Process for recycling polythiourethanes, thio compounds, and use thereof

Abstract

The invention relates to a process for recycling polythiourethanes. According to the invention, polythiourethanes are depolymerized in the presence of monofunctional thiols. Thiol is subsequently removed from the obtained oligomer mixture by applying negative pressure, resulting in polythiourethane. The process allows polythiourethanes to be easily virtually completely recycled.

Description

[0001] Bruno Bock GmbH and Friedrich Schiller University Jena

[0002] Lawyer's file = 223bb01.wo

[0003] Description

[0004] Processes for the recycling of polythiourethanes, thio compounds and their use

[0005] The invention relates to a process for the chemical recycling of polythiourethanes as well as to the resulting thio compounds and their use.

[0006] Polythiourethanes are well-known polymers that can exist in linear or branched form, or even as a polymer network. Polythiourethanes are used in a wide variety of applications, including organic glasses, such as spectacle lenses or optical lenses, coatings, paints, adhesives, or potting compounds, as well as foams for use as insulation materials.

[0007] Since polythiourethanes often exist as a polymer network in the corresponding applications, traditional mechanical recycling, as is common for thermoplastics, is not possible. Molded articles or coatings made of linear or branched polythiourethanes are also often not readily recyclable, as they contain additives that must be removed before recycling. Therefore, polythiourethanes are often not recyclable using conventional methods, and thermal recycling, i.e., incineration, often remains the only option.

[0008] To date, only a few initial approaches have been described in the literature that allow the recycling of polythiourethanes. Polythiourethanes are reversible at elevated temperatures of approximately 120 °C and in the presence of catalysts (e.g., dibutyltin dilaurate, sodium tetraphenylborate with 1-methylimidazole), meaning that the thiourethane bonds undergo exchange reactions. Since the bonds exchange within the polymer network, the network density remains constant; the polymers can therefore be classified as vitrimers. These polymers show, for example, self-healing or shape memory behavior (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).

[0009] These properties were also demonstrated in polythiourethane-urethane networks containing both thiourethane and urethane bonds. 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, YZ. Wang, "Adaptable strategy to fabricate self-healable and reprocessable poly(thiourethane-urethane) elastomers via reversible thiol-isocyanate click chemistry", Macromolecules 2020, 53, 4284-4293).

[0010] Similar results were also obtained for thioureas (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).

[0011] The depolymerization of polyurethanes or polythiourethanes and their reaction with di- or polyamines to form oligomeric urea compounds is described in DE 10 2011 008 535 A1.

[0012] Crosslinked polythiourethanes were depolymerized with an excess of trithiols in acetone solution (S. Huang, M. Podgörski, X. Han, CN 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 the idea of ​​a circular economy and the principles of sustainability. Acetone, for example, is used as a solvent, which requires complex separation. In addition, wastewater and other waste products are generated that must be disposed of; this is further complicated by the fact that this wastewater contains large amounts of table salt.

[0013] Solvolysis with methanol has also been performed for polythiourethane networks (L. Li, X. Chen, J.M. 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 laboriously separated from the resulting solution. However, direct repolymerization is not possible. The reaction is not sustainable because it uses the problematic solvent dichloromethane, and the long reaction times are hardly feasible for commercial use.

[0014] Furthermore, a polythiourethane based on a cyclic monomer of carbonyl sulfide (COS) and methylaziridine was prepared (S. Wu, M. Luo, DJ

[0015] 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). Upon heating the polymer, a cyclic monomer can reform. However, structural variations of the polymer are not possible with this method, and the aliphatic, linear polythiourethane does not exhibit mechanical properties comparable to cross-linked polymers, e.g., those based on aromatic isocyanates.

[0016] The invention is based on the object of creating a process for the chemical recycling of polythiourethanes which enables the direct production of repolymerizable monomers and / or oligomers which can be repolymerized again without the need for complicated purification of the resulting monomer / oligomer mixture.

[0017] A further object of the invention is to provide a process for the chemical recycling of polythiourethanes which is simple to carry out, does not involve complicated processing steps, follows the principles of sustainability and which allows the reuse of polythiourethanes in the sense of a circular economy.

[0018] These objects are achieved by the method according to claim 1.

[0019] Preferred variants of the process according to the invention are described in subclaims 2 to 12.

[0020] The invention relates to a process for the recycling of polythiourethanes comprising the following measures: a) initial charging of a mixture of polythiourethane and monofunctional thiol and optionally a polar aprotic solvent, wherein at least one mole of monofunctional thiol is used per mole of thiourethane bond of the polythiourethane, b) depolymerization of the polythiourethane by treating the mixture from step a) at a first reaction temperature, whereby di- or higher-functional thiols are formed from the polythiourethane and monomeric and oligomeric thiourethanes terminated with monofunctional thiols, c) optionally separating impurities from the mixture obtained in step b) and / or from solvent, d) optionally adding di- or higher-functional isocyanate and di- or higher-functional thiol, and e) treating the mixture from step b), c) or d) at a second reaction temperature which is lower,is equal to or greater than the first reaction temperature, under a pressure reduced compared to step b), c) or d), whereby the monofunctional thiol is removed from the mixture and polymerization of the monomeric and oligomeric thiourethanes from step b) and any compounds added in step d) takes place. A monofunctional thiol is used in the process according to the invention. Furthermore, the monofunctional thiol is removed from the reaction mixture during the repolymerization.

[0021] The polythiourethanes used in the invention can be linear, branched, or crosslinked. Polythiourethane networks are preferred.

[0022] Examples of linear polythiourethanes are polymers with at least 80 mol%, based on the total amount of the polymer, of structural units of the formula (I)

[0023] [-SR 1 -S-CO-NH-R 2 -NH-CO] m- (I) and optionally with up to 20 mol%, based on the total amount of the polymer, of structural units of the formula (Ha) or (Hb)

[0024] [-OR 3 -O-CO-NH-R 4 -NH-CO] n - (Ha)

[0025] [-NR 9a -R 9 -NR 9a -CO-NH-R 10 -NH-CO] n - (Hb) where R 1 , R 2 , R 3 , R 4 , R 9 and R 10 are independently divalent organic radicals, in particular alkylene, cycloalkylene, arylene, aralkylene or heterocyclylene,

[0026] R 9a is hydrogen or a monovalent organic radical, in particular hydrogen, alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl, and very particularly preferably hydrogen or Ci-C6-alkyl, or the radicals R 9a and R 9together with the two nitrogen atoms form a piperidinyl radical, 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 an integer of at least 1, in particular from 1 to 5, with the proviso that R 1 , R 2 , R 3 , R 4 , R 9 , R 9a and R 10 can also take on different meanings within a molecule within the given definitions.

