CA2244486C - Polyisocyanates containing iminooxadiazine dione groups and a process for their preparation - Google Patents

Abstract

The present invention relates to a process for the preparation of polyisocyanates by oligomerizing isocyanates corresponding to formula I (OCN-CH2)X (I) wherein X represents the residue obtained by removing the OCN-CH2 group from a monomeric polyisocyanate, wherein the residue contains 3 to 20 carbon atoms and at least one NCO group, in the presence of hydrogen-polyfluoride oligomerization catalysts corresponding to formula II Mn+ n[F-((HF)m] (II) wherein M represents an n-valent cation and m is >= 0.1. The present invention is also directed to the polyisocyanates obtained by this process.

Description

LeA 32514 US V12.06.1998 POLYISOCYANATES CONTAINING IMINOOXADIAZINE DIONE
GROUPS AND A PROCESS FOR THEIR PREPARATION
BACKGROUND OF THE INVENTION
Field of the Invention The present invention relates to a process for the preparation of polyisocyanates con-taining iminooxadiazine dione groups in the presence of fluorine-containing catalysts and to the resulting polyisocyanates.

Description of the Prior Art The oligomerization and polymerization of isocyanates, particularly with the forma-tion of NCO dimer and trimer structures, is not new. If these oligomers and polymers contain free NCO groups, which may optionally be blocked with blocking agents, they are extraordinarily high quality starting materials for the preparation of a multiplicity of polyurethane resins and coating agents.

A number of industrial processes for the preparation of these polyisocyanates are known and may be found, e.g., in H.J. Laas et al,.J. Prakt. Chem. 1994, 336, 185 ff.
The majority of the above-mentioned isocyanate modifications are considerably accel-erated or are only possible by the use of various catalysts. Many catalysts simultane-ously catalyze the formation of several different types of oligomerization reactions.
This may be advantageous if the preparation of mixtures of the oligomers with differ-ent structures is desired.

However, the opposite is also frequently the case. The simultaneous presence of NCO-reactive reaction partners in addition to the isocyanate groups of the isocyanate to be oligomerized sometimes has an adverse effect on the desired oligomerization reaction or on the properties of the product obtained. Also, the simultaneous forma-LeA 32514 US

tion of structural groups other than those of the pure NCO oligomers does not al-ways take place smoothly and completely under the optimum conditions for the for-mation of the desired group.

The presence of C02, for example, in the tetraalkylammonium hydroxide-catalyzed trimerization of hexamethylene diisocyanate (HDI) prevents the formation of a clear, high-quality product (DE-A 3,806,276).

Alcohols are frequently used as solvents for the oligomerization catalyst.
They, also catalyzed by this catalyst, react with the isocyanate to be oligomerized to form allo-phanate groups via an intermediate urethane stage. Sometimes additional amounts of alcohol are added if products with a higher allophanate content are desired.
Al-lophanate groups derived from monofunctional alcohols have a low viscosity and, like uretdiones, are useful as reactive thinners for the preparation of coating compositions having a low VOC content. VOC's are volatile organic compounds, i.e., the com-pounds given off from the paint or coating in the gaseous form during curing.

The allophanatization of the above-mentioned alcohols takes place simultaneously with trimerization and is catalyzed by typical trimerization catalysts such as tetra-alkylammonium hydroxides, carboxylates or carbonates. However, residual urethane groups formed from the corresponding alcohol often remain in the product and reduce the NCO functionality and, thus, reduce the quality of the resulting resins.

The advantages of uretdiones and allophanates in terms of the viscosity and VOC
content are offset by a lower NCO functionality, which often results in a loss of qual-ity in the end products. For example, the resulting paint films have insufficient solvent resistance. Here is the advantage of trimers apparent since even the lowest molecular oligomer is a crosslinking agent, i.e., it has an NCO functionality of 3.

Another example of a process, which also has the disadvantage of forming mixtures of wanted and unwanted reaction products, is the phosphine-catalyzed oligomerization of aliphatic diisocyanates. Apart from the sensitivity to air of alkyl phosphines, their LeA 32514 US

unpleasant physiological properties and the need to operate with comparatively high concentrations during oligomerization, mixtures of various types of isocyanate oli-gomers are formed. These oligomers differ greatly in terms of their composition de-pending to a large extent on the starting isocyanate used and on the reaction condi-tions chosen as set forth in Example 1, hereinafter.

Compare also H. J. Laas et al., J. Prakt. Chem. 1994, 336, 196 ff.

To obtain lower viscosity product requires dimerization of the isocyanates, while a product having a higher NCO functionality is obtained by trimerization. It has now become apparent that with phosphine catalysis, a molar ratio of trimer [calculated as (NCO)3, molecular weight 126] to dimer [calculated as (NCO)2, molecular weight 84] of less than 5:1 cannot be shifted to a higher ratio of trimer without the simulta-neous formation of uretoneimines.

Uretonimines are a rather unwanted class of compounds in aliphatic polyisocyanate chemistry since they dissociate to form the starting isocyanate at an even lower tem-perature than the structurally similar uretdiones. The uretonimines are formed by the reaction of an isocyanate group with a carbodiimide group. Uretonimines may be present in a dynamic equilibrium with carbodiimides at room temperature.

If an isocyanate group from a monomeric isocyanate reacts with the carbodiimide group to form the uretonimine group, the dissociation of the uretonimine groups will result in a latent residual monomer problem. For reasons of occupational hygiene, products containing uretonimine groups cannot be used for the production of poly-urethane coatings. This is why reference is also repeatedly made in the (patent) litera-ture to carry out the phosphine-catalyzed oligomerization of monomeric diisocyanates at the lowest possible temperature (compare H. J. Laas et al., J. Prakt.
Chem., 1994, 336, 196).

LeA 32514 US

There have been many attempts to obtain high quality, low viscosity products that are stable towards dissociation, but which have an optimum NCO functionality that is higher than 3.

At the present time the trimer may be obtained by a low conversion trimerization process such that the main product obtained is the trimer composed of three mole-cules of diisocyanate. The trimer may also be obtained from a high conversion process by separating it by extraction or distillation from its by-products. Neither process is advantageous from an econoniic viewpoint. In the former process the low conversion rate results in an enormous loss in resin yield and a large energy requirement, mainly caused by the monomer separation required after trimerization. In the latter process the extraction and distillation processes result in higher costs and to the production of higher viscosity fractions.

