A method for preparing a conductive hydrogel sensor based on fluorine-containing polyionic liquid

Abstract

This invention discloses a method for preparing a conductive hydrogel sensor based on a fluorinated polyionic liquid, comprising the following steps: (1) adding a fluorinated organic halide to aminomethyl methacrylate, stirring, reacting under an inert atmosphere for 48-72 h, recrystallizing with anhydrous ethanol, and vacuum drying to obtain a fluorinated cationic monomer; (2) dissolving lithium bis(trifluoromethanesulfonyl)imide in deionized water, adding the fluorinated cationic monomer thereto, stirring and reacting at 0°C, separating the liquids, washing the lower oily liquid with deionized water, and vacuum drying to obtain a fluorinated polymerizable ionic liquid; (3) adding a hydrophobic ionic liquid medium and a photoinitiator to the fluorinated polymerizable ionic liquid, stirring until dissolved, transferring to a transparent and sealed mold, and irradiating with ultraviolet light for 2-6 h to form a conductive hydrogel sensor based on a fluorinated polyionic liquid, which has high strength, dryness resistance, swelling resistance, and self-healing properties.

Description

Technical Field

[0001] This invention belongs to the field of hydrogel technology, specifically relating to a method for preparing a conductive hydrogel sensor based on a fluorinated polyionic liquid. Background Technology

[0002] Conductive hydrogels, due to their excellent flexibility and conductivity, can respond rapidly to various external stimuli and generate corresponding electrical signal changes, making them one of the most promising materials in the field of flexible electronics. However, their application in flexible electronic devices still faces some challenges. First, due to their high water content, conductive gels often exhibit poor mechanical properties; second, they suffer from poor stability in extreme environments. To address these issues, many researchers in recent years have improved the environmental resistance of materials by constructing fluorinated polyionic liquid gels. The basic research approach involves mixing unsaturated quaternary ammonium salts (or imidazole salts) with lithium bis(trifluoromethanesulfonyl)imide to prepare fluorinated polymerizable ionic liquids, and then homopolymerizing or copolymerizing these liquids with other monomers to obtain fluorinated polyionic liquid gels with a certain degree of hydrophobicity. Although these methods can improve the hydrophobicity of the material to some extent by introducing hydrophobic counterions (such as bis(trifluoromethanesulfonyl)imide ions), the interaction between the fluorinated counterions and the polymer monomers is weak, and it is difficult to construct a strong molecular network by relying solely on low amounts of fluorinated counterions, resulting in limited improvement in the mechanical properties of the gel. Therefore, how to enhance the intermolecular interaction between fluorinated counterions and monomers, develop conductive gels with high strength and toughness, extreme environmental stability and high sensitivity, and expand their application in the field of flexible electronics has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a method for preparing a conductive hydrogel sensor based on a fluorinated polyionic liquid. First, a fluorinated polymerizable quaternary ammonium salt is prepared, which is then reacted with a fluorinated anionic compound to prepare a polymerizable ionic liquid. Utilizing the network structure of the fluorinated polymerizable ionic liquid, which exhibits synergistic physical and chemical cross-linking, multiple reversible non-covalent interactions (such as electrostatic interactions, ion-dipole dipole-dipole interactions, etc.) are introduced to prepare a conductive gel that possesses high strength, resistance to drying, resistance to swelling, and self-healing properties.

[0004] A method for preparing a conductive hydrogel sensor based on a fluorinated polyionic liquid includes the following steps: (1) Preparation of fluorine-containing cationic monomer: Add fluorine-containing organic halide to amino methacrylate, stir, react under an inert atmosphere for 48-72 h, recrystallize with anhydrous ethanol, and dry under vacuum to obtain fluorine-containing cationic monomer; (2) Preparation of fluorine-containing polymerizable ionic liquid: Lithium bis(trifluoromethanesulfonylimide) is dissolved in deionized water, the fluorine-containing cationic monomer is added to it, the reaction is stirred at 0°C, the liquid is separated, the lower oily liquid is washed with deionized water and dried under vacuum to obtain fluorine-containing polymerizable ionic liquid; (3) Preparation of conductive hydrogel sensor: Add hydrophobic ionic liquid medium and photoinitiator to the fluorine-containing polymerizable ionic liquid, stir until dissolved, transfer to a transparent and sealed mold, and irradiate with ultraviolet light for 2-6 h to form a conductive hydrogel sensor based on fluorine-containing polyionic liquid.

