Isocyanate-terminated prepolymer

Abstract

Embodiments of the present disclosure are directed towards an isocyanate-terminated prepolymer that is the reaction product of a poly(propoxylated diol) and a stochiometric excess, relative the poly(propoxylated diol), of an isocyanate having at least 70 wt.% monomeric methylene diphenyl diisocyanate. The poly(propoxylated diol) is formed in the presence of a modified multi-metal cyanide alkoxylation catalyst and has an average hydroxyl number of 5 to 140 mg KOH / g. The isocyanate-terminated prepolymer has an NCO group content of from 2 wt.% to 20 wt.% based on a total weight of the isocyanate-terminated prepolymer.

Description

Isocyanate-Terminated PrepolymerField of Disclosure

[0001] Embodiments of the present disclosure are directed to prepolymers and in particular isocyanate-terminated prepolymers for use in polyurethane compositions.Background

[0002] Poly(propoxylated diols) are a type of polyether polyol containing multiple ether linkages. They are formed by the addition of propylene oxide to a diol initiator, which results in a polymer having a repeating structure of propylene oxide units end capped by hydroxyl groups. In industry, poly(propoxylated diols) are important isocyanate-reactive components in polyurethane compositions used in coatings, adhesives, sealants, and elastomer applications.

[0003] On a commercial scale, poly(propoxylated diols) are formed using anionic potassium hydroxide (KOH) catalysts, which assist in the ring-opening polymerization process. KOH catalysts, while well-known to produce propylene oxide diols, need to be removed via intensive finishing processes prior to using the poly(propoxylated diols) in the final polyurethane composition. Additionally, monols are formed in varying amounts, leading to a lower overall polyol functionality and average molecular weight. This leads to increased cost and bottlenecked production volumes, but also causes deleterious effects in the performance of isocyanate-terminated prepolymers, which are a primary outlet for such poly(propoxylated diols).

[0004] As is known in the art, isocyanate-terminated prepolymers find wide usage as single component, moisture-curing species that have great applicability in coatings and binders, and as primary active reagents in adhesives and sealants. Isocyanate-terminated prepolymers should have sufficiently workable viscosities, reasonable open times, and desirable kinetics in achieving a tack-free cure. They should also provide suitable mechanical properties such as tear and tensile strength, as well as elongation.

[0005] Therefore, there is a need for improved production of poly(propoxylated diols) for use in forming isocyanate-terminated prepolymers that can be used in preparing polyurethane compositions.Summary

[0006] The present disclosure provides for isocyanate-terminated prepolymers made from poly(propoxylated diols) of various molecular weights produced by the action of a modified multi-metal cyanide alkoxylation catalyst, where the moisture-cured products formed using the isocyanate-terminated prepolymers often show enhanced mechanical performance versus those prepolymers made with commercially available, KOH-produced poly(propoxylated diols).

[0007] Specifically, there is provided an isocyanate-terminated prepolymer that includes a reaction product of a poly(propoxylated diol) formed in the presence of a modified multi-metal cyanide alkoxylation catalyst of Formula I:M1b[M2(CN)r(X1)t]c[M5(X2)6]d • nM4xA1y • pM3wA2zFormula I where M1and M4each represent a metal ion independently selected from Zn2+, Fe2+, Co2+, Ni2+, Mo4+, Mo6+, Al3+, V4+, V5+, Sr2+, W4+, W6+, Mn2+, Sn2+, Sn4+, Pb2+, Cu2+, La3+, and Cr3+; M2and M5each represent a metal ion independently selected from Fe3+, Fe2+, Co3+, Co2+, Cr2+, Cr3+, Mn2+, Mn3+, Ir3+, Ni2+, Rh3+, Ru2+, V4+, V5+, Ni2+, Pd2+, and Pt2+; M3represents at least one magnesium, Group 3 - Group 15 metal, or lanthanide series metal or semi-metal ion; X1represents a group other than cyanide that coordinates with the M2ion; X2represents a group other than cyanide that coordinates with the M5ion; A1represents a halide, nitrate, sulfate, carbonate, cyanide, oxalate, thiocyanate, isocyanate, perchlorate, isothiocyanate, an alkanesulfonate, an arylenesulfonate, trifluoromethanesulfonate, or a Ci-4 carboxylate; A2represents least one alkoxide, aryloxy, carboxylate, acyl, pyrophosphate, phosphate, thiophosphate, amide, oxide, siloxide, hydride, carbamate, or hydrocarbon anion; b, c and d are each numbers that reflect an electrostatically neutral complex, provided that b and c each are greater than zero; x and y are integers that balance the charges in the metal salt M3xA1y; r is an integer from 4 to 6; t is an integer from 0 to 2; n is a number from 0 and 20; p is from 0.002 to 10; and w and z are integers that balance the charges in the metal salt M3ZA2Z, provided that w is from 1 to 4; wherein the poly(propoxylated diol) has an average hydroxyl number of 5 to 140 mg KOH / g; and a stoichiometric excess, relative the poly(propoxylated diol), of an isocyanate having at least 70 wt.% monomeric methylene diphenyl diisocyanate, where the wt.% is based on the total weight of the isocyanate; and wherein the isocyanate-terminated prepolymer has an NCO group content of from 2 wt.% to 20 wt.% based on a total weight of the isocyanate-terminated prepolymer.Detailed Description

