Bisphenol curing agent containing spirocyclic bisboronic acid ester group, vegetable oil-based epoxy resin and preparation method and application thereof

Abstract

The present invention provides a bisphenol curing agent, a vegetable oil-based epoxy resin and its preparation method and application containing a spiro-bis-boronic acid ester group, and belongs to the field of fine chemical technology. The present invention is based on the method designed by cross-linking network structure, by dehydration condensation of 4-hydroxyphenylboronic acid and pentaerythritol, a spiro-boronic acid ester-based diphenol is prepared in one step, which is used to improve the structural performance of epoxy adhesive. In the present invention, spiro-boronic acid ester-based diphenol and bisphenol F both contain a double benzene ring structure, which is conducive to improving the rigidity of the epoxy adhesive molecular structure and contributing to the structural cohesive strength. At the same time, the B-O bond has high bond energy and associative reversible cross-linking characteristics, which can improve the bonding strength and reprocessing performance of the vegetable oil-based epoxy resin, and can significantly improve the structure of the epoxy adhesive. The vegetable oil-based epoxy resin prepared not only has better bonding strength, but also has good degradation performance and reprocessing performance.

Description

Technical Field

[0001] The present invention relates to the technical field of fine chemicals, and in particular to a bisphenol curing agent containing a spirocyclic bisboronic acid ester group, a vegetable oil-based epoxy resin, and a preparation method and application thereof. Background Art

[0002] Epoxy adhesives are one of the most widely used adhesive materials. Due to their excellent performance, adjustable structure, and simple preparation, they are used in a variety of fields, including aerospace, automotive manufacturing, wind turbine blades, and structural high-performance resins. Depending on the needs of the application scenario, current research on epoxy adhesives focuses on improving the adhesive's application performance by modifying and curing the cross-linking network. This mainly includes epoxy adhesive reinforcement and toughening modification, the preparation of high-strength epoxy adhesives, the preparation of low-temperature / fast-curing high-strength epoxy adhesives, the preparation of high-temperature resistant epoxy adhesives, and the preparation of water-resistant epoxy adhesives. Based on the demand for materials in various fields, lightweight and high-strength standards have become increasingly important, requiring adhesives to possess excellent bonding strength to meet the structural requirements of the material.

[0003] At present, the performance modification of epoxy adhesives mainly focuses on the following aspects: (1) cross-linking network modification, which is to improve the structural properties of epoxy adhesives and thus improve the bonding performance by designing the structure of epoxy monomers or curing agents, such as introducing hyperbranched structures; (2) blending modification, which is to blend epoxy adhesives with other adhesives with specific excellent properties to improve the shortcomings of epoxy adhesives and improve the bonding performance of epoxy adhesives; (3) nano-hybrid modification, which is to use nano-fillers as reinforcing elements to improve the structural properties of epoxy adhesives and achieve improved bonding performance.

[0004] Patent CN202211122212.8 "A high-strength single-component epoxy adhesive composition and its preparation method" obtains a high-strength epoxy adhesive by designing a toughening agent and then compounding a curing agent, diluent, filler and other synergistically modified epoxy resin cross-linking system. However, most of the currently disclosed methods have complex processes and complex additives, which are not conducive to industrial applications. In addition, epoxy resins are mainly petroleum-based products and do not meet the current "dual carbon" requirements (or such as CN201310675056.2 "A high-strength adhesive and its preparation method and its use"). At the same time, in adhesives prepared from bio-based environmentally friendly materials such as epoxy vegetable oil, the bonding strength is much different from that of petroleum-based epoxy adhesives (such as CN202410260521.4 "A plasma-modified chitosan-cured epoxy soybean oil wood adhesive and its preparation method and application"). In addition, with the increase in the application of epoxy adhesives, after the product completes its service life, the high bonding strength makes it impossible to degrade and remove the colloid, making it difficult to reprocess and apply it, and the recycling of materials cannot be achieved.

