Cationic polyester and preparation method thereof

Abstract

The invention provides cationic polyester and a preparation method thereof, and relates to the technical field of modified polyester. According to the cationic polyester disclosed by the invention, on the basis that dimethyl isophthalate-5-sulfonate is added during preparation, aliphatic dimethyl dicarboxylate is continuously added, and the addition amounts of the dimethyl isophthalate-5-sulfonate and the aliphatic dimethyl dicarboxylate are controlled; the polyester can have better spinning performance and better dyeing performance at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of modified polyesters, and relates to a cationic polyester and a preparation method thereof. Background Art

[0002] The macromolecular chain segments of PET polyesters belong to rigid chain segments. Therefore, the molecules inside PET fibers are arranged neatly and tightly, and it is difficult for dyes to enter the interior of the fibers, resulting in difficult dyeing and affecting the application of PET polyesters in textile shoes and clothing. By introducing a comonomer, sodium 5-sulfoisophthalate, into the copolymer molecular chain of PET polyesters, good adsorption of cationic dyes can be achieved, and the dyeing performance of polyester fibers is improved. However, there are still problems such as insufficient depth and low dye exhaustion rate in dyeing dark colors of the resulting fibers and / or fabrics. Chinese Patent CN86104826A discloses that when synthesizing polyesters from DMT and ethylene glycol, dimethyl 3,5-benzenedisulfonate and aliphatic dicarboxylic acid ethylene glycol polyesters with 6 to 10 carbon atoms are added for block copolymerization, and the addition amount of the aliphatic dicarboxylic acid ethylene glycol polyester cannot be less than 5%. It is also recorded that if aliphatic dicarboxylic acid dimethyl esters or aliphatic dicarboxylic acids are directly added for random copolymerization, the melting point of the prepared copolyester will decrease and the heat resistance will be poor. Chinese Patent CN102061533A discloses that a titanium-based catalyst is used instead of a conventional antimony-based catalyst during the synthesis of polyester polymers. Relative to the total amount of the fiber-forming polymer, the addition amount of the copolymerization component aliphatic dicarboxylic acid is 1.5 to 9 wt%, and the addition amount of sodium 5-sulfoisophthalate is 0.9 to 3.7 wt%.

[0003] For cationic polyesters, it is required not only to have good dyeing performance but also not to have an adverse impact on the properties of the polyesters, and basically maintain the original properties such as mechanical strength and melting point, so as not to cause adverse effects on melt spinning and applications.

[0004] However, for polyesters to have good dyeing performance, it is necessary to disrupt the crystalline structure and / or rigid structure of the polyesters to a certain extent, but this will also cause a decrease in the properties of the polyesters such as melting point, mechanical strength, and spinnability. Therefore, there is a contradictory relationship. Summary of the Invention

[0005] The applicant unexpectedly found that by using a sulfonate comonomer and dimethyl aliphatic dicarboxylate as comonomers and controlling the usage amounts of the sulfonate comonomer and dimethyl aliphatic dicarboxylate within a certain range, the dyeing performance of PET polyesters can be significantly improved without affecting their mechanical strength, melting point and other properties. Based on this, the present invention provides a cationic polyester and a preparation method thereof.

[0006] The technical solution of the present invention is as follows:

[0007] A cationic polyester is obtained by preparing with the following raw material components:

[0008] A-1) Dimethyl terephthalate;

[0009] A-2) Dimethyl isophthalate-5-sulfonate and / or bis(2-hydroxyethyl) isophthalate-5-sulfonate;

[0010] A-3) Dimethyl C2-C10 aliphatic dicarboxylate;

[0011] A-4) Ethylene glycol;

[0012] The weight of the raw material component A-2) is 1-4% of the weight of the raw material component A-1);

[0013] The weight of the raw material component A-3) is 1.5-4% of the weight of the raw material component A-1).

[0014] Preferably, the weight of the raw material component A-2) is 1.5-2.5% of the weight of the raw material component A-1);

[0015] The weight of the raw material component A-3) is 1.5-2.5% of the weight of the raw material component A-1).

[0016] Preferably, the ratio of the sum of the moles of the raw material components A-1), A-2) and A-3) to the moles of the raw material component A-4) is 1:1.1-2.

[0017] Preferably, the dimethyl C2-C8 aliphatic dicarboxylate has the structure shown in the following formula (1),

[0018] CH3OOC(CH2) n COOCH3(1)

[0019] where n = 0-8.

