Method for recycling polythiourethanes, thio compounds and their uses

Abstract

Method for recycling polythiourethanes, thio compounds and their uses This paper describes a method for recycling polythiourethane. For this purpose, the polythiourethane is depolymerized in the presence of a difunctional or higher functional thiol. Difunctional and / or higher functional isocyanates, epoxides, or ethylenically unsaturated compounds are then added to the resulting monomer and oligomer mixture, optionally together with difunctional and / or higher functional thiols. The reaction mixture is then repolymerized. This method allows complete recycling of polythiourethane in a simple and practical manner.

Description

[Technical Field]

[0001] The present invention relates to a method for chemically recycling polythiourethanes and thio compounds arising during their production, and to uses thereof. [Background technology]

[0002] Polythiourethanes are well-known polymers that exist as linear or branched chains or as polymer networks. They are used in a variety of applications, including organic glasses, e.g., eyeglass and optical lenses, paints, lacquers, adhesives, casting compounds, and foams for thermal insulation.

[0003] Polythiourethanes often exist as polymer networks in relevant applications, making them impossible to recycle mechanically like thermoplastics. Furthermore, moldings and coatings made from linear or branched polythiourethanes often cannot be easily recycled because they contain additives that must be separated before recycling. Therefore, polythiourethanes often cannot be recycled by conventional methods, and thermal recycling, or incineration, is often the only option.

[0004] Only a few early approaches to making polythiourethanes recyclable have been described in the literature. Polythiourethanes are reversible, i.e., undergo substitution reactions of the thiourethane bonds, at high temperatures, e.g., around 120 °C, in the presence of catalysts (e.g., dibutyltin dilaurate, sodium tetraphenylborate with 1-methylimidazole). As bonds within the polymer network are replaced, the network density remains constant, and the polymers are considered to belong to the vitrimer class of materials. These polymers exhibit properties such as self-healing and shape memory (F. Gamardella, F. Guerrero, S. De la Flor, X. Ramis, A. Serra, “A new class of vitrimers based on aliphatic poly(thiourethane) networks with shape memory and permanent shape reconfiguration”, Eur. Polym. J. 2020, 122, 109361; F. Gamardella, A. Serra, X. Ramis, S. De la Flor, “Actuator behavior of tailored poly(thiourethane) shape memory thermosets”, Polymers 2021, 13, 1571).

[0005] These properties were also evident in polythiourethane-urethane networks, which contain both thiourethane and urethane linkages. The reversibility of the former, in particular, allows for recycling (C.-J. Fan, Z.-B. Wen, Z.-Y. Xu, Y. Xiao, D. Wu, K.-K. Yang, Y.-Z. Wang, “Adaptable strategy to fabricate self-healable and reprocessable poly(thiourethane-urethane) elastomers via reversible thiol-isocyanate click chemistry”, Macromolecules 2020, 53, 4284-4293).

[0006] Similar results have been obtained with thiourea (H. Feng, N. Zheng, W. Peng, C. Ni, H. Song, Q. Zhao, T. Xie, “Upcycling of dynamic thiourea thermoset polymers by intrinsic chemical strengthening”, Nat. Commun. 2022, 13, 397).

[0007] The depolymerization of polyurethanes or polyurethanes and their conversion into oligomeric urea compounds by reaction with diamines or polyamines is described in DE 10 2011 008 535 A1.

[0008] Cross-linked poly(thiourethane) was depolymerized using excess trithiol in acetone solution (S. Huang, M. Podgorski, X. Han, C.N. Bowman, “Chemical recycling of poly(thiourethane) thermosets enabled by dynamic thiourethane bonds”, Polym. Chem. 2020, 11, 6879-6883). However, this is a complex process that contradicts circular economy ideas and sustainability principles. For example, acetone is used as a solvent, which must be separated at great expense. Furthermore, wastewater and waste products are generated and must be treated, and this wastewater contains large amounts of common salts, further exacerbating the problem.

[0009] Solvolysis of polythiourethane networks with methanol was also performed (L. Li, X. Chen, JM Torkelson, “Reprocessable polymer networks via thiourethane dynamic chemistry: Recovery of cross-link density after recycling and proof-of-principle solvolysis leading to monomer recovery”, Macromolecules 2019, 52, 8207-8216). The thiol can be separated from the resulting solution through a complex process. However, direct repolymerization is not possible in this case. This reaction is unsustainable due to the use of dichloromethane, a problematic solvent, and the long reaction time makes it hardly suitable for commercial use.

[0010] Furthermore, polythiourethanes based on the cyclic monomers carbonyl sulfide (COS) and methylaziridine have been prepared. (S. Wu, M. Luo, DJ Darensbourg, D. Zeng, Y. Yao, X. Zuo, X. Hu, D. Tan, “Non-isocyanate and catalyst-free synthesis of a recyclable polythiourethane with cyclic structure”, ACS Sustainable Chem. Eng. 2020, 8, 5693-5703) When the polymer is heated, the cyclic monomers can be reformed. However, this method does not allow for structural modification of the polymer, and aliphatic, linear polythiourethanes do not exhibit mechanical properties comparable to those of crosslinked polymers based on aromatic isocyanates. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] DE102011008535A1 [Non-patent literature]

[0012] [Non-Patent Document 1] F. Gamardella, F. Guerrero, S. De la Flor, X. Ramis, A. Serra, “A new class of vitrimers based on aliphatic poly(thiourethane) networks with shape memory and permanent shape reconfiguration”, Eur. Polym. J. 2020, 122, 109361 [Non-patent document 2] “Actuator behavior of tailored poly(thiourethane) shape memory thermosets,” Polymers 2021, 13, 1571

Outdoor Tools3

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Direct Environment 5

Outdoor Configuration6

[0013] The present invention aims to create a method for the chemical recycling of polythiourethane (polythiourea) that allows the direct production of monomers and / or oligomers that can be repolymerized and used as reactants in other reactions, without the need for complex purification of the resulting monomer / oligomer mixture.

[0014] The present invention also aims to create a method for the chemical recycling of polythiourethanes that is easy to implement, does not involve complex processing steps, complies with the principles of sustainability and allows for the recycling of polythiourethanes in the context of a circular economy. [Means for solving the problem]

[0015] These problems are solved by the method according to claim 1. Preferred variants of the method according to the invention are set forth in claims 2-14.

[0016] The present invention relates to a method for recycling polythiourethane, comprising the steps of: a) providing a mixture of polythiourethane and difunctional or higher functional thiol, and optionally difunctional or higher functional polar proton reactive solvent, wherein: using at least one mole of a difunctional or higher functional thiol per mole of thiourethane linkage of the polythiourethane; b) depolymerizing the polythiourethane by treating the mixture from step a) at a first reaction temperature, thereby producing difunctional or higher functional thiols from the polythiourethane and difunctional or higher functional thiol-terminated monomeric and oligomeric thiourethanes; c) optionally separating impurities from the mixture obtained in step b); d) adding a difunctional or higher functional isocyanate or epoxide- or ethylenically unsaturated compound and, optionally, a difunctional or higher functional thiol to the mixture from step b) or c), e) treating the mixture from step d) at a second reaction temperature that is lower than, equal to, or higher than the first reaction temperature, thereby polymerizing the monomeric and oligomeric thiourethanes from step b) and polymerizing the compounds added in step d) and any reactive solvent that is optionally present, with the proviso that the depolymerization in step b) and the polymerization in step e) are carried out in the presence of a bulk or difunctional or higher functional polar proton reactive solvent.

[0017] In the process according to the invention, difunctional or higher functional thiols are used in the depolymerization step b), which, together with the reactants and, if necessary, reactive solvents added in step d), become constituents of the repolymerized product, preferably a repolymerized polyurethane.

