Preparation of polyisocyanates containing iminooxadiazinedione groups and their use

Description

The present invention relates to a novel process for preparing polyisocyanates containing iminooxadiazinedione groups by a partial trimerization of (cyclo)aliphatic diisocyanate in the presence of at least one oligomerization catalyst from the group of pentafluorobenzoates and to the use of the thus obtainable polyisocyanates containing iminooxadiazinedione groups as a polyisocyanate component in polyurethane coatings.

Processes for partially or fully trimerizing (cyclo)aliphatic polyisocyanates for preparing polyisocyanates containing iminooxadiazinedione groups or cellular or compact polyurethanes having isocyanurate groups are known and are described in numerous literature publications.

These state-of-the-art processes are summarized in H. J. Laas et al, J. Prakt. Chem. 1994, 336, 185 ff.

EP-A 962455, 962454, 896009, 798299, 447074, 379914, 339396, 315692, 295926 and 235388 disclose processes which lead to products with a high proportion of iminooxadiazinedione groups (asymmetric isocyanate trimers).

Suitable catalysts are, for example, fluoride or poly(hydrogen)fluoride [F- x (HF) _m ], preferably with quaternary phosphonium cations as counterions, wherein m is a number between 0,001 till 20, preferably 0,5 till 5, very preferably 1.

EP2976373 discloses a catalyst kit comprising a trimerization catalyst for the asymmetric trimerization of polyisocyanates and a catalyst poison for the trimerization catalyst. Possible catalyst poisons, i.e. , stoppers, are quite generally anhydrous acids having a pKa value below 3.2.

However, disadvantages of these prior art processes are that the reactivity of the catalyst, is low, caused, among other things, by partially decomposition of the catalyst and toxicity of the catalysts containing fluoride is high.

It is an object of the present invention to provide a process for the preparation of polyisocyanates containing a high content of iminooxadiazinedione groups which is characterized by a higher reactivity and lower toxicity. Catalyst should be employable over a wide temperature range, should have a good solubility in the reaction mixture and should have less tendency to decompose. This object is achieved by a process for preparing polyisocyanates containing iminooxadiazinedione groups by at least reacting at least one (cyclo)aliphatic diisocyanate in the presence of at least one oligomerization catalyst, wherein the oligomerization catalyst is a salt containing pentafluorobenzoate as anion.

A further object of the present invention relates to the use of the thus obtainable polyisocyanates containing iminooxadiazinedione groups as a polyisocyanate component in polyurethane coatings.

Oligomerization catalysts are salts containing pentafluorobenzoate as anion. Pentafluorobenzoate is shown in formula (I)

Suitable cations may in principle be any species known to be catalytically active with respect to isocyanates. These cations may ensure good solubility in the isocyanate medium. Preference is being given to tetraalkylammonium, tetraalkylphosphonium, guanidinium, sulfonium, imidazoli- um, benzotriazolium and pyridinium. Especially preferred are cations according to formula (II) wherein

X is nitrogen or phosphorus and

R ¹ , R ² , R ³ and R ⁴ may each independently be the same or different and are each a straight- chain or branched optionally substituted, preferably not substituted Ci- to C2o-alkyl group, an optionally substituted, preferably not substituted C5- to Ci2-cycloalkyl group, an optionally substituted, preferably not substituted C7- to Cw-aralkyl group, or an optionally substituted, preferably not substituted Ce-Cw-aryl group, or two or more of the R ¹ to R ⁴ radicals together form a 4-, 5- or 6-membered alkylene chain or, together with a nitrogen atom, form a 5- or 6-membered ring which may also contain an additional nitrogen or oxygen atom as a bridge member, or together form a multimembered, preferably six-membered, polycyclic system, preferably bicyclic system, which may also contain one or more additional nitrogen atoms, oxygen atoms or oxygen and nitrogen atoms as bridge members.

