Thermoplastic polyamide as well as preparation method and application thereof

Abstract

The invention discloses thermoplastic polyamide as well as a preparation method and application thereof, and the preparation method comprises the following steps: mixing a carboxyl monomer, a hydroxyl monomer, 3, 6-dioxa-1, 8-octane dithiol, a catalyst and a solvent, carrying out sulfydryl-olefin click reaction under the protection of inert gas, and carrying out post-treatment to obtain the thermoplastic polyamide, wherein the structural formula of the carboxyl monomer is shown in the specification, and the structural formula of the hydroxyl monomer is shown in the specification; the mass ratio of the carboxyl monomer to the hydroxyl monomer to the 3, 6-dioxa-1, 8-octane dithiol is (9.7 to 14.2) to (1.3 to 5.2) to 5.5. The invention provides high molecular weight bio-based functional polyamide prepared through mercapto click polymerization, the polyamide has reactive side groups including carboxyl and hydroxyl, so that new chemical covalent bonds are formed in the high-temperature processing process, a polymer network is converted from a linear type to a cross-linked type, and further the cementing performance is enhanced.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, specifically to a thermoplastic polyamide, its preparation method, and its applications. Background Technology

[0002] Polyamides, linked by amide bonds, possess excellent heat resistance, chemical stability, and mechanical properties due to their unique molecular structure. These advantages enable polyamides to be used in a wide range of applications, including automotive, electrical and electronic, sports and leisure, coatings, and engineering. Based on the length of the molecular chain, polyamides can be divided into two categories: long-chain nylons and short-chain nylons. Notably, long-chain fatty acids in vegetable oils (such as castor oil and tung oil) can be chemically converted into bio-based long-chain nylons. This route has been successfully implemented, reducing the reliance of plastics production on fossil resources. However, the cost of bio-based long-chain nylons remains high, which limits their further development to some extent. Therefore, how to enhance the value of bio-based long-chain nylons through molecular structure design, thereby promoting the healthy development of the bio-based industry, has become a significant challenge facing both academia and industry.

[0003] Building upon traditional polyamides, functional polyamides can be developed by introducing hydroxyl, carboxyl, amino, and halogen groups into their molecular structure. This improves or endows materials with new physical, chemical, or biological properties, resulting in excellent hydrolysis resistance, UV stability, and biocompatibility. The development of functional polyamides not only meets the needs of high-end manufacturing and specific applications but also brings higher added value to the products themselves. However, a significant problem in functional polyamide research is that the introduction of functional groups often limits the polymerization reaction conditions, leading to low molecular weight and unsatisfactory performance in the resulting materials. Therefore, exploring new synthetic strategies for functional polyamides and achieving the controllable construction of high molecular weight functional polyamides remains a research topic of practical significance.

[0004] Reversible covalent crosslinking network technology has brought about a revolutionary change to thermosetting resins, enabling crosslinked materials to be reprocessable and effectively avoiding the resource waste and environmental damage caused by single-use resins. Zhang Mingqiu et al. classified reversible covalent resins into two categories: general reversible covalent resins (A+B...). C+D or A+B C) Dynamically reversible covalent resins. Compared to conventional reversible covalent networks, dynamically reversible covalent networks offer the ability to reprocess products while maintaining the integrity of the network structure, making them widely favored by researchers and the market. However, it is undeniable that the reprocessing of dynamically reversible covalent networks is essentially based on the exchange mechanism of covalent bonds. This process typically requires higher temperatures and longer times, inevitably negatively impacting the processing efficiency and performance of cross-linked plastics. Therefore, how to skillfully balance the relationship between the covalent cross-linking network and processing efficiency to achieve effective processing of dynamically reversible covalent cross-linked resins has become an important research trend.

