EP2081978A1

EP2081978A1 - Compositions for making a negative mould

Info

Publication number: EP2081978A1
Application number: EP07846770A
Authority: EP
Inventors: Hartmut Nefzger; Erika Bauer; Michael Ludewig; Matthias Schaub; Klaus-Dieter Nehren; Michael Freckmann; Holger Urbas
Original assignee: Heraeus Kulzer GmbH
Current assignee: Kulzer GmbH
Priority date: 2006-11-25
Filing date: 2007-11-23
Publication date: 2009-07-29
Also published as: DE102006055739A1; US20080146695A1; US20100022739A1; WO2008061774A1; CA2670203A1; WO2008061651A1

Abstract

The present invention relates to compositions for making a negative mould which are based on polyether derivatives, a process for producing them and their use.

Description

impression materials

The present invention relates to molding compositions based on polyether derivatives, a process for their preparation and their use.

Polyether derivative-based impression materials used in the dental field have long been known. According to the prior art, pastes are used whose components comprise, for example, polyether polyols, polyisocyanates and aminosiloxanes, as well as fillers and other auxiliaries.

The crosslinking of the masses takes place, for example, by the hydrolysis of alkoxy-silane groups by ambient or deliberately added moisture and subsequent crosslinking to form siloxane groups.

The requirements for dental impression materials are very high. EP-A 0 269 819, inter alia, mentions a pleasant taste and odor, aesthetic appearance, good storage stability, good handleability, precision of the impressions, useful hardening characteristics and dimensionally stable shaped bodies under ambient conditions. Furthermore, such compositions must not contain any irritating or toxic components. Cured masses must of course have a good compression set behavior and preferably have no hysteresis under tensile stress. In addition, they must be economically advantageous to produce.

Previous solutions to this problem include, for example, alginate impression materials with the disadvantage of a comparatively strong shrinkage. Polysulfϊd Abformas- sen are dark colored and also contain lead or copper compounds as catalysts. Polyether impression compounds contain ethyleneimine crosslinkers. Polysiloxane impression compounds occasionally give erroneous imprints due to the moisture in the oral cavity.

The closest prior art is disclosed in EP-A 1 245 601 and EP-A 0 269 819. According to EP-A 1 245 601, the preparation of an NCO prepolymer from a polyol and an aliphatic, cycloaliphatic or aromatic polyisocyanate is first described, characterized in that one waives any metal catalysis. This also applies to the second stage of the reaction of this NCO prepolymer with secondary amine-terminated aminoalkylalkoxysilane.

This approach is of course not universally applicable, especially not if the polyol used for the NCO prepolymer has not exclusively or at least predominantly primary OH groups. It is known to the person skilled in the art that, in particular when cycloaliphatic diisocyanates, such as, for example, are used. Isophorone diisocyanate with polyether polyols which do not have exclusively or predominantly primary OH groups, resulting from this doctrine economically unacceptably long reaction times for the preparation of prepolymer. Incidentally, this also applies to the reaction of such NCO prepolymers with amine-terminated aminoalkylalkoxysilane. Here are even with example

Dibutyltin dilaurate catalysis undergo long-lasting and therefore uneconomical phases, during which free amine is present alongside free isocyanate. For dental applications, the more reactive aromatic polyisocyanates are eliminated from the outset because of their toxicity. Free isocyanate, be it aromatic or aliphatic in nature, is, of course, basically just as unacceptable in dental applications as is an excess of aminosiloxane exceeding an absolute minimum. In addition, free isocyanates are also unacceptable because, over time, e.g. After compounding with additives and auxiliaries, would continue to react slowly, whereby the consistency of the pastes changed slowly and thus the storage stability could not be guaranteed.

Some of the latter aspects are already described in EP-A 0 269 819. However, EP-A 0 269 819 does not describe whether and, if appropriate, which type of catalysts are to be used advantageously for the reaction of the NCO groups. In two embodiments, only tin octoate is used. However, tin compounds cause the problem of corrosion effects when stored in certain packaging materials such as aluminum tubes or tubular bags based on aluminum. In addition, toxicological concerns have recently been voiced against organotin compounds in recent years. There is therefore a need for dental impression materials which preferably contain no tin compounds in which, however, the content of tin compounds is at least limited to a minimum, for example 5 ppm, ie of the order of magnitude of about 10% of those currently customary in the art Amount are limited. In the teaching of EP-A 0 269 819, no solution to this problem can be seen.

