WO1994004586A1

WO1994004586A1 - Flexible, moulded, hot cured, low firmness polyurethane foams

Info

Publication number: WO1994004586A1
Application number: PCT/EP1993/002120
Authority: WO
Inventors: Robert Baumann; Christopher Wickham Noakes; Sylvie Renée PIQUE
Original assignee: Dow Europe S.A.; Polyol International B.V.
Priority date: 1992-08-14
Filing date: 1993-08-10
Publication date: 1994-03-03
Also published as: GB9217309D0

Abstract

Flexible, moulded, hot cured, low firmness polyurethane foams are prepared by reacting a polyol composition comprising a polyether polyol, a monohydroxy polyether, water, a tertiary amine catalyst and an organometallic catalyst with an organic polyisocyanate wherein the monohydroxy polyether is a monohydroxy polyoxyalkylene adduct containing more than 50 % by weight of propylene oxide and having a molecular weight of less than 1000. These foams have lower firmness and higher air flow values as compared with foams prepared using the same or similar composition which contains monohydroxy polyether which has no more than 50 % by weight of propylene oxide and/or a molecular weight greater than 1000. These low firmness foams are useful as upholstery materials or as cushions or squabs in vehicle seats.

Description

FLEXIBLE, MOULDED, HOT CURED, LOW FIRMNESS POLYURETHANE

FOAMS

The present invention relates to reduced firmness, flexible, hot c cured, moulded polyurethane foams having excellent air flow properties while retaining good processing and other physical property characteristics.

Flexible hot cured, moulded polyurethane foams are the , ₀ product of a reaction of an isocyanate with a polyol formulation typically containing polyether polyols, water, a foam stabilizer and catalysts. Other additives such as fire retardants, auxiliary blowing agents, fillers, dyes, pigments and antioxidants may also be used. Those skilled in the art know that the density of the foam can be controlled by regulating the 15 amount of water in the formulation. The reaction of water with isocyanate liberates carbon dioxide gas which causes expansion of the foam. Raising the amount of water in the polyol formulation (with a corresponding increase in the amount of isocyanate to maintain the same stoichiometric reaction ratio), decreases the foam density, but raises the

20 amount of urea linkages in the foam, which contribute to increased foam firmness. For years, reduced firmness foams have been produced by incorporating an auxiliary blowing agent into the polyol formulation. The most commonly used auxiliary blowing agents are halogen n - containing low boiling point liquids such as CFC 1 1. The use of this type of auxiliary blowing agents is now seen as undesirable due to concern about their environmental effects. It is well known that when CFC 1 1 or any other previously used auxiliary blowing agent is replaced by additional water blowing, the corresponding flexible polyurethane foams become harder at comparable densities.

The use of monofunctional hydroxyl terminated materials such as monofunctional alcohols, monofunctional ethers and monofunctional esters in the preparation of polyurethane foams is well known in the art.

Journal of Elastomers and Plastics, Arceneaux et al, p.63, Vol. 14 (1982) describe the effect of monohydroxy polyethers of equivalent weight of up to 719, on the load bearing properties of flexible slabstock foams. Arceneaux et al have found that the addition of monohydroxy polyethers of equivalent weight of up to 719 to the foaming formulations results in foams which have improvement in elongation properties but unacceptable load bearing, tear resistance and compressive and tensile strength properties.

