Inherently heat-conductive flame-retardant recycled epoxy resin and preparation method thereof

Abstract

The application belongs to the technical field of flame-retardant polymers, and particularly relates to an intrinsic heat-conducting flame-retardant recycled epoxy resin and a preparation method thereof. The preparation method comprises the following steps: (1) diethanolamine is reacted with 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) to obtain an intermediate A; (2) the intermediate A is subjected to polycondensation reaction with phenylphosphonic acid to obtain a terminal phosphonic acid group polyester flame retardant (PEF); (3) 4,4'-diphenol is epoxidized to obtain a liquid crystal epoxy precursor LEP; and (4) the PEF, the LEP and 3,3'-dithiodipropionic acid are mixed and heated and cured to prepare the epoxy resin. The prepared epoxy resin has intrinsic heat conduction, flame retardation and high efficiency recycling, and is a highly potential polymer material.

Description

Technical Field

[0001] This invention relates to the field of flame-retardant polymer technology, and more specifically to an intrinsically thermally conductive, flame-retardant recyclable epoxy resin and its preparation method. Background Technology

[0002] Epoxy resins, as a widely used thermosetting resin, have been extensively applied in aerospace, adhesives, electronic packaging, coatings, and composite materials, becoming an indispensable part of modern industry. However, epoxy resins are flammable materials, easily generating large amounts of heat and toxic gases when burned, limiting their application in high-safety fields. Furthermore, the non-recyclability of traditional thermosetting epoxy resins leads to large accumulations of waste, contradicting the principles of green manufacturing. Although significant progress has been made in epoxy resin recycling, with each recycling cycle, material properties inevitably decline to varying degrees, severely restricting their sustainable application in high-performance fields. Therefore, developing a flame-retardant epoxy resin with high recyclability is a critical issue that urgently needs to be addressed.

[0003] Conventional epoxy resins are amorphous and have poor thermal conductivity, typically below 0.2 W / (m·K), which cannot meet the high thermal conductivity requirements of high-density electronic devices and thermal management materials. In recent years, with the increasing integration of electronic devices and the promotion of green environmental protection policies, the development of epoxy resin materials with high thermal conductivity has become a research hotspot. Although some studies have attempted to improve thermal conductivity by filling with thermally conductive fillers (such as alumina and boron nitride) or introducing phosphorus- or nitrogen-containing structures to improve flame retardant properties, these strategies often have the following problems: adding thermally conductive fillers may reduce the mechanical properties and transparency of the material, and interfacial thermal resistance limits the thermal conductivity efficiency; externally added flame retardants are prone to migration and precipitation, affecting the long-term stability of the material.

[0004] Therefore, there is an urgent need to develop an epoxy resin system that combines intrinsic thermal conductivity, flame retardancy, and high recyclability to achieve synergistic optimization of thermal management, safety, and sustainability. Currently, relevant technologies remain relatively limited. Summary of the Invention

[0005] In view of this, the present invention provides an intrinsically thermally conductive and flame-retardant recyclable epoxy resin and its preparation method. The epoxy resin prepared by the present invention has excellent intrinsic thermal conductivity and flame-retardant properties, high recycling efficiency, and great application potential.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing an intrinsically thermally conductive and flame-retardant recyclable epoxy resin, characterized by comprising the following steps:

[0008] (1) Synthesize intermediate A containing phosphenanthrene and tertiary amine groups;

[0009] (2) An end-phosphate-based polyester flame retardant (PEF) was synthesized using intermediate A;

[0010] (3) A liquid crystal epoxy precursor (LEP) was synthesized using 4,4'-biphenyl.

[0011] (4) Mix the end-phosphate polyester flame retardant, liquid crystal epoxy precursor and 3,3'-dithiodipropionic acid in a certain proportion, pour into a mold and heat to cure to obtain epoxy resin.

[0012] Preferably, intermediate A in step (1) is prepared by reacting diethanolamine with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

[0013] Preferably, the reaction conditions for step (1) are as follows: under nitrogen conditions, diethanolamine, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), paraformaldehyde (POM) and chloroform are added to a reaction vessel and reacted for a period of time. After the reaction is completed, the mixture is slowly cooled to room temperature, the product is filtered, washed and vacuum dried to obtain a transparent gel-like product, which is intermediate A.

[0014] Preferably, the molar ratio of diethanolamine to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 1:1, and the mass percentage of paraformaldehyde is 10%-20%; the reaction time is 10-24 h at 40-65°C; and the vacuum drying is 6-12 h at 130-150°C.

[0015] The above process can be represented by the following chemical reaction equation:

[0016] .

[0017] Preferably, the phosphate-terminated polyester flame retardant in step (2) is prepared by a polycondensation reaction of intermediate A and phenylphosphonic acid, and has the characteristic structure shown in Formula 1:

[0018]

[0019] Formula 1.