The same applies to EP-A 0 096 249, EP-A 0 158 893, US-A 4,374,237 and US-A 3,632,557, DE-A 4 307 024, EP-A 0 687 280, DE-A 4 439 769, DE-A. A 10 201 703, EP-A 1 563 822, EP-A 1 563 823 as well as for EP-A 1 226 808, EP-A 1 402 873 and EP-A 1 081 191.

Furthermore, EP-A 0 269 819 teaches that preferably those polyethers are used which have predominantly, ie up to 90%, primary OH end groups based on all OH end groups. The only polyether polyols of economic relevance are, in addition to the polytetrahydrofurans, those which are prepared from ethylene oxide and / or propylene oxide. Polytetrahydrofurans are less suitable for dental applications because they have a phase transition in the region of room temperature, which leads to the fact that the flow and thus the processing properties are undesirably strongly temperature-dependent in the range of the application temperature. In addition, disadvantageously their high compared to ethylene-propylene oxide based types. Of course, in the case of ethylene-propylene oxide-based polyethers, high proportions of primary OH groups are only obtained by polymerizing relatively high proportions of ethylene oxide units, if appropriate in admixture with propylene oxide as the end block, onto polypropylene oxide in the preparation of such polyethers. This structure in turn leads to an undesirably high hydrophilicity, which has a strongly negative effect on the water absorption behavior and thus the storage stability of the pastes produced therewith. Desirable in this regard It is therefore to be able to use polyether with as few ethylene oxide structural elements and still ensure reasonable reaction times.

It is an object of the present invention to provide an impression mass system based on silane-terminated polyether derivatives for the dental sector

To provide, which contains as possible no tin compounds or has a maximum content of tin compounds of <5 ppm, this impression system must be economical to manufacture and meet all the above-mentioned requirements of dental impression materials.

Surprisingly, it has now been found that this object can be achieved outstandingly with the aid of silane-terminated polyethers which are prepared essentially or completely without catalysis by tin compounds.

The invention therefore provides silane-terminated polyether derivatives obtainable by reaction of

a.) largely linear polyether polyols with predominantly secondary OH

Groups with the aid of catalysts with b.) Diisocyanates

to prepolymers having an NCO content of 0.5 to 6 wt .-% NCO, preferably 1 to 4 wt .-% NCO and further reaction of these prepolymers in a second reaction step with

c.) compounds containing amino groups of the general formula (i)

HNR- (CH ₂ ) H-SiR ₁ R ₂ R ₃ , (i)

wherein

R is hydrogen or - (CH ₂ VSiRiR ₂ R ₃ , n is an integer from 1 to 6 and at least one of the groups R ₁ , R ₂ , R _{3 has} the structure (-OC _p H _2p ) _q -OR 4,

where p assumes the values of 2 to 5, preferably 3, and q assumes values of 0 to 100, preferably 0 to 4, and

R _{4 represents} a substituent selected from the group comprising alkyl, ayryl, arylaklyl, vinyl or vinylcarbonyl

and

the remaining groups R ₁ , R ₂ , R _{3 are} alkoxy radicals having 1 to 4 C atoms,

be implemented such that the NCO value is less than 0.001 wt .-% NCO and the proportion of free amino groups in the range of 0.5 to 50 mmol, preferably 1 to

15, more preferably 0.5 to 5 mmol of amine groups per kg of the thus obtained silane-terminated polyether derivative is set.

Another object of the invention is a process for the preparation of silane-terminated polyether derivatives, characterized in that

a.) largely linear polyether polyols with predominantly secondary OH groups with the aid of catalysts with b.) Diisocyanates

to prepolymers having an NCO content of 0.5 to 6 wt .-% NCO, preferably 1 to 4 wt .-% NCO and the further reaction of these prepolymers in a second reaction step with

c.) compounds containing amino groups of the general formula (i)

HNR- (CH ₂ ) _n -SiRiR ₂ R ₃ , (i) Wonn

R is hydrogen or - (CH ₂ VSiR ₁ R ₂ R ₃ , n is an integer from 1 to 6 and at least one of the groups R ₁ , R ₂ , R _{3 has} the structure (-O-CpH _2p ) _q -OR ₄ .

and

In the following the invention will be described in more detail.

