Cationic-π-action degradable tough epoxy resin and preparation method thereof

Abstract

The present invention discloses a degradable tough epoxy resin containing a cation-π effect and a preparation method thereof, wherein the epoxy resin is composed of a multi-arm thiol containing an ester group, an ionic liquid containing an unsaturated double bond and a cation-π effect, and an epoxy resin. The present invention can combine the multi-arm thiol containing an ester group and the ionic liquid of the unsaturated double bond with the epoxy resin through a light-heat dual curing process to construct a degradable epoxy resin system with high toughness, and the whole method is green, simple and easy to operate. The energy dissipation capacity of the epoxy resin containing the cation-π effect when subjected to external stimuli is significantly improved, and the cation-π action sites uniformly dispersed in the network play a key role in the balance of stiffness and toughness under repeated loading-unloading cycles. In addition, the ester group in the structure makes the synthesized epoxy resin have excellent degradation performance, and the hydrogen atoms in the imidazole can form intermolecular hydrogen bonds with the ester group, accelerate the degradation process of the resin, and achieve rapid degradation under amine / alkaline conditions.

Description

Technical Field

[0001] The present invention relates to an epoxy resin and a preparation method thereof, in particular to an ester group-cation-π-acting degradable tough epoxy resin and a preparation method thereof. Background Art

[0002] There is a trade-off between strength and toughness in most materials, and increasing their crosslink density often leads to embrittlement, especially in thermosetting materials. Epoxy resin, as one of the most commonly used thermosetting resins, has been widely used in various fields, such as aerospace, transportation, and electronics. Generally, highly crosslinked epoxy resins have excellent properties such as high modulus, strength, and heat resistance. However, the three-dimensional crosslinked network structure after curing limits the slippage of the molecular chains, resulting in the unfavorable consequences of high brittleness and poor crack propagation resistance, ultimately causing permanent damage such as material failure. In the past few decades, methods of improving the toughness of resins by incorporating elastomers, thermoplastics, interpenetrating networks, and adding nanofillers have been widely studied. However, in most cases, the introduction of flexible structures inevitably leads to a sacrifice in material strength. Therefore, how to achieve improved ductility without sacrificing mechanical strength still requires in-depth research.

[0003] Recent studies of naturally toughened materials have revealed that their toughness stems from reversible chemical bonds and multi-layered structures within the molecules. Non-covalent interactions, which do not require additional energy for bond breakage and recombination, are considered promising approaches for dissipating energy. Non-covalent interactions, such as hydrogen bonds, metal coordination bonds, and host-guest interactions, have been widely exploited through structural design in materials such as elastomers and hydrogels, achieving significant breakthroughs in the development of highly tough materials. This demonstrates that the sacrificial strategy provided by non-covalent interactions offers a practical solution for designing highly tough polymers. Notably, for materials with such properties, mechanical deformation of the cross-linked network should be fully reversible at low strains. Therefore, sufficient molecular mobility is required to maintain the sacrificial effect when the external force is removed, and a certain amount of covalent crosslinking between chains is required to provide a restorative force. Epoxy resins have a highly rigid benzene ring structure, and the poor energy dissipation and segment mobility resulting from this rigid structure are likely to limit the implementation of this sacrificial strategy in epoxy resins. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a cation-π-containing degradable tough epoxy resin and a preparation method thereof. The present invention can combine ester-containing multi-arm thiol, unsaturated double-bond ionic liquid with epoxy resin through a simple light-heat dual curing process to construct a degradable epoxy resin system with high toughness. The whole method is green, simple and easy to operate. The energy dissipation capacity of the epoxy resin containing cation-π effect is significantly improved when subjected to external stimuli. The cation-π action sites uniformly dispersed in the network play a key role in the balance between stiffness and toughness under repeated loading-unloading cycles. In addition, the ester group in the structure gives the synthesized epoxy resin excellent degradation performance. The hydrogen atoms in the imidazole can form intermolecular hydrogen bonds with the ester group, accelerate the degradation process of the resin, and achieve rapid degradation under amine / alkaline conditions. Among them, the aminolysis solution can be recycled and participated in the re-curing of the epoxy resin, which has huge economic and environmental advantages in the fields of recyclable thermosetting resins and their composite materials.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] An ionic liquid containing an unsaturated double bond and a cation-π interaction has the following molecular structure formula:

[0007]

[0008] Wherein, R is not limited to Cl - Br - , I - Br 3- , BF 4- PF 6- 、FSI - TFSI - 、SbF6 - 、TfS - OH - 、CO3 2- , HCO 3- 、FeCl 4- 、AlCl 4- 、ZnCl 2- 、CuCl 2- 、SO-、SDd - SHd - PB 2- R1 is an ionic liquid that can form a cation-π effect, but is not limited to a benzene ring, hexafluorobenzene, etc.

