Preparation method of polybenzoxazine molded at room temperature and capable of being reprocessed

Abstract

The invention discloses a preparation method of room-temperature molded and reprocessable polybenzoxazine, and relates to the technical field of high polymer material preparation. Comprising the following steps: 1, dissolving 3-aminopropyl alkoxy silane or 3-aminopropyl methyl alkoxy silane and a polyphenol compound in an organic solvent, reacting at the temperature of 0-100 DEG C until complete dissolution, adding paraformaldehyde, adding anhydrous magnesium sulfate to remove water after the reaction is finished, standing, filtering, and removing the solvent to obtain 3-aminopropyl alkoxy silane; the method comprises the following steps: step 1, preparing a benzoxazine monomer containing siloxy and phenolic hydroxyl (Ph-OH), step 2, placing the benzoxazine monomer in a room temperature environment for molding to obtain a sample molded at room temperature, and step 3, heating and curing the sample molded at room temperature under the curing temperature condition of 60-300 DEG C, and 4, during reprocessing, crushing the cured polybenzoxazine in a crusher, and carrying out hot press molding again in a hot press.

Description

Technical Field

[0001] The present invention discloses a method for preparing polybenzoxazine that can be formed and reprocessed at room temperature, and relates to the technical field of polymer material preparation. Background Art

[0002] Polybenzoxazines, a new commercial thermosetting resin, have attracted widespread attention due to their high heat resistance, good flame retardancy, and low water absorption. They are typically synthesized via thermally induced ring-opening polymerization of benzoxazine monomers. However, the relatively stable six-membered heterocyclic ring of the oxazine ring makes it less reactive, and their ring-opening polymerization typically requires relatively high temperatures, generally exceeding 200°C, which greatly limits their application in low-temperature manufacturing. At the same time, polybenzoxazines have been widely used in structural and insulating materials due to their high-temperature resistance, solvent resistance, dimensional stability, and excellent insulation properties. However, existing polybenzoxazines contain irreversible covalent crosslinks, making them insoluble and infusible after curing, making them insoluble in reprocessing and recycling, resulting in resource waste and environmental pollution. Summary of the Invention

[0003] The present invention addresses the problems of the prior art and provides a method for preparing a polybenzoxazine that can be molded and reprocessed at room temperature, and a benzoxazine resin that can be molded and reprocessed at room temperature.

[0004] The specific scheme proposed by the present invention is:

[0005] The present invention provides a method for preparing polybenzoxazine that can be formed and reprocessed at room temperature, comprising:

[0006] Step 1: dissolving 3-aminopropyl alkoxysilane or 3-aminopropyl methyl alkoxysilane and a polyphenol compound in an organic solvent, reacting at a temperature of 0-100°C until completely dissolved, adding paraformaldehyde, adding anhydrous magnesium sulfate to remove water after the reaction, standing and filtering, removing the solvent, and then vacuum drying to obtain a benzoxazine monomer.

[0007] Step 2: Place the benzoxazine monomer in a room temperature environment to form a sample formed at room temperature.

[0008] Step 3: Heat and cure the sample formed at room temperature at a temperature of 60-300°C.

[0009] Step 4: During reprocessing, the solidified polybenzoxazine is broken into pieces in a crusher and re-molded in a hot press.

[0010] Furthermore, the organic solvent in step 1 of the method for preparing a room-temperature moldable and reprocessable polybenzoxazine comprises one or more of chloroform, toluene, dioxane, ethanol, and dichloromethane.

[0011] Furthermore, the polyphenolic compound in step 1 of the method for preparing a room-temperature moldable and reprocessable polybenzoxazine includes bisphenol A, kaempferol, hydroquinone, catechol, and pyrogallol.

[0012] Furthermore, in step 1 of the method for preparing a room-temperature moldable and reprocessable polybenzoxazine, the molar ratio of 3-aminopropylalkoxysilane or 3-aminopropylmethylalkoxysilane, the polyphenol compound and paraformaldehyde is 1:1:(1-10).

