Process for producing a monool or polyol comprising a polyoxymethylene block

Description

[0001] The present invention describes a process for preparing a monol or polyol comprising a polyoxymethylene block.

[0002] Block copolymers containing polyoxymethylene units in addition to other polymer and polycondensate units are described, for example, in JP 2007 211082 A, WO 2004 / 096746 A1, GB 807589, EP 1 418 190 A1, US 3,754,053, US 3,575,930, US 2002 / 0016395, EP 3 129 419 B1 and JP 04-306215.

[0003] EP 3 653 657 A1 discloses a process for preparing prepolymers comprising a polyoxymethylene block, prepolymers obtainable by such a process and mixtures of these prepolymers with OH-reactive compounds, preferably polyisocyanates.

[0004] US 3575930 A describes a process for producing NCO prepolymers by reacting low-molecular-weight polymeric formaldehyde (pFA) with an excess of diisocyanates. The low-molecular-weight pFA fractions are obtained by extraction with boiling dioxane (bp 101 °C) and subsequent filtration and are not storable. Furthermore, an energy-intensive azeotropic distillation step with benzene is necessary to remove water from the low-molecular-weight pFA fractions in solution before the low-molecular-weight polymeric formaldehyde can be reacted with diisocyanates. Furthermore, the described azeotropic distillation and the reaction of pFA with diisocyanates take place at relatively high temperatures, resulting in decomposition reactions that form significant amounts of monomeric formaldehyde.

[0005] DE 26 49 800 describes a process for producing polyoxymethylene in the presence of catalysts, in which gaseous, anhydrous formaldehyde is introduced into a reaction medium containing an organic solvent such as n-heptane and a polymeric catalyst. Polyoxymethylene refers to formaldehyde polymers with a molecular weight of at least 10,000 g / mol.

[0006] EP 3 498 743 A1 discloses a process for producing a prepolymer containing polyoxymethylene groups, comprising the step of reacting a polyol component, wherein the polyol component comprises a polyoxymethylene containing OH end groups, with a compound reactive toward OH groups, wherein the reaction is carried out in the presence of an ionic fluorine compound. In the examples, a monofunctional isocyanate is used as the OH-reactive compound, so that as a result of the reaction of the polyoxymethylene containing OH end groups with the monofunctional isocyanate, no NCO functionalities necessary for the subsequent PU reaction remain in the prepolymer.

[0007] WO 2004 / 096746 A1 discloses the reaction of formaldehyde oligomers with alkylene oxides or isocyanates. A formalin solution is first evaporated at 80 °C and 120 mbar and then reacted with propylene oxide in the presence of a basic catalyst, forming low-molecular-weight adducts of two molecules of propylene oxide and two molecules of formaldehyde.

[0008] WO 2014 / 095679 A1 discloses a process for preparing NCO-modified polyoxymethylene block copolymers, comprising the step of polymerizing formaldehyde in a reaction vessel in the presence of a catalyst, wherein the polymerization of formaldehyde is further carried out in the presence of a starter compound having at least 2 Zerewitinoff-active H atoms to obtain an intermediate product, which is reacted with an isocyanate.

[0009] EP 3498743 A1 describes a process for producing a prepolymer containing polyoxymethylene groups, comprising the step of reacting a polyol component with a compound reactive toward OH groups, wherein the polyol component comprises a polyoxymethylene containing OH end groups whose OH end groups are not part of carboxyl groups. The reaction is carried out in the presence of an ionic fluorine compound, wherein the ionic fluorine compound is a coordinatively saturated compound. A disadvantage of this process is that fluorine compounds must be removed before the prepolymers are converted into polyurethane foams, as they can have a negative effect on the foam formation reactions.

[0010] WO 2020 / 099601 A1 discloses a process for producing an NCO-terminated prepolymer using reactive Soxhlet extraction, in which a solution consisting of polymeric formaldehyde in an aprotic solvent with a boiling point of less than or equal to 60 °C at 1 bara is transferred from a first container to a second container containing a polyisocyanate and converted into the NCO-terminated prepolymer. The solvent is continuously recycled from the second container to the first container.

[0011] US 1948069 A discloses a process for producing soluble paraformaldehyde by azeotropic distillation of a mixture of an aqueous formaldehyde solution and organic solvents, wherein in the specific embodiment, an azeotropic distillation of an approximately 40 vol% aqueous formaldehyde solution is carried out with ethyl acetate at 69 to 70°C and the resulting paraformaldehyde is separated from the solution by filtration or gentle pressing and then dried at 100°C.

[0012] US 2,823,237 discloses a process for producing highly soluble paraformaldehyde, wherein a methanolic formaldehyde solution with a water content of not more than 10 wt.% is distilled in vacuo at a temperature of 10 °C to 35 °C.

[0013] According to the current state of the art, the conversion of polymeric formaldehyde is either carried out at relatively high temperatures, which leads to depolymerization of the polymeric formaldehyde compounds, or additional fluorine-containing compounds must sometimes be added as solubilizers to improve the solubility of the poorly soluble polymeric formaldehyde, which can interfere with subsequent reactions such as the polyurethaneization reaction and must be removed in an additional process step. Furthermore, the use of methanolic formaldehyde solutions is also disclosed, although monofunctional methanol reduces the average functionality of the prepolymer.In addition, a high proportion of physically bound water in formaldehyde solutions is disadvantageous for the subsequent reaction of hydroxyl-containing formaldehyde with hydroxyl-reactive compounds such as polyisocyanates to form prepolymer compounds, preferably NCO-terminated prepolymers, since significant amounts of urea are formed as a result of the undesirable side reaction of the water with the polyisocyanate.

[0014] Based on the prior art, the object arose to provide an easily scalable and thermally gentle process for converting sparingly soluble polymeric formaldehydes or formalin solutions into technically processable, readily soluble polyols with an adjustable number of oxymethylene repeat units, without the addition of unnecessary solubilizers or monofunctional cosolvents, so that the soluble compounds are chemically stable and thus storable, and can also be used directly in downstream reactions such as, for example, for the production of reactive prepolymer compounds, preferably NCO-terminated prepolymers. The monols or polyols according to the invention comprising a polyoxymethylene block should also have a proportion of physically bound water of less than 2.0 wt.%, preferably less than 1.0 wt.%, particularly preferably less than 0.5 wt.-%, so that urea formation is reduced as an undesirable side reaction in the subsequent reaction of the monol or polyol with polyisocyanates to form NCO-terminated prepolymers. Another aspect of the process according to the invention is the reduction of solvent requirements.

[0015] According to the invention, the object is achieved by a process for producing a monol or polyol comprising a polyoxymethylene block according to claim 1, the monol or polyol according to claim 11, a process for producing a prepolymer according to claim 13 and the resulting prepolymer according to claim 14, as well as a process for producing a reaction product, preferably a polyurethane, according to claim 15. Advantageous further developments are specified in the subclaims. They can be combined as desired unless the context clearly indicates otherwise.

[0016] According to the invention, this object is achieved by a process for producing a monol or polyol comprising a polyoxymethylene block, preferably a polyol comprising a polyoxymethylene block, the process comprising the following steps: i) providing a formaldehyde-containing mixture (A) containing formaldehyde in a polar solvent (A) and optionally in a polar solvent (C); ii) adding a non-polar solvent (B) to the formaldehyde-containing solution i) or a formaldehyde-containing suspension i) to form a mixture ii); iii) removing the solvent (A), the solvent (B) and optionally the solvent (C) from the mixture ii) to form a monol or polyol comprising a polyoxymethylene block, wherein the removal of the solvent (A), the solvent (B) and optionally the solvent (C) in step iii) takes place at a temperature of 0 °C to 80 °C, preferably from 30 °C to 60 °C and a pressure of 0.01 °mbara to 5000 °mbara, preferably from 0.1 °mbara to 2000 °mbara, particularly preferably from 1 mbara to 1000 mbara and most preferably from 1 mbara to 500 mbara; wherein the solvent (A) is different from the solvent (B); and wherein the solvent (B) and optionally the solvent (C) do not contain any OH-reactive functional groups and do not themselves react with OH-reactive compounds.

[0017] The use of the word "one" in connection with countable quantities here and below is to be understood as a number only if this is clear from the context (e.g., by the phrase "exactly one"). Otherwise, expressions such as "one polymeric formaldehyde compound" etc. always also include embodiments in which two or more polymeric formaldehyde compounds etc. are used.