European Patent 0 386 974 A2 (PMC Inc.) teaches the use of a variety of monohydroxy materials in the preparation of flexible free rise polyurethane foams. Monohydroxy materials can be alcohols, polyesters or polyethers. Useful monohydroxy polyethers are derived from the reaction of a monofunctional alcohol with propylene oxide and/or ethylene oxide and have the molecular weight from 100 to 3000. The reference teaches that the use of these monohydroxy materials results in a foam having decreased firmness at a given density. Most of the examples in this reference show the use of linear alcohols such as hexanol, or mixtures of linear alcohols such as n-dodecanol, n- tetradecanol and other longer chain linear alcohols. Only two monohydroxy polyethers (a 1700 molecular weight monohydroxy polyether made from a 50/50 blend of ethylene oxide and propylene oxide and a 550 molecular weight monohydroxy polyether made from ethylene oxide). are exemplified in this reference (see, page 9, Table 4, Formulations C and F) Use of either of these two monohydroxy polyethers produced lower firmness foam but the air flow properties of the foams so produced are significantly reduced Formulation A (Control) containing no monohydroxy polyether produced the foam having air flow( SCFM) of 2 4, while Formulations C and F containing 15 parts of a 1700 molecular weight monohydroxy polyether made from a 50/50 blend of ethylene oxide and propylene oxide and 15 parts of a 550 molecular weight monohydroxy polyether made from ethylene oxide, respectively produced foams having air flows (SCFM) 0.6 and 0.3, respectively, which would be generally considered as unacceptable by the industry.

0 European Patent 0 361 334 A2 (The Dow Chemical Company) teaches preparation of soft polyurethane foams by reacting polyisocyanates with polyol compositions containing polyether mono- alcohols in the presence of trimenzation catalyst and water as blowing agent Polyether mono-alcohols are prepared by reacting an alkylene

15 oxide such as ethylene oxide, 1 ,2-propylene oxide, 1 ,2- and 2,3-butylene oxide, styrene oxide, or mixtures thereof with a mono-hydπc initiator such as aliphatic, cycloaliphatic or aromatic monohydπc alcohols having 1 to 12 carbon atoms, and aliphatic, cycloaliphatic or aromatic ethers, of

„ _ monoether glycols having 2 to 6 carbon atoms in the glycol moiety, and dimethyl, -ethyl, -propyl or -butyl ethers of tπols such as glycerol and ^' tπmethylolpropane. Suitable polyether mono-alcohols have a molecular weight of at least 800, preferably from 800 to 3000. The soft polyurethane foams prepared using these polyether mono-alcohols in

25 the presence of trimenzation catalyst and water as the blowing agent are said to exhibit comparable properties to those of foams prepared using conventional polyol compositions and CFC blowing agents. However, while no air flow properties of these foam are mentioned in this reference, it is known that trimenzation catalysts can negatively influence air flow characteristics of the foam

US Patent 3,875,086 (Ramey et al) describes the use of monohydroxy polyether chain stoppers prepared by reacting a monohydroxy initiator with propylene oxide or propylene oxide and ethylene oxide to reduce and control the hardness of polyurethane elastomers, and to improve the flowability of reactants used to produce flexible polyurethane foams.

US Patent 3,457,203 (Cohen et al) describes preparation of a hydrophilic polyurethane foam, where the use of "water soluble r oxyethylated monofunctional compounds" enhances the water absorption of the sponges produced.

British Patent 1 ,066,759 (Elekal) also describes a method of producing hydrophilic polyurethane foam sponges for domestic and _{ι n} industrial use, by incorporating a monoalkoxypolyethylene glycol in the foam.

A definite need exists in the industry for a method in which flexible, moulded, hot cured, lower firmness polyurethane foams can be

. ,_ made, without losing important air flow properties while other foam properties are acceptable and comparable with conventionally made foams. Surprisingly, it has now been found that by using particular low molecular weight monohydroxy polyethers lower firmness polyurethane foams having excellent air flow values are produced.

20

Accordingly, the present invention concerns a process for preparing a flexible, moulded, hot cured, low firmness polyurethane foam comprising reacting a polyol composition comprising a polyether polyol, a monohydroxy polyether, water, a tertiary amine catalyst and an