According to the process according to the invention for the preparation of silane-terminated polyether derivatives, substantially linear polyether polyols having more than 80% secondary OH groups with the aid of zinc catalysts are reacted in a first reaction step by reaction with aliphatic polyisocyanates to give a prepolymer having an NCO group. Content of 0.5 to 6 wt .-% NCO, preferably 1 to 4% by weight of NCO reacted. Substantially linear polyether polyols having more than 80% secondary OH groups are those polyols which are prepared by ring-opening polymerization from epoxides, eg ethylene and propylene oxide, preferably entirely or predominantly propylene oxide, with the aid of, for example, KOH or double metal catalysts (DMC) as catalysts, using reactive hydrogen atoms starters from the group of polyalcohols and polyamines, and water. These substantially linear polyether polyols are those having a hydroxy functionality of from 1.95 to 2.3, preferably from 1.96 to 2.06. Preference is given to divalent starters, such as, for example, ethylene glycol, 1,2-propylene glycol,

Propylene glycol-1,3, diethylene glycol, butylene glycol-1,4, butylene glycol-2,3, 1,6-hexanediol, glycerol, 1,1,1-trimethylolpropane and water. Starters according to the invention also comprise mixtures of a plurality of starters, wherein the starter mixtures are composed so that polyether polyols having an OH functionality of not more than 2.5 are formed, preferably not more than 2.2.

If more than one epoxide is used, the polymerization can be carried out either in blocks or mixed. However, preference is given to the use of only one epoxide, particularly preferably propylene oxide, and also mixtures of two epoxides, the mixtures consisting predominantly of propylene oxide. Polyether polyols according to the invention are further characterized in that they have number-average molecular weights of 150 to 20,000 Da, preferably 500 to 6500 Da, more preferably 800 to 5500. Of course, mixtures of at least two polyether polyols can be used advantageously, in which case the number average molecular weight of Mixture in the prescribed range is.

Examples of aliphatic polyisocyanates are 4,4'-methylenebis (cyclohexyl isocyanate), ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-1,3-diisocyanate, cyclohexane 1,4-diisocyanate or 1-isocyanato, 3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI). They may be used singly or in admixture, but particularly preferred is IPDI. The polyethers according to the invention are prepared in a first reaction stage with polyisocyanates according to the prior art at temperatures in the range of 60 to 150 ° C., preferably 80 to 110 ° C., preferably using a protective gas, more preferably nitrogen, at atmospheric pressure to reduced pressure, preferably normal pressure, converted to NCO prepolymers, wherein a solvent inert to NCO groups can be used, but preferably is carried out without a solvent.

To accelerate the reaction, catalysts are used according to the invention.

Preferred catalysts, if appropriate catalyst mixtures, are characterized in that the silane-terminated polyether derivatives have maximum amounts of 5 ppm tin compound. Preference is given to the use of catalysts which have wholly or predominantly zinc as the metal atom. Examples of catalysts according to the invention are zinc acetate, zinc acetate, zinc lactate, zinc stearate, zinc undecylenate

Zinc di-tert-butylsalicylate, zinc acetylacetonate and zinc neodecanoate. The catalysts are advantageously used in amounts of 0.5 to 10 mg Zn / kg prepolymer.

The prepolymers of the invention have NCO contents of 0.5 to 6 wt .-% NCO, preferably 1 to 4 wt .-% NCO.

The prepolymer formation is considered complete when the practically determined NCO content reaches the theoretically calculated NCO value.

The NCO prepolymers according to the invention are then reacted in a second reaction stage with alkoxysilylmonoamines. Suitable Alkoxysüylmono- amines are known. Examples are the technically readily available γ-aminopropyl-tri-C _t -Ci-alkoxysilane or bis (3-Ci-C ₄ -alkoxysilylpropyl) amines, such as γ-aminopropyltrimethoxysilane and γ-Arninopropyltriethoxysilan.

The reaction of NCO prepolymer and alkoxysilylmonoamine to give reactive silane-terminated polyether derivatives is carried out in such a way that in the silane terminated polyether derivative no NCO is more detectable and the proportion of free amino groups in the range of 0.5 to 50 mmol, preferably 1 to 15, more preferably 0.5 to 5 mmol of amine groups per kg of silane-terminated polyether derivatives.

According to the invention, these specifications are preferably achieved by initially setting a stoichiometric excess of alkoxysilylmonoamine which is mathematically suitable for setting the NCO value to 0 and the amine value to a value of preferably 0.5 to 5 mmol per kg of silane-terminated polyether derivative, at elevated temperatures Temperature, preferably at least 50 ° C, stirred and allowed to react. Both free amine and free isocyanate are found at this stage of the reaction.

