Water-absorbing, swelling elastomers and process for their production

Abstract

The application provides a water-absorbing and swelling elastomer and a preparation method thereof. The elastomer raw material comprises a polybasic acid and / or an anhydride, a polyol, a soft segment structure monomer, a crosslinking agent and an ester monomer. The polybasic acid and / or anhydride comprises one or more than one combination of terephthalic acid, isophthalic acid, phthalic acid and phthalic anhydride. The crosslinking agent is a product obtained by reacting an unsaturated polybasic acid or anhydride with a polyol, wherein the number of carbon atoms in the main chain of the unsaturated polybasic acid or anhydride is not higher than 6, and the number of carbon atoms in the main chain of the polyol is not higher than 6. The ester monomer is a tri-ester containing a hydrogen atom at a position a. The crosslinking agent used in the application can undergo a Michael addition reaction with the tri-ester containing a hydrogen atom at the position a, and the degree of crosslinking can be controlled through the reaction, so that the final elastomer has excellent water absorption performance, and the elastomer after water absorption still maintains good structural mechanical properties.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of synthetic high polymer elastomer, and particularly relates to a water-absorbing and swelling elastomer and a preparation method thereof. BACKGROUND

[0002] The water-absorbing and swelling elastomer is a novel functional polymer material having the functions of both elastic sealing and water-absorbing and swelling, and has the performance of fast water absorption while maintaining the high elasticity of rubber. The water-absorbing mechanism of the water-absorbing and swelling elastomer is as follows: the elastic matrix is mainly composed of high-polymerization-degree carbon and hydrogen chain segments, and is a hydrophobic substance. When the hydrophilic groups or hydrophilic components are introduced into the matrix, the water molecules will enter the matrix and form a strong affinity with the hydrophilic groups in the elastomer, and the hydrophilic substances in the elastomer are dissolved or swollen, so that the osmotic pressure difference is formed between the inside and outside of the elastomer. The pressure difference promotes the penetration of water into the elastomer. The hydrophilic substances continuously absorb water, and the elastomer is deformed. When the anti-deformation force of the elastomer and the osmotic pressure difference are equal, the balance is reached, that is, the maximum swelling rate of static water is reached, and the water-absorbing and swelling effect is relatively stable.

[0003] At present, there are mainly two methods for preparing the water-absorbing and swelling elastomer: physical blending and chemical grafting. The water-absorbing and swelling elastomer prepared by physical blending is obtained by physically blending the elastomer and the water-absorbing resin. The water-absorbing and swelling elastomer prepared by chemical grafting is obtained by grafting the hydrophilic groups or chain segments onto the elastomer macromolecule through chemical reaction.

[0004] Compared with the physical blending method, the water-swellable elastomer prepared by the chemical grafting method has the advantages of good microcosmic compatibility, high strength, and good repeated performance. However, the grafting reaction is difficult and the process is complicated. At present, most of the water-swellable elastomers in the prior art are prepared by the physical blending method, and there are few reports on the chemical grafting. Patent application CN115403738A discloses a preparation method of a water-swelling polyurethane elastomer. Polyethylene glycol and 4,4-dicyclohexyl methane diisocyanate are rapidly reacted in the presence of a catalyst to form a polyurethane prepolymer. Silver nanowires and 4,4-dihydroxy diphenyl disulfide are reacted to form a composite chain extending liquid which has the functions of chain extending and crosslinking. The composite chain extending liquid is added to the prepolymer for polymerization reaction. After 12 hours of chain extending reaction, the reaction liquid is dried to obtain the water-swelling polyurethane elastomer. This method requires a large amount of N,N-dimethylformamide solvent, and the solvent needs to be recovered and treated. The whole process is relatively complex. Patent application CN111285971A discloses a preparation method of a water-swellable rubber. The invention first swells chlorinated polyethylene rubber with hydrophilic monomer N-vinyl pyrrolidone containing an initiator and a crosslinking agent, and then performs free radical polymerization to obtain polyvinyl pyrrolidone / chlorinated polyethylene water-swellable rubber. However, this method uses free radical polymerization, which makes the polymerization degree uncontrollable. SUMMARY

[0005] In order to solve the problems of the prior art, the present application provides a water-swellable elastomer and a preparation method thereof.

