MXPA99006168A - Microporous polymeric foams made with silicon or germanium based monomers - Google Patents

Abstract

Disclosed are polymeric foam materials obtained using monomers based on silicon and/or germanium. The copolymerization of silicon- or germanium-based monomers provide foams that have low glass transition temperatures and low densities. These foams also exhibit relatively high yield stress values, which make the foams suitable for absorption of fluids, particularly aqueous fluids such as urine and menses (when the foams are rendered hydrophilic). The foams have a variety of other uses, including insulation applications.

Description

MICROPOROUS POLYMERIC FOAMS MADE WITH MONOMERS BASED ON SILICON OR GERMANIUM FIELD OF THE INVENTION This application relates to open-cell, microporous polymeric foams made using monomers based on silicon or germanium.

BACKGROUND OF THE INVENTION The development of microporous foams has been the subject of substantial commercial interest. These foams have found utility in various applications, such as thermal, acoustic, electrical, and mechanical insulators (e.g., for damping), absorbent materials, filters, membranes, ink carriers, dyes, lubricants, and lotions, making articles of flotation and the like. References describing these uses and properties of the foams include Oerte !, G. "Polyurethane Handbook" Hanser Publishers, Munich, 1985, and Gibson, L.J .; Ashby, M.F. "Structures and Properties of Cellular Solids" Pergamon Press, Oxford, 1988. The term "Isolator" refers to any material that reduces the transfer of energy from one location to another. The term "absorbent" refers to materials that imbibe or retain or distribute fluids, usually liquids, an example being a sponge. The term "filter" refers to materials that pass a fluid, either gas or liquid, while retaining impurities within the material by size exclusion. Other uses for the foams are generally obvious to one skilled in the art. For many uses, the composite material and generally conflicting requirements are placed on the foam itself. These may include (1) low density, (2) flexibility, (3) resistance (compression and traction), (4) aperture, and (5) control of morphology. Low density foams are more efficient since most uses require a certain volume and a low density foam will impose less mass to meet this objective. Flexible foams are typically generated by maintaining a > glass transition temperature (Tg) of the relatively low foam. Resistance is a parameter that is inevitably sacrificed to achieve either a lower Tg or a lower density. The strength can be effectively generated by including interlacing agents which link the polymer chains of the foam together in a manner that confers a degree of resistance to deformation and the ability to recover from deformation, for example, elasticity. The opening and morphology are controlled mainly by the method of formation and curing of the foam. Accordingly, it would be desirable to be able to make a high cell surface, open cell polymeric foam material that: (1) has the lowest density consistency with the other requirements imposed on the foam; (2) be flexible; (3) be resistant; (4) has a generally open cell structure; and (5) can be manufactured to control the size of the cells produced within the foam.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to polymeric foams comprising comonomers based on silicon and / or germanium. The term "comonomer" is used herein to denote that these required comonomers are going to be generally used with other comonomers that may or may not contain silicon and / or germanium. These polymeric foams are preferably prepared by polymerization of certain water-in-oil emulsions having a relatively high ratio of water phase to oil phase, commonly known in the art as high internal phase emulsions, or "HIPE". As used herein, the polymeric foam materials resulting from the polymerization of these emulsions are referred to herein as HIPE foams. The HIPE foam materials of the present invention comprise a non-ionic polymeric foam structure generally flexible, semi-flexible or rigid, of open cells connected internally. The comonomers used to form the HIPE generally must be relatively insoluble in the aqueous phase of the emulsion. Polymeric foam structures derived from? HiPE comprise at least about 5%, based on the weight of the foam, of one or more comonomers selected from the group consisting of silicon-containing comonomers, germanium-containing comonomers, and mixtures thereof, Preferably, the foams of the present invention will have: A) a density less than about 0.10 g / cm3; B) a vitreous transition temperature (Tg) between about -40 ° and 90 ° C; and C) an elastic stress value of at least about 0.25 psi. The present invention relates to foams prepared by polymerization of a HIPE comprising a discontinuous water phase and a continuous oil phase, wherein the water to oil ratio is at least about 10: 1. The water phase usually contains an electrolyte and a water initiator. The oil phase generally consists of substantially water insoluble monomers polymerizable by free radicals, including at least one comonomer containing silicon and / or germanium, an emulsifier, and other optional ingredients defined below. The monomer containing the silicon and / or germanium are selected to confer the desired properties in the resulting polymeric foam, for example, low density, a glass transition (Tg) of between about -40 ° and 90 ° C, sufficient mechanical integrity to the final intended use, and an open cell microporous morphology.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 of the drawings is a photomicrograph (250 X amplification) of a section of a polymeric foam representative of the present invention, made from a HIPE having a weight ratio of water to oil of 60: 1 and formed at 55 ° C, wherein the monomer component consists of a weight ratio of 55:33:12 of 2-ethylhexyl acrylate (EHA): divinylbenzene (DVB, 42.9% divinylbenzene and approximately 60% ethyl styrene): tetrakis (3-methacryloxyethoxy) silan, and where emulsifier was used in 10% (by weight of the oil phase) of monoleate of diglycerol (DGMO). Figure 2 of the drawings is a photomicrograph (1000 X amplification) of the foam of Figure 1.

DETAILED DESCRIPTION OF THE INVENTION I. Polymeric Foams Containing Silicon and / or Germanium The polymeric foams of the present invention are composed of specific combinations of monomers, which to a greater extent control the final properties of the foam. The types of monomers used fall within the following three broad categories: (1) monomers that help maintain a desirable Tg in the resulting polymer, (2) monomers that help confer "stiffness" to the resulting polymer, referred to herein as "monomers" of hardening ", and (3) monomers having di-, tri-, tetra- and higher functionality utilize in conferring the entanglement within the resulting polymer, herein referred to as interlayers. These interleavers are particularly critical in achieving the desired compression strength or modulus and / or the elasticity that is required for many of the foam applications. Applicants have discovered that, surprisingly, monomers containing silicon and / or germanium are particularly useful in areas (1) and (3) above. For example, a comonomer such as (3-acryloxypropyl) metii-bis- (trimethylsiloxy) silane (hereinafter referred to as APMTS) 'forms polymers having the desirably low Tg. As another example, an interlayer such as tetrakis (2-methacryloxyethyloxy) silane (hereinafter referred to as KTMES) forms polymers that are effectively entangled to have the desired compressive strength and elasticity without increasing the Tg of the resulting polymeric foam to a undesirable degree. The general class of these compounds is described more fully below, although these two are presented as being generally illustrative, non-limiting examples of the invention. It is understood that both of these two representative examples are used as comonomers with other comonomers to confer the desired properties in the final foam. The ability of these comonomers based on silicon and / or germanium to confer the desired strength without undesirably increasing the Tg is taught in relation to the molecular flexibility associated with the bonds attached to the Si and / or Ge atom. This flexibility is seen in the polysiloxanes, which have very low Tg. In contrast, comonomers that confer resistance while lacking sufficient molecular flexibility tend to increase Tg. Examples include divinylbenzene, an interlayer where higher levels can increase polymer resistance while also increasing Tg. Tg is an important criterion in the use of any polymer. Although in some applications a relatively high Tg may be desired, in general this is achieved more easily than obtaining a correspondingly low Tg in a polymer without sacrificing other properties, such as strength, to an undesirable degree. Applicants have found that the comonomers used in the present invention are particularly useful in maintaining a comparatively low Tg while also conferring sufficient strength for many uses in the final product. The polymers constituting the present foams comprise from about 0.5% to about 30% elemental silicon or germanium, or a combination of the two. Preferably, the polymer will comprise from about 1% to about 15%, more preferably from about 2% to about 10%, of these elements. Although the foams can be described in terms of their elemental silicon / germanium content, it is understood that these elements are covalently bonded to other polymerizable groups and are introduced into the foam polymer in the form of silicon / germanium containing comonomers. .

