Preparation method of melamine formaldehyde oligomer

Abstract

The invention discloses a preparation method of a melamino-formaldehyde oligomer, and belongs to the technical field of organic synthesis. According to the method, melamine and paraformaldehyde are taken as raw materials and react in phosphite ester or phosphate ester to prepare the melamine formaldehyde oligomer. The prepared melamine formaldehyde oligomer can be used as a nitrogen flame retardant. The method is safe, simple and environment-friendly to operate. The method has the advantages of cheap initial raw materials, simple operation, simple process, energy saving and high raw material conversion rate, and can realize large-scale production of the melamino-formaldehyde oligomer.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic synthesis, and particularly relates to a method for preparing melamine formaldehyde oligomers. Background Art

[0002] Melamine Formaldehyde resin (MF), also known as melamine resin, is obtained by reacting melamine with formaldehyde under alkaline conditions to obtain hydroxymethyl melamine, and then heating it under acidic conditions.

[0003]

[0004] Melamine Formaldehyde resin

[0005] Because it releases a large amount of nitrogen during combustion and can decompose to form a dense carbon layer to isolate air, it has good flame retardant properties.

[0006] 1) Zhou Zonghua [1] et al. used melamine and aqueous formaldehyde as raw materials, and sodium hydroxide solution and hydrochloric acid solution were used as alkaline catalyst and acidic catalyst respectively to study the effects of different reaction conditions on the reaction and product properties. The reaction is shown in Figure S-1.

[0007]

[0008] S-1

[0009] 2) Heng Zhu [2] et al. synthesized ethylene glycol modified melamine formaldehyde resin using ethylene glycol, paraformaldehyde and melamine as raw materials, and then prepared rigid polyurethane foam using ethylene glycol modified melamine formaldehyde resin, polyol and polyisocyanate. The reaction is shown in Figure S-2.

[0010]

[0011] S-2

[0012] 3) Anil Kumar and Vimal Katiyar [3] studied the polymerization reaction of melamine and formaldehyde at high temperature. Three processes of the polymerization reaction were determined: the first step is the reaction of formaldehyde with water to form HOCH2OH intermediate, the second step is the addition reaction of this intermediate with melamine to obtain hydroxymethyl melamine, and finally the intermediate of the second step reacts with itself or with melamine to undergo a condensation reaction to obtain a dimer or polymer chain. The structural formula is shown in Figure S-3.

[0013]

[0014] S-3

[0015] 4) Bunichiro Tomita of the University of Tokyo [4] Methylene di- and tri-melamine formaldehyde resin was synthesized using monohydroxymethyl melamine and melamine as raw materials (pH = 4 - 5, t = 70 °C), and its structure is shown in Figure S-4. The structure of this compound was confirmed by carbon-13 nuclear magnetic resonance spectroscopy.

[0016]

[0017] S-4

[0018] It can be seen that the existing synthesis processes of methyl ether bridge or methylene bridge melamine formaldehyde resins or the synthesis processes of polyol-modified melamine formaldehyde resins all use NaOH solution and hydrochloric acid as the basic catalyst and acidic catalyst, and achieve the synthesis and modification of melamine formaldehyde resins through the hydroxymethylation and etherification of melamine. These processes have the disadvantages of cumbersome operation and high free formaldehyde content.

[0019] References

[0020] [1] Zhou Zonghua, Qin Jun. Research on the synthesis reaction of melamine resin [J]. China Plastics Industry, 1989, (05): 10 - 13.

[0021] [2] Heng Z, Shiai X. Preparation of Flame-Retardant Rigid Polyurethane Foams by Combining Modified Melamine-Formaldehyde Resin and Phosphorus Flame Retardants [J]. ACS Omega, 2020, 5(17): 9658 - 9667.

[0022] [3] Anil Kumar, Vimal Katiyar. Modeling and Experimental Investigation of Melamine-Formaldehyde Polymerization [J]. Macromolecules, 1990, 23(16): 3729 - 3736.

