Benzoxazine reactive diluent as well as preparation method and application thereof

Abstract

The invention discloses a benzoxazine reactive diluent which is characterized in that an N atom on an oxazine ring is connected with a benzene ring, the benzene ring is provided with a substituent R2, and the benzene ring connected with the oxazine ring is provided with a substituent R1 at the ortho-position of O on the oxazine ring. The preparation method comprises the following steps of: mixing aromatic monophenol with ortho-substituted phenolic groups, aromatic monoamine with substituent groups and paraformaldehyde which are used as raw materials according to a molar ratio of 1: (1-1.5): (2-2.8), adding 1-10 times of volume of organic solvent, reacting for 1-2 hours at 70-90 DEG C, filtering, washing, and drying to obtain the polyformaldehyde. And then cooling, suction filtration, washing and vacuum drying are performed respectively to obtain the liquid monobenzoxazine reactive diluent at room temperature. The reactive diluent provided by the invention solves the problem of two-phase incompatibility caused by using styrene as a benzoxazine diluent in a traditional method. In addition, the problem that the heat resistance of a cured product is easily reduced due to the use of a non-benzoxazine reactive diluent is solved, and the good heat resistance of polybenzoxazine can be fully exerted.

Description

Technical Field

[0001] The invention relates to the technical field of thermosetting resins, and in particular to a reactive diluent for a thermosetting resin system, and in particular to the structure of a reactive diluent for a benzoxazine system and a preparation method thereof. Background Art

[0002] Benzoxazine resin is a thermosetting resin. The monomer can be cross-linked by ring opening under heating or under the action of catalyst to form polybenzoxazine, which is widely used in the fields of construction, electronic packaging, aerospace, and automobile industry.

[0003] As is known to all, for thermosetting resins, different processing techniques have different requirements for resin viscosity. Some processing techniques require a specific range of viscosity, so the viscosity of the resin is very important. For this reason, various methods for adjusting the viscosity of the resin have been developed. Typical methods include active diluent method and inactive diluent method. For epoxy resin, which is also a thermosetting resin, both active diluent method and inactive diluent method have been studied a lot, and the diluent system is very rich. Different diluents can be selected to adjust the viscosity according to the requirements of the processing technology. However, for benzoxazine, research in this area is relatively scarce at present. There are two main types of known benzoxazine diluents. Inactive diluents are mainly organic solvents, including acetone, chloroform, ether, butanone and dichloromethane, which can effectively reduce the viscosity of the benzoxazine system, but the main problem is that the solvent is difficult to completely remove, and it is easy to form bubbles during the material molding process, resulting in surface defects and internal voids in the material, thereby bringing quality risks to the product. The active diluent is mainly styrene (Liu Xiangdong, Biobased composites prepared using an environmentally friendly water-slurry methodology, Industrial & Engineering Chemistry Research, 2018 Vol. 57 No. 23). Styrene has a better effect on adjusting the viscosity of benzoxazine, but there are two main problems: first, styrene and benzoxazine do not react with each other, but each polymerizes to form polybenzoxazine and polystyrene. There are two polymer networks in the curing system, which are prone to deterioration of material properties due to phase separation. Secondly, the heat resistance of polystyrene itself is poor, which is much lower than the heat resistance of polybenzoxazine. Using styrene for benzoxazine diluent will reduce the heat resistance of the final material. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to provide a reactive diluent for diluting the benzoxazine system, which can maintain the performance and heat resistance of the benzoxazine material. Another technical problem to be solved by the present invention is to provide a preparation method of the diluent. And to provide the application of the diluent.

[0005] The technical solution of the present invention is:

[0006] A benzoxazine active diluent, wherein the N atom on the oxazine ring is connected to a benzene ring, the benzene ring carries a substituent R2, and the benzene ring connected to the oxazine ring is connected to a substituent R1 at the ortho position of the O atom on the oxazine ring; the molecular structure of the diluent is as follows:

[0007]

[0008] The R1 is an alkyl chain, and R2 is an alkyl chain or an alkyl chain containing an ether bond. R2 is an alkyl chain or an alkyl chain containing an ether bond, and can be located at the ortho, meta, or para position of the N atom of the benzoxazine ring, but preferably at the meta and para positions.

[0009] R1 must be located in the ortho position of the O atom of the benzoxazine ring. If the substituent R1 is located in the ortho, para or meta position of the phenolic hydroxyl group, the melting point of the resin is often high, and due to the regular structure, the resin is easy to crystallize at room temperature and is not suitable for use as a reactive diluent.

[0010] According to the benzoxazine reactive diluent of the present invention, preferably, the R1 is an alkyl chain of no more than three carbon atoms; and the length of the R2 chain is no more than 5 carbon atoms.

