A protective coating with a full-process synergistic inhibition function of degradation and a preparation method thereof

Abstract

The application provides a protective coating with deterioration whole-process synergistic inhibition function and a preparation method thereof. The protective coating is prepared from a chain extender, a polyurethane prepolymer and a bisphenol A epoxy resin in a molar ratio of 3:2:3 under certain conditions. In the protective coating, the 4-position NCO bond of the NCO-terminated polyurethane prepolymer is combined with the borate ester bond introduced by the chain extender to form a boron-nitrogen coordination bond; and the 2-position NCO bond of the NCO-terminated polyurethane prepolymer is combined with the bisphenol A type epoxy resin matrix through a hydroxyl group. The protective coating with deterioration whole-process synergistic inhibition function provided by the application adopts a brand-new idea, introduces the chain extender and the epoxy resin matrix into the polyurethane prepolymer respectively, forms a repairable three-level network structure system, and significantly improves the high-efficiency toughening function. The aforementioned protective coating is applied to the surface of concrete and steel structure, and realizes effective protection under extreme environmental conditions such as corrosion resistance and impact resistance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of organic composite materials, and relates to a protective coating, in particular to a protective coating with a synergistic inhibition function in the whole deterioration process and a preparation method. BACKGROUND

[0002] In coastal engineering, building materials such as concrete and steel structures are corroded by harsh environmental factors, which is the main reason for the premature failure of the structure; corrosion protection can significantly improve the service life and greatly reduce the cost. Common corrosion protection strategies include surface coating, covalent surface chemical modification, corrosion-resistant material corrosion inhibitor, and electrochemical protection. Among them, surface polymer coating has a wide range of applications, good protection effect, and simple operation, and is recognized as the most effective and widely used protection method. Compared with other protection technologies, surface coating protection technology can well block the penetration of corrosive ions in the external environment, and provide excellent corrosion protection by completely isolating the external environment from the protected substrate.

[0003] In surface coating protection technology, epoxy coatings are widely used due to their excellent protection of building materials under harsh conditions, which is due to the excellent properties of epoxy resin materials: mechanical properties, electrical insulation, corrosion resistance, chemical stability, etc. However, epoxy resin itself has the disadvantages of poor impact toughness, high brittleness, high internal stress, high repair frequency, and high cost, which makes it unable to meet the high protection standards of harsh environments. Many scholars have conducted modification research on the epoxy matrix to enhance the properties of the epoxy resin to meet more stringent service conditions. However, the existing coating protection technology still has the following unavoidable shortcomings: (1) the mechanical properties of the protective coating are poor, the protection effect cannot meet the demand, the deformation recovery ability under external force is poor, and the application range is limited; (2) the modification and toughening effect of traditional toughening technology cannot meet the expected value, the toughening range is small, and if the epoxy matrix is excessively modified, the mechanical strength, modulus and thermal stability of the epoxy resin system will be reduced. Therefore, how to optimize the mechanical properties of the epoxy coating at the same time is a technical problem that needs to be solved in the existing technology. SUMMARY

[0004] In view of the problems existing in the surface coating protection technology in the prior art, the present application provides a protective coating with a synergistic inhibition function in the whole deterioration process and a preparation method. The protective coating with a synergistic inhibition function in the whole deterioration process disclosed by the present application adopts a new idea, introduces a chain extender and an epoxy resin matrix into a polyurethane prepolymer respectively, forms a repairable three-level network structure system, and significantly improves the high-efficiency toughening function; the aforementioned protective coating is applied to the surface of concrete and steel structure, and effective protection under extreme environmental conditions such as corrosion resistance and impact resistance is realized.

