Aliphatic polycarbonate adhesives containing photoresponsive groups and their preparation methods

Abstract

This invention discloses an aliphatic polycarbonate adhesive containing photoresponsive groups and its preparation method, relating to the field of smart adhesive technology. This invention uses aliphatic polycarbonate as the polymer backbone and small-molecule photoresponsive groups as initiators to prepare a repairable and recyclable smart adhesive material via ring-opening polymerization. Adhesion and cleaning experiments on different substrates show that the obtained aliphatic polycarbonate elastomer containing photoresponsive groups exhibits very strong adhesive strength (0.22 MPa to 11.2 MPa). This type of adhesive can be quickly and effectively cleaned when the external environment changes, and can be used as a reversible adhesive.

Description

Technical Field

[0001] This invention relates to smart adhesive materials, specifically to aliphatic polycarbonate adhesives containing photoresponsive groups and their preparation methods. Background Technology

[0002] Aliphatic polycarbonate materials are difficult to process and mold, have poor multifunctionality, and require a large amount of energy for recycling, resulting in serious resource waste and environmental pollution. Because these materials have long been unable to achieve green and sustainable development, they have attracted considerable attention from researchers. In recent years, intelligent polymer elastomers with self-healing capabilities have been widely researched and developed in various fields such as human body sensors, wound healing, and adhesion. With the rapid development of multifunctional and increasingly stimulus-responsive driven materials with biomimetic self-healing capabilities, intelligent and adaptive driven materials for long-term application are expected to be used in complex environments. Although a thermally decomposable aliphatic polycarbonate adhesive with low residual carbon after sintering and degreasing ability even in relatively low-temperature non-oxidizing atmospheres has been reported in Chinese invention patents CN111032729B and CN109415502B, this type of adhesive cannot achieve strong adhesive strength and intelligent bonding processes, and no reports of intelligent aliphatic polycarbonate adhesives have been found in existing patents. Therefore, it is necessary to explore novel aliphatic polycarbonate adhesives. Furthermore… Combining a material's self-healing capabilities with high adhesion is particularly attractive because it can significantly improve the overall performance of adhesives and has a wide range of applications. However, in practical applications, a completely clean surface is difficult or sometimes impossible to achieve simultaneously, which often leads to adhesion failure of conventional adhesives. Summary of the Invention

[0003] To address the aforementioned technical problems, the purpose of this invention is to provide a light-responsive, rapidly repairing smart adhesive, solving the problems of limited functionality, slow self-healing efficiency, and low bonding strength of current aliphatic polycarbonate structures. Simultaneously, this invention provides an adhesive method with ultra-strong bonding strength, solving the current limitations of achieving smart bonding and rapid cleaning, which has broad application prospects in the field of smart bonding.

[0004] In this invention, photoresponsive units (including but not limited to azobenzene and its derivatives, stilbene, Schiff bases, spiropyrans, and other photoresponsive compounds) are selected as functional initiators, and aliphatic polycarbonate is used as the polymer backbone. During polymerization, these units provide a large number of physical crosslinking groups, and as the polymerization reaction proceeds, further physical crosslinking interactions are formed, thereby enhancing self-healing properties. Furthermore, since the photoresponsive units possess photoisomerization properties, this provides the possibility of achieving multifunctionality in the synthesized materials and offers a theoretical basis for the development of smart adhesives.

[0005] The aliphatic polycarbonate monomers involved in this invention are commercially widely used and patented aliphatic polycarbonate monomers (e.g., those reported in Chinese Invention Patent ZL 201310363003.7). Ring-opening polymerization (ROP) of cyclic carbonate monomers is the most efficient and convenient method for preparing high molecular weight polycarbonates with low dispersion coefficients. Trimethylene carbonate (TMC) is one of the most studied cyclic carbonate monomers. To optimize its performance and expand its applications in biomedicine, various functional groups, such as hydroxyl, carboxyl, and amino groups, are often introduced into its outer ring through chemical modification, resulting in a variety of functionalized cyclic carbonate monomers, the general structural formula of which is shown in Formula I.