[0009] A method for preparing the above-mentioned ionic liquid containing an unsaturated double bond and a cation-π reaction is prepared according to the following reaction process:

[0010]

[0011] Step 1: dissolve the reactant with R1 group and N-vinyl imidazole in an appropriate amount of solvent 1, and stir at room temperature to 88°C for 6 to 72 hours, wherein:

[0012] The structural formula of the reactant with R1 group is:

[0013]

[0014] The molar ratio of the reactant with the R1 group to N-vinylimidazole is 1.01 to 2:1;

[0015] The solvent 1 is not limited to one of acetonitrile, tetrahydrofuran, methanol, ethanol, dioxane, and dichloromethane;

[0016] Step 2: precipitating the reaction mixture in step 1 in solvent 2 and centrifuging, wherein:

[0017] The solvent 2 is not limited to one of ether, n-hexane, petroleum ether, and ethyl acetate;

[0018] The number of centrifugation is 3 to 5 times, each time for 3 to 10 minutes;

[0019] Step 3: Collect the product and dry it to a constant weight under vacuum to obtain an ionic liquid containing an unsaturated double bond and a cation-π reaction.

[0020] A cation-π-interaction degradable tough epoxy resin is composed of a multi-arm thiol containing an ester group, an ionic liquid containing an unsaturated double bond and a cation-π interaction, and an epoxy resin, wherein:

[0021] The multi-arm thiol containing an ester group is not limited to pentaerythritol (thioglycolate), pentaerythritol tetrakis (3-mercaptopropionate), dipentaerythritol hexa (3-mercaptopropionate), trimethylolpropane tris (3-mercaptopropionate), bis (thioglycolate) glycol ester, etc., and the structure contains an ester group and the number of thiol groups is ≥ 2. When used, it can be one or more, and the multi-arm thiol is not limited to three-arm, four-arm, six-arm, etc.

[0022] The molar ratio of the epoxy group to the mercapto group is 1:1, and the molar ratio of the unsaturated double bond to the mercapto group is 0.1 to 1:1;

[0023] The epoxy resin is one or more of glycidyl ether, glycidyl ester, glycidyl amine, aliphatic epoxy resin, alicyclic epoxy resin, trifunctional epoxy resin, tetrafunctional epoxy resin, phenolic epoxy resin, o-cresol epoxy resin, and nitrogen-containing epoxy resin.

[0024] A method for preparing the above-mentioned cationic-π-containing degradable tough epoxy resin, according to Figure 1Preparation as shown in the reaction scheme:

[0025] The specific steps are as follows:

[0026] A one-pot method is used to mix a photoinitiator, a multi-arm thiol containing an ester group, an ionic liquid containing an unsaturated double bond and a cation-π interaction with an epoxy resin, and generate a degradable tough epoxy resin containing a cation-π interaction through light-heat dual curing crosslinking, wherein:

[0027] The photoinitiator includes one or more of free radical, cationic, anionic and ring-opening metathesis polymerization photoinitiators, but is not limited to one or more of IHT-PI 910, 659, 907, MBF, TPO, IHT-PI 4265, IHT-PI 1000, IHT-PI 500, benzoin, benzoin dimethyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin butyl ether, benzophenone, 2,4-dihydroxybenzophenone, diaryl iodonium salt, triaryl iodonium salt, alkyl iodonium salt, and isopropylphenylferrocenium hexafluorophosphate, and the added amount is 0.1-3wt% of the mass of the thiol;

[0028] The first stage of the light-heat dual curing crosslinking is UV curing, the selected wavelength is 365nm, and the irradiation time is 5 to 60 minutes; after completing the first stage curing, it is transferred to an oven for the second stage curing, the curing temperature is 25 to 200°C, and the curing time is 60 to 360 minutes.

