Oligomeric acid stabilizers

Abstract

An oligomeric di(monophosphate) acid stabilizer conforming to the structure of formula (II) wherein n is n > 3. And a method for producing the acid stabilizer and a polyurethane prepolymer containing the acid stabilizer.

Description

Technical Field

[0001] This invention generally relates to an oligomer acid stabilizer and a method for preparing and using such an acid stabilizer to stabilize polyurethane prepolymers. Background Technology

[0002] Polyurethane prepolymers are versatile compounds well-known in the art and commonly used in the production of polyurethane materials. They are formed by the reaction of polyols (such as polyester polyols or polyether polyols) with isocyanates (typically aromatic or aliphatic diisocyanates). This reaction produces highly reactive intermediates known as prepolymers. Polyurethane prepolymers have low molecular weights and a large number of isocyanate groups, making them suitable for subsequent polymerization reactions. These prepolymers serve as building blocks for a wide range of polyurethane applications, including foams, adhesives, coatings, elastomers, and sealants. Their customizable properties allow for the tuning of physical properties (such as flexibility, stiffness, and chemical resistance), enabling the formulation of specific polyurethane products to meet diverse industrial and consumer needs.

[0003] Polyurethane prepolymers typically require the addition of acid stabilizers to ensure their stability and performance. Acid stabilizers play a crucial role in preventing premature curing or gelation of prepolymers during storage and transportation. These stabilizers function by neutralizing residual alkali present in the prepolymer formulation, which would otherwise catalyze undesirable reactions leading to premature crosslinking. By inhibiting alkali-catalyzed reactions, the stabilizer extends the shelf life of the polyurethane prepolymer, making it easier to handle, store, and subsequently process. Additionally, acid stabilizers help maintain the required reactivity of the prepolymer during the manufacturing process, ensuring consistent product quality and performance. Overall, the addition of acid stabilizers is essential for ensuring the long-term stability and usability of polyurethane prepolymers, enabling the efficient production of high-quality polyurethane products. Prepolymers without such stabilizers are prone to premature reaction of the isocyanate groups. This can result in poor thermal stability of the prepolymer, producing cured products with inferior properties, and in extreme cases, may cause gelation of the reactor during production.

[0004] Polyurethane prepolymers are typically stabilized using acyl chlorides (such as benzoyl chloride) or phosphoric acid. Both of these prepolymer stabilizers have drawbacks, especially in the production of low-free (LF) monomer prepolymers (i.e., prepolymers with less than 1 wt%, less than 0.5 wt%, less than 0.1 wt%, or less than 0.05 wt% free isocyanate monomers). For example, LF prepolymers are produced by removing diisocyanate monomers from the prepolymer using a continuous distillation process at high temperature and low pressure. Benzoyl chloride is unsuitable as a stabilizer for the production of LF prepolymers due to its high volatility. Phosphoric acid is less volatile than benzoyl chloride. However, a significant amount of acid is lost during the distillation process. This results in the formation of acidic distillates and vacuum exhaust streams that are corrosive to metal equipment. Another disadvantage of phosphoric acid is that it catalyzes the depolymerization of poly(tetramethylene ether) glycol (PTMEG) prepolymers to form tetrahydrofuran (THF) monomers. THF is volatile and flammable, and its presence in the prepolymer is highly undesirable.

[0005] European patent application EP0856551A1 references the use of polyphosphoric acid as an acid stabilizer for polyurethane prepolymers. However, several issues remain associated with the use of polyphosphoric acid as a stabilizer for prepolymers, particularly for the production of LF prepolymers. Polyphosphoric acid is a mixture of phosphoric acid with a relatively small amount of phosphoric acid condensation product. There are two common grades of polyphosphoric acid. The grade with a 105% determination (based on phosphoric acid) contains approximately 4.8% condensation product. The grade with a 115% determination (based on phosphoric acid) contains approximately 13.1% condensation product.

[0006] In the process of preparing LF prepolymers, some phosphoric acid from polyphosphoric acid is removed from the prepolymer during the distillation of free monomers. This results in the formation of acidic distillates and vacuum exhaust streams that are corrosive to metal equipment. Like phosphoric acid, polyphosphoric acid catalyzes the depolymerization of PTMEG prepolymers to form THF. For the reasons mentioned above, and because THF can cause a solvent odor in the prepolymer and may lead to microbubble formation in cast elastomer parts, the presence of THF in the prepolymer is problematic.