In these compounds, a straight-chain or branched, not substituted Ci- to C2o-alkyl group is, for example, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, 2,4,4-trimethylpentyl, nonyl, dodecyl, eicosyl, decyl, 1 , 1-dimethylpropyl, 1 ,1 -dimethylbutyl or 1 , 1 ,3,3-tetramethylbutyl, an optionally substituted C5- to Ci2-cycloalkyl group is cyclopentyl, cyclohexyl, cyclooctyl, cyclododecyl, methylcyclopentyl, dimethylcyclopentyl, methylcyclohexyl, dimethylcyclohexyl, diethylcyclohexyl, butylcyclohexyl, methoxycyclohexyl, di methoxycyclohexyl, diethoxycyclohexyl, butylthiocyclohexyl, chlorocyclohexyl, dichlorocyclohexyl, dichlorocyclopentyl, or else a saturated or unsaturated bicyclic system, for example norbornyl or norbornenyl, an optionally substituted C7- to Cw-aralkyl group is, for example, benzyl, 1 -phenylethyl, 2-phenylethyl, a,a-dimethylbenzyl, benzhydryl, p-tolylmethyl, 1-(p-butylphenyl)ethyl, o-, m- or p-chlorobenzyl, 2,4-dichlorobenzyl, o-, m- or p-methoxybenzyl or o-, m- or p-ethoxybenzyl, an optionally substituted Ce-Cw-aryl group is, for example, phenyl, 2-, 3- or 4-methylphenyl, a-naphthyl or [3-naphthyl, an optionally substituted Ci-C2o-alkyl optionally interrupted by one or more oxygen and/or sulfur atoms and/or one or more substituted or unsubstituted imino groups or substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles is, for example, 2-carboxyethyl, 2-cyanoethyl, 2-cyanopropyl, 2-methoxycarbonylethyl, 2-ethoxycarbonylethyl, 2-butoxycarbonylpropyl, 1 ,2-di(methoxycarbonyl)ethyl, 2-methoxyethyl, 2-ethoxyethyl, 2-butoxy- ethyl, diethoxymethyl, diethoxyethyl, 1 ,3-dioxolan-2-yl, 1 ,3-dioxan-2-yl, 2-methyl-1,3-dioxolan-2- yl, 4-methyl-1 ,3-dioxolan-2-yl, 2-isopropoxyethyl, 2-butoxypropyl, 2-octyloxyethyl, chloromethyl, 2-chloroethyl, trichloromethyl, trifluoromethyl, 1 ,1-dimethyl-2-chloroethyl, 2-methoxyisopropyl, 2-ethoxyethyl, butylthiomethyl, 2-dodecylthioethyl, 2-phenylthioethyl, 2,2,2-trifluoroethyl, 2-hy- droxyethyl, 2-hydroxypropyl, 3-hydroxypropyl, 4- hydroxy butyl, 6- hydroxy hexyl, 1 -hydroxy- 1 ,1 -dimethylmethyl, 2-hydroxy-2,2-dimethylethyl, 2-phenoxyethyl, 2-phenoxypropyl, 3-phenoxy- propyl, 4-phenoxybutyl, 6-phenoxyhexyl, 2-methoxyethyl, 2-methoxypropyl, 3-methoxypropyl, 4-methoxybutyl, 6-methoxyhexyl, 2-ethoxyethyl, 2-ethoxypropyl, 3-ethoxypropyl, 4-ethoxybutyl or 6-ethoxyhexyl, and

Ce- to Ci2-aryl optionally interrupted by one or more oxygen atoms and/or sulfur atoms and/or one or more substituted or unsubstituted imino groups or substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles is, for example tolyl, xylyl, 4- di-phenylyl, chlorophenyl, dichlorophenyl, trichlorophenyl, difluorophenyl, methylphenyl, dime- thyl-phenyl, tri methyl phenyl, ethylphenyl, diethylphenyl, isopropylphenyl, tert-butylphenyl, do- decyl-phenyl, methoxyphenyl, dimethoxyphenyl, ethoxyphenyl, hexyloxyphenyl, methylnaphthyl, isopropylnaphthyl, chloronaphthyl, ethoxynaphthyl, 2,6-dimethylphenyl, 2,4,6-trimethylphenyl, 2,6-dimethoxyphenyl, 2,6-dichlorophenyl, 4-bromophenyl, 2- or 4-nitrophenyl, 2,4- or 2,6-dinitro- phenyl, 4-dimethylaminophenyl, 4-acetylphenyl, methoxyethylphenyl or ethoxymethylphenyl.

Examples of R ¹ to R ⁴ are in each case independently methyl, ethyl, 2-hydroxyethyl, 2-hydroxy- propyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, dodecyl, phenyl, a- or p-naphthyl, benzyl, cyclopentyl or cyclohexyl.

When two or more of the R ¹ to R ⁴ radicals form a ring, these may be, for example, 1 ,4-butylene, 1 ,5-pentylene, 3-oxa-1 ,5-pentylene, 3-aza-1 ,5-pentylene or 3-methyl-3-aza-1 ,5-pentylene.

Preferred R ¹ to R ⁴ radicals are each independently methyl, ethyl, 2-hydroxyethyl, 2-hydroxy- propyl, propyl, isopropyl, n-butyl, tert-butyl, hexyl, octyl, 2-ethylhexyl, nonyl, decyl, dodecyl, phenyl and benzyl, particular preference is given to methyl, ethyl, n-butyl, octyl, decyl, dodecyl, phenyl and benzyl, very particular preference is given to methyl, ethyl, n-butyl, octyl, decyl, dodecyl and in particular methyl, n-butyl, octyl, decyl and dodecyl.

In one embodiment of the present invention all radicals R ¹ to R ⁴ are hydrocarbons without any atoms other than carbon or hydrogen.

Examples of such ammonium cations are tetraoctylammonium, tetramethylammonium, tetraethylammonium, tetra-n-butylammonium, trimethylbenzylammonium, triethylbenzylammonium, tri-n-butylbenzylammonium, trimethylethylammonium, trimethyloctylammonium, trimethyldec- ylammonium, trimethyldodecylammonium, benzyldimethyloctylammonium, benzyldimethyldecylammonium, benzyldimethyldodecylammonium, tri-n-butylethylammonium, triethylmethylammonium, tri-n-butylmethylammonium, diisopropyldiethylammonium, diisopropylethylmethylammonium, diisopropylethylbenzylammonium, N,N-dimethylpiperidinium, N,N-dimethylmor- pholinium, N,N-dimethylpiperazinium or N-methyldiazabicyclo[2.2.2]octane. Preferred alkylammonium ions are tetraoctylammonium, tetramethylammonium, tetraethylammonium and tet- ra-n-butylammonium, particular preference is given to tetramethylammonium and tetraethylammonium and very particular preference is given to tetra-n-butylammonium.

