WO2022073835A1

WO2022073835A1 - Method for producing polyurethane foams or hydrogels by employing amine chain extenders

Info

Publication number: WO2022073835A1
Application number: PCT/EP2021/076899
Authority: WO
Inventors: Jim Thompson; Jan SUETTERLIN; Marc-Stephan Weiser; Sascha Plug; Rafael METHLING; Sebastian Doerr
Original assignee: Covestro Deutschland Ag
Priority date: 2020-10-05
Filing date: 2021-09-30
Publication date: 2022-04-14

Abstract

The invention provides a process for producing polyurethane foams or hydrogels, in which compositions comprising A) isocyanate-functional prepolymers obtainable by the reaction of A1)low molecular weight diisocyanates of molar mass from 140 to 278 g/mol, with A2)polyalkylene oxides having an OH functionality of two or more, A3)optionally further isocyanate-reactive components differing from A2); B) water in an amount of at least 2% by weight, based on the total weight of the composition; C) optionally polyisocyanates obtainable by reaction of at least two low molecular, preferably aliphatic diisocyanates, wherein the diisocyanates having a molar mass of 140 to 278 g/mol, D) optionally catalysts; E) optionally salts of weak acids, the corresponding free acids of which have a pKA in water at 25°C of ≥ 3.0 and ≤ 14.0; F) optionally surfactants; and G) optionally mono- or polyhydric alcohols or polyols; H) optionally hydrophilic polyisocyanates obtainable by reaction of H1) low molecular weight diisocyanates of molar mass from 140 to 278 g/mol and/or polyisocyanates preparable therefrom and having an average isocyanate functionality of 2 to 6 with H2) monohydroxyfunctional polyalkylene oxides of OH number from 10 to 250 and of oxyethylene unit content from 50 to 100 mol%, based on the total amount of the oxyalkylene groups present, I) a polyamine with at least two amine groups or two ammonium groups, preferably a diamine, are provided, optionally foamed and cured, wherein the isocyanate containing components, especially components A), C) and H), do not exceed a residual diisocyanate content of 8% by weight, based on the total weight of the polyurethane foam or hydrogel and wherein the ratio of amine groups stemming from component I) to isocyanate groups of all components A) to I) is in a range of 0.1 to 1.2. These foams or hydrogels are used in wound dressings, cosmetic articles or incontinence products.

Description

Method for producing polyurethane foams or hydrogels by employing amine chain extenders

The invention provides a process for producing polyurethane foams or polyurethane hydrogels, in which compositions comprising A) isocyanate-functional prepolymers obtainable by the reaction of Al) low molecular weight diisocyanates of molar mass from 140 to 278 g/mol, with A2) polyalkylene oxides having an OH functionality of two or more and optionally A3) further isocyanate-reactive components differing from A2); B) water in an amount of at least 2% by weight, based on the total weight of the composition; C) optionally polyisocyanates composed of at least two low molecular weight, aliphatic diisocyanates; D) optionally catalysts: E) optionally salts of weak acids, the corresponding free acids of which have a pKA in water at 25°C of > 3.0 and < 14.0; F) optionally surfactants; G) optionally mono- or polyhydric alcohols or polyols; H) optionally hydrophilic polyisocyanates; I) a polyamine, are provided, wherein the ratio of amine groups to isocyanate groups of all components A) to I) is in a range of 0.1 to 1.2. Also the foams and hydrogels thus produced and the uses thereof are part of the invention.

Water absorbing polyurethanes are useful for many applications such as foam or hydrogel based wound dressings, incontinence pads or hydrogel contact lenses. Foams are highly porous materials with low density. In the case of wound dressing foams, densities are often around 100 g/L. With increasing density the material may be called a porous hydrogel until it is a pure and compact hydrogel without any visible pores. There is no sharp boundary between the two extremes. Regardless of terminology, regarding foams and hydrogels, important mechanical properties, such as tensile strength at break, drastically decline upon swelling of the foams or hydrogels when coming into contact with fluids. Especially, for the application in wound dressings, water absorbing polyurethanes in the form of foams or hydrogels that retain high wet-tensile-strength-at-break (oB.wet) despite good water absorption are desirable.

Since the density of the material, like foams or hydrogels, has also a strong influence on the mechanical properties it is not easy to say which basic materials would directly reach the goal of retaining wet high wet-tensile-strength-at-break (oB.wet) and good water absorption. Solely, comparing absolute values of wet-tensile-strength-at-break (oB.wet) for the different materials like low density foams, high density foams and hydrogels, does not allow for assessing the mechanical performance of the polymer material they are made of. However, dividing OB.wet by density (D) delivers a value that accounts for density differences and therefore normalizes the value of wet-tensile-strength-at-break (oB.wet) with respect to the density. However, it is not desirable to increase wet-tensile-strength-at-break (oB.wet) by simply reducing water absorption of the material because water absorption is an essential feature for the application in wound dressings and incontinence pads of these polymeric materials. Consequently, a material at low density with high water absorption that displays high OB.wet is desirable.

When absorbing water, the material swells. Here, swelling was described as an expansion factor S in one dimension, i.e., the increase of a cross-section of a sample can be described by a factor S². Since tensile stress depends on the tensile force per cross-sectional area and water does not contribute to the tensile stress it is expected that wet-tensile-strength-at-break (oB.wet) drops by at least the factor S². Based on these considerations the term (oB,wet/D)-S² is useful to assess the performance of the material of the foam or hydrogel in the wet state independent from density and extent of swelling.

Foams with good wet-tensile-strength-at-break (oB.wet) are already known. For instance, a foam from prepolymer example 4 of US2006142529 was synthesized (comparative example 1 in this document) and used to obtain a foam with an excellent (oB,wet/D)-S² value of 0.61. However, all foams in US2006142529 were synthesized from prepolymers that were not distilled after synthesis, hence, containing more than at least 8% residual diisocyanate. Due to the low vapor pressure of diisocyanate monomers foam or hydrogel manufacturers require an exhaustion system for safe manufacturing of foams and hydrogels.

Another disadvantage of the prepolymers in US2006142529 is that they are based on aromatic isocyanates. Furthermore, for many manufacturing processes it is desirable to use prepolymers with viscosities lower than 25000 mPas, preferably lower than 10000 mPas. Many aromatic prepolymers do not meet this requirement. Moreover, removing the residual diisocyanate by distillation will lead to a further drastic increase of viscosity. An additional disadvantage of aromatic prepolymers is that foams produced from aromatic prepolymers are inherently yellowing.

All foams in US2006142529 are based on aromatic isocyanates and contain > 8% monomeric diisocyanates. Similar foams are known from US3903232, US4137200 and US5849850.

Prior art documents EP2143744, EP2470580 EP2632501 and WO19137879, describe foams produced from aliphatic isocyanate prepolymers where the residual diisocyanate was removed via distillation. However, good wet strength performance was not mentioned in any of them.

None of the prior art mention amines as component for the production of polyurethane foams.

An aim that has not been achieved to date in the production of polyurethane foams or hydrogels, especially in the use thereof in medical applications, is to provide an efficient process and allows for a cost efficient processability leading to a foam with good and almost unchanged properties both in dry and in wet state.

Furthermore, it was an aim to provide compositions for the production of foams that allow the manufacturing of foams or hydrogels that provide high water absorption and/or high wet-tensile- strength-at-break (oB.wet), especially high values of (oB,wet/D)-S².

One aim of the present invention was that of at least partly overcoming at least one disadvantage of the prior art. Furthermore, it was a goal to find favourable prepolymers that are easily pumpable and show good properties when mixed with components comprising water.

