WO1996026915A1

WO1996026915A1 - Novel di- and polyamino compounds for use in the preparation of polyurethane materials

Info

Publication number: WO1996026915A1
Application number: PCT/EP1996/000340
Authority: WO
Inventors: Guy Leon Jean Ghislain Biesmans; Gonda Van Essche
Original assignee: Imperial Chemical Industries Plc
Priority date: 1995-02-27
Filing date: 1996-01-23
Publication date: 1996-09-06
Also published as: JPH11501621A; EP0812310A1

Abstract

Fluorinated diaminodiphenyl methane compounds and conversion of these compounds into polyols and polyisocyanates, which in turn can be used in the preparation of polyurethane foams, powders or aerogels.

Description

Novel di- and polyamino compounds for use in the preparation of polyurethane materials

The present invention relates to novel di- and polyamino compounds that can be used for preparing polyols and polyisocyanates, which in turn can be used in the synthesis of polyurethane materials. The present invention relates also to the polyols, polyisocyanates and polyurethane materials obtained by using said compound.

It is well known to manufacture polyurethane materials of a cellular or non- cellular, flexible or rigid nature by reacting organic polyisocyanates having two or more isocyanate groups per molecule with compounds containing a plurality of isocyanate reactive groups, for example polyols and polyamines, in the presence, where required, of other components such as blowing agents, cross-linking agents, catalysts and surfactants. These polyurethane materials may take the form of adhesives, coatings, elastomers, fibres, films, foams, thermoplastics, powders, xerogels, aerogels and the like.

Polyols for use in preparing polyurethanes are usually prepared by reacting an initiator compound having a plurality of active hydrogen atoms (alcohols or amines) with an alkylene oxide (usually propylene oxide). A suitable initiator compound is diammodiphenylmethane (methylenedianiline) . Polyamines for use in preparing polyurethanes are obtained by converting the hydroxyl end-groups of the polyols to amino end-groups.

Organic polyisocyanates for use in preparing polyurethanes are conventionally manufactured by reacting phosgene with the corresponding organic polyamines. Thus the starting materials for diisocyanatodiphenylmethane (MDI) and its homologues, are the mixtures of isomers and homologues of diaπαnodiphenylmethane that are formed by the condensation reaction of formaldehyde and aniline.

A problem encountered when preparing polyurethane or polyisocyanurate aerogels (as described in, e.g., WO 95/03358) is the limited solubility of known organic polyisocyanates in CO_ and/or hydro (chloro) fluorocarbons, especially at pressures below 100 bar.

A problem encountered when preparing polyurethane foams blov.n witn (cyclo)alkanes is the limited solubility of these blowing agents in the known organic polyisocyanates.

We have now found novel polyamino compounds suitable for use in the preparation of polyols and polyisocyanates, and thus also polyurethane materials. The polyisocyanates derived from these novel polyamino compounds have a higher solubility in C0_ and hydro(chloro) fluorocarbons than the conventional polyisocyanates and dissolve (cyclo) alkanes better than the conventional polyisocyanates.

Thus according to the present invention compounds corresponding to general formula (I)

wherein: n, n' and n" each independently represent an integer of from 0 to 4 , at least one of n, n' and n" not being equal to 0; m represents an integer of from 0 to 8, preferably from 0 to 4; and wherein the amino substituents are situated in ortho, meta or para position with regard to the methylene substituent; with the exception of bis (2, 3, 5, 6-tetrafluoro-4-amιnophenyl)methane and bis (3-fluoro-4-amιnophenyl)methane.

Bis (2, 3, 5, 6-tetrafluoro-4-amιnophenyl)methane is described in JP 02/138155 for use m the preparation of epoxy resins and fluorine-containing rubber Bis (3-fluoro-4-amιnophenyl (methane is described in US 3456037 for use in the preparation of polyurethane elastomers.

Preferably m equals 0.

Preferred compounds according to formula (I) are listed below in table 1

TABLE 1

Preferred compound according to formula (I) for use in the preparation of polyurethane materials are compound (1.1) and compound (1.9) .

