Water-soluble polyesters, processes for their preparation and use

Abstract

The application relates to the field of high polymer chemical industry and discloses a water-soluble polyester as well as a preparation method and application thereof. The intrinsic viscosity of the water-soluble polyester is 0.50-0.55 dL / g, the shear viscosity is 50-60 Pa.s under the condition that the temperature is 288 DEG C and the shear rate is 6000 s ‑1 The preparation method of the water-soluble polyester comprises the following steps: under the condition that a titanium catalyst exists, reacting a binary acid monomer with a binary alcohol monomer to obtain a reactant I; and reacting the reactant I with isophthalic acid bis-hydroxyethyl ester-5-sodium sulfonate and polyethylene glycol. The water-soluble polyester has specific intrinsic viscosity and shear viscosity, and when applied to the preparation process of island-in-sea fibers, the distribution uniformity of the sea phase and the island phase can be effectively ensured, and the distribution of the sea phase and the island phase in the fibers is uniform, and the opening speed is fast and stable.

Description

Technical Field

[0001] This invention relates to the field of polymer chemistry, specifically to a water-soluble polyester, its preparation method, and its applications. Background Technology

[0002] Domestic polyester production capacity has been increasing year by year, and conventional polyester and fibers are showing a trend of oversupply. Developing functional polyesters has become an important measure to expand polyester applications and improve differentiation. Water-soluble polyester (COPET) is a polyester that can dissolve in hot (alkaline) water, produced by adding modifying components during polyester synthesis. Currently, water-soluble polyester chips are mainly used in the production of island-of-sea composite microfibers. Other applications include microporous and quick-drying fibers, improved dyeing fibers, and alkali reduction treatment of fabrics.

[0003] Water-soluble polyester is mainly used as a dissolution component in the spinning industry for ultrafine composite spinning of chemical fibers. Compared with mechanical and solvent-based peeling methods, this water-soluble peeling method has significant advantages, yielding finer and more uniform ultrafine fibers. Compared with solvent-based peeling, it avoids the drawbacks of using various toxic and environmentally polluting solvents, requiring only hot alkaline solutions for peeling, which is beneficial for industrial implementation and meets environmental protection requirements. Ultrafine denier fibers prepared using water-soluble polyester have advantages such as soft hand feel, good smoothness, moisture absorption and perspiration wicking, and high strength, and are therefore widely used in fields such as simulated leather, high-end fabrics, sportswear, and special drawing paper.

[0004] To prepare water-soluble polyesters, previous research has focused on the preparation process and raw materials. Many patents concentrate on the formulation of water-soluble polyesters. For example, CN107602832A and CN106674508A disclose water-soluble polyesters made from functional raw materials such as terephthalic acid (PTA), isophthalic acid (IPA), ethylene glycol (EG), sodium bis(hydroxyethyl) isophthalate-5-sulfonate (SIPE), and polyethylene glycol (PEG). CN105669959A uses itaconic acid and its sulfonated product, sodium itaconic acid sulfonate, instead of the traditional... A novel water-soluble polyester (PBIINa) is synthesized by direct esterification polycondensation using hydrophilic monomers containing benzene rings and diacids, with the addition of 1,4-butanediol. CN104371096A describes a process using terephthalic acid, ethylene glycol, neopentyl glycol, polyethylene glycol, ethylene glycol-5-sulfonate sodium isophthalate, and aliphatic diacids as monomers, antimony trioxide or antimony acetate as catalysts, and trimethyl phosphate as a stabilizer. The process involves esterification, polymerization, and post-treatment to obtain the water-soluble polyester. While these patents all investigate the formulation of water-soluble polyesters, the broad range of monomer studies leads to significant differences in the thermal and water-soluble properties of the resulting polyesters. This affects the stability of the spinning and fiber-opening processes in practical applications and may further result in uneven separation of the sea-phase and island-phase in the island-island yarn after alkali-soluble fiber opening. In addition, CN1438274A and CN101407946A respectively add 4-8 mol% or 11-20% isophthalic acid (IPA) during the polymerization process of producing water-soluble polyester. Such a high content of IPA will lead to a deterioration in the crystallization properties of water-soluble polyester, affecting the processing of island yarn and causing abnormal phenomena such as defects and breaks.

[0005] To reduce heavy metal pollution during the fiber opening process, CN103130996A discloses an alkali-soluble polyester and its preparation method. The polyester contains repeating units synthesized from terephthalic acid and ethylene glycol, wherein the content of sodium dimethyl isophthalate-5-sulfonate is equivalent to 2-8 mol% of the total dicarboxylic acid units, and the content of metal elements other than sodium in the polyester is below 3 ppm. The addition of sodium dimethyl isophthalate-5-sulfonate, organic sulfonic acid as a catalyst, and organic amine compound as a regulator during the polycondensation stage, coupled with excessively high polycondensation temperatures, may lead to SIPE self-polymerization during actual production, resulting in polymer bursting.

[0006] In summary, although water-soluble polyester has developed a complete set of technologies for synthesis, spinning, weaving, fiber opening, and dyeing and finishing as a soluble component for island fiber composite spinning after many years of development, it has not yet formed a unified product standard due to its high polymerization difficulty and stringent requirements for spinning conditions. Therefore, abnormal phenomena such as drying adhesion and uneven fiber opening exist in the actual production process. In order to overcome these problems, water-soluble polyester needs to meet the following four requirements: (1) From the perspective of reaction process, the key to water-soluble polyester process is to select appropriate catalysts and functional monomers to make the polycondensation reaction stable and prevent the phenomenon of rapid polymerization caused by excessive self-polymerization of monomers; (2) In terms of the performance of water-soluble polyester, it is necessary to ensure that there is a suitable glass transition temperature and crystallization rate to prevent adhesion and poor fiber performance during the use of water-soluble polyester; (3) In the island fiber forming process, it is necessary to ensure that the box pressure of water-soluble polyester and conventional polyester is similar and that the island phase structure of spinning is uniform; (4) The fiber opening process should be fast and stable, and the pollution of process wastewater to the environment should be minimized as much as possible.

[0007] Therefore, considering the current research status of water-soluble polyesters, developing water-soluble polyesters with stable polycondensation reaction, crystallization properties not much different from conventional polyesters, low heavy metal content, easy solubility in alkaline water and stable rate has certain market prospects and environmental benefits. Summary of the Invention

[0008] The purpose of this invention is to overcome a series of technical problems existing in the prior art, such as the easy self-polymerization of monomers during the polycondensation process of water-soluble polyester, the low glass transition temperature and crystallinity causing the chips to easily stick together, the uneven distribution of marine island phases due to unstable pressure during spinning, and the inability to guarantee uniform and stable fiber opening. This invention provides a water-soluble polyester, its preparation method, and its application.