[0006]

[0007] In the aliphatic carbonate monomers shown in Formula I, M1 is a hydrogen atom or a methyl group; M2 is selected from hydrogen atom, cyano, carboxyl, ester, substituted or unsubstituted C1-C15 alkyl, substituted or unsubstituted C6-C20 aryl, substituted or unsubstituted C1-C15 alkoxy, substituted or unsubstituted C1-C15 heteroalkyl, substituted or unsubstituted C6-C20 heteroaryl, wherein the heteroalkyl is at least one C-substituted alkyl or cycloalkyl group, and the alkyl, aryl, alkoxy, heteroalkyl, and heteroaryl groups may have one or more substituents, including but not limited to hydroxyl, cyano, carboxyl, mercapto, carbonyl, ester, and phenyl.

[0008] The aliphatic carbonate monomers used in this invention include, but are not limited to, trimethylene carbonate (TMC), 5-methyl-5-benzyloxycarbonyl trimethylene carbonate (MBC), 5-benzyloxy-trimethylene carbonate (BTMC), and 5-methyl-5-carboxyl-trimethylene carbonate (MCC), as shown below:

[0009]

[0010] The photoresponsive groups involved in this invention include, but are not limited to, stilbene, azobenzene, Schiff bases, and other compounds that can undergo cis-trans isomerization under light of a certain wavelength or at a specific temperature, as shown in Formulas II to IV:

[0011]

[0012] In the stilbene-based photoresponsive compounds represented by Formula ⅠⅠ, the azobenzene-based photoresponsive compounds represented by Formula Ⅲ, and the Schiff base-based photoresponsive compounds represented by Formula Ⅳ, R1 is a hydrogen atom or a C1-C12 alkyl group; the terminal group R2 is a para-substituted C1-C12 n-alkyl or n-alkoxy, nitro, cyano, or carboxyl group; and R3 is a hydrogen atom or a cyano group.

[0013] This invention uses photoresponsive groups to initiate the ring-opening polymerization of aliphatic carbonate monomers to prepare aliphatic polycarbonate elastomers with photoresponsive groups at the terminal positions, the structures of which are shown in Formula V-Formula VⅠⅠ.

[0014]

[0015] In aliphatic polycarbonate elastomers with photoresponsive groups at the terminal positions as shown in Formula V-VII, M1 is a hydrogen atom or a methyl group; M2 is a hydrogen atom, cyano group, carboxyl group, ester group, substituted or unsubstituted C1-C15 alkyl group, substituted or unsubstituted C6-C20 aryl group, substituted or unsubstituted C1-C15 alkoxy group, substituted or unsubstituted C1-C15 heteroalkyl group, or substituted or unsubstituted C6-C20 heteroaryl group, wherein the heteroalkyl group is at least one C with an O The alkyl or cycloalkyl group may be S- or N-substituted, and the alkyl, aryl, alkoxy, heteroalkyl, or heteroaryl group may have one or more substituents, including but not limited to hydroxyl, cyano, carboxyl, mercapto, carbonyl, ester, and phenyl groups; n represents the degree of polymerization (number of repeating units), preferably an integer from 107 to 300, i.e., the polymer molecular weight is between 30,000 and 90,000; the terminal group R2 is a para-substituted C1-C12 n-alkyl or n-alkoxy, nitro, cyano, or carboxyl group.

[0016] Polymerization methods for obtaining V-type VⅠⅠ polymers include, but are not limited to, coordination ring-opening polymerization, solution ring-opening polymerization, ring-opening metathesis polymerization (ROMP), and in-situ blending.

[0017] Specifically, the present invention uses photoresponsive groups as functional initiators to initiate the ring-opening polymerization of aliphatic carbonate monomers. The polymerization reaction steps are generally similar to the preparation method disclosed in Chinese invention patent ZL 201310363003.7.

[0018] This invention provides an aliphatic polycarbonate adhesive with ultra-strong adhesive strength containing specific photoresponsive groups at its ends, and its preparation and application methods are as follows:

[0019] (1) Preparation of aliphatic polycarbonate elastomers with end-position photoresponsive groups

[0020] A certain amount of photoresponsive groups are used as functional initiators to initiate the ring-opening polymerization of aliphatic carbonate monomers, preparing aliphatic polycarbonate elastomers with photoresponsive groups at their terminals. The dynamic bonds constituting the target elastomer network include, but are not limited to, hydrogen bonding, disulfide bonds, Diels-Alde interactions, hydrophobic association interactions, host-guest interactions, and boron-oxygen bonds. The molar ratio of aliphatic carbonate monomer to photoresponsive initiator is in the range of 10:1 to 1000:1, the reaction temperature is in the range of 80 to 130℃, the reaction time is in the range of 24 to 48 h, and organic solvents such as tetrahydrofuran, dichloromethane, ethanol, and methanol can be used.

