Process for the preparation of light stable polyisocyanates containing allophanate groups.

The present invention relates to a new process for the preparation of light-colored lightfast allophanate groups (cyclo) aliphatic polyisocyanates, and the use of the polyisocyanates obtainable by this process as a structural component in the production of polyurethane plastics.

Processes for the preparation of polyisocyanates containing allophanate groups have already been described in GB-PS 994 890, US-PS 3 769 318, EP-B 0 000 016, EP-B 0 000 194 and EP-A-0 303 150.

According to GB-PS 994 890, polyisocyanates containing urethane groups from simple mono- or polyhydric alcohols and organic polyisocyanates, in particular diisocyanates, are heated by heating to elevated temperatures or in the presence of catalysts such as metal carboxylates, metal chelates or tertiary amines with further amounts of organic polyisocyanates, preferably diisocyanates, until the isocyanate content calculated for complete conversion of the urethane groups is reached. The exact constitution of the reaction products cannot be given with certainty according to the teaching of the British patent. From the measured NCO values ​​of the reaction mixtures or The end products isolated therefrom are concluded that these are essentially allophanate polyisocyanates.

As was shown in a comparative example, purely thermal reaction according to GB-PS 994 890 gives strongly colored products which, according to 13 C-NMR spectroscopy, not only allophant polyisocyanates, but also considerable amounts of uretdione, urea and biuret polyisocyanates, which are caused by side reactions such as dimerization and biuretization arise, and contain unreacted urethanes. This can be explained by the fact that when the reaction is stopped at the NCO content calculated for complete allophanatization, a urethane group remains unreacted in the reaction mixture for each NCO group reacted by the side reaction.

The catalysts described in GB-PS 994 890 such as metal carboxylates, metal chelates and tertiary amines have long been known as dimerization and / or trimerization catalysts for isocyanates, so that the occurrence of such side reactions occurs to a considerable extent in the reaction of urethane groups with isocyanates to allophanates, such as shown in Comparative Examples 3 and 4, is quite understandable. It is not apparent from the patent specification under which conditions and / or with the aid of which catalysts pure allophanate polyisocyanates can be produced. Nor can it be deduced under what conditions light-colored light-fast products can be obtained.

The problem of making allophanate polyisocyanates that are not accompanied by dimeric and trimeric polyisocyanates is addressed in U.S. Patent No. 3,769,318. According to this patent, allophanate-containing polyisocyanates which have at least one aromatically bound isocyanate group are prepared by reacting N-substituted carbamic acid esters with isocyanates in the presence of alkylating sulfuric or sulfonic acid esters. According to a special variant, this method is carried out in the presence of certain metal compounds. In the long relevant list, the description also mentions tin (II) octoate, but this salt is not used in any specific embodiment. The prior publication thus does not provide any indication that tin compounds of the type mentioned below by way of example are to be selected from the long list of suitable metal compounds for the preparation of pure (cyclo) aliphatic polyisocyanates containing allophanate groups.

EP-B 0 000 016 and EP-A 0 303 150 describe purely thermal reaction of urethanes with organic polyisocyanates to form allophanate polyisocyanates. As can be seen from Comparative Example 1, purely thermal reactions of urethanes and isocyanates lead to side reactions to a considerable extent and to discoloration of the products.

EP-B 0 000 194 describes a process for the preparation of allophanate polyisocyanates with aliphatically and / or cycloaliphatically bound isocyanate groups, in which compounds containing urethane groups are reacted with polyisocyanates with aliphatically and / or cycloaliphatically bound isocyanate groups in the presence of strong acids. The presence of strong acids such as hydrogen chloride largely suppresses side reactions such as trimerization and biuretization, but the products obtained are discolored and tend to darken when they are left to stand for a long time (Comparative Example 2).

The prior art cited does not provide any suggestions as to how high-quality, in particular light-fast, ie (cyclo) aliphatic allophanate polyisocyanates could be obtained. However, since it had to be assumed that such polyisocyanates represent valuable starting materials for the production of lightfast polyurethane lacquers, it was the object of the invention to provide a process for the production of such allophanate polyisocyanates.

Surprisingly, this object was achieved by carrying out the reaction between aliphatic or cycloaliphatic polyisocyanates and compounds containing urethane groups in the presence of certain tin compounds described in more detail below. The process products according to the invention are distinguished by a low number of ferns, high lightfastness and color stability and, moreover, by a comparatively low viscosity and represent valuable starting materials for the production of polyurethane plastics, in particular polyurethane lacquers.

The present invention relates to a process for the preparation of allophanates containing aliphatic and / or cycloaliphatic isocyanate groups by reacting organic compounds containing urethane groups with organic polyisocyanates with aliphatic and / or cycloaliphatic isocyanate groups, characterized in that the reaction is carried out in the presence of tin compounds .

The present invention also relates to the use of the polyisocyanates obtainable by this process as a structural component in the production of polyurethane plastics, in particular crosslinking resin for two-component polyurethane lacquers which may be used in blocked form.

Starting materials for the process according to the invention are (i) organic compounds containing urethane groups and (ii) organic polyisocyanates with aliphatic and / or cycloaliphatic bound isocyanate groups.

The compounds containing urethane groups to be used in the process according to the invention are any compounds which may contain isocyanate groups and which have 1 to 70, preferably 1 to 40% by weight of urethane groups (calculated as CHNO₂, molecular weight = 59), and which are preferably Except for the urethane groups, there are no other H-active groups that are reactive towards isocyanate groups. Compounds containing urethane groups, for example, which have been obtained by reacting amines containing primary amino groups with chloroformic acid esters are suitable. However, the compounds containing urethane groups are preferably reaction products of isocyanates, in particular polyisocyanates, with organic hydroxyl compounds, ie alcohols or phenols, preferably alcohols.

