Field

[0001] The present disclosure generally relates to porous polymeric membranes.

Summary

[0002] In a first aspect, a porous polymeric membrane is provided. The porous polymeric membrane includes a) a first outer surface having a patterned array of first pores having irregularly shaped perimeters; b) an opposing second outer surface having a plurality of second pores; and c) a polymeric matrix extending between the first outer surface and the second outer surface. The polymeric matrix defines a plurality of through holes that extend between the first pores and the second pores.

[0003] In a second aspect, a method is provided. The method includes applying a casting solution to a tooling structure having a major surface and a patterned array of protrusions extending orthogonally therefrom, to form a layer of the casting solution. The casting solution includes a polymer component and a solvent system. The method further includes contacting the layer of the casting solution with a nonsolvent fluid to solidify the polymer component and form a porous polymeric membrane; and removing the porous polymeric membrane from the tooling structure, thereby providing a porous polymeric membrane. The porous polymeric membrane includes 1) a first outer surface having a patterned array of first pores having irregularly shaped perimeters that do not correspond to a shape of a top of the plurality of protrusions; 2) an opposing second outer surface having a plurality of second pores; and 3) a polymeric matrix extending between the first outer surface and the second outer surface. The polymeric matrix defines a plurality of through holes that extend between the first pores and the second pores.

[0004] The above summary of the present disclosure is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The description that follows more particularly exemplifies illustrative embodiments. In several places throughout the application, guidance is provided through lists of examples, which examples may be used in various combinations. In each instance, the recited list serves only as a representative group and should not be interpreted as an exclusive list. Brief Description of the Drawings

[0005] FIG. 1 is a schematic perspective view of an exemplary porous polymeric membrane according to the present disclosure.

[0006] FIG. 2A is a scanning electronic microscopy (SEM) image of a portion of a first surface of an exemplary infiltrated three-dimensional article according to the present disclosure.

[0007] FIG. 2B is an SEM image of a portion of a second surface of the exemplary infiltrated three-dimensional article of FIG. 2A.

[0008] FIG. 3 is a flow chart of an exemplary method according to the present disclosure

[0009] FIG. 4 is a schematic cross-sectional schematic of a porous polymeric membrane formed on a tooling structure in which pores on a surface of the membrane do not correspond to a shape of a top of the tooling structure protrusions.

[0010] FIG. 5 is a schematic cross-sectional schematic of a tooling structure having protrusions with a stem and a head for use in methods according to the present disclosure.

[0011] While the above-identified figures set forth various embodiments of the disclosure, other embodiments are also contemplated, as noted in the description. In all cases, this disclosure presents the invention by way of representation and not limitation. The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number.

Detailed Description

[0012] Glossary

[0013] The term “diameter” refers to the longest distance measurable along a cross-section of an element (e.g., pore, through hole, protrusion head, protrusion stem). An average diameter is the average of 25 or more measured diameters.

[0014] The term “microporous” refers to having multiple pores that have an average dimension (in some cases, diameter) of up to 500 micrometers. At least some of the multiple pores should have a dimension on the order of or larger than the wavelength of visible light. For example, at least some of the pores should have a dimension (in some cases, diameter) of at least 400 nanometers. Pore size is measured by measuring bubble point according to ASTM F-316-80. [0015] The thickness of a membrane should be understood to be its smallest dimension. It is generally referred to as the “z” dimension and refers to the distance between the major surfaces of the membrane.

[0016] The term “upstanding” with regard to the tooling protrusions refers to posts that protrude from a major surface and includes posts that stand perpendicular to the major surface and posts that are at an angle to the major surface other than 90 degrees.

[0017] As used herein, “aliphatic group” means a saturated or unsaturated linear, branched, or cyclic hydrocarbon group. This term is used to encompass alkyl, alkenyl, and alkynyl groups, for example. “Alkyl” means a linear or branched, cyclic or acyclic, saturated monovalent hydrocarbon having from one to thirty-two carbon atoms, e.g., methyl, ethyl, 1 -propyl, 2-propyl, pentyl, and the like. “Alkylene” means a linear saturated divalent hydrocarbon having from one to twelve carbon atoms or a branched saturated divalent hydrocarbon radical having from three to twelve carbon atoms, e.g., methylene, ethylene, propylene, 2-methylpropylene, pentylene, hexylene, and the like. Each of “alkenyl” and “ene” refers to a monovalent linear or branched unsaturated aliphatic group with one or more carbon-carbon double bonds, e.g., vinyl.

[0018] As used herein, the term “(meth)acrylate” is a shorthand reference to acrylate, methacrylate, or combinations thereof, “(meth)acrylic” is a shorthand reference to acrylic, methacrylic, or combinations thereof, and “(meth)acryl” is a shorthand reference to acryl and methacryl groups. “Acryl” refers to derivatives of acrylic acid, such as acrylates, methacrylates, acrylamides, and methacrylamides. By “(meth)acryl” is meant a monomer or oligomer having at least one acryl or methacryl groups, and linked by an aliphatic segment if containing two or more groups. As used herein, “(meth)acrylate-functional compounds” are compounds that include, among other things, a (meth)acrylate moiety.

[0019] As used herein, the term or prefix “micro” refers to at least one dimension defining a structure or shape being in a range from 1 micrometer to 1 millimeter. For example, a microstructure may have a height or a width that is in a range from 1 micrometer to 1 millimeter.

[0020] As used herein, a “resin” contains all polymerizable components (monomers, oligomers and/or polymers) being present in a hardenable composition. The resin may contain only one polymerizable component compound or a mixture of different polymerizable compounds.

[0021] As used herein, the term “glass transition temperature” (T _g ), of a polymer refers to the transition of a polymer from a glassy state to a rubbery state and can be measured using Differential Scanning Calorimetry (DSC), such as at a heating rate of 10 °C per minute in a nitrogen stream. A suitable DSC method and mode of analysis is as described in Matsumoto, A. et. al., J. Polym. Sci. A., Polym. Chem. 1993, 31, 2531-2539.

