Colorless transparent liquid rubber and preparation method thereof

Abstract

The invention relates to colorless transparent liquid rubber and a preparation method thereof, and the preparation method comprises the following steps: adding an olefin monomer, a structure regulator and a non-polar organic solvent into a reaction container, uniformly stirring, adding an initiator, and carrying out an anionic polymerization reaction; the molar ratio of the structure regulator to the initiator is (0.5-10): 1; after the reaction is finished, monocarboxylic acid with the carbon atom number of 4-8 is added as a terminator, and the molar ratio of the monocarboxylic acid to the initiator is (1.1-1.2): 1; adding an antioxidant; and removing the solvent in the reaction system to obtain colorless and transparent liquid rubber. Compared with the prior art, the method has the advantages that after the anionic polymerization initiated by the lithium salt is finished, the monocarboxylic acid is directly added into the polymerization reaction solution for termination, a colorless and transparent liquid rubber product is successfully prepared, and after the liquid rubber is aged at a certain temperature, the appearance of the liquid rubber is still clear and transparent.

Description

Technical Field

[0001] This invention belongs to the field of synthetic rubber technology, and in particular relates to a colorless and transparent liquid rubber and its preparation method. Background Technology

[0002] Liquid rubber generally has an average molecular weight between 500 and 100,000 and is an oligomer that is a viscous, flowing liquid at room temperature. Compared to traditional rubber products, liquid rubber has advantages such as good flowability, ease of processing, and continuous production, and is known as the "new generation of gold rubber." It is mainly used in the production of cast elastomers, aerospace seals, adhesives, high-performance tires, potting materials, waterproof and anti-corrosion materials, and integrated circuit packaging. Among them, diene-based liquid rubbers (liquid polybutadiene, styrene-butadiene, and isoprene rubbers) account for more than 70% of the liquid rubber market share.

[0003] The main production methods for liquid rubber include free radical polymerization and anionic polymerization. Free radical polymerization produces liquid rubber with low 1,2-vinyl content and relatively low purity, while anionic polymerization can produce liquid rubber with a vinyl content of over 80%. The initiators used are generally organometallic compounds, with butyllithium being the most widely used industrially. Because anionic polymerization is a living initiator, a terminator must be added after the reaction; otherwise, coupling between active macromolecules will occur, leading to an increase in polymer molecular weight. Commonly used terminators are polar compounds such as water or alcohols (e.g., ethanol, methanol, isopropanol). However, when water or alcohol is used for termination, it reacts with organolithium compounds to form lithium hydroxide or alkoxylithium. This can cause the liquid rubber to turn yellow, and the lithium hydroxide or alkyllithium can form insoluble microparticles in the liquid rubber, making it opaque and affecting its appearance. These insoluble microparticles can also affect downstream processing applications. In addition, lithium hydroxide and alkoxylithium are highly alkaline and can react with antioxidants, affecting their anti-aging properties. This leads to changes in the properties of liquid rubber during heating, storage, and use, especially yellowing, which greatly limits the product's application range. Therefore, it is necessary to remove lithium hydroxide or alkoxylithium from the product, or select appropriate terminators to ensure that the reaction product with alkyllithium is colorless and does not harm the product's performance.

[0004] Patent US6222008 discloses a method for removing residual catalysts from hydrogenated liquid diene rubber by contacting an aqueous solution of water and carbon dioxide or an inorganic acid (such as phosphoric acid, sulfuric acid, etc.) with the rubber solution followed by the addition of ammonia. This method requires extraction and centrifugation, and necessitates heating water to agglomerate the rubber, making the process cumbersome and energy-intensive. Patent US4136088 reports a method for extracting catalyst residues by adding an aqueous solution of isopropanol; this method also suffers from low production efficiency and cumbersome solvent recovery. Patent US4595749 discloses a method for removing metal catalysts using an oxidant and dicarboxylic acid, where the dicarboxylic acid is dissolved in toluene, resulting in environmental pollution and difficulty in solvent recovery. Furthermore, this method requires overnight settling of the solution for catalyst separation, leading to low production efficiency. CN102702408A discloses a method for preparing diene-based liquid rubber, proposing that adding a straight-chain organic diacid or a solution of a straight-chain organic diacid to the polymerization system after the polymerization reaction can effectively improve the color of the liquid diene rubber. However, the straight-chain organic diacids used in this method are all solids, and they all need to be dissolved in solvents such as water, polar solvents, or a mixture of polar and non-polar solvents before use. Anionic polymerization generally uses non-polar solvents for polymerization. Using this method for termination requires dissolving the organic diacid into a liquid first. Therefore, water and other polar solvents will be introduced during the termination process, increasing the difficulty of post-processing of the liquid rubber. Moreover, after termination with a diacid, when the amount of catalyst is large, the formed lithium dicarboxylic acid is a solid particle that will be suspended in the liquid rubber, affecting the transparency of the liquid rubber.

