DE1954093B2 - Process for the preparation of polymeric organic isocyanates - Google Patents

Description

The present invention relates to an improved process for the preparation of organic isocyanurates increased stability

The trimerization of organic isocyanates, especially aromatic polyisocyanates, in the presence of aliphatic Isocyanates using aliphatic, araliphatic or mixed aliphatic-araliphatic Phosphine is known. The method allows the production of free isocyanate groups Isocyanurates, especially those isocyanurates which are free aromatic and aliphatic at the same time Have NCO groups. These isocyanate trimers are particularly suitable for relative production light-stable adhesives, paints, elastomers and foams. For the production of the trimerization products however, it is necessary to carry out the polymerization reaction accurately and with reproducible properties to finish quickly at a predetermined point. To such a sharp stop of the trimerization reaction To achieve the desired degree of polymerization, the reaction mixture J5 Compounds added that cancel the effectiveness of the catalyst. As such catalyst poisons are anhydrous hydrogen chloride, benzoyl chloride, acetyl chloride, dimethyl sulfate, methyl p-toluene sulfonate, Mixtures of the last two compounds mentioned and other compounds are known (FR-PS 15 10 342). However, these catalyst poisons have the disadvantage that their addition to the reaction mixture Action of the catalyst does not stop immediately and completely, so that in general a Reheating is required to completely deactivate the catalyst, creating a sharp controlled termination of the polymerization reaction is impossible. In addition, isocyanurates exhibit that under Using the said catalyst poisons produced the undesirable property at Storage to age, which in particular results in an undesirable increase in viscosity and discoloration which makes products noticeable.

The reference Ulimann's Encyklopadie der "Technische Chemie", 3rd edition, Vol. 9, Urban & Schwarzenberg-Verlag, Munich, Berlin (1957), page 270, discusses the influence of sulfur compounds on metal catalysts, such as those used, for. B. used in hydrogenation or oxidation reactions bo reach. Any indication of a suitable catalyst / catalyst poison combination for the Trimerization of organic polyisocyanates cannot be found in this reference.

The in Literature "Mechanisms of Sulfur t>^r>Reactions", McGraw-Hill Publishers, New York (1962), page 158, mentioned reaction of phosphines with elemental sulfur, a conceivable Under many of the highly reactive phosphines, no can Provide reference to the process according to the invention described below, since the reference on the one hand does not provide any details with regard to the kinetics of the reaction taking place between phosphines and elemental sulfur and on the other hand in the original literature on which the cited reference is based (reports of the German Chemical Society 10 [ 1877], pages 810-812) it is expressly stated that, for example phenylphosphine at ordinary temperature reacts very slowly with sulfur, and that the reaction se! bst is very slow in view of this, highlighted in the literature when heated to 100 ⁰ C The inertia of sulfur was to be assumed that sulfur acts as a catalyst gate poison would have to be far more unsuitable than the catalyst poisons listed in FR-PS 15 10 342.

As has now been found, surprisingly, it is still possible to address the above-mentioned disadvantages Avoid using the reaction mixture as a catalyst poison elemental sulfur is added.

The present invention thus relates to a process for the preparation of polymeric isocyanates by polymerization of organic polyisocyanates in the presence of a phosphine as a catalyst and Termination of the polymerization reaction by subsequent addition of a catalyst poison, characterized in that that sulfur is used as a catalyst poison.

One to three moles of sulfur per mole are generally required to terminate the polymerization reaction used catalyst required.

Any aliphatic, cycloaliphatic, araliphatic or aromatic polyisocyanates. Suitable isocyanates are in particular those the general formula

R (NCO),

in which R denotes an aliphatic, cycloaliphatic, araliphatic or aromatic hydrocarbon, which optionally has an indifferent substituent and χ is an integer from 2 to 4, in particular 2 to 3. Examples of suitable aromatic polyisocyanates are

2,4- and 2,6-diisocyanatotoluene

and mixtures thereof,

4,4'-diisocyanatodiphenylmethane,

Phenylene diisocyanates,

4-tert-butyl-m-phenylene diisocyanate,

l-methoxyphenylene-2,4-diisocyanate,

Diphenyl-4,4'-diisocyanai,

1,5-diisocyanatonaphthalene,

1,4-diisocyanatonaphthalene,

4,4 ', 4 "-Triisocyanato-triphenylmethane,

Tris (p-isocyanatophenyl) thiophosphate

and similar connections
called.