[0009] During their research, the inventors of this invention unexpectedly discovered that, within a specific environmentally friendly catalyst reaction system, by matching the dosage of each raw material component, reaction conditions, and the content of specific components in the obtained water-soluble polyester, the resulting water-soluble polyester can possess stable water solubility, crystallinity, and processing properties. Simultaneously, by strictly controlling the intrinsic viscosity and shear viscosity of the water-soluble polyester within a specific range, it can effectively ensure the formation of a stable island-island phase distribution during the island-island yarn forming process, improving the uniformity of the island-island phase distribution and the fiber opening speed. The inventors further discovered that at a temperature of 288℃ and a shear rate of 6000s, [the following conditions are met / are achieved]. -1 The shear viscosity under certain conditions, and its application in the production of island-island fibers (where the water-soluble polyester is the marine phase), at a high shear rate of 6000 s⁻¹. -1Under these conditions, the shear viscosity ratio between the water-soluble polyester and the conventional polyester used for the island phase can be used as a key control indicator for the water-soluble polyester to ensure the uniformity of the marine and island phase structures during the subsequent island-island yarn forming process, and to achieve fast and stable fiber opening speed. Based on the above findings, this invention is proposed.

[0010] To achieve the above objectives, the first aspect of the present invention provides a water-soluble polyester having an intrinsic viscosity of 0.50-0.55 dL / g, and a viscosity that is suitable for use at a temperature of 288°C and a shear rate of 6000 s. -1 The shear viscosity under the given conditions is 50-60 Pa·s.

[0011] A second aspect of the present invention provides a method for preparing a water-soluble polyester, the method comprising the following steps:

[0012] (1) Under the condition of the presence of a titanium catalyst, the dicarboxylic acid monomer and the diol monomer are reacted to obtain reactant I;

[0013] (2) React the reactant I with sodium bis(hydroxyethyl) isophthalate-5-sulfonate and polyethylene glycol in the reaction II;

[0014] Of which, based on a total amount of 100 parts by weight of the dicarboxylic acid monomer and the diol monomer, the amount of the titanium catalyst is 0.0015-0.003 parts by weight, the amount of sodium dihydroxyethyl isophthalate-5-sulfonate is 4.5-7 parts by weight, and the amount of polyethylene glycol is 4.5-7 parts by weight.

[0015] The third aspect of the present invention provides the application of the above-described water-soluble polyester and the water-soluble polyester obtained by the above method in the production of chemical fibers.

[0016] A fourth aspect of the present invention provides a method for producing island-island fibers, the method comprising the following steps: using the above-described water-soluble polyester and / or the water-soluble polyester obtained by the above method as the marine phase, and using conventional polyester as the island phase; wherein, at a temperature of 288°C and a shear rate of 6000 s... -1 Under these conditions, the ratio of the shear viscosity of the water-soluble polyester to that of the conventional polyester is 0.8-0.9:1.

[0017] The water-soluble polyester provided by this invention is a fast-dissolving, environmentally friendly polyester with specific intrinsic viscosity and shear viscosity. When applied to the spinning process, it can form a specific shear viscosity ratio with conventional polyester, effectively ensuring the uniform distribution of the marine phase (the water-soluble polyester provided by this invention) and the island phase (conventional polyester), thereby achieving the goal of uniform distribution of the marine and island phases in the fiber and fast and stable fiber opening speed. Furthermore, the glass transition temperature and semi-crystallization period of the water-soluble polyester provided by this invention are close to those of conventional polyester, resulting in better processing performance. Moreover, its water solubility is significantly better than that of conventional polyester, and its heavy metal content is significantly reduced.

[0018] The method for preparing water-soluble polyester provided by this invention features a stable polycondensation reaction and a simple drying process, making it suitable for industrial production. Attached Figure Description

[0019] Figure 1 This is a cross-sectional view of the island phase of the water-soluble polyester prepared in Example 1 when used as a marine precursor fiber.

[0020] Figure 2 This is a cross-sectional view of the island phase of the polyester obtained in Comparative Example 2 when it is used as a marine precursor fiber.

[0021] Figure 3 This is a microscopic morphology image of the water-soluble polyester prepared in Example 1 after alkali reduction treatment when used as a marine garter belt.

[0022] Figure 4 This is a microscopic morphology image of the polyester obtained in Comparative Example 2 after alkali reduction treatment when used as a marine phase. Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] The first aspect of this invention provides a water-soluble polyester having an intrinsic viscosity of 0.50-0.55 dL / g, and a viscosity that is suitable for use at a temperature of 288°C and a shear rate of 6000 s. -1 The shear viscosity under the given conditions is 50-60 Pa·s.

[0025] In this invention, intrinsic viscosity was tested and characterized according to section 5.1 of GB / T14190-2017 "Test Method for Fiber Grade Polyester Chips"; shear viscosity was obtained by testing the rheological properties of the samples using a capillary rheometer, wherein the capillary die diameter was 1 mm, the aspect ratio L / D = 16, the inlet angle was 90°, the test temperature was 288℃, and the shear rate was 6000 s. -1 .

[0026] The water-soluble polyester provided by this invention has specific intrinsic viscosity and shear viscosity. When applied to the formation of island-island yarn, it can effectively ensure the formation of a stable island-island phase distribution, improve the uniformity of the island-island phase distribution in the fiber and the fiber opening speed.

[0027] According to the present invention, preferably, the intrinsic viscosity of the water-soluble polyester is 0.515-0.53 dL / g, and it is suitable for use at a temperature of 288°C and a shear rate of 6000 s. -1 The shear viscosity under the given conditions is 52-58.5 Pa·s.

[0028] To realize the application of the water-soluble polyester provided by this invention in the production of chemical fibers, especially island-island fibers, the water-soluble polyester, in addition to having specific intrinsic viscosity and shear viscosity, should also possess stable water solubility, crystallization properties, and processing properties. Preferably, the water-soluble polyester has a glass transition temperature of 55-68°C, a semi-crystallization period of 2-4 minutes, and a water solubility greater than or equal to 51.6% under alkali reduction process conditions of 100°C, 1 wt% alkali content, and 45 minutes. The glass transition temperature and melt crystallization rate of this water-soluble polyester are close to those of conventional polyesters, and it exhibits good processing properties.

