Flame-retardant polyhydroxy melamine derivative and preparation method thereof

Abstract

The invention discloses a flame-retardant polyhydroxy melamine derivative and a preparation method thereof, and belongs to the field of high polymer material synthesis. According to the preparation method disclosed by the invention, 2, 2-dimethylolpropionic acid methyl ester and hexamethylol melamine are taken as raw materials, and melamine is modified through transesterification. Compared with the prior art, the product quality can be greatly improved, so that the product meets the production requirements of high-transparency epoxy resin and polyester resin, and the method has very good popularization and application values.

Description

Technical Field

[0001] This invention relates to the field of polymer material synthesis, specifically providing a flame-retardant polyhydroxy melamine derivative and its preparation method. Background Technology

[0002] Epoxy and polyester resins are widely used in aerospace, electronics, and composite materials industries due to their excellent mechanical properties, adhesive properties, and electrical insulation. However, because these resins are mainly composed of carbon, hydrogen, and oxygen, their limiting oxygen index (LOI) is usually low, making them highly flammable, which limits their application in environments with stringent fire protection requirements.

[0003] Melamine has an extremely high nitrogen content (approximately 66%), and at high temperatures it can decompose to release nitrogen gas (a non-combustible gas) and promote carbon formation, making it a recognized green and highly efficient flame retardant. However, ordinary melamine has poor solubility and is difficult to directly participate in resin polymerization.

[0004] In their paper "Synthesis and characterization of solvent-free hybrid alkyd resin with hyperbranched melamine core," Gungor Gunduz, Nagehan Keskin, and others synthesized a hyperbranched monomer with terminal hydroxyl groups by reacting hexamethylol melamine (HMM) with 2,2-dimethylolpropionic acid (DMPA). However, because the reaction was carried out under acidic conditions with acidic catalysts such as p-toluenesulfonic acid (p-TSA), water was generated during the reaction, and the reaction temperature needed to reach 140°C. The raw material, hexamethylol melamine (HMM), is highly thermosensitive. Under high temperature and acidic conditions, the hydroxymethyl groups between HMM molecules readily undergo self-condensation to form ether bonds, leading to a sudden increase in viscosity or even "burst polymerization" (gelation) in the later stages of the reaction. Furthermore, prolonged exposure to temperatures above 140°C inevitably results in thermal oxidation of the product, causing the final resin to have a yellowish or darker color. This is a fatal flaw for epoxy resin applications requiring high transparency, severely limiting the product's application areas. Summary of the Invention

[0005] This invention addresses the shortcomings of the prior art by providing a method for preparing flame-retardant polyhydroxy melamine derivatives suitable for industrial-scale production.

[0006] The technical solution adopted by this invention to solve its technical problem is: a method for preparing flame-retardant polyhydroxy melamine derivatives, characterized by using methyl 2,2-dimethylolpropionate and hexamethylol melamine as raw materials, and obtaining the terminal hydroxyl monomer shown in Formula I through transesterification reaction. .

[0007] Preferably, the method for preparing the flame-retardant polyhydroxy melamine derivative of the present invention includes: S1. Add measured amounts of hexamethylol melamine, methyl 2,2-dimethylolpropionate, and alkaline catalyst to the dispersant and react at 75~100℃ for 5~8 hours; S2. Neutralize the alkaline catalyst, allow it to stand and separate into phases, and remove low-boiling substances from the lower layer to obtain the terminal hydroxyl monomer shown in Formula I.

[0008] Preferably, the molar ratio of hexamethylol melamine to methyl 2,2-dimethylol propionate is 1:6~7, and particularly preferably 1:6~6.3.

[0009] Preferably, the dispersant is toluene or xylene, and the amount of dispersant used is 4 to 10 times the mass of hexamethylolmelamine, particularly preferably 6 to 10 times.

[0010] Preferably, the alkaline catalyst is potassium hydroxide or sodium hydroxide, and the amount of alkaline catalyst used is 1% to 2% of the mass of hexamethylolmelamine, particularly preferably 1.8% to 2%.

[0011] Preferably, the reaction temperature in step S1 is 80~90℃ and the reaction time is 5.5~6.5 hours.

[0012] Preferably, the base catalyst is neutralized with formic acid, acetic acid, benzoic acid or hydrochloric acid, and particularly preferably with acetic acid or formic acid.

[0013] Preferably, after neutralizing the alkaline catalyst, the mixture is allowed to stand at 40~60℃ for phase separation, and more preferably at 47~53℃.

[0014] Preferably, the lower layer of low-boiling substances is removed by vacuum concentration. The vacuum degree of vacuum concentration is preferably -0.095±0.01MPa.

[0015] This invention uses methyl 2,2-dimethylolpropionate and hexamethylol melamine as raw materials to prepare the terminal hydroxyl monomer shown in Formula I through transesterification. Compared with the prior art, it has the following outstanding advantages: (i) The product is of high quality and can meet the production requirements of high-transparency epoxy resin and polyester resin. (ii) The reaction conditions are low, which makes it easier to promote and apply. Attached Figure Description

[0016] The invention will be further described below with reference to the accompanying drawings.

