Thin films, methods of making the same, optical devices, and optoelectronic devices

Abstract

This application provides a thin film, a method for preparing the same, an optical device, and a photoelectric device. The thin film includes a crosslinked polymer comprising polymer units and photoresponsive groups connected to the polymer units. The crosslinked polymer can undergo a decrosslinking reaction under irradiation with light of a first wavelength to generate a polymer matrix and photoresponsive crosslinked monomers; the crosslinked polymer can also undergo a crosslinking reaction under irradiation with light of a second wavelength or the action of a catalyst to generate the crosslinked polymer, where the second wavelength is different from the first wavelength. This can improve the quality of the thin film.

Description

Technical Field

[0001] This application relates to the field of materials technology, specifically to a thin film and its preparation method, optical devices, and optoelectronic devices. Background Technology

[0002] Optical thin films are commonly used in optical or optoelectronic devices, such as lenses, displays, cameras, or projectors, as optical functional layers to perform dimming functions. Optical thin films are typically made from transparent polymer materials, and the fabrication process usually includes: melt extrusion, stretching and orientation, and cooling and setting. During this process, it is necessary to control the switching between crosslinking and decrosslinking states of the polymer molecules in the optical thin film to obtain high-quality films. However, if crosslinking is not performed during the melt extrusion stage, the film is prone to problems such as uneven flow, film thickness fluctuations, and surface ripples. If crosslinking is too strong during the melt extrusion stage, stretching and orientation are restricted, the film is prone to brittleness or insufficient orientation, resulting in uneven optical properties. Summary of the Invention

[0003] This application provides a thin film comprising a crosslinked polymer, the crosslinked polymer comprising polymer units and photoresponsive groups connected to the polymer units; The crosslinked polymer can undergo a decrosslinking reaction under irradiation with light of a first wavelength to generate a polymer matrix and a photoresponsive crosslinking monomer; the crosslinked polymer can undergo a crosslinking reaction under irradiation with light of a second wavelength or under the action of a catalyst to generate the crosslinked polymer, wherein the second wavelength is different from the first wavelength.

[0004] In some embodiments, the mass ratio of the polymer matrix to the photoresponsive crosslinking monomer in the film ranges from 10 to 500.

[0005] In some embodiments, the photoresponsive group includes one or more of the following: pyrazolopyrazolidine group, azo group, anthracene group, metal coordinating group, coumarin group, diarylvinyl group, and photoactivated carbonyl-imine group.

[0006] In some embodiments, the catalyst comprises an inorganic base catalyst.

[0007] In some embodiments, the polymer matrix includes one or more of polymethyl methacrylate, polycarbonate, cyclic olefin polymer, polyimide, polyethylene terephthalate, and polyvinyl alcohol.

[0008] In some embodiments, the thin film further includes a photoinitiator.

[0009] In some embodiments, the mass ratio of the polymer matrix to the photoinitiator ranges from 200 to 10000.

[0010] This application also provides a method for preparing a thin film, comprising: Photoresponsive crosslinking monomers are added to a polymer matrix to form a lightly crosslinked polymer. The lightly cross-linked polymer is irradiated with light of a first wavelength, causing the lightly cross-linked polymer to undergo a decross-linking reaction to generate a polymer matrix and a photoresponsive cross-linking monomer, thus obtaining a decross-linked polymer; The uncrosslinked polymer is subjected to an extension treatment so that the molecular chains of the uncrosslinked polymer are aligned with the extension direction to obtain an extended polymer; The extended polymer is dissolved or melted, and then irradiated with light of a second wavelength different from the first wavelength or coated with a catalyst, so that the polymer matrix and photoresponsive crosslinking monomers in the extended polymer undergo a crosslinking reaction to form a crosslinked polymer.

[0011] In some embodiments, the addition of a photoresponsive crosslinking monomer to the polymer matrix to react and form a lightly crosslinked polymer includes: The polymer matrix and the photoresponsive crosslinking monomer are melt-mixed and extruded at 200-250°C to form a lightly crosslinked polymer. Alternatively, the polymer matrix and the photoresponsive crosslinking monomer are melt-mixed and extruded at 200-250°C to form a copolymer, and the copolymer is subjected to light, heat or catalyst treatment to cause an addition reaction to form a lightly crosslinked polymer.

[0012] In some embodiments, the photoresponsive group includes one or more of the following: pyrazolopyrazolidine group, azo group, anthracene group, metal coordinating group, coumarin group, diarylvinyl group, and photoactivated carbonyl-imine group; In some embodiments, the polymer matrix includes one or more of polymethyl methacrylate, polycarbonate, cyclic olefin polymer, polyimide, polyethylene terephthalate, and polyvinyl alcohol.

