Dynamic cross-linked polyurethane with photodegradability and remoldability as well as preparation method and application of dynamic cross-linked polyurethane

Abstract

The invention discloses dynamic cross-linked polyurethane with photodegradability and remoldability as well as a preparation method and application thereof, and belongs to the technical field of high polymer materials, the dynamic cross-linked polyurethane is obtained by polymerizing a chain extender, a cross-linking agent, polymer polyol and polyisocyanate, the chain extender and the cross-linking agent both contain acetoacetate oxime bonds, and the polymer polyol and the polyisocyanate are polymerized to obtain the dynamic cross-linked polyurethane with photodegradability and remoldability. During polymerization, acetoacetate oxime bonds react with isocyanate to generate acetoacetate oximido carbamate in a cross-linked network of polyurethane, and the acetoacetate oximido carbamate is a dynamic covalent bond and is beneficial to remodeling of polyurethane; a photodegradable element is designed in the chain extender, so that the photodegradation of the polyurethane is facilitated; the polyurethane not only has good mechanical properties, but also has recycling performance and controllable photodegradation performance, which is of great significance to promotion of sustainable development of polyurethane.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to a dynamically crosslinked polyurethane with photo-degradability and remoldability, and a preparation method and application thereof. Background Art

[0002] Polyurethane has a microphase separation structure (including flexible segments and rigid segments), and its mechanical behavior can be regulated through structural design, and it continues to play an important role in fields such as automobile manufacturing, textile processing, and architectural decoration. It takes hundreds of years for polyurethane to be completely degraded in the natural environment, resulting in increasingly serious problems of microplastic pollution and ecological chain toxicity accumulation. How to alleviate the problem of polyurethane waste polluting the environment is a highly challenging problem.

[0003] At present, the main method for recycling and reusing polyurethane is the chemical recycling method, which realizes degradation by adding a degradation agent to waste polyurethane plastics. For example, Chinese Patent CN 106700126 A discloses a method for recycling polyurethane by self-catalyzed degradation. Polyurethane waste and a degradation agent are added into a reaction kettle, stirred and mixed evenly under nitrogen protection, and at the same time, a heat transfer oil furnace is used to raise the temperature to 160 - 220°C for a degradation reaction for 0.5 - 3 h, and then the temperature is controlled at 160 - 220°C and the vacuum degree is 1 - 1000 mbar to vacuum off the excess degradation agent (which can be recycled), and the temperature is lowered to 80°C to directly obtain the degradation product. This method requires strict degradation conditions, is troublesome to operate, and has a complex process.

[0004] In the prior art, bio-based polyester polyols (such as polycaprolactone) are also introduced into the structure of polyurethane to improve the biodegradability of polyurethane. For example, Chinese Patent CN 115181233 A discloses a dendrimeric polycaprolactone-based polyurethane film with adjustable degradation and its preparation method. A novel stimulus-responsive and controllable degradation dendrimeric polycaprolactone diol is prepared through molecular design, and then it reacts with a diisocyanate to synthesize a dendrimeric polymer prepolymer, and then a chain extender is introduced to prepare a dendrimeric polycaprolactone-based polyurethane film with adjustable degradation. Functionalized polycaprolactone segments are introduced into the polyurethane, and the film undergoes a thermosensitive phase change by regulating the temperature. Above the phase transition temperature, the degradation of the film is inhibited under acidic conditions and can be rapidly degraded under alkaline conditions. The degradation path of the polyurethane material disclosed in this patent is strongly dependent, and it is difficult to adapt to the natural environment. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a dynamically crosslinked polyurethane with photo-degradability and remoldability, and a preparation method and application thereof. The polyurethane not only has good mechanical properties, but also has recycling and reusing properties and controllable photo-degradability.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A dynamically cross-linked polyurethane with photodegradability and remodelability, wherein the structural formula of the dynamically cross-linked polyurethane is: ; The dynamic cross-linked polyurethane is obtained by polymerizing a chain extender, a cross-linking agent, a polymer polyol and polyisocyanate.

[0007] Furthermore, the structural formula of the chain extender is: .

[0008] The structural formula of the cross-linking agent is: .

[0009] 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.

[0010] The polymer polyol is selected from polycaprolactone polyol, preferably polycaprolactone diol.

[0011] The present invention also provides a method for preparing the photodegradable and remodelable dynamic cross-linked polyurethane, 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 photodegradable and remodelable dynamic cross-linked polyurethane.

[0012] 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.

[0013] The mass ratio of the catalyst to the polymer polyol is 0.1-1:1000.