II. General Characteristics of the Foam The polymeric foams of the present invention are of relatively open cell. This means that the individual cells of the foam are in complete communication, not obstructed with the adjacent cells. The cells, in said substantially open cell foam structures, have intercell openings or "windows" that connect one cell to another within the foam structure. These foam structures of substantially open cell will generally have a cross-linked character, the individual cells being defined by a plurality of mutually connected, three-dimensionally branched frames. The strands of the polymeric material forming these branched webs can be referred to as "poles". Open cell foams having a typical post-type structure are shown by way of example in the photomicrographs of Figures 1 and 2. As used in the present invention, a foam material is an "open cell" if at least 80% of the cells in the foam structure that are at least 1μm in size are in fluid communication with at least one adjacent cell. These polymeric foams can be generally hydrophobic to inhibit the passage of aqueous fluids through the foam, or hydrophilic to promote the imbibition of the aqueous fluids in the foam. The hydrophobic / hyalophilic properties of the internal surfaces of the foam structures are controlled by post-polymerization treatment methods of the foam. As used herein, the term "hydrophilic" is used to refer to surfaces that are wettable by the aqueous fluids deposited thereon. Hydrophilic capacity and wettability are typically defined in terms of the contact angle and surface tension of the fluids and the solid surfaces involved. This is discussed in detail in the publication of the American Chemical Society entitled "Contact Angle, Wetting and Adhesion" edited by Robert F. Gould (Copyright 1964), which is hereby incorporated by reference. A surface is said to be wetted by a fluid (ie, hydrophilic) when any contact angle between the fluid and the surface is less than 90 °, or when the fluid tends to spread spontaneously across the surface, both conditions coexisting normally. Conversely, a surface that is "hydrophobic" is considered if the contact angle is greater than 90 ° and the fluid does not spontaneously spread across the surface. The foams used according to the present invention are easily optimized to confer the desired properties in each specific application. As examples, these foams can be microcellular (<10 μm) up to moderate cell diameters (ca. 150 μm); low density (0.10 g / cm3) at very low density (0.004 g / cm3); from rigid to flexible (from Tg raised to low Tg (subambiente), corresponding); and from strong to weak. The foams may be provided as continuous sheets, rigid thick boards, and particles of various sizes, specific shapes, etc., as required for their final use. However, these optimized foams avoid some of the deficiencies associated with the foaming methods described hereinafter. That is, they generally contain little or no nitrogen or sulfur in such a way that the incineration does not normally produce harmful gases, does not require CFC materials, volatile organic compounds (VCC) during manufacture, are generally photostable, are easily producible in large quantities with reasonable economy such as, be it, plan, roll, particle foam, and the like.

A. Vitreous Transition Temperature A key parameter of the foams of the present invention is its glass transition temperature (Tg). The Tg represents the midpoint of the transition between the vitreous and elastic states of the polymer. Foams that have a Tg greater than the temperature of useThey can be very strong, but they will also be very rigid and potentially susceptible to fracture. Such foams typically also take a long time to recover to the expanded state after being stored in the compressed state for extended periods. Although the end use of a particular foam is an important factor when determining the desired Tg of the foam, the preferred foams are those having a Tg of about 15 ° to about 50 ° C. More preferred are foams having a Tg of from about 20 ° to about 40 ° C. The comonomers containing silicon and / or germanium described hereinafter are particularly useful in developing polymers with low Tg. The method to determine the Tg by Mechanical Dynamic Analysis (DMA) is described in the section METHODS OF TEST, below.

B. B. Foam Density Another important property of the foams of the present invention is their density. The "foam density" (ie in grams of foam per cubic centimeter of foam volume in the air) is specified here on a dry basis, unless otherwise indicated. Any suitable gravimetric procedure that will provide a mass determination of the solid foam material per unit volume of foam structure can be used to measure the density of the foam. For example, an ASTM gravimetric process described more fully in the Test Methods section of U.S. Patent 5,387,207 (Dyer et al.), Issued February 7, 1995 (incorporated herein by reference) is a method that It can be used for density determination. Although the foams can be made with virtually any density varying from below that of the air to just less than the bulk density of the polymer from which it is made, the foams of the present invention are more useful when they have a dry density in the expanded state less than about 0.10 g / cm3, preferably between about 0.08 and about 0.004 g / cm3, more preferably between about 0. 004 and approximately 0.001 gr / cm3, and most preferably 0.002 gr / cm3, approximately.

C. Cell Size Foam cells, and especially cells that are formed by polymerizing an oil phase containing monomer surrounding water phase droplets relatively free of monomer, will often have a substantially spherical shape. The size or "diameter" of said spherical cells is a parameter commonly used to characterize foams in general. Since the cells in a given sample of polymer foam will not necessarily be of approximately the same size, an average cell size, ie the average cell diameter, will usually be specified. A number of techniques are available to determine the average cell size of the foams. The most useful technique, without emotion, to determine the cell size of the foam involves a simple measurement based on the scanning electron photomicrograph of a foam sample. Figure 1, for example, shows a typical HIPE foam structure, according to the present invention. Superimposed over the photomicrograph is a scale representing a dimension of 100 μm. Said scale can be used to determine the average cell size through an image analysis procedure. The measurements of cell size given herein are based on the average cell size in number of the foam, for example, as shown in Figure 1. The foams of the present invention will preferably have an average cell size in number not greater than about 150 μm, more preferably from about 10 to about 100 μm, and most preferably from about 15 to 35 μm. as with the other characteristics of the foam, the preferred average cell size for a given foam will be dictated in part by its anticipated end use.