[0013] In some embodiments, the value of the first wavelength ranges from 250 nm to 480 nm; In some embodiments, the value of the second wavelength ranges from 250 nm to 480 nm; In some embodiments, the catalyst comprises an inorganic base catalyst.

[0014] This application also provides an optical device including the aforementioned thin film.

[0015] In some embodiments, the optical device includes a lens.

[0016] This application also provides an optoelectronic device, including the aforementioned thin film.

[0017] In some embodiments, the optoelectronic device includes one or more of a camera module, a display module, a photovoltaic module, and a projector.

[0018] The beneficial effects of this application include: In this embodiment, the crosslinked polymer in the film includes photoresponsive groups. The crosslinked polymer can undergo crosslinking or decrosslinking reactions through light irradiation or catalysis. Therefore, the film in this embodiment can undergo crosslinking or decrosslinking reactions under relatively mild conditions of light irradiation or catalysis. Furthermore, when this characteristic of the film is applied to the film preparation process, the reaction conditions can be controlled to allow the crosslinked polymer in the film to undergo light crosslinking during the melt extrusion stage, thereby avoiding defects such as uneven flow or film thickness fluctuations during the melt extrusion stage. Then, before the stretching and orientation stage, the crosslinked polymer in the film is controlled to undergo a decrosslinking reaction to avoid insufficient orientation due to crosslinking restrictions during stretching and orientation, which would lead to uneven optical properties. After the stretching and orientation is completed, the film can be further controlled to undergo recrosslinking to achieve film shaping.

[0019] Additional aspects and advantages of this application will be set forth in part in the description which follows, and will become apparent from the description or may be learned by practice of this application. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0021] Figure 1 The diagram shown is a schematic representation of the steps in a thin film preparation method provided in an exemplary embodiment of this application. Detailed Implementation

[0022] The present application will be described more fully below with reference to the accompanying drawings in which embodiments are illustrated.

[0023] While terms such as "first," "second," etc., can be used to describe various components, such components are not limited by these terms. These terms are only used to distinguish one component from another and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more. Where there is no conflict, the features in the embodiments described below in this application may complement or combine with each other.

[0024] In the accompanying drawings, the dimensions and thicknesses of the elements may be enlarged for better understanding, clarity, and ease of description. However, this application is not limited to the dimensions and thicknesses shown in the drawings. The thicknesses of layers, films, panels, areas, and other elements may be exaggerated in the drawings for clarity. Example embodiments are shown in the drawings, wherein the same reference numerals denote the same elements.

[0025] Currently, optical thin films are typically prepared using thermally reversible systems (such as the Diels-Alder reaction) and UV-curing systems. Thermally reversible systems achieve light crosslinking during melt extrusion and decrosslinking during stretching and orientation by controlling temperature. However, these systems suffer from high temperatures, high energy consumption, and slow reaction times for both triggering and decrosslinking reactions. UV-curing systems trigger crosslinking reactions through UV light irradiation. However, UV light irradiation in these systems is concentrated, has poor penetration, and often induces yellowing or excessive surface crosslinking.

[0026] This application provides a thin film and its preparation method, an optical device, and an optoelectronic device, which aim to solve or improve the above-mentioned technical problems.

[0027] This application provides a thin film comprising a crosslinked polymer, the crosslinked polymer comprising polymer units and photoresponsive groups connected to the polymer units; the crosslinked polymer is capable of undergoing a decrosslinking reaction under irradiation with light of a first wavelength to generate a polymer matrix and a photoresponsive crosslinked monomer; the crosslinked polymer is capable of undergoing a crosslinking reaction with the polymer matrix under irradiation with light of a second wavelength or under the action of a catalyst to generate the crosslinked polymer, the second wavelength being different from the first wavelength.

[0028] In this embodiment, the crosslinked polymer in the film includes photoresponsive groups. The crosslinked polymer can undergo crosslinking or decrosslinking reactions through light irradiation or catalysis. Therefore, the film in this embodiment can undergo crosslinking or decrosslinking reactions under relatively mild conditions of light irradiation or catalysis. Furthermore, when this characteristic of the film is applied to the film preparation process, the reaction conditions can be controlled to allow the crosslinked polymer in the film to undergo light crosslinking during the melt extrusion stage, thereby avoiding defects such as uneven flow or film thickness fluctuations during the melt extrusion stage. Then, before the stretching and orientation stage, the crosslinked polymer in the film is controlled to undergo a decrosslinking reaction to avoid insufficient orientation due to crosslinking restrictions during stretching and orientation, which would lead to uneven optical properties. After the stretching and orientation is completed, the film can be further controlled to undergo recrosslinking to achieve film shaping.

