LU101916B1

LU101916B1 - Use of low-phosphorus crosslinker in preparation of polyurethane film

Info

Publication number: LU101916B1
Application number: LU101916A
Authority: LU
Inventors: Hong Chi; Tianduo Li
Original assignee: Univ Qilu Technology
Priority date: 2019-12-05
Filing date: 2020-07-13
Publication date: 2021-01-15
Also published as: CN110872370A; CN110872370B

Abstract

The present disclosure provides use of a low-phosphorus crosslinker in the preparation of polyurethane film. The structural formula of the low-phosphorus crosslinker is: NH2 H2N NH9 . A method for synthesizing a polyurethane film is: polyisocyanate and polyol are prepolymerized to obtain a prepolymer, and a crosslinking reaction between a low-phosphoras crosslinker and a prepolymer is performed in a mold to obtain a polyurethane film. A low-phosphoras crosslinker is used to synthesize a polyurethane film in the present disclosure, so that the polyurethane film has good flame retardant performance and shape-memory performance.

Description

Use of low-phosphorus crosslinker in preparation of polyurethane film LU101916 | Field of the Invention | The present disclosure pertains to a field of film materials, and relates to use of a | low-phosphorus crosslinker in the preparation of a polyurethane film. | Background of the Invention | The description herein only provides the background information related to the present | disclosure, and does not necessarily constitute the prior art. | Polyurethane (PU) has many characteristics which make it become a high-performance | polymer material. Polyurethane has been used in a wide range of industrial applications, | including biomedicine, construction, automobile, textile, thermoplastic and thermosetting | polyurethanes. Thermoplastic polyurethane (TPU) is promising in various strong elastomers, | because of its fine-tuning structure and the microphase separation between soft and hard | segments. Thermosetting polyurethane is an important kind of materials with high thermal . stability. The basic chemistry of thermosetting polyurethane depends on the reaction between . isocyanate-terminated prepolymers, bifunctional chain extenders and crosslinkers. One kind . of unique polyurethane prepolymer consists of a polyester soft segment (SS) and a . diisocyanate hard segment (HS). Most of the chain extenders are polyester or polyether | polyols with long segments, which extend the linear segments of the polymer and have a | significant influence on the distribution and crosslinking of the soft and hard segments in the . molecules. Acting as a crosslinking center, the crosslinker has a relatively stable structure | which can provide a tough skeleton for the PU network and form a good crosslinking . network structure, which is a key material with excellent mechanical property. In this | environment, the properties of the crosslinker are very important because they can . significantly affect the degree of reaction and thus the properties of the thermosetting ; material. Different types of crosslinkers are used in the curing reaction of polyurethane, | including hydroxyl-terminated polyesters, poly(ester amides), amine-terminated polyamides, | etc. Using these crosslinkers will improve the appearance and properties of polyurethane, | such as scratch hardness, adhesion, flexibility, and water resistance. | Polyurethane has excellent properties, such as flexibility, mechanical property, chemical | resistance, dimensional stability, etc. However, one of its main disadvantages is the . flammability, which limits its further application. The improvement of flame retardance of | PU has become an important issue in the development of new polymer materials. The main | flame retardants of PU are halogen compounds such as pentabromodiphenyl ether, | chloroethyl phosphate, etc., which give PU excellent flame retardance. However, such flame |

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2 | retardants will release a lot of toxic gases when burned, which will pollute the environment LU101916 | and harm the health of people.

Therefore, there is a particular need for environmentally | friendly flame retardant additives with good flame retardance. | An article entitled “Preparation and Research of High-Performance Shape-Memory |

"Transparent Polyurethane” published by Zhang Junrui, et al. in “Chemical Research and | Application” disclosed that: many transparent polyurethane films with shape-memory effect | were prepared by using commercially available hydroxyacrylic resin and isocyanate as the | main raw materials through adding polycaprolactone diol, and their deformation recovery | temperature can be adjusted continuously and controllably.

