Benzoxazine monomer based on 2, 4-dihydroxy benzaldehyde as well as preparation method and application of benzoxazine monomer

Abstract

The invention discloses a benzoxazine monomer based on 2, 4-dihydroxy benzaldehyde as well as a preparation method and application of the benzoxazine monomer, and belongs to the technical field of resin synthesis. The benzoxazine monomer is prepared by taking the 2, 4-dihydroxy benzaldehyde, the 3-aminophenylacetylene and the formaldehyde as raw materials, the synthesis method is simple, the yield is relatively high, and the benzoxazine monomer has a large-scale production prospect. The preparation method comprises the following steps: dissolving 2, 4-dihydroxy benzaldehyde and 3-aminophenylacetylene in an organic solvent, dropwise adding formaldehyde, carrying out heating reflux, reacting, filtering, and carrying out reduced pressure evaporation to obtain a liquid benzoxazine monomer. And then, polymerizing the obtained benzoxazine monomer at a high temperature, so as to prepare the polybenzoxazine-based resin.

Description

Technical Field

[0001] The present invention belongs to the technical field of resin materials, and particularly relates to a benzoxazine monomer based on 2,4-dihydroxybenzaldehyde, a preparation method thereof, and an application thereof. Background Art

[0002] Polybenzoxazine resin (abbreviated as PBO resin) is a kind of high-molecular material with excellent properties, and has received extensive attention in the fields of aerospace, automobiles, electronics, and composite materials in recent years. It belongs to thermosetting resins such as epoxy resins and phenolic resins, and has many excellent performance advantages, especially outstanding in heat resistance, mechanical properties, and processing properties.

[0003] Traditional phenolic resins need to be catalyzed by acids or bases during the polymerization process, which not only increases the complexity of the production process, but also releases harmful gases such as formaldehyde during the reaction process, causing pollution. The polymerization reaction of polybenzoxazine resin can proceed spontaneously without an external catalyst, and almost no small molecules are released during the curing process. This characteristic makes PBO resin more environmentally friendly during the production process, and there is almost no shrinkage or expansion after curing, thus effectively improving the dimensional stability and quality of the final product. Therefore, it better meets the requirements of practical applications.

[0004] Although polybenzoxazine resin performs well in many aspects, there are still some technical challenges to fully realize its industrial application: First is the cost issue. The production cost of polybenzoxazine resin is relatively high, mainly due to the complexity of its synthesis process and the high price of raw materials. To achieve its large-scale application, reducing the production cost is an urgent problem to be solved. Researchers are looking for cheaper and more easily available raw materials to reduce the production cost of PBO resin. Second is the performance balance: Although PBO resin has certain advantages in curing, thermal stability, flame retardancy, etc., few products can achieve an ideal balance in these aspects at the same time. For example, although PBO resin has high thermal stability, its flame retardancy may be insufficient in some cases, or it cannot fully meet the use requirements under different performance requirements. Therefore, how to optimize these performances, especially under the multiple requirements of high temperature, flame retardancy, and mechanical properties, is still an urgent problem to be solved.

[0005] By introducing different functional groups or adjusting the molecular structure of polybenzoxazine resin through molecular design, the cost and performance can be balanced. The introduction of certain functional groups can improve its flame retardancy, plasticization, antioxidant property, etc., but how to maintain the basic advantages of the material without affecting its other performances is the current research focus. By reasonably designing and adjusting the functional groups, preparing new polybenzoxazine resins with excellent performances will greatly enhance its competitiveness in the application market. Summary of the Invention

[0006] Common benzoxazine resins often have a relatively high curing temperature. Therefore, it is of great significance to design a benzoxazine resin with a low curing temperature. Combining the properties of common functional groups and the benzoxazine curing mechanism, the present invention designs to introduce hydroxyl groups and aldehyde groups into the benzoxazine resin to achieve the purpose of reducing the curing temperature.

[0007] One of the purposes of the present invention is to provide a benzoxazine monomer based on 2,4-dihydroxybenzaldehyde, and its structural formula is as follows:

[0008]

[0009] Another purpose of the present invention is to provide a preparation method of the above-mentioned benzoxazine monomer, specifically: dissolving 2,4-dihydroxybenzaldehyde and 3-aminophenylacetylene in an organic solvent, dropwise adding formaldehyde, heating under reflux, filtering after the reaction, and evaporating under reduced pressure to obtain a liquid benzoxazine monomer.

[0010] Further, the molar ratio of 2,4-dihydroxybenzaldehyde, 3-aminophenylacetylene and formaldehyde is 1:(1-1.2):(2-4).

[0011] Further, the organic solvent is selected from at least one of toluene, acetonitrile, dichloromethane, dichloroethane, chloroform, n-hexane, tetrahydrofuran, methanol, ethanol, polyethylene glycol.

