Oligomeric acid stabilizer

Abstract

An oligomeric di-monophosphate acid stabilizer conforming to the structure of formula (II); where n is where n is ≥ 3. As well as the process for making such an acid stabilizer and polyurethane prepolymers containing the acid stabilizer.

Description

[0001] OLIGOMERIC ACID STABILIZER

[0002] FIELD OF THE INVENTION

[0003] The present invention relates generally to an oligomeric acid stabilizer as well as the process for making and using such acid stabilizer in the stabilization of polyurethane prepolymers.

[0004] BACKGROUND OF THE INVENTION

[0005] A polyurethane prepolymer is a versatile chemical compound well known in the art commonly used in the production of polyurethane materials. It is formed through the reaction of polyols, such as polyester or polyether polyols, with isocyanates, typically aromatic or aliphatic diisocyanates. The reaction creates a highly reactive intermediate product known as a prepolymer. Polyurethane prepolymers possess a low molecular weight and a high number of isocyanate groups, making them suitable for subsequent polymerization reactions. These prepolymers serve as the building blocks for a wide range of polyurethane applications, including foams, adhesives, coatings, elastomers, and sealants. Their customizable nature enables the tailoring of physical properties, such as flexibility, hardness, and chemical resistance, allowing for the formulation of specific polyurethane products to suit diverse industrial and consumer needs. Polyurethane prepolymers often require the addition of an acid stabilizer to ensure their stability and performance. Acid stabilizers play an important role in preventing premature curing or gelling of the prepolymer during storage and transportation. These stabilizers function by neutralizing residual base present in the prepolymer formulation, which could otherwise catalyze the unwanted reactions leading to premature crosslinking. By inhibiting base catalyzed reactions, the stabilizer extends the shelf life of polyurethane prepolymers, allowing for convenient handling, storage, and subsequent processing. Additionally, acid stabilizers help maintain the desired reactivity of the prepolymer during the manufacturing process, ensuring consistent product quality and performance. Overall, the incorporation of an acid stabilizer is vital to ensure the long-term stability and usability of polyurethane prepolymers, enabling efficient production of high-quality polyurethane products. Prepolymers that do not contain such stabilizers are prone to the premature reaction of the isocyanate groups. This can result in prepolymers that have poor heat stability, produce cured products with inferior properties and in extreme cases can result in the gelation of a reactor during production.

[0006] Polyurethane prepolymers are typically stabilized with acid chlorides, such as benzoyl chloride, or phosphoric acid. Both of these prepolymer stabilizers have deficiencies, especially in the production of low free (LF) monomer prepolymers, i.e., a prepolymer having less than 1 wt%, less than 0.5 wt%, less than 0.1 wt % or less than 0.05 wt % free isocyanate monomer. LF prepolymers are produced for example using a continuous distillation process to remove diisocyanate monomers from prepolymers at elevated temperature and low pressure. Benzoyl chloride cannot be used as a stabilizer for the production of LF prepolymers, due to its high volatility. Phosphoric acid is less volatile than benzoyl chloride. Nevertheless, significant amounts of acid are lost during the distillation process. This results in the formation of an acidic distillate and vacuum exhaust streams that are corrosive to metal equipment. Another disadvantage of phosphoric acid is that it catalyzes the reversion of Poly(tetramethylene ether) glycol (PTMEG) prepolymers to tetrahydrofuran (THF) monomer. THF is volatile and flammable and its presence in prepolymers is highly undesirable.

[0007] European Patent application, EP0856551A1, cites the use of poly phosphoric acid as an acid stabilizer for polyurethane prepolymers. However there remains a number of problems associated with the use of polyphosphoric acid as a stabilizer for prepolymers and especially as a stabilizer for the production of LF prepolymers. Polyphosphoric acid is a mixture of phosphoric acid and a relatively small amount of phosphoric acid condensation product. There are two common grades of polyphosphoric acid. The grade of polyphosphoric acid with the 105 % assay (on a phosphoric acid basis) contains about assay (on a phosphoric acid basis) contains about 13.1 % of the condensation product.

[0008] Some of the phosphoric acid from the polyphosphoric will be removed from the prepolymer during the distillation of free monomer from the prepolymer in the process of preparing LF prepolymer. This results in the formation of an acidic distillate and vacuum exhaust streams that are corrosive to metal equipment. Polyphosphoric acid, like phosphoric acid, catalyzes the reversion of PTMEG prepolymers to THF. The presence of THF in prepolymers is problematic for the reasons mentioned above and since it can cause the prepolymer to have a solvent odor and can cause the formation of microbubbles in cast elastomer parts.

