A dopo-based derivative monomer, a preparation method and application thereof

Abstract

The application relates to a DOPO-based derivative monomer, a preparation method and application thereof, and belongs to the technical field of organic synthesis. The application takes p-methoxycarbonyl benzaldehyde and methyl p-bromobenzoate as raw materials, and prepares and synthesizes DOPO-bis (4-carboxyl phenyl) through an ester group protection-halogenation activation-DOPO nucleophilic bond formation-ester hydrolysis reaction. The application solves the defects that the existing DOPO-based copolymer monomer structure has low polymerization activity, single function, and the modified polyester is difficult to consider heat resistance, flame retardance and aging resistance by means of DOPO skeleton modification and monomer structure design, improves the structural uniqueness of the monomer and the industrialization feasibility of the preparation process, and does not need special raw materials or equipment adaptation. The method has the advantages of high monomer preparation yield and excellent copolymerization reaction efficiency, realizes the synergistic improvement of heat resistance, flame retardance and aging resistance, and expands the application range of polyester injection products.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, and in particular relates to a DOPO-based derivative monomer, its preparation method, and its application. Background Technology

[0002] Polyesters are widely used in electronics, automotive parts, and other fields due to their excellent mechanical and processing properties. However, their inherent flammability makes them prone to causing fires, with a limiting oxygen index (LOI) of only 21% and a vertical flammability rating of UL94V-2. Therefore, flame retardant modification is a core requirement for expanding their applications. DOPO, as a halogen-free phosphorus-containing flame retardant, combines high thermal stability with environmental friendliness. It can improve flame retardancy through a synergistic mechanism of char formation and smoke suppression, avoiding the environmental risks of brominated flame retardants and the compatibility defects of inorganic flame retardants. However, DOPO contains only PH bonds and lacks copolymerizable functional groups. Physical blending is prone to migration, loss, and phase separation, which can disrupt the mechanical uniformity of polyester. Therefore, structural modification is needed to introduce active sites to achieve covalent bonding.

[0003] Meanwhile, as electronic and electrical appliances become smaller and more powerful, the operating temperature of internal components has risen to 90-120℃. Traditional polyesters, such as PET, have a glass transition temperature close to 67℃, at which they are prone to softening and deformation, failing to meet the requirements of high-temperature resistant components such as connectors and insulating skeletons. Furthermore, with the trend towards lightweight materials, applications such as automotive engines require higher heat resistance from surrounding high-temperature components, further highlighting the urgency of heat-resistant modification of polyesters. Currently, the market size of flame-retardant and heat-resistant polyesters is gradually growing in the fields of high-temperature flame-retardant components for electronic and electrical appliances and peripheral materials for automotive engines. Moreover, with the deepening of halogen-free flame-retardant regulations and the increasing performance requirements of high-end equipment, polyester materials that combine flame retardancy and heat resistance will gradually replace traditional modified polyesters, capturing a larger share of the high-end market.

[0004] Existing research on polyester DOPO modification has significant limitations. It's difficult to simultaneously achieve both flame retardancy and heat resistance in DOPO-based flame retardants. Materials prepared often fail to maintain good heat resistance, aging resistance, and processability while ensuring flame retardancy. For example, the existing technical paper "Study on the Synthesis Kinetics of PET Based on DOPO-based Flame Retardants" reports that the steric hindrance effect of DDP significantly reduces the rate constant of the polycondensation reaction, affecting polymer product performance. Patent CN105669760B discloses an organophosphorus phenanthrene derivative, prepared by reacting glycerol ester derivatives obtained from the esterification of glycerol with carboxylic acid / acyl chloride derivatives with organophosphorus phenanthrene compounds. This method can be used to improve the flame retardancy of polyesters such as PET and PBT, as well as polyamide engineering plastics such as PA6 and PA66. However, this preparation method suffers from low reaction efficiency and a need for improvement in product yield.

[0005] Therefore, there is an urgent need to develop a DOPO-based monomer with a mild and environmentally friendly synthesis process, while also possessing multiple excellent properties such as high temperature resistance and anti-aging properties, to meet the needs of high-end electronics and automotive fields. Summary of the Invention

[0006] To address the shortcomings of existing technologies and to solve the problems of low polymerization activity and limited functionality of DOPO monomers, as well as the poor environmental friendliness of monomer synthesis in DOPO-based polyester modification technologies, which fail to simultaneously improve heat resistance, flame retardancy, and aging resistance, this invention aims to design and provide a mild and environmentally friendly DOPO-based diacid monomer for synthesis, and its application in polyester copolymerization. This invention offers advantages such as high monomer yield and excellent copolymerization efficiency, achieving a balanced optimization of flame retardancy, heat resistance, and processing performance in polyester materials, meeting the needs of high-end electronics and automotive industries.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] On one hand, the present invention provides a DOPO-based derivative monomer, wherein the DOPO-based derivative monomer is DOPO-bis(4-carboxyphenyl) (abbreviated as DOPO-MDCA), and its structural formula is shown in Formula I below:

[0009] Formula I.

