METHOD OF PREPARATION

The present invention relates to isocyanate group containing admixtures having reduced organometallic and base catalyzed reactivity. The present invention particularly relates to isocyanate group containing admixtures wherein a reactivity adjusting agent is employed to slow the rate of forming a urethane or an isocyanurate group.

It has long been known that compounds having an isocyanate group (hereinafter isocyanates) can react with compounds having active hydrogens. Examples of such reactions include the reaction of an isocyanate group and an amine to form a urea, the reaction of an isocyanate group and water to form an amine, and the reaction of an isocyanate group and an alcohol to form a urethane. It is also known that compounds which contain more than one isocyanate group and compounds which contain more than one active hydrogen can react to form polymers. The most versatile of these polymers are polyurethanes prepared from formulations containing di- or poly-isocyanates and macroglycols.

Urethane group containing compounds prepared from formulations including monofunctional isocyanates are also useful compounds. For example, mono-isocyanates such as butyl isocyanate and phenyl isocyanate can be used to prepare products ranging from pharmaceuticals to herbicides. However, by far, the largest use of isocyanates is in the production of polyurethanes.

Polyurethanes can be prepared by reacting a di- or poly-functional active hydrogen containing compound wherein the active hydrogen group is a hydroxyl with a di- or poly-isocyanate. Isocyanate compounds are commonly prepared by phosgeπating amines. For example, polymethylene polyphenyl polyisocyanate (PMDI) is commercially prepared by phosgenating mixtures of methylene-bridged polyphenyl polyamines. By-products of the phosgenation reaction include chlorine bearing compounds, many of which are acidic. Acidic compounds can interfere with organometallic and base catalyzed reactions of active hydrogens and isocyanates, generally by slowing down the rate of reaction between isocyanate groups

and active hydrogens- Because of this, there have been many efforts to decrease the acidity of poly- and di-isocyanates during their manufacture.

Efforts on the part of industry to reduce acidity in poly- and di-isocyanates have generally been successful. In some cases these efforts have been too successful. It has sometimes been found desirable to reintroduce acidity into poly- and di-isocyanates. For example, U.S. Patent 3,523,106 to Davidson discloses that hydrogen chloride gas (HCI) or an acid chloride such as benzoyl chloride can be added to organic isocyanates to increase the rate forthe reaction of an organic isocyanate and a polyol- U.S. Patent 3,640,886 to Conker discloses adding a small amount of N,N'-disubstituted carbamoyl chloride to an organic isocyanate for similar purposes- Adding HCI to certain isocyanate containing compounds can cause undesirable properties to manifest, for example, adding HCI to PMDI can increase the rate at which the PMDI will increase in viscosity upon storage.

Modern conventional isocyanates often have very low levels of acidity. One problem observed with these very low acid isocyanates is that they often can react with active hydrogen containing compounds too quickly-

Therefore, it would be desirable to prepare isocyanates by admixing therewith an agent which would decrease the organometallic and base catalyzed reactivity of the isocyanates. It would also be desirable to prepare PMDI isocyanates having decreased organometallic and base catalyzed reactivity that do not subsequently undergo an accelerated growth in viscosity.

In one aspect, the present invention is a composition of an isocyanate group containing admixture having reduced organometallic and base catalyzed reactivity comprising an admixture prepared by admixing an isocyanate reactivity adjusting agent selected from the group consisting of phosphoryl chloride, phosphoryl bromide, phosphorus trichloride and phosphorus tribromide and mixtures thereof, and an isocyanate group containing compound, wherein the isocyanate reactivity adjusting agent is present at an acidity concentration of from 0-15to 21-15 mill-equivalents (meq) of acidic halide per kilogram (kg) of isocyanate.

