A cross-linked castor oil resin with remodeling properties and its preparation method and application

Abstract

The invention discloses a cross-linked castor oil resin with remodelability, a preparation method thereof, and an application thereof, belonging to the technical field of polymer materials. First, acetoacetoxime castor oil is prepared, and then the acetoacetoxime castor oil is dissolved in an organic solvent. An isocyanate cross-linking agent and a catalyst are added, mixed evenly, and dried to obtain the cross-linked castor oil resin with remodelability. The acetoacetoxime carbamate formed in the structure after cross-linking is a new type of dynamic covalent bond with remodelability. The resin can be reshaped multiple times by hot pressing and maintains good mechanical properties, which is of great significance for promoting the sustainable development of polymer materials.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and particularly relates to a cross-linked castor oil resin with remodeling properties, a preparation method and an application thereof. Background Art

[0002] Traditional thermosetting resins possess excellent mechanical properties and dimensional stability due to their inherent covalent crosslinking network. However, these irreversible covalent bonds also render thermosetting resins insoluble and insoluble, making them difficult to reshape. New materials with reshapeability not only possess the excellent mechanical properties and dimensional stability of thermosetting resins but also possess self-healing and shape memory capabilities. These materials hold great potential for applications in smart manufacturing, sensors, electronic skin, and other fields.

[0003] The raw materials used to prepare resins mainly come from non-renewable petroleum-based resources. How to develop sustainable new polymer materials using renewable biomass resources as raw materials is gradually attracting the attention of researchers.

[0004] Castor oil is an abundant and inexpensive industrial vegetable oil. Being inedible, it does not compete with the food industry for resources, thus aligning with the principles of biomass material development. Its chemical structure contains reactive groups such as esters, hydroxyls, and carbon-carbon double bonds, which provide a foundation for chemical modification, structural design, and high-value utilization. Castor oil is currently used in the preparation of polymer products such as sealants, pharmaceuticals, cosmetics, and coatings.

[0005] Chinese patent CN 111925504A discloses a castor oil-based polyurethane acrylic resin and a preparation method and application thereof. The preparation method comprises the following steps: (1) reacting a reactive diluent, an isocyanate, and castor oil as raw materials until the mass fraction of the isocyanate group in the feed reaches half of the theoretical value before the reaction starts, thereby obtaining an isocyanate semi-blocked intermediate; (2) reacting the isocyanate semi-blocked intermediate obtained in step (1) with a hydroxy acrylate, adding an antioxidant until the isocyanate group content is less than 0.5%, and adding anhydrous ethanol for blocking, thereby obtaining a castor oil-based polyurethane acrylic resin.

[0006] Chinese patent CN 107353393A discloses a castor oil-modified polyurethane resin and a preparation method thereof. The castor oil-modified polyurethane resin is composed of the following components in the following proportions: 10-20 parts by weight of polyol A, 20-40 parts by weight of polyol B, 8-10 parts by weight of castor oil, 20-45 parts by weight of isocyanate, 5-8 parts by weight of a hydrophilic chain extender, 1-3 parts by weight of a diol chain extender, 3-5 parts by weight of a diamine chain extender, 6-7 parts by weight of a salt-forming agent, 100-200 parts by weight of a solvent A, and 8-16 parts by weight of a solvent B.

[0007] Although the above-mentioned prior art discloses some resins prepared using castor oil as a raw material, these resins are not remodelable, have a high discard rate after use, and cause environmental pollution. Summary of the Invention

[0008] To address the above technical issues, the present invention provides a remodelable cross-linked castor oil resin, its preparation method, and its application. This resin is obtained by cross-linking acetoacetoxime castor oil with an isocyanate cross-linking agent. The acetoacetoxime carbamate formed in the cross-linked structure represents a novel dynamic covalent bond and offers remodelability. This resin can be reshaped multiple times using hot pressing while maintaining excellent mechanical properties, which is of great significance for promoting the sustainable development of polymer materials.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing a cross-linked castor oil resin with remodeling properties, comprising the following steps:

[0011] (1) Preparation of acetoacetate oxime castor oil;

[0012] (2) Dissolve acetoacetic acid oxime castor oil in an organic solvent, add an isocyanate crosslinking agent and a catalyst, mix well, and dry to obtain a remodelable cross-linked castor oil resin.

