POLYURETHANE FOAMS FOR COMFORT APPLICATIONS

Abstract

Polyurethane foams that are hydrophilic but exhibit low compression set are made from a combination of MDI and TDI prepolymers, water, and a polymeric polyol. Optionally, the foams are manufactured by incorporating a phase-change material into the foam formulation. The phase-change material does not require encapsulation.

Description

POLYURETHANE FOAMS FOR COMFORT APPLICATIONS FIELD OF INVENTION This invention relates to flexible polyurethane foams that are useful in comfort applications such as pillows, mattresses, mattress toppers, and seat cushions. BACKGROUND OF THE INVENTION Polyurethane foams are used extensively to manufacture cushioning materials, particularly for bedding and seating. One problem with these foams is that they are not very effective at conducting heat. Therefore, the heat emitted by a user is trapped by the foam in areas close to the user's body. This results in a localized increase in temperature that the user often perceives as uncomfortable. Several approaches have been proposed to address this problem. Increasing the porosity of the foam to allow air to flow in and out more easily helps considerably. Making the foam more hydrophilic allows moisture, such as perspiration, to be wicked away from the wearer's body more effectively, thus contributing to a greater sense of comfort. So-called gel technology is used to impart a cool-to-the-touch feel, which is important at the point of sale. i1 ΓΑηη / ζζηζ / Ε / γίΛΐ Ref. 336606 None of these approaches has been entirely satisfactory. Foams that are highly porous and have high airflow rates are permeable, but may lack the necessary load-bearing characteristics. Hydrophilic foams tend to have poor compression set. This leads to the foam becoming permanently deformed during regular use, sagging or forming depressions. Formulation modifications to reduce compression set tend to reduce airflow. Hydrophilic foams also lack the desired cool feel at the point of sale. Phase-change materials or gels are frequently used to impart a cooling sensation. These materials have a melting or phase-transition temperature at approximately room temperature or slightly higher. They effectively absorb body heat upon contact as the material undergoes its phase change. This results in a cooling sensation upon initial touch. Gels are used as surface stoppers or infused into foams. Gels are not permeable and therefore do not effectively transfer heat. Once gels warm up to body temperature, they tend to trap heat rather than dissipate it. They also tend to be sticky and are therefore commonly encapsulated within polymer films. This further reduces their permeability, exacerbating the problem. A polyurethane foam is sought that exhibits good moisture absorption along with low compression set for use in bedding and other comfort applications. Ideally, the foam also exhibits high airflow and a cool feel. DETAILED DESCRIPTION OF THE INVENTION This invention is, in one aspect, a flexible polyurethane foam comprising a reaction product of a reaction mixture comprising: a) an isocyanate mixture comprising a) a first isocyanate-functionalized prepolymer, wherein the first isocyanate-functionalized prepolymer is a reaction product of at least one hydroxyl-terminated ethylene oxide polymer and optionally a hydroxyl-functionalized branching agent and / or hydroxyl-functionalized chain extender with an excess of diphenylmethane diisocyanate, wherein the diphenylmethane diisocyanate is at least 50 wt% 4,4'-diphenylmethane diisocyanate, a-2) optionally diphenylmethane diisocyanate, wherein components a-1) and a-2) together have an isocyanate content of 5 to 15 wt% and contain 30 to 75 wt% oxyethylene units, based on the combined weight of components a-1) and a-2), and components a-1) and a-2) together constitute 40 to 60% of the total weight of the isocyanate mixture, a-3) a second prepolymer with isocyanate functionality,whose second isocyanate-functionalized prepolymer is a reaction product of at least one hydroxyl-terminated ethylene oxide polymer and a hydroxy-functionalized branching agent having at least three hydroxyl groups per molecule and a hydroxyl equivalent weight of up to 250 g / equivalent with an excess of toluene diisocyanate, and a-4) optionally toluene diisocyanate, wherein a-3) and a-4) together have an isocyanate content of 5 to 15 wt% and contain 30 to 75 wt% of oxyethylene units, based on the combined weight of components a-3) and a-4) and 2 to 5 wt% of residues of the hydroxyl-functionalized branching agent, based on the combined weight of components a-3) and a-4); components a-3) and a-4) together constitute 40 to 60% of the total weight of the isocyanate mixture; and components a-1), a-2), a-3) and a-4) together constitute the total weight of the isocyanate mixture; b) water; c) at least one polymeric polyol comprising polymeric particles dispersed in at least one base polyol, the base polyol being a polyether having at least 50% by weight of oxypropylene units and a hydroxyl equivalent weight i1 ΓΑηη / ζζηζ / Ε / γίΛΐ of 500 to 3000 g / equivalent; d) optionally a poly(ethylene oxide), the poly(ethylene oxide) being a homopolymer of ethylene oxide or a random and / or block copolymer of at least 80 wt% ethylene oxide and up to 20 wt% another alkylene oxide, the poly(ethylene oxide) having a number average molecular weight of 400 to 1200 g / mol; at least one of e) and f), wherein e) is at least one silicone surfactant; and f) is at least one higher ethylene oxide / alkylene oxide block copolymer, the block copolymer containing 40 to 90 wt% of oxyethylene units and having a number-average molecular weight of 1500 to 12,000 g / mol; and optionally (g) at least one phase-change material having a melting or glass transition temperature of 25 to 37 °C and containing no isocyanate groups or isocyanate-reactive groups; where i) the isocyanate mixture constitutes 40 to 65% of the combined weights of the components ag; ii) water constitutes 15 to 41% of the combined weights of the ag components; iii) the at least one polymeric polyol constitutes 8 to 20% of the combined weights of the ag components and the polymeric particles constitute 0.5 to 10% of the combined weights of i1 CAnn / zznz / E / YiAi i1 CAnn / zznz / E / YiAi the ag components; iv) poly(ethylene oxide) when present constitutes up to 5% of the combined weights of the ag components; (v) at least one silicone surfactant constitutes 0 to 3% of the combined weights of the components; vi) the at least one higher ethylene oxide / alkylene oxide block copolymer constitutes 0 to 3% of the combined weights of the components ag; vii) the at least one phase change material constitutes up to 15% of the combined weights of the ag components and viii) the ag components constitute at least 95% of the weight of the reaction mixture. Flexible polyurethane foams produced according to the invention have an unusual combination of properties that makes the foam particularly desirable for bedding, seating, and other comfort applications where the foam is exposed to body heat and / or water vapor evaporating from a human user's body. These properties include very low compression set, good moisture absorption behavior, and suitable density. In preferred embodiments, they also exhibit good airflow and / or non-zero latent heat in the temperature range of 25 to 37°C. The good airflow and non-zero latent heat result in a cooling characteristic of the foam. The foam, or an article containing the foam, can, in such applications, support at least a portion of a human user's weight. The invention is also a method for manufacturing a flexible polyurethane foam, comprising A. To form a reaction mixture by mixing: a) an isocyanate mixture comprising a-1) a first isocyanate-functional prepolymer, wherein the first isocyanate-functional prepolymer is a reaction product of at least one hydroxyl-terminated ethylene oxide polymer and optionally a hydroxyl-functional branching agent and / or a hydroxyl-functional chain extender with an excess of diphenylmethane diisocyanate, wherein the diphenylmethane diisocyanate is at least 50 wt% 4,4'-diphenylmethane diisocyanate by weight, a-2) optionally diphenylmethane diisocyanate, wherein components a-1) and a-2) together have an isocyanate content of 5 to 15 wt% and contain 30 to 75 wt% oxyethylene units, based on the combined weight of components a-1) and a-2), and components a-1) and a-2) together constitute 40 to 60 wt% of the total weight of the isocyanate mixture, a-3) a second prepolymer with isocyanate functionality,whose second isocyanate-functionalized prepolymer is a reaction product of at least one hydroxyl-terminated ethylene oxide polymer and a hydroxy-functionalized branching agent having at least three hydroxyl groups per molecule and a hydroxyl equivalent weight of up to 250 g / equivalent with an excess of toluene diisocyanate, and a-4) optionally toluene diisocyanate, wherein a-3) and a-4) together have an isocyanate content of 5 to 15 wt% and contain 30 to 75 