A dynamic cross-linked polyurethane with photodegradability and remodelability, and its preparation method and application

Abstract

The invention discloses a dynamic cross-linked polyurethane with photodegradability and remodelability, a preparation method and application thereof, and belongs to the technical field of polymer materials. The dynamic cross-linked polyurethane is obtained by polymerizing a chain extender, a cross-linking agent, a polymer polyol and a polyisocyanate, wherein the chain extender and the cross-linking agent both contain acetoacetate oxime bonds. During polymerization, the acetoacetate oxime bonds react with the isocyanate to generate acetoacetate oxime carbamate in the cross-linked network of the polyurethane. The acetoacetate oxime carbamate is a dynamic covalent bond that facilitates the remodeling of the polyurethane. In addition, a photodegradable unit is designed in the chain extender to facilitate the photodegradation of the polyurethane. The polyurethane not only has good mechanical properties, but also has recycling and reuse properties and controllable photodegradation properties, which is of great significance for promoting the sustainable development of polyurethane.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and in particular relates to a dynamically cross-linked polyurethane with photodegradability and remodelability, and a preparation method and application thereof. Background Art

[0002] Polyurethane (PU) possesses a microphase-separated structure (comprising flexible and rigid segments), whose mechanical behavior can be manipulated through structural design. It continues to play a vital role in automotive manufacturing, textile processing, architectural decoration, and other fields. However, PU takes hundreds of years to fully degrade in the natural environment, leading to increasingly serious microplastic pollution and toxic accumulation throughout the ecosystem. Alleviating the environmental impact of PU waste is a significant challenge.

[0003] Currently, the main method for polyurethane recycling and reuse is chemical recovery, which involves adding a degradation agent to discarded polyurethane plastics to achieve degradation. For example, Chinese patent CN 106700126 A discloses a polyurethane autocatalytic degradation recovery method. Polyurethane waste and a degradation agent are added to a reactor and stirred under nitrogen for uniform mixing. The temperature is then raised to 160-220°C using a thermal oil furnace for a degradation reaction of 0.5-3 hours. Excess degradation agent (which can be recycled) is then removed under vacuum conditions at a controlled temperature of 160-220°C and a vacuum of 1-1000 mbar. The degradation product is then directly obtained by cooling the temperature to 80°C. This method requires strict degradation conditions, is cumbersome to operate, and is complex.

[0004] Prior art has also introduced bio-based polyester polyols (such as polycaprolactone) into the polyurethane structure to enhance its biodegradability. For example, Chinese Patent CN 115181233 A discloses a controllably degradable dendritic polycaprolactone polyurethane film and its preparation method. Through molecular design, a novel stimuli-responsive, controllably degradable dendritic polycaprolactone diol is prepared. This is then reacted with a diisocyanate to synthesize a dendritic polymer prepolymer. A chain extender is then introduced to produce the controllably degradable dendritic polycaprolactone polyurethane film. The functionalized polycaprolactone segments introduced into the polyurethane film can be manipulated to induce a temperature-sensitive phase transition. Above the phase transition temperature, degradation of the film is suppressed under acidic conditions, while degradation is rapid under alkaline conditions. However, the polyurethane material disclosed in this patent is highly dependent on its degradation pathway, making it difficult to adapt to natural environments. Summary of the Invention

[0005] To address the above technical issues, the present invention provides a photodegradable and remodelable dynamically cross-linked polyurethane, its preparation method, and application. The polyurethane not only has good mechanical properties, but also has recyclability and controllable photodegradability.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A dynamically cross-linked polyurethane with photodegradability and remodelability, wherein the structural formula of the dynamically cross-linked polyurethane is:

[0008] ;

[0009] The dynamic cross-linked polyurethane is obtained by polymerizing a chain extender, a cross-linking agent, a polymer polyol and polyisocyanate.

[0010] Furthermore, the structural formula of the chain extender is: .