[0013] The preparation method specifically comprises the following steps:

[0014] (1) Acetoacetate castor oil is mixed with glacial acetic acid, and a sodium nitrite aqueous solution is added dropwise at -5-0°C. After the addition is completed, the mixture is stirred for 12-24 hours, and acetoacetate oxime castor oil is obtained through post-treatment;

[0015] (2) Dissolve acetoacetic acid oxime castor oil in an organic solvent, add an isocyanate crosslinking agent and a catalyst, mix well, and dry to obtain a remodelable cross-linked castor oil resin.

[0016] In step (1), the preparation method of the acetoacetate castor oil is as follows: castor oil and tert-butyl acetoacetate are uniformly mixed, stirred at 90-140°C for 1-3 hours, and acetoacetate castor oil is obtained through post-treatment.

[0017] Furthermore, the molar ratio of castor oil to tert-butyl acetoacetate is 1:3-6.

[0018] The post-treatment method is: pouring the reaction solution into petroleum ether to precipitate and wash multiple times, and drying the precipitate to constant weight.

[0019] In step (1), the molar ratio of acetoacetate castor oil, glacial acetic acid and sodium nitrite is 1:6-9:3-6.

[0020] In step (1), the post-treatment method is: extraction with ethyl acetate, washing the organic phase with sodium bicarbonate aqueous solution until neutral, and then concentrating and drying.

[0021] In step (2), the isocyanate cross-linking agent is selected from one of 4,4'-diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate, decanediisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

[0022] In step (2), the catalyst is selected from one of diisopropylamine, dimethylisopropylamine, dibutyltin dilaurate, 4-dimethylaminopyridine, 1,8-diazabicyclo[5,4,0]undec-7-ene, and 1,5-diazabicyclo[4.3.0]non-5-ene.

[0023] In step (2), the organic solvent is selected from one of tetrahydrofuran, dichloromethane, chloroform, 1,4-dioxane, toluene, and xylene.

[0024] In step (2), the drying conditions are: keeping warm at 40-80 °C for 48-72 h.

[0025] In step (2), the molar ratio of the acetoacetic acid ester oxime castor oil to the isocyanate cross-linking agent is 4:3-6; the mass ratio of the acetoacetic acid ester oxime castor oil to the catalyst is 1000:1-10.

[0026] The present invention also provides a remodelable cross-linked castor oil resin prepared according to the preparation method, which can be remodeled and used multiple times.

[0027] The present invention also provides the use of cross-linked castor oil resin with remodeling properties in preparing new materials with remodeling properties, which can be used to prepare polymer products such as sealants, medicines, cosmetics and coatings.

[0028] The present invention provides a method for preparing a remodelable cross-linked castor oil resin. First, acetoacetate oxime castor oil is prepared using acetoacetate castor oil as a raw material. Then, the castor oil is subjected to a cross-linking reaction under the action of an isocyanate cross-linking agent. After the cross-linking reaction, acetoacetate oxime carbamate is formed in the structure. The acetoacetate oxime carbamate is a new type of dynamic covalent bond with remodelability. The resin can be remodeled multiple times by hot pressing, maintains good mechanical properties, and can be recycled and reused.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1) The present invention prepares acetoacetate oxime castor oil by continuously modifying the hydroxyl groups in the castor oil structure. This method is different from the method of modifying ketone or aldehyde groups into oxime groups. The preparation method is simple and convenient for post-processing.

[0031] 2) The acetoacetate oxime carbamate generated by the reaction of acetoacetate oxime with isocyanate in the present invention is confirmed to be a new type of dynamic covalent bond with remodelability.

