Preparation method of polyacetal polyol and application of polyacetal polyol in PU system

Abstract

The present invention relates to a method for preparing a polyacetal polyol, comprising the step (i) of reacting a compound (D1) having at least one OH group with a compound (C1) selected from the group consisting of vinyl ethers, aldehydes and acetals in the presence of a solid acid catalyst; a polyacetal polyol obtained in the process; the use of a polyacetal polyol obtained or obtainable according to said process; and a process for the preparation of polyurethanes.

Description

[0001] The present invention relates to a process for preparing a polyacetal polyol, comprising step (i): reacting a compound (D1) having at least one OH group with a compound (C1) in the presence of a solid acid catalyst, wherein the compound (C1) is selected from the group consisting of vinyl ethers, aldehydes and acetals; the polyacetal polyol obtained in the process; the use of the polyacetal polyol obtainable or obtained according to the process; and a process for preparing a polyurethane.

[0002] Polyurethane materials, as an important class of plastic materials, are used in numerous applications across a variety of industries, owing to their high strength, long service life and the ability to be customized for specific end - use applications. In addition, when compared with certain industrial plastic materials, polyurethane materials are more environmentally friendly and sustainable, for example due to their use in energy - efficient end - use applications such as thermal insulation applications (e.g., building and pipe insulation), and in applications for lightweight design of components. Due to the growing demand and production of PU materials, a large amount of PU waste is generated every year, which is either incinerated or ultimately sent to landfills, causing serious environmental problems. However, polyurethane materials are difficult to recycle via mechanical or chemical recycling methods.

[0003] Chemical recycling of polyurethanes can be carried out, for example, by glycolysis (chemical decomposition of urethanes by the active hydrogen atoms present in the glycol structure), but this method requires a large amount of energy, harsh reaction conditions (such as high temperatures above 220 °C), a large excess of glycol, shows limited selectivity, and produces a highly complex mixture of polyols and oligomers that is difficult or even impossible to separate (Polym. Degard. Stab. 2002, 75, 413 - 421; Polym. Degard. Stab. 2004, 147 - 151; ChemSusChem 2020, 13, 3835, 3843). The polyurethane industry still needs to develop other methods to simplify the recycling process of polyurethane materials, thereby reducing the total amount of energy, time, machinery and reagents required for recycling such materials.

[0004] For example, introducing special functional groups or smart monomers into the polymer enables the resulting polymer to be depolymerized by a simple method, thereby reducing the difficulty of implementing the recycling process of the material. Several suitable monomers for synthesizing polyurethanes that can be easily depolymerized are described in the literature.

[0005] T. Hashimoto et al. (J. Appl. Polym. Sci., 2016, 133, 44088) described a method for synthesizing polyols via the polyaddition reaction of various mono vinyl ethers with diols using p-toluenesulfonic acid (PTSA) as a homogeneous catalyst. The resulting polyols were used to synthesize degradable PU elastomers. This method required a large amount of organic solvents (THF, dichloromethane), resulting in the formation of a large amount of cyclic acetal by-products, and the catalyst present in the form of salt had to be removed by extraction.

[0006] Z. Petrovic et al. (J. Polym. Environ., 2009, 17, 123–130) described a method for synthesizing polyols via the bulk polyaddition reaction of triethylene glycol divinyl ether with diols using oxalic acid as a catalyst (i.e., a homogeneous catalyst) at 80 °C. The polyols can also be used to synthesize polyurethanes. This method only caused a small amount of cyclic acetal to form as a by-product. Due to the presence of the salt formed by the acid and DABCO, the polyols were turbid. In this case, the main drawback was that the salt would remain in the polyols, which might have a potential negative impact on the reactivity and properties of the PU, and the degree of influence depended on the type of PU system.

[0007] WO 2021 / 236385 A1 discloses a method for synthesizing polyols suitable for preparing polyurethanes, which is achieved via the bulk polyaddition reaction of triethylene glycol divinyl ether (TEGDVE) with diols using p-toluenesulfonic acid as a homogeneous catalyst at 40 °C. When using 1,4-butanediol or smaller diols as monomers, this method also results in the formation of a large amount of by-products. In addition, colored polyols are obtained. In this case, the main drawback is also that the salts used to neutralize the catalyst and the excess amine will remain in the polyols, which may have a negative impact on the reactivity, stability, and properties of the PU.

[0008] The main problem associated with using acids such as oxalic acid and p-toluenesulfonic acid as homogeneous catalysts is that the acids must be neutralized after the reaction. Usually, DABCO, DMCHA, or KOH is used for neutralization, and the salts formed should be removed from the polyols. This not only adds an extra step, but also poses a major problem in filtering out the formed salts. An alternative is to purify the polyols by extraction, but this method is hardly feasible on an industrial scale.

[0009] The object of the present invention is to provide polyols for preparing polyurethanes, which enable the polyurethanes to be easily decomposed under mild conditions and can be prepared with high purity by a simple method.

[0010] According to the present invention, the above problems are solved by a method for preparing a polyacetal polyol, which method comprises step (i): reacting a compound (D1) having at least one OH group with a compound (C1) in the presence of a solid acid catalyst, wherein the compound (C1) is selected from the group consisting of vinyl ethers, aldehydes, and acetals.

[0011] It has been unexpectedly found that the use of a solid acid catalyst allows the preparation of polyols containing acetal groups by a simple method and, preferably, also allows minimizing side reactions. Surprisingly, when using 1,4-butanediol or a smaller diol as the monomer, the formation of cyclic acetals can be significantly reduced. In addition, when using monomers having five or more carbon atoms, the amount of cyclic products is negligible.

[0012] Furthermore, it has been found that the polyacetal polyol can be easily separated from the catalyst.

[0013] The resulting polyacetal polyol can be used in various polyurethane elastomers and thermosetting materials. Polyurethanes based on acetal-containing polyols exhibit good properties and stability under standard conditions. On the other hand, the instability of the acetal group in a very low pH medium can be used to achieve the smooth depolymerization of polyurethanes under mild conditions (e.g., treatment with an acidic aqueous solution at a low temperature (e.g., up to 90 °C)) to obtain corresponding small molecule monomers (e.g., ethylene glycol, butanediol, etc.) that can be separated using standard separation techniques. This method also allows for the easier separation of small molecule monomers from other additives (such as flame retardants, surfactants, etc.). The recycled monomers can be reused for the synthesis of the native polymer (i.e., "recycled monomers"), thereby enabling the "closed-loop" recycling of polyurethanes.

[0014] Furthermore, the method according to the present invention also allows for the synthesis of fully biobased polyacetal polyols provided that commercially available biobased compounds (such as ethylene glycol, propylene glycol, butanediol, and glycerol) are used as raw materials.

[0015] It has been found that solid acid catalysts can be used in the synthesis and catalytic reaction of polyacetal polyols. In the context of the present invention, a solid catalyst is a catalyst that remains substantially in a solid state under the conditions of the process, in particular in the solid state under the reaction conditions of step (i) of the process according to the present invention. Generally, the catalyst is insoluble in the reaction mixture. The catalyst can be used in a continuous process or a batch process. A significant advantage of such a solid heterogeneous catalyst is that it can be easily removed by simple filtration after the reaction. Thus, polyols with extremely low acid values can be obtained, such as acid values below 0.2 mg KOH / g, more preferably below 0.1 mg KOH / g, even more preferably below 0.05 mg KOH / g, and most preferably below 0.03 mg KOH / g. In addition, after filtration, the catalyst can be washed, dried and reused multiple times. According to the present invention, the continuous production of polyols can also be achieved using the solid acid catalyst.

[0016] According to the present invention, the process comprises step (i): reacting a compound (D1) having at least one OH group with a compound (C1) in the presence of a solid acid catalyst. The compound (C1) is selected from the group consisting of vinyl ethers, aldehydes and acetals.

[0017] The compound (D1) has at least one OH group and may also have additional functional groups, in particular additional OH groups. Preferably, the compound (D1) has from 1 to 8, preferably from 2 to 6, more preferably from 2 to 4, particularly preferably from 2 to 3 OH groups, and most preferably 2 OH groups. Water, acids (such as dicarboxylic acids, tricarboxylic acids) and / or their esters can also be used as the compound (D1).

[0018] Suitable compounds (D1) can have, for example, a functionality of from 1 to 8, preferably from 2 to 3. According to another embodiment, the present invention also relates to a process for preparing polyacetal polyols as disclosed above, wherein the compound (D1) has a functionality of from 1 to 8, preferably from 2 to 3.

[0019] Suitable compounds (D1) can have, for example, a molecular weight of less than 5000 g / mol, preferably less than 2000 g / mol, more preferably less than 1000 g / mol, even more preferably less than 500 g / mol and most preferably less than 200 g / mol.

[0020] According to another embodiment, the present invention also relates to a process for preparing polyacetal polyols as disclosed above, wherein the compound (D1) has a molecular weight of less than 5000 g / mol.

[0021] Unless otherwise specified, in the context of the present invention, the molecular weight can be determined via 1It can be determined by H-NMR end-group quantification or can be calculated from the OH number according to EN ISO 4629-1:2016.

[0022] Suitable compounds (D1) can be particularly selected from the group consisting of monoalcohols, diols and triols having 1 to 20 carbon atoms, preferably selected from the group consisting of monoalcohols, diols and triols having 1 to 18 carbon atoms, preferably 2 to 12 carbon atoms and even more preferably 2 to 6 carbon atoms. According to another embodiment, the present invention thus also relates to a process for preparing a polyacetal polyol as disclosed above, wherein the compound (D1) is selected from the group consisting of monoalcohols, diols and triols having 1 to 18 carbon atoms, preferably selected from the group consisting of monoalcohols, diols and triols having 2 to 6 carbon atoms.

[0023] Suitable are, for example, aliphatic diols such as butanediol, pentanediol, hexanediol or decanediol and the corresponding isomers, preferably pentanediol and / or hexanediol, especially hexanediol. In addition to these alcohols, other monoalcohols, diols or polyols can also be used, for example those having a molecular weight of 62 g / mol to 400 g / mol. Examples are monoethylene glycol, 1,2- or 1,3-propanediol, 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, PTHF250, bisphenol compounds, and mixtures of polyols.Suitable active hydrogen compounds can be, for example, 1,2-, 1,3- and 1,4-butanediol, butane-2,3-diol, pentane-1,2-diol, pentane-1,3-diol, pentane-1,4-diol, pentane-1,5-diol, pentane-2,3-diol, pentane-2,4-diol, hexane-1,2-diol, hexane-1,3-diol, hexane-1,4-diol, hexane-1,5-diol, hexane-2,5-diol, 1,6-hexanediol, heptane-1,2-diol, 1,7-heptanediol, 1,8-octanediol, 1,2-octanediol, 1,9-nonanediol, 1,2-decanediol, 1,10-decanediol, 1,2-dodecanediol, 1,12-dodecanediol, 1,5-hexadiene-3,4-diol, 2,2-bis(4-hydroxycyclohexyl)propane, neopentyl glycol (2,2-dimethylpropane-1,3-diol), 2,2-diethylpropane-1,3-diol, 2-methyl-2-ethylpropane-1,3-diol, 2-methyl-2,4-pentanediol, 2,4-dimethyl-2,4-pentanediol, 2-ethyl-1,3-hexanediol, 2,5-dimethyl-2,5-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, pinacol, diethylene glycol, triethylene glycol, dipropylene glycol and tripropylene glycol, 1,1-dimethylethane-1,2-diol, 2-butyl-2-ethyl-1,3-propanediol, 2-ethyl-1,3-propanediol, neopentyl glycol, neopentyl glycol hydroxypivalate, 2-ethyl-1,3-hexanediol, 2,4-diethyloctane-1,3-diol, cyclic aliphatic diol compounds having 3 to 14 carbon atoms, such as tetramethylcyclobutanediol, 1,2-, 1,3- and 1,4-cyclohexanediol, 1,1-, 1,2-, 1,3- and 1,4-cyclohexanedimethanol, 1,2-, 1,3- or 1,4-cyclooctanediol, 4,8-bis(hydroxymethyl)tricyclo[5.2.1.02,6]decane, norbornanediol, pinanediol, decahydronaphthalenediol, 2,2-bis(4-hydroxycyclohexyl)propane, bis(4-hydroxycyclohexyl)isopropane; aromatic diols such as 2,5-bis(hydroxymethyl)furan, 3,4-bis(hydroxymethyl)furan, bis(2-hydroxyethyl) terephthalate, 1,4-benzenediol, hydroquinone bis(2-hydroxyethyl) ether, bisphenol A, bisphenol AP, bisphenol AF, bisphenol B, bisphenol BP, bisphenol C, bisphenol C2, bisphenol E, bisphenol F, bisphenol G, bisphenol M, bisphenol S, bisphenol P, bisphenol PH, bisphenol TMC, bisphenol Z, tetrabromobisphenol A, and aliphatic alcohols having 2 to 20 carbon atoms and additional functional groups, or mixtures of two or more of the above compounds.

[0024] Particularly preferably, the alcohol component includes monoethylene glycol, 1,2 - propanediol, 1,3 - propanediol, 1,4 - butanediol, 1,5 - pentanediol, 1,6 - hexanediol, 1,7 - heptanediol, 1,8 - octanediol, 1,9 - nonanediol or 1,10 - decanediol, especially 1,4 - butanediol, 1,5 - pentanediol and 1,6 - hexanediol. In addition, preferred diols are diethylene glycol and dipropylene glycol.

[0025] According to the present invention, compounds having one free OH group and one or more protected OH groups can also be used as compound (D1).

