A high-strength insulating Schiff base degradable epoxy resin material and preparation method thereof

Abstract

The present invention belongs to the technical field of epoxy resins, and particularly relates to a Schiff base group-containing degradable epoxy resin material with high strength and insulation and a preparation method thereof. The present invention adopts a stepwise reaction. First, the molecular structure design and functional building block construction of the Schiff base segment are carried out, and then the Schiff base building block is introduced between the molecular chains of the crosslinked network through the chain extension modification of the resin molecules, so as to endow the epoxy resin material with high-efficiency degradation ability in acidic solutions, and deep carrier traps are constructed in the crosslinked network to regulate the transport behavior of carriers in the network, thereby improving the insulation performance of the epoxy resin material. In addition, the synergistic effect of the rigid polybenzene ring structure and the flexible polyether bonds in the intermolecular Schiff base segment, as well as the adjustable length of the Schiff base segment, also realizes the controllability of the packing density of the molecular chains in the epoxy crosslinked network, enhances the mechanical strength of the epoxy resin material, and meets the high service performance requirements of the high-degradation epoxy resin material in a high-insulation service environment.

Description

Technical Field

[0001] The invention belongs to the field of degradable epoxy resin modification, and particularly relates to a high-strength insulating Schiff base degradable epoxy resin material and a preparation method thereof. Background Art

[0002] Epoxy resin is used as a core material for precision electronic device packaging, advanced electrical equipment manufacturing, and high-end power equipment insulation due to its excellent insulation, mechanical and chemical stability. However, after epoxy resin is cross-linked and cured, it forms a highly stable three-dimensional cross-linked network structure, making it difficult to degrade and recycle epoxy resin materials. my country's annual consumption of electrical epoxy can reach hundreds of thousands of tons. The environmental pollution and waste of resources caused by the retirement and disposal of thermosetting epoxy resin materials have become a major problem that needs to be solved urgently.

[0003] In response to the degradation and recycling problems of thermosetting epoxy resin materials, in 2011, French scholar Liberle proposed a revolutionary new technology for epoxy resin degradation. By introducing dynamic covalent bonds that can undergo dynamic exchange reactions into epoxy resin molecules. By applying specific external stimuli, the exchange reaction between the dynamic covalent bonds in the epoxy resin cross-linking network and the external medium is triggered, the directional breakage of the chemical bonds in the resin network is achieved, and the epoxy cross-linking network is efficiently deconstructed. However, although the introduction of dynamic covalent bonds in the epoxy resin cross-linking network gives the epoxy resin material high degradation characteristics, it also becomes an "unstable factor" in the network, which will lead to a decrease in the electrical, mechanical, thermal and other service performance of the epoxy resin material, especially when the epoxy resin material is operated for a long time in scenarios with high insulation requirements such as power equipment. The high insulation service environment is another key challenge for the long-term reliability of epoxy resin materials. Therefore, the synergy between the high degradability and high service performance of epoxy resin materials is a major problem that needs to be broken through.

[0004] In response to the above-mentioned problem of synergistic performance of epoxy resin materials, existing research has achieved a balance between the degradability and other service performance of epoxy resin materials by constructing a multi-level interlocking covalent adaptive cross-linking network. It mainly introduces multiple dynamic covalent bonds in the cross-linking network, and according to the stimulus response characteristics of different dynamic covalent bonds, while achieving the degradable functionalization of epoxy resin materials, it further takes into account the mechanical and thermal properties of epoxy resin materials. However, this epoxy resin material is not for high-insulation application scenarios, and there are no high requirements for the insulation performance of epoxy resin materials. Moreover, the glass transition temperature of this epoxy resin material is only 103°C at most, which cannot meet the long-term operation performance requirements of the material under the coupling of electrical, mechanical, and thermal fields. Therefore, for the high-insulation operation scenarios of epoxy resin materials, it is very important to propose an effective method that takes into account the degradation and service performance of epoxy insulation materials. Summary of the invention

[0005] In view of the above problems, one of the objects of the present invention is to provide a method for preparing a Schiff base-based degradable epoxy resin material with high strength insulation, by constructing Schiff base segments that can undergo dynamic exchange reactions between the molecular chains of the epoxy cross-linked network, and based on the structural design of the interchain Schiff base segments and the optimization of the number of segments, to achieve coordinated regulation of the multi-dimensional properties of the highly degradable epoxy resin material, and to achieve coordinated improvement of the mechanical and insulation properties of the degradable epoxy material constructed based on the interchain Schiff base segments.

[0006] To achieve the above object, the present invention adopts the following technical scheme: a method for preparing a high-strength insulating Schiff base degradable epoxy resin material, comprising the following steps:

[0007] S1. Weigh a Schiff base building block, an epoxy resin and a phase transfer catalyst in a molar ratio of (0.1-0.3): 1: (0.001-0.003); the molecular structure of the Schiff base building block is:

[0008] ;

[0009] Among them, the R group is C 6 H 4 , C 12 H 8 O.C 13 H 10 , C 15 H 14 and C 13 H 8 F 6 One of;

[0010] The epoxy resin and the Schiff base building block are mixed, stirred and dissolved at 90-120°C to form a uniform mixed solution, a phase transfer catalyst is added, the heating temperature is adjusted to 130-160°C, stirring is continued at this temperature for 6-12 hours, and cooling is performed after the reaction is completed to obtain the Schiff base chain extension modified epoxy resin;

[0011] S2. Weigh the Schiff base chain-extending modified epoxy resin, the anhydride curing agent and the amine accelerator in a mass ratio of 100:(60-90):(0.005-0.015);

[0012] The epoxy resin modified by Schiff base chain extension and the acid anhydride curing agent are placed in a reaction kettle, heated and stirred at 80-120°C to form a uniform mixed liquid, the mixed liquid is subjected to a first degassing treatment, an amine accelerator is added during the treatment, and the degassed mixed liquid is poured into a preheated mold, subjected to a second degassing treatment, cured, cooled to room temperature and then demolded, thereby obtaining an epoxy insulating material with interchain Schiff base segments.

[0013] Further improvement on the preparation method of Schiff base degradable epoxy resin material with high strength insulation:

[0014] Preferably, the epoxy resin described in step S1 is one or a combination of two or more of glycidyl ether, glycidyl ester, aliphatic and alicyclic epoxy resins.

[0015] Preferably, the phase transfer catalyst described in step S1 is one or a combination of two or more of onium salts, open-chain polyethers, tertiary amines, crown ethers, thioethers and quaternary ammonium salts.

[0016] Preferably, the anhydride curing agent described in step S2 is one or a combination of two or more of phthalic anhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride and methylnadic anhydride.

[0017] Preferably, the amine accelerator described in step S2 is one or a combination of two or more of aliphatic amines, alicyclic amines, aromatic amines and heterocyclic amine accelerators.

[0018] Preferably, the specific processes of the first degassing treatment, the second degassing treatment and curing in step S2 are as follows: The mixed material liquid is degassed at a vacuum degree of 0.08 - 0.1 MPa for 10 - 120 min, the amine accelerator is added, and then vacuum degassing is continued for 5 - 20 min. The vacuum condition is removed, and the first degassing treatment ends; then the mixed material liquid is poured into a mold preheated to 80 - 120 °C, placed under heating conditions of 120 - 140 °C for 5 - 30 min to complete the second degassing treatment, and then pre-cured at 120 - 140 °C for 3 - 9 h, and then post-cured at 150 - 170 °C for 3 - 18 h.

[0019] Preferably, the preparation method of the Schiff base building block described in step S1 is as follows:

[0020] S11. Weigh kojic acid, diamine compound and p-toluenesulfonic acid in a molar ratio of 2: (0.8 - 1.2): (0.02 - 0.1);

[0021] S12. Dissolve kojic acid and diamine compound in benzene according to the above molar ratio, and magnetically stir until completely dissolved under heating conditions of 40 - 80 °C. Then add the catalyst p-toluenesulfonic acid, adjust the heating temperature to 60 - 140 °C for reflux condensation for 12 - 24 h. After the reaction ends, filter and rotary evaporate the excess benzene to obtain the Schiff base building block product.

[0022] Preferably, the diamine compound described in steps S11 and S12 is one or a combination of two or more of 4,4'-diaminodiphenyl ether, p-phenylenediamine, 4,4'-methylenedianiline, 4,4'-(2,2-propylidene)dianiline, and 4,4'-(perfluoropropane-2,2-diyl)dianiline.

[0023] Preferably, in steps S1 and S12, the progress of the chain extension modification reaction is tracked by thin layer chromatography.

[0024] The second object of the present invention is to provide a high-strength insulating Schiff base degradable epoxy resin material prepared by the preparation method of the high-strength insulating Schiff base degradable epoxy resin material described in any one of the above.

