Benzoxazine acetal derivatives for production of recyclable polymers

Abstract

What is described is a benzoxazine derivative of the formula (I), and also a process for producing a benzoxazine derivative of the invention, and likewise a kit for production of a recyclable polymer and the use of a benzoxazine derivative of the invention or a kit of the invention for the production of a recyclable polymer, and also a recyclable polymer based on polybenzoxazine or polybenzoxazine derivative, a process for producing a recyclable polymer of the invention, and the use of a recyclable polymer of the invention as plastic and / or adhesive and / or matrix resin for a composite material.

Description

[0001] Fraunhofer Society for the Promotion of Applied Research, registered association, Hansastraße 27 c, 80686 Munich

[0002] Benzoxazine derivative and use and process for the preparation thereof and recyclable polymer and use and process for the preparation thereof

[0003] The present invention relates to a benzoxazine derivative. The invention further relates to a process for producing a benzoxazine derivative according to the invention. The invention also relates to a kit for producing a recyclable polymer and to the use of a benzoxazine derivative according to the invention or a kit according to the invention for producing a recyclable polymer. The invention also relates to a recyclable polymer based on polybenzoxazine or polybenzoxazine derivative, a process for producing a recyclable polymer according to the invention, and the use of a recyclable polymer according to the invention as a plastic and / or adhesive and / or matrix resin for a composite material. The invention is defined in the appended claims. Preferred aspects of the present invention will become apparent from the following description, including the examples.To the extent that certain embodiments are designated as preferred for one aspect of the invention, the corresponding statements also apply to the other aspects of the present invention, mutatis mutandis. Preferred individual features of aspects of the invention (as defined in the claims and / or disclosed in the description) can be combined with one another and are preferably combined with one another, unless otherwise apparent to the person skilled in the art from the present text in the individual case.

[0004] The landfilling of composite materials such as glass fiber reinforced plastic (GRP) or carbon fiber reinforced plastic (CFRP) is regulated by the current EU Landfill Regulation (Directive 99 / 31 / EC) with the aim of reducing the release of organic materials into the environment. The recycling of multi-material systems, such as those found in fiber reinforced plastics and composite materials in general, is not possible using the plastics conventionally used for this purpose. The three-dimensional network structure of the typically used thermoset polymer systems, such as phenolic resins, vinyl esters, unsaturated polyester resins (UP), and epoxy resins (EP), as matrix systems, prevents the matrix from being dissolved and thus separated from the fibers and other components.

[0005] Benzoxazines and benzoxazine-based composites are used in the aerospace sector due to their thermal resistance and mechanical stability. Their properties have the potential to replace phenolic resins and, in some cases, epoxies. In addition to suitable material properties for the application, the demand for degradable and thus recyclable thermosets is growing rapidly.

[0006] The following solutions are known in the field of degradable resin systems, especially for use in composite materials:

[0007] In the state of the art (cf. a) Zhang et al., Recent advances in recyclable thermosets and thermoset composites based on covalent adaptable networks, J. Mat. Sci Technology 2021 , 92, 75-87; DOI: 10.1016 / j.jmst.2021 .03.043; b) Mulcahy et al., Debondable adhesives and their use in recycling, Green Chem., 2022, 24, 36), the class of vitrimers based on dynamic covalent chemistry has been described as an approach to recyclable polymers, and the use of these polymers as matrix systems for composites has been demonstrated. The original mechanism of the dynamic transesterification reaction based on the pioneering work of Ludwig Leibler in 2011, partly in the presence of catalysts, has been applied to epoxides (cf. a) Capelot, M.; Montarnal, D.; Tournilhac, F.; Leibler, L. Metal-catalyzed transesterification for healing and assembling of thermosets. J.Am. Chem. Soc. 2012, 134, 7664-7667; b) Capelot, M.; Cease and desist, MM; Tournilhac, F.; Leibler, L.Catalytic Control of the Vitrimer Glass Transition. ACS Macro Lett. 2012, 1 , 789- 792) und Benzoxazine (vgl. a) Antoine Adjaoud et al, Polybenzoxazines: a sustainable platform for the design of fast responsive and catalyst-free vitrimers based on trans-esterifica- tion exchanges, Polym. Chem., 2021 ,12, 3276-3289 DOI: 10.1039 / d1 py00324k; b) W02021250024A1 , c) WO2022122735A1) übertragen.

[0008] VITRIMAX™ are dynamic polymer networks based on a dynamic polyimine and EP-based polymer network from MALLINDA. As is typical for vitrimers, VITRIMAX polymer networks are characterized by reprocessability when heated above the glass transition temperature, stress relaxation, reversible molding, weldability, and closed-loop recycling of fully cured materials (see Taynton, P.; Ni, H.; Zhu, C.; Yu, K.; Loob, S.; Jin, Y.; Qi, HJ; Zhang, W. Repairable Woven Carbon Fiber Composites with Full Recyclability Enabled by Malleable Polyimine Networks. Adv. Mater. 2016, 28, 2904-2909).