[0009] At the time of the invention a need therefore existed to find an acid stabilizer suitable for use prepolymers including the use in LF prepolymer production processes.

[0010] It has been surprisingly found that polypropane ether di-monophosphate (herein referred to as “oligomeric di-monophosphate” or “ODMP”) is a di-mono phosphoric ester end-capped polyether polymer. It is a nonvolatile, high molecular weight acid stabilizer suitable for use in the production of LF prepolymers and cannot enter the distillate or vacuum exhaust streams. LF PTMEG prepolymers made using ODMP as an acid stabilizer have good storage stability and have a much lower propensity for THF formation than those made using phosphoric acid.

[0011] BRIEF SUMMARY OF THE INVENTION

[0012] There is broadly contemplated, in accordance with at least one presently preferred embodiment of the present invention, an oligomeric acid stabilizer conforming to the structure of formula (I): where n is greater than or equal to 3, and Rl, R2, R3 and R4 are independently selected from the group consisting of

[0013] Hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, aryl, aralkyl, and alkaryl, but where at least one of Rl, R2, R3 and R4 is Hydrogen.

[0014] There is also broadly contemplated, in accordance with at least one presently preferred embodiment of the present invention, an oligomeric di-monophosphate acid stabilizer (ODMP) conforming to the structure of formula (II):

[0015] (ii), where n is greater than or equal to 3, or any salt forms thereof.

[0016] In addition, in another embodiment there is a polyurethane prepolymer composition comprising an oligomeric di-monophosphate acid stabilizer conforming to the structure of formula (II).

[0017] In another embodiment of the present invention there is a process for stabilizing a polyurethane prepolymer formed of the reaction of an isocyanate and polyol components, comprising the steps of adding ODMP to the isocyanate component prior to its reaction with the polyol component.

[0018] In another embodiment of the present invention there is a process for stabilizing a polyurethane prepolymer formed of the reaction of an isocyanate and polyol components, comprising the steps of adding ODMP to the polyol component prior to its reaction with the diisocyanate polyol component.

[0019] In another embodiment of the present invention there is a process for stabilizing a polyurethane prepolymer formed of the reaction of an isocyanate and polyol components, comprising the steps of adding ODMP to the prepolymer after the reaction of the diisocyanate and polyol components are completed.

[0020] BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0021] Figure 1 provides a graph of THF stability of a MDI prepolymer as a function of acid type at a fixed level. Figure 2 provides a graph of THF stability of a TDI prepolymer as a function of acid type and level.

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] ODMP can be made using readily available starting materials and by standard reaction equipment and processes within the knowledge of those skilled in the art of chemical synthesis. In one approach, ODMP can be made from polypropane ether didichlorophosphate (“ODCP”). Broadly stated, ODCP is itself formed by reacting polypropane ether glycol with excess phosphorous oxychloride. The excess phosphorous oxychloride is distilled from the reaction product under vacuum to give high purity ODCP. The polypropane ether di-dichlorophosphate is added to excess water dissolved in acetone. Thereafter the acetone and excess water is distilled off yielding the polypropane ether di-dichlorophosphate. The synthesis can be represented by the following reactions (A) and (B): The polypropane ether di -monophosphate has a number average molecular weight of 300 to 10,000 and preferably 350 to 5,000.

[0024] The polypropane ether glycol (or polypropanediol) of the invention can be obtained commercially. It may be selected from the 250, 500, 1000, 2000 or the 2700 MW grades and have a repeating number, n, that can range from 3 to 48. In an embodiment from 5 to 25 and in another embodiment of about 9.