[0025] Compared with the prior art, the following beneficial effects are achieved:

[0026] 1) In order to overcome the difficulty in achieving the coordinated service performance of electricity, mechanics, heat, etc. of epoxy materials while realizing the degradable functionalization of epoxy materials in the prior art, and being unable to meet the performance requirements for long-term operation of epoxy materials in high-insulation scenarios. The present invention provides a method for synergistically improving the insulation and mechanical properties of a degradable epoxy resin material based on the construction of Schiff base segments between chains. By constructing Schiff base segments that can undergo dynamic exchange reactions between the molecular chains of the epoxy crosslinked network, and based on the structural design and optimization of the number of Schiff base segments between chains, the high service performance requirements of high-degradation epoxy resin materials in a high-insulation service environment are achieved. The main design ideas are as follows:

[0027] The present invention adopts a step-by-step reaction. First, the molecular structure design and functional building block construction of the Schiff base segment are carried out to construct a rigid polybenzene ring Schiff base building block with pH-responsive characteristics, and this Schiff base segment is introduced between the molecular chains of the crosslinked network through the chain extension modification of the resin molecule to endow the epoxy resin material with high-efficiency degradation ability in acidic solutions. At the same time, the introduction of the Schiff base segment between chains can also construct deep carrier traps in the crosslinked network, thereby regulating the transport behavior of carriers in the crosslinked network and inhibiting the proliferation of carriers inside the material under high electric fields, realizing the enhancement of the insulation performance of the epoxy crosslinked network. At the same time, through the construction of the Schiff base segment between molecular chains, more flexible ether bonds and a rigid polybenzene ring structure between chains are introduced into the resin main chain. The synergistic effect of the highly rigid polybenzene ring structure and multiple flexible ether bonds in the Schiff base segment between chains, as well as the adjustable length of the Schiff base segment, also realizes the controllability of the packing density of molecular chains in the epoxy crosslinked network, achieving the coordination of rigidity and flexibility of the epoxy crosslinked network, thereby being able to synergistically enhance the mechanical strength of the epoxy insulating material. The steric effect of the rigid polybenzene ring structure can also inhibit the free rotation of segments in the crosslinked network, improve the cooperative torsional barrier of segments in the network, and cause a certain improvement in the thermal performance of the epoxy crosslinked network.

[0028] 2) The Schiff base segments constructed between the molecular chains of the epoxy crosslinked network prepared by the present invention have pH-responsive characteristics. The -C=N dynamic covalent bonds within the segments can break chemical bonds in an acidic solution, thereby achieving the purpose of depolymerizing the epoxy crosslinked network. At the same time, the response of the -C=N dynamic covalent bond to temperature also endows the epoxy crosslinked network with dynamics, and thus the thermal reshaping and damage self-healing characteristics of the epoxy insulating material can be realized.

[0029] The present invention constructs Schiff base segments with both high electron affinity and low vertical ionization energy between the molecular chains of the epoxy crosslinked network. The introduction of this Schiff base segment can create deep carrier traps within the epoxy crosslinked network, increase the density of carrier traps, and then regulate the transport behavior of carriers within the epoxy crosslinked network, inhibit the proliferation of carriers inside the epoxy material under high fields, and improve the insulation performance of the epoxy crosslinked network. At the same time, the adjustable length of the Schiff base segments within the epoxy crosslinked network also endows the epoxy crosslinked network with a higher molecular chain packing density, thereby reducing the proportion of free volume within the crosslinked network and weakening the motion response ability of dipoles to the electric field, and thus the dielectric performance of the epoxy insulating material can be improved.

[0030] The rigid polycyclic benzene conjugate structure, flexible freely rotatable methylene group, and ether bonds introduced on the resin molecular chains of the present invention can endow the epoxy insulating material with more excellent mechanical strength. Specifically, the chain extension modification of epoxy resin introduces more ether bonds on the molecular main chain, which can improve the ductility of the epoxy crosslinked network. At the same time, the introduction of rigid benzene rings and cyclohexenyl groups on the resin molecular chains also increases the overall rigidity of the crosslinked network. The epoxy crosslinked network with the cooperation of rigidity and flexibility also endows the epoxy insulating material with higher mechanical strength and ductility.

[0031] The Schiff base segments constructed between the molecular chains within the epoxy crosslinked network of the present invention exhibit a certain degree of conjugation. Therefore, the overall structure of the segment has relatively high rigidity, which can, to a certain extent, inhibit the free rotation of flexible groups such as ether bonds on the resin molecular chains, thereby increasing the cooperative torsional barrier of the segments within the crosslinked network. At the same time, the construction of the Schiff base segments also introduces more -C=N crosslinking sites within the crosslinked network, and the -C=N double bond has higher rigidity compared to the ester bond formed by the crosslinking of epoxy groups and anhydrides. This also makes the epoxy crosslinked network have a higher glass transition temperature after constructing the inter-chain Schiff base segments, and also makes the epoxy insulating material have a higher service temperature. Description of the Drawings

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0033] Figure 1 is the nuclear magnetic resonance of the Schiff base building block in Example 1 1 H;

[0034] Figure 2 is the nuclear magnetic resonance of the Schiff base building block in Example 1 13 C;

[0035] Figure 3 is the nuclear magnetic resonance of the Schiff base building block in Example 4 1 H;

[0036] Figure 4 is the nuclear magnetic resonance of the Schiff base building block in Example 4 13 C;

[0037] Figure 5 is the nuclear magnetic resonance of the Schiff base building block in Example 4 19 F;

[0038] Figure 6 is the epoxy crosslinked network with Schiff base segments constructed between molecular chains in Example 2;

[0039] Figure 7 is the mass change curve during the degradation process of the epoxy insulation material samples prepared in Examples 1, 3, 5, 6, 7, 8 and Comparative Examples 1-3. Detailed implementation manners

[0040] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0041] To better understand the above technical solutions, the following will describe the above technical solutions in detail in conjunction with the accompanying drawings of the specification and specific embodiments.

[0042] Example 1

[0043] This example provides a preparation method of a high-strength insulating Schiff base degradable epoxy resin material, which specifically includes the following steps:

[0044] Step 1: Synthesis of Schiff base building block:

[0045] Weigh 2 mol of kojic acid, 1 mol of 4,4'-diaminodiphenyl ether, and 0.04 mol of p-toluenesulfonic acid respectively. Dissolve kojic acid and 4,4'-diaminodiphenyl ether in benzene, and completely dissolve the two by magnetic stirring under heating at 60 °C. Then add p-toluenesulfonic acid to the completely dissolved mixed solution. At this time, adjust the heating temperature to 120 °C and carry out condensation reflux for 12 h. Use thin-layer chromatography tracking method to track the reaction situation in real time. After the reaction is completed, filter and rotary evaporate to remove the excess benzene solvent to obtain the Schiff base building block product 1.

[0046] Step 2: Schiff base chain extension modification reaction of epoxy resin:

[0047] Weigh 0.1 mol of Schiff base building block, 1 mol of bisphenol A epoxy resin, and 0.001 mol of benzyltriethylammonium chloride respectively. Stir and dissolve the epoxy resin and the Schiff base building block at 120 °C respectively to form a homogeneous mixed solution. Add the phase transfer catalyst benzyltriethylammonium chloride to the mixed solution, and adjust the heating temperature to 160 °C. Continue to stir at this heating temperature for 9 h. And track the chain extension modification reaction by thin-layer chromatography. After the reaction is completed, the Schiff base chain extension modified bisphenol A epoxy resin can be obtained.

[0048] Step 3: Construction of epoxy cross-linked network containing Schiff base segments:

[0049] Weigh 100 g of Schiff base chain extension modified bisphenol A epoxy resin, 66 g of phthalic anhydride curing agent, and 0.005 g of DMP-30 accelerator respectively. Put the Schiff base segment chain extension modified bisphenol A epoxy resin and the phthalic anhydride curing agent into the reaction kettle and heat and stir at 100 °C. After mixing into a homogeneous liquid phase, carry out degassing treatment under a vacuum degree of 0.1 MPa. After degassing for 30 min, add the DMP-30 accelerator to the mixed material liquid and continue vacuum degassing for 5 min. Remove the vacuum condition, pour the above mixed material liquid into a mold preheated to 100 °C, and degas in an oven at 130 °C for 10 min. Select pre-curing at 130 °C / 6 h and post-curing at 160 °C / 6 h. After the program curing is completed, the sample is naturally cooled to room temperature and demolded to obtain a high-strength insulating Schiff base degradable epoxy resin material.

