A compound based on a bisimidazole skeleton and a phosphaphenanthrene group, and its preparation method and application

Abstract

The present invention discloses a compound based on a biimidazole skeleton and a phosphaphenanthrene group, as well as a preparation method and application thereof. The compound has the following structural formula: #imgabs0#. The compound based on a biimidazole skeleton and a phosphaphenanthrene group provided by the present invention exerts a flame retardant and promoting effect through the biimidazole skeleton and the phosphaphenanthrene group, can dilute the reactivity of CDI for easy processing, and can be quickly miscible with epoxy resin at only 70°C. The operation is simple and the energy consumption is low. The product is green and halogen-free, meeting the environmental protection requirements of flame-retardant epoxy resin production. At the same time, the epoxy resin exhibits excellent physical and mechanical properties and heat resistance while obtaining high flame retardancy.

Description

Technical Field

[0001] The present invention relates to the technical field of flame retardants, and in particular to a compound based on a bisimidazole skeleton and a phosphaphenanthrene group, and a preparation method and application thereof. Background Art

[0002] As a thermosetting polymer resin, epoxy resin is widely used in various industrial and engineering conditions due to its good bonding strength, high thermal stability, excellent insulation properties, outstanding chemical resistance and outstanding mechanical properties. However, unmodified epoxy resin is very flammable, which seriously limits its use in fields with high flame retardancy requirements, such as electronics and aerospace.

[0003] Currently, flame retardant modification of epoxy resins is primarily achieved through the addition of flame retardants. These agents can be categorized as additive or reactive based on their mode of action. Reactive flame retardants are preferred over additive flame retardants due to their long-lasting flame retardancy and minimal degradation of resin properties. 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) is an emerging reactive organophosphorus flame retardant with high flame retardancy, potentially replacing the most widely used but environmentally unfriendly halogen flame retardants in epoxy resins. DOPO is also a novel halogen-free flame retardant intermediate containing a PH bond, making it highly reactive towards olefins, epoxy bonds, and carbonyl groups, enabling direct flame retardant modification of epoxy resins. However, due to the steric hindrance of the benzene ring in DOPO, its reaction with epoxy resin requires relatively high temperatures, making this process time-consuming and energy-intensive, with minimal success. For example, in Novel phosphorus-containing epoxy resins Part I. Synthesis and properties, Wang et al. mentioned a phosphorus-containing epoxy resin. The introduction of DOPO as a reactive flame retardant requires a high temperature reaction of 160°C for 150 minutes, and the LOI is only 27% at a high phosphorus loading of 1.69 wt%. The phosphorus-containing epoxy resin mentioned by Zhang et al. in Preparation of flame retarded epoxy resins containing DOPO group needs to be synthesized by the reaction of DOPO and epoxy bonds under the condition of a reaction of 130°C for 120 minutes. When the phosphorus content in the system is 1.5 wt%, it only reaches the UL-94 V-1 level, and the mechanical properties and heat resistance are also deteriorated to a certain extent.

[0004] Therefore, it is urgent to provide a new flame retardant to solve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned technical deficiencies and propose a compound based on a bisimidazole skeleton and a phosphaphenanthrene group, as well as its preparation method and application, to solve the technical problems in the prior art that the process of introducing DOPO into epoxy resin is time-consuming and energy-consuming, the flame retardancy of the epoxy resin is insufficiently improved, and the mechanical properties and heat resistance are deteriorated.

[0006] In a first aspect, the present invention provides a compound based on a bisimidazole skeleton and a phosphaphenanthrene group, having the following structural formula:

[0007] .

[0008] In a second aspect, the present invention provides a method for preparing a compound based on a bisimidazole skeleton and a phosphaphenanthrene group, comprising the following steps:

[0009] Compounds based on bisimidazole skeleton and phosphaphenanthrene group were synthesized by nucleophilic addition reaction using N'N-carbonyldiimidazole and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide as raw materials.

