Phosphorus-silicon type Schiff base derivative flame retardant as well as preparation method and application thereof

Abstract

The invention discloses a phosphorus-silicon type Schiff base derivative flame retardant and a preparation method and application thereof.The preparation method comprises the steps that salicylaldehyde and 1, 3-bis (3-aminopropyl)-1, 1, 3, 3-tetramethyldisiloxane react to obtain silicon-containing Schiff base, then P-H on hypophosphorous acid substances and-C = N-on the silicon-containing Schiff base are subjected to an addition reaction, and the phosphorus-silicon type Schiff base derivative flame retardant is obtained. The phosphorus-silicon type Schiff base derivative flame retardant is prepared. The flame retardant contains a plurality of groups such as-OH,-NH-and the like, can achieve molecular-level dispersion in a high polymer material, and plays an efficient flame-retardant role. The flame retardant has a gas-phase and condensed-phase dual-phase flame retardant effect: in the gas phase, the effects of dilution and free radical capture are exerted; and in a condensed phase, char formation can be promoted and a barrier effect can be exerted. In addition, due to the existence of organic silicon, a compact carbon layer with a specific-Si-O-bond or-Si-C-bond of siloxane can be generated during combustion, the protection effect of oxygen isolation and heat insulation is achieved, and the condensed phase flame retardant effect is enhanced. The phosphorus-silicon type Schiff base derivative flame retardant has a wide application prospect and can be applied to flame-retardant modification of polyurethane and epoxy resin.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to a phosphorus-silicon Schiff base derivative flame retardant, a preparation method thereof and an application thereof. Background Art

[0002] Schiff base is a class of organic compounds containing an imine group -C=N-. It is formed by the dehydration condensation of primary amines and carbonyl compounds. Patents with publication numbers CN 106496065 A, CN 106748879 A and CN 106496065 A respectively introduce the preparation methods of o-phenylenediamine Schiff base, p-nitrobenzaldehyde Schiff base and aryl Schiff base. It can be seen that the synthesis process of Schiff base compounds has simple steps, easy-to-control reaction conditions and high yields; the imine group has a planar triangular structure, the N atom belongs to sp2 hybridization, has a lone pair of electrons, and its hybrid orbitals are prone to deformation, making Schiff base and its derivatives widely used in the field of material modification. In recent years, Schiff base compounds have begun to be widely used in the field of flame retardant materials. Patents with publication numbers CN 108948348 A, CN 108794745 A, CN 109111571 A and CN 109111570 A disclose the synthesis of triazine-based Schiff base flame retardants and phosphorus-containing Schiff base flame retardants; Patent Nos. CN 113337006 A and CN113264960 A disclose the preparation of phosphorus-containing Schiff base derivative flame retardants by the reaction of active hydrogen on 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and Schiff base. Hypophosphite flame retardants, as a kind of phosphorus-based flame retardants, have the advantages of high efficiency, low smoke, non-toxic and halogen-free, and are widely used in the field of flame retardancy. For example, aluminum diethyl hypophosphite (ADP) disclosed in the US patent US7635785 (2009) applied by Clariant Corporation of Germany and 2-carboxyethyl phenylphosphinic acid (CEPPA) disclosed in the US patent US4081463 (1978) applied by Monsanto Company, etc.

[0003] For a long time, in the field of flame retardancy, silicon-based flame retardants exist as synergists for other flame retardants. Introducing silicon elements can improve the flame retardancy efficiency. The patent with publication number CN 109734898 B discloses a novel phosphorus, nitrogen and silicon-containing flame retardant for the flame retardancy of polyamide 6. The patent with patent number CN 202210484808.6 discloses a POSS-based flame retardant containing phosphorus, nitrogen and silicon elements and a method thereof. In the existing research, the research on combining silicon-containing Schiff base and hypophosphite into one molecule through chemical reaction has not been reported; in this application, salicylaldehyde, 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane and hypophosphite substances are used as reactants to synthesize a phosphorus-silicon Schiff base derivative flame retardant. SUMMARY OF THE INVENTION

