Depolymerization of polyurethanes: regeneration of isocyanates via chemical recycling

Abstract

The present invention discloses a one-step polyurethane (PU) depolymerization to recover isocyanates and regenerate both thermoplastic and thermoset PU. The process uses a halide-containing boron compound to react at mild conditions (e.g., in toluene lt; and directly depolymerizing the PU into isocyanate at the temperature of 100 DEG C). Furthermore, the depolymerization of both model PU and commercially available PU having molecular weight distribution and thermomechanical properties equivalent to the original PU with a yield of at most 50% and the regeneration of PU using recovered isocyanates are disclosed herein.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 318,123, filed on March 9, 2022, the entire disclosure of which is incorporated herein by reference in its entirety for all purposes.

[0003] Statement Regarding Federally Funded Research

[0004] This invention was made with government support awarded by the National Science Foundation under Grant Nos. NSF GCR 1934887 and NSF DMR 2004682. The government has certain rights in this invention. Background Art

[0005] Polyurethane (PU) is a class of polymers that is widely present because they provide a variety of available thermomechanical properties that can be customized by selecting monomers and additives for manufacturing. In overall polymer production, PU ranks sixth, and the global market is expected to grow from $70.7B in 2020 to $94.6B in 2028, with a compound annual growth rate (CAGR) of 3.8%. Conventional PU is polymerized by isocyanates, polyols / macro diols, and low molecular weight diols / chain extenders. The production of PU causes environmental and human health problems because most common diisocyanates used for PU manufacturing, such as methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI), are classified as carcinogens, mutagens, and reproductive toxicants. Exposure to these compounds is associated with asthma, dermatitis, conjunctivitis, respiratory diseases, and acute poisoning. In addition, isocyanates are prepared by reacting amines with phosgene (a highly toxic substance). Despite the hazards associated with its production, PU is a versatile material used in everyday products such as footwear, refrigerators, foams, mattresses, carpets, furniture, adhesives, coatings, composites, aircraft, windmills, and many other products.

[0006] The widespread use of PU materials has resulted in a large amount of end-of-life PU and post-production waste, most of which is landfilled or incinerated, and recycling these waste streams is challenging. Currently, PU recycling strategies can be categorized as mechanical recycling or thermochemical recycling. Mechanical recycling is the most common method for recycling thermoplastic PU, and involves grinding solid PU waste into particles, which are then recombined into PU foam or used as fillers in new products. This technology typically degrades the PU and results in a material with inferior thermomechanical properties compared to the original PU, and additives or compatibilizers are usually added to the recyclate to facilitate blending with the original polymer. However, when it comes to thermosetting PU, mechanical recycling fails due to the network structure of the polymer.

[0007] In contrast to mechanical methods, thermochemical recycling involves deconstructing PU waste into monomers or other small molecules. The most common PU chemical recycling methods are hydrolysis, aminolysis, hydrogenolysis, and glycolysis. In hydrolysis, PU reacts with steam at high temperature (>200°C) in the presence of an alkaline catalyst, resulting in the generation of amines, polyols, and carbon dioxide. For aminolysis, ammonia or fatty amines are used for deconstruction, and amines, polyols, ureas, and carbamates are produced. Although this method involves milder reaction conditions than other chemical recycling methods, the complex separation steps hinder its industrial application. Recently, catalytic hydrogenolysis of PU waste has emerged as a chemical recycling technology that employs external hydrogen and transition metal catalysts, particularly transition metal pincer complexes, in combination with a base to deconstruct PU materials into corresponding diamine and polyol parts. Finally, in glycolysis, PU waste is deconstructed by reacting with diols or triols (e.g., ethylene glycol or glycerol) in the temperature range of 180°C-240°C to form polyols that can be incorporated into new PU materials. Among these chemical recycling methods, only glycolysis is applied on an industrial scale and none of the above mentioned technologies is able to recover isocyanates, a key component for PU synthesis.

[0008] Therefore, robust strategies are needed to recover isocyanates from PU deconstruction and thereby reduce the dependence on petrochemical feedstocks, especially highly hazardous compounds such as phosgene, while increasing the recyclability of PU materials. Summary of the invention

[0009] This article discloses a method for depolymerizing polyurethane materials, which can use an organic boron compound as a depolymerizing agent under mild reaction conditions to recover isocyanate and regenerate PU materials ( Figure 1A Laboratory-made and commercially sourced thermoset and thermoplastic polyurethanes composed of aromatic isocyanates have been depolymerized using the techniques disclosed below, and the recovered isocyanates have been used to regenerate new PU materials having molecular weights and thermomechanical properties equivalent to those of the virgin materials.

[0010] In aspects of the present invention, a method for depolymerizing a polyurethane in a single step to provide a regenerated isocyanate compound is provided. The method comprises contacting the polyurethane with a depolymerizing agent in the presence of a solvent and a Lewis base. The depolymerizing agent may include a halide-containing boron compound, and the regenerated isocyanate mixture may include a mixture of the regenerated isocyanate compound and at least one of an adduct of a polyol and a halide-containing boron compound, an adduct of a chain extender and a halide-containing boron compound, a residual amount of a Lewis base, or an acid-base adduct.

[0011] In embodiments, the method can be used to depolymerize thermoplastic polyurethanes or thermoset polyurethanes, as shown in the following structures:

[0012]

[0013] in:

[0014] R' is H or C1-C10 alkyl;

[0015] Each R1 is independently:

[0016] (i) an unsubstituted or substituted alkylene group having 2 to 75 carbon atoms, wherein one or more carbon atoms in the alkylene group may be substituted by an oxygen atom, a nitrogen atom or a sulfur atom, provided that only a carbon atom is directly bonded to each of the two NH groups in the polyurethane backbone; or

[0017] (ii) an unsubstituted or substituted aromatic group having 6 to 75 carbon atoms;

[0018] or

[0019] (iii) an unsubstituted or substituted heteroaromatic group having 4 to 75 carbon atoms; or

[0020] (iv) an unsubstituted or substituted cycloalkyl-containing group having 4 to 75 carbon atoms;

[0021] or

[0022] (v) an unsubstituted or substituted heterocyclic alkyl group having 4 to 75 carbon atoms; or

[0023] (vi) any combination thereof;

[0024] R2 and R3 are independently selected from alkylene groups having 2 to 75 carbon atoms, wherein:

[0025] One of R2 or R3 is an alkylene group having 2 to 5 carbon atoms, and the other of R2 or R3 is an oligomeric or polymeric segment having 6 to 75 carbon atoms, and

[0026] one or more carbon atoms are optionally substituted with oxygen atoms, nitrogen atoms or sulfur atoms, provided that only a carbon atom is directly bonded to each of the terminal oxygen atoms in the polyurethane backbone;

[0027] x, y, z, m, n and r are each independently 1 to 200, and p is 3 to 100, and

[0028] The depolymerizing agent is relative to the urethane ( urethane ) bonds are present in an amount of 0.3 to 3 molar equivalents.

[0029] In embodiments of the methods disclosed above, the halide-containing boron compound is selected from a halogenated organoborane compound or a boron trihalide. In embodiments, the halogenated organoborane compound may include one or more of β-chlorocatecholborane, β-bromocatecholborane, β-fluorocatecholborane, and β-iodocatecholborane.

[0030] In another embodiment of the method, the Lewis base may include one or more of triethylamine, pyridine, dimethylaminopyridine, triethylenediamine, diisopropylethylamine, other trialkylamines, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), amidine derivatives, lithium diisopropylamide, and quinuclidine. In an embodiment, the solvent may include one or more of toluene, hexane, heptane, pentane, benzene, and cyclohexane.