[0032] 3) The present invention imparts good remodelability to the cross-linked castor oil resin by introducing acetoacetate oxime carbamate into the cross-linked network. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The preparation route of acetoacetate oxime castor oil is shown below;

[0034] Figure 2 This is the H NMR spectrum of acetoacetoxymethylene castor oil (A) and acetoacetoxymethylene castor oil (B). The solvent used for NMR measurement is DSMSO- d 6;

[0035] Figure 3 is the stress-strain curve of the cross-linked castor oil resin in Examples 1 to 3;

[0036] Figure 4 The stress relaxation curves and activation energies of AOxCOU-1.0 in Example 1 at different test temperatures are shown;

[0037] Figure 5 : The stress-strain curves of AOxCOU-1.0 before and after remodeling in Example 1;

[0038] Figure 6 This is the H NMR spectrum of the acetoacetate oxime carbamate small molecule AB in the experimental example. The solvent used for NMR measurement is DSMSO- d 6;

[0039] Figure 7 This is a small molecule model reaction and nuclear magnetic resonance hydrogen spectrum. The solvent used for nuclear magnetic resonance measurement is DSMSO- d 6. DETAILED DESCRIPTION

[0040] The present invention is described in detail below with reference to the embodiments. Example 1

[0041] A method for preparing a remodelable cross-linked castor oil resin comprises the following steps:

[0042] (1) Preparation of acetoacetate castor oil: Weigh castor oil (9.33 g, 10 mmol) and tert-butyl acetoacetate (6.32 g, 40 mmol) in a round-bottom flask equipped with a stirrer and mix them evenly. Stir at 130 °C for 3 h. After the reaction is completed, pour the solution into a large amount of petroleum ether to precipitate and wash it several times. The precipitate is dried to a constant weight, which is acetoacetate castor oil.

[0043] (2) Preparation of acetoacetoxymethylene castor oil: Weigh acetoacetoxymethylene castor oil (11.85 g, 10 mmol) and glacial acetic acid (4.8 g, 80 mmol), mix well, and cool to -5 °C. Then, add dropwise 10 mL of 27.6% sodium nitrite (2.76 g, 40 mmol) in water and react for 12 h. Then, add ethyl acetate to the solution and extract it several times. The organic phase is retained and washed with sodium bicarbonate aqueous solution until neutral. Finally, it is dried by rotary evaporation to constant weight to obtain acetoacetoxymethylene castor oil.

[0044] (3) Preparation of remodelable cross-linked castor oil resin: Acetoacetate oxime castor oil (5.1 g, 4 mmol) was weighed and dissolved in 80 mL of 1,4-dioxane. Then, decanediisocyanate (1.18 g, 6 mmol) and dibutyltin dilaurate (0.006 g) were added in sequence. After mixing evenly, the solution was poured into a polytetrafluoroethylene mold and placed in a 60 °C forced air drying oven for 72 h to obtain an acetoacetate oxime carbamate cross-linked castor oil film, which was recorded as AOxCOU-1.0.

[0045] The hydrogen nuclear magnetic resonance spectrum of the acetoacetate castor oil prepared in this example is as follows: Figure 2 As shown in Figure B, the nuclear magnetic resonance hydrogen spectrum of acetoacetate oxime castor oil is as follows Figure 2 As shown in Figure A, compared with that of acetoacetate-oxime castor oil, the H NMR spectrum of acetoacetate-oxime castor oil shows that the signal peaks at 2.16 ppm and 3.5 ppm disappear, while new signal peaks appear at 2.33 ppm and 13.2 ppm, indicating that the acetoacetate group has been modified into acetoacetate-oxime group, proving that acetoacetate-oxime castor oil was successfully prepared. Example 2

[0046] The other steps were the same as in Example 1, except that the amount of decanediisocyanate added was changed to 0.94 g (4.8 mmol). The resulting acetoacetate oxime carbamate cross-linked castor oil film was designated as AOxCOU-0.8. Example 3

[0047] The other steps were the same as in Example 1, except that the amount of decanediisocyanate added was changed to 0.71 g (3.6 mmol). The resulting acetoacetate oxime carbamate cross-linked castor oil film was designated as AOxCOU-0.6. Example 4

