. Table 1 shows that there is no pore structure of Example 1 ; a closed pore structure in Example 2; a mixed pore structure in Example 3 having both open and closed pores; an open pore structure in Example 4; and aggregate structures of spherulitic domains formed in both Examples 5 and 6. Table 1 shows that adding 10 wt% of solvent still results in the desired increase in crystallinity, but is not enough to form interconnected pores through the sample. Increasing the solvent concentration to greater than 10 wt% results in the formation of interconnected, open pores through the polyamide composition. At 40 wt% and greater, larger aggregates of the spherulites are formed and at 50 wt% the interconnected nature of the spherulites is greatly reduced and there was an incomplete polymerization of the cyclic caprolactam monomer.

[0047] FIG. 1 shows an SEM image of the polyamide composition of Example 4. FIG. 1 shows that the composition has a spherulitic morphology, where the individual spherulites have a length scale of about 10 micrometers. FIG. 1 further shows that the multiple spherulites can comprise submicron sized fibrillated domains, see the connected spherulites in the boxed portion of the image.

[0048] The temperature profile versus time of the polymerization of ε-caprolactam of Examples 1 and 4 was measured using a thermocouple present in the solution during polymerization. The temperature profiles of Examples 1 and 4 are shown in FIG. 2 and FIG. 3, respectively. FIG. 2 illustrates that at the polymerization temperature of 150 °C, an exotherm of about 20 °C is produced. As the crystallization temperature of polyamide 6 is at about 150 °C, the polymer produced during the exotherm is primarily in the amorphous phase. Surprisingly, FIG. 3 illustrates that the presence of the solvent is capable of reducing the exotherm such that the reaction temperature is maintained below 150 °C. Without being bound by theory, it is believed that the polymerization forms an increased amount of crystalline polyamide by maintaining the reaction temperature below the crystallization temperature of 150 °C.

[0049] The crystallinity of the polyamide compositions of Examples 1 and 4 are shown in Table 2, where the crystallinity was determined using both DSC on the first heating scan and WAXS. Table 2 clearly shows, from both the DSC data and the WAXS data, that the increased crystallinity that is achieved when the cyclic lactam monomer is polymerized in the presence of a solvent.

Crystallinity (wt%) 40.5 42.02 46.0 - 57.8 39.7

Examples 7-12: Effect of solvent on the polyamide composition

[0050] Examples 7-12 were prepared in accordance with Example 4, except that the solvent was varied. In Examples 7-9, solvents having a boiling point less than the

polymerization temperature were used and in Examples 10-12, solvents having a boiling point greater than or equal to the polymerization temperature were used. Examples 7-9 all showed an open pore structure, whereas Examples 10-12 all resulted in closed pore structure.

[0051] Tables 1 and 2 show that the polyamide compositions prepared in the presence of the solvent all have higher melting temperatures and increased crystallinity, exhibiting a 50 to 60% increase relative to the polyamide composition of Example 1.

Example 13 : Uniaxial compression of polyamide compositions

[0052] Uniaxial compression testing was carried out as described above on the polyamide compositions of Examples 1, 4, 7, and 8. The results are illustrated in FIG. 4 and the modulus and yield stress are shown in Table 2. FIG. 4 shows that the polyamide compositions show yielding and strain hardening prior to progressive buckling that is dictated by the geometry of pores and their packing density. FIG. 4 also shows that the linear modulus of the polyamide compositions prepared in the presence of a solvent is less than the composition of Example 1, prepared in the absence of a solvent, presumably due to the higher porosity of Examples 4, 7, and 8. Example 14: Moisture uptake of polyamide compositions

[0053] Moisture absorption tests of the polyamide compositions of Examples 1 and 4 were performed by putting the compositions in a closed desiccator with 100 mL of water. The closed desiccator had a relative humidity of 65% and a temperature of 70 °C. The compositions were periodically weighed over two weeks to measure the moisture uptake (Wu) by using Equation (IV).

Moisture uptake, Wu = ^χ 100% (IV)

In Equation (IV), W, is the initial (dry) weight of the sample and W _t is the weight of the sample measured at a time, t. The moisture uptake is shown in FIG. 5.

[0054] FIG. 5 shows that the water uptake of Example 1 reaches its maximum moisture uptake (-7%) in 96 hours and reaches a plateau at 144 hours. In contrast to the water uptake of Example 1, FIG. 5 shows a significant reduction in water uptake of Example 4, where Example 4 exhibits a reduction in moisture uptake by more than 40% relative to that of Example 1. The lower moisture absorption in Example 4 can be attributed to their higher crystallinity, which is about 50% higher than that of Example 1.

