Preparation method and application of resin for PBO fiber reinforced bulletproof composite material

Abstract

The invention discloses a preparation method and application of epoxy resin for bulletproof composite materials. First, an epoxy resin monomer with a phenylene benzoxazole structure is synthesized; secondly, a dendritic macromolecule crosslinking agent with an active group at the end is synthesized; finally, the bulletproof composite material is molded by a dipping method and a hot pressing method. The invention adopts an epoxy resin with a phenylene benzoxazole structure as a matrix. The invention adopts a dendritic macromolecule with an active group such as an amino group or a carboxyl group at the end as a curing agent. The spherical three-dimensional structure of the dendritic macromolecule can reduce the shrinkage rate of the epoxy cured product, and the active group can directly participate in the curing reaction to form a three-dimensional network structure. The numerous terminal functional groups can also accelerate the curing reaction speed. At the same time, controlling the size and spherical structure of the dendritic macromolecule plays a toughening role on the epoxy resin.

Description

Technical Field

[0001] The invention relates to the field of epoxy resin preparation, and in particular to a preparation method and application of a resin for a PBO fiber reinforced bulletproof composite material. Background Art

[0002] Bulletproof composite materials are a type of high-impact materials with fibers as reinforcements and resin matrix as adhesives. PBO fiber is the abbreviation of poly(p-phenylene benzobisoxazole) fiber, which has high specific strength and high specific energy absorption value. It is a high-performance fiber with application prospects in bulletproof composite materials besides aramid fiber and ultra-high molecular weight polyethylene fiber. Epoxy resin is widely used in fiber-reinforced resin-based composite materials due to its excellent mechanical properties, chemical stability, adhesion, processing performance, etc. However, its application has problems such as brittleness after curing, poor impact resistance, and easy cracking. Therefore, structural design and toughening modification of epoxy resin suitable for PBO fiber bulletproof composite materials are technical problems that need to be solved urgently.

[0003] For example, the patent with publication number CN106478712A discloses a preparation method of an epoxy-terminated paraphenylene benzobisoxazole precursor, which improves the interfacial bonding strength with PBO fibers, but the toughness of the resin matrix still needs to be improved. The patent with publication number CN114875522A discloses a toughened liquid-molded epoxy resin ternary composite fiber and its preparation method, which improves the toughness of the composite material, but the compatibility with PBO fibers needs to be improved.

[0004] Although the existing technologies have improved the interface bonding between PBO fiber and resin and the toughness of epoxy resin, there is no report on toughened epoxy resin specifically used for PBO fiber bulletproof composite materials. Therefore, in response to this technical gap, this patent innovatively discloses a preparation method and application of resin for bulletproof composite materials, based on the structure of PBO fiber, epoxy resin monomer is designed and synthesized, and dendritic macromolecular crosslinking agent is used to cure, toughen and impact-modify epoxy resin. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a preparation method and application of epoxy resin for bulletproof composite materials, carry out structural design and monomer synthesis of epoxy resin, and improve the impact resistance of PBO fiber bulletproof composite materials through the toughening effect of cross-linking agent.

[0006] In order to achieve the above-mentioned purpose, the preparation method of the epoxy resin for bullet-proof composite material of the present invention comprises the following steps: firstly, synthesizing an epoxy resin monomer having a phenylene benzoxazole structure; secondly, synthesizing a dendritic macromolecular crosslinking agent having an active group at the end; and finally, performing molding processing of the bullet-proof composite material by a dipping method and a hot pressing method.

[0007] In order to solve the compatibility problem between PBO fiber and epoxy resin, the present invention adopts epoxy resin with phenylene benzoxazole structure as the matrix. The epoxy resin retains the benzene ring skeleton of bisphenol to ensure that its mechanical properties are less affected, and at the same time introduces benzoxazole structure through dehydration condensation reaction to form π-π interaction with the surface of PBO fiber, thereby improving the interface bonding between PBO fiber and epoxy resin.

[0008] In order to solve the problem of high brittleness of epoxy resin after curing, the present invention adopts dendritic macromolecules with active groups such as amino groups and carboxyl groups at the ends as curing agents. The spherical three-dimensional structure of the dendritic macromolecules can reduce the shrinkage rate of epoxy cured products, and the active groups can directly participate in the curing reaction to form a three-dimensional network structure. The numerous terminal functional groups can also accelerate the curing reaction speed. At the same time, controlling the size and spherical structure of the dendritic macromolecules has a toughening effect on the epoxy resin.

[0009] A method for preparing a resin for a PBO fiber-reinforced bulletproof composite material comprises the following steps:

[0010] (1) Synthesis of epoxy resin monomers with phenylene benzoxazole structure:

[0011] Step 1: adding concentrated nitric acid dropwise to the stirred toluene, bisphenol compound and glacial acetic acid solution, and after the reaction and post-treatment, obtaining a product of yellow powder, namely the nitrobisphenol compound;

[0012] Step 2: adding the nitrated bisphenol compound, anhydrous ethanol, FeCl3·6H2O and activated carbon into a reactor equipped with a mechanical stirrer and a reflux condenser, dropping N2H4·H2O into the mixture, refluxing the reaction mixture and cooling it, and post-treating the product to obtain a white precipitate, which is the amino bisphenol compound;

[0013] Step 3: adding an aminated bisphenol compound, a carboxyl-containing phenolic compound and phosphorus pentoxide to a mixed solution of polyphosphoric acid and methanesulfonic acid, stirring the mixture, and performing post-treatment to obtain a product that is a phenolic compound having a bisbenzoxazole structure;

[0014] Step 4: adding a phenolic compound having a bisbenzoxazole structure and epichlorohydrin to a NaOH aqueous solution, reacting at 55-75° C. for 3-24 hours, and obtaining a brown viscous liquid after post-treatment after the reaction is completed, which is an epoxy resin monomer having a phenylene benzoxazole structure;