[0008] The present disclosure provides for an isocyanate-tipped prepolymer derived from the direct reaction of a poly (propox ylated polyol) with an isocyanate. The poly(propoxylated polyol) is formed in the presence of a modified multi-metal cyanide alkoxylation (MMC) catalyst, as provided herein, which provides the resulting polyether polyol both a reduction in its unsaturation level along, an average hydroxyl number of 5 to 140 mg KOH / g and a polydispersity of less than 1.5.

[0009] In forming the isocyanate-tipped prepolymer, the isocyanate is used in a stochiometric excess, relative the poly(propoxylated diol), where the isocyanate has at least 70 wt.% monomeric methylene diphenyl diisocyanate (MDI), where the wt.% is based on the total weight of the isocyanate. The resulting isocyanate-terminated prepolymer has an NCO group content of from 2 wt.% to 20 wt.% based on a total weight of the isocyanate-terminated prepolymer. Notably, the isocyanate -terminated prepolymer excludes low molecular weight diols and does not require the use of a dispersing agent (e.g,, does not include a dispersing agent).

[0010] The isocyanate-terminated prepolymer described herein offers several advantages over conventional KOH-derived analogues. The isocyanate-terminated prepolymer can achieve higher weight average molecular weights (e.g., a value of at least 2 kDa, among others), which are unattainable through KOH-based processes. Additionally, the use of the MMC catalyst allows for isocyanate-terminated prepolymers that do not require low molecular weight chain extenders, such as those typically needed in two-part polyurethane ( K ) systems. The isocyanate-terminated prepolymers are useful in a wide variety of applications, including as one-part (IK) moisture curing systems, such as IK binders, IK sealants, or IK adhesives. The isocyanate-terminated prepolymers are also useful in 2K systems, such as 2K adhesives. As the prepolymers are designed for moisture cure, they are distinct from 2K amine-curing systems as are known.

[0011] For the embodiments, the isocyanate-terminated prepolymer includes a reaction product of a poly(propoxylated diol) formed in the presence of a modified multi-metal cyanide alkoxylation (MMC) catalyst of Formula I:M1b[M2(CN)r(X1)t]c[M5(X2)6]d • nM4xA1y • pM3wA2zFormula Iwhere: M1and M4each represent a metal ion independently selected from Zn2+, Fe2+, Co2+, Ni2+, Mo4+, Mo6+, Al3+, V4+, V5+, Sr2+, W4+, W6+, Mn2+, Sn2+, Sn4+, Pb2+, Cu2+, La3+, and Cr3+; M2and M5each represent a metal ion independently selected from Fe3+, Fe2+, Co3+, Co2+, Cr2+, Cr3+, Mn2+, Mn3+, Ir3+, Ni2+, Rh3+, Ru2+, V4+, V5+, Ni2+, Pd2+, and Pt2+; M3represents at least one magnesium, Group 3 - Group 15 metal, or lanthanide series metal or semi-metal ion; X1represents a group other than cyanide that coordinates with the M2ion; X2represents a group other than cyanide that coordinates with the M5ion; A1represents a halide, nitrate, sulfate, carbonate, cyanide, oxalate, thiocyanate, isocyanate, perchlorate, isothiocyanate, an alkanesulfonate, an arylenesulfonate, trifluoromethanesulfonate, or a Ci-4 carboxylate; A2represents least one alkoxide, aryloxy, carboxylate, acyl, pyrophosphate, phosphate, thiophosphate, amide, oxide, siloxide, hydride, carbamate, or hydrocarbon anion; b, c and d are each numbers that reflect an electrostatically neutral complex, provided that b and c each are greater than zero; x and y are integers that balance the charges in the metal salt M3xA1y; r is an integer from 4 to 6; t is an integer from 0 to 2; n is a number from 0 and 20; p is from 0.002 to 10; and w and z are integers that balance the charges in the metal salt M3ZA2Z, provided that w is from 1 to 4.

[0012] Methods of forming the MMC catalyst of Formula I can be found in U. S. Pat. Pub. 2021 / 0198425 Al, which is incorporated herein in by reference its entirety.