[0011] The structural formula of the cross-linking agent is: .

[0012] The polyisocyanate is selected from one of 4,4'-diphenylmethane diisocyanate, toluene diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, decanediisocyanate, 4,4'-dicyclohexylmethane diisocyanate and cyclohexane dimethylene diisocyanate.

[0013] The polymer polyol is selected from polycaprolactone polyol, preferably polycaprolactone diol.

[0014] The present invention also provides a method for preparing the dynamically cross-linked polyurethane with photodegradability and remodelability, which comprises the following steps: dissolving a polymer polyol, a polyisocyanate and a catalyst in an organic solvent, reacting at 50-70°C under nitrogen protection for at least 1 hour, then adding a chain extender, continuing the reaction for at least 1 hour, and finally adding a cross-linking agent. After sufficient stirring, the film is cast and dried to obtain the dynamically cross-linked polyurethane with photodegradability and remodelability.

[0015] Furthermore, the molar ratio of the polymer polyol, polyisocyanate, chain extender, and cross-linking agent is 1:2-4:0.2-1.5:0.4-2.0.

[0016] The mass ratio of the catalyst to the polymer polyol is 0.1 to 1:1000.

[0017] After adding the cross-linking agent, stirring was continued for 0.5 h.

[0018] The preparation method of the chain extender comprises the following steps:

[0019] (1-1) 2,6-bis(hydroxymethyl)-p-cresol, 2-nitrobenzyl bromide, and potassium carbonate were stirred and mixed in N,N-dimethylformamide, and reacted at 20-30°C for at least one hour. After post-treatment, the intermediate 1 was obtained.

[0020] (1-2) Intermediate 1 is reacted with tert-butyl acetoacetate at 130-150 °C for 2-4 h, and then post-treated to obtain intermediate 2.

[0021] (1-3) The intermediate product 2 is mixed with glacial acetic acid, and a sodium nitrite aqueous solution is added dropwise at -5 °C. After the addition is complete, the reaction is stirred for 12-24 h. After post-treatment, the chain extender is obtained.

[0022] Furthermore, in step (1-1), the molar ratio of 2-nitrobenzyl bromide, 2,6-bis(hydroxymethyl)-p-cresol and potassium carbonate is 1:1.0~1.3:3~7.

[0023] In step (1-2), the molar ratio of the intermediate product 1 to tert-butyl acetoacetate is 1:1.1~2.0.

[0024] In step (1-3), the molar ratio of the intermediate product 2, glacial acetic acid, and sodium nitrite is 1:4~6:2~4.

[0025] The preparation method of the cross-linking agent comprises the following steps:

[0026] (2-1) Trimethylolpropane and tert-butyl acetoacetate were reacted at 130–150 °C for 2–4 h, and the intermediate 3 was obtained after post-treatment.

[0027] (2-2) The intermediate product 3 is mixed with glacial acetic acid, and a sodium nitrite aqueous solution is added dropwise at -10 to 0 °C. After the addition is complete, the reaction is stirred for 12 to 24 h. The cross-linking agent is obtained through post-treatment.

[0028] Furthermore, in step (2-1), the molar ratio of trimethylolpropane to tert-butyl acetoacetate is 1:1.1~2.0.

[0029] In step (2-2), the molar ratio of the intermediate product 3, glacial acetic acid and sodium nitrite is 1:6~9:3~6.

[0030] The present invention also provides application of the dynamic cross-linked polyurethane with photodegradability and remodelability in the preparation of new materials.

[0031] The present invention provides a dynamic cross-linked polyurethane with photodegradability and remodelability, which is obtained by polymerizing a chain extender, a cross-linker, a polymer polyol and a polyisocyanate. The chain extender and the cross-linker both contain acetoacetate oxime bonds. During polymerization, the acetoacetate oxime bonds react with the isocyanate to generate acetoacetate oxime carbamate in the cross-linked network of the polyurethane. The acetoacetate oxime carbamate is a dynamic covalent bond that facilitates the remodeling of the polyurethane. In addition, a photodegradable unit is designed in the chain extender to facilitate the photodegradation of the polyurethane.