[0015] (2) Synthesis of dendrimer crosslinkers with active groups at the ends:

[0016] Dissolve the tert-butyloxycarbonyl carbonyl protected straight-chain amino acids (amino acids with carbon atoms of 3, 6, 8, and 11) in a certain amount of DMF, then add the condensing agents HBTU and HOBt, and stir for 5 minutes in an ice-water bath to mix them evenly. Then add the acid-binding agent N-methylmorpholine and the dendritic central unit octaamino POSS hydrochloride, slowly warm the reaction to room temperature and continue the reaction at room temperature for 24 hours. After the reaction is completed, pour the yellow-green solution obtained by the reaction into deionized water, and a white precipitate will appear after slight stirring. The precipitate obtained by centrifugation is washed with deionized water and acetonitrile and purified by column chromatography. The chromatographic stationary phase is 200-300 mesh silica gel, and the mobile phase is a mixed solvent of dichloromethane / methanol = 9 / 1. The yield is about 67%-92%, and the initial product obtained is white crystalline. The initial product is dissolved in dichloromethane, and hydrogen chloride gas is passed through at 30-50°C for BOC deprotection treatment. The final product is distilled under reduced pressure to remove volatiles to obtain a colorless or light yellow oily liquid, which is a dendritic macromolecular crosslinking agent with an amino active group at the end.

[0017] The resin for the PBO fiber reinforced bulletproof composite material comprises an epoxy resin monomer with a phenylene benzoxazole structure and a dendritic macromolecular crosslinking agent with an amino active group at the end.

[0018] In step 1, the bisphenol compound is any one of bisphenol A, bisphenol F and bisphenol S.

[0019] In step 1, the reaction: the reaction temperature is controlled to be 0-5°C, and the mixture is stirred at this temperature for 0.5-2 hours, the mixture is heated to 15-35°C, and the mixture is stirred for 1-3 hours.

[0020] In step 1, the post-treatment includes: filtering the solid and washing it with cold water, and drying the product under vacuum at 85-95° C. for 8-16 hours.

[0021] In step 2, N2H4·H2O is added dropwise to the mixture within 20 to 40 minutes.

[0022] In step 2, the reaction mixture is refluxed at 70-80° C. for 4-6 hours and then cooled.

[0023] In step 2, post-treatment includes: filtering the precipitate and recrystallizing the product with dilute hydrochloric acid.

[0024] In step 3, the carboxyl-containing phenolic compound is any one of p-hydroxybenzoic acid, o-hydroxybenzoic acid, m-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 2,4-dihydroxybenzoic acid, and 4-hydroxy-2-methylbenzoic acid.

[0025] In step 3, the mixture is stirred at 35-45° C. for 0.5-2 hours.

[0026] In step 3, post-treatment includes filtering the solid and washing it with anhydrous ethanol until it is neutral.

[0027] In step 4, the reaction is carried out at 60-70° C. for 3-24 hours.

[0028] The post-treatment comprises: standing still after the reaction is completed, collecting the organic phase with a separatory funnel, removing the upper alkaline water, washing the organic phase with boiling water for several times, and dehydrating and drying to obtain a brown viscous liquid.

[0029] In step (2), the dendrimer cross-linking agent is any one of POSS-Cn-NH2 and POSS-Cn-COOH;

[0030] The n is any one of 3, 6, 8, and 11.

[0031] More preferably, (1) the epoxy resin monomer having a phenylene benzoxazole structure is synthesized using the following technical scheme:

[0032] Step 1: Add concentrated nitric acid dropwise to the stirred toluene, bisphenol compound and glacial acetic acid solution, control the reaction temperature to 0-5°C, and stir the mixture at this temperature for 1 hour. Allow the mixture to warm to room temperature and stir the mixture for 2 hours. Filter the solid and wash with cold water. Dry the product under vacuum at 90°C for 12 hours to obtain a yellow powder, which is the nitrobisphenol compound.

[0033] Step 2: Add the above nitrobisphenol compound, anhydrous ethanol, FeCl3·6H2O and activated carbon into a flask equipped with a mechanical stirrer and a reflux condenser. Add N2H4·H2O dropwise to the mixture within 30 minutes, reflux the reaction mixture at 75°C for 5 hours and then cool to room temperature. Filter the precipitate and recrystallize the product with dilute hydrochloric acid to obtain a white precipitate. The product is an aminobisphenol compound.

[0034] Step 3: Add the above-mentioned aminated bisphenol compound, carboxyl-containing phenolic compound and phosphorus pentoxide to a mixed solution of polyphosphoric acid and methanesulfonic acid, and stir the mixture for 1 hour at 40° C. Filter the solid and wash it with anhydrous ethanol until it is neutral, and the product is a phenolic compound with a bisbenzoxazole structure.

[0035] Step 4: Add the above phenolic compound with a bisbenzoxazole structure and epichlorohydrin to a NaOH solution and react at 65°C for 3-24 hours. After the reaction is completed, let it stand, collect the organic phase using a separatory funnel, remove the upper alkaline water, wash the organic phase with boiling water several times, and dehydrate and dry to obtain a brown viscous liquid, which is an epoxy resin monomer with a phenylene benzoxazole structure.

[0036] According to the present invention, the bisphenol compound is any one of bisphenol A, bisphenol F and bisphenol S.

[0037] According to the present invention, the carboxyl-containing phenolic compound is any one of p-hydroxybenzoic acid, o-hydroxybenzoic acid, m-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 2,4-dihydroxybenzoic acid, and 4-hydroxy-2-methylbenzoic acid.