[0018] The polythiourethanes used in the present invention may be linear, branched, or crosslinked, with polythiourethane networks being preferred.

[0019] Examples of linear polythiourethanes have structural units of formula (I) that are at least 80 mol % of the polymer, based on the total amount of polymer: [ka] optionally having up to 20 mol % of structural units of formula (IIa) or formula (IIb), based on the total amount of the polymer; [ka] where R 1 , R 2 , R 3 , R 4 , R 9 and R 10 are, independently of one another, a divalent organic residue, in particular an alkylene, cycloalkylene, arylene, aralkylene or heterocyclylene, R 9a is hydrogen or a monovalent organic residue, in particular hydrogen, alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl, most preferably hydrogen or C1-C6-alkyl, or a residue R 9a and R 9 together with the two nitrogen atoms to form a piperidinyl residue m is an integer of at least 10, preferably from 10 to 100,000 and in particular from 15 to 1,000, and n is at least 1, in particular an integer from 1 to 5; However, R 1 , R2 , R 3 , R 4 , R 9 , R 9a and R 10 , can have different meanings within a molecule within a given definition.

[0020] Examples of branched polythiourethane or polymer networks are polymers comprising at least 80 mol % of structural units of formula (III), based on the total amount of polymer, [ka] optionally up to 20 mol %, based on the total amount of the polymer, of structural units of formula (IIa) and / or formula (IIb) and / or formula (IVa) and / or formula (IVb), [ka] where R 5 is an (o+1)-valent organic residue, in particular an (o+1)-valent alkyl, cycloalkyl, aryl, or heterocyclyl residue, where R 6 is a (p+1)-valent organic residue, in particular a (p+1)-valent alkyl, cycloalkyl, aryl, or heterocyclyl residue, R 3 , R 4 , R 9 and R 10 are, independently of one another, a divalent organic residue, in particular alkylene, cycloalkylene, arylene, aralkylene or heterocyclyl, R 9a and R 11a are, independently of one another, hydrogen or a monovalent organic residue, in particular hydrogen, alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl, particularly preferably hydrogen or C-C-alkyl, or a residue R 9a and R 9 together with the two nitrogen atoms form a piperidinyl residue, R 7 and R 11are, independently of one another, a (q+1)-valent organic residue, in particular a (q+1)-valent alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl residue, Alternatively, residue R 11a and R 11 together with the two nitrogen atoms form a piperidinyl residue, R 8 and R 12 are, independently of each other, an (r+1)-valent organic residue, in particular an (r+1)-valent alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl residue, m is an integer of at least 10, preferably an integer of 10 to 100,000, in particular an integer of 15 to 1,000, n is an integer of at least 1, in particular an integer from 1 to 5; o and p are independently 1 to 10, preferably 1, 2 or 3, provided that R 3 , R 4、 R 5 , R 6 , R 7 , R 8 , R 9 , R 9a , R 10 , R 11 , R 11a , R 12 , o, p, q and r may have different meanings within a molecule within the given definition; o and / or p occur at least once per molecule and are 2 to 10, preferably 2 or 3, and q and / or r, if present, may have different meanings within the molecule within the given definitions; q and r each independently represent 1 to 10, preferably 1, 2 or 3.

[0021] The polythiourethanes used in accordance with the present invention and the polymers produced by repolymerization may be homopolymers or copolymers.

[0022] The difference between branched polythiourethanes and polythiourethane networks is that the former are thermoplastic polymers with some branching points, whereas polymer networks consist of dimensionally linked polymer chains, where wide-mesh crosslinks between the main chains lead to elastomers and close-mesh crosslinks between the main chains lead to duromers.

[0023] Polymer networks made of polythiourethanes form a subgroup of duromers (thermosets) and are characterized by vitrimer properties. This is a class of plastics derived from classical duromers and has strong similarities to them. Vitrimers are made of covalently bonded networks and can change topology through thermally activated bond exchange reactions. Vitrimers are strong glass formers. At high temperatures, they flow and behave like viscoelastic liquids. At low temperatures, the exchange reactions are frozen and the vitrimers behave like classical duromers.

[0024] As used herein, when one of the residues is alkyl, the alkyl group may be branched or unbranched. The alkyl group typically contains up to 20 carbon atoms, preferably up to 10 carbon atoms. Examples of alkyl groups are methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, 2-ethylhexyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl, or n-eicosyl. Alkyl groups having 1 to 6 carbon atoms are particularly preferred. Alkyl groups having multiple carbon atoms may optionally have one or more non-adjacent oxygen atoms and / or one or more non-adjacent carboxylic acid ester residues -CO-O- in the chain. Thus, the term alkyl also includes (poly)alkylether and (poly)alkylester groups. Alkyl groups can be optionally substituted, for example, with alkoxy, cycloalkyl, aryl, heterocyclyl, halogen, carboxyl ester, carboxyl amide, sulfonate ester, sulfonamide, or alkylcarbonyl.

[0025] In this specification, when one of the residues is cycloalkyl, the cycloalkyl group is typically a cyclic group containing 3 to 8, preferably 5, 6, or 7, ring carbon atoms, each of which can be independently substituted. Examples of substituents include an alkyl group or two alkyl groups, which can form a ring together with the ring carbon atoms to which they are attached. Examples of cycloalkyl groups are cyclopropyl, cyclopentyl, or cyclohexyl. The cycloalkyl group can be optionally substituted with, for example, alkyl, alkoxy, cycloalkyl, aryl, heterocyclyl, halogen, carboxyl ester, carboxyl amide, sulfonate ester, sulfonate amide, or alkylcarbonyl.

[0026] In this specification, when one of the residues is aryl, the aryl group is typically a cyclic aromatic group containing 5 to 14 ring carbon atoms, each of which can be independently substituted. Examples of substituents include an alkyl group or two alkyl groups, which, together with the ring carbon atoms to which they are attached, may form another ring. Examples of aryl groups are naphthyl, biphenyl, anthryl, or, in particular, phenyl. The aryl group can be optionally substituted with, for example, alkyl, alkoxy, cycloalkyl, aryl, heterocyclyl, halogen, carboxyl ester, carboxyl amide, sulfonate ester, sulfonate amide, or alkylcarbonyl.

[0027] In this specification, when one of the residues is aralkyl, the aralkyl group is usually an aryl group with at least one alkyl group covalently bonded as defined above.The aralkyl group can be substituted on the aromatic ring with, for example, alkyl group or halogen atom.The example of the aralkyl group is benzyl group.The alkyl group can be substituted with, for example, alkyl, alkoxy, cycloalkyl, aryl, heterocyclyl, halogen, carboxyl ester, carboxyl amide, sulfonic acid ester, sulfonic acid amide or alkylcarbonyl as needed.

[0028] As used herein, when one of the residues is heterocyclyl, it is typically a cyclic group having 3 to 10 ring carbon atoms and at least one ring heteroatom, each of which may be substituted independently of the other. Examples of substituents include an alkyl group or two alkyl groups, which, together with the ring carbon atoms to which they are attached, may form a further ring. Examples of heteroatoms include oxygen, nitrogen, or sulfur. Examples of heterocyclyl groups are furyl, thienyl, pyrrolyl, imidazolyl, pyridyl, piperidinyl, or isocyanurate. The heterocyclyl group may be aromatic or non-aromatic. The heterocyclic group may optionally be substituted, for example, with alkyl, alkoxy, cycloalkyl, aryl, halogen, carboxyl ester, carboxyl amide, sulfonate ester, sulfonate amide, or alkylcarbonyl.

[0029] As used herein, when one of the residues is a halogen, this refers to a covalently bonded fluorine, chlorine, bromine, or iodine atom, with chlorine being preferred.

