JPH059451B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF THE INVENTION This invention relates to flexible polyurethane foams. Flexible polyurethane foams made using TDI (toluene diisocyanate) have been produced for many years, especially for cushions and pine tresses. However, for hydrophilic foams used in medical or personal care applications, the TDI in the foam is
(methylene diphenyl isocyanate) is desirable because TDI has a high vapor pressure and relatively high toxicity, which requires special precautions during processing and use. Furthermore, TDI-based foams can be hydrolyzed and weakened during sterilization or storage in humid containers. For example, TDI-based hydrophilic foams can be liquefied after several cycles at 120° C. in a steam autoclave. Also
TDI-based hydrophilic foams swell excessively when wetted to more than about 100% by volume. Typical polyurethane foams are manufactured from MDI. These forms are rigid or semi-rigid due to the MDI imparting crystallinity. In UK Patent No. 874430, at least two
A flexible polyurethane foam is produced by reacting a polyether polyol having 2 hydroxyl groups and a polyisocyanate mixture consisting of a diarylmethane diisocyanate and 5 to 10% by weight of a polyisocyanate with 2 or more functionalities in the presence of a small amount of water. is manufactured.
A catalyst can be used in any embodiment. These foams have properties that are not hydrophilic and sufficient to transport large amounts of fibers, fillers, disinfectants, and other water-dispersible ingredients into foams used for medical or personal protection applications. The disadvantage is that it does not absorb a large amount of water. The term hydrophilic as used herein means that the foam product is capable of absorbing 15 to 20 times its weight in water. A further disadvantage with any catalyst is that undesirable catalyst residues may remain. In U.S. Pat. No. 4,237,240, diphenylmethane diisocyanate is highly resistant by reacting with a polyester polyol or a mixture of polyester polyols and polyether polyols having a polyester polyol content of at least 60% by weight of the polyol mixture, and a small amount of water. Soft MDI-based foams with load bearing and high energy absorption capacity have been manufactured. Catalysts are used as indicated in the claims. In addition to these foams having the disadvantage of containing undesirable catalyst residues in the foam similar to those of UK Patent No. 874,430 mentioned above, they require the use of more expensive polyester polyols. do. In British Patent No. 1209058, a polyisocyanate of at least 10% is capped with propylene oxide to give hydrolytic stability.
Flexible hydrophilic polyurethane foams can be produced by reaction with polyether polyols containing % by weight of block copolymers of ethylene oxide. This process requires the use of at least one divalent tin salt of a fatty acid and/or at least one tertiary amine as catalyst. Although the foam products produced in this way are hydrophilic, they have the disadvantage that they not only absorb only small amounts of water, but also require the use of block copolymers. Furthermore, therein MDI, which is hydrophobic, to produce hydrophilic foam products.