[0014] After adding the cross-linking agent, stirring was continued for 0.5 h.

[0015] 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 are stirred and mixed in N,N-dimethylformamide, reacted at 20-30 °C for at least h, and post-treated to obtain the intermediate 1; (1-2) The intermediate product 1 is reacted with tert-butyl acetoacetate at 130-150 °C for 2-4 h, and the intermediate product 2 is obtained after post-treatment; (1-3) Mix the intermediate product 2 with glacial acetic acid, and dropwise add an aqueous solution of sodium nitrite at -5 °C. After the addition is complete, stir and react for 12 - 24 h, and obtain the chain extender after post-treatment.

[0016] Further, in step (1-1), the molar ratio of benzyl 2-nitrobenzenesulfonate, 2,6-bis(hydroxymethyl)-p-cresol, and potassium carbonate is 1:1.0 - 1.3:3 - 7.

[0017] In step (1-2), the molar ratio of the intermediate product 1 tert-butyl acetoacetate is 1:1.1 - 2.0.

[0018] In step (1-3), the molar ratio of the intermediate product 2, glacial acetic acid, and sodium nitrite is 1:4 - 6:2 - 4.

[0019] The preparation method of the crosslinking agent includes the following steps: (2-1) React trimethylolpropane with tert-butyl acetoacetate at 130 - 150 °C for 2 - 4 h, and obtain the intermediate product 3 after post-treatment; (2-2) Mix the intermediate product 3 with glacial acetic acid, and dropwise add an aqueous solution of sodium nitrite at -10 - 0 °C. After the addition is complete, stir and react for 12 - 24 h, and obtain the crosslinking agent after post-treatment.

[0020] Further, in step (2-1), the molar ratio of trimethylolpropane to tert-butyl acetoacetate is 1:1.1 - 2.0.

[0021] In step (2-2), the molar ratio of the intermediate product 3, glacial acetic acid, and sodium nitrite is 1:6 - 9:3 - 6.

[0022] The present invention also provides the application of the dynamically crosslinked polyurethane with photo-degradability and remoldability in the preparation of new materials.

[0023] The dynamically crosslinked polyurethane with photo-degradability and remoldability provided by the present invention is obtained by polymerizing a chain extender, a crosslinking agent, a polymer polyol, and a polyisocyanate. Both the chain extender and the crosslinking agent contain an acetoacetate oxime bond. When polymerizing, the acetoacetate oxime bond reacts with the isocyanate to generate an acetoacetate oxime carbamate in the crosslinked network of the polyurethane, which is a dynamic covalent bond and helps the remolding of the polyurethane; and a photo-degradable motif is designed in the chain extender, which helps the photo-degradation of the polyurethane.

[0024] The preparation method of the dynamically crosslinked polyurethane with photodegradability and remoldability provided by the present invention is as follows: First, a chain extender with acetoacetate oxime bonds and photodegradable units, and a crosslinking agent with acetoacetate oxime bonds are synthesized, and then they are applied to the synthesis process of polyurethane. During the polymerization reaction, the acetoacetate oxime bonds in the chain extender and the crosslinking agent react with polyisocyanate to form acetoacetate oxime carbamate. The prepared crosslinked polyurethane can be reshaped multiple times by hot pressing, and can also be degraded under ultraviolet light irradiation.

[0025] Compared with the prior art, the present invention has the following beneficial effects: 1) The dynamically crosslinked polyurethane with photodegradability and remoldability provided by the present invention integrates dynamic oxime carbamate bonds and photodegradable units into the crosslinked polyurethane network, realizing the degradation mechanism of "ultraviolet light-triggered macroscopic disintegration". This dynamically crosslinked polyurethane has both photodegradability and remoldability.

[0026] 2) The structure design of the dynamically crosslinked polyurethane with photodegradability and remoldability provided by the present invention is reasonable. Both the chain extender and the crosslinking agent used in the polymerization contain acetoacetate oxime groups. The acetoacetate oxime carbamate formed by their reaction with isocyanate is a new type of dynamic covalent bond, which helps to reshape the polyurethane; and the chain extender also contains photodegradable units, and the polyurethane prepared therefrom has high-efficiency controllable photodegradation performance.

[0027] 3) The preparation methods of the chain extender and the crosslinking agent provided by the present invention are mild and the post-treatment is convenient, which is different from the method of modifying keto or aldehyde groups into oxime groups.