Low viscosity aliphatic polyisocyanates having the optimum functionality can also be prepared by alternative reactions, e.g., by the reaction of silylated alcohols with iso-cyanatoalkanoic acid chlorides (Ch. Zwiener, L. Schmalstieg, M. Sonntag, K.
Nacht-kamp, and J. Pedain, Farbe und Lack, 1991, 1052-1057 and the literature cited therein). A disadvantage of this process is that the isocyanatoalkanoic acid chlorides are not available industrially and can be difficult to handle. The process could be im-plemented only with a large expenditure for equipment that cannot be justified by the expected advantages of the products, essentially the low viscosity of the polyiso-cyanates.

Based on the preceding discussion, the development of a process for isocyanate oli-gomerization, which does not involve the disadvantages cited above, would be ex-tremely desirable. Accordingly, it is an object of the present invention to develop a process for the oligomerization of di- and polyisocyanates that results in dissociation resistant, low viscosity products which have a high NCO functionality.

This object may be obtained with the process according to the present invention as discussed hereinafter.

LeA 32514 US CA 02244486 1998-08-03 SUMMARY OF THE INVENTION

The present invention relates to a process for the preparation of polyisocyanates by oligomerizing isocyanates corresponding to formula I
(OCN-CH2)X (I) wherein X represents the residue obtained by removing the OCN-CH2 group from a monomeric polyisocyanate, wherein the residue contains 3 to 20 carbon atoms and at least one NCO group, in the presence of hydrogen-polyfluoride oligomerization catalysts corresponding to formula II

Mn+ nLF- ( (BY)m] (II) wherein M represents an n-valent cation n is 1, 2, 3... 6, preferred is I and 2 and m is > 0.1.

The present invention is also directed to the polyisocyanates obtained by this process.
DETAILED DESCRIPTION OF THE INVENTION
Hydrogen (poly)fluorides catalysts, which are suitable for carrying out the process of the invention, are those corresponding to formula II

LeA 32514 US

wherein m is > 0.1, preferably >0.5 and more preferably m>1, and M represents an n-valent cation or cation mixture, n = 1, 2, 3...6, preferred is 1 and 2, preferably an ammonium or phosphonium cation, more preferably a tetraalkylammonium cation.

Preferred catalysts for carrying out the process according to the invention are tetra-organyl-ammonium or phosphonium hydrogen polyfluorides corresponding to formula III

R4E+ [F- . (HF)m] (III) wherein E represents N or P, R represents the same or different aliphatic, cycloaliphatic, araliphatic or aro-matic radicals which have 1 to 25 carbon atoms and may optionally be substi-tuted with 0, N or halogen and m is as defined above.

Especially preferred as catalysts for carrying out the process according to the inven-tion are tetraalkylammonium hydrogen polyfluorides corresponding to formula III
wherein E represents N, R represents the same or different aliphatic, cycloaliphatic or araliphatic radicals which have I to 20 carbon atoms and may optionally be substituted with 0, N
or halogen and LeA 32514 US

m is as defined above.

Examples of these catalysts are benzyltrimethylammonium hydrogen polyfluorides corresponding to formula IV:

C6H5CH2(CH3)3N+[F- - (HF)m] (IV), and tetraalkylammonium hydrogen polyfluorides corresponding to formula V:
R4N+[F- . (HIF)m] M, wherein R represents the same or different aliphatic or cycloaliphatic radicals having 1 to 20 carbon atoms and m is defined as above.

Catalysts used in particular preference are tetraalkylammonium hydrogen polyflu-orides corresponding to formula (VI):

R3(R!)N+[F- . (HT)m] (VI) wherein R represents the same or different aliphatic radicals having 1 to 15 carbon atoms, R' represents an aliphatic radical having I to 4 carbon atoms and m is as defined above.

Since it is known from numerous literature examples that acids and acid derivatives are reliable "stopping-agents" for trimerization reactions (H.J. Laas et al., J. Prakt.

LeA 32514 US

Chem. 1994, 336, 185 ff, other citations therein), it is surprising that the catalytic ac-tivity of the catalysts is not destroyed by the addition of the mineral acid, HF, for ex-ample, to quaternary ammonium or phosphonium fluorides.

Hydrogen (poly)fluorides may either be obtained commercially in some cases or can easily be prepared in any stoichiometry by mixing appropriate fluorides with the de-sired quantity of HF.

The form in which hydrogen fluoride is added is unimportant. It may be in the pure form, i.e., in the liquid or gaseous aggregate state. HF solutions, e.g., in protic or aprotic organic solvents are also easy to handle. HF-amine complexes, e.g., with amines such as triethylamine, pyridine or melamine, are also available commercially and relatively safe to handle.

Unlike free hydrogen fluoride, which has physiologically unpleasant properties, hy-drogen polyfluorides are not problematic. The physiological hazard potential is also removed from any HF residues that might be present in the products according to the invention because HF reacts with isocyanates to form carbamoylfluorides as described in G.D. Buckley, H. A. Piggott and A. J. E. Welch, J. Chem. Soc., 1945, 864-865).

The amount of HF in the catalyst systems may vary widely. Thus, it is not important whether HF is present in the form of monohydrogen difluorides (m = n = 1 in formula I), dihydrogen trifluorides (n = 1, m= 2 in formula I) etc., or their potassium salts with the appropriate stoichiometry (Hollemann-Wiberg), Lehrbuch der Anorganischen Chemie, 91st -100th ed., W. de Gruyter Verlag, Berlin, New York, 1985, p. 408, footnote 50), or mixtures of the latter with excess fluoride on the one hand and HF on the other hand. The optimum design of a polyfluoride catalyst may differ depending upon particular requirements and the isocyanate to be oligomerized; however, this optimization may easily be determined by preliminary tests. It is not important for carrying out the process according to the invention whether the catalyst is soluble in the mono- or polyisocyanate to be oligomerized (homogeneous catalysis) or insoluble (heterogeneous catalysis). Other substances may be added during catalysis, such as LeA 32514 US

amines, alcohols, phenols, solvents for the catalyst and/or the isocyanate, antioxidants, and matrices for the adsorptive or covalent bonding of the catalyst. The hydrogen fluoride required for the formation of hydrogen (poly)fluorides may also be added separately, optionally in dissolved form, to the starting isocyanate before or during trimerization. Also, any substances that yield hydrogen fluoride under the conditions of catalysis may be used to prepare the products according to the invention.
For ex-ample, carbamoyl fluorides are suitable as a source of HF, preferably those that can be generated by addition of HF to the isocyanate to be oligomerized.