[0020] Preferably, the conditions for the polycondensation reaction are as follows: intermediate A and phenylphosphonic acid are added to a flask equipped with a stirrer and a vacuum distillation device, the oil bath is heated to 160-200℃ and reacted for 2-6 h, and the water produced in the reaction is removed by vacuum distillation; the molar ratio of intermediate A to phenylphosphonic acid is (0.35-0.8):1.

[0021] The above process can be represented by the following chemical reaction equation:

[0022] .

[0023] Preferably, the liquid crystal epoxy precursor in step (3) is prepared by epoxidation of 4,4'-biphenyl.

[0024] The reaction conditions are as follows: Under nitrogen atmosphere, 4,4'-biphenyl hydroquinone is added to the reaction vessel, followed by epichlorohydrin and tetrabutylammonium bromide in a certain mass ratio. The mixture is heated to 60-80℃ and reacted for 2-4 h. Then, a strong alkali aqueous solution with a concentration of 30-50wt% is added dropwise, and the reaction is continued for 1-3 h. The solid is obtained by filtration, washed with water and ethanol in sequence, and dried under vacuum at 70-90℃ for 12-24 h to obtain the liquid crystal epoxy precursor.

[0025] The mass ratio of 4,4'-biphenyl to epichlorohydrin is 1:(3~4), and the amount of tetrabutylammonium bromide added is 0.5%-2% of the total mass of 4,4'-biphenyl and epichlorohydrin.

[0026] The above process can be represented by the following chemical reaction equation:

[0027] .

[0028] Preferably, the ratio of the number of epoxy groups in the liquid crystal epoxy precursor to the number of carboxyl groups in the terminal phosphate polyester flame retardant and 3,3'-dithiodipropionic acid in step (4) is 1:(0.8-1.2).

[0029] Preferably, the heating and curing in step (4) is carried out by hot pressing curing, and the hot pressing conditions are: 150℃, 10 MPa for 6 hours.

[0030] Another object of the present invention is to provide an intrinsically thermally conductive and flame-retardant recycled epoxy resin prepared by the above-described method for preparing the recycled epoxy resin.

[0031] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The synthesis method of the end-phosphate polyester flame retardant (PEF) in this invention is simple, does not require the participation of solvents, does not require complicated post-processing steps, and only water is generated as a by-product.

[0033] (2) The prepared epoxy resin material has excellent intrinsic thermal conductivity and flame retardancy.

[0034] (3) The prepared epoxy resin has triple dynamic covalent bonds, excellent physical remodeling properties, and can be processed more than 5 times. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0036] Figure 1 The 1H NMR spectrum of flame retardant intermediate A in Example 1;

[0037] Figure 2 The 1H NMR spectrum of the terminal phosphate-based polyester flame retardant (PEF1) in Example 1;

[0038] Figure 3 The stress relaxation curves are for Example 1 and Comparative Examples 1, 2, and 3.

[0039] Figure 4 This is a digital photograph physically reconstructed as shown in Example 1. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Example 1:

[0042] 1. First, flame retardant intermediate A containing phosphenanthrene groups was synthesized. Under nitrogen atmosphere, diethanolamine (19.2 g, 0.2 mol), DOPO (43.2 g, 0.2 mol), paraformaldehyde (9 g), and chloroform (200 mL) were added to a reaction vessel and reacted at 55 °C for 12 h. After the reaction was completed, the mixture was slowly cooled to room temperature. The product was filtered, and the residue was repeatedly washed with ethanol and then dried under vacuum at 130 °C for 6 h to obtain a transparent gel-like product, which was intermediate A.

[0043] 2. Under nitrogen conditions, intermediate A (33.3 g, 0.1 mol) and phenylphosphonic acid (31.6 g, 0.2 mol) were added to a flask equipped with a stirring and vacuum distillation apparatus, and reacted in an oil bath at 180 °C for 4 h to obtain end-phosphate polyester flame retardant (PEF1).

[0044] 3. Under nitrogen atmosphere, 30 g of 4,4'-biphenyl hydroquinone was added to a reaction vessel, followed by 90 g of epichlorohydrin and 1 g of tetrabutylammonium bromide. The mixture was heated to 80 °C and reacted for 3 h. Then, 50 g of 40 wt% sodium hydroxide aqueous solution was added dropwise, and the reaction was continued for 1 h. After the reaction was completed, the solid was filtered and washed with water and ethanol, and dried under vacuum at 80 °C for 4 h to obtain LEP.

[0045] 4. Mix and dissolve the above 10 g LEP, 4.9 g 3,3'-dithiodipropionic acid and 6.2 g PEF1 at 150°C, quickly pour into a mold, and cure at 10 MPa and 150°C for 6 h.

