Low-melting toughened copolyester chip and preparation method thereof

Abstract

The application belongs to the technical field of polymer material preparation, and provides a low-melting-point toughened copolyester chip and a preparation method thereof; firstly, a hyperbranched polyester with a surface rich in terminal carboxyl functional groups is prepared through core growth of a polybasic acid alcohol and terminal functionalization reaction of an acid anhydride; another is a linear chain extender with long flexible segments and both ends also functionalized by carboxyl, which is obtained by terminal esterification reaction on a polyether glycol; then, in the synthesis process of the main polyester, aromatic dibasic acid components and polyhydric alcohol components are subjected to multi-stage melt polycondensation under the action of a composite catalyst system, and the above hyperbranched polyester and the chain extender are introduced into the reaction system in the form of a slurry, through the polycondensation process, the functional additives are covalently bonded to the copolyester main chain, forming an integrated network reinforcing structure, so that the copolyester chip has the characteristics of low melting point and excellent toughness.

Description

Technical Field

[0001] This invention belongs to the field of polymer material preparation technology, and relates to a low-melting-point toughened copolyester chip and its preparation method. Background Technology

[0002] Low-melting-point copolyesters, as an important class of thermoplastic polymers, have been widely used in hot melt adhesives, functional fibers, and composite matrixes due to their excellent adhesive properties, controllable melting temperature, and good chemical stability. However, conventional low-melting-point copolyester materials often have problems in their molecular structure, such as a high proportion of rigid segments and insufficient molecular chain flexibility. This results in high brittleness, poor impact resistance, and poor tear strength after curing.

[0003] To improve the toughness of low-melting-point copolyesters, existing technologies typically employ physical blending, which involves mechanically mixing the copolyester with various elastomers or rubber-plastic toughening agents in the molten state. While this method is simple, the inherent thermodynamic incompatibility between the polyester matrix and the toughening agent often leads to weak interphase bonding, uneven dispersion of the toughening phase, and a tendency for phase separation. This unstable microstructure prevents effective stress transfer between phase interfaces when the material is subjected to external impact, resulting in limited toughening effects and potentially sacrificing the material's strength and thermal stability. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a low-melting-point toughened copolyester chip and its preparation method. By synthesizing a carboxyl-terminated polyester and a carboxyl-terminated chain extender with long flexible chain segments, and introducing the above two functional additives into the reaction system during the main copolyester polycondensation reaction, the additives are chemically bonded to the polymer backbone through subsequent deep polycondensation, forming a stable molecular-level toughening network, thereby endowing the final chip with excellent toughness and mechanical properties, thus meeting the needs of actual production.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing low-melting-point toughened copolyester chips, the method comprising:

[0007] S1, dimethylolpropionic acid, pyromellitic dianhydride and p-toluenesulfonic acid are mixed and reacted, and succinic anhydride is added to react to obtain carboxyl-terminated hyperbranched polyester;

[0008] S2, polyethylene glycol, succinic anhydride, pyridine, triethylamine and anhydrous toluene are mixed and reacted to obtain a long flexible chain extender with carboxyl groups at both ends;

[0009] S3 involves mixing and reacting terephthalic acid, isophthalic acid, ethylene glycol, diethylene glycol, manganese acetate tetrahydrate ethylene glycol solution with phosphorous acid, adding end-carboxyl hyperbranched polyester and end-carboxyl long flexible chain extender, and then adding antimony trioxide to obtain a low-melting-point toughened copolyester chip.

[0010] Specifically, it includes:

[0011] S1, mix dimethylolpropionic acid, pyromellitic dianhydride and p-toluenesulfonic acid, under nitrogen atmosphere, adjust the temperature to the first temperature for reaction, after the reaction is completed, vacuum is drawn and maintained, then vacuum is removed and nitrogen protection is maintained, adjust the temperature to the second temperature, add succinic anhydride and stir the reaction, after the reaction is completed, cool, crush and dissolve in acetone, pour in deionized water to precipitate, filter and dry to obtain carboxyl-terminated hyperbranched polyester.