[0005] Therefore, in view of the problems existing in the above-mentioned technologies, a new method for preparing liquid rubber is still needed to obtain colorless and transparent liquid rubber with no significant change in appearance after aging. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies, such as low production efficiency and difficulty in ensuring the transparency of liquid rubber, by providing a colorless and transparent liquid rubber and its preparation method.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] This invention provides a method for preparing a colorless and transparent liquid rubber, comprising the following steps:

[0009] S1: Add olefin monomers, structure modifiers, and nonpolar organic solvents to a reaction vessel, stir until homogeneous, and then add an initiator to carry out anionic polymerization; the molar ratio of the structure modifier to the olefin monomer is (0.5-10):1;

[0010] S2: After the reaction is complete, add a monocarboxylic acid with 4-8 carbon atoms as a terminator. The molar ratio of the monocarboxylic acid to the initiator is (1.1-1.2):1.

[0011] S3: Add antioxidant; then remove the solvent from the reaction system to obtain a colorless and transparent liquid rubber with a number average molecular weight of 500-50000.

[0012] Further, in step S1, the concentration of the olefin monomer is 5-30 wt%.

[0013] Furthermore, the reaction temperature of the anionic polymerization reaction is 10-150℃, and the reaction time is 20-120 min.

[0014] Further, in step S1, the olefin monomer includes one or more of butadiene, styrene, or isoprene, preferably butadiene.

[0015] Further, in step S1, the initiator includes one or more of n-butyllithium, sec-butyllithium, isobutyllithium, and tert-butyllithium, preferably n-butyllithium.

[0016] Further, in step S1, the structure modifier includes one or more of ethers, amines, or organometallic compounds.

[0017] Furthermore, the ethers include one or more of 2,2-(2-tetrahydrofuranyl)propane, diethyl ether, di-n-propyl ether, diisopropyl ether, di-n-butyl ether, tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, or triethylene glycol dimethyl ether.

[0018] Furthermore, the amines include one or more of trimethylamine, triethylamine, N,N,N,N-tetramethylethylenediamine, N-methylmorpholine, N-ethylmorpholine, N-phenylmorpholine, or hexamethylphosphophthalimide.

[0019] Furthermore, the organometallic compound includes one or more of sodium tetrahydrofuranol, sodium pentooxy, sodium tert-pentoxy, sodium menthol, potassium tert-butoxy, or barium 2-ethylhexyloxy.

[0020] Further, in step S1, the nonpolar organic solvent includes one or more of cyclopentane, cyclohexane, n-hexane, n-pentane, n-heptane, raffinate oil, or hydrogenated gasoline, preferably cyclopentane.

[0021] Further, in step S2, the monocarboxylic acid includes one or more of butyric acid, 2-methylpropionic acid, valeric acid, 2-methylbutyric acid, 3-methylbutyric acid, hexanoic acid, 2-methylvaleric acid, 3-methylvaleric acid, 4-methylvaleric acid, heptanoic acid, 2-methylhexanoic acid, 2-ethylhexanoic acid, 3-methylhexanoic acid, 4-methylhexanoic acid, 5-methylhexanoic acid, or octanoic acid.

[0022] Furthermore, in step S2, the mixing and contact time between the monocarboxylic acid and the polymerization product is not less than 1 minute.