[0018] The invention is explained in detail below. Various embodiments can be combined with one another as desired, unless the context clearly indicates otherwise to a person skilled in the art.

[0019] According to the common technical definition, a monol is understood to be a compound having one terminal hydroxyl group, whereas a polyol is understood to be a compound having more than one terminal hydroxyl group, preferably 2 to 10, particularly preferably from 2 to 5, very particularly preferably from 2 to 3 terminal hydroxyl groups.

[0020] According to the invention, a polyol comprising a polyoxymethylene block is preferably prepared.

[0021] In one embodiment of the process according to the invention, the formaldehyde-containing mixture (A) is obtainable by mixing polymeric formaldehyde with the polar solvent (A) and optionally the polar solvent (C). Depending on the concentration or solubility of the polymeric formaldehyde in the polar solvent (A) and optionally the polar solvent (C), the result is the formaldehyde-containing suspension i) or a formaldehyde-containing solution i), preferably a formaldehyde-containing suspension i).

[0022] In one embodiment of the process according to the invention, the formaldehyde-containing mixture (A) is a formaldehyde-containing solution i) or a formaldehyde-containing suspension i), preferably a formaldehyde-containing suspension i).

[0023] In one embodiment of the process according to the invention, the proportion of formaldehyde in the polar solvent (A) in step i) is 1 wt.% to 99 wt.%, preferably 10 wt.% to 50 wt.%, particularly preferably 15 wt.%-40 wt.%.

[0024] In one embodiment of the process according to the invention, the formaldehyde-containing mixture (A) is the formaldehyde-containing solution i).

[0025] According to the common technical definition, a solution is a homogeneous mixture of at least two substances in which a solid, liquid or gaseous substance (solvate such as polymeric formaldehyde) is homogeneously distributed in a mostly liquid solvent (solvent such as solvent (A) and / or solvent (C)).

[0026] In one embodiment of the process according to the invention, the proportion of formaldehyde in the formaldehyde-containing solution is i) 1 wt.% to 50 wt.%, preferably 10 wt.% to 45 wt.%, particularly preferably 10 wt.% to 40 wt.%.

[0027] In a preferred embodiment of the process according to the invention, the formaldehyde-containing solution i) is prepared by dissolving 1 wt.% to 40 wt.%, preferably 10 wt.% to 35 wt.% of the polymeric paraformaldehyde in water as polar solvent (A).

[0028] In an alternative embodiment of the process according to the invention, a formalin solution is used as the formaldehyde-containing solution i). The formalin solution is preferably an aqueous, methanol-containing formalin solution with a formaldehyde content of 1 wt.% to 50 wt.%, preferably 10 wt.% to 45 wt.%, particularly preferably 10 wt.% to 40 wt.%, and a methanol content of less than 5 wt.%, preferably less than 3 wt.%, and particularly preferably 1.5 wt.%.

[0029] In an alternative embodiment of the process according to the invention, the formaldehyde-containing mixture (A) is the formaldehyde-containing suspension i).

[0030] According to general technical knowledge, a suspension is understood to be a heterogeneous mixture of a liquid such as solvent (A) and / or solvent (C) and solid particles distributed therein, such as polymeric formaldehyde, whereby phase boundaries result between the dispersed particles and the liquid.

[0031] In an alternative embodiment of the process according to the invention, the proportion of formaldehyde in the formaldehyde-containing suspension is i) 10 wt.% to 99 wt.%, preferably 50 wt.% to 95 wt.%, particularly preferably 60 wt.%-90 wt.%.

[0032] In one embodiment of the process according to the invention, the formaldehyde-containing mixture (A) is obtainable by mixing polymeric formaldehyde with the polar solvent (A) and optionally the polar solvent (C).

[0033] In one embodiment of the process according to the invention, polymeric formaldehyde is used, wherein the polymeric formaldehyde has m terminal hydroxyl group and m is a natural number of two or more, preferably of 2 or 3.

[0034] Suitable polymeric formaldehyde for the process according to the invention are, in principle, those oligomeric and polymeric forms of formaldehyde which have at least one, preferably at least two, terminal hydroxyl groups for reaction with the OH-reactive groups of an OH-reactive compound. The term "terminal hydroxyl group" is understood, according to the invention, to mean, in particular, a terminal hemiacetal functionality which arises as a structural feature upon polymerization of the formaldehyde. For example, the starter compounds can be oligomers and polymers of formaldehyde of the general formula HO-(CH 2 O) n -H, where n is a natural number ≥ 2 and polymeric formaldehyde typically has n > 8 repeating units.

[0035] Polymeric formaldehyde suitable for the process according to the invention generally has molar masses of 62 to 30,000 g / mol, preferably from 62 to 12,000 g / mol, particularly preferably from 242 to 6,000 g / mol and very particularly preferably from 242 to 3,000 g / mol and comprises from 2 to 1,000, preferably from 2 to 400, particularly preferably from 8 to 200 and very particularly preferably from 8 to 100 oxymethylene repeat units. The polymeric formaldehyde used in the process according to the invention typically has a functionality (F), ie has a terminal hydroxyl group, of 2 to 3, but in certain cases these can also be more highly functional, ie have a functionality > 3. Preferably, open-chain polymeric formaldehyde with terminal hydroxyl groups is used in the process according to the invention, which has a functionality of 2 to 10, preferably of 2 to 5, particularly preferably of 2 to 3.Most preferably, linear polymeric formaldehyde having a functionality of 2 with two terminal hydroxyl groups is used in the process according to the invention. The functionality F corresponds to the number of terminal OH end groups (terminal hydroxyl groups m) per molecule.

[0036] The production of polymeric formaldehyde, which is used for the process according to the invention, can be carried out by known processes (cf. e.g. M. Haubs et al., 2012, Polyoxymethylenes, Ullmann's Encyclopedia of Industrial Chemistry; G. Reus et al., 2012, Formaldehyde, ibid ) .The polymeric formaldehyde can in principle also be used in the form of a copolymer in the process according to the invention, wherein, in addition to formaldehyde, for example, 1,4-dioxane or 1,3-dioxolane are copolymerized as comonomers. Further suitable formaldehyde copolymers for the process according to the invention are copolymers of formaldehyde and trioxane with cyclic and / or linear formals, such as, for example, butanediol formal, epoxides or cyclic carbonates (cf., for example, EP 3 080 177 B1). It is also conceivable that higher homologous aldehydes, such as, for example, acetaldehyde, propionaldehyde, etc., are incorporated into the formaldehyde polymer as comonomers. It is also conceivable that polymeric formaldehyde according to the invention is again prepared starting from H-functional starter compounds; in particular, polymeric formaldehyde with a hydroxyl end group functionality F > 2 can be obtained by using polyfunctional starter compounds (cf., for example,WO 1981001712 A1, Bull. Chem. Soc. J., 1994, 67, 2560-2566, US 3436375, JP 03263454, JP 2928823).

[0037] Formaldehyde is known to polymerize even in the presence of small traces of water. Therefore, in aqueous solution, depending on the concentration and temperature of the solution, a mixture of oligomers and polymers of different chain lengths forms, which are in equilibrium with molecular formaldehyde and formaldehyde hydrate. So-called paraformaldehyde precipitates from the solution as a white, poorly soluble solid and is usually a mixture of linear formaldehyde polymers with 8 to 100 oxymethylene repeat units.

[0038] A particular advantage of the process according to the invention is that either aqueous formalin solution or polymeric formaldehyde, so-called paraformaldehyde, both of which are commercially available in large quantities and at low cost and have a favorable CO2 balance, can be used directly.

[0039] A polyoxymethylene group (polyoxymethylene block (POM)) within the meaning of the invention denotes a polymeric structural unit -(CH 2 -O-) x , where x is an integer ≥ 2, which contains at least one CH 2 group bonded to two oxygen atoms, which is connected to further methylene groups or other polymeric structures via at least one of the oxygen atoms. Polyoxymethylene blocks -(CH 2 -O-) x preferably contain an average of x ≥ 3 to x ≤ 25, more preferably an average of x ≥ 4 to x ≤ 18, and particularly preferably an average of x ≥ 5 to x ≤ 12 oxymethylene units.