Further examples of ammonium cations are described in WO2021/122508. Described are cyclic ammonium cations of the formula III where Y is a linear or branched C2-C20 segment which is substituted by a hydroxyl group in the 2 position to the charge-bearing nitrogen atom and optionally bears further substituents and is optionally interrupted by heteroatoms from the group of oxygen, sulfur, nitrogen and aromatic rings and optionally has further rings, and the N-bonded substituents R5 and R6 are either independently identical or different, substituted or unsubstituted, optionally branched, aliphatic C1-C20 radicals, aromatic C6-C20 radicals or araliphatic C7-C20 radicals or the N-bonded substituents R5 and R6 form a ring segment X with one another for which the same or different definition given above for Y is applicable, with the proviso that X has a hydroxyl group as substituent in the 2 position to the charge-bearing nitrogen atom or does not have a hydroxyl group as substituent in the 2 position to the charge-bearing nitrogen atom.

In a further embodiment the sum of carbon atoms in the radicals R ¹ to R ⁴ is at least 11 , particularly preferred at least 13, very particularly preferred at least 15.

In another embodiment of the present invention one radical out of the four radicals R ¹ to R ⁴ is a substituted Ci-C2o-alkyl the other three radicals being hydrocarbons.

Examples of such ammonium cations are 2-hydroxyethyl trimethylammonium, 2-hydroxypropyl trimethylammonium, 2-hydroxyethyl triethylammonium, 2-hydroxypropyl triethylammonium, 2-hydroxyethyl tri-n-butylammonium, 2-hydroxypropyl tri-n-butylammonium, 2-hydroxyethyl di- methyl benzyl ammonium, 2-hydroxypropyl dimethyl benzyl ammonium, N-(2-hydroxyethyl),N- methyl morpholinium, N-(2-hydroxypropyl),N-methyl morpholinium or 3-hydroxy quinuclidine, preferably 2-hydroxyethyl trimethylammonium, 2-hydroxypropyl trimethylammonium, 2-hydroxy- ethyl dimethyl benzyl ammonium and 3-hydroxy quinuclidine, very preferably 2-hydroxyethyl trimethylammonium and 2-hydroxypropyl trimethylammonium and particularly preferably 2-hy- droxypropyl trimethylammonium.

Ammonium ions containing ring systems are, for example, methylated, ethylated or benzylated piperazines, piperidines, morpholines, quinuclidines or triethylenediamines.

However, this embodiment is less preferred than the embodiment with all radicals R ¹ to R ⁴ being hydrocarbons.

Preferred phosphonium ions are tetramethyl phosphonium, tetrabutyl phosphonium, tetraoctyl phosphonium, and tetradecyl phosphonium, trihexyl(tetradecyl)phosphonium, triisobu- tyl(methyl)phosphonium, tributyl(tetradecyl)phosphonium, tri-n-butylethylphosphonium, tribu- tyl(octyl)phosphonium, tetra-n-butylphosphonium and mixtures thereof. Specifically, preferred is tetra-n-butyl phosphonium.

Tetrabutyl phosphonium, tetrabutyl ammonium and trimethylbenzyl ammonium are the most preferred cations.

The inventive process is preferably carried out at a temperature of from 20° C to 120° C, preferably 40-80 °C, very preferably 50-70 °C.

The oligomerization catalysts which can be used in accordance with the invention can be prepared by known processes, e.g., as described in EP1727842.

The oligomerization catalyst may be used in substance, as solution or as suspension.

Preferably the oligomerization catalyst is used in substance. In another embodiment the oligomerization catalyst is dissolved in a solvent before the addition to the (cyclo)aliphatic diisocyanate.

When the catalyst is used as a solution, depending on the solubility in the solvent used, a solution having a dilution of generally 90 - 20%, preferably 90 - 50%, more preferably 85 - 55% and most preferably 70 - 80% by weight catalyst content is established. In principle, suitable solvents are those in which the catalyst has a good solubility. Preferred solvents are alcohols, toluene, xylene, cyclic ethers, carboxylic esters and ketones or mixtures. Very preferred solvents are alcohols comprising methanol, isopropanol or containing at least 6 carbon atoms, more preferred 2-ethyl hexan-1-ol and 2-propyl heptan-1-ol.

The oligomerization catalysts used may also be mixtures with other known oligomerization catalysts, and these may be mixed in broad ratios, for example in ratios of from 90:10 to 10:90, preferably from 80:20 to 20:80 and more preferably from 60:40 to 40:60.

To prepare the polyisocyanates containing iminooxadiazinedione groups, the oligomerization catalysts, depending on their catalytic activity, are appropriately used in very small effective amounts which can be determined experimentally in a simple manner.

In general, the oligomerization catalysts are used in the process according to the invention in an amount of from 1 ppm to 1 %, preferably from 20 ppm to 500 ppm, very preferably from 50 ppm to 500 ppm, most preferably from 50 ppm to 300 ppm based on the (cyclo)aliphatic diisocyanates.