[0038] Taking bisphenol A as the bisphenol compound and p-hydroxybenzoic acid as the carboxyl-containing phenol compound as an example, the epoxy resin monomer synthesis reaction equation of the present invention is as follows:

[0039]

[0040] (2) The dendrimer crosslinker having an active group at the end is synthesized by the following steps:

[0041] Dissolve the tert-butyloxycarbonyl carbonyl protected straight-chain amino acids (amino acids with carbon atoms of 3, 6, 8, and 11) in a certain amount of DMF, then add the condensing agents HBTU and HOBt, and stir for 5 minutes in an ice-water bath to mix them evenly. Then add the acid-binding agent N-methylmorpholine and the dendritic central unit octaamino POSS hydrochloride, slowly warm the reaction to room temperature and continue the reaction at room temperature for 24 hours. After the reaction is completed, pour the yellow-green solution obtained by the reaction into deionized water, and a white precipitate will appear after slight stirring. The precipitate obtained by centrifugation is washed with deionized water and acetonitrile and purified by column chromatography. The chromatographic stationary phase is 200-300 mesh silica gel, and the mobile phase is a mixed solvent of dichloromethane / methanol = 9 / 1. The yield is about 67%-92%, and the initial product obtained is white crystalline. The initial product is dissolved in dichloromethane, and hydrogen chloride gas is passed through at 30-50°C for BOC deprotection treatment. The final product is distilled under reduced pressure to remove volatiles to obtain a colorless or light yellow oily liquid, which is a dendritic macromolecular crosslinking agent with an amino active group at the end.

[0042] According to the present invention, the amino acid is aminopropionic acid, aminocaproic acid, aminocaprylic acid, or aminoundecanoic acid.

[0043] The dendrimer cross-linking agent synthesis reaction formula of the present invention is as follows:

[0044]

[0045] (3) The method for forming and processing bulletproof composite materials is as follows:

[0046] The dendritic macromolecular crosslinking agent synthesized above with active groups at the end is added to the epoxy resin monomer with phenylene benzoxazole structure in a stoichiometric ratio, stirred evenly and vacuum degassed to obtain epoxy resin glue. PBO fiber fabric is immersed in the above epoxy resin glue, and then dried at 35-45°C (more preferably 40°C) to obtain PBO fiber prepreg. The PBO fiber prepreg is layered in a certain order and hot pressed to obtain a bulletproof composite material.

[0047] According to the present invention, the hot pressing temperature is 80-120° C., the pressure is 5-10 MPa, and the time is 2-6 hours.

[0048] Compared with the prior art, the present invention has the following advantages:

[0049] The present invention adopts an epoxy resin with a phenylene benzoxazole structure as a matrix. The epoxy resin retains the benzene ring skeleton of bisphenol to ensure that its mechanical properties are less affected. At the same time, the benzoxazole structure is introduced through a dehydration condensation reaction to form a π-π interaction with the surface of the PBO fiber, thereby improving the interface bonding between the PBO fiber and the epoxy resin. In order to solve the problem of large brittleness of the epoxy resin after curing, the present invention adopts a dendritic macromolecule with active groups such as amino and carboxyl groups at the end as a curing agent. The spherical three-dimensional structure of the dendritic macromolecule can reduce the shrinkage rate of the epoxy cured product, and the active group can directly participate in the curing reaction to form a three-dimensional network structure. The numerous terminal functional groups can also accelerate the curing reaction speed, and at the same time, the size and spherical structure of the dendritic macromolecule are controlled to toughen the epoxy resin. The ballistic performance of the PBO fiber bulletproof composite material is improved by molding and processing by a dipping method and a hot pressing method. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 The interlaminar shear strength test results of each embodiment and comparative example;

[0051] Figure 2 The impact toughness test results of each embodiment and comparative example are shown;

[0052] Figure 3 The bulletproof V50 value test results of each embodiment and comparative example are shown. DETAILED DESCRIPTION

[0053] The present invention will be further described below in conjunction with specific implementation examples.

[0054] Embodiment 1:

[0055] (1) Synthesis of epoxy resin monomer with phenylene benzoxazole structure:

[0056] Step 1: Add concentrated nitric acid (15 mL) dropwise to a stirred solution of toluene (75 mL), 2,2-bis(4-hydroxyphenyl)propane (15.0 g) and glacial acetic acid (50 mL) over 1 hour at 0°C, and stir the mixture for 1 hour. Warm the mixture to room temperature 25°C and stir the mixture for 2 hours. Filter and wash the solid with cold water. Dry the product under vacuum at 90°C for 12 hours to obtain a yellow powder.

[0057] Step 2: Add 2,2'-bis(4-hydroxy-3-nitrophenyl)propane (6.4 g), anhydrous ethanol (80 mL), FeCl3·6H2O (0.2 g) and activated carbon (1.5 g) to a 250 mL flask with a mechanical stirrer and a reflux condenser. Add N2H4·H2O (15 mL) dropwise to the mixture over 30 minutes. Reflux the reaction mixture at 75°C for 5 hours. Cool the reaction mixture to room temperature 25°C and filter the precipitate. Recrystallize the product with dilute hydrochloric acid to obtain a white precipitate.

[0058] Step 3: Add 2,2'-bis(4-hydroxy-3-aminophenyl)propane (25.8 g), p-hydroxybenzoic acid (27.6 g) and phosphorus pentoxide (11.2 g) to 100 mL of a mixed solution of polyphosphoric acid and methanesulfonic acid, and stir the mixture at 40° C. for 1 hour. Filter the solid and wash with 100 mL of anhydrous ethanol until neutral to obtain a white powder.

[0059] Step 4: Add 4,4'-(propane-2,2-diylbis(benzo[d]oxazole-5,2-diyl))diphenol (47.6g) and epichlorohydrin (23.5g) to 150mL 10% NaOH solution and react at 65°C for 24h. After the reaction is completed, let it stand and use a separatory funnel to collect the organic phase. After removing the upper alkaline water, wash the organic phase with boiling water several times, dehydrate and dry to obtain a brown viscous liquid, which is an epoxy resin monomer with a phenylene benzoxazole structure. The synthetic product was verified by Fourier infrared characterization to be consistent with the design, v (cm -1 )=3030,2930,1691,1640,1505,1363,1330,1222,1059,1021,980,935,851,824,796,737.