[0032] The present invention provides a method for preparing a dynamically cross-linked polyurethane with photodegradability and remodelability. The method comprises the following steps: first, synthesizing a chain extender having an acetoacetate oxime bond and a photodegradable unit, and a cross-linking agent having an acetoacetate oxime bond. These are then applied to the polyurethane synthesis process. During the polymerization reaction, the acetoacetate oxime bonds in the chain extender and the cross-linking agent react with polyisocyanate to generate acetoacetate oxime carbamate. The prepared cross-linked polyurethane can be remodeled multiple times by hot pressing, and can also be degraded under ultraviolet light.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1) The dynamically cross-linked polyurethane with photodegradability and remodelability provided by the present invention integrates dynamic oxime urethane bonds and photodegradable elements into the cross-linked polyurethane network to achieve a degradation mechanism of "ultraviolet light-triggered macroscopic disintegration". The dynamically cross-linked polyurethane is both photodegradable and remodelable.

[0035] 2) The structural design of the photodegradable and remodelable dynamic cross-linked polyurethane provided by the present invention is reasonable. The chain extender and cross-linker used in the polymerization both contain acetoacetate oxime groups. The acetoacetate oxime carbamate generated by the reaction with isocyanate is a new type of dynamic covalent bond that helps to remodel the polyurethane. The chain extender also contains a photodegradable unit, and the polyurethane prepared therefrom has efficient and controllable photodegradation performance.

[0036] 3) The preparation method of the chain extender and cross-linking agent provided by the present invention is mild and convenient for post-processing, which is different from the method of modifying ketone or aldehyde groups into oxime groups.

[0037] 4) The photodegradable and remodelable dynamic cross-linked polyurethane provided by the present invention not only has good mechanical properties, but also has recycling and reuse properties and controllable photodegradation properties, which is of great significance for promoting the sustainable development of polyurethane. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The synthetic route for the chain extender (5-methyl-2-(2-nitrobenzyloxy)-1,3-phenylene)bismethylenebis(acetoacetate oxime) is provided;

[0039] Figure 2 The synthetic route for the cross-linking agent 2-ethyl-2-[(acetoacetate oxime)methyl]propane-1,3-diylbis(acetoacetate oxime);

[0040] Figure 3 A preparation roadmap for cross-linked polyurethane;

[0041] Figure 4 is the H NMR spectrum of the chain extender;

[0042] Figure 5 is the H NMR spectrum of the cross-linking agent;

[0043] Figure 6 is the stress-strain curve of the cross-linked polyurethane in the embodiment;

[0044] Figure 7 The storage modulus and loss factor curves of the cross-linked polyurethane in the examples, wherein Figure A is Example 1, Figure B is Example 2, Figure C is Example 3, and Figure D is Example 4;

[0045] Figure 8 : The stress-strain curves of the cross-linked polyurethane before and after remodeling in Example 1;

[0046] Figure 9 Figures 2 and 3 are experimental diagrams of UV degradation of cross-linked polyurethane, where (a) the polyurethane of Example 1 was not irradiated with 365 nm light, (b) the polyurethane of Example 1 was irradiated with 365 nm light for 2 h, and (c) the polyurethane of Comparative Example 1 was irradiated with 365 nm light for 2 h. The solvent was tetrahydrofuran.