[0005] The technical scheme of the present application:

[0006] A method for preparing a protective coating with a synergistic inhibition function throughout the whole deterioration process, comprising the following steps:

[0007] (1) A certain amount of chain extender, polyurethane prepolymer and bisphenol A epoxy resin are weighed according to the molar ratio of 3:2:3; the chain extender is a mixture of N-(3-dimethylaminopropyl)-N,N-diisopropanolamine (HDB) and 2,2'-(1,4-phenylene)-bis[4-(4-hydroxybutyl)-1,3,2-dioxaborinane] (DPA) according to the molar ratio of 1:1. HDB is introduced as a chain extender to introduce a reversible borate ester bond, and the flexible ethyl segment enhances the flow of the borate ester. DPA, as a chain extender, not only provides N coordination bonds, but also combines with the polyurethane prepolymer to promote the formation of boron-nitrogen coordination bonds. The polyurethane prepolymer is an NCO-terminated polyurethane prepolymer.

[0008] (2) The chain extender is mixed with the polyurethane prepolymer and reacted at 50-70℃ for 4-5h to fully react the 4-position NCO bond of the polyurethane prepolymer molecular chain. This step increases the chain length and folding of the polyurethane prepolymer by introducing the chain extender into it, and also introduces a self-repairing functional bond to significantly improve its mechanical properties.

[0009] (3) Bisphenol A epoxy resin is added to the system after step (2), heated to 90-120℃, and reacted for 4-5h to react the 2-position NCO bond of the polyurethane prepolymer, obtaining a composite modified epoxy resin, i.e. a protective coating with a synergistic inhibition function throughout the whole deterioration process. By controlling the temperature, the present application ensures that the 2,4-position NCO bonds of the polyurethane prepolymer participate in the reaction at the right time, so that the two end NCO bonds can participate in the chain extension reaction and grafting reaction respectively, and the crosslinking density of the epoxy resin cured product is not affected after toughening in this way.

[0010] The NCO-terminated polyurethane prepolymer is obtained by (a) reacting toluene diisocyanate TDI and polyethylene glycol PEG200; or (b) reacting toluene diisocyanate TDI and castor oil. The specific operation of (a) is as follows: polyethylene glycol PEG200 is dehydrated, TDI is added according to the molar ratio of PEG200:TDI=1:1, then stirred at 90-120℃ for 4h to obtain the NCO-terminated polyurethane prepolymer. The specific operation of (b) is as follows: castor oil is dehydrated, TDI is added according to the molar ratio of castor oil:TDI=1:2.8, then stirred at 90-120℃ for 4h to obtain the NCO-terminated polyurethane prepolymer.

[0011] The protective coating is prepared by the method as described above. In the protective coating, the 4-position NCO bond of the NCO-terminated polyurethane prepolymer is combined with the borate bond introduced by the chain extender to form a boron-nitrogen coordination bond; and the 2-position NCO bond of the NCO-terminated polyurethane prepolymer is combined with the bisphenol A type epoxy resin matrix through a hydroxyl group. The polyurethane prepolymer is synthesized by using a flexible long-chain polyol, the borate bond is introduced by adding a chain extender, and the boron-nitrogen coordination bond (B-N) is formed by adding a nitro compound, thereby forming a secondary network structure. On this basis, the secondary network structure is grafted into the epoxy resin, the proportion of the soft segment in the epoxy resin is significantly increased, the coordination between molecules promotes the formation of a tertiary network structure, and the mechanical properties of the material are greatly improved. At the same time, the B-N coordination bond and the urethane hydrogen act as sacrificial bonds, which are broken under external force to dissipate energy and release and recover after release. The formation of the internal coordination bond causes the folding of the PU main chain, and the destruction of the coordination bond causes the unfolding and sliding of the polymer network, thereby improving the toughness of the material and greatly improving the brittleness and easy breaking of the traditional epoxy material.

[0012] The application of the protective coating as described above in concrete protection or steel structure protection. The specific operation is as follows: the protective coating is mixed and stirred with an epoxy curing agent at a weight ratio of 4:1-2:1 under the temperature condition of 0-30 DEG C, is brushed on the surface of concrete or steel structure within 20 min, is air-dried at room temperature for 3-5 h, and is hardened and shaped.