[0030] As used herein, when one of the residues is alkylene, the alkylene group may be either branched or unbranched. An alkylene group corresponds to the definition given for an alkyl group, with the modification that the molecular residues are linked by two covalent bonds instead of one. Alkylene groups having multiple carbon atoms may optionally have one or more non-adjacent oxygen atoms and / or one or more non-adjacent carboxylic acid ester residues -CO-O- in the chain. Thus, the term alkylene also includes (poly)alkylene ether and (poly)alkylene ester groups. Alkylene groups having 2 to 20 carbon atoms, especially those having 2 to 12 carbon atoms, are particularly preferred, and those having 1 to 3 non-adjacent oxygen atoms in the alkylene chain are especially preferred.

[0031] As used herein, when one of the residues is cycloalkylene, the cycloalkylene group is typically a cyclic group containing 3 to 8, preferably 5, 6, or 7, ring carbon atoms, each of which may be substituted independently of the other. The cycloalkylene group corresponds to the definition of a cycloalkyl group, modified in that the group is attached to the rest of the molecule via two covalent bonds instead of one. Cyclohexylene is particularly preferred.

[0032] As used herein, when one of the residues is arylene, the arylene group is typically a cyclic aromatic group containing 5 to 14 ring carbon atoms, each of which may be independently substituted. The arylene group corresponds to the definition given for the aryl group, modified in that the group is attached to the rest of the molecule via two covalent bonds instead of one. Phenylene is particularly preferred.

[0033] In this specification, when one of the residues is aralkylene, the aralkylene group is typically an arylene group, as defined above, with at least one alkylene group covalently bonded thereto.The alkylene group corresponds to the definition given for aralkyl group, with the modification that the group is bonded to the rest of the molecule via two covalent bonds instead of one covalent bond.Benzylene is particularly preferred.

[0034] In this specification, when one of the residues is a heterocycle, the heterocycle is typically a cyclic group having 3 to 10 ring carbon atoms and at least one ring heteroatom, each of which may be independently substituted. The heterocycle corresponds to the definition of a heterocyclyl group, with the modification that it is bonded to the rest of the molecule via two covalent bonds instead of one. Isocyanurates are particularly preferred.

[0035] Tertiary or higher alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl residues correspond to the above definitions of alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl, subject to the modification that these groups are attached to the rest of the molecule via three or more covalent bonds instead of one.

[0036] The polythiourethanes used in the present invention can be prepared using conventional polymerization processes, such as bulk, solution, emulsion, or suspension polymerization, procedures known to those skilled in the art.

[0037] The polythiourethanes used in the present invention can be prepared, for example, by polymerizing diisocyanates of formula (V) and / or higher functional isocyanates of formula (VI) with dithiols of formula (VII) and / or higher functional thiols of formula (VIII). [ka] where R 1 , R 2 , R 5 , R 6 , o and p have the meanings defined above.

[0038] Optionally, the reaction mixture can contain up to 20 mole % of additional polyisocyanates of formulae (IX), (X), (XI) and / or (XII), based on the total amount of polyisocyanates of formulae (V) and (VI). [ka] where R 4 , R 8 , R 10 , R 12 and r has the meaning defined above.

[0039] Optionally, the reaction mixture can contain up to 20 mole % of polyhydroxy or polyamine compounds of formula (XIII), (XIV), (XV) and / or (XVI), based on the total amount of thiols of formula (VII) and (VIII). [ka] where R 3 , R 7 , R 9 , R 9a , R 11 , R 11a and q has the meaning defined above.

[0040] Instead of or in addition to difunctional or higher functional isocyanates, it is also possible to use blocked higher functional isocyanates, which can be converted to isocyanates by heating. Examples of suitable blocking agents include, inter alia, alcohols, phenols, amines, oximes, amides, imides, imidazoles, pyrazoles and triazoles.

[0041] The monomers required to prepare the polythiourethanes used in this invention are known and commercially available or can be synthesized using standard organic chemistry methods. They can be monomers produced by petrochemical and / or bio-based methods.

[0042] The chain length, degree of branching, and crosslink density of the polythiourethanes used in the present invention can be adjusted by selecting the type and amount of monomers, and methods for doing so are known to those skilled in the art.

[0043] The polythiourethanes used in the present invention may contain additives typically used with such polymers. Examples include processing aids or additives that impart specific properties to the polymer. For example, dyes, pigments, heat stabilizers, glass or carbon fibers, fillers, antioxidants, UV stabilizers, antistatic agents, lubricants, biocides, preservatives, or foaming agents.

[0044] The method according to the invention comprises carrying out a depolymerization. For this purpose, the polythiourethane is combined with a difunctional and / or higher functional thiol (step b). The depolymerization can be carried out in the presence or absence of a difunctional and / or higher functional polar proton-reactive solvent.

[0045] The depolymerization is preferably carried out in the absence of a solvent.

[0046] The polythiourethane can be used in any form, whether as a substance (bulk), in solution, in suspension or as a paste. Preferably, the process is carried out using a substance, in particular a pulverized polythiourethane in the form of a powder or pellets.

[0047] Solvents that can be used in the process according to the invention are difunctional or even higher functional protic polar compounds that are liquid at room temperature (25° C.).

[0048] Difunctional or higher functional proton polar reactive solvents include difunctional aliphatic alcohols having at least two hydroxy groups, such as ethylene glycol, propylene glycol or tetramethylene glycol, polyethylene glycol, or polypropylene glycol or polytetramethylene glycol having at least two alkylene glycol repeat units, or primary and secondary di-, tri- or tetra-amines, such as ethylenediamine, propylenediamine or butylenediamine or diaminopolyethylene glycol, diaminopolypropylene glycol or copolymers thereof.

[0049] A compound of formula (XVII) is used as a bifunctional or even higher functional thiol in step b). [ka] where R 14is a (t+1)-valent organic residue, in particular a (t+1)-valent alkyl-, cycloalkyl-, aryl-, aralkyl- or heterocyclyl residue, where t is an integer greater than or equal to 1, preferably 1 to 9, and in particular 1 to 3.

[0050] Difunctional thiols and higher functional thiols, or mixtures of different difunctional or higher functional thiols, can also be used.

[0051] The thiols used can be based on petrochemical or bio-based feedstocks containing functional groups suitable for thiol functionalization. These suitable functional groups include, for example, unsaturated carbon-carbon bonds, epoxide groups, or halogens. These functional groups can be introduced into the starting compound by one or more intermediate steps.

[0052] The thiol is used in an equimolar amount, or preferably in a molar excess. The amount of thiol is selected so that in the mixture of polythiourethane and thiol, at least 1 mole of thiol is present per mole of thiourethane bond in the polythiourethane. Preferably, 1 to 100 moles, particularly 1.5 to 50 moles of thiol are used per mole of thiourethane bond in the polythiourethane.

[0053] The depolymerization can be carried out at a temperature of 20 to 220° C. The preferred reaction temperature is in the range of 30 to 210° C., particularly 50 to 200° C.

[0054] The duration of the depolymerization reaction can vary over a wide range, typically from 5 minutes to 60 hours, preferably from 10 minutes to 30 hours, and especially from 10 minutes to 20 hours.

[0055] A catalyst can be used for the depolymerization. These catalysts can be those also used in the production of polythiourethane. Examples include basic catalysts, such as tertiary amines, such as diisopropylethylamine or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), phosphines, such as triphenylphosphine, or heavy metal compounds, especially organotin compounds, such as dibutyltin dilaurate.

[0056] When a catalyst is used, the proportion of the catalyst in the reaction mixture is typically 0.01 to 10 mol %, and preferably 0.1 to 3 mol %, based on the amount of thiol.

[0057] Depolymerization is preferably carried out in bulk (in the mass) in the absence of solvents or dispersants.

[0058] Preferably, the reaction mixture consists solely of polythiourethane, thiol, and optionally catalyst.