[0009] For epoxides, a degradable network based on disulfide bonds is known in the state of the art (cf. a) Ruiz de Luzuriaga, A.; Martin, R.; Markaide, N.; Rekondo, A.; Cabanero, G.; Rodriguez, J.; Odriozola, I. Epoxy resin with exchangeable disulfide crosslinks to obtain reprocessable, repairable and recyclable fiber-reinforced thermoset composites. Mater. Horiz. 2016, 3, 241-247; b) Post, W.; Cohades, A.; Michaud, V.; van der Zwaag, S.; Garcia, SJ Healing of a glass fiber reinforced composite with a disulphide containing organic-inorganic epoxy matrix. Compos. Sei. Technol. 2017, 152, 85-93). In addition to the potential for reprocessing and self-healing for repair processes known for dynamic polymer networks, the disulfide unit allows for the dissolution of the polymer networks and thus recycling. A chemical reagent is required for the degradation process. The concept has also been applied to benzoxazines (cf. a) A. Trejo-Machin et al.A cardanol-based polybenzoxazine vitrimer: recycling, reshaping and reversible adhesion, Polym. Chem. 2020, 11 , 7026-7034; b) WO2021180562A1).

[0010] The use of cleavable ketal groups has been described for degradable epoxies based on the RecyclaminO technology (US10214479B2) developed by Connora Technologies (Hayward, CA, USA) and commercialized by Aditya Birla. Recyclamin® is used as an amine hardener for epoxies. The resulting epoxy contains cleavable groups that allow degradation of the polymer and polymer network to a thermoplastic epoxy under mild conditions. The resulting plastics and composites based on them are limited to epoxies and are characterized by low glass transition temperatures and limited thermal stability. Their application is currently restricted to the production of GRP structures with moderate mechanical and low thermal requirements (e.g., for rotor blade manufacturing).

[0011] Aditya Birla has expanded the system and integrated cleavable groups such as acetals, ketals, and silanes into the epoxy structure (see WO 2020 / 161538 A1). The degradable epoxy monomers are polymerized with conventional amines, resulting in epoxy-based polymer networks that can be dissolved under slightly acidic conditions in the presence of an organic solvent and at temperatures of 130°C (using 5% acetic acid). The temperatures to be used depend on the concentration and strength of the acid used.

[0012] The use of diacetal groups has also been demonstrated in polyurethanes (PU) with a resulting glass transition temperature (Tg) of 130°C (cf. High-Performance, Biobased, Degradable Polyurethane Thermoset and Its Application in Readily Recyclable Carbon Fiber Composites ACS Sustainable Chem. Eng. 2020, 8, 30, 11162-11170) as well as in epoxides with resulting Tg's in the range of 160-170°C (cf. Ma, S.; Wei, J.; Jia, Z.; Yu, T.; Yuan, W.; Li, Q.; Wang, S.; You, S.; Liu, R.; Zhu, J. Readily recyclable, high-performance thermosetting materials based on a lignin-derived spiro diacetal trigger. J. Ma- ter.Chem. A 2019, 7, 1233-1243). The polymers based on PU and EP could be degraded under mild acidic conditions.

[0013] Polybenzoxazines (PBz) are thermoset polymers characterized by low shrinkage, very good thermal stability, low water absorption, and high glass transition temperatures (Tg up to 350 °C). Due to the high crosslinking based on covalent and non-covalent bonds, PBz are typically brittle. Furthermore, due to the lower reactivity of the oxazine ring compared to epoxides, curing temperatures of up to 250 °C are necessary for thermal ring-opening polymerization (cf. NN Ghosh, B. Kiskan, Y. Yagci, Prog. Polym. Sci. 2007, 32, 1344). Among other approaches, the prior art describes the use of amines as additional curing components that influence both the polymerization temperature and the toughness of the benzoxazines.

[0014] In the state of the art, the N-CH2-X (X = O, N, S) bond, which is formed in PBz alongside the Mannich bond, is described as significantly more reactive and thus accessible for reversible reactions and thus as a structural unit for dynamic polymer networks (cf. Zhang et al., "Unexpected Healability of an ortho-Blocked Polybenzoxazine Resin," ACS Macro Letters 2019, 8, 506-511). The reversibility of a PBz is described by Lei Zhang et al. in a PBz polymer network with a predominantly phenoxy structure and the resulting N-CH2-O bond. This approach can be realized using a benzoxazine monomer with a blocked ortho position, which prevents the thermodynamically favored rearrangement to the phenolic structure with Mannich bonds. The phenoxy to phenol rearrangement typically occurs at 160°C.The work shows that a phenoxy-like N-CH2-O group exhibits dynamic binding properties that can be realized exclusively in ortho-blocked benzoxazine monomers.

