CA1334848C

CA1334848C - Process for the production of polyisocyanates which contain isocyanurate groups

Info

Publication number: CA1334848C
Application number: CA 606858
Authority: CA
Inventors: William E. Slack
Original assignee: Miles Inc
Current assignee: Bayer Corp
Priority date: 1988-08-05
Filing date: 1989-07-27
Publication date: 1995-03-21
Anticipated expiration: 2012-03-21
Also published as: GB8917746D0; GB2221465A

Abstract

The present invention is directed to a process for the preparation of a polyisocyanate having isocyanurate structure which comprises heating an organic diisocyanate to a temperature of from 100 to 275°C in the presence of a catalytic amount of an organic compound containing at least one aliphatic tertiary amine group and at least one aliphatic hydroxy group and having a molecular weight of no more than about 500 for a period of from about 0.1 minute to about 360 minutes.

Description

13~4848 PROCESS FOR THE PRODUCTION OF POLYISOCYANATES
WHICH CONTAIN ISOCYANURATE GROUPS
BACKGROUND OF THE INVENTION
Numerous processes for the production of isocyanurate-containing polyisocyanates are known.
Typical of such processes are those described in U.S.
Patents 3,248,372, 3,330,828, 3,645,979 and 3,996,223.
Typical of the catalysts described are tertiary amines such as N,N-dialkylethanolamines (U.S. 3,248,372), alkali metal and alkaline metal compounds (U.S.
3,330,828), organic phosphines (U.S. 3,645,9793, and mixtures of Mannich bases and carbamic acid esters (U.S.
3,996,223). Although these references broadly indicate that reaction temperatures ranging from as low as -40C
to as high as 200C can be used, in the examples the temperatures used are generally less than 150C, with relatively long reaction times. Thus, U.S. 3,248,372 utilizes temperatures of from 70 to 140C, with reaction times ranging from 10 to almost 15 hours. U.S.
3,330,828 exemplifies reaction temperatures of from 30 to 65C with reaction times ranging from 10 minutes to almost 5 hours. U.S. 3,645,979 exemplifies reaction temperatures of from 60 to 120C, with reaction times ranging from 6 minutes to over 5 hours. Finally, U.S.
3,996,223 exemplifies reaction temperatures of from 70 to 150C with reaction times ranging from 30 minutes to 6 hours.
As is apparent, many different compounds have been used as catalysts. Furthermore, with both aliphatic and aromatic diisocyanates, temperatures of less than 100C are typically used due to the instability of the catalysts at higher temperatures. In addition the same catalyst cannot generally be used to trimerize both aliphatic and aromatic diisocyanates.

133~848 Catalysts which contain both tertiary amine groups and aliphatic hydroxy groups are known and are used in the production of polyisocyanurate foams. See, e.g., U.S. Patents 3,824,239, 3,824,240 and 4,026,840.
DESCRIPTION OF THE lNV ~:N LION
The present invention is directed to a process for the preparation of a polyisocyanate, and preferably a liquid polyisocyanate, having an isocyanurate structure which comprises heating an organic 10 diisocyanate to a temperature of from 100 to 275C in the presence of a catalytic amount of an organic compound containing at least one aliphatic tertiary amine group and at least one aliphatic hydroxy group and having a molecular weight of no more than about 500 for 15 a period of from about 0.1 minute to about 360 minutes.
Starting isocyanates suitable for use in the present invention include substantially any aromatic, aliphatic and cycloaliphatic diisocyanate. In general, such diisocyanates are represented by the formula:
R(NCO)2 in which R represents an organic group obtainable by removal of the isocyanate groups from an organic 25 diisocyanate having a molecular weight of from about 112 to 1000, and preferably from about 140 to 400.
Preferred diisocyanates are those in which R represents a divalent aliphatic hydrocarbon group having from 4 to 18 carbon atoms, a divalent cycloaliphatic hydrocarbon 30 group having from 5 to 15 carbon atoms, or a divalent araliphatic hydrocarbon group having from 7 to 15 carbon atoms. Examples of the organic diisocyanates which are particularly suitable for the process include tetramethylene diisocyanate; 1,6-hexamethylene 35 diisocyanate, dodecamethylene diisocyanate;