[0010] Secondly, this invention provides a method for preparing a DOPO-based derivative monomer. This invention synthesizes the target monomer through a four-step reaction: "ester protection - halogenation activation - DOPO nucleophilic bonding - ester hydrolysis," specifically including the following steps:

[0011] Weigh p-methoxycarbonylbenzaldehyde and methyl p-bromobenzoate, and react them with magnesium shavings in an anhydrous solvent, i.e., Grignard reagent addition reaction, to prepare bis(p-methoxycarbonylphenyl)methanol; the ester group is protected to prevent the carboxyl group from being deactivated in subsequent reactions.

[0012] Di(p-methoxycarbonylphenyl)methanol was weighed and subjected to a halogenation reaction with a halogenating reagent and a catalyst to obtain bis(p-methoxycarbonylphenyl) halomethane; a leaving group (Cl or Br) was introduced through the halogenation reaction to provide an active site for the nucleophilic attack of DOPO.

[0013] Weigh out bis(p-methoxycarbonylphenyl) halomethane, DOPO and an acid-binding agent and carry out a heating and reflux reaction in an organic solvent to form PC bonds, and obtain an ester-protected DOPO intermediate;

[0014] The DOPO intermediate was hydrolyzed under alkaline solution conditions, and after acidification, the ester group was converted into a carboxyl group. After separation and purification, DOPO-bis(4-carboxyphenyl) was obtained, with the full name 10-[(4,4'-dicarboxyphenyl)methyl]-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

[0015] In the preparation method described above, the anhydrous solvent is anhydrous tetrahydrofuran or anhydrous diethyl ether;

[0016] The molar ratio of p-methoxycarbonylbenzaldehyde to methyl p-bromobenzoate is 1:(1.0~1.2);

[0017] The molar ratio of methyl p-bromobenzoate to magnesium shavings is 1:(1.1~1.3);

[0018] The reaction conditions are: reaction temperature -5~25℃, reaction time 2~5h.

[0019] In the preparation method described above, the halogenated reagent is selected from at least one of thionyl chloride, phosphorus oxychloride, or hydrobromic acid;

[0020] The molar ratio of the halogenating reagent to bis(p-methoxycarbonylphenyl)methanol is (1.1~1.5):1;

[0021] The catalyst is selected from at least one of methanesulfonic acid, p-toluenesulfonic acid, or concentrated phosphoric acid;

[0022] The amount of catalyst used is 1% to 5% of the mass of bis(p-methoxycarbonylphenyl)halomethane;

[0023] The conditions for the halogenation reaction are: reaction temperature 20~60℃, reaction time 1~3h.

[0024] In the preparation method described above, the acid-binding agent is selected from at least one of triethylamine, diisopropylethylamine, or pyridine.

[0025] The organic solvent is toluene or xylene;

[0026] The molar ratio of the bis(p-methoxycarbonylphenyl) halomethane to DOPO is 1:(1.0~1.1);

[0027] The molar ratio of the acid-binding agent to bis(p-methoxycarbonylphenyl) halomethane is (1.0~1.5):1;

[0028] The conditions for the heating and reflux reaction are: reaction temperature 80~120℃, reaction time 4~8h.

[0029] In the preparation method described above, the alkaline solution is an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide.

[0030] The amount of solute in the alkaline solution is 2.0 to 3.0 times the molar amount of the DOPO intermediate;

[0031] The conditions for the hydrolysis reaction are: hydrolysis temperature 60~100℃, hydrolysis time 3~6h;

[0032] The acidification is carried out to pH 2-3;

[0033] The separation and purification methods are filtration, water washing, vacuum drying, or recrystallization.

[0034] Thirdly, the present invention provides the application of the DOPO-based derivative monomer in the preparation of flame-retardant, heat-resistant, and aging-resistant polyester materials.

[0035] Fourthly, the present invention provides a method for preparing a flame-retardant, heat-resistant, and aging-resistant polyester material, wherein the DOPO-based derivative monomer and the polyester monomer are subjected to esterification or transesterification reaction and polycondensation reaction in sequence under the action of a catalyst to obtain a flame-retardant, heat-resistant, and aging-resistant polyester.

[0036] The method for preparing a flame-retardant, heat-resistant, and aging-resistant polyester material, wherein the DOPO-based derivative monomer accounts for 5% to 20% of the molar amount of the polyester monomer, allows for the control of the flame-retardant and heat-resistant properties of the polyester.

[0037] Preferably, the polyester monomer is PET, PBT or PTT.