[0010] In a third aspect, the present invention provides the use of the above-mentioned compound based on a bisimidazole skeleton and a phosphaphenanthrene group as a flame retardant accelerator for epoxy resin.

[0011] In a fourth aspect, the present invention provides the use of the above-mentioned compound based on a bisimidazole skeleton and a phosphaphenanthrene group as a flame retardant curing agent for epoxy resin.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] The compound based on a bisimidazole skeleton and a phosphaphenanthrene group provided by the present invention exerts flame retardant and promoting effects through the bisimidazole skeleton and the phosphaphenanthrene group, can dilute the reactivity of CDI for easy processing, can be quickly miscible with epoxy resin at only 70°C, is simple to operate and has low energy consumption, and the product is green and halogen-free, meeting the environmental protection requirements of flame-retardant epoxy resin production. At the same time, the epoxy resin exhibits excellent physical and mechanical properties and heat resistance while obtaining high flame retardancy. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 FTIR spectra of CDI, DOPO and DOPO-CDI prepared in Example 1 of the present invention;

[0015] Figure 2 DOPO and DOPO-CDI prepared in Example 1 of the present invention 31 P NMR spectrum;

[0016] Figure 3 DOPO-CDI prepared in Example 1 of the present invention 1 H NMR spectra;

[0017] Figure 4 Scanning electron micrographs of the combustion carbon residue of epoxy resin obtained by adding different amounts of DOPO-CDI prepared in Example 1 of the present invention; wherein the mass fractions of DOPO-CDI from left to right are 0 wt%, 3.0 wt%, 4.5 wt%, and 6.0 wt%, respectively; a, b, c, and d correspond to low magnifications, respectively; a1, b1, c1, and d1 correspond to high magnifications, respectively;

[0018] Figure 5 This is a bar graph showing the tensile strength of epoxy resins obtained at different addition amounts of DOPO-CDI prepared in Example 1 of the present invention;

[0019] Figure 6 This is a bar graph showing the bending strength of epoxy resins obtained at different addition amounts of DOPO-CDI prepared in Example 1 of the present invention;

[0020] Figure 7 This is a bar graph showing the impact strength of epoxy resins obtained at different addition amounts of DOPO-CDI prepared in Example 1 of the present invention;

[0021] Figure 8 The impact cross-section electron micrograph (a) of pure epoxy resin (Neat EP) and the impact cross-section electron micrograph (b) of epoxy resin to which 3 wt % of DOPO-CDI prepared in Example 1 of the present invention was added (EP / DOPO-CDI 3.0);

[0022] Figure 9 The infrared spectra of the carbon residues after combustion of pure epoxy resin (Neat EP) and epoxy resin added with 6 wt% of DOPO-CDI prepared in Example 1 of the present invention (EP / DOPO-CDI 6.0);

[0023] Figure 10 This is a full-time mass spectrum of the thermal decomposition of DOPO-CDI prepared in Example 1 of the present invention;

[0024] Figure 11 This is a mass spectrum of imidazole fragments generated by thermal decomposition of DOPO-CDI prepared in Example 1 of the present invention;

[0025] Figure 12 This is the mass spectrum of the DOPO fragment produced by thermal decomposition of DOPO-CDI prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0027] In the current research field of epoxy resin flame retardancy, most flame retardants (including DOPO, etc.) often need to be stirred at a high temperature above 130°C when introduced into epoxy resin (such as bisphenol A diglycidyl ether (DEGBA)). This process is often time-consuming and energy-consuming with little effect, resulting in low flame retardancy efficiency and adversely affecting the mechanical properties and heat resistance of the epoxy resin.

[0028] N'N-Carbonyldiimidazole (CDI) is a highly reactive imidazole compound. Due to its low cost, availability, and low toxicity during the reaction process, it is widely used in the biopharmaceutical field and is often used as an important intermediate in chemical synthesis. Further research by the inventors has also revealed that CDI can be used as an epoxy resin additive. This is because CDI contains highly reactive imidazole groups, which can promote the curing of epoxy resins. Epoxy resins synthesized via the imidazole anionic polymerization mechanism also exhibit excellent thermal stability and acid and alkali resistance. However, CDI's excessive reactivity can easily lead to premature curing of epoxy resins during processing due to its short working time, which limits its application in the epoxy resin field.