[0040] For the purposes of the invention, a polyoxymethylene block is also understood to mean blocks which contain small proportions of further repeating units made up of monomeric and / or oligomeric units other than the oxymethylene repeating units, the proportion of these units generally being less than 25 mol%, preferably less than 10 mol%, preferably less than 5 mol%, based on the total amount of monomer units contained in the block. According to general technical knowledge (cf. G. Reus et al., 2012, Formaldehyde, Ullmann's Encyclopedia of Industrial Chemistry; 2012), these repeating units made up of monomeric and / or oligomeric units other than the oxymethylene repeating units are, for example, free water or water bound in the polyoxymethylene block.

[0041] In a preferred embodiment, the polyoxymethylene block does not contain any further portions of further repeating units made up of monomeric and / or oligomeric units other than the oxymethylene repeating units.

[0042] In one embodiment of the process according to the invention, the polar solvent (A) has a boiling point of <300 °C, preferably <250, particularly preferably <200 °C and very particularly preferably <150 °C at 1 bara.

[0043] In a preferred embodiment of the process according to the invention, the polar solvent (A) is one or more compounds and is selected from the group consisting of water, glycerol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butanediol, preferably water, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, and particularly preferably water.

[0044] In a particularly preferred embodiment of the process according to the invention, the polar solvent (A) is water.

[0045] In the process according to the invention, the non-polar solvent (B) contains no OH-reactive functional groups and does not react with OH-reactive compounds. According to the invention, nitromethane, acetonitrile, methyl acetate, 1,3-dioxolane, ethyl formate, dimethoxymethane, tetrahydrofuran, ethyl acetate, 1,4-dioxane, methyl propanoate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and 2-butanone are not non-polar solvents.

[0046] In one embodiment of the process according to the invention, the non-polar solvent (B) has a boiling point of <300 °C, preferably <250, particularly preferably <200 °C and very particularly preferably <150 °C at 1 bara.

[0047] In one embodiment of the process according to the invention, the non-polar solvent (B) forms an azeotrope with the solvent (A), preferably with water, under the process conditions according to the invention in steps ii) and iii).

[0048] In one embodiment of the process according to the invention, the non-polar solvent (B) is one or more compound(s) and is selected from the group consisting of trichloromethane, trichloroethene, 1,2-dichloroethane, 1-bromopropane, 1-bromobutane, 1-bromo-2-methylpropane, 1-chloro-2-methylpropane, 1,2-dichloropropane, carbon tetrachloride, dichloromethane, isopropyl acetate, propyl acetate, butyl acetate, isobutyl acetate, propyl formate, butyl formate, isobutyl formate, propyl propionate, ethyl propionate, isopentyl acetate, butyl propionate, butyl butyrate, butyl ethyl ether, dibutyl ether, diethyl ether, benzene, toluene, styrene, m-xylene, p-xylene, o-xylene, ethylbenzene, isopropenylbenzene, isopropylbenzene, cyclohexene, n, iso-hexene, n, iso-heptene, 2-methyl-1,3-butadiene, methylenecyclobutane, 2-methyl-2-butene, hexane, cyclohexane, heptane, methylcyclohexane, octane, 2,2,4-trimethylpentane, nonane, decane, petroleum ether, preferably trichloromethane,Trichloroethene, 1,2-dichloroethane, 1-bromopropane, 1-bromobutane, 1-bromo-2-methylpropane, 1-chloro-2-methylpropane, 1,2-dichloropropane, carbon tetrachloride, dichloromethane, butyl ethyl ether, dibutyl ether, diethyl ether, benzene, toluene, styrene, m-xylene, p-xylene, o-xylene, ethylbenzene, isopropenylbenzene, isopropylbenzene, cyclohexene, n, iso-hexene, n, iso-heptene, 2-methyl-1,3-butadiene, methylenecyclobutane, 2-methyl-2-butene, hexane, cyclohexane, heptane, methylcyclohexane, octane, 2,2,4-trimethylpentane, nonane, decane, petroleum ether, particularly preferably benzene, toluene, m-xylene, p-xylene, o-xylene, hexane, cyclohexane, heptane, methylcyclohexane and most preferably p-xylene, cyclohexane, methylcyclohexane and toluene.

[0049] In the process according to the invention, the polar solvent (C) does not contain any OH-reactive functional groups and does not react with OH-reactive compounds.

[0050] In one embodiment of the process according to the invention, the polar solvent (C) forms an azeotrope with solvent (A), preferably with water, under process conditions in step i).

[0051] In one embodiment of the process according to the invention, the polar solvent (C) is one or more compounds and is selected from the group consisting of nitromethane, acetonitrile, methyl acetate, 1,3-dioxolane, ethyl formate, dimethoxymethane, tetrahydrofuran, ethyl acetate, 1,4-dioxane, methyl propanoate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 2-butanone, preferably nitromethane, ethyl acetate, methyl propanoate, ethyl formate, particularly preferably ethyl acetate.

[0052] In one embodiment of the method according to the invention, step i) comprises the following steps: i-1) Providing the formaldehyde-containing solution i) in the solvent (A), preferably water i-2) Optionally adding a polar solvent (C) to the formaldehyde-containing solution i) i-3) Reducing the solvent (A) and optionally the solvent (C) to form a formaldehyde-containing suspension i-3).

[0053] In one embodiment of the process according to the invention, the volumetric ratio of the polar solvent (A) added in step i-1) to the polar solvent (C) added in step i-2) is from 0.02:1 to 50:1, preferably from 0.02:1 to 10:1.

[0054] In one embodiment of the process according to the invention, the reduction of the solvent (A) and optionally of the solvent (C) in step i-3) takes place at a temperature of 0 °C to 80 °C, preferably from 30 °C to 60 °C and at a pressure of 0.01 °mbara to 5000 °mbara, preferably from 0.1 °mbara to 2000 °mbara, particularly preferably from 1 mbara to 1000 mbara and very particularly preferably from 1 mbara to 500 mbara and for 15 min to 40 h, preferably 60 min to 30 h, particularly preferably 120 min to 20 h.

[0055] In a preferred embodiment of the process according to the invention, step i) further comprises the following steps: i-4) Addition of a polar solvent (C) to the formaldehyde-containing suspension i-3) to form a formaldehyde-containing mixture i-4), i-5) Reduction of the solvent (A) and optionally of the solvent (C) from the formaldehyde-containing mixture i-4) to form a formaldehyde-containing suspension i-5).

[0056] In one embodiment of the process according to the invention, the reduction of the solvent (A) and the solvent (C) in step i-3) and step i-5) is carried out at a temperature of 0 °C to 80 °C, preferably from 30 °C to 60 °C and at a pressure of 0.01 °mbara to 5000 °mbara, preferably from 0.1 °mbara to 2000 °mbara, particularly preferably from 1 mbara to 1000 mbara and very particularly preferably from 1 mbara to 500 mbara and for 15 min to 40 h, preferably 60 min to 30 h, particularly preferably 120 min to 20 h.

[0057] In step ii), the non-polar solvent (B) is added to the formaldehyde-containing solution i) or formaldehyde-containing suspension i) to form a mixture ii), wherein the addition can be carried out continuously or discontinuously. Continuous addition is understood to mean a volume flow of the solvent (B) in step ii) of > 0 mL / min, wherein the volume flow is constant or can be varied. Discontinuous addition, on the other hand, also means interim volume flows V(2) of 0 mL / min between two successive volume flows V(1) and V(3) with > 0 mL / min in step ii). One such embodiment for the discontinuous addition is the stepwise addition of the solvent (B).

[0058] In one embodiment of the process according to the invention, the volumetric ratio of the non-polar solvent (B) added in step ii) to the polar solvent (A) and solvent (C) added in step i) is from 500:1 to 0.1:1, preferably from 200:1 to 0.5:1.

[0059] In step iii), the solvent (A), the solvent (B) and optionally the solvent (C) are removed from the mixture ii) to form an oxymethylene group-containing monol or polyol, preferably polyol, at a temperature of 0 °C to 80 °C, preferably from 30 °C to 60 °C and a pressure of 0.01 °mbara to 5000 °mbara, preferably from 0.1 °mbara to 2000 °mbara, particularly preferably from 1 mbara to 1000 mbara and very particularly preferably from 1 mbara to 500 mbara, wherein the removal can be carried out continuously or discontinuously, preferably continuously.

