A twice-reinforced polyurethane film and a method for preparing the same
By introducing H-COF and HEMA into the polyurethane prepolymer solution, and utilizing light-triggered in-situ polymerization of HEMA and nano-confined crosslinking of H-COF, the problem of strength-toughness trade-off and mechanical property degradation of elastomers is solved, realizing a polyurethane film with high strength, high toughness and long-term durability, suitable for flexible electronic packaging and protective windows.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- LANZHOU INSTITUTE OF CHEMICAL PHYSICS CHINESE ACADEMY OF SCIENCES
- Filing Date
- 2026-02-02
- Publication Date
- 2026-05-19
AI Technical Summary
Existing elastomers suffer from a strength-toughness trade-off and rapid degradation of mechanical properties during use, leading to premature component failure and even catastrophic accidents.
A two-dimensional organic framework structure H-COF and 2-hydroxyethyl methacrylate (HEMA) containing carbon-carbon double bonds were introduced into a polyurethane prepolymer solution. The in-situ polymerization of HEMA was triggered by light to construct a second-stage crosslinking network. The hydrogen bonds and nanopore structure of H-COF were used for physical confinement and crosslinking to form a covalently reinforced skeleton.
It achieves high strength and high toughness in polyurethane films, enabling in-situ self-reinforcement under mild conditions, maintaining long-term durability, and significantly improving mechanical properties, making it suitable for flexible electronic packaging, protective windows, and intermediate layers in composite structures.
Smart Images
Figure CN121628042B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of polyurethane materials technology, and particularly relates to a polyurethane film that can be reinforced twice and its preparation method. Background Technology
[0002] Elastomers have become indispensable industrial materials due to their high elasticity and wide range of applications, but the inherent strength-toughness trade-off remains a challenge. More importantly, rapid degradation of mechanical properties during use can lead to premature component failure, significantly shortening service life and even causing catastrophic accidents. Overcoming these limitations requires elastomers to possess not only excellent initial properties but also long-term operational stability. Supramolecular interactions, particularly hydrogen bonds, play a crucial role in enhancing mechanical properties because their dynamic association and dissociation contribute to efficient energy dissipation. However, excessively high hydrogen bond density can weaken network integrity, thereby impairing overall performance. Therefore, achieving a balance between dynamic bond bonding and structural robustness remains a core challenge. Summary of the Invention
[0003] To address the aforementioned technical problems, this invention provides a polyurethane film capable of secondary reinforcement and its preparation method. This polyurethane film exhibits high strength and high toughness. This invention aims to solve the strength-toughness trade-off problem inherent in existing elastomers and the issue of rapid degradation of mechanical properties during service, providing an elastomer that can achieve in-situ self-reinforcement under mild conditions and possesses both high strength, high toughness, and long-term durability, along with its preparation method.
[0004] To achieve the above objectives, the present invention adopts the following technical solution:
[0005] A method for preparing a polyurethane film capable of secondary reinforcement includes the following steps:
[0006] S0: Adding a two-dimensional organic framework structure H-COF to a polyurethane prepolymer solution;
[0007] S1: Add a chain extender to the polyurethane prepolymer solution and carry out a chain extension reaction for 1-6 hours; the molar ratio of diisocyanate to polyol in the polyurethane prepolymer solution is 1.1-2.2:1; the chain extender is a small molecule diamine chain extender; the molar ratio of the small molecule diamine chain extender to the polyol is 0.05-1.05:1;
[0008] S2: Cool the reaction system obtained in step S1 to 60°C, add 2-hydroxyethyl methacrylate to the cooled reaction system, and continue the reaction for 1-6 hours; the molar ratio of hydroxyl groups to polyols in the added 2-hydroxyethyl methacrylate is 0.05-1.5:1; in this step, 2-hydroxyethyl methacrylate is introduced into the reaction system by reacting with the active groups on the polyurethane prepolymer or the extended polyurethane chain segments;
[0009] S3: A photoinitiator is added to the reaction system obtained in step S2 to obtain the target polyurethane composite system solution; the amount of the photoinitiator is 1-10% of the lipid content of the reaction system obtained in step S2;
[0010] S4: Defoaming treatment is performed on the target polyurethane composite system solution obtained in step S3 to obtain a film-forming liquid;
[0011] S5: The film-forming solution obtained in step S4 is subjected to film-forming treatment to obtain a wet film, and the wet film is subjected to drying treatment;
[0012] S6: Polyurethane film can be obtained by irradiating the dried film with light. Under the action of light, the C=C bond in 2-hydroxyethyl methacrylate undergoes in-situ polymerization.
[0013] A polyurethane film that can be re-reinforced, wherein the polyurethane film has an amorphous structure and its tensile strength increases by 50% to 400% after being irradiated with ultraviolet light.
[0014] The beneficial effects of this invention are as follows:
[0015] (1) In the process of polyurethane prepolymer synthesis, the polyurethane film of the present invention introduces 2-hydroxyethyl methacrylate (HEMA) units containing carbon-carbon double bonds (C=C), so that while forming the first stage polyurethane network, potential photopolymerizable reaction sites are pre-embedded in the polyurethane chain segments; then the polyurethane film after film formation is treated by light irradiation, and the in-situ polymerization of HEMA-derived C=C bonds is triggered without changing the macroscopic size and molding state, thereby constructing the second stage crosslinking network, thereby achieving "secondary reinforcement" of the material and achieving simultaneous improvement of strength and toughness.