[0015] N-CH2-N bonds are known in the art from the copolymerization of benzoxazines with amines (cf. Sun et al., A curing system of benzoxazine with amine: reactivity, reaction mechanism and material properties, RSC Adv. 2015, 5, 19048). Due to the presence of difunctional amines, BA-a cured at 120 or 150°C with curing rates similar to epoxy / amine systems and significantly faster and at lower temperatures than the conventional benzoxazine BA-a. The reaction of the oxazine ring with an amine results in an N-CH2-N zwitterionic bond, which has been described as reversible. Upon further heating, the structure decomposes irreversibly to the iminium ion, which results in the phenoxy and phenol structure known for benzoxazines at elevated temperatures.Similar benzoxazine / amine mixtures with dynamic properties below 160°C and a structure dominated by the formation of irreversible Mannich bonds were described by Shuai Zhang et al. (cf. S. Zhang et al., Facile preparation of lightweight and robust polybenzoxazine foams, Ind. Eng. Chem. Res. 2020, 59, 7575-7583).

[0016] For the cleavable benzoxazine described by Wang et al., a diacetal unit is introduced into the benzoxazine monomer as a cleavable group via the phenol component (see P. Wang et al., High heat-resistant and degradable polybenzoxazines with a diacetal structure, ACS Sustainable Chem. Eng. 2021, 9, 7913-7921). The resulting polymers are characterized by high thermal stability and can exhibit Tg values ​​of over 301 °C. They can be cleaved under mild, acidic conditions. However, the phenol derivative used for this purpose has a high melting point, which complicates processing and monomer synthesis.

[0017] Against the background of the prior art, the primary object of the present invention was to provide a monomer from which recyclable polymers can be produced, as well as to provide a corresponding recyclable polymer; while simultaneously overcoming one or more disadvantages described in the prior art in connection with the production and properties of such recyclable polymers.

[0018] Further objects arise from the following description and the patent claims.

[0019] The primary object of the present invention is achieved by a benzoxazine derivative having the formula (I) where

[0020] R 1 , R 2 , R 3 , R 4 , R 5 , R e , R 7 and R 8 are the same or different and each represents an organic residue or H,

[0021] R 9is a functional organic group, preferably an alkylene group having 1 to 23 carbon atoms, particularly preferably an alkylene group having 1 to 2 carbon atoms;

[0022] R 10 , R 11 and R 12 are the same or different and each represents an organic radical or H, preferably each an organic radical, where R 12preferably is or comprises a benzoxazine unit or is preferably selected from the group consisting of aminoalkyl group, aliphatic or aromatic vinyl group, aliphatic or aromatic propargyl group, siloxane group and oligosiloxane group. Recyclable polymers (or recyclable polybenzoxazines or polybenzoxazine derivatives) can be produced from the benzoxazine derivative according to the invention, which polymers are advantageously characterized by degradability under mild conditions (which enables easy recycling of the polymers) with simultaneous high glass transition temperatures (Tg) and good thermomechanical properties as well as good thermal stability. Furthermore, the benzoxazine derivatives according to the invention are characterized by significantly better processing and the possibility of lowering the polymerization temperature compared to benzoxazine derivatives comprising acetal or ketal groups known from the prior art.

[0023] The advantages of the benzoxazine derivative according to the invention result in particular from the fact that the benzoxazine derivative comprises (at least) one (cleavable) acetal or ketal group which is linked to the nitrogen atom of the benzoxazine structure, whereby the benzoxazine derivative according to the invention differs substantially from benzoxazine derivatives with acetal or ketal groups known from the prior art (for example, the benzoxazine derivatives described in P. Wang et al., High heat-resistant and degradable polybenzoxazines with a diacetal structure, ACS Sustainable Chem. Eng. 2021, 9, 7913-7921).

[0024] The benzoxazine derivative according to the invention can be processed as a one-component system and converted into a recyclable (cleavable) polybenzoxazine by heating in a ring-opening polymerization.

[0025] Alternatively, the benzoxazine derivative of the invention can be polymerized in a copolymerization with other benzoxazine monomers (e.g., bisphenol A or F-based benzoxazine from Huntsman Advanced Materials). Using the benzoxazine derivative of the invention, both recyclable or degradable homopolymers and recyclable or degradable copolymers can be obtained.

