Patent Publication Number: US-2022213372-A1

Title: (co)polymer matrix composites comprising thermally-conductive particles and endothermic particles and methods of making the same

Description:
BACKGROUND 
     Integrated circuits, active and passive components, optical disk drives, batteries, and motors generate heat during use. To prolong the long term, as well as continuous, use of the devices, the heat must be dissipated. Finned metal blocks and heat spreaders containing heat pipes are commonly used as heat sinks to dissipate the heat generated by devices during use. Materials commonly used for providing a thermal bridge between the heat generating components and heat sinks/heat spreaders include gel masses, liquid to solid phase change compounds, greases, and pads that are mechanically clamped between, for example, a printed circuit board (PCB) and heat sink. 
     Thermally-conductive materials, incorporated into adhesives (e.g., heat-activated, hot-melt and pressure-sensitive adhesives) are sometimes used to provide an adhesive bond between a heat generating component and a heat sink/heat spreader so that no mechanical clamping is required. Such thermal interface materials often exhibit good heat conduction characteristics compared to unfilled or lightly filled adhesive compositions, but may not exhibit good heat absorption or heat dissipation characteristics compared to metal heat sinks or heat spreader. Thermal management is often done via heat transfer materials and combinations of both active and passive cooling with air or conductive heat transfer to liquid-cooled interfaces. 
     Porous films and membranes foams are generally made via a phase separation process, and therefore typically have relatively small, uniform, pore sizes, and different pore morphologies as compared to foams. The pores on porous films are typically open such that gas, liquid, or vapor can pass from one major surface though the open pores to the other opposed, major surface. Porous films and membranes foams can be made via several phase separation processes, but are typically made via solvent induced phase separation or thermally induced phase separation. 
     SUMMARY 
     Managing charging and discharging of battery systems is often done via electronic battery management systems. Thermal management is often done via heat transfer materials and combinations of both active and passive cooling with air or heat transfer liquid interfaces. 
     Additionally, some pollution control elements and fire protection devices use endothermic materials in their construction. Endothermic materials are known to absorb heat at certain temperatures. This is often accompanied by a phase change mechanism. Some endothermic materials expand due to chemicals that are imbibed within particles, while others expand due to the nature of the mineral or ore they contain. The temperature range at which the expansion occurs can vary depending on the endothermic material and/or the intercalated chemistry. 
     Porous (co)polymeric films generally have high flexibility and can provide intimate contact or cushioning between hard plastics or metal. Trapped air, however, is naturally considered an insulator against heat conduction, and porous materials featuring trapped air are typically not suitable for heat dissipation. Alternative lightweight, flexible materials and approaches for conducting, absorbing and/or dissipating heat, particularly in compact (e.g., handheld) electronic devices are desired. 
     Additional options to deliver or otherwise provide endothermic materials, in combination with thermally-conductive materials, more particularly in particulate form (i.e., as particles), are desired. Porous films generally have the flexibility and can provide intimate contact or cushion between hard plastics or metal. Trapped air, however, is naturally considered an insulator against heat conduction and porous materials featuring trapped air are typically not suitable for heat dissipation. Alternative materials and approaches for dissipating or conducting heat are desired. 
     The present disclosure describes various exemplary embodiments of highly particle-loaded (co)polymer matrix composites which exhibit high thermal conductivity. Further incorporation of endothermic particles can additionally enable the composite to absorb heat and thereby act as heat absorbers or heat sinks. 
     Thus in one aspect, the present disclosure describes a (co)polymer matrix composite including a porous (co)polymeric network structure, a plurality of thermally-conductive particles and a plurality of endothermic particles distributed within the (co)polymeric network structure, wherein the thermally-conductive particles and the endothermic particles are present in a range from 15 to 99 (in some embodiments, in a range from 25 to 98, 50 to 98, 75 to 98, or even 93 to 97) weight percent, based on the total weight of the (co)polymer matrix composite (excluding any solvent). 
     In some exemplary embodiments, the (co)polymer matrix composite volumetrically expands by at least 10% (in some embodiments at least 20%, 30%, 40% or even 50%) of its initial volume when exposed to a temperature of at least 135 (in some embodiments, at least 150, 175, or even at least 200; in some embodiments, in a range from 135 to 400, or even 200 to 400) ° C. 
     In some such embodiments, the percent volume expansion of the (co)polymeric matrix composites is improved by compressing the (co)polymeric matrix composite, thereby increasing the density of the unexpanded (co)polymer matrix composite. 
     In another aspect, the present disclosure describes a first method of making (co)polymer matrix composites described herein, the method comprising combining (e.g., heating, mixing and/or blending) a thermoplastic (co)polymer, a solvent, a plurality of thermally-conductive particles, a plurality of intumescent particles and optionally a plurality of endothermic particles to provide a slurry; forming the slurry in to an article (e.g., a layer); heating the article in an environment to retain at least 90 (in some embodiments, at least 91, 92, 93, 94, 95, 96, 97, 98, 99, or even at least 99.5) percent by weight of the solvent in the article, based on the weight of the solvent in the article, and solubilize at least 50 (in some embodiments, at least 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, or even 100) percent of the thermoplastic (co)polymer, based on the total weight of the thermoplastic (co)polymer; and inducing phase separation of the thermoplastic (co)polymer from the solvent to provide the (co)polymer matrix composite. 
     The desired article is formed before the (co)polymer becomes miscible with the solvent and the phase separation is a thermally induced phase separation (TIPS) process. 
     In a further aspect, the present disclosure describes a second method of making (co)polymer matrix composites described herein, the method comprising combining (e.g., heating, mixing and/or blending) a thermoplastic (co)polymer, a solvent for the thermoplastic (co)polymer, a plurality of thermally-conductive particles, and a plurality of endothermic particles to form a suspension of the thermally-conductive and endothermic particles in a miscible thermoplastic (co)polymer-solvent solution; inducing phase separation of the thermoplastic (co)polymer from the solvent; and removing at least a portion of the solvent to provide the (co)polymer matrix composite. 
     In the second method, the (co)polymer is miscible with the solvent before the desired article is formed. In the second method, phase separation is achieved via solvent induced phase separation (SIPS) using a wet or dry process, or thermally induced phase separation methods. 
     The (co)polymer matrix composites described herein may be useful, for example, as fillers, thermal interface materials, and thermal management materials, for example, in electronic devices, more particularly mobile handheld electronic devices, power supplies, and batteries. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure may be more completely understood by consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying figures, in which: 
         FIG. 1  is a schematic of an exemplary (co)polymer matrix composite described herein. 
         FIG. 2  is a schematic of another exemplary (co)polymer matrix composite described herein. 
         FIG. 3  is a schematic of another exemplary (co)polymer matrix composite described herein. 
         FIGS. 4, 5, 6, 7 and 8  show scanning electron microscope (SEM) micrographs of cross-sections of exemplary (co)polymer matrix composites (Examples 3A, 4A, 5A, 6A and 7, respectively) described herein. 
     
    
    