133~848 cyclohexane-1,3- and -1,4-diisocyanate; l-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate or IPDI); bis-(4-isocyanato-cyclohexyl)-methane; 1,3- and 1,4-bis-(isocyanato-5 methyl)cyclohexane; bis-(4-isocyanato-3-methyl-cyclohexyl)-methane; and ~ '-tetramethyl-xylylene diisocyanate. Preferred diisocyanates are 1,6-hexa-methylene diisocyanate, isophorone diisocyanate and bis(4-isocyanatocyclohexyl)-methane. Mixtures of 10 diisocyanates can, of course, be used. In addition to the organic diisocyanates containing aliphatically-and/or cycloaliphatically- bound isocyanate groups previously set forth, it is also possible in accordance with the present invention to use aromatic diisocyanates 15 wherein R represents a difunctional aromatic hydrocarbon radical having from 6 to 15 carbon atoms. Suitable aromatic diisocyanates include 2,4-diisocyanato toluene, 2,6-diisocyanato toluene, and mixtures of these isomers;
4,4'-diisocyanato diphenyl methane and its isomeric 20 mixtures with 2,4'- and optionally 2,2'-diisocyanato diphenyl methane; and 1,5-diisocyanato naphthalene. In addition it is possible according to the present invention to use mixtures of aromatic and aliphatic isocyanates.
The catalysts of the present invention are organic compounds which have molecular weights of no more than about 500 and which contain at least one aliphatic tertiary amine group and at least one aliphatic hydroxy group. Specific compounds include 30 N,N,N'-trimethylaminoethylethanolamine;
N,N'-dimethyl-N,N'-bis(hydroxyethyl)ethylene diamine;
N-hydroxyethyl-N,N',N'-tetramethyldiethylene triamine;
dimethyl-ethanolamine; N,N,N',N'-tetramethyl-amino-2-propanol; triethanolamine; N-methyl-35 diethanolamine; 1-(2-hydroxyethyl)pyrrolidine;

l-methyl-2-pyrrolidine ethanol; N,N-diethylethanolamine;
N-isopropyldiethanolamine; N-t-butyldiethanolamine; N-piperidine-ethanol; 4-(2-hydroxyethyl)morpholine;
N-ethyldiethanolamine; l-[N,N-bis(2-hydroxyethyl)amino]-5 2-propanol; 1,4-piperazine-diethanol;
triisopropanolamine; 3-(~-hydroxyethyl)-oxazolidine;
l-piperazine propanol; and the like. Preferred are those compounds having molecular weights of less than about 250 and containing only one tertiary amine group.
When carrying out the process of the invention, the amount of catalyst used is generally less than one percent by weight (based on the combined weight of the isocyanate and catalyst) and is preferably used in an amount of from about 0.1 to about 0.9 percent by weight 15 and most preferably from about 0.3 to about 0.7 percent by weight.
The reaction in accordance with the present invention is carried out at a temperature of from 100C
to 275C, preferably at a temperature of from 125C to 20 250C, and most preferably at a temperature of from 150C to 250C. The reaction is carried out for a period of from about 0.1 minutes to about 360 minutes, preferably for from about 1 to about 180 minutes and most preferably for from about 3 to about 10 minutes.
25 (These times exclude the heat-up and cool down periods).
In general, the higher the temperature, the shorter the reaction time. It is also preferred that the reaction be carried out in the absence of oxygen because the product thus formed is substantially improved with 30 respect to color.
In the practice of the present invention, the diisocyanate is introduced into a reaction vessel and the catalyst is added thereto. Appropriate reaction vessels are known in the art. It is preferred, however, 35 that a hot tube plug flow reaction be used.