[0013] Furthermore, in step 3 of the method for preparing a room-temperature moldable and reprocessable polybenzoxazine, the sample formed at room temperature is heated and cured in one or more atmospheres of air, nitrogen or inert gas, and the curing is carried out by heating at a temperature of 60-300°C, wherein the curing can be further carried out at temperatures of 140°C, 160°C, 180°C, 200°C, 220°C, 240°C and 260°C, each for 2 hours, to obtain a fully cross-linked polybenzoxazine.

[0014] Furthermore, in step 4 of the method for preparing a room-temperature moldable and reprocessable polybenzoxazine, the polybenzoxazine is ground into powder during reprocessing, and the hot pressing temperature is set to 30-350° C., the pressure is set to 0.1-100 MPa, and the hot pressing time is set to 0.1-24 hours.

[0015] The present invention also applies the benzoxazine resin prepared by the method for preparing the room-temperature-molded and reprocessable polybenzoxazine to the field of preparing structural materials and insulating materials.

[0016] The benefits of the present invention are:

[0017] The present invention enables room-temperature benzoxazine molding, exhibiting a dual effect through the Ph-OH group: on the one hand, it catalyzes the condensation reaction of silanol groups at room temperature to form a Si-O-Si pre-crosslinked network, allowing the benzoxazine to complete room-temperature curing and molding within 48 hours, exhibiting excellent mechanical properties; on the other hand, it promotes the ring-opening reaction of some oxazine rings and introduces dynamic Si-O-Ph bonds after complete crosslinking and curing, thereby enabling the polybenzoxazine resin to be reprocessed and molded, breaking through technical barriers and possessing broad market prospects. At the same time, the room-temperature molding ability of the benzoxazine resin monomer containing Ph-OH groups and silanol groups prepared by the present invention provides a solution to the difficulty of thermosetting resins in molding at lower temperatures. Furthermore, the polybenzoxazine crosslinked with dynamic Si-O-Ph bonds prepared after complete crosslinking and curing imparts high thermal stability and reprocessability to the material, contributing to the development of environmentally friendly, high-performance materials and resource recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, some simple drawings are provided below to represent the sample data during the implementation of the present invention.

[0019] Figure 1 Schematic diagram of the preparation of the room temperature moldable and reprocessable polybenzoxazine in Example 1.

[0020] Figure 2 Schematic diagram of the preparation of polybenzoxazine that can be molded and reprocessed at room temperature in Example 2.

[0021] Figure 3 This is the monomer characterization of benzoxazine in Example 1.

[0022] Figure 4 This is the FT-IR spectrum of the benzoxazine monomer formed at room temperature in Example 1.

[0023] Figure 5 This is the tensile strength test of the benzoxazine monomer after room temperature molding in Example 1.

[0024] Figure 6 This is the FT-IR spectrum of the room temperature formed benzoxazine heated and cured in Example 1.

[0025] Figure 7 Schematic diagram of the reprocessing of the fully cured polybenzoxazine in Example 1.

[0026] Figure 8 This is the tensile strength test of the fully cured polybenzoxazine in Example 1.

[0027] Figure 9 This is the TGA test of the fully cured polybenzoxazine in Example 1.

[0028] Figure 10 This is the DMA test of the fully cured polybenzoxazine in Example 1.

[0029] Figure 11 This is the monomer characterization of benzoxazine in Example 2.

[0030] Figure 12 This is the FT-IR spectrum of the benzoxazine monomer formed at room temperature in Example 2.

[0031] Figure 13 Schematic diagram of the reprocessing of the fully cured polybenzoxazine in Example 9. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0033] Example 1

[0034] This embodiment provides a method for preparing polybenzoxazine that can be formed at room temperature and reprocessed, and the specific steps include:

[0035] Step 1: 3-aminopropyltriethoxysilane and bisphenol A were dissolved in chloroform, stirred evenly, and stirred at 50°C for 30 minutes. After they were completely dissolved, paraformaldehyde was added, and then reacted at 70°C for 5 hours. After the reaction, the solvent was removed and the benzoxazine monomer was obtained after vacuum drying.

