HK1066783B - Preparation of polyisocyanates containing uretdione groups - Google Patents

Description

Preparation of polyisocyanates containing uretdione groups

Cross reference to related patent applications

According to 35U.SC. § 119(a) to (d), the present application claims priority from German patent application No.10254878.1 filed 11, 25, 2002.

Technical Field

The present invention relates to the use of cycloalkylphosphines as catalysts for the dimerization of isocyanates and to a process for preparing polyisocyanates containing uretdione groups.

Background

There have been few attempts to prepare aliphatic polyisocyanates containing uretdione groups and as far as possible free from by-products, using catalysts whose catalytic selectivity is only very little, or even not at all, dependent on temperature and conversion.

Aliphatic isocyanates which contain uretdione groups, have a low by-product content and are based on optionally branched, linear aliphatic diisocyanates are characterized by a particularly low viscosity; products based on cycloaliphatic diisocyanates can be used as internally blocked crosslinkers in coating systems, which can avoid the removal of the product.

Tris (dialkylamino) phosphine (DE-A3030513) shows very good selectivity for the formation of uretdione groups (uretdione selectivity), optionally together with a cocatalyst (DE-A3437635). But due to the oxide of phosphorus (V): such as hexamethylphosphoric triamide, have serious drawbacks represented by high carcinogenic potential, and the technical usefulness of tris (dialkylamino) phosphine is limited. For example, DE-A3739549 discloses a method for catalyzing the dimerization of NCO with 4-dialkylamino-pyridines, such as 4-Dimethylaminopyridine (DMAP), but the formation of uretdione is selective only in the case of specific cycloaliphatic isocyanates, such as isophorone diisocyanate (IPDI). Linear aliphatic isocyanates, such as Hexamethylene Diisocyanate (HDI) and branched, linear aliphatic isocyanates, such as trimethylhexane diisocyanate (TMDI) and methylpentane diisocyanate (MPDI), when used in combination with DMAP and its related compounds, give rise to particularly highly colored heterogeneous reaction products.

DE-A1670720 discloses the preparation of aliphatic polyisocyanates containing uretdione groups, in which the catalysts used are tertiary phosphines or boron trifluoride containing at least one aliphatic substituent and adducts thereof, respectively. It is mentioned that a high percentage of uretdione groups in the product can only be obtained at low conversion and reaction temperatures of 50 to 80 ℃ with concomitant formation of isocyanate trimers (isocyanurates and iminooxadiazinediones), and that, especially at relatively high temperatures, other by-products such as carbodiimides or uretonimines, which are particularly prone to cleavage (irriptive) due to the tendency to precipitate monomeric isocyanates during storage, are also formed.

To terminate the reaction at low conversions, the phosphine catalyst was deactivated by alkylation with dimethyl sulfate (ED-A1670720) or methyl tosylate (EP-A377177), and unreacted monomers were subsequently removed from the product. This deactivation reaction requires temperatures up to 60 ℃ and, owing to the long reaction times, leads to a delay in the actual termination of the uretdione formation reaction and, overall, therefore to increased formation of by-products.

According to the teaching of DE-A1954093, the above-mentioned problems can be overcome by using elemental sulphur as a terminating agent. The reaction is stopped instantaneously regardless of the reaction temperature. However, the amount of sulfur required is difficult to determine due to partial catalyst deactivation during the catalytic reaction. For example, an excessive amount of the catalyst poison used leads to polyisocyanate products having unfavorable properties such as clouding and problems of affecting the reuse of unreacted monomers due to contamination with sulfur.

It is therefore an object of the present invention to provide a process for preparing isocyanates containing uretdione groups which exhibits a higher selectivity for uretdione formation (uretdione selectivity) and an equal or higher monomer conversion, while the tendency to form uretonimines is significantly reduced, compared with the prior art.

Disclosure of Invention

It is an object of the present invention to provide a process for preparing polyisocyanates containing uretdione groups, which comprises reacting at least one organic isocyanate, a catalyst containing at least one phosphine which contains at least one cycloaliphatic group directly attached to the phosphorus atom, optionally one or more solvents, and optionally one or more additives.