It has also been found that use of hydroxy compounds such as alcohols and diols (or their urethane derivatives) will significantly enhance the catalytic activity of the catalysts used.
When the reaction is carried out at a temperature greater than 200C, a trimer-modified isocyanate is formed which is storage stable at 25C
and, therefore, there is no need for the addition of an acidic stopper. However, when the reaction is carried 10 out at a lower temperature (i.e., less than 200C), the addition of an acidic stopper such as hydrogen chloride (one equivalent of acidic compound per equivalent of tertiary amine group) is required when the ratio of tertiary nitrogen to NCO group is greater than 0.01 15 and/or when the ratio of total hydroxy group to NCO
group is greater than 0.02.
Several observations have been made when following the present invention:
1. The catalyst lose most of their activity at higher temperatures (200C or more) after a short time. (See Example 10 vs. 46 or 9 vs. 47; Examples 1, 5, 6, 7). Therefore, the addition of a stopper is not necessary.
2. The catalysts can be used as trimerization catalysts for both aromatic and aliphatic isocyanates. The catalysts can be used to make mixed trimer products. (See Example 95).

3. The presence of oxygen inhibits the catalyst and causes darkly colored products (see Examples 64-67).

4. The catalysts give, with N2 purging, darker colored products at higher temperatures.
For example, at 250C a color of APHA of more than 200, while at 150C, APHA is 35.

- 13348~8 5. Hydroxy groups (or their urethane derivative) enhance the activity of these catalysts. The hydroxy groups can first be converted to urethane groups (Example 4) or added and heated directly to the reaction temperature (Example 2).

6. The catalysts, when mixed with isocyanates at ambient temperature (~25C) are stable for extended periods of time yet still keep their reactivity at high temperature (>100C) as long as the ratio of tertiary nitrogens to NCO groups is less than 0.01 and/or the ratio of total hydroxy groups to NCO groups is less than 0.02. (See Examples 68-71).

7. In general, the more removed the OH group is from the tertiary nitrogen group the less reactive the catalyst. (Compare Examples 10 and 12).

8. In general, the less sterically hindered the tertiary nitrogen and the more OH
groups present in the molecule, the more reactive the catalyst. (Compare Example 48 to Example 24).

9. Relative to point 2 above, the amino alcohols appear to be better high temperature catalysts for aliphatic isocyanates than aromatic isocyanates which is the opposite of what is found normally.
(Examples 48 and 86). However, at lower temperatures (<200C), the reverse is true.
(Compare Examples 91 and 92 to Examples 56, 57 and 58).
The invention is further illustrated but is not 35 intended to be limited by the following examples in -` 1334848 which all parts and percentages are by weight unless otherwise specified.
All the examples were purged with dry nitrogen to eliminate water vapor and oxygen. The latter 5 inhibits the catalyst and causes darker colored products.
Example 1 To a 250 ml 3-neck flask were added 100 grams of hexamethylene diisocyanate and 0.3 grams of 10 triethanolamine. The stirred reaction mixture was heated over a 4 minute period to 250C, held for 2 minutes, then cooled over a 6 minute period to below 70C. The resulting clear liquid had an % NCO content of 40.0% (this % NCO did not change after 40 months 15 storage at 25C). An IR analysis of the mixture gave strong absorptions at 1692 cm 1 and 1466 cm 1 indicative of trimer. Unreacted hexamethylene diisocyanate was removed by thin layer distillation to afford a liquid product with a viscosity of 4030 mPa.s at 25C and an 20 isocyanate content of 21.5%. The product contained 0.05% unreacted hexamethylene diisocyanate.
Example 2 To a 250 ml 3-neck flask were added 100 grams of hexamethylene diisocyanate, 0.4 grams of 25 N-methyldiethanolamine, and 0.4 g n-butanol. The stirred reaction mixture was heated over a 4 minute period to 250C, held for 2 minutes and then cooled over a 6 minute period to below 70C. The resulting clear liquid had an % NCO content of 34.0%. An IR analysis 30 indicated trimerization.
Example 3 To a 250 ml 3-neck flask were added 100 grams of hexamethylene diisocyanate and 0.4 grams of N-methyl-diethanolamine. The reaction mixture was stirred at 35 25C until all the hydroxy groups had been converted to 1'3348~8 urethane groups affording an NCO content of 49.5%. The stirred reaction mixture was then heated over a 4 minute period to 250C, held for 2 minutes and then cooled over a 6 minute period to below 70C. The resulting clear 5 liquid had an % NCO content for 39.3. An IR analysis indicated trimerization.
Example 4 To a 250 ml 3-neck flask were added 100 grams of hexamethylene diisocyanate, 0.4 grams of N-methyl-10 diethanolamine, and 0.4 grams n-butanol. The reaction mixture was stirred at 25C until all the hydroxy groups had been converted to urethane groups affording an NCO
content of 49.1%. The stirred reaction mixture was then heated over a 4 minute period to 250C, held for 2 15 minutes and then cooled over a 6 minute period to below 70C. The resulting clear liquid had an % NCO content of 35.4%. An IR analysis indicated trimerization.
Example 5 To a feed tank was added a mixture of 100 parts 20 hexamethylene diisocyanate, 0.4 parts n-butanol and 0.2 parts l-(2-hydroxyethyl) pyrrolidine. This material was then pumped, at 25C, through a hot tube plug flow reactor at 265C. The heat-up from 25C to 265C
required 2.1 minutes. The reaction mixture was 25 maintained at 265C for 2.3 minutes and then quench cooled to 40C. The isocyanate content of the resulting reaction mixture was 41.9%. The unreacted hexamethylene diisocyanate was removed by thin layer distillation to af~ord a clear liquid product with a viscosity of 3390 30 mPa.s at 25C and an isocyanate content of 21.0%. The %
NCO did not change after 8 months storage at 25C. The product contained 0.4% unreacted hexamethylene diisocyanate.