D. Specific Surface Area Another important parameter of the foams is their specific surface area, which is determined by both the dimensions of the cell units in the foam and by the density of the polymer, and is therefore a way to quantify the i total amount of solid surface provided by the foam. The specific surface area is determined by measuring the amount of capillary consumption of a liquid of a low surface tension (e.g. ethanol), which occurs within a foam sample of a known mass and dimensions. A detailed description of said method for determining the specific surface area of the foam through the capillary suction method is set forth in the Test Methods section of the United States patent.

United States 5,387,207 (Dyer et al.), Issued February 7, 1995, which is incorporated herein by reference. Other similar tests can be used to determine the specific surface area with the foams present. The foams of the present invention have a specific surface area of at least about 0.01 m2 / cm 3, preferably of at least about 0.025 m2 / cm 3.

E. Elastic stress The elastic stress is determined in a stress-strain experiment conducted on the foam at a temperature and tension regime (in the compressed mode). The elastic stress is the stress in the transition from the linear elastic region to the highland region of the stress-strain curve. The elastic stress is indicative of the general resistance properties of the polymeric foam at the temperature of interest. For many applications, higher elastic stress values are desirable at a given density and Tg of foam. The foams of the present invention preferably will have an elastic stress value of at least about 0.25 psi, preferably at least about 0.5 psi.