[0031] In an embodiment of the method, the depolymerization is carried out at a temperature of 20°C to 150°C in an inert environment comprising one or more of nitrogen (N2), argon, helium, and dry air.

[0032] In another embodiment of the method, the polyol can include poly(tetramethylene glycol), polyethylene glycol, polyethylene glycol trimethylolpropane triether, polypropylene glycol, or a combination thereof, and the chain extender can include 1,4-butanediol, glycerol, ethylene glycol, 1,6-hexanediol, or a combination thereof.

[0033] In yet another embodiment of the method, the method may further include separating the recovered isocyanate from the regenerated isocyanate mixture by treating the regenerated isocyanate mixture with at least one of chromatography, distillation (e.g., vacuum distillation), differential extraction, or crystallization.

[0034] In another aspect of the invention, disclosed herein is a method of forming a polyurethane comprising reacting a separated, recovered isocyanate with one or more polyols and / or a chain extender in the presence of a polymerization catalyst and an optional solvent. In an embodiment, the polymerization catalyst may include a tin-containing catalyst or an amine catalyst. In an embodiment, the tin-containing catalyst may include dibutyltin dilaurate, dioctyltin dilaurate, dioctyl carboxylate, stannous octoate, or a mixture thereof, and the amine catalyst may include 1,4-diazabicyclo[2.2.2]octane (DABCO), dimethylethanolamine, triethylenediamine, or a mixture thereof.

[0035] Another aspect of the invention disclosed herein is a composition comprising a polyurethane prepared from separated recycled isocyanates and halide-containing boron compounds. In an embodiment, the composition may also include a solvent. In another embodiment, the composition may also include one or more of virgin polyurethane, an inert filler, and an additive. In an embodiment, the composition may have a biobased content of 20% to 100% according to ASTM-D6866.

[0036] Another aspect of the invention is an article comprising the composition as disclosed above.

[0037] Another aspect of the invention disclosed herein is a method comprising: providing a regenerated isocyanate mixture obtained by the method for depolymerizing polyurethane as disclosed above; purifying the regenerated isocyanate mixture compounds by at least one of chromatography, distillation (e.g., vacuum distillation), differential extraction, or crystallization to obtain isolated recovered isocyanate compounds; and forming a recycled polyurethane by reacting the recovered isocyanate compounds with one or more polyols in the presence of a catalyst, wherein the one or more polyols include recycled polyols, bio-derived polyols, petroleum-based polyols, or mixtures thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1A An exemplary one-step polyurethane depolymerization and isocyanate regeneration and repolymerization according to an embodiment of the present invention is shown.

[0039] Figure 1B The general chemical structures of thermoplastic polyurethanes and thermoset polyurethanes are shown.

[0040] Figure 2A A schematic diagram illustrating the synthesis of polyurethane by varying the diisocyanate and the chain extender is shown.

[0041] Figure 2B A schematic diagram illustrating an exemplary depolymerization reaction of a laboratory-synthesized hexamethylene diisocyanate (HDI)-based polyurethane (1.56 g) in the presence of β-chlorocatecholborane (0.52 g), triethylamine (0.7 mL) and toluene (10 mL) at a temperature of 85° C. according to an embodiment of the present invention is shown.

[0042] Figure 2C Shows Figure 2B ATR-FTIR spectra of an exemplary HDI-based polyurethane (solid line) and the depolymerization reaction product mixture (dashed line) are shown in FIG.

[0043] Figure 2D The results of gas chromatography-mass spectrometry (GC-MS) are shown. Figure 2BAnalysis of the product mixture.

[0044] Figure 3A Shown are the ATR-FTIR spectra of a model thermoplastic polyurethane (PU1) before depolymerization, after depolymerization, after isocyanate purification and after repolymerization.

[0045] Figure 3B Shown are ATR-FTIR spectra of a commercial thermoplastic polyurethane (CPU1) before depolymerization, after depolymerization, after isocyanate purification and after repolymerization. For clarity, the spectra are vertically offset.

[0046] Figure 4A Shown are gel permeation chromatography (GPC) chromatograms of thermoplastic polyurethanes: laboratory synthesized (PU1) and commercially obtained (CPU1).

[0047] Figure 4B Differential Scanning Calorimetry (DSC) thermograms (exotherms) of a laboratory synthesized thermoplastic polyurethane (PU1) and a commercially available thermoplastic polyurethane (CPU1) are shown.

[0048] FIG. 5A to FIG. 5C Shown are nuclear magnetic resonance (NMR) spectra of isocyanates recovered from laboratory synthesized thermoplastic polyurethane (PU1) and commercially available thermoplastic polyurethane (CPU1), thermosetting polyurethane (PU2) and commercially available thermosetting polyurethane (CPU2), as well as pure MDI and toluene diisocyanate (TDI) for reference.

[0049] Fig. 6A and Figure 6B Shown are (A): ATR-FTIR spectra of a model thermosetting material (PU2) before depolymerization (black), after depolymerization, after isocyanate purification, and after repolymerization; and (B): ATR-FTIR spectra of a commercially available thermosetting material (CPU2) before depolymerization, after depolymerization, after isocyanate purification (blue), and after repolymerization. For clarity, the spectra are vertically offset.

[0050] Figure 7 Shown are GPC chromatograms of repolymerized thermosetting polyurethanes from a laboratory synthesized thermosetting polyurethane (PU2) and a commercially available thermosetting polyurethane (CPU2).

[0051] Figure 8 The DSC thermograms (exotherms) of the starting thermoset polyurethane (PU2) and the resynthesized polyurethane (RPU2) are shown.

[0052] Fig.9A and Fig. 9BShown are: (A): GPC chromatograms of remanufactured PUs prepared from isolated MDI (RPU1, RPU3), with molecular weights calculated relative to a series of poly(methyl methacrylate) standards; and (B): DSC curves (exotherms) of resynthesized polymers RPU1 and RPU3. For clarity, the curves are vertically offset.

[0053] Fig. 10A and Fig. 10B Shown are (A): ATR-FTIR spectrum of thermoplastic polyurethane (PU1) after depolymerization using boron trichloride as a depolymerizing agent; and (B): Nuclear magnetic resonance (NMR) spectrum of the product mixture after the depolymerization reaction, which shows signals from isocyanate, polyol and chain extender. DETAILED DESCRIPTION

[0054] As used herein, the term "virgin polyurethane" refers to a polyurethane produced from isocyanates derived directly from petrochemical feedstocks (such as natural gas or crude oil) or plant-based biomass feedstocks.

[0055] As used herein, the term "alkylene" refers to a saturated aliphatic hydrocarbon group, such as ethyl, n-propyl, isopropyl, n-butyl, sec-butyl or tert-butyl, and the alkyl group may have a substituent or may not have a substituent. The term "substituted alkylene" refers to an alkyl group bonded to a substituent; additional substituents are not particularly limited. Examples of additional substituents include alkyl, halogen, aryl and heteroaryl, and the same applies in the following description. Alkyl groups substituted with halogen are also referred to as haloalkyl. The number of carbon atoms in the alkylene group is not particularly limited, and is preferably 2 to 75, or 3 to 50, or 5 to 35, or 5 to 25, or 5 to 20, or 5 to 10.

[0056] As used herein, the term "cycloalkyl-containing group" refers to an alkylene group containing a saturated alicyclic hydrocarbon moiety, such as cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, norbornyl or adamantyl. The cycloalkyl-containing group may have a substituent or may not have a substituent. The number of carbon atoms in the cycloalkyl-containing group is not particularly limited, and is preferably 4 to 75, or 3 to 50, or 5 to 35, or 5 to 25, or 5 to 20.

