EP0000348A1 - Polyuret polyisocyanates, preparation thereof and their use in the preparation of polyurethanes. - Google Patents

Abstract

The present invention relates to new polyurethane polyisocyanates, a process for their preparation which consists in reacting primary or secondary monoamines with excess amounts of organic diisocyanates to form triuret or higher polyuret groups, and the use of the new compounds as Isocyanate component in the manufacture of polyurethane plastics.

Description

The present invention relates to a novel process for the production of organic polyisocyanates containing polyurethane groups, the most important polyisocyanates obtainable by this process and the use of the process products as an isocyanate component in the production of polyurethane plastics.

Polyisocyanates containing biuret groups are known and find practical use as raw materials for high-quality, lightfast coatings. For example, they can be made from diisocyanates and water (DT-AS 1 101 394), hydrogen sulfide (DT-AS 1 165 580), formic acid (DT-AS 1 174 760), tertiary alcohols (DT-AS 1 543 178, DT-AS 1 931 055), monoamines (DT-OS 2 308 015) or polyamines (DT-OS 2 261 065).

These prior art processes for the production of biuret polyisocyanates have a number of disadvantages.

In most of the processes, some of the isocyanate groups initially form amino groups with over continue reacting liquid diisocyanate via the corresponding diisocyanate ureas to biuret polyisocyanates. The conversion of the isocyanate groups into amino groups is always accompanied by the formation of gaseous by-products such as carbon dioxide, carbon monoxide, carbon sulfoxide or olefins, the removal of which can lead to exhaust gas problems. In the heterogeneous reaction of diisocyanates with water, there is also the risk of the formation of insoluble polyureas, which are difficult to separate. The reaction of diisocyanates with tertiary alcohols, which is used industrially for the production of biuret polyisocyanates, has the further disadvantage that relatively high temperatures are necessary for the urethane cleavage to convert the isocyanate groups into amino groups. Of particular disadvantage, however, is the fact that in these processes some of the isocyanate groups of the diisocyanate used as the starting material must first be destroyed with the formation of amines.

According to DT-OS 2 261 065, the direct reaction of polyamines with diisocyanates leads to biuret polyisocyanates without elimination of volatile by-products and without conversion of isocyanate groups into amino groups. In this process, however, considerable practical difficulties arise, particularly when using technically easily accessible starting materials such as hexamethylene diamine and hexamethylene diisocyanate, since the high reactivity of the amino groups with respect to the isocyanate groups means that the tendency to form insoluble polyureas is very great and thus to completion in most cases the implementation of uneconomically long reheating of the reaction mixture at high temperature is necessary, which leads to a strong loading impairment of the properties of the process products, especially their inherent color.

In all of the prior art processes, the transition from diisocyanates to biuret polyisocyanates takes place under the disadvantages mentioned. The further reaction to polyurethane polyisocyanates is not observed.

It was therefore the object of the present invention to provide a new process which allows the preparation of high-quality modified polyisocyanates which combine the advantages of the biuretplyisocyanates in a simple manner, without the process having the disadvantages mentioned of the processes of the prior art is affected by technology.

This object was surprisingly achieved by reacting certain organic monoamines, described in more detail below, with excess amounts of certain diisocyanates, described in more detail below, under certain reaction conditions described in more detail below.

The present invention relates to a process for the preparation of modified, triuret or higher polyuret groups having organic polyisocyanates, characterized in that primary or secondary monoamines with excess amounts of organic diisocyanates with formation of triuret or higher polyuret groups and incorporating the with respect to Implementation of indifferent residue of the amine in the process product brings to reaction.

in welcher

• R₁ und R₂ für gleiche oder verschiedene Reste stehen und aliphatische Kohlenwasserstoffreste mit 1-20 Kohlenstoffatomen oder cycloaliphatische Kohlenwasserstoffreste-mit 4-20 Kohlenstoffatomen bedeuten, oder wobei die beiden Reste zusammen mit dem Stickstoffatom einen gegebenenfalls weitere Heteroatome aufweisenden heterocyclischen Ring mit 5-6 Ringgliedern bilden können,
• R₃ und R₄ für gleiche oder verschiedene Reste stehen und aliphatische oder cycloaliphatische Kohlenwasserstoffreste mit 4-20 Kohlenstoffatomen bedeuten und
• n eine Zahl von 2 bis 8 bedeutet.