The compounds according to formula (I) are obtained by the acid condensation of the corresponding fluorinated aniline(s) and formaldehyde. Two different fluorinated anilines may be used and also a mixture of a fluorinated aniline and a non- luorinated aniline. Methods for performing this reaction are known in the art. When two different fluorinated anilines are used mixtures of different compounds according to formula (I) are obtained.

Compounds according to formula (I) are useful in the preparation of polyurethane based materials. They can be used as such and have the function of, for example, amme chain extenders (especially in flexible foam applications) or they can be converted into polyols and/or polyisocyanates which in turn can be converted into polyurethane based materials.

Therefore the present invention also provides polyol compositions obtainable by oxyalkylation of a compound of formula (I) and optionally a second initiator.

The polyol compositions according to the present invention may contain oxyalkylene units derived from propylene oxide, ethylene oxide and butylene oxide. These oxyalkylene units may be partially or fully fluorinated. When both propylene and ethylene oxides are employed in the oxyalkylation, they may be reacted either simultaneously or sequentially with the compound according to formula (I). It is preferred that the ethylene oxide content does not exceed 70 * of the total alkylene oxide units on a molar basis.

In conjunction with the compound of formula (I) another initiator may be used in the formation of the polyol compositions according to the present invention.

Suitable co-initiators include: water and polyols, for example ethylene glycol, propylene glycol and their oligomers, glycerol, tπmethylolpropane, triethanolamine, pentaerythritol, sorbitol and sucrose; polyamines, for example ethylene diamine, tolylene diarmne, diaminodiphenylmethane and polymethylene polyphenylene polyamines; and ammoalcohols, for example ethanolamine, triisopropanolamine and diethanolamine; and mixtures of such initiators.

Polyols having hydroxyl values in the range 30 to 680 mg KOH/g can be prepared, preferably in the range 30 to 620 mg KOH/g and more preferably in the range 300 to 500 mg KOH/g.

The method for making the polyol compositions according to the present invention basically follows prior art modes of making polyether polyols. The oxyalkylation is performed in the presence of ionic catalysts as known in the art. The amount of catalyst utilised may vary over a wide weight percentage based on tne weight of the initiator(s) . Usually an amount of catalyst ranging from about 0.01 to about 5 weight - is employed, based on the weight of the initiator. More often, the amount employed is 0.1-2 -, and most often 0.3-1 Ϊ.

Usually basic catalysts are used. Potassium hydroxide or sodium hydroxide are most preferred. Other metal hydroxides .such as cesium hydroxide) or tertiary amines can also be used. Acid catalysis is also possible. Lewis-acids like boron trifluoride, stannic chloride, or combinations of ferric chloride with thionyl chloride are preferred.

The amount of alkylene oxide added to the compound of formula (I) and the optional co-initiator may range over a wide range of about 1-100 moles of alkylene oxide per mole of initiator. More often, 1-50 moles of alkylene oxide are reacted per mole of initiator.

The temperature of reaction may range from about 50°C to about 200^CC, and is preferably from 80°C to 150°C.

Where the polyol compositions are intended for use in the preparation of rigid polyurethane foams, the polyols should have average hydroxyl numbers in the range from 300 to 880 mg KOH/g, especially in the range from 300 to 500 mg KOH/g, and a hydroxyl functionality in the range from 2 to 8, especially m the range from 3 to 6, preferably 4.

Where the polyol compositions are intended for use in the preparation of flexible foams, tne polyols should have a molecular weight in the range from 1000 to 10000, preferably from 3000 to 7500, and a number average functionality in the range from 2 to 4.

The present invention also provides polyisocyanate compositions obtainable by phosgenation cf compounds of formula (I) .

Thus according tc the present invention there is provided a novel compound corresponding to formula (II)

wherein n, n', n" and m have the meanings as defined above.

Preferreα compounds according to formula (II) are bis (3, 5-dιfluoro-4- lsocyana opher.yl methane (compound II.1) and bis .2, 3, 5, 6-tetrafluoro-4- lsocyanatopher. l methane (compound II. Si .

The phosgenation s performed according to methods generally known in the art, such as described, for example, in US 4297294, DE 3744001 and GB

1218360.

