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 The research and development leading to the subject matter disclosed herein was not federally sponsored.
 This invention relates to acoustical insulation for a variety of applications such as buildings, and especially for floors.
 In subdivided buildings such as apartment buildings, townhouses, condominiums, hotels and office buildings, it is important to provide good acoustical insulation between adjoining units and/or between floors. In many jurisdictions, building codes mandate certain standards of acoustical insulation between adjoining tenants and/or adjoining floors. To meet these standards, insulating materials are often incorporated into walls, ceilings and floors.
 To minimize the transmission of noise between floors, so-called “floating floor” constructions are becoming common. A “floating floor” construction includes a structural subfloor, which is weight-bearing. A “floating floor” sits atop of the structural subfloor but is not affixed to it and it is also separated from the connecting side walls. A flexible material separates the structural floor and the side walls from the floating floor. This flexible material is selected to have a low stiffness, leading to a low resonance frequency of the floating floor system. This provides insulation against ambient sounds that have higher frequencies.
 The acoustical insulation in a floating floor installation must satisfy several simultaneous demands. It must be soft enough that the system's natural resonance frequency is low. It must bear the weight of the floating floor and additional weight such as furniture and building occupants. As it will usually be walked over as it is installed and the floating floor is installed above it, the insulating material must withstand high, temporary, localized pressures without substantial permanent deformation. As insulating material is normally in place for years or decades, it must maintain its acoustical insulating properties for long periods of time. It must also be chemically stable, and not decompose or release harmful or irritating compounds to the surrounding environment.
 A commonly used insulating material in floating floor installations are foam boards made from expanded elastified polystyrene (EPS) beads. In order to be soft enough to provide acceptable acoustical insulation, these EPS boards are made in such a way that the individual expanded EPS beads are only weakly adhered to each other. As a result of the poor bead adhesion, the boards are very fragile unless they are thicker than about 17 millimeters (mm). This fragility leads to difficulties in handling the EPS boards. The thickness of the EPS boards also increases the cost and takes up otherwise habitable space.
 When thinner insulating material is desired, polyethylene foam sheets are often used instead of expanded EPS sheet. However, these sheets are not satisfactory in long-term creep behavior.
 Thus, it would be desirable to provide an alternative acoustical insulating material for use in building walls and, especially floors.
 The FIGURE is a cross-section of a floating floor construction containing a layer of acoustical insulation according to the invention.
 In a first aspect, this invention is an improvement in a building construction wherein foam acoustical insulation is installed in a wall, ceiling or floor of said building construction, the improvement comprising using as said acoustical insulation a polymeric foam of a polymer blend including (a) at least one alkenyl aromatic polymer, (b) at least one α-olefin polymer and (c) an effective amount of a compatibilizer to compatibilize said alkenyl aromatic polymer and said α-olefin polymer at the relative proportions thereof that are present in said polymer blend.
 In a second aspect, this invention is an improvement to a floating flooring system. The flooring system comprises a structural subfloor having a floating floor overlaid upon it and a polymeric foam underlayment installed between said structural subfloor and said floating floor. The polymeric foam is a cellular polymer blend including (a) at least one alkenyl aromatic polymer, (b) at least one α-olefin polymer and (c) an effective amount of a compatibilizer to compatibilize said alkenyl aromatic polymer and said α-olefin polymer at the relative proportions thereof that are present in said polymer blend.
 In a third aspect, this invention is the use as acoustical insulation in a building construction of a cellular polymer blend including (a) at least one alkenyl aromatic polymer, (b) at least one α-olefin polymer and (c) an effective amount of a compatibilizer to compatibilize said alkenyl aromatic polymer and said α-olefin polymer at the relative proportions thereof that are present in said polymer blend.
 In a fourth aspect, this invention is an acoustical foam comprising (a) at least one alkenyl aromatic polymer, (b) at least one α-olefin polymer and (c) an effective amount of a compatibilizer to compatibilize said alkenyl aromatic polymer and said α-olefin polymer at the relative proportions thereof that are present in said polymer blend, said foam having a density of from about 10-60 kg/m
 In a fifth aspect, this invention is a method for improving the acoustical performance of a building construction, comprising installing a wall, polymeric foam in a wall, ceiling or floor of said building construction, wherein the polymeric foam of a polymer blend including (a) at least one alkenyl aromatic polymer, (b) at least one α-olefin polymer and (c) an effective amount of a compatibilizer to compatibilize said alkenyl aromatic polymer and said α-olefin polymer at the relative proportions thereof that are present in said polymer blend.
 In this invention, a polymeric foam made from a blend of an alkenyl aromatic polymer and an α-olefin polymer may be used as acoustical insulation in a building construction. The blend also contains a polymeric compatibilizer for the alkenyl aromatic polymer and the α-olefin polymer.