Drawings

FIG. 1 shows a graph of conversion as a function of refractive index; and

fig. 2 shows a graph of refractive index as a function of time.

Detailed Description

It has now been found that cycloalkylphosphines having at least one cycloaliphatic radical attached directly to the phosphorus have a better selectivity in the formation of uretdiones (uretdionization) starting from organic isocyanates and over a wider temperature range than the phosphines with linear aliphatic substituents used hitherto for this purpose. Furthermore, when the catalysts used according to the invention are used, it has been found that the tendency to form uretonimines is particularly low and that there is a particularly positive influence on the storage properties of the polyisocyanates prepared.

The invention provides the use of a phosphine having at least one cycloaliphatic radical attached directly to the phosphorus as a catalyst for the formation of uretdiones ("uretdiones") in the isocyanate dimerization.

The phosphines used according to the invention are phosphines of the formula I:

formula I

Wherein

R¹Is optionally mono or multiple C₁～C₁₂Alkyl-or alkoxy-substituted C₃～C₂₀And R²，R³Independently of one another are optionally mono-or poly-C₁～C₁₂Alkyl-or alkoxy-substituted C₃～C₂₀Cycloaliphatic radical of (A) or (C)₁～C₂₀Linear or branched aliphatic radical of (1).

Among them, preferred is

R¹Is optionally mono or multiple C₁～C₁₂Alkyl-substituted cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl,

R²，R³independently of one another are optionally mono-or poly-C₁～C₁₂Alkyl-substituted cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl or aliphatic C₂～C₈An alkyl group.

Examples of cycloaliphatic phosphines for use according to the invention are: cyclopentyl dimethylphosphine, cyclopentyl diethylphosphine, cyclopentyl di-n-propylphosphine, cyclopentyl di-isopropylphosphine, cyclopentyl dibutylphosphine, where "butyl" may represent all isomers, i.e. n-butyl, isobutyl, 2-butyl, tert-butyl and cyclobutyl, cyclopentyl dihexylphosphine (all isomeric hexyl radicals), cyclopentyl dioctylphosphine (all isomeric octyl radicals), dicyclopentyl methylphosphine, dicyclopentyl ethylphosphine, dicyclopentyl-n-propylphosphine, dicyclopentyl-isopropylphosphine, dicyclopentyl-butylphosphine (all isomeric butyl radicals), dicyclopentyl-hexylphosphine (all isomeric hexyl radicals), dicyclopentyl-octylphosphine (all isomeric octyl radicals), Tricyclopentylphosphine, cyclohexyl-dimethylphosphine, cyclohexyl-di-ethylphosphine, cyclohexyl-di-n-propylphosphine, cyclohexyl-di-isopropylphosphine, cyclohexyl-dibutylphosphine (all isomeric butyl groups), cyclohexyl-dihexylphosphine (all isomeric hexyl groups), cyclohexyl-dioctylphosphine (all isomeric octyl groups), dicyclohexyl-methylphosphine, dicyclohexyl-ethylphosphine, dicyclohexyl-n-propylphosphine, dicyclohexyl-isopropylphosphine, dicyclohexyl-butylphosphine (all isomeric butyl groups), dicyclohexyl-hexylphosphine (all isomeric hexyl groups), dicyclohexyl-octylphosphine (all isomeric octyl groups) and tricyclohexylphosphine.

As catalysts for the formation of uretdiones, they can be used individually, in any desired mixtures with one another or in mixtures with other primary, secondary and/or tertiary alkyl, aralkyl and/or arylphosphines.

The invention further provides a process for preparing polyisocyanates containing uretdione groups, in which

a) At least one organic isocyanate,

b) a catalyst comprising at least one phosphine having at least one cycloaliphatic group attached directly to the phosphorus,

c) optionally a solvent, and

d) optional additives

And (4) reacting.

