Method for removing monoisocyanates from organic solution

Abstract

Monoisocyanate impurities are removed from a process stream obtained when solvent is separated from a polyisocyanate product. The monoisocyanates are reacted with amine compounds at specific molar ratios to produce ureas. The ureas can be discarded by burning, landfilling or otherwise. Alternatively the ureas can be recycled back into the polyisocyanate manufacturing process, where they are formed into biuret compounds that can remain with the polyisocyanate product.

Claims

1. A method for removing phenyl isocyanate from an organic solvent, comprising the steps of: a) contacting i) a starting solution containing at least 85 weight percent, based on the weight of the starting solution, of one or more organic solvents inert to reaction with isocyanate and amine groups and 1.5 to 15 weight percent, based on the weight of the starting solution, of phenyl isocyanate, with ii) at least one amine selected from the group consisting of aniline, MDA and PMDA, in proportions sufficient to provide 0.01 to 0.8 equivalents of primary and/or secondary amino groups per equivalent of isocyanate groups in the starting solution; and b) reacting at least a portion of the phenyl isocyanate with at least a portion of the amine to form a slurry of the one or more urea compounds in the one or more organic solvents.

2. The method of claim 1 wherein the starting solution and amine are combined in proportions sufficient to provide 0.2 to 0.75 equivalents of primary and/or secondary amino groups per equivalent of isocyanate groups in the starting solution.

3. The method of claim 1 wherein step a) is performed by adding the amine to the starting solution in two or more increments or continuously.

4. The method of claim 1 further comprising a step of reacting at least a portion of the one or more urea compounds with a polyisocyanate to form one or more biuret compounds.

5. The method of claim 1, further comprising recycling at least a portion of the one or more urea compounds into an MDI and/or polymeric MDI manufacturing process, which MDI and/or polymeric MDI manufacturing process comprises a step of reacting a polyamine with phosgene in solution in a process solvent to produce an MDI and/or polymeric MDI product and a step of separating the MDI and/or polymeric MDI product from the process solvent, wherein the recycling of at least a portion of the one or more urea compounds into the MDI and/or polymeric MDI manufacturing process is performed downstream of the step of reacting the polyamine with phosgene in the process solvent, and the one or more urea compounds react with a portion of the polyisocyanate product to form one or more biuret compounds during the step of separating the MDI and/or polymeric MDI product from the process solvent.

6. The method of claim 1 further comprising the step of c) separating at least a portion of the one or more organic solvents from the one or more urea compounds.

7. The method of claim 1 wherein the amine is aniline.

8. An MDI and/or polymeric MDI manufacturing process, comprising the steps of: a) reacting aniline with formaldehyde in a solvent to produce a mixture of MDA, PMDA and unreacted aniline in the solvent; b) distilling aniline from the mixture produced in step a) to produce a process stream containing the solvent, MDA, PMDA and residual aniline; c) phosgenating the process stream from step b) to form an isocyanate process stream containing the solvent, MDI, one or more polymethylene polyphenylisocyanates that have at least three phenyl isocyanate groups and phenyl isocyanate; d) separating MDI and polymethylene polyphenylisocyanates that have at least three phenyl isocyanate groups and phenyl isocyanate from the isocyanate process stream obtained in step c) by distillation to produce a solvent stream containing at least a portion of the solvent, 0.2 to 10 weight percent phenyl isocyanate based on the weight of the solvent stream and 0.0001 to 5 weight percent, based on the weight of the solvent stream, of MDI and/or one or more polymethylene polyphenylisocyanates that have at least three phenyl isocyanate groups; e) combining the solvent stream obtained in step d) with aniline at a ratio of 0.01 to 0.8 moles of aniline per mole of phenyl isocyanate and reacting at least a portion of the aniline with phenyl isocyanate to form urea compounds; f) recycling the urea compounds and optionally the solvent in the solvent stream into the manufacturing process downstream from step c) and into step d), whereby at least a portion of the urea compounds react during step d) with at least a portion of the MDI and/or one or more polymethylene polyphenylisocyanates that have at least three phenyl isocyanate groups to form biuret compounds.