[0005] Moreover, there is a contradiction between high bonding strength and degradability and reprocessability, and the existing technology cannot achieve the integration of the above properties through structural design modification. Currently, there is a technology that realizes the reprocessing of epoxy adhesives by constructing epoxy hot melt adhesives, such as CN112877014B "An epoxy resin hot melt adhesive and its preparation method", which uses urea-pyrimidone as a functional structure to achieve repeated bonding. However, there are no relevant reports on the unified integration of high bonding strength, reprocessability and degradability of bio-based epoxy resin adhesives. Therefore, how to take into account the high bonding strength, rapid degradation and repeated bonding performance of adhesives is the focus and difficulty of the current development of the adhesive industry. Summary of the Invention

[0006] The purpose of the present invention is to provide a bisphenol curing agent containing a spirocyclic bisboronic acid ester group, a plant oil-based epoxy resin, and a preparation method and application thereof. In view of the current situation where high-strength epoxy cross-linking network cannot be balanced with degradation performance and reprocessing performance, a bio-based epoxy resin adhesive is prepared that has high bonding strength, rapid degradation, and repeated bonding (reprocessing) performance.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a bisphenol curing agent containing a spiro-bis-boronate group. The bisphenol curing agent containing a spiro-bis-boronate group is prepared from 4-hydroxyphenylboric acid and pentaerythritol in a molar ratio of 2-2.2:1. The structure of the bisphenol curing agent containing a spiro-bis-boronate group is shown in formula (I):

[0009]

[0010] The present invention also provides a method for preparing a bisphenol curing agent containing a spirocyclic bisboronic acid ester group, comprising the following steps:

[0011] 4-Hydroxyphenylboric acid, pentaerythritol and anhydrous ethanol are mixed, heated for reaction, and rotary evaporated to obtain a bisphenol curing agent containing a spirocyclic bisboronic acid ester group.

[0012] Preferably, the molar volume ratio of pentaerythritol to anhydrous ethanol is 1 mol:0.5-1 L; the temperature of the heating reaction is 50-70° C., and the heating reaction time is 12-24 h.

[0013] The present invention also provides a method for preparing a plant oil-based epoxy resin using a bisphenol curing agent containing a spirocyclic bisboronic acid ester group, comprising the following steps:

[0014] Epoxidized soybean oil, a bisphenol curing agent containing a spirocyclic bisboronic acid ester group, a curing agent, a catalyst and anhydrous ethanol are stirred and mixed, heated under negative pressure for reaction, degassed and dried to obtain a vegetable oil-based epoxy resin.

[0015] Preferably, the curing agent includes one of bisphenol F, bisphenol A, and bisphenol S; and the catalyst includes one of imidazole, acrylic anhydride, aniline, benzyldimethylamine, and phenol.

[0016] Preferably, the molar volume ratio of the epoxidized soybean oil, the bisphenol curing agent containing a spirocyclic bisboronic acid ester group, the curing agent, and anhydrous ethanol is: epoxidized soybean oil: bisphenol curing agent containing a spirocyclic bisboronic acid ester group: curing agent: anhydrous ethanol = 1 mol: 0-2 mol: 0-2 mol: 1-1.5 L; the amount of the catalyst used is 0-20% by weight of the epoxidized soybean oil.

[0017] Preferably, the pressure of the heating reaction under the negative pressure condition is 0.1-0.5 MPa; the heating reaction temperature is 70-100° C.; and the heating reaction time is 30-60 min.

[0018] Preferably, the heat drying temperature is 120-160° C. and the time is 6 hours.

[0019] The present invention also provides a plant oil-based epoxy resin prepared by the method for preparing the plant oil-based epoxy resin.

[0020] The present invention also provides a use of a vegetable oil-based epoxy resin as an adhesive.

[0021] The beneficial effects of the present invention compared with the prior art are:

[0022] (1) This invention, based on a cross-linked network structure design method, synthesizes a novel spiro borate structure that can be used as a curing agent to improve the structural properties of epoxy adhesives. By dehydrating and condensing 4-hydroxyphenylboronic acid with pentaerythritol, a spiro borate-based diphenol is prepared in one step. This compound serves as the primary functional unit for structural modification.