[0047] Figure 10 This is the H NMR spectrum of the acetoacetate oxime carbamate small molecule AB in Experimental Example 1;

[0048] Figure 11 This is a small molecule model reaction and H NMR spectrum. DETAILED DESCRIPTION

[0049] The present invention is described in detail below with reference to the embodiments. Example 1

[0050] A method for preparing a dynamically cross-linked polyurethane with photodegradability and remodelability comprises the following steps:

[0051] (1) Synthetic chain extender:

[0052] (1-1) 2-Nitrobenzyl bromide (2.16 g, 10 mmol), 2,6-bis(hydroxymethyl)-p-cresol (1.85 g, 11 mmol), and potassium carbonate (6.91 g, 50 mmol) were mixed in 100 mL of N,N-dimethylformamide and stirred at 25°C for 2 h. After the reaction, the mixture was filtered and the filtrate was poured into water to precipitate. The precipitate was separated by column chromatography using a 2:1 volume ratio of petroleum ether and ethyl acetate as the eluent and dried to obtain intermediate 1.

[0053] (1-2) Intermediate 1 (3.03 g, 10 mmol) and tert-butyl acetoacetate (4.75 g, 30 mmol) were mixed and stirred at 150°C for 3 h. The residual fraction after vacuum distillation was washed with n-hexane and dried to obtain Intermediate 2.

[0054] (1-3) Intermediate product 2 (4.71 g, 10 mmol) and glacial acetic acid (3.00 g, 50 mmol) were mixed, and 6 mL of a 23% aqueous solution of sodium nitrite (1.38 g, 20 mmol) was added dropwise at -5 °C. The mixture was stirred for 12 h. After the reaction, the mixture was extracted with ethyl acetate and the organic phase was washed with a saturated sodium bicarbonate solution until neutral. The organic phase was then dried over anhydrous sodium sulfate, concentrated by rotary evaporation, and dried to a constant weight to obtain the chain extender (5-methyl-2-(2-nitrobenzyloxy)-1,3-phenylene)bismethylenebis(acetoacetate oxime). Its H NMR spectrum is shown in Figure 2. Figure 4 shown. 1 H NMR (500 MHz, DMSO- d 6) δ 13.37(s, 2H), 8.20(t, J = 7.3 Hz, 1H), 8.09 (d, J = 7.9 Hz, 1H), 7.87 (t, J = 7.4Hz, 1H), 7.65 (t, J = 7.9 Hz, 1H), 7.38 – 7.25 (m, 2H), 5.35 – 5.18 (m, 6H), 2.39 – 2.22 (m, 9H).

[0055] (2) Synthetic cross-linking agent:

[0056] (2-1) Trimethylolpropane (6.71 g, 50 mmol) and tert-butyl acetoacetate (47.46 g, 300 mmol) were mixed and stirred at 150°C for 3 h. The residual fraction after vacuum distillation was washed with n-hexane and dried to obtain intermediate 3.

[0057] (2-2) Intermediate product 3 (7.73 g, 20 mmol) and glacial acetic acid (10.8 g, 180 mmol) were mixed, and 36 mL of a 23% aqueous solution of sodium nitrite (8.28 g, 120 mmol) was added dropwise at -5 °C. The mixture was stirred for 12 h. After the reaction, the mixture was extracted with ethyl acetate and the organic phase was washed with a saturated sodium bicarbonate solution until neutral. The organic phase was then dried over anhydrous sodium sulfate, concentrated by rotary evaporation, and dried to a constant weight to obtain the crosslinker 2-ethyl-2-[(acetoacetate oxime)methyl]propane-1,3-diylbis(acetoacetate oxime). Its H NMR spectrum is shown in Figure 2. Figure 5 shown. 1 H NMR (500 MHz, DMSO- d 6) δ13.37 (d, J = 6.7 Hz, 3H), 4.20 (s, 6H), 2.36 (s, 9H), 1.48 – 1.37 (m, 2H), 0.82 (dt, J = 11.4, 7.5 Hz, 3H).

