Process for the cleavage of low and medium molecular weight carboxylic rubber with terminal aldehyde groups

Abstract

The scheme provides a cleavage method of low molecular weight aldehyde carboxyl rubber, which comprises the following steps: dissolving rubber in an organic solvent to obtain a rubber solution; heating the rubber solution, adding sodium metavanadate solution and mixing uniformly to obtain a mixed solution; adding hydrogen peroxide drop by drop into the mixed solution until the cleavage reaction is completed to obtain a reaction solution, wherein the molar ratio of the total amount of hydrogen peroxide to the carbon-carbon double bond in the rubber is (1.2-2.5):1; and treating the reaction solution to obtain low molecular weight aldehyde carboxyl rubber. The method can reduce the cost, improve the environmental protection, significantly improve the functional group content and reaction efficiency of the product, and provide a better choice for the large-scale production and application of low molecular weight aldehyde carboxyl rubber.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fine polymer chemicals and its manufacturing, in particular to a cracking method of low-molecular-weight terminal aldehyde carboxyl rubber with aldehyde group or carboxyl group or hydroxyl group at the chain end. BACKGROUND

[0002] Liquid rubber with terminal functional groups (such as aldehyde group, carboxyl group, hydroxyl group, etc.) has become a research hotspot in the field of fine polymer chemicals due to its wide application in adhesives, sealants, composites and other fields. Its preparation methods mainly include free radical polymerization, anionic polymerization, ring-opening metathesis polymerization (ROMP) and high polymer degradation, etc. However, each preparation method has its limitations:

[0003] Free radical polymerization is divided into free radical solution polymerization and free radical emulsion polymerization. Free radical solution polymerization requires the use of bifunctional initiators (such as ACVA, peroxypentanedioic acid), the reaction temperature is relatively high (70-115℃), the product molecular weight distribution is wide (1.5-2.1), and the microstructure is mainly 1,4-addition, which limits the performance adjustment of the material. For example, Sibert et al. prepared carboxyl-terminated polybutadiene by free radical solution polymerization of butadiene using 4,4-azo-bis-(4-cyanopentanoic acid) (ACVA) as initiator and tert-butyl alcohol as solvent, the reaction temperature was 70℃ and 80℃, the product molecular weight was 2000-5000, and the molecular weight distribution was 1.5-2.1. For another example, Niu Weidong et al. prepared carboxyl-terminated polybutadiene liquid rubber by free radical solution polymerization using peroxypentanedioic acid as initiator and anhydrous ethanol or acetone as solvent, the polymerization temperature was 105-115℃, the product molecular weight decreased with increasing polymerization temperature, and the butadiene unit in the molecular chain was mainly 1,4-addition structure. Although free radical emulsion polymerization has low cost and is easy to operate continuously, the product is mainly trans-1,4 structure, has high viscosity, poor low temperature resistance, and non-uniform crosslinking network, which is not conducive to subsequent application.

[0004] Anionic polymerization uses alkali metal as initiator to initiate butadiene polymerization, and the polymer with metal ion active end group is obtained by anionic polymerization. The metal ion active end group can be further converted into various functional groups by further reaction. After the reaction of metal ion active end group with carbon dioxide or diacid anhydride and acid treatment, the polymer with carboxyl group at the end is obtained. Urcmeck et al. prepared carboxyl-terminated polybutadiene by anionic polymerization, and the carboxylation rate (actual carboxyl content / theoretical carboxyl content) of the product was greater than 90%. However, this method has strict requirements on reaction conditions (such as strict drying of CO2 to avoid deactivation of active end group), and the microstructure of the product is difficult to accurately control, which makes it difficult to scale up production.

[0005] Ring-opening metathesis polymerization refers to the polymerization method in which double bonds in cyclic olefins break and open in the presence of a catalyst, resulting in a polymer with double bonds in the main chain. Using cyclic olefins as monomers, ring-opening polymerization in the presence of a catalyst (such as Grubbs catalyst) can prepare terminally functionalized polybutadiene. Although the reaction mechanism of ring-opening metathesis polymerization is simple, the stereoselectivity mechanism is not well understood, and the product structure exhibits a certain degree of randomness.