     In the drawings, like reference numerals indicate like elements. While the above-identified drawing, which may not be drawn to scale, sets forth various embodiments of the present disclosure, other embodiments are also contemplated, as noted in the Detailed Description. In all cases, this disclosure describes the presently disclosed disclosure by way of representation of exemplary embodiments and not by express limitations. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of this disclosure. 
     DETAILED DESCRIPTION 
     For the following Glossary of defined terms, these definitions shall be applied for the entire application, unless a different definition is provided in the claims or elsewhere in the specification. 
     Glossary 
     Certain terms are used throughout the description and the claims that, while for the most part are well known, may require some explanation. Therefore, it should understood that: 
     The term “homogeneous” means exhibiting only a single phase of matter when observed at a macroscopic scale. 
     The terms “(co)polymer” or “(co)polymers” includes homopolymers and copolymers, as well as homopolymers or copolymers that may be formed in a miscible blend, e.g., by coextrusion or by reaction, including, e.g., transesterification. The term “copolymer” includes random, block and star (e.g., dendritic) copolymers. 
     The term “(meth)acrylate” with respect to a monomer, oligomer or means a vinyl-functional alkyl ester formed as the reaction product of an alcohol with an acrylic or a methacrylic acid. 
     The term “endothermic particles,” as used herein, means particles comprising bound water, wherein the bond water desorbs at a temperature of at least 90° C., or particles comprising a crystalline or semi-crystalline material (e.g., a crystalline or semi-crystalline (co)polymer) that undergoes a crystalline to amorphous melt transition (i.e., exhibits a melting temperature) of at least 90° C. 
     The term “miscible” as used herein refers to the ability of substances to mix in all proportions (i.e., to fully dissolve in each other at any concentration), forming a solution, wherein for some solvent-(co)polymer systems heat may be needed for the (co)polymer to be miscible with the solvent. By contrast, substances are immiscible if a significant proportion does not form a solution. For example, butanone is significantly soluble in water, but these two solvents are not miscible because they are not soluble in all proportions. 
     The term “phase separation,” as used herein, refers to the process in which particles are uniformly dispersed in a homogeneous (co)polymer-solvent solution that is transformed (e.g., by a change in temperature or solvent concentration) into a continuous three-dimensional (co)polymer matrix composite. 
     The term “thermally-conductive particles,” as used herein, means particles having a thermal conductivity greater than 2 W/(m° K). 
     The term “adjacent” with reference to a particular layer means joined with or attached to another layer, in a position wherein the two layers are either next to (i.e., adjoined to) and directly contacting each other, or contiguous with each other but not in direct contact (i.e., there are one or more additional layers intervening between the layers). 
     Terms of orientation such as “atop”, “on”, “over,” “covering”, “uppermost”, “underlying” and the like for the location of various elements in the disclosed coated articles, refer to the relative position of an element with respect to a horizontally-disposed, upwardly-facing substrate. However, unless otherwise indicated, it is not intended that the substrate or articles should have any particular orientation in space during or after manufacture. For purposes of clarity and without intending to be unduly limited thereby, the tape sheets or strips in a group of any two sequentially stacked sheets or strips are referenced as an overlying tape sheet and an underlying tape sheet with the adhesive layer of the overlying tape sheet adhered to the front or first face of the backing of the underlying tape sheet. 
     The terms “overlay” or “overlaying” describe the position of a layer with respect to a substrate or layer of a multi-layer article of the present disclosure, we refer to the layer as being atop the substrate or other element, but not necessarily contiguous to either the substrate or the other element. 
     The term “separated by” to describe the position of a layer with respect to other layers, refers to the layer as being positioned between two other layers but not necessarily contiguous to or adjacent to either layer. 
     The terms “about” or “approximately” with reference to a numerical value or a shape means+/−five percent of the numerical value or property or characteristic, but expressly includes the exact numerical value. For example, a viscosity of “about” 1 Pa-sec refers to a viscosity from 0.95 to 1.05 Pa-sec, but also expressly includes a viscosity of exactly 1 Pa-sec. Similarly, a perimeter that is “substantially square” is intended to describe a geometric shape having four lateral edges in which each lateral edge has a length which is from 95% to 105% of the length of any other lateral edge, but which also includes a geometric shape in which each lateral edge has exactly the same length. 
     The term “substantially” with reference to a property or characteristic means that the property or characteristic is exhibited to a greater extent than the opposite of that property or characteristic is exhibited. For example, a substrate that is “substantially” transparent refers to a substrate that transmits more radiation (e.g., visible light) than it fails to transmit (e.g., absorbs and reflects). Thus, a substrate that transmits more than 50% of the visible light incident upon its surface is substantially transparent, but a substrate that transmits 50% or less of the visible light incident upon its surface is not substantially transparent. 
     As used in this specification and the appended embodiments, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to fine fibers containing “a compound” includes a mixture of two or more compounds. As used in this specification and the appended embodiments, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     As used in this specification, the recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.8, 4, and 5). 
     Unless otherwise noted, all parts, percentages, ratios, etc. used in the specification are expressed based on the weight of the ingredients. Weight percent, percent by weight, % by weight, wt. % and the like are synonyms that refer to the amount of a substance in a composition expressed as the weight of that substance divided by the weight of the composition and multiplied by 100. 
     Unless otherwise indicated, all numbers expressing quantities or ingredients, measurement of properties and so forth used in the specification and embodiments are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached listing of embodiments can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings of the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claimed embodiments, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. 
     Exemplary embodiments of the present disclosure may take on various modifications and alterations without departing from the spirit and scope of the present disclosure. Accordingly, it is to be understood that the embodiments of the present disclosure are not to be limited to the following described exemplary embodiments, but is to be controlled by the limitations set forth in the claims and any equivalents thereof. 
     Various exemplary embodiments of the disclosure will now be described with particular reference to the Drawings. Exemplary embodiments of the present disclosure may take on various modifications and alterations without departing from the spirit and scope of the disclosure. Accordingly, it is to be understood that the embodiments of the present disclosure are not to be limited to the following described exemplary embodiments, but are to be controlled by the limitations set forth in the claims and any equivalents thereof. 
     (Co)polymer Matrix Composites 
     In one aspect, the present disclosure describes a (co)polymer matrix composite comprising: 
     a porous (co)polymeric network structure; and 
     a plurality of thermally-conductive particles and a plurality of endothermic particles distributed within the (co)polymeric network structure, wherein the endothermic and thermally-conductive particles are present in a range from 15 to 99 (in some embodiments, in a range from 25 to 98, 50 to 98, 75 to 98, or even 93 to 97) weight percent, based on the total weight of endothermic particles and the (co)polymer (excluding any solvent). 
     In some exemplary embodiments, the (co)polymer matrix composite volumetrically expands by at least 10% (in some embodiments at least 20%, 30%, 40% or even 50%) of its initial volume when exposed to a temperature of at least 135 (in some embodiments, at least 150, 175, or even at least 200; in some embodiments, in a range from 135 to 400, or even 200 to 400) ° C. 
     In some such embodiments, the percent volume expansion of the (co)polymeric matrix composites is improved by compressing the (co)polymeric matrix composite thereby increasing the density of the unexpanded (co)polymer matrix composite. 
     In certain exemplary embodiments, (co)polymeric matrix composites described herein, have first and second planar, opposed major surfaces. In some embodiments, (co)polymer matrix composites described herein, have first and second opposed major surfaces, wherein the first major surface is nonplanar (e.g., curved). Referring to  FIG. 1 , exemplary (co)polymer matrix composite described herein  100  has first and second opposed major surfaces  101 ,  102 . First major surface  101  is nonplanar. 
     Planar and nonplanar major surfaces can be provided, for example, by coating or extruding the slurry onto a patterned substrate (e.g., a liner, a belt, a mold, or a tool). Alternatively, for example, a die with a shaped slot can be used to form nonplanar surfaces during the coating or extrusion process. Alternatively, for example, the structure can be formed after the phase separation has occurred before, and/or after, the solvent is removed by molding or shaping the layer with a patterned tool. 
     In some embodiments, (co)polymer matrix composites described herein, have first protrusions extending outwardly from the first major surface, and in some embodiments, second protrusions extending outwardly from the second major surface. In some embodiments, the first protrusions are integral with the first major surface, and in some embodiments, the second protrusions are integral with the second major surface. Exemplary protrusions include at least one of a post, a rail, a hook, a pyramid, a continuous rail, a continuous multi-directional rail, a hemisphere, a cylinder, or a multi-lobed cylinder. In some embodiments, the protrusions have a cross-section in at least one of a circle, a square, a rectangle, a triangle, a pentagon, other polygons, a sinusoidal, a herringbone, or a multi-lobe. 
     Referring to  FIG. 2 , exemplary (co)polymer matrix composite described herein  200  has first protrusions  205  extending outwardly from first major surface  201  and optional second protrusions  206  extending outwardly from second major surface  202 . 
     Protrusions can be provided, for example, by coating or extruding between patterned substrate (e.g., a liner, a belt, a mold, or a tool). Alternatively, a die with a shaped slot can be used to form protrusions during the coating or extrusion process. Alternatively, for example, the structure can be formed after the phase separation has occurred, by molding or shaping the film between patterned tools. 
     In some embodiments, (co)polymer matrix composite described herein, have first depressions extending into the first major surface, and in some embodiments, second depressions extending into the second major surface. Exemplary depressions include at least one of a groove, a slot, an inverted pyramid, a hole (including a thru or blind hole), or a dimple. 
     Referring to  FIG. 3 , exemplary (co)polymer matrix composite described herein  300  has first depressions  307  extending into first major surface  301  and optional second depressions  308  extending into second major surface  302 . Depressions can be provided, for example, by coating or extruding between a patterned substrate (e.g., a liner, a belt, a mold, or a tool). Alternatively, for example, a die with a shaped slot can be used to form depressions during the coating or extrusion process. Alternatively, for example, the structure can be formed after the phase separation has occurred, before and/or after, the solvent is removed by molding or shaping the film between patterned tools. 
     In some exemplary embodiments, these shaped two- or three-dimensional structures can improve compression by deforming and or bending to provide increased compression and contact force between heat transfer surfaces. As heat transfer surfaces expand or contract this compression or spring like action created by the surfaces can improve thermal conductivity by improving surface to surface contact. Alternatively, increased surface area caused by certain shapes can increase convective heat transfer. This can be a benefit where heat is being conducted to a fluid or air rather than a second heat absorbing surface or heat sink. 
     In some exemplary embodiments, (co)polymer matrix composites described herein further comprise a reinforcement or support structure (e.g., attached to the (co)polymer matrix composite, partial therein, and/or therein). Exemplary reinforcements or support structures include fibers, strands, nonwovens, woven materials, fabrics, mesh, and films. 
     Reinforcement/support structures such as nonwovens, wovens, mesh, fibers, etc. can be imbibed with, laminated or adhered to thermally conductive polymer composites to help improve mechanical durability. In some embodiments it can be advantageous for these supports to also be thermally conductive. Thus, metal foils and meshes are particularly, useful as are carbon fibers, glass fibers, and or flame-resistant (co)polymeric fibers (e.g., oriented poly(acrylo)nitrile (OPAN) fibers or poly(penylene)sulfide (PPS) fibers. 
     The reinforcement, for example, can be laminated to the (co)polymer matrix composite thermally, adhesively, or ultrasonically. The reinforcement, for example, can be imbedded within the (co)polymer matrix composite during the coating or extrusion process. The reinforcement, for example, can be between the major surfaces of the composite, on one major surface, or on both major surfaces. More than one type of reinforcement can be used. 
     The (co)polymeric network structure may be described as a porous (co)polymeric network or a porous phase-separated (co)polymeric network. Generally, the porous (co)polymeric network (as-made) includes an interconnected porous (co)polymeric network structure comprising a plurality of interconnected morphologies (e.g., at least one of fibrils, nodules, nodes, open cells, closed cells, leafy laces, strands, nodes, spheres, or honeycombs). The interconnected (co)polymeric structures may adhere directly to the surface of the particles and act as a binder for the particles. In this regard, the space between adjacent particles (e.g., particles or agglomerate particles) may include porous (co)polymeric network structures, as opposed to a solid matrix material, thereby providing desired porosity. 
     In some embodiments, the (co)polymeric network structure may include a 3-dimensional reticular structure that includes an interconnected network of (co)polymeric fibrils. In some embodiments, individual fibrils have an average width in a range from 10 nm to 100 nm (in some embodiments, in a range from 100 nm to 500 nm, or even 500 nm to 5 micrometers). 