[0060] Here, the temperature for removing the solvent (A), the solvent (B) and optionally the solvent (C) in step iii) corresponds to the temperature of the mixture ii) and the pressure of the apparatus containing the mixture ii) in step iii).

[0061] In one embodiment of the process according to the invention, in step iv) the solvent mixture comprising the polar solvent (A), the non-polar solvent (B) and optionally the polar solvent (C) from step iii) is separated, resulting in a first fraction comprising the polar solvent (A) and / or the polar solvent (C) and a second fraction comprising the non-polar solvent (B).

[0062] The separation of the solvents can be carried out by means of distillative and / or extractive methods known to the person skilled in the art, wherein for the process according to the invention, in particular density and polarity differences of the first fraction comprising the polar solvent (A) and / or the polar solvent (C), preferably consisting of the polar solvent (A) and / or the polar solvent (C), and the second fraction comprising the non-polar solvent (B), preferably consisting of the non-polar solvent (B), are used.

[0063] In one embodiment of the process according to the invention, in step v), the second fraction comprising the solvent (B) consisting of the non-polar solvent (B) is recycled and is added in step ii) to the formaldehyde-containing solution i) or formaldehyde-containing suspension i) to form a mixture ii). This recirculation procedure consisting of steps ii) to v) allows a significant amount of the non-polar solvent (B) to be saved.

[0064] In a further embodiment, the first fraction comprising the polar solvent (A) and / or the polar solvent (C) can also be recycled in step v), and in step i), specifically step i-1) for the polar solvent (A), and in step i-3) the polar solvent (C) can be added again. This recirculation procedure consisting of steps i) to v) allows a significant amount of the polar solvent (A) and / or the polar solvent (C) to be saved.

[0065] The recycling of the polar solvent (A) and / or the non-polar solvent (B) and optionally the polar solvent (C) in step v) can be carried out continuously or discontinuously (stepwise).

[0066] In a first embodiment, the invention relates to a process for producing a monol or polyol comprising a polyoxymethylene block, preferably a polyol comprising a polyoxymethylene block, the process comprising the following steps: i) providing a formaldehyde-containing mixture (A) containing formaldehyde in a polar solvent (A) and optionally in a polar solvent (C); ii) adding a non-polar solvent (B) to the formaldehyde-containing solution i) or a formaldehyde-containing suspension i) to form a mixture ii); iii) removing the solvent (A), the solvent (B) and optionally the solvent (C) from the mixture ii) to form the monol or polyol comprising a polyoxymethylene block, wherein the removal of the solvent (A), the solvent (B) and optionally the solvent (C) in step iii) takes place at a temperature of 0 °C to 80 °C, preferably from 30 °C to 60 °C and a pressure of 0.01 °mbara to 5000 °mbara, preferably from 0.1 °mbara to 2000 °mbara, particularly preferably from 1 mbara to 1000 mbara and most preferably from 1 mbara to 500 mbara;wherein the solvent (A) is different from the solvent (B); and wherein the solvent (B) and optionally the solvent (C) do not contain any OH-reactive functional groups and do not themselves react with OH-reactive compounds.

[0067] In a second embodiment, the invention relates to a process according to the first embodiment, wherein the formaldehyde-containing mixture (A) is obtainable by mixing polymeric formaldehyde with the polar solvent (A) and optionally the polar solvent (C).

[0068] In a third embodiment, the invention relates to a process according to the first or second embodiment, wherein the polar solvent (A) is one or more compounds and is selected from the group consisting of water, glycerol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butanediol, preferably water, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, and particularly preferably water.

[0069] In a fourth embodiment, the invention relates to a process according to any one of the first to third embodiments, wherein the non-polar solvent (B) is one or more compound(s) and is selected from the group consisting of trichloromethane, trichloroethene, 1,2-dichloroethane, 1-bromopropane, 1-bromobutane, 1-bromo-2-methylpropane, 1-chloro-2-methylpropane, 1,2-dichloropropane, carbon tetrachloride, dichloromethane, isopropyl acetate, propyl acetate, butyl acetate, isobutyl acetate, propyl formate, butyl formate, isobutyl formate, propyl propionate, ethyl propionate, isopentyl acetate, butyl propionate, butyl butyrate, butyl ethyl ether, dibutyl ether, diethyl ether, benzene, toluene, styrene, m-xylene, p-xylene, o-xylene, ethylbenzene, isopropenylbenzene, Isopropylbenzene, cyclohexene, n, iso-hexene, n, iso-heptene, 2-methyl-1,3-butadiene, methylenecyclobutane, 2-methyl-2-butene, hexane, cyclohexane, heptane, methylcyclohexane, octane, 2,2,4-trimethylpentane,Nonane, decane, petroleum ether, preferably trichloromethane, trichloroethene, 1,2-dichloroethane, 1-bromopropane, 1-bromobutane, 1-bromo-2-methylpropane, 1-chloro-2-methylpropane, 1,2-dichloropropane, carbon tetrachloride, dichloromethane, butyl ethyl ether, dibutyl ether, diethyl ether, benzene, Toluene, styrene, m-xylene, p-xylene, o-xylene, ethylbenzene, isopropenylbenzene, isopropylbenzene, cyclohexene, n, iso-hexene, n, iso-heptene, 2-methyl-1,3-butadiene, methylenecyclobutane, 2-methyl-2-butene, hexane, cyclohexane, heptane, Methylcyclohexane, octane, 2,2,4-trimethylpentane, nonane, Decane, petroleum ether, particularly preferably benzene, toluene, m-xylene, p-xylene, o-xylene, hexane, cyclohexane, heptane, methylcyclohexane and very particularly preferably p-xylene, cyclohexane, methylcyclohexane and toluene.

[0070] In a fifth embodiment, the invention relates to a process according to any one of the first to fourth embodiments, wherein the non-polar solvent (B) forms an azeotrope with the solvent (A), preferably with water, under the process conditions according to the invention in steps ii) and iii).

[0071] In a sixth embodiment, the invention relates to a process according to one of the first to fifth embodiments, wherein the formaldehyde-containing mixture (A) is a formaldehyde-containing solution i) or a formaldehyde-containing suspension i), preferably a formaldehyde-containing suspension i).

[0072] In a seventh embodiment, the invention relates to a process according to any one of the first to sixth embodiments, wherein the proportion of formaldehyde in the polar solvent (A) in step i) is 1 wt.% to 99 wt.%, preferably 10 wt.% to 50 wt.%, particularly preferably 15 wt.%-40 wt.%.

[0073] In an eighth embodiment, the invention relates to a process according to any one of the first to seventh embodiments, wherein the formaldehyde-containing mixture (A) is the formaldehyde-containing solution i) and is prepared by dissolving polymeric paraformaldehyde in the polar solvent (A).

[0074] In a ninth embodiment, the invention relates to a process according to any one of the first to eighth embodiments, wherein the formaldehyde-containing mixture (A) is the formaldehyde-containing solution i).

[0075] In a tenth embodiment, the invention relates to a process according to the ninth embodiment, wherein the proportion of formaldehyde in the formaldehyde-containing solution is i) 1 wt.% to 50 wt.%, preferably 10 wt.% to 45 wt.%, particularly preferably 10 wt.% to 40 wt.%.

[0076] In an eleventh embodiment, the invention relates to a process according to the ninth or tenth embodiment, wherein the formaldehyde-containing solution i) is prepared by dissolving 1 wt.% to 40 wt.%, preferably 10 wt.% to 35 wt.% of the polymeric paraformaldehyde in water as polar solvent (A).

[0077] In a twelfth embodiment, the invention relates to a process according to the first to eighth embodiments, wherein the formaldehyde-containing mixture (A) is the formaldehyde-containing suspension i).

[0078] In a thirteenth embodiment, the invention relates to a process according to the twelfth embodiment, wherein the proportion of formaldehyde in the formaldehyde-containing suspension i) is 10 wt.% to 99 wt.%, preferably 50 wt.% to 95 wt.%, particularly preferably 60 wt.%-90 wt.%.