[0026] According to the present invention, compounds having three or more OH groups can also be used as compound (D1). Suitable ones are, for example, 1,2,4 - butanetriol, trimethylolethane, 1,2,6 - hexanetriol, trimethylolethane, butane - 1,2,3,4 - tetrol, benzene - 1,2,3 - triol, xylose, deoxyribose, mannose, sorbose, tagatose, galactose, ribose, fructose, mannitol, sorbitol, fucitol, galactitol, iditol, xylitol, volemitol, glycerol, glucose, sucrose, pentaerythritol, dipentaerythritol, diglycerol or trimethylolpropane, and alkoxylated derivatives of compounds having three or more OH groups.

[0027] Also suitable are polyether diols and higher functionality polyether alcohols, especially polyethylene glycol HO(CH2CH2O)n - H, higher polypropylene glycol HO(CH[CH3]CH2O)n - H, where n is an integer and n ≥ 4, for example 4 to 20; polyethylene glycol - polypropylene glycol, more particularly those having 4 to 20 repeating units, and the sequence of ethylene oxide units and propylene oxide units can be a block or random sequence; polybutylene glycol, more particularly those having 4 to 20 repeating units; and poly - 1,3 - propanediol, more particularly those having 4 to 20 repeating units. Suitable compounds can have a functionality of 1 to 6, preferably 2 to 6.

[0028] Among the polyester polyols used as component D1, preferred are polyester polyols based on the following diol components and dicarboxylic acid components, the diol components being selected from the group consisting of butanediol, neopentyl glycol, hexanediol, ethylene glycol, diethylene glycol and mixtures thereof, and the dicarboxylic acid components being selected from the group consisting of adipic acid, glutaric acid, succinic acid, phthalic acid, isophthalic acid and combinations thereof. Particularly preferred are polyester polyols based on ethylene glycol and / or butanediol and / or neopentyl glycol and / or hexanediol with adipic acid and / or phthalic acid and / or isophthalic acid.

[0029] Suitable polyester polyols also include polycaprolactones, especially poly-C4-C12-caprolactones, in particular polycaprolactone (PCL). Polycaprolactones refer to aliphatic polyesters that can be obtained by ring-opening polymerization of lactones, especially C4-C12-lactones, in particular ε-caprolactone (ε-caprolactone). Polycaprolactone has a repeating monomer unit of the general formula (1) [-O-CHR-(CH2)m-CO-], where m is from 4 to 10, m = 4 in the case of caprolactone, and R is hydrogen. In the context of the present invention, the term polycaprolactone is understood to refer to both homopolymers of ε-caprolactone and copolymers of ε-caprolactone. Suitable copolymers are, for example, copolymers of ε-caprolactone with monomers selected from the group consisting of lactic acid, lactide, glycolic acid, and glycollide. Polyester polyols are common components, for example, they can be obtained from Ullmanns der technischen Chemie [Ullmann’s Encyclopedia of Industrial Chemistry], 4th edition, volume 19, pages 62 to 65.

[0030] In the context of the present invention, mixtures of two or more aliphatic diols can also be used.

[0031] According to step (i), compound (D1) and (C1) react under suitable conditions. (C1) is selected from the group consisting of vinyl ethers, aldehydes, and acetals. According to the present invention, the reaction can be selected from the group consisting of addition polymerization, polycondensation, or transacetalization reactions. The suitable reaction conditions for this reaction are known in principle to those skilled in the art. The addition polymerization is usually carried out at 0 °C to 150 °C, more preferably at 10 °C to 120 °C, more preferably at 10 °C to 90 °C, even more preferably at 15 °C to 70 °C, and most preferably at 20 °C to 50 °C. The polycondensation and transacetalization reactions are carried out at temperatures above 0 °C, usually at 0 °C to 250 °C, more preferably at 10 °C to 150 °C, more preferably at 20 °C to 110 °C, even more preferably at 25 °C to 90 °C, and most preferably at 40 °C to 90 °C.

[0032] Generally, the solid acid catalyst is solid under the reaction conditions of step (i). According to another embodiment, the present invention relates to a method for preparing a polyacetal polyol, comprising step (i): reacting a compound (D1) having at least one OH group with a compound (C1) in the presence of a solid acid catalyst, wherein the compound (C1) is selected from the group consisting of vinyl ethers, aldehydes, and acetals, and wherein the catalyst is in a solid state under the reaction conditions of step (i).

[0033] According to another embodiment, the invention thus also relates to a process for preparing a polyacetal polyol as disclosed above, wherein the reaction according to step (i) is a polyaddition reaction, a polycondensation reaction or a transacetalization reaction.

[0034] In the case where the compound (C1) is selected from vinyl ethers, suitable compounds are, for example, divinyl ethers such as 1,4-butanediol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether or 1,4-cyclohexanedimethanol divinyl ether; hydroxy-functional monovinyl ethers such as ethylene glycol vinyl ether, 1,4-butanediol vinyl ether, diethylene glycol vinyl ether, 1,6-hexanediol vinyl ether or 1,4-cyclohexanedimethanol vinyl ether. Monovinyl ethers or divinyl ethers of polytetrahydrofuran (such as PTHF 250 or PTHF 1000) having a molecular weight in the range from 200 g / mol to 1400 g / mol can also be used, monovinyl ethers such as ethyl vinyl ether, 2-ethylhexyl vinyl ether, tetraethylene glycol methyl vinyl ether, dodecyl vinyl ether, and vinyl ethers generally containing between 3 and 20 carbon atoms. Suitable vinyl ethers can be prepared, for example, from the compounds (D1) as disclosed above by known techniques.

[0035] In the context of the present invention, mixtures of two or more vinyl ethers can also be used.

[0036] In the case where the compound (C1) is selected from aldehydes, such aldehydes are aliphatic aldehydes, such as mono-aliphatic aldehydes having 4 to 12 carbon atoms, or aromatic aldehydes, such as benzaldehyde. Suitable compounds also include, for example, dialdehydes, such as glutaraldehyde, glyoxal, terephthalaldehyde; trialdehydes; or aldehydes having additional functional groups, such as hydroxy-functionalized aldehydes, such as vanillin, 7-hydroxy-3,7-dimethyloctanal, 2-hydroxybenzaldehyde, 4-hydroxybenzaldehyde, 2,3-dihydroxybenzaldehyde, hydroxymethylfurfural, lactaldehyde, 3-hydroxybutyraldehyde, hydroxypivalaldehyde, 5-hydroxymethyl-2-furaldehyde. Particularly suitable compounds are mono-aldehydes, such as straight-chain aliphatic mono-aldehydes, such as formaldehyde, paraformaldehyde, trioxane, acetaldehyde, paraldehyde, propionaldehyde, valeraldehyde, hexanal, heptanal and aldehydes having no more than 12 carbon atoms, 2-trans-hexenal, 4-heptenal, 3-ethoxy-2-methylacrolein; branched-chain aliphatic mono-aldehydes, such as 2-ethylhexanal, 2-methylvaleraldehyde, isobutyraldehyde, 2-methylbutyraldehyde, 2,2-dimethylpropanal, 3-methylvaleraldehyde, 4-methylvaleraldehyde, 2-ethylbutyraldehyde, phenylpropanal, cyclohexanecarboxaldehyde, 2,2-dimethylbutyraldehyde, 3,3-dimethylbutyraldehyde, 3-methylbutyraldehyde; aromatic mono-aldehydes, such as benzaldehyde, 4-methoxybenzaldehyde or phenylacetaldehyde, 4-isopropylbenzaldehyde, furfural, anisaldehyde, 1-naphthaldehyde; and aliphatic ketones, such as cyclopentanone, 2,3-butanedione, 2,6-dimethyl-4-heptanone, 5-methyl-2-hexanone, acetone, methylhept-5-en-2-one, diethyl ketone, cyclododecanone, methyl ethyl ketone; aromatic ketones, such as acetophenone, 1-phenyl-1-pentanone, benzophenone; and ketones containing other functional groups, such as 3-hydroxyacetophenone and 3-hydroxybutanone. More preferred aldehydes (C1) are mono-aldehydes, such as benzaldehyde, heptanal, valeraldehyde; and aldehyde precursors, such as paraldehyde and paraformaldehyde.

[0037] In the context of the present invention, mixtures of two or more aldehydes can also be used.

[0038] In the case where the compound (C1) is selected from acetals, suitable compounds are, for example, acetals such as aliphatic acetals having one or more acetal groups, for example dimethoxymethane, 1,1 - dimethoxyethane, 1,1 - diethoxyethane, 1,1 - diethoxypropane, 1,1,3,3 - tetramethoxypropane, butanedial bis(dimethyl acetal), 2 - chloro - 1,1 - diethoxyethane, isobutyraldehyde diethyl acetal, methylglyoxal 1,1 - dimethyl acetal, nonanal diethyl acetal, 1,1,2 - trimethoxyethane; aromatic acetals such as benzaldehyde dimethyl acetal, 4 - methoxybenzaldehyde dimethyl acetal, phenylacetaldehyde dimethyl acetal, 2 - furfural diethyl acetal; or diacetals such as 1,1,3,3 - tetramethoxypropane and tetrahydro - 2,5 - dimethoxyfuran; and ketals such as 1,1 - dimethoxycyclohexane, 2,2 - diethoxypropane, 1,1 - dimethoxycyclopentane and acetone dibutyl ketal. More preferred acetals (C1) are monoacetals such as dimethoxymethane, 1,1 - diethoxyethane, 1,1 - diethoxypropane and benzaldehyde dimethyl acetal.

[0039] According to another embodiment, the present invention also relates to a process for the preparation of the polyacetal polyol as disclosed above, wherein the compound (C1) is selected from the group consisting of divinyl ethers and monovinyl ethers.

[0040] In the context of the present invention, mixtures of two or more acetals or ketals can also be used.

[0041] According to another embodiment, the present invention also relates to a process for the preparation of the polyacetal polyol as disclosed above, wherein the compound (C1) is selected from the group consisting of straight - chain aliphatic aldehydes, branched - chain aliphatic aldehydes, aromatic aldehydes and ketones.

[0042] According to another embodiment, the present invention thus also relates to a process for the preparation of the polyacetal polyol as disclosed above, wherein the compound (C1) is selected from the group consisting of aliphatic acetals, aromatic acetals and ketals.

[0043] According to the present invention, the reaction is carried out in the presence of a solid acid catalyst.

[0044] In the context of the present invention, a solid acid is a solid having acidic sites on its (internal and external) surface, on which basic substances can undergo chemisorption. Preferably, in the context of the present invention, according to the definitions of Brønsted and Lewis, a solid acid has a tendency to release protons or accept electron pairs. The solid acid catalysts applicable in the context of the present invention may differ in their chemical composition, the number, type and strength of the acidic sites, and physical properties such as specific surface area and porosity, and thus the accessibility of the catalytically active sites.

[0045] In the context of the present invention, suitable solid acid catalysts preferably have a specific surface area of at least 10 m 2 / g, in particular at least 100 m 2 / g, and more preferably at least 200 m 2 / g.

[0046] Furthermore, suitable solid acid catalysts preferably have an acidity of at least 0.10 mmol / g, in particular at least 0.15 mmol / g, and more preferably at least 0.20 mmol / g, which is determined by the acid amount measured by the ammonia TPD (temperature programmed desorption) method as described in the examples.

[0047] In addition, suitable solid acid catalysts preferably have medium-strength acid sites, the corresponding T max measured by the ammonia TPD method is in the range of 340 °C to 380 °C.

[0048] Solid acid catalysts applicable in the context of the present invention include aluminosilicates or silicoaluminates, such as zeolites, silicoaluminophosphates, amorphous aluminosilicates, clays. Suitable zeolites are, for example, microporous aluminosilicates with an ordered structure (BEA type, MOR type...). In the context of the present invention, aluminosilicates in an amorphous form, with a lower degree of structural order and weaker acidity, such as ASA (amorphous silica-alumina) catalysts, can also be used. Clay catalysts belonging to the class of silicates with a certain acidity, or mesoporous aluminosilicate materials (such as MCM-22) can also be used. In addition, silica-alumina hydrates and corresponding oxides, such as the "Siral" and "Siralox" materials purchased from Sasol, can be used in the context of the present invention.

[0049] Suitable catalysts also include acidic metal oxides and metal oxide mixtures, such as titanium dioxide, zirconium dioxide, niobium pentoxide, solid phosphoric acid, sulfated zirconia, or heteropolyoxometalates.

[0050] Another class of suitable solid acid catalysts that can be used are polymers and resins containing acidic structural units, such as polystyrene with sulfonic acid groups. An example of such a cation exchange resin is Amberlyst 15.

[0051] Additional suitable catalysts can be metal-organic frameworks (MOFs), as described, for example, in the following documents: US 5,648,508; EP-A-0 709 253; M. O’Keeffe et al., J. Sol. State Chem., 152 (2000) pages 3-20; H. Li et al., Nature 402 (1999) page 276 seq.; M. Eddaoudi et al., Topics in Catalysis 9 (1999) pages 105-111; B. Chen et al., Science 291 (2001) pages 1021-1023.

