Bio-based epoxy monomer containing Schiff base structure, preparation method and application of bio-based epoxy monomer, bio-based epoxy resin containing Schiff base structure, and preparation method and application of bio-based epoxy resin

Abstract

The invention provides a bio-based epoxy monomer containing a Schiff base structure, a preparation method and application of the bio-based epoxy monomer, bio-based epoxy resin containing the Schiff base structure, and a preparation method and application of the bio-based epoxy resin, and relates to the technical field of epoxy resin. The bio-based epoxy monomer containing the Schiff base structure provided by the invention contains the Schiff base structure, and based on high bond energy and dynamic characteristics of the Schiff base, the thermal stability, flame retardant property and mechanical property of the bio-based epoxy resin containing the Schiff base structure prepared by taking the monomer as a raw material are synergistically improved. Moreover, the bio-based epoxy monomer containing the Schiff base structure, provided by the invention, is relatively small in molecular weight, relatively high in epoxy value, few in side chain substituent groups, simple in structure, relatively high in symmetry and simple in curing process with a curing agent, and the obtained bio-based epoxy resin containing the Schiff base structure is high in glass transition temperature and excellent in mechanical property and thermal stability; and the dynamic cross-linked network shows good dynamic performance, and has huge application potential in the fields of flame retardance, self-repairing and degradable recycling.

Description

Technical Field

[0001] The invention belongs to the technical field of epoxy resins, and relates to a bio-based epoxy monomer containing a Schiff base structure, a preparation method and application thereof, and a bio-based epoxy resin containing a Schiff base structure, a preparation method and application thereof. Background Art

[0002] Epoxy resin is a polymer material containing two or more epoxy groups in its molecular structure. Compared with other thermosetting plastics, epoxy resin has better chemical and mechanical stability and can be made into a variety of materials such as packaging materials, coatings, injection molding materials, adhesives, etc., and is widely used in daily life and various fields of the national economy. There are many types of epoxy resins, among which bisphenol A epoxy resin (DGEBA) can be mass-produced due to its simple synthesis process, and its output accounts for more than 85% of the total epoxy resin.

[0003] Bisphenol A (BPA) is the main raw material of the most widely used DGEBA, and its main source is petroleum. With the increasingly serious problem of petroleum depletion in recent years, humans have to redevelop green, environmentally friendly and sustainable biomass-based materials in order to replace non-renewable fossil resources and alleviate the problem of petroleum shortage. In addition, BPA, as an endocrine disruptor, can cause endocrine disorders and seriously threaten human health. Therefore, it is urgent to develop renewable resources to prepare new bio-based epoxy resins to replace commercial epoxy resins from petroleum sources.

[0004] In recent years, a large number of bio-based epoxy resins have been synthesized from various biomass resources. There are many monophenolic substances in nature, which create convenient conditions for the synthesis of bio-based epoxy monomers. At present, there are reports on Schiff base structure syringaldehyde epoxy monomers. The Schiff base structure syringaldehyde bisphenol monomers are prepared by reacting biomass syringaldehyde with amino compounds. The Schiff base structure syringaldehyde bisphenol monomers are reacted with epichlorohydrin under a phase transfer catalyst, and then sodium hydroxide solution is added for ring-opening reaction to obtain the Schiff base structure syringaldehyde epoxy monomer. However, the thermal stability of the epoxy resin prepared by the above-mentioned Schiff base structure syringaldehyde epoxy monomer is not good enough. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a bio-based epoxy monomer containing a Schiff base structure, a preparation method and application thereof, a bio-based epoxy resin containing a Schiff base structure, and a preparation method and application thereof. The bio-based epoxy resin containing a Schiff base structure prepared using the bio-based epoxy monomer containing a Schiff base structure provided by the present invention as a raw material has excellent thermal stability.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a bio-based epoxy monomer containing a Schiff base structure, having a structure shown in Formula I:

[0008]

[0009] The present invention also provides a method for preparing the bio-based epoxy monomer containing a Schiff base structure described in the above technical solution, comprising the following steps:

[0010] The bio-based bisphenol monomer, epichlorohydrin and a phase transfer catalyst are mixed to perform a ring-opening reaction, and then an alkali metal hydroxide is added to perform a ring-closing reaction to obtain the bio-based epoxy monomer containing a Schiff base structure;

[0011] The structural formula of the bio-based bisphenol monomer is as follows:

[0012] Preferably, the molar ratio of the bio-based bisphenol monomer to epichlorohydrin is 1:2.5-10;

[0013] The phase transfer catalyst includes one or more of organic ammonium halides, organic ammonium hydrogen sulfates, pyridine and organic amines;

[0014] The molar ratio of the bio-based bisphenol monomer to the phase transfer catalyst is 1:0.0125-0.2;

[0015] The ring-opening reaction temperature is 40 to 100°C, and the time is preferably 1 to 6 hours;

[0016] The molar ratio of the bio-based bisphenol monomer to the alkali metal hydroxide is 1:0.5-2;

[0017] The alkali metal hydroxide is used in the form of an alkali metal hydroxide aqueous solution, and the mass concentration of the alkali metal hydroxide aqueous solution is 30-50%;

[0018] The temperature of the ring-closing reaction is less than 0° C., and the time is preferably 2 to 8 hours.