[0060] (2) Synthesis of dendrimer crosslinkers with active groups at the ends:

[0061] 378g (0.20mol) BOC-β-alanine was dissolved in 3L DMF, and then 761g (1mol) HBTU and 298g (2.1mol) HOBt were added, and stirred for 5min in an ice-water bath to make it evenly mixed. Subsequently, 364g (3.6mol) N-methylmorpholine and 234g (0.2mol) octaamino POSS hydrochloride were added, and the reaction slowly warmed to room temperature and continued to react at room temperature for 24h. After the reaction was completed, the yellow-green solution obtained by the reaction was poured into 200L deionized water, and a white precipitate was obtained after slight stirring. The white precipitate was obtained by suction filtration, and the precipitate was washed with deionized water and acetonitrile and purified by column chromatography. The chromatographic stationary phase was 200-300 mesh silica gel, and the mobile phase was a mixed solvent of dichloromethane / methanol = 6 / 1. The yield was 82%, and the initial product obtained was white crystals. The initial product was dissolved in dichloromethane and deprotected by passing hydrogen chloride gas at 35°C. The final product was distilled under reduced pressure to remove volatiles to obtain a colorless oily liquid, which was a dendritic macromolecular crosslinker with an amino active group at the end. The synthesized structure was characterized by nuclear magnetic resonance spectroscopy and was consistent with the design. 1 H NMR(POSS-C3-NH2,DMSO-d6,500MHz,ppm),7.79(8H,s,CH2NHCOCH2),8.74(16H,t,NH2),3.01(16H,t,CH2CH2NH CO), 2.96(16H,t,CH2CH2NH), 2.44(16H,t,NHCOCH2CH2), 1.54-1.39(32H,m,CH2CH2CH2), 0.59(16H,br,SiCH2).

[0062] (3) Bulletproof composite material molding and processing:

[0063] The dendritic macromolecular crosslinking agent synthesized above with active groups at the end is added to the epoxy resin monomer with phenylene benzoxazole structure in a stoichiometric ratio, stirred evenly and vacuum degassed to obtain epoxy resin glue. PBO fiber fabric is immersed in the above epoxy resin glue and then dried at 40°C to obtain PBO fiber prepreg. The PBO fiber prepreg is layered in a certain order and hot-pressed at a temperature of 80°C and a pressure of 10MPa for 3 hours to obtain a bulletproof composite material.

[0064] Embodiment 2:

[0065] (1) Synthesis of epoxy resin monomer with phenylene benzoxazole structure:

[0066] Step 1: Add concentrated nitric acid (15 mL) dropwise to a stirred solution of toluene (75 mL), 2,2-bis(4-hydroxyphenyl)propane (15.0 g) and glacial acetic acid (50 mL) over 1 hour at 0°C, and stir the mixture for 1 hour. Warm the mixture to room temperature 25°C and stir the mixture for 2 hours. Filter and wash the solid with cold water. Dry the product under vacuum at 90°C for 12 hours to obtain a yellow powder.

[0067] Step 2: Add 2,2'-bis(4-hydroxy-3-nitrophenyl)propane (6.4 g), anhydrous ethanol (80 mL), FeCl3·6H2O (0.2 g) and activated carbon (1.5 g) to a 250 mL flask with a mechanical stirrer and a reflux condenser. Add N2H4·H2O (15 mL) dropwise to the mixture over 30 minutes. Reflux the reaction mixture at 75°C for 5 hours. Cool the reaction mixture to room temperature 25°C and filter the precipitate. Recrystallize the product with dilute hydrochloric acid to obtain a white precipitate.

[0068] Step 3: Add 2,2'-bis(4-hydroxy-3-aminophenyl)propane (25.8 g), p-hydroxybenzoic acid (27.6 g) and phosphorus pentoxide (11.2 g) to 100 mL of a mixed solution of polyphosphoric acid and methanesulfonic acid, and stir the mixture at 40° C. for 1 hour. Filter the solid and wash with 100 mL of anhydrous ethanol until neutral to obtain a white powder.

[0069] Step 4: Add 4,4'-(propane-2,2-diylbis(benzo[d]oxazole-5,2-diyl))diphenol (47.6g) and epichlorohydrin (23.5g) to 150mL 10% NaOH solution and react at 65°C for 12h. After the reaction is completed, let it stand and use a separatory funnel to collect the organic phase. After removing the upper alkaline water, wash the organic phase with boiling water several times, dehydrate and dry to obtain a brown viscous liquid, which is an epoxy resin monomer with a phenylene benzoxazole structure. The synthetic product was verified by Fourier infrared characterization to be consistent with the design, v (cm -1 )=3030,2930,1691,1640,1505,1363,1330,1222,1059,1021,980,935,851,824,796,737.

[0070] (2) Synthesis of dendrimer crosslinkers with active groups at the ends:

[0071] 462g (2mol) BOC-6-aminocaproic acid was dissolved in 3L DMF, and then 761g (1mol) HBTU and 298g (2.1mol) HOBt were added, and stirred for 5min in an ice-water bath to make it evenly mixed. Subsequently, 364g (3.6mol) N-methylmorpholine and 234g (0.2mol) octaamino POSS hydrochloride were added, and the reaction slowly warmed to room temperature and continued to react at room temperature for 24h. After the reaction was completed, the yellow-green solution obtained by the reaction was poured into 20L deionized water, and a white precipitate appeared after slight stirring. The precipitate obtained by centrifugation was washed with deionized water and acetonitrile and purified by column chromatography. The chromatographic stationary phase was 200-300 mesh silica gel, and the mobile phase was a mixed solvent of dichloromethane / methanol = 9 / 1. The yield was 85%, and the initial product obtained was white crystals. The initial product was dissolved in dichloromethane and deprotected by passing hydrogen chloride gas at 40°C. The final product was distilled under reduced pressure to remove volatiles to obtain a colorless oily liquid, which was a dendritic macromolecular crosslinker with an amino active group at the end. The synthesized structure was characterized by nuclear magnetic resonance spectroscopy and was consistent with the design. 1 H NMR(POSS-C6-NH2,DMSO-d6,500MHz,ppm):7.77(8H,d,CH2NHCOCH2),8.76(16H,t,NH2),3.01(16H,d,CH2CH2NHCO),2.88(16 H,d,CH2CH2NH2),2.04(16H,t,NHCOCH2CH2),1.54-1.39(32H,m,CH2CH2CH2),1.20(16H,m,CH2CH2CH2),0.59(16H,s,SiCH2).