The process according to the invention is appropriately carried out at a temperature in the range from 20 to 120°C and reaction times of 10 min to 6 hours, preferably of from 20 min to 3 hours, more preferably of from 20 min to 2 hours. At temperatures above 150°C, discoloration of the polyisocyanates containing iminooxadiazinedione groups may occur, for example in the case of prolonged reaction times. The temperature is preferably such that the reactivity of the catalyst is sufficiently high. The temperature is preferably such that the share of iminooxadiazinedione versus standard isocyanurate is not dropping too far. The optimum temperature range is given above.

The oligomerization may be carried out continuously, semicontinuously or batchwise, preferably continuously.

In a batch process, in general, it is unimportant which components are initially charged or added. Usually, the isocyanate to be trimerized is at least partly, preferably fully, initially charged and the at least one catalyst is added slowly and/or in portions, then brought to the desired reaction temperature, and the remainder of the catalyst is added, if appropriate in portions.

An alternative preparation variant proceeds as follows: a batchwise process is performed in a stirred reactor. The mixture of diisocyanate and catalyst is initially charged typically at approx. 40°C. After- wards, the oligomerization is initiated by increasing the temperature of the reaction mixture to from 50 to 120°C, preferably to from 50 to 80°C. Alternatively, the catalyst may also be metered in after the diisocyanate has attained the temperature necessary for the reaction. The oligomerization is generally exothermic. The catalyst is preferably dissolved in a suitable solvent and to use it in this form.

The continuous oligomerization may appropriately be carried out continuously in a reaction coil with continuous, simultaneous metering of diisocyanate and the catalyst at from 40 to 120°C and within from 30 seconds to 4 hours. A reaction coil having a small diameter leads to the achievement of high flow rates and consequently good mixing. It is also advantageous to heat the diisocya- nate/catalyst mixture to from approx. 50 to 60°C before entry into the reaction coil. For more precise metering and optimal mixing of the catalyst, it is also advantageous to dissolve the catalyst in a suitable solvent. In principle, suitable solvents are those in which the catalyst has a good solubility.

The continuous trimerization may also be carried out in a multiple reactor cascade. The reaction is stopped in the last reactor of the cascade or in e.g., a static mixer.

Typically, the reaction is carried out under a gas or gas mixture which is inert under the reaction conditions, for example those having an oxygen content of below 2%, preferably below 1 %, more preferably below 0.5% by volume, most preferably no oxygen. Preference is given to nitrogen, argon, nitrogen-noble gas mixtures; particular preference is given to nitrogen.

Once the desired degree of trimerization, i.e. NCO content, or degree of reaction (based on the NCO content before the reaction) of the iminooxadiazinedione /(cyclo)aliphatic diisocyanate reaction mixture has been attained, the degree of reaction appropriately being in the range of from 5 to 40% of the NCO groups, preferably from 8 to 30% of the NCO groups, very preferably from 10 to 20% of the NCO groups, and for which typically reaction times of from 0.05 to 4 hours, preferably from 10 min to 3 hours, are required, the oligomerization reaction may be ended, for example, by deactivating the oligomerization catalyst.

Preferably the catalyst poison contains at least one acid having a pKa value below 4.0, preferably below 2.0.

Suitable catalyst poisons are inorganic acids or acid esters, for example hydrogen chloride, phosphorous acid, dialkyl phosphorous acids, preferably bis-2-ethyl-hexyl phosphorous acid and bis-butyl-phosphorous acid, phosphoric acid, carbonyl halides, preferably acetyl chloride or benzoyl chloride, sulfonic acids or esters, preferably methanesulfonic acid, p-toluene sulfonic acid, methyl or ethyl p-toluene sulfonate, p-dodecyl benzyl-toluol-sulfonic acid, m- chloroperbenzoic acid.

More preferably the catalyst poison acid ester containing phosphorus or sulfur, very preferably the catalyst poison is para-toluene sulfonic acid or p-dodecyl benzenesulfonic acid.

The catalyst poisons may, based on the oligomerization catalysts, be used in equivalent or excess amounts, and the smallest effective amount, which can be determined experimentally, is preferred simply for economic reasons. For example, the catalyst poison is used in a ratio to the oligomerization catalyst of 0.7:1 - 1.5:1 mol/mol and very particularly preferably 0.9:1 - 1.2:1 mol/mol, most preferably 1 :1.

The addition of the catalyst poison depends upon the type of the catalyst poison. For instance, liquid catalyst poisons such as dibutylphosphate or di-2-ethylhexyl-phosphate may be added as a solution in a solvent.

Solid catalyst poisons are preferably added in diluted form as a solution or suspension, preferably as a solution.

Solvents preferably are reactive towards NCO groups.

Preferably alcohols are used as solvents.

The alcohol may be a primary, secondary, or tertiary alcohol. Primary alcohols are for example 2-ethyl-1 -butanol, 2-ethyl-hexane-1-ol; n-octan-1-ol; nonan-1-ol; 2-n-propyl-n-heptane-1-ol; n- decan-1-ol; iso-decan-1 -ol [C9-C11-alcohol mixture (C10 rich; “iso-decanol)]; 2-butyl-octan-1-ol; undecane-1-ol; iso-tridecan-1-ol; 2-hexyl-decanol, dodecan-1-ol, 1-tridecyl alcohol, tetradecan- 1-ol, pentadecyl alcohol, hexadecyl alcohol, octadecyl alcohol. Alcohols may as well be mixtures of different molecular composition as of different chain lengths.