[0058] (3) Preparation of dynamic cross-linked polyurethane with photodegradability and remodelability: Polycaprolactone diol (4 g, 2 mmol), isophorone diisocyanate (1.78 g, 8 mmol) and 0.001 g dibutyltin dilaurate catalyst were dissolved in 40 mL tetrahydrofuran and reacted at 60 °C under nitrogen protection for 1 h. Then, a chain extender (0.79 g, 1.5 mmol) was added and the reaction continued for 1 h. Finally, a cross-linker (1.42 g, 3 mmol) was added and stirred for 0.5 h. The mixture was poured into a mold by solution casting. After 72 h at 40 °C, a cross-linked polyurethane was obtained. Example 2

[0059] The rest is the same as in Example 1, except that step (3) is changed to:

[0060] Polycaprolactone diol (4 g, 2 mmol), isophorone diisocyanate (1.78 g, 8 mmol) and 40 μL dibutyltin dilaurate catalyst were dissolved in 40 mL tetrahydrofuran and reacted at 60 °C under nitrogen for 1 h. Then, a chain extender (1.26 g, 2.4 mmol) was added and the reaction continued for 1 h. Finally, a crosslinker (1.14 g, 2.4 mmol) was added and stirred for 0.5 h. The mixture was then poured into a mold by solution casting. Cross-linked polyurethane was obtained after 72 h at 40 °C. Example 3

[0061] The rest is the same as in Example 1, except that step (3) is changed to:

[0062] Polycaprolactone diol (4 g, 2 mmol), 4,4'-dicyclohexylmethane diisocyanate (1.05 g, 4 mmol) and 40 uL dibutyltin dilaurate catalyst were dissolved in 40 mL N,N-dimethylformamide and reacted at 60 °C under nitrogen for 1 h. Then, a chain extender (0.26 g, 0.5 mmol) was added and the reaction continued for 1 h. Finally, a crosslinker (0.47 g, 1.0 mmol) was added and stirred for 0.5 h. The mixture was then poured into a mold by solution casting. Cross-linked polyurethane was obtained after 72 h at 80 °C. Example 4

[0063] The rest is the same as in Example 1, except that step (3) is changed to:

[0064] Polycaprolactone diol (4 g, 2 mmol), 4,4'-dicyclohexylmethane diisocyanate (1.05 g, 4 mmol) and 40 uL dibutyltin dilaurate catalyst were dissolved in 40 mL N,N-dimethylformamide and reacted at 60 °C under nitrogen for 1 h. Then, a chain extender (0.42 g, 0.8 mmol) was added and the reaction continued for 1 h. Finally, a crosslinker (0.38 g, 0.8 mmol) was added and stirred for 0.5 h. The mixture was then poured into a mold by solution casting. Cross-linked polyurethane was obtained after 72 h at 80 °C. Comparative Example 1

[0065] A method for preparing a cross-linked polyurethane comprises the following steps:

[0066] Polycaprolactone diol (4 g, 2 mmol) and isophorone diisocyanate (1.78 g, 8 mmol) were dissolved in 40 mL of tetrahydrofuran and reacted under nitrogen at 60 °C for 1 h. Ethylene glycol (0.09 g, 1.5 mmol) was then added and the reaction continued for 1 h. Finally, trimethylolpropane (0.4 g, 3 mmol) was added and stirred thoroughly. The mixture was then poured into a mold using a solution casting method and allowed to stand at 40 °C for 72 h to obtain a comparative cross-linked polyurethane.

[0067] Test Example 1

[0068] The cross-linked polyurethane obtained in each embodiment was tested using a universal electronic tensile testing machine and a dynamic thermomechanical analyzer. The stress-strain curves are shown in FIG. Figure 6As shown in the figure, the greater the amount of isocyanate used, the greater the breaking strength of the cross-linked polyurethane and the lower the breaking elongation. For example, the breaking strengths of Examples 1 and 3 are 15.3 MPa and 9.65 MPa, respectively, and the breaking elongations are 760% and 855%, respectively. This indicates that isocyanate increases the content of the hard segment in the polyurethane. When the amount of isocyanate used remains unchanged, increasing the amount of cross-linker will also increase the breaking strength of the polyurethane and reduce the breaking elongation. For example, the breaking strengths of Examples 1 and 2 are 15.3 MPa and 13.4 MPa, respectively, and the breaking elongations are 760% and 842%, respectively. This is because the cross-linker enhances the interaction between the chains.

