PROCESS FOR CARBODIIMIDIZATION

Abstract

The invention relates to polycarbodiimides and to a process for their preparation using special catalysts.

Claims

1. A process for preparing polyisocyanates comprising carbodiimide groups, comprising a first step wherein at least one monomeric di- or polyisocyanate, is subjected to a carbodiimidization reaction in the presence of at least one phosphetane-1-oxide of the general formula I ##STR00002## wherein R is a monovalent organic radical having 1 to 6 carbon atoms, and a second step wherein the phosphetane-1-oxide is removed from the reaction product of the first step.

2. The process of claim 1, wherein the phosphetane-1-oxide is selected from the group consisting of 1,2,2,3,4,4-hexamethylphosphetane-1-oxide, 1-ethyl-2,2,3,4,4-pentamethylphosphetane-1-oxide, 1-phenyl-2,2,3,4,4-pentamethylphosphetane-1-oxide, and mixtures thereof.

3. The process of claim 1, wherein the at least one monomeric di- or polyisocyanate is selected from the group consisting of aliphatic, cycloaliphatic, araliphatic and aromatic di- or polyisocyanates.

4. The process of claim 3, wherein aliphatic, cycloaliphatic or araliphatic monomeric di- or polyisocyanates are used in the process and the carbodiimidization reaction is effected in the presence of ≤20 ppm by weight carbodiimidization catalyst, wherein the carbodiimidization catalyst is the phosphetane-1-oxide of the general formula I, in a mixture with ≤80% by weight, based on the amount of phosphetane-1-oxides, of further compounds catalyzing the carbodiimidization reaction that are different from phosphetane-1-oxides of the formula I.

5. The process of claim 4, wherein the carbodiimidization catalyst is exclusively the phosphetane-1-oxide of the general formula I.

6. The process of claim 1, wherein the carbodiimidization reaction is carried out at a temperature in the range from 130 to 230° C.

7. The process of claim 1, wherein the carbodiimidization reaction is carried out in the presence of at least one solvent.

8. The process of claim 7, wherein the solvent has a boiling point under standard pressure (1013 mbar) of ≥120° C.

9. The process of claim 7, wherein the solvent and the phosphetane-1-oxide according to formula I are removed together from the reaction mixture obtained from the first step in a distillation step.

10. The process of claim 1, wherein the second step is carried out by distillation at a pressure less than 1013 mbar.

11. A polyisocyanate comprising carbodiimide groups having a phosphorus content of ≤100 ppm, determined by elemental analysis (ICP-OES, DIN ISO 17025), made by the process according of claim 1.

12. The polyisocyanate of claim 11, wherein 1,2,2,3,4,4-hexamethylphosphetane-1-oxide is used as phosphetane-1-oxide of the formula I.

13. The process of claim 1 wherein the phosphetane-1-oxide is removed from the reaction product of the first step by distillation.

14. The process of claim 3, wherein aromatic monomeric di- or polyisocyanates are used in the process and the carbodiimidization reaction is effected in the presence of 0.1 to 3.0% by weight carbodiimidization catalyst, and wherein the carbodiimidization catalyst is the phosphetane-1-oxide of the general formula I, in a mixture with ≤80% by weight, based on the amount of phosphetane-1-oxides, of further compounds catalyzing the carbodiimidization reaction that are different from phosphetane-1-oxides of the formula I.

15. The process of claim 14, wherein the carbodiimidization catalyst is exclusively the phosphetane-1-oxide of the general formula I.

16. The process of claim 3, wherein aromatic monomeric di- or polyisocyanates are used in the process and the carbodiimidization reaction is effected in the presence of 0.1 to 2.0% by weight carbodiimidization catalyst, and wherein the carbodiimidization catalyst is the phosphetane-1-oxide of the general formula I, in a mixture with ≤80% by weight, based on the amount of phosphetane-1-oxides, of further compounds catalyzing the carbodiimidization reaction that are different from phosphetane-1-oxides of the formula I.

17. The process of claim 16, wherein the carbodiimidization catalyst is exclusively the phosphetane-1-oxide of the general formula I.