is not indicated and the resulting foam will contain undesirable catalyst residues. It is an object of the present invention to provide improved flexible polyurethane foams made from prepolymers containing MDI only as an isocyanate source. It is an object of the present invention to provide improved flexible polyurethane foams that may further contain higher amounts of fibers, fillers, disinfectants, or other water-dispersible ingredients. A further object is to produce a soft hydrophilic foam of white color for use in medical health care applications. Furthermore, it can be stored indefinitely and used as a carrier for water-dispersible components, and only as a source of isocyanate, which will also yield a hydrophilic foam product when mixed with approximately equal amounts of water. The aim is to produce polyurethane prepolymers with MDI and its derivatives. Furthermore, it is an object to produce polyurethane prepolymers having MDI and its derivatives only as isocyanate source, which have viscosity stability over time. It is also an object to produce polyurethane prepolymers having up to 50% by weight of isocyanates and having MDI and its derivatives only as the isocyanate source which will give rise to flexible foams. These and other objects will become apparent from the description of the invention below. Water-absorbing flexible foams for medical or personal care applications can be made from isocyanate-capped prepolymers using MDI derived from isocyanates as the sole isocyanate. This foam can be manufactured in two embodiments. One specific example, hereinafter abbreviated as specific example A, uses a monomeric polyol crosslinking agent, and the other specific example, abbreviated as specific example B, uses a polymeric polyol. In this application, a patent is claimed only for Specific Example B among these, and Specific Example A will be explained only for reference. In Example A, Union Carbide
1 mole of a prepolymer having at least one poly( _oxyC2-4 alkylene) diol having a molecular weight of at least about 1100 and having at least 50% by weight of oxylene groups, such as Carbowax, Trioltrimethylolpropane. a monomeric polyol crosslinker having 3 or 4 hydroxyl equivalents per hydroxyl, and an isocyanate product having a functionality of 2.0 or higher, such as a methylene bis(fluoride) having a functionality of approximately 2.1 and hereinafter abbreviated as MDI. produced from a mixture of isocyanates including derivatives of enyl isocyanate) and MDI
The foam is made from MDI based on Isonatel 43-L from Upjohn Polymer Chemicals. In Example B, Union Carbide
At least one poly(oxyethylene) having a relatively low molecular weight of less than 2000, such as Carbowax 1000, and containing a diol having at least 50% by weight, preferably at least 80% by weight of oxyethylene groups.
Prepolymers with _C2-4 alkylene): polymeric poly( _oxyC2-4 alkylene) polyols having 3 or 4 hydroxyl equivalents per mole and having a relatively high molecular weight of at least 500. Crosslinking agents, e.g. Triol TEP990, Union
Poly(oxyethylene) triol of approximately 900 molecular weight from Carbide or POLY G76−120,
Oxyethylene-capped poly(oxypropylene) triol of approximately 1400 molecular weight from Olin;
Isocyanate products with a functionality of 2.0 or higher made from a mixture of isocyanates including derivatives of bis(phenyl isocyanate) and MDI, such as Upjohn with a functionality of approximately 2.1.
The foam is made from MDI based on Isonate 143-L from Polymer Chemicals. The composition produces a white foam that is aesthetically pleasing and desirable for medical and health care applications. One of the important features of these prepolymer compositions is that the amount of isocyanate, such as Isonate 143-L, is less than 50% of the weight of the prepolymer in Example A, typically 38-46%; In Example B, the content may be limited to 37 to 48% of the prepolymer. The amount of isocyanate component required is reduced in Example A as the average molecular weight of the diol component increases, so this molecular weight is greater than 1100. When using trimethylolpropane as a monomeric crosslinking agent, the preferred molecular weight of the diol is
1200-1400, and the diol contains at least 80% by weight of oxyethylene groups. The diol used in a preferred embodiment is a mixture of two diols having different molecular weights. For example, one diol can have a molecular weight of 1000 and the other 1450. In Example B, the amount of isocyanate component required is reduced as the average molecular weight of the polymeric polyol crosslinking component increases, so this molecular weight is greater than 500. When using Carbowax 1000, which has a molecular weight of about 1000 as the diol, a suitable polymeric polyol crosslinker has a molecular weight of about 1000.
Poly, a triol with a molecular weight of 1400
It is G176−120. The actual free MDI content can be adjusted higher or lower in this isocyanate-containing product as long as the functionality remains above 2.0. For example, additional pure MDI can be added. Prepolymers with moderate viscosity and good viscosity stability include relatively low molecular weight polyether polyols, MDI-containing isocyanate products such as Isonate 143-L, and trimethylolpropane (TMOP) as the monomeric crosslinker. It can be manufactured using However, when this prepolymer is mixed with water, the resulting foam is typically a white, semi-rigid foam that is suitable for use as an abrasive sponge, but for use as a cushion or soft foam. is not suitable for For example, if the MDI-containing form is Isonate143-L,
Carbowax1000 and trimethylolpropane (TMOP) as a crosslinking agent that gives strength to the foam
Manufactured using. No. 10/1981, part of related patents of U.S. Patent No. 220,562, dated December 29, 1980.