Therefore, it was a goal to produce foams or hydrogels by a fast and safe process which retain their hydrophilicity and ability to swell, especially as indicated by an edge length expansion factor S of at least 1.05. Furthermore, it was a goal that the wet elongation at break of the produced foams or hydrogels should be higher than 50%. In the particular case of foams with densities lower than 200 g/L the absolute wet-tensile-strength-at-break (oB.wet) should be at least 19 kPa.

A further goal of the invention was to provide foams with good wet strength performance as indicated by (oB,wet/D)-S² values of at least 0.30, especially together with the properties and production features as mentioned above.

Furthermore, a high performing material which is characterized by a high (oB.wet) despite low density and high water absorption was a goal of the invention.

It has been found that, surprisingly, the combination of features of the subject-matter of Claim 1 was able to solve at least one of the mentioned problems or have reached the mentioned aims.

The invention firstly relates to a process for producing polyurethane foams or hydrogels, in which compositions comprising

A) isocyanate-functional prepolymers obtainable by the reaction of

Al) low molecular weight diisocyanates of molar mass from 140 to 278 g/mol, with

A2) polyalkylene oxides having an OH functionality of two or more, preferably within a range from 2 to 6, preferably within a range from 2 to 5, or preferably 2 to 4,

A3) optionally further isocyanate-reactive components differing from A2) ;

B) water in an amount of at least 2% by weight, preferably of at least 3% by weight, more preferably of at least 5% by weight, or preferably of at least 10% by weight, based on the total weight of the composition or preferably within a range from 2% to 40% by weight, or preferably within a range from 5% to 30% by weight, or preferably within a range from 10% to 25% by weight, based on the total weight of the composition;

C) optionally polyisocyanates obtainable by reaction of at least two low molecular, preferably aliphatic diisocyanates, wherein the diisocyanates having a molar mass of 140 to 278 g/mol;

D) optionally catalysts;

E) optionally salts of weak acids, the corresponding free acids of which have a pKA in water at

F) optionally surfactants; and

G) optionally mono- or polyhydric alcohols or polyols;

H) optionally hydrophilic polyisocyanates obtainable by reaction of

Hl) low molecular weight diisocyanates of molar mass from 140 to 278 g/mol and/or polyisocyanates preparable therefrom and having an average isocyanate functionality of 2 to 6 with

H2) monohydroxyfunctional polyalkylene oxides of OH number from 10 to 250 and of oxy ethylene unit content from 50 to 100 mol%, based on the total amount of the oxyalkylene groups present,

I) a polyamine with at least two amine groups or two ammonium groups, preferably a diamine; are provided, eventually foamed and cured, wherein the ratio of amine groups stemming from component I) to isocyanate groups of all components A) to I) is in a range of 0.1 to 1.2 wherein the isocyanate containing components, especially components A), C) and H), do not exceed a residual diisocyanate content of 8% by weight, based on the total weight of the polyurethane foam or hydrogel.

Preferably, the prepolymers A) have a residual monomer content of below 1% by weight, preferably below 0.8% by weight, more preferably below 0.75% by weight, especially preferably below 0.5% by weight, based on the total weight of the prepolymer.

Preferably, the components A), C) and H) have a residual diisocyanate content of below 5% by weight, more preferably below 3% by weight, especially preferably below 2% by weight, even more preferably below 0.5% by weight, most preferably below 0.1% by weight, based on the total weight of the components A), C) and H).

The residual diisocyanate content according to the invention means the content of diisocyanates which have a molar mass from 140 to 278 g/mol.

In the preparation of the isocyanate-functional prepolymers A), the amounts of polyalkylene oxides A2), the optionally further isocyanate-reactive components, differing from A2), A3), and the low molecular weight, preferably aliphatic diisocyanates Al) are preferably adjusted such that, for every 1 mol of OH groups of the combined components A2) and A3), there are provided 1.1 to 20 mol, preferably 1.5 to 10 mol and more preferably 2 to 5 mol of NCO groups of the low molecular weight, preferably aliphatic diisocyanate Al).

In the preparation of the isocyanate-functional prepolymers A), the amounts of polyalkylene oxides A2), the optionally further isocyanate-reactive components A3) and the low molecular weight, preferably aliphatic diisocyanates Al) are preferably adjusted such that, for every 1 mol of isocyanate reactive groups of the combined components A2) and A3), there are provided 1.1 to 20 mol, preferably 1.5 to 10 mol and more preferably 2 to 5 mol of NCO groups of the low molecular weight, preferably aliphatic diisocyanate Al).

The reaction can be effected in the presence of urethanization catalysts such as tin compounds, zinc compounds, amines, guanidines or amidines, or in the presence of allophanatization catalysts such as zinc compounds.

Other catalysts as mentioned later as representative of component D) may also be present when reacting components Al) to A3) to receive the prepolymer Al). However, it is preferred not to use a catalyst when reacting component Al) to A3).

The reaction is typically performed at 25°C to 140°C, preferably 60°C to 100°C.

If excess isocyanate has been employed, preferably the excess of low molecular weight, preferably aliphatic diisocyanate is then removed, preferably by thin-fdm distillation using a thin-fdm evaporator.

Before, during and after the reaction or the distillative removal of the excess diisocyanate, preference is given to adding acidic or alkylating stabilizers, such as benzoyl chloride, isophthaloyl chloride, methyl tosylate, chloropropionic acid, HC1, dibutyl phosphate or antioxidants such as di-tert-butylcresol or tocopherol.

Preferably, the NCO content of the isocyanate-functional prepolymers A) is 1.5% to 8% by weight.

Examples of low molecular weight, aliphatic diisocyanates of component Al) are hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), butylene diisocyanate (BDI), pentamethylene diisocyanate (PDI), bisisocyanatocyclohexylmethane (HMDI), 2,2,4-trimethylhexamethylene diisocyanate, bisisocyanatomethylcyclohexane, bisisocyanatomethyltricyclodecane, xylene diisocyanate, tetramethylxylylene diisocyanate, norbomane diisocyanate, cyclohexane diisocyanate or diisocyanatododecane, preference being given to hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), butylene diisocyanate (BDI), pentamethylene diisocyanate (PDI), and bis(isocyanatocyclohexyl)methane (HMDI). Particular preference is given to hexamethylene diisocyanate and pentamethylene diisocyanate.

If aromatic diisocyanates are used as component Al), these are preferably toluene 2,4-diisocyanate (2,4- TDI), toluene 2,6-diisocyanate (2,6-TDI) or 2,2 ’-methylene diphenyl diisocyanate (2,2’-MDI), 2.4'- methylene diphenyl diisocyanate (2,4’-MDI), 4,4 ’-methylene diphenyl diisocyanate (4,4’-MDI), or mixtures of at least two of these. Polyalkylene oxides of component A2) may be any polyalkylene oxides that the person skilled in the art would use for the purpose. Examples of these are selected from the group consisting of polyethylene oxide, polypropylene oxide, polytetrahydrofuran or a mixture of at least two of these. Polyalkylene oxides of component A2) are preferably copolymers of ethylene oxide and propylene oxide having an oxyethylene unit content, based on the total amount of the oxyalkylene groups present, of 50 to 100 mol%, preferably 60 to 90 mol%, started from polyols or amines. Preferred starters of this kind are selected from the group consisting of ethylene glycol, propane-1, 3-diol, propane-1,2 diol (propylene glycol), dipropylene glycol, butane- 1,4-diol, glycerol, trimethylolpropane (TMP), sorbitol, pentaerythritol, triethanolamine, ammonia and ethylenediamine, or a mixture of at least two of these.

The polyalkylene oxides of component A2) typically have number-average molecular weights of 250 to 10 000 g/mol, preferably of 300 to 2800 g/mol, more preferably 350 to 1500 g/mol.