[0036] Step 2: Place the benzoxazine monomer in a constant temperature and humidity chamber for molding at a temperature of 35°C and a humidity of 60%;

[0037] Step 3: Curing the benzoxazine formed at room temperature by heating at a temperature of 60-300° C. under a nitrogen atmosphere;

[0038] Step 4: The solidified benzoxazine sample was crushed in a grinder, and then sieved through a sieve to obtain a benzoxazine resin with a particle size of 60 mesh. The benzoxazine resin was then re-molded in a hot press at a temperature of 250°C, a pressure of 30 MPa, and a pressing time of 5 hours.

[0039] Benzoxazine monomer characterization Figure 3 As shown:

[0040] 1 H-NMR (400MHz, Chloroform-d, ppm): δ=0.65(t,2H,N-CH2-CH2-CH2-Si), 1.20(t,9H,Si-℃H2-CH3), 1.59(s,6H,C-(CH3)2), 1.68(m,2H,N-CH2 -CH2-CH2-Si), 2.74(t,2H,N-CH2-CH2-CH2-Si), 3.81(m,6H,Si-O-CH2-CH3), 3.91(s,2H,O-CH2-N), 4.81(s,2H,Ar-CH2-N), 6.64-7.07(benzene ring).

[0041] 13C-NMR (400MHz, Chloroform-d, ppm): δ = 153.93, 151.77, 143.26, 127.87, 126.26, 125.49,119.21,115.77,114.85(benzene ring),82.25(O-CH2-N),58.50(Si-O-CH2-CH3),5 4.27(N-CH2-CH2-CH2-Si),50.43(Ar-CH2-N),41.67(Ar-C-Ar),31.13(Ar-C-CH3 ), 21.37(N-CH2-CH2-CH2-Si), 18.30(Si-O-CH2-CH3), 7.82(N-CH2-CH2-CH2-Si).

[0042] 29 Si-NMR (400MHz, Chloroform-d, ppm): δ=-45.06.

[0043] FT-IR (KBr, cm -1 ): 1498 (trisubstituted benzene ring stretching vibration), 1228 (CO-C asymmetric stretching vibration), 1072 (Si-OC stretching vibration), 935 (oxazine ring).

[0044] The FT-IR spectrum of benzoxazine monomer at room temperature is as follows Figure 4 As shown:

[0045] Figure 4 This is the FT-IR spectrum of benzoxazine monomer during room temperature molding. As the curing time increases, the characteristic absorption peak of Si-O-CH2-CH3 (1072cm -1 ) intensity significantly attenuated, while 1000-1100cm -1 The broad peaks attributable to the Si-O-Si chain gradually increased within the range, indicating that Si-O-CH2-CH3 underwent hydrolysis and condensation to form a Si-O-Si cross-linked network. -1 ) continued to decrease, and after 48h at 958cm -1 The characteristic absorption peak of the Si-O-Ph bond appears at 100 nm. This phenomenon indicates that during the room-temperature molding process of the BA-mtes-OH monomer, a certain amount of Si-O-CH2-CH3 in the monomer undergoes hydrolysis in the air, cross-linking with each other to form Si-O-Si chains. The Ph-OH groups in the monomer catalyze the ring-opening reaction of the oxazine ring, releasing more Ph-OH groups.

[0046] The tensile strength test of benzoxazine monomer after room temperature molding is as follows Figure 5 As shown:

[0047] Figure 5 Comparisons of stress-strain curves and tensile strengths of virgin and reprocessed benzoxazine monomer room-temperature molded samples are presented. The tensile strengths of the virgin and three-reprocessed samples were 30.05 MPa, 31.21 MPa, 30.51 MPa, and 32.42 MPa, respectively. Mechanical property retentions were 103.86%, 101.53%, and 107.88%, respectively. This mechanical property retention is greater than 100%, demonstrating excellent mechanical property retention in benzoxazine monomer room-temperature molded samples.