[0020] A method for preparing a cationic polyester according to any one of the above embodiments, adding each of the raw material components to a reactor, and successively performing a transesterification reaction and a condensation reaction to obtain the cationic polyester.

[0021] Preferably, a transesterification catalyst is added during the transesterification reaction, and the weight of the transesterification catalyst is 200-500 ppm of the sum of the weights of the raw material components;

[0022] Preferably, the transesterification catalyst is selected from divalent metal acetates.

[0023] More preferably, an anti-ether agent is also added during the transesterification reaction, and the weight of the anti-ether agent is 200-500 ppm of the sum of the weights of the raw material components;

[0024] Preferably, the ether inhibitor is selected from alkali metal acetates.

[0025] Preferably, the condensation reaction includes a preliminary condensation reaction and a final condensation reaction that are carried out successively;

[0026] The temperature of the preliminary condensation reaction is 250 - 265 °C, and the vacuum degree does not exceed 500 Pa.

[0027] More preferably, the temperature of the final condensation reaction is 265 - 285 °C, and the vacuum degree does not exceed 100 Pa.

[0028] Preferably, a condensation catalyst and a heat stabilizer are added during the condensation reaction;

[0029] Preferably, the condensation catalyst is selected from antimony-based catalysts; the heat stabilizer is selected from phosphorus-based heat stabilizers.

[0030] The beneficial effects of the present invention are as follows:

[0031] (1) In the preparation of PET polyester of the present invention, two comonomers, namely a sulfonate comonomer and a dimethyl aliphatic dicarboxylate, are added, and the amounts of the two comonomers are controlled, so that PET polyester with good dyeing performance can be obtained, and there is basically no influence on the melting point, mechanical properties, spinnability, etc. of the polyester.

[0032] (2) In the present invention, the molar ratios of the ester raw materials (raw material component A-1), raw material component A-2), and raw material component A-3)) to ethylene glycol are further controlled, and a cationic polyester with good performance can be obtained by using a conventional catalyst in the polyester synthesis. Specific Embodiments

[0033] The technical solutions of the present invention are further described and illustrated below through specific embodiments.

[0034] On the one hand, the present invention provides a cationic polyester, which is obtained by preparing with the following raw material components:

[0035] A-1) Dimethyl terephthalate DMT;

[0036] A-2) Dimethyl 5-sulfoisophthalate and / or bis(2-hydroxyethyl) 5-sulfoisophthalate;

[0037] A-3) Dimethyl C2-C10 aliphatic dicarboxylate;

[0038] A-4) Ethylene glycol;

[0039] The weight of raw material component A-2) is 1 - 4% of the weight of raw material component A-1);

[0040] The weight of raw material component A-3) is 1.5-4% of the weight of raw material component A-1).

[0041] The above raw material components A-1), A-2) and A-3) are all dimethyl esters. They can first undergo transesterification reactions with raw material component A-4) to respectively form hydroxyethyl ester compounds, which is beneficial to subsequent condensation reactions and generates a cationic polyester with a relatively uniform distribution of functional groups (sulfonates, C2-C10 aliphatic dicarboxylic esters). In the present invention, by adding raw material components A-2) and A-3) with sulfonate structures to the raw material components and controlling the addition amounts of raw material components A-2) and A-3), it is found that polyester fibers or polyester-containing fabrics with good dyeing ability and dyeing stability can be obtained with basically no impact on the properties of the polyester (such as melting point, mechanical strength, etc.), solving the contradiction problem between the dyeing performance of polyester and properties such as melting point and mechanical strength in the prior art. The dyeing performance of the cationic polyester of the present invention mainly comes from raw material component A-2), and raw material component A-3) can play a role in deepening the dyeing, and they work together synergistically, making the cationic polyester of the present invention have good dyeing performance and dyeing stability. If the content of raw material component A-2) is too small (for example, the weight of raw material component A-2) is 0.5% of the weight of raw material component A-1)), it is not conducive to the improvement of dyeing performance. If the content of raw material component A-2) is too high (for example, the weight ratio of raw material component A-2) to raw material component A-1) reaches 4.5% or higher), the sulfonate groups may self-polymerize to generate colloidal impurities, reducing the spinnability of the polyester. For example, the breakage rate during the spinning process increases significantly. If the content of raw material component A-3) is too small (for example, the weight of raw material component A-3) is 1% of the weight of raw material component A-1)), the effect of deepening the dyeing is not obvious. If the content of raw material component A-3) is too much (for example, the weight ratio of raw material component A-3) to raw material component A-1) reaches 4.5% or higher), the polyester chips turn yellow and the melting point drops significantly, which is not conducive to spinning, the breakage rate during spinning is high, and the mechanical strength of the fibers decreases significantly.

