Graft copolymer, and preparation method therefor and use thereof

Abstract

The present invention provides a graft copolymer, and a preparation method therefor and a use thereof. The graft copolymer comprises an isobutylene-maleic anhydride copolymer segment and a polyisobutylene segment grafted to an isobutylene-maleic anhydride copolymer, and the water contact angle of the graft copolymer is 75°-117°. The graft copolymer of the present invention has both hydrophilicity and hydrophobicity, is suitable for nanofluids of non-polar systems, and maintains good stability and dispersibility.

Description

A graft copolymer, its preparation method and application

[0001] This application claims priority to Chinese Patent Application No. 202411800801.6, filed on December 9, 2024, entitled "A graft copolymer and its preparation method and application", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to the field of petrochemicals, specifically to a graft copolymer, its preparation method, and its application. Background Technology

[0003] Under the "dual carbon" goal and with the "reducing oil and increasing chemicals" strategy, chemical products are gradually shifting towards high-end, green, and diversified development. Isobutylene-maleic anhydride copolymer is a chemical product prepared through free radical copolymerization. Its raw materials, isobutylene and maleic anhydride, both originate from the C4 fraction of petroleum cracking, offering advantages such as low raw material prices and abundant supply. Isobutylene-maleic anhydride copolymers contain abundant anhydride groups, allowing for further chemical modification to impart new functions and increase their added value. Different molecular weights of isobutylene-maleic anhydride copolymers have different applications. For example, low molecular weight isobutylene-maleic anhydride copolymers can be used as scale inhibitors, dispersants, and water-reducing agents in cement slurries, while medium molecular weight isobutylene-maleic anhydride copolymers can be used as adhesives for wood and paper processing, and as emulsion polymerization stabilizers. However, isobutylene-maleic anhydride copolymer is an alternating copolymer and the copolymer composition cannot be adjusted, resulting in high polarity and rigidity of the copolymer segments. Therefore, it is usually used as a hydrophilic material, and its application range is limited. For example, when applied to non-polar systems, it generally suffers from poor dispersibility and poor stability.

[0004] With the gradual development of macromolecular engineering, the chemical structures of polymers have become more sophisticated. Among them, graft copolymers are copolymers composed of main chains and branches with different properties through chemical bonding. These copolymers usually combine the characteristics of both materials, resulting in a richer range of polymer properties. According to "Preparation and Electrochemical Performance of a Double Lithium Salt Comb Polymer Electrolyte" in Vol. 42, No. 9, pp. 2861-2868 of the *Journal of Chemical Research in Chinese Universities* and "A Multifunctional Amphiphilic Polymer as a Platform for Surface-functionalizing Metallic and Other Inorganic Nanostructures" in Vol. 175, pp. 137-151 of *Faraday Discussions*, for graft copolymers with maleic anhydride copolymers as the main chain, polyethylene glycol monomethyl ether is often chosen as the copolymer branch. However, because both exhibit hydrophilicity, the application range of the resulting graft copolymers is still somewhat limited.

[0005] According to the articles "Influence of temperature on the colloidal stability of polymer-coated gold nanoparticles in cell culture media" in *Small*, Volume 12, Issue 13, pp. 1723-1731, and "Colloidal stability of surface chemistry are key factors for the composition of the protein corona of inorganic gold nanoparticles" in *Advanced Functional Materials*, Volume 27, Issue 42, pp. 170-1956, comb-like polymers can be prepared by reacting higher aliphatic amines with isobutylene-maleic anhydride copolymers or their derivatives. This process achieves the organic combination of polar maleic anhydride copolymer segments and nonpolar alkyl chains, reducing the proportion of polar hydrophilic groups and increasing the hydrophobicity of the copolymer. However, higher aliphatic amines are expensive, making this method unsuitable for large-scale production. Furthermore, the dispersibility and stability of these polymers in nonpolar systems require further improvement.

[0006] Therefore, how to prepare a graft copolymer with both hydrophilicity and hydrophobicity based on isobutylene-maleic anhydride copolymer, and improve its dispersibility and stability in nonpolar systems, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] This invention provides a graft copolymer, its preparation method, and its application, which combines hydrophilicity and hydrophobicity, is suitable for use in non-polar nanofluid systems, and maintains good stability and dispersibility.

[0008] In one aspect, the present invention provides a graft copolymer comprising isobutylene-maleic anhydride copolymer segments and polyisobutylene segments grafted onto the isobutylene-maleic anhydride copolymer segments, wherein the water contact angle of the graft copolymer is 75° to 117°.

[0009] According to one embodiment of the present invention, the graft copolymer is prepared by esterification reaction of isobutylene-maleic anhydride copolymer and hydroxyl-terminated polyisobutylene, wherein the hydroxyl-terminated polyisobutylene is copolymerized from polyisobutylene having unsaturated end groups and mercapto alcohol.

[0010] According to one embodiment of the present invention, the number average molecular weight of the isobutylene-maleic anhydride copolymer is 5,000 to 400,000 g / mol; and / or, the ratio of the weight average molecular weight to the number average molecular weight of the isobutylene-maleic anhydride copolymer is 2.5 to 3.15; and / or, the number average molecular weight of the polyisobutylene having unsaturated end groups is 1,000 to 5,000 g / mol; and / or, the mercapto alcohol includes 2-mercaptoethanol.

[0011] According to one embodiment of the present invention, the isobutylene-maleic anhydride copolymer segment is the main chain in the graft copolymer, and the polyisobutylene segment is the branch chain; and / or, the grafting rate of the polyisobutylene segment in the graft copolymer is 1% to 38%.

[0012] In another aspect, the present invention provides a method for preparing a graft copolymer, comprising the following steps: mixing isobutylene-maleic anhydride copolymer and hydroxyl-terminated polyisobutylene in an organic solvent to obtain a first mixed solution, and then performing an esterification reaction to obtain the graft copolymer.

[0013] According to one embodiment of the present invention, the organic solvent includes one or more of N,N-dimethylformamide and dimethyl sulfoxide; and / or, the first mixed solution is a homogeneous solution; and / or, the sum of the mass percentages of isobutylene-maleic anhydride copolymer and hydroxyl-terminated polyisobutylene in the first mixed solution is 10% to 40%; and / or, the reaction temperature of the esterification reaction is 70 to 140°C, and the reaction time is 2 to 12 hours.