[0069] Storage modulus and loss factor curves are as follows Figure 7 As shown in the figure, increasing the amount of isocyanate and crosslinking agent will increase the glass transition temperature of the crosslinked polyurethane. For example, from Example 1 to Example 4, the glass transition temperatures are 34.7°C, 28.8°C, -6.6°C and -13.9°C, respectively.

[0070] Test Example 2

[0071] The cross-linked polyurethane prepared in Example 1 was crushed and then subjected to hot pressing using a flat vulcanizer. The instrument parameters were set at 10 MPa, 80°C, and 1 hour. After the hot pressing operation was completed, the film was cooled and removed.

[0072] The stress-strain curve after multiple hot pressing reshaping is shown in Figure 2. Figure 8 As shown in the figure, it can be seen that the fracture strength and elongation at break after two hot pressing reshapings are only slightly lower than those before reshaping, proving that it still has good mechanical properties after reshaping.

[0073] However, the cross-linked polyurethane prepared in Comparative Example 1 could not be reshaped using the same method as above.

[0074] Test Example 3

[0075] 0.13 g of the cross-linked polyurethane prepared in Example 1 was immersed in 10 mL of tetrahydrofuran solvent and irradiated with 365 nm light for 2 h. The cross-linked polyurethane was dissolved in tetrahydrofuran. Figure 9 As shown in Figure (b), the cross-linked polyurethane that has not been irradiated with light can only swell in tetrahydrofuran, as shown in Figure (b). Figure 9 As shown in Figure (a).

[0076] The cross-linked polyurethane prepared in Comparative Example 1 can only swell even if it is exposed to light for the same time after the same operation. Figure 9This is shown in Figure (c) of the figure. This is because the chain extender (5-methyl-2-(2-nitrobenzyloxy)-1,3-phenylene)bismethylenebis(acetoacetate oxime) decomposes under ultraviolet light, destroying the cross-linked network structure of the polyurethane, making it soluble in tetrahydrofuran.

[0077] Experimental Example 1

[0078] To confirm that the acetoacetate oxime carbamate of the present invention is a new type of dynamic covalent bond, the present invention conducted the following experiments:

[0079] Ethyl acetoacetate oxime small molecule A (3.18 g, 20 mmol) and n-butyl isocyanate B (1.98 g, 20 mmol) were weighed and mixed evenly in 50 mL of petroleum ether. Then 0.001 g of dibutyltin dilaurate was added and stirred at room temperature for 24 hours. After the reaction was completed, column chromatography was used for separation (the volume ratio of petroleum ether to ethyl acetate was 4:1) with the eluent being ethyl acetate and petroleum ether in a volume ratio of 2:1 to obtain acetoacetate oxime carbamate small molecule AB. Its H NMR spectrum is as follows: Figure 10 shown. 1 H NMR (500 MHz, DMSO- d 6) δ 7.98 (t, J = 5.9 Hz, 1H), 4.41 – 4.29 (m, 2H), 3.11 (q, J = 6.7 Hz, 2H), 2.48 (d, J = 1.1 Hz, 3H), 1.47 (p, J = 7.2 Hz, 2H), 1.36 – 1.20 (m, 6H), 0.95 – 0.83 (m, 3H).