Secondary alcohols are for example 3-decanol or 4-decanol.

Preferably the alcohol is a primary alcohol. Preferred alcohols are 2-ethyl hexanol and 2-n- propyl heptan-1-ol, very preferred 2-ethyl-hexan-1-ol.

The alcohol may be monofunctional, difunctional or trifunctional. Difunctional alcohols are for example 2-ethyl-1 ,3-hexandiol, neopentyl glycol, 1 ,6- hexanediol, 1 ,7-heptanediol, 1 ,8-octa- nediol, 1 ,9-nonanediol and 1 ,10-decanediol; branched aliphatic diols such as 3-methyl[1]1 ,5- pentanediol, 2-methyl-1 ,8-octanediol, and 2,2-diethyl-1 ,3-propanediol; cyclic aliphatic diols such as 1 ,2-cyclohex[1]anediol, 1 ,4-cyclohexanediol, 1 ,2-cyclohexanedimethanol, 1 ,4-cyclohexane- dimethanol, 1 ,3-cyclobutanediol, 2,2,4,4,-te[1]tramethyl-1 ,3-cyclobutanediol, hydrogenated bisphenol A, isosorbide, isomannide, andisoidide, 2-propyl-1 ,3-heptandiol, 2,4-diethyloctan-1 ,3- diol, and cycloaliphatic diols, containing 6 to 20 carbon atoms, preferably b is- (4- hydroxy cy cl o- hexan)isopropyliden, tetramethylcyclobutandiol, 1 ,2-, 1 ,3- Oder 1 ,4-cyclohexandiol, cyclooctan- diol, norbornandiol, 2,2-bis(4-hydroxycyclohexyl)propan, 1 ,1-, 1 ,2-, 1 ,3- and 1 ,4-cyclohexan- dimethanol. Mixtures between primary alcohols and secondary alcohols are possible as well, preferably the mixture of 2-ethyl-hexane-1-ol or 2-n-propyl-n-heptane-1-ol with 2-ethyl-1,3-hexandiol, preferably the first one. Preferably the alcohol is monofunctional.

The alcohol may be linear or branched, preferably the alcohol is branched.

The alcohol may be aliphatic or cycloaliphatic. A cyclic alcohol may be cyclo hexanediol or cyclohexane dimethanol. Preferably the alcohol is aliphatic.

The alcohols may be alkoxylated, for example, ethoxylated, propoxylated or butoxylated. Preferably the alcohol is not alkoxylated.

Alkoxylated alcohols may be for example triethyleneglycol, dipropyleneglycol, 2-butoxyethanol 2-butoxypropanol, triethylenglycol monoethylether, diiethylenglycol monopropylether, eth- ylenglycol monopentylether, dipropyleneglycol monoethylether, propyleneglycol monopropylether, propyleneglycol monopentylether, poly-THF as poly THF 250, poly-THF 650, poly-THF 1000, poly-THF 1800, poly-THF 1000 poly-THF 2000, poly-THF 2900, 2,2,4-trimethyl-1 ,3- pentandiol, 1,4-cyclohexanedimethanol, 1 ,3-cyclohexanedimethanol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

The alcohol may be saturated or unsaturated. Unsaturated alcohols may be for example cis-9- hexadecenol or c/s,c/s-9,12-octadecadien-1-ol. Preferably the alcohol is saturated.

The solution may contain further solvents, e.g., further alcohols, toluene, xylene, cyclic ethers, carboxylic esters and ketones or mixtures thereof. In the preferred form, only alcohol is used.

The alcohols used may also be mixtures of alcohols.

The catalyst poisons are generally added at ambient temperature but might be preheated to the reaction temperature.

The polyisocyanates containing iminooxadiazinedione groups which are prepared by the process according to the invention may be freed of any solvent or diluent present and/or preferably of excess, unconverted (cyclo)aliphatic diisocyanates in a manner known per se, for example by thin-film distillation at a temperature of from 100 to 180°C, if appropriate under reduced pressure, if appropriate additionally while passing through inert stripping gas, or extraction, so that the polyisocyanates containing iminooxadiazinedione groups are obtainable with a content of monomeric diisocyanates of, for example, below 1.0% by weight, preferably below 0.5% by weight, more preferably below 0.3% by weight, even more preferably below 0.2% by weight and in particular not more than 0.1% by weight. The polyisocyanates containing iminooxadiazinedi- one groups are suitable, for example, for coatings, preparing Pll foams, cellular or compact elastomers, casting compositions and adhesives.

Without removal of the excess monomeric diisocyanates, the polyisocyanates containing iminooxadiazinedione groups are suitable, for example, for preparing Pll foams, cellular or compact elastomers, casting compositions and adhesives. The monomer-free and monomer- containing polyisocyanates containing iminooxadiazinedione groups may also be modified in a manner known per se by introducing, for example, urethane, allophanate, urea, biuret, isocy- anurate and/or carbodiimide groups, and/or the isocyanates may be capped with suitable capping agents.

The process according to the invention can be used to oligomerize any organic diisocyanates having aliphatic, cycloaliphatic, or aliphatic and cycloaliphatic isocyanate groups or mixtures thereof.

