DE1954093C3 - 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 in particular aromatic polyisocyanates in the presence of aliphatic isocyanates using aliphatic more araliphatic or mixed aliphatic-araliphatic Phosphines 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. About a dull, sharp stop to the trimerization reaction To achieve the desired degree of polymerization, have been the reaction mixture Compounds added that neutralize 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 Use of the mentioned catalyst poisons produced have the undesirable property of aging on storage, which is particularly evident in a unwanted increase in viscosity and discoloration of the products noticeable.

The literature parts of Ulimann's Encyklopadie der technical chemistry, 3rd edition ßd. 9, Urban & Schwarzenberg-Verlag, Munich, Berlin (1957), Page 270, discusses the influence of sulfur compounds on metal catalysts, such as those used e.g. B. at Hydrogenation or oxidation reactions are used. Any indication of a suitable one Catalyst / catalyst poison combination for the trimerization of organic polyisocyanates not to be found in this reference.

Also that in the literature reference “Mechanisms of Sulfur Reactions ”, McGraw-Hill-Verlag, New York (1962), page 158, reaction of phosphines mentioned with elementary *! Sulfur, one of many conceivable

Reaction of the highly reactive phosphines cannot indicate the inventive concept described below Mediate method, since the reference on the one hand no details regarding the kinetics of the between phosphines and elemental sulfur provides and there on the other hand in the reaction the original literature on which the cited literature is based (reports of the Deutsche Chemischen Gesellschaft 10 [1877], pages 810-812) expressly emphasizes that, for example, phenylphosphine at ordinary temperature reacts only very gradually with sulfur, and that the reaction itself at Heating to 100 ° C. is slow. In view of this inertia of sulfur, which has been emphasized in the literature, it was to be assumed that sulfur as a catalyst poison would have to be far more unsuitable than those listed in FR-PS 1510 342 Catalyst poisons.

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

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.

To terminate the polymerization reaction, one to three moles of sulfur per mole are generally required! 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 ^^ - diisocyanate,
Diphenyl ^ '- diisocyanate,

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,
I ^ -Tetramethylene diisocyanal,

., 6-mexamethylene diisocyanate.
l, 5-diisocyanato-2,2-dimethylpentane,
1,3-xylylene diisocyanate,
1,4-xylylindiisocyanate,
Cydohexylen-1,) - diisocyanate and

1 ^^ - Trisocyanatocyclohexane
called.

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

Any desired phosphines can be used as catalyst in the process according to the invention, such as, for example, aliphatic, araliphatic or mixed aliphatic aromatic phosphines. Suitable are e.g. B. Trialkylphosphine viz trimethylphosphine, triethylphosphine. Tri-n-propyiphosphine, tri-iso-propylphosphine, 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 percent by weight, based on the reaction mixture, of catalysts are added.

The method according to the invention can be carried out in the presence or absence of solvents. When using solvents a somewhat higher content of catalyst is preferably used. Suitable inert organic solvents are z. B. dioxane, esters such as methyl acetate, ethyl acetate, butyl acetate and methyl glycol acetate; Ketones like 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, the reaction at -20 to + 100 ° C, is preferably performed at 20 to 60 ⁰ C. Unusually high temperatures should be avoided in order to counteract the formation of carbodiimides and discoloration of the reaction mixture. The reaction can be carried out at any pressure, but is preferably carried out at atmospheric pressure.

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

Those produced by the process of the invention Compounds can have one or more isocyanurate nuclei in the molecule. she are particularly suitable for the production of adhesives and paints. Elastomers and foams as well as Hardener for polyester lacquers. The isocyanurates are preferably used in 50 to 70% solutions. Suitable solvents for this are esters, ketones and hydrocarbons.

Examples
example 1

(1 A, comparative test) In a suitable reaction vessel, 1300 parts by weight of an 80/20 isomer mixture of 2,4- and 2,6-DiisocyanatotoluoI together 2600 parts by weight Hexai nethylendiisocyanat at 60 ⁰ C is heated; then 0.78 parts by weight of tri-n-butylphosphine are added. The temperature of the reaction mixture is kept at 60 ° C. by cooling slightly. After about 45 hours, the reaction mixture has an NCO content of about 36%. At this time, the reaction by the addition of 1.56 parts by weight of a mixture of dimethyl sulfate and methyl-p-toluenesulfonate, and brief heating to 100 ⁰ C is brought to a standstill during this post-heating the reaction sounds from only slowly, which is the falling of a further NCO content noticeable The unreacted monomer mixture is finally removed by distillation at a pressure of 1 mm Hg and a temperature of 175 to 180 "C in a thin-film evaporator. 2065 parts by weight of a brittle yellowish resin with an NCO content of 19.8 are obtained %.

(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 at 60 ⁰ C ervärmt; then 0.78 parts by weight of tri-n-butylphosphine are added. The temperature of the reaction mixture is kept at 60 ° C. by cooling slightly. 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 is finally removed by distillation at a pressure of 1 mm Hg and a temperature of 175 to 180 ^0C. 2221 parts by weight of a brittle yellowish resin with an NCO content of 20.0% are obtained.

The resins obtained according to I A and I B become 60% solutions each made in ethyl acetate. The aging stability of the solutions is determined by measurement the increase in viscosity as a function of time.

Solution from aging

No.% NCO ViskosilSt

c C at 2 r C

Aging after 21 months

Temperature viscosity

cP at 25 ° C

increase

Colour

Gardner number

IA
I ß

I!, 36
11.75

684
41!

2550
1170

J7J%
28J%

An eo% solution in ethyl acetate according to 1 A but using 3.12 parts by weight of a mixture of dimethyl sulfate and methyl p-toluenesulfonate The resin produced shows an increase in viscosity of 574 cP after storage for 21 months at 25 ° C on 226OcP. The color of the solution corresponds to the Gardner color number 5, the 293% increase in viscosity proves that even an increased addition of the known catalyst poison does not produce satisfactory results It follows from this that the termination of the reaction m by the addition of sulfur leads to aging-stable and weaker colored products.

Example 2

336 g of hexamethylene diisocyanate are mixed with 1.2 g of tri-n-butylphosphine and the mixture is ^{stirred at 50 to 60 °} C. for about eight hours. The NCO content has then fallen from 493% to 35 to 36%. The reaction is stopped by addition of 0.2 g of sulfur and distilling the low-viscosity reaction product of two times 2 "on a thin film evaporator (vacuum 0.3 Torr, circulating flow temperature of the heating medium 160 to 170 ⁰ C), there are 161 grams of distillate and 170 g of polymer with obtained an NCO content of 21.1% and a content of free hexamethylene diisocyanate of less than 1%. The viscous yellowish liquid shows absorption in the IR spectrum at 2.75,3,4,4,4,5,68,53,6,85,7,45,9,2,1 \ , 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 to a solution of 500 g of 2,4-toluene diisocyanate in 500 g of butyl acetate with thorough stirring. The temperature rises to 50 to 60 ° C. The mixture is stirred at this temperature for 30 to 40 hours and an NCO content of 9.0 to 9.5% is achieved. The reaction is stopped by adding 0.5 g of sulfur at 50 to 60 ⁰ C terminated Any small amounts of unreacted sulfur in the reaction mixture by Fvration for example through a pressure filter to be removed after cooling.

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