wt% of oxyethylene units, based on the combined weight of components a3) and a-4) and 2 to 5 wt% of residues of the hydroxyl-functionalized branching agent, based on the combined weight of components a-3) and a-4); Components a-3) and a-4) together constitute 40 to 60% of the total weight of the isocyanate mixture; and components a-1), a-2), a-3) and a-4) together constitute the total weight of the isocyanate mixture; b) water; c) at least one polymeric polyol comprising polymeric particles dispersed in at least one base polyol, the base polyol being a polyether having at least 50% by weight of oxypropylene units and a hydroxyl equivalent weight of 500 to 3000 g / equivalent; d) optionally a poly(ethylene oxide), the poly(ethylene oxide) is a homopolymer of ethylene oxide or a random and / or block copolymer of at least 80 wt% ethylene oxide and up to 20 wt% another alkylene oxide, the poly(ethylene oxide) having a number average molecular weight of 400 to 1200 g / mol; at least one of e) and f), wherein e) is at least one silicone surfactant; and f) is at least one higher ethylene oxide / alkylene oxide block copolymer, the block copolymer containing 40 to 90 wt% of oxyethylene units and having a number-average molecular weight of 1500 to 12,000 g / mol; and optionally (g) at least one phase-change material having a melting or glass transition temperature of 25 to 37 °C and containing no isocyanate groups or isocyanate-reactive groups; where i) the isocyanate mixture constitutes 40 to 65% of the combined weights of the components ag; ii) water constitutes 15 to 41% of the combined weights of the ag components; iii) the at least one polymeric polyol constitutes 8 to 20% of the combined weights of the ag components and the polymeric particles constitute 0.5 to 10% of the combined weights of the ag components; iv) poly(ethylene oxide) when present constitutes up to 5% of the combined weights of the ag components; 1¡ FRnn / zznz / E / YiAi (v) at least one silicone surfactant constitutes 0 to 3% of the combined weights of the components; vi) the at least one higher ethylene oxide / alkylene oxide block copolymer constitutes 0 to 3% of the combined weights of the components ag; vii) at least one phase change material constitutes up to 15% of the combined weights of components ag and viii) components ag constitute at least 95% of the weight of the reaction mixture and B. react the reaction mixture to produce the foam. Component a-1) of the isocyanate mixture is an isocyanate-terminated first prepolymer, which is a reaction product of at least one ethylene oxide hydroxyl-terminated polymer and optionally a hydroxyl-containing branching and / or chain-extending agent with an excess of diphenylmethane diisocyanate (MDI). At least 50% by weight of the MDI is the 4,4' isomer. In some embodiments, the 4,4' isomer constitutes at least 60% or at least 70% by weight of the diphenylmethane diisocyanate used to prepare the prepolymer. Up to 100% of the diphenylmethane diisocyanate may be the 4,4' isomer. The 2,4' isomer, if present, may constitute at least 5%, at least 10%, or at least 15% by weight of the diphenylmethane diisocyanate. The 2,2' isomer, if present, can constitute up to 5%, or up to 2% of the weight of the diphenylmethane diisocyanate used to make the prepolymer. The ethylene oxide polymer is conveniently a hydroxyl-terminated ethylene oxide homopolymer or a random or block copolymer of ethylene oxide and hydroxyl-terminated 1,2-propylene oxide. The polyether may contain, for example, at least 50% or at least 60% by weight of oxyethylene groups and up to 100% by weight of oxyethylene groups. One polyether of particular interest is a homopolymer of poly(ethylene oxide). Another is a random or block copolymer of ethylene oxide and 1,2-propylene oxide containing 50 to 99%, preferably 60 to 95%, of oxyethylene groups and correspondingly 5 to 50%, preferably 5 to 40%, of methyloxyethylene (oxypropylene) groups. The polyether may nominally contain, for example, an average of 2 to 4 hydroxyl groups per molecule. A preferred nominal average hydroxyl functionality is 2 to 3, and a more preferred nominal average hydroxyl functionality is 2 to 2.5 or 2 to 2.25. The nominal functionality refers to the number of oxyalkylable groups in the starting compound used in the production of the polyether(s). A primary amino group is considered to contain 2 oxyalkylable sites for the purposes of this invention. The hydroxyl equivalent weight of the polyether is preferably at least 300 or at least 450, and may be, for example, up to 6000, up to 3000, or up to 2000 g / equivalent. A particularly preferred equivalent weight range is from 500 to 1800 g / equivalent. All hydroxyl equivalent weights in this description are determined by titration methods such as ASTM D4274-99. A mixture of two or more polyethers, as described above, can be used to prepare the first isocyanate-terminated prepolymer. The isocyanate-functionalized prepolymer is conveniently prepared by mixing the MDI with the polyether(s) and subjecting the mixture to conditions under which a portion of the isocyanate groups react with the hydroxyl groups of the polyether(s) to form urethane linkages. A hydroxyl-containing branching and / or chain-extending agent is optionally present when the isocyanate-functionalized prepolymer is formed. Such a branching or chain-extending agent may have a hydroxyl equivalent weight of up to 250 or up to 125, and may have at least 3 (preferably 3-8, 3-6, or 3-4) hydroxyl groups per molecule in the case of a branching agent and exactly two hydroxyl groups per molecule in the case of a chain-extending agent. If present, they are present in an amount of up to 5, preferably up to 2, parts by weight per 100 parts by weight of the polyether(s). FRnn / zznz / E / YiAi This prepolymer formation reaction is conveniently carried out at an elevated temperature (such as 60 to 180 °C) and preferably under an inert atmosphere such as nitrogen, helium, or argon. An excess of isocyanate groups over hydroxyl groups is provided; in some embodiments, the MDI, the polyether(s), and the optional branching agent and / or chain extender are combined in a ratio of 0.95 to 1.5, specifically 0.95 to 1.25 mol of the polyisocyanate per equivalent of hydroxyl groups. The reaction generally continues until the prepolymer reaches a constant isocyanate content, indicating the consumption of essentially all the hydroxyl groups of the polyether. The first isocyanate-terminated prepolymer is preferably prepared in the substantial absence of a urethane catalyst, i.e., a catalyst for the reaction of an isocyanate group with a hydroxyl group to form a urethane. In particular, the reaction mixture for forming the first functional isocyanate prepolymer preferably contains no more than 1 part per million by weight of metals and no more than 100 parts per million by weight of amine compounds. The resulting isocyanate-terminated prepolymer contains equally small amounts of such materials (if any). The polyether(s) are preferably not amine-initiated and do not contain amine groups that exhibit urethane catalyst activity. The product of the prepolymer formation reaction may contain a certain amount of unreacted MDI, which, when present, forms all or part of component a-2) of the isocyanate mixture. The MDI may be combined separately with the first isocyanate-functionalized prepolymer and / or with the other ingredients of the isocyanate mixture, if desired. The first isocyanate-functionalized prepolymer and any free MDI in the isocyanate mixture together have an isocyanate content of 5 to 15%, based on the combined weight of the first isocyanate-functionalized prepolymer and free MDI. The isocyanate content may be at least 6% or at least 7% by weight and may be, for example, up to 12% or up to 10% by weight on the same basis. The isocyanate content can be determined using well-established titration methods. The first isocyanate-functionalized prepolymer and any free MDI in the isocyanate blend together contain 30 to 70 percent by weight of oxyethylene units, based on the combined weight of the first isocyanate-functionalized prepolymer and free MDI. The oxyethylene unit content may be at least 40 percent by weight, at least 50 percent by weight, or at least 55 percent by weight, and 70 percent by weight or up to 65 percent by weight, on the same basis. The percentage of oxyethylene units is a calculated i1 ΓΑηη / ζζηζ / E / γίΛΐ value, determined using the relationship: %oxietilenoala2j t CAnn / zznz / E / YiAi %oxietilertOpex pesopepesOpG-l· 'pesofrj^ce-^pesoMDj where %oxietilenoai,a2, is the weight percentage of oxyethylene groups in components a-1 and a-2 of the isocyanate mixture, %oxietilenopees is the weight percentage of oxyethylene groups in the polyether(s) used to make the first isocyanate functional prepolymer, wtpees is the weight of the polyether(s) used to make the first isocyanate functional prepolymer, wtbr,ce is the weight of all branching agents and chain extenders used to make the first isocyanate functional