The deformation recovery | temperature and shape-memory effect of polyurethane films were measured, and their | shape-memory function was characterized.

The research results show that the polyurethane : prepared by hydroxyacrylic resin and polycaprolactone diol has shape-memory function, and : the polyurethane prepared by hydroxyacrylic resin has high deformation recovery | temperature and is brittle at room temperature; the polyurethane prepared by | polycaprolactone diol has low deformation recovery temperature and is soft at room | temperature; the transparent polyurethane with shape-memory effect which is adjustable | continuously in this temperature range can be prepared by reasonable combination of | hydroxyacrylic resin and polycaprolactone diol; when the content of polycaprolactone diol is | high, polyurethane will have a poor shaping effect at room temperature after deformation. | The method for preparing the transparent polyurethane film was as follows: the : hydroxyacrylic resin and polycaprolactone diol were dissolved in butyl acetate, and then the i metered amounts of isocyanate and a catalyst (dibutyltin dilaurate, accounting for 0.01wt% of | the mass fraction of the reactant and solvent) were added, with an equivalent ratio of Ë NCO/OH of 1.2:1 in the system, and a solid content of about 80wt%. The mixed components | were poured into an aluminum-foil weighing plate, and cured in an 80°C oven for 48h, and ; then placed at room temperature for 7 days, with a coating thickness of 0.4-0.5 mm after : drying.

The five polyurethane films were named PU1, PU2, PU3, PU4, PUS.

In this paper, Ë dibutyltin dilaurate used as a catalyst has strong biological toxicity as an organic tin catalyst. : When one is poisoned by dibutyltin dilaurate acutely, it mainly manifests as symptoms of the | central nervous system, including headache, dizziness, fatigue, depression, nausea, etc.; when | exposing for a long time, it can cause neurasthenia syndrome.

It can cause contact dermatitis | and allergic dermatitis on the skin.

Since dibutyltin dilaurate has the above toxicity, its use as ' an organic tin catalyst is not environment friendly.

After research by the inventors of the | present disclosure, it was found that the curing time of 7 days at room temperature during the | preparation of the transparent polyurethane film is too long to be used in production, and the Ë polyurethane has poor flame retardance.

LU101916 Summary of the invention | In order to solve the problems of the prior art, the purpose of the present disclosure is to | provide use of a low-phosphorus crosslinker in the preparation of polyurethane film, which | not only enhances the flame retardance of polyurethane, but also the shape-memory | performance and resistance of polyurethane. | In order to realize the above purpose, the technical solutions of the present disclosure are: | In one aspect, use of a low-phosphorus crosslinker in the preparation of polyurethane film is | disclosed, the structural formula of the low-phosphorus crosslinker is: | NH, | 0 z | O LN. _.O | I 10 | N ~ N | HN oF | NH . | In another aspect, a method for synthesizing a polyurethane film is disclosed, polyisocyanate | and polyol are prepolymerized to obtain a prepolymer, and a crosslinking reaction between a | low-phosphorus crosslinker and the prepolymer is performed in a mold to obtain a ; polyurethane film, wherein the structural formula of the low-phosphorus crosslinker is: | 0 2 | Oo. ] >N, 0 | N oN © | HN Oo Pr | First, the present disclosure prepared a polyurethane film in the absence of a catalyst, which | avoids the biological toxicity caused by the use of dibutyltin dilaurate as a catalyst and | improves the environmental protection; and simultaneously significantly reduces the time for ; preparing a transparent polyurethane film.

Second, the present disclosure uses a / low-phosphorus crosslinker, which can improve the flame retardance of polyurethane while ;

4 | keeping its other properties.

LU101916 |

In a third aspect, a polyurethane film prepared by the synthetic method above is disclosed. |

In a fourth aspect, use of the above polyurethane film in construction, automobile and/or | textile is disclosed. |

The beneficial effects of the present disclosure are: | The polyurethane film synthesized in the present disclosure not only has shape-memory | performance, but also has resistance due to the presence of phosphazene derivatives.