[0019] The present invention also provides the use of the bio-based epoxy monomer containing the Schiff base structure described in the above technical solution in the preparation of epoxy resin.

[0020] The present invention also provides a bio-based epoxy resin containing a Schiff base structure, and the raw materials for preparing the bio-based epoxy resin include the bio-based epoxy monomer and curing agent described in the above technical solution.

[0021] Preferably, the curing agent includes one or more of an organic amine curing agent, a carboxylic acid curing agent and an acid anhydride curing agent;

[0022] The mass of the curing agent accounts for 10 to 40% of the mass of the bio-based epoxy monomer.

[0023] Preferably, the preparation raw material further comprises a promoter, and the promoter comprises one or more of 2,4,6-tris(dimethylaminomethyl)phenol, 1,5,7-triazabicyclo[4.4.0]decene-5-ene, imidazole, zinc acetylacetonate and 2-methyl-4-ethylimidazole;

[0024] The mass of the accelerator accounts for 0.01 to 10% of the mass of the bio-based epoxy monomer.

[0025] The present invention also provides a method for preparing the bio-based epoxy resin containing a Schiff base structure described in the above technical solution, comprising the following steps: mixing a bio-based epoxy monomer and a curing agent, and curing to obtain the bio-based epoxy resin containing a Schiff base structure.

[0026] Preferably, the curing includes sequentially performing a first curing and a second curing; the temperature of the first curing is 40 to 120° C., and the time is 1 to 10 hours; the temperature of the second curing is 80 to 200° C., and the time is 1 to 10 hours; the temperature of the second curing is higher than the temperature of the first curing;

[0027] When the prepared raw materials further include an accelerator, the mixing is mixing the bio-based epoxy monomer, the curing agent and the accelerator.

[0028] The present invention also provides the use of the bio-based epoxy resin containing a Schiff base structure described in the above technical solution or the bio-based epoxy resin containing a Schiff base structure prepared by the preparation method described in the above technical solution in flame retardant materials, self-healing materials or degradable and recyclable materials.

[0029] The bio-based epoxy monomer containing a Schiff base structure provided by the present invention contains a Schiff base structure. Based on the high bond energy and dynamic characteristics of the Schiff base, the thermal stability, flame retardancy and mechanical properties of the bio-based epoxy resin containing a Schiff base structure prepared using the monomer as a raw material are synergistically improved. Moreover, the bio-based epoxy monomer containing a Schiff base structure provided by the present invention has a small molecular weight, a high epoxy value, few side chain substitution groups, a simple structure, a high symmetry, and a simple curing process with a curing agent. The obtained bio-based epoxy resin containing a Schiff base structure has a high glass transition temperature, excellent mechanical properties and thermal stability, and a dynamic cross-linked network exhibits good dynamic properties, and has great application potential in the fields of flame retardancy, self-repairing, and degradable recycling.

[0030] The Schiff base structure in the bio-based epoxy monomer containing the Schiff base structure provided by the present invention has dynamic chemical properties, and is cured by carboxylic acid curing agent, anhydride curing agent and amine curing agent to form a cross-linked network structure containing dynamic imine bonds and dynamic ester bonds, which synergistically improves the dynamic performance of the epoxy resin cross-linked network. The strategy of applying dynamic chemistry to epoxy resins in the present invention can expand the multifunctionality of epoxy resins while designing high-performance epoxy resins on the molecular structure, thereby solving the problem of "insoluble and infusible" and difficult to recycle after cross-linking and curing of thermosetting epoxy resins. The present invention introduces reversible dynamic covalent bonds into the network of bio-based epoxy resins containing Schiff base structures, and then induces the network structure of thermosetting resins to crack or rearrange through changes in the external environment, so that it has certain degradability and recyclability, which is of great significance for the development of recyclable bio-based epoxy resins to replace traditional thermosetting resins.

[0031] As shown in the test results of the embodiment, the Schiff base structure contained in the bio-based epoxy resin containing Schiff base structure prepared by the present invention has a carbon residue rate of ≥20% at 800°C (N2 atmosphere), a thermal weight loss temperature of 5% ≥260°C, and a glass transition temperature of up to 152°C, which is almost the same as that of commercial bisphenol A epoxy resin, and can replace traditional bisphenol A epoxy resin in some application scenarios.

[0032] The method for preparing the bio-based epoxy monomer containing a Schiff base structure provided by the present invention has simple process, simple operation, low production cost, is green and environmentally friendly, and is suitable for industrial production.