Examples of aliphatic, cycloaliphatic or araliphatic polyisocyanates are

Ethylene diisocyanate,

1,4-tetramethylene diisocyanate,

1,6-hexamethylene diisocyanate,

l, 5-diisocyanato-2,2-dimethylpentane,

1,3-xylene diisocyanate,

1,4-xylylene diisocyanate,

Cyclohexylene-1,3-diisocyanate and

1 AS-triisocyanatocyclohexane
called

Preferred polyisocyanates to be used as starting material are 2,4-diisocyanatotoluene, its Mixtures with 2,6-diisocyanatotoluene, hexamethylene diisocyanate and mixtures of an aromatic polyisocyanate with an aliphatic, cycloaliphatic or araliphatic polyisocyanate, the ratio of aliphatically to aromatically bound NCO groups is chosen so that in the starting mixture ι ο per aromatic NCO group at least 0.25 aliphatic NCO groups, preferably more than 1 aliphatic NCO groups, in particular up to 10 aliphatic groups NCO groups are present.

Any phosphines can be used as a catalyst in the process according to the invention, such as B. aliphatic, araliphatic or mixed aliphatic-aromatic phosphines. Suitable are e.g. B. Trialkylphosphine such as trimethylphosphine, triethylphosphine, tri-n-propyJphosphine, tri-iso-propy] pbosphine, Ethyldibutylphosphine, tri-n-butylphosphine, tri-isobutylphosphine, Tri-tert-butylphosphine, tribenzylphosphine, dimethyl-benzylphosphine and dimethyl-phenylphosphine. Phosphines in which 2 alkyl groups form a ring, such as. B. P-butyl-phosphacyclopentane are also suitable. The amount of catalyst can vary within wide limits. In general 0.001 to 10.0 percent by weight, preferably 0.001 to 1.0 percent by weight, in particular 0.01 to 0.1 Percentage by weight of catalysts based on the reaction mixture was added.

The process according to the invention can be carried out in the presence or absence of solvents will. If solvents are used, a somewhat higher content of catalyst is preferred used. Suitable inert organic solvents are, for. B. dioxane, esters such as methyl acetate, ethyl acetate, Butyl acetate and methyl glycol acetate; Ketones such as acetone, methyl ethyl ketone and cyclohexanone; aromatic, aliphatic or chlorinated hydrocarbons with the exception of carbon tetrachloride.

The trimerization reaction can take place at different reaction temperatures. Generally will the reaction is carried out at -20 to + 100.degree. C., preferably at 20 to 60.degree. Unusually high temperatures should be avoided to prevent the formation of carbodiimides and discoloration of the reaction mixture to counteract. The reaction can be carried out at any pressure, but is preferably atmospheric Pressure carried out.

Unreacted monomeric starting material can be separated after the reaction has ended such as B. distillation or extraction can be removed.

The compounds prepared by the process according to the invention can either be or have several isocyanurate nuclei in the molecule. They are particularly suitable for the production of adhesives, Lacquers, elastomers and foams as well as hardeners for polyester lacquers. The isocyanurates are coming preferably used in 50 to 70% solutions. Suitable solvents for this are esters, ketones and Hydrocarbons.

Examples
example 1

(1 A, comparative experiment) 1300 parts by weight of an 80/20 isomer mixture are placed in a suitable reaction vessel from 2,4- and 2,6-diisocyanatotoluene together with 2600 parts by weight of hexamethylene diisocyanate heated to 60 ° C; then 0.78 parts by weight of tri-n-buiylphosphine are added. The temperature of the reaction mixture is kept at 60 ° C. by cooling slightly. After about The reaction mixture has an NCO content of approx. 36% for 4.5 hours. At this point the Reaction by adding 1.56 parts by weight of a mixture of dimethyl sulfate and methyl p-toluenesulfonate and briefly heated to 100 ° C to a standstill. During this reheating sounds the reaction takes place only slowly, which is noticeable in a further drop in the NCO content. The unreacted monomer mixture is finally distilled at a pressure of 1 mm Hg and a temperature of 175 to 180 ° C in a thin film evaporator. You get 2065 Parts by weight of a brittle yellowish resin with an NCO content of 19.8%.

