Benzoxazine derivative and application and preparation method thereof as well as recyclable polymer and application and preparation method thereof

Abstract

Described is a benzoxazine derivative of formula (I) # imgabs0 # (I), also a method for producing a benzoxazine derivative according to the invention, and a kit for producing a recoverable polymer and the use of a benzoxazine derivative according to the invention or a kit according to the invention for producing a recoverable polymer, a recoverable polymer based on polybenzoxazine or polybenzoxazine derivatives, a method for producing a recoverable polymer according to the invention and the use of a recoverable polymer according to the invention as a matrix resin for plastics and / or adhesives and / or composites are also described.

Description

Technical Field

[0001] The present invention relates to a benzoxazine derivative. It also relates to a method for preparing the benzoxazine derivative according to the invention. It also relates to a kit for preparing a recyclable polymer and the use of a benzoxazine derivative according to the invention or a kit according to the invention for preparing a recyclable polymer. The present invention also relates to a recyclable polymer based on polybenzoxazine or a polybenzoxazine derivative, a method for preparing the recyclable polymer according to the invention, and the use of the recyclable polymer according to the invention as a plastic and / or adhesive and / or matrix resin for a composite material. Background Art

[0002] The present invention is defined in the accompanying claims. Preferred aspects of the invention are also apparent from the following description together with the examples. Where a particular design solution is described as preferred for one aspect of the invention, the corresponding embodiments also apply mutatis mutandis to the other aspects of the invention. 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 a person skilled in the art would infer otherwise from the present disclosure in individual cases.

[0003] The landfill disposal of composite materials, such as glass-fiber-reinforced plastics (GFRP) or carbon-fiber-reinforced plastics (CFRP), is addressed under current EU landfill regulations (Directive 99 / 31 / EC), the goal of which is to reduce the introduction of organic materials into the environment. Material and raw material recycling for multi-material systems, such as those typically found in fiber-reinforced plastics and composite materials, is not feasible due to the plastics typically used for these applications. The three-dimensional network structure of thermosetting polymer systems, such as phenolic resins, vinyl esters, unsaturated polyester resins (UP), and epoxy resins (EP), commonly used as matrix systems, does not allow the matrix to be dissolved and thus separated from the fibers and other components.

[0004] Benzoxazines and benzoxazine-based composites are used in the aerospace sector due to their thermal and mechanical stability. Due to their properties, they have the potential to replace phenolic resins and partially replace epoxy resins. In addition to material properties suitable for the application, the demand for biodegradable and therefore recyclable thermoset materials is increasing dramatically.

[0005] In the field of degradable resin systems, in particular for use in composite materials, the following solutions are known:

[0006] In the prior art (see a) Zhang et al., Recent advances in recyclable thermosets and thermoset composites based on covalent adaptable networks, J. Mat. SciTechnology 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), methods based on dynamic covalent chemistry of glassy polymers (Vitrimers) as recyclable polymers are described, and these polymers have been shown to be useful as matrix systems for composites.The original mechanism of dynamic transesterification based on the pioneering work of Ludwig Leibler in 2011 (partly in the presence of catalysts) has been transferred to epoxy resins (see a) Capelot, M.; Montarnal, D.; Tournilhac, F.; Leibler, L., Metal-catalyzed transesterification for healing and assembly of thermosets, J. Am. Chem. Soc. 2012, 134, 7664–7667; b) Capelot, M.; Unterlass, M.M.; Tournilhac, F.; Leibler, L., Catalytic Control of the Vitrimer Glass Transition, ACS Macro Lett. 2012, 1, 789–792) and benzoxazines (see a) Antoine Adjaoud et al., Polybenzoxazines: a sustainable platform for the design of fast responsive and catalyst-free vitrimers based on trans-esterification exchanges, Polym. Chem., 2021, 12, 3276-3289 DOI: 10.1039 / d1py00324k; a) WO2021250024A1, c) WO2022122735A1).

[0007] VITRIMAX TMThe VITRIMAX polymer network is based on a dynamic polyimine and EP-based polymer network from Malleable. As is known for glass-like polymers, the VITRIMAX polymer network features reprocessability upon heating above the glass transition temperature, stress relaxation, reversible molding, weldability, and closed-loop recycling of the fully cured material (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).