     In some embodiments, the thermally-conductive particles, endothermic particles and optional endothermic particles are dispersed within the (co)polymeric network structure, such that an external surface of the individual units of the particles (e.g., individual particles or individual agglomerate particles) is mostly uncontacted, or uncoated, by the (co)polymeric network structure. In this regard, in some embodiments, the average percent areal coverage of the (co)polymeric network structure on the external surface of the individual particles (i.e., the percent of the external surface area that is in direct contact with the (co)polymeric network structure) is not greater than 50 (in some embodiments, not greater than 40, 30, 25, 20, 10, 5, or even not greater than 1) percent, based on the total surface area of the external surfaces of the individual particles. Although not wanting to be bound by theory, it is believed that the large, uncontacted surface area coating on the particles enables increased particle-to-particle contact upon compression and therefore increases thermal conductivity. 
     In some embodiments, the (co)polymeric network structure does not penetrate internal porosity or internal surface area of the individual particles (e.g., individual particles or individual agglomerate particles) are mostly uncontacted, or uncoated, by the (co)polymeric network structure. 
     As-made (co)polymer matrix composites described herein (i.e., prior to any compression or other post formation densification), typically have a density of at least 0.3 (in some embodiments, in a range from 0.3 to 2.3, 0.3 to 2.1, 0.3 to 1.5, or even 0.3 to 1 g/cm 3 . 
     In some embodiments, the thermal conductivity of the (co)polymer matrix composites is improved by compressing the (co)polymer matrix composites thereby increasing the density of the (co)polymer matrix composite. In some embodiments, the compression can take place at elevated temperatures (e.g., above the glass transition temperature of the (co)polymer matrix, or even, in some embodiments, above the melting point of the (co)polymer matrix). In some embodiments, (co)polymer matrix composites have a density of at least 1 (in some embodiments, at least 2, 3, 4, 5, 6, 7, 8, 9, or even at least 10; in some embodiments, in the range from 1 to 10, 1 to 9, 3 to 8, or even 4 to 7) g/cm 3 . In other embodiments, compressed (co)polymer matrix composites have a density of at least 0.3 (in some embodiments, in a range from 0.3 to 2.3, 0.3 to 2.1, 0.3 to 1.5, or even 0.3 to 1 g/cm 3 . 
     In some embodiments, (co)polymer matrix composites described herein have a porosity of at least 5 (in some embodiments, in a range from 10 to 80, 20 to 70, or even 30 to 60) percent. 
     In some embodiments, (co)polymer matrix composites described herein have a porosity less than 80 (in some embodiments, in a range from 0 to 80, 0 to 70, 0 to 60, 10 to 80, 10 to 70, 10 to 60, 10 to 50, 10 to 40, 10 to 30, or even 5 to 20) percent. 
     In some exemplary embodiments, the thermally-conductive particles and the endothermic particles are present in a single layer comprised of the (co)polymer matrix composite. In certain such embodiments, the thermally-conductive particles and the endothermic particles may be substantially homogenously distributed within the layer. 
     In other exemplary embodiments, the thermally-conductive particles are present in a first layer comprised of the (co)polymer matrix composite, and the endothermic particles are present in a second layer adjacent to the first layer. Optionally, the second layer adjoins the first layer. 
     In additional exemplary embodiments, the thermally-conductive particles are present in a first layer comprised of the (co)polymer matrix composite having opposed first and second major surfaces, and the endothermic particles are present in a second layer overlaying and adjacent to the first major surface of the first layer and a third layer overlaying and adjacent to the second major surface of the first layer. Optionally, the second layer adjoins the first major surface, and the third layer adjoins the second major surface. 
     In further exemplary embodiments, the endothermic particles are present in a first layer comprised of the (co)polymer matrix composite having opposed first and second major surfaces, and the thermally-conductive particles are present in a second layer overlaying and adjacent to the first major surface of the first layer and in a third layer overlaying and adjacent to the second major surface of the first layer. Optionally, the second layer adjoins the first major surface, and the third layer adjoins the second major surface. 
     It will be understood that various ordering and arrangements of multiple layers comprising one or both of the thermally-conductive particles and the endothermic particles are within the scope of the present disclosure. 
     (Co)polymers 
     In some embodiments, the (co)polymeric network structure may comprise, consist essentially of, or consist of at least one thermoplastic (co)polymer. Exemplary thermoplastic (co)polymers include polyurethane, polyester (e.g., polyethylene terephthalate, polybutylene terephthalate, and polylactic acid), polyamide (e.g., nylon 6, nylon 6,6, nylon 12 and polypeptide), polyether (e.g., polyethylene oxide and polypropylene oxide), polycarbonate (e.g., bisphenol-A-polycarbonate), polyimide, polysulphone, polyethersulphone, polyphenylene oxide, polyacrylate (e.g., thermoplastic (co)polymers formed from the addition (co)polymerization of monomer(s) containing an acrylate functional group), poly(meth)acrylate (e.g., thermoplastic (co)polymers formed from the addition (co)polymerization of monomer(s) containing a (meth)acrylate functional group), polyolefin (e.g., polyethylene and polypropylene), styrene and styrene-based random and block copolymer, chlorinated (co)polymer (e.g., polyvinyl chloride), fluorinated (co)polymer (e.g., polyvinylidene fluoride; (co)polymers of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride; (co)polymers of ethylene, tetrafluoroethylene; hexafluoropropylene; and polytetrafluoroethylene), and (co)polymers of ethylene and chlorotrifluoroethylene, or a combination thereof. 
     In some embodiments, thermoplastic (co)polymers include homopolymers or copolymers (e.g., block copolymers or random copolymers). In some embodiments, thermoplastic (co)polymers include a mixture of at least two thermoplastic (co)polymer types (e.g., a mixture of polyethylene and polypropylene or a mixture of polyethylene and polyacrylate). In some embodiments, the (co)polymer may be at least one of polyethylene (e.g., ultra-high molecular weight polyethylene), polypropylene (e.g., ultra-high molecular weight polypropylene), polylactic acid, poly(ethylene-co-chlorotrifluoroethylene) and polyvinylidene fluoride, or a combination thereof. 
     In certain exemplary embodiments, the porous (co)polymeric network structure comprises at least one of polyacrylonitrile, polyurethane, polyester, polyamide, polyether, polycarbonate, polyimide, polysulfone, polyphenylene oxide, polyacrylate, poly(meth)acrylate, polyolefin, polysiloxane, poly(meth)acrylosiloxane, styrene or styrene-based random and block (co)polymer, chlorinated (co)polymer, fluorinated (co)polymer (e.g., polyvinylidene fluoride), or (co)polymers of ethylene and chlorotrifluoroethylene, or a combination thereof. 
     In further exemplary embodiments, the porous (co)polymeric network structure advantageously comprises a crosslinked polysiloxane (co)polymer (e.g., a crosslinked poly(meth)acrylosiloxane copolymer). In certain such exemplary embodiments, the crosslinked polysiloxane (co)polymer may be advantageously used to provide a (co)polymeric network structure that exhibits a low activation temperature (e.g., activating at a temperature of less than 150° C., less than 140° C., less than 130° C., less than 120° C., less than 110° C., or even less than 10° C.) for the incorporated endothermic particles. 
     In some embodiments, the thermoplastic (co)polymer is a single thermoplastic (co)polymer (i.e., it is not a mixture of at least two thermoplastic (co)polymer types). In some embodiments, the thermoplastic (co)polymers consist essentially of, or consist of polyethylene (e.g., ultra-high molecular weight polyethylene). 
     In some embodiments, the thermoplastic (co)polymer used to make the (co)polymer matrix composites described herein are particles having a particle size less than 1000 (in some embodiments, in a range from 1 to 10, 10 to 30, 30 to 100, 100 to 200, 200 to 500, 500 to 1000) micrometers. 
     In some embodiments, the porous (co)polymeric network structure comprises a (co)polymer having a number average molecular weight in a range from 5×10 4  to 1×10 7  (in some embodiments, in a range from 1×10 6  to 8×10 6 , 2×10 6  to 6×10 6 , or even 3×10 6  to 5×10 6 ) g/mol. For purposes of the present disclosure, the number average molecular weight can be measured by known techniques in the art (e.g., gel permeation chromatography (GPC)). GPC may be conducted in a suitable solvent for the thermoplastic (co)polymer, along with the use of narrow molecular weight distribution (co)polymer standards (e.g., narrow molecular weight distribution polystyrene standards). 
     Thermoplastic (co)polymers are generally characterized as being partially crystalline, exhibiting a melting point. In some embodiments, the thermoplastic (co)polymer may have a melting point in a range from 120 to 350 (in some embodiments, in a range from 120 to 300, 120 to 250, or even 120 to 200) ° C. The melting point of the thermoplastic (co)polymer can be measured by known techniques in the art (e.g., the on-set temperature measured in a differential scanning calorimetry (DSC) test, conducted with a 5 to 10 mg sample, at a heating scan rate of 10° C./min., while the sample is under a nitrogen atmosphere). 
     In some embodiments, the (co)polymeric network structure is a continuous network structure (i.e., the (co)polymer phase comprises a structure that is open cell with continuous voids or pores forming interconnections between the voids, extending throughout the structure). In some embodiments, at least 2 (in some embodiments, at least 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, or even, 100) percent of the (co)polymer network structure, by volume, may be a continuous (co)polymer network structure. It should be noted that for purposes of the present disclosure, the portion of the volume of the (co)polymer matrix composite made up of the particles is not considered part of the (co)polymeric network structure. In some embodiments, the (co)polymer network extends between two particles forming a network of interconnected particles. 
     Solvents 
     The solvent (e.g., a first solvent) is selected such that it forms a miscible (co)polymer-solvent solution. In some cases, elevated temperatures may be required to form the miscible (co)polymer-solvent solution. The solvent may be a blend of at least two individual solvents. In some embodiments, when the (co)polymer is a polyolefin (e.g., at least one of polyethylene and polypropylene), the solvent may be, for example, at least one of mineral oil, tetralin, decalin, orthodichlorobenzene, cyclohexane-toluene mixture, dodecane, paraffin oil/wax, kerosene, isoparaffinic fluids, p-xylene/cyclohexane mixture (1/1 wt./wt.), camphene, 1,2,4 trichlorobenzene, octane, orange oil, vegetable oil, castor oil, palm kernel oil, or a combination thereof. In some embodiments, when the (co)polymer is polyvinylidene fluoride, the solvent may be, for example, at least one of ethylene carbonate, propylene carbonate, or 1,2,3 triacetoxypropane, or a combination thereof. 
     In some embodiments, the solvent may be removed, for example, by evaporation. High vapor pressure solvents being particularly suited to this method of removal. If, however, the first solvent has a low vapor pressure, it may be desirable to have a second solvent, of higher vapor pressure, to extract the first solvent, followed by evaporation of the second solvent. For example, in some embodiments, when mineral oil is used as a first solvent, isopropanol at elevated temperature (e.g., about 60° C.) or a blend of methyl nonafluorobutyl ether (C 4 F 9 OCH 3 ), ethylnonafluorobutyl ether (C 4 F 9 OC 2 H 5 ), and trans-1,2-dichloroethylene (available, for example, under the trade designation “NOVEC 72DE” from 3M Company (St. Paul, Minn.) may be used as a second solvent to extract the first solvent, followed by evaporation of the second solvent. In some embodiments, when at least one of vegetable oil or palm kernel oil is used as the first solvent, isopropanol at elevated temperature (e.g., about 60° C.), may be used as the second solvent. In some embodiments, when ethylene carbonate is used as the first solvent, water may be used as the second solvent. 
     In some embodiments, small quantities of other additives can be added to the (co)polymer matrix composite to impart additional functionality or act as processing aids. These include viscosity modifiers (e.g., fumed silica, block (co)polymers, and wax), plasticizers, thermal stabilizers (e.g., such as available, for example, under the trade designation “IRGANOX 1010” from BASF, Ludwigshafen, Germany), antimicrobials (e.g., silver and quaternary ammonium), flame retardants, antioxidants, dyes, pigments, and ultraviolet (UV) stabilizers, or a combination thereof. 
     In some embodiments, (co)polymer matrix composites described herein, are in the form of a layer having a thickness in a range from 50 to 11000 micrometers, wherein the thickness excludes the height of any protrusions extending from the base of the layer. 
     In some embodiments, the porous (co)polymeric network structure is produced by an induced phase separation of a miscible thermoplastic (co)polymer-solvent solution. In some embodiments, induced phase separation is at least one of thermally induced phase separation or solvent induced phase separation. 
     Particles 
     The thermally-conductive particles and endothermic particles are generally present in a range from 15 to 99 (in some embodiments, in a range from 25 to 98, 50 to 98, 75 to 98, or even 93 to 97) weight percent, based on the total weight of the (co)polymer matrix composite (excluding any optional solvent). 
     Thermally-Conductive Particles 
     Exemplary thermally conductive particles include conductive carbon, metals, semiconductors, and ceramics. 
     In some embodiments, the thermally conductive particles comprise electrically non-conductive particles (e.g., ceramic particles comprising boron nitride, aluminum trihydrate, silica carbide, and metal oxides (e.g., aluminum oxide and iron oxide)). 
     In some embodiments, the thermally conductive particles comprise electrically conductive particles such as carbon particles such as carbon black, graphite or graphene; and metal particles comprising at least one metal selected from aluminum, copper, nickel, platinum, silver and gold, or a combination thereof. 
     In some embodiments, the thermally conductive particles comprise a mixture of two or more particle types selected from carbon black, graphite, graphene, aluminum, copper, silver, graphite, diamond, SiC, Si 3 N 4 , MN, BeO, MgO, Al 2 O 3 , aluminum hydroxide, aluminum oxyhydroxide, hexagonal boron nitride (h-BN), cubic boron nitride (c-BN), ZnO, natural aluminosilicate, and synthetic aluminosilicate, or a combination thereof. 
     Exemplary sizes of the thermally conductive particles range from 1-100s of nanometers to 1-100s of micrometers in size. Exemplary shapes of the thermally conductive particles include irregular, platy, acicular, spherical shapes, and as well as agglomerated forms. Agglomerates can range in size, for example, from a few micrometers up to, and including, a few millimeters. The particles can be mixed to have multimodal size distributions which may, for example, allow for optimal packing density. 