[0042] For raw material component A-2), the sulfonate is preferably sodium sulfonate, such as sodium 5-sulfoisophthalate dimethyl ester and / or sodium 5-sulfoisophthalate bis(2-hydroxyethyl) ester. For the weight ratio of raw material component A-2) to raw material component A-1), by way of example, it can be any value among 1%, 1.2%, 1.3%, 1.5%, 1.7%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.7%, 2.8%, 3%, 3.2%, 3.4%, 3.5%, 3.7%, 3.8%, 4%, etc. or any value between them, without any particular limitation. Further, the weight of raw material component A-2) can be 1.5-2.5% of the weight of raw material component A-1).

[0043] For the weight ratio of raw material component A-3) relative to raw material component A-1), by way of example, it can be any value among 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.7%, 2.8%, 3%, 3.2%, 3.3%, 3.5%, 3.7%, 3.8%, 4%, etc. or any value between them, without any particular limitation. Further, the weight of raw material component A-3) is 1.5 - 2.5% of the weight of raw material component A-1).

[0044] In some embodiments, the ratio of the sum of the molar amounts of raw material component A-1), raw material component A-2), and raw material component A-3) to the molar amount of raw material component A-4) is 1:1.1 - 2. Within this ratio range, it is beneficial for the transesterification reaction to proceed. Raw material component A-1), raw material component A-2), and raw material component A-3) are converted into compounds of hydroxyethyl esters, and the excess ethylene glycol can be removed by vacuum distillation in the subsequent pre-condensation stage. By way of example, the ratio can be any value among 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, etc. or any value between them, without any particular limitation.

[0045] In some embodiments, the C2-C8 aliphatic dicarboxylic acid dimethyl ester has the following structure as shown in formula (1):

[0046] CH3OOC(CH2) n COOCH3 (1)

[0047] Wherein, n = 0 - 8.

[0048] By way of example, the C2-C8 aliphatic dicarboxylic acid dimethyl ester can be dimethyl oxalate, dimethyl 1,3-propanedicarboxylate, dimethyl 1,6-hexanedicarboxylate, dimethyl 1,9-nonanedicarboxylate, dimethyl 1,4-butanedicarboxylate, dimethyl 1,8-octanedicarboxylate, etc. Further, the above n = 1 - 4, that is, the C2-C8 aliphatic dicarboxylic acid dimethyl ester can be dimethyl 1,3-propanedicarboxylate, dimethyl 1,6-hexanedicarboxylate, dimethyl 1,4-butanedicarboxylate, etc.

[0049] On the other hand, the present invention also provides a method for preparing the cationic polyester described in any one of the above embodiments. Each raw material component is added to a reactor, and transesterification reaction and condensation reaction are carried out in sequence to obtain the cationic polyester. By using the above raw material components A-1), A-2), A-3) and A-4), the cationic polyester can be obtained through transesterification reaction and condensation reaction. During the transesterification reaction, a transesterification catalyst is added, and the weight of the transesterification catalyst is 200-500 ppm of the sum of the weights of each raw material component. For example, it can be 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm, 500 ppm, etc., and preferably 400 ppm; the transesterification catalyst is selected from divalent metal acetates, such as acetates of divalent metals like calcium, magnesium, zinc, manganese, titanium, antimony, etc. In the present invention, the temperature of the transesterification reaction is not particularly limited and can be 170-240°C, and it can be carried out under normal pressure.

[0050] In some embodiments, an anti-ether agent is also added during the transesterification reaction, and the weight of the anti-ether agent is 200-500 ppm of the sum of the weights of each raw material component. For example, it can be 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm, 500 ppm, etc., and preferably 400 ppm; the anti-ether agent is selected from alkali metal acetates, such as sodium acetate, potassium acetate, lithium acetate, and preferably sodium acetate.

[0051] In some embodiments, the condensation reaction includes a pre-condensation reaction and a final condensation reaction carried out in sequence;

[0052] The temperature of the pre-condensation reaction is 250-265°C, and the vacuum degree does not exceed 500 Pa.