[0048] The FT-IR spectrum of room temperature formed benzoxazine heated and cured is shown in Figure 6 As shown:

[0049] Figure 6 The curing behavior of benzoxazine room temperature molded samples at different curing temperatures is shown. In the low temperature stage, the temperature is <200℃, 935cm -1 The presence of the COC characteristic absorption peak of the oxazine ring at 3125-3643 cm indicates that the ring-opening reaction has not yet been completed. -1 The broad peaks gradually increasing in the range are attributed to the formation of Ph-OH groups (oxazine ring opening products). -1 The attenuation of the trisubstituted benzene ring vibration peak at 1482 cm -1 The simultaneous increase in the signal intensity of the tetrasubstituted benzene ring peak at 935cm 2 confirms that the benzoxazine molecules cross-link through the ring-opening reaction to form a polybenzoxazine cross-linked network. When the temperature rises to 200℃, the characteristic peak of the oxazine ring (935cm 2) -1 ) almost disappears, indicating the completion of the ring-opening reaction. In the high temperature post-curing stage (200-260℃), 958cm -1 The characteristic peak of Si-O-Ph bond at the -1 ) strength decreased, indicating that the residual Si-O-CH2-CH3 reacted with Ph-OH to form a larger number of dynamic Si-O-Ph bonds. Experimental data showed that after gradient thermal curing, the material transformed from a partially cross-linked benzoxazine room temperature molded sample to a fully cross-linked polybenzoxazine network with a high density of dynamic bonds.

[0050] Schematic diagram of reprocessing of fully cured polybenzoxazine Figure 7 As shown:

[0051] Figure 7 This image shows the reprocessing process of a fully cured benzoxazine sample. The cured sample was crushed in a crusher and sieved through a screen to obtain a powder sample. As can be seen in the image, the powder is light yellow with no black spots. The powder sample was placed in a mold and hot-pressed. The resulting reprocessed sample is transparent and has a smooth cross-section.

[0052] The tensile strength of fully cured polybenzoxazine was tested as follows: Figure 8 As shown:

[0053] Figure 8 =The tensile strength of the fully cured polybenzoxazine (PBZ) sample and the three-times-processed sample is 48.49 MPa, 47.49 MPa, 47.90 MPa, and 46.79 MPa, respectively. The mechanical property retention rates are 97.9%, 98.8%, and 96.5%, respectively. These data demonstrate that fully cured polybenzoxazine exhibits excellent mechanical properties and mechanical property retention.

[0054] TGA test of fully cured polybenzoxazine Figure 9 As shown:

[0055] The TGA curves of the fully cured polybenzoxazine original and reprocessed samples show the thermal stability of the material. d5 and T d10 Reaching 336℃ and 364℃ respectively, Y 800 As high as 57.3%, compared with the traditional bisphenol A / aniline benzoxazine (T d5 =302℃, T d10 =327℃, Y 800 =31.0%) is significantly improved. In air environment, the T d5 and T d10 Further increase to 367℃ and 416℃, Y 800 The significant enhancement of thermal performance is due to the increase in its crosslinking density. First, the Si-O-Si bonds formed in the room temperature pre-curing stage provide preliminary crosslinking, and the Ph-OH groups released by the complete ring opening of the oxazine ring during the high-temperature curing process condense with Si-O-CH2-CH3 to form high-density Si-O-Ph dynamic bonds. The bond energy (452kJ / mol) is significantly higher than that of the traditional CN bond (305kJ / mol), which effectively inhibits the high-temperature segment dissociation. Compared with the unmodified polybenzoxazine, the fully cured polybenzoxazine still shows excellent cyclic stability. After three processing, T d5 It only dropped by 4.5%, which is significantly better than the reversible cross-linking system reported in the literature. This is due to the heat resistance advantage of the Si-O-Ph dynamic bond and the tight cross-linking structure of the system.