[0059] During the depolymerization step, polythiourethane is degraded to form oligomeric and monomeric compounds. These compounds are then reacted with thiols to convert them into thiol-terminated monomeric and thiol-terminated thiourethane oligomers. This is shown schematically in Figure 1. The composition of the reaction mixture at the end of the depolymerization step, and therefore the length of the individual fragments or the number of thiourethane repeat units in the resulting oligomers, depends on the molar ratio of thiol to starting compound.

[0060] In addition to monomeric difunctional or higher functional thiourethanes, there are also thiol-capped oligomeric thiourethanes. These are usually oligomers having 2 to 16, preferably 2 to 8, and especially 2 to 6 thiourethane units per molecule. Typically, more than 50%, especially more than 80%, of all oligomers have a degree of oligomerization of 2 to 16.

[0061] The initial reaction mixture (step a) is typically a solid or a mixture of solids and liquids, or a solution or dispersion of the reactants in a solvent. Depolymerization produces a mixture of monomers and oligomers, which may still contain solid components from the initial mixture. At the end of the depolymerization process, a stirrable mixture is always present, preferably a liquid.

[0062] In step b) of the depolymerization process, the starting polythiourethane is decomposed to produce monomers and oligomers, i.e., thiourethane monomers and thiourethane oligomers.

[0063] The monomers and oligomers have a mercapto group of formula (XVIII) which is attached to the rest of the molecule via a thioisocyanate group. [ka] where w is an integer of 1 or more, preferably 1 to 9, particularly 1 to 3; R 14 and t have the meanings defined above, w is less than t, y is an integer with value t+1-w.

[0064] These mercapto groups can also have different meanings within the molecule within the given definition.

[0065] If desired, the oligomer may be modified with residues R 5 The molecule may further have a free mercapto group of formula -SH attached to it via

[0066] The monomer is a compound of formula (XIX) or (XX) derived from a polyisocyanate. [ka] where R 2 , R 6 , R 14 and t has the meaning defined above; p is 2 to 10, preferably 2 or 3.

[0067] The oligomer is a compound of formula (XXI) or a compound comprising structural units of formula (XXII) derived from at least two polyisocyanates [ka] where R 1 , R 2 , R 14 has the meaning defined above, R 5 is an (x+z2+1)-valent organic residue, in particular an (x+z2+1)-valent alkyl-, cycloalkyl-, aryl- or heterocyclyl residue, R 6 is a (z1+1)- or (z2+1)-valent organic residue, in particular a (z1+1)-valent alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl residue, s is an integer of 1 to 15, preferably an integer of 1 to 12; x is an integer between 0 and 9, z1 and z2 are integers from 1 to 10, x+z2 is an integer between 1 and 10, However, R 1 , R 2 , R 5 , R 6 , R 14 , t, x, z1 and z2 may also have different meanings within the molecule within the given definitions, provided that the oligomer of formula (XXII) has a further group of formula (XVIII) linked to the oligomer via a thioisocyanate group.

[0068] The oligomers having structural units of formula (XXII) preferably comprise at least 25 mol %, in particular at least 50 mol % and especially 80 mol %, based on the total amount of the oligomers of these structural units.

[0069] The oligomer containing structural units of formula (XXII) may optionally comprise up to 20 mole % based on the oligomer of structural units of formula (IVa) or (IVb) above.

[0070] In addition to the residue of formula (XVIII), the oligomer may also contain amino end groups derived from isocyanates. These end groups have the structure of formula (XXIII): [ka] where R 6 and p has the meaning defined above, z3 is an integer from 1 to 10.

[0071] The proportion of these amino end groups is up to a maximum of 30 mol %, preferably up to 10 mol % and in particular up to 0 mol %, based on the total amount of end groups in the molecule.

[0072] Some species formed by depolymerization from a mixture of monomeric and oligomeric cleavage fragments are described below by way of example.

[0073] The mixture contains monomers of formula (XIX) or (XX) above. Additionally, the mixture includes dimers, trimers, and similar higher oligomers thereof.

[0074] Examples of possible dimers are compounds of formula (XXIV), (XXVa) or (XXVb) [ka]

[0075] Further examples of monomers, dimers and trimers derived from trifunctional isocyanates and difunctional mercaptans are given below.

[0076] The difunctional mercaptan is [ka] It is characterized by:

[0077] Trifunctional isocyanates are [ka] It is characterized by:

[0078] [ka]

[0079] The composition of the monomeric and oligomeric degradation fragments is novel and is also the subject of the present invention.

[0080] The proportion of the decomposition fragments (cleavage fragments) of the monomer of formula (XIX) or (XX) in the composition may be 0 to 100 mol % based on the total amount of the decomposition fragments in the composition.

[0081] The proportion of oligomeric decomposition fragments of formula (XXI) or (XXII) in the composition may also be 0 to 100 mol % based on the total amount of decomposition fragments in the composition.

[0082] The proportion of monomers and oligomers in the composition can be controlled by the amount of thiol used in step b).

[0083] The invention also relates to the use of these compositions for the preparation of polythiourethanes, for the preparation of copolymers containing polythiourethane groups, or as curing agents for epoxides or for compounds containing ethylenically unsaturated groups.

[0084] Compositions of monomeric and oligomeric fragments are preferred, but exclude monomeric and thiourethane oligomers obtained by depolymerization of polythiourethane networks derived from 4,4'-methylenebis-(cyclohexyl isocyanate) and ethoxylated trimethylolpropane-tris-(3-mercaptopropionic acid).

[0085] Particularly preferably, R 1 and R 2 are each independently an alkylene, cycloalkylene, arylene, aralkylene, or heterocyclylene; R 5 is an (x+z2+1)-valent alkyl-, cycloalkyl-, aryl-, aralkyl-, or heterocyclyl residue, and R 6 is a (z+1)-valent alkyl-, cycloalkyl-, aryl-, aralkyl-, or heterocyclyl residue, and R 14 is a(t+1)-valent alkyl-, cycloalkyl-, aryl-, aralkyl- or heterocyclyl residue, x+z2 is 1, 2 or 3, and t is an integer from 1 to 9, in particular from 1 to 3, and is the composition of monomeric and oligomeric decomposition fragments.

[0086] R 1 is cycloalkylene, arylene, aralkylene or heterocyclylene, especially arylene, and R 5 Also preferred are compositions of monomeric and oligomeric decomposition fragments in which is a (x+z 2+1)-valent cycloalkyl-, aryl-, aralkyl- or heterocyclyl residue, in particular a (x+z 2+1)-valent aryl residue.

[0087] Also preferred are compositions of monomeric and oligomeric degradation fragments that do not contain structural units of formula (IIa), (IIb), (IVa) and / or (IVb).

[0088] After depolymerization, the resulting oligomeric mixture can be freed from unwanted additives (step c), for example by filtration or distillation, or by other separation operations known to those skilled in the art.

[0089] The oligomer mixtures thus produced can be repolymerized into polymers such as polythiourethanes either immediately after their preparation or at a later time after interruption. Alternatively, oligomer mixtures containing free mercaptan groups can be used as reactants in other reactions, such as polycondensation with dicarboxylic acids or as curing agents for epoxy compounds or compounds containing ethylenically unsaturated groups.

[0090] In the process according to the invention, difunctional and / or higher functional isocyanates, difunctional and / or higher functional epoxides, difunctional and / or higher functional compounds containing ethylenically unsaturated groups and, if desired, difunctional and / or higher functional thiols are added to the monomer / oligomer mixture (step d).

[0091] Difunctional and higher functional isocyanates or mixtures of different difunctional or higher functional isocyanates can also be used, as can difunctional or higher functional epoxides and difunctional or higher functional compounds containing ethylenically unsaturated groups.

[0092] Additionally, mixtures of compounds containing isocyanates, epoxides and / or ethylenically unsaturated groups may also be used.