The phosgenation can take place both continuously and discontmuously. The phosgenation car. take place in two steps according to the well-known cold/hot phosgenation principle or in one step according to the hot phosgenation principle.

Inert organic compounds are used as solvent. Suitable solvents include aliphatic, cycloaliphatic and aromatic hydrocarbons, halogenated hydrocarbons, nitro-substituted hydrocarbons, aliphatic-aromatic ethers, aromatic ethers, carboxylic acid esters, carboxylic acid nitriles, sulfone, phosphoric acid halogenide and phosphoric acid ester. Chlorobenzene and ortho dichlorobenzene have been generally accepted as the most commonly used solvents.

Further the phosgenation can take place at normal or slightly elevated pressure.

The phosgene is added to the composition in an amount of 1 to 10 times, in particular 1.05 to 6 times the stoichiometric amount.

Catalysts such as dimethylformamide and acid acceptors such as pyridme can accelerate the phosgenation. Further processing of the reaction mixture after the phosgenation involves the recovery of gaseous substances (hydrogen chloride and excess of phosgene) and multistage distillation to separate the solvent. The isocyanate itself can then be recovered by means of extraction, crystallisation, distillation or sublimation.

The isocyanates according to formula (II) can be post-reacted; they can be trimerised, urea-modified, allophonate-modified, biuret-modified or they can be prepolymeπsed (i.e. reacted with polyols, etc.). In any of these forms they can then be used in the preparation of polyurethane based materials.

The polyol compositions and polyisocyanate compositions resulting from compounds according to formula (I) can be used in a conventional manner in order to prepare polyurethane materials. The polyurethane materials can be solid (e.g. elastomers) or they can be cellular. The polyurethane material can be in the form of rigid foams, flexible foams, self-skinning foams, elastomers, thermoplastic polyurethane (TPU) , powders, xerogels, aerogels or as coatings, adhesives, sealants and binders.

The term "polyurethane materials" as used herein is meant to also include urethane-modifled polyisocyanurate materials, polyisocyanurate materials, polyurea materials, polyallophanate materials and polybiuret materials.

In general, polyurethane preparation involves reacting a polyol composition with an organic polyisocyanate in the presence of a foaming agent in the case of polyurethane foam preparation, and usually, catalysts, surfactants and other known additives.

A polyol composition according to the present invention may be reacted with a conventional polyisocyanate composition, or a polyisocyanate composition according to the present invention may be reacted with a conventional polyol composition. Alternatively a polyol composition according to the present invention may be reacted with a polyisocyanate composition according to the present invention.

Further the polyol composition used may comprise a mixture of different types of polyols, including conventional polyols and polyols according to the present invention; similarly the polyisocyanate composition used may comprise a mixture of different types of polyisocyanates, including conventional polyisocyanates and polyisocyanates according to the invention.

Conventional polyisocyanates for use in the polyurethane forming process include aliphatic, cycloaliphatic, araliphatic and aromatic polyisocyanates as proposed in the literature. Of particular importance are aromatic diisocyanates such as tolylene and diphenylmethane dnsocyanate in the well known pure, modified and crude forms, in particular the so-called MDI variants and the mixtures of diphenylmethane dnsocyanate(s) and oligomers thereof known in the art as "crude" or "polymeric" MDI.

The polyisocyanates used in the polyurethane forming process can be in the form of a prepolymer, or in the form of a trimerised isocyanate or a modified (urea, allophonate, biuret) isocyanate.

Preferred polyisocyanates for the preparation of rigid polyurethane foams are those having an average nominal functionality of 2.4-3.0 and in particular of 2.4-2.9.

Preferred polyisocyanates for the preparation of flexible and integral skin foams and for microcellular elastomers are those having an average nominal functionality of 2.0 to 2.4.

In particular MDI based polyurethane prepolymers and semi- or quasi- prepolymers having an NCO value of 5 to 31 - by weight may be used.