[0013] The beneficial effects of the present application are as follows:

[0014] (1) The protective coating described in the present application proposes a brand-new idea, i.e. introducing a chain extender and an epoxy resin matrix into a polyurethane prepolymer respectively to form a repairable tertiary network structure system, which significantly improves the high-efficiency toughening function; and thus the effective protection of concrete and steel structure under extreme environmental conditions such as corrosion resistance and impact resistance is realized.

[0015] (2) The protective coating of the present application has an elongation at break of 21%, which is increased by 83% compared with a pure epoxy coating; the tensile strength is increased to 36 MPa, which is increased by 38% compared with a pure epoxy coating; and the impact toughness is 30 MPa, which is increased by more than 45% compared with a pure epoxy coating.

[0016] (3) The protective coating described in the present application not only has good mechanical properties, but also can be self-repaired; the first strength recovery rate after being subjected to a prestress or a pre-damage is as high as 95%, and after 13 times of "loading-recovery-loading", the initial strength can still be recovered by 51%. BRIEF DESCRIPTION OF DRAWINGS

[0017] The accompanying drawings are provided to illustrate the present application. Figure 1 The accompanying drawings are provided to illustrate the present application.

[0018] Figure 1 is a micrograph of a protective coating system according to the present application. Figure 2 Figure 2 is a micrograph of a protective coating system according to the present application.

[0019] Figure 3 is a micrograph of a protective coating system according to the present application. Figure 3 Figure 4 is a micrograph of a protective coating system according to the present application.

[0020] Figure 5 is an infrared spectrum of a polyurethane prepolymer, chain extender modified polyurethane, and composite modified epoxy coating according to Example 1. Figure 4 Figure 6 is a micrograph of a protective coating system according to the present application.

[0021] Figure 7 is a micrograph of a protective coating system according to the present application.

[0022] The present application is further described in conjunction with the following examples.

[0023] Example 1: Preparation and application of a protective coating with a synergistic inhibition function throughout the entire degradation process

[0024] A method for preparing a protective coating with a synergistic inhibition function throughout the entire degradation process, comprising the following steps:

[0025] (1) A certain amount of chain extender, NCO-terminated polyurethane prepolymer, and bisphenol A epoxy resin are weighed according to a molar ratio of 3:2:3. The chain extender is N-(3-dimethylaminopropyl)-N,N-diisopropanolamine and 2,2'-(1,4-phenylene)-bis[4-(4-hydroxybutyl)-1,3,2-dioxaborolane]. The NCO-terminated polyurethane prepolymer is obtained by reacting toluene diisocyanate (TDI) and polyethylene glycol (PEG200). The specific operation is as follows: polyethylene glycol (PEG200) is dehydrated, TDI is added according to a molar ratio of PEG200:TDI = 1:1, and then stirred at 90°C for 4h to obtain the NCO-terminated polyurethane prepolymer.

[0026] (2) The chain extender is mixed with the polyurethane prepolymer, and reacted at 50°C for 5h to make the 4-position NCO bond of the polyurethane prepolymer chain fully react with the borate bond introduced by the chain extender to form a boron-nitrogen coordination bond.

[0027] (3) Bisphenol A epoxy resin is added to the system after step (2), heated to 120°C, and reacted for 5h to make the 2-position NCO bond of the polyurethane prepolymer react, so that the 2-position NCO bond of the polyurethane prepolymer is combined with the bisphenol A type epoxy resin matrix through the hydroxyl group to obtain a composite modified epoxy resin, i.e. a protective coating with a synergistic inhibition function throughout the entire degradation process.

[0028] ​The aforementioned protective coating is applied to concrete protection. Specifically, the protective coating and phenolic amine curing agent are mixed at a weight ratio of 4:1 at 20°C until homogeneous. The mixture is then applied to the concrete or steel structure surface within 20 minutes and allowed to air dry at room temperature for 5 hours to harden and set.

[0029] Example 2: Preparation and application of a protective coating with synergistic inhibition of degradation throughout the entire process.