[0013] Preferably, for Formula I, M1and M4each represent a metal ion independently selected from Zn2+and Fe2+; M2and MBeach represent a metal ion independently selected from Fe3+, Fe2+, Co3+and Co2+; M3represents Ga'>)+, I l+, In'^+, Mn^+and Al^+; X1and X2are preferably water and / or alcohols. More preferably, for Formula I, M1and M4are each Zn2+; M2and MBare each independently selected from Co3+and Co2+; M3is most preferably Al+3.

[0014] The use of the MMC catalyst, as provided herein, allows obtaining poly(propoxylated diols) with improved retention of starter functionality. This enables enhanced mechanical properties in the article obtained from the isocyanate-terminated prepolymer after cure, versus similar KOH-derived analogues. The poly(propoxylated diol) formed in the presence of the MMC catalyst of Formula I can be prepared a process that includes combining the MMC catalyst with an alcoholic starter compound and the propylene oxide, along with other possible alkylene oxides, to form a polymerization mixture, and then subjecting thepolymerization mixture to polymerization conditions, as provided in U. S. Pat. Pub. 2021 / 0198425 Al. Briefly, the polymerization can be performed using a starter compound, as are known, which helps to provide molecular weight control and to establish the number of hydroxyl groups of the resulting poly(propoxylated diol) (e.g., 2 hydroxyl groups). The starter compound may have a hydroxyl equivalent weight less than that of the resulting poly(propoxylated diol), it may have a hydroxyl equivalent weight of from 30 to 500 or more. The equivalent weight may be up to 500. up to 250, up to 125, and / or up to 100.

[0015] Exemplary starters include, but are not limited to, ethylene glycol, propylene glycol, 1,4-butane diol, 1,6-hexane diol, 1,8-octane diol, cyclohexane dimethanol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, phenol and polyphenolic starters such as bisphenol A and alkoxylates (such as ethoxylates and / or propoxylates) of any of these that have a hydroxyl equivalent weight less than that of the product of the polymerization.

[0016] The poly (propoxy lated diol) is formed from a monomer composition comprising at least 70 wt.% propylene oxide, where the wt.% is based on the total weight of the monomer composition. For example, the poly(propoxylated diol) can be formed from a monomer composition comprising at least 70 wt.% to 100 wt.% propylene oxide, where the wt.% is based on the total weight of the monomer composition. Preferably, the poly(propoxylated diol) is formed from a monomer composition comprising at least 80 wt.% to 100 wt.% propylene oxide, where the wt.% is based on the total weight of the monomer composition. More preferably, the poly (propoxy lated diol) is formed from a monomer composition comprising at least 90 wt.% to 100 wt.% propylene oxide, where the wt.% is based on the total weight of the monomer composition. The poly(propoxylated diol) can also be formed from a monomer composition comprising 100 wt.% propylene oxide. In other words, the poly(propoxylated diol) is a homopropoxylate diol when the poly(propoxylated diol) is formed from a monomer composition comprising 100 wt.% propylene oxide.

[0017] The propylene oxide may be 1,2-propylene oxide. When wt.% values of the propylene oxide are below 100 wt.%, other suitable monomers that can be used in producing the poly(propoxylated diol) can include, but not limited to, one or more of ethylene oxide. 1,2- butane oxide, 2-methyl- 1,2- butaneoxide, 2,3-butane oxide, tetrahydrofuran, epichlorohydrin, hexane oxide, styrene oxide, divinylbenzene dioxide, a glycidyl ether such as Bisphenol A diglycidyl ether, allyl glycidyl ether, or other polymerizable oxirane.

[0018] The polymerization typically is performed at an elevated temperature. The polymerization mixture temperature may be, for example, 80 to 220 °C (c.g., from 120 to 190 °C). The polymerization reaction can be performed at superatmospheric pressures, but can be performed at atmospheric pressure or even sub-atmospheric pressures. A preferred pressure is 0 to 10 atmospheres, especially 0-6 atmospheres, gauge pressure. The polymerization preferably is performed under vacuum or under an inert atmosphere such as a nitrogen, helium or argon atmosphere.

[0019] Enough of the catalyst of Formula 1 may be used to provide a reasonable polymerization rate, but it is generally desirable to use as little of the catalyst as possible consistent with reasonable polymerization rates, as this both reduces the cost for the catalyst and, if the catalyst levels are low enough, can eliminate the need to remove catalyst residues from the product. Using lower amounts of catalysts also reduces the residual metal content of the product. The amount of catalyst may be from 1 to 5000 ppm based on the weight of the product. The amount of catalyst may be at least 2 ppm. at least 5 ppm. at least 10 ppm, at least 25 ppm, or up to 500 ppm or up to 200 ppm or up to 100 ppm, based on the weight of the product. The amount of catalyst may be selected to provide 0.25 to 20, 0.5 to 10, 0.5 to 1 or 0.5 to 2.5 parts by weight cobalt per million parts by weight of the product.

