Controllably thermally expandable polyimine resins containing dynamic covalent bonds and methods of making the same

Abstract

This invention belongs to the field of functional materials technology, specifically a controllable thermal expansion polyimide resin containing dynamic covalent bonds and its preparation method. The controllable thermal expansion polyimide resin of this invention is prepared from amino monomers and aldehyde monomers containing dibenzo-8-membered ring units, and its structure contains dibenzo-8-membered ring structural units and dynamic imine bonds. The dibenzo-8-membered ring units contribute to the low coefficient of thermal expansion of the polyimide, while the dynamic imine bonds endow the polyimide with properties such as reprocessability and biodegradability. The coefficient of thermal expansion of the polyimide is adjusted by changing the crosslinking density and the content of the dibenzo-8-membered rings. The polyimide resin prepared by this invention exhibits excellent heat resistance, thermal stability, and mechanical properties; it also has good solvent resistance. Furthermore, it can degrade under acidic conditions, and the degraded monomers can be recycled to form polyimide films. It can be widely used in encapsulation materials, energy-absorbing materials, and self-healing materials.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, specifically relating to controllable thermal expansion polyimide resin and its preparation method. Background Technology

[0002] Polymer materials are diverse and possess advantages such as ease of processing, low cost, and lightweight, making them widely used in daily life. However, polymer materials are difficult to degrade and have low recycling rates. Waste polymer materials from daily life and production, such as waste plastics and rubber, persist in the environment, causing significant pollution. Microplastics generated from waste plastics can enter the human body through the ecosystem, posing a threat to human health. Thermosetting polymer materials have a cross-linked network structure, and their excellent thermal and mechanical properties make them widely used in many fields. However, compared to the re-plasticization and processing of thermoplastic polymers, thermosetting polymers are insoluble and infusible, making them more difficult to recycle. Currently, one of the development directions for polymer materials is greening, improving recycling rates, and ensuring that they degrade after entering the environment and do not accumulate. Introducing reversible covalent bonds into the polymer cross-linked network is an effective way to achieve the green development of thermosetting polymer materials. Compared to traditional thermosetting polymers, cross-linked network materials containing dynamic covalent bonds have reprocessable and self-healing properties, which stem from the reversible reactions of dynamic covalent bonds. Therefore, by constructing dynamic covalent bonds, the processing properties of thermosetting polymer materials can approach those of thermoplastic polymer materials, while exhibiting higher thermal and mechanical properties than thermoplastic polymer materials.

[0003] Furthermore, compared to metallic and inorganic non-metallic materials, polymers have a higher coefficient of thermal expansion, limiting their application range. For example, in electronic devices, polymer materials are bonded to metallic or inorganic non-metallic substrates; if the coefficients of thermal expansion do not match, the materials are prone to failure during use. Common methods to reduce the coefficient of thermal expansion of polymers include adding fillers with low coefficients of thermal expansion and controlling the polymer's chemical structure and aggregate structure. Composite materials prepared with added fillers are prone to cracking and failure due to compatibility issues. Traditional methods of adjusting polymer structure and aggregate state cannot guarantee reprocessability while reducing the coefficient of thermal expansion, because the polymer's aggregate structure changes after dynamic covalent bond reshaping or repair.

[0004] The inventors, in collaboration with Jennifer Lu from the University of California, reported a cross-linked polyarylamide exhibiting significant negative expansion behavior (Shen Xingyuan, PhD dissertation, Fudan University, 2016). Conformational changes in the dibenzo-8-membered ring unit within the polymer network were shown to be related to anomalous negative thermal expansion (Nat. Chem. 2013, 5, 1035). The dibenzo-8-membered ring primarily exhibits a boat conformation at low temperatures, transitioning to a chair conformation at higher temperatures. In fact, molecular structure significantly influences its conformational transitions. Based on this mechanism, the inventors subsequently obtained polyarylamides with positive, zero, and negative thermal expansion (Macromolecules, 2018, 51, 8477). Simultaneously, the inventors developed a synthetic route for functional monomers containing dibenzo-8-membered ring units and prepared linear polyarylamides exhibiting negative expansion behavior (Macromolecules, 2018, 51, 1377). Based on extensive synthesis, monomers containing dibenzo-8-membered rings with multiple functional groups were prepared, which can be used to explore more high-performance resins with low / negative thermal expansion behavior. Based on the unique conformational transformation of the dibenzo-8-membered ring unit, the prepared negative or low expansion polymer materials can be endowed with functions that are difficult to achieve in other low-expansion polymer materials, such as the reprocessable properties described in this invention.