[0029] Based on this, the present invention is proposed.

[0030] In a first aspect, the present invention provides a compound based on a bisimidazole skeleton and a phosphaphenanthrene group (DOPO-CDI), having the following structural formula:

[0031] .

[0032] The compound based on a bisimidazole skeleton and a phosphaphenanthrene group (DOPO-CDI) provided by the present invention exerts flame retardant and promoting effects through the bisimidazole skeleton and the phosphaphenanthrene group, can dilute the reactivity of CDI for easy processing, can be quickly miscible with epoxy resin at only 70°C, is simple to operate and has low energy consumption, and the product is green and halogen-free, which can meet the environmental protection requirements of flame-retardant epoxy resin production.

[0033] In a second aspect, the present invention provides a method for preparing a compound based on a bisimidazole skeleton and a phosphaphenanthrene group, comprising the following steps:

[0034] Using N'N-carbonyldiimidazole (CDI) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as raw materials, a compound based on a bisimidazole skeleton and a phosphaphenanthrene group was synthesized via a nucleophilic addition reaction. The reaction formula is as follows:

[0035] .

[0036] The invention adopts DOPO and CDI to synthesize DOPO-CDI by a simple nucleophilic addition one-step method. The raw materials of the whole preparation process are cheap and easily available, the reaction conditions are mild, the preparation process has low toxicity, the reaction process is convenient and fast, the yield is high, and the production cost is low.

[0037] In this embodiment, the molar ratio of N'N-carbonyldiimidazole to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 1:(1-2), including but not limited to 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2, etc.

[0038] In this embodiment, the temperature of the nucleophilic addition reaction is 80-100°C, including but not limited to 80°C, 85°C, 90°C, 95°C, 100°C, etc.; the time of the nucleophilic addition reaction is 6-12h, including but not limited to 6h, 7h, 8h, 9h, 10h, 11h, 12h, etc.

[0039] In this embodiment, the nucleophilic addition reaction is carried out in the presence of a solvent.

[0040] Preferably, the solvent is one of N,N-dimethylformamide (DMF), toluene, tetrahydrofuran, and dioxane.

[0041] Preferably, the usage ratio of N'N-carbonyldiimidazole to the solvent is (0.1-0.5) g:1 ml, including but not limited to 0.1 g:1 ml, 0.2 g:1 ml, 0.3 g:1 ml, 0.4 g:1 ml, 0.5 g:1 ml, etc.

[0042] In this embodiment, the nucleophilic addition reaction is carried out under stirring and a protective atmosphere. The present invention does not limit the type of protective atmosphere, and those skilled in the art can select it according to actual circumstances. For example, the protective atmosphere can be nitrogen, argon, etc.

[0043] In this embodiment, after the nucleophilic addition reaction is completed, the process further comprises: extracting the crude product with a dichloromethane and water system, and drying the upper aqueous phase to obtain a pure product.

[0044] In some specific embodiments of the present invention, the method for preparing the compound based on a bisimidazole skeleton and a phosphaphenanthrene group comprises the following steps:

[0045] The solvent is divided into two parts, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and N'N-carbonyldiimidazole are dissolved in one part of the solvent respectively to obtain a 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide solution and an N'N-carbonyldiimidazole solution;

[0046] Under stirring at 80-100° C., a 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide solution is added dropwise to an N'N-carbonyldiimidazole solution. After the addition is complete, the reaction is continued for 6-12 hours. After the reaction is completed, the solvent is evaporated to obtain a compound based on a biimidazole skeleton and a phosphaphenanthrene group.

[0047] Preferably, the dropping time is 2-6 hours, including but not limited to 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, etc.