[0033] The method for preparing the bio-based epoxy resin containing a Schiff base structure provided by the present invention has simple process, simple operation, low production cost, is green and environmentally friendly, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a hydrogen nuclear magnetic resonance spectrum of a novel bio-based epoxy resin containing a Schiff base structure prepared in Example;

[0035] Figure 2 The dynamic mechanical curve (DMA) diagram of the bio-based epoxy resin containing a Schiff base structure prepared in Example 4;

[0036] Figure 3 This is a thermogravimetric analysis (TGA) curve of the bio-based epoxy resin containing a Schiff base structure prepared in Example 4;

[0037] Figure 4 The dynamic thermomechanical curve diagram of the bio-based epoxy resin containing a Schiff base structure prepared in Example 5;

[0038] Figure 5 This is a thermogravimetric analysis curve of the bio-based epoxy resin containing a Schiff base structure prepared in Example 5;

[0039] Figure 6 The dynamic thermomechanical curve diagram of the bio-based epoxy resin containing a Schiff base structure prepared in Example 6;

[0040] Figure 7 This is a thermogravimetric analysis curve of the bio-based epoxy resin containing a Schiff base structure prepared in Example 6;

[0041] Figure 8 The dynamic thermomechanical curve of the bio-based epoxy resin containing a Schiff base structure prepared in Example 7;

[0042] Fig. 9 This is a thermogravimetric analysis curve of the bio-based epoxy resin containing a Schiff base structure prepared in Example 7;

[0043] Fig.10 The dynamic thermomechanical curve of the bio-based epoxy resin containing a Schiff base structure prepared in Example 8;

[0044] Fig.11 This is a thermogravimetric analysis curve of the bio-based epoxy resin containing a Schiff base structure prepared in Example 8. DETAILED DESCRIPTION

[0045] The present invention provides a bio-based epoxy monomer containing a Schiff base structure, having a structure shown in Formula I:

[0046]

[0047] The bio-based epoxy monomer containing a Schiff base structure provided by the present invention contains a Schiff base structure. Based on the high bond energy and dynamic characteristics of the Schiff base, the thermal stability, flame retardancy and mechanical properties of the bio-based epoxy resin containing a Schiff base structure prepared with the monomer as a raw material are synergistically improved. Moreover, the bio-based epoxy monomer containing a Schiff base structure provided by the present invention has a small molecular weight, a high epoxy value, few side chain substitution groups, a simple structure, a high symmetry, and a simple curing process with a curing agent. The obtained bio-based epoxy resin containing a Schiff base structure has a high glass transition temperature, excellent mechanical properties and thermal stability, and a dynamic cross-linked network exhibits good dynamic properties, and has great application potential in the fields of flame retardancy, self-repair and degradable recycling. The present invention also provides a method for preparing a bio-based epoxy monomer containing a Schiff base structure described in the above technical scheme, comprising the following steps: mixing a bio-based bisphenol monomer (denoted as VHMBA), epichlorohydrin and a phase transfer catalyst, performing a ring-opening reaction, and then adding an alkali metal hydroxide for a ring-closing reaction to obtain the bio-based epoxy monomer containing a Schiff base structure (denoted as VHMBA-EP);

[0048] The structural formula of the bio-based bisphenol monomer is as follows:

[0049] In the present invention, unless otherwise specified, the raw materials used in the present invention are preferably commercially available products.

[0050] In the present invention, the molar ratio of the bio-based bisphenol monomer to epichlorohydrin is preferably 1:2.5-10, and in specific embodiments may be 1:2.5, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10.

[0051] In the present invention, the phase transfer catalyst preferably includes one or more of organic ammonium halides, organic ammonium hydrogen sulfates, pyridine and organic amines; the organic ammonium halides preferably include one or more of tetrabutylammonium bromide, tetrabutylammonium chloride, benzyltriethylammonium chloride, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride and tetradecyltrimethylammonium chloride; the organic ammonium hydrogen sulfate preferably includes tetrabutylammonium hydrogen sulfate; the organic amine preferably includes tributylamine. In the present invention, the molar ratio of the bio-based bisphenol monomer to the phase transfer catalyst is preferably 1:0.0125-0.2, and in specific embodiments it can be 1:0.0125, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.1, 1:0.15 or 1:0.2.

[0052] In the present invention, the mixing of the bio-based bisphenol monomer (denoted as VHMBA), epichlorohydrin and a phase transfer catalyst preferably includes: dissolving the bio-based bisphenol monomer in epichlorohydrin, stirring and mixing, and then adding the phase transfer catalyst for mixing. In the present invention, the stirring and mixing temperature is 20 to 60°C, and in specific embodiments, it can be 20°C, 25°C, 30°C, 40°C, 50°C or 60°C; the stirring and mixing time is preferably 10 to 40 minutes, and in specific embodiments, it can be 10 minutes, 20 minutes, 30 minutes or 40 minutes.

[0053] In the present invention, the temperature of the ring-opening reaction is preferably 40-100°C, and in specific embodiments it can be 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C; the time of the ring-opening reaction is preferably 1-6h, and in specific embodiments it can be 1h, 2h, 3h, 4h, 5h or 6h.

[0054] In the present invention, the molar ratio of the bio-based bisphenol monomer to the alkali metal hydroxide is preferably 1:0.5-2, and in specific embodiments, it can be 1:0.5, 1:1, 1:1.5 or 1:2. In the present invention, the alkali metal hydroxide preferably includes at least one of sodium hydroxide and potassium hydroxide. In the present invention, the alkali metal hydroxide is preferably used in the form of an alkali metal hydroxide aqueous solution, and the mass concentration of the alkali metal hydroxide aqueous solution is preferably 30-50%, and in specific embodiments, it can be 30%, 35%, 40%, 45% or 50%.