25 organometallic catalyst with an organic poiyisocyanate wherein the monohydroxy polyether is a monohydroxy polyoxyalkylene adduct containing more than 50% by weight of propylene oxide and having a molecular weight of less than 1000, preferably from 150 to 750. The flexible, moulded, hot cured, low firmness polyurethane foam thus prepared has lower firmness and higher air flow value as compared with a foam prepared using the same or similar composition containing monohydroxy polyether which has no more than 50% by weight of propylene oxide and/or a molecular weight greater than 1 ,000. In another embodiment, the present invention concerns a flexible, moulded, hot cured, low firmness polyurethane foam which is the reaction product of a polyol composition comprising a polyether polyol, a monohydroxy polyether, water, a tertiary amine catalyst and an organometallic catalyst with an organic poiyisocyanate wherein the monohydroxy polyether is a monohydroxy polyoxyalkylene adduct containing more than 50% by weight of propylene oxide and having a molecular weight of less than 1000, preferably from 150 to 750, and wherein the foam has lower firmness and higher air fiow value as compared with a foam of the same or similar composition containing monohydroxy polyether which has no more than 50% .by weight of propylene oxide.

Polyether polyois which can be used in the present invention are well known in the art, are readily available and include the addition products of alkylene oxides with polyhydric compounds having from 2 to 8 active hydrogen containing groups per molecule. Examples of polyhydric compounds that are suitable as starting materials for making the alkylene oxide adducts comprise, for example, water, glycerol, trimethylolpropane, pentaerythritol, hexanetriol, hexitol, heptitol, sorbitol, sucrose, amine compounds , such as ethylene diamine and aminoethylpiperazine, and mixtures of two of more of the aforementioned compounds. The alkylene oxide adducts of the polyhydric initiator can be prepared using techniques well known to those skilled in the art of preparing polyether polyols.

Other suitable polyether polyols are those known as polymer polyols or grafted polyols, such as those modified by copolimerizing with styrene or mixtures of styrene with acrylonitrale (known as S/AN copolymer polyols), or combinations of amines or olamines with isocyanates (known as PHD or PIPA copolymer polyols). These modified polyether polyols are commercially available.

Preferred polyether polyols for use in this invention are the addition products of alkylene oxides with polyhydric compounds having s .

2 to 4 active nydrogen containing groups per molecule and wnerein the addition product has a hydroxyi number of from 20 to 120, preferably from 20 to 80.

The polyol component can comprise of a mixture of one or more polyether polyols and/or one or more polymer polyols whereby the preferred composition contains at least one polyether polyol which is trifunctional. Illustrative of such a polyether polyol, for example, is glycerine which is alkoxylated with one or a combination of oxides including ethylene oxide, in a block or random form so as to provide a polyether polyol containing from 20 to 90, preferably from 35 to 90 percent primary hydroxyi and having a hydroxyi number from 20 to 100.

The polyol component of the polyol composition is present in an amount of between 75 to 98, preferably from

80 to 97 percent by weight of the total polyol composition.

Preferred monohydroxy polyoxyalkylene adducts useful in the present invention can be prepared by the reaction of a monohydroxy initiator with propylene oxide and an additional alkylene oxide, preferably ethylene oxide. The resulting monohydroxy polyoxyalkylene adduct should contain more than 50% by weight of propylene oxide. Examples of suitable initiators include aliphatic, cycloaliphatic or aromatic monohydroxy alcohols having 1 to 12 carbon atoms and aliphatic, cycloaliphatic or aromatic ethers of monoether glycols having 2 to 6 carbon atoms in the glycol moiety and dimethyl, -ethyl, -propyl, or -butyl ethers of triols such as glycerol and trimethylolpropane. The monohydroxy initiator may also be combined with a polyol initiator, which on reaction with an alkylene oxide produces a monohydroxy polyether in admixture with the polyol. Exemplary of a polyol initiator is glycerine. Illustrative of suitable monohydroxy initiators are, for example, methanol, ethanol, propanol, butanol and alkylene oxide adducts of these alcohols.

