Low-melting-point thermo-oxidative aging resistant polyester chip and preparation method thereof

Abstract

The invention provides a low-melting-point thermo-oxidative aging resistant polyester chip and a preparation method thereof, and belongs to the technical field of low-melting-point polyester chips. Based on a low-melting-point matrix modified by copolymerization and a first static defense line, an anchored antioxidant monomer is covalently bonded to a polymer main chain during synthesis, the defects that a traditional antioxidant is easy to migrate and short in aging are overcome, and aging degradation can be inhibited for a long time; according to the second dynamic repair mechanism, a carbodiimide repair agent is introduced and can recognize and reconnect a broken chain when the molecular chain is broken due to material aging, so that the reduction of the molecular weight is effectively inhibited; the two assistants form efficient synergism: static prevention reduces damage and reduces burden for the repairing agent; and the repairing function makes up the generated damage, overcomes the limitation of a pure antioxidant system, and finally endows the material with more durable and reliable comprehensive performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of low-melting-point polyester chips, and relates to a low-melting-point heat-resistant and oxygen-aging-resistant polyester chip and a preparation method thereof. BACKGROUND

[0002] Polyester materials have become key materials in the fields of engineering plastics, special fibers and functional films due to their excellent comprehensive performance. However, in harsh application scenarios such as automobiles, electronics and new energy, traditional polyesters face two major challenges: first, the high melting point of the polyester leads to high processing energy consumption and is prone to thermal degradation during processing; second, the molecular structure of the polyester is prone to aging in a high-temperature oxygen environment, which leads to molecular chain rupture and performance degradation, severely limiting the reliability of long-term service. To address these challenges, existing technologies usually adopt two strategies: reducing the melting point through copolymerization modification, and adding small-molecule antioxidants to delay aging. However, both strategies have obvious shortcomings: first, copolymerization modification improves the processability but often sacrifices part of the thermal stability; second, traditional small-molecule antioxidants are added through physical blending, which has problems such as migration, volatilization and extraction, resulting in a gradual loss of protection effect over time and the inability to provide stable protection throughout the life cycle. More critically, this traditional stabilization method is a passive “defense” mechanism that can only delay the occurrence of degradation but cannot repair the molecular chain rupture damage that has already occurred, and the degradation of material performance is irreversible. SUMMARY

[0003] To address the above problems, the purpose of the present application is to provide a low-melting-point heat-resistant and oxygen-aging-resistant polyester chip and a preparation method thereof. The present application constructs a dual-protection system that synergistically combines static prevention and dynamic repair. The base resin is a low-melting-point copolyester modified by copolymerization, which introduces asymmetric monomers to disrupt the molecular chain regularity, achieve more moderate processing conditions and reduce thermal degradation. During its synthesis stage, an anchor-type thiophenol antioxidant monomer is anchored to the polymer main chain through a covalent bond. This constitutes a static defense line, solving the problems of easy migration and short time efficiency of traditional antioxidants, providing intrinsic antioxidant protection for the material and effectively inhibiting the occurrence of aging degradation; a carbodiimide repair agent is introduced, which can recognize and reconnect the broken chains when the material ages and the molecular chains break, effectively inhibiting the decrease in molecular weight; the two functional additives form a high-efficiency synergy: the preventive effect of the anchor antioxidant greatly reduces the occurrence of damage, reducing the burden on the repair agent; and the repair agent can compensate for a small amount of damage that has already occurred, overcoming the limitations of traditional antioxidant systems, thereby endowing the polyester material with more durable and reliable comprehensive performance.

[0004] To achieve this purpose, the present application adopts the following technical solutions:

[0005] In a first aspect, the present application provides a method for preparing low-melting-point heat-resistant and oxygen-aging-resistant polyester chips, which comprises:

[0006] S1: 4,4'-dithiodianiline and salicylaldehyde are added to ethanol, and glacial acetic acid is added to obtain reaction liquid A, which is stirred and reacted under nitrogen protection, and solid is precipitated and cooled, filtered, washed, and dried to obtain a sulfur-containing bis-Schiff base skeleton intermediate; the sulfur-containing bis-Schiff base skeleton intermediate is added to dimethyl sulfoxide, and ethylene carbonate, potassium carbonate, and tetrabutylammonium bromide are added to obtain reaction liquid B, which is stirred and reacted to obtain a pretreatment liquid, which is poured into deionized water, filtered, washed, purified, and dried to obtain an anchor-type sulfur phenolic antioxidant monomer;

[0007] S2: A dichloromethane dispersion solution of 1,3-adamantanediamine is prepared, and tert-butyl isocyanate is added under ice water bath and nitrogen protection to obtain reaction liquid C, which is stirred and reacted, filtered, washed, and dried to obtain a diurea intermediate; the diurea intermediate and triethylamine are added to dichloromethane to obtain a suspension, and a phosphorus oxychloride dichlorobenzene solution is added in an ice water bath to obtain reaction liquid D, which is stirred and reacted at room temperature, distilled under reduced pressure, and the crude product is added to toluene with phospholane, and then reacted after warming, cooled, filtered, distilled under reduced pressure, and dried to obtain a carbodiimide repair agent;

[0008] S3: An acid, an alcohol, and a composite catalyst are mixed to obtain reaction liquid E, the acid is terephthalic acid and isophthalic acid, and the alcohol is ethylene glycol, isosorbide, and the anchor-type sulfur phenolic antioxidant monomer, which is reacted at a first temperature under nitrogen protection and a first pressure, and then warmed to a second temperature while the pressure is reduced to a second pressure, to obtain a polyester melt containing an anchor-type antioxidant;

[0009] S4: The carbodiimide repair agent is added to the polyester melt containing the anchor-type antioxidant at a third temperature, and a mixed melt is obtained by stirring in a twin-screw extruder, which is extruded through the extruder head and pelletized to obtain low-melting-point heat-resistant and oxygen-aging-resistant polyester chips.

[0010] As a preferred technical solution of the present application, in step S1, the molar ratio of 4,4'-dithiodianiline to salicylaldehyde is 1:(2.0-2.2), for example, it can be 1:2.00, 1:2.02, 1:2.04, 1:2.06, 1:2.08, 1:2.10, 1:2.12, 1:2.14, 1:2.16, 1:2.18, or 1:2.20, but is not limited to the listed values, and other values not listed in this range are also applicable.

