Application of Lewis Acidic Deep Eutectic Solvents in the Catalytic Synthesis of Polymerized Rosin-based Epoxy Resin

Abstract

The present invention belongs to the technical field of the synthesis of polymerized rosin-based epoxy resins, and particularly relates to the application of Lewis acidic deep eutectic solvents in the catalytic synthesis of polymerized rosin-based epoxy resins. In the present invention, a Lewis acidic deep eutectic solvent is used as a catalyst, and polymerized rosin reacts with epichlorohydrin to carry out an esterification reaction, and the esterification reaction product reacts with a ring-closing agent sodium hydroxide to carry out a ring-closing reaction to generate a polymerized rosin-based epoxy resin; the Lewis acidic deep eutectic solvent includes a hydrogen bond acceptor and a hydrogen bond donor, the hydrogen bond donor includes choline chloride, and the Lewis acid of the hydrogen bond acceptor is CrCl<subgt;3< / subgt>·6H<subgt;2< / subgt>O, CoCl<subgt;2< / subgt>·6H<subgt;2< / subgt>O or AlCl<subgt;3< / subgt>·6H<subgt;2< / subgt>O. The polymerized rosin-based epoxy resin prepared by the present invention has good thermal stability. After curing, the stability of the polymerized rosin-based epoxy resin is enhanced and the crosslinking degree is increased, and the polymerized rosin-based epoxy resin exhibits good compressibility and toughness.

Description

Technical Field

[0001] The present invention belongs to the technical field of the synthesis of polymerized rosin-based epoxy resins, and particularly relates to the application of Lewis acidic deep eutectic solvents in the catalytic synthesis of polymerized rosin-based epoxy resins. Background Art

[0002] In recent years, the growing environmental and economic problems as well as the limited nature of petrochemical resources have promoted the research and development of bio-based materials. Extracting raw materials from natural resources to prepare bio-based materials and thus replace petrochemical-based materials not only meets the industrial requirements for coordinated development with the environment but also further promotes the sustainable development of processes and products. China is rich in natural rosin resources, and rosin is one of its main components.

[0003] Epoxy resins usually contain two or more epoxy groups in their molecules and are a class of versatile chemical materials widely used in fields such as coatings, adhesives, composite materials, and electronic components. Currently, the commercially used epoxy resins are mainly petroleum-based epoxy resins, most of whose raw materials are aromatic compounds and phenolic compounds, which are relatively expensive. Moreover, the catalysts for catalytic reactions cannot be recycled, and the properties of the obtained epoxy resins are not good. Therefore, the preparation of economical and environmentally friendly bio-based epoxy resins, especially rosin-based epoxy resins, has always attracted the attention of researchers. To improve the hardness of epoxy resins, rosin can be dimerized to form polymerized rosin, which is then used to make polymerized rosin-based epoxy resins.

[0004] In the preparation reaction of epoxy resins, the catalysts mainly used are quaternary ammonium salt catalysts, tertiary amine catalysts, metal complex catalysts, organic acids or organic acid salt catalysts. The biggest problem with the catalysts used in this reaction is that they cannot be recycled, which does not conform to the concept of green environmental protection; moreover, for the polymerized rosin-based epoxy resins prepared in related technologies, their epoxy values, thermal stabilities, compressibilities, and toughness still cannot meet the existing requirements.

[0005] Therefore, using natural resources as raw materials to find a green and environmentally friendly catalyst for the preparation of bio-based epoxy resins with high epoxy values, high thermal stabilities, and high toughness is of great significance for industrial production. Summary of the Invention

[0006] In order to solve the technical problems in the prior art that the catalysts used for preparing polymerized rosin-based epoxy resins cannot be recycled, and the epoxy values, thermal stabilities, compressibilities, and toughness of the prepared polymerized rosin-based epoxy resins still cannot meet the existing requirements, the present invention provides the application of Lewis acidic deep eutectic solvents in the catalytic synthesis of polymerized rosin-based epoxy resins.

