METHOD FOR PRODUCING ISOCYANURATES FROM URETDIONES

Abstract

The invention relates to a process of preparing allophanate- and/or thioallophanate group-containing compounds comprising the following steps: reacting A) at least one component having at least one uretdione group with B) at least one component having at least one hydroxyl and/or thiol group, in the presence C) of at least one catalyst, containing a structural element of the general formulae (I) and/or (II), wherein R1, R2, R3, R4, R5 and R6 independently of each other represent the same or different radicals meaning saturated or unsaturated, linear or branched, aliphatic, cycloaliphatic, araliphatic or aromatic organic radicals with 1 to 18 carbon atoms that are substituted or unsubstituted and/or have heteroatoms in the chain, the radicals being capable of forming, even when combined with each other and optionally together with an additional heteroatom, rings with 3 to 8 carbon atoms that can optionally be further substituted, wherein R3, R4, R5 and R6 independently of each other also can represent hydrogen, and R7 represents hydrogen or a carboxylate anion (COO—), the at least one component A) having at least one uretdione group being polyaddition compounds A2) that can be obtained by reacting isocyanate-functional uretdione groups A1) with alcohols and/or amines that have a free isocyanate group content of less than 5 wt. % in their solvent-free form.

Claims

1. A process for producing isocyanurate-containing compounds comprising reaction of A) at least one substantially isocyanate-free component comprising at least one uretdione group in the presence of B) at least one catalyst containing a structural element of general formulae (I) and/or (II) ##STR00004## in which R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 independently of one another stand for identical or different radicals which represent saturated or unsaturated, linear or branched, aliphatic, cycloaliphatic, araliphatic or aromatic organic radicals having 1 to 18 carbon atoms which are substituted or unsubstituted and/or have heteroatoms in the chain, wherein the radicals may also in combination with one another optionally together with a further heteroatom form rings having 3 to 8 carbon atoms which may optionally be further substituted, wherein R.sup.3, R.sup.4, R.sup.5 and R.sup.6 may independently of one another also represent hydrogen and R.sup.7 represents hydrogen or a carboxylate anion (COO.sup.−).

2. The process as claimed in claim 1, characterized in that component A) is a polyaddition compounds obtained by oligomerization of monomeric isocyanates and/or by reaction of isocyanate-functional uretdione-containing compounds with alcohols and/or amines.

3. The process as claimed in claim 2, characterized in that component A) is a uretdione-containing compounds based on one selected from the group consisting of PDI, HDI, IPDI, NBDI, XDI, and H.sub.12-MDI.

4. The process as claimed in claim 2, characterized in that component A) is a polyaddition compounds obtained by reaction of isocyanate-functional, uretdione-containing compounds with at least difunctional polyols in the molecular weight range 62 to 22 000 and optionally monoalcohols while maintaining an equivalent ratio of isocyanate groups to isocyanate-reactive groups of 1.0:0.9 to 0.5:1.

5. The process as claimed in claim 1, characterized in that component B) is a compounds of general formulae (I) and/or (II), in which R.sup.1 and R.sup.2 independently of one another are identical or different radicals which represent saturated or unsaturated, linear or branched, aliphatic, cycloaliphatic, araliphatic or aromatic organic radicals which have 1 to 12 carbon atoms, are substituted or unsubstituted and/or have heteroatoms in the chain, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 represent hydrogen and wherein R.sup.7 represents hydrogen or a carboxylate anion (COO.sup.−).

6. The process as claimed in claim 1, characterized in that component B) is a compounds of general formulae (I) and/or (II), in which R.sup.1 and R.sup.2 independently of one another are identical or different radicals which represent saturated or unsaturated, linear or branched, aliphatic organic radicals having 1 to 12 carbon atoms, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 represent hydrogen and R.sup.7 represents hydrogen or a carboxylate anion (COO.sup.−).

7. The process as claimed in claim 1, characterized in that catalyst B) is an imidazolium salts of general formula (I) where R.sup.7 represents a carboxylate anion.

8. The process as claimed in claim 1, characterized in that catalyst B) is selected from the group consisting of 1,3-dimethylimidazolium 2-carboxylate, 1-ethyl-3-methylimidazolium 2-carboxylate, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium 2-carboxylate, and/or 1-butyl-3-methylimidazolium acetate.

9. The process as claimed in claim 1, characterized in that component B) is present in an amount of 0.001% to 15% by weight, based on the total weight of components A) and B), excluding any solvents, auxiliaries or additives present in these components.