[0027] Examples of branched polythiourethanes or polymer networks are polymers containing at least 80 mol%, based on the total amount of the polymer, of structural units of the formula (III)

[0028] [-SR 5 -(S-CO-NH-R 6 -(NH-CO)p) o ] m- (III) and optionally with up to 20 mol%, based on the total amount of the polymer, of structural units of formula (Ha) and / or formula (IIb) and / or formula (IVa) and / or formula (IVb)

[0029] [-OR 3 -O-CO-NH-R 4 -NH-CO] n - (Ha)

[0030] [-NR 9a -R 9 -NR 9a -CO-NH-R 10 -NH-CO] n - (llb)

[0031] [-OR 7 -(O-CO-NH-R 8 -(NH-CO) r )q] n - (IVa)

[0032] [-(NR 11a -R 11 -(NR 11a -CO-NH-R 12 -(NH-CO) r )q] n - (IVb) where R 5 is an (o+1 )-valent organic radical, in particular an (o+1 )-valent alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl radical,

[0033] R 6 is a (p+1)-valent organic radical, in particular a (p+1)-valent alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl radical,

[0034] R 3 , R 4 , R 9 and R 10 are independently divalent organic radicals, in particular alkylene, cycloalkylene, arylene, aralkylene or heterocyclic,

[0035] R 9a and R 11a independently of one another are hydrogen or monovalent organic radicals, in particular hydrogen, alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl, and very particularly preferably hydrogen or Ci-Cß-alkyl, or the radicals R 9a and R 9 together with the two nitrogen atoms form a piperidinyl radical, R 7 and R 11 independently of one another are (q+1 )-valent organic radicals, in particular (q+1 )-valent alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl radicals, or the radicals R 11a and R 11 together with the two nitrogen atoms form a piperidinyl residue,

[0036] R 8 and R 12are independently of one another (r+1)-valent organic radicals, in particular (r+1)-valent alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl radicals, m is an integer of at least 10, preferably from 10 to 100,000 and in particular from 15 to 1,000, n is an integer of at least 1, in particular from 1 to 5, o and p are independently of one another 1 to 10, preferably 1, 2 or 3, with the proviso 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 can also take on different meanings within a molecule within the framework of the given definitions, that o and / or p is 2 to 10, preferably 2 or 3, at least once per molecule, that q and / or r - if present - can also take on different meanings within a molecule within the framework of the given definitions, and that q and r are 1 to 10, preferably 1, 2 or 3.

[0037] The polythiourethanes used according to the invention and the polymers produced by repolymerization can be homopolymers or copolymers.

[0038] The difference between branched polythiourethanes and polythiourethane networks is that the former are thermoplastic polymers with more or fewer branching points, whereas polymer networks consist of dimensionally interconnected polymer chains. Loose cross-linking between the main chains leads to elastomers, while tight cross-linking between the main chains leads to thermosets.

[0039] Polymer networks made of polythiourethanes form a subgroup of thermosets and are characterized by vitrimeric behavior. This is a class of plastics derived from and strongly similar to traditional thermosets. Vitrimers are composed of covalent networks that can change their topology through thermally activated bond exchange reactions. Vitrimers are strong glass formers. At high temperatures, they flow and behave like a viscoelastic fluid. At low temperatures, the exchange reactions are frozen, and the vitrimers behave like traditional thermosets.

[0040] If one of the radicals denotes alkyl in this description, the alkyl group can be either branched or unbranched. An alkyl group typically contains one to twenty carbon atoms, preferably one to ten 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 with one to six carbon atoms are particularly preferred. Alkyl groups with multiple carbon atoms may optionally contain one or more non-adjacent oxygen atoms and / or one or more non-adjacent carboxylic acid ester residues -CO-O- in the chain. The term "alkyl" therefore also includes (poly)alkyl ether groups and (poly)alkyl esters.Alkyl groups may optionally be substituted, for example with alkoxy, cycloalkyl, aryl, heterocyclyl, halogen, carboxyl ester, carboxylamide, sulfonic acid ester, sulfonic acid amide or alkylcarbonyl.

[0041] If one of the radicals in this description denotes cycloalkyl, the cycloalkyl group is typically a cyclic group containing three to eight, preferably five, six, or seven, ring carbon atoms, each of which may be independently substituted. Examples of substituents are alkyl groups or two alkyl groups that, together with the ring carbon atoms to which they are attached, may form another ring. Examples of cycloalkyl groups are cyclopropyl, cyclopentyl, or cyclohexyl. Cycloalkyl groups may optionally be substituted, for example with alkyl, alkoxy, cycloalkyl, aryl, heterocyclyl, halogen, carboxyl ester, carboxylamide, sulfonic acid ester, sulfonic acid amide, or alkylcarbonyl.

[0042] If one of the radicals in this description is aryl, the aryl group is typically a cyclic aromatic group containing five to fourteen ring carbon atoms, each of which may be independently substituted. Examples of substituents are alkyl groups or two alkyl groups that, 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. Aryl groups may optionally be substituted, for example with alkyl, alkoxy, cycloalkyl, aryl, heterocyclyl, halogen, carboxyl ester, carboxylamide, sulfonic acid ester, sulfonic acid amide, or alkylcarbonyl.

[0043] If one of the radicals in this description denotes aralkyl, the aralkyl group is typically an aryl group, where aryl has already been defined above, to which at least one alkyl group is covalently bonded. The aralkyl group can be substituted on the aromatic ring, for example, with alkyl groups or with halogen atoms. An example of an aralkyl group is benzyl. Aralkyl groups can optionally be substituted, for example, with alkyl, alkoxy, cycloalkyl, aryl, heterocyclyl, halogen, carboxyl ester, carboxylamide, sulfonic acid ester, sulfonic acid amide, or alkylcarbonyl.