[0006] The object of the present application is achieved by the following technical solutions:

[0007] A water-swellable elastomer, the elastomer raw material comprises, polybasic acid and / or anhydride, polyol, soft segment structure monomer, crosslinking agent, ester monomer, the polybasic acid and / or anhydride comprises one or more than one combination of terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydride, the crosslinking agent is the product obtained by the reaction of unsaturated polybasic acid or anhydride with the main chain carbon atom number not more than 6 and polyol with the main chain carbon atom number not more than 6; the ester monomer is a triester containing hydrogen atoms in the alpha position.

[0008] Preferably, the polyol with the main chain carbon atom number not more than 6 comprises one or more than one of trimethylolpropane, trimethylolethane, pentaerythritol, and the unsaturated polybasic acid or anhydride with the main chain carbon atom number not more than 6 comprises one or more than one combination of pyromellitic anhydride, maleic anhydride, itaconic acid, fumaric acid.

[0009] Preferably, the ester monomer comprises one or more than one of triethyl citrate, tripropyl citrate, triethyl methane tricarboxylate, and triethyl 1,1,2-ethane tricarboxylate.

[0010] Preferably, the cross-linking agent and the ester monomer are added in an amount of 1% to 24% of the total amount of the raw materials (molar ratio).

[0011] Preferably, the polybasic acid and / or anhydride further comprises one or more than one combination of 1,4-cyclohexane dicarboxylic acid, adipic acid, sebacic acid, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, itaconic acid, fumaric acid; and the polyol comprises one or more than one arbitrary combination of ethylene glycol, 1,2-propanediol, 1,4-butanediol, neopentyl glycol, 1,4-cyclohexane dimethanol.

[0012] Preferably, the soft segment structure monomer comprises one or more than one combination of polyethylene glycol, polypropylene glycol, polycarbonate diol.

[0013] Preferably, the elastomer raw material further comprises a catalyst, which includes but is not limited to one or more than one combination of sodium acetate, zinc acetate, manganese acetate, antimony acetate, tetrabutyl titanate, isopropyl titanate, dibutyl tin oxide, dibutyl tin dilaurate, ethylene glycol antimony, antimony trioxide, sodium ethoxide, sodium hydride, sodium amide, benzoyl peroxide.

[0014] Preferably, the preparation method of any one of the water-absorbing and swelling elastomers comprises the following steps:

[0015] S1, reacting an unsaturated polybasic acid or anhydride with a main chain carbon atom number of not more than 6 with a polyol with a main chain carbon atom number of not more than 6 to prepare a cross-linking agent;

[0016] S2, preparing a polyester elastomer by bulk melt copolymerization of the cross-linking agent prepared in S1 and other raw materials.

[0017] Preferably, S1 comprises the following steps:

[0018] S11, putting the polyol with a main chain carbon atom number of not more than 6 into a reaction kettle, rapidly heating to 85-90°C for melting;

[0019] S12, putting the unsaturated polybasic acid or anhydride with a main chain carbon atom number of not more than 6 into the reaction kettle for esterification at 80-90°C;

[0020] S13, adding deionized water, cooling to 0-5°C and placing for 24 hours or more to obtain a white precipitate;

[0021] S14, filtering the obtained white precipitate, vacuum drying to obtain a white solid in powder form, which is the desired cross-linking agent;

[0022] S2 comprises the following steps:

[0023] S21, the raw materials except the crosslinking agent and the esterification catalyst are put into a stainless steel reactor, stirred under nitrogen protection, and rapidly heated to 100-150 DEG C to mix thoroughly;

[0024] S22, gradually heated to 170-190 DEG C for 2-3 hours, and then heated to 200-225 DEG C for reaction, and the reaction is stopped when the esterification rate is greater than 95 %;

[0025] S23, the crosslinking agent prepared in S1 is put into the reactor, and the temperature is controlled at 225-240 DEG C, and the pressure is gradually reduced to below 100 Pa for polycondensation reaction;

[0026] S24, sampling analysis is carried out, the stirring is stopped when the viscosity of the polymer reaches 1 dl / g, the vacuum is eliminated, and the material is discharged under pressure to obtain a water-absorbing elastomer.