According to a particular embodiment of the process according to the invention, urethanes prepared in situ from phenols or alcohols and excess amounts of aliphatic or cycloaliphatic polyisocyanates are used as starting materials. The reaction mixture obtained in this reaction then already contains the second main component of the process according to the invention, the aliphatic or cycloaliphatic polyisocyanate, which had been used in excess in the production of urethane. The preferred compounds containing urethane groups to be used as starting materials in the process according to the invention include those of the general formula<chemistry id="chem0001" num="0001"><img file="EP0682012A1_D0001.tif" /></chemistry> in which<dl id="dl0001"><dt>A</dt><dd>represents a radical such as is obtained by removing the hydroxyl groups from an n-valent organic compound which has hydroxyl groups and which, apart from the hydroxyl groups, has no further groups which are reactive toward isocyanate groups,</dd><dt>R₁</dt><dd>represents a radical as obtained by removing the isocyanate groups from a diisocyanate with aliphatic and / or cycloaliphatic bound isocyanate groups and</dd><dt>n</dt><dd>represents an integer from 1 to 4,</dd></dl> or mixtures of compounds of the formula mentioned containing urethane groups with up to 50% by weight, based on the mixture as a whole, of higher homologues of these compounds formed by chain extension reactions.

These urethanes which are particularly preferably used in the process according to the invention and contain isocyanate groups generally contain 1 to 40% by weight of urethane groups and 1 to 30% by weight of isocyanate groups, the radicals A and R 1 being (cyclo) aliphatic hydrocarbon radicals .

In accordance with these statements, the urethanes of the general formula mentioned which are preferably to be used in the process according to the invention and which have isocyanate groups are preferably reacted with compounds of the formula having hydroxyl groups         A (OH)_nwith diisocyanates of the formula         R₁ (NCO) ₂ obtained, the reactants being used in a ratio corresponding to an NCO / OH equivalent ratio of at least 1.1: 1, preferably at least 1.8: 1 and particularly preferably 2: 1 to 24: 1.

Likewise possible, but less preferred, would be the use of compounds containing urethane groups, which by reaction of compounds containing hydroxyl groups A (OH)_n with monoisocyanates and / or higher than difunctional polyisocyanates, optionally in a mixture with diisocyanates, and which may not have any free isocyanate groups.

The starting materials containing urethane groups for the process according to the invention are prepared by the well-known methods of polyurethane chemistry, ie in particular by simply heating the starting materials to 40 to 150 ° C., preferably 50 to 100 ° C.

If appropriate, the reaction can be carried out with catalysis using the known urethanization catalysts, but is preferably carried out without a catalyst or using catalysts such as are used for the allophanatization reaction, as described below.

As polyhydroxy compounds A (OH)_n can both phenols such. B. phenol, α-naphthol, cresol, resorcinol or trishydroxybenzenes as well as alcoholic hydroxyl organic compounds. Such compounds containing alcoholic hydroxyl groups are preferred over the phenols mentioned by way of example.

About these preferred alcoholic hydroxyl compounds A (OH)_n belong<ul id="ul0001" list-style="none"><li>1. Low molecular weight, optionally ether bridging 1-4-valent aliphatic alcohols in the molecular weight range 32-250 such as. B. Methanol, ethanol, propanol, isopropanol, allyl alcohol, isomeric butanols, pentanols, hexanols and heptanols, 2-ethylhexanol, fatty alcohols with 10 - 20 carbon atoms, ethanediol, 1,2- and 1,3-propanediol, 1,2-, 1, 3- and 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6- and 2,5-hexanediol, 3-methyl-1,5-pentanediol, 2-methyl-2-propyl-1,3- propanediol, 2,2-diethyl-1,3-propanediol, 2-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, trimethyl-1,6-hexanediol, 1,10- Decanediol, 1,12-dodecanediol, 2-methyl-1,4-butanediol, 2-methyl-1,3-propanediol, glycerol, butanetriol, 2-hydroxymethyl-2-methyl-1,3-propanediol, 1,2,6-hexanetriol, trimethylolethane, trimethylolpropane, Pentaerythritol, ethylene glycol monoalkyl or aryl ether, propylene glycol monoalkyl ether, diethylene glycol, triethylene glycol, tetraethylene glycol,</li><li>2nd Cycloaliphatic 1-4-valent alcohols in the molecular weight range 86-250, such as. B. Cyclopentanol, cyclohexanol, methylcyclohexanol, trimethylcyclohexanol, 4-tert-butylcyclohexanol, menthol, borneol and isoborneol, 2-hydroxydecalin, 1,2-, 1,3- and 1,4-cyclohexanediol, 2,4-dihydroxy-1,1 , 3,3-tetramethylcyclobutane, 1,4-bis (hydroxymethyl) cyclohexane, bis (4-hydroxycyclohexyl) methane, 2,2-bis (4-hydroxycyclohexyl) propane, 2,4-bis ( 4-hydroxycyclohexyl) -2-methylpentane, furfuryl and tetrahydrofurfuryl alcohol, bis (hydroxymethyl) norbornane, bis (hydroxymethyl) tricyclodecane,</li><li>3rd Araliphatic 1-4-valent alcohols in the molecular weight range 108-300, such as B. benzyl alcohol, phenylethyl alcohol, 3-phenylpropanol or 4,4'-bis (2-hydroxyethyl) diphenylmethane or</li><li>4th 1-4 hydroxyl-containing polythioethers, polyacetals, polycarbonates or in particular polyesters or polyethers of the type known per se in polyurethane chemistry with average molecular weights of 250 to 5000, preferably 300 to 2000. Suitable polyester polyols include, for example, the known reaction products of dihydric and, if appropriate, additionally trihydric alcohols, such as those of those already mentioned under 1, which correspond to the statements made. type mentioned by way of example with undersized amounts of polyvalent, preferably dihydric carboxylic acids or their anhydrides such as adipic acid, phthalic acid, isophthalic acid, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, maleic anhydride, and / or dimeric or trimeric oleic acids. Hydroxyl group-containing polycaprolactones of the type known per se can also be used as polyester polyols. The polyether polyols are the known alkoxylation products of suitable starter molecules, for example the polyhydric alcohols mentioned above under 1 or mixtures of such alcohols. In the alkoxylation, ethylene oxide and / or propylene oxide are preferably used alone, in a mixture and / or in blocks.</li></ul>

The simple aliphatic alcohols mentioned under 1. and the polyester or polyether polyols mentioned under 4. are preferably used in the process according to the invention.