[0093] The proportion of difunctional and / or higher functional isocyanate, epoxide or ethylenically unsaturated group-containing compound added in step d) is typically selected so that 0.01 to 500 mol, in particular 0.2 to 100 mol, of isocyanate, epoxide or ethylenically unsaturated group is obtained from the added isocyanate, epoxide or ethylenically unsaturated group-containing compound per mol of mercaptan group in the monomer / oligomer mixture from step b2).

[0094] The repolymerization in step e) can also be carried out using the same catalyst as in step b) of depolymerization.

[0095] When a catalyst is used, the proportion of the catalyst in the reaction mixture in step e) is typically 0.01 to 10 mol %, preferably 0.1 to 3 mol %, based on the amount of thiol.

[0096] The repolymerization in step e) can be carried out at a temperature of 20 to 220° C. The preferred reaction temperature is in the range of 30 to 210° C., particularly in the range of 50 to 200° C.

[0097] The duration of the repolymerization reaction in step e) can vary over a wide range. Typically, the repolymerization reaction can last from 5 minutes to 60 hours, preferably from 10 minutes to 30 hours, and especially from 10 minutes to 20 hours.

[0098] The pressure during the repolymerization reaction of step e) can vary widely. It is possible to work under vacuum, atmospheric pressure or superatmospheric pressure. Preferably, the operation is carried out at atmospheric pressure.

[0099] The repolymerization in step e) is preferably carried out in bulk without solvent or dispersant.

[0100] Typically, the reaction mixture in the repolymerization stage of step e) consists solely of a mixture of monomers and oligomers from the depolymerization, added difunctional and / or higher functional compounds containing isocyanate, epoxy, and / or ethylenically unsaturated groups, and, optionally, a catalyst and / or, optionally, a difunctional polar proton-reactive solvent.

[0101] Alternatively, difunctional and / or higher functionality thiols can be added to the monomer and oligomer mixture from the depolymerization prior to the repolymerization in step d), forming a repolymer together with the monomers and oligomers from step b) and the difunctional and / or higher functionality isocyanate, epoxy and / or ethylenically unsaturated group-containing compounds from step d).

[0102] The proportion of difunctional and / or higher functional thiols added in step d) is typically selected so that the total proportion of mercapto groups in the reaction mixture corresponds approximately to the total proportion of isocyanate, epoxide and / or ethylenically unsaturated groups in the reaction mixture. Typically, 0.5 to 1.5 moles, in particular 0.8 to 1.2 moles, of isocyanate, epoxide and / or ethylenically unsaturated groups in the reaction mixture corresponds to 1 mole of mercaptan groups in the reaction mixture.

[0103] In this variant, the reaction mixture in the repolymerization stage of step e) consists solely of a mixture of monomers and oligomers from the depolymerization, added thiols and isocyanates, epoxides and / or compounds containing ethylenically unsaturated groups, and, if desired, a catalyst.

[0104] Preferably, a higher temperature is selected for the repolymerization stage in step e) than for the depolymerization stage.

[0105] After completion of the repolymerization of step e), the reaction mixture is cooled to deactivate any catalyst present.

[0106] The resulting repolymer can then be subjected to a molding process, or it can be crushed, for example crushed into pellets or crushed into a powder, before further processing.

[0107] The reaction can be carried out in a conventional stirred reactor, disperser, rapid mixer, jet-jet disperser, reaction extruder, extruder or mixer-kneader.

[0108] The depolymerization can be carried out separately from the repolymerization, preferably in a different reactor.

[0109] The process according to the invention can be carried out batchwise or continuously, with the batch process being preferred.

[0110] Suitable difunctional or higher functional isocyanates are all known aliphatic, cycloaliphatic, aromatic or aromatic isocyanates, aromatic di- or polyisocyanates being preferred.

[0111] For the preparation or repolymerization of the polythiourethanes used in the present invention, the following isocyanates are preferred: Phenyl diisocyanate, phenyl triisocyanate, toluene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, diphenyl ether diisocyanate, alkylene diisocyanates such as tetra-, penta-, hexa-, octamethylene diisocyanate, alkylene triisocyanates such as tetra-, penta-, hexa-, octamethylene triisocyanate and trimers thereof, xylylene di- or tri-isocyanate, mono-, di-, tri-, or tetramethyl xylene diisocyanate, Silylene di- or triisocyanate, dicyclohexylmethane diisocyanate, dicyclohexyl ether diisocyanate, cyclohexyl di- or tri-isocyanate, mono-, di-, tri-, or tetraalkylcyclohexyl diisocyanates, such as isophorone diisocyanate, norbornane diisocyanate, triphenylmethane triisocyanate, biphenyl diisocyanate, isocyanurate-tris-N-alkylene isocyanate, or naphthalene di- or tri-isocyanate. Mixtures of two or more of these compounds can also be used. The isocyanates used can be obtained from petrochemical and bio-based processes.

[0112] Instead of the above-mentioned difunctional or higher functional isocyanates, it is also possible to use their blocked variants, such as isocyanates blocked with alcohols, phenols, amines, oximes, amides, imidazoles, pyrazoles and triazoles, which can be converted to isocyanates by heating.

[0113] For the preparation or repolymerization of the polythiourethanes according to the invention, the following isocyanates are particularly preferably used: 4,4'-diphenylmethane diisocyanate, 1,4-phenylene diisocyanate, 1,4-xylylene diisocyanate, toluylene-2,4-diisocyanate, toluylene-2,6-diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, hexane-1,6-diisocyanate and its trimer, isophorone diisocyanate, norbornane diisocyanate, tetramethylxylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, triisocyanatononane, and cyclohexane-1,4-diisocyanate.

[0114] The following epoxides are preferably used for the repolymerization in step e): Polyglycidyl esters, polyglycidyl ethers, and alicyclic epoxides are preferred, especially those having, on average, more than one epoxy group directly bonded to an oxygen or nitrogen atom. Examples of such epoxides include polyglycidyl esters and poly(β-methylglycidyl) esters, which can be obtained by reacting a compound having two or more carboxylic acid groups per molecule with epichlorohydrin, glycerol dichlorohydrin, or β-methylepichlorohydrin in the presence of an alkali. Such polyglycidyl esters can be derived from aliphatic polycarboxylic acids such as oxalic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, or dimerized or trimerized linoleic acid; aliphatic polycarboxylic acids such as tetrahydrophthalic acid, 4-methyltetrahydrophthalic acid, hexahydrophthalic acid, 4-methylhexahydrophthalic acid; and aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid.

[0115] Further examples include polyglycidyl ethers and poly(β-methylglycidyl) ethers, which can be obtained by reacting a compound containing at least two free alcoholic and / or phenolic hydroxyl groups per molecule with an appropriate epichlorohydrin under alkaline conditions or in the presence of an acidic catalyst, followed by treatment with alkali. These ethers can be prepared from acyclic alcohols such as ethylene glycol, diethylene glycol and polymeric poly(oxyethylene) glycols, propane-1,2-diol and poly(oxypropylene) glycol, propane-1,3-diol, butane-1,4-diol, poly(oxytetramethylene) glycol, pentane-1,5-diol, hexane-1,6-diol, hexane-2,4,6-triol, glycerin, 1,1,1-trimethylolpropane, pentaerythritol, sorbitol, and polyepichlorohydrin; cycloaliphatic alcohols such as resorcitol, quinitol, bis(4-hydroxycyclohexyl)methane, 2,2-bis(4-hydroxycyclohexyl)propane, 1,1-bis(hydroxymethyl)cyclohex-3-ene, and the like; and alcohols having an aromatic nucleus such as 2,4-(dihydroxymethyl)benzene. They can also be prepared from mononuclear phenols such as resorcinol and hydroquinone, polynuclear phenols such as bis(4-hydroxyphenyl)methane, 4,4'-dihydroxydiphenyl, 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane, and novolaks formed from aldehydes (e.g., formaldehyde, acetaldehyde, chloral, furfural, etc.) and phenols (e.g., phenol itself and phenols substituted in the ring with chlorine atoms or alkyl groups containing up to 9 carbon atoms, e.g., 4-chlorophenol, 2-methylphenol, 4-tert-butylphenol, etc.).