In another aspect, the present invention is a method for preparing a composition of an isocyanate group containing admixture having reduced organometallic and base catalyzed reactivity comprising admixing an isocyanate reactivity adjusting agent selected from the group consisting of phosphoryl chloride, phosphoryl bromide, phosphorus trichloride and phosphorus tribromide and mixtures thereof, and an isocyanate group containing compound, wherein the isocyanate reactivity adjusting agent is present at an acidity concentration of from 0.15 to 21-15 meq of acidic halide per kg of isocyanate group containing compound. In yet another aspect, the present invention is a polymer prepared from a formulation comprising (1) a di- and/or poly-isocyanate, (2) an active hydrogen containing compound, and (3) an isocyanate reactivity adjusting agent selected from the group consisting of phosphoryl chloride, phosphoryl bromide, phosphorus trichloride and phosphorus

tribromide and mixtures thereof, wherein the isocyanate reactivity adjusting agent is present at an acidity concentration of from 0.15 to 21.15 meq of acidic halide per kg of isocyanate. Another aspect of the present invention is a method for preparing a polymer comprising mixing (1) a di- or poly-isocyanate, (2) an active hydrogen containing compound, and (3) an isocyanate reactivity adjusting agent selected from the group consisting of phosphoryl chloride, phosphoryl bromide, phosphorus trichloride and phosphorus tribromide and mixtures thereof wherein the isocyanate reactivity adjusting agent is present at an acidity concentration of from 0.15 to 21.15 meq of acidic halide per kg of the di- and/or poly- isocyanate. The isocyanate reactivity adjusting agents of the present invention can be advantageously mixed with a mono-, di- and/or poly-isocyanate to slow the rate of an organometallic or base catalyzed reaction between a mono-, di- and/or poly-isocyanate and a polyol. Phosphoryl chloride, for example, is a liquid reactivity adjusting agent and can be mixed more easily with a liquid di- and/or poly-isocyanate than can be a gas or solid reactivity adjusting agent. As a liquid, it can also be removed by stripping. In the case of PMDI, the isocyanate reactivity adjusting agents of the present invention can be advantageously employed to reduce the rate of organometallic and base catalyzed reaction between PMDI and a polyol without undesirable increases in the rate of PMDI viscosity growth during storage and handling. The composition of an isocyanate group containing admixture of the present invention is an admixture of an isocyanate and an isocyanate reactivity adjusting agent selected from the group consisting of phosphoryl chloride, phosphoryl bromide, phosphorus trichloride and phosphorus tribromide and mixtures thereof. The amount of isocyanate reactivity adjusting agent used will vary with the application to which the resultant isocyanate group containing admixture will be put and the amount of acidic materials already present in the isocyanate. However, generally, the amount of isocyanate reactivity adjusting agent used in preparing the composition of the present invention will preferably be that required to achieve an acidic halide concentration of from 0.15 to 21.15, more preferably from 0.30 to 14.10, and most preferably from 0.55 to 1 1.50 milliequivalents (meq) acidic halide per kg of isocyanate group containing compound.

The composition of an isocyanate group containing admixture of the present invention can be prepared by admixing an isocyanate reactivity adjusting agent and an isocyanate. Any isocyanate which is reactive with an active hydrogen compound can be used to prepare the compositions of the present invention. For example, methyl isocyanate, ethyl isocyanate, propyl isocyanate, butyl isocyanate, phenyl isocyanate and the like, and mixtures thereof can be admixed with an isocyanate reactivity adjusting agent to prepare the composition of the present invention. Any such mono-isocyanate can be so used.