[0057] As used herein, the term "heterocycloalkyl-containing group" refers to an alkylene group containing an aliphatic ring having at least one atom (e.g., N, O, and / or S) other than carbon in the ring, such as a piperazine ring, a pyrrolidine ring, a pyrrolidone ring, an azetidine ring, a morpholine ring, a dioxane ring, a tetrahydrofuran ring, an oxirane ring, a pyran ring, a piperidine ring, or a cyclic amide, and the group containing the heterocycloalkyl may have a substituent or may not have a substituent. The number of carbon atoms in the group containing the heterocycloalkyl is not particularly limited, and is preferably 4 to 75, or 4 to 60, or 5 to 50, or 5 to 35, or 5 to 25, or 5 to 20.

[0058] As used herein, the term "aromatic-containing group" refers to an alkylene group containing a cyclic aromatic group, such as phenyl, biphenyl, terphenyl, naphthyl, fluorenyl, benzofluorenyl, dibenzofluorenyl, phenanthryl, anthracenyl, triphenylenyl, benzanthryl, The aromatic group may be substituted with 1-2-nitro-2-nitro-1-ol, 1-2-nitro-2-ol, 1-2-nitro-2-ol, 1-2-nitro-3-ol, 1-2-nitro-4-ol, 1-2-nitro-5-ol, 1-2-nitro-6-ol, 1-2-nitro-7-ol, 1-2-nitro-8-ol, 1-2-nitro-9-ol, 1-2-nitro-10-ol, 1-2-nitro-20-ol, 1-2-nitro-3 ...8-ol, 1-2-nitro-9-ol, 1-2-nitro-10-ol, 1-2-nitro-3-ol, 1-2-nitro-8-ol, 1-2-nitro-9-ol, 1-2-nitro-10-ol, 1-2-nitro-3-ol, 1-2-nitro-8-ol, 1-2-nitro-9-ol, 1-2-nitro-10-ol

[0059] In a substituted phenyl group having two adjacent carbon atoms each having a substituent, the substituent may form a ring structure. The resulting group may correspond to any one or more of a "substituted phenyl group", an "aryl group having a structure in which two or more rings are fused", and a "heteroaryl group having a structure in which two or more rings are fused", depending on the structure.

[0060] As used herein, the term "heteroaromatic-containing group" refers to an alkylene group containing a cyclic aromatic group having one or more atoms other than carbon (e.g., N, O and / or S) in the ring, such as pyridyl, furyl, thienyl, quinolyl, isoquinolyl, pyrazinyl, pyrimidinyl, pyridazinyl. The heteroaromatic-containing group may have a substituent or may not have a substituent. The number of carbon atoms in the heteroaromatic-containing group is not particularly limited, and is preferably 4 to 75, or 4 to 60, or 5 to 50, or 5 to 35, or 5 to 25, or 5 to 20.

[0061] As used herein, the term "halo" refers to an atom selected from fluorine, chlorine, bromine and iodine.

[0062] As used herein, "biobased content" is determined according to ASTM-D6866 and is based on the same concepts as radiocarbon dating, but without the use of an age equation. 14 C) compared to the radiocarbon ( 14 C) is analyzed based on the ratio of the amount of carbon present in the sample to the amount of carbon present in the sample. The ratio is reported in percentages in the unit of "pMC" (percentage of modern carbon), where modern or current is defined as 1950. If the material analyzed is a mixture of current radiocarbon and fossil carbon (not containing radiocarbon), the pMC value obtained is directly related to the amount of biomass material present in the sample. Combining fossil carbon with current carbon in the material will result in a dilution of the current pMC content. By assuming that 107.5pMC represents current biomass material and 0pMC represents petroleum derivatives, the measured pMC value of the material will reflect the ratio of the two component types. 100% of the material derived from current plants / trees will produce a radiocarbon signal close to 107.5pMC. If the material is diluted with 50% petroleum derivatives, it will obtain a radiocarbon signal close to 54pMC. The biomass content result is derived by specifying that 100% is equal to 107.5pMC and specifying that 0% is equal to 0pMC. At this point, a sample measuring 99pMC will give an equivalent biological content result of 93%.

[0063] According to aspects of the present invention, disclosed herein is a method for depolymerizing polyurethane in a single step to provide a regenerated isocyanate compound. The method includes contacting the polyurethane with a depolymerizing agent in the presence of a solvent and a Lewis base. Any suitable depolymerizing agent can be used, including but not limited to a halide-containing boron compound, such as a halogenated organic borane compound or a boron trihalide. The regenerated isocyanate mixture may include a mixture of the regenerated isocyanate compound and at least one of the following: an adduct of a polyol and a halide-containing boron compound, an adduct of a chain extender and a halide-containing boron compound, a residual amount of a Lewis base, or an acid-base adduct. In an embodiment, the regenerated isocyanate mixture may include a mixture of the regenerated isocyanate compound and at least two, or at least three, or all four of the following: an adduct of a polyol and a halide-containing boron compound, an adduct of a chain extender and a halide-containing boron compound, a residual amount of a Lewis base, or an acid-base adduct.

[0064] In embodiments, the polyurethane is a thermoplastic polyurethane or a thermoset polyurethane, such as Figure 1B The structure shown in FIG. Figure 1BIn the general structure of the polyurethane shown in , R' can be hydrogen or C1-C10, or C1-C8, or C1-C5, or C1-C3 alkyl; each R1 is independently (i) an unsubstituted or substituted alkylene group having 2 to 75, or 2 to 50, or 2 to 25, or 2 to 15, or 2 to 10 carbon atoms, wherein one or more carbon atoms in the alkylene group may be substituted by an oxygen atom, a nitrogen atom, or a sulfur atom, provided that only the carbon atom is directly bonded to each of the two NH groups in the polyurethane backbone; or (ii) an unsubstituted or substituted aromatic-containing group having 6 to 75, or 6 to 50, or 6 to 35, or 6 to 25, or 6 to 20 carbon atoms; or (iii) an unsubstituted or (iv) an unsubstituted or substituted cycloalkyl-containing group having 4 to 75, or 3 to 60, or 5 to 50, or 5 to 35, or 5 to 25, or 5 to 20 carbon atoms; or (v) an unsubstituted or substituted heterocycloalkyl-containing group having 4 to 75, or 3 to 60, or 5 to 50, or 5 to 35, or 5 to 25, or 5 to 20 carbon atoms; or (vi) a combination thereof; and x, y, z, m, n and r are each independently 1 to 200, and p is 3 to 100. R2 and R3 can be independently selected from alkylene groups having at least 2 carbon atoms, wherein one of R2 and R3 can be an alkylene group having 2 to 10 carbon atoms, and the other of R2 and R3 can be an oligomeric or polymeric segment having at least 6, or 10, or 25, or 35, or 50, or 60, or 75 carbon atoms; one or more carbon atoms are optionally substituted with oxygen atoms, nitrogen atoms or sulfur atoms, provided that only carbon atoms are directly bonded to each of the terminal oxygen atoms in the polyurethane backbone.

[0065] In an embodiment, at least one of R2 and R3 comprises a polyether, a polyester, a thioether, a polyether comprising at least one thioether group, a polyimide, or a combination thereof.

[0066] In an embodiment, the amount of depolymerizing agent used exceeds the amount of urethane bonds present in the polyurethane, which is calculated as described below. In another embodiment, the depolymerizing agent is present in an amount of 0.1 to 10, or 0.2 to 6, or 0.3 to 3 molar equivalents relative to the urethane bonds. As used herein, the molar amount of urethane bonds is calculated from the molar amount of isocyanate used to synthesize the thermoplastic and thermosetting PUs made in the laboratory. It should be noted that, as used herein, the molar amount of urethane bonds is an estimate.