[0053] In the condensation reaction, through two steps of pre-condensation and final condensation, the reaction temperature of pre-condensation is slightly lower than that of final condensation. The pre-condensation reaction is mainly to remove the remaining ethylene glycol, the generated small molecule alcohols and small molecule oligomers and other low-boiling substances such as raw materials or by-products that are not conducive to the condensation reaction. There is no particular limitation on the time of the pre-condensation reaction. Considering the reaction effect and reaction efficiency comprehensively, the time can be about 30 min, such as 25-35 min. For example, it can be 25 min, 27 min, 28 min, 30 min, 32 min, 33 min, 35 min, etc. Further, the temperature of the pre-condensation reaction is 255-265°C.

[0054] In some embodiments, the temperature of the final condensation reaction is 265 - 285°C, and the vacuum degree does not exceed 100 Pa. Under the conditions of the final condensation reaction, it is beneficial to accelerate the condensation reaction and promote the timely discharge of small-molecule by-products of condensation. Further, the temperature of the final condensation reaction is 275 - 285°C. The end point of the final condensation reaction can be judged by the stirring power, which is well-known to those skilled in the art.

[0055] In some embodiments, a condensation catalyst and a heat stabilizer are added during the condensation reaction; the condensation catalyst is selected from antimony-based catalysts, such as antimony glycolate, antimony trioxide, etc., and the added weight of the antimony-based catalyst can be 600 - 800 ppm of the weight of DMT; the heat stabilizer is selected from phosphorus-based heat stabilizers, such as trimethyl phosphate, and the added weight of the phosphorus-based heat stabilizer can be 300 - 400 ppm of the weight of DMT.

[0056] The technical solutions of the present invention are further described and illustrated according to the following embodiments. Unless otherwise specified, the parts mentioned in the following embodiments are parts by weight.

[0057] Example 1

[0058] The raw material components are: 100 parts of DMT, 2.5 parts of sodium 5-sulfoisophthalate dimethyl ester SIPM, 1.5 parts of dimethyl succinate DMSu, and ethylene glycol EG. The ratio of the sum of the molar numbers of DMT, SIPM, and DMSu to the molar number of EG is 1:1.4.

[0059] The weight of the manganese acetate catalyst is 400 ppm of the sum of the weights of the raw material components, the weight of the sodium acetate is 400 ppm of the sum of the weights of the raw material components, the weight of the antimony glycolate is 700 ppm of the weight of DMT, and the weight of the trimethyl phosphate is 400 ppm of the weight of DMT.

[0060] Under normal pressure, EG and DMSu are put into the reaction kettle, the stirrer (frequency 30 Hz) is started, and then DMT, SIPM, manganese acetate catalyst and sodium acetate are added. The temperature is raised to 210 - 230 °C for transesterification reaction. When the temperature rises to about 180 - 190 °C, the temperature in the transesterification process tower and the top temperature will rise. When the top temperature rises to about 70 °C, the top cooling water is turned on for cooling. Methanol goes out through the top of the tower, then is cooled by the condenser and collected in the collection tank. When the methanol evaporation amount reaches about 95% of the theoretical value, keep the reaction kettle at normal pressure, add antimony glycolate and trimethyl phosphate stabilizer into the kettle, raise the stirrer frequency from 30 Hz to 50 Hz, stop the top cooling water, reduce the pressure to a vacuum degree not exceeding 500 Pa, raise the temperature to 255 - 265 °C, keep warm for 30 min to remove low-boiling substances, then continue to reduce the pressure to a vacuum degree not exceeding 100 Pa, raise the temperature to 275 - 285 °C, continue stirring until the stirrer power reaches 1.8 KW, reduce the stirrer frequency to 30 Hz, then continue stirring until the stirrer power rises to 1.5 KW, stop the polycondensation reaction, stop vacuum pumping, fill nitrogen into the reaction kettle to normal pressure, and discharge the material. When discharging, the melt is cooled by cooling water when flowing out and then introduced into the cutting chamber for pelletizing to obtain polyester chips.

[0061] Example 2

[0062] The difference between this example and Example 1 is that in Example 1, the amount of DMSu is adjusted from 1.5 parts to 2.5 parts. The remaining steps remain unchanged.

[0063] Example 3

[0064] The difference between this example and Example 1 is that in Example 1, the amount of DMSu is adjusted from 1.5 parts to 4 parts. The remaining steps remain unchanged.

[0065] Comparative Example 1

[0066] The difference between this comparative example and Example 1 is that in Example 1, the amount of DMSu is adjusted from 1.5 parts to 4.5 parts. The remaining steps remain unchanged.