[0116] Epoxides in which some or all of the epoxide groups are not terminal can also be used, such as vinylcyclohexene dioxide, limonene dioxide, dicyclopentadiene dioxide, 4-oxatetracyclo[6.2.1.02,7.03,5]undec-9-yl glycidyl ether, bis(4-oxatetracyclo[6.2.1.02,7.03,5]undec-9-yl) ether of ethylene glycol, 3,4-epoxycyclohexylmethyl-3',4'epoxycyclohexanecarboxylate, and its 6,6 1 -dimethyl derivatives such as bis(3,4-epoxycyclohexane-carboxylate) of ethylene glycol, 3-(3,4-epoxycyclohexyl)-8,9-epoxy-2,4-dioxaspiro[5,5]undecane and epoxidized copolymers of butadiene with ethylenic compounds such as styrene and vinyl acetate can also be used.

[0117] Epoxy resins with various types of 1,2-epoxy groups attached to heteroatoms can be used, such as the glycidyl ethers and glycidyl esters of salicylic acid. Mixtures of epoxy resins can also be used.

[0118] Particularly preferred for the repolymerization in step e) are the following epoxides: Polyglycidyl esters, polyglycidyl ethers of 2,2-bis(4-hydroxyphenyl)propane, or novolacs formed from formaldehyde and phenols, or phenols substituted in the ring with chlorine atoms or alkyl hydrocarbon groups containing 1 to 9 carbon atoms and having a 1,2-epoxy content of at least 0.5 equivalents per kg, and 3,4-epoxycyclohexylmethyl-3',4'epoxycyclohexanecarboxylate.

[0119] The following compounds containing ethylenically unsaturated groups are suitable for use in the repolymerization in step e): Allyl compounds, vinyl compounds, ethylenically unsaturated carboxylic acids or derivatives thereof, such as esters or amides thereof.

[0120] The allyl compounds include organic compounds having at least one allyl group, preferably two or more allyl groups. These include, in particular, esters of unsaturated carboxylic acids with allyl alcohol, N-allyl alcohol compounds, polyallyl ethers, polyallylamine, or allyl esters of phosphoric acid. Mixtures of allyl compounds can also be used.

[0121] Particularly preferred for the repolymerization in step e) are the following allyl compounds: Allyl (meth)acrylate, maleic acid diallyl ester, triallyl cyanurate, pentaerythri- and tetraallyl ether, polyethylene glycol diallyl ether, monoethylene glycol diallyl ether, glycerol di- and triallyl ether, polyallyl ether, sorbitol-based polyallyl ethers, and their ethoxylated variants, tetraallyloxyethane, triallylamine or tetraallylethylenediamine.

[0122] Vinyl compounds include organic compounds containing at least one, preferably two or more, vinyl groups. These include, in particular, vinyl ethers or vinyl esters of aliphatic monocarboxylic acids, especially acetic acid. Mixtures of vinyl compounds can also be used.

[0123] Ethylenically unsaturated carboxylic acids and derivatives thereof include organic compounds having at least one, preferably two or more, ethylenically unsaturated groups and one or more carboxyl groups, or esters or amides thereof.

[0124] These include, in particular, mono- or dicarboxylic acids having one or two ethylenically unsaturated groups, or their esters or amides, such as esters of ethylenically unsaturated carboxylic acids with mono- or higher-functional alcohols, or amides of ethylenically unsaturated carboxylic acids with mono- or higher-functional amides. Mixtures of ethylenically unsaturated carboxylic acids and their derivatives can also be used.

[0125] Particularly preferred for the repolymerization in step e) are the following derivatives of ethylenically unsaturated carboxylic acids: Acrylates and methacrylates of monohydric alcohols, such as alkyl esters of acrylic or methacrylic acid, in particular methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, pentyl methacrylate, hexyl methacrylate, and 2-ethylhexyl methacrylate.

[0126] Acrylates and methacrylates of polyhydric alcohols, such as ethylene glycol diacrylate, triethylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, butanediol-1,4-diacrylate, pentamethylene glycol diacrylate, neopentyl glycol diacrylate, hexamethylene glycol diacrylate, 1,1,1-trimethylolpropane triacrylate, pentaerythritol tetraacrylate, and the corresponding methacrylates. Other suitable polyfunctional materials are the reaction products of hydroxyalkyl acrylates or methacrylates with isocyanate-terminated prepolymers derived from polyols and polyisocyanates.

[0127] Acrylamides and methacrylamides based on mono- or polyvalent amines, such as N-methylacrylamide and N-methylmethacrylamide, N,N'-methylenebisacrylamide and N,N'-methylenebismethacrylamide.

[0128] Other preferred compounds containing ethylenically unsaturated groups are esters of epoxy resins with carboxylic acids having polymerizable (meth)acrylic groups, such as acrylic acid, methacrylic acid, dimers of acrylic and methacrylic acid, and adducts of hydroxyalkyl acrylates or methacrylates with polycarboxylic acid anhydrides, such as adducts of 2-hydroxyethyl methacrylate or 2-hydroxypropyl acrylate with polycarboxylic acid anhydrides.

[0129] For the preparation or depolymerization of the polythiourethanes used in the present invention or for repolymerization, the following difunctional or even higher functional thiols are preferred: Phenyldithiol, phenyltrithiol, toluenedithiol, toluentrithiol, diphenylmethanedithiol, diphenyletherdithiol, alkylenedithiols such as di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-, undeca-, and dodecamethylenedithiol, alkylenetriols and tetrathiols such as terpenethiol, myrsentriol, farnesenetriol, alkyleneetherdithiol, xylylenedithiol, mono-, di-, tri-, or tetramethylxylylenedithiol, dicyclohexylmethanedithiol, dicyclohexyletherdithiol, cyclohexylmethylmethanedithiol, dicyclohexyletherdithiol, Sildithiol, mono-, di-, tri-, or tetraalkylcyclohexyldithiol, triphenylmethanetrithiol, biphenyldithiol, isocyanurate-tris-N-alkylenethiol, naphthalenedithiol, naphthalenetrithiol, di-, tri-, or tetraesters of di-, tri-, or tetrahydric alcohols with mercaptoalkanoic acids, especially 3-mercaptopropionic acid or thioglycolic acid with di-, tri-, or tetrahydric aliphatic alcohols, such as ethylene glycol, diethylene glycol ether, trimethylolpropane, its ethoxylated or propoxylated derivatives, pentaerythritol, and polycaprolactone. Mixtures of two or more of these compounds can also be used.

[0130] For the preparation or depolymerization of the polythiourethanes used in the present invention or for repolymerization, the following difunctional or even higher functional thiols are particularly preferred: Hexanedithiol, dodecanedithiol, limonenedithiol, millicentrithiol, farnesenethiol, pentaerythritol-tetra-(3-mercaptopropionate), trimethylolpropane-tri-(3-mercaptopropionate), tris-[2-(3-mercaptopropionyl-oxy)ethyl]isocyanurate, ethylene glycol-di-(3-mercaptopropionate), diethylene glycol ether-di-(3-mercaptopropionate), dipentaerythritol hexa-(3-mercaptopropionate), ethoxylated trimethylolpropane-tri-(3-mercaptopropionate), propoxylated trimethylolpropane-tri-(3-mercaptopropionate), and polycaprolactone-tetra-(3-mercaptopropionate).

