Preparation method and application of thermoplastic processable and controllable degradation photo-crosslinking polyester

Abstract

The application relates to a preparation method and application of a repeatable thermoplastic processing and controllable degradation photo-crosslinking polyester. The photo-crosslinking polyester material is prepared by crosslinking a low-molecular-weight biodegradable polyester modified by 1,2-dithiolane groups through ultraviolet irradiation. The 1,2-dithiolane groups can undergo ring-opening polymerization under ultraviolet irradiation to form a biodegradable polyester material crosslinked by a disulfide bond. Compared with linear biodegradable polyester materials, the crosslinked biodegradable polyester material has better high-temperature dimensional stability. Based on the high-temperature exchangeability and reduction stimulus responsiveness of the disulfide bond, the photo-crosslinking polyester material can not only be repeatedly thermally processed, but also be quickly de-crosslinked under a reduction condition to generate a low-molecular-weight biodegradable polyester, and the low-molecular-weight biodegradable polyester can be quickly biodegraded, so that controllable and rapid degradation is realized. The polyester material prepared in the application is easy to reshape, the modified raw material is safe, nontoxic and renewable, and no additional crosslinking agent is needed.

Description

Technical Field

[0001] This invention relates to the field of polyester materials, specifically to a method for preparing and applying a reusable thermoplastic processing and controllable degradation photocrosslinked polyester. Background Technology

[0002] Cross-linked polymers exhibit superior mechanical properties, heat resistance, and chemical stability compared to linear polymers. However, the presence of the cross-linking network makes them difficult to reshape after molding, hence they are often referred to as thermosetting materials. These materials are difficult to recycle after disposal, leading to environmental pollution and resource waste. Using dynamic covalent cross-linking instead of traditional permanent covalent cross-linking can impart thermoplasticity similar to linear polymers to cross-linked polymers, and is considered a promising method for addressing the difficulty in recycling cross-linked polymers (Science, 2011, 334, 965-968; Prog. Polym. Sci. 2021, 113, 101353). However, although dynamic covalent cross-linked polymers can be repeatedly processed and reshaped, most are difficult to degrade, resulting in continued environmental pollution even after they cannot be reprocessed. Introducing dynamic covalent cross-linking into biodegradable polyester materials can enhance their mechanical properties and stability, and allow them to degrade in the environment even after mechanical recycling is no longer possible, thus solving the aforementioned problems. However, the introduction of cross-linked networks slows down the degradation rate of biodegradable polyester materials. Currently, the slow degradation rate of biodegradable polyester materials (e.g., polylactic acid can only degrade under 60-degree composting conditions, and the degradation time is as long as 2 months) is causing increasingly serious microplastic pollution problems, which also limits the widespread use of biodegradable polyester materials represented by polylactic acid.

[0003] Currently, there is a lack of a method for preparing and applying cross-linked polyester materials that can be repeatedly thermoplasticized while also achieving controlled and rapid degradation. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a method for preparing and applying a reusable thermoplastic processing and controllable degradation photocrosslinked polyester.

[0005] To address the problems of the prior art, the present invention provides the following technical solution:

[0006] A method for preparing a reusable thermoplastic processable and controllably degradable photocrosslinked polyester, the method comprising the following steps:

[0007] (1) Under Steglich esterification reaction conditions, a low molecular weight biodegradable polyester polyol and a carboxylic acid derivative of 1,2-dithionecyclopentane were reacted and purified to obtain a low molecular weight biodegradable polyester with 1,2-dithionecyclopentane group end-capped modification.

[0008] (2) After dissolving the 1,2-dithionyl pentyl group-terminated low molecular weight biodegradable polyester in a solvent, it was placed in a mold and crosslinked by ultraviolet light to obtain a reusable thermoplastic processing and controllable degradable photocrosslinked polyester.

[0009] Furthermore, the low molecular weight biodegradable polyester polyol is one or a mixture of two or more of polylactic acid polyol, polypropylene carbonate polyol, polycaprolactone polyol, and biodegradable polyester polyol obtained by polycondensation of dicarboxylic acid and diol.

[0010] Furthermore, the weight-average molecular weight of the low molecular weight biodegradable polyester polyol does not exceed 5 kDa.

[0011] Furthermore, the general structural formula of the carboxylic acid derivative of the 1,2-dithionecyclopentane is as follows:

[0012] Where n = 0 - 10.