[0012] S2, polyethylene glycol, succinic anhydride, pyridine, triethylamine and anhydrous toluene are mixed, and the mixture is refluxed at the third temperature under a nitrogen atmosphere. After the reaction is completed, it is cooled to room temperature, the reaction solution is poured into anhydrous diethyl ether to precipitate, filtered and redissolved in dichloromethane, washed successively with dilute hydrochloric acid and saturated brine until the pH of the aqueous layer is 5.5-6.5, dried with anhydrous magnesium sulfate, rotary evaporated and vacuum dried to obtain a long flexible chain extender with carboxyl groups at both ends;

[0013] S3, terephthalic acid, isophthalic acid, ethylene glycol, diethylene glycol, manganese acetate tetrahydrate ethylene glycol solution are mixed with phosphorous acid, under nitrogen atmosphere, the temperature is adjusted to the fourth temperature and stirred during reaction, the temperature is further adjusted to the fifth temperature and the gas pressure is adjusted to the target gas pressure and maintained, the end-carboxyl hyperbranched polyester and the end-carboxyl long flexible chain extender are pre-dispersed into a slurry with hot ethylene glycol and then added, then antimony trioxide is added, the temperature is adjusted to the sixth temperature and vacuum is maintained, then the temperature is lowered to the seventh temperature and discharged, air-cooled and pelletized, and dried to obtain a low melting point toughened copolyester chip.

[0014] First, in step S1, the synthesis of carboxyl-terminated hyperbranched polyester is a two-stage process. The first stage is the construction of the hyperbranched framework, the core of which is a self-condensation reaction. One carboxyl group in a dimethylolpropionic acid molecule undergoes an acid-catalyzed esterification reaction with one of the two hydroxyl groups in another molecule, removing one molecule of water and forming an ester bond. Since each molecule of dimethylolpropionic acid contributes one reactive carboxyl group and two reactive hydroxyl groups, as the reaction continues, the molecular chain grows in a non-linear manner, forming a three-dimensional dendritic topology with numerous branches, thus forming a highly branched polyester intermediate. High temperature and a nitrogen atmosphere facilitate the removal of byproduct water from the system, promoting the shift of equilibrium towards esterification. The subsequent vacuum step further forcibly removes residual water and small molecules, driving an increase in the degree of polymerization, ultimately forming a hyperbranched polyester intermediate with ester bonds as the linking elements and a surface rich in unreacted terminal hydroxyl groups. The second stage is end-group functionalization, the mechanism of which is a nucleophilic addition ring-opening reaction. When succinic anhydride is added, the terminal hydroxyl groups on the surface of the hyperbranched polyester act as nucleophiles. Their lone pair electrons attack an electron-deficient carbonyl carbon on the succinic anhydride ring, causing the carbonyl-oxygen bond to break and the anhydride ring to open, thereby obtaining a hyperbranched polymer with a surface covered by carboxyl groups.

[0015] Secondly, in step S2, the preparation mechanism of the end-carboxyl long flexible chain extender is similar to the end-group functionalization described above. As a linear diol, polyethylene glycol exhibits enhanced nucleophilicity at its end-chain primary hydroxyl groups under the action of the alkaline catalysts pyridine and triethylamine. These enhanced nucleophilic hydroxyl groups also attack the carbonyl carbon of succinic anhydride, initiating nucleophilic acyl substitution. By using an excess of succinic anhydride, it is ensured that both ends of the polyethylene glycol are functionalized, ultimately forming a linear macromolecule with a flexible polyether as the main chain and a carboxyl functional group attached to each end. Subsequent acid washing and water washing steps are to remove the catalyst and unreacted succinic anhydride to obtain a pure target product.