The monohydroxy initiators are reacted with an alkylene oxide comprising propylene oxide and an additional alkylene oxide such as ethylene oxide, 1 ,2-butylene oxide, and 2,3-butylene oxide or mixtures of two or more additional alkylene oxiαes, in the presence of one or more catalysts using techniques known to those skilled in the art of preparing polyether polyols. Preferred alkylene oxides are mixtures or random block feedings of 1 ,2-propylene oxide and ethylene oxide. The resulting monohydroxy polyoxialkylene adduct should contain more than 50% by weight of propylene oxide The choice of catalysts used in the preparation of the monohydroxy polyoxyalkylene adducts are well known to those skilled in the art of preparing polyether polyols. Preferred catalysts are compounds of the group I and group II metals of the Peπodic Table Illustrative examples of suitable catalysts are, for example, sodium hydroxide, potassium hydroxide, and barium hydroxide

Suitable monohydroxy polyoxyalkylene adducts useful in the present invention contain more than 50% by weight of propylene oxide and have a molecular weight of less than 1000, preferably from 150 to 750. By way of illustration, examples of such monohydroxy polyoxyalkylene adducts are those which can be prepared by the reaction of n-butanol with propylene oxide to give a product with a molecular

_ weight from 190 to 250 Another example, for example, are the monohydroxy polyoxyalkylene adducts which can be prepared by the reaction of n-butanol with a mixed oxide feed comprising ethylene oxide and at least 60% of propylene oxide to to give a product with a molecular weight of 550 to 650. This monohydroxy polyoxyalkylene adduct can be

25 further reacted with additional amount of ethylene oxide to produce the product containing more than 50% by weight of propylene oxide and having a molecular weight of 550 to 650

Mixtures of two or more of the aforementioned monohydroxy 30 polyoxyalkylene adducts are also suitable for use in the present invention

The monohydroxy polyoxyalkylene adduct component of the polyol composition of the present invention is present in an amount of from 0.5 to 25, preferably from 1 to 15 parts by weight of the total polyol composition.

Tertiary amines and organometallic compounds are used as catalysts in the present invention. Tertiary amines are conventionally used as catalysts in the production of polyurethane foams, illustrative tertiary amines which can be used in the present invention include triethylene diamine, pentamethyldiethylenetriamine, N- ethylmorpholine, N-2-dimethylethylenemorpholine, bis(dimethyl- aminoethyl) ether and other compounds well known to those skilled in the art. Such tertiary amines are used in amounts of from 0.01 to 1.5 parts by weight of total polyol present. Preferably they are used in amounts of from 0.03 to 1.5 parts. Mixtures of two or more amines may also be employed in the present invention.

Organometallic compounds are also conventionally used. as catalysts in the production of polyurethane foams, illustra¬ tive organometallic compounds which can be used as catalysts in the present invention include carboxylic acids salts such as dibutyl tin dilaurate and dibutyl tin maleate and the like. The organic metal catalyst is normally used in amounts of from 0.01 to 0.5, preferably from 0.03 to 0.5 part by weight per 100 parts by weight of total polyol present. The preferred organometallic catalyst for use in the present invention is stannous octoate.

Preferably, when a mixture of tertiary amine catalysts are used, alone or in conjunction with other catalysts, any trimerization catalyst present amongst the tertiary amine catalysts makes up only a minor portion of said tertiary amine catalysts, non-trimerization tertiary amine catalysts being present in a greater amount.

The organic polyisocyanates which are useful in the present invention include those containing at least about two isocyanate groups per molecule. Preferably, the isocyanate employed contains an average of from about 2.0 to about 3.0 isocyanate groups per molecule. Suitable isocyanates include aromatic polyisocyanates, aliphatic, cycloaliphatic and heterocyclic polyisocyanates used alone or in admixture. The preferred isocyanates used in the practice of this invention are aromatic polyisocyanates and include the toluene diisocyanates, especially 2,4-and 2,6-toluene diisocyanate (TDI) as well as any desired mixture of these isomers, 2,4'- and 4,4'-dιphenylmethane diisocyanate (MDl) as well as any desired mixture of these isomers, oiigomers of MDl (polymeric MDl), polymethylene polyphenyl polyisocyanates (commonly referred to as " crude MDl "), mixtures of TDI and polymeric MDl and mixtures of the these polyisocyanates Prepolymers of the above poiyisocyanate (e.g. with polyether polyols, glycols or mixtures of these) can also be used in the present invention