[0008] For epoxy resins, degradable networks based on disulfide bonds are known from the prior art (see a) Ruiz de Luzuriaga, A.; Martin, R.; Markaide, N.; Rekondo, A.; Cabañero, G.; Rodríguez, 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 fibre reinforced composite with a disulphide containing organic-inorganic Epoxymatrix (Repair of glass fiber-reinforced composites containing organic-inorganic epoxy disulfides), Compos. Sci. Technol. 2017, 152, 85–93). In addition to the self-healing potential known for dynamic polymer networks for reprocessing and repair processes, the disulfide units also allow for the decomposition of the polymer network, enabling recycling. Chemical agents are required for degradation. This concept has also been applied to benzoxazines (see a) A. Trejo-Machin et al., Acardanol-based polybenzoxazine vitrimer: recycling, reshaping and reversible adhesion, Polym. Chem. 2020, 11, 7026–7034; b) WO2021180562A1).

[0009] The use of cleavable ketal groups has been described for degradable epoxy resins based on the Recyclamin® technology (US Pat. No. 10214479B2) developed by Connora Technologies (Hayward, California, USA) and commercialized by Aditya Birla. Recyclamin® is used as an amine hardener for epoxy resins. The resulting epoxy resins contain cleavable groups that allow the polymer and polymer network to degrade into thermoplastic epoxy resins under mild conditions. The resulting plastics and composites based on them are limited to epoxy resins and are characterized by a low glass transition temperature and limited thermal stability. Currently, applications are limited to the production of GFK structures with moderate mechanical and low thermal requirements (e.g., for rotor blades).

[0010] Aditya Birla has expanded upon this system and incorporated cleavable groups such as acetals, ketals, and silanes into the epoxy resin structure (see WO 2020 / 161538 A1). These degradable epoxy monomers are polymerized with conventional amines to produce an epoxy-based polymer network that decomposes under mildly acidic conditions in the presence of organic solvents at temperatures of 130°C (using 5% acetic acid). The temperature to be applied depends on the concentration and strength of the acid used.

[0011] Furthermore, the use of diacetal groups has been demonstrated in polyurethanes (PUs) with a glass transition temperature (Tg) of 130°C (see High-Performance, Biobased, Degradable Polyurethane Thermoset and Its Application in Readily Recyclable Carbon Fiber Composites, ACS Sustainable Chem. Eng. 2020, 8, 30, 11162–11170) and in epoxy resins resulting in Tgs in the 160–170°C range (see Readily recyclable, high-performance thermosetting materials based on alignin-derived spiro diacetal by Ma, S.; Wei, J.; Jia, Z.; Yu, T.; Yuan, W.; Li, Q.; Wang, S.; You, S.; Liu, R.; Zhu, J.). The PU and EP-based polymers are capable of degradation under weak acidic conditions.

[0012] Polybenzoxazine (PBz) is a thermosetting polymer characterized by low shrinkage, very good thermal stability, low water absorption, and a high glass transition temperature (Tg up to 350°C). Due to the high degree of crosslinking based on covalent and non-covalent bonds, PBz is generally brittle. Furthermore, due to the lower reactivity of the oxazine ring compared to epoxy resins, thermal ring-opening polymerization requires curing temperatures of up to 250°C (see 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 agent components to influence the polymerization temperature and toughness of benzoxazines.

[0013] Prior art has described N-CH2-X (X = O, N, S) bonds in PBz (PBz) as significantly more reactive, thus amenable to reversible reactions and thus as building blocks for dynamic polymer networks (see Zhang et al., "Unexpected Healability of an ortho-Blocked Polybenzoxazine Resin," ACS Macro Letters 2019, 8, 506-511). Lei Zhang et al. described the reversibility of PBz in a PBz polymer network with a predominantly phenoxy structure and resulting N-CH2-O bonds. This approach is achieved by using benzoxazine monomers with blocked ortho positions, which inhibit the thermodynamically preferred rearrangement to a phenolic structure with a Mannich bond. The rearrangement from the phenoxy group to the phenol typically occurs at 160°C. This work demonstrates that the phenoxy-type N-CH2-O group possesses dynamic bonding properties, which can only be achieved in ortho-blocked benzoxazine monomers.