Mixtures of the aforementioned hydroxyl compounds can of course also be used. This is even a preferred embodiment of the process according to the invention, since the functionality of the polyisocyanate containing allophanate groups can be varied as desired by using a mixture of hydroxyl compounds of different functionality.

According to the invention, such diisocyanates of the formula are preferably used to prepare the compounds containing urethane groups as starting materials for the process according to the invention and as reactants for these compounds         R₁ (NCO) ₂ used for which<dl id="dl0002"><dt>R₁</dt><dd>represents an aliphatic hydrocarbon radical having 2 to 20, preferably 6 to 10, carbon atoms, a cycloaliphatic hydrocarbon radical having 4 to 20, preferably 6 to 15 carbon atoms or a xylylene radical.</dd></dl>

Examples of such isocyanates are 1,2-diisocyanatoethane, 1,4-diisocyanatobutane, 1,6-diisocyanatohexane, 1,11-diisocyanatoundecane, 2,2,4- and 2,4,4-trimethyl-1,6-diisocyanatohexane, 1 Isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane (isophorone diisocyanate), 1,3-diisocyanatocyclobutane, 1,3- and 1,4-diisocyanatocyclohexane, 4,4'-bis (isocyanatocyclohexyl) methane, 1,2-bis (isocyanatomethyl) cyclobutane, 1,3- and 1,4-bis (isocyanatomethyl) cyclohexane, Hexahydro-2,4- and / or 2,6-diisocyanatotoluene, bis-isocyanatomethylnorbornane (mixture of isomers), 1-isocyanato-4 (3) -isocyanatomethyl-1-methylcyclohexane or p-xylylene diisocyanate. Such diisocyanates are used both in the preparation of the compounds containing urethane groups to be used according to the invention and as their reactants. 1,6-Diisocyanatohexane and isophorone diisocyanate are particularly preferred.

In the preparation of the compounds containing the starting materials serving as urethane groups, but not as their reactants in the process according to the invention, monoisocyanates such as. B. n-hexyl isocyanate or cyclohexyl isocyanate may be used, although this is less preferred.

Higher than difunctional aliphatic or cycloaliphatic polyisocyanates can also be used or used both in the preparation of the compounds containing urethane groups as starting materials and as their reactants. Examples of such polyisocyanates are the isocyanurate group-containing trimerization products of 1,6-diisocyanatohexane or of isophorone diisocyanate.

Any mixtures of the isocyanates mentioned can be used both in the preparation of the starting materials containing urethane groups and as their reactants, with the restriction that it is advisable to dispense with the use of monoisocyanates as reactants for the compounds containing urethane groups, since the NCO Functionality of the process products according to the invention would be reduced. The functionality of the process products according to the invention can be varied by selecting certain mixing ratios of the isocyanate components and by choosing the mixing ratio of different hydroxyl compounds.

Essential to the invention is the use of tin compounds in the reaction of the compounds containing urethane groups with the isocyanate component to form the corresponding allophanates containing isocyanate groups.

These tin compounds are tin salts and organotin compounds. Tin compounds which are soluble in the reaction mixture and have a tin content of 10 to 65% by weight, such as, in particular, tin (II) and organotin salts of organic acids and tin (II) halides are preferred. Examples of the preferred tin compounds are tin (II) chloride, bromide, iodide, tin (II) octanoate, tin (II) -2-ethylhexanoate and dibutyltin dilaurate. Tin (II) salts of organic acids such as, for example, tin (II) n-octanoate or tin (II) -2-ethylhexanoate are particularly preferred.

The tin compounds are used in the process according to the invention in amounts of 0.001-5.0, preferably 0.01-1.0% by weight, based on the total weight of the reactants.

The tin compounds can be incorporated into the reaction mixture by any method. For example, it is possible to mix the tin compound with the compound containing hydroxyl groups before the compound containing urethane groups is prepared. It is also possible, if the two-stage process is used, to mix the tin compound into the reaction mixture only before the compounds containing allophanate groups are prepared.

To carry out the process according to the invention, the reactants are generally used in amounts such that 2 to 50, preferably 3 to 12, isocyanate groups of the polyisocyanate component are present in each urethane group of the compound containing urethane groups. In the case of the production of the compound containing urethane groups in situ, a corresponding excess of the isocyanate component is accordingly used.

The reaction according to the invention is generally carried out in the temperature range between 50 and 140 ° C. The course of the reaction according to the invention can be followed by determining the NCO content of the reaction mixture. The reaction can be stopped at any time, for example by cooling to room temperature.

In the preferred variant of the process according to the invention in which the starting compound having urethane groups is prepared in situ, the procedure is generally as follows:

The diisocyanate, which is preferably used as the isocyanate component, is initially introduced at 50-80 ° C. and the hydroxyl component is added dropwise in liquid form with thorough stirring. If the same isocyanate or isocyanate mixture is to be used for urethane formation and allophanate formation, it is easiest to use it in such an excess from the start that the NCO / OH equivalent ratio is 3: 1 and 12: 1.