[0131] When reactive solvents are used in addition to difunctional or higher functional thiols, they are typically aliphatic or aromatic di- or polyhydroxy compounds. Diols, triols, or tetrols, or mixtures thereof, are preferred. Polyether alcohols are preferred as polyhydroxy compounds.

[0132] In a preferred embodiment of the process according to the invention, the depolymerization in step b) and the repolymerization in step e) are carried out in bulk.

[0133] In a further preferred embodiment of the process according to the invention, the depolymerization in step b) and the repolymerization in step e) are carried out in the presence of a catalyst.

[0134] The catalyst is preferably selected from the group consisting of tertiary amines, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), phosphines or organotin compounds.

[0135] In a further preferred embodiment of the process according to the present invention, the first reaction temperature and the second reaction temperature are in the range of 30°C to 210°C, preferably 50°C to 200°C.

[0136] In a further preferred embodiment of the process according to the invention, in step a) 1.5 to 50 mol of difunctional or higher functional thiol are used per mole of thiourethane bond of the polythiourethane.

[0137] In a further preferred embodiment of the process according to the invention, oligomeric polyurethanes having 2 to 16 repeating units are produced in the depolymerization step.

[0138] In a particularly preferred embodiment of the method according to the invention, the di-, tri- or tetrafunctional thiol used in step a) is preferably hexanedithiol, dodecanedithiol, pentaerythritol-tetra-(3-mercaptopropionate), trimethylpropane-tri-(3-mercapto-propionate), tris-[2-(3-mercaptopropionyloxy)ethyl]-isocyanurate, ethylene glycol-di-(3-mercaptopropionate), dipentaerythritol-hexa-(3-mercaptopropionate), diethylene glycol ether-di-(3-mercaptopropionate), dipentaerythritol-hexa-(3-mercaptopropionate), ethoxylated trimethylpropane-tri-(3-mercaptopropionate), propoxylated trimethylpropane-tri-(3-mercaptopropionate), polycaprolactone tetra-(3-mercaptopropionate) or a mixture of two or more thereof.

[0139] In a particularly preferred embodiment of the process according to the invention, in steps d) and e), difunctional or higher functional isocyanates are used, in particular selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 1,4-phenylene diisocyanate, 1,4-xylylene diisocyanate, toluylene-2,4-diisocyanate, toluylene-2,6-diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, hexane-1,6-diisocyanate and its trimer, isophorone diisocyanate, norbornane diisocyanate, pentamethylene diisocyanate and its trimer, tetramethylxylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, triisocyanatononane, cyclohexane-1,4-diisocyanate or mixtures of two or more thereof.

[0140] A particularly preferred embodiment of the process according to the invention is one in which a polythiourethane network is used in step a).

[0141] A further particularly preferred embodiment of the process according to the invention is one in which the thiol from the polythiourethane obtained in step b) is a trifunctional or higher functional thiol, preferably a trifunctional thiol.

[0142] In step a), polythiourethanes are preferably used which are polythiourethane networks composed of biobased monomers.

[0143] Furthermore, it is preferred that the difunctional or higher functional thiol used in step a) is a bio-based raw material and / or that the difunctional or higher functional isocyanate or epoxide or ethylenically unsaturated compound used in step d) is a bio-based raw material.

[0144] The polythiourethanes obtained by the repolymerization according to the invention, like their starting products, can be used in a wide variety of technical fields. They can also be molded into shapes of any design. Examples of these are fibers, films, or molded articles, which can be obtained from the polythiourethanes obtained by the repolymerization according to the invention by molding processes such as injection molding, pressing, foam injection molding, gas-assisted injection molding, blow molding, film casting, calendaring, nitrating, or coating of any substrate. [Brief explanation of the drawings]

[0145] [Figure 1] FIG. 1 illustrates an exemplary method according to the invention.

[0146] This diagram shows step A, which precedes the method according to the invention. This involves the synthesis of a polythiourethane network (from a higher-functionality thiol; here a trithiol, shown as an example of a higher-functionality isocyanate, here a diisocyanate). The recycling of the polythiourease is shown in steps B and C, where the polythiourethane network is depolymerized using a difunctional thiol to a mixture of monomers or oligomers (step B). After the addition of a higher-functionality isocyanate, in this case a diisocyanate, the mixture is repolymerized to a polymer network (step C).

[0147] Depolymerization and subsequent repolymerization with a difunctional thiol, as shown in Figure 1, uses a difunctional thiol (e.g., hexanedithiol, dodecanedithiol, ethylene glycol bis(3-mercaptopropionate)) to repolymerize the polythiourethane network for recycling. Higher-functional thiols can also be used. Depolymerization is preferably performed in bulk. Only a slight excess of thiol is used. The reaction temperature is 20-220°C, ideally 50-200°C. A catalyst can be used, for example, for the reaction of DBU with triphenylphosphine or an organotin compound. For repolymerization, the monomer / oligomer mixture is heated after adding another higher-functional isocyanate, such as pentamethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, or methylene diphenyl isocyanate. This re-forms the polythiourethane network. [Example]

[0148] The following examples illustrate the process according to the invention without limiting it.

[0149] Synthesis of polythiourethane: Synthesis of poly(pentaerythritol tetrakis(2-mercaptoacetate)-co-hexamethylene diisocyanate) 44 g of pentaerythritol tetrakis(2-mercaptoacetate) (0.102 mol) was mixed with 34.3 g of hexamethylene diisocyanate (0.204 mol) and left at room temperature for 3 days. The colorless solid was ground using a laboratory mill (IKA A10 basic). DSC: Tg = 63°C Elemental analysis: Calculated value [%]: C: 45.30 H: 5.77 N: 7.29 S: 16.68 Measurement value [%]: C:45.49 H:5.94 N:7.56 S:16.35

[0150] Example 1: Decomposition and repolymerization of ethylene glycol bis(2-mercaptoacetate) 537 mg of polythiourethane network (pentaerythritol tetrakis(2-mercaptoacetate)-co-hexamethylene diisocyanate; 1 / 2 ratio; 0.70 mmol (calculated as the pentaerythritol tetrakis(2-mercaptoacetate) repeat unit) was mixed with ethylene glycol bis(2-mercaptoacetate) (881 mg; 4.19 mmol) in a microwave vial. The vessel was hermetically sealed, and the mixture was stirred at 150 °C for 3.5 h.

[0151] 425 mg of the resulting solution (0.21 mmol, calculated as the pentaerythritol tetrakis(2-mercaptoacetate) repeating unit) was mixed with 13 mg of dibutyltin dilaurate (0.02 mmol) and 211 mg of hexamethylene diisocyanate (1.26 mmol). The mixture was heated to 100°C for 10 seconds to obtain a homogeneous solution. The mixture was then stirred at room temperature until gelation occurred, followed by curing at 50°C for 24 hours. A colorless solid was formed. DSC: Tg = 35°C Elemental analysis: Calculated value [%]: C: 44.65 H: 5.84 N: 7.37 S: 16.88 Measurement value [%]: C:45.33 H:6.05 N:7.64 S:16.74

[0152] Example 2: Decomposition and repolymerization of ethylene glycol bis(2-mercaptoacetate) and ethylene glycol: 225 mg of polythiourethane network (pentaerythritol tetrakis(2-mercaptoacetate) / hexamethylene diisocyanate; ratio 1 / 2; 0.29 mmol (calculated in pentaerythritol tetrakis(2-mercaptoacetate) repeat units) was mixed with ethylene glycol bis(2-mercaptoacetate) (308 mg; 1.46 mmol) and ethylene glycol (91 mg; 1.46 mmol) in a microwave vial. The vessel was hermetically sealed, and the mixture was stirred at 150 °C for 3 h.