IL Foam Uses The polymeric foams of the present invention will have numerous end uses. For example, foams can be prepared to be absorbent materials, particularly for water-based fluids such as urine and menses. These foams - can be prepared to have structural characteristics similar to the HIPE-derived foams described in, for example, the co-pending patent application of the United States Serial No. 08 / 563,866 (DesMarais et al., Filed October 13, 1995); U.S. Patent No. 5,387,207 (Dyer et al., issued February 7, 1995); U.S. Patent No. 5,550,167 (DesMarais, issued August 27, 1996); and U.S. Patent No. 5,563,179 (DesMarais et al., issued October 8, 1996); each of which is incorporated by reference here. These absorbent foams can be included in absorbent articles such as baby diapers, feminine hygiene articles (e.g. tampons, catamenial pads), adult incontinence articles, and the like, such as those described in the copending patent applications. and issued patents mentioned above. The foams can also be prepared to be useful as insulators. These foams will have structural characteristics (e.g., cell size, density, Tg) similar to the foams described in the co-pending United States patent application Serial No. 08 / 472,447 (Dyer et al., Filed June 7, 1995 ) and the copending US Patent Application Serial No. 08 / 484,727 (DesMarais et al., filed June 7, 1995, both of which are incorporated by reference herein.) Polymeric foams can also be used for filter media. fluids (liquid or gas) to remove impurities Other uses of the foams include membranes, ink carriers, dyes, lubricants, lotions, life saving products, and other uses generally obvious to one skilled in the art. lll. Preparation of Polymeric Foams from HIPE using Monomers Containing Silicon and / or Germanium A. In General The polymeric foams according to the present invention are preferably prepared by the polymerization of HIPE. The relative amounts of the water and oil phases used to form the HIPEs are, among many other parameters, important for determining the structural, mechanical and performance properties of the resulting polymeric foams. In particular, the water to oil ratio in the emulsion can influence the density, the cell size and the specific surface area of the foam and dimensions of the poles that form the foam. The emulsions used to prepare the HIPE foams will generally have a volume to weight ratio of water to oil phase of at least about 10: 1 to, preferably from about 2.5: 1 to about 250: 1, more preferably from about 25: 1 to about 75: 1, and most preferably about 50: 1. The process for obtaining these foams comprises the steps of: A) forming a water-in-oil emulsion under low shear mixing of: 1) an oil phase comprising: a) from about 80 to about 98% by weight of a a rnonomer component capable of forming a copolymer having a Tg value of about -40 ° C to about 90 ° C, the monomer component comprising: i) at least about 5% by weight of a material selected from the group consisting of of one or more comonomers containing silicon, one or more comonomers containing germanium, and mixtures thereof; ii) from about 0 to about 70% by weight of a monofunctional monomer substantially water-soluble, capable of forming a homopolymer having a Tg of about 40 ° C or less; iii) from about 0% to about 70% by weight of a monofunctional comonomer substantially insoluble in water, capable of imparting resistance approximately equivalent to that provided by styrene; iv) from about 0% to about 50% by weight of a first polyfunctional crosslinking agent, substantially insoluble in water, selected from divinylbenzenes and analogs thereof; and v) from 0 to about 15% by weight of a second polyfunctional crosslinking agent, substantially insoluble in water, selected from the group consisting of diacrylates and dimethacrylates of diols and analogs thereof; and b) from about 2 to about 20% by weight of an emulsifying component, which is soluble in the oil phase, and which is suitable for forming a stable emulsion of water in oil 2) a water phase comprising about 0.1% to about 20% by weight of a water-soluble electrolyte; 3) a volume to weight ratio of water phase to oil phase of at least about 10: 1; and B) polymerizing the monomer component in the oil phase of the oil in water emulsion to form a polymeric foam material. The polymeric foam material can then be thoroughly washed and dehydrated to provide a dry, hydro-ooic foam. Alternatively, the foam can be made hydrophilic by suitable surface treatment with any of one or more hydrophilizing agents, including calcium chloride and similar salts, residual emulsifiers used to stabilize HIPE, and other wetting agents well known to those skilled in the art. The technique. Hydrophilizing treatments are described in, for example, U.S. Patent No. 5,387,207 (Dyer et al., Issued February 7, 1995) (see especially column 22 to column 24), which is incorporated herein by reference. These foams can be formed as desired. Typically, this configuration will comprise slicing in relatively thin sheets. These sheets may optionally be compressed, for example, continuously through pressure spaces, in a thin state and wound into rolls. The compressible sheets will retain their relatively thin compressed state until they are unwound, applied as desired, and either heated above their activation temperature (usually above the Tg of the polymer) or allowed to remain for a relatively long period of time , for example, of several weeks or months, depending on the ambient temperature, as described in the copending United States patent application Serial No. 08 / 484,727 (DesMarais et al., filed June 7, 1995). Alternatively, the shapes can be conferred by the formation of the container in which the HIPE is cured to form the polymeric foam material. Alternatively, the cured foam can be cut into cubes, shredded, milled or otherwise crushed into pieces of small particles for further use. 1. Components of the Oil Phase The continuous oil phase of the HIPE comprises monomers that are potimized to form the solid foam structure. This monomer component is formulated to be capable of forming a copolymer having a Tg of from about -40 ° C to about 90 ° C, and preferably from about 15 ° to about 50 ° C, more preferably from about 20 ° to about 40 ° C. ° C. (The method for determining Tg by Dynamic Mechanical Analysis (DMA) is described in the Test Methods section below). This monomer component includes at least one of a comonomer, at a level of at least about 5%, which contains silicon and / or germanium. Preferably the monomer component will include from about 8% to about 50%, more preferably from about 10% to about 30%, of a comonomer or comonomers containing silicon and / or germanium. The levels of these comonomers less than about 5% were found to induce minimally measurable changes in the properties of the foam. This monomer component further includes: (a) at least one functional monomer whose atactic amorphous polymer has a Tg of about 40 ° C or less (see Brandup, J., Immergut, EH, "Polymer Handbook", 2nd edition, Wiley-lnterscience, New York, NY, 1975, 111-139), hereinafter referred to as a "Tg reducing monomer"; (b) at least one monofunctional comonomer for improving the stiffness or the breaking strength of the foam, hereinafter referred to as a "hardening monomer"; (c) a first polyfunctional interlacing agent; and / or (d) optionally a second polyfunctional crosslinking agent. The comonomers described above in sections (a), (b) and (c) may also contain silicon and / or germanium to meet the level requirements for these elements in the formulation. The selection of particular types and amounts of monofunctional monomers and comonomers and polyfunctional crosslinking agents may be important for the performance of HIPE absorbent foams, which have the desired combination of structure and mechanical properties, which make these materials suitable for use in the present invention. The monofunctional monomer components containing silicon and / or germanium include the myriad types. These may include comonomers designed to serve as Tg reducing monomers, as defined above. The examples generally include monomers having at least one pendant group that is reactive in the free radical polymerizations. Non-limiting examples of these pendant groups include acrylates, methacrylates, acrylamides, methacrylamides, styryls, dienes, vinyl sulfones, and the like. These pendant groups are well known to those skilled in the art. Attached to these pendant groups will be a portion containing at least one silicon and / or germanium atom functionalized appropriately. Non-limiting examples of these portions include dimethylsiloxanes, germanoxanes, silanes and germanians. Preferred examples are the silicon-containing Tg reducing monomers, which contain di and trisiloxane portions, for example, the groups -Si (CH3) 2 -) - 0-Si (CH3) 2- and -Si (CH3) 2 -) - 0-Si (CH3) 2-OSi (CH3) 2-. These portions provide an exceptionally flexible side chain in the pendant reactive group which, after polymerization, induces a strong Tg reducing effect on a weight basis. It has been found by experimentation that at least 5% of these monomers should be used to exert the desired influence. Since these monomers typically contain between about 10% and about 40% elemental silicon and / or germanium, the amount of silicon and / or elemental germanium in the formulation will typically be at least about 0.5%. The upper range in the amount of silicon and / or germanium used in the formulation, is governed by the maximum amount of these comonomers that can be used, which is 100% times the maximum level of silicon and / or germanium possible in the comonomer while retaining the reactive pendant group, which is approximately 50% in the case of Germanic irimethyl vinyl. Specific non-limiting examples of the monomers include (3-acryloxypropyl) -methylbis- (trimethylsiloxy) silane, allythiisopropyl silane, allyltriphenyl silane, bis (trimethylsilyl) taconate, p- (t-butyldimethylsiloxy) styrene, methacrylamido-propyltriethoxysilane, methacryloxyethoxytrimethylsilane, (methacryloxymethyl) -dimethylethoxysilane, methacryloxytrimethyl silane, (2,4-pentadienyl) trimethylsilane, styrylethyltrimethoxysilane, 3- (N-styrylmethyl-2-aminoethylamino) propyltrimethoxy silane hydrochloride, (m, p -vinylbenzoyloxy) trimethylsilane, vinytrimethyl silane, vinyl dimethylethyl silane, vinylpentamethyldisiloxane, vinyl trifluoromethyl dimethyl silane, vinyltris (trimethylsiloxy) silane, and German vinyltriethyl. Although each of these examples will vary in their propensity to serve as a Tg reducing monomer, each may find the specific advantage of achieving a specific Tg for a polymeric foam needed for a particular end use. The monomer component may include one or more of Tg reducing monomers that do not contain silicon and / or germanium, which tend to impart rubber-like properties to the resulting polymeric foam structure. Such monomers can produce high molecular weight atactic amorphous polymers (greater than 10,000), having a Tg of about 40 ° C or less. Monomers of this type include, for example, (C4-C14) alkyl acrylates such as butyl acrylate, hexyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, (lauryl) acrylate, dodecyl, isodecyl acrylate, tetradecyl acrylate, aryl acrylates and alkaryl acrylates such as benzyl acrylate, nonylphenyl acrylate, (C6-C16) alkyl methacrylates such as hexyl methacrylate, octyl methacrylate, nonyl methacrylate, methacrylate decyl, isodecyl methacrylate, dodecyl (lauryl) methacrylate, tetradecyl methacrylate, alkyl styrenes (C4-C12) such as pn-octylstyrene, acrylamides such as N-octadecyl acrylamide, isoprene, butadiene, and combinations of such monomers. Of these monomers, the most preferred are isodecyl acrylate, dodecyl acrylate, and 2-ethylhexylate acuate. The monofunctional monomers will generally comprise from 0 to about 70%, more preferably from about 20 to 60%, by weight of the monomer component. The monomer component used in the oil phase of the HIPE may also comprise one or more monofunctional comonomers capable of imparting rigidity approximately equivalent to that provided by styrene to the resulting polymeric foam structure. The stiffer foams exhibit the ability to deform substantially without failure. These types of monofunctional comonomer may include styrene-based comonomers (see fig., styrene and ethyl styrene), or other types of monomers such as methyl methacrylate, wherein related homopolymer is known for its illustrative rigidity. The preferred monofunctional comonomer of this type is a styrene-based monomer, the most preferred monomers of this type being styrene and ethyl styrene.