After the urethane reaction - controlled by determining the NCO content - the temperature is increased to 80-140 ° C and the catalyst (the tin compound) is added. The mixture is stirred until the NCO content has dropped to the value calculated for complete allophanatization.

However, the catalyst (the tin compound) can also be initially introduced together with the isocyanate or metered in together with the hydroxyl compound.

If the polyisocyanate containing allophanate groups is to be freed from excess diisocyanate, this is done either by thin-layer distillation or by fractional extraction, for example using n-hexane or cyclohexane as the extractant.

When carrying out the process according to the invention, the nature and proportions of the starting materials are generally chosen so that at least two allophanates containing isocyanate groups, ie allophanate polyisocyanates, are formed as process products. Process products of this type are distinguished by excellent stability during thin-film treatment, even at temperatures of 180 ° C. and more. The side and equilibration reactions observed in polyisocyanates with uretdione or biuret structure do not occur, which lead to annoying caking and an increase in viscosity.

The method according to the invention is suitable for continuous implementation. In this case, several reactors are advantageously connected in series in the form of a cascade. Diisocyanate, hydroxyl compound and catalyst are continuously metered into the first reactor. Setting the temperature and throughput ensures that the reaction is complete when it leaves the last reactor. The raw product then passes through a thin film evaporator, where it is freed from excess diisocyanate. This is returned to the first reactor.

The process products according to the invention are distinguished by a low color number, high light fastness and color stability and a comparatively low viscosity.

In particular, the excellent storage stability of the allophanate polyisocyanates according to the invention, freed from excess starting isocyanate, should also be emphasized. The products of the process according to the invention show no tendency to split off monomeric starting isocyanate and, in this point in particular, advantageously differ from known polyisocyanates containing uretdione or biuret groups.

The process products according to the invention are valuable starting materials for the production of polyurethane plastics by the isocyanate polyaddition process, in particular for the production of one- or two-component polyurethane coatings. When the process products according to the invention are used in a form blocked with known blocking agents for isocyanate groups, the process products according to the invention are also particularly suitable for the production of polyurethane stoving lacquers.

Preferred reactants for the process products according to the invention, optionally in blocked form, in the production of polyurethane lacquers are the polyhydroxy polyesters, polyhydroxy polyacrylates known per se in polyurethane lacquer technology and optionally low molecular weight, polyhydric alcohols. Suitable reactants of this type are described, for example, in DE-AS 2 304 893.

The proportions in which the optionally blocked polyisocyanates according to the invention and the reaction partners mentioned are reacted in the production of polyurethane lacquers are generally chosen so that 0.8-3, preferably 0.9-1, to an (optionally blocked) isocyanate group 1 Hydroxyl, amino, mercapto and / or carboxyl groups are omitted.

To accelerate the curing, the catalysts customary in isocyanate chemistry can be used in a known manner, such as, for. B. tert. Amines such as triethylamine, pyridine, methylpyridine, benzyldimethylamine, N, N-dimethylcyclohexylamine, N-methylpiperidine, pentamethyldiethylene triamine, N, N'-endoethylene piperazine, N, N'-dimethylpiperazine, etc., metal salts such as iron (III) chloride, zinc chloride, zinc -2-ethylhexanoate, tin (II) -2-ethylhexanoate, dibutyltin dilaurate, molybdenum glycolate, etc.

The allophanate polyisocyanates can also be used in one-component paints. Humidity curing produces glossy, high-quality coatings. If necessary, undersized amounts of OH components, especially the OH-functional reactants already mentioned, can also be used. They are used in an amount such that at least 1.25, preferably 1.5 to 10, NCO groups are accounted for by one OH group. The catalysts mentioned can also be used in one-component paints.

When the allophanate polyisocyanates are used in stoving lacquers, the NCO groups are blocked in whole or in part in a known manner. The polyisocyanate is with a suitable blocking agent, preferably at elevated temperature (z. B. 40 to 140 ° C) optionally in the presence of a suitable catalyst, such as. B. tert. Amines, metal salts such as zinc 2-ethylhexanoate, tin (II) -2-ethylhexanoate, dibutyltin dilaurate or alkali metal phenolate reacted.

Suitable blocking agents are, for example: Monophenols such as phenol, the cresols, the trimethylphenols, the tert. Butylphenols; tertiary alcohols such as tert-butanol, tert-amyl alcohol, dimethylphenylcarbinol; easily enol-forming compounds such as acetoacetic ester, acetylacetone, malonic acid derivatives such as malonic diester with 1 to 8 carbon atoms in the alcohol residues; secondary aromatic amines such as N-methylaniline, the N-methyltoluidines, N-phenyltoluidine, N-phenylxylidine; Imides such as succinimide; Lactams such as ε-caprolactam, δ-valerolactam; Oximes such as butanone oxime, cyclohexanone oxime; Mercaptans such as methyl mercaptan, ethyl mercaptan, butyl mercaptan, 2-mercaptobenzthiazole, α-naphthyl mercaptan, dodecyl mercaptan.

For the preparation of the paint binders, blocked polyisocyanate, polyfunctional reaction partner, catalyst and, if appropriate, the usual additives, such as, for. B. pigments, dyes, fillers and leveling agents with one another using a conventional mixing unit, for. B. dissolver, well mixed and homogenized either with or without solvent and diluent.

The paints and coatings can be in solvent-free liquid form or in solution or from the melt, or in solid form by the usual methods such. B. brushing, rolling, pouring, spraying, the vortex sintering process or the electrostatic powder spraying process can be applied to the object to be coated.

The lacquers containing the polyisocyanates according to the invention produce films which adhere surprisingly well to metallic substrates, are particularly lightfast, stable to heat color and very abrasion-resistant and, if they are used in air-drying lacquers, dry particularly quickly, even at temperatures around 0.degree. In addition, they are characterized by great hardness, elasticity, very good chemical resistance, high gloss, excellent weather resistance and good pigmentability.