[0005] This invention proposes a method for synthesizing a polyimide resin containing dynamic covalent bonds and a dibenzo-8-membered ring structure, achieving for the first time simultaneously a low coefficient of thermal expansion and reprocessability of a thermosetting polymer material. The dynamic covalent bonds in the polyimide resin endow it with remodeling, self-healing, and biodegradable recyclable properties, while the dibenzo-8-membered ring structure reduces the coefficient of thermal expansion of the polyimide. The prepared polyimide resin exhibits excellent thermal and mechanical properties, and its coefficient of thermal expansion is adjustable within the range of 5–50 ppm / K, showing broad application prospects. Summary of the Invention

[0006] The purpose of this invention is to provide a controllable thermal expansion polyimide resin containing dynamic covalent bonds with excellent thermal and mechanical properties, and a method for preparing the same.

[0007] The controllable thermal expansion polyimide resin containing dynamic covalent bonds proposed in this invention is a polyimide resin containing dibenzo-eight-membered ring structural units. It uses amino monomers containing dibenzo-eight-membered ring structures as raw materials, which react with aldehyde monomers. During the preparation process, the thermal expansion coefficient of the polyimide is adjusted by controlling the crosslinking density and the content of the dibenzo-eight-membered rings. The specific process is as follows:

[0008] The amino monomer and aldehyde monomer are dissolved in N-methyl-2-pyrrolidone and reacted by heating on a hot plate while the solvent is evaporated. The reaction is first held at 100-120°C for 2-4 hours, and then transferred to an oven and held at 150-200°C for 8-12 hours to obtain polyimide resin.

[0009] Wherein, when the aldehyde monomer is triphenylformaldehyde, the amino monomer comprises two components, the first component of the amino monomer being an amino monomer (Ⅰ) containing a dibenzo-eight-membered ring structure, with the structural formula:

[0010]

[0011] R1 and R2 are any one of H, methyl, ethyl, propyl, or butyl; R3 and R4 are Any one of methyl, ethyl, propyl, or butyl;

[0012] The second component of the amino monomer is compound (II), with the general formula:

[0013] Where R is Any one of them;

[0014] When the amino monomer is compound (Ⅰ), the aldehyde monomer comprises two components. The first component of the aldehyde monomer is the difunctional monomer terephthalaldehyde, with the following structural formula:

[0015]

[0016] The second component of the aldehyde monomer is the trifunctional monomer methyltriphenylaldehyde, with the following structural formula:

[0017]

[0018] During the curing reaction, adjusting the ratio of the two components in the amino monomer changes the content of the dibenzo-eight-membered ring structure in the polyimide resin, thereby adjusting the coefficient of thermal expansion of the obtained polyimide resin; similarly, changing the type and amount of aldehyde monomer can also adjust the coefficient of thermal expansion of the obtained polyimide resin.

[0019] In this invention, when the aldehyde monomer is triphenylaldehyde, the proportion of the second component compound (II) in the total amino monomer is controlled to be 0-80% (preferably 5-80%), and the coefficient of thermal expansion is adjustable between 5-50 ppm / K.

[0020] In this invention, when the amino monomer is compound (Ⅰ), the proportion of difunctional aldehyde monomer to total aldehyde monomer is controlled to be 0-100% (preferably 5-100%), thereby changing the crosslinking density of the polyimide crosslinking network. The coefficient of thermal expansion is adjustable between 5 and 35 ppm / K.

[0021] The preparation method of the controllable thermal expansion polyimide resin containing dynamic covalent bonds proposed in this invention includes the following specific steps:

[0022] The amino monomer and aldehyde monomer are dissolved in N-methyl-2-pyrrolidone and reacted by heating on a hot plate while the solvent is evaporated. The reaction is first carried out at 100-120°C for 2-4 hours, and then transferred to an oven and carried out at 150-200°C for 2-4 hours to obtain polyimide resin.