[0006] In comparison, polymer degradation methods are characterized by simple operation and controllable reaction. Our research group previously developed a method for the controllable pyrolysis of cis-butadiene rubber based on polymer degradation (Zhou Qinzhuo. Controllable preparation of terminal (poly)hydroxyl polybutadiene liquid rubber based on oxidative pyrolysis of cis-butadiene rubber [D]. Zhejiang: Zhejiang University, 2016.). Using H5IO6 as an oxidant to oxidize high molecular weight cis-butadiene rubber yields either highly cis-terminated hydroxyl polybutadiene liquid rubber or hydroxyl-terminated polybutadiene liquid rubber. The high molecular weight cis-butadiene rubber is quantitatively epoxidized in solution with m-chloroperoxybenzoic acid, and then H5IO6 is added to pyrolyze the epoxidized cis-butadiene rubber at the epoxy bond, yielding low molecular weight aldehyde-terminated polybutadiene (ATPB). The aldehyde groups at both ends of the ATPB chain are then reduced or oxidized to obtain hydroxyl-terminated or carboxyl-terminated polybutadiene liquid rubber. The reaction equation is shown below:

[0007] .

[0008] The reaction mechanism of this controlled pyrolysis method for cis-butadiene rubber is well-defined and has virtually no side reactions. Furthermore, since both epoxidation and H5IO6 pyrolysis are quantitative reactions, the molecular weight of the product can be controlled by adjusting the epoxy ratio. However, this method still has limitations: H5IO6 is environmentally harmful and can pollute water bodies; it is also costly and poses certain flammability, toxicity, and explosion hazards, making it unsuitable for large-scale industrial production. Additionally, the aldehyde group generation efficiency of this method depends on the rubber epoxidation rate; at low epoxidation rates, the aldehyde group content is low (aldehyde group to double bond ratio is only 0.16), making it difficult to meet the requirements for highly active end groups.

[0009] Therefore, it is necessary to find an environmentally friendly catalyst that can be used for large-scale industrial production to replace H5IO6 in the preparation of low to medium molecular weight terminal aldehyde carboxyl rubber. Summary of the Invention

[0010] The purpose of this invention is to provide a pyrolysis method for low- to medium-molecular-weight aldehyde- and carboxyl-terminated rubbers. By using NaVO3 as a catalyst and optimizing the reaction pathway, the method significantly improves the functional group content and reaction efficiency of the product while reducing costs and enhancing environmental friendliness. This provides a better option for the large-scale production and application of low- to medium-molecular-weight aldehyde- and carboxyl-terminated rubbers.

[0011] To achieve the above objectives, this technical solution provides a method for pyrolyzing low to medium molecular weight aldehyde- and carboxyl-terminated rubber, comprising the following steps:

[0012] The rubber is dissolved in an organic solvent to obtain a rubber solution;

[0013] After heating the adhesive solution, add sodium metavanadate solution and mix thoroughly to obtain a mixture.

[0014] Hydrogen peroxide was added dropwise to the mixture until the pyrolysis reaction was completed, and the reaction solution was obtained. The total amount of hydrogen peroxide used and the molar ratio of carbon-carbon double bonds in the rubber were (1.2~2.5):1.

[0015] The reaction solution was processed to obtain low to medium molecular weight terminal aldehyde and carboxyl rubber.

[0016] This scheme specifically selects sodium metavanadate as a catalyst, which can generate VO under acidic conditions. 2+ Active species can efficiently mediate the oxidative cracking of rubber by hydrogen peroxide. Using sodium metavanadate as a catalyst not only has the advantages of low cost and environmental friendliness, but also can facilitate the oxidation and decomposition of rubber by hydrogen peroxide. 2+ It directly interacts with the carbon-carbon double bonds of polybutadiene rubber to achieve one-step oxidative cleavage, eliminating the need for intermediate steps such as epoxidation and simplifying the reaction pathway.

[0017] The reaction process for the pyrolysis method of low to medium molecular weight terminal aldehyde and carboxyl rubbers in this scheme is as follows:

[0018] .

[0019] Specifically, sodium metavanadate generates VO in an acidic system. 2+ Active species, this VO 2+ The active species, acting as oxygen carriers, mediate the reaction between hydrogen peroxide and the carbon-carbon double bonds in polybutadiene rubber, via VO2+. 2+ The attack of reactive species on the carbon-carbon double bond and the transfer of oxygen directly trigger the oxidative breakage of the carbon-carbon double bond, eliminating the need for intermediate steps such as epoxidation. This completes the cleavage of the rubber molecular chain in one step, ultimately forming functional groups such as aldehyde, carboxyl, and hydroxyl groups at the chain ends. This catalytic oxidation mechanism avoids the limitations of the traditional periodic acid (H5IO6) oxidative cleavage method, which relies on the degree of epoxidation. This makes the oxidative cleavage process more direct and efficient, significantly increasing the content of functional groups (especially aldehyde groups) in the products, while reducing environmental harm and production costs.