[0007] To solve the above technical problems, the present invention adopts the following technical solutions:

[0008] Application of Lewis acidic deep eutectic solvent in catalytic synthesis of polymerized rosin-based epoxy resin. Using Lewis acidic deep eutectic solvent (DES) as a catalyst, esterification reaction occurs between polymerized rosin and epichlorohydrin (ECH), and then the esterification reaction product reacts with the ring-closing agent sodium hydroxide to undergo a ring-closing reaction to produce polymerized rosin-based epoxy resin.

[0009] The Lewis acidic deep eutectic solvent includes a hydrogen bond acceptor and a hydrogen bond donor. The hydrogen bond donor includes choline chloride (ChCl), and the hydrogen bond acceptor includes a Lewis acid, and the Lewis acid can preferably be CrCl3·6H2O, CoCl2·6H2O or AlCl3·6H2O.

[0010] The metal atom in the catalyst Lewis acidic deep eutectic solvent combines with the oxygen atom in epichlorohydrin, promoting the ring-opening of the epoxy group in epichlorohydrin, thereby promoting the esterification reaction; the esterification reaction product reacts with the ring-closing agent sodium hydroxide to undergo a ring-closing reaction to produce polymerized rosin-based epoxy resin. The reaction route map is as follows:

[0011]

[0012] In the esterification reaction process of the present invention, the weight of the Lewis acidic deep eutectic solvent is 20 - 40% of the weight of the polymerized rosin, and the weight of the epichlorohydrin is 2 - 6 times the weight of the polymerized rosin.

[0013] Furthermore, the conditions of the esterification reaction are that the reaction temperature is 90 - 115 °C and the reaction time is 4 - 6 h.

[0014] In the ring-closing reaction of the present invention, the sodium hydroxide can be in the form of fixed particles, and the weight of the sodium hydroxide is 10 - 20% of the weight of the polymerized rosin.

[0015] Furthermore, the conditions of the ring-closing reaction are that the reaction temperature is 60 - 90 °C and the reaction time is 2 - 4 h.

[0016] Furthermore, the preparation method of the polymerized rosin-based epoxy resin further includes an optimization step: after the esterification reaction is completed, the deep eutectic solvent is recovered and can be recycled, and the reaction solution enters the next ring-closing reaction; after the ring-closing reaction is completed, the excessive epichlorohydrin in the filtrate is recovered and reused, and the product is a brownish-yellow viscous liquid polymerized rosin-based epoxy resin.

[0017] The epoxy value of the polymerized rosin-based epoxy resin prepared by the present invention can reach 0.209 mol / 100 g.

[0018] Secondly, the present invention also provides a preparation method of the Lewis acidic deep eutectic solvent, specifically, a hydrogen bond acceptor and a hydrogen bond donor are heated and stirred to react until a homogeneous transparent liquid is formed, thus obtaining the Lewis acidic deep eutectic solvent.

[0019] Furthermore, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 2:1 - 4:1; the formation conditions of the deep eutectic solvent are a temperature of 80 °C and a time of 4 h.

[0020] Even further, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 3:1.

[0021] The present invention provides an application of the Lewis acidic deep eutectic solvent in the catalytic synthesis of polymerized rosin-based epoxy resin. In the present invention, the Lewis acidic deep eutectic solvent is used as a catalyst, and polymerized rosin and epichlorohydrin undergo an esterification reaction, and the esterification reaction product and the ring-closing agent sodium hydroxide undergo a ring-closing reaction to generate polymerized rosin-based epoxy resin. Compared with the related prior art, the technical solution of the present invention has the following beneficial effects:

[0022] The preparation method and raw materials of the catalyst Lewis acidic deep eutectic solvent provided by the present invention are simple. During the preparation process, the atom utilization rate is 100%, no by-products are generated, which conforms to the design concept of green chemistry. The hydrogen bond donor choline chloride and a specific Lewis acid hydrogen bond acceptor are assembled to obtain the Lewis acidic deep eutectic solvent described in the present invention. The Lewis acidic deep eutectic solvent can adjust the acid strength of the deep eutectic solvent as a catalyst, providing an appropriate acid strength for the catalytic synthesis reaction of polymerized rosin-based epoxy resin. The Lewis acidic deep eutectic solvent catalytic system has a self-separation characteristic, realizing the reaction-separation integration in the process of catalytic synthesis of polymerized rosin-based epoxy resin. The catalyst has good recyclability and structural stability. The polymerized rosin-based epoxy resin prepared by using the Lewis acidic deep eutectic solvent has good thermal stability. After curing, the stability of the polymerized rosin-based epoxy resin is enhanced and the crosslinking degree is increased, and the polymerized rosin-based epoxy resin exhibits good compressibility and toughness. Description of the Drawings