[0030] Unlike Example 1,

[0031] (1) The chain extender is N-(3-dimethylaminopropyl)-N,N-diisopropanolamine and 2,2'-(1,4-phenylene)-bis[4-(4-hydroxybutyl)-1,3,2-dioxaborane]. The NCO-terminated polyurethane prepolymer is obtained by reacting toluene diisocyanate (TDI) and polyethylene glycol (PEG200). Specifically, PEG200 is dehydrated, TDI is added at a molar ratio of PEG200:TDI = 1:1, and then the mixture is stirred at 120°C for 4 hours to obtain the NCO-terminated polyurethane prepolymer.

[0032] (2) Mix the chain extender with the polyurethane prepolymer and react at 70°C for 4 hours to allow the NCO bond at the 4-position of the polyurethane prepolymer molecular chain to react fully.

[0033] (3) Add bisphenol A epoxy resin to the system after the reaction in step (2), heat to 90°C and react for 4 hours to react the NCO bond at the 2-position of the polyurethane prepolymer to obtain a composite modified epoxy resin, which is a protective coating with synergistic inhibition function throughout the degradation process.

[0034] The aforementioned protective coating is applied to steel structure protection. Specifically, the protective coating and phenolic amine curing agent are mixed at a weight ratio of 3:1 at 15°C until homogeneous. The mixture is then applied to the concrete or steel structure surface within 20 minutes and allowed to air dry at room temperature for 5 hours to harden and set.

[0035] Example 3: Preparation and application of a protective coating with synergistic inhibition of the entire degradation process

[0036] Unlike Example 1,

[0037] (1) The chain extender is N-(3-dimethylaminopropyl)-N,N-diisopropanolamine and 2,2'-(1,4-phenylene)-bis[4-(4-hydroxybutyl)-1,3,2-dioxaborolane]. The NCO-terminated polyurethane prepolymer is obtained by reaction of toluene diisocyanate TDI and castor oil. The specific operation is as follows: the castor oil is dehydrated, TDI is added according to the molar ratio of castor oil: TDI = 1:2.8, then stirred at 90°C for 4h to obtain the NCO-terminated polyurethane prepolymer.

[0038] (2) The chain extender is mixed with the polyurethane prepolymer, and reacted at 50°C for 4h to make the 4-position NCO bond of the polyurethane prepolymer chain fully react, to obtain a chain extender modified polyurethane prepolymer.

[0039] (3) Bisphenol A epoxy resin is added to the system after step (2) reaction, heated to 120°C and reacted for 4h to make the 2-position NCO bond of the polyurethane prepolymer react, to obtain a composite modified epoxy resin, i.e. a protective coating with synergistic inhibition function throughout the deterioration process.

[0040] The foregoing protective coating is applied to concrete protection. The specific operation is as follows: the protective coating is mixed with a phenolic amine curing agent at a weight ratio of 2:1 at a temperature of 10°C, and stirred uniformly, and applied to the surface of concrete or steel structure within 20min, and air dried at room temperature for 3h, and hardened to form.

[0041] Example 4: Preparation and application of protective coating with synergistic inhibition function throughout the deterioration process

[0042] Different from example 1,

[0043] (1) The chain extender is N-(3-dimethylaminopropyl)-N,N-diisopropanolamine and 2,2'-(1,4-phenylene)-bis[4-(4-hydroxybutyl)-1,3,2-dioxaborolane]. The NCO-terminated polyurethane prepolymer is obtained by reaction of toluene diisocyanate TDI and castor oil. The specific operation is as follows: the castor oil is dehydrated, TDI is added according to the molar ratio of castor oil: TDI = 1:2.8, then stirred at 120°C for 4h to obtain the NCO-terminated polyurethane prepolymer.

[0044] (2) The chain extender is mixed with the polyurethane prepolymer, and reacted at 70°C for 5h to make the 4-position NCO bond of the polyurethane prepolymer chain fully react, to obtain a chain extender modified polyurethane prepolymer.

