Phenolic fluorescent copolyesters and methods for making the same

Abstract

The application provides a phenol-based fluorescent copolyester and a preparation method thereof, and belongs to the field of functional polymers, wherein the preparation method comprises the following steps: adding dimethyl terephthalate, ethylene glycol, 2,5-dihydroxy dimethyl terephthalate, an ester exchange reaction catalyst and a polycondensation reaction catalyst into a reaction kettle, performing ester exchange reaction after protection gas is introduced, and obtaining an ester exchange product; heating the reaction kettle, performing polycondensation reaction, and obtaining a copolyester; cooling, solidifying and granulating the copolyester, and obtaining the phenol-based fluorescent copolyester. The application realizes structure and essence type fluorescent modification of the material by introducing the phenol-based monomer 2,5-dihydroxy dimethyl terephthalate with a specific conjugate structure into a conventional polyethylene terephthalate polymerization system, and chemically bonding the light-emitting functional group to the polyester molecular main chain in the form of a covalent bond through an ester exchange-melt copolymerization process.

Description

Technical Field

[0001] This application relates to the field of functional polymer technology, specifically to a phenol-based fluorescent copolyester and its preparation method. Background Technology

[0002] Polyethylene terephthalate (PET), as a polyester material with excellent comprehensive properties, has been widely used in fibers, films, and packaging. However, with the increasing demand for materials in high-end fields such as optical sensing, fluorescent anti-counterfeiting, biomarking, and functional luminescent fibers, the inherent limitation of ordinary PET materials in lacking fluorescent functionality is becoming increasingly prominent. This restricts its in-depth application in scenarios requiring specific identification, monitoring, or decorative functions through fluorescent properties.

[0003] Currently, the construction of fluorescent polyester materials mainly relies on two strategies: exogenous doping and chemical bonding. However, both have significant limitations. Exogenous doping typically involves introducing organic fluorescent dyes or inorganic phosphors into the polyester matrix through melt or solution blending. While simple to operate, this strategy easily leads to fluorescent molecule aggregation and quenching, as well as macroscopic phase separation. Furthermore, small-molecule dyes are prone to migration and leaching, resulting not only in poor fluorescence stability but also impairing the mechanical strength of the matrix. Chemical bonding, which typically involves introducing fluorescent groups into the molecular chain through modification grafting or copolymerization of functional monomers, can inhibit migration at its source. However, it often faces problems such as cumbersome synthesis steps and harsh reaction conditions. The introduced large-volume side groups can also disrupt the regularity of polyester segments, leading to decreased thermal stability and processing fluidity. Existing technologies still struggle to efficiently and stably introduce fluorescent functionality while simultaneously maintaining the intrinsic processability and mechanical strength of the polyester.

[0004] To address the aforementioned issues, it is necessary to develop a modified polyester that combines fluorescent properties with mechanical strength to meet the processing and application requirements of polyester materials. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides a phenol-based fluorescent copolyester and its preparation method. This method introduces 2,5-dihydroxydimethyl terephthalate (DDTH) into a copolymer system of dimethyl terephthalate (DMT) and ethylene glycol (EG), firmly bonding the DDTH monomer to the polyester backbone through chemical bonds, thereby achieving a uniform and stable distribution of fluorescent units at the molecular level. This process synthesizes a novel copolyester with inherent fluorescent properties in one step. By controlling the amount of DDTH introduced, the fluorescence intensity can be effectively controlled. While imparting a long-lasting and stable fluorescent effect to the material, it strives to maintain the good thermal properties and spinnability of the polyester, providing an innovative and efficient preparation route for the development of novel fluorescent anti-counterfeiting materials, optical sensing elements, and functional luminescent fibers.

[0006] To achieve the above objectives, in a first aspect, embodiments of this application provide a method for preparing a phenol-based fluorescent copolyester, comprising: Dimethyl terephthalate, ethylene glycol, 2,5-dihydroxyterephthalate, transesterification catalyst and polycondensation catalyst were added to a reaction vessel, and a transesterification reaction was carried out after a protective gas was introduced to obtain the transesterification product. The reactor is heated to carry out a polycondensation reaction to obtain a copolyester; The copolyester was cooled, cured, and granulated to obtain phenol-based fluorescent copolyester.

[0007] Furthermore, the mass ratio of dimethyl terephthalate to 2,5-dihydroxyterephthalate is 1:(0.025-0.1); and / or, The ratio of the total molar amount of dimethyl terephthalate and 2,5-dihydroxyterephthalate to the molar amount of ethylene glycol is 1:(1.5-2.5).