[0029] In this invention, the glass transition temperature (Tg) and the semi-crystallization period (t) are... 1 / 2 The differential scanning calorimetry (DSC) method was used for testing and calculation. The specific procedure was as follows: Under nitrogen protection, DSC thermal analysis was performed by raising the temperature from 25℃ to 290℃ at a rate of 10℃ / min, holding for 5 min, then lowering it to 25℃ at a rate of 400℃ / min, followed by another raising the temperature from 25℃ to 290℃ at a rate of 10℃ / min, holding for 5 min, and finally lowering it to 100℃ at a rate of 10℃ / min. The glass transition temperature Tg was calculated based on the second heating curve, and the half-crystallization period t during the melting and crystallization process was calculated using the crystallinity of the melting and crystallization peak. 1 / 2 The alkali reduction process refers to the solubility of water-soluble polyester after treating it in an alkaline solution with an alkali content of 1 wt% at 100°C for 45 minutes.

[0030] According to the present invention, preferably, the water-soluble polyester contains sodium bis(hydroxyethyl) isophthalate-5-sulfonate units, polyethylene glycol units, and titanium. The sodium bis(hydroxyethyl) isophthalate-5-sulfonate units refer to the groups formed after the esterification of sodium bis(hydroxyethyl) isophthalate-5-sulfonate; the polyethylene glycol units refer to the groups formed after the esterification of polyethylene glycol; and the titanium comes from a titanium-based catalyst used in the synthesis of the water-soluble polyester.

[0031] According to the present invention, preferably, the polyethylene glycol unit is selected from at least one of PEG1500 unit, PEG2000 unit and PEG4000 unit; more preferably, it is PEG2000 unit.

[0032] In this invention, the contents of sodium diethyl isophthalate-5-sulfonate units and polyethylene glycol units in the water-soluble polyester can be obtained by nuclear magnetic resonance (NMR) spectroscopy, and the content of titanium can be obtained by elemental analysis. Preferably, the content of sodium diethyl isophthalate-5-sulfonate units is 6-8 wt%, the content of polyethylene glycol units is 6-8 wt%, and the content of titanium is 0.0003-0.0005 wt%. The inventors have found that under this preferred embodiment, the water-soluble polyester exhibits characteristics such as low heavy metal content, rapid water solubility, good processing performance, and stable and uniform fiber opening, resulting in significant functionalization and environmental benefits.

[0033] According to the present invention, the water-soluble polyester can be prepared by using a variety of raw material components to form a specific catalyst reaction system, so as to possess the aforementioned specific intrinsic viscosity, shear viscosity, and stable water solubility, crystallinity, and processability. Preferably, the raw material components of the water-soluble polyester contain a diacid monomer, a diol monomer, sodium bis(hydroxyethyl) isophthalate-5-sulfonate, polyethylene glycol, and a titanium-based catalyst; wherein the titanium-based catalyst serves as a catalyst for the esterification reaction of the diacid monomer and the diol monomer.

[0034] According to the present invention, preferably, the dicarboxylic acid monomer is selected from at least one of terephthalic acid, isophthalic acid and adipic acid; more preferably, it is terephthalic acid.

[0035] According to the present invention, preferably, the diol monomer is ethylene glycol and / or pentanediol; more preferably, it is ethylene glycol.

[0036] According to the present invention, preferably, the polyethylene glycol is selected from at least one of PEG1500, PEG2000 and PEG4000; more preferably, it is PEG2000.

[0037] According to the present invention, preferably, the titanium-based catalyst is tetrabutyl titanate and / or titanium glycolate; more preferably, it is tetrabutyl titanate.

[0038] In this invention, the above-mentioned dicarboxylic acid monomer, diol monomer, sodium bis(hydroxyethyl) isophthalate-5-sulfonate, polyethylene glycol, and titanium catalyst are all commercially available or can be prepared by methods disclosed in the prior art.

[0039] A second aspect of the present invention provides a method for preparing a water-soluble polyester, the method comprising the following steps:

[0040] (1) Under the condition of the presence of a titanium catalyst, the dicarboxylic acid monomer and the diol monomer are reacted to obtain reactant I;

[0041] (2) React the reactant I with sodium bis(hydroxyethyl) isophthalate-5-sulfonate and polyethylene glycol in the reaction II;

[0042] Of which, based on a total amount of 100 parts by weight of the dicarboxylic acid monomer and the diol monomer, the amount of the titanium catalyst is 0.0015-0.003 parts by weight, the amount of sodium dihydroxyethyl isophthalate-5-sulfonate is 4.5-7 parts by weight, and the amount of polyethylene glycol is 4.5-7 parts by weight.

[0043] The method for preparing water-soluble polyester in this invention is simple and suitable for industrial production. By limiting the amounts of titanium-based catalyst, sodium diethyl isophthalate-5-sulfonate (SIPE), and polyethylene glycol (PEG) in the preparation process, the content of titanium, SIPE units, and PEG units in the water-soluble polyester can be controlled, resulting in a content of 6-8 wt% for sodium diethyl isophthalate-5-sulfonate units (SIPE units), 6-8 wt% for polyethylene glycol units (PEG units), and 0.0003-0.0005 wt% for titanium. This results in an intrinsic viscosity of 0.5-0.55 dL / g at a temperature of 288°C and a shear rate of 6000 s⁻¹. -1 The shear viscosity under the given conditions is 50-60 Pa·s.

[0044] According to the present invention, preferably, the intrinsic viscosity of the water-soluble polyester is 0.515-0.53 dL / g, and is suitable for use at a temperature of 288°C and a shear rate of 6000 s. -1 The shear viscosity under the given conditions is 52-58.5 Pa·s.

[0045] According to the present invention, preferably, the glass transition temperature of the water-soluble polyester is 55-68°C, the semi-crystallization period is 2-4 min, and the water solubility is greater than or equal to 51.6% under the alkali reduction process conditions of 100°C, 1 wt% alkali content, and 45 min time.

[0046] According to the present invention, preferably, the dicarboxylic acid monomer is selected from at least one of terephthalic acid, isophthalic acid and adipic acid; more preferably, it is terephthalic acid.

[0047] According to the present invention, preferably, the diol monomer is ethylene glycol and / or pentanediol; more preferably, it is ethylene glycol.

[0048] According to the present invention, preferably, the polyethylene glycol is selected from at least one of PEG1500, PEG2000 and PEG4000; more preferably, it is PEG2000.

[0049] According to the present invention, preferably, the titanium-based catalyst is tetrabutyl titanate and / or titanium glycolate; more preferably, it is tetrabutyl titanate.