[0023] This invention terminates the polymerization reaction after lithium-based anionic polymerization by directly adding a C4-C8 monocarboxylic acid (CCA), not limited to straight-chain CCAs but including branched CCAs, to the polymerization reaction solution. This effectively terminates the polymerization reaction without affecting the effectiveness of the antioxidant in the liquid rubber. The monocarboxylic acid must have at least 4 carbon atoms. Carboxylic acids with fewer than 4 carbon atoms are too acidic, resulting in relatively strong basic lithium carboxylate, which significantly impacts the antioxidant. Conversely, monocarboxylic acids with more than 8 carbon atoms are too weakly acidic, resulting in poor termination and a higher likelihood of lithium carboxylate precipitation, requiring a longer termination time. Furthermore, the addition of the monocarboxylic acid must be carried out under inert gas protection, and the amount added should be 1.1-1.2 times the molar amount of the initiator in the reaction system. Insufficient addition of the monocarboxylic acid will not achieve the termination effect; while excessive addition will result in too much residual monocarboxylic acid in the liquid rubber, affecting its viscosity and other properties.

[0024] Further, in step S3, the antioxidant includes one or more of 2,4-bis(n-octylthimethylene)-6-methylphenol, 2,6-di-tert-butyl-p-methylphenol, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl) phosphite, octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, tris(2,4-di-tert-butylphenyl) phosphite, 2,6-di-tert-butyl-p-cresol, tert-butylcatechol, and 2,2'-methylene-bis(4-methyl-6-tert-butylphenol), preferably 2,4-bis(n-octylthimethylene)-6-methylphenol.

[0025] Further, in step S3, the amount of antioxidant added is 0.05-2 wt% of the amount of olefin monomer added.

[0026] Furthermore, in step S3, the solvent in the polymer solution is removed by vacuum distillation.

[0027] The present invention also provides a colorless and transparent liquid rubber prepared by the above preparation method.

[0028] Furthermore, the liquid rubber remains colorless and transparent even after being heated and aged at 60-80℃ for 4-6 hours.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) After the anionic polymerization initiated by lithium salt is completed, the present invention terminates the polymerization reaction by directly adding a monocarboxylic acid containing a certain carbon chain to the polymerization reaction solution, and successfully obtains a colorless and transparent liquid rubber product. After aging at a certain temperature, the appearance of the liquid rubber remains clear and transparent.

[0031] (2) The monocarboxylic acid added after polymerization can include straight-chain or branched carboxylic acids, which can effectively terminate the polymerization reaction without affecting the effect of antioxidants in liquid rubber; and the number of carbon atoms and the amount added of the monocarboxylic acid must be within a certain range in order to achieve both a good polymerization reaction termination effect and a colorless and transparent appearance.

[0032] (3) This invention provides a simple, fast and effective method for terminating anionic polymerization. After termination, it does not harm the performance of the product and is colorless in appearance. The terminating agent is readily available, inexpensive, and easy to transport in industrial applications.

[0033] (4) The present invention does not require the organic monocarboxylic acid to be dissolved into liquid in advance. After the monocarboxylic acid is added to the polymer reaction solution, no particulate matter will be formed suspended in the liquid rubber. The liquid rubber as a whole is clear and transparent, which will not affect the downstream processing and application of the colorless and transparent liquid rubber.

[0034] (5) The post-polymerization treatment method of the present invention does not require heating water to agglomerate the rubber, nor does it require complex catalyst separation, extraction and other processes. It only requires adding a monocarboxylic acid directly to the reaction liquid system to terminate the reaction and adding an antioxidant to prevent aging. The operation is simple and greatly improves production efficiency. Attached Figure Description

[0035] Figure 1 This is the GPC spectrum of the liquid rubber prepared in Example 1 of the present invention.

[0036] Figure 2 This is an image of the appearance of the liquid rubber sample after aging, prepared in Example 1 of the present invention.

[0037] Figure 3 This is an image of the aged liquid rubber sample prepared in Comparative Example 1.

[0038] Figure 4 The image shows the appearance of the liquid rubber sample prepared in Comparative Example 2.

[0039] Figure 5 The image shows the GPC spectrum of the liquid rubber prepared in Comparative Example 3. Detailed Implementation

[0040] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0041] Unless otherwise specified, the reagents, methods, instruments, and equipment used in this invention are conventional in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0042] In the following embodiments, the butadiene used is 1,3-butadiene; the structure modifier used is 2,2-(2-tetrahydrofuranyl)propane, abbreviated as DTHFP; and the catalyst used is n-butyllithium.

