Reactive polyurethane formulations with a low monomer content

Abstract

A reactive polyurethane formulation suitable for use as a sealant, coating, binder, encapsulant, grout or adhesive, said formulation comprising polyurethane prepolymers having free isocyanate groups and having less than 1%, preferably less than 0.5%, more preferably less than 0.1% by weight free diisocyanate monomers based on the total weight of the formulation.

Description

[0001]P136513PC00 Title: Reactive polyurethane formulations with a low monomer content TECHNICAL FIELD OF THE INVENTION The present invention relates to reactive polyurethane formulations with a low diisocyanate monomer content suitable for but not limited to sealant, coating, encapsulant, binder, grouting and adhesive applications. The present invention further relates to a method for reducing the amount of residual diisocyanate monomers in a reactive polyurethane formulation, whilst maintaining adhesive, sealant performance and product stability. The present invention further relates to the use of the reactive polyurethane formulation as sealant, adhesive, encapsulant, binder, grouting or coating. BACKGROUND OF THE INVENTION Polyurethane based adhesives and sealants are known in the art. Sealants based on PU-chemistry, also known in the field as reactive polyurethane prepolymer formulations, are comprising in most instances di- isocyanate monomer compounds which nowadays are recognized as a health risk and hence desired to be avoided. Recently, a new European law under the REACH Regulation (Regulation EC / 1907 / 2006 concerning the Registration, Evaluation, Authorization and Restriction of Chemicals) came into force which stipulates that isocyanate monomers cannot be used as substances on their own, as constituents in other substances or in mixtures for industrial and professional use unless the concentration of these isocyanate monomers individually is less than 0.1 % by weight, or certain training and labelling requirements are complied with. In preparing a polyurethane prepolymer, an organic diisocyanate monomer is reacted with a polyol, usually employing a stoichiometric excess of the diisocyanate monomer (an NCO:OH ratio greater than 1:1, usually about 2:1 or greater). The use of such an excess of diisocyanate monomer results in an undesirable amount of unreacted volatile diisocyanate monomer compounds in the prepolymer reaction product mixture. However, two phenomena appear to be associated with a reduced concentration of diisocyanate monomers in a polyurethane prepolymer formulations e.g., when used as sealant. First of all, a significant loss of hardness and other physical properties during storage is observed. The diisocyanate monomers scavenge protic nucleophiles (i.e. methanol) that otherwise react with the isocyanate groups of the prepolymer(s), end- capping them and thereby reducing the hardness of the sealant after curing. This end-capping process proceeds slowly and manifests itself after one to several weeks of storage. Secondly, a significant loss of adhesion on aluminum (and potential other metallic and non-metallic surfaces) is observed. Monomers quickly migrate to and bind with the metal surface and act as anchoring points for the prepolymer to adhere too. Several techniques have been described in the art as useful for reducing the amount of diisocyanate monomer in the prepolymer reaction product mixture. For example, US 4,182,825 describes a process for distilling the prepolymer reaction product under vacuum conditions to reduce the amount of diisocyanate monomer. US 4,061,662 describes a process for the removal of unreacted diisocyanate from prepolymers by passing the prepolymer reaction product through a column containing a molecular sieve. US 4,385,171 describes a method for the removal of unreacted diisocyanate from polyurethane prepolymers by co-distilling the prepolymer reaction product with a compound which boils at a temperature greater than the boiling point of the diisocyanate. US 4,888,442 describes a two-step process consisting of a first step of distilling the prepolymer reaction product to remove the bulk of the diisocyanate and then, in the second step, a solvent is added to the distilled prepolymer reaction product and the resultant mixture is passed through an agitated thin-film evaporator. US 4,288,577 describes the removal of unreacted methylene bis(4- phenyl isocyanate) (MDI) via solvent extraction with hexane. WO 1997 / 046603 discloses a process for reducing the amount of residual organic diisocyanate monomer in a polyurethane prepolymer reaction product mixture which comprises distilling the polyurethane prepolymer reaction product mixture in the presence of a combination of at least one inert first solvent with a boiling point below the boiling point of the residual organic diisocyanate monomer and at least one inert second solvent with a boiling point above the boiling point of the residual organic diisocyanate monomer, at a temperature which exceeds the vaporization temperature of the residual organic diisocyanate monomer and which is below the decomposition temperature of the polyurethane prepolymer. It is known that in the distillation of diisocyanate monomers from polyurethane prepolymers, high temperatures must be avoided to prevent decomposition reactions in the prepolymer. Furthermore, diisocyanate monomers with high melting points, such as para-phenylene diisocyanate (PPDI), have not been easily removed from polyurethane prepolymers using above known procedures such as distillation. US 6515164 B1 reports the synthesis of a low-monomer polyurethane prepolymer by combining a diisocyanate with unequally reactive isocyanate groups (TDI) with a diisocyanate with equally reactive isocyanate groups (MDI). This procedure, however, requires a cumbersome twostep synthesis wherein the addition of MDI needs to occur the moment the most reactive isocyanate groups of TDI have been consumed by the hydroxyl groups of a polyhydric alcohol. US2004 / 0162385 discloses a process for obtaining a low monomer polyurethane prepolymer by reacting a monomeric asymmetrical diisocyanate such as 2,4'-MDI, containing less than 5% 4,4'-MDI and 2,2'- MDI, the 2,2'-MDI content being under 0,4%, with a polyhydric alcohol such as a diol with a molecular weight of 60 g / mol to 2000 g / mol. Similarly, EP2155797B1 describes the use of 2,4-TDI to prepare polyurethane prepolymers with a TDI monomer content of no more than 0,1% by weight. Above methods to reduce or eliminate the presence of diisocyanate monomers in reactive polyurethane formulations do not give an alternative for the advantages originating from the presence of these diisocyanate monomers such as reducing loss of matrix strength during storage. It is also known that diisocyanate monomers in reactive polyurethane formulations migrate quickly to and bind easily with the metal surface and act as anchoring points for the polyurethane prepolymer to adhere to the metal surface. Also, for this advantage there is no alternative given in above cited prior art. As such there is hence a need for a method to eliminate or at least drastically reduce the amount of diisocyanate monomer compounds in a reactive polyurethane formulation suitable for use as a sealant or adhesive thereby however retaining the properties such as good adhesion to especially metal surfaces and avoiding reduction of hardness of the sealant (or adhesive) after storage. GOAL OF THE INVENTION It is the goal of the invention to provide reactive polyurethane formulations with a low diisocyanate monomer content suitable for sealant and adhesive applications without losing the advantages originating from the presence of diisocyanate monomers such as no loss of hardness and other physical properties during storage and good adhesion on range of surface, particularly metal surfaces such as aluminum. More in particular it is a goal to provide reactive polyurethane formulations with a low diisocyanate monomer content below 1 wt%, preferably below 0.5 wt%, more preferably below 0.1 wt% based on the total weight of the reactive formulation. It is a further goal to provide a method for reducing the amount of residual diisocyanate monomers in a reactive polyurethane formulation. The present invention further relates to the use of the reactive polyurethane formulation according to the invention as a sealant, adhesive, binder, encapsulant, grout or coating and a method for sealing, binding, coating, encapsulating, grouting or adhering substrates using the reactive polyurethane formulation of the invention. DETAILED DESCRIPTION The current invention provides reactive polyurethane formulations suitable for use as a sealant, binder, encapsulant, coating, grout or adhesive wherein the reactive polyurethane formulations have low amounts of diisocyanate monomer compounds below 1 wt%, preferably below 0.5 wt%, more preferably below 0.1 wt% based on the total weight of the reactive formulation. It was surprisingly found that the reactive polyurethane formulation of the invention is a stable formulation over time with good adhesion properties on metal surfaces such as aluminum and the formulation may be further optimized to fit specific applications to enhance the strength of said formulation, to avoid a significant loss of hardness and other physical properties during storage. It was surprisingly found that by combining a polyisocyanate composition having free isocyanate groups originating from diisocyanate monomers with defined amounts of moisture sensitive substances of which at least one hydrolysis product is isocyanate reactive and preferably react faster with diisocyanate monomers making it possible to achieve a reactive polyurethane