[0016] (2) This invention provides a UV-triggered nano-confined reinforcement strategy. In one embodiment, hydrazone-bonded covalent organic framework materials (H-COFs) are introduced into the elastomer network in a low amount. The high-density hydrogen bonding of these materials fixes the polymer chains, and the nanopore structure forms physical confinement and physical cross-linking, thereby restricting chain segment movement, improving stress transmission, and inhibiting crack propagation. Furthermore, under UV irradiation, the unsaturated groups (e.g., C=C groups) carried by the elastomer chain ends / side groups undergo confined free radical polymerization or confined cross-linking reactions within the COF nanochannels, transforming the original dynamic supramolecular network into a composite network structure with a covalently reinforced framework, thereby achieving in-situ reinforcement and structural stabilization of the material.
[0017] (3) The polyurethane film of the present invention is suitable for flexible electronic packaging, protective windows and composite structure intermediate layers, etc., and provides a new functional material solution with mechanical properties that can be adjusted as needed. Attached Figure Description
[0018] Figure 1 The XRD curves are of the polyurethane film in Example 1 that was not exposed to ultraviolet light and the polyurethane film that was exposed to ultraviolet light for 10 min and 20 min, respectively.
[0019] Figure 2 The XRD curves are of the polyurethane film in Example 2 that was not exposed to ultraviolet light and the polyurethane film that was exposed to ultraviolet light for 10 min and 20 min, respectively.
[0020] Figure 3 The XRD curves are of the polyurethane film in Example 3 that was not exposed to ultraviolet light and the polyurethane film that was exposed to ultraviolet light for 10 min and 20 min, respectively.
[0021] Figure 4 The XRD curves are of the polyurethane film in Example 4 that was not exposed to ultraviolet light and the polyurethane film that was exposed to ultraviolet light for 10 min and 20 min, respectively.
[0022] Figure 5 The XRD curves of the polyurethane film in Example 1 that was not exposed to ultraviolet light and the polyurethane film that was exposed to ultraviolet light for 10 min and 20 min, respectively, are compared.
[0023] Figure 6 The stress-strain curves are for the polyurethane film in Example 1 that was not exposed to ultraviolet light and for the polyurethane films that were exposed to ultraviolet light for 10 min and 20 min, respectively.
[0024] Figure 7The stress-strain curves are for the polyurethane film in Example 2 that was not exposed to ultraviolet light and for the polyurethane films that were exposed to ultraviolet light for 10 min and 20 min, respectively.
[0025] Figure 8 The stress-strain curves are for the polyurethane film in Example 3 that was not exposed to ultraviolet light and for the polyurethane films that were exposed to ultraviolet light for 10 min and 20 min, respectively.
[0026] Figure 9 The stress-strain curves are for the polyurethane film in Example 4 that was not exposed to ultraviolet light and for the polyurethane films that were exposed to ultraviolet light for 10 min and 20 min, respectively.
[0027] Figure 10 The stress-strain curves of the polyurethane film in Example 1 that was not exposed to ultraviolet light and the polyurethane films that were exposed to ultraviolet light for 10 min and 20 min, respectively, are compared.
[0028] Figure 11 This is a schematic diagram showing the stress magnitude of each sample in Examples 1 to 3.
[0029] Figure 12 This is a schematic diagram of the toughness of each sample in Examples 1 to 3.
[0030] Figure 13 This is a schematic diagram showing the stress magnitude of the sample in Example 4.
[0031] Figure 14 This is a schematic diagram of the toughness of the sample in Example 4.
[0032] Figure 15 The thermogravimetric curves are shown for the polyurethane film in Example 1 that was not exposed to ultraviolet light and for the polyurethane film that was exposed to ultraviolet light for 10 min and 20 min, respectively.
[0033] Figure 16 The thermogravimetric curves are shown for the polyurethane film in Example 2 that was not exposed to ultraviolet light and for the polyurethane film that was exposed to ultraviolet light for 10 min and 20 min, respectively.
[0034] Figure 17 The thermogravimetric curves are shown for the polyurethane film in Example 3 that was not exposed to ultraviolet light and for the polyurethane film that was exposed to ultraviolet light for 10 min and 20 min, respectively.
[0035] Figure 18 The thermogravimetric curves are shown for the polyurethane film in Example 4 that was not exposed to ultraviolet light and for the polyurethane film that was exposed to ultraviolet light for 10 min and 20 min, respectively.
[0036] Figure 19The thermogravimetric curves of the polyurethane film without ultraviolet light and the polyurethane film irradiated with ultraviolet light for 10 min and 20 min, respectively, are shown in Comparative Example 1.
[0037] Figure 20 A comparison of AFM phase diagrams of Example 1 after treatment with different illumination times.
[0038] Figure 21 A comparison of AFM phase diagrams of Example 2 after treatment with different illumination times.
[0039] Figure 22 A comparison of AFM phase diagrams of Example 3 after treatment with different illumination times.
[0040] Figure 23 A comparison of AFM phase diagrams of Example 4 after treatment with different illumination times.