[0056] Fully cured polybenzoxazine DMA Figure 10 As shown:

[0057] Figure 10 The DMA results show that the T of the fully cured polybenzoxazine original sample is gAs high as 369℃ (based on tanδ peak), it is worth noting that after three reprocessing, the T g 360℃, 362℃ and 370℃ respectively, significantly surpassing the traditional aniline-based polybenzoxazine (T g =150°C). Its excellent heat resistance is attributed to its unique multi-stage crosslinked network. First, Si-O-Si bonds formed during room temperature molding act as pre-crosslinks, increasing the crosslink density. Second, during hot pressing, dynamic Si-O-Ph bonds exchange with Ph-OH groups to form new dynamic Si-O-Ph bonds, which not only repair processing damage but also optimize the network topology through bond rearrangement. Compared to systems that rely solely on oxazine ring crosslinking, the introduction of Si-O-Si and Si-O-Ph bonds significantly improves the material's heat resistance.

[0058] Example 2

[0059] This embodiment provides a method for preparing polybenzoxazine that can be formed at room temperature and reprocessed, and the specific steps include:

[0060] Step 1: Dissolve 3-aminopropylmethyldiethoxysilane and bisphenol A in chloroform, stir evenly, and stir at 50°C for 30 minutes. After they are completely dissolved, add paraformaldehyde, and then react at 70°C for 5 hours. After the reaction, remove the solvent and vacuum dry to obtain a benzoxazine monomer;

[0061] Step 2: Place the benzoxazine monomer in a constant temperature and humidity chamber for molding at a temperature of 35°C and a humidity of 60%;

[0062] Step 3: Curing the benzoxazine formed at room temperature by heating in an air atmosphere at a temperature of 60-300°C;

[0063] Step 4: The solidified benzoxazine sample was crushed in a grinder, and then sieved through a sieve to obtain a benzoxazine resin with a particle size of 60 mesh. The benzoxazine resin was then re-molded in a hot press at a temperature of 250°C, a pressure of 30 MPa, and a pressing time of 5 hours.

[0064] Benzoxazine monomer characterization Figure 11 As shown:

[0065] 1H-NMR (400MHz, CDCl3, ppm): δ = 6.64-7.06 (7H, benzene ring), 4.81 (s, 2H, Ar-CH2-N), 3.92 (s, 2H, O-CH2-N), 3.76 (m, 4H, Si-O-CH2-CH3), 2.74 (t, 2H, N-CH2-CH2 -CH2-Si),1.64(m,2H,N-CH2-CH2-CH2-Si),1.59(s,6H,C-(CH3)2),1.19(t,6H,Si-OCH2-CH3),0.62(t,2H,N-CH2-CH2-CH2-Si),0.12(s,3H,Si-CH3).

[0066] 13 C-NMR (400 MHz, CDCl3, ppm): δ = 153.98, 151.82, 143.23, 142.71, 142.51, 127.88, 126.29, 125.44, 119.25, 115.76, 114.83 (benzene ring), 82.28 (O-CH2-N), 58.24 (Si-O-CH2-CH3), 54.47 (N-CH2-CH2-CH2-Si),50.52(Ar-CH2-N),41.67(Ar-C-Ar),31.13(Ar-C-CH3),21.56(N- CH2-CH2-CH2-Si), 18.40(Si-O-CH2-CH3), 11.29(N-CH2-CH2-CH2-Si), -4.81(Si-CH3).

[0067] 29 Si-NMR (400MHz, CDCl3, ppm): δ=-45.7.

[0068] FT-IR (KBr, cm -1 ):3176-3530 (Ph-OH group), 1497 (trisubstituted benzene ring stretching vibration), 1228 (COC asymmetric stretching vibration), 1072 (Si-OC stretching vibration), 930 (oxazine ring).

[0069] The FT-IR spectrum of benzoxazine monomer at room temperature is as follows Figure 12 As shown:

[0070] In order to show the specific changes of benzoxazine monomer during room temperature molding, the monomer was placed in a constant temperature and humidity chamber, and samples were taken out every 12 hours for testing. In the FT-IR spectrum during room temperature molding, the characteristic absorption peak (1074cm -1) gradually decreases with the extension of room temperature storage time, and at 1000cm -1 -1100cm -1 The characteristic peak corresponding to the Si-O-Si chain gradually increases. -1 The characteristic peak of the oxazine ring at 958cm is also decreasing. When placed at room temperature for 36h and 48h, the oxazine peak gradually decreases to constant. At the same time, when placed at room temperature for 36h, the peak at 958cm -1 Characteristic peaks for Si-O-Ph bonds begin to appear at 36 hours. This preliminary study suggests that during the room-temperature molding process, a certain amount of Si-O-CH2-CH3 within the monomer undergoes hydrolysis in air, crosslinking to form Si-O-Si chains. Simultaneously, in the presence of Ph-OH groups, the oxazine ring undergoes partial ring opening to generate Ph-OH groups. Ultimately, after 36 hours, the characteristic infrared peaks remain essentially unchanged, demonstrating that the changes within the system have stabilized.