See U.S. patent application Ser.
Because TMOP has such a low equivalent weight of 44.7, the prepolymer requires a large amount of the isocyanate component, Isonate 143-L, to cap all the hydroxy groups. The amount of isocyanate is on the order of 50-55% by weight, which makes the foam relatively stiff and hydrophobic. In Example A, the poly( _oxyC2-4 alkylene) diol and the monomeric crosslinking agent include, for example,
It has been found that in MDI-containing systems containing TMOP, the isocyanate component can be advantageously reduced by increasing the average molecular weight of the poly( _oxyC2-4 alkylene) diol component to a molecular weight value of 1100 or higher. These diols preferably have at least 80% by weight of ethyleneoxy groups. The resulting soft foam retains its physical properties even when treated with steam in an autoclave at 120° C. for 5 hours, and this foam shows a significant reduction in its swelling properties compared to the TDI foam.
TDI-based hydrophobic foam has a 100%
% by volume, but the foam in embodiment A of the invention swells only 30-60% when wetted. Furthermore, it has been found in Example B that the isocyanate content in MDI-containing systems using relatively low molecular weight diols with molecular weights below 2000 can be advantageously reduced by increasing the molecular weight of the polyol crosslinker. Instead of using TMOP with a molecular weight of 134, a high molecular weight poly( _oxyC2-4 alkylene) triol or tetrol with a molecular weight of about 500 to 2000 is used. A suitable example is Poly G176-120, a triol with a molecular weight of about 1400. The resulting soft foam retains its physical properties even when treated with steam for 5 hours at 120°C in an autoclave.
This foam also exhibits a significant reduction in its swelling properties compared to the TDI foam. TDI-based hydrophobic foam has 100% volume when wetted
However, the foam in embodiment B of the invention swells only about 30-75% when wetted. In both Examples A and B, by reducing the content of isocyanate such as Isonate 143-L, the resulting foam is more than 50% Isonate 143-L.
L content, it is pliable and resilient compared to semi-rigid, non-resilient foams. By increasing the molecular weight of the diol
The amount of Isonate 143-L required can be reduced to such an extent that the ratio of isocyanate to hydroxyl functionality (known as the isocyanate index) can be reduced from 3.5/1 to about 3/1, and this change It contributes to the flexibility of the product. Flexibility is best characterized by the bending modulus, but the tensile modulus, which is more easily obtained at 1% elongation, can be used to roughly classify these forms as soft and supple [1.41 Kg/
cm ² ], strong but flexible (modulus between 1.41 and 2.82 Kg/cm ² ), and semi-rigid or rigid (modulus greater than 2.82 Kg/cm ² ). In both Examples A and B, preferred isocyanates containing products with a functionality of 2.0 or higher are diphenylmethane diisocyanate, abbreviated as MDI, and mixtures of isocyanates, including derivatives of MDI. Commercial products meeting this requirement are prepared by reacting MDI to form the carbodiimide and then reacting this material again to form the trifunctional cycloaddition product.
There is Isonate143L. The mixture of MDI, carbodiimide and cycloaddition product are in equilibrium. The mixture of components A and B below constitutes the 143L system. Here

The term derivative of diphenylmethane diisocyanate as used herein refers to a product prepared from MDI as a starting material. This would include addition products, dimers and trimers. This would not include materials such as polymethylene polyphenyl isocyanate that are not made from MDI. Prepolymer techniques in producing foams require mixing with approximately equal amounts of water. This requires that the prepolymer be hydrophilic,
And that is why at least some poly(oxyethylene) containing diol must be used in making the prepolymer prepared from Isonate 143-L. The desired viscosity for good mixing and foaming with water is in the range of about 10,000 to 35,000 cp, preferably about 20,000 cp at 25°C. Both the viscosity and hydrophilicity of the prepolymer are controlled by proper selection of polyol type and molecular weight. This prepolymer must not become too thick during storage. After an accelerated storage test of 2 weeks at 80°C, it was found to be sufficiently storage stable if the viscosity did not rise above 100,000 cp (measured at 25°C). For a flexible foam to be used in many applications, it must have a tensile strength of at least 1.41 Kg/ ^cm2 , approximately 0.048 to 0.096
It should have a foam density of g/cc and an elongation at break of at least 100%, with higher elongation values being preferred. In one example in Example A an elongation at 200% failure was obtained, while in Example B
An elongation at failure of 250% was obtained in the example. The diol used is a poly( _oxyC2-4 alkylene) containing at least 50% by weight of oxyethylene groups.