[0020] The polymerization reaction may be performed in any type of vessel that is suitable for the pressures and temperatures encountered and can be done in a continuous, semi¬ batch or batch process. In a continuous or semi-batch process, the vessel should have one or more inlets through which the propylene oxide, other monomers and starter compound and catalyst can be introduced during the reaction. In a continuous process, the reactor vessel should contain at least one outlet through which a portion of the partially polymerized reaction mixture can be withdrawn. In a semi-batch operation, propylene oxide (and optionally additional starter and catalyst) is added during the reaction, but product usually is not removed until the polymerization is completed. A tubular reactor that has multiple points for injecting the starting materials, a loop reactor, and a continuous stirred tank reactor (CTSR) are all suitable types of vessels for continuous or semi-batch operations. The reactor should be equipped with a means of providing or removing heat, so the temperature of the reaction mixture can be maintained within the required range. Suitable means include various types of jacketing for thermal fluids, various types of internal or external heaters, and the like. A cook-down step performed on continuouslywithdrawn product is conveniently conducted in a reactor that prevents significant back-mixing from occurring, Plug flow operation in a pipe or tubular reactor is a preferred manner of performing such a cook-down step.

[0021] The poly(propoxylated diol) has an average hydroxyl number of 5 to 140 mg KOH / g. Preferably, the poly(propoxylated diol) has an average hydroxyl number of 10 to 110 mg KOH / g. In addition, the poly(propoxylated diol) has a number average molecular weight of 800 to 22,000 g / mol. The hydroxyl number can be measured by any number of known techniques, such as ASTM D4274-23.

[0022] The poly(propoxylated diol) formed in the presence of the MMC catalyst has a poly dispersity of less than 1.15. Preferably, the poly(propoxylated diol) formed in the presence of the MMC catalyst has a polydispersity in a range of 1.01 to 1.15. Poly dispersity can be measured using any number of known techniques, including gel permeation chromatography, as is known in the art.

[0023] The isocyanate-terminated prepolymer is the reaction product of the poly(propoxylated diol), as provided herein, and a stochiometric excess, relative the poly(propoxylated diol), of an isocyanate having at least 70 wt.% monomeric methylene diphenyl diisocyanate (MDI), where the wt.% is based on the total weight of the isocyanate. For example, the isocyanate-terminated prepolymer is the reaction product of the poly(propoxylated diol), as provided herein, and a stochiometric excess, relative the poly(propoxylated diol), of an isocyanate having 70 wt.% to 100 wt.% MDI, where the wt.% is based on the total weight of the isocyanate. Other values for the range of the isocyanate are also possible, which can include 75 wt.% to 100 wt.% MDI; 80 wt.% to 100 wt.% MDI; 85 wt.% to 100 wt.% MDI; 90 wt.% to 100 wt.% MDI; and 95 wt.% to 100 wt.% MDI, where the wt.% is based on the total weight of the isocyanate. The monomeric MDI can include isomers of MDI (e.g., 4,4’-MDI, 2,4’-MDI and / or 2,2’ -MDI), as are known. Examples of the monomeric MDI can include pure MDI and crude MDI, where the crude MDI provides a mixture of MDI isomers. Preferably, the isocyanate is pure monomeric MDI, in particular 4,4’ -MDI. Other examples of monomeric MDI can include a 50:50 (vol:vol) isomer mix of 4,4'-MDI and 2,4'-MDI. In other words, the isocyanate comprises equal parts 4,4’ -MDI and 2,4’ -MDI. In addition, other isomer mix values of 4,4'-MDI and 2,4'-MDI are possible, including: 55:45; 60:40; 65:35; 70:30; 75:25; 80:20; 85:15; 90:10; 95:5; 45:55; and 40:60, among others, where the ratios are based on volume (e.g., vokvol).

[0024] In addition to the at least 70 wt.% monomeric MDI, it is possible for the isocyanate used in forming the isocyanate-terminated prepolymer to include up to 30 wt.% of one or more of a second isocyanate. For example, the isocyanate used in forming the isocyanate-terminated prepolymer can include from 0.01 wt.% to 30 wt.% of one or more of a second isocyanate; from 1 wt.% to 30 wt.% of one or more of a second isocyanate; from 1 wt.% to 20 wt.% of one or more of a second isocyanate; from 1 wt.% to 10 wt.% of one or more of a second isocyanate; from 5 wt.% to 30 wt.% of one or more of a second isocyanate; from 5 wt.% to 20 wt.% of one or more of a second isocyanate; from 5 wt.% to 10 wt.% of one or more of a second isocyanate; from 10 wt.% to 30 wt.% of one or more of a second isocyanate; and from 20 wt.% to 30 wt.% of one or more of a second isocyanate. For the various embodiments, the wt.% of the combination of the at least 70 wt.% monomeric MDI and the second isocyanate totals 100 wt.% of the isocyanate used in forming the isocyanate-terminated prepolymer. The average nominal functionality of the isocyanate is preferably between about 2.0 and 2.2, and is most preferably about 2.0.