Its | structural characteristics are characterized by Fourier transform infrared spectroscopy | (FT-IR) and "H-NMR.

Then, PUs with different percentages of CP are prepared and studied. |

The shape-memory behavior is characterized by DMA, and the micro-scale combustion ; calorimeter (MCC) shows that the addition of CP changes the thermal degradation behavior ;

and enhances the flame retardance of PU. | Brief Description of the Drawings |

The accompanying drawings forming part of the present disclosure are used to provide a | further understanding of the present disclosure.

The exemplary examples and descriptions of | the present disclosure are used to explain the present disclosure, and do not constitute an | undue limitation on the present disclosure. |

Fig.1 is a schematic diagram of synthesis of hexa(acetylaminophenyl)cyclotriphosphazene in |

Example 1 of the present disclosure; | Fig.2 is an FTIR spectrogram of a polyurethane film in Example 3 of the present disclosure; |

Fig. 3 is a loss factor curve of polyurethane with different ACP contents in an example of the ; present disclosure; !

Fig. 4 is a storage modulus curve of polyurethane with different ACP contents in an example Ë of the present disclosure; | Fig. 5 is the tensile strength curve of a polyurethane film; :

Fig. 6 is the elongation curve of the polyurethane film; |

Fig. 7 is a three-dimensional diagram of 50% tensile stress of the PU-1 content polyurethane; |

Fig. 8 is a three-dimensional diagram of 70% tensile stress of PU-2 content polyurethane; |

Fig. 9 is a three-dimensional diagram of 70% tensile stress of PU-1 content polyurethane; ‘ Fig. 10 is a three-dimensional diagram of 30% tensile stress of the PU-2 CP content / polyurethane; )

Fig. 11 is a nuclear magnetic diagram of a hexa(acetylaminophenyl) cyclotriphosphazene | (CPAC); |

Fig. 12 is a nuclear magnetic diagram of an amine-terminated cyclophosphazene (ACP); .

Fig. 13 is a high-resolution mass spectrogram of LU101916 hexa(acetylaminophenyl)cyclotriphosphazene (CPAC); | Fig. 14 is a high-resolution mass spectrogram of amine-terminated cyclophosphazene (ACP). | 5 Detailed Description of the Embodiments | It should be noted that the following detail descriptions are exemplary and are intended to | provide further explanations of the present disclosure.

Unless otherwise indicated, all | technical and scientific terms used herein have the same meaning as commonly understood | by those skilled in the technical field to which the present disclosure belongs. | It should be noted that the terms used herein are only to describe particular embodiments and | are not intended to limit exemplary embodiments according to the present disclosure.

As | used herein, the singular form is also intended to include the plural form, unless clearly | indicated in the content.

Besides, it should also be understood that when the terms | “comprising” and/or “including” are used in this specification, they indicate the presence of | features, steps, operations, devices, components, and/or combinations thereof. | In view of the problem that the existing polyurethane has poor flame retardance, the present | disclosure proposes use of a low-phosphorus crosslinker in the preparation of a polyurethane | A typical embodiment of the present disclosure provides use of a low-phosphorus crosslinker | in the preparation of a polyurethane film.

The structural formula of the low-phosphorus : crosslinker is | NH | IN Eo | Another embodiment of the present disclosure provides a method for synthesizing a | polyurethane film, polyisocyanate and polyol are prepolymerized to obtain a prepolymer, and : acrosslinking reaction between a low-phosphorus crosslinker and the prepolymer is | performed in a mold to obtain a polyurethane film, wherein the structural formula of the | low-phosphorus crosslinker is: |

| 6 NH, LU101916

“a © 1

NH | ono CT | ry io |

NH, |

First, the present disclosure prepared a polyurethane film without a catalyst, which avoids the | biological toxicity caused by the use of dibutyltin dilaurate as a catalyst and improves the | environmental protection; and simultaneously significantly reduces the time for preparing a | transparent polyurethane film.