[0027] The crosslinking agent used in the application can undergo Michael addition reaction with the tri-ester containing hydrogen atoms in the alpha position, and the crosslinking degree can be controlled through this reaction. The prepared crosslinking agent retains unreacted terminal carboxyl groups, increases the number of hydrophilic groups, facilitates the diffusion of water molecules more easily and faster, and makes the final elastomer have excellent water absorption performance. Meanwhile, the elastomer after water absorption still maintains good structural mechanical properties. DETAILED DESCRIPTION

[0028] The technical scheme of the application is specifically described below with examples, and the application discloses a water-absorbing elastomer and a preparation method thereof.

[0029] The raw materials of the water-absorbing elastomer include polybasic acid and / or anhydride, polyol, soft segment structure monomer, crosslinking agent, and ester monomer. The polybasic acid and / or anhydride includes one or more than one combination of terephthalic acid, isophthalic acid, phthalic acid, and phthalic anhydride. In the application, the polybasic acid and / or anhydride includes the following combinations: polybasic acid, anhydride, combination of polybasic acid and anhydride, and phthalic anhydride as the anhydride of phthalic acid. Generally, when selected, phthalic anhydride and phthalic acid are selected alternatively.

[0030] Further, the polybasic acid and / or anhydride also selectively includes one or more than one combination of 1,4-cyclohexane dicarboxylic acid, adipic acid, sebacic acid, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, itaconic acid, and fumaric acid; and the polyol includes one or more than one arbitrary combination of ethylene glycol, 1,2-propanediol, 1,4-butanediol, neopentyl glycol, and 1,4-cyclohexane dimethanol.

[0031] The cross-linking agent is added in an amount of 1% to 24% (molar ratio) of the total amount of the ester monomer. The elastomer raw material further comprises a catalyst, which includes but is not limited to one or more than one combination of sodium acetate, zinc acetate, manganese acetate, antimony acetate, tetrabutyl titanate, isopropyl titanate, dibutyl tin oxide, dibutyl tin dilaurate, ethylene glycol antimony, antimony trioxide, sodium ethoxide, sodium hydride, sodium amide, and benzoyl peroxide.

[0032] The ester monomer is a tri-ester containing hydrogen atoms in the alpha position, which can include one or more than one combination of triethyl citrate, tripropyl citrate, triethyl methane tricarboxylate, and triethyl 1,1,2-ethane tricarboxylate. The soft segment structure monomer includes one or more than one combination of polyethylene glycol, polypropylene glycol, and polycarbonate diol.

[0033] The cross-linking agent is a product obtained by reacting an unsaturated polybasic acid or anhydride with a main chain carbon atom number of not more than 6 with a polyhydric alcohol with a main chain carbon atom number of not more than 6. The polyhydric alcohol with a main chain carbon atom number of not more than 6 includes one or more than one combination of trimethylolpropane, trihydroxymethylethane, and pentaerythritol. The unsaturated polybasic acid or anhydride with a main chain carbon atom number of not more than 6 includes one or more than one combination of pyromellitic anhydride, maleic anhydride, itaconic acid, and fumaric acid.

[0034] The application further discloses a preparation method of any one of the water-absorbing and swelling elastomers, which comprises the following steps: preparing the cross-linking agent, and preparing the elastomer.