However, preferably, the isocyanate is a di- and/or poly-isocyanate. In the practice of the present invention, the isocyanate can be advantageously selected from organic polyisocyanates, modified polyisocyanate mixtures, and isocyanate-based prepolymers. These can include aliphatic, cycloaliphatic and preferably muitivalent isocyanates such as 1 ,6- hexamethylenediisocyanate; 1-isocyanato-3,5,5-trimethyl-1 ,3-iso-cyanatomethyl-cyclohexane; 2,4- and 2,6-hexahydro-toluenediisocyanate, as well as the corresponding isomeric mixtures; 4,4'-, 2,2'- and 2,4'-dicyclohexyl-methylenediisocyanate, as well as the corresponding isomeric mixtures; 2,4- and 2,6-toluenediisocyanate (TDI) and the corresponding isomeric mixtures; 4,4'-, 2,4'- and 2,2'-methylene diphenyldiisocyanate (MDI) and the corresponding isomeric mixtures; mixtures of 4,4'-, 2,4'- and 2,2'-MDI and PMDI; and mixtures of PMDI and TDI. Also advantageously used for preparing the compositions of the present invention are the so-called modified muitivalent isocyanates, i.e., products which are obtained through chemical reactions of the above diϊsocyanates and/or polyisocyanates. Exemplary are polyisocyanates containing esters, ureas, biurets, allophanates and preferably uretonimines; isocyanurate and/or urethane group containing diisocyanates; and/or polyisocyanates- Individual examples are aromatic polyisocyanates containing urethane groups, preferably having isocyanate group contents of from 2 to 40 weight percent, more preferably from 20 to 35 weight percent, obtained by reaction of diisocyanates and/or polyisocyanates with, for example, lower molecular weight diols, triols, oxyalkylene glycols, dioxyalkylene glycols or polyoxyalkylene glycols having molecular weights up to about 800. Polyester diols and triols can also be used- These polyols can be employed individually or in mixtures as di- and/or polyoxyalkylene glycols. For example, diethylene glycols, dipropylene glycols, polyoxyethylene glycols, polyoxypropyfene glycols and polyoxypropylenepolyoxyethylene glycols can be used. Suitable also are prepolymers having isocyanate group contents of from 2 to 30 weight percent, more preferably from 15 to 25 weight percent. Liquid polyisocyanates containing uretonimine groups and/or isocyanurate rings, having isocyanate group contents of from 8 to 40 weight percent, more preferably from 20 to 35 weight percent, can also be used. These include, for example, polyisocyanates based on 4,4'-, 2,4'- and/or 2,2'-MDI and the corresponding isomeric mixtures, 2,4- and/or 2,6-TDl and the corresponding isomeric mixtures, 4,4'-, 2,4'- and 2,2'-MDI and the corresponding isomeric mixtures; mixtures of MDI and PMDI and mixtures of TDI and MDI and/or PMDI.

Also useful in the present invention are: (ϊ) polyisocyanates containing uretonimine groups and/or urethane groups, from 4,4'-MDI or a mixture of 4,4'- and 2,4'-MDI having an isocyanate group content of from 8 to 33 weight percent; (ii) prepolymers having an isocyanate group content of from 10 to 30 weight percent, based on the weight of the prepolymer, prepared by the reaction of polyoxy-alkylene polyols, having a functionality of preferably from 2 to 4and a molecular weight of from 600 to 15,000 with 4,4'-MDI orwith a

mixture of 4,4'- and 2,4'-MDI and mixtures of (i) and (ii); and (iii) 2,4- and 2,6-TDI and the corresponding isomeric mixtures.

PMDI in any of its forms can also be used and is preferred. In this case it preferably has an equivalent weight of from 125 to 200, more preferably from 130 to 150, and an average functionality of greater than or equal to about 2. The viscosity of the PMDI component is preferably from 25 (0.025 Pa.s) to 5,000 (5 Pa.s) centi poise, but values from 25 (0.025 Pa.s) to 2,500 cps (2.5 Pa.s) at 25^ are preferred for ease of processing. Similar viscosities are preferred where alternative isocyanates are selected.

In preparing the composition of an isocyanate group containing admixture of the present invention, an isocyanate and an isocyanate reactivity adjusting agent are admixed. This admixture can be prepared by any means known by those skilled in the art of preparing such admixtures to be useful for preparing an evenly dispersed admixture of a liquid or solid in an isocyanate. For example, the isocyanate reactivity adjusting agent can be directly added to a vessel containing an isocyanate and then the vessel can be agitated, stirred or the like, for a period of time sufficient to evenly disperse the isocyanate reactivity adjusting agent throughout the vessel. Alternatively, the isocyanate reactivity adjusting agent can be first admixed with a relatively small amount of isocyanate or a solvent to prepare a concentrate, and the concentrate added to the vessel of isocyanate as described hereinabove. Advantageously, an isocyanate reactivity adjusting agent of the present invention can generally be contacted with isocyanates in high concentration without undesirable loss of properties or production of significant amounts of undesirable impurities.

