A photoresponsive epoxy resin based on azopyridine structure and preparation method and photoresponsive method thereof

Abstract

The invention discloses a photoresponsive epoxy resin based on an azopyridine structure, and its preparation method is as follows: the amino derivatives containing azopyridine structure and epoxy resin monomer are dissolved in N, N-dimethylformamide, poured into a mold, and after drying the solvent at 50 ° C in an oven, heated to 120-160 ° C for curing reaction for 4-5h to obtain a photoresponsive epoxy resin. The photoresponsive method of the photoresponsive epoxy resin is: the epoxy resin is stretched 5%-100% at 70-150 ° C and then cooled to room temperature, and the epoxy resin is deformed under ultraviolet light irradiation of 340-380nm, and the deformed position is continuously irradiated with visible light of 420-460nm, and the epoxy resin returns to its original state. The preparation method of the photoresponsive epoxy resin based on the azopyridine structure prepared by the present invention is simple, the curing temperature is low, the curing reaction time is short, and the material has excellent mechanical properties, shape memory properties and photoresponsive properties, and has broad application prospects in the field of smart materials.

Description

Technical Field

[0001] The present invention relates to the technical field of photoresponsive materials, in particular to a photoresponsive epoxy resin based on an azopyridine structure, and a preparation method and a photoresponsive method thereof. Background Art

[0002] Stimuli-responsive polymer materials, a type of polymer-based smart material, are highly sensitive to external stimuli such as temperature, pH, light, and voltage. These stimuli can cause reversible or irreversible changes in the material's structure or state, imparting specialized functionalities. These specialized functionalities can meet specific material needs. Compared to other responsive behaviors, photoresponsiveness offers advantages such as rapid response, remote controllability, lack of byproducts, and safety and reliability. This makes it widely applicable in areas such as photo-orientation, photo-control, and surface relief gratings. Photo-braking materials, which simulate biological motion through reversible deformation in response to light, have widespread applications in the field of biomimetic biology. For example, photo-braking devices can mimic human movements such as crawling / walking, rolling, grasping, jumping, and swimming. Therefore, photo-braking materials hold great promise for future applications.

[0003] Epoxy resins have excellent mechanical properties, chemical resistance, and thermal stability, and are widely used in construction, coatings, decoration, electronics, and industrial molds. Relatively little research has been conducted on epoxy resins for photoresistance. Reported photoresistance epoxy resins are primarily obtained by curing azobenzene-containing epoxy monomers generated by azophenyldiphenol and epichlorohydrin with long-chain alkyl diacids. For example, Michael R. Kessler (ACS Appl. Mater. Interfaces 2016, 8, 15750-15757) and Yue Zhao (Adv. Mater. 2017, 29, 1606467 and Adv. Mater. 2018, 30, 1706597) respectively obtained photoresponsive epoxy resins by curing azobenzene-containing epoxy monomers with sebacic acid and dodecane diacid at high temperatures. Because carboxylic acid-cured epoxy resins require high temperatures, their preparation requires not only a reaction of an azobenzene-containing epoxy monomer with a long-chain alkyl diacid in a solvent at 145°C for nearly 12 hours, followed by another 12 hours of heating to remove the solvent, but also subsequent hot pressing of the polymer pellets at 180°C. This high reaction temperature, long reaction time, and complex preparation process limit the material's application. Summary of the Invention

[0004] In order to solve the problems of existing photoactivated epoxy resins such as high curing temperature, long curing time, and complex curing process, the present invention provides a method for preparing a photoresponsive epoxy resin material with low curing temperature, short curing time, and simple process.

[0005] The photoresponsive epoxy resin based on an azopyridine structure provided by the present invention is prepared by a curing reaction of an amino derivative containing an azopyridine structure and an epoxy resin monomer at a molar ratio of 1:(1-2) at 120-160° C. for 4-5 hours.

[0006] The molecular structural formula of the amino derivative containing azopyridine structure is as follows:

[0007]

[0008] Wherein, R1 is one of the following structural formulas:

[0009]

[0010] The value range of m is 1-11.

[0011] The general molecular structure formula of the epoxy resin monomer is:

[0012]

[0013] Wherein, R2 is one of the following structural formulas:

[0014]

[0015] The value range of n is 1-10.