     In some embodiments, the thermally conductive particles have an average particle size (average length of longest dimension) in a range from 100 nm to 2 mm (in some embodiments, in a range from 200 nm to 1000 nm). 
     In some embodiments, the thermally conductive particles have bimodal or trimodal distribution. Multimodal distributions of particles can allow for higher packing efficiency, improved particle-to-particle contact and thereby improved thermal conductivity. 
     Endothermic Particles 
     Exemplary endothermic particles comprise an endothermic material that comprise a solid phase that transitions to a gas or liquid phase upon heating which results in absorption of heat. In some embodiments, the particles break down during the absorption of heat. “Endothermic material” refers to a compound that absorbs heat, typically by releasing water of hydration, by going through a phase change that absorbs heat (i.e., liquid to gas), or by other chemical change where the reaction requires a net absorption of heat to take place. Typically, the endothermic particles have an endotherm of at least 200 J/g. 
     Exemplary endothermic particles comprise at least one of sodium bicarbonate, calcium sulfate dihydrate, aluminum trihydrate, magnesium sulfate octahydrate, ammonium oxalate, sodium metasilicate pentahydrate, sodium silicate a crystalline wax, a crystalline (co)polymer, a semi-crystalline (co)polymer, or a combination thereof. 
     Exemplary sizes of the endothermic particles range from 1-100s of nanometers to 1-100s of micrometers in size. Exemplary shapes of the endothermic particles include irregular, platy, acicular, spherical shapes, and as well as agglomerated forms. Agglomerates can range in size, for example, from a few micrometers up to and including a few millimeters. The particles can be mixed to have multimodal size distributions which may, for example, allow for optimal packing density. 
     In some embodiments, the endothermic particles have an average particle size (average length of longest dimension) in a range from 300 nm to 700 micrometers (in some embodiments, in a range from 5 micrometers to 300 micrometers, 5 micrometers to 150 micrometers, or even 1 micrometer to 300 micrometers). 
     In some embodiments, the endothermic particles comprise first and second, different (i.e., different compositions or microstructures, or particle sizes) endothermic particles. In some embodiments, the first endothermic particles comprise sodium bicarbonate, calcium sulfate dihydrate, aluminum trihydrate, magnesium sulfate octahydrate, ammonium oxalate, or sodium silicate, and wherein the second endothermic particles comprise sodium bicarbonate, calcium sulfate dihydrate, aluminum trihydrate, magnesium sulfate octahydrate, ammonium oxalate, sodium metasilicate pentahydrate, or sodium silicate. 
     In some embodiments, the first endothermic particles have an average particle size (average length of longest dimension) in a range from 300 nm to 700 micrometers (in some embodiments, in a range from 5 micrometers to 300 micrometers, 5 micrometers to 150 micrometers, or even 1 micrometer to 300 micrometers) and the second endothermic particles have an average particle size (average length of longest dimension) in a range from 300 nm to 700 micrometers (in some embodiments, in a range from 5 micrometers to 300 micrometers, 5 micrometers to 150 micrometers, or even 1 micrometer to 300 micrometers). 
     In some embodiments, the endothermic particles are present in a range from 15 to 99 (in some embodiments, in a range from 25 to 98, 50 to 98, 75 to 98, or even 93 to 97) weight present, and the second endothermic particles are present in a range from 15 to 99 (in some embodiments, in a range from 25 to 98, 50 to 98, 75 to 98, or even 93 to 97) weight percent, based on the total weight of the first and second endothermic particles. 
     Methods of Making the (Co)polymer Matrix Composite 
     Various methods may be used to make the (co)polymer matrix composites of the present disclosure. 
     First Method 
     In another aspect, the present disclosure describes a first method of making (co)polymer matrix composites described herein, the method comprising: 
     combining (e.g., mixing or blending) a thermoplastic (co)polymer, a solvent, a plurality of thermally-conductive particles, and a plurality of endothermic particles to provide a slurry; 
     forming the slurry in to an article (e.g., a layer); 
     heating the article in an environment to retain at least 90 (in some embodiments, at least 91, 92, 93, 94, 95, 96, 97, 98, 99, or even at least 99.5) percent by weight of the solvent in the article, based on the weight of the solvent in the article, and solubilize at least 50 (in some embodiments, at least 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, or even 100) percent of the thermoplastic (co)polymer, based on the total weight of the thermoplastic (co)polymer; and inducing phase separation of the thermoplastic (co)polymer from the solvent to provide the (co)polymer matrix composite. 
     In the first method, the desired article is formed before the (co)polymer becomes miscible with the solvent and the phase separation is a thermally induced phase separation (TIPS) process. 
     In the TIPS process, elevated temperature is used to make a nonsolvent become a solvent for the (co)polymer, then the temperature is lowered returning the solvent to a nonsolvent for the (co)polymer. Effectively, the hot solvent becomes the pore former when sufficient heat is removed and it loses its solvating capacity. The solvent used in the thermal phase separation process can be volatile or nonvolatile. 
     Surprisingly, in the first method to make a (co)polymer matrix composite, the relatively high particle loadings allow a slurry to be made that can be shaped into a layer, that maintains its form as the solvent is heated to become miscible with the (co)polymer. The solvent used is normally volatile and is later evaporated. 
     Typically, the maximum particle loading that can be achieved in traditional particle-filled composites (dense (co)polymeric films, adhesives, etc.), is not more than about 40 to 60 vol. %, based on the volume of the particles and binder. Incorporating more than 60 vol. % particles into traditional particle-filled composites typically is not achievable because such high particle loaded materials cannot be processed via coating or extrusion methods and/or the resulting composite becomes very brittle. 
     Traditional composites also typically fully encapsulate the particles with binder, preventing access to the particle surfaces and minimizing potential particle-to-particle contact. Surprisingly, the high levels of solvent and the phase separated morphologies obtained with the methods described herein, enable relatively high particle loadings with relatively low amounts of high molecular weight binder. The through-porous. phase-separated morphologies also allow samples to be breathable at relatively low to relatively high particle concentrations. The high particle loading also helps minimize the formation of thin non-porous (co)polymer layer that can form during phase separation. Moreover, the (co)polymer matrix composites described herein are relatively flexible and tend not to shed particles. Although not wanting to be bound by theory, it is believed that another advantage of embodiments of (co)polymer matrix composites described herein, is that the particles are not fully coated with binder enabling a high degree of particle surface contact, without masking due to the porous nature of the binder. It should be noted that compression of the layer can significantly enhance the particle-to-particle contact. The high molecular weight binder also does not readily flow in the absence of solvent, even at elevated temperatures (e.g., 135° C.). 
     In the first method using a TIPS process to make a (co)polymer matrix composite, the solvent used is normally nonvolatile, but in some exemplary embodiments, the solvent is advantageously selected to be a volatile solvent or may comprise a mixture of a least one non-volatile solvent and at least one volatile solvent. 
     If the particles are dense, typically the slurry is continuously mixed or blended to prevent or reduce settling or separation of the (co)polymer and/or particles from the solvent. In some embodiments, the slurry is degassed using techniques known in the art to remove entrapped air. 
     The slurry can be formed in to an article using techniques known in the art, including knife coating, roll coating (e.g., roll coating through a defined nip), and coating through any number of different dies having the appropriate dimensions or profiles. 
     In some embodiments of the first method, combining is conducted at at least one temperature below the melting point of the (co)polymer and below the boiling point of the solvent. 
     In some embodiments of the first method, heating is conducted at at least one temperature above the melting point of the miscible thermoplastic (co)polymer-solvent solution, and below the boiling point of the solvent. 
     In some embodiments of the first method, inducing phase separation is conducted at a temperature less than the melting point of the (co)polymer in the slurry. Although not wanting to be bound, it is believed that in some embodiments, solvents used to make a miscible blend with the (co)polymer can cause melting point depression in the (co)polymer. The melting point described herein includes below any melting point depression of the (co)polymer solvent system. 
     In some embodiments of the first method, the solvent is a blend of at least two individual solvents. In some embodiments, when the (co)polymer is a polyolefin (e.g., at least one of polyethylene or polypropylene), the solvent may be at least one of mineral oil, tetralin, decalin, 1,2-orthodichlorobenzene, cyclohexane-toluene mixture, dodecane, paraffin oil/wax, kerosene, p-xylene/cyclohexane mixture (1/1 wt./wt.), camphene, 1,2,4 trichlorobenzene, octane, orange oil, vegetable oil, castor oil, or palm kernel oil. In some embodiments, when the (co)polymer is polyvinylidene fluoride, the solvent is at least one of ethylene carbonate, propylene carbonate, or 1,2,3 triacetoxypropane. 
     In some embodiments of the first method, the (co)polymeric network structure may be formed during phase separation. In some embodiments, the (co)polymeric network structure is provided by an induced phase separation of a miscible thermoplastic (co)polymer-solvent solution. In some embodiments, the phase separation is induced thermally (e.g., via thermally induced phase separation (TIPS) by quenching to a lower temperature than used during heating). Cooling can be provided, for example, in air, liquid, or on a solid interface, and varied to control the phase separation. The (co)polymeric network structure may be inherently porous (i.e., have pores). The pore structure may be open, enabling fluid communication from an interior region of the (co)polymeric network structure to an exterior surface of the (co)polymeric network structure and/or between a first surface of the (co)polymeric network structure and an opposing second surface of the (co)polymeric network structure. 
     In some embodiments of the method described herein, the weight ratio of solvent to (co)polymer is at least 9:1. In some embodiments, the volume ratio of particles to (co)polymer is at least 9:1. In some embodiments, and for ease of manufacturing, it may be desirable to form a layer at room temperature. Typically, during the layer formation using phase separation, relatively small pores are particularly vulnerable to collapsing during solvent extraction. The relatively high particle to (co)polymer loading achievable by the methods described herein may reduce pore collapsing and yield a more uniform defect-free (co)polymer matrix composite. 
     In some embodiments, the first method further comprises removing at least a portion (in some embodiments, at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, 99.5, or even 100 percent by weight of the solvent, based on the weight of the solvent in the formed article) of the solvent from the formed article, after inducing phase separation of the thermoplastic (co)polymer from the solvent. 
     In some embodiments of the first method, at least 90 percent by weight of the solvent, based on the weight of the solvent in the formed article, is removed, wherein the formed article, before removing at least 90 percent by weight of the solvent, based on the weight of the solvent in the formed article, of the solvent has a first volume, wherein the formed article, after removing at least 90 percent by weight of the solvent, based on the weight of the solvent in the formed article, has a second volume, and wherein the difference between the first and second volume (i.e., (the first volume minus the second volume) divided by the first volume times 100) is less than 10 (in some embodiments, less than 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.75, 0.5, or even less than 0.3) percent. 
     Volatile solvents can be removed from the (co)polymer matrix composite, for example, by allowing the solvent to evaporate from at least one major surface of the (co)polymer matrix composite. Evaporation can be aided, for example, by the addition of at least one of heat, vacuum, or air flow. Evaporation of flammable solvents can be achieved in a solvent-rated oven. If the first solvent, however, has a low vapor pressure, a second solvent, of higher vapor pressure, may be used to extract the first solvent, followed by evaporation of the second solvent. For example, in some embodiments, when mineral oil is used as a first solvent, isopropanol at elevated temperature (e.g., about 60° C.) or a blend of methyl nonafluorobutyl ether (C 4 F 9 OCH 3 ), ethylnonafluorobutyl ether (C 4 F 9 OC 2 H 5 ), and trans-1,2-dichloroethylene (available under the trade designation “NOVEC 72DE” from 3M Company, St. Paul, Minn.) may be used as a second solvent to extract the first solvent, followed by evaporation of the second solvent. In some embodiments, when at least one of vegetable oil or palm kernel oil is used as the first solvent, isopropanol at elevated temperature (e.g., about 60° C.) may be used as the second solvent. In some embodiments, when ethylene carbonate is used as the first solvent, water may be used as the second solvent. 
     In some embodiments of the first method, the article has first and second major surfaces with ends perpendicular to the first and second major surfaces, and the ends are unrestrained (i.e., without the need for restraints during extraction) during the solvent removal. This can be done, for example, by drying a portion of a layer without restraint in an oven. Continuous drying can be achieved, for example, by drying a long portion of a layer supported on a belt as it is conveyed through an oven. Alternatively, to facilitate removal of non-volatile solvents, for example, a long portion of a layer can be continuously conveyed through a bath of compatible volatile solvent thereby exchanging the solvents and allowing the layer to be subsequently dried without restraint. Not all the non-volatile solvent, however, need be removed from the layer during the solvent exchange. Small amounts of non-volatile solvents may remain and act as a plasticizer to the (co)polymer. 
     In some embodiments of the first method, the formed, phase separated article after the solvent removal, has a porosity of at least 5 (in some embodiments, at least 10, 20, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or even at least 90; in some embodiments, in a range from 25 to 90) percent. This porosity is caused by the phase separation of the (co)polymer from the solvent, which initially leaves no unfilled voids, as the pores in the (co)polymer matrix composite are filled with solvent. After the solvent is completely or partly removed, void spaces in the (co)polymer matrix composite are exposed. The particle-to-particle interactions can minimize the collapse or deformation of the porous (co)polymer matrix composite from capillary-induced negative pressures from the solvent drying process. 