In another aspect, the present invention is a poiyurethane prepared from a formulation comprising a di- and/or poly-isocyanate, an isocyanate reactivity adjusting agent, and an active hydrogen containing compound. The active hydrogen containing compound can be any active hydrogen containing compound which can be used to prepare a poiyurethane or a polyisocyanurate. Active hydrogen containing compounds most commonly used in poiyurethane production are those compounds having at least two hydroxyl groups. Those compounds are referred to herein as polyols. Representatives of suitable polyols are generally known and are described in such publications as High Polymers, Vol. XVI, "Polyurethanes, Chemistry and Technology" by Saunders and Frisch, Interscience Publishers, New York, Vol. I, pp. 32-42, 44-54 (1962) and Vol. II, pp. 5-6,198-199 (1964); Organic Polymer Chemistry by K. J. Saunders, Chapman and Hall, London, pp. 323-325 (1973); and Developments in Polyurethanes, Vol. I, J. M. Burst, ed., Applied Science Publishers, pp. 1-76 (1978). However, any active hydrogen containing compound can be used to prepare the polymer of the present invention. Examples of such materials include those selected from the following classes of compositions, alone or in admixture: (a) alkylene oxide adducts of polyhydroxyalkanes; (b) alkylene oxide adducts of non-reducing sugars and sugar derivatives; (c) alkylene oxide adducts of phosphorus

and polyphosphorus acids; and (d) alkylene oxide adducts of polyphenols. Polyols of these types are referred to herein as "base polyols".

Examples of alkylene oxide adducts of polyhydroxyalkanes useful herein are adducts of ethylene glycol, propylene glycol, 1,3-dihydroxypropane, 1,4-dihydroxybutane, and 1,6-dihydroxyhexane, glycerol, 1,2,4-trihydroxybutane, 1,2,6-trihydroxyhexane, 1 ,1,1- trimethylolethane, 1,1,1-trimethyloIpropane, pentaerythritol, polycaprolactone, xylitol, arabitol, sorbitol, mannitol, and the like. Preferred herein as alkylene oxide adducts of polyhydroxyalkanes are the ethylene oxide adducts of trihydroxyalkanes- Other useful adducts include ethylene diamine, glycerin, ammonia, 1,2,3,4-tetrahydroxy butane, fructose, and sucrose-

Also preferred are poly(oxypropylene) glycols, triols, tetrols and hexols and any of these that are capped with ethylene oxide- These polyols also include poly(oxypropylene- oxyethylene)polyois. The oxyethylene content should preferably comprise less than 80 weight percent of the total and more preferably less than 40 weight percent. The ethylene oxide, when used, can be incorporated in any way along the polymer chain, for example, as internal blocks, terminal blocks, or randomly distributed blocks, or any combination thereof.

The base polyols described hereinabove can contain small amounts of "inherent" unsaturation, i.e., unsaturation due to the isomerization of propylene oxide to allyl alcohol during the manufacture of the polyol- In some cases it may be desirable to include additional unsaturation in the polyols.

Another preferred class of polyols are "copolymer polyols", which are base polyols containing stably dispersed polymers such as acrylonitrile-styrene copolymers. Production of these copolymer polyols can be from reaction mixtures comprising a variety of other materials, including, for example, catalysts such as azobisisobutyronitrile; copolymer polyol stabilizers; and chain transfer agents such as isopropanol.

Yet another class of polyols preferred for the present invention are the "so called" polyester polyols- These active hydrogen containing compounds are generally prepared by the condensation of di-carboxylic acids with dialchohols or by homopolymerization of cyclic esters- Included in this class of di-carboxylic acid ester polyols are polyadipicacid esters of butanediol, polyterepthalate acid esters of ethylene glycol and the like. An exampleof a homopolymer of a cyclic ester polyol is poly ε-caprolactone. Polyols having both polyether character and polyester character may also be used to prepare the polyurethanes of the present invention.