[0041] Figure 24 A comparison of the AFM phase diagrams of Comparative Example 1 after processing with different illumination times.
[0042] Figure 25 This is a schematic diagram of the H-COF structure. Detailed Implementation
[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.
[0044] The raw materials and equipment used in the embodiments of this application are all commercially available, and there are no special requirements unless otherwise specified.
[0045] This invention proposes a method for preparing UV-triggered, secondary-reinforced polyurethane. Upon UV irradiation, terminal carbon-carbon double bonds (C=C) undergo free radical polymerization, transforming the dynamic supramolecular network into a covalently reinforced structure. This synergistic mechanism endows the material with superior mechanical properties, while the UV nanochannel effect accelerates shape memory recovery and enhances fluorescence, thereby enabling adaptive actuation and optical readout. This work establishes a generalizable design principle for developing ultra-durable, multifunctional elastomers with long-term durability.
[0046] This invention provides a method for preparing a polyurethane film that can be reinforced twice, comprising the following steps:
[0047] S0: Preparation of polyurethane prepolymer solution; The viscosity of the polyurethane prepolymer solution prepared in this invention is 500-1000 mPa·s;
[0048] Preparation of H-COF dispersion; wherein H-COF is a covalent organic framework material linked by hydrazone bonds, and the structure of H-COF is as follows: Figure 25 As shown, it is constructed by the condensation of multifunctional aromatic aldehyde structural units and hydrazine / hydrazinoyl structural units, forming a large number of hydrazone-linking motifs (e.g., -C(=O)-NH-N=CH- or their equivalent structures) within the framework, thus forming a stable covalent skeleton with periodically repeating units. The skeleton is also rich in hydrogen bond donor / acceptor sites, including nitrogen (C=N) of imine in hydrazones, oxygen (C=O) of carbonyl groups in amide / hydrazide structures, and -NH- groups, enabling H-COF to form an internal hydrogen bond network and generate multi-point hydrogen bonds with polymer segments to achieve strong interfacial bonding and segment fixation. In addition, H-COF has a regular ordered porous structure and forms continuous nanochannels. The pores are periodically distributed inside the material, which can exert a spatial confinement effect on polymer segments or reactive groups, inhibiting disordered migration and promoting stress transfer and structural stability.
[0049] S1: After the prepolymer is prepared, a small-molecule diamine chain extender is added to the system. The chain extender includes one or more of malondihydrazide, dihydrazide p-benzoic acid, and isophthalohydrazide. Preferably, the chain extender is first dissolved in a certain amount of organic solvent (the organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide) to obtain a homogeneous chain extender solution. Then, under a protective atmosphere (e.g., nitrogen) at 40-100 °C, the chain extender solution is slowly added to the prepolymer solution, and the reaction is continued with stirring for 1-6 h to complete the chain extension reaction and form a polyurethane main chain with a certain molecular weight and initial network structure.
[0050] S2: Add 2-hydroxyethyl methacrylate (HEMA) containing carbon-carbon double bonds to the mixed system after the chain extension reaction, and continue stirring at 40-100 °C under a nitrogen atmosphere for 1-6 h, so that HEMA is introduced into the system by reacting with the active groups on the prepolymer or the chain-extended polyurethane segments.
[0051] S3: Subsequently, a photoinitiator is added to the system obtained in step S2. Preferably, the photoinitiator is selected from one or more of 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenyl-prop-1-one, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and 2,2-dimethoxy-2-phenylacetylbenzene. The photoinitiator is uniformly dispersed under stirring conditions to obtain the target polyurethane composite system solution.
[0052] S4: Perform degassing treatment on the mixed solution obtained in step S3 to fully remove residual bubbles in the system and obtain a uniform film-forming solution without obvious bubble defects.
[0053] S5: The film-forming liquid is uniformly poured onto the surface of a pre-prepared polytetrafluoroethylene mold or substrate. The thickness of the wet film is adjusted by a scraper or casting method. The mold is then placed in an environment of 60-100 ℃ to dry for 24-72 h to basically completely remove the organic solvent, thereby obtaining a film sample with uniform thickness and smooth surface, which provides a substrate for subsequent ultraviolet light irradiation secondary enhancement treatment.
[0054] S6: Irradiate the thin film sample, preferably with ultraviolet light.
[0055] The preparation of the polyurethane prepolymer solution in step S0 specifically includes the following steps:
[0056] S01: Select polyester and / or polyether polyols as the soft segment component. The number average molecular weight of the polyols is 1000-3000, preferably selected from one or more combinations of polycarbonate diol, polycaprolactone diol, and polytetrahydrofuran diol. Add the polyols to a three-necked flask equipped with a mechanical stirrer, thermometer, and nitrogen inlet / outlet. Stir for 60-150 min under nitrogen protection in an oil bath at 100-150 °C to fully remove moisture from the system and complete the pre-drying treatment.
[0057] S02: After the dehydration process is completed, add a certain amount of organic solvent to the three-necked flask. The organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide. Continue stirring for 30-120 min to fully dissolve the polyol and form a homogeneous and transparent polyol solution.