[0048] The raw materials of the present invention (N'N-carbonyldiimidazole, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and solvent) are all dehydrated or dried before use.

[0049] In a third aspect, the present invention provides the use of the above-mentioned compound based on a bisimidazole skeleton and a phosphaphenanthrene group as a flame retardant accelerator for epoxy resin.

[0050] The compound based on a biimidazole skeleton and a phosphaphenanthrene group of the present invention can be introduced into epoxy resin as an epoxy resin flame retardant accelerator at low temperature and in a short time, and can also reduce the curing temperature and shorten the curing time. After being introduced into the epoxy resin curing system, a high-performance flame-retardant epoxy resin with high strength, high toughness and high thermal stability can be produced.

[0051] In this embodiment, the compound having a biimidazole skeleton and a phosphaphenanthrene group accounts for 2-10% of the total mass of the epoxy resin system (i.e., epoxy resin + curing agent + compound having a biimidazole skeleton and a phosphaphenanthrene group), including but not limited to 2%, 4%, 6%, 8%, and 10%.

[0052] In this embodiment, the compound having a bisimidazole skeleton and a phosphaphenanthrene group is dissolved in the epoxy resin at a temperature of 65-80° C., preferably 70° C., for 3-10 minutes, preferably 5 minutes.

[0053] In this embodiment, the curing conditions are: pre-curing at 70-110° C. for 0.5-1 h, then curing at 120-150° C. for 0.5-2 h, and finally curing at 170-190° C. for 1-3 h.

[0054] In a fourth aspect, the present invention provides the use of the above-mentioned compound based on a bisimidazole skeleton and a phosphaphenanthrene group as a flame retardant curing agent for epoxy resin.

[0055] When the compound based on the bisimidazole skeleton and the phosphaphenanthrene group is used as an epoxy resin flame retardant curing agent and is introduced into the epoxy resin, the temperature is low and the time is short, and the compound has a latent curing effect.

[0056] In this embodiment, the compound having a biimidazole skeleton and a phosphaphenanthrene group accounts for 2-10% of the total mass of the epoxy resin system (i.e., epoxy resin + compound having a biimidazole skeleton and a phosphaphenanthrene group), including but not limited to 2%, 4%, 6%, 8%, and 10%.

[0057] In this embodiment, the compound having a bisimidazole skeleton and a phosphaphenanthrene group is dissolved in the epoxy resin at a temperature of 65-80° C., preferably 70° C., for 3-10 minutes, preferably 5 minutes.

[0058] In this embodiment, the curing conditions are: pre-curing at 60-80° C. for 0.5-1 h, then curing at 110-130° C. for 0.5-2 h, and finally curing at 170-190° C. for 1-3 h.

[0059] In the present invention, it should be noted that the compounds of the present invention having a bisimidazole skeleton and a phosphaphenanthrene group do not limit the applicable epoxy resin system, and those skilled in the art can select according to actual conditions. For example, the epoxy resin can be bisphenol A glycidyl ether, and the curing agent can be 4,4'-diaminodiphenylmethane, dicyandiamide, etc.

[0060] Example 1 Preparation of DOPO-CDI

[0061] After pre-treatment of the DMF solvent and the two raw materials to remove water, 60g of DOPO was dissolved in 150ml of DMF. 45g of CDI and 50ml of DMF were added to a 500ml three-necked flask and dissolved under heating and magnetic stirring under a nitrogen atmosphere. Once the CDI was completely dissolved and the temperature in the flask stabilized at 90°C, the DOPO-DMF solution was slowly added dropwise to the flask via a constant pressure funnel. The addition was complete within 4 hours and the reaction was continued for 8 hours before removal. The solvent was evaporated to dryness to obtain the crude product DOPO-CDI. DOPO-CDI is a deep red semisolid that dissolves rapidly in epoxy resin under heating. In the subsequent examples and comparative examples, the crude product was used directly as a curing agent or accelerator. If the crude product requires purification, it can be extracted with dichloromethane and water to remove trace amounts of unreacted raw materials. The upper aqueous phase was then dried to obtain the pure product.