[0044] If one of the radicals in this description is heterocyclyl, it is typically a cyclic group with three to ten ring carbon atoms and at least one ring heteroatom, each of which may be independently substituted. Examples of substituents are alkyl groups, or two alkyl groups which, together with the ring carbon atoms to which they are attached, may form another ring. Examples of heteroatoms are oxygen, nitrogen, or sulfur. Examples of heterocyclyl groups are furyl, thienyl, pyrrolyl, imidazolyl, pyridyl, piperidinyl, or isocyanurate. Heterocyclyl groups can be aromatic or non-aromatic. Heterocyclyl groups can optionally be substituted, for example with alkyl, alkoxy, cycloalkyl, aryl, halogen, carboxyl ester, carboxylamide, sulfonic acid ester, sulfonic acid amide, or alkylcarbonyl.

[0045] If one of the radicals in this description represents a halogen, it means a covalently bonded fluorine, chlorine, bromine, or iodine atom. Chlorine is preferred.

[0046] If one of the radicals denotes alkylene in this description, the alkylene group can be either branched or unbranched. Alkylene groups correspond to the definition given for alkyl groups, with the modification that the group is attached to the rest of the molecule via two covalent bonds instead of one covalent bond. Alkylene groups with multiple carbon atoms can optionally have one or more non-adjacent oxygen atoms and / or one or more non-adjacent carboxylic acid ester radicals -CO-O- in the chain. The term alkylene therefore also encompasses (poly)alkylene ether groups and (poly)alkylene ester groups. Particular preference is given to alkylene groups with two to twenty, in particular with two to twelve, carbon atoms, in particular those which have one to three non-adjacent oxygen atoms in the alkylene chain.

[0047] If one of the radicals in this description denotes cycloalkylene, the cycloalkylene group is typically a cyclic group containing three to eight, preferably five, six, or seven, ring carbon atoms, each of which may be independently substituted. Cycloalkylene groups correspond to the definition given for cycloalkyl groups, with the modification that the group is attached to the rest of the molecule via two covalent bonds instead of one. Cyclohexylene is particularly preferred.

[0048] If one of the radicals in this description denotes arylene, the arylene group is typically a cyclic aromatic group containing five to fourteen ring carbon atoms, each of which may be independently substituted. Arylene groups correspond to the definition given for aryl groups, except that the group is attached to the rest of the molecule via two covalent bonds instead of one. Phenylene is particularly preferred.

[0049] If one of the radicals in this description denotes aralkylene, the aralkylene group is typically an arylene group, where arylene has already been defined above, to which at least one alkylene group is covalently bonded. Aralkylene groups correspond to the definition given for aralkyl groups, 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.

[0050] If one of the radicals in this description denotes heterocycles, the heterocycle group is typically a cyclic group with three to ten ring carbon atoms and at least one ring heteroatom, each of which may be independently substituted. Heterocycle groups correspond to the definition given for heterocyclyl groups, with the modification that the group is attached to the rest of the molecule via two covalent bonds instead of one. Isocyanurate is particularly preferred.

[0051] Trivalent or higher alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl radicals correspond to the definitions given above for alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl, with the modification that these groups are attached to the rest of the molecule by three or more covalent bonds instead of one covalent bond.

[0052] The polythiourethanes used according to the invention can be prepared using conventional polymerization processes. Examples include bulk polymerization, solution polymerization, or emulsion or suspension polymerization. These procedures are known to those skilled in the art. The polythiourethanes used according to the invention can be prepared, for example, by polymerizing diisocyanates of formula (V) and / or higher-functionality isocyanates of formula (VI) with dithiols of formula (VII) and / or with higher-functionality thiols of formula (VIII).

[0053] OCN-R 2 -NCO (V), OCN-R 6 -(NCO) P (VI),

[0054] HS-R 1 -SH (VII), HS-R 5 -(SH) O (VIII), where R 1 , R 2 , R 5 , R 6 , o and p have the meaning defined above.

[0055] If appropriate, the reaction mixture may contain a total of up to 20 mol%, based on the total amount of polyisocyanates of the formulas (V) and (VI), of further polyisocyanates of the formulas (IX), (X), (XI) and / or (XII)

[0056] OCN-R 4 -NCO (IX), OCN-R 8 -(NCO) r (X),

[0057] OCN-R 10 -NCO (XI), OCN-R 12 -(NCO) r (XII), where R 4 , R 8 , R 10 , R 12 and r have the meaning defined above.

[0058] Optionally, the reaction mixture may contain a total of up to 20 mol.%, based on the total amount of thiols of the formulas (VII) and (VIII), of polyhydroxy compounds or of polyamine compounds of the formulas (XIII), (XIV), (XV) and / or (XVI)

[0059] HO-R 3 -OH (XIII), HO-R 7 -(OH) q (XIV),

[0060] HR 9a NR 9 -NR9a H (XV), HR 11a NR 11 -(NR 11a H) q (XVI), where R 3 , R 7 , R 9 , R 9a , R 11 , R 11a and q have the meaning defined above. Instead of or in addition to the di- or higher-functional isocyanates, it is also possible to use blocked multifunctional isocyanates, which can be converted into isocyanates by heating. Blocking agents include, in particular, alcohols, phenols, amines, oximes, amides, imides, imidazoles, pyrazoles, and triazoles.

[0061] The monomers required for the production of the polythiourethanes used in the invention are known and are commercially available or can be synthesized using standard organic chemistry methods. These may be monomers produced by petrochemical and / or bio-based processes.

[0062] The chain length, degree of branching, and crosslinking density of the polythiourethanes used in the invention can be adjusted by selecting the type and amount of monomers. The procedures for this are known to those skilled in the art.

[0063] The polythiourethanes used according to the invention may contain additives typically used together with such polymers. Examples include processing aids or additives that impart specific properties to the polymers. Examples include dyes, pigments, heat stabilizers, glass or carbon fibers, fillers, antioxidants, UV stabilizers, antistatic agents, lubricants, biocides, preservatives, or blowing agents.