[0029] A method for degrading the above-mentioned cationic-π-containing degradable toughened epoxy resin comprises the following steps:

[0030] An alkaline solvent or amine capable of immersing the resin is added to a cationic-π-containing degradable toughened epoxy resin, and the resin is heated and stirred at 50 to 150° C. until the resin is completely degraded, wherein:

[0031] The amount of the alkaline solvent or amine is at least 0.8 times the mass of the cationic-π-containing degradable toughened epoxy resin;

[0032] The alkaline solution is not limited to one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, potassium carbonate, cesium carbonate, sodium thiosulfate, ammonia water, ammonium bicarbonate, etc., and the concentration is 0.5 to 6 mol / L;

[0033] The amine is not limited to one or more of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, ethylenediamine, butanediamine, hexamethylenediamine, meta-xylylenediamine and the like.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] 1. The present invention adopts a one-pot method to synthesize an epoxy resin system containing ester groups and cationic-π interactions. The whole process is simple, has high yield, and fast reaction rate. The dynamically reversible cationic-π interaction cross-linking sites can increase the energy dissipation of the resin system through the bond breaking-recombination process when subjected to external force.

[0036] 2. The resin obtained by the present invention after curing not only has excellent mechanical properties, but also has good application in degradation and recycling. The rich ester groups in the structure and the adjustable glass transition temperature enable the series of resins prepared by the present invention to achieve rapid degradation under non-harsh conditions. The degradation conditions are amine / alkaline conditions. The aminolysis solution can also be used in the re-curing process of the epoxy resin, and will not generate a secondary pollution source to the environment. It is an economically feasible industrial production route. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The figure shows the preparation flow chart of cationic-π-interacting degradable tough epoxy resin. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further described below with reference to the embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the scope of protection of the present invention.

[0039] Example 1: Ionic Liquid I Containing Unsaturated Double Bonds and Cationic-π Interactions

[0040] 14.8 g of benzyl chloride and 10 g of N-vinylimidazole were dissolved in 30 mL of acetonitrile, stirred, and heated for 12 hours. The reaction mixture was then precipitated in diethyl ether and centrifuged three times at 10,000 rpm for 10 minutes each. Finally, the yellow liquid ionic liquid I was collected and dried under vacuum to a constant weight with a yield of approximately 90%. The molecular structure is as follows:

[0041]

[0042] Example 2: Ionic Liquid II Containing Unsaturated Double Bonds Interacting with Cation-π

[0043] 45 g of 2,3,4,5,6-pentafluorobenzyl bromide and 19 g of N-vinylimidazole were dissolved in 200 mL of acetonitrile, stirred, and heated for 12 hours. The reaction mixture was then precipitated in diethyl ether and centrifuged three times at 10,000 rpm for 10 minutes each. Finally, the white solid ionic liquid II was collected and dried under vacuum to a constant weight with a yield of approximately 90%. The molecular structure is as follows:

[0044]

[0045] Example 3: High-Toughness Degradable Thermosetting Resin 1

[0046] At room temperature, 10 g of epoxy resin E51, 1 wt% of photoinitiator 2,4-dihydroxybenzophenone, 10.5 g of pentaerythritol tetrakis(3-mercaptopropionate) and 4.6 g of ionic liquid I were mixed evenly, degassed in a vacuum oven, and further transferred to a PTFE mold pre-coated with a release agent. The mixture was first irradiated under a 365 nm UV lamp for 15 min, and then heated in a 75 ° C oven for 2 h to completely cure. After cooling to room temperature, a high-toughness biodegradable epoxy resin I was obtained. Its thermodynamic properties are shown in Table 1.

[0047] Table 1 Thermodynamic properties of epoxy resin I

[0048]

[0049]

[0050] Example 4: High-toughness degradable thermosetting resin II

[0051] At room temperature, 10 g of epoxy resin E51, 1 wt% of photoinitiator 2,4-dihydroxybenzophenone, 7.3 g of trimethylolpropane tris(3-mercaptopropionate) and 5 g of ionic liquid I were mixed evenly, degassed in a vacuum oven, and further transferred to a PTFE mold pre-coated with a release agent. The mixture was first irradiated under a 365 nm UV lamp for 15 min, and then heated in an oven at 100 ° C for 2 h to completely cure. After cooling to room temperature, a high-toughness biodegradable epoxy resin I was obtained. Its thermodynamic properties are shown in Table 2.