[0023] Figure 1 It is the infrared spectrum of the deep eutectic solvent [CrCl3·6H2O][ChCl]3;

[0024] Figure 2 It is the nuclear magnetic spectrum of the deep eutectic solvent [CrCl3·6H2O][ChCl]3;

[0025] Figure 3 It is the thermogravimetric spectrum of the deep eutectic solvent [CrCl3·6H2O][ChCl]3;

[0026] Figure 4The infrared spectrogram of the polymerized rosin-based epoxy resin obtained in Example 2;

[0027] Figure 5 The thermogravimetric spectrogram of the polymerized rosin-based epoxy resin obtained in Example 2;

[0028] Figure 6 The thermogravimetric analysis spectrogram of the cured polymerized rosin-based epoxy resin;

[0029] Figure 7 The DSC characterization spectrograms of the polymerized rosin-based epoxy resin before and after curing;

[0030] Figure 8 The tensile-strain diagram of the polymerized rosin-based epoxy resin cured with HHPA;

[0031] Figure 9 The tensile-strain diagram of E-44 epoxy resin cured with HHPA. Specific Embodiments

[0032] The present invention discloses the application of Lewis acidic deep eutectic solvents in the catalytic synthesis of polymerized rosin-based epoxy resins. Those skilled in the art can draw on the content of this article and appropriately modify the process parameters to achieve it. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and those related can obviously make changes or appropriate alterations and combinations to the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0033] In order to enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below in conjunction with specific embodiments.

[0034] Unless otherwise specified, the following test methods are all conventional methods. Unless otherwise specified, the test materials and chemical reagents used can be easily obtained from commercial companies, and can be purchased from Shanghai Titan Scientific Co., Ltd., Shanghai Aladdin Biochemical Technology Co., Ltd., Sinopharm Chemical Reagent Co., Ltd., Shanghai Macklin Biochemical Co., Ltd., etc. The experimental instruments used can be purchased from Shanghai Liangping Instrument Co., Ltd., Bruker Corporation of Germany, Netzsch of Germany, Gongyi Yingyu Yuhua Instrument Factory, Kunshan Hechuang Ultrasonic Instrument Co., Ltd., Ningbo Jiemasen Electric Co., Ltd., etc.

[0035] Unless otherwise specified, the epoxy value of the polymerized rosin-based epoxy resin was determined by the HCl-acetone method. The specific steps for epoxy value determination were as follows: 0.5 g of the polymerized rosin-based epoxy resin was taken in a 250 mL conical flask, 25 mL of HCl-acetone solution was added to completely dissolve the polymerized rosin-based epoxy resin. After dissolution, it was left for 1 h, then 4-5 drops of 1% phenolphthalein indicator were added, and finally, it was titrated with an ethanol solution of NaOH until the solution turned pink and the color did not disappear within 30 s. At the same time, a blank was titrated under the above conditions. The calculation method of the epoxy value is shown in Formula 1:

[0036]

[0037] E: epoxy value (mol / 100 g), V1: volume of ethanol solution of NaOH consumed by the blank sample (mL), V2: volume of ethanol solution of NaOH consumed by the known mass sample (mL), C: molar concentration of ethanol solution of NaOH (mol / L), m: mass of the sample (g).

[0038] The curing and test specimen preparation method of the polymerized rosin-based epoxy resin described in the present invention was as follows: The polymerized rosin-based epoxy resin, the curing agent HHPA (hexahydrophthalic anhydride), and a small amount of catalyst (2-ethyl-4-methylimidazole) were dissolved in the solvent acetone to obtain a homogeneous solution. Then it was poured into a mold and placed in a vacuum oven set at 50 °C to remove the solvent acetone, and it was cured at 120 °C, 150 °C, and 180 °C for 2 h, 2 h, and 1 h respectively. After curing, it was cooled to room temperature, and the sample was carefully separated from the mold to obtain a rectangular parallelepiped specimen with dimensions of 80×10×4 mm 3 and the specimen was stored for the next mechanical property test.