The following examples illustrate the invention. All percentages relate to percentages by weight.

<b>Examples</b>

Example 1:

74 g (1 mol) of n-butanol were added dropwise at 70 ° C. to 336 g (2 mol) of 1,6-diisocyanatohexane (HDI) and the mixture was stirred for one hour, the reaction mixture having an NCO content of 30.7%, that of corresponds to complete urethanization. After the temperature had been raised to 100 ° C., 0.1 g (0.02% on reaction mixture) of tin (II) -2-ethylhexanoate was added. The mixture was stirred at 100 ° C. for 2 h until an NCO content of 20.5% was reached, which corresponds to complete allophanatization. With the aid of 13 C-NMR spectroscopy, the isocyanate secondary products in the reaction mixture were recorded quantitatively (see Table 1). The mixture was then worked up by thin-layer distillation, giving 334 g (81.4%) of a product with an NCO content of 12.9%, a viscosity of 890 mPas at 23 ° C. and a Hazen color number of 20.

Comparative Example 1

(catalyst-free, according to GB-PS 994 890)

336 g (2 mol) HDI and 74 g (1 mol) n-butanol were stirred at 70 ° C. until the NCO content of the reaction mixture was 30.7% (complete urethanization). The temperature was then raised to 150 ° C. and the mixture was stirred at this temperature for 24 h, as a result of which the NCO content of the reaction mixture was 22.3%, which corresponds to the extensive allophanatization. The isocyanate secondary products were determined quantitatively with the aid of 13 C-NMR spectroscopy (see Table 1). Since the reaction mixture was colored strongly yellow, it was not worked up by distillation.

Comparative Example 2

(according to EP-B 0 000 194, hydrogen chloride as catalyst):

336 g (2 mol) HDI and 74 g (1 mol) n-butanol were reacted at 70 ° C until urethane (NCO content 30.7%). After increasing the temperature to 100 ° C., 4.1 g (1%) of hydrogen chloride (in the form of an 8% solution of hydrogen chloride in HDI - formation of the carbamoyl chloride) were added. The mixture was stirred for 5 h at 100 ° C., an NCO content of 20.5% being achieved, which corresponds to complete allophanatization. The reaction mixture was analyzed using 13 C-NMR spectroscopy (Table 1) and worked up by thin-layer distillation. 332 g (81%) of a pale yellow product with an NCO content of 12.9%, a viscosity of 930 mPas at 23 ° C. and a Hazen color number of 50 were obtained. After 2 weeks of storage, the Hazen color number was 150.<tables id="tabl0001" num="0001"><table frame="all"><title>Table 1</title><tgroup cols="4" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row><entry namest="col1" nameend="col4" align="center">13 C NMR spectroscopic analysis</entry></row><row><entry namest="col1" nameend="col1" rowsep="0" align="center">Structure [% by weight]</entry><entry namest="col2" nameend="col2" rowsep="0" align="center">example 1</entry><entry namest="col3" nameend="col4" align="center">Comparative example</entry></row><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" align="center">1</entry><entry namest="col4" nameend="col4" align="center">2</entry></row><row><entry namest="col1" nameend="col1" align="left">Urethane</entry><entry namest="col2" nameend="col2" align="center">-</entry><entry namest="col3" nameend="col3" align="center">19,2</entry><entry namest="col4" nameend="col4" align="center">10,5</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Allophanate</entry><entry namest="col2" nameend="col2" align="center">97,8</entry><entry namest="col3" nameend="col3" align="center">65,0</entry><entry namest="col4" nameend="col4" align="center">82,4</entry></row><row><entry namest="col1" nameend="col1" align="left">Uretdione</entry><entry namest="col2" nameend="col2" align="center">-</entry><entry namest="col3" nameend="col3" align="center">3,3</entry><entry namest="col4" nameend="col4" align="center">1,6</entry></row><row><entry namest="col1" nameend="col1" align="left">Isocyanurate</entry><entry namest="col2" nameend="col2" align="center">2,2</entry><entry namest="col3" nameend="col3" align="center">-</entry><entry namest="col4" nameend="col4" align="center">1,6</entry></row><row><entry namest="col1" nameend="col1" align="left">urea</entry><entry namest="col2" nameend="col2" align="center">-</entry><entry namest="col3" nameend="col3" align="center">6,2</entry><entry namest="col4" nameend="col4" align="center">1,0</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Biuret</entry><entry namest="col2" nameend="col2" align="center">-</entry><entry namest="col3" nameend="col3" align="center">6,3</entry><entry namest="col4" nameend="col4" align="center">3,0</entry></row></tbody></tgroup></table></tables>

13 C NMR spectroscopic analyzes were carried out using a Bruker AMX-500 spectrometer at 125.76 MHz with proton noise decoupling (PND). Dimethylsulfoxide-d₆, tetramethylsilane (TMS) was used as solvent and ²H- "lock" was internal standard. The structures were assigned using the carbonyl carbon atom signals at 148-160 ppm (compared to TMS). The molar proportions obtained were converted to% by weight.

Example 2:

In a 2 l three-necked flask, 75 g (0.5 mol) of triethylene glycol were added dropwise to 1008 g (6 mol) of 1,6-diisocyanatohexane (HDI) at 70 ° C. in the course of 30 min. After a further 30 min at 70 ° C., the NCO content of the reaction mixture was 42.7%, which corresponds to the complete conversion of the OH groups to urethane groups. After raising the temperature to 100 ° C, 0.3 g (0.03%) of stannous (II) -2-ethylhexanoate was added. After 3 hours at 100 ° C., the NCO content of the reaction mixture corresponded to a complete conversion of the urethane groups to allophanate groups with 38.8%. The crude product was subjected to thin film distillation. 422 g of an almost colorless product (Hazen color number 25) with a viscosity of 1300 mPas at 23 ° C. and an NCO content of 18.8% were obtained. The composition of the product was examined by gel chromatography (Table 2).