     In some embodiments of the first method, no solvent is removed from the formed article (even after inducing phase separation of the thermoplastic (co)polymer from the solvent). This can be accomplished, for example, by using a non-volatile solvent (e.g., mineral oil or wax) and not completing the extraction/evaporation step. 
     Second Method 
     In another aspect, the present disclosure describes a second method of making (co)polymer matrix composites described herein, the method comprising: 
     combining (e.g., mixing or blending) a thermoplastic (co)polymer, a solvent for the thermoplastic (co)polymer, a plurality of thermally-conductive particles, and a plurality of endothermic particles to form a suspension of the thermally-conductive and endothermic particles in a miscible thermoplastic (co)polymer-solvent solution; 
     inducing phase separation of the thermoplastic (co)polymer from the solvent; and 
     removing at least a portion of the solvent to provide the (co)polymer matrix composite. 
     In the second method, the (co)polymer is miscible with the solvent before the desired article is formed. In the second method, phase separation is achieved via solvent induced phase separation (SIPS) using a wet or dry process, or thermally induced phase separation methods. 
     In the SIPS wet process, the solvent dissolving the (co)polymer is exchanged with a nonsolvent to induce phase separation. The new exchanging solvent in the system becomes the pore former for the (co)polymer. In the SIPS dry process, the solvent dissolving the (co)polymer is evaporated to induce phase separation. In the dry process, a nonsolvent is also solubilized in the solution by the solvent dissolving the (co)polymer. This nonsolvent for the (co)polymer becomes the pore former for the (co)polymer as the solubilizing solvent evaporates. The process is considered a “dry process” because no additional exchange liquids are used. The nonsolvent is also normally volatile but has a boiling point at least 30° C. lower than the solvent. 
     In the second method to make a (co)polymer matrix composite by the wet or dry SIPS process, the solvents are normally nonvolatile for the wet process and volatile for the dry process. However, in some exemplary embodiments of either the wet or dry SIPS process, the solvent may advantageously comprise a mixture of a least one non-volatile solvent and at least one volatile solvent. 
     In some embodiments, the second method further comprises adding the thermally-conductive particles and/or the endothermic particles and the optional endothermic particles to the miscible (co)polymer-solvent solution, prior to phase separation. The (co)polymeric network structure may be formed during the phase separation of the process. In some embodiments, the (co)polymeric network structure is provided via an induced phase separation of a miscible thermoplastic (co)polymer-solvent solution. In some embodiments, the phase separation is induced thermally (e.g., via thermally induced phase separation (TIPS) by quenching to lower temperature), chemically (e.g., via solvent induced phase separation (SIPS) by substituting a poor solvent for a good solvent), or change in the solvent ratio (e.g., by evaporation of one of the solvents). 
     Other phase separation or pore formation techniques known in the art, such as discontinuous (co)polymer blends (also sometimes referred to as (co)polymer assisted phase inversion (PAPI)), moisture induced phase separation, or vapor induced phase separation, can also be used. The (co)polymeric network structure may be inherently porous (i.e., have pores). The pore structure may be open, enabling fluid communication from an interior region of the (co)polymeric network structure to an exterior surface of the (co)polymeric network structure and/or between a first surface of the (co)polymeric network structure and an opposing second surface of the (co)polymeric network structure. 
     In some embodiments of the second method, the (co)polymer in the miscible thermoplastic (co)polymer-solvent solution has a melting point, wherein the solvent has a boiling point, and wherein combining is conducted at at least one temperature above the melting point of the miscible thermoplastic (co)polymer-solvent solution, and below the boiling point of the solvent. 
     In some embodiments of the second method, the (co)polymer in the miscible thermoplastic (co)polymer-solvent solution has a melting point, and wherein inducing phase separation is conducted at at least one temperature less than the melting point of the (co)polymer in the miscible thermoplastic (co)polymer-solvent solution. The thermoplastic (co)polymer-solvent mixture may be heated to facilitate the dissolution of the thermoplastic (co)polymer in the solvent. After the thermoplastic (co)polymer has been phase separated from the solvent, at least a portion of the solvent may be removed from the (co)polymer matrix composite using techniques known in the art, including evaporation of the solvent or extraction of the solvent by a higher vapor pressure, second solvent, followed by evaporation of the second solvent. 
     In some embodiments, in a range from 10 to 100 (in some embodiments, in a range from 20 to 100, 30 to 100, 40 to 100, 50 to 100, 60 to 100, 70 to 100, 80 to 100, 90 to 100, 95 to 100, or even 98 to 100) percent by weight of the solvent, and second solvent, if used, may be removed from the (co)polymer matrix composite. 
     The solvent is typically selected such that it is capable of dissolving the (co)polymer and forming a miscible (co)polymer-solvent solution. Heating the solution to an elevated temperature may facilitate the dissolution of the (co)polymer. In some embodiments, combining the (co)polymer and solvent is conducted at at least one temperature in a range from 20° C. to 350° C. The endothermic particles may be added at any or all of the combining, before the (co)polymer is dissolved, after the (co)polymer is dissolved, or at any time there between. 
     In some embodiments, the solvent is a blend of at least two individual solvents. In some embodiments, when the (co)polymer is a polyolefin (e.g., at least one of polyethylene or polypropylene), the solvent may be at least one of mineral oil, paraffin oil/wax, camphene, orange oil, vegetable oil, castor oil, or palm kernel oil. In some embodiments, when the (co)polymer is polyvinylidene fluoride, the solvent is at least one of ethylene carbonate, propylene carbonate, or 1,2,3 triacetoxypropane. 
     In some embodiments, the solvent may be removed, for example, by evaporation, high vapor pressure solvents being particularly suited to this method of removal. If the first solvent, however, has a low vapor pressure, a second solvent, of higher vapor pressure, may be used to extract the first solvent, followed by evaporation of the second solvent. For example, in some embodiments, when mineral oil is used as a first solvent, isopropanol at elevated temperature (e.g., about 60° C.) or a blend of methyl nonafluorobutyl ether (C 4 F 9 OCH 3 ), ethylnonafluorobutyl ether (C 4 F 9 OC 2 H 5 ), and trans-1,2-dichloroethylene (available under the trade designation “NOVEC 72DE” from 3M Company (St. Paul, Minn.) may be used as a second solvent to extract the first solvent, followed by evaporation of the second solvent. In some embodiments, when at least one of vegetable oil or palm kernel oil is used as the first solvent, isopropanol at elevated temperature (e.g., about 60° C.) may be used as the second solvent. In some embodiments, when ethylene carbonate is used as the first solvent, water may be used as the second solvent. 
     Typically, in the phase separation process, the blended mixture is formed in to a layer prior to solidification of the (co)polymer. The (co)polymer is dissolved in solvent (that allows formation of miscible thermoplastic-solvent solution), and the endothermic particles dispersed to form a blended mixture, that is formed into an article (e.g., a layer), followed by phase separation (e.g., temperature reduction for TIPS, solvent evaporation or solvent exchange with nonsolvent for SIPS). The layer-forming may be conducted using techniques known in the art, including, knife coating, roll coating (e.g., roll coating through a defined nip), and extrusion (e.g., extrusion through a die (e.g., extrusion through a die having the appropriate layer dimensions (i.e., width and thickness of the die gap))). In one exemplary embodiment, the mixture has a paste-like consistency and is formed in to a layer by extrusion (e.g., extrusion through a die having the appropriate layer dimensions (i.e., width and thickness of the die gap)). 
     After forming the slurry in to a layer, where the thermoplastic (co)polymer is miscible in its solvent, the (co)polymer is then induced to phase separate. Several techniques may be used to induce phase separation, including at least one of thermally induced phase separation or solvent induced phase separation. Thermally induced phase separation may occur when the temperature at which induced phase separation is conducted is lower than the combining temperature of the (co)polymer, solvent, and endothermic particles. This may be achieved by cooling the miscible (co)polymer-solvent solution, if combining is conducted near room temperature, or by first heating the miscible (co)polymer-solvent solution to an elevated temperature (either during combining or after combining), followed by decreasing the temperature of the miscible (co)polymer-solvent solution, thereby inducing phase separation of the thermoplastic (co)polymer. 
     In both cases, the cooling may cause phase separation of the (co)polymer from the solvent. Solvent induced phase separation can be conducted by adding a second solvent, a poor solvent for the (co)polymer, to the miscible (co)polymer-solvent solution or may be achieved by removing at least a portion of the solvent of the miscible (co)polymer-solvent solution (e.g., evaporating at least a portion of the solvent of the miscible (co)polymer-solvent solution), thereby inducing phase separation of the (co)polymer. Combination of phase separation techniques (e.g., thermally induced phase separation and solvent induced phase separation), may be employed. 
     Thermally induced phase separation, may be advantageous, as it also facilitates the dissolution of the (co)polymer when combining is conducted at an elevated temperature. In some embodiments, thermally inducing phase separation is conducted at at least one temperature in a range from 5 to 300 (in some embodiments, in a range from 5 to 250, 5 to 200, 5 to 150, 15 to 300, 15 to 250, 15 to 200, 15 to 130, or even 25 to 110) ° C. below the combining temperature. 
     After inducing phase separation, at least a portion of the solvent may be removed, thereby forming a porous (co)polymer matrix composite layer having a (co)polymeric network structure and an endothermic material distributed within the thermoplastic (co)polymer network structure. 
     The solvent may be removed by evaporation, high vapor pressure solvents being particularly suited to this method of removal. If the first solvent, however, has a low vapor pressure, a second solvent, of higher vapor pressure, may be used to extract the first solvent, followed by evaporation of the second solvent. In some embodiments, in a range from 10 to 100 (in some embodiments, in a range from 20 to 100, 30 to 100, 40 to 100, 50 to 100, 60 to 100, 70 to 100, 80 to 100, 90 to 100, 95 to 100, or even 98 to 100) percent by weight of the solvent, and second solvent, if used, may be removed from the (co)polymer matrix composite. 
     Optional Additional Processing Steps 
     In some embodiments, the first and second methods further comprise compressing the (co)polymer matrix composite. That is, after inducing phase separation, the formed (co)polymeric network structure may be compressed, for example, to tune the air flow resistance of the (co)polymer matrix composite. Compression of the (co)polymer matrix composite may be achieved, for example, by conventional calendaring processes known in the art. 
     In some embodiments, where the network structure is plastically deformed by at least a compressive force, vibratory energy may be imparted during the application of the compressive force. In some of these embodiments, the (co)polymer composite is in the form of a strip of indefinite length, and the applying of a compressive force step is performed as the strip passes through a nip. A tensile loading may be applied during passage through such a nip. For example, the nip may be formed between two rollers, at least one of which applies the vibratory energy; between a roller and a bar, at least one of which applies the vibratory energy; or between two bars, at least one of which applies the vibratory energy. The applying of the compressive force and the vibratory energy may be accomplished in a continuous roll-to-roll fashion, or in a step-and-repeat fashion. In other embodiments, the applying a compressive force step is performed on a discrete layer between, for example, a plate and a platen, at least one of which applies the vibratory energy. In some embodiments, the vibratory energy is in the ultrasonic range (e.g., 20 kHz), but other ranges are considered to be suitable. For further details regarding plastically deforming the network structure, see co-pending application having U.S. Ser. No. 62/578,732, filed Oct. 30, 2017, the disclosure of which is incorporated by reference. 
     In some embodiments, the density of the compressed (co)polymer matrix composite is at least 1 (in some embodiments, at least 2.5, or even at least 1.75; in some embodiments, in the range from 1 to 1.75, or even 1 to 2.5) g/cm 3  after compression. 
     In some embodiments, compressing the (co)polymeric matrix composite increases its density by increasing the particle-to-particle contact. This increase in density can increase the amount of endothermic per unit volume. 
     In some embodiments, (co)polymer matrix composite described herein can be wrapped around a 0.5 mm (in some embodiments, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 1 cm, 5 cm, 10 cm, 25 cm, 50 cm, or even 1 meter) rod without breaking. 
     Various unexpected results and advantages are obtained in exemplary embodiments of the disclosure. These and other unexpected results and advantages are within the scope of the following exemplary embodiments. 
     Listing of Exemplary Embodiments 
     1A. A (co)polymer matrix composite comprising: 
     a porous (co)polymeric network structure; 
     a plurality of thermally-conductive particles and a plurality of endothermic particles distributed within the (co)polymeric network structure, wherein the thermally-conductive particles and endothermic particles are present in a range from 15 to 99 (in some embodiments, in a range from 25 to 98, 50 to 98, 75 to 98, or even 93 to 97) weight percent, based on the total weight of the thermally-conductive particles, the endothermic particles and the (co)polymer (excluding any solvent); and optionally wherein 
     the (co)polymer matrix composite volumetrically expands by at least 10% (in some embodiments at least 20%, 30%, 40% or even 50%) of its initial volume when exposed to a temperature of at least 135 (in some embodiments, at least 150, 175, or even at least 200; in some embodiments, in a range from 135 to 400, or even 200 to 400) ° C. 
     2A. The (co)polymer matrix composite of Exemplary Embodiment 1A, wherein the (co)polymer matrix composite has a density of at least 0.3 (in some embodiments, in a range from 0.3 to 2.3, 0.3 to 2.1, 0.3 to 1.5, or even 0.3 to 1) g/cm 3 .
 