[0052] The metal ions forming the metal-organic framework material used according to the invention are preferably selected from groups Ia, IIa, IIIa, IVa to VIIIa and Ib to VIb of the Periodic Table of the Elements. Among these metals, Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb and Bi, Zn, Cu, Ni, Pd, Pt, Ru, Rh and Co are specifically mentioned. Regarding the metal ions of the aforementioned elements, Mg + , Ca 2+ , Sr 2+ , Ba 2+ , Sc 3+ , Y 3+ , Ti 4+ , Zr 4+ , Hf 4+ , V 4+ , V 3+ , V 2+ , Nb 3+ , Ta 3+ , Cr 3+ , Mo 3+ , W 3+ , Mn 3+ , Mn 3+ Mn 2+ , Re 3+ , Re 2+ , Fe 3+ , Fe 2+ , Ru 3+ , Ru 2+ , Os 3+ , Os 2+ , Co 3+ Co 2+ , Rh 2+ , Rh +, Ir 2+ , Ir + , Ni 2 + , Ni + , Pd 2+ , Pd + , Pt 2+ , Pt, Cu + , Cu + , Ag + , Au, Zn 2+ , Cd 2+ , Hg 2+ , Al 3+ , Ga 3+ , In 3+ , Tl 3+ , Si 4+ , Ge 4+ , Ge 2 + , Sn 4+ , Sn 2+ , Pb 4+ , Pb 2 +, As 5+ , As 3+ , As + , Sb 5+ , Sb 3+ , Sb + , Bi + , Bi 3+ and Bi + . In another embodiment, the metal or metal ion in the metal-organic framework has a molecular geometry selected from the group consisting of trigonal planar, tetrahedral, square planar, trigonal bipyramidal, square pyramidal, octahedral, trigonal prismatic, pentagonal bipyramidal, paddlewheel, and anti-prismatic.

[0053] At least bidentate organic ligands present in the metal-organic framework material are capable of coordinating with metal ions. Such ligands are known to those skilled in the art. The at least bidentate organic ligand is preferably selected from: i) an alkyl group having 1 to 10 carbon atoms, ii) an aryl group having 1 to 5 benzene rings, iii) alkylamines and arylamines bearing the following groups: one or more alkyl groups having 1 to 10 carbon atoms, and / or one or more aryl groups having 1 to 5 benzene rings, these groups being covalently substituted by at least one functional group X capable of coordinating with metal ions, where X is selected from the group consisting of: CO2H, CS2H, NO2, S03H, Si(OH)3, Ge(OH)3, Sn(OH)3, Si(SH)4, Ge(SH)4, Sn(SH)3, PO3H, AsO3H, AsO4H, P(SH)3, As(SH)3, CH(RSH)2, C(RSH)3, CH(RNH2)2, C(RNH2)3, CH(ROH)2, C(ROH)3, CH(RCN)2, C(RCN)3, where R is an alkyl group having 1 to 5 carbon atoms, or an aryl group consisting of 1 to 2 benzene rings; and CH(SH)2, C(SH)3, CH(NH2)2, C(NH2)2, CH(OH)2, C(OH)3, CH(CN)2 and C(CN)3. WO 02 / 088148 discloses bidentate organic ligands belonging to the class of aromatic compounds, and these aromatic compounds may bear one or more substituents. The content on pages 8 - 14 of WO02 / 088148 is incorporated herein by reference in its entirety.

[0054] Preferred catalysts are selected from the group comprising mixed oxides (aluminosilicates) containing alumina and silica. These materials can be obtained by co-precipitation or controlled hydrolysis of salts (e.g., using Al(NO3)3·9H2O and / or NaAlO2 and / or AlCl3 as aluminum precursors, and tetraethoxysilane (TEOS) as the silicon precursor), and both the aluminum precursor and the silicon precursor can be alkoxides. Suitable materials can also be obtained as naturally occurring materials, such as clays, which, after activation with inorganic acids (such as HCl, H2SO4 or HNO3), act as solid acid catalysts, for example.

[0055] Suitable catalysts can be selected, for example, from catalysts obtained by a method comprising calcining a precursor of an oxide of one or more elements selected from the group consisting of Ge, Sn, B, Al, Ga, Zn, Cu, Fe, Mn, Ni, Cr, Mo, P, S, W, Nb, Ti, Zr, Hf, Y, La, Ce, Yb, and Si at a temperature in the range of 150°C to 1150°C to obtain an oxide; silica-alumina hydrate; a clay compound containing Si and Al; a zeolite having a structure selected from the group consisting of BEA, EMT, ERI, EUO, FAU, HEU, LTA, LTL, MAZ, MOR, MTW, NES, OFF, and TON; or a cation exchange resin.

[0056] According to another embodiment, the present invention thus also relates to a method for preparing a polyacetal polyol as disclosed above, wherein the solid acid catalyst is selected from the group consisting of

[0057] - a catalyst obtained by a method comprising calcining a precursor of an oxide of one or more elements selected from the group consisting of Ge, Sn, B, Al, Ga, Zn, Cu, Fe, Mn, Ni, Cr, Mo, P, S, W, Nb, Ti, Zr, Hf, Y, La, Ce, Yb, and Si at a temperature in the range of 150°C to 1150°C to obtain an oxide;

[0058] - silica-alumina hydrate

[0059] - a clay compound containing Si and Al;

[0060] - a zeolite having a structure selected from the group consisting of BEA, EMT, ERI, EUO, FAU, HEU, LTA, LTL, MAZ, MOR, MTW, NES, OFF, and TON;

[0061] - a cation exchange resin;

[0062] - a MOF catalyst.

[0063] Particularly suitable are those selected from clay compounds, mixed oxides, and MOF catalysts.

[0064] The method according to the invention comprises step (i) and may also comprise additional steps, in particular purification steps or separation steps. Preferably, after the reaction according to step (i), the solid catalyst is separated from the reaction mixture. The catalyst can be separated, for example, by filtration. The catalyst separated from the reaction mixture can also be subjected to a purification step (such as a washing step) and can also be reused in the method. The method may also comprise additional washing steps.

[0065] Typically, a reaction mixture is obtained in step (i). The product, as well as unreacted starting materials such as compound (D1) and / or (C1) or by-products such as cyclic acetals, can be separated by suitable separation methods such as a distillation step.

[0066] According to another embodiment, the invention thus also relates to a process for preparing a polyacetal polyol as disclosed above, wherein the process comprises one or more separation steps selected from the group consisting of filtration, distillation and washing.

[0067] By the process according to the invention, a polyacetal polyol is obtained. The polyacetal polyol obtained can have one or more acetal groups and OH end groups, for example from 1 to 8 OH end groups, preferably from 1 to 6, more preferably from 1 to 5, from 2 to 5, from 2 to 4, in particular from 2 to 3 OH end groups or 2 OH end groups. Preferably, the polyacetal polyol has a molecular weight in the range up to 12,000 g / mol, in particular up to 10,000 g / mol, for example in the range from 500 g / mol to 8,000 g / mol, preferably in the range from 500 g / mol to 8000 g / mol, more preferably in the range from 800 g / mol to 6000 g / mol, in particular in the range from 1000 g / mol to 5000 g / mol, this molecular weight being calculated from the OH number in accordance with EN ISO 4629-1:2016. The hydroxyl value of the polyacetal polyol can be in the range from 10 mg KOH / g to 1200 mg KOH / g, preferably in the range from 10 mg KOH / g to 600 mg KOH / g, more preferably in the range from 15 mg KOH / g to 500 mg KOH / g, in particular in the range from 15 mg KOH / g to 400 mg KOH / g and most preferably in the range from 20 mg KOH / g to 250 mg KOH / g.

[0068] According to another aspect, the invention also relates to a polyacetal polyol obtainable or obtained by a process for preparing a polyacetal polyol as disclosed above.

[0069] It has been found that the polyacetal polyol according to the invention is suitable for the preparation of polyurethanes. The resulting polyurethanes can be depolymerized using mild conditions. According to another aspect, the invention also relates to the use of a polyacetal polyol obtainable or obtained by a process for preparing a polyacetal polyol as disclosed above or a polyacetal polyol according to the invention for the preparation of polyurethanes.

[0070] Processes for preparing polyurethanes are in principle known. Typically, a polyol component is reacted with an isocyanate component.

[0071] Typically, polyurethanes are prepared using a method comprising the steps of: mixing (a) a polyisocyanate, (b) a polyol composition comprising a polymeric compound having isocyanate-reactive groups, (c) a catalyst, and optionally (d) a blowing agent, (e) a chain extender and / or crosslinking agent, and (f) auxiliaries and / or additives to form a reaction mixture, and subsequently reacting the reaction mixture to produce a polyurethane. The polyacetal polyol can be used as such or in combination with one or more additional polyols.

[0072] In the context of the present invention, "polyurethane" includes all known polyisocyanate addition products. These polyurethanes include the addition products of isocyanates with alcohols, as well as modified polyurethanes that may contain isocyanurate, urethane, urea, carbodiimide, uretonimine, and biuret structures, and also include additional isocyanate addition products. According to the present invention, these polyurethanes particularly include solid polyisocyanate addition products, such as elastomers based on polyisocyanate addition products, thermoplastic PU elastomers, thermosetting plastics, and foams, such as soft foams, semi-rigid foams, rigid foams, or integral skin foams. In addition, polyurethane coatings, adhesives, and sealants are also included. "Polyurethane" is further understood to mean polymer blends comprising polyurethanes and other polymers, and foams made from these polymer blends.

[0073] According to another aspect, the present invention also relates to a method for preparing a polyurethane, which method comprises at least step (I)

[0074] (I) reacting a polyacetal polyol obtained or obtainable according to the method for preparing a polyacetal polyol as disclosed above or a polyacetal polyol according to the present invention with at least one polyisocyanate.

[0075] According to step (I), the polyacetal polyol is contacted with at least one polyisocyanate preferably having an average of at least 1.5 isocyanate groups, which polyisocyanate is also referred to hereinafter as component (a). Additional components can be added in this method, such as: (b) other polymeric compounds having isocyanate-reactive groups, (c) a catalyst, (d) an optional blowing agent, (e) a chain extender or crosslinking agent, and (f) additives.

[0076] For the purposes of the present invention, in principle any polyisocyanate can be used in step (I). In the context of the present invention, the polyisocyanate (a) is also referred to as "isocyanate". That is to say, the at least one isocyanate contains a plurality of NCO functional groups, for example 2, 3 or 4 NCO functional groups, or any value or range of values therein. It should be understood that the at least one polyisocyanate includes both monomeric diisocyanates, i.e., compounds having 2 NCO functional groups, and oligomeric forms thereof having on average more than 2 NCO functional groups, for example from 2 to 4 NCO functional groups.

[0077] The isocyanate (a) used for producing the polyurethane according to the present invention includes all polyisocyanates known for producing polyurethanes. These polyisocyanates include aliphatic, cycloaliphatic and aromatic divalent or polyvalent isocyanates known from the prior art, and any desired mixtures thereof. Examples include 2,2'-, 2,4'- and 4,4'-diphenylmethane diisocyanate, mixtures of monomeric diphenylmethane diisocyanate and polynuclear homologues of diphenylmethane diisocyanate (polymeric MDI), isophorone diisocyanate (IPDI) or its oligomers, 2,4- or 2,6-toluene diisocyanate (TDI) or mixtures thereof, tetramethylene diisocyanate or its oligomers, pentamethylene diisocyanate, hexamethylene diisocyanate (HDI) or its oligomers, H12-MDI, naphthylene diisocyanate (NDI), or mixtures thereof.

[0078] Preference is given to 2,4- and / or 2,6-toluene diisocyanate (TDI) or mixtures thereof, monomeric diphenylmethane diisocyanate and / or polynuclear homologues of diphenylmethane diisocyanate (polymeric MDI), and mixtures thereof. Other possible isocyanates are described, for example, in "Kunststoffhandbuch", Volume 7, "Polyurethane", Carl Hanser Verlag, 3rd Edition 1993, Chapters 3.2 and 3.3.2.

[0079] The isocyanate can be used in the form of a polyisocyanate prepolymer. These polyisocyanate prepolymers can be obtained by reacting an excess of the above polyisocyanate (component (a)) with a polymeric compound having isocyanate-reactive groups (b) and / or chain extenders (e) at a temperature of from 20 °C to 100 °C, preferably about 80 °C, to provide the polyisocyanate prepolymer.

[0080] Polymeric compounds having isocyanate-reactive groups (b) and chain extenders (e) are known to those skilled in the art and are described, for example, in "Kunststoffhandbuch [Plastics Handbook], Volume 7, Polyurethane [Polyurethanes]", Carl Hanser Verlag, 3rd edition 1993, Chapter 3.1. Thus, examples of polymeric compounds having isocyanate-reactive groups that can also be used are the polymeric compounds having isocyanate-reactive groups described under (b) below. If an isocyanate prepolymer is used as the isocyanate (a), its isocyanate content (NCO content) is preferably greater than 5% by weight, more preferably from 10% to 45% by weight, still more preferably from 12% to 40% by weight, particularly preferably from 15% to 35% by weight, especially from 15% to 30% by weight, and most preferably from 15% to 25% by weight. The determination of the NCO content in weight percentages is done by standard chemical titration analysis known to those skilled in the art, and thus the present invention is not limited by any such method.

[0081] According to another embodiment, the present invention also relates to the method as disclosed above, wherein the isocyanate is selected from the group consisting of aliphatic diisocyanates, cycloaliphatic diisocyanates, aromatic diisocyanates or aromatic / aliphatic oligomeric or polymeric isocyanates.