[0021] (2) Application of aliphatic polycarbonate adhesives with end-position photoresponsive groups

[0022] To induce adhesion in aliphatic polycarbonate elastomers containing photoresponsive groups, an elastomer sample prepared in step (1) was placed on a substrate of a certain area. The sample was then directly irradiated with ultraviolet light (at a specific intensity and duration) or subjected to specific thermal radiation to form a uniform liquid layer. Another substrate was then placed on the liquid layer, and pressure was applied to the substrate before the sample returned to a solid state, causing the two substrates to adhere together. The substrate may include, but is not limited to, substrates made of glass, polymers (such as polycarbonate), metals (such as iron, aluminum, copper, etc.), or ceramics (such as zirconium oxide). Generally, the light intensity is 50–100 W, and the irradiation time is 120–600 s; the thermal radiation temperature is 37–100 °C, and the time is 120–600 s.

[0023] This invention utilizes photoresponsive groups as initiators to prepare a highly efficient, self-healing, and controllable smart adhesive aliphatic polycarbonate adhesive. This adhesive exhibits excellent self-healing behavior, including short repair time, high repair efficiency, excellent ductility, and strong mechanical strength. Utilizing its self-healing properties, the pulverized material can be recycled and processed into any shape an unlimited number of times through ultraviolet or thermal radiation. Furthermore, this material also possesses excellent impact resistance and moisture and corrosion resistance in harsh environments.

[0024] Compared with existing inventions, the present invention has the following advantages:

[0025] (1) The method of the present invention is simple and easy to implement, and the raw material resources are abundant, which is conducive to realizing industrial production.

[0026] (2) The aliphatic polycarbonate involved in the preparation process of this invention has good biocompatibility, no acidic substances are generated during the degradation process, and no side effects are produced, which can significantly improve its multifunctionality.

[0027] (3) The properties of the aliphatic polycarbonate segments involved in the preparation process of this invention can be controlled and adjusted, so that the properties of the prepared material are controllable.

[0028] (4) The elastomer material prepared by the present invention can achieve a dual response effect, that is, it can achieve both light response and rapid thermal response effect for self-repair and recycling.

[0029] (5) The elastomer adhesive prepared by this invention can rapidly self-heal, and the self-healing time is significantly shortened with the increase of light or heat radiation intensity. The complete self-healing time is only 1 to 10 minutes.

[0030] (6) The elastomeric adhesive prepared by this invention can bond multiple different substrates and exhibits strong bonding strength. Furthermore, because this type of adhesive can respond quickly to light and temperature, it can achieve intelligent bonding and rapid, effective post-bonding cleaning. Attached Figure Description

[0031] Figure 1 The structure of the aliphatic polycarbonate adhesive polymer prepared in Example 1 of this invention is shown.

[0032] Figure 2 This is a demonstration experiment of the self-healing behavior of the aliphatic polycarbonate elastomer prepared in Example 2 of the present invention. In this experiment, a shows the self-healing behavior of the elastomer under an optical microscope, b shows the self-healing behavior of the elastomer under an atomic force microscope, and c shows the stress-strain curves of the elastomer at different self-healing times.

[0033] Figure 3 This invention demonstrates the environmental stability and recyclability of the aliphatic polycarbonate elastomer prepared in Example 3 of this invention. (a) shows the proportion of hydrogen bonds in the elastomer and water vapor under full molecular dynamics simulation, (b) shows the corrosion resistance of the elastomer over a wide pH range, (c) shows the stress-strain curve of the elastomer after 14 recycling cycles, and (d) shows the crosslinking density of the elastomer before and after recycling.

[0034] Figure 4 This demonstrates the bonding performance of the aliphatic polycarbonate adhesive prepared in Example 4 of the present invention on different substrates. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to the embodiments.