[0005] Preferably, in step (3), when adding the hydrophobic ionic liquid medium and the photoinitiator, a crosslinking agent is also required.

[0006] Preferably, the fluorinated organohalide is at least one of 1,1,1-trifluoro-3-iodopropane, 4-(trifluoromethyl)bromobenzyl bromide, or trifluoroiodomethane.

[0007] Preferably, the hydrophobic ionic liquid medium is at least one of 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazoline tetrafluoroborate, or 1-butyl-3-methylimidazoline hexafluorophosphate.

[0008] Preferably, in step (1), the volume ratio of the aminomethacrylate to the fluorinated organic halide is 1:(0.5-5).

[0009] Preferably, in step (2), the mass ratio of lithium bis(trifluoromethanesulfonylimide) to the fluorinated cationic monomer is 1:(0.1-5).

[0010] Preferably, in step (3), the ratio of the fluorinated polymerizable ionic liquid, the hydrophobic ionic liquid medium, the crosslinking agent, and the photoinitiator is 1 mL: (25-500) μL: (10-80) mg.

[0011] Preferably, when adding the crosslinking agent in step (3), the ratio of the fluorinated polymerizable ionic liquid, the hydrophobic ionic liquid medium, the crosslinking agent, and the photoinitiator is 1 mL: (25-500) μL: (0.2-5) μL: (10-80) mg.

[0012] Preferably, the aminomethacrylate is at least one of dimethylaminoethyl methacrylate or diethylaminoethyl methacrylate.

[0013] Preferably, the crosslinking agent is at least one of N,N′-methylenebisacrylamide, ethylene glycol dimethacrylate, or divinylbenzene.

[0014] Preferably, the photoinitiator is at least one of 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone or ethyl (2,4,6-trimethylbenzoyl)phenylphosphonate.

[0015] Preferably, the vacuum drying conditions are 40-70 °C for 12-48 h.

[0016] Advantages of this invention: The gel prepared by this invention is prepared by reacting aminomethyl acrylate with fluorinated halides to obtain a polymerizable quaternary ammonium salt with high fluorine content. The quaternary ammonium salt is then reacted with fluorinated anionic compounds to prepare a fluorinated polymerizable ionic liquid. Then, a hydrophobic ionic liquid medium is added to regulate the interaction and control the balance between the mechanical properties, conductivity and anti-swelling properties of the gel material. The polymerized conductive hydrogel has high strength, dryness resistance, swelling resistance and self-healing properties. Attached Figure Description

[0017] Figure 1 Stress-strain diagrams of the hydrogels of Example 1, Example 10, and Comparative Example 1 are shown. Figure 2 The bar chart shows the Young's modulus and toughness of the hydrogels from Examples 1, 10, and Comparative Example 1. Figure 3 Stress-strain diagrams of the hydrogels in Example 1 and Comparative Example 2; Figure 4 Stress-strain diagrams of the hydrogels in Example 1 and Comparative Example 3; Figure 5 The bar chart shows the fracture strength and self-healing efficiency of the hydrogel in Example 1. Figure 6 Conductivity diagram of the polyionic liquid gel prepared in Example 1; Figure 7 Swelling diagrams of the polyionic liquid gel prepared in Example 1 in different solvents. Detailed Implementation Example 1

