Preparation method of intramolecular synergistic macromolecular antioxidant

Abstract

The invention discloses a preparation method of a macromolecular antioxidant, which comprises the following two steps: carrying out esterification reaction on 3, 5-di-tert-butyl-4-hydroxyphenyl propionic acid and N-hydroxymethyl acrylamide to obtain a micromolecular hindered phenol antioxidant 3-(3, 5-di-tert-butyl-4-hydroxyphenyl) propionic acid acrylamide methyl ester (AHP) with double bonds; the preparation method comprises the following steps: carrying out free radical polymerization reaction on double bonds in AHP and N-phenylmaleimide (NPMI) to obtain a macromolecular antioxidant PAN with hindered phenol and tertiary amine groups; the PAN provided by the invention is subjected to a DPPH free radical scavenging ability test with a commercially available antioxidant 1010, has the same scavenging rate with AO1010 under a certain concentration, and has relatively high antioxidant performance.

Description

Technical Field

[0001] The invention relates to the field of intramolecular synergistic macromolecular synthesis, in particular to a method for synthesizing an antioxidant containing a hindered phenol group and a tertiary amine group. Background Art

[0002] Polyamide 6 (PA6) has a regular molecular chain and high crystallinity, and its amide group (NHCO) is polar, thus forming hydrogen bonds between the molecular chains. Therefore, PA6 has the advantages of high strength, good toughness, good wear resistance, corrosion resistance, easy molding, and easy processing, and is widely used in the automotive and electrical and electronic industries. However, the carbon-hydrogen bond on the methylene group close to the amide group (NHCO) is the weakest bond and is easily affected by environmental factors such as heat, oxygen, and light, resulting in a series of pyrolysis reactions, breaking the main chain of the polymer, and then reducing the relative molecular weight, continuously deteriorating the physical and chemical properties of the material, thereby significantly limiting the application of PA6 products. Therefore, improving the thermal oxidative aging of PA6 has become a research hotspot.

[0003] Adding antioxidants to PA6 is the most effective way to prevent its thermal oxidative aging. Adding a small amount of antioxidants can effectively slow down the thermal oxidative aging process of its products and extend its service life. Generally speaking, according to the different structures, properties and functions of common antioxidants, they can be divided into three categories: amine antioxidants, hindered phenol antioxidants and auxiliary antioxidants.

[0004] Hindered phenolic antioxidants are some phenolic compounds with steric hindrance. The mechanism of action is as follows: the phenolic hydroxyl group, a free radical trap on the antioxidant, reacts with the peroxy or alkoxy group generated by the amide group of PA6, reacting with it to form a stable compound, preventing the free radical from grabbing hydrogen to break the molecular chain further, thereby protecting the polymer chain from the influence of free radicals and delaying the thermal oxidative aging of polyamide. Due to its significant anti-thermal aging effect and significant reduction in environmental pollution, hindered phenolic antioxidants have received significant attention and developed rapidly.

[0005] However, the molecular weight of the antioxidant commonly used in PA6 is 500-1000g / mol. Due to its low molecular weight, it is easy to volatilize or migrate from the matrix material during processing or long-term use. In order to solve these problems, the common method is to synthesize high molecular weight antioxidants.

[0006] Xie et al. combined 2,6-di-tert-butyl-4-hydroxymethylphenol (DBHMP) with per-2,3-acetyl-β-cyclodextrin (β-CDcore) and synthesized a star-shaped macromolecular antioxidant (β-CD-DBHMP) in two steps. The resulting β-CD-DBHMP furfural has good thermal oxidation stability and good extraction resistance in the NR matrix ("Synthesis and antioxidant properties of a star-shaped macromolecular antioxidant based on β-cyclodextrin", Xie H. et al., Materials Letters 2015, 151, 72-74).

[0007] Currently, there is no method for synthesizing intramolecular synergistic macromolecular antioxidants using hindered phenols and tertiary amine groups. Summary of the invention

[0008] The purpose of the present invention is to provide a method for synthesizing an intramolecular synergistic macromolecular antioxidant. The present invention can use low-cost 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid and N-hydroxymethyl acrylamide to prepare a small molecule hindered phenol structure 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid acrylamide methyl ester (AHP) containing a double bond, which is simple to operate, has a high yield and strong repeatability; the present invention uses the carbon-carbon double bond in the synthesized new small molecule antioxidant AHP and the carbon-carbon double bond of N-phenylmaleimide (NPMI) for free radical copolymerization to synthesize a macromolecular antioxidant containing a hindered phenol group and a tertiary amine group, and the antioxidant also contains a heat-resistant group, integrates antioxidant performance and heat-resistant performance, and has great significance for the innovation of antioxidants.