The amount of catalyst used in the process of the present invention depends mainly on the target reaction rate and ranges from 0.01 to 3 mol%, preferably from 0.05 to 2 mol%, based on the total amount of moles of isocyanate and moles of catalyst used.

In the process of the invention, it can be used undiluted or in solution in a solvent. Suitable solvents here include, for example, all compounds which do not react with phosphines, such as aliphatic or aromatic hydrocarbons, alcohols, ketones, esters and ethers. Preference is given to using undiluted phosphines in the process of the invention.

As isocyanates for use according to the invention, it is possible in a) to use essentially all known organic isocyanates, which have been prepared by phosgenation or by phosgene-free processes and which can be used individually or in any desired mixtures with one another.

Preference is given to using aliphatic, cycloaliphatic or araliphatic di-or polyisocyanates having an NCO functionality of 2 or more.

Particularly preferred for use are optionally branched, aliphatic diisocyanates, which may optionally contain cyclic groups and have an isocyanate group attached to one primary carbon atom. Examples thereof are butane diisocyanate, pentane diisocyanate, hexane diisocyanate, heptane diisocyanate, octane diisocyanate, nonane diisocyanate, decane diisocyanate, undecane diisocyanate and dodecane diisocyanate, and any isomer of the above-mentioned compounds may also be used.

Particular mention may be made of Hexamethylene Diisocyanate (HDI), methylpentane diisocyanate (MPDI), trimethylhexane diisocyanate (TMDI), bis (isocyanatomethyl) cyclohexane (H)₆XDI) and norbornane diisocyanate (NBDI), either individually or in any desired mixtures with one another.

Furthermore, isophorone diisocyanate (IPDI), bis (isocyanatocyclohexyl) methane (H) can also be used in the process of the invention₁₂MDI), bis (isocyanatomethyl) benzene (ditolyl diisocyanate, XDI) and bis (2-isocyanatoprop-2-yl) benzene (tetramethylxylene diisocyanate, TMXDI).

The process of the invention is carried out at a reaction temperature of from 0 ℃ to 120 ℃, preferably from 0 ℃ to 100 ℃, more preferably from 0 ℃ to 80 ℃, most preferably from 0 ℃ to 60 ℃.

The method of the present invention is carried out so that the conversion of NCO groups is 1 to 100 mol%, preferably 5 to 90 mol%, more preferably 10 to 60 mol%, most preferably 10 to 50 mol%.

To obtain NCO conversions < 100 mol%, the reaction can be stopped at the desired degree of conversion.

After the desired degree of conversion, suitable catalyst poisons for terminating the reaction include essentially all those which have been disclosed to date (DE-A1670667, 1670720, 1934763, 1954093, 3437635, U.S. Pat. No. 5, 4614785), such as alkylating agents (e.g.dimethyl sulfate, methyl tosylate), organic or inorganic peroxides, acid chlorides and also sulfur, which, where appropriate, react with the catalyst at elevated reaction temperatures (variant A).

After deactivation of the reaction mixture according to variant A, the unreacted monomers and/or the deactivated catalyst can be separated off.

The reaction process can also be terminated without chemically deactivating the catalyst. For this purpose, the active catalyst is separated from the reaction mixture immediately after the desired conversion has been reached, in order to prevent further reaction of by-products which may have formed (scheme B).

According to variant B, unreacted residual monomers can be separated from the treated reaction mixture simultaneously with or subsequently to the separation of the catalyst.

In the process of the present invention, unreacted monomers, catalyst and/or other undesired components may be separated from the reaction mixture, for example, by any known separation means such as distillation, extraction or crystallization/filtration. In the embodiment of thin film distillation, distillation is suitably preferred. Of course, two or more of these techniques may be used in combination.

According to variant B, the catalyst is preferably removed by distillation in order to terminate the reaction, in which case, where appropriate, unreacted monomers can be removed simultaneously.

During the work-up of the reaction terminated according to variant A or B, the residual monomers present are preferably removed by distillation.

