Process for Preparing Carbodiimides

Abstract

The invention relates to a novel process for preparing carbodiimides comprising the steps of a) carbodiimidization of isocyanates in the presence of a catalyst, b) separation of the catalyst and/or monomeric isocyanate from the carbodiimide by distillation or extraction to obtain a crude carbodiimide comprising monomeric isocyanate, c) addition of one or more alcohols and partial or complete reaction of the alcohol with the monomeric isocyanate of the crude carbodiimide.

Claims

1. A process for preparing carbodiimides of formula (I) ##STR00003## in which n is a number from 1 to 500, R.sup.I is C.sub.1-C.sub.24 alkylenes and/or C.sub.5-C.sub.12 cycloalkylenes, C.sub.1-C.sub.12-alkyl-substituted or C.sub.1-C.sub.24-oxyalkyl-substituted cycloalkylenes, C.sub.1-C.sub.12-alkyl-substituted arylenes, C.sub.1-C.sub.24-oxyalkyl-substituted arylenes, C.sub.7-C.sub.18-alkylaryl-substituted arylenes and optionally C.sub.1-C.sub.12-alkyl-substituted arylenes bridged via C.sub.1-C.sub.8 alkylene groups and having a total of 8 to 30 carbon atoms, and arylene and R.sup.II, R.sup.III identically or independently of one another are C.sub.1-C.sub.24-alkyl- and/or C.sub.5-C.sub.24-cyclo- or C.sub.1-C.sub.12-alkyl-substituted or C.sub.1-C.sub.24-oxyalkyl-substituted cycloalkyls, C.sub.1-C.sub.12-alkyl-substituted or C.sub.1-C.sub.24-oxyalkyl-substituted aryls, C.sub.7-C.sub.18-alkylaryl-substituted aryls and optionally C.sub.1-C.sub.12-alkyl-substituted aryls bridged via C.sub.1-C.sub.8 alkylene groups and having a total of 8 to 30 carbon atoms, and aryl, comprising the steps of: a) carbodiimidization of isocyanates in the presence of a catalyst to give a reaction mixture comprising carbodiimide and monomeric isocyanate, b) at least partial separation of the catalyst and/or monomeric isocyanate from the reaction mixture comprising carbodiimide and monomeric isocyanate by distillation or extraction to obtain a crude carbodiimide comprising monomeric isocyanate, and c) addition of one or more alcohols to the crude carbodiimide comprising monomeric isocyanate and partial or complete reaction of the alcohol with the monomeric isocyanate of the crude carbodiimide.

2. The process according to claim 1, wherein in step c), based on the amount of carbodiimide present, 0.1%-5% by weight of alcohol(s) is added.

3. The process according to claim 1, wherein the addition and/or reaction of the alcohol in step c) is effected at temperatures in the range from 140-200? C.

4. The process according to claim 1, wherein the alcohols used are aliphatic and/or aromatic alcohols.

5. The process according to claim 1, wherein the reaction mixture product from step a) is filtered between step a) and step b).

6. The process according to claim 1, wherein the addition and/or reaction in step c) is effected while stirring.

7. The process according to claim 1, wherein the carbodiimides correspond to formula (II), ##STR00004## in which R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 identically or independently of one another are H, C.sub.1-C.sub.20 alkyl, C.sub.3-C.sub.20 cycloalkyl, C.sub.6-C.sub.15 aryl and/or C.sub.7-C.sub.15 aralkyl, R.sup.7=C.sub.1-C.sub.18 alkylene, C.sub.5-C.sub.18 cycloalkylene, C.sub.1-C.sub.20-alkyl-substituted arylene and/or C.sub.7-C.sub.18 aralkylene.

8. The process according to claim 7, wherein n is a number in the range from 1 to 50.

9. The process according to claim 1, wherein the distillation in step b) is effected at temperatures of from 140? C. to 200? C.

10. The process according to claim 1, wherein the distillation in step b) is conducted at a pressure of from 0.1 to 50 mbar.