In addition, the polyalkylene oxides of component A2) have OH functionalities of 2 to 6, preferably of 2 to 5, more preferably of 2 to 4.

Preferably, component A3) is a polyol. More preferably, A3) is a diol.

Preferably, A3) is linear, especially a linear diol. Preferably, component A3) is selected from the group consisting of 1,2-ethandiol, 2-(2-hydroxyethoxy)ethan-l-ol, 1,2 propanediol, 1,3 propanediol, 1,2 butanediol, 1,3 butanediol, 1,4 butanediol, 1,2 pentanediol, 1,3 pentanediol, 1,4 pentanediol, 1,5 pentanediol, 1,2 hexanediol, 1,3 hexanediol, 1,4 hexanediol, 1,5 hexanediol, 1,6 hexanediol, 1,2 heptanediol, 1,3 heptanediol, 1,4 heptanediol, 1,5 heptanediol, 1,6 heptanediol, 1,7 heptanediol, 1,2 octanediol, 1,3 octanediol, 1,4 octanediol, 1,5 octanediol, 1,6 octanediol, 1,7 octanediol, 1,8 octanediol, 1,2 nonanediol, 1,3 nonanediol, 1,4 nonanediol, 1,5 nonanediol, 1,6 nonanediol, 1,7 nonanediol, 1,8 nonanediol, 1,9 nonanediol, 1,2 decanediol, 1,3 decanediol, 1,4 decanediol, 1,5 decanediol, 1,6 decanediol, 1,7 decanediol, 1,8 decanediol, 1,9 decanediol, 1,10 decanediol, 1,2 undecanediol, 1,3 undecanediol, 1,4 undecanediol, 1,5 undecanediol, 1,6 undecanediol, 1,7 undecanediol, 1,8 undecanediol, 1,9 undecanediol, 1,10 undecanediol, 1,11 undecanediol, 1,2 dodecanediol, 1,3 dodecanediol, 1,4 dodecanediol, 1,5 dodecanediol, 1,6 dodecanediol, 1,7 dodecanediol, 1,8 dodecanediol, 1,9 dodecanediol, 1,10 dodecanediol, 1,11 dodecanediol, 1,12 dodecanediol or mixtures of at least two thereof. Most preferably, A3) is selected from the group consisting of 1,2-ethandiol, 2- (2-hydroxyethoxy)ethan-l-ol, 1,3 propanediol, 1,4 butanediol, 1,6 hexanediol, 1,8 octanediol, 1,10 decanediol, 1,12 dodecanediol or mixtures of at least two thereof.

Further components for A3), in principle, preference is given to using any of the mono- and polyhydric alcohols or mono- and polyfunctional amines that are known per se to the person skilled in the art, and mixtures thereof. These are mono- or polyhydric alcohols or polyols that are different to those of the component A2), such as ethanol, propanol, butanol, decanol, tridecanol, hexadecanol, ethylene glycol, neopentyl glycol, trimethylolpropane, glycerol, pentaerythritol, monofunctional polyether alcohols and polyester alcohols, polyetherdiols and polyesterdiols or mixtures of at least two of these. Examples of mono- or polyfunctional amines include butylamine, ethylenediamine or amine-terminated polyalkylene glycols (e.g. Jeffamine®).

In the preparation of the prepolymer A), it is possible to use catalysts as described for component D) for example.

Water as component B) is employed in at least 2% by weight, preferably of at least 5% by weight, or preferably of at least 10% by weight, or preferably within a range from 2% to 40% by weight, or preferably within a range from 5% to 30% by weight, or preferably within a range from 10% to 25% by weight, based on the total weight of the composition.

Any compounds of component C) that are optionally to be used are polyisocyanates obtainable by reaction of low molecular weight diisocyanates having amolar mass of 140 to 278 g/mol, such as biurets, oxadiazinetrione, allophanates, isocyanurates, iminooxadiazinediones or uretdiones of the aforementioned low molecular weight diisocyanates. Preference is given to using preferably aliphatic diisocyanates for component C). Preferably, the 4-membered or 6-membered ring oligomers of low molecular weight diisocyanates have a functionality within a range from 2 to 6, or preferably within a range from 2.1 to 5.5, or preferably within a range from 2.5 to 5.

Preferably, the component C) has a residual diisocyanate content of below 1% by weight, preferably below 0.8% by weight, more preferably below 0.75% by weight, especially preferably below 0.5% by weight, based on the total weight of the component C).

Examples of low molecular weight, aliphatic diisocyanates of component C) are hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), butylene diisocyanate (BDI), pentamethylene diisocyanate (PDI), bisisocyanatocyclohexylmethane (HMDI), 2,2,4-trimethylhexamethylene diisocyanate, bisisocyanatomethylcyclohexane, bisisocyanatomethyltricyclodecane, xylene diisocyanate, tetramethylxylylene diisocyanate, norbomane diisocyanate, cyclohexane diisocyanate or diisocyanatododecane, preference being given to hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), butylene diisocyanate (BDI), pentamethylene diisocyanate (PDI), and bis(isocyanatocyclohexyl)methane (HMDI). Particular preference is given to PDI, HDI, IPDI, very particular preference to hexamethylene diisocyanate and pentamethylene diisocyanate.

If aromatic polyisocyanates are used as component C), these are preferably toluene 2,4-diisocyanate (2,4-TDI), toluene 2,6-diisocyanate (2,6-TDI) or 2,2’-methylene diphenyl diisocyanate (2,2’-MDI), 2,4 ’-methylene diphenyl diisocyanate (2,4 ’-MDI), 4,4 ’-methylene diphenyl diisocyanate (4,4 ’-MDI), or mixtures of at least two of these. The content of isocyanate groups elevated by the use of component C) ensures better foaming since more CO2 is formed in the isocyanate-water reaction.

To accelerate the urethane formation, catalysts can be used in component D). These are typically the compounds known to the person skilled in the art from polyurethane technology. Preference is given here to compounds from the group consisting of catalytically active metal salts, amines, amidines and guanidines. Examples include dibutyltin dilaurate (DBTL), tin acetate, 1,8- diazabicyclo[5.4.0]undecene-7 (DBU), l,5-diazabicyclo[4.3.0]nonene-5 (DBN), 1,4- diazabicyclo[3.3.0]octene-4 (DBO), N-ethylmorpholine (NEM), triethylenediamine (DABCO), pentamethylguanidine (PMG), tetramethylguanidine (TMG), cyclotetramethylguanidine (TMGC), n- decyltetramethylguanidine (TMGD), n-dodecyltetramethylguanidine (TMGDO), dimethylaminoethyltetramethylguanidine (TMGN), 1,1,4,4,5,5-hexamethylisobiguanidine (HMIB), phenyltetramethylguanidine (TMGP) and hexamethyleneoctamethylbiguanidine (HOBG), dimethylaminopropylamine (DMAPA).

Preference is given to the use of amines, amidines, guanidines or mixtures thereof as catalysts of component D). In addition, preference is also given to the use of l,8-diazabicyclo[5.4.0]undecene-7 (DBU), l,5-diazabicyclo[4.3.0]nonene-5 (DBN), triethylenediamine (DABCO).

It is preferred not to use catalysts at all.

As component E) it is optionally possible to use salts of weak acids, the corresponding free acids of which have a pKA in water at 25°C of > 3.0 and < 14.0. Examples of suitable salts of weak acids are potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate and sodium hydrogencarbonate, sodium acetate, potassium acetate, sodium citrate, potassium citrate, sodium benzoate, potassium benzoate, also including any desired mixtures of these salts. It is preferable when the salts of weak acids are selected from the group of sodium hydroxide, sodium hydrogencarbonate and sodium carbonate. In this case, the result is a particularly short reaction time.