[0007] Therefore, at the time of this invention, there was a need to find an acid stabilizer suitable for prepolymers (including those used in the LF prepolymer production process).

[0008] Surprisingly, polypropane ether di-monophosphate (referred to herein as "oligomeric di-monophosphate" or "ODMP") was found to be a di-monophosphate-terminated polyether polymer. It is a non-volatile, high-molecular-weight acid stabilizer suitable for the production of LF prepolymers and does not enter the distillate or vacuum exhaust stream. LF PTMEG prepolymers prepared using ODMP as an acid stabilizer exhibited better storage stability and a significantly lower tendency to form THF compared to prepolymers prepared using phosphoric acid. Summary of the Invention

[0009] According to at least one currently preferred embodiment of the present invention, an oligomeric acid stabilizer conforming to formula (I) is widely envisioned:

[0010] Where n is greater than or equal to 3, and

[0011] R1, R2, R3, and R4 are independently selected from the group consisting of: hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, aryl, aralkyl, and alkylaryl, but at least one of R1, R2, R3, and R4 is hydrogen.

[0012] According to at least one currently preferred embodiment of the invention, oligomeric di-monophosphate acid stabilizers (ODMPs) conforming to formula (II) are also broadly envisioned: , Where n is greater than or equal to 3, or any salt form thereof.

[0013] In another embodiment, there is a polyurethane prepolymer composition comprising an oligomeric diazo (monophosphate) stabilizer conforming to the structure of formula (II).

[0014] In another embodiment of the invention, there is a method for stabilizing a polyurethane prepolymer formed by the reaction of an isocyanate and a polyol component, comprising the step of adding ODMP to the isocyanate component before the isocyanate component reacts with the polyol component.

[0015] In another embodiment of the invention, there is a method for stabilizing a polyurethane prepolymer formed by the reaction of isocyanate and polyol components, comprising the step of adding ODMP to the polyol component before the polyol component reacts with the diisocyanate polyol component.

[0016] In another embodiment of the invention, there is a method for stabilizing a polyurethane prepolymer formed by the reaction of isocyanate and polyol components, comprising the step of adding ODMP to the prepolymer after the reaction of the diisocyanate and polyol components is completed. Attached Figure Description

[0017] Figure 1 A graph showing the variation of THF stability of MDI prepolymers with acid type (at a fixed level) is provided.

[0018] Figure 2 A graph showing the variation of THF stability of TDI prepolymers with acid type and level is provided. Detailed Implementation

[0019] ODMP can be prepared using readily available starting materials and through standard reaction equipment and processes known to those skilled in the art of chemical synthesis. In one method, ODMP can be prepared from polypropane ether di-dichlorophosphate (“ODCP”). In general, ODCP itself is formed by reacting polypropane ether diol with excess phosphorus oxychloride. The excess phosphorus oxychloride is distilled off from the reaction product under vacuum to obtain high-purity ODCP. Polypropane ether di-dichlorophosphate is added to excess water dissolved in acetone. Subsequently, the acetone and excess water are distilled off to obtain polypropane ether di-dichlorophosphate. The synthesis can be represented by the following reactions (A) and (B):

[0020] The number average molecular weight of the polypropane ether di(monophosphate) is from 300 to 10,000, and preferably from 350 to 5,000.

[0021] The polypropylene ether glycol (or polypropylene glycol) of the present invention is commercially available. It can be selected from MW grades of 250, 500, 1000, 2000 or 2700, and the repetition number n can range from 3 to 48. In one embodiment, it is 5 to 25, and in another embodiment, it is about 9.

[0022] The ODMP acid stabilizer of the present invention is used to stabilize polyurethane prepolymers, particularly LF polyurethane prepolymers.