1~4848 Example 6 The procedure of Example S was repeated using 100 parts of hexamethylene diisocyanate, 1.5 parts of n-butanol and 0.15 parts of 1-(2-hydroxyethyl) 5 pyrrolidine. The isocyanate content of the resulting reaction mixture was 38.6%. The unreacted hexamethylene diisocyanate was removed by thin layer distillation to afford a clear liquid product with a viscosity of 4710 mPa.s at 25C and an isocyanate content of 19.5%. The %
10 NCO did not change after 8 months storage at 25C. The product contained 0.4% unreacted hexamethylene diisocyanate.
Example 7 To a feed tank was added a mixture of 100 parts 15 hexamethylene diisocyanate, 4.4 parts n-butanol and 0.02 parts 1-(2-hydroxyethyl) pyrrolidine. This material was then pumped, at 25C, through a preheater which brought the mixture to about 160C. The mixture then entered a stirred overflow reactor purged with nitrogen and was 20 held at 260C for an average residence time of 3.4 minutes. The overflow material was quench cooled to about 40C and was found to have a 38.6% NCO content.
Unreacted hexamethylene diisocyanate was removed by thin layer distillation to afford a clear liquid product with 25 a viscosity of 1910 mPa.s at 25C and an isocyanate content of 18.0%. The % NCC did not change after 8 months storage at 25C. The product contained l.Qh unreacted hexamethylene diisocyanates.
Examples 8-57 Using the procedure described in Example 2 above, the following trimerizations of aliphatic isocyanates were carried out using the specified reagents and conditions set forth in the table. HX is hexAmethylene diisocyanate.

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O O -`- 1334848 Examples 64 and 65 The procedure of Example 2 was repeated except there was no purging of this reaction vessel with nitrogen before or during the reaction. To 100 parts of 5 hexamethylene diisocyanate was added 0.4 parts of triethanolamine. The isocyanate content of the resulting reaction mixture after being heated at 250G
for 2 minutes was 43.3%. The reaction was repeated except the reaction vessel was purged with dry nitrogen 10 before and during the reaction to afford an isocyanate content of 33.7%.
Examples 66 and 67 The procedure of Examples 64 and 65 was repeated except triethanolamine was replaced by 0.4 15 parts of N-methyldiethanolamine. The resulting % NCO
with no nitrogen purging was 46.0% and with nitrogen purging was 40.6%.
Examples 68, 69, 70 and 71 To a 2-liter 3-neck flask were added 1000 grams 20 of hexamethylene diisocyanate, 4.0 grams triethanolamine and 4.0 grams n-butanol. The stirred reaction mixture was held at 50C for 1 hour, then cooled to ambient temperature while being purged with dry nitrogen. After one hour, 100 grams (having a titrated NCO content of 25 48.6% compared to a theoretical NCO of 48.7%) of this material was heated at 250C for 2 minutes as described in Example 2 to afford on cooling a clear solution with an NCO content of 34.6%. After 24 hours another sample (having an NCO content of 48.6%) was heated at 250C for 30 2 minutes to give an NC0 content of 32.2%. The process was repeated after 8 and 108 days (initial % NCO
starting mix in both runs was 48.6%) to afford 34.4% and 32.2% NCO, respectively.