After about 2 hours, the amine and the NCO content is determined hourly. The conversion is deemed terminated when one of the values from two consecutive measurements is unchanged. If the amine value is in the desired range and at the same time the NCO value is 0, the product is ready. If the amine value is zero and the NCO value is> 0, an amount of alkoxysilylmonoamine sufficient to raise the amine value within a range of 0.5 to 5 mmol of amine groups per kg is added.

If the amine value is above the desired range and the NCO value is zero, an amount of aliphatic monoisocyanate is metered, which is mathematically sufficient to lower the amine value in the desired range.

The use of the aliphatic monoisocyanate in place of (alternatively) EPDI with at least one very slowly reacting NCO group, represents a significant time advantage.

In a further variant according to the invention, the state of a silane-terminated polyether derivative having an NCO value of zero and an amine value in the range from 0.5 to 5 mmol of amine groups per kg of silane-terminated polyether derivative is achieved by initially using a superstoichiometric amount of alkoxysilylmonoamine if necessary, by adding the same, the amine group content to values greater than 2 mmol of amine groups per kg of polyurethane mass, particularly preferably 2 to 5 mmol of amine groups per kg of polyurethane composition sets constant and that this over 2 mmol value by adding a stoichiometric relative to the amine groups amount of an aliphatic isocyanate, preferably monoisocyanate having at least 2 carbon atoms, preferably at least 6 carbon atoms, such as 1 -n-Ocylisocyanat, 1-n-decyl isocyanate, 1-n-dodecyl isocyanate or 1-stearyl isocyanate reacted with respect to the proportion of free amino groups to values below 2 mmol / kg.

Of course, by the method according to the invention, other than the o.g. Status can be adjusted in terms of NCO value and amine group concentration.

The impression materials of the invention based on silane-terminated polyether derivatives are, in order to bring them into an administrable form, provided according to the prior art with other auxiliaries and additives.

Examples include: fillers, dyes, pigments, thickeners, surfactants, odors and flavorings, and thinners.

For the Abbindereaktion in the oral cavity water is required. In order to set practicable setting times acids are added as catalytically active components. Dental impression materials according to the invention are preferably offered as two-component systems, one component containing the silane-terminated polyether derivatives and optionally further auxiliaries and additives and the other component water, one or more acidic components and optionally auxiliaries and additives. It is surprising that

the described silane-terminated poly-ether derivatives prepared under Zn catalysis have a molecular weight distribution comparable to those of silane-terminated polyether derivatives which have been prepared by catalysis of tin compounds and have tin compound contents of> 5 ppm;

- The systems according to the invention have a comparable or more favorable storage stability;

- Are obtained with the silane-terminated polyether derivatives according to the invention molding compounds that meet the basic requirements for impression materials and not differ significantly in their physical and application properties profile of the compositions of the prior art with levels of tin compounds> 5 ppm.

The following examples further illustrate the invention and show the related technical effects.

Example 1 (according to the invention): Preparation of the polyurethane compositions

Was heated 2553 g of a previously dehydrated in a water jet vacuum polypropylene oxide having an OH number of 28 mgKOH / g (Acclaim ^® 4200N (Bayer Material Science AG) to 100 ⁰ C, gave under stirring under inert gas within 2 minutes 236 g of isophorone diisocyanate (IPDI After 5 minutes, 100 mg of zinc di-tert-butylsalicylate were added and the mixture was stirred at 100 ° C. for about 2 hours and the NCO content of the NCO prepolymer was determined to be 1.20% by weight of NCO (theoretical) : 1.28% by weight) was allowed to cool to 40 ° C and again determined the NCO content (1.20 wt .-% NCO).

To this viscous reaction mass 170 g Dynasilan Ameo ^® (Degussa AG adhesive TP 3023) were incubated at 40 ⁰ C is stirred in. After 2 hours and after 3 hours, the proportion of free amine was determined to be 0.5 mmol amine / kg. An additional 1 g Dynasilan Ameo was stirred in, the amine content being determined after 2 hours and after 3 hours to 0.4 mmol amine / kg.

It was stirred for a further 2 g Dynasilan Ameo ^®, wherein the amine content after 2 and 3 hours to 0.3 mmol amine / kg was determined.

It was stirred for a further 4 g Dynasilan Ameo ^®, wherein the amine content after 2 and 3 hours to 1.8 mmol amine / kg is determined. The increase in the proportion of free amine after the last addition of Dynasilan ^®

Ameo indicates that all NCO groups have reacted.