3A. The (co)polymer matrix composite of any preceding Exemplary Embodiment, wherein the (co)polymer matrix composite has a porosity of at least 5 (in some embodiments, in a range from 10 to 80, 20 to 70, or even 30 to 60) percent.
 
4A. The (co)polymer matrix composite of any preceding Exemplary Embodiment, wherein the thermally-conductive particles comprise at least one of electrically non-conductive particles or electrically-conductive particles, further wherein the electrically non-conductive particles are ceramic particles selected from the group consisting of boron nitride, aluminum trihydrate, silicon carbide, silicon nitride, metal oxides, metal nitrides, and combinations thereof; and the electrically-conductive particles are carbon particles selected from the group consisting of carbon black, graphite, graphene and combinations thereof, and/or metal particles selected from the group consisting of aluminum, copper, nickel, silver, platinum, gold, and combinations thereof, additionally wherein the endothermic particles comprise at least one of sodium bicarbonate, calcium sulfate dihydrate, aluminum trihydrate, magnesium sulfate octahydrate, ammonium oxalate, sodium metasilicate pentahydrate, sodium silicate, a crystalline wax, a crystalline (co)polymer, a semi-crystalline (co)polymer, or a combination thereof.
 
5A. The (co)polymer matrix composite of any preceding Exemplary Embodiment, wherein the thermally-conductive particles exhibit a number average particle size (average length of longest dimension) in a range from 500 nm to 7000 micrometers (in some embodiments, in a range from 70 micrometers to 300 micrometers, 300 micrometers to 800 micrometers, 800 micrometers to 1500 micrometers, or even 1500 micrometers to 7000 micrometers), and the endothermic particles exhibit a number average particle size (average length of longest dimension) in a range from 500 nm to 7000 micrometers (in some embodiments, in a range from 70 micrometers to 300 micrometers, 300 micrometers to 800 micrometers, 800 micrometers to 1500 micrometers, or even 1500 micrometers to 7000 micrometers).
 
6A. The (co)polymer matrix composite of any preceding Exemplary Embodiment, wherein the thermally-conductive particles are present at a weight fraction in a range from 15 to 99 (in some embodiments, in a range from 25 to 98, 50 to 98, 75 to 98, or even 93 to 97) weight percent, and wherein the endothermic particles are present at a weight fraction in a range from 15 to 99 (in some embodiments, in a range from 25 to 98, 50 to 98, 75 to 98, or even 93 to 97) weight percent, based on the total weight of the (co)polymer matrix composite.
 
7A. The (co)polymer matrix composite of any preceding Exemplary Embodiment, wherein the porous (co)polymeric network structure comprises at least one of polyurethane, polyester, polyamide, polyether, polycarbonate, polyimide, polysulfone, polyethersulfone, polyphenylene oxide, polyacrylate, poly(meth)acrylate, polyacrylonitrile, polyolefin, styrene or styrene-based random and block (co)polymer, chlorinated (co)polymer, fluorinated (co)polymer (e.g., polyvinylidene fluoride), or (co)polymers of ethylene and chlorotrifluoroethylene.
 
8A. The (co)polymer matrix composite of any preceding Exemplary Embodiment, wherein the porous (co)polymeric network structure comprises a phase separated plurality of interconnected morphologies (e.g., at least one of fibrils, nodules, nodes, open cells, closed cells, leafy laces, strands, nodes, spheres, or honeycombs).
 
9A. The (co)polymer matrix composite of any preceding Exemplary Embodiment, wherein the porous (co)polymeric network structure comprises a (co)polymer having a number average molecular weight in a range from of 5×10 4  to 1×10 7  (in some embodiments, in a range from 1×10 6  to 8×10 6 , 2×10 6  to 6×10 6 , or even 3×10 6  to 5×10 6 ) g/mol.
 
10A. The (co)polymer matrix composite of any preceding Exemplary Embodiment, wherein the (co)polymer matrix composite is in the form of a layer having a thickness in a range from 50 to 7000 micrometers.
 
11A. The (co)polymer matrix composite of any preceding Exemplary Embodiment, wherein the porous (co)polymeric network structure is produced by an induced phase separation of a miscible thermoplastic (co)polymer-solvent solution.
 
12A. The (co)polymer matrix composite of Exemplary Embodiment 11A, wherein induced phase separation is at least one of thermally induced phase separation and solvent induced phase separation.
 
13A. The (co)polymer matrix composite of any preceding Exemplary Embodiment, having first and second planar, opposed major surfaces.
 
14A. The (co)polymer matrix composite of any preceding Exemplary Embodiment, having first and second opposed major surfaces, wherein the first major surface is nonplanar (e.g., curved or protrusions with no planar surface there between).
 
15A. The (co)polymer matrix composite of either Exemplary Embodiment 13A or 14A, wherein the first major surface has first protrusions extending outwardly from the first major surface. In some embodiments, the protrusions are integral with the first major surface.
 
16A. The (co)polymer matrix composite of Exemplary Embodiment 15A, wherein the first protrusions are at least one of a post, a rail, a hook, a pyramid, a continuous rail, a continuous multi-directional rail, a hemisphere, a cylinder, or a multi-lobed cylinder.
 
17A. The (co)polymer matrix composite of any of Exemplary Embodiments 13A to 16A, wherein the first major surface has first depressions extending into the first major surface.
 