The "stiffness" monofunctional comonomer will usually comprise from about 0 to about 70%, preferably from about 20% to about 50%, most preferably from about 30% to about 50 &, by weight of the monomer component. In certain cases, the "stiffness" comonomer may also impart the desired rubber type properties to the resulting polymer. For said comonomers, the amount of these that can be included in the monomer component will be that of the typical monomer and comonomer combination. The monomer component contains a first polyfunctional crosslinking agent (and optionally a second agent.) As with the monofunctional monomers and comonomers, the selection of the particular type and amount of the crosslinking agent or agents is very important for the performance of the preferred polymeric foams having the desired combination of structural and mechanical properties It has also been found that these crosslinkers may advantageously contain silicon and / or germanium The first polyfunctional crosslinking agent can be selected from monomers containing silicon and / or germanium. relatively central silicon and / or germanium atom functionalized with at least two of the pendant reactive groups described above The preferred examples have 3 or 4 pendant reactive groups and are based on silicon, although also germanium can be generally substituted. Limitations incl uyen tetraalyl silane (abbreviated "TAS"), tetrakis (2-methacryloxyethoxy) silane ("TKMES"), 1,3-bis (3-methacryloxypropyl) tetramethyl-disiloxane ("BMPTDS"), and 1, 3, 5-trivinyl-1, 1, 3,5,5-pentamethyltrisiloxane ("TVPTS"). Other non-limiting examples include dimethoxydialyl silane, bis (2-allyoxymethyl) -1-trimethylsiloxybutane, bis (methacryloxy) diphenylsilane, bis (methacryloxy) dimethyl silane, bis (4-styryl) dimethylsilane, diallyldiphenylsilane, diallyldimethylsilane, 1,3-diallyltetramethyldisiloxane, divinyltetramethyldisiloxane, hexavinyldisiloxane, bis (2-allyloxymethyl) phenethyl) -tetramethyldisiloxane, 1,5-divinylhexamethyltrisiloxane, and German tetralil. It has been found by experimentation that these interleavers can be used to harden the polymer efficiently without unduly increasing the Tg of the polymer, which can not be desired in all cases. The polyfunctional "crosslinker" comonomer containing silicon and / or germanium will normally comprise from about 5 to about 80%, preferably from about 10% to about 60%, most preferably from about 25% to about 40%, by weight of the monomer component . The first polyfunctional crosslinking agent can also be selected from a wide variety of comonomers containing two or more activated vinyl groups, such as divinylbenzenes and analogs thereof. Analogs of the dibinylbenzenes useful herein include, but are not limited to, trivinylbenzenes, divinyltoiuens, divinyxylenes, divinylnaphthalenes, divinilaiquirbenzenes, divinylphenanthrenes, divinylbiphenyls, divinyl diphenylmethans, divinylbenzyl, divinylphenyl ethers, divinyl diphenyl sulfides, divinylfurans, divinyl sulfide, divinyl sulfone, and mixtures thereof. Divinylbenzene is typically available as a mixture with ethyl styrene in proportions of about 55:45. These proportions can be modified in order to enrich the oil phase with one or the other component. In general, it is advantageous to enrich the mixture with the ethyl styrene component, while simultaneously reducing the amount of styrene in the monomer mixture. The preferred ratio of divinylbenzene to ethyl styrene is approximately 30:70 and 55:45, most preferably from 35:65 to 45:55, approximately. The inclusion of higher levels of ethyl styrene imparts the required rigidity without increasing the Tg of the resulting copolymer to the extent that the styrene does. This first interlacing agent in general can be included in the oil phase of the HIPE in an amount of from about 2% to about 50%, preferably from about 10% to about 35%, and most preferably from about 15% to about 25%, by weight of the monomer component (in a base to 100%). The second optional crosslinking agent can be selected from polyfunctional acrylates or methacrylates selected from the group consisting of diacrylates or dimethacrylates of diols and analogs thereof. These crosslinking agents include methacrylates, acrylamides, methacrylamides and mixtures thereof. These include di-, tri-, and tetra-acrylates, as well as di-, tri-, and tetra-methacrylates, di-, tri-, and tetra-acrylamides, as well as di-, tri-, and tetra-methacrylamides; and mixtures of these crosslinking agents. Suitable acrylate and methacrylate crosslinking agents can be derived from diols, triols and tetraols including 1,10-decanediol, 1,8-octanediol, 1,6-hexanediol, 1,4-butanediol, 1,3-butanediol, 1, 4-but-2-eneodiol, ethylene glycol, diethylene glycol, trimethylolpropane, pentaerythritol, hydroquinone, catechol, resorcinol, triethylene glycol, polyethylene glycol, sorbitol, and the like. (The acrylamide and rneamideamide crosslinking agents can be derived from the equivalent diamines, triamines, and tetramines). Preferred diols have at least 2, preferably at least 4, and most preferably 6 carbon atoms. This second crosslinking agent can generally be included in the oil phase of the HIPE in an amount of from 0 to about 15% by weight of the monomer component. The main portion of the oil base of the HIPEs will comprise the aforementioned monomers, comonomers and crosslinking agents. It is essential that these monomers, comonomers and crosslinking agents are substantially insoluble in water, so that they are mainly soluble in the oil phase and not in the water phase. The use of said substantially insoluble monomers in water ensures that HIPEs of appropriate characteristics and stability will be obtained. Of course, it is highly preferred that the monomers, comonomers and crosslinking agents used herein are of the type such that the resulting polymeric foam is suitably non-toxic and appropriate and chemically stable. These monomers, comonomers and crosslinking agents should preferably have little or no toxicity if present at very low residual concentrations, during the processing and / or use of the post-polymerization foam.