[0023] (2) The present invention modifies epoxy soybean oil by compounding spiroborate-based diphenol with bisphenol F. The spiroborate-based diphenol and bisphenol F curing agent are beneficial to significantly improve the bonding strength. First, both materials contain a double benzene ring structure, which is beneficial to improving the molecular structural rigidity of the epoxy adhesive and contributing to the structural cohesive strength. Secondly, the spiroborate group in the spiroborate-based diphenol is a double six-membered ring structure, which has a structural strength gain effect similar to that of the benzene ring, further improving the cohesive strength. At the same time, the electron-deficient boron atoms in the spiroborate-based diphenol tend to combine with donor groups and nucleophiles that are abundant on the surfaces of various substrates, thereby improving the interfacial bonding activity and contributing to the interfacial bonding performance. The simultaneous optimization of cohesive strength and interfacial bonding performance synergistically shares excellent bonding strength.

[0024] In addition to the aforementioned adhesive strength-boosting properties, the BO bond also exhibits associative reversible crosslinking, endowing the three-dimensional crosslinked network with reprocessability, resulting in the adhesive exhibiting repeatable bonding properties. Furthermore, the BO bond possesses a high bond energy (809 kJ / mol), avoiding the structural strength impairment often associated with other dynamic bonding groups. The dynamic reversible crosslinking properties of BO allow for structural degradation under acidic conditions, enabling the degradable removal of the colloidal material.

[0025] (3) The present invention is based on the spirocyclic borate group to achieve a significant improvement in the structure of the epoxy adhesive. The prepared plant oil-based epoxy resin not only has better bonding strength, but also has good degradation and reprocessing properties. DETAILED DESCRIPTION

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0028] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0029] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0030] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0031] The present invention prepares a plant oil-based epoxy resin with good bonding strength, while taking into account degradation performance and reprocessing performance. The preparation is mainly divided into two steps. The specific method is as follows:

[0032] (1) Preparation of bisphenol curing agent containing spirocyclic bisboronic acid ester group:

[0033] 4-hydroxyphenylboronic acid, pentaerythritol and anhydrous ethanol are mixed, heated for reaction, and rotary evaporated to obtain a bisphenol curing agent containing a spirocyclic bisboronic acid ester group;

[0034] (2) A method for a vegetable oil-based epoxy resin, comprising the following steps:

[0035] Epoxidized soybean oil, a bisphenol curing agent containing a spirocyclic bisboronic acid ester group, a curing agent, a catalyst and anhydrous ethanol are stirred and mixed, heated under negative pressure for reaction, degassed and dried to obtain a vegetable oil-based epoxy resin.

[0036] The structure of bisphenol F used in the following examples is as follows:

[0037]

[0038] Example 1

[0039] Example 1 of the present invention provides a method for preparing a bisphenol curing agent containing a spirocyclic bisboronic acid ester group, which specifically comprises the following steps:

[0040] 2 mol of 4-hydroxyphenylboric acid, 1 mol of pentaerythritol, and 1 L of anhydrous ethanol were mixed, reacted at 50° C. for 24 h, and rotary evaporated to obtain a bisphenol curing agent containing a spirocyclic bisboronic acid ester group.

[0041] Example 2

[0042] Example 2 of the present invention provides a method for preparing a plant oil-based epoxy resin using a bisphenol curing agent containing a spirocyclic bisboronic acid ester group, which specifically includes the following steps:

[0043] 1 mol of epoxy soybean oil (calculated here as containing 4 epoxy groups in one structure), 0.8 mol of bisphenol curing agent containing spirocyclic bisboronic acid ester group, 1.2 mol of bisphenol F, 20% imidazole by weight of epoxy soybean oil, and 1.5 L of anhydrous ethanol were stirred and mixed, reacted at 100 ° C for 60 min under a negative pressure of 0.1 MPa, degassed, and baked at 120 ° C for 6 h to obtain a vegetable oil-based epoxy resin.