[0025] The ODMP acid stabilizer of the invention is useful in the stabilization of polyurethane prepolymers and particularly LF polyurethane prepolymers. More broadly it may also be noted that polypropane ether di-dichlorophosphate is a versatile reactive intermediate. As an example, it can be reacted with 0.01 to 3.99 equivalents of an alcohol or alcohols (optionally with a solvent) to make after hydrolysis a material that contains both acid and ester groups. The alcohols can be chosen from alkyl, alkenyl, alkynyl, cycloalkyl, aryl, aralkyl, and alkaryl. The ester groups can be used to modify the solubility properties of the acidic compound. The intermediate can also be reacted with active hydrogen compounds, including (but not limited to) acids, alcohols, amines, phenols or thiols to make fully or partially substituted materials that may be useful in the stabilization of polyurethane prepolymers and particularly LF polyurethane prepolymers. ODMP according to the structure of formula (II) is a particular species of the genus represented by the structure of formula (I) above. The synthesis can be represented by the following reactions (C) and (D): (C)

[0026] A polyurethane prepolymer composition comprising an oligomeric di- monophosphate acid stabilizer conforming to the structure of formula (II) above, can be prepared through the reaction of readily available starting materials and by standard reaction equipment and processes within the knowledge of those skilled in the art of prepolymer synthesis.

[0027] ODMP can be added to the prepolymer during manufacture or afterward. In one embodiment, a prepolymer is stabilized with ODMP which is added to isocyanate monomer prior to the prepolymer forming reaction thereof with polyol and prior to any subsequent distillation in the case of LF prepolymer production for example.

[0028] It can be appreciated that there is no particular restriction on the prepolymer, or mixture of prepolymers, that can be used in the present invention, nor is there a particular restriction on the polyols or diisocyanate monomers or polyols that can be used in the preparation of the prepolymer. The diisocyanate component for preparation of the prepolymer may include aromatic and aliphatic diisocyanate monomers or polymers. Aromatic diisocyanates are well known and are widely used in the preparation of polyurethanes. Aromatic diisocyanate monomers useful in the practice of the present invention include 2,4'- and 4,4'-methylene-bis-(phenyl isocyanate) (MDI), 2,4- and 2,6-toluene diisocyanate (TDI), para-phenylene diisocyanate (PPDI), tolidene diisocyanate (TODI), naphthalene- 1,5- diisocyanate (NDI), diphenyl 4,4'-diisocyanate, and mixtures thereof. Aliphatic diisocyanate monomers include 1,6-hexane diisocyanate (HDI), dibenzyl 4,4'- diisocyanate, isophorone diisocyanate (IPDI), 1,3- and 1,4-xylene diisocyanates, 1,6- hexamethylene diisocyanate, 1,3'- and l,4'-cyclohexyl diisocyanate (CHDI), the three geometric isomers of 1,1 '-methylene-bis(4-isocyanatocyclohexane) (H12MDI), and mixtures thereof.

[0029] In one embodiment, the diisocyanate monomers are aromatic diisocyanates namely monomeric MDI. With respect to the polyol component of the prepolymer various polyols can be employed. Polyols include compounds having more than one hydroxyl, amino, or thiol functional groups or combinations thereof. The formation of such polyols is well known in the art. Such polyols may contain ester, ether, amide, aliphatic, acrylic, polylactic acid, polyglycolic acid, metal, metalloid and other functionalities as also known to those skilled in the art. In various embodiments, the polyol may comprise one or more of polyether polyols, polyester polyols, polybutadiene polyols, polycarbonate polyols, polycaprolactone polyols, polyacrylate polyols, polylactic acid, polyglycolic acid, and polyols containing blocks of different types of esters, ethers, amides, and / or other repeating groups or segments, and mixtures or combinations thereof. In some embodiments the polyols have a molecular weight ranging from 100 to 10,000, in one embodiment, from 225 to 6,000, and in another embodiment from 250 to 3,000.

[0030] In this context, molecular weight refers to the number average molecular weight in Daltons which as used herein is calculated via Hydroxyl number measurement by ASTM E222-94 method.

[0031] In various embodiments, the polyol may comprise glycols, triols, and / or higher average hydroxyl functionality and having molecular weights ranging, for example, from 50 to 600, and in another embodiment from 55 to 300, and in another from 60 to 200. Such polyols may include in one embodiment lower molecular weight polyols. The average hydroxyl functionality can range from about 2 to 8, preferably about 2 to 3 and more preferably from about 2 to 2.5. Such glycols or triols may include, for example, ethylene glycol, isomers of propylene glycol, isomers of butane diol, isomers of pentanediol, isomers of hexanediol, trimethylolpropane, pentaerythritol, poly(tetramethylene ether) glycol, poly(trimethylene ether) glycol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, and mixtures thereof.