[0067] According to an embodiment, the depolymerizing agent can be a halide-containing boron compound, such as a halogenated organoborane compound or a boron trihalide. Any suitable halogenated organoborane compound can be used, including but not limited to β-chlorocatechol borane, β-bromocatechol borane, β-fluorocatechol borane, β-iodocatechol borane or a combination thereof. Examples of boron trihalides include boron trifluoride, boron trichloride, boron tribromide and boron triiodide.

[0068] In another embodiment, the Lewis base may include one or more of triethylamine, pyridine, dimethylaminopyridine, triethylenediamine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), other amidine derivatives, diisopropylethylamine, other non-nucleophilic alkylamines, lithium diisopropylamide, and quinuclidine.

[0069] Any suitable solvent may be used. In embodiments, the solvent is a non-polar solvent including, but not limited to, toluene, hexane, heptane, benzene, cyclohexane, or combinations thereof.

[0070] According to various embodiments, the depolymerization can be carried out at a temperature of 10° C. to 200° C., or 20° C. to 150° C., or 40° C. to 100° C. The depolymerization can be carried out for any suitable amount of time, for example, 5 min to 24 h, or 10 min to 12 h, or 15 min to 6 h, or 20 min to 5 h. It should be noted that the time for which the depolymerization is carried out depends on the temperature at which the depolymerization is carried out.

[0071] In an embodiment, the step of depolymerization is carried out in an inert environment such as nitrogen (N2), argon, helium or a combination thereof. In another embodiment, the depolymerization is carried out in dry air substantially free of moisture. In yet another embodiment, the depolymerization is carried out under vacuum.

[0072] According to an embodiment of the present invention, the polyol comprises poly(tetrahydrofuran), polyethylene glycol, polyethylene glycol trimethylolpropane triether, polypropylene glycol or a combination thereof. In another embodiment, the chain extender comprises 1,4-butanediol, glycerol, ethylene glycol, 1,6-hexanediol or a combination thereof.

[0073] Suitable examples of adducts of polyols and halogenated organic borane compounds include, but are not limited to, catechol boron ethers. Suitable examples of adducts of chain extenders and halogenated organic boron compounds include, but are not limited to, catechol boron ethers such as dicatechol boron ethyl ether. Suitable examples of acid-base adducts include, but are not limited to, triethylamine hydrochloride and dimethylaminopyridinium salts. Based on the total amount of Lewis base relative to the amount of depolymerizing agent, the residual amount of Lewis base can be present in 1% to 30% by mass, 1% to 10% by mass, or 1% to 5% by mass. Based on the total amount of the reaction mixture, the adduct of a polyol and a halide-containing boron compound, the adduct of a chain extender and a halide-containing boron compound, or the acid-base adduct can be present in an amount of 5% to 90% by mass, or 10% to 85% by mass, or 15% to 75% by mass.

[0074] In aspects of the invention, the method may further include a step of separating the recovered isocyanate from the regenerated isocyanate mixture by treating the regenerated isocyanate mixture with at least one of chromatography, distillation (e.g., vacuum distillation), differential extraction, or crystallization. In an embodiment, the step of separating the recovered isocyanate compound from the regenerated isocyanate mixture is performed after the step of depolymerizing the polyurethane.

[0075] Another aspect of the invention is a process for forming a polyurethane comprising contacting the separated recovered isocyanate from the process as disclosed above with one or more polyols and / or chain extenders in the presence of a polymerization catalyst and optionally a solvent.

[0076] In embodiments, the step of contacting the separated recovered isocyanate further comprises contacting the separated recovered isocyanate first with a polymerization catalyst and a polyol at a first temperature of 20°C to 120°C, or 20°C to 90°C, or 60°C to 70°C for a first amount of time of 5 min to 12 h, or 10 min to 5 h, or 15 min to 1 h to form a prepolymer. The prepolymer is then chain extended to form a high molecular weight polymer by adding one or more chain extenders to the reaction mixture and stirring at a second temperature of 20°C to 120°C, or 50°C to 120°C, or 90°C to 110°C for a second amount of time of 10 min to 48 h, or 15 min to 24 h, or 30 min to 16 h, or 1 h to 6 h. In embodiments, the polymerization catalyst and polyol are dissolved in the same solvent as the separated recovered isocyanate.

[0077] Any suitable polymerization catalyst can be used, such as a tin-containing catalyst or an amine catalyst. Suitable examples of tin-containing catalysts can include dibutyltin dilaurate, dioctyltin dilaurate, dioctyl carboxylate, stannous octoate or a mixture thereof. Any suitable amine catalyst can be used, including but not limited to 1,4-diazabicyclo [2.2.2] octane (DABCO), dimethylethanolamine, triethylenediamine or a mixture thereof.

[0078] In an embodiment, the optional solvent is the same as the solvent used in the step of depolymerizing the polyurethane. And in another embodiment, the optional solvent is different from the solvent used in the step of depolymerizing the polyurethane. Suitable examples of optional solvents include, but are not limited to, N,N-dimethylformamide, N,N-dimethylacetamide, or tetrahydrofuran.

[0079] In another aspect of the present invention, the composition may include polyurethane and halide-containing boron compounds prepared according to the method disclosed above. The composition may include any suitable amount of polyurethane, such as at least 1 mass %, or 2 mass %, or 5 mass %, or 10 mass %, or 25 mass %, or 50 mass %, or 75 mass %, 90 mass %, or 95 mass % based on the total mass of the composition. In an embodiment, the halide-containing borane compound may be present in the composition in an amount of at least 0.1ppm, or 0.10ppm, or 10ppm, or 100ppm, or 1000ppm, as detected by energy dispersive X-ray spectroscopy (EDX) or inductively coupled plasma optical emission spectroscopy (ICP-OES). In another embodiment, the composition may also include trace amounts of polyols and halide-containing boron compound adducts, chain extenders and halide-containing boron compound adducts, residual amounts of Lewis bases, or at least one of acid-base adducts, such as disclosed above. As used herein, trace amounts refer to less than 1000 ppm, or less than 500 ppm, or less than 100 ppm, or less than 50 ppm, or less than 10 ppm, or less than 1 ppm, or less than 0.5 ppm, or less than 0.1 ppm.

[0080] In aspects of the present invention, the composition may further include one or more of virgin polyurethane, inert fillers and additives. Virgin polyurethane may be present in any suitable amount, for example, 0% to 90%, or 0% to 50%, or 0% to 25% based on the total amount of the composition.

[0081] Suitable examples of inert fillers include, but are not limited to, biomass, lignin, cellulose, natural or synthetic fibers, silica, or recycled polymers. The inert filler may be present in any suitable amount, such as 0% to 80%, or 1% to 50%, or 1% to 25%, based on the total amount of the composition.

[0082] Suitable examples of additives include, but are not limited to, antioxidants, processing aids, lubricants, plasticizers, tackifiers, flame retardants, dyes, or stabilizers. The additives may be present in any suitable amount, for example, 0% to 60%, or 0% to 20%, or 0% to 5%, based on the total amount of the composition.

[0083] In an embodiment, the composition has a bio-based content of 20% to 80% according to ASTM-D6866.

[0084] In aspects of the invention, an article comprises a composition as disclosed herein.