(1 B, method of the invention) In a suitable reaction vessel, 1300 parts by weight of an 80/20 isomer mixture of 2,4- and 2,6-diisocyanatotoluene with 2600 parts by weight of hexamethylene diisocyanate to 6O ⁰ C is heated; then 0.78 parts by weight of tri-n-butylphosphine are added. With slight cooling the temperature of the reaction mixture is kept at 6O ⁰ C. After about 4.5 hours the reaction mixture has an NCO content of about 36%. At this point the reaction is stopped by adding 0.2 parts by weight of sulfur. Reheating is not necessary here, as the sulfur causes the reaction to stop immediately. A further decrease in the NCO content after the addition of sulfur cannot be determined. The unreacted monomer mixture is finally removed by distillation at a pressure of 1 mm Hg and a temperature of 175 to 180.degree. 2221 parts by weight of a brittle yellowish resin with an NCO content of 20.0% are obtained.

60% solutions in ethyl acetate are prepared from the resins obtained according to 1 A and 1 B. the The aging stability of the solutions is determined by measuring the increase in viscosity as a function of time certainly.

Solution from aging

No.% NCO viscosity

cP at 25 ° C

Aging after 21 months

Temperature viscosity cP at 25 ° C

increase

colour

Gardner number

IA 11.36 084 20 ° C 2550 373% 5 IB il.75 413 20 ° C 1170 283% 3

A 60% solution in ethyl acetate of a resin prepared according to 1 A but using 3.12 parts by weight of a mixture of dimethyl sulfate and methyl p-toluenesulfonate shows a viscosity increase of 574 cP - to 226 ° C after storage for 21 months at 25 ° C. The color of the solution corresponds to the Gardner Color 5. 293% strength increase in viscosity shows that an increased addition of the known catalyst poison leads ^r gebnissen no satisfactory E. It follows from this that the termination of the reaction by the addition of sulfur leads to more aging-stable and less colored products.

Example 2

336 g of hexamethylene diisocyanate are added to 1.2 g of tri-n-butylphosphine and stirred for approximately eight hours at 50 to 6O ⁰ C. The NCO content has then decreased from 49.5% to 35 to 36%. The reaction is stopped by adding 0.2 g of sulfur and the low-viscosity reaction product is distilled twice over a thin-film evaporator (vacuum 0.3 Torr, circulation temperature of the heating medium 160 to 170 ° C). 161 g of distillate and 170 g of polymer with an NCO content of 21.1% and a content of free hexamethylene diisocyanate of less than 1% are obtained. The viscous yellowish liquid shows absorption in the IR spectrum at 2.75,3,4,4,4,5,68,5,9,6,85,7,45,9,2,11,6, 12,75 and 13.05 µ. The band at 4.6 μ, which is characteristic of the carbodiimides, is completely absent. Molecular weight 500 to 510.

Example 3

3 g of tri-n-butylphosphine are added with thorough stirring to a solution of 500 g of 2,4-tolylene diisocyanate in 500 g of butyl acetate. The temperature rises to 50 to 6O ⁰ C. The mixture is stirred at this temperature for 30 to 40 hours and reached an NCO content of 9.0 to 9.5%. The reaction is terminated by addition of 0.5 g of sulfur at 50 to 6O ⁰ C. Any small amounts of unreacted sulfur are, after cooling the reaction mixture by filtration, for. B. removed via a pressure nutsche.

Claims (1)

Claim: Process for the preparation of polymeric isocyanates by polymerizing organic polyisocyanates in the presence of a phosphine as a catalyst and termination of the polymerization reaction by subsequent addition of a catalyst poison, characterized in that sulfur is used as a catalyst poison. ι ο