[0022] As used herein, “thermoplastic” refers to a polymer that flows when heated sufficiently above its glass transition point and become solid when cooled.

[0023] As used herein, “thermoset” refers to a polymer that permanently sets upon curing and does not flow upon subsequent heating. Thermoset polymers are typically crosslinked polymers.

[0024] The words “preferred” and “preferably” refer to embodiments of the disclosure that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the disclosure.

[0025] In this application, terms such as “a”, “an”, and “the” are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terms “a”, “an”, and “the” are used interchangeably with the term “at least one.” The phrases “at least one of’ and “comprises at least one of’ followed by a list refers to any one of the items in the list and any combination of two or more items in the list.

[0026] As used herein, the term “or” is generally employed in its usual sense including “and/or” unless the content clearly dictates otherwise. The term “and/or” means one or all of the listed elements or a combination of any two or more of the listed elements.

[0027] Also herein, all numbers are assumed to be modified by the term “about” and preferably by the term “exactly.” As used herein in connection with a measured quantity, the term “about” refers to that variation in the measured quantity as would be expected by the skilled artisan making the measurement and exercising a level of care commensurate with the objective of the measurement and the precision of the measuring equipment used. Also herein, the recitations of numerical ranges by endpoints include all numbers subsumed within that range as well as the endpoints (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

[0028] As used herein as a modifier to a property or attribute, the term “generally”, unless otherwise specifically defined, means that the property or attribute would be readily recognizable by a person of ordinary skill but without requiring absolute precision or a perfect match (e.g., within +/- 20 % for quantifiable properties). The term “substantially”, unless otherwise specifically defined, means to a high degree of approximation (e.g., within +/- 10% for quantifiable properties) but again without requiring absolute precision or a perfect match. Terms such as same, equal, uniform, constant, strictly, and the like, are understood to be within the usual tolerances or measuring error applicable to the particular circumstance rather than requiring absolute precision or a perfect match.

[0029] In membrane technology, it is preferred to combine high selectivity with high flux. In the case of filtration membranes (e.g., in biopharma processing) this translates into the challenge to generate membranes with uniform pores with a high pore number density on large scale with simple techniques. Block copolymers have been widely studied in this regard due to their ability to self-assemble into regular structures, which can lead to high pore densities. However, block copolymer methodologies tend to suffer from few significant limitations, including a limited set of chemistries and a high cost for the block copolymers.

[0030] It has been discovered that a “cast and precipitate” (CAP) process, which combines micro- or nano-replication and membrane formation in one step, can be used to form porous polymeric membranes having both high selectivity and high flux. Here, a polymer solution cast on to a tooling structure that includes upstanding projections is subjected to nonsolvent induced phase separation (NIPS) while in contact with the tooling surface. As the polymer precipitates, the thickness shrinkage associated with the process is enough to pierce through the post in order to form through holes. The lateral shrinkage allows the polymer film to be easily released from the tool. Unlike other microfabrication approaches that require post-treatment such as etching or heat treatment to achieve through holes, CAP allows etch-free single step continuous fabrication. CAP processes are generally compatible with any ternary pairs of polymer-solvent-nonsolvent, which can be a significant advantage from each of a commercialization and scale-up perspective.

[0031] It has been unexpectedly discovered that a suitable tooling surface can include protrusions that have both a head and a stem, wherein the formed porous polymeric membrane can be removed from the protrusions without walls of the through holes being destroyed by the head, as discussed in greater detail below.

Porous Polymeric Membranes

[0032] In a first aspect, a porous polymeric membrane is provided. The porous polymeric membrane comprises:

[0033] a) a first outer surface having a patterned array of first pores having irregularly shaped perimeters;

[0034] b) an opposing second outer surface having a plurality of second pores; and

[0035] c) a polymeric matrix extending between the first outer surface and the second outer surface, the polymeric matrix defining a plurality of through holes that extend between the first pores and the second pores. [0036] Referring to FIG. 1, a porous polymeric membrane 100 comprises a first outer surface 110 having a patterned array of first pores 120 having irregularly shaped perimeters; an opposing second outer surface 130 having a plurality of second pores 140; and a polymeric matrix 150 extending between the first outer surface 110 and the second outer surface 130. The polymeric matrix 150 defines a plurality of through holes 160 that extend between the first pores 120 and the second pores 140, the through holes being bound by walls 170. In this case, the patterned array comprises a grid of pores that are spaced (approximately) equally from adjacent pores, located in rows and columns. Any deliberate pattern useful for filtration is suitable for the array. In the embodiment illustrated in FIG. 1, the plurality of second pores 140 have regularly shaped perimeters, e.g., circular perimeters. Further, the first pores 120 have a size (e.g., diameter) that is smaller than the size (e.g., diameter) of the second pores 140 and generally include a group of four small pores instead of one larger pore.

[0037] The term “irregular” with respect to the perimeter of a pore refers to the perimeter having a shape that is uneven or unbalanced. Often, the perimeter of an irregularly shaped pore is asymmetric due to the lack of evenness or balance in an otherwise symmetric shape (e.g., equilateral triangle, circle, square, etc.). For instance, an irregular circular pore has a perimeter that is not a perfect circle, see, e.g., the pore indicated by reference number 224 in FIG. 2A. For a plurality of pores to meet the definition of having irregularly shaped perimeters, it is not necessary for every single pore to have an irregular shape, but rather 25% or greater of the pores in the plurality of pores have irregularly shaped perimeters, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90% or greater of the pores in the plurality of pores have irregularly shaped perimeters. Pore shape and/or size can be determined using any commonly known microscopic methods. For example, optical microscopy or scanning electron microscopy can be used in combination with any image analysis software. For example, software commercially available as free ware under the trade designation “IMAGE J” from NIH, Bethesda, MD.