[0085] In another aspect of the invention, there is an integrated process comprising the steps of providing a regenerated isocyanate mixture obtained by reacting a polyurethane with a depolymerizing agent in the presence of a solvent and a Lewis base; purifying the regenerated isocyanate mixture by at least one of chromatography, distillation (e.g., vacuum distillation), differential extraction, or crystallization to obtain a separated recovered isocyanate compound; and forming a recycled polyurethane by reacting the recovered isocyanate with one or more polyols in the presence of a catalyst, wherein the one or more polyols include recycled polyols, bio-derived polyols, petroleum-based polyols, or mixtures thereof.

[0086] Model diurethane deconstruction

[0087] The objective of the present invention is to recover isocyanates directly from PU and a depolymerizing agent capable of efficiently converting urethane / carbamate bonds in the polymer into isocyanate groups in a single step. Previous literature has reported the use of catechol borane halides and boron halides for the deconstruction of small molecule urethane / diurethanes with near quantitative conversion. As a proof of concept, an aromatic diurethane (DU1) was synthesized from MDI and methanol (not shown) and the compound was deconstructed using β-chlorocatechol borane in the presence of triethylamine with toluene as solvent at 80°C and ambient pressure. The successful deconstruction of DU1 and the reformation of MDI were confirmed by ATR-FTIR and NMR spectroscopy (not shown). The ATR-FTIR spectrum showed a 300 nm wavelength at ~2270 cm -1 The peaks at 1730–1690 cm-1 correspond to the –N=C=O stretching (not shown). -1 、3300cm -1 and 1500cm -1 The characteristic urethane peaks of -C=O stretching, -NH stretching and -NH bending at 100 Å disappeared. Additional experiments were performed using β-chlorocatechol borane without a Lewis base (i.e., triethylamine) and using a Lewis base (i.e., triethylamine) without β-chlorocatechol borane as controls, and further details can be found in Comparative Examples 1 and 2 disclosed below.

[0088] Thermoplastic PU depolymerization

[0089] Two thermoplastic PUs (PU1 (laboratory synthesized) and CPU1 (commercially available)) were depolymerized using the same method as used for the model diurethane deconstruction, as disclosed below in Example 1. PU1 was synthesized using MDI as the hard segment, poly(tetramethylene oxide) (PTMO) as the soft segment, and 1,4-butanediol (BDO) as the chain extender ( Figure 2A ; Table 1), and CPU1 (MDI-based PU) was purchased from a commercial supplier and the additives were removed by dissolution and precipitation before use. PU1 was successfully synthesized by Figure 3A The ATR-FTIR spectrum shown in confirms that at 2270 cm -1 The disappearance of the isocyanate peak at 1730-1690 cm -1 ), urethane-NH stretch (~3300cm -1 ), and urethane-NH bending (~1500cm -1 ) peak confirmed the formation of PU. Similarly, CPU1 was characterized by ATR-FTIR spectroscopy and showed the same characteristic urethane peak ( Figure 3B The molecular weights of the two thermoplastic PUs were determined by gel permeation chromatography (GPC). Figure 4A and Table 1), and differential scanning calorimetry (DSC) was performed to evaluate the thermal properties of the materials (e.g., glass transition temperature [T g ] and crystallization / melting behavior), such as Figure 4B Shown in.

[0090] Table 1: Composition details of the synthesized polyurethanes

[0091]

[0092]

[0093] The synthesized thermoplastic polyurethane (PU1) and the commercially sourced thermoplastic polyurethane (CPU1) were successfully depolymerized using β-chlorocatechol borane in the presence of triethylamine at 80 °C in toluene, as Figure 2B The formation of MDI was confirmed by ATR-FTIR spectroscopy and at 2270 cm -1 The appearance of the -N=C=O stretching peak at 100° and the disappearance of the characteristic urethane peaks from -C=O stretching, -NH stretching, and -NH bending are consistent in both cases ( Figure 3A and Figure 3B). The regenerated isocyanate compound was separated by column chromatography to obtain a white solid, which was characterized by ATR-FTIR and 1 H NMR spectroscopy characterization. ATR-FTIR spectra all showed ∼2270 cm -1 The peak corresponding to –N=C=O stretching ( Figure 3A and Figure 3B ), confirming the presence of isocyanate. Figure 5A Showing white solid 1 H NMR spectrum (in CDCl3) with the spectrum of a pure MDI standard as reference. The isolated MDI yield of PU1 was 23%. For CPU1, it is difficult to report the isolated yield because the initial content of MDI in the commercially sourced thermoplastic polyurethane is unknown. About 58 mg of MDI was obtained from 500 mg of CPU1 material after column chromatography (12 wt.% yield based on the amount of polyurethane (CPU1)).

[0094] The depolymerization reactions of both PU1 and CPU1 produce MDI; however, product characterization of CPU1 is significantly more challenging than that of PU1 because the composition of commercially sourced samples is unknown. For example, the ATR-FTIR spectrum of depolymerized CPU1 exhibited some characteristic urethane peaks, indicating incomplete conversion to isocyanate. In addition, excess β-chlorocatechol borane and triethylamine were used for the depolymerization of PU1 and CPU1, but the unknown composition and presence of residual additives (e.g., antioxidants, processing aids, etc.) in CPU1 may interfere with the depolymerization or react with the formed isocyanate to produce by-products. The yields between PU1 and CPU1 cannot also be directly compared because the MDI content is not the same and is unknown in the case of CPU1. In addition, aliphatic isocyanate-based thermoplastic PUs synthesized using hexamethylene diisocyanate (HDI) as the hard segment, PTMO as the soft segment, and BDO as the chain extender were successfully depolymerized using β-chlorocatechol borane in the presence of triethylamine at 80°C in toluene, as shown in FIG. Figure 2B The formation of HDI was confirmed by ATR-FTIR spectroscopy and at 2270 cm -1 The appearance of the -N=C=O stretching peak at , and the disappearance of the characteristic urethane peaks from -C=O stretching, -NH stretching, and -NH bending are consistent with previous observations ( Figure 2C In addition, the presence of HDI in the product mixture was confirmed by gas chromatography-mass spectrometry (GC-MS) ( Figure 2D ).

[0095] Depolymerization of thermosetting PU

[0096] Thermoset PU is difficult to recycle by any common recycling technology, but the β-chlorocatechol borane-based depolymerization technology has been demonstrated for both a laboratory-synthesized thermoset polyurethane (PU2) and a commercially-sourced thermoset polyurethane (CPU2). The same depolymerization conditions were applied to both thermoset materials and the formation of the corresponding isocyanate was confirmed by ATR-FTIR spectroscopy ( Fig. 6A and Figure 6B The ATR-FTIR spectrum indicated the appearance of the characteristic -N=C=O stretching peak and the disappearance of the urethane -C=O stretching peak, -NH stretching peak and -NH bending peak. The isocyanate was separated by column chromatography. MDI was recovered from PU2 with a yield of 20% (isocyanate yield) and analyzed by ATR-FTIR and 1 H NMR spectra (respectively Fig. 6A and Figure 5C ) characterization. For CPU2, TDI was similarly separated by column chromatography and isolated in a yield of <5 wt.% based on the total amount of polymer. TDI was also characterized by ATR-FTIR and 1 H NMR spectroscopy. ATR-FTIR spectrum shows -N=C=O stretching peak ( Figure 6B ), and the NMR spectrum is comparable to that of the authentic standard ( Figure 5C ).