[0023] [4] Bunichiro Tomita, Shiro Hato. Melamine-Formaldehyde Resins: Constitutional Characterization by Fourier Transform 13C-NMR Spectroscopy[J], Journal of Polymer Science, 1979, 17: 3205-3215. Summary of the Invention

[0024] In order to solve the above technical problems, the present invention provides a method for preparing a melamine formaldehyde oligomer. Without adding a catalyst, melamine and paraformaldehyde react at high temperature in a solvent to obtain a melamine formaldehyde oligomer, which has the characteristics of low-cost and easily available raw materials, low cost, no pollution, and high conversion rate. The reaction is shown in Figure S-5.

[0025] The technical solution adopted by the present invention is as follows: A method for preparing a melamine formaldehyde oligomer, comprising the following steps:

[0026]

[0027] Add melamine and a solvent into a flask, start stirring, and add paraformaldehyde in portions. Carry out a condensation reaction at 165 °C - 175 °C to obtain a melamine formaldehyde oligomer;

[0028] In the condensation reaction, the molar ratio of melamine to paraformaldehyde is 1:1 - 1.5.

[0029] Further, paraformaldehyde is added in 2 - 3 portions during the condensation reaction.

[0030] Further, the solvent is one or a mixture of more than one of dimethyl phosphite, trimethyl phosphite, dimethyl phosphate, trimethyl phosphate, diethyl phosphite, triethyl phosphite, diethyl phosphate, and triethyl phosphate.

[0031] Specifically, for the synthesis of the melamine formaldehyde oligomer: Add melamine and diethyl phosphite into a 250 mL three-necked flask equipped with a thermometer, a stirring device, and a reflux device. Start stirring and heat up. During the process, add paraformaldehyde in 3 portions and carry out a condensation reaction at 170 °C to obtain a melamine formaldehyde oligomer.

[0032] The beneficial effects of the present invention are as follows: This method uses melamine and paraformaldehyde as raw materials to react in phosphite or phosphate ester to obtain a melamine formaldehyde oligomer. The obtained melamine formaldehyde oligomer can be used as a nitrogen-based flame retardant. The method of the present invention is safe, simple, and environmentally friendly in operation. The starting materials of this method are cheap, the operation is simple, the process is simple, energy is saved, the raw material conversion rate is high, and large-scale production of melamine formaldehyde oligomers can be realized. Description of the Drawings

[0033] Figure 1 It is the infrared spectra of melamine and the melamine formaldehyde oligomer.

[0034] Figure 2 It is the mass spectrum of melamine formaldehyde oligomer.

[0035] Figure 3 It is the graph of crucible combustion residue. Specific Embodiments

[0036] The present invention will be further described below by way of examples. However, these examples are merely exemplary and do not constitute any limitation to the protection scope of the present invention. The following non-limiting examples can enable those of ordinary skill in the art to understand the present invention more comprehensively, but do not limit the present invention in any way. In the following examples, unless otherwise specified, the experimental methods used are all conventional methods, and the materials, reagents, etc. used can be purchased from chemical reagent companies.

[0037] Example 1

[0038] Melamine (3.15 g) and dimethyl phosphite (20.7 g) were added into a 250 mL three-necked flask equipped with a thermometer, a stirring device and a reflux device. Stirring was started and the temperature was raised. Paraformaldehyde (0.75 g) was added in 3 portions during the process. The condensation reaction was carried out at 170 °C. As the reaction proceeded, the system became viscous. After 10 min of reaction, 75 ml of ethanol was added. The mixture was filtered, washed and dried to obtain a white solid powder with a yield of 95.4%. The infrared spectra of melamine and melamine formaldehyde oligomer are shown in Figure 1 . IR (KBr, cm -1 -1): 3367 (-NH2), 2980, 1460 (-CH2-), 1542, 1339, 827 (triazine ring skeleton), 1041 (-C-N-).

[0039] The mass spectrum of melamine formaldehyde oligomer is shown in Figure 2 . m / z = 265.1383 (n = 1, [M+H] + , theoretical value 265.1386), m / z = 403.2037 (n = 2, [M+H] + , theoretical value 403.2040).