Foaming agents which may be used include carbon dioxide-evolving compounds such as water and inert low boiling compounds having a boiling point of above -70^CC at atmospheric pressure. Suitable inert blowing agents include those well known and described in the art, for example, hydrocarbons, dialkyl ethers, alkyl alkanoates, aliphatic and cycloaliphatic hydrofluorocarbons, hydrochiorofluoroca bons, chlorofluorocarbons, hyαrochlorocarbons and fluorine-containing ethers.

Catalysts include the usual tertiary amines, tin compounds and metal salts of carboxylic acids whilst useful surfactants include siloxane-oxyalkylene copolymers and conventional non-ionic types. Other useful additives include fire-retardants, for example, trιs-2-chloroethyl phosphate and dimethyl methylphosphonate. In operating the polyurethane forming process the known one-shot, full prepolymer or semi-prepolymer techniques may be used together with conventional mixing methods and the foams and elastomers may be prepared in the form of mouldings, cavity fillings, sprayed foam, frothed foam, slabstock foam or laminates with other materials such as hardboard, plasterboard, plastics, paper or metals.

It is convenient in many applications to provide the components for polyurethane production in pre-blended formulations based on each of the primary polyisocyanate and polyol components. In particular, many reaction systems employ a polyol formulation which contains the major additives such as the blowing agent and the catalyst in addition to the polyol component or components.

When the compounds according to formula (I) are used as chain extenders in the polyurethane forming process they are conveniently added to the pre- blended polyol formulation in an amount of from 0.1 to 20 parts by weight based on the total polyol composition. In case flexible foams are prepared according to the prepolymer process the compounds according to the invention may be used as chain extenders either as the sole isocyanate-reactive ingredient (apart from water in case water is used as blowing agent) or together with other isocyanate-reactive ingredients, like other chain extenders and high molecular weight polyol m relatively small amounts.

Polyisocyanate compositions according to the present invention are especially useful for preparing polyurethane baseα aerogels according to the process described in WO 95/03358 (incorporated herein by reference) and polyurethane based porous materials according to the processes described in WO 95/00530 (incorporated herein by reference). Generally these materials are prepared by dissolving an organic polyisocyanate (usually in an amount of 1 to 25 * by weight) in a suitable solvent tsuch as a hydrofluorocarbon) . A suitable trimerisation catalyst is added hereto in a weight ratio isocyanate/catalyst of between 3 and 5000 (preferably between 5 and 1000 and most preferably between 10 and 500) and the mixture is thoroughly mixed. Thereafter it is left in a quiescent state until a sol-gel is obtained which is dried by super critical drying in case of an aerogel or by flash-off (sudden release of pressure) in case of a powder.

Using the present polyisocyanate compositions instead of conventional polyisocyanates m the preparation of polyurethane based aerogels leads to lower density of the oDtained aerogels.

The invention will be further illustrated with respect to the following specific examples, which are given by way of illustration and not as limitations of the scope of this invention.

EXAMPLE 1: Preparation of compound 1.1

A 250 ml 3-necked flask was fitted with a reflux condenser, an addition funnel and a nitrogen gas flow. 0.426 moles (54.95 g) of 2,6- difluoroanilme and 50 ml of t-butanol were charged into the flask and heated to 50°C under mechanical stirring. 0.20 moles (20.0 g) of a 30 % aqueous solution of formaldehyde was added dropwise and stirred magnetically for hour at 50°C. The mixture was allowed to cool to room temperature and transferred to a Parr-reactor where 0.18 mole (18.5 g) of hydrochloric acid, 35 % in 60 ml t-butanol, was fed at 40°C. The temperature was then increased to 125°C for 2 4 hours. The pressure went up to 6 bar. The product was allowed to cool to room temperature and then charged into a 500 ml flask, fitted with a reflux condenser, an addition funnel and a nitrogen flow. To neutralise the product 0.18 mole (7.2 g) of a 50 ⁱ aqueous solution of sodium hydroxide was added dropwise at 50°C. The mixture was stirred for 1 hour resulting in phase separation. The solids were filtered off and washed with dichloromethane to dissolve the product. The dichloromethane was dried over MgSO, and stripped off on a rotavapor. The remaining product was recrystallised from cyclohexane. Overall yield was 80 ϊ . This product was converted into the corresponding fluorinated dnsocyanate (compound II.1) following standard phosgenation procedures.