Suitable aliphatic diisocyanates have advantageously from 3 to 16 carbon atoms, preferably from 4 to 12 carbon atoms, in the linear or branched alkylene radical, and suitable cycloaliphatic diisocyanates have advantageously from 4 to 18 carbon atoms, preferably from 6 to 15 carbon atoms, in the cycloalkylene radical. Examples include: 1,4-diisocyanatobutane, 2-ethyl-1,4-diisocyanatobutane, 1,5-diisocyanatopentane (PDI), 2-methyl-1 ,5-diisocyanatopentane, 2,2-dimethyl-1 ,5-diisocyanatopentane, 2-propyl-2-ethyl-1 ,5- diisocyanato-pentane, 2-butyl-2-ethyl- 1 ,5-diisocyanatopentane, 2-alkoxymethylene-1 ,5-diiso- cyanatopentane, 3-methyl-, 3-ethyl-1,5-diisocyanatopentane, hexamethylene 1 ,6-diisocyanate (HDI), 2,4,4- or 2,2, 4-tri-methylhexamethylene 1,6-diisocyanate, 1,7-diisocyanatoheptane, 1,8- diisocyanatooctane, 1,10-diisocyanatodecane, 1 ,12-diisocyanatododecane, 4,4’-diisocyanatodicyclohexylmethane, 2,4’-diisocyanatodicyclohexylmethane, and also mixtures of the diisocyanato dicyclohexyl methane isomers, 1,3-diisocyanatocyclohexane and also isomer mixtures of diisocyanato cyclohexanes and 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane. The (cyclo)aliphatic diisocyanates used are preferably hexamethylene diisocyanate (HDI), pentamethylene diisocyanate (PDI), 5-isocyanato-1-(isocyanatomethyl)-1,3,3-trimethylcyclohexane (IPDI), 2-methyl pentane 1,5-diisocyanate, 2, 4, 4-trimethyl-1,8-hexane diisocyanate, 2,2,4-trimethyl-1,6-hexane diisocyanate and 4-isocyanatomethyl-1.8-octane, very preferably hexamethylene 1,6-diisocy- anate (HDI) and 1,5-diisocyanatopentane (PDI).

It will be appreciated that the oligomerization catalysts also catalyze the trimerization of aromatic isocyanates but are preferred for (cyclo)aliphatic isocyanates. The inventive process may be used for the oligomerization of (cyclo)aliphatic diisocyanates prepared by any processes, for example by a phosgene-free process route or one proceeding with the use of phosgene.

The (cyclo)aliphatic diisocyanates which can be used in accordance with the invention may be prepared by any processes, for example by phosgenating the appropriate diamines and thermally dissociating the dicarbamoyl chlorides formed as an intermediate. (Cyclo)aliphatic diisocyanates prepared by phosgene-free processes do not contain any chlorine compounds as byproducts and therefore contain, because of the preparation, a fundamentally different byproduct spectrum.

It will be appreciated that mixtures of isocyanates which have been prepared by the phosgene process and by phosgene-free processes may also be used.

The (cyclo)aliphatic diisocyanates which can be used in the process according to the invention and are obtainable by a phosgene-free process and especially by thermal dissociation of (cycloaliphatic dicarbamic esters are not restricted, and preference is given in particular to selecting diisocyanates obtainable by thermal dissociation of (cyclo)aliphatic dicarbamic esters from the group of hexamethylene 1,6-diisocyanate, 2-butyl-2-ethylpentamethylene 1,5-di isocyanate and 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane.

In a preferred embodiment of the invention, isocyanate monomers are used which have a total chlorine content of 800 ppm by weight or less, preferably 400 ppm by weight or less, most preferably 200 ppm by weight or less.

In a preferred embodiment of the invention, isocyanate monomers are used which have a hydrolyzable chlorine content of 100 ppm by weight or less, more preferably 50, 25, respectively 20 ppm by weight or less.

Polyisocyanates containing iminooxadiazinedione groups and prepared by these process variants are suitable preferentially for producing polyurethane coatings, for example textile and leather coatings, for polyurethane dispersions and adhesives, and find use in particular as a polyisocyanate component in one- and two-component polyurethane systems for high-grade, weather-resistant polyurethane coatings. These preferably are high-solids or water borne coatings.

Coating formulations obtained are suitable for coating substrates such as wood, wood veneer, paper, cardboard, paperboard, textile, film, leather, nonwoven, plastics surfaces, glass, ceramic, mineral building materials, such as molded cement blocks and fiber-cement slabs, or metals, which in each case may optionally have been precoated or pretreated.

Coating compositions of this kind are suitable as or in interior or exterior coatings, i.e. , in those applications where there is exposure to daylight, preferably of parts of buildings, coatings on (large) vehicles and aircraft, and industrial applications, utility vehicles in agriculture and construction, decorative coatings, bridges, buildings, power masts, tanks, containers, pipelines, power stations, chemical plants, ships, cranes, posts, sheet piling, valves, pipes, fittings, flanges, couplings, halls, roofs, and structural steel, furniture, windows, doors, woodblock flooring, can coating and coil coating, for floor coverings, such as in parking levels or in hospitals and in particular in automotive finishes, as OEM and refinish application. ppm and percentage data used in this document relate, unless stated otherwise, to percentages by weight and ppm by weight.

The examples which follow are intended to illustrate the invention, but not restrict it to these examples.