[0036] The instruments and characterization methods used in the examples are as follows:

[0037] (1) Differential Scanning Calorimetry (DSC)

[0038] The German NETZSCH DSC-204 differential calorimeter was used. Test method: N2 was used as the protective gas, and a disposable aluminum crucible was used to hold the sample. The heating and cooling rates were both 10℃ / min.

[0039] (2) Polarizing optical microscope (POM)

[0040] The polarizing optical microscopy (POM) was performed on a Zeiss Axio Scope A1 microscope equipped with a Linkam LTSE420 thermal platform.

[0041] (3) Atomic force microscopy (AFM)

[0042] The atomic force microscope images were obtained on a Bruker instrument in tapping mode (cantilever model: TESP-V2, Bruker).

[0043] Example 1

[0044] 1. Selection of photoresponsive initiator materials

[0045]

[0046] The photoresponsive initiator used in this embodiment is n-butylazophenol as shown in the above formula. The synthesis process is as follows: p-n-butylaniline is dissolved in a hydrochloric acid solution of a certain concentration and stirred in an ice-water bath; then, sodium nitrite is dissolved in deionized water and added dropwise to the above solution to generate a diazonium salt; then, a certain mass of sodium hydroxide particles is dissolved in deionized water, and after dissolution, a certain mass of phenol solution is added to the sodium hydroxide solution; finally, the mixed solution is added dropwise to the reaction system; after the reaction is completed, hydrochloric acid solution is added dropwise to make the pH of the system 3-5, filtered, dried by blowing air and then vacuum dried for 24-48 hours to synthesize n-butylazophenol.

[0047] 2. Preparation of aliphatic polycarbonate elastomers with terminal azophenyl groups

[0048] 10 g (40 mmol) of aliphatic carbonate monomer 5-methyl-5-benzyloxycarbonyltrimethylene carbonate (MBC) was placed into a dry and clean silanization polymerization tube. Then, 0.08–4 mmol of initiator n-butylazophenol was added to the polymerization tube (multiple parallel experiments were conducted within a molar ratio of n-butylazophenol to aliphatic carbonate monomer of 1:500–1:10). Following this, 10 μL of catalyst stannous octoate solution was added dropwise. The polymerization tube was evacuated, purged four times with nitrogen, sealed, and reacted in an oil bath at 130 °C for 30 h. After polymerization, the prepared sample was placed in a large amount of dichloromethane solvent for 48 h to dissolve unreacted monomers, with fresh dichloromethane solvent replaced every 24 h. Subsequently, the sample was deswollen with ethanol, and the deswollen sample was dried in a vacuum oven for four days to constant weight, yielding a pale yellow solid material.

[0049] 3. Application of aliphatic polycarbonate adhesives with terminal azophenyl groups

[0050] In an area of ​​0.25cm 2 ~1.00cm 2 A 0.22 g aliphatic polycarbonate elastomer with terminal azophenyl groups was placed on a substrate (including but not limited to glass, polycarbonate, iron, aluminum, zirconium oxide, etc.). The elastomer was then directly irradiated with ultraviolet light for 600 s, or subjected to thermal radiation (temperature ~50°C) for 300 s to form a uniform liquid sample layer. Then, another substrate (0.25 cm²) was placed on the liquid layer. 2 ~1.00cm 2 The samples were then left at room temperature for 24 hours before further testing. Generally, the light intensity was 50–100 W and the illumination time was 120–600 s, the temperature range was 37–100 °C, and the duration was 120–600 s. Pressure (0.1 N–10 N) was applied to the substrate before the sample returned to a solid state. The adhered substrate was then stored at room temperature for a certain period (12–48 hours) for further testing.

[0051] like Figure 1 As shown, aliphatic carbonate monomers contain benzene ring groups. Azobenzene small molecules are selected as functional initiators, and azobenzene is designed into the end positions of the aliphatic polycarbonate via bulk coordination polymerization. As the monomer chains are continuously initiated, oligomers are formed. Subsequently, by controlling the molecular weight and distribution width of the polymer, when the benzene ring groups in the polymer side chains reach the critical crosslinking point, due to the high chemical kinetics of the benzene ring groups, the network will form from the physical crosslinking points in the polymer side chains. When the material is subjected to external stimuli, the condensed state of the elastic network will be altered, optical isomerization will occur (the chemical structure will change from trans to cis), thereby leading to changes in the thermal and mechanical behavior of the material.