The polyol composition is advantageously reacted with a poiyisocyanate as described above such that the ratio of isocyanate groups of the poiyisocyanate to the active hydrogen containing groups of the polyol composition including water is from 0.8. 1 to 1.2 1 and preferably from 0.85: 1 to 1.15 1

Water is used as a blowing agent . The reaction of water with isocyanate liberates carbon dioxide which causes the foam to expand, thus acting as a blowing agent. Water can be present in the polyol composition in an amount from 1 to 8, preferably from 2 to 6, most preferably 3 to 5 parts by weight per 100 parts by weight of total polyol present.

Supplementary blowing agents can also be employed in the present invention. Such suitable supplementary blowing agents include liquids having a boiling point in the range from 0 to 80 °C. Exemplary useful supplementary blowing agents include halogenated hydrocarbons such as dichlorodifluorome-thane, chlorotπfluoromethane, tπchlorofluoromethane and tπchloro-ethane. Should supplementary blowing agents be used, the preferred types are the so called "soft" chlorofluorocarbons which contain at least one hydrogen atom per molecule

The polyol composition may also contain one or more foam stabilizers or surfactants or cell stability or other cell size control agents Such materials are well known in the art In general , representative foam stabilizers are alkoxysilanes, polysilylphosphonates, polydimethyl- siloxanes, the condensates of ethylene oxide with a hydrophobic base formed by condensing propylene oxide with propylene glycol, the alkylene oxide adducts of ethylene diamine, and the polyoxyalkylene esters of long chain fatty acids and sorbitan, and (siloxaneoxyalkylene) block copolymers.

Examples of suitable surfactants and stabilizers are theTegostab BF2370, Tegostab B8002 and Tegostab BF4900 products sold by Th. Goldschmidt. Similar products are sold by Union Carbide Corp., Air Products and Dow Corning.

The foam stabilizer, surfactant, cell stability or other cell control agent is generally used in amounts from 0.1 to 2.0 parts by weight per 100 parts by weight of hydroxyi group containing compounds in the polyol composition. Mixtures of one one or more stabilizers and/or one or more surfactants may also be used.

In addition to the above mentioned components, the foam formulation may also contain any number of a variety of additives conventionally used in the production of polyurethane foams such as fire retardants, anti oxidants, dyes, pigments and fillers. Crosslinkers may also be used within the scope of the invention to modify foam properties. These additives and crosslinkers are used in amounts well known to skilled persons.

According to the present invention the reaction components may be reacted by the known single-step process by reacting all the ingredients together at once, by the prepolymer process or by the so called "quasi-prepolymer method" . In the single-step process the foams are normally produced with the aid of a low or high pressure machine. The polyol components are either metered separately or in pre mixtures to a mixing head where they are combined with a metered poiyisocyanate to give the polyurethane reacting mixture. This mixture may be poured or injected into a mould or container as required. The mould temperature on pouring is usually between 30 to 60 °C. Alternatively the foams can be prepared by the so called " quasi- prepoiymer" method. In this method a portion of the polyoi component is reacted in the absence of catalysts with the poiyisocyanate component in a proportion so as to react up to 30 percent of the free isocyanate groups in the reaction product. To prepare the foam the remaining portion of the polyol component, water, and other components are reacted with the partially reacted isocyanate using similar types of machines.

The moulded foams are cured at a temperature of between 60 to 250 °C conveniently for a period of time between 5 and 20 minutes, before demoulding.

The polyurethane foams prepared according to the present invention are flexible products having densities from 15 to 120, preferably from 20 to 100, and most preferably from 20 to 80 kilograms per cubic meter and having air flow value of at least 1 , preferably more than 1.4, as measured by the ISO 7231 method. These polyurethane foams are used, for example, as upholstery materials or as cushions or squabs in automotive seating.