Second, the present disclosure uses a low-phosphorus l crosslinker, which can improve the flame retardance of polyurethane while keeping its other | properties. | The polyisocyanate described in the present disclosure is a compound containing at least two . isocyanate groups, for example: isophorone diisocyanate (IPDI), toluene diisocyanate (MDI), . m-xylylene diisocyanate (XDI), etc. | The polyol described in the present disclosure is a compound containing at least two . hydroxyl groups, for example: polyethylene glycol 200 (PEG-200), polyethylene glycol 300 | (PEG-300), polyethylene glycol 400 (PEG-400) , polyethylene glycol 600 (PEG-600), . polyethylene glycol 800 (PEG-800), heptapolyethylene glycol, diethylene glycol, Ë di(2-hydroxypropyl) ether, triethylene glycol, ethyl glycol di(propylene glycol-block-ethylene glycol) ether, 1,5-pentanediol, pentaethylene glycol, etc. | In one or more examples of this embodiment, the prepolymerized condition is: heating under | an inert atmosphere.

The inert atmosphere refers to an atmosphere formed by gas with | relatively stable chemical properties, such as nitrogen, helium, and argon.

When the inert | atmosphere is provided by nitrogen, the synthesis cost can be reduced. . In one or more examples of this embodiment, the prepolymerized temperature is 50 to 70°C, | and the reaction time is 50 to 70 min. | In one or more examples of this embodiment, the temperature of the crosslinking reaction is ; 50 to 70°C, and the reaction time is 40 to 50h. ‘ In one or more examples of this embodiment, a solution of a low-phosphorus crosslinker is | added to the prepolymer and mixed homogeneously to obtain a mixed solution.

The mixed | solution is cast onto a mold, to evaporate the solvent, and a crosslinking reaction is . performed on the evaporated liquid layer. |

| 7

In these examples, the solvent in the low-phosphorus crosslinker solution is LU101916 N,N-dimethylformamide. | In one or more examples of this embodiment, the method for preparing the low-phosphorus | crosslinker includes using hexachlorocyclotriphosphazene and 4-acetylaminophenol as raw | materials to obtain the low-phosphorus crosslinker according to the following reaction route: | HaCOCHN NHCOCHz HN NH, | hs + on—_3-nncoots — ucoc—{_Y-o-r ro") -wooon, — no eo a | ar’ + c'e, | 1 Q HN NH, | In these examples, the substitution reaction of hexachlorocyclotriphosphazene and | 4-acetylaminophenol is performed to obtain intermediate 1, and alcoholysis reaction is | performed on intermediate 1 to obtain a low-phosphorus crosslinker. | In these examples, the molar ratio of hexachlorocyclotriphosphazene to 4-acetylaminophenol is 1:6.5-7.5. | In these examples, the condition of substitution reaction is: heating to reflux with potassium | carbonate. | In these examples, the condition of alcoholysis is: heating the reaction in methanol solution Ë of NaOH. | A third embodiment of the present disclosure provides a polyurethane film prepared by the ; above synthetic method. , The fourth embodiment of the present disclosure provides use of the above polyurethane film Ë in construction, automobile and/or textile. ; In order to make those skilled in the art understand the technical solutions of the present Ë disclosure more clearly, the technical solutions of the present disclosure will be described in À detail below in conjunction with particular examples. | The raw materials used in the examples of the present disclosure are as follows: | N3P3Cls (hexachlorocyclotriphosphazene), 4-acetylaminophenol, K2CO3, NaOH, | hexamethylene diisocyanate, polypropylene glycol-400 are all available from Shanghai Ë Maclean Biochemical Technology Co., Ltd. | The acetone solution is available from Fuyu reagent.