9. The manufacturing process of claim 8 wherein step e) is performed by adding the aniline to the solvent stream obtained in step d) in two or more increments or continuously at a temperature of at least 80? C.

Description

COMPARATIVE SAMPLES A AND B

(1) Stock solutions are prepared to emulate a process stream obtained from a polymeric MDI production facility after separation of the polyisocyanate product from the reaction solvent. The stock solution contains 0.05% of a mixture of the 2,4- and 4,4-isomers of MDI, approximately 2% phenyl isocyanate (exact amounts as measured by high pressure chromatography reported below) and the balance, monochlorobenzene.

Comp. Sample A

(2) Under nitrogen and with stirring, a quantity of the stock solution is combined at room temperature with 4,4-diaminodiphenyl methane (MDA) at a ratio of 1 equivalent of isocyanate groups to 1 equivalent of amino groups. A thick, barely stirrable white slurry forms within about 2 minutes. This slurry is heated to reflux, refluxed for 8 minutes and then cooled to room temperature. The phenyl isocyanate concentration is reduced from 2.15% to 0.044%. However, the slurry that forms is too thick to handle in most industrial equipment.

Comp. Sample B

(3) Comparative Sample A is repeated, except this time the stock solution is diluted with more monochlorobenzene in a 1:19 ratio prior to being combined with the MDA. This reduces the phenyl isocyanate concentration to about 0.1 percent. The amount of MDA is reduced proportionately. Heating to reflux is begun immediately and reflux is achieved after 16 minutes. Samples are taken at that time and periodically thereafter for analysis by high pressure liquid chromatography (HPLC). Particles do not form until about 30 minutes after the reaction mixture is brought to reflux. Results are as indicated in Table 1:

(4) TABLE-US-00001 TABLE 1 Reaction Time Phenyl Isocyanate MDI (minutes) Concentration, % concentration, % 0 0.1 0.0025 16 (Start of Reflux) 0.1 None detected 106 0.09 None detected 166 0.06 None detected 346 0.03 None detected

(5) By diluting the system, the problem of a thick slurry can be avoided. However, as the data in Table 1 shows, MDA reacts every slowly with phenyl isocyanate in such a dilute system. Approximately three hours are needed to reduce the amount of phenyl isocyanate by half.

EXAMPLES 1-3 AND COMPARATIVE SAMPLES C AND D

Comp Sample C

(6) Under nitrogen and with stirring, a quantity of the stock solution is combined at room temperature with aniline at a ratio of 1 equivalent of isocyanate groups to 1 equivalent of amino groups. A thick, barely stirrable white slurry forms within 1 minute. This slurry is heated to reflux. 106 minutes after the aniline and stock solution are combined, another 0.49 equivalent of aniline per starting equivalent of isocyanate groups is added and refluxing is continued. Samples are taken thereafter for analysis. Results are as indicated in Table 2:

(7) TABLE-US-00002 TABLE 2 Reaction Phenyl Time Isocyanate Aniline (minutes) Concentration, % Concentration, % Comment 0 2.1 10 0.4 0.30 Start of reflux 40 0.2 0.24 70 0.07 0.08 136 0.03 0.8 Additional aniline added after 106 minutes 223 0.02 0.9

(8) As the data in Table 2 shows, good conversion of phenyl isocyanate is seen but aniline is not all consumed. In addition, the thick slurry can be processed only with difficulty. Unreacted phenyl isocyanate is present even after further addition of aniline.