[0097] Thermoset PUs have historically been difficult to recycle, and the application of this depolymerization technology can play a major role in improving the recyclability of thermoset PUs. However, the isocyanate yields from the two thermoset PUs (PU2 and CPU2) (20 wt.% and <5 wt.%) are slightly lower than those from the thermoplastic PUs (PU1 and CPU1) (23 wt.% and 12 wt.%), respectively. This difference may stem from the inability of the depolymerizer to enter the thermoset material, while choosing a solvent that better swells the thermoset PU or grinding the thermoset material more finely to increase the surface area can lead to higher conversion. The presence of additives in CPU2 may also have a negative impact on conversion similar to the thermoplastic case. In addition, due to the relatively high solubility of TDI in most organic solvents commonly used for column chromatography (e.g., toluene, ethyl acetate, and hexane), the separation of TDI from CPU2 is significantly easier than the separation of MDI from other PUs. Therefore, the development of improved separation techniques for separating isocyanates from these depolymerization mixtures can significantly improve yields.

[0098] PU synthesized using recycled MDI / TDI

[0099] The recycled isocyanate from PU1, CPU1, PU2 and CPU2 was used to regenerate new PU materials (RPU1 to RPU4; see Table 2) with the same composition as PU1 (PTMO macrodiol and BDO chain extender). The conversion of isocyanate and -OH functional groups to urethane bonds was confirmed for each system by ATR-FTIR spectroscopy, as shown in Figure 3A , Figure 4B , Fig. 6A and Figure 6B In all cases, the -N=C=O stretching peak disappears and the characteristic urethane peak reappears. GPC was used to measure the molecular weight distribution of the resynthesized PU, and the weight average molecular weight (Mw) value was 20800 g / mol to 6900 g / mol, with a dispersion of The thermal properties of the resynthesized PUs were also evaluated by DSC (Table 2). g and a melting temperature (T m ) show similar thermal transitions with slight variations for each transition. In addition, neither RPU1 nor RPU3 exhibits hard segment T at higher temperatures. g However, the thermal transition of RPU2 is different from that of RPU1 and RPU3. RPU2 exhibits a T of -65 °C. g , -25℃ crystallization temperature (T c ), the melting point of the soft segment at 18°C ​​(T m ), and two T of the hard segment at 103°C and 148°C g However, the reasons for the missing and / or additional transitions are unclear ( Fig. 9B and Figure 8 ).

[0100] Table 2: Composition details and key properties of the resynthesized PU.

[0101]

[0102]

[0103] It should be noted from Table 2 that the separated recycled isocyanates were used to resynthesize thermoplastic polyurethanes; however, for RPU3 from commercial PU, the measured weight average molecular weight is significantly lower than that of the starting PU (17700 g / mol (RPU3) vs. 32600 g / mol (CPU1)). This difference can be explained by impurities in the recycled isocyanate leading to mismatched stoichiometry, and more careful purification of the isocyanate can achieve better control of the molecular weight. In addition, further recycling of the resynthesized PUs was not explored, but considering the equivalence in terms of molecular weight and thermal properties, they are expected to behave similarly to the original PUs with the same composition.

[0104] in conclusion

[0105] A "one-step" technology for the depolymerization and regeneration of thermoplastic polyurethane (PU) materials and thermosetting polyurethane (PU) materials is reported for the first time, and is applied to both laboratory-made PU and commercially sourced PU. The method uses inexpensive halide-containing boron compounds as depolymerization agents and directly produces isocyanates under mild reaction conditions (<100°C and ambient pressure). Based on the starting isocyanate content or the amount of starting polymer, the isocyanate is separated at a yield of up to 23wt.%, and is used to regenerate new PU materials with molecular weight and thermomechanical properties equivalent to the original PU. In general, this new recycling method enables the recyclability of conventional PU and can minimize the need for the production of new isocyanates.

[0106] In this specification, embodiments have been described in a manner that enables a clear and concise description to be written, but it is intended and understood that embodiments may be combined or separated differently without departing from the present invention. For example, it is understood that all preferred features described herein may be applied to all aspects of the present invention described herein.

[0107] Example

[0108] Embodiments of the present invention will now be described. The technical scope of the present invention is not limited to the embodiments described below.

[0109] Material

[0110] All solvents used were purchased from Sigma-Aldrich. All dry solvents were purchased from Sigma-Aldrich. Unless otherwise stated, all chemicals used were purchased from Sigma-Aldrich. Dibutyltin dilaurate (DBTDL) was stored under dry nitrogen and used as received. Anhydrous N,N-dimethylacetamide (DMAc), anhydrous methanol, anhydrous dichloromethane, and anhydrous toluene were used as received. Poly(tetrahydrofuran) (PTMO; Mn: 2,000 g / mol) was dehydrated and degassed under vacuum at 80°C for 24 h and stored under a dry nitrogen (N2) atmosphere before use. 1,4-Butanediol (BDO) was vacuum distilled and stored under dry nitrogen before use. Methylene diphenyl diisocyanate (MDI) purchased from TCI America was vacuum distilled and stored under dry N2 before use. β-Chlorocatechol borane was purchased from TCI and used as received. Triethylamine was used as received. Boron trichloride (about 13% in toluene, about 1.0 mol / L) was purchased from TCI and used as received. CPU1 (MDI-based PU) was obtained from a commercial supplier (Lubrizol) and the additives were removed by dissolution and precipitation before use.

[0111] Characterization

[0112] Attenuated Total Reflectance Fourier Transform Infrared (ATR-FT-IR)

[0113] ATRFT-IR spectra were recorded on a Thermo Nicolet NEXUS 670 FTIR spectrometer using a mercury cadmium telluride (MCT) detector.

[0114] Gel Permeation Chromatography (GPC)

[0115] The number average molecular weight (Mn), weight average molecular weight (Mw) and molecular weight distribution (dispersity) of soluble polymers were determined in DMAc using a TOSOH EcoSEC Elite GPC instrument (HLC-8420) equipped with a refractive index (RI) detector. The DMAc mobile phase contained 0.5 wt.% LiBr. A series of 8 nearly monodisperse poly(methyl methacrylate) (PMMA) standards (Agilent Technologies) with molecular weight values ​​ranging from 1840 g / mol to 2210000 g / mol were used to calibrate the instrument.

[0116] NMR spectroscopy

[0117] 1 H NMR spectra were obtained on a Bruker AV 400 MHz or AVIII 600 MHz spectrometer.

[0118] Thermal analysis (DSC)

[0119] Thermal analysis of polyurethane was performed using a TA Instruments Discovery Series DSC instrument. -1 Three heating cycles and two cooling cycles were performed at -90°C and 200°C with a heating / cooling rate of 1.18°C. The data from the second heating cycle are presented.

[0120] method

[0121] Calculated molar amount of urethane bonds in polyurethane :

[0122] The molar amount of urethane bonds is calculated as follows:

[0123] Weight of laboratory-made thermoplastic polyurethane PU1 for depolymerization: 500 mg

[0124] Calculated amount of isocyanate (MDI) in 500 mg of PU1 (in mg): 153 mg mmol of isocyanate (MDI) in 500 mg of PU1: 0.611 mmol

[0125] Considering that one MDI molecule has two isocyanate functional groups (-NCO), mmol of urethane bonds = 2 × mmol of isocyanate (MDI) in 500 mg of PU1 ≡ 2 × 0.611 mmol = 1.222 mmol

[0126] β-chlorocatechol borane is used in excess of urethane bond, for example, the molar ratio of urethane bond:β-chlorocatechol borane is 1:1.25.

[0127] Thus, for 1.222 mmol of urethane, 1.5275 mmol of β-chlorocatechol borane was used (1.222*1.25=1.5275 mmol).

[0128] Reference Example 1: Synthesis of Model Diaminoester DU1

[0129] 4,4'-methylenephenylene diisocyanate (MDI) (4.8mmol) was added to an excess of dry methanol (5mL) while stirring at room temperature. The formation of a white precipitate was observed, and the reaction was stirred at 65°C for 18h. Then, the excess organic solvent was concentrated under reduced pressure. The product was separated and purified by column chromatography. 1H NMR (600MHz, DMSO-d6, δppm): 9.51 (s, 2H, -NHCOO), 7.34 (d, 4H, ArH), 7.09 (d, 4H, ArH), 3.79 (s, 2H, ArCH2Ar), 3.64 (s, 6H, -OCH3).