 Any numerical values recited herein include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and any higher value. As an example, if it is stated that the amount of a component or a value of a process variable such as, for example, temperature, pressure, time and the like is, for example, from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, it is intended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. are expressly enumerated in this specification. For values which are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner. Unless otherwise stated, all ranges include both endpoints and all numbers between the endpoints.
 All references herein to elements or metals belonging to a certain Group refer to the Periodic Table of the Elements published and copyrighted by CRC Press, Inc., 1989. Any reference to the Group or Groups shall be to the Group or Groups as reflected in this Periodic Table of the Elements using the IUPAC system for numbering groups.
 “Hydrocarbyl” means any aliphatic, cycloaliphatic, aromatic, aryl substituted aliphatic, aryl-substituted cycloaliphatic, aliphatic substituted aromatic, or aliphatic substituted cycloaliphatic groups. “Hydrocarbyloxy” means a hydrocarbyl group having an oxygen linkage between it and the carbon atom to which it is attached. “Aliphatic” means a compound having a straight- or branched-chain arrangement of its carbon atoms.
 “Copolymer” means a polymer having polymerized therein monomeric units derived from two different monomers.
 “Interpolymer” means a polymer having polymerized therein monomeric units derived from at least two different monomers. This includes, for example, copolymers, terpolymers and tetrapolymers. “Monomeric unit” refers to a polymer backbone portion that is derived from a single monomer.
 Alkenyl Aromatic Polymer
 For purposes of this invention, an alkenyl aromatic polymer is a melt-processable polymer or melt processable impact-modified polymer in the form of polymerized monovinylidene aromatic monomers as represented by the structure:
 wherein R is hydrogen or an alkyl radical that preferably has no more than three carbon atoms and Ar is an aromatic group. R is preferably hydrogen or methyl, most preferably hydrogen. Aromatic groups Ar include phenyl and naphthyl groups. The aromatic group Ar may be substituted. Halogen (such as Cl, F, Br), alkyl (especially C
 The alkenyl aromatic polymer may be a homopolymer of a monovinylidene aromatic monomer as described above. Polystyrene homopolymers are the most preferred alkenyl aromatic polymers. Interpolymers of two or more monovinylidene aromatic monomers are also useful.
 Although not critical, the alkenyl aromatic polymer may have a high degree of syndiotactic configuration; i.e., the aromatic groups are located alternately at opposite directions relative to the main chain that consists of carbon-carbon bonds. Homopolymers of monovinylidene aromatic polymers that have syndiotacticity of 75% r diad or greater or even 90% r diad or greater as measured by
 The alkenyl aromatic polymer may also contain repeating units derived from one or more other monomers that are copolymerizable with the monovinylidene aromatic monomer. Suitable such monomers include N-phenyl maleimide; acrylamide; ethylenically unsaturated nitriles such as acrylonitrile and methacrylonitrile; ethylenically unsaturated carboxylic acids and anhydrides such as acrylic acid, methacrylic acid, fumaric anhydride and maleic anhydride; esters of ethylenically unsaturated acids such as C
 In addition, the alkenyl aromatic polymers include those modified with rubbers to improve their impact properties. The modification can be, for example, through blending, grafting or polymerization of a monovinylidene aromatic monomer (optionally with other monomers) in the presence of a rubber compound. Examples of such rubbers are homopolymers of C
 Preferred impact modified alkenyl aromatic polymers are prepared by dissolving the rubber into the monovinylidene aromatic monomer and any comonomers and polymerizing the resulting solution, preferably while agitating the solution so as to prepare a dispersed, grafted, impact modified polymer having rubber domains containing occlusions of the matrix polymer dispersed throughout the resulting polymerized mass. In such products, polymerized monovinylidene aromatic monomer forms a continuous polymeric matrix. Additional quantities of rubber polymer may be blended into the impact modified polymer if desired.
 Commercial PS (polystyrene), HIPS (high impact polystyrene), ABS (acrylonitrile-butadiene-styrene) and SAN (styrene-acrylonitrile) resins that are melt processable are particularly useful in this invention.
 The alkenyl aromatic polymer has a molecular weight such that it can be melt processed with a blowing agent to form a cellular foam structure. Preferably, the alkenyl aromatic polymer has a melting temperature of about 60° C. to about 310° C. A number average molecular weight of about 60,000 to about 350,000, preferably from about 100,000 to about 300,000, is particularly suitable. In the case of an impact modified polymer, these molecular weight numbers refer to molecular weight of the matrix polymer (i.e., the continuous phase polymer of a monovinylidene aromatic monomer).
