GB2063248A

GB2063248A - Process for Preparing Stable Mono-isocyanate Mono- unsaturated Urethane Monomers

Info

Publication number: GB2063248A
Application number: GB8025814A
Authority: GB
Original assignee: Witco Chemical Corp
Current assignee: Witco Corp
Priority date: 1979-11-16
Filing date: 1980-08-07
Publication date: 1981-06-03
Also published as: DE3025227A1; FR2469398A1; FR2469398B1; GB2063248B

Abstract

A process for preparing urethane monomers comprising: reacting an unsaturated hydroxylated compound with an excess of a diisocyanate; and removing substantially all of the excess diisocyanate by vacuum stripping at elevated temperatures. The liquid product displays excellent stability and may be stored and shipped without deterioration, and the final homopolymerized product exhibits good tensile and elongation characteristics as well as good solvent resistance.

Description

SPECIFICATION Process for Preparing Stable Mono-isocyanate Mono-unsaturated This invention relates to unsaturated urethane monomers. Specifically, this invention relates to a process for preparing novel stable mono-isocyanate mono-unsaturated terminated urethane monomer products.

In the past, urethane monomers were prepared by ( 1 ) first reacting a di- or polyfunctional hydroxyl compound with a diisocyanate in the ratio of one mole of diisocyanate per hydroxyl, thus producing a di- or polyfunctional NCO terminated compound. This in turn is further reacted with a mono-hydroxyl mono-unsaturated compound, such as hydroxy-propyl methacrylate, in the ratio of one isocyanate group per hydroxyl group to produce the final desired product; (2) the product was made by reversing the order of addition by adding the mono-unsaturated mono-hydroxyl to the diisocyanate followed by the addition of the di or polyfunctional hydroxyl compound, or (3) all the compounds were added at one time.

In U.S. Patent No. 2,958,704, there is disclosed a method of preparing monoalkenyl urethane monoisocyanates, wherein essentially one mole of diisocyanate is reacted with one mole of hydroxylated compound.

While such prior art techniques provide urethane monomers suitable for polymerization to polyurethane, particularly foamed polyurethanes, such monomers or polymers made therefrom, were often unstable and unsuitable for storage or long term shipment as there tended to be homopolymerizations, primarily due to the presence of excess isocyanate.

We have now developed a process for the preparation of a novel urethane monomer product which is stable, which is significantly less toxic than most conventional monomers, which can be prepared by an economic process and which is useful in preparing polyurethanes.

Accordingly, the present invention provides a process for preparing urethane monomers comprising: reacting an unsaturated hydroxylated compound with an excess of a diisocyanate; and removing substantially all of the excess diisocyanate by vacuum stripping at elevated temperatures.

The present invention recognizes that in substantially molar equivalent hydroxyl-diisocyanate reactions of the prior art, an excess of about 5 to 6% by weight of diisocyanate remained unreacted, which in effect indicates the formation of diunsaturated products. In urethane polymers formed according to the prior art there were also many short, segmented highly cross-linked parts in the formed polymer.

This can best be illustrated by examining the hydroxypropyl methacrylate (HMPA)-toluene diisocyanate (TDI) reaction as follows:

HPMA--TDI reaction product (terminal mono-unsaturated mono-isocyanate) By calculation, this product would have %NCO content of NCO 42 %NCO= x100 or xiOOor ----x100=13.2 HPMA--TDI 318 However, this following diunsaturated product

% NCO = 84 x 100 = 13.2% 636 would have the same 13.2% NCO. The only way that this difference could be shown would be to analytically determine the free TDI level.

The present invention contemplates the elimination of the toxic unreacted isocyanate while retaining the desirable precursor properties.

In accordance with the present invention the elimination of substantially all of the free isocyanate, and at the very least a reduction to less than about 1% by weight of the isocyanate is achieved. More preferably the reduction is down to less than 0.5% by weight. It has been found that the most preferred method of blocking the formation of diunsaturate is by stripping the reaction product. That is, the reaction product is subject to vacuum stripping at elevated temperature, generally at 1-5 mm Hg vacuum and at temperatures in the range of from 1 500 F to 2500F, by the use of a Votatord9, for instance.

It is an important part of the present invention that the diisocyanate be present in an excess amount and preferably an excess of 20%, or more, by weight of the hydroxylated compound. The reaction of the diisocyanate with the hydroxylated compound is generally at relatively low temperatures, of about ambient temperatures, and up to about 1000C, to complete the reaction.

Representative hydroxylated compounds which may be used in the present invention include hydroxyalkyl acrylates and hydroxyalkyl methacrylates, wherein the alkyl group preferably lower C16 alkyl, including such compounds as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate.

Suitable diisocyanates which may be used in the present invention include those diisocyanates well-known in urethane chemistry. Particularly suitable are the aryl, arylalkyl, and like diisocyanates, toluene diisocyanate being preferred.