[0012] Further, the organic solvent is toluene.

[0013] Further, the temperature of the heating under reflux is 85-100 °C.

[0014] Another purpose of the present invention is to provide a polybenzoxazine resin prepared by curing the above-mentioned benzoxazine monomer.

[0015] Further, the curing process is: placing the benzoxazine monomer in a mold, heating at 80 °C for 1 h, heating at 100 °C for 1 h, heating at 110 °C for 1 h, and heating at 120 °C for 1 h to obtain the polybenzoxazine resin.

[0016] Beneficial effects: The present invention provides a benzoxazine monomer based on 2,4-dihydroxybenzaldehyde and a polybenzoxazine resin. The synthesis method of the benzoxazine monomer provided by the present invention is simple, and the product can be obtained in a high yield through a one-step reaction. Compared with the conventional benzoxazine resin, the polybenzoxazine resin prepared by the present invention can obtain a benzoxazine resin with the advantages of low curing temperature, high char yield and high thermal stability at the same time. Brief Description of the Drawings

[0017] Figure 1 It is the infrared spectrum before and after curing of the benzoxazine monomer prepared in Example 1. In the figure, the characteristic absorption peak at 3314 cm -1 can be attributed to the stretching vibration of C-H of the alkynyl group and disappears after curing. The characteristic absorption peak at 3438 cm -1 can be attributed to the O-H stretching vibration, the characteristic absorption peak at 3273 cm -1 can be attributed to the C-H stretching vibration on the benzene ring, and the characteristic absorption peak at 1259 cm -1 can be attributed to the asymmetric stretching of C-O-C of the oxazine ring, while the characteristic vibration peak at 930 cm -1 can be attributed to the oxazine ring and decreases sharply after curing, indicating that the oxazine ring has completed ring-opening polymerization.

[0018] Figure 2 It is the polybenzoxazine resin prepared in Example 13.

[0019] Figure 3 It is the DSC curve of the benzoxazine monomer prepared in Example 1.

[0020] Figure 4 It is the TGA curve of the polybenzoxazine resin prepared in Example 13.

[0021] Figure 5 It is the TGA curve of the polybenzoxazine resin prepared in Example 14.

[0022] Figure 6 It is the TGA curve of the polybenzoxazine resin prepared in Example 15.

[0023] Figure 7 It is the combustion test result of the polybenzoxazine resin prepared in Example 13.

[0024] Figure 8 It is the MCC curve of the polybenzoxazine resin prepared in Example 13. Specific Embodiments

[0025] The preferred embodiments of the present invention will be described in detail below in conjunction with the examples. It should be understood that the following examples are given only for illustrative purposes and are not used to limit the scope of the present invention. Those skilled in the art can make various modifications and substitutions to the present invention without departing from the purpose and spirit of the present invention.

[0026] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0027] Unless otherwise specified, the materials, reagents, etc. used in the following examples can all be obtained from commercial sources.

[0028] Example 1

[0029] Dissolve 2,4-dihydroxybenzaldehyde (1.3812 g, 10 mmol) and 3-aminophenylacetylene (1.1715 g, 10 mmol) completely in toluene (25 ml), then dropwise add formaldehyde (0.6006 g, 20 mmol). Heat under reflux at 90 °C for about 10 h. Monitor by thin-layer chromatography. When the solution turns yellow, filter to obtain the filtrate, and evaporate under reduced pressure to obtain a brown viscous liquid product with a yield of 88%.

[0030] Example 2

[0031] Dissolve 2,4-dihydroxybenzaldehyde (1.3812 g, 10 mmol) and 3-aminophenylacetylene (1.1715 g, 10 mmol) completely in toluene (25 ml), then dropwise add formaldehyde (0.9009 g, 30 mmol). Heat under reflux at 90 °C for about 10 h. Monitor by thin-layer chromatography. When the solution turns yellow, filter to obtain the filtrate, and evaporate under reduced pressure to obtain a brown viscous liquid product with a yield of 70%.

[0032] Example 3

[0033] Dissolve 2,4-dihydroxybenzaldehyde (1.3812 g, 10 mmol) and 3-aminophenylacetylene (1.4058 g, 12 mmol) completely in toluene (25 ml), then dropwise add formaldehyde (0.6006 g, 20 mmol). Heat under reflux at 90 °C for about 10 h. Monitor by thin-layer chromatography. When the solution turns yellow, filter to obtain the filtrate, and evaporate under reduced pressure to obtain a brown viscous liquid product with a yield of 65%.

[0034] Example 4

[0035] Dissolve 2,4-dihydroxybenzaldehyde (1.3812 g, 10 mmol) and 3-aminophenylacetylene (1.4058 g, 12 mmol) completely in toluene (25 ml), then dropwise add formaldehyde (0.9009 g, 30 mmol). Heat under reflux at 90 °C for about 10 h. Monitor by thin-layer chromatography. When the solution turns yellow, filter to obtain the filtrate, and evaporate under reduced pressure to obtain a brown viscous liquid product with a yield of 73%.