[0153] The resulting solution was mixed with 12 mg of dibutyltin dilaurate (0.02 mmol) and 493 mg of hexamethylene diisocyanate (2.93 mmol). The mixture was heated to 100°C for 10 seconds to obtain a homogeneous solution. The mixture was then stirred at room temperature until gelation occurred, followed by curing at 60°C for 24 hours. A colorless solid was formed. Elemental analysis: Calculated value [%]: C: 46.94 H: 6.45 N: 8.82 S: 11.77 Measurement value [%]: C:47.46 H:6.50 N:9.08 S:11.53

Claims

1. 1. A method for recycling polythiourethane, comprising the steps of: a) providing a mixture of a polythiourethane and a difunctional or higher functional thiol, and optionally a difunctional or higher functional polar proton reactive solvent, wherein: using at least one mole of difunctional or higher functional thiol per mole of thiourethane linkage in the polythiourethane; b) depolymerizing the polythiourethane by treating the mixture from step a) at a first reaction temperature, thereby producing difunctional or higher functional thiols from said polythiourethane and difunctional or higher functional thiol terminated monomeric and oligomeric thiourethanes; c) optionally separating impurities from the mixture obtained in step b); d) adding a difunctional or higher functional isocyanate or epoxide compound or an ethylenically unsaturated compound and, optionally, a difunctional or higher functional thiol to the mixture from step b) or c), e) treating the mixture from step d) at a second reaction temperature which is lower than, equal to, or higher than the first reaction temperature, thereby polymerizing the monomers and oligomeric thiourethanes from step b), the compounds added in step d) and any reactive solvents present, with the proviso that the depolymerization in step b) and the polymerization in step e) are carried out in bulk or in the presence of a difunctional or higher functional polar proton reactive solvent; The method comprising:

2. 2. The process according to claim 1, characterized in that the depolymerization in step b) and the polymerization in step e) are carried out in bulk.

3. 3. The process according to claim 1, wherein the depolymerization in step b) and the polymerization in step e) are carried out in the presence of a catalyst.

4. 4. The method of claim 3, wherein the catalyst is selected from the group consisting of a tertiary amine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), a phosphine, or an organotin compound.

5. 5. The method according to claim 1, wherein the first reaction temperature and the second reaction temperature are in the range of 20 to 220°C, preferably 50 to 200°C.

6. 6. The method according to claim 1, wherein in step a) 1.5 to 50 moles of difunctional or higher functional thiol are used per mole of thiourethane bond in the polythiourethane.

7. 7. The method according to claim 1, wherein the oligomeric polythiourethane from step b) has from 2 to 16 repeating units.

8. The thiol used in step a) is a di-, tri- or tetrafunctional thiol, preferably hexanedithiol, dodecanedithiol, limonenedithiol, myrcentrithiol, farnesenetetrathiol, pentaerythritol-tetra-(3-mercaptopropionate), trimethylolpropane-tri-(3-mercaptopropionate), tris-[2-(3-mercaptopropionyloxy)ethyl]-isocyanurate, ethylene glycol-di ...

2. The method of claim 1, wherein the hydroxyl group is selected from the group consisting of diethylene glycol ether-di-(3-mercaptopropionate), diethylene glycol ether-di-(3-mercaptopropionate), dipentaerythritol hexa-(3-mercaptopropionate), ethoxylated trimethylolpropane-tri-(3-mercaptopropionate), propoxylated trimethylolpropane-tri-(3-mercaptopropionate), polycaprolactone-tetra-(3-mercaptopropionate), or a mixture of two or more thereof.

9. 2. The process according to claim 1, characterized in that in step d) difunctional or higher functional isocyanates are used.

10. 10. The method of claim 9, wherein the isocyanate used in step d) is selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 1,4-phenylene diisocyanate, 1,4-xylylene diisocyanate, toluylene-2,4-diisocyanate, toluylene-2,6-diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, hexane-1,6-diisocyanate or a trimer thereof, isophorone diisocyanate, norbornane diisocyanate, pentamethylene diisocyanate, tetramethylxylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, triisocyanatononane, cyclohexane-1,4-diisocyanate, or a mixture of two or more thereof.

11. 11. The method according to claim 1, wherein the polythiourethane used in step a) is a polythiourethane network.

12. 12. The method according to claim 11, characterized in that in step b) the thiol obtained from the polythiourethane is a trifunctional or higher functional thiol, preferably a trifunctional thiol.

13. 13. The method according to claim 1, wherein in step a) a polythiourethane is used which is a polythiourethane network composed of biobased monomers.

14. 14. The method according to claim 1, wherein the difunctional or higher functional thiol used in step a) is a bio-based raw material and / or the difunctional or higher functional isocyanate or epoxide or ethylenically unsaturated compound used in step d) is a bio-based raw material.

15. A composition comprising a monomer of formula (XIX) and / or an oligomer of formula (XXI) or a composition comprising a monomer of formula (XX) and / or an oligomer comprising a structural unit of formula (XXII), 【Chemistry 1】 In the formula, R １ and R ２ are each independently a divalent organic residue, R ５ is an organic residue with a valence of (x+z2+1), R ６ is a (z1+1)-valent or (z2+1)-valent organic residue, R １４ is a (t+1)-valent organic residue, t is an integer of 1 or greater, p is 2 to 10, preferably 2 or 3; s represents an integer from 1 to 15; x is an integer from 0 to 9; z1 and z2 each independently represent an integer of 1 to 10, the sum of x and z2 is an integer from 1 to 10, However, R １ , R ２ , R ５ , R ６ , R １４ , t, x, z1 and z2 may have different meanings within a molecule within the given definition, The oligomer of formula (XXII) has an additional residue of formula (XVIII) attached to the oligomer via a thioisocyanate group: 【Chemistry 2】 In the formula, w is an integer of 1 or more, R １４ and t has the meaning defined above; w is smaller than t, y is an integer having a value of t+1-w, the proportion of the monomer of formula (XIX) and the oligomer of formula (XXI) in the composition can be from 0 to 100 mol %, based on the total amount of these compounds, the sum of these compounds always being 100 mol %, The proportion of the monomer of formula (XX) and the oligomer comprising a structural unit of formula (XXII) in the composition can be 0 to 100 mol % based on the total amount of these compounds, and the sum of these compounds is always 100 mol %.

16. R １ and R ２ are each independently alkylene, cycloalkylene, arylene, aralkylene or heterocyclylene, R ５ is an (x+z2+1)-valent alkyl-, cycloalkyl-, aryl-, aralkyl-, or heterocyclyl residue, and R ６ is a (z1+1)- or (z2+1)-valent alkyl-, cycloalkyl-, aryl-, aralkyl-, or heterocyclyl residue, and R １４ 16. The composition according to claim 15, characterized in that x is a (t+1)-valent alkyl-, cycloalkyl-, aryl-, aralkyl- or heterocyclyl residue, x+z2 are each independently 1, 2 or 3, and t is an integer from 1 to 9, in particular an integer from 1 to 3.

17. 16. The composition of claim 15, wherein the monomers and oligomers obtained by depolymerization of polythiourethane networks derived from 4,4'-methylene-bis-(cyclohexyl isocyanate) and ethoxylated trimethylolpropane-tris-(3-mercaptopropionate) are excluded.

18. R １ is cycloalkylene, arylene, aralkylene or heterocyclylene, especially arylene, and R ５ 16. The composition according to claim 15, wherein is a (x+z2+1)-valent cycloalkyl-, aryl-, aralkyl- or heterocyclyl residue, in particular a (x+z2+1)-valent aryl residue.

19. 16. Use of the composition according to claim 15 for the preparation of polythiourethanes, for the preparation of copolymers containing polythiourethane groups, or as a curing agent for epoxy compounds or compounds containing ethylenically unsaturated groups.

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