prepolymer, and wímdi is the weight of the MDI used to make the first isocyanate functional prepolymer plus any other MDI present in the isocyanate mixture. Component a-3) of the isocyanate mixture is a second isocyanate-terminated prepolymer, which is a reaction product of at least one hydroxyl-terminated ethylene oxide polymer and a hydroxyl-containing branching agent with an excess of toluene diisocyanate (TDI). The TDI may be the 2,4-, 2,5-, or 2,6- isomer, or a mixture of two or more of these. In some embodiments, the TDI is a mixture of 50 to 85% of the 2,4- isomer, the remainder being the 2,6- isomer. The hydroxyl-terminated ethylene oxide polymer is as described above in relation to the first isocyanate-functionalized prepolymer. The branching agent is generally as described with respect to the first prepolymer with isocyanate functionality. It has at least three hydroxyl groups per molecule and, in some embodiments, has 3-8, 3-6, or 3-4 hydroxyl groups per molecule. Its hydroxyl equivalent weight can be up to 250, up to 125, or up to 80. Examples include glycerin, trimethylolpropane, trimethylolethane, sorbitol, mannitol, sucrose, pentaerythritol, erythritol, triethanolamine, and alkoxylates of any or more of the above that have the aforementioned hydroxyl equivalent weight. The amount of branching agent is selected so that the residues of the branching agent constitute 2 to 5%, preferably 3 to 5%, of the combined weight of components a-3) and a-4). The weight of the residues is calculated from those of the starting materials used in the preparation of components a-3) and a-4), as follows: jt CANn / zznz / E / YiAi Wt — % branching agent pesobr+ pesope+ pesoce+ pesoTDIx 100% where Wttr is the weight of the branching agents used to make component a-3), Wtpees is the weight of the polyether used to make component a-3), Wtce is the weight of any chain extender used to make component a-3), and Wtdi is the combined weight of the TDI used to make component a-3) plus the weight of component a-4) (if present). The second isocyanate-terminated prepolymer is conveniently prepared in a manner analogous to that described above for the first isocyanate-terminated prepolymer, by substituting MDI for TDI. The second isocyanate-terminated prepolymer is preferably prepared in the substantial absence of a urethane catalyst, i.e., a catalyst for the reaction of an isocyanate group with a hydroxyl group to form a urethane. In particular, the reaction mixture for forming the second isocyanate-terminated prepolymer preferably contains no more than 1 part per million by weight of metals and no more than 100 parts per million by weight of amine compounds. Consequently, the resulting second isocyanate-terminated prepolymer contains similarly small amounts of such materials (if any).As before, the polyether(s) are preferably not amine initiated and do not otherwise contain amine groups that exhibit urethane catalyst activity. The product of the prepolymer formation reaction may contain a certain amount of unreacted TDI, which, when present, forms all or part of component a-4) of the isocyanate mixture. The TDI may be combined separately with the second isocyanate-functionalized prepolymer and / or with the other ingredients of the isocyanate mixture, if desired. The second isocyanate-functionalized prepolymer and any free TDI in the isocyanate mixture together have an isocyanate content of 5 to 15%, based on the combined weight of the second isocyanate-functionalized prepolymer and free TDI. The isocyanate content may be at least 6% or at least 7% by weight and may be, for example, up to 12% or up to 10% by weight on the same basis. The second isocyanate-functionalized prepolymer and any free TDI in the isocyanate mixture together contain 30 to 70 percent by weight of oxyethylene units, based on the combined weight of the second isocyanate-functionalized prepolymer and free TDI. The oxyethylene unit content may be at least 40 percent by weight or at least 50 percent by weight, on the same basis. The percentage of oxyethylene units is a calculated value, determined in a manner analogous to that described above, by substituting the weight of TDI with the weight of MDI. The isocyanate mixture constitutes 40 to 65% of the combined weights of the components. In some embodiments, the isocyanate mixture constitutes at least 45% of the combined weights of the components and up to 62.5%, up to 60%, or up to 55% of these. Water (component b)) constitutes 15-41% of the combined weights of the components ag. Water may constitute at least 17%, at least 19%, or at least 20% of these and may constitute up to 35% or up to 30% of these. The polymeric polyol (component c) is a dispersion of polymer particles in a liquid base polyol, where the base polyol forms a continuous base. Some or all of the polymer particles may be grafted onto the base polyol. The polymeric polyol may also include one or more stabilizers, onto which some or all of the polymer particles may be grafted. The base polyol is one or more polyethers having a hydroxyl equivalent weight of 500 to 3000 g / equivalent. The hydroxyl equivalent weight may be at least 800, at least 1000, or at least 1200, and may be, for example, up to 2500, up to 2000, or up to 1800 g / equivalent. The base polyol is a polymer or copolymer of propylene oxide containing at least 50 wt% oxypropylene units. Propylene oxide homopolymers and random and / or block copolymers of 50 to 99 wt% propylene oxide and 1 to 50 wt% ethylene oxide are particularly useful base polyols. The base polyol can have a nominal functionality of i1 CAnn / zznz / E / YiAi to 6, especially 2 to 4 and with the maximum preference 2 to 3. The actual functionality may be somewhat lower than the nominal functionality in some cases. A particularly preferred base polyol type is prepared by homopolymerizing propylene oxide or randomly copolymerizing 75-99.9 wt% propylene oxide and correspondingly 0.1 to 25 wt% ethylene oxide in a di- or trifunctional initiator, and optionally capping the resulting polyether with up to 30 wt% (based on total product weight) ethylene oxide to form a base polyol having mainly primary hydroxyl groups. The dispersed polymeric particles may constitute, for example, at least 1, at least 5 or at least 10 percent of the total weight of the polymeric polyol and may constitute, for example, up to 60 percent, up to 50 percent, up to 40 percent, up to 30 percent or up to 20 percent of the total weight of these. The polymer particles dispersed in some formulations have particle sizes from 100 nm to 25 pm, more typically from 250 nm to 10 pm. Preferably, at least 90% by volume of the dispersed polymer particles have sizes within these ranges. Particle sizes are taken as diameters of spheres having an equivalent volume. Particle size measurements can be obtained by laser diffraction methods, using equipment such as a Beckman-Coulter LX 13320 laser diffraction particle size analyzer. The dispersed polymer particles may be, for example, polyurea, polyurethane, and / or polyhydrazide, and / or a polymer of one or more vinyl monomers. Useful vinyl monomers include, for example, various polyolefins (such as ethylene polymers and copolymers), various polyesters, various polyamides, various polycarbonates, various acrylic and / or methacrylate ester polymers and copolymers, a styrene homopolymer or copolymer, an acrylonitrile homopolymer or copolymer, and the like. In some embodiments, the dispersed particles are styrene-acrylonitrile copolymer particles. At least a portion of the dispersed polymer particles is preferably grafted onto at least a portion of a stabilizer and / or the base polyol molecules that form the continuous phase. Polyurea particle dispersions can be prepared by reacting a primary or secondary amine with a polyisocyanate in the presence of the base polyol. Methods for producing polyurea dispersions are described, for example, in WO 2012 / 154831. Polyurethane particle dispersions can be prepared by reacting a low equivalent weight polyol or amino alcohol with a polyisocyanate in the presence of the base polyol i1 CAnn / zznz / E / YiAi. Methods for producing such dispersions are described, for example, in US 4,305,857, WO 94 / 20558, WO 2012 / 154820. Dispersions of polymerized vinyl monomers can be prepared by in-situ polymerization of such monomers in the base polyol. Such methods are described in, for example, USP 4,513,124, USP 4,588,830, USP 4,640,935, and USP 5,854,386. Alternatively, dispersions of this type can be formed by a melt dispersion process, in which a previously formed vinyl polymer is melted and dispersed in the base polyol. Methods of this type are described in USP 6,613,827 and WO 2009 / 155427. Polymer polyols constitute at least 8 percent of the combined weights of components ag. In some embodiments, the polymer polyol(s) constitute at least 9 percent of these. The polymer polyol(s) constitute up to 20 percent of the combined weights of components ae and may constitute up to 18 percent, up to 15 percent, or up to 12 