18A. The (co)polymer matrix composite of Exemplary Embodiment 17A, wherein the first depressions are at least one of a groove, a slot, an inverted pyramid, a hole (including a thru or blind hole), or a dimple.
 
     19A. The (co)polymer matrix composite of any of Exemplary Embodiments 15A to 18A, wherein the second major surface has second protrusions extending outwardly from the second major surface. 
     20A. The (co)polymer matrix composite of Exemplary Embodiment 19A, wherein the second protrusions are at least one of a post, a rail, a hook, a pyramid, a continuous rail, a continuous multi-directional rail, a hemisphere, a cylinder, or a multi-lobed cylinder.
 
21A. The (co)polymer matrix composite of any of Exemplary Embodiments 19A to 20A, wherein the second major surface has second depressions extending into the second major surface.
 
22A. The (co)polymer matrix composite of Exemplary Embodiment 21A, wherein the second depressions are at least one of a groove, a slot, an inverted pyramid, a hole (including a thru or blind hole), or a dimple.
 
23A. The (co)polymer matrix composite of any preceding Exemplary Embodiment, further comprising a reinforcement (e.g., attached to the (co)polymer matrix composite, partial therein, and/or therein).
 
24A. The (co)polymer matrix composite of any preceding Exemplary Embodiment, that can be wrapped around a 0.5 mm (in some embodiments, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 1 cm, 5 cm, 10 cm, 25 cm, 50 cm, or even 1 meter) rod without breaking.
 
25A. The (co)polymer matrix composite of of any of Exemplary Embodiments 1A to 9A, wherein the thermally-conductive particles and the endothermic particles are present in a single layer.
 
26A. The (co)polymer matrix composite of any of Exemplary Embodiments 1A to 9A, wherein the thermally-conductive particles are present in a first layer, and the endothermic particles are present in a second layer adjacent to the first layer, optionally wherein the second layer adjoins the first layer.
 
27A. The (co)polymer matrix composite of any of Exemplary Embodiments 1A to 9A, wherein the thermally-conductive particles are present in a first layer having opposed first and second major surfaces, and the endothermic particles are present in a second layer overlaying and adjacent to the first major surface of the first layer, and a third layer overlaying and adjacent to the second major surface of the first layer, optionally wherein the second layer adjoins the first major surface, and the third layer adjoins the second major surface.
 
28A. The (co)polymer matrix composite of any of Exemplary Embodiments 1A to 9A, wherein the endothermic particles are present in a first layer having opposed first and second major surfaces, and the thermally-conductive particles are present in a second layer overlaying and adjacent to the first major surface of the first layer and a third layer overlaying and adjacent to the second major surface of the first layer, optionally wherein the second layer adjoins the first major surface, and the third layer adjoins the second major surface.
 
29A. The (co)polymer matrix composite of any preceding Exemplary Embodiment, comprising at least one of a viscosity modifier (e.g., fumed silica, block (co)polymers, and wax), a plasticizer, a thermal stabilizer (e.g., such as available, for example, under the trade designation “IRGANOX 1010” from BASF, Ludwigshafen, Germany), an antimicrobial (e.g., silver and quaternary ammonium), a flame retardant, an antioxidant, a dye, a pigment, or an ultraviolet (UV) stabilizer.
 
1B. A method of making the (co)polymer matrix composite of any preceding Exemplary Embodiment, the method comprising:
 
     combining (e.g., heating, mixing and/or blending) a thermoplastic (co)polymer, a solvent, a plurality of thermally-conductive particles, and a plurality of endothermic particles to provide a slurry; 
     forming the slurry in to an article (e.g., a layer); 
     heating the article in an environment to retain at least 90 (in some embodiments, at least 91, 92, 93, 94, 95, 96, 97, 98, 99, or even at least 99.5) percent by weight of the solvent in the article, based on the weight of the solvent in the article, and solubilize at least 50 (in some embodiments, at least 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, or even 100) percent of the thermoplastic (co)polymer, based on the total weight of the thermoplastic (co)polymer; and 
     inducing phase separation of the thermoplastic (co)polymer from the solvent to provide the (co)polymer matrix composite. 
     2B. The method of Exemplary Embodiment 1B, further comprising removing at least a portion (in some embodiments, at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, 99.5, or even 100 percent by weight of the solvent, based on the weight of the solvent in the formed article) of the solvent from the formed article after inducing phase separation of the thermoplastic (co)polymer from the solvent.
 
3B. The method of Exemplary Embodiment 2B, wherein at least 90 percent by weight of the solvent, based on the weight of the solvent in the formed article, is removed, wherein the formed article, before removing at least 90 percent by weight of the solvent, based on the weight of the solvent in the formed article, of the solvent has a first volume, wherein the formed article, after removing at least 90 percent by weight of the solvent, based on the weight of the solvent in the formed article, has a second volume, and wherein the difference between the first and second volume (i.e., (the first volume minus the second volume) divided by the first volume times 100) is less than 10 (in some embodiments, less than 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.75, 0.5, or even less than 0.3) percent.
 
4B. The method of Exemplary Embodiment 3B, wherein the article has first and second major surfaces with ends perpendicular to the first and second major surfaces, and where the ends are unrestrained during the solvent removal.
 
5B. The method of either Exemplary Embodiment 3B or 4B, wherein the formed article after the solvent removal, has a porosity at least 5 (in some embodiments, at least 10, 20, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or even at least 90; in some embodiments, in a range from 25 to 90) percent.
 
6B. The method of Exemplary Embodiment 1B, wherein no solvent is removed from the formed article (even after inducing phase separation of the thermoplastic (co)polymer from the solvent).
 
7B. The method of any preceding B Exemplary Embodiment, wherein inducing phase separation includes thermally induced phase separation.
 
8B. The method of any preceding B Exemplary Embodiment, wherein the (co)polymer in the slurry has a melting point, wherein the solvent has a boiling point, and wherein combining is conducted below the melting point of the (co)polymer in the slurry, and below the boiling point of the solvent.
 
9B. The method of any preceding B Exemplary Embodiment, wherein the (co)polymer in the slurry has a melting point, and wherein inducing phase separation is conducted at less than the melting point of the (co)polymer in the slurry.
 
10B. The method of any preceding B Exemplary Embodiment, further comprising compressing the (co)polymer matrix composite.
 
11B. The method of any of Exemplary Embodiments 1B to 9B, further comprising applying vibratory energy to the (co)polymer matrix composite simultaneously with the applying a compressive force.
 
12B. The method of any preceding B Exemplary Embodiment, wherein the porous (co)polymeric network structure comprises at least one of polyacrylonitrile, polyurethane, polyester, polyamide, polyether, polycarbonate, polyimide, polysulfone, polyethersulfone, polyphenylene oxide, polyacrylate, poly(meth)acrylate, polyolefin, styrene or styrene-based random and block (co)polymer, chlorinated (co)polymer, fluorinated (co)polymer, or (co)polymers of ethylene and chlorotrifluoroethylene.
 
13B. The method of any preceding B Exemplary Embodiment, wherein the porous (co)polymeric network structure comprises a plurality of interconnected morphologies (e.g., at least one of fibrils, nodules, nodes, open cells, closed cells, leafy laces, strands, nodes, spheres, or honeycombs).
 
14B. The method of any preceding B Exemplary Embodiment, wherein the porous (co)polymeric network structure is produced by an induced phase separation of a miscible thermoplastic (co)polymer-solvent solution.
 
15B. The method of Exemplary Embodiment 14B, wherein inducing phase separation includes thermally induced phase separation.
 
1C. A method of making the (co)polymer matrix composite of any preceding A Exemplary Embodiment, the method comprising:
 
     combining (e.g., heating, mixing and/or blending) a thermoplastic (co)polymer, a solvent for the thermoplastic (co)polymer, a plurality of thermally-conductive particles, and a plurality of endothermic particles to form a suspension of endothermic particles in a miscible thermoplastic (co)polymer-solvent solution; 
     inducing phase separation of the thermoplastic (co)polymer from the solvent; and 
     removing at least a portion of the solvent to provide the (co)polymer matrix composite. 
     2C. The method of Exemplary Embodiment 1C, wherein inducing phase separation includes at least one of thermally induced phase separation or solvent induced phase separation.
 
3C. The method of Exemplary Embodiment 1C, wherein the (co)polymer in the miscible thermoplastic (co)polymer-solvent solution has a melting point, wherein the solvent has a boiling point, and wherein combining is conducted above the melting point of the miscible thermoplastic (co)polymer-solvent solution, and below the boiling point of the solvent.
 
4C. The method of any preceding C Exemplary Embodiment, wherein the (co)polymer in the miscible thermoplastic (co)polymer-solvent solution has a melting point, and wherein inducing phase separation is conducted at less than the melting point of the (co)polymer in the miscible thermoplastic (co)polymer-solvent solution.
 
5C. The method of any preceding C Exemplary Embodiment, further comprising compressing the (co)polymer matrix composite.
 
6C. The method of any of Exemplary Embodiments 1C to 4C, further comprising applying vibratory energy to the (co)polymer matrix composite simultaneously with the applying a compressive force.
 
7C. The method of any preceding C Exemplary Embodiment, wherein the porous (co)polymeric network structure comprises at least one of polyacrylonitrile, polyurethane, polyester, polyamide, polyether, polycarbonate, polyimide, polysulfone, polyethersulfone, polyphenylene oxide, polyacrylate, poly(meth)acrylate, polyolefin, styrene or styrene-based random and block (co)polymer, chlorinated (co)polymer, fluorinated (co)polymer, or (co)polymers of ethylene and chlorotrifluoroethylene.
 
8C. The method of any preceding C Exemplary Embodiment, wherein the porous (co)polymeric network structure comprises a plurality of interconnected morphologies (e.g., at least one of fibrils, nodules, nodes, open cells, closed cells, leafy laces, strands, nodes, spheres, or honeycombs).
 
1D. An article (e.g., a thermal interface material, a thermally initiated fuse or a fire stop device) comprising the (co)polymer matrix composite of any preceding A Exemplary Embodiment.
 
     Various advantages and embodiments 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. 
     The operation of the present disclosure will be further described with regard to the following detailed examples. These examples are offered to further illustrate the various specific and preferred embodiments and techniques. It should be understood, however, that many variations and modifications may be made while remaining within the scope of the present disclosure. 
     EXAMPLES 
     These Examples are merely for illustrative purposes and are not meant to be overly limiting on the scope of the appended claims. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the present disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. 
     Test Methods 
     Air Flow Resistance Test 
     Air flow resistance was measured using a densometer (obtained as Model 4110 from Gurley Precision Instruments, Troy, N.Y.) with a timer (obtained as Model 4320 from Gurley Precision Instruments). A sample was clamped in the tester. The timer and photo eye were reset and the cylinder was released, allowing air to pass through a 1 square inch (6.5 cm 2 ) circle with a constant force of 4.88 inches (12.4 cm) of water (1215 N/m 2 ). The time to pass 50 mL of air was recorded. 
     Bubble Point Pressure Test 
     Bubble point pressure is a commonly used technique to characterize the largest pore in a porous membrane. This technique is a modification to ASTM F316-03 (2006), “Standard Test Methods for Pore Size Characteristics of Membrane Filters by Bubble Point and Mean Flow Pore Test,” the entire disclosure of which is incorporated herein by reference and includes an automated pressure controller and flow meter to quantify when the bubble point pressure had been reached. 
     Discs 47 mm in diameter were cut and samples soaked in IPA to fully fill and wet out the pores within the sample. The wet samples were then placed in a holder (47 mm; Stainless Holder Part #2220 from Pall Corporation (Port Washington, N.Y.). Pressure was slowly increased on the top of the sample using a pressure controller and gas flow was measured on the bottom with a gas flow meter. The pressure was recoded when there was a significant increase in flow from the baseline flow rate. This was reported as the bubble point pressure pounds per square inch (psi) (centimeters of mercury, cm Hg or Pascals, Pa). 
     Density and Porosity Test 
     The density of a sample was calculated using a method similar to ASTM F-1315-17 (2017), “Standard Test Method for Density of a Sheet Gasket Material,” the entire disclosure of which is incorporated herein by reference, by cutting a 47 mm diameter disc, weighing the disc on an analytical balance of suitable resolution (typically 0.0001 gram), and measuring the thickness of the disc on a thickness gauge (obtained as Model 49-70 from Testing Machines, Inc. (New Castle, Del.) with a dead weight of 7.3 psi (50.3 KPa) and a flat anvil of 0.63 inch (1.6 cm) diameter, with a dwell time of about 3 seconds and a resolution of +/−0.0001 inch. The density was then calculated by dividing the mass by the volume, which was calculated from the thickness and diameter of the sample. With the known densities and weight fractions of the components of the (co)polymer matrix composite, the theoretical density of the (co)polymer matrix composite was calculated by the rule of mixtures. Using the theoretical density and the measured density, the porosity was calculated as: 
       Porosity=[1−(measured density/theoretical density)]×100.
 