10. A composition containing at least one substantially isocyanate-free polyaddition compound A) obtainable by reaction of isocyanate-functional uretdione-containing compounds with alcohols and/or amines and at least one catalyst B) having an imidazolium or imidazolinium structure which comprises a structural element of general formulae (I) and/or (II) as claimed in claim 1, and optionally further auxiliary and additive substances.

11. The use of compositions as claimed in claim 10 for producing polyurethane plastics or coating formulations.

12. A polyurethane plastic obtained from an optionally heat-cured composition as claimed in claim 10.

13. A shaped article made of a polyurethane plastic as claimed in claim 12.

14. A coating formulation containing compositions as claimed in claim 10.

15. A substrate coated with a heat-cured coating formulation as claimed in claim 14.

Description

EXAMPLES

[0101] All percentages are based on weight, unless stated otherwise.

[0102] NCO contents were determined titrimetrically in accordance with DIN EN ISO 11909:2007-05.

[0103] All viscosity measurements were taken with a Physica MCR 51 rheometer from Anton Paar Germany GmbH (DE) according to DIN EN ISO 3219:1994-10 at a shear rate of 250 s.sup.−1.

[0104] Residual monomer contents were measured in accordance with DIN EN ISO 10283:2007-11 by gas chromatography with an internal standard.

[0105] The compositions of the uretdione model compounds were determined by gel permeation chromatography based on DIN 55672-1:2016-03 (gel permeation chromatography (GPC)—part 1: tetrahydrofuran (THF) as eluent) with the modification that a flow rate of 0.6 ml/min rather than 1.0 ml/min was used. The proportions of the different oligomers from the chromatograms in area % which were determined with software assistance were in each case approximately equated with proportions in % by weight. Konig pendulum damping was determined in accordance with DIN EN ISO 1522:2007-04 on glass plates.

[0106] The uretdione reaction products formed during curing of the compositions according to the invention were determined using proton-decoupled .sup.13C-NMR spectra (recorded using CDCl.sub.3 solvent on a Bruker DPX-400 instrument). The structural elements relevant to the present invention have the following chemical shifts (in ppm): uretdione: 157.1; urethane: 156.3; isocyanurate: 148.4.

[0107] IR spectra were recorded using the Bruker Alpha-P IR FT-IR spectrometer. A matrix FM from Bruker with a 3 mm diamond head probe was used for in-situ IR measurements. The spectra were analyzed using Bruker OPUS 7.0 spectroscopy software.

[0108] Solvent resistance was determined using xylene as a typical coatings solvent. To this end a small amount of the solvent was added to a test tube and provided with a cotton pad at the opening so that an atmosphere saturated with xylene was formed inside the test tube. The test tube was subsequently placed with the cotton pad on the coating surface and remained there for 5 minutes. Once the solvent had been wiped off, the film was examined for destruction/softening/loss of adhesion. (0=no change, 5=film destroyed)

[0109] Starting Compounds

[0110] Production of an HDI Uretdione Model Compound (HDI-UD1)

Production of 1,3-bis(6-isocyanatohexyl)-1,3-diazetidine-2,4-dione

[0111] According to the process described in example 1 of EP-A 0 789 017 1,3-bis(6-isocyanatohexyl)-1,3-diazetidine-2,4-dione (ideal bis(6-isocyanatohexyl)uretdione) was produced by tributylphosphine-catalyzed oligomerization of 1,6-diisocyanatohexane (HDI) and subsequent distillative workup. [0112] NCO content: 25.0% [0113] Monomeric HDI: <0.03% [0114] Viscosity (23° C.): 28 mPas

[0115] Analysis by gel permeation chromatography (GPC) reveals the following composition:

TABLE-US-00001 HDI uretdione (n = 2): 99.2% (according to GPC) HDI isocyanurate (n = 3): 0.4% (according to GPC) higher oligomers: 0.4% (according to GPC)

Production of the dimethylurethane of bis(6-isocyanatohexyl)uretdione

[0116] 10 g (0.0595 eq) of the above-described HDI uretdione were dissolved in 30 ml of dichloromethane, admixed with 2 g (0.0625 mol) of methanol and stirred at 40° C. under dry nitrogen until isocyanate was no longer detectable by IR spectroscopy after 8 h. Dichloromethane and excess methanol were then removed using a rotary evaporator. The dimethylurethane of bis(6-isocyanatohexyl)uretdione (HDI-UD1) was obtained as a colorless solid. There were no longer any free isocyanate groups detectable by IR spectroscopy (no isocyanate absorption band at 2270 cm.sup.−1). [0117] Uretdione group content: 21.0% (calculated as C.sub.2N.sub.2O.sub.2, molecular weight 84)

[0118] Production of an HDI Polyuretdione (HDI-UD2)