percent of these. The dispersed polymer particles constitute from 0.5 to 10% of the combined weights of the components. The dispersed polymer particles may constitute at least 1%, at least 2%, or at least 4% of these and up to 8% of these. The polymeric polyol preferably contains no more than 5 parts per million by weight or no more than 1 part per million by weight of metals and no more than 100 parts per million of amine compounds. The base polyol(s) are preferably not amine-initiated and do not contain amine groups that exhibit urethane catalyst activity. Poly(ethylene oxide) (component d) is a homopolymer of ethylene oxide or a random and / or block copolymer of alkylene oxides, of which at least 80 wt% is ethylene oxide and up to 20 wt% is one or more other alkylene oxides. The other alkylene oxide, when present, may include or be 1,2-propylene oxide. Poly(ethylene oxide) may have a molecular weight of 400 to 1200 g / mol per GPC. Preferably, it contains at least one hydroxyl group per molecule. Preferably, it nominally contains at least two hydroxyl groups per molecule and up to six, up to four, or up to three hydroxyl groups per molecule. Useful silicone surfactants (component e)) are self-dispersible and / or water-soluble. Useful silicone surfactants include block copolymers having at least one polysiloxane block and at least one polyether block. Such block copolymers may be, for example, AB or BAB type copolymers, where A represents the polysiloxane block and each B represents a polyether block. Such a block copolymer may be a graft-type pendant structure in which multiple polyether blocks depend on a polysiloxane block. Each polyether block is preferably an ethylene oxide homopolymer or copolymer. An ethylene oxide copolymer may be a copolymer of ethylene oxide and propylene oxide. The silicone surfactant may contain, for example, 20 to 80 wt% of polysiloxane, 20 to 75 wt% of polymerized ethylene oxide, and 0 to 50 wt% of polymerized propylene oxide, based on the total weight of the silicone surfactant. A more preferred silicone surfactant contains 20 to 80 wt% of polysiloxane, 20 to 75 wt% of polymerized ethylene oxide, and 0 to 20 wt% of polymerized propylene oxide. An even more preferred silicone surfactant contains 25 to 50 wt% of polysiloxane, 50 to 75 wt% of polymerized ethylene oxide, and 0 to 10 wt% of polymerized propylene oxide. Suitable silicone surfactants are commercially available and include, for example, water-soluble surfactants sold by Momentive Performance Products under the product designation Silwet®. This includes, for example, Silwet® surfactants L-7002, L-7200, L-7230, L-7600, L-7604, L-7605, and L7657. Silicone surfactants constitute 0 to 3% of the combined weights of the active ingredients. Silicone surfactants may constitute at least 0.5%, at least 0.75%, or at least 1% of these and may constitute up to 2.5% or 2% of 1¡ FRnn / zznz / E / YiAi these . The block copolymer of ethylene oxide and a higher alkylene oxide (component f) contains one or more oxyethylene blocks and one or more blocks of a polymerized higher alkylene oxide. The higher alkylene oxide may be, for example, 1,2-propylene oxide, 1,2-butylene oxide, or a mixture thereof. Such block copolymers may contain, for example, 40 to 90 wt% of oxyethylene units and have number-average molecular weights of 1500 to 12,000 g / mol (by gel permeation chromatography against polystyrene standards). Such block copolymers may have one or more hydroxyl groups, such as 1 to 4 hydroxyl groups or 2 to 4 hydroxyl groups. Examples of suitable block copolymers include those sold by The Dow Chemical Company under the trade name Tergitol™, and those sold by BASF under the trade name Pluronics™. The block copolymer of ethylene oxide and a higher alkylene oxide preferably contains no more than 5 parts per million by weight or no more than 1 part per million by weight of metals and no more than 100 parts per million of amine compounds. It is preferably not initiated with an amine. The ethylene oxide and higher alkylene oxide block copolymer may constitute 0 to 3% of the combined weights of the components. It may constitute at least 0.5%, at least 0.75%, or at least 1% of this, and may constitute up to 2.5% or up to 2% of this. The phase change material (component g) is one or more materials having a melting or glass transition temperature of 25 to 37 °C and not containing isocyanate groups or isocyanate-reactive groups. The phase change material may be or contain, for example, any one or more natural or synthetic waxes, such as polyethylene wax, beeswax, lanolin, carnauba wax, candelilla wax, uricuri wax, sugarcane wax, jojoba wax, epicuticular wax, coconut wax, petroleum wax, or paraffin wax. The phase change material preferably has a melting temperature of 25 to 32 °C, especially 28 to 32 °C. The phase change material is preferably not encapsulated, i.e., it is not contained within a film or other container that forms a physical barrier between the phase change material and the remaining ingredients of the reaction mixture. The phase change material, when present, constitutes up to 15% of the combined weights of the ag components. In some embodiments, it constitutes at least 1%, at least 2%, or at least 2.5% of this, and in some embodiments, it constitutes up to 12.5% ​​or up to 10% of this. The reaction mixture may contain one or more optional ingredients in addition to the components described above. Such optional ingredients, if present, constitute together no more than 5% of the weight of the reaction mixture. Suitable optional ingredients include one or more branching agents and / or chain extenders as described above in relation to the preparation of quasi-prepolymers, but may be omitted. The reaction mixture may also contain various ingredients such as colorants, antioxidants, preservatives, biocides, fragrances, thickening agents (such as xanthan gum, various water-soluble cellulose ethers, or polyacrylamide), mixing aids, wetting agents (when fillers are present), and the like. If present, these preferably constitute up to 10% or up to 5% of the total weight of the reaction mixture. The reaction mixture for making polyurethane foam preferably lacks a curing catalyst, i.e., a catalyst for the reaction of isocyanate groups to water and / or alcohol groups. In particular, the reaction mixture preferably contains no more than 5 parts per million, and preferably no more than 1 part per million, by weight of metals and no more than 100 parts per million by weight of amine compounds. The reaction mixture may contain, in addition to the ag components, one or more solid components such as fillers and reinforcing materials. Examples of fillers include clays, diatomaceous earth, calcium carbonate, wollastonite, ground polymer particles, wood flour, cork flour, glass or other ceramic particles, and various types of natural and synthetic fibers, which may be interwoven, woven, or entangled if desired. Such solid components may constitute up to 75 percent of the total weight of the reaction mixture. Polyurethane foam is made by combining the ingredients to form a reaction mixture and subjecting the resulting reaction mixture to conditions in which the quasi-prepolymer with isocyanate functionality and one or more bg components react to form the flexible polyurethane foam. The ingredients ag can be combined in any order, although it is preferable to add the polyisocyanate mixture last or simultaneously with the other ingredients to avoid a premature reaction before the remaining ingredients can be added. Thus, for example, components bg can be combined first, followed by the addition of the polyisocyanate mixture. Alternatively, components ag can all be combined at once. It is also possible to form components be in several subcombinations that combine when the polyisocyanate mixture is added. Optional ingredients that are reactive with isocyanate or water-soluble (i1 ΓΑηη / ζζηζ / E / γίΛΐ) can be added together with the water or separately. Curing occurs spontaneously upon mixing water with the polyisocyanate mixture, so a wide range of conditions is suitable for the reaction. The curing temperature can be as low as 0 °C or as high as, for example, 100 °C. Temperatures close to or slightly elevated from room temperature are perfectly adequate and generally preferred. Therefore, the curing temperature can be at least 15 °C or at least 20 °C and up to 50 °C, 40 °C, or 35 °C. The curing reaction produces carbon dioxide gas, which forms cells and expands the reaction mixture as curing takes place. The curing step, on the other hand, can be carried out in an open container, where the rising foam expands against the weight of the atmosphere and / or the weight of a thin film. This free-rising process can be achieved by distributing the reaction mixture in a container where it rises and cures. The curing step can be carried out in a closed container, such as a closed mold, in which the expansion is limited by the internal dimensions of the cavity to produce a foam that has a size and