[0014] N—CH—N bonds are known from the prior art from the copolymerization of benzoxazine with amines (see Sun et al., Acuring system of benzoxazine with amine: reactivity, reaction mechanism and material properties, RSC Adv. 2015, 5, 19048). Due to the presence of the difunctional amine, BA-a cures at 120°C or 150°C at a similar rate to epoxy / amine systems, and significantly faster and at lower temperatures than conventional benzoxazines BA-a. The reaction of the oxazine ring with the amine produces an N—CH—N zwitterionic bond, which is described as reversible. Upon further heating, this structure irreversibly decomposes into an iminium ion, which, at elevated temperatures, produces the phenoxy and phenol structures known for benzoxazines. Shuai Zhang et al. described similar benzoxazine / amine mixtures that exhibit dynamic properties below 160°C and form structures dominated by irreversible Mannich bridges (see S. Zhang et al., Facile preparation of lightweight and robust polybenzoxazine foams, Ind. Eng. Chem. Res. 2020, 59, 7575-7583).

[0015] In the case of the cleavable benzoxazines described by Wang et al., a diacetal unit is introduced as a cleavable group into the benzoxazines monomer via a phenol component (see P. Wang et al., High heat-resistant and degradable polybenzoxazines with a diacetal structure, ACS Sustainabl Chem. Eng. 2021, 9, 7913-7921). The resulting polymers are characterized by high thermal stability and can have a Tg exceeding 301°C. They can be cleaved under mild acidic conditions. However, the phenol derivatives used for this purpose are characterized by a high melting point, which makes processing and monomer synthesis difficult. Summary of the Invention

[0016] Against the backdrop of the prior art, the main purpose of the present invention is to provide a monomer capable of preparing a recyclable polymer, and to provide a corresponding recyclable polymer; while overcoming one or more shortcomings associated with the preparation of such recyclable polymers and their properties in the prior art.

[0017] Other objects follow from the following and from the claims.

[0018] The main object of the present invention is achieved by benzoxazine derivatives having the following formula (I):

[0019] (I),

[0020] in

[0021] - R 1 、R 2 、R 3 、R 4 、R 5 、R 6 、R 7 and R 8 are the same or different and represent an organic residue or H, respectively;

[0022] - R 9 is an organic functional group, preferably an alkylene group having 1 to 23 carbon atoms, particularly preferably an alkyl group having 1 to 2 carbon atoms;

[0023] - R 10 、R 11 and R 12 are the same or different and represent an organic residue or H, preferably represent an organic residue,

[0024] where R 12 It is preferably or comprises a benzoxazine unit, or is preferably selected from the group consisting of: aminoalkyl groups, aliphatic or aromatic vinyl groups, aliphatic or aromatic propargyl groups, siloxane groups and oligosiloxane groups.

[0025] The benzoxazine derivatives according to the present invention enable the preparation of recyclable polymers (or recyclable polybenzoxazines or polybenzoxazine derivatives) that are advantageously characterized by their ability to degrade under mild conditions (which enables simple recycling of the polymers), combined with a high glass transition temperature (Tg) and good thermomechanical properties and thermal stability. Furthermore, compared to benzoxazine derivatives known from the prior art that contain acetal or ketal groups, the benzoxazine derivatives according to the present invention are distinguished by significantly better processing and the possibility of lowering the polymerization temperature.

[0026] The advantages of the benzoxazine derivatives according to the invention arise in particular from the fact that the benzoxazine derivatives contain (at least) one (cleavable) acetal group or ketal group linked to the nitrogen atom of the benzoxazine structure, whereby the benzoxazine derivatives according to the invention are essentially different from the benzoxazine derivatives having acetal groups or ketal groups known from the prior art (e.g., the benzoxazine derivatives described in P. Wang et al., "High heat-resistant and degradable polybenzoxazines with a diacetal structure," ACS Sustainabel Chem. Eng. 2021, 9, 7913-7921).

[0027] The benzoxazine derivatives according to the invention can be processed as a one-component system and converted into recyclable (cleavable) polybenzoxazines by heating in a ring-opening polymerization.

[0028] Alternatively, the benzoxazine derivatives according to the present invention can be copolymerized with other benzoxazine monomers (e.g., bisphenol A or F-based benzoxazine from Huntsman Advanced Materials). In other words, using the benzoxazine derivatives according to the present invention, both recyclable or degradable homopolymers and copolymers can be obtained.