[0023] The polyimide resin prepared by this invention exhibits excellent heat resistance, thermal stability, and mechanical properties; it also possesses good solvent resistance and can degrade under acidic conditions. The degraded monomers can be recycled to produce polyimide films. This dynamically covalently bonded, controllable thermal expansion resin can be applied not only to precision devices with stringent dimensional stability requirements but also to the fabrication of energy-absorbing and self-healing materials. It can be widely used in any of the fields of encapsulation materials, energy-absorbing materials, and self-healing materials, or to regulate the thermal expansion behavior of other materials. Attached Figure Description

[0024] Figure 1 The curves showing the change rate of length of the polyimide resin obtained in Examples 1-5 as a function of temperature are shown.

[0025] Figure 2 The curves showing the change rate of length of the polyimide resin obtained in Examples 6-9 as a function of temperature are shown.

[0026] Figure 3 The appearance of the polyimide resin obtained in Example 1 before and after remolding.

[0027] Figure 4 The stress-strain curves of the polyimide resin obtained in Example 1 before and after remolding are shown.

[0028] Figure 5 The curves showing the change rate of length of the polyimide resin obtained in Example 1 before and after remolding as a function of temperature are shown. Detailed Implementation

[0029] The present invention will be further illustrated by the following examples.

[0030] Example 1: Preparation of low-expansion polyimide resin

[0031] An amino monomer containing a dibenzo-eight-membered ring (166.3 mg, 0.32 mmol) and tris(benzoxyl)aldehyde (33.7 mg, 0.21 mmol) were dissolved in N-methyl-2-pyrrolidone (2 mL). The reaction was carried out by heating on a hot plate while the solvent was evaporated. The reaction was first carried out at 100–120 °C for 2–4 hours, and then transferred to an oven and carried out at 150–200 °C for 8–12 hours to obtain polyimide resin.

[0032] The structural formula of the amino monomer containing the dibenzo-eight-membered ring is as follows:

[0033]

[0034] Example 2, Preparation of low-expansion polyimide resin

[0035] An amino monomer containing a dibenzo-eight-membered ring (165.3 mg, 0.31 mmol), terephthalaldehyde (5.9 mg, 0.04 mmol), and mesitylenealdehyde (28.8 mg, 0.18 mmol) were dissolved in N-methyl-2-pyrrolidone (2 mL). The reaction was carried out by heating on a hot plate while the solvent was evaporated. The reaction was first carried out at 100–120 °C for 2–4 hours, and then transferred to an oven and carried out at 150–200 °C for 8–12 hours to obtain polyimide resin.

[0036] The structural formula of the amino monomer containing the dibenzo-eight-membered ring is as follows:

[0037]

[0038] Example 3, Preparation of low-expansion polyimide resin

[0039] An amino monomer containing a dibenzo-eight-membered ring (163.6 mg, 0.31 mmol), terephthalaldehyde (15.5 mg, 0.12 mmol), and mesitylenealdehyde (19.9 mg, 0.12 mmol) were dissolved in N-methyl-2-pyrrolidone (2 mL). The reaction was carried out by heating on a hot plate while the solvent was evaporated. The reaction was first carried out at 100–120 °C for 2–4 hours, and then transferred to an oven and carried out at 150–200 °C for 8–12 hours to obtain polyimide resin.

[0040] The structural formula of the amino monomer containing the dibenzo-eight-membered ring is as follows:

[0041]

[0042] Example 4: Preparation of low-expansion polyimide resin

[0043] An amino monomer containing a dibenzo-eight-membered ring (161.5 mg, 0.30 mmol), terephthalaldehyde (29.6 mg, 0.22 mmol), and mestrialdehyde (8.9 mg, 0.06 mmol) were dissolved in N-methyl-2-pyrrolidone (2 mL). The reaction was carried out by heating on a hot plate while the solvent was evaporated. The reaction was first carried out at 100–120 °C for 2–4 hours, and then transferred to an oven and carried out at 150–200 °C for 8–12 hours to obtain polyimide resin.