[0038] As mentioned above, it has been unexpectedly discovered that a tooling surface used in cast and precipitate processes can include protrusions that have both a head and a stem and that the formed porous polymeric membrane can be removed from the protrusions without walls of the through holes being destroyed by the heads of the protrusions. In some cases, removal of the porous polymeric membrane does form a tear in the perimeter of at least some of the pores on the first outer surface or the second outer surface as the membrane passes over the heads. For instance, FIG. 2A shows a tear 222 in the perimeter of a pore 220 on a surface 210 of a porous polymeric membrane 200. An advantage of employing protrusions that have both a head and a stem is that the head can assist in securing the layer of casting solution in place on the tooling structure during the precipitation process to form the porous polymeric membrane (e.g., if submerged in a nonsolvent fluid), thus decreasing the chance that the membrane will separate from the tooling structure undesirably early.

[0039] In certain embodiments, the first pores and the second pores have perimeters that are different from each other in at least one of shape (e.g., regular versus irregular) or size. FIGS. 2A- 2B provide an example of first pores 220 and second pores 240 that have different pore sizes. More particularly, FIG. 2A is a scanning electron microscope (SEM) image of a portion of a first surface 210 of a porous polymeric membrane 200 formed of polyethersulfone including a plurality of first pores 220 having irregularly shaped perimeters. Through holes 260 and the polymeric matrix 250 are visible through at least some of the first pores 220. FIG. 2B is an SEM image of a portion of a second surface 230 of the polymeric membrane 200 including a plurality of second pores 240. The plurality of second pores 240 have both a different shape (irregular ovals) and a different size (smaller) than the plurality of first pores 220 in FIG. 2A. This was achieved by applying a layer of casting solution on a tooling structure that had a thickness greater than the height of the protrusions. The protrusions had a shape of a head on a stem, in particular a T-shape, and outer edges of the head tended to form the second pores 240. For instance, the four second pores 240 indicated in FIG. 2B each correspond to a location of four edges of the head (e.g., the top of the “T”) of one stem. In this embodiment, the second pores 240 have an average area that is less than half of an average area of the first pores 220. In alternate embodiments, optionally the first pores have an average area that is less than half of an average area of the second pores.

[0040] Further, in the embodiment shown in FIGS. 2A-2B, the polymeric matrix 250 that is located adjacent to the through holes 260 and extends between the first surface 210 and the second surface 230 is porous. In alternate embodiments, the polymeric matrix located adjacent to the through holes is nonporous. Often, the distance between adjacent through holes affects whether or not the polymeric matrix is porous, with small distances (e.g., less than 10 micrometers) being more likely to have nonporous polymeric matrices.

[0041] In certain embodiments, first pores and second pores may have similar pore sizes but different pore shapes. For instance, a plurality of first pores can have irregularly shaped perimeters (e.g., irregular circles), whereas a plurality of second pores can have a different shape (e.g., regular circles) than the plurality of first pores. This can be achieved by applying a layer of casting solution on a tooling structure that has a thickness smaller than the height of the protrusions. The protrusions may have a shape of a head on a stem, and removal of the porous polymeric membrane from the tooling structure tends to deform the perimeters of at least some of the first pores to result in them having irregularly shaped perimeters.

[0042] Often, at least one of the through holes, first pores, or second pores of a porous polymeric membrane have an average diameter of 1 micrometer or greater, 2 micrometers or greater, 3 micrometers, 5 micrometers, 7 micrometers, 10 micrometers, 12 micrometers, 15 micrometers, 20 micrometers, 25 micrometers, 30 micrometers, 35 micrometers, 40 micrometers, 45 micrometers, 50 micrometers, 60 micrometers, 70 micrometers, 80 micrometers, 90 micrometers, 100 micrometers, 110 micrometers, 120 micrometers, 120 micrometers, 140 micrometers, or 150 micrometers or greater; and 500 micrometers or less, 475 micrometers, 450 micrometers, 425 micrometers, 400 micrometers, 375 micrometers, 350 micrometers, 325 micrometers, 300 micrometers, 275 micrometers, 250 micrometers, 225 micrometers, 200 micrometers, 190 micrometers, 180 micrometers, 170 micrometers, or 160 micrometers or less. In many embodiments, the through holes have an average diameter of 1 micrometer to 500 micrometers or 10 micrometers to 300 micrometers. For convenience, the average diameter of the through holes is typically determined at either the first outer surface or the second outer surface of the porous polymeric membrane. Depending on how the porous polymeric membrane was made, the diameter of the through holes may vary between the first outer surface and the second outer surface through the thickness of the porous polymeric membrane, e.g., when a tooling structure has protrusions with cross-sections that vary along the height of the protrusions. In select embodiments, the through holes are isoporous. Isoporous through holes may be provided by employing a tooling structure that has protrusions of the same size.

[0043] The porous polymeric membrane has a thickness between the first outer surface and the second outer surface of 1 micrometer or greater, 2 micrometers, 5 micrometers, 7 micrometers, 10 micrometers, 12 micrometers, 15 micrometers, 20 micrometers, 25 micrometers, 30 micrometers, 35 micrometers, 40 micrometers, 45 micrometers, 50 micrometers, 60 micrometers, 70 micrometers, 80 micrometers, 90 micrometers, 100 micrometers, 125 micrometers, 150 micrometers, 175 micrometers, 200 micrometers, 225 micrometers, 250 micrometers, 275 micrometers, 300 micrometers, 325 micrometers, 350 micrometers, 400 micrometers, 450 micrometers, or 500 micrometers or greater; and 5 millimeters (mm) or less, 4.5 mm, 4 mm, 3.5 mm, 3 mm, 2.5 mm, 2 mm, 1.5 mm, 1 mm, 950 micrometers, 900 micrometers, 850 micrometers, 800 micrometers, 750 micrometers, 700 micrometers, 650 micrometers, 600 micrometers, 550 micrometers, 500 micrometers, 450 micrometers, 400 micrometers, 350 micrometers, 300 micrometers, 250 micrometers, or 200 micrometers or less. [0044] The through holes/first pores have a density on the first outer surface imparted by the density of protrusions on a major surface of the tooling structure employed to prepare the porous polymeric membrane. In some embodiments, the density of the first pores and through holes on the first outer surface is 50 per square centimeter (cm ² ) or greater, 75 per cm ² , 100 per cm ² , 125 per cm ² , 150 per cm ² , 175 per cm ² , 200 per cm ² , 225 per cm ² , or 250 per cm ² or greater. An upper maximum of density of through holes and first pores is limited by the diameters of the heads of the protrusions on the tooling structure. More particularly, if the heads of the protrusions get too close together (or touch) it will be difficult to successfully remove the porous polymeric matrix from the tooling structure with intact through holes and/or pores.