[0040] Example 2

[0041] Melamine (3.15 g) and diethyl phosphite (20.7 g) were added into a 250 mL three-necked flask equipped with a thermometer, a stirring device and a reflux device. Stirring was started and the temperature was raised. Paraformaldehyde (0.75 g) was added in 3 portions during the process. The condensation reaction was carried out at 165 °C. As the reaction proceeded, the system became viscous. After 10 min of reaction, 75 ml of ethanol was added. The mixture was filtered, washed and dried to obtain a white solid powder with a yield of 87.3%.

[0042] Example 3

[0043] Melamine (3.15 g) and dimethyl phosphate (20.5 g) were added into a 250 mL three-necked flask equipped with a thermometer, a stirring device and a reflux device. Stirring was started and the temperature was raised. During the process, paraformaldehyde (0.75 g) was added in three portions. The condensation reaction was carried out at 175 °C. As the reaction proceeded, the system became viscous. After 10 min of reaction, 75 ml of ethanol was added. After filtration, washing and drying, a white solid powder was obtained with a yield of 92.3%.

[0044] Example 4

[0045] Melamine (4.7 g) and diethyl phosphate (20.7 g) were added into a 250 mL three-necked flask equipped with a thermometer, a stirring device and a reflux device. Stirring was started and the temperature was raised. During the process, paraformaldehyde (1.125 g, 0.025 mol) was added in three portions. The condensation reaction was carried out at 170 °C. As the reaction proceeded, the system became viscous. After 10 min of reaction, 75 ml of ethanol was added. After filtration, washing and drying, a white solid powder was obtained with a yield of 89.3%.

[0046] Example 5

[0047] Melamine (3.15 g) and diethyl phosphite (41.4 g) were added into a 250 mL three-necked flask equipped with a thermometer, a stirring device and a reflux device. Stirring was started and the temperature was raised. During the process, paraformaldehyde (0.75 g) was added in three portions. The condensation reaction was carried out at 170 °C. As the reaction proceeded, the system became viscous. After 10 min of reaction, 75 ml of ethanol was added. After filtration, washing and drying, a white solid powder was obtained with a yield of 90.7%.

[0048] The melamine formaldehyde oligomer in Example 1 was subjected to a combustion experiment in a crucible, as Figure 3 shown Figure 3 In the figure, melamine is on the left, and the char residue after combustion of the melamine formaldehyde oligomer in the crucible is on the right. After combustion, melamine leaves a yellow solid, and a large amount of smoke is formed during the combustion process, and it does not have flame retardancy; after combustion, the melamine formaldehyde oligomer forms a dense carbon layer, and a large amount of smoke is generated during combustion, and a burning match cannot ignite the smoke, indicating that the melamine formaldehyde oligomer can prevent the spread of flame and inhibit combustion during combustion, and has certain flame retardant properties.

[0049] The above examples are only used to illustrate the present invention. Any equivalent transformation and improvement based on the technical solution of the present invention should not be excluded from the protection scope of the present invention.

Claims

1. A preparation method of a melamine formaldehyde oligomer, characterized in that, It includes the following steps: ； Add melamine and a solvent into a flask, start stirring, add paraformaldehyde in portions, and carry out a condensation reaction at 165 °C - 175 °C to obtain a melamine formaldehyde oligomer; In the condensation reaction, the molar ratio of melamine to paraformaldehyde is 1:1 - 1.

5.

2. The preparation method of a melamine formaldehyde oligomer according to claim 1, characterized in that: Paraformaldehyde is added in 2 - 3 portions during the condensation reaction.

3. The preparation method of a melamine formaldehyde oligomer according to claim 1, characterized in that: The solvent is one or a mixture of more than one of dimethyl phosphite, trimethyl phosphite, dimethyl phosphate, trimethyl phosphate, diethyl phosphite, triethyl phosphite, diethyl phosphate, and triethyl phosphate.

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