[0029] In some embodiments, the mass ratio of the polymer matrix to the photoresponsive crosslinking monomer in the film ranges from 10 to 500. Therefore, by introducing a trace amount of the photoresponsive crosslinking monomer into the polymer matrix, the crosslinking and decrosslinking of the film can be controlled by light or a catalyst. In some examples, when the mass fraction of the polymer matrix is ​​100 parts, the mass fraction of the photoreversible crosslinking monomer can be 0.2 to 10 parts.

[0030] In some preferred embodiments, the mass ratio of the polymer matrix to the photoresponsive crosslinking monomer in the film ranges from 100 to 500. This configuration results in a lower amount of photoresponsive crosslinking monomer, which, on the one hand, facilitates the formation of a lightly crosslinked network between the polymer monomer and the photoresponsive crosslinking monomer, avoiding the increased brittleness caused by excessive crosslinking due to high content of the photoresponsive crosslinking monomer, or the possibility that insufficient compatibility between the photoresponsive crosslinking monomer and the polymer matrix could lead to agglomeration and macroscopic phase separation during curing, thus compromising the uniformity of the film. For example, the mass ratio of the polymer matrix to the photoresponsive crosslinking monomer in the film can be 100, 200, 300, 400, or 500.

[0031] In some embodiments, the photoresponsive group includes one or more of the following: pyrazolopyrazolidine group, azo group, anthracene group, metal coordinating group, photoactivated carbonyl-imine group, and coumarin group.

[0032] In some embodiments, the photoresponsive group includes a pyrazolopyrazolidinedione group. In this case, dibromodiphenyl ether (including a pyrazolopyrazolidinedione group) can be used as a crosslinking agent. The polymer matrix and dibromodiphenyl ether can undergo a crosslinking reaction under the action of a catalyst to achieve crosslinking of the polymer matrix within the film. That is, the polymer matrix reacts to form a lightly crosslinked polymer, which is beneficial for uniform and stable film formation during melt extrusion. Then, light of a first wavelength can be used to irradiate the lightly crosslinked polymer to cause a decrosslinking reaction, resulting in a decrosslinked polymer matrix and a photoresponsive crosslinking monomer. The film can then be stretched and oriented so that the molecular chains align along the extension direction. The catalyst can then be reused to cause the polymer matrix and the crosslinking agent to undergo a crosslinking reaction, rebuilding the crosslinking network. Exemplarily, the first wavelength ranges from 250 nm to 480 nm. Specifically, the first wavelength (hv1) can be from 400 nm to 440 nm, for example, 415 nm. Catalysts include inorganic base catalysts, such as Cs₂CO₃ (cesium carbonate), K₂CO₃ (potassium carbonate), and Na₂CO₃ (sodium carbonate). An exemplary reaction (taking the reaction of polyethylene glycol acrylate with dibromodiphenyl ether as an example) is as follows: In some embodiments, the photoresponsive group includes an azo group. The photoresponsive mechanism of the azo group is photoinduced cis-trans isomerization. Specifically, when the azo group is in the trans configuration (initial state, left figure below), the azo group has a linear extended structure that can connect the polymer matrix to each other. That is, at this time, the polymer matrix reacts to form a lightly cross-linked polymer, and the film is in a lightly cross-linked state, which is beneficial for uniform film flow during melt extrusion and relatively stable film thickness. When the azo group is irradiated with light of a first wavelength, the azo group changes from a stable trans configuration to a cis configuration. The cis configuration changes to a curved structure, which shortens the effective distance between the two ends of the molecule, weakens its bridging ability, and causes some cross-linking points to fail, that is, some cross-linking points to de-crosslink. Then, the film can be stretched and oriented so that the molecular chains are aligned with the extension direction. Then, the azo group can be irradiated with light of a second wavelength, causing the azo group to switch from the cis configuration back to the trans configuration, rebuilding the cross-linked network. For example, the values ​​of both the first and second wavelengths are in the range of 250 nm to 480 nm. Specifically, the first wavelength (hv1) can be 400 nm to 440 nm, and the second wavelength (hv2) can be 320 nm to 380 nm. An exemplary reaction formula (taking azobenzene as an example) is as follows: In some embodiments, the photoresponsive group includes anthracene groups. When a polymer with anthracene groups on its side chains is irradiated with light of a first wavelength, the two anthracene groups undergo photodimerization to form a four-membered ring bridging structure, an "anthracene dimer," which connects the different polymer chains, forming a crosslink. When irradiated with light of a second wavelength, the formed four-membered ring undergoes a reverse reaction, causing the dimer to cleave back into two independent anthracene groups. Thus, the crosslinking and decrosslinking states of the film during preparation can be controlled by controlling the reaction conditions. Exemplarily, the first wavelength (hv1) can be greater than 300 nm, and the second wavelength (hv2) can be less than 300 nm, for example, 254 nm.