It is a diol. Thus, if the diol includes oxypropylene or oxybutylene or mixtures thereof, a small amount of oxyethylene must also be present. Preferred diols in Example A are those having at least 80% by weight oxyethylene groups. In some preferred embodiments of embodiment A, the diol is manufactured by Union Carbide.
It has been found that using a mixture of Carbowax 1000 and Carbowax 1450 is satisfactory;
It is also within the scope of this embodiment to use formulations of any of the more preferred poly(oxyethylene) diols having number average molecular weights in the range of 1000-2000, preferably 1200-1400. The average molecular weight of all diols in these examples will be at least about 1100. Advantageously, the foam produced by using a blend of approximately equimolar amounts of these two diols has low volume swelling and low density. Although it is within the scope of Example A to use any monomeric polyol as a crosslinker, polyol crosslinkers having 3 or 4 hydroxyl equivalents per mole are more preferred. These include trimethylolpropane, trimethylolethane, glycerol, triethanolamine, pentaerythritol or mixtures of these polyols. The most preferred is the formula is trimethylolpropane, TMOP. For example B, Union as the diol
Carbowax1000 by Carbide or
It has been found that using Carbowax 1450 is satisfactory in preferred embodiments, but
It is also within the scope of this embodiment to use any poly(oxyethylene) diol having a number average molecular weight in the range of 2000, preferably 1000 to 1500. Although it is within the scope of Example B to use any polymeric polyol as the crosslinking agent, more preferred have 3 or 4 hydroxyl equivalents per mole and at least
A polymeric poly( _oxyC2-4 alkylene) polyol crosslinker with a number average molecular weight of 500 or a mixture of these polymeric polyols. Most preferred is Poly G76-120, an oxyethylene capped poly(oxypropylene) triol of approximately 1400 molecular weight. Here, the oxyethylene moiety is presumed to contain a block of oxyethylene units bonded to the center of the polyoxypropylene core. It is also believed that the polyol crosslinker can be constructed from random copolymers of these units. The density and physical properties of the foams of Examples A and B appear to be affected by polyol content. If it is desired to obtain a stiffer and less rubbery foam with lower density, the amount of polyol is increased. Similarly, if a higher density and more elasticity is desired, the amount of polyol is reduced.
A practical amount of polyol crosslinker having 3 or 4 hydroxy functionality is such that 2 to 35% of the hydroxyl content of the diol and polyol mixture originates from the polyol. The preferred range for good soft foam is from polyol to 10
~30% hydroxyl. The polyol in Example B is a polymeric polyol, and generally a relatively small amount of polymeric polyol is used to maintain the fluidity of the prepolymer. When expressing the amount of polyol crosslinker in terms of the amount of diol present, the diol and polyol crosslinker are present in a molar ratio of about 4:1 to 8:1 in Example A, and in Example B the polymeric When the amount of polyol crosslinker is expressed in terms of the larger amount of diol present, the diol and polyol crosslinker are present in a molar ratio of about 30:1 to 8:1. In Example A, Carbowax 1000 has an equivalent weight of 500 per hydroxyl group, while TMOP, which has a molecular weight of 134, has an equivalent weight of 500 per hydroxyl group.