In addition to the more traditional polyols described hereinabove, the present invention can be prepared with other active hydrogen containing compounds- For example, the present invention may be prepared with thio-alchohols and amine terminated compounds. In both cases, however, the inherent acid character of the thio-alchohols and the inherent basic character of the amine containing compounds will lessen the relative effectiveness of the

isocyanate reactivity adjusting agents of the present invention. In the case of the thiols, the already high level of acidity would require a substantial amount of reactivity adjusting agent to be added to significantly change the relative acidity level thereof. In the case of the amine terminated active hydrogen compounds, the reactivity adjusting agents would be, to some degree, tied up by the amines. Therefore, a quantity of reactivity adjusting agent added to an amine-isocyanate admixture would have comparatively less effect on the rate of reaction thereof compared to the same amount of reactivity adjusting agent added to a hydroxyl- isocyanate admixture.

The poiyurethane composition of the present invention can be prepared by a method wherein a poiyurethane formulation comprising a di- and/or poly-isocyanate, an active hydrogen containing compound, and an isocyanate reactivity adjusting agent are admixed. The order of admixing the components is not important except that the di- and/or poly- isocyanate and the active hydrogen containing compound are preferably not reacted prior to admixing one or the other with the isocyanate reactivity adjusting agent. The active hydrogen containing compound or the di- and/or poly-isocyanate can be first mixed with the isocyanate reactivity adjusting agents of the present invention without a significant loss of properties in the resulting poiyurethane nor production of a significant amount of undesirable impurities. The compositions of isocyanate containing admixtures of the present invention are desirably diminished in organometallic and base catalyzed reactivity. The reaction rate for forming a urethane group is often undesirably slow. Therefore, an organometallic catalyst or tertiary amine catalyst is often part of a formulation used to prepare a urethane containing compound. For example, poiyurethane formulations are typically catalyzed by incorporating into the formulation a catalyst in an amount suitable to increase the rate of reaction between an isocyanate and a active hydroxyl species. Although a wide variety of materials is known to be useful for this purpose, the most widely used and preferred catalysts are the tertiary amine catalysts and the organotin catalysts.

Examples of the tertiary amine catalysts include, for example, triethylenediamine, N-methyl morpholine, N-ethyl morpholine, diethyl ethanolamine, N-coco morpholine, 1- methyl-4-dimethylaminoethyl piperazine, 3-methoxy-N-dimethylpropylamine, N,N-diethyl-3- diethyl aminopropylamine, dimethylbenzyl amine and the like. Tertiary amine catalysts are advantageously employed in an amount from 0.01 to 2 percent by weight of the polyol formulation.

Examples of organotin catalysts include dimethyltin dilaurate, dibutyltin dilaurate, dioctyltin dilaurate, stannous octoate and the like. Other examples of effective catalysts include those taught in, for example, U.S. Patent No. 2,846,408 to Brochhagen, etal. Preferably the organotin catalyst is employed in an amount from 0.001 to 0.5 percent by weight of the the active hydrogen containing compound formulation.

Polyisocyanurate compositions can be directly prepared with formulations including the isocyanate reactivity adjusting agents of the present invention. However, just as with the rate of urethane group formation, the rate of formation of isocyanurate groups can also be undesirably slow- Therefore, the formulations of the present invention can also include those catalysts which catalyze the formation of isocyaπurates such as those mentioned in

Saunders and Frisch, Polyurethanes, Chemistry and Technology in 1 High Polymers Vol. XVI, pp. 94-97 (1962). Such catalysts are referred to herein as trimerization catalysts. Examples of trimerization catalysts include aliphaticand aromatic tertiary amine compounds, organometallic compounds, alkali metal salts of carboxylic acids, phenols and symmetrical triazine derivatives. Preferred catalysts are potassium salts of carboxylic acids such as potassium octoate and tertiary amines such as, for instance, 2,4.6-tris(dimethyl aminomethyl) phenol.