[0043] Example 1:

[0044] This embodiment provides a colorless and transparent liquid rubber, and the specific preparation method is as follows:

[0045] Under high-purity nitrogen protection, 900 g of cyclohexane and 100 g of butadiene were added to a 2 L polymerization reactor, followed by 16.6 mmol of 2,2-(2-tetrahydrofuranyl)propane, and the mixture was stirred for 10 min. The reactor temperature was maintained at 25 °C, and then 16.6 mmol of n-butyllithium was added. The polymerization reaction was maintained at 25 °C for 60 min. After polymerization, 18.3 mmol of hexanoic acid was added to terminate the reaction for 20 min, followed by 1 g of the antioxidant 2,4-bis(n-octylthionyl)-6-methylphenol. The polymerization mixture was then subjected to vacuum distillation to obtain a colorless and transparent liquid polybutadiene product.

[0046] The final liquid polybutadiene was sampled and characterized for molecular weight and molecular weight distribution by gel permeation chromatography (GPC). Figure 1 As shown, the liquid rubber prepared in this embodiment has a number-average molecular weight of 6500 and a dispersibility coefficient of 1.01.

[0047] like Figure 2 As shown, an appropriate amount of the above liquid polybutadiene rubber was placed in a 70°C oven for aging for 5 hours, and the liquid polybutadiene rubber still appeared colorless and transparent.

[0048] Example 2:

[0049] This embodiment provides a colorless and transparent liquid rubber, and the specific preparation method is as follows:

[0050] Under high-purity nitrogen protection, 900g of cyclohexane and 100g of butadiene were added to a 2L polymerization reactor, followed by 16.6mmol of 2,2-(2-tetrahydrofuranyl)propane, and the mixture was stirred for 10 minutes. The reactor temperature was maintained at 25°C, and then 16.6mmol of n-butyllithium was added. During the polymerization reaction, the temperature was maintained at 25°C for 60 minutes. After polymerization, 19.1mmol of hexanoic acid was added to terminate the reaction for 10 minutes, followed by 1g of the antioxidant 2,4-bis(n-octylthionyl)-6-methylphenol. The polymerization mixture was then subjected to vacuum distillation to obtain a colorless and transparent liquid polybutadiene product. An appropriate amount of the above liquid polybutadiene rubber was placed in an 80°C oven for aging for 6 hours, and the liquid polybutadiene rubber remained colorless and transparent.

[0051] Example 3:

[0052] This embodiment provides a colorless and transparent liquid rubber, and the specific preparation method is as follows:

[0053] Under high-purity nitrogen protection, 900g of cyclohexane and 100g of butadiene were added to a 2L polymerization reactor, followed by 16.6mmol of 2,2-(2-tetrahydrofuranyl)propane, and the mixture was stirred for 10 minutes. The reactor temperature was maintained at 25°C, and then 16.6mmol of n-butyllithium was added. During the polymerization reaction, the temperature was maintained at 25°C for 60 minutes. After polymerization, 19.9mmol of hexanoic acid was added to terminate the reaction for 3 minutes, followed by 1g of the antioxidant 2,4-bis(n-octylthionyl)-6-methylphenol. The polymerization mixture was then subjected to vacuum distillation to obtain a colorless and transparent liquid polybutadiene product. An appropriate amount of the above liquid polybutadiene rubber was placed in an 85°C oven for aging for 4 hours, and the liquid polybutadiene rubber remained colorless and transparent.

[0054] Example 4:

[0055] This embodiment provides a colorless and transparent liquid rubber, and the specific preparation method is as follows:

[0056] Under high-purity nitrogen protection, 900g of cyclohexane and 100g of butadiene were added to a 2L polymerization reactor, followed by 16.6mmol of 2,2-(2-tetrahydrofuranyl)propane, and the mixture was stirred for 10 minutes. The reactor temperature was maintained at 25°C, and then 16.6mmol of n-butyllithium was added. During the polymerization reaction, the temperature was maintained at 25°C for 60 minutes. After polymerization, 19.9mmol of butyric acid was added to terminate the reaction for 3 minutes, followed by 1g of the antioxidant 2,4-bis(n-octylthionyl)-6-methylphenol. The polymerization mixture was then subjected to vacuum distillation to obtain a colorless and transparent liquid polybutadiene product. An appropriate amount of the above liquid polybutadiene rubber was placed in an 80°C oven for aging for 4 hours, and the liquid polybutadiene rubber remained colorless and transparent.