Example 1

(9) Under nitrogen and with stirring, a quantity of the stock solution at reflux is combined with aniline (also at reflux) at a ratio of 1 equivalent of isocyanate groups to 0.62 equivalent of amino groups. This slurry is maintained at reflux. The refluxing solution turns hazy after 20 minutes at reflux. Samples are taken periodically for analysis. Gas chromatography-mass spectrometry on the product at 167 minutes (final product) confirms the presence of the unreacted aniline. Results are as indicated in Table 3:

(10) TABLE-US-00003 TABLE 3 Reaction Time Phenyl Isocyanate Aniline (minutes) Concentration, % Concentration, % 0 1.86 0 1 1.34 0.48 24 0.56 0.01 167 0.58 0.01

(11) The urea compounds produced in the foregoing reaction are recovered by vacuum filtration and dried under vacuum (100? C./16 hours) until a constant weight is obtained. Under nitrogen, 0.3 gram of the urea compounds are combined with 29.7 grams of a polymeric MDI (2.7 average isocyanate functionality, 134 isocyanate equivalent weight), heated with stirring to 100? C. over 12 minutes and held at that temperature for 22 minutes. The temperature is then increased over 6 minutes to 125? C. and held at that temperature for an hour. The isocyanate equivalent weight of the biuret-containing product is measured by titration. Matrix-Assisted Laser Desorption/Ionization Mass Spectral (MALDI-TOF MS) analysis confirms the presence of biuret structure.

(12) For comparison, the polymeric MDI by itself is subjected to the same handling and heating profile.

(13) The viscosity of the biuret-containing product and the heated polymeric MDI each are measured on a plate-and-cone rheometer at 25.6? C., with a 40 mm cone and a 54 ?m gap. Molecular weights are measured on each by GPC against a 1000 MW polyethylene glycol standard, using a 1% w/v solution in anhydrous methanol.

(14) Results of the foregoing testing are as indicated in Table 4.

(15) TABLE-US-00004 TABLE 4 Heat-treated Sample Ex. 1 Polymeric MDI Isocyanate equivalent weight 134.7 132.8 Viscosity, Pa .Math. s 0.24 0.21 M.sub.n 456 451 M.sub.w 584 573 MP 332 332 M.sub.z 855 823 Polydispersity 1.28 1.27

(16) As the data in Table 4 shows, the biuret-modified polymeric MDI has properties that are minimally changed from those of the unmodified isocyanate product.

Example 2

(17) Example 1 is repeated, this time reducing the amount of aniline further so as to provide only 0.495 equivalent of amino groups per equivalent of isocyanate groups. A thin, easily stirrable slurry forms after about 1 minute. Samples are taken periodically for analysis with results as indicated in Table 5:

(18) TABLE-US-00005 TABLE 5 Reaction Time Phenyl Isocyanate Aniline (minutes) Concentration, % Concentration, % 0 2.05 0 12 (start of reflux) 1.1 0.03 72 1.1 0.04 192 1.2 0.04

Example 3

(19) Example 1 is repeated, this time reducing the amount of aniline still further so as to provide only 0.256 equivalent of amino groups per equivalent of isocyanate groups. A thin, easily stirrable slurry forms after about 4 minutes. Samples are taken periodically for analysis with results as indicated in Table 6:

(20) TABLE-US-00006 TABLE 6 Reaction Time Phenyl Isocyanate Aniline (minutes) Concentration, % Concentration, % 0 2.1 0 11 (start of reflux) 1.4 0.02 71 1.6 0.03 131 1.7 0.02

Comp. Sample D

(21) Example 1 is repeated again, this time reducing the amount of aniline still further so as to provide only 0.099 equivalent of amino groups per equivalent of isocyanate groups. Particles are not seen in the refluxing solution until samples are removed and cooled for analysis. 1,3-Diphenylurea is observed in the gas chromatographic analyses starting with the sample from the 13 minute reaction time. Results of periodic analysis are as indicated in Table 7:

(22) TABLE-US-00007 TABLE 7 Reaction Time Phenyl Isocyanate Aniline (minutes) Concentration, % Concentration, % 0 2.1 0 13 (start of reflux) 1.9 0.04 73 1.9 0.03 433 2.0 0.02

(23) Only a minor amount of the phenyl isocyanate is removed, and aniline still remains in the product.