[0004] An object of the present invention is to provide a phosphorus-silicon Schiff base derivative flame retardant in view of the deficiencies of the prior art. This flame retardant can be molecularly dispersed in polymer materials and play an efficient flame retardant role. In the gas phase, on the one hand, it can play a dilution role by releasing water and ammonia through the combustion of phenolic hydroxyl groups and amino groups. On the other hand, the phosphorus oxy free radicals released by the combustion of hypophosphorous acid substances in it play a free radical capture role. In the condensed phase, on the one hand, the hypophosphorous acid substances in it generate phosphoric acid to promote carbon formation of the material and play a flame retardant effect in the condensed phase. On the other hand, the phenolic substances and aldehyde substances generated by pyrolysis during the combustion process can continue to obtain phenolic resin through an addition reaction during the heating process and can play an excellent barrier effect in the condensed phase. This flame retardant not only has a dual-phase flame retardant effect in the gas phase and the condensed phase, but also, due to the presence of organosilicon, an inorganic oxygen barrier and heat insulation protective layer with unique -Si-O- bonds or -Si-C- bonds will be formed during combustion, preventing the volatilization of small molecules decomposed from the material and inhibiting the decomposition of the material, thereby achieving the purpose of flame retardancy, low smoke, and low toxicity.

[0005] The chemical structure of the phosphorus-silicon Schiff base derivative flame retardant of the present invention is shown in structural formula (Ⅰ):

[0006]

[0007] R1 is

[0008] Another object of the present invention is to provide a preparation method of the above-mentioned phosphorus-silicon Schiff base derivative flame retardant.

[0009] The preparation method includes the following steps:

[0010] Step (1). Add the protic organic solvent of salicylaldehyde (shown in structural formula Ⅱ) to the protic organic solvent of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (shown in structural formula Ⅲ), and stir at 60 - 80 °C for 2 - 4 hours under the protection of an inert gas.

[0011]

[0012] Step (2). Add the protic organic solvent of hypophosphorous acid substances to the protic organic solvent after the reaction in step (1), and stir at 60 - 80 °C for 8 - 10 hours under the protection of an inert gas;

[0013] The concentration of salicylaldehyde in a protic organic solvent is 1.0 - 3.0 mol / L, the concentration of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane in a protic organic solvent is 0.5 - 1.5 mol / L, the concentration of hypophosphorous acid in a protic organic solvent is 1.0 - 3.0 mol / L, and the three use the same protic organic solvent. The molar ratio of the added salicylaldehyde, 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, and hypophosphorous acid is: 2:1:2;

[0014] The hypophosphorous acid is one or more of hypophosphorous acid, methyl hypophosphorous acid, ethyl hypophosphorous acid, tert-butyl hypophosphorous acid, ethoxy hypophosphorous acid, phenyl hypophosphorous acid, and benzyl hypophosphorous acid.

[0015] The inert gas is nitrogen or argon;

[0016] The protic organic solvent is one of methanol, ethanol, propanol, formic acid, acetic acid, and formamide;

[0017] After the reaction in step (3) is completed, through suction filtration, washing, and drying, the target product, the phosphorus-silicon Schiff base derivative flame retardant (as shown in structural formula I), is obtained.

[0018] The salicylaldehyde, 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, hypophosphorous acid, and protic organic solvent in the present invention are all industrial products and can be obtained through market purchase.

[0019] In the present invention, salicylaldehyde and 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane undergo an aldehyde-amine condensation reaction to obtain a silicon-containing Schiff base with a characteristic group -C=N-. Then, it undergoes an addition reaction with the active hydrogen connected to the phosphorus atom on a hypophosphorous acid-based substance to obtain a phosphorus-silicon type Schiff base derivative flame retardant. This flame retardant has the following characteristics: (1) The flame retardant contains multiple -OH, -NH- and other groups, which can interact intermolecularly with certain polymer materials, such as forming intermolecular hydrogen bonds with thermoplastic polyurethane elastomers and crosslinking reactions with epoxy resins, so as to achieve molecular-level dispersion in polymer materials and play an efficient flame retardant role. (2) It has a gas-phase and condensed-phase dual-phase flame retardant effect. In the gas phase, on the one hand, it plays a dilution role by releasing water and ammonia through the combustion of phenolic hydroxyl groups and amine groups. On the other hand, the hypophosphorous acid-based substance releases phosphorus-oxygen free radicals during combustion to play a free radical capture role. In the condensed phase, on the one hand, the hypophosphorous acid-based substance generates phosphoric acid to promote carbonization of the material and play a flame retardant effect in the condensed phase. On the other hand, the phenolic substances and aldehyde substances generated by pyrolysis during the combustion process can continue to undergo an addition reaction to obtain phenolic resin during heating, which can play an excellent barrier effect in the condensed phase. (3) In addition, due to the presence of organosilicon, a dense carbon layer with unique -Si-O- bonds or -Si-C- bonds of siloxane will be formed during combustion, playing a role of oxygen isolation and heat insulation protection, and enhancing the condensed-phase flame retardant effect.