[0026] A benzoxazine derivative according to the invention having the formula (Ia) is preferred

[0027] where

[0028] - R 1 , R 2 , R 3 , R 4 , R 5 , R e , R 7 , R 8 , R 14 , R 15 , R 18 , R 17 , R 18 , R 19 , R 20 and R 21 are the same or different and each represents an organic radical or H; - R 9 and R 13are the same or different and each has a functional organic

[0029] group, preferably an alkylene group having 1 to 23 carbon atoms, particularly preferably an alkylene group having 1 to 2 carbon atoms;

[0030] R 10 and R 11 are the same or different and each represents an organic radical or H, preferably each represents an organic radical. Also preferred is a benzoxazine derivative according to the invention, wherein

[0031] R 1 and R 2 or R 2 and R 3 or R 3 and R 4 are linked together to form a ring structure, preferably a heterocyclic ring structure of at least 5 atoms and / or

[0032] R 18 and R 19 or R 19 and R 20 or R 20 and R 21are linked together to form a ring structure, preferably a heterocyclic ring structure of at least 5 atoms, and / or one or more, preferably all, of the radicals R 1 , R 2 , R 3 , R 4 , R 5 , R e , R 7 , R 8 , R 14 , R 15 , R 18 , R 17 , R 18 , R 19 , R 20 and R 21 are independently selected from the group consisting of H, alkyl group having preferably 1 to 15 carbon atoms, alkoxy group having preferably 1 to 10 carbon atoms and ester group and / or

[0033] R 10 and / or R 11 an alkyl group having 1 to 10 carbon atoms or an alkoxy group having 1 to 10 carbon atoms or R 10 and R 11 are linked together to form a ring structure of at least 5 carbon atoms.

[0034] Also preferred is a benzoxazine derivative according to the invention, wherein

[0035] - R 5 , R 8 , R 7 , R 8 , R 14 , R 15 , R 18 and R 17 each represent H,

[0036] - R 9 and R 13 each represent an ethylene group, and

[0037] - R 10 and R 11 each represent a methyl group.

[0038] Also preferred according to the invention is a benzoxazine derivative according to the invention, wherein R 10 and R 11 represent an organic residue and R 12 represents an organic residue or H.

[0039] This requires that the two residues R 10 and R 11form a ketal, and it has surprisingly been found that these ketals exhibit some, several, or all of the properties described above to a particularly high degree. This also applies, for example, to improved recycling behavior, which simplifies the latter.

[0040] Also preferred is a benzoxazine derivative according to the invention, wherein the benzoxazine derivative has the formula (1), (2), (3), (4) or (5)

[0041] Part of the invention is also a process for producing a benzoxazine derivative according to the invention or preferably according to the invention (as defined above and in the claims), comprising the step of reacting one or more phenol derivatives or phenol with one or more amino acetals, preferably one or more amino ketals, particularly preferably diamino ketal, in the presence of an aldehyde, preferably in the presence of paraformaldehyde. In the process according to the invention for producing a benzoxazine derivative according to the invention or preferably according to the invention, the acetal or ketal group is introduced into the benzoxazine derivative to be produced via the amine component (and not via the phenol component). This results in the advantages already explained above for the resulting benzoxazine derivative.Furthermore, this approach allows for a simpler synthesis of the benzoxazine derivative as well as easier processing of the resulting benzoxazine derivative.

[0042] The process according to the invention for preparing a benzoxazine derivative according to the invention or preferably according to the invention is preferably carried out in a one-step reaction.

[0043] The properties of the benzoxazine derivative to be prepared according to the invention or preferably according to the invention (as well as the properties of the polymer that can be prepared using this benzoxazine derivative) can be additionally adapted to the respective requirements of the benzoxazine derivative (or to the polymer to be prepared therefrom) by appropriate selection of the phenol derivatives.

[0044] Part of the invention is also a kit for producing a recyclable polymer (or for producing a recyclable polybenzoxazine or polybenzoxazine derivative), comprising

[0045] - at least one aminoacetal, preferably at least one aminoketal, particularly preferably diaminoketal, and

[0046] - at least one benzoxazine monomer, preferably a benzoxazine derivative according to the invention or preferably according to the invention (as defined above and in the claims).

[0047] Such a kit according to the invention, which is typically present as a two-component system, allows for the simple production of a recyclable polymer (or a recyclable polybenzoxazine or polybenzoxazine derivative) without the need for further monomer design or synthesis. The production of a recyclable polymer (or a recyclable polybenzoxazine or polybenzoxazine derivative) can be achieved by mixing the components of the kit according to the invention and subsequent thermal ring-opening polymerization.