EXAMPLE 4

(24) Under nitrogen and with stirring, a quantity of the stock solution is combined at room temperature with aniline and a polymeric MDA at a ratio of 1 equivalent of isocyanate groups to 0.045 equivalent of aniline and 0.205 equivalent of polymeric MDA. The polymeric MDA contains about 40-45 weight-% methylene dianiline (o,o-, o,p- and p,p-isomers). The remaining 55-60 weight-% are oligomers that have 3 or more aniline groups. This polymeric MDA contains 9.835 milliequivalents nitrogen per gram and 0.0305 milliequivalent tertiary amine per gram.

(25) A thin white slurry forms within 1 minute. This slurry is heated to reflux. Samples are taken periodically thereafter for analysis. HPLC analysis of a sample from 376 minutes of reaction reveals that no polymeric MDI is present. Results are as indicated in Table 8:

(26) TABLE-US-00008 TABLE 8 Reaction Time Phenyl Isocyanate Aniline (minutes) Concentration, % Concentration, % 0 2.2 16 (start of reflux) 1.7 0.02 46 1.7 0.02 256 1.7 0.03 376 1.8 0.03

COMPARATIVE EXAMPLES E AND F

Comp. Ex. E

(27) Under nitrogen and with stirring, a quantity of the stock solution is combined at room temperature with water at a ratio of 1 equivalent of isocyanate groups to 0.262 equivalent of water. This slurry is heated to reflux. Samples are taken periodically thereafter for analysis. The reaction solution remains transparent throughout the reaction. Results are as indicated in Table 9:

(28) TABLE-US-00009 TABLE 9 Reaction Time Phenyl Isocyanate Aniline (minutes) Concentration, % Concentration, % 0 2.1 15 (start of reflux) 2.1 0.013 75 2.2 0.011 315 2.2 0.012

(29) Comp. Ex. F is performed in the same manner, except the ratio of isocyanate to water is 1:0.252 and heating is only to 80? C. The reaction solution again remains transparent throughout the reaction. Results are as indicated in Table 10:

(30) TABLE-US-00010 TABLE 10 Reaction Time Phenyl Isocyanate Aniline (minutes) Concentration, % Concentration, % 0 2.1 11 (start of reflux) 2.1 0 71 2.1 0 311 2.2 0

(31) Comparative Samples E and F show the effect of using water to attempt to remove phenyl isocyanate. Very little conversion of the phenyl isocyanate is seen and, at reflux, very little aniline is produced.

EXAMPLES 5-9

Ex. 5

(32) Under nitrogen and with stirring, a quantity of the stock solution is combined at room temperature with a polymeric MDA as described in previous examples, at a ratio of 1 equivalent of isocyanate groups to 0.250 equivalent of polymeric MDA. A thin white slurry forms as soon as the stock solution and polymeric MDA are combined. This slurry is heated to reflux. Samples are taken periodically thereafter for analysis. No polymeric MDA is detected by HPLC analysis after 378 minutes of reaction time. Results are as indicated in Table 11:

(33) TABLE-US-00011 TABLE 11 Reaction Time Phenyl Isocyanate (minutes) Concentration, % 0 2.1 18 (start of reflux) 1.6 78 1.6 378 1.6

(34) About 25% of the phenyl isocyanate is removed rapidly in this process, with complete consumption of polymeric MDA. In addition, the slurry remains easily stirrable and can be processed without difficulty at industrial scale.

Ex. 6

(35) Example 5 is repeated except an equivalent ratio of 1 equivalent of isocyanate groups to 0.502 equivalent of polymeric MDA is used. As with Ex. 5, a thin, easily stirrable slurry forms immediately upon contacting the stock solution and polymeric MDA. No polymeric MDA is detected by HPLC analysis by 196 minutes of reaction time. Results of periodic analysis are indicated in Table 12.

(36) TABLE-US-00012 TABLE 12 Reaction Time Phenyl Isocyanate (minutes) Concentration, % 0 2.0 16 (start of reflux) 1.1 76 1.0 196 1.0

(37) By increasing the amount of polymeric MDA to about one half equivalent per equivalent of isocyanates, a greater amount of phenyl isocyanate is removed. Again, complete removal of polymeric MDA is seen and the slurry remains thin and easily handled.