[0011] In some optional embodiments, the mass-volume ratio of 4,4'-dithiodianiline to ethanol is 1 g: (15-25) mL, for example, it can be 1 g: 15 mL, 1 g: 16 mL, 1 g: 17 mL, 1 g: 18 mL, 1 g: 19 mL, 1 g: 20 mL, 1 g: 21 mL, 1 g: 22 mL, 1 g: 23 mL, 1 g: 24 mL or 1 g: 25 mL, but not only limited to the listed values, other values not listed in the range are also applicable.

[0012] In some optional embodiments, the amount of glacial acetic acid is 0.1-0.5% of the total mass of 4,4'-dithiodianiline and salicylaldehyde, for example, it can be 0.10%, 0.14%, 0.18%, 0.22%, 0.26%, 0.30%, 0.34%, 0.38%, 0.42%, 0.46% or 0.50%, but not only limited to the listed values, other values not listed in the range are also applicable.

[0013] In some optional embodiments, the temperature of the stirring reaction of reaction solution A is 70-80°C, for example, it can be 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C or 80°C, but not only limited to the listed values, other values not listed in the range are also applicable.

[0014] In some optional embodiments, the time of the stirring reaction of reaction solution A is 4-8h, for example, it can be 4.0h, 4.4h, 4.8h, 5.2h, 5.6h, 6.0h, 6.4h, 6.8h, 7.2h, 7.6h or 8.0h, but not only limited to the listed values, other values not listed in the range are also applicable.

[0015] In some optional embodiments, after the stirring reaction of reaction solution A, the solid is precipitated by cooling to 0-10°C, for example, it can be cooled to 0°C, 1°C, 2°C, 3°C, 4°C, 5°C, 6°C, 7°C, 8°C, 9°C or 10°C, but not only limited to the listed values, other values not listed in the range are also applicable.

[0016] In some optional embodiments, the temperature of reaction solution B is 60-80°C, for example, it can be 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C, but not only limited to the listed values, other values not listed in the range are also applicable.

[0017] In some alternative embodiments, the molar ratio of the sulfur-containing bis-Schiff base skeleton intermediate to ethylene carbonate is 1: (1-1.2), which can be 1:1, 1:1.02, 1:1.04, 1:1.06, 1:1.08, 1:1.1, 1:1.12, 1:1.14, 1:1.16, 1:1.18 or 1:1.2, but is not limited to the listed values, and other values not listed within the range are also applicable.

[0018] In some alternative embodiments, the amount of potassium carbonate added is 1-3% of the mass of the sulfur-containing bis-Schiff base skeleton intermediate, which can be 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8% or 3.0%, but is not limited to the listed values, and other values not listed within the range are also applicable.

[0019] In some alternative embodiments, the amount of tetrabutylammonium bromide added is 1-5% of the mass of the sulfur-containing bis-Schiff base skeleton intermediate, which can be 1.0%, 1.4%, 1.8%, 2.2%, 2.6%, 3.0%, 3.4%, 3.8%, 4.2%, 4.6% or 5.0%, but is not limited to the listed values, and other values not listed within the range are also applicable.

[0020] In some alternative embodiments, the stirring reaction time of the reaction solution B is 1-2h, which can be 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2h, but is not limited to the listed values, and other values not listed within the range are also applicable.

[0021] In some alternative embodiments, the volume ratio of deionized water to pretreatment solution is (10-20):1, which can be 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1 or 20:1, but is not limited to the listed values, and other values not listed within the range are also applicable.

[0022] As a preferred technical solution of the present application, in step S2, the mass-volume ratio of 1,3-adamantanediamine to dichloromethane is 1g:(20-40)mL, which can be 1g:20mL, 1g:22mL, 1g:24mL, 1g:26mL, 1g:28mL, 1g:30mL, 1g:32mL, 1g:34mL, 1g:36mL, 1g:38mL or 1g:40mL, but is not limited to the listed values, and other values not listed within the range are also applicable.

[0023] In some alternative embodiments, the molar ratio of 1,3-adamantanediamine to tert-butyl isocyanate is 1:(2-2.2), for example, it can be 1:2.00, 1:2.02, 1:2.04, 1:2.06, 1:2.08, 1:2.10, 1:2.12, 1:2.14, 1:2.16, 1:2.18 or 1:2.20, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0024] In some optional embodiments, the reaction temperature of the reaction liquid C is 20-30°C, for example, it can be 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C or 30°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0025] In some optional embodiments, the reaction time of the reaction solution C is 10-14 h, for example, it can be 10.0 h, 10.4 h, 10.8 h, 11.2 h, 11.6 h, 12.0 h, 12.4 h, 12.8 h, 13.2 h, 13.6 h or 14.0 h, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0026] In some alternative embodiments, the molar ratio of the diurea intermediate to triethylamine is 1:(4-5), for example, it can be 1:4.0, 1:4.1, 1:4.2, 1:4.3, 1:4.4, 1:4.5, 1:4.6, 1:4.7, 1:4.8, 1:4.9 or 1:5.0, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0027] In some optional embodiments, the molar ratio of the diurea intermediate to phosphorus oxychloride is 1:(2.2-2.8), for example, it can be 1:2.20, 1:2.26, 1:2.32, 1:2.38, 1:2.44, 1:2.50, 1:2.56, 1:2.62, 1:2.68, 1:2.74 or 1:2.80, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0028] In some optional embodiments, the reaction solution D is stirred at room temperature for 20-28 hours, for example, 20.0 hours, 20.8 hours, 21.6 hours, 22.4 hours, 23.2 hours, 24.0 hours, 24.8 hours, 25.6 hours, 26.4 hours, 27.2 hours, or 28.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0029] In some optional embodiments, the amount of phosphacyclopentane fed is 0.1-0.5% of the mass of the crude product, for example, it can be 0.1%, 0.14%, 0.18%, 0.22%, 0.26%, 0.3%, 0.34%, 0.38%, 0.42%, 0.46% or 0.5%, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0030] In some optional embodiments, the crude product and phosphacyclopentane are added to toluene and then heated to 120-160°C, for example, 120°C, 124°C, 128°C, 132°C, 136°C, 140°C, 144°C, 148°C, 152°C, 156°C or 160°C, but not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0031] In some optional embodiments, the crude product and phosphacyclopentane are added to toluene and reacted at elevated temperature for 2-4 hours, for example, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours, or 4 hours, but are not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0032] As a preferred technical solution of the present invention, in step S3, the molar ratio of the acid to the alcohol is 1:(1.1-1.4), for example, it can be 1:1.10, 1:1.13, 1:1.16, 1:1.19, 1:1.22, 1:1.25, 1:1.28, 1:1.31, 1:1.34, 1:1.37 or 1:1.40, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] In some optional embodiments, the molar fraction of the acid, mesophthalic acid, is 15-25%, for example, it can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24% or 25%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0034] In some alternative embodiments, the molar fraction of isosorbide in the alcohol is 3-8%, for example, it can be 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5% or 8.0%, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0035] In some optional embodiments, the molar fraction of the anchored thiophenol antioxidant monomer in the alcohol is 0.5-2.0%, for example, it can be 0.50%, 0.65%, 0.80%, 0.95%, 1.10%, 1.25%, 1.40%, 1.55%, 1.70%, 1.85% or 2.00%, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0036] In some optional embodiments, the amount of the composite catalyst is 200-400 ppm of the total mass of the acid and alcohol, for example, 200 ppm, 220 ppm, 240 ppm, 260 ppm, 280 ppm, 300 ppm, 320 ppm, 340 ppm, 360 ppm, 380 ppm or 400 ppm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0037] In some optional embodiments, the mass ratio of antimony trioxide to cobalt acetate in the composite catalyst is 1:0.1.