[0020] The low to medium molecular weight aldehyde- and carboxyl-terminated rubbers synthesized in this method have a molecular weight (Mn) between 5000 and 20000 g / mol, a molecular weight distribution index (PDI) below 2.5, and all chain ends are aldehyde, carboxyl, or hydroxyl groups, with ester or epoxy groups within the chain. (VOC) 2+Under the synergistic effect of catalysis and H2O2 oxidation, carbon-carbon double bonds break and preferentially form aldehyde groups (-CHO). Some aldehyde groups can be further oxidized to form carboxyl groups (-COOH) or reduced to form hydroxyl groups (-CH2OH). The acidic environment and mild conditions of the reaction system inhibit the formation of other non-target functional groups, ensuring that the chain ends are mainly composed of aldehyde, carboxyl, or hydroxyl groups.

[0021] In some embodiments, the aldehyde content ranges from 0.05 to 1.28, the carboxyl content ranges from 0.10 to 1.53, the hydroxyl content ranges from 0.08 to 2.42, the ester content ranges from 0.05 to 1.61, and the epoxy content ranges from 0.00 to 0.84.

[0022] It is important to note that the structure of the oxidative pyrolysis products of H5IO6 is related to the epoxidation rate. Under low epoxidation rates, the ratio of aldehyde groups to carbon-carbon double bonds is only 0.16, while the oxidative pyrolysis products involving NaVO3 have the highest aldehyde content of 1.28, which is significantly better than the oxidative pyrolysis results of H5IO6. This is because the pyrolysis of H5IO6 relies on the epoxidation rate of the rubber, and under low epoxidation rates, it cannot generate products with a high aldehyde content. In contrast, the catalytic mechanism of NaVO3 involves VO2... + The loading of O reacts with the double bond, directly oxidizing and cracking the rubber. The degree of oxidative cracking is not limited by the degree of other reactions. At the same time, the activation process of the catalyst is simple and inexpensive, requiring only a small amount of hydrogen peroxide. To achieve the same degree of oxidative cracking, the cost of the NaVO3-catalyzed rubber oxidative cracking method is only 94% of that of the H5IO6 oxidative cracking method, which greatly reduces the cost of oxidative cracking and provides inexpensive reactants for subsequent reactions.

[0023] In some embodiments, the organic solvent for dissolving polybutadiene rubber is selected from any or a combination of tetrahydrofuran, 1,2-dichloroethane, and n-hexane. These organic solvents have excellent dissolving ability for polybutadiene rubber, and can uniformly disperse the rubber to form a stable adhesive solution, ensuring sufficient contact with sodium metavanadate solution and hydrogen peroxide in the subsequent process, and providing a uniform reaction environment for the oxidative pyrolysis reaction.

[0024] In some embodiments, the concentration of the adhesive solution is 0.001~0.4 g / mL. Preferably, the concentration of the adhesive solution is 0.033 g / mL. The concentration of the adhesive solution directly affects the dispersion state of the rubber molecular chains in the solvent. When the concentration is too high, the rubber molecular chains are prone to entanglement and aggregation, making it difficult for the sodium metavanadate solution and hydrogen peroxide to uniformly contact the carbon-carbon double bonds, resulting in incomplete local reactions and a wider molecular weight distribution of the product. On the other hand, if the concentration is too low, it will reduce the density of reaction sites per unit volume, slow down the reaction rate, and increase the amount of solvent used and the cost of subsequent purification, which is not conducive to industrial production. Furthermore, the concentration of the adhesive solution also affects the viscosity of the reaction system. If the concentration is too high, the viscosity of the system will increase sharply, making stirring difficult, reducing the efficiency of heat and mass transfer, and potentially causing local overheating or side reactions. If the concentration is too low, the viscosity of the system will be insufficient, making it difficult to maintain a stable reaction environment, and the reaction conditions may be changed due to the excessively fast solvent evaporation rate. Limiting the concentration range can ensure that the viscosity of the system is moderate, facilitating operations such as stirring and adding reagents, and improving the stability and repeatability of the process.