The present invention also relates to the preferred compounds of the formula obtainable by this process

in which

• R ₁ and R ₂ stand for identical or different radicals and mean aliphatic hydrocarbon radicals with 1-20 carbon atoms or cycloaliphatic hydrocarbon radicals with 4-20 carbon atoms, or the two radicals together with the nitrogen atom optionally having a further heteroatomic heterocyclic ring with 5-6 Can form ring members,
• R ₃ and R _{4 represent the} same or different radicals and are aliphatic or cycloaliphatic hydrocarbon radicals having 4-20 carbon atoms and
• n represents a number from 2 to 8.

Finally, the present invention also relates to the use of the modified polyisocyanates obtainable by the process according to the invention as an isocyanate component in the production of polyurethane plastics by the isocyanate polyaddition process.

• 1. Aromatische Monoamine mit primären oder sekundären Aminogruppen, z.B. Anilin, N-Methylanilin, N-Äthylanilin oder N-Butylanilin. Derartige aromatische Amine sind jedoch im Vergleich zu den nachstehend beispielhaft genannten Aminen weniger bevorzugt.
• 2. Monoamine der Formel
  
  in welcher
  • R₁ und R₂ die bereits oben angegebene Bedeutung haben und wobei R₁ in Ergänzung der oben gemachten Definition auch für Wasserstoff stehen kann.

Starting materials for the process according to the invention are any primary or secondary amino groups which are organic compounds which are otherwise inert under the conditions of the process according to the invention. These include

• 1. Aromatic monoamines with primary or secondary amino groups, for example aniline, N-methylaniline, N-ethylaniline or N-butylaniline. However, such aromatic amines are less preferred compared to the amines exemplified below.
• 2. Monoamines of the formula
  
  in which
  • R ₁ and R _{2 have} the meaning already given above and where R ₁ can also stand for hydrogen in addition to the definition given above.

Monoamines of the formula mentioned are preferably used in which R ₁ and R _{2 are} identical or different radicals and are aliphatic hydrocarbon radicals having 1-4 carbon atoms, where R ₁ can also represent hydrogen or in which R ₁ and R ₂ together with form a piperidine residue on the nitrogen atom.

Very particularly preferred starting materials are the secondary monoamines corresponding to the above definition. Any mixtures of the amines mentioned can also be used.
Specific examples of preferred or particularly preferred for the method according to the invention
Suitable monoamines are: methylamine, ethylamine, propylamine, isopropylamine, isomeric butylamines, pentylamine, hexylamine, cyclohexylamine, dodecylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, bis- (2-ethylhexyl) amine, N-methylcyclohexylamine, N-ethylamine, cyclohexylamine -Methyloctadecylamine, pyrrolidine, piperidine etc.

When carrying out the process according to the invention, modified polyisocyanates containing triuret or higher polyuret groups are formed from the monoamines mentioned above and the diisocyanates mentioned below by way of example, in which the rest of the amine which is indifferent to the reaction is incorporated. This reaction proceeds via the intermediates of the compounds having urea groups which form from the amines and the diisocyanates or of compounds which have compounds with further diisocyanate and biuret groups which form from the urea groups. Intermediate stages are therefore the monourea monoisocyanates formed by addition of one mole of amine and one mole of diisocyanate, or also of bisheas formed from two moles of amine and one mole of diisocyanate, or the biuret polyisocyanates formed from these and further diisocyanate. A logical consequence of this fact is, of course, that as a starting material according to a modification of the method according to the invention, this also, for example, in a separate operation from the at monoamines mentioned by way of example and the intermediates prepared below by way of example isocyanates can be used. Of course, the type of manufacture of these intermediates is of no importance here. It would of course also be conceivable to use as the starting material in the process according to the invention the reaction product containing urea groups from one mole of hexamethylene-bis-carbamic acid chloride and 2 moles of a monoamine which corresponds to the reaction product containing urea groups from one mole of hexamethylene diisocyanate and 2 moles of the same monoamine.