[0016] The specific preparation method of the above-mentioned photoresponsive epoxy resin based on azopyridine structure is as follows:

[0017] The amino derivative containing an azopyridine structure and the epoxy resin monomer are dissolved in N,N-dimethylformamide in a molar ratio of 1:1, poured into a mold, and the solvent is dried in an oven at 50°C, and then heated to 120-160°C for a curing reaction for 4-5 hours to obtain a photoresponsive epoxy resin.

[0018] The synthesis method of the azodipyridinylamine derivative is as follows: at room temperature, azodipyridinyl chloride is dissolved in dry dichloromethane, a flexible long-chain diamine is added, and the mixture is synthesized under the catalytic condition of triethylamine.

[0019] Preferably, the flexible long-chain diamine is one of polysiloxane, polyetheramine, and polyethylene glycol diamine with a molecular weight of 100-800.

[0020] The photoresponsive method of the azopyridine-based photoresponsive epoxy resin comprises the following steps: stretching the epoxy resin by 5% to 100% at 70-150° C. and then cooling it to room temperature; irradiating the epoxy resin with 340-380 nm ultraviolet light to deform the epoxy resin; and continuously irradiating the deformed position with 420-460 nm visible light to restore the epoxy resin to its original shape.

[0021] Compared with the prior art, the present invention is beneficial in that:

[0022] First, the present invention incorporates a photoactive azobispyridine structure into the photoresponsive epoxy resin. Through the photoresponsive reversible cis-trans isomerization of the azobispyridine structure, the epoxy resin material achieves photoactivation. Upon irradiation with 340-380nm ultraviolet light, the resulting epoxy resin deforms. Further irradiation with 420-460nm visible light restores the deformed area to its original shape. Using light as a stimulus, the material offers advantages such as remote, contactless control, precise positioning, and instantaneous switching.

[0023] Secondly, the photoresponsive epoxy resin of the present invention is obtained by curing an amino derivative containing an azodipyridine structure with an epoxy resin monomer at 120-160°C for 4-5 hours. Compared with previously reported photoresponsive epoxy resins, the curing temperature is lower, the curing time is significantly shortened, and the curing process is simpler.

[0024] Third, the photoresponsive epoxy resin of the present invention has a higher crosslink density and a tensile strength of 37.3 MPa, approximately 60% higher than the aforementioned photoactivated azobenzene epoxy resin. This material exhibits excellent mechanical properties, shape memory properties, and photoresponsiveness, and has broad application prospects in the field of smart materials.

[0025] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 , H NMR spectrum of sodium azopyridine dicarboxylate.

[0027] Figure 2 , infrared spectrum of azopyridinediamine derivative Abpy-PEA.

[0028] Figure 3 , UV absorption spectrum of azopyridinediamine derivative Abpy-PEA.

[0029] Figure 4 , DSC diagram of epoxy E51 and azopyridinediamine derivative before curing.

[0030] Figure 5 , DSC graph of epoxy E51 after curing with azopyridinediamine derivative.

[0031] Figure 6 , Infrared spectrum of the photoresponsive epoxy resin film E51 / Abpy-PEA based on azopyridine structure.

[0032] Figure 7, Photoresponse diagram of photoresponsive epoxy resin film E51 / Abpy-PEA based on azopyridine structure.

[0033] Figure 8 , diagram of the shape memory process of the photoresponsive epoxy resin film E51 / Abpy-PEA based on azopyridine structure.

[0034] Figure 9 , stress-strain curve of photoresponsive epoxy resin film E51 / Abpy-PEA based on azopyridine structure.

[0035] Figure 10 , infrared spectra of epoxy E51 and terminated azopyridinediamine E51 / Terminated Abpy-PEA.

[0036] Figure 11 , DSC graph of epoxy E51 before reaction with terminated azopyridine diamine E51 / Terminated Abpy-PEA.

[0037] Figure 12 , DSC graph after the reaction of epoxy E51 and terminated azopyridine diamine E51 / Terminated Abpy-PEA. DETAILED DESCRIPTION

[0038] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0039] Example 1

[0040] A method for preparing a photoresponsive epoxy resin based on an azopyridine structure, comprising the following steps:

[0041] (1) Preparation of azopyridinedicarboxylic acid

[0042] Weigh 9g of 6-aminonicotinic acid into a round-bottom flask. Prepare a 10% sodium hydroxide aqueous solution and add 45ml to the flask. Stir magnetically until uniform. Add 135ml of NaClO solution dropwise in an ice-water bath over approximately 15 minutes. Stir in an ice-water bath for 1 hour. After 1 hour, add an additional 90ml of NaClO solution and continue reacting in the ice-water bath for 3 hours.