[0035] Trimethylolpropane trimaleic acid monoester

[0036] 1 mol of trimethylolpropane is first put into a reaction kettle, and then rapidly heated to 85-90°C. After the trimethylolpropane is melted, 3 mol of maleic anhydride is put into the reaction kettle, and esterification is performed at 90°C for 4 h. Then, deionized water is added, and the temperature is reduced to 0-5°C for 24 h to obtain white precipitates. The white precipitates are filtered and vacuum dried to obtain white powdery solids, namely the trimethylolpropane trimaleic acid monoester, and the structural formula is as shown in the following formula:

[0037]

[0038] Trimethylolpropane triitaconic acid monoester

[0039] Firstly, 1 mol of trimethylolpropane is put into a reaction kettle, and quickly heated to 85-90℃, after melting, 3 mol of itaconic acid is put into the reaction kettle, and esterification is carried out at 90℃ for 4 hours, then deionized water is added, and the temperature is reduced to 0-5℃ and placed for 24 hours to obtain white precipitate, which is filtered and vacuum dried to obtain white powder, i.e. trimethylolpropane trimaleic acid monoester, and the structure of the trimethylolpropane triitaconic acid monoester is shown as follows:

[0040]

[0041] In the preparation of the water-absorbing and swelling elastomer of the present application, the reaction mechanism and conditions of the crosslinking agent used are basically the same, and the following two crosslinking agents are taken as examples to prepare the water-absorbing and swelling elastomer:

[0042] Example 1:

[0043] 1.95 mol of terephthalic acid, 1.95 mol of isophthalic acid, 0.1 mol of triethyl citrate, 3.6 mol of ethylene glycol, 1.8 mol of neopentyl glycol, 0.6 mol of polyethylene glycol, 0.08 g of tetrabutyl titanate, and 0.10 g of zinc acetate are put into a 2L stainless steel reaction kettle, and stirred at a speed of 100 rpm under nitrogen protection, and after being quickly heated to 100-150℃ and fully mixed, the temperature is gradually increased to 180℃ and reacted for 2 hours, and then the temperature is increased to 200-225℃ and reacted for 2.5 hours, and the reaction is stopped when the esterification rate is >95%.

[0044] In the above reaction kettle, 0.1 mol of trimethylolpropane trimaleic acid monoester and 0.08 g of sodium ethoxide are added, and then the temperature is continuously increased and the pressure is slowly reduced to adjust the speed to 60 rpm, and the temperature is controlled between 225-240℃, and the pressure is gradually reduced to below 100 Pa for polycondensation reaction. When the viscosity of the polymer reaches 1 dl / g, stop stirring, eliminate vacuum, and pressurize to discharge to obtain a polyester elastomer.

[0045] Example 2:

[0046] 1.8 mol of terephthalic acid, 1.8 mol of isophthalic acid, 0.4 mol of triethyl citrate, 3.6 mol of ethylene glycol, 1.8 mol of neopentyl glycol, 0.6 mol of polyethylene glycol, 0.08 g of tetrabutyl titanate, and 0.10 g of zinc acetate are put into a 2L stainless steel reaction kettle, and stirred at a speed of 100 rpm under nitrogen protection, and after being quickly heated to 100-150℃ and fully mixed, the temperature is gradually increased to 180℃ and reacted for 2 hours, and then the temperature is increased to 200-225℃ and reacted for 2.5 hours, and the reaction is stopped when the esterification rate is >95%.

[0047] In the above reaction kettle, 0.4 mol of trimethylolpropane tris-maleic acid monoester and 0.08 g of sodium ethoxide were added, and the temperature was then increased while slowly reducing the pressure to adjust the rotation speed to 60 rpm, with the temperature controlled at 225-240°C, and the polycondensation reaction was carried out by gradually reducing the pressure to below 100 Pa. Sampling analysis was performed, and when the polymer viscosity reached 1 dl / g, the stirring was stopped, the vacuum was eliminated, and the product was discharged by pressurization to obtain a water-absorbing and swelling elastomer.