[0014] According to one embodiment of the present invention, the method for preparing the hydroxyl-terminated polyisobutylene includes: mixing polyisobutylene with unsaturated end groups, mercapto alcohol, and photoinitiator in a solvent, and then subjecting the mixture to a click chemical reaction under ultraviolet light to obtain the hydroxyl-terminated polyisobutylene.

[0015] According to one embodiment of the present invention, the photoinitiator includes 2,2-dimethoxy-2-phenylacetophenone; and / or, the solvent includes one or more of dichloromethane and trichloromethane; and / or, the reaction temperature of the click chemistry reaction is 0-8°C and the reaction time is 10-40 min.

[0016] In another aspect, the present invention provides a nanofluid comprising nano-alumina, a nonpolar solvent, and a graft copolymer prepared according to the above-described method for preparing the graft copolymer.

[0017] According to one embodiment of the present invention, the mass ratio of the graft copolymer to the volume ratio of the nonpolar solvent is 0.025 g: 10 mL to 0.2 g: 10 mL.

[0018] The implementation of this invention has at least the following beneficial effects: By grafting non-polar polyisobutylene onto the surface of a polar isobutylene-maleic anhydride copolymer, a novel graft copolymer based on the isobutylene-maleic anhydride copolymer is obtained. Furthermore, by adjusting the ratio of polar to non-polar segments in the copolymer, the water-sensory angle of the graft copolymer is kept within the range of 75° to 117°. This graft copolymer is simple to prepare, low in cost, and achieves an organic combination of polar and non-polar segments, possessing both hydrophilic and hydrophobic properties. Introducing polyisobutylene onto the surface of the isobutylene-maleic anhydride copolymer weakens its rigidity. Therefore, the graft copolymer of this invention can be used as a dispersant to promote the dispersion of polar nanoparticles in non-polar solvents, resulting in a long-term stable and uniformly dispersed nanofluid that can be applied in heat transfer media, coatings, and other fields. Attached Figure Description

[0019] Figure 1 is the infrared spectrum of the graft copolymer in Example 1;

[0020] Figure 2 shows the water contact angles of isobutylene-maleic anhydride copolymer (IBMA) in Comparative Example 1 and graft copolymer (IBMA-g-PIB) in Example 2. Detailed Implementation

[0021] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] This invention provides a graft copolymer comprising isobutylene-maleic anhydride copolymer segments and polyisobutylene segments grafted onto the isobutylene-maleic anhydride copolymer, wherein the water contact angle of the graft copolymer is 75° to 117°.

[0023] According to the inventors' research, compared to isobutylene-maleic anhydride copolymers, a new graft copolymer is obtained by grafting polyisobutylene onto the surface of isobutylene-maleic anhydride copolymers. This allows for the combination of polar isobutylene-maleic anhydride copolymer segments with non-polar polyisobutylene segments. Furthermore, the hydrophilicity or hydrophobicity of the graft copolymer can be controlled by adjusting the grafting rate of the non-polar polyisobutylene and the length of the polyisobutylene segments, thereby enabling the water angle of the graft copolymer to be within the range of 75° to 117°, thus giving the graft copolymer both hydrophilic and hydrophobic properties. By introducing polyisobutylene onto the surface of the isobutylene-maleic anhydride copolymer, the rigidity of the isobutylene-maleic anhydride copolymer is weakened. Moreover, polyisobutylene is inexpensive and its preparation method is simple, thus resulting in a low preparation cost for this graft copolymer.

[0024] Therefore, the above-mentioned graft copolymer has both hydrophilic and hydrophobic properties, and can be used as a dispersant to promote the dispersion of nanoparticles, thus it can be widely used in the fields of nanofluid preparation, lubricant additives, dye dispersion and other fields.

[0025] In some embodiments, the water contact angle of the graft copolymer can be 75° to 117°, for example, a range of 75°, 82°, 95°, 97°, 98°, 108°, 110°, 115°, 117° or any combination thereof.

[0026] In some embodiments, the graft copolymer can be prepared by esterification of isobutylene-maleic anhydride copolymer (IBMA) and hydroxyl-terminated polyisobutylene (PIB-OH), wherein the hydroxyl-terminated polyisobutylene is copolymerized from polyisobutylene (HR-PIB) with unsaturated end groups and mercapto alcohol.

[0027] Specifically, polyisobutylene with unsaturated end groups and mercapto alcohols are polymerized by addition reaction (thiol-ene click chemistry) to generate hydroxyl-terminated polyisobutylene. Isobutylene-maleic anhydride copolymer and hydroxyl-terminated polyisobutylene are then esterified to generate a novel graft copolymer, wherein the polyisobutylene ends contain primary hydroxyl groups and each end group contains a sulfur unit.

[0028] In some embodiments, the number average molecular weight of the isobutylene-maleic anhydride copolymer can be 5,000 to 400,000 g / mol, for example, a range consisting of 5,000 g / mol, 100,000 g / mol, 200,000 g / mol, 300,000 g / mol, 400,000 g / mol, or any two of these. Preferably, the number average molecular weight of the isobutylene-maleic anhydride copolymer can be 5,000 to 300,000 g / mol, for example, a range consisting of 5,000 g / mol, 100,000 g / mol, 200,000 g / mol, 300,000 g / mol, or any two of these.

[0029] Furthermore, the weight-average molecular weight to number-average molecular weight ratio of the isobutylene-maleic anhydride copolymer is 2.5 to 3.15, for example, 2.5, 2.57, 2.60, 2.64, 2.69, 2.70, 2.80, 2.81, 2.89, 2.90, 3.00, 3.10, 3.13, 3.15 or any combination thereof, and the specific weight-average molecular weight to number-average molecular weight ratio of the isobutylene-maleic anhydride copolymer can be 2.57 to 3.13.

[0030] Furthermore, the number-average molecular weight of polyisobutylene with unsaturated end groups can be 1000–5000 g / mol, for example, 1000 g / mol, 2000 g / mol, 3000 g / mol, 4000 g / mol, 5000 g / mol or any two of these ranges. Preferably, the number-average molecular weight of polyisobutylene with unsaturated end groups can be 1000–3000 g / mol, for example, 1000 g / mol, 2000 g / mol, 3000 g / mol or any two of these ranges.