[0008] Furthermore, the transesterification catalyst is anhydrous zinc acetate, and the mass ratio of the transesterification catalyst to dimethyl terephthalate is (0.0001-0.001):1; and / or, The catalyst for the polycondensation reaction is antimony trioxide, and the mass ratio of the polycondensation catalyst to dimethyl terephthalate is (0.0001-0.001):1.

[0009] Furthermore, the transesterification reaction after introducing a protective gas includes: A protective gas is introduced into the reactor and pressurized to 140 kPa-160 kPa. Then the pressure is released to atmospheric pressure, the valve is closed, and the protective gas is introduced again. This process is repeated three times. The protective gas includes at least one of nitrogen and argon.

[0010] Furthermore, the temperature of the reactor in the transesterification reaction is 190℃-220℃, and the temperature of the process tower in the transesterification reaction is 65℃-75℃; and / or, In the transesterification reaction, the reactor temperature was gradually increased from 8℃ / h to 12℃ / h.

[0011] Furthermore, the transesterification reaction is carried out under stirring; and / or, The transesterification reaction is stopped when the amount of water produced reaches 90% of the theoretical amount.

[0012] Furthermore, the temperature of the reactor in the polycondensation reaction is 260℃-280℃, and the temperature of the reactor in the polycondensation reaction is gradually increased to 280℃ at a rate of 2℃ / min.

[0013] Furthermore, the polycondensation reaction is carried out under gradient decompression conditions, including multiple consecutive decompression stages. In each decompression stage, the pressure of the reactor is reduced by 15kPa-25kPa, i.e., maintained at that pressure for 10min-20min, and the cycle continues until the pressure of the reactor is ≤-0.1MPa.

[0014] Furthermore, the polycondensation reaction is carried out under stirring. The torque value of the stirrer during the polycondensation reaction is monitored. When the torque value reaches 2.5-2.7 Nm, the polycondensation reaction is stopped and the reactor is restored to atmospheric pressure.

[0015] Secondly, embodiments of this application provide a phenol-based fluorescent copolyester, which is prepared by the above-described method for preparing phenol-based fluorescent copolyester.

[0016] The beneficial technical effects of this application are as follows: In this application, 2,5-dihydroxyterephthalate (DDTH) is precisely introduced into a copolymer system of dimethyl terephthalate (DMT) and ethylene glycol (EG) at a specific ratio. Using direct transesterification and subsequent high-temperature polycondensation, the phenolic DDTH monomer with a specific conjugated structure is chemically bonded to the polyester backbone, achieving a uniform and stable distribution of fluorescent units at the molecular level, thus realizing structurally-inherent fluorescent modification of the material. Furthermore, because it is firmly bonded to the polymer chain, the fluorescence function is durable and stable. This method imparts bright and tunable fluorescent properties to the polyester while retaining the good thermal properties of the matrix resin and improving its tensile strength and impact resistance. Moreover, the process does not require the use of large amounts of harmful organic solvents, making it environmentally friendly. By controlling the amount of DDTH introduced, the fluorescence intensity can be effectively controlled, providing an innovative and efficient preparation route for developing novel fluorescent anti-counterfeiting materials, optical sensing elements, and functional luminescent fibers.

[0017] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0019] Figure 1 This is a synthetic route diagram for the phenol-based fluorescent copolyester of this application.

[0020] Figure 2 These are the fluorescence excitation and fluorescence emission spectra of the phenol-based fluorescent copolyester prepared in Example 1 of this application.

[0021] Figure 3 These are the fluorescence excitation and fluorescence emission spectra of the phenol-based fluorescent copolyester prepared in Example 2 of this application.

[0022] Figure 4 These are the fluorescence excitation and fluorescence emission spectra of the phenol-based fluorescent copolyester prepared in Example 3 of this application. Detailed Implementation

[0023] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0025] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0026] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0027] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0028] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0029] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0030] Unless otherwise specified, the terms "comprising" and "including" as used in this application are open-ended. For example, "comprising" and "including" may mean that other components not listed may also be included or contained.