[0048] Example 3:

[0049] In a 2L stainless steel reaction kettle, 1.5 mol of terephthalic acid, 1.5 mol of isophthalic acid, 1 mol of triethyl citrate, 3.6 mol of ethylene glycol, 1.8 mol of neopentyl glycol, 0.6 mol of polyethylene glycol, 0.08 g of tetrabutyl titanate, and 0.10 g of zinc acetate were added, and stirring was performed at 100 rpm under nitrogen protection, and after rapid heating to 100-150°C to mix thoroughly, the temperature was gradually increased to 180°C for 2 hours, and then to 200-225°C for 2.5 hours, and the reaction was terminated when the esterification rate was >95%.

[0050] In the above reaction kettle, 1 mol of trimethylolpropane tris-itaconic acid monoester and 0.08 g of sodium ethoxide were added, and the temperature was then increased while slowly reducing the pressure to adjust the rotation speed to 60 rpm, with the temperature controlled at 225-240°C, and the polycondensation reaction was carried out by gradually reducing the pressure to below 100 Pa. Sampling analysis was performed, and when the polymer viscosity reached 1 dl / g, the stirring was stopped, the vacuum was eliminated, and the product was discharged by pressurization to obtain a water-absorbing and swelling elastomer.

[0051] Example 4:

[0052] In a 2L stainless steel reaction kettle, 1 mol of terephthalic acid, 1 mol of isophthalic acid, 2 mol of triethyl citrate, 3.6 mol of ethylene glycol, 1.8 mol of neopentyl glycol, 0.6 mol of polyethylene glycol, 0.08 g of tetrabutyl titanate, and 0.10 g of zinc acetate were added, and stirring was performed at 100 rpm under nitrogen protection, and after rapid heating to 100-150°C to mix thoroughly, the temperature was gradually increased to 180°C for 2 hours, and then to 200-225°C for 2.5 hours, and the reaction was terminated when the esterification rate was >95%.

[0053] In the above reaction kettle, 2 mol of trimethylolpropane tris-maleic acid monoester and 0.08 g of sodium ethoxide were added, and the temperature was then increased while slowly reducing the pressure to adjust the rotation speed to 60 rpm, with the temperature controlled at 225-240°C, and the polycondensation reaction was carried out by gradually reducing the pressure to below 100 Pa. Sampling analysis was performed, and when the polymer viscosity reached 1 dl / g, the stirring was stopped, the vacuum was eliminated, and the product was discharged by pressurization to obtain a water-absorbing and swelling elastomer.

[0054] Example 5: 1 mol of terephthalic acid, 1 mol of isophthalic acid, 2 mol of triethyl citrate, 3.6 mol of ethylene glycol, 1.8 mol of neopentyl glycol, 0.6 mol of polyethylene glycol, 0.08 g of tetrabutyl titanate, and 0.10 g of zinc acetate were put into a 2-L stainless steel reaction vessel, and stirred at 100 rpm under nitrogen. After mixing sufficiently by rapid heating to 100-150°C, the temperature was gradually increased to 180°C, and the reaction was carried out for 2 hours. Then, the temperature was increased to 200-225°C, and the reaction was carried out for 2.5 hours. When the esterification rate was more than 95%, the reaction was terminated.

[0055] After 2 mol of trimethylolpropane tricottonate and 0.08 g of sodium ethoxide were added to the above reaction vessel, the temperature was further increased, and the pressure was slowly reduced while the rotation speed was adjusted to 60 rpm. The condensation reaction was carried out at 225-240°C under a pressure of less than 100 Pa. When the viscosity of the polymer reached 1 dl / g, the stirring was stopped, the vacuum was eliminated, and the product was discharged by pressurization to obtain a water-absorbing and swelling elastomer.