[0029] Preferred are benzoxazine derivatives according to the present invention having the following formula (Ia)

[0030] (Ia),

[0031] in

[0032] - R1 、R 2 、R 3 、R 4 、R 5 、R 6 、R 7 、R 8 、R 14 、R 15 、R 16 、R 17 、R 18 、R 19 、R 20 and R 21 are the same or different and represent an organic residue or H, respectively;

[0033] - R 9 and R 13 are the same or different and each represents an organic functional group, preferably an alkylene group having 1 to 23 carbon atoms, particularly preferably an alkyl group having 1 to 2 carbon atoms;

[0034] - R 10 and R 11 are the same or different and each represents an organic residue or H, preferably each represents an organic residue.

[0035] Likewise preferred are benzoxazine derivatives according to the invention in which

[0036] R 1 and R 2 or R 2 and R 3 or R 3 and R 4 are linked to each other so as to form a cyclic structure, preferably a heterocyclic structure consisting of at least 5 atoms;

[0037] and / or

[0038] R 18 and R 19 or R 19 and R 20 or R 20 and R 21 are linked to each other so as to form a cyclic structure, preferably a heterocyclic structure consisting of at least 5 atoms;

[0039] and / or

[0040] Residue R 1 、R 2 、R 3 、R 4 、R 5 、R 6 、R 7 、R 8、R 14 、R 15 、R 16 、R 17 、R 18 、R 19 、R 20 and R 21 One or more, preferably all, of the group independently of one another are selected from: H, an alkyl group having preferably 1 to 15 carbon atoms, an alkoxy group having preferably 1 to 10 carbon atoms, and an ester group;

[0041] and / or

[0042] R 10 and / or R 11 represents 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 to each other to form a ring structure consisting of at least 5 carbon atoms.

[0043] Also preferred are benzoxazine derivatives according to the invention, wherein

[0044] - R 5 、R 6 、R 7 、R 8 、R 14 、R 15 、R 16 and R 17 Respectively represent H,

[0045] - R 9 and R 13 represent vinyl, and

[0046] - R 10 and R 11 represent methyl groups respectively.

[0047] Furthermore, preference is given according to the invention to benzoxazine derivatives according to the invention in which R 10 and R 11 represents an organic residue and R 12 represents an organic residue or H.

[0048] This means that the two residues R 10 and R 11 Ketals are formed, wherein surprisingly it has been found that these ketals have one or more or all of the above-mentioned properties. This also applies, for example, to improved performance in recycling, which simplifies recycling.

[0049] Also preferred are benzoxazine derivatives according to the invention, wherein the benzoxazine derivative has the formula (1), (2), (3), (4) or (5):

[0050] (1),

[0051] (2),

[0052] (3),

[0053] (4),

[0054] (5).

[0055] Part of the present invention is also a process for preparing a benzoxazine derivative according to the invention or preferably according to the invention (as defined above and in the claims), said process comprising the following steps:

[0056] One or more phenol derivatives or phenol

[0057] and

[0058] one or more aminoacetals, preferably one or more aminoketals, particularly preferably bisaminoketals,

[0059] In the presence of an aldehyde, the reaction is preferably carried out in the presence of paraformaldehyde.

[0060] During the process according to the invention for preparing the benzoxazine derivative according to the invention, or preferably according to the invention, the acetal or ketal groups are introduced into the benzoxazine derivative to be prepared via the amine component (rather than via the phenol component). This results in the advantages of the benzoxazine derivatives obtained, as already explained above. Furthermore, the process allows for simpler synthesis of benzoxazine derivatives and easier processing of the benzoxazine derivatives obtained.

[0061] Preferably, the process according to the invention for preparing the benzoxazine derivatives according to the invention or preferably according to the invention is carried out in a one-step reaction.

[0062] By correspondingly selecting the phenol derivative, the properties of the benzoxazine derivative according to the invention or preferably according to the invention to be prepared (and the properties of the polymers preparable using them) can additionally be adapted to the respective requirements placed on the benzoxazine derivative (or the polymer to be prepared therefrom).

[0063] Also part of the present invention is a kit for preparing a recyclable polymer (or for preparing a recyclable polybenzoxazine or polybenzoxazine derivative), comprising:

[0064] - at least one aminoacetal, preferably at least one aminoketal, particularly preferably a bisaminoketal, and

[0065] - 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).

[0066] This kit according to the invention, which is usually present as a two-component system, allows the preparation of recyclable polymers (or recyclable polybenzoxazines or polybenzoxazine derivatives) in a simple manner without requiring further monomer design or further monomer synthesis beforehand.

[0067] The preparation of recyclable polymers (or the preparation of recyclable polybenzoxazines or polybenzoxazine derivatives) can in this case be achieved by mixing the components of the kit according to the invention and subsequently carrying out a thermal ring-opening polymerization.