[0045] The polymeric matrix comprises polyethersulfone, polypropylene, polysulfone, polyacrylonitrile, a cellulose ester, a polyimide, a polyamide, poly(vinylidene fluoride), or poly (tetrafluoroethylene). In select embodiments, the polymeric matrix comprises polyethersulfone or amorphous nylon. Suitable commercially available polyethersulfones are from BASF (Wyandotte, MI) under the trade designation “ULTRASON E6020” and “ULTRASON E7020”. A suitable commercially available amorphous nylon is from Evonik Industries (Essen, Germany) under the trade designation “TROGAMID CX9704”.

Methods

[0046] In a second aspect, the present disclosure provides a method comprising:

[0047] applying a casting solution to a tooling structure comprising a major surface and a patterned array of protrusions extending orthogonally therefrom, to form a layer of the casting solution, the casting solution comprising a polymer component and a solvent system;

[0048] contacting the layer of the casting solution with a nonsolvent fluid to solidify the polymer component and form a porous polymeric membrane; and

[0049] removing the porous polymeric membrane from the tooling structure, thereby providing a porous polymeric membrane comprising:

[0050] 1) a first outer surface having a patterned array of first pores having irregularly shaped perimeters that do not correspond to a shape of a top of the plurality of protrusions;

[0051] 2) an opposing second outer surface having a plurality of second pores; and

[0052] 3) a polymeric matrix extending between the first outer surface and the second outer surface, the polymeric matrix defining a plurality of through holes that extend between the first pores and the second pores. [0053] Referring to FIG. 3, a flow chart is provided of an exemplary method according to the present disclosure. The method comprises Step 310 to apply a casting solution to a tooling structure comprising a major surface and a patterned array of protrusions extending orthogonally therefrom, to form a layer of the casting solution, the casting solution comprising a polymer component and a solvent system. In certain embodiments, the layer of the casting solution has a thickness smaller than the height of the protrusions while in other embodiments, the layer of the casting solution has a thickness equal to the height of the protrusions. Typically employing a casting solution layer thickness of equal or smaller height than the protrusion height results in a precipitated membrane having a thickness smaller than the protrusion height due to shrinkage during the precipitation process. In certain embodiments, the layer of the casting solution has a thickness larger than the height of the protrusions. Advantageously, by employing a casting solution layer having a thickness larger than the height of the protrusions can result in a porous polymeric membrane having pores that are smaller than the size of the top of the protrusions (e.g., the size of heads of the protrusions), such as shown in FIG. 2B and described above. The casting solution may be applied to the tooling structure by any suitable means, for instance and without limitation, roller coating, flow coating, dip coating, spin coating, spray coating, knife coating, or die coating.

[0054] Typically, the casting solution comprises a solids content of 5 percent by weight (wt.%) or greater, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, or 15 wt.% or greater; and 50 wt.% or less, 47 wt.%, 45 wt.%, 42 wt.%, 40 wt.%, 37 wt.%, 35 wt.%, 32 wt.%, 30 wt.%, 29 wt.%, 28 wt.%, 27 wt.%, 26 wt.%, 25 wt.%, 24 wt.%, 23 wt.%, 22 wt.%, 21 wt.%, 20 wt.%, 19 wt.%, 18 wt.%, 17 wt.%, 16 wt.%, 15 wt.%, 14 wt.%, 13 wt.%, or 12 wt.% or less. At a solids content of less than 5 wt.%, the resulting porous polymeric membrane tends to shrink to such an extent that the through holes are substantially larger than the size of the protrusions of the tooling structure. At a solids content of greater than 50 wt.%, tends to result in too high of a viscosity to successfully cast on the tooling structure.

[0055] Any polymer-solvent-nonsolvent combination that forms a polymeric membrane in a cast and precipitate process is suitable for use in methods according to the present disclosure. For instance, the polymer component optionally comprises polyethersulfone, polypropylene, polysulfone, polyacrylonitrile, a cellulose ester, a polyimide, a polyamide (e.g., an amorphous nylon), poly(vinylidene fluoride), or poly(tetrafluoroethylene). In select embodiments, the polymer component comprises polyethersulfone or amorphous nylon, the solvent system comprises dimethyl sulfoxide, and the nonsolvent fluid comprises water. [0056] Some examples of solvents for the casting solution may include water, dimethyl formamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidinone, tetramethylurea, acetone, methyl ethyl ketone, methyl acetate, ethylacetate and other alkyl acetates, dimethylsulfoxide and combinations thereof. The solvent may be oligomeric or polymeric in nature forming a polymer blend with the polymer component. The solvent may comprise more than one solvent, a blend of solvents, or a nonsolvent for phase inversion. A nonsolvent is a material that is miscible in the solvent of the dope formulation, but which, by itself, is insoluble with the polymer or may cause coagulation of the polymer. The nonsolvent may be added to a solvent to influence the rate of a phase inversion or aid in the development of a microstructure.

[0057] The selection of a solvent for a casting solution to provide a stable homogeneous solution for casting in the formation of membranes involves basic principles of polymer solubility.