It has an equivalent weight of 45. Since Isonate 143L is used to attach the hydroxyl groups, the amount of isocyanate required is very strongly influenced by the amount of TMOP, and thus the amount of TMOP is adjusted relatively carefully. In example B, if the molecular weight of the polyol is too high, the hydroxyl concentration is very low and it takes a very long time to react the starting materials. On the other hand, the molecular weight takes a very long time. On the other hand, when the molecular weight is very low and low molecular weight diols are used, large amounts of isocyanate are required and stiff foams result. In Example B, Carbowax 1000 has an equivalent weight of 500 per hydroxyl group, while Poly G76-120, which has a molecular weight of 1400, has an equivalent weight of 467 per hydroxyl group.
Since Isonate 143L is used to bind hydroxyl groups, the amount of isocyanate required is very strongly influenced by the amount of Poly G76-120, and thus the amount of Poly G76-120 should be adjusted relatively carefully. . Practicable amounts in both Examples A and B are such that the isocyanate index is between 2.5 and 3.5, preferably between 2.8 and 3.2, with very good results being obtained at 3.1. Higher ratios result in lower polymer viscosity, lower foam density and less swellability, but are also costly and reduce flexibility and elongation. During the preparation of the prepolymer, one isocyanate group of the polyisocyanate component reacts with one hydroxyl group, and the remaining isocyanate groups remain unreacted. These free isocyanate groups on the prepolymer then react with water to form polyurea bonds, simultaneously increasing the molecular weight and liberating _CO2 to produce a foamed product. When reacting the components in both Examples A and B to form the prepolymer, it is advantageous to measure the amount of isocyanate by titration after the reaction has run for about 1 hour. Based on this knowledge, titration can determine the additional reaction time needed to reduce the amount of isocyanate to approximately the theoretical amount at which all hydroxyl groups will react with the isocyanate. If the reaction is continued to further reduce the amount of isocyanate, the viscosity of the prepolymer increases, making it more difficult to subsequently mix the prepolymer with water. Excessive reaction of the prepolymer components also causes an increase in foam density as well as a decrease in the water absorption properties of the resulting foam. The surfactant is chosen to obtain a foam with the correct cell size, shape, and good appearance without crushing or splitting. Surfactants known to be useful with polyurethane foams can be used here. Examples of suitable surfactants include block copolymers of oxyethylene and oxypropylene, such as Wyandotte,
Manufactured by BASF Wyabdotte Corp. of Michigan.
There are Pluronic Polyol surfactants. A preferred surfactant is Pruronic L-62. A preferred method for producing polyurethane foams is to add about the same amount of aqueous suspension to the prepolymer;
The next step is to mix the two together. The composition of this aqueous suspension can also be expressed based on 100 parts of prepolymer resin. Thus, 100 parts of water per 100 parts of resin is expressed as 100 phr of water.
The quantity ratio of prepolymer mixture to aqueous suspension can vary within a wide range. However, if the amount of aqueous suspension is too large, the strength of the resulting foam will be reduced. On the other hand, if the amount of aqueous suspension is reduced too much, it will not be possible to add enough fiber and filler fed through this aqueous suspension. A preferred method of foaming the prepolymer includes an aqueous suspension, such as 2% Pluronic L-62 surfactant.
There is a method of heating the solution as well as the prepolymer to a temperature of approximately 35°C. These are poured or pumped together in a ratio of about 80 parts by weight of prepolymer to about 100 parts by weight of the aqueous suspension and immediately attached to a mechanical stirrer, such as an impeller attached to a drill motor. (blade) for up to 30 seconds. During this time, complete mixing occurs, but not enough to cause a chemical reaction. This mixture is immediately poured into a mold where it is allowed to heat up and harden the foam product. Fibers can be added to the aqueous phase for insert into the foam composition to provide additional structural rigidity. Polyester fibers are particularly advantageous and can be chopped to about 1.27 cm or less. For aqueous suspensions, the fibers can be added in varying amounts, but it is preferred that they do not constitute more than about 10% by weight, since higher amounts will make it difficult to pump the suspension. This is because it becomes difficult. Also, polymeric suspending agents or thickening agents can be added to maintain dual functionality. Firstly, it prevents water from flowing out of the fibers and retains the suspended components so that the fibers do not float. Second, the thickening agent acts as a wetting agent for the fibers so that they do not become tangled, dehydrated, or crushed as they pass through the mixing pump. Examples of thickening agents include Polyox
Made by WSR, Natroso, Xanthan gum, and Dow.