[0068] The benzoxazine monomer included in the kit according to the present invention can be a benzoxazine monomer known from the prior art (e.g., a bisphenol A / anilinobenzoxazine monomer). Preferably, the benzoxazine monomer included in the kit according to the present invention is a benzoxazine derivative according to the present invention or preferably according to the present invention (as defined above and in the claims). That is, for the purposes of the present invention, the term "benzoxazine monomer" refers to both benzoxazine and a benzoxazine derivative.

[0069] Part of the present 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 producing a recyclable polymer (or for producing a recyclable polybenzoxazine or polybenzoxazine derivative).

[0070] Also part of the present invention is a recyclable polymer based on polybenzoxazine or a polybenzoxazine derivative (or a recyclable polybenzoxazine or a polybenzoxazine derivative) comprising acetal groups, preferably ketal groups, wherein the recyclable polymer (or recyclable polybenzoxazine or a polybenzoxazine derivative) is obtainable by a synthesis comprising the following steps:

[0071] a.1) providing a benzoxazine derivative according to the invention or preferably according to the invention (as defined above and in the claims);

[0072] or

[0073] a.2) preparing benzoxazine derivatives according to the invention (as defined above and in the claims);

[0074] or

[0075] a.3) mixing at least one aminoacetal, preferably at least one aminoketal, particularly preferably a bisaminoketal, with at least one benzoxazine monomer, preferably according to the invention and preferably a benzoxazine derivative according to the invention (as defined above and in the claims);

[0076] b) polymerizing (preferably thermal ring-opening polymerization) 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.

[0077] The recyclable polymer according to the present invention (or the recyclable polybenzoxazine or polybenzoxazine derivative according to the present invention) is characterized in that i) the polymer backbone has a benzoxazine-type, preferably phenolic, structure; and ii) (cleavable) acetal groups or ketal groups are embedded in the benzoxazine structure via an amine component.

[0078] 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 combined with a high glass transition temperature and good thermomechanical properties.

[0079] Preferred is a recyclable polymer (or recyclable polybenzoxazine or polybenzoxazine derivative) according to the present invention, wherein the recyclable polymer (or recyclable polybenzoxazine or polybenzoxazine derivative)

[0080] Has dynamic characteristics;

[0081] and / or

[0082] Degradable or soluble under acidic conditions, preferably in 25% acetic acid at 80°C (particularly preferably within 4 hours, more preferably within one hour);

[0083] and / or

[0084] having a glass transition temperature (Tg) of greater than 80°C, preferably greater than 100°C, particularly preferably 115°C or above;

[0085] and / or

[0086] It is thermally stable at a temperature of 170°C, preferably at a temperature of 200°C.

[0087] For the purposes of the present invention, covalently crosslinked polymers are considered dynamic or have dynamic properties if the covalently linked sites can be dynamically broken and reconnected due to appropriate stimuli, preferably changes in temperature and / or pressure in the present case (see Jin et al., "Recent Advances in Dynamic Covalent Chemistry," Chemical Society Reviews, Vol. 42, 2013, pp. 6634-6654). Due to these chemical properties, such polymer networks allow stress relaxation, shaping, and reprocessing, and have self-healing properties.

[0088] Therefore, in a preferred design, the recyclable polymer according to the present invention (or the recyclable polybenzoxazine or polybenzoxazine derivative according to the present invention) is a polymer that is degradable under mild conditions and has dynamic properties.

[0089] For the purposes of the present invention, "thermally stable" means that no decomposition of the polymer can be detected at the corresponding temperature. The thermal stability at the stated temperature can be determined by thermogravimetric analysis (TGA) and / or dynamic differential scanning calorimetry (DSC), preferably as described in Example 6 below.

[0090] Part of the present invention is also a process for preparing a recyclable polymer (or recyclable polybenzoxazine or polybenzoxazine derivative) according to the invention or preferably according to the invention, as defined above and in the claims, comprising the following steps:

[0091] a.1) providing a benzoxazine derivative according to the invention or preferably according to the invention (as defined above and in the claims);

[0092] or

[0093] a.2) preparing benzoxazine derivatives according to the invention (as defined above and in the claims);

[0094] or

[0095] a.3) mixing at least one aminoacetal, preferably at least one aminoketal, particularly preferably a bisaminoketal, with at least one benzoxazine monomer, preferably according to the invention and preferably a benzoxazine derivative according to the invention (as defined above and in the claims);

[0096] 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.