[0011] The R1 is preferably an alkyl chain with no more than three carbon atoms, such as methyl, ethyl and propyl. When the alkyl chain length exceeds three carbon atoms, it can still be used as a benzoxazine active diluent, but the heat resistance of the system will be sharply reduced after curing. However, it can be used as an active diluent for benzoxazine systems that do not require high temperature resistance.

[0012] When the chain length of R2 exceeds 5 carbon atoms, it can still be used as a benzoxazine active diluent, but the heat resistance of the system will decrease sharply after curing. However, it can be used as an active diluent for benzoxazine systems that do not require high temperature resistance.

[0013] According to the benzoxazine active diluent of the present invention, preferably, R2 is selected from one of the following structures:

[0014]

[0015] According to the benzoxazine active diluent of the present invention, preferably, the benzoxazine active diluent is liquid at room temperature, and its melting point ranges from -20 to 30°C.

[0016] The present invention also provides a method for preparing the above-mentioned benzoxazine active diluent, comprising the following steps:

[0017] (1) adding a monophenol with a substituent R1, a monoamine with a substituent R2, polyformaldehyde, and 1-10 times the volume of an organic solvent in a molar ratio of 1:1-1.5:2-2.8, mixing and dissolving evenly, reacting at 70-90° C. for 1-2 hours, and then heating to 100-130° C. for 6-8 hours; wherein R1 is an alkyl chain, and R2 is an alkyl chain or an alkyl chain containing an ether bond;

[0018] (2) The system is cooled, filtered, washed and vacuum dried to obtain a liquid monobenzoxazine monomer.

[0019] The present invention provides a method for preparing the above-mentioned benzoxazine active diluent, using a monophenol with a substituent R1, a monoamine with a substituent R2, and paraformaldehyde as raw materials, and reacting to prepare benzoxazine that can be used as an active diluent. The chemical reaction equation is as follows:

[0020]

[0021] According to the method for preparing a benzoxazine active diluent of the present invention, preferably, the monophenol with substituent R1 is an aromatic phenol with substituent R1; the monoamine with substituent R2 is an aromatic amine compound with substituent R2. Here, whether it is a monoamine or a monophenol, there can be only one benzene ring.

[0022] According to the method for preparing a benzoxazine active diluent of the present invention, preferably, in the monophenol with substituent R1, the substituent R1 is located at the ortho position of the phenolic hydroxyl group.

[0023] According to the method for preparing a benzoxazine reactive diluent of the present invention, preferably, R1 is an alkyl chain of no more than three carbon atoms; and the length of the R2 chain is no more than 5 carbon atoms.

[0024] According to the method for preparing a benzoxazine active diluent of the present invention, preferably, the solvent is an organic solvent that can dissolve reactants and products, so that the reaction system is a homogeneous system. The solvent in the above steps is selected differently depending on the different phenol and amine compounds. More preferably, it is one or a mixture of several of dioxane, toluene, xylene, dimethylformamide, dimethyl sulfoxide, etc.

[0025] In the washing process in the above steps, sodium hydroxide solution is used for washing first, and then a large amount of deionized water is used for washing until the pH value reaches neutral. More preferably, the concentration of the sodium hydroxide solution is 0.1-1 mol / L.

[0026] Furthermore, the R2 is located at the meta position and the para position of the amine group of the aromatic amine compound.

[0027] The present invention also provides the use of the above-mentioned benzoxazine active diluent in adjusting the viscosity of benzoxazine.

[0028] The present invention develops a new monobenzoxazine with a specific structure as an active diluent. This monobenzoxazine diluent is different from a styrene-based active diluent. First, this diluent is also a benzoxazine. During the curing process, due to the cross-linking of the benzoxazine ring, the system forms a uniform cross-linked network and does not produce a phase separation phenomenon. Secondly, since only one polymer, polybenzoxazine, exists in the system after curing, the heat resistance of the cured product will not be reduced, and the good heat resistance of polybenzoxazine can be fully utilized. The problem of reducing the heat resistance of the material caused by the styrene diluent method is solved.

[0029] Beneficial effects:

[0030] (1) The present invention uses a new liquid benzoxazine with a specific structure as an active diluent. This diluent is also a benzoxazine. During the curing process, the benzoxazine undergoes ring-opening crosslinking to form a uniform crosslinked network without phase separation. After curing, the system is a homogeneous network. This solves the problem of two-phase incompatibility caused by using styrene as a benzoxazine diluent in the traditional method.