[0050] According to the present invention, preferably, the weight ratio of the diacid monomer to the diol monomer is 1-2.5:1; more preferably, it is 1.5-1.9:1. The inventors have found that, under this preferred embodiment, it is advantageous to achieve stable water solubility, crystallinity, and processing properties in the water-soluble polyester, while also limiting the intrinsic viscosity and shear viscosity within a specific range, thereby improving the uniformity of marine island phase distribution and fiber opening speed in the fiber.

[0051] According to the present invention, more preferably, the amounts of sodium diethyl isophthalate-5-sulfonate and polyethylene glycol in the water-soluble polyester are similar, and the ratio of sodium diethyl isophthalate-5-sulfonate to polyethylene glycol in the preparation process of the water-soluble polyester is preferably 0.79-1.26:1, and more preferably 0.95-1.05:1.

[0052] According to the present invention, preferably, the conditions for reaction I in step (1) include at least: a temperature of 230-260°C, an absolute pressure of 0.2-0.4 MPa, and a time of 60-240 min. The inventors have found that under this preferred embodiment, it is advantageous to achieve stable water solubility, crystallinity, and processing properties in the water-soluble polyester, while also limiting the intrinsic viscosity and shear viscosity to a specific range.

[0053] According to the present invention, preferably, the reaction II process in step (2) includes: first performing a pre-condensation reaction and then performing a final condensation reaction. The inventors have found that, under this preferred embodiment, it is beneficial to improve the stability of water-soluble polyesters.

[0054] According to the present invention, preferably, the conditions for the pre-condensation reaction include at least: a heating reaction at a temperature of 260-275°C, an absolute pressure of 0.1-100 kPa, and a time of 40-50 min. The inventors have found that, under this preferred embodiment, it is advantageous to combine the reaction process with the dosage of each raw material, so that the resulting water-soluble hydrogel has specific intrinsic viscosity and shear viscosity, achieving the characteristics of rapid water solubility, good processing performance, and stable and uniform fiber opening in the water-soluble polyester.

[0055] According to the present invention, preferably, the conditions for the final polycondensation reaction include at least: a temperature of 270-285°C, an absolute pressure of less than 100 Pa, and a time of 70-85 min. The time of the final polycondensation reaction can be controlled by accumulating the time after the stirring current of the reactor reaches a set value. The inventors have found that, under this preferred embodiment, it is advantageous to combine the reaction process with the amount of each raw material, so that the resulting water-soluble hydrogel has specific intrinsic viscosity and shear viscosity, and the water-soluble polyester has the characteristics of rapid water solubility, good processing performance, and stable and uniform fiber opening.

[0056] In this invention, the method for preparing the water-soluble polyester further includes: extruding, pelletizing, and drying reactant II obtained from the polycondensation reaction. The extrusion, pelletizing, and drying methods can employ conventional techniques and equipment.

[0057] According to a particularly preferred embodiment of the present invention, a method for preparing water-soluble polyester includes the following steps:

[0058] (1) In the presence of tetrabutyl titanate, terephthalic acid and ethylene glycol are mixed at a weight ratio of 1.5-1.9:1 and reacted at a temperature of 230-260℃ and an absolute pressure of 0.2-0.4MPa for 60-240 min to obtain reactant I.

[0059] (2) After mixing reactant I with sodium dihydroxyethyl isophthalate-5-sulfonate (SIPE) and PEG2000, the mixture is first heated to a temperature range of 260-275℃ for 40-50 min under an absolute pressure of 0.1-100 kPa, and then subjected to a final polycondensation reaction at a temperature of 270-285℃ and an absolute pressure below 100 Pa. After the stirring current reaches the set value, the cumulative polycondensation time is 70-85 min to obtain reactant II. Reactant II is then extruded, pelletized, and dried to obtain water-soluble polyester.

[0060] Of these, the amount of tetrabutyl titanate is 0.0015-0.003 wt%, SIPE is 4.5-7 wt%, and PEG2000 is 4.5-7 wt%, relative to the total weight of terephthalic acid and ethylene glycol; the ratio of SIPE to PEG2000 is 0.95-1.05:1.

[0061] The water-soluble polyester provided by this invention is a rapidly water-soluble, environmentally friendly polyester with specific intrinsic viscosity and shear viscosity. When applied in the spinning process, it can form a specific shear viscosity ratio with conventional polyester, effectively ensuring the uniform distribution of the marine phase (the water-soluble polyester provided by this invention) and the island phase (conventional polyester), thereby achieving the goal of uniform distribution of the marine and island phases in the fiber and fast and stable fiber opening speed. Based on this, a third aspect of this invention provides the application of the above-mentioned water-soluble polyester and the water-soluble polyester prepared by the above method in the production of chemical fibers. The chemical fibers can be island-island fibers, etc.

[0062] A fourth aspect of the present invention provides a method for producing island-island fibers, the method comprising the following steps: using the above-described water-soluble polyester and / or the water-soluble polyester prepared according to the above method as the marine phase, and using conventional polyester as the island phase; wherein, at a temperature of 288°C and a shear rate of 6000 s... -1 Under these conditions, the ratio of the shear viscosity of the water-soluble polyester to that of the conventional polyester is 0.8-0.9:1. The island-island fibers produced by this method are beneficial in ensuring a stable island-island phase distribution during the island-island yarn forming process, resulting in good fiber opening.

[0063] In this invention, the spinning method can adopt conventional spinning methods or equipment. For example, the above-mentioned water-soluble polyester is dried to become the marine phase and conventional polyester is dried to become the island phase. The island-island yarn is prepared by spinning using an island-island yarn spinning device. The marine phase and island phase are fed into two screws, A and B, respectively, to prepare the marine phase and island phase of the fiber. The feed speed of screw A is 12-18 Hz and the feed speed of screw B is 32-28 Hz, so that the weight ratio of marine phase in the fiber is 25-35% and the spinning speed is 2800-3200 m / min.

[0064] When evaluating the spinning process of island-island fibers, the cross-section of the raw yarn was observed under a microscope to show a clear and uniformly distributed marine and island phases. The raw yarn was then stretched to prepare garter fabric. The garter fabric was then subjected to alkali reduction treatment in hot alkaline water to prepare ultrafine fibers. The weight loss rate of the garter after alkali reduction treatment was tested to be 31-33%, and the fiber opening condition of the garter was observed to be good using electron microscopy.