[0018] A method for preparing a conductive hydrogel sensor based on a fluorinated polyionic liquid includes the following steps: (1) Preparation of fluorine-containing cationic monomer: Take 6.67 mL of dimethylaminoethyl methacrylate, add 5.86 mL of 1,1,1-trifluoro-3-iodopropane, stir, react under nitrogen atmosphere for 48 h, recrystallize with anhydrous ethanol, and dry under vacuum at 50 °C for 24 h to obtain fluorine-containing cationic monomer. (2) Preparation of fluorine-containing polymerizable ionic liquid: 4.73g of lithium bis(trifluoromethanesulfonylimide) was dissolved in deionized water, and 5.94g of the fluorine-containing cationic monomer was added to it. The mixture was stirred rapidly at 0°C, separated, and the lower oily liquid was washed with deionized water and dried under vacuum at 50°C for 24h to obtain fluorine-containing polymerizable ionic liquid. (3) Preparation of conductive hydrogel sensor: Take 500 μL of the fluorine-containing polymerizable ionic liquid, add 60 μL of 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide, 0.225 μL of divinylbenzene, and 10 mg of 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone, stir until dissolved, transfer to a transparent and sealed mold, and irradiate with ultraviolet light for 2 h to form a conductive hydrogel sensor based on fluorine-containing polyionic liquid. Example 2

[0019] Diethylaminoethyl methacrylate was used instead of dimethylaminoethyl methacrylate, and everything else was the same as in Example 1. Example 3

[0020] Trifluoroiodomethane was used instead of 1,1,1-trifluoro-3-iodopropane, and everything else was the same as in Example 1. Example 4

[0021] 4-(trifluoromethyl)benzyl bromide was used instead of 1,1,1-trifluoro-3-iodopropane, and everything else was the same as in Example 1. Example 5

[0022] In step (2), 2.37 g of lithium bis(trifluoromethanesulfonylimide) was used, and the rest was the same as in Example 1. Example 6

[0023] In step (3), 25 μL of 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imine is used, divinylbenzene is not added, and the rest is the same as in Example 1. Example 7

[0024] In step (2), 2.97g of fluorine-containing cationic monomer is used, and the rest is the same as in Example 1. Example 8

[0025] In step (3), ethylene glycol dimethacrylate is selected as the crosslinking agent instead of divinylbenzene, and the rest is the same as in Example 1. Example 9

[0026] In step (3), 25 μL of 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide is used, and the rest is the same as in Example 1. Example 10

[0027] In step (3), 75 μL of 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide is used, and the rest is the same as in Example 1. Example 11

[0028] In step (3), 100 μL of 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide is used, and the rest is the same as in Example 1. Example 12

[0029] In step (3), 25 μL of 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide and 0.15 μL of divinylbenzene are used, and the rest is the same as in Example 1. Example 13

[0030] In step (3), 25 μL of 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide and 0.75 μL of divinylbenzene are used, and the rest is the same as in Example 1. Example 14

[0031] In step (3), 25 μL of 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide and 1.5 μL of divinylbenzene are used, and the rest is the same as in Example 1. Example 15

[0032] A method for preparing a conductive hydrogel sensor based on a fluorinated polyionic liquid includes the following steps: (1) Preparation of fluorine-containing cationic monomer: Take 6.67 mL of dimethylaminoethyl methacrylate, add 3.34 mL of 1,1,1-trifluoro-3-iodopropane, stir, react under nitrogen atmosphere for 72 h, recrystallize with anhydrous ethanol, and dry under vacuum at 50 °C for 24 h to obtain fluorine-containing cationic monomer; (2) Preparation of fluorine-containing polymerizable ionic liquid: 4.73g of lithium bis(trifluoromethanesulfonylimide) was dissolved in deionized water, and 0.473g of the fluorine-containing cationic monomer was added to it. The mixture was stirred rapidly at 0°C, separated, and the lower oily liquid was washed with deionized water and dried under vacuum at 50°C for 24h to obtain fluorine-containing polymerizable ionic liquid. (3) Preparation of conductive hydrogel sensor: Take 500 μL of the fluorinated polymerizable ionic liquid, add 12.5 μL of 1-ethyl-3-methylimidazolium tetrafluoroborate, 0.1 μL of N,N′-methylenebisacrylamide, and 5 mg of 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone, stir until dissolved, transfer to a transparent and sealed mold, and irradiate with ultraviolet light for 2 h to form a conductive hydrogel sensor based on fluorinated polyionic liquid. Example 16