[0033] An exemplary reaction formula (using anthracene as an example) is as follows: In some embodiments, the anthracene group may also be an anthrone group, an anthraquinone group, etc.

[0034] In some embodiments, the photoresponsive group includes a metal coordinating group. Under different light irradiation conditions, the electronic structure or coordination state of the central metal ion in the metal coordinating group undergoes a direct and reversible change. This enables the decrosslinking of the crosslinked polymer and the crosslinking of the polymer matrix. In some examples, the metal coordinating group may include a ruthenium coordinating group or an iron coordinating group.

[0035] In some embodiments, the photoresponsive group includes a coumarin group. When irradiated with light of a first wavelength, the coumarin group undergoes a [2+2] cycloaddition reaction to form cyclobutane crosslinks, i.e., a crosslinking reaction occurs. When irradiated with light of a second wavelength, the reaction proceeds in reverse, i.e., a decrosslinking reaction occurs, the cyclobutane structure breaks down, and the film returns to its initial state. Similarly to the aforementioned embodiments, the crosslinking and decrosslinking states of the film during the preparation process can be controlled by controlling the reaction conditions. Exemplarily, the first wavelength (hv1) can be greater than 300 nm, for example, 365 nm, and the second wavelength (hv2) can be less than 300 nm, for example, 254 nm.

[0036] An exemplary reaction formula (using anthracene as an example) is as follows: In some embodiments, the photoresponsive group includes a diarylvinyl group. Similar to an azo group, the diarylvinyl group undergoes isomerization transitions between open-ring and closed-ring states under irradiation with light of different wavelengths, allowing the diarylvinyl group to be formed at crosslinking points. When the diarylvinyl group is in the open-ring state, the crosslinking bonds are easily broken, resulting in a decrosslinked state of the polymer molecules, which is beneficial for sufficient film stretching and orientation. When the diarylvinyl group is in the closed-ring state, the planar structure is better, resulting in a stable crosslinked state of the polymer molecules, which is beneficial for uniform and stable film thickness throughout during melt extrusion. Exemplarily, the first wavelength (hv1) can be in the range of 297~405nm, for example, 300nm or 313nm, and the second wavelength (hv2) can be in the range of 420~480nm, for example, 435nm or 470nm.

[0037] An exemplary reaction formula (using anthracene as an example) is as follows: In some embodiments, the photoresponsive group includes a photoactivated carbonyl-imine group, which can be photo-induced E / Z isomerization using the C=N double bond itself. Light energy of a specific wavelength drives the imine bond to switch between two geometries (E and Z), thereby achieving crosslinking and de-crosslinking. Exemplarily, the first wavelength (hv1) can be in the range of 412 nm to 442 nm, for example, 432 nm, and the second wavelength (hv2) can be in the range of 320 nm to 360 nm, for example, 340 nm.

[0038] An exemplary reaction (taking photoinduced Z / E isomerization of hydrazone as an example) is as follows: In some embodiments, the polymer matrix includes one or more of polymethyl methacrylate, polycarbonate, cyclic olefin polymers, polyimide, polyethylene terephthalate, and polyvinyl alcohol. Preferably, the polymer matrix can be a light-transmitting polymer. Thus, the film provided in this embodiment can function as a light-functional layer in optical or optoelectronic devices.

[0039] In some embodiments, the film further includes a photoinitiator. The photoinitiator decomposes upon absorbing light energy to generate free radicals or ions, thereby assisting in initiating crosslinking or decrosslinking reactions. In some examples, the photoinitiator may be Irgacure 819 (phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide), azobisisobutyronitrile (AIBN), or Irgacure 261 (iron aromatic salt), etc.

[0040] In some embodiments, the mass ratio of the polymer matrix to the photoinitiator ranges from 200 to 10000. With this configuration, the photoinitiator can promote crosslinking or decrosslinking reactions in the film.