formulation suitable for use as a sealant or adhesive wherein said formulation has less than 1%, preferably less than 0.5%, more preferably less than 0.1% by weight free diisocyanate monomers based on the total weight of the formulation and wherein said formulation has surprisingly good adhesion properties on metal surfaces such as aluminum, loss of hardness and other physical properties during storage is avoided compared to state of the art reactive polyurethane formulations having low diisocyanate monomers. To successfully overcome the problems associated with a low diisocyanate monomer concentration (reduced adhesion, loss of matrix strength during storage), it was surprisingly found that the re-introduction of diisocyanate monomers and the conversion of them during the process of making the reactive polyurethane formulation into small non-monomeric species, that these “modified” isocyanate non-monomer species will take over the role of the original diisocyanate monomers. This was achieved by combining a polyisocyanate composition which comprises the original diisocyanate monomers (such as 2,2’-MDI, 2,4’-MDI, 4,4’-MDI or 2,4- or 2,6- TDI or mixtures thereof) with well-defined moisture sensitive substances of whose at least one hydrolysis product is isocyanate reactive in the presence of defined amounts of water. Because of the difference in reactivity between the NCO ‘s of the polyisocyanate prepolymer used in the reactive polyisocyanate formulation of the present invention and the NCO’s of the free isocyanate groups of isocyanate monomers, the reaction of isocyanate reactive hydrolysis products (such as silanol / methanol, amines) is assumed to occur preferably with the free isocyanate groups of the isocyanate monomers leaving the isocyanate prepolymers unaffected. For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combination of all or some of the features described. Terminology used for describing particular embodiments is not intended to limit the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms and mixed forms as well, unless the context clearly indicates otherwise. The term "and / or" includes any and all combinations of one or more of the associated listed items. It will be understood that the terms "comprises" and / or "comprising" specify the presence of stated features but do not exclude the presence or addition of one or more other features. Likewise, it will be understood that when a connection between structures or components is described, this connection may be established directly or through intermediate structures or components unless specified otherwise (or if chemically impossible). As used herein, the term “adhesive” and “adhesive formulation” or “coating” and “coating formulation” refers to a formulation having adhesive or coating properties to bond e.g. the material to a substrate or multiple substrates. As used herein, the term “sealant” and “sealant formulation” refers to a formulation having sealing properties, mostly used to seal the gap between adjacent, non-touching substrates. It might be used e.g. to make the gap between substrates watertight or airtight. As used herein, the term “encapsulant” and “encapsulant formulation” refers to a formulation having encapsulating properties, coating, enclosing and binding particularly particulate matter. As used herein, the term “grout” and “grouting formulation” refers to a formulation having adhesive and edge-to-edge filling properties (paver joints) such as in tile to wall adhesion. As used herein, the term “binder” and “binder formulation” refers to a formulation having adhesive-like properties such that multiple substrates are held together. As used herein, the term “diisocyanate monomer” refers to a compound with following structure: O=C=N-R-N=C=O, whereby the group R is an aliphatic or aromatic hydrocarbon unit of unspecified length. R does not contain urethane, urea, uretdione, biuret, allophanate carbodiimide, uretonimine, or isocyanurate linkages (i.e. the diisocyanate entity is not the result of prepolymerisation of a parent diisocyanate). Such species have a molecular weight less than 600, preferably less than 400, more preferably less than 300 g / mol. As used herein, the term “polyisocyanate” refers to a compound containing multiple (2 or more) isocyanate functional groups, including all isomeric structures of said materials mixtures thereof. As used herein, the term “polymeric MDI” and “pMDI” refers to MDI which contains 20 to 80 wt% monomeric 4,4'-methylene diphenyl isocyanate (MDI) or mixed diisocyanate monomers; the rest consists of higher molecular weight MDI oligomers and MDI homologues. As used herein the term “asymmetric polyisocyanates” and “asymmetric diisocyanates” refer to polyisocyanates or diisocyanates that have unequally reactive isocyanate groups (i.e. isophorone diisocyanate, 2-4 toluene diisocyanate). In contrast, 4,4’ methylene diphenyl diisocyanate (4,4’ MDI) is regarded as a symmetric diisocyanate since both its isocyanate groups are equally reactive. As used herein, the term “average reactivity”, refers to the weighted numerical average of the reactivities of constituent parts in that component of the formulation, based upon molar contents, it is an estimate of how a blend of different reactive materials will behave as a whole. As used herein, the term “viscosity”, refers to a measure of a fluid’s resistance to flow and hence describing the internal friction of a moving fluid. Viscosity measurements are described in multiple handbooks or standards, such as ISO 3219-2. As used herein, the term “density”, refers to a compounds mass per unit of volume. Herein the term “density” is measured according to ISO 2811-1 unless otherwise specified. As used herein the term “Shore A hardness” is the surface hardness of a material as measured according to ISO48-4:2018. As used herein, the term “wt%”, or “weight percentage”, or “percentage by weight”, refers to the mass fraction of a compound in a mixture, composition or formulation divided by the total mass of said mixture, composition or formulation multiplied by 100 and is expressed as a percentage between 0 and 100. As used herein E100%-Alu (value given in N / mm²) refers to the force F recorded in the force / extension diagram at a tensile strain of 100%, measured according to ISO 8339, divided by the initial cross section area S of an aluminum test specimen as defined in ISO 13640. As used herein Smax - Alu (value given in N / mm2) refers to the maximal force F recorded in the force / extension diagram measured according to ISO 8339, divided by the initial cross section area S of an aluminum test specimen as defined in ISO 13640. As used herein dl% at Smax -Alu refers to the elongation calculated by: [(width of the aluminum test specimen at Smax - original width of the test specimen) / (original width of the test specimen)] x 100, according to ISO 8339. As used herein dl% at Break - Alu refers to the elongation at break calculated by: [(final width of the aluminum test specimen - original width of the test specimen) / (original width of the test specimen)] x 100, according to ISO 8339. As used herein Coh refers to Cohesive Failure, which is defined as failure exclusively in the adhesive material (visual assessment). As used herein TL refers to Thin Layer Failure, which is defined as failure exclusively in the subsurface layer of the adhesive material (visual assessment). As used herein Adh refers to Adhesion Layer Failure, which is defined as failure exclusively in the adhesion layer between the adhesive and the substrate (visual assessment). As used herein the expression "isocyanate-reactive groups" as used herein refers to groups having active hydrogen atoms capable of reacting with NCO groups from isocyanates e.g. active hydrogen atoms in hydroxyl and amine groups present in the reactive compositions. As used herein the expression “functionality” refers to the average nominal functionality is used herein to indicate the theoretical number average functionality. As used herein, the term “weight ratio” as used in the reactive polyurethane formulation is expressed in a form X:Y wherein X represents the weight amount of a first compound and Y represents the weight amount of a second compound. As used herein, the term “molar ratio” as used in the reactive polyurethane formulation is expressed in a form X:Y wherein X represents the molar amount of the first compound (or a reactive group) and Y represents the molar amount of a second compound (or a reactive group). As used herein, the term “non-reactive”, refers to a compound that is mixed into the reactive polyurethane formulation that does not react with any of the compounds present in said reactive polyurethane formulation. As used herein, the term “excess moles of diisocyanate monomers” refers to the moles of diisocyanate monomer that need to be converted according to the invention to ensure that the mass concentration of all diisocyanate monomers in the reactive polyurethane formulation after mixing is below 1 wt%, preferably below 0.5 wt% or most preferably below 0.1 wt% based on the total weight of the reactive polyurethane formulation. The combining and mixing of the polyisocyanates and the other ingredients to form the reactive polyurethane formulation of the invention preferably is to be conducted at ambient pressure and at a temperature between 5°C and 95°C and more preferably between 15°C and 60 °C in order to avoid undesired premature reactions as much as possible. Accordingly, the invention provides a reactive polyurethane formulation suitable for use as a sealant, encapsulant, binder, grout, coating or adhesive, said formulation comprising polyurethane prepolymers having free isocyanate groups