EXAMPLE 2: Solubility tests

The solubility of some blowing agents in standard polymeric MDI (SUPRASEC DNR available from Imperial Chemical Industries; SUPRASEC is a trademark of Imperial Chemical Industries ) was compared with the solubility of these compounds in a mixture of standard polymeric MDI and 2 * of compound II.1. The results are given in Table 2. The solubility is indicated in - by weight.

TABLE 2 solubility in SUPRASEC solubility in SUPRASEC DNR + DNR 2 ' II.1

HCFC 141b 100 Ϊ 100 * cyclopentane 28 - 30 * n-pentane 9 - 10 - EXAMPLE 3: Polyurethane foam preparation

Polyurethane foams were prepared from the formulations indicated in Table 3 below. Various properties of the obtained foams were measured; the results are also given in Table 3.

The following ingredients were used:

DALTOLAC XR 159 being a polyether polyol available from Imperial Chemical

Industries; DALTOLAC XR 144 being a polyether polyol available from Imperial Chemical

Industries;

DALTOLAC R 130 being a polyether polyol available from Imperial Chemical

Industries;

DALTOLAC R 170 being a polyether polyol available from Imperial Chemical Industries;

DALTOCEL F 455 being a polyether polyol available from Imperial Chemical

Industries;

DALTOLAC XR 124 being a polyether polyol available from Imperial Chemical

Industries; NIAX Al being a catalyst available from Union Carbide;

SFC being a catalyst available from Imperial Chemical Industries;

TEGOSTAB B 8423 being a surfactant available from Goldschmidt;

RS 201 being a surfactant available from Union Carbide;

L 6900 being a surfactant available from Union Carbide; DESMORAPID PV being a catalyst available from Bayer;

SUPRASEC DNR being polymeric MDI available from Imperial Chemical

Industries;

ISO being a mixture of SUPRASEC DNR and 2 r by weight of compound II.1.

DALTOLAC, DALTOCEL and SUPRASEC are trademarks of Imperial Chemical Industries.

TABLE 3

Ref 1 Foam 1 Ref 2 Foam 2

DALTOLAC XR 159 pbw 33.00 33.00 28.50 28.50

DALTOLAC XR 144 pbw 30.00 30.00

DALTOLAC R 130 pbw 31.00 31.00

DALTOLAC R 170 pbw 60.00 60.00

DALTOCEL F 455 pbw 1.50 1.50

DALTOLAC XR 124 pbw 10.00 10.00 NIAX Al pbw 0.30 0.30

SFC pbw 1.20 1.20 3.20 3.20

TEGOSTAB B8423 pbw 1.00 1.00

RS 201 pbw 1.00 1.00

L 6900 pbw 2.50 2.50

DESMORAPID PV pbw 0.40 0.40 water pbw 2.20 2.20 1.94 1.94 cyclopentane pbw 12.00 12.00

HCFC 141b pbw 37.80 37.80

SUPRASEC DNR pbw 140.00 184.16

ISO pbw 140.00 184.16

Index 107 107 129 129

Cream Time sec 10 10 10 10

String Time sec 55 53 42 40

End of Rise Time sec 110 110 90 85

Free Rise Density kg/πr 26.1 26.3 26.1 25.3

Overall Density kg/m^J 32.7 32.9 33.4 33.2

Core Density kg/m 29.7 29.6 30.2 29.8

Closed Cell Content % 92.9 94.6 93.8 95.8

Compression strength at kPa 140.4 139.7 131.4 133.1 10 * (mean)

Modulus (mean) MPa 3.5 3.4 3.2 3.3

Lambda value

Initial mW/mK 22.2 21.8 18.5 18.8

After 7 days at 70°C mW/mK 25.8 25.8 21.9 22.9

After 21 days at 70°C mW/mK 27.6 27.5 23.6 24.2

After 35 days at 70°C mW/mK 27.8 27.6 24.1 24.6

These examples show that foam properties are not detrimentally influenced when fluorinated polyisocyanates according to the present invention are used in the preparation of the foam.