According to the process of the invention, a broad range of high-quality, very valuable polyisocyanates for polyurethane applications has become accessible in a simple man-ner by using polyfluoride catalysts. In addition, the presence of carbon dioxide, re-gardless of whether it is present only in traces or in a relatively high concentration, does not affect the process according to the invention as demonstrated hereinafter in Example 4.

It is particularly surprising that polyfluoride catalysis are suitable for the preparation of polyisocyanates corresponding to formula VII containing iminooxadiazine dione groups ("asymmetrical trimers") z ~ Rs R~N N (VII), R'-N1~1_ O'1~ O

wherein LeA 32514 US CA 02244486 1998-08-03 Rl, R2, R3 represent the same or different radicals obtained by removing the iso-cyanate group from a monomeric polyisocyanate corresponding to the formula OCN-CH2)X
wherein X is as defined above.

This class of compounds has been the subject of little investigation previously. The first representative, 3,5-dimethyl-2-methylimino-4,6-diketo-1,3,5-oxadiazine (R1=R2=
R3= Me in Fig. VII), is obtained in addition to the isomeric isocyanurate by Slotta and Tschesche by the triethylphosphine-catalyzed trimerization of methylisocyanate (Chem. Ber. 1927, 60, 295). According to A. Etienne, G. Lonchambon, P.
Girardeau and G. Durand, C. R. Acad. Sci. Ser. C 277 1973, 795), it is said to be obtainable in a better yield by trimerization with the same catalyst in 1,2-dichloroethane. 5-methyl-2-methylimino-3-phenyl-4,6-diketo-1,3,5-oxadiazine is obtained in a 31% yield in ad-dition to other products during the reaction of methyliminocarbonic acid diphenylester with tosylisocyanate as by-product (E. Schaumann, J. Dietz, E. Kausch and G.
C.
Schmerse, Chem. Ber. 1987, 120, 339). Oxadiazinium salts, structurally related to the iminooxadiazine diones, are obtained as a by-product from the reaction of methyl-and isopropylisocyanate with antimony pentachloride and oxalyl chloride, ethyloxalyl chloride and methylchloroformate (A. Hamed, A. Ismail, M. G. Hitzler and J. C.
Jochims, J. Prakt. Chem. 1995, 337, 385-390).
As has been surprisingly found and which could not have been predicted from the prior art, the most striking peculiarity of the liquid iminooxadiazine diones, which may be obtained from HDI according to the invention, is the significantly lower viscosity compared with the corresponding isocyanurate isomer. The same applies to the melt and solution viscosities of the polyisocyanates that are solid at room temperature, for example, those prepared from cycloaliphatic diisocyanates as demonstrated hereinafter in Example 8.

LeA 32514 US

There are references to the formation of iminooxadiazine diones as a minor secondary reaction product during the catalyzed oligomerization of aliphatic isocyanates. How-ever, the physical and chemical properties of polyisocyanates with an iminooxadiazine dione structure are previously unknown. It is disclosed in DE-A 1,670,720 (page 5, lines 1-5) that during the phosphine-catalyzed uretdione formation ("dimerization") of aliphatic diisocyanates, "other by-products such as alkylamino-dialkyloxadiazine diones, carbodiimides and uretonimines are formed in an increasing quantity in addition to isocyanurates at relatively high temperatures and mainly with relatively lengthy exposure to high temperatures and with a low catalyst concentration...". More precise details about the amounts of these by-products cannot be found in this publication.

We have found that neither the controlled preparation of dimers (uretdiones) nor trimers (isocyanurates, iminooxadiazine diones) is possible by phosphine catalysis, and that the production of carbodiimides/ uretonimines at relatively high temperatures is unavoidable. The molar proportion of iminooxadiazine dione in the product and the ratio of isocyanurate to iminooxadiazine dione remains virtually constant regardless of the reaction conditions as demonstrated in Example I hereinafter.
Therefore, the statements made in DE-A 1,670,720 are only partly correct.

The fact that carbodiimides and uretonimines are an undesired class of compounds in aliphatic polyisocyanate chemistry has previously been explained.
DE-A 3,902,078 describes a process according for the trimerization of (cyclo)aliphatic diisocyanates using quaternary ammonium and phosphonium fluorides in the presence of carbon dioxide, in which iminooxadiazine diones are also produced in minor amounts (page 4, lines 51-52) in addition to oxadiazine triones and iso-cyanurates. The proportion thereof, based on the trimer content, is not more than 25 mole %. The same catalyst system and its use for the preparation of polyisocyanates having isocyanurate groups is described in EP-A 0,355,479. However, there is no LeA 32514 US

reference in this publication to either the proportional formation of iminooxadiazine diones or to products having a lower viscosity.

Therefore, it is unknown that the use of fluorides in the absence of CO2 promotes to a somewhat greater degree the formation of imino-oxadiazine diones, compared with processes of the prior art. To the contrary the teachings of DE-A 3,902,078 suggest that the formation of iminooxadiazine dione is linked to the presence of CO2 during the reaction and, thus, to the simultaneous formation of oxadiazine triones (from 2 moles of NCO and one mole of C02).
As shown by the examples of EP-A 0,355,479 which relate to HDI trimerizations, dynamic viscosities (measured at 23 C) of 2000, 35,000 and 2,500 mPa.s can be ob-tained using the fluoride catalyst systems described for HDI trimerizations having a resin yield of 22, 60 and 25%, respectively. The isocyanurate polyisocyanates ob-tained by catalysis with quaternary ammonium hydroxides according to the disclosure of DE-A 3,806,276 have viscosity values of about 1500 and 9,800 mPa.s at 23 C
with HDI trimer yields of 32 and 52% respectively. (compare DE-A 3,806,276, Examples 11 and 9, respectively.). Consequently, the HDI trimers obtained by fluoride catalysis according to EP-A 0,355,479 do not represent an improvement in terms of viscosity.
A connection between the amount of iminooxadiazine dione in the trimer mixture, fluoride catalysis and the viscosity of the resins could not be predicted by a skilled artisan.