The following designations, symbols, terms and abbreviations are used in the Examples below:

Polyol A is an ethylene oxide, propylene oxide mixed feed adduct of glycerine, ethylene oxide capped to give an hydroxyi number of 56 and a primary hydroxyi content of 40%

Monol A is a monohydroxy polyalkylene adduct

(propylene oxide/ethylene oxide adduct of methanol) having the propylene oxide content greater than 50% and having a hydroxyi number of 37.5. (i.e. molecular weight of 1490)

Monol B is a monohydroxy polyalkylene adduct

(propylene oxide/ethylene oxide adduct of butanol) having the propylene oxide content greater than 50% and a hydroxyi number of 89 (i.e., a molecular weight of 630)

Monol C is a monohydroxy polyalkylene adduct

(propylene oxide/ethylene oxide adduct of c methanol) having the propylene oxide content greater than 50% and a hydroxyi number of 295 (i.e. a molecular weight of 190)

Dabco 33LV a 33 percent solution of triethylene diamine in , _n dipropylene glycol sold by Air Products and

Chemicals Inc.

Dabco XDM is N,N-dimethylethyl-N-morpholine sold by Air Products Chemical Inc.

15 Niax AI is 70% bis(2-dimethylaminoethyl)ether solution in DPG sold by Union Carbide Corp.

Polycat 5 is pentamethyldiethylenetriamine sold by Air

Products and Chemicals Inc.

20

NEM is N-ethylmorpholine sold , e.g., by Air

Products and Chemicals Inc. and Texaco

SO is stannous octoate

25

BF-2370 is silicone surfactant sold by Th. Goldschmidt under the trademark Tegostab BF2370

B-8002 is silicone surfactant sold by Th. Goldschmidt under the trademark Tegostab B-8002

30

L-620 is silicone surfactant sold by Union Carbide

Corp. as Union Carbide Surfactant L-620

T-80 is a 80:20 mixture of the 2,4- and 2,6-toluene diisocyanate isomers sold by the Dow Chemical Company under the trademark Voranate T80.

CFD is Comoression Force Deflection

Properties of the polyurethane foams give in the Examples below are determined according to the following test methods:

Core Density DIN 53420

Air Flow ISO 7231 (on AMSCOR foam porosity instrument)

CFD DIN 53577

Resilience ASTM D 3574

Compression Set DIN 53572

SAG factor calculated as the ratio of the CFD at 65% compression divided by the CFD at 25% compression using DIN 53577 test method.

Index is the ratio of the amount of reactive isocyanate groups in the reaction mixture divided by the amount of active hydrogen groups in the reaction mixture multiplied by 100.

The following examples are given to illustrate the invention and should not be interpreted as limiting it in any way. Unless stated otherwise, all parts and percentages are given by weight . EXAMPLES 1 TO 3 AND COMPARATIVE EXAMPLES C-1 TO C-2

The polyurethane foams were produced by pouring foam formulations shown in Table 1 below into a square aluminium mould using a low pressure pouring machine, allowing the foam to rise and then curing it at 160 °C for about 10 minutes. The mould pouring temperature was around 35 °C. Foam properties are shown in Table 1 below

Table 1.

Note: Comparative Examples C-1 and C-2 are not examples of this invention As can be seen from Table 1 , foams prepared in Examples 1 to 3 exhibit superior air flow characteristics and lower firmness even at higher SO level, as indicated by the CFD values at 40% than foams prepared in Comparative Examples C-1 and C-2 using no monohydroxy polyoxyalkylene adduct and monohydroxy polyoxyalkylene adduct which is outside the scope of the present invention, respectively. Other properties of the foams prepared in Examples 1 to 3 are acceptable.

1 6

EXAMPLE 4 AND COMPARATIVE EXAMPLES C-3 TO C-4

Polyurethane foams were prepared using hand mixed formulations shown in Table 2 below. As seen from the data shown in Table 2 below, low molecular weight monohydroxy polyoxyalkylene adduct exhibits the strong influence on the air flow characteristics and foam firmness (CLD at 40%) in high density foams. The air low characteristics of the foams prepared using no monohydroxy polyoxyalkylene adduct or conventional monohydroxy polyoxyalkylene adduct (Monol A) are considerably lower than that of the foam prepared using the monohydroxy polyoxyalkylene adduct of this invention, even with the addition of a blowing catalyst such as Polycat 5, while the foam of Example 4 meets the requirements for air flow at high densities (with reduced firmness).