[0044] Example 3

[0045] Example 3 of the present invention provides a method for preparing a vegetable oil-based epoxy resin using a bisphenol curing agent containing a spirocyclic bisboronate group. The difference from Example 2 is that in Example 3, the amount of the bisphenol curing agent containing a spirocyclic bisboronate group is 2 mol, and the amount of bisphenol F is 0 mol.

[0046] Example 4

[0047] Example 4 of the present invention provides a method for preparing a vegetable oil-based epoxy resin using a bisphenol curing agent containing a spirocyclic bisboronate group. The difference from Example 2 is that in Example 4, the amount of the bisphenol curing agent containing a spirocyclic bisboronate group is 0.4 mol, and the amount of bisphenol F is 1.6 mol.

[0048] Example 5

[0049] Example 5 of the present invention provides a method for preparing a vegetable oil-based epoxy resin using a bisphenol curing agent containing a spirocyclic bisboronate group. The difference from Example 2 is that in Example 5, the amount of the bisphenol curing agent containing a spirocyclic bisboronate group is 1.2 mol, and the amount of bisphenol F is 1.4 mol.

[0050] Example 6

[0051] Example 6 of the present invention provides a method for preparing a vegetable oil-based epoxy resin using a bisphenol curing agent containing a spirocyclic bisboronate group. The difference from Example 2 is that in Example 6, the amount of the bisphenol curing agent containing a spirocyclic bisboronate group is 1.6 mol, and the amount of bisphenol F is 2 mol.

[0052] Comparative Example 1

[0053] Comparative Example 1 of the present invention provides a method for preparing a vegetable oil-based epoxy resin. The difference from Example 2 is that in Comparative Example 1, the amount of the bisphenol curing agent containing a spirocyclic bisboronic acid ester group is 0 mol, and the amount of bisphenol F is 2 mol.

[0054] Test Example 1

[0055] Test Example 1 of the present invention tested the bonding strength performance of the vegetable oil-based epoxy resins prepared in Examples 2 to 6 and Comparative Example 1. The prepared vegetable oil-based epoxy resins were coated on the surface of the substrate, and another substrate was covered on top. After clamping, the adhesive was cured at 120°C and 140°C for 2 hours each to test the shear bonding strength of the cured adhesive. The specific results are shown in Table 1.

[0056] Table 1 Bonding strength properties of different vegetable oil-based epoxy resins

[0057] Grouping Bonding strength Example 2 16.24±0.81MPa Example 3 10.57±1.68MPa Example 4 12.96±0.90MPa Example 5 14.03±0.15MPa Example 6 12.84±1.47MPa Comparative Example 1 8.33±0.64MPa

[0058] As shown in Table 1, when a bisphenol curing agent containing a spirocyclic bisborate group is added, the bonding strength of the vegetable oil-based epoxy resin prepared by the present invention as an adhesive is significantly improved.

[0059] Test Example 2

[0060] Test Example 2 of the present invention tested the repeated bonding performance of the vegetable oil-based epoxy resins prepared in Examples 2 to 6 and Comparative Example 1. The bonded specimens that were broken after the tensile strength test in Test Example 1 were stacked in their original positions and re-bonded using a hot press at 140°C and 3 MPa for 1 hour. The strength test was performed according to the method of Test Example 1. The results are shown in Table 2.

[0061]

[0062] As shown in Table 2, when a bisphenol curing agent containing a spirocyclic bisborate group is added, the vegetable oil-based epoxy resin prepared by the present invention can be used as an adhesive for repeated bonding, and the reprocessing performance is significantly improved.