[0031] In addition, mercapto alcohols may include 2-mercaptoethanol, which has a small relative molecular weight and can participate more efficiently in the reaction to generate terminal hydroxyl polyisobutylene.

[0032] In some embodiments, the isobutylene-maleic anhydride copolymer segment is the main chain and the polyisobutylene segment is the branch chain in the graft copolymer, realizing the organic combination of polar and non-polar segments, and possessing both hydrophilic and hydrophobic properties. This makes it more suitable for the graft copolymer to be used as a dispersant in non-polar systems, improving its dispersibility and stability in non-polar systems.

[0033] In this embodiment of the invention, the grafting rate of polyisobutylene in the graft copolymer refers to the ratio of the amount of polyisobutylene segments to the amount of repeating units in the isobutylene-maleic anhydride copolymer segments.

[0034] Specifically, the isobutylene-maleic anhydride copolymer is an alternating copolymer, wherein the molecular weight of the repeating unit is approximately equal to the sum of the molecular weight of isobutylene and the molecular weight of maleic anhydride.

[0035] Furthermore, the grafting rate of polyisobutylene in the graft copolymer can be from 1% to 38%, for example, a range of 1%, 2%, 5%, 10%, 20%, 28%, 30%, 38%, or any combination thereof.

[0036] In some embodiments, the grafting rate of polyisobutylene can be 5% to 36%, for example, a range of 5%, 10%, 15%, 20%, 25%, 28%, 30%, 35%, 36% or any two thereof, which is more conducive to the application of the graft copolymer to non-polar systems and further improves the dispersibility and stability of the graft copolymer in non-polar systems.

[0037] The present invention also provides a method for preparing the above-mentioned graft copolymer, which may include the following steps: mixing isobutylene-maleic anhydride copolymer and hydroxyl-terminated polyisobutylene in an organic solvent to obtain a first mixed solution, and then performing an esterification reaction to obtain the graft copolymer.

[0038] In a specific implementation, isobutylene-maleic anhydride copolymer and hydroxyl-terminated polyisobutylene can be dissolved together in an organic solvent, and under heating conditions, the isobutylene-maleic anhydride copolymer and hydroxyl-terminated polyisobutylene in the first mixed solution undergo an esterification reaction to obtain a graft copolymer.

[0039] Specifically, the organic solvent includes any organic solvent that can co-dissolve isobutylene-maleic anhydride copolymer and hydroxyl-terminated polyisobutylene without interfering with their esterification reaction.

[0040] In some embodiments, the organic solvent may include one or more of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO).

[0041] Furthermore, the first mixed solution can be a homogeneous solution.

[0042] Furthermore, the sum of the mass percentages of the isobutylene-maleic anhydride copolymer and the hydroxyl-terminated polyisobutylene in the first mixed solution can be 10% to 40%, for example, 10%, 20%, 30%, 40%, or any combination thereof.

[0043] In addition, the reaction temperature of the esterification reaction can be 70 to 140°C, for example, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C or any combination thereof; the reaction time can be 2h to 12h, for example, 2h, 4h, 6h, 8h, 10h, 12h or any combination thereof.

[0044] In practice, isobutylene-maleic anhydride copolymer and hydroxyl-terminated polyisobutylene can be dissolved together in an organic solvent in a round-bottom flask and stirred until a homogeneous solution is formed. Under heating conditions, the isobutylene-maleic anhydride copolymer and hydroxyl-terminated polyisobutylene in the homogeneous solution (first mixed solution) formed above undergo an esterification reaction to generate a graft copolymer. Then, ethanol is added to it until a precipitate is formed. The precipitate is washed with n-hexane and placed under reduced pressure until a constant weight is reached to obtain the graft copolymer.

[0045] In some embodiments, the preparation method of hydroxyl-terminated polyisobutylene may include: mixing polyisobutylene with unsaturated end groups, mercapto alcohol, and photoinitiator in a solvent, and then subjecting the mixture to a click chemical reaction under ultraviolet light to obtain hydroxyl-terminated polyisobutylene.

[0046] Specifically, the ultraviolet light source can come from a medium-pressure Hg lamp.

[0047] In practice, polyisobutylene with unsaturated end groups, mercapto alcohol, and photoinitiator can be dissolved in a solvent simultaneously, and hydroxyl-terminated polyisobutylene can be obtained after undergoing a thiol-ene click chemical reaction under ultraviolet light irradiation.

[0048] Specifically, the mass percentage of photoinitiator in the solvent can be 1%.

[0049] Specifically, photoinitiators include any known photoinitiator that enables polyisobutylene and mercaptools with unsaturated end groups to undergo a thiol-ene click chemistry reaction under UV light irradiation.

[0050] In some embodiments, the photoinitiator may include 2,2-dimethoxy-2-phenylacetophenone (i.e., DMPA, or photosensitizer 651).

[0051] Generally, the solvent can include any organic solvent that can co-dissolve polyisobutylene, mercapto alcohol, and photoinitiator with unsaturated end groups without interfering with the thiol-ene click chemistry reaction.

[0052] In some embodiments, the solvent may include one or more of dichloromethane and trichloromethane.

[0053] In addition, the reaction temperature of the click chemical reaction can be 0 to 8°C, for example, 0°C, 2°C, 4°C, 6°C, 8°C or any combination thereof; the reaction time can be 10 to 40 min, for example, 10 min, 20 min, 30 min, 40 min or any combination thereof.

[0054] In practice, polyisobutylene with unsaturated end groups, mercapto alcohol, and photoinitiator can be dissolved in a solvent in a round-bottom flask and stirred until a homogeneous solution is formed. The homogeneous solution in the round-bottom flask is then subjected to click chemical reaction by ultraviolet light irradiation in an ice-water bath to obtain hydroxyl-terminated polyisobutylene. The solution containing hydroxyl-terminated polyisobutylene in the round-bottom flask is then directly used in the subsequent preparation of graft copolymers.

[0055] In practice, after the homogeneous solution in the round-bottom flask undergoes a click chemical reaction under ultraviolet light irradiation in an ice-water bath to obtain terminal hydroxyl polyisobutylene, the solvent in the round-bottom flask can be removed under reduced pressure. The remaining solid in the round-bottom flask is then dissolved in hexane to form a solution. The resulting solution is washed three times with methanol to remove unreacted mercaptools, photoinitiators, and other small molecule impurities. The solution is then placed under reduced pressure until constant weight is achieved to obtain terminal hydroxyl polyisobutylene.

