Polylactic acid oligomer with fluorescence effect, preparation method thereof and polylactic acid-based high molecular material

Abstract

The application discloses a polylactic acid oligomer with fluorescence effect, a preparation method of the polylactic acid oligomer and a polylactic acid-based high polymer material, and belongs to the technical field of polymer materials. The polylactic acid oligomer with fluorescence effect is prepared by directly initiating controllable ring-opening polymerization of lactide by using active amino groups in an organic fluorescent small molecule, and the polylactic acid oligomer is further blended with commercially available polylactic acid to prepare a polylactic acid-based high polymer material with fluorescence effect and chemical circulation. The polylactic acid oligomer is chemically composed of organic fluorescent small molecules and homogenized polylactic acid molecular chains, so that the polylactic acid oligomer has excellent compatibility and dispersibility in the polylactic acid base material. The homogenized polylactic acid molecular chains in the polylactic acid oligomer are connected to the luminophore amino groups in the organic fluorescent small molecules instead of the luminophore, so that the polylactic acid oligomer can present the same fluorescence intensity as the corresponding organic fluorescent small molecule, and the fluorescence intensity can be adjusted according to different fluorescence wavelengths to present diversification.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a polylactic acid oligomer with fluorescence effect, a method for preparing the same, and a polylactic acid-based polymer material with fluorescence effect and chemical recyclability. Background Technology

[0002] Fluorescent materials, due to their ability to absorb light of specific wavelengths and excite high-brightness, high-color-purity fluorescence, are widely used in daily consumer goods, industrial signage, stationery, textile printing and dyeing, and security and anti-counterfeiting fields. The huge consumer market has led to a rapidly increasing demand for fluorescent materials, particularly for polymer fluorescent masterbatches and products used as carriers. However, the matrix of most mainstream fluorescent materials in the current consumer market is made of petroleum-based polymers such as polyethylene, polypropylene, and polystyrene. These materials are chemically stable in the natural environment and are difficult to degrade. If these products are not effectively recycled after their service life, they will remain in the environment as solid waste for a long time, eventually breaking down into "microplastics," posing a serious and persistent pollution threat to soil and aquatic ecosystems, which runs counter to the global promotion of green and sustainable development concepts.

[0003] To address the aforementioned environmental problems, researchers have begun seeking alternatives to traditional petroleum-based plastics using renewable bio-based materials. Among numerous bio-based materials, polylactic acid (PLA) is considered one of the most promising environmentally friendly alternatives due to its excellent biocompatibility, complete biodegradability, and good processing performance. Therefore, developing fluorescent materials based on PLA is considered an ideal solution to fundamentally address the environmental pollution problems caused by the disposal of fluorescent products. By compositing organic fluorescent small molecules or fluorescent pigments with a PLA matrix, novel environmentally friendly materials that combine fluorescence functionality with full biodegradability can be prepared, achieving greening from raw materials to end products. For example, patent CN117417565A discloses the direct addition of fluorescent carbon dots to a PLA chloroform solution, followed by casting, vacuum drying, and finally obtaining a fluorescent PLA composite film. However, conventional organic fluorescent small molecules or fluorescent pigments have poor compatibility with the PLA matrix, easily leading to migration and precipitation of the organic fluorescent small molecules or fluorescent pigments, resulting in decreased fluorescence intensity, insufficient stability, and affecting the material's mechanical properties.

[0004] To address these issues, strategies such as microencapsulation, core-shell structures, and micro / nano construction have been extensively explored. For example, patents CN114457489A and CN114457489B disclose the preparation of fluorescent dye microcapsules and transparent microspheres, their physical blending with a polylactic acid (PLA) matrix, and the fabrication of fluorescent PLA fiber fabrics with a core-shell structure using melt spinning equipment. The fluorescence color can be altered by adjusting the amount of microcapsules used. On the other hand, fluorescent molecules are introduced into PLA chains through chemical grafting modification. For instance, patents CN110452368A, CN110452368B, CN110591069A, and CN110591069B disclose the synthesis of hydroxylated macromolecular initiators via active anionic polymerization, the use of these initiators to synthesize PLA with terminal hydroxyl groups, and the grafting of carboxyl-containing fluorescent small molecules to the PLA ends via esterification dehydration condensation reactions to prepare fluorescent polymer materials. Another patent, CN118273000A, discloses a chemical modification method to convert recycled waste polylactic acid (PLA) products into allyl-terminated low-molecular-weight PLA, followed by a Michael addition reaction to graft N-aminoethylpiperazine onto the allyl ends of the PLA molecular chain to prepare fluorescent PLA. However, existing methods generally suffer from poor material compatibility, high toxicity of some raw materials, and complex processes. Therefore, developing high-performance, highly stable, safe, and easily processed fluorescent PLA materials has become an important research direction in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a fluorescent polylactic acid (PLA) oligomer, its preparation method, and a fluorescent and chemically recyclable PLA-based polymer material. This invention utilizes a fluorescent PLA oligomer and commercially available PLA, blended and then processed to obtain a fluorescent and chemically recyclable PLA-based polymer material. The fluorescent PLA oligomer is prepared via a lactide ring-opening polymerization reaction, and its structure consists of homogeneous PLA molecular chains composed of repeating dehydrated lactic acid structural units bonded to small organic fluorescent molecules. The synthesis method used in this invention is controllable and uses commercially available raw materials. Furthermore, this fluorescent PLA oligomer exhibits excellent compatibility and dispersibility in commercially available PLA due to the presence of homogeneous PLA molecular chains. Fluorescent and chemically recyclable polylactic acid-based polymers can be prepared using solution and / or melt blending methods commonly used in the field. These materials not only retain the original biodegradable, processable, recyclable, and biosafety properties of commercially available polylactic acid, but also exhibit high fluorescence brightness and adjustable fluorescence intensity. Furthermore, the preparation process is simple and inexpensive, demonstrating excellent prospects in the application fields of fluorescent polymer materials.