[0055] In the present invention, the temperature of the ring-closing reaction is preferably ≤0°C, preferably -5 to 0°C, and in specific embodiments it can be -5°C, -4°C, -3°C, -2°C, -1°C or 0°C; the time of the ring-closing reaction is preferably 2 to 8h, and in specific embodiments it can be 2h, 3h, 4h, 5h, 6h, 7h or 8h.

[0056] In the present invention, the mechanism of the ring-opening reaction and the ring-closing reaction is as follows:

[0057]

[0058] After completing the ring-closure reaction, the present invention preferably further comprises: subjecting the obtained ring-closure reaction feed liquid to organic solvent extraction, washing the obtained organic phase with water until it is neutral, removing the solvent, and obtaining the bio-based epoxy monomer containing the Schiff base structure. In the present invention, the organic solvent preferably includes one or more of methanol, ethanol, dichloromethane, N,N-dimethylformamide and N-methylpyrrolidone. In the present invention, the water washing preferably includes deionized water washing. The present invention does not specifically limit the method for removing the solvent, and the method for removing the solvent well known to those skilled in the art can be used to remove water and organic solvent.

[0059] In the present invention, the preparation method of the bio-based bisphenol monomer preferably comprises the following steps: neutralizing vanillin amine hydrochloride, and then performing an amine-aldehyde condensation reaction with vanillin to obtain the bio-based bisphenol monomer. Specifically, vanillin amine hydrochloride is mixed with an alcohol solvent, and an alkaline reagent is added for neutralization to obtain a neutralization reaction liquid; the neutralization reaction liquid is subjected to an amine-aldehyde condensation reaction with a vanillin solution to obtain the bio-based bisphenol monomer. The preparation route is as follows:

[0060]

[0061] The invention mixes vanillin amine hydrochloride with an alcohol solvent, adds an alkaline reagent for neutralization, and obtains a neutralization reaction liquid.

[0062] In the present invention, the alcohol solvent preferably includes one or more of methanol, ethanol, isopropanol and ethylene glycol; the molar ratio of the vanillin amine hydrochloride to the alcohol solvent is preferably 1:6.5-40, and in specific embodiments it can be 1:6.5, 1:10, 1:15, 1:20, 1:23, 1:25, 1:30, 1:35 or 1:40.

[0063] In the present invention, the alkaline agent preferably includes at least one of an alkali metal carbonate and an alkali metal hydroxide; the alkali metal hydroxide preferably includes at least one of sodium hydroxide and potassium hydroxide; the alkali metal carbonate preferably includes at least one of potassium carbonate and sodium carbonate; the molar ratio of the vanillin amine hydrochloride to the alkaline agent is preferably: 0.3 to 3, and in specific embodiments it can be 1:0.3, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5 or 1:3.

[0064] In the present invention, the mixing time is preferably 5 to 10 minutes, and in specific embodiments can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes or 10 minutes; the mixing temperature is preferably room temperature.

[0065] In the present invention, the neutralization temperature is preferably 30-80°C, and in specific embodiments it can be 30°C, 40°C, 50°C, 60°C, 70°C or 80°C; the neutralization time is preferably 10-60 min, and in specific embodiments it can be 10 min, 20 min, 30 min, 40 min, 50 min or 60 min.

[0066] After obtaining the neutralization reaction liquid, the present invention conducts an amine-aldehyde condensation reaction between the neutralization reaction liquid and a vanillin solution to obtain a bio-based bisphenol monomer.

[0067] In the present invention, the molar ratio of vanillinamine hydrochloride to vanillin is preferably 1:0.65-4, and in specific embodiments can be 1:0.65, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5 or 1:4.

[0068] In the present invention, the solvent in the vanillin solution preferably includes an alcohol solvent, and the alcohol solvent preferably includes one or more of methanol, ethanol, isopropanol and ethylene glycol; the molar ratio of vanillin to solvent in the vanillin solution is preferably 1:3-20, and in specific embodiments it can be 1:3, 1:5, 1:10, 1:15 or 1:20.

[0069] In the present invention, the temperature of the amine-aldehyde condensation reaction is preferably 30-80°C, and in specific embodiments it can be 30°C, 40°C, 50°C, 60°C, 70°C or 80°C; the time of the amine-aldehyde condensation reaction is preferably 1-8h, and in specific embodiments it can be 1h, 2h, 3h, 4h, 5h, 6h, 7h or 8h.

[0070] After the amine-aldehyde condensation reaction is completed, the present invention preferably further comprises: pouring the reaction solution obtained by the amine-aldehyde condensation reaction into petroleum ether for precipitation, filtering, and drying the obtained solid component to obtain a bio-based bisphenol monomer. In the present invention, the drying temperature is preferably 30 to 100°C, and in specific embodiments it can be 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C; the drying time is preferably 4 to 24 hours, and in specific embodiments it can be 4 hours, 10 hours, 15 hours, 20 hours or 24 hours.

[0071] The present invention uses bio-based raw material vanillin as the starting material for preparing bio-based bisphenol monomers, thereby avoiding the harm to the environment and human health caused by the release of bisphenol A (BPA) in traditional epoxy resins from the source.

[0072] The present invention also provides the use of the bio-based epoxy monomer containing the Schiff base structure described in the above technical solution in the preparation of epoxy resin.