[0044] The structural formula of the amino monomer containing the dibenzo-eight-membered ring is as follows:

[0045]

[0046] Example 5: Preparation of low-expansion polyimide resin

[0047] An amino monomer containing a dibenzo-eight-membered ring (159.8 mg, 0.30 mmol) and terephthalaldehyde (40.2 mg, 0.30 mmol) were dissolved in N-methyl-2-pyrrolidone (2 mL). The reaction was carried out by heating on a hot plate while the solvent was evaporated. The reaction was first carried out at 100-120 °C for 2-4 hours, and then transferred to an oven and carried out at 150-200 °C for 8-12 hours to obtain polyimide resin.

[0048] The structural formula of the amino monomer containing the dibenzo-eight-membered ring is as follows:

[0049]

[0050] Example 6: Preparation of low-expansion polyimide resin

[0051] An amino monomer containing a dibenzo-eight-membered ring (153.9 mg, 0.29 mmol), 4,4'-diaminodiphenylmethane (14.3 mg, 0.07 mmol), and tris(benzoxyl)aldehyde (39.0 mg, 0.24 mmol) were dissolved in N-methyl-2-pyrrolidone (2 mL). The reaction was carried out by heating on a hot plate while the solvent was evaporated. The reaction was first carried out at 100–120 °C for 2–4 hours, and then transferred to an oven and carried out at 150–200 °C for 8–12 hours to obtain polyimide resin.

[0052] The structural formula of the amino monomer containing the dibenzo-eight-membered ring is as follows:

[0053]

[0054] Example 7, Preparation of low-expansion polyimide resin

[0055] An amino monomer containing a dibenzo-eight-membered ring (112.5 mg, 0.21 mmol), 4,4'-diaminodiphenylmethane (41.9 mg, 0.21 mmol), and mesitylenealdehyde (45.6 mg, 0.28 mmol) were dissolved in N-methyl-2-pyrrolidone (2 mL). The reaction was carried out by heating on a hot plate while the solvent was evaporated. The reaction was first carried out at 100–120 °C for 2–4 hours, and then transferred to an oven and carried out at 150–200 °C for 8–12 hours to obtain polyimide resin.

[0056] The structural formula of the amino monomer containing the dibenzo-eight-membered ring is as follows:

[0057]

[0058] Example 8, Preparation of low-expansion polyimide resin

[0059] An amino monomer containing a dibenzo-eight-membered ring (57.1 mg, 0.11 mmol), 4,4'-diaminodiphenylmethane (85.0 mg, 0.43 mmol), and tris(benzoxyl)aldehyde (57.9 mg, 0.36 mmol) were dissolved in N-methyl-2-pyrrolidone (2 mL). The reaction was carried out by heating on a hot plate while the solvent was evaporated. The reaction was first carried out at 100–120 °C for 2–4 hours, and then transferred to an oven and carried out at 150–200 °C for 8–12 hours to obtain polyimide resin.

[0060] The structural formula of the amino monomer containing the dibenzo-eight-membered ring is as follows:

[0061]

[0062] Example 9, Preparation of low-expansion polyimide resin

[0063] 4,4'-Diaminodiphenylmethane (129.4 mg, 0.65 mmol) and mesitylenealdehyde (70.6 mg, 0.44 mmol) were dissolved in N-methyl-2-pyrrolidone (2 mL). The reaction was carried out by heating on a hot plate while the solvent was evaporated. The reaction was first carried out at 100-120 °C for 2-4 hours, and then transferred to an oven and carried out at 150-200 °C for 8-12 hours to obtain polyimide resin.

[0064] The thermal expansion properties of the polyimide resins obtained in Examples 1-5 were tested, and the results are as follows: Figure 1 As shown. Depending on the crosslinking density in the polyimide resin, the coefficients of thermal expansion of Examples 1-5 range from 7.9 to 31.4 ppm / K within a temperature range of 0 to 150°C.

[0065] The polyimide resins obtained in Examples 1 and 2 have thermal expansion coefficients of 7.9 and 8.1 ppm / K, respectively, which match the thermal expansion coefficients of metals and inorganic non-metals. When used as composite materials, they can avoid material failure caused by mismatch in thermal expansion coefficients.

[0066] The thermal expansion properties of the polyimide resins obtained in Examples 6-9 were tested, and the results are as follows: Figure 2 As shown. Depending on the content of dibenzo-octane rings in the polyimide resin, the coefficients of thermal expansion of Examples 6-9 range from 20.2 to 49.2 ppm / K within the temperature range of 0-150°C.