[0009] The technical solution of the present invention is a method for preparing a small molecule antioxidant containing a double bond, comprising the following steps: the first step is to take 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid, a catalyst and a dehydrating agent and place them in anhydrous dichloromethane, stir them in an ice bath for 2 hours, then add N-hydroxymethyl acrylamide, react for a certain time at 20°C, and after the reaction is completed, perform column purification, and dry the obtained solid to obtain a small molecule antioxidant AHP. AHP and NPMI are dissolved in xylene, and then an initiator AIBN is added, and the reaction is carried out at a certain temperature for 5 hours. After the reaction is completed, anhydrous ethanol is added, and the precipitated solid is dried to obtain a macromolecular antioxidant PAN.

[0010] In the aforementioned preparation method of the small molecule antioxidant containing double bonds, the mixture of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid and N-hydroxymethyl acrylamide reacts stably at 20°C, and the molar ratio of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid to N-hydroxymethyl acrylamide is 1:1.5.

[0011] The catalyst is 4-dimethylaminopyridine (DMAP), and the dehydrating agent is one or more of dicyclohexylcarbodiimide (DCC), diisopropylcarbodiimide (DIC) and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDCI). The molar ratios of the catalyst DMAP and the dehydrating agent to 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid are 1:10 and 1.2:1, respectively.

[0012] In the above-mentioned preparation method of small molecule antioxidant containing double bonds, the concentration of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid and N-hydroxymethyl acrylamide in anhydrous dichloromethane solution is 0.7 mol / L. The reaction time of the reaction system is 6-30 hours, preferably 24 hours.

[0013] In the aforementioned method for preparing the macromolecular antioxidant containing hindered phenol groups and tertiary amine groups, the molar ratio of AHP to NPMI is 1.5:1-1:1.5, preferably 1:1.5.

[0014] In the aforementioned method for preparing the macromolecular antioxidant containing hindered phenol groups and tertiary amine groups, the molar ratio of the initiator to the total monomers is 3%-5%, preferably 4%.

[0015] In the aforementioned method for preparing the macromolecular antioxidant containing hindered phenol groups and tertiary amine groups, the concentration of AHP and NPMI in the xylene solution is 0.3-0.7 mol / L, preferably 0.7 mol / L.

[0016] In the aforementioned method for preparing the macromolecular antioxidant containing hindered phenol groups and tertiary amine groups, the reaction temperature of the reaction system is 90-110°C, preferably 110°C.

[0017] Beneficial effects of the present invention:

[0018] The antioxidant designed by the present invention has three characteristics: (1) Improved molecular weight: controlled within 3k-8k, reducing the aggravated aging of PA6 caused by the migration of antioxidants in actual use; (2) Intramolecular synergy: hindered phenol and hindered amine exist in one molecule, which has a synergistic effect and greatly improves the antioxidant efficiency; (3) Increased content of hindered phenol per mole: each antioxidant molecule contains multiple antioxidant groups, which improves the antioxidant effect of a single antioxidant. The design of the new antioxidant refers to the two characteristics of the multi-hindered phenol structure and high molecular weight per mole of the commercially available antioxidant 1010. On the one hand, the content of antioxidant per mole of the designed new antioxidant will be more, thereby improving the antioxidant efficiency of a single antioxidant molecule; on the other hand, the problem of insufficient antioxidant long-term effectiveness and greatly reduced antioxidant efficiency caused by the easy migration of traditional antioxidants in the matrix material due to their small molecular weight will be solved.

[0019] In summary, the present invention can synthesize a macromolecular antioxidant with intramolecular synergy, has a simple process, is highly operable, and has the advantages of improving the antioxidant effect and long-term antioxidant capacity of the antioxidant; the macromolecular antioxidant with intramolecular synergy of the present invention has a novel molecular structure, which is of great significance for promoting the sustainable development of antioxidants. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the structural characterization of the small molecule antioxidant AHP;

[0021] Figure 2 It is a characterization of the thermal stability of small molecule antioxidant AHP;

[0022] Figure 3 It is the structural characterization of the macromolecular antioxidant PAN;

[0023] Figure 4 This is a graph showing the free radical scavenging rates of the macromolecular antioxidant PAN and the commercially available antioxidant 1010.

