DE1092007B - Process for the preparation of polyisocyanates containing a carbodiimide isocyanate adduct - Google Patents

Description

Process for the preparation of a carbodiimide isocyanate adduct containing polyisocyanates carbodiimides, which in the thermal decomposition of aromatic isocyanates are not very stable (Chem. Rev., 53 [1953, P. 145). Carbodiimides made from 4,4'-diisocyanatodiphenylmethane are highly polymeric and insoluble and firm (Am. Soc., 80 [1958], pp. 5496). It is also known that carbodiimides Form adducts with isocyanates (German Auslegeschrift 1 012 601), which when heated split again into carbodiimide and isocyanate.

The invention relates to a process for the production of polyfunctional Isocyanates of the diphenylmethane series, the adducts of carbodiimides and isocyanates contain.

In the condensation of aniline with formaldehyde essentially fall the following amines of the diphenylmethane series: 2,4'-diaminodiphenylmethane 1 bis 3010, 4,4'-diaminodiphenylmethane 70 to 85 0 / ,, 2,4-bis (4-aminobenzyl) aniline 10 up to 20%, tetra-, penta- and hexafunctional diphenylmethane bases 3 to 80 / o.

You can use the mixture or individual enriched or pure Form isolated components of the same phosgenate in a known manner or enrichment or isolate individual components only after phosgenation has taken place.

The amines of the diphenylmethane series can be obtained by known processes, z. B. according to German Patent 94927, dissolved in an inert solvent, convert with phosgene into the corresponding polyisocyanates. That after eliminating the excess phosgene and evaporation of the solvent remaining crude product or a pure polyisocyanate of the diphenylmethane series should be more than 90 0 /, of total nitrogen in the form of isocyanate groups.

According to the present method, it is possible in a single operation, starting from mixtures of polyfunctional, aromatic amines, such as those used in condensation of aniline with formaldehyde or substances that split off formaldehyde in mineral acids Solution are formed to produce stable, polyfunctional isocyanates, which In addition to free isocyanate groups, also blocked isocyanate groups in the form of carbodiimide-isocyanate adducts contain.

The process is characterized in that the known in Way, polyisocyanates prepared by phosgenation of the corresponding amines subjecting the diphenylmethane series to a heat treatment at temperatures above 150 "C, up to a maximum of 330/0 of the isocyanate groups present due to carbodiimide formation have been consumed, and then cooled to room temperature.

The polyisocyanate (s) are at normal or reduced Pressure from 150 to 3000 C, preferred 180 to 220 "C, heated, with cleavage of Carbon dioxide is observed. They are formed to a small extent according to the equation RNCO + OCNR + RN = C = NR + CO2 R = substituted phenyl radical with enlarged molecules Carbodiimide.

The reaction takes place autocatalytically, i. i.e., the forming Carbodiimides catalyze the further decomposition of isocyanate groups. The time dependency the carbodiimide formation can approximately be represented by a parabola: g = 100 t2 where g is the proportion of unreacted isocyanate groups, based on the initial concentration = 100, t is the time in hours and a essentially depends on the decomposition temperature and to a lesser extent dependent on the composition of the isocyanate mixture Factor means.

At a decomposition temperature of 220 "C, the factor a is between 0.1 and 0.6 and at a decomposition temperature of 1800 C between 0.01 and 0.06, corresponding to a 100/0 decomposition at 2200 C in 4 to 10 hours and at 1800 C in 13 to 32 hours.

In order to obtain still liquid or at least meltable products, may not exceed 50% of the isocyanate groups originally present to form carbodiimide-isocyanate adducts implemented.

As soon as a maximum of 330 /, of the isocyanate groups to be converted have been consumed by the carbodiimide reaction, the polyisocyanate becomes carbodiimide -Mixture cooled to room temperature. Carbodiimide groups react at room temperature free isocyanate groups in a molar ratio of 1: 1, with a further increase in the size of the molecule occurs, so that the above-mentioned at most 500/0 of the originally existing Isocyanate groups are consumed.

The carbodiimide isocyanate adducts absorb light in the infrared Range at 5.76 to 5.78 p and at 7.24 to 7.22 p.

The products obtained have the following advantages: They are excellent suitable for the production of foams, especially rigid foams.

They have an extremely low vapor pressure, practically no odor and are non-toxic.

They show against unmodified 4,4'-diisocyanatodiphenylmethane improved shelf life and less or no tendency to crystallize.

Example 1 From an amine mixture consisting of 2 parts of 2,4'-diaminodiphenylmethane, 85 parts of 4,4'-diaminodiphenylmethane, 12 parts of 2,4-bis- (4-aminobenzyl) -aniline and 3 parts of more than three-functional diphenylmethane bases are reacted with Phosgene obtained in chlorobenzene solution, a mixture of polyisocyanates whose Total nitrogen - after evaporation of the solvent - to 95.8% in the isocyanate groups is included.

The crude isocyanate is heated to 1890 ° C. while stirring. After 41/2 Hours are still 89.8 01o of the total nitrogen to be found in NCO groups. The mixture is cooled to 20 ° C. After a post-reaction period of 10 hours, only 86.20 / 0 des are left Total nitrogen in free NCO groups.

The product remains liquid at room temperature.

Example 2 An amine mixture of 1 part 2,4'-diaminodiphenylmethane, 76 parts of 4,4'-diaminodiphenylmethane, 15 parts of 2,4-bis (4-aminobenzyl) aniline, 8 parts of tetra-, penta- and hexafunctional diphenylmethane bases can be used with a yield of 96.50 / ,, based on the amino groups used, to the corresponding React isocyanate mixture. The concentrate freed from the solvent is under heated to 2000 C for 3 hours in a vacuum of 50 torr, the isocyanate nitrogen drops to 91.00 / 0 of total nitrogen. 15 hours later it is at room temperature An isocyanate nitrogen of 89.5% was found in the sample held. The product crystallizes no longer.

Example 3 Pure, distilled 4,4'-diisocyanatodiphenylmethane is heated for 11 hours at 2200 C, the N CO content, expressed in parts from the equivalent weight 42, from 33.5 to 25.80 :, decreases. After standing for 24 hours At room temperature the crystalline solidified end product still contains 22.8% free NCO groups.

Claims (1)

PATENT CLAIM: Process for the production of a calbodiimide isocyanate adduct containing polyisocyanates, characterized in that in a known manner polyisocyanates of the diphenylmethane series produced by phosgenation of the corresponding amines subjected to heat treatment at temperatures above 150 "C, up to the maximum 330/0 of the isocyanate groups present have been consumed by carbodiimide formation and then cools to room temperature.