[0046] The material passed the UL 94 vertical burning test (V-0 rating); the limiting oxygen index (LOI) was 33.5%; the thermal conductivity was 1.12 W / (m·K); the tensile strength was 22.5 MPa; the stress relaxation time at 190℃ was 58 s; the tensile strength after five physical recycling cycles was 20.3 MPa; and the thermal conductivity after five physical recycling cycles was 1.08 W / (m·K).

[0047] Example 2:

[0048] 10 g LEP, 8.2 g PEF1 and 4.2 g 3,3'-dithiodipropionic acid prepared in Example 1 were mixed and stirred to dissolve at 150°C, and then quickly poured into a mold and cured at 10 MPa and 150°C for 6 h.

[0049] The material was tested and found to meet the UL 94 vertical burning test V-0 rating; the limiting oxygen index (LOI) was 34.3%; the thermal conductivity was 1.15 W / (m·K); the tensile strength was 21.3 MPa; the stress relaxation time at 190℃ was 61 s; the tensile strength after five physical recycling cycles was 19.6 MPa; and the thermal conductivity after five physical recycling cycles was 1.09 W / (m·K).

[0050] Example 3:

[0051] 1. Under nitrogen conditions, intermediate A (40 g, 0.12 mol) and phenylphosphonic acid (31.6 g, 0.2 mol) prepared in the examples were added to a flask equipped with a stirring and vacuum distillation apparatus, and reacted in an oil bath at 180°C for 4 h to obtain end-phosphate polyester flame retardant (PEF2).

[0052] 2. Mix and dissolve 10 g LEP, 4.9 g 3,3'-dithiodipropionic acid and 6.2 g PEF2 prepared in Example 1 at 150°C, quickly pour into a mold, and cure at 10 MPa and 150°C for 6 h.

[0053] The material passed the UL 94 vertical burning test (V-0 rating); the limiting oxygen index (LOI) was 33.0%; the thermal conductivity was 1.16 W / (m·K); the tensile strength was 21.5 MPa; the stress relaxation time at 190℃ was 56 s; the tensile strength after five physical recycling cycles was 19.4 MPa; and the thermal conductivity after five physical recycling cycles was 1.1 W / (m·K).

[0054] Comparative Example 1:

[0055] 1. Mix and dissolve 5 g of E51 (bisphenol A type epoxy resin, epoxy value: 0.51 mol / 100 g) and 1.9 g of adipic acid at 150℃.

[0056] 2. Pour the above mixture into a metal mold and cure at 150 °C for 6 hours to obtain a thermosetting epoxy resin.

[0057] Tests showed that the material had no UL 94 vertical burning rating; a limiting oxygen index (LOI) of 21.4%; a thermal conductivity of 0.56 W / (m·K); a tensile strength of 34.3 MPa; and no stress relaxation behavior at 190°C, making it impossible to physically recycle.

[0058] Comparative Example 2:

[0059] 1. Mix and dissolve 5 g of E51 and 2.7 g of 3,3'-dithiodipropionic acid at 150°C.

[0060] 2. Pour the above mixture into a metal mold and cure at 150°C for 6 hours to obtain a thermosetting epoxy resin.

[0061] The material was tested and found to have no UL 94 vertical burning rating; a limiting oxygen index (LOI) of 22.0%; a thermal conductivity of 0.58 W / (m·K); a tensile strength of 23.4 MPa; a stress relaxation time of 222 s at 190°C; a tensile strength of 11.5 MPa after five physical recycling cycles; and a thermal conductivity of 0.42 W / (m·K) after five physical recycling cycles.

[0062] Comparative Example 3:

[0063] 1. Mix and dissolve 5 g of LEP prepared in Example 1 and 3.5 g of 3,3'-dithiodipropionic acid at 150°C.

[0064] 2. Pour the above mixture into a metal mold and cure at 150°C for 6 hours to obtain a thermosetting epoxy resin.

[0065] The material was tested and found to have no UL 94 vertical burning rating; a limiting oxygen index (LOI) of 22.3%; a thermal conductivity of 0.98 W / (m·K); a tensile strength of 24.2 MPa; a stress relaxation time of 233 s at 190°C; a tensile strength of 11.1 MPa after five physical recycling cycles; and a thermal conductivity of 0.66 W / (m·K) after five physical recycling cycles.