[0062] By FTIR, 1 H NMR, 31 The structure of the purified DOPO-CDI was characterized by P NMR. The test results are shown in Figure 1-3 .

[0063] See also Figure 1 ,pass Figure 1 It can be seen that in the infrared spectrum of DOPO-CDI, the wave number is 750cm -1and 1220cm -1 They are the absorption peaks of Ar-H and P=O in the DOPO group, 1050 cm -1 The absorption peak is derived from the CN bond in the CDI group. In addition, the absorption peak at 1750cm -1 and 1730cm -1 The C=O doublet peak disappears due to the nucleophilic attack of PH, and a peak at 3300 cm -1 A broad hydroxyl peak at 3500 cm-1.

[0064] See also Figure 2-3 ,pass Figure 2-3 It can be seen that the area and position of each NMR absorption peak correspond one to one with the chemical structure of DOPO-CDI, further proving the successful synthesis of DOPO-CDI.

[0065] Example 2 DOPO-CDI is directly used as a flame retardant curing agent for epoxy resin

[0066] The prepared DOPO-CDI was added to an epoxy resin (bisphenol A glycidyl ether, DEGBA) at a 6wt% mass fraction and dissolved with stirring at 70°C until a homogeneous system with the bisphenol A glycidyl ether was formed. After vacuum degassing, the mixture could be cast or stored properly after cooling to room temperature. To ensure uniformity in the cured resin, a certain degree of fluidity was required during the initial curing phase. Therefore, the curing cycle was set as a pre-cure at 70°C for 1 hour, a cure at 120°C for 1 hour, and a cure at 180°C for 2 hours.

[0067] The cured samples fully meet the characteristics of imidazole-cured products, showing high thermal stability, a glass transition temperature Tg of 162°C, high flame retardancy, an oxygen index of 36.5%, and passing the UL-94 V-0 rating.

[0068] Example 3: DOPO-CDI used as an accelerator in epoxy resin / 4,4'-diaminodiphenylmethane (DDM) curing system

[0069] First, the epoxy resin was heated to 90°C. An appropriate amount of DDM was added based on the equimolar ratio of active hydrogen and epoxy based on the epoxy equivalent of the epoxy resin. Once dissolved into a homogeneous and transparent solution, the oil bath temperature was lowered to 70°C. After the system temperature stabilized, 3.0% of the total system mass fraction (3 wt%) of the prepared DOPO-CDI was added and stirred until homogeneous and transparent. The specific formula is shown in Table 1. The sample was removed and vacuum-degassing was performed, and then cast and cured. The curing procedure was 70°C for 1 hour, 120°C for 1 hour, and 180°C for 2 hours. The sample to be tested was numbered EP / DOPO-CDI 3.0.

[0070] Example 4 DOPO-CDI is used as an accelerator for epoxy resin / dicyandiamide curing system

[0071] After heating the epoxy resin to 70°C, add dicyandiamide (calculated according to the epoxy equivalent) and disperse it evenly. Then add the prepared DOPO-CDI and stir until the DOPO-CDI is completely dissolved and the system is uniform. Then take it out and pour it into the mold after vacuum degassing, or wait for it to cool to room temperature and store it properly. The curing procedure is 110°C for 1 hour, 150°C for 1 hour, and 180°C for 2 hours.

[0072] Due to the promoting effect of DOPO-CDI, the curing exothermic peak of the epoxy resin / dicyandiamide system with the introduction of 6wt% DOPO-CDI is reduced to 140℃.

[0073] Example 5 DOPO-CDI is used as an accelerator for epoxy resin / DDM curing system

[0074] Similar to Example 3, in order to explore the effect of dosage on performance, the addition amount of DOPO-CDI was adjusted to 4.5 wt %. The specific formula is shown in Table 1, and the sample to be tested is numbered EP / DOPO-CDI 4.5.