[0048] The benzoxazine monomer comprised in the kit according to the invention can be a benzoxazine monomer known from the prior art (for example, a bisphenol A / aniline-based benzoxazine monomer). Preferably, the benzoxazine monomer comprised in the kit according to the invention is a benzoxazine derivative according to the invention or preferably according to the invention (as defined above and in the claims). The term "benzoxazine monomer" in the context of the present invention therefore refers to both benzoxazines and benzoxazine derivatives.

[0049] Part of the invention is also the use of a benzoxazine derivative according to the invention or preferably according to the invention (as defined above and in the claims) or a kit according to the invention for the production of a recyclable polymer (or for the production of a recyclable polybenzoxazine or polybenzoxazine derivative).

[0050] Part of the invention is also a recyclable polymer based on polybenzoxazine or polybenzoxazine derivative (or a recyclable polybenzoxazine or polybenzoxazine derivative) comprising acetal groups, preferably ketal groups, wherein the recyclable polymer (or the recyclable polybenzoxazine or polybenzoxazine derivative) is obtainable by a synthesis comprising a.1) providing a benzoxazine derivative according to the invention or preferably according to the invention (as defined above and in the claims) or a.2) producing a benzoxazine derivative according to the invention (as defined above and in the claims) or a.3) Mixing at least one aminoacetal, preferably at least one aminoketal, particularly preferably diaminoketal, and at least one benzoxazine monomer, preferably a benzoxazine derivative according to the invention or preferably according to the invention (as defined above and in the claims); b) Polymerization (preferably thermal ring-opening polymerization) of the benzoxazine derivative provided in step a.1) or of the benzoxazine derivative prepared in step a.2) or of the mixture prepared in step a.3), optionally in the presence of one or more further benzoxazine monomers.

[0051] The recyclable polymer according to the invention (or the recyclable polybenzoxazine or polybenzoxazine derivative according to the invention) is characterized in that i) the polymer backbone has a benzoxazine-typical, preferably phenolic, structure, and ii) the (cleavable) acetal or ketal groups are incorporated into the benzoxazine structure via the amine component.

[0052] The recyclable polymer according to the invention (or the recyclable polybenzoxazine or polybenzoxazine derivative according to the invention) is further characterized by degradability under mild conditions while simultaneously having a high glass transition temperature and good thermomechanical properties.

[0053] Preference is given to a recyclable polymer according to the invention (or recyclable polybenzoxazine or polybenzoxazine derivative), wherein the recyclable polymer (or the recyclable polybenzoxazine or polybenzoxazine derivative) has dynamic properties and / or is degradable or soluble under acidic conditions, preferably in 25% acetic acid at 80°C (particularly preferably within 4 hours, more preferably within one hour), and / or has a glass transition temperature (Tg) of more than 80°C, preferably of more than 100°C, particularly preferably of 115°C or more, and / or is (still) thermally stable at a temperature of 170°C, preferably at a temperature of 200°C.

[0054] For the purposes of the present invention, covalently cross-linked polymers are referred to as having dynamic properties if they allow the covalent bonding sites to dynamically separate and reconnect as a result of an appropriate stimulus, in the case of the present invention preferably by varying the temperature and / or pressure (cf. "Recent advances in dynamic covalent chemistry" by Jin et al. in Chemical Society Reviews, Vol. 42, 2013, pp. 6634-6654). Due to this chemical property, such polymer networks allow for stress relaxation, shaping, and reprocessing, and exhibit self-healing properties.

[0055] The recyclable polymer according to the invention (or the recyclable polybenzoxazine or polybenzoxazine derivative according to the invention) thus enables, in a preferred embodiment, the realization of a polymer which is degradable under mild conditions and which simultaneously has dynamic properties.

[0056] Thermally stable, in the context of the present invention, means that no decomposition of the polymer can (yet) be detected at the corresponding temperature. The presence of thermal stability at the stated temperatures can be determined, for example, by thermogravimetric analysis (TGA) and / or differential scanning calorimetry (DSC), preferably as explained in Example 6 below.

[0057] Part of the invention is also a process for producing a recyclable polymer according to the invention or preferably according to the invention (or a recyclable polybenzoxazine or polybenzoxazine derivative), as defined above and in the claims, comprising the following steps: a.1) providing a benzoxazine derivative according to the invention or preferably according to the invention (as defined above and in the claims), or a.2) producing a benzoxazine derivative according to the invention (as defined above and in the claims) or a.3) mixing at least one amino acetal, preferably at least one amino ketal, particularly preferably diamino ketal, and at least one benzoxazine monomer, preferably a benzoxazine derivative according to the invention or preferably according to the invention (as defined above and in the claims); b) polymerization (preferably thermal ring-opening polymerization) of the benzoxazine derivative provided in step a.1) or of the benzoxazine derivative provided in step a.2) prepared benzoxazine derivative or the mixture prepared in step a.3), optionally in the presence of one or more further benzoxazine monomers.