[0052] Table 2 Thermodynamic properties of epoxy resin II

[0053] project performance Tensile strength (MPa) 15±2 Tensile modulus (GPa) 1.0±0.2 Tensile strain (%) 100±20 <![CDATA[T g (℃)]]> 60～70 <![CDATA[T d5％ (℃)]]> 290～300

[0054] Example 5: High-toughness degradable thermosetting resin III

[0055] At room temperature, 10 g of epoxy resin E51, 1 wt% of photoinitiator 2,4-dihydroxybenzophenone, 9.5 g of dipentaerythritol hexa(3-mercaptopropionate) and 5 g of ionic liquid I were mixed evenly, degassed in a vacuum oven, and further transferred to a PTFE mold pre-coated with a release agent. First, it was irradiated under a UV lamp with a wavelength of 365 nm for 15 min, and then heated in an oven at 75 ° C for 2 h to completely cure. After cooling to room temperature, a high-toughness biodegradable epoxy resin III was obtained, whose thermodynamic properties are shown in Table 3.

[0056] Table 3 Thermodynamic properties of epoxy resin III

[0057] project performance Tensile strength (MPa) 40±5 Tensile modulus (GPa) 2±0.2 Tensile strain (%) 25±5 <![CDATA[T g (℃)]]> 100～120 <![CDATA[T d5％ (℃)]]> 320～350

[0058] Example 6: High-toughness degradable thermosetting resin IV

[0059] At room temperature, 10 g of epoxy resin E51, 1 wt% of photoinitiator 2,4-dihydroxybenzophenone, 10.5 g of pentaerythritol tetrakis(3-mercaptopropionate) and 8 g of ionic liquid II were mixed evenly, degassed in a vacuum oven, and further transferred to a PTFE mold pre-coated with a release agent. First, it was irradiated under a UV lamp with a wavelength of 365 nm for 30 minutes, and then heated in an oven at 100°C for 2 hours to completely cure. After cooling to room temperature, a high-toughness biodegradable epoxy resin IV was obtained.

[0060] Example 7: Degradable Thermosetting Resin I

[0061] Add 1g of high-toughness degradable thermosetting resin I and 2g of diethylenetriamine to a 50mL glass bottle and stir at 100°C for 2h to completely degrade and obtain a clear and transparent yellow solution with a certain viscosity. Use 1.1g of this yellow solution and 6.0g of epoxy resin E-51 for curing. The curing procedure is 24h at room temperature and 1h at 100°C. The mechanical property retention rate of the obtained degradable thermosetting resin I is 80% of that of the high-toughness degradable thermosetting resin I cured with diethylenetriamine.

[0062] Example 8: Degradable Thermosetting Resin II

[0063] Add 1g of high-toughness degradable thermosetting resin I and 2g of ethylenediamine to a 50mL glass bottle and stir at 100°C for 2h to completely degrade and obtain a clear and transparent yellow solution with a certain viscosity. Use 0.5g of this yellow solution and 5.0g of epoxy resin E-51 for curing. The curing procedure is 24h at room temperature and 1h at 100°C. The mechanical property retention rate of the obtained degradable thermosetting resin II is 85% of that of the high-toughness degradable thermosetting resin I cured with ethylenediamine.

[0064] Example 9: Degradation and recovery of degradable thermosetting resin III

[0065] Add 1g of degradable thermosetting resin I and 2g of m-xylenediamine to a 50mL glass bottle and stir at 100°C for 4h to completely degrade and obtain a clear and transparent yellow solution with a certain viscosity. Use 1.8g of this yellow solution and 5.6g of epoxy resin E-51 to cure at 80°C for 6h. The mechanical property retention rate of the obtained degradable thermosetting resin III is 90% of that of the high-toughness degradable thermosetting resin I cured with m-xylenediamine.

[0066] Example 10: Degradable Thermosetting Resin IV

[0067] Add 1 g of high-toughness degradable thermosetting resin I and 0.5 mol / L NaOH solution into a 50 mL glass bottle and stir at 100 °C for 6 h. The solution will be completely degraded to obtain a clear and transparent orange solution.