[0038] Fifthly, the present invention provides a flame-retardant, heat-resistant, and aging-resistant polyester material, obtained by the aforementioned preparation method.

[0039] Preferably, a flame-retardant, heat-resistant, and aging-resistant polyester material comprises: terephthalic acid, DOPO-MDCA, a diol, and a catalyst, subjected to an esterification-pre-polymerization-polymerization reaction; after the reaction, granulation and drying are performed to obtain the flame-retardant and heat-resistant polyester material. The diol is ethylene glycol or isosorbide.

[0040] The flame-retardant, heat-resistant, and aging-resistant polyester material has a limiting oxygen index (LOI) ≥23%, a vertical flammability rating of UL94V-0, and a glass transition temperature (T0). g With a temperature of ≥82.2℃, which is 5~30℃ higher than that of unmodified polyester of the same type, it is suitable for preparing high-temperature resistant and flame-retardant electronic and electrical components, high-temperature resistant parts around automobile engines, high-temperature food packaging materials, or high-temperature resistant and flame-retardant fibers.

[0041] Mechanism of action of the present invention: (1) Flame retardancy: The phosphenanthrene ring of DOPO-bis(4-carboxyphenyl) monomer decomposes at high temperature to generate phosphoric acid substances, forming a dense flame retardant carbon layer on the surface of the material, isolating oxygen and heat, forming condensed phase flame retardancy; at the same time, the released phosphorus-containing free radicals can capture active free radicals in the combustion process, terminate the chain combustion reaction, form gas phase flame retardancy, and achieve gas phase-condensed phase synergistic flame retardancy. (2) High temperature resistance: The rigid conjugated structure of the phosphenanthrene ring (DOPO skeleton) and benzene ring of the monomer of the present invention, after being introduced into the polyester main chain, will restrict the flexibility of the molecular chain, increase the packing density of the molecular chain, thereby increasing the glass transition temperature and heat distortion temperature; at the same time, the large conjugated system enhances the intermolecular interaction, reduces the thermal motion activity of the molecular chain, and further improves the thermal stability. (3) Aging resistance: The DOPO phosphoranthroline and benzene ring of the DOPO-bis(4-carboxyphenyl) monomer of this invention form a large π conjugated system, which can absorb 280-350nm ultraviolet light and disperse energy, reduce the free radical degradation reaction initiated by ultraviolet light, and delay the yellowing and embrittlement of the material; the rigid skeleton of the benzene ring restricts the movement of the molecular chain, reducing the exposure and degradation sites of the molecular chain under thermo-oxidative conditions; at the same time, the phosphorus-oxygen bond and the benzene ring have high bond energy, which are not easy to break under thermo-oxidative conditions, thus avoiding molecular chain degradation.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. The DOPO-bis(4-carboxyphenyl) (DOPO-MDCA) prepared by this invention has a well-defined structure, containing two carboxyl groups that can efficiently copolymerize with polyester monomers, exhibiting excellent compatibility with the polyester molecular chain. The dual carboxyl group active sites significantly enhance the copolymerization efficiency with PET, solving the problem of low polymerization activity of traditional DOPO monomers. Furthermore, the phosphorus atom is connected to the rigid heterocycle of DOPO through a stable PC bond, preventing phosphorus migration and facilitating subsequent improvement of polyester T. g It lays the foundation for the structure and has outstanding high-temperature resistance.

[0044] 2. The synthesis route of the DOPO-bis(4-carboxyphenyl) monomer prepared by this invention is simple and controllable. Each step uses conventional commercial raw materials and is compatible with existing PET copolymerization production lines. The reaction conditions are mild, and the product has high purity after separation and purification. The industrial production cost is low and the operation is strong. It solves the problem that existing PET copolymers cannot simultaneously achieve heat resistance, flame retardancy and aging resistance, and the products are difficult to adapt to high temperature and complex working conditions.

[0045] 3. When the DOPO-bis(4-carboxyphenyl) monomer prepared in this invention participates in PET copolymerization, the rigid phosphorus heterocycle and benzene ring structure of DOPO are simultaneously embedded in the polyester backbone, significantly increasing the rotational resistance within the molecular chain and lowering the glass transition temperature (Tg) of the modified polyester. g Compared to unmodified polyester of the same type, it is an improvement and greatly expands the application range of polyester in medium and high temperature environments.

[0046] 4. This invention achieves a limiting oxygen index (LOI) of ≥28% and a vertical flammability rating of UL94V-0 for modified polyester through a synergistic mechanism of “condensed phase char formation + gas phase free radical suppression”. Furthermore, phosphorus is stably bound to the main chain through PC bonds, eliminating the risk of migration and loss, thus effectively improving the flame retardant performance of the material.