and having less than 1%, preferably less than 0.5%, more preferably less than 0.1% by weight free diisocyanate monomers based on the total weight of the formulation, said formulation obtained by combining and / or mixing at least the following ingredients: (i) 11-40%, preferably 15-35%, more preferably 18-33% byweight of a polyisocyanate composition (a) and comprising polyurethane prepolymers formed by reacting at least one polyol with at least one polyisocyanate, wherein the at least one polyisocyanate is used in an amount such that the NCO groups are present in molar excess relative to the hydroxyl groups of the at least one polyol and the NCO / OH ratio is in the range 1.4:1 – 3:1, preferably in the range 1.8:1 to 2.2:1; and (ii) 0.1 up 3 %, preferably 0.1-2%, more preferably 0.1-1% byweight of a polyisocyanate composition (b) having a functionality equal to or greater than 2 and containing 20 up to 100 %, preferably 35-100% by weight free diisocyanate monomers based on the total weight of polyisocyanate composition (b), and(iii) 0.01 up 5 %, preferably 0.01-3%, more preferably 0.01-2%by weight of at least one moisture sensitive compound (c) of whose hydrolysis products give at least one monofunctional isocyanate-reactive compound (d), and (iv) water, and(v) optionally 0 up 80%, and preferably 0 to 50% by weight offillers, and (vi) optionally an amount of latent hardener sufficient for its atleast 1 hydrolysis product to react with at least 30%, more preferably at least 50% and most preferably at least 70% of the polyisocyanate composition (a), and (vii) optionally further additives or mixtures of additivesselected from but not limited to rheology modifiers, pigments, plasticizers, catalysts, solvents, UV stabilizers, light stabilizers, acid scavengers, adhesion promotors and biocides wherein the % by weight of polyisocyanate composition (a), polyisocyanate composition (b), the at least one moisture sensitive compound (c), the optional latent hardener, fillers and further optional additives is based on the total weight of the reactive polyurethane formulation, and wherein the average isocyanate reactivity of the free isocyanate groups originating from polyisocyanate composition (a) towards water and / or the at least one isocyanate reactive hydrolysis products (d) is lower compared to the average isocyanate reactivity of the free isocyanate groups originating from the polyisocyanate composition (b) towards water or / and the at least one isocyanate reactive hydrolysis products (d), and wherein the molar ratio of the excess moles of diisocyanate monomer compounds present in polyisocyanate composition (a) and (b) towards the moles of isocyanate reactive products selected from water and the at least one hydrolysis product from the moisture sensitive compound (c) is in the range 3:1 – 0.6:1 preferably 2:1 – 0.6:1 and more preferably 1.1:1 – 0.6:1, most preferably 0.6:1 such that the final monomer content in the polyurethane formulation is below 1%, preferably below 0.5%, more preferably below 0.1% by weight free diisocyanate monomers based on the total weight of the reactive polyurethane formulation and the excess moles of diisocyanate monomer compounds refer to the moles of diisocyanate monomer in polyisocyanate composition (a) and / or (b) that need to be converted by reaction with water and monofunctional polyisocyanate reactive compound (d) to ensure that the mass concentration of all diisocyanate monomers in the reactive polyurethane formulation after mixing is below 1 wt%, preferably below 0.5 wt% or most preferably below 0.1 wt% based on the total weight of the reactive polyurethane formulation, and wherein the excess moles of diisocyanate monomer compounds refer to the moles of diisocyanate monomer in polyisocyanate composition (a) and / or (b) that need to be converted by reaction with water and monofunctional polyisocyanate reactive compound (d) to ensure that the mass concentration of all diisocyanate monomers in the reactive polyurethane formulation after mixing is below 1 wt%, preferably below 0.5 wt% or most preferably below 0.1 wt% based on the total weight of the reactive polyurethane formulation. The molar ratio of the excess moles of diisocyanate monomer compounds present in polyisocyanate composition (a) and (b) towards the moles of isocyanate reactive products selected from water and the at least one hydrolysis product from the moisture sensitive compound (c) may be for example about 3:1, preferably about 2:1, more preferably about 1:1, most preferably about 0.6:1 such that the final monomer content in the polyurethane formulation is below 1%, preferably below 0.5%, more preferably below 0.1% by weight free diisocyanate monomers based on the total weight of the reactive polyurethane formulation According to embodiments, the water required in the reactive polyurethane formulation may be added as an additive but may also originate from atmospheric moisture or as contamination in the ingredients used or as a result of condensation products of some of the ingredients, or any other source. Polyisocyanate compounds Part of the invention is based on the difference in reactivity of the isocyanate groups in the polyisocyanate compounds towards isocyanate reactive groups. For example, the NCO functional groups in the different MDI isomers (2,2´-, 2,4´- and 4,4´-MDI) will show different reactivity towards the isocyanate reactive hydrolysis products (d) originating from the moisture sensitive compound (c). In that respect, the NCO groups in a polyisocyanate made from 2,4-toluene diisocyanate (2,4-TDI)) show a lower reactivity towards the isocyanate reactive groups in the isocyanate reactive hydrolysis products (d) and water compared to the reactivity of the NCO groups in a polyisocyanate made from 4,4´-MDI towards the isocyanate reactive groups in the isocyanate reactive hydrolysis products (d) and water. According to the teaching of this invention, the polyisocyanates in polyisocyanate composition (b) comprise isocyanate monomer compounds which have higher average reactivity towards isocyanate-reactive groups compared to the on average slower reacting (remaining) NCO groups of the polyurethane prepolymer compounds in polyisocyanate composition (a). As a preferred embodiment, polyisocyanate composition (b) and polyisocyanate composition (a) are derived from the following diisocyanate monomer combinations: 2,4’-MDI / 4,4’-MDI / pMDI : 2,4-TDI / 2,6-TDI ; 2,4’- MDI / 4,4’-MDI / pMDI : IPDI ; 2,4’-MDI / 4,4’-MDI / pMDI : 1,6-HDI : 2,4’- MDI / 4,4’-MDI / pMDI : H12MDI ; 2,4’-MDI / 4,4’-MDI / pMDI : TXMDI; 2,4- TDI / 2,6-TDI : IPDI ; 2,4-TDI / 2,6-TDI : 1,6-HDI ; 2,4-TDI / 2,6-TDI : H12MDI ; 2,4-TDI / 2,6-TDI : TXMDI; 1,5-NDI : IPDI ; 1,5-NDI : 1,6-HDI ; 1,5-NDI : H12MDI,1,5-NDI : TXMDI wherein 2,4’MDI / 4,4’-MDI / pMDI refers to either pure 4,4’-MDI or to the 50:50 mixture of 2,4’-MDI / 4,4’-MDI and all intermediate mixtures or to polymeric MDI and all mixtures with 2,4’-MDI and / or 4,4’-MDI ; wherein 2,4-TDI / 2,6-TDI refers to pure 2,4-TDI or the 80:20 mixture of 2,4-TDI and 2,6-TDI or all intermediate mixtures, wherein IPDI refers to isophorone diisocyanate, wherein 1,6-HDI refers to 1,6- hexamethyelen diisocyanate, wherein H12MDI refers to hydrogenated MDI, wherein 1,5-NDI refers to 1,5-naphthylene diisocyanate and wherein TXMDI refers to tetramethylxylylene diisocyanate. Polyisocyanate composition (a) Polyisocyanate composition (a) comprises a known and reducible amount of free isocyanate monomers on the total weight of polyisocyanate composition (a) and is comprising polyurethane prepolymers formed by reacting at least one polyol with at least one polyisocyanate, wherein the at least one polyisocyanate is used in an amount such that the NCO groups are present in molar excess relative to the hydroxyl groups of the at least one polyol and the NCO / OH ratio is in the range 1.4:1 – 3:1, preferably in the range 1.8:1 to 2.2:1. The polyisocyanate compounds in poly-isocyanate composition (a) are preferably selected from asymmetric aromatic and (cyclo)aliphatic di- isocyanates such as toluene diisocyanate, more preferably 2,4-toluene di- isocyanate (2,4-TDI)) or asymmetric methylene diphenyl diisocyanate (MDI) selected from 2,4'-methylenediphenyl diisocyanate (2,4’ MDI) and 2,2'- methylenediphenyl diisocyanate (2,2’ MDI), isophorone diisocyante (IPDI) or 2,6-hexamethylene diisocyanate (2,6-HDI), 2,4’-HMDI (hydrogenated 2,4’ MDI). The polyisocyanate compounds in polyisocyanate composition (a) may comprise symmetric diisocyanates such as diisocyanates selected from 4,4'-methylenediphenyl diisocyanate (MDI) with the precaution that any unreacted diisocyanates in polyisocyanate composition (a) after forming the polyurethane prepolymer are removed by distillation before combining with the remaining ingredients to form the reactive polyurethane formulation if the invention. The polyisocyanate compounds in polyisocyanate composition (a) may comprise polyisocyanates selected from asymmetric diisocyanates and symmetric diisocyanates or mixtures thereof with the precaution that any unreacted diisocyanates in polyisocyanate composition (a) after forming the polyurethane prepolymer are removed by distillation before combining with the remaining ingredients to form the reactive polyurethane formulation if the invention. Polyisocyanate composition (b) Polyisocyanate composition (b) is comprising polyisocyanate compounds having a functionality equal to or greater than 2. Preferably the average functionality of polyisocyanate composition (b) is equal to or greater than 2 and is containing 20 up to 100 %, preferably 35-100% by weight free diisocyanate monomers based on the total weight of polyisocyanate composition (b). Said free diisocyanate monomer compounds are preferably selected from 2,2´-, 2,4´- and 4,4´-MDI, pMDI and aliphatic isocyanates. According to preferred embodiments, polyisocyanate composition (b) is comprising polymeric MDI (pMDI). pMDI in general is a mixture of polymethylene polyphenyl polyisocyanate isomers, diphenylmethane di- isocyanate isomers, triisocyanates, and other higher functional oligomers. The diphenylmethane diisocyanate in the polymeric MDI may include one or more isomers selected from 2,4’ and 4,4’ MDI isomers. Typically, commercially available pMDI is a mixture that contains 20–80% by weight isocyanate monomers as well as oligomers containing 3–6 rings and other minor isomers, such as the 2,2’-isomer. According to preferred embodiments polyisocyanate composition (b) is selected from polymeric MDI wherein polymeric MDI comprises at least 30% up to 45% by weight diisocyanate monomers based on the total weight of polyisocyanate composition (b). According to embodiments, the hardness stability (loss in Shore A during storage) of the reactive polyurethane formulation may be improved by a higher concentration of pMDI in polyisocyanate composition (b) and / or a higher prepolymer concentration (originating from polyisocyanate composition (a)) in the reactive polyurethane formulation. Polyols used in polyisocyanate composition (a) The polyol used to form the polyurethane prepolymers in polyisocyanate composition (a) is preferably selected from aromatic or aliphatic or cycloaliphatic polyether, aromatic or non-aromatic polyester polyol or polyhydroxybutylene, more preferably a polyoxyalkylene polyether or polyester polyol. Said polyoxyalkylene polyether polyols may be produced, for example, by the base catalyzed addition of an alkylene oxide to an initiator molecule containing an average of two or more active hydrogens (limitations may be aromatic, aliphatic, cycloaliphatic, saturated or unsaturated and may optionally contain heteroatoms such as, but not limited to nitrogen and sulfur). Examples of alkylene oxide include but are not limited to ethylene oxide, propylene oxide, butylene oxide, amylene oxide, mixtures thereof, tetrahydrofuran, alkylene oxide-tetrahydrofuran mixtures, epihalohydrins, and aralkylene oxides such as styrene oxide. Suitable initiators include aliphatics, cycloaliphatics and aromatics and mixtures thereof, such as but not limited to ethylene glycol, propylene glycol, dipropylene glycol, trimethylene glycol, 1,2-butanediol, 1,3- butanediol, 1,4-butanediol, 1,2-pentanediol, 1,4-pentanediol, 1,5- pentanediol, 1,6-hexanediol, 1,7-heptanediol, glycerol, 1,1,1- trimethylolpropane, 1,1,1-trimethylolethane, 1,2,6-hexanetriol, a-methyl glucoside, pentaerythritol, and sorbitol and mixtures thereof. The polyoxyalkylene polyether or polyester polyols may have either primary, secondary or tertiary hydroxyl groups but more preferably primary or secondary hydroxyl groups. Included among the polyether polyols are polyoxyethylene glycol, polyoxypropylene glycol, polyoxybutylene glycol, polytetramethylene glycol, block copolymers, for example, combinations of polyoxypropylene and polyoxyethylene glycols, poly-1,2- oxybutylene and polyoxyethylene glycols, poly-1,4-oxybutylene and polyoxyethylene glycols, and random copolymer glycols prepared from blends of two or more alkylene oxides or by the sequential addition of two or more alkylene oxides. A further aspect of the invention includes optional use of bio- based polyether and polyester polyols, …. Examples include castor oil based, soya oil based, lignin-based polyether and polyester or polyhydric polyols. In one of the preferred embodiments of the invention the polyether polyols used in polyisocyanate composition (a) to form the polyurethane prepolymers have nominally 2 to 6 hydroxyl groups and are produced from the polymerization of EO, PO and BO as homopolymers, mixed polymers (random or block), having a number-average molecular weight of about 62 to 25000, preferably about 800 to 20000, and most preferably 800 to 10000. In another preferred embodiment of the invention the polyester polyols used in the polyisocyanate composition (a) are composed of C2-18 polyols, with C2_6 polyacids, having a number-average molecular weight of about 150 to 8000, preferably about 800 to 4000. Moisture sensitive compound (c) Suitable moisture sensitive compounds (c) whose at least one hydrolysis product is isocyanate reactive and capable of reacting with the diisocyanate monomers in the reactive polyisocyanate formulation include all materials known by those skilled in the art, such as but not limited to: ^Compounds comprising at least one reactive alkoxysilylgroup. Suitable examples include vinyl trialkoxysilanes, tetraethoxysilanes, N- (methyldimethoxysilylmethyl)-O- methylcarbamate, (methacryloyloxymethyl)silanes, methoxymethylsilanes, ^Orthoformic esters, suitable examples include trimethylorthoformate, triethyl orthoformate, … ^Mono-isocyanates, suitable examples include p-Toluenesulfonyl isocyanate (pTSI) and mono-oxazolidines, suitable examples include 3-ethyl-2-methyl-2-(3- methylbutyl)-1,3-oxazolidine, 3-butyl-2-(heptan-3-yl)-1,3- oxazolidine, … and combination thereof. Fillers According to preferred embodiments, the reactive polyurethane formulation may further comprise at least one filler. The at least one filler is usually introduced based on its physical properties such as density and particle size. The at least one filler is provided to modify the rheological as well as the technical properties of the reactive polyurethane formulation as well as the final fully cured material. The at least one filler may have a density between 0.001-11 g / cm³, between 0.1-5 g / cm³ or between 0.1-4 g / cm³. The at least one filler can be any filler, described to date, that is preferably compatible, more in particular dispersible, with the reactive polyurethane formulation and / or that can be easily re-dispersed such as by manual shaking. Suitable fillers include but are not limited to inorganic or organic fillers such as ground or participated calcium carbonate optionally coated with an organic material such as, but not limited to, fatty acids, stearic acid, baryte (heavy spar), talcs, quartz flours, quartz sand, dolomites, wollastonites, kaolins, calcined kaolins, mica (potassium aluminum silicate), molecular sieves, aluminum oxides, aluminum hydroxides, magnesium hydroxide, silicas including finely divided silicas from pyrolysis processes, industrially produced carbon blacks, graphite, metal powders such as aluminum, copper, iron, silver or steel, PVC and other plastic powders or hollow spheres, titanium dioxide, glass bubbles, perlite, expanded thermoplastic microspheres, silicate ceramic microspheres, vermiculite platelets, cements, gypsum, fly ashes, graphite, graphene, metal powders, for example of aluminum, copper, iron, silver or steel ,or any combination thereof. Commercial examples of calcium carbonate include Hakuenka®CCR, Hakuenka®CCR S10, ImerCarb®20S, ImerSeal®36S, ImerSeal®50s, ImerSeal®96S, Omyabond®520, Omyacarb®2t, Polycarb®88s or any combination thereof. Commercial examples of glass bubbles include 3M glass bubbles K1, 3M glass bubbles K25, 3M glass bubbles K32, Poraver®0.04 - 0.125, or any combination thereof. Other commercially available fillers include Dicalite®GPE-18, Expancel®920 DE 40 d30, Expancel®920 DE 40 d25, sumfoam®KU powder P300, fillite®160, microlite®FPSV, or any combination thereof. Preferably the fillers are selected from grounded or participated calcium carbonate, silicas or titanium dioxide. Typically, the amount of the filler, when present, is from 1 wt% to 80 wt%, more preferably from 5 wt% to 60 wt%, most preferably from 10 wt% to 50 wt%, relative to the total weight of reactive polyurethane formulation. Latent hardeners A “latent hardener” refers to a substance having at least two groups that are reactive toward isocyanates, at least one, preferably both, of which are blocked in terms of its reactivity and is activatable by means of moisture. In other words, at least one of the isocyanate reactive groups in the latent hardener becomes reactive toward isocyanate groups after they have been activated by means of moisture. A suitable latent hardener is a blocked amine having a blocked, hydrolytically activatable amino group and at least one further reactive group selected from the group consisting of hydroxyl group, mercapto group, secondary amino group, primary amino group and preferably blocked, hydrolytically activatable amino group. Chemically blocked amines release amino groups on contact with moisture and react rapidly with the isocyanate groups without formation of carbon dioxide. Latent hardeners used are usually compounds having aldimine, ketimine or oxazolidine groups. Any latent hardeners which overlap in chemistry with the above defined moisture sensitive compounds are for calculation purposes only regarded as latent hardeners in the current invention and are not counted as moisture sensitive compounds. The reactive polyurethane formulation may comprise further additive compounds to further modify the adhesive or sealant properties and / or appearance of the reactive polyurethane formulation according to the need of the application. Additive compounds generally comprise, based on the total weight of the reactive polyurethane formulation, 0-50 wt%, preferably 0-30 wt%, more preferably 0-15 wt% in the reactive polyurethane formulation. Examples of additive compounds include pigments or dyes (to address the color), rheology modifiers (to influence the flow behavior), stabilizers (to stabilize against oxidation, heat, light or UV radiation), catalysts (to facilitate the adhesive network formation, and / or to induce crosslinking), adhesion promotors, tackifiers, flame retardants, surface- active substances, biocides or combinations thereof. Pigments and / or dyes Suitable pigments include any pigment known to date that is preferably compatible with the reactive polyurethane formulation such as titanium dioxide or carbon black. Suitable dyes include any dye known to date that is preferably compatible with the reactive polyurethane formulation of the invention. Rheology modifiers Suitable rheology modifiers (also referred to as rheology control agents) include thixotropy agents, such as but not limited to fumed silica, amide wax, sheet silicate such as but not limited to bentonite, a derivative of castor oil, hydrogenated castor oil, polyamide waxes, polyurethanes, urea compounds, cellulose ethers, hydrophobically modified polyoxyethylenes, or any combination thereof. Stabilizers Suitable stabilizers include stabilizers described to date that are compatible with the reactive polyurethane formulation of the present invention such as hindered amine light stabilizers (HALS), UV stabilizers and antioxidants. Commercial examples include but are not limited to: irganox®1135, tinuvin®571, tinuvin®765, geniosil®stab F, irganox®1010, irganox®245, tinuvin®326, tinuvin®5151, tinuvin®770, addworks®IBC 760, eversorb®HP5, tinuvin®312, eversorb®H1, eversorb®HP3, eversorb®HP4, hostavin®N30P. Catalysts Suitable catalysts include but not limited to metalorganiccompounds, basic nitrogen or phosphorus compounds. Suitable metalorganic compounds comprise compounds of mercury, tin, titanium, zirconium, aluminum or zinc, barium, nickel, hafnium, platinum, ruthenium. Said metalorganic catalyst may comprise an organotin compound, an inorganic tin salt or tin compound derivatives. Commonly the tin compound in said catalyst is bivalent or tetravalent. Examples of inorganic tin salts include tin(II) chloride, tin(IV) chloride, or any combination thereof. Examples of organotin compounds include 1,3- dicarbonyl compounds of bivalent or tetravalent tin, for example, the acetylacetonates such as di(n-butyl)tin(IV) di(acetylacetonate), di(n- octyl)tin(IV) di(acetylacetonate), (n-octyl)(n-butyl)tin(IV) di(acetylacetonate); the dialkyl tin(IV) dicarboxylates, for example, di-n-butyltin dilaurate, di-n- butyltin maleate, di-n-butyltin diacetate, di-n-octyltin dilaurate, di-n- octyltin diacetate, or the corresponding dialkoxylates, for example, di-n- butyltin dimethoxide; oxides of tetravalent tin, for example, dialkyltin oxides, such as, for example, di-n-butyltin oxide and di-n-octyltin oxide; and the tin(II) carboxylates such as tin(II) octoate or tin(II) phenolate. Examples of tin compound derivatives include tin compounds of ethyl silicate, dimethyl maleate, diethyl maleate, dioctyl maleate, dimethyl phthalate, diethyl phthalate, dioctyl phthalate, such as, for example, di(n-butyl)tin(IV) di(methyl maleate), di(n-butyl)tin(IV) di(butyl maleate), di(n-octyl)tin(IV) di(methyl maleate), di(n-octyl)tin(IV) di(butyl maleate), di(n-octyl)tin(IV) di(isooctyl maleate); and di(n-butyl)tin(IV) sulfide, (n-butyl)2-Sn(SCH2COO), (n-octyl)2-Sn(SCH2COO), (n-octyl)2-Sn(SCH2CH2COO), (n-octyl)2- Sn(SCH2CH2COOCH2CH2OCOCH2S), (n-butyl)2-Sn(SCH2COO-i-C8H17)2, (n-octyl)2-Sn(SCH2COO-i-C8H17)2, and (n-octyl)2-Sn(SCH2COO-n-C8H17)2. Nitrogen-containing compounds suitable as catalysts are in particular amines, especially tertiary amines such as, but not limited to N- ethyl-diisopropylamine, N,N,N’,N’-tetramethylalkylenediamines, 1 ,4- diazabicyclo[2.2.2]octane, 2,2’-dimorpholinodiethylether (DMDEE); amidines such as especially 1 ,8- diazabicyclo[5.4.0]undec-7-ene (DBU), 1 ,5- diazabicyclo[4.3.0]non-5-ene (DBN), 6-dibutylamino1,8-diazabicyclo- [5.4.0]undec-7-ene; guanidines such as especially tetramethylguanidine, 2- guanidino-benzimidazole, acetylacetone- guanidine, 3-di-o-tolyl-guanidine, 2-tert-butyl-1,1,3,3-tetramethyl guanidine; and imidazoles, in particular N- (3-trimethoxysilylpropyl)-4,5-dihydroimidazole and N-(3- triethoxysilylpropyl)-4,5-dihydroimidazole. Nitrogen or phosphorus containing catalyst compounds are especially imidazoles, pyridines, phosphazene bases, secondary or tertiary amines, hexahydrotriazines, biguanides, guanidines, or amidines. Non limitative examples of commercially available catalysts suitable for use in the reactive polyurethane formulation of the present invention include: Metatin®700 series as manufactured by Acima®, Switzerland, the TIB KAT®series such as but not limited to TIB KAT®223, 226, 218 as manufactured by TIB Chemicals AG. If the reactive polyurethane formulation contains latent hardeners, suitable catalysts for the hydrolysis of the latent hardeners are acids, especially organic acids, especially aromatic carboxylic acids such as benzoic acid, 2-nitrobenzoic acid or salicylic acid. Also suitable are combinations of different catalysts. Typically, the amount of the catalyst, when present, is from 0.005 wt% to 10 wt%, more preferably from 0.05 wt% to 3 wt%, calculated on the total weight of the reactive polyurethane formulation. Plasticizers The reactive polyurethane formulation of the present invention may further comprise optionally at least one plasticizer compound to reduce the viscosity and to facilitate application of reactive polyurethane formulation. The plasticizer compound can be any compound described to date for that purpose that is preferably compatible with the reactive polyurethane formulation. Among plasticizers suitable for use in the reactive polyurethane formulation of the present invention are phthalic acid ester compounds such as dibutyl phthalate, diisononyl phthalate (DINP), diheptyl phthalate, di(2- ethylhexyl)phthalate, diisodecyl phthalate (DIDP), and butyl benzyl phthalate; terephthalic acid ester compounds such as bis(2-ethylhexyl)-1,4- benzenedicarboxylate; non-phthalic ester compounds such as 1,2- cyclohexane dicarboxylic acid diisononyl ester, aliphatic polycarboxylic acid ester compounds such as dioctyl adipate, dioctyl sebacate, dibutyl sebacate, diisodecyl succinate, and tributyl acetylcitrate; unsaturated fatty acid ester compounds such as butyl oleate and methyl acetyl ricinoleate; alkyl sulfonic acid phenyl esters; phosphoric acid ester compounds such as tricresyl phosphate and tributyl phosphate; trimellitic acid ester compounds; chlorinated paraffin; hydrocarbon oils such as alkyl diphenyl and partially hydrogenated terphenyl; process oil; and epoxy plasticizers such as epoxidized soybean oil and benzyl epoxystearate. Also, polymer plasticizers may be used as plasticizers suitable for use in the reactive polyurethane formulation of the present invention, such as but not particularly limited to, vinyl polymers obtained by polymerizing vinyl monomers by various methods; esters of polyalkylene glycols, such as diethylene glycol dibenzoate, triethylene glycol dibenzoate, and pentaerythritol ester; polyester plasticizers formed from dibasic acids (e.g. sebacic acid, adipic acid, azelaic acid, phthalic acid) and divalent alcohols (e.g. ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol); polyethers such as polyether polyols (e.g. polyethylene glycol, polypropylene glycol, and polytetramethylene glycol having a number average molecular weight of 500 or more, or even 1000 or more) and derivatives obtained by converting the hydroxyl groups of these polyether polyols into ester groups, ether groups, or the like; polystyrenes such as polystyrene and poly-α-methylstyrene; polybutadiene, polybutene, polyisobutylene, butadiene-acrylonitrile, and polychloroprene. Non limitative examples of commercially available plasticizers suitable for use in the method of the present invention include: Eastman®168 available from Eastman Chemical Company, Jayflex®DINP, Jayflex®DIUP, Jayflex®DIDP available from ExxonMobil Chemical, Mesamoll®available from Lanxess, Hexamoll®DINCH available from BASF AG, Desmophen®2060 BD available from Covestro, VORANOL®available from DOW and (di)benzoates such as Benzoflex®2088, Benzoflex®284 (Eastman) and triacetin (Eastman). Typically, the amount of the plasticizer, when present, is from 0,1 wt% to 80 wt%, more preferably from 0,1 wt% to 50% wt%, relative to the total weight of the reactive polyurethane formulation. Flame retardants Suitable flame retardants are known in the art of adhesives and may include but are not limited to aluminum hydroxide and / or magnesium hydroxide, or organic phosphoric esters such as triethyl phosphate, tricresyl phosphate, triphenyl phosphate, diphenyl cresyl phosphate, isodecyl diphenyl phosphate, tris(1,3-dichloro-2-propyl) phosphate, tris(2- chloroethyl) phosphate, tris(2-ethylhexyl) phosphate, tris(chloroisopropyl) phosphate, tris(chloropropyl) phosphate, isopropylated triphenyl phosphate, mono-, bis- or tris(isopropylphenyl) phosphates of different degrees of isopropylation, resorcinol bis(diphenyl phosphate), bisphenol A bis(diphenyl phosphate) or ammonium polyphosphates. Adhesion promotors The reactive polyurethane formulation may optionally comprise adhesion promotors to further increase the performance of the reactive polyurethane formulation towards the substrates to be bonded, coated or sealed. The at least one adhesion promoter can be any adhesion promoter described to date for that purpose which is compatible with the reactive polyurethane formulation of the present invention. Any adhesion promotors which overlap in chemistry with the above defined moisture sensitive compounds are for calculation purposes only regarded as adhesion promotors in the current invention and are not counted as moisture sensitive compounds. Preferred but non-limiting adhesion promoters optionally suitable for use in the present invention are aminosilanes, epoxy