18. The process of claim 1, wherein the carbodiimidization reaction is carried out at a temperature in the range from 140 to 210° C.

19. A polyisocyanate containing comprising carbodiimide groups having a phosphorus content of ≤25 ppm, determined by elemental analysis (ICP-OES, DIN ISO 17025), made by the process of claim 1.

20. A polyisocyanate containing comprising carbodiimide groups having a phosphorus content of ≤20 ppm, determined by elemental analysis (ICP-OES, DIN ISO 17025), made by the process of claim 1.

Description

EXAMPLES

Example 1: Comparative Example

[0039] Catalyst: Phospholene Oxide

[0040] To H.sub.12MDI (20.0 g, 75.8 mmol, 1.0 eq) in chlorobenzene (2.22 g) was added phospholene oxide at a mole fraction of xCat=1.5%. The reaction mixture was heated to 150° C. and samples of ˜500 mg were taken at regular intervals to determine the NCO.sub.t value. From the NCO values determined, the conversion of the free isocyanate groups to carbodiimide groups was calculated according to

Conversion.sub.t=(NCO.sub.t=0−NCO.sub.t)/NCO.sub.t=0

where NCO.sub.t is the measured NCO value at time t and NCO.sub.t=0 is the NCO value at time t=0. In addition, the TOF (turnover frequency) at time t was calculated according to

TOF.sub.t=(n(NCO).sub.t−n(NCO).sub.t=0/(n(Cat)*t)

where n(NCO).sub.t is the amount of NCO groups at time t and n(NCO).sub.t=0 is the amount of NCO groups at time t=0. n(Cat) is the amount of catalyst and t is the reaction time. The results are shown in the table below.

TABLE-US-00001 Reaction time/h Conversion/% TOF/s.sup.−1 00:00 0.0 00:30 13.5 0.0097 01:00 22.6 0.0081 01:30 25.2 0.0060 03:05 42.5 0.0050 04:00 51.4 0.0046 05:00 57.0 0.0041 06:00 64.1 0.0038

Example 2: Inventive

[0041] Catalyst: Phosphetane Oxide

[0042] The procedure was as described above, with the difference that 1,2,2,3,4,4-hexamethylphosphetane-1-oxide was used as catalyst. The results are shown in the table below.

TABLE-US-00002 Reaction time/h Conversion/% TOF/s−1 00:00 0.0 00:30 1.4 0.0009 01:00 4.1 0.0013 01:30 6.7 0.0015 03:45 16.6 0.0015 04:15 18.6 0.0014 06:00 25.9 0.0014

Example 3: Comparative Example

[0043] To H.sub.12MDI (20.0 g, 75.8 mmol, 1.0 eq) in chlorobenzene (2.22 g) was added phospholene oxide (0.20 g). The reaction mixture was heated to 200° C. for 8 h. A distillation head was then attached and the mixture was distilled at 200° C. and 20 mbar. The residue was investigated for P content by elemental analysis and a value of 480 mg/kg was found, which corresponds to 18% of the original amount of catalyst.

Example 4: Inventive

[0044] To H.sub.12MDI (20.0 g, 75.8 mmol, 1.0 eq) in chlorobenzene (2.22 g) was added 1-ethyl-2,2,3,4,4-pentamethylphosphetane-1-oxide (0.20 g). The reaction mixture was heated to 200° C. for 8 h. A distillation head was then attached and the mixture was distilled at 200° C. and 20 mbar. The residue was investigated for P content by elemental analysis and a value of 200 mg/kg was found, which corresponds to 11% of the original amount of catalyst.

Example 5: Inventive

[0045] To H.sub.12MDI (20.0 g, 75.8 mmol, 1.0 eq) in chlorobenzene (2.22 g) was added 1,2,2,3,4,4-hexamethylphosphetane-1-oxide (0.20 g). The reaction mixture was heated to 200° C. for 8 h. A distillation head was then attached and the mixture was distilled at 200° C. and 20 mbar. The residue was investigated for P content by elemental analysis and a value of 18 mg/kg was found, which corresponds to 1% of the original amount of catalyst.