[0025] Examples of the second isocyanate include one or more of other organic aliphatic and aromatic di- and poly-isocyanates, such as 2,4- and 2,6-toluene diisocyanate and mixtures thereof; modified aromatic isocyanates such as those prepared by reaction of isocyanates with themselves or with reactive low molecular weight or oligomeric species; polymeric MDI; and the various aliphatic and cycloaliphatic isocyanates such as 1,6-hexane diisocyanate, 1,8-octane diisocyanate, 2,4- and 2,6-methylcyclohexane diisocyanate, 2,2'-, 2,4'- and 4,4'-dicyclohexylmethane diisocyanate, and isophorone diisocyanate. Modified aliphatic and cycloaliphatic isocyanates may also be used.

[0026] As discussed herein, the poly(propoxylated diol), as provided herein, is reacted in a stochiometric excess, relative the poly(propoxylated diol), with the isocyanate having at least 70 wt.% monomeric MDI, where the wt.% is based on the total weight of the isocyanate. The resulting isocyanate-terminated prepolymer has an isocyanate (NCO) group content of from 2 wt.% to 20 wt.% based on a total weight of the isocyanate-terminated prepolymer. In addition, the resulting isocyanate-terminated prepolymer has an NCO group content can also have values ranging from 2 wt.% to 16 wt.% based on a total weight of the isocyanate-terminated prepolymer; from 2 wt.% to 15 wt.% based on a total weight of the isocyanate-terminated prepolymer; from 2 wt.% to 12 wt.% based on a total weight of the isocyanate-terminatedprepolymer; from 2 wt.% to 11 wt.% based on a total weight of the isocyanate-terminated prepolymer; and from 3 wt.% to 10 wt.% based on a total weight of the isocyanate-terminated prepolymer.

[0027] The isocyanate-terminated prepolymer has a weight average molecular weight of at least 2 kDa. For example, the isocyanate-terminated prepolymer has a weight average molecular weight of 2 kDa to 30 kDa. Weight average molecular weights and number average molecular weights can be measured by any number of known techniques, such as chromatographic methods, which include gel permeation chromatograph or size exclusion chromatography with the use of polystyrene styrene standards, as are known in the art.

[0028] The isocyanate-terminated prepolymer can be used in a variety of applications, including as a moisture-cured elastomer that is the reaction product of the isocyanate-terminated prepolymer, as provided herein, and water. Specifically, the isocyanate-terminated prepolymer can be useful in the areas of IK adhesives or IK sealants, where the latter includes moisture-curable sealants, or moisture curable binders. For example, the isocyanate-terminated prepolymers are useful as IK moisture-cure binders, where the isocyanate-terminated prepolymer with relatively its low NCO % content (e.g., in the range from 2 to 12 %) can cure by reaction with moisture, usually moisture in the atmosphere. The isocyanate-terminated prepolymers of the present disclosure are also useful in 2K systems, such as 2K adhesives.EXAMPLES

[0029] The Examples (EX) and Comparative Examples (CE) are formed using the materials listed in Table 1. All materials were commercially obtained and used as received unless otherwise noted. For the CE and EXX, all parts are by weight, unless otherwise noted.Table 1 - MaterialsDescription Source Polyol A Homopropoxylate diol made using KOH asalkoxylation catalyst, average OH number 110mgKOH / g.Polyol B Homopropoxylate diol made with KOH, average OHnumber 56 mgKOH / g.Polyol C Homopropoxylate diol made with KOH, average OHnumber 28 mgKOH / g.Polyol D Homopropoxylate diol made with MMC (OH# 104) - Mn= 1126 / PDI = 1.04Polyol E Homopropoxylate diol made with MMC (OH# 53) —Mn= 2066 / PDI = 1.05Polyol F Homopropoxylate diol made with MMC (OH# 27.4) - Mn= 3966 / PDI = 1.13Polyol G Homopropoxylate diol made with MMC (OH# 10.5) - Mn= 8418 / PDI = 1.14Dabco® Stannous Octoate Metal Catalyst Evonik T-9Amine 2,2-dimorpholinodiethylether (DMDEE) Sigma catalyst Aldrich Isocyanate monomeric methylene diphenyl diisocyanate (MDI) -50:50 mixture of 2,4’- and 4,4’ -isomers

[0030] Polyol D-G were prepared as follows. The modified multi-metal cyanide (MMC) catalyst was produced according to procedures reported in U. S. Pat. Pub. 2021 / 0198425.