Comparative Example 3

(According to GB-PS 994 890, zinc naphthenate as catalyst as in Example 5 of the GB-PS):

1008 g (6 mol) 1,6-diisocyanatohexane (HDI) and 75 g (0.5 mol) triethylene glycol were reacted as in Example 2 until the urethanization was complete (NCO content 42.7%). Then 1.15 g of zinc naphthenate were added. Within 8 hours at 50 ° C the NCO content dropped to 38.8%. After working up by thin-layer distillation, a brown-yellow product with an NCO content of 20.4% and a viscosity at 25 ° C. of 1350 mPas was obtained. GPC analysis see Table 2.

Comparative Example 4

(According to GB-PS 994 890, tertiary amine as catalyst as in Example 4 of the GB-PS):

As in Comparative Example 3 above, the urethane solution was prepared, then 1.15 g of diazabicyclooctane was added and the mixture was stirred at 70 ° C. for 24 hours. The theoretical NCO drop was only reached after a further 16 h at 120 ° C. After working up, a deep yellow oil with a viscosity of 1050 mPas at 25 ° C. and an NCO content of 20.2% was obtained. GPC analysis see Table 2. <tables id="tabl0002" num="0002"><table frame="all"><title>Table 2</title><tgroup cols="4" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row><entry namest="col1" nameend="col4" align="center">Gel chromatographic analysis</entry></row><row><entry namest="col1" nameend="col1" rowsep="0" align="center">Component [area%]</entry><entry namest="col2" nameend="col2" rowsep="0" align="center">Example 2</entry><entry namest="col3" nameend="col4" align="center">Comparative example</entry></row><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" align="center">3</entry><entry namest="col4" nameend="col4" align="center">4</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">HDI</entry><entry namest="col2" nameend="col2" align="center">0,2</entry><entry namest="col3" nameend="col3" align="center">0,7</entry><entry namest="col4" nameend="col4" align="char" char=",">0,5</entry></row><row><entry namest="col1" nameend="col1" align="left">Dimeric diisocyanate</entry><entry namest="col2" nameend="col2" align="center">0,5</entry><entry namest="col3" nameend="col3" align="center">1,5</entry><entry namest="col4" nameend="col4" align="center">6,3</entry></row><row><entry namest="col1" nameend="col1" align="left">Trimer diisocyanate</entry><entry namest="col2" nameend="col2" align="center">2,9</entry><entry namest="col3" nameend="col3" align="center">10,6</entry><entry namest="col4" nameend="col4" align="center">11,3</entry></row><row><entry namest="col1" nameend="col1" align="left">Bisurethane from 1 mol triethylene glycol and 2 mol diisocyanate</entry><entry namest="col2" nameend="col2" align="center">1,0</entry><entry namest="col3" nameend="col3" align="center">10,3</entry><entry namest="col4" nameend="col4" align="center">10,3</entry></row><row><entry namest="col1" nameend="col1" align="left">Monourethane monoallophanate</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /></row><row><entry namest="col1" nameend="col1" align="left">1 moles of triethylene glycol and 3 moles of diisocyanate</entry><entry namest="col2" nameend="col2" align="center">1,6</entry><entry namest="col3" nameend="col3" align="center">9,8</entry><entry namest="col4" nameend="col4" align="center">15,6</entry></row><row><entry namest="col1" nameend="col1" align="left">Bisallophanate from 1 mol triethylene glycol and 4 mol diisocyanate</entry><entry namest="col2" nameend="col2" align="center">31,9</entry><entry namest="col3" nameend="col3" align="center">20,8</entry><entry namest="col4" nameend="col4" align="center">12,2</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Sum of all polymer homologous compounds</entry><entry namest="col2" nameend="col2" align="center">61,9</entry><entry namest="col3" nameend="col3" align="center">46,3</entry><entry namest="col4" nameend="col4" align="center">43,8</entry></row></tbody></tgroup></table></tables>

Examples 3-13:

see tables 3 and 4

<tables id="tabl0003" num="0003"><table frame="all"><title>Table 3</title><tgroup cols="7" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="22.50mm" /><colspec colnum="2" colname="col2" colwidth="22.50mm" /><colspec colnum="3" colname="col3" colwidth="22.50mm" /><colspec colnum="4" colname="col4" colwidth="22.50mm" /><colspec colnum="5" colname="col5" colwidth="22.50mm" /><colspec colnum="6" colname="col6" colwidth="22.50mm" /><colspec colnum="7" colname="col7" colwidth="22.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col7" align="center">Examples 3 - 8 (analogous to example 1):</entry></row><row><entry namest="col1" nameend="col1" align="left">example</entry><entry namest="col2" nameend="col2" align="center">3</entry><entry namest="col3" nameend="col3" align="center">4</entry><entry namest="col4" nameend="col4" align="center">5</entry><entry namest="col5" nameend="col5" align="center">6</entry><entry namest="col6" nameend="col6" align="center">7</entry><entry namest="col7" nameend="col7" align="center">8</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Isocyanate</entry><entry namest="col2" nameend="col2" align="center">HDI</entry><entry namest="col3" nameend="col3" align="center">HDI</entry><entry namest="col4" nameend="col4" align="center">HDI</entry><entry namest="col5" nameend="col5" align="center">HDI</entry><entry namest="col6" nameend="col6" align="center">HDI</entry><entry namest="col7" nameend="col7" align="center">HDI</entry></row><row><entry namest="col1" nameend="col1" align="left">alcohol</entry><entry namest="col2" nameend="col2" align="center">n-BuOH</entry><entry namest="col3" nameend="col3" align="center">n-BuOH</entry><entry namest="col4" nameend="col4" align="center">n-BuOH</entry><entry namest="col5" nameend="col5" align="center">n-BuOH</entry><entry namest="col6" nameend="col6" align="center">n-BuOH</entry><entry namest="col7" nameend="col7" align="center">n-BuOH</entry></row><row><entry namest="col1" nameend="col1" align="left">NCO / OH</entry><entry namest="col2" nameend="col2" align="center">4,0</entry><entry namest="col3" nameend="col3" align="center">6,0</entry><entry namest="col4" nameend="col4" align="center">8,0</entry><entry namest="col5" nameend="col5" align="center">10,0</entry><entry namest="col6" nameend="col6" align="center">4,0</entry><entry namest="col7" nameend="col7" align="center">10,0</entry></row><row><entry namest="col1" nameend="col1" align="left">catalyst</entry><entry namest="col2" nameend="col2" align="center">A</entry><entry namest="col3" nameend="col3" align="center">A</entry><entry namest="col4" nameend="col4" align="center">A</entry><entry namest="col5" nameend="col5" align="center">A</entry><entry namest="col6" nameend="col6" align="center">B</entry><entry namest="col7" nameend="col7" align="center">B</entry></row><row><entry namest="col1" nameend="col1" align="left">[%]</entry><entry namest="col2" nameend="col2" align="center">0,04</entry><entry namest="col3" nameend="col3" align="center">0,02</entry><entry namest="col4" nameend="col4" align="center">0,02</entry><entry namest="col5" nameend="col5" align="center">0,02</entry><entry namest="col6" nameend="col6" align="center">0,05</entry><entry namest="col7" nameend="col7" align="center">0,05</entry></row><row><entry namest="col1" nameend="col1" align="left">Reaction temperature [° C]</entry><entry namest="col2" nameend="col2" align="center">110</entry><entry namest="col3" nameend="col3" align="center">110</entry><entry namest="col4" nameend="col4" align="center">110</entry><entry namest="col5" nameend="col5" align="center">110</entry><entry namest="col6" nameend="col6" align="center">110</entry><entry namest="col7" nameend="col7" align="center">110</entry></row><row><entry namest="col1" nameend="col1" align="left">Response time [h]</entry><entry namest="col2" nameend="col2" align="center">2</entry><entry namest="col3" nameend="col3" align="center">3</entry><entry namest="col4" nameend="col4" align="center">2</entry><entry namest="col5" nameend="col5" align="center">1,5</entry><entry namest="col6" nameend="col6" align="center">4</entry><entry namest="col7" nameend="col7" align="center">1,5</entry></row><row><entry namest="col1" nameend="col1" align="left">NCO_End [%]</entry><entry namest="col2" nameend="col2" align="center">20,3</entry><entry namest="col3" nameend="col3" align="center">29,1</entry><entry namest="col4" nameend="col4" align="center">33,8</entry><entry namest="col5" nameend="col5" align="center">36,7</entry><entry namest="col6" nameend="col6" align="center">20,8</entry><entry namest="col7" nameend="col7" align="center">36,6</entry></row><row><entry namest="col1" nameend="col1" align="left">yield_resin [%]</entry><entry namest="col2" nameend="col2" align="center">80,7</entry><entry namest="col3" nameend="col3" align="center">58,9</entry><entry namest="col4" nameend="col4" align="center">46,0</entry><entry namest="col5" nameend="col5" align="center">38,9</entry><entry namest="col6" nameend="col6" align="center">76,9</entry><entry namest="col7" nameend="col7" align="center">39,2</entry></row><row><entry namest="col1" nameend="col1" align="left">NCO_resin [%]</entry><entry namest="col2" nameend="col2" align="center">12,7</entry><entry namest="col3" nameend="col3" align="center">15,3</entry><entry namest="col4" nameend="col4" align="center">17,4</entry><entry namest="col5" nameend="col5" align="center">18,6</entry><entry namest="col6" nameend="col6" align="center">12,5</entry><entry namest="col7" nameend="col7" align="center">17,8</entry></row><row><entry namest="col1" nameend="col1" align="left">Viscosity [mPas]</entry><entry namest="col2" nameend="col2" align="center">870</entry><entry namest="col3" nameend="col3" align="center">200</entry><entry namest="col4" nameend="col4" align="center">160</entry><entry namest="col5" nameend="col5" align="center">140</entry><entry namest="col6" nameend="col6" align="center">1050</entry><entry namest="col7" nameend="col7" align="center">240</entry></row><row><entry namest="col1" nameend="col1" align="left">Hazen color number</entry><entry namest="col2" nameend="col2" align="center">25</entry><entry namest="col3" nameend="col3" align="center">25</entry><entry namest="col4" nameend="col4" align="center">30</entry><entry namest="col5" nameend="col5" align="center">25</entry><entry namest="col6" nameend="col6" align="center">40</entry><entry namest="col7" nameend="col7" align="center">40</entry></row><row