[0065] In this invention, the conventional polyester can be a commercially available polyester commonly used for preparing island-of-the-sea fibers, or a polyester prepared by conventional methods in the art. Exemplarily, the preparation method of the conventional polyester includes the following steps: mixing antimony glycolate catalyst, terephthalic acid (PTA), and ethylene glycol (EG) at a weight ratio of 1:2800-3200:1600-2000, and carrying out a conventional esterification reaction under conditions of a gauge pressure of 0.2-0.3 MPa and a temperature of 200-300°C; after the esterification reaction, carrying out a pre-condensation reaction at 260-275°C for 40-50 min, and finally controlling the condensation reaction temperature at 270-285°C for a final condensation reaction, with an absolute pressure below 100 Pa, and accumulating a condensation time of 100-110 min after the stirring current in the reactor reaches the set value; the melt is then extruded by a melt pump, pelletized, and dried to obtain the conventional polyester.

[0066] The present invention will be described in detail below through embodiments.

[0067] In the following examples, unless otherwise specified, the raw materials and reagents used are all conventional commercial products.

[0068] In the following examples, the titanium content in the polyester was determined using elemental analysis; the contents of sodium diethyl isophthalate-5-sulfonate (SIPE) units and polyethylene glycol (PEG) units were analyzed using 1H NMR spectroscopy, with deuterated trifluoroacetic acid as the solvent. 1 1H NMR testing was performed, and the content of SIPE and PEG units was calculated based on the integral area of ​​the corresponding characteristic peaks of the copolyester. The conversion rate of SIPE or PEG = (content calculated by NMR / theoretical amount added) × 100%.

[0069] The intrinsic viscosity was tested and characterized according to section 5.1 of GB / T14190-2017 Test Method for Fiber Grade Polyester Chips.

[0070] The glass transition temperature (Tg) and the semi-crystallization period (t) mentioned above 1 / 2 The differential scanning calorimetry (DSC) method was used for testing and calculation. The specific procedure was as follows: Under nitrogen protection, DSC thermal analysis was performed by raising the temperature from 25℃ to 290℃ at a rate of 10℃ / min, holding for 5 min, then lowering it to 25℃ at a rate of 400℃ / min, followed by another raising the temperature from 25℃ to 290℃ at a rate of 10℃ / min, holding for 5 min, and finally lowering it to 100℃ at a rate of 10℃ / min. The glass transition temperature Tg was calculated based on the second heating curve, and the half-crystallization period t during the melting and crystallization process was calculated using the crystallinity of the melting and crystallization peak. 1 / 2 .

[0071] The shear viscosity was obtained by testing the rheological properties of the sample using a capillary rheometer. The capillary orifice diameter was 1 mm, the aspect ratio L / D = 16, the inlet angle was 90°, the test temperature was 288°C, and the shear rate was 6000 s⁻¹. -1 .

[0072] The alkali reduction process involves treating water-soluble polyester in an alkaline solution at 100°C with an alkali content of 1 wt% for 45 minutes.

[0073] Example 1

[0074] 5000g of terephthalic acid (PTA), 3000g of ethylene glycol (EG), and 0.191g of tetrabutyl titanate catalyst were added to a 20L general-purpose polymerization reactor. The reaction was carried out for 200min under the conditions of gauge pressure 0.25MPa and temperature 250℃ to obtain reactant I. After reaction I was completed, 471g of SIPE and 471g of PEG2000 were added to reactant I in sequence. The reaction was carried out at an absolute pressure of 0.1-100Kpa and a temperature range of 260-275℃ for 45min. Finally, the polycondensation reaction temperature was controlled at 278℃ and the absolute pressure was below 100Pa for the final polycondensation reaction. After the stirring current of the reactor reached the set value, the cumulative polycondensation time was 75min to obtain reactant II. Reactant II (melt) was extruded, pelletized, and dried by a melt pump to obtain 6725g of water-soluble polyester.

[0075] The water-soluble polyester prepared in Example 1 was subjected to... 1 ¹H NMR analysis showed that the chemical shifts of the sulfonate groups in the characteristic SIPE unit were δ = 8.97 and δd = 9.06, while the chemical shifts of the PEG unit were δ = 3.96 and δf = 4.11.

[0076] Example 2

[0077] 5000g of terephthalic acid (PTA), 3000g of ethylene glycol (EG), and 0.145g of tetrabutyl titanate catalyst were added to a 20L general-purpose polymerization reactor. The reaction was carried out for 80 minutes under the conditions of gauge pressure of 0.3MPa and temperature of 230℃ to obtain reactant I. After the reaction was completed, 551g of SIPE and 551g of PEG 2000 were added to reactant I in sequence. The reaction was carried out at an absolute pressure of 0.1-100Kpa and a temperature range of 260-275℃ for 40 minutes. Finally, the polycondensation reaction temperature was controlled at 270℃ and the absolute pressure was below 100Pa for the final polycondensation reaction. After the stirring current of the reactor reached the set value, the cumulative polycondensation time was 78 minutes to obtain reactant II. Reactant II (melt) was extruded, pelletized, and dried by a melt pump to obtain 6855g of water-soluble polyester.

[0078] Example 3

[0079] 5000g of terephthalic acid (PTA), 3000g of ethylene glycol (EG), and 0.187g of tetrabutyl titanate catalyst were added to a 20L general-purpose polymerization reactor. The reaction was carried out for 240min under the conditions of gauge pressure of 0.1MPa and temperature of 260℃ to obtain reactant I. After the reaction was completed, 394g of SIPE and 394g of PEG2000 were added to reactant I in sequence. The reaction was carried out at an absolute pressure of 0.1-100Kpa and a temperature range of 260-275℃ for 50min. Finally, the polycondensation reaction temperature was controlled at 285℃ and the absolute pressure was below 100Pa for the final polycondensation reaction. After the stirring current of the reactor reached the set value, the cumulative polycondensation time was 82min to obtain reactant II. Reactant II (melt) was extruded, pelletized, and dried by a melt pump to obtain 6571g of water-soluble polyester.

[0080] Example 4

[0081] 5000g of terephthalic acid (PTA), 3000g of ethylene glycol (EG), and 0.141g of tetrabutyl titanate catalyst were added to a 20L general-purpose polymerization reactor. The reaction was carried out for 150min under the conditions of gauge pressure of 0.25MPa and temperature of 250℃ to obtain reactant I. After the reaction was completed, 432g of SIPE and 432g of PEG2000 were added to reactant I in sequence. The reaction was carried out at an absolute pressure of 0.1-100Kpa and a temperature range of 260-275℃ for 45min. Finally, the polycondensation reaction temperature was controlled at 278℃ and the absolute pressure was below 100Pa for the final polycondensation reaction. After the stirring current of the reactor reached the set value, the cumulative polycondensation time was 80min to obtain reactant II. Reactant II (melt) was extruded, pelletized, and dried by a melt pump to obtain 6647g of water-soluble polyester.