[0041] In some preferred embodiments, the mass ratio of the polymer matrix to the photoinitiator ranges from 800 to 10000. A smaller proportion and lower dosage of the photoinitiator results in fewer free radicals being generated instantaneously during the reaction. This means that individual free radicals have more opportunities to undergo longer chain growth reactions with monomer molecular chains, which is beneficial for increasing the molecular weight of the crosslinked polymer. Simultaneously, it avoids the photoinitiator remaining as an impurity in the polymer due to excessive dosage, which could lead to yellowing of the film or the generation of an odor. Furthermore, excessive photoinitiator dosage can result in an excessively high concentration of free radicals, exacerbating chain termination reactions, leading to incomplete polymerization and excessive crosslinking, which in turn reduces the material's hardness and toughness. Therefore, this embodiment, by controlling the dosage of the photoinitiator, helps to improve the quality of the crosslinked polymer.

[0042] In some embodiments, the thickness of the film ranges from 50 to 200 μm. For example, the thickness of the film can be 50 μm, 70 μm, 100 μm, or 150 μm.

[0043] Based on the same inventive concept, this application also provides a method for preparing a thin film, see [link to relevant documentation]. Figure 1 As shown, 100 represents a polymer unit and 200 represents a photoresponsive group. The preparation method includes the following steps: S100: A photoresponsive crosslinking monomer is added to the polymer matrix to form a lightly crosslinked polymer, such as... Figure 1 As shown in (a).

[0044] S200: The lightly cross-linked polymer is irradiated with light of a first wavelength, causing a decrosslinking reaction that generates a polymer matrix and photoresponsive crosslinking monomers, resulting in a decrosslinked polymer, such as... Figure 1 As shown in (b).

[0045] S300: The decrosslinked polymer is subjected to an extension treatment, causing the molecular chains of the decrosslinked polymer to align along the extension direction, resulting in an extended polymer, such as... Figure 1 As shown in (c).

[0046] S400: The extended polymer is dissolved or melted, and irradiated with light of a second wavelength different from the first wavelength, or a catalyst is coated on the surface of the extended polymer, so that the polymer matrix and photoresponsive crosslinking monomers in the extended polymer undergo a crosslinking reaction to form a crosslinked polymer, such as... Figure 1 As shown in (d).

[0047] In this embodiment, crosslinking or decrosslinking reactions can occur under different reaction conditions by utilizing photoresponsive groups. By controlling the reaction conditions, the polymer matrix in the film is further controlled to be in a lightly crosslinked state during the melt extrusion stage, so as to achieve the most uniform and stable thickness throughout the melt-extruded film. Then, irradiation with a specific wavelength is used to decrosslink the polymer matrix in the film, facilitating the stretching treatment of the film and aligning the molecular chains in the film along the stretching direction. Finally, the film is irradiated with another specific wavelength or a catalyst is used to cause the polymer matrix to crosslink again, resulting in a film with relatively stable properties and morphology.

[0048] In some embodiments, the addition of a photoresponsive crosslinking monomer to the polymer matrix in step S100 to form a lightly crosslinked polymer specifically includes: S110: The polymer matrix and the photoresponsive crosslinking monomer are melt-mixed and extruded at 200~250°C to form a lightly crosslinked polymer.

[0049] In this embodiment, the temperature of the melt mixing has reached the condition for the polymer matrix in the film to undergo a light crosslinking reaction. Therefore, no other reaction conditions are needed to activate the crosslinking reaction. For example, when the photoresponsive group includes a pyrazolopyrazolide group or an azo group, light crosslinking can be achieved by mixing the polymer matrix with the photoresponsive crosslinking monomer during melt extrusion.

[0050] Furthermore, when the melt-mixing extrusion temperature is in the range of 200~250℃, since this temperature range is much higher than the glass transition temperature, the mixture after mixing the polymer matrix and the photoresponsive crosslinking monomer can soften and flow, which is beneficial for the uniform dispersion of small molecules such as photoresponsive crosslinking monomers and photoinitiators. This allows for slight crosslinking with the polymer matrix to form a light crosslinked network. In other words, a temperature greater than or equal to 200℃ avoids insufficient melting or uneven mixing. Simultaneously, a temperature less than or equal to 250℃ avoids excessive temperature leading to polymer matrix decomposition or side reactions, or even premature over-crosslinking, resulting in difficulties in subsequent stretching and orientation. Preferably, in this embodiment, the temperature value can be 200℃, 210℃, 220℃, 230℃, 240℃, or 250℃.