[0024] Figure 5 Mechanical curves of PA6 composites at different aging times: (a) tensile strength (b) notched impact strength DETAILED DESCRIPTION

[0025] Example 1

[0026] Preparation of small molecule antioxidant AHP: 5.004g of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid (HPPA) (18mmol) and 0.2196g of 4-dimethylaminopyridine (DMAP) (1.8mmol) were dissolved in 40mL of anhydrous dichloromethane at 0℃ and nitrogen atmosphere, and stirred for 10min; 4.14g of 1-ethyl-3 (3-dimethylpropylamine) carbodiimide (EDCI) (21.6mmol) was dissolved in 40mL of anhydrous dichloromethane, and the solution was slowly dripped into the reaction system. After stirring for 2h, 2.727g of N-hydroxymethyl acrylamide (NMA) (27mmol) was dissolved in 10mL of anhydrous dichloromethane and dripped into the reaction system; the reaction system was reacted at 20℃ for 24 hours, and nitrogen was protected during the reaction. After the reaction, column purification was performed, and the obtained solid was dried to obtain a small molecule antioxidant AHP.

[0027] The preparation method of the macromolecular antioxidant containing hindered phenol and tertiary amine groups is as follows: 1.5 mol of the prepared AHP and 1 mol of NPMI are dissolved in 10 mL of xylene, and then 0.125 mol of initiator AIBN is added, and the reaction is carried out at 110° C. for 5 hours. After the reaction is completed, anhydrous ethanol is added, and the precipitated solid is dried to obtain the macromolecular antioxidant PAN.

[0028] Example 2

[0029] Preparation of small molecule antioxidant AHP: At 0°C and nitrogen atmosphere, 5.004g of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid (HPPA) (18mmol), 2.727g of N-hydroxymethyl acrylamide (NMA) (27mmol) and 0.2196g of 4-dimethylaminopyridine (DMAP) (1.8mmol) were dissolved in 50mL of anhydrous dichloromethane. After stirring for 10min, 4.14g of 1-ethyl-3(3-dimethylpropylamine)carbodiimide (EDCI) (21.6mmol) was dissolved in 40mL of anhydrous dichloromethane. The solution was slowly dripped into the reaction system and stirred for 2h. The reaction system was allowed to react at 20°C for 24h, with nitrogen protection during the reaction. After the reaction, column purification was performed.

[0030] Preparation method of macromolecular antioxidant containing hindered phenol and tertiary amine groups: (1) 1.083g AHP (3mmol) and 0.519g N-phenylmaleimide (NPMI) (3mmol) are dissolved in 12mL xylene in a three-necked round-bottom flask; (2) N2 is continuously introduced into the flask, and the solvent is heated to 76°C for 30min until the two monomers are fully dissolved; (3) 0.0295g (3%; 0.18mmol) AIBN is added to the reaction system and reacted at 90°C for 24h. After the reaction is completed, anhydrous ethanol is added, and the precipitated solid is dried to obtain the macromolecular antioxidant PAN.

[0031] Application Example 1

[0032] The ability of PAN and commercial antioxidant 1010 to capture active free radicals was tested by the DPPH method. The operation steps are as follows:

[0033] 1) Preparation of DPPH solution: Accurately weigh 3.9 mg DPPH powder, dissolve it in a beaker with a small amount of anhydrous ethanol, transfer it to a 50 mL volumetric flask to make up the volume, shake well, and prepare a DPPH solution with a molar concentration of 2×10-4 mol / L, and place it in a dark box for use.