In the case of forming a foam, to improve foam formation, foam stability or the properties of the resulting polyurethane foam, compounds of component F) may be used, where such additives may in principle be any of the anionic, cationic, amphoteric and nonionic surfactants that are known per se, and mixtures of these. Preference is given to using alkyl polyglycosides, EO/PO block copolymers, alkyl or aryl alkoxylates, siloxane alkoxylates, esters of sulfosuccinic acid and/or alkali metal or alkaline earth metal alkanoates or mixtures of at least two of these. Particular preference is given to using EO/PO block copolymers. Preference is given to using solly the EO/PO block copolymers as component F).

In addition, to improve the foam or hydrogel properties of the resulting polyurethane foam, compounds of component G) may be used. These are in principle all the mono- and polyhydric alcohols that are known per se to the person skilled in the art, and mixtures of these. These are mono- or polyhydric alcohols or polyols, such as ethanol, propanol, butanol, decanol, tridecanol, hexadecanol, ethylene glycol, neopentyl glycol, butanediol, hexanediol, decanediol, trimethylolpropane, glycerol, pentaerythritol, monofunctional polyether alcohols and polyester alcohols, polyetherdiols and polyesterdiols or mixtures of at least two of these.

In the preparation of the hydrophilic polyisocyanates H), the ratio of the monohydroxyfunctional polyalkylene oxides H2) to the low molecular weight diisocyanates Hl) is typically adjusted such that, for every 1 mol of OH groups of the monohydroxyfunctional polyalkylene oxides, there are 1.25 to 20 mol, preferably 2 to 15 mol and more preferably 5 to 13 mol of NCO groups of the low molecular weight diisocyanate Hl). This is followed by allophanatization or biuretization and/or isocyanurate formation or uretdione formation. If the polyalkylene oxides H2) are bonded to the preferably aliphatic diisocyanates Hl) via urethane groups, allophanatization preferably takes place thereafter. It is further preferable that isocyanate structural units are formed.

A preferred alternative preparation of the hydrophilic polyisocyanates H) is typically effected by reaction of 1 mol of OH groups of the monohydroxyfunctional polyalkylene oxide component H2) with 1.25 to 20 mol, preferably with 2 to 15 mol and more preferably 5 to 13 mol of NCO groups of a polyisocyanate Hl) having an isocyanate functionality of 2 to 6, based on aliphatic or aromatic diisocyanates, preferably aliphatic diisocyanates. Examples of such polyisocyanates Hl) are biuret structures, isocyanurates or uretdiones based on preferably aliphatic diisocyanates. The polyisocyanate Hl) and the polyalkylene oxide H2) are preferably joined to one another via a urethane group or a urea group, preference being given particularly to linkage via urethane groups.

Preferably, the component H) has a residual diisocyanate content of below 1% by weight, preferably below 0.8% by weight, more preferably below 0.75% by weight, especially preferably below 0.5% by weight, based on the total weight of the component H).

The polyamine, preferably the diamine of component I) can be any polyamine that the person skilled in the art would select for the process to form a foam or hydrogel. Preferably, the polyamine of component I) comprises secondary or primary amine groups or both, more preferably solely primary amine groups. Preferably, the polyamine is able to react with an NCO-group by building a urea group. Preferably, the amine groups are terminally positioned. Preferably, the polyamine has a molecular weight in a range of from 50 to 400 g/mol, more preferably in a range of from 60 to 300 g/mol. Preferably, the backbone of the diamine is a hydrocarbon chain without hetero atoms. Preferably, the backbone of the polyamine is a linear hydrocarbon chain. A linear hydrocarbon chain, according to the invention is an unbranched alkylene-group. Preferably, the polyamine is linear and comprises secondary amine groups. More preferably, the polyamine is linear and comprises primary amine groups. Preferably, the polyamine is a diamine which is linear and comprises secondary amine groups. More preferably, the polyamine is a diamine which is linear and comprises primary amine groups

Preferably, the polyamine has at least two ammonium groups. Preferably, the polyamine is provided at least partially in the form of an ammonium salt like ammoniumformate or ammoniumhydrogencarbonate, more preferably as an ammoniumhydrogencarbonate.

The component I) is preferably selected from the group consisting of a diamine or a triamine or both. Examples of a triamine are diethylenetriamine and dipropylenetriamine.

The component I) preferably comprises a diamine which is selected from the group consisting of 1,2- ethane diamine 1,3-propane diamine, 1,4- butane diamine, 1,5-pentamethylenediamine, 1,6- hexamethylenediamine, 1,7-heptamethylenediamine, 1,8 -octamethylenediamine, 1,10- decamethylenediamine, 1, 12-dodecamethylenediamine or a mixture of at least two thereof.

In a preferred embodiment, component I) comprises an aliphatic polyamine, preferably an aliphatic diamine, more preferably a linear aliphatic diamine as the polyamine I).

Preferably, the diamine is selected from the group consisting of 1,3-butane diamine, 1,4- propane diamine, 1,5-pentamethylenediamine, 1,6-hexamethylenediamine, 1,7-heptamethylenediamine, 1,8- octamethylenediamine, 1,10-decamethylendiamine, 1,12-dodecamethylendiamine or a mixture of at least two thereof.

Preferably, the polyamine I) is provided as ammonium salt, more preferably as ammoniumhydrogencarbonate .

In a preferred embodiment, the component I) comprises the polyamine as ammonium salt, preferably as ammoniumhydrogencarbonate or ammoniumformate, more preferably as ammonium salt of 1,6- hexamethylenediamine, especially preferably as hexane- 1,6-diammonium hydrogencarbonate. Preferably, the hydrogenecarbonate is used as the anion of the ammoniumhydrogencarbonate. In the case hydrogenecarbonate is used as the anion of the ammonium salt, the ammoniumhydrogencarbonate salt can be formed by the addition of carbon dioxide, for example in the form of dry ice either as solid or fluid, to an aqueous solution of the polyamine. The ammonium salt is in equilibrium with a small amount of the un-protonated amine of the polyamine I). By reacting un-protonated amine of the component I) with at least component A), C) and H) new un-protonated amine is reformed from the rest ammonium salt. Carbondioxide evolves as gas during this process.

In a preferred embodiment the isocyanate-containing components, especially components A), C) and H), have a total isocyanate content within a range from 2% to 12% by weight, more preferably in a range from 2% to 10% by weight, even more preferably in a range from 2% to 8% by weight, based on the total amount of the isocyanate-containing components.

Preferably, the isocyanate-containing components, especially components A), C) and H) have a content of urethane groups of 1.0 to 3.5 mol/kg, based on the total amount of the isocyanate-containing components. Preferably, the isocyanate-containing components, especially components A), C) and H), have a total isocyanate content within a range from 3% to 7% by weight or preferably within a range from 4% to 6.5% by weight, and preferably a content of urethane groups within a range from 1.5 to 3.0 mol/kg, or preferably within a range from 1.7 to 2.8 mol/kg, based in each case on the total amount of the isocyanate-containing components.

Preference is given to using aliphatic diisocyanates in the production of polyurethane foams or hydrogels of the invention. More particularly, preference is given to using exclusively aliphatic diisocyanates for components Al), C) and Hl).

Preference is given to using linear diisocyanates in the production of polyurethane foams or hydrogels of the invention. More particularly, preference is given to using exclusively linear diisocyanates for components Al), C) and Hl).

The reaction is typically performed at 25°C to 140°C, preferably at 60°C to 100°C.

If excess low molecular weight diisocyanate has been employed, the excess of low molecular weight, preferably aliphatic diisocyanate is then removed, preferably by thin-fdm distillation.