[0017] Appendix Figure 1This is a flowchart illustrating the preparation process of the flame-retardant polyhydroxy melamine derivative of this invention. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this should not be construed as limiting the invention. Unless otherwise defined, the test reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods unless otherwise specified.

[0019] This invention uses methyl 2,2-dimethylolpropionate and hexamethylol melamine as raw materials, and modifies melamine through transesterification to obtain the terminal hydroxyl monomer compound shown in Formula I:

[0020] As attached Figure 1 As shown, the preparation method is as follows: S1. Add the measured amounts of hexamethylol melamine, methyl 2,2-dimethylolpropionate, and alkaline catalyst to the dispersant, stir slowly, and carry out the transesterification reaction at a constant temperature of 75~100℃ for 5~8 hours. S2. Neutralize the base catalyst with an acid of equal molar amount to the catalyst, allow it to stand and separate into phases, and concentrate the lower layer under reduced pressure to remove low-boiling substances to obtain the terminal hydroxyl monomer shown in Formula I.

[0021] Example 1: 15.3 g of hexamethylolmelamine, 44.5 g of methyl 2,2-dimethylolpropionate, 0.3 g of sodium hydroxide, and 100 g of toluene were added to a four-necked reaction flask. The reaction was carried out at 85 °C, and the system gradually changed from a white powder to complete dissolution. After 6 hours, 0.45 g of acetic acid was added to neutralize the catalyst, and the mixture was cooled to 50 ± 3 °C and allowed to stand for phase separation. The upper toluene phase was recycled. The lower product phase was evaporated under a vacuum of -0.095 MPa to obtain 49.3 g of a colorless and transparent liquid with a hydroxyl value of 671 mg KOH / g.

[0022] Example 2:

[0023] 30.6 g of hexamethylolmelamine, 91 g of methyl 2,2-dimethylolpropionate, 0.6 g of potassium hydroxide, and 300 g of DMSO were added to a four-necked reaction flask. The reaction was carried out at 85 °C, and the system gradually changed from a white powder to complete dissolution. After 6 hours, 0.45 g of acetic acid was added to neutralize the catalyst, and the mixture was cooled to 50 ± 3 °C and allowed to stand for phase separation. The upper DMSO phase was recycled. The lower product phase was evaporated under a vacuum of -0.095 MPa to obtain 100.1 g of a colorless and transparent liquid with a hydroxyl value of 684 mg KOH / g.

[0024] Comparative Example 1: The only difference from Example 1 is the amount of toluene added to the reaction system.

[0025] The following products were obtained with different amounts of toluene:

[0026] Comparative Example 2: The only difference from Example 1 is the reaction temperature.

[0027] The following products were obtained at different temperatures:

[0028] Comparative Example 3: The only difference from Example 1 is the acid reagent used to neutralize the base catalyst in step S2.

[0029] Different acid reagents yielded the following products:

[0030] The embodiments described above are merely preferred embodiments of the present invention. Ordinary variations and substitutions made by those skilled in the art within the scope of the technical solutions of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a flame-retardant polyhydroxy melamine derivative, characterized in that, Using methyl 2,2-dimethylolpropionate and hexamethylol melamine as raw materials, a terminal hydroxyl monomer as shown in Formula I was obtained through transesterification. 。 2. The preparation method according to claim 1, characterized in that, include: S1. Add measured amounts of hexamethylol melamine, methyl 2,2-dimethylolpropionate, and alkaline catalyst to the dispersant and react at 75~100℃ for 5~8 hours; S2. Neutralize the alkaline catalyst, allow it to stand and separate into phases, and remove low-boiling substances from the lower layer to obtain the terminal hydroxyl monomer shown in Formula I.

3. The preparation method according to claim 2, characterized in that, The molar ratio of hexamethylol melamine to methyl 2,2-dimethylolpropionate is 1:6~7.

4. The preparation method according to claim 2, characterized in that, The dispersant is toluene or xylene, and the amount of dispersant used is 4 to 10 times the mass of hexamethylolmelamine.

5. The preparation method according to claim 2, characterized in that, The alkaline catalyst is potassium hydroxide or sodium hydroxide, and the amount of alkaline catalyst used is 1% to 2% of the mass of hexamethylolmelamine.

6. The preparation method according to claim 2, characterized in that, The alkaline catalyst is neutralized with formic acid, acetic acid, benzoic acid or hydrochloric acid.

7. The preparation method according to claim 2, characterized in that, Phase separation was carried out by standing at 40~60℃; The lower layer of low-boiling substances is removed by vacuum concentration.

8. The flame-retardant polyhydroxy melamine derivative obtained by the preparation method according to any one of claims 1-7.

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