[0013] Furthermore, the feed ratio of the low molecular weight biodegradable polyester polyol and the carboxylic acid derivative of 1,2-dithionecyclopentane is calculated based on the molar ratio of carboxyl groups to hydroxyl groups, which is 1:1.2 to 1:0.8.

[0014] Furthermore, the wavelength of the ultraviolet light is 300-400nm, and the illumination time is 10-120min.

[0015] Furthermore, the solvent mentioned in step (2) is one or more of tetrahydrofuran, dichloromethane, chloroform, and acetone.

[0016] The remodeling method for the reusable thermoplastic and controllable degradable photocrosslinked polyester prepared by the above-described method includes the following steps: crushing the reusable thermoplastic and controllable degradable photocrosslinked polyester and molding it at 150-180°C for 5-20 minutes.

[0017] The controlled degradation method for the reusable thermoplastic and controllable photocrosslinked polyester prepared by the above preparation method includes the following steps: immersing the reusable thermoplastic and controllable photocrosslinked polyester in a THF solution containing NaBH4 for degradation, wherein the concentration of NaBH4 is not less than 0.5 mg / ml and the immersion time is not more than 1 hour; and then composting the product after washing the degradation product with water.

[0018] The reusable thermoplastic processing and controllable degradation photocrosslinked polyester prepared by the above-described method can be applied in the fields of plastics, coatings, adhesives, water-resistant materials, and biomedicine.

[0019] Beneficial Effects: This invention uses a bio-based 1,2-dithiocyclopentane carboxylic acid derivative to end-cap and modify a low molecular weight biodegradable polyester, which is then crosslinked with ultraviolet light to obtain a crosslinked biodegradable polyester material containing disulfide bonds. Compared with linear biodegradable polyester materials, crosslinked biodegradable polyester materials have better high-temperature dimensional stability, which can broaden the application range of biodegradable polyester materials. In addition, disulfide bonds can undergo exchange reactions under high-temperature conditions, thereby giving crosslinked polyester materials the ability to be reshaped and overcoming the problem of traditional crosslinked polyester materials being difficult to reprocess. Furthermore, disulfide bonds can break under reducing conditions to generate thiol groups. Therefore, the photocrosslinked polyester material prepared by this invention can also rapidly degrade into oligomers under reducing conditions after disposal, and the oligomers can be rapidly biodegraded, thereby achieving controllable and rapid degradation, overcoming the problem of slow and uncontrollable degradation of plastics by traditional biodegradable polyesters. In addition, the modified raw material of the photocrosslinked polyester material of this invention is a bio-based molecule, which has the characteristics of being safe, non-toxic, and renewable. Moreover, this invention does not use any external crosslinking agent, overcoming the problem of crosslinking agent migration. The method of crosslinking with ultraviolet light also has the advantages of simple operation and low energy consumption.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] (1) This invention uses a carboxylic acid derivative of 1,2-dithionecyclopentane to end-modify a low molecular weight biodegradable polyester, and then crosslinks it with ultraviolet light to obtain a crosslinked polyester material that can be repeatedly thermoplasticized and controlled to degrade, thus overcoming the problems of traditional crosslinked polyester materials that cannot be repeatedly thermoplasticized and whose degradation is uncontrollable.

[0022] (2) Compared with linear biodegradable polyester materials, the photocrosslinked polyester material of the present invention has better high-temperature dimensional stability.

[0023] (3) The present invention uses low molecular weight biodegradable polyester. Compared with high molecular weight biodegradable polyester, its polymerization process and equipment are simpler, and the ultraviolet light irradiation crosslinking method is environmentally friendly and convenient.

[0024] (4) The carboxylic acid derivative of 1,2-dithionecyclopentane used in this invention is a bio-based compound, which is renewable, safe and non-toxic. Furthermore, this invention does not use any external crosslinking agent, thus avoiding the problem of crosslinking agent migration. Attached Figure Description

[0025] Figure 1 The above are the 1H NMR spectra of the biodegradable polyester polyol before and after modification in Example 1.

[0026] Figure 2 The UV-Vis absorption spectra of the low molecular weight biodegradable polyester end-capped with 1,2-dithionyl groups in Example 1 before and after UV irradiation are shown.

[0027] Figure 3 Photograph of photocrosslinked polyester

[0028] Figure 4 The image shows the difference scanning calorimetry (DSC) curves before and after UV irradiation of the low molecular weight biodegradable polyester end-capped with 1,2-dithionyl groups in Example 1.