[0079] In a fourteenth embodiment, the invention relates to a process according to any one of the eighth to thirteenth embodiments, wherein polymeric formaldehyde is used and the polymeric formaldehyde has a terminal hydroxyl group and m is a natural number of two or more, preferably of 2 or 3.

[0080] In a fifteenth embodiment, the invention relates to a method according to any one of the first to fourteenth embodiments, wherein step i) comprises the following steps: i-1) Providing a formaldehyde-containing solution i) in the solvent (A), preferably water i-2) Optionally adding a polar solvent (C) to the formaldehyde-containing solution i) i-3) Reducing the solvent (A) and optionally the solvent (C) to form a formaldehyde-containing suspension i-3).

[0081] In a sixteenth embodiment, the invention relates to a process according to the fifteenth embodiment, wherein the volumetric ratio of the polar solvent (A) added in step i-1) to the polar solvent (C) added in step i-2) is from 0.02:1 to 50:1, preferably from 0.02:1 to 10:1.

[0082] In a seventeenth embodiment, the invention relates to a process according to the fifteenth or sixteenth embodiment, wherein the reduction of the solvent (A) and optionally of the solvent (C) in step i-3) is carried out at a temperature of 0 °C to 80 °C, preferably from 30 °C to 60 °C and at a pressure of 0.01 °mbara to 5000 °mbara, preferably from 0.1 °mbara to 2000 °mbara, particularly preferably from 1 mbara to 1000 mbara and very particularly preferably from 1 mbara to 500 mbara and for 15 min to 40 h, preferably 60 min to 30 h, particularly preferably 120 min to 20 h.

[0083] In an eighteenth embodiment, the invention relates to a method according to any one of the fifteenth to seventeenth embodiments, wherein step i) further comprises the following steps: i-4) Addition of a polar solvent (C) to the formaldehyde-containing suspension i-3) to form a formaldehyde-containing mixture i-4), i-5) Reduction of the solvent (A) and optionally the solvent (C) from the formaldehyde-containing mixture i-4) to form a formaldehyde-containing suspension i-5),

[0084] In a nineteenth embodiment, the invention relates to a process according to any one of the first to eighteenth embodiments, wherein the volumetric ratio of the non-polar solvent (B) added in step ii) to the polar solvent (A) and solvent (C) added in step i) is from 500:1 to 0.1:1, preferably from 200:1 to 0.5:1.

[0085] In a twentieth embodiment, the invention relates to a process according to any one of the first to nineteenth embodiments, wherein the polar solvent (C) is one or more compounds and is selected from the group consisting of nitromethane, acetonitrile, methyl acetate, 1,3-dioxolane, ethyl formate, dimethoxymethane, tetrahydrofuran, ethyl acetate, 1,4-dioxane, methyl propionate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 2-butanone, preferably nitromethane, ethyl acetate, methyl propionate, and ethyl formate, particularly preferably ethyl acetate.

[0086] In a twenty-first embodiment, the invention relates to a method according to one of the first to twentieth embodiments, wherein the method further comprises the following steps: iv) Separating the solvent mixture comprising the polar solvent (A), the non-polar solvent (B) and optionally the polar solvent (C) from step iii) v) Recycling the non-polar solvent (B) to step ii) Examples Connections used:

[0087] Granuform (polymeric formaldehyde): (Granuform®< M or Granuform®< 96, (formaldehyde content according to the manufacturer 94.5 - 96.5 wt.%), Prefere Paraform GmbH & Co. KG). Formalin: Formaldehyde solution in water (formaldehyde content according to the manufacturer 32.05 wt.%, methanol content 1.26 wt.%, Covestro Deutschland AG). Ethyl acetate-1 (> 98%, Julius Hoesch GmbH & Co. KG, no pretreatment). Ethyl acetate-2 (> 99.5%, Sigma-Aldrich, dried over CaH 2 , distilled, and stored over a 4 Å molecular sieve). Cyclohexane (> 99%, Acros Organics, no pretreatment). Toluene (> 98%, Julius Hoesch GmbH & Co. KG, no pretreatment). p-Xylene (> 99%, Sigma-Aldrich, no pretreatment) TDI (Desmodur T 100, toluene-2,4-diisocyanate, > 99%, Covestro Deutschland AG, no pretreatment) n -Pentane (> 99%, Acros Organics, dried over 4 Å molecular sieve) Dibutyltin dilaurate (95%, Sigma-Aldrich, no pretreatment) DMSO-d6 (99.80% D, Euriso-Top GmbH, dried over 4 Å molecular sieve) Dimethoxymethane, DMM (99.9%, Sigma-Aldrich Chemie GmbH, dried over CaH 2 , distilled and stored over 4 Å molecular sieve) Dioxane (> 99%, Sigma-Aldrich, no pretreatment) Benzene (> 99%, Sigma-Aldrich, no pretreatment) Method description:

[0088] Structure of the azeotropic rectification: A 250 mL three-neck flask is equipped with a KPG stirrer and connected to a Dean-Stark adapter (water separator). The entire apparatus is vacuum-tight, and the Dean-Stark adapter is additionally cooled to 0 °C with a cryostat.

[0089] 1< H-NMR spectroscopy:The measurements were performed on a Bruker Avance III 300 (300 MHz) or Bruker Avance III 400 (400 MHz); the calibration of the chemical shifts was performed relative to the residual proton signal (DMSO-d6: δ 1< H = 2.50 ppm); the multiplicity of the signals was given as follows: s = singlet, m = multiplet.

[0090] Polyoxymethylene group content: The average content of polyoxymethylene groups n in the polyol comprising a polyoxymethylene block was determined using 1< H-NMR spectroscopy by integrating the characteristic proton signals. The characteristic signals of the hydroxyl end groups (OH) are in the range of 6.5-5.7 ppm. The characteristic signals of the polyoxymethylene groups (OCH 2 ) are in the range of 5.05-4.4 ppm. After the integral of the OH signal was normalized to two, the content of polyoxymethylene groups n in the polyols according to the invention comprising a polyoxymethylene block can be calculated using the following formula: n − = Integral OCH 2 2

[0091] Free water content: The physically bound water content (free water content) of the inventive polyols comprising a polyoxymethylene block was determined using 1< H-NMR spectroscopy. The ratios of the corresponding signals (OH [δ 1< H 6.5-5.7 ppm], H 2 O [δ 1< H 3.33 ppm]) were determined by integration, and the water content was calculated using the following formula: Wassergehalt % = MW H 2 O n × MW OCH 2 + MW H 2 O × Integral OH Integral H 2 O + MW H 2 O × 100 %

[0092] NCO prepolymer / urea ratio: The selectivity for NCO prepolymer formation was determined as the molar ratio between product (NCO prepolymer) and byproduct (urea) in the product mixture. The NCO prepolymer / urea ratio was determined using 1< H NMR spectroscopy by integrating the corresponding signals (NH groups of carbamate units of the prepolymer [δ 1< H 9.89 ppm], NH groups of urea [δ 1< H 8.72 ppm]). NCO Präpolymer / Harnstoff Verhältnis − = Integral NH Präpolymer Integral NH Harnstoff

[0093] The integral of the NH groups of the prepolymer was normalized to 100.

[0094] Polyol (comprising a polyoxymethylene block) Sales: The conversion of polyol (comprising a polyoxymethylene block) in the reaction with TDI was determined using 1< H NMR spectroscopy. The characteristic signals of the hydroxyl end groups (OH [δ 1 < H 6.5-5.7 ppm]) were considered for this purpose. The integral of the characteristic signals of the polyoxymethylene groups in direct proximity to the carbamate unit (OCH 2 * [δ 1 < H 5.34 ppm]) was normalized to four. If no signals of the hydroxyl end groups were observed after the reaction (the total integral of the range 6.5-5.7 ppm was <0.1), the conversion of polyol (comprising a polyoxymethylene block) was assumed to be >95%.

[0095] Determination of particle size distribution:Woven wire mesh sieves (frame diameter 100 mm, standards: ISO 3310-1 / ASTM E11) are stacked on top of each other in decreasing mesh size. The sample material (pFA) is placed on the coarsest wire mesh sieve, and the sieves are secured in a sieving machine (Retsch AS 200 basic). The sieves are vibrated for 30 minutes, and the mass fractions of the individual fractions are determined. The mass of the smallest fraction that has passed all sieve sizes (<45 µm) is determined as the difference between the initial weight and the sum of all other weighed fractions. Examples of the production process of polyols comprising a polyoxymethylene block Example 1: Azeotropic rectification of a formaldehyde-containing suspension i) with cyclohexane as non-polar solvent (B)

[0096] A pressure bottle was filled with Granuform (15.0 g) and deionized water (30 mL). Heating the reaction mixture to 110 °C for approximately 10 hours yielded a clear formaldehyde solution (approximately 32 wt% formaldehyde).