[0058] S03: Naturally cool the above mixture to 60-100 °C, and add diisocyanate under a nitrogen atmosphere. The diisocyanate is preferably selected from one or more of hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (MDI), and 4,4'-dicyclohexylmethane diisocyanate (HMDI). Simultaneously, measure a certain amount of organic solvent (preferably the same system as the aforementioned solvent), dissolve the diisocyanate, and add it dropwise to the reaction system. Add the catalyst dibutyltin dilaurate (DBTDL), ensuring the catalyst amount effectively promotes the reaction without initiating gelation. Stir the reaction at 60-100 °C for 2-5 h under nitrogen protection. During this time, adjust the amount of organic solvent added appropriately to control the viscosity of the system and prevent premature gelation, obtaining a polyurethane prepolymer solution containing terminal isocyanate groups.
[0059] Example 1:
[0060] (1) First, weigh 6.00g of PCDL-2000 polycarbonate diol and place it in a three-necked flask. Heat and stir at 120°C under a nitrogen atmosphere in an oil bath for 2 hours to fully remove moisture from the system and complete the pre-drying treatment.
[0061] (2) After the polycarbonate diol has been dehydrated, add 10 mL of N,N-dimethylformamide to the three-necked flask as a reaction solvent, and continue stirring for about 30 min to fully dissolve it and form a uniform and transparent polyester polyol solution.
[0062] (3) Cool the above mixture naturally to about 80°C, add 10 mg H-COF to 40 mL N,N-dimethylformamide and disperse to obtain H-COF dispersion; then add the dispersion to the polyester polyol solution and mix evenly.
[0063] (4) Under a continuous nitrogen atmosphere, 1.58 g of 4,4'-dicyclohexylmethane diisocyanate was first added to a three-necked flask, followed by 0.10 g of dibutyltin dilaurate as a catalyst. The mixture was stirred at 80 °C for about 3 h to obtain a polyurethane prepolymer solution containing terminal isocyanate groups.
[0064] (5) After the prepolymer is prepared, weigh 0.297 g of malondihydrazide, dissolve it in 20 mL of dimethyl sulfoxide, stir and mix it evenly, and then add it to the above prepolymer solution under nitrogen protection and continue the chain extension reaction for 1 h.
[0065] (6) Cool to 60°C, add 0.195g of 2-hydroxyethyl methacrylate (HEMA) to the mixture, and continue stirring for 3 hours.
[0066] (7) Finally, add 0.15g of photoinitiator 1-hydroxycyclohexylphenyl ketone to obtain the target polyurethane composite system solution.
[0067] (8) After the reaction is completed, the resulting mixture is vacuumed to remove residual bubbles from the system and obtain a uniform film-forming solution without obvious bubbles.
[0068] (9) Pour the above film-forming liquid evenly into a pre-prepared polytetrafluoroethylene mold, and dry the mold at 80°C for 48 hours to completely remove the solvent, and obtain a polyurethane film sample with uniform thickness, which is recorded as Example 1.
[0069] Example 2:
[0070] (1) First, weigh 6.00g of PCDL-2000 polycarbonate diol and place it in a three-necked flask. Heat and stir at 120°C under a nitrogen atmosphere in an oil bath for 2 hours to fully remove moisture from the system and complete the pre-drying treatment.
[0071] (2) After the polycarbonate diol has been dehydrated, add 10 mL of N,N-dimethylformamide to the three-necked flask as a reaction solvent, and continue stirring for about 30 min to fully dissolve it and form a uniform and transparent polyester polyol solution.
[0072] (3) Under a continuous nitrogen atmosphere, 1.58 g of 4,4'-dicyclohexylmethane diisocyanate was first added to a three-necked flask, followed by 0.10 g of dibutyltin dilaurate as a catalyst. The mixture was stirred at 80 °C for about 3 h to obtain a polyurethane prepolymer solution containing terminal isocyanate groups.
[0073] (4) Under a continuous nitrogen atmosphere, 1.58 g of 4,4'-dicyclohexylmethane diisocyanate was first added to a three-necked flask, followed by 0.10 g of dibutyltin dilaurate as a catalyst. The mixture was stirred at 80 °C for about 3 h to obtain a polyurethane prepolymer solution containing terminal isocyanate groups.
[0074] (5) After the prepolymer is prepared, weigh 0.198 g of malondihydrazide, dissolve it in 20 mL of dimethyl sulfoxide, stir and mix it evenly, and then add it to the above prepolymer solution under nitrogen protection and continue the chain extension reaction for 1 h.
[0075] (6) Cool to 60°C, add 0.39g of 2-hydroxyethyl methacrylate (HEMA) to the mixture, and continue stirring for 3 hours.
[0076] (7) Finally, add 0.15g of photoinitiator (1-hydroxycyclohexylphenyl ketone) to obtain the target polyurethane composite system solution.
[0077] (8) After the reaction is completed, the resulting mixture is vacuumed to remove residual bubbles from the system and obtain a uniform film-forming solution without obvious bubbles.
[0078] (9) Pour the above film-forming liquid evenly into a pre-prepared polytetrafluoroethylene mold, and dry the mold at 80°C for 48 hours to completely remove the solvent, and obtain a polyurethane film sample with uniform thickness, which is recorded as Example 2.
[0079] Example 3:
[0080] (1) First, weigh 6.00g of PCDL-2000 polycarbonate diol and place it in a three-necked flask. Heat and stir at 120°C under a nitrogen atmosphere in an oil bath for 2 hours to fully remove moisture from the system and complete the pre-drying treatment.