[0031] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0032] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0033] With the increasing demand for materials in high-end fields such as optical sensing, fluorescent anti-counterfeiting, biomarking, and functional luminescent fibers, the inherent defect of ordinary PET materials lacking fluorescence functionality is becoming increasingly prominent. This limits their in-depth application in scenarios requiring specific identification, monitoring, or decorative functions through fluorescence properties. Currently, the construction of fluorescent polyester materials mainly relies on two strategies: exogenous doping and chemical bonding, but both have significant limitations. The exogenous doping strategy typically introduces organic fluorescent dyes or inorganic phosphors into the polyester matrix through melt or solution blending. Although simple to operate, this strategy easily leads to the aggregation and quenching of fluorescent molecules and macroscopic phase separation; moreover, small molecule dyes are prone to migration and leakage, resulting not only in poor fluorescence stability but also damage to the mechanical strength of the matrix. The chemical bonding strategy typically introduces fluorescent groups into the molecular chain through modification grafting or functional monomer copolymerization. Although it can inhibit migration at the source, it often faces problems such as cumbersome synthesis steps and harsh reaction conditions; the introduced large-volume side groups may also disrupt the regularity of polyester chain segments, leading to a decrease in its thermal stability and processing fluidity. Existing technologies still struggle to efficiently and stably introduce fluorescent functionality while simultaneously maintaining the processability and mechanical strength of polyester.

[0034] To address the aforementioned technical problems, embodiments of this application provide a method for preparing a phenol-based fluorescent copolyester, comprising: Dimethyl terephthalate, ethylene glycol, 2,5-dihydroxyterephthalate, transesterification catalyst and polycondensation catalyst were added to a reaction vessel, and a transesterification reaction was carried out after a protective gas was introduced to obtain the transesterification product. The reactor is heated to carry out a polycondensation reaction to obtain a copolyester; The copolyester was cooled, cured, and granulated to obtain phenol-based fluorescent copolyester.

[0035] In the technical solution of this application, 2,5-dihydroxyterephthalate (DDTH) is precisely introduced into a copolymer system of dimethyl terephthalate (DMT) and ethylene glycol (EG) in a specific ratio. Using direct transesterification and high-temperature polycondensation processes, 2,5-dihydroxyterephthalate is chemically bonded to the polyester backbone, achieving a uniform and stable distribution of fluorescent units at the molecular level. Figure 1 This is the synthetic route diagram of the phenol-based fluorescent copolyester of this application. This process synthesizes a novel copolyester with inherent fluorescent properties in one step. By controlling the amount of dimethyl 2,5-dihydroxyterephthalate introduced, the fluorescence intensity can be effectively controlled. While giving the material a long-lasting and stable fluorescent effect, it strives to maintain the good thermal properties and mechanical strength of the polyester. This provides an innovative and efficient preparation route for the development of novel fluorescent anti-counterfeiting materials, optical sensing elements and functional luminescent fibers.

[0036] It can be explained that the benzene ring and carbonyl group in dimethyl 2,5-dihydroxyterephthalate provide a rigid conjugated skeleton, creating conditions for excited electron transitions. The two para-positioned methyl ester groups act as electron-withdrawing groups, pulling on the electron cloud of the benzene ring. The two para-positioned phenolic hydroxyl groups act as electron-donating groups, pushing electrons towards the benzene ring and carbonyl group. Under photon excitation, charge transfers from the phenolic hydroxyl end to the methyl ester end. When the excited state returns to the ground state, energy is released in the form of light, thus producing fluorescence.

[0037] In some embodiments, the mass ratio of dimethyl terephthalate to dimethyl 2,5-dihydroxyterephthalate is 1:(0.025-0.1).

[0038] In this embodiment, the phenolic hydroxyl groups of the 2,5-dihydroxyterephthalate molecule form intramolecular hydrogen bonds with adjacent ester carbonyl groups, generating strong solid-state fluorescence. By controlling the mass ratio of dimethyl terephthalate to dimethyl 2,5-dihydroxyterephthalate to 1:(0.025-0.1), the luminescent units at this ratio can produce sufficient fluorescence brightness while reducing aggregation-induced quenching that may result from excessively high luminescent unit concentration, thereby maintaining the quantum yield level and reducing energy dissipation. Copolymerizing a small amount of dimethyl 2,5-dihydroxyterephthalate at this ratio can maintain the regularity and crystallinity of the PET molecular chain, reduce oxidation and cross-linking that may be caused by excessive phenolic hydroxyl groups, and achieve a balance between luminescent performance and mechanical strength.

[0039] In some embodiments, the ratio of the total molar amount of dimethyl terephthalate and 2,5-dihydroxyterephthalate to the molar amount of ethylene glycol is 1:(1.5-2.5).

[0040] In this embodiment, the molar ratio of the total amount of dimethyl terephthalate and 2,5-dihydroxyterephthalate to the molar amount of ethylene glycol is controlled at 1:(1.5-2.5). Excess ethylene glycol promotes the conversion of the methoxy groups of dimethyl terephthalate and 2,5-dihydroxyterephthalate to hydroxyethyl groups in the transesterification equilibrium reaction, thereby increasing the purity of the transesterification reaction products. Simultaneously, ethylene glycol also acts as a solvent, reducing the viscosity of the reaction system, promoting mass and heat transfer, and accelerating the transesterification reaction rate.