Example 15: Filtration using a porous polyamide composition

[0055] In order to characterize the open porous morphology of the polyamide compositions, a filtration test was carried out using a dead-end filtration setup. A coffee suspension was filtrated through a 1 mm thick sample of the polyamide composition of Example 4 and the filtrates were characterized by SEM after filtration. SEM images show the accumulation of coffee particles on the surface of the samples as well as in the channels of the interconnected pores.

[0056] Set forth below are various non-limiting embodiments of the present disclosure.

[0057] Embodiment 1 : A polyamide composition, comprising: an anionically polymerized polyamide; wherein the polyamide composition has a crystallinity of greater than or equal to 45 wt% as determined by DSC; and a porosity of greater than or equal to 10 vol% as determined based on a density of the polyamide composition.

[0058] Embodiment 2: The polyamide composition of Embodiment 1, wherein the crystallinity is greater than or equal to 50 wt%.

[0059] Embodiment 3 : The polyamide composition of Embodiment 1, wherein the crystallinity is 45 to 75 wt%. [0060] Embodiment 4: The polyamide composition of any one or more of the preceding embodiments, wherein the porosity is 10 to 50 vol%.

[0061] Embodiment 5 : The polyamide composition of any one or more of the preceding embodiments, wherein the polyamide composition has an open pore structure. For example, wherein the polyamide composition has an interconnected pore structure.

[0062] Embodiment 6: The polyamide composition of any one or more of the preceding embodiments, wherein the polyamide composition has a water uptake of less than or equal to 5 wt%. The water uptake can be the weight percent increase based on the initial water free weight of the polyamide composition.

[0063] Embodiment 7: The polyamide composition of any one or more of the preceding embodiments, wherein the anionically polymerized polyamide has a weight average molecular weight of 2,000 to 100,000 Da as measured by gel permeation

chromatography based on polystyrene standards.

[0064] Embodiment 8: The polyamide composition of any one or more of the preceding embodiments, wherein the anionically polymerized polyamide has a weight average molecular weight of 5,000 to 50,000 Da as measured by gel permeation

chromatography based on polystyrene standards.

[0065] Embodiment 9: The polyamide composition of any one or more of the preceding embodiments, wherein the anionically polymerized polyamide is derived from a cyclic lactam monomer comprising β-propiolactam, γ-butyrolactam, δ-valerolactam, ε- caprolactam, enantholactam, caprylolactam, laurolactam, β,β-dimethylpropiolactam, α,α- dimethylpropiolactam, amylolactam, or a combination comprising at least one of the foregoing.

[0066] Embodiment 10: The polyamide composition of any one or more of the preceding embodiments, wherein the anionically polymerized polyamide is derived from a cyclic lactam monomer comprising ε-caprolactam.

[0067] Embodiment 1 1 : The polyamide composition of any one or more of the preceding embodiments, wherein the polyamide composition further comprises an additive, a second polymer different from the anionically polymerized polyamide, or a combination comprising at least one of the foregoing.

[0068] Embodiment 12: A method of making any one or more of the preceding polyamide compositions, comprising: anionically polymerizing a monomer mixture comprising a cyclic lactam monomer, a solvent in which the cyclic lactam monomer is soluble, a catalyst, and an activator to form the anionically polymerized polyamide.

[0069] Embodiment 13 : The method of Embodiment 12, wherein the cyclic lactam monomer comprises β-propiolactam, γ-butyrolactam, δ-valerolactam, ε-caprolactam, enantholactam, caprylolactam, laurolactam, β,β-dimethylpropiolactam, α,α- dimethylpropiolactam, amylolactam, or a combination comprising at least one of the foregoing.

[0070] Embodiment 14: The method of Embodiment 12, wherein the cyclic lactam monomer comprises ε-caprolactam.

[0071] Embodiment 15: The method of any one or more of Embodiments 12 to 14, wherein greater than or equal to 100 mg of the cyclic lactam monomer can be dissolved in 1 milliliter of solvent at 23 °C.

[0072] Embodiment 16: The method of any one or more of Embodiments 12 to 15, wherein the solvent comprises methyl tert-butyl ether, isopropyl ether, an alkanol, a polyol, an aromatic hydrocarbon, a carboxylate, diphenyl ether, biphenyl, an alkyl-substituted lactam, n-nonane, a-pinene, n-decane, or a combination comprising at least one of the foregoing.