[0028] 4) The dynamically crosslinked polyurethane with photodegradability and remoldability provided by the present invention not only has good mechanical properties, but also has recycling and reusing properties and controllable photodegradation properties, which is of great significance for promoting the sustainable development of polyurethane. Description of the Drawings

[0029] Figure 1 It is the synthetic route diagram of the chain extender (5-methyl-2-(2-nitrobenzyloxy)-1,3-phenylene)bis(methylene)bis(acetoacetate oxime); Figure 2 It is the synthetic route diagram of the crosslinking agent 2-ethyl-2-[(acetoacetate oxime)methyl]propane-1,3-diyl bis(acetoacetate oxime); Figure 3 It is the preparation route diagram of the crosslinked polyurethane; Figure 4 It is the nuclear magnetic resonance hydrogen spectrum diagram of the chain extender; Figure 5 It is the nuclear magnetic resonance hydrogen spectrum diagram of the crosslinking agent; Figure 6Stress-strain curve of the crosslinked polyurethane in the example; Figure 7 Storage modulus and loss factor curves of the crosslinked polyurethane in the example, where, Figure A - Example 1, Figure B - Example 2, Figure C - Example 3, Figure D - Example 4; Figure 8 Stress-strain curves of the crosslinked polyurethane in Example 1 before and after reshaping; Figure 9 UV light degradation experimental diagram of the crosslinked polyurethane, where, (a) The polyurethane in Example 1 was not irradiated with 365 nm light, (b) The polyurethane in Example 1 was irradiated with 365 nm light for 2 h, (c) The polyurethane in Comparative Example 1 was irradiated with 365 nm light for 2 h; The solvent was tetrahydrofuran; Figure 10 1H NMR spectrum of the small molecule AB of acetoacetate oxime carbamate in Experimental Example 1; Figure 11 Small molecule model reaction and 1H NMR spectrum. Detailed implementation mode

[0030] The present invention will be described in detail below in conjunction with the examples. Example 1

[0031] A preparation method of a dynamically crosslinked polyurethane with photo-degradability and reshaping property, comprising the following steps: (1) Synthesize the chain extender: (1-1) Mix 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) in 100 mL of N,N-dimethylformamide evenly, and stir and react at 25 °C for 2 h. After the reaction is completed, filter the mixed solution by suction, and pour the filtrate into water to precipitate. The precipitate is separated by column chromatography, and the eluent is a mixed solution composed of petroleum ether and ethyl acetate according to a volume ratio of 2:1, and dried to obtain Intermediate Product 1.

[0032] (1-2) Mix Intermediate Product 1 (3.03 g, 10 mmol) and tert-butyl acetoacetate (4.75 g, 30 mmol), and stir and react at 150 °C for 3 h. The residual components after vacuum distillation are poured into n-hexane for washing and drying to obtain Intermediate Product 2.

[0033] (1 - 3) The intermediate 2 (4.71 g, 10 mmol) and glacial acetic acid (3.00 g, 50 mmol) were mixed, and an aqueous solution of sodium nitrite (1.38 g, 20 mmol) with a mass concentration of 23% in 6 mL was added dropwise at -5 °C, followed by stirring for 12 h. After the reaction, extraction was carried out with ethyl acetate, and the organic phase was washed with saturated sodium bicarbonate solution until neutral, then dried over anhydrous sodium sulfate, concentrated by rotary evaporation and dried to constant weight to obtain the chain extender (5-methyl-2-(2-nitrobenzyloxy)-1,3-phenylene)bis(methylene)bis(acetoacetate oxime). Its nuclear magnetic resonance hydrogen spectrum is shown as 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).

[0034] (2) Synthesis of the crosslinking agent: (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 component after vacuum distillation was poured into n-hexane for washing and drying to obtain intermediate 3.

[0035] (2-2) Intermediate 3 (7.73 g, 20 mmol) and glacial acetic acid (10.8 g, 180 mmol) were mixed, and an aqueous solution of sodium nitrite (8.28 g, 120 mmol) with a mass concentration of 23% in 36 mL was added dropwise at -5 °C, followed by stirring for 12 h. After the reaction, extraction was carried out with ethyl acetate, and the organic phase was washed with saturated sodium bicarbonate solution until neutral, then dried over anhydrous sodium sulfate, concentrated by rotary evaporation and dried to constant weight to obtain the crosslinking agent 2-ethyl-2-[(acetoacetate oxime)methyl]propane-1,3-diyl bis(acetoacetate oxime). Its nuclear magnetic resonance hydrogen spectrum is shown as 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).