[0097] The polymerization in step b) is usually initiated by elevated temperature. The level of the temperature(s) used for polymerization or curing, and correspondingly the duration of holding the 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).

[0098] Furthermore, part of the present invention is the use of a recyclable polymer according to the invention and preferably according to the invention (or a recyclable benzoxazine or polybenzoxazine derivative), as defined above and in the claims, as:

[0099] plastic;

[0100] and / or

[0101] Adhesives;

[0102] and / or

[0103] The matrix resin of the composite material is preferably the matrix resin of the fiber-reinforced composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0104] Hereinafter, the present invention will be described in detail according to examples and drawings. Herein, the examples described below should be used to describe and explain the present invention in detail, but not to limit its scope. DETAILED DESCRIPTION

[0105] Example 1: Preparation of benzoxazine derivatives according to the present invention

[0106] 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 hours). After the reaction was complete (as monitored by 80 MHz NMR or TLC), the reaction mixture was cooled to room temperature. The solvent was removed under reduced pressure to obtain the crude product. The crude product was dissolved in 100 mL of chloroform and washed with 2 × 100 mL of aqueous sodium hydroxide solution (1 mol / L). The organic phase was separated, dried over Na2SO4, and the solvent was removed on a rotary evaporator under reduced pressure at a bath temperature of 60°C.

[0107] Benzoxazine derivatives were prepared using the following phenol derivatives: (i) sesamol, (ii) ethyl phloretin acetate, (iii) guaiacol, (iv) o-cresol, and (v) p-cresol. Unlike the above preparation procedure, a 5-fold scaled-down synthesis was used for the preparation of benzoxazine derivatives using sesamol.

[0108] Table 1 below lists the phenol derivatives used and the benzoxazine derivatives obtained therefrom.

[0109] Table 1

[0110]

[0111] Example 2: Preparation of a recyclable polymer according to the present invention from the benzoxazine derivative prepared in Example 1

[0112] Recyclable polymers were prepared from the benzoxazine derivatives prepared in Example 1. To this end, the benzoxazine derivatives were polymerized or cured in each case by aging in a circulating air oven at 150° C. for 2 hours and then at 180° C. for a further 2 hours.

[0113] Example 3: Preparation of a recyclable polymer according to the present invention from benzoxazine monomer and diaminoketal

[0114] 7.4 g (16 mmol) of bisphenol A / anilinobenzoxazine monomer (BA-a) available under the trade name ARALDITE® MT35600 from Huntsman Advanced Materials (M = 462.6 g / mol) was added to the mixture.

[0115] (BA-a)

[0116] Homogenize or mix with 2.6 g (16 mmol) of diaminoketal (CAS No. 127090-71-5, M = 162.23 g / mol) in the melt at 110° C. for about 10 minutes.

[0117] The mixture thus prepared was polymerized or cured by aging in a forced air oven initially at 120° C. for 2 hours and subsequently at 150° C. for a further 2 hours.

[0118] Example 4: Investigation of the thermomechanical properties of polymers according to the invention and not according to the invention

[0119] Thermomechanical properties of the following polymers were investigated with the aid of Dynamic Mechanical Analysis (DMA):

[0120] - Polybenzoxazine obtained by polymerizing or curing bisphenol A / anilinobenzoxazine monomers under the trade name ARALDITE® MT35600 from Huntsman Advanced Materials at 180°C for 2 hours and then at 200°C for 2 hours (not according to the present invention, hereinafter and in Figure 1 also referred to as “conventional polybenzoxazines” in

[0121] - Epoxy resin system, named EP YDL 5557 + THR 9357 , from CTP Advanced Materials Ltd., where the epoxy resin system was prepared in accordance with the manufacturer's instructions by combining the resin components (YDL 5557 ) and curing agent component (THR 9357 ) were mixed in a weight ratio of 100:30 and cured 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, hereinafter and in Figure 1 Also known as "EP YDL 5557 + THR 9357 ”);

[0122] - a recyclable polymer, prepared according to Example 3 above (hereinafter also referred to as "degradable polybenzoxazine 1" according to the present invention and in the accompanying drawings);

[0123] - A 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 (also referred to as "degradable polybenzoxazine 2 according to the invention hereinafter and in the figures)

[0124] The results of DMA performed in the temperature range of 25°C to 200°C are Figure 1 Shown in.