[0058] The polymerization in step b) is usually initiated by elevated temperatures. The temperature(s) used for polymerization or curing, as well as the duration of the respective temperature(s), can vary depending on the viscosity and reactivity of the benzoxazine or amine used (or the possible additional use of (other) nucleophiles such as thiols).

[0059] Part of the invention is also the use of a polymer according to the invention or preferably according to the invention recyclable polymer (or a recyclable polybenzoxazine or polybenzoxazine derivative), as defined above and in the claims, as

[0060] Plastic and / or

[0061] Adhesive and / or

[0062] Matrix resin for a composite material, preferably for a fiber composite material.

[0063] The invention is explained in more detail below with reference to examples and the accompanying figures. The examples given below are intended to describe and explain the invention in more detail without limiting its scope. Example 1: Preparation of Benzoxazine Derivatives According to the Invention

[0064] Diaminoketal 30.8 mmol, 1 eq) and a phenol derivative (61.6 mmol, 2 eq) were dissolved in 100 mL of EtOH. Paraformaldehyde (125 mmol, 4.05 eq) was added, and the suspension was heated to reflux with stirring in an oil bath (for approximately 4.5 h). After completion of the reaction (verified by 80 MHz NMR or TLC), the

[0065] The reaction mixture was cooled to room temperature. The solvent was removed under reduced pressure, yielding the crude product. The crude product was dissolved in 100 mL of chloroform and washed with 2 x 100 mL of aqueous sodium hydroxide solution (1 mol / L). The organic phase was separated, dried over Na2SO4, and the solvent was removed under reduced pressure on a rotary evaporator at a bath temperature of 60 °C.

[0066] Benzoxazine derivatives were prepared using the following phenol derivatives: (i) sesamol, (ii) ethyl phloretinate, (iii) guaiacol, (iv) o-cresol, (v) p-cresol. Deviating from the preparation procedure described above, a 5-fold smaller synthesis batch was chosen for the preparation of the benzoxazine derivative using sesamol. Table 1 below lists the phenol derivatives used and the resulting benzoxazine derivatives.

[0067] Table 1

[0068]

[0069] Objective 2: Production of inventive recyclable polymers from the benzoxazine derivatives prepared in Example 1

[0070] Recyclable polymers were produced from the benzoxazine derivatives prepared in Example 1. For this purpose, the benzoxazine derivatives were polymerized or cured by aging in a convection oven for two hours at 150 °C and then for a further two hours at 180 °C.

[0071] Example 3: Preparation of a recyclable polymer according to the invention from a benzoxazine monomer and diaminoketal

[0072] 7.4 g (16 mmol) of the bisphenol A / aniline-based benzoxazine monomer (BA-a) with the trade name ARALDITE® MT35600 from Huntsman Advanced Materials (M = 462.6 g / mol) were homogenized or mixed together with 2.6 g (16 mmol) of diaminoketal (CAS: 127090-71-5, M = 162.23 g / mol) in the melt at 110°C for approximately 10 min.

[0073] The mixture thus prepared was polymerized or cured by aging in a circulating air oven for two hours at 120 °C and then for a further two hours at 150 °C.

[0074] Example 4: Investigation of the thermomechanical properties of polymers according to the invention and not according to the invention

[0075] The thermomechanical properties of the following polymers were investigated using dynamic thermomechanical analysis (DMA):

[0076] Polybenzoxazine obtained by polymerizing or curing the bisphenol A / aniline-based benzoxazine monomer with the trade name ARALDITE® MT35600 from Huntsman Advanced Materials for initially 2 hours at 180 °C and then for a further 2 hours at 200 °C (not according to the invention, also referred to below and in Fig. 1 as “conventional polybenzoxazine”);

[0077] Epoxy system designated EP YDL5557 + THR9357 from CTP Advanced Materials GmbH, wherein the epoxy system was prepared according to the manufacturer's instructions by mixing the resin component (YDL5557) with the hardener component (THR9357) in a weight ratio of 100:30 and curing at room temperature, see also https: / / cetepox.de / wp-content / uploads / 2020 / 08 / TDS-Epotec-YDL5557-THR9357-Rev.00.pdf (not according to the invention, also referred to below and in Fig. 1 as "EP YDL5557 + THR9357"); recyclable polymer, prepared according to Example 3 above (according to the invention, also referred to below and in the figures as "degrPolybenzoxazine 1"); Recyclable polymer, prepared according to Example 2 above using the benzoxazine derivative according to the invention prepared in Example 1 using the phenol derivative p-cresol (according to the invention, hereinafter and in the figures also referred to as “degrPolybenzoxazine 2”).

[0078] The results of the DMA performed in a temperature range of 25 °C to 200 °C are shown in Fig. 1.