[0082] Example 5

[0083] 5000g of terephthalic acid (PTA), 3000g of ethylene glycol (EG), and 0.235g of tetrabutyl titanate catalyst were added to a 20L general-purpose polymerization reactor. Reaction I was carried out for 150min under the conditions of gauge pressure of 0.25MPa and temperature of 250℃. After reaction I was completed, 401g of SIPE and 502g of PEG2000 were added sequentially. The reaction was carried out at an absolute pressure of 0.1-100Kpa and a temperature range of 260-275℃ for 45min. Finally, the polycondensation reaction temperature was controlled at 278℃ and the absolute pressure was below 100Pa for the final polycondensation reaction. After the stirring current of the reactor reached the set value, the cumulative polycondensation time was 75min to obtain reactant II. Reactant II (melt) was extruded, pelletized, and dried by a melt pump to obtain 6686g of water-soluble polyester.

[0084] Example 6

[0085] Water-soluble polyester was prepared according to the method of Example 1, except that the amount of SIPE was replaced with 502g, the amount of PEG2000 was replaced with 401g, and the cumulative polycondensation time after the stirring current of the reactor reached the set value was replaced with 70min; 6686g of water-soluble polyester was obtained.

[0086] Example 7

[0087] Water-soluble polyester was prepared according to the method of Example 1, except that PEG2000 was replaced with PEG1500; 6725g of water-soluble polyester was obtained.

[0088] Example 8

[0089] A water-soluble polyester was prepared according to the method of Example 1, except that tetrabutyl titanate was replaced with titanium glycolate with an equimolar titanium element content; 6725g of water-soluble polyester was obtained.

[0090] Comparative Example 1

[0091] 5000g of terephthalic acid (PTA), 3000g of ethylene glycol (EG), and 1.6624g of antimony glycol catalyst were added to a 20L general-purpose polymerization reactor. Esterification was carried out for 200min under a gauge pressure of 0.25MPa and a temperature of 250℃. After the esterification reaction, the temperature was increased for 45min under an absolute pressure of 0.1-100Kpa and a temperature range of 260-275℃. Finally, the polycondensation reaction was carried out at a final polycondensation reaction temperature of 278℃ and an absolute pressure below 100Pa. After the stirring current of the reactor reached the set value, the cumulative polycondensation time was 105min. The melt was extruded by a melt pump, pelletized, and dried to obtain 5783g of polyester (hereinafter referred to as conventional polyester).

[0092] Comparative Example 2

[0093] 5000g of terephthalic acid (PTA), 3000g of ethylene glycol (EG), and 0.185g of tetrabutyl titanate catalyst were added to a 20L general-purpose polymerization reactor. The reaction was carried out for 200min under the conditions of gauge pressure of 0.25MPa and temperature of 250℃ to obtain reactant I. After the reaction was completed, 358g of SIPE and 358g of PEG2000 were added to reactant I in sequence. The reaction was carried out at an absolute pressure of 0.1-100Kpa and a temperature range of 260-275℃ for 45min. Finally, the polycondensation reaction temperature was controlled at 278℃ and the absolute pressure was below 100Pa for the final polycondensation reaction. After the stirring current of the reactor reached the set value, the cumulative polycondensation time was 85min to obtain reactant II. Reactant II (melt) was extruded, pelletized, and dried by a melt pump to obtain 6499g of polyester.

[0094] Comparative Example 3

[0095] 5000g of terephthalic acid (PTA), 3000g of ethylene glycol (EG), and 0.200g of tetrabutyl titanate catalyst were added to a 20L general-purpose polymerization reactor. The reaction was carried out for 200min under the conditions of gauge pressure 0.25MPa and temperature 250℃ to obtain reactant I. After reaction I was completed, 635g of SIPE and 635g of PEG2000 were added to reactant I in sequence. The reaction was carried out at an absolute pressure of 0.1-100Kpa and a temperature range of 260-275℃ for 45min. Finally, the polycondensation reaction temperature was controlled at 278℃ and the absolute pressure was below 100Pa for the final polycondensation reaction. After the stirring current of the reactor reached the set value, the cumulative polycondensation time was 45min to obtain reactant II. Reactant II (melt) was extruded, pelletized, and dried by a melt pump to obtain 7053g of polyester.

[0096] Comparative Example 4

[0097] 5000g of terephthalic acid (PTA), 3000g of ethylene glycol (EG), and 0.191g of tetrabutyl titanate catalyst were added to a 20L general-purpose polymerization reactor. The reaction was carried out for 200min under the conditions of gauge pressure 0.25MPa and temperature 250℃ to obtain reactant I. After reaction I was completed, 471g of SIPE and 471g of PEG2000 were added to reactant I in sequence. The reaction was carried out at an absolute pressure of 0.1-100Kpa and a temperature range of 260-275℃ for 45min. Finally, the polycondensation reaction temperature was controlled at 278℃ and the absolute pressure was below 100Pa for the final polycondensation reaction. After the stirring current of the reactor reached the set value, the cumulative polycondensation time was 64min to obtain reactant II. Reactant II (melt) was extruded, pelletized, and dried by a melt pump to obtain 6725g of polyester.

[0098] Comparative Example 5

[0099] Polyester was prepared according to the method of Comparative Example 4, except that the cumulative polycondensation time after the stirring current in the reactor reached the set value was replaced with 91 min; 6725 g of polyester was obtained.

[0100] Comparative Example 6

[0101] 5000g of terephthalic acid (PTA), 3000g of ethylene glycol (EG), and 0.120g of tetrabutyl titanate catalyst were added to a 20L general-purpose polymerization reactor. The reaction was carried out for 200min under the conditions of gauge pressure 0.25MPa and temperature 250℃ to obtain reactant I. After reaction I was completed, 471g of SIPE and 471g of PEG2000 were added to reactant I in sequence. The reaction was carried out at an absolute pressure of 0.1-100Kpa and a temperature range of 260-275℃ for 45min. Finally, the polycondensation reaction temperature was controlled at 278℃ and the absolute pressure was below 100Pa for the final polycondensation reaction. After the stirring current of the reactor reached the set value, the cumulative polycondensation time was 120min to obtain reactant II. Reactant II (melt) was extruded, pelletized, and dried by a melt pump to obtain 6725g of polyester.