[0050] Comparative Example 1

[0051] This comparative example provides a method for constructing an unchain-extended modified bisphenol A epoxy cross-linked network, which specifically includes the following steps:

[0052] Weigh 100 g of bisphenol A epoxy resin, 80 g of phthalic anhydride curing agent, and 0.005 g of DMP-30 accelerator respectively. Put the bisphenol A epoxy resin and phthalic anhydride curing agent into a reaction kettle and heat and stir at 100 °C. After mixing into a homogeneous liquid phase, perform degassing treatment under a vacuum of 0.1 MPa. After degassing for 30 min, add DMP-30 accelerator to the mixed material liquid and continue vacuum degassing for 5 min. Remove the vacuum condition, pour the above mixed material liquid into a mold preheated to 100 °C, and degas in an oven for 10 min. Select pre-curing at 130 °C / 6 h and post-curing at 160 °C / 6 h. After the program curing is completed, the sample is naturally cooled to room temperature and then demolded to obtain bisphenol A epoxy insulating material, and the properties of the epoxy insulating material are tested and characterized.

[0053] Example 2

[0054] This example provides a preparation method of a high-strength insulating Schiff base degradable epoxy resin material, which specifically includes the following steps:

[0055] Step 1: Synthesis of Schiff base building block:

[0056] Weigh 2 mol of kojic acid, 1 mol of p-phenylenediamine, and 0.04 mol of p-toluenesulfonic acid respectively. Dissolve kojic acid and p-phenylenediamine in benzene, and completely dissolve the two in benzene by magnetic stirring under heating at 60 °C. Then add p-toluenesulfonic acid to the completely dissolved mixed solution. At this time, adjust the heating temperature to 120 °C and carry out condensation reflux. Continue magnetic stirring at this temperature for 12 h, and use thin-layer chromatography tracking method to track the reaction situation in real time. After the reaction is completed, filter and rotary evaporate the excess benzene solvent to obtain Schiff base building block product 2.

[0057] Step 2: Schiff base chain extension modification reaction of epoxy resin:

[0058] Weigh 0.1 mol of Schiff base building block, 1 mol of bisphenol A epoxy resin, and 0.001 mol of benzyltriethylammonium chloride respectively. Stir and dissolve the epoxy resin and Schiff base building block at 120 °C respectively to form a homogeneous mixed solution. Add the phase transfer catalyst benzyltriethylammonium chloride to the mixed solution, and further adjust the heating temperature to 160 °C. Continue stirring at this heating temperature for 9 h. After the reaction is completed, Schiff base chain extension modified bisphenol A epoxy resin can be obtained.

[0059] Step 3: Construction of epoxy cross-linked network containing Schiff base segments:

[0060] Weigh 100 g of bisphenol A epoxy resin modified by Schiff base chain extension, 66 g of phthalic anhydride curing agent, and 0.005 g of DMP-30 accelerator respectively. Put the bisphenol A epoxy resin modified by Schiff base chain extension and the phthalic anhydride curing agent into a reaction kettle and heat and stir at 100 °C. After mixing into a uniform liquid phase, carry out degassing treatment under a vacuum degree of 0.1 MPa. After degassing for 30 min, add DMP-30 accelerator to the mixed material liquid and continue vacuum degassing for 5 min. Remove the vacuum condition, pour the above mixed material liquid into a mold preheated to 100 °C, and degas in an oven at 130 °C for 10 min. Adopt pre-curing at 130 °C / 6 h and post-curing at 160 °C / 6 h. After the program curing is completed, the sample is naturally cooled to room temperature and then demolded to obtain a high-strength insulating Schiff base-based degradable epoxy resin material.

[0061] Example 3

[0062] This example provides a preparation method of a high-strength insulating Schiff base-based degradable epoxy resin material, which specifically includes the following steps:

[0063] Step 1: Synthesis of Schiff base building blocks:

[0064] Weigh 2 mol of kojic acid, 1 mol of 4,4'-methylenedianiline, and 0.04 mol of p-toluenesulfonic acid respectively. Dissolve kojic acid and 4,4'-methylenedianiline in benzene, and completely dissolve the two in benzene by magnetic stirring under heating at 60 °C. Then add p-toluenesulfonic acid to the completely dissolved mixed solution. At this time, adjust the heating temperature to 120 °C and carry out condensation reflux. Continue magnetic stirring at this temperature for 12 h, and use thin-layer chromatography tracking method to track the reaction situation in real time. After the reaction is completed, filter and rotary evaporate the excess benzene solvent to obtain the Schiff base building block product 3.

[0065] Step 2: Schiff base chain extension modification reaction of epoxy resin:

[0066] Weigh 0.1 mol of Schiff base building block, 1 mol of bisphenol A epoxy resin, and 0.001 mol of benzyltriethylammonium chloride respectively. Stir and dissolve the epoxy resin and the Schiff base building block at 120 °C respectively to form a uniform mixed solution. Add the phase transfer catalyst benzyltriethylammonium chloride to the mixed solution, and further adjust the heating temperature to 160 °C. Continue stirring at this heating temperature for 9 h. After the reaction is completed, the bisphenol A epoxy resin modified by Schiff base chain extension can be obtained.

[0067] Step 3: Construction of an epoxy cross-linked network containing Schiff base segments:

[0068] Weigh 100 g of bisphenol A epoxy resin modified by Schiff base chain extension, 66 g of phthalic anhydride curing agent, and 0.005 g of DMP-30 accelerator respectively. Put the bisphenol A epoxy resin modified by Schiff base chain extension and phthalic anhydride curing agent into a reaction kettle and heat and stir at 100 °C. After mixing into a uniform liquid phase, carry out degassing treatment under a vacuum of 0.1 MPa. After degassing for 30 min, add DMP-30 accelerator to the mixed material liquid and continue vacuum degassing for 5 min. Remove the vacuum condition, pour the above mixed material liquid into a mold preheated to 100 °C, and degas in an oven at 130 °C for 10 min. Adopt pre-curing at 130 °C / 6 h and post-curing at 160 °C / 6 h. After the program curing is completed, the sample is naturally cooled to room temperature and then demolded to obtain a high-strength insulating Schiff base-based degradable epoxy resin material.

[0069] Example 4

[0070] This example provides a preparation method of a high-strength insulating Schiff base-based degradable epoxy resin material, which specifically includes the following steps:

[0071] Step 1: Synthesis of Schiff base building block:

[0072] Weigh 2 mol of kojic acid, 1 mol of 4,4'-(perfluoropropane-2,2-diyl)dianiline, and 0.04 mol of p-toluenesulfonic acid respectively. Dissolve kojic acid and 4,4'-(perfluoropropane-2,2-diyl)dianiline in benzene, and completely dissolve the two in benzene by magnetic stirring under heating at 60 °C. Then add p-toluenesulfonic acid to the completely dissolved mixed solution. At this time, adjust the heating temperature to 120 °C and carry out condensation reflux. Continue magnetic stirring at this temperature for 12 h, and use thin-layer chromatography tracking method to track the reaction situation in real time. After the reaction is completed, filter and rotary evaporate the excess benzene solvent to obtain the Schiff base building block product 4.

[0073] Step 2: Schiff base chain extension modification reaction of epoxy resin:

[0074] Weigh 0.1 mol of Schiff base building block, 1 mol of bisphenol A epoxy resin, and 0.001 mol of benzyltriethylammonium chloride respectively. Stir and dissolve the epoxy resin and Schiff base building block at 120 °C respectively to form a uniform mixed solution. Add the phase transfer catalyst benzyltriethylammonium chloride to the mixed solution, and further adjust the heating temperature to 160 °C. Continue stirring at this heating temperature for 9 h. After the reaction is completed, the bisphenol A epoxy resin modified by Schiff base chain extension can be obtained.

[0075] Step 3: Construction of epoxy cross-linked network containing Schiff base chain segments:

[0076] Weigh 100 g of the epoxy resin modified by Schiff base chain extension, 66 g of phthalic anhydride curing agent, and 0.005 g of DMP-30 accelerator respectively. Put the bisphenol A epoxy resin modified by Schiff base chain extension and the phthalic anhydride curing agent into a reaction kettle and heat and stir at 100 °C. After mixing into a homogeneous liquid phase, carry out degassing treatment under a vacuum degree of 0.1 MPa. After degassing for 30 min, add DMP-30 accelerator to the mixed material liquid and continue vacuum degassing for 5 min. Remove the vacuum condition, pour the above mixed material liquid into a mold preheated to 100 °C, and degas in an oven at 130 °C for 10 min. Adopt pre-curing at 130 °C / 6 h and post-curing at 160 °C / 6 h. After the program curing is completed, the sample is naturally cooled to room temperature and then demolded to obtain a high-strength insulating Schiff base-based degradable epoxy resin material.