[0075] Example 6 DOPO-CDI used as an accelerator for epoxy resin / DDM curing system

[0076] Similar to Example 3, in order to explore the effect of dosage on performance, the addition amount of DOPO-CDI was adjusted to 6 wt %. The specific formula is shown in Table 1, and the sample to be tested is numbered EP / DOPO-CDI 6.0.

[0077] Comparative Example 1

[0078] To better characterize the impact of DOPO-CDI on the overall performance of epoxy resins, a pure epoxy resin / DDM curing system was prepared. The epoxy resin was first heated to 90°C. An appropriate amount of DDM, based on the epoxy equivalent weight of the epoxy resin, was added. Once dissolved into a homogeneous, transparent solution, the solution was removed and immediately poured into a mold for curing after vacuum degassing. The specific formulation is shown in Table 1. Because there was no curing-accelerating component, the curing schedule was set to 100°C for 2 hours, 150°C for 2 hours, and 180°C for 2 hours for ease of comparison. The tested sample was designated Neat EP.

[0079] Comparative Example 2

[0080] To demonstrate the superiority of DOPO-CDI over DOPO, an epoxy resin / DDM curing system with direct addition of DOPO was prepared. DEGBA was first heated to 100°C, 3 wt% DOPO was added, and dissolved within 1 hour to achieve a homogeneous system. DDM was then added for curing, with the same curing schedule of 100°C for 2 hours, 150°C for 2 hours, and 180°C for 2 hours. The sample to be tested was designated EP / DOPO 3.0.

[0081] In order to study the effect of DOPO-CDI on the performance of epoxy resin and explore its mechanism, a representative aromatic amine curing agent DDM was selected and combined with DGEBA (epoxy value 0.51 mol / 100 g) as the main curing system for testing and research. The test results are shown in Tables 1-3 and Figure 4-12 .

[0082] Among them, the limiting oxygen index (LOI) test is carried out according to the ASTM D2863 standard; the vertical burning (UL-94) test is based on the ISO-1210 standard; and the combustion behavior of EP is characterized using a cone calorimeter, and the test is based on the ISO 5660 standard.

[0083] Table 1 Formula of pure epoxy resin and flame retardant epoxy resin

[0084] sample Bisphenol A diglycidyl ether E51 (wt%) DDM (wt%) DOPO-CDI (wt%) DOPO (wt%) P(wt%) Neat EP 80 20 0 0 0 EP / DOPO-CDI 3.0 77.6 19.4 3.0 0 0.25 EP / DOPO-CDI 4.5 76.4 19.1 4.5 0 0.37 EP / DOPO-CDI 6.0 75.2 18.8 6.0 0 0.49 EP / DOPO 3.0 77.6 19.4 0 3.0 0.43

[0085] Table 2 Comprehensive performance comparison of Examples 3, 5, 6 and Comparative Examples 1 and 2

[0086] sample P(wt%) LOI(%) UL-94 Glass transition temperature / ℃ Curing exothermic peak / ℃ Neat EP 0 25 NR 152.9 163 EP / DOPO-CDI 3.0 0.25 36.8 V-1 165.6 139 EP / DOPO-CDI 4.5 0.37 37.0 V-0 163.5 142 EP / DOPO-CDI 6.0 0.49 37.5 V-0 156.9 144 EP / DOPO 3.0 0.43 32.6 V-1 148.2 158

[0087] Table 3 Comparison of combustion behaviors of Examples 3, 5, 6 and Comparative Example 1

[0088] sample Neat EP EP / DOPO-CDI3.0 EP / DOPO-CDI4.5 EP / DOPO-CDI6.0 TTI(s) 50 51 46 45 PHRR(KW / m 2 , 1822.8 1334.3 1105.9 991.7 THR(MJ / m 2 ) 91.3 73.1 68.4 66.7 FIGRA(KW / m 2 ·s) 11.13 9.10 7.52 6.89 Av-COY(kg / kg) 0.089 0.085 0.087 0.091 Off-CO2Y(kg / kg) 2.16 1.72 1.63 1.64 TSP(m 2 ) 20.0 18.5 17.9 16.4