There are polyacrylamides such as Separan AP30 that have a molecular weight of about 1 million. Suitable suspending or thickening agents include BFGoodrich
Carbopol resin manufactured by Chemical Co., e.g.
Carbopol934, Cardopol940 and especially
There is Carbopol941. Since Carbopol resin is an acrylic acid polymer with acidic moieties, neutralizing agents such as sodium or ammonium hydroxide can be added. It is advantageous to increase the viscosity of the aqueous phase when adding ammonium hydroxide to Carbopol as a neutralizing agent. Also, ammonium hydroxide
Being cheaper than Carbopol, more economical compositions can be produced with the same degree of thickening properties and less Carbopol is used. Depending on any fibers, fillers, disinfectants, pigments, thickeners, or other water-soluble or water-dispersible ingredients that may be included, the best surfactants are highly hydrophobic silicone types, such as L- 520 (Union
carbide) or other silicone surfactants to extremely hydrophilic types, such as Brij-58 (ICI-
America) or other Brij, Span, or ICI
Tween products can be varied from.
Nonionic surfactants for general use;
For example, Pluronics, especially L-62, L-72, L-92,
P-75 or P-85 (BASF-Wyandotte) is preferred. The use of these surfactants is well known to those familiar with the composition of polyurethane foam products. A water adsorption test is conducted by cutting the foam sample into a rectangle with a size of 2.54 x 7.62 x 12.70 cm. Submerge the item in water and hold the item until it stops dripping. The ratio of wet weight to dry weight is the water adsorption rate. Although the basic features of the present invention have been shown, the following Reference Examples 1 to 4 are shown to explain special examples of Example A, and Examples 1 to 5 are special examples of Example B. This is shown to explain. Reference example 1 Carbowax1000 (174g, 0.174mol),
A mixture of Carbowax 1450 (249 g, 0.172 mol) and trimethylolpropane (6.1 g, 0.045 mol) was dried by heating at 70° C. for 2 hours under a vacuum of 2 Torr. Add 365 g of Isonte-143L (isocyanate) to this dry and degassed polyol mixture.
2.56 equivalents) were added. The temperature was maintained at 70° C. for 70 minutes to complete the reaction. This product has an isocyanate content of 2.18 meq/g and at 25°C.
It was a pale yellow liquid with a viscosity of 23,000 cp.
After storing the sample at 80 °C for 2 weeks, the product was 25
It thickened only up to 40,000 cp at ℃. When 80 g of the product heated at 35° C. is stirred with 100 ml of a 2% solution of Pluronic L-62, a nonionic surfactant manufactured by Wyandotte, it has a density of 4.1 pounds per cubic foot and is soft and pliable. , a form is produced which is hydrophilic, the properties of which are summarized in Table 1.