[0029] Figure 5 The creep-recovery curve of Example 1 at 80°C

[0030] Figure 6 Comparison of hot pressing before and after reshaping Example 1

[0031] Figure 7 Photograph of degradation example 1 Detailed Implementation

[0032] The present invention will be further described below with reference to the embodiments.

[0033] Test method description:

[0034] 1. The modification of polyester polyol was successfully confirmed by 1H NMR spectroscopy.

[0035] 2. Successful ring opening of the five-membered ring and successful photocrosslinking were confirmed by ultraviolet-visible absorption spectroscopy.

[0036] 3. Determine the appearance and transparency of the photocrosslinked polyester film through photographs.

[0037] 4. Through T g The increase indicates that crosslinking improves the thermodynamic properties of low molecular weight polyester.

[0038] 5. The creep recovery curve demonstrates that photocrosslinked polyester has excellent high-temperature dimensional stability.

[0039] 6. The repeatability of photocrosslinked polyester was determined by crushing and hot pressing molding experiments.

[0040] 7. The rapid cleavage of disulfide bonds in the reducing agent demonstrates its controllable and rapid degradation properties.

[0041] The present invention will now be described in detail with reference to specific test examples. It should be noted that the following test examples are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0042] The polylactic acid diol and triol used in the experiment were from Fengyuan Futailai Co., Ltd., polycaprolactone diol and polycaprolactone triol were from Aladdin, polypropylene carbonate diol was from Zhejiang Huafeng Environmental Protection Materials Co., Ltd., 1,2-dithiopentane-3-carboxylic acid and 1,2-dithiopentane-3-propionic acid were from Leyan Reagent, dicyclohexylcarbodiimide and 4-dimethylaminopyridine were from Adamas, and other reagents were from Sinopharm unless otherwise specified.

[0043] Example 1

[0044] (1) Polylactic acid diol (M w =3kDa) 20g, lipoic acid 2.75g (hydroxyl to carboxyl ratio of 1:1) were dissolved in dichloromethane to a clear and transparent solution, and then dicyclohexylcarbodiimide was added as a dehydrating agent for the Steglich esterification reaction, and then 4-dimethylaminopyridine was added as a catalyst. The reaction was carried out at 25°C for 24h. The product was washed three times with 1N hydrochloric acid solution, saturated sodium bicarbonate solution, water and anhydrous ethanol respectively, and then vacuum dried to obtain 1,2-dithiocyclopentyl group-terminated modified low molecular weight polylactic acid. (2) 1g of the above 1,2-dithiocyclopentyl group-terminated modified low molecular weight polylactic acid was dissolved in 10ml of tetrahydrofuran and placed in a mold. It was irradiated under a 365nm wavelength ultraviolet lamp (50W) for 60min.

[0045] Example 2

[0046] The specific process is the same as in Example 1, except that the mass of lipoic acid in step (1) is replaced with 3.30g (the ratio of hydroxyl to carboxyl groups is 1:1.2).

[0047] Example 3

[0048] The specific process is the same as in Example 1, except that the mass of lipoic acid in step (1) is replaced with 2.20g (the ratio of hydroxyl to carboxyl groups is 1:0.8).

[0049] Example 4

[0050] The specific process is the same as in Example 1, except that in step (1), polylactic acid diol is replaced with polylactic acid triol (M). w =3kDa), with a mass of 20g, of which 4.12g is lipoic acid (hydroxyl to carboxyl ratio of 1:1).

[0051] Example 5

[0052] The specific process is the same as in Example 1, where polylactic acid diol (M) is used in step (1). w =3kDa) replaced with polylactic acid diol (M w=5kDa), and the mass of lipoic acid is correspondingly changed to 1.65g (hydroxyl to carboxyl ratio of 1:1).

[0053] Example 6

[0054] The specific process is the same as in Example 1, where polylactic acid diol (M) is used in step (1). w =3kDa) replaced with polylactic acid diol (M w =2kDa), the mass of lipoic acid is changed to 4.12g (hydroxyl to carboxyl ratio is 1:1), and the solvent in step (2) is changed to acetone.

[0055] Example 7

[0056] The specific process is the same as in Example 1, except that polylactic acid diol is replaced with polycaprolactone diol (M). w =3kDa), and in step (2), the solvent is changed to trichloromethane.