[0064] The process according to the invention comprises carrying out a depolymerization. For this purpose, polythiourethane is combined with a monofunctional thiol (step b). The depolymerization can be carried out in the presence or absence of a polar aprotic solvent.

[0065] The depolymerization preferably takes place in the absence of a solvent. The polythiourethane can be in the form of a solvent, a solution, a suspension, or a paste, and can be used in any desired form. Preferably, the process is carried out in the form of a solvent, and in particular, comminuted polythiourethane is used, for example, as a powder or in the form of pellets.

[0066] Solvents that can be used in the process according to the invention are aprotic polar compounds that are liquid at room temperature (25 °C).

[0067] Polar aprotic solvents include ketones, e.g. acetone, lactones, e.g. gamma-butyrolactone, lactams, e.g. α / -methyl-2-pyrrolidone, nitriles, e.g. acetonitrile, nitro compounds, e.g. nitromethane, tertiary carboxamides, e.g. dimethylformamide or dimethylacetamide, urea derivatives, e.g. tetramethylurea or dimethylpropyleneurea (DMPU), sulfoxides, e.g. dimethyl sulfoxide (DMSO), sulfones, e.g. sulfolane, or carbonic acid esters, e.g. dimethyl carbonate or ethylene carbonate.

[0068] In step b) a compound of formula (XVII) is used as monofunctional thiol

[0069] R 13 -SH (XVII), where R 13 is a monovalent organic radical, in particular alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl.

[0070] Mixtures of different monofunctional thiols can also be used.

[0071] The thiols used can be based on petrochemical or bio-based raw materials that contain functionalities suitable for thiofunctionalization. These suitable functionalities include, for example, unsaturated carbon-carbon bonds, epoxy groups, or halogens. These functionalities can also be introduced into the starting compound through one or more intermediate steps.

[0072] The thiol is used in an equimolar amount or, preferably, in a molar excess. The amount of thiol is selected such that a mixture of polythiourethane and thiol is present in which at least one mole of thiol is present per mole of thiourethane bond in the polythiourethane. Preferably, 1 to 100 moles, in particular 1.5 to 50 moles, of thiol are used per mole of thiourethane bond in the polythiourethane.

[0073] Depolymerization can be carried out at temperatures between 20 and 220 °C. Preferred reaction temperatures are in the range of 30 and 210 °C, especially in the range of 50 and 200 °C.

[0074] The duration of the depolymerization reaction can vary widely. Typically, the depolymerization reaction can last from 5 minutes to 60 hours, preferably from 10 minutes to 30 hours, and especially from 10 minutes to 20 hours.

[0075] A catalyst can be used for the depolymerization. These catalysts can be those also used for the production of polythiourethanes. Examples include basic catalysts such as tertiary amines, e.g., diisopropylethylamine or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), phosphines such as triphenylphosphine, or heavy metal compounds, especially organic tin compounds such as dibutyltin dilaurate.

[0076] If a catalyst is used, the proportion of catalysts in the reaction mixture is typically 0.01 to 10 mol%, based on the amount of the reaction mixture, preferably 0.1 to 3 mol%.

[0077] Depolymerization preferably takes place in bulk, i.e., in the absence of solvents or dispersants. The reaction mixture preferably consists only of polythiourethane, thiol, and optionally a catalyst.

[0078] In the depolymerization step, the polythiourethane is cleaved, forming oligomeric and monomeric compounds. These are converted by reaction with the thiol into thiol-terminated monomers 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 thus the length of the individual cleavage fragments or the number of thiourethane repeat units in the resulting oligomers, is determined by the molar ratio of thiol to the starting compound.

[0079] In addition to monomeric di- or higher-functional thiourethanes, thiol-capped oligothiourethanes are also available. These are generally oligomers with 2 to 16, preferably 2 to 8, and especially 2 to 6 thiourethane units in the molecule. Typically, more than 50%, especially more than 80%, of all oligomers have degrees of oligomerization of 2 to 16.

[0080] The initial reaction mixture (step a) is usually a mixture of solids or of solids and liquids, or a solution or dispersion of reactants in a solvent. Depolymerization results in an oligomer mixture, which may still contain solid components from the starting mixture. At the end of depolymerization, a stirrable mixture is always obtained. This mixture is preferably liquid.

[0081] During depolymerization, in step b) monomers and / or oligomers, i.e. thiourethane monomers and / or thiourethane oligomers, are produced from the starting polythiourethanes by cleavage.

[0082] The monomers and oligomers have mercapto groups of formula (XVIII) which are linked to the rest of the molecule via thioisocyanate groups R 13 -S- (XVIII) where R 13has the meaning defined above. These mercapto groups can also take on different meanings within a molecule within the given definitions.

[0083] Optionally, the oligomers may contain free mercapto groups of the formula -SH, which are attached via the radical R 5 are connected to the molecule.

[0084] The monomers are compounds of formulas (XIX) or (XX) derived from a polyisocyanate

[0085] R 13 -S-CO-NH-R 2 -NH-CO-SR 13 (XIX),

[0086] R 13 -S-CO-NH-R 6 -(NH-CO-SR 13 ) P (XX), where R 2 , R 6 and R 13 have the meaning defined above, and p is 2 to 10, preferably 2 or 3.