It is surprising that according to the invention a significant increase in the iminooxa-diazine dione proportion in the trimer mixture is possible, which results in a drastic reduction in the viscosity of said products.

As shown by our own investigations into HDI trimerization with the fluoride catalyst systems described above, the iminooxadiazine dione proportion in the trimer mixture is never greater than 25%, and is generally below 20%, even when the preparation conditions of the polyisocyanate (co-catalyst, temperature, cation, etc.) are varied as demonstrated in Example 2 hereinafter. On a very general level, it is virtually impos-LeA 32514 US

sible to derive meaningful conclusions regarding the viscosity of a certain compound or class of compounds based on the structure or the NCO functionality of other com-pounds or types of compounds.

Although polyisocyanates having a relatively low NCO functionality, such as uretdi-ones or allophanates prepared from monofunctional alcohols, usually have a lower viscosity than polyisocyanates with a fairly high functionality, such as isocyanurates, this relationship may also be reversed. For example, 1,3,5-tris(6-isocyanato-hexyl)isocyanurate, which has a viscosity of about 700 mPa.s at 23 C, has a substan-tially lower dynamic viscosity than the structurally related, but only NCO-difunctional 3,5-bis(6-isocyanatohexyl)-1-oxadiazine trione, which has a viscosity of about mPa.s at 23 C (Example 3).

Another advantage of the polyisocyanates according to the invention having an iminooxadiazine dione structure is that even when exposed to high temperatures for a relatively long time, they do not exhibit any tendency to dissociate back to the mono-meric structural components on which they are based, usually diisocyanates.
Even such high-boiling compounds as N,N',N"-tris(6-isocyanatohexyl)iminooxadiazine di-one can thus be separated from higher molecular weight by-products of the HDI
trimer mixtures according to the invention both by distillation and extraction without undergoing decomposition or rearrangement to the isomeric isocyanurate.

The products according to the invention have a substantially lower viscosity than 1,3,5-tris-(6-isocyanatohexyl)isocyanurate, which has a viscosity of 700 mPa.s at 23 C as demonstrated in Example 6 hereinafter. Therefore, N,N'N"-tris-(6-iso-cyanatohexyl) iminooxadiazine dione is the NCO-trifunctional oligomer of hex-amethylene diisocyanate having the lowest viscosity. The same applies to asymmetri-cal trimers (iminooxadiazine diones) of other di- and polyisocyanates.

Catalyst concentrations, based on the weight of the starting isocyanate and the weight of the fluoride ion, of less than 0.1% by weight, preferably less than 0.05%
by weight, are used to carry out the process according to the invention. To oligomerize NCO

LeA 32514 US

group-containing, linear aliphatic diisocyanates, such as HDI, less than 50 ppm may be sufficient, based on the weight of the fluoride anion and the diisocyanate used.

The process according to the invention may be carried out at a temperature 0 to 250 C, preferably 20 to 180 C and more preferably 40 to 120 C, 'in the condensed phase or in the gaseous phase. The process may be continued until there is a quanti-tative conversion of the isocyanate groups of the starting isocyanate, or the process may be terminated at any degree of conversion, preferably after 10 to 90%, more preferably after 20 to 60% of the monomeric diisocyanate has been oligomerized.

All known prior art methods may be used to terminate the reaction, i.e. to inactivate the catalyst system. These methods include the addition of up to stoichiometric quantities of acids or acid derivatives, such as benzoyl chloride, acid esters of acids containing phosphorus or sulfur, these acids themselves, but not HF);
absorptive bonding of the catalyst followed by separation by filtration; and thermal deactivation.
Compared to phosphine catalysis, the critical advantage of the polyfluoride catalysis according to the invention is that, apart from the substantially lower catalyst concen-tration required for oligomerization, there is no tendency to form carbodiimide and/or uretdione groups, even at high temperatures.

Compared with catalysis by quaternary ammonium hydroxides, carboxylates, carbonates and fluorides, the process according to the invention has several advan-tages. It is possible to operate in homogeneous catalysis with substantially more con-centrated catalyst solutions and even pure polyfluorides because these catalysts are liquid or soluble in the isocyanate to be oligomerized. Therefore, secondary reactions with the catalyst solvent are not of concern. The exothermic reactions and turbidity due to spontaneous excessive crosslinking, which is difficult to influence and fre-quently observed during the use of the previously mentioned catalysts, hardly ever occur. The storage stability of the polyfluoride catalysts and its solutions, even at ele-vated temperature, is improved.

LeA 32514 US

According to a particular, continuous embodiment of the process of the invention, oligomerization may be carried out in a tubular reactor. In this case, the reduced ten-dency of the polyfluoride catalysts to form gel particles spontaneously in the product, despite application in highly concentrated solution or as a pure active substance, is an advantage.

Suitable starting compounds for carrying out the process according to the invention include monomeric diisocyanates and polyisocyanates corresponding to the formula I
(OCN-CH2)X

wherein X represents the residue obtained by removing the OCN-CH2 group from a monomeric polyisocyanate, wherein the residue contains 3 to 20 carbon atoms and at least one NCO group.

While this residue must contain 3 to 20 carbon atoms and at least one NCO
group, it may optionally also contain heteroatoms such as N, 0 and S.

Examples of suitable groups, X, include the regio- and stereoisomers of mono-, di-and tri- isocyanato-propyl, -butyl, -pentyl [e.g., (OCN-CH2)X = hexamethylene diiso-cyanate (HDI), 2-methylpentane-1,5-diisocyanate, etc.], -hexyl, -octyl [e.g., (OCN-CH2)X = 4-isocyanatomethyl-1,8-octane diisocyanate], -nonyl, -decyl, -alkoxyalkyl, -cyclohexyl, -(methyl)cyclohexyl [e.g., (OCN-CH2)X = 3(4)-isocyanatomethyl-l-methylcyclohexyl-isocyanate (IMCI)], -(dimethyl)cyclohexyl, (trimethyl)cyclohexyl [e.g., (OCN-CH2)X = isophorone diisocyanate (IPDI)], -ethylcyclohexyl, -propyl-cyclohexyl, (-methyl)phenyl, (-methyl)cyclohexyl and -methyl-isocyanatocyclohexyl.
The process for preparing these polyisocyanates is not critical for their use in accor-dance with the present invention, i.e., they may be produced with or without the use of phosgene.