Table 2

Note: Comparative Examples C-3 to C-4 are not examples of this invention EXAMPLE 5 AND COMPARATIVE EXAMPLE C-5

Polyurethane foams were prepared using hand mixed formulations shown in Table 3 below. As seen from the data shown in Table 3, the foam prepared using the lower molecular weight monohydroxy polyalkylene adduct of the present invention (Monol C) exhibits far better air flow characteristics and lower firmness than the foam prepared using conventional, higher molecular weight monohydroxy polyalkylene adduct (Monol A). At the same time, compression sets and SAG factors of the foams are comparable.

Table 3

Note: Comparative Example C-5 is not an example of this invention EXAMPLES 6 AND 7

The polyurethane foams were produced by pouring foam formulations shown in Table 4 below into real production moulds. These Examples demonstrate that the properties of the foams prepared in real production moulds using the low molecular weight monohydroxy polyoxyalkylene adducts of the present invention do not deteriorate. In particular the foams remained porous as shown by the similar and high air flow values while foams processing characteristics were good, without brittleness or crumbliness and with good skin retention.

Table 4

* An aluminium laboratory 25 litre mould. ** A rear squab production mould, volume around 70 litres thickness up to 120 mm.

Claims

1. A process for the preparation of a flexible, moulded, hot cured, low firmness polyurethane foam comprising reacting a polyol composition comprising a polyether polyol, a monohydroxy polyether, water, a tertiary amine catalyst and an organometallic catalyst with an organic poiyisocyanate characterised in that the monohydroxy polyether is a monohydroxy polyoxyalkylene adduct containing greater than 50% by weight of propylene oxide and having a molecular weight of less than 1000.

2. The process of Claim 1, wherein said monohydroxy polyoxyalkylene adduct has a molecular weight of from 150 to 750.

3. The process of Claim 1 or Claim 2, wherein said monohydroxy polyoxyalkylene adduct is prepared by the reaction of a monohydroxy initiator with propylene oxide and ethylene oxide.

4. The process of Claim 3, wherein said monohydroxy polyoxyalkylene adduct is prepared by the reaction of n- butanol with propylene oxide and ethylene oxide.

5. The process of Claim 4, wherein said monohydroxy polyoxyalkylene adduct is present in an amount of from 1 to 25 parts by weight of the total polyol composition.

6. The process of Claim 5, wherein water is present in an amount of from 1 to 8 parts by weight per 100 parts by weight of the polyol composition.

7. The process of Claim 6, wherein a liquid having a boiling point in the range of from 0. to 80°C is used as a supplementary blowing agent.

8. A flexible, moulded, hot cured, low firmness polyurethane foam which is the reaction product of a polyol composition comprising a polyether polyol, a monohydroxy polyether, water, a tertiary amine catalyst and an organometallic catalyst with an organic poiyisocyanate characterised in that the monohydroxy polyether is a monohydroxy polyoxyalkylene adduct containing more than 50% by weight of propylene oxide and having a molecular weight of less than 1000.

9. The polyurethane foam of Claim 8, wherein said monohydroxy polyoxyalkylene adduct has a molecular weight of from 150 to 750.

10. The polyurethane foam of Claim 8 or Claim 9, wherein said monohydroxy polyoxyalkylene adduct is prepared by the reaction of a monohydroxy initiator with propylene oxide and ethylene oxide.

11. The polyurethane foam of any one of Claims 8 to 10 wherein said monohydroxy polyoxyalkylene adduct is used in an amount of from 1 to 25 parts by weight of the total polyol composition.

12. The polyurethane foam of any one of Claims 8 to 11, wherein the foam is cured at a temperature of between 60 and

250°C.