rowsep="1"><entry namest="col1" nameend="col7" align="justify">Catalyst: A = tin (II) -2-ethylhexanoate B = tin (II) chloride</entry></row></tbody></tgroup></table></tables><tables id="tabl0004" num="0004"><table frame="all"><title>Table 4</title><tgroup cols="6" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="26.25mm" /><colspec colnum="2" colname="col2" colwidth="26.25mm" /><colspec colnum="3" colname="col3" colwidth="26.25mm" /><colspec colnum="4" colname="col4" colwidth="26.25mm" /><colspec colnum="5" colname="col5" colwidth="26.25mm" /><colspec colnum="6" colname="col6" colwidth="26.25mm" /><thead valign="top"><row><entry namest="col1" nameend="col6" align="center">Examples 9-13 (analogous to Example 1):</entry></row><row><entry namest="col1" nameend="col1" align="left">example</entry><entry namest="col2" nameend="col2" align="center">9</entry><entry namest="col3" nameend="col3" align="center">10</entry><entry namest="col4" nameend="col4" align="center">11</entry><entry namest="col5" nameend="col5" align="center">12</entry><entry namest="col6" nameend="col6" align="center">13</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Isocyanate</entry><entry namest="col2" nameend="col2" align="center">HDI</entry><entry namest="col3" nameend="col3" align="center">HDI</entry><entry namest="col4" nameend="col4" align="center">IPDI</entry><entry namest="col5" nameend="col5" align="center">IPDI</entry><entry namest="col6" nameend="col6" align="center">IPDI</entry></row><row><entry namest="col1" nameend="col1" align="left">alcohol</entry><entry namest="col2" nameend="col2" align="center">MeOH</entry><entry namest="col3" nameend="col3" align="center">EtOH</entry><entry namest="col4" nameend="col4" align="center">n-BuOH</entry><entry namest="col5" nameend="col5" align="center">n-BuOH</entry><entry namest="col6" nameend="col6" align="center">n-BuOH</entry></row><row><entry namest="col1" nameend="col1" align="left">NCO / OH</entry><entry namest="col2" nameend="col2" align="center">8,0</entry><entry namest="col3" nameend="col3" align="center">8,0</entry><entry namest="col4" nameend="col4" align="center">6,0</entry><entry namest="col5" nameend="col5" align="center">8,0</entry><entry namest="col6" nameend="col6" align="center">10,0</entry></row><row><entry namest="col1" nameend="col1" align="left">catalyst</entry><entry namest="col2" nameend="col2" align="center">A</entry><entry namest="col3" nameend="col3" align="center">A</entry><entry namest="col4" nameend="col4" align="center">A</entry><entry namest="col5" nameend="col5" align="center">A</entry><entry namest="col6" nameend="col6" align="center">A</entry></row><row><entry namest="col1" nameend="col1" align="left">[%]</entry><entry namest="col2" nameend="col2" align="center">0,05</entry><entry namest="col3" nameend="col3" align="center">0,05</entry><entry namest="col4" nameend="col4" align="center">0,1</entry><entry namest="col5" nameend="col5" align="center">0,1</entry><entry namest="col6" nameend="col6" align="center">0,1</entry></row><row><entry namest="col1" nameend="col1" align="left">Reaction temperature [° C]</entry><entry namest="col2" nameend="col2" align="center">110</entry><entry namest="col3" nameend="col3" align="center">110</entry><entry namest="col4" nameend="col4" align="center">110</entry><entry namest="col5" nameend="col5" align="center">110</entry><entry namest="col6" nameend="col6" align="center">110</entry></row><row><entry namest="col1" nameend="col1" align="left">Response time [h]</entry><entry namest="col2" nameend="col2" align="center">2</entry><entry namest="col3" nameend="col3" align="center">2,5</entry><entry namest="col4" nameend="col4" align="center">6</entry><entry namest="col5" nameend="col5" align="center">3,5</entry><entry namest="col6" nameend="col6" align="center">3</entry></row><row><entry namest="col1" nameend="col1" align="left">NCO_End [%]</entry><entry namest="col2" nameend="col2" align="center">34,9</entry><entry namest="col3" nameend="col3" align="center">35,0</entry><entry namest="col4" nameend="col4" align="center">23,1</entry><entry namest="col5" nameend="col5" align="center">26,2</entry><entry namest="col6" nameend="col6" align="center">28,0</entry></row><row><entry namest="col1" nameend="col1" align="left">yield_resin [%]</entry><entry namest="col2" nameend="col2" align="center">48,1</entry><entry namest="col3" nameend="col3" align="center">47,2</entry><entry namest="col4" nameend="col4" align="center">56,8</entry><entry namest="col5" nameend="col5" align="center">41,9</entry><entry namest="col6" nameend="col6" align="center">38,0</entry></row><row><entry namest="col1" nameend="col1" align="left">NCO_resin [%]</entry><entry namest="col2" nameend="col2" align="center">18,6</entry><entry namest="col3" nameend="col3" align="center">18,4</entry><entry namest="col4" nameend="col4" align="center">13,4</entry><entry namest="col5" nameend="col5" align="center">13,8</entry><entry namest="col6" nameend="col6" align="center">14,2</entry></row><row><entry namest="col1" nameend="col1" align="left">Viscosity [mPas]</entry><entry namest="col2" nameend="col2" align="center">540</entry><entry namest="col3" nameend="col3" align="center">270</entry><entry namest="col4" nameend="col4" align="center">230*</entry><entry namest="col5" nameend="col5" align="center">200*</entry><entry namest="col6" nameend="col6" align="center">180*</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Hazen color number</entry><entry namest="col2" nameend="col2" align="center">30</entry><entry namest="col3" nameend="col3" align="center">30</entry><entry namest="col4" nameend="col4" align="center">50</entry><entry namest="col5" nameend="col5" align="center">40</entry><entry namest="col6" nameend="col6" align="center">50</entry></row></tbody></tgroup><tgroup cols="6" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="26.25mm" /><colspec colnum="2" colname="col2" colwidth="26.25mm" /><colspec colnum="3" colname="col3" colwidth="26.25mm" /><colspec colnum="4" colname="col4" colwidth="26.25mm" /><colspec colnum="5" colname="col5" colwidth="26.25mm" /><colspec colnum="6" colname="col6" colwidth="26.25mm" /><tbody valign="top"><row><entry namest="col1" nameend="col6" align="justify">* = 70% solution in methoxypropylacetate</entry></row><row><entry namest="col1" nameend="col6" align="justify">Catalyst: A = tin (II) -2-ethylhexanoate B = tin (II) chloride</entry></row></tbody></tgroup></table></tables>