[0119] 1000 g (5.95 eq) of the above-described ideal bis(6-isocyanatohexyl) uretdione (NCO content: 25.0%) were dissolved in 800 g of butyl acetate, 4.6 g (0.2% by weight) of a 10% solution of dibutyltin dilaurate (DBTL) in butyl acetate were added and the mixture was heated to 60° C. under dry nitrogen and with stirring. A mixture of 347.5 g (4.76 eq) of 2,2,4-trimethylpentane-1,3-diol and 154.7 g (1.19 eq) of 2-ethyl-1-hexanol was added dropwise to this solution over 2 hours. After a stirring time of 48 hours at 60° C. the NCO content was <0.1%. A practically colorless solution of an HDI polyuretdione crosslinker (HDI-UD2) was obtained. [0120] NCO content: <0.1% [0121] Uretdione group content: 10.8% (calculated as C.sub.2N.sub.2O.sub.2, molecular weight 84) [0122] Uretdione functionality: 5 (calculated) [0123] Solids content: about 65%

[0124] Viscosity (23° C.): 1400 mPas

Production of a PDI uretdione model compound (PDI-UD1)

Production of 1,3-bis(5-isocyanatopentyl)-1,3-diazetidine-2,4-dione

[0125] According to the process described in example 1 of EP-A 0 789 017 1,3-bis(5-isocyanatopentyl)-1,3-diazetidine-2,4-dione (ideal bis(5-isocyanatopentyl)uretdione) was produced by tributylphosphine-catalyzed oligomerization of 1,5-diisocyanatopentane (PDI) instead of 1,6-diisocyanatohexane (HDI) and subsequent distillative workup. [0126] NCO content: 27.3% [0127] Monomeric PDI: 0.03% [0128] Viscosity (23° C.): 22 mPas

[0129] Analysis by gel permeation chromatography (GPC) reveals the following composition:

TABLE-US-00002 HDI uretdione (n = 2): 98.7% (according to GPC) HDI isocyanurate (n = 3): 0.7% (according to GPC) higher oligomers: 0.6% (according to GPC)

Production of the dimethyl urethane of bis(5-isocyanatopentyl)uretdione (PDI-UD1)

[0130] 10 g (0.065 eq) of the above-described PDI uretdione were dissolved in 30 ml of dichloromethane, admixed with 2 g (0.068 mol) of methanol and stirred at 40° C. under dry nitrogen until isocyanate was no longer detectable by IR spectroscopy after 8 h. Dichloromethane and excess methanol were then removed using a rotary evaporator. The dimethylurethane of bis(5-isocyanatopentyl)uretdione (PDI-UD1) was obtained as a colorless solid. There were no longer any free isocyanate groups detectable by IR spectroscopy (no isocyanate absorption band at 2270 cm.sup.−1).

[0131] Uretdione group content: 22.3% (calculated as C.sub.2N.sub.2O.sub.2, molecular weight 84)

[0132] Catalysts [0133] 1-Ethyl-3-methylimidazolium acetate (97%), Sigma-Aldrich Chemie GmbH, Munich, DE [0134] 1-Ethyl-3-methylimidazolium-(L)-(+) lactate (95%), Sigma-Aldrich Chemie GmbH, Munich, DE [0135] 1-Ethyl-3-methylimidazolium 2-carboxylate, produced by the process described in Chem. Eur. J. 2016, 22, 16292-16303 [0136] 1-Ethyl-3-methylimidazolium hydrogencarbonate (96%), Alfa Chemistry, New York, USA

Example 1

[0137] In an oven-dried and pressure-resistant reaction vial 70 mg (0.40 mmol) of 1-ethyl-3-methylimidazolium acetate together with 800.0 mg (2.00 mmol) of the HDI uretdione model compound (HDI-UD1) were dissolved in 10.0 ml of absolute tetrahydrofuran (THF). The reaction vessel was closed and the contents then stirred at 80° C. for one hour. After removal of the solvent in high vacuum the residue was extracted with 30 mL of water and 50 mL of ethyl acetate. The aqueous phase was separated off and extracted a further three times with 50 ml of ethyl acetate in each case. The combined organic phases were washed with 100 ml of saturated NaCl solution, dried over MgSO.sub.4, filtered and the solvent removed under vacuum. Obtained as product in quantitative yield (800 mg) was a white solid which according to .sup.13C NMR was the trimethylurethane of tris(6-isocyanatohexyl) isocyanurate. Uretdione signals were no longer detectable. In situ IR measurements did not indicate the presence of free isocyanate groups at any time during the reaction.