Another essential component of the oil phase is an emulsifying component comprising at least one primary emulsifier. Primary emulsifiers are well known to those skilled in the art. Particularly preferred emulsifiers include Span 20®, Span 40®, Span 60® and Span 80®. These are nominally sorbitan esters derived from lauric, myristic, stearic and oleic acids, repsectively. Other preferred emulsifiers include diglycerol esters derived from monooleate acids, monomiristate, monopalmitate, monoisostearate. A preferred emulsifier is ditallowdimethyl ammonium methyl sulfate. Mixtures of these emulsifiers are also particularly useful, as they are purified versions of each, specifically sorbitan esters that contain minimum levels of isosorbide and polyol impurities. When an optional secondary emulsifier (s) is (are) included in the emulsifying component, it is in a weight ratio of primary to secondary emulsifier of from about 50: 1 to about 1: 4, preferably from 30: 1 to 2: 1, approximately. As indicated above, those skilled in the art will recognize that any suitable emulsifier (s) may be used in the processes for making the foams of the present invention. For examples, see U.S. Patent No. 5,387,307 and U.S. Patent No. 5,563,179. The oil phase used to form the HIPE comprises from about 80 to about 98% by weight of the monomer component and from about 2 to about 20% by weight of the emulsifier component. Preferably, the oil phase will comprise from about 90 to about 97% by weight of a monomer component and from about 3 to about 10% by weight of the emulsifying component. The oil phase can also contain other optional components. One such optional component is an oil-soluble polymerization initiator of the general type well known to those skilled in the art, such as described in U.S. Patent 5,290,820 (Bass et al.), Issued on the 1st. March 1994, which is incorporated herein by reference. A preferred optional component is an antioxidant such as a Disabled Amine Light Stabilizer (HALS) such as bis- (1, 2,2,5,5-pentamethylpyridinyl) sebacate (Tinuvin-765®) or Disabled Phenolic Stabilizers (HPS). ) such as lrganox-1076® and t-butylhydroxy-quinone. Another optional component includes is a plasticizer such as dioctyl azelate, dioctyl sebacate or dioctyl adipate. Yet another optional ingredient is filler particles or fillers that can harden the polymer and / or increase its thermally insulating properties. Exemplary filler particles include aluminum, titanium dioxide, carbon black, graphite, calcium carbonate, talc, and the like. Generally, particles that help make the polymer opaque in the infrared region are preferred, such as carbon black and graphite. Other optional components include dyes (colorant or pigments), fluorescent agents, opacifying modifiers, chain transfer agents, and the like. 2. Components of the Water Phase The discontinuous water internal phase of the HIPE is generally an aqueous solution containing one or more dissolved components. A dissolved essential component of the water phase is a water soluble electrolyte. The dissolved electrolyte minimizes the tendency of monomers, comonomers and crosslinkers that are mainly soluble in oil to also dissolve in the water phase. This, in turn, is believed to minimize the degree to which the polymeric material fills the cell windows in the adjoining oil / water surfaces formed by the droplets of the water phase during polymerization. Thus, the presence of the electrolyte and the ionic strength resulting from the water phase is believed to determine if and to what degree the resulting preferred polymeric foams can be open cell. Any electrolyte capable of imparting ionic resistance to the water phase can be used. Preferred electrolytes are mono-, di- or trivalent organic salts, such as water-soluble halides, for example, chlorides, nitrates and sulfates of alkali metals or alkaline earth metals. Examples include sodium chloride, calcium chloride, sodium sulfate and magnesium sulfate. Calcium chloride is most preferred for use in the preparation of HIPE. Generally, the electrolyte will be used in the water phase of the HIPEs at a concentration in the range of about 0.2 to about 20% by weight of the water phase. Most preferably, the electrolyte will comprise from about 1 to about 20% by weight of the water phase. The HIPEs will also contain a polymerization initiator. Said initiator component is generally added to the water phase of the HIPEs and can be any free radical, water soluble, conventional initiator. These include peroxygen compounds such as sodium, potassium and ammonium persulfates, hydrogen peroxide, sodium peracetate, sodium percarbonate and the like. Conventional redox initiator systems can also be used. Such systems are formed by combining the above peroxygen compounds with reducing agents such as sodium bisulfite, L-ascorbic acid or ferrous salts. The initiator may be present in an amount of up to 20 mol% based on the total moles of polymerizable monomers present in the oil phase. Most preferably, the initiator is present in an amount of about 0.001 to about 10 mol% based on the total moles of the polymerizable monomers in the oil phase. 3. Hydrophilizing Surfactants and Hydratable Salts The polymer that forms the HIPE foam structure will preferably be substantially free of polar functional groups. This means that the polymeric foam will have a relatively hydrophobic character. When these foams are to be used as insulating materials, water resistance is generally a desired characteristic. The removal of the residual emulsifier and / or the salt resulting from the polymerization is generally desired in a manner described more fully hereinafter.

B. Processing Conditions for Obtaining HIPE Foams The preparation of foams typically involves the steps of: 1) forming a highly stable internal phase emulsion (HIPE); 2) polymerizing / curing this suitable emulsion to form a solid polymeric foam structure; 3) optionally washing the solid polymeric foam structure to remove the original waste water phase, emulsifier, salts, from the polymeric foam structure; 4) after dehydrating this polymer foam structure; and 5) optionally hydrophilizing the foam. 1. HIPE Formation HIPE is formed by combining the oil phase and water components in the previously specified ratios. The oil phase will typically contain the monomers, comonomers, interleavers and emulsifiers of requirement, as well as optional components such as plasticizers, antioxidants, flame retardants, and chain transfer agents. The water phase will typically contain electrolytes and polymerization initiators. The HIPE can be formed from the combined oil and water phases by subjecting them to shear agitation. The shear agitation is also applied to such a degree and for a time necessary to form a stable emulsion. Said process can be conducted in either intermittent or continuous form, and is generally carried out under suitable conditions to form an emulsion, wherein the droplets of the water phase are dispersed to such an extent that the resulting polymeric foam will have the structural characteristics of requirement. Emulsification of the oil and water phase combination will often involve the use of a mixing or stirring device, such as a pin propellant. A preferred method for forming said HIPEs involves a continuous process that combines and emulsifies the oil and water phases of requirement. In said process, a liquid stream comprising the oil phase is formed. Consequently, a liquid stream comprising the water phase is also formed. Then, the two streams are combined in a suitable mixing chamber or zone, so that the pre-specified water-to-oil phase weight ratios are obtained. In the mixing zone or chamber, the combined streams are generally subjected to low shear agitation provided, for example, through a pin driver of suitable configurations and dimensions. The shear stress will typically be applied to the combined water / oil phase stream at an appropriate rate. Once formed, the stable liquid HIPE can then be removed from the chamber or mixing zone. This preferred method for forming HIPEs through a continuous process is described in more detail in U.S. Patent 5,149,720 (DesMarais et al.), Issued September 22, 1992, which is incorporated herein by reference. See also application of the co-pending United States of America series No. 08 / 370,694, filed January 10, 1995 by T. DesMarais (incorporated herein by reference), which describes an improved continuous process having a recirculation circuit for the HIPE 2. Polymerization / Healing of HIPE The formed HIPE will generally be collected or emptied into a suitable container, container or reaction region, which will be polymerized or cured. In one embodiment, the reaction vessel is constructed of polyethylene, from which finally the polymerized / cured solid foam material can be easily removed for further processing after the polymerization / cure has been performed to the desired degree. The temperature at which the HIPE is emptied into the container is generally about equal to the polymerization / cure temperature. Suitable polymerization / curing conditions will vary depending on the monomer and other development of the oil and water phases of the emulsion (especially the emulsifier systems used), and the type and amounts of polymerization initiators used. Frequently, however, suitable polymerization / cure conditions will involve maintaining the HIPE at elevated temperatures approximately above 30 ° C, preferably above 35 ° C, for a period ranging from about 2 to 64 hours , most preferably from 4 to 48 hours, approximately. HIPE can also be cured in stages as described in U.S. Patent 5,189,070 (Brownscombe et al.), Issued February 23, 1993, which is incorporated herein by reference. An open-cell, porous water-filled HIPE foam is typically obtained after polymerization / cure in a reaction vessel, such as a tray or cup. This polymerized HIPE foam is typically cut or sliced into a sheet-like shape. Polymerized HIPE foam sheets are easier to process during the subsequent steps of treatment / washing and dehydration, as well as to prepare the HIPE foam for use in insulation materials. The polymerized HIPE foam is typically cut / sliced to provide a cut thickness in the range of about 0.2032 cm to about 6.25 cm. 3. HIPE Foam Treatment / Washing The solid polymerized HIPE foam formed will generally be filled with the wastewater phase material to prepare the HIPE. The residual water phase material (generally an aqueous electrolyte solution, residual emulsifier, and polymerization initiator) can be removed before further processing and use of the foam. The removal of this original water phase material will usually be done by compressing the foam structure to compress the residual liquid, and / or by washing the foam structure with water or other aqueous washing solutions. Frequently, several compression and washing steps will be used, v. gr., from 2 to 4 cycles. It is preferable that the water used in this wash be heated to at least about the Tg of the polymer to maintain its flexibility and docility during compression dewatering and to reduce and prevent damage to the foam structure. 4. Dehydration of the Foam After the HIPE foam has been treated / washed, it will be dehydrated. Dehydration can be achieved by compressing the foam to squeeze the residual water, subjecting the foam and water at the same temperature from about 60 ° to about 200 ° C, or by microwave treatment, by thermal dehydration in vacuum or by a combination of compression and drying / microwave / vacuum dewatering techniques. These HIPE foams are typically compressively dehydrated to a thickness of about 1/3 (33%) or less of their fully expanded thickness. The dehydration step will generally be performed until the HIPE foam is ready to use and is as dry as practicable. Frequently, said compression dehydrated foams will have a water content (moisture) of from about 1% to about 15%, more preferably from about 5% to about 10% by weight, on a dry weight basis.