Ex. 7

(38) Example 5 is repeated again except an equivalent ratio of 1 equivalent of isocyanate groups to 0.681 equivalent of polymeric MDA is used. Once again, a thin, easily stirrable slurry forms immediately upon contacting the stock solution and polymeric MDA. Results of periodic analysis are indicated in Table 13. No polymeric MDA is detected by HPLC analysis after 47 minutes of reaction time or thereafter.

(39) TABLE-US-00013 TABLE 13 Reaction Time Phenyl Isocyanate (minutes) Concentration, % 0 2.0 17 (start of reflux) 0.8 47 0.6 77 0.6 257 0.6

(40) By increasing the amount of added amine to 0.681 equivalent per equivalent of isocyanates, about 70% of the phenyl isocyanate is consumed, with complete consumption of polymeric MDA. The slurry is thin and easily processed.

Ex. 8

(41) Under nitrogen and with stirring, a quantity of the stock solution is heated to reflux. Separately, a quantity of a 3.3%-wt. solution of the polymeric MDA in chlorobenzene is heated to reflux. The refluxing solutions are combined at a ratio of 1 equivalent of isocyanate groups to 0.638 equivalent of amino groups and held at reflux. Once again, a thin, easily stirrable slurry forms within about 30 seconds. Results of periodic analysis are indicated in Table 14. No polymeric MDA is detected by HPLC analysis after one minute of reaction time or at any later time.

(42) TABLE-US-00014 TABLE 14 Reaction Time Phenyl Isocyanate (minutes) Concentration, % 0 1.8 1 0.9 21 0.5 71 0.5 157 0.5

(43) In this experiment, over half the phenyl isocyanate is removed within one minute of reaction time. Almost 75% is removed within 21 minutes, with complete consumption of polymeric MDA. The slurry is thin and easily processed.

(44) The urea compounds are removed from the solvent and dried as described in Example 1. 0.3 gram of the urea compounds are combined with 29.7 grams of a polymeric MDI (2.7 average isocyanate functionality, 134 isocyanate equivalent weight) and heated as described in Example 1. The properties of the resulting biuret-modified polyisocyanate are as indicated in Table 15. The properties of the starting polyisocyanate, similarly handled and heat-treated, are again provided for purposes of comparison.

(45) TABLE-US-00015 TABLE 15 Heat-treated Sample Ex. 1 Polymeric MDI Isocyanate equivalent weight 134.8 132.8 Viscosity, Pa .Math. s 0.29 0.21 M.sub.n 460 451 M.sub.w 596 573 MP 333 332 M.sub.z 881 823 Polydispersity 1.30 1.27

(46) As before, the biuret-modified polymeric MDI has properties that are only slightly changed from those of the unmodified isocyanate product.

Ex. 9

(47) Example 5 is repeated again, except the equivalent ratio of 1 equivalent of isocyanate groups to 0.543 equivalent of polymeric MDA is used, and the reaction mixture is stirred at room temperature instead of being heated to reflux. A solution forms which becomes a thin, easily stirrable slurry forms after about 3 minutes. Results of periodic analysis are indicated in Table 16. No polymeric MDA is detected by HPLC analysis at 338 minutes of reaction time.

(48) TABLE-US-00016 TABLE 16 Reaction Time Phenyl Isocyanate (minutes) Concentration, % 0 1.9 4 1.6 27 1.1 84 1.0 338 1.0

(49) Even at room temperature, almost half the phenyl isocyanate is removed in 84 minutes of reaction time. Complete removal of polymeric MDA is observed when sampled at 338 minutes. The thin slurry is easily handled in industrial equipment.

EXAMPLES 10A AND 10B

Ex. 10A

(50) A solution of 98% monochlorobenzene, 1.89% phenyl isocyanate and 0.11 wt. % MDI is combined with neat aniline in an amount to provide 0.7 equivalent of amino groups per equivalent of isocyanate groups. The resulting reaction mixture is heated at reflux for 2 hours and cooled to room temperature.