 α-Olefin Polymer
 The α-olefin polymer is a polymer or interpolymer containing repeated units derived by polymerizing an α-olefin. The α-olefin polymer contains essentially no polymerized monovinylidene aromatic monomers and no sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers. Particularly suitable α-olefins have from 2 to about 20 carbon atoms, preferably from 2 to about 8 carbon atoms, and include ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and the like. Preferred α-olefin polymers are homopolymers of ethylene or propylene and interpolymers of ethylene with a C
 Particularly suitable α-olefin polymers include low density polyethylene (LDPE), which term is used herein to designate polyethylene homopolymers made in a high pressure, free radical polymerization process. These LDPE polymers are characterized by having a high degree of long chain branching. LDPE useful in this invention preferably has a density of about 0.910 to 0.940 g/cc (ASTM D792) and a melt index from about 0.02 to about 100 grams per 10 minutes, preferably from 0.1 to about 50 grams per 10 minutes (as determined by ASTM Test Method D 1283, condition 190° C./2.16 kg).
 The so-called linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) products are also useful herein. These polymers are homopolymers of polyethylene or copolymers thereof with one or more higher α-olefins and characterized by the near or total absence (less than 0.01/1000 carbon atoms) of long chain branching. LLDPE and HDPE are made in a low pressure process employing conventional Ziegler-Natta type catalysts, as described in U.S. Pat. No. 4,076,698. LLDPE and HDPE are generally distinguished by the level of α-olefin comonomer that is used in their production, with LLDPE containing higher levels of comonomer and accordingly lower density. Suitable LLDPE polymers having a density of from about 0.85 to about 0.940 g/cc (ASTM D 792) and a melt index (ASTM D 1238, condition 190° C./2.16 kg) of about 0.01 to about 100 grams/10 minutes. Suitable HDPE polymers have a similar melt index, but have a density of greater than about 0.940 g/cc.
 Another suitable α-olefin polymer includes polypropylene. High melt strength polypropylene resins are preferred. The propylene polymer material may be comprised solely of one or more propylene homopolymers, one or more propylene copolymers, and blends of one or more of each of propylene homopolymers and copolymers; propylene homopolymers are preferred. The propylene polymer preferably has a weight average molecular weight (M
 Another suitable type of α-olefin polymer are LLDPE polymers having a homogeneous distribution of the comonomer, as are described, for example, in U.S. Pat. No. 3,645,992 to Elston and U.S. Pat. Nos. 5,026,798 and 5,055,438 to Canich.
 Yet another type of α-olefin polymer are substantially linear olefin polymers as described in U.S. Pat. Nos. 5,272,236 and 5,278,272, incorporated herein by reference. The substantially linear olefin polymer is advantageously a homopolymer of a C
 In addition, α-olefin polymers that have been subjected to coupling or light crosslinking treatments are useful herein, provided that they remain melt processable. Such grafting or light crosslinking techniques include silane grafting as described in U.S. Pat. No, 4,714,716 to Park; peroxide coupling as described in U.S. Pat. No. 4,578,431 to Shaw et al., and irradiation as described in U.S. Pat. No 5,736,618 to Poloso. Preferably, the treated polymer has a gel content of less than 10%, more preferably less than 5%, most preferably less than 2% by weight, as determined by gel permeation chromatography. Treatment of this type is of particular interest for HIDPE, LLDPE or substantially linear polyethylene copolymers, as it tends to increase the melt tension and melt viscosity of those polymers to a range that improves their ability to be processed into foam in an extrusion process.
 Polymeric Compatibilizer
 The polymer blend further contains a polymeric compatibilizer for the alkenyl aromatic polymer and the α-olefin polymer. The polymeric compatibilizer can be of any type, provided that it prevents macroscopic phase separation of the polymer blend, and the polymer blend is melt processable to form a foam. Without the compatibilizer, the alkenyl aromatic polymer and the α-olefin polymer are difficult to blend and difficult to foam. The compatibilizer enhances the mixing between the polymeric components. Suitable compatibilizers include certain aliphatic α-olefin/monovinylidene aromatic interpolymers, hydrogenated or non-hydrogenated monovinylidene aromatic/conjugated diene block (including diblock and triblock) copolymers, and styrene/olefin graft copolymers.