[0041] In some embodiments, the transesterification catalyst is anhydrous zinc acetate, and the mass ratio of the transesterification catalyst to dimethyl terephthalate is (0.0001-0.001):1.

[0042] In this embodiment, anhydrous zinc acetate is used as the catalyst for the transesterification reaction. By polarizing the carbonyl group of the ester, it promotes the nucleophilic attack of ethylene glycol, reduces the activation energy required for the transesterification reaction, and facilitates its efficient execution. The thermochromic and oxidative coloration caused by zinc ions under transesterification conditions is less pronounced than with other catalysts, and the hue of the generated BHET is typically pure white or slightly yellow, which is beneficial for maintaining the pure color of the transesterification product. Controlling the mass ratio of the transesterification catalyst to dimethyl terephthalate to (0.0001-0.001):1 balances the transesterification reaction rate with the etherification of ethylene glycol itself, maintains the melting point and thermal stability of the transesterification product, reduces the potential formation of phenolic complexes due to excessive metal catalyst, and maintains the product's appearance, color, and fluorescence purity.

[0043] The catalyst for the polycondensation reaction is antimony trioxide, and the mass ratio of the polycondensation catalyst to dimethyl terephthalate is (0.0001-0.001):1.

[0044] In this embodiment, antimony trioxide is used as a catalyst for the polycondensation reaction to accelerate the process. Controlling the mass ratio of the polycondensation catalyst to dimethyl terephthalate to (0.0001-0.001):1 enhances the activity of the polycondensation reaction while preserving the fluorescence properties of the luminescent copolymer.

[0045] In some embodiments, transesterification after introducing a protective gas includes: A protective gas is introduced into the reactor and pressurized to 140 kPa-160 kPa. Then the pressure is released to atmospheric pressure, the valve is closed, and the protective gas is introduced again. This process is repeated three times. The protective gas includes at least one of nitrogen and argon.

[0046] In this embodiment, the air in the reactor was replaced with a protective gas three times. Because the flash point of ethylene glycol is easily reached during the transesterification reaction, replacing the gas with a protective gas dilutes the oxygen concentration, reducing the risk of explosion. Simultaneously, it reduces the possibility of the phenolic hydroxyl groups present in dimethyl 2,5-dihydroxyterephthalate in the reactor being oxidized to form colored quinone structures, thereby protecting the fluorescent structure of the comonomer.

[0047] In some embodiments, the temperature of the reactor in the transesterification reaction is 190°C-220°C, and the temperature of the process tower in the transesterification reaction is 65°C-75°C.

[0048] In this embodiment, the temperature of the reactor in the transesterification reaction is controlled at 190℃-220℃, and the temperature of the process tower in the transesterification reaction is controlled at 65℃-75℃. Within this temperature range, the reactor can melt and disperse dimethyl terephthalate and 2,5-dihydroxyterephthalate in ethylene glycol to form a homogeneous melt. This reactor temperature range is higher than the boiling point of methanol but lower than the boiling point of ethylene glycol, which promotes the release of methanol generated in the reaction as a gaseous phase, thus promoting the forward progress of the transesterification reaction. As the transesterification reaction progresses to the later stages, the concentration of reactant monomers further decreases. Increasing the reactor temperature can increase the reaction rate and remove excess methanol. The purpose of setting the process tower temperature to 65℃-75℃ is to allow the methanol generated during the transesterification reaction to enter the esterification condenser in gaseous form, while simultaneously allowing the ethylene glycol vapor generated during the transesterification process to flow back to the reactor. During the transesterification reaction, some ethylene glycol vapor reaches the process tower, causing the process tower temperature to be higher than the actual set value. As the reaction proceeds, when the ethylene glycol has essentially reacted completely, the temperature of the process tower will decrease significantly.

[0049] In some embodiments, the reactor temperature in the transesterification reaction is gradually increased from 8°C / h to 12°C / h.

[0050] In this embodiment, the reactor for the transesterification reaction is heated at a rate of 8°C / h to 12°C / h. Different stages of the polycondensation reaction serve different functions. In the initial stage of the polycondensation reaction, dimethyl terephthalate and 2,5-dihydroxyterephthalate are melt-dispersed in ethylene glycol. Stable heating avoids localized overheating of the reactor and reduces evaporation of ethylene glycol in the early stages of the reaction. As the transesterification reaction proceeds, methanol gradually escapes in gaseous form; stable heating promotes the stable and continuous discharge of methanol. In the later stages of the transesterification reaction, stable heating increases the conversion rate of dimethyl ester end groups, resulting in a transesterification product with a uniform structure.