     Thermal Conductivity Test 
     The thermal conductivity of the films was measured according to ASTM D5470 (“Standard Test Method for Thermal Transmission Properties of Thermally Conductive Electrical Insulation Materials”), the entire disclosure of which is incorporated herein by reference, using the Thermal Interface Material Tester Model TIM1300 from AnalysisTech (Wakefield, Mass.). 33 mm discs were cut out of the densified squares using a hole punch. The test temperature was 50° C. and the applied test pressure was set to 100 psi. The instruments&#39; thickness gauge was used to measure the thickness of the sample during testing. A thin layer of thermal grease (Thermal Grease 120 Series, Wakefield Thermal Solutions, Pelham, N.H.) is applied to the samples before placing them into the TIM tester to reduce the contact resistance between test surfaces and sample surfaces (increased surface wet-out). 
     Endothermic Test 
     A differential scanning calorimeter (obtained under the trade designation “DSC Q2000” from TA Instruments, New Castle, Del.) was used to measure the endothermic properties of materials. The unit had prior been calibrated using an Indium powder reference run at 10° C./min. Samples were run at a ramp rate of 10° C./min. under a nitrogen flow of 20 ml/min. 10 milligrams of the sample were placed into an aluminum pan and the sample was run in a non-sealed condition. An endothermic response was recorded. Integration of the area under the curve allows for the calculation of the amount of energy removed per unit weight (J/g) for the composite structure. 
     Cross-Section Inspection Test 
     A scanning electron microscope (SEM) digital image of a cross-section of the polymer matrix composites were taken with an SEM (obtained under the trade designation “PHENOM” from FEI Company, Hillsboro, Oreg.). The cross-sectional sample was prepared by liquid nitrogen freeze fracturing followed by gold sputter coating with a sputter coater (obtained under the trade designation “EMITECH K550X” from Quorum Technologies (Laughton East Sussex, England). 
     Illustrative (Co)polymer Matrix Composite Articles 
     Example 1A 
     More than 23 grams of sodium bicarbonate (obtained under the trade designation “SODIUM BICARBONATE, 7412-12” from Macron Fine Chemicals, Center Valley, Pa.) and more than 23 grams of boron nitride agglomerates (obtained under the trade designation “BORON NITRIDE AGGLOMERATES, 3M COOLING FILLERS AGGLOMERATES 50M” from 3M Company (St. Paul, Minn.) were placed in a lab oven (obtained under the trade designation “DESPATCH RFD1-42-2E” from Despatch (Minneapolis, Minn.), at 225° F. (107° C.) for 2 hours to dry. 
     A plastic mixing cup (obtained under the trade designation “MAX 300 LONG CUP” for a speed mixer obtained under the trade designation “SPEEDMIXER DAC600.2 VAC-LR,” from FlackTek, Inc. (Landrum, S.C.) was charged with 3.5 grams of an ultra-high molecular weight polyethylene (UHMWPE) (obtained under the trade designation “GUR-2126” from Celanese Corporation, Irving, Tex.), 23 grams of dried sodium bicarbonate (obtained under the trade designation “SODIUM BICARBONATE, 7412-12” from Macron Fine Chemicals (Center Valley, Pa.), 23 grams of dried boron nitride agglomerates (obtained under the trade designation “BORON NITRIDE AGGLOMERATES, 3M COOLING FILLERS AGGLOMERATES 50M” from 3M Company (St. Paul, Minn.), and 60.5 grams of paraffin (obtained under the trade designation “ISOPAR G” from Brenntag Great Lakes, Inc. (Wauwatosa, Wis.) and was mixed at 800 rpm and 50 mbar for 60 seconds, followed by 1200 rpm and 50 mbar for 60 seconds, followed by 800 rpm and 50 mbar for 60 seconds, followed by 0 rpm and 50 mbar for 15 seconds in the “SPEEDMIXER DAC600.2 VAC-LR”. 
     The slurry was removed from the mixer, stirred by hand to remove material from the walls of the cup and then applied with a scoop at room temperature (about 25° C.) to a 3 mil (75 micrometer) heat stabilized biaxially-oriented polyethylene terephthalate (PET) liner, then a 3 mil (75 micrometer) heat stabilized biaxially-oriented PET liner was applied on top to sandwich the slurry. The selection of a specific heat stabilized biaxially-oriented PET liner is not critical. 
     Two 1 mm thick aluminum sheets were placed between the PET liners along opposite edges, overlapping the PET liners by roughly 0.5 inches. A flat metal bar, long enough to rest on both aluminum sheets, was run over the PET liners to spread the slurry to the 1 mm thickness of the aluminum sheets. Progressive multiple passes with increasing downward pressure of the flat metal bar were used to flatten the slurry. 
     The aluminum sheets were removed from between the PET liners. The sandwiched, formed slurry was placed on an aluminum tray and placed in a lab oven (obtained under the trade designation “DESPATCH RFD1-42-2E” from Despatch, Inc. (Minneapolis, Minn.), at 135° C. (275° F.) for 5 minutes to activate (i.e., to allow the UHMWPE to dissolve into the solvent forming a single phase). The tray with the activated, sandwiched, formed slurry was removed from the oven and allowed to air cool to ambient temperature (about 25° C.), forming a solvent filled polymer matrix composite. Both the top and bottom liners were removed exposing the polymer matrix composite to air. 
     The polymer matrix composite was then placed back on a PET liner on the tray, and the tray was inserted into the lab oven (“DESPATCH RFD1-42-2E”) from Despatch, Inc. (Minneapolis, Minn.), at 100° C. (215° F.) for an hour. After evaporation, the polymer matrix composite was removed from the oven, allowed to cool to ambient temperature, and characterized. 
     The resulting polymer matrix composite was 41.4 mils (1.05 mm) thick, had a measured density of 0.584 g/cm 3  (as determined by the “Density and Porosity Test”), a Gurley air flow of 10.7 sec/50 cm3 (as determined by the “Air Flow Resistance Test”), and an endotherm of 53.23 J/g (as determined by the “Endothermic Test”). 
     Example 1B 
     Example 1B was prepared and tested as described in Example 1A except a 1.5″×1.5″ square was cut from the film. The square was placed between the two release liners, and then between two sheet metal plates. This layup was placed in a hydraulic press (obtained under the trade designation “WABASH-GENESIS MODEL G30H-15-LP” from Wabash MPI (Wabash, Ind.) and compressed at 15 tons (147 kN) at ambient temperature (about 25° C.) for 60 seconds. 
     The resulting polymer matrix composite was 12.2 mils (0.310 mm) thick, had a measured density of 0.265 g/cm 3  (as determined by the “Density and Porosity Test”), and a thermal conductivity of 2.61 W/m° K (as determined by the “Thermal Conductivity Test”). 
     Example 2A 
     Example 2A was prepared and tested as described in Example 1A, except the slurry consisted of 3.5 grams of UHMWPE, 23 grams of dried calcium sulfate dihydrate, (obtained under the trade designation “CALCIUM SULFATE DIHYDRATE, ACS, 98.0-102.0% POWDER, 36700” from Alfa Aesar, Haverhill Mass.), 23 grams of dried boron nitride agglomerates (obtained under the trade designation “BORON NITRIDE AGGLOMERATES, 3M COOLING FILLERS AGGLOMERATES 50M” from 3M Company (St. Paul, Minn.), and 56 grams of paraffin (obtained under the trade designation “ISOPAR G” from Brenntag Great Lakes, Inc. (Wauwatosa, Wis.). 
     The resulting polymer matrix composite was 32.2 mils (0.817 mm) thick, had a measured density of 0.621 g/cm 3  (as determined by the “Density and Porosity Test”), a Gurley air flow of 9.3 sec/50 cm3 (as determined by the “Air Flow Resistance Test”), a K L  bubble point of 3.4 psi (as determined by the “Bubble Point Pressure Test”) using mineral oil in place of IPA, and an endotherm of 105.76 J/g (as determined by the “Endothermic Test”). 
     Example 2B 
     Example 2B was prepared and tested as described in Example 2A, then densified as described in Example 1B. The resulting polymer matrix composite was 10.4 mils (0.264 mm) thick, had a measured density of 0.225 g/cm 3  (as determined by the “Density and Porosity Test”), and a thermal conductivity of 2.12 W/m° K (as determined by the “Thermal Conductivity Test”). 
     Example 3A 
     Example 3A was prepared as described in Example 1A, except Example 3A is a 2-layer film (layers A&amp;B). A plastic mixing cup for layer A was charged with 3.5 grams of UHMWPE, 23.25 grams of dried boron nitride agglomerates, 20 grams of expandable graphite (obtained under the trade designation “ASBURY 3772” from Asbury Carbons, Inc. (Asbury, N.J.), and 45.5 grams of paraffin. 
     The slurry for layer B was prepared in a separate plastic mixing cup in the same manner as layer A, except it contained 4 grams of UHMWPE, 46.5 grams of dried calcium sulfate dihydrate, and 42 grams of paraffin. Each plastic cup was mixed at 800 rpm and 50 mbar for 60 seconds, followed by 1200 rpm and 50 mbar for 60 seconds, followed by 800 rpm and 50 mbar for 60 seconds, followed by 0 rpm and 50 mbar for 15 seconds in the “SPEEDMIXER DAC600.2 VAC-LR”. 
     The slurry for layer A was removed from the mixer, stirred by hand to remove material from the walls of the cup and then applied with a scoop at room temperature (about 25° C.) to the PET liner, then the other PET liner was applied on top to sandwich the slurry. Two 1 mm thick aluminum sheets were placed between the PET liners along opposite edges, overlapping the PET liners by roughly 0.5 inches. A flat metal bar, long enough to rest on both aluminum sheets, was run over the PET liners to spread the slurry to the 1 mm thickness of the aluminum sheets. Progressive multiple passes with increasing downward pressure of the flat metal bar were used to flatten the slurry. 
     The aluminum sheets were removed from between the PET liners. The sandwiched, formed slurry was placed on an aluminum tray and placed in a lab oven, at 135° C. (275° F.) for 5 minutes to activate (i.e., to allow the UHMWPE to dissolve into the solvent forming a single phase). The tray with the activated, sandwiched, formed slurry was removed from the oven and allowed to air cool to ambient temperature (about 25° C.), forming a solvent filled polymer matrix composite. Both the top and bottom liners were removed exposing the polymer matrix composite to air on top. 
     The polymer matrix composite layer A was then placed back on a PET liner. The slurry for layer B was applied on top of the activated layer A, then the second PET liner was applied on top of layer B. Four 1 mm thick aluminum sheets were placed between the PET liners along opposite edges (2 sheets per side), overlapping the PET liners by roughly 0.5 inches. A flat metal bar, long enough to rest on both aluminum sheets, was run over the PET liners to spread the slurry layer B to 1 mm thick. Progressive multiple passes with increasing downward pressure of the flat metal bar were used to flatten the slurry. 
     The aluminum sheets were removed from between the PET liners. The sandwiched, formed slurry was placed on an aluminum tray and placed in a lab oven, at 135° C. (275° F.) for 5 minutes to activate. The tray with the activated sandwiched, formed slurry was removed from the oven and allowed to air cool to ambient temperature (about 25° C.), forming a solvent filled polymer matrix composite. Both the top and bottom liners were removed exposing the polymer matrix composite to air on top. The tray was inserted into the lab oven at 100° C. (215° F.) for an hour. After evaporation, the polymer matrix composite was removed from the oven, allowed to cool to ambient temperature, and characterized. 
     The resulting polymer matrix composite was 80.6 mils (2.047 mm) thick, had a measured density of 0.6868 g/cm 3 , a Gurley air flow of 435.6 sec/50 cm 3 , a K L  bubble point of 5.92 psi, and an endotherm of 87.12 J/g. Referring to  FIG. 4 , a photomicrograph obtained using the Cross-section Inspection Test on the (co)polymer matrix composite is shown. 
     Example 3B 
     Example 3B was prepared and tested as described in Example 3A, then densified as described in Example 1B. The resulting polymer matrix composite was 31.4 mils (0.797 mm) thick, had a measured density of 1.74 g/cm 3 , and a thermal conductivity of 0.375 W/m° K. 
     Example 4A 
     Example 4A was prepared and tested as described in Example 3A, except the slurry for layer A contained 4 grams of UHMWPE, 46.5 grams of dried boron nitride agglomerates, and 63 grams of paraffin. The slurry for layer B was also prepared as described in Example 3A, except it contained 4 grams of UHMWPE, 46.5 grams of calcium sulfate dihydrate, and 42 grams of paraffin. 
     The resulting polymer matrix composite was 83.5 mils (2.121 mm) thick, had a measured density of 0.625 g/cm 3 , a Gurley air flow of greater than 5 min/50 cm 3 , a K L  bubble point of 5.18 psi, and an endotherm of 101 J/g. Referring to  FIG. 5 , a photomicrograph obtained using the Cross-section Inspection Test on the (co)polymer matrix composite is shown. 
     Example 4B 
     Example 4B was prepared and tested as described in Example 4A, then densified as described in Example 1B. The resulting polymer matrix composite was 27.7 mils (0.703 mm) thick, had a measured density of 0.6 g/cm 3 , and a thermal conductivity of 0.418 W/m° K. 
     Example 5A 
     Example 5A was prepared and tested as described in Example 4A except Example 5 is a 3-layer film (layers A, B, and A). The slurries for Example 5 were identical to the slurries prepared in example 4A. The slurries were coated and activated as described in example 5A up to the point where layer B is activated. After activating layer B, another layer A slurry was coated and activated on top of layer B, using the same methods described for layer B in Example 3A. 
     The resulting polymer matrix composite was 134.5 mils (3.416 mm) thick, had a measured density of 0.612 g/cm 3 , a Gurley air flow of 65.8 sec/50 cm 3 , a K L  bubble point of 6.98 psi, and an endotherm of 73.6 J/g. Referring to  FIG. 6 , a photomicrograph obtained using the Cross-section Inspection Test on the (co)polymer matrix composite is shown. 
     Example 5B 
     Example 5B was prepared and tested as described in Example 5A, then densified as described in Example 1B. The resulting polymer matrix composite was 44.5 mils (1.130 mm) thick, had a measured density of 0.965 g/cm 3 , and a thermal conductivity of 0.597 W/m° K. 
     Example 6A 
     Example 6A was prepared and tested as described in Example 5A except Example 6A is a 3-layer film (layers A, B, and C). The slurries for Example 6A were prepared in the same manner described in example 3, except the slurry components were different. The slurry for layer A consisted of 4 grams of UHMWPE, 46.5 grams of dried boron nitride agglomerates (dried using the methods described for Example 1A), and 63 grams of paraffin. The slurry for layer B was prepared in a separate plastic mixing cup and contained 4 grams of UHMWPE, 46.5 grams of dried calcium sulfate dihydrate (dried using the methods described for Example 1A), and 42 grams of paraffin. The slurry for layer C was prepared in a separate plastic mixing cup and contained 8 grams of UHMWPE, 93 grams of aluminum shot RSA600 (obtained under the trade designation “ALUMINUM PARTICLES, RSA-600-2N CAST ALUMINUM SHOT” from Transmet Corp. (Columbus, Ohio), and 21 grams of paraffin. 
     The slurries were coated and activated as described in example 3 up to the point where layer B is activated. After activating layer B, the layer C slurry was coated and activated on top of layer B, using the same methods described for layer B in example 3. 
     The resulting polymer matrix composite was 132.4 mils (3.362 mm) thick, had a measured density of 1.0738 g/cm 3 , a Gurley air flow of 3.3 sec/50 cm 3 , and an endotherm of 50.3 J/g. Referring to  FIG. 7 , a photomicrograph obtained using the Cross-section Inspection Test on the (co)polymer matrix composite is shown. 
     Example 6B 
     Example 6B was prepared and tested as described in Example 6A, then densified as described in Example 1B. The resulting polymer matrix composite was 55.7 mils (1.414 mm) thick, had a measured density of 1.208 g/cm 3 , and a thermal conductivity of 0.831 W/m° K 
     Example 7 
     Example 7 is a single-layer film made using two different components (components A &amp; B) that react to form a solid film. For component A, a “MAX 300 LONG” plastic mixing cup was charged with 16 grams of part 1 of a 2-part silicone (obtained under the trade designation “TWO-PART, PT-CATALYZED SILICONE, 3M ESPE IMPRINT 3 LIGHT BODY” from 3M Company (St. Paul, Minn.), 8 grams of dried boron nitride agglomerates (dried using the methods described for Example 1A), and 8 grams of sodium metasilicates (obtained under the trade designation “SODIUM METASILICATES PARTICLES, METSO PENTABEAD 20” from PQ Corporation (Malvern, Pa.). Component B was prepared in a separate plastic missing cup and consisted of 16 grams of part 2 of a 2-part silicone, 8 grams of dried boron nitride agglomerates (dried using the methods described for Example 1A), and 8 grams of “SODIUM METASILICATES PARTICLES, METSO PENTABEAD 20”. 
     Both components were mixed in their respective cups by hand for 1 minute at room temperature using a wooden stirrer stick. Then component A was scooped into the container for component B and both components were mixed together at room temperature using a wooden stirrer stick. The doughy mixture was applied with a scoop at room temperature (about 25° C.) to a PET liner, then another PET liner was applied on top to sandwich the dough. Two 1 mm thick aluminum sheets were placed between the PET liners along opposite edges, overlapping the PET liners by roughly 0.5 inches. 
     A roller, long enough to rest on both aluminum sheets, was rolled over the top PET liner to spread the doughy mixture to the 1 mm thickness of the aluminum sheets. Progressive multiple passes with increasing downward pressure of the roller were used to flatten the dough. Once the doughy mixture was sufficiently flat, it was allowed to rest for 10 minutes so that the silicone binder could cure. After resting, the aluminum sheets were removed, and the PET liners were stripped from the finished sample. 
     Example 7 was tested using the same test methods described in Example 1A &amp; Example 1B. The resulting polymer matrix composite was 12.22 mils (0.310 mm) thick, had a measured density of 1.543 g/cm 3 , a Gurley air flow of 3.03 sec/50 cm 3 , an endotherm of 27.74 J/g, and a thermal conductivity of 1.44 W/m° K. Referring to  FIG. 8 , a photomicrograph obtained using the Cross-section Inspection Test on the (co)polymer matrix composite is shown. 
     Example 8 
     Example 8 is a single-layer film made using two different components (components A &amp; B) that react to form a solid film. For component A, a “MAX 300 LONG” plastic mixing cup was charged with 2 grams of part 1 of a 2-part silicone, 2.5 grams of aluminum shot (obtained under the trade designation “ALUMINUM PARTICLES, RSA-400-2N CAST ALUMINUM SHOT” from Transmet Corp. (Columbus, Ohio), and 8 grams of sodium metasilicates. Component B was prepared in a separate plastic mixing cup and consisted of 2 grams of part 2 of a 2-part silicone, 2.5 grams of aluminum shot, and 8 grams of sodium metasilicates. 
     Both components were mixed in their respective cups by hand for 1 minute at room temperature using a wooden stirrer stick. Then component A was scooped into the container for component B and both components were mixed together at room temperature using a wooden stirrer stick. The doughy mixture was applied with a scoop at room temperature (about 25° C.) to a PET liner, then another PET liner was applied on top to sandwich the dough. Two 1 mm thick aluminum sheets were placed between the PET liners along opposite edges, overlapping the PET liners by roughly 0.5 inches. A roller, long enough to rest on both aluminum sheets, was rolled over the top PET liner to spread the doughy mixture to the 1 mm thickness of the aluminum sheets. 
     Progressive multiple passes with increasing downward pressure of the roller were used to flatten the dough. Once the doughy mixture was sufficiently flat, it was allowed to rest for 10 minutes so that the silicone binder could cure. After resting, the aluminum sheets were removed, and the PET liners were stripped from the finished sample. 
     Example 8 was tested using the same test methods described in Example 1A &amp; Example 1B. The resulting polymer matrix composite was 120.8 mils (3.07 mm) thick, had an endotherm of 801.02 J/g, and a thermal conductivity of 0.919 W/m° K. 
     Example 9 
     Example 9 is a single-layer film made using two different components (components A &amp; B) that react to form a solid film. For component A, a “MAX 300 LONG” plastic mixing cup was charged with 16 grams of part 1 of a 2-part silicone, 8 grams of aluminum shot, and 8 grams of sodium metasilicates. Component B was prepared in a separate plastic missing cup and consisted of 16 grams of part 2 of a 2-part silicone, 8 grams of aluminum sho, and 8 grams of sodium metasilicates. Both components were mixed in their respective cups by hand for 1 minute at room temperature using a wooden stirrer stick. Then component A was scooped into the container for component B and both components were mixed together at room temperature using a wooden stirrer stick. The doughy mixture was applied with a scoop at room temperature (about 25° C.) to a PET liner, then another PET liner was applied on top to sandwich the dough. 
     Two 1 mm thick aluminum sheets were placed between the PET liners along opposite edges, overlapping the PET liners by roughly 0.5 inches. A roller, long enough to rest on both aluminum sheets, was rolled over the top PET liner to spread the doughy mixture to the 1 mm thickness of the aluminum sheets. Progressive multiple passes with increasing downward pressure of the roller were used to flatten the dough. Once the doughy mixture was sufficiently flat, it was allowed to rest for 10 minutes so that the silicone binder could cure. After resting, the aluminum sheets were removed, and the PET liners were stripped from the finished sample. 
     Example 9 was tested using the same test methods described in Example 1A &amp; Example 1B. The resulting polymer matrix composite had a thermal conductivity of 1.34 W/m° K. 
     Example 10A 
     Example 10A was prepared and tested as described in Example 1A, except the slurry consisted of 3.5 grams of UHMWPE, 46.5 grams of dried calcium sulfate dihydrate (dried using the methods described in Example 1A), and 46.5 grams of paraffin. The resulting polymer matrix composite was 47.3 mils (1.201 mm) thick, had a measured density of 0.762 g/cm 3 , a Gurley air flow of 1.2 sec/50 cm 3 , a K L  bubble point of 9.56 psi, and an endotherm of 162.5 J/g. 
     Example 10B 
     Example 10B was prepared and tested as described in Example 10A, then densified as described in Example 1B. The resulting polymer matrix composite was 17.5 mils (0.444 mm) thick, had a measured density of 0.379 g/cm 3 , and a thermal conductivity of 0.464 W/m° K. 
     Example 11A 
     Example 11A was prepared and tested as described in Example 1A, except the slurry consisted of 4 grams of UHMWPE, 46.5 grams of dried boron nitride (dried using the methods described in Example 1A), and 63 grams of paraffin. The resulting polymer matrix composite was 47 mils (1.194 mm) thick, had a measured density of 0.509 g/cm 3 , a Gurley air flow of 6.9 sec/50 cm 3 , and an endotherm of 17.85 J/g. 
     Example 11B 
     Example 11B was prepared and tested as described in Example 11A, then densified as described in Example 1B. The resulting polymer matrix composite was 11.5 mils (0.292 mm) thick, had a measured density of 0.249 g/cm 3 , and a thermal conductivity of 1.739 W/m° K. 
     Example 12A 
     A 300 ml aluminum mixing cup was charged with 35.0 grams of wax paraffin (obtained under the trade designation WAX PARAFFIN W1018 from Spectrum Chemical Mfg. Corp. (Gardena, Calif.). The aluminum cup was placed on a hot plate (obtained under the trade designation “RCTBASIC” from IKA Works, Inc. (Wilmington, N.C.) for 15 min to heat the material to 160° F. (71° C.). Next, 11.2 grams of UHMWPE and 211.0 grams of aluminum shot were added to the aluminum cup. The materials were mixed by hand using a tongue depressor for 3 min while the jar remained on the hot plate. The slurry was dispensed into a “MAX 300 LONG” plastic mixing cup and mixed at 1200 RPM for 30 seconds under vacuum at 50 mBar. A PET liner was placed onto a 78.74 mil (2 mm) aluminum plate. 
     The aluminum plate with the PET liner are placed on top a hot plate to preheat both to 160° F. (71° C.). The slurry was cast onto the PET liner while still hot, then another PET liner was placed on top to sandwich the slurry. The slurry was spread between the PET liners by using a notch bar set to a gap of 66 mils (1.68 mm). The notch bar rails were wider than the PET liner to obtain an effective wet film thickness of approximately 60 mils (1.52 mm). Progressive multiple passes with increasing downward pressure of the notch bar were used to flatten the slurry. The sandwiched, formed slurry was placed on an aluminum tray and placed in a lab oven, at 135° C. (275° F.) for 5 minutes to activate (i.e., to allow the UHMWPE to dissolve into the solvent forming a single phase). After activation, the films were removed from the oven and cooled down to ambient temperature (about 25° C.). 
     Example 12A was tested using the same test methods described in Example 1A &amp; Example 1B. The resulting polymer matrix composite was 73.2 mils (1.86 mm) thick, had a measured density of 2.231 g/cm 3 , and an endotherm of 33.12 J/g. 
     Example 12B 
     Example 12B was prepared and tested as described in Example 12A, then densified as described in Example 1B. The resulting polymer matrix composite was 55.0 mils (1.40 mm) thick, had a measured density of 2.332 g/cm 3 , and a thermal conductivity of 5.93 W/m° K. 
     Reference throughout this specification to “one embodiment,” “certain embodiments,” “one or more embodiments” or “an embodiment,” whether or not including the term “exemplary” preceding the term “embodiment,” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the certain exemplary embodiments of the present disclosure. Thus, the appearances of the phrases such as “in one or more embodiments,” “in certain embodiments,” “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the certain exemplary embodiments of the present disclosure. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. 
     While the specification has described in detail certain exemplary embodiments, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these embodiments. Accordingly, it should be understood that this disclosure is not to be unduly limited to the illustrative embodiments set forth hereinabove. In particular, as used herein, the recitation of numerical ranges by endpoints is intended to include all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). In addition, all numbers used herein are assumed to be modified by the term “about.” 
     Furthermore, all publications and patents referenced herein are incorporated by reference in their entirety to the same extent as if each individual publication or patent was specifically and individually indicated to be incorporated by reference. Various exemplary embodiments have been described. These and other embodiments are within the scope of the following claims.