In the case of polyisocyanates prepared according to the invention which may still contain free, unreacted monomers, such as are important, for example, in the further processing to NCO-blocked products or uretdione curing agents with low or no NCO content, for example for powder coatings, it is possible to carry out the monomer isolation first after termination (variants A and B).

For the treatment of the process of the present invention, the process is independent of whether it is carried out as a whole, or as a partial batch, or continuously.

Furthermore, stabilizers and additives which are customary in polyisocyanate chemistry can be added at any desired point in time in the process of the invention. Examples which may be mentioned are: antioxidants, such as sterically hindered phenols (2, 6-di-tert-butylphenol, 4-methyl-2, 6-di-tert-butylphenol), for example, light stabilizers, such as HALS amines, triazoles, etc., weak acids or catalysts for the NCO-OH reaction, for example, dibutyltin Dilaurate (DBTL).

Furthermore, it is possible to add the small amounts of catalyst poison used in variant A to the product worked up in accordance with variant B, in order to increase the reverse dissociation stability during storage of the product, and in order to reduce the tendency toward formation of by-products and/or to reduce further reaction of free NCO groups.

The products prepared by the process of the invention and based on optionally branched or linear aliphatic di-or polyisocyanates which do not contain cycloalkyl substituents are light-coloured and have a viscosity of < 1000mPas/23 ℃. If cycloaliphatic and/or araliphatic di-or polyisocyanates are used, the resulting resins have a high viscosity, even as solids (viscosity > 10000mPas/23 ℃).

In the form of low monomer contents, i.e.after removal of unreacted monomers, the products according to the invention have an NCO content of < 30% by weight, preferably < 25% by weight.

The polyisocyanates prepared by the process of the invention can be used as starting materials for the production, for example of mouldings (foamed articles, where appropriate), paints, coatings, adhesives or auxiliaries, it being possible, where appropriate, for free, non-uretdionized NCO groups present to be blocked.

Suitable methods for blocking free, non-uretdionized NCO groups include all those known to the person skilled in the art. As blocking agents, it is possible in particular to use phenols (such as phenol, nonylphenol, cresol), oximes (such as butanone oxime, cyclohexanone oxime), lactams (such as epsilon-caprolactam), secondary amines (such as diisopropylamine), pyrazoles (such as dimethylpyrazole), imidazoles, triazoles or malonates and acetates.

The substantially by-product-free polyisocyanates containing uretdione groups, prepared by the process according to the invention, are particularly suitable for the preparation of one-or two-component polyurethane coatings, in admixture with suitable, other, existing di-or polyisocyanates, such as di-and polyisocyanates containing biuret, urethane, allophanate, isocyanurate and iminooxadiazinedione groups.

Likewise, polyisocyanates prepared in accordance with the present invention based on optionally branched, linear aliphatic isocyanates are preferably used as reaction diluents for reducing the viscosity of relatively high viscosity polyisocyanate resins.

For the reaction of the polyisocyanates prepared according to the invention into polyurethanes, it is possible to use any compounds containing at least two reactive isocyanate functions, alone or in combination with one another in the form of mixtures (isocyanate-reactive binders).

Preference is given to using one or more isocyanate-reactive binders which are known per se from polyurethane chemistry, such as polyols or polyamines. As polyhydroxyl compounds, particular preference is given to using polyester-, polyether-, polyacrylate-and/or polycarboxylic acid-polyols, where appropriate low molecular weight polyols may also be added.

The equivalent ratio of non-uretdionized isocyanate groups to isocyanate-reactive functional groups of the isocyanate-reactive binder, which may also have been blocked, is from 0.8 to 3, and sometimes from 0.8 to 2, where appropriate, and the isocyanate-reactive functional groups are OH-, NH-or COOH.

It is possible to use an excess of isocyanate-reactive binder, since, where appropriate, at elevated temperature and/or with the addition of a catalyst, cleavage of the uretidione ring leads to the release of more NCO groups which can react with the excess of isocyanate-reactive functional groups. As a result, the network density of the polymer formed is increased, while the properties of the polymer are favorably influenced.