[0020] This phosphorus-silicon type Schiff base derivative flame retardant has a wide application prospect and can be used for flame retardant modification of polyurethanes and epoxy resins. Brief Description of the Drawings

[0021] Figure 1 Comparison of the char residues after combustion of the flame retardant TPU materials prepared in the control example and Example 1 (a1, a2: control example, b1, b2: Example 1);

[0022] Figure 2 Elemental analysis comparison of the char residues after combustion of the flame retardant TPU materials prepared in the control example and Example 1. Detailed Description of the Invention

[0023] The technical solutions of the present invention will be further described in detail below with reference to the drawings and specific examples.

[0024] Control Example

[0025] 3.00 g (0.05 mol) of ethylenediamine was added to a 250 ml four-necked flask equipped with a reflux condenser and a stirrer. Then, 12.21 g (0.1 mol) of salicylaldehyde and 50 ml of absolute ethanol were added to the four-necked flask. The temperature of the system was raised to 70 °C using an oil bath, and the reaction was carried out for 2 h under a nitrogen atmosphere. Then, 14.21 g (0.1 mol) of phenylphosphinic acid was dissolved in 50 ml of absolute ethanol under ultrasonic dispersion at 45 °C and added to the above four-necked flask. Keeping the reaction temperature unchanged, the reaction was continued for 10 h under a nitrogen atmosphere, and then the system was cooled to room temperature. The mixture was initially filtered, and the obtained solid was washed 5 times with absolute ethanol. The obtained product was dried in a vacuum oven at 80 °C for 12 h to obtain a silicon-free Schiff base derivative flame retardant, which was used as a control example. The structural formula is as follows:

[0026]

[0027] Example 1

[0028] 12.44 g (0.05 mol) of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane was added to a 250 ml four-necked flask equipped with a reflux condenser and a stirrer. Then, 12.21 g (0.1 mol) of salicylaldehyde and 50 ml of absolute ethanol were added to the four-necked flask. The temperature of the system was raised to 70 °C using an oil bath, and the reaction was carried out for 2 h under a nitrogen atmosphere. Then, 14.21 g (0.1 mol) of phenylphosphinic acid was dissolved in 50 ml of absolute ethanol under ultrasonic dispersion at 45 °C and added to the above four-necked flask. Keeping the reaction temperature unchanged, the reaction was continued for 10 h under a nitrogen atmosphere, and then the system was cooled to room temperature. The mixture was initially filtered, and the obtained solid was washed 5 times with absolute ethanol. The obtained product was dried in a vacuum oven at 80 °C for 12 h to obtain the target product - a phosphorus-silicon type Schiff base derivative flame retardant with a yield of 65.0%. It and the silicon-free Schiff base derivative flame retardant prepared in the control example were used for flame-retarding TPU materials, and the flame-retarding char-forming effects are compared as attached Figure 1 shown, and the retention of silicon elements is as attached Figure 2 shown. Table 1 shows some cone calorimeter test results of the flame retardants prepared in the control example and Example 1 for flame-retarding TPU materials.

[0029] Table 1

[0030]

[0031] Example 2

[0032] 24.88 g (0.1 mol) of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane was added to a 500 ml four-necked flask equipped with a condensing reflux device and a stirring device. Then, 24.42 g (0.2 mol) of salicylaldehyde and 100 ml of absolute ethanol were added to the four-necked flask. The temperature of the system was raised to 70 °C using an oil bath device, and the reaction was carried out for 2 h under a nitrogen atmosphere. Then, 13.20 g (0.2 mol) of hypophosphorous acid was dissolved in 100 ml of absolute ethanol under the condition of ultrasonic dispersion at 45 °C and added to the four-necked flask. Keeping the reaction temperature unchanged, the reaction was continued for 10 h under a nitrogen atmosphere, and then the system was cooled to room temperature. The mixture was preliminarily filtered, and the obtained solid was washed 5 times with absolute ethanol. The obtained product was dried in a vacuum oven at 80 °C for 12 h to obtain the target product, a phosphorus-silicon Schiff base derivative flame retardant, with a yield of 68.9%.