LeA 32514 US CA 02244486 2005-04-26 It may also be advantageous to use mixtures of certain polyisocyanates in the process according to the invention, for example, in order to comply in an optimum manner with the range of requirements of the relevant product or product mixture. In many applications, such as coatings for automobiles (esp. OEM), mixtures of isocyanurate polyisocyanates based on linear aliphatic diisocyanates (e.g., HDI) and cycloaliphatic diisocyanates (e.g., IPDI or H12MDI (Desmodur W, a commercial product of Bayer AG) are used. These mixtures are usually prepared by mixing the individual iso-cyanurate polyisocyanates. However, it may also be advantageous to prepare them by simultaneous co-trimerization from the corresponding mixture of monomeric compo-nents (EP-A 0,047,452).

Certain prior art isocyanurate polyisocyanates based on cycloaliphatic diisocyanates are solid under ambient conditions and sometimes have such a high melt viscosity that monomer separation by thin film distillation is difficult and requires the use of solvents and/or flow improvers during thin film distillation. Unless low degrees of conversion (resin yield) and/or reduced NCO functionality are acceptable, commercially available isocyanurate polyisocyanates having solids contents of about 70% and prepared from cycloaliphatic diisocyanates generally have viscosities, measured at 23 C, of 1000 to 10,000 mPa.s.

However, if mixtures of linear aliphatic diisocyanates, such as HDI, and cycloaliphatic diisocyanates, such as IPDI, are trimerized according to the process of the invention with (partial) formation of iminooxadiazine diones, even at room temperature, free-flowing products (viscosity less than 100 000 mPa.s at 23 C) are obtained.
These products also exhibit a drastically more rapid fall in viscosity in solution when solvent is added when compared to the corresponding prior art products as demonstrated in Example 7 hereinafter. Corresponding prior art products are those having the same or similar NCO functionality, diisocyanate basis and average molecular weight.

The products obtained by the process according to the invention are valuable starting materials for the preparation of optionally foamed plastics, paints, coatings, adhesives and additives. In view of their reduced solution and melt viscosity compared to prod-*trade-mark LeA 32514 US

ucts based predominantly on isocyanurate polyisocyanate, the products according to the invention are particularly suitable for the preparation solvent-free, solvent borne or water-dispersible, one- and two-component polyurethane coating compositions, in which the isocyanate groups may be present in the blocked form. The resulting coatings equally good or an improved range of properties compared to the prior art products. The products according to the invention based on HDI, even in high dilu-tion in paint solvents, are more stable towards the occurrence of flocculation or tur-bidity than the corresponding prior art products predominantly containing isocy-anurate groups. Their resistance to the effect of atmospheric moisture (skin formation in open containers) is also better than the prior art products.

The products according to the invention may be used in the pure form or in combina-tion with other prior art isocyanate derivatives, e.g., polyisocyanates containing uret-dione, biuret, allophanate, isocyanurate and/or urethane groups, in which the free NCO groups may optionally be blocked or deactivated with blocking agents.

The invention is further illustrated but is not intended to be limited by the following examples in which all parts and percentages are by weight unless otherwise specified.
EXAMPLES

Unless otherwise specified, all parts and percentages are by weight.

Mole % details were determined by NMR spectroscopy and always relate, unless otherwise specified, to the sum of the NCO secondary products. The measurements were carried out on the DPX 400 device made by Brucker on approx. 5% (1H-NMR) and approx. 50% (13C-NMR) samples in dry CDC13 at a frequency of 400 MHz (1H-NNIR) and 100 MHz (13C-NMR), respectively. The reference chosen for the ppm scale was small quantities of tetramethylsilane in the solvent with a 1H-chem.
shift of 0 ppm (IH-NMR) and the solvent itself (CDC13) with a shift of 77.0 ppm (13C-NMR). Data for the chemical shift of the compounds suitable were taken from the literature (compare D. Wendisch, H. Reiff and D. Dieterich, Die Angewandte Mak-LeA 32514 US

romolekulare Chemie 141, 1986, 173-183 and the literature cited therein), and by measuring model substances. The 3,5-dimethyl-2-methylimino-4,6-diketo-1,3,5-oxadiazine obtainable in an approx. 70% yield from methylisocyanate with catalysis with approx. 3% tri-n-butyl phosphine in accordance with the process described by Slotta and Tschesche in Chem. Ber. 1927, 60, 295 has the following NMR-chem.
shifts (in ppm): 3.09; 3.08 and 2.84 (1H-NMR, CH3) and 148.3; 144.6 and 137.3 (13C-NMR. C=O/C=N). The products according to the invention with an iminooxadiazine dione structure have very similar 13C-NMR chem. shifts of the C=O/C=N atoms and were undoubtedly to be distinguished from those of other iso-cyanate secondary products. HDI-based oxadiazine triones were identified in the 13C-NMR spectrum i.a. by two signals at 147.8 and 143.9 ppm for the ring-C=O
atoms;
the commercial product measured was Baymicrori Oxa WM 06 from Bayer AG.

The dynamic viscosities were determined at 23 C with the VT 550 viscometer made by Haake. Measurements were taken at different shear speeds to ensure that the flow properties of the polyisocyanate mixtures according to the invention described, as well as those of the comparison products conform to the ideal Newtonian fluid.
Therefore, the shear speed was not stated.

The residual monomer contents were determined by gas chromatography.
All the reactions were carried out under a nitrogen atmosphere.
*trade-mark LeA 32514 US

Example 1- Comparison example of phosphine catalysis (not according to the in-vention) 3 samples were prepared. In each case 200 g(1.19 mol) of freshly distilled HDI
were stirred for one hour at 60 C first under reduced pressure (0.1 mbar) to remove dis-solved gases, then dry nitrogen was passed through, and 3 g (14.8 mmol) of tri-n-butylphosphine (Acros) were added at the following temperatures a) 60 C, b) 120 C and c) 180 C

and reacted under a nitrogen atmosphere until the refractive index of the crude solu-tion set forth in Table 1 was reached. The reactions were each terminated by the ad-dition of 4 g (26 mmol) of p-toluenesulfonic acid methyl ester (Merck) and continued stirring for one hour at 80 C.