[0025] In some embodiments, the adhesive solution is heated to 60-65°C, sodium metavanadate solution is added, and the mixture is stirred at 5000-7000 rpm until it is homogeneous to obtain a mixed solution.

[0026] Preferably, the adhesive solution is heated to 60°C, then sodium metavanadate solution is added and stirred at 6000 rpm until the mixture is homogeneous to obtain a mixed solution.

[0027] In some embodiments, a sodium metavanadate solution is added to the adhesive solution under normal pressure.

[0028] In some embodiments, the sodium metavanadate solution is an acidic solution to facilitate the formation of VO from sodium metavanadate in the solution. 2+ Active species, thereby mediating the oxidative pyrolysis reaction of rubber by hydrogen peroxide.

[0029] In some embodiments, the pH of the sodium metavanadate solution is 1 to 2, preferably, the pH of the sodium metavanadate solution is 1.

[0030] The sodium metavanadate solution in this scheme is prepared on-site, that is, it is prepared using glacial acetic acid, hydrochloric acid, hydrogen peroxide and sodium metavanadate solid as raw materials.

[0031] In some embodiments, glacial acetic acid is used as a solvent. Hydrochloric acid and hydrogen peroxide are added to the solvent, followed by the addition of sodium metavanadate solid. The mixture is stirred until homogeneous and fully reacted to obtain a sodium metavanadate solution. The molar ratio of hydrogen peroxide to sodium metavanadate solid is (0.01~4):1.

[0032] In some embodiments, 30% hydrogen peroxide is selected.

[0033] In some embodiments, the reaction time is 10-20 min. Preferably, the reaction time is 15 min.

[0034] In some embodiments, hydrogen peroxide is added dropwise to the mixture for 3-5 hours until the pyrolysis reaction is completed to obtain a reaction solution, wherein the total amount of hydrogen peroxide used and the molar ratio of carbon-carbon double bonds in the rubber is (1.2-2.5):1.

[0035] Preferably, the molar ratio of the total amount of hydrogen peroxide used to the carbon-carbon double bonds in the rubber is 2.4:1. Hydrogen peroxide, as an oxidant, needs to react with the carbon-carbon double bonds in the rubber molecular chain to achieve chain breakage. A molar ratio of 1.2~2.5:1 ensures sufficient oxidant to oxidize and break down the carbon-carbon double bonds as much as possible, avoiding incomplete reactions due to insufficient hydrogen peroxide. This ensures that the product molecular weight can be stably reduced to the target range. If the ratio is too low, insufficient oxidation of the double bonds will lead to a higher product molecular weight and a wider distribution, failing to meet the design requirements for medium and low molecular weights. If the ratio is too high, it may cause over-oxidation or non-selective reactions, resulting in irregular chain breakage, disordered functional group types (such as generating too many non-target oxygen-containing groups), and even destruction of existing terminal aldehyde and carboxyl groups, reducing product activity. The range of 1.2~2.5:1 ensures sufficient cleavage while reducing side reactions and maintaining the controllability of the product structure.

[0036] In some embodiments, the rubber is any one of butadiene rubber, solution-polymerized styrene-butadiene rubber, butyl rubber, and nitrile rubber.

[0037] In some embodiments, the supernatant obtained by centrifuging the reaction solution is purified by 1,2-dichloroethane solution, rotary evaporation and vacuum drying after filtration.

[0038] Compared with existing technologies, this technical solution has the following characteristics and beneficial effects:

[0039] Compared to the traditional periodic acid (H5IO6) oxidative cracking method, this scheme uses sodium metavanadate (NaVO3) as a catalyst and hydrogen peroxide as an oxidant. The reagents used are inexpensive and readily available, which significantly reduces production costs (the cost is only 94% of that of the periodic acid method when achieving the same degree of oxidative cracking). At the same time, it avoids the water pollution, combustion, and toxicity risks of periodic acid, which is more in line with the development needs of green chemical industry and is suitable for large-scale industrial production.