[0077] Examples 1, 2, 3 and 4 are compared to explore the influence of the conjugated structure of Schiff base chain segments between molecular chains on the properties of epoxy materials.

[0078] Example 5

[0079] This example provides a preparation method of a high-strength insulating Schiff base-based degradable epoxy resin material, which specifically includes the following steps:

[0080] Step 1: Synthesis of Schiff base building blocks:

[0081] Weigh 2 mol of kojic acid, 1 mol of 4,4'-diaminodiphenyl ether, and 0.04 mol of p-toluenesulfonic acid respectively. Dissolve kojic acid and 4,4'-diaminodiphenyl ether in benzene, and completely dissolve the two in benzene by magnetic stirring under heating at 60 °C. Then add p-toluenesulfonic acid to the completely dissolved mixed solution. At this time, adjust the heating temperature to 120 °C and carry out condensation reflux. Continue magnetic stirring at this temperature for 12 h, and use thin-layer chromatography tracking method to track the reaction situation in real time. After the reaction is completed, filter and rotary evaporate the excess benzene solvent to obtain the Schiff base building block product 5.

[0082] Step 2: Schiff base chain extension modification reaction of epoxy resin:

[0083] Weigh 0.2 mol of Schiff base building blocks, 1 mol of bisphenol A epoxy resin, and 0.002 mol of benzyltriethylammonium chloride respectively. Stir and dissolve the epoxy resin and Schiff base building blocks at 120 °C respectively to form a homogeneous mixed solution. Add the phase transfer catalyst benzyltriethylammonium chloride to the mixed solution, and further adjust the heating temperature to 160 °C. Continue stirring at this heating temperature for 9 h. After the reaction is completed, the bisphenol A epoxy resin modified by Schiff base chain extension can be obtained.

[0084] Step 3: Construction of an epoxy cross-linked network containing Schiff base chain segments:

[0085] Weigh 100 g of the epoxy resin modified by Schiff base chain extension, 53 g of phthalic anhydride curing agent, and 0.005 g of DMP-30 accelerator respectively. Put the bisphenol A epoxy resin modified by Schiff base chain extension and the phthalic anhydride curing agent into a reaction kettle and heat and stir at 100 °C. After mixing into a homogeneous liquid phase, carry out degassing treatment under a vacuum of 0.1 MPa. After degassing for 30 min, add DMP-30 accelerator to the mixed material liquid, and continue vacuum degassing for 5 min. Remove the vacuum condition, pour the above mixed material liquid into a mold preheated to 100 °C, and degas in an oven at 130 °C for 10 min. Select pre-curing at 130 °C / 6 h and post-curing at 160 °C / 6 h. After the programmed curing is completed, the sample is naturally cooled to room temperature and demolded, and a high-strength insulating Schiff base-based degradable epoxy resin material is obtained.

[0086] Example 6

[0087] This example provides a preparation method of a high-strength insulating Schiff base-based degradable epoxy resin material, which specifically includes the following steps:

[0088] Step 1: Synthesis of Schiff base building blocks:

[0089] Weigh 2 mol of kojic acid, 1 mol of 4,4'-diaminodiphenyl ether, and 0.04 mol of p-toluenesulfonic acid respectively. Dissolve kojic acid and 4,4'-diaminodiphenyl ether in benzene, and completely dissolve the two in benzene by magnetic stirring under heating at 60 °C. Then add p-toluenesulfonic acid to the completely dissolved mixed solution. At this time, adjust the heating temperature to 120 °C and carry out condensation reflux. Continue magnetic stirring at this temperature for 12 h, and use thin-layer chromatography tracking method to track the reaction situation in real time. After the reaction is completed, filter and rotary evaporate the excess benzene solvent to obtain the Schiff base building block product 6.

[0090] Step 2: Schiff base chain extension modification reaction of epoxy resin:

[0091] Weigh 0.3 mol of Schiff base building blocks, 1 mol of bisphenol A epoxy resin, and 0.003 mol of benzyltriethylammonium chloride respectively. Stir and dissolve the weighed epoxy resin and Schiff base building blocks at 120 °C respectively to form a homogeneous mixed solution. Add the phase transfer catalyst benzyltriethylammonium chloride to the mixed solution, and further adjust the heating temperature to 160 °C. Continue stirring at this heating temperature for 9 h. After the reaction is completed, the bisphenol A epoxy resin modified by Schiff base chain extension can be obtained.

[0092] Step 3: Construction of an epoxy crosslinked network containing Schiff base segments:

[0093] Weigh 100 g of the epoxy resin modified by Schiff base chain extension, 39 g of phthalic anhydride curing agent, and 0.005 g of DMP-30 accelerator respectively. Put the bisphenol A epoxy resin modified by Schiff base chain extension and phthalic anhydride curing agent into a reaction kettle and heat and stir at 100 °C. After mixing into a homogeneous liquid phase, carry out degassing treatment under a vacuum degree of 0.1 MPa. After degassing for 30 min, add DMP-30 accelerator to the mixed material liquid, and continue vacuum degassing for 5 min. Remove the vacuum condition, pour the above mixed material liquid into a mold preheated to 100 °C, and degas in an oven at 130 °C for 10 min. Select pre-curing at 130 °C / 6 h and post-curing at 160 °C / 6 h. After the programmed curing is completed, the sample is naturally cooled to room temperature and then demolded, and a high-strength insulating Schiff base-based degradable epoxy resin material is obtained.

[0094] Comparisons are made among Examples 1, 5, and 6 to explore the influence of the content of Schiff base chain segments between molecular chains on the properties of epoxy materials. In Examples 1, 5, and 6, due to the change in the content of Schiff base building blocks after resin chain extension modification, the epoxy value of the epoxy resin after chain extension modification will change, which leads to corresponding changes in the content of the epoxy resin curing agent components. The contents of phthalic anhydride curing agent in Examples 1, 5, and 6 are 66 g, 53 g, and 39 g in sequence.

[0095] Example 7

[0096] This example provides a preparation method of a high-strength insulating Schiff base-based degradable epoxy resin material, which specifically includes the following steps:

[0097] Step 1: Synthesis of Schiff base building blocks:

[0098] Weigh 2 mol of kojic acid, 1 mol of 4,4'-diaminodiphenyl ether, and 0.04 mol of p-toluenesulfonic acid respectively. Dissolve the weighed kojic acid and 4,4'-diaminodiphenyl ether in benzene, and completely dissolve the two in benzene by magnetic stirring under heating at 60 °C. Then add p-toluenesulfonic acid to the completely dissolved mixed solution. At this time, adjust the heating temperature to 120 °C and carry out condensation reflux. Continue magnetic stirring at this temperature for 12 h, and use thin-layer chromatography tracking method to track the reaction situation in real time. After the reaction is completed, filter and rotary evaporate the excess benzene solvent to obtain the Schiff base building block product 7.

[0099] Step 2: Schiff base chain extension modification reaction of epoxy resin:

[0100] Weigh 0.1 mol of Schiff base building block, 1 mol of bisphenol F epoxy resin, and 0.001 mol of benzyltriethylammonium chloride respectively. Stir and dissolve the epoxy resin and the Schiff base building block at 120 °C respectively to form a homogeneous mixed solution. Add the phase transfer catalyst benzyltriethylammonium chloride to the mixed solution, and further adjust the heating temperature to 160 °C. Continue stirring at this heating temperature for 9 h. After the reaction is completed, bisphenol F epoxy resin modified by Schiff base chain extension can be obtained.

[0101] Step 3: Construction of epoxy cross-linked network containing Schiff base segments:

[0102] Weigh 100 g of bisphenol F epoxy resin modified by Schiff base segment chain extension, 76 g of phthalic anhydride curing agent, and 0.005 g of DMP-30 accelerator respectively. Put the bisphenol F epoxy resin modified by Schiff base segment chain extension and the phthalic anhydride curing agent into a reaction kettle and heat and stir at 100 °C. After mixing into a homogeneous liquid phase, carry out degassing treatment under a vacuum degree of 0.1 MPa. After degassing for 30 min, add DMP-30 accelerator to the mixed material liquid, and continue vacuum degassing for 5 min. Remove the vacuum condition, pour the above mixed material liquid into a mold preheated to 100 °C in advance, and degas in an oven at 130 °C for 10 min. Select pre-curing at 130 °C / 6 h and post-curing at 160 °C / 6 h. After the program curing is completed, the sample is naturally cooled to room temperature and demolded, and a high-strength insulating Schiff base degradable epoxy resin material is prepared.