[0051] In some embodiments, the transesterification reaction is carried out under stirring.

[0052] In this embodiment, dimethyl terephthalate and 2,5-dihydroxyterephthalate are melt-dispersed in ethylene glycol by stirring, which increases the contact area, accelerates the reaction between the dimethyl terephthalate monomer and ethylene glycol, and promotes the uniform distribution of the light-emitting units.

[0053] In some embodiments, the transesterification reaction is stopped when the amount of water discharged from the transesterification reaction reaches 90% of the theoretical amount of water discharged.

[0054] In this embodiment, the theoretical water yield was determined based on the feed amounts of dimethyl terephthalate monomer, 2,5-dihydroxydimethyl terephthalate monomer, and ethylene glycol, and calculated assuming all methyl ester groups and hydroxyl groups participated in the reaction. The theoretical water yield was actually the methanol distillation yield. The transesterification reaction is reversible. When the methanol production reaches approximately 90% of the theoretical value, the forward reaction rate has decreased significantly, the reactant concentration is very low, the product concentration is very high, and the system is very close to the thermodynamic equilibrium point at that temperature. If the temperature is maintained for a prolonged period to achieve the final 10% conversion rate, the side reaction of intermolecular dehydration of ethylene glycol to form diethylene glycol will be drastically accelerated, leading to a decrease in the product's melting point, thermal stability, and strength. Simultaneously, prolonged exposure to extreme high-temperature conditions can easily cause thermal oxidation and condensation of phenolic hydroxyl groups, resulting in yellowing and fluorescence quenching of the product.

[0055] In some embodiments, the temperature of the reactor in the polycondensation reaction is 260°C-280°C, and the reactor temperature is gradually increased to 280°C at a rate of 2°C / min.

[0056] In this embodiment, the temperature of the polycondensation reaction is controlled between 260℃ and 280℃. Within the temperature range of 260℃ to 270℃, excess ethylene glycol and methanol in the reactor are removed, resulting in a low molecular weight and low viscosity of the polymer. Within the temperature range of 270℃ to 280℃, chain growth reaction mainly occurs, and the molecular weight of the polymer gradually increases. Simultaneously, to protect the phenolic hydroxyl groups, the temperature needs to be controlled below 280℃ to reduce potential thermal damage.

[0057] In some embodiments, the polycondensation reaction is carried out under gradient decompression conditions, including multiple successive decompression stages. In each decompression stage, the pressure of the reactor is reduced by 15 kPa to 25 kPa, i.e., maintained at that pressure for 10 min to 20 min, and the cycle continues until the pressure of the reactor is ≤ -0.1 MPa.

[0058] In this embodiment, the reactor is subjected to gradient decompression to control the boiling rate of ethylene glycol at a stable level, achieving gentle removal of ethylene glycol, promoting the forward polycondensation reaction, and improving the safety of the reaction system. During the decompression process, each pressure reduction of 15-25 kPa in the reactor, maintained at that pressure for 10-20 minutes, facilitates the reaction and diffusion of dimethyl ester melt and ethylene glycol, promoting a steady increase in the molecular weight of the copolymer. Decompression until the reactor pressure is ≤-0.1 MPa achieves complete removal of ethylene glycol, increasing the molecular weight and purity of the polycondensation product.

[0059] In some embodiments, the polycondensation reaction is carried out under stirring. The torque value of the stirrer during the polycondensation reaction is monitored. When the torque value reaches 2.5-2.7 Nm, the polycondensation reaction is stopped and the reactor is restored to atmospheric pressure.

[0060] In this embodiment, stirring ensures uniform removal of ethylene glycol from the melt in the reactor, promoting uniform growth of the copolymer's molecular chains. Simultaneously, uniform heat transfer reduces the risk of condensation reactions of phenolic hydroxyl groups due to localized overheating, maintaining the integrity of the copolymer's fluorescent structure. Torque reflects the copolymer's viscosity; when the torque value reaches 2.5-2.7 Nm, the copolymer's molecular weight reaches an ideal state, achieving a balance between the copolymer's fluorescent properties and mechanical strength.

[0061] Secondly, embodiments of this application provide a phenol-based fluorescent copolyester, which is prepared by the above-described method for preparing phenol-based fluorescent copolyester.

[0062] It is understood that the phenol-based fluorescent copolyester has all the beneficial effects of the above-mentioned preparation methods of the phenol-based fluorescent copolyester, and will not be elaborated here.