[0031] A jacketed glass reactor (8 L volume) equipped with dual pitch blades was heated to 30 °C and purged with flowing nitrogen under atmospheric pressure. An aqueous solution of t-BuOH (2862.5 g, 17.0 wt.% t-BuOH) was loaded in the reactor. Catalox Ba (4.6 g) was then added to the reactor and allowed to stir for 10 min. Water (321.0 g) was added thereafter to rinse the funnel used for adding alumina solids. In a 1 L jar, potassium hexacyanocobaltate (93.4 g) was added to water (800 g) and sonicated until the salt was completely dissolved. This solution was added to the reactor contents and mixed at 400 RPM. An aqueous ZnCh solution (1824 g, 50 wt.% ZnCh) was added sub-surface using a peristaltic pump at the rate of 25 mL / min. Based on the availability of the spectrometer, the reactive precipitation was monitored using Raman spectroscopy. The mixture was allowed to stir at 30 °C, 400 RPM for 2 h. P4000LM (4000 MW propoxylate, 22.5 g) was added to the reactor and this mixture was stirred at 400 RPM for 1 h. The wet cake was isolated using a spin tube centrifuge (4000 RPM, 1 h) and redispersed in a stirred tank in a wash solution for 1 h at 400 RPM. This step was repeated 3x to wash the byproduct, KC1, which is detrimental to catalyst activity. The wash concentrations were:i. Wash solution 1: 3382.2 g total, 49.7 wt% t-BuOH, 0.7 wt% P4000LM ii. Wash solution 2: 2182.2 g total, 64.3 wt% t-BuOH, 1.0 wt% P4000LM iii. Wash solution 3: 1794.4 g total, 97.2 wt% t-BuOH, 0.6 wt% P4000LM

[0032] The final wet cake was dried in a vacuum oven at 0.1 torr and 50 °C to constant weight. The dried cake was then crushed using a mortar and pestle to give the fine catalyst powder (117.6 g) and sieved through 150-micron mesh using a Rotovap. The catalyst was stored in nitrogen purge box. Elemental composition is shown in Table 2.Table 1. Elemental composition of Lab Scale Modified Double Metal Cyanide Catalyst Complex by NAA.Catalyst ID Zn, Co, K, Cl, Al, Zn: Co Al: Co wt% wt% wt% wt% wt%Modified MetalCatalyst24.4 10.5 0.22 2.6 1.6 2.09 0.34

[0033] The d50of the MMC powder is 7.4 mm (Beckmann-Coulter particle size analyzer) and the surface are as determined by N2physisorption (Micromeritics ASAP instrument) is 19.7 m2 / g.Table 3. Prepolymer formulations with target and measured %NCO and prepolymer viscosity at 25 °C.OH CE CE CE CE CE E CEF EX EX EX EX EX EX EX EXReagentnr A B C D 1 2 3 4 5 6 7 8 Polyol A 110 X XPolyol B 56 X XPolyol C 28 X XPolyol D 104 X XPolyol E 53 X XPolyol F 27.4 X XPolyol G 10.5 X X Isocyanate to target 3% 10% 3% 10% 3% 10% 3% 10% 3% 10 3% 10% 3% 10% %NCO %Measured %NCO 3.1 10.0 3.00 9.97 3.08 10.0 2.97 10.0 3.00 9.8 3.0 10.0 3.00 9.901 3 8 0 5 0 0Viscosity (Pa*s) 265 8.50 27.5 2.57 9.70 1.88 431 9.5 35.6 3.1 13. 2.3 17.1 5.77

[0034] The prepolymers listed in Table 3 were prepared by reacting the Polyol with the Isocyanate in the required ratio to reach the target NCO %. Each reaction forming CE A - CE F and EX 1 - EX 8 in Table 2 was carried out as follows. The polyol (pre-dried to water content <200ppm) was charged into a 4-neck round bottom flask equipped with a mechanical stirrer, thermocouple, and nitrogen inlet. Isocyanate was then added to the reactor. The polyol andisocyanate mixture were mixed for 5 mins under nitrogen. The mixed solution was heated to 75 °C slowly and the temperature change of the reaction mix was recorded. The reaction mix was maintained at 75 °C for 2 hours then monitoring the reaction for completion by measuring the NCO%. 50 ppm of the stannous octoate metal catalyst was introduced to promote reaction completion. After the target NCO% was reached, the reaction was cooled down to 40 °C and was transferred into a plastic jar for further evaluation.