[0033] A method for preparing a conductive hydrogel sensor based on a fluorinated polyionic liquid includes the following steps: (1) Preparation of fluorine-containing cationic monomer: Take 6.67 mL of dimethylaminoethyl methacrylate, add 33.35 mL of 1,1,1-trifluoro-3-iodopropane, stir, react under nitrogen atmosphere for 48 h, recrystallize with anhydrous ethanol, and dry under vacuum at 50 °C for 24 h to obtain fluorine-containing cationic monomer. (2) Preparation of fluorine-containing polymerizable ionic liquid: 4.73g of lithium bis(trifluoromethanesulfonylimide) was dissolved in deionized water, and 23.65g of the fluorine-containing cationic monomer was added to it. The mixture was stirred rapidly at 0°C, separated, and the lower oily liquid was washed with deionized water and dried under vacuum at 50°C for 24h to obtain fluorine-containing polymerizable ionic liquid. (3) Preparation of conductive hydrogel sensor: Take 500 μL of the fluorinated polymerizable ionic liquid, add 250 μL of 1-butyl-3-methylimidazolium hexafluorophosphate, 2.5 μL of ethylene glycol dimethacrylate and 40 mg of ethyl (2,4,6-trimethylbenzoyl)phenylphosphonate, stir until dissolved, transfer to a transparent and sealed mold, and irradiate with ultraviolet light for 6 h to form a conductive hydrogel sensor based on fluorinated polyionic liquid. Example 17

[0034] Divinylbenzene was not added; otherwise, it was the same as in Example 1.

[0035] Comparative Example 1 The same as in Example 1 was used, but without the addition of 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide.

[0036] Comparative Example 2 Choline chloride glycerol ionic liquid was used instead of 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imine, otherwise it was the same as in Example 1.

[0037] Comparative Example 3 A hydrogel based on a hexane polyionic liquid was prepared by replacing 1,1,1-trifluoro-3-iodopropane with n-hexane bromide. This hydrogel contains fluorine only in the counterion phase and not in the main chain, as detailed below: (1) Preparation of n-hexane cationic monomer: 6.67 mL of dimethylaminoethyl methacrylate was added to a round-bottom flask, 5.62 mL of bromohexane was added, and the mixture was stirred and reacted under a nitrogen atmosphere for 48 h. The mixture was recrystallized from anhydrous ethanol and dried under vacuum at 50 °C for 24 h to obtain n-hexane cationic monomer. (2) Preparation of hexane polymerizable ionic liquid: 4.73 g of lithium bis(trifluoromethanesulfonylimide) was dissolved in deionized water, and 5.25 g of the hexane cationic monomer was added. The mixture was stirred rapidly at 0 °C, separated into layers, and the lower oily liquid was washed with deionized water and dried under vacuum at 50 °C for 24 h to obtain hexane polymerizable ionic liquid. (3) Preparation of n-hexane polyionic liquid gel: Take 500 μL of the n-hexane polymerizable ionic liquid, add 60 μL of 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide, 0.225 μL of divinylbenzene, and 10 mg of photoinitiator 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone, stir until dissolved, transfer to a transparent and sealed mold, and irradiate with ultraviolet light for 2 h to form a conductive hydrogel sensor based on n-hexane polyionic liquid.

[0038] Performance testing 1. Mechanical performance testing The stress-strain curves of Examples 1, 10, and 17, and Comparative Examples 1-3 were tested using an electronic universal testing machine. Simultaneously, the toughness and Young's modulus of Examples 1, 10, 17, and Comparative Example 1 were also tested. (See attached table.) Figure 1-4 ; Depend on Figure 1 It can be seen that the hydrogels prepared in Examples 1, 10, and 17 of the present invention have a certain degree of flexibility, while Comparative Example 1 has no elasticity. Depend on Figure 2 It can be seen that the Young's modulus of Comparative Example 1 is 200 MPa, which is much greater than that of Examples 1 and 10 and 17, proving that the present invention endows the polyionic liquid gel with a certain degree of flexibility and its mechanical properties are adjustable. Depend on Figure 3 It can be seen that Example 1 has better toughness compared to Comparative Example 2; Depend on Figure 4 It can be seen that Example 1 has better toughness and fracture strength compared with Comparative Example 3, proving that the mechanical properties of the polyionic liquid gel in this invention are superior to those of the n-hexane ionic liquid gel. The fluorinated polymerizable ionic liquid gel in Example 1 contains fluorine not only in its counterion but also in its main chain; its molecular structure is as follows: , The molecular structure of the hexane polymerizable ionic liquid gel in Comparative Example 3 is as follows:

[0039] It contains only fluorine in the counterion and not in the main chain; therefore, the fluorinated polyionic liquid gel of Example 1 has more ion-dipole interactions between molecules compared with the n-hexane ionic liquid gel of Comparative Example 3. In addition, the hydrogel of Example 1 has more fluorine atoms, which gives it better mechanical properties.

[0040] Meanwhile, the fracture strength and elongation at break of Examples 2, 3, 4, 6, 15, 16, and 17 were tested, and their structures are shown in Table 1.

[0041] Table 1. Fracture strength and elongation at break of different embodiments .

[0042] 2. Self-healing performance testing The gel sample was cut in half and then the two parts were reassembled along the cut surface. The sample was allowed to self-heal at 25°C for 24 hours. Examples 1-17 were all self-healing, while Comparative Examples 1, 2 and 3 did not have self-healing ability. Mechanical tensile tests were performed on the self-healing samples of Example 1 to determine the self-healing efficiency ( The formula for () is as follows: in, It is the fracture strength of the sample after self-healing. It is the fracture strength of the original sample; See results Figure 5 ; Depend on Figure 5 It can be seen that Example 1 still has good mechanical strength after five cycles of self-healing test. The average fracture strength of the five self-healing tests is 1079.64 KPa, and the average self-healing efficiency can reach 53.42%.

[0043] 3. Conductivity testing The conductivity of the hydrogel of Example 1 was measured using a KEITHLEY 2400 digital source potentiometer (2.1V). The prepared hydrogel sample was a cuboid. The hydrogel of Example 1 was fixed to a human finger and vocal cords, respectively. Conductivity tests were performed by measuring the deformation caused by the extension and bending of the finger and the vibration of the vocal cords when pronouncing "hello," and the changes in relative resistance were recorded. (See attached figure). Figure 6 ; The relative resistance is defined as DR / R0 = (R-R0) / R0, where R0 represents the initial resistance without strain and R represents the real-time resistance after deformation. Depend on Figure 6It was found that when the finger was bent at 30°, 60°, and 90°, the ΔR / R0 of the gel reached 2.1%, 4.0%, and 6.5%, respectively, indicating that the gel can produce an accurate signal response, and the signal exhibits obvious regularity and stability. When the word "hello" was emitted, a regular relative resistance change curve of the polyionic liquid gel could be observed. These results demonstrate that the hydrogel possesses good conductivity in strain response. This property shows great potential application prospects in fields such as soft electronic materials and wearable sensors.

[0044] 4. Testing for resistance to special environments Swelling test: Samples from Example 1 with a cut mass of 0.6 g were immersed in 150 mL of different solvents (distilled water, 1 mol / L HCl solution, 1 mol / L NaOH solution, petroleum ether, n-hexane, and white oil, respectively). The samples were weighed periodically, and their stability in special environments was characterized by calculating the swelling rate. The results are shown in [Figure number missing]. Figure 7 ; The expansion ratio (SR) is estimated using the following formula: m0 is the original weight of the sample, and m is the weight after soaking for a certain period of time. Both are in g. Depend on Figure 7 It was found that the gel only swelled slightly in 1 mol / L HCl solution (representing a strong acid) and distilled water, with a swelling degree of about 4.5%. In 1 mol / L NaOH solution (representing a strong alkali), the gel showed a slight decreasing trend in mass, but the mass loss was only 10% after 30 days. Meanwhile, the polyionic liquid gel showed almost no mass change after immersion in petroleum ether, n-hexane, and white oil for 30 days, demonstrating excellent stability. Therefore, it can be seen that the hydrogel prepared by the present invention can exhibit excellent stability in special environments.