The poiyurethane compositions of the present invention can be prepared with di- and/or poly-isocyanates, di- and/or poly-alchohols, and other additional additives- For example, the polyurethanes of the present invention can be prepared with a blowing agent to produce a foam. In addition to blowing agents, the formulations can also include such additives as surfactants, catalysts, fillers, pigments, flame retardants, mold release agents, mixtures of the above, and any other material known by those skilled in the art of preparing polyurethanes to be useful in preparing poiyurethane products.

The isocyanate group containing admixtures of the present invention can have desirably reduced organometallic catalyzed and basic catalyzed reactivity. Such reactivity can be measured by any method known to those skilled in the art of measuring isocyanate reactivity- For example, this reactivity can be determined by measuring the time from mixing of a polyisocyanate or an admixture of polyisocyanates with an active hydrogen compound until specific phenomena are observed in a forming poiyurethane or foam. Materials containing a high concentration of acidity tend either to not foam at all, or to fail to timely cure, with the resultthatthey remain tacky- Commonly employed measurements of foam forming ability include:

a) Cream time: the time in seconds from mixing until foaming begins, determined by observing when gas first begins to separate from the admixture; b) Gel time: the time in seconds from mixing until the foaming admixture first begins to produce "strings" adhering to a wooden spatula quickly inserted and removed from the foaming admixture; c) Tack-free time: the time in seconds from mixing until the foam surface loses its sticky quality-

A reactive isocyanate containing admixture will have low values corresponding to relatively shorttimes for a foam to form. Conversely, materials which fail to foam or take a long time to form a foam are relatively unreactive. Therefore, foams prepared from formulations having no

reactivity adjusting agents can have shorter cream, gel and tack-free times than those prepared from formulations including the reactivity adjusting agents of the present invention. In the practice of the present invention, an isocyanate group containing admixture with a desired level of acidity can be prepared by admixing an isocyanate with an isocyanate reactivity adjusting agent under conditions such that the initial acidity of the isocyanate and the acidity added to it by means of adding isocyanate reactivity adjusting agent equals the desired level of acidity. Acidity levels can be estimated and isocyanate reactivity adjusting agent additions made based on calculated acidity yields, but, in order to prepare the isocyanate group containing admixture of the present invention, acidity levels are desirably measured.

Acidity in isocyanates can be measured as meq of acidic halide per kg of isocyanate. The acidity concentration of isocyanates can be measured by any suitable method. A preferred method for measuring acidity consists of placing from 2 to 10 grams of an isocyanate sample (S) into a beaker. The sample is first dissolved by stirring with 75 milliliters of toluene and methanol 1 : 1 , then the sample is further diluted with another 75 milliliters of toluene and methanol 1 : 1. The beaker is covered with a watch glass and placed on a hot plate set for about 230° C. The solution in the beaker is stirred and heated for exactly 7 minutes. The solution should be boiling for about the last two minutes of the heating period. The beaker is then removed from the hot plate and cooled. The solution in the beaker can be titrated by any suitable means, for instance, by use of an autotitrator. The titrant is preferably 0.03 N potassium hydroxide. The resultant titration should produce an "S" shaped curve. A blank is then run under the same conditions and the volume (V) of titrant consumed is determined. Parts per million (ppm) hydrogen chloride iscalculated using the formula: ppm HCI = ((V-B) x N x 3.65) x (1/S) x (1 x 104) wherein V represents the milliliters of potassium hydroxide titrant consumed by the sample; B represents the milliliters of titrant consumed bythe blank; N represents the normality of the titrant; and S represents the weight in grams of the isocyanate material placed into the beaker. Meq(s) of acidic halide per kg of isocyanate can be calculated bythe following formula: meq acidic halide/kg isocyanate = ppm HCI/35.5 In one embodiment, the present invention can be prepared employing PMDI without undesirable increases in viscosity growth rates. It is known that adjusting the acidity of PMDI with HCI can often cause viscosity growth rates to accelerate, thereby shortening the shelf life of PMDI products so prepared. The reactivity adjusting agents of the present invention can be employed without a substantial increase in viscosity growth rates. The viscosity of PMDI can be measured by any means known to those skilled in the art of testing the physical properties of PMDI. For example, PMDI viscosity can be measured utilizing a calibrated capillary viscometer.