[0063] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0064] I. Preparation Method Example 1 Dimethyl terephthalate and 2,5-dihydroxyterephthalate were weighed out at a mass ratio of 1:0.025. Then, ethylene glycol was weighed out at a ratio of 1:2 to the total molar amount of dimethyl terephthalate and 2,5-dihydroxyterephthalate. Anhydrous zinc acetate and antimony trioxide were weighed out as catalysts at 0.05% of the mass of dimethyl terephthalate. After checking the reactor's seal, weighed ethylene glycol terephthalate, ethylene glycol, dimethyl 2,5-dihydroxyterephthalate, anhydrous zinc acetate, and antimony trioxide were added to the reactor. Nitrogen gas was introduced into the reactor, and after the pressure reached 150 kPa, the valve was opened to release the pressure. After reaching atmospheric pressure, the valve was closed, and nitrogen gas was introduced into the reactor again. This process was repeated three times to purge the air from the reactor. The temperatures of the reactor and process tower were raised to 190℃ and 70℃ respectively to carry out the transesterification reaction. During the reaction, the stirrer was turned on and the stirring speed was set to 100 rpm. During this reaction, the temperature was increased by 10℃ every hour. The esterification reaction was considered to be completed when the amount of water produced reached 90% of the theoretical amount. Close the valve between the reactor and the process tower, and turn off the heating switch of the process tower. Open the valve between the reactor and the polycondensation condenser to enter the polycondensation stage. Then, increase the reactor temperature by 20°C every 10 minutes until it reaches 280°C. During the polycondensation process, turn on the vacuum pump and maintain the pressure at 20 kPa for 15 minutes until it reaches -0.1 MPa. During the polycondensation process, pay attention to the torque of the stirrer. The reaction ends when the stirring torque reaches 2.6 Nm. Turn off the vacuum pump and pressurize to atmospheric pressure. The prepared copolyester melt was discharged from the reactor, cooled and solidified, and then pelletized to obtain the phenol-based fluorescent copolyester of Example 1.

[0065] Example 2 Unlike Example 1, the mass ratio of dimethyl terephthalate to 2,5-dihydroxyterephthalate was 1:0.05, while the remaining steps were largely the same, resulting in the phenol-based fluorescent copolyester of Example 2.

[0066] Example 3 Unlike Example 1, the mass ratio of dimethyl terephthalate to 2,5-dihydroxyterephthalate was 1:0.1, while the remaining steps were largely the same, resulting in the phenol-based fluorescent copolyester of Example 3.

[0067] Comparative Example 1 Unlike Example 1, dimethyl 2,5-dihydroxyterephthalate was not added, but the remaining steps were largely the same, resulting in the copolyester of Comparative Example 1.

[0068] Comparative Example 2 Unlike Example 1, dimethyl terephthalate was replaced with dimethyl succinate, while the remaining steps were largely the same, resulting in the copolyester of Comparative Example 2.

[0069] II. Testing Methods Material properties were tested on the phenol-based fluorescent copolyesters prepared in Examples 1-3 and the copolyesters prepared in Comparative Examples 1-2.

[0070] 1. Fluorescence Spectroscopy Analysis: Under dry and light-protected conditions, a steady-state fluorescence spectrometer (model: Edinbursh-FLS 1000, UK) was used to perform fluorescence spectral analysis on the copolyester, adjusting the excitation spectrum range to 300nm-500nm and the emission spectrum range to 450-600nm. First, the excitation spectrum was measured to determine the peak wavelength and peak intensity. Then, at the specified excitation wavelength, the emission spectrum of the sample was measured, and its peak wavelength and peak intensity were recorded. 2. Quantum Yield: Quantum yield was determined using a steady-state fluorescence spectrometer (model: Edinbursh-FLS1000, UK) combined with the integrating sphere method under ambient temperature and light-protected conditions. The excitation wavelength was set to 400 nm, and the emission spectrum scanning range was 450-650 nm. Since the obtained copolyester was a solid powder, no solvent was required during the entire test, nor was a blank solvent control necessary. The photomultiplier tube voltage of the instrument was automatically adjusted to ensure consistent test parameters for all samples.

[0071] 2. Mechanical Properties: Tensile properties of the samples were tested using an Instron electronic tensile testing machine. Tensile specimens with dimensions of 40mm × 5mm × 2mm were prepared from the obtained copolyester. Tensile tests were conducted at a rate of 5mm / min according to GB / T 1040.2-2022 "Determination of Tensile Properties of Plastics - Part 2: Test Conditions for Molded and Extruded Plastics". The tensile strength and elongation at break were recorded, and the tests were repeated 5 times, with the average value taken.