[0102] Comparative Example 7

[0103] 5000g of terephthalic acid (PTA), 3000g of ethylene glycol (EG), and 0.285g of tetrabutyl titanate catalyst were added to a 20L general-purpose polymerization reactor. The reaction was carried out for 200min under the conditions of gauge pressure of 0.25MPa and temperature of 250℃ to obtain reactant I. After the reaction was completed, 471g of SIPE and 471g of PEG2000 were added to reactant I in sequence. The reaction was carried out at an absolute pressure of 0.1-100Kpa and a temperature range of 260-275℃ for 45min. Finally, the polycondensation reaction temperature was controlled at 278℃ and the absolute pressure was below 100Pa for the final polycondensation reaction. After the stirring current of the reactor reached the set value, the cumulative polycondensation time was 46min to obtain reactant II. Reactant II (melt) was extruded, pelletized, and dried by a melt pump to obtain 6725g of polyester.

[0104] Test Example 1

[0105] Using the water-soluble polyesters or polyesters prepared in Examples 1-8 and Comparative Examples 1-7 as samples, the heavy metal content (wt%), SIPE content (wt%), and polyethylene glycol content (wt%) in each sample were calculated. The intrinsic viscosity of each sample was also tested at a temperature of 288°C and a shear rate of 6000 s. -1 Shear viscosity, glass transition temperature Tg, and half-crystallization period t under the given conditions. 1 / 2 The water solubility under the alkali reduction process conditions is shown in Table 1.

[0106] Table 1

[0107]

[0108] As can be seen from the data in Table 1, the water-soluble polyesters obtained by the preparation method provided by the present invention in Examples 1-8 have a heavy metal content reduced by more than 95% compared with the conventional polyester provided in Comparative Example 1, and are highly environmentally friendly. Under the conditions of 100°C, 1.0% alkali content, and 45 min alkali reduction process, the water solubility is more than 51.6%, which is more than 250 times higher than the water solubility of the conventional polyester prepared in Comparative Example 1, and has the characteristic of rapid water solubility. At the same time, the glass transition temperature and melt crystallization rate of the water-soluble polyesters prepared in Examples 1-8 are close to those of the conventional polyester prepared in Comparative Example 1, so the processing performance is better.

[0109] Test Example 2

[0110] The water-soluble polyester or polyester obtained in Examples 1-8 and Comparative Examples 2-7 were used as the sea phase, and conventional polyester (the polyester obtained in Comparative Example 1) was used as the island phase. After drying, island-island yarns were prepared using an island-island yarn spinning device. The sea phase and island phase were fed into two screws, A and B, respectively, to prepare the sea phase and island phase of the fiber. The feed speed of screw A was 15.00 Hz, and the feed speed of screw B was 35.00 Hz, so that the weight ratio of the sea phase in the fiber was 30%, and the spinning speed was 3000 m / min. The cross-section of the yarn was observed under a microscope. Among them, when the water-soluble polyester obtained in Example 1 was used as the sea phase, the cross-section of the island phase of the island-island yarn was as follows. Figure 1 As shown, it exhibits a clear and uniformly distributed marine and island phase morphology. When the polyester prepared in Comparative Example 2 is used as the marine phase, the island phase cross-section of the island precursor is as follows: Figure 2 As shown, it exhibits adhesion between marine and island facies (see details). Figure 2 (The part circled in the middle).

[0111] The shear viscosity ratios of the water-soluble polyesters or polyesters prepared in Examples 1-8 and Comparative Examples 2-7 and the conventional polyester (the polyester prepared in Comparative Example 1) were calculated and are shown in Table 2.

[0112] The island-island precursor yarns obtained above were drawn at a speed of 450 m / min and a draw ratio of 1.85. After weaving the drawn yarns into stockings, the weight loss rate of the stockings was tested under alkali reduction processing conditions. The microstructure (island-island phase separation) of the stockings after alkali reduction treatment was observed by electron microscopy, and the results are shown in Table 2. Specifically, when the water-soluble polyester obtained in Example 1 was used as the island phase, the microstructure of the stockings after alkali reduction treatment was as follows: Figure 3 As shown, its fiber opening is uniform and complete, and the fiber opening condition is good. When the polyester obtained in Comparative Example 2 is used as the marine phase, the microstructure of the garter belt after alkali reduction treatment is as follows. Figure 4 As shown, its fiber opening is uneven.

[0113] Table 2

[0114] serial number Shear viscosity ratio Original wire cross-sectional distribution % water solubility of garter belt Garment lace unraveling condition Example 1 0.90 Marine and island facies are evenly distributed. 32.5 good Example 2 0.80 Marine and island facies are evenly distributed. 33.0 good Example 3 0.88 Marine and island facies are evenly distributed. 31.8 good Example 4 0.84 Marine and island facies are evenly distributed. 32.5 good Example 5 0.82 Marine and island facies are evenly distributed. 32.8 good Example 6 0.89 Marine and island facies are evenly distributed. 32.7 good Example 7 0.90 Marine and island facies are evenly distributed. 32.7 good Example 8 0.90 Marine and island facies are evenly distributed. 32.6 good Comparative Example 1 1.00 / / / Comparative Example 2 0.76 Marine and island facies adhesion 18.9 Uneven Comparative Example 3 1.08 Marine and island facies adhesion 38.5 Excessive reduction Comparative Example 4 0.73 Marine and island facies adhesion 28.4 Uneven, incomplete Comparative Example 5 1.16 Marine and island facies adhesion 19.8 Uneven, incomplete Comparative Example 6 0.60 Marine and island facies adhesion 24.9 Uneven, incomplete Comparative Example 7 1.14 Marine and island facies adhesion 31.2 Uneven, incomplete

[0115] As can be seen from the data in Table 2, the sea-island yarns prepared using the water-soluble polyesters obtained in Examples 1-8 as the sea-phase material exhibit clear interfaces between the sea-phase and island-phase on the cross-section, and the garters prepared from the drawn yarns show uniform fiber opening after alkali reduction. -1 The ratio of the shear viscosity under the specified conditions to that of the conventional polyester prepared in Comparative Example 1 is (0.8-0.9):1, which ensures the uniformity of the marine and island phase structures when applied to island-island yarns. This results in the uniform dispersion of the marine and island phases in island-island yarns prepared using the water-soluble polyesters obtained in Examples 1-8 after alkali reduction processing.