[0006] Specifically, the present invention provides the following technical solution:

[0007] The first aspect of this invention provides a polylactic acid oligomer with a fluorescent effect.

[0008] Polylactic acid oligomers exhibiting fluorescence have the structure shown in formula (I):

[0009] Formula (I)

[0010] Where m is 1 or 2, n is 10~120, A is the electron acceptor, and π is the π bridge (benzene ring structure).

[0011] Furthermore, the relative molecular mass of the fluorescent polylactic acid oligomer is greater than 800 g / mol and less than 8900 g / mol. The relative molecular mass of the fluorescent polylactic acid oligomer is the sum of the relative molecular mass of the organic fluorescent small molecules and the total relative molecular mass of the polylactic acid molecular chain segments. The total relative molecular mass of the polylactic acid molecular chain segments can be adjusted by changing the total number of dehydrated lactic acid repeating units (i.e., the total degree of polymerization), which actually depends on the number of active amino groups in the organic fluorescent small molecules and the molar ratio of amino groups to lactide monomers. In ring-opening polymerization, when the molar ratio of initiating groups to polymerizing monomers is too high, the polymer chain growth exhibits non-steady-state characteristics and significantly enhanced randomness, leading to a wider molecular weight distribution of the polymer and significant batch-to-batch differences in the polymerized products. Therefore, this invention optimizes the degree of polymerization of polylactic acid (PLA) molecular segments obtained by polymerization initiated by each amino group on the organic fluorescent small molecule, i.e., the n value in the structure shown in formula (I) is greater than or equal to 10. Combined with the calculation of molecule 1, which has the smallest relative molecular mass, the lower limit of the relative molecular mass of the PLA oligomer with fluorescence effect is preferably defined. As the n value increases, the chain growth during ring-opening polymerization becomes more controllable, and the increased length of the PLA molecular segment can also improve the compatibility of the PLA oligomer with fluorescence effect in the application matrix. However, excessively long PLA molecular segments can lead to a decrease in the fluorescence brightness of the PLA oligomer with fluorescence effect. Therefore, this invention optimizes the upper limit of the relative molecular mass of the PLA oligomer with fluorescence effect by calculating the molecular weight range of the oligomer concept and molecule 3, which has the largest relative molecular mass.

[0012] The second aspect of this invention provides a method for preparing a polylactic acid oligomer with a fluorescent effect as described in the first aspect. The method involves melting and mixing an organic fluorescent small molecule and lactide, then adding a catalyst. Under the action of the catalyst, the active amino group in the organic fluorescent small molecule directly initiates the controlled ring-opening polymerization of lactide to generate a polylactic acid oligomer with a fluorescent effect. The organic fluorescent small molecule is a D-π-A type fluorescent molecule, comprising an electron acceptor, an electron donor, and a π-bridge. The electron donor is an amino group (-NH2), with at least one amino group, preferably one or two. The electron acceptor is an electron-deficient group that readily accepts electrons, including one or more of -NH2, -COOR, -CN, -CH3, -COR, -NO2, and -C3H7, preferably -CN. R is an alkyl group, preferably -CH3.

[0013] Preferably, the organic fluorescent small molecule has the structure shown in formula (II):

[0014] Equation (II)

[0015] Wherein, R1 is one of -H, -NH2, -COOR, -CN, -NO2, -CH3 and -COR; R2 is one of -H, -COOR, -CH3, -NH2, -COR, and -CN; R3 is one of -H, -CN, -NO2, -COOR, and -C3H7; R4 is one of -H, -COOR, -NH2, -CN, and -CH3; R5 is one of -H, -NO2, -COOR, -COR, -NH2, -CH3, and -CN; R1, R2, R3, R4, and R5 cannot all be -H. If any one of R1, R2, R3, and R5 is -NH2, the others cannot all be -H.

[0016] More preferably, the specific chemical structural formula of the organic fluorescent small molecule is one of the following structural formulas:

[0017] (Molecule 1: p-aminobenzonitrile)

[0018] (Molecular 2: 3'-aminoacetophenone)

[0019] (Molecular 3: Dimethyl 5-aminoisophthalate).

[0020] (Molecular 4: Dimethyl 2-aminoterephthalate).

[0021] (Molecular 5: 3-aminobenzonitrile)

[0022] (Molecular 6: 2-aminobenzonitrile)

[0023] (Molecular 7: Dimethyl 3-amino-phthalate)

[0024] (Molecular 8: Dimethyl 2-aminoisophthalate)

[0025] (Molecular 9: 2-amino-3-methylbenzonitrile)

[0026] (Molecular 10: Dimethyl 4-aminophthalate).