[0073] The present invention also provides a bio-based epoxy resin containing a Schiff base structure, and the raw materials for preparing the bio-based epoxy resin include the bio-based epoxy monomer and curing agent described in the above technical solution.

[0074] In the present invention, the curing agent preferably includes one or more of an organic amine curing agent, a carboxylic acid curing agent and an anhydride curing agent; the organic amine curing agent preferably includes one or more of pentamethylenediamine, isophoronediamine, metaphenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone and 4,4'-dithiodiphenylamine; the carboxylic acid curing agent preferably includes one or more of adipic acid, suberic acid and sebacic acid. In the present invention, the anhydride curing agent preferably includes one or more of succinic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic anhydride and trimellitic anhydride. In the present invention, the mass of the curing agent preferably accounts for 10-40% of the mass of the bio-based epoxy monomer, and in specific embodiments it can be 10%, 12.8%, 15%, 20%, 24.8%, 25%, 30%, 31.2%, 35%, 36.6%, 38% or 40%.

[0075] In the present invention, the raw materials for preparing the bio-based epoxy resin containing a Schiff base structure preferably also include an accelerator, and the accelerator preferably includes one or more of 2,4,6-tris(dimethylaminomethyl)phenol, 1,5,7-triazabicyclo[4.4.0]decene-5-ene, imidazole, zinc acetylacetonate, and 2-methyl-4-ethylimidazole. In the present invention, the mass of the accelerator preferably accounts for 0.01 to 10% of the mass of the bio-based epoxy monomer, and in specific embodiments, it can be 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 3.4%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0076] In the present invention, the glass transition temperature of the bio-based epoxy resin containing a Schiff base structure is preferably ≥95°C, more preferably 95-152°C, and in a specific embodiment, it can be 95°C, 122°C, 125°C, 148°C or 152°C; the storage modulus of the bio-based epoxy resin containing a Schiff base structure at 30°C is preferably ≥2700MPa, more preferably 2700-4823MPa, and in a specific embodiment, it can be 2700MPa, 3758MPa, 4490MPa, 4654MPa or 4823MPa; the 5% thermal weight loss temperature (N 2 atmosphere) is preferably ≥260°C, and in specific embodiments it can be 260°C, 270°C, 273°C, 284°C or 295°C; the residual carbon rate of the bio-based epoxy resin containing a Schiff base structure at 800°C (N2 atmosphere) is preferably ≥20%, more preferably 20-36%, and in specific embodiments it can be 20%, 26%, 30%, 35% or 36%; the static tensile strength of the bio-based epoxy resin containing a Schiff base structure at room temperature is preferably ≥55MPa, more preferably 55-71MPa, and in specific embodiments it can be 55MPa, 65MPa, 67MPa, 70MPa or 71MPa.

[0077] The Schiff base structure in the bio-based epoxy monomer containing the Schiff base structure provided by the present invention has dynamic chemical properties, and is cured by a carboxylic acid curing agent and an anhydride curing agent to form a cross-linked network structure containing dynamic imine bonds and dynamic ester bonds, which synergistically improves the dynamic performance of the epoxy resin cross-linked network. The strategy of applying dynamic chemistry to epoxy resins in the present invention can expand the multifunctionality of epoxy resins while designing high-performance epoxy resins on the molecular structure, thereby solving the problem of "insoluble and infusible" and difficult to recycle after cross-linking and curing of thermosetting epoxy resins. The present invention introduces reversible dynamic covalent bonds into the network of bio-based epoxy resins containing Schiff base structures, and then induces the network structure of thermosetting resins to crack or rearrange through changes in the external environment, so that it has certain degradability and recyclability, which is of great significance for the development of recyclable bio-based epoxy resins to replace traditional thermosetting resins.

[0078] The present invention also provides a method for preparing the bio-based epoxy resin containing a Schiff base structure described in the above technical solution, comprising the following steps: mixing a bio-based epoxy monomer and a curing agent, and curing to obtain the bio-based epoxy resin containing a Schiff base structure.

[0079] In the present invention, the mixing temperature is preferably 25-120°C, and in specific embodiments can be 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C. The present invention has no special limitation on the mixing time, as long as the raw materials can be mixed evenly.

[0080] In the present invention, when the raw materials for preparing the bio-based epoxy resin containing a Schiff base structure also include an accelerator, the mixing is preferably mixing the bio-based epoxy monomer, the curing agent and the accelerator, more preferably mixing the bio-based epoxy monomer and the accelerator, and mixing the resulting mixture with the curing agent.

[0081] After the mixing is completed, the present invention preferably further comprises vacuum degassing the mixed solution obtained by the mixing, and then performing subsequent curing. In the present invention, the temperature of the vacuum degassing is preferably 25 to 120°C, and in specific embodiments it can be 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C, and the temperature of the vacuum degassing is preferably the same as the temperature of the mixing; the time of the vacuum degassing is preferably 30 to 60 minutes, and in specific embodiments it can be 30 minutes, 40 minutes, 50 minutes or 60 minutes; the vacuum degassing is preferably carried out in an oven.