[0081] (2) After the polycarbonate diol has been dehydrated, add 20 mL of N,N-dimethylformamide to the three-necked flask as a reaction solvent and continue stirring for about 30 min to fully dissolve it and form a uniform and transparent polyester polyol solution.
[0082] (3) Cool the above mixture naturally to about 80°C, add 10 mg H-COF to 40 mL N,N-dimethylformamide and disperse to obtain H-COF dispersion; then add the dispersion to the polyester polyol solution and mix evenly.
[0083] (4) Under a continuous nitrogen atmosphere, 1.58 g of 4,4'-dicyclohexylmethane diisocyanate was first added to a three-necked flask, followed by 0.10 g of dibutyltin dilaurate as a catalyst. The mixture was stirred at 80 °C for about 3 h to obtain a polyurethane prepolymer solution containing terminal isocyanate groups.
[0084] (5) After the prepolymer is prepared, weigh 0.099 g of malondihydrazide, dissolve it in 20 mL of dimethyl sulfoxide, stir and mix it evenly, and then add it to the above prepolymer solution under nitrogen protection and continue the chain extension reaction for 1 h.
[0085] (6) Cool to 60°C, add 0.585g of 2-hydroxyethyl methacrylate (HEMA) to the mixture, and continue stirring for 3 hours.
[0086] (7) Finally, add 0.15g of photoinitiator: 1-hydroxycyclohexylphenyl ketone to obtain the target polyurethane composite system solution.
[0087] (8) After the reaction is completed, the resulting mixture is vacuumed to remove residual bubbles from the system and obtain a uniform film-forming solution without obvious bubbles.
[0088] (9) Pour the above film-forming liquid evenly into a pre-prepared polytetrafluoroethylene mold, and dry the mold at 80°C for 48 hours to completely remove the solvent, and obtain a polyurethane film sample with uniform thickness, which is recorded as Example 3.
[0089] Example 4:
[0090] (1) First, weigh 6.00g of PCDL-2000 polycarbonate diol and place it in a three-necked flask. Heat and stir at 120°C under a nitrogen atmosphere in an oil bath for 2 hours to fully remove moisture from the system and complete the pre-drying treatment.
[0091] (2) After the polycarbonate diol has been dehydrated, add 20 mL of N,N-dimethylformamide to the three-necked flask as a reaction solvent and continue stirring for about 30 min to fully dissolve it and form a uniform and transparent polyester polyol solution.
[0092] (3) Cool the above mixture naturally to about 80°C. Under a continuous nitrogen atmosphere, first add 1.58g of 4,4'-dicyclohexylmethane diisocyanate to a three-necked flask, then add 0.10g of dibutyltin dilaurate as a catalyst. Stir the reaction at 80°C for about 3 hours to obtain a polyurethane prepolymer solution containing terminal isocyanate groups.
[0093] (4) After the prepolymer is prepared, the system is cooled to 60°C, and 0.78g of 2-hydroxyethyl methacrylate (HEMA) is added to the mixture. Stirring continues for 3 hours.
[0094] (5) Finally, add 0.15g of photoinitiator: 1-hydroxycyclohexylphenyl ketone to obtain the target polyurethane composite system solution.
[0095] (6) After the reaction is completed, the resulting mixture is vacuumed to remove residual bubbles from the system and obtain a uniform film-forming solution without obvious bubbles.
[0096] (7) Pour the above film-forming liquid evenly into a pre-prepared polytetrafluoroethylene mold, and dry the mold at 80°C for 48 hours to completely remove the solvent, and obtain a polyurethane film sample with uniform thickness, which is recorded as Example 4.
[0097] Comparative Example 1:
[0098] (1) First, weigh 6.00g of PCDL-2000 polycarbonate diol and place it in a three-necked flask. Heat and stir at 120°C under a nitrogen atmosphere in an oil bath for 2 hours to fully remove moisture from the system and complete the pre-drying treatment.
[0099] (2) After the polycarbonate diol has been dehydrated, add 20 mL of N,N-dimethylformamide to the three-necked flask as a reaction solvent and continue stirring for about 30 min to fully dissolve it and form a uniform and transparent polyester polyol solution.
[0100] (3) Cool the above mixture naturally to about 80°C. Under a continuous nitrogen atmosphere, first add 1.58g of 4,4'-dicyclohexylmethane diisocyanate to a three-necked flask, then add 0.10g of dibutyltin dilaurate as a catalyst. Stir the reaction at 80°C for about 3 hours to obtain a polyurethane prepolymer solution containing terminal isocyanate groups.
[0101] (4) After the prepolymer is prepared, weigh 0.396 g of malondihydrazide, dissolve it in 20 mL of dimethyl sulfoxide, stir and mix it evenly, and then add it to the above prepolymer solution under nitrogen protection and continue the chain extension reaction for 1 h.
[0102] (5) Finally, add 0.15g of photoinitiator: 1-hydroxycyclohexylphenyl ketone to obtain the target polyurethane composite system solution.
[0103] (6) After the reaction is completed, the resulting mixture is vacuumed to remove residual bubbles from the system and obtain a uniform film-forming solution without obvious bubbles.
