PROCESS OF PREPARING ALLOPHANATE- AND/OR THIOALLOPHANATE GROUP-CONTAINING COMPOUNDS

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 R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 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 R.sup.3, R.sup.4, R.sup.5 and R.sup.6 independently of each other also can represent hydrogen, and R.sup.7 represents hydrogen or a carboxylate anion (COO.sup.−), 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 at least one of an allophanate and a thioallophanate-containing compound, the process comprising reacting A) at least one component comprising at least one uretdione group with B) at least one component comprising at least one of a hydroxyl group and a thiol group in the presence of C) at least one catalyst containing a structural element of at least one of formulae (I) and (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 are 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 and optionally 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.−), wherein the at least one component A) comprising at least one uretdione group is selected from polyaddition compounds A2) obtainable by reaction of isocyanate-functional uretdione-containing compounds A1) with alcohols and/or amines which in solvent-free form have a content of free isocyanate groups of less than 5% by weight.

2. The process as claimed in claim 1, wherein the component A1) is selected from the group consisting of uretdione-containing compounds based on PDI, HDI, IPDI, XDI, NBDI, and H.sub.12-MDI which preferably have an average NCO functionality of at least 1.6 and have a content of uretdione structures (calculated as C.sub.2N.sub.2O.sub.2, molecular weight=84) of 10% to 25% by weight.

3. The process as claimed in claim 1, wherein the polyaddition compounds A2) is selected from the group consisting of compounds obtained by reaction of isocyanate-functional, uretdione-containing compounds A1) 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 2:1 to 0.5:1.

4. The process as claimed in claim 2, wherein the uretdione-containing polyaddition compounds A2) in solvent-free form have a content of free isocyanate groups of less than 2% by weight.

5. The process as claimed in claim 1, wherein component B) is selected from at least difunctional polyols in the molecular weight range 62 to 22 000.

6. The process as claimed in claim 1, wherein components A) and B) are employed in amounts such that for each uretdione group of component A) there are 0.5 to 2.0 hydroxyl and/or thiol groups of component B).

7. The process as claimed in claim 1, wherein component C) is selected from catalysts containing a structural element of general formulae (I) and/or (II), in which R.sup.1 and R.sup.2 independently of one another stand forare 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.−).

8. The process as claimed in claim 1, wherein component C) is selected from the group consisting of catalysts containing a structural element 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.−).

9. The process as claimed in claim 1, wherein catalyst C) is selected from the group consisting of imidazolium salts of 1,3-dimethylimidazolium 2-carboxylate, 1-ethyl-3-methylimidazolium 2-carboxylate, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium 2-carboxylate, and 1-butyl-3-methylimidazolium acetate.

10. The process as claimed in claim 1, wherein component C) 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 and auxiliary or additive substances present in these components.

11. A composition containing at least one component A) comprising at least one uretdione group, at least one component B) comprising at least one thiol group and at least one catalyst C) having an imidazolium or imidazolinium structure and optionally further auxiliary and additive substances or containing at least one at least one polyaddition compound A2) which in solvent-free form has a content of free isocyanate groups of less than 5% by weight, at least one component B) comprising at least one hydroxyl and/or thiol group and at least one catalyst C) having an imidazolium or imidazolinium structure and optionally further auxiliary and additive substances.

12. (canceled)

13. A coating formulation containing the compositions as claimed in claim 11.

14. A substrate coated with the coating formulation as claimed in claim 13.

15. A polyurethane plastic obtained from the composition as claimed in claim 11.

16. The process as claimed in claim 2, wherein the uretdione-containing polyaddition compounds A2) in solvent-free form have a content of free isocyanate groups of less than 1% by weight.

17. The process as claimed in claim 2, wherein the uretdione-containing polyaddition compounds A2) in solvent-free form are isocyanate-free.

18. The substrate as claimed in claim 14, wherein the composition is heat-cured.

19. The polyurethane plastic as claimed in claim 15, wherein the composition is heat-cured.

Description

EXAMPLES

[0105] All percentages are based on weight, unless stated otherwise.