[0056] This invention also provides a nanofluid comprising nano-alumina, the above-mentioned graft copolymer, and a non-polar solvent. This nanofluid can be applied to heat transfer media, coatings, and other fields.

[0057] Specifically, the nonpolar solvent is an organic solvent, which may include alkane solvents. In some embodiments, the alkane solvent includes one or more of cyclohexane, n-hexane, and n-heptane.

[0058] In some embodiments, the mass ratio of the graft copolymer to the volume ratio of the nonpolar solvent is 0.01 g:10 mL to 0.2 g:10 mL, for example, 0.01 g:10 mL, 0.025 g:10 mL, 0.05 g:10 mL, 0.1 g:10 mL, 0.15 g:10 mL, 0.2 g:10 mL, or any range of two of the aforementioned values. Preferably, the mass ratio of the graft copolymer to the volume ratio of the nonpolar solvent is 0.025 g:10 mL to 0.2 g:10 mL, for example, 0.025 g:10 mL, 0.05 g:10 mL, 0.1 g:10 mL, 0.15 g:10 mL, 0.2 g:10 mL, or any range of two of the aforementioned values, which is beneficial for maintaining the stability of the nanofluid.

[0059] In some embodiments, the preparation of the nanofluid specifically includes: adding nano-alumina and graft copolymer to a non-polar solvent and sonicating for 30 min to obtain a long-lasting, stable and uniformly dispersed alumina nanofluid. The mass ratio of nano-alumina to the volume ratio of the non-polar solvent can be 0.05 g: 10 mL to 0.4 g: 10 mL, for example, 0.05 g: 10 mL, 0.1 g: 10 mL, 0.2 g: 10 mL, 0.3 g: 10 mL, 0.4 g: 10 mL, or any range of two of the aforementioned values.

[0060] Generally, the volume of the nanofluid is approximately equal to the volume of the nonpolar solvent. That is, the mass ratio of nano-alumina to the volume ratio of the nanofluid can be 0.05g:10mL to 0.4g:10mL, for example, 0.05g:10mL, 0.1g:10mL, 0.2g:10mL, 0.3g:10mL, 0.4g:10mL, or any range of two of the aforementioned values. The mass ratio of the graft copolymer to the volume ratio of the nanofluid can be 0.025g:10mL to 0.2g:10mL, for example, 0.025g:10mL, 0.05g:10mL, 0.1g:10mL, 0.15g:10mL, 0.2g:10mL, or any range of two of the aforementioned values.

[0061] The present invention will be further described below through specific embodiments.

[0062] Example 1

[0063] 1. Preparation of hydroxyl-terminated polyisobutylene (end-group modification of polyisobutylene with unsaturated end groups)

[0064] 20g of polyisobutylene with unsaturated end groups (from BASF, catalog number [missing information]) with a number-average molecular weight of 2300g / mol was used. 2300 g of 2-mercaptoethanol, 0.2 g of 2,2-dimethoxy-2-phenylacetophenone (1 wt% relative to polyisobutylene with unsaturated end groups) and 50 mL of CHCl3 were dissolved together in a 100 mL round-bottom flask and stirred until a homogeneous solution was formed. The homogeneous solution formed in the round-bottom flask was placed in an ice-water bath at 0 °C and irradiated with ultraviolet light using a medium-pressure Hg lamp for 20 min to obtain a solution containing hydroxyl-terminated polyisobutylene. Then, the solvent in the solution containing hydroxyl-terminated polyisobutylene was removed under reduced pressure, and the solid remaining in the round-bottom flask was dissolved in hexane to form a solution. The resulting solution was washed three times with methanol and then placed under reduced pressure until constant weight was reached to obtain hydroxyl-terminated polyisobutylene (PIB-OH2.3k). The end group conversion rate of hydroxyl-terminated polyisobutylene was 100% as determined by 1H NMR spectroscopy.

[0065] 2. Synthesis of isobutylene-maleic anhydride copolymer and polyisobutylene graft copolymer (IBMA-g-PIB)

[0066] 5 g of isobutylene-maleic anhydride copolymer with a number-average molecular weight of 5000 g / mol, denoted as IBMA5k, with a weight-average molecular weight to number-average molecular weight ratio (Mw / Mn) of 2.81, was dissolved together with 10 g of prepared PIB-OH2.3k in 35 g of DMF (i.e., 37 mL) in a 100 mL round-bottom flask and stirred until a homogeneous solution was formed. The combined mass percentage of isobutylene-maleic anhydride copolymer and hydroxyl-terminated polyisobutylene in the resulting solution was 30%. This solution was heated at 120 °C for 4 h, and ethanol was added until a precipitate formed. The precipitate was washed three times with n-hexane and placed under reduced pressure until constant weight was achieved to obtain the graft copolymer.

[0067] The grafting rate of IBMA-g-PIB was determined to be 10% by titration. The resulting graft copolymer was designated IBMA5k-g10-PIB2.3k, with a water contact angle of 97°. Compared to IBMA5k, the water contact angle of IBMA5k-g28-PIB2.3k was increased by 32°, indicating that the hydrophobicity of the graft copolymer of Example 1 was improved compared to the isobutylene-maleic anhydride copolymer.

[0068] Figure 1 shows the infrared spectrum of the obtained graft copolymer. The absorption peaks at 1776 cm⁻¹ and 1853 cm⁻¹ are attributed to the stretching vibrations of the two carbonyl groups (C=O) on the anhydride; the peak at 933 cm⁻¹ is characteristic of five-membered ring anhydrides; the peak near 2950 cm⁻¹ is attributed to the stretching vibrations of the methyl and methylene groups; the peak at 3350 cm⁻¹ is attributed to the hydroxyl (-OH) group in the carboxyl group generated by the grafting reaction; and the peaks at 1388 cm⁻¹ and 1365 cm⁻¹ are characteristic of the branched polyisobutylene skeleton. This demonstrates that hydroxyl-terminated polyisobutylene has been successfully grafted onto the branches of the isobutylene-maleic anhydride copolymer.