[0057] Example 8

[0058] The specific process is the same as in Example 1, except that polylactic acid diol is replaced with hydroxyl-terminated polybutylene succinate (M). w =3kDa), and in step (2), the solvent is changed to trichloromethane.

[0059] Example 9

[0060] The specific process is the same as in Example 1, except that in step (1), polylactic acid diol is replaced with polypropylene carbonate diol (M). w =3kDa), and in step (2), the solvent is changed to dichloromethane.

[0061] Example 10

[0062] The specific process is the same as in Example 1, except that lipoic acid is replaced with 1,2-dithiazane-3-carboxylic acid, with a mass of 2.00g (hydroxyl to carboxyl ratio of 1:1).

[0063] Example 11

[0064] The specific process is the same as in Example 1, except that lipoic acid is replaced with 1,2-dithiazane-3-undecanoic acid, with a mass of 3.31g (hydroxyl to carboxyl ratio of 1:1).

[0065] Example 12

[0066] The specific process is the same as in Example 1, except that in step (2), the illumination is changed to 120 min under a 365 nm ultraviolet lamp (50 W).

[0067] Example 13

[0068] The specific process is the same as in Example 1, except that in step (2), the illumination is changed to 10 minutes of illumination under a 200W ultraviolet lamp with a wavelength of 365nm.

[0069] Remodeling Example 1

[0070] The photocrosslinked polylactic acid material prepared in Example 1 was pulverized and molded at 160°C for 15 min.

[0071] Remodeling Example 2

[0072] The specific process is the same as in Remodeling Example 1, except that the molding temperature is changed to 150℃ and the time is changed to 20 minutes.

[0073] Remodeling Example 3

[0074] The specific process is the same as in Remodeling Example 1, except that the molding temperature is changed to 180℃ and the time is changed to 5 minutes.

[0075] Remodeling Example 4

[0076] The specific process is the same as in Remodeling Example 1, except that the photocrosslinked polylactic acid material prepared in Example 1 is replaced with the photocrosslinked polycaprolactone material prepared in Example 7.

[0077] Remodeling Example 5

[0078] The specific process is the same as in Remodeling Example 1, except that the photocrosslinked polylactic acid material prepared in Example 1 is replaced with the photocrosslinked polypropylene carbonate material prepared in Example 9.

[0079] Degradation Example 1

[0080] The photocrosslinked polylactic acid material (100 μm thick) prepared in Example 1 was immersed in a THF solution containing NaBH4 (0.5 mg / mL) for 60 min.

[0081] Degradation Example 2

[0082] The specific process is the same as in Degradation Example 1, except that the concentration of NaBH4 is changed to 1 mg / mL and the soaking time is changed to 30 min.

[0083] Comparative Example 1

[0084] 1g of low molecular weight polylactic acid diol (M w =3kDa) was dissolved in 10ml of tetrahydrofuran and then placed in a mold to evaporate the solvent and form a film.

[0085] Figure 1 The NMR spectra of the biodegradable polyester polyol before and after modification in Example 1 demonstrate the successful preparation of a low molecular weight biodegradable polyester with 1,2-dithionyl pentyl group end-capping modification. Figure 2The images show the UV absorption spectra of the low molecular weight biodegradable polyester modified with 1,2-dithionyl pentane end-capsulation in Example 1 before and after UV irradiation. As can be seen from the images, the UV absorption peak of the sample before irradiation is around 330 nm, while the UV absorption peak at this location disappears after irradiation. This proves that after UV irradiation, the 1,2-dithionyl pentane end-capsulation ring-opens and forms disulfide crosslinks. Figure 3 The image shows a photograph of the photocrosslinked polyester material. As can be seen from the image, the photocrosslinked polyester material prepared in this invention exhibits excellent transparency. Table 1 lists the gel fraction of the photocrosslinked polyester material, showing that the photocrosslinked polyester material prepared in this invention has a good network structure and a gel fraction higher than 85%. Figure 4 The differential scanning calorimetry (DSC) curves of the sample before and after light irradiation in Example 1 show that, compared with Comparative Example 1, the glass transition temperature of the sample after crosslinking in Example 1 increased by 15°C. Figure 5 The creep-recovery curve of Example 1 at 80°C shows that the sample does not creep and the strain can be completely recovered after the stress is removed. This indicates that the photocrosslinked polylactic acid material prepared by the present invention has good high-temperature dimensional stability, while commercial linear polylactic acid will undergo obvious creep and permanent deformation above the glass transition temperature (~55°C). Figure 6 The photograph of Remodeling Example 1 shows that even though Example 1 has a gel fraction as high as 89%, it can still be hot-pressed into a transparent and complete film sample, which demonstrates that the photocrosslinked polyester material prepared by the present invention has good remodeling ability. Figure 7 The photograph of degradation example 1 shows that the photocrosslinked polyester material prepared in this invention can be rapidly degraded into oligomers dissolved in tetrahydrofuran under conditions of a small amount of NaBH4. Gel permeation chromatography determined the weight-average molecular weight of the degraded material to be approximately 3 kDa, indicating that the sample degradation was relatively complete. Low-molecular-weight biodegradable polyesters can rapidly degrade under composting or enzymatic degradation conditions. Therefore, the degradation of photocrosslinked polyesters can be controlled by using reducing agents, and rapid degradation can be achieved.