[0023] More broadly, it can also be noted that polypropylene ether di(dichlorophosphate) is a versatile reaction intermediate. As an example, it can react with one or more alcohols (optionally, in the case of a solvent) in amounts ranging from 0.01 to 3.99 equivalents to obtain a material containing both acid and ester groups after hydrolysis. The alcohols can be selected from alkyl alcohols, alkenyl alcohols, alkynyl alcohols, cycloalkyl alcohols, aryl alcohols, aralkyl alcohols, and alkylaryl alcohols. The ester groups can be used to modify the solubility properties of acidic compounds. The intermediate can also react with active hydrogen compounds, including (but not limited to) acids, alcohols, amines, phenols, or thiols, to prepare materials that can be used to stabilize polyurethane prepolymers, particularly LF polyurethane prepolymers, in a fully or partially substituted manner. ODMP according to the structure of formula (II) is a specific species of a genus represented by the structure of formula (I) above. The synthesis can be represented by the following reactions (C) and (D):

[0024] Polyurethane prepolymer compositions comprising oligomeric diazo (monophosphate) acid stabilizers conforming to formula (II) above can be prepared by reacting readily available starting materials and by standard reaction equipment and processes known to those skilled in the art of prepolymer synthesis.

[0025] ODMP can be added to the prepolymer during or after manufacturing. In one embodiment, ODMP is used to stabilize the prepolymer; ODMP is added to the isocyanate monomer before the prepolymer formation reaction of the isocyanate monomer with the polyol, and before any subsequent distillation (e.g., in the case of LF prepolymer production).

[0026] It is understood that there are no particular limitations on the prepolymers or mixtures of prepolymers that can be used in this invention; nor are there any particular limitations on the polyols or diisocyanate monomers or polyols that can be used to prepare the prepolymers.

[0027] The diisocyanate component used to prepare the prepolymer may include aromatic and aliphatic diisocyanate monomers or polymers. Aromatic diisocyanates are well known and widely used in the preparation of polyurethanes. Aromatic diisocyanate monomers that can be used in the practice of this invention include 2,4'- and 4,4'-methylene bis(phenyl isocyanate) (MDI), 2,4- and 2,6-toluene diisocyanate (TDI), terephthalic diisocyanate (PPDI), bitoluidine diisocyanate (TODI), naphthalene-1,5-diisocyanate (NDI), 4,4'-diphenyl diisocyanate, and mixtures thereof. Aliphatic diisocyanate monomers include three geometric isomers of 1,6-hexamethylene diisocyanate (HDI), 4,4'-dibenzyl diisocyanate, isophorone diisocyanate (IPDI), 1,3- and 1,4-xylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,3'- and 1,4'-cyclohexyl diisocyanate (CHDI), and 1,1'-methylenebis(4-isocyanate cyclohexane) (H12MDI), as well as mixtures thereof.

[0028] In one embodiment, the diisocyanate monomer is an aromatic diisocyanate, namely, monomer MDI.

[0029] For the polyol component of the prepolymer, various polyols can be used. Polyols include compounds having more than one hydroxyl, amino, or thiol functional group or a combination thereof. The formation of such polyols is well known in the art. Such polyols may contain esters, ethers, amides, aliphatic, acrylic, polylactic acid, polyglycolic acid, metals, metalloids, and other functional groups known to those skilled in the art. In several embodiments, the polyol may include one or more of the following: 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 molecular weight of the polyol ranges 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, as used herein, which is calculated by determining the hydroxyl value using the ASTM E222-94 method.

[0031] In several embodiments, the polyol may include diols, triols, and / or polyols with higher average hydroxyl functionality, having a molecular weight range, for example, from 50 to 600, and in another embodiment from 55 to 300, and in yet another from 60 to 200. In one embodiment, such polyols may include polyols with lower molecular weights. The average hydroxyl functionality may range from about 2 to 8, preferably from about 2 to 3, and more preferably from about 2 to 2.5. Such diols or triols may include, for example, ethylene glycol, propylene glycol isomers, butanediol isomers, pentanediol isomers, hexanediol isomers, 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 polyol used to prepare the prepolymer is a polyester polyol type compound. These polyols are prepared by conventional methods using combinations of dicarboxylic acids and diols known in the art, such as succinates, adipates, or other esters. Esters can also be prepared by the condensation reaction of hydroxycarboxylic acids (e.g., lactic acid or glycolic acid). Esters can also be prepared from acyl chlorides. Exemplary polyester polyols are poly(adipate) glycol, poly(hexyl adipate) glycol, poly(ethylene adipate) glycol (PEAG), poly(diethylene adipate) glycol, poly(ethylene adipate / propylene adipate) glycol, poly(trimethylolpropane / hexamethylene adipate) glycol, poly(ethylene adipate / butyl adipate) glycol, poly(butyl adipate) glycol, poly(hexyl adipate / neoprene adipate) glycol, poly(butylene adipate / hexyl adipate) glycol (PBHAG), poly(neoprene adipate) glycol, and mixtures thereof, copolymers (including block copolymers and random copolymers), and terpolymers thereof.