[0005] Chinese patent application CN117089074A discloses an ultra-low temperature bio-based polyamide hot melt adhesive and its preparation method. The structural formula of the hot melt adhesive is shown below: Where at least one R is It is a biomass hot melt adhesive obtained by functionalizing fatty acid polyamide monomers. It has excellent bonding strength and weather resistance, but its mechanical properties are not ideal and its bonding strength is poor. Summary of the Invention

[0006] The technical problem to be solved by this invention is how to improve the mechanical properties and adhesive properties of thermoplastic polyamides.

[0007] The present invention solves the above-mentioned technical problems through the following technical means: A method for preparing a thermoplastic polyamide includes the following steps: mixing a carboxyl monomer, a hydroxyl monomer, 3,6-dioxa-1,8-octanedithiol, a catalyst, and a solvent, carrying out a mercapto-olefin click reaction under an inert gas protection, and then performing post-treatment to obtain the thermoplastic polyamide; The structural formula of the carboxyl monomer is as follows: The structural formula of the hydroxyl monomer is as follows: The mass ratio of the carboxyl monomer, hydroxyl monomer, and 3,6-dioxa-1,8-octanedithiol is 9.7-14.2:1.3-5.2:5.5.

[0008] Preferably, the catalyst is azobisisobutyronitrile; the solvent is tetrahydrofuran.

[0009] Preferably, the reaction is carried out at a temperature of 65°C for 24 hours.

[0010] Preferably, the mass ratio of the carboxyl monomer, hydroxyl monomer, and 3,6-dioxa-1,8-octanedithiol is 11.2-14.2:1.3-3.9:5.5.

[0011] Preferably, the mass ratio of the carboxyl monomer, hydroxyl monomer, and 3,6-dioxa-1,8-octanedithiol is 11.2:3.9:5.5.

[0012] Preferably, the post-processing includes precipitating the product in methanol, filtering to obtain a white product; drying the white product and dissolving it in tetrahydrofuran, repeating the above steps of precipitating in methanol, and filtering and drying.

[0013] Preferably, the process further includes heating the post-processed product under vacuum.

[0014] Preferably, the heating temperature is 120-160℃ and the heating time is 0.1-2h.

[0015] The present invention also proposes a thermoplastic polyamide, which is prepared by the aforementioned method for preparing thermoplastic polyamide.

[0016] Preferably, the number average molecular weight of the thermoplastic polyamide is 23600-30600 g / mol.

[0017] The present invention also proposes an application of the aforementioned thermoplastic polyamide as a hot melt adhesive.

[0018] The present invention also proposes a hot melt adhesive containing the aforementioned thermoplastic polyamide.

[0019] The advantages of this invention are: This invention proposes a high-molecular-weight bio-based functional polyamide prepared via mercapto-click polymerization. This polyamide possesses reactive side groups, including carboxyl and hydroxyl groups, which enable the formation of new covalent bonds during high-temperature processing, transforming the polymer network from linear to cross-linked and thus enhancing its bonding properties. By precisely adjusting the proportion of functional groups in the polymer, the thermodynamic properties of the material can be effectively modified. Furthermore, the functional groups in the polymer can be induced by heating, thereby achieving a transformation of the polymer network from linear to cross-linked. This strategy can reduce the processing difficulty of dynamically reversible covalently cross-linked resins in practical applications. Moreover, the hydroxyl ester cross-linked network formed after thermal induction in the functional polyamide not only enhances the material's adhesive properties but also maintains its reprocessability, solving the problems of difficult processing and low bonding performance of current thermosetting polyamide hot melt adhesives. This invention provides a new approach for the preparation of functional polyamides and novel dynamically reversible covalent resins, and is expected to provide direction for the high-value development of bio-based materials.