[0130] Reference Example 2: Conversion of urethane / carbamate into General Procedure for Isocyanates

[0131] DU1 (200 mg) and anhydrous toluene (2 mL) were added to a round-bottom flask. Triethylamine (0.21 mL) and β-chlorocatechol borane (235 mg) were dissolved in 2 mL of anhydrous toluene, and the solution was added dropwise to the polymer solution. The resulting mixture was heated at 80 ° C for 2 h. After the reaction, an aliquot from the reaction mixture was analyzed by ATR-FTIR spectroscopy using a highly sensitive MCT detector.

[0132] Reference Example 3: General procedure for the synthesis of polyurethane PU1

[0133] To minimize side reactions with water, all polymerizations were performed in a glove box. In a typical reaction, an excess of MDI (2.58 g, 15.3 mmol) was placed in a round-bottom flask equipped with an addition funnel, and 5 mL of DMAc was added to the round-bottom flask. PTMO (5.12 g, 5.1 mmol) and 5 drops of DBTDL were dissolved in another 25 mL of DMAc and added to the addition funnel. The PTMO / catalyst solution was slowly (within 1 h) added to the MDI solution. The reaction mixture was then stirred at 65 ° C for 3 h to form a prepolymer. The prepolymer was then chain extended to form a high molecular weight polymer by adding a chain extender BDO (0.923 g, 10.2 mmol) to the reaction mixture and stirring at 85 ° C for 24 h. The reaction mixture was precipitated into a large excess of warm distilled water, and the resulting polyurethane was washed with methanol and dried under dynamic vacuum until constant weight.

[0134] Example 1: Depolymerization of Thermoplastic Polyurethane

[0135] Thermoplastic polyurethane PU1 (500mg) is added to a round-bottom flask with 10mL of anhydrous toluene. The mixture is stirred at 20°C for 12h. A solution of triethylamine (0.21mL) and β-chlorocatechol borane (235mg) in 5mL of toluene is added dropwise to the polymer solution, and the resulting mixture is refluxed at 80°C for 2h. After the reaction, aliquots from the reaction mixture are analyzed by ATR-FTIR spectrometry using a highly sensitive MCT detector. The isocyanate compound regenerated is separated by column chromatography with a 23wt.% yield (isocyanate compound yield of the recovery separated).

[0136] A depolymerization procedure similar to that used for PU1 was used for a commercially available thermoplastic polyurethane (CPU1), which was freed of additives by dissolution and precipitation prior to use. About 58 mg of isolated, recovered MDI was obtained from 500 mg of CPU1 material.

[0137] Example 2: Depolymerization of Thermoset Polyurethane Using β-Chlorocatechol Borane

[0138] A depolymerization procedure similar to that for PU1 was used for synthesized thermosetting polyurethane (PU2) and commercially purchased thermosetting polyurethane (CPU2). PU2 was synthesized using MDI, PTMO and glycerol, and CPU2 was obtained from a kitchen sponge made using TDI. The CPU2 sample was washed three times with tetrahydrofuran to remove any organic soluble additives and / or dyes, and dried at 40° C. under a dynamic vacuum before depolymerization. The same depolymerization conditions (excessive β-chlorocatechol borane, triethylamine and toluene at 80° C.) were applied to both thermosetting materials, and the formation of the corresponding isocyanate was confirmed by ATR-FTIR spectroscopy ( FIG. 4 ). About 30 mg of separated recovered MDI was obtained from 500 mg of CPU2 material. About 10 mg of separated recovered MDI was obtained from 500 mg of CPU2 material.

[0139] Example 3: Effect of temperature on product yield

[0140] Polyurethane CPU1 (500mg) is added to a round-bottom flask with 10mL of anhydrous toluene. A solution of triethylamine (0.21mL) and β-chlorocatechol borane (235mg) in 5mL of anhydrous toluene is added dropwise to the polymer solution, and the resulting mixture is stirred for 2h at a certain temperature (0°C, 50°C, 80°C or 100°C), as summarized in Table 3. After each reaction is completed, aliquots are analyzed by ATR-FTIR spectroscopy using a highly sensitive MCT detector. The regenerated isocyanate compound is separated by column chromatography, with a yield (isolated yield) of 6.8-12wt.% based on the amount of polyurethane (CPU1).

[0141] Table 3: Yield changes with temperature

[0142]

[0143] Example 4: Effect of Catalyst

[0144] A similar depolymerization procedure as that used for PU1 (MDI-based polyurethane with PTMO and BDO) in Example 1 was used, but boron trichloride was used instead of β-chlorocatechol borane. The amounts of CPU1 and triethylamine remained the same as in Example 1. 444 μL of boron trichloride in toluene was used for the reaction. The temperature and reaction time also remained the same as in Example 1. After the reaction, an aliquot from the depolymerization reaction mixture was analyzed by ATR-FTIR spectroscopy and the isocyanate was observed at 2270 cm -1 The characteristic peak at Fig. 10A Characterization of the depolymerization reaction mixture by NMR spectroscopy showed signals from isocyanate, polyol and chain extender ( Fig. 10B ).

[0145] Example 5: Synthesis of polyurethane (RPU1 to RPU4) using isocyanate recovered from PU1, PU2, CPU1 and CPU2 General procedures

[0146] Using the isocyanates recovered from PU1, PU2, CPU1 and CPU2 obtained in Examples 1 and 2, polyurethane was synthesized according to the procedure described in Reference Example 2. However, after the PTMO / catalyst solution was slowly added to the MDI solution, the reaction was stirred at 65°C for 25 minutes to form a prepolymer. The prepolymer was then chain extended to form a high molecular weight polymer by adding BDO to the reaction mixture and stirring at 100°C for 34 hours. The reaction mixture was precipitated into a large excess of cold methanol and dried under dynamic vacuum until constant weight. The experimental details are summarized in Table 4 below.

[0147] Table 4: Repolymerization of recovered isocyanate

[0148] sample RPU1 RPU2 RPU3 RPU4 Isocyanate recovered from PU1 PU2 CPU1 CPU2 Isocyanate MDI MDI MDI TDI Polyols PTMO PTMO PTMO PTMO Chain Extender BDO BDO BDO BDO Temperature (in °C) (T1, T2) 65,100 6,585 65,100 6,585 Prepolymer time 25min 3h 25min 3h Time (in hours); Chain extension 34 24 34 24

[0149] Comparative Example 1: Depolymerization reaction using only Lewis base, with addition of depolymerizing agent

[0150] To test whether the addition of a base alone is sufficient to promote the formation of isocyanates, the depolymerizing agent was omitted and a blank reaction was performed in toluene at 80°C. For the reaction, PU2 (250 mg) was soaked in 3 mL of toluene to swell the crosslinked polymer, and triethylamine (0.2 mL) was added. According to an embodiment of the present invention, the mixture was heated to 80°C and allowed to react for 2 h. As expected, ATR-FTIR analysis confirmed the absence of isocyanates, which was confirmed by the IR spectrum at ~2270 cm -1 The absence of a peak at is apparent, highlighting the importance of the organoboron reagent.