To facilitate the crosslinking reaction of the polyisocyanates prepared according to the invention with isocyanate-reactive binders, any catalyst known from polyurethane chemistry can be used. By way of example, metal salts such as dibutyltin (IV) dilaurate, tin (II) bis (2-ethyl-hexanoate), bismuth (III) tris (2-ethylhexanoate), zinc (II) bis (2-ethylhexanoate) or zinc chloride and tertiary amines such as 1, 4-diazabicyclo [2.2.2] octane, triethylamine or benzyldimethylamine may be employed.

In the formulation stage, the optionally blocked polyisocyanates prepared according to the invention, the isocyanate-reactive binders, the catalysts and, where appropriate, customary external auxiliaries such as pigments, fillers, additives, levelling assistants, defoamers and/or matting agents, etc., are mixed with one another and, where appropriate, homogenized with solvents in customary mixing devices such as sand mills.

Suitable solvents include all customary paint solvents known per se, such as ethyl and butyl acetate, ethylene or propylene glycol monomethyl ether, monoethyl or monopropyl ether acetate, 2-butanone, 4-methyl-2-pentanone, cyclohexanone, toluene, xylene, solvent naphtha, N-methylpyrrolidone, etc.

The coating can be applied to the product to be coated in the form of a solution or in molten form, if appropriate also in solid form (powder coating), in the usual manner, for example by means of dispersion, roller coating, pouring, spraying, dipping, sintering by means of a fluidized bed or electrostatic spraying.

Suitable substrates include all materials of known construction, in particular metals, wood, plastics and ceramics.

Examples

Unless otherwise stated, all percentages are to be understood as being by weight (percent by weight).

The NCO content of the resins described in the examples according to the invention and in the comparative examples was determined by titration in accordance with DIN 53185.

Dynamic viscosity (Visco) was determined at 23 ℃ using a rotational viscometer550, Thermo Haake GmbH, D-76227 Karlsruhe). To ensure that the rheology of the polyisocyanates prepared according to the invention and of the products of the comparative examples was determined at different shear rates, it was not necessary to state the shear rates, since they are consistent with the rheology of ideal Newtonian fluids.

The symbol "mol%" or the molar ratio of different types of structures to one another is based on measurements by NMR spectroscopy. Unless otherwise specified, it refers in each case to the sum of the types of structures formed by modification reactions (oligomerization reactions) from the previously free NCO groups of the isocyanate to be modified. The sample at a concentration of about 50% by weight was dissolved in dry CDCl₃In D, or about 80% by weight of the sample₆In DMSO at a proton frequency of 400 or 700MHz¹³Measurement of C-NMR (¹³C-NMR: 100 or 176MHZ, relaxation hysteresis: 4 seconds, 2000 scans, spectrometer: DPX 400, AVC 400 or DRX 700, Bruker GmbH, D-76287 Rheinstetten). On the ppm scale, a small amount of tetramethylsilane is added to the solvent, the tetramethylsilane being present in a small amount¹³The chemical shift of C was 0ppm, while that of the solvent itself was 77.0ppm (CDCl)₃) Or 43.5ppm (D)₆-DMSO)。

Unless otherwise specified, each reaction was carried out with HDI as a reactant.

Example 1:

in the presence of the amounts of catalyst indicated in Table 1 and at the stated temperatures, in nitrogen, in septum-sealed glass vessels,10g of freshly distilled, degassed HDI were stirred (magnetic stirrer) at regular intervals by measuring the refractive index of the reaction mixture (starting material) (at 20 ℃ and the optical frequency of the D-line of the sodium spectrum, n)_D ²⁰) The progress of the reaction was determined. (n of starting ═ unconverted ═ pure HDI)_D ²⁰＝1.4523)。

Table 1: reaction parameters

^*: based on the amount of HDI used

Abbreviations:

TBP: tri-n-butylphosphine (Comparative experiment)

CHDHP: cyclohexyl-di-n-hexylphosphine (C)Experiments of the invention)

DCPBP: dicyclopentyl-butylphosphine (Experiments of the invention

TCPP: tricyclopentylphosphine (a)Experiments of the invention

N of the starting material for different catalysts by recording calibration curves based on relatively large batches processed synthetically by distillation at different degrees of conversion_D ²⁰The value of (d) and the yield of the resin [% ]]In connection with this, the present invention is,or simply referred to as yield hereinafter. At yields up to about 80%, a nearly linear relationship between the two variables is obtained, independent of catalyst and reaction temperature (FIG. 1), so the resin yield is always determined by measuring the refractive index in situ.