[0036] Example 5

[0037] Dissolve 2,4-dihydroxybenzaldehyde (1.3812 g, 10 mmol) and 3-aminophenylacetylene (1.1715 g, 10 mmol) completely in toluene (25 ml), then dropwise add formaldehyde (0.6006 g, 20 mmol). Heat under reflux at 85 °C for about 10 h. Monitor by thin-layer chromatography. When the solution turns yellow, filter to obtain the filtrate, and evaporate under reduced pressure to obtain a brown viscous liquid product with a yield of 67%.

[0038] Example 6

[0039] Dissolve 2,4-dihydroxybenzaldehyde (1.3812 g, 10 mmol) and 3-aminophenylacetylene (1.1715 g, 10 mmol) completely in toluene (25 ml), then dropwise add formaldehyde (0.6006 g, 20 mmol). Heat under reflux at 100 °C for about 10 h. Monitor by thin layer chromatography. When the solution turns yellow, filter to obtain the filtrate, and evaporate under reduced pressure to obtain a brown viscous liquid product with a yield of 85%.

[0040] Example 7

[0041] Dissolve 2,4-dihydroxybenzaldehyde (1.3812 g, 10 mmol) and 3-aminophenylacetylene (1.1715 g, 10 mmol) completely in toluene (25 ml), then dropwise add formaldehyde (1.2012 g, 40 mmol). Heat under reflux at 100 °C for about 10 h. Monitor by thin layer chromatography. When the solution turns yellow, filter to obtain the filtrate, and evaporate under reduced pressure to obtain a brown viscous liquid product with a yield of 83%.

[0042] Example 8

[0043] In this example, 2,4-dihydroxybenzaldehyde is replaced by 2,4-dihydroxyacetophenone.

[0044] Dissolve 2,4-dihydroxyacetophenone (1.5216 g, 10 mmol) and 3-aminophenylacetylene (1.1715 g, 10 mmol) completely in toluene (25 ml), then dropwise add formaldehyde (0.6006 g, 20 mmol). Heat under reflux at 100 °C for about 10 h. Monitor by thin layer chromatography. When the solution turns yellow, filter to obtain the filtrate, and evaporate under reduced pressure to obtain a brown viscous liquid product with a yield of 82%.

[0045] Example 9

[0046] In this example, 2,4-dihydroxybenzaldehyde is replaced by m-hydroxybenzaldehyde.

[0047] Dissolve m-hydroxybenzaldehyde (1.2212 g, 10 mmol) and 3-aminophenylacetylene (1.1715 g, 10 mmol) completely in toluene (25 ml), then dropwise add formaldehyde (0.6006 g, 20 mmol). Heat under reflux at 100 °C for about 12 h. Monitor by thin layer chromatography, filter to obtain the filtrate, extract with NaOH (1 mol / L, 100 ml), and evaporate the organic phase under reduced pressure to obtain a brown viscous liquid product with a yield of 71%.

[0048] Example 10

[0049] In this example, 2,4-dihydroxybenzaldehyde was replaced with curcumin.

[0050] Curcumin (3.6838 g, 10 mmol) and 3-aminophenylacetylene (1.1715 g, 10 mmol) were completely dissolved in toluene (25 ml), and then formaldehyde (1.2012 g, 40 mmol) was added dropwise. The mixture was heated under reflux at 100 °C for about 10 h, monitored by thin-layer chromatography, filtered to obtain a filtrate, and evaporated under reduced pressure to obtain a brown viscous liquid product with a yield of 66%.

[0051] Example 11

[0052] 2,4-Dihydroxybenzaldehyde (1.3812 g, 10 mmol) and 3-aminophenylacetylene (1.1715 g, 10 mmol) were completely dissolved in 1,4-dioxane (25 ml), and then formaldehyde (0.6006 g, 20 mmol) was added dropwise. The mixture was heated under reflux at 100 °C for about 10 h, monitored by thin-layer chromatography, filtered to obtain a filtrate, and evaporated under reduced pressure to obtain a brown viscous liquid product with a yield of 60%.

[0053] Example 12

[0054] 2,4-Dihydroxybenzaldehyde (1.3812 g, 10 mmol) and 3-aminophenylacetylene (1.1715 g, 10 mmol) were completely dissolved in ethanol (25 ml), and then formaldehyde (0.6006 g, 20 mmol) was added dropwise. The mixture was heated under reflux at 100 °C for about 10 h, monitored by thin-layer chromatography, filtered to obtain a filtrate, and evaporated under reduced pressure to obtain a brown viscous liquid product with a yield of 63%.