 Examples of suitable aliphatic α-olefin/monovinylidene interpolymers include the substantially random interpolymers prepared by polymerizing i) ethylene and/or one or more α-olefin monomers and ii) one or more vinyl or vinylidene aromatic monomers and/or one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers, and optionally iii) other polymerizable ethylenically unsaturated monomer(s). The interpolymer contains, for example, in polymerized form, from about 35 to about 99 mole percent of monomer type i), about 1 to about 65 mole percent of monomer type ii), and up to 30 mole percent of monomer type iii). Preferably, the interpolymer contains from about 45-97 mole percent of monomer type i), about 3-55 mole percent of monomer type ii) and no more than 20 mole percent of monomer type iii). The interpolymer advantageously has a melt flow index (190° C./2.16 kg) of about 0.1 to 50 g/10 min and a molecular weight distribution which is a weight average molecular weight/number average molecular weight (M
 Examples of suitable α-olefin include for example, α-olefins containing from 3 to about 20, preferably from 3 to about 12, more preferably from 3 to about 8 carbon atoms. Particularly suitable are ethylene, propylene, butene-1, 4-methyl-1-pentene, hexene-1 or octene-1 or ethylene in combination with one or more of propylene, butene-1, 4-methyl-1-pentene, hexene-1 or octene-1. These α-olefins do not contain an aromatic, hindered aliphatic or cycloaliphatic moieties.
 Other optional polymerizable ethylenically unsaturated monomer(s) include norbomene and C
 Vinyl or vinylidene aromatic monomers which can be employed to prepare the interpolymers include, for example, those represented by the following formula:
 wherein R
 By the terms “sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene compounds”, it is meant addition polymerizable vinyl or vinylidene monomers corresponding to the formula:
 wherein A
 The substantially random interpolymers include the pseudo-random interpolymers as described in EP-A-0,416,815 by James C. Stevens et al., (equivalent to U.S. Pat. No. 5,872,201) and U.S. Pat. No. 5,703,187 by Francis J. Timmers, both of which are incorporated herein by reference in their entirety. The substantially random interpolymers are conveniently made by polymerizing a mixture of polymerizable monomers in the presence of one or more metallocene or constrained geometry catalysts in combination with various cocatalysts. Preferred operating conditions for such polymerization reactions are pressures from atmospheric up to 3000 atmospheres and temperatures from −30° C. to 200° C. Polymerizations and unreacted monomer removal at temperatures above the autopolymerization temperature of the respective monomers may result in formation of some amounts of homopolymer polymerization products resulting from free radical polymerization.
 Examples of catalysts and methods for preparing the substantially random interpolymers are disclosed in European Application Nos. EP-A-416,815; EP-A-514,828; allowed U.S. application Ser. No. 09/302,067; as well as U.S. Pat. Nos. 5,055,438; 5,057,475; 5,096,867; 5,064,802; 5,132,380; 5,189,192; 5,321,106; 5,347,024; 5,350,723; 5,374,696; 5,399,635; 5,470,993; 5,703,187; 5,721,185; 5,929,154; 6,013,819; and 6,048,909. All of the foregoing are fully incorporated herein by reference.
 The substantially random α-olefin/vinyl aromatic interpolymers can also be prepared by the methods described in JP 07/278230 employing as catalysts compounds shown by the general formula:
 where Cp
 The substantially random α-olefin/vinyl aromatic interpolymers can also be prepared by the methods described by John G. Bradfute et al. (W. R. Grace & Co.) in WO 95/32095; by R. B. Pannell (Exxon Chemical Patents, Inc.) in WO 94/00500; and in
 Also of interest are the substantially random interpolymers which comprise at least one α-olefin/vinyl aromatic/vinyl aromatic/α-olefin tetrad disclosed in WO 98/09999 by Francis J. Timmers et al. These interpolymers contain additional signals in their carbon-13 NMR spectra with intensities greater than three times the peak to peak noise. These signals appear in the chemical shift range 43.70-44.25 ppm and 38.0-38.5 ppm. Specifically, major peaks are observed at 44.1, 43.9, and 38.2 ppm. A proton test NMR experiment indicates that the signals in the chemical shift region 43.70-44.25 ppm are methine carbons and the signals in the region 38.0-38.5 ppm are methylene carbons.
 It is believed that these new signals are due to sequences involving two head-to-tail vinyl aromatic monomer insertions preceded and followed by at least one α-olefin insertion, e.g. an ethylene/styrene/styrene/ethylene tetrad wherein the styrene monomer insertions of said tetrads occur exclusively in a 1,2 (head to tail) manner. It is understood by one skilled in the art that for such tetrads involving a vinyl aromatic monomer other than styrene and an α-olefin other than ethylene that the ethylene/vinyl aromatic monomer/vinyl aromatic monomer/ethylene tetrad will give rise to similar carbon-13 NMR peaks but with slightly different chemical shifts.