[0063] Test Example 3

[0064] Test Example 3 of the present invention tested the repeated bonding performance of the vegetable oil-based epoxy resins prepared in Examples 2 to 6 and Comparative Example 1. The specific method is as follows:

[0065] 2 volumes of water were added to 8 volumes of tetrahydrofuran solvent, and HCl was added to make the final concentrations of the solution 0.1, 0.5, and 1.0 M, respectively. At temperatures of 20 and 50° C., the vegetable oil-based epoxy resins prepared in Examples 2 to 6 and Comparative Example 1 were added, and the time for complete degradation of the epoxy resins was recorded. The results are shown in Table 3.

[0066] Table 3 Degradation properties of vegetable oil epoxy adhesives

[0067] Grouping 0.1M HCl, 20°C 0.5M HCl, 20°C 1M HCl, 20°C 1M HCl, 50°C Example 2 752 minutes 560 minutes 325 minutes 125 minutes Example 3 488 minutes 400 minutes 264 minutes 88 minutes Example 4 1020 mins 850 minutes 765 minutes 690 minutes Example 5 690 minutes 490 minutes 300 minutes 110 minutes Example 6 510 minutes 430 minutes 286 minutes 98 minutes Comparative Example 1 - - - -

[0068] As shown in Table 3, when a bisphenol curing agent containing a spirocyclic bisboronic acid ester group is added, the vegetable oil-based epoxy resin prepared in the present invention has the characteristic of rapid degradation.

[0069] 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 principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A bisphenol curing agent containing a spirocyclic bisboronic acid ester group, characterized in that: The bisphenol curing agent containing a spirocyclic bisboronic acid ester group is prepared from 4-hydroxyphenylboric acid and pentaerythritol in a molar ratio of 2-2.2:

1. The structure of the bisphenol curing agent containing a spirocyclic bisboronic acid ester group is shown in formula (I): .

2. A method for preparing the bisphenol curing agent containing a spirocyclic bisboronic acid ester group according to claim 1, characterized in that: The steps include: 4-Hydroxyphenylboric acid, pentaerythritol and anhydrous ethanol are mixed, heated for reaction, and rotary evaporated to obtain a bisphenol curing agent containing a spirocyclic bisboronic acid ester group.

3. The method for preparing a bisphenol curing agent containing a spirocyclic bisboronic acid ester group according to claim 2, wherein: The molar volume ratio of pentaerythritol to anhydrous ethanol is 1 mol:0.5-1 L; the temperature of the heating reaction is 50-70° C., and the heating reaction time is 12-24 h.

4. A method for preparing a vegetable oil-based epoxy resin using the bisphenol curing agent containing a spirocyclic bisboronic acid ester group according to claim 1, characterized in that: The steps include: The epoxy soybean oil, the compound of formula (I), the curing agent, the catalyst and the anhydrous ethanol are stirred and mixed, heated under negative pressure to react, degassed and dried to obtain the vegetable oil-based epoxy resin; The curing agent is selected from one of bisphenol F, bisphenol A and bisphenol S; The catalyst is selected from one of imidazole, acrylic anhydride, aniline, benzyldimethylamine and phenol.

5. The method for preparing a vegetable oil-based epoxy resin according to claim 4, wherein: The molar volume ratio of the epoxidized soybean oil, the compound of formula (I), the curing agent, and anhydrous ethanol is: epoxidized soybean oil: the compound of formula (I): the curing agent: anhydrous ethanol = 1 mol: 0-2 mol: 0-2 mol: 1-1.5 L; the amount of the catalyst used is 0-20% by weight of the epoxidized soybean oil.

6. The method for preparing a vegetable oil-based epoxy resin according to claim 4, wherein: The pressure of the heating reaction under the negative pressure condition is 0.1-0.5 MPa; the heating temperature is 70-100° C., and the heating time is 30-60 min.

7. The method for preparing a vegetable oil-based epoxy resin according to claim 4, wherein: The temperature of the heat drying is 120-160° C. and the time is 6 hours.

8. A vegetable oil-based epoxy resin prepared by the method for preparing a vegetable oil-based epoxy resin according to any one of claims 4 to 7.

9. Use of the vegetable oil-based epoxy resin according to claim 8 as an adhesive.

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