[0043] After the reaction is completed, the resulting mixture is filtered through a funnel, and the resulting filtrate is treated with NaOH pellets and filtered again. The solids obtained from the two filtrations are dissolved in 250 ml of a 1 mol / L NaOH solution to obtain a red solution. The solution is poured into a round-bottom flask, heated to 50°C, and treated with activated carbon for 30 minutes. The resulting solution is cooled to room temperature and filtered through SiO2 powder. The resulting solution is acidified with concentrated hydrochloric acid to a pH of 3-4. The pink precipitate obtained during the acidification process is filtered, washed to neutrality, and dried to obtain azopyridinedicarboxylic acid.

[0044] The reaction equation is as follows:

[0045]

[0046] Figure 1 This is the H NMR spectrum of sodium azopyridine dicarboxylate. Since the dicarboxylic acid is insoluble in deuterated water, it was converted to its sodium salt using sodium carbonate and then dissolved in deuterated water for analysis. The shifts in the graph are: δ = 4.7 ppm (durated water), 8.92-8.93 ppm (2H), 8.34-8.37 ppm (2H), and 7.87-7.89 ppm (2H).

[0047] (2) Preparation of azopyridine dichloride

[0048] Grind dried azopyridinedicarboxylic acid into a powder. Weigh 1 g of azopyridinedicarboxylic acid into a round-bottom flask. In a fume hood, measure 15 ml of thionyl chloride solution and add it to the same round-bottom flask. Set up the experimental apparatus and place a drying tube filled with potassium carbonate particles on top of the condenser. Set the reaction temperature to 78°C and the reaction time to 12 hours under magnetic stirring.

[0049] After the reaction is completed, the resulting solution is subjected to rotary evaporation to remove unreacted thionyl chloride in the system. The solid obtained after rotary evaporation is ultrasonically dissolved with an appropriate amount of dichloromethane and then filtered using a sand core funnel. The resulting filtrate is poured into a round-bottom flask of known weight and subjected to rotary evaporation to obtain a certain amount of azopyridine dichloride. The reaction equation is as follows:

[0050]

[0051] (3) Preparation of azopyridinediamine Abpy-PEA

[0052] In a round-bottom flask, weigh 2.57g of polyether diamine (molecular weight 400), add 1.43ml of triethylamine, and sonicate with 21.4ml of dichloromethane. Then, add 14.3ml of dichloromethane to 1g of azopyridine dichloride obtained in the previous step and sonicate. Place the round-bottom flask in an ice bath under nitrogen. Slowly add the azopyridine dichloride solution dropwise to the flask using a syringe. After the addition is complete, purge with nitrogen for 2 minutes. The reaction time is 24 hours.

[0053]

[0054] After the reaction is complete, the solution is rotary evaporated, and the resulting solid is added to tetrahydrofuran and rotary evaporated twice more to remove the triethylamine. During the final rotary evaporation, the solution is poured into a round-bottom flask of known weight to determine the mass of azopyridinediamine (Abpy-PEA). Finally, the solution is pumped with an oil pump for 15-20 minutes to remove the remaining tetrahydrofuran. The reaction equation is as follows:

[0055] Figure 2 This is the infrared spectrum of the azopyridine diamine derivative Abpy-PEA, in which: 3488cm -1 It is the stretching vibration absorption peak of -NH2 and -NH- in amide, 1644cm -1 and 1374cm -1 They are the stretching vibration absorption peaks of -C=O- and -CN- in the amide bond, 1544 cm -1 It is the stretching vibration absorption peak of -N=N- in the azopyridine structure, 1105cm -1 It is the stretching vibration absorption peak of the ether bond -COC-, 2927cm -1 ,2973cm -1 ,2873cm -1 They are the stretching vibration absorption peaks of -CH-, -CH3, and -CH2- respectively.

[0056] Figure 3 This is the ultraviolet absorption spectrum of the azopyridinediamine derivative Abpy-PEA. In the figure, the absorption peak of the azo trans structure is at 365nm, and the absorption peak of the azo cis structure is at 450nm.