Examples

Cat1 : 2,3,4,5,6-pentafluorobenzoate trimethyl benzylammonium

8,0g of 2,3,4,5,6-pentafluorobenzoic acid (Sigma Aldrich) were diluted in 20g Methanol using a magnetic stirrer. 15,8g of trimethylbenzylammonium hydorixe (10wt% solution in methanol - Sigma Aldrich) were slowly added within 15 minutes. The solution was stirred at room temperature for 8Hours. The solution was finally distilled using a rotary evaporator (40°C and 40 mBar for 2 hours. H-NMR confirmed the formation of 2,3,4,5,6-pentafluorobenzoic acid trimethyl benzylammonium with a residual methanol content of 20wt%.

Cat2: 2,3,4,5,6-pentafluorobenzoate tetrabutylphosphonium

To 1,25g Tetrabutylphosphonium hydroxide (40 wt% in water from Sigma Aldrich) were added 383,58mg of 2,3,4,5,6-Pentafluorobenzoic acid (Sigma Aldrich). The reaction was stirred overnight at room temperature and the residual water was lyophilized over 24 hours. A clean product was detected using 1 H-NMR (D2O).

Cat3: 2,3,4,5,6-pentafluorobenzoate tetrabutylammonium

To 1,25g Tetrabutylammonium hydroxide (40 wt% in water from Sigma Aldrich) were added 408,66mg of 2,3,4,5,6-Pentafluorobenzoic acid (Sigma Aldrich). The reaction was stirred overnight at room temperature and the residual water was lyophilized over 24 hours. A clean product was detected using 1 H-NMR (D2O). CatA: 2,3,4,5-tetrafluorobenzoatetrimethyl benzylammonium

The synthesis described in Cat1 was repeated whereby : 2,3,4,5-tetrafluorobenzoic acid was used as starting material instead of 2,3,4,5,6-pentafluorobenzoic acid trimethyl benzylammonium. H-NMR confirmed the formation of 2,3,4,5,6-pentafluorobenzoic acid trimethyl benzylammonium with a residual methanol content of 20wt%.

CatB: 2,3,4-trifluorobenzoate trimethyl benzylammonium

The synthesis described in Cat1 was repeated whereby : 2,3,4-trifluorobenzoic acid was used as starting material instead of 2,3,4,5,6-pentafluorobenzoic acid trimethyl benzylammonium. H- NMR confirmed the formation of 2,3,4,5,6-pentafluorobenzoic acid trimethyl benzylammonium with a residual methanol content of 15wt%.

CatC: 2,4,5-trifluorobenzoate trimethyl benzylammonium

The synthesis described in Cat1 was repeated whereby : 2,4,5-trifluorobenzoic acid was used as starting material instead of 2,3,4,5,6-pentafluorobenzoic acid trimethyl benzylammonium. H- NMR confirmed the formation of 2,3,4,5,6-pentafluorobenzoic acid trimethyl benzylammonium with a residual methanol content of 15wt%.

CatD: 2,3,6-trifluorobenzoate acid trimethyl benzylammonium

The synthesis described in Cat1 was repeated whereby : 2,3,6-trifluorobenzoic acid was used as starting material instead of 2,3,4,5,6-pentafluorobenzoic acid trimethyl benzylammonium. H- NMR confirmed the formation of 2,3,4,5,6-pentafluorobenzoic acid trimethyl benzylammonium with a residual methanol content of 5wt%.

CatE: 2,6-difluorobenzoate trimethyl benzylammonium

The synthesis described in Cat1 was repeated whereby : 2,6-difluorobenzoic acid trimethyl benzylammonium was used as starting material instead of 2,3,4,5,6-pentafluorobenzoic acid trimethyl benzylammonium. H-NMR confirmed the formation of 2,3,4,5,6-pentafluorobenzoic acid trimethyl benzylammonium with a residual methanol content of 5wt%.

CatF: tetrabutylammonium benzoate (Sigma Aldrich)

OLIGOMERIZATION EXAMPLE

Cat1 :

819,0 grams of freshly distillated HDI were charged to a 1L, 4-neck round bottom flask equipped with a thermometer (coupled with a temperature regulated oil-bath), mechanical stirring, a cold- water condenser and nitrogen inlet. The reaction was degassed using vacuum at 60°C. Upon stirring 300ppm Cat1 were added, and the reaction mixture was maintained around at 60°C (maximal temperature below 65°C). After 50 minutes the NCO content reached 44,3% and the reaction was stopped using a stoichiometric amount of para-toluolsulfonic acid (40wt% in isopropanol). After distillation of the unreacted HDI using a thin film evaporator (165 °C / 2 mbar) a polyisocyanate with a viscosity of 935 mPa.s (23°C) and a NCO content of 23,6% is obtained. 13C NMR analysis revealed that iminooxadiazinedione I (iminooxadiazinedione + Isocyanurate) ratio was 43%

Cat2:

194,4mg Cat2 was charged to flame-dried Schlenk tube under argon and 525, 5mg n- hexylisocyanate (Sigma Aldrich), which was purified by destination under inert conditions and stored under an argon atmosphere at 4 °C, was added. The color changed from colorless to yellow and gas was formed. The reaction was stirred at 60 °C. 1H NMR after 1 hour revealed a complete conversion of HMI to 37mol% tri-n-hexylisocyanurate and 63mol% tri-n- hexyliminooxadiozinedione