(51) The reaction mixture is then vacuum filtered on a fritted glass funnel (10-16 micron pore size) to remove precipitated urea compounds. 4.23 grams of urea compounds are recovered.

Ex. 10B

(52) Example 10A is repeated without filtering off the urea compounds. Instead, the reaction mixture is rotoevaporated to remove the solvent, leaving the urea compounds behind. 5.65 grams of dry urea compounds are obtained.

(53) These results indicate that filtration only removes about 75% of the urea compounds.

EXAMPLE 11

(54) Under a nitrogen atmosphere, a 2% solution (197.12 grams) of phenyl isocyanate (33.33 milliequivalents) in chlorobenzene is added to a 3 neck, 500 milliliter, round bottom, glass reactor equipped with a chilled condenser (?2? C.), thermocouple-heating mantle-temperature controller assembly, overhead nitrogen inlet (0.2 liter per minute), and magnetic stirring. The magnetically stirred solution is heated to 100? C. Aniline (10.0 milliequivalents, amine to isocyanate equivalent ratio 0.3:1) is injected subsurface. Three minutes after injection of aniline the transparent solution becomes an easily stirred white slurry. The resulting reaction mixture is stirred at 100? C. for 60 minutes after the aniline is injected. The aniline concentration falls below measurable values within 10 minutes after the aniline injection. Phenyl isocyanate falls to 1.33% by weight after about 40 minutes and remains approximately at that level.

(55) Approximately 12 grams of reaction mixture is removed for these analysis within the first 60 minutes after the aniline injection, at which time a second injection of aniline (9.74 milliequivalents) is made. The ratio of amine equivalents to isocyanate equivalents after the second aniline injection, prior to any reaction, is approximately 0.49:1. The ratio of total equivalents of aniline added in the two injections to the number of equivalents of phenyl isocyanate in the starting solution is approximately 0.6:1.

(56) The reaction continues to be stirred at 100? C. Twenty-two minutes after the second aniline injection, the concentration of phenyl isocyanate is 0.79 weight percent and the amount of aniline is below the level of detection. The concentration of phenyl isocyanate stabilizes at about 0.70 weight percent 40-60 minutes after the second aniline addition.

EXAMPLE 12

(57) Under a nitrogen atmosphere, a 2.01% solution (197.58 grams) of phenyl isocyanate (33.18 milliequivalents) in chlorobenzene is added to a 3 neck, 500 milliliter, round bottom, glass reactor equipped with a chilled condenser (?2? C.), thermocouple-heating mantle-temperature controller assembly, overhead nitrogen inlet (0.2 liters per minute), and magnetic stirring. The magnetically stirred solution is heated to 100? C. Aniline (5.82 milliequivalents, approximately 0.175 equivalent per equivalent of phenyl isocyanate) is injected subsurface. Nine minutes after injection of aniline the transparent solution becomes an easily stirred white slurry. A cumulative 10 minutes after the first aniline injection, a second injection of aniline (5.83 milliequivalents, approximately 0.213 equivalent per equivalent of remaining phenyl isocyanate) is made. A cumulative 20 minutes after the first aniline injection a third injection of aniline (5.79 milliequivalents, approximately 0.269 equivalent per equivalent of remaining phenyl isocyanate) is made. A cumulative 30 minutes after the first aniline injection a fourth injection of aniline (5.82 milliequivalents, about 0.370 equivalent per equivalent of remaining phenyl isocyanate) is made. The total amount of aniline added in the four injections is 0.7 equivalent per equivalent of phenyl isocyanate in the starting solution. The temperature is maintained at 100? C. with stirring throughout the process.

(58) The phenyl isocyanate concentration is reduced to 0.53% 10 minutes after the fourth aniline injection. Aniline concentration is 0.02% at that time. By 20 minutes after the fourth aniline injection the phenyl isocyanate concentration is 0.49% and the amount of remaining aniline is below the detection limit.