[0106] NCO contents were determined titrimetrically in accordance with DIN EN ISO 11909:2007-05.

[0107] All viscosity measurements were recorded with a Physica MCR 51 rheometer from Anton Paar Germany GmbH (DE) according to DIN EN ISO 3219:1994-10 at a shear rate 5 of 250 s-1.

[0108] Residual monomer contents were measured in accordance with DIN EN ISO 10283:2007-11 by gas chromatography with an internal standard.

[0109] 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.

[0110] König pendulum damping was determined in accordance with DIN EN ISO 1522:2007-04 on glass plates.

[0111] 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 individual structural elements have the following chemical shifts (in ppm): uretdione: 157.1; isocyanurate: 148.4; allophanate: 155.7 and 153.8.

[0112] 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 lacquer 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)

[0113] Starting Compounds

[0114] Production of an HDI Uretdione Model Compound (HDI-UD1)

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

[0115] 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.

[0116] NCO content: 25.0%

[0117] Monomeric HDI: <0.03%

[0118] Viscosity (23° C.): 28 mPas

[0119] 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 (HDI-UD1)

[0120] 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.

[0121] Uretdione group content: 21.0% (calculated as C.sub.2N.sub.2O.sub.2, molecular weight 84)

[0122] Production of an HDI Polyuretdione Crosslinker (HDI-UD2)

[0123] 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 80° 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 16 hours at 80° C. the NCO content was <0.2%. A practically colorless solution of an HDI polyuretdione crosslinker (HDI-UD2) was obtained.

[0124] NCO content: 0.16%

[0125] Uretdione group content: 10.8% (calculated as C.sub.2N.sub.2O.sub.2, molecular weight 84) Uretdione functionality: 5 (calculated)

[0126] Solids content: about 65%

[0127] Viscosity (23° C.): 1400 mPas

[0128] Production of a PDI Uretdione Model Compound (PDI-UD1)

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

[0129] 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.

[0130] NCO content: 27.3%

[0131] Monomeric PDI: 0.03%

[0132] Viscosity (23° C.): 22 mPas

[0133] 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)

[0134] 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).

[0135] Uretdione group content: 22.3% (calculated as C.sub.2N.sub.2O.sub.2, molecular weight 84)

[0136] Catalysts

[0137] 1-Ethyl-3-methylimidazolium acetate (97%), Sigma-Aldrich Chemie GmbH, Munich, DE

[0138] 1,3-dimethylimidazolium 2-carbon/late, produced by the process described in J. Org. Chem. 73, 14, 5582-5584

[0139] 1-Ethyl-3-methylimidazolium 2-carbon/late, produced by the process described in Chem. Eur. J. 2016, 22, 16292-16303

Example 1

[0140] In an oven-dried and pressure-resistant reaction vial 6.8 mg (0.04 mmol) of 1-ethyl-3-methylimidazolium acetate together with 28.2 mg (0.21 mmol) of 2-(2-ethoxyethoxy)ethanol (Carbitol) were dissolved in 1.0 ml of absolute tetrahydrofuran (THF). Then 80.0 mg (0.20 mmol) of the HDI uretdione model compound (HDI-UD1) were added and the contents of the closed reaction vessel were stirred at 80° C. for one hour. After removal of the solvent under high vacuum the .sup.13C NMR spectrum of the mixture showed complete conversion of the employed uretdione to allophanate and isocyanurate groups. The molar ratio of allophanate to isocyanurate groups was 90:10.

Example 2

[0141] In an oven-dried and pressure-resistant reaction vial 8.1 mg (0.04 mmol) of 1,3-dimethylimidazolium 2-carbon/late together with 28.2 mg (0.21 mmol) of Carbitol were dissolved in 1.0 ml of absolute THF. Then 80.0 mg (0.20 mmol) of the HDI uretdione model compound (HDI-UD1) were added and the contents of the closed reaction vessel were stirred at 80° C. for one hour. After removal of the solvent under high vacuum the .sup.13C NMR spectrum of the mixture showed complete conversion of the employed uretdione to allophanate and isocyanurate groups. The molar ratio of allophanate to isocyanurate groups was 87:13.