[0072] (3) Bulletproof composite material molding and processing:

[0073] The dendritic macromolecular crosslinking agent synthesized above with active groups at the end is added to the epoxy resin monomer with phenylene benzoxazole structure in a stoichiometric ratio, stirred evenly and vacuum degassed to obtain epoxy resin glue. PBO fiber fabric is immersed in the above epoxy resin glue and then dried at 40°C to obtain PBO fiber prepreg. The PBO fiber prepreg is layered in a certain order and hot-pressed at a temperature of 80°C and a pressure of 10MPa for 3 hours to obtain a bulletproof composite material.

[0074] Embodiment 3:

[0075] (1) Synthesis of epoxy resin monomer with phenylene benzoxazole structure:

[0076] Step 1: Add concentrated nitric acid (15 mL) dropwise to a stirred solution of toluene (75 mL), 4,4-dihydroxydiphenylmethane (12.5 g) and glacial acetic acid (50 mL) over 1 hour at 0°C, and stir the mixture for 1 hour. Warm the mixture to room temperature 25°C and stir the mixture for 2 hours. Filter and wash the solid with cold water. Dry the product under vacuum at 90°C for 12 hours to obtain a yellow powder.

[0077] Step 2: Add 4,4'-methylenebis(2-nitrophenol) (5.8 g), anhydrous ethanol (80 mL), FeCl3·6H2O (0.2 g) and activated carbon (1.5 g) to a 250 mL flask with a mechanical stirrer and a reflux condenser. Add N2H4·H2O (15 mL) dropwise to the mixture over 30 minutes. Reflux the reaction mixture at 75°C for 5 hours. Cool the reaction mixture to room temperature 25°C and filter the precipitate. Recrystallize the product with dilute hydrochloric acid to obtain a white precipitate.

[0078] Step 3: Add 4,4'-methylenebis(2-aminophenol) (23.4 g), p-hydroxybenzoic acid (24.7 g) and phosphorus pentoxide (10.8 g) to 100 mL of a mixed solution of polyphosphoric acid and methanesulfonic acid, and stir the mixture at 40° C. for 1 hour. Filter the solid and wash with 100 mL of anhydrous ethanol until neutral to obtain a white powder.

[0079] Step 4: Add 4,4'-(methylenebis(benzo[d]oxazole-5,2-diyl))diphenol (43.9g) and epichlorohydrin (21.2g) to 150mL 10% NaOH solution and react at 65°C for 24h. After the reaction is completed, let it stand and use a separatory funnel to collect the organic phase. After removing the upper alkaline water, wash the organic phase with boiling water several times and dehydrate to obtain a brown viscous liquid, which is an epoxy resin monomer with a phenylene benzoxazole structure. The synthetic product was verified by Fourier infrared characterization to be consistent with the design, v (cm -1 )=3030,2930,1691,1640,1505,1363,1330,1222,1059,1021,980,935,851,824,796,737.

[0080] (2) Synthesis of dendrimer crosslinkers with active groups at the ends:

[0081] 518g (2mol) of homemade C8-Boc was dissolved in 3L DMF, and then 761g (10mol) HBTU and 298g (21mol) HOBt were added, and stirred for 5min in an ice-water bath to make it evenly mixed. Subsequently, 364g (36mol) N-methylmorpholine and 234g (2mol) octaamino POSS hydrochloride were added, and the reaction slowly warmed to room temperature and continued to react at room temperature for 24h. After the reaction was completed, the yellow-green solution obtained by the reaction was poured into 2L deionized water, and a white precipitate appeared after slight stirring. The precipitate obtained by centrifugation was washed with deionized water and acetonitrile and purified by column chromatography. The chromatographic stationary phase was 200-300 mesh silica gel, and the mobile phase was a mixed solvent of dichloromethane / methanol = 6 / 1. The initial product was a white solid, Rf = 0.6, and the yield was 62.0%. The initial product was dissolved in dichloromethane and deprotected by passing hydrogen chloride gas at 40°C. The final product was distilled under reduced pressure to remove volatiles to obtain a colorless oily liquid, which was a dendritic macromolecular crosslinker with an amino active group at the end. The synthesized structure was characterized by nuclear magnetic resonance spectroscopy and was consistent with the design. 1 H NMR(POSS-C8-NH2,DMSO-d6,500MHz,ppm):7.79(8H,s,CH2NHCOCH2),8.75(16H,s,NH2),3.00(16H,s,CH2CH2NHCO),2.88(16H,s,CH2CH2NH2),2 .05(16H,t,NHCOCH2CH2),1.52-1.39(32H,m,CH2CH2CH2),1.30-1.39(112H,m,CH3,CH2CH2CH2),1.22(48H,s,CH2CH2CH2),0.58(16H,s,SiCH2).

[0082] (3) Bulletproof composite material molding and processing:

[0083] The dendritic macromolecular crosslinking agent synthesized above with active groups at the end is added to the epoxy resin monomer with phenylene benzoxazole structure in a stoichiometric ratio, stirred evenly and vacuum degassed to obtain epoxy resin glue. PBO fiber fabric is immersed in the above epoxy resin glue and then dried at 40°C to obtain PBO fiber prepreg. The PBO fiber prepreg is layered in a certain order and hot-pressed at a temperature of 80°C and a pressure of 10MPa for 3 hours to obtain a bulletproof composite material.