Example 2

[0138] In an oven-dried and pressure-resistant reaction vial 8.4 mg (0.04 mmol) of 1-ethyl-3-methylimidazolium-(L)-(+) lactate together with 80.0 mg (0.20 mmol) of the HDI uretdione model compound (HDI-UD1) were dissolved in 1.0 ml of absolute tetrahydrofuran (THF). The reaction vessel was closed and the contents then stirred at 80° C. for one hour. Obtained as product after removal of the solvent under high vacuum was a pale yellow oil which according to .sup.13C NMR was the trimethyl urethane of tris(6-isocyanatohexyl) isocyanurate. Uretdione signals were no longer detectable. In situ IR measurements did not indicate the presence of free isocyanate groups at any time during the reaction.

Example 3

[0139] In an oven-dried and pressure-resistant reaction vial 6.16 mg (0.04 mmol) of 1-ethyl-3-methylimidazolium 2-carboxylate together with 80.0 mg (0.20 mmol) of the HDI uretdione model compound (HDI-UD1) were dissolved in 1.0 ml of absolute tetrahydrofuran (THF). The reaction vessel was closed and the contents then stirred at 80° C. for one hour. Obtained as product after removal of the solvent under high vacuum was a pale yellow oil which according to .sup.13C NMR was the trimethyl urethane of tris(6-isocyanatohexyl) isocyanurate. Uretdione signals were no longer detectable. In situ IR measurements did not indicate the presence of free isocyanate groups at any time during the reaction.

Example 4

[0140] In an oven-dried and pressure-resistant reaction vial 71.7 mg (0.40 mmol) of 1-ethyl-3-methylimidazolium hydrogencarbonate together with 800 mg (2.00 mmol) of the HDI uretdione model compound (HDI-UD1) were dissolved in 10 ml of absolute tetrahydrofuran (THF). The reaction vessel was closed and the contents then stirred at 80° C. for one hour. The solvent was then removed under high vacuum and the obtained crude product was worked up by the process described in example 1. Obtained as product in quantitative yield (800 mg) was a white solid which according to .sup.13C NMR was the trimethyl urethane of tris(6-isocyanatohexyl) isocyanurate. Uretdione signals were no longer detectable. In situ IR measurements did not indicate the presence of free isocyanate groups at any time during the reaction.

Example 5

[0141] In an oven-dried and pressure-resistant reaction vial 6.16 mg (0.04 mmol) of 1-ethyl-3-methylimidazolium 2-carboxylate together with 80.0 mg (0.20 mmol) of the HDI uretdione model compound (HDI-UD1) were dissolved in 1.0 ml of absolute tetrahydrofuran (THF). The reaction vessel was closed and the contents then stirred at 80° C. for one hour. Obtained as product after removal of the solvent under high vacuum was a pale yellow oil which according to .sup.13C NMR was the trimethyl urethane of tris(6-isocyanatohexyl) isocyanurate. Uretdione signals were no longer detectable. In situ IR measurements did not indicate the presence of free isocyanate groups at any time during the reaction.

Example 6

[0142] In an oven-dried and pressure-resistant reaction vial 0.05 g (0.3 mmol) of 1-ethyl-3-methylimidazolium acetate together with 0.53 g (1.4 mmol) of the PDI uretdione model compound (PDI-UD1) were dissolved in 10.6 ml of absolute tetrahydrofuran (THF). The reaction vessel was closed and the contents then stirred at 80° C. for one hour. Obtained as product after removal of the solvent under high vacuum was a light yellow oil which according to .sup.13C NMR was the trimethyl urethane of tris(5-isocyanatohexyl) isocyanurate. Uretdione signals were no longer detectable. In situ IR measurements did not indicate the presence of free isocyanate groups at any time during the reaction.

Example 7 (Inventive and Comparative)

[0143] 100 g (0.128 eq) of the 65% solution of the HDI polyuretdione crosslinker (HDI-UD2) in butyl acetate were mixed with 3 g (0.018 mol) of 1-ethyl-3-methylimidazolium acetate as catalyst to afford a coating formulation and applied to a degreased glass plate using a film applicator in applied film thickness of 150 μm.

[0144] After flashing off at room temperature for 15 minutes the coating was cured at 100° C. over 40 min. This afforded a hard, elastic and completely transparent coating having a pendulum hardness of 135 s and a xylene resistance of 1-2.

[0145] FIG. 1 shows the IR spectrum (AU: absorption units, WN: wavenumber) of the coating formulation before (a) and after (b) curing. It is apparent that the uretdione groups (d) (band at about 1780 cm.sup.−1) originally present in addition to urethane groups (c) have completely disappeared in the cured coating film. Instead, an isocyanurate band (e) appears at about 1670 cm.sup.−1. Isocyanate groups (band at about 2270 cm.sup.−1) are not detectable.