Before, during and/or after the reaction or the distillative removal of the excess diisocyanate, it is possible to add acidic or alkylating stabilizers, such as benzoyl chloride, isophthaloyl chloride, methyl tosylate, chloropropionic acid, HC1 or antioxidants such as di-tert-butylcresol or tocopherol.

The NCO content of the hydrophilic polyisocyanates H) is preferably 0.3% to 23% by weight, more preferably 2% to 21% by weight and most preferably 3% to 18% by weight.

Examples of low molecular weight, aliphatic diisocyanates of component Hl) are hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), butylene diisocyanate (BDI), pentamethylene diisocyanate (PDI), bisisocyanatocyclohexylmethane (HMDI), 2,2,4-trimethylhexamethylene diisocyanate, bisisocyanatomethylcyclohexane, bisisocyanatomethyltricyclodecane, xylene diisocyanate, tetramethylxylylene diisocyanate, norbomane diisocyanate, cyclohexane diisocyanate or diisocyanatododecane, preference being given to hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), butylene diisocyanate (BDI), pentamethylene diisocyanate (PDI), and bis(isocyanatocyclohexyl)methane (HMDI). Particular preference is given to PDI, HDI, IPDI, very particular preference to hexamethylene diisocyanate and pentamethylene diisocyanate.

If aromatic diisocyanates are used as component Hl), these are preferably toluene 2,4-diisocyanate (2,4- TDI), toluene 2,6-diisocyanate (2,6-TDI) or 2,2 ’-methylene diphenyl diisocyanate (2,2’-MDI), 2.4'- methylene diphenyl diisocyanate (2,4’-MDI), 4,4 ’-methylene diphenyl diisocyanate (4,4’-MDI), or mixtures of at least two of these.

Examples of higher molecular weight polyisocyanates H2) are polyisocyanates having an average isocyanate functionality of 2 to 6 with isocyanurate, urethane, allophanate, biuret, iminooxadiazinetrione, oxadiazinetrione and/or uretdione groups, based on the preferably aliphatic and/or cycloaliphatic diisocyanates mentioned in the paragraph above.

Components H2) used are preferably higher molecular weight compounds with biuret, iminooxadiazinedione, isocyanurate and/or uretdione groups, based on hexamethylene diisocyanate, isophorone diisocyanate and/or 4,4'-diisocyanatodicyclohexylmethane. Preference is further given to isocyanurates. Very particular preference is given to structures based on hexamethylene diisocyanate.

The monohydroxyfunctional polyalkylene oxides H2) have an OH number of 15 to 250, preferably of 28 to 112, and an oxyethylene unit content of 50 to 100 mol%, preferably of 60 to 100 mol%, based on the total amount of the oxyalkylene groups present.

Monohydroxyfunctional polyalkylene oxides in the context of the invention are understood to mean compounds that have only one isocyanate-reactive group, i.e. one group that can react with an NCO group.

The preparation of polyalkylene oxides H2) by alkoxylation of suitable starter molecules is known from the literature (e.g. Ullmanns Encyclopadie der technischen Chemie [Ullmann's Encyclopedia of Industrial Chemistry], 4th edition, volume 19, Verlag Chemie, Weinheim p. 31-38). Suitable starter molecules are especially saturated monoalcohols such as methanol, ethanol, n-propanol, isopropanol, n- butanol, isobutanol, sec-butanol, diethylene glycol monobutyl ether, and aromatic alcohols such as phenol or monoamines such as diethylamine. Preferred starter molecules are saturated monoalcohols of the aforementioned type. Particular preference is given to using diethylene glycol monobutyl ether or n- butanol as starter molecules.

The monohydroxyfunctional polyalkylene oxides H2) typically have number-average molecular weights of 220 to 3700 g/mol, preferably of 250 to 2800 g/mol, or preferably of 300 to 2000 g/mol. The monohydroxyfunctional polyalkylene oxides H2) preferably have an OH group as isocyanatereactive group.

Typically, components A) to I) are used in the following amounts:

100 parts by weight of isocyanate-functional prepolymers A)

0. 1 to 200 parts by weight of water or a nonaqueous isocyanate-reactive component B)

0 to 30 parts by weight of heterocyclic oligomers C)

0 to 1 part by weight of catalysts D)

0 to 5 parts by weight of salts of weak acids, the corresponding free acids of which have a pKA in water at 25°C of > 3.0 and < 14.0 E)

0 to 10 parts by weight of surfactants F)

0 to 20 parts by weight of alcohols G)

0.5 to 50 parts by weight of hydrophilic polyisocyanate component H) polyamine I) in an amount wherein the ratio of amine groups stemming from component I) to isocyanate groups of all components A) to I) is in a range of 0.1 to 1.2.

Preferably, components A) to I) are used in the following amounts:

100 parts by weight of isocyanate-functional prepolymers A)

0. 1 to 100 parts by weight of water or a nonaqueous isocyanate-reactive component B)

1 to 20 parts by weight of heterocyclic oligomers C)

0 to 1 part by weight of catalysts D)

0 to 5 parts by weight of surfactants F)

0 to 10 parts by weight of alcohols G)

1 to 25 parts by weight of hydrophilic polyisocyanates H) polyamine I) in an amount wherein the ratio of amine groups stemming from component I) to isocyanate groups of all components A) to I) is in a range of 0.1 to 1.2.

More preferably, components A) to I) are used in the following amounts:

100 parts by weight of isocyanate-functional prepolymers A)

1 to 60 parts by weight of water or a nonaqueous isocyanate-reactive component B) 2 to 15 parts by weight of heterocyclic oligomers C)

0 to 0.5 part by weight of catalysts D)

0 part by weight of salts of weak acids, the corresponding free acids of which have a pKA in water at 25°C of > 3.0 and < 14.0 E)

0 to 3 parts by weight of surfactants F)

0 part by weight of alcohols G)

2 to 15 parts by weight of hydrophilic polyisocyanates H) polyamine I) in an amount wherein the ratio of amine groups stemming from component I) to isocyanate groups of all components A) to I) is in a range of 0.1 to 1.2.

In a preferred embodiment of the process according to the invention, the NCO content of the isocyanate- functional prepolymers A) is 1.5% to 8% by weight, more preferably 2% to 7.5% by weight and most preferably 3% to 7% by weight.

In a preferred embodiment of the process according to the invention, prepolymer A) has a proportion by weight of low molecular weight diisocyanates having a molar mass of 140 to 278 g/mol of below 1.0% by weight, preferably of below 0.5% by weight, preferably of below 0.3% by weight, or preferably of below 0.1% by weight, based on the Prepolymer A). The proportion by weight of low molecular weight diisocyanates is preferably adjusted via distillation.

In a preferred embodiment of the process according to the invention, aliphatic isocyanates are used as component Al), more preferably exclusively aliphatic isocyanates. Examples of aliphatic isocyanates have already been mentioned above. Preferred aliphatic isocyanates are HDI or IPDI or mixtures thereof, especially preferred HDI. By utilizing aliphatic isocyanates as component Al) the aim can be reached to provide non-yellowing foams or hydrogels, especially for the production of wound dressings.

In a preferred embodiment of the process according to the invention, linear diisocyanates in the production of polyurethane foams or hydrogels are used. More particularly, preference is given to using exclusively linear diisocyanates for components Al), C) and Hl).

In a preferred embodiment of the process according to the invention, the isocyanate-functional prepolymer A has a viscosity a viscosity at RT/ 23°C/ 25°C, determined according to DIN 53019 of < 50 000 mPas, preferably of < 25 000 mPas, or preferably of < 10 000 mPas, or preferably within a range from 100 to 20 000 mPas.