[0031] (2) There is only a polybenzoxazine network in the solidified material, which solves the problem of heat resistance of the solidified material and can give full play to the good heat resistance of polybenzoxazine. After the obtained diluent is added to the benzoxazine resin, the room temperature viscosity of the obtained material is lower than 10Pa·s (the room temperature viscosity can be further lower than 5Pa·s), and the 5% thermal decomposition temperature of the solidified material is above 300°C. In the prior art, styrene is generally used as a diluent. Since the decomposition temperature of polystyrene is around 250°C, the heat resistance of the benzoxazine solidified material prepared by the technology of the present invention is greatly improved compared with the prior art.

[0032] (3) The problem of bubbles and internal voids in the material molding process caused by solvent residue when using solvent as an inactive diluent is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 1HNMR spectrum of the benzoxazine diluent obtained in Example 1;

[0034] Figure 2 ESI mass spectrum of the benzoxazine diluent obtained in Example 1;

[0035] Figure 3 1HNMR spectrum of the benzoxazine diluent obtained in Example 2;

[0036] Figure 4 ESI mass spectrum of the benzoxazine diluent obtained in Example 2;

[0037] Figure 5 1HNMR spectrum of the benzoxazine diluent obtained in Example 3;

[0038] Figure 6 ESI mass spectrum of the benzoxazine diluent obtained in Example 3; DETAILED DESCRIPTION

[0039] The following provides a specific implementation of the novel monobenzoxazine resin that can be used as a reactive diluent and the preparation method thereof of the present invention.

[0040] Example 1

[0041] In a single-necked flask equipped with magnetic stirring and condensation reflux, add o-cresol (0.1mol, 10.8g), o-anisidine (0.1mol, 12.3g), polyformaldehyde (0.2mol, 6g) and 100ml dioxane, stir evenly and heat to 70°C. After reacting for 1h, heat to 100°C and continue to react for 6h. After the reaction is completed, wait for the system to cool and filter. Pour the liquid sample obtained by filtration into 0.5mol / L sodium hydroxide solution, and then pour the bottom liquid into deionized water for washing. The organic phase after separation is placed in a vacuum oven and dried for 8h to obtain a liquid benzoxazine monomer. After the diluent obtained in this embodiment is added to the benzoxazine resin, the room temperature viscosity of the obtained material is 0.5Pa·s, the peak curing temperature is 227°C, and the 5% thermal decomposition temperature of the cured product is 343°C.

[0042] The structural formula of the benzoxazine monomer in this embodiment is:

[0043]

[0044] The benzoxazine in this example was characterized by NMR, using deuterated DMSO as solvent and tetramethylsilane (TMS) as internal standard, and the obtained 1 HNMR spectrum, see attached Figure 1 .

[0045] Attached Figure 1 The absorption peaks of aromatic protons appear at 8.04-6.69 ppm, and the peaks at 5.41 ppm (O-CH2-N) and 4.56 ppm (Ar-CH2-N) prove the formation of oxazine ring. The single peaks at 2.11 ppm and 3.68 ppm correspond to the characteristic peaks of hydrogen atoms of methyl and methoxy groups on the benzene ring, respectively.

[0046] Attached Figure 2This is the ESI mass spectrum. The theoretical mass-to-charge ratio of the monomer is 255, which is consistent with the measured molecular ion peak, proving that the diluent was successfully synthesized.

[0047] Example 2

[0048] In a single-necked flask equipped with magnetic stirring and condensation reflux, o-cresol (0.1mol, 10.8g), p-methoxyaniline (0.1mol, 12.3g), polyformaldehyde (0.2mol, 6g) and 100ml dioxane were added, stirred evenly and heated to 90°C. After reacting for 1h, the temperature was raised to 100°C and the reaction was continued for 7h. After the reaction was completed, the system was cooled and filtered, and the liquid sample obtained by filtration was poured into a 0.5mol / L sodium hydroxide solution, and then the bottom liquid was poured into deionized water for washing. The organic phase after separation was placed in a vacuum oven and dried for 8h to obtain a liquid benzoxazine monomer. After the diluent obtained in this embodiment was added to the benzoxazine resin, the room temperature viscosity of the obtained material was 0.8Pa·s, the peak curing temperature was 202°C, and the 5% thermal decomposition temperature of the cured product was 346°C.

[0049] The structural formula of the benzoxazine monomer in this embodiment is:

[0050]

[0051] The benzoxazine in this example was characterized by NMR, using deuterated DMSO as solvent and tetramethylsilane (TMS) as internal standard, and the obtained 1 HNMR spectrum, see attached Figure 3 .

[0052] Attached Figure 3 The absorption peaks of aromatic protons appear at 8.04-6.69 ppm, and the peaks at 5.39 ppm (O-CH2-N) and 4.54 ppm (Ar-CH2-N) prove the formation of oxazine ring. The single peaks at 2.09 ppm and 3.67 ppm correspond to the characteristic peaks of hydrogen atoms of methyl and methoxy groups on the benzene ring, respectively.