[0033] In one embodiment, poly(tetramethylene ether) glycol (PTMEG) polyol and aromatic diisocyanate are used as isocyanate components. Compared with prepolymers conventionally prepared using phosphoric acid, the LF PTMEG-based prepolymer prepared using the ODMP acid stabilizer of the present invention exhibits improved storage stability and a much lower tendency to form THF.

[0034] While preferred embodiments of the invention have been described herein, it should be understood that the invention is not limited to these precise embodiments, and that various other changes and modifications can be made to it by those skilled in the art without departing from the scope or spirit of the invention. As used in this specification and the appended claims, unless expressly specified otherwise, the singular forms “a,” “an,” and “described” include plural references. The following examples illustrate the practice of the invention but are not intended to limit its scope.

[0035] Example

[0036] Synthesis of polypropane ether di(dichlorophosphate)

[0037] Add 276.1 g (1.801 mol, 5.402 equivalents) of phosphoryl chloride to a 500 mL round-bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, feeding funnel, and gas inlet and outlet adapters. A steady stream of nitrogen is passed through the reactor into a bubbler filled with mineral oil. The bubbler outlet is connected to a water trap to remove acid from the outlet stream. Add 100.0 g of polypropylene glycol (MW = 555.4 g / mol, 0.1801 mol, 0.3601 equivalents) to the feeding funnel. Add the polyol over a 50-minute period without external heating. At the end of the addition period, the batch temperature reaches 40°C, and external heating is applied. The batch is heated to 50°C, and after 4 hours, HCl gas production ceases, indicating the reaction is complete. Cool the batch to room temperature and store it overnight under nitrogen protection.

[0038] A 500 mL round-bottom flask was assembled for vacuum distillation. Phosphoryl chloride was collected in a 500 mL vacuum trap placed in a Dewar flask and cooled using a mixture of dry ice and acetone. Pressure and temperature were adjusted to achieve stable boiling within the flask. The contents of the flask were maintained at 50°C and 2.5 mbar for 4 hours. 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.

[0039] The structure of the product was confirmed to be polypropylene ether di(dichlorophosphate) by 1H, 13C, and 31P {1H} NMR. 1H and 31P {1H} NMR spectral analysis showed that the distillate was essentially pure phosphoryl chloride.

[0040] Synthesis of polypropane ether di(monophosphate)

[0041] 100 g of acetone and 52.1 g (2.891 mol, 2.891 equivalent) of water were added to a 250 mL round-bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, feeding funnel, gas inlet and outlet adapters. A steady stream of nitrogen was passed through the reactor into a bubbler containing mineral oil. The outlet of the bubbler was connected to a water trap to remove acid from the outlet stream. 114.0 g of polypropylene ether di(dichlorophosphate) (MW = 789.1 g / mol, 197.29 g / equivalent, 0.144 mol, 0.578 equivalent) was added to the feeding funnel. Polypropylene 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. HCl gas production ceased within 10 minutes, indicating that the reaction was complete.

[0042] A 500 mL round-bottom flask was assembled for vacuum distillation. Acetone and water were collected in a 500 mL vacuum trap placed in a Dewar flask and cooled using a mixture of dry ice and acetone. The pressure and temperature were adjusted to achieve a stable boil within the flask. Distillation continued for five hours until it ceased to boil (2.9 mbar / 50°C). The product contained 200 ppm of water and was a clear, light straw-colored viscous liquid.

[0043] The structure of the product was confirmed by 1H, 13C and 31P {1H} NMR spectroscopy analysis to be polypropylene ether di(monophosphate).

[0044] Attempted Synthesis of Polypropylene Ether Di-Dichlorophosphate

[0045] 240.4 g (1.568 mol, 4.704 equivalents) of phosphoryl chloride was charged into a 500 mL round-bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, feeding funnel, gas inlet and outlet adapters. A steady stream of nitrogen was passed through the reactor into a bubbler containing mineral oil. The outlet of the bubbler was connected to a water trap to remove acid from the outlet stream. 159.6 g of polypropylene ether glycol (MW = 1018 g / mol, 0.1568 mol, 0.3136 equivalents) was charged into the feeding funnel. 25 mL of polyol was added to the reactor. The temperature did not change, and no HCl gas was released. The mixture was heated, and at 58°C, a slow release of HCl gas was observed. The mixture was heated to 80°C, and the remaining polyol was added. Within 30 minutes, the solution turned black, and the temperature began to rise rapidly. The reaction was stopped. The results indicate that the side reactions compete with phosphorylation.