EXAMPLE 4

2.25 g of a polyisocyanate mixture containing 85 % by weight of polymeric MDI (SUPRASEC 2185 available from Imperial Chemical Industries) and 15 % by weight of fluorinated dnsocyanate II.1 was added into a glass jar. A second glass jar contained an homogeneous solution of 72.71 g CH₂C1_ and 0.045 ml catalyst TMR (available from Air Products). The two mixtures were added together and shaked vigorously for a short period of time to ensure full irascibility of the chemicals.

The obtained reaction mixture was left in a quiscent state. After 3 hours gelation occurred and after 24 hours a solid gel was obtained which was supercritically dried. A white hard matrix of medium elasticity having a density of 137 kg_/ , a surface area of 473 m /g and a pore size of 21.9 nm, was obtained.

The same procedure was followed but using only polymeric MDI and no fluorinated polyisocyanate. A white hard matrix of low elasticity having a density of 183 kg/m, a surface area of 431 m'/g and a pore size of 23.9 nm, was obtained.

This example shows that by using a fluorinated polyisocyanate lower density aerogel/powders are obtained.

E<AMPLE 5

5 g of compound II 1 was dissolved in 95 g of A 22 and 0 1 g of Polycat 41 (available from Air Products) was added. After thorough mixing a turbid solution was formed. A white powder formed over 24 hours and precipitated out of the A 22 solution. The A 22 was released by means of evaporation into the air The particle size of the powder was less than 1 μ as determined by SEM.

EXAMPLE 6

3 g of compound II.1 was dissolved in 97 g of dichloromethane. To this mixture 0.06 g of catalyst TMR (available from Air Products) was added while stirring. The πxture was left to gel for 24 hours. The opaque sol-gel was solvent exchanged to liquid CO and supercritically dried from CO . A fine powder was obtained with a specific surface area of 28 m /g and a compact density of 60 kg/m EXAMPLE 7: Preparation of compound 1.3

Example 1 was repeated using 0.341 mole of 2,6-difluoroaniline and 0.085 mole 2, -difluoroaniline. 26 g of a mixture of different species with as main component compound 1.3 was formed.

Following standard phosgenation procedures the corresponding isocyanate was prepared with a yield of 70%.

EXAMPLE 8: Preparation of compound 1.4

Example 1 was repeated using 0.21 mole 2,6-dιfluoroanιline and 0.21 mole 2, 5-difluoroanιlme to give compound 1.4. The ratio between 2,5/2,6 and 2,5/2,5 coupling was 2.4/1. Traces of 2,6/2,6 coupling adducts were found as well.

Following standard phosgenation procedures the product was converted into isocyanate with a yield of 50ι.

EXAMPLE 9: Preparation of compound 1.5

Example 1 was repeated with 0.21 mole aniline and 0.21 mole 2,6- difluoroamline. Product 1.5 was formed but contained highly insoluble polymeric species.

EXAMPLE 10: Preparation of compound 1.7

Example 1 was repeateσ with 0.42 mole 2, 3, 6-trιfluoroanιlιne. The yield of compound 1.7 was 40-.

This product was converted into the corresponding isocyanate using standard phosgenation procedures.

EXAMPLE 11: Preparation of compound 1.9

Example 1 was repeated using 0.42 mole 2, 3, 5, 6-tetrafluoroanilιne to give compound 1.9 with 45- yield.

This product was converted into the corresponding isocyanate with a yield of 50* (corpound II.9).

EXAMPLE 12

Example 4 was repeated employing mixtures of compound II.1 and SUPRASEC DNR (available from Imperial Chemical Industries) in weight ratio of 1/99, 5/95 and 10/9C. The results obtained on the final aerogel are given in Table 4. Table 4

weight ratio II.1/SUPRASEC DNR 1/99 5/95 10/90 density kg/m³ 175 172 155 specific surface area πr/g 700 650 665

EXAMPLE 13

Example 4 was repeated using a mixture of compound II.9 and SUPRASEC DNR (weight ratio 5/95) employing a solvent mixture of dichloromethane and acetone in a weight ratio of 90/10. The final aerogel had a density of 118 kg/rn^ and a specific surface area of 430 πr/g.