The present invention includes the production of a broad range of mono-isocyanate, monounsaturated urethane polymer precursors, such as the monoalkenyl urethane monoisocyanates: monoallyl urethane of 2,4 - tolylene diisocyanate, the monomethallyl urethane of 2,4 - tolylene diisocyanate, the mono( 1 ,4-butanediol monovinyl ether) urethanes of 2,4 - tolylene diisocyanate, the mono (ethyiene glycol monomethacrylate)urethane of 2,4 - tolylene diisocyanate and the monoallyl urethane of 1,8 - diisocyanato - p - methane.

In carrying out the reaction to produce the monoalkenyl urethane monoisocyanates various inert diluents may also be employed at the ambient (250C) temperatures of the reactions. Inert diluents which are useful in the prqcess of this invention include aromatic hydrocarbons such as benzene, toluene and the xylenes; halogenated hydrocarbons such as chloro-benzene and bromobenzene; halogenated aliphatic hydrocarbons such as chloroform and carbon tetrachloride; and others such as diethyl ether, dioxane and tetrahydrofuran. Any solvent which will not react with either the diisocyanate or the alcohol can be used as a diluent.

The following examples illustrate the present invention.

Example To a 10 gallon reactor. 12,008 grams of 80/20 2,4-2,6 toluene diisocyanate (TDI) was added along with 0.02 grams of the methyl ether of hydroquinone (MEHR). Shotwise, 7912 grams of hydroxypropyl methacrylate (HPM) was added to the reactor to maintain the exotherm at 800C. After all the HPM had been added the reaction was then held at 800C for two hours. After two hours the reactor mixture was cooled and stripped. Before stripping, the prepolymer had an NCO content of 1 7.9 percent and a viscosity of 700 cps at 25or. The prepolymer was stripped through a Votator(D at the rate of fourteen pounds per hour. The holding tank was at room temperature, the Votators jacket was 3250F, the stripper temperature 2000F, the overhead temperature 1 800F with a vacuum of 3.0 millimeters, and rotor speed of 2400 rpm. The yield was 16,125 grams of stripped prepolymer having 13.6% NCO and a viscosity of 9,450 cps at 250C. 2,750 grams of TDI was stripped during this run.

The NCO content of the prepolymer of Run 1 was not initially sufficiently low, so the procedure as aforesaid was repeated with the vacuum on the rotator lowered to 1.0-1.7 mm and the rate decreased to 8.72 pounds per hour. This procedure (Run 2) gave a lower yield of prepolymer 1 5,11 5 grams, with slightly more stripped TDI, (2835 grams) and an NCO content of 12.36%.

The NCO content indicated that both Run 1 and Run 2 were not totally stripped of free TDI so a third run was tried. Run 3 consisted of 14,750 grams of Run 2 product and 9,185 grams of Run 1 product. These were placed in the reactor, mixed, and heated to 800 C. This mixture was then stripped as above with the result that 580 grams additional TDI was stripped. The yield was 21, 975 grams, the percent NCO was 11.56, the viscosity 6600 cps at 250C, and of the most importance was the free monomer content had been reduced to 0.24% by weight.

The Run 3 product above with its low monomer content and relatively low viscosity is stable and easily handled to convert many polyols with active hydrogens into unsaturated polyurethanes which could then be further reacted by free radical polymerization to useful end products.

All of the materials utilized in the foregoing example are commercial grade.

It is to be recognized that the novel stable urethane monomers made by this invention may be incorporated in the known urethane polymer applications.

As is well known in the art, the unsaturated hydroxyl compound may be substituted by other alkenyl compound having an active hydrogen such as allylamine or acrylic acid, for instance, to yield a terminal monounsaturated, mono-isocyanate product.

Claims

1. A process for preparing urethane monomers comprising: reacting an unsaturated hydroxylated compound with an excess of a diisocyanate; and removing substantially all of the excess diisocyanate by vacuum stripping at elevated temperatures.

2. A process as claimed in claim 1 wherein the hydroxylated compound is mono-hydroxylated.

3. A process as claimed in claim 1 or claim 2 wherein a temperature in the range of from 1 500F to 2500F is employed while vacuum stripping.

4. A process as claimed in any one of the preceding claims wherein the vacuum stripping is carried out at from 1 to 5 mm Hg.

5. A process as claimed in any one of the preceding claims wherein at least 20% by weight excess of the diisocyanate is employed.

6. A process as claimed in any one of the preceding claims wherein the hydroxylated compound is a hydroxyalkyl acrylate.

7. A process as claimed in any one of the preceding claims wherein the diisocyanate is toluene diisocyanate.

8. A process as claimed in any one of the preceding claims wherein the reaction of the unsaturated hydroxylated compound with the diisocyanate is carried out in the presence of a diluent.

9. A process as claimed in claim 1 substantially as hereinbefore described with reference to the Example.

10. A product prepared by a process as claimed in any one of the preceding claims.

11. A product as claimed in claim 10 which has an isocyanate content of less than 0.5% by weight.

12. A polyurethane when formed from a product as claimed in claim 10 or claim 11.

13. A modification af the process claimed in any one of claims 1 to 8 wherein an alkenyl compound having an active amine or carboxyl group is substituted for the unsaturated hydroxylated compound.