[0046] Attempted Synthesis of Polytetramethylene Ether Di(Dichlorophosphate)

[0047] 277.7 g (1.811 mol, 5.433 equivalents) of phosphoryl chloride was charged into a 500 mL round-bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, feeding funnel, gas inlet and outlet adapters. A steady stream of nitrogen was passed through the reactor into a bubbler containing mineral oil. The outlet of the bubbler was connected to a water trap to remove acid from the outlet stream. 122.3 g of polytetramethylene ether glycol (MW = 675 g / mol, 0.1812 mol, 0.3624 equivalents) was charged into the feeding funnel. The polyol was added dropwise to the reactor, but almost no reaction occurred. The mixture was heated to 70°C, and slow generation of HCl gas was observed. A gel-like substance formed, and the mixture became a slurry. The reaction was terminated. The results indicate that a side reaction competes with phosphorylation.

[0048] An Attempted Synthesis of Polyethylene Ether Di-Dichlorophosphate

[0049] 287.1 g (1.872 mol, 5.617 equivalent) of phosphoryl chloride was charged into a 500 mL round-bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, feeding funnel, gas inlet and outlet adapters. A steady stream of nitrogen was passed through the reactor into a bubbler containing mineral oil. The outlet of the bubbler was connected to a water trap to remove acid from the outlet stream. 112.9 g of polyethylene ether glycol (MW = 603 g / mol, 0.1872 mol, 0.3745 equivalent) was charged into the feeding funnel. 20 mL of polyol was added dropwise to the reactor, and a mild exothermic reaction occurred. The remaining polyol was added dropwise in 10 mL increments, and the mixture was heated to 60°C in 5°C increments. A steady release of HCl gas was observed. After 5 hours, the reaction appeared to be complete, and the reaction mixture turned dark. The batch was cooled to room temperature and stirred overnight under nitrogen protection.

[0050] A 500 mL round-bottom flask was assembled for vacuum distillation. Phosphoryl chloride was collected in a 500 mL vacuum trap placed in a Dewar flask and cooled using a mixture of dry ice and acetone. Pressure and temperature were adjusted to achieve stable boiling within the flask. The contents of the flask were maintained at 50°C and 2.9 mbar for 4 hours. The product was a black liquid containing small black particles and was stored under nitrogen. The distillate was a colorless, transparent liquid and was stored under nitrogen.

[0051] ¹H, ¹³C, and ³¹P {¹H} NMR spectroscopy analysis of the soluble fraction of the product indicated significant degradation. The average length of the PEG chain decreased from an average of 13.67 monomer units in the starting polyol to 2.26 monomer units in the reaction product. The end groups of the reaction product contained approximately 54% phosphorylated end groups and approximately 46% -OCH₂CH₂Cl end groups. ¹H, ¹³C, and ³¹P {¹H} NMR spectroscopy analysis showed that the distillate was a mixture of phosphoryl chloride (75%) and 1,4-dioxane (25%). The presence of 1,4-dioxane in the distillate indicates that the polyethylene glycol chains degraded in the acidic reaction medium.

[0052] Prepolymer distillation

[0053] In an ideal prepolymer distillation process, all acids in the crude prepolymer are retained in the stripped prepolymer. In practical prepolymer distillation processes, acid loss can occur through vacuum degassing, distillate stream, chemical reactions, and physical splashing of residues into the distillate stream.

[0054] Acid loss during distillation can cause problems for both product quality and equipment maintenance. - Industrial prepolymer distillation processes are continuous operations.

[0055] - The diisocyanate monomers distilled off were recovered and used to prepare subsequent batches of prepolymers.

[0056] - For low molecular weight volatile acids, a large amount of the acid is removed from the residue and co-distilled with the monomer.

[0057] - For low molecular weight volatile acids, the acid levels in the distillate and crude product increase with each subsequent batch of prepolymer. High levels of acid in the prepolymer are known to cause color problems.