 These interpolymers can be prepared by conducting the polymerization at temperatures of from about −30° C. to about 250° C. in the presence of such catalysts as those represented by the formula:
 wherein: each C
 wherein each R is independently, each occurrence, H, hydrocarbyl, silahydrocarbyl, or hydrocarbylsilyl, containing up to about 30 preferably from 1 to about 20 more preferably from 1 to about 10 carbon or silicon atoms or two R groups together form a divalent derivative of such group. Preferably, R independently each occurrence is (including where appropriate all isomers) hydrogen, methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, phenyl or silyl or (where appropriate) two such R groups are linked together forming a fused ring system such as indenyl, fluorenyl, tetrahydroindenyl, tetrahydrofluorenyl, or octahydrofluorenyl.
 Particularly preferred catalysts include, for example, racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl) zirconium dichloride, racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl) zirconium 1,4-diphenyl-1,3-butadiene, racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenyl-indenyl) zirconium di-C1-4 alkyl, racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl) zirconium di-C1-4 alkoxide, or any combination thereof and the like.
 It is also possible to use the following titanium-based constrained geometry catalysts, [N-(1,1-dimethylethyl)-1,1-dimethyl-1-[(1,2,3,4,5-q)-1,5,6,7-tetrahydro-s-indacen-1-yl]silanaminato(2-)-N]titanium dimethyl; (1-indenyl)(tert-butylamido)dimethylsilane titanium dimethyl; ((3-tert-butyl)(1,2,3,4,5-η)-1-indenyl)(tert-butylamido) dimethylsilane titanium dimethyl; and ((3-iso-propyl)(1,2,3,4,5-η)-1)-1-indenyl)(tert-butyl amido) dimethylsilane titanium dimethyl, or any combination thereof and the like.
 Further preparative methods for the interpolymers used in the present invention have been described in the literature. Longo and Grassi (
 While preparing the substantially random interpolymer, an amount of atactic vinyl aromatic homopolymer may be formed due to homopolymerization of the vinyl aromatic monomer at elevated temperatures. The presence of vinyl aromatic homopolymer is in general not detrimental for the purposes of the present invention and can be tolerated. The vinyl aromatic homopolymer may be separated from the interpolymer, if desired, by extraction techniques such as selective precipitation from solution with a non solvent for either the interpolymer or the vinyl aromatic homopolymer. For the purpose of the present invention it is preferred that no more than 30 weight percent, preferably less than 20 weight percent based on the total weight of the interpolymers of atactic vinyl aromatic homopolymer is present.
 Blends of an alkenyl aromatic polymer with an α-olefin polymer using an α-olefin/monovinylidene aromatic interpolymer as a compatibilizer are described in U.S. Pat. No. 5,460,818 incorporated herein by reference. Those blends are suitable for use herein.
 Monovinylidene aromatic/conjugated diene block copolymers include diblock and triblock copolymers of, for example, styrene and one or more conjugated dienes such as butadiene, isoprene or norbomene. The proportion of units derived from the monovinylidene aromatic monomer is, for example, from 10 to 80% by weight and preferably from 30 to 60% by weight. These advantageously have a molecular weight, as measured by viscosity against a polystyrene standard, of about 3,000 to 800,000 and preferably from 10,000 to 100,000. These block copolymers can be hydrogenated, as described in U.S. Pat. No. 4,020,025, and the hydrogenated forms can also be used. The double bonds in the backbone of the polymer may be hydrogenated to the extent of 90% or more. Suitable styrene/olefin graft copolymers are also described in U.S. Pat. No. 4,020,025 and in German Published Application 1,495,813, both included herewith by reference.
 Preferred interpolymers are substantially random ethylene-styrene interpolymers. Such polymers preferably have a styrene content from about 20 to about 70 wt % measured as described, for example, in U.S. Pat. No. 6,048,909 to Chaudhary. Most preferred are interpolymers such as those marketed by The Dow Chemical Company under the INDEX™ tradename. These interpolymers have a higher damping ratio than either the ethylene or the styrene components alone. A damping ratio, also called loss tangent (tgε), is a ratio between loss modulus (viscous component of the deformation) versus storage modulus (elastic component of the deformation.)
 The polymer blend contains, for example, from about 10%, preferably from about 20%, more preferably from about 25%, most preferably from about 35% up to about 90%, preferably up to about 80%, and more preferably up to about 75%, and even more preferably up to about 70% by weight alkenyl aromatic polymer. A high concentration of alkenyl aromatic polymer tends to improve mechanical properties but decrease softness. The blend contains, for example, from about 10%, preferably from about 20%, more preferably from about 25%, most preferably from about 35% up to about 75%, preferably up to about 60%, more preferably up to about 50% by weight of the α-olefin polymer. A high concentration of α-olefin polymer tends to improve softness but may hinder post-load recovery and creep performance. The blend preferably contains from about 1%, more preferably from about 2%, most preferably from about 3%, even more preferably from about 5%, preferably from about 10% to about 60%, preferably to about 50%, more preferably to about 40%, even more preferably to about 30% by weight of the compatibilizer. The polymeric compatibilizer tends to improve damping properties, but a high concentration may decrease strength. All percentages in this paragraph are based on the combined weight of alkenyl aromatic polymer, α-olefin polymer, and compatibilizer. The polymer blend can be prepared by simple melt blending. If desired, the individual polymers can be separately charged into an extruder together with blowing agent and other auxiliaries to form the polymer blend as part of the foam-making process. Alternatively, the polymer blend can be made separately prior to the foaming process. The dispersion of the polymer components should be uniform.