[0045] (3) To the system after step (2) reaction, add bisphenol A epoxy resin, heat to 90°C, and react for 5h, so that the 2-position NCO bond of the polyurethane prepolymer reacts, to obtain a composite modified epoxy resin, i.e. a protective coating with a synergistic inhibition function in the whole deterioration process.

[0046] The foregoing protective coating is applied to the protection of steel structures. The specific operation is as follows: the protective coating is mixed with a phenolic amine curing agent at a weight ratio of 2:1 under the temperature condition of 0°C, and is uniformly stirred, and is brushed on the surface of concrete or a steel structure within 20 min, and is air-dried at room temperature for 3h, and is hardened and shaped.

[0047] Example 5: Preparation and application of a protective coating with a synergistic inhibition function in the whole deterioration process

[0048] Different from example 1, the chain extender is N-(3-dimethylaminopropyl)-N,N-diisopropanolamine and 2,2'-(1,4-phenylene)-bis[4-(4-hydroxybutyl)-1,3,2-dioxaborolane].

[0049] (1) The chain extender is N-(3-dimethylaminopropyl)-N,N-diisopropanolamine and 2,2'-(1,4-phenylene)-bis[4-(4-hydroxybutyl)-1,3,2-dioxaborolane]. The NCO-terminated polyurethane prepolymer is obtained by the reaction of toluene diisocyanate TDI and polyethylene glycol PEG200. The specific operation is as follows: polyethylene glycol PEG200 is subjected to dehydration treatment, TDI is added at a molar ratio of PEG200:TDI=1:1, and then the NCO-terminated polyurethane prepolymer is obtained by stirring at 100°C for 4.5h.

[0050] (2) The chain extender is mixed with the polyurethane prepolymer, and the 4-position NCO bond of the polyurethane prepolymer is fully reacted by reacting at 60°C for 4.5h.

[0051] (3) To the system after step (2) reaction, add bisphenol A epoxy resin, heat to 100°C, and react for 4.5h, so that the 2-position NCO bond of the polyurethane prepolymer reacts, to obtain a composite modified epoxy resin, i.e. a protective coating with a synergistic inhibition function in the whole deterioration process.

[0052] The foregoing protective coating is applied to the protection of steel structures. The specific operation is as follows: the protective coating is mixed with a phenolic amine curing agent at a weight ratio of 2:1 under the temperature condition of 0°C, and is uniformly stirred, and is brushed on the surface of concrete or a steel structure within 20 min, and is air-dried at room temperature for 3h, and is hardened and shaped.

[0053] Example 6: Infrared spectrum of a polyurethane prepolymer, a chain extender modified polyurethane, and a composite modified coating

[0054] The infrared spectrum of the polyurethane prepolymer, the chain extender modified polyurethane of step (1) in Examples 1-5 and the final composite modified coating were characterized, and the results were consistent. The following will be described by taking Example 1 as an example, and the details are shown in Figure 4 .

[0055] As can be seen from Figure 4 , after the reaction of the chain extender with the polyurethane prepolymer, the characteristic vibration peak of urethane appears at 3318 cm -1 , the characteristic vibration peak of borate appears at 657 cm -1 , indicating that after step (1), the polyurethane containing dynamic borate ester bonds is successfully synthesized. In addition, the characteristic vibration peak of boron-nitrogen coordination bond appears at 1240 cm -1 , indicating that the reaction of the borate bond in the chain extender with the polyurethane prepolymer promotes the coordination of boron and nitrogen. At the same time, the characteristic peak of isocyanate still exists at 2250 cm -1 , indicating that the reaction product still has free isocyanate groups (NCO-) that can participate in subsequent grafting reactions.

[0056] As can be seen from the infrared spectrum of the composite modified coating, the characteristic peak of isocyanate (NCO-) completely disappears at 2242-2273 cm -1 , and the characteristic peak of borate bond appears at 660 cm -1 , the characteristic vibration peak of boron-nitrogen coordination bond appears at 1230 cm -1 , and the characteristic peak of urethane appears at 1678 cm -1 . This indicates that after step (2), the grafting reaction of the bisphenol A epoxy resin with the chain extender modified polyurethane prepolymer occurs, and a new substance, i.e., the composite modified epoxy coating, is synthesized.