At the same (molar) concentration, tri-n-butylphosphine (TBP) gave a higher reaction rate than the catalyst used according to the invention. The catalysts of the invention are less active due to the increased number of cycloalkyl groups bonded to P, but at the same time are much more selective with respect to the formation of uretdione. As a result, TBP is always used in lower amounts than the cycloalkylphosphine to maintain comparable reaction rates. A further factor is that when TBP is used, the relatively rapid reaction is initiated followed by rapid catalyst deactivation, as evident by the small slope of the time/yield curve as the reaction proceeds (the salewer). In contrast, with cycloalkyl-substituted phosphines, a substantially more uniform reaction regime can be obtained, although the yield is still high (FIG. 2). The amount of catalyst used in all cases in example 1 depends only on the target reaction rate. Within the above-mentioned range, the catalyst concentration had no detectable effect on the selectivity of the reaction, as can be confirmed by comparative experiments with higher concentrations of TBP at different temperatures.

To examine the correlation of temperature and catalyst to uretdione selectivity, when n_D ²⁰When the values reached 1.4550, 1.4670, 1.4740 and 1.4830, 0.5ml of the reaction mixture was removed under nitrogen, respectively, corresponding to resin yields of about 15, 35, 45 and 60% (see FIG. 1), these samples were transferred to an NMR tube, followed by the addition of 1% D of benzoyl chloride₆0.15ml of DMSO solution (phosphine inactivated) with¹³C-NMR spectrum was analyzed.

For better observation of the selectivity, the parameter U/T is defined as the molar ratio of the uretdione structure to the sum of the two trimeric structures (isocyanurate and iminooxadiazinedione). The U/T values associated with the above yields (about 15, 35, 45 and 60 wt%, respectively) are listed in tables 2-5.

Table 2: U/T selectivity as a function of catalyst and reaction temperature at a yield of about 15 wt.%

Table 3: U/T selectivity as a function of catalyst and reaction temperature at a yield of about 35 wt.%

Table 4: U/T selectivity as a function of catalyst and reaction temperature at a yield of about 45 wt.%

Table 5: U/T selectivity as a function of catalyst and reaction temperature at a yield of about 60 wt.%

Table 6: mol% of uretonimine formed in the reaction product at a yield of about 15% by weight as a function of catalyst and reaction temperature

Table 7: at a yield of about 35 wt.%, the mol% of uretonimine formed in the reaction product is related to the catalyst and the reaction temperature

Table 8: the mol% of uretonimine formed in the reaction product at a yield of about 45 wt.% is related to the catalyst and the reaction temperature

Table 9: the mol% of uretonimine formed in the reaction product at a yield of about 60% by weight is a function of the catalyst and the reaction temperature

Abbreviations:

TBP: tri-n-butylphosphine (Comparative experiment)

CHDHP: cyclohexyl-di-n-hexylphosphine (C)Experiments of the invention)

DCPBP: dicyclopentyl-butylphosphine (Experiments of the invention)

TCPP: tricyclopentylphosphine (a)Experiments of the invention)

n.n.: by passing¹³No detection by C-NMR Spectroscopy

From the above tables it can be concluded that for a given yield and low levels of uretonimine in the product, the uretdione selectivity of the catalyst of the invention is generally higher than in the case of tri-n-butylphosphine (TBP). Also, with the catalysts of the invention, at relatively high reaction temperatures, it is notable that the formation of uretonimines is particularly low, which is always reduced to a greater extent than with TBP.