[0086] Table 1

[0087] Example 1 89±2.3 Example 4 86±1.9 Example 7 90±0.9 Example 8 92±1.1 Example 9 85±0.7

[0088] a The gel fraction was determined by Soxhlet extraction in dichloromethane for 24 hours.

Claims

1. A method for preparing a reusable thermoplastic processable and controllably degradable photocrosslinked polyester, characterized in that, The preparation method includes the following steps: (1) Under Steglich esterification reaction conditions, a low molecular weight biodegradable polyester polyol and a carboxylic acid derivative of 1,2-dithionecyclopentane were reacted and purified to obtain a low molecular weight biodegradable polyester with 1,2-dithionecyclopentane group end-capped modification. (2) After dissolving the 1,2-dithionyl pentyl group-terminated low molecular weight biodegradable polyester in a solvent, it was placed in a mold and crosslinked by ultraviolet light to obtain a reusable thermoplastic processing and controllable degradable photocrosslinked polyester. The low molecular weight biodegradable polyester polyol is one or a mixture of two or more of the following: polylactic acid polyol, polypropylene carbonate polyol, polycaprolactone polyol, and biodegradable polyester polyol obtained by polycondensation of dicarboxylic acid and diol. The weight-average molecular weight of the low molecular weight biodegradable polyester polyol does not exceed 5 kDa. The general structural formula of the carboxylic acid derivatives of 1,2-dithionecyclopentane is: , where n = 0-10.

2. The method for preparing a reusable thermoplastic processing and controllable degradation photocrosslinked polyester as described in claim 1, characterized in that, The feed ratio of the low molecular weight biodegradable polyester polyol and the carboxylic acid derivative of 1,2-dithionecyclopentane is calculated based on the molar ratio of carboxyl groups to hydroxyl groups, which is 1:1.2 to 1:0.

8.

3. The method for preparing a reusable thermoplastic processing and controllable degradation photocrosslinked polyester as described in claim 1, characterized in that, The wavelength of the ultraviolet light is 300-400 nm, and the illumination time is 10-120 min.

4. The method for preparing a reusable thermoplastic processing and controllable degradation photocrosslinked polyester as described in claim 1, characterized in that, The solvent mentioned in step (2) is one or more of tetrahydrofuran, dichloromethane, trichloromethane, and acetone.

5. A method for reshaping a reusable thermoplastic processing and controllably degradable photocrosslinked polyester prepared by any one of claims 1 to 4, characterized in that, The steps include: crushing the reusable thermoplastic processing and controllable degradable photocrosslinked polyester, and then molding it at 150~180 ℃ for 5~20 min.

6. A method for controlling the degradation of the reusable thermoplastic processing and controllably degradable photocrosslinked polyester prepared by any one of claims 1 to 4, characterized in that, The steps include: immersing the reusable thermoplastic and controllable degradable photocrosslinked polyester in a THF solution containing NaBH4 for degradation, wherein the concentration of NaBH4 is not less than 0.5 mg / ml and the immersion time is not more than 1 hour; and then composting the product after washing it with water.

7. The application of the reusable thermoplastic processing and controllable degradation photocrosslinked polyester prepared by the preparation method according to any one of claims 1 to 4, characterized in that, The reusable thermoplastic processing and controllable degradable photocrosslinked polyester described herein has applications in the fields of plastics, coatings, adhesives, water-resistant materials, and biomedical materials.

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