[0058] - For low molecular weight volatile acids, the acidity of the distilled prepolymer will be a function of the distillation conditions (feed rate, vacuum, and temperature). This will cause changes in the reactivity of the prepolymer when the material is processed into a polyurethane product using a curing agent.

[0059] For low molecular weight volatile acids, the acid content in the prepolymer produced at the beginning of the production cycle will be relatively low. As the production cycle continues, the acid level in the distilled monomers will increase. All other things being equal, the acid level in the prepolymer will increase slowly during the production cycle. This can lead to batch-to-batch variations in the reactivity of the prepolymer when the material is processed into a polyurethane product using a curing agent.

[0060] Highly acidic distillates and exhaust gases can corrode metal equipment such as pipes, pumps, and containers.

[0061] Abbreviations and Notes

[0062] - MDI = 4,4'-methylene diphenyl diisocyanate

[0063] - PTMEG = Poly(tetramethylene ether)diol

[0064] - OAC (oligoacyl chloride) is a diacyl chloride-terminated polyether polymer. It is synthesized internally (in a house, in a laboratory) from isophthaloyl chloride and PTMEG-650.

[0065] - ODMP (oligomeric di(monophosphate)) is a di(monophosphate)-terminated polyether polymer. It is synthesized internally from phosphoryl chloride and poly(propylene glycol).

[0066] - 85% phosphoric acid is a low molecular weight (98 g / mol) acid and contains 15% water.

[0067] - 115% phosphoric acid is primarily phosphoric acid and is also known as poly(phosphoric acid). It contains approximately 87% phosphoric acid. It also contains pyrophosphate, smaller amounts of triphosphate, etc. 115% is based on the amount of phosphoric acid (before dehydration).

[0068] - EHAP is a low molecular weight acid. It is a mixture containing approximately 42% 2-ethylhexyl phosphate (mono-EHAP) (MW = 210 g / mol) and 55% bis(2-ethylhexyl) phosphate (MW = 322 g / mol).

[0069] - The crude prepolymer is the material fed into the distillation process and is rich in diisocyanate monomers.

[0070] - The prepolymer or residue after stripping 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%.

[0071] - The distillate is the volatile fraction of the crude prepolymer. It is primarily a diisocyanate monomer, but also contains other components, including volatile acids such as benzoyl chloride, EHAP, and phosphoric acid.

[0072] Examples 1 through 8 demonstrate the advantages of using ODMP in the prepolymer distillation process. ODMP is the only acid stabilizer that possesses both high acid retention and the ability to produce prepolymers with good THF stability.

[0073] Example 1 - This Invention: Distillation Stability of ODMP

[0074] MDI (5739 g, 45.86 equivalents) was loaded into a 12.0 L round-bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, and gas inlet and outlet adapters. A stable nitrogen stream was passed through the reactor during the synthesis. ODMP (3.12 g, 3.53 μe / g on residue) was added to the MDI and mixed for 15 min. This was followed by PTMEG-1000 (3261 g, 6.552 equivalents). PTMEG-1000 was added to ensure the batch temperature did not exceed 75°C. The reaction was carried out at 70 ± 5°C for 2 h, and then stored overnight in a forced convection oven at 50°C before distillation. Unreacted MDI was removed by scraped-film distillation. Data are summarized in Table 1.

[0075] Example 2 - Comparative Example: Distillation Stability of EHAP

[0076] MDI (4000 g, 31.97 equivalents) was loaded into a 12.0 L round-bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, and gas inlet and outlet adapters. A stable nitrogen stream was passed through the reactor during the synthesis. EHAP (5.89 g, 3.50 microequivalents / g on residue) was added to the MDI and mixed for 15 minutes. This was followed by PTMEG-1000 (2245 g, 4.529 equivalents). PTMEG-1000 was added to ensure the batch temperature did not exceed 75°C. The reaction was carried out at 70 ± 5°C for 2 hours, and then stored overnight in a forced convection oven at 50°C before distillation. Unreacted MDI was removed by scraped-film distillation. Data are summarized in Table 1.