Polymer solvents may be categorized as good solvents, nonsolvents, and poor solvents. Good solvents are those in which the interactions (forces) between the polymer molecules and solvent molecules are greater than the forces of attraction between one polymer molecule and another polymer molecule. The reverse is true for nonsolvents. Poor solvents are those in which the interactions between the polymer and solvent are equal to the forces of attraction between one polymer and another polymer molecule. Good solvents dissolve substantial amounts of polymer and may be miscible with the polymer at concentrations of at least 5 weight percent, whereas poor solvents may or may not be miscible, depending upon the molecular weight of the polymer and the type of solvent. For example, when polyethersulfone is the polymer, examples of good solvents for polyethersulfone include dimethylacetamide, dioxane, dimethylsulfoxide, N-methyl-2- pyrrolidinone, chloroform, tetramethylurea, formic acid, and tetrachloroethane. Another method for evaluating solvents for polymer solubility includes Hildebrand solubility parameters. These parameters refer to a solubility parameter represented by the square root of the cohesive energy density of a material, having units of (pressure) ^{1 2} , and being equal to (AH-RT) ^1/2 V ^1/2 where AH is the molar vaporization enthalpy of the material, R is the universal gas constant, T is the absolute temperature, and V is the molar volume of the solvent. Hildebrand solubility parameters are tabulated for solvents in: Barton, A. F. M., “Handbook of Solubility and Other Cohesion Parameters”, 2nd Ed., CRC Press, Boca Raton, FL. (1991); for monomers and representative polymers in “Polymer Handbook”, 4th Ed., J. Brandrup & E. H. Immergut, Eds. John Wiley, NY, pp. VII 675-714 (1999); and for many commercially available polymers in Barton, A. F. M., “Handbook of Polymer-Liquid Interaction Parameters and Solubility Parameters”, CRC Press, Boca Raton, FL. (1990). [0058] The method also comprises Step 320 to contact the layer of the casting solution with a nonsolvent fluid to solidify the polymer component and form a porous polymeric membrane. Suitable nonsolvents can be determined as described above in detail. Additionally, the method comprises Step 330 to remove the porous polymeric membrane from the tooling structure (e.g., by peeling off the tooling structure), thereby providing a porous polymeric membrane.

[0059] The porous polymeric membrane comprises 1) a first outer surface having a patterned array of first pores having irregularly shaped perimeters that do not correspond to a shape of a top of the plurality of protrusions; 2) an opposing second outer surface having a plurality of second pores; and 3) a polymeric matrix extending between the first outer surface and the second outer surface. Further, the polymeric matrix defines a plurality of through holes that extend between the first pores and the second pores. The porous polymeric membrane may be according to any embodiment of the first aspect described in detail above.

[0060] Referring to FIG. 4, a schematic cross-sectional schematic illustration is provided of a porous polymeric membrane 400 formed on a tooling structure 490 in which pores on a first outer surface 410 of the membrane 400 do not correspond to a shape of a top 484 of the tooling structure 490 protrusions 480. Rather, the pores correspond to a shape of a stem 482 of the protrusions 480 and the stem 482 has a different shape than the top (e.g., head) 484. The pores in the illustration of FIG. 4 are filled with the protrusions 480 because the porous polymeric membrane 400 has yet to be removed from the tooling structure 490. A second, opposing outer surface 430 of the membrane 400 is located adjacent to the tooling structure 490.

[0061] Often, the protrusions of a tooling structure comprise a stem (e.g., post) and a head, in which the stem extends generally orthogonally from the major surface of the tooling structure and the head is disposed distal to the major surface of the tooling structure. In embodiments where the protrusions comprise a head on a stem, preferably the first pores of the resulting porous polymeric membrane have an average pore size that is smaller than the head of the protrusions.

[0062] In certain embodiments, the protrusions comprise a T-shape, a nail shape, a mushroom shape (e.g., with a circular or oval head enlarged with respect to the stem), or combinations thereof. For example, as illustrated in FIG. 5, the tooling structure 510 may comprise a backing 514 having a first side 516 and a second side 518 opposite the first side 516. Upstanding stems 520 extend from the first side 516 of the backing 514, such that each stem 520 has a proximal end 522 contiguous with the first side 516 of the backing 514 and a distal end (i.e., head) 524 opposite the proximal end 522. The distal ends 24 of the posts 20 need not all be the same shape and/or orientation within a given tooling structure 510. Although the stems 520 in FIG. 5 are arranged perpendicular to the backing 514, the stems 520 could also be slanted at an angle to the backing 514, e.g., an angle between 45 and 90 degrees, between 60 and 90 degrees, or between 75 and 90 degrees.

[0063] The material composition of the tooling structure includes an organic polymer. The organic polymer is not particularly limiting and comprise either a thermoplastic polymer or a thermoset polymer. Exemplary thermoplastic polymers include polyolefin homopolymers such as polyethylene, polypropylene, and polybutylene, copolymers of ethylene, propylene and/or butylenes, and copolymers and blends thereof; copolymers containing ethylene such as ethylene vinyl acetate and ethylene acrylic acid; polyesters such as polyethylene terephthalate), polyethylene butyrate and polyethylene napthalate; polyamides such as poly(hexamethylene adipamide); polyurethanes; polycarbonates; poly(vinyl alcohol); ketones such as polyetheretherketone; polyphenylene sulfide; and mixtures thereof. In some embodiments, the thermoplastic is a polyolefin (e.g., polyethylene, polypropylene, polybutylene, ethylene copolymers, propylene copolymers, butylene copolymers, and copolymers and blends of these materials), a polyester and combinations thereof. In select embodiments, the tooling structure is formed of polypropylene or a crosslinked (meth)acrylate polymer.