[0082] The term "aliphatic diisocyanate" refers to a molecule having two isocyanate groups attached to an acyclic saturated hydrocarbon group usually containing 4 to 18 carbon atoms. Examples of aliphatic diisocyanates include, but are not limited to, tetramethylene-1,4-diisocyanate, pentamethylene-1,5-diisocyanate, hexamethylene-1,6-diisocyanate, decamethylene diisocyanate, 1,12-dodecane diisocyanate, 2,2,4-trimethyl-hexamethylene diisocyanate, 2,4,4-trimethyl-hexamethylene diisocyanate, 2-methyl-1,5-pentamethylene diisocyanate, etc., and mixtures thereof. Preferred aliphatic diisocyanates are pentamethylene-1,5-diisocyanate, hexamethylene-1,6-diisocyanate, 2,2,4-trimethyl-hexamethylene-1,6-diisocyanate and 2,4,4-trimethyl-hexamethylene-1,6-diisocyanate and mixtures thereof.

[0083] The term "alicyclic diisocyanate" refers to a molecule having two isocyanate groups attached to a saturated hydrocarbon group with at least one cyclic moiety. Alicyclic diisocyanates typically contain from 6 to 18 carbon atoms. Examples of alicyclic diisocyanates include, but are not limited to, cyclobutane-1,3-diisocyanate, 1,2-, 1,3- and 1,4-cyclohexane diisocyanate, 2,4- and 2,6-diisocyanato-1-methylcyclohexane (i.e., 2,4- and 2,6-hexahydrotoluene diisocyanate), 4,4'- and 2,4'-dicyclohexyl diisocyanate, isocyanatomethylcyclohexane isocyanate, isocyanatoethylcyclohexane isocyanate, bis(isocyanatomethyl)cyclohexane, 4,4'-diisocyanatodicyclohexylmethane (12-MDI), isophorone diisocyanate, and mixtures thereof. Preferred alicyclic diisocyanates are 1,2-, 1,3- and 1,4-cyclohexane diisocyanate, 2,4- and 2,6-diisocyanato-1-methylcyclohexane, 4,4'- and 2,4'-dicyclohexyl diisocyanate, bis(isocyanatomethyl)cyclohexane, 4,4'-diisocyanatodicyclohexylmethane (12-MDI), isophorone diisocyanate, and mixtures thereof. Isophorone diisocyanate is typically a mixture, especially a mixture of cis- and trans-isomers, usually in a mass ratio of 60:40 to 80:20, more particularly 70:30 to 75:25, especially about 75:25.

[0084] The term "aromatic diisocyanate" refers to a molecule having two isocyanate groups attached directly and / or indirectly to an aromatic ring. Aromatic diisocyanates typically have from 8 to 18 carbon atoms. Examples of aromatic diisocyanates include, but are not limited to, 1,2-, 1,3- and 1,4-phenylene diisocyanate, naphthylene-1,5-diisocyanate, 2,4- and 2,6-toluene diisocyanate, 2,4'-, 4,4'- and 2,2'-diphenyl diisocyanate, 2,2'-, 2,4'- and 4,4'-diphenylmethane diisocyanate, 1,2-, 1,3- and 1,4-benzenedimethyl diisocyanate and m-tetramethylbenzenedimethyl diisocyanate (TMXDI) and mixtures thereof. Preferred aromatic diisocyanates are 2,4- and 2,6-toluene diisocyanate, 2,4'-, 4,4'- and 2,2'-diphenyl diisocyanate, 2,2'-, 2,4'- and 4,4'-diphenylmethane diisocyanate, 1,2-, 1,3- and 1,4-benzenedimethyl diisocyanate, m-tetramethylbenzenedimethyl diisocyanate (TMXDI), and mixtures thereof.

[0085] The relative amounts of the isocyanate composition are preferably chosen such that the molar ratio of NCO groups to the isocyanate-reactive groups (i.e., active hydrogen groups) present in the polyol composition provided in step (I) can vary depending on the NCO content of the polyurethane to be prepared. Generally, the NCO group content of the resulting product is in the range of 0.1% to 35% by weight.

[0086] According to step (I), the polyoxymethylene polyol is reacted with at least one isocyanate. According to the invention, additional compounds commonly used in the preparation of polyurethanes can be used. For example, the polyoxymethylene polyol can be mixed with additional compounds for use in the polyol composition.

[0087] The polyol composition (b) can, for example, comprise from 1% to 100% by weight, based on the composition, of the polyoxymethylene polyol according to the invention. Depending on the composition of the polyol composition, the properties of the resulting polyurethane can be affected. According to one embodiment of the invention, the polyol composition can comprise from 50% to 100% by weight, based on the composition, of the polyoxymethylene polyol. According to an alternative embodiment, the polyol composition can also comprise from 1% to 25% by weight, based on the composition, of the polyoxymethylene polyol.

[0088] The polyol composition (b) can also comprise additional compounds having at least one functional group containing active hydrogen which is reactive with an isocyanate group.

[0089] The term "active hydrogen" refers to a compound having at least one functional group which is capable of reacting with an isocyanate group in an addition reaction to form a chemical bond between the carbon atom of the isocyanate group and one of the atoms of the functional group. These functional groups are also referred to as "active hydrogen functional groups" or "isocyanate-reactive groups". Typical active hydrogen functional groups of active hydrogen compounds are hydroxyl groups (OH), mercapto groups (SH), primary amino groups (NH2) and secondary amino groups (NH). The above functional groups will react with an isocyanate group to form a urethane, urea or thiocarbamate group, respectively. Preferably, additional polyols are used according to the invention.

[0090] In principle, any polyol conventionally used for preparing polyurethanes can be used. The type of polyol can depend on the desired purpose of the application. Suitable polyol compounds are polyester polyols, specifically including aliphatic polyester polyols and aliphatic-aromatic polyester polyols, polyester carbonate polyols, polyether ester polyols, aliphatic polycarbonate polyols, polyacrylate polyols, polyolefin polyols, aliphatic polyether alcohols, and mixtures thereof. In a preferred group of embodiments, the polyol is selected from polyester polyols, especially aliphatic polyester polyols and aliphatic-aromatic polyester polyols, aliphatic polycarbonate polyols, aliphatic polyether alcohols, and mixtures thereof. Specifically, the polyol composition comprises a polyester polyol and / or an aliphatic polyether polyol as described herein. In particular, the polyol is selected from polyester polyols, aliphatic polyether polyols, and combinations thereof.

[0091] Preferably, the average molecular weight of the polyol is less than 10,000 g / mol. This molecular weight is determined using 1 1H-NMR end-group quantification, or can be calculated from the OH number according to EN ISO 4629-1:2016.

[0092] The polyester alcohols suitable as polyols are specifically aliphatic polyester alcohols and aliphatic / aromatic polyester alcohols, i.e., polyester alcohols based on a dicarboxylic acid component selected from aliphatic dicarboxylic acids, cycloaliphatic dicarboxylic acids, aromatic dicarboxylic acids, and combinations thereof and a diol component selected from aliphatic diols, cycloaliphatic diols, and polyether polyols.

[0093] The aliphatic diols suitable for preparing polyester polyols generally have 2 to 20 carbon atoms, especially 3 to 10 carbon atoms. Examples of aliphatic diols are ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,3-pentanediol, 2,4-pentanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 1,5-hexanediol, 1,6-hexanediol, 2,5-hexanediol, 1,2-heptanediol, 1,7-heptanediol, 1,8-octanediol, 1,2-octanediol, 1,9-nonanediol, 1,2-decanediol, 1,10-decanediol, 1,2-dodecanediol, 1,12-dodecanediol, 1,5-hexadiene-3,4-diol, neopentyl glycol (2,2-dimethylpropane-1,3-diol), 2,2-diethylpropane-1,3-diol, 2-methyl-2-ethylpropane-1,3-diol, 2-methyl-2,4-pentanediol, 2,4-dimethyl-2,4-pentanediol, 2-ethyl-1,3-hexanediol, 2,5-dimethyl-2,5-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, pinacol, diethylene glycol, triethylene glycol, dipropylene glycol, and tripropylene glycol.

[0094] The alicyclic diols suitable for the preparation of polyester polyols usually have 4 to 20 carbon atoms, especially 5 to 10 carbon atoms. Examples of alicyclic diols are cyclopentanediol, cyclohexane-1,4-diol, cyclohexane-1,2-dimethanol, cyclohexane-1,3-dimethanol, cyclohexane-1,4-dimethanol, and 2,2,4,4-tetramethylcyclobutane-1,3-diol. Also suitable as diols for the preparation of polyester polyols are polyether diols, especially polyethylene glycols HO(CH2CH2O)n-H, higher polypropylene glycols HO(CH[CH3]CH2O)n-H, where n is an integer and n≥4, for example 4 to 20; polyethylene glycol-polypropylene glycols, more particularly those having 4 to 20 repeating units, and the sequence of ethylene oxide units and propylene oxide units can be a block or random sequence; polybutylene glycols, more particularly those having 4 to 20 repeating units; and poly-1,3-propylene glycols, more particularly those having 4 to 20 repeating units.

[0095] Preferred dicarboxylic acids for the preparation of polyester polyols are aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid; alicyclic dicarboxylic acids preferably having 8 to 12 carbon atoms such as tetrahydrophthalic acid, hexahydrophthalic acid, cyclohexanedicarboxylic acid; aliphatic dicarboxylic acids preferably having 3 to 40 carbon atoms such as malonic acid, succinic acid, 2-methylsuccinic acid, glutaric acid, 2-methylglutaric acid, 3-methylglutaric acid, α-ketoglutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, tridecanedioic acid, fumaric acid, 2,2-dimethylglutaric acid, suberic acid, diglycolic acid, oxaloacetic acid, glutamic acid, aspartic acid, itaconic acid, and maleic acid; and dimer fatty acids such as dimer fatty acids of octadecadienoic acid or dimer fatty acids obtained by dimerization of other polyunsaturated fatty acids or fatty acid mixtures [CAS 61788-89-4].

[0096] The dicarboxylic acids used for the preparation of polyester polyols can be the free acids or their ester derivatives. The derivatives are preferably understood as the corresponding acid anhydrides; monoalkyl esters and dialkyl esters, preferably mono- and di-C1-C4 alkyl esters, more preferably monomethyl esters and dimethyl esters; and the corresponding monoethyl esters and diethyl esters; also mono vinyl esters and divinyl esters; and mixed esters, examples being mixed esters having different C1-C4 alkyl components.

[0097] Among the polyester polyols, polyester polyols based on a diol component and a dicarboxylic acid component are preferred. The diol component is selected from the group consisting of butanediol, neopentyl glycol, hexanediol, ethylene glycol, diethylene glycol, and mixtures thereof. The dicarboxylic acid component is selected from the group consisting of adipic acid, phthalic acid, isophthalic acid, and combinations thereof. Particularly preferred are polyester polyols based on butanediol and / or neopentyl glycol and / or hexanediol and adipic acid and / or phthalic acid and / or isophthalic acid.

[0098] Suitable polyester polyols as polyols also include polyesters, especially poly-C4-C12-lactones, in particular polycaprolactone (PCL). Polyester is an aliphatic polyester that can be obtained by ring-opening polymerization of lactones, especially C4-C12-lactones, in particular ε-caprolactone (ε-caprolactone). Polycaprolactone has a repeating monomer unit of the general formula (1) [-O-CHR-(CH2)m-CO-], where m is from 4 to 10, m = 4 in the case of caprolactone, and R is hydrogen. In the context of the present invention, the term polycaprolactone is understood to refer to both the homopolymer of ε-caprolactone and the copolymer of ε-caprolactone. Suitable copolymers are, for example, copolymers of ε-caprolactone with monomers selected from the group consisting of lactic acid, lactide, glycolic acid, and glycolide. Polyester polyols are common components. For example, they can be obtained from Ullmanns der technischen Chemie [Ullmann’s Encyclopedia of Industrial Chemistry], 4th edition, volume 19, pages 62 to 65.

[0099] Suitable aliphatic polyether polyols for use as polyols are, for example, addition products of C2-C4-alkylene oxides such as ethylene oxide, propylene oxide, 1,2-epoxybutane, 2,3-epoxybutane or 2-methyloxirane. Further suitable polymeric polyols (b) are aliphatic polyether polyols obtainable by the condensation of polyaliphatic alcohols and aliphatic polyether polyols obtainable by the alkoxylation of polyaliphatic alcohols, amines and amino alcohols. Suitable polyols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, trimethylolpropane, glycerol, pentaerythritol, triethanolamine (or tris(2-hydroxyethyl)amine), sorbitol, or mixtures of these polyols. Suitable polyether alcohols generally have a hydroxyl functionality in the range from 1.5 to 5.0, more preferably in the range from 1.8 to 4 and in particular in the range from 1.8 to 2.5. Suitable polyether alcohols preferably have a hydroxyl value in the range from 20 mg KOH / g to 600 mg KOH / g, more preferably in the range from 25 mg KOH / g to 400 mg KOH / g and in particular in the range from 30 mg KOH / g to 250 mg KOH / g. In the context of the present invention, the OH value is measured in accordance with EN ISO 4629-1:2016, unless otherwise stated.

[0100] Generally speaking, their number average molecular weight Mn is in the range from 400 g / mol to 10,000 g / mol, preferably from 500 g / mol to 6,000 g / mol and more preferably from 1,000 g / mol to 3,000 g / mol, and this molecular weight can be determined using 1 end-group quantification by 1H-NMR spectroscopy or can be calculated from the number of hydroxyl groups in accordance with EN ISO 4629-1:2016.

[0101] Preferred polyether components (b) are polyethylene oxide polyols, polypropylene oxide polyols, polypropylene oxide-ethylene oxide copolymer polyols and polytetrahydrofuran polyols (poly-THF) having a molecular weight Mn of from 400 g / mol to 10,000 g / mol, preferably from 500 g / mol to 6,000 g / mol and more preferably from 800 g / mol to 3,000 g / mol. In this case, particularly low molecular weight polyether polyols can be water-soluble in the case of a correspondingly high OH content.