[0077] Example 3 - Comparative Example: Distillation Stability of Phosphoric Acid

[0078] MDI (5765 g, 46.07 equivalents) was loaded into a 12.0 L round-bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, and gas inlet and outlet adapters. A stable nitrogen stream was passed through the reactor during the synthesis. 85% phosphoric acid (1.95 g, 3.51 microequivalents / g on residue) was added to the MDI and mixed for 15 minutes. This was followed by PTMEG-1000 (3235 g, 6.528 equivalents). PTMEG-1000 was added to ensure the batch temperature did not exceed 75°C. The reaction was carried out at 70 ± 5°C for 2 hours, and then stored overnight in a forced convection oven at 50°C before distillation. Unreacted MDI was removed by scraped-film distillation. Data are summarized in Table 1.

[0079] In Examples 1 to 3, the wiped-film evaporator was operated with a jacket temperature of 160°C, a feed rate of 1 to 2 liters per hour, and a vacuum between 0.01 mbar and 1.0 mbar.

[0080] Table 1. Acid stability in LF monomer distillation process

[0081] The results in Table 1 are shown below: - 44% of EHAP was lost during the distillation process.

[0082] - 33% of phosphoric acid was lost during the distillation process.

[0083] In contrast, only about 5% of ODMP is lost during distillation. ODMP is a polymer with an average molecular weight of 700 g / mol. Due to its high molecular weight, ODMP cannot be distilled from the prepolymer.

[0084] - All prepolymers listed in Table 1 have good NCO stability.

[0085] - Prepolymers produced using EHAP and ODMP acid stabilizers have low levels of THF.

[0086] - Prepolymers produced using phosphoric acid have high levels of THF.

[0087] Examples 1 to 3 demonstrate the advantages of using ODMP as an acid stabilizer in low free monomer distillation processes.

[0088] Example 4 - Comparative Example: Distillation Stability Without Acid Addition

[0089] Low-acid TDI (4554 g, 52.30 equivalents) was loaded into a 12.0 L round-bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, and gas inlet and outlet adapters. A stable nitrogen stream was passed through the reactor during synthesis. No acid was added to the monomer. PTMEG / diol (4446 g, 17.43 equivalents) was added to keep the batch temperature below 75°C. The reaction was carried out at 70 ± 5°C for 2 hours, followed by overnight storage in a forced convection oven at 50°C. Unreacted TDI was removed by scraped-film distillation. Data are summarized in Table 2.

[0090] Example 5 - Comparative Example: Distillation Stability of Benzoyl Chloride

[0091] High-acid TDI (4554 g, 52.30 equivalents) was loaded into a 12.0 L round-bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, and gas inlet and outlet adapters. A stable nitrogen stream was passed through the reactor during synthesis. The monomer contained PhCOCl (2.46 g, 539 ppm, 2.38 μeq / g acid as HCl on residue). PTMEG / diol (4446 g, 17.43 equivalents) was added to keep the batch temperature below 75°C. The reaction was carried out at 70 ± 5°C for 2 hours, followed by overnight storage at 50°C in a forced convection oven. Unreacted TDI was removed by scraped-film distillation. Data are summarized in Table 2.

[0092] Example 6 - Comparative Example: Distillation Stability of OAC

[0093] Low-acid TDI (4554 g, 52.30 equivalents) was loaded into a 12.0 L round-bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, and gas inlet and outlet adapters. A stable nitrogen stream was passed through the reactor during synthesis. Oligoacryl chloride (1.57 g, 214 ppm, 0.434 μe / g acid residue, as HCl) was added to the TDI. PTMEG / diol (4446 g, 17.43 equivalents) was added to ensure the batch temperature did not exceed 75°C. The reaction was carried out at 70 ± 5°C for 2 hours, followed by overnight storage at 50°C in a forced convection oven. Unreacted TDI was removed by scraped-film distillation. Data are summarized in Table 2.

[0094] In Examples 4 to 6, the wiped-film evaporator was operated with a jacket temperature of 140°C, a feed rate of 1 L / h to 2 L / h, and a vacuum between 0.01 mbar and 1.0 mbar.

[0095] Table 2. Acid stability in the LF TDI process

[0096] The results in Table 2 are shown below: - The crude prepolymer prepared without acid failed the 24-hour / 100°C NCO stability test.

[0097] - Crude prepolymers prepared with benzoyl chloride or oligoacryl chloride have good NCO stability.

[0098] - The distilled prepolymer prepared without the addition of acid failed the 24-hour / 100°C NCO stability test.

[0099] - The distilled prepolymer prepared with benzoyl chloride failed the 24-hour / 100°C NCO stability test. The data indicate that benzoyl chloride was co-distilled with TDI monomer and / or reacted with the prepolymer.