[0036] (3) Preparation of dynamically crosslinked polyurethane with photo - degradability and remoldability: Dissolve polycaprolactone diol (4 g, 2 mmol), isophorone diisocyanate (1.78 g, 8 mmol) and 0.001 g of dibutyltin dilaurate catalyst in 40 mL of tetrahydrofuran. React under nitrogen protection at 60 °C for 1 h, then add the chain extender (0.79 g, 1.5 mmol) and continue to react for 1 h. Finally, add the crosslinking agent (1.42 g, 3 mmol) and continue stirring for 0.5 h. Then, use the solution casting film - forming method to pour into a mold. After 72 h at 40 °C, the crosslinked polyurethane is obtained. Example 2

[0037] Others are the same as Example 1, except that step (3) is changed to: Dissolve polycaprolactone diol (4 g, 2 mmol), isophorone diisocyanate (1.78 g, 8 mmol) and 40 μL of dibutyltin dilaurate catalyst in 40 mL of tetrahydrofuran. React under nitrogen protection at 60 °C for 1 h, then add the chain extender (1.26 g, 2.4 mmol) and continue to react for 1 h. Finally, add the crosslinking agent (1.14 g, 2.4 mmol) and continue stirring for 0.5 h. Then, use the solution casting film - forming method to pour into a mold. After 72 h at 40 °C, the crosslinked polyurethane is obtained. Example 3

[0038] Others are the same as Example 1, except that step (3) is changed to: Dissolve polycaprolactone diol (4 g, 2 mmol), 4,4’ - dicyclohexylmethane diisocyanate (1.05 g, 4 mmol) and 40 μL of dibutyltin dilaurate catalyst in 40 mL of N,N - dimethylformamide. React under nitrogen protection at 60 °C for 1 h, then add the chain extender (0.26 g, 0.5 mmol) and continue to react for 1 h. Finally, add the crosslinking agent (0.47 g, 1.0 mmol) and continue stirring for 0.5 h. Then, use the solution casting film - forming method to pour into a mold. After 72 h at 80 °C, the crosslinked polyurethane is obtained. Example 4

[0039] Others are the same as Example 1, except that step (3) is changed to: 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 protection for 1 h. Then, a chain extender (0.42 g, 0.8 mmol) was added and the reaction continued for 1 h. Finally, a cross-linking agent (0.38 g, 0.8 mmol) was added and stirred for 0.5 h. Then, the solution was poured into a mold by a solution casting film forming method. After 72 h at 80 °C, a cross-linked polyurethane was obtained. Comparative Example 1

[0040] A method for preparing a cross-linked polyurethane comprises the following steps: 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 protection at 60 °C for 1 h. Then, ethylene glycol (0.09 g, 1.5 mmol) was added and the reaction continued for 1 h. Finally, trimethylolpropane (0.4 g, 3 mmol) was added and stirred thoroughly. Then, the solution was poured into a mold by a solution casting film forming method. After standing at 40 °C for 72 h, a comparative cross-linked polyurethane was obtained. Test Example 1

[0041] The cross-linked polyurethane obtained in each embodiment was tested using a universal electronic tensile machine and a dynamic thermomechanical analyzer. The stress-strain curves are shown in FIG. Figure 6 As shown in the figure, the more isocyanate is used, the greater the breaking strength of the cross-linked polyurethane is, and the lower the breaking elongation is. 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, which indicates that isocyanate increases the content of the hard segment in the polyurethane. When the amount of isocyanate is unchanged, increasing the amount of cross-linking agent 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, because the cross-linking agent enhances the interaction between the chains.

[0042] Storage modulus and loss factor curves are shown in 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. Test Example 2

[0043] After the crosslinked polyurethane prepared in Example 1 was crushed, a hot pressing operation was carried out using a flat vulcanizing machine, and the instrument parameters were set to 10 MPa, 80 °C, and 1 h. After the hot pressing operation was completed, the temperature was lowered and the film was taken out.

[0044] The stress-strain curves after multiple hot pressing and reshaping are as Figure 8 shown. It can be seen from the figure that after two hot pressing and reshaping, the fracture strength and elongation at break only decreased slightly compared with those before reshaping, proving that it still has good mechanical properties after reshaping.

[0045] However, the crosslinked polyurethane prepared in Comparative Example 1 could not be reshaped by the same method above. Test Example 3

[0046] 0.13 g of the crosslinked polyurethane prepared in Example 1 was immersed in 10 mL of tetrahydrofuran solvent. After being irradiated with 365 nm light for 2 h, the crosslinked polyurethane dissolved in tetrahydrofuran, as shown in Figure 9 (b) in the figure, while the unirradiated crosslinked polyurethane could only swell in tetrahydrofuran, as shown in Figure 9 (a) in the figure.