[0097] The formaldehyde solution was concentrated to 87 wt.% using a rotary evaporator: the bath temperature was 40 °C, the distillation pressure was between 40 and 60 mbar with a pressure reduction of 5 mbar per 45 min. The distillation time was 3 hours. The resulting cloudy suspension (approx. 17.3 g) was then transferred to the azeotropic rectification setup and treated with cyclohexane (75 mL). The water from the formaldehyde solution was then further removed by azeotropic rectification at 40 °C under reduced pressure (240-250 mbar). After 25 hours, a suspension of the polyol comprising a polyoxymethylene block in cyclohexane was obtained. The product was collected by filtration as a colorless solid and then dried. A sample of the obtained product (polyol comprising a polyoxymethylene block) was completely dissolved in DMSO-d6 and subsequently characterized by 1< H-NMR spectroscopy: Polyoxymethylene group content: n = 9.0. Free water content: 0.3 wt.%. Example 2 (comparison): Azeotropic rectification of a formaldehyde-containing suspension i) with ethyl acetate as solvent (C)

[0098] A pressure bottle was filled with Granuform (15.0 g) and deionized water (30 mL). Heating the reaction mixture to 110 °C for approximately 10 hours yielded a clear formaldehyde solution (approximately 32 wt% formaldehyde).

[0099] The formaldehyde solution was concentrated to 87 wt.% using a rotary evaporator: the bath temperature was 40 °C, the distillation pressure was between 40 and 60 mbar with a pressure reduction of 5 mbar per 45 min. The distillation time was 3 hours. The resulting cloudy suspension (approx. 17.3 g) was immediately transferred to the azeotropic rectification setup and treated with ethyl acetate-1 (75 mL). The water from the formaldehyde solution was further removed by azeotropic rectification at 40 °C under reduced pressure (240-250 mbar). After 25 hours, a suspension of the polyol comprising a polyoxymethylene block in ethyl acetate was obtained. The product was collected by filtration as a colorless solid and then dried. A sample of the resulting polyol comprising a polyoxymethylene block was completely dissolved in DMSO-d6 and subsequently characterized by 1< H-NMR spectroscopy: Polyoxymethylene group content: n = 5.5. Free water content: 5.6 wt.%. Example 3: Azeotropic rectification of a formaldehyde-containing suspension i) with p -Xylene as a non-polar solvent (B)

[0100] A pressure bottle was filled with Granuform (15.0 g) and deionized water (30 mL). Heating the reaction mixture to 110 °C for approximately 10 hours yielded a clear formaldehyde solution (approximately 32 wt% formaldehyde).

[0101] The formaldehyde solution was concentrated to 87 wt.% using a rotary evaporator: the bath temperature was 40 °C, the distillation pressure was between 40 and 60 mbar with a pressure reduction of 5 mbar / 45 min. The distillation time was 3 hours. The resulting cloudy suspension (approx. 17.3 g) was immediately transferred to the azeotropic rectification setup and p-xylene (75 mL). The water from the formaldehyde solution was further removed by azeotropic rectification at 40 °C under reduced pressure (40 mbar). After 20 hours, a suspension of the polyol comprising a polyoxymethylene block in p- Xylene was obtained. The product was collected by filtration as a colorless solid and then dried. A sample of the resulting polyol, comprising a polyoxymethylene block, was completely dissolved in DMSO-d6 and subsequently characterized using 1< H-NMR spectroscopy: Polyoxymethylene group content: n = 9.1. Free water content: 0.2 wt.%. Example 4 (Comparison): Azeotropic rectification of a formaldehyde-containing suspension i) without addition of an additional non-polar solvent (B)

[0102] A pressure bottle was filled with Granuform (15.0 g) and deionized water (30 mL). Heating the reaction mixture to 110 °C for approximately 10 hours yielded a clear formaldehyde solution (approximately 32 wt% formaldehyde).

[0103] The formaldehyde solution was concentrated to 87 wt.% using a rotary evaporator: the bath temperature was 40 °C, the distillation pressure was between 40 and 60 mbar with a pressure reduction of 5 mbar / 45 min. The distillation time was 3 hours. The resulting cloudy suspension (approx. 17.3 g) was immediately transferred to the azeotropic rectification setup. No additional solvent was added. The water from the formaldehyde solution was further removed by distillation at 40 °C under reduced pressure (40 mbar). After 20 hours, the polyol comprising a polyoxymethylene block was obtained as a colorless solid. A sample of the resulting product was completely dissolved in DMSO-d6 and subsequently characterized using 1< H-NMR spectroscopy: Polyoxymethylene group content: n = 7.9. Free water content: 6.9 wt.%. Example 5: Azeotropic rectification of a formaldehyde-containing suspension i) with toluene as a non-polar solvent (B)

[0104] A pressure bottle was filled with Granuform (15.0 g) and deionized water (30 mL). Heating the reaction mixture to 110 °C for approximately 10 hours yielded a clear formaldehyde solution (approximately 32 wt% formaldehyde).

[0105] The formaldehyde solution was concentrated to 87 wt.% using a rotary evaporator: the bath temperature was 40 °C, the distillation pressure was between 40 and 60 mbar with a pressure reduction of 5 mbar / 45 min. The distillation time was 3 hours. The resulting cloudy suspension (approx. 17.3 g) was immediately transferred to the azeotropic rectification setup and mixed with toluene (75 mL). The water from the formaldehyde solution was further removed by azeotropic rectification at 40 °C under reduced pressure (90 mbar). After 20 hours, a suspension of the polyol comprising a polyoxymethylene block in toluene was obtained. The product was collected by filtration as a colorless solid and then dried. A sample of the resulting product was completely dissolved in DMSO-d6 and subsequently characterized using 1< H NMR spectroscopy: Polyoxymethylene group content: n = 8.8. Free water content: 0.3 wt.%. Example 6: Azeotropic rectification of a formaldehyde-containing suspension i) with toluene as a non-polar solvent (B)

[0106] Formalin (45.0 g) was concentrated to 87 wt.% using a rotary evaporator. The bath temperature was 40 °C, and the distillation pressure was between 40 and 60 mbar, with a pressure reduction of 5 mbar / 45 min. The distillation time was 3 hours. The resulting cloudy suspension (approx. 17.3 g) was immediately transferred to the azeotropic rectification setup and treated with toluene (75 mL). The water from the formaldehyde solution was further removed by azeotropic rectification at 40 °C under reduced pressure (90 mbar). After 20 hours, a suspension of the polyol comprising a polyoxymethylene block in toluene was obtained. The product was collected by filtration as a colorless solid and then dried. A sample of the resulting product was completely dissolved in DMSO-d6 and subsequently characterized using 1< H NMR spectroscopy: Polyoxymethylene group content: n = 8.5. Free water content: 0.4 wt.%. Example 7: Azeotropic rectification of a formaldehyde-containing solution i) with toluene as a non-polar solvent (B)

[0107] A pressure bottle was filled with Granuform (15.0 g) and deionized water (30 mL). Heating the reaction mixture to 110 °C for approximately 10 hours yielded a clear formaldehyde solution (approximately 32 wt% formaldehyde).

[0108] The formaldehyde solution was transferred to the azeotropic rectification setup and mixed with toluene (75 mL). The water from the formaldehyde solution was removed by azeotropic rectification at 40 °C under reduced pressure (90 mbar). After 40 hours, a suspension of the polyol containing a polyoxymethylene block in toluene was obtained. The product was collected by filtration as a colorless solid and then dried. A sample of the resulting product was completely dissolved in DMSO-d6 and subsequently characterized using 1< H NMR spectroscopy: Polyoxymethylene group content: n = 9.0. Free water content: 0.4 wt.%. Example 8: Azeotropic rectification of a formaldehyde-containing suspension i) with ethyl acetate as polar solvent (C) and cyclohexane as non-polar solvent (B)

[0109] A pressure bottle was filled with Granuform (15.0 g) and deionized water (30 mL). Heating the reaction mixture to 110 °C for approximately 10 hours yielded a clear formaldehyde solution (approximately 32 wt% formaldehyde).