[0034] 2) Prepare the sample solution to be tested: accurately weigh 0.0591g antioxidant 0715-1, 0.0509g antioxidant 0715-7, 0.0295g antioxidant 1010, and 0.022g antioxidant BHT, dissolve them respectively with a small amount of anhydrous ethanol, transfer them to a 250mL volumetric flask to make up the volume, shake well, and prepare two antioxidant solutions with a phenolic hydroxyl concentration of 4×10-4mol / L. Use a pipette to transfer 5mL, 10mL, 15mL, 20mL, 25mL, and 37.5mL of the antioxidant solution with a phenolic hydroxyl concentration of 4×10-4mol / L into a 50mL volumetric flask, add anhydrous ethanol to the scale, shake well, and prepare antioxidant solutions with phenolic hydroxyl concentrations of 0.4×10-4mol / L, 0.8×10-4mol / L, 1.2×10-4mol / L, 1.6×1010-4mol / L, 2×10-4mol / L, and 3×10-4mol / L, respectively. In this article, the ratio of phenolic hydroxyl concentration to DPPH solution concentration c(OH) / c(DPPH)=0.2, 0.4, 0.6, 0.8, 1.0, and 1.5 is used to represent five different concentrations of antioxidants.

[0035] 3) Add 1.5mL DPPH solution and 1.5mL ethanol solution to test tube No. 1 as the test group (As); add 1.5mL of the sample solution to be tested and 1.5mL of anhydrous ethanol solution to test tube No. 2 as the control group (Ac); add 1.5mL DPPH solution and 1.5mL of sample solvent solution to test tube No. 3 as the blank group (Ab). After fully mixing, use an ultraviolet spectrophotometer to measure the absorbance value at a wavelength of 517nm (sample solvent zero calibration).

[0036] The experimental results are as follows Figure 4 , at a certain concentration, has the same scavenging rate as AO1010 and has higher antioxidant properties.

[0037] Application Example 2

[0038] Two PA6 / antioxidant composite materials were prepared by extrusion molding process by adding 5g antioxidant PAN into 1kg PA6. The antioxidant properties were studied by thermal oxidative aging at 150℃. The mechanical properties after thermal oxidative aging were shown in Figure 2. Figure 5 shown.

Claims

1. An intramolecular synergistic macromolecular antioxidant, characterized in that: The antioxidant structural formula is shown below: Where n is 5-12.

2. The method for preparing an intramolecular synergistic macromolecular antioxidant according to claim 1, characterized in that: The invention comprises the following steps: (1) a method for preparing a small molecule antioxidant containing a double bond: 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid, a catalyst and a dehydrating agent are placed in anhydrous dichloromethane, stirred in an ice bath, and then N-hydroxymethyl acrylamide is added for reaction. After the reaction is completed, the reaction is performed through a column for purification, and the obtained solid is dried to obtain a small molecule antioxidant 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid acrylamide methyl ester (AHP); (2) the obtained AHP and N-phenylmaleimide (NPMI) are dissolved in xylene, and then an initiator AIBN is added for reaction. After the reaction is completed, anhydrous ethanol is added, and the precipitated solid is dried to obtain a macromolecular antioxidant.

3. The method for preparing a small molecule antioxidant AHP according to claim 1, characterized in that: The molar ratio of the 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid to N-hydroxymethyl acrylamide is 1:1.

5.

4. The method for preparing a small molecule antioxidant AHP according to claim 1, characterized in that: The catalyst is 4-dimethylaminopyridine (DMAP), and the dehydrating agent is one or more of dicyclohexylcarbodiimide (DCC), diisopropylcarbodiimide (DIC) and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDCI).

5. The method for preparing a small molecule antioxidant AHP according to claim 1, characterized in that: The molar ratio of the catalyst to 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid is 1:10, and the molar ratio of the dehydrating agent to 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid is 1.2:

1.

6. The method for preparing a small molecule antioxidant AHP according to claim 1, characterized in that: The concentration of the 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid and N-hydroxymethyl acrylamide in the anhydrous dichloromethane solution is 0.7 mol / L.

7. The method for preparing a small molecule antioxidant AHP according to claim 1, characterized in that: The reaction time after adding N-hydroxymethyl acrylamide in step (1) is 6-30 hours.

8. The method for preparing a macromolecular antioxidant PAN according to claim 1, characterized in that: The molar ratio of the AHP to the NPMI is 1.5:1-1:1.5; the concentration of the AHP and the NPMI in the xylene solution is 0.3-0.7 mol / L.

9. The method for preparing a macromolecular antioxidant PAN according to claim 1, characterized in that: The molar ratio of the initiator to the total monomers is 3%-5%.

10. The method for preparing a macromolecular antioxidant PAN according to claim 1, characterized in that: The reaction temperature in step (2) is 90-110°C, preferably 110°C.

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