[0035] As seen, the data in Table 3 shows good agreement between the target and measured NCO%. It is also noted that the CE prepolymers prepared using polyols A, B, and C are designed to be compared respectively with the EX prepolymers prepared using polyols D, E, F. In addition, Table 3 includes prepolymers prepared also using polyol G, characterized by a very low OH number (relative to the other polyols used in EX), which is enabled thanks to the fact that the polyol was prepared using the MMC catalyst. The CE using a similar polyol to Polyol G, but prepared using KOH catalyst, was not included since such polyol would contain a very large amount of monols from unsaturation, making it unsuitable for the application.Table 4 - Reactivity of CE and EX Prepolymers Expressed as Open TimeCE CE CE CE CE CE EX EX EX EX EX EX EX EXExample A B C D E F 1 2 3 4 5 6 7 8 Target 3% 10% 3% 10% 3% 10% 3% 10% 3% 10% 3% 10% 3% 10% %NCOOpen Time 2h 2h 6h 3h n.d. Ih 5h Ih 3h Ih 1.5h 3h 4.5h 3h24m 24m 7m 12m 45m 10m 30m 55m Tensile 482 n.d. 306 2106 148 791 645 1940 401 7281 501 3197 1782 2371 %Elongation n.d. n.d. 545 500 141 246 700 200 908 690 2198 682 1832 410 Stress @ 208 n.d. 162 640 112 676 245 1216 180 1219 177 813 153 868 100%Tear 123 n.d. 104 334 44 200 133 321 123 352 161 254 164 191

[0036] Table 4 reports the reactivity of the various CE and EX prepolymers expressed as open time. The results indicate some fluctuations but overall, the reactivities of the CE are similar’ to those of the EX. CE E is the exception, as it failed to achieve proper cure. The physical mechanical properties are averages of testing performed in triplicate on the cured polymer obtained after moisture curing of the prepolymers listed in Table 2.

[0037] Despite similarities in their syntheses to achieve prepolymers at the targeted isocyanate content, all prepolymers made with KOH polyol (CE A - CE F) showed the following general characteristics compared to their MMC-derived counterparts (EX 1 - EX 6) after moisture curing the prepolymer: the prepolymers made with KOH polyol showed worse tensile strength; worse elongation and worse tear strength.

[0038] In more detail, CE A and CE B despite multiple attempts to achieve a “defect-free” moisture cure film displayed the following: CE B formed too many bubbles under the same test conditions as EX 2 and while it showed similar curing kinetics, it failed to provide films upon curing which were suitable for material property testing. Comparing CE A versus EX 1 (similar prepolymers but respectively based on KOH catalyzed polyol and on MMC catalyzed polyol), showed that EX 1 had a better performance as compared to CE A. CE C had lower tear, tensile and elongation properties than EX 3. CE D had lower tear, tensile, and elongation properties than EX 4. CE E showed significantly slower curing kinetics than EX 5 and while tack-free, remained somewhat gelatinous and failed to cure to the same extent as EX 5 in a reasonable time-frame and had failed mechanical testing results. EX 5 showed instead good cure kinetics and suitable mechanical properties in the cured film. CE F had lower tensile strength, elongation and tear strength than EX 6. EX 7 and EX 8 showed that cured films with suitable mechanical properties can be made from prepolymers based on the lOkDa poly(propoxylate diol) made with the MMC: as mentioned, the comparable KOH catalyzed polyol and the corresponding prepolymer were not prepared as they would have resulted in very poor performance (incomplete curing, poor mechanical properties).Tests

[0039] Determination of NCO content: the NCO contents of the prepolymers were determined by titration following the procedure of ASTM D5155 (Determination of the Isocyanate Content of Aromatic Isocyanates). The isocyanate in a sample was allowed to react with excess of di-n-butyl amine (DBA). After the reaction was complete, the excess DBA was determined by back titration with standard hydrochloric acid.

[0040] Viscosity Measurement: viscosity of the prepolymer was measured following ASTM D445 by using an AR2000 Rheometer from TA Instruments. Approximately 0.5 mL of sample was dispensed onto the Peltier plate on the Rheometer equipped with a 40 mm diameter1° steel cone geometry (54 μm gap). After the removal of excess material, the viscosity test was performed by recording the viscosity isothermal of 25 °C and a shear rate of 10 s-1.

[0041] Open time measurement: performed using a mechanical recorder following ASTM D5895. The prepolymer was mixed with certain amount of DMDEE catalyst. A coating with a wet film thickness of -150 mils was applied to a glass panel. Immediately after application, the panel was affixed to a Gardner BYK drying time recorder and the stylus was lowered onto the wet film. Measurements were performed at 77 °F and 50 % relative humidity.

[0042] Mechanical property testing of thin films: Prepolymer with DMDEE catalyst was pre-mixed using flacktek mixer. Films of -25 mil thickness was prepared by drawing down the prepolymer onto a polypropylene substrate using a drawdown bar. The films were moisture cured for seven days (temperature 22-24 °C, humidity 40-45%) before testing for mechanical properties. Tensile properties were measured on micro-tensile bar samples (ASTM D1708) that were prepared from cured plaques and cut with a “dog-bone” shape. Tensile properties were measured with a Monsanto Tensiometer from Alpha Technologies at a rate of 5 in / min.