Example 3

[0142] In an oven-dried and pressure-resistant reaction vial 6.2 mg (0.04 mmol) of 1-ethyl-3-methylimidazolium 2-carbon/late together with 28.2 mg (0.21 mmol) of Carbitol were dissolved in 1.0 ml of absolute THF. Then 80.0 mg (0.20 mmol) of the HDI uretdione model compound (HDI-UD1) were added and the contents of the closed reaction vessel were stirred at 80° C. for one hour. After removal of the solvent under high vacuum the .sup.13C NMR spectrum of the mixture showed complete conversion of the employed uretdione to allophanate and isocyanurate groups. The molar ratio of allophanate to isocyanurate groups was 88:12.

Example 4

[0143] In an oven-dried and pressure-resistant reaction vial 0.05 g (0.3 mmol) of sodium ethyldithiocarbonate together with 0.23 g (1.7 mmol) of Carbitol were dissolved in 12.1 ml of absolute tetrahydrofuran (THF). Then 0.61 g (1.6 mmol) of the PDI uretdione model compound (PDI-UD1) were added and the contents of the closed reaction vessel were stirred at 24° C. for one hour. After removal of the solvent under high vacuum the .sup.13C NMR spectrum of the mixture showed complete conversion of the employed uretdione to allophanate and isocyanurate groups. The molar ratio of allophanate to isocyanurate groups was 90:10.

Example 5

Inventive and Comparative

[0144] 100 g (0.559 eq) of a commercially available, aromatics-free branched polyester polyol having a solids content of 75% in butyl acetate and an OH content of 9.5% based on solid resin, obtainable under the name Desmophen 775 XP (Covestro Deutschland AG, Leverkusen, DE), were mixed with 197.6 g (0.254 eq) of the HDI polyuretdione crosslinker (HDI-UD2) corresponding to an equivalent ratio of hydroxyl groups to uretdione groups of 1.1:1 to afford a coating formulation which, after addition of 3.0 g (18.2 mmol, 1.0%) of 1-ethyl-3-methylimidazolium acetate as catalyst, was applied to a degreased glass sheet using a film applicator in an applied film thickness of 150 μm.

[0145] For comparison, by the same process 100 g of Desmophen 775 XP and 197.6 g of the HDI polyuretdione crosslinker (HDI-UD2), likewise corresponding to an equivalent ratio of hydroxyl groups to uretdione groups of 1.1:1, were used to produce a coating formulation and after addition of 2.9 g (18.8 mmol, 1.0%) of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as catalyst said formulation was applied to a degreased glass sheet using a film applicator in an applied film thickness of 150 μm.

[0146] After flashing off at room temperature for 15 minutes both coatings were cured at 100° C. over 30 min. In both cases, hard, elastic and completely transparent coatings were obtained, which differed as follows:

TABLE-US-00003 1-ethyl-3-methylimidazolium DBU Catalyst acetate (inventive) (comparative) Visual assessment good slight structure Flow color colorless yellow Pendulum damping 103 s 79 s Xylene resistance 2 5

Example 6

[0147] 51.4 g (0.421 eq) of pentaerythritol tetrakis(3-mercaptopropionate) (solids content: 100%, SH content: 26%), available under the name THIOCURE PETMP (Bruno Bock Chemische Fabrik GmbH & Co. KG, Marschacht, DE), were mixed with 148.6 g (0.191 eq) of the HDI polyuretdione crosslinker (HDI-UD2) corresponding to an equivalent ratio of thiol groups to uretdione groups of 1.1:1 to afford a coating formulation which, after addition of 2.0 g (12.1 mmol, 1.0%) of 1-ethyl-3-methylimidazolium acetate as catalyst, was applied to a degreased glass sheet using a film applicator in an applied film thickness of 150 μm. After flashing off at room temperature for 15 minutes the coating was cured at 100° C. over 30 min.

[0148] A smooth, colorless transparent coating was obtained which had pendulum damping of 160 s and a xylene resistance of 1-2.