[0116] In the formation of island-island yarn, water-soluble polyester and conventional polyester melts are combined to form fiber precursors with an island-island structure. Therefore, it is crucial to ensure that the two melts have suitable shear viscosity to guarantee a uniform distribution of the island and marine phases. Excessive difference in shear viscosity between the two melts can lead to uneven distribution and adhesion of the island and marine phases, resulting in uneven alkali reduction during subsequent yarn splitting. Furthermore, to ensure sufficient processing and performance properties, the glass transition temperature (Tg) must not be too low; otherwise, filament adhesion will occur during processing. A slightly faster melt crystallization rate is also necessary to maintain fiber strength. During the subsequent alkali reduction treatment of island-island yarn fabrics, users aim to minimize the heavy metal content in the polyester.

[0117] The polyester prepared in Comparative Example 1 has the properties of a conventional polyester. The results show that the water solubility of the water-soluble polyesters prepared in Examples 1-8 is more than 250 times higher than that of conventional polyesters.

[0118] The test results of Comparative Examples 2 and 3 show that both excessively high and excessively low SIPE and PEG contents will affect the water solubility and processing properties of the obtained polyester. When the content is too low, the water solubility rate of the polyester will decrease, and when the content is too high, the polymerization reaction will be too fast and the shear viscosity of the polyester will be high, which will result in uneven cross-sectional distribution of the island filament and excessive weight reduction.

[0119] The test results of Comparative Examples 4 and 5 show that excessively high or low viscosity of environmentally friendly polyester will disrupt the melt pressure balance of island filaments, resulting in uneven distribution of marine and island phases, which will also affect the stability of alkali reduction in kelp filaments.

[0120] Comparative Example 6 shows that when the catalyst content in the polyester synthesis system is too low, it will seriously affect the polymerization rate and the processing performance of the resulting water-soluble polyester will be poor. Comparative Example 7 shows that when the catalyst content is too high, the polymerization rate will be too fast, resulting in poor stability of the copolymerization reaction and thus poor performance of the resulting water-soluble polyester.

[0121] Based on the performance requirements of island-sea fiber, the preparation method of water-soluble polyester provided in Examples 1-8 is adopted. By matching the amount of each raw material component, the reaction conditions and the content of specific components in the obtained water-soluble polyester, the water-soluble polyester has the characteristics of low heavy metal content, rapid water solubility, good processing performance and stable and uniform fiber opening, and has significant functionalization and greening effects.

[0122] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A water-soluble polyester, characterized in that, The intrinsic viscosity of the water-soluble polyester is 0.50-0.55 dL / g, and it is suitable for use at a temperature of 288℃ and a shear rate of 6000 s. -1 The shear viscosity under the conditions is 50-60 Pa·s; the water solubility of the water-soluble polyester under the conditions of alkali reduction process at 100℃, alkali content of 1wt%, and time of 45min is greater than or equal to 51.6%; the glass transition temperature of the water-soluble polyester is 55-68℃, and the semi-crystallization period is 2-4min. The water-soluble polyester contains sodium diethyl isophthalate-5-sulfonate units, polyethylene glycol units, and titanium; in the water-soluble polyester, the content of sodium diethyl isophthalate-5-sulfonate units is 6-8 wt%, the content of polyethylene glycol units is 6-8 wt%, and the content of titanium is 0.0003-0.0005 wt%. The method for preparing the water-soluble polyester includes the following steps: (1) Under the condition of the presence of a titanium catalyst, the dicarboxylic acid monomer and the diol monomer are reacted to obtain reactant I; (2) Reactant I is reacted with sodium bis(hydroxyethyl) isophthalate-5-sulfonate and polyethylene glycol in reaction II; the process of reaction II includes: first performing a pre-condensation reaction and then performing a final condensation reaction; the conditions for the pre-condensation reaction include at least the following: the temperature is increased to 260-275℃, the absolute pressure is 0.1-100 kPa, and the time is 40-50 min; the conditions for the final condensation reaction include at least the following: the temperature is 270-285℃, the absolute pressure is below 100 Pa, and the time is 70-85 min; Of which, based on a total amount of 100 parts by weight of the dicarboxylic acid monomer and the diol monomer, the amount of the titanium catalyst is 0.0015-0.003 parts by weight, the amount of sodium dihydroxyethyl isophthalate-5-sulfonate is 4.5-7 parts by weight, and the amount of polyethylene glycol is 4.5-7 parts by weight. The polyethylene glycol unit is selected from at least one of PEG1500 unit, PEG2000 unit and PEG4000 unit; the dicarboxylic acid monomer is selected from at least one of terephthalic acid, isophthalic acid and adipic acid; the diol monomer is ethylene glycol and / or pentanediol.

2. The water-soluble polyester according to claim 1, characterized in that, The intrinsic viscosity of the water-soluble polyester is 0.515-0.53 dL / g, and it is suitable for use at a temperature of 288℃ and a shear rate of 6000 s. -1 The shear viscosity under the given conditions is 52-58.5 Pa·s.

3. The water-soluble polyester according to claim 1 or 2, characterized in that, The polyethylene glycol unit is a PEG2000 unit.

4. The water-soluble polyester according to claim 1, characterized in that, The dicarboxylic acid monomer is terephthalic acid; The diol monomer is ethylene glycol; The titanium-based catalyst is tetrabutyl titanate and / or titanium glycol.

5. The water-soluble polyester according to claim 4, characterized in that, The titanium-based catalyst is tetrabutyl titanate.

6. The water-soluble polyester according to claim 1, characterized in that, The weight ratio of the dicarboxylic acid monomer to the diol monomer is 1-2.5:

1.

7. The water-soluble polyester according to claim 6, characterized in that, The weight ratio of the dicarboxylic acid monomer to the diol monomer is 1.5-1.9:

1.

8. The water-soluble polyester according to claim 7, characterized in that, The ratio of sodium bis(hydroxyethyl) isophthalate-5-sulfonate to polyethylene glycol is 0.79-1.26:

1.

9. The water-soluble polyester according to claim 8, characterized in that, The ratio of sodium bis(hydroxyethyl) isophthalate-5-sulfonate to polyethylene glycol is 0.95-1.05:

1.

10. The water-soluble polyester according to claim 1, characterized in that, The conditions for reaction I in step (1) include at least the following: temperature of 230-260℃, absolute pressure of 0.2-0.4MPa, and time of 60-240min.

11. The use of the water-soluble polyester according to any one of claims 1 to 10 in the production of chemical fibers.

12. A method for producing island-of-sea fibers, characterized in that, The method includes the following steps: using the water-soluble polyester according to any one of claims 1 to 10 as the marine phase and a conventional polyester as the island phase; wherein, at a temperature of 288°C and a shear rate of 6000 s... -1 Under these conditions, the ratio of the shear viscosity of the water-soluble polyester to that of the conventional polyester is 0.8-0.9:1.

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