[0032] In another embodiment of the invention the polyols useful for making prepolymer are compounds of the polyester polyol type. These polyols are prepared by conventional methods using a combination of diacids and diols that are known in the art, for example succinate, adipate or other esters. The esters may also be prepared by the condensation reaction of hydroxyl carboxylic acids, for example lactic or glycolic acids. Esters may also be prepared from acyl chlorides. Illustrative of the polyester polyols are poly(adipate) glycol, poly(hexamethylene adipate) glycol, polyethylene adipate) glycol (PEAG), poly(diethylene adipate) glycol, poly(ethylene / propylene adipate) glycol, poly(trimethylolpropane / hexamethylene adipate) glycol, poly(ethylene / butylene adipate) glycol, poly(butylene adipate) glycol, poly(hexamethylene / neopentyl adipate) glycol, poly(butylene / hexamethylene adipate) glycol (PBHAG), poly(neopentyl adipate) glycol, and mixtures, copolymers (including block and random copolymers) and terpolymers thereof.

[0033] In one embodiment the use of poly(tetramethylene ether) glycol (PTMEG) polyol with an aromatic diisocyanate as the isocyanate component. LF PTMEG based prepolymers made with the inventive ODMP acid stabilizer show improved storage stability and have a much lower propensity for THF formation than those conventionally made using phosphoric acid.

[0034] Although the preferred embodiments of the present invention are described herein, it is to be understood that the invention is not limited to that precise embodiment, and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention. As used in this description and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the content clearly dictates otherwise. The following examples are illustrative of a practice of the invention, but are not meant as limiting the scope of the invention.

[0035] EXAMPLES

[0036] Synthesis of polypropane ether di-dichlorophosphate

[0037] 276.1 g (1.801 mol, 5.402 eq.) of phosphoryl chloride was charged to a 500 mL round bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, addition funnel, gas inlet and outlet adaptors. A steady flow of nitrogen gas was passed through the reactor to a bubbler that contained mineral oil. The outlet of the bubbler was connected to a water trap to remove acid from the outlet gas stream.

[0038] 100.0 g of polypropanediol (MW = 555.4 g / mol, 0.1801 mol, 0.3601 eq.) was charged to the addition funnel. The polyol was added over a 50 minute period without external heating. The batch temperature reached 40°C at the end of the addition period and external heating was applied. The batch was heated to 50°C and after 4 hours HC1 gas generation had stopped, which indicated the reaction was complete. The batch was cooled to room temperature and stored overnight under a nitrogen pad.

[0039] The 500 mb round bottom flask was equipped for vacuum distillation. The phosphoryl chloride was collected in a 500 mL vacuum trap that was placed in a Dewar flask and cooled with a dry ice acetone mixture. The pressure and temperature were adjusted such that steady boiling occurred in the flask. The contents of the flask were maintained at 50°C for 4 hours and 2.5 mbar. The product was a clear light straw colored liquid and was stored under nitrogen. The distillate was a clear colorless liquid and was stored under nitrogen.

[0040] The structure of the product was confirmed to be polypropane ether didichlorophosphate by 1H, 13C, and 31P{ 1H} NMR. The distillate was essentially pure phosphoryl chloride by 1H and 31P{1H} NMR spectroscopy.

[0041] Synthesis of polypropane ether di-monophosphate

[0042] 100 g of acetone and 52.1 g (2.891 mol, 2.891 eq.) of water was charged to a 250 mL round bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, addition funnel, gas inlet and outlet adaptors. A steady flow of nitrogen gas was passed through the reactor to a bubbler that contained mineral oil. The outlet of the bubbler was connected to a water trap to remove acid from the outlet gas stream.

[0043] 114.0 g of polypropane ether di-dichlorophosphate (MW = 789.1 g / mol, 197.29 g / eq, 0.144 mol, 0.578 eq.) was charged to the addition funnel. Polypropane ether di- dichlorophosphate was added dropwise over a 40 minute period without external heating. The reaction was vigorous and the batch temperature reached 56°C at the end of the addition period. Within 10 minutes, HC1 gas generation had stopped, which indicated the reaction was complete. The 500 mL round bottom was equipped for vacuum distillation. Acetone and water were collected in a 500 mL vacuum trap that was placed in a Dewar flask and cooled with a dry ice acetone mixture. The pressure and temperature were adjusted such that steady boiling occurred in the flask. The distillation continued for five hours until boiling was absent (2.9 mbar / 50°C). The product contained 200 ppm water and was a clear light straw colored viscous liquid.