[0039] Example 1

[0040] The hydrogen bond acceptor CrCl3·6H2O, CoCl2·6H2O, AlCl3·6H2O and the hydrogen bond donor choline chloride were added to a 25 mL single-necked round-bottom flask at a molar ratio of 1:3, and magnetically stirred for 4 h under an 80 °C oil bath heating to obtain the Lewis acidic deep eutectic solvents [CrCl3·6H2O][ChCl]3, [CoCl2·6H2O][ChCl]3, [AlCl3·6H2O][ChCl]3. The above Lewis acidic deep eutectic solvents were characterized by infrared and nuclear magnetic resonance, which proved the successful preparation of the above Lewis acidic deep eutectic solvents. The infrared spectrum and nuclear magnetic resonance spectrum of the deep eutectic solvent [CrCl3·6H2O][ChCl]3 are shown in Figure 1 and Figure 2 . Figure 1It is shown that in the infrared spectrum of ChCl, it can be clearly observed that at 3258.40 cm -1 is the peak of the active hydrogen in -OH. It can be seen from the infrared spectrum of DES that after successfully synthesizing DES[CrCl3·6H2O][ChCl]3, the peak of the active hydrogen in -OH has an obvious red shift, moving towards lower wavenumbers. This shift indicates the formation of hydrogen bonds in DES[CrCl3·6H2O][ChCl]3.

[0041] Figure 2 It is shown that the peak of the active hydrogen in -OH of ChCl is at 5.55 ppm, the peak of H on -CH3 in ChCl is at 3.13 ppm, the peak of H on -CH2 near the methyl group in ChCl is at 3.40 ppm, and the peak of H on -CH2 near -OH in ChCl is at 3.81 ppm. The appearance of the same type of peaks can also be observed in the NMR spectrum of DES. After synthesizing DES, due to the hydrogen bond effect between DES, the chemical shift of the peaks increases. The peak of the active hydrogen in -OH becomes 5.58 ppm, the peak of H on -CH3 becomes 3.38 ppm, and the characteristic peaks of H on -CH2 near the methyl group and -OH are 3.44 and 3.84 ppm respectively. In summary, the acidic deep eutectic solvent [CrCl3·6H2O][ChCl]3 is successfully prepared.

[0042] Figure 3 Figure 10 is the thermogravimetric spectrum of the DES catalyst [CrCl3·6H2O][ChCl]3. It can be clearly observed from the figure that in the range of 0 - 800 °C, the acidic deep eutectic solvent [CrCl3·6H2O][ChCl]3 has only one obvious weight loss. There is no weight loss within 100 °C, indicating no loss of moisture. The melting point of CrCl3·6H2O is 83 °C, but there is no weight loss within 100 °C, indicating that the interaction between CrCl3·6H2O and ChCl enhances its melting point. The weight loss of the catalyst at 230 °C is only 6.5%. In short, the thermal decomposition temperature of DES is above 140 °C. The above conclusions show that DES[CrCl3·6H2O][ChCl]3 has good thermal stability and meets the relevant conditions of the reaction temperature of this system.

[0043] The infrared and NMR characterization diagrams of other Lewis acidic deep eutectic solvents also prove that the acidic deep eutectic solvents [CoCl2·6H2O][ChCl]3 and [AlCl3·6H2O][ChCl]3 are successfully prepared, and the thermogravimetric spectra also show that [CoCl2·6H2O][ChCl]3 and [AlCl3·6H2O][ChCl]3 have good thermal stability.

[0044] Example 2

[0045] The Lewis acidic deep eutectic solvent [CrCl3·6H2O][ChCl]3 prepared in Example 1 was used to catalyze the synthesis of polymerized rosin-based epoxy resin: 10 g of polymerized rosin and 50 g of epichlorohydrin were weighed, heated and dissolved, and then 3 g of the catalyst [CrCl3·6H2O][ChCl]3 prepared in Example 1 was added. The reaction was carried out at 115 °C for 6 h. After standing for a while, the catalyst and the upper reaction liquid were automatically separated into layers. After phase separation, the catalyst in the lower layer could be recycled.

[0046] The product of the upper reaction liquid was transferred into a 50 mL round-bottom flask, 1.5 g of solid granular sodium hydroxide was added, and the reaction was carried out at 75 °C for 3.5 h until the pH of the system no longer decreased. After the reaction was completed, the sodium chloride solid was filtered. The filtrate was washed with water and distilled to obtain the product.

[0047] The product was characterized by infrared spectroscopy. The infrared spectrum was as Figure 4 , and by comparing with the infrared spectrum of polymerized rosin, it can be seen that a relatively broad peak appeared in the polymerized rosin-based epoxy resin at 3432.54 cm -1 , which might be the characteristic peak of the hydroxyl group in the part where the dicarboxyl addition product did not undergo ring closure. The characteristic peak at 1695.74 cm -1 of polymerized rosin disappeared due to the reaction of the carboxyl group with the epoxy group and became the characteristic peak of the ester group in the polymerized rosin-based epoxy resin at 1725.53 cm -1 . And at 889.16 cm -1 , the characteristic absorption peak of the epoxy group was also observed. The above shows that the carboxyl group in the polymerized rosin in the product did interact with ECH, and the product formed was polymerized rosin-based epoxy resin. The epoxy value of the polymerized rosin-based epoxy resin prepared in this example was 0.209 mol / 100 g.

[0048] The polymerized rosin-based epoxy resin obtained in this example was subjected to thermogravimetric analysis. The thermogravimetric spectrum was as Figure 5 . Within 100 °C, the polymerized rosin-based epoxy resin was very stable and there was no weight loss. When the temperature was raised to 200 °C, the weight loss was 10%, and this part of the weight loss might be due to the residual small amount of polymerized rosin in the product. When the temperature was further heated to 325 °C, the weight loss rate of the polymerized rosin-based epoxy resin reached the maximum, and its weight loss was about 40%. It can be seen that the thermal decomposition temperature of the polymerized rosin-based epoxy resin in this example was above 100 °C, so it had good thermal stability.

[0049] Figure 6 This was the thermogravimetric analysis spectrum of the cured polymerized rosin-based epoxy resin, compared with the uncured polymerized rosin-based epoxy resin ( Figure 5) Compared with the thermogravimetric spectrum of , the initial weight loss temperature of the cured polymerized rosin-based epoxy resin increases. When the heating temperature rises to about 250 °C, its weight loss is 10%, indicating that the thermal stability of the cured polymerized rosin-based epoxy resin has been enhanced.

[0050] Figure 7 Figure shows the DSC (Differential Scanning Calorimetry) characterization spectra of the polymerized rosin-based epoxy resin before and after curing. The measured data in the figure are the glass transition temperatures (Tg) of the specimens. The glass transition temperature of the epoxy resin is one of the important indicators to measure its performance. The glass transition temperature refers to the temperature at which the epoxy resin changes from a solid state to a flowing state. The Tg of the polymerized rosin-based epoxy resin before curing is relatively low at 5.6 °C, while the Tg of the cured polymerized rosin-based epoxy resin rises to 24.9 °C. The height of Tg is closely related to the molecular weight of the polymer. The increase in Tg indicates that the curing reaction increases the crosslinking degree of the polymerized rosin-based epoxy resin, so its molecular weight also increases accordingly.

[0051] The polymerized rosin-based epoxy resin prepared in this example was cured with HHPA and analyzed as follows. Figure 8 Figure shows the tensile-strain diagram of the polymerized rosin-based epoxy resin cured with HHPA. The results show that the elongation at break of this material is 7.6% and the tensile strength is 1.78 MPa. Figure 9 Figure shows the tensile-strain diagram of the commercial E-44 epoxy resin after curing. It can be observed that the tensile strength of the E-44 epoxy resin is 1.25 MPa and the elongation at break is less than 1%. Thus, it can be seen that the polymerized rosin-based epoxy resin can compensate for the disadvantages of ordinary epoxy resins such as low hardness and poor toughness, showing good compressibility and toughness, so it is easier to process and is suitable for the production of light products.