[0047] 5. The technical solution of this invention has multiple performance synergistic advantages. While utilizing the flame retardancy of DOPO, it also takes advantage of its rigid structure to design and introduce a large rigidity conjugated monomer to achieve the functions of heat resistance, flame retardancy and anti-aging, thus making up for the shortcomings of the single function of traditional DOPO monomer. Attached Figure Description

[0048] Figure 1 This is a flowchart illustrating the preparation process of DOPO-MDCA according to the present invention;

[0049] Figure 2 The nuclear magnetic resonance spectrum of DOPO-MDCA obtained in Example 1 is shown. Detailed Implementation

[0050] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. It should be noted that, unless otherwise specified, the technical means used in the following examples are conventional means well known to those skilled in the art, and the raw materials used are all commercially available conventional products. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various modifications or alterations to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0051] The following are the test methods for the relevant performance indicators in each embodiment and comparative example:

[0052] (1) Monomer purity: The purity was determined by high performance liquid chromatography. 0.05±0.001g of DOPO-MDCA sample was weighed and dissolved in 25mL of N,N-dimethylformamide solvent. After complete dissolution, the solution was filtered and set aside. The mobile phase was a methanol-water mixture (volume ratio 70:30), the flow rate was set to 1.0 mL / min, and the column temperature was controlled at 30℃. A standard curve was plotted using DOPO-MDCA standard. The mass fraction corresponding to the peak area of ​​the sample was calculated by the external standard method, which is the monomer purity.

[0053] (2) Intrinsic viscosity: The test was carried out in accordance with the standard GB / T14190-2017. 0.125±0.005g of sample was weighed and dissolved in 25mL of a mixed solution of phenol and 1,1,2,2-tetrachloroethane (mass ratio 1:1). The solvent and the dissolved solution were then tested and calculated at 25℃ using an Ubbelohde viscometer.

[0054] (3) Melting point and glass transition temperature: under nitrogen protection, the sample was characterized by differential scanning calorimetry (DSC, TA-Q20). 5 mg of the dry sample was heated to 290 °C at a rate of 10 °C / min and held for 10 min to remove the thermal history. Then it was cooled to 0 °C at a rate of 10 °C / min and held for 3 min. Then it was heated to 290 °C at a rate of 10 °C / min.

[0055] (4) Polymer thermal aging yellowing test: According to the relevant method for determining the yellow index of plastics ASTM D1925, the sample was placed in a 125℃ forced-air oven, and the yellow index was measured periodically. The change value ΔYI after 500 hours was calculated.

[0056] (5) Flame retardant performance: the oxygen index was measured according to ISO 4589-1984; the droplet condition was measured according to UL-94.

[0057] In the following examples, Examples 1-6 describe the preparation of DOPO-based derivative monomers, and Examples 7-12 describe the preparation of flame-retardant, heat-resistant, and aging-resistant polyester materials. Figure 1 This is a flowchart illustrating the preparation process of the DOPO-based derivative monomer of this invention.

[0058] Example 1:

[0059] A method for preparing a DOPO-based derivative monomer specifically includes the following steps:

[0060] (1) Weigh 1 mol of p-methoxycarbonylbenzaldehyde and 1 mol of p-bromobenzoate, and react them with 1.1 mol of magnesium shavings in an anhydrous solvent at 10 °C for 3 h to prepare bis(p-methoxycarbonylphenyl)methanol.

[0061] (2) Weigh the bis(p-methoxycarbonylphenyl)methanol obtained above and sulfoxide (the molar ratio of sulfoxide to bis(p-methoxycarbonylphenyl)methanol is 1.3:1), methanesulfonic acid (the amount of catalyst is 1% of the mass of bis(p-methoxycarbonylphenyl) halomethane) and carry out the halogenation reaction at 40°C for 2 hours to obtain bis(p-methoxycarbonylphenyl) halomethane.

[0062] (3) Weigh the bis(p-methoxycarbonylphenyl) halomethane, DOPO and acid-binding agent obtained in the above step and heat them in an organic solvent at 100°C under reflux for 6 h to form PC bonds and obtain ester-protected DOPO intermediate; wherein the molar ratio of bis(p-methoxycarbonylphenyl) halomethane to DOPO is 1:1; the molar ratio of acid-binding agent to bis(p-methoxycarbonylphenyl) halomethane is 1.2:1.

[0063] (4) The DOPO intermediate was hydrolyzed in an aqueous sodium hydroxide solution (the amount of solute in the alkaline solution was twice the molar amount of the DOPO intermediate) at 80°C for 4 hours. After acidification to pH=2, the purity was 99.0~99.5%. After separation and purification, DOPO-bis(4-carboxyphenyl) was obtained. Figure 2 The nuclear magnetic resonance spectrum shown confirms the successful synthesis of the DOPO-bis(4-carboxyphenyl) structure shown in Formula 1.

[0064] Example 2:

[0065] A method for preparing a DOPO-based derivative monomer specifically includes the following steps:

[0066] (1) Weigh 1 mol of p-methoxycarbonylbenzaldehyde and 1.1 mol of p-bromobenzoate, and react them with 1.43 mol of magnesium shavings in anhydrous solvent at 10 °C for 3 h to prepare bis(p-methoxycarbonylphenyl)methanol.

[0067] (2) Weigh the bis(p-methoxycarbonylphenyl)methanol obtained above and thionyl chloride (the molar ratio of thionyl chloride to bis(p-methoxycarbonylphenyl)methanol is 1.1:1), methanesulfonic acid (the amount of catalyst is 2% of the mass of bis(p-methoxycarbonylphenyl) halomethane) and carry out the halogenation reaction at a temperature of 40°C for 2 hours to obtain bis(p-methoxycarbonylphenyl) halomethane.

[0068] (3) Weigh the bis(p-methoxycarbonylphenyl) halomethane, DOPO and acid-binding agent obtained in the above step and heat them in an organic solvent at 100°C under reflux for 6 h to form PC bonds and obtain ester-protected DOPO intermediate; wherein the molar ratio of bis(p-methoxycarbonylphenyl) halomethane to DOPO is 1:1.1; the molar ratio of acid-binding agent to bis(p-methoxycarbonylphenyl) halomethane is 1:1.

[0069] (4) The DOPO intermediate was hydrolyzed in an aqueous sodium hydroxide solution (the amount of solute in the alkaline solution was 3 times the molar amount of the DOPO intermediate) at 80°C for 4 hours. After acidification to pH=2, the purity was 98.8~99.3%. After separation and purification, DOPO-bis(4-carboxyphenyl) was obtained.

[0070] Example 3:

[0071] A method for preparing a DOPO-based derivative monomer specifically includes the following steps:

[0072] (1) Weigh 1 mol of p-methoxycarbonylbenzaldehyde and 1.2 mol of p-bromobenzoate, and react them with 1.44 mol of magnesium shavings in anhydrous solvent at 10 °C for 3 h to prepare bis(p-methoxycarbonylphenyl)methanol.

[0073] (2) Weigh the bis(p-methoxycarbonylphenyl)methanol obtained above and thionyl chloride (the molar ratio of thionyl chloride to bis(p-methoxycarbonylphenyl)methanol is 1.5:1), methanesulfonic acid (the amount of catalyst is 5% of the mass of bis(p-methoxycarbonylphenyl) halomethane) and carry out the halogenation reaction at a temperature of 40°C for 2 hours to obtain bis(p-methoxycarbonylphenyl) halomethane.

[0074] (3) Weigh the bis(p-methoxycarbonylphenyl) halomethane, DOPO and acid-binding agent obtained in the above step and heat them in an organic solvent at 100°C under reflux for 6 h to form PC bonds and obtain ester-protected DOPO intermediate; wherein, the molar ratio of bis(p-methoxycarbonylphenyl) halomethane to DOPO is 1:1.05; the molar ratio of acid-binding agent to bis(p-methoxycarbonylphenyl) halomethane is 1.5:1.

[0075] (4) The DOPO intermediate was hydrolyzed in an aqueous sodium hydroxide solution (the amount of solute in the alkaline solution was 2.5 times the molar amount of the DOPO intermediate) at 80°C for 4 hours. After acidification to pH=2, the purity was 98.5~99.0%. After separation and purification, DOPO-bis(4-carboxyphenyl) was obtained.

[0076] Example 4:

[0077] A method for preparing a DOPO-based derivative monomer specifically includes the following steps:

[0078] (1) Weigh 1 mol of p-methoxycarbonylbenzaldehyde and 1 mol of p-bromobenzoate, and react them with 1.1 mol of magnesium shavings in an anhydrous solvent at -5℃ for 5 h to prepare bis(p-methoxycarbonylphenyl)methanol.

[0079] (2) Weigh the bis(p-methoxycarbonylphenyl)methanol obtained above and phosphorus oxychloride (the molar ratio of thionyl chloride to bis(p-methoxycarbonylphenyl)methanol is 1.3:1), and concentrated phosphoric acid catalyst (the amount of catalyst is 1% of the mass of bis(p-methoxycarbonylphenyl) halomethane) and carry out the halogenation reaction at 20°C for 3 hours to obtain bis(p-methoxycarbonylphenyl) halomethane.

[0080] (3) Weigh the bis(p-methoxycarbonylphenyl) halomethane, DOPO and acid-binding agent obtained in the above step and heat them in an organic solvent at 80°C under reflux for 8 hours to form PC bonds and obtain ester-protected DOPO intermediate; wherein the molar ratio of bis(p-methoxycarbonylphenyl) halomethane to DOPO is 1:1; the molar ratio of acid-binding agent to bis(p-methoxycarbonylphenyl) halomethane is 1.2:1.