[0082] In the present invention, the curing preferably includes a first curing and a second curing in sequence, and the temperature of the second curing is preferably higher than the temperature of the first curing. In the present invention, the temperature of the first curing is preferably 40 to 120°C, and in specific embodiments, it can be 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C; the time of the first curing is preferably 1 to 10 hours, and in specific embodiments, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours. In the present invention, the temperature of the second curing is preferably 80-200°C, and in specific embodiments, it can be 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C; the time of the second curing is preferably 1-10h, and in specific embodiments, it can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h. In the present invention, the curing is preferably carried out in a mold, and the mold is preferably preheated before use, and the preheating temperature is preferably 40-120°C, and in specific embodiments, it can be 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C; the preheating temperature is preferably the same as the temperature of the first curing.

[0083] The method for preparing the bio-based epoxy resin containing a Schiff base structure provided by the present invention has simple process, simple operation, low production cost, is green and environmentally friendly, and is suitable for industrial production.

[0084] The present invention also provides the use of the bio-based epoxy resin containing a Schiff base structure described in the above technical solution or the bio-based epoxy resin containing a Schiff base structure obtained by the preparation method described in the above technical solution in flame retardant materials, self-healing materials or degradable and recyclable materials. The bio-based epoxy resin containing a Schiff base structure provided by the present invention has a high glass transition temperature, excellent mechanical properties and thermal stability, and a dynamic cross-linked network exhibits good dynamic properties. It has great application potential in the fields of flame retardancy, self-healing and degradable recycling, and is of great significance for the development of recyclable bio-based epoxy resins to replace traditional thermosetting resins.

[0085] The bio-based epoxy monomer containing a Schiff base structure, its preparation method and application, and the bio-based epoxy resin containing a Schiff base structure, its preparation method and application provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0086] Example 1

[0087] (1) Preparation of bio-based bisphenol monomer (VHMBA): Vanillin amine hydrochloride (0.1 mol) was dissolved in methanol (2.3 mol) and mixed for 10 min, then anhydrous potassium carbonate (0.1 mol) was added, the temperature was raised to 55°C and stirred for 30 min to obtain a neutralization reaction solution; vanillin (0.1 mol) was dissolved in methanol (1.2 mol), the obtained vanillin solution was added to the neutralization reaction solution, and the reaction was carried out at 55°C for 4 h. After the reaction, the reaction solution was poured into petroleum ether for precipitation, filtered, and the obtained solid component was placed in a vacuum oven at 80°C and dried for 12 h to obtain VHMBA (24.8 g, yield 87%).

[0088] (2) Preparation of bio-based epoxy monomer containing Schiff base structure (VHMBA-EP): VHMBA (0.1 mol) was dissolved in epichlorohydrin (1.0 mol), stirred at 40°C for 30 min, tetrabutylammonium bromide (10.3 mmol) as a phase transfer catalyst was added, the temperature was raised to 80°C for reaction for 2 h, cooled to room temperature and then treated in an ice bath. When the temperature dropped below 0°C, a 40% by mass aqueous solution of sodium hydroxide (0.2 mol) was added, and the system was kept at this temperature for reaction for 5 h, extracted with ethyl acetate, and the obtained organic phase was washed with deionized water until neutral, and the ethyl acetate was completely removed by rotary evaporation to obtain VHMBA-EP (32.3 g, yield 81%).

[0089] Example 2

[0090] (1) Preparation of bio-based bisphenol monomer (VHMBA): Dissolve vanillin amine hydrochloride (0.1 mol) in methanol (2.3 mol) and mix for 10 min, then add anhydrous potassium carbonate (0.1 mol). Heat to 60°C and stir for 30 min to obtain a neutralization reaction solution; then dissolve vanillin (0.1 mol) in methanol (1.2 mol), add the obtained vanillin solution to the neutralization reaction solution, and react at 60°C for 6 h. After the reaction is completed, pour the reaction solution into petroleum ether for precipitation, filter, filter, and place the obtained solid component in a vacuum oven at 80°C to dry for 12 h to obtain VHMBA (25.8 g, yield 90%).

[0091] (2) Preparation of bio-based epoxy monomer containing Schiff base structure (VHMBA-EP): VHMBA (0.1 mol) was dissolved in epichlorohydrin (1.0 mol), stirred at 60°C for 30 min, tetrabutylammonium bromide (10.3 mmol) as a phase transfer catalyst was added, the temperature was raised to 80°C for reaction for 4 h, cooled to room temperature and then treated in an ice bath. When the temperature dropped below 0°C, a 40% by mass aqueous solution of sodium hydroxide (0.2 mol) was added, and the system was kept at this temperature for reaction for 5 h, extracted with ethyl acetate, and the obtained organic phase was washed with deionized water until neutral, and the ethyl acetate was removed by rotary evaporation to obtain VHMBA-EP (31.5 g, yield 79%).

[0092] Example 3

[0093] (1) Preparation of bio-based bisphenol monomer (VHMBA): Dissolve vanillin amine hydrochloride (0.1 mol) in methanol (2.3 mol) and mix for 10 min, then add anhydrous potassium carbonate (0.1 mol). Heat to 60°C and stir for 30 min to obtain a neutralization reaction solution; then dissolve vanillin (0.1 mol) in methanol (1.2 mol), add the obtained vanillin solution to the neutralization reaction solution, and react at 60°C for 6 h. After the reaction is completed, pour the reaction solution into petroleum ether for precipitation, filter, filter, and place the obtained solid component in a vacuum oven at 80°C to dry for 12 h to obtain VHMBA (25.8 g, yield 90%).