silanes, ureido silanes, acryl silanes, alkyl silanes, sulfur silanes, vinyl silanes, chloro silanes, (meth)acryloylsilanes, anhydridosilanes, carbamatosilanes, iminosilanes, oligomeric forms of these silanes, adducts formed from primary aminosilanes with epoxysilanes or (meth)acryloylsilanes or anhydridosilanes, amino-functional alkylsilsesquioxanes, cyanuric chloride and derivates or a combination thereof. Suitable aminosilane adhesion promoters include but are not limited to 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, aminomethyltrimethoxysilane, aminomethyltriethoxysilane, 3- aminopropylmethyldiethoxysilane, (N-2-aminoethyl)-3- aminopropyltrimethoxysilane, (N-2-aminoethyl)-3- aminopropyltriethoxysilane, diethylenetriaminopropyltrimethoxysilane, phenylaminomethyl-trimethoxysilane, (N-2-aminoethyl)-3- aminopropylmethyldimethoxysilane, 3-(N- phenylamino)propyltrimethoxysilane, 3- piperazinylpropylmethyldimethoxysilane, 3-(N,N- dimethylaminopropyl)aminopropylmethyldimethoxysilane, tri[(3- triethoxysilyl)propyl]amine, tri[(3-trimethoxysilyl)propyl]amine, and the oligomers thereof, 3-(N,N-dimethylamino)propyltrimethoxysilane, 3-(N,N- dimethylamino)-propyltriethoxysilane, (N,N- dimethylamino)methyltrimethoxysilane, (N,N- dimethylamino)methyltriethoxysilane, bis(3-trimethoxysilyl)propylamine, bis(3-triethoxysilyl)propylamine, and combinations thereof. Suitable epoxy silane adhesion promoters include but are not limited to 3-Glycidoxypropyltrimethoxysilane, 3- Glycidoxypropyltriethoxysilane, 3-Glycidoxypropylmethyldiethoxysilane, 2- (3,4-epoxycyclohexyl)ethyltrimethoxysilane. Suitable ureido silane adhesion promoters include but are not limited to 3-Ureidopropyltrimethoxysilane, 3-Ureidopropyltriethoxysilane. Suitable acryl silanes adhesion promoters include but are not limited to 3-Methacryloxypropyltrimethoxysilane, 3- Methacryloxypropylmethyldimethoxysilane. Suitable alkyl silanes adhesion promoters include but are not limited to Methyltrimethoxysilane, Methyltris-(methylethylketoxime)silane, n-octyltriethoxysilane, n-octyltrimethoxysilane, n-Propyltrimethoxysilane, Phenyltrimethoxysilane. Suitable chloro silane adhesion promoters include but are not limited to 3-Chloropropyltrimethoxysilane, 3-Chloropropyltriethoxysilane. Suitable sulfur silanes adhesion promoters include but are not limited to 3-Mercaptopropyltrimethoxysilane, 3- Mercaptopropylmethyldimethoxysilane, 3- Thiocyanatopropyltriethoxysilane. Suitable optional surface-active substances include a wetting agent, a levelling agent, a de-aerating agent, a defoamer or any combination thereof. Suitable optional biocides include an algicide, a fungicide or a substance that inhibits fungal growth, or a combination thereof and / or other substances customarily used in curable reactive polyurethane formulations. According to a further aspect of the invention, the use of the reactive polyurethane formulation according to the invention as an adhesive formulation is disclosed. According to a further aspect of the invention, the use of the reactive polyurethane formulation according to the invention as a sealant formulation is disclosed. According to a further aspect of the invention, the use of the reactive polyurethane formulation according to the invention as a coating formulation is disclosed. According to a further aspect of the invention, the use of the reactive polyurethane formulation according to the invention as an encapsulant formulation is disclosed. According to a further aspect of the invention, the use of the reactive polyurethane formulation according to the invention as a binder formulation is disclosed. According to a further aspect of the invention, the use of the reactive polyurethane formulation according to the invention as a grouting formulation is disclosed. According to a further aspect, an adhesive, sealant, coating, encapsulant, binder, grouting formulation comprising the reactive polyurethane formulation according to the invention and having less than 1 %, preferably less than 0.5 %, more preferably less than 0.1% by weight free diisocyanate monomers based on the total weight of the formulation is disclosed. According to a further aspect, a method of making a reactive polyurethane formulation suitable for use as an adhesive, sealant, coating, encapsulant, binder, grouting formulation having less than 1 %, preferably less than 0.5 %, more preferably less than 0.1% by weight free diisocyanate monomers based on the total weight of the formulation is disclosed, said method comprising at least the steps of mixing the ingredients (i) - (vii) of the reactive polyurethane formulation. The ingredients (ii) –(vii) may be combined and / or mixed before adding polyisocyanate composition (a). It is important for the corresponding end-applications that the reactive polyurethane formulation as detailed above remains substantially free of moisture during further storage in order to avoid premature crosslinking. Additional water scavengers can be employed to effect this requirement, but it is imperative that adequate and suitable packaging is used to exclude water as much as possible. EXAMPLES The monomeric diisocyanate content was determined by Currenta GmbH with the validated DIN EN ISO / IEC 17025 compliant method CAM- 0642303-18E (HPLC-MS / MS). Viscosity was measured with a TA®Instruments Discovery HR-2 rheometer (25mm parallel plate, 1 mm gap, shear rate 1 s-1) over a temperature range from 20 °C to 80 °C, with a ramp rate of 5 °C / min. A shore A hardness test was carried out 1 day after preparation of the reactive sealant formulation and after 4 weeks (1 month) of storage of the reactive sealant formulation in moisture tight cartridge in an oven at 40 °C. A difference in shore A hardness of 5 units or more between the 2 test values was considered significant. Preparation of Prepolymers Isocyanate terminated prepolymers were prepared by charging the ingredients into a clean 5-liter, 3-neck flaks equipped with an overhead stirrer, a thermocouple, and a nitrogen inlet. As a general procedure, the polyols were introduced first into the flask and homogeneously mixed while heated to 50 °C. Next, the diisocyanate monomer was introduced, where after the mixture was further stirred and homogenized. Subsequently, the catalyst was added together with any other necessary additives, and the mixture was heated to 70 °C. Reaction progress was monitored using ATR-FTIR or titration (ASTM D2572-19). Distillation of Prepolymers A glass short path evaporator (VTA) with an evaporative surface of 0,04 m² was used to remove diisocyanate monomers, especially diphenylmethane 4,4’-diisocyanate (MDI). To improve the efficiency of the distillation process, approximately 20% by weight of dimethyl phthalate was added to the prepolymer. The distillation was performed with a jacket temperature of 180 °C, a pressure 0,07 mbar, and a distillate condensation temperature of 30 °C. Mostly, a residual monomer concentration equal to or below 0,1 % by weight could be attained after one pass. If not, a second pass was performed, with following temperature and pressure settings: jacket temperature 170 °C pressure 0,07 mbar, distillate condensation temperature 50 °C. Prepolymer 1 (MDI based) 2029 g of Desmophen®2060 BD and 2029 g of Desmophen®4042 BT were reacted with 941 g of Desmodur®44M flakes to give a prepolymer with an NCO content of 3% by weight, a viscosity of 90 Pa.s at 20 °C and a residual diphenylmethane 4,4’-diisocyanate (MDI) concentration of 4.4% by weight. Prepolymer 2 (MDI based, distilled) 1279 g of Desmophen®2060 BD and 1279 g of Desmophen®4042 BT were reacted with 1441 g of Desmodur®44M flakes to give a prepolymer with an NCO content of 10% by weight and a viscosity of 4 Pa.s at 20 °C. The unreacted diphenylmethane 4,4’-diisocyanates were removed by short path distillation. Prior to distillation the prepolymer was mixed with 800 g of dimethyl phthalate. The prepolymer after distillation had an NCO content of 2.7% by weight, a viscosity of 20 Pa.s at 20°C and residual MDI content of 0.05% by weight. Prepolymer 3 (TDI based) 1228 g of Voranol®CP4755 and 2456 g of Acclaim®4200, spiked with 0.14 g of orthosphoric acid, 85% aqueous, were reacted with 311 g Desmodur®T80. The prepolymer thus obtained had an NCO content of 1.6% by weight, a viscosity of 16 Pa.s at 20 °C and a residual toluene diisocyanate (TDI) content of 0.14% by weight. Prepolymer 4 (TDI based) 3505 g of Desmophen®4042 BT, spiked with 0.27 g of orthosphoric acid, 85% aqueous, was reacted with 489 g of Desmodur®T80. The prepolymer thus obtained had an NCO content of 2.87% by weight, a viscosity of 18 Pa.s at 20 °C and a residual toluene diisocyanate (TDI) content of 0.60% by weight. PU White Paste In a planetary mixing vessel (Netzsch Planetary Mixing and Kneading Machine PMH 10) 1410 g of Mesamoll®(plasticizer) and 100 g of EFKA®8350 (dispersing agent) were charged. Next, 2492 g Tronox®R-FK-2 (titanium dioxide) was added and the resulting slurry was vigorously mixed for 15 minutes while applying vacuum suction. Afterwards, and additional 998 g of Mesamoll®was added, followed by an additional 10-minute mixing step with vacuum suction. Thixotropic Paste A solution of 14.09% by weight n-butylamine in DIDP was prepared. A solution of 24.11% by weight Desmodur®44M flakes in DIDP was prepared by melting the MDI flakes in DIDP, heated to 50 °C under nitrogen atmosphere. The amine solution was added dropwise to the MDI solution, while stirring vigorously and using ice-water cooling to keep the temperature below 120 °C. The resulting white paste-like material was stirred for an additional 30 minutes. Reactive Polyurethane Formulations For each composition, the ingredients in Table 1, Table 2 