shape corresponding to that of the mold cavity. The amount of water in the reaction mixture is much greater than the amount of isocyanate groups in the i1 CAnn / zznz / E / YiAi isocyanate mixture. Because of this, the cured foam often contains a significant amount of moisture, which may be at least partially in the form of a liquid contained within the foam cells. A drying step may be performed to remove some or all of this excess water. This drying stage can be carried out, for example, by passing a dry gas through the foam, allowing the foam to settle in a dry atmosphere, and / or heating the foam to a temperature of, for example, 50 to 150 °C. Drying can be carried out until any desired moisture content is achieved. In some embodiments, drying is carried out until a constant foam weight is reached, indicating the removal of all residual water from the foam. The foam of the invention can have a foam density after drying of, for example, 40 to 144 kg / m³, measured in accordance with ASTM D3574. A significant advantage of this invention is that foam densities of 80 kg / m³ and lower are readily obtained. In some embodiments, the foam density is 48 to 80 kg / m³. When dried, the foam of the invention exhibits low compression set in addition to low foam density. Compression set is measured in accordance with ASTM D-3774:D on skinless 5 x 5 x 2.54 cm specimens. The specimen thicknesses are measured with a micrometer. The specimens are placed between steel plates, compressed to 1% of their original thickness, and aged under compression at 70°C for 22 hours. The specimens are then removed from the testing apparatus and allowed to recover to room temperature for 30 minutes before their thicknesses are remeasured. Compression set is calculated as [100% x (original thickness - final thickness)] to original thickness. Compression set is typically less than 10%. In preferred embodiments, compression set may be 8% or less, 6% or less, or even 5% or less. The foam of the invention containing a phase-change material (component g), when dried to a constant weight as described above, can exhibit a latent heat at 27°C, measured by differential scanning calorimetry, of at least 2.5 J / g. Its latent heat can be at least 4 J / g, at least 8 J / g, at least 10 J / g, or at least 14 J / g at that temperature. In some embodiments, the latent heat can be as much as 25 J / g, as much as 30 J / g, or even higher at that temperature. The foam of the invention can exhibit an airflow of at least 0.8 l / s as measured according to ASTM D3574 Test G. The airflow can be at least 1.2 l / s or at least 1.4 l / s and can be, for example, up to 5 l / s or up to 4 l / s. In some formulations, the foam exhibits a moisture absorption time of 5 seconds or less, preferably 4 seconds or less. The moisture absorption time is measured on skinless 5 x 5 x 2.54 cm samples dried to a constant weight. Three milliliters of room-temperature water are slowly poured onto the top surface of the foam sample from a pipette, and the amount of time required for the foam to absorb the water is recorded as the absorption time. The foam of the invention is useful for bedding, seating, and other comfort applications. Comfort applications include those in which, during use, the foam is exposed to body heat or water vapor evaporating from the body of a human user. The foam, or an article containing the foam in such applications, often supports at least a portion of a human user's weight and is compressed during use. Examples of such comfort applications include pillows; mattress toppers, mattresses, quilts, furniture and / or car seats; padding; insulating clothing, and the like. Another application of interest is padding for limb prostheses. The following examples are provided to illustrate the invention, but are not intended to limit its scope. All parts and percentages are by weight unless otherwise stated. Polyisocyanate 1 is manufactured by first preheating a mixture of 57.9 parts of a poly(ethylene oxide) homopolymer with a molecular weight average of 1000 g / mol and 3.8 parts of trimethylolpropane to 80 °C. Separately, 33.8 parts of an 80 / 20 mixture of 2,4- and 2,6-toluene diisocyanate (TDI) are heated to 40 °C. 0.004 parts of benzoyl chloride are added to the TDI. The polyol mixture is added to the TDI, and the resulting reaction mixture is heated to 74 °C until a constant isocyanate content of 8% is achieved. An additional 4.4 parts of TDI are then mixed in. The resulting product is cooled to below 60 °C. The isocyanate content is measured as 9.45–10.3 wt% according to ASTM D5155. The viscosity is measured as 18,000–21,000 mPa·s at 25 °C according to ASTM D4065. Polyisocyanate 1 contains approximately 95.6 wt% of a TDI prepolymer, and the polyols, approximately 3.8 percent by weight of branching agent residues (trimethylolpropane) and approximately 4.4 percent by weight of free TDI. Polyisocyanate 1 contains 57.9% oxyethylene units by calculation. Polyisocyanate 2 is prepared by first preheating to 80 °C a mixture of 32 parts of a number-average molecular weight poly(ethylene oxide) homopolymer of 1000 g / mol and 13 parts of a nominally trifunctional random copolymer of number-average molecular weight 5000 g / mol of propylene oxide and ethylene oxide, containing 75% oxyethylene units. Separately, 35 parts of a 79 / 21 mixture of 4,4'- and 2,4'-diphenylmethane diisocyanate (MDI) are heated to 55 °C. 0.003 parts of benzoyl chloride are added to the MDI. The polyol and MDI mixture is combined, and the resulting reaction mixture is heated to 75 °C until a constant isocyanate content is achieved. The resulting product is cooled to below 60 °C. The isocyanate content is measured as 7% by weight in accordance with ASTM D5155. Polyisocyanate 2 contains an MDI prepolymer and polyols and a small amount of free MDI.Polyisocyanate 2 contains 61.75% oxyethylene units, calculated. The viscosity of polyisocyanate 2 is approximately 20,000 cps at 25 °C. Polyisocyanate 3 is prepared by first preheating a mixture of 71.1 parts of a number-average molecular weight poly(ethylene oxide) homopolymer and 1.1 parts of trimethylolpropane to 80 °C. Separately, 27.8 parts of an 80 / 20 mixture of 2,4- and 2,6-toluene diisocyanate (TDI) are heated to 40 °C. 0.007 parts of benzoyl chloride are added to the TDI. The polyol mixture is added to the TDI, and the resulting reaction mixture is heated to 74 °C until a constant isocyanate content of 6.25% is achieved. The resulting product is cooled to below 60 °C. Polyisocyanate 3 contains a TDI prepolymer and the polyols. A small amount of free TDI may be present. Polyisocyanate 3 contains 66.2% oxyethylene units and approximately 1.1 per i1 CAnn / zznz / E / YiAi percent by weight of branching agent residues. Polyisocyanate 4 is prepared by first preheating a mixture of 66.2 parts of a number-average molecular weight poly(ethylene oxide) homopolymer and 2.4 parts of trimethylolpropane to 80 °C. Separately, 30.4 parts of an 80 / 20 mixture of 2,4- and 2,6-toluene diisocyanate (TDI) are heated to 40 °C. 0.05 part of benzo-4,4-thiobis(6-tert-butyl-m-cresol) is added to the TDI. The polyol mixture is added to the TDI, and the resulting reaction mixture is heated to 74 °C until a constant isocyanate content is achieved. One part of dicyclohexylmethane-4,4'-diisocyanate is mixed in. The resulting product is cooled to below 60 °C. The isocyanate content is measured as 6.8% by weight according to ASTM D5155. Polyisocyanate 3 contains a prepolymer of TDI and polyols, and may contain a small amount of free TDI and / or a small amount of free dicyclohexylmethane-4,4'-diisocyanate. Polyisocyanate 4 contains approximately 66.2% by weight of oxyethylene units and approximately 2.4% of branching agent residues. Polyisocyanate 5 is prepared by first preheating a nominally difunctional propylene oxide homopolymer, weight equivalent 1000, to 80 °C. Separately, 35 parts of a 69 / 31 mixture of 4,4'- and 2,4'-diphenylmethane diisocyanate (MDI) are heated to 55 °C. 0.003 parts of benzoyl chloride are added to the MDI. The polyol and MDI mixture is combined, and the resulting reaction mixture is heated to 75 °C until a constant isocyanate content of 7% is reached. The resulting product is cooled to below 60 °C. Polyisocyanate 5 contains an MDI prepolymer and polyols, and free MDI. Polyisocyanate 5 does not contain oxyethylene units. Surfactant A is an organosilicone surfactant marketed by Momentive Performance Materials under the trade name Silwet®. Surfactant B is a triblock copolymer of ethylene oxide / propylene oxide / ethylene oxide. The central poly(propylene oxide) block of the copolymer has a molecular weight of 1750. The outer poly(ethylene oxide) blocks constitute 80% of the total weight of the copolymer. The copolymer has a nominal hydroxyl functionality of 2. The PGM (phase change material) is an unencapsulated paraffin wax that has a melting temperature of 28 °C. CPP is a polymer polyol with a hydroxyl number of approximately 22. The base polyol is a nominally trifunctional copolymer of