[0027] (Molecular 11: Methyl 3-acetyl-4-aminobenzoate).

[0028] (Molecular 12: 4-nitro-o-phenylenediamine)

[0029] (Molecular 13: 4-amino-2-methylbenzonitrile)

[0030] (Molecular 14: 3,5-diaminobenzonitrile)

[0031] (Molecular 15: Dimethyl 4-aminoisophthalate).

[0032] (Molecular 16: 2-amino-3-nitrobenzenenitrile)

[0033] (Molecular 17: 2-amino-5-(1-methylethyl)benzonitrile).

[0034] Polylactic acid oligomers with fluorescence effects can exhibit the fluorescence color emitted by the organic fluorescent small molecules themselves. In some preferred embodiments, the organic fluorescent small molecules can be selected according to the target brightness and emission wavelength requirements of the polylactic acid oligomers, thereby obtaining polylactic acid oligomers with fluorescence effects that have strong fluorescence brightness and small wavelength shift. In this invention, the preferred organic fluorescent small molecules are D-π-A type organic fluorescent small molecules containing one or two amino groups. The presence of one or two amino groups as initiating groups enables the prepared fluorescent polylactic acid oligomers to exhibit a linear structure similar to commercially available polylactic acid. Furthermore, it allows for the control of secondary amide content in the fluorescent polylactic acid oligomers at a low level, avoiding the high content of alkaline secondary amides that would hinder the controllable synthesis of fluorescent polylactic acid oligomers. It also prevents excessive alkalinity due to secondary amide accumulation during the thermal processing of fluorescent polylactic acid oligomers / polylactic acid blends, thus ensuring good structural stability of the fluorescent polylactic acid oligomers and their chemically recyclable polylactic acid-based polymer products during storage and processing. In addition, the preferred organic fluorescent small molecules are all commercially available and readily available, requiring no additional modification or customization. More importantly, the selected organic fluorescent small molecules cover different fluorescence intensities, meaning that the synthesized polylactic acid oligomers can perfectly exhibit the fluorescence intensity inherent in the organic fluorescent small molecules themselves.

[0035] Specifically, the preparation method of polylactic acid oligomers with fluorescent effects includes the following steps:

[0036] Step (1): Add the selected organic fluorescent small molecule and lactide monomer to the reaction flask, then heat to 110~120 ℃ under an inert atmosphere and stir continuously for 15~20 minutes. After the lactide is completely melted and mixed evenly with the organic fluorescent small molecule, cool the resulting organic fluorescent small molecule / lactide mixture to room temperature.

[0037] Step (2): Add the catalyst to the organic fluorescent small molecule / lactide mixture obtained in step (1), and then carry out the lactide ring-opening polymerization reaction under the protection of an inert atmosphere, controlling the reaction temperature at 120~130 ℃ and the reaction time at 24~48 hours;

[0038] Step (3): Cool the crude product obtained in step (2) to room temperature, add dichloromethane to completely dissolve it, then add the resulting solution dropwise to ice-cold methanol to precipitate and separate by vacuum filtration. Repeat this dissolution-precipitation cycle several times, and dry the purified product to constant weight to obtain the polylactic acid oligomer with fluorescent effect. Preferably, the purified product is vacuum dried at 40 °C to constant weight.

[0039] Furthermore, in step (1), the molar ratio of the organic fluorescent small molecule to the lactide monomer is 1:5~60. The molar ratio of the organic fluorescent small molecule to the lactide monomer directly affects the relative molecular mass of the polylactic acid oligomer with fluorescence effect and the length of the polylactic acid molecular chain segment therein. The present invention sets this molar ratio within the preferred range, which can reduce the non-steady state and randomness of chain growth during ring-opening polymerization, ensure the controllability of the synthesis of polylactic acid oligomer with fluorescence effect, and at the same time maintain the fluorescence brightness of the polylactic acid oligomer with fluorescence effect at a high level.

[0040] Furthermore, the catalyst used in step (2) can be selected from one or more of stannous octoate, stannous chloride, zinc lactate, zinc chloride, and zinc acetate. These catalysts catalyze the ring-opening polymerization of lactide through a highly efficient coordination-intercalation mechanism. This system exhibits high selectivity and controllability, with few side reactions, thus enabling the preparation of fluorescent polylactic acid oligomers with controllable molecular weight, narrow distribution, high purity, and no non-cyclic byproducts. In terms of biosafety, zinc is an essential trace element for the human body, and the zinc ions remaining after catalysting are essentially non-toxic; while stannous catalysts such as stannous octoate are widely used in industry, and their safety at catalyst concentrations has been certified by the US FDA. Based on comprehensive performance and safety, stannous octoate is a more preferred catalyst of this invention.

[0041] Furthermore, in step (2), the molar ratio of catalyst to lactide monomer is 1.1~1.3:1000. The catalyst selected in this invention has extremely high catalytic activity, and even at such a low dosage (approximately one-thousandth of the molar amount of monomer), it can still significantly improve monomer conversion, shorten reaction time, and increase the final yield. In addition, the low initial catalyst dosage, combined with the subsequent multi-step dissolution-precipitation purification process, can effectively remove metal residues in the product, further reducing the metal ion content in the polymer, thereby ensuring its excellent biosafety.