[0057] (4) Preparation of photoresponsive epoxy resin film E51 / Abpy-PEA

[0058] Preparation of photoresponsive epoxy resin film using azopyridine diamine derivatives and epoxy resin: Weigh 0.128g of bisphenol A epoxy resin and 0.17g of azopyridine diamine derivative (Abpy-PEA) (molar ratio 2:1) in the same glass bottle, add 3ml of N,N-dimethylformamide (DMF) for ultrasonic dissolution; pour the evenly dispersed solution into the mold and put it into a 50°C oven for drying. After a period of time, it is cured: the oven is heated to 120°C within 10 minutes and maintained for 2 hours, and then the oven is heated to 160°C within 10 minutes and maintained for 2 hours. After curing is completed, the film is removed with tweezers, checked for defects such as bubbles, and then stored. The chemical reaction formula is as follows:

[0059]

[0060] Figure 4 This is the DSC graph of epoxy E51 and azobispyridine diamine derivative before curing. The information in the figure proves that the curing reaction temperature of epoxy E51 and azobispyridine diamine derivative is around 150°C.

[0061] Figure 5 This is the DSC graph after curing epoxy E51 with azobispyridine diamine derivatives. The information in the figure proves that the glass transition temperature of the epoxy resin obtained after curing epoxy E51 with azobispyridine diamine derivatives is about 42°C.

[0062] Figure 6 The infrared spectrum of the photoresponsive epoxy resin film E51 / Abpy-PEA based on azopyridine structure is shown in the figure: 3424cm -1 It is the stretching vibration absorption peak of -NH2 and -NH- in amide, 1644cm -1 and 1374cm -1 They are the stretching vibration absorption peaks of -C=O and -CN- in the amide bond, 1509cm -1 It is the stretching vibration absorption peak of -N=N- in the azopyridine structure, 1105cm -1 It is the stretching vibration absorption peak of the ether bond -COC-, 1249cm -1 、921cm -1 and 829cm -1 It is the characteristic peak of epoxy group, 2969cm -1 、2871cm -1 and 2929cm -1 They are the stretching vibration absorption peaks of -CH3, -CH2-, and -CH- respectively.

[0063] Figure 7This is the photoresponse graph of the azopyridine-based photoresponsive epoxy resin film E51 / Abpy-PEA. A 3.1 cm long strip was stretched and oriented at 50°C. The film was then grasped with tweezers and exposed to 365 nm UV light. Deformation of the film is clearly observed where it is illuminated, bending toward the source. This phenomenon demonstrates that under 365 nm UV light, the azopyridine structure transforms from a stable trans-form to a cis-form, demonstrating the photoresponsive epoxy resin film's ability to undergo photoinduced deformation.

[0064] Figure 8 This is a diagram of the shape memory process of the photoresponsive epoxy resin film E51 / Abpy-PEA based on the azopyridine structure. In the figure, before orientation, the original length of the photoresponsive epoxy resin film spline was 2.1 cm; after external force stretching and orientation at 50°C, the length of the film spline was 3.6 cm; after the external force was removed and the stretched spline was placed in ice water to cool, the spline became 3.5 cm; finally, after the spline was placed in a 50°C environment, the spline returned to 2.3 cm. By calculating the fixation rate R of the photoresponsive epoxy resin film f and response rate R r , and get R f =93%, R r =86%, indicating that the film has excellent shape memory function.

[0065] Figure 9 This figure shows the stress-strain curve of the azopyridine-based photoresponsive epoxy film E51 / Abpy-PEA. The resulting photoresponsive epoxy film was trimmed into long strips for tensile testing. The specimens were 5 mm wide, 0.25 mm thick, and had an original marking of 11.73 mm. The tensile rate was 20 mm / min. Five tests were repeated, and the average results were taken. At a tensile rate of 20 mm / min, the photoresponsive epoxy film exhibited an average maximum tensile stress of 39.8 N, an average elastic modulus of 617.96 MPa, an average tensile strength of 37.3 MPa, an average elongation at break of 54.4%, and a tensile stress at break of 0.65 MPa. Conventional epoxy films made from E51 have an elongation at break of 36%.

[0066] Example 2

[0067] The method for preparing azopyridinedicarboxylic acid and azopyridine dichloride is the same as steps (1) and (2) of Example 1.

[0068] (3) Preparation of blocked azopyridinediamine

[0069] Dissolve 0.235g of acrylonitrile in 10ml of anhydrous methanol and 2.3g of azopyridinediamine in 2ml of anhydrous methanol. Add the methanol solution of azopyridinediamine dropwise to the acrylonitrile solution in anhydrous methanol over 30 minutes in an ice bath. After the addition is complete, return the reaction to room temperature and stir magnetically for 24 hours.