 The polymer blend or any component thereof can contain additives that do not undesirably interfere with the foaming process or the acoustical properties of the resulting foam. Antioxidants, colorants, fillers, dyes, slip agents, flame retardants and the like are common such additives.
 A foam for use in this invention is conveniently made from the polymer blend through an extrusion process. The polymer blend or the individual constituents thereof are advantageously fed into the heated barrel of an extruder, which is maintained above the crystalline melting temperature of the constituents of the blend. Optionally, auxiliary components such as nucleating agents are mixed into the blend. An expanding agent is mixed with the molten polymer blend under pressure and the resulting mixture extruded though a die to an area of lower pressure where the mixture expands and cools to form a cellular structure. Generally, the mixture is cooled to within +/−20° C. of the highest crystalline melting point or glass transition temperature of the components of the polymer blend before extrusion. Optionally, the extruded foam is made using an accumulating extrusion process as described in U.S. Pat. No. 4,323,528 to Collins et al.
 Expanding agents include both physical and chemical blowing agents. Physical blowing agents include gasses and liquids that volatilize under the conditions of the foaming process, whereas chemical blowing agents produce a gas under the condition of the foaming process through some chemical means, usually decomposition. Particularly suitable physical blowing agents include halocarbons containing 1 or 2 carbon atoms such as methyl chloride, ethyl chloride, dichloromonofluoromethane, trichlorofluoromethane, monofluoromonochloromethane, 1,1,2-trifluorotrichloroethane, 1,1,2,2-tetrafluorodichlorethane, 1,2,2,2-tetrafluoroethane, and 1,2,2-trifluoroethane. Also suitable are saturated or unsaturated hydrocarbons containing from 3 to 8 carbon atoms such as propane, n-butane, isobutane, pentane, hexane, octane, propene, 1-butene, 1-pentene, isopentane and 2,2-dimethylbutane. Carbon dioxide, nitrogen, argon, water and the like are also useful. Mixtures of these physical expanding agents can be used. Chemical blowing agents include, for example, azodicarbonamide, dinitrosopentamethylene tetramine, benzenesulfonyl hydrazide and toluene sulfonyl hydrizide. Isobutane is a highly preferred blowing agent.
 A nucleating agent (or cell control agent) can be used to help control the size of the cells. Cell control agents include finely particulate solids such as talc as well as mixtures of sodium bicarbonate with citric acid or sodium citrate. The foam advantageously has a cell size in the range of from 0.1 mm, preferably from 0.2 mm, more preferably from about 0.3 mm, to about 10 mm, preferably to about 5 mm, more preferably to about 2.5 mm as measured by ASTM D 3756.
 In addition, a stability control agent such as glycerol monostearate, stearyl stearamide or the like can be used to modify the rate at which the blowing agent escapes from the cells of the foam after the foam is cooled. The use of such stability control agents is described, for example, in U.S. Pat. Nos. 3,644,230 to Cronin and 4,395,510 to Park.
 As the foam may be used in buildings, for example as acoustical insulation, it preferably will also contain a flame retardant which functions to extinguish flames or at least slow the spread of fire in the foam. Flame retardants are well known, and include brominated organic compounds such as are described in U.S. Pat. No. 4,446,254 to Nakae. Preferred flame retardants include hexabromocyclohexane and blends with a chlorinated paraffin and/or a synergist such as antimony trioxide, dicumyl and polycumyl.
 It is often desirable to accelerate the aging of the foam in order to remove the blowing agent from the cells before shipping or using the foam. This is particularly true with hydrocarbon or other flammable blowing agents. Accelerated aging can be accomplished through perforation techniques as described in U.S. Pat. No. 5,242,016 to Kolosowski, through heat aging (including but not limited to the conditions described in U.S. Pat. No. 5,059,376 to Pontiff), or a combination of both techniques.