The NCO value at this time was determined to be 0 wt% NCO. The amine content determined after a further 24 hours was constant at 1.8 mmol amine / kg.

Example 2 (according to the invention): Preparation of the polyurethane compositions

Was heated 2550 g of a previously dehydrated in a water-jet vacuum polypropylene oxide having an OH number of 28 mgKOH / g (Acclaim ^® 4200N (Bayer Material Science AG) to 100 ⁰ C, gave under stirring under inert gas within 2 minutes 283 g of isophorone diisocyanate (IPDI ) was added. After 5 minutes, 80 mg of zinc-di- tert.butylsalicylat were added. the mixture is stirred for about 2 hours at 100 ⁰ C and determined the NCO content of the NCO prepolymer to 1.83 wt .-% NCO (theor .: 1.89% by weight). The mixture was allowed to cool to 40 ° C and again determined the NCO content (1.83 wt .-% NCO).

At that tough reaction mass 273 g Dynasylan ^® Ameo were stirred at 40 °. After 2 and 3 hours, the amount of free amine was determined to be 1.99 mmol A / min.

Further determination of the free content after 24 hours showed a free amine content of 1.98 mmol amine / kg. The NCO value at this time was determined to be 0 wt% NCO

Comparative Example 1 (VBl not according to the invention)

The same procedure was used as in Example 1, but instead of Zn-tert-butyl-salicylate, 150 mg of dibutyltin dilaurate were added as catalyst. After stirring at 100 ° C. for 2 hours, the NCO content of the NCO prepolymer was determined to be 1.25% by weight of NCO (theoretical: 1.28% by weight). The mixture was allowed to cool to 40 ^° C. and again determined the NCO content (1.25% by weight).

NCO).

At that tough reaction mass 180 g Dynasylan ^® Ameo were stirred at 40 ⁰ C. After 2 hours and after 3 hours, the proportion of free amine was determined to be 0.11 mmol amine / kg. It was stirred an additional 2.7 g Dynasilan Ameo ^®, wherein the amine content after 2

Hours and after 3 hours to 2.96 mmol amine / kg was determined. 0.45 g of octyl isocyanate was stirred in, the amine content being determined to be 1.74 mmol amine / kg after 2 and 3 hours. The NCO value at this time was determined to be 0 wt% NCO. The amine content determined after a further 24 hours was constant at 1.74 mmol amine / kg.

Comparative Example 2 (VB2 not according to the invention)

The same procedure was used as in Example 1, but instead of zinc tert-butyl salicylate, 150 mg of dibutyltin dilaurate were added as catalyst. After stirring for 2 hours at 100 ^° C., the NCO content of the NCO prepolymer was determined to be 1.82% by weight of NCO (theoretical: 1.89% by weight). The mixture was allowed to cool to 40 ⁰ C and again determined the NCO content (1.82 wt .-% NCO).

At that tough reaction mass 269 g Dynasylan ^® Ameo were stirred at 40 ° C. After 2 hours and after 3 hours, the proportion of free amine was determined to be 0.3 mmol amine / kg.

It was stirred an additional 1 g Dynasilan Ameo ^®, wherein the amine content after 2 hours and after 3 hours to 1.52 mmol of amine / kg was determined. The NCO value at this time was determined to be 0 wt% NCO.

To evaluate the molecular weight distribution, investigations were carried out by gel permeation chromatography. It was evident that the molecular weight distributions of Bl are broadly consistent with VBl and that of B2 with VB2.

Investigation of storage stability

The products of Examples 1, 2 and Comparative Examples VB 1 and VB 2 were packaged airtight and stored at 60 ° C. To assess the storage stability, the change in viscosity was determined.

The silane-terminated polyether derivatives used according to the invention are distinguished by a similar or lower viscosity change and thus by a comparable or higher storage stability:

Table 1: Determination of the storage stability of silane-terminated polyether derivatives

Table 1 shows that, according to the invention, it is possible to obtain systems whose storage stabilities are at least equally superior to those conventionally catalyzed on prolonged storage.

Formulation Examples:

A. Preparation of the basic components

In a laboratory dissolver, 20 parts by weight of the silane-terminated polyether derivatives with 20 parts by weight of dibenzyltoluene, 56 parts by weight of quartz flour and 4 parts by weight hydrogenated castor oil for 3 h at a pressure <50 mbar to a homogeneous pasty mass mixed.

B. The preparation of the catalyst component takes place in accordance with DE-AlO 104 079.

Example 3.