[0089] Please refer to Tables 1-3. It can be seen from Tables 1-3 that the pure epoxy resin NeatEP without the addition of DOPO-CDI of the present invention exhibits the lowest flame retardancy, corresponding to Example 1, the flame retardant epoxy resin EP / DOPO 3.0 with direct addition of DOPO exhibits lower flame retardancy, corresponding to Example 2, while EP / DOPO-CDI 3.0, EP / DOPO-CDI 4.5 and EP / DOPO-CDI 6.0 correspond to Examples 3, 5 and 6, respectively.

[0090] Tables 2 and 3 show that the addition of DOPO-CDI to the EP / DDM epoxy curing system improves the flame retardancy and fire safety of the epoxy resin to varying degrees. The exceptionally high flame retardancy is attributed to the synergistic flame retardancy of PN and the unique degradation behavior of the imidazole backbone. Furthermore, the introduction of DOPO-CDI improves epoxy resin processing performance and heat resistance, making it superior to DOPO in various aspects.

[0091] See also Figure 4 ,pass Figure 4 It can be seen that the carbon residue produced after combustion of the epoxy resin matrix with the addition of DOPO-CDI shows a trend of gradually becoming denser with the increase of the amount of DOPO-CDI added, indicating that its condensed phase flame retardant effect also increases accordingly.

[0092] See also Figure 5-7 ,pass Figure 5-7 It can be seen that the epoxy resin system after adding DOPO-CDI has higher strength and toughness, and the tensile strength and flexural strength increase with the increase of DOPO-CDI addition, but after adding DOPO-CDI, the impact strength decreases with the increase of DOPO-CDI addition.

[0093] See also Figure 8 ,pass Figure 8 It can be seen that the introduction of DOPO-CDI makes the impact fracture surface of the epoxy resin matrix rougher, proving that it absorbs more impact energy and thus has greater toughness.

[0094] See also Figure 9 ,pass Figure 9 It can be seen that the addition of DOPO-CDI enables the epoxy resin matrix to produce a large number of dense graphite layers during the combustion process, achieving condensed phase flame retardancy.

[0095] See also Figure 10-12 ,pass Figure 10-12 It can be seen that the thermal decomposition of DOPO-CDI releases a large amount of flame retardant substances, such as imidazole and DOPO, into the air, indicating that the addition of DOPO-CDI to epoxy resin is beneficial to the gas phase flame retardancy of the epoxy resin matrix.

[0096] Compared with the prior art, the present invention has the following beneficial effects:

[0097] (1) The DOPO-CDI of the present invention has good processing performance and can form a homogeneous system with bisphenol A glycidyl ether by stirring at 70°C for 5 minutes.

[0098] (2) The DOPO-CDI of the present invention has a wide range of applications and can be used as an epoxy resin curing accelerator or as a standalone epoxy resin curing agent. When used as an epoxy resin curing accelerator, it has a promoting effect on a variety of epoxy resin curing systems. When used as an epoxy resin curing agent, it has a longer processing time than CDI and exhibits a latent curing effect, allowing it to be stored at room temperature for 10 days.

[0099] (3) When the DOPO-CDI of the present invention is used in a DDM / EP curing system, the epoxy resin can be cured and formed in 10 minutes at 100°C. Under laboratory conditions, the epoxy resin can be further cured by means of pre-curing and post-curing to obtain optimal performance. In actual production, the curing procedure can be further adjusted according to energy consumption requirements.

[0100] (4) The epoxy resin to which the DOPO-CDI of the present invention is added exhibits excellent physical and mechanical properties and heat resistance while achieving high flame retardancy.

[0101] (5) The present invention reduces the excessive reactivity of CDI through chemical modification to facilitate its introduction into epoxy resin, thereby expanding the application of this pharmaceutical intermediate in the field of epoxy resin.