[0044] The structure of the product was confirmed to be polypropane ether dimonophosphate by 1H, 13C, and 31P{1H} NMR spectroscopy.

[0045] Attempted synthesis of polypropylene ether di-dichlorophosphate 240.4 g (1.568 mol, 4.704 eq.) of phosphoryl chloride was charged to a 500 mL round bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, addition funnel, gas inlet and outlet adaptors. A steady flow of nitrogen gas was passed through the reactor to a bubbler that contained mineral oil. The outlet of the bubbler was connected to a water trap to remove acid from the outlet gas stream.

[0046] 159.6 g of polypropylene ether glycol (MW = 1018 g / mol, 0.1568 mol, 0.3136 eq.) was charged to the addition funnel. 25 mL of the polyol was charged to the reactor. There was no change in temperature and no HC1 gas evolution. The mixture was heated and at 58°C and slow HC1 gas evolution was noticed. The mixture was heated to 80°C and the remainder of the polyol was charged. Within 30 minutes the solution became black and the temperature started to rapidly increase. The reaction was aborted. The results show that side reactions were competing with phosphorylation.

[0047] Attempted synthesis of polytetramethylene ether di -dichlorophosphate

[0048] 277.7 g (1.811 mol, 5.433 eq.) of phosphoryl chloride was charged to a 500 mL round bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, addition funnel, gas inlet and outlet adaptors. A steady flow of nitrogen gas was passed through the reactor to a bubbler that contained mineral oil. The outlet of the bubbler was connected to a water trap to remove acid from the outlet gas stream.

[0049] 122.3 g of polytetramethylene ether glycol (MW = 675 g / mol, 0.1812 mol, 0.3624 eq.) was charged to the addition funnel. The polyol was added drop wise to the reactor and little reaction occurred. The mixture was heated to 70°C and a slow generation of HC1 gas was observed. A gel like material formed and the mixture became a slurry. The reaction was aborted. The results show that side reactions were competing with phosphorylation.

[0050] Attempted synthesis of polyethylene ether di -dichlorophosphate

[0051] 287.1 g (1.872 mol, 5.617 eq.) of phosphoryl chloride was charged to a 500 mL round bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, addition funnel, gas inlet and outlet adaptors. A steady flow of nitrogen gas was passed through the reactor to a bubbler that contained mineral oil. The outlet of the bubbler was connected to a water trap to remove acid from the outlet gas stream.

[0052] 112.9 g of polyethylene ether glycol (MW = 603 g / mol, 0.1872 mol, 0.3745 eq.) was charged to the addition funnel. 20 mL of the polyol was added dropwise to the reactor and a mild exothermic reaction occurred. The remainder of the polyol was added dropwise in 10 mL amounts and the mixture was heated in 5°C increments to 60°C. A steady evolution of HC1 gas was noted. After 5 hours the reaction appeared complete and the reaction mixture developed a dark color. The batch was cooled to room temperature and stirred overnight under a nitrogen pad. The 500 mL round bottom flask was equipped for vacuum distillation. The phosphoryl chloride was collected in a 500 mL vacuum trap that was placed in a Dewar flask and was cooled with a dry ice acetone mixture. The pressure and temperature were adjusted such that steady boiling occurred in the flask. The contents of the flask were maintained at 50°C for 4 hours and 2.9 mbar. The product was a black liquid that contained small black particles and was stored under nitrogen. The distillated was a clear colorless liquid and was stored under nitrogen.

[0053] 1H, 13C, and 3 IP { 1H} NMR spectroscopy of the soluble portion of the product showed that significant degradation had occurred. The average PEG chain length decreased from an average of 13.67 monomer units in the starting polyol to 2.26 monomer units in the reaction products. The end groups of the reaction product contained about 54 % of the phosphorylated end groups and about 46 % of -OCH2CH2C1 end groups. 1H, 13C, and 31P{ 1H} NMR spectroscopy showed that the distillate was a mixture of phosphoryl chloride (75 %) and 1,4-di oxane (25 %). The presence of 1,4- dioxane in the distillate shows that the polyethylene glycol chain was degraded in the acidic reaction media.

[0054] Prepolymer Distillation

[0055] In an ideal prepolymer distillation process all of the acid in the crude prepolymer would remain in the stripped prepolymer. In real prepolymer distillation processes acid losses can occur through the vacuum exhaust, the distillate stream, chemical reaction and the physical splashing of the residue into the distillate stream.