[0016] Finally, in step S3, in the initial stage, terephthalic acid and isophthalic acid react with excess ethylene glycol and diethylene glycol under the catalysis of manganese acetate to generate oligomers such as ethylene glycol terephthalate and diethylene glycol terephthalate, and remove a large amount of water. The introduction of isophthalic acid disrupts the regularity of the polymer chain, which is the structural basis for obtaining a low melting point, while phosphorous acid acts as a heat stabilizer to prevent side reactions and degradation at high temperatures. When the reaction proceeds to the pre-condensation stage, the system is mainly composed of oligomers with terminal hydroxyl groups. At this time, the prepared carboxyl-terminated hyperbranched polyester and the long flexible chain extender with carboxyl groups at both ends are added in the form of ethylene glycol slurry. After adding the catalyst antimony trioxide and entering the high-temperature and high-vacuum condensation stage, a covalent bonding reaction occurs: on the one hand, the terminal carboxyl groups of the additive react with a large number of terminal hydroxyl groups in the system to undergo esterification; on the other hand, under high temperature and strong catalysis, the terminal carboxyl groups of the additive and the newly generated ester bonds react with the ester bonds on the polyester chain to undergo transesterification. This allows the hyperbranched polyester to function as a multifunctional multibranched / star-branched copolyester structure, while the long flexible chain extender, as a flexible bridge segment, is chemically bonded to the copolyester backbone, ultimately forming a single homogeneous copolymer with an intramolecularly toughened, complex branched or network structure, rather than a physical blend.

[0017] As a preferred embodiment of the present invention, in S1, the mass ratio of dimethylolpropionic acid, pyromellitic dianhydride, p-toluenesulfonic acid, and succinic anhydride is 100:(10-18):(0.3-0.8):(100-120), for example, it can be 100:(10, 10.8, 11.6, 12.4, 13.2, 14.0, 14.8, 15.6, 16.4, 17.2, or 18.0):(0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, or 0.8):(100, 102, 104, 106, 108, 110, 112, 114, 116, 118, or 120), but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0018] In some alternative embodiments, the first temperature is 145-155°C, for example, it can be 145°C, 146°C, 147°C, 148°C, 149°C, 150°C, 151°C, 152°C, 153°C, 154°C or 155°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0019] In some alternative embodiments, the reaction time at the first temperature is 1.5-3 hours, for example, 1.5 hours, 1.65 hours, 1.8 hours, 1.95 hours, 2.1 hours, 2.25 hours, 2.4 hours, 2.55 hours, 2.7 hours, 2.85 hours, or 3.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0020] In some optional embodiments, the vacuuming period is 0.5-1h, for example, it can be 0.5h, 0.55h, 0.6h, 0.65h, 0.7h, 0.75h, 0.8h, 0.85h, 0.9h, 0.95h or 1.0h, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0021] In some alternative embodiments, the second temperature is 120-130°C, for example, it can be 120°C, 121°C, 122°C, 123°C, 124°C, 125°C, 126°C, 127°C, 128°C, 129°C or 130°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0022] In some optional embodiments, the reaction time for adding succinic anhydride and stirring is 0.5-1.0 h, for example, it can be 0.5 h, 0.55 h, 0.6 h, 0.65 h, 0.7 h, 0.75 h, 0.8 h, 0.85 h, 0.9 h, 0.95 h or 1.0 h, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0023] As a preferred embodiment of the present invention, in S2, the number-average molecular weight (M) of the polyethylene glycol is... n The range is 1500-4000, for example, it can be 1500, 2000, 3000 or 4000, but it is not limited to the listed values. Other unlisted values ​​within this range also apply.

[0024] In some optional embodiments, the mass ratio of polyethylene glycol, succinic anhydride, pyridine, triethylamine, and anhydrous toluene is 100:(12-30):(1-3):(0.2-0.5):(400-600), for example, it can be 100:(12, 13.8, 15.6, 17.4, 19.2, 21, 22.8, 24.6, 26.4, 28.2, or 30):(1.0, 1.2, 1.4, 1.6, 1.8, ... 2.0, 2.2, 2.4, 2.6, 2.8 or 3.0: (0.2, 0.23, 0.26, 0.29, 0.32, 0.35, 0.38, 0.41, 0.44, 0.47 or 0.5): (400, 420, 440, 460, 480, 500, 520, 540, 560, 580 or 600), but not limited to the listed values; other unlisted values ​​within this range also apply.