[0103] Comparative Example 2

[0104] This comparative example provides a method for constructing an unextended modified bisphenol F epoxy cross-linked network, which specifically includes the following steps:

[0105] Weigh 100 g of bisphenol F epoxy resin, 80 g of phthalic anhydride curing agent, and 0.005 g of DMP-30 accelerator respectively. Put the bisphenol A epoxy resin and the phthalic anhydride curing agent into a reaction kettle and heat and stir at 100 °C. After mixing into a homogeneous liquid phase, carry out degassing treatment under a vacuum degree of 0.1 MPa. After degassing for 30 min, add DMP-30 accelerator to the mixed material liquid, and continue vacuum degassing for 5 min. Remove the vacuum condition, pour the above mixed material liquid into a mold preheated to 100 °C in advance, and degas in an oven for 10 min. Select pre-curing at 130 °C / 6 h and post-curing at 160 °C / 6 h. After the program curing is completed, the sample is naturally cooled to room temperature and demolded to obtain a bisphenol F epoxy insulating material, and the performance of the epoxy insulating material is tested and characterized.

[0106] Example 8

[0107] This example provides a preparation method of a high-strength insulating Schiff base degradable epoxy resin material, which specifically includes the following steps:

[0108] Step 1: Synthesis of Schiff base building block:

[0109] Weigh 2 mol of kojic acid, 1 mol of 4,4'-diaminodiphenyl ether, and 0.04 mol of p-toluenesulfonic acid respectively. Dissolve kojic acid and 4,4'-diaminodiphenyl ether in benzene, and completely dissolve the two in benzene by magnetic stirring under heating at 60 °C. Then add p-toluenesulfonic acid to the completely dissolved mixed solution. At this time, adjust the heating temperature to 120 °C and carry out condensation reflux. Continue magnetic stirring at this temperature for 12 h, and use thin-layer chromatography tracking method to track the reaction situation in real time. After the reaction is completed, filter and rotary evaporate to remove the excess benzene solvent to obtain the Schiff base building block product 8.

[0110] Step 2: Schiff base chain extension modification reaction of epoxy resin:

[0111] Weigh 0.1 mol of Schiff base building block, 1 mol of bisphenol AF epoxy resin, and 0.001 mol of benzyltriethylammonium chloride respectively. Stir and dissolve the epoxy resin and the Schiff base building block at 120 °C respectively to form a homogeneous mixed solution. Add the phase transfer catalyst benzyltriethylammonium chloride to the mixed solution, and further adjust the heating temperature to 160 °C. Continue stirring at this heating temperature for 9 h. After the reaction is completed, the bisphenol AF epoxy resin modified by Schiff base chain extension can be obtained.

[0112] Step 3: Construction of epoxy cross-linked network containing Schiff base segments:

[0113] Weigh 100 g of bisphenol AF epoxy resin modified by Schiff base segment chain extension, 68 g of phthalic anhydride curing agent, and 0.005 g of DMP-30 accelerator respectively. Put the bisphenol AF epoxy resin modified by Schiff base segment chain extension and the phthalic anhydride curing agent into a reaction kettle and heat and stir at 100 °C. After mixing into a homogeneous liquid phase, carry out degassing treatment under a vacuum degree of 0.1 MPa. After degassing for 30 min, add the DMP-30 accelerator to the mixed material liquid, continue vacuum degassing for 5 min, remove the vacuum condition, and the degassing treatment is completed; pour the above mixed material liquid into a mold preheated to 100 °C, and degas in an oven at 130 °C for 10 min. Select pre-curing at 130 °C / 6 h and post-curing at 160 °C / 6 h. After the programmed curing is completed, the sample is naturally cooled to room temperature and demolded, and the high-strength insulating Schiff base-based degradable epoxy resin material is prepared.

[0114] Comparative Example 3

[0115] This comparative example provides a method for constructing an unmodified epoxy cross-linked network of bisphenol AF, which specifically includes the following steps:

[0116] Weigh 100 g of bisphenol AF epoxy resin, 80 g of phthalic anhydride curing agent, and 0.005 g of DMP-30 accelerator respectively. Put the bisphenol AF epoxy resin and phthalic anhydride curing agent into a reaction kettle and heat and stir at 100 °C. After mixing into a uniform liquid phase, carry out degassing treatment under a vacuum degree of 0.1 MPa. After degassing for 30 min, add DMP-30 accelerator to the mixed material liquid and continue vacuum degassing for 5 min. Remove the vacuum condition, pour the above mixed material liquid into a mold preheated to 100 °C, and degas in an oven for 10 min. Select pre-curing at 130 °C / 6 h and post-curing at 160 °C / 6 h. After the program curing is completed, the sample is naturally cooled to room temperature and demolded to obtain bisphenol AF epoxy insulating material, and the performance of the epoxy insulating material is tested and characterized.

[0117] Comparisons were made between Comparative Examples 1, 2, 3 and Examples 1, 7, 8 to explore the performance improvement effect of Schiff base segments on the chain extension modification of different epoxy resins.

[0118] Example 9

[0119] This example provides a preparation method of a high-strength insulating Schiff base degradable epoxy resin material, which specifically includes the following steps:

[0120] Step 1: Synthesis of Schiff base building blocks:

[0121] Weigh 2 mol of kojic acid, 1 mol of 4,4'-(2,2-propylidene) diphenylamine, and 0.04 mol of p-toluenesulfonic acid respectively. Dissolve kojic acid and 4,4'-(2,2-propylidene) diphenylamine in benzene, and completely dissolve the two by magnetic stirring under heating at 60 °C. Then add p-toluenesulfonic acid to the completely dissolved mixed solution. At this time, adjust the heating temperature to 120 °C and carry out reflux condensation for 12 h, and use thin-layer chromatography tracking method to track the reaction situation in real time. After the reaction is completed, filter and rotary evaporate the excess benzene solvent to obtain the Schiff base building block product 9.

[0122] Step 2: Schiff base chain extension modification reaction of epoxy resin:

[0123] Weigh 0.1 mol of Schiff base building block, 1 mol of bisphenol A epoxy resin, and 0.001 mol of benzyltriethylammonium chloride respectively. Stir and dissolve the epoxy resin and Schiff base building block at 120 °C respectively to form a uniform mixed solution, add the phase transfer catalyst benzyltriethylammonium chloride to the mixed solution, and adjust the heating temperature to 160 °C. Continue stirring at this heating temperature for 9 h. And track the chain extension modification reaction by thin-layer chromatography, and the Schiff base chain extension modified bisphenol A epoxy resin can be obtained after the reaction is completed.

[0124] Step 3: Construction of epoxy cross-linked network containing Schiff base segments:

[0125] Weigh 100 g of bisphenol A epoxy resin modified by Schiff base chain extension, 60 g of phthalic anhydride curing agent, and 0.005 g of DMP-30 accelerator respectively. Put the bisphenol A epoxy resin modified by Schiff base chain segment and phthalic anhydride curing agent into a reaction kettle and heat and stir at 100 °C. After mixing into a homogeneous liquid phase, carry out degassing treatment under a vacuum of 0.1 MPa. After degassing for 120 min, add DMP-30 accelerator to the mixed liquid, and continue vacuum degassing for 10 min. Remove the vacuum condition, pour the mixed liquid into a mold preheated to 80 °C, and degas in an oven at 130 °C for 10 min. Select pre-curing at 120 °C / 9 h and post-curing at 170 °C / 3 h. After the programmed curing is completed, the sample is naturally cooled to room temperature and demolded, and a high-strength insulating Schiff base-based degradable epoxy resin material is obtained.

[0126] Example 10

[0127] This example provides a preparation method of a high-strength insulating Schiff base-based degradable epoxy resin material, which specifically includes the following steps:

[0128] Step 1: Synthesis of Schiff base building blocks:

[0129] Weigh 2 mol of kojic acid, 0.8 mol of 4,4'-(2,2-propylidene) diphenylamine, and 0.02 mol of p-toluenesulfonic acid respectively. Dissolve kojic acid and 4,4'-(2,2-propylidene) diphenylamine in benzene, and completely dissolve the two by magnetic stirring under heating at 40 °C. Then add p-toluenesulfonic acid to the completely dissolved mixed solution. At this time, adjust the heating temperature to 80 °C and carry out condensation reflux for 12 h, and use thin-layer chromatography tracking method to track the reaction situation in real time. After the reaction is completed, filter and rotary evaporate the excess benzene solvent to obtain 10 Schiff base building block products.