[0072] 3. Thermal properties: The samples were tested using a thermogravimetric analyzer under a nitrogen atmosphere. The nitrogen flow rate was set to 20 mL / min, and the samples were heated from room temperature to 800℃ at a rate of 10℃ / min. The change in sample mass with temperature was recorded throughout the process to obtain the thermogravimetric curve, and the residual mass at the 5% thermogravimetric temperature and 800℃ was calculated.

[0073] III. Analysis of Test Results for Each Embodiment and Comparative Example Table 1. Optical performance test results of Examples 1-3 and Comparative Examples 1-2 Note: "—" indicates that it was not detected, or that a valid value could not be given due to the signal being too low.

[0074] Table 2. Test results of mechanical and thermal properties of Examples 1-3 and Comparative Examples 1-2 Results analysis: Figures 2-4The fluorescence excitation and emission spectra of the phenol-based fluorescent copolyesters prepared in Examples 1-3 are shown in Table 1. As can be seen from Table 1, with the increase of DDTH content, the fluorescence emission peak of the phenol-based fluorescent copolyester shifted from 467 nm to 472 nm, showing a slight redshift trend, and the luminescence intensity showed a pattern of first increasing and then decreasing. Among them, the copolyester with 2.5% DDTH content in Example 1 exhibited the highest fluorescence emission intensity (3.6 × 10⁻⁶) under 365 nm excitation light. 6 (au). The introduction of DDTH significantly improved the fluorescence quantum yield of the copolyester. In Example 2, the copolyester with 5% DDTH content exhibited the best luminescence efficiency, with a quantum yield as high as 52.33%. While the quantum yield decreased slightly as the DDTH content further increased to 10%, it still remained at a relatively high level of 45.37%. These results demonstrate that the DDTH copolyester described in this invention possesses excellent fluorescence properties and has the potential for application in the field of high-value-added optical materials.

[0075] The pure PET sample obtained in Comparative Example 1 was characterized for fluorescence performance under the same test conditions as in Example 1. The results showed that the pure PET sample did not exhibit a significant fluorescence emission peak under UV excitation, and its fluorescence signal was extremely weak, making it impossible to accurately measure its fluorescence quantum yield, directly demonstrating its lack of effective fluorescence response. This comparative result confirms that conventional PET materials themselves possess almost no intrinsic fluorescence properties. However, this invention, by embedding the phenolic monomer DDTH with a specific structure into the polyester molecular backbone via chemical covalent bonds, successfully achieves a fundamental modification of the optical properties of polyester materials from scratch. The significant fluorescence signals exhibited by the series of copolyesters prepared in Examples 1-3 of this invention originate from the introduced DDTH structural units, thus fully demonstrating the uniqueness and inventiveness of the technical solution of this invention in endowing polyester materials with durable and stable fluorescence functionality.

[0076] Comparative Example 2 replaced dimethyl terephthalate (DMT) used in this application with dimethyl succinate (DSS), that is, replaced aromatic dimethyl ester with aliphatic dimethyl ester. The resulting copolymer did not show a significant fluorescence emission peak under UV excitation, and its fluorescence signal was extremely weak, making it impossible to accurately measure its fluorescence quantum yield. This directly demonstrates that it lacks effective fluorescence response characteristics. The reason is that during the thermal motion of the flexible aliphatic chains composed of DMT, the excited-state energy absorbed by the luminescent monomer DDTH is consumed through non-radiative transitions; furthermore, DMT lacks a benzene ring and cannot generate solid-state fluorescence by forming intramolecular hydrogen bonds with the luminescent monomer DDTH.

[0077] The polyesters prepared in Comparative Examples 1-2 exhibited tensile strengths of 38 MPa-48 MPa and elongation at break of 320%-530%, indicating that the polyester material possesses good flexibility but limited strength. In Comparative Example 2, dimethyl succinate replaced dimethyl terephthalate, and the flexible aliphatic chain replaced the original rigid benzene ring of PET, further reducing its tensile strength and increasing its elongation at break. The copolyesters prepared in Examples 1-3 achieved tensile strengths of 72 MPa-93 MPa and elongation at break of 25%-65%, indicating that their internal structure is highly rigid and possesses a certain degree of resistance to deformation. Compared to Comparative Example 1, the phenol-based fluorescent copolyesters prepared in Examples 1-3 showed an increase in tensile strength of approximately 50%-94%; their elongation at break was at a moderate level, still higher than that of brittle materials. They transformed from a material with excellent ductility but insufficient strength into a material with high rigidity, impact resistance, and a more balanced comprehensive mechanical property, meeting a wider range of structural applications.