[0110] The formaldehyde solution was concentrated to 87 wt.% using a rotary evaporator. The bath temperature was 40 °C, and the distillation pressure was between 40 and 60 mbar, with a pressure reduction of 5 mbar per 45 min. The distillation time was 3 hours. The resulting cloudy suspension (approx. 17.3 g) was immediately transferred to the azeotropic rectification setup and treated with ethyl acetate-1 (75 mL). The water from the formaldehyde solution was further removed by azeotropic rectification at 40 °C under reduced pressure (240-250 mbar). After 20 hours, cyclohexane was added to the resulting suspension (150 mL). The mixture was distilled at 240-250 mbar and 40 °C for 5 hours, while 150 mL of cyclohexane was added portionwise to the mixture during this time. The product was obtained by filtration as a colorless solid and then dried.A sample of the obtained product was completely dissolved in DMSO-d6 and subsequently characterized by 1< H-NMR spectroscopy: . Polyoxymethylene group content: n = 8.2. Free water content: 0.3 wt.%. Table 1: Summary of the number-average number of polyoxymethylene repeating units n and the free water content for polyols containing polyoxymethylene blocks for different process conditions. Example LM (A) Mixture (A) LM (B) LM (C) T(iii) [°C] p(iii) [mbar] t(iii) [h] na)< w(H 2 O) [wt.%] b)< 1 H2O suspension Cyclohexane - 40 240-250 25 9.0 0.3 2 (cf.) H2O suspension - ESEE 40 240-250 25 5.5 5.6 3 H2O suspension p-xylene 40 40 20 9.1 0.2 4 (cf.) H2O suspension - - 40 40 20 7.9 6.9 5 H2O suspension toluene 40 90 20 8.8 0.3 6 H2O suspension toluene 40 90 20 8.5 0.4 7 H2O Solution toluene 40 90 40 9.0 0.4 8 H2O suspension Cyclohexane ESEE 40 240-250 25 8.2 0.3 a) n number-average number of polyoxymethylene repeating units, b) w(H 2 O) free water content determined by proton resonance spectroscopy (cf.) Comparative example Table 2 Determination of the particle size distribution for the polyol containing a polyoxymethylene block prepared according to Example 1 and Example 8. Particle sizes [µm] Example 1 [wt.%] Example 8 [wt.%] <45 1.13 4.77 45-125 29.21 39.07 125-250 8.64 51.47 250-500 14.98 4.36 500-1000 10.45 0.26 1000-2000 17.87 0.07 >2000 17.72 0 Examples of the preparation process of isocyanate group-terminated prepolymers comprising a polyoxymethylene block by reacting the polyols comprising a polyoxymethylene block according to Examples 1 to 6 with toluene-2,4-diisocyanate Example 9:

[0111] Polyol comprising a polyoxymethylene block (1.0 g) from Example 1 was suspended by stirring in ethyl acetate-2 (10 mL) for approximately 10 hours at room temperature. Subsequently, an excess of toluene-2,4-diisocyanate (approx. 12 g) in the presence of a dibutyltin dilaurate catalyst (10-40 mg) was initially charged to another reaction vessel, and the previously obtained suspension was added dropwise at 40 °C. The reaction mixture was stirred for a further hour at 40 °C. The solvent (ethyl acetate) was removed under reduced pressure in a cold trap, and the residue was thoroughly washed with dried n-pentane (3-4 times), yielding the reaction product as a colorless solid. NCO prepolymer / urea ratio: 100 / 9. Polyol comprising a polyoxymethylene block. Conversion: >95%. Example 10 (comparison):

[0112] Polyol comprising a polyoxymethylene block (1.0 g) from Example 2 was suspended by stirring in ethyl acetate-2 (10 mL) for approximately 10 hours at room temperature. Subsequently, an excess of toluene-2,4-diisocyanate (approx. 12 g) in the presence of a dibutyltin dilaurate catalyst (10-40 mg) was initially charged to another reaction vessel, and the previously obtained suspension was added dropwise at 40 °C. The reaction mixture was stirred for a further hour at 40 °C. The solvent (ethyl acetate) was removed under reduced pressure in a cold trap, and the residue was thoroughly washed with dried n-pentane (3-4 times), yielding the reaction product as a colorless solid. NCO prepolymer / urea ratio: 100 / 105. Polyol comprising a polyoxymethylene block. Conversion: >95%. Example 11:

[0113] Polyol comprising a polyoxymethylene block (1.0 g) from Example 3 was suspended by stirring in ethyl acetate-2 (10 mL) for about 10 hours at room temperature. Subsequently, an excess of toluene-2,4-diisocyanate (about 12 g) in the presence of a dibutyltin dilaurate catalyst (10-40 mg) was placed in another reaction vessel, and the previously obtained suspension was added dropwise at 40 °C. The reaction mixture was stirred for a further hour at 40 °C. The solvent (ethyl acetate) was removed under reduced pressure in a cold trap, and the residue was washed with dried n -Pentane was completely washed (3-4 times) and the reaction product was obtained as a colorless solid. NCO prepolymer / urea ratio: 100 / 7. Polyol comprising a polyoxymethylene block. Conversion: >95%. Example 12 (comparison):

[0114] Polyol comprising a polyoxymethylene block (1.0 g) from Example 4 was suspended by stirring in ethyl acetate-2 (10 mL) for approximately 10 hours at room temperature. Subsequently, an excess of toluene-2,4-diisocyanate (approx. 12 g) in the presence of a dibutyltin dilaurate catalyst (10-40 mg) was initially charged to another reaction vessel, and the previously obtained suspension was added dropwise at 40 °C. The reaction mixture was stirred for a further hour at 40 °C. The solvent (ethyl acetate) was removed under reduced pressure in a cold trap, and the residue was thoroughly washed with dried n-pentane (3-4 times), yielding the reaction product as a colorless solid. NCO prepolymer / urea ratio: 100 / 117. Polyol comprising a polyoxymethylene block. Conversion: >95%. Example 13:

[0115] Polyol comprising a polyoxymethylene block (1.0 g) from Example 5 was suspended by stirring in ethyl acetate-2 (10 mL) for about 10 hours at room temperature. Subsequently, an excess of toluene-2,4-diisocyanate (about 12 g) in the presence of a dibutyltin dilaurate catalyst (10-40 mg) was placed in another reaction vessel, and the previously obtained suspension was added dropwise at 40 °C. The reaction mixture was stirred for a further hour at 40 °C. The solvent (ethyl acetate) was removed under reduced pressure in a cold trap, and the residue was washed with dried n -Pentane was completely washed (3-4 times) and the reaction product was obtained as a colorless solid. NCO prepolymer / urea ratio: 100 / 10. Polyol comprising a polyoxymethylene block. Conversion: >95%. Example 14:

[0116] Polyol comprising a polyoxymethylene block (1.0 g) from Example 6 was suspended by stirring in ethyl acetate-2 (10 mL) for about 10 hours at room temperature. Subsequently, an excess of toluene-2,4-diisocyanate (about 12 g) in the presence of a dibutyltin dilaurate catalyst (10-40 mg) was placed in another reaction vessel, and the previously obtained suspension was added dropwise at 40 °C. The reaction mixture was stirred for a further hour at 40 °C. The solvent (ethyl acetate) was removed under reduced pressure in a cold trap, and the residue was washed with dried n -Pentane was completely washed (3-4 times) and the reaction product was obtained as a colorless solid. NCO prepolymer / urea ratio: 100 / 14. Polyol comprising a polyoxymethylene block. Conversion: >95%. Example 15 (Comparison): Reaction of pFA (Granuform ®< M) with toluene diisocyanate (TDI) according to Example 2 of US 3575930 A1 (reproduction of US3575930, Example 2)

[0117] Paraformaldehyde pFA (Granuform®< M, 10 g) was boiled in a flask with 90 g of dioxane for 2 min and filtered. The resulting solution was treated with 20 mL of benzene and dried by azeotropic distillation. Subsequently, 16.7 g of TDI were added, and the reaction mixture was heated to 91 °C for 6 h. In contrast to Example 2 of US 3575930 A1, no polymeric product could be filtered directly from the reaction solution. Even after removal of the volatile components at 35 °C and 10 mbar, no polymeric product or NCO prepolymer was obtained. The 1< H NMR spectrum of this yellow residue showed only signals attributable to TDI. No formation of polymers with NCO groups or NCO prepolymers could be observed.