propylene oxide and ethylene oxide with a hydroxyl number of 36.5; the oxyethylene content of the base polyol is approximately 20% by weight. The dispersed phase consists of styrene-acrylonitrile particles. The solids content (weight of the styrene-acrylonitrile particles) is approximately 40% by weight. Poly(EO) is a nominally trifunctional ethylene oxide homopolymer initiated with glycerin that has a number of hydroxyls of 270 mg KOH / g and a numerical average molecular weight of 624 g / mol. Polyurethane foams are manufactured using the ingredients listed in Table 1-4. The polyisocyanate in each case is combined at room temperature with the remaining ingredients in a high-speed laboratory mixer for 20 seconds. The resulting reaction mixture is poured into an open mold lined with a polyethylene sheet. The foams rise and cure in the mold. When dimensionally stable, the foams are demolded and cured under ambient conditions for at least 24 hours. Skins are removed from the foams before sampling for property testing. The moisture absorption time is measured on skinless 5 x 5 x 2.54 cm samples dried to a constant weight. Three milliliters of room temperature water are slowly dropped onto the upper surface of the foam sample from a pipette, and the amount Density is measured in accordance with ASTM D3574A. Compressive strain is determined using three core specimens of 2 χ 2 χ 1 (5.08 cm χ 5.08 cm χ ρρηη / ζζηζ / Ε / γίΛΐ 2.54 cm). The samples are measured with a litematic micrometer for thickness and placed between steel plates with 0.1 in. (2.54 mm) spacers to measure 90% deflection. The foams are aged in an oven at 70 °C for 22 hours. After 22 hours, the specimens are removed and allowed to recover for 30 minutes before taking the final measurement in accordance with ASTM D3574: D. Airflow is measured on crushed foam samples according to ASTM D3574: G. Latent heat is measured using differential scanning calorimetry. The K factor is measured using a Laser Comp thermal flow meter at a mean test temperature of 7.5 °F and a test temperature differential of 40 °F. Comparative samples AE Comparative AE samples are prepared from recipes as set out in Table 1. The foam test results are as indicated in Table 1. Table 1 FRnn / zznz / E / YiAi Ingredient Parts by weight Ex.A* Ex. B* Ex. C* Ex. D* Ex. E* Water 29.5 29.5 29.5 29.5 29.5 Surfactant A 1.75 1.75 1.75 1.75 1.75 Surfactant B 1.75 1.75 1.75 1.75 1.75 CPP 17 17 17 17 17 PCM 0 0 0 0 0 Poly(EO) 0 0 0 0 0 Polyisocyanate 1 0 15 0 0 25 Polyisocyanate 2 50 35 25 25 0 Polyisocyanate 3 0 0 25 0 0 Polyisocyanate 4 0 0 0 25 0 Polyisocyanate 5 0 0 0 0 25 Test Results Moisture Absorption, s 4 4 4 4 4 Density lb / ft3 (kg / m3) 5.05 (80.8) 4.85 (77.6) 5.40 (86.4) 5.35 (85.6) 7.40 (118.4) Air Flow, l / s (scfm) 1.63 (0.77) 2.43 (1.14) 2.09 (0.98) 1.57 (0.74) 3.46 (1.63) Compressive strain at 90%, % 88.8 31.2 84.6 57.4 86.3 Latent heat at 27 °C (J / g) 0 0 0 0 0 Factor k 0.3 0.3 0.3 0.3 0.3 *This is not an example of the invention. These foams are manufactured without a phase-change material to simplify formulations and to isolate the effects of various polyisocyanate compositions. The latent heats at 27 °C in each case reflect the absence of a phase-change material. As shown in Table 1, the foam properties depend largely on the polyisocyanate selection, in unpredictable ways. Polyisocyanate 2 (Comp. A) by itself results in a foam with extremely high compression set. When Polyisocyanates 1 and 2 are used together in a 30 / 70 ratio (Comp. B), compression set improves, although the compression set of 31.2% is still too high for this foam to be useful in bedding applications. A 50 / 50 mix of Polyisocyanate 2 with Polyisocyanate 3 (Comp. C) or Polyisocyanate 4 (Comp. D) leads to high compression set; the airflow of Comp. D also decreases. A 50 / 50 mix of Polyisocyanate 1 and Polyisocyanate 5 (Comp. E) produces very poor compression set. Taken together, these results demonstrate a high degree of variability in foam properties due to changes in the polyisocyanate; none of the polyisocyanates is suitable for achieving low compression set. Examples 1-3. Comparative Samples 1-3 are prepared from recipes as set out in Table 2. The foam test results for these samples are as shown in Table 2. 1¡ FRnn / zznz / E / YiAi ρρηη / ζζηζ / Ε / γίΛΐ Table 2 Ingredient Parts by Weight Ex. 1 Ex. 2 Ex. 3 Water 29.5 31.25 31.25 Surfactant A 1.75 0 1.75 Surfactant B 1.75 1.75 0 CPP 17 17 17 PCM 0 0 0 Poly(EO) 0 0 0 Polyisocyanate 1 25 25 25 Polyisocyanate 2 25 25 25 Results Moisture absorption, s 4 4 4 Density lb / ft3 (kg / m3) 4.61 (73.8) 4.58 (73.3) 4.78 (76.5) Air flow, l / s (scfm) 3.04 (1.43) 0.3 (0.14) 1.09 (0.51) 90 % of Compressive strain, % 9.7 9.2 7.2 Latent heat at 27 °C (J / g) 0 0 0 Factor k 0.3 0.3 0.3 These results demonstrate the effect of using a mixture 50 / 50 of Polyisocyanates 1 and 2, along with three different surfactant packages. Example 1 is a direct comparison with Comparative Sample C (Table 1). The difference is a higher level of branching in the TDI prepolymer of Example 1 (Prepolymer 1, 3.8 wt% branching agent) compared to the TDI prepolymer of Comparative Sample C (Prepolymer 3, 1.1 wt% branching agent). The more highly branched Prepolymer 1 leads to a drastic reduction in compressive strain (9.7% vs. 84.6% for Comparative Sample C). Example 1 compared to Sample Comp. B demonstrates the effect of the ratio of components a-1) plus a-2) to components a-3) plus a-4). Too much of the a-3) plus a-4) component leads to a large increase in compressive strain (31.2% for Sample Comp. B vs. only 9.7% for Example 1). Examples 2 and 3 show the effect of using only one of the surfactants A and B. Very low compressive strains are obtained in all Examples 1-3, but the air flows are much lower when only one of the surfactants is present, as in Examples 2 and 3. The latent heat at 27 °C is zero due to the lack of a phase-change material. Comparative samples F and G Comparative samples F and G are prepared from recipes as shown in Table 3. The foam test results are as indicated in Table 3. Table 3 1¡ FRnn / zznz / E / YiAi Ingredient Parts by weight Ex. F* Ex. G* Water 29.5 29.5 Surfactant A 1.75 1.75 Surfactant B 1.75 1.75 CPP 25 5 PCM 0 0 Poly(EO) 0 0 Polyisocyanate 1 25 25 Polyisocyanate 2 25 25 Results Moisture absorption, s 4 4 Density lb / ft3 (kg / m3) 4.77 (76.3) 4.95 (79.2) Air flow, 1 / s (scfm) 3.94 (1.85) 8.4 (3.95) 90 % compression strain, % 14.7 84.6 Latent heat at 27 °C (J / g) 0 0 k factor 0.3 0.3 i1 CAnn / zznz / E / YiAi *Not an example of the invention. Comparative Examples F and G illustrate the effect of increasing (Comp. F) or decreasing (Comp. G) the amount of polymer polyol along with the 50 / 50 blend of Polyisocyanates 1 and 2, compared to Ex. 1 (Table 2). Compressive strain increases slightly for Sample Comp. F. Even at this moderately increased level, compressive strain is higher than desired for bedding applications. Compressive strain becomes extremely high in the Sample comp. G. Again, the latent heat is zero in all cases due to the lack of phase change material. Examples 4-8 Examples 4-8 are prepared from recipes as set out in Table 4. The foam test results are the i1 CAnn / zznz / E / YiAi indicated in Table 4. Table 4 Ingredient Parts by Weight Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Water 24.5 29.5 27.0 22.5 24.5 Surfactant A 1.75 1.75 1.75 1.75 1.75 Surfactant B 1.75 1.75 1.75 1.75 1.75 CPP 17 17 15 13 15 PCM 5 0 2.5 10 5 Poly(EO) 0 5 2 2 2 Polyisocyanate 1 25 25 25 25 25 Polyisocyanate 2 25 25 25 25 25 Results Moisture absorption, s 4 4 4 4 4 Density lb / ft3 (kg / m3) 4.14 (66.2) 4.07 (65.1) 4.27 (68.3) 4.52 (72.3) 4.93 (78.9) Air flow, l / s (scfm) 1.55 (0.73) 5.3 (2.49) 4.28 (2.01) 1.84 (0.86) 3.05 (1.43) 90% compression strain, % 2.7 3.8 2.8 2.9 4.2 Latent heat at 27 °C (J / g) 14.9 0 4.7 20.1 14.1 k factor 0.3 0.3 0.3 0.3 0.3 *This is not an example of the invention. All Examples 4-8 exhibit very low compressive strains. The presence of the phase-change material in Example 4 has three effects, as shown in comparison with Example 1. The compressive strain becomes even lower than in Example 1, and a positive latent heat is observed at 27 °C. Some loss of airflow is also observed. Example 5 shows the effect of including component f) in the reaction mixture, in the absence of a phase-change material. Compared to Example 1, the compressive strain is significantly lower, and a higher airflow is obtained. The latent heat at 27 °C is zero due to the lack of a phase-change material. Examples 6-8 show the effect of including both component f) and the phase-change material. Compressive strains are extremely low, and airflows are improved compared to Example 4, which has the phase-change material but no component f). This is observed even at a very high level of phase-change material (Ex. 7). The airflows for Examples 6 and 8 are comparable to or greater than those of Example 1, despite the presence of the phase-change material. It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.