[0053] Attached Figure 4 This is the ESI mass spectrum. The theoretical mass-to-charge ratio of the monomer is 255, which is consistent with the measured molecular ion peak, proving that the diluent was successfully synthesized.

[0054] Example 3

[0055] In a single-necked flask equipped with magnetic stirring and condensation reflux, o-cresol (0.1mol, 10.8g), p-butylaniline (0.1mol, 14.9g), polyformaldehyde (0.2mol, 6g) and 100ml of dioxane were added, stirred evenly and heated to 80°C. After reacting for 1h, the temperature was raised to 100°C and the reaction was continued for 8h. After the reaction was completed, the system was cooled and filtered, and the liquid sample obtained by filtration was poured into a 0.5mol / L sodium hydroxide solution, and then the bottom liquid was poured into deionized water for washing. The organic phase after separation was placed in a vacuum oven and dried for 8h to obtain a liquid benzoxazine monomer. After the diluent obtained in this embodiment was added to the benzoxazine resin, the room temperature viscosity of the obtained material was 0.7Pa·s, the peak curing temperature was 221°C, and the 5% thermal decomposition temperature of the cured product was 327°C.

[0056] The structural formula of the benzoxazine monomer in this embodiment is:

[0057]

[0058] The benzoxazine in this example was characterized by NMR, using deuterated DMSO as solvent and tetramethylsilane (TMS) as internal standard, and the obtained 1 HNMR spectrum, see attached Figure 5 .

[0059] Attached Figure 6 In the figure, the absorption peaks of aromatic protons appear at 8.04-6.69 ppm, and the peaks at 5.42 ppm (O-CH2-N) and 4.57 ppm (Ar-CH2-N) prove the formation of oxazine ring. The single peak at 2.07 ppm corresponds to the characteristic peak of methyl hydrogen on the benzene ring.

[0060] The signals in the range of 0.68-1.64 ppm correspond to the characteristic peaks of hydrogen of long alkyl side chains.

[0061] Attached Figure 6 The figure is the ESI mass spectrum. The theoretical mass-to-charge ratio of the monomer is 281, which is consistent with the measured molecular ion peak, proving that the diluent was successfully synthesized.

[0062] The above embodiments are only for illustrating the basic features of the concept of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the concept of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A benzoxazine active diluent, characterized in that: The N atom on the oxazine ring is connected to a benzene ring, the benzene ring carries a substituent R2, and the benzene ring connected to the oxazine ring is connected to a substituent R1 at the ortho position of the O atom on the oxazine ring; the molecular structure of the diluent is as follows: The R1 is an alkyl chain, and R2 is an alkyl chain or an alkyl chain containing an ether bond.

2. A benzoxazine reactive diluent according to claim 1, characterized in that: The R1 is an alkyl chain of no more than three carbon atoms; the length of the R2 chain is no more than 5 carbon atoms.

3. A benzoxazine reactive diluent according to claim 1, characterized in that: R2 is selected from one of the following structures:

4. The benzoxazine reactive diluent according to claim 1, characterized in that: The melting point of the benzoxazine active diluent is in the range of -20 to 30°C.

5. The method for preparing a benzoxazine active diluent according to claim 1, characterized in that: The steps include: (1) adding a monophenol with a substituent R1, a monoamine with a substituent R2, polyformaldehyde, and 1-10 times the volume of an organic solvent in a molar ratio of 1:1-1.5:2-2.8, mixing and dissolving evenly, reacting at 70-90° C. for 1-2 hours, and then heating to 100-130° C. for 6-8 hours; wherein R1 is an alkyl chain, and R2 is an alkyl chain or an alkyl chain containing an ether bond; (2) The system is cooled, filtered, washed and vacuum dried to obtain a liquid monobenzoxazine monomer.

6. The method for preparing a benzoxazine reactive diluent according to claim 5, characterized in that: The monophenol with substituent R1 is an aromatic phenol with substituent R1; the monoamine with substituent R2 is an aromatic amine compound with substituent R2.

7. The method for preparing a benzoxazine reactive diluent according to claim 5, characterized in that: In the monophenol with substituent R1, the substituent R1 is located at the ortho position of the phenolic hydroxyl group; and the R2 is located at the meta position and para position of the amine group of the aromatic amine compound.

8. The method for preparing a benzoxazine reactive diluent according to claim 5, characterized in that: The organic solvent can dissolve reactants and products, making the reaction system a homogeneous system.

9. The method for preparing a benzoxazine reactive diluent according to claim 5 or 8, characterized in that: The organic solvent is selected from one or more of the following components: dioxane, toluene, xylene, dimethylformamide, and dimethyl sulfoxide.

10. Use of the benzoxazine active diluent according to claim 1 in adjusting the viscosity of benzoxazine.

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