[0094] (2) Preparation of bio-based epoxy monomer containing Schiff base structure (VHMBA-EP): VHMBA (0.1 mol) was dissolved in epichlorohydrin (1.0 mol), stirred at 40°C for 30 min, tetrabutylammonium bromide (10.3 mmol) as a phase transfer catalyst was added, the temperature was raised to 80°C for reaction for 2 h, cooled to room temperature and then treated in an ice bath. When the temperature dropped below 0°C, a 40% by mass aqueous solution of sodium hydroxide (0.2 mol) was added, and the system was kept at this temperature for reaction for 5 h, extracted with ethyl acetate, and the obtained organic phase was washed with deionized water until neutral, and the ethyl acetate was completely removed by rotary evaporation to obtain VHMBA-EP (32.3 g, yield 81%).

[0095] Figure 1 This is the hydrogen nuclear magnetic resonance spectrum of the bio-based epoxy monomer prepared in Example 3. It can be seen that the present invention successfully prepared a bio-based epoxy monomer having a structure shown in Formula I.

[0096] Epoxy value test: the theoretical epoxy value of VHMBA-EP prepared in Example 1 is 0.501 mol / 100 g, and the actual tested epoxy value is 0.470 mol / 100 g; the theoretical epoxy value of VHMBA-EP prepared in Example 2 is 0.501 mol / 100 g, and the actual tested epoxy value is 0.480 mol / 100 g; the theoretical epoxy value of VHMBA-EP prepared in Example 3 is 0.501 mol / 100 g, and the actual tested epoxy value is 0.460 mol / 100 g.

[0097] Example 4

[0098] Preparation of a bio-based epoxy resin containing a Schiff base structure: 1.56 g of a curing agent, 4,4'-dithiodiphenylamine, and 5 g of VHMBA-EP prepared in Example 1 were mixed evenly at 80° C., bubbles were removed by vacuum at 80° C. for 30 min, and the mixture was poured into a mold that had been preheated in a 100° C. forced air oven, first cured at 100° C. for 4 h, then cured at 150° C. for 4 h, and then demolded after cooling to room temperature to obtain a bio-based epoxy resin containing a Schiff base structure.

[0099] The glass transition temperature of the bio-based epoxy resin containing Schiff base structure is 148℃, and the storage modulus at 30℃ is 3758MPa (see Figure 2 ); The 5% thermal weight loss temperature under N2 atmosphere reaches 260°C, and the residual carbon rate at 800°C is 36% (see Figure 3 ); the static tensile strength at room temperature is 70MPa.

[0100] Example 5

[0101] Preparation of a bio-based epoxy resin containing a Schiff base structure: 0.64 g of curing agent 1,5-pentanediamine and 5 g of VHMBA-EP prepared in Example 1 were mixed evenly at 25°C, the bubbles were removed by vacuum at 25°C for 20 min, and the mixture was poured into a mold that had been preheated in a 60°C forced air oven. The mixture was first cured at 60°C for 6 h, and then second cured at 120°C for 10 h. The mixture was cooled to room temperature and then demolded to obtain a bio-based epoxy resin containing a Schiff base structure.

[0102] The glass transition temperature of the bio-based epoxy resin containing Schiff base structure is 125℃, the storage modulus at 30℃ is 4823MPa, and the elasticity (see Figure 4 ); The 5% thermal weight loss temperature under N2 atmosphere reaches 270°C, and the residual carbon rate at 800°C is 26% (see Figure 5 ); The static tensile strength at room temperature is 65MPa.

[0103] Example 6

[0104] Preparation of a bio-based epoxy resin containing a Schiff base structure: 1.24 g of curing agent 4,4'-diaminodiphenylmethane and 5 g of VHMBA-EP prepared in Example 1 were mixed evenly at 90°C, and then the bubbles were removed by vacuum at 90°C for 30 minutes. The mixture was then poured into a mold that had been preheated in a 100°C forced air oven, first cured at 120°C for 4 hours, and second cured at 150°C for 2 hours. The mixture was cooled to room temperature and then demolded to obtain a bio-based epoxy resin containing a Schiff base structure.

[0105] The glass transition temperature of the bio-based epoxy resin containing Schiff base structure is 152°C, and the storage modulus at 30°C is 2700MPa (see Figure 6 ). The 5% thermal weight loss temperature under N2 atmosphere reaches 295℃, and the residual carbon rate at 800℃ is 20% (see Figure 7 ); The static tensile strength at room temperature is 67MPa.

[0106] Example 7

[0107] Preparation of a bio-based epoxy resin containing a Schiff base structure: 0.3 g of zinc acetylacetonate and 5 g of VHMBA-EP prepared in Example 2 were mixed uniformly at 100° C., and then 1.25 g of a curing agent, succinic anhydride, was added. After the prepolymer was completely mixed, bubbles were removed by vacuum at 90° C. for 30 min, and then the mixture was poured into a mold that had been preheated in a 120° C. forced air oven. The mixture was first cured at 120° C. for 4 h, and then secondly cured at 150° C. for 6 h. After cooling to room temperature, the mixture was demolded to obtain a bio-based epoxy resin containing a Schiff base structure.