Claims

1. A flexible polyurethane foam, characterized in that it comprises a reaction product of a reaction mixture comprising a) an isocyanate mixture comprising a-1) a first isocyanate-functional prepolymer, wherein the first isocyanate-functional prepolymer is a reaction product of at least one hydroxyl-terminated ethylene oxide polymer and optionally a hydroxyl-functional branching agent and / or hydroxyl-functional chain extender with an excess of diphenylmethane diisocyanate, wherein the diphenylmethane diisocyanate is at least 50% by weight 4,4'-diphenylmethane diisocyanate, a-2) optionally diphenylmethane diisocyanate, wherein components a-1) and a-2) together have an isocyanate content of 5 to 15% by weight and contain 30 to 75% by weight oxyethylene units, based on the combined weight of components a-1) and a-2), and the components a-1) and a-2) together constitute 40 to 60% of the total weightof the isocyanate mixture, i1 ΓΑηη / ζζηζ / E / γίΛΐ a-3) a second isocyanate-functional prepolymer, wherein the second isocyanate-functional prepolymer is a reaction product of at least one hydroxyl-terminated ethylene oxide polymer and a hydroxyl-functional branching agent having at least three hydroxyl groups per molecule and a hydroxyl equivalent weight of up to 250 g / equivalent with an excess of toluene diisocyanate, and a-4) optionally toluene diisocyanate, wherein a-3) and a-4) together have an isocyanate content of 5 to 15 wt% and contain 30 to 75 wt% of oxyethylene units, based on the combined weight of components a3) and a-4), and 2 to 5 wt% of residues of the hydroxyl-functional branching agent, based on the weight combined of components a-3) and a-4); components a-3) and a-4) together constitute 40 to 60% of the total weight of the isocyanate mixture; and components a-1), a-2), a-3) anda-4) together constitute the total weight of the isocyanate mixture; b) water; c) at least one polymeric polyol comprising polymeric particles dispersed in at least one base polyol, the base polyol being a polyether having at least 50 wt% of oxypropylene units and a hydroxyl equivalent weight of 500 to 3000 g / equivalent; d) optionally a poly(ethylene oxide), the poly(ethylene oxide) being a homopolymer of i1 CAnn / zznz / E / YiAi ethylene oxide or a random and / or block copolymer of at least 80 wt% ethylene oxide and up to 20 wt% another alkylene oxide, the poly(ethylene oxide) having a number-average molecular weight of 400 to 1200 g / mol; at least one of e) and f), wherein e) is at least one silicone surfactant; yf) is at least one higher ethylene oxide / alkylene oxide block copolymer, the block copolymer containing 40 to 90 wt% of oxyethylene units and having an average molecular weight innumber of 1500 to 12,000 g / mol; and optionally g) at least one phase-change material having a melting or glass transition temperature of 25 to 37 °C and containing no isocyanate groups or isocyanate-reactive groups; wherein i) the isocyanate mixture constitutes 40 to 65% of the combined weights of components ag; ii) water constitutes 15 to 41% of the combined weights of components ag; iii) the at least one polymeric polyol constitutes 8 to 20% of the combined weights of components ag and the polymeric particles constitute 0.5 to 10% of the combined weights of components ag; iv) poly(ethylene oxide) when present constitutes up to 5% of the combined weights of components i1 CAnn / zznz / E / YiAi ag; (v) at least one silicone surfactant constitutes 0 to 3% of the combined weights of components ag; (vi) at least one ethylene oxide / higher alkylene oxide block copolymer constitutes 0 to 3% of the weightscombined weights of the ag components; vii) at least one phase change material constitutes up to 15% of the combined weights of the ag components and viii) the ag components constitute at least 95% of the weight of the reaction mixture.