The following examples and comparative examples are intended to be illustrative of the present invention- However, these examples and comparative examples are not intended to limit the scope of the present invention and should not be so interpreted.

Example 1

A sample of PMDI (PAPI 88*) having an initial viscosity of 153 centipoise at 25° C and an initial acidity of 140 parts per million as HCI (3.84 meq of acidic halide/kg isocyanate) was admixed with sufficient phosphoryl chloride to increase acidity by 84 parts per million (2.30 meq acidic halide/kg isocyanate). (*PAPI 88 is a trade designation of The ^' Dow Chemical Company.) This PMDI was used to prepare a poiyurethane by admixing it with an active hydrogen admixture, the admixture formulation containing 100 parts of VORANOL446* (a propoxylated sucrose/glycerine polyol), 1.5 parts of DABCO DC-193* (a silicone surfactant), 1.61 parts of DABCO 33LV* (trϊethylene diamine catalyst), and 40 parts of a chlorof luorocarbon blowing agent (R-11). (*VORANOL446 is a trade designation of the Dow Chemical Company; *DABCO DC-193 is a trade designation of Air Products and Chemicals, Inc.; and *DABCO 33LV is a trade designation of Air Products and Chemicals, Inc.) 132.1 grams of PMDI were mixed with 143.11 grams of active hydrogen admixture. Results for reactivity were recorded in Table 1 following the examples-

Example 2

A sample was prepared substantially as in Example 1 except that sufficient phosphoryl chloride was added to increase acidity by 234 parts per million (6.42 meq acidic halide/kg isocyanate)- Results for reactivity were recorded in Table 1 following the examples-

Comparative Example 3

A sample ^' as prepared substantially as in Example 1 except that acidity was increased by means of adding HCI- Acidity was increased by 84 parts per million (2-30 meq acidic halide/kg isocyanate)- Results for reactivity were recorded in Table 1 following the examples.

Comparative Example 4

A sample was prepared substantially as in Example 1 except that acidity was increased by means of adding HCI- Acidity was increased by 234 parts per million (6-42 meq acidic halide/kg isocyanate)- Results for reactivity were recorded in Table 1 following the examples.

Comparative Example 5

A sample was prepared substantially as in Example 1 except that acidity was not increased. Results for reactivity were recorded in Table 1 following the examples.

Example 6 A sample of PMDI having an initial viscosity of 153 centi poise at 25° C and an initial acidity of 140 parts per million as HCI (3.84 meq halide/kg isocyanate) was admixed with sufficient phosphoryl chloride to increase acidity by 84 parts per million (2.30 meq acidic halide/kg isocyanate). This sample was stored at 50° C for twelve weeks. Viscosity was measured periodically and recorded in Table 2 following the examples.

Example 7

A sample was prepared substantially as in Example 6 except that sufficient phosphoryl chloride was added to increase acidity by 234 parts per million(6.42 meq acidic halide/kg isocyanate). Results for viscosity were recorded in Table 2 following the examples.

Comparative Example 8

A sample was prepared substantially as in Example 6 except that acidity was increased by means of adding HCI. Acidity was increased by 84 parts per million (2.30 meq acidic halide/kg isocyanate). Results for viscosity were recorded in Table 2 following the examples.

Comparative Example 9

A sample was prepared substantially as in Example 6 except that acidity was increased by means of adding HCI. Acidity was increased by 234 parts per million (6.42 meq acidic halide/kg isocyanate). Results for viscosity were recorded in Table 2 following the examples.

Comparative Example 10

A sample was prepared substantially as in Example 1 except that acidity was not increased. Results for viscosity were recorded in Table 2 which follows.

Table 1

^fc not an example of the present invention.

Table 2

"not an example of the present invention.