[0102] Aliphatic polycarbonate polyols suitable as polyols can be obtained by the reaction of a carbonic acid derivative (such as diphenyl carbonate, dimethyl carbonate or phosgene) with a diol. Such useful diols include, for example, ethylene glycol, 1,2-propanediol and 1,3-propanediol, 1,3-butanediol and 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, neopentyl glycol, 1,4-bis(hydroxymethyl)cyclohexane, 2-methylpropane-1,3-diol, 2,2,4-trimethylpentane-1,3-diol, dipropylene glycol, polypropylene glycol, dibutylene glycol, polybutylene glycol, and lactone-modified diols. The diol component preferably contains 40% to 100% by weight of 1,6-hexanediol and / or hexanediol derivatives, preferably those having ether or ester groups and terminal OH groups, such as products obtained by reacting 1 mol of hexanediol with at least 1 mol, preferably 1 mol to 2 mol of ε-caprolactone, or dihexanediol or trihexanediol obtained by self-etherification of hexanediol. Polyether polycarbonate polyols can also be used. Among the aliphatic polycarbonate polyols, polycarbonate polyols based on dimethyl carbonate and hexanediol and / or butanediol and / or ε-caprolactone are preferred. Polycarbonate polyols based on dimethyl carbonate and hexanediol and / or ε-caprolactone are very particularly preferred. The preferred polycarbonate polyols have a molecular weight Mn of 400 g / mol to 10,000 g / mol, preferably 500 g / mol to 5,000 g / mol, determined by gel permeation chromatography as described above.

[0103] Additional compounds can be added in step (I), which can be, for example, one or more additional active hydrogen compounds, which will also be collectively referred to hereinafter as chain extenders and / or crosslinkers (e). Generally speaking, the active hydrogen compounds have a molecular weight of at most 500 g / mol. Suitable active hydrogen compounds can have 2, 3 or 3, preferably 2 functional groups capable of reacting with isocyanate groups, which are specifically selected from OH, NH2 or SH. Specifically, suitable compounds should be selected as specific compounds with a molecular weight of at most 400 g / mol and only 2 OH groups in each molecule as the sole functional group.

[0104] Specifically, the active hydrogen compound may be selected from aliphatic diol compounds having 2 to 20 carbon atoms, such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,1-dimethylethane-1,2-diol, 2-butyl-2-ethyl-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-methyl-1,3-propanediol, neopentyl glycol, neopentyl glycol hydroxypivalate, 1,2-butanediol, 1,3-butanediol- and 1,4-butanediol, 1,6-hexanediol, 1,10-decanediol, 2-ethyl-1,3-hexanediol, 2,4-diethyloctane-1,3-diol; cyclic aliphatic diol compounds having 3 to 14 carbon atoms, such as tetramethylcyclobutanediol, 1,2-cyclohexanediol, 1,3-cyclohexanediol and 1,4-cyclohexanediol, 1,1-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol and 1,4-cyclohexanedimethanol, 1,2-cyclooctanediol, 1,3-cyclooctanediol or 1,4-cyclooctanediol, norbornanediol, pinanediol, decahydronaphthalenediol, 2,2-bis(4-hydroxycyclohexyl)propane, bis(4-hydroxycyclohexyl)isopropane; and aliphatic amino alcohols having 2 to 20 carbon atoms, such as monoethanolamine, diethanolamine, monopropanolamine, dipropanolamine, N-methyldiethanolamine and N-methyldipropanolamine.

[0105] Particularly preferred are compounds selected from aliphatic diols having 2 to 12 carbon atoms, such as ethylene glycol, 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol.

[0106] According to the present invention, a chain extender having an acetal group may also be used.

[0107] In the context of the present invention, compounds having a molecular weight of at most 500 g / mol and having 3 or more OH groups per molecule as the sole functional group may also be used as the crosslinking agent (e). According to the present invention, a crosslinking agent having an acetal group may also be used. Suitable compounds are, for example, glycerol and trimethylolpropane.

[0108] Additional additives and / or auxiliaries can be used as component (f). Preferably, the liquid mixture of polyol compounds provided in step (I) contains less than 10% of organic compounds that do not have any active hydrogen functional groups and are thus inert under the reaction conditions. These compounds generally have a molecular weight of at most 200 g / mol and are also referred to as "organic solvents". Examples of organic solvents include, but are not limited to, ketones having 3 to 8 carbon atoms, especially aliphatic or cycloaliphatic ketones having 3 to 8 carbon atoms, such as acetone, methyl ethyl ketone, cyclohexanone, and isobutyl methyl ketone; and aliphatic or cycloaliphatic ethers, such as tetrahydrofuran, dioxane, or di-C1-C4-alkyl ethers of mono-, di- or trialkylene glycols, such as diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, tripropylene glycol dimethyl ether; esters, such as C4-C8 lactones, such as butyrolactone, valerolactone, or caprolactone; aliphatic ether esters, such as C1-C4 alkoxy-C2-C4 alkyl acetates and propionates, such as methoxypropyl acetate; or carbonates, such as ethylene carbonate, dimethyl carbonate, diethyl carbonate; N-alkyl-2-pyrrolidones, such as N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, or higher homologues; and mixtures thereof. Specifically, the liquid mixture of polyol compounds provided in step (I) does not contain any organic compounds that do not have any active hydrogen functional groups, or contains less than 2% by weight of such compounds, more preferably less than 1% by weight of such compounds, particularly less than 0.5% by weight of such compounds.

[0109] The liquid mixture can contain additional components, such as a catalyst (c) that catalyzes the formation of polyurethanes from the reactive components contained in the liquid mixture and the isocyanate compound. Based on the total weight of the liquid mixture, the amount of the catalyst will generally not exceed 5% by weight and will typically be in the range of 0.1% by weight to 3% by weight. Suitable catalysts include, but are not limited to, tin compounds, such as stannous octoate, dibutyltin dilaurate, bismuth neodecanoate, or bismuth dioctoate, and tertiary amines, such as dimethylbenzylamine, trimethylamine, 1,4-diazabicyclo[2.2.2]octane, or any other catalyst known to those skilled in the art that promotes the formation of urethane groups through the reaction of the hydroxyl groups in compounds (b) and (e) with the isocyanate groups of the isocyanate compound (a). Additional catalysts are described, for example, in Houben-Weyl, Methoden der Organischen Chemie, Volume XIV / 2, Thieme-Verlag, Stuttgart 1963, page 60f, and Ullmanns der Technischen Chemie, 4th Edition, Volume 19 (1981), page 306.

[0110] Typical catalysts (c) that can be used in the production of polyurethanes include, for example: amidines such as 2,3-dimethyl-3,4,5,6-tetrahydropyrimidine, tertiary amines such as triethylamine, tributylamine, dimethylbenzylamine, N-methyl-, N-ethyl- and N-cyclohexylmorpholine, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethylbutanediamine, N,N,N',N'-tetramethylethylenediamine, pentamethyldiethylenetriamine, tetramethyldiaminoethyl ether, bis(dimethylaminopropyl)urea, dimethylpiperazine, 1,2-dimethylimidazole, 1-azabicyclo[3.3.0]octane and preferably 1,4-diazabicyclo[2.2.2]octane, and alkanolamine compounds such as triethanolamine, triisopropanolamine, N-methyl- and N-ethyldiethanolamine, and dimethylethanolamine. Examples of catalyst-incorporable substances that can be used are bis(dimethylaminopropyl)urea, bis(N,N-dimethylaminoethoxyethyl)carbamate, dimethylaminopropylurea, N,N,N-trimethyl-N-hydroxyethylbis(aminopropyl ether), N,N,N-trimethyl-N-hydroxyethylbis(aminoethyl ether), diethylethanolamine, bis(N,N-dimethyl-3-aminopropyl)amine, dimethylaminopropylamine, 1-(3-aminopropyl)pyrrolidine, 3-dimethylaminopropyl-N,N-dimethylpropane-1,3-diamine, dimethyl-2-(2-aminoethoxyethanol), (1,3-bis(dimethylamino)propan-2-ol), N,N-bis(3-dimethylaminopropyl)-N-isopropanolamine, bis(dimethylaminopropyl)-2-hydroxyethylamine, N,N,N-trimethyl-N-(3-aminopropyl)-bis(aminoethyl ether), 1,4-diazabicyclo[2.2.2]octane-2-methanol and 3-dimethylaminopropyl diisopropanolamine, or mixtures thereof. Organometallic compounds are also envisaged, preferably organotin compounds such as tin(II) salts of organic carboxylic acids, for example tin(II) acetate, tin(II) octoate, tin(II) ethylhexanoate and tin(II) laurate, and dialkyltin(IV) salts of organic carboxylic acids, for example dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate and dioctyltin diacetate; and bismuth carboxylates such as bismuth(III) neodecanoate, bismuth 2-ethylhexanoate and bismuth octoate, or mixtures thereof. The organometallic compounds can be used alone or preferably in combination with strongly basic amines.

[0111] The polyurethanes obtained according to the method can be dense materials which can be used, for example, as adhesives. The polyurethanes can also be polyurethane foams.

[0112] When the polyurethane according to the invention is in the form of a polyurethane foam, the reaction mixture according to the invention further comprises a blowing agent (d). Any known blowing agent for the production of polyurethanes can be used. These blowing agents can include chemical blowing agents and / or physical blowing agents. Such blowing agents are described, for example, in "Kunststoffhandbuch [Plastics Handbook], Volume 7, Polyurethane [Polyurethanes]", Carl Hanser Verlag, 3rd edition 1993, Chapter 3.4.5. "Chemical blowing agent" is to be understood as meaning a compound which forms a gaseous product by reaction with the isocyanate. Examples of such blowing agents are water or carboxylic acids. "Physical blowing agent" is to be understood as meaning a compound which is dissolved or emulsified in the raw materials for polyurethane production and vaporizes under the conditions of polyurethane formation. Examples thereof include hydrocarbons, halogenated hydrocarbons and other compounds, such as perfluorinated alkanes (such as perfluorohexane), chlorofluorocarbons, and ethers, esters, ketones, acetals and / or liquid carbon dioxide. The blowing agent can be used in any desired amount. The blowing agent is preferably used in an amount such that the resulting polyurethane foam has a density of from 10 g / L to 850 g / L, particularly preferably from 20 g / L to 800 g / L and in particular from 25 g / L to 500 g / L. A blowing agent containing water is particularly preferably used.

[0113] It is also possible to use further auxiliaries and / or additives (f). Any known auxiliary substances and additive substances for the production of polyurethanes can be used. Examples include surface-active substances, foam stabilizers, cell regulators, release agents, fillers, dyes, pigments, flame retardants, hydrolysis stabilizers, substances which inhibit fungi and bacteria, and antioxidants. Such substances are known and are described, for example, in "Kunststoffhandbuch, Volume 7, Polyurethane", Carl Hanser Verlag, 3rd edition 1993, Chapters 3.4.4 and 3.4.6 to 3.4.11.

[0114] Step (I) generally comprises mixing these compounds and then heating the mixture thus obtained until the compounds are mutually soluble. The mixing and heating can be carried out simultaneously or successively. Suitable conditions are in principle known to the person skilled in the art, depending on the components used and the materials prepared.

[0115] The mixing can be carried out, for example, at room temperature, but can also be carried out at elevated temperature, for example at a temperature of at least 50 °C, particularly at a temperature in the range from 50 °C to 150 °C.

[0116] The reaction conditions for polyurethane formation will depend on the reactivity of the components present in the polyol composition, the reactivity of the isocyanate, and the presence of a catalyst.

[0117] Preferably, step (I) is carried out at least in the initial stage under conditions of an organic solvent free of hydrogen-free active groups. Thus, based on the total weight of the reactants fed to the reactor, the amount of the organic solvent (i.e., an organic compound having no active hydrogen functional groups and a molecular weight of at most 200 g / mol) in the reactants fed to the reactor is preferably less than 1% by weight, particularly less than 0.1% by weight or 0. However, depending on the reaction conditions and the components used in the process, solvents such as acetone may also be used.

[0118] According to another aspect, the present invention also relates to polyurethanes obtainable or obtained according to the method for preparing polyurethanes as disclosed above.

[0119] According to another aspect, the present invention also relates to a method for recycling polyurethanes obtained according to the method disclosed above or polyurethanes according to the present invention, the method comprising at least the following steps

[0120] (x) treating the polyurethane with a solution having a pH value in the range of 0 to 6.

[0121] Thus, in one embodiment, the present invention relates to a method for recycling polyurethane materials. Specifically, the method comprises: contacting the polyurethane material with an acidic solution and allowing at least a portion of the polyurethane material to decompose into a recovered raw material composition.

[0122] The acidic aqueous solution used in the method may contain any acidic compound as long as its pH value is less than or equal to about 6, preferably less than 4, particularly less than 2. In certain embodiments, the acidic solution may further contain other components in addition to the acidic compound. These components may include solvents such as alcohols, THF, toluene or other solvents.

[0123] The method may further comprise additional steps, particularly subsequent steps after step (x).

[0124] For example, one or more of the following steps may be implemented:

[0125] - separating the obtained liquid phase and solid hard segment phase, optionally also separating the resulting gas phase;

[0126] - neutralizing the acidic liquid phase using a base or an ion exchange resin;

[0127] - separating water and the resulting components using distillation, precipitation or extraction;

[0128] -Depolymerize the solid-state hard segment phase, achieved, for example, by hydrolysis, for example, carried out under conditions where the pH value is greater than 7, particularly where the pH value is greater than 10, for example, implemented in 1-methylimidazole, or in the presence of strong bases (such as KOH, NaOH, tBuOK), organic bases (such as TBD, DBU, DABCO, DMAP, etc.) or organic salts based on such bases (for example, DBU-acetate).