[0020] The linear polymer obtained by this invention has reactive functional groups on its side chains. High-temperature processing allows these functional groups to react, enabling the transformation of the hot melt adhesive from a linear polymer to a cross-linked polymer. Because the polymer network is linear before processing, it exhibits excellent processing fluidity, facilitating processing. The covalent bonds formed after cross-linking enhance the bonding performance, while also avoiding the processing difficulties encountered when directly using thermosetting polymers as hot melt adhesives. Attached Figure Description

[0021] Figure 1 The NMR spectra of the monomers in Examples 1 and 2 of this invention are shown below. Figure 2 Gel permeation chromatograms of the products of Examples 3, 4, 5, 6 and 7 of this invention; Figure 3 Differential scanning calorimetry (DSC) spectra of the products from Examples 3, 4, 5, 6, and 7 of this invention; Figure 4 The uniaxial tensile curves are those of the products from Examples 3, 4, 5, 6, and 7 of this invention. Figure 5 The Young's modulus and fracture toughness of the products of Examples 3, 4, 5, 6 and 7 of this invention; Figure 6 This is a temperature-varying frequency scanning spectrum of the transformation process from the product of Example 6 to the product of Example 8 of the present invention; Figure 7 The image shows the physical product of the repeated hot pressing and the uniaxial tensile curve of the product in Example 8 of this invention. Figure 8 The product of Example 8 of this invention is the Arrhenius equation curve fitted according to the relaxation time; Figure 9 The bonding properties of the products of Examples 6 and 8 of this invention on different substrates; Figure 10 This demonstrates the repeatability of the bonding performance of the product in Example 8 of this invention on different substrates. Figure 11 The above are the synthesis route diagrams for embodiments 3, 4, 5, 6, 7 and 8 of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0024] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0025] The oxadithiol used below is 3,6-dioxa-1,8-octanedithiol, with the structural formula: .

[0026] Example 1 Take 237.9 g of methyl undecanoate, 44.6 g of 1,3-diamino-2-propanol, and 145 ml of tetrahydrofuran and add them to a 1000 ml round-bottom flask. Purge the flask with a continuously flowing stream of high-purity nitrogen for 40 min. Then add 5 ml of 30% (wt) sodium methoxide solution, followed by incubation at 65°C. o The reaction was carried out in an oil bath at temperature C for 24 hours. After the reaction was completed, the temperature was gradually increased to 90°C. o C was then purified by removing tetrahydrofuran, followed by cooling and dissolution in methanol. The solution was then recrystallized and filtered in a refrigerator. This recrystallization and filtration process was repeated three times, and the product was dried to obtain monomer A, whose structural formula is [insert structural formula here]. .

[0027] Example 2 21.1 g of monomer A prepared in Example 1, 6 g of succinic anhydride, 0.2 g of 4-dimethylaminopyridine, and 25 ml of tetrahydrofuran were added to a 250 ml round-bottom flask. Under magnetic stirring, the reaction was gradually heated to 65 °C. o After reaction C for 24 hours, 25 ml of tetrahydrofuran and 10 ml of water were added to a round-bottom flask, and the reaction was continued for 8 hours. The product was then poured into dichloromethane and washed three times each with saturated sodium bicarbonate and sodium chloride solutions. After drying with anhydrous sodium sulfate, the product was filtered and dried to obtain monomer B, whose structural formula is [structural formula missing]. .

[0028] Example 3 15.7 g of monomer B, 5.5 g of oxadithiol, 150 mg of azobisisobutyronitrile, and 50 mL of tetrahydrofuran prepared in Example 2 were added to a 250 mL single-necked round-bottom flask. After sealing the flask, it was purged with high-purity nitrogen gas at room temperature for 30 min. After purging, the temperature was raised to 65 °C. o After reaction C, the product was reacted for 24 hours. After the reaction was complete, the precipitate was placed in 500 mL of methanol and filtered to obtain a white product. The white product was dried and dissolved in 50 mL of tetrahydrofuran. The methanol precipitation step was repeated, and the product was filtered and dried again to obtain polyamide.