[0081] (4) The DOPO intermediate was hydrolyzed in an aqueous sodium hydroxide solution (the amount of solute in the alkaline solution was twice the molar amount of the DOPO intermediate) at 100°C for 3 hours. After acidification to pH=2, the purity was 99.2~99.5%. After separation and purification, DOPO-bis(4-carboxyphenyl) was obtained.

[0082] Example 5:

[0083] A method for preparing a DOPO-based derivative monomer specifically includes the following steps:

[0084] (1) Weigh 1 mol of p-methoxycarbonylbenzaldehyde and 1.1 mol of p-bromobenzoate, and react them with 1.43 mol of magnesium shavings in anhydrous solvent at 15 °C for 2.5 h to prepare bis(p-methoxycarbonylphenyl)methanol.

[0085] (2) Weigh the bis(p-methoxycarbonylphenyl)methanol obtained above and phosphorus oxychloride (the molar ratio of sulfoxide to bis(p-methoxycarbonylphenyl)methanol is 1.3:1), p-toluenesulfonic acid catalyst (the amount of catalyst is 5% of the mass of bis(p-methoxycarbonylphenyl) halomethane) and carry out the halogenation reaction at 60°C for 1 h to obtain bis(p-methoxycarbonylphenyl) halomethane.

[0086] (3) Weigh the bis(p-methoxycarbonylphenyl) halomethane, DOPO and acid-binding agent obtained in the above step and heat them in an organic solvent at 120°C under reflux for 4 h to form PC bonds and obtain ester-protected DOPO intermediate; wherein the molar ratio of bis(p-methoxycarbonylphenyl) halomethane to DOPO is 1:1.1; the molar ratio of acid-binding agent to bis(p-methoxycarbonylphenyl) halomethane is 1:1.

[0087] (4) The DOPO intermediate was hydrolyzed in an aqueous sodium hydroxide solution (the amount of solute in the alkaline solution was 3 times the molar amount of the DOPO intermediate) at 60°C for 6 hours. After acidification to pH=2, the purity was 98.6~99.1%. After separation and purification, DOPO-bis(4-carboxyphenyl) was obtained.

[0088] Example 6:

[0089] A method for preparing a DOPO-based derivative monomer specifically includes the following steps:

[0090] (1) Weigh 1 mol of p-methoxycarbonylbenzaldehyde and 1.2 mol of p-bromobenzoate, and react them with 1.44 mol of magnesium shavings in anhydrous solvent at 25 °C for 2 h to prepare bis(p-methoxycarbonylphenyl)methanol.

[0091] (2) Weigh the bis(p-methoxycarbonylphenyl)methanol obtained above and thionyl chloride (the molar ratio of thionyl chloride to bis(p-methoxycarbonylphenyl)methanol is 1.3:1), methanesulfonic acid (the amount of catalyst is 5% of the mass of bis(p-methoxycarbonylphenyl) halomethane) and carry out the halogenation reaction at a temperature of 40°C for 2 hours to obtain bis(p-methoxycarbonylphenyl) halomethane.

[0092] (3) Weigh the bis(p-methoxycarbonylphenyl) halomethane, DOPO and acid-binding agent obtained in the above step and heat them in an organic solvent at 90°C under reflux for 5 h to form PC bonds and obtain ester-protected DOPO intermediate; wherein, the molar ratio of bis(p-methoxycarbonylphenyl) halomethane to DOPO is 1:1.05; the molar ratio of acid-binding agent to bis(p-methoxycarbonylphenyl) halomethane is 1.5:1.

[0093] (4) The DOPO intermediate was hydrolyzed in an aqueous sodium hydroxide solution (the amount of solute in the alkaline solution was 2.5 times the molar amount of the DOPO intermediate) at 70°C for 5 hours. After acidification to pH=2, the purity was 98.7~99.2%. After separation and purification, DOPO-bis(4-carboxyphenyl) was obtained.

[0094] Example 7: Preparation of flame-retardant, heat-resistant, and aging-resistant polyester materials

[0095] The DOPO-based derivative monomers prepared in Example 1 were weighed and added to a polymerization reactor according to the proportions shown in Table 1 below: terephthalic acid (PTA), purified DOPO-bis(4-carboxyphenyl) functional monomer (DOPO-MDCA), ethylene glycol (EG), and esterification catalyst. Under nitrogen protection, the temperature was raised to 240-250℃ for esterification, and the reaction was carried out at approximately 240℃ for 3 hours. Then, a polycondensation reaction was performed at 280℃ and a pressure ≤50Pa to obtain a flame-retardant, heat-resistant, and aging-resistant polyester material.

[0096] Example 8:

[0097] Weigh the DOPO-based derivative monomers prepared in Example 2 and prepare them according to the proportions shown in Table 1 below. The preparation process is the same as in Example 7 to obtain flame-retardant, heat-resistant, and aging-resistant polyester materials.

[0098] Example 9:

[0099] Weigh the DOPO-based derivative monomers prepared in Example 3 and prepare them according to the proportions shown in Table 1 below. The preparation process is the same as in Example 7 to obtain flame-retardant, heat-resistant and aging-resistant polyester materials.

[0100] Example 10:

[0101] Weigh the DOPO-based derivative monomers prepared in Example 4 and prepare them according to the proportions shown in Table 1 below. The preparation process is the same as in Example 7 to obtain flame-retardant, heat-resistant, and aging-resistant polyester materials.

[0102] Example 11:

[0103] Weigh the DOPO-based derivative monomers prepared in Example 5 and prepare them according to the proportions shown in Table 1 below. The preparation process is the same as in Example 7 to obtain flame-retardant, heat-resistant, and aging-resistant polyester materials.

[0104] Example 12:

[0105] Weigh the DOPO-based derivative monomers prepared in Example 6 and prepare them according to the proportions shown in Table 1 below. The preparation process is the same as in Example 7 to obtain flame-retardant, heat-resistant, and aging-resistant polyester materials.

[0106] Comparative Example 1:

[0107] The preparation method is the same as in Example 7, except that no DOPO or DOPO-based derivative monomers are added.

[0108] Comparative Example 2:

[0109] The preparation method is the same as in Example 7, except that the DOPO-based derivative monomer of the present invention is replaced with the DOPO derivative (DOPO-HPIMP) with the structure of formula (II).

[0110] Equation (II).

[0111] Comparative Example 3:

[0112] The preparation method is the same as in Example 7, except that DOPO is used instead of the DOPO-based derivative monomer of the present invention.

[0113] Special Note: The parameters used in this invention, such as esterification temperature, esterification reaction time, polycondensation reaction temperature, polycondensation reaction pressure, and the molar ratio of terephthalic acid to ethylene glycol, are conventional parameters for PET preparation, and their specific values ​​are not significantly different from those in existing technologies. Therefore, this invention only selects one set of optimal parameters for illustrative purposes. Performance tests were conducted on the obtained polyester materials, and the results are shown in Table 1 below.

[0114] Table 1. Physical properties of flame-retardant polyester

[0115] Example 7 3000 0.65 82.2 245.4 392.6 18 23 Level V-2 Example 8 5000 0.64 85.1 236.6 391.3 15 26 Level V-1 Example 9 8000 0.60 89.3 222.6 387.6 12 28 V-0 level Example 10 10000 0.62 92.4 212.8 387.1 8 31 V-0 level Example 11 12000 0.64 95.4 202.5 385.4 6 33 V-0 level Example 12 15000 0.62 100.3 186.0 383.1 4 35 V-0 level Comparative Example 1 0 0.68 78.1 258.2 395.0 25 21 Non-flame retardant Comparative Example 2 10000 0.55 88.6 208.3 375.2 20 27 Level V-1 Comparative Example 3 10000 0.52 85.3 210.5 370.4 22 25 Level V-2

[0116] The data shows that the DOPO-MDCA flame retardant monomers prepared in Examples 1-6, when added at phosphorus contents of 3000~15000ppm, produce polyester materials with excellent physical properties: limiting oxygen index (LOI) ≥23%, vertical burning reaches UL94 V-0 level when phosphorus content ≥8000ppm, glass transition temperature ≥82.2℃, heat resistance is improved compared to unmodified Comparative Example 1, and heat resistance and flame retardancy are excellent, making it suitable for the preparation of high-temperature flame retardant parts.

[0117] Comparative Examples 1-3 (Comparative Example 1 had no flame retardant, and Comparative Examples 2-3 all had a phosphorus content of 10,000 ppm) all performed worse than Example 10 with the same phosphorus content. Specifically, Comparative Example 1, lacking any added flame retardant and therefore lacking the synergistic flame-retardant effect of phosphorus-based gas-condensed phase flame retardancy, had a limiting oxygen index of only 21%, no flame retardant rating, and no rigid conjugated structure, resulting in heat resistance and aging resistance at the polyester baseline level. Comparative Example 2 used DOPO-HPIMP, which, although containing hydroxyl active sites, had poor compatibility with the polyester system and low reactivity. Its rigid phosphaphenanthrene skeleton could not effectively embed into the main chain to restrict molecular chain thermal motion, resulting in relatively lower heat resistance. The low charring rate and lack of a synergistic charring biphenyl ring structure mean that this structure can only achieve single-phase flame suppression. It cannot form a dense char layer at high temperatures, resulting in poor charring properties and low flame retardant efficiency. Its flame retardant performance is inferior to that of Example 10. Furthermore, the hydroxyl group is prone to initiating side reactions, leading to a decrease in the intrinsic viscosity of the material. The absence of a large π conjugated system also makes its aging and yellowing resistance far inferior to that of Example 10. Comparative Example 3 uses small molecule DOPO, which lacks copolymerizable active functional groups and has extremely poor compatibility with the polyester matrix. It is prone to agglomeration and volatilization, and phosphorus cannot exist stably in the polyester system. Therefore, it cannot play an effective flame retardant role, nor can it positively improve the heat resistance of the polyester. Thus, its performance is the worst.