11. The process according to claim 1, wherein the catalyst in step a) is selected from the group consisting of phospholene oxides, phospholidines, phospholine oxides, and also the sulfides thereof, tertiary amines, basic metal compounds, alkali metal oxides, alkali metal hydroxides, alkaline earth metal oxides, alkaline earth metal hydroxides, alkoxides, phenoxides, metal carboxylates and non-basic organometallic compounds.

12. The process according to claim 1, wherein the carbodiimidization is effected in the presence of a solvent.

13. The process according to claim 1, wherein the isocyanates used are 1,3,5-triisopropylphenyl diisocyanate (TRIDI), 2,6-diisopropylphenyl isocyanate (DIPI) and/or 2,4,6-triisopropylphenyl isocyanate (TRIPI).

14. The process according to claim 1, wherein following step c) excess alcohol is removed by distillation.

15. The process according to claim 1, wherein, after step c), carbodiimides are obtained which have a content of monomeric isocyanate of less than 1000 ppm.

Description

WORKING EXAMPLES

Determination of the Residual Isocyanate Monomer Content

[0043] The residual isocyanate monomer content was determined by means of HPLC after reaction with a reagent solution (1-pyridyl-2-piperazine in 100 ml of THF). The eluent used was a mixture of ammonium acetate solution and methanol. Calibration was performed beforehand with various concentrations of the monomeric isocyanate.

[0044] Example carbodiimide: Carbodiimide of the formula (II) with R.sup.7=triisopropylphenylene, R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and R.sup.6=isopropyl and n=approx. 18

Example 1: Carbodiimidization

[0045] A mixture of 1,3,5-triisopropylphenyl diisocyanate (TRIDI) and 2,4,6-triisopropylphenyl isocyanate (TRIPI) was carbodiimidized in the presence of approx. 0.2% of methylphospholene oxide at 160? C., until an NCO content of <1% was achieved. The reaction product was distilled for 2 h at 160? C. and 10 mbar.

Example 2: Batch Distillation

[0046] The carbodiimide from Example 1 was distilled in a stainless steel tank for 5 h over a short distillation bridge. The temperatures in the distillation tank were in a range from 160? C. to 180? C., the final pressure was approx. 10 mbar.

Example 3: Distillation Via Thin-Film/Short-Path Evaporator

[0047] The carbodiimide from Example 1 was distilled by means of a thin-film/short-path evaporator combination at approx. 180? C. and 1 mbar.

Example 4: Recrystallization

[0048] The carbodiimide from Example 1 was dissolved in toluene at 60? C. in a stainless steel tank and then recrystallized from acetone at 10-20? C. After filtration, the pulverulent carbodiimide was dried for several hours in a dryer at a reduced pressure of 10 mbar.

Example 5: Reaction with Alcohol

[0049] To the carbodiimide from Example 1 was added in a stainless steel tank 0.5% 2-ethylhexanol and the mixture was stirred at 160? C. for approx. 30 min.

Example 6: Reaction with Alcohol

[0050] To the carbodiimide from Example 1 was added in a stainless steel tank 2.0% 2-ethylhexanol and the mixture was stirred at 160? C. for approx. 30 min.

[0051] The residual content of monomeric isocyanate was determined by means of HPLC. The colour was determined according to the CIE L*a*b* method ISO 11664-4. The b value was evaluated.

[0052] The results are listed in Table 1 below.

TABLE-US-00001 TABLE 1 Characteristics Monomeric isocyanate TRIPI in ppm, Yield Example Colour, CIELab (target <1000 ppm) (%) 1 (comp.) 6 approx. 1800 >95 2 (comp.) 10 approx. 1300 >95 3 (comp.) 8 <100 >90 4 (comp.) <4 <100 <60 5 (inv.) 6 approx. 700 >95 6 (inv.) 6 <100 >95 comp.: comparative example, inv.: according to the invention

[0053] As can be seen from Table 1, the residual isocyanate monomer content cannot be achieved in the simple batch distillation method even after very long distillation times. Moreover, this results in a marked deterioration in the product colour. The desired quality characteristics are first achieved by means of recrystallization or by means of a thin-film/short-path evaporator combination; however, these methods are complex and are associated with losses in yield. The simple reaction with small amounts of alcohol (here 2-ethylhexanol) leads to the desired results while avoiding the disadvantages of the known processes.