IV. Test Methods A. Dynamic Mechanical Analysis (DMA) The DMA was used to determine the Tg of the polymers including the polymeric foams. The sample disks were analyzed using Rheometrics RSA-II dynamic mechanical analyzer equipment, in a compression mode using parallel plates with a diameter of 25 mm. The instrument parameters used were the following: Temperature step from approximately 120 ° C to -50 ° C in steps of 2.5 ° C, depending on the precision needed to define the transition point. Soaking intervals between temperature changes of 120-160 seconds Dynamic voltage setting at 0.7% Frequency setting at 1.0 radians / second Fixing of self-tension in dynamic force mode of static force tracking with an initial static force setting at 5 g. The glass transition temperature was taken as the maximum point of the loss tangent curve (tan [d]) against temperature.

B. Elastic stress Elastic stress can be quantified by compressing a sample of foam at a specific rate and at a specific temperature, and measuring the resistance exerted by that sample on compression. Typically, the data is formatted as a stress curve on the Y axis and stress on the X axis. These graphs typically show an initial linear response followed by a rapid fall in additional compressive strength at a point named "point transferor or deformation ". The transfer point is defined as the intersection of the lines formed by the linear regions before and after the transfer point. Elastic stress is the value of effort at that intersection. The analysis is performed using the same equipment defined in the preceding section (Rheometrics RSA-II) operating in a constant voltage mode. In this mode, the temperature is set at 31 ° C and the voltage regime is set at 0.1% / second. The sample is maintained at this temperature for at least 5 minutes before the initiation of compression to bring it to the defined temperature. The experiment is continued for 10 minutes in compression followed by 10 minutes at the same rate of tension in the reverse direction. The data analysis is conducted as described above.

C. Density Density is the weight of a given sample divided by its volume and can be determined by any appropriate normal method. The density measurements used here involved weighing the cylindrical samples (disks) used in the previous measurements, which have a diameter of 2.54 cm. The thickness of the sample was determined by measurement. The density was then calculated using the density equation = weight (mg) / (0.507 x thickness (mm) expressed in units of mg / cm3.) Samples were typically washed in water and 2-propanol to remove salt and residual emulsifier. from the sample before these measurements The measured densities conformed close to what was expected from the water to oil ratio of the HIPE, from which the particular foam was derived, for example, density = (I / (W: O + 1)) in units of g / cm3.

V. Specific Examples The following examples illustrate the specific preparation of HIPE foams useful in the present invention.

EXAMPLES 1 to 5 Preparation of the Foams from HIPE Examples 1 to 5 are illustrative of low density foams having the desirably low Tg and desirably high elastic stress achieved by using a silicon-containing Tg reducing comonomer.

A) Preparation of HIPE The water phase consisting of 10% calcium chloride (anhydrous) and 0.05% potassium persulfate (initiator) was prepared. The oil phase was prepared according to the monomer ratios described in Table I, all of which include an emulsifier to form the HIPE.

The preferred emulsifier used in these examples is diglycerol monooleate (DGMO) used at a level of 5 to 10% by weight of the oil phase. The diglycerol monooleate emulsifier (Grindsted Products; Braband, Denmark) comprises approximately 81% diglycerol monooleate, 1% other diglycerol monoesters, 3% polyglycerols, and 15% other polyglycerol esters, imparts an interfacial tension value of the oil phase / water phase minimum of approximately 2.7 dynes / cm and has a critical aggregation concentration of approximately 2.9% by weight. To form the HIPE, the oil phase is placed in a 3-inch diameter plastic cup. The water phase is placed in an addition funnel, jacketed, maintained at approximately 50 ° C. The contents of the plastic cup are agitated using a Cafrano RZR50 agitator equipped with a six paddle stirrer that rotates at approximately 300 rpm (adjustable by the operator as needed). At a rate of addition sufficient to add the water phase in a period of about 2 to 5 minutes, the water phase is added into the plastic cup with constant stirring. The cup is moved up or down as needed to shake the HIPE as it forms to incorporate the entire water phase into the emulsion.

B) Polymerization / Healing of HIPE The HIPE inside the 3-inch plastic cups are capped and placed in an oven set at 65oC during the night to cure and provide a foam of Polymeric HIPE.