[0033] Example 3

[0034] 12.44 g (0.05 mol) of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane was added to a 250 ml four-necked flask equipped with a condensing reflux device and a stirring device. Then, 12.21 g (0.1 mol) of salicylaldehyde and 50 ml of methanol were added to the four-necked flask. The temperature of the system was raised to 60 °C using an oil bath device, and the reaction was carried out for 4 h under a nitrogen atmosphere. Then, 6.60 (0.1 mol) of hypophosphorous acid was dissolved in 50 ml of methanol under the condition of ultrasonic dispersion at 45 °C and added to the four-necked flask. Keeping the reaction temperature unchanged, the reaction was continued for 8 h under a nitrogen atmosphere, and then the system was cooled to room temperature. The mixture was preliminarily filtered, and the obtained solid was washed 5 times with methanol. The obtained product was dried in a vacuum oven at 80 °C for 12 h to obtain the target product, a phosphorus-silicon Schiff base derivative flame retardant, with a yield of 35.4%.

[0035] Example 4

[0036] 12.44 g (0.05 mol) of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane was added to a 250 ml four-necked flask equipped with a condensing reflux device and a stirring device. Then, 12.21 g (0.1 mol) of salicylaldehyde and 50 ml of propanol were added to the four-necked flask. The temperature of the system was raised to 80 °C using an oil bath device, and the reaction was carried out for 2 h under a nitrogen atmosphere. Then, 14.21 g (0.1 mol) of phenylphosphinic acid was dissolved in 50 ml of propanol under the condition of ultrasonic dispersion at 45 °C and added to the four-necked flask. Keeping the reaction temperature unchanged, the reaction was continued for 10 h under a nitrogen atmosphere, and then the system was cooled to room temperature. The mixture was preliminarily filtered, and the obtained solid was washed 5 times with propanol. The obtained product was dried in a vacuum oven at 90 °C for 12 h to obtain the target product, a phosphorus-silicon Schiff base derivative flame retardant, with a yield of 55.5%.

[0037] Example 5

[0038] 12.44 g (0.05 mol) of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane was added to a 250 ml four-necked flask equipped with a condensing reflux device and a stirring device. Then, 12.21 g (0.1 mol) of salicylaldehyde and 50 ml of methanol were added to the four-necked flask. The temperature of the system was raised to 60 °C using an oil bath device, and the reaction was carried out for 4 h under a nitrogen atmosphere. Then, 11.01 g (0.1 mol) of ethoxyphosphinic acid was dissolved in 50 ml of methanol under the condition of ultrasonic dispersion at 45 °C and added to the four-necked flask. Keeping the reaction temperature unchanged, the reaction was continued for 10 h under a nitrogen atmosphere, and then the system was cooled to room temperature. The mixture was preliminarily filtered, and the obtained solid was washed 5 times with methanol. The obtained product was dried in a vacuum oven at 80 °C for 12 h to obtain the target product, a phosphorus-silicon Schiff base derivative flame retardant, with a yield of 66.7%.

[0039] Example 6

[0040] 24.88 g (0.1 mol) of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane was added to a 500 ml four-necked flask equipped with a condenser reflux device and a stirring device. Then, 24.42 g (0.2 mol) of salicylaldehyde and 100 ml of absolute ethanol were added to the four-necked flask. The temperature of the system was raised to 70 °C using an oil bath device, and the reaction was carried out for 2 h under a nitrogen atmosphere. Then, 28.42 g (0.2 mol) of phenylphosphinic acid was dissolved in 100 ml of absolute ethanol under the condition of ultrasonic dispersion at 45 °C and added to the four-necked flask. Keeping the reaction temperature unchanged, the reaction was continued for 8 h under a nitrogen atmosphere, and then the system was cooled to room temperature. The mixture was preliminarily filtered, and the obtained solid was washed 5 times with absolute ethanol. The obtained product was dried in a vacuum oven at 80 °C for 12 h to obtain the target product, a phosphorus-silicon Schiff base derivative flame retardant, with a yield of 59.3%.

[0041] Example 7

[0042] 12.44 g (0.05 mol) of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane was added to a 250 ml four-necked flask equipped with a condenser reflux device and a stirring device. Then, 12.21 g (0.1 mol) of salicylaldehyde and 50 ml of formic acid were added to the four-necked flask. The temperature of the system was raised to 70 °C using an oil bath device, and the reaction was carried out for 2 h under a nitrogen atmosphere. Then, 14.21 g (0.1 mol) of phenylphosphinic acid was dissolved in 50 ml of formic acid under the condition of ultrasonic dispersion at 45 °C and added to the four-necked flask. Keeping the reaction temperature unchanged, the reaction was continued for 8 h under a nitrogen atmosphere, and then the system was cooled to room temperature. The mixture was preliminarily filtered, and the obtained solid was washed 5 times with formic acid. The obtained product was dried in a vacuum oven at 100 °C for 12 h to obtain the target product, a phosphorus-silicon Schiff base derivative flame retardant, with a yield of 45.6%.