[0029] Example 4 Take 1.3g of monomer A sample prepared in Example 1, 14.2g of monomer B sample prepared in Example 2, 5.5g of oxadithiol, 150mg of azobisisobutyronitrile, and 50mL of tetrahydrofuran and add them to a 250ml single-necked round-bottom flask. After sealing the flask, purge it with high-purity nitrogen gas at room temperature for 30min. After the purging is complete, raise the temperature to 65°C. o After reaction C, the product was reacted for 24 hours. After the reaction was complete, the precipitate was placed in 500 mL of methanol and filtered to obtain a white product. The white product was dried and dissolved in 50 mL of tetrahydrofuran. The methanol precipitation step was repeated, and the product was filtered and dried again to obtain polyamide.

[0030] Example 5 Take 2.6 g of monomer A sample prepared in Example 1, 12.7 g of monomer B sample prepared in Example 2, 5.5 g of oxadithiol, 150 mg of azobisisobutyronitrile, and 50 mL of tetrahydrofuran and add them to a 250 mL single-necked round-bottom flask. After sealing the flask, purge it with high-purity nitrogen gas at room temperature for 30 min. After the purging is complete, raise the temperature to 65 °C. o After reaction C, the product was reacted for 24 hours. After the reaction was complete, the precipitate was placed in 500 mL of methanol and filtered to obtain a white product. The white product was dried and dissolved in 50 mL of tetrahydrofuran. The methanol precipitation step was repeated, and the product was filtered and dried again to obtain polyamide.

[0031] Example 6 Take 3.9 g of monomer A sample prepared in Example 1, 11.2 g of monomer B sample prepared in Example 2, 5.5 g of oxadithiol, 150 mg of azobisisobutyronitrile, and 50 mL of tetrahydrofuran and add them to a 250 mL single-necked round-bottom flask. After sealing the flask, purge it with high-purity nitrogen gas at room temperature for 30 min. After the purging is complete, raise the temperature to 65 °C. o After reaction C, the product was reacted for 24 hours. After the reaction was complete, the precipitate was placed in 500 mL of methanol and filtered to obtain a white product. The white product was dried and dissolved in 50 mL of tetrahydrofuran. The methanol precipitation step was repeated, and the product was filtered and dried again to obtain polyamide.

[0032] Example 7 Take 5.2 g of monomer A sample prepared in Example 1, 9.7 g of monomer B sample prepared in Example 2, 5.5 g of oxadithiol, 150 mg of azobisisobutyronitrile, and 50 mL of tetrahydrofuran and add them to a 250 mL single-necked round-bottom flask. After sealing the flask, purge it with high-purity nitrogen gas at room temperature for 30 min. After the purging is complete, raise the temperature to 65 °C. o After reaction C, the product was reacted for 24 hours. After the reaction was complete, the precipitate was placed in 500 mL of methanol and filtered to obtain a white product. The white product was dried and dissolved in 50 mL of tetrahydrofuran. The methanol precipitation step was repeated, and the product was filtered and dried again to obtain polyamide.

[0033] Example 8 Take 20g of the polyamide sample prepared in Example 6, place it in a vacuum drying oven, evacuate the oven to a vacuum state, and then heat it to 160°C. o C, react for 1 hour. After the reaction is complete, cool it to room temperature and remove it.

[0034] The polymerization scheme of the polymer is as follows Figure 11 As shown, by controlling the feed ratios of Examples 1 and 2 during polymer synthesis, the one-step preparation methods of Examples 3, 4, 5, 6, and 7 can be achieved. It is important to note that from Examples 4 to 7, the side groups in the polymer network simultaneously possess both carboxyl and hydroxyl groups. The simultaneous presence of these two functional groups provides the possibility for subsequent crosslinking. Furthermore, after polymer crosslinking, the hydroxyl groups present in the polymer system can undergo dynamic exchange reactions with the covalently crosslinked ester groups, which provides a theoretical basis for the self-reinforcing properties and reprocessability of thermoplastic polyamide hot melt adhesives.