Diisocyanates suitable for the process according to the invention are any organic diisocyanates which, apart from the isocyanate groups, have no further groups which are reactive under the reaction conditions of the process according to the invention. Both the classic aromatic diisocyanates of polyurethane chemistry such as 2,4-diisocyanatotoluene, 2,6-diisocyanatotoluene, mixtures consisting of these isomers or 4,4'-diisocyanatodiphenylmethane are suitable. However, diisocyanates with aliphatic and / or cycloaliphatic isocyanate groups are preferably used, in particular those in which the two isocyanate groups are linked via aliphatic hydrocarbon radicals with 4-12 carbon atoms or via cycloaliphatic hydrocarbon radicals with 4-15 carbon atoms, the aliphatic or cycloaliphatic hydrocarbon chains being interrupted by ester groups or can be substituted, such as: 1,4-diisocyanatobutane, 1,6-diisocyanatohexane, 2,4,4-trimethyl-1,6-di-isocyanatohexane, 1,11-diisocyanatoundecane, 3-isocyanatomethyl-3,5, 5-trimethylcyclohexyl isocyanate, 4,4'-cyclohexane diisocyanate, 4,4'- Dicyclohexylmethane diisocyanate, 1,2-bis (isocyanatomethyl) cyclobutane or 6-isocyanatocaproic acid 2-isocyanatoethyl ester. Hexamethylene diisocyanate is preferably used.

Of course, diisocyanate mixtures can also be used, e.g. a urea or a biuret are first produced from a diisocyanate with a monofunctional amine, which then form polyurets with another diisocyanate.

While the reaction of amines with diisocyanates to form the corresponding ureas or biurets is part of the known prior art, no technically usable method has yet been disclosed which allows the addition reaction between amine and isocyanate to be continued beyond the intermediate stage of the corresponding biurets. This is due to the sluggishness of reaction of the biurets to organic diisocyanates, which can only be overcome by using suitable catalysts.

The catalysts to be used according to the invention are proton-releasing strong acids which react with isocyanates, in particular with aliphatic or cycloaliphatic isocyanates, to form a mixed acid anhydride, the carbamic acid corresponding to the isocyanate and the proton-releasing acid being the acids represent the mixed acid anhydride. Such acids HX (X = acid residue after proton cleavage) suitable for the process according to the invention react with isocyanates Y-NCO to form adducts of the formula Y-NH-CO-X, which are mixed anhydride of the carbamic acid Y-NH-COOH and Acid HX can be seen.

Examples suitable
Ter acids are hydrogen halides such as hydrogen fluoride, hydrogen chloride, hydrogen bromide or hydrogen iodide, chlorosulfonic acid, fluorosulfonic acid, sulfuric acid, alkanesulfonic acids such as methanesulfonic acid or perhalogenated alkanesulfonic acids such as trifluoromethanesulfonic acid. Hydrogen chloride is the preferred acid to be used in the process according to the invention. Instead of the acids, both the ammonium salts corresponding to the acids with the amines used as starting material or the mixed carbamic acid anhydrides corresponding to the acids, in particular carbamic acid chlorides, the diisocyanates used as starting material or any other isocyanate can of course be used in the process according to the invention. In general, the catalysts are used in amounts of 0.001-10, preferably 0.01-1.0% by weight, based on the total weight of the reactants.

It is possible to carry out the process according to the invention, in particular using the acids mentioned as examples, as catalysts at relatively low temperatures in the range from approximately O-140 ° C., the reaction leading to the triuret and Reaction products containing polyurethane groups generally takes place in the range between 90 and 140 ° C. The catalysis according to the invention with the acids mentioned by way of example thus permits, under mild reaction conditions, the preparation of isocyanate addition products having polyurethane groups from organic diisocyanates and organic monoamines or urea groups or compounds having biuret groups formed from monoamines and diisocyanates. When the process according to the invention is carried out using monoamines as starting materials, there are no readily volatile by-products because of the mild reaction conditions; in particular, even when using primary monoamines as starting materials, no monoisocyanates corresponding to these monoamines are formed. The remainder of the monoamines, which are indifferent to the implementation of the invention, thus always forms part of the process products of the invention.

When carrying out the process according to the invention using monoamines as starting materials, these and the diisocyanates are generally used in proportions which have an NCO / NH molar ratio of 5.5: 1 to 100: 1, preferably 6: 1 to 30: 1, correspond. When using starting materials containing urea groups, ie mono urea monoisocyanates or bis-ureas formed from monoamines and diisocyanates, appropriate quantitative ratios are used, taking into account that in the starting materials containing urea groups already monoamines and diisocyanates in a molar ratio of 1: 1 or 2: 1 are present. These monoamines and diisocyanates, which are present in the form of the starting materials containing urea groups, go into the Calculation of the amine: diisocyanate ratio. The same statements apply mutatis mutandis when starting materials containing biuret groups are used, as they result from the reaction of the intermediate products containing urea groups with further diisocyanate.