[0078] The 5% thermogravimetric temperature (TWT) is the lowest temperature at which a material begins to undergo significant thermal degradation, characterizing its thermal stability. The copolyesters prepared in Examples 1-3 had 5% TWTs of 403.3℃-407.4℃, which, compared to the 409.5℃ TWT of the PET matrix resin prepared in Comparative Example 1, indicate that their thermal stability remains at a comparable level.

[0079] In summary, this application precisely introduces dimethyl 2,5-dihydroxyterephthalate (DDTH) into a copolymer system of dimethyl terephthalate (DMT) and ethylene glycol (EG) at a specific ratio. Using direct transesterification and subsequent high-temperature polycondensation, the phenolic DDTH monomer with a specific conjugated structure is firmly bonded to the polyester backbone via chemical bonds. This method imparts bright and tunable fluorescent properties to the copolyester while retaining the good thermal properties of the matrix resin and improving tensile strength and impact resistance.

[0080] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing embodiments by combining some of the constituent elements, are also included in the scope of this application without departing from the spirit of this application.

[0081] Furthermore, although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing a phenol-based fluorescent copolyester, characterized in that, include: Dimethyl terephthalate, ethylene glycol, 2,5-dihydroxyterephthalate, transesterification catalyst and polycondensation catalyst were added to a reaction vessel, and a transesterification reaction was carried out after a protective gas was introduced to obtain the transesterification product. The reactor is heated to carry out a polycondensation reaction to obtain a copolyester; The copolyester is cooled, cured, and granulated to obtain the phenol-based fluorescent copolyester.

2. The method for preparing phenol-based fluorescent copolyester according to claim 1, characterized in that, The mass ratio of the dimethyl terephthalate to the dimethyl 2,5-dihydroxyterephthalate is 1:(0.025-0.1); and / or, The ratio of the total molar amount of dimethyl terephthalate and dimethyl 2,5-dihydroxyterephthalate to the molar amount of ethylene glycol is 1:(1.5-2.5).

3. The method for preparing phenol-based fluorescent copolyester according to claim 1, characterized in that, The transesterification catalyst is anhydrous zinc acetate, and the mass ratio of the transesterification catalyst to the dimethyl terephthalate is (0.0001-0.001):1; and / or, The polycondensation catalyst is antimony trioxide, and the mass ratio of the polycondensation catalyst to the dimethyl terephthalate is (0.0001-0.001):

1.

4. The method for preparing phenol-based fluorescent copolyester according to claim 1, characterized in that, The transesterification reaction following the introduction of a protective gas includes: A protective gas is introduced into the reactor and pressurized to 140 kPa-160 kPa, then depressurized to atmospheric pressure, the valve is closed, and the protective gas is introduced again. This process is repeated three times. The protective gas includes at least one of nitrogen and argon.

5. The method for preparing phenol-based fluorescent copolyester according to claim 1, characterized in that, The temperature of the reactor in the transesterification reaction is 190℃-220℃, and the temperature of the process tower in the transesterification reaction is 65℃-75℃; and / or, In the transesterification reaction, the reactor temperature is gradually increased from 8℃ / min to 12℃ / min.

6. The method for preparing phenol-based fluorescent copolyester according to claim 1, characterized in that, The transesterification reaction is carried out under stirring; and / or, The transesterification reaction is stopped when the amount of water discharged reaches 90% of the theoretical discharge amount.

7. The method for preparing phenol-based fluorescent copolyester according to claim 1, characterized in that, The temperature of the reactor in the polycondensation reaction is 260℃-280℃, and the temperature of the reactor in the polycondensation reaction is gradually increased by 2℃ / min-3℃ / min.

8. The method for preparing phenol-based fluorescent copolyester according to claim 1, characterized in that, The polycondensation reaction is carried out under gradient decompression conditions, including multiple consecutive decompression stages. In each decompression stage, the pressure of the reactor is reduced by 15 kPa to 25 kPa, i.e., maintained at that pressure for 10 min to 20 min, and the cycle continues until the pressure of the reactor is ≤ -0.1 MPa.

9. The method for preparing phenol-based fluorescent copolyester according to claim 1, characterized in that, The polycondensation reaction is carried out under stirring. The torque value of the stirrer during the polycondensation reaction is monitored. When the torque value reaches 2.5 Nm-2.7 Nm, the polycondensation reaction is stopped and the reactor is restored to atmospheric pressure.

10. A phenol-based fluorescent copolyester, characterized in that, It is prepared by the method for preparing phenol-based fluorescent copolyester according to any one of claims 1-9.

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