[0130] Step 2: Schiff base chain extension modification reaction of epoxy resin:

[0131] Weigh 0.1 mol of Schiff base building blocks, 1 mol of bisphenol A epoxy resin, and 0.001 mol of benzyltriethylammonium chloride respectively. Stir and dissolve the epoxy resin and Schiff base building blocks at 90 °C respectively to form a homogeneous mixed solution. Add the phase transfer catalyst benzyltriethylammonium chloride to the mixed solution, and adjust the heating temperature to 130 °C, and continue stirring at this heating temperature for 12 h. And track the chain extension modification reaction by thin-layer chromatography method, and the Schiff base chain extension modified bisphenol A epoxy resin can be obtained after the reaction is completed.

[0132] Step 3: Construction of epoxy crosslinked network containing Schiff base segments:

[0133] Weigh 100 g of bisphenol A epoxy resin modified by Schiff base chain extension, 90 g of phthalic anhydride curing agent, and 0.015 g of DMP-30 accelerator respectively. Put the bisphenol A epoxy resin modified by Schiff base chain segment and phthalic anhydride curing agent into a reaction kettle and heat and stir at 120 °C. After mixing into a uniform liquid phase, carry out degassing treatment under a vacuum degree of 0.1 MPa. After degassing for 10 min, add DMP-30 accelerator to the mixed material liquid and continue vacuum degassing for 20 min. Remove the vacuum condition, pour the mixed material liquid into a mold preheated to 100 °C, and degas in an oven at 140 °C for 5 min. Select pre-curing at 140 °C / 3 h and post-curing at 150 °C / 18 h. After the programmed curing is completed, the sample is naturally cooled to room temperature and demolded to obtain a high-strength insulating Schiff base-based degradable epoxy resin material.

[0134] Example 11

[0135] Step 1: Synthesis of Schiff base building block:

[0136] Weigh 2 mol of kojic acid, 1.2 mol of 4,4'-(2,2-propylidene)dianiline, and 0.1 mol of p-toluenesulfonic acid respectively. Dissolve kojic acid and 4,4'-(2,2-propylidene)dianiline in benzene and completely dissolve the two by magnetic stirring under heating at 80 °C. Then add p-toluenesulfonic acid to the completely dissolved mixed solution. At this time, adjust the heating temperature to 140 °C and carry out condensation reflux for 24 h, and use thin-layer chromatography tracking method to track the reaction situation in real time. After the reaction is completed, filter and rotary evaporate the excess benzene solvent to obtain Schiff base building block product 11.

[0137] Step 2: Schiff base chain extension modification reaction of epoxy resin:

[0138] Weigh 0.3 mol of Schiff base building block, 1 mol of bisphenol A epoxy resin, and 0.003 mol of benzyltriethylammonium chloride respectively. Stir and dissolve the epoxy resin and Schiff base building block at 120 °C respectively to form a uniform mixed solution. Add the phase transfer catalyst benzyltriethylammonium chloride to the mixed solution, and adjust the heating temperature to 160 °C, and continue stirring at this heating temperature for 6 h. And track the chain extension modification reaction by thin-layer chromatography method, and the Schiff base chain extension modified bisphenol A epoxy resin can be obtained after the reaction is completed.

[0139] Step 3: Construction of epoxy crosslinked network containing Schiff base chain segment:

[0140] Weigh 100 g of bisphenol A epoxy resin modified by Schiff base chain extension, 80 g of phthalic anhydride curing agent, and 0.01 g of DMP-30 accelerator respectively. Put the bisphenol A epoxy resin modified by Schiff base chain segment extension and phthalic anhydride curing agent into a reaction kettle and heat and stir at 80 °C. After mixing into a homogeneous liquid phase, carry out degassing treatment under a vacuum degree of 0.08 MPa. After degassing for 30 min, add DMP-30 accelerator to the mixed material liquid and continue vacuum degassing for 5 min. Remove the vacuum condition, pour the mixed material liquid into a mold preheated to 120 °C in advance, and degas in an oven at 120 °C for 30 min. Select pre-curing at 130 °C / 6 h and post-curing at 160 °C / 6 h. After the program curing is completed, the sample is naturally cooled to room temperature and demolded, and a high-strength insulating Schiff base-based degradable epoxy resin material is obtained.

[0141] A comparison is formed among Examples 9, 10, and 11 to explore the influence of the synthesis material ratio and process parameters of Schiff base building blocks on the improvement effect of the chain extension modification performance of epoxy resin.

[0142] The testing methods for the examples or comparative examples of this application are as follows:

[0143] Testing of epoxy value of epoxy resin: Determine the epoxy value of epoxy resin before and after Schiff base chain extension modification according to the testing requirements of GB-T1677-2008:

[0144] ;

[0145] In the formula, V—the volume of the standard sodium hydroxide solution consumed by the sample, ml; V 0 —the volume of the standard sodium hydroxide solution consumed by the blank sample, ml; C—the equivalent concentration of the sodium hydroxide standard solution, mol / L; W—the mass of the sample, g.

[0146] Testing of AC breakdown strength: According to the testing standard of the national standard GB / T 1408.1-2016 "Test Methods for Electrical Strength of Insulating Materials", measure the breakdown strength of the sample under short-term electric field action at a voltage rising speed of 2 kV / s. The measurement ambient temperature is 25 °C, the test sample is a disc with a diameter of 100 mm and a thickness of 1 mm, the test voltage frequency is 50 Hz, 3 finished products are taken for each sample, 3 points are tested for each sample, 9 breakdown data can be obtained for each sample, the test results are averaged, and the Weibull distribution is used for breakdown strength calculation.

[0147] Tensile Strength Test: According to the test standard of GB / T 2567-2021 "Test Methods for Properties of Resin Castings", a universal mechanical testing machine was used to measure the elastic modulus, tensile strength, tensile elongation and fracture toughness of the specimens. The test specimens were prepared by casting according to the technical conditions specified in GB / T 2567-2008. The test temperature was 25°C and the relative humidity was 50%. When measuring the tensile strength, the test speed was 10 mm / min, and the arbitration test speed was 2 mm / min. When measuring other properties, the test speed was 2 mm / min. Each type of specimen was tested 3 times, and the measurement results were averaged.

[0148] Glass Transition Temperature Test: According to the test standard of GB / T 40396-2021 "Test Method for Glass Transition Temperature of Polymer Matrix Composites - Dynamic Mechanical Analysis (DMA)", a dynamic thermomechanical analyzer was used to test the glass transition temperature of the material. The test mode was single and double cantilever mode. The test conditions were air atmosphere, the heating rate was 5°C / min, the loading frequency was 1 Hz, heating from room temperature to 250°C, cooling to room temperature and then heating to 250°C again at the same rate until the modulus change tended to be flat, and the program heating was ended. The glass transition temperature of the test material specimen was obtained by processing the test curve.

[0149] Chemical Degradation Performance Test: Epoxy material samples with the same mass and size were selected and placed in a degradation reactor, and chemical degradation was carried out in a degradation solution at 100°C. The degradation rate of the material was calculated based on the degradation time required for all the epoxy material samples to degrade. Five sets of specimens were taken for each group, and the degradation rate was the average of the five sets of specimens.

[0150] Figure 1 is the nuclear magnetic resonance of the Schiff base block in Example 1 1 H; Figure 2 is the nuclear magnetic resonance of the Schiff base block in Example 1 13 C; Figure 3 is the nuclear magnetic resonance of the Schiff base block in Example 4 1 H; Figure 4 is the nuclear magnetic resonance of the Schiff base block in Example 4 13 C; Figure 5 is the nuclear magnetic resonance of the Schiff base block in Example 4 19 F. The performance characterization results of the epoxy insulating materials obtained in Examples 1 to 11 and Comparative Examples 1 to 3 are shown in Tables 1 to 2.

[0151] Among them, in Example 1, 4,4-diaminodiphenyl ether was selected as the diamine compound to construct the Schiff base chain segment, and the bisphenol A epoxy resin modified by chain extension with it was used as the resin matrix to obtain the epoxy insulating material after crosslinking and curing. Comparative Example 1 is the bisphenol A epoxy resin without Schiff base chain segment extension modification and the epoxy insulating material obtained after its crosslinking and curing. In Examples 1, 2, 3, 4, and 9, different diamine compounds were respectively selected, and Schiff base chain segments with different conjugated structures were constructed therefrom. Then, the bisphenol A epoxy resin was modified by chain extension through them, and Schiff base chain segments with different polybenzene ring conjugated structures were introduced between the molecular chains of the epoxy crosslinking network to realize the regulation of the service performance of the epoxy crosslinking network. In Examples 1, 5, and 6, the content of the Schiff base chain segment constructed between the molecular chains in the crosslinking network was changed to comparatively explore the influence of the content of the Schiff base chain segment between the molecular chains on the service performance of the epoxy crosslinking network. In Examples 1, 7, and 8, bisphenol A, bisphenol F, and bisphenol AF type epoxy resins were respectively selected as the resin matrix to explore the compatibility of the Schiff base chain segment with the epoxy resin system and the improvement effect of the construction of the chain segment between the molecular chains on the performance of the epoxy insulating material after crosslinking and curing. In Examples 9, 10, and 11, by adjusting the synthesis raw material ratio and process parameters of the Schiff base building block, a comparison was formed among the three examples to explore the influence of the synthesis material ratio and process parameters of the Schiff base building block on the improvement effect of the epoxy resin chain extension modification performance.