[0087] The oligomers are compounds of formula (XXI) or compounds containing structural units of formula (XXII) derived from at least two polyisocyanates

[0088] R 13 -S-CO-NH-R 2 -NH-CO-(SR 1 -S-CO-NH-R 2 -NH-CO-) S SR 13 (XXI)

[0089] (R 13 S-CO-NH) W (SH) X (NH-CO-SR 13 ) y where R 1 , R 2 and R 13 have the meaning defined above, R 5 is a (x+z2+1)-valent organic radical, in particular a (x+z2+1)-valent alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl radical,

[0090] R 6a (w+z1+1)-valent or a (y+z2+1)-valent organic radical, in particular a (w+z1+1)-valent or a (y+z2+1)-valent alkyl, cycloalkyl, aryl, aralkyl radical or heterocyclyl radical, s is an integer from 1 to 15, preferably from 1 to 12, w, x and y are integers from 0 to 9, z1 and z2 are integers from 1 to 10, the sum w+z1 is an integer from 1 to 10, the sum x+z2 is an integer from 1 to 10, the sum y+z2 is an integer from 1 to 10. with the proviso that R 1 , R 2 , R 5 , R 6 , R 13 , w, x, y, z1 and z2 can also have different meanings within a molecule within the framework of the given definitions, and that the oligomer of formula (XXII) has further groups of formula (XVIII) which are linked to the oligomer via thioisocyanate groups

[0091] The oligomers with the structural units of formula (XXII) preferably contain at least 80 mol%, in particular 100 mol%, based on the total amount of the oligomer, of these structural units.

[0092] The oligomers containing the structural units of formula (XXII) may optionally contain up to 20 mol%, based on the oligomer, of structural units of the above-mentioned formulas (IVa) or (IVb).

[0093] In addition to the residues of formula (XVIII), the oligomers may also contain amino end groups derived from the isocyanates. These end groups have the structure of formula (XXIII).

[0094] (H2N) z3 -R 6 -(NHCO)pi Z 3- (XXIII), wherein R 6 and p have the meanings defined above, and z3 represents an integer from 1 to 10.

[0095] The proportion of these amino end groups is up to 30 mol%, preferably up to 10 mol% and in particular 0 mol%, based on the total amount of end groups in the molecule.

[0096] Some species formed by depolymerization from the mixture of monomeric and oligomeric cleavage pieces are described below as examples.

[0097] The mixture contains monomers of the above-mentioned formulas (XIX) or (XX). Furthermore, the mixture contains dimers, trimers, and their analogous higher oligomers.

[0098] An example of possible dimers are compounds of the formulas (XXIV), (XXVa) or (XXVb)

[0099] R 13 -S-CO-NH-R 2 -NH-CO-SR 1 -S-CO-NH-R 2 -NH-CO-SR 13 (24)

[0100] (R 13 -S-CO-NH)2-R 6 -NH-CO-SR 5 -S-CO-NH-R 6 -(NH-CO-SR 13 )2(XXVa),

[0101] R 13 -S-CO-NH-R 6-NH-CO-SR 5 -S-CO-NH-R 6 -(NH-CO-SR 13 )2(XXVb),

[0102] Further examples of monomers, dimers and trimers derived from trifunctional isocyanates and monofunctional mercaptans are listed below.

[0103] The monofunctional mercaptans are marked by — —.

[0104] The trifunctional isocyanates are characterized by . Monomer

[0105] The compositions of monomeric and / or oligomeric cleavage pieces are novel and are also the subject of the present invention.

[0106] The proportion of monomeric cleavage fragments of formula (XIX) or (XX) in the composition can be from 0 to 100 mol%, based on the total amount of cleavage fragments in the composition. The proportion of oligomeric cleavage fragments of formula (XXI) or (XXII) in the composition can also be from 0 to 100 mol%, based on the total amount of cleavage fragments in the composition.

[0107] The proportion of monomers and oligomers in the composition can be controlled by the amount of thiol used in step b). The invention also relates to the use of these compositions for the production of polythiourethanes or copolymers containing polythiourethane groups.

[0108] Preferred are compositions of monomeric and oligomeric cleavage pieces in which R 1 and R 2 independently of one another are alkylene, cycloalkylene, arylene, aralkylene or heterocyclylene, R 5a (x+z2+1 )-valent alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl radical, R 6 a (w+z1 +1 )-valent alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl radical, R 13 is an alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl radical, and w+z1, x+z2 and y+z2 independently of one another are 1, 2 or 3.

[0109] Particularly preferred are compositions of monomeric and oligomeric cleavage pieces, wherein R 1 Cycloalkylene, arylene, aralkylene or heterocyclylene, especially arylene and and R 5 a (x+z2+1 )-valent cycloalkyl, aryl, aralkyl or heterocyclyl radical, in particular a (x+z2+1 )-valent aryl radical.

[0110] Also preferred are compositions of monomeric and oligomeric cleavage pieces which do not contain structural units of the formula (IIa), (IIb), (IVa) and / or (IVb).

[0111] After depolymerization, the resulting oligomer mixture can be freed from unwanted additives and / or solvent (step c). This can be done, for example, by filtration or distillation, or by other separation operations known to those skilled in the art.

[0112] The oligomer mixture thus prepared can be repolymerized into a polymer, e.g., a polythiourethane, immediately after its preparation or after an interruption at any later time. During repolymerization of the oligomer mixture, the monomer / oligomer mixture is placed under reduced pressure after optional addition of a catalyst so that the thiol can be removed, with simultaneous repolymerization occurring (step e).

[0113] For the repolymerization in step e), the same catalysts can be used as for the depolymerization in step b).

[0114] If a catalyst is used, the proportion of catalysts in the reaction mixture is typically 0.01 to 10 mol%, based on the amount of the reaction mixture, preferably 0.1 to 3 mol%.

[0115] The repolymerization in step e) can be carried out at temperatures between 20 and 220°C. Preferred reaction temperatures are in the range of 30 to 210°C, in particular in the range of 50 to 200°C.

[0116] The duration of the repolymerization reaction in step e) can vary widely. 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.

[0117] The pressure during the repolymerization reaction in step e) is below atmospheric pressure. Typically, the pressure in the repolymerization stage is 0.01 to 0.9 atm, preferably 0.05 to 0.5 atm.

[0118] The repolymerization in step e) is preferably carried out in bulk, i.e. in the absence of solvents or dispersants.

[0119] As a rule, the reaction mixture in the repolymerization stage in step e) consists only of the monomer and oligomer mixture from the depolymerization and, optionally, a catalyst. Alternatively, in a preceding step d), di- and / or higher-functional thiol and di- and / or higher-functional isocyanate can be added to the monomer and oligomer mixture from the depolymerization before the repolymerization in step e. These di- and / or higher-functional isocyanates, together with the monomers and oligomers from step b), form a repolymer. The proportion of such additional polymerizable components in the reaction mixture is typically up to 90 wt. %, based on the total amount of the reaction mixture.