[0057] Example 7: Mechanical property test of the composite modified epoxy protective coating prepared in Examples 1-5

[0058] The composite modified epoxy protective coating prepared in Examples 1-5 and the pure epoxy protective coating as a control were respectively subjected to tensile test by using a tensile testing machine and impact test by using a pendulum testing machine, and the results are shown in Table 1.

[0059] As can be seen from Table 1, the elongation at break of the protective coating prepared in Examples 1-5 is 14.11-20.99%, which is increased by 23-83% compared with the pure epoxy coating; the maximum tensile strength is 28.70-36.00 MPa, which is increased by 10-38% compared with the pure epoxy protective coating; and the impact toughness is 28.55-30.00 MPa, which is increased by 38-45% compared with the pure epoxy protective coating.

[0060] Table 1: Mechanical property test results of the composite modified epoxy protective coating prepared in Examples 1-5 and the control

[0061] Elongation at break Maximum tensile strength Impact resistance Example 1 14.11％ 28.70 MPa 28.55 MPa Example 2 16.40％ 29.48 MPa 28.73 MPa Example 3 17.89％ 36.00 MPa 30.00 MPa Example 4 17.09％ 33.91 MPa 28.68 MPa Example 5 20.99％ 35.22 MPa 29.33 MPa Pure epoxy protective coating 11.47％ 26.09 MPa 20.68 MPa

[0062] Example 8: Repair performance test of the composite modified epoxy protective coating prepared in Examples 1-5

[0063] Tensile test was performed on the composite modified epoxy protective coating prepared in Examples 1-5 by a tensile testing machine, pre-stress simulation was performed by loading to 60% of the maximum tensile stress, and 2-3h room temperature standing recovery was performed after pre-stress or pre-damage effect, and 13 experiments were continuously performed. The tensile stress after recovery is shown in Table 2.

[0064] As shown in Table 2, the first strength recovery rate of the composite modified epoxy protective coating prepared in Examples 1-5 is 95-98%, and after 13 times of "loading-recovery-loading", it can still recover 45-51% of the initial maximum tensile stress.

[0065] Table 2 Repair performance test results of the composite modified epoxy protective coating prepared in Examples 1-5

[0066] Example 1 Example 2 Example 3 Example 4 Example 5 Maximum tensile strength 28.70 MPa 29.48 MPa 36.00 MPa 33.91 MPa 35.22 MPa 1st recovery 27.22 MPa 28 MPa 34.18 MPa 32.19 MPa 34.46 MPa 2nd recovery 26.63 MPa 27.56 MPa 33.77 MPa 31.68 MPa 34.41 MPa 3rd recovery 26.05 MPa 27.1 MPa 33.33 MPa 31.27 MPa 34.01 MPa 4th recovery 25.54 MPa 26.54 MPa 32.98 MPa 30.56 MPa 33.88 MPa 5th recovery 25.01 MPa 26 MPa 32.45 MPa 30.11 MPa 33.29 MPa 6th recovery 24.17 MPa 25.33 MPa 31.55 MPa 29.69 MPa 32.74 MPa 7th recovery 23.34 MPa 24.37 MPa 30.82 MPa 28.74 MPa 31.6 MPa 8th recovery 22.37 MPa 23.05 MPa 29.1 MPa 27.33 MPa 30.21 MPa 9th recovery 21.56 MPa 22.35 MPa 28.11 MPa 26.25 MPa 29.01 MPa 10th recovery 20.4 MPa 20.25 MPa 26.13 MPa 25.13 MPa 27.22 MPa 11th recovery 18.55 MPa 18.74 MPa 24.25 MPa 23.01 MPa 25.14 MPa 12th recovery 15.36 MPa 17.22 MPa 21.1 MPa 20.77 MPa 23.51 MPa 13th recovery 12.88 MPa 14.7 MPa 16.4 MPa 16.95 MPa 17.96 MPa