[0051] In other embodiments, step S100, which involves adding a photoresponsive crosslinking monomer to the polymer matrix to form a lightly crosslinked polymer, specifically includes: S120: The polymer matrix and the photoresponsive crosslinking monomer are melt-mixed and extruded at 200~250°C to form a copolymer. The copolymer is then subjected to light, heat or catalyst treatment to cause an addition reaction to form a lightly crosslinked polymer.

[0052] In this embodiment, during the melt mixing process, the polymer matrix can undergo a copolymerization reaction to generate a copolymer. Furthermore, treatment with light, heat, or a catalyst can further induce a crosslinking reaction in the copolymer to achieve light crosslinking. For example, when the photoresponsive group includes anthracene groups, during melt extrusion, the anthracene groups polymerize with the polymer matrix to obtain a copolymer. Then, through light treatment, the anthracene groups undergo a [4+4] cycloaddition reaction to generate a dimer structure, forming a low-density crosslinked network. Further, similar to the aforementioned embodiment, when the melt mixing extrusion temperature is within the range of 200~250℃, insufficient melting and uneven mixing, polymer decomposition, or other side reactions can be avoided. Preferably, in this embodiment, the temperature value can be 200℃, 210℃, 220℃, 230℃, 240℃, or 250℃.

[0053] Similarly to the foregoing embodiments, in some embodiments of the thin film preparation method provided in this application, the photoresponsive group includes one or more of the following: pyrazolopyrazolidine group, azo group, anthracene group, metal coordinating group, coumarin group, diarylvinyl group, and photoactivated carbonyl-imine group.

[0054] In some embodiments, the polymer matrix includes one or more of polymethyl methacrylate, polycarbonate, cyclic olefin polymer, polyimide, polyethylene terephthalate, and polyvinyl alcohol.

[0055] In some embodiments, the first wavelength ranges from 250 nm to 480 nm. It should be noted that the specific value of the first wavelength can be adaptively designed according to the type of photoresponsive group, selecting the corresponding wavelength range in which the photoresponsive group can undergo decrosslinking reaction, so as to achieve a higher reaction efficiency of the decrosslinking reaction.

[0056] In some embodiments, the second wavelength ranges from 250 nm to 480 nm. Similarly, the second wavelength, like the first wavelength, can be adaptively designed according to the type of photoresponsive group, selecting the corresponding wavelength range where the photoresponsive group can undergo crosslinking reactions to achieve higher reaction efficiency in the crosslinking reaction.

[0057] In some embodiments, the catalyst comprises an inorganic base catalyst.

[0058] This application also provides an optical device, including the thin film provided in the foregoing embodiments.

[0059] In some embodiments, the optical element may be a lens. The thin film may be a lens element or an anti-reflective coating on a lens element.

[0060] This embodiment also provides an optoelectronic device, including the thin film provided in the foregoing embodiments.

[0061] In some embodiments, the optoelectronic device can be one or more of a camera module, a display module, a photovoltaic module, and a projector. The thin film can be an optical compensation film, a reflective film, or a protective film in an optical device. For example, it can be a polarizer, a reflective film, a film layer composition of an optical microcavity structure, or an encapsulation layer.

[0062] For example, the display module includes an LCD display module, which includes a backlight module, a lower polarizer, a thin-film transistor substrate, a liquid crystal layer, a light filter, and an upper polarizer stacked sequentially. The thin film provided in this embodiment can be used to form the structure in the upper or lower polarizer. In other examples, the display module includes an OLED display module, which includes a substrate, a backplane, a light-emitting device, an encapsulation layer, a polarizer, a touch layer, and a cover plate stacked sequentially. At least one of the encapsulation layer and the polarizer includes the thin film provided in this embodiment.

[0063] To facilitate understanding, this application provides specific examples of several thin film preparation methods for further explanation.

[0064] Example 1 Step 1, Material Preparation Stage: Polymethyl methacrylate (PMMA, Mw≈1.2×10⁻⁶) 6100 parts of photoresponsive crosslinking monomer (in this embodiment, it can be dibromodimethylamine) 0.8 parts of photoinitiator (Irgacure 819 or a similar system) 0.05 parts of the film. In some embodiments, a stabilizer may also be added to the film to stabilize its properties.

[0065] Step 2, Melt Extrusion and Initial Crosslinking Stage: After mixing the materials from Step 1, melt-mix them at 220°C and cool them with a cooling roller to obtain a semi-transparent film with a thickness of approximately 80 μm. At this stage, a lightly crosslinked polymer is formed, with a gel fraction of 8-10% and a film surface roughness Ra < 4 nm.