Unreacted monomer was then removed from the crude products by thin film distil-lation at 120 C/0.1 mbar in a short-path evaporator. The product composition was then determined by NMR spectroscopy and the residual monomer content was de-termined by gas chromatography. The latter was determined again after 3 weeks' storage at 20-25 C (room temperature) followed by 2 weeks' storage at 50 C in a drying cabinet. All of the analytical results are summarized in Table 1.

Table 1- Results of the tributylphosphine-catalyzed HDI oligomerization at various temperatures ~
Test 20 Resin Viscosity Residual Carbodi- Uretdiones Isocyanurates Iminooxadia-Molar Molar nD Yield [mpa.s] monomer imides/ [mole%] [mole%] zine ratio of ratio of [%] content uretone- diones trimer 3) isocyanurates C~
[%] imines [mole%] To dimers to [mole%] (uretdiones) iminooxa-diazine diones y la 1.4732 46.3 240 0.1/0.1/ n.d. 69 22 9 0.45 2.4 0.21) lb 1.4731 40.0 1250 0.3/0.3/ 3 28 47 22 2.5 2.1 0.4 1) lc 1.4768 39.4 5200 2.7/3.8/ 54 4 30 12 10.5 2.5 5.41) Residual monomer content after work up/storage for three weeks at 20-25 C room temperature/further storage for 2 weeks at 50 C
2) n.d. = note detectable 3) Trimers = sun of isocyanurates and iminooxadiazine diones LeA 32514 US

Example 2 - Comparison example of fluoride catalysis (not according to the inven-tion) 4 samples were prepared. In each case 200 g(1.19 mol) of freshly distilled HDI
were stirred for one hour at 60 C firstly under reduced pressure (0.1 mbar) to remove dis-solved gases, then dry nitrogen was passed through and the mixture treated as fol-lows:

a) Approx. 900 ppm, based on the weight of the catalyst and HDI used (which corresponded to approx. 44 ppm of fluoride, F-), of an approx. 8% catalyst solution of methyl(trialkyl)ammonium fluoride (alkyl groups were Cg-Clp) in 2-ethyl-1,3-hexane diol (prepared as described in DE-A 39 02 078 (U.S. Pat-ent 5,013,838), Example 1, or in S. Dermeik and Y. Sasson, J. Org. Chem. 54 1989, 4827-4829 and the literature described therein) were added at 80 C.
The temperature rose to a maximum of 105 C and stirring was carried out until an NCO content of 41.2% was obtained. The reaction was then stopped by adding 0.9 g of phosphoric acid di-n-butylester, stirring was continued for another hour at 60 C, and unreacted monomer was then removed by thin film distillation in a short path evaporator (120 C/0.1 mbar). The analysis was then carried out as described in Example 1. The results are set forth in Table 2.

b) The procedure described in a) was followed except that an amount of 110 ppm, based on the weight of the catalyst and HDI (which corresponded to ap-prox. 18 ppm of fluoride, F-), of an approx. 5% solution of tetramethylammo-nium fluoride tetrahydrate [Me4N+F-xH2O] (Aldrich) in n-butanol was used as the catalyst. The trimerization reaction was carried out at a temperature of 60-70 C until the NCO content was 39.1% and terminated by the addition of 0.132 g of phosphoric acid di-n-butylester.

The procedure described in a) was followed except that an amount of approx.
190 ppm, based on the weight of the catalyst and HDI (which corresponded to approx. 22 ppm of fluoride, F-), of an approx. 8% solution of tetraethylam-LeA 32514 US

monium fluoride hydrate [Et4N+F-xH2O] (Aldrich) in n-butanol was used as the catalyst. The trimerization was carried out at a temperature of 70-150 C
until the NCO content was 39.9% and terminated by the addition of 0.312 g of phosphoric acid di-n-butylester.

d) The procedure described in a) was followed except that an amount of approx.
160 ppm, based on the weight of the catalyst and HDI (which corresponded to approx. 16 ppm of fluoride, F-), of an approx. 5% solution of benzyltrimethyl-ammonium fluoride hydrate (Aldrich) in 2-ethyl-1,3-hexane diol [Bz(Me)3N+F-xII2O] (Janssen) was used as the catalyst. The trimerization was carried out until the NCO content was 3 5.1 % and terminated by the ad-dition of 0.03 g of phosphoric acid di-n-butylester.

As can be seen from Table 2, the molar iminooxadiazine dione proportion in the trimer mixture (sum of isocyanurate and iminooxadiazine dione) was still well below 30%.

LeA 32514 US

Table 2 - The result of fluoride-catalyzed trimerization of HDI

Iminooxa Isocyanurates Urethanes Allophanates Uretdiones Carbodiimide Ratio Test -diazine B [mole%] [mole-%] [mole-%] [mole%] /Uretonimines A : B
diones A [mole%]
[mole%]
3a 14 68 n.d. 13 5 n.d. 17:83 3b 18 74 n.d. 5 3 n.d. 20:80 3c 21 69 2 5 3 n.d. 23:77 3d 15 69 2 10 4 n.d. 18:82 1) n.d. = non detectable LeA 32514 t Examgle 3- Comparison 2 samples were prepared.

a) 1500 g of an HDI-isocyanurate polyisocyanate having an NCO content of 23.5% and a viscosity of 1380 mPa.s were prepared as described in DE-A
3,806,276 (Canadian 1,335,990). This product was treated by thin film distil-lation in a short-path evaporator at a pressure of 0.05 mbar and a temperature of the heating medium of 220 C. 364 g of distillate was obtained from which monomeric HDI was then removed by thin film distillation at 120 C/0.05 mbar. The resulting colorless liquid contained at least 98%, based on com-bined IR, NMR and GPC analytical methods of the ideal isocyanurate trimer, i.e., three molecules of HDI (1,3,5-tris(6-isocyanatohexyl) isocyanurate). The product had a viscosity of 700 + 10 mPa.s at 23 C. This viscosity is consis-tent with data known from the literature and set forth in WO-A 93/07 183. In these examples the viscosities were measured at 25 C on less pure "ideal iso-cyanurate" fractions.

b) 1500 g of an HDI oxadiazine trione polyisocyanate having an NCO content of 22.5% and a viscosity of 2560 mPa.s (commercial product Baymicrori Oxa WM 06 from Bayer AG) were prepared as described in DE-A 1,670,666 (U.S.
Patent 3,748,329). This product was treated by thin film distillation in a short-path evaporator at a pressure of 0.05 mbar and a temperature of the heating medium of 220 C. 1092 g of distillate was obtained from which monomeric HDI was then removed by thin film distillation at 120 C/0.05 mbar. The resulting colorless liquid contained at least 98%, based on combined IR, NMR
and GPC analytical methods, of 3,5-bis(6-isocyanatohexyl)-1-oxadiazine trione composed of two molecules of HDI and one molecule of CO2. The product had a viscosity of 1200 + 20 mPa.s at 23 C. No comparative data is available from the literature for this oxadiazine trione product.