• Man legt das Diisocyanat in einem geeigneten Reaktionsgefäß vor und gibt das Amin bei Temperaturen von O-100°C zu. Dabei beträgt das NCO/NH-Molverhältnis im allgemeinen 6:1 bis 30:1. Feste Amine werden über einen beheizten und flüssige Amine über einen normalen Tropftrichter dosiert. Gasförmige Amine werden eventuell zusammen mit einem Inertgasstrom in. das Diisocyanat eingeleitet. Es bilden sich spontan die entsprechenden Harnstoffe. Bei Einsatz von primären Aminen fallen diese meistens zunächst aus und gehen durch Weiterreaktion zu Biureten bei 80-120°C in Lösung. Bei Einsatz von sekundären Aminen bleibt die Reaktion bei Abwesenheit des Katalysators auf der Stufe der zumeist in überschüssigem Diisocyanat nicht vollständig löslichen Harnstoffe stehen. Die Katalysatorzugabe kann zu jedem Zeitpunkt der Reaktion erfolgen. Man kann ihn z.B. mit dem Diisocyanat vorlegen, ihn als Ammoniumsalz mit den Aminen eindosieren oder ihn erst nach Beendigung der _Vorreaktion zu Harnstoff- oder Biuretisocyanaten zugeben. Danach wird das Reaktionsgemisch auf 90-140°C erhitzt und der Reaktionsverlauf durch Kontrolle der NCO-Gehaltsabnahme verfolgt. Bei Verwendung von flüchtigen Katalysatoren, z.B. Chlorwasserstoff, kann zur Vermeidung von bei höheren Temperaturen möglichen Katalysatorverlusten unter Druck gearbeitet werden.

The procedure for carrying out the process according to the invention is generally as follows:

• The diisocyanate is placed in a suitable reaction vessel and the amine is added at temperatures of 0-100 ° C. The NCO / NH molar ratio is generally 6: 1 to 30: 1. Solid amines are dosed via a heated and liquid amine through a normal dropping funnel. Gaseous amines are possibly introduced into the diisocyanate together with an inert gas stream. The corresponding ureas form spontaneously. When primary amines are used, they usually precipitate out first and dissolve through further reaction to biurets at 80-120 ° C. When secondary amines are used, the reaction remains in the absence of the catalyst at the stage of the ureas, which are usually not completely soluble in excess diisocyanate. The catalyst can be added at any time during the reaction. You can put it for example with the diisocyanate present, be metered him as ammonium salt with the amines or him orreaktion admit to urea or Biuretisocyanaten only after the _V. The reaction mixture is then heated to 90-140 ° C. and the course of the reaction is monitored by checking the decrease in NCO content. When using volatile catalysts, such as hydrogen chloride, can be used to avoid possible catalyst at higher temperatures losses are worked under pressure.

If the decrease in NCO corresponds to the desired "degree of polyurethaneization": ie, if the desired amount of NCO groups has been reacted per amino group, the reaction is terminated. This is done simply by cooling the reaction mixture to 20-50 ° C. The reaction times required depend on the nature of the starting materials on temperature and in particular of the _A rt and amount of catalyst used. They are generally 1-20, preferably 2-8, hours. After the reaction has ended, clear, colorless to slightly yellowish reaction solutions are obtained.

The reactions are usually ended at a point in time when an average of about 3 NCO groups are used per amino group. The products then have an average functionality of 3.5, taking into account the polymer homologue. However, it is possible to achieve a higher "degree of polyuretization", i.e. to implement 4 and more NCO groups per amino group. However, the viscosities of the products then increase quickly.

The catalyst is generally removed by distilling the reaction mixture in vacuo. If hydrogen halides are used as catalysts, removal, in particular in the case of smaller amounts of catalyst, can also be carried out by adding equimolar amounts of propylene oxide. It is also possible to remove the catalyst by, for example, thin-layer evaporation if the crude isocyanate is freed from excess diisocyanate. The distillate of thin-film distillation, which is then next to the diisocyanate contains the catalyst, can be reused as starting material.

If the removal of excess diisocyanate is provided, it is usually carried out by thin-layer evaporation; however, it can also be extracted by extraction of the reaction mixture with suitable solvents, e.g. Hexane, heptane etc. can be achieved.

The crude isocyanates can be used as such. In most cases, however, they are preferably freed from monomeric isocyanate fractions by thin-layer evaporation or extraction. The monomer-free products are light yellow oils or solid resins; the NCO content is 10-22%.

The process is ideal for a continuous implementation. In these cases, several reaction vessels are cascaded together. In the first reaction vessel, the starting products diisocyanate and amine are mixed at about 60 ° C. The catalyst is added at about 80 ° C. in the second reaction vessel. In the third and optionally further reaction vessels, the further reaction to the polyisocyanate takes place at about 90-140 ° C., the desired degree of “polyurethaneisation” being set by controlling the temperature and the residence time.