[0118] NCO prepolymer / urea ratio: not determinable. Example 16 (Comparison): Reaction of Granuform ®< M with DMM and toluene-2,4-diisocyanate (TDI) by reactive Soxhlet extraction (EP 3653657 A1, Ex. 1)

[0119] 10.5 g of Granuform®< M was placed in the extraction thimble of a Soxhlet extractor. Polymeric formaldehyde was extracted by Soxhlet extraction with dimethoxymethane (DMM) as the solvent (200 mL) under reflux (60 °C oil bath temperature) and reacted with an excess of TDI (12.1 g) in the flask below. After 66 hours of extraction, the solvent was removed under reduced pressure, and the residue was washed with dried n-pentane, yielding the reaction product as a colorless solid.

[0120] NCO prepolymer / urea ratio: 100 / 36. Example 17 (Comparison): Preparation of a carbamate-protected polyoxymethylene polyol by reacting paraformaldehyde with 4-tolyl isocyanate using a fluoride salt (EP349743 A1, Example 1):

[0121] A flask was charged with 450 mg (1 mmol) of paraformaldehyde in 15 mL of dioxolane. 315 mg (1 mmol) of tetrabutylammonium fluoride trihydrate (NBu4F x 3H2O, TBAF) and 6 mg (0.01 mmol) of dubityltin dilaurate (DBTL) were added to the suspension, and the mixture was heated to 60 °C with stirring. 1070 mg (8 mmol) of 4-tolyl isocyanate was added to the mixture, and the reaction mixture was stirred for 15 minutes at 5000 rpm. A white solid was separated from the upper liquid phase. The solvent was removed from the liquid phase under partial vacuum, and the product mixture was obtained as a white solid. Yield: 1200 mg (29% considering 720 mg of urea and 260 mg of TBAF).

[0122] NCO prepolymer / urea ratio: 100 / 1043. Table 3: Comparison of NCO prepolymer to urea ratios and conversions for isocyanate group-terminated prepolymers. Example Polyol comprising a polyoxymethylene block of T [°C] T [min] NCO prepolymer / urea ratio Polyol comprising a polyoxymethylene block conversion [%] 9 Example 1 40 60 100 / 9 >95 10 (cf.) Example 2 (cf.) 40 60 100 / 105 >95 11 Example 3 40 60 100 / 7 >95 12 (cf.) Example 4 (cf.) 40 60 100 / 117 >95 13 Example 5 40 60 100 / 10 >95 14 Example 6 40 60 100 / 14 >95 15 (cf.) - 91 360 - nb 16 (cf.) - 60 3960 100 / 36 nb 17 (cf.) - 60 180 100 / 1043 nb nb: not determined.

Claims

1. Method for preparing a monol or polyol comprising a polyoxymethylene block, preferably a polyol comprising a polyoxymethylene block, the method comprising the following steps: i) providing a formaldehyde-containing mixture (A) containing formaldehyde in a polar solvent (A) and optionally in a polar solvent (C); ii) adding a nonpolar solvent (B) to the formaldehyde-containing solution i) or to a formaldehyde-containing suspension i) to form a mix ii); iii) removing the solvent (A), the solvent (B) and optionally the solvent (C) from the mix ii) to form the monol or polyol comprising a polyoxymethylene block, wherein the solvent (A), the solvent (B) and optionally the solvent (C) are removed in step iii) at a temperature from 0°C to 80°C, preferably from 30°C to 60°C, and a pressure from 0.01 °mbara to 5000 °mbara, preferably from 0.1 °mbara to 2000 °mbara, particularly preferably from 1 mbara to 1000 mbara, and most preferably from 1 mbara to 500 mbara; wherein the solvent (A) is not the same as the solvent (B); and wherein the solvent (B) and optionally the solvent (C) do not contain any OH-reactive functional groups and do not themselves react with OH-reactive compounds.

2. Method according to claim 1, wherein the formaldehyde-containing mixture (A) is obtainable by mixing polymer formaldehyde with the polar solvent (A) and optionally the polar solvent (C).

3. Method according to claim 1 or 2, wherein the polar solvent (A) is one or more compounds and is selected from the group consisting of water, glycerol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butanediol, preferably water, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, and particularly preferably water.

4. Method according to any of claims 1 to 3, wherein the nonpolar solvent (B) is one or more compounds and is selected from the group consisting of trichloromethane, trichloroethene, 1,2-dichloroethane, 1-bromopropane, 1-bromobutane, 1-bromo-2-methylpropane, 1-chloro-2-methylpropane, 1,2-dichloropropane, carbon tetrachloride, dichloromethane, isopropyl acetate, propyl acetate, butyl acetate, isobutyl acetate, propyl formate, butyl formate, isobutyl formate, propyl propionate, ethyl propionate, isopentyl acetate, butyl propionate, butyl butyrate, butyl ethyl ether, dibutyl ether, diethyl ether, benzene, toluene, styrene, m-xylene, p-xylene, o-xylene, ethyl benzene, isopropenyl benzene, isopropyl benzene, cyclohexene, n, isohexene, n, isoheptene, 2-methyl-1,3-butadiene, methylenecyclobutane, 2-methyl-2-butene, hexane, cyclohexane, heptane, methylcyclohexane, octane, 2,2,4-trimethylpentane, nonane, decane, petroleum ether, preferably trichloromethane, trichloroethene, 1,2-dichloroethane, 1-bromopropane, 1-bromobutane, 1-bromo-2-methylpropane, 1-chloro-2-methylpropane, 1,2-dichloropropane, carbon tetrachloride, dichloromethane, butyl ethyl ether, dibutyl ether, diethyl ether, benzene, toluene, styrene, m-xylene, p-xylene, o-xylene, ethyl benzene, isopropenyl benzene, isopropyl benzene, cyclohexene, n, isohexene, n, isoheptene, 2-methyl-1,3-butadiene, methylenecyclobutane, 2-methyl-2-butene, hexane, cyclohexane, heptane, methylcyclohexane, octane, 2,2,4-trimethylpentane, nonane, decane, petroleum ether, particularly preferably benzene, toluene, m-xylene, p-xylene, o-xylene, hexane, cyclohexane, heptane, methylcyclohexane, and very particularly preferably p-xylene, cyclohexane, methylcyclohexane and toluene.

5. Method according to any of claims 1 to 4, wherein the formaldehyde-containing mixture (A) is a formaldehyde-containing solution i) or a formaldehyde-containing suspension i), preferably a formaldehyde-containing suspension i).

6. Method according to any of claims 1 to 5, wherein step i) comprises the following steps: i-1) providing a formaldehyde-containing solution i) in the solvent (A), preferably water i-2) optionally adding a polar solvent (C) to the formaldehyde-containing solution i) i-3) reducing the solvent (A) and optionally the solvent (C) to form a formaldehyde-containing suspension i-3).

7. Method according to claim 6, wherein step i) further comprises the following steps: i-4) adding a polar solvent (C) to the formaldehyde-containing suspension i-3) to form a formaldehyde-containing mixture i-4), i-5) reducing the solvent (A) and optionally the solvent (C) from the formaldehyde-containing mixture i-4) to form a formaldehyde-containing suspension i-5).

8. Method according to any of claims 1 to 7, wherein the polar solvent (C) is one or more compounds and is selected from the group consisting of nitromethane, acetonitrile, methyl acetate, 1,3-dioxolane, ethyl formate, dimethoxymethane, tetrahydrofurane, ethyl acetate, 1,4-dioxane, methyl propionate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 2-butanone, preferably nitromethane, ethyl acetate, methyl propionate and ethyl formate, particularly preferably ethyl acetate.

9. Method according to any of claims 1 to 8, wherein the method also comprises the following steps: iv) separating the solvent mixture comprising the polar solvent (A), the nonpolar solvent (B) and optionally the polar solvent (C) from step iii) v) returning the nonpolar solvent (B) to step ii).