[0069] Example 2

[0070] The difference between the preparation method of the graft copolymer and Example 1 is that the number-average molecular weight of the polyisobutylene with unsaturated end groups used in the preparation of the hydroxyl-terminated polyisobutylene is 1300 g / mol (from BASF, catalog number [missing information]). 1300), 1.8 g of 2-mercaptoethanol was added, and the irradiation time of the medium-pressure Hg lamp was 15 min. The resulting hydroxyl-terminated polyisobutylene was labeled as PIB-OH1.3k (the end-group conversion rate of the hydroxyl-terminated polyisobutylene was 100% as measured by 1H NMR spectroscopy).

[0071] Another difference lies in the synthesis process of the graft copolymer. 5g of IBMA5k and 15g of the prepared PIB-OH1.3k were dissolved together in 60g of DMF (64mL) to form a homogeneous solution, which was then reacted at 100℃ for 6 hours. The total mass percentage of the isobutylene-maleic anhydride copolymer and the hydroxyl-terminated polyisobutylene in the homogeneous solution was 25%. The grafting rate of IBMA-g-PIB was determined to be 28% by titration. The resulting graft copolymer was designated IBMA5k-g28-PIB1.3k. Infrared spectral characterization of the graft copolymer showed that the hydroxyl-terminated polyisobutylene had been successfully grafted onto the side chains of the isobutylene-maleic anhydride copolymer.

[0072] As shown in Figure 2, the water contact angle (WCA) of the main chain IBMA5k is 65°, and the water contact angle of IBMA5k-g28-PIB1.3k is 108°. Compared with IBMA5k, the water contact angle of IBMA5k-g28-PIB1.3k is increased by 43°, which indicates that the hydrophobicity of the graft copolymer in Example 2 is improved compared with the isobutylene-maleic anhydride copolymer.

[0073] Example 3

[0074] The difference between the preparation method of the graft copolymer and that of Example 2 is that, in the synthesis of the graft copolymer, 5g of IBMA5k and 20g of the obtained PIB-OH1.3k were dissolved in 60g of DMF (i.e., 64mL) to form a homogeneous solution and reacted at 100°C for 8h. The total mass percentage of isobutylene-maleic anhydride copolymer and hydroxyl-terminated polyisobutylene in the homogeneous solution was 29%. The grafting rate of the obtained IBMA-g-PIB was determined to be 36% by titration. The obtained graft copolymer is designated as IBMA5k-g36-PIB1.3k, and its water contact angle is 117°. Compared with IBMA5k, the water contact angle of IBMA5k-g28-PIB2.3k is increased by 52°, which indicates that the hydrophobicity of the graft copolymer in Example 3 is improved compared with that of the isobutylene-maleic anhydride copolymer. Infrared spectral characterization of the graft copolymer showed that hydroxyl-terminated polyisobutylene had been successfully grafted onto the side chains of the isobutylene-maleic anhydride copolymer.

[0075] Example 4

[0076] The difference between the preparation method of the graft copolymer and that in Example 1 is that the HR-PIB used in the preparation of the hydroxyl-terminated polyisobutylene is from BASF, catalog number [missing information]. The product was PIB-OH1.0k, with a number average molecular weight of 1000 g / mol, 2.3 g of 2-mercaptoethanol was added, 35 mL of CH2Cl2 was used as the solvent, and the irradiation time of the medium-pressure Hg lamp was 10 min. The end group conversion rate of the product was 95% as determined by 1H NMR spectroscopy.

[0077] Another difference lies in the synthesis of the graft copolymer. In this process, 5g of isobutylene-maleic anhydride copolymer (denoted as IBMA15k, Mw / Mn = 2.64) with a number-average molecular weight of 15000g / mol and 12g of the prepared PIB-OH1.0k were dissolved in 60mL of a mixed solvent of decane and DMF (decane to DMF volume ratio 2:1) to form a homogeneous solution, which was then reacted at 110℃ for 5h. The sum of the mass percentages of the isobutylene-maleic anhydride copolymer and the hydroxyl-terminated polyisobutylene in the homogeneous solution was 26%. The grafting rate of IBMA-g-PIB was determined to be 25% by titration. The resulting graft copolymer was denoted as IBMA15k-g25-PIB1.0k, and its water contact angle was 98°. Infrared spectral characterization of the graft copolymer showed that the hydroxyl-terminated polyisobutylene had been successfully grafted onto the branches of the isobutylene-maleic anhydride copolymer.

[0078] Example 5

[0079] The preparation method of the graft copolymer differs from that in Example 1 in that the irradiation time with a medium-pressure Hg lamp is 10 min in the preparation of the terminal hydroxyl polyisobutylene. The resulting product is PIB-OH2.3k (the end-group conversion rate of this product was measured to be 95% by 1H NMR spectroscopy).

[0080] Another difference lies in the synthesis of the graft copolymer. In this process, 5g of isobutylene-maleic anhydride copolymer (denoted as IBMA50k, Mw / Mn = 2.57) with a number-average molecular weight of 50,000 g / mol and 5g of PIB-OH2.3k were dissolved together in 40mL of a mixed solution of decane and DMSO (decane to DMSO volume ratio 1:1) to form a homogeneous solution, which was then reacted at 80℃ for 10h. The sum of the mass percentages of the isobutylene-maleic anhydride copolymer and the hydroxyl-terminated polyisobutylene in the homogeneous solution was 21%. The grafting rate of IBMA-g-PIB was determined to be 5% by titration. The resulting graft copolymer was denoted as IBMA50k-g5-PIB2.3k, and its water contact angle was 82°. Infrared spectral characterization of the graft copolymer showed that the hydroxyl-terminated polyisobutylene had been successfully grafted onto the branches of the isobutylene-maleic anhydride copolymer.

[0081] Example 6

[0082] The difference between the preparation method of the graft copolymer and that in Example 1 is that in the preparation of the terminal hydroxyl polyisobutylene, after obtaining the CHCl3 solution containing PIB-OH2.3k, the entire solution is directly applied to the subsequent graft copolymer reaction.