[0080] Small molecule AB (2.5 mg, 0.01 mmol) and phenylethyl isocyanate C (1.4 mg, 0.01 mmol) were weighed and dissolved in 0.6 mL of anhydrous DSMSO- d 6 were mixed evenly and the nuclear magnetic resonance hydrogen spectra were obtained at 110 °C at different time intervals. Figure 11 As shown in the figure, the signal peak intensity of the C-NH-C of the AB molecule at 7.97 ppm decreases with the extension of reaction time, while the signal peak intensity of the C-NH-C of the AC molecule at 8.08 ppm gradually increases. This confirms that acetoacetoxycarbamate can undergo a reversible cleavage-formation reaction under certain temperature conditions, that is, acetoacetoxycarbamate is a dynamic covalent bond.

[0081] As can be seen from the above, the cross-linked polyurethane provided by the present invention has photodegradation properties and structural remodeling properties, and can be treated by ultraviolet light irradiation or hot pressing remodeling methods to reduce the degree of pollution of polyurethane waste to the environment.

[0082] The above-mentioned detailed description of a dynamically cross-linked polyurethane with photodegradability and remodelability, its preparation method and application with reference to the embodiments is illustrative rather than restrictive. Several embodiments can be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A dynamically cross-linked polyurethane with photodegradability and remodelability, characterized in that: The dynamic cross-linked polyurethane is obtained by polymerizing a chain extender, a cross-linking agent, a polymer polyol and a polyisocyanate; The structural formula of the chain extender is: The structural formula of the cross-linking agent is:

2. The dynamically cross-linked polyurethane with photodegradability and remodelability according to claim 1, characterized in that: The polyisocyanate is selected from one of 4,4'-diphenylmethane diisocyanate, toluene diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, decanediisocyanate, 4,4'-dicyclohexylmethane diisocyanate and cyclohexane dimethylene diisocyanate.

3. The dynamically cross-linked polyurethane with photodegradability and remodelability according to claim 1, characterized in that: The polymer polyol is selected from polycaprolactone polyol.

4. A method for preparing a dynamically cross-linked polyurethane having photodegradability and remodelability according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: dissolving a polymer polyol, a polyisocyanate and a catalyst in an organic solvent, reacting at 50-70° C. under nitrogen protection for at least 1 hour, then adding a chain extender, continuing the reaction for at least 1 hour, and finally adding a crosslinking agent. After sufficient stirring, the mixture is cast into a film, and after drying, a dynamic crosslinked polyurethane with photodegradability and remodelability is obtained.

5. The preparation method according to claim 4, characterized in that The molar ratio of the polymer polyol, polyisocyanate, chain extender and cross-linking agent is 1:2-4:0.2-1.5:0.4-2.

0.

6. The preparation method according to claim 4, characterized in that The preparation method of the chain extender comprises the following steps: (1-1) 2,6-bis(hydroxymethyl)-p-cresol, 2-nitrobenzyl bromide, and potassium carbonate were stirred and mixed in N,N-dimethylformamide, and reacted at 20-30°C for at least 1 h. After post-treatment, the intermediate 1 was obtained. (1-2) Intermediate product 1 is reacted with tert-butyl acetoacetate at 130-150°C for 2-4 hours, and intermediate product 2 is obtained after post-treatment; (1-3) The intermediate product 2 was mixed with glacial acetic acid, and a sodium nitrite aqueous solution was added dropwise at -5°C. After the addition was completed, the reaction was stirred for 12 to 24 hours, and the chain extender was obtained through post-treatment.

7. The preparation method according to claim 4, characterized in that The preparation method of the cross-linking agent comprises the following steps: (2-1) Trimethylolpropane and tert-butyl acetoacetate are reacted at 130-150°C for 2-4 hours, and the intermediate 3 is obtained after post-treatment; (2-2) The intermediate product 3 is mixed with glacial acetic acid, and a sodium nitrite aqueous solution is added dropwise at -10 to 0°C. After the addition is complete, the reaction is stirred for 12 to 24 hours, and the cross-linking agent is obtained through post-treatment.

8. Use of the photodegradable and remodelable dynamically cross-linked polyurethane as claimed in claim 1 in material preparation.

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