[0066] In Comparative Examples 1, 2, and 3, which do not contain PEF, the UL-94 test results were all unrated. However, in Examples 1, 2, and 3, which contain PEF, the UL-94 test results were all rated V-0, indicating that PEF can effectively improve flame retardant performance. Figure 3 The stress relaxation curves show that Comparative Example 1, lacking any dynamic covalent bonds, exhibits no stress relaxation behavior and is therefore unsuitable for physical recycling. Comparative Examples 2 and 3, after adding a curing agent containing disulfide bonds, show stress relaxation behavior, but contain only one type of dynamic covalent bond, resulting in poor retention of mechanical properties after physical recycling. In Examples 1, 2, and 3, PEF contains a tertiary amine structure, enabling in-situ catalysis of transesterification. The terminal phosphate group of PEF reacts with the epoxy to form a β-hydroxy phosphate structure. Therefore, Examples 1, 2, and 3 contain a triple dynamic covalent bond of β-hydroxy ester, β-hydroxy phosphate, and disulfide bonds, exhibiting excellent retention of mechanical properties after physical recycling. Comparative Examples 1 and 2, lacking LEP, have low thermal conductivity. Comparative Example 3, using liquid crystal epoxy resin LEP, shows a significantly improved thermal conductivity. The addition of PEF in Examples 1, 2, and 3 further enhances the thermal conductivity. In summary, the epoxy resins prepared in Examples 1, 2 and 3 possess intrinsic thermal conductivity, flame retardancy and high recycling efficiency.

[0067] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0068] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing an intrinsically thermally conductive and flame-retardant recyclable epoxy resin, characterized in that, Includes the following steps: (1) Synthesize intermediate A containing phosphenanthrene and tertiary amine groups; (2) An end-phosphate-based polyester flame retardant was synthesized using intermediate A; (3) A liquid crystal epoxy precursor was synthesized using 4,4'-biphenyl. (4) Mix the end-phosphate polyester flame retardant, liquid crystal epoxy precursor and 3,3'-dithiodipropionic acid in a certain proportion, pour into a mold and heat to cure to obtain epoxy resin. Intermediate A in step (1) is prepared by reacting diethanolamine with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; The reaction conditions for step (1) are as follows: under nitrogen conditions, diethanolamine, 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide, paraformaldehyde and chloroform are added to the reaction vessel and reacted for a period of time. After the reaction is completed, the mixture is slowly cooled to room temperature, the product is filtered, washed and vacuum dried to obtain a transparent gel-like product, which is intermediate A. The phosphate-terminated polyester flame retardant described in step (2) is prepared by a polycondensation reaction of intermediate A and phenylphosphonic acid, and has the characteristic structure shown in Formula 1: Formula 1; The liquid crystal epoxy precursor in step (3) is prepared by epoxidation of 4,4'-biphenyl. The reaction conditions are as follows: Under nitrogen atmosphere, 4,4'-biphenyl hydroquinone is added to the reaction vessel, followed by epichlorohydrin and tetrabutylammonium bromide in a certain mass ratio. The mixture is heated to 60-80℃ and reacted for 2-4 h. Then, a strong alkali aqueous solution with a concentration of 30-50wt% is added dropwise, and the reaction is continued for 1-3 h. The solid is obtained by filtration, washed with water and ethanol in sequence, and dried under vacuum at 70-90℃ for 12-24 h to obtain the liquid crystal epoxy precursor. The mass ratio of 4,4'-biphenyl to epichlorohydrin is 1:(3~4), and the amount of tetrabutylammonium bromide added is 0.5%-2% of the total mass of 4,4'-biphenyl and epichlorohydrin.

2. The method for preparing an intrinsically thermally conductive and flame-retardant recyclable epoxy resin according to claim 1, characterized in that, The molar ratio of diethanolamine to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 1:1, and the mass percentage of paraformaldehyde is 10%-20%; the reaction time is 10-24 h at 40-65℃; and the vacuum drying is 6-12 h at 130-150℃.

3. The method for preparing an intrinsically thermally conductive and flame-retardant recyclable epoxy resin according to claim 1, characterized in that, The conditions for the polycondensation reaction are as follows: intermediate A and phenylphosphonic acid are added to a flask equipped with a stirrer and a vacuum distillation device, the oil bath is heated to 160-200℃ and reacted for 2-6 h, and the water produced in the reaction is removed by vacuum distillation; the molar ratio of intermediate A to phenylphosphonic acid is (0.35-0.8):

1.

4. The method for preparing an intrinsically thermally conductive and flame-retardant recyclable epoxy resin according to claim 1, characterized in that, The ratio of the number of epoxy groups in the liquid crystal epoxy precursor to the number of carboxyl groups in the terminal phosphate polyester flame retardant and 3,3'-dithiodipropionic acid in step (4) is 1:(0.8-1.2).

5. The method for preparing an intrinsically thermally conductive and flame-retardant recyclable epoxy resin according to claim 1, characterized in that, In step (4), the heating and curing process is carried out by hot pressing. The hot pressing conditions are: 150℃ and 10 MPa for 6 hours.

6. An intrinsically thermally conductive and flame-retardant recyclable epoxy resin, characterized in that, It is prepared by the method of preparing intrinsically thermally conductive and flame-retardant recyclable epoxy resin according to any one of claims 1-5.

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