[0067] As can be seen from the above, the mechanical properties of the composite modified epoxy protective coating prepared in Examples 1-5 of the present application are significantly improved. Among them, the elongation at break is increased to 21%, which is increased by 83% compared with the pure epoxy coating; the tensile strength is increased to 36MPa, which is increased by 38% compared with the pure epoxy coating; the impact toughness reaches 30MPa, which is increased by more than 45% compared with the pure epoxy coating. In addition, the composite modified epoxy protective coating prepared in Examples 1-5 of the present application can be self-repaired; after 13 times of "loading-recovery-loading", it can still recover 51% of the initial strength. This is because the protective coating described in the present application introduces the chain extender and the epoxy resin matrix into the polyurethane prepolymer respectively, forming a repairable three-level network structure system, which significantly improves its high-efficiency toughening function, producing an unpredictable technical effect.

Claims

1. A method for preparing a protective coating with synergistic inhibition of degradation throughout the entire process, characterized in that: Includes the following steps: (1) Weigh appropriate amounts of chain extender, NCO-terminated polyurethane prepolymer and bisphenol A epoxy resin according to a molar ratio of 3:2:3; (2) Mix the chain extender with the polyurethane prepolymer and react at 50-70℃ for 4-5 h to allow the NCO bond at position 4 of the polyurethane prepolymer molecular chain to react fully; (3) Add bisphenol A epoxy resin to the system after the reaction in step (2), heat to 90-120℃ and react for 4-5 h to allow the NCO bond at position 2 of the polyurethane prepolymer to react, and obtain a composite modified epoxy resin, which is a protective coating with synergistic inhibition function throughout the degradation process; The chain extender is a mixture of N-(3-dimethylaminopropyl)-N,N-diisopropanolamine and 2,2'-(1,4-phenylene)-bis[4-(4-hydroxybutyl)-1,3,2-dioxaborane] in a molar ratio of 1:

1.

2. The method for preparing the protective coating according to claim 1, characterized in that: The NCO-terminated polyurethane prepolymer is obtained by reacting (a) toluene diisocyanate (TDI) with polyethylene glycol (PEG200); or (b) toluene diisocyanate (TDI) with castor oil.

3. The method for preparing the protective coating according to claim 2, characterized in that: The specific operation of (a) is as follows: polyethylene glycol PEG200 is dehydrated, TDI is added at a molar ratio of PEG200:TDI=1:1, and then stirred at 90-120℃ for 4h to obtain NCO-terminated polyurethane prepolymer.

4. The method for preparing the protective coating according to claim 2, characterized in that: The specific operation of (b) is as follows: dehydrate the castor oil, add TDI at a molar ratio of castor oil:TDI=1:2.8, and then stir for 4 hours at 90-120℃ to obtain NCO-terminated polyurethane prepolymer.

5. The protective coating prepared by the method according to any one of claims 1-4.

6. The protective coating according to claim 5, characterized in that: The NCO bond at the 4-position of the NCO-terminated polyurethane prepolymer combines with the borate ester bond introduced by the chain extender to form a boron-nitrogen coordination bond; the NCO bond at the 2-position of the NCO-terminated polyurethane prepolymer combines with the bisphenol A type epoxy resin matrix through hydroxyl groups.

7. The application of the protective coating as described in claim 5 or 6, characterized in that: The specific application is for concrete protection or steel structure protection.

8. The application of the protective coating according to claim 7, characterized in that: The specific operation of the concrete protection or steel structure protection is as follows: the protective coating described in claim 5 or 6 is mixed with the epoxy curing agent at a weight ratio of 4:1-2:1 under the temperature condition of 0-30℃, and then brushed onto the concrete or steel structure surface within 20 minutes. It is then air-dried at room temperature for 3-5 hours to harden and form.

9. The application of the protective coating according to claim 7, characterized in that: The epoxy curing agent is a phenolic amine curing agent.

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