Hydroxyalkyl Tertiary Amine Catalysts for Isocyanate Reactions

1. Field of the Invention

The present invention relates to the general field of basic catalysis of organic reactions and is particularly concerned with catalysts for promotion of reactions involving organic isocyanates as in the production of polyisocyanurates and polyurethanes.

2. Prior Art

It is well known in the art that tertiary amines are good catalysts for production of polyurethanes. Also certain hydroxyalkyl tertiary amines have been advocated for polyurethane production. In particular, dimethyl ethanolamine has been employed for such purpose but it suffers from the drawbacks of relatively high volatility and its poor gel and curing properties. To overcome these deficiencies dimethyl ethanolamine is more generally employed as a cocatalyst with other known superior tertiary amine polyurethane catalysts such as diazabicyclo-octane.

Tertiary amines, however, are not generally effective as polyisocyanurate catalysts. The use of hydroxyethyl tertiary amines as polyisocyanurate catalysts have been mentioned but only in conjunction with alkylene oxides or as adducts of polyisocyanates, as in U.S. Pat. No. 3,786,030. Hydroxyethyl tertiary amines as such, as exemplified by dimethyl ethanol amine, were not known to be effective as polyisocyanurate catalysts.

In recent patents (U.S. Pat. Nos. 3,824,239 and 3,824,240) it is disclosed that certain hydroxyalkylamines are effective as trimerization catalysts for isocyanates, but the compounds disclosed in these patents are limited generally to those in which the hydroxyalkylamine function is associated with an aromatic triazine nuclear structure, which structures in themselves demonstrate good trimerization activity.

It has now been discovered that certain hydroxyalkyl tertiary amines having at least one primary hydroxyethyl group and at least two tertiary nitrogen atoms in the molecule, are not only excellent gelling and curing catalysts in polyurethanes but also exhibit unexpectedly effective catalytic activity in trimerization of organic isocyanates and in carbo-diimide formation from organic isocyanates. It was also unexpectedly found that the hydroxyl group of these tertiary amines plays an important role in the overall activity of the catalysts of the present invention and that particularly those compounds having a primary hydroxyl group possess far superior activity over those of similar structure having a secondary or tertiary hydroxyl group.

More particularly, it has now been found, in accordance with the present invention, that compounds of the general formula ##STR2## exhibit unexpectedly high catalytic activity in isocyanate reactions such as in the production of polyurethanes and polyisocyanurates. In the above formula (I) preferred compounds are those in which

Y= CH.sub.3 or Z

z= ch.sub.2 ch.sub.2 oh

n= 1 or 2

Compounds of the described formula may be prepared by methods generally known in the art, such as by reaction of an alkanolamine with formaldehyde and formic acid following the known Leuckhardt synthesis procedure (Surrey, A. R., "Name Reactions in Organic Chemistry", 2d. ed., (1961) pp 157-159).

Among the preferred catalysts of the present invention which can be prepared by the classical Leuckhardt synthesis are: ##STR3## The isomeric forms of III and IV and similarly structured compounds in accordance with Formula I are effective also.

In the preparation of urethane resins any of the compounds of the present invention can be used as the sole catalyst or as cocatalyst with other tertiary amines such as with triethylene diamines, or in conjunction with the known organometallic polyurethane catalysts such as those comprising salts or complexes with tin, lead or antimony. Any of the known polyols heretofore suggested for reaction with polyisocyanates for polyurethane production may be used with the catalysts of the invention, including polyether and polyester glycols, without significant departure except for the catalyst, from known formulations and procedures. Thus, the polyols can be based on glycol, glycerine, or higher polyols and may contain other functional groups as those polyols based on sucrose or the so called amine polyols. The hydroxy function of the polyol may be primary or secondary or a mixture of both of these. In general there can be employed any polyol having at least two active hydrogen atoms responding to the Zerewitinoff test.

In the practice of the invention in trimerization reactions for production of polyisocyanurates, as well as in polyurethane formation, the usual blowing agents, surfactants, fire retardants, fillers and other customary additives may be used in the formulation. The hydroxyalkyl tertiary amine catalysts of the invention can be used alone in that form or in their carboxylic acid salt form; also these may be used in conjunction with other cocatalysts such as potassium carboxylates. The compounds of the invention can be reacted with mono- or poly-functional organic isocyanates to form corresponding adducts and these adducts employed as catalysts. In the preparation of isocyanurates, it is also known to include in addition to the isocyanates to be polymerized, other resins such as epoxies and epoxynovolac resins, or simple alkylene oxides. Such formulations can also be employed with the catalysts of the present invention.

The isocyanates that can be employed in preparation of resins according to the invention include carbocyclic isocyanates such as tolylene diisocyanate (TDI) and the technical grades of isomeric tolylene diisocyanates commercially available, as well as diphenyl methane diisocyanate; polymeric isocyanates, isothiocyanates, aliphatic and cycloaliphatic isocyanates.