 The foam formulation is advantageously selected so that the foam has a density of from about 5 kg/m
 The foam is conveniently extruded in the form of sheet or plank material having a thickness of from about 1, preferably from about 1.5, more preferably about 2, most preferably about 3 to about 200, preferably to about 100, more preferably to about 50 mm. Due to room height and door height restrictions, the desired thickness requirement is usually less than or equal to about 10 mm when the foam is used as acoustical insulation. Thinner extrusions can be used in multiple layers if desired to achieve desired acoustical insulation. Thicker extrusions can be cut down to lesser thickness. The width of the sheet is not critical, although larger widths tend to reduce labor in installing the foam as acoustical insulation. Widths of up to 3 meters or more are suitable, with preferred widths being from about 0.1 to 2 meters.
 The final foam for use by the consumer, either before or after elastification as described below, preferably has a dynamic modulus of no greater than 1,500 kN/m
 The dynamic modulus, and therefore the dynamic stiffness, of a foam can be reduced somewhat by mechanically stressing the foam, such as by compression. This process is referred to herein as “elastification”. Elastification tends to open cells and to crease cell struts so that the foam is softened and the dynamic stiffness correspondingly reduced. Compression is readily accomplished by, for example, compressing the foam by about 30-95% of its original thickness through a pair of rollers or under any kind of compression system. Multiple compressions may be done in order to achieve a desired softness (as indicated by dynamic modulus).
 The foam advantageously has an open cell content of at least 10 volume %, preferably at least 15 volume %, more preferably at least 20 volume %, up to 100 volume %, preferably up to about 95 volume %, more preferably up to about 90 volume % as measured per ASTM D 2856 Procedure A. In some cases, foams with less than 10 volume % open cells may also be suitable.
 The foam may be used as a layer of acoustical insulation in a floor or wall construction. A layer of the foam is installed in the wall or floor at which acoustical insulation is desired. The foam layer can be installed in the ceiling, wall or floor between weight-bearing structures and exposed surfaces. For vertical installations, the foam can be held in place with adhesives or mechanical devices such as nails, screws, staples or rivets. For horizontal installations, it is often not necessary to secure the foam to the underlying structure, although it may be so secured if desired.
 The floating floor system illustrated in
 As shown in
 In all cases, screed
 Acoustical foam layer
 Because acoustical foam layer
 The following examples are provided to illustrate the invention but are not intended to limit to scope thereof. All parts and percentages are by weight unless otherwise indicated.
 I. Preparation and Testing of Ethylene-styrene Interpolymers (ESI-1 and ESI-2)
 The ESI's may be prepared as described in column 17, line 15 through column 20, line 3 of U.S. Pat. No. 6,048,909 which is herein incorporated by reference. The melt flow or melt index measurements, and analysis of the styrene content in the ESI interpolymers may be determined, for example, as described in column 14, line 28 through column 17, line 11 of U.S. Pat. No. 6,048,909 which is also incorporated by reference.
 For ESI-1, the reactor temperature is 104.9° C., the solvent flow is 665 lb./hr, the ethylene flow is 123 lb./hr, the hydrogen flow is 1525 standard cubic centimeters/minute and the styrene flow is 110 lb./hr. The cocatalyst is tris(pentafluorophenyl)borane. A modified methylaluminoxane (MMAO) commercially available from Akzo Nobel as MMAO-3A (CAS# 146905-79-5) is also used. The boron to titanium ratio in the cocatalyst and catalyst is 3.6:1, and the MMAO/titanium ratio is 6.0. Sufficient catalyst is used to obtain the desired conversion rate. ESI-1 contains 39.9 wt-% (15.2 mole-%) copolymerized styrene and 0.6 weight percent atactic polystyrene homopolymer. Its melt index is 0.63 g/10 minutes (190° C./2.16 kg). ESI-2 contains 44.7 wt-% copolymerized styrene and 10.2 weight percent atactic polystyrene homopolymer. Its melt index is 1.5 g/10 minutes (190° C./2.16 kg).
 II. Foam Preparation
 A foam suitable for use in the present invention is made using a screw type extruder having a feeding zone, a metering, a mixing zone, heating zones, three cooling zones. A rectangular shaped die is mounted at the end of the cooling zones.
 Pellets of polystyrene homopolymer having a M
 Foam Example 2 is prepared by compressing a portion of foam Example 1 by 70% of its original thickness under a press at a speed of 500 mm/minute and immediately releasing the pressure at the same rate. Foam Example 3 is prepared by compressing a portion of foam Example 1 by 85% in the same way. Foam Example 4 is prepared by compressing a portion of foam Example 1 by 92% in the same way.
 Foam Example 5 is prepared in the same manner as foam Example 1, except the weight ratio of PS/PE/ESI-1 is 40/50/10, and it is compressed by 70% in the mariner described for Example 2. Foam Example 6 is prepared in the same way as Foam Example 5, except it is compressed by 90%.
 Foam Examples 7 and 8 are prepared in the same way as Foam Examples 5 and 6, respectively, except that the weight ratio of PS/PE/ESI-1 is 40/55/5.