[0064] Any number of current methods can be used to make the tooling structure, such as by feeding a molten resin containing the organic polymer and any additional ingredients between a nip formed by two rolls or a nip formed between a die face and roll surface, with at least one of the rolls having cavities. The cavities may be the inverse shape of a protrusion having a stem and a head or may be the inverse shape of a post without a head. Pressure provided by the nip forces the resin into the cavities. In some embodiments, a vacuum can be used to evacuate the cavities for easier filling. The nip is typically sufficiently wide such that a continuous backing is formed over the cavities. The mold surface and cavities can optionally be air or water cooled before stripping the integrally formed backing and posts from the mold, such as by a stripper roll. If the protrusions formed upon exiting the cavities do not have heads, heads can be subsequently formed by a capping method as described in U.S. Pat. No. 5,077,870 (Melbye et al.). Typically, the capping method includes deforming the tip portions of the protrusions using heat and/or pressure. The heat and pressure, if both are used, could be applied sequentially or simultaneously.

[0065] Other suitable tool rolls include those formed from a series of plates defining a plurality of protrusion-forming cavities about its periphery such as those described, for example, in U.S. Pat. No. 4,775,310 (Fischer). Cavities may be formed in the plates by drilling or photoresist technology, for example. Still other suitable tool rolls may include wire-wrapped rolls, which are disclosed along with their method of manufacturing, for example, in U.S. Pat. No. 6,190,594 (Gorman et al.). Another exemplary method for forming a thermoplastic backing with protrusions includes using a flexible mold belt defining an array of post-shaped cavities as described in U.S. Pat. No. 7,214,334 (Jens et al.). Yet other useful methods for forming a thermoplastic backing with protrusions can be found in U.S. Pat. Nos. 6,287,665 (Hammer); 7,198,743 (Tuma); and 6,627,133 (Tuma).

[0066] Another useful method for forming protrusions with heads on a thermoplastic backing is profile extrusion described, for example, in U.S. Pat. No. 4,894,060 (Nestegard). Typically, in this method a thermoplastic flow stream is passed through a patterned die lip (e.g., cut by electron discharge machining) to form a web having ridges that extend in the machine direction, slicing the ridges in a direction perpendicular to the machine direction, and stretching the web in the machine direction to form separated projections. The ridges may form protrusion precursors and exhibit the cross-sectional shape of stems with heads to be formed. The thermoplastic backing of the tooling structure made by this method has stretch-induced molecular orientation.

[0067] Illustrative examples of suitable thermoset polymers for the tooling structure include for instance and without limitation, crosslinked acrylate such as mono- or multi-functional acrylates or acrylated epoxies, acrylated polyesters, and acrylated urethanes blended with mono- and multifunctional monomers are typically preferred. These polymers are typically preferred for one or more of the following reasons: high thermal stability, environmental stability, and clarity, plus excellent release from a tooling or mold.

[0068] Other illustrative examples of materials suitable for forming the tooling structure are reactive resin systems capable of being crosslinked by a free radical polymerization mechanism by exposure to actinic radiation, for example, electron beam, ultraviolet light, or visible light. Additionally, these materials may be polymerized by thermal means with the addition of a thermal initiator such as benzoyl peroxide. Radiation-initiated cationically polymerizable resins also may be used. Reactive resins suitable for forming the tooling structure may be blends of photoinitiator and at least one compound bearing an acrylate group. Preferably the resin blend contains a monofunctional, a difunctional, or a polyfunctional compound to ensure formation of a crosslinked polymeric network upon irradiation. Illustrative examples of resins that are capable of being polymerized by a free radical mechanism that can be used herein include acrylic-based resins derived from epoxies, polyesters, polyethers, and urethanes, ethylenically unsaturated compounds, aminoplast derivatives having at least one pendant acrylate group, isocyanate derivatives having at least one pendant acrylate group, epoxy resins other than acrylated epoxies, and mixtures and combinations thereof. The term acrylate is used here to encompass both acrylates and methacrylates. U.S. Pat. 4,576,850 (Martens) discloses examples of crosslinked resins that may be used in tooling structures of the present disclosure. Further, polymerizable resins of the type disclosed in, for example, U.S. Patent 7,61 1,251 (Thakkar) may be used in tooling structures of the present disclosure.

[0069] Ethylenically unsaturated resins include both monomeric and polymeric compounds that contain atoms of carbon, hydrogen and oxygen, and optionally nitrogen, sulfur, and the halogens may be used herein. Oxygen or nitrogen atoms, or both, are generally present in ether, ester, urethane, amide, and urea groups. Ethylenically unsaturated compounds preferably have a molecular weight of less than about 4,000 and preferably are esters made from the reaction of compounds containing aliphatic monohydroxy groups, aliphatic polyhydroxy groups, and unsaturated carboxylic acids, such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, iso-crotonic acid, maleic acid, and the like. Such materials are typically readily available commercially and can be readily cross linked.

[0070] Some illustrative examples of compounds having an acrylic or methacrylic group that are suitable for use in the tooling structure are listed below:

[0071] (1) Monofunctional compounds:

[0072] ethylacrylate, n-butylacrylate, isobutylacrylate, 2-ethylhexylacrylate, n-hexylacrylate, n- octylacrylate, isooctyl acrylate, bornyl acrylate, tetrahydrofurfuryl acrylate, 2-phenoxyethyl acrylate, and N,N-dimethylacrylamide;

[0073] (2) Difunctional compounds:

[0074] 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, neopentylglycol diacrylate, ethylene glycol diacrylate, triethyleneglycol diacrylate, tetraethylene glycol diacrylate, and diethylene glycol diacrylate; and

[0075] (3) Polyfunctional compounds:

[0076] trimethylolpropane triacrylate, glyceroltriacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, and tris(2-acryloyloxyethyl)isocyanurate. Monofunctional compounds typically tend to provide faster penetration of the material of the overlay fdm and difunctional and polyfunctional compounds typically tend to provide more crosslinked, stronger bonds at the interface between the cube comer elements and overlay fdm. Some representative examples of other ethylenically unsaturated compounds and resins include styrene, divinylbenzene, vinyl toluene, N-vinyl formamide, N-vinyl pyrrolidone, N-vinyl caprolactam, monoallyl, polyallyl, and polymethallyl esters such as diallyl phthalate and diallyl adipate, and amides of carboxylic acids such as N,N-diallyladipamide. [0077] Illustrative examples of photopolymerization initiators that can be blended with acrylic compounds in tooling structures of the present disclosure include the following: benzil, methyl o- benzoate, benzoin, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, etc., benzophenone/tertiary amine, acetophenones such as 2,2-diethoxyacetophenone, benzyl methyl ketal, 1 -hydroxy cyclohexylphenyl ketone, 2- hydroxy-2-methyl-l-phenylpropan-l-one, l-(4- isopropylphenyl)-2 -hydroxy-2 -methylpropan- 1 -one, 2-benzyl-2-N,N-dimethylamino- 1 -(4- morpholinophenyl)-l-butanone, 2, 4, 6-trimethylbenzoyl -diphenylphosphine oxide, 2-methyl-l- 4(methylthio), phenyl -2 -morpholino- 1 -propanone, bis(2,6-dimethoxybenzoyl)(2,4,4- trimethylpentyl)phosphine oxide, etc. The compounds may be used individually or in combination.

[0078] Cationically polymerizable materials including but are not limited to materials containing epoxy and vinyl ether functional groups may be used herein. These systems are photoinitiated by onium salt initiators, such as triarylsulfonium, and diaryliodonium salts.

[0079] In some embodiments, the thickness of the backing of the tooling structure is up to about 400, 250, 150, 100, 75 or 50 micrometers, such as 30 to 225 micrometers, 50 to 200 micrometers, or 100 to 150 micrometers. In some embodiments, the stems have a maximum height (above the backing) of up to 5 mm, 3 mm, 1.5 mm, 1 mm, 500 micrometers, 400 micrometers, 300 micrometers, 200 micrometers, or 100 micrometers, and, in some embodiments a minimum height of at least about 5 micrometers, 10 micrometers, 25 micrometers, 50 micrometers, 75 micrometers, 100 micrometers, 125 micrometers, 150 micrometers, 175 micrometers, or 200 micrometers. In some embodiments, the stems have an aspect ratio (that is, a ratio of height to width at the widest point) of at least about 2: 1, 3: 1, or 4: 1.

[0080] The protrusions (measured at the widest point of the stems) may have an average diameter of 1 micrometer or greater, 2 micrometers or greater, 3 micrometers, 5 micrometers, 7 micrometers, 10 micrometers, 12 micrometers, 15 micrometers, 20 micrometers, 25 micrometers, 30 micrometers, 35 micrometers, 40 micrometers, 45 micrometers, 50 micrometers, 60 micrometers, 70 micrometers, 80 micrometers, 90 micrometers, 100 micrometers, 110 micrometers, 120 micrometers, 120 micrometers, 140 micrometers, or 150 micrometers or greater; and 500 micrometers or less, 475 micrometers, 450 micrometers, 425 micrometers, 400 micrometers, 375 micrometers, 350 micrometers, 325 micrometers, 300 micrometers, 275 micrometers, 250 micrometers, 225 micrometers, 200 micrometers, 190 micrometers, 180 micrometers, 170 micrometers, or 160 micrometers or less. In many embodiments, the protrusions have an average diameter of 1 micrometer to 500 micrometers or 10 micrometers to 300 micrometers. Exemplary Embodiments

[0081] In a first embodiment, the present disclosure provides a porous polymeric membrane. The porous polymeric membrane comprises a) a first outer surface having a patterned array of first pores having irregularly shaped perimeters; b) an opposing second outer surface having a plurality of second pores; and c) a polymeric matrix extending between the first outer surface and the second outer surface. The polymeric matrix defines a plurality of through holes that extend between the first pores and the second pores.

[0082] In a second embodiment, the present disclosure provides a porous polymeric membrane according to the first embodiment, wherein the through holes have an average diameter of 1 micrometer to 500 micrometers or 10 micrometers to 300 micrometers.

[0083] In a third embodiment, the present disclosure provides a porous polymeric membrane according to the first embodiment or the second embodiment, wherein the plurality of second pores have regularly shaped perimeters.

[0084] In a fourth embodiment, the present disclosure provides a porous polymeric membrane according to any of the first through third embodiments, wherein the polymeric matrix located adjacent to the through holes is porous.

[0085] In a fifth embodiment, the present disclosure provides a porous polymeric membrane according to any of the first through third embodiments, wherein the polymeric matrix located adjacent to the through holes is nonporous.

[0086] In a sixth embodiment, the present disclosure provides a porous polymeric membrane according to any of the first through fifth embodiments, wherein the through holes are isoporous.

[0087] In a seventh embodiment, the present disclosure provides a porous polymeric membrane according to any of the first through sixth embodiments, having a thickness between the first outer surface and the second outer surface of 1 micrometer or greater.

[0088] In an eighth embodiment, the present disclosure provides a porous polymeric membrane according to any of the first through seventh embodiments, wherein the through holes have a density on the first outer surface of 50 per square centimeter or greater.

[0089] In a ninth embodiment, the present disclosure provides a porous polymeric membrane according to any of the first through eighth embodiments, wherein the polymeric matrix comprises polyethersulfone, polypropylene, polysulfone, polyacrylonitrile, a cellulose ester, a polyimide, a polyamide, poly(vinylidene fluoride), or polytetrafluoroethylene). [0090] In a tenth embodiment, the present disclosure provides a porous polymeric membrane according to any of the first through ninth embodiments, wherein the polymeric matrix comprises polyethersulfone or amorphous nylon.

[0091] In an eleventh embodiment, the present disclosure provides a porous polymeric membrane according to any of the first through tenth embodiments, wherein the first pores have an average area that is less than half of an average area of the second pores.