[0035] pass Figure 1 The characteristic peaks of Example 1 in the NMR spectrum are consistent with the peak positions of its structural formula, indicating the successful preparation of the product of Example 1. Based on this, a substitution reaction of the hydroxyl groups on the monomer of Example 1 can achieve the addition of carboxyl functional groups as in Example 2. Through comparison... Figure 1 The NMR spectra of the products of Examples 1 and 2 show that the characteristic peak at position a disappears after the reaction, and a new characteristic peak is formed at position f, which indicates the successful conversion of the product of Example 1 to the product of Example 2.

[0036] By adjusting the different proportions of monomers used in Examples 1 and 2, one-step preparation methods can be achieved for Examples 3, 4, 5, 6, and 7. For example... Figure 2 As shown, molecular weight tests were performed on the products of Examples 3, 4, 5, 6 and 7. It can be seen that the prepared polymers all have a number average molecular weight greater than 20,000 g / mol, thus demonstrating the successful copolymerization of the monomers of Example 1 and Example 2.

[0037] The thermal properties of the products from Examples 3, 4, 5, 6, and 7 were tested using differential scanning calorimetry. It can be seen that the melting point of the polymers from Example 3 to Example 7 exhibits a phenomenon of first decreasing and then increasing. This is because the polymer in Example 3 has all carboxyl groups as side groups. The hydrogen bonding interactions between the side chains and the uniformity of the side chains endow its molecular chain with high regularity, thus showing a relatively high melting point. With the introduction of the monomer from Example 1 in Example 4, the hydroxyl groups disrupted the regularity of the original side groups, thereby lowering its melting point. However, it is worth noting that as the content of introduced hydroxyl groups increases, the melting point of the examples shows a gradual increasing trend. This is mainly attributed to the gradually strengthening intermolecular forces between the introduced hydroxyl groups and the polymer chains. In addition, the changes in crystallization temperature and melting point of the products in each example show a consistent regularity.

[0038] The tensile method is consistent with that disclosed in Chinese patent application CN 117089074 A, namely, using a UTM2502 electronic universal testing machine for mechanical tensile testing. Each group of samples was cut into dumbbell shapes using a cutter of the same specification, and then subjected to mechanical testing. The tensile speed for the sample testing at room temperature was 50 mm / min. Figure 4 Uniaxial tensile testing of the products from the examples revealed that Example 3 exhibited excellent mechanical properties. Example 4 showed significant softening due to the introduction of hydroxyl groups in the side chains; however, the polymer gradually became stronger with increasing hydroxyl content. To more intuitively illustrate this phenomenon, as shown... Figure 5 As shown, it can be seen that with the introduction of hydroxyl groups in the examples, the Young's modulus of the polymer first decreases and then increases. Correspondingly, the fracture toughness of the polymer shows that Example 3 is greater than Examples 4 and 5, Example 6 reaches the maximum, and Example 7 shows a decrease. This is because the initial amount of hydroxyl groups introduced is small, disrupting the original chain regularity. However, at this point, the hydrogen bonds formed by the hydroxyl groups are insufficient to enhance performance, leading to a decrease in toughness. As the hydroxyl content reaches the level of Example 6, the dual enhancement of performance through crystallization and hydrogen bonds achieved improved toughness. However, when the hydroxyl content continues to increase, the mechanical property curve of Example 7 reflects that the polymer has transformed from an elastomer to a rigid plastic, with a decrease in elongation at break, and consequently, a decrease in toughness.

[0039] like Figure 6 As shown, frequency scans were performed on the product of Example 6 at different temperatures. It can be seen that Example 6 at 100... o At temperature C, even after 5000 s, the loss modulus is still much greater than the storage modulus, indicating that the polymer remains in a fluid state at this temperature. However, when the temperature rises to 120°C... o At 6800s, the storage modulus will exceed the loss modulus, and as the temperature further increases to 140... o C and 160 oC, the time when the storage modulus is greater than the loss modulus decreases to 1500s and 480s. This indicates that with increasing temperature, the rate of cross-linking reaction within the polymer network intensifies, and the rate of polymer transformation from a linear network to a cross-linked network is accelerated. This is because the hydroxyl and carboxyl groups on the side groups of Example 6 can react with each other at high temperatures to form ester groups, causing the polymer network to transform from linear to cross-linked, thereby achieving the preparation of Example 8.