[0052] Example 3

[0053] The Lewis acidic deep eutectic solvent [CoCl2·6H2O][ChCl]3 prepared in Example 1 was used to catalyze the synthesis of polymerized rosin-based epoxy resin: Weigh 10 g of polymerized rosin and 60 g of epichlorohydrin, heat and dissolve them, then add 4 g of the catalyst [CoCl2·6H2O][ChCl]3 prepared in Example 1, and react at 115 °C for 6 h; After standing for a while, the catalyst and the upper reaction liquid automatically separate into layers. After phase separation, the catalyst in the lower layer can be recycled.

[0054] Transfer the product of the upper reaction liquid into a 50 mL round-bottom flask, add 2 g of solid sodium hydroxide particles, and react at 90 °C for 4 h until the pH of the system no longer decreases. After the reaction is completed, filter the sodium chloride solid, and the filtrate is washed with water and distilled to obtain the product polymerized rosin-based epoxy resin. The epoxy value of the product polymerized rosin-based epoxy resin is 0.175 mol / 100 g.

[0055] Example 4

[0056] The Lewis acidic deep eutectic solvent [AlCl3·6H2O][ChCl]3 prepared in Example 1 was used to catalyze the synthesis of polymerized rosin-based epoxy resin: Weigh 10 g of polymerized rosin and 20 g of epichlorohydrin. After heating and dissolving, add 2 g of the catalyst [AlCl3·6H2O][ChCl]3 prepared in Example 1, and react at 90 °C for 4 h; After standing for a while, the catalyst and the upper reaction liquid are automatically separated into layers. After phase separation, the catalyst in the lower layer can be recycled.

[0057] Transfer the product of the upper reaction liquid into a 50 mL round-bottom flask, add 1 g of solid sodium hydroxide particles, and react at 60 °C for 2 h until the pH of the system no longer decreases. After the reaction is completed, filter the sodium chloride solid, and the filtrate is washed with water and distilled to obtain the product. The epoxy value of the product, polymerized rosin-based epoxy resin, is 0.190 mol / 100 g.

[0058] Example 5

[0059] Different types of catalysts in Table 1 were used to catalyze the synthesis of polymerized rosin-based epoxy resin. The epoxy values of the finally obtained polymerized rosin-based epoxy resin and the recovery rates of the catalysts are shown in Table 1.

[0060] Table 1 Catalytic activity data of different catalysts

[0061]

[0062] Reaction conditions: 10 g of polymerized rosin, 40 g of ECH, 3 g of DES, esterification reaction temperature and time 105 °C, 6 h, ring-closing reaction temperature and time 70 °C, 3.5 h, 1 g of NaOH.

[0063] A series of different acidic deep eutectic solvents were obtained by combining different hydrogen bond donors and different hydrogen bond acceptors, and they were used to catalyze the synthesis of polymerized rosin-based epoxy resin. The data in Table 1 show that when CrCl3·6H2O was used alone to catalyze the synthesis of polymerized rosin-based epoxy resin, the epoxy value of the obtained product was relatively low, and the catalyst could not be recycled. For other acidic DES catalysts (Entry 2 - Entry 7), the highest epoxy value of the polymerized rosin-based epoxy resin obtained by the catalytic reaction was only 0.084 mol / 100 g. The epoxy value is one of the important indicators for evaluating the quality of polymerized rosin-based epoxy resin. The higher the epoxy value, the better the catalytic effect of the catalyst.

[0064] The Lewis acidic deep eutectic solvent catalysts obtained by combining the hydrogen bond acceptors Lewis acids [CrCl3·6H2O], [AlCl3·6H2O], and [CoCl2·6H2O] described in the present invention with only the specific hydrogen bond donor choline chloride are used for catalyzing the synthesis of polymerized rosin-based epoxy resin, and the epoxy value of the obtained product and the recovery rate of the catalyst are relatively good.