[0125] The thermomechanical properties of the recyclable polymers "degradable polybenzoxazine 1" and "degradable polybenzoxazine 2" according to the present invention are superior to those of the degradable epoxy resin "EP YDL" not according to the present invention. 5557 + THR 9357 Here, the glass transition temperature (Tg = 115°C) of “degradable polybenzoxazine 2” is significantly higher than that of “EP YDL 5557 + THR 9357” (= 64 °C). Compared with “degradable polybenzoxazine 2”, the Tg of “degradable polybenzoxazine 1” is lower (= 84.5 °C), which may be attributed to the relatively high content of diaminoketal in terms of stoichiometry.

[0126] Example 5: Degradability and Recyclability Study of Polymers According to the Invention and Not According to the Invention

[0127] The biodegradability and recyclability of the following polymers were investigated with the aid of dissolution tests:

[0128] - "conventional polybenzoxazines" (not according to the invention),

[0129] - "EP YDL 5557 + THR 9357 "(not according to the invention),

[0130] - "degradable polybenzoxazine 1" (according to the invention),

[0131] - "Degradable polybenzoxazine 2" (according to the present invention).

[0132] For a detailed description of the individual polymers, see the corresponding explanation of Example 4. Unlike the parameters described in Example 4, the "EP YDL 5557 + THR 9357 Cured at 80°C.

[0133] For the dissolution test, the polymer samples were subjected to 25% aqueous acetic acid at 80°C. In addition, for the control test "EP YDL 5557 + THR 9357 The hydrolytic and chemical stability of the degradable polybenzoxazine 1, degradable polybenzoxazine 2, and degradable polybenzoxazine 1 were investigated by aging in water at 80°C for 19 h and in methyl ethyl ketone (MEK) at 80°C for 19 h. The test results are summarized in Table 2.

[0134] Table 2

[0135]

[0136] (Containing ketal groups) polymer "EP YDL 5557 + THR 9357 "," "degradable polybenzoxazine 1," and "degradable polybenzoxazine 2," respectively, dissolved in 25% aqueous acetic acid at 80°C after 4 hours. "Conventional polybenzoxazine" showed no dissolution in 25% aqueous acetic acid within the observed time.

[0137] When compared with water and methyl ethyl ketone (MEK), “EP YDL 5557 + THR 9357 No changes in the aggregation state were observed for "degradable polybenzoxazine 1" and "degradable polybenzoxazine 2" after 19 hours.

[0138] Example 6: Study on the thermal stability of the polymer according to the present invention

[0139] The thermal stability of the polymers "degradable polybenzoxazine 1" and "degradable polybenzoxazine 2" according to the present invention was determined using thermogravimetric analysis (TGA) and dynamic differential scanning calorimetry (DSC). For a detailed description of these two polymers, see the corresponding explanation of Example 4.

[0140] TGA measurements were performed in a 20% oxygen atmosphere at a heating rate of 5 K / min in the temperature range of 3°C5 to 550°C. DSC measurements were performed at a heating rate of 10 K / min in the temperature range of 0 to 220°C.

[0141] Figure 2 The DSC test results show the temperature-dependent normalized heat flow. Glass transition temperatures can be detected for "degradable polybenzoxazine 1" and "degradable polybenzoxazine 2." Furthermore, no endothermic or exothermic processes are observed until 220°C.

[0142] The results of the TGA test are Figure 3 Thermogravimetric analysis shows the temperature-dependent mass loss in %. Standards use the temperatures at which the mass loss reaches 1% (T1%) and 5% (T5%) to describe the thermal stability of polymers. The following values were determined for the polymers "degradable polybenzoxazine 1" and "degradable polybenzoxazine 2" according to the invention:

[0143] - "Degradable Polybenzoxazine 1": T 1% = 184°C, T 5% = 227°C;

[0144] - "Degradable Polybenzoxazine 2": T 1% = 230°C, T 5% = 240°C.

[0145] Therefore, the polymers “degradable polybenzoxazine 1” and “degradable polybenzoxazine 2” according to the invention are thermally stable at least up to 184° C. (for “degradable polybenzoxazine 1”) or 230° C. for “degradable polybenzoxazine 2”, respectively.