[0038] In some alternative embodiments, the first pressure is 0.1-0.4 MPa, for example, it can be 0.10 MPa, 0.13 MPa, 0.16 MPa, 0.19 MPa, 0.22 MPa, 0.25 MPa, 0.28 MPa, 0.31 MPa, 0.34 MPa, 0.37 MPa or 0.40 MPa, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0039] In some alternative embodiments, the first temperature is 240-260°C, for example, it can be 240°C, 242°C, 244°C, 246°C, 248°C, 250°C, 252°C, 254°C, 256°C, 258°C or 260°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0040] In some optional embodiments, the reaction time of the reaction solution E at the first temperature is 3-4 hours, for example, it can be 3.0 hours, 3.1 hours, 3.2 hours, 3.3 hours, 3.4 hours, 3.5 hours, 3.6 hours, 3.7 hours, 3.8 hours, 3.9 hours or 4.0 hours, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0041] In some alternative embodiments, the second temperature is 270-280°C, for example, it can be 270°C, 271°C, 272°C, 273°C, 274°C, 275°C, 276°C, 277°C, 278°C, 279°C or 280°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0042] In some alternative embodiments, the second pressure is 50-100 Pa, for example, it can be 50 Pa, 55 Pa, 60 Pa, 65 Pa, 70 Pa, 75 Pa, 80 Pa, 85 Pa, 90 Pa, 95 Pa or 100 Pa, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0043] In some alternative embodiments, the viscosity of the reaction solution E reacting to the polyester melt at the second temperature is 0.6-0.8 dL / g, for example, it can be 0.60 dL / g, 0.62 dL / g, 0.64 dL / g, 0.66 dL / g, 0.68 dL / g, 0.70 dL / g, 0.72 dL / g, 0.74 dL / g, 0.76 dL / g, 0.78 dL / g or 0.80 dL / g, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0044] As a preferred technical solution of the present invention, in step S4, the third temperature is 250-270℃, for example, it can be 250℃, 252℃, 254℃, 256℃, 258℃, 260℃, 262℃, 264℃, 266℃, 268℃ or 270℃, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0045] In some optional embodiments, the amount of the carbodiimide repair agent added is 1-1.5% of the mass of the polyester melt containing the anchoring antioxidant, for example, it can be 1.00%, 1.05%, 1.10%, 1.15%, 1.20%, 1.25%, 1.30%, 1.35%, 1.40%, 1.45% or 1.50%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0046] Secondly, the present invention provides a low-melting-point heat-resistant and oxygen-aging-resistant polyester chip prepared by the aforementioned preparation method.

[0047] This application aims to prepare a heat- and oxygen-resistant polyester by constructing a synergistic protection system: firstly, a reactive antioxidant monomer is integrated into the polymer backbone to build a durable intrinsic protective capability; secondly, a molecular chain repair agent is added to the material matrix to endow the material with the function of actively repairing itself when damaged, thereby achieving comprehensive and long-term stabilization from source prevention to process repair.

[0048] First, this application prepares an anchored thiophenol antioxidant monomer, providing polyester materials with a long-lasting antioxidant capability against migration. The anchored thiophenol antioxidant monomer possesses multiple structural units with free radical scavenging and peroxide decomposition capabilities, including aromatic etherified hydroxyl groups, imine groups, and disulfide bonds, which are beneficial for the synergistic passivation of free radicals and unstable peroxides that initiate degradation. Furthermore, its molecule is modified with primary alcohol hydroxyl groups that can participate in polymerization. This allows it to be covalently embedded into the polymer backbone during the polyester synthesis stage. This chemical anchoring method reduces the risk of volatility and short protective life of traditional small-molecule antioxidants, and facilitates the formation of a more durable static protective system within the material.

[0049] Secondly, this application prepares a carbodiimide repair agent, the purpose of which is to endow polyester materials with dynamic protective capabilities for self-repair after aging damage occurs. This repair agent employs a rigid adamantane backbone with high thermal stability, which is beneficial for maintaining the relative stability of its activity and structure during high-temperature processing and long-term service; carbodiimide groups sensitive to acidic substances (especially carboxyl groups) are introduced at the functional ends. When the polyester material undergoes molecular chain breakage due to aging and generates new terminal carboxyl groups, these pre-dispersed carbodiimide repair agent molecules can preferentially recognize and react with them, generating acylurea structures, thereby achieving a certain degree of reconnection of some broken chain segments. This active repair mechanism can effectively inhibit the decrease in the molecular weight of the material and maintain its mechanical properties.