13348~8 Examples 72-92 Using the procedure described in Example 2 above the following trimerization of aromatic isocyanates were carried out using the specified 5 reagents and conditions set forth in the following table. MDI is methylene bis(phenylisocyanate).

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--24 ~-133~848 Example 93 To a 250 ml 3-neck flask were added 100 grams of hexamethylene diisocyanate, 2.7 grams 1,3-propanediol, and 0.3 grams 1-(2-hydroxyethyl) 5 pyrrolidine. The stirred reaction mixture was heated over a 5 minute period to 125C. After 3 hours at 125C, the NCO content had dropped to 30.4%. At this time, 0.022 grams of hydrogen chloride (~210 ppm) was added. After 0.5 hours at 125C the NCO content was 10 30.4% and after an additional 0.5 hours at 125C, the NCO content was unchanged from the previous reading.
Example 94 (Compare to 91 and 92) To a 250 ml 3-neck flask were added 100 grams of MDI, 1.4 grams 1,3-propanediol and 0.2 grams 15 1-(2-hydroxyethyl) pyrrolidine. The stirred reaction mixture was heated over a 5 minute period to 125C.
After 2 minutes at 125C, the NCO content was 32.2%. At this time 0.022 grams of hydrogen chloride (~210 ppm) was added. After 0.5 hours at 125C the NCO content was 20 31.8% and after an additional 0.5 hours at 125C the NCO
content was unchanged from the previous reading.
Example 95 To a 250 ml 3-neck flask were added 49.1 grams of hexamethylene diisocyanate, 50.9 grams of 2,4-toluene 25 diisocyanate and 0.2 grams of N-methylethanolamine. The stirred reaction mixture was heated over a 4 minute period to 200C. After 10 minutes at 200C, the reaction mixture was cooled over a 2 minute period to 50C. The resulting clear yellow liquid had a 40.1% NCO
30 content. Using HPLC analysis, the polymeric trimer product was found to have an aliphatic component of about 30%.
Although the invention has been described in detail in the foregoing for the purpose of illustration, 35 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

1. A process for the preparation of a polyisocyanate having isocyanurate structure which comprises heating an organic diisocyanate to a temperature of from 100 to 275°C in the presence of a catalytic amount of an organic compound containing at least one aliphatic tertiary amine group and at least one aliphatic hydroxy group and having a molecular weight of no more than about 500 for a period of from about 0.1 minute to about 360 minutes.

2. The process of Claim 1 wherein said organic compound has a molecular weight of less than about 250 and contains only one tertiary amine group.

3. The process of Claim 1 wherein the amount of said organic compound used is less than one percent by weight, based on the combined weight of the isocyanate and said compound.

4. The process of Claim 3, wherein said compound is used in an amount of from about 0.1 to about 0.9 percent by weight.

5. The process of Claim 4, wherein said compound is used in an amount of from about 0.3 to about 0.7 percent by weight.

6. The process of Claim 1 wherein said temperature is from 125°C to 250°C.

7. The process of Claim 6 wherein said temperature is from 150°C to 250°C.

8. The process of Claim 1 wherein the reaction is carried out for a period of from about 1 to about 180 minutes.

9. The process of Claim 8 wherein said period is from about 3 to about 10 minutes.

10. The process of Claim 1 wherein the reaction is conducted in the absence of oxygen.