[0057] Example 5:

[0058] This embodiment provides a colorless and transparent liquid rubber, and the specific preparation method is as follows:

[0059] Under high-purity nitrogen protection, 900g of cyclohexane and 100g of butadiene were added to a 2L polymerization reactor, followed by 16.6mmol of 2,2-(2-tetrahydrofuranyl)propane, and the mixture was stirred for 10 minutes. The reactor temperature was maintained at 25°C, and then 16.6mmol of n-butyllithium was added. During the polymerization reaction, the temperature was maintained at 25°C for 60 minutes. After polymerization, 19.9mmol of octanoic acid was added to terminate the reaction for 3 minutes, followed by 1g of the antioxidant 2,4-bis(n-octylthionyl)-6-methylphenol. The polymerization mixture was then subjected to vacuum distillation to obtain a colorless and transparent liquid polybutadiene product. An appropriate amount of the above liquid polybutadiene rubber was placed in an 80°C oven for aging for 5 hours, and the liquid polybutadiene rubber remained colorless and transparent.

[0060] Example 6:

[0061] This embodiment provides a colorless and transparent liquid rubber, and the specific preparation method is as follows:

[0062] Under high-purity nitrogen protection, 900g of cyclohexane and 100g of butadiene were added to a 2L polymerization reactor, followed by 16.6mmol of 2,2-(2-tetrahydrofuranyl)propane, and the mixture was stirred for 10 minutes. The reactor temperature was maintained at 25°C, and then 16.6mmol of n-butyllithium was added. During the polymerization reaction, the temperature was maintained at 25°C for 60 minutes. After polymerization, 19mmol of 2-methylhexanoic acid was added to terminate the reaction for 3 minutes, followed by 1g of the antioxidant 2,4-di(n-octylthionyl)-6-methylphenol. The polymerization mixture was then subjected to vacuum distillation to obtain a colorless and transparent liquid polybutadiene product. An appropriate amount of the above liquid polybutadiene rubber was placed in an 80°C oven for aging for 5 hours, and the liquid polybutadiene rubber remained colorless and transparent.

[0063] Comparative Example 1:

[0064] This comparative example provides a liquid rubber, and the specific preparation method is as follows:

[0065] Polymer preparation was performed using the anionic polymerization method described in Example 1. The difference was that after polymerization, 19.9 mmol of propionic acid was added to terminate the polymerization for 3 minutes, followed by the addition of 1 g of antioxidant 2,4-bis(n-octylthionyl)-6-methylphenol. The polymerization mixture was then subjected to vacuum distillation to obtain a colorless, transparent liquid polybutadiene product. An appropriate amount of the above liquid polybutadiene rubber was placed in an 80°C oven for 5 hours. Figure 3 As shown, the liquid polybutadiene rubber has a yellowish appearance and is no longer a colorless and transparent liquid rubber.

[0066] Comparative Example 2:

[0067] This comparative example provides a liquid rubber, and the specific preparation method is as follows:

[0068] The polymer was prepared according to the anionic polymerization method described in Example 1. The difference was that after polymerization, 19 mmol of nonanoic acid was added to terminate the polymerization for 3 minutes, followed by the addition of 1 g of the antioxidant 2,4-bis(n-octylthionyl)-6-methylphenol. The polymerization mixture was then subjected to vacuum distillation. Figure 4 As shown, the obtained liquid polybutadiene product is translucent. Because the carbon chain of nonanoic acid is too long, lithium nonanoate precipitate is formed, which makes the sample appear translucent and prevents the formation of colorless and transparent liquid rubber.

[0069] Comparative Example 3:

[0070] This comparative example provides a liquid rubber, and the specific preparation method is as follows:

[0071] The polymer was prepared using the anionic polymerization method described in Example 1. The difference was that after polymerization, 16.6 mmol of hexanoic acid was added to terminate the polymerization for 3 min, followed by the addition of 1 g of antioxidant 2,4-bis(n-octylthiomethylene)-6-methylphenol. The polymerization mixture was then subjected to vacuum distillation to obtain a colorless and transparent liquid polybutadiene product.

[0072] The liquid rubber product finally obtained in this comparative example was subjected to GPC testing. Figure 5 As shown, the results revealed a small number of macromolecular peaks in the GPC spectrum, indicating that the amount of monocarboxylic acid added was insufficient, resulting in incomplete termination and coupling between active molecules.