[0050] The base resin in this application is a copolymer-modified low-melting-point copolyester, which optimizes the material's processing properties and makes it an ideal platform for carrying functional units. By introducing isophthalic acid and bio-based isosorbide, two nonlinear and asymmetric comonomers, into the polymer backbone, the regularity of the traditional molecular chain is intentionally disrupted, thereby reducing the material's crystallinity and melting point. This modification allows the material to be melt-processed under milder temperature conditions, reducing production energy consumption, minimizing thermal degradation during processing, and broadening its application potential in heat-sensitive fields. During polymerization, anchored antioxidant monomers are introduced as functional comonomers, completing the construction of a functionalized low-melting-point matrix.

[0051] In this application, there is also a functional synergy between the anchored antioxidant monomer and the carbodiimide repair agent. This is a dual and progressive protection mechanism: First, the anchored antioxidant monomer, anchored to the polyester backbone, constitutes the first line of defense, inhibiting and delaying aging degradation at its source through a preventative mechanism. Second, for unavoidable molecular chain damage, the carbodiimide repair agent dispersed in the matrix activates the second line of defense, actively compensating for the damage already caused. The preventative effect of the anchored antioxidant monomer reduces the repair pressure on the carbodiimide repair agent, enabling it to maintain its activity for a longer period; while the repair effect of the carbodiimide repair agent compensates for the inability of a simple antioxidant system to reverse performance degradation. Through this synergy, the polyester material prepared in this application can achieve more durable and reliable overall performance.

[0052] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0053] This application introduces an anchored thiophenol antioxidant monomer to impart long-lasting and migration-resistant antioxidant properties to polyester materials. This monomer contains reactive hydroxyl groups at both ends that can participate in polymerization, while the center integrates multiple highly efficient antioxidant groups. During polyester synthesis, it can be chemically anchored to the polymer backbone through covalent bonds, reducing the risks of easy migration and short-lived effects associated with traditional small-molecule antioxidants, and facilitating the construction of a durable static protective system within the material.

[0054] This application introduces a carbodiimide repair agent to endow polyester materials with dynamic self-repair capabilities in response to aging damage. This repair agent combines a highly thermally stable structure with carbodiimide. When the polymer breaks down due to aging and generates terminal carboxyl groups, the pre-dispersed repair agent reacts with these groups to form an acylurea structure, thereby achieving a certain degree of reconnection of some broken chain segments, effectively inhibiting molecular weight decline and maintaining the mechanical properties of the material.

[0055] In this application, the base resin is a low-melting-point copolyester. Through copolymerization modification, asymmetric monomers (isophthalic acid and isosorbide) are introduced to disrupt the molecular chain regularity, thereby lowering its melting point. This modification allows the material to be processed under milder conditions, reduces thermal degradation, and broadens its application areas. Simultaneously, anchored antioxidant monomers are directly introduced during the polymerization stage, completing the construction of a functionalized low-melting-point matrix.

[0056] In this application, the anchored antioxidant monomer serves as the first line of defense, providing static prevention by inhibiting and delaying aging degradation at its source and reducing molecular chain damage. The carbodiimide repair agent serves as the second line of defense, providing dynamic repair to compensate for existing molecular chain breakage. The two work synergistically: the preventative mechanism reduces the burden on the repair agent, while the repair mechanism compensates for the inability of a simple antioxidant system to reverse performance degradation, ultimately achieving more durable and reliable overall performance. Detailed Implementation

[0057] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The embodiments described herein are specific implementations of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limiting the implementation of the present invention or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of this application. These technical solutions include technical solutions that employ any obvious substitutions and modifications made to the embodiments described herein.

[0058] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone further purification or processing.

[0059] Example 1

[0060] This embodiment provides a low-melting-point heat- and oxygen-aging-resistant polyester chip and its preparation method. The preparation method of the low-melting-point heat- and oxygen-aging-resistant polyester chip specifically includes the following steps:

[0061] S1: 4,4'-Dithiodiphenylamine and salicylaldehyde were added to ethanol at a molar ratio of 1:2.15, where the mass-to-volume ratio of 4,4'-dithiodiphenylamine to ethanol was 1 g:18 mL. Glacial acetic acid was added to obtain reaction solution A, where the amount of glacial acetic acid added was 0.4% of the total mass of 4,4'-dithiodiphenylamine and salicylaldehyde. The reaction was stirred at 72°C for 5 h under nitrogen protection. The mixture was cooled to 2°C to precipitate a solid, which was then filtered, washed, and dried to obtain a sulfur-containing bis-Schiff base intermediate. The sulfur-containing bis-Schiff base intermediate was then added to dimethyl methacrylate... In sulfone, ethylene carbonate, potassium carbonate, and tetrabutylammonium bromide were added at 75°C to obtain reaction solution B, wherein the molar ratio of sulfur-containing bis-Schiff base skeleton intermediate to ethylene carbonate was 1:1, the amount of potassium carbonate added was 2.5% of the mass of sulfur-containing bis-Schiff base skeleton intermediate, and the amount of tetrabutylammonium bromide added was 2% of the mass of sulfur-containing bis-Schiff base skeleton intermediate. The reaction was stirred for 1 hour to obtain a pretreatment solution, which was poured into deionized water, wherein the volume ratio of deionized water to pretreatment solution was 12:1. After filtration, washing, purification, and drying, the anchored thiophenol antioxidant monomer was obtained.