In a preferred embodiment of the process the components A), C) and H) have a residual diisocyanate content of below 5% by weight, preferably below 3% by weight, more preferably below 2% by weight, especially preferably below 0.5% by weight, most preferably below 0. 1% by weight based on the total weight of the components A), C) and H). By decreasing the residual diisocyanate content the aim was reached to provide a process for the production of polyurethane foams or hydrogels from prepolymer formulations that may be handled without health risks. This is very important if foams are produced in a mass production where persons work that are not adapted to handle risky chemicals.

In a preferred embodiment of the process according to the invention, at least the following steps are conducted:

I), preparing the prepolymer A) from components Al), A2) and optionally A3), optionally D),

II). optionally mixing components A), C) and H) and other isocyanate-containing components to obtain a prepolymer mixture,

III). optionally adding A3) and optionally D),

IV). optionally mixing component B) with all other components, especially D), E), F) G) and I), apart from the prepolymer mixture,

V). mixing the prepolymer mixture obtained in I) to III) with the mixture from IV).

Preferably, the temperature in at least one of steps I), to IV). is chosen within a range from 2 to 70°C, or preferably within a range from 10 to 50°C, or preferably from 20 to 40°C.

In step IV). components B), D), E), F), G) and I) may be provided separately or in any combination and order to the mixture of step II). or III).

Preferably, the mixture, after step IV)., is applied to a substrate and allowed to cure. The curing is preferably conducted at a temperature within a range from 20 to 50°C. With the aid of convection ovens or infrared dryers, the curing and simultaneous drying can also be conducted in higher temperature ranges, for example between 50 and 200°C.

The polyurethane foams or hydrogels according to the invention are preferably produced by mixing components A), produced from components Al), A2) and optionally A3) and optionally D), optionally with C) and/or H), in any sequence, and then with a mixture of B) and I) and optionally D), E), F), G), foaming the mixture and curing, preferably by chemical crosslinking. Preferably, components A), C) and H) are pre-mixed with one another. Any salts E) to be used and any surfactants F) are preferably added to the reaction mixture in the form of their aqueous solutions, preferably together with component B).

The foaming can in principle be effected by means of the carbon dioxide formed in the reaction of the isocyanate groups with water, but the use of other blowing agents is likewise possible. For instance, it is also possible in principle to use blowing agents from the class of the hydrocarbons such as C3-C6- alkanes, e.g. butanes, w-pentane, /.so-pcntanc. cyc/o-pcntanc. hexanes or the like or halogenated hydrocarbons such as dichloromethane, dichloromonofluoromethane, chlorodifluoroethanes, 1,1- dichloro-2,2,2-trifluoroethane, 2,2-dichloro-2-fluoroethane, especially chlorine-free hydrofluorocarbons such as difluoromethane, trifluoromethane, difluoroethane, 1,1,1,2-tetrafluoroethane, tetrafluoroethane (R 134 or R 134a), 1,1,1,3,3-pentafluoropropane (R 245 fa), 1,1, 1,3,3, 3-hexafluoro- propane (R 256), 1,1,1,3,3-pentafluorobutane (R 365 mfc), heptafluoropropane or else sulfur hexafluoride. Mixtures of these blowing agents are also usable.

The subsequent curing is typically performed at 23°C.

In a preferred embodiment of the process according to the invention, the oxyethylene unit content of A2 is > 50% by weight, or preferably > 55% by weight, or preferably > 60% by weight, based on the total amount of the oxyalkylene groups present.

Preferably, there is a molar ratio of NCO groups to OH groups in the reaction of components Al) to A4) to give the isocyanate-functional prepolymer A) of < 5, or preferably of < 4, or preferably of < 3, or preferably within a range from 1 to 5, or preferably within a range from 1.5 to 4.5.

In a preferred embodiment of the process according to the invention, the polyalkylene oxide A2) has an OH number within a range from 25 to 450 mg KOH/g, preferably within a range from 50 to 400, or preferably within a range from 75 to 250.

Moreover, the present invention further provides the polyurethane foams or hydrogels produced by the process according to the invention, and for the use of the hydrophilic, preferably aliphatic polyurethane foams or hydrogels as a constituent of a wound dressing, a cosmetic article or an incontinence product.

As already described above, the polyurethane foams or hydrogels according to the invention are preferably produced by mixing components A), produced from components Al), A2) and optionally A3), optionally D), optionally with C) and/or H), in any sequence, and then with a mixture of B) and I) and optionally D), E), F), G), foaming the mixture and curing, preferably by chemical crosslinking. Preferably, components A), C) and H) are pre-mixed with one another. Any salts E) to be used and any surfactants F) are preferably added to the reaction mixture in the form of their aqueous solutions. Preferably, the polyurethane foams or hydrogels according to the invention are hydrophilic and have preferably aliphatic units.

In the case of forming foams, the polyurethane foams according to the invention or the polyurethane foams produced in accordance with the invention preferably have a porous, at least partly open-cell structure with cells in communication with one another. The density of the polyurethane foams is preferably 50 to 300 g/1. The polyurethane foams have good mechanical strength and high elasticity. Typically, tensile strengthdry values are greater than 40 kPa, elongation at break values greater than 30% with a density in the range from 50 to 300 g/1 (determination in each case by the standards as described later under Methods).

After the production, the polyurethane foams can be processed by methods known per se to give essentially two-dimensional or thin three-dimensional materials which can then be used, for example, as a constituent of a wound dressing, of a cosmetic article or of an incontinence product. In general, for this purpose, slabstock foams are cut to the desired thickness by standard methods, to obtain two- dimensional materials having a thickness of typically from 10 pm to 5 cm, preferably from 0.1 mm to 1 cm, more preferably from 0.1 mm to 6 mm, most preferably from 0.2 mm to 6 mm.

With the aid of suitable casting techniques, the two-dimensional materials described can alternatively be obtained directly by application and optionally foaming of the composition according to the invention to a substrate, for example an optionally pretreated paper, a film, a nonwoven or a textile.

In a preferred variant, for this purpose, a mixture of the starting materials as described in the PCT application numbered WO 2011/006608 is applied to a substrate by means of a coating bar, and then the optional foaming follows after the coating. The gap height of the coating bar is generally in the range from 0.2 to 20 mm, preferably from 0.5 to 5 mm and most preferably from 0.8 to 2 mm. The film width of the coating bar to be used can be matched to the particular end use. Examples are film widths between 10 and 5000 mm, preferably between 20 and 2000 mm.

Preference is given to a casting method in which, while the polyurethane foam or hydrogels is being cast to a layer or a substrate, a further layer is applied to the top side of the polyurethane foam or hydrogel, preferably before the polyurethane foam or hydrogel has dried. Such a process is described in the patent application with application number EP 17156493.3 and can likewise be employed here.

The polyurethane foams generally contain only a small water-extractable proportion of not more than 2% by weight, preferably of not more than 1% by weight, meaning that they contain only very small amounts of chemically unbound constituents.

Moreover, the polyurethane foams or hydrogels may be bonded, laminated or coated with further materials, for example based on hydrogels, (semi-)permeable films, foam films, coatings, hydrocolloids or other foams.

The polyurethane foams or hydrogels according to the invention are particularly suitable for production of wound dressings. The polyurethane foams or hydrogels here may be in direct or indirect contact with the wound. However, preference is given to using the polyurethane foams or hydrogels in direct contact with the wound in order to assure, for example, optimal absorption of wound fluid. The polyurethane foams or hydrogels that are used as wound dressing must additionally be sterilized in a further process step. For sterilization, the processes known per se to the person skilled in the art are used, in which sterilization is effected by thermal treatment, chemical substances such as oxyethylene, or irradiation, for example by gamma irradiation. The irradiation can optionally be effected under protective gas atmosphere. The polyurethane foams or hydrogels according to the invention made from preferably aliphatic diisocyanates, especially component Al) and optionally Hl), have the great advantage that they are not discoloured on irradiation, especially on irradiation with gamma rays.