[0025] In some alternative embodiments, the third temperature is 110-115°C, for example, it can be 110°C, 110.5°C, 111°C, 111.5°C, 112°C, 112.5°C, 113°C, 113.5°C, 114°C, 114.5°C or 115°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0026] In some alternative embodiments, the reflux reaction time is 3-6 hours, for example, 3.0 hours, 3.3 hours, 3.6 hours, 3.9 hours, 4.2 hours, 4.5 hours, 4.8 hours, 5.1 hours, 5.4 hours, 5.7 hours, or 6.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0027] As a preferred embodiment of the present invention, in S3, the mass ratio of the terephthalic acid, isophthalic acid, ethylene glycol, diethylene glycol, manganese acetate tetrahydrate ethylene glycol solution to phosphorous acid is (700-900):(100-300):(400-600):(20-80):(0.56-1.66), for example, it can be (700, 720, 740, 760, 780, 800, 8... 20, 840, 860, 880 or 900: (100, 120, 140, 160, 180, 200, 220, 240, 260, 280 or 300): (400, 420, 440, 460, 480, 500, 520, 540, 560, 580 or 600), but not limited to the listed values, other unlisted values ​​within this range also apply.

[0028] In some optional embodiments, the mass ratio of the terephthalic acid, diethylene glycol, manganese acetate tetrahydrate ethylene glycol solution to phosphorous acid is (700-900):(20-80):(0.56-1.66):(0.03-0.2), for example, it can be (700, 720, 740, 760, 780, 800, 820, 840, 860, 880 or 900):(20, 26, 32, 38, 44, 50). 56, 62, 68, 74 or 80: (0.56, 0.67, 0.78, 0.89, 1, 1.11, 1.22, 1.33, 1.44, 1.55 or 1.66): (0.03, 0.05, 0.07, 0.09, 0.11, 0.13, 0.15, 0.17, 0.19 or 0.2), but not limited to the listed values; other unlisted values ​​within this range also apply.

[0029] In some optional embodiments, the mass fraction of the manganese acetate tetrahydrate ethylene glycol solution is 20 wt.%.

[0030] In some optional embodiments, the fourth temperature is 225-245°C, for example, it can be 225°C, 227°C, 229°C, 231°C, 233°C, 235°C, 237°C, 239°C, 241°C, 243°C or 245°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0031] In some optional embodiments, the reflux stirring reaction time is 2-5 hours, for example, 2.0 hours, 2.3 hours, 2.6 hours, 2.9 hours, 3.2 hours, 3.5 hours, 3.8 hours, 4.1 hours, 4.4 hours, 4.7 hours or 5.0 hours, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0032] In some optional embodiments, the fifth temperature is 255-265°C, for example, it can be 255°C, 256°C, 257°C, 258°C, 259°C, 260°C, 261°C, 262°C, 263°C, 264°C or 265°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0033] In some alternative embodiments, the target pressure is 20-40 kPa, for example, it can be 20 kPa, 22 kPa, 24 kPa, 26 kPa, 28 kPa, 30 kPa, 32 kPa, 34 kPa, 36 kPa, 38 kPa or 40 kPa, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0034] In some optional embodiments, the target pressure is maintained for 30-60 minutes, for example, 30 minutes, 33 minutes, 36 minutes, 39 minutes, 42 minutes, 45 minutes, 48 ​​minutes, 51 minutes, 54 minutes, 57 minutes or 60 minutes, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0035] In some optional embodiments, the mass ratio of terephthalic acid to carboxyl-terminated hyperbranched polyester is (700-900):(5-18), for example, it can be (700, 720, 740, 760, 780, 800, 820, 840, 860, 880 or 900):(5, 6.3, 7.6, 8.9, 10.2, 11.5, 12.8, 14.1, 15.4, 16.7 or 18), but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0036] In some optional embodiments, the mass ratio of terephthalic acid, the long flexible chain extender with carboxyl groups at both ends, and antimony trioxide is (700-900):(30-100):(0.22-0.38), for example, it can be (700, 720, 740, 760, 780, 800, 820, 840, 860, 880 or 900):(30, 37, 44, 51, 58, 65, 72, 79, 86, 93 or 100):(0.22, 0.236, 0.252, 0.268, 0.284, 0.3, 0.316, 0.332, 0.348, 0.364 or 0.38), but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0037] In some optional embodiments, the sixth temperature is 268-276°C, for example, it can be 268°C, 268.8°C, 269.6°C, 270.4°C, 271.2°C, 272.0°C, 272.8°C, 273.6°C, 274.4°C, 275.2°C or 276°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0038] In some optional embodiments, the vacuuming duration is 30-90 min, for example, 30 min, 36 min, 42 min, 48 min, 54 min, 60 min, 66 min, 72 min, 78 min, 84 min or 90 min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0039] In some optional embodiments, the seventh temperature is 255-265°C, for example, it can be 255°C, 256°C, 257°C, 258°C, 259°C, 260°C, 261°C, 262°C, 263°C, 264°C or 265°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0040] In a second aspect, the present invention provides a low-melting-point toughened copolyester chip prepared by the preparation method described in the first aspect.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows: By introducing pre-synthesized hyperbranched toughening agent and long flexible chain extender into the reaction system during the polyester melt polycondensation stage, the present invention achieves chemical bonding of toughening components at the molecular level, solving the technical defects of traditional physical blending methods such as weak interfacial bonding force, easy migration of toughening phase and phase separation due to poor compatibility, and forming a uniform and stable single-phase system; in the constructed molecular network, the hyperbranched polyester acts as a three-dimensional stress dispersion node, while the long flexible chain extender acts as a flexible bridge, which can efficiently absorb and dissipate external impact energy and improve the toughness of copolyester chips. Detailed Implementation