[0062] S2: Prepare a dichloromethane dispersion of 1,3-adamantanediamine, wherein the mass-to-volume ratio of 1,3-adamantanediamine to dichloromethane is 1 g: 25 mL. Add tert-butyl isocyanate under ice-water bath and nitrogen protection to obtain reaction solution C, wherein the molar ratio of 1,3-adamantanediamine to tert-butyl isocyanate is 1:2.1. Stir the reaction at 22 °C for 11 h, filter, wash, and dry to obtain a diurea intermediate. Add the diurea intermediate and triethylamine to dichloromethane to obtain a suspension. A solution of diurea intermediate to triethylamine in a 1:4.2 molar ratio was prepared by adding a dichlorotoluene solution of phosphorus oxychloride to a solution of phosphorus oxychloride in an ice-water bath to obtain reaction solution D, in which the molar ratio of diurea intermediate to phosphorus oxychloride was 1:2.4. The mixture was stirred at room temperature for 22 h, then distilled under reduced pressure. The crude product and phosphazene were added to toluene, with the amount of phosphazene added being 0.4% of the mass of the crude product. The mixture was heated to 140 °C and reacted for 3 h. After cooling, the mixture was filtered, distilled under reduced pressure, and dried to obtain the carbodiimide repair agent.

[0063] S3: An acid, an alcohol, and a composite catalyst are mixed to obtain a reaction solution E. The acid is terephthalic acid and isophthalic acid, and the alcohol is ethylene glycol, isosorbide, and an anchored thiophenol antioxidant monomer. The molar ratio of acid to alcohol is 1:1.2; the molar fraction of isophthalic acid is 18%; the molar fraction of isosorbide in the alcohol is 4%, and the molar fraction of the anchored thiophenol antioxidant monomer is 1.0%. The amount of composite catalyst is 250 ppm of the total mass of acid and alcohol. The mass ratio of antimony trioxide to cobalt acetate in the composite catalyst is 1:0.1. Under nitrogen protection and a first pressure of 0.2 MPa, the reaction is carried out at a first temperature of 245°C for 3.2 h. Then, the temperature is raised to a second temperature of 272°C, and the pressure is lowered to a second pressure of 60 Pa. The reaction continues until the viscosity reaches 0.65 dL / g to obtain a polyester melt containing an anchored antioxidant.

[0064] S4: At a third temperature of 255℃, carbodiimide repair agent is added to the polyester melt containing anchoring antioxidant and stirred in a twin-screw extruder to obtain a mixed melt. The amount of carbodiimide repair agent added is 1.1% of the mass of the polyester melt containing anchoring antioxidant. The melt is extruded through the extruder die head and pelletized to obtain low melting point heat-resistant and oxygen-aging resistant polyester chips.

[0065] Example 2

[0066] This embodiment provides a low-melting-point heat- and oxygen-aging-resistant polyester chip and its preparation method. The preparation method of the low-melting-point heat- and oxygen-aging-resistant polyester chip specifically includes the following steps:

[0067] S1: 4,4'-Dithiodiphenylamine and salicylaldehyde were added to ethanol at a molar ratio of 1:2.0, where the mass-to-volume ratio of 4,4'-dithiodiphenylamine to ethanol was 1 g:25 mL. Glacial acetic acid was added to obtain reaction solution A, where the amount of glacial acetic acid added was 0.1% of the total mass of 4,4'-dithiodiphenylamine and salicylaldehyde. The reaction was carried out under nitrogen protection at 80°C with stirring for 8 hours. The mixture was cooled to 10°C to precipitate a solid, which was then filtered, washed, and dried to obtain a sulfur-containing bis-Schiff base intermediate. The sulfur-containing bis-Schiff base intermediate was then added to dimethyl sulfoxide. In the reaction, ethylene carbonate, potassium carbonate, and tetrabutylammonium bromide were added at 60°C to obtain reaction solution B, wherein the molar ratio of sulfur-containing bis-Schiff base intermediate to ethylene carbonate was 1:1.1, the amount of potassium carbonate added was 1% of the mass of sulfur-containing bis-Schiff base intermediate, and the amount of tetrabutylammonium bromide added was 5% of the mass of sulfur-containing bis-Schiff base intermediate. The reaction was stirred for 1.3 h to obtain a pretreatment solution, which was poured into deionized water, wherein the volume ratio of deionized water to pretreatment solution was 20:1. After filtration, washing, purification, and drying, the anchored thiophenol antioxidant monomer was obtained.

[0068] S2: Prepare a dichloromethane dispersion of 1,3-adamantanediamine, wherein the mass-to-volume ratio of 1,3-adamantanediamine to dichloromethane is 1 g:40 mL. Add tert-butyl isocyanate under ice-water bath and nitrogen protection to obtain reaction solution C, wherein the molar ratio of 1,3-adamantanediamine to tert-butyl isocyanate is 1:2.2. Stir the reaction at 30 °C for 14 h, filter, wash, and dry to obtain a diurea intermediate. Add the diurea intermediate and triethylamine to dichloromethane to obtain a suspension. A solution of phosphorus oxychloride in dichlorotoluene was added to a floating liquid in which the molar ratio of diurea intermediate to triethylamine was 1:5 to obtain reaction solution D, in which the molar ratio of diurea intermediate to phosphorus oxychloride was 1:2.8. The mixture was stirred at room temperature for 28 h, and then distilled under reduced pressure. The crude product and phosphazene were added to toluene, with the amount of phosphazene added being 0.3% of the mass of the crude product. The mixture was heated to 150 °C and reacted for 3.5 h. After cooling, the mixture was filtered, distilled under reduced pressure, and dried to obtain the carbodiimide repair agent.

[0069] S3: Acid, alcohol, and composite catalyst are mixed to obtain reaction solution E. The acid is terephthalic acid and isophthalic acid, and the alcohol is ethylene glycol, isosorbide, and anchored thiophenol antioxidant monomer. The molar ratio of acid to alcohol is 1:1.4; the molar fraction of isophthalic acid is 25%; the molar fraction of isosorbide in the alcohol is 8%, and the molar fraction of anchored thiophenol antioxidant monomer is 2.0%. The amount of composite catalyst is 400 ppm of the total mass of acid and alcohol. The mass ratio of antimony trioxide to cobalt acetate in the composite catalyst is 1:0.1. Under nitrogen protection and a first pressure of 0.4 MPa, the reaction is carried out at a first temperature of 260°C for 4 hours. Then, the temperature is raised to a second temperature of 280°C, and the pressure is lowered to a second pressure of 100 Pa. The reaction continues until the viscosity is 0.8 dL / g to obtain a polyester melt containing anchored antioxidant.