Excess diisocyanate and the catalyst are removed, for example, using a coiled tube evaporator combined with a downstream thin-film evaporator. The distillates consisting of diisocyanate and catalyst are combined and returned to the process. The polyisocyanate is obtained as a residue of the thin film distillation.

As already stated, monoisocyanates are not split off when the process according to the invention is carried out. However, it can take place in part if the process product according to the invention is freed from excess diisocyanate at elevated temperature (about 170 ^° C.) by thin-layer evaporation after the reaction has ended. For this reason, when using primary monoamines as starting materials, it is recommended to remove the excess, unreacted diisocyanate by extraction with suitable solvents, such as n-hexane. If secondary monoamines are used as starting materials, such an extraction is not necessary, since in this case the elimination of monoisocyanate is impossible due to the different structure of the reaction products.

When carrying out the process according to the invention, the properties of the modified polyisocyanates obtained, in particular their NCO functionality, NCO content, and the viscosity can be adjusted not only by selecting the suitable starting materials but also particularly simply by adjusting the "degree of polyuretization", i.e. the number of NCO groups converted per amino group can be controlled.

In the preferred use of secondary monoamines, in particular with amino groups bound by aliphatic or cycloaliphatic and aliphatic or cycloaliphatic diisocyanates, the preferred process products according to the invention of the formula given at the outset are obtained. In the particularly preferred use of dialkylamines with C iC ₄ alkyl radicals or of piperidine, and of hexamethylene Diisocyanate as starting materials in carrying out the process according to the invention results in the particularly preferred process products according to the invention of the general formula mentioned, in which the radicals R _i -R ₄ correspond to the above definition of the particularly preferred starting materials and in which n stands for a number from 2 to 8.

The process products according to the invention can be used in particular as an isocyanate component in the production of polyurethane plastics by the ilocyanate polyaddition process. They are suitable for the production of polyurethane foams as well as for the production of elastomers, coatings or bonds. In particular when using the process products according to the invention for the first-mentioned field of application, it is often unnecessary to distill off the excess diisocyanate after the reaction according to the invention has ended. The monomer-free process products according to the invention are excellent raw materials for producing high-quality, weatherproof and lightfast coatings. This applies in particular to the process products according to the invention which have been produced using only aliphatic or cycloaliphatic starting materials.

With regard to the use of the process products according to the invention as "lacquer isocyanates", their excellent compatibility with commercially available polyhydroxy polyacrylates should be emphasized in particular. Another advantage of the process products according to the invention over known biuret polyisocyanates is that in particular the products prepared from secondary amines are stable against monomer cleavage, ie that the monomer content of the polyisocyanates according to the invention does not increase even during storage at elevated temperature (50 ° C.).

example 1

In a 4 1 four-necked flask equipped with a stirrer, reflux condenser and contact thermometer, 135 g (3 mol) of dimethylamine were introduced into 3024 g (18 mol) of 1,6-diisocyanatohexane with a blanket of nitrogen, the temperature in the reaction vessel rising to approx. 60 ° C. The corresponding urea formed, which, apart from small residual amounts, was dissolved after the amine addition had ended. 7 g (0.19 mol) of hydrogen chloride in 100 g of 1,6-diisocyanatohexane were then added to the reaction mixture and the temperature was raised to 100.degree. The NCO content of the now clear reaction solution was 44% (corresponding to a consumption of 1 NCO group per amino group). After 2 hours the NCO content was 40% (corresponding to a consumption of 2 NCO groups per amino group) and after 4 hours to 35% (corresponding to a consumption of 3.3 NCO groups per amino group, corresponding to n = 2.3 ) decreased. The reaction solution was cooled to 50 ° C. and 11 g (0.19 mol) of propylene oxide were added to bind the hydrolyzable chlorine. The subsequent thin-layer distillation gave 1600 g of 1,6-diisocyanatohexane as the distillate and 1540 g of polyurethane polyisocyanate as the residue (NCO content = 19.5%; viscosity at 25 ° C = 5000 mPa.s; residual content of monomeric 1,6-diisocyanatohexane = 0 , 60%).

Based on the control of the _M onomerengehalts of product samples that were stored for extended periods at 50 ° C, it was found that the polyisocyanate against Monomerenrückspaltung is stable.