[0152] Table 1 Comparison of performance parameters of epoxy resin after Schiff base chain extension modification in examples

[0153] ;

[0154] As shown in Table 1, by measuring the epoxy value of the epoxy resin after Schiff base chain extension modification, it can be found that compared with Comparative Example 1 after modification, in Examples 1, 2, 3, 4, and 9, after the molecular chain extension modification of the epoxy resin, the epoxy value of the epoxy resin will decrease to a certain extent. This is because of the growth of the resin molecular chain after chain extension and the decrease in the content of epoxy groups on the resin main chain. And in Examples 1, 5, and 6, by changing the content of the Schiff base chain extension modifier during the epoxy resin chain extension process, the epoxy value of the modified epoxy resin will gradually decrease accordingly. In Examples 1, 7, and 8, the modification of the Schiff base chain extension modifier has a good chain extension modification effect on different epoxy resins, which also shows the compatibility of the developed Schiff base chain extension modifier with the epoxy resin system. The measured epoxy value of the epoxy resin after chain extension is basically consistent with the theoretical epoxy value.

[0155] In addition, combined with Figures 1 to 5 the nuclear magnetic resonance of the Schiff base building blocks synthesized in Example 1 and Example 4 1 H, 13 C, and 19Analysis of the F spectrum shows that there is a good correspondence between the molecular structural formula of the synthesized Schiff base block and the H, C, and F atoms at the corresponding chemical shifts in the nuclear magnetic resonance spectrum. This also indicates that the Schiff base block synthesized in the above examples and the chain extension modification reaction of the epoxy resin are consistent with the expectations. Examples 1, 2, 3, 4, and 9 respectively selected diamine compounds with different structures and constructed Schiff base chain segments with different conjugated structures. Corresponding to the molecular structural formula of the Schiff base block, the R group is successively C 6 H 4 、C 12 H 8 O, C 13 H 10 、C 13 H 8 F 6 and C 15 H 14 . The influence law of the Schiff base block structure between the resin molecular chains on the service performance of the epoxy cross-linked network was verified. In Examples 1, 5, and 6, the content of the Schiff base chain segment between the molecular chains in the cross-linked network was further changed to explore the influence of the content of the Schiff base chain segment between the chains on the service performance of the epoxy cross-linked network. In Examples 1, 7, and 8, bisphenol A, bisphenol F, and bisphenol AF type epoxy resins were respectively selected as the resin matrix to explore the compatibility of the Schiff base chain segment with the epoxy resin system and the improvement effect of the construction of the chain segment between the molecular chains on the performance of the cross-linked and cured epoxy insulating material, and the universality of this method for improving the performance of epoxy resin was verified. In Examples 9, 10, and 11, by changing the ratios of kojic acid, diamine compounds, and p-toluenesulfonic acid in the Schiff base block and further adjusting the synthesis process parameters of the Schiff base block, the influence law of the above variables on the service performance of the epoxy cross-linked network was studied, and the optimal raw material ratio of the Schiff base block and the optimal synthesis process parameters were obtained.

[0156] It can also be found by measuring the viscosity value of the epoxy resin after Schiff base chain extension modification that, compared with the epoxy resin without chain extension modification (Comparative Examples 1, 2, and 3), the viscosity value of the epoxy resin after Schiff base chain extension modification will increase to a certain extent. Moreover, by comparing the viscosity values of the epoxy resin after chain extension with different contents of the Schiff base chain extender in Examples 1, 5, and 6, it can be seen that as the content of the chain extender increases, the viscosity of the epoxy resin will increase accordingly. The increase in the viscosity of the epoxy resin matrix after chain extension modification can, to a certain extent, inhibit the sedimentation of inorganic reinforcing fillers in the resin because the gravitational force and suspension force of the inorganic reinforcing fillers in the vertical direction in the resin matrix can be balanced. This has important practical significance for the development of high-performance epoxy composite insulating materials for high-end power equipment.

[0157] Table 2 Performance comparison of epoxy insulating materials in examples and comparative examples

[0158] ;

[0159] As shown in Table 2, through the comparative analysis of the multi-dimensional properties of the epoxy insulating materials in the comparative examples and the examples, it can be seen that constructing Schiff base segments between the molecular chains of the crosslinked network can effectively improve the insulation, mechanical, thermal, and chemical degradation properties of the epoxy materials.

[0160] Figure 6 is the epoxy crosslinked network with Schiff base segments constructed between the molecular chains in Example 2; in terms of the dielectric strength of the epoxy insulating material, the dielectric strength of the unmodified bisphenol A epoxy material in Comparative Example 1 was only 35.13 kV / mm, but after constructing Schiff base segments between the molecular chains of the crosslinked network, the dielectric strength of the epoxy material was significantly improved. The results of Comparative Example 1, Examples 1, 5, and 6 show that as the number of Schiff base segments constructed between the molecular chains increases, the dielectric strength of the epoxy material will show a trend of first increasing and then decreasing. When the molar ratio of epoxy resin to Schiff base segment is 1:0.2, the dielectric strength of the epoxy material is the highest, reaching 39.19 kV / mm, which is 11.5% higher than that of the epoxy insulating material without Schiff base segments constructed. This is also related to the influence of the introduction of deep traps of carriers in the network on the carrier transport behavior. The performance results of Comparative Example 1 and the epoxy materials in Examples 1, 2, 3, 4, and 9 show that by changing the molecular structure of the Schiff base segment, different depths of carrier traps can be constructed between the molecular chains of the crosslinked network, realizing the regulation of the carrier transport behavior in the epoxy crosslinked network, and thus improving the dielectric strength of the epoxy insulating material. When 4,4'-(perfluoropropane-2,2-diyl)dianiline is selected as the diamine compound to construct the Schiff base building block and introduced into the epoxy crosslinked network, the dielectric strength of the epoxy insulating material can reach 42.38 kV / mm, an increase of nearly 20%. In addition, when the Schiff base building block is used to chain-extend and modify bisphenol F and bisphenol AF epoxy resins, the dielectric strength of the epoxy insulating material has a certain increase compared with that before modification. This also shows that this technical method has good adaptability to the enhancement of the properties of the epoxy resin system, and it also shows that this technical method is a general method for improving the properties of epoxy resins. This technical method has good reference significance for the development of epoxy resin materials with high degradation and high insulation synergy for high-end power equipment.

[0161] In terms of the tensile strength of the epoxy insulating material, the tensile strength of the unmodified bisphenol A epoxy insulating material in Comparative Example 1 was only 73.2 MPa. However, after constructing Schiff base segments in the crosslinked network in Examples 1, 2, 3, 4, and 9, the tensile strength of the epoxy insulating material was significantly improved. The highest tensile strength of the epoxy material could reach 86.7 MPa, which was a 18.4% increase compared to the unmodified state. This was also related to the combined effect of the rigid Schiff base segments between the chains and the flexible ether bonds on the chains. When more Schiff base segments were introduced between the molecular chains, the tensile strength of the epoxy insulating material showed a changing pattern of first increasing and then decreasing. When the molar ratio of epoxy resin to Schiff base modifier was 1:0.2, the highest tensile strength of the epoxy insulating material could reach 89.1 MPa.

[0162] The significant increase in the tensile strength of the epoxy insulating material also further reduced the cracking risk during the operation of the material, and provided guarantee for the safe and stable long-term operation of power equipment. At the same time, the Schiff base chain extension modification had a significant effect on enhancing the properties of bisphenol F and bisphenol AF type epoxy resins. Among them, the tensile strength of the bisphenol F epoxy insulating material was increased from 76.1 MPa to 82.7 MPa, and the bisphenol AF epoxy insulating material was increased from 70.2 MPa to 81.3 MPa, with the maximum increase amplitude of 15.8%.