[0070] S4: At a third temperature of 270℃, carbodiimide repair agent is added to polyester melt containing anchoring antioxidant and stirred in a twin-screw extruder to obtain a mixed melt. The amount of carbodiimide repair agent added is 1.5% of the mass of polyester melt containing anchoring antioxidant. The melt is extruded through the extruder die head and pelletized to obtain low melting point heat-resistant and oxygen-aging resistant polyester chips.

[0071] Example 3

[0072] This embodiment provides a low-melting-point heat- and oxygen-aging-resistant polyester chip and its preparation method. The preparation method of the low-melting-point heat- and oxygen-aging-resistant polyester chip specifically includes the following steps:

[0073] S1: 4,4'-Dithiodiphenylamine and salicylaldehyde were added to ethanol at a molar ratio of 1:2.1, where the mass-to-volume ratio of 4,4'-dithiodiphenylamine to ethanol was 1 g:22 mL. Glacial acetic acid was added to obtain reaction solution A, where the amount of glacial acetic acid added was 0.2% of the total mass of 4,4'-dithiodiphenylamine and salicylaldehyde. The reaction was carried out under nitrogen protection at 78°C with stirring for 7 h. The mixture was cooled to 8°C to precipitate a solid, which was then filtered, washed, and dried to obtain a sulfur-containing bis-Schiff base skeleton intermediate. The sulfur-containing bis-Schiff base skeleton intermediate was then added to dimethyl sulfoxide... Ethylene carbonate, potassium carbonate, and tetrabutylammonium bromide were added at 65°C to obtain reaction solution B, wherein the molar ratio of sulfur-containing bis-Schiff base skeleton intermediate to ethylene carbonate was 1:1.2, the amount of potassium carbonate added was 1.5% of the mass of sulfur-containing bis-Schiff base skeleton intermediate, and the amount of tetrabutylammonium bromide added was 4% of the mass of sulfur-containing bis-Schiff base skeleton intermediate. The reaction was stirred for 1.5 h to obtain a pretreatment solution, which was poured into deionized water, wherein the volume ratio of deionized water to pretreatment solution was 18:1. The solution was filtered, washed, purified, and dried to obtain anchored thiophenol antioxidant monomer.

[0074] S2: Prepare a dichloromethane dispersion of 1,3-adamantanediamine, wherein the mass-to-volume ratio of 1,3-adamantanediamine to dichloromethane is 1 g:35 mL. Add tert-butyl isocyanate under ice-water bath and nitrogen protection to obtain reaction solution C, wherein the molar ratio of 1,3-adamantanediamine to tert-butyl isocyanate is 1:2.15. Stir the reaction at 28 °C for 13 h, filter, wash, and dry to obtain a diurea intermediate. Add the diurea intermediate and triethylamine to dichloromethane to obtain... A suspension, wherein the molar ratio of diurea intermediate to triethylamine is 1:4.8, is added to a dichlorotoluene solution of phosphorus oxychloride in an ice-water bath to obtain reaction solution D, wherein the molar ratio of diurea intermediate to phosphorus oxychloride is 1:2.6. The mixture is stirred at room temperature for 26 h, and then distilled under reduced pressure. The crude product and phosphazene are added to toluene, wherein the amount of phosphazene added is 0.1% of the mass of the crude product. The mixture is heated to 120 °C and reacted for 2 h. After cooling, the mixture is filtered, distilled under reduced pressure, and dried to obtain the carbodiimide repair agent.

[0075] S3: Acid, alcohol, and composite catalyst are mixed to obtain reaction solution E. The acid is terephthalic acid and isophthalic acid, and the alcohol is ethylene glycol, isosorbide, and anchored thiophenol antioxidant monomer. The molar ratio of acid to alcohol is 1:1.3; the molar fraction of isophthalic acid is 22%; the molar fraction of isosorbide in the alcohol is 7%, and the molar fraction of anchored thiophenol antioxidant monomer is 1.5%. The amount of composite catalyst is 350 ppm of the total mass of acid and alcohol. The mass ratio of antimony trioxide to cobalt acetate in the composite catalyst is 1:0.1. Under nitrogen protection and a first pressure of 0.3 MPa, the reaction is carried out at a first temperature of 255°C for 3.8 h. Then, the temperature is raised to a second temperature of 278°C, and the pressure is lowered to a second pressure of 90 Pa. The reaction continues until the viscosity reaches 0.75 dL / g to obtain a polyester melt containing anchored antioxidant.

[0076] S4: At a third temperature of 265°C, carbodiimide repair agent is added to polyester melt containing anchoring antioxidant and stirred in a twin-screw extruder to obtain a mixed melt. The amount of carbodiimide repair agent added is 1.4% of the mass of polyester melt containing anchoring antioxidant. The melt is extruded through the extruder die head and pelletized to obtain low melting point heat-resistant and oxygen-aging resistant polyester chips.

[0077] Example 4

[0078] This embodiment provides a low-melting-point heat- and oxygen-aging-resistant polyester chip and its preparation method. The preparation method of the low-melting-point heat- and oxygen-aging-resistant polyester chip specifically includes the following steps:

[0079] S1: 4,4'-Dithiodiphenylamine and salicylaldehyde were added to ethanol at a molar ratio of 1:2.2, where the mass-to-volume ratio of 4,4'-dithiodiphenylamine to ethanol was 1 g:15 mL. Glacial acetic acid was added to obtain reaction solution A, where the amount of glacial acetic acid added was 0.5% of the total mass of 4,4'-dithiodiphenylamine and salicylaldehyde. The reaction was carried out under nitrogen protection at 70°C with stirring for 4 h. The mixture was cooled to 0°C to precipitate a solid, which was then filtered, washed, and dried to obtain a sulfur-containing bis-Schiff base intermediate. The sulfur-containing bis-Schiff base intermediate was then added to dimethyl sulfoxide. In the reaction, ethylene carbonate, potassium carbonate, and tetrabutylammonium bromide were added at 80°C to obtain reaction solution B, wherein the molar ratio of sulfur-containing bis-Schiff base skeleton intermediate to ethylene carbonate was 1:1.08, the amount of potassium carbonate added was 3% of the mass of sulfur-containing bis-Schiff base skeleton intermediate, and the amount of tetrabutylammonium bromide added was 1% of the mass of sulfur-containing bis-Schiff base skeleton intermediate. The reaction was stirred for 2 hours to obtain a pretreatment solution, which was poured into deionized water, wherein the volume ratio of deionized water to pretreatment solution was 10:1. The solution was filtered, washed, purified, and dried to obtain anchored thiophenol antioxidant monomer.