[0084] Embodiment 4:

[0085] (1) Synthesis of epoxy resin monomer with phenylene benzoxazole structure:

[0086] Step 1: Add concentrated nitric acid (15 mL) dropwise to a stirred solution of toluene (75 mL), 2,2-bis(4-hydroxyphenyl)propane (15.0 g) and glacial acetic acid (50 mL) over 1 hour at 0°C, and stir the mixture for 1 hour. Warm the mixture to room temperature 25°C and stir the mixture for 2 hours. Filter and wash the solid with cold water. Dry the product under vacuum at 90°C for 12 hours to obtain a yellow powder.

[0087] Step 2: Add 2,2'-bis(4-hydroxy-3-nitrophenyl)propane (6.4 g), anhydrous ethanol (80 mL), FeCl3·6H2O (0.2 g) and activated carbon (1.5 g) to a 250 mL flask with a mechanical stirrer and a reflux condenser. Add N2H4·H2O (15 mL) dropwise to the mixture over 30 minutes. Reflux the reaction mixture at 75°C for 5 hours. Cool the reaction mixture to room temperature 25°C and filter the precipitate. Recrystallize the product with dilute hydrochloric acid to obtain a white precipitate.

[0088] Step 3: Add 2,2'-bis(4-hydroxy-3-aminophenyl)propane (25.8 g), p-hydroxybenzoic acid (27.6 g) and phosphorus pentoxide (11.2 g) to 100 mL of a mixed solution of polyphosphoric acid and methanesulfonic acid, and stir the mixture at 40° C. for 1 hour. Filter the solid and wash with 100 mL of anhydrous ethanol until neutral to obtain a white powder.

[0089] Step 4: Add 4,4'-(propane-2,2-diylbis(benzo[d]oxazole-5,2-diyl))diphenol (47.6g) and epichlorohydrin (23.5g) to 150mL 10% NaOH solution and react at 65°C for 12h. After the reaction is completed, let it stand and use a separatory funnel to collect the organic phase. After removing the upper alkaline water, wash the organic phase with boiling water several times, dehydrate and dry to obtain a brown viscous liquid, which is an epoxy resin monomer with a phenylene benzoxazole structure. The synthetic product was verified by Fourier infrared characterization to be consistent with the design, v (cm -1 )=3030,2930,1691,1640,1505,1363,1330,1222,1059,1021,980,935,851,824,796,737.

[0090] (2) Synthesis of dendrimer crosslinkers with active groups at the ends:

[0091] 602g (20mol) of homemade C11-Boc was dissolved in 3L DMF, and then 761g (10mol) HBTU and 298g (21mol) HOBt were added, and stirred for 5min in an ice-water bath to make it evenly mixed. Subsequently, 364g (36mol) N-methylmorpholine and 234g (2mol) octaamino POSS hydrochloride were added, and the reaction slowly warmed to room temperature and continued to react at room temperature for 24h. After the reaction was completed, the yellow-green solution obtained by the reaction was poured into 20L deionized water, and a white precipitate appeared after slight stirring. The precipitate was separated by filtration, washed with deionized water and acetonitrile, and purified by column chromatography. The chromatographic stationary phase was 200-300 mesh silica gel, and the mobile phase was a mixed solvent of dichloromethane / methanol = 6 / 1. The initial product was a white solid, Rf = 0.6, and the yield was 58.0%. The initial product was dissolved in dichloromethane and deprotected by passing hydrogen chloride gas at 40°C. The final product was distilled under reduced pressure to remove volatiles to obtain a colorless oily liquid, which was a dendritic macromolecular crosslinker with an amino active group at the end. The synthesized structure was characterized by nuclear magnetic resonance spectroscopy and was consistent with the design. 1 H NMR(POSS-C11-NH2,DMSO-d6,500MHz,ppm):7.79(8H,s,CH2NHCOCH2),8.74(16H,s,NH2),2.99(16H,s,CH2CH2NHCO),2.87( 16H,d,CH2CH2NH2), 2.04(16H,t,NHCOCH2CH2), 1.45(32H,s,CH2CH2CH2), 1.22(112H,s,CH2CH2CH2), 0.58(16H,s,SiCH2).

[0092] (3) Bulletproof composite material molding and processing:

[0093] The dendritic macromolecular crosslinking agent synthesized above with active groups at the end is added to the epoxy resin monomer with phenylene benzoxazole structure in a stoichiometric ratio, stirred evenly and vacuum degassed to obtain epoxy resin glue. PBO fiber fabric is immersed in the above epoxy resin glue and then dried at 40°C to obtain PBO fiber prepreg. The PBO fiber prepreg is layered in a certain order and hot-pressed at a temperature of 80°C and a pressure of 10MPa for 3 hours to obtain a bulletproof composite material.

[0094] Embodiment 5:

[0095] (1) Synthesis of epoxy resin monomer with phenylene benzoxazole structure:

[0096] Step 1: Add concentrated nitric acid (15 mL) dropwise to a stirred solution of toluene (75 mL), 2,2-bis(4-hydroxyphenyl)propane (15.0 g) and glacial acetic acid (50 mL) over 1 hour at 0°C, and stir the mixture for 1 hour. Warm the mixture to room temperature 25°C and stir the mixture for 2 hours. Filter and wash the solid with cold water. Dry the product under vacuum at 90°C for 12 hours to obtain a yellow powder.