[0083] Another difference lies in the synthesis of the graft copolymer. 8g of isobutylene-maleic anhydride copolymer (denoted as IBMA30k, Mw / Mn = 2.69) with a number-average molecular weight of 30000g / mol was dissolved in 40mL of DMSO and then directly mixed with the aforementioned CHCl3 solution containing PIB-OH2.3k to obtain a homogeneous solution. The sum of the mass percentages of the isobutylene-maleic anhydride copolymer and the hydroxyl-terminated polyisobutylene in the homogeneous solution was 19%, and the mixture was reacted at 70℃ for 12h. The grafting rate of IBMA-g-PIB was determined to be 14% by titration. The resulting graft copolymer is denoted as IBMA30k-g14-PIB2.3k, and its water contact angle is 105°. Infrared spectral characterization of the graft copolymer showed that the hydroxyl-terminated polyisobutylene had been successfully grafted onto the side chains of the isobutylene-maleic anhydride copolymer.

[0084] Example 7

[0085] The difference between the preparation method of the graft copolymer and that in Example 1 is that in the preparation of the terminal hydroxyl polyisobutylene, the CH3Cl solution containing PIB-OH2.3k is directly applied to the subsequent graft copolymer reaction.

[0086] Another difference lies in the synthesis of the graft copolymer. In this process, 10g of isobutylene-maleic anhydride copolymer (denoted as IBMA50k, Mw / Mn = 2.57) with a number-average molecular weight of 50000g / mol was dissolved in 60g of DMF (64mL), and then mixed with 10mL of the aforementioned CH3Cl solution containing PIB-OH2.3k to obtain a homogeneous solution. The sum of the mass percentages of the isobutylene-maleic anhydride copolymer and the hydroxyl-terminated polyisobutylene in the resulting homogeneous solution was 16%, and the mixture was reacted at 80℃ for 10h. The grafting rate of IBMA-g-PIB was determined to be 2% by titration. The resulting graft copolymer is denoted as IBMA50k-g2-PIB2.3k, and its water contact angle is 75°. Infrared spectral characterization of the graft copolymer showed that the hydroxyl-terminated polyisobutylene had been successfully grafted onto the side chains of the isobutylene-maleic anhydride copolymer.

[0087] Example 8

[0088] The preparation method of the graft copolymer differs from that in Example 1 in that, during the synthesis of the graft copolymer, 10g of isobutylene-maleic anhydride copolymer (denoted as IBMA100k, Mw / Mn = 2.89) with a number average molecular weight of 100,000 g / mol and 20g of the obtained PIB-OH2.3k were dissolved together in 60g of DMF (i.e., 64mL) to form a homogeneous solution, and reacted at 100℃ for 8h. The total mass percentage of isobutylene-maleic anhydride copolymer and hydroxyl-terminated polyisobutylene in the homogeneous solution was 33%. The grafting rate of the obtained IBMA-g-PIB was determined to be 10% by titration. The obtained graft copolymer is denoted as IBMA100k-g10-PIB2.3k, and its water contact angle is 95°. The infrared spectral characterization results of the graft copolymer show that hydroxyl-terminated polyisobutylene has been successfully grafted onto the side chains of the isobutylene-maleic anhydride copolymer.

[0089] Example 9

[0090] The preparation method of the graft copolymer differs from that in Example 1 in that, during the synthesis of the graft copolymer, 7g of isobutylene-maleic anhydride copolymer (denoted as IBMA250k, Mw / Mn = 3.13) with a number-average molecular weight of 250,000 g / mol and 20g of the obtained PIB-OH2.3k were dissolved together in 60g of DMF (i.e., 64mL) to form a homogeneous solution, and reacted at 100℃ for 8h. The total mass percentage of isobutylene-maleic anhydride copolymer and hydroxyl-terminated polyisobutylene in the homogeneous solution was 31%. The grafting rate of the obtained IBMA-g-PIB was determined to be 16% by titration. The obtained graft copolymer is denoted as IBMA250k-g16-PIB2.3k, and its water contact angle is 110°. The infrared spectral characterization results of the graft copolymer show that hydroxyl-terminated polyisobutylene has been successfully grafted onto the side chains of the isobutylene-maleic anhydride copolymer.

[0091] Example 10

[0092] The preparation method of the graft copolymer differs from that in Example 1 in that, during the synthesis of the graft copolymer, 6g of isobutylene-maleic anhydride copolymer (denoted as IBMA300k, Mw / Mn = 2.94) with a number-average molecular weight of 300,000 g / mol and 20g of the obtained PIB-OH2.3k were dissolved together in 60g of DMF (i.e., 64mL) to form a homogeneous solution, and reacted at 100℃ for 8h. The total mass percentage of isobutylene-maleic anhydride copolymer and hydroxyl-terminated polyisobutylene in the homogeneous solution was 30%. The grafting rate of the obtained IBMA-g-PIB was determined to be 20% by titration. The obtained graft copolymer is denoted as IBMA300k-g20-PIB2.3k, and its water contact angle is 115°. The infrared spectral characterization results of the graft copolymer show that hydroxyl-terminated polyisobutylene has been successfully grafted onto the side chains of the isobutylene-maleic anhydride copolymer.

[0093] Example 11

[0094] 0.1 g of nano-alumina and 0.05 g of IBMA15k-g25-PIB1.0k graft copolymer (prepared in Example 4) were sequentially added to 10 mL of cyclohexane solution to obtain a mixed system. After sonication for 30 min, the absorbance of the mixed system was observed using a UV-Vis spectrophotometer (Agilent 8453UV-vis, Agilent Technologies, USA). The absorbance value measured immediately after sonication was taken as 100%. The absorbance values ​​corresponding to 6 h, 12 h, 18 h, 24 h, 48 h, 72 h, 96 h, and 120 h were 100%, 100%, 100%, 100%, 99%, 98%, 97%, and 97%, respectively. The absorbance of the mixed system could be maintained above 95%, indicating that using the graft copolymer as a dispersant can make nano-alumina stable and uniformly dispersed in cyclohexane for a long time.

[0095] Example 12

[0096] 0.1 g of nano-alumina and 0.05 g of IBMA15k-g25-PIB1.0k graft copolymer (prepared in Example 4) were sequentially added to 10 mL of n-hexane liquid to obtain a mixed system. After sonication for 30 min, the absorbance of the system was observed using a UV-Vis spectrophotometer. The absorbance measured immediately after sonication was taken as 100%. The absorbance corresponding to 6 h, 12 h, 18 h, 24 h, 48 h, 72 h, 96 h, and 120 h were 100%, 100%, 100%, 100%, 99%, 99%, 98%, and 98%, respectively. The absorbance of the mixed system could be maintained above 95%, indicating that using the graft copolymer as a dispersant can make nano-alumina stable and uniformly dispersed in n-hexane for a long time.