[0056] The loss of acid during distillation is problematic for both product quality and equipment maintenance:

[0057] Industrial prepolymer distillation processes are operated continuously.

[0058] The distilled diisocyanate monomer is recycled and used to make subsequent batches of prepolymer.

[0059] In the case of low molecular weight volatile acids, significant amounts of acid are removed from the residue and co-distill with the monomer.

[0060] In the case of low molecular weight volatile acids, the acid level in the distillate and the crude will increase with each subsequent batch of prepolymer. High levels of acid in prepolymers are known to cause color problems.

[0061] In the case of low molecular weight volatile acids, the acidity of the distilled prepolymer will be a function of the distillation conditions (feed rate, vacuum level and temperature). This can cause variations in prepolymer reactivity when processing the material with curatives into polyurethane products. In the case of low molecular weight volatile acids, the prepolymers produced at the start of a production campaign will be relatively depleted in acid. As the production campaign continues, the acid level in the distilled monomer will increase. Holding all other variables constant, the acid level in the prepolymer will slowly increase during a production campaign. This can cause batch to batch variations in prepolymer reactivity when processing the material with curatives into polyurethane products.

[0062] Highly acidic distillate and exhaust streams can cause corrosion of metal equipment, such as pipes, pumps and vessels.

[0063] Acronyms and comments - MDI = 4, 4’-methylene diphenyl diisocyanate

[0064] PTMEG = poly(tetramethylene ether) glycol

[0065] OAC (oligomeric acid chloride) is a di-acid chloride end capped polyether polymer. It was synthesized in house from isophthaloyl di-chloride and PTMEG-650.

[0066] ODMP (oligomeric di -monophosphate) is a di-mono phosphoric ester end capped poly ether polymer. It was synthesized in house starting from phosphoryl chloride and poly(propanediol). 85 % Phosphoric acid is a low molecular weight (98 g / mol) acid and contains 15

[0067] % water.

[0068] 115 % phosphoric acid is primarily phosphoric acid and is also known as poly(phosphoric acid). It contains about 87 % phosphoric acid. It also contains pyrophosphoric acid, a lesser amount of triphosphoric acid and so on. The 115 % is based on the calculated amount of phosphoric acid (before dehydration).

[0069] EHAP is a low molecular acid. It is a mixture containing about 42 % 2- ethylhexyl phosphate (mono-EHAP) (MW = 210 g / mol) and 55 % bis-2-ethylhexyl phosphate (MW = 322 g / mol). - Crude prepolymer is the material that is fed into the distillation process and is rich in diisocyanate monomer.

[0070] Stripped prepolymer or residue is the non-volatile portion of the crude prepolymer. The diisocyanate monomer level is less than 1.0 % , preferably less than 0.5 % and most preferably less than 0.1 %. - Distillate is the volatile portion of the crude prepolymer. It is mostly diisocyanate monomer, but includes other components, including volatile acids such as benzoyl chloride , EHAP and phosphoric acid. Examples 1 to 8 show the advantages of using ODMP in the prepolymer distillation process. ODMP is the only acid stabilizer that has both high acid retention and produces prepolymers with good THF stability.

[0071] Example 1 - Inventive: Distillation Stability of ODMP MDI (5739 g, 45.86 eq) was charged to a 12.0 L round bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, gas inlet and outlet adaptors. A steady flow of nitrogen was passed through the reactor during the synthesis. ODMP (3.12 g, 3.53 peq / g on residue) was charged to the MDI and mixed for 15 minutes. This was followed by PTMEG-1000 (3261 g, 6.552 eq). The PTMEG-1000 was added such that the batch temperature did not exceed 75°C. The reaction was run for 2 hours at 70±5°C and stored at 50°C overnight in a forced convection oven before distillation. The unreacted MDI was removed by wiped film distillation. The data is summarized in Table 1.

[0072] Example 2 - Comparative: Distillation Stability of EHAP MDI (4000 g, 31.97 eq) was charged to a 12.0 L round bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, gas inlet and outlet adaptors. A steady flow of nitrogen was passed through the reactor during the synthesis. EHAP (5.89 g, 3.50 peq / g on residue) was charged to the MDI and mixed for 15 minutes. This was followed by PTMEG-1000 (2245 g, 4.529 eq). The PTMEG-1000 was added such that the batch temperature did not exceed 75°C. The reaction was run for 2 hours at 70±5°C and stored at 50°C overnight in a forced convection oven before distillation. The unreacted MDI was removed by wiped film distillation. The data is summarized in Table 1.