[0151] Based on current observations and existing literature, and without wishing to be bound by any particular theory, it is believed that base-promoted deprotonation of the urethane group, followed by nucleophilic substitution of Cl by the urethane, and rearrangement within the resulting urethane-chlorocatechol borane complex leads to the formation of the isocyanate. It is important to note that the formation of isocyanates from urethanes is challenging because highly reactive isocyanates tend to recombine with alcohols. However, the depolymerizing agents used for the conversion of urethane to isocyanate functional groups act as capping agents for the alcohol, preventing it from recombination with the isocyanate and preventing the reaction from proceeding in the reverse direction.

[0152] Comparative Example 2: Depolymerization using only a depolymerizing agent with the addition of a Lewis base

[0153] Another control experiment was carried out using β-chlorocatechol borane in the absence of a base. Polyurethane CPU1 (500 mg) was added to a round-bottom flask with 10 mL of anhydrous toluene. The mixture was stirred at 20 ° C for 12 h. β-chlorocatechol borane (235 mg) in 5 mL of anhydrous toluene was added dropwise to the polymer solution, and the resulting mixture was stirred at 80 ° C for 2 h. ATR-FTIR analysis showed the presence of isocyanate. However, after purification by column chromatography using ethyl acetate / hexane, the isolated yield was <6% (wt.%, based on the amount of polyurethane (CPU1)).

[0154] Comparative Example 3: Depolymerization using a polar solvent

[0155] Another control experiment was performed using β-chlorocatechol borane and base, but DMAc was used as solvent and the reaction was carried out at 150°C. The amounts of all reactants remained the same as in Example 1. A depolymerization procedure similar to that used for the depolymerization of PU1 in Example 1 was used, but DMAc (15 mL) was used as solvent and the reaction was carried out at 150°C. After the reaction, an aliquot from the depolymerization reaction mixture was analyzed by ATR-FTIR spectroscopy and no isocyanate was observed at 2270 cm -1 The characteristic peak at , which means that depolymerization did not occur in DMAc.

[0156] Although the invention is illustrated and described herein with reference to particular embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made to the details within the metes and bounds of equivalents of the claims without departing from the invention.

[0157] Although preferred embodiments of the present invention have been shown and described herein, it should be understood that these embodiments are provided by way of example only. Without departing from the spirit of the present invention, those skilled in the art will be able to imagine many variations, changes and substitutions. Therefore, the appended claims are intended to cover all these variations that fall within the spirit and scope of the present invention.

Claims

1. A method for depolymerizing a polyurethane in a single step to provide a regenerated isocyanate compound, the method comprising contacting the polyurethane with a depolymerizing agent in the presence of a solvent and a Lewis base, wherein the depolymerizing agent comprises a halide-containing boron compound, and The regenerated isocyanate mixture comprises a mixture of a regenerated isocyanate compound and at least one of the following: an adduct of a polyol and the halide-containing boron compound, an adduct of a chain extender and the halide-containing boron compound, a residual amount of the Lewis base, or an acid-base adduct.

2. The method according to claim 1, wherein the polyurethane is a thermoplastic polyurethane or a thermosetting polyurethane, represented by the following structure: R' is H or C1-C10 alkyl; Each R1 is independently: (i) an unsubstituted or substituted alkylene group having 2 to 75 carbon atoms, wherein one or more carbon atoms in the alkylene group may be substituted by an oxygen atom, a nitrogen atom or a sulfur atom, provided that only carbon atoms are directly bonded to each of the two NH groups in the polyurethane backbone; or (ii) an unsubstituted or substituted aromatic group having 6 to 75 carbon atoms; or (iii) an unsubstituted or substituted heteroaromatic group having 4 to 75 carbon atoms; or (iv) an unsubstituted or substituted cycloalkyl-containing group having 4 to 75 carbon atoms; or (v) an unsubstituted or substituted heterocyclic alkyl group having 4 to 75 carbon atoms; or (vi) any combination thereof; R2 and R3 are independently selected from alkylene groups having at least 2 carbon atoms, wherein: (i) one of R2 or R3 is an alkylene group having 2 to 5 carbon atoms, and the other of R2 or R3 is an oligomeric or polymeric segment having at least 6 carbon atoms, and (ii) one or more carbon atoms are optionally substituted with oxygen atoms, nitrogen atoms or sulfur atoms, provided that only a carbon atom is directly bonded to each of the terminal oxygen atoms in the polyurethane backbone; x, y, z, m, n and r are each independently 1 to 200, and p is 3 to 100, and The depolymerizing agent is present in an amount of 0.3 to 3 molar equivalents relative to the urethane bond.

3. The method according to claim 1 or 2, wherein the halide-containing boron compound is selected from a halogenated organoborane compound or a boron trihalide. 4 . The method according to claim 3 , wherein the halogenated organic borane compound comprises one or more of β-chlorocatechol borane, β-bromocatechol borane, β-fluorocatechol borane and β-iodocatechol borane.

5. The method according to any one of claims 1 to 4, wherein the Lewis base comprises one or more of triethylamine, pyridine, dimethylaminopyridine, triethylenediamine, diisopropylethylamine, other trialkylamines, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), amidine derivatives, lithium diisopropylamide and quinuclidine.

6. The method according to any one of claims 1 to 5, wherein the solvent comprises one or more of toluene, hexane, heptane, pentane, benzene and cyclohexane.

7. The process according to any one of claims 1 to 6, wherein the depolymerization is carried out at a temperature of 20°C to 150°C.

8. The method according to any one of claims 1 to 7, wherein the depolymerization is carried out in an inert environment comprising one or more of nitrogen, argon, helium and dry air.

9. The method of any one of claims 1 to 8, wherein the polyol comprises poly(tetramethylene glycol), polyethylene glycol, polyethylene glycol trimethylolpropane triether, polypropylene glycol, or a combination thereof, and The chain extender comprises 1,4-butanediol, glycerol, ethylene glycol, 1,6-hexanediol or a combination thereof.

10. The method of any one of claims 1 to 9, further comprising separating the recovered isocyanate from the regenerated isocyanate mixture by treating the regenerated isocyanate mixture with at least one of chromatography, distillation, differential extraction or crystallization.

11. A process for forming a polyurethane comprising reacting the separated recovered isocyanate from the process according to claim 10 with one or more polyols and / or chain extenders in the presence of a polymerization catalyst and optionally a solvent.

12. The method of claim 11, wherein the polymerization catalyst comprises a tin-containing catalyst or an amine catalyst.

13. The method according to claim 12, wherein the tin-containing catalyst comprises dibutyltin dilaurate, dioctyltin dilaurate, dioctyl carboxylate, stannous octoate or a mixture thereof, and The amine catalyst comprises 1,4-diazabicyclo[2.2.2]octane (DABCO), dimethylethanolamine, triethylenediamine, or a mixture thereof.

14. A composition comprising the polyurethane prepared according to the method of claim 10 and a halide-containing boron compound.

15. The composition of claim 14, wherein the composition further comprises a solvent.

16. The composition according to claim 14 or 15, wherein the composition further comprises one or more of virgin polyurethane, an inert filler and an additive.

17. The composition of any one of claims 14 to 16, wherein the composition has a bio-based content according to ASTM-D6866 of 20% to 100%.

18. An article comprising the composition according to any one of claims 14 to 17.

19. A method comprising: (i) providing a regenerated isocyanate mixture obtained by the depolymerization process according to any one of claims 1 to 9; (ii) purifying the regenerated isocyanate mixture by at least one of chromatography, distillation, differential extraction or crystallization to obtain a separated recovered isocyanate compound; as well as (iii) forming a recycled polyurethane by reacting the recovered isocyanate compound with one or more polyols in the presence of a catalyst, wherein the one or more polyols comprise recycled polyols, bio-derived polyols, petroleum-based polyols, or mixtures thereof.

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