[0066] Step 3, decrosslinking stage: The film obtained in step 2 is irradiated with light at a wavelength of 450 nm for 30 seconds. Some photo-responsive crosslinks in the system break, and the chain segment mobility is restored. At this time, the elastic modulus of the molten film decreases by about 40%, which is beneficial for the reorientation of molecular chains during the stretching stage.

[0067] Step 4: Stretching and Re-crosslinking Fixation Stage: The film obtained in Step 3 is stretched longitudinally by 2.5 times and laterally by 1.6 times at 120°C, and then irradiated with light at a wavelength of 420 nm for 60 seconds. This causes the crosslinking bonds to reform and fix the molecular orientation. Compared with conventional uncrosslinked PMMA films, the film obtained in this embodiment has a surface hardness increased from 2H to 4H, a thermal shrinkage rate of <0.3%, and good refractive index uniformity (Δn<5×10⁻⁶). -4 Experimental results show that the film obtained in this embodiment has an approximately 30% improvement in flatness, a 25% reduction in tensile residual stress, and a film thickness fluctuation of less than ±2μm.

[0068] Example 2 Step 1, Material Preparation Stage: Polycarbonate (PC, Mw≈8×10 5 100 parts of photoresponsive crosslinking monomer (in this embodiment, it can be a crosslinking monomer containing an azo group) 0.8 parts of photoinitiator (Irgacure 819 or a similar system) 0.05 parts of photoinitiator.

[0069] Step 2, Melt Extrusion and Initial Crosslinking Stage: After mixing the materials from Step 1, melt-mix them at 240°C and cool them with a cooling roller to obtain a semi-transparent film with a thickness of approximately 100 μm. At this point, a lightly crosslinked polymer is formed.

[0070] Step 3, decrosslinking stage: The film obtained in step 2 is irradiated with light at a wavelength of 430 nm for 40 seconds. Some photo-responsive crosslinks in the system break, and the chain segment mobility is restored. At this time, the elastic modulus of the molten film decreases, which is beneficial for the reorientation of molecular chains during the stretching stage.

[0071] Step 4: Stretching and Re-crosslinking Fixation Stage: The film obtained in Step 3 is stretched longitudinally by 2.0 times at 130°C, and then irradiated with light at a wavelength of 410 nm for 90 seconds. Crosslinking bonds reform, fixing the molecular orientation. Compared with conventional uncrosslinked PC films, the film obtained in this embodiment exhibits approximately 40% lower surface roughness, 1H higher hardness, 20% higher stretching orientation retention, and no obvious optical interference fringes.

[0072] Example 3 Step 1, Material Preparation Stage: 95 parts of methyl methacrylate (MMA), 5 parts of photoresponsive crosslinking monomer (in this example, it can be 9-anthracenylmethyl methacrylate (AMA)), and 0.2 parts of photoinitiator (azobisisobutyronitrile (AIBN)).

[0073] Step two, melt extrusion and initial crosslinking stage: After mixing the materials from step one, melt-mix them at 210℃ and cool them with a cooling roller to obtain a semi-transparent film with a thickness of approximately 70 μm. This forms an anthrone-modified PMMA copolymer (PMMA-g-Anthracene) with an anthrone substitution rate of approximately 4-6 mol%, and a molecular weight ≈ 1.0 × 10⁻⁶. 6 The copolymer was extruded at 210°C to form a transparent film with a thickness of approximately 70 μm. Under <260 nm ultraviolet light irradiation for 60 s, the anthrone side chains underwent a [4+4] cycloaddition reaction to form a dimer structure, resulting in a lightly crosslinked polymer. The gel fraction of this film was approximately 10%.

[0074] Step 3, Decrosslinking Stage: The film obtained in Step 2 is irradiated with light at a wavelength of 350 nm for 30 seconds. The anthrone dimer is reversibly cleaved into monomers, the crosslinking bonds break, and the chain segment mobility is restored. In this stage, the storage modulus decreases by about 35%, the molecular chain orientation increases, and biaxial stretching is facilitated.

[0075] Step 4: Stretching and Re-crosslinking Fixation Stage: The film obtained in Step 3 is stretched longitudinally by 2.2 times and laterally by 1.5 times at 115°C, and then irradiated with light at a wavelength of 260 nm for 90 seconds. The anthrone groups undergo a second dimerization reaction, forming a stable crosslinked network and fixing the molecular orientation. Compared with conventional uncrosslinked MMA films, the film obtained in this embodiment has a surface hardness increased to 4H, a thermal shrinkage rate of <0.4%, and an optical uniformity Δn <6×10⁻⁶. -4 .