[0047] However, after the same operation was carried out on the crosslinked polyurethane prepared in Comparative Example 1, even after being irradiated for the same time, it could only swell, as shown in Figure 9 (c) in the figure. This is because the chain extender (5-methyl-2-(2-nitrobenzyloxy)-1,3-phenylene) bis(methylene) bis(acetoacetate oxime) decomposes under ultraviolet light, destroying the polyurethane crosslinked network structure, so it can be dissolved in tetrahydrofuran. Experimental Example 1

[0048] To confirm that the acetoacetate oxime-based carbamate described in the present invention is a novel dynamic covalent bond, the following experiments were carried out in the present invention: Weighed ethyl acetoacetate oxime small molecule A (3.18 g, 20 mmol) and n-butyl isocyanate B (1.98 g, 20 mmol) and mixed them evenly in 50 mL of petroleum ether. Then, 0.001 g of dibutyltin dilaurate was added and stirred at room temperature for 24 h. After the reaction ended, column chromatography separation was carried out (the volume ratio of petroleum ether to ethyl acetate was 4:1), and the eluent was ethyl acetate and petroleum ether with a volume ratio of 2:1 to obtain the acetoacetate oxime-based carbamate small molecule AB, and its nuclear magnetic resonance hydrogen spectrum is as Figure 10 shown. 1 H NMR (500 MHz, DMSO- d 6) δ7.98 (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).

[0049] Weigh small molecule AB (2.5 mg, 0.01 mmol) and phenethyl isocyanate C (1.4 mg, 0.01 mmol) and mix them evenly in 0.6 mL of anhydrous DMSO- d 6. The proton nuclear magnetic resonance spectra are obtained at 110 °C at different intervals as shown in Figure 11 the figure. The signal peak intensity of the C-NH-C of the AB molecule at 7.97 ppm decreases with the prolongation of the 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 the acetoacetate oxime-based carbamate can undergo a reversible cleavage-formation reaction under certain temperature conditions, that is, the acetoacetate oxime-based carbamate is a dynamic covalent bond.

[0050] As can be seen from the above, the crosslinked polyurethane provided by the present invention has photo-degradation performance and structure remodeling performance, and can be treated by ultraviolet irradiation or hot pressing remodeling methods to reduce the environmental pollution degree of polyurethane waste.

[0051] The above detailed description of a dynamically crosslinked polyurethane with photo-degradability and remolding property, its preparation method and application with reference to the embodiments is illustrative rather than restrictive. Several embodiments can be listed within the defined scope. Therefore, changes and modifications without departing from the general concept of the present invention should fall within the protection scope of the present invention.

Claims

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

2. The dynamically crosslinked polyurethane with photodegradability and recyclability according to claim 1, characterized in that, The structural formula of the chain extender is as follows: .

3. The dynamically crosslinked polyurethane with photo-degradability and reprocessability according to claim 1, characterized in that, The structural formula of the crosslinking agent is as follows: .

4. The dynamically crosslinked polyurethane with photodegradability and remoldability according to claim 1, wherein 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.

5. The dynamically crosslinked polyurethane with photodegradability and remoldability according to claim 1, wherein The polymer polyol is selected from polycaprolactone polyols.

6. A preparation method of a dynamically crosslinked polyurethane having photo-degradability and plasticity as described in any one of claims 1-5, characterized in that, The preparation method comprises the following steps: dissolving polymer polyol, polyisocyanate and 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 crosslinking agent is cast into a film, and after drying, a dynamic crosslinked polyurethane with photodegradability and remodelability is obtained.

7. The preparation method according to claim 6, characterized in that, The molar ratio of the polymer polyol, polyisocyanate, chain extender and crosslinking agent is 1:2-4:0.2-1.5:0.4-2.

0.

8. The preparation method according to claim 6, wherein 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 are stirred and mixed in N,N-dimethylformamide, reacted at 20-30 °C for at least h, and post-treated to obtain the intermediate 1; (1-2) The intermediate product 1 is reacted with tert-butyl acetoacetate at 130-150 °C for 2-4 h, and the intermediate product 2 is obtained after post-treatment; (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 to 24 h, and the chain extender is obtained after post-treatment.

9. The preparation method according to claim 6, 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 h, and the intermediate product 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 h, and the cross-linking agent is obtained through post-treatment.

10. Use of the dynamically cross-linked polyurethane with photodegradability and remodelability as claimed in claim 1 in the preparation of new materials.

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