[0040] Furthermore, the aldehyde generation efficiency of the traditional periodic acid oxidative cleavage method depends on the rubber epoxidation rate. At low epoxidation rates, the ratio of aldehyde groups to double bonds is only 0.16. In this scheme, NaVO3 is converted into aldehydes via VO3. 2+The loaded oxygen reacts directly with the double bonds of rubber, and the degree of oxidative cleavage is not limited by other reactions. The aldehyde content of the product can reach up to 1.28, and the content of functional groups such as carboxyl, hydroxyl, and ester groups is also at a high level, which can provide more active reactants for subsequent end-group modification. Moreover, under the catalysis of NaVO3, hydrogen peroxide can complete the oxidative cleavage of rubber in one step, making the reaction path simpler, and the reaction conditions mild and easy to control, which can effectively improve production efficiency.

[0041] The number-average molecular weight of the low-to-medium molecular weight terminal aldehyde-carboxyl rubbers obtained by this method can be stably controlled within the range of 5000~20000 g / mol, with a molecular weight distribution index (PDI) below 2.5, meeting the application requirements of low-to-medium molecular weight liquid rubbers. Furthermore, this method is applicable to various rubber types, including butadiene rubber, solution-polymerized styrene-butadiene rubber, butyl rubber, and nitrile rubber. By adjusting the reaction parameters, the product structure can be flexibly controlled, expanding its application scenarios in the field of fine polymer chemicals. Attached Figure Description

[0042] Figure 1 The above is the 1H NMR spectrum of the medium-to-high molecular weight, highly reactive polybutadiene with aldehyde and carboxyl groups at the ends, prepared in Example 1.

[0043] Figure 2 The above is the 1H NMR spectrum of the medium-to-high molecular weight, highly reactive polybutadiene with aldehyde and carboxyl groups at the ends, prepared in Example 2.

[0044] Figure 3 The above is the 1H NMR spectrum of the medium-to-high molecular weight, highly reactive polybutadiene with aldehyde and carboxyl groups at the ends, prepared in Example 3.

[0045] Figure 4 The 1H NMR spectrum of the medium-to-high molecular weight, highly reactive polybutadiene with aldehyde and carboxyl groups at the ends, prepared in Example 4.

[0046] Figure 5 The above is the 1H NMR spectrum of the medium-to-high molecular weight, highly reactive polybutadiene with aldehyde and carboxyl groups at the ends, prepared in Example 5.

[0047] Figure 6 This is a comparison diagram showing the 1H NMR spectra of the products from Comparative Example 1 and Example 2. Detailed Implementation

[0048] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0049] Experimental description:

[0050] Polymer structure analysis: The structure was determined using a nuclear magnetic resonance spectrometer (Bruker AVANCE NEO-500MHz) with deuterated chloroform as the solvent.

[0051] Polymer number-average molecular weight (M n The determination of molecular weight distribution index (PDI) was performed by gel permeation chromatography (Waters Alliance e2695), using tetrahydrofuran as solvent and narrow-distribution polystyrene as standard. The polymer concentration was 1-10 mg / mL and the solvent flow rate was 1 mL / min.

[0052] Example 1

[0053] 2.4 g of polybutadiene rubber was dissolved in 72 mL of 1,2-dichloroethane solution and kept at a constant temperature of 60 °C. Sodium metavanadate solution (pH=1, nNaVO3:nH2O2=1:2) was added, followed by slow dropwise addition of hydrogen peroxide (30 wt%). The reaction was carried out at 60 °C for 4 h. The molar ratio of the total amount of hydrogen peroxide used to the carbon-carbon double bond units in the polybutadiene rubber was 2.4:1. After the reaction was complete, the reaction solution was centrifuged to obtain the supernatant. The remaining catalyst was removed by filtration, and the supernatant was dried by rotary evaporation to obtain aldehyde-terminated / carboxyl-terminated polybutadiene liquid rubber. The product's M... n The value is 6365, and the PDI is 1.98.

[0054] The NMR spectra of the product of Example 1 and butadiene rubber were compared as follows: Figure 1 As shown, the obtained rubber has been attached with aldehyde, carboxyl, and hydroxyl groups. The rubber obtained in Example 1 has an aldehyde content of 0.44%, a carboxyl content of 0.57%, a hydroxyl content of 0.47%, an ester content of 0.52%, and an epoxy content of 0.22%.