and Table 3 were mixed in the amounts specified using a Rochem®SpeedMixer DAC 600.2. Comparative sealant formulations RPF1 – RPF3 RPF 1 RPF 2 RPF3 Prepolymer 1 17.3% Prepolymer 2 18.9% 17.3% Prepolymer 3 6.7% 7.3% 6.7% Chalk122.6% 22.5% 32.5% PU White Paste 7.1% 7.1% 7.1% PVC Solvin®373 9.9% 9,9% 5.8% Plasticizer – DIDP22.6% 0,35% 0% pTSI 0.2% 0.2% 0.2% Thixotropic Paste 28.3% 28.2% 25.0% UV Stabilizer30.4% 0.4% 0.4% Adhesion Promotor40.3% 0.3% 0.3% Aldirez®BH 2.4% 2.8%2,4%Salicylic acid solution 2,2% 2,2% 2,2% Shore A hardness 30 26 29 Shore A hardness – 1 month 30 17 E100% - Alu (N / mm²) 0.33 0.35 0.41 Smax – Alu (N / mm²) 0.59 0.37 0.66 dl% at Smax -Alu 776 267 640 dl% at Break – Alu 800 269 642 Failure Mode TL Adh Adh Residual Monomer Concentration 0,77% 0,02% 0,02% (calculated) 1 Ground calcium carbonate – 5 µm 2 Diisodecyl Phthalate 3 Lowilite®UV B1260 4 trimethoxy[3-(oxiran-2-ylmethoxy)propyl]silane Table 1 Table 1 illustrates comparative sealant formulations which either have a (too) high monomer content or have a low monomer content achieved using state of the art distillation processes to remove the diisocyanate monomers. Comparative sealant formulation 1 (noted as RPF1) is prepared with a standard MDI prepolymer (noted as Prepolymer 1) having a diisocyanate monomer content (MDI) of 4.4 wt% based on the total weight of the reactive sealant formulation. It can be seen as a “state of the art” reference sealant formulation. Comparative sealant formulation 2 (noted as RPF2) and comparative sealant formulation 3 (noted as RPF3,) have been prepared with a distilled MDI prepolymer (noted as Prepolymer 2). Both the standard MDI prepolymer and the distilled MDI prepolymer have the same polyol composition. Table 1 further illustrates that diisocyanate monomer removal significantly impacted the adhesion on aluminum as illustrated for RPF 1 versus RPF 2. Formula adjustments, such as the removal of plasticizer and the reduction of thixotropic paste, can improve the adhesion on aluminum, but do not resolve the loss in matrix strength, as is proven by the decline in shore A hardness during a 1-month storage (RPF3). Sealant formulations according to the invention In this example the results of 4 sealant formulas according to the invention are shown in Table 2. Inventive sealant formulation 1 (RPF4) comprises 25.17 wt% Prepolymer 3, a bis-oxazolidine latent hardener (Incozol®EH), 0.38 wt% pMDI and 0.25 wt% VTMS based on the total weight of the reactive polyurethane formulation. Inventive sealant formulation 2 (RPF5) has a similar composition to inventive sealant formulation 1 (RPF4) but a lower prepolymer 3 and thixotropic paste concentration, and a higher concentration of PVC. Inventive sealant formulations 3 and 4 (noted as RPF6 and RPF7) comprises Prepolymer 3, a secondary prepolymer (Prepolymer 4) and a bis- aldimine latent hardener (Aldirez®BH from Incorez). Inventive sealant formulation 3 comprises pTSI and VTMS as moisture sensitive compound while inventive sealant formulation 4 comprises only pTSI as moisture sensitive compound. All 4 sealant formulations (RPF4 – RPF7) were hardness stable during storage and performed well in aluminum joints (ISO 8339). Notice that the amount of polymeric MDI needed to ensure a stable formula was impacted by the type of latent hardener (Incozol®EH versus Aldirez®BH).EX2713_99_1 EX2713_99_2 EX3081_36_2 EX3081_50RPF4 RPF5 RPF6 RPF7 Prepolymer 3 25.17% 21.60% 16.50% 17.96% Prepolymer 4 5.50% 5.98% Chalk135.15% 35.64% 35.75% 22.63% PU White Paste 8.64% 8.76% 8.88% 7.12% PVC Solvin®373 1.68% 8.58% 4.64% 9.89% pTSI 0.13% 0.22% Vinyl 0.25% 0.26% 0.12% trimethoxysilane Polymeric MDI 0.24% 0.25% 0.50% 0.50% Thixotropic 25.17% 21.60% 23.65% 28.23% Paste UV Stabilizer 0.10%20.10%20.10%20.42%3Adhesion 0.23% 0.24% 0.24% 0.24% Promotor4Incozol®EH 3.19% 2.82% Aldirez®BH 2.00% 2.10% Salicylic acid 0.17% 0.18% 2.00% 2.17% solution Shore A 33 34 30 23 hardness Shore A 33 30 30 25 hardness – 1m E100% - Alu 0.61 0.62 0.48 0.46 (N / mm²) Smax – Alu 0.84 1.05 0.71 0.65 (N / mm²) dl% at Smax - 354 528 552 557 Alu dl% at Break – 364 532 571 581 Alu Failure Mode Coh Coh Coh Coh Residual Monomer Concentration 2,2’-MDI < 0.001% < 0.001% < 0.001% < 0.001% 2,4’-MDI < 0.001% < 0.001% 0,004% 0.005% 4,4’-MDI 0.001% 0.001% 0,020% 0.035% 2,4-TDI < 0.001% < 0.001% 0,003% 0.003% 2,6-TDI 0.002% 0.002% 0.010% 0.014% ^ Monomers50.001% 0.001% 0.037% 0.057% 1 Ground calcium carbonate – 5 µm 2 Tinuvin®292 3 Lowilite®UV B1260 4 trimethoxy[3-(oxiran-2-ylmethoxy)propyl]silane 5 sum of the diisocyanate monomers by weight Table 2 Sealant formulations according to the invention In this example the results for 3 sealant formulations according to the invention are illustrated in Table 3. Inventive sealant formulation 5 (noted RPF8), 6 (noted as RPF 9) and 7 (noted as RPF10) have an identical composition, except the polymeric MDI concentration. Notice that the initial shore A hardness value was similar for all 3 formulations, when the hardness test was set up one day after production of the sealant, but that the formulations with a polymeric MDI concentration below 0.5% by weight, exhibited significant loss of hardness, when measured after a 1-month of storage at room temperature. In addition, the performance in aluminum joints (ISO 8339) was likewise correlated with the polymeric MDI concentration. These examples illustrate the importance of choosing the optimal polymeric MDI concentration considering the desired maximal monomer content in the sealant and its performance in stability. EX3081_33_8 EX3081_33_3 EX3081_33_7RPF8 RPF9 RPF10 Prepolymer 3 18.70% 18.70% 18.70% Prepolymer 4 3.30% 3.30% 3.30% Chalk138% 38% 37.8% PU White Paste 8.88% 8.87% 8.84% PVC Solvin® 3734.64% 4.64% 4.64%pTSI 0.13% 0.13% 0.13% Polymeric MDI 0.13% 0.25% 0.50% Thixotropic Paste 21.66% 21.62% 21.55% UV Stabilizer20.10% 0.10% 0.10% Adhesion Promotor30.24% 0.24% 0.24% Aldirez®BH 2.21% 2.21% 2.21% Salicylic acid solution42.00% 2.00% 2.00% Shore A hardness 37 36 38 Shore A hardness – 1m 8 23 36E100% - Alu (N / mm²) 0.53 0.55 0.62 Smax – Alu (N / mm²) 0.54 0.61 0.69 dl% at Smax -Alu 164% 197% 247% dl% at Break – Alu 146% 199% 281% Failure Mode TL Adh TL 1 Ground calcium carbonate – 5 µm2Tinuvin®292 3 trimethoxy[3-(oxiran-2-ylmethoxy)propyl]silane 45% by weight of salicylic acid in dioctyl adipate Table 3 Calculus Example RPF 7 (see Table 2) is composed of 17.95% of prepolymer 3, which has a TDI monomer concentration of 0.14% and 5.98% of prepolymer 4 which has a TDI monomer concentration of 0.60%. Furthermore, RPF 7 contains 0.50% polymeric MDI, with an NCO value of 31% by weight and an MDI monomer concentration of 40% by weight. In addition, 0.22% by weight of para- toluenesulfonylisocyanate (pTSI) is also added. It is assumed that pTSI reacts fast with water present in the formulation and is converted to paratoluenesulfonylamide (pTSA). pTSA itself has the capacity to endcap an isocyanate group. If polymeric MDI and pTSI are mixed with some or all of the water containing ingredients in the formulation (chalk, thixotropic paste, plasticizer, PU white paste) than the minimal required amount of water (^^^^%^^2^^) to reduce the total monomer concentration to 0,1% by weight can be calculated as follows: Equation 1 With ^^^^^^^^^^^^the molecular weight of pTSI; ^^^^^^^^^^the molecular weight of an isocyanate group and ^^^^^^2^^the molecular weight of water. q is the extent of the reaction in the isocyanate groups of pMDI and is defined as follows: With [^^^^^^^^^^^^^^]0the initial concentration of pMDI isocyanate groups and with [^^^^^^^^^^^^^^]∞the concentration of pMDI isocyanate groups after all the pTSI and water has reacted. For pMDI with its equally reactive isocyanate groups, the mass fraction free (diisocyanate) monomers present after reaction is equal to: ^^^^% ^^^^^^^^^^^^%^^^^^^ ^^^^ ^^^^^^^^(1 − ^^)2 Equation 3 With ^^^^%^^^^^^ ^^^^ ^^^^^^^^the weight fraction of MDI in pMDI. Since the target monomer concentration in the reactive polyurethane formula is set to 0.1% by weight, this requirement imposes that: (^^^^%^^^^^^^^^^^^^^^^^^^^ − ^^^^%^^^^^^^^^^3^^^^%^^^^^^^^^^^^^^^^^^^^^^^^3 − ^^^^%^^^^^^^^^^4^^^^%^^^^^^^^^^^^^^^^^^^^^^^^4)= ^^^^% ^^^^% (2 ^^^^^^^^ ^^^^^^ ^^^^ ^^^^^^^^ 1 − ^^)Equation 4 With ^^^^%^^^^^^^^^^3the weight fraction of Prepolymer 3, ^^^^%^^^^^^^^^^^^^^^^^^^^^^^^3the weight fraction diisocyanate monomers in Prepolymer 3, ^^^^%^^^^^^^^^^4the weight fraction of Prepolymer 4, ^^^^%^^^^^^^^^^^^^^^^^^^^^^^^4the weight fraction of diisocyanate monomers in Prepolymer 4. Rearrangement of the formula gives an expression in q: with the requirement that: Equation 7 Input of the actual amounts into Equation 1 and Equation 5 gives: In addition, the molar ratio excess diisocyanate monomers to water is equal to 0.6:1, while the molar ratio excess diisocyanate monomers to pTSI isequal to: 0.4:1. Thus, a calculated concentration 0.03 wt% of water is required to ensure that RPF 7 has a diisocyanate monomer concentration of 0.1 wt%. This number can be used as a guideline to indicate whether the raw materials contain sufficient moisture when preparing the reactive polyurethane formulation. In the case that the moisture sensitive compound (c) is an organotrialkoxysilane, such as vinyltrimethoxysilane, we assume for calculation purposes, that on average 1 mole of vinyltrimethoxysilane reacts with 1,5 moles of water, releasing 1,5 moles of methanol. For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described. Of course, it is to be appreciated that any one of the above embodiments or processes may be combined with one or more other embodiments or processes to provide even further improvements in finding and matching designs and advantages.