[0055] Example 13

[0056] The benzoxazine monomer prepared in Example 1 was poured into a mold and heated at 80 °C for 1 h, 100 °C for 1 h, 110 °C for 1 h, and 120 °C for 1 h to obtain a cured polybenzoxazine resin, as Figure 2 shown.

[0057] Example 14

[0058] The benzoxazine monomer prepared in Example 8 was poured into a mold and heated at 100 °C for 1 h, 120 °C for 1 h, 140 °C for 2 h, and 160 °C for 2 h to obtain a cured polybenzoxazine resin.

[0059] Example 15

[0060] The benzoxazine monomer prepared in Example 9 was poured into a mold and heated at 100 °C for 1 h, 120 °C for 1 h, 140 °C for 2 h, and 160 °C for 2 h to obtain the cured polybenzoxazine resin.

[0061] Test Example 1

[0062] Testing instrument: NETZSCH STA449F3 synchronous thermal analyzer

[0063] Experimental method: The thermal curing process of the benzoxazine monomer in Example 1 was studied by DSC. As Figure 3 shown, the curing starting point of the benzoxazine monomer was 148.11 °C, and the maximum exothermic temperature was 177.87 °C.

[0064] Test Example 2

[0065] Testing instrument: NETZSCH STA449F3 synchronous thermal analyzer

[0066] Experimental method: The thermal weight loss process of the polybenzoxazine resin in Example 13 was studied by TGA. As Figure 4 shown, the temperature at which the polybenzoxazine resin lost 5% of its weight was 360 °C, the temperature at which it lost 10% of its weight was 432 °C, and the char residue rate at 800 °C was 67%.

[0067] Test Example 3

[0068] Testing instrument: NETZSCH STA449F3 synchronous thermal analyzer

[0069] Experimental method: The thermal weight loss process of the polybenzoxazine resin in Example 14 was studied by TGA. As Figure 5 shown, the temperature at which the polybenzoxazine resin lost 5% of its weight was 306 °C, the temperature at which it lost 10% of its weight was 392 °C, and the char residue rate at 800 °C was 42%, which was much lower than that of the polybenzoxazine resin in Example 13.

[0070] Test Example 4

[0071] Testing instrument: NETZSCH STA449F3 synchronous thermal analyzer

[0072] Experimental method: The thermal weight loss process of the polybenzoxazine resin in Example 15 was studied by TGA. As Figure 6 shown, the temperature at which the polybenzoxazine resin lost 5% of its weight was 176 °C, the temperature at which it lost 10% of its weight was 188 °C, and the char residue rate at 800 °C was 49%, which was much lower than that of the polybenzoxazine resin in Example 13.

[0073] Test Example 5

[0074] Experimental method: The polybenzoxazine resin of Example 13 was subjected to a vertical burning test. As Figure 7 shown, the polybenzoxazine resin was subjected to two 10-second burning tests. During the burning process, no molten droplets dripped, and the flame immediately extinguished after the heat source was removed, meeting the V0 standard of UL-94.

[0075] Test Example 6

[0076] Experimental method: The polybenzoxazine resin of Example 13 was subjected to a microcalorimetry test. As Figure 8 shown, the heat release rate (HRC) was 19.9 J / g·K, and the total heat release (THR) was 2.8 kJ / g.

Claims

1. A benzoxazine monomer based on 2,4-dihydroxybenzaldehyde, the structural formula of which is as follows:

2. The method for preparing the benzoxazine monomer according to claim 1, characterized in that: 2,4-dihydroxybenzaldehyde and 3-aminophenylacetylene are dissolved in an organic solvent, formaldehyde is added dropwise, heated to reflux, filtered after reaction, and evaporated under reduced pressure to obtain a liquid benzoxazine monomer.

3. The preparation method according to claim 2, characterized in that: The molar ratio of the 2,4-dihydroxybenzaldehyde, 3-aminophenylacetylene and formaldehyde is 1:(1-1.2):(2-4).

4. The preparation method according to claim 2, characterized in that: The organic solvent is selected from at least one of toluene, acetonitrile, dichloromethane, dichloroethane, chloroform, n-hexane, tetrahydrofuran, methanol, ethanol, and polyethylene glycol.

5. The preparation method according to claim 4, characterized in that: The organic solvent is toluene.

6. The preparation method according to claim 2, characterized in that: The heating reflux temperature is 85-100°C.

7. A polybenzoxazine resin, characterized in that: The benzoxazine monomer according to claim 1 is cured and prepared.

8. The polybenzoxazine resin according to claim 7, characterized in that The curing process is as follows: placing the benzoxazine monomer in a mold, heating at 80° C. for 1 hour, heating at 100° C. for 1 hour, heating at 110° C. for 1 hour, and heating at 120° C. for 1 hour to obtain the polybenzoxazine resin.

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