[0080] S2: Prepare a dichloromethane dispersion of 1,3-adamantanediamine, wherein the mass-to-volume ratio of 1,3-adamantanediamine to dichloromethane is 1 g: 20 mL. Add tert-butyl isocyanate under ice-water bath and nitrogen protection to obtain reaction solution C, wherein the molar ratio of 1,3-adamantanediamine to tert-butyl isocyanate is 1:2. Stir the reaction at 20 °C for 10 h, filter, wash, and dry to obtain a diurea intermediate. Add the diurea intermediate and triethylamine to dichloromethane to obtain a suspension. A solution of phosphorus oxychloride in dichlorotoluene was added to a floating liquid in which the molar ratio of diurea intermediate to triethylamine was 1:4 to obtain reaction solution D, in which the molar ratio of diurea intermediate to phosphorus oxychloride was 1:2.2. The mixture was stirred at room temperature for 20 h, and then distilled under reduced pressure. The crude product and phosphazene were added to toluene, with the amount of phosphazene added being 0.5% of the mass of the crude product. The mixture was heated to 160 °C and reacted for 4 h. After cooling, the mixture was filtered, distilled under reduced pressure, and dried to obtain the carbodiimide repair agent.

[0081] S3: Acid, alcohol, and composite catalyst are mixed to obtain reaction solution E. The acid is terephthalic acid and isophthalic acid, and the alcohol is ethylene glycol, isosorbide, and anchored thiophenol antioxidant monomer. The molar ratio of acid to alcohol is 1:1.1; the molar fraction of isophthalic acid is 15%; the molar fraction of isosorbide in the alcohol is 3%, and the molar fraction of anchored thiophenol antioxidant monomer is 0.5%. The amount of composite catalyst is 200 ppm of the total mass of acid and alcohol. The mass ratio of antimony trioxide to cobalt acetate in the composite catalyst is 1:0.1. Under nitrogen protection and a first pressure of 0.1 MPa, the reaction is carried out at a first temperature of 240°C for 3 hours. Then, the temperature is raised to a second temperature of 270°C, and the pressure is lowered to a second pressure of 50 Pa. The reaction continues until the viscosity is 0.6 dL / g to obtain a polyester melt containing anchored antioxidant.

[0082] S4: At a third temperature of 250°C, carbodiimide repair agent is added to the polyester melt containing anchoring antioxidant and stirred in a twin-screw extruder to obtain a mixed melt. The amount of carbodiimide repair agent added is 1% of the mass of the polyester melt containing anchoring antioxidant. The melt is extruded through the extruder die head and pelletized to obtain low-melting-point heat-resistant and oxygen-aging resistant polyester chips.

[0083] Comparative Example 1

[0084] This comparative example provides a low-melting-point heat-resistant and oxygen-aging-resistant polyester chip. The difference between this example and Example 1 is that no carbodiimide repair agent is added, while the other operating steps and process parameters are exactly the same as in Example 1.

[0085] Comparative Example 2

[0086] This comparative example provides a low-melting-point heat-resistant and oxygen-aging-resistant polyester chip. The difference between this example and Example 1 is that no anchored thiophenol antioxidant monomer is added. All other operating steps and process parameters are exactly the same as in Example 1.

[0087] Comparative Example 3

[0088] This comparative example provides a low-melting-point heat-resistant and oxygen-aging-resistant polyester chip. The difference from Example 1 is that a traditional small-molecule antioxidant is used to replace the anchored thiophenol antioxidant monomer, and a carbodiimide repair agent is added simultaneously in step S4. Other operating steps and process parameters are exactly the same as in Example 1.

[0089] The performance of the low-melting-point heat-resistant and oxygen-aging-resistant polyester chips of Examples 1-4 and Comparative Examples 1-3 was tested, and the specific process is as follows:

[0090] The melting point of the sample was tested according to ISO 11357-3;

[0091] The initial intrinsic viscosity and the characteristic viscosity after aging treatment of the test samples were determined according to GB / T14190-2017, and their retention rate was calculated.

[0092] The yellowing index of the sample was tested according to ASTM E313;

[0093] Based on the initial tensile strength and elongation at break of the test sample according to ASTM D638, as well as the tensile strength and elongation at break after aging treatment, calculate its retention rate.

[0094] The test results are shown in Table 1.

[0095] Table 1. Test results of the low melting point heat- and oxygen-aging resistant polyester chips of Examples 1-4 and Comparative Examples 1-3

[0096]

[0097] As shown in Table 1, the test results of Example 1 and Comparative Example 1 indicate that without the addition of the carbodiimide repair agent, the system lacks the "dynamic repair" function. Although the anchored antioxidant monomer can still effectively inhibit most of the degradation from the source, molecular chain breakage is still inevitable during long-term thermo-oxidative aging. This cumulative and irreversible molecular chain breakage damage leads to the deterioration of material properties, a decrease in intrinsic viscosity retention, and a sharp decline in molecular weight, resulting in a drastic deterioration in material toughness and a drop in elongation at break retention. Simultaneously, molecular chain breakage also leads to a decrease in tensile strength retention. The increased active end groups generated by degradation trigger side reactions, increasing the yellowing index.

[0098] As shown in Table 1, the test results of Example 1 and Comparative Example 2 indicate that without the addition of anchored thiophenol antioxidant monomers, the first line of "static prevention" is missing. The material degrades under thermo-oxidative conditions, producing a large number of chromophores, thus increasing its yellowing index. Although the carbodiimide repair agent continuously "repairs" newly formed chain breaks during this process, delaying the collapse of molecular weight to some extent, this "damage-repair" mode cannot prevent the matrix itself from being severely oxidized. Deep oxidative damage to the polymer matrix weakens its ability to withstand deformation, resulting in a decrease in both tensile strength retention and elongation at break retention.