[0055] Example 2

[0056] 2.4 g of butadiene rubber was dissolved in 72 mL of tetrahydrofuran solution and kept at a constant temperature of 60 °C. Sodium metavanadate solution (pH=1, nNaVO3:nH2O2=1:1) was added, followed by slow dropwise addition of hydrogen peroxide (30 wt%). The reaction was carried out at 60 °C for 4 h, with the total amount of hydrogen peroxide used in a molar ratio of 2.4:1 to the carbon-carbon double bond units in the polybutadiene rubber. After the reaction was complete, the reaction solution was centrifuged to obtain the supernatant. The remaining catalyst was removed by filtration, and the supernatant was dried by rotary evaporation to obtain aldehyde-terminated / carboxyl-terminated polybutadiene liquid rubber. The product's M... n The value is 14760, and the PDI is 2.15.

[0057] The NMR spectra of the product from Example 2 and butadiene rubber were compared as follows:Figure 2 As shown, the rubber obtained in Example 2 has been attached with aldehyde, carboxyl, and hydroxyl groups. The rubber obtained in Example 2 has an aldehyde content of 0.61%, a carboxyl content of 0.70%, a hydroxyl content of 0.88%, an ester content of 1.48%, and an epoxy content of 0.33%.

[0058] Example 3

[0059] 2.4 g of butadiene rubber was dissolved in 72 mL of tetrahydrofuran solution and kept at a constant temperature of 60 °C. Sodium metavanadate solution (pH=2, nNaVO3:nH2O2=1:2) was added, followed by slow dropwise addition of hydrogen peroxide (30 wt%). The reaction was carried out at 60 °C for 4 h, with the total amount of hydrogen peroxide used in a molar ratio of 2.4:1 to the carbon-carbon double bond units in the polybutadiene rubber. After the reaction was complete, the reaction solution was centrifuged to obtain the supernatant. The remaining catalyst was removed by filtration, and the supernatant was dried by rotary evaporation to obtain aldehyde-terminated / carboxyl-terminated polybutadiene liquid rubber. The product's M... n The value is 19041, and the PDI is 2.18.

[0060] The NMR spectra of the product from Example 3 and butadiene rubber were compared as follows: Figure 3 As shown, the rubber obtained in Example 3 has been attached with aldehyde, carboxyl, and hydroxyl groups. The rubber obtained in Example 3 has an aldehyde content of 0.66%, a carboxyl content of 0.41%, a hydroxyl content of 1.08%, an ester content of 0.34%, and an epoxy content of 0.22%.

[0061] Example 4

[0062] 2.4 g of butadiene rubber was dissolved in 36 mL of a mixed solution of 1,2-dichloroethane and 36 mL of tetrahydrofuran, and the solution was kept at a constant temperature of 60 °C. After adding sodium metavanadate solution (pH=2, nNaVO3:nH2O2=1:1), hydrogen peroxide (30 wt%) was slowly added dropwise to the rubber solution. The reaction was carried out at 60 °C for 4 h. The total amount of hydrogen peroxide used was in a molar ratio of 2.4:1 to the carbon-carbon double bond units in the polybutadiene rubber. After the reaction was complete, the reaction solution was centrifuged to obtain the supernatant. The remaining catalyst was removed by filtration, and the supernatant was dried by rotary evaporation to obtain aldehyde-terminated / carboxyl-terminated polybutadiene liquid rubber. The product's M... n The value is 12491, and the PDI is 2.19.

[0063] The NMR spectra of the product from Example 4 and butadiene rubber were compared as follows: Figure 4 As shown, the rubber obtained in Example 4 has been attached with aldehyde, carboxyl, and hydroxyl groups. The rubber obtained in Example 4 has an aldehyde content of 0.42%, a carboxyl content of 0.46%, a hydroxyl content of 0.49%, an ester content of 0.07%, and an epoxy content of 0.17%.

[0064] Example 5

[0065] 2.4 g of solution-polymerized styrene-butadiene rubber was dissolved in 72 mL of 1,2-dichloroethane solution and kept at a constant temperature of 60 °C. Sodium metavanadate solution (pH=1, nNaVO3:nH2O2=1:2) was added, followed by slow dropwise addition of hydrogen peroxide (30 wt%). The reaction was carried out at 60 °C for 4 h, with the total amount of hydrogen peroxide used in a molar ratio of 2.4:1 to the carbon-carbon double bond units in the polybutadiene rubber. After the reaction was complete, the reaction solution was centrifuged to obtain the supernatant. The supernatant was filtered to remove the remaining catalyst, and then dried by rotary evaporation to obtain aldehyde-terminated / carboxyl-terminated polybutadiene liquid rubber. The product's M... n The value is 17322, and the PDI is 1.92.