[0120] In step d), mixtures of difunctional and higher-functional isocyanates, or of different difunctional isocyanates, or of different higher-functional isocyanates can also be used. The same applies to difunctional or higher-functional thiols.

[0121] In this variant, the reaction mixture in the repolymerization stage preferably consists only of monomer and oligomer mixture from the depolymerization, added thiols and isocyanates, and optionally catalyst.

[0122] Preferably, a higher temperature is chosen in the repolymerization stage in step e) than in the depolymerization stage.

[0123] After completion of the repolymerization in step e), the reaction mixture is cooled and any catalyst present is inactivated.

[0124] The resulting repolymer can then be subjected to a molding process. Alternatively, the resulting repolymer can be crushed, for example, formed into pellets or ground into powder before being subjected to further processing.

[0125] The reactions can be carried out in conventional stirred reactors, dispersers, high-speed mixers, jet dispersers, reaction extruders, extruders, or mixer-kneaders. Depolymerization can be carried out separately from repolymerization, preferably in different reactors.

[0126] The process according to the invention can be carried out batchwise or continuously. Batchwise processes are preferred.

[0127] Suitable di- or higher-functional isocyanates are all known aliphatic, cycloaliphatic, araliphatic or aromatic isocyanates, with aromatic di- or polyisocyanates being preferred.

[0128] The following isocyanates are preferably used for the preparation of the polythiourethanes used according to the invention or for repolymerization:

[0129] Phenyl diisocyanates, phenyl triisocyanates, toluene diisocyanates, toluene triisocyanates, diphenylmethane diisocyanates, diphenyl ether diisocyanates, alkylene diisocyanates such as tetra-, penta-, hexa-, and octamethylene diisocyanate or their trimers, alkylene ether diisocyanates or triisocyanates, xylylene diisocyanates or triisocyanates, mono-, di-, tri-, or tetramethylxylylene diisocyanates or triisocyanates, dicyclohexylmethane diisocyanates, dicyclohexyl ether diisocyanates, cyclohexyl diisocyanates or triisocyanates, mono-, di-, tri-, or tetraalkylcyclohexyl diisocyanates such as isophorone diisocyanate, norbornane diisocyanate, triphenylmethane triisocyanates, biphenyl diisocyanates, isocyanurate tris-N-alkylene isocyanates, or naphthalene diisocyanates or triisocyanates. Mixtures of two or more of these compounds may also be used. The isocyanates used can come from petrochemical as well as bio-based processes.

[0130] Instead of the above-mentioned di- or higher-functional isocyanates, their blocked variants can also be used. Examples of these are isocyanates that have been blocked with alcohols, phenols, amines, oximes, amides, imides, imidazoles, pyrazoles, and triazoles and can be converted into isocyanates by heating. Particularly preferred for the preparation of the isocyanates used according to the invention are

[0131] Polythiourethanes or the following isocyanates are used for repolymerization:

[0132] 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, the trimer of Hexane-1,6-diisocyanate, Isophorone diisocyanate, Norbornane diisocyanate, Tetramethylxylylene diisocyanate, 4,4'-Dicyclohexylmethane diisocyanate, Triisocyanatononane and Cyclohexane-1,4-diisocyanate.

[0133] The following di- or higher-functional thiols are preferably used for production or repolymerization:

[0134] Phenyldithiols, phenyltrithiols, toluene dithiols, toluene trithiols, diphenylmethane dithiols, diphenyl ether dithiols, alkylenedithiols, such as di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-, undeca- and dodecamethylene dithiols, alkylene tri- and tetrathiols such as terpene thiols, Myrcentrithiol, farnesene tetrathiol, alkylene ether dithiols, xylylenedithiols, mono-, di-, tri- or tetramethylxylylenedithiols, dicyclohexylmethane dithiols, dicyclohexyl ether dithiols, cyclohexyl dithiols, mono-, di-, tri- or tetraalkylcyclohexyl dithiols, triphenylmethane trithiols, biphenyl dithiols, Isocyanurate-tr / s-AZ-alkylene thiols, Naphthalenedithiols, naphthalenetrithiols, di-, tri- or tetraesters of mercaptoalkanoic acids with di-, tri- or tetrahydric alcohols, in particular di-, tri- or tetraesters of 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 may also be used.

[0135] The following di- or higher-functional thiols are particularly preferably used for the preparation or repolymerization: hexanedithiol, dodecanedithiol, limonenedithiol, myrcenedithiol, farnesene tetrathiol, pentaerythritol tetra(3-mercaptopropionate), trimethylolpropane tri(3-mercaptopropionate), tr / s-[2-(3-mercaptopropionyloxy)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).

[0136] The following monofunctional thiols are preferably used for depolymerizing the polythiourethanes used according to the invention:

[0137] Phenylthiols, toluenethiols, xylylthiols, alkylthiols, such as alkylthiols with one to twelve carbon atoms, mono-, di-, tri-, or tetramethylxylylthiols, cyclohexylthiols, mono-, di-, tri-, or tetraalkylcyclohexylthiols, naphthalenethiols, esters of mercaptoalkanoic acids with monohydric alcohols, especially esters of 3-mercaptopropionic acid or thioglycolic acid with monohydric aliphatic alcohols, such as methanol or ethanol. Mixtures of two or more of these compounds can also be used.

[0138] The following monofunctional thiols are particularly preferably used for depolymerizing the polythiourethanes used according to the invention:

[0139] Ethanethiol, 1-propanethiol, 2-propanethiol, hexanethiol, thiophenol or alkyl esters of 3-mercaptopropionic acid or thioglycolic acid.

[0140] In preferred embodiments of the process according to the invention, the depolymerization in step b) and the repolymerization in step e) are carried out in substance.

[0141] In further preferred embodiments 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. This catalyst is preferably selected from the group consisting of alkali metal hydroxide, tertiary amine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), phosphine, or organic tin compounds.

[0142] In further preferred embodiments of the process according to the invention, the first reaction temperature and the second reaction temperature are in the range between 30 °C and 210 °C, preferably between 50 and 200 °C.

[0143] In additional preferred embodiments of the process according to the invention, 1.5 to 50 moles of the monofunctional thiol are used in step a) per mole of thiourethane bond of the polythiourethane.

[0144] In further preferred embodiments of the process according to the invention, oligomeric polythiourethanes having two to sixteen repeat units are produced in the depolymerization stage.

[0145] In a particularly preferred embodiment of the process according to the invention, monofunctional thiols selected from the group of alkylthiols having two to ten carbon atoms, in particular ethanethiol, 1-propanethiol, 2-propanethiol, hexanethiol, thiophenol, alkyl esters of 3-mercaptopropionic acid or thioglycolic acid or mixtures of two or more thereof, are used in step a).

[0146] Particularly preferred embodiments of the process according to the invention are those in which polythiourethane networks are used in step a).

[0147] Also preferred are processes in which a polythiourethane is used in step a), which is a polythiourethane network composed of bio-based monomers. Further preferred are processes in which the monofunctional thiol used in step a) is a bio-based raw material and / or in which the di- or higher-functional isocyanate or thiol used in step d) is a bio-based raw material.

[0148] Further particularly preferred embodiments of the process according to the invention are those in which the thiol obtained from the polythiourethane in step b) is a tri- or higher-functional, preferably a trifunctional thiol.

[0149] The polythiourethanes obtained by repolymerization according to the invention, like their starting materials, can be used in a wide variety of technical fields. The polythiourethanes can be formed into molded parts of any shape. Examples include fibers, films, or molded articles obtainable from the polythiourethane produced by repolymerization according to the invention by any molding process, for example, by injection molding, compression molding, foam injection molding, gas injection molding, blow molding, film casting, calendering, lamination, or coating of any substrate.

[0150] Figure 1 illustrates the method according to the invention by way of example.

[0151] This figure depicts step A preceding the process according to the invention. This involves the synthesis of polythiourethane networks (from multifunctional thiols; shown here as an example for trithiols, and multifunctional isocyanates; shown here as an example for diisocyanates). The recycling of these polythiourethanes is depicted in steps B and C. The polythiourethane networks are depolymerized into the monomers or a mixture of oligomers using a monofunctional thiol (step B). The mixture is repolymerized into a polymer network by splitting off and removing the thiol (step C).

[0152] The depolymerization with a monofunctional thiol shown in Figure 1 and the subsequent repolymerization can be carried out as follows: The polythiourethane networks are depolymerized for recycling with the aid of a monofunctional thiol (e.g., thioglycolic acid, butyl 3-mercaptopropionate, 3-mercaptopropionic acid). The depolymerization preferably takes place in bulk. The thiol is used in excess. The reaction temperature here is between 20 and 220 °C, ideally between 50 and 200 °C. A catalyst can be used for the reaction, for example, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) or DBU with triphenylphosphine, or organic tin compounds. For repolymerization, the monomer / oligomer mixture is heated after optional addition of the catalyst, and the thiol is removed under vacuum. This regenerates the polythiourethane network.

[0153] The following examples illustrate the process according to the invention without limiting it

[0154] Synthesis of a polythiourethane: Poly(Pentaeryth r'\to\-tetrakis(2-mercaptoacetate)-co-hexamethylene diisocyanate):

[0155] 44 g of pentaerythritol tetraacetate (0.102 mol) were stirred with 34.3 g of hexamethylene diisocyanate (0.204 mol) and then allowed to stand at room temperature for 3 days. The colorless solid was ground using a laboratory mill (IKA A10 basic).

[0156] DSC: T g = 63 °C.

[0157] Elemental analysis:

[0158] Calculated [%]: C: 45.30 H: 5.77 N: 7.29 S: 16.68

[0159] Found [%]: C: 45.49 H: 5.94 N: 7.56 S: 16.35

[0160] Example 1: Degradation with 1-hexanethiol and repolymerization:

[0161] 188 mg polythiourethane network (pentaerythritol-tefra / s(2-mercaptoacetate)-co-

[0162] Hexamethylene diisocyanate (ratio 1 / 2; 0.24 mmol (calculated based on pentaerythritol tetrakis(2-mercaptoacetate) repeating unit) was added to 1-hexanethiol (145 mg; 1.22 mmol) and 0.57 mL of dry dimethylformamide in a microwave vial. The vial was sealed airtight, and the mixture was stirred at 200 °C for 20 minutes.

[0163] To the resulting solution, 1.60 g of pentaerythritol tetraacetate (2-mercaptoacetate) (3.70 mmol) and 1.29 g of hexamethylene diisocyanate (7.67 mmol) were added. The mixture was heated to 70 °C with stirring and a vacuum of 0.1 mbar was applied. After the volatile components had evaporated, the colorless gel was cured overnight at 60 °C and 4 mbar.

[0164] For 2 degradation with 1-hexanethiol and repolymerization:

[0165] 28 mg of polythiourethane network (pentaerythritol tetrakis(2-mercaptoacetate)-co-hexamethylene diisocyanate; ratio 1 / 2; 0.04 mmol (calculated per pentaerythritol tetrakis(2-mercaptoacetate) repeating unit) were added to a microwave vial containing 1-hexanethiol (22 mg; 0.18 mmol) and 0.50 mL of dry dimethylformamide. The vial was sealed hermetically, and the mixture was stirred at 200 °C for 40 minutes.

[0166] To the resulting solution, 61 mg of pentaerythritol tetrachloride (2-mercaptoacetate) (0.14 mmol) and 50 mg of hexamethylene diisocyanate (0.30 mmol) were added. The mixture was heated to 70 °C with stirring and a vacuum of 0.1 mbar was applied. After the volatile components had evaporated, the colorless gel was cured overnight at 60 °C and 4 mbar.