[0073] Embodiment 17: The method of any one or more of Embodiments 12 to 16, wherein the solvent comprises benzene, toluene, meta-xylene, ortho-xylene, para-xylene, or a combination comprising at least one of the foregoing.

[0074] Embodiment 18: The method of any one or more of Embodiments 12 to 17, wherein the anionically polymerizing occurs at a polymerization temperature and wherein the solvent has a boiling point that is less than a polymerization temperature.

[0075] Embodiment 19: The method of any one or more of Embodiments 12 to 18, wherein the anionically polymerizing occurs at a polymerization temperature and wherein the solvent has a boiling point that is less than or equal to the polymerization temperature minus 5 °C.

[0076] Embodiment 20: The method of any one or more of Embodiments 12 to 19, wherein the monomer mixture comprises 2 to 50 wt% of the solvent based on the total weight of the monomer mixture.

[0077] Embodiment 21 : The method of Embodiment 20, wherein the monomer mixture comprises 10 to 40 wt% of the solvent based on the total weight of the monomer mixture. [0078] Embodiment 22: The method of any one or more of Embodiments 12 to 21, wherein the monomer mixture comprises 1 to 6 wt% of the catalyst based on the total weight of the monomer mixture.

[0079] Embodiment 23 : The method of any one or more of Embodiments 12 to 22, wherein the monomer mixture comprises 1 to 4 wt% of the activator based on the total weight of the monomer mixture.

[0080] Embodiment 24: The method of any one or more of Embodiments 12 to 23, wherein the anionically polymerizing comprises reaction injection molding.

[0081] Embodiment 25: The method of any one or more of Embodiments 12 to 24, further comprising forming a powder from the polyamide composition.

[0082] Embodiment 26: A powder comprising the polyamide composition of any one or more of the preceding embodiments.

[0083] Embodiment 27: A method comprising, 3D printing the powder of

Embodiment 26.

[0084] Embodiment 28: A method comprising, extruding a melt comprising a thermoplastic polymer and the powder of Embodiment 26.

[0085] Embodiment 29: An article comprising the polyamide composition of any one or more of Embodiments 1 to 24.

[0086] Embodiment 30: The article of Embodiment 29, wherein the article is a filter.

[0087] While the disclosure has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.

[0088] In general, the disclosure can alternately comprise, consist of, or consist essentially of, any appropriate components herein disclosed. The disclosure can additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any components, materials, ingredients, adjuvants or species used in the prior art compositions or that are otherwise not necessary to the achievement of the function and/or objectives of the present disclosure. [0089] The terms "a" and "an" do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The term "or" means "and/or" unless clearly indicated otherwise by context. The term "combination" is inclusive of blends, mixtures, alloys, reaction products, and the like. Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this invention belongs. Also, a list comprising "at least one or more of the foregoing" means that the list is inclusive of each element individually, as well as combinations of two or more elements of the list, and combinations of at least one element of the list with like elements not named.

[0090] Reference throughout the specification to "an embodiment", "another embodiment", "some embodiments", and so forth, means that a particular element (e.g., feature, structure, step, or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments. The terms "first," "second," and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another.

[0091] In general, the compositions, methods, and articles can alternatively comprise, consist of, or consist essentially of, any ingredients, steps, or components herein disclosed. The compositions, methods, and articles can additionally, or alternatively, be formulated, conducted, or manufactured so as to be devoid, or substantially free, of any ingredients, steps, or components not necessary to the achievement of the function or objectives of the present claims.

[0092] Unless specified to the contrary herein, all test standards are the most recent standard in effect as of the filing date of this application, or, if priority is claimed, the filing date of the earliest priority application in which the test standard appears.

[0093] "About" as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with

measurement of the particular quantity (e.g., the limitations of the measurement system). For example, "about" can mean within one or more standard deviations. "About" is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. [0094] The endpoints of all ranges directed to the same component or property are inclusive of the endpoints, are independently combinable, and include all intermediate points and ranges. For example, ranges of "up to 25 wt%, or 5 to 20 wt%" is inclusive of the endpoints and all intermediate values of the ranges of "5 to 25 wt%," such as 10 to 23 wt%, etc.

[0095] All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.

[0096] While particular embodiments have been described, alternatives,

modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.