[0065] Using common Lewis acids (ZnCl2, SnCl2, FeCl3, InCl3) as hydrogen bond acceptors and ChCl as hydrogen bond donors to form acidic DES catalysts and applying them to the reaction of polymerized rosin-based epoxy resin, the epoxy value and catalyst recovery rate data of the obtained polymerized rosin-based epoxy resin are shown in Table 2.

[0066] Table 2 Catalytic activities of different catalysts

[0067]

[0068] Reaction conditions: 10 g of polymerized rosin, 40 g of ECH, 3 g of DES, esterification reaction temperature and time 105 °C, 6 h, ring-closing reaction temperature and time 70 °C, 3.5 h, 1 g of NaOH.

[0069] The data in Table 2 show that the catalysts [FeCl3·6H2O][ChCl]3, [ZnCl2][ChCl]3, etc. in Table 2 have poor catalytic effects, the epoxy value of the product is relatively low, and the catalyst cannot be recycled and reused. The Lewis acidic deep eutectic solvents [CrCl3·6H2O][ChCl], [CoCl2·6H2O][ChCl], and [AlCl3·6H2O][ChCl]3 described in the present invention catalyze the reaction to obtain epoxy values of epoxy resin of 0.197 mol / 100 g, 0.178 mol / 100 g, and 0.192 mol / 100 g respectively under non-optimal conditions, and the recovery rates are 89.3%, 91.8%, and 93.8% respectively. The Lewis acidic deep eutectic solvent catalyst provided by the present invention, the hydrogen bond donor choline chloride only combines with the specific hydrogen bond acceptors Lewis acids [CrCl3·6H2O], [AlCl3·6H2O], and [CoCl2·6H2O] to obtain the Lewis acidic deep eutectic solvent catalyst, which not only has good catalytic effects, but also the catalyst can be recycled, overcomes the disadvantage that the catalyst for preparing polymerized rosin-based epoxy resin by traditional catalysts cannot be recovered, and also provides a new idea for catalytic preparation of other bio-based epoxy resins.

[0070] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. Application of Lewis acidic deep eutectic solvents in catalytic synthesis of polymerized rosin-based epoxy resin, characterized in that: Using a Lewis acidic deep eutectic solvent as a catalyst, polymerized rosin reacts with epichlorohydrin in an esterification reaction, and the esterification reaction product reacts with the ring-closing agent sodium hydroxide in a ring-closing reaction to produce a polymerized rosin-based epoxy resin; The Lewis acidic deep eutectic solvent includes a hydrogen bond acceptor and a hydrogen bond donor. The hydrogen bond donor includes choline chloride, and the hydrogen bond acceptor includes a Lewis acid. The Lewis acid is selected from CrCl3·6H2O, CoCl2·6H2O or AlCl3·6H2O; During the esterification reaction, the weight of the Lewis acidic deep eutectic solvent is 20-40% of the weight of the polymerized rosin, and the weight of the epichlorohydrin is 2-6 times the weight of the polymerized rosin; The conditions for the esterification reaction are that the reaction temperature is 90-115 °C and the reaction time is 4-6 h; During the ring-closing reaction, the weight of the sodium hydroxide is 10-20% of the weight of the polymerized rosin; The conditions for the ring-closing reaction are that the reaction temperature is 60-90 °C and the reaction time is 2-4 h; After the esterification reaction, the deep eutectic solvent is recovered and recycled, and the reaction solution enters the next ring-closing reaction; after the ring-closing reaction, the excess epichlorohydrin in the filtrate is recovered and reused, and the product is a brownish-yellow viscous liquid polymerized rosin-based epoxy resin.

2. The application according to claim 1, characterized in that: The epoxy value of the produced polymerized rosin-based epoxy resin can reach 0.209 mol / 100 g.

3. The application according to claim 1, characterized in that: The preparation method of the Lewis acidic deep eutectic solvent is that the hydrogen bond acceptor and the hydrogen bond donor are heated and stirred for reaction until a homogeneous transparent liquid is formed, that is, the Lewis acidic deep eutectic solvent is obtained.

4. The application according to claim 3, characterized in that: The molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 2:1-4:1; the formation conditions of the deep eutectic solvent are a temperature of 80 °C and a time of 4 h.

5. The application according to claim 4, wherein: The molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 3:1.

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