[0068] Example 11: Degradable Thermosetting Resin V

[0069] Add 1g of high-toughness degradable thermosetting resin I and 1mol / L NaOH solution into a 50mL glass bottle and stir at 100℃ for 2h. It can be completely degraded to obtain a clear and transparent orange solution.

[0070] Example 12: Degradable Thermosetting Resin VI

[0071] Add 1g of high-toughness degradable thermosetting resin I and 1mol / L NaOH solution into a 50mL glass bottle and stir at room temperature for 7 days to completely degrade and obtain a clear and transparent light yellow solution.

[0072] Example 13: Degradable Thermosetting Resin VII

[0073] Add 1g of high-toughness degradable thermosetting resin IV and 1mol / L NaOH solution into a 50mL glass bottle and stir at 100℃ for 2h to completely degrade and obtain a clear and transparent yellow solution.

[0074] Example 14: Degradable Thermosetting Resin VIII

[0075] Add 1g of high-toughness degradable thermosetting resin IV and 2g of triethylenetetramine solution into a 50mL glass bottle and stir at 100℃ for 4h to completely degrade and obtain a clear and transparent yellow solution.

Claims

1. A cationic-π-containing degradable tough epoxy resin, characterized in that The epoxy resin is composed of a multi-arm thiol containing an ester group, an ionic liquid containing an unsaturated double bond and a cation-π reaction, and an epoxy resin, wherein: The ionic liquid containing an unsaturated double bond and a cation-π interaction has the following molecular structure formula: Where R is Cl - Br - R1 is one of a benzene ring and hexafluorobenzene; The multi-arm thiol is one or more of pentaerythritol (thioglycolate), pentaerythritol tetrakis (3-mercaptopropionate), dipentaerythritol hexa (3-mercaptopropionate), trimethylolpropane tris (3-mercaptopropionate), and bis (thioglycolate) ethylene glycol ester; The molar ratio of the epoxy group to the thiol group is 1:1, and the molar ratio of the unsaturated double bond to the thiol group is 0.1 to 1:1; The epoxy resin is one or more of glycidyl ether, glycidyl ester, glycidyl amine, aliphatic epoxy resin, alicyclic epoxy resin, trifunctional epoxy resin, tetrafunctional epoxy resin, phenolic epoxy resin, o-cresol epoxy resin, and nitrogen-containing epoxy resin.

2. A method for preparing the cationic-π-containing degradable tough epoxy resin according to claim 1, characterized in that The method comprises the following steps: A one-pot method is used to mix a photoinitiator, a multi-arm thiol containing an ester group, an ionic liquid containing an unsaturated double bond and a cation-π interaction with an epoxy resin, and generate a degradable tough epoxy resin containing a cation-π interaction through light-heat dual curing crosslinking, wherein: The first stage of the light-heat dual curing crosslinking is UV curing, the wavelength selected is 365 nm, and the irradiation time is 5 to 60 minutes; after the first stage of curing is completed, it is transferred to the oven for the second stage of curing, and the curing temperature is 25 to 200 o C, curing time is 60~360 min.

3. The method for preparing a cation-π-containing degradable tough epoxy resin according to claim 2, wherein The photoinitiator is one or more of free radical, cationic, anionic and ring-opening metathesis polymerization photoinitiators, and the added amount is 0.1-3 wt% of the mass of the thiol.

4. A method for degrading the cationic-π-degradable toughened epoxy resin according to claim 1, characterized in that The method comprises the following steps: An alkaline solvent or amine capable of immersing the resin is added to the cationic-π-action degradable tough epoxy resin, and the resin is heated and stirred at 50-150° C. until the resin is completely degraded.

5. The method for degrading a cation-π-containing degradable tough epoxy resin according to claim 4, characterized in that The amount of the alkaline solvent or amine is at least 0.8 times the mass of the cationic-π-containing degradable tough epoxy resin; the alkaline solution is one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, potassium carbonate, cesium carbonate, sodium thiosulfate, ammonia water, and ammonium bicarbonate, with a concentration of 0.5 to 6 mol / L; the amine is one or more of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, ethylenediamine, butanediamine, hexamethylenediamine, and meta-xylylenediamine.

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