Example 2:

1500g of HDI were freed from dissolved gases by stirring at 60 ℃ for 1 hour under reduced pressure (0.5mbar) in a stirred vessel, then cooled to 40 ℃ under nitrogen blanket, and subsequently: 2-A: 6.0g TBP: (Comparative experiment) or 2-B: 21.0g DCPBP (Inventive experiment).

The stirring was continued at 40 ℃ and the increase in conversion was monitored by measuring the degree of refraction. When n is_D ²⁰The reaction product was worked up by distillation in a flash evaporator at a pressure of 0.3mbar in the upstream pre-evaporator at a heated medium temperature of 130 ℃ (pre-evaporator) and 140 ℃ (thin film evaporator) to reach about 1.4630 (target conversion). The distillate was then brought to the starting amount with fresh, degassed HDI under nitrogen, stirred repeatedly at 40 ℃ until the refractive index mentioned above was reached, and the product was then worked up as described above. This procedure was repeated a total of 7 times. In all cases, the desired reaction times are given in Table 10 and the data relating to the isolated resins are given in Table 11.

Table 10: reaction times (hh: mm) for experiments 2-A and-B when the target conversion was reached

Table 11: data relating to the resins obtained in the experiments (average of 8 experiments)

6-A: comparative experiment, 6-B: experiments of the invention

The reaction conditions observed with the catalyst DCPBS of the invention are substantially more uniform than with TBP. This is of great importance for the practical application of phosphines in a continuously operated process. In addition, in the process of the present invention, since the uretdione fraction is higher, a resin of lower viscosity can be obtained in higher yield. In addition, the resins prepared according to the invention are characterized by a lower content of HDI.

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Claims (10)

1. A process for dimerizing isocyanates comprising reacting an isocyanate-functional compound in the presence of a phosphine containing at least one cycloaliphatic radical directly attached to phosphorus as catalyst to form uretdiones, with the proviso that the reaction is carried out in the absence of urea and/or amide,

wherein the phosphine is a phosphine of formula I:

wherein

R¹Represents optionally a single or multiple C₁～C₁₂Alkyl-or alkoxy-substituted C₃～C₂₀A cycloaliphatic radical of, and

R²and R³Independently of one another, from optionally mono-or poly-C₁～C₁₂Alkyl-or alkoxy-substituted C₃～C₂₀And a linear or branched C₁～C₂₀The fatty group of (2).

2. The process of claim 1, wherein the phosphine is selected from the group consisting of cyclopentyl dimethyl phosphine, cyclopentyl diethyl phosphine, cyclopentyl di-n-propyl phosphine, cyclopentyl di-isopropyl phosphine, cyclopentyl dibutyl phosphine, cyclopentyl dihexyl phosphine, cyclopentyl dioctyl phosphine, dicyclopentyl methyl phosphine, dicyclopentyl ethyl phosphine, dicyclopentyl n-propyl phosphine, dicyclopentyl isopropyl phosphine, dicyclopentyl butyl phosphine, dicyclopentyl hexyl phosphine, dicyclopentyl octyl phosphine, tricyclopentyl phosphine, cyclohexyl dimethyl phosphine, cyclohexyl di-ethyl phosphine, cyclohexyl di-n-propyl phosphine, cyclohexyl di-isopropyl phosphine, cyclohexyl dibutyl phosphine, cyclohexyl dihexyl phosphine, cyclohexyl di-n-propyl phosphine, cyclohexyl di-isopropyl phosphine, cyclohexyl di-butyl phosphine, cyclohexyl di-hexyl phosphine, cyclopentyl di-n-propyl phosphine, cyclopentyl di-butyl phosphine, cyclopentyl di-n-propyl phosphine, cyclopentyl di-butyl phosphine, cyclopentyl, Cyclohexyl-dioctylphosphine, dicyclohexyl-methylphosphine, dicyclohexyl-ethylphosphine, dicyclohexyl-n-propylphosphine, dicyclohexyl-isopropylphosphine, dicyclohexyl-butylphosphine, dicyclohexyl-hexylphosphine, dicyclohexyl-octylphosphine, and tricyclohexylphosphine.