[0163] In terms of the glass transition temperature of the epoxy insulating material, the glass transition temperature of the unmodified bisphenol A epoxy insulating material in Comparative Example 1 was only 136 °C. In Examples 1, 5, and 6, when 4,4-diaminodiphenyl ether was selected as the diamine compound to construct rigid conjugated Schiff base segments between the molecular chains of the crosslinked network, the glass transition temperature of the epoxy insulating material was the highest when the molar ratio of resin to Schiff base chain extension modifier was 1:0.3, reaching 162 °C. This also indicated that the introduction of rigid Schiff base segments enhanced the overall rigidity of the crosslinked network, and more Schiff base segments between the chains had a stronger inhibitory effect on the free rotation of the groups in the network, increasing the cooperative torsion barrier and significantly improving the glass transition temperature of the epoxy crosslinked network. Designing and constructing Schiff base segments with different rigidities and chain lengths in Examples 1, 2, 3, 4, and 9 had a certain effect on improving the thermal properties of the epoxy insulating material. When different Schiff base segments were introduced into the network, the glass transition temperature of the epoxy insulating material was in the range of 145 - 152 °C. The Schiff base segments constructed with 4,4'-(perfluoropropane-2,2-diyl)dianiline had a better effect on increasing the glass transition temperature of the epoxy insulating material. This might also be related to CF in the chain segment 3The group has a higher chemical bond energy, which is related to stability. In addition, the intermolecular Schiff base segments constructed within the crosslinked network have a significant enhancing effect on the glass transition temperature of epoxy insulating materials. Among them, the glass transition temperatures of bisphenol F and bisphenol AF epoxy insulating materials are increased by 6.7% and 7.7% respectively. The increase in the glass transition temperature of epoxy insulating materials further expands the service scenario range of the materials.

[0164] Figure 7 It is the mass change curve during the degradation process of the epoxy insulating material samples prepared in Examples 1, 3, 5, 6, 7, 8 and Comparative Examples 1-3. In terms of the chemical degradation of epoxy insulating materials, by comparing the degradation rates of unmodified and Schiff base chain-extended modified epoxy insulating material samples in a 0.1 M hydrochloric acid / methanol solution (hydrochloric acid: methanol = 1:9), it can be found that the chemical degradation rate of the unmodified epoxy crosslinked network (Comparative Examples 1, 2, and 3) in the weak acid degradation agent is only 0.008 - 0.015 g / h. This indicates that the epoxy insulating material hardly has the ability of chemical degradation in the degradation agent. When constructing Schiff base segments responsive to pH in the epoxy crosslinked network, the chemical degradation rate of the epoxy crosslinked network will increase from 0.008 - 0.015 g / h to 0.25 - 0.31 g / h. Its chemical degradation rate has been significantly improved, showing an order-of-magnitude change. Moreover, as the content of the Schiff base segments constructed within the epoxy crosslinked network increases, the depolymerization ability of the epoxy crosslinked network also increases accordingly. The chemical degradation rate of the epoxy insulating material further increases from 0.27 g / h to 0.35 g / h. This may be because the Schiff base segments responsive to pH changes within the epoxy crosslinked network replace the original epoxy-anhydride crosslinking sites, resulting in a significant improvement in the depolymerization ability of the epoxy crosslinked network. In addition, for bisphenol F and bisphenol AF epoxy resins, after constructing Schiff base segments within the epoxy crosslinked network, the degradation rates of the epoxy insulating materials in a 0.1 M hydrochloric acid / methanol mixed solution also show obvious improvements. Among them, the chemical degradation rates of bisphenol F and bisphenol AF epoxy insulating materials reach 0.25 g / h and 0.29 g / h respectively, which also indicates the general effectiveness of this technical method in improving the chemical degradation ability of epoxy resin systems. Overall, constructing Schiff base segments in the epoxy crosslinked network has a significant promoting effect on the degradation performance of insulating materials.

[0165] It should be noted that, in this document, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising one..." does not exclude the presence of additional identical elements in the process, method, article or device comprising said element.

[0166] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0167] Those skilled in the art should understand that the above are only several specific embodiments of the present invention, rather than all embodiments. It should be pointed out that many variations and improvements can be made for those of ordinary skill in the art, and all variations or improvements that do not exceed the scope of the claims should be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a high-strength insulating Schiff base degradable epoxy resin material, characterized in that: The steps include: S1. Weigh a Schiff base building block, an epoxy resin and a phase transfer catalyst in a molar ratio of (0.1-0.3): 1: (0.001-0.003); the molecular structure of the Schiff base building block is: , wherein the R group is one of -C6H4-, -C6H4-O-C6H4-, -C6H4-CH2-C6H4-, -C6H4-C(CH3)2-C6H4- and -C6H4-C(CF3)2-C6H4-; The epoxy resin and the Schiff base building block are mixed, stirred and dissolved at 90-120°C to form a uniform mixed solution, a phase transfer catalyst is added, the heating temperature is adjusted to 130-160°C, stirring is continued at this temperature for 6-12 hours, and cooling is performed after the reaction is completed to obtain the Schiff base chain extension modified epoxy resin; S2. Weigh the Schiff base chain-extending modified epoxy resin, the anhydride curing agent and the amine accelerator in a mass ratio of 100:(60-90):(0.005-0.015); The epoxy resin modified by Schiff base chain extension and the acid anhydride curing agent are placed in a reaction kettle, heated and stirred at 80-120°C to form a uniform mixed liquid, the mixed liquid is subjected to a first degassing treatment, an amine accelerator is added during the treatment, and the degassed mixed liquid is poured into a preheated mold, subjected to a second degassing treatment, cured, cooled to room temperature and then demolded, thereby obtaining an epoxy insulating material with interchain Schiff base segments.

2. The method for preparing the high-strength insulating Schiff base degradable epoxy resin material according to claim 1, characterized in that: The epoxy resin described in step S1 is one or a combination of two or more of glycidyl ether, glycidyl ester, aliphatic and alicyclic epoxy resins.

3. The method for preparing the high-strength insulating Schiff base degradable epoxy resin material according to claim 1, characterized in that: The phase transfer catalyst described in step S1 is one or a combination of two or more of onium salts, open-chain polyethers, tertiary amines, crown ethers, thioethers and quaternary ammonium salts.

4. The method for preparing the high-strength insulating Schiff base degradable epoxy resin material according to claim 1, characterized in that: The anhydride curing agent described in step S2 is one or a combination of two or more of phthalic anhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride and methylnadic anhydride.

5. The method for preparing the high-strength insulating Schiff base degradable epoxy resin material according to claim 1, characterized in that: The amine accelerator described in step S2 is one or a combination of two or more of aliphatic amines, alicyclic amines, aromatic amines, and heterocyclic amine accelerators.

6. The method for preparing the high-strength insulating Schiff base degradable epoxy resin material according to claim 1, 4 or 5, characterized in that: The specific process of the first degassing treatment, the second degassing treatment and the curing in step S2 is as follows: the mixed liquid is degassed at a vacuum degree of 0.08-0.1 MPa for 10-120 min, an amine accelerator is added, and the vacuum degassing is continued for 5-20 min, and the vacuum condition is removed, and the first degassing treatment is completed; The mixed liquid is then poured into a mold preheated to 80-120°C, placed under heating conditions at 120-140°C for 5-30 minutes to complete the second degassing treatment, and then pre-cured at 120-140°C for 3-9 hours, and then post-cured at 150-170°C for 3-18 hours.

7. The method for preparing the high-strength insulating Schiff base degradable epoxy resin material according to claim 1, 2 or 3, characterized in that: The preparation method of the Schiff base building block in step S1 is as follows: S11, weighing kojic acid, a diamine compound and p-toluenesulfonic acid in a molar ratio of 2: (0.8-1.2): (0.02-0.1); S12. Dissolve kojic acid and diamine compounds in benzene according to the above-mentioned molar ratio, and stir them magnetically at 40-80°C until they are completely dissolved. Then add p-toluenesulfonic acid as a catalyst, adjust the heating temperature to 60-140°C, condense and reflux for 12-24 hours, and after the reaction is completed, filter and evaporate excess benzene to obtain a Schiff base building block product.

8. The method for preparing the high-strength insulating Schiff base degradable epoxy resin material according to claim 7, characterized in that: The diamine compound in step S11 and step S12 is one or a combination of two or more of 4,4'-diaminophenyl ether, p-phenylenediamine, 4,4'-methylenedianiline, 4,4'-(2,2-propylenediyl)diphenylamine and 4,4'-(perfluoropropane-2,2-diyl)diphenylamine.

9. The method for preparing the high-strength insulating Schiff base degradable epoxy resin material according to claim 1, characterized in that: In step S1, the progress of the chain extension modification reaction is tracked by thin layer chromatography.

10. The method for preparing the high-strength insulating Schiff base degradable epoxy resin material according to claim 7, characterized in that: In step S12, the progress of the chain extension modification reaction is tracked by thin layer chromatography.

11. A high-strength insulating Schiff base degradable epoxy resin material obtained by the method for preparing the high-strength insulating Schiff base degradable epoxy resin material according to any one of claims 1 to 10.

Images