Ë Ethanol and N,N-dimethylformamide are all available from Sinopharm Group. : ;

Tris(2-aminoethyl)amine is available from Shanghai Aladdin X -_ xample Sa | . . ; 2g, | The synthetic steps of the amine-terminated cyclophosphazene crossh 0, © {i | ; : | 0, ry (1) Synthesis of hexa(acetylaminophenyl) cyclotriphosphazene ç > Li 1 mmol N3P3Cls, 7.2 mmol 4-acetylaminophenol, 10.8 mmol K2COs we y in 60 mL acetone solution and heated to reflux for 70-100 h: then the vola i the product were evaporated under vacuum and the residue was washed wi if times, 20mL each time; washed with ethanol twice, SmL each time; finally w i hexane three times, 5mL each time; the resulting white solid I was vacuum-drieda 4 for 48-72 h, to obtain hexa(acetylaminophenyl)cyclotriph e—. > tylaminophenyl)cyclotriphosphazene, as shown in F 188. à (2) Synthesis of amine-terminated cyclophosphazene en

0.5 mmol hexa(acetylaminophenyl)cyclotriphosphazene and 44%-45% by weight of NaAOH = | were added to 20 mL methanol solution, and heated under reflux for 20-30 h, and filtered to * obtain a white solid II. Then the white solid II was washed with water three times, 80-200 mL. © | each time, then washed with ethanol three times, 5 mL each time, and finally washed with Ÿ hexane three times, 5 mL each time. After washed, it was vacuum-dried at 40-60°C for 48-72 i h, to obtain amine-terminated cyclophosphazene crosslinker, as shown in Figs. 12 and 14. | The process for synthesizing hexa(acetylaminophenyl)cyclotriphosphazene is shown in Fig. Ÿ Example 2 | Synthesis of pure polyurethane film > 2 mmol hexamethylene diisocyanate and 1 mmol polypropylene glycol 400 were mixed and . heated at 65°C for 60 min under nitrogen gas to obtain a prepolymer; | Then 5 wt% tris(2-aminoethyl)amine was dissolved in 15mL N,N-dimethylformamide, and | the resulting solution was added to the prepolymer, and stirred evenly with magnetic force; | then the solution was cast onto the PTFE mold, to evaporate the solvent, and the crosslinking | was performed on the evaporated liquid layer at 60°C for 48 hours. After crosslinking, a | 3 he polyurethane film with a network as the final product was obtained, and referred to as PU. . Example 3 | Synthesis of polyurethane film | 2 mmol hexamethylene diisocyanate and 1 mmol polypropylene glycol 400 were mixed and | heated at 65°C for 60 min under nitrogen gas to obtain a prepolymer; | Then 5 wt% amine-terminated cyclophosphazene was dissolved in N,N-dimethylformamide, |

| and the resulting solution was added to the prepolymer, and stirred evenly, then the solution LU101916 | was cast onto the PTFE mold, to evaporate the solvent, and the crosslinking was performed ; | on the evaporated liquid layer at 60°C for 48 hours. Then, a polyurethane film with a network | as the final product was obtained, and referred to as PU-1. | 5 Example 4 | This example is the same as Example 3, except that the amount of amine-terminated | cyclophosphazene is 10 wt%, and the final product is referred to as PU-2. | Example 5 | This example is the same as Example 3, except that the amount of amine-terminated | cyclophosphazene is 15 wt%, and the final product is referred to as PU-3. / Example 6 | This example is the same as Example 3, except that the amount of amine-terminated | cyclophosphazene is 20 wt%, and the final product is referred to as PU-4. | Example 7 | This example is the same as Example 3, except that the amount of amine-terminated | cyclophosphazene is 30 wt%, and the final product is referred to as PU-5. ; | The infrared spectrum was recorded on a Perkin Elmer 2000 Fourier Transform Infrared | (FTIR) spectrometer using Fourier Transform Infrared Spectroscopy (FT-IR), and the : frequency range of FT-IR was 4000-500 cm‘. | The nuclear magnetic resonance spectra was recorded as proton nuclear magnetic resonance | (*H-NMR) spectra using the Bruker AMX-400 spectrometer in DMSO at a frequency of 400 ' High-resolution mass spectra was recorded by using ultraflextreme™ MALDI TOF/TOF | (Bruker America). | Tensile test was performed on the computer-controlled electronic universal testing machine | (WDW-02 Shanghai Shangyi) at room temperature, and the spline of the PU film was | stretched with a force of SN per minute. | Dynamic mechanical analysis (DMA) measurement was performed using DMA Q800 of TA | Instruments with a tensile mode. À frequency of 1 Hz was used in all measurements. The | sample was loaded on a fixture and measured at a heating rate of 5 °C min”! under nitrogen. | The sample size is 30mm X 5mm. | The pyrolysis combustion flow calorimeter (PCFC) test was performed using FAA | Microscale combustion calorimeter (Fire Testing Technology, UK). 50.5 samples were | heated from 100°C to 700°C at a heating rate of 1°C/s with a flow rate of 80 mL/min.