[0118] In summary, the DOPO-MDCA monomer of this invention has a dicarboxyl structure, which can be copolymerized with PTA and EG and firmly bonded to the polyester backbone through chemical bonds, effectively solving the defects of traditional flame retardants. The overall performance of the prepared polyester material is superior to that of the prior art.

Claims

1. A DOPO-based derivative monomer, characterized in that, The DOPO-based derivative monomer is DOPO-bis(4-carboxyphenyl), and its structural formula is shown in Formula I below: Formula I.

2. The method for preparing a DOPO-based derivative monomer as described in claim 1, characterized in that, Includes the following steps: Weigh p-methoxycarbonylbenzaldehyde and methyl p-bromobenzoate, and react them with magnesium shavings in an anhydrous solvent to prepare bis(p-methoxycarbonylphenyl)methanol; Weigh out bis(p-methoxycarbonylphenyl)methanol and react it with a halogenating reagent and a catalyst to give bis(p-methoxycarbonylphenyl)methane haloacetate; Weigh out bis(p-methoxycarbonylphenyl) halomethane, DOPO and an acid-binding agent and carry out a heating and reflux reaction in an organic solvent to obtain an ester-protected DOPO intermediate; The DOPO intermediate was hydrolyzed under alkaline solution conditions, and after acidification, separation and purification, DOPO-bis(4-carboxyphenyl) was obtained.

3. The preparation method according to claim 2, characterized in that, The anhydrous solvent is anhydrous tetrahydrofuran or anhydrous diethyl ether; The molar ratio of p-methoxycarbonylbenzaldehyde to methyl p-bromobenzoate is 1:(1.0~1.2); The molar ratio of methyl p-bromobenzoate to magnesium shavings is 1:(1.1~1.3); The reaction conditions are: reaction temperature -5~25℃, reaction time 2~5h.

4. The preparation method according to claim 2, characterized in that, The halogenated reagent is selected from at least one of thionyl chloride, phosphorus oxychloride, or hydrobromic acid. The molar ratio of the halogenating reagent to bis(p-methoxycarbonylphenyl)methanol is (1.1~1.5):1; The catalyst is selected from at least one of methanesulfonic acid, p-toluenesulfonic acid, or concentrated phosphoric acid; The amount of catalyst used is 1% to 5% of the mass of bis(p-methoxycarbonylphenyl)halomethane; The conditions for the halogenation reaction are: reaction temperature 20~60℃, reaction time 1~3h.

5. The preparation method according to claim 2, characterized in that, The acid-binding agent is selected from at least one of triethylamine, diisopropylethylamine, or pyridine; The organic solvent is toluene or xylene; The molar ratio of the bis(p-methoxycarbonylphenyl) halomethane to DOPO is 1:(1.0~1.1); The molar ratio of the acid-binding agent to bis(p-methoxycarbonylphenyl) halomethane is (1.0~1.5):1; The conditions for the heating and reflux reaction are: reaction temperature 80~120℃, reaction time 4~8h.

6. The preparation method according to claim 2, characterized in that, The alkaline solution is an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide; The amount of solute in the alkaline solution is 2.0 to 3.0 times the molar amount of the DOPO intermediate; The conditions for the hydrolysis reaction are: hydrolysis temperature 60~100℃, hydrolysis time 3~6h; The acidification is carried out to pH 2-3; The separation and purification methods are filtration, water washing, vacuum drying, or recrystallization.

7. The application of the DOPO-based derivative monomer as described in claim 1 in the preparation of flame-retardant, heat-resistant, and aging-resistant polyester materials.

8. A method for preparing a flame-retardant, heat-resistant, and aging-resistant polyester material, characterized in that, Flame-retardant, heat-resistant, and aging-resistant polyester is prepared by copolymerization of the DOPO-based derivative monomer as described in claim 1 and polyester monomer.

9. The method for preparing a flame-retardant, heat-resistant, and aging-resistant polyester material as described in claim 8, characterized in that, The DOPO-based derivative monomer accounts for 5% to 20% of the molar amount of the polyester monomer.

10. A flame-retardant, heat-resistant, and aging-resistant polyester material, characterized in that, Obtained by the preparation method described in claim 8.

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