[0067] Comparative Example 2

[0068] The difference between this comparative example and Example 1 is that in Example 1, the amount of DMSu is adjusted from 1.5 parts to 1.0 parts. The remaining steps remain unchanged.

[0069] Example 4

[0070] The difference between this example and Example 1 is that in Example 1, the amount of SIPM is adjusted from 2.5 parts to 1.5 parts. The remaining steps remain unchanged.

[0071] Example 5

[0072] The difference between this example and Example 1 is as follows: in Example 1, the amount of SIPM is adjusted from 2.5 parts to 1 part, and the remaining steps remain unchanged.

[0073] Example 6

[0074] The difference between this example and Example 1 is as follows: in Example 1, the amount of SIPM is adjusted from 2.5 parts to 4 parts, and the remaining steps remain unchanged.

[0075] Comparative Example 3

[0076] The difference between this comparative example and Example 1 is as follows: in Example 1, the amount of SIPM is adjusted from 2.5 parts to 0.5 parts, and the remaining steps remain unchanged.

[0077] Comparative Example 4

[0078] The difference between this comparative example and Example 1 is as follows: in Example 1, the amount of SIPM is adjusted from 2.5 parts to 4.5 parts, and the remaining steps remain unchanged.

[0079] Example 7

[0080] The difference between this example and Example 1 is as follows: in Example 1, the amount of SIPM is adjusted from 2.5 parts to 2 parts, and the amount of DMSu is adjusted from 1.5 parts to 2 parts, and the remaining steps remain unchanged.

[0081] Example 8

[0082] The difference between this example and Example 1 is as follows: in Example 1, the amount of SIPM is adjusted from 2.5 parts to 1.5 parts, and the amount of DMSu is adjusted from 1.5 parts to 2.5 parts, and the remaining steps remain unchanged.

[0083] Example 9

[0084] The difference between this example and Example 1 is as follows: in Example 1, DMSu is replaced with 1,6 - hexanediol dimethyl ester of equal weight, and the remaining steps remain unchanged.

[0085] Example 10

[0086] The difference between this example and Example 1 is as follows: in Example 1, DMSu is replaced with 1,3 - propanediol dimethyl ester of equal weight, and the remaining steps remain unchanged.

[0087] The polyester chips of Examples 1 - 10 and Comparative Examples 1 - 4 were respectively dried to remove surface water at 65 - 70 °C, and then crystallized using a drum dryer to obtain spinning dry chips. The melting point and intrinsic viscosity of the dry chips were tested. The melting point was tested using a DSC differential scanning calorimeter. The intrinsic viscosity was tested in accordance with the provisions of GB / T 14190 - 2017, and the solvent used was a phenol / tetrachloroethane solution with a weight ratio of 1:1.

[0088] The dry chips are spun at a spinning speed of 2,750 m / min at 288 °C to produce POY, and the yarn breakage rate is evaluated. The requirement for the breakage rate is that the number of breaks per kilometer should not exceed 5 for qualification, and more than 5 is unqualified.

[0089] The above-mentioned POYs are texturized under the conditions of an upper heating box at 180 °C, a draft ratio of 1.78, a D / Y ratio of 1.78, and a polyurethane Pu disc of 1-5-1 to produce deeply dyed DTY. The breaking strength of the DTY is detected. The breaking strength is tested according to the provisions of GB / T 14344-2008.

[0090] The above-mentioned DTYs are knitted into sock linings by a weft knitting machine. After degreasing treatment, they are dyed at 120 °C for 40 min to obtain black fabrics, and the L value, K / S value, and light fastness of the fabrics are measured. The lower the L value and the higher the K / S value, the deeper the dyeing and the better the dyeing ability. It is required that the L value does not exceed 20 and the K / S value is not less than 21. The light fastness is tested according to the national standard GB / T 8427-2019, and for dark colors, a requirement of ≥4 grades is considered qualified. The L value and K / S value are tested using a Datacolor 800 colorimeter.

[0091] Dyeing process:

[0092] Dye composition: 0.3% ED-gl yellow, 0.6% ED-GR red, 3% ED-RNT black, 1.5 g / L of sodium sulfate, 0.5 g / L of anti-dust agent, 0.5 g / L of HAC;

[0093] First, the fabric is degreased, and then the fabric is placed in a dyeing vat. The dye is dropped in according to a liquor ratio of 1:15 using a metering instrument; when the temperature is 30 °C, the dyeing vat is placed in a temperature control box and slowly heated at a heating rate of 1.5 °C / min to 120 °C. Then, after holding at 120 °C for 40 min, the fabric in the dyeing vat is taken out, washed, dried, and the L value and K / S value of the fabric are measured using a colorimeter.