[0129] This is completed in the presence. Suitable conditions are, for example, disclosed in WO 2010 / 130652 A2;

[0130] -Separate the water and the resulting components using distillation, precipitation, or extraction.

[0131] According to one embodiment, all steps are carried out to separate the resulting components.

[0132] Suitable acids for step (x) are generally inorganic acids and organic acids. Examples of inorganic acids are hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, boric acid, hydrobromic acid, and examples of organic acids are oxalic acid, formic acid, acetic acid, citric acid, benzoic acid, dicarboxylic acids (such as adipic acid, glutaric acid, or succinic acid), methanesulfonic acid, and p-toluenesulfonic acid.

[0133] Although it is desirable to immerse the entire polyurethane material to be decomposed in an acidic solution, in some embodiments, only a part of the polyurethane material is brought into contact with the acidic solution. In these embodiments, the remaining part of the polyurethane material (i.e., the part not in contact with the acidic solution) will not decompose. In other words, the present disclosure also contemplates partial recycling of the polyurethane material.

[0134] There are also various methods to promote the depolymerization process and ultimately promote the decomposition of the polyurethane material into various components including the recycled raw material composition. Generally, the polyurethane is crushed using suitable methods (such as cutting or grinding) before depolymerization. Generally, once the polyurethane material is immersed in the acidic solution, it can be stirred using techniques known in the art. Additionally, heat can be applied to one or both of the acidic solution and the polyurethane material to promote the depolymerization process. For example, the acidic solution in which the polyurethane material is immersed can be heated to a temperature in the range of 60 °C to 100 °C. Only when necessary can the material be heated to a temperature above 100 °C, for example, 100 °C to 200 °C. The total amount of time required to decompose the polyurethane material into the recycled raw material composition can vary depending on many factors, such as the thickness of the polyurethane material.

[0135] The method may include additional steps, such as a separation step of separating the resulting liquid and solid phases, or a neutralization purification step, for example by distillation, precipitation or extraction. Residues (such as the remaining part of the polyurethane hard segment phase) can be processed in a separate recycling step, for example by treating these residues with a solution (such as an alkaline solution). For example, the alkaline solution in which the hard segment phase is immersed can be heated to a temperature in the range of 60 °C to 200 °C. In certain embodiments, the alkaline solution may further contain other components in addition to the alkaline compound. These components may include solvents such as alcohols, THF, toluene or other solvents.

[0136] The recovered materials (such as the recovered diol compound) can then be used as raw materials for preparing the original native polyol or other materials.

[0137] The method of the present disclosure is capable of converting certain polyurethane materials into raw material compounds, which can be used as reactive ingredients in the preparation of the original native polyol or in the preparation of another material (such as another type of polyurethane material or another polymer type). This method of recycling the original polyurethane material is energy-efficient and can result in a significant reduction in the total amount of polyurethane material ultimately landfilled.

[0138] Further embodiments of the present invention can be found in the claims and the examples. It should be understood that the features of the subject matter / method / use according to the present invention described above and set forth below can be used not only in the combinations specified in each case, but also in other combinations without departing from the scope of the present invention. For example, combinations of preferred features with particularly preferred features or combinations of features not further characterized with particularly preferred features, etc. are thus implicitly covered even if the combination is not explicitly mentioned.

[0139] Illustrative embodiments of the present invention are listed below, but these do not limit the present invention. In particular, the present invention also covers those embodiments resulting from the combinations generated by the dependent references and thus specified below.

[0140] 1. A method for preparing a polyacetal polyol, comprising step (i): reacting a compound (D1) having at least one OH group with a compound (C1) in the presence of a solid acid catalyst, wherein the compound (C1) is selected from the group consisting of vinyl ethers, aldehydes and acetals.

[0141] 2. The method according to embodiment 1, wherein the compound (D1) has a molecular weight of less than 5000 g / mol, preferably less than 2000 g / mol, particularly less than 1000 g / mol, and more preferably less than 500 g / mol.

[0142] 3. The method according to embodiment 1 or 2, wherein the compound (D1) has a functionality of 1 to 8, preferably 2 to 3.

[0143] 4. The method according to any one of embodiments 1 to 3, wherein the reaction according to step (i) is an addition polymerization reaction, a polycondensation reaction or a transacetalization reaction.

[0144] 5. The method according to any one of embodiments 1 to 4, wherein the solid acid catalyst is selected from the group consisting of

[0145] - a catalyst obtained by a method comprising calcining a precursor of an oxide of one or more elements selected from the group consisting of Ge, Sn, B, Al, Ga, Zn, Cu, Fe, Mn, Ni,

[0146] Cr, Mo, P, S, W, Nb, Ti, Zr, Hf, Y, La, Ce, Yb and Si at a temperature in the range of 150 °C to 1150 °C to obtain an oxide;

[0147] - silica-alumina hydrate

[0148] - a clay compound containing Si and Al;

[0149] - a zeolite having a structure selected from the group consisting of BEA, EMT, ERI, EUO, FAU, HEU, LTA, LTL, MAZ, MOR, MTW, NES, OFF and TON;

[0150] - a cation exchange resin;

[0151] - a MOF catalyst.

[0152] 6. The method according to any one of embodiments 1 to 5, wherein the compound (D1) is selected from the group consisting of monohydric alcohols, dihydric alcohols and trihydric alcohols having 1 to 20 carbon atoms, preferably selected from the group consisting of monohydric alcohols, dihydric alcohols and trihydric alcohols having 2 to 6 carbon atoms.

[0153] 7. The method according to any one of embodiments 1 to 6, wherein the compound (C1) is selected from the group consisting of divinyl ethers and monovinyl ethers.

[0154] 8. The method according to any one of embodiments 1 to 6, wherein the compound (C1) is selected from the group consisting of linear aliphatic aldehydes, branched aliphatic aldehydes, aromatic aldehydes and ketones.

[0155] 9. The method according to any one of embodiments 1 to 6, wherein the compound (C1) is selected from the group consisting of aliphatic acetals, aromatic acetals and ketals.

[0156] 10. The method according to any one of embodiments 1 to 9, wherein the method comprises one or more separation steps selected from the group consisting of filtration, distillation, and washing.

[0157] 11. A polyacetal polyol obtainable or obtained by the method according to any one of embodiments 1 to 10.

[0158] 12. The polyacetal polyol according to embodiment 11, wherein the polyacetal polyol has at least one acetal group and 1 to 8 hydroxyl end groups.

[0159] 13. The polyacetal polyol according to embodiment 11 or 12, wherein the hydroxyl value of the polyacetal polyol is in the range of 10 mg KOH / g to 1200 mg KOH / g.

[0160] 14. A polyacetal polyol obtainable or obtained by a method comprising step (i), wherein step (i) is reacting a compound (D1) having at least one OH group with a compound (C1) in the presence of a solid acid catalyst, and wherein the compound (C1) is selected from the group consisting of vinyl ethers, aldehydes, and acetals.

[0161] 15. The polyacetal polyol according to embodiment 14, wherein the compound (D1) has a molecular weight of less than 5000 g / mol, preferably less than 2000 g / mol, particularly less than 1000 g / mol, and more preferably less than 500 g / mol.

[0162] 16. The polyacetal polyol according to embodiment 14 or 15, wherein the compound (D1) has a functionality of 1 to 8, preferably 2 to 3.

[0163] 17. The polyacetal polyol according to any one of embodiments 14 to 16, wherein the reaction according to step (i) is an addition polymerization reaction, a polycondensation reaction, or a transacetalization reaction.

[0164] 18. The polyacetal polyol according to any one of embodiments 14 to 17, wherein the solid acid catalyst is selected from the group consisting of

[0165] - a catalyst obtained by a method comprising calcining a precursor of an oxide of one or more elements selected from the group consisting of Ge, Sn, B, Al, Ga, Zn, Cu, Fe, Mn, Ni, Cr, Mo, P, S, W, Nb, Ti, Zr, Hf, Y, La, Ce, Yb, and Si at a temperature in the range of 150 °C to 1150 °C to obtain an oxide;

[0166] - silica-alumina hydrate

[0167] - Clay compounds containing Si and Al;

[0168] - Zeolites having a structure selected from the group consisting of BEA, EMT, ERI, EUO, FAU, HEU, LTA, LTL, MAZ, MOR, MTW, NES, OFF, and TON;

[0169] - Cation exchange resins;

[0170] - MOF catalysts.

[0171] 19. The polyacetal polyol according to any one of embodiments 14 to 18, wherein the compound (D1) is selected from the group consisting of monohydric alcohols, dihydric alcohols, and trihydric alcohols having 1 to 20 carbon atoms, preferably selected from the group consisting of monohydric alcohols, dihydric alcohols, and trihydric alcohols having 2 to 6 carbon atoms.

[0172] 20. The polyacetal polyol according to any one of embodiments 14 to 19, wherein the compound (C1) is selected from the group consisting of divinyl ethers and monovinyl ethers.

[0173] 21. The polyacetal polyol according to any one of embodiments 14 to 20, wherein the compound (C1) is selected from the group consisting of linear aliphatic aldehydes, branched aliphatic aldehydes, aromatic aldehydes, and ketones.

[0174] 22. The polyacetal polyol according to any one of embodiments 14 to 19, wherein the compound (C1) is selected from the group consisting of aliphatic acetals, aromatic acetals, and ketals.

[0175] 23. The polyacetal polyol according to any one of embodiments 14 to 22, wherein the method includes one or more separation steps selected from the group consisting of filtration, distillation, and washing.

[0176] 24. Use of the polyacetal polyol obtained or obtainable by the method according to any one of embodiments 1 to 10 or the polyacetal polyol according to any one of embodiments 11 to 23 for the preparation of polyurethanes.

[0177] 25. A method for preparing a polyurethane, at least including step (I)

[0178] (I) Reacting the polyacetal polyol obtained or obtainable by the method according to any one of embodiments 1 to 10 or the polyacetal polyol according to any one of embodiments 11 to 23 with at least one isocyanate.

[0179] 26. The polyurethane obtained or obtainable by the method according to embodiment 25.

[0180] 27. A method for recycling the polyurethane obtained according to the method of embodiment 15 or the polyurethane according to embodiment 26, comprising at least the following steps

[0181] (x) treating the polyurethane with a solution having a pH value in the range of 0 to 6.

[0182] 28. The method according to embodiment 27, wherein the method comprises one or more of the following steps:

[0183] - separating the obtained liquid phase and solid hard segment phase, and optionally also separating the resulting gas phase;

[0184] - neutralizing the acidic liquid phase using an alkali or an ion exchange resin;

[0185] - separating water and the resulting components using distillation, precipitation or extraction.

[0186] 29. A method for preparing a polyacetal polyol, comprising step (i): reacting a compound (D1) having at least one OH group with a compound (C1) in the presence of a solid acid catalyst, wherein the compound (C1) is selected from the group consisting of vinyl ethers, aldehydes and acetals, and wherein the catalyst is in a solid state under the reaction conditions of step (i).

[0187] 30. A method for preparing a polyacetal polyol, comprising step (i): reacting a compound (D1) having at least one OH group with a compound (C1) in the presence of a solid acid catalyst, wherein the compound (C1) is selected from the group consisting of vinyl ethers, aldehydes and acetals, and wherein the solid acid catalyst is selected from the group consisting of

[0188] - a catalyst obtained by a method comprising calcining a precursor of one or more oxides selected from the group consisting of Ge, Sn, B, Al, Ga, Zn, Cu, Fe, Mn, Ni, Cr, Mo, P, S, W, Nb, Ti, Zr, Hf, Y, La, Ce, Yb and Si at a temperature in the range of 150 °C to 1150 °C to obtain an oxide;

[0189] - silica-alumina hydrate

[0190] - a clay compound containing Si and Al;

[0191] - a zeolite having a structure selected from the group consisting of BEA, EMT, ERI, EUO, FAU, HEU, LTA, LTL, MAZ, MOR, MTW, NES, OFF and TON;

[0192] - a cation exchange resin;

[0193] - MOF catalyst.

[0194] 31. The method according to claim 29 or 30, wherein the compound (D1) has a molecular weight of less than 5000 g / mol, preferably less than 2000 g / mol, particularly less than 1000 g / mol, and more preferably less than 500 g / mol.

[0195] 32. The method according to any one of claims 29 to 31, wherein the compound (D1) has a functionality of 1 to 8, preferably 2 to 3.

[0196] 33. The method according to any one of claims 29 to 32, wherein the reaction according to step (i) is a addition polymerization reaction, a polycondensation reaction or a transacetalization reaction.

[0197] 34. The method according to any one of claims 29 to 33, wherein the solid acid catalyst is selected from the group consisting of

[0198] - a catalyst obtained by a method comprising calcining a precursor of one or more oxides selected from the group consisting of Ge, Sn, B, Al, Ga, Zn, Cu, Fe, Mn, Ni, Cr, Mo, P, S, W, Nb, Ti, Zr, Hf, Y, La, Ce, Yb and Si at a temperature in the range of 150 °C to 1150 °C to obtain an oxide;

[0199] - silica-alumina hydrate

[0200] - a clay compound containing Si and Al;

[0201] - a zeolite having a structure selected from the group consisting of BEA, EMT, ERI, EUO, FAU, HEU, LTA, LTL, MAZ, MOR, MTW, NES, OFF and TON;

[0202] - a cation exchange resin;

[0203] - MOF catalyst.