[0167] Example 3: Degradation with 1-hexanethiol and repolymerization:

[0168] 1.46 g of polythiourethane network (pentaerythritol tetrakis(2-mercaptoacetate)-co-hexamethylene diisocyanate; ratio 1 / 2; 1.89 mmol (calculated per pentaerythritol tetrakis(2-mercaptoacetate) repeating unit)) were added to a microwave vial with 1-hexanethiol (1.12 g; 9.46 mmol) and 2.63 mL of dry dimethylformamide. The vial was sealed hermetically, and the mixture was stirred at 200 °C for 60 minutes. 110 mg of pentaerythritol tetrakis(2-mercaptoacetate) (0.25 mmol) and 96 mg of hexamethylene diisocyanate (0.57 mmol) were added to 408 mg of the resulting solution (containing 207 mg of substance). The mixture was heated to 70 °C while stirring. 9 C and a vacuum of 0.1 mbar was applied. After the volatile components had evaporated, the colorless gel was cured overnight at 60 °C and 4 mbar vacuum.

Claims

Patent claims 223bb01.wo 1 . A process for the recycling of polythiourethane comprising the following measures: a) initial charge of a mixture of polythiourethane and monofunctional thiol and optionally a polar aprotic solvent, wherein at least one mole of monofunctional thiol is used per mole of thiourethane bond of the polythiourethane, b) depolymerization of the polythiourethane by treating the mixture from step a) at a first reaction temperature, whereby di- or higher-functional thiols from the polythiourethane and monomeric and oligomeric thiourethanes terminated with monofunctional thiols are formed, c) optionally separating impurities and / or solvent from the mixture obtained in step b), d) optionally adding di- or higher-functional isocyanate and di- or higher-functional thiol, and e) treating the mixture from step b), c) or d) at a second reaction temperature which is lower,is equal to or greater than the first reaction temperature, under reduced pressure compared to step b), c) or d), whereby the monofunctional thiol is removed from the mixture and polymerization of the monomeric and oligomeric thiourethanes from step b) and of the compounds optionally added in step d) takes place.

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

3. Process according to at least one of claims 1 or 2, characterized in that the depolymerization in step b) and the polymerization in step e) are carried out in the presence of a catalyst.

4. Process according to claim 3, characterized in that the catalyst is selected from the group consisting of tertiary amine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), phosphine or organic tin compounds.

5. The process according to at least one of claims 1 to 4, characterized in that the first reaction temperature and the second reaction temperature are in the range between 20°C and 220°C, preferably between 50 and 200°C.

6. Process according to at least one of claims 1 to 5, characterized in that 1.5 to 50 moles of the monofunctional thiol are used per mole of thiourethane bond of the polythiourethane in step a).

7. Process according to at least one of claims 1 to 6, characterized in that the oligomeric polythiourethanes from step b) have two to sixteen repeat units.

8. The process according to claim 1, characterized in that the monofunctional thiol used in step a) is selected from the group of alkylthiols having two to ten carbon atoms, in particular ethanethiol, 1-propanethiol, 2-propanethiol, hexanethiol, thiophenol, alkyl esters of 3-mercaptopropionic acid or thioglycolic acid or mixtures of two or more thereof.

9. Process according to at least one of claims 1 to 8, characterized in that the polythiourethane used in step a) is a polythiourethane network.

10. The process according to claim 9, characterized in that the thiol obtained from the polythiourethane in step b) is a tri- or higher-functional, preferably a trifunctional thiol.

11. Process according to at least one of claims 1 to 10, characterized in that in step a) a polythiourethane is used which has a • Polythiourethane network composed of bio-based monomers.

12. The process according to at least one of claims 1 to 10, characterized in that the monofunctional thiol used in step a) is a bio-based raw material and / or that the di- or higher-functional isocyanate or thiol optionally used in step d) are bio-based raw materials.

13. Compositions containing monomers of formula (XIX) and / or oligomers of formula (XXI) or containing monomers of formula (XX) and / or oligomers containing structural units of formula (XXII) R 13 -S-CO-NH-R 2 -NH-CO-SR 13 (XIX), R 13 -S-CO-NH-R 6 -(NH-CO-SR 13 ) P (XX), R 13 -S-CO-NH-R 2 -NH-CO-(SR 1 -S-CO-NH-R 2 -NH-CO-) S SR 13 (XXI) where R 1 and R 2are independently divalent organic radicals, R 5 is a (x+z2+1 )-valent organic residue, R 6 is a (w+z1+1)-valent or a (y+z2+1)-valent organic residue, R 13 is a monovalent organic radical, w, x and y are independently integers from 0 to 9, z1 and z2 are independently integers from 1 to 10, the sum w+z1 is an integer from 1 to 10. the sum x+z2 is an integer from 1 to 10. the sum y+z2 is an integer from 1 to 10. with the proviso that R 1 , R 2 , R 5 , R 6 , R 13 , w, x, y, z1 and z2 can also have different meanings within a molecule within the given definitions, that the oligomer of formula (XXII) contains further radicals R 13which are linked to the oligomer via thioisocyanate groups, that the proportion of the monomers of the formula (XIX) and the oligomers of the formula (XXI) in the composition can be 0 to 100 mol%, based on the total amount of these compounds, the sum of these compounds always being 100 mol%, and that the proportion of the monomers of the formula (XX) and the oligomers containing the structural units of the formula (XXII) in the composition can be 0 to 100 mol%, based on the total amount of these compounds, the sum of these compounds always being 100 mol%.

14. Compositions according to claim 13, characterized in that R 1 and R 2 independently of one another are alkylene, cycloalkylene, arylene, aralkylene or heterocyclylene, R 5 a (x+z2+1 )-valent alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl radical, R 6a (w+z1 +1 )-valent or a (y+z2+1 )-valent alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl radical, R 13 is an alkyl, cycloalkyl, aryl, aralkyl or heterocyclyl radical, and w+z1, x+z2 and y+z2 independently of one another are 1, 2 or 3.

15. Compositions according to claim 14, characterized in that R 1 Cycloalkylene, arylene, aralkylene or heterocyclylene, especially arylene and and R 5 a (x+z2+1 )-valent cycloalkyl, aryl, aralkyl or heterocyclyl radical, in particular a (x+z2+1 )-valent aryl radical.

16. Use of the compositions according to claim 13 for the preparation of polythiourethanes or for the preparation of copolymers containing polythiourethane groups.

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