Likewise possible is addition, incorporation or coating of or with antimicrobial, pharmaceutical or biological active ingredients or other additives that have a positive effect, for example in relation to wound healing and the avoidance of microbial contamination.

A further aspect of the invention is a polyurethane foam or polyurethane hydrogel which as obtained according to the process according to the invention as described above.

A further aspect of the invention is a wound dressing or an incontinence product which is obtainable using polyurethane foams or hydrogels according to the invention.

Raw materials

Desmodur® H

Desmodur® H, hexamethylenediisocyanate. The content of hexamethylenediisocyanate is > 98.2% by weight commercial product of Covestro Deutschland AG.

Desm ophen® L 300

Polyethylene glycol, prepared by ethoxylation of propylene glycol, OH-number: 190 mg KOH / g, commercial product of Covestro Deutschland AG

Polyfethyleneglycol-ran-propylenglvcol)

Poly(ethyleneglycol-ran-propylenglycol) is a difunctional polyether (MERCK). The molar mass and fraction of ethylene oxide units were determined via ¹ H-NMR spectroscopy in deutorated chloroform solvent to be 1870 g/mol and 80.4%, respectively.

Dibtuyl phosphate commercial product of Merck, _Germany, purity > 97%.

Hexamethylene diamine: commercial product of ABCR, Germany, purity 98%.

Sodium hydrogen carbonate; commercial product of KRAFT, Germany,

Pluronic PE 6800: commercial product of BASF, Ludwigshafen, Germany dry ice: commercial product of Nippon Gases, Germany

Methods

Percentages denote weight percentages unless stated otherwise.

Viscosity

Viscosities of prepolymers were determined according to DIN 53019-1-2008-09. Unless stated otherwise the temperature was 23 °C.

OH-numbers

The OH numbers were determined according to the method of DIN 53240-2:2007-11.

NCO content

NCO contents were determined according to DIN-EN ISO 11909-2007-05. pH-value pH was measured using a Knick 765 Calimatic pH-meter at 23 °C.

Residual diisocyanate content

Residual diisocyanate contents were determined according to DIN EN ISO 10283:2007.

Foam/Hydrogel height

The height of foam samples was measured by a compressed air caliper connected to a display (Heidehain MT25P).

Measurement of foam/hydrogel density (D)

Foam samples of the dimensions 5 x 5 cm were punched out of the foam sheet. The sample height was determined as described previously at five locations and averaged. Subsequently, the samples were weighed using a Mettler Toledo XS603S balance and the density (D) was calculated.

Determination of urethane content

For the present invention, the urethane content can be calculated from the stoichiometry of the urethane-forming reaction between hydroxyl groups and isocyanate groups. Since the hydroxyl groups are fully converted to urethane groups in all examples, the following formula can be used for calculation: % by wt. of hydroxyl component ■ OHN

Urethane content = - -₇ -

5610M mol where OHN denotes hydroxyl number of the hydroxyl component used or the corresponding average value for multiple components. Examples of possible hydroxyl components are mono- or polyfunctional alcohols or polyols. Specific examples are described under Al), A3), G) or H2).

In the case of subsequent removal of urethane-free components from the product mixture, for example by a distillation process, there is an increase in the polyol content and hence also in the urethane content of the product mixture.

Calculation example with reference to Prepolymer 4

Urethane content before distillation:

63.71 - 190 mol

Urethane content = - -₇ - = 2.16 - —

5610 M kg mol

Urethane content after distillation:

70.07 - 190 mol

Urethane content = - -₇ - = 2.37 - —

5610 M kg mol

It will be apparent to the person skilled in the art that the formula utilized here has to be modified or extended if, for example, reactants that already contain urethane groups are used, other urethane-forming reactions are used or competing reactions can occur (for example urea formation in the presence of amines).

Measurement of swelling (edge length expansion factor (SI)

Immediately after measuring the liquid absorption according to DIN EN 13726-1:2002 the edge lengths of the swollen samples were determined. From the resulting 4 values an average edge length was calculated. The edge length expansion factor S was calculated as follows

S = (average edge length after swelling in cm)/5cm-

Elongation at break and tensile strength at break

Elongation at break (eb, wet) and wet-tensile-strength-at-break (ob.wet) in the wet (swollen) state were determined according to DIN EN ISO 527-2 except for the following deviations. The samples were immersed in deionized water for 30 min prior to punching out the tensile specimens. The wet specimen height needed for the calculation of the wet-tensile-strength-at-break (ob.wet) could not be measured reliably due to the caliper sinking into the extremely soft specimen. Therefore, the wet foam height was estimated from the dry foam height and the edge length expension according to the formula h(wet sample) = h(dry sample) ■ edge length expansion factor

Examples

Prepolymer 1 (according to US2006142529, example 4)

133.5 g of Desmodur 24 MI and 133.5 g Desmodur 44 M were heated to 70 °C. Over the course of 2 h 733.3 g of a Poly(ethyleneglycol-ran-propylenglycol) were added dropwise while stirring. The reaction mixture stirred at 70 °C for another 4 h until a constant NCO content of 5.4% was reached. The product had a viscosity of 29900 mPas. The urethane content was calculated to be 0.80 mol/kg.

Prepolymer 2

168 g of HDI and 0.5 g of dibutyl phosphate were heated to 80 °C. Over the course of 1 h 296 g of Desmophen L300 were added dropwise while stirring. The reaction mixture stirred at 80 °C for another

3.5 h until an NCO content of 8.8% was reached. The product had a viscosity of 2100 mPas. The urethane content was calculated to be 2.2 mol/kg.

Prepolymer 3

2431 g of HDI and 3.0 g of dibutyl phosphate were heated to 80 °C. Over the course of 1 h 569 g of Desmophen L300 were added dropwise while stirring. The reaction mixture stirred at 80 °C for another 3 h until an NCO content of 35.7% was reached. Excess HDI was removed via distillation employing a thin film evaporator at 140 °C and about 0.6 mbar. A clear prepolymer with an NCO content of 8.8%, a viscosity of 710 mPas and a residual monomer content of 0.02% was obtained. The urethane content was calculated to be 2.2 mol/kg.

Prepolymer 4 (according to WO19137879, example 1)

1680 g of HDI and 5.0 g of dibutyl phosphate were heated to 80 °C. Over the course of 1 h 2960 g of Desmophen L300 were added dropwise while stirring. The reaction mixture stirred at 80 °C for another

3.5 h until an NCO content of 9.1% was reached. Excess HDI was removed by a thin film evaporator at 140 °C and about 0.7 mbar. A clear prepolymer with an NCO content of 5.0% and a viscosity of 5140 mPas was obtained and a residual diisocyanate content of 0.03% was obtained. The urethane content was calculated to be 2.4 mol/kg. Aqueous phase 1 (not inventive)

1.5 g Pluronic PE 6800 were dissolved in 73.5 g deionized water.

Aqueous phase 2 (not inventive)

48 g Pluronic PE 6800, 13 g sodium hydrogencarbonate and 4 g citric acid monohydrate were dissolved in 935 g deionized water.

Aqueous phase 3 (not inventive)

65 g Pluronic PE 6800 and 18 g sodium hydrogencarbonate were dissolved in 935 g deionized water.

Aqueous phase 4 (inventive)

3.30 g hexamethylene diamine was dissolved in 18.19 g deionized water. Dry ice was added stepwise until the pH dropped below 9.3 indicating full conversion of hexamethylene diamine to the corresponding hydrogen carbonate salt. Finally, 1.20 g of Pluronic PE 6800 were dissolved in the aqueous solution.