Example 2

Analogously to Example 1, 3024 g (18 mol) of 1,6-diisocyanatohexane were reacted with 225 g (5 mol) of dimethylamine with the addition of 7 g (0.19 mol) of hydrogen chloride. After 7 hours, the NCO content of the reaction mixture was 27.4% (corresponding to a consumption of 3 NCO groups per amino group (n = 2)). After the thin-layer evaporation, 2150 g of polyisocyanate were obtained in addition to 1000 g of 1,6-diisocyanatohexane (NCO content = 16.2%; viscosity at 25 ^° C. = 30,000 mPas; residual monomer content = 0.3%).

Example 3

Analogously to Example 1, 1008 g (6 mol) of 1,6-diisocyanatohexane were reacted with 45 g (1 mol) of dimethylamine with the addition of 3 g (0.08 mol) of hydrogen chloride. After 6 hours the NCO content of the reaction mixture had dropped to 28% (corresponding to a degree of conversion of 5 NCO groups per amino group (n = 4)). The viscosity of the crude isocyanate was 200 mPa · s / 25 ° C.

Example 5 (usage example)

154 g of a 65% solution of a strongly branched polyester based on phthalic anhydride and trimethylolpropane (hydroxyl content 8%) in ethyl glycol acetate / xylene (1: 1) were added after adding 1 g of a tertiary amine as catalyst and 0.4 g of cellulose butyrate propionate diluted as a leveling agent with 220 g of a solvent mixture of methyl ethyl ketone, butyl acetate, ethyl glycol acetate and toluene (4: 1: 4: 1). 135 g of a 75% strength solution of the polyisocyanate from Example 1 in ethyl glycol acetate / xylene (1: 1) were added (NCO / OH molar ratio = 1: 1). The finished paint solution was then applied to steel sheets where the paint films cured at room temperature. The fully cured clear lacquer films were scratch-resistant, elastic and resistant to solvents such as toluene, ethyl glycol acetate, ethyl acetate or acetone. They also had the following characteristics:

Example 6 (usage example)

154 g of the polyester solution described in Example 5 were processed with 100 g of titanium dioxide (rutile type) to form a paste. In addition to the catalyst and leveling agent, 120 g of the solvent mixture already described were added to this paste. The mixture thus obtained was mixed with 135 g of a 75% solution of the polyisocyanate from Example 1 in ethyl glycol acetate / xylene (1: 1) and applied in a thin layer to steel sheets. The paint films containing pigment hardened completely at room temperature. They were characterized by scratch resistance and solvent resistance and had the following properties compared to the clear lacquer films:

Claims (8)

1) Process for the preparation of modified, triuret or higher polyuret organic polyisocyanates, characterized in that primary or secondary monoamines with excess amounts of organic diisocyanates with formation of triuret or higher polyuret groups and incorporating the rest of the indifferent to the reaction Brings amine into the process product to react. 2) Process according to claim 1, characterized in that aliphatic or cycloaliphatic monoamines or mixtures thereof are used as monoamines. 3) Process according to claims 1 and 2, characterized in that aliphatic and / or cycloaliphatic diisocyanates are used as organic diisocyanates. 4) Modification of the process according to claims 1-3, characterized in that instead of the amines, the urea and / or biuret groups thereof, and the reaction products with organic diisocyanates which are indifferent to the reaction of the amines, are used. 5) Process according to claim 1 to 4, characterized in that one carries out the reaction in the presence of strong acids forming a mixed carbamic acid anhydride with isocyanates. 6) Compounds of the formula

in which R ₁ and R ₂ stand for identical or different radicals and mean aliphatic hydrocarbon radicals with 1-20 carbon atoms or cycloaliphatic hydrocarbon radicals with 4-20 carbon atoms, or where the two radicals together with the nitrogen atom optionally have a further heteroatomic heterocyclic ring with 5-6 ring members can form R ₃ and R _{4 represent the} same or different radicals and are aliphatic or cycloaliphatic hydrocarbon radicals having 4-20 carbon atoms and n represents a number from 2 to 8. 7) Compounds of the formula according to claim 6, wherein R ₁ and R _{2 represent} identical or different radicals and represent an aliphatic hydrocarbon radical with 1-4 carbon atoms or together with the nitrogen atom a piperidine radical, R ₃ and R ₄ each represent hexamethylene radicals and n stands for a number from 2 to 8. 8) Use of the modified polyisocyanates accessible as claimed in claim 1 as an isocyanate component in the production of polyurethane plastics by the isocyanate polyaddition process.