*trade-mark LeA 32514 US

Example 4- According to the invention a) catalyst preparation To 2.3 g (49 mmole) of potassium fluoride, dissolved in 50 g of methanol con-taining 1% water, are added 16 g (47,6 mmole) Aliquat 336 (Fluka), dissol-ved in 50 g methanol of the same quality as mentioned above. The mixture is stirred at room temperature for 24 hours and filtered. Another 2.3 g of potas-sium fluoride is added to the filtrate and stirring is continued for another hours. Inorganic salts are filtered off and the filtrate is concentrated at room temperature in vacuo (0.1 torr) on a rotavap until no more solvent (methanol) is distilled off and then filtered again. The fluoride content of the remaining, clear and slightly yellow liquid amounts to 2.7% (as detected with an ion-sensitive electrode). The residual chlorine content is 0.2% (elemental analysis).
0.95 g (14.2 mmole) of a 30% HF solution in iso-propanol are added dropwise with stirring and cooling to 0 C to 10 g (14.2 mmole Fluoride) of the quater-nary ammonium fluoride solution described above. The fluoride content (F-, not total fluorine (!) of the final catalyst solution amounts to 2.5%, referring to approximately 50 - 60% catalyst of formula R3(ME)N+[HF2)-, R is, referring to the Fluka catalogue, C8 to Clp, with C8 being preferred. This solution is used as a catalyst for the trimerization reactions set forth below.

b) trimerization 200 g(1.19 mol) of freshly distilled HDI were saturated with carbon dioxide at room temperature (20-25 C) by vigorously passing a stream of CO2 through the HDI for one hour. The HDI was heated to 60 C, then approx. 400 ppm, based on the weight of the catalyst and HDI (which corre-sponded to approx. 19 ppm of fluoride, F-), of the above mentioned catalyst solution were added. The temperature rose to a maximum of 80 C and stir-ring was continued until an NCO content of 41.2% was obtained. The reaction was terminated by the addition of 0.9 g of phosphoric acid di-n-butylester, stirring was continued for another hour at 60 C and the unreacted monomer LeA 32514 US

was finally removed by thin film distillation in a short-path evaporator (120 C/0.1 mbar). A colorless, clear resin was obtained having an NCO con-tent of 22.8% which, according to analysis by NMR spectroscopy, had the following composition: approx. 4 mole % uretdione, approx. 6 mole % oxadi-azine trione, approx. 54 mole % isocyanurates and approx. 36 mole %
iminooxadiazine diones. Carbodiimides and uretonimines were not detectable.
This example shows that in contrast to HDI trimerization with quaternary ammonium hydroxides as described in DE-A 3,806,276, it is possible according to the present invention to operate without difficulty in the presence of C02, provided that the pres-ence of small amounts of oxadiazine trione in the resin are not troublesome for the corresponding application.

When this example was repeated using benzyltrimethylammonium hydroxide in an alcoholic solution and with the same quaternary ammonium fluoride described above, except that the HF addition was omitted, turbid solutions containing gel particles in some cases were obtained immediately after the addition of the catalyst. These solu-tions were not suitable for the preparation of high-quality, clear HDI-based polyiso-cyanate resins.
Example 5 - According to the invention a) 2000 g of HDI were initially pretreated in the manner described in Example 2.
The catalyst from Example 4 (in an amount of 12 ppm of fluoride, based of weight of HDI used) was then added dropwise in portions at an internal tem-perature of 50 C over a period of 90 min such that the internal temperature did not exceed 65 C. When the NCO content of the mixture was 43.0%, 0.3 g of dibutylphosphate were added, the mixture stirred for a further hour at 50 C and then worked up as described in Example 4. 520 g, which corre-sponded to a resin yield of 26%, of a colorless trimer mixture having the fol-lowing properties were obtained:

NCO content: 23.6%

LeA 32514 US

Viscosity: 1050 mPa.s Residual monomer content: 0.17% HDI
Hazen color index according to DIN 53 409: 56 APHA
Molar ratio of iminooxadiazine diones to isocyanurates: 0.8:1 Carbodiimides and uretonimines were not detectable.

b) Example 5a) was repeated at a reaction temperature of 150 C (a temperature which causes the formation of carbodiimides and uretonimines when using phosphine catalysts for HDI oligomerization) and terminated after an NCO
content of the crude product of 39.0% was obtained. The resulting product had an NCO content of 22.1 %, a residual monomer content of 0.1 % and a vis-cosity of 1900 mPa.s, and was obtained in a resin yield of approx. 41%.
Carbodiimides and uretonimines were not detectable.

Example 6- According to the invention 500 g of the product obtained according to Example 5a) were distilled and purified under the same conditions set forth in Example 3. 180 g of a mixture were obtained, which contained more than 98% of pure HDI trimers, i.e., 1,3,5-tris(6-isocyanato-hexyl)isocyanurate and N,N'N"-tris-(6-isocyanatohexyl) iminooxadiazine dione) hav-ing the same ratio of isocyanurate to iminooxadiazine dione as the starting oligomer mixture. The viscosity of this mixture was 390 mPa.s at 23 C and its NCO
content was 25.0%. The residual monomer content was 0.1%, which only changed insignifi-cantly (0.18%) after storage for three weeks at 50 C in a drying cabinet.
Carbodi-imides and uretonimines were not detectable.