[0048] The other steps were the same as those in Example 1, except that step (3) was as follows: 5.1 g of acetoacetoxymethylene castor oil (4 mmol) was weighed and dissolved in 80 mL of toluene. Isophorone diisocyanate (0.89 g, 4 mmol) and 4-dimethylaminopyridine (0.005 g) were then added to the mixture. After mixing evenly, the solution was poured into a polytetrafluoroethylene mold and placed in an 80°C forced air drying oven for 72 h to obtain an acetoacetoxymethylene carbamate cross-linked castor oil film. The film was tested for tensile strength and had a breaking strength of 9.2 MPa and an elongation at break of 87%. Example 5

[0049] The other steps were the same as those in Example 1, except that step (3) was as follows: 5.1 g of acetoacetoxymethylene castor oil (4 mmol) was weighed and dissolved in 80 mL of tetrahydrofuran. 4,4'-dicyclohexylmethane diisocyanate (1.3 g, 5 mmol) and diisopropylamine (0.009 g) were then added to the mixture. After mixing evenly, the solution was poured into a polytetrafluoroethylene mold and placed in a 40°C forced air drying oven for 72 h to obtain an acetoacetoxymethylene carbamate cross-linked castor oil film. The tensile test showed that the breaking strength was 8.5 MPa and the elongation at break was 103%. Comparative Example 1

[0050] Castor oil (3.7 g, 4 mmol) was dissolved in 80 mL of tetrahydrofuran. Hexamethylene diisocyanate (1.01 g, 6 mmol) and dibutyltin dilaurate (0.004 g) were then added. After mixing thoroughly, the solution was poured into a polytetrafluoroethylene mold and placed in a 40°C forced air drying oven for 72 h. This yielded a cross-linked castor oil film free of acetoacetoxycarbamate. Tensile testing revealed a breaking strength of 5.7 MPa and an elongation at break of 168%. The film was then crushed and hot-pressed using a flat-plate vulcanizer at 10 MPa, 100°C, and 1 h. After the hot-pressing operation was complete and the film cooled, it remained a crushed film, demonstrating that the cross-linked castor oil film free of acetoacetoxycarbamate could not be reshaped.

[0051] Test Example 1

[0052] The three films obtained in Examples 1-3 were subjected to tensile tests, and the stress-strain curves were as follows: Figure 3As the diisocyanate content increases, the breaking strength of the film increases from 3.55 MPa (AOxCOU-0.6) to 7.06 MPa (AOxCOU-1.0), while the elongation at break decreases from 214% to 132%. This is primarily due to the fact that a higher amount of isocyanate increases the cross-linking network density.

[0053] The stress relaxation curves of AOxCOU-1.0 at different temperatures are shown in Figure 2. Figure 4 As shown in the figure, although there is a cross-linked network inside AOxCOU-1.0, the stress can be relaxed to 0 within the test temperature range, which shows that the topological structure of the cross-linked network can be reshaped.

[0054] Test Example 2

[0055] After the AOxCOU-1.0 film was crushed, it was hot-pressed using a flat-plate vulcanizer with the instrument parameters set at 10 MPa, 100°C, and 1 hour. After the hot-pressing operation was completed, the film was cooled and removed.

[0056] The stress-strain curve after multiple hot pressing reshaping is as follows Figure 5 As shown in the figure, the fracture strength (6.65 MPa) and elongation at break (113%) of AOxCOU-1.0 after three hot pressing reshaping processes were only slightly lower than those before reshaping (7.06 MPa, 133%), proving that it still has good mechanical properties after reshaping.

[0057] Experimental example

[0058] In order to explore the mechanism of the remodeling property of cross-linked castor oil resin, the present invention conducted the following experiments:

[0059] Ethyl acetoacetate oxime small molecule A (3.18 g, 20 mmol) and n-butyl isocyanate B (1.98 g, 20 mmol) were weighed and mixed evenly in 50 mL of petroleum ether. Then 0.001 g of dibutyltin dilaurate was added and stirred at room temperature for 24 h. After the reaction was completed, silica gel column was used to separate and remove impurities. The eluent was ethyl acetate and petroleum ether in a volume ratio of 2:1 to obtain acetoacetate oxime carbamate small molecule AB. Its nuclear magnetic resonance hydrogen spectrum is as follows Figure 6 As shown by Figure 6 It can be seen that AB was successfully prepared. 1 H NMR (500 MHz, DMSO- d 6) δ7.98 (t, J = 5.9 Hz, 1H), 4.41 – 4.29 (m,2H), 3.11 (q, J = 6.7 Hz, 2H), 2.48 (d, J = 1.1 Hz, 3H), 1.47 (p, J = 7.2 Hz,2H), 1.36 – 1.20 (m, 5H), 0.95 – 0.83 (m, 3H).