[0104] (7) The above film-forming liquid was poured evenly into a pre-prepared polytetrafluoroethylene mold, and the mold was dried at 80°C for 48 hours to completely remove the solvent, resulting in a polyurethane film sample with uniform thickness, which was designated as Comparative Example 1.
[0105] Experimental results and analysis:
[0106] 1. XRD curves of polyurethane films
[0107] To obtain structural information about the polyurethane films of this invention, X-ray diffraction (XRD) tests were performed on the film samples of Examples 1 to 4 to analyze their crystallinity and microphase separation. Therefore, Cu Kα radiation (λ = 1.5418 Å) was used to perform XRD tests on an Ultima IV diffractometer, with a 2θ range of 5° to 90° and a scan rate of 2° / min.
[0108] Figure 1 The XRD curves are of the polyurethane film in Example 1 that was not exposed to ultraviolet light and the polyurethane film that was exposed to ultraviolet light for 10 min and 20 min, respectively. Figure 2 The XRD curves are of the polyurethane film in Example 2 that was not exposed to ultraviolet light and the polyurethane film that was exposed to ultraviolet light for 10 min and 20 min, respectively. Figure 3 The XRD curves are of the polyurethane film in Example 3 that was not exposed to ultraviolet light and the polyurethane film that was exposed to ultraviolet light for 10 min and 20 min, respectively. Figure 4 The XRD curves are of the polyurethane film in Example 4 that was not exposed to ultraviolet light and the polyurethane film that was exposed to ultraviolet light for 10 min and 20 min, respectively. Figure 5 The XRD curves of the polyurethane film in Example 1 that was not exposed to ultraviolet light and the polyurethane film that was exposed to ultraviolet light for 10 min and 20 min, respectively, are compared.
[0109] from Figures 1 to 4 This shows the changes in the internal microstructure of the polymer caused by ultraviolet light irradiation. For example... Figure 5 As shown, for Comparative Example 1 without HEMA, its diffraction curve exhibits only broad and gentle scattering peaks throughout the 2θ range, without sharp diffraction peaks, indicating that this system is predominantly amorphous and possesses amorphous characteristics. In contrast, as... Figure 4As shown, in Example 4 containing HEMA, a distinct diffraction peak can be observed at 2θ≈23.4° when unirradiated, indicating the presence of a certain degree of localized ordered stacking or microcrystalline regions in the system. As the UV irradiation time increases, the peak intensity of this diffraction peak gradually weakens until it basically disappears, and the peak shape changes from sharp to broad. This indicates that the carbon-carbon double bonds derived from HEMA undergo free radical polymerization under UV irradiation, breaking the original localized ordered structure and allowing the polyurethane segments to rearrange and transform into a more uniform amorphous or fine phase structure.
[0110] The XRD results above show that the polymerizable double bonds introduced by HEMA induce significant structural reorganization in the polyurethane film under UV light triggering, confirming the regulatory effect of the UV crosslinking process on the polyurethane network at the structural level. Combining the XRD patterns of Examples 1-3, it can be seen that these films are dominated by broad, diffuse peaks, with no obvious diffraction peaks, indicating low crystallinity and an overall amorphous structure. This is consistent with the high transparency exhibited macroscopically by the films of Examples 1-3, and also provides a structural basis for their excellent strength and toughness during tensile deformation.
[0111] 2. Mechanical properties of polyurethane films
[0112] To effectively evaluate the mechanical properties of the prepared polyurethane materials, stress-strain curve tests were performed on all samples from Examples 1-4 and Comparative Example 1. Test standard: GB / T 1040-2006; test speed: 100 mm / min; test environment: 25℃.
[0113] Test results are available Figures 6 to 14 .in Figure 6 The stress-strain curves are for the polyurethane film in Example 1 that was not exposed to ultraviolet light and for the polyurethane films that were exposed to ultraviolet light for 10 min and 20 min, respectively. Figure 7 The stress-strain curves are for the polyurethane film in Example 2 that was not exposed to ultraviolet light and for the polyurethane films that were exposed to ultraviolet light for 10 min and 20 min, respectively. Figure 8 The stress-strain curves are for the polyurethane film in Example 3 that was not exposed to ultraviolet light and for the polyurethane films that were exposed to ultraviolet light for 10 min and 20 min, respectively. Figure 9 The stress-strain curves are for the polyurethane film in Example 4 that was not exposed to ultraviolet light and for the polyurethane films that were exposed to ultraviolet light for 10 min and 20 min, respectively. Figure 10 The stress-strain curves of the polyurethane film in Example 1 that was not exposed to ultraviolet light and the polyurethane films that were exposed to ultraviolet light for 10 min and 20 min, respectively, are compared. Figure 11 This is a summary diagram of the stress magnitudes for each sample in Examples 1 to 3; Figure 12This is a summary diagram of the toughness of each sample in Examples 1 to 3.
[0114] from Figures 6 to 12 It can be seen that tensile tests conducted under different ultraviolet irradiation conditions confirm the improvement in mechanical properties brought about by the secondary reinforcement effect. Uniaxial stress-strain curves ( Figure 6-12 The results show a clear trend of increased UV dependence. For polyurethane films containing HEMA, UV irradiation significantly alters the deformation pattern and load-bearing capacity of the material: as the irradiation time increases, the slope of the curve gradually increases in the initial stage, indicating an improvement in network stiffness; simultaneously, the stress continues to rise before fracture without a significant yield plateau, indicating that the material can maintain continuous strain hardening behavior under large strain.