[0073] Example 3 - Comparative: Distillation Stability of Phosphoric Acid

[0074] MDI (5765 g, 46.07 eq) was charged to a 12.0 L round bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, gas inlet and outlet adaptors. A steady flow of nitrogen was passed through the reactor during the synthesis. 85 % Phosphoric Acid (1.95 g, 3.51 peq / g on residue) was charged to the MDI and mixed for 15 minutes. This was followed by PTMEG-1000 (3235 g, 6.528 eq). The PTMEG- 1000 was added such that the batch temperature did not exceed 75 °C. The reaction was run for 2 hours at 70±5°C and stored at 50°C overnight in a forced convection oven before distillation. The unreacted MDI was removed by wiped film distillation. The data is summarized in Table 1.

[0075] In Examples 1 to 3 the wipe film evaporator was operated using a jacket temperature of 160°C, the feed rate was between 1 to 2 L / hr and the vacuum was operated between 0.01 mbar to 1.0 mbar. Table 1. Acid Stability in the LF monomer Distillation Process

[0076] The results in Table 1 shows the following:

[0077] 44 % of EHAP is lost in the distillation process.

[0078] 33 % of phosphoric acid is lost in the distillation process.

[0079] In contrast, only about 5 % of the ODMP is lost in the distillation process. ODMP is a polymer with an average molecular weight of 700 g / mol. It is not possible to distill ODMP from the prepolymer, due to its high molecular weight.

[0080] All the prepolymers listed in Table 1 have good NCO stability.

[0081] Prepolymers produced with EHAP and ODMP acid stabilizers have a low levels of THE

[0082] The prepolymer produced with phosphoric acid has a high level of THF.

[0083] Examples one through three demonstrate the advantages of using ODMP as a an acid stabilizer in the low free monomer distillation process.

[0084] Example 4 - Comparative: Distillation Stability in the Absence of Added Acid Low acid TDI (4554 g, 52.30 eq) was charged to a 12.0 L round bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, gas inlet and outlet adaptors. A steady flow of nitrogen was passed through the reactor during the synthesis. No acid was added to the monomer. PTMEG / Diol (4446 g, 17.43 eq) was added such that the batch temperature did not exceed 75°C. The reaction was run for 2 hours at 70±5°C and stored at 50°C overnight in a forced convection oven. The unreacted TDI was removed by wiped film distillation. The data is summarized in Table 2. Example 5 - Comparative: Distillation Stability of Benzoyl Chloride

[0085] High acid TDI (4554 g, 52.30 eq) was charged to a 12.0 L round bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, gas inlet and outlet adaptors. A steady flow of nitrogen was passed through the reactor during the synthesis. The monomer contained PhCOCl (2.46 g, 539 ppm, 2.38 peq / g acid as HC1 on residue). PTMEG / Diol (4446 g, 17.43 eq) was added such that the batch temperature did not exceed 75°C. The reaction was run for 2 hours at 70±5°C and stored at 50°C overnight in a forced convection oven. The unreacted TDI was removed by wiped film distillation. The data is summarized in Table 2. Example 6 - Comparative: Distillation Stability of OAC

[0086] Low acid TDI (4554 g, 52.30 eq) was charged to a 12.0 L round bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, gas inlet and outlet adaptors. A steady flow of nitrogen was passed through the reactor during the synthesis. Oligomeric acid chloride (1.57 g, 214 ppm, 0.434 peq / g acid as HC1 on residue) was added to the TDI. PTMEG / Diol (4446 g, 17.43 eq) was added such that the batch temperature did not exceed 75°C. The reaction was run for 2 hours at 70±5°C and stored at 50°C overnight in a forced convection oven. The unreacted TDI was removed by wiped film distillation. The data is summarized in Table 2. In Examples 4 to 6 the wipe film evaporator was operated using a jacket temperature of 140°C, the feed rate was between 1 to 2 L / hr and the vacuum was operated between 0.01 mbar to 1.0 mbar.

[0087] Table 2, Acid Stability in the LF TDI Process

[0088] The results in Table 2 shows the following:

[0089] The crude prepolymer made without acid fails the 24 hrs. / 100°C NCO stability test.

[0090] The crude prepolymer made with benzoyl chloride or oligomeric acid chloride have good NCO stability.

[0091] The distilled prepolymer made without added acid fails the 24 hrs. / 100°C NCO stability test.

[0092] The distilled prepolymer made with benzoyl chloride fails the 24 hrs. / 100°C NCO stability test. The data suggests that the benzoyl chloride is being co-distilled with TDI monomer and / or reacting with the prepolymer.

[0093] The distilled prepolymer made with oligomeric acid chloride fails the 24 hrs. / 100°C NCO stability test. The molecular weight of the oligomeric acid chloride is too high to co-distill with the TDI monomer. The data suggests that the oligomeric acid chloride is reacting with the prepolymer. Example 7 - THF and NCO Stability as Function of Acid Type

[0094] MDI (3151 g, 25.19 eq) was charged to a 12.0 L round bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, gas inlet and outlet adaptors. A steady flow of nitrogen was passed through the reactor during the synthesis. PTMEG-2000 (5847 g, 5.755 eq) was added such that the batch temperature did not exceed 85°C. The reaction was run for 2 hours at 80±5°C and stored at 50°C overnight in a forced convection oven. The NCO of the prepolymer was 8.30 %. The material was then blended with the acids listed below. Samples were charged to 33 mL borosilicate vials and heat aged for 24 hours at 100°C. The data is summarized in Table 3 and shown in Figure 1.

[0095] Table 3. THF and NCO Stability as a Function of Acid Type

[0096] Table 3 shows the following:

[0097] All the prepolymers had good NCO stability.

[0098] The prepolymers containing 85 % H3PO4 and 115 % H3PO4 had poor THF stability. - The prepolymers containing ODMP, EHAP and benzoyl chloride had good THF stability.

[0099] Example 8 - THF and NCO Stability as a Function of Acid Type and

[0100] Concentration

[0101] Low acid TDI (3893 g, 44.70 eq) was charged to a 12.0 L round bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, gas inlet and outlet adaptors. A steady flow of nitrogen was passed through the reactor during the synthesis. PTMEG / Diol (5522 g, 22.13 eq) was added such that the batch temperature did not exceed 75°C. The reaction was run for 2 hours at 70±5°C and stored at 50°C overnight in a forced convection oven. The NCO was 9.34 %. The material was then blended with ODMP, H3PO4 and EHAP at different levels. Samples were charged to 33 mL borosilicate vials and heat aged for 24 hours at 100°C. The samples with no added acid gelled when heat aged for 24 hours at 100°C. The data is summarized in Tables 4 to 6 and shown in Figure 2.

[0102] Table 4. THF and NCO Stability as a Function of ODMP Level

[0103] Table 5. THF and NCO Stability as a Function of H3PO4 Level

[0104]

[0105] Table 6. THF and NCO Stability as a Function of EHAP Level

[0106] High NCO TDI PTMEG prepolymers are most prone to acid catalyzed reversion to THF. The results in Tables 4 to 6 shows the following:

[0107] All the prepolymers have good NCO stability.

[0108] The prepolymer without added acid had poor NCO stability.

[0109] The prepolymer containing HjPO^ad poor THF stability.

[0110] The prepolymers containing ODMP and EHAP had similar and good THF Stability.

Claims

What is claimed is:

1. An acid stabilizer composition comprising an oligomeric di-monophosphate conforming to the structure of formula (II):where n is > 3 or any salt forms thereof.

2. The composition accoridng to Claim 1, wherein the oligomeric di-monophosphate has a number average molecular weight of 300 to 10,000.

3. A polyurethane prepolymer composition comprising an acid stabilizer composition having an oligomeric di-monophosphate conforming to the structure of formula (II):(II), where n is > 3, or any salt forms thereof.

4. The composition accoridng to Claim 3, wherein the acid stablizer is present in a an amount of 5 to 1000 ppm relative to the total weight of the prepolymer.

5. A process for stabilizing a polyurethane prepolymer, comprising the steps of adding the acid stabilizer to the diisocyanate monomer before crude synthesis, or adding the acid stabilizer to the polyol before crude synthesis or adding the acid stabilizer to the crude prepolymer after synthesis or any combination of the three.

6. An acid stabilizer composition comprising an oligomeric di-monophosphate conforming to the structure of formula (I):where n is greater than or equal to 3, and where Rl, R2, R3 and R4 are independently selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, aryl, aralkyl, and alkaryl, but where at least one of Rl, R2, R3 and R4 is hydrogen.

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