[0073] In summary, this invention, after the anionic polymerization initiated by lithium salts, terminates the polymerization reaction by directly adding a monocarboxylic acid containing a certain carbon chain to the polymerization solution, successfully producing a colorless and transparent liquid rubber product. Furthermore, after aging at a certain temperature, the liquid rubber retains its clear and transparent appearance. Monocarboxylic acid, as an effective terminator, can effectively stop the polymerization reaction without affecting the effectiveness of antioxidants in the liquid rubber; moreover, the number of carbon atoms and the amount of monocarboxylic acid added must be within a certain range to achieve both a good polymerization termination effect and a colorless and transparent appearance.

[0074] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a colorless and transparent liquid rubber, characterized in that, Includes the following steps: S1: Add olefin monomers, structure modifiers, and nonpolar organic solvents to a reaction vessel, stir until homogeneous, and then add an initiator to carry out anionic polymerization; the molar ratio of the structure modifier to the initiator is (0.5-10):1; S2: After the reaction is complete, add a monocarboxylic acid with 4-8 carbon atoms as a terminator. The molar ratio of the monocarboxylic acid to the initiator is (1.1-1.2):

1. S3: Add antioxidant; then remove the solvent from the reaction system to obtain a colorless and transparent liquid rubber with a number average molecular weight of 500-50000.

2. The method for preparing a colorless and transparent liquid rubber according to claim 1, characterized in that, In step S1, the concentration of the olefin monomer is 5-30 wt%. The anionic polymerization reaction is carried out at a temperature of 10-150℃ for a time of 20-120 min.

3. The method for preparing a colorless and transparent liquid rubber according to claim 1, characterized in that, In step S1, the olefin monomer includes one or more of butadiene, styrene, or isoprene; The initiator includes one or more of n-butyllithium, sec-butyllithium, isobutyllithium, and tert-butyllithium.

4. The method for preparing a colorless and transparent liquid rubber according to claim 1, characterized in that, In step S1, the structure modifier includes one or more of ethers, amines, or organometallic compounds; The ethers include one or more of 2,2-(2-tetrahydrofuranyl)propane, diethyl ether, di-n-propyl ether, diisopropyl ether, di-n-butyl ether, tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, or triethylene glycol dimethyl ether; The amines include one or more of trimethylamine, triethylamine, N,N,N,N-tetramethylethylenediamine, N-methylmorpholine, N-ethylmorpholine, N-phenylmorpholine, or hexamethylphosphophthalimide; The organometallic compound includes one or more of sodium tetrahydrofuranol, sodium pentooxy, sodium tert-pentoxy, sodium menthol, potassium tert-butoxy, or barium 2-ethylhexyloxy.

5. The method for preparing a colorless and transparent liquid rubber according to claim 1, characterized in that, In step S1, the nonpolar organic solvent includes one or more of cyclopentane, cyclohexane, n-hexane, n-pentane, n-heptane, raffinate oil, or hydrogenated gasoline.

6. The method for preparing a colorless and transparent liquid rubber according to claim 1, characterized in that, In step S2, the monocarboxylic acid includes one or more of butyric acid, 2-methylpropionic acid, valeric acid, 2-methylbutyric acid, 3-methylbutyric acid, hexanoic acid, 2-methylvaleric acid, 3-methylvaleric acid, 4-methylvaleric acid, heptanoic acid, 2-methylhexanoic acid, 2-ethylhexanoic acid, 3-methylhexanoic acid, 4-methylhexanoic acid, 5-methylhexanoic acid, or octanoic acid.

7. The method for preparing a colorless and transparent liquid rubber according to claim 1, characterized in that, In step S2, the mixing and contact time between the monocarboxylic acid and the polymerization product is not less than 1 minute.

8. The method for preparing a colorless and transparent liquid rubber according to claim 1, characterized in that, In step S3, the antioxidant includes one or more of the following: 2,4-bis(n-octylthionyl)-6-methylphenol, 2,6-di-tert-butyl-p-methylphenol, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl) phosphite, octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, tris(2,4-di-tert-butylphenyl) phosphite, 2,6-di-tert-butyl-p-cresol, tert-butylcatechol, and 2,2'-methylenebis(4-methyl-6-tert-butylphenol).

9. The method for preparing a colorless and transparent liquid rubber according to claim 1, characterized in that, In step S3, the amount of antioxidant added is 0.05-2 wt% of the amount of olefin monomer added.

10. A colorless and transparent liquid rubber prepared by any one of the preparation methods of claims 1-9.

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