2. The flexible polyurethane foam according to claim 1, characterized in that the phase change material comprises any one or more of a natural or synthetic wax such as polyethylene wax, beeswax, lanolin, carnauba wax, candelilla wax, uricuri wax, sugar cane wax, jojoba wax, epicuticular wax, coconut wax, petroleum wax or paraffin wax.

3. The flexible polyurethane foam according to claim 1 or 2, characterized in that the phase change material constitutes 2.5 to 10 percent of the total weight of the components.

4. The flexible polyurethane foam according to any of the preceding claims, characterized in that components a-1) and a-2) together constitute 45 to 55% of the weight of the isocyanate mixture and components a-3) and a-4) together constitute 55 to 45% of the weight of the isocyanate mixture.

5. The flexible polyurethane foam according to any of the preceding claims, characterized in that the silicone surfactant and the higher ethylene oxide / alkylene oxide block copolymer each constitute 0.5 to 3% of the combined weights of the components.

6. The flexible polyurethane foam according to any of the preceding claims, characterized in that the silicone surfactant contains 25 to 70% by weight of polysiloxane, 10 to 75% by weight of polymerized ethylene oxide and 0 to 10% by weight of polymerized propylene oxide, based on the weight of the silicone surfactant.

7. The flexible polyurethane foam according to any of the preceding claims, characterized in that the higher ethylene oxide / alkylene oxide block copolymer contains 40 to 90% oxyethylene units and has a number-average molecular weight of 1500 to 12,000.

8. The flexible polyurethane foam according to any of the preceding claims, characterized in that the poly(ethylene oxide) constitutes 0.5 to 5% of the combined weights of the components.

9. A method for making a flexible polyurethane foam, characterized in that it comprises A. forming a reaction mixture by mixing: i1 CAnn / zznz / E / YiAi a) an isocyanate mixture comprising a-1) a first isocyanate functional prepolymer, wherein the first isocyanate functional prepolymer is a reaction product of at least one hydroxyl-terminated ethylene oxide polymer and optionally a hydroxyl-functional branching agent and / or a hydroxyl-functional chain extender with an excess of diphenylmethane diisocyanate, wherein the diphenylmethane diisocyanate is at least 50 wt% 50 wt% 4,4'-diphenylmethane diisocyanate, a-2) optionally diphenylmethane diisocyanate, wherein components a-1) and a-2) together have an isocyanate content of 5 to 15 wt% and contain 30 to 75 wt% oxyethylene units, based on the combined weight of the components a-1) and a-2), and components a-1) and a-2) together constitute 40 a60% of the total weight of the isocyanate mixture, a-3) a second isocyanate-functionalized prepolymer, wherein the second isocyanate-functionalized prepolymer is a reaction product of at least one ethylene oxide hydroxyl-terminated polymer and a hydroxyl-functionalized branching agent having at least three hydroxyl groups per molecule and a hydroxyl equivalent weight of up to 250 g / equivalent with an excess of toluene diisocyanate, and 11 FRnn / zznz / E / YiAi a-4) optionally toluene diisocyanate, wherein a-3) and a-4) together have an isocyanate content of 5 to 15% by weight and contain 30 to 75% by weight of oxyethylene units, based on the combined weight of components a-3) and a-4), and 2 to 5% by weight of residues of the hydroxyl-functionalized branching agent, based on the combined weight of components a-3) and a-4); components a-3) and a-4) together constitute 40 to 60% of the total weight of the isocyanate mixture; and the componentsa-1), a-2), a-3) and a-4) together constitute the total weight of the isocyanate mixture; b) water; c) at least one polymeric polyol comprising polymeric particles dispersed in at least one base polyol, the base polyol being a polyether having at least 50 wt% of oxypropylene units and a hydroxyl equivalent weight of 500 to 3000 g / equivalent; d) optionally a poly(ethylene oxide), the poly(ethylene oxide) being an ethylene oxide homopolymer or a random and / or block copolymer of at least 80 wt% ethylene oxide and up to 20 wt% another alkylene oxide, the poly(ethylene oxide) having a number-average molecular weight of 400 to 1200 g / mol; at least one of e) and f), wherein e) is at least one silicone surfactant; yf) is at least one higher ethylene oxide / alkylene oxide block copolymer, the i1 CAnn / zznz / E / YiAi block copolymer containing 40 to 90 wt% of oxyethylene units and having a weightnumber average molecular weight of 1500 to 12,000 g / mol; and optionally (g) at least one phase-change material having a melting or glass transition temperature of 25 to 37 °C and containing no isocyanate groups or isocyanate-reactive groups; wherein (i) the isocyanate mixture constitutes 40 to 65% of the combined weights of components (ag); (ii) water constitutes 15 to 41% of the combined weights of components (ag); (iii) the at least one polymeric polyol constitutes 8 to 20% of the combined weights of components (ag) and the polymeric particles constitute 0.5 to 10% of the combined weights of components (ag); (iv) poly(ethylene oxide), when present, constitutes up to 5% of the combined weights of components (ag); (v) at least one silicone surfactant constitutes 0 to 3% of the combined weights of the components; (vi) at least one ethylene oxide / higher alkylene oxide block copolymer constitutes 0 to 3% of the weightscombined of the components ag; vii) at least one phase change material constitutes i1 CAnn / zznz / E / YiAi up to 15% of the combined weights of the components ag and viii) the components ag constitute at least 95% of the weight of the reaction mixture and B. react the reaction mixture to produce the foam.

10. The method according to claim 9, characterized in that the phase change material constitutes 2.5 to 10 percent of the total weight of the components and the phase change material comprises one or more of a natural or synthetic wax, such as polyethylene wax, beeswax, lanolin, carnauba wax, candelilla wax, uricuri wax, sugar cane wax, jojoba wax, epicuticular wax, coconut wax, petroleum wax, or paraffin wax.

11. The method according to any of claims 9-10, characterized in that the silicone surfactant and the higher ethylene oxide / alkylene oxide block copolymer each constitute 0.5 to 3% of the combined weights of the components, the silicone surfactant contains 25 to 70% by weight of polysiloxane, 10 to 75% by weight of polymerized ethylene oxide and 0 to 10% by weight of polymerized propylene oxide, based on the weight of the silicone surfactant, and the higher ethylene oxide / alkylene oxide block copolymer contains 40 to 90% of oxyethylene units and has an average molecular weight of 1500 to 12,000.

12. A pad, characterized in that it comprises a flexible polyurethane foam in accordance with any of claims 1-8.

13. The pad according to claim 12, characterized in that it is a pillow, mattress cover, mattress, quilt, furniture seat or backrest, car seat or backrest; bedspread or insulating article of clothing, or a pad for a limb prosthesis.

14. The pad according to claim 12 or 13, characterized in that the flexible polyurethane foam, when dried to a constant weight, has a density of 48 to 80 kg / m3 and a compression deformation of 10% or less.

15. The pad according to any of claims 12-14, characterized in that the flexible polyurethane foam, when dried to a constant weight, exhibits a latent heat of at least 2.5 J / ga 27°K and a moisture absorption time of 5 seconds or less.