【table】

Table Reference Examples 2-4 These examples illustrate foams obtained using different prepolymer compositions. The composition is shown in Table 1, and the properties of the foam are shown in Table 1. In reference example 2, increasing the average molecular weight of the diol and using a small amount of isocyanate resulted in a foam with higher density and greater capacity for water. In Reference Example 3, the amount of TMOP crosslinker was reduced and the isocyanate index
Increased to 3.4 to maintain strength. However, the ratio of diol to triol is outside the scope of this invention and thus this is a comparative example. Although a stiff foam was obtained, it was not possible to determine the water adsorption ratio since it did not absorb water and became wet. In Reference Example 4, a single diol,
Carbowax 1450 was used with TMOP as crosslinker. A good flexible hydrophilic foam with high elongation, good water holding capacity and water vapor resistance was obtained. Example 1 Carbowax1000 (412g, 0.412mol) and Poly
A mixture of G176-120 (28 g, 0.02 mol) was dried by heating at 70° C. for 2 hours under a vacuum of 2 Torr. To this dried and degassed polyol mixture was added 349 g of Isonate 143L (2.45 equivalents of isocyanate). The temperature was maintained at 70° C. for 80 minutes to complete the reaction. This product is 1.96 meq/
It was a pale yellow liquid with an isocyanate content of 100 g and a viscosity of 27000 cp at 25°C. This sample
After 2 weeks of storage at 80°C, the product was stored at 25°C.
It thickened only to 43,000 cp. When 80 g of the product heated at 35° C. is stirred with 100 ml of a 2% solution of Pluronic L-62, a nonionic surfactant manufactured by Wyandotte, it has a density of 3.9 pounds per cubic foot and is soft and pliable. , a form is produced which is hydrophilic, the properties of which are summarized in Table 1.

【table】

【table】

TABLE Examples 2-5 These samples illustrate foams obtained using different prepolymer compositions. The composition is shown in Table 1, and the foam properties are shown in Table 1. In Example 2, the amount of triol was decreased and the isocyanate index was increased instead to produce a product with lower viscosity and lower foam density and swelling factor. In Example 3, the amounts of triol and isocyanate were further increased while good foam properties were maintained. In Example 4, the molecular weight of the Carbowax diol was reduced to 1450, while the amount of isocyanate was reduced to only 37% by weight of the total composition while maintaining good foam properties. In Example 5, Carbowax 1450 was also used, but the isocyanate index was increased from 3.0 to 3.5 to reduce the density of the foam and improve its swelling factor.

Claims (1)

[Scope of Claims] 1. an aqueous phase and (a) at least 50% by weight of oxyethylene groups and
(b) _{diphenylmethane} diisocyanate, and diphenylmethane diisocyanate; diphenylmethane diisocyanate-containing isocyanate products having a functionality of 2.0 or more consisting of a mixture of isocyanates including derivatives of enylmethane diisocyanate, and (c) having 3 or 4 hydroxyl equivalents per mole and having at least 500 a polymeric poly(oxyC _2-4 alkylene) polyol crosslinking agent, having a number average molecular weight of The polyol crosslinking agent has hydroxy equivalents ranging from 5 to 50% of the total hydroxy equivalents in the diol and polyol.
A resin phase consisting of a prepolymer present to constitute 35 mol % and with a ratio of isocyanate equivalents to total hydroxyl equivalents of 2.5:1 to 3.5:1 is mixed together and reacted. A flexible polyurethane foam based on methylene diphenyl isocyanate produced by 2. The foam of claim 1, wherein the poly( _oxyC2-4 alkylene) diol has a nominal number average molecular weight of between 600 and 2000, and the diol has at least 80% by weight of oxyethylene groups. . 3 Poly(oxyethylene) triol having a molecular weight of 900 as a polymeric polyol crosslinking agent, and
oxyethylene capped poly(oxypropylene) triol with a molecular weight of 1400,
and mixtures thereof. 4. The foam of claim 3, wherein the polymeric polyol crosslinker comprises blocks of oxyethylene and oxypropylene units. 5. The foam of claim 1, wherein the isocyanate product is a modified diphenylmethane diisocyanate containing high percentages of pure diphenylmethane diisocyanate and small amounts of carbodiimide and carbodiimide cycloaddition products. 6. The foam of claim 1 further comprising reinforcing fibers which are polyester fibers having a length of 1.27 cm or less, and further comprising a thickening agent or suspending agent.