Claims

What is claimed is:

1. An isocyanate-terminated prepolymer, comprising:a reaction product of:a poly(propoxylated diol) formed in the presence of a modified multi-metal cyanide alkoxylation catalyst of Formula I:MibtM^CW tlctM6^2)^ • nM S • pM3wA2zFormula I wherein:M1and M4each represent, a metal ion independently selected from Zn2+, Fe2+, Co2+, Ni2+, Mo4+, Mo6+, Al3+, V4+, V5+, Sr2+, W4+, W6+, Mn2+, Sn2+, Sn4+, Pb2+, Cu2+, La3+, and Cr3+;M2and M5each represent a metal ion independently selected from Fe3+, Fe2+, Co3+, Co2+, Cr2+, Cr3+, Mn2+, Mn3+, Ir3+, Ni2+, Rh3+, Ru2+, V4+, V5+, Ni2+, Pd2+, and Pt2+;M3represents at least one magnesium, Group 3 — Group 15 metal, or lanthanide series metal or semi-metal ion;X1represents a group other than cyanide that coordinates with the M2ion;X2represents a group other than cyanide that coordinates with the M5ion;A1represents a halide, nitrate, sulfate, carbonate, cyanide, oxalate, thiocyanate, isocyanate, perchlorate, isothiocyanate, an alkanesulfonate, an arylenesulfonate, trifluoromethanesulfonate, or a Ci-4 carboxylate;A2represents least one alkoxide, aryloxy, carboxylate, acyl, pyrophosphate, phosphate, thiophosphate, amide, oxide, siloxide, hydride, carbamate, or hydrocarbon anion;b, c and d are each numbers that reflect an electrostatically neutral complex, provided that b and c each are greater than zero;x and y are integers that balance the charges in the metal salt MFA'--;r is an integer from 4 to 6;t is an integer from 0 to 2;n is a number from 0 and 20;p is from 0.002 to 10; andw and z are integers that balance the charges in the metal salt M3ZA2Z, provided that w is from 1 to 4;wherein the poly(propoxylated diol) has an average hydroxyl number of 5 to 140 mg KOH / g; anda stochiometric excess, relative the poly(propoxylated diol), of an isocyanate having at least 70 wt.% monomeric methylene diphenyl diisocyanate, where the wt.% is based on the total weight of the isocyanate; and wherein the isocyanate-terminated prepolymer has an NCO group content of from 2 wt.% to 20 wt.% based on a total weight of the isocyanate-terminated prepolymer.

2. The isocyanate-terminated prepolymer of claim 1, wherein for the modified multi-metal cyanide alkoxylation catalyst:M1and M4are each Zn2+;M2and M5each represent a metal ion independently selected from Co3+and Co2+; and M3is Al3+.

3. The isocyanate-terminated prepolymer of any one of claims 1-2, wherein the poly(propoxylated diol) has a number average molecular weight of 800 to 22,000 g / mol.

4. The isocyanate-terminated prepolymer of any one of claims 1-3, wherein the poly(propoxylated diol) is formed from a monomer composition comprising at least 70 wt.% propylene oxide, wherein the wt.% is based on the total weight of the monomer composition.

5. The isocyanate-terminated prepolymer of any one of claims 1-4, wherein the reaction product is formed with the stochiometric excess of the isocyanate and a polyol composition having at least 70 wt.% of the poly(propoxylated diol), wherein the wt.% is based on the total weight of the polyol composition.

6. The isocyanate-terminated prepolymer of any one of claims 1-5, wherein the poly(propoxylated diol) formed in the presence of the modified multi-metal cyanide alkoxylation catalyst has a poly dispersity of less than 1.15.

7. The isocyanate-terminated prepolymer of any one of claims 1 -6, wherein the monomeric methylene diphenyl diisocyanatc comprises equal parts 4,4’ -methylene diphenyl diisocyanatc and 2,4’ -methylene diphenyl diisocyanate.

8. The isocyanate-terminated prepolymer of any one of claims 1-7, wherein the isocyanate-terminated prepolymer has a weight average molecular weight of at least 2 kDa.

9. The isocyanate-terminated prepolymer of any one of claims 1-8, wherein the poly(propoxylated diol) is a homopropoxylate diol.

10. The isocyanate-terminated prepolymer of any one of claims 1-9, wherein the isocyanate-terminated prepolymer has an NCO group content of from 2 wt.% to 15 wt.% based on a total weight of the isocyanate-terminated prepolymer; or wherein the isocyanate-terminated prepolymer has an NCO group content of from 2 wt.% to 11 wt.% based on a total weight of the isocyanate-terminated prepolymer.

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