C. Foam Washing and Dehydration The cured HIPE foam was removed from the cup as a cylinder 3 inches in diameter and approximately 4 inches long. The foam at this point has a residual water phase (containing dissolved emulsifiers, electrolyte, initiator residues, and initiator) of about 50-60 times (50-60 X) the weight of the polymerized monomers. The foam was sliced in a food slicer to provide circular pieces of about 3 to about 8 mm thick. These pieces are washed in distilled water and compressed to remove 3 to 4 times the water. These are further washed in 2-propanol and compressed approximately 3 to 4 times. The pieces are then dried in an oven set at 65 ° C for 1 to 2 hours. In some cases, the foams crush when dried and must be dried by freezing the swollen state with water to recover the fully expanded foams. Various shapes and sizes of foams can be prepared in a similar manner by the use of appropriately shaped containers in which the HIPE is cured and / or the appropriate cut or formed. The process for preparing the foams of the present invention may also be a continuous process, such as that described in U.S. Patent No. 5,149,720, issued September 22, 1992 to DesMarais et al., Or the co-pending application for the patent. of the United States Serial No. 08 / 370,694, filed by DesMarais on January 10, 1995, the disclosure of each of which is incorporated herein by reference. Specific non-limiting examples of the combinations of the comonomers for making the foams of the present invention are shown in Tables 1 and 2.

Table 1. Composition and Properties of the Foam EHA - 2-ethylhexyl acrylate, available from Aldrich Chemical Corp., Milwaukee, Wl. DVB - divinyl benzene, based on 39-42% purity with 58-61% ethyl styrene impurity; available from Dow Chemical Corp., of Midland, Ml. AETMS-2- (acryloxyethoxy) trimethylsilane. APTMS - (3-acryloxypropyl) methylbis- (trimethylsiloxy) silane. All the silicon and germanium compounds used herein were obtained from Gelest, Inc. of Tuliytown, Pa, unless otherwise indicated.

EXAMPLES 6 to 14 Examples 6 to 14 are illustrative of low density foams having the desirably low Tg and desirably high elastic stress achieved by using a polyfunctional silicon-containing crosslinking agent. The foams are prepared using the process described for making foams of Examples 1 to 5, and the components of the oil phase described in Table 2.

Table 2. Composition and Properties of the Foam ISO Isoprene; available from Aldrich Chemical Corp. Because isoprene boils at 33 ° C, the preparation of the HIPE for example 13 is carried out at -5 ° C and the container is cured in a pressurized pressure vessel at 30 psi with argon. The pressure vessel is placed in the curing oven set at 65 ° C for two days to effect curing. BMAPTD 1, 3-bis (3-methylacri! Oxypropyl) t'3-tetramethyl-disiloxane. TUPMTS • 1, 3,5-trivinil-1, 1, 3,5,5-pentamethyltrisiloxane. TAS - tetra-allyl silane TKMES - Tetrakis (methacryloxyethoxy) silane. NM - not measured All silicon and germanium compounds used herein were obtained from Gelest, Inc. of Tullytown, Pa, unless otherwise indicated. In other examples, other alkyl acrylates are used in partial or total substitution for EHA, other crosslinkers are used in total partial replacement for DVB, related analogs are used where germanium is used in partial or total substitution of silicon, and are used other emulsifiers including the disodium dimethyl ammonium methylisulfate in partial or total substitution by the DGMO, as described above.

Claims (10)

1. A polymeric foam material comprising at least 5%, based on the weight of the foam, of one or more comonomers selected from the group consisting of silicon-containing comonomers, germanium-containing comonomers, and mixtures thereof, characterized in that the polymeric foam material has: a) a density less than 0.10 g / cm3; b) a glass transition temperature (Tg) of -40oC to 90oC; and c) a vault of elastic stress of at least 0.25 psi.

2. The polymeric foam according to claim 1, further characterized in that the foam is hydrophilic and is capable of acquiring and distributing aqueous fluids.

3. The polymeric foam material according to claim 2, further characterized in that the foam has a specific surface area of at least 0.01 m / cm3, preferably at least 0.025 m2 / cm3.

4. The polymeric foam material according to any of claims 1 to 3, further characterized in that the foam has a Tg of 15 ° to 50 ° C.

5. The polymeric foam material according to any of claims 1 to 4, further characterized in that the foam has an average cell size of not more than 150 μm.

6. The polymeric foam material according to any of claims 1 to 5, further characterized in that the foam is hydrophobic.

The polymeric foam material according to any of claims 1 to 6, further characterized in that the foam has an average cell size of 10 μm to 100 μm, preferably 15 μm to 35 μm.

8. The polymeric foam material according to claim 6 or claim 7, characterized in that the foam has one has a Tg of 15 ° to 50 ° C.

9. A polymeric foam material obtained by polymerizing an emulsion of water in oil of high internal phase, characterized in that the foam comprises at least 5%, based on the weight of the foam, of one or more comonomers selected from the group consisting of silicon-containing comonomers, germanium-containing comonomers, and mixtures thereof

10. The polymeric foam according to any of claims 1 to 9, characterized in that the foam is prepared by the process comprising the steps of : A) forming a water-in-oil emulsion under low shear mixing of: 1) an oil phase comprising: a) from 80% to 98% by weight of a monomer component capable of forming a copolymer having a Tg value from about -40 ° C to about 90 ° C, the monomer component comprising: i) at least 5% by weight of a material selected from the group consisting of one or more comonomers which contain silicon, one or more comonomers containing germanium, and mixtures thereof; ii) from 0% to 70% by weight of a monofunctional monomer substantially insoluble in water, capable of forming a homopolymer having a Tg of about 40 ° C or less; * iii) from 0% to 70% by weight of a monofunctional comonomer substantially insoluble in water, capable of imparting resistance approximately equivalent to that provided by styrene; iv) from 0% to 50% by weight of a first polyfunctional crosslinking agent, substantially insoluble in water, selected from divinylbenzenes and analogs thereof; and v) from 0% to 15% by weight of a second polyfunctional crosslinking agent, substantially insoluble in water, selected from the group consisting of diacrylates and dimethacrylates of diols and analogs thereof; and b) from 2% to 20% by weight of an emulsifying component, which is soluble in the oil phase, and which is suitable for forming a stable emulsion of water in oil 2) a water phase comprising 0.1% at 20% by weight of a water-soluble electrolyte; 3) a volume to weight ratio of water phase to oil phase of at least 10: 1; and B) polymerizing the monomer component in the oil phase of the oil in water emulsion to form a polymeric foam material.