Structural characterization of polyurethane film with FT-IR |

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10 | After the successful synthesis of ACP, it was used as a crosslinker to prepare a series of LU101916 | polyurethane films. The characteristics of the infrared spectrum are shown in Fig. 2. It can be | seen from Fig. 2 that the P=N and P=O stretching vibration peaks at 1177 cm”! and 955 cm”! | do not appear in pure PU, and the P=N and P=O stretching vibration peaks at 1177 cm”! and | 955 cm appear after the addition of compound ACP. This proves that ACP participates in the | reaction. ; Dynamic mechanical thermal analysis | DMA is an excellent tool for studying relaxation related to structure | Fig. 3 depicts the storage modulus (E”) curves of different copolymerization systems. In all | curves, E’ goes down sharply over a wide range. At low temperature, the copolymer has glass | properties. In this case, the molecular segment motion will be frozen, but E’ is still high. As | the temperature increases, the frozen segment structure will start to gradually relax, and | above 50°C, all the E’ of the copolymerization systems tend to keep balance. | PU-2 has the highest E’ in the three copolymerization systems, while PU-1 copolymerization | system has the lowest E’. Compared with PU-1, it has greater crosslinking, due to the higher | addition and versatility of ACP molecules. Therefore, PU-2 has a relatively high E’. .

The glass transition temperature (Tg) corresponding to the tan § peak on the loss factor (tan | 9) curve of all copolymers is shown in Fig. 4. Tg is related to the soft segment structure in the = structure. Therefore, when the molar ratios of HDI and PPG in the polyurethane network are | the same, PU-1 and PU-2 have almost the same Tg. At the same time, the content of ACP | crosslinker is added. The relative proportion of hard segments and the crosslinking density of | the polyurethane network are increased, resulting in shorter and wider peaks of tan 5. | Evaluation of mechanical property and shape-memory performance: .

The data of tensile strength and elongation of composite materials are shown in Figs. 6 and 7. à It can be seen from Figs. 6 and 7 that the mechanical property of the composite materials | decreases with the increase of the crosslinker. As the crosslinker increases, the crosslinking | between polymer chains increases, thus the rigidity increases, and the corresponding tensile | length and elongation at break decrease. Therefore, it is known that the obtained material has | improved mechanical properties. The shape-memory effect was not found in the experiment | of polyurethane prepared by tri(2-aminoethyl)amine crosslinker. | In order to evaluate the performance of the material system as a shape-memory polymer, a | controlled force mode of DMA measurement was performed on PU-1 and PU-2 by the | present disclosure. As shown in Figs. 7-10, PU-1 and PU-2 were initially heated to Tians = | 70°C. At this elevated temperature, the entanglement of the PPG molecular chain is removed, | so that the polymer is likely to deform. The samples are subjected to strains with different |