Claims

1. A method for preparing a conductive hydrogel sensor based on a fluorinated polyionic liquid, characterized in that: Includes the following steps: (1) Preparation of fluorine-containing cationic monomer: Add fluorine-containing organic halide to amino methacrylate, stir, react under an inert atmosphere for 48-72 h, recrystallize with anhydrous ethanol, and dry under vacuum to obtain fluorine-containing cationic monomer; (2) Preparation of fluorine-containing polymerizable ionic liquid: Lithium bis(trifluoromethanesulfonylimide) is dissolved in deionized water, the fluorine-containing cationic monomer is added to it, the reaction is stirred at 0°C, the liquid is separated, the lower oily liquid is washed with deionized water and dried under vacuum to obtain fluorine-containing polymerizable ionic liquid; (3) Preparation of conductive hydrogel sensor: Add hydrophobic ionic liquid medium and photoinitiator to the fluorine-containing polymerizable ionic liquid, stir until dissolved, transfer to a transparent and sealed mold, and irradiate with ultraviolet light for 2-6 h to form a conductive hydrogel sensor based on fluorine-containing polyionic liquid.

2. The method for preparing a conductive hydrogel sensor based on a fluorinated polyionic liquid according to claim 1 or 2, characterized in that: In step (3), a crosslinking agent also needs to be added when adding the hydrophobic ionic liquid medium and the photoinitiator.

3. The method for preparing a conductive hydrogel sensor based on a fluorinated polyionic liquid according to claim 1 or 2, characterized in that: The fluorinated organohalide is at least one of 1,1,1-trifluoro-3-iodopropane, 4-(trifluoromethyl)bromobenzyl bromide, or trifluoroiodomethane.

4. The method for preparing a conductive hydrogel sensor based on a fluorinated polyionic liquid according to claim 1 or 2, characterized in that: The hydrophobic ionic liquid medium is at least one of 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imine, 1-ethyl-3-methylimidazoline tetrafluoroborate, or 1-butyl-3-methylimidazoline hexafluorophosphate.

5. The method for preparing a conductive hydrogel sensor based on a fluorinated polyionic liquid according to claim 1 or 2, characterized in that: In step (1), the volume ratio of aminomethacrylate to fluorinated organic halide is 1:(0.5-5).

6. The method for preparing a conductive hydrogel sensor based on a fluorinated polyionic liquid according to claim 1 or 2, characterized in that: In step (2), the mass ratio of lithium bis(trifluoromethanesulfonylimide) to the fluorinated cationic monomer is 1:(0.1-5).

7. The method for preparing a conductive hydrogel sensor based on a fluorinated polyionic liquid according to claim 1 or 2, characterized in that: In step (3), the ratio of the fluorinated polymerizable ionic liquid, the hydrophobic ionic liquid medium, and the photoinitiator is 1 mL: (25-500) μL: (10-80) mg.

8. The method for preparing a conductive hydrogel sensor based on a fluorinated polyionic liquid according to claim 2, characterized in that: In step (3), the ratio of the fluorinated polymerizable ionic liquid, the hydrophobic ionic liquid medium, the crosslinking agent, and the photoinitiator is 1 mL: (25-500) μL: (0.2-5) μL: (10-80) mg.

9. The method for preparing a conductive hydrogel sensor based on a fluorinated polyionic liquid according to claim 1 or 2, characterized in that: The aminomethacrylate is at least one of dimethylaminoethyl methacrylate or diethylaminoethyl methacrylate.

10. The method for preparing a conductive hydrogel sensor based on a fluorinated polyionic liquid according to claim 1 or 2, characterized in that: The crosslinking agent is at least one of N,N′-methylenebisacrylamide, ethylene glycol dimethacrylate, or divinylbenzene; the photoinitiator is at least one of 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone or ethyl (2,4,6-trimethylbenzoyl)phenylphosphonate.

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