[0108] The glass transition temperature of the bio-based epoxy resin containing Schiff base structure is 122℃, and the storage modulus at 30℃ is 4654MPa (see Figure 8 ); The 5% thermal weight loss temperature under N2 atmosphere reaches 284°C, and the residual carbon rate at 800°C is 35% (see Fig. 9 ); The static tensile strength at room temperature is 71MPa.

[0109] Example 8

[0110] Preparation of a bio-based epoxy resin containing a Schiff base structure: 0.17 g of 1,5,7-triazabicyclo[4.4.0]decene-5-ene and 5 g of VHMBA-EP prepared in Example 2 were mixed uniformly at 80° C., and then 1.83 g of adipic acid as a curing agent was added. After the prepolymer was completely mixed, bubbles were removed by vacuum at 80° C. for 30 min and then poured into a mold that had been preheated in a 120° C. forced air oven. The mixture was first cured at 120° C. for 4 h and then cured at 160° C. for 6 h. After cooling to room temperature, the mixture was demolded to obtain a bio-based epoxy resin containing a Schiff base structure.

[0111] The glass transition temperature of the bio-based epoxy resin containing Schiff base structure is 95°C, and the storage modulus at 30°C is 4490MPa (see Fig.10 ). The 5% thermal weight loss temperature under N2 atmosphere reaches 273℃, and the residual carbon rate at 800℃ is 30% (see Fig.11 ); The static tensile strength at room temperature is 55MPa.

[0112] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A bio-based epoxy monomer containing a Schiff base structure, having a structure shown in Formula I:

2. The method for preparing the bio-based epoxy monomer containing a Schiff base structure according to claim 1, comprising the following steps: The bio-based bisphenol monomer, epichlorohydrin and a phase transfer catalyst are mixed to perform a ring-opening reaction, and then an alkali metal hydroxide is added to perform a ring-closing reaction to obtain the bio-based epoxy monomer containing a Schiff base structure; The structural formula of the bio-based bisphenol monomer is as follows:

3. The preparation method according to claim 2, characterized in that: The molar ratio of the bio-based bisphenol monomer to epichlorohydrin is 1:2.5-10; The phase transfer catalyst includes one or more of organic ammonium halides, organic ammonium hydrogen sulfates, pyridine and organic amines; The molar ratio of the bio-based bisphenol monomer to the phase transfer catalyst is 1:0.0125-0.2; The ring-opening reaction temperature is 40 to 100°C, and the time is preferably 1 to 6 hours; The molar ratio of the bio-based bisphenol monomer to the alkali metal hydroxide is 1:0.5-2; The alkali metal hydroxide is used in the form of an alkali metal hydroxide aqueous solution, and the mass concentration of the alkali metal hydroxide aqueous solution is 30-50%; The temperature of the ring-closing reaction is less than 0° C., and the time is preferably 2 to 8 hours.

4. Use of the bio-based epoxy monomer containing a Schiff base structure according to claim 1 in the preparation of epoxy resin.

5. A bio-based epoxy resin containing a Schiff base structure, wherein the raw materials for preparing the bio-based epoxy resin include the bio-based epoxy monomer according to claim 1 and a curing agent.

6. The bio-based epoxy resin containing a Schiff base structure according to claim 5, characterized in that: The curing agent includes one or more of an organic amine curing agent, a carboxylic acid curing agent and an acid anhydride curing agent; The mass of the curing agent accounts for 10 to 40% of the mass of the bio-based epoxy monomer.

7. The bio-based epoxy resin containing a Schiff base structure according to claim 5, characterized in that: The preparation raw materials also include a promoter, which includes one or more of 2,4,6-tris(dimethylaminomethyl)phenol, 1,5,7-triazabicyclo[4.4.0]decene-5-ene, imidazole, zinc acetylacetonate and 2-methyl-4-ethylimidazole; The mass of the accelerator accounts for 0.01 to 10% of the mass of the bio-based epoxy monomer.

8. The method for preparing the bio-based epoxy resin containing a Schiff base structure according to any one of claims 5 to 7, comprising the following steps: The bio-based epoxy monomer and the curing agent are mixed and cured to obtain the bio-based epoxy resin containing the Schiff base structure.

9. The preparation method according to claim 8, characterized in that: The curing includes sequentially performing a first curing and a second curing; the temperature of the first curing is 40 to 120° C., and the time is 1 to 10 hours; the temperature of the second curing is 80 to 200° C., and the time is 1 to 10 hours; the temperature of the second curing is higher than the temperature of the first curing; When the prepared raw materials further include an accelerator, the mixing is mixing the bio-based epoxy monomer, the curing agent and the accelerator.

10. Use of the bio-based epoxy resin containing a Schiff base structure according to any one of claims 5 to 7 or the bio-based epoxy resin containing a Schiff base structure obtained by the preparation method according to any one of claims 8 to 9 in flame retardant materials, self-healing materials or degradable and recyclable materials.

Images