The various base components were mixed with the catalyst component in a weight ratio of 5: 1. Working times (according to DIN EN ISO 4823), hardnesses according to Shore A (according to DIN 5305), and tear strengths (according to DIN 53504) were determined on the blends. The compositions according to the invention in each case matched the property profile of the tin-catalyzed compounds. The tin-free impression materials according to the invention fulfill the essential requirements for dental impression materials (according to ISO 4823). Table 2: Formulations for the preparation of dental impression materials and evaluation of important properties

Claims

claims:

1. Silane-terminated polyether derivatives, obtainable by reaction of

a.) largely linear polyether polyols with predominantly secondary

OH groups with the aid of catalysts with b.) Diisocyanates

to prepolymers having an NCO content of 0.5 to 6 wt .-% NCO, preferably 1 to 4 wt .-% NCO and further reaction of these prepolymers in a second reaction step

c.) compounds containing amino groups of the general formula (i)

HNR- (CH ₂ VSiRiR ₂ R ₃ , (i)

wherein

R is hydrogen or - (CH ₂ ) _n -SiRiR ₂ R ₃ , n is an integer from 1 to 6 and at least one of the groups Ri, R ₂ , R _{3 has} the structure (-OC _p H _2P ) _q -OR ₄ .

R _{4 represents} a substituent selected from the group comprising alkyl, ayryl, arylalkyl, vinyl or vinylcarbonyl

and the remaining groups R ₁ , R ₂ , R _{3 are} alkoxy radicals having 1 to 4 C atoms,

be implemented such that the NCO value is less than 0.001 wt .-% NCO and the proportion of free amino groups in the range of 0.5 to 50 mmol A-mingruppen per kg of the thus obtained silane-terminated polyether derivative is set.

2. Silane-terminated polyether derivatives according to claim 1, characterized in that the proportion of free amino groups in the range of 1 to 15 mmol amine groups per kg of the silane-terminated polyether derivative thus obtained is set.

3. Silane-terminated polyether derivatives according to claim 1, characterized gekennzeichet that the proportion of free amino groups in the range of 0.5 to 5 mmol Ammgruppen per kg of the thus obtained silane-terminated polyether derivative is set.

4. A process for the preparation of silane-terminated polyether derivatives, characterized in that

a.) substantially linear polyether polyols with predominantly secondary OH

Groups with the aid of catalysts with b.) Diisocyanates

c.) compounds containing amino groups of the general formula (i)

HNR- (CH ₂ VSiR ₁ R ₂ R ₃ , (i) embedded image in which

R is hydrogen or - (CH ₂₎ H-SiR ₁ R ₂ R _3, n is an integer from 1 to 6 and at least one of the groups Ri, R _2, R _3, the structure (-O-C _p H _2p) _q -OR ₄ ,

and

be implemented such that the NCO value is less than 0.001 wt .-% NCO and the proportion of free amino groups in the range of 0.5 to 50 mmol, preferably 1 to 15, particularly preferably 0,

5 - 5 mmol amine groups per kg of the thus obtained silane-terminated polyether derivative is set.

A method according to claim 4, characterized in that for the production of

NCO prepolymers tin compounds in proportions of at most 5 ppm and at least one further catalytic active species, preferably zinc salts, preferably from the group zinc di-tert-butyl salicylate, zinc acetylacetonate and zinc neodecanoate, can be used.

6. The method according to claim 4, characterized in that the NCO prepolymers are produced using amounts of catalyst of 0.5 to 10 mg Zn / kg.

7. The method according to claim 4, characterized in that the NCO prepolymers are prepared at temperatures of 60 to 150 ° C, preferably 80 to 110 ⁰ C, under protective gas, preferably nitrogen.

8. The method according to claim 4, characterized in that the adjustment of the NCO value and the amine group concentration to values below

0.001 wt .-% NCO and at the same time greater than 2 mmol amine groups per kg, more preferably 2 to 5 mmol amine groups per silane-terminated polyether derivative using an aliphatic isocyanate, preferably monoisocyanate having at least 2 carbon atoms, preferably at least 6 carbon atoms, more preferably substances selected from the

Group consisting of 1-n-ocyl isocyanate, 1-n-decyl isocyanate, 1-n-Ocylisocyanat or 1-stearyl isocyanate.

9. Use of polyurethane compositions according to claims 1 to 6 for the production of impression materials.

10. Use according to claim 9, characterized in that it is the impression materials for dental applications

11. Use according to claim 9, characterized in that the materials are in the form of two separate components which are mixed before use.