Aqueous phase 5 (inventive)

6.60 g hexamethylene diamine was dissolved in 23.70 g deionized water. Dry ice was added stepwise until the pH dropped below 9.3 indicating full conversion of hexamethylene diamine to the corresponding hydrogen carbonate salt. Finally, 1.20 g of Pluronic PE 6800 were dissolved in the aqueous solution.

Preparation of foams

The prepolymers from the examples were placed into a 500 mL PP beaker (Sarstedt, Germany) and stirred using Disperlux green 037 stirrer at 930 rpm for 15 seconds. Subsequently, a defined amount of aqueous phase (see Table 1) was added. It was stirred for another 5 seconds. Then the mixture was coated on a release paper (Felix Schoeller Y 05200) using a 1500 pm coating bar. After 40 seconds a pin holed release paper (Felix Schoeller Y05200) was placed on top. The foam was allowed to dry over night at 23°C.

020PF30009-Foreign Countries

- 23 -

Table 1. Properties of foams prepared from prepolymers 1 to 4 and aqueous phases 1 and 5

As already explained in the introduction the term (oB,wet/D)-S² is useful to assess the wet-tensile-strength- at-break (ob.wet) independent from density and extent of swelling. Table 1 summarizes the properties of foams 1 to 6 prepared from different prepolymers and aqueous phases.

Aliphatic prepolymers containing more than 1% residual diisocyanate like comparative example 2 in this document can be used to produce foams with excellent wet strength performance as indicated by the outstanding (oB,wet/D)-S² value of 1.42. Similar prepolymers that differ only by the subsequent removal of the residual diisocyanate monomer are known. For instance, example 1 of WO19137879 leads to a prepolymer that retained a rather low viscosity of 5140 mPas after distillation. However, the (oB,wet/D)-S² value of foams produced from this prepolymer dropped drastically to 0.28 (see non- inventive example 4 as described above in table 1). In order to verify that this drop can be attributed to the presence of residual diisocyanate rather than the change in chemical composition of the product accompanying the distillation process (HDI content and polyol content) comparative prepolymer 3 was designed in a way that it resembles the chemical composition of prepolymer 4 (similar HDI and polyol content of 35% and 65%, respectively) but differs in the fact that the residual diisocyanate was removed via distillation.

It can be summarized that prepolymers that allow production of foams with good wet-tensile-strength- at-break (ob.wet) performance as indicated by high (oB,wet/D)-S² values were known in prior art but the reason for the good performance could be attributed to the presence of residual diisocyanates in these disclosed formulations which are often not desirable because of different reasons as mentioned before.

Aromatic foam 1 and aliphatic foam 2 show excellent (oB,wet/D)-S² values > 0.30 but were prepared from the respective prepolymers 1 and 2 that contain more than 8% monomeric diisocyanates (component Al). Prepolymers 3 and 4 contain less than 8% diisocyanates because residual diisocyanate was removed by distillation.

Foam 4 was prepared via a non-inventive method without a polyamine as component I). The (ob,wet/D)-S² value was only 0.28. Foam 5 was prepared employing a polyamine as component I) in an amount that resulted in a NH/NCO-ratio of 0.4. Due to component I) the (ob,wet/D)-S² value increased to 0.40. Foam 6 was prepared by further increasing the amount of component I) until a NH/NCO-ratio of 0.8 was reached. As a result (ob,wet/D)-S² further increased to 0.50. Consequently, it could be demonstrated that employing component I) effectively increases (oB,wet/D)-S². Surprisingly, it could be shown that a foam with good (ob,wet/D)-S² value could be reached even with low residual diisocyanate amounts.

Claims

- 25 - Claims

1. A process for producing polyurethane foams or polyurethane hydrogels, in which compositions comprising

A) isocyanate-functional prepolymers obtainable by the reaction of

A2) polyalkylene oxides having an OH functionality of two or more,

A3) optionally further isocyanate-reactive components differing from A2);

B) water in an amount of at least 2% by weight, based on the total weight of the composition;

D) optionally catalysts;

E) optionally salts of weak acids, the corresponding free acids of which have a pKA in water at 25°C of > 3.0 and < 14.0;

F) optionally surfactants;

G) optionally mono- or polyhydric alcohols or polyols;

H) optionally hydrophilic polyisocyanates obtainable by reaction of

Hl) low molecular weight diisocyanates of molar mass from 140 to 278 g/mol and/or polyisocyanates preparable therefrom and having an average isocyanate-functionality of 2 to 6 with

H2) monohydroxyfunctional polyalkylene oxides of OH number from 10 to 250 and of oxyethylene unit content from 50 to 100 mol%, based on the total amount of the oxyalkylene groups present;

I) a polyamine with at least two amine groups or two ammonium groups, preferably a diamine; are provided, optionally foamed and cured wherein the isocyanate containing components, especially components A), C) and H), do not exceed a residual diisocyanate content of 8% by weight, based on the total weight of the polyurethane foam or hydrogel and wherein the ratio of amine groups stemming from component I) to isocyanate groups of all components A) to I) is in a range of 0.1 to 1.2.

2. The process according to claim 1, wherein component I) comprises an aliphatic polyamine, preferably a linear aliphatic diamine as polyamine. The process according to any of claims 1 or 2, wherein component I) comprises the polyamine as ammonium salt, preferably as ammoniumhydrogencarbonate or ammoniumformate, more preferably as ammonium salt of 1,6-hexamethylendiamine, especially preferably as hexane- 1,6- diammonium hydrogencarbonate. The process according to either of the preceding claims, wherein the isocyanate-containing components, especially components A), C) and H), have a total isocyanate content within a range from 2% to 12% by weight, based on the total amount of the isocyanate-containing components, especially on the total amount of components A), C) and H). The process according to either of the preceding claims, wherein the NCO content of the isocyanate-functional prepolymers A) is 1.5% to 8% by weight, more preferably 2% to 7.5% by weight and most preferably 3% to 7% by weight. The process according to either of the preceding claims, wherein prepolymer A) has a proportion by weight of low molecular weight diisocyanates having a molar mass of 140 to 278 g/mol of below 1.0% by weight, based on the total mass of the prepolymer A). The process according to either of the preceding claims, wherein aliphatic diisocyanates are used as component Al). The process according to either of the preceding claims, wherein linear diisocyanates are used as component Al). The process according to any of the preceding claims, wherein the isocyanate-functional prepolymer A) has a viscosity at RT/ 23 °C/ 25 °C, determined according to DIN 53019, of < 50 000 mPas. The process according to any of the preceding claims, wherein the isocyanate containing components, especially components A), C) and H), do not exceed a residual diisocyanate content of 5% by weight, more preferably below 1% by weight, most preferably below 0.1% by weight, based on the total weight of the polyurethane foam or hydrogel. The process according to any of the preceding claims, wherein the following steps are conducted:

I). preparing the prepolymer A) from components Al), A2) and optionally A3) and optionally

D),

II). optionally mixing components A), C) and H) and other isocyanate-containing components to obtain a prepolymer mixture, III), optionally adding A4) and optionally D),

IV). optionally mixing component B) and I) with all other components, especially D), E), F) and G), apart from the prepolymer mixture,

V). mixing the prepolymer mixture obtained in I), to III), with the mixture from IV).. The process according to any of the preceding claims, wherein the oxyethylene unit content of A2) is > 50% by weight, based on the total amount of the oxyalkylene groups present. The process according to any of the preceding claims, wherein the polyalkylene oxide A2) has an OH number within a range from 25 to 450 mg KOH/g. A polyurethane foam or a polyurethane hydrogel obtained by a process according to any of the preceding claims. A wound dressing, a cosmetic article or an incontinence product obtainable using polyurethane foams or hydrogels according to claim 14, or produced according to any of claims 1 to 13.