[0115] The results showed that the films irradiated with ultraviolet light for 10 minutes in Examples 2 and 3 exhibited significant peak values in both strength and toughness. For example, the tensile strength increased from 28.25 MPa and 13.40 MPa to 72.01 MPa and 57.47 MPa, respectively, and the toughness increased from 155.86 MJ·m. -3 and 81.05 MJ·m -3 Increased to 223.83 MJ·m -3 and 118.76 MJ·m -3 After further extending the irradiation time to 20 minutes, although the strength was still significantly higher than that of the original sample, the toughness decreased, indicating that excessive irradiation leads to excessively high crosslinking density and limited elongation at break, thus causing a certain degree of "over-hardening" effect. In contrast, the initial network of Example 1 already had high strength and toughness, and moderate ultraviolet irradiation only brought slight enhancement, with the overall morphology of the curve remaining stable.
[0116] For Example 4 containing HEMA, the secondary reinforcement effect was the most significant. Figure 13 Tensile strength increased from 6.43 MPa (original) to 27.59 MPa (after 10 min of UV irradiation) and 49.56 MPa (after 20 min of UV irradiation), while toughness increased from 2.86 MJ·m. -3 Significantly increased to 20.81 MJ·m -3 and 44.30 MJ·m -3 The mechanical properties improved by an order of magnitude, indicating that ultraviolet light irradiation triggered free radical polymerization, which built additional cross-linking points and physical entanglements inside the film, forming a more compact and extensible multi-network structure.
[0117] However, for Comparative Example 1 without HEMA, regardless of whether it was subjected to ultraviolet irradiation, its stress-strain curves almost overlapped, the tensile strength fluctuated only slightly within the range of 41.72-46.77 MPa, and the toughness remained stable at 159.33-171.81 MJ·m. -3 This indicates that in the absence of polymerizable double bonds, UV irradiation is unlikely to induce significant network reconstruction. This is highly consistent with the structural reorganization observed in the aforementioned XRD / scattering tests, jointly demonstrating that UV light can significantly improve the strength and toughness of thin films without sacrificing transparency and processability through the polymerization of HEMA-derived carbon-carbon double bonds.
[0118] 3. Thermal properties of polyurethane films
[0119] To effectively evaluate the thermal properties of the prepared polyurethane materials, thermogravimetric analysis was performed on all samples from Examples 1-4 and Comparative Example 1.
[0120] Test temperature range: room temperature - 600℃, heating rate: 10℃ / min
[0121] The results are as follows Figures 15 to 19 As shown. Figure 15 The thermogravimetric curves are shown for the polyurethane film in Example 1 that was not exposed to ultraviolet light and for the polyurethane film that was exposed to ultraviolet light for 10 min and 20 min, respectively. Figure 16 The thermogravimetric curves are shown for the polyurethane film in Example 2 that was not exposed to ultraviolet light and for the polyurethane film that was exposed to ultraviolet light for 10 min and 20 min, respectively. Figure 17 The thermogravimetric curves are shown for the polyurethane film in Example 3 that was not exposed to ultraviolet light and for the polyurethane film that was exposed to ultraviolet light for 10 min and 20 min, respectively. Figure 18 The thermogravimetric curves are shown for the polyurethane film in Example 4 that was not exposed to ultraviolet light and for the polyurethane film that was exposed to ultraviolet light for 10 min and 20 min, respectively. Figure 19 The thermogravimetric curves of the polyurethane film without ultraviolet light and the polyurethane film irradiated with ultraviolet light for 10 min and 20 min, respectively, are shown in Comparative Example 1.
[0122] From such Figures 15-19 It can be seen that the mass of Examples 1 to 4 and Comparative Example 1 remained almost unchanged within the range of room temperature to approximately 300°C, indicating that the material has good thermal stability under normal and medium temperature conditions. During the weight loss stage, corresponding to the thermal decomposition of the polyurethane backbone, the curves under different UV irradiation times were generally similar. However, Examples 3 and 4 showed a slight increase in decomposition temperature and a slight increase in residual char after UV irradiation, indicating that secondary crosslinking did not weaken the thermal stability of the film, and some formulations even brought a slight improvement in heat resistance.
[0123] After the introduction of H-COF into the system, H-COF, on the one hand, forms multi-point interactions with polyurethane segments through the high-density hydrogen bond sites in the backbone, and generates confinement and physical cross-linking effects through its nanopores, effectively restricting the thermal motion and disordered migration of segments and improving stress transmission; on the other hand, under UV irradiation, the terminal C=C groups can undergo confined free radical polymerization in the COF nanochannels, further transforming the dynamic supramolecular network into a more stable covalently reinforced structure.
[0124] 4. Atomic Force Microscopy (AFM) Phase Diagram Analysis
[0125] To investigate the effect of ultraviolet light irradiation on the microstructure of polyurethane films, atomic force microscopy (AFM) phase diagram characterization was performed on samples from Examples 1 to 4 and Comparative Example 1. Figures 20-24 The AFM phase diagram visually reveals the regulatory effect of UV-triggered HEMA polymerization on the microphase structure of polyurethane—achieving a “secondary enhancement” of mechanical properties by refining hard domains, increasing crosslinking density, and promoting phase compatibility.