[0071] Example 3

[0072] This embodiment provides a method for preparing polybenzoxazine that can be formed at room temperature and reprocessed, and the specific steps include:

[0073] Step 1: 3-aminopropyltriethoxysilane and bisphenol A were dissolved in chloroform, stirred evenly, and stirred at 50°C for 30 minutes. After they were completely dissolved, paraformaldehyde was added, and then reacted at 70°C for 5 hours. After the reaction, the solvent was removed and the benzoxazine monomer was obtained after vacuum drying.

[0074] Step 2: Place the benzoxazine monomer in a constant temperature and humidity chamber for molding at a temperature of 25°C and a humidity of 50%;

[0075] Step 3: Curing the benzoxazine formed at room temperature by heating at a temperature of 60-300° C. under an argon atmosphere;

[0076] Step 4: The solidified benzoxazine sample was crushed in a grinder, and then sieved through a sieve to obtain a benzoxazine resin with a particle size of 60 mesh. The benzoxazine resin was then hot-pressed in a hot press with a temperature of 300°C, a pressure of 25 MPa, and a pressing time of 6 hours.

[0077] The characterization of the benzoxazine monomer and the FT-IR spectrum of the benzoxazine monomer formed at room temperature are similar to those in Examples 1 and 2.

[0078] Example 4

[0079] This embodiment provides a method for preparing polybenzoxazine that can be formed at room temperature and reprocessed, and the specific steps include:

[0080] Step 1: Dissolve 3-aminopropylmethyldiethoxysilane and bisphenol A in chloroform, stir evenly, and stir at 50°C for 30 minutes. After they are completely dissolved, add paraformaldehyde, and then react at 70°C for 5 hours. After the reaction, remove the solvent and vacuum dry to obtain a benzoxazine monomer;

[0081] Step 2: Place the benzoxazine monomer in a constant temperature and humidity chamber for molding at a temperature of 25°C and a humidity of 50%;

[0082] Step 3: Curing the benzoxazine formed at room temperature by heating under a nitrogen atmosphere;

[0083] Step 4: The solidified benzoxazine sample was crushed in a grinder, and then sieved through a sieve to obtain a benzoxazine resin with a particle size of 60 mesh, which was then re-hot-pressed in a hot press at a temperature of 300°C, a pressure of 25 MPa, and a pressing time of 8 hours.

[0084] The characterization of the benzoxazine monomer and the FT-IR spectrum of the benzoxazine monomer formed at room temperature are similar to those in Examples 1 and 2.

[0085] Example 5

[0086] This embodiment provides a method for preparing polybenzoxazine that can be formed at room temperature and reprocessed, and the specific steps include:

[0087] Step 1: 3-aminopropyltriethoxysilane and bisphenol A were dissolved in chloroform, stirred evenly, and stirred at 50°C for 30 minutes. After they were completely dissolved, paraformaldehyde was added, and then reacted at 70°C for 5 hours. After the reaction, the solvent was removed and the benzoxazine monomer was obtained after vacuum drying.

[0088] Step 2: Place the benzoxazine monomer in a constant temperature and humidity chamber at a temperature of 25°C and a humidity of 70%;

[0089] Step 3: Curing the benzoxazine formed at room temperature by heating at a temperature of 60-300° C. under a nitrogen atmosphere;

[0090] Step 4: The solidified benzoxazine sample was crushed in a grinder, and then sieved through a sieve to obtain a benzoxazine resin with a particle size of 60 mesh, which was then re-hot-pressed in a hot press at a temperature of 300°C, a pressure of 30 MPa, and a pressing time of 5 h.