[0204] 35. The method according to any one of claims 29 to 34, wherein the compound (D1) is selected from the group consisting of monohydric alcohols, diols and triols having 1 to 20 carbon atoms, preferably selected from the group consisting of monohydric alcohols, diols and triols having 2 to 6 carbon atoms.

[0205] 36. The method according to any one of claims 29 to 35, wherein the compound (C1) is selected from the group consisting of divinyl ethers and monovinyl ethers.

[0206] 37. The method according to any one of claims 29 to 36, wherein the compound (C1) is selected from the group consisting of linear aliphatic aldehydes, branched aliphatic aldehydes, aromatic aldehydes and ketones.

[0207] 38. The method according to any one of claims 29 to 37, wherein the compound (C1) is selected from the group consisting of aliphatic acetals, aromatic acetals and ketals.

[0208] 39. The method according to any one of claims 29 to 38, wherein the method comprises one or more separation steps selected from the group consisting of filtration, distillation and washing.

[0209] 40. A polyacetal polyol obtainable or obtained by the method according to any one of claims 29 to 39.

[0210] 41. The polyacetal polyol according to claim 40, wherein the polyacetal polyol has at least one acetal group and 1 to 8 hydroxy end groups.

[0211] 42. The polyacetal polyol according to claim 40 or 41, wherein the hydroxyl value of the polyacetal polyol is in the range of 10 mg KOH / g to 1200 mg KOH / g.

[0212] 43. Use of a polyacetal polyol obtainable or obtained by the method according to any one of claims 29 to 39 or a polyacetal polyol according to any one of claims 40 to 42 for the preparation of a polyurethane.

[0213] 44. A method for the preparation of a polyurethane, comprising at least step (I)

[0214] (I) reacting a polyacetal polyol obtainable or obtained by the method according to any one of claims 29 to 39 or a polyacetal polyol according to claim 11 with at least one isocyanate.

[0215] 45. A polyurethane obtainable or obtained by the method according to claim 44.

[0216] 46. A method for recycling a polyurethane obtainable by the method according to claim 44 or a polyurethane according to claim 45, comprising at least the following steps

[0217] (x) treating the polyurethane with a solution having a pH in the range of 0 to 6.

[0218] 47. The method according to claim 46, wherein the method comprises one or more of the following steps:

[0219] - Separating the obtained liquid and solid hard segment phases, and optionally also separating the obtained gas phase;

[0220] - Neutralizing the acidic liquid phase using an alkali or an ion exchange resin;

[0221] - Separating water and the obtained components using distillation, precipitation or extraction.

[0222] The present invention is further described by way of examples. The examples relate to practical and in some cases preferred embodiments of the present invention, which do not limit the scope of the present invention. Examples

[0223] I. Materials Used

[0224] 1. Catalysts

[0225] 1.1 Siral 70, a mixed oxide / hydroxide of silica and alumina (Al2O3 / SiO2 ratio of 30 / 70), purchased from Sasol (Germany)

[0226] Specific surface area S determined by nitrogen adsorption method BET [m 2 / g] 375

[0227] Acidity determined by ammonia TPD method: amount [mmol / g] 0.70

[0228] Acidity determined by ammonia TPD method: T max [℃] 202 and 362

[0229] 1.2 K10, an aluminosilicate catalyst, acid-activated natural bentonite, purchased from Clariant (Germany)

[0230] Specific surface area S determined by nitrogen adsorption method BET [m 2 / g] 236

[0231] Acidity determined by ammonia TPD method: amount [mmol / g] 0.24

[0232] Acidity determined by ammonia TPD method: T max [℃] 194 and 360

[0233] 1.3 Basolite C-300: MOF (copper benzene-1,3,5-tricarboxylate) provided by BASF SE (Germany)

[0234] Specific surface area S determined by nitrogen adsorption method BET [m 2 / g] 1500 - 2100

[0235] Particle size distribution (D50) [μm] 15.96

[0236] II. Examples

[0237] 1. Polyacetal polyol 1

[0238] 1,4 - Butanediol (B14) and 1,4 - butanediol divinyl ether (B14 DVE) were dried using molecular sieve for at least 48 hours and then reserved. 85.4 g of dried 1,4 - butanediol was added to a 500 ml three - necked round - bottom flask equipped with an argon inlet, a mechanical stirrer, a thermocouple, and a dropping funnel. 2.4 g of K10 catalyst was added to B14. The reaction mixture was heated to 30 °C, and the mechanical stirrer was set to 450 rpm to completely suspend the catalyst particles in the reaction mixture. 114.8 g of B14 DVE was loaded into the dropping funnel. B14 DVE was added dropwise to the reaction mixture, and the addition was completed after about 30 minutes. The reaction temperature was kept constant at 30 °C. After a total reaction time of 90 minutes, the polyaddition was completed. The reaction mixture was vacuum - filtered to remove the solid catalyst, and the filtered solution was then dried using a rotary evaporator at 65 °C and under reduced pressure (18 mbar) for 2 hours. The resulting product was a clear and colorless polyacetal polyol with a hydroxyl value of 116.9 mg KOH / g and an acid value of less than 0.1 mg KOH / g.

[0239] The removed K10 catalyst by filtration was washed with diethyl ether and then placed in a nitrogen oven and dried at 50 °C. Subsequently, this catalyst could be reused for at least two more reactions, and the hydroxyl value and acid value of the resulting polyacetal polyol were similar to those of the above - mentioned initial polyol.

[0240] Polyacetal polyol 2

[0241] 1,4 - butanediol (B14) and 1,4 - butanediol divinyl ether (B14 DVE) were dried using molecular sieves for at least 48 hours and then reserved for use. Approximately 367 g of dried 1,4 - butanediol was added to a 1 L three - necked round - bottom flask equipped with an argon inlet, a mechanical stirrer, a thermocouple, and a dropping funnel. 19.1 g of Siral 70 catalyst was added to B14. The reaction mixture was heated to 30 °C, and the mechanical stirrer was set to 450 rpm to completely suspend the catalyst particles in the reaction mixture. 573 g of B14 DVE was charged into the dropping funnel. B14 DVE was added dropwise to the reaction mixture, and the addition was completed in about 60 minutes. The reaction temperature was maintained at 30 °C. After a total reaction time of 6 hours, the polycondensation was completed. The reaction mixture was vacuum - filtered to remove the solid catalyst. The filtered solution was then dried using a rotary evaporator at 65 °C and under reduced pressure (18 mbar) for 4 hours. The resulting product was a clear, colorless polyacetal polyol with a hydroxyl value of 58 mg KOH / g and an acid value of 0.03 mg KOH / g.

[0242] The removed Siral 70 catalyst by filtration was washed with diethyl ether and then placed in a nitrogen oven and dried at 50 °C. Subsequently, this catalyst could be reused for at least four more reactions, and the hydroxyl value and acid value of the resulting polyacetal polyol were similar to those of the original polyol above.

[0243] 3. Polyacetal polyol 3

[0244] Diethylene glycol divinyl ether (DEG DVE) was dried using molecular sieves for at least 48 hours and then reserved for use. 101 g of 1,6 - hexanediol (H16) was added to a 500 ml three - necked round - bottom flask equipped with an argon inlet, a mechanical stirrer, a thermocouple, and a dropping funnel. 3 g of K10 catalyst was added to H16. The reaction mixture was heated to 45 °C to melt H16, and the mechanical stirrer was set to 450 rpm to suspend the catalyst particles in the reaction mixture. 110.1 g of DEG DVE was charged into the dropping funnel. DEG DVE was added dropwise, and the addition was completed in about 15 minutes. During the addition of DEG DVE, the reaction temperature slowly decreased from 45 °C to 30 °C and then remained at 30 °C. After a total reaction time of 3 hours, the polycondensation was completed. The reaction mixture was vacuum - filtered to remove the solid catalyst, and the filtered solution was then dried using a rotary evaporator at 65 °C and under reduced pressure (18 mbar) for 2 hours. The resulting product was a clear, colorless polyacetal polyol with a hydroxyl value of 97 mg KOH / g and an acid value of less than 0.1 mg KOH / g.

[0245] 4. Polyacetal polyol 4

[0246] 80 g of 1,6 - hexanediol (H16) was added to a 250 ml three - necked round - bottom flask equipped with an argon inlet, a Dean - Stark water separator, and a thermocouple. 5.8 g of Siral 70 catalyst and 30 g of paraldehyde were added. 20 g of hexane was added as a water - carrying agent for the Dean - Stark water separator. The reaction mixture was heated to 75 °C, and the magnetic stirrer was set at 450 rpm to suspend the catalyst particles in the reaction mixture. After a reaction time of 22 hours, the polycondensation reaction was complete and all the acetaldehyde was consumed. The reaction mixture was vacuum - filtered to remove the solid catalyst, and the filtered product was then dried using a rotary evaporator at 65 °C and under reduced pressure (18 mbar) for 2 hours. The resulting product was a clear, colorless polyacetal polyol with a hydroxyl value of 153 mg KOH / g and an acid value of 0.01 mg KOH / g.

[0247] 5. Polyacetal polyol 5

[0248] 45 g of 1,6 - hexanediol (H16) was added to a 250 ml three - necked round - bottom flask equipped with an argon inlet, a Dean - Stark water separator, and a thermocouple. 2.57 g of Basolite C - 300 MOF catalyst and 30 g of benzaldehyde were added. 20 g of hexane was added as a water - carrying agent for the Dean - Stark water separator. The reaction mixture was heated to 77 °C, and the magnetic stirrer was set at 450 rpm to suspend the catalyst particles in the reaction mixture. After a reaction time of 16 hours, the reaction mixture was vacuum - filtered to remove the solid catalyst. Subsequently, the polyol was placed in a rotary evaporator and dried first at 65 °C under reduced pressure (10 mbar) for 2 hours and then heated to 110 °C and dried for another 2 hours. The resulting product was a clear, colorless polyacetal polyol with a hydroxyl value of 76 mg KOH / g and an acid value of 0.07 mg KOH / g.

[0249] 6. Polyacetal polyol 6

[0250] 64 g of 1,6 - hexanediol (H16) was added to a 250 ml round - bottom flask.

[0251] 1.85 g of K10 catalyst and 89 g of 1,1 - diethoxypropane were added. The flask was connected to a rotary evaporator and heated to 60 °C at a pressure of 750 mbar and maintained for 1 hour. Subsequently, the pressure was gradually reduced step - by - step every hour, first to 450 mbar, then to 250 mbar, and finally to 20 mbar. After 20 hours, the reaction mixture was vacuum - filtered to remove the solid catalyst. The filtered product was then dried using a rotary evaporator at 65 °C and under reduced pressure (18 mbar) for 2 hours. The resulting product was a transparent polyacetal polyol with a hydroxyl value of 76 mg KOH / g and an acid value of 0.04 mg KOH / g.

[0252] 7. Polyacetal polyol 7

[0253] Diethylene glycol divinyl ether (DEG DVE) was dried using molecular sieve for at least 48 hours and then reserved. 120 g of 1,6 - hexanediol (H16) and 17 g of trimethylolpropane were added to a 500 ml three - necked round - bottom flask equipped with an argon inlet, a mechanical stirrer, a thermocouple, and a dropping funnel. 3.6 g of K10 catalyst was added to the mixture. The mechanical stirrer was set at 450 rpm to suspend the catalyst particles in the reaction mixture, and the reaction mixture was heated to 50 °C. 161 g of DEG DVE was charged into the dropping funnel. The addition of DEG DVE was carried out dropwise and the addition was completed in about 15 minutes. During the addition of DEG DVE, the reaction temperature slowly decreased from 50 °C to 30 °C and was maintained at 30 °C. After a total reaction time of 22 hours, the reaction mixture was vacuum - filtered to remove the solid catalyst, and the filtered solution was then dried using a rotary evaporator at 65 °C and under reduced pressure (18 mbar) for 2 hours. The resulting product was a clear colorless polyacetal polyol with a hydroxyl value of 83 mg KOH / g and an acid value of less than 0.1 mg KOH / g.

[0254] 8. Acetal - containing chain extender

[0255] 72 g of 1,1 - diethoxypropane was added to a 250 ml round - bottom flask. Added

[0256] 2.42 g of K10 catalyst and 50.5 g of 2 - hydroxyethyl acetate (purity 60%, purchased from TCI Europa). The flask was fitted to a rotary evaporator and heated to 55 °C at a pressure of 750 mbar and maintained for 1 hour. Subsequently, the pressure was gradually reduced, first to 450 mbar, then to 250 mbar, and finally to 20 mbar. After an 8 - hour reaction time, the reaction mixture was vacuum - filtered to remove the solid catalyst. The filtered product was then vacuum - distilled at 120 °C and 2 mbar for 1 hour. Approximately 125 g of anionic exchange resin (Amberlyst A26), together with 100 g of methanol and 20 g of water, was added to the non - volatile part. The mixture was heated to 60 °C and maintained for 2 hours, then filtered, and then evaporated at 90 °C and under reduced pressure (2 mbar) to obtain a clear liquid product.