[0040] like Figure 7 As shown, the sheet of product from Example 8 can be cut into smaller pieces and then hot-pressed again under a pressure of 500N to obtain a polymer film, indicating that it has reprocessable properties (it belongs to a cross-linked network and is generally not reprocessable). Uniaxial tensile testing revealed that the polymer film of Example 8 did not degrade in performance after three repeated processing steps, indicating that it is feasible to adjust the polymer network from linear to cross-linked through side groups. In addition, as... Figure 8 As shown, stress relaxation experiments were conducted on Example 8, and the results showed that the fitting results of its relaxation time and relaxation temperature followed the Arrhenius equation, which also indicates that the cross-linked network has excellent reprocessability.

[0041] Based on this, overlap shear tests were performed on the products of Examples 6 and 8. Samples were cut into 12.5mm × 25mm pieces and placed between substrates, bonded at 120°C for 30 minutes, and then subjected to uniaxial tensile testing on an Instron instrument at a speed of 5mm / min. Figure 9 As shown, under the same overlapping surface conditions, the bonding strength of Example 8 is significantly higher than that of Example 6. This is because the transformation of the polymer from a linear to a cross-linked network enhances the cohesive force of the bond, thereby improving its bonding performance. Furthermore, Example 8 also exhibits excellent bonding performance on both copper and aluminum sheets. Repeated bonding tests were performed on the product of Example 8, as follows... Figure 10 As shown, the product of Example 8 was repeatedly bonded to stainless steel sheets, copper sheets, and aluminum sheets three times without any decrease in bonding performance, indicating that the polymer has excellent repeatable bonding performance.

[0042] The amounts of materials used in each embodiment are shown in the table below:

[0043] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for the preparation of a thermoplastic polyamide, characterized in that: The method comprises the following steps: carboxyl monomer, hydroxyl monomer, 3,6-dioxane-1,8-octane dithiol, catalyst and solvent are mixed, and a mercapto-olefin click reaction is carried out under inert gas protection, and post-treatment is carried out to obtain the thermoplastic polyamide; The carboxyl monomer has a structural formula of The hydroxyl monomer has a structural formula of The mass ratio of the carboxyl monomer, the hydroxyl monomer and 3,6-dioxa-1,8-octane dithiol is 9.7-14.2:1.3-5.2:5.

5.

2. The process for the preparation of thermoplastic polyamide according to claim 1, characterized in that: the catalyst is azobisdimethyl isobutyronitrile; and the solvent is tetrahydrofuran.

3. The process for the preparation of thermoplastic polyamide according to claim 1, characterized in that: The temperature of the reaction is 65 DEG C, and the time is 24 h.

4. The process for the preparation of thermoplastic polyamide according to claim 1, characterized in that: The mass ratio of the carboxyl monomer, hydroxyl monomer and 3,6-dioxane-1,8-octane dithiol is 11.2-14.2:1.3-3.9:5.

5.

5. The process for the preparation of thermoplastic polyamide according to claim 1, characterized in that: The mass ratio of the carboxyl monomer, hydroxyl monomer and 3,6-dioxane-1,8-octane dithiol is 11.2:3.9:5.

5.

6. The process for the preparation of thermoplastic polyamide according to any one of claims 1 to 5, characterized in that: The product obtained after post-treatment is further heated under vacuum.

7. The process for the preparation of thermoplastic polyamide according to claim 6, characterized in that: The temperature of the heating is 120-160 DEG C, and the time is 0.1-2 h.

8. A thermoplastic polyamide characterized by: The thermoplastic polyamide is prepared by the method according to any one of claims 1-7.

9. The thermoplastic polyamide according to claim 8 is used as hot melt adhesive.

10. A hot melt adhesive characterized by: The thermoplastic polyamide according to claim 8 is contained.

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