[0079] The inventive recyclable polymers "degrPolybenzoxazine 1" and "degrPolybenzoxazine 2" exhibit thermomechanical properties that exceed the properties of the non-inventive degradable epoxide "EP YDL5557 + THR9357." In particular, "degrPolybenzoxazine 2" exhibits a significantly higher Tg (= 115 °C) than "EP YDL5557 + THR9357" (= 64 °C). The lower Tg of "degrPolybenzoxazine 1" (= 84.5 °C) compared to "degrPolybenzoxazine 2" can be attributed to the stoichiometric and thus comparatively high content of the diamino ketal.

[0080] The degradability and recyclability of the following polymers were investigated by means of dissolution tests: “conventional polybenzoxazine” (not according to the invention),

[0081] “EP YDL5557 + THR9357” (not according to the invention),

[0082] “degrPolybenzoxazine 1” (according to the invention),

[0083] "degrPolybenzoxazine 2" (according to the invention). Regarding the specifications for the individual polymers, reference is made to the corresponding explanations for Example 4. Deviating from the specifications given in Example 4, the "EP YDL5557 + THR9357" was cured at 80 °C for the tests conducted in Example 5.

[0084] For the dissolution tests, the polymer samples were each exposed to aqueous 25% acetic acid at 80 °C. In addition, the hydrolytic and chemical stability of the polymers "EP YDL5557 + THR9357," "degrPolybenzoxazine 1," and "degrPolybenzoxazine 2" was investigated in control tests by aging in water for 19 hours at 80 °C and by aging in methyl ether ketone (MEK) for 19 hours at 80 °C. The test results are summarized in Table 2. Table 2 The (ketal group-containing) polymers "EP YDL5557 + THR9357", "degrPolybenzoxazine 1", and "degrPolybenzoxazine 2" each dissolved after four hours in aqueous 25% acetic acid at 80 °C. The "conventional polybenzoxazine" showed no dissolution in aqueous 25% acetic acid during the observed time.

[0085] In the control tests in water and MEK, no change in the state of aggregation was observed for “EP YDL5557 + THR9357”, “degrPolybenzoxazin 1” and “degrPolybenzoxazin 2” after 19 h. the thermal stability of

[0086] The thermal stability was determined using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) for the inventive polymers "degrPolybenzoxazine 1" and "degrPolybenzoxazine 2." For the specifications of the two polymers, please refer to the corresponding explanations for Example 4.

[0087] TGA measurements were performed at a heating rate of 5 K / min over a temperature range of 35 to 550 °C in a 20% oxygen atmosphere. DSC measurements were performed at a heating rate of 10 K / min over a temperature range of 0 to 220 °C.

[0088] Fig. 2 shows the normalized heat flow as a function of temperature as a result of the DSC analysis. The glass transition temperatures can be detected for "degrPolybenzoxazine 1" and "degrPolybenzoxazine 2." Furthermore, no endothermic or exothermic processes are visible up to a temperature of 220 °C.

[0089] The results of the TGA measurements are shown in Fig. 3. The thermogravimetric analysis shows the mass loss in % as a function of temperature. The temperatures at which the mass loss occurs at 1% (Ti%) and 5% (Ts%) are typically used to describe the thermal stability of polymers. The following values ​​were determined for the inventive polymers "degrPolybenzoxazine 1" and "degrPolybenzoxazine 2":

[0090] .degrPolybenzoxazine 1“: Ti% = 184 °C, Ts% = 227 °C;

[0091] .degrPolybenzoxazine 2" Ti% = 230 °C, Ts% = 240 °C. The inventive polymers "degrPolybenzoxazine 1" and "degrPolybenzoxazine 2" are thus thermally stable at least up to a temperature of 184 °C (for "degrPolybenzoxazine 1") or 230 °C for "degrPolybenzoxazine 2".