Claims

1. A benzoxazine derivative having formula (I), （I）， in - R 1 、R 2 、R 3 、R 4 、R 5 、R 6 、R 7 and R 8 are the same or different and represent an organic residue or H, respectively; - R 9 is an organic functional group, preferably an alkylene group having 1 to 23 carbon atoms, particularly preferably an alkyl group having 1 to 2 carbon atoms; - R 10 、R 11 and R 12 are the same or different and represent an organic residue or H, preferably represent an organic residue, where R 12 It is preferably or comprises a benzoxazine unit, or is preferably selected from the group consisting of: an aminoalkyl group, an aliphatic or aromatic vinyl group, an aliphatic or aromatic propargyl group, a siloxane group and an oligosiloxane group.

2. The benzoxazine derivative according to claim 1, which has formula (Ia) (It), in - R 1 、R 2 、R 3 、R 4 、R 5 、R 6 、R 7 、R 8 、R 14 、R 15 、R 16 、R 17 、R 18 、R 19 、R 20 and R 21 are the same or different and represent an organic residue or H, respectively; - R 9 and R 13 are the same or different and each represents an organic functional group, preferably an alkylene group having 1 to 23 carbon atoms, particularly preferably an alkyl group having 1 to 2 carbon atoms; - R 10 and R 11 are the same or different and each represents an organic residue or H, preferably each represents an organic residue.

3. The benzoxazine derivative according to claim 1 or claim 2, wherein R 1 and R 2 or R 2 and R 3 or R 3 and R 4 are linked to each other so as to form a cyclic structure, preferably a heterocyclic structure consisting 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 to each other so as to form a cyclic structure, preferably a heterocyclic structure consisting of at least 5 atoms; and / or Residue R 1 、R 2 、R 3 、R 4 、R 5 、R 6 、R 7 、R 8 、R 14 、R 15 、R 16 、R 17 、R 18 、R 19 、R 20 and R 21 One or more, preferably all, of the group independently of one another are selected from: H, an alkyl group having preferably 1 to 15 carbon atoms, an alkoxy group having preferably 1 to 10 carbon atoms, and an ester group; and / or R 10 and / or R 11 represents 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 to each other to form a ring structure consisting of at least 5 carbon atoms.

4. The benzoxazine derivative according to any one of the preceding claims, wherein - R 5 、R 6 、R 7 、R 8 、R 14 、R 15 、R 16 and R 17 Respectively represent H, - R 9 and R 13 represent vinyl, and - R 10 and R 11 represent methyl groups respectively.

5. The benzoxazine derivative according to any one of the preceding claims, wherein R 10 and R 11 represents an organic residue and R 12 represents an organic residue or H.

6. The benzoxazine derivative according to any one of the preceding claims, wherein the benzoxazine derivative has formula (1), (2), (3), (4) or (5) （1）， （2）， （3）， （4）， （5）。 7. A process for preparing a benzoxazine derivative as defined in any one of claims 1 to 6, said process comprising the steps of: One or more phenol derivatives or phenol and one or more aminoacetals, preferably one or more aminoketals, particularly preferably bisaminoketals, In the presence of an aldehyde, the reaction is preferably carried out in the presence of paraformaldehyde.

8. A kit for preparing a recyclable polymer, the kit comprising: - at least one aminoacetal, preferably at least one aminoketal, particularly preferably a bisaminoketal; 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 a kit as defined in claim 8 for the preparation of a recyclable polymer.

10. A recyclable polymer based on polybenzoxazine or a polybenzoxazine derivative, said recyclable polymer comprising acetal groups, preferably ketal groups, wherein said recyclable polymer is obtainable by a synthesis comprising the following steps: 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 aminoacetal, preferably at least one aminoketal, particularly preferably a bisaminoketal, with 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. The recyclable polymer according to claim 10, wherein the recyclable polymer have dynamic characteristics, and / or Degradable or soluble under acidic conditions, preferably in 25% acetic acid at 80°C; and / or having a glass transition temperature of greater than 80°C, preferably greater than 100°C, particularly preferably 115°C or above, and / or It is thermally stable at a temperature of 170°C, preferably at a temperature of 200°C.

12. A process for preparing a recyclable polymer as defined in any one of claims 9 to 10, said process comprising the steps of: 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 aminoacetal, preferably at least one aminoketal, particularly preferably a bisaminoketal, with 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.

13. Use of a recyclable polymer as defined in any one of claims 10 to 11 as: plastic; and / or Adhesives; and / or The matrix resin of the composite material is preferably the matrix resin of the fiber-reinforced composite material.

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