[0066] The NMR spectra of the product from Example 5 and butadiene rubber were compared as follows: Figure 5 As shown, the rubber obtained in Example 5 has been attached with aldehyde, carboxyl, and hydroxyl groups. The rubber obtained in Example 5 has an aldehyde content of 0.05%, a carboxyl content of 0.10%, a hydroxyl content of 0.09%, an ester content of 0.08%, and an epoxy content of 0.00%.

[0067] Comparative Example 1

[0068] 2.4 g of butadiene rubber was dissolved in 72 mL of tetrahydrofuran solution, and an appropriate amount of H₅IO₆ was added at room temperature. The reaction was allowed to proceed for a period of time. After post-treatment, the product was characterized by 1H NMR spectroscopy. The 1H NMR spectra of the products from Comparative Example 1 and Example 2 were compared as follows: Figure 6 As shown, under the condition of 1% epoxidation rate, the ratio of aldehyde group to carbon-carbon double bond in the product obtained by H5IO6 oxidative pyrolysis is only 0.16, while the aldehyde group content in the product obtained by NaVO3 oxidative pyrolysis is 1.28.

[0069] Those skilled in the art should understand that the technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0070] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for preparing low to medium molecular weight terminal aldehyde-carboxyl rubber, characterized in that, Includes the following steps: The rubber was dissolved using an organic solvent to obtain a rubber solution; After heating the adhesive solution, sodium metavanadate solution is added and mixed evenly to obtain a mixed solution. Sodium metavanadate solution is an acidic solution. Glacial acetic acid is used as the solvent. Hydrochloric acid and hydrogen peroxide are added to the solvent, and then sodium metavanadate solid is added. The mixture is stirred evenly and reacted fully to obtain sodium metavanadate solution. The molar ratio of hydrogen peroxide to sodium metavanadate solid is (0.01~4):

1. Hydrogen peroxide was added dropwise to the mixture until the pyrolysis reaction was completed, and the reaction solution was obtained. The total amount of hydrogen peroxide used and the molar ratio of carbon-carbon double bonds in the rubber were (1.2~2.5):

1. The reaction solution was processed to obtain low to medium molecular weight aldehyde-carboxyl rubber, wherein the molecular weight Mn of the low to medium molecular weight aldehyde-carboxyl rubber is between 5000 and 20000 g / mol, the molecular weight distribution index PDI is less than 2.5, the chain ends are all aldehyde, carboxyl or hydroxyl groups, and the chain contains ester or epoxy groups.

2. The method for preparing low to medium molecular weight terminal aldehyde and carboxyl rubber according to claim 1, characterized in that, The aldehyde content ranges from 0.05 to 1.28, the carboxyl content ranges from 0.10 to 1.53, the hydroxyl content ranges from 0.08 to 2.42, the ester content ranges from 0.05 to 1.61, and the epoxy content ranges from 0.00 to 0.

84.

3. The method for preparing low to medium molecular weight terminal aldehyde-carboxyl rubber according to claim 1, characterized in that, The organic solvent for dissolving the rubber is selected from any one or a combination of tetrahydrofuran, 1,2-dichloroethane, and n-hexane.

4. The method for preparing low to medium molecular weight terminal aldehyde and carboxyl rubber according to claim 1, characterized in that, The rubber is any one of butadiene rubber, solution-polymerized styrene-butadiene rubber, butyl rubber, and nitrile rubber.

5. The method for preparing low to medium molecular weight terminal aldehyde-carboxyl rubber according to claim 1, characterized in that, The concentration of the adhesive solution is 0.001~0.4g / mL.

6. The method for preparing low to medium molecular weight terminal aldehyde-carboxyl rubber according to claim 1, characterized in that, Heat the adhesive solution to 60-65℃, add sodium metavanadate solution, and stir at 5000-7000 rpm until the mixture is homogeneous to obtain the final mixture.

7. The method for preparing low to medium molecular weight terminal aldehyde and carboxyl rubber according to claim 1, characterized in that, The supernatant was obtained by centrifuging the reaction liquid. After filtering the supernatant, it was purified with 1,2-dichloroethane solution, rotary evaporated and vacuum dried.

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