Cat 3:

178,3mg Cat3 was charged to flame-dried Schlenk tube under argon and 500, Omg n- hexylisocyanate (Sigma Aldrich), which was purified by destination under inert conditions and stored under an argon atmosphere at 4 °C, was added. The color changed from colorless to yellow and gas was formed. The reaction was stirred at 60 °C. 1H NMR after 1 hour revealed a complete conversion of HMI to 68mol% tri-n-hexylisocyanurate and 32mol% tri-n- hexyliminooxadiozinedione

Cat A:

798,0 grams of freshly distillated HDI were charged to a 1L, 4-neck round bottom flask equipped with a thermometer (coupled with a temperature regulated oil-bath), mechanical stirring, a cold- water condenser and nitrogen inlet. The reaction was degassed using vacuum at 60°C. Upon stirring 2425ppm CatA were added, and the reaction mixture was maintained around at 60°C (maximal temperature below 65°C). After 110 minutes the NCO content reached 43,7% and the reaction was stopped using a stoichiometric amount of para-toluolsulfonic acid (40wt% in isopropanol). After distillation of the unreacted HDI using a thin film evaporator (165 °C / 2 mbar) a polyisocyanate with a viscosity of 2060 mPa.s (23°C) and a NCO content of 22,6% is obtained. 13C NMR analysis revealed that iminooxadiazinedione I (iminooxadiazinedione + Isocyanurate) ratio was 5%. Cat B:

799,0 grams of freshly distillated HDI were charged to a 1L, 4-neck round bottom flask equipped with a thermometer (coupled with a temperature regulated oil-bath), mechanical stirring, a cold- water condenser and nitrogen inlet. The reaction was degassed using vacuum at 60°C. Upon stirring 2634ppm Cat B were added, and the reaction mixture was maintained around at 60°C (maximal temperature below 65°C). After 133 minutes the NCO content reached 42,4% and the reaction was stopped using a stoichiometric amount of para-toluolsulfonic acid (40wt% in isopropanol). After distillation of the unreacted HDI using a thin film evaporator (165 °C / 2 mbar) a polyisocyanate with a viscosity of 2650 mPa.s (23°C) and a NCO content of 22,1% is obtained. 13C NMR analysis revealed that iminooxadiazinedione I (iminooxadiazinedione + Isocyanurate) ratio was 10%.

Cat C:

829,0 grams of freshly distillated HDI were charged to a 1L, 4-neck round bottom flask equipped with a thermometer (coupled with a temperature regulated oil-bath), mechanical stirring, a cold- water condenser and nitrogen inlet. The reaction was degassed using vacuum at 60°C. Upon stirring 2465ppm Cat C were added, and the reaction mixture was maintained around at 60°C (maximal temperature below 65°C). After 91 minutes the NCO content reached 43,2% and the reaction was stopped using a stoichiometric amount of para-toluolsulfonic acid (40wt% in isopropanol). After distillation of the unreacted HDI using a thin film evaporator (165 °C / 2 mbar) a polyisocyanate with a viscosity of 2060 mPa.s (23°C) and a NCO content of 22,4% is obtained. 13C NMR analysis revealed that iminooxadiazinedione I (iminooxadiazinedione + Isocyanurate) ratio was 5%.

Cat D:

801,0 grams of freshly distillated HDI were charged to a 1 L, 4-neck round bottom flask equipped with a thermometer (coupled with a temperature regulated oil-bath), mechanical stirring, a cold- water condenser and nitrogen inlet. The reaction was degassed using vacuum at 60°C. Upon stirring 1500ppm Cat D were added, and the reaction mixture was maintained around at 60°C (maximal temperature below 65°C). After 165 minutes the NCO content reached 49,8% The temperature was then increased to 80°C and an additional 1000ppm Cat D was added. After an additional 160 min, the NCO content reached 49,7% indicating that almost no reaction which indicated that no or limited reaction took place.

Cat E:

798,0 grams of freshly distillated HDI were charged to a 1L, 4-neck round bottom flask equipped with a thermometer (coupled with a temperature regulated oil-bath), mechanical stirring, a cold- water condenser and nitrogen inlet. The reaction was degassed using vacuum at 60°C. Upon stirring 2600ppm Cat E were added, and the reaction mixture was maintained around at 60°C (maximal temperature below 65°C). After 240 minutes the NCO content reached 49,9% which indicated that no or limited reaction took place.

Cat F:

900,0 grams of freshly distillated HDI were charged to a 1L, 4-neck round bottom flask equipped with a thermometer (coupled with a temperature regulated oil-bath), mechanical stirring, a cold- water condenser and nitrogen inlet. The reaction was degassed using vacuum at 60°C. Upon stirring 600ppm Cat F were added, and the reaction mixture was maintained around at 60°C (maximal temperature below 65°C). After 150 minutes the NCO content reached 41,2% and the reaction was stopped using a stoichiometric amount of di-2-ethyl-hexylphosphate). After distillation of the unreacted HDI using a thin film evaporator (165 °C / 2 mbar) a polyisocyanate with a viscosity of 2450 mPa.s (23°C) and a NCO content of 22,1% is obtained. 13C NMR analysis revealed that iminooxadiazinedione I (iminooxadiazinedione + Isocyanurate) ratio was less than 1%.