[0042] 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 those that make any obvious substitutions and modifications to the embodiments described herein.

[0043] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone any further purification treatment.

[0044] Example 1

[0045] This embodiment provides a low-melting-point toughened copolyester chip and its preparation method, the preparation method specifically including the following steps:

[0046] S1, 100.0g of dimethylolpropionic acid, 10.0g of pyromellitic dianhydride and 0.5g of p-toluenesulfonic acid were mixed and reacted at 145°C for 2.0h under a nitrogen atmosphere. After the reaction was completed, a vacuum was applied and maintained for 1.0h. Then the vacuum was removed and nitrogen protection was maintained. The temperature was adjusted to 125°C and 120g of succinic anhydride was added and stirred for 0.8h. After the reaction was completed, the mixture was cooled, crushed and dissolved in acetone. The precipitate was poured into deionized water, filtered and dried to obtain a carboxyl-terminated hyperbranched polyester.

[0047] S2, add 100.0g of polyethylene glycol (M n =1500), 30.0g succinic anhydride, 2.0g pyridine, 0.2g triethylamine and 500.0g anhydrous toluene were mixed, and the mixture was refluxed at 115℃ for 3.0h under a nitrogen atmosphere. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was poured into anhydrous diethyl ether to precipitate, filtered and redissolved in dichloromethane. The solution was washed successively with dilute hydrochloric acid and saturated brine until the pH of the aqueous layer was 5.5. The solution was then dried with anhydrous magnesium sulfate, and then dried by rotary evaporation and vacuum drying to obtain a long flexible chain extender with carboxyl groups at both ends.

[0048] S3, 700g terephthalic acid, 200g isophthalic acid, 600g ethylene glycol, 20g diethylene glycol, 0.56g of 20wt.% manganese acetate tetrahydrate ethylene glycol solution, and 0.1g phosphorous acid were mixed. Under a nitrogen atmosphere, the temperature was adjusted to 245°C and refluxed with stirring for 3.0h. The temperature was then adjusted to 265°C and the pressure was adjusted to 20kPa and maintained for 40min. 18g of end-carboxyl hyperbranched polyester and 50g of end-carboxyl long flexible chain extender were pre-dispersed in hot ethylene glycol to form a slurry and added. Then 0.38g of antimony trioxide was added. The temperature was adjusted to 268°C and vacuum was maintained for 30min. Subsequently, the temperature was lowered to 255°C and discharged. The product was air-cooled, pelletized, and dried to obtain a low-melting-point toughened copolyester chip.