Claims

Patent claims: 1 . Benzoxazine derivative with the formula (I) where R 1 , R 2 , R 3 , R 4 , R 5 , R e , R 7 and R 8 are the same or different and each represents an organic residue or H, R 9 is a functional organic group, preferably an alkylene group having 1 to 23 carbon atoms, particularly preferably an alkylene group having 1 to 2 carbon atoms; - R 10 , R 11 and R 12 are the same or different and each contain an organic radical or H, preferably each an organic radical, where R 12 preferably is or comprises a benzoxazine unit or is preferably selected from the group consisting of aminoalkyl group, aliphatic or aromatic vinyl group, aliphatic or aromatic propargyl group, siloxane group and oligosiloxane group. Benzoxazine derivative according to claim 1, having the formula (Ia) where - R 1 , R 2 , R 3 , R 4 , R 5 , R e , R 7 , R 8 , R 14 , R 15 , R 18 , R 17 , R 18 , R 19 , R 20 and R 21 are the same or different and each represents an organic radical or H; R 9 and R 13 are the same or different and each represents a functional organic group, preferably an alkylene group having 1 to 23 carbon atoms, particularly preferably an alkylene group having 1 to 2 carbon atoms; R 10 and R 11 are the same or different and each represents an organic radical or H, preferably each represents an organic radical. Benzoxazine derivative according to claim 1 or claim 2, wherein R 1 and R 2or R 2 and R 3 or R 3 and R 4 are linked together to form a ring structure, preferably a heterocyclic ring structure of at least 5 atoms and / or R 18 and R 19 or R 19 and R 20 or R 20 and R 21 are linked together to form a ring structure, preferably a heterocyclic ring structure of at least 5 atoms and / or one or more, preferably all, of the radicals R 1 , R 2 , R 3 , R 4 , R 5 , R e , R 7 , R 8 , R 14 , R 15 , R 18 , R 17 , R 18 , R 19 , R 20 and R 21are independently selected from the group consisting of H, alkyl group having preferably 1 to 15 carbon atoms, alkoxy group having preferably 1 to 10 carbon atoms and ester group and / or R 10 and / or R 11 an alkyl group having 1 to 10 carbon atoms or an alkoxy group having 1 to 10 carbon atoms or R 10 and R 11 are linked together to form a ring structure of at least 5 carbon atoms. Benzoxazine derivative according to any one of the preceding claims, wherein - R 5 , R e , R 7 , R 8 , R 14 , R 15 , R 18 and R 17 each represent H, - R 9 and R 13 each represent an ethylene group, and - R 10 and R 11 each represent a methyl group. Benzoxazine derivative according to one of the preceding claims, wherein R 10 and R11 represent an organic residue and R 12 represents an organic radical or H. Benzoxazine derivative according to any one of the preceding claims, wherein the benzoxazine derivative has the formula (1), (2), (3), (4) or (5) 7. A process for preparing a benzoxazine derivative as claimed in any one of claims 1 to 6, comprising the step of reacting one or more phenol derivatives or phenol with one or more aminoacetals, preferably one or more aminoketals, particularly preferably diaminoketal, in the presence of an aldehyde, preferably in the presence of paraformaldehyde.

8. Kit for producing a recyclable polymer, comprising - at least one aminoacetal, preferably at least one aminoketal, particularly preferably diaminoketal, and - at least one benzoxazine monomer, preferably a benzoxazine derivative as defined in any one of claims 1 to 6.

9. Use of a benzoxazine derivative as defined in any one of claims 1 to 6 or of a kit as defined in claim 8 for the preparation of a recyclable polymer.

10. A recyclable polymer based on polybenzoxazine or polybenzoxazine derivative comprising acetal groups, preferably ketal groups, wherein the recyclable polymer is obtainable by a synthesis comprising a.1) providing a benzoxazine derivative as defined in any one of claims 1 to 6, or a.2) preparing a benzoxazine derivative as defined in claim 7, or a.3) mixing at least one amino acetal, preferably at least one amino ketal, particularly preferably diamino ketal, and at least one benzoxazine monomer, preferably a benzoxazine derivative as defined in any one of claims 1 to 6; b) polymerizing the benzoxazine derivative provided in step a.1) or the benzoxazine derivative prepared in step a.2) or the mixture prepared in step a.3), optionally in the presence of one or more further benzoxazine monomers.

11. Recyclable polymer according to claim 10, wherein the recyclable polymer has dynamic properties and / or is degradable or soluble under acidic conditions, preferably in 25% acetic acid at 80°C, and / or has a glass transition temperature of more than 80°C, preferably of more than 100°C, particularly preferably of 115°C or more, and / or is thermally stable at a temperature of 170°C, preferably at a temperature of 200°C.

12. A process for producing a recyclable polymer as defined in any one of claims 9 to 10, comprising the following steps: a.1) providing a benzoxazine derivative as defined in any one of claims 1 to 6, or a.2) producing a benzoxazine derivative as defined in claim 7, or a.3) mixing at least one aminoacetal, preferably at least one aminoketal, particularly preferably diaminoketal, and at least one benzoxazine monomer, preferably a benzoxazine derivative as defined in any one of claims 1 to 6; b) polymerization of the benzoxazine derivative provided in step a.1) or the benzoxazine derivative prepared in step a.2) or the mixture prepared in step a.3), optionally in the presence of one or more further benzoxazine monomers.

13. Use of a recyclable polymer as defined in any one of claims 10 to 11 as Plastic and / or Adhesive and / or Matrix resin for a composite material, preferably for a fiber composite material.

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