[0126] In summary, the UV-induced secondary reinforcement process significantly improves mechanical properties without significantly reducing the thermal stability of the polyurethane film. Some embodiments even show a certain improvement in heat resistance, meaning that the material has good thermal reliability during actual processing and use.
[0127] It will be readily understood by those skilled in the art that parts not described in detail in this specification are well-known in the field. The above embodiments are provided merely for the purpose of describing the invention and are not intended to limit the scope of the invention. The scope of the invention is defined by the appended claims. All equivalent substitutions and modifications made without departing from the spirit and principles of the invention should be covered within the scope of the invention.
Claims
1. A method for preparing a polyurethane film capable of secondary reinforcement, characterized in that, Includes the following steps: S0: A two-dimensional organic framework structure H-COF is added to a polyurethane prepolymer solution. The H-COF is a covalent organic framework material with hydrazone bonds, which is constructed by the condensation of multifunctional aromatic aldehyde structural units and hydrazine / hydrazinoyl structural units. A large number of hydrazone bond motifs are formed in the framework, thus forming a stable covalent skeleton with periodic repeating units. The skeleton is also rich in hydrogen bond donor / acceptor sites, so that H-COF can form an internal hydrogen bond network and generate multi-point hydrogen bond interactions with polymer segments to achieve strong interfacial bonding and segment fixation. H-COF has a regular ordered porous structure and forms continuous nanochannels. The channels are periodically distributed inside the material, which has a spatial confinement effect on polymer segments or reactive groups, inhibiting disordered migration and promoting stress transfer and structural stability. S1: Add a chain extender to the polyurethane prepolymer solution and carry out a chain extension reaction for 1-6 hours; the molar ratio of diisocyanate to polyol in the polyurethane prepolymer solution is 1.1-2.2:1; the chain extender is a small molecule diamine chain extender; the molar ratio of the small molecule diamine chain extender to the polyol is 0.05-1.05:1; S2: Cool the reaction system obtained in step S1 to 60°C, add 2-hydroxyethyl methacrylate to the cooled reaction system, and continue the reaction for 1-6 hours; the molar ratio of hydroxyl groups to polyols in the added 2-hydroxyethyl methacrylate is 0.05-1.5:1; in this step, 2-hydroxyethyl methacrylate is introduced into the reaction system by reacting with the active groups on the polyurethane prepolymer or the extended polyurethane chain segments; S3: A photoinitiator is added to the reaction system obtained in step S2 to obtain the target polyurethane composite system solution; the amount of the photoinitiator is 1-10% of the mass of the reaction system obtained in step S2; S4: Defoaming treatment is performed on the target polyurethane composite system solution obtained in step S3 to obtain a film-forming liquid; S5: The film-forming solution obtained in step S4 is subjected to film-forming treatment to obtain a wet film, and the wet film is subjected to drying treatment; S6: Polyurethane film can be obtained by irradiating the dried film with light. Under the action of light, the C=C bond in 2-hydroxyethyl methacrylate undergoes in-situ polymerization.
2. The method for preparing a secondary reinforceable polyurethane film according to claim 1, characterized in that, Steps S1 and S2 are performed at 40-100℃.
3. The method for preparing a secondary reinforceable polyurethane film according to claim 1, characterized in that, The addition of the chain extender is accomplished by adding a chain extender solution, wherein the solvent of the chain extender solution is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.
4. The method for preparing a secondary reinforceable polyurethane film according to claim 1, characterized in that, Both steps S1 and S2 are performed under a protective atmosphere.
5. The method for preparing a secondary reinforceable polyurethane film according to claim 1, characterized in that, The photoinitiator mentioned in step S3 is one or more of 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenyl-prop-1-one, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.
6. The method for preparing a secondary reinforceable polyurethane film according to claim 1, characterized in that, The defoaming process in step S4 uses vacuum defoaming.
7. The method for preparing a secondary reinforceable polyurethane film according to claim 1, characterized in that, The molar ratio of isocyanate to polyol in the polyurethane prepolymer solution is 2.0-2.1:1; the molar ratio of the small molecule diamine chain extender to the polyol is 0.25-0.75:1; the molar ratio of hydroxyl groups to the polyol in the 2-hydroxyethyl methacrylate is 0.5-1.5:1; and the amount of photoinitiator is 1-5% of the mass of the reaction system obtained in step S2.
8. The method for preparing a secondary reinforceable polyurethane film according to any one of claims 1 to 7, characterized in that, The polyurethane prepolymer solution is a polyurethane prepolymer solution containing terminal isocyanate groups.
9. The method for preparing a secondary reinforceable polyurethane film according to any one of claims 1 to 7, characterized in that, The viscosity of the polyurethane prepolymer solution is 500-1500 mPa·s.
10. A polyurethane film capable of secondary reinforcement, characterized in that, The re-reinforceable polyurethane film is prepared by the preparation method of the re-reinforceable polyurethane film according to any one of claims 1 to 9, and the re-reinforceable polyurethane film has an amorphous structure.