Compounds corresponding to Formula I and illustrative of Formulae II, III and IV, employed as catalyst in certain of the formulations in Examples below, were produced in the following manner:

A. N,N,N'trimethylaminoethylethanolamine (Formula II)

In a resin kettle (or flask) was charged 1 mole of aminoethylethanolamine (AEEA) and to it was added slowly 5 moles of formic acid and 3.5 moles of 40% aqueous formaldehyde. The mixture was then heated on a steam bath until the evolution of carbon dioxide ceased. The mixture was then cooled in a water bath and sodium hydroxide added with stirring until phase separation occurred. The top layer (the amine layer) was isolated and distilled. The fraction distilled at 195.degree.-200.degree. C. was collected as the product and weighed 90 grams. The product had the following properties:

B. Preparation of N,N'dimethyl N,N'bis hydroxyethylethylenediamine ##STR5##

Procedure:

The procedure in A. above was followed. 74g of N,N'bis hydroxyethylethylenediamine were reacted with 70g of 88% formic acid and 100cc of 40% aqueous formaldehyde. After work up of the reaction mixture the fraction distilling at 145.degree. C. and 4 mm Hg was collected as the product amounting to about 60 grams.

C. Preparation of tetramethylhydroxyethyldiethylenetriamine ##STR7##

The procedure in A. above was followed. The quantities reacted were

70g of crude hydroxyethyl diethylene triamine

250g of 88% formic acid

320g of 40% aqueous formaldehyde

After work-up the fraction distilling at 95.degree.-120.degree. C. and 3mm Hg was collected, 77.4 grams, as the product mixture.

The refractive index at 22.degree. C. = 1.4644

The following examples are illustrative of various formulations that can be employed in practice of the invention, without being limited thereto:

A. Into a flask equipped with a thermowell there was charged 11.9 parts by weight of phenyl isocyanate. To this was added 0.12 parts (1% by weight of isocyanate) of trimethylaminoethylethanolamine (TMAEEA). A thermocouple was put in place and the mixture agitated for a few seconds then allowed to stand. After about 80 minutes a sudden reaction took place accompanied by an exotherm that drove the temperature from 100.degree. to 250.degree. F. (about 37.8.degree. to 121.degree. C.) and the whole mixture turned into a solid mass. After washing with methanol, a melting point determination was made and found to be 284.degree.-285.degree. C. (the literature reports 282.degree. C. as the melting point of phenylisocyanurate). Infrared spectrum showed for this product the same characteristic bands as those reported in the literature for phenyl isocyanurate.

B. The run above was repeated increasing the amount of TMAEEA catalyst to 2% by weight of the isocyanate. This time the reaction was spontaneous with hardly any induction period. The product was likewise identified as phenyl isocyanurate.

C. A number of similar runs were made except that other amines and hydroxylamines respectively were substituted for the TMAEEA catalyst previously employed. The results are summarized in Table I below:

The above components were processed in conventional (one-shot) manner to produce a molded polyurethane semi-rigid foam of the type used in crash pads and instrument panels.

The various catalysts and quantities employed in the runs made using the foregoing formulation are recorded in Table 2 below, together with the time required for complete filling of the test mold, which was in the form of a maze with reversing paths from the point of introduction of the resin mixture.

The formulation below was employed for production of a highly resilient water-blown polyurethane foams, using different amine catalysts.

The data as to cream time (C.T.), rise time (R.T.) and hard gel time (H.G.T.) in the runs made with the different catalysts are reported in Table 3 below:

The following formulation was employed in making a flexible polyester polyurethane foam of the water-blown type by the one-shot method

The results obtained are reported in Table 4 below in comparison to a typical catalyst employed in such formulations.

It appears from the results reported in Table 4 above that TMAEEA is more active than the control even when using 55% less catalyst. Also the TMAEEA catalyst permits wide latitude in concentration for processing polyester polyol foams.

The following formulation was employed in the preparation of a water-blown polyether polyurethane foam by the one-shot method.

The results obtained are reported in Table 5 below compared with those using a typical catalyst employed in such formulations.

A number of isocyanurate foams were prepared using the following formulation:

The properties of the foams obtained with different proportions of TMAEEA are reported in Table 6 below. Comparison of these with a sample of a commercial isocyanurate foam--code 25 (Upjohn)--is also reported in Table 6.

A series of runs were carried out to test the activity of various amine catalysts in several concentrations, in the preparation of polyisocyanurate foams by the conventional "one-shot" method. The standard formulation employed in each of these runs comprised:

The results are reported in Table 7 below:

While both the monohydroxyethyl ethylene diamine compound (a) and the bis hydroxy ethyl ethylene diamine compound (b) gave good foams, these are not equivalent in activity as will be seen from the comparison of these in Table 8 below, employed in production of the polyisocyanurate in accordance with Example 7.

It is also noted that the foams obtained with catalyst (b) while acceptable did not rise to desired height obtained with the TMAEEA (a) catalyst.

The utility of the novel catalysts of the invention in forming carbodiimides from isocyanates was shown by the following test.

In a flask connected to three successive saturated solutions of barium hydroxide there were charged 34.7 parts by weight of 2.4 toluene diisocyanate and 0.8 parts to 1.0 parts of TMAEEA. The mixture was agitated by shaking for a few minutes upon which a rapid exothermic reaction occurred generating a considerable amount of CO.sub.2, evidenced by the barium carbonate precipated in the connecting flasks. The foamed toluene diisocyanate polymer formed was examined by infrared spectroscopy and found to contain a substantial amount of carbodiimides groupings which showed up as bands at 2120- 2140 cm.sup.-1.

While in the formulations of the foregoing examples TMAEEA is employed for the most part as the preferred catalyst according to the invention, it will be understood that other catalysts conforming to formula I may be similarly employed, particularly the compounds corresponding to formulae III and IV.