3. A process for preparing polyisocyanates containing uretdione groups, which comprises reacting

a) At least one organic isocyanate,

b) a catalyst comprising at least one phosphine having at least one cycloaliphatic group attached directly to the phosphorus,

c) optionally one or more solvents, and

d) optionally one or more additives

Provided that the reaction is carried out in the absence of urea and/or amide,

wherein the phosphine is a phosphine of formula I:

wherein

R¹Represents optionally a single or multiple C₁～C₁₂Alkyl-or alkoxy-substituted C₃～C₂₀A cycloaliphatic radical of, and

R²and R³Independently of one another, from optionally mono-or poly-C₁～C₁₂Alkyl-or alkoxy-substituted C₃～C₂₀And a linear or branched C₁～C₂₀The fatty group of (2).

4. The process of claim 3, wherein the phosphine is selected from the group consisting of cyclopentyl dimethyl phosphine, cyclopentyl diethyl phosphine, cyclopentyl di-n-propyl phosphine, cyclopentyl di-isopropyl phosphine, cyclopentyl dibutyl phosphine, cyclopentyl dihexyl phosphine, cyclopentyl dioctyl phosphine, dicyclopentyl methyl phosphine, dicyclopentyl ethyl phosphine, dicyclopentyl n-propyl phosphine, dicyclopentyl isopropyl phosphine, dicyclopentyl butyl phosphine, dicyclopentyl hexyl phosphine, dicyclopentyl octyl phosphine, tricyclopentyl phosphine, cyclohexyl dimethyl phosphine, cyclohexyl di-ethyl phosphine, cyclohexyl di-n-propyl phosphine, cyclohexyl di-isopropyl phosphine, cyclohexyl dibutyl phosphine, cyclohexyl dihexyl phosphine, cyclohexyl di-n-propyl phosphine, cyclohexyl di-isopropyl phosphine, cyclohexyl di-butyl phosphine, cyclohexyl di-hexyl phosphine, cyclopentyl di-n-propyl phosphine, cyclopentyl di-butyl phosphine, cyclopentyl di-n-propyl phosphine, cyclopentyl di-butyl phosphine, cyclopentyl, Cyclohexyl-dioctylphosphine, dicyclohexyl-methylphosphine, dicyclohexyl-ethylphosphine, dicyclohexyl-n-propylphosphine, dicyclohexyl-isopropylphosphine, dicyclohexyl-butylphosphine, dicyclohexyl-hexylphosphine, dicyclohexyl-octylphosphine, and tricyclohexylphosphine.

5. A process as claimed in claim 3, wherein the catalyst is used in an amount of from 0.01 to 3 mol%, based on the sum of the moles of isocyanate and the moles of catalyst used.

6. The process of claim 3 wherein the at least one organic isocyanate is a di-or polyisocyanate selected from the group consisting of aliphatic isocyanates, cycloaliphatic isocyanates and arylaliphatic isocyanates having an NCO functionality of 2 or greater.

7. The process of claim 6 wherein the isocyanate is one or more selected from the group consisting of hexamethylene diisocyanate, methylpentane diisocyanate, trimethylhexane diisocyanate, bis (isocyanatomethyl) -cyclohexane, norbornane diisocyanate, isophorone diisocyanate, bis (isocyanatocyclohexyl) methane, bis (isocyanatomethyl) benzene and bis (2-isocyanatoprop-2-yl) benzene.

8. The method of claim 3, wherein the one or more additives are one or more selected from the group consisting of antioxidants, light stabilizers, and weak acids.

9. The process of claim 8 wherein the light stabilizer is a hindered amine light stabilizer.

10. The method according to claim 3, wherein the solvent is one or more selected from the group consisting of aliphatic hydrocarbons, aromatic hydrocarbons, alcohols, ketones, esters, and ethers.