[0060] Small molecule AB (2.5 mg, 0.01 mmol) and phenylethyl isocyanate C (1.4 mg, 0.01 mmol) were weighed and dissolved in 0.6 mL of anhydrous DSMSO- d 6 were mixed evenly and the nuclear magnetic resonance hydrogen spectra were obtained at 110 °C at different time intervals. Figure 7 As shown, from Figure 7 It can be seen that the signal peak intensity of the C-NH-C of the AB molecule at 7.97 ppm decreases with the extension of reaction time, while the signal peak intensity of the C-NH-C of the AC molecule at 8.08 ppm gradually increases. This confirms that acetoacetoxycarbamate can undergo a reversible cleavage-formation reaction under certain temperature conditions, that is, acetoacetoxycarbamate is a dynamic covalent bond.

[0061] As can be seen from the above, the reason why the cross-linked castor oil resin provided by the present invention has remodeling properties is that after the acetoacetoxime castor oil undergoes a cross-linking reaction under the action of an isocyanate cross-linking agent, acetoacetoxime carbamate is formed in the structure, which is a new type of dynamic covalent bond with remodeling properties. The resin can be remodeled multiple times by hot pressing and can still maintain good mechanical properties after multiple remodeling.

[0062] The above-mentioned detailed description of a remodelable cross-linked castor oil resin, its preparation method and application with reference to the embodiments is illustrative rather than restrictive. Several embodiments can be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a cross-linked castor oil resin with remodeling properties, characterized in that: The preparation method comprises the following steps: (1) Acetoacetate castor oil is mixed with glacial acetic acid, and a sodium nitrite aqueous solution is added dropwise at -5-0°C. After the addition is completed, the mixture is stirred for 12-24 hours, and acetoacetate oxime castor oil is obtained through post-treatment; (2) Dissolve acetoacetic acid oxime castor oil in an organic solvent, add an isocyanate crosslinking agent and a catalyst, mix well, and dry to obtain a remodelable cross-linked castor oil resin.

2. The preparation method according to claim 1, characterized in that In step (1), the molar ratio of acetoacetate castor oil, glacial acetic acid and sodium nitrite is 1:6-9:3-6.

3. The preparation method according to claim 1, characterized in that In step (2), the isocyanate cross-linking agent is selected from one of 4,4'-diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate, decanediisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

4. The preparation method according to claim 1, characterized in that In step (2), the catalyst is selected from one of diisopropylamine, dimethylisopropylamine, dibutyltin dilaurate, 4-dimethylaminopyridine, 1,8-diazabicyclo[5,4,0]undec-7-ene, and 1,5-diazabicyclo[4.3.0]non-5-ene.

5. The preparation method according to claim 1, characterized in that In step (2), the organic solvent is selected from one of tetrahydrofuran, dichloromethane, chloroform, 1,4-dioxane, toluene, and xylene.

6. The preparation method according to claim 1, characterized in that In step (2), the drying conditions are: keeping warm at 40-80°C for 48-72 hours.

7. The preparation method according to any one of claims 1 to 6, characterized in that In step (2), the molar ratio of the acetoacetate oxime castor oil to the isocyanate cross-linking agent is 4:3-6; the mass ratio of the acetoacetate oxime castor oil to the catalyst is 1000:1-10.

8. The cross-linked castor oil resin with remodelability obtained by the preparation method according to any one of claims 1 to 7.

9. Use of the cross-linked castor oil resin with remodeling properties as claimed in claim 8 in preparing a material with remodeling properties.

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