[0052] Example 2

[0053] 1. Same as step 1 in Example 1;

[0054] 2. Same as step 2 in Example 1;

[0055] 3. Conduct repeatability tests to accurately quantify self-healing efficiency.

[0056] Take a certain area (0.10 cm²) 2 ~1.00cm 2 The aliphatic polycarbonate elastomer material samples containing azophenyl groups at the ends of the sample were cut with a scalpel blade, and at least three parallel samples were recorded. Each sample was completely cut into four pieces with a cross-shaped slit, and the cut interfaces were gently joined together with a light force (0.01N to 0.1N).

[0057] like Figure 2 As shown, the self-healing behavior of the created scratch "cross" was investigated by thermal irradiation. The results showed that under ultraviolet (light intensity 50–100 W and irradiation time 0–600 s) or thermal irradiation (37–100 °C) conditions, the scratch "cross" gradually disappeared with increasing repair time (0–600 s), and the damaged scars completely disappeared within 10–240 s (see Figure 1). Figure 2 (a) The three-dimensional self-healing behavior of the material was tested using atomic force microscopy, revealing that the damaged areas of the material had clearly visible depressions before repair (see [reference]). Figure 2 (a) and (b) of b); after external environmental stimulation, the depressed area is repaired (will Figure 2 (c) and (d) of b).

[0058] In summary, aliphatic polycarbonate elastomers with terminal azophenyl groups not only exhibit excellent self-healing behavior but also achieve a repair efficiency of over 90% (see [link to original text]). Figure 2 (c) This can be explained as follows: when the material interface is damaged, the physical cross-linking bonds at the damaged site are broken. After applying external stimuli, the optical isomerization ability of the synthesized elastomer is activated, which leads to a change in the condensed state of the material and promotes the movement of chain segments. The hydrophobic association interaction with the damaged interface is rearranged, so the broken interface is automatically repaired under the synergistic effect (optical isomerization and non-covalent bonds).

[0059] Example 3

[0060] 1. Same as step 1 in Example 1;

[0061] 2. Same as step 2 in Example 1;

[0062] 3. To evaluate the environmental stability and recyclability of aliphatic polycarbonate elastomer materials with terminal azophenyl groups, samples of a certain mass (0.1 g to 3 g) were placed in acidic or alkaline solutions with pH values ​​of 1 to 12, and the changes in surface morphology and mass loss were observed. Subsequently, the tensile strength after 0 to 20 cycles was evaluated.

[0063] The specific steps for the swelling experiment of elastomer materials in acidic or alkaline solutions with pH values ​​of 1–12 are as follows: Weigh the dried elastomer material to a constant weight, then immerse it in the solvent. Replace the solvent with fresh solvent after a certain period of time. After 3–5 days, remove the material, wipe the surface dry with filter paper, and weigh it again. The formula for calculating the swelling ratio (SR) of the elastomer material is:

[0064]

[0065] Among them, W s W represents the equilibrium swelling mass of the elastomer in dichloromethane or water. d This represents the initial weight of the elastomer.

[0066] like Figure 3 As shown in (a), in the polymer / water system, the water molecules in the network behave similarly to "free" water, having almost no effect on the original non-covalent bonds in the polymer. This indicates that water molecules cannot break the hydrophobic association between molecules in the polymer system, and the synthesized elastomer exhibits excellent moisture resistance. Furthermore, over a wide pH range, after immersion for 0–3 days, the swelling ratio (SR) and mass loss rate of this type of material show almost no change, demonstrating its corrosion resistance (e.g., ...). Figure 3 As shown in (b)). This type of material has excellent recycling capacity (more than 10 cycles), and its tensile strength first increases and then decreases with the increase of the number of cycles (as shown in the figure). Figure 3 As shown in (c), this can be explained by the crosslinking density first increasing and then decreasing (as shown in the middle). Figure 3 As shown in (d), the rearranged non-covalent bonds experienced chain fatigue with increasing recycling cycles.