Claims

CLAIMS1. A reactive polyurethane formulation suitable for use as a sealant,coating, binder, encapsulant, grout or adhesive, said formulation comprising polyurethane prepolymers having free isocyanate groups and having less than 1%, preferably less than 0.5%, more preferably less than 0.1% by weight free diisocyanate monomers based on the total weight of the formulation, said formulation obtained by combining at least following ingredients: (i) 11 - 40 %, preferably 15 - 35%, more preferably 18 - 33% byweight of a polyisocyanate composition (a) and comprising polyurethane prepolymers formed by reacting at least one polyol with at least one polyisocyanate, wherein the at least one polyisocyanate is used in an amount such that the NCO groups are present in molar excess relative to the hydroxyl groups of the at least one polyol and the NCO / OH ratio is in the range 1.4 - 3, preferably in the range 1.8 - 2.2; and (ii) 0.1 - 3 %, preferably 0.1 - 2%, more preferably 0.1 - 1% byweight of a polyisocyanate composition (b) having a functionality equal to or greater than 2 and containing 20 up to 100 %, preferably 35 - 100% by weight free diisocyanate monomers based on the total weight of polyisocyanate composition (b), and (iii) 0.01 - 5 %, preferably 0.01 - 3%, more preferably 0.01 - 2%by weight of at least one moisture sensitive compound (c) of whose hydrolysis products give at least one monofunctional isocyanate reactive compound (d), and (iv) water, and(v) optionally 0 - 80%, and preferably 0 - 50% by weight offillers, and (vi) optionally an amount of latent hardener sufficient for itsat least 1 hydrolysis product to react with at least 30%, more preferably at least 50% and most preferably at least 70% of the polyisocyanate composition (a), and (vii) optionally further additives or mixtures of additivesselected from but not limited to rheology modifiers, pigments, plasticizers, catalysts, solvents, UV stabilizers, light stabilizers, acid scavengers, adhesion promotors and biocides wherein the % by weight of polyisocyanate composition (a), polyisocyanate composition (b), the at least one moisture sensitive compound (c), the optional latent hardener, fillers and further optional additives is based on the total weight of the reactive polyurethane formulation, and wherein the average isocyanate reactivity of the free isocyanate groups originating from polyisocyanate composition (a) towards water and / or the at least one isocyanate reactive hydrolysis products (d) is lower compared to the average isocyanate reactivity of the free isocyanate groups originating from the polyisocyanate composition (b) towards water or / and the at least one isocyanate reactive hydrolysis products (d), and wherein the molar ratio of the excess moles of diisocyanate monomer compounds present in polyisocyanate composition (a) and (b) towards the moles of isocyanate reactive products selected from water and the at least one hydrolysis product from the moisture sensitive compound (c) is in the range 3:1 – 0.6:1 preferably 2:1 – 0.6:1 and more preferably 1.1:1 – 0.6:1, most preferably 0.6:1 such that the final diisocyanate monomer content in the polyurethane formulation is below 1% , preferably below0.5%, more preferably below 0.1% by weight based on the total weight of the formulation, and wherein the excess moles of diisocyanate monomer compounds refer to the moles of diisocyanate monomer in polyisocyanate composition (a) and / or (b) that need to be converted by reaction with water and polyisocyanate reactive compound (d) to ensure that the mass concentration of all diisocyanate monomers in the reactive polyurethane formulation after mixing is below 1 wt%, preferably below 0.5 wt% or most preferably below 0.1 wt% based on the total weight of the reactive polyurethane formulation.

2. The reactive polyurethane formulation according to claim 1,wherein the polyisocyanate in polyisocyanate composition (a) is selected from asymmetric diisocyanates, preferably selected from toluene diisocyanate, more preferably 2,4-toluene diisocyanate (2,4-TDI)) or asymmetric methylenediphenyl diisocyanate (MDI) selected from 2,4'- methylenediphenyl diisocyanate (2,4’ MDI).

3. The reactive polyurethane formulation according to claim 1,wherein the polyisocyanate in polyisocyanate composition (a) is selected from symmetric diisocyanates, preferably selected from 4,4'- methylenediphenyl diisocyanate (MDI) with the precaution that any unreacted diisocyanates in polyisocyanate composition (a) after forming the polyurethane prepolymer are removed, to any desired extent by distillation.

4. The reactive polyurethane formulation according to any offoregoing claims wherein polyisocyanate composition (a) comprises polyisocyanates selected from asymmetric diisocyanates and symmetric diisocyanates with the precaution that any unreacted diisocyanates in polyisocyanate composition (a) after forming the polyurethane prepolymer are removed, to any desired extent by distillation.

5. The reactive polyurethane formulation according to any offoregoing claims, wherein polyisocyanate composition (b) is comprising polymeric MDI, more preferably polyisocyanate composition (b) is selectedfrom polymeric MDI which comprises at least 20% up to 50% by weight diisocyanate monomers based on the total weight of polyisocyanate composition (b).

6. The reactive polyurethane formulation according to any offoregoing claims, wherein the moisture sensitive compound (c) is selected from compounds comprising at least one reactive alkoxysilyl group, preferably selected from vinyl trialkoxysilanes, tetraalkoxysilanes, N- (methyldimethoxysilylmethyl)-O-methylcarbamate, (methacryloyloxymethyl)silanes, methoxymethylsilanes, more preferably selected from vinyltrimethoxysilane or vinyltriethoxysilane.

7. The reactive polyurethane formulation according to any offoregoing claims 1-5, wherein the moisture sensitive compound (c) is selected from orthoformic esters such as trimethyl orthoformate and triethyl orthoformate.

8. The reactive polyurethane formulation according to any offoregoing claims 1-5, wherein the moisture sensitive compound (c) is selected from mono-isocyanates such as p-Toluenesulfonyl isocyanate (pTSI) or mono-oxazolidines such as 3-ethyl-2-methyl-2-(3-methylbutyl)-1,3- oxazolidine, 3-butyl-2-(heptan-3-yl)-1,3-oxazolidine.

9. The reactive polyurethane formulation according to any offoregoing claims, wherein the optional adhesion promoter is selected from an aminosilane, an epoxy silane, an ureido silane, an acryl silane, an alkyl silane, a chloro silane, a sulfur silane, a vinyl silane, or a combination thereof.

10. The reactive polyurethane formulation according to any offoregoing claims, further comprising optionally, based on the total weight of the formulation, 0-50 wt%, preferably 0-30 wt%, more preferably 0-15 wt% further additive compounds wherein the additive compounds are selected from a filler, a pigment, a dye a stabilizer, a catalyst, a rheology controlagent, a tackifier, a flame retardant, a surface-active substance, a biocide or a combination thereof.

11. Use of the reactive polyurethane formulation according to any offoregoing claims as a sealant formulation, an adhesive formulation, an encapsulant formulation, a grouting formulation or a binder formulation.

12. Use according to claim 11 to improve adhesion to metal surfacesand avoiding reduction of hardness of the sealant formulation, the adhesive formulation, the encapsulant formulation, the grouting formulation or the binder formulation after storage.

13. A formulation comprising the reactive polyurethane formulationaccording to any of claims 1-10 and having less than 1 %, preferably less than 0.5 %, more preferably less than 0.1% by weight free diisocyanate monomers based on the total weight of the formulation.

14. A method of making formulation according to claim 13, saidmethod comprising at least the steps of combining and / or mixing the ingredients (i) - (vii) according to any of claims 1-10.

15. The method according to claim 14 wherein the ingredients (ii) –(vii) are mixed before adding polyisocyanate composition (a) to the reactive polyurethane formulation according to any of claims 1-10.

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