[0092] In a twelfth embodiment, the present disclosure provides a method. The method comprises applying a casting solution to a tooling structure comprising a major surface and a patterned array of protrusions extending orthogonally therefrom, to form a layer of the casting solution. The casting solution comprises a polymer component and a solvent system. The method further comprises contacting the layer of the casting solution with a nonsolvent fluid to solidify the polymer component and form a porous polymeric membrane; and removing the porous polymeric membrane from the tooling structure, thereby providing a porous polymeric membrane. The porous polymeric membrane comprises 1) a first outer surface having a patterned array of first pores having irregularly shaped perimeters that do not correspond to a shape of a top of the plurality of protrusions; 2) an opposing second outer surface having a plurality of second pores; and 3) a polymeric matrix extending between the first outer surface and the second outer surface. The polymeric matrix defines a plurality of through holes that extend between the first pores and the second pores.

[0093] In a thirteenth embodiment, the present disclosure provides a method according to the twelfth embodiment, wherein the protrusions comprise a stem and a head, in which the stem extends orthogonally from the major surface of the tooling structure and the head is disposed distal to the major surface of the tooling structure.

[0094] In a fourteenth embodiment, the present disclosure provides a method according to the thirteenth embodiment, wherein the protrusions comprise a T-shape, a nail shape, a mushroom shape, or combinations thereof.

[0095] In a fifteenth embodiment, the present disclosure provides a method according to the thirteenth embodiment or the fourteenth embodiment, wherein the first pores have an average pore size that is smaller than the head of the protrusions.

[0096] In a sixteenth embodiment, the present disclosure provides a method according to any of the twelfth through fourteenth embodiments, wherein the layer of the casting solution has a thickness smaller than the height of the protrusions. [0097] In a seventeenth embodiment, the present disclosure provides a method according to any of the twelfth through fourteenth embodiments, wherein the layer of the casting solution has a thickness equal to the height of the protrusions.

[0098] In an eighteenth embodiment, the present disclosure provides a method according to any of the twelfth through fifteenth embodiments, wherein the layer of the casting solution has a thickness larger than the height of the protrusions.

[0099] In a nineteenth embodiment, the present disclosure provides a method according to any of the twelfth through eighteenth embodiments, wherein the casting solution comprises a solids content of 5 percent by weight to 50 percent by weight.

[00100] In a twentieth embodiment, the present disclosure provides a method according to any of the twelfth through eighteenth embodiments, wherein the polymer component comprises polyethersulfone, polypropylene, polysulfone, polyacrylonitrile, a cellulose ester, a polyimide, a polyamide, poly(vinylidene fluoride), or polytetrafluoroethylene).

[00101] In a twenty-first embodiment, the present disclosure provides a method according to any of the twelfth through twentieth embodiments, wherein the polymer component comprises polyethersulfone or amorphous nylon, the solvent system comprises dimethyl sulfoxide, and the nonsolvent fluid comprises water.

[00102] In a twenty-second embodiment, the present disclosure provides a method according to any of the twelfth through twenty-first embodiments, wherein the tooling structure is formed of polypropylene or a crosslinked (meth)acrylate polymer.

[00103] In a twenty-third embodiment, the present disclosure provides a method according to any of the twelfth through twenty-second embodiments, wherein the protrusions have an average diameter of 1 micrometer to 500 micrometers or 10 micrometers to 300 micrometers.

[00104] In a twenty-fourth embodiment, the present disclosure provides a method according to any of the twelfth through twenty-third embodiments, wherein the porous polymeric membrane is according to any of the first through eleventh embodiments.

[00105] Advantages and embodiments of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention. All parts and percentages are by weight unless otherwise indicated. EXAMPLES

[00106] Unless otherwise noted or apparent from the context, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight.

[00107] Commercially available polyethersulfone (PES), available from BASF, Wyandotte, MI, under trade designation “ULTRASON E6020”, was used as a polymer for membrane fabrication. N-Methyl pyrrolidone (NMP), available from BASF, Wyandotte, MI, was selected as solvent. Deionized water was selected as a non-solvent. 10 wt.% of PES was dissolved in NMP using a speed mixer at room temperature until a homogeneous clear solution was obtained. After that the solution was left standing overnight at 60 °C to remove any entrapped bubbles.

[00108] The structured surface used to make the membrane was a mechanical fastener strip prepared from an ethylene-propylene copolymer available from Dow Chemical Company, Midland, MI, under the trade designation “C700-35N” using the method described in U.S. Pat. No. 5,845,375 (Miller et al.). The mechanical fastener strips were arranged in a staggered array. The posts were conical in shape. The distal tips of the posts were deformed with a textured heated surface to form grooved caps such as that disclosed in U.S. Pat. No. 6,708,378 (Parellada et al.) or U.S. Pat. No. 5,868,987 (Kampfer et al.).

[00109] The membranes were prepared by casting the homogeneous PES solution on to the structured surface using a doctor blade such that the scraping action touched the top of the caps and excess PES solution above the caps was wiped off. The structured surface coated with the PES solution was then immersed into deionized water at 25 °C immediately. Upon immersion, the PES solution slowly solidified into an opaque film that was still attached to the structured surface. The solidified film was slowly peeled from the structured surface and stored in deionized water at 25 °C until further analysis. The structured surface had a height of 350 micrometers where the PES solution could be cast. Note that the initial casting thickness of the membrane was dependent on the height of the structured surface itself and other structured surfaces with a higher or a lower height are also thought to be useful to prepare membranes of varying thicknesses.

[00110] SEM analysis was conducted using a JEOL JSM-6510LV Scanning Electron Microscope. The membrane samples were placed in refrigerator for 24 hours and then small samples were cut and mounted on the sample holder, each coated with platinum to provide conductivity, and images were captured. Portions of the samples imaged are shown in FIGS. 2A and 2B described above.

[00111] Foreseeable modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention. This invention should not be restricted to the embodiments that are set forth in this application for illustrative purposes.