[0100] - The distilled prepolymer prepared using oligoacrylamide chloride failed the 24-hour / 100°C NCO stability test. The molecular weight of the oligoacrylamide chloride is too high to co-distill with the TDI monomer. The data indicate that the oligoacrylamide chloride reacts with the prepolymer.

[0101] Example 7 - Variation of THF and NCO stability with acid type

[0102] MDI (3151 g, 25.19 equivalents) was loaded into a 12.0 L round-bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, and gas inlet and outlet adapters. A stable nitrogen stream was passed through the reactor during synthesis. PTMEG-2000 (5847 g, 5.755 equivalents) was added to ensure the batch temperature did not exceed 85°C. The reaction was carried out at 80 ± 5°C for 2 hours, followed by overnight storage in a forced convection oven at 50°C. The NCO content of the prepolymer was 8.30%. The material was then blended with the acids listed below. Samples were loaded into 33 mL borosilicate glass vials and heat-aged at 100°C for 24 hours. Data are summarized in Table 3 and are as follows: Figure 1 As shown.

[0103] Table 3. Stability of THF and NCO varies with acid type

[0104] Table 3 is shown below: - All prepolymers exhibit good NCO stability.

[0105] Prepolymers containing 85% H3PO4 and 115% H3PO4 have poor THF stability.

[0106] - Prepolymers containing ODMP, EHAP and benzoyl chloride exhibit good THF stability.

[0107] Example 8 - Variation of THF and NCO stability with acid type and concentration

[0108] Low-acid TDI (3893 g, 44.70 equivalents) was loaded into a 12.0 L round-bottom flask equipped with a mechanical stirrer, electric heating mantle, thermocouple, and gas inlet and outlet adapters. A stable nitrogen stream was passed through the reactor during synthesis. PTMEG / diol (5522 g, 22.13 equivalents) was added, ensuring the batch temperature did not exceed 75°C. The reaction was carried out at 70 ± 5°C for 2 hours, followed by overnight storage in a forced convection oven at 50°C. The NCO content was 9.34%. The material was then blended with different levels of ODMP, H3PO4, and EHAP. Samples were loaded into 33 mL borosilicate glass vials and heat-aged at 100°C for 24 hours. Samples without added acid gelled upon heat aging at 100°C for 24 hours. Data are summarized in Tables 4 to 6, and as shown in Tables 4 to 6. Figure 2 As shown.

[0109] Table 4. Variation of THF and NCO stability with ODMP level

[0110] Table 5. Stability of THF and NCO with H3PO4 level

[0111] Table 6. Variation of THF and NCO stability with EHAP level

[0112] High-NCO TDI PTMEG prepolymers are most susceptible to acid-catalyzed depolymerization to form THF. The results are shown in Tables 4 to 6 below. - All prepolymers exhibit good NCO stability.

[0113] - Prepolymers without added acid have poor NCO stability.

[0114] - Prepolymers containing H3PO4 have poor THF stability.

[0115] - Prepolymers containing ODMP and EHAP have similar and good THF stability.

Claims

1. An acid stabilizer composition comprising an oligomeric di(monophosphate) conforming to formula (II): ， Where n≥3, or any salt form thereof.

2. The composition according to claim 1, wherein the number-average molecular weight of the oligomeric di(monophosphate) is from 300 to 10,000.

3. A polyurethane prepolymer composition comprising an acid stabilizer composition having an oligomeric di(monophosphate) having a structure conforming to formula (II): ， Where n≥3, Or any salt form thereof.

4. The composition according to claim 3, wherein the amount of acid stabilizer present is from 5 ppm to 1000 ppm relative to the total weight of the prepolymer.

5. A method for stabilizing polyurethane prepolymers, comprising the following steps: An acid stabilizer is added to the diisocyanate monomer prior to crude synthesis; or an acid stabilizer is added to the polyol prior to crude synthesis. Alternatively, an acid stabilizer may be added to the crude prepolymer after synthesis; or any combination of the three.

6. An acid stabilizer composition comprising an oligomeric di(monophosphate) conforming to formula (I): Where n is greater than or equal to 3, and R1, R2, R3 and R4 are independently selected from the group consisting of: hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, aryl, aralkyl and alkylaryl, but at least one of R1, R2, R3 and R4 is hydrogen.

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