[0067] Example 4

[0068] 1. Same as step 1 in Example 1;

[0069] 2. Same as step 2 in Example 1;

[0070] 3. Same as step 3 in Example 1;

[0071] like Figure 4As shown, the adhesion strength (0.22 MPa to 11.2 MPa) of the synthesized elastomer to different substrates (including but not limited to polycarbonate (PC), glass, iron, zirconium oxide (ZrO2), and pigskin) was evaluated by shear tests. Peel adhesion tests on different substrates revealed that the elastomer exhibits very strong adhesion strength; for example, the adhesion strengths on clean Fe, zirconium oxide, and glass substrates were 1.8 MPa, 4.3 MPa, and 4.8 MPa, respectively. The strongest adhesion occurred on the polycarbonate substrate (adhesion strength of 11.2 MPa). This may be due to the surface of polycarbonate and its similar chemical structure, which promotes penetration between the polycarbonate substrate and the surface of this type of polycarbonate elastomer, leading to more physical interlocking. The strong adhesion of the synthesized elastomer to different substrates is attributed to the excellent synergistic effect between optical isomerization and non-covalent bonds, resulting in changes in the condensed state of the material.

[0072] The above detailed description is a specific description of feasible embodiments of the invention. These embodiments are not intended to limit the scope of protection of the invention. All equivalent implementations or modifications that do not depart from the invention should be included within the scope of protection of the invention.

[0073] Furthermore, those skilled in the art can make various modifications, additions, and substitutions in other forms and details within the scope and spirit of the claims of this invention. Of course, all such modifications, additions, and substitutions made in accordance with the spirit of this invention should be included within the scope of protection claimed by this invention.

Claims

1. A method for preparing an aliphatic polycarbonate containing photoresponsive groups, wherein a photoresponsive compound of formula II, III or IV is used as an initiator to initiate the ring-opening polymerization of an aliphatic carbonate monomer of formula I to obtain an aliphatic polycarbonate containing photoresponsive groups of formula V, VI or VII. in, M1 is a hydrogen atom or a methyl group; M2 is a hydrogen atom, a cyano group, a carboxyl group, an ester group, a substituted or unsubstituted C1~C15 alkyl group, a substituted or unsubstituted C6~C20 aryl group, a substituted or unsubstituted C1~C15 alkoxy group, a substituted or unsubstituted C1~C15 heteroalkyl group, or a substituted or unsubstituted C6~C20 heteroaryl group; R1 is a hydrogen atom; R2 is a C1~C12 n-alkyl or n-alkoxy group, a nitro group, a cyano group, or a carboxyl group; R3 is a hydrogen atom or a cyano group; n represents the degree of polymerization.

2. The preparation method according to claim 1, characterized in that, The heteroalkyl group is at least one C-substituted alkyl or cycloalkyl group, wherein the substituted C1-C15 alkyl group, the substituted C6-C20 aryl group, the substituted C1-C15 alkoxy group, the substituted C1-C15 heteroalkyl group, and the substituted C6-C20 heteroaryl group have one or more substituents selected from hydroxyl, cyano, carboxyl, mercapto, carbonyl, ester, and phenyl groups.

3. The preparation method according to claim 1, characterized in that, The aliphatic polycarbonate containing photoresponsive groups has a molecular weight between 30,000 and 90,000.

4. The preparation method according to claim 1, characterized in that, The aliphatic carbonate monomer represented by Formula I is selected from one or more of the following compounds: 。 5. The preparation method according to claim 1, characterized in that, The molar ratio of the aliphatic carbonate monomer to the photoresponsive compound is in the range of 10:1 to 1000:1, and the polymerization reaction temperature is in the range of 80 to 130°C.

6. The use of aliphatic polycarbonate containing photoresponsive groups obtained by any of the preparation methods described in claims 1 to 5 as an adhesive.

7. The application as described in claim 6, characterized in that, The aliphatic polycarbonate containing photoresponsive groups is placed on the substrate to be bonded, and then subjected to ultraviolet irradiation or heat radiation to form a uniform liquid layer. Then, another substrate to be bonded is placed on the liquid layer and pressure is applied to make the two substrates adhere together.

8. The application as described in claim 7, characterized in that, The substrate is selected from glass, polymer, metal, and ceramic.

9. The application as described in claim 7, characterized in that, The intensity of the ultraviolet irradiation is 50~100 W, and the irradiation time is 120~600 s; the temperature of the thermal radiation is 37~100℃, and the time is 120~600 s.

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