[0097] Step 2: Add 2,2'-bis(4-hydroxy-3-nitrophenyl)propane (6.4 g), anhydrous ethanol (80 mL), FeCl3·6H2O (0.2 g) and activated carbon (1.5 g) to a 250 mL flask with a mechanical stirrer and a reflux condenser. Add N2H4·H2O (15 mL) dropwise to the mixture over 30 minutes. Reflux the reaction mixture at 75°C for 5 hours. Cool the reaction mixture to room temperature 25°C and filter the precipitate. Recrystallize the product with dilute hydrochloric acid to obtain a white precipitate.

[0098] Step 3: Add 2,2'-bis(4-hydroxy-3-aminophenyl)propane (25.8 g), p-hydroxybenzoic acid (27.6 g) and phosphorus pentoxide (11.2 g) to 100 mL of a mixed solution of polyphosphoric acid and methanesulfonic acid, and stir the mixture at 40° C. for 1 hour. Filter the solid and wash with 100 mL of anhydrous ethanol until neutral to obtain a white powder.

[0099] Step 4: Add 4,4'-(propane-2,2-diylbis(benzo[d]oxazole-5,2-diyl))diphenol (47.6g) and epichlorohydrin (23.5g) to 150mL 10% NaOH solution and react at 65°C for 12h. After the reaction is completed, let it stand and use a separatory funnel to collect the organic phase. After removing the upper alkaline water, wash the organic phase with boiling water several times, dehydrate and dry to obtain a brown viscous liquid, which is an epoxy resin monomer with a phenylene benzoxazole structure. The synthetic product was verified by Fourier infrared characterization to be consistent with the design, v (cm -1 )=3030,2930,1691,1640,1505,1363,1330,1222,1059,1021,980,935,851,824,796,737.

[0100] (2) Synthesis of dendrimer crosslinkers with active groups at the ends:

[0101] 236g (0.68mol) (S)-2,6-di-tert-butoxycarbonylaminocaproic acid (BOC-Lys(BOC)-OH) was dissolved in 2000mL N,N-dimethylformamide (DMF), and then 139g (1.36mol) N-methylmorpholine (NMM) was added. A mixture of 144g (0.68mol) carbodiimide (EDCI) and 101g (0.75mol) 1-hydroxybenzotriazole (HOBT) was added under ice bath. After activation for 30min, 50g (0.043mol) POSS amino hydrochloride was added. The reaction was gradually warmed to room temperature and the reaction lasted for 24h. After the reaction was completed, a yellow solution was obtained, which was poured into 1000mL (0.50mol / L) of citric acid-water solution, and a white precipitate was produced after the two were mixed. The white precipitate was obtained by filtering with a Buchner funnel, and the white precipitate was washed with acetonitrile and purified by a chromatographic column. The stationary phase of the silica gel column is 200-300 mesh silica gel, and the mobile phase is a dichloromethane / methanol mixed solvent with a volume ratio of 15:1. The initial product obtained has a white crystalline appearance and a yield of 90%. The initial product is dissolved in dichloromethane and subjected to a BOC deprotection treatment at 45°C by passing hydrogen chloride gas. The final product is distilled under reduced pressure to remove volatiles to obtain a colorless oily liquid, which is a dendritic macromolecular cross-linking agent with an amino active group at the end. The synthesized structure is characterized by nuclear magnetic resonance spectroscopy and is consistent with the design. 1 HNMR(POSS-Lys-NH2,DMSO-d6,500MHz,ppm),8.70(16H,t,CHNH2),8.36(1H,t,CH2NH),3.79(8H,t,CH(CH2)NHCO) ,2.99(32H,t,CH2CH2NH-Boc),2.83(16H,t,CH(CH2)NHCO),1.54-1.39(48H,m,CH2CH2CH2),0.52(16H,t,SiCH2).

[0102] (3) Bulletproof composite material molding and processing:

[0103] The dendritic macromolecular crosslinking agent synthesized above with active groups at the end is added to the epoxy resin monomer with phenylene benzoxazole structure in a stoichiometric ratio, stirred evenly and vacuum degassed to obtain epoxy resin glue. PBO fiber fabric is immersed in the above epoxy resin glue and then dried at 40°C to obtain PBO fiber prepreg. The PBO fiber prepreg is layered in a certain order and hot-pressed at a temperature of 120°C and a pressure of 5MPa for 2 hours to obtain a bulletproof composite material.

[0104] Comparative Example:

[0105] The commercially available E51 epoxy resin and curing agent H256 were mixed evenly in a mass ratio of 100:30 and then vacuum degassed to obtain epoxy resin glue. The PBO fiber fabric was immersed in the above epoxy resin glue and then dried at 40°C to obtain PBO fiber prepreg. The PBO fiber prepreg was layered in a certain order and hot-pressed at a temperature of 120°C and a pressure of 5MPa for 2 hours to obtain a bulletproof composite material.

[0106] The bulletproof composite material prepared by the above method improves the interface compatibility between epoxy resin and PBO fiber by introducing p-phenylene benzobisoxazole structure into epoxy resin monomer; dendritic macromolecular crosslinking agent is used as epoxy resin toughening curing agent to improve the impact resistance of the composite material. Compared with the composite material made of ordinary commercially available epoxy resin, the interlaminar shear strength, impact toughness and bulletproof V50 value of the composite material prepared by the method of the present invention are greatly improved.

[0107] The interlaminar shear strength test results of each embodiment and comparative example are as follows: Figure 1 As shown, the interlaminar shear strength of the PBO fiber / epoxy resin composite material prepared by the method of the present invention is significantly improved compared with the PBO fiber composite material prepared by ordinary epoxy resin.

[0108] The impact toughness test results of each embodiment and comparative example are as follows: Figure 2 As shown, the impact toughness of the PBO fiber / epoxy resin composite material prepared by the method of the present invention is significantly improved compared with the PBO fiber composite material prepared by ordinary epoxy resin.

[0109] The test results of the bulletproof V50 values ​​of the embodiments and comparative examples are as follows: Figure 3 As shown, the bulletproof V50 value of the PBO fiber / epoxy resin composite material prepared by the method of the present invention is significantly improved compared with the PBO fiber composite material prepared by ordinary epoxy resin.