Slresse, I I TH. mally fix thj -— , CSS 15 released ang 5 COOled to „19°C ) + the . - un Strain, Material reta; der cong an ed to 70°C. th ; RS à signify, » 116 material relea ant portion of shape, whi Ses a fixed strain Of the | a ; and r | > Which shows a certain d CtUrns to its orte: | certain degree o recove O ItS origina] | Flame retardance | Micro-scale combustion calorimeter (MCC) based | ygen consumption calorimetry is a \ well-known pyrolysis combustion flow calorime FC). With a few milligrams of | samples, MCC can quickly and easily provide key flammability parameters of the material, | such as peak heat release rate (pHRR), total heat release (THR), and peak heat release (HR). | The corresponding data of pure PU and PU with different ACP composite content are shown |. in Table 1. It can be observed that the addition of CP reduces the pHRR, THR and HR value | of PU, which proves that the addition of ACP functions to improve the flame retardance of | polyurethane. | Table 1 MCC values of polyurethane with different ACP content | HR Capacity(j/g-k) Peak HR (W/g) | Total HR(kj/g) | The ab tent 1 ferred embodiments of th t discl d t © above contents are ONLY prererred embodiments oI the present disclosure, and are no intended to limit the present disclosure.

For those skilled in the art, the present disclosure may have various modifications and changes.

Any modification, equivalent replacement, improvement, etc made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

Claims LU101916

1. Use of a low-phosphorus crosslinker in the preparation of a polyurethane film, characterized in that the structural formula of the low-phosphorus crosslinker is: NH,

NH 0 2 O. ] Pa N, rn O

TL NH, NH, .

2. A method for synthesizing a polyurethane film, characterized in that polyisocyanate and polyol are prepolymerized to obtain a prepolymer, and a crosslinking reaction between a low-phosphorus crosslinker and a prepolymer is performed in a mold to obtain a polyurethane film, wherein the structural formula of the low-phosphorus crosslinker is: |

O

TL NH, NH, .

3. The method for synthesizing the polyurethane film according to claim 2, characterized in that the prepolymerized condition is: heating under an inert atmosphere; the inert atmosphere is nitrogen gas.

4. The method for synthesizing the polyurethane film according to claim 2, characterized in that the prepolymerized temperature is 60-70°C and the reaction time is 50-70 min.

5. The method for synthesizing the polyurethane film according to claim 2, characterized in that the temperature of the crosslinking reaction is 55-65°C.

6. The method for synthesizing the polyurethane film according to claim 2, characterized in that a solution of a low-phosphorus crosslinker is added to the prepolymer and mixed homogenously to obtain a mixed solution, the mixed solution is cast onto a mold, to

| | evaporate solvent, and a crosslinking reaction is performed on the evaporated liquid layer; LU101916 | preferably, the solvent in the low-phosphorus crosslinker solution is | N,N-dimethylformamide. Ë

7. The method for synthesizing the polyurethane film according to claim 2, characterized in .

that the method for preparing the low-phosphorus crosslinker comprises using : hexachlorocyclotriphosphazene and 4-acetylaminophenol as raw materials to obtain the Ë low-phosphorus crosslinker according to the following reaction route: | H3COCHN NHCOCH; HN NH, | otre + on_3-nncocHs _> Hacocum—(_}-0--"5"o{)—ncocts a ano eo Thm | R N.p:N "RÉ | er a do oh |

8. The method for synthesizing the polyurethane film according to claim 7, characterized in ‘ that the substitution reaction of hexachlorocyclotriphosphazene and 4-acetylaminophenol is A performed to obtain intermediate 1, and alcoholysis reaction is performed to intermediate 1 to | obtain a low-phosphorus crosslinker; . preferably, the molar ratio of hexachlorocyclotriphosphazene to 4-acetylaminophenol is .

1:6.5-7.5; . preferably, the condition of substitution reaction is: heating to reflux with potassium | carbonate; | preferably, the condition of alcoholysis is: heating the reaction in methanol solution of . NaOH. |

9. A polyurethane film, being prepared by the synthetic method according to any one of . claims 2 to 8. |

10. Use of the polyurethane film of claim 9 in construction, automobile and/or textile. |