[0102] The specific embodiments of the present invention described above do not limit the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A compound based on a bisimidazole skeleton and a phosphaphenanthrene group, characterized in that: It has the following structural formula: 。 2. A method for preparing a compound based on a bisimidazole skeleton and a phosphaphenanthrene group as claimed in claim 1, characterized in that: The following steps are involved: Compounds based on bisimidazole skeleton and phosphaphenanthrene group were synthesized by nucleophilic addition reaction using N'N-carbonyldiimidazole and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide as raw materials.

3. The method for preparing a compound based on a bisimidazole skeleton and a phosphaphenanthrene group according to claim 2, wherein: The molar ratio of N'N-carbonyldiimidazole to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 1:(1-2); and / or, The temperature of the nucleophilic addition reaction is 80-100° C., and the time of the nucleophilic addition reaction is 6-12 hours.

4. The method for preparing a compound based on a bisimidazole skeleton and a phosphaphenanthrene group according to claim 2, wherein: The nucleophilic addition reaction is carried out in the presence of a solvent; wherein, The solvent is one of N,N-dimethylformamide, toluene, tetrahydrofuran, and dioxane; and / or, The usage ratio of the N'N-carbonyldiimidazole to the solvent is (0.1-0.5) g:1 ml.

5. The method for preparing a compound based on a bisimidazole skeleton and a phosphaphenanthrene group according to claim 2, wherein: After the nucleophilic addition reaction is completed, the method further comprises: extracting the crude product through a system of dichloromethane and water, and drying the upper aqueous phase to obtain a pure product.

6. The method for preparing a compound based on a bisimidazole skeleton and a phosphaphenanthrene group according to claim 2, wherein: The following steps are involved: The solvent is divided into two parts, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and N'N-carbonyldiimidazole are dissolved in one part of the solvent respectively to obtain a 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide solution and an N'N-carbonyldiimidazole solution; The 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide solution is added dropwise to the N'N-carbonyldiimidazole solution under stirring at 80-100° C. The addition time is 2-6 hours. After the addition is completed, the reaction is continued for 6-12 hours. After the reaction is completed, the solvent is evaporated to obtain a compound based on a biimidazole skeleton and a phosphaphenanthrene group.

7. Use of the compound based on a bisimidazole skeleton and a phosphaphenanthrene group as claimed in claim 1 as a flame retardant accelerator for epoxy resin.

8. The use of the compound based on a bisimidazole skeleton and a phosphaphenanthrene group as a flame retardant accelerator for epoxy resin according to claim 7, characterized in that: The compound of the bisimidazole skeleton and the phosphaphenanthrene group accounts for 2-10% of the total mass of the epoxy resin, the curing agent, the bisimidazole skeleton and the phosphaphenanthrene group; and / or, The compound containing the bisimidazole skeleton and the phosphaphenanthrene group is dissolved in the epoxy resin at a temperature of 65-80° C. for 3-10 minutes; and / or, The curing conditions are: pre-curing at 70-110° C. for 0.5-1 h, curing at 120-150° C. for 0.5-2 h, and finally curing at 170-190° C. for 1-3 h.

9. Use of the compound based on a bisimidazole skeleton and a phosphaphenanthrene group as claimed in claim 1 as a flame retardant curing agent for epoxy resin.

10. The use of the compound based on a bisimidazole skeleton and a phosphaphenanthrene group as a flame retardant curing agent for epoxy resin according to claim 9, characterized in that: The compound having a biimidazole skeleton and a phosphaphenanthrene group accounts for 2-10% of the total mass of the epoxy resin and the compound having a biimidazole skeleton and a phosphaphenanthrene group; and / or, The compound containing the bisimidazole skeleton and the phosphaphenanthrene group is dissolved in the epoxy resin at a temperature of 65-80° C. for 3-10 minutes; and / or, The curing conditions are: pre-curing at 60-80° C. for 0.5-1 h, curing at 110-130° C. for 0.5-2 h, and finally curing at 170-190° C. for 1-3 h.

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