 Foam Example 9 is prepared in the same way as Foam Example 5, except the PS/PE/ESI-1 ratio is 45/45/10.
 Foam Example 10 is prepared in the same manner as Foam Example 1, except the foam density is somewhat lower. Foam Example 11 is prepared by compressing Foam Example 10 by 70%, using the method described for Foam Example 2.
 Foam Example 12 is prepared in the same manner as Foam Example 10, but at a slightly higher density.
 Foam Examples 13 and 14 are made in the same manner as Examples 1 and 4, respectively, except that ESI-2 is substituted for ESI-1, a 0.7 g/10 min. melt index polyethylene is substituted for the polyethylene, and a polystyrene of MW=192,000 is substituted for the polystyrene used in Examples 1 and 4, the amount of isobutane is 10 parts per hundred parts resin, and 0.06 part per hundred Irganox 1010 is used as the antioxidant.
 The density, cell size, open cell content, dynamic modulus and dynamic stiffness of all Foam Examples are determined. They are as reported in the following table. In addition, creep is measured for each foam after exposure for 1000 hours to loads of 2.5 kPa (kN/m
 For comparison, the properties of a polyethylene foam (Comparative Example A) are provided in the following table.
TABLE 1 Creeps Ex. Elastifi- Thick- % Open 2.5 3.5 5.0 No. PS/PE/ESI Density cation ness Cell Size Cells DM DS kPa kPa kPa A* PE 37 0 10 ND 0 455 81 14 ND ND 1 40/40/20 25.6 0 10 1.11 71.3 622 62 4.8 4.3 6.6 2 40/40/20 25.6 70 10 1.11 71.3 404 40 6.2 7.3 13.3 3 40/40/20 25.6 85 10 1.11 71.3 384 38 7.3 10.9 12.7 4 40/40/20 25.6 92 10 1.11 71.3 390 39 7.3 10.6 18.7 5 40/50/10 33.7 70 10 0.66 56 380 38 4.4 6.4 11.7 6 40/50/10 33.7 90 10 0.66 56 310 31 ND 9.1 13.6 7 40/55/5 31.8 70 10 0.56 66 510 51 ND 5.6 8.9 8 40/55/5 31.8 90 10 0.56 66 410 41 ND 6.1 10.1 9 45/45/10 22.8 70 10 1.02 75 310 31 5.5 11.7 ND 10 40/40/20 24.3 0 10 1.44 82 390 39 7.8 8.6 11 11 40/40/20 24.3 70 10 1.44 82 331 33 8.5 12.8 21.7 12 40/40/20 24.6 0 10 1.25 76 415 42 8.9 12.1 12.1 13 40/40/20 27.9 0 10 1.12 39 986 99 ND 4.9 6.3 14 40/40/20 27.8 92 9.14 1.17 57.4 380 42 ND 5.8 14.9
 Table 2 shows acoustic and mechanical properties of a foam prepared as described in Example 1 at various thicknesses.
TABLE 2 Acoustic and Mechanical Performance of Impact Sound Insulation Sheet Thickness (mm) 3 5 10 Dynamic Stiffness (MN/m 105 65 40 Dynamic Modulus (MN/m 0.315 0.325 0.4 Impact Sound Improvement ΔLw (dB) 18 21 24 Thickness recovery dL-dB % 10% 10% 10% Creep @ 3.5 kPa % 7.3% 7.3% 7.3%
 Table 3 shows creep data over time (up to about 1000 hours) for a 10 mm thick foam prepared as described in Example 1. For comparison, the properties of a 5 mm thick polyethylene foam (Comparative Example B) are also provided.
TABLE 3 Comparative Examples Example B 15 16 17 Load = 2.5 kPa Load = 2.5 kPa Load = 3.75 kPa Load = 5.0 kPa Time Creep Time Creep Time Creep Time Creep (hours) (%) (hours) (%) (hours) (%) (hours) (%) 0.08 7.4 0.02 2.8 0.02 2.4 0.02 3.4 0.2 7.6 0.2 3.4 23 5.3 23 8.9 0.5 7.7 23 4.8 45 5.7 45 9.8 1 7.9 45 5.1 430 6.7 330 12.0 24 9.2 100 5.3 1000 7.6 1000 14.1 48 10.1 210 5.6 168 12.2 1000 6.2 336 13.3 504 13.8 1056 14.5
 As can be seen from the data in the foregoing tables, foam made from the ternary blend in accordance with this invention therefore has a large advantage in long term deformation properties (creep) and typically has a low dynamic modulus, making it more suitable than LDPE foam for use as acoustical insulation in applications that expose the foam to prolonged weight-bearing.