[0091] The characterization of the benzoxazine monomer and the FT-IR spectrum of the benzoxazine monomer formed at room temperature are similar to those in Examples 1 and 2.

[0092] Example 6

[0093] This embodiment provides a method for preparing polybenzoxazine that can be formed at room temperature and reprocessed, and the specific steps include:

[0094] Step 1: Dissolve 3-aminopropylmethyldiethoxysilane and bisphenol A in chloroform, stir evenly, and stir at 50°C for 30 minutes. After they are completely dissolved, add paraformaldehyde, and then react at 70°C for 5 hours. After the reaction, remove the solvent and vacuum dry to obtain a benzoxazine monomer;

[0095] Step 2: Place the benzoxazine monomer in a constant temperature and humidity chamber at 0°C and 40% humidity;

[0096] Step 3: Curing the benzoxazine formed at room temperature by heating in an air atmosphere at a temperature of 60-300°C;

[0097] Step 4: The solidified benzoxazine sample was crushed in a grinder, and then sieved through a sieve to obtain a 60-mesh benzoxazine resin, which was then re-hot-pressed in a hot press at a temperature of 300°C, a pressure of 30 MPa, and a pressing time of 6 hours.

[0098] The characterization of the benzoxazine monomer and the FT-IR spectrum of the benzoxazine monomer formed at room temperature are similar to those in Examples 1 and 2.

[0099] Example 7

[0100] This embodiment provides a method for preparing polybenzoxazine that can be formed at room temperature and reprocessed, and the specific steps include:

[0101] Step 1: 3-aminopropyltriethoxysilane and bisphenol A were dissolved in chloroform, stirred evenly, and stirred at 50°C for 30 minutes. After they were completely dissolved, paraformaldehyde was added, and then reacted at 70°C for 5 hours. After the reaction, the solvent was removed and the benzoxazine monomer was obtained after vacuum drying.

[0102] Step 2: Place the benzoxazine monomer in a constant temperature and humidity chamber for molding at a temperature of 0°C and a humidity of 40%;

[0103] Step 3: Curing the benzoxazine formed at room temperature by heating at a temperature of 60-300° C. under a nitrogen atmosphere;

[0104] Step 4: The solidified benzoxazine sample was crushed in a grinder, and then sieved through a sieve to obtain a benzoxazine resin with a particle size of 60 mesh, which was then re-hot-pressed in a hot press at a temperature of 300°C, a pressure of 30 MPa, and a pressing time of 5 h.

[0105] The characterization of the benzoxazine monomer and the FT-IR spectrum of the benzoxazine monomer formed at room temperature are similar to those in Examples 1 and 2.

[0106] Example 8

[0107] This embodiment provides a method for preparing polybenzoxazine that can be formed at room temperature and reprocessed, and the specific steps include:

[0108] Step 1: Under nitrogen protection, 3-aminopropyltriethoxysilane and catechol were dissolved in chloroform, stirred evenly, and stirred at 50°C for 30 minutes. After they were completely dissolved, paraformaldehyde was added, and then reacted at 80°C for 5 hours. After the reaction, the solvent was removed and the benzoxazine monomer was obtained after vacuum drying.

[0109] Step 2: Place the benzoxazine monomer in a constant temperature and humidity chamber at a temperature of 35°C and a humidity of 60%;

[0110] Step 3: Curing the benzoxazine formed at room temperature by heating under a nitrogen atmosphere;

[0111] Step 4: Crush the solidified benzoxazine sample in a grinder, then sieve out 60-mesh benzoxazine resin, which can be re-hot-pressed in a hot press at a temperature of 250°C, a pressure of 20 MPa, and a pressing time of 3 hours.

[0112] The characterization of the benzoxazine monomer and the FT-IR spectrum of the benzoxazine monomer formed at room temperature are similar to those in Examples 1 and 2.