[0067] The polyimide resin obtained in Example 1 was subjected to a reprocessability test. The shredded polyimide film could be re-hot-pressed into a film under the catalysis of the primary amine, exhibiting plasticity. The actual object is shown in Figure 3.

[0068] Tensile tests were performed on the polyimide resin obtained in Example 1 to compare the mechanical properties before and after reshaping. The stress-strain curves are shown below. Figure 4 As shown, the tensile properties of the samples after the first and second reshaping were not significantly different from those of the original samples, and their stress-strain curves showed a high degree of overlap, indicating that the mechanical properties of the polyimide resin did not decrease after repeated processing.

[0069] The thermal expansion properties of the polyimide resin obtained in Example 1 were tested, and the thermal expansion properties before and after remolding were compared, such as... Figure 5 As shown, polyimide still exhibits low thermal expansion after primary and secondary reshaping, with thermal expansion coefficients of 13.7 ppm / K and 12.6 ppm / K, respectively, indicating that the DBCOD units in its structure can still undergo conformational transformation.

Claims

1. A controlled thermal expansion poly(ylimine) resin containing dynamic covalent bonds, characterized in that, The process involves using an amino monomer containing a dibenzo-8-membered ring structure as a raw material, which reacts with an aldehyde monomer. The thermal expansion coefficient of the polyimide is adjusted by controlling the crosslinking density and the content of the dibenzo-8-membered ring. The specific process is as follows: The amino monomer and aldehyde monomer are dissolved in N-methyl-2-pyrrolidone and reacted by heating on a hot plate while the solvent is evaporated. The reaction is first held at 100~120℃ for 2~4 hours, and then transferred to an oven and held at 150~200℃ for 8~12 hours to obtain polyimide resin. When the aldehyde monomer is terphenylaldehyde, the amino monomer comprises one component (first component) or two components (first and second components). The first component of the amino monomer is an amino monomer (Ⅰ) containing a dibenzo-eight-membered ring structure, with the following structural formula: ； R1 and R2 are any one of H, methyl, ethyl, propyl, or butyl; R3 and R4 are Any one of them; The second component of the amino monomer is compound (II) with the general formula: ; R is any one of the following: When the amino monomer is compound (Ⅰ), the aldehyde monomer includes a first component or two components, a first component and a second component. The first component of the aldehyde monomer is the difunctional monomer terephthalaldehyde, with the following structural formula: ； The second component of the aldehyde monomer is the trifunctional monomer methyltriphenylaldehyde, with the following structural formula: ； During the reaction, the thermal expansion coefficient of polyimide resin is adjusted by changing the ratio of the two components in the amino monomer to change the content of the dibenzo-eight-membered ring structure in the polyimide resin; the thermal expansion coefficient of polyimide resin is also adjusted by changing the type and amount of aldehyde monomer.

2. The controlled thermal expansion poly(ylimine) resin containing dynamic covalent bonds according to claim 1, characterized in that, When the aldehyde monomer is triphenylaldehyde, the proportion of the second component compound (II) in the total amino monomer is controlled to be 0-80%, and the coefficient of thermal expansion is adjustable between 5-50 ppm / K.

3. The controlled thermal expansion poly(ylimine) resin containing dynamic covalent bonds according to claim 1, characterized in that, When the amino monomer is compound (Ⅰ), the proportion of difunctional aldehyde monomers in the total aldehyde monomers is controlled to be 0~100%, and the crosslinking density of the polyimide crosslinking network is changed, and the coefficient of thermal expansion is adjustable between 5~35 ppm / K.

4. A method for preparing a controllable thermal expansion polyimide resin containing dynamic covalent bonds as described in any one of claims 1-3, characterized in that, The specific steps are as follows: Dissolve the amino monomer and aldehyde monomer in N-methyl-2-pyrrolidone, and react them by heating on a hot plate while evaporating and removing the solvent. First, react at 100~120℃ for 2~4 hours, and then transfer to an oven and keep at 150~200℃ for 2~4 hours to obtain polyimide resin.

5. The application of a controllable thermal expansion polyimide resin containing dynamic covalent bonds as described in any one of claims 1-3 in any of the fields of encapsulation materials, energy-absorbing materials, and self-healing materials.

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