[0049] Example 2

[0050] This embodiment provides a low-melting-point toughened copolyester chip and its preparation method, the preparation method specifically including the following steps:

[0051] S1, 100.0g of dimethylolpropionic acid, 18.0g of pyromellitic dianhydride and 0.8g of p-toluenesulfonic acid were mixed and reacted at 155°C for 1.5h under a nitrogen atmosphere. After the reaction was completed, a vacuum was applied and maintained for 0.5h. Then the vacuum was removed and nitrogen protection was maintained. The temperature was adjusted to 130°C and 100g of succinic anhydride was added and stirred for 1.0h. After the reaction was completed, the mixture was cooled, crushed and dissolved in acetone. Deionized water was poured in to precipitate the mixture. The mixture was filtered and dried to obtain a carboxyl-terminated hyperbranched polyester.

[0052] S2, 100.0g of polyethylene glycol (M n=4000), 12.0g succinic anhydride, 1.0g pyridine, 0.5g triethylamine and 400g anhydrous toluene were mixed, and the mixture was refluxed at 110℃ for 6.0h under a nitrogen atmosphere. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was poured into anhydrous diethyl ether to precipitate, filtered and redissolved in dichloromethane. The solution was washed successively with dilute hydrochloric acid and saturated brine until the pH of the aqueous layer was 6.5. The solution was then dried with anhydrous magnesium sulfate, and then dried by rotary evaporation and vacuum drying to obtain a long flexible chain extender with carboxyl groups at both ends.

[0053] S3: 900g terephthalic acid, 100g isophthalic acid, 400g ethylene glycol, 60g diethylene glycol, 1.66g of ethylene glycol solution containing 20wt.% manganese acetate tetrahydrate, and 0.03g phosphorous acid were mixed. Under a nitrogen atmosphere, the mixture was refluxed and stirred at 225°C for 5.0h. The temperature was then adjusted to 255°C and the pressure was adjusted to 40kPa and maintained for 30min. 5g of end-carboxyl hyperbranched polyester and 100g of end-carboxyl long flexible chain extender were pre-dispersed in hot ethylene glycol and added to the mixture. Then, 0.22g of antimony trioxide was added. The temperature was adjusted to 276°C and vacuum was maintained for 90min. Subsequently, the temperature was lowered to 265°C and the mixture was discharged. The product was then air-cooled, pelletized, and dried to obtain a low-melting-point toughened copolyester chip.

[0054] Example 3

[0055] This embodiment provides a low-melting-point toughened copolyester chip and its preparation method, the preparation method specifically including the following steps:

[0056] S1, 100.0g of dimethylolpropionic acid, 15.0g of pyromellitic dianhydride and 0.3g of p-toluenesulfonic acid were mixed and reacted at 150°C for 3.0h under a nitrogen atmosphere. After the reaction was completed, a vacuum was applied and maintained for 0.8h. Then the vacuum was removed and nitrogen protection was maintained. The temperature was adjusted to 120°C and 110g of succinic anhydride was added and stirred for 0.5h. After the reaction was completed, the mixture was cooled, crushed and dissolved in acetone. The precipitate was poured into deionized water, filtered and dried to obtain a carboxyl-terminated hyperbranched polyester.

[0057] S2, 100.0g of polyethylene glycol (M n =2000), 25.0g succinic anhydride, 3.0g pyridine, 0.4g triethylamine and 600g anhydrous toluene were mixed and refluxed at 112℃ for 4.0h under a nitrogen atmosphere. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was poured into anhydrous diethyl ether to precipitate, filtered and redissolved in dichloromethane. The solution was washed successively with dilute hydrochloric acid and saturated brine until the pH of the aqueous layer was 5.8. The solution was then dried with anhydrous magnesium sulfate, rotary evaporated and vacuum dried to obtain a long flexible chain extender with carboxyl groups at both ends.