[0257] 9. Bis - acetal - containing chain extender diol

[0258] 103 g of trimethylolpropane (TMP) was added to a 250 ml three-necked round-bottom flask equipped with an argon inlet, a Dean-Stark water separator and a thermocouple. 1.81 g of K10 catalyst and 38.6 g of a 50 wt% aqueous glutaraldehyde solution were added. 20 g of hexane was added as the water-carrying agent for the Dean-Stark water separator. The reaction mixture was heated to 77 °C and the magnetic stirrer was set at 450 rpm to suspend the catalyst particles in the reaction mixture. After 21 h, the reaction mixture was vacuum filtered to remove the solid catalyst. The product was washed with water to remove free TMP. The washed product was then dried using a rotary evaporator at 65 °C and under reduced pressure (18 mbar) for 6 h to obtain propane-1,3-diylbis(5-ethyl-1,3-dioxane-2,5-diyl)dimethanol as a clear colorless liquid with a hydroxyl value of 318 mg KOH / g and an acid value of less than 0.1 mg KOH / g.

[0259] 10. Synthesis of PU materials containing polyacetal polyols

[0260] The polyacetal polyol 2 from Example 2 was used for the synthesis of PU elastomers. Both the polyol and 1,4-butanediol were dried in a vacuum oven at 80 °C for 4 h. 27.88 g of polyacetal polyol 2, 2.23 g of 1,4-butanediol and 0.0275 g of 1,4-diazabicyclo[2.2.2]octane were placed in a 100 ml beaker and mixed at 80 °C under argon protection using a mechanical stirrer at 250 rpm. 9.89 g of 4,4’-MDI was added to the polyol component. After mixing for 1 min, the temperature reached 110 °C, and then the mixture was poured into a Teflon mold preheated to 120 °C. After 20 min, the material was transferred to a nitrogen oven and further cured at 80 °C for 16 h.

[0261] 11. PU depolymerization

[0262] 18.8 g of the PU material synthesized in Example 10 was cut into small pieces (2 mm × 4 mm × 40 mm) and placed in a 100 ml round-bottom flask equipped with a water-cooled condenser. 25 g of a 0.1 M aqueous hydrochloric acid solution was added and the mixture was heated to 80 °C and maintained for 8 h while stirring using a magnetic stirrer at 300 rpm. Subsequently, the resulting solid PU hard segment phase was filtered to be separated from the solution in quantitative yield and further depolymerized as described below. The remaining aqueous phase was transferred to a 250 ml flask containing 4 g of an anion exchange resin (Amberlyst A26). The mixture was stirred at room temperature for 15 min and the resin was filtered off. After evaporating the water at 70 °C and under reduced pressure (20 mbar) for two hours, 8.6 g (yield 91%) of 1,4-butanediol was obtained, with a purity of 98% as determined by 1 1H NMR.

[0263] Depolymerization of the PU hard segment phase: 6.3 g of the separated PU hard segment phase was added to a 20 ml round-bottom flask equipped with a water-cooled condenser. 2 g of water and 2.6 g of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) were added, and the mixture was heated in an oil bath at 150 °C for 48 hours while stirring at 100 rpm using a magnetic stirrer. The temperature of the mixture was slowly increased from 100 °C to 130 °C, and the solid liquefied. After the mixture was cooled to room temperature, it was washed with hot water, and the aqueous phase was filtered and dried to obtain a mixture of 1,4-butanediol and TBD. The insoluble part was subjected to vacuum distillation at 300 °C and 2 mbar under reduced pressure, and then the distillate was dried to obtain 3.05 g (yield 83%) of 4,4'-diaminodiphenylmethane (MDA), with a purity of 98% according to 1 1H NMR detection. Further, the mixture of 1,4-butanediol and TBD was diluted with water and transferred to a 250 ml flask containing 55 g of a cation exchange resin (Amberlyst 36). The mixture was stirred at room temperature for 15 minutes, and the resin was removed by filtration. After evaporating the water at 70 °C and under reduced pressure (20 mbar) for two hours, 1.54 g (yield 92%) of 1,4-butanediol was obtained, with a purity of 97% according to 1 1H NMR detection.

[0264] 12. Comparative Example 1. Polyacetal polyol C1

[0265] Triglycol divinyl ether (TEG DVE) was dried using molecular sieves for at least 48 hours and then used. 114 g of dipropylene glycol, 172 g of dried TEG DVE, and 13.6 g of trimethylolpropane were added to a 500 ml three-necked round-bottom flask equipped with an argon inlet, a mechanical stirrer, and a thermocouple. Subsequently, 0.63 g of oxalic acid was added to the mixture, and the reaction mixture was heated to 80 °C. The mechanical stirrer was set at 450 rpm. After 5 hours, 0.9 g of 1,4-diazabicyclo[2.2.2]octane was added to the reaction mixture to neutralize the acid catalyst. The resulting product was an opaque white polyacetal polyol with a hydroxyl value of 58 mg KOH / g and an acid value of 2.2 mg KOH / g.

[0266] 13. Comparative Example 2. Polyacetal polyol C2

[0267] The polypropylene glycol with a molecular weight of 450 g / mol and triethylene glycol divinyl ether (TEG DVE) were dried using a molecular sieve for at least 48 hours and then reserved for use. 345.8 g of polypropylene glycol was added to a 500 ml three-necked round-bottom flask equipped with an argon inlet, a mechanical stirrer, and a thermocouple. Subsequently, 0.094 g of p-toluenesulfonic acid was added to the flask, and the reaction mixture was heated to 40 °C. The mechanical stirrer was set at 450 rpm. After 4.5 hours, 0.5 g of N,N-dimethylcyclohexylamine was added to the reaction mixture to neutralize the acid catalyst. The resulting product was an orange polyacetal polyol still containing catalyst salts, and its hydroxyl value was 61 mg KOH / g.

[0268] 14. Comparative Example 3. Synthesis of PU material containing PTHF2000

[0269] PTHF 2000 and 1,4-butanediol were dried in a vacuum oven at 80 °C for 4 hours. 28.09 g of PTHF2000, 2.20 g of butanediol, and 0.03 g of 1,4-diazabicyclo[2.2.2]octane were added to a 100 ml beaker and mixed at 250 rpm with a mechanical stirrer under argon protection at 80 °C. 9.71 g of 4,4’-MDI was added to the polyol component. After mixing for 1 minute, the temperature reached 110 °C, and then the mixture was poured into a Teflon mold preheated to 120 °C. After 20 minutes, the material was transferred to a nitrogen oven and further cured at 80 °C for 16 hours.

[0270] 15. Comparative Example 4. Hydrolysis of PU material containing PTHF2000

[0271] 15 g of the PU material synthesized in Comparative Example 2 was cut into small pieces (2 mm × 4 mm × 40 mm) and placed in a 100 ml round-bottom flask equipped with a water-cooled condenser. 20 g of 0.1 M hydrochloric acid aqueous solution was added, and the mixture was heated to 80 °C and maintained for 8 hours while stirring at 300 rpm using a magnetic stirrer. The material remained intact and showed no signs of degradation.

[0272] III. Methods Used :

[0273] 1. Ammonia TPD method: Experimental procedure

[0274] Place approximately 200 mg to 500 mg of the sample in an AutoChem TPD device and pre-treat the material by heating it to 600 °C at a heating rate of 20 K / min in nitrogen. After holding the sample at 600 °C for 10 minutes, cool it to 100 °C and perform ammonia adsorption at this temperature. Then evaporate the excess ammonia at 100 °C. The ammonia temperature-programmed desorption experiment is carried out in the range of 100 °C to 600 °C with a heating rate of 10 K / min and held at 600 °C for 30 minutes. The desorbed gas is continuously monitored using a TCD detector and a mass spectrometer. After calibration, the concentration or number of acidic sites in the range of 100 °C to 600 °C is obtained, with the unit of mmol / g. Deconvolution of the signal allows determination of the acidic site strength corresponding to the temperature, which is the temperature (T max ) at which (one or more) maxima are observed on the curve. If peaks or shoulders are found in the TPD curve in the range of 340 °C to 380 °C, the sample has medium acid strength sites, and the lower the acid strength, the lower the corresponding T max value, and the higher the acid strength, the higher the corresponding T max value.

[0275] 2. Analyze the specific surface area according to DIN ISO 9277.

[0276] 3. Determine the properties of the polyol using the following methods: The hydroxyl number is determined according to the phthalic acid method EN ISO 4629-1:2016, and the result is expressed in mg KOH / g. The acid value is determined according to DIN EN ISO 2114, and the result is expressed in mg KOH / g.

[0277] Cited References :

[0278] Polym. Degard. Stab. 2002, 75, 413 - 421

[0279] Polym. Degard. Stab. 2004, 147 - 151

[0280] ChemSusChem 2020, 13, 3835, 3843

[0281] T. Hashimoto et al., J. Appl. Polym. Sci., 2016, 133, 44088

[0282] Z. Petrovic et al., J Polym Environ., 2009, 17, 123 - 130

[0283] WO 2021 / 236385 A1

[0284] Ullmanns der technischen Chemie[Ullmann’s Encyclopedia of Industrial Chemistry], 4th edition, volume 19, pp. 62 to 65;p. 306.

[0285] US 5,648,508

[0286] EP - A - 0 709 253

[0287] M.O’Keeffe et al., J.Sol.State Chem., 152(2000) p.3 - 20

[0288] H.Li et al., Nature 402(1999) p.276seq.

[0289] M.Eddaoudi et al., Topics in Catalysis 9(1999) p.105 - 111

[0290] B.Chen et al., Science 291(2001) p.1021 - 23

[0291] WO 02 / 088148

[0292] “Kunststoffhandbuch”, Volume 7, “Polyurethane”, Carl Hanser Verlag, 3rd edition 1993, chapters 3.1, 3.2 and 3.3.2, 3.4.4, 3.4.5 and 3.4.6 to 3.4.11

[0293] Houben - Weyl, Methoden der Organischen Chemie, Vol.XIV / 2, Thieme - Verlag, Stuttgart 1963, p.60f.

[0294] WO 2010 / 130652 A2。

Claims

1. A method for preparing a polyacetal polyol, comprising step (i): reacting a compound (D1) having at least one OH group with a compound (C1) in the presence of a solid acid catalyst, wherein the compound (C1) is selected from the group consisting of vinyl ethers, aldehydes, and acetals.

2. The method according to claim 1, wherein the compound (D1) has a molecular weight of less than 5000 g / mol, preferably less than 2000 g / mol, particularly less than 1000 g / mol, and more preferably less than 500 g / mol.

3. The method according to claim 1 or 2, wherein the compound (D1) has a functionality of 1 to 8, preferably 2 to 3.

4. The method according to any one of claims 1 to 3, wherein the reaction according to step (i) is a polyaddition reaction, a polycondensation reaction, or a transacetalization reaction.

5. The method according to any one of claims 1 to 4, wherein the solid acid catalyst is selected from the group consisting of - a catalyst obtained by a method comprising calcining a precursor of one or more oxides selected from the group consisting of Ge, Sn, B, Al, Ga, Zn, Cu, Fe, Mn, Ni, Cr, Mo, P, S, W, Nb, Ti, Zr, Hf, Y, La, Ce, Yb, and Si at a temperature in the range of 150 °C to 1150 °C to obtain an oxide; - silica-alumina hydrate - a clay compound containing Si and Al; - a zeolite having a structure selected from the group consisting of BEA, EMT, ERI, EUO, FAU, HEU, LTA, LTL, MAZ, MOR, MTW, NES, OFF, and TON; - a cation exchange resin; - a MOF catalyst.

6. The method according to any one of claims 1 to 5, wherein the compound (D1) is selected from the group consisting of monohydric alcohols, diols, and triols having 1 to 20 carbon atoms, preferably selected from the group consisting of monohydric alcohols, diols, and triols having 2 to 6 carbon atoms.

7. The method according to any one of claims 1 to 6, wherein the compound (C1) is selected from the group consisting of divinyl ethers and monovinyl ethers.

8. The method according to any one of claims 1 to 6, wherein the compound (C1) is selected from the group consisting of linear aliphatic aldehydes, branched aliphatic aldehydes, aromatic aldehydes, and ketones.

9. The method according to any one of claims 1 to 6, wherein the compound (C1) is selected from the group consisting of aliphatic acetals, aromatic acetals, and ketals.

10. The method according to any one of claims 1 to 9, wherein the method comprises one or more separation steps selected from the group consisting of filtration, distillation, and washing.

11. A polyacetal polyol obtainable or obtained by the method according to any one of claims 1 to 10.

12. The polyacetal polyol according to claim 11, wherein the polyacetal polyol has at least one acetal group and 1 to 8 hydroxyl end groups.

13. The polyacetal polyol according to claim 11 or 12, wherein the hydroxyl value of the polyacetal polyol is in the range of 10 mg KOH / g to 1200 mg KOH / g.

14. Use of a polyacetal polyol obtainable or obtained by the method according to any one of claims 1 to 10 or a polyacetal polyol according to any one of claims 11 to 13 for the preparation of polyurethanes.

15. A method for the preparation of polyurethanes, comprising at least step (I) (I) Reacting a polyacetal polyol obtainable or obtained by the method according to any one of claims 1 to 10 or a polyacetal polyol according to claim 11 with at least one isocyanate.

16. A polyurethane obtainable or obtained by the method according to claim 15.

17. A method for recycling a polyurethane obtainable or obtained by the method according to claim 15 or a polyurethane according to claim 16, comprising at least the following steps (x) Treating the polyurethane with a solution having a pH in the range of 0 to 6.

18. The method according to claim 17, wherein the method comprises one or more of the following steps: - Separating the obtained liquid phase and the solid hard segment phase, optionally also separating the resulting gas phase; - Neutralizing the acidic liquid phase using an alkali or an ion exchange resin; - Separating water and the resulting components using distillation, precipitation or extraction.