[0113] Example 9

[0114] This embodiment provides a method for preparing polybenzoxazine that can be formed at room temperature and reprocessed, and the specific steps include:

[0115] Step 1: 3-aminopropyltriethoxysilane and bisphenol A were dissolved in chloroform, stirred evenly, and stirred at 50°C for 30 minutes. After they were completely dissolved, paraformaldehyde was added, and then reacted at 70°C for 5 hours. After the reaction, the solvent was removed and the benzoxazine monomer was obtained after vacuum drying.

[0116] Step 2: Place the benzoxazine monomer in a constant temperature and humidity chamber for molding at a temperature of 35°C and a humidity of 60%;

[0117] Step 3: Curing the benzoxazine formed at room temperature by heating under a nitrogen atmosphere;

[0118] Step 4: Crush the solidified benzoxazine sample in a grinder, then sieve out 60-mesh benzoxazine resin, which can be re-hot-pressed in a hot press with a temperature of 100°C, a pressure of 15 MPa, and a pressing time of 5 hours.

[0119] Schematic diagram of reprocessing of fully cured benzoxazine Figure 13 As shown:

[0120] Figure 13 This image shows the reprocessing of a fully cured benzoxazine sample. The fully cured benzoxazine sample was ground into powder using a crusher and then hot-pressed to obtain a transparent reprocessed sample. This process was repeated three times, resulting in a transparent sample with a smooth cross-section. This demonstrates that the sample powder can heal into a single piece.

[0121] The above are preferred embodiments of the present invention. Within the scope of the technical solution of the present invention, the type and amount of reagents used can be adjusted according to actual conditions to achieve the result of degradation of the polybenzoxazine resin.

[0122] Unless otherwise specified, all reagents involved in the method of the present invention were purchased through regular channels or obtained as gifts.

[0123] The above embodiments are merely preferred embodiments for the purpose of fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

Claims

1. A method for preparing a room temperature moldable and reprocessable polybenzoxazine, characterized in that include: Step 1: dissolving 3-aminopropyl alkoxysilane or 3-aminopropyl methyl alkoxysilane and a polyphenol compound in an organic solvent, reacting at a temperature of 0-100°C until completely dissolved, adding paraformaldehyde, adding anhydrous magnesium sulfate to remove water after the reaction, standing and filtering, removing the solvent, and then vacuum drying to obtain a benzoxazine monomer containing a silaneoxy group and a Ph-OH group. Step 2: Place the benzoxazine monomer in a room temperature environment to form a sample formed at room temperature. Step 3: Heat and cure the sample formed at room temperature at a temperature of 60-300°C. Step 4: During reprocessing, the solidified polybenzoxazine is broken into pieces in a crusher and re-molded in a hot press.

2. The method for preparing a room temperature moldable and reprocessable polybenzoxazine according to claim 1, characterized in that The organic solvent in step 1 includes one or more of chloroform, toluene, dioxane, ethanol, and dichloromethane.

3. The method for preparing a room-temperature moldable and reprocessable polybenzoxazine according to claim 1, wherein the polyphenol compound in step 1 comprises bisphenol A, kaempferol, hydroquinone, catechol, and pyrogallol.

4. The method for preparing a room-temperature moldable and reprocessable polybenzoxazine according to claim 1, wherein the molar ratio of the 3-aminopropylalkoxysilane or 3-aminopropylmethylalkoxysilane, the polyphenol compound, and the paraformaldehyde in step 1 is 1:1:(1-10).

5. The method for preparing a room temperature moldable and reprocessable polybenzoxazine according to claim 1, characterized in that In step 3, the sample formed at room temperature is heated and cured in one or more atmospheres of air, nitrogen or inert gas at a temperature of 60-300° C. to obtain a fully cross-linked polybenzoxazine.

6. The method for preparing a room temperature moldable and reprocessable polybenzoxazine according to claim 1, characterized in that During the further processing in step 4, the polybenzoxazine is ground into powder, and the hot pressing temperature is set to 30-350° C., the pressure is set to 0.1-100 MPa, and the hot pressing time is set to 0.1-24 hours.

7. The benzoxazine resin prepared by the method for preparing a room temperature moldable and reprocessable polybenzoxazine according to claims 1 to 6 is used in the field of preparing structural materials and insulating materials.

Images