[0097] Example 13

[0098] 0.1 g of nano-alumina and 0.05 g of IBMA15k-g25-PIB1.0k graft copolymer (prepared in Example 4) were sequentially added to 10 mL of n-heptane liquid to obtain a mixed system. After sonication for 30 min, the absorbance of the system was observed using a UV-Vis spectrophotometer. The absorbance measured immediately after sonication was taken as 100%. The absorbances corresponding to 6 h, 12 h, 18 h, 24 h, 48 h, 72 h, 96 h, and 120 h were 100%, 100%, 100%, 99%, 98%, 98%, 97%, and 96%, respectively. The absorbance of the mixed system could be maintained above 95%, indicating that using the graft copolymer as a dispersant can make nano-alumina stable and uniformly dispersed in n-hexane for a long time.

[0099] Example 14

[0100] 0.1 g of nano-alumina and 0.01 g of IBMA15k-g25-PIB1.0k graft copolymer (prepared in Example 4) were sequentially added to 10 mL of cyclohexyl liquid to obtain a mixed system. After sonication for 30 min, the change in absorbance of the mixed system was observed using a UV-Vis spectrophotometer. The absorbance value measured immediately after sonication was taken as 100%. When the amount of IBMA15k-g25-PIB1.0k added was 0.01 g, the absorbance of the mixed system after 6 h, 12 h, 18 h, 24 h, 48 h, 72 h, 96 h, and 120 h were 100%, 100%, 98%, 95%, 82%, 78%, 75%, and 68%, respectively.

[0101] Example 15

[0102] The difference from Example 14 is that the amount of IBMA15k-g25-PIB1.0k graft copolymer (obtained in Example 4) was adjusted to 0.02g. The absorbance of the mixed system after 6h, 12h, 18h, 24h, 48h, 72h, 96h, and 120h was 100%, 100%, 100%, 98%, 95%, 92%, 90%, and 88%, respectively.

[0103] Example 16

[0104] The difference from Example 14 is that the amount of IBMA15k-g25-PIB1.0k graft copolymer (obtained in Example 4) was adjusted to 0.025g. The absorbance after 6h, 12h, 18h, 24h, 48h, 72h, 96h, and 120h was 100%, 100%, 100%, 99%, 98%, 97%, 95%, and 95%, respectively. The absorbance of the system can be maintained above 95%.

[0105] Example 17

[0106] The difference from Example 14 is that the amount of IBMA15k-g25-PIB1.0k graft copolymer (obtained in Example 4) was adjusted to 0.1g, and the absorbance of the mixed system after 6h, 12h, 18h, 24h, 48h, 72h, 96h, and 120h was 100%, 100%, 100%, 100%, 99%, 99%, 99%, and 98%, respectively.

[0107] Example 18

[0108] The difference from Example 14 is that the amount of IBMA15k-g25-PIB1.0k graft copolymer (obtained in Example 4) was adjusted to 0.2g, and the absorbance of the mixed system after 6h, 12h, 18h, 24h, 48h, 72h, 96h, and 120h was 100%, 100%, 100%, 100%, 99%, 99%, and 98%, respectively.

[0109] Example 19

[0110] 0.1 g of nano-alumina and 0.05 g of IBMA50k-g2-PIB2.3k graft copolymer (prepared in Example 7) were sequentially added to 10 mL of cyclohexyl liquid to obtain a mixed system. After sonication for 30 min, the absorbance of the mixed system was observed using a UV-Vis spectrophotometer. The absorbance measured immediately after sonication was taken as 100%. The absorbances corresponding to 6 h, 12 h, 18 h, 24 h, 48 h, 72 h, 96 h, and 120 h were 100%, 98%, 97%, 92%, 86%, 73%, 70%, and 62%, respectively. It can be seen that the grafting rate of the graft copolymer directly affects its dispersion performance.

[0111] Example 20

[0112] 0.1 g of nano-alumina and 0.05 g of IBMA5k-g36-PIB1.3k graft copolymer (prepared in Example 3) were sequentially added to 10 mL of cyclohexyl liquid to form a mixed system. After sonication for 30 min, the absorbance of the system was observed using a UV-Vis spectrophotometer. The absorbance measured immediately after sonication was taken as 100%. The absorbances corresponding to 6 h, 12 h, 18 h, 24 h, 48 h, 72 h, 96 h, and 120 h were 100%, 100%, 100%, 100%, 100%, 99%, and 99%, respectively. It can be seen that the absorbance of the mixed system can be maintained above 95%, indicating that using BMA5k-g36-PIB1.3k graft copolymer as a dispersant can make nano-alumina stable and uniformly dispersed in non-polar solvents for a long time.

[0113] Comparative Example 1

[0114] The water contact angle of the IBMA5k (Mw / Mn=2.81) membrane with a number average molecular weight of 5000 g / mol is 65°.

[0115] Comparative Example 2

[0116] 5 g of IBMA15k (number-average molecular weight 15000 g / mol, Mw / Mn = 2.64) and 10 g of polyethylene glycol monomethyl ether (mPEG, number-average molecular weight 1000 g / mol) were dissolved in 50 g of N,N-dimethylformamide (DMF) to form a mixture. The total mass percentage of isobutylene-maleic anhydride copolymer and polyethylene glycol monomethyl ether in this mixture was 23%. The mixture was reacted at 110 °C for 5 h. The grafting rate of the obtained IBMA-g-mPEG was determined to be 25% by titration. The resulting graft copolymer was designated IBMA15k-g25-mPEG1.0k, and its water contact angle was 52°.

[0117] Comparative Example 3

[0118] 0.1 g of nano-alumina was added to 10 mL of cyclohexyl liquid to form a mixture. The mixture was sonicated for 30 min and then allowed to stand. The absorbance of the system was observed using a UV-Vis spectrophotometer (Agilent 8453UV-vis, Agilent Technologies, USA). The absorbance value measured immediately after sonication was considered 100%. After 20 min, the absorbance of the system decreased to 25%, indicating that nano-alumina cannot be uniformly and stably dispersed in non-polar solvents without a dispersant.