[0058] S3. 850g terephthalic acid, 300g isophthalic acid, 550g ethylene glycol, 80g diethylene glycol, 1.0g of ethylene glycol solution containing 20wt.% manganese acetate tetrahydrate, and 0.20g phosphorous acid were mixed. Under a nitrogen atmosphere, the temperature was adjusted to 230°C and stirred for 2.0h. The temperature was then adjusted to 260°C and the pressure was adjusted to 30kPa and maintained for 60min. 10g of end-carboxyl hyperbranched polyester and 30g of end-carboxyl long flexible chain extender were pre-dispersed in hot ethylene glycol to form a slurry and added to the mixture. Then, 0.30g of antimony trioxide was added. The temperature was adjusted to 272°C and vacuum was maintained for 60min. Subsequently, the temperature was lowered to 260°C and the mixture was discharged. It was then air-cooled, pelletized, and dried to obtain a low-melting-point toughened copolyester chip.

[0059] Example 4

[0060] This embodiment provides a low-melting-point toughened copolyester chip and its preparation method, the preparation method specifically including the following steps:

[0061] S1, 100.0g of dimethylolpropionic acid, 12.0g of pyromellitic dianhydride and 0.6g of p-toluenesulfonic acid were mixed and reacted at 152°C for 2.5h under a nitrogen atmosphere. After the reaction was completed, a vacuum was applied and maintained for 0.6h. Then the vacuum was removed and nitrogen protection was maintained. The temperature was adjusted to 128°C and 105g of succinic anhydride was added and stirred for 0.6h. After the reaction was completed, the mixture was cooled, crushed and dissolved in acetone. The precipitate was poured into deionized water, filtered and dried to obtain a carboxyl-terminated hyperbranched polyester.

[0062] S2, 100.0g of polyethylene glycol (M n =3000), 18.0g succinic anhydride, 2.5g pyridine, 0.3g triethylamine and 450g anhydrous toluene were mixed, and the mixture was refluxed at 114℃ for 5.0h under a nitrogen atmosphere. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was poured into anhydrous diethyl ether to precipitate, filtered and redissolved in dichloromethane. The solution was washed successively with dilute hydrochloric acid and saturated brine until the pH of the aqueous layer was 6.3. The solution was then dried with anhydrous magnesium sulfate, and then dried by rotary evaporation and vacuum drying to obtain a long flexible chain extender with carboxyl groups at both ends.

[0063] S3, 750g terephthalic acid, 250g isophthalic acid, 450g ethylene glycol, 40g diethylene glycol, 1.2g of ethylene glycol solution containing 20wt.% manganese acetate tetrahydrate, and 0.15g phosphorous acid were mixed. Under a nitrogen atmosphere, the temperature was adjusted to 240°C and stirred for 4.0h. The temperature was then adjusted to 258°C and the pressure was adjusted to 35kPa and maintained for 45min. 15g of end-carboxyl hyperbranched polyester and 80g of end-carboxyl long flexible chain extender were pre-dispersed in hot ethylene glycol to form a slurry and added to the mixture. Then, 0.35g of antimony trioxide was added. The temperature was adjusted to 270°C and vacuum was maintained for 75min. Subsequently, the temperature was lowered to 258°C and the mixture was discharged. It was then air-cooled, pelletized, and dried to obtain a low-melting-point toughened copolyester chip.

[0064] Comparative Example 1

[0065] This comparative example provides a low-melting-point toughened copolyester chip and its preparation method. The difference between this example and Example 1 is that the mass of the carboxyl-terminated hyperbranched polyester in S3 is 0, while the other process parameters and operating conditions are exactly the same as in Example 1.

[0066] Comparative Example 2

[0067] This comparative example provides a low-melting-point toughened copolyester chip and its preparation method. The difference between this example and Example 1 is that the mass of the carboxyl-terminal long flexible chain extender in S3 is 0, while the other process parameters and operating conditions are exactly the same as in Example 1.

[0068] Comparative Example 3

[0069] This comparative example provides a low-melting-point toughened copolyester chip and its preparation method. The difference between this example and Example 1 is that the mass of the carboxyl-terminated hyperbranched polyester in S3 and the carboxyl-terminated long flexible chain extender at both ends are 0. Other process parameters and operating conditions are exactly the same as in Example 1.

[0070] Performance testing:

[0071] Melting point test: The melting point of the low melting point toughened copolyesters prepared in Examples 1-4 and Comparative Examples 1-3 was tested according to ISO 11357-3.