EXAMPLE 13

(59) Under a nitrogen atmosphere, a 4.50% solution (198.79 grams) of phenyl isocyanate (75.1 milliequivalents) in chlorobenzene is added to a 3 neck, 500 milliliter, round bottom, glass reactor equipped with a chilled condenser (?2? C.), thermocouple-heating mantle-temperature controller assembly, overhead nitrogen inlet (0.2 liters per minute), and magnetic stirring. The magnetically stirred solution is heated to 100? C. Aniline (4.90 grams, 52.57 milliequivalents per equivalent of phenyl isocyanate) is injected subsurface. About 10 seconds after injection of aniline the transparent solution becomes a thick, but easily stirred, white slurry. The aniline is 0.7 equivalent per equivalent of phenyl isocyanate in the starting solution. The temperature is maintained at 100? C. with stirring throughout the process. The phenyl isocyanate concentration is reduced to 1.67% 10 minutes after the aniline injection. Aniline concentration is 0.15% at that time. By 20 minutes after the aniline injection the phenyl isocyanate concentration is 1.41% and the amount of remaining aniline is 0.026%.

EXAMPLES 14-16 AND COMPARATIVE SAMPLES G AND H

Ex. 14

(60) A solution containing 20.44 grams of a mixture of the 2,4- and 4,4-isomers of MDI, 406.77 grams of phenyl isocyanate and 19.906 kilograms of chlorobenzene is reacted with 234.30 grams of aniline at 157? C. under pressure for 180 minutes to a final phenyl isocyanate concentration of 0.53%. Urea compounds produced in the forgoing reaction are recovered by rotary evaporation of a portion of the product slurry and dried under vacuum (100? C./25 hours) to a constant weight. Under nitrogen, 0.0200 gram of the urea compounds are combined with 199.98 grams of a polymeric MDI (2.7 average isocyanate functionality, 134 isocyanate equivalent weight), heated with stirring to 125? C. over 14 minutes and held at that temperature for 15 minutes.

Ex. 15

(61) Under nitrogen, 0.2000 gram of the urea compounds described in Ex. 14 are combined with 199.80 grams of the polymeric MDI described in Ex. 14, heated with stirring to 125? C. over 14 minutes and held at that temperature for 15 minutes.

Ex. 16

(62) 3.0149 grams of the product from Ex. 15 and 27.1320 grams of polymeric MDI (described in Ex. 14) are mixed together.

Comp. Sample G

(63) For comparison, the polymeric MDI by itself (described in Ex. 14) is subjected to the same handling and heating profile. Thus, 200.00 grams of polymeric MDI are heated with stirring to 125? C. over 14 minutes and held at that temperature for 15 minutes.

Comp. Sample H

(64) The polymeric MDI described in Ex. 14 is tested without any treatment or modification.

(65) The isocyanate equivalent weight (IEW) of the products obtained from Examples 14-16 and Comparative Samples G and H are measured by titration. The viscosity of each are measured on a plate-and-cone rheometer at 25.6? C., with a 40 mm cone and a 54 ?m gap. Molecular weights are measured on each by GPC against a 1000 MW polyethylene glycol standard, using a 1% w/v solution in anhydrous methanol. Results of the foregoing testing are as indicated in Table 17.

(66) TABLE-US-00017 TABLE 17 Comp. Comp. Sample Ex. 14 Ex. 15 Ex. 16 Sample G Sample H IEW 133.74 133.52 133.69 133.86 133.82 Viscosity, Pa .Math. s 0.206 0.214 0.200 0.206 0.197 M.sub.w 583 577 580 570 579 Polydispersity 1.33 1.32 1.33 1.31 1.33

(67) As the data in Table 17 shows, the biuret-modified polymeric MDI products of Examples 14-16 have properties that are minimally changed from those of the unmodified isocyanate product. Polymeric MDI with greater amounts of biuret-modification may beneficially be diluted with fresh polymeric MDI.