[0056] Example 6: 0.8 mol of terephthalic acid, 0.8 mol of isophthalic acid, 2.4 mol of triethyl citrate, 3.6 mol of ethylene glycol, 1.8 mol of neopentyl glycol, 0.6 mol of polyethylene glycol, 0.08 g of tetrabutyl titanate, and 0.10 g of zinc acetate were put into a 2-L stainless steel reaction vessel, and stirred at 100 rpm under nitrogen. After mixing sufficiently by rapid heating to 100-150°C, the temperature was gradually increased to 180°C, and the reaction was carried out for 2 hours. Then, the temperature was increased to 200-225°C, and the reaction was carried out for 2.5 hours. When the esterification rate was more than 95%, the reaction was terminated.

[0057] After 2.4 mol of trimethylolpropane tricottonate and 0.08 g of sodium ethoxide were added to the above reaction vessel, the temperature was further increased, and the pressure was slowly reduced while the rotation speed was adjusted to 60 rpm. The condensation reaction was carried out at 225-240°C under a pressure of less than 100 Pa. When the viscosity of the polymer reached 1 dl / g, the stirring was stopped, the vacuum was eliminated, and the product was discharged by pressurization to obtain a water-absorbing and swelling elastomer.

[0058] Comparative Example 1-1:

[0059] This comparative example provides a water-absorbing and swelling polyester elastomer in which a crosslinking agent is added at the same time as other raw materials (radical polymerization occurs). The preparation method is as follows:

[0060] Put 1 mol of terephthalic acid, 1 mol of isophthalic acid, 2 mol of trimethylolpropane trimaleate monoester, 3.6 mol of ethylene glycol, 1.8 mol of neopentyl glycol, 0.6 mol of polyethylene glycol, 0.08 g of tetrabutyl titanate, 0.10 g of zinc acetate, and 0.10 g of benzoyl peroxide into a 2L stainless steel reaction kettle, and stir at a speed of 100 rpm under nitrogen protection. After rapid heating to 100-150°C and fully mixing, gradually heat to 180°C and react for 2 hours, then heat to 200-225°C and react for 2.5 hours. When the esterification rate is >95%, stop the reaction. Continue to heat and slowly reduce the pressure to adjust the speed to 60 rpm, and control the temperature at 225-240°C. Gradually reduce the pressure to below 100 Pa to perform the polycondensation reaction. Take a sample for analysis, and when the viscosity of the polymer reaches 1 dl / g, stop stirring, eliminate the vacuum, and pressurize to discharge the material to obtain a water-absorbing and swelling elastomer.

[0061] Comparative Example 1-2

[0062] This comparative example has the same formulation and reaction time as Comparative Example 1-1.

[0063] Comparative Example 1-3

[0064] This comparative example has the same formulation and reaction time as Comparative Example 1-1.

[0065] Performance Test

[0066] The polyester elastomers obtained in Example 1-6 and the comparative examples were tested for performance according to relevant standards:

[0067] 1. IV (Intrinsic Viscosity): GB / T 14190-2008 Test Methods for Fiber Grade Polyester Chips (PET).

[0068] 2. Tensile Strength: The tensile strength was tested according to GB / T 528-2009.

[0069] 3. Elongation at Break: The elongation at break was tested according to GB / T 528-2009.

[0070] 4. Water Immersion: The test sample was placed in deionized water at room temperature for 72 hours, and the tensile strength and elongation at break were measured again to calculate the tensile strength retention rate and elongation at break retention rate.

[0071] 5. Volume Expansion Rate Test: Tested according to GB / T 18173.3-2014 Appendix A.

[0072] The results are shown in the following table:

[0073]

[0074]

[0075] Generally, the cross-linking degree of the elastomer increases with the increase of the cross-linking agent, the internal network points of the elastomer structure increase, and the water absorption increases, but if the cross-linking degree is too high, the internal space of the structure is greatly reduced, the elastomer cannot absorb water and swell, and the water absorption rate decreases; therefore, the controllable cross-linking degree is particularly important.

[0076] As can be seen from the examples and comparative examples, the controllable cross-linking degree not only makes the water absorption controllable, but also makes the mechanical properties of the elastomer after water absorption controllable. Comparative example 1-1, comparative example 1-2 and comparative example 1-3 demonstrate the importance of the controllable cross-linking degree. The cross-linking agent product described in the application has abundant unsaturated double bonds, which not only can react as a cross-linking agent, but also contains end carboxyl groups, which can increase the number of hydrophilic groups, and is conducive to the easier and faster diffusion of water molecules.