[0076] It should be understood that the embodiments described herein should be considered in a descriptive sense only and not for limiting purposes. The description of features or aspects within each embodiment should generally be considered as other similar features or aspects that may be used in other embodiments. Although one or more embodiments have been described with reference to the accompanying drawings, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope defined by the claims and their equivalents.

Claims

1. A thin film, characterized in that, The crosslinked polymer includes polymer units and photoresponsive groups connected to the polymer units; The crosslinked polymer can undergo a decrosslinking reaction under irradiation with light of a first wavelength to generate a polymer matrix and a photoresponsive crosslinking monomer; the crosslinked polymer can undergo a crosslinking reaction under irradiation with light of a second wavelength or under the action of a catalyst to generate the crosslinked polymer, wherein the second wavelength is different from the first wavelength.

2. The thin film according to claim 1, characterized in that, The mass ratio of the polymer matrix to the photoresponsive crosslinking monomer in the film ranges from 10 to 500.

3. The thin film according to claim 1, characterized in that, The photoresponsive groups include one or more of the following: pyrazolopyrazolidine group, azo group, anthracene group, metal coordinating group, coumarin group, diarylvinyl group, and photoactivated carbonyl-imine group.

4. The thin film according to claim 1, characterized in that, The catalyst includes inorganic base catalysts.

5. The thin film according to claim 1, characterized in that, The polymer matrix includes one or more of polymethyl methacrylate, polycarbonate, cyclic olefin polymer, polyimide, polyethylene terephthalate, and polyvinyl alcohol.

6. The thin film according to claim 1, characterized in that, The thin film also includes a photoinitiator.

7. The thin film according to claim 6, characterized in that, The mass ratio of the polymer matrix to the photoinitiator ranges from 200 to 10000.

8. A method for preparing a thin film, characterized in that, include: Photoresponsive crosslinking monomers are added to a polymer matrix to form a lightly crosslinked polymer. The lightly cross-linked polymer is irradiated with light of a first wavelength, causing the lightly cross-linked polymer to undergo a decross-linking reaction to generate a polymer matrix and a photoresponsive cross-linking monomer, thus obtaining a decross-linked polymer; The uncrosslinked polymer is subjected to an extension treatment so that the molecular chains of the uncrosslinked polymer are aligned with the extension direction to obtain an extended polymer; The extended polymer is dissolved or melted, and then irradiated with light of a second wavelength different from the first wavelength or coated with a catalyst, so that the polymer matrix and photoresponsive crosslinking monomers in the extended polymer undergo a crosslinking reaction to form a crosslinked polymer.

9. The preparation method according to claim 8, characterized in that, The process of adding a photoresponsive crosslinking monomer to the polymer matrix to form a lightly crosslinked polymer includes: The polymer matrix and the photoresponsive crosslinking monomer are melt-mixed and extruded at 200-250°C to form a lightly crosslinked polymer. Alternatively, the polymer matrix and the photoresponsive crosslinking monomer are melt-mixed and extruded at 200-250°C to form a copolymer, and the copolymer is subjected to light, heat or catalyst treatment to cause an addition reaction to form a lightly crosslinked polymer.

10. The preparation method according to claim 8, characterized in that, The photoresponsive groups include one or more of the following: pyrazolopyrazolidine group, azo group, anthracene group, metal coordinating group, coumarin group, diarylvinyl group, and photoactivated carbonyl-imine group; And / or, the polymer matrix includes one or more of polymethyl methacrylate, polycarbonate, cyclic olefin polymer, polyimide, polyethylene terephthalate, and polyvinyl alcohol.

11. The preparation method according to claim 8, characterized in that, The first wavelength ranges from 250nm to 480nm; And / or, the value of the second wavelength ranges from 250nm to 480nm; And / or, the catalyst includes an inorganic base catalyst.

12. An optical device, characterized in that, Includes the thin film as described in any one of claims 1 to 7.

13. The optical device according to claim 12, characterized in that, The optical device includes a lens.

14. An optoelectronic device, characterized in that, Includes the thin film as described in any one of claims 1 to 7.

15. The optoelectronic device according to claim 14, characterized in that, The optoelectronic devices include one or more of the following: camera module, display module, photovoltaic module, and projector.

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