[0072] Toughness test: The low melting point toughened copolyesters prepared in Examples 1-4 and Comparative Examples 1-3 were subjected to toughness test according to ISO 180.

[0073] The test results are shown in Table 1.

[0074] Table 1. Test results of low-melting-point toughened copolyesters in Examples 1-4 and Comparative Examples 1-3

[0075] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Melting point (°C) 178.8 181.4 180.6 179.5 182.3 205.1 209.4 <![CDATA[Toughness (kJ / m 2 )]])]> 9.2 8.9 9.1 9.1 7.4 7.1 4.8

[0076] As shown in Table 1, compared to Example 1, the melting point of Comparative Example 1 increased while its toughness decreased; the melting point of Comparative Example 2 increased while its toughness decreased; and the melting point of Comparative Example 3 increased while its toughness decreased. This is because in Comparative Example 1, the mass of the terminal carboxyl hyperbranched polyester is 0, which affects the crystallinity and lattice regularity. Simultaneously, the loss of multi-point branching and entanglement reduces energy dissipation and shear yielding capacity at the crack tip, resulting in decreased toughness. In Comparative Example 2, the mass of the terminal carboxyl long flexible chain extender is 0, lacking the flexible chain bridging segments of the terminal carboxyl long flexible chain extender, allowing for more complete crystal growth, thus increasing the melting point and decreasing toughness. In Comparative Example 3, the mass of both the terminal carboxyl hyperbranched polyester and the terminal carboxyl long flexible chain extender is 0, increasing crystallinity. However, the absence of flexible chain bridging segments and multi-point branching and entanglement results in an increased melting point and decreased toughness.

[0077] 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 method for preparing low-melting-point toughened copolyester chips, characterized in that, The preparation method includes: S1, dimethylolpropionic acid, pyromellitic dianhydride and p-toluenesulfonic acid are mixed and reacted, and succinic anhydride is added to react to obtain carboxyl-terminated hyperbranched polyester; S2, polyethylene glycol, succinic anhydride, pyridine, triethylamine and anhydrous toluene are mixed and reacted to obtain a long flexible chain extender with carboxyl groups at both ends; S3 involves mixing and reacting terephthalic acid, isophthalic acid, ethylene glycol, diethylene glycol, manganese acetate tetrahydrate ethylene glycol solution with phosphorous acid, adding end-carboxyl hyperbranched polyester and end-carboxyl long flexible chain extender, and then adding antimony trioxide to obtain a low-melting-point toughened copolyester chip. The mass ratio of dimethylolpropionic acid, pyromellitic dianhydride, p-toluenesulfonic acid, and succinic anhydride is 100:(10-18):(0.3-0.8):(100-120). The mass ratio of terephthalic acid, isophthalic acid and ethylene glycol is (700-900):(100-300):(400-600). The mass ratio of terephthalic acid to carboxyl-terminated hyperbranched polyester is (700-900):(5-18). The mass ratio of the terephthalic acid, the long flexible chain extender with carboxyl groups at both ends, and antimony trioxide is (700-900): (30-100): (0.22-0.38).

2. The method for preparing low-melting-point toughened copolyester chips according to claim 1, characterized in that, In S2: The number average molecular weight of the polyethylene glycol is 1500-4000.

3. The method for preparing low-melting-point toughened copolyester chips according to claim 1, characterized in that, In S2: The mass ratio of polyethylene glycol, succinic anhydride, pyridine, triethylamine and anhydrous toluene is 100:(12-30):(1-3):(0.2-0.5):(400-600).

4. The method for preparing low-melting-point toughened copolyester chips according to claim 1, characterized in that, In S3: The mass ratio of the ethylene glycol solution containing terephthalic acid, diethylene glycol, and manganese acetate tetrahydrate to phosphorous acid is (700-900):(20-80):(0.56-1.66):(0.03-0.2).

5. The method for preparing low-melting-point toughened copolyester chips according to claim 1, characterized in that, In S3: The mass fraction of the manganese acetate tetrahydrate ethylene glycol solution is 20 wt.%.

6. A low-melting-point toughened copolyester chip obtained by the preparation method according to any one of claims 1-5.