[0070] After the reaction is completed, the resulting solution is subjected to rotary evaporation, and an appropriate amount of tetrahydrofuran is added to dissolve and rotary evaporation to remove the methanol therein; the remaining tetrahydrofuran is removed with an oil pump. The reaction equation is as follows:

[0071]

[0072] (4) Preparation of photoresponsive epoxy resin films

[0073] Preparation of photoresponsive epoxy resin film using blocked azopyridine diamine and epoxy resin: 0.25g of bisphenol A epoxy resin and 0.085g of blocked azopyridine diamine (molar ratio of 1:1) were placed in the same glass bottle, and 3ml of DMF was added for ultrasonic dissolution; the evenly dispersed solution was poured into a mold and placed in a 50°C oven for drying. After drying, the film was heated and cured. The curing program was set as follows: first, the temperature was raised to 200°C, maintained for 2 hours, and then the temperature was raised to 265°C for curing for 2 hours. After curing, the film was removed with tweezers and stored after inspection. The reaction equation is as follows:

[0074]

[0075] Figure 10 The infrared spectrum of epoxy E51 and terminated azopyridine diamine E51 / Terminated Abpy-PEA is the same as that of Example 1. Figure 6 Compared with the infrared absorption spectrum of E51 / Abpy-PEA, the infrared absorption spectrum of E51 / Abpy-PEA has the following peaks at 2146 cm- -1 The peak at the center is the stretching vibration absorption peak of -C≡N, indicating that the experimental process of acrylonitrile-terminated Abpy-PEA has been completed.

[0076] Figure 11 This is the DSC graph before the reaction of epoxy E51 and blocked azopyridine diamine E51 / Terminated Abpy-PEA. The peak temperature in the graph indicates that the curing temperature of E51 and blocked Abpy-PEA is 264°C.

[0077] Figure 12This is the DSC of the reaction between epoxy E51 and terminated azopyridine diamine E51 / Terminated Abpy-PEA. It can be clearly observed in the figure that the glass transition temperature of the film is 20°C, which also indicates that the curing is complete.

[0078] In summary, the present invention achieves the photoactivation effect of a photoresponsive epoxy resin by introducing an azopyridine structure into the epoxy resin backbone and leveraging the photoresponsive properties of the azopyridine structure. The azopyridine-based photoresponsive epoxy resin prepared by the present invention has a simple preparation method, low curing temperature, and short curing reaction time. Furthermore, the material exhibits excellent mechanical properties, shape memory properties, and photoresponsiveness, and has broad application prospects in the field of smart materials.

[0079] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a photoresponsive epoxy resin based on an azopyridine structure, characterized in that: The amino derivative containing azopyridine structure and epoxy resin monomer are dissolved in N,N-dimethylformamide, poured into a mold, dried in an oven at 50°C, and then heated to 120-160°C for curing reaction for 4-5 hours to obtain a photoresponsive epoxy resin; the molar ratio of the amino derivative containing azobispyridine structure to the epoxy resin monomer is 1:(1-2); the molecular structure formula of the amino derivative containing azopyridine structure is as follows: In the formula, R1 is one of the following structural formulas: The value range of m is 1-11; The synthesis method of the azodipyridinylamine derivative comprises the following steps: dissolving azodipyridinyl chloride in dry dichloromethane at room temperature, adding a flexible long-chain diamine, and synthesizing the product under the catalytic condition of triethylamine; the flexible long-chain diamine is a polysiloxane or polyetheramine with a molecular weight of 100-800.

2. The method for preparing a photoresponsive epoxy resin based on azopyridine structure according to claim 1, characterized in that: The general molecular structure formula of the epoxy resin monomer is: In the formula, R2 is one of the following structural formulas: The value range of n is 1-10.

3. The method for preparing a photoresponsive epoxy resin based on azopyridine structure according to claim 1, characterized in that: The flexible long-chain diamine is polyethylene glycol diamine with a molecular weight of 100-800.

4. A photoresponsive epoxy resin based on an azopyridine structure, characterized in that: The method is prepared according to any one of claims 1 to 3.

5. A photoresponsive method for a photoresponsive epoxy resin based on an azopyridine structure as claimed in claim 4, characterized in that: The epoxy resin is stretched by 5%-100% at 70-150°C and then cooled to room temperature. Under the irradiation of 340-380nm ultraviolet light, the epoxy resin is deformed. The deformed position is further irradiated with 420-460nm visible light, and the epoxy resin returns to its original state.

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