[0099] As shown in Table 1, the test results of Example 1 and Comparative Example 3 indicate that when using traditional small-molecule antioxidants to replace anchored antioxidant monomers, the traditional antioxidants and carbodiimide repair agents work synergistically to provide good protection in the early stages of aging. However, as the aging time increases, the small-molecule antioxidants, due to their physical instability, are gradually depleted or lost through volatilization and migration, resulting in a decrease in their effective concentration. Consequently, they are unable to maintain the same level of protective effect as anchored antioxidants throughout the entire aging cycle, and their degradation rate is relatively accelerated. Therefore, after long-term aging, all performance indicators, such as yellowing index, intrinsic viscosity retention rate, tensile strength retention rate, and elongation at break retention rate, decrease.

[0100] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A process for the production of low melting heat- resistant, oxygen-aging resistant polyester chips, characterized in that, The preparation method comprises: S1: 4,4'-dithiodianiline and salicylaldehyde are added into ethanol, and glacial acetic acid is added to obtain reaction liquid A, under the protection of nitrogen, the reaction is stirred, solid is precipitated and cooled, filtered, washed, and dried to obtain a sulfur-containing bis-Schiff base skeleton intermediate; the sulfur-containing bis-Schiff base skeleton intermediate is added into dimethyl sulfoxide, ethylene carbonate, potassium carbonate and tetrabutylammonium bromide are added to obtain reaction liquid B, the reaction is stirred to obtain a pretreatment liquid, which is poured into deionized water, filtered, washed, purified, and dried to obtain an anchor type sulfenol antioxidant monomer; S2: a dichloromethane dispersion solution of 1,3-adamantanediamine is prepared, and tert-butyl isocyanate is added under the protection of an ice water bath and nitrogen to obtain reaction liquid C, the reaction is stirred, filtered, washed, and dried to obtain a diurea intermediate, the diurea intermediate and triethylamine are added into dichloromethane to obtain a suspension, a phosphorus oxychloride dichlorobenzene solution is added in an ice water bath to obtain reaction liquid D, the reaction is stirred at room temperature, the crude product is distilled under reduced pressure, the crude product and phosphorus heterocyclic pentane are added into toluene, the reaction is carried out after being heated, cooled, filtered, distilled under reduced pressure, and dried to obtain a carbodiimide repair agent; S3: an acid, an alcohol, and a composite catalyst are mixed to obtain reaction liquid E, the acid is terephthalic acid and isophthalic acid, the alcohol is ethylene glycol, isosorbide, and the anchor type sulfenol antioxidant monomer, the reaction is carried out at a first temperature under the protection of nitrogen and a first pressure, then the temperature is increased to a second temperature, and the pressure is reduced to a second pressure, to obtain a polyester melt containing an anchor type antioxidant; S4: the polyester melt containing the anchor type antioxidant is added with the carbodiimide repair agent at a third temperature, and a mixed melt is obtained by stirring in a twin-screw extruder, and the mixed melt is extruded through a head of the extruder, and pelletized to obtain low-melting-point heat-resistant and aging-resistant polyester chips.

2. A process for the preparation of low melting point heat resistant and oxidation aged polyester chips as claimed in claim 1, wherein, In S1: The molar ratio of the 4,4'-dithiodianiline to the salicylaldehyde is 1:(2.0-2.2).

3. The process for the preparation of low melting point heat resistant and oxidation aged polyester chips as claimed in claim 1, wherein, In S1: The mass-volume ratio of the 4,4'-dithiodianiline to the ethanol is 1g:(15-25)mL; The feeding amount of the glacial acetic acid is 0.1-0.5% of the total mass of the 4,4'-dithiodianiline and the salicylaldehyde.

4. The process for the preparation of low melting point heat resistant and oxidation aged polyester chips as claimed in claim 1, wherein, In S1: The molar ratio of the sulfur-containing bis-Schiff base skeleton intermediate to the ethylene carbonate is 1:(1-1.2); The feeding amount of the potassium carbonate is 1-3% of the mass of the sulfur-containing bis-Schiff base skeleton intermediate; The feeding amount of the tetrabutylammonium bromide is 1-5% of the mass of the sulfur-containing bis-Schiff base skeleton intermediate.

5. The process for the preparation of low melting point heat resistant and oxidation aged polyester chips as claimed in claim 1, wherein, In S2: The mass-volume ratio of the 1,3-adamantanediamine to the dichloromethane is 1g:(20-40)mL; The molar ratio of the 1,3-adamantanediamine to the tert-butyl isocyanate is 1:(2-2.2).

6. The process for the preparation of low melting point heat resistant and oxidation aged polyester chips as claimed in claim 1, wherein, In S2: The molar ratio of the diurea intermediate to the triethylamine is 1:(4-5); The molar ratio of the diurea intermediate to the phosphorus oxychloride is 1:(2.2-2.8).

7. The process for the preparation of low melting point heat resistant and oxidation aged polyester chips as claimed in claim 1, wherein, In S3: The molar ratio of the acid to the alcohol is 1:(1.1-1.4); The molar fraction of the isophthalic acid in the acid is 15-25%; The molar fraction of the isosorbide in the alcohol is 3-8%; The molar fraction of the anchor type sulfenol antioxidant monomer in the alcohol is 0.5-2.0%.

8. The process for the preparation of low melting point heat resistant and oxidation aged polyester chips as claimed in claim 1, wherein, In S3: The amount of the composite catalyst is 200-400 ppm of the total mass of the acid and the alcohol; The mass ratio of the diantimony trioxide to the cobalt acetate in the composite catalyst is 1:0.

1.

9. The process for the preparation of low melting point heat resistant and oxidation aged polyester chips as claimed in claim 1, wherein, In S4: The third temperature is 250-270 DEG C; The amount of the carbodiimide restorer added is 1-1.5% of the mass of the polyester melt containing the anchor-type antioxidant.

10. A low-melting heat-resistant and oxygen-aged polyester chip prepared by the preparation method according to any one of claims 1-9.

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