Repeating this example increasing the catalyst level to 0.075 ml gave an aerogel with a density of 67 kg/m- and a specific surface area of 172 m'Vg.

Claims

Compound corresponding to general formula (I)

wherein: n, n' and n" each independently represent an integer of from 0 to 4, at least one of n, n' and n" not being equal to 0; m represents an integer of from 0 to 8; and wherein the ammo substituents are situated in ortho, meta or para position with regard to the methylene substituent; with the exception of bis (2,

3, 5, 6-tetrafluoro-4-aminophenyl)methane and bis (3-fluoro-4-aminophenyl)methane.

Compound according to claim 1 wherein m equals 0.

Method for preparing compounds as defined in claim 1 or 2 comprising the step of acid condensation of aniline and formaldehyde, wherein at least one fluorinated aniline is used.

4. Polyol compositions, obtainable by oxyalkylation of (a) initiato (s. characterised in that at least one of the initiators is a compound corresponding to formula (I)

wherein: n, n' and n" each independently represent an integer of from 0 to 4, at least one of n, r.' and n" not being equal to 0; m represents an integer of from 0 to 8; and wherein the amino substituents are situated in ortho, meta or para position with regard to the methylene substituent.

Method for preparing a polyol composition by oxyalkylation of (a) initiator (s) , characterised in that at least one of the initiators is a compound corresponding to formula (I)

wherein: n, n' and n" each independently represent an integer of from 0 to 4, at least one of n, n' and n" not being equal to 0; m represents an integer of from 0 to 8; and wherein the amino substituents are situated in ortho, meta or para position with regard to the methylene substituent.

Polyisocyanate corresponding to general formula (II)

wherein: n, n' and n" each independently represent an integer of from 0 to 4, at least one of n, n' and n" not being equal to 0; m represents an integer of from 0 to 8; and wherein the isocyanato substituents are situated in ortho, meta or para position with regard to the methylene substituent.

Polyisocyanate according to claim 6 wherein m equals 0.

Polyisocyanate according to claim 7, being bis (3, 5-difluoro-4-isocyanatophenyl) methane or bis (2, 3, 5, 6-tetrafluoro- 4 -isocyanatophenyl) methane.

Method for preparing a polyisocyanate as defined in any one of claims 6 to 8 by phosgenation of a compound corresponding to general formula

wherein : n, n' and n" each independently represent an integer of from 0 to 4, at least one of n, n¹ and n" not being equal to 0; m represents an integer of from 0 to 8; and wherein the amino substituents are situated in ortho, meta or para position with regard to the methylene substituent.

10. Method for preparing a polyurethane material by reacting a polyol composition with a polyisocyanate composition, characterised in that the polyol composition comprises a polyol as defined in claim 4 or/and the polyisocyanate composition comprises a polyisocyanate as defined in any one of claims 6 to 8.

11. Method according to claim 10 wherein said polyurethane material is a rigid foam.

12. Method for preparing a polyisocyanurate material by trimerismg a polyisocyanate composition, characterised in that the polyisocyanate composition comprises a polyisocyanate as defined in any one of claims 6 to 8.

13. Method for preparing a polyurethane material by reacting a polyol with a polyisocyanate in the presence of a chain extender, characterised in that the chain extender is a compound as defined in claim 1 or 2.

14. Polyol composition containing a chain extender in an amount of from 0.1 to 20 parts by weight based on the total composition, characterised in that the chain extender is a compound as defined in claim 1 or 2.

15. Method for preparing an aerogel comprising the steps of a) mixing an organic polyisocyanate and an isocyanate trimerisation catalyst in a suitable solvent, b) maintaining said mixture in a quiescent state for a sufficiently long period of time to form a polymeric gel, and c) supercritically drying the obtained gel, characterised in that the organic polyisocyanate comprises a compound as defined in any one of claims 6 to 8.

16. Polyurethane based material obtainable by the method as defined any one of claims 10, 11, 12, 13 and 15.