[0043] Example 8

[0044] 12.44 g (0.05 mol) of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane was added to a 250 ml four-necked flask equipped with a condenser reflux device and a stirring device. Then, 12.21 g (0.1 mol) of salicylaldehyde and 50 ml of absolute ethanol were added to the four-necked flask. The temperature of the system was raised to 70 °C using an oil bath device, and the reaction was carried out for 4 h under a nitrogen atmosphere. Then, 15.61 g (0.1 mol) of benzylphosphinic acid was dissolved in 50 ml of absolute ethanol under the condition of ultrasonic dispersion at 45 °C and added to the four-necked flask. Keeping the reaction temperature unchanged, the reaction was continued for 10 h under a nitrogen atmosphere, and then the system was cooled to room temperature. The mixture was preliminarily filtered, and the obtained solid was washed 5 times with absolute ethanol. The obtained product was dried in a vacuum oven at 80 °C for 12 h to obtain the target product, a phosphorus-silicon Schiff base derivative flame retardant, with a yield of 59.8%.

[0045] The limiting oxygen index values of the flame retardant TPU materials prepared in each example are shown in Table 2.

[0046] Table 2

[0047]

[0048]

[0049] The above-described embodiments are only some preferred solutions of the present invention, but they are not intended to limit the present invention. Those of ordinary skill in the relevant technical field can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all technical solutions obtained by adopting equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A phosphorus-silicon Schiff base derivative flame retardant, whose chemical structural formula is as follows: Among them, R1 is 2. The preparation method of the phosphosilicon-based Schiff base derivative flame retardant according to claim 1, characterized in that, The following steps are included: Step (1): Add a protic organic solvent containing salicylaldehyde to a protic organic solvent containing 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, and stir at 60-80°C for 2-4 hours in an inert gas atmosphere to obtain an intermediate product, silicon-containing Schiff base; Step (2): Add a protic organic solvent containing hypophosphorous acid substances to the intermediate product, silicon-containing Schiff base, and stir at 60-80°C for 8-10 hours under the protection of an inert gas; Step (3): The product obtained after the reaction is filtered, washed, and vacuum dried to obtain a phosphorus-silicon Schiff base derivative flame retardant; The above protic organic solvents are all the same kind of protic organic solvent.

3. The preparation method of the phosphosilicon Schiff base derivative flame retardant according to claim 2, characterized in that, The hypophosphorous acid substances are one of hypophosphorous acid, methyl hypophosphorous acid, ethyl hypophosphorous acid, tert-butyl hypophosphorous acid, ethoxy hypophosphorous acid, phenyl hypophosphorous acid, and benzyl hypophosphorous acid.

4. The preparation method of the phosphosilicon-based Schiff base derivative flame retardant according to claim 2, wherein, The concentration of the protic organic solvent containing 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane is 0.5-1.5 mol / L.

5. The preparation method of the phosphosilicon Schiff base derivative flame retardant according to claim 2, wherein, The concentration of the protic organic solvent containing salicylaldehyde is 1.0-3.0 mol / L.

6. The preparation method of the phosphosilicon Schiff base derivative flame retardant according to claim 2, wherein, The concentration of hypophosphite in the protic organic solvent containing hypophosphorous acid substances is 1.0-3.0 mol / L.

7. The preparation method of the phosphosilicon Schiff base derivative flame retardant according to claim 2, characterized in that, The molar ratio of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, salicylaldehyde, and hypophosphorous acid substances is 1:2:

2.

8. The preparation method of the phosphosilicon Schiff base derivative flame retardant according to claim 2, characterized in that, The inert gas is nitrogen or argon.

9. The preparation method of the phosphosilicon-based Schiff base derivative flame retardant according to claim 2, characterized in that, The protic organic solvent is one of methanol, ethanol, propanol, formic acid, acetic acid, and formamide.

10. The application of the phosphosilicon Schiff base derivative flame retardant according to claim 1, characterized in that, It is used for flame retardant modification of polyurethane or epoxy resin.

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