[0110] The above are only embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing a resin for a PBO fiber-reinforced bulletproof composite material, characterized in that: The following steps are involved: (1) Synthesis of epoxy resin monomers with phenylene benzoxazole structure: Step 1: adding concentrated nitric acid dropwise to the stirred toluene, bisphenol compound and glacial acetic acid solution, and after the reaction and post-treatment, obtaining a product of yellow powder, namely the nitrobisphenol compound; Step 2: adding the nitrated bisphenol compound, anhydrous ethanol, FeCl3·6H2O and activated carbon into a reactor equipped with a mechanical stirrer and a reflux condenser, dropping N2H4·H2O into the mixture, refluxing the reaction mixture and cooling it, and post-treating the product to obtain a white precipitate, which is the amino bisphenol compound; Step 3: adding an aminated bisphenol compound, a carboxyl-containing phenolic compound and phosphorus pentoxide to a mixed solution of polyphosphoric acid and methanesulfonic acid, stirring the mixture, and performing post-treatment to obtain a product that is a phenolic compound having a bisbenzoxazole structure; Step 4: adding a phenolic compound having a bisbenzoxazole structure and epichlorohydrin to a NaOH aqueous solution, reacting at 55-75° C. for 3-24 hours, and obtaining a brown viscous liquid after post-treatment after the reaction is completed, which is an epoxy resin monomer having a phenylene benzoxazole structure; (2) Synthesis of dendrimer crosslinkers with active groups at the ends: A tert-butyloxycarbonyl protected straight-chain amino acid, the carbon number of the straight-chain amino acid is 3, 6, 8, 11, is dissolved in a solvent, and then a condensing agent is added, and the mixture is mixed evenly in an ice-water bath, and then an acid-binding agent N-methylmorpholine and a dendritic central unit octaamino POSS hydrochloride are added, and the temperature is raised to 15-35° C. and the reaction is continued for 18-30 hours. After the reaction is completed, the yellow-green solution obtained by the reaction is poured into deionized water, and a white precipitate appears after stirring. The precipitate is obtained by centrifugation, washed with deionized water and acetonitrile, and purified by column chromatography. The obtained initial product is a white crystal. The initial product is dissolved in dichloromethane, and hydrogen chloride gas is passed at 30-50° C. to carry out a BOC protection treatment. The final product is subjected to reduced pressure distillation to remove volatiles to obtain a colorless or light yellow oily liquid, which is a dendritic macromolecular cross-linking agent with an amino active group at the end; The resin for the PBO fiber reinforced bulletproof composite material comprises an epoxy resin monomer with a phenylene benzoxazole structure and a dendritic macromolecular crosslinking agent with an amino active group at the end.

2. The method for preparing a resin for PBO fiber reinforced bulletproof composite material according to claim 1, characterized in that: In step 1, the bisphenol compound is any one of bisphenol A, bisphenol F, and bisphenol S; In step 1, the reaction: controlling the reaction temperature to 0-5°C, stirring the mixture at the temperature for 0.5-2 hours, raising the temperature of the mixture to 15-35°C, and stirring the mixture for 1-3 hours; In step 1, the post-treatment includes: filtering the solid and washing it with cold water, and drying the product under vacuum at 85-95° C. for 8-16 hours.

3. The method for preparing a resin for PBO fiber reinforced bulletproof composite material according to claim 1, characterized in that: In step 2, N2H4·H2O is added dropwise to the mixture within 20 to 40 minutes; In step 2, the reaction mixture is refluxed at 70-80° C. for 4-6 hours and then cooled; In step 2, post-treatment includes: filtering the precipitate and recrystallizing the product with dilute hydrochloric acid.

4. The method for preparing a resin for PBO fiber reinforced bulletproof composite material according to claim 1, characterized in that: In step 3, the carboxyl-containing phenolic compound is any one of p-hydroxybenzoic acid, o-hydroxybenzoic acid, m-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 2,4-dihydroxybenzoic acid, and 4-hydroxy-2-methylbenzoic acid.

5. The method for preparing a resin for PBO fiber reinforced bulletproof composite material according to claim 1, characterized in that: In step 3, stirring the mixture at 35-45° C. for 0.5-2 hours; In step 3, post-treatment includes filtering the solid and washing it with anhydrous ethanol until it is neutral.

6. The method for preparing a resin for PBO fiber reinforced bulletproof composite material according to claim 1, characterized in that: In step 4, react at 60-70°C for 3-24h; The post-treatment comprises: standing still after the reaction is completed, collecting the organic phase with a separatory funnel, removing the upper alkaline water, washing the organic phase with boiling water for several times, and dehydrating and drying to obtain a brown viscous liquid.

7. The method for preparing a resin for PBO fiber reinforced bulletproof composite material according to claim 1, characterized in that: In step (2), the dendrimer crosslinker having an amino active group at the end is POSS-Cn-NH2; The n is any one of 3, 6, 8, and 11.

8. Use of the resin for PBO fiber reinforced ballistic-proof composite materials prepared by the preparation method according to any one of claims 1 to 7 in the preparation of ballistic-proof composite materials.

9. The use according to claim 8, characterized in that: include: Adding a dendrimer crosslinker having an active group at the end into an epoxy resin monomer having a phenylene benzoxazole structure in a stoichiometric ratio, stirring evenly and then vacuum degassing to obtain an epoxy resin glue solution; The PBO fiber fabric is immersed in epoxy resin glue and then dried at 35-45°C to obtain a PBO fiber prepreg. The PBO fiber prepreg is layered in sequence and hot pressed to obtain a bullet-proof composite material.

10. The use according to claim 9, characterized in that: The hot pressing temperature is 80-120°C, the pressure is 5-10MPa, and the time is 2-6 hours.

Images