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

[0095] Table 1

[0096]

[0097] In the above Comparative Example 1, the breakage rate reaches 8 breaks per kilometer; in the above Comparative Example 4, the colloid content in the prepared polyester chips is on the high side, and the breakage rate is more than 11 breaks per kilometer, which is seriously unqualified.

[0098] Therefore, as can be seen from the results in Table 1 above, in the synthesis of PET polyester in the present invention, by controlling the amounts of dimethyl isophthalate-5-sulfonate and dimethyl C2-C8 aliphatic dicarboxylate, polyester chips with relatively high melting points and intrinsic viscosities are obtained. The fibers after spinning have relatively high mechanical strength, the spinning effect is good, and the dyeing performance and stability of the fabric are good. Therefore, in order to improve the dyeing performance of PET, on the basis of adding dimethyl isophthalate-5-sulfonate during the preparation of PET polyester, continuing to add a certain amount of dimethyl C2-C8 aliphatic dicarboxylate helps to improve the dark color performance of polyester fabrics.

[0099] As described above, the basic principles, main features, and advantages of the present invention have been shown and described. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments are only preferred embodiments of the present invention, and the scope of implementation of the present invention cannot be defined thereby. That is, equivalent changes and modifications made according to the scope of the present invention patent and the content of the specification should still fall within the scope covered by the present invention. The scope of protection required by the present invention is defined by the appended claims and their equivalents.

Claims

1. A cationic polyester, characterized in that, Obtained by preparing from the following raw material components: A-1) Dimethyl terephthalate; A-2) Dimethyl isophthalate-5-sulfonate and / or bis(2-hydroxyethyl) isophthalate-5-sulfonate; A-3) C2-C10 aliphatic dicarboxylic acid dimethyl ester; A-4) Ethylene glycol; The weight of the raw material component A-2) is 1-4% of the weight of the raw material component A-1); The weight of the raw material component A-3) is 1.5-4% of the weight of the raw material component A-1).

2. The cationic polyester according to claim 1, characterized in that, The weight of the raw material component A-2) is 1.5-2.5% of the weight of the raw material component A-1); The weight of the raw material component A-3) is 1.5-2.5% of the weight of the raw material component A-1).

3. The cationic polyester according to claim 1, characterized in that, The ratio of the sum of the moles of the raw material components A-1), A-2) and A-3) to the moles of the raw material component A-4) is 1:1.1-2.

4. The cationic polyester according to claim 1, wherein The C2-C8 aliphatic dicarboxylic acid dimethyl ester has the structure shown in the following formula (1), CH3OOC(CH2) n COOCH3(1) wherein, n = 0-8.

5. A method for preparing the cationic polyester according to any one of claims 1-4, characterized in that, Add each of the above raw material components into a reactor, and carry out transesterification reaction and condensation reaction in sequence to obtain the cationic polyester.

6. The preparation method of the cationic polyester according to claim 5, characterized in that, During the transesterification reaction, a transesterification catalyst is added, and the weight of the transesterification catalyst is 200-500 ppm of the sum of the weights of each of the above raw material components; Preferably, the transesterification catalyst is selected from divalent metal acetates.

7. The preparation method of the cationic polyester according to claim 6, characterized in that, During the transesterification reaction, an anti-ether agent is also added, and the weight of the anti-ether agent is 200-500 ppm of the sum of the weights of each of the above raw material components; Preferably, the anti-ether agent is selected from alkali metal acetates.

8. The preparation method of the cationic polyester according to claim 5, characterized in that, The condensation reaction includes a pre-condensation reaction and a final condensation reaction carried out in sequence; The temperature of the pre-condensation reaction is 250-265 °C, and the vacuum degree does not exceed 500 Pa.

9. The preparation method of the cationic polyester according to claim 8, wherein, The temperature of the final condensation reaction is 265-285 °C, and the vacuum degree does not exceed 100 Pa.

10. The preparation method of the cationic polyester according to claim 5, characterized in that, During the condensation reaction, a condensation catalyst and a heat stabilizer are added; Preferably, the condensation catalyst is selected from antimony-based catalysts; the heat stabilizer is selected from phosphorus-based heat stabilizers.

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