Example 7 - According to the invention A mixture of 84 g(0.5 mol) of HDI and 111 g(0.5 mol) of isophorone diisocyanate (IPDI) was added to a 250 ml four-necked flask equipped with an internal thermome-ter, stirrer, reflux condenser, gas inlet tube and metering device for the catalyst solu-tion,. The mixture was freed from gases dissolved in the diisocyanate mixture initially LeA 32514 US

at room temperature and a pressure of approx. 0.1 mbar for 1 hour, and then heated to an internal temperature of 60 C while a weak stream of nitrogen was passed through the mixture. 1.614 g of a solution of 0.5 g of tetraethylammonium fluoride hydrate (Aldrich) and 0.2 g of hydrogen fluoride in 5.6 g of 2-ethyl-1,3-hexane diol were then added in portions at this temperature over a period of approx. 20 minutes such that the internal temperature did not exceed 70 C. Trimerization was then car-ried out at 60-70 C until the NCO content of the mixture was 34.2%. The reaction was terminated by adding 0.181 g of di-n-butylphosphate and stirring for 1 hour at 60 C. Unreacted monomeric diisocyanates were then removed by thin film distilla-tion in a short-path evaporator at 0.1 mbar and a temperature of the heating medium of 170 C. 62.4 g of a clear and virtually colorless resin was obtained (corresponding to a yield of 32%). The pure product had a viscosity of 26500 mPa.s, an NCO
con-tent of 18.8% and residual monomer contents of 0.13% of HDI and 0.27% of IPDI.
The molar ratio of iminooxadiazine diones to isocyanurates was approx. 1:1.
Carbodi-imides and uretonimines were not detectable.

Example 8 - According to the invention a) 100 g (0.51 mol) of 1,3-bis(isocyanatomethyl)cyclohexane (Aldrich) were first pretreated as described in Example 2 and then trimerized to an NCO content of 36.5% by the incremental addition of the catalyst described in Example 4 (a total of 42 ppm of fluoride) at 58-60 C for 3 hours. The reaction was termi-nated by the addition of 100 mg of di-n-octylphosphate, stirring was continued for another hour at 60 C and unreacted 1,3-bis(isocyanatomethyl)cyclohexane was removed by thin film distillation in a short-path evaporator at 0.2 mbar and a temperature of the heating medium of 140 C. 33.8 g of a clear and vir-tually colorless resin was obtained (corresponding to a yield of 33.8%). The pure product had an NCO content of 19.8% and was still just free flowing at room temperature (20-25 C). The viscosity of the 80% solution in n-butylace-tate was 1670 mPa.s and the NCO content was 15.8%. The residual monomer content was 0.13% of 1,3-bis(isocyanatomethyl)cyclohexane. Analysis of the solid resin by NMR spectroscopy provided the following composition: ap-LeA 32514 US

prox. 8 mole % uretdiones, approx. 44 mole % isocyanurates and approx. 48 mole % iminooxadiazine diones. Carbodiimides and uretonimines were not de-tectable.

b) Example 8a) was repeated with the exception that 240 pprn, based on 100%
solids catalyst and the weight of the starting diisocyanate, of a solution of ben-zyltrimethyl-ammonium hydroxide (supplied as a 40% solution in methanol by Aldrich and diluted to 10% active substance with n-butanol) was used as the catalyst. The resulting product, which did not did not contain iminooxadiazine dione groups, had the following properties:

Resin yield: 34.0%
NCO content: 19.3%
Viscosity of the 80% solution in n-butyl acetate: 2800 mPa.s Residual monomer content: 0.2% 1,3-bis(isocyanatomethyl)cyclohexane The analysis of the solid resin by NMR spectroscopy provided the following compo-sition: approx. 4 mole % uretdiones, approx. 1 mole % urethanes, approx. 4 mole %
allophanates and approx. 91 mole % isocyanurates.
Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Claims (18)

1. A process for the preparation of a polyisocyanate containing iminooxadiazine dione groups which comprises oligomerizing a compound corresponding to formula I

(OCN-CH2)X (I) wherein X represents the residue obtained by removing the OCN-CH2 group from a monomeric polyisocyanate, wherein the residue contains 3 to 20 carbon atoms and at least one NCO group, in the presence of a hydrogen-polyfluoride oligomerization catalyst corresponding to formula II

M n+ n[F- (HF)m] (II) wherein M represents an n-valent cation, m is >= 0.1 and n is 1-6.

2. The process of Claim 1 wherein said oligomerization catalyst is a tetraorganyl-ammonium or phosphonium hydrogen polyfluoride corresponding to formula III

R4E+ [F-.(HF)m] (III) wherein E represents N or P and R represents the same or different aliphatic, cycloaliphatic, araliphatic or aromatic radicals which have 1 to 25 carbon atoms and may optionally be substituted with O, N or halogen.

3. The process of Claim 2 wherein E represents N, R represents the same or different aliphatic, cycloaliphatic, araliphatic or aromatic radicals which have 1 to 20 carbon atoms and may optionally be substituted with O, N or halogen.

4. The process of Claim 1 wherein said oligomerization catalyst is benzyl-trimethylammonium hydrogen polyfluoride corresponding to formula IV:
C6H5CH2(CH3)3N+[F-.(HF)m] (IV).

5. The process of Claim 1 wherein said oligomerization catalyst is a tetra-alkylammonium hydrogen polyfluoride corresponding to formula V:

R4N+[F-.(HF)m] (V), wherein R represents the same or different aliphatic or cycloaliphatic radicals having 1 to 20 carbon atoms.

6. The process of Claim 1 wherein said oligomerization catalyst is a tetra-alkylammonium hydrogen polyfluoride corresponding to formula VI:

R3(R')N+[F-.(HF)m] (VI), wherein R represents the same or different aliphatic radicals having 1 to 15 carbon atoms and R' represents an aliphatic radical having 1 to 4 carbon atoms.

7. The process of Claim 1 wherein m is >= 0.5.

8. The process of Claim 1 wherein m is >= 1Ø

9. The process of Claim 2 wherein m is >= 0.5.

10. The process of Claim 2 wherein m is >= 1Ø

11. The process of Claim 3 wherein m is >= 0.5.

12. The process of Claim 3 wherein m is >= 1Ø

13. The process of Claim 4 wherein m is >= 0.5.

14. The process of Claim 4 wherein m is >= 1Ø

15. The process of Claim 5 wherein m is >= 0.5.

16. The process of Claim 5 wherein m is >=1Ø

17. The process of Claim 6 wherein m is >= 0.5.

18. The process of Claim 6 wherein m is >= 1Ø