[0077] The application further utilizes the Michael addition method to graft the cross-linking agent into the elastomer structure, and realizes the controllable cross-linking degree by controlling the amount of the cross-linking agent, so that the final product has good water absorption performance and still maintains good mechanical properties after water absorption.

[0078] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the application, but not to limit it; although the application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the application.

Claims

1. A water-swellable elastomer, characterized in that: The elastomer raw materials include polyacids and / or anhydrides, polyols, soft segment structural monomers, crosslinking agents, and ester monomers. The polyacids and / or anhydrides include one or more of terephthalic acid, isophthalic acid, phthalic acid, and phthalic anhydride. The crosslinking agent is a product obtained by reacting an unsaturated polyacid or anhydride having no more than 6 carbon atoms in the main chain with a polyol having no more than 6 carbon atoms in the main chain. The ester monomer is a tribasic ester containing a hydrogen atom at the a position. The crosslinking agent is trimethylolpropane trimaleate or trimethylolpropane triitaconate. The soft segment structural monomers include polyethylene glycol and polypropylene glycol. The elastomer raw materials also include a catalyst, which includes sodium ethoxide. The ester monomer includes one or more of triethyl citrate, tripropyl citrate, methanetricarboxylic acid triethyl ester, and 1,1,2-ethanetricarboxylic acid triethyl ester. The added amounts of the crosslinking agent and the ester monomer are both 1% to 24% of the total feed amount by molar ratio.

2. The water-swellable elastomer according to claim 1, characterized in that: The polyacid and / or anhydride also includes one or more combinations of 1,4-cyclohexanedicarboxylic acid, adipic acid, sebacic acid, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, itaconic acid, and fumaric acid; the polyol includes one or more combinations of ethylene glycol, 1,2-propylene glycol, 1,4-butanediol, neopentyl glycol, and 1,4-cyclohexanedimethanol.

3. The method for preparing a water-swellable elastomer according to any one of claims 1 to 2, wherein: The steps include: S1, reacting an unsaturated polyacid or anhydride having a main chain carbon number not exceeding 6 with a polyol having a main chain carbon number not exceeding 6 to prepare a crosslinking agent; S2. The cross-linking agent prepared in S1 is reacted with other raw materials through bulk melt copolymerization to obtain a polyester elastomer.

4. The method for preparing a water-swellable elastomer according to claim 3, wherein: The S1 comprises the following steps: S11, adding a polyol having a main chain carbon number of not more than 6 into a reaction kettle, and rapidly heating it to 85-90°C for melting; S12, adding an unsaturated polyacid or anhydride having a main chain carbon number of not more than 6 into a reaction kettle and esterifying at 80-90°C; S13, add deionized water, cool to 0-5°C and let stand for more than 24 hours to obtain a white precipitate; S14, filtering the obtained white precipitate and vacuum drying to obtain a powdery white solid which is the desired cross-linking agent; The S2 comprises the following steps: S21, adding the raw materials except the cross-linking agent and the esterification catalyst into a stainless steel reactor, stirring under nitrogen protection and rapidly heating to 100-150° C. for thorough mixing; S22, gradually raising the temperature to 170-190°C and reacting for 2-3 hours, then raising the temperature to 200-225°C and continuing the reaction. The reaction is terminated when the esterification rate is greater than 95%; S23, adding the cross-linking agent prepared in S1 into the reactor, continuing to heat and stir while slowly reducing the pressure, controlling the temperature between 225 and 240°C, and gradually reducing the pressure to below 100 Pa to carry out polycondensation reaction; S24. Take samples for analysis. When the polymer viscosity reaches 1 dl / g, stop stirring, eliminate the vacuum, and pressurize the material to obtain a water-swellable elastomer.

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