[0119] Comparative Example 4

[0120] 0.1 g of nano-alumina and 0.05 g of IBMA15k-g25-mPEG1.0k graft copolymer (Comparative Example 2) were sequentially added to 10 mL of cyclohexyl liquid to obtain a mixed system. After sonication for 30 min, the change in absorbance of the system was observed using a UV-Vis spectrophotometer. The absorbance value measured immediately after sonication was regarded as 100%. After 20 min, the absorbance of the system decreased to 27%, indicating that when the branched chain becomes the polar segment mPEG, it is impossible to make the nano-alumina uniformly and stably dispersed in a non-polar solvent.

[0121] As can be seen from Examples 1 to 10, the graft copolymers prepared in the examples include an isobutylene-maleic anhydride copolymer backbone and polyisobutylene side chains grafted onto the isobutylene-maleic anhydride copolymer. The grafting rate of the polyisobutylene segments in the graft copolymer is 1% to 38%, and the water contact angle of the graft copolymer is 75° to 117°. It has both hydrophilic and hydrophobic properties, is suitable for use in non-polar nanofluid systems, and maintains good stability and dispersibility.

[0122] In Examples 1-10, compared to Comparative Examples 1 and 2, the water contact angle of the grafted copolymers was improved by grafting non-polar polyisobutylene onto the surface of the polar isobutylene-maleic anhydride copolymer. More specifically, compared to IBMA5k in Comparative Example 1, the water contact angle of the grafted copolymers obtained by grafting PIB-OH onto IBMA5k in Examples 1-3 was increased by 32° to 52°. This indicates that the hydrophobicity of the grafted copolymers in Examples 1-3 was improved compared to IBMA5k, which is beneficial for their application in non-polar nanofluid systems, maintaining good stability and dispersibility.

[0123] Compared to Comparative Example 4 (using the graft copolymer prepared in Comparative Example 2, with a polar isobutylene-maleic anhydride copolymer as the main chain and polar polyethylene glycol monomethyl ether as the side chain), Examples 11, 19, and 20 respectively used the graft copolymers prepared in Examples 4, 7, and 3, including the polar isobutylene-maleic anhydride copolymer main chain and the side chains of non-polar polyisobutylene segments. These copolymers possess both hydrophilic and hydrophobic properties, making them suitable for use in non-polar nanofluid systems while maintaining good stability and dispersibility. Compared to Example 19 (using the graft copolymer prepared in Example 7 with a 2% grafting rate of polyisobutylene segments), Examples 11 and 20 respectively used the graft copolymers prepared in Examples 4 and 3. By further controlling the grafting rate of polyisobutylene segments in the graft copolymers from 5% to 36%, their stability and dispersibility were further improved when applied to non-polar nanofluid systems.

[0124] Compared to Comparative Example 3, Examples 11 to 18 added graft copolymers to the nanofluid, which made the nano-alumina stable and uniformly dispersed in non-polar solvents for a long time, thus improving the stability of the nanofluid.

[0125] Compared with Examples 14 and 15, Examples 11 and 16 to 18, by further controlling the mass ratio of the graft copolymer to the volume ratio of the nonpolar solvent to 0.025 g: 10 mL to 0.2 g: 10 mL, can further extend the time for uniform dispersion of nano-alumina in nonpolar fluid.

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A graft copolymer, characterized in that, It includes isobutylene-maleic anhydride copolymer segments and polyisobutylene segments grafted onto the isobutylene-maleic anhydride copolymer segments, wherein the water contact angle of the grafted copolymer is 75° to 117°.

2. The graft copolymer according to claim 1, characterized in that, The graft copolymer is prepared by esterification of isobutylene-maleic anhydride copolymer and hydroxyl-terminated polyisobutylene, wherein the hydroxyl-terminated polyisobutylene is copolymerized from polyisobutylene with unsaturated end groups and mercapto alcohol.

3. The graft copolymer according to claim 2, characterized in that, The number-average molecular weight of the isobutylene-maleic anhydride copolymer is 5000-400000 g / mol; And / or, the weight-average molecular weight to number-average molecular weight ratio of the isobutylene-maleic anhydride copolymer is 2.5 to 3.15; And / or, the number-average molecular weight of the polyisobutylene having unsaturated end groups is 1000 to 5000 g / mol; And / or, the mercapto alcohol includes 2-mercaptoethanol.

4. The graft copolymer according to claim 1, characterized in that, In the graft copolymer, the isobutylene-maleic anhydride copolymer segment is the main chain, and the polyisobutylene segment is the branch chain. And / or, the grafting rate of the polyisobutylene segments in the graft copolymer is 1% to 38%.

5. A method for preparing the graft copolymer according to any one of claims 1-4, characterized in that, Includes the following steps: The graft copolymer is prepared by mixing isobutylene-maleic anhydride copolymer and hydroxyl-terminated polyisobutylene in an organic solvent to obtain a first mixed solution, followed by esterification.

6. The method for preparing the graft copolymer according to claim 5, characterized in that, The organic solvent includes one or more of N,N-dimethylformamide and dimethyl sulfoxide; And / or, the first mixed solution is a homogeneous solution; And / or, the sum of the mass percentages of isobutylene-maleic anhydride copolymer and hydroxyl-terminated polyisobutylene in the first mixed solution is 10% to 40%. And / or, the esterification reaction is carried out at a temperature of 70–140°C for a time of 2–12 h.

7. The method for preparing the graft copolymer according to claim 5 or 6, characterized in that, The method for preparing the terminal hydroxyl polyisobutylene includes: mixing polyisobutylene with unsaturated end groups, mercapto alcohol, and photoinitiator in a solvent, and then conducting a click chemical reaction under ultraviolet light to obtain the terminal hydroxyl polyisobutylene.

8. The method for preparing the graft copolymer according to claim 7, characterized in that, The photoinitiator includes 2,2-dimethoxy-2-phenylacetophenone; And / or, the solvent includes one or more of dichloromethane and trichloromethane; And / or, the reaction temperature of the click chemical reaction is 0–8°C, and the reaction time is 10–40 min.

9. A nanofluid, characterized in that, The graft copolymer includes nano-alumina, a non-polar solvent, and the graft copolymer prepared by any one of claims 1 to 4 or any one of claims 5 to 8.

10. The nanofluid according to claim 9, characterized in that, The mass ratio of the graft copolymer to the volume ratio of the nonpolar solvent is 0.025 g: 10 mL to 0.2 g: 10 mL.

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