[0042] Furthermore, the lactide monomer is selected from L-lactide, D-lactide, meso-lactide, or any combination thereof. The lactide monomer of this invention can be obtained directly through commercial channels or prepared by means of methods commonly used by those skilled in the art. L-lactide is a more preferred monomer.

[0043] Furthermore, the inert atmosphere includes, but is not limited to, one of nitrogen, argon, and helium.

[0044] The third aspect of the present invention provides a polylactic acid-based polymer material with fluorescence effect and chemical recyclability, comprising the polylactic acid oligomer with fluorescence effect described in the first aspect and commercially available polylactic acid, wherein the amount of polylactic acid oligomer with fluorescence effect added is 5 wt.%-20 wt.% of commercially available polylactic acid with a commercial brand.

[0045] The specific method for preparing a fluorescent and chemically recyclable polylactic acid (PLA)-based polymer material involves adding a fluorescent PLA oligomer to commercially available PLA via solution blending and / or melt blending. The amount of the fluorescent PLA oligomer added is 0.5-20 wt.%, preferably 5 wt.%. The fluorescent PLA oligomer described in this invention has the same dehydrated lactic acid repeating unit structure as commercially available PLA, and this homogeneous structural feature ensures excellent compatibility between the two in organic solvent dissolved state, heated molten state, and room temperature solid state. The organic solvents used in the solution blending process include, but are not limited to, dichloromethane and trichloromethane, and the melt blending temperature can be set according to temperature settings commonly used by those skilled in the art.

[0046] In this invention, commercially available polylactic acid (PLA) with commercial brands can be selected, such as NatureWorks' Ingeo™ series, TotalEnergies Corbion's Luminy® series, Zhejiang Hisun Biomaterials' REVODE series, Anhui Fengyuan's FY series, and Jilin COFCO's JSC series. The fluorescent PLA oligomer described in this invention can be blended into commercially available PLA to prepare a fluorescent and chemically recyclable PLA-based polymer material. This material retains the excellent properties of PLA itself, meeting the needs of injection molding, spinning, blown film production, 3D printing, and chemical recycling.

[0047] The third aspect concerns the application of fluorescent and chemically recyclable polylactic acid (PLA)-based polymers in textiles (such as protective clothing and sportswear), environmentally friendly products (such as garbage bags and packaging bags), daily necessities and household goods (such as toys, stationery, and home decorations), 3D printing materials, and medical supplies (such as fluorescent PLA nanospheres for drug delivery, cell labeling, and in vitro diagnostics). The fluorescent and chemically recyclable PLA-based polymer is a PLA-based masterbatch, which can be supplemented with appropriate additives as needed during the aforementioned specific applications.

[0048] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0049] This invention provides a polylactic acid (PLA)-based polymer material with fluorescent effects and chemical recyclability. Structurally, this material consists of fluorescent small molecules chemically bonded to PLA molecular chains. Because its molecular chains are homogeneous with commercially available PLA, this material exhibits excellent compatibility and dispersibility within a PLA matrix, achieving uniform blending without any heterogeneous additives. This not only ensures that the original biodegradability and processability of the blended substrate are not compromised, but also makes its chemical recycling pathway completely consistent with that of ordinary PLA. Therefore, blends made from this material and commercially available PLA perfectly inherit the excellent recycling characteristics and low-carbon properties of PLA.

[0050] The synthesis method of the fluorescent polylactic acid oligomers described in this invention offers high controllability, and all raw materials used are commercially available, making it suitable for industrial application. Furthermore, the selected catalyst does not bond to the product molecular chain during the reaction, and after purification, it exhibits extremely low metal residue, thus ensuring excellent biocompatibility after blending with commercially available polylactic acid. Crucially, the polylactic acid chain in this oligomer is chemically bonded to the amino groups of the organic fluorescent small molecule, having only a slight impact on its fluorescence brightness, allowing the oligomer to essentially retain the high luminescence intensity of the small molecule itself. Simultaneously, by adjusting the mass ratio of oligomers of different molecular weights in the blend system, the fluorescence brightness of the final material can be flexibly controlled, thereby achieving the advantage of diversified brightness control in the field of polylactic acid-based polymers with fluorescent effects and chemical recyclability. Attached Figure Description

[0051] Figure 1 The reaction equation for the polylactic acid oligomer with fluorescence effect prepared in Example 1 is shown below.

[0052] Figure 2 The proton NMR spectrum of the polylactic acid oligomer with fluorescence effect prepared in Example 1 ( 1 H NMR).

[0053] Figure 3 Fourier transform infrared (FTIR) spectrum of the polylactic acid oligomer with fluorescence effect prepared in Example 1.

[0054] Figure 4 Gel permeation chromatogram (GPC) of the polylactic acid oligomer with fluorescence effect prepared in Example 1.

[0055] Figure 5 The image shows a dichloromethane solution of polylactic acid oligomer with fluorescence prepared in Example 1 and its stability evaluation.

[0056] Figure 6 The image shows a solution of polylactic acid oligomer with fluorescence under ultraviolet light and its stability evaluation, prepared in Example 1.

[0057] Figure 7 The reaction equation for the polylactic acid oligomer with fluorescence effect prepared in Example 14 is shown.

[0058] Figure 8 The image shows the melt-spun product of the bio-based polymer material with fluorescence effect and chemical recyclability prepared in Example 1, and the actual product under ultraviolet light.

[0059] Figure 9 The image shows the electrospinning product of the bio-based polymer material with fluorescence effect and chemical recyclability prepared in Example 3, and the actual product under ultraviolet light. Detailed Implementation

[0060] The technical solution of the present invention will be further described in detail below with reference to several preferred embodiments and accompanying drawings. These embodiments are implemented based on the technical solution of the invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. It should be understood that the specific embodiments described herein are merely used to clearly and completely explain the technical solution of the present invention and are not intended to limit the present invention. 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.

[0061] It should be noted that all raw materials and reagents used in this invention are available from conventional commercial sources, and there are no special restrictions on the manufacturers from which they are purchased. Here, for the purpose of effective comparative analysis between the examples and comparative examples, the commercially available polylactic acid used in the preparation of the fluorescent and chemically recyclable bio-based polymer material is exemplarily selected as NatureWorks' Ingeo™ 4032D.

[0062] Example 1

[0063] This embodiment provides a polylactic acid-based polymer material with fluorescence effect and chemical recyclability, and its specific preparation process is as follows:

[0064] First, p-aminobenzonitrile (3 mmol) and L-lactide monomer (90 mmol) were weighed and added to a reaction flask, with a molar ratio of organic fluorescent small molecule to L-lactide monomer of 1:30. The mixture was then heated to 120 °C under nitrogen atmosphere and stirred continuously for 30 minutes until the L-lactide monomer was completely melted and uniformly mixed with the organic fluorescent small molecule. The resulting mixture was then cooled to room temperature. Next, stannous octoate catalyst (0.099 mmol) was added to the aforementioned organic fluorescent small molecule / L-lactide mixture, with a molar ratio of catalyst to lactide monomer of 1.1:1000. The mixture was then subjected to a ring-opening polymerization reaction at 125 °C for 24 hours under nitrogen atmosphere. After the reaction was completed, the crude product was cooled to room temperature and dichloromethane was added to dissolve it completely. The resulting solution was then added dropwise to 20 times the volume equivalent of ice-cold methanol to precipitate and separated by filtration. This dissolution-precipitation cycle was repeated three times. Finally, the purified product was dried under vacuum at 40 °C to constant weight to obtain the polylactic acid oligomer with fluorescent effect in this example.

[0065] When preparing a bio-based polymer material with fluorescent effect and chemical recyclability, the amount of polylactic acid oligomer with fluorescent effect added is 20 wt.% of commercially available polylactic acid. That is, 2 g of the polylactic acid oligomer with fluorescent effect prepared by the above reaction and 10 g of commercially available polylactic acid are weighed, dissolved in 70 mL of dichloromethane, and stirred and mixed at room temperature for 6 h. The resulting solution is then poured into a mold and dried completely to obtain a bio-based polymer material with fluorescent effect and chemical recyclability.

[0066] The synthesis reaction equation for the polylactic acid oligomer with fluorescence effect provided in this embodiment is as follows: Figure 1 As shown, and its chemical structure is obtained through 1 H NMR test ( Figure 2 ) and FTIR test ( Figure 3 ) for analysis. From Figure 2 It can be seen that the polylactic acid oligomers with fluorescent effects prepared in this embodiment 1 The 1H NMR spectrum contained characteristic peaks of methyl and methine protons belonging to polylactic acid (PLA) molecular chains, as well as characteristic peaks belonging to protons on the aromatic rings of small organic fluorescent molecules, confirming the successful preparation of the fluorescent PLA oligomer. Furthermore, calculations showed that the yield of this fluorescent PLA oligomer was 93.2%. Figure 3 It can be seen that the polylactic acid oligomer with fluorescence effect prepared in this embodiment has the same infrared characteristic peaks as commercially available polylactic acid, including the C=O stretching vibration peak (1758 cm⁻¹). -1 ), COC asymmetric stretching vibration peak (1180 cm⁻¹) -1), COC symmetric stretching vibration peak (1081 cm⁻¹) -1 The asymmetric bending vibration peak of methyl CH (1455 cm⁻¹) -1 ) and symmetrical bending vibration peak (1359 cm) -1 The asymmetric stretching vibration peak of methyl CH (2997 cm⁻¹) -1 ) and symmetrical stretching vibration peak (2946 cm) -1 This indicates that the prepared polylactic acid oligomers exhibiting fluorescence have a homogeneous structure with commercially available polylactic acid, meaning they both contain repeating dehydrated lactic acid structural units. Furthermore, the infrared spectrum of the fluorescent polylactic acid oligomers also reveals a C≡N stretching vibration region (2225 cm⁻¹). -1 ), CH stretching vibration peak in the benzene ring (3070 cm⁻¹) -1 ) and the out-of-plane bending vibration region of CH in the substituted benzene ring (857-790 cm) -1 This confirms the presence of characteristic structures of small organic fluorescent molecules. Furthermore, the infrared spectra of polylactic acid oligomers exhibit distinct amide I and II characteristic peak regions (1640-1500 cm⁻¹). -1 ), and at 3454 cm -1 The presence of a significant NH stretching vibration peak in the aromatic secondary amide indicates that the amino group in the organic fluorescent molecule reacts with lactide to form an amide group.

[0067] Figure 4 The GPC curves of the fluorescent polylactic acid oligomers prepared in this embodiment are shown. No obvious double peaks or tailing phenomena were observed, indicating that the synthesis and preparation of the fluorescent polylactic acid oligomers have good controllability. Fluorescence emission spectroscopy tests revealed that the fluorescence emission wavelengths of the fluorescent polylactic acid oligomers prepared in Examples 1-17 were all within the blue wavelength range, which is basically consistent with the color of the organic fluorescent small molecule used. This indicates that the bonding of the polylactic acid molecular chain did not or slightly affected the characteristics of the chromophore in the organic fluorescent small molecule, and also reflects the scientific validity and effectiveness of the strategy of preparing fluorescent polylactic acid oligomers by initiating the ring-opening polymerization of lactide using the auxochrome amino group in the organic fluorescent small molecule. Figure 5 and Figure 6 It can be seen that the polylactic acid oligomer with fluorescence effect prepared in this embodiment has excellent solubility in dichloromethane. The resulting clear and transparent solution contains no solid particles or precipitates, and it still maintains its original state after standing for 24 hours under room temperature and ultraviolet light irradiation, respectively. This reflects the excellent structural stability of the polylactic acid oligomer with fluorescence effect, and also indicates that the organic fluorescent small molecules and polylactic acid molecular chains are chemically bonded rather than physically blended.

[0068] Example 2

[0069] This embodiment provides a polylactic acid-based polymer material with fluorescence effect and chemical recyclability, and its specific preparation steps are as follows:

[0070] First, 2 mmol of 3'-aminoacetophenone and 60 mmol of D-lactide monomer were weighed and added to a reaction flask, with a molar ratio of organic fluorescent small molecule to D-lactide monomer of 1:30. The mixture was then heated to 120 °C under argon atmosphere and stirred continuously for 20 minutes until the D-lactide monomer was completely melted and uniformly mixed with the organic fluorescent small molecule. The resulting mixture was then cooled to room temperature. Next, 0.072 mmol of stannous chloride catalyst was added to the aforementioned organic fluorescent small molecule / D-lactide mixture, with a molar ratio of catalyst to lactide monomer of 1.2:1000. The mixture was then subjected to a ring-opening polymerization reaction at 120 °C for 48 hours under argon atmosphere. After the reaction was completed, the crude product was cooled to room temperature and dichloromethane was added to dissolve it completely. The resulting solution was then added dropwise to 20 times the volume equivalent of ice-cold methanol to precipitate and separated by filtration. This dissolution-precipitation cycle was repeated three times. Finally, the purified product was dried under vacuum at 40 °C to constant weight to obtain the polylactic acid oligomer with fluorescent effect in this example.

[0071] In preparing a bio-based polymer material with fluorescent and chemically recyclable properties, the amount of fluorescent polylactic acid oligomer added was 15 wt.% of commercially available polylactic acid. Specifically, 1.5 g of the fluorescent polylactic acid oligomer prepared in the above reaction and 10 g of commercially available polylactic acid were weighed and premixed at room temperature, then vacuum dried at 75 °C for 24 hours. The dried premix was then added to a torque rheometer preheated to 190 °C and melt-blended at this temperature at a mixing speed of 45 rpm for 8 minutes. After extrusion, cooling, and pelletizing, the bio-based polymer material with fluorescent and chemically recyclable properties was obtained.

[0072] Example 3

[0073] This embodiment provides a polylactic acid-based polymer material with fluorescence effect and chemical recyclability, and its specific preparation steps are as follows:

[0074] First, 2 mmol of dimethyl 5-aminoisophthalate and 120 mmol of D-lactide monomer were weighed and added to a reaction flask, with a molar ratio of organic fluorescent small molecule to meso-lactide monomer of 1:60. The mixture was then heated to 120 °C under nitrogen atmosphere and stirred continuously for 20 minutes until the meso-lactide monomer was completely melted and uniformly mixed with the organic fluorescent small molecule. The resulting mixture was then cooled to room temperature. Next, 0.156 mmol of zinc lactate catalyst was added to the aforementioned organic fluorescent small molecule / D-lactide mixture, with a molar ratio of catalyst to lactide monomer of 1.3:1000. The mixture was then subjected to a ring-opening polymerization reaction at 120 °C for 48 hours under helium atmosphere. After the reaction was completed, the crude product was cooled to room temperature and dichloromethane was added to dissolve it completely. The resulting solution was then added dropwise to 20 times the volume equivalent of ice-cold methanol to precipitate and separated by filtration. This dissolution-precipitation cycle was repeated three times. Finally, the purified product was dried under vacuum at 40 °C to constant weight to obtain the polylactic acid oligomer with fluorescent effect in this example.

[0075] When preparing a bio-based polymer material with fluorescent effect and chemical recyclability, the amount of polylactic acid oligomer with fluorescent effect added is 10 wt.% of commercially available polylactic acid. That is, 1 g of the polylactic acid oligomer with fluorescent effect prepared by the above reaction and 10 g of commercially available polylactic acid are weighed, dissolved in 70 mL of dichloromethane, and stirred and mixed at room temperature for 6 h. The resulting solution is then poured into a mold and dried completely to obtain a bio-based polymer material with fluorescent effect and chemical recyclability.

[0076] Example 4

[0077] This embodiment provides a polylactic acid-based polymer material with fluorescence effect and chemical recyclability. Except that the organic fluorescent small molecule is 2-aminoterephthalate dimethyl ester, and the amount of polylactic acid oligomer with fluorescence effect added is 5 wt.% of commercially available polylactic acid, everything else is the same as in Example 1.

[0078] Example 5

[0079] This embodiment provides a polylactic acid-based polymer material with fluorescence effect and chemical recyclability. Except that the organic fluorescent small molecule is 3-aminobenzonitrile, and its dosage is changed to 2 mmol, the dosage of lactide is changed to 80 mmol, and the amount of polylactic acid oligomer with fluorescence effect added is 5 wt.% of commercially available polylactic acid, everything else is the same as in Example 1.

[0080] Example 6

[0081] This embodiment provides a polylactic acid-based polymer material with fluorescence effect and chemical recyclability. Except that the organic fluorescent small molecule is 2-aminobenzonitrile, the amount of acrylic resin is changed to 15 mmol, and the amount of polylactic acid oligomer with fluorescence effect added is 5 wt.% of commercially available polylactic acid. All other aspects are the same as in Example 2.

[0082] Example 7

[0083] This embodiment provides a polylactic acid-based polymer material with fluorescence effect and chemical recyclability. Except that the organic fluorescent small molecule is 3-amino-phthalate dimethyl ester, the catalyst is zinc acetate, and the amount of polylactic acid oligomer with fluorescence effect added is 5 wt.% of commercially available polylactic acid, everything else is the same as in Example 1.

[0084] Example 8

[0085] This embodiment provides a polylactic acid-based polymer material with fluorescence effect and chemical recyclability. Except that the organic fluorescent small molecule is dimethyl 2-aminoisophthalate, and its dosage is changed to 2 mmol, the dosage of lactide is changed to 80 mmol, and the amount of polylactic acid oligomer with fluorescence effect added is 5 wt.% of commercially available polylactic acid. All other aspects are the same as in Example 1.

[0086] Example 9

[0087] This embodiment provides a polylactic acid-based polymer material with fluorescence effect and chemical recyclability. Except that the organic fluorescent small molecule is 2-amino-3-methylbenzonitrile, and the amount of polylactic acid oligomer with fluorescence effect added is 5 wt.% of commercially available polylactic acid, everything else is the same as in Example 2.

[0088] Example 10

[0089] This embodiment provides a polylactic acid-based polymer material with fluorescence effect and chemical recyclability. Except that the organic fluorescent small molecule is dimethyl 4-aminophthalate, and its dosage is changed to 2 mmol, the dosage of acrylic acid is changed to 10 mmol, and the amount of polylactic acid oligomer with fluorescence effect added is 5 wt.% of commercially available polylactic acid. All other aspects are the same as in Example 1.

[0090] Example 11

[0091] This embodiment provides a polylactic acid-based polymer material with fluorescence effect and chemical recyclability. Except that the organic fluorescent small molecule is methyl 3-acetyl-4-aminobenzoate, and the amount of polylactic acid oligomer with fluorescence effect added is 5 wt.% of commercially available polylactic acid, everything else is the same as in Example 1.

[0092] Example 12

[0093] This embodiment provides a polylactic acid-based polymer material with fluorescence effect and chemical recyclability. Except that the organic fluorescent small molecule is 4-nitro-o-phenylenediamine, the amount of which is changed to 1 mmol, the amount of lactide is changed to 60 mmol, and the amount of polylactic acid oligomer with fluorescence effect is 5 wt.% of commercially available polylactic acid. All other aspects are the same as in Example 1.

[0094] Example 13

[0095] This embodiment provides a polylactic acid-based polymer material with fluorescence effect and chemical recyclability. Except that the organic fluorescent small molecule is 4-amino-2-methylbenzonitrile, and the amount of polylactic acid oligomer with fluorescence effect added is 5 wt.% of commercially available polylactic acid, everything else is the same as in Example 2.

[0096] Example 14

[0097] This embodiment provides a polylactic acid-based polymer material with fluorescence effect and chemical recyclability, except that the organic fluorescent small molecule is 3,5-diaminobenzonitrile, the amount of which is changed to 2 mmol, the amount of lactide is changed to 40 mmol, the catalyst is zinc chloride, and the amount of polylactic acid oligomer with fluorescence effect added is 5 wt.% of commercially available polylactic acid. All other aspects are the same as in Example 1.

[0098] Example 15

[0099] This embodiment provides a polylactic acid-based polymer material with fluorescence effect and chemical recyclability. Except that the organic fluorescent small molecule is dimethyl 4-aminoisophthalate, the amount of polylactic acid oligomer with fluorescence effect added is 5 wt.% of commercially available polylactic acid, and everything else is the same as in Example 1.

[0100] Example 16

[0101] This embodiment provides a polylactic acid-based polymer material with fluorescence effect and chemical recyclability. Except that the organic fluorescent small molecule is 2-amino-3-nitrobenzonitrile, and the amount of polylactic acid oligomer with fluorescence effect added is 5 wt.% of commercially available polylactic acid, everything else is the same as in Example 1.

[0102] Example 17

[0103] This embodiment provides a polylactic acid-based polymer material with fluorescence effect and chemical recyclability. Except that the organic fluorescent small molecule is 2-amino-5-(1-methylethyl)benzonitrile, and the amount of polylactic acid oligomer with fluorescence effect added is 5 wt.% of commercially available polylactic acid, everything else is the same as in Example 2.

[0104] Comparative Example 1

[0105] In Comparative Example 1, the preparation of polylactic acid oligomers was the same as in Example 1, except that the organic small molecule was replaced with diaminomaleitrile.

[0106] Comparative Example 2

[0107] In Comparative Example 2, the preparation of polylactic acid oligomers was the same as in Example 1, except that the organic small molecule was replaced with aniline.

[0108] Comparative Example 3

[0109] In the preparation of polylactic acid oligomer in Comparative Example 3, the amount of p-aminobenzonitrile was changed to 2 mmol and the amount of lactide was changed to 5 mmol. At this time, the molar ratio of organic fluorescent small molecule to lactide monomer was 1:2.5. Everything else was the same as in Example 1.

[0110] Application Example 1 (Melt spinning)

[0111] The fluorescent and chemically recyclable polylactic acid-based polymer materials prepared in Examples 1-17 were placed in the mixing chamber of a torque rheometer and melt-mixed at 180 °C and 60 rpm for 10 min. The melt was then pumped to a spinning assembly at a rate of 2.0 mL / min using a gear pump and extruded through a 0.3 mm diameter spinneret to form a melt stream. While cooling in room temperature air, the extruded stream was stretched and oriented at a draw ratio of 1:8, and finally collected by a winding roller at 200 rpm. This fiber can be woven into clothing with fluorescent properties.

[0112] Figure 8 The polylactic acid-based polymer material prepared by solution blending in Example 1 exhibits good spinnability and can be melt-spun into polylactic acid fibers with fluorescent effects. This demonstrates that the polylactic acid-based polymer material prepared in Example 1 with fluorescent effects and chemical recyclability retains the original processing properties of commercially available polylactic acid.

[0113] Application Example 2 (Electrospinning)

[0114] The fluorescent and chemically recyclable polylactic acid-based polymer materials prepared in Examples 1-17 were dissolved in a DCM / DMF mixed solvent (8:2, v / v) to prepare a 10 wt% solution. The solution was stirred for 12 hours and then allowed to stand for 1 hour to defoam. The solution was then transferred to a syringe and electrospinning was initiated. The electrospinning voltage was 20 kV, the receiving distance was 16 cm, the feed rate was set to 1.0 mL / h, and the rotational speed of the receiving roller was maintained at approximately 300 rpm.

[0115] Figure 9The polylactic acid-based polymer material prepared by solution blending in Example 3 exhibits good spinnability and can be electrospun into a polylactic acid fiber membrane with a fluorescent effect. This demonstrates that the polylactic acid-based polymer material prepared in Example 3 with a fluorescent effect and chemical recyclability still retains the original processing properties of commercially available polylactic acid.

[0116] Test characterization:

[0117] The polylactic acid oligomers with fluorescent effects prepared in the above examples and comparative examples, as well as the products obtained in application examples 1 and 2, were characterized by testing, as detailed below:

[0118] Chemical structure characterization: Fluorescent polylactic acid oligomers were dissolved in deuterated chloroform, and their structures were then analyzed using a JNM-ECZ600R / S1 nuclear magnetic resonance spectrometer. 1 ¹H NMR spectra. The methylene proton peak (4.3 ppm) attached to the terminal hydroxyl group and the methylene proton peak (5.2 ppm) not attached to the terminal hydroxyl group in the polylactic acid molecular chain were analyzed and identified. The integrated areas I of the two peaks were obtained by integration. 5.2 and I 4.3 In polylactic acid oligomers exhibiting fluorescence, the number of repeating dehydrated lactic acid units (total degree of polymerization) is equal to the ratio of the integral areas of the two peaks (I0). 5.2 / I 4.3 Add one. The NMR calculation value of the relative molecular mass of polylactic acid oligomers with fluorescence effect is equal to the relative molecular mass of the dehydrated lactic acid unit multiplied by the total degree of polymerization plus the relative molecular mass of the organic fluorescent small molecule.

[0119] Fluorescence performance testing: The emission wavelength, fluorescence intensity, and other performance indicators of the products obtained in Case 1 and 2 were tested using a fluorescence spectrophotometer.

[0120] The relative molecular mass and total degree of polymerization of the polylactic acid oligomers prepared in Examples 1-17 and Comparative Examples 1-3 are shown in Table 1. The fluorescence intensity and linear density of the polylactic acid fibers obtained by melt spinning in Application Example 1 are shown in Table 2. The fluorescence intensity and fiber diameter (nm) of the polylactic acid fiber membrane obtained by electrospinning in Application Example 2 are shown in Table 3.

[0121] Table 1

[0122] As can be seen from the data in Table 1, the polylactic acid oligomers with fluorescence effects prepared in each embodiment and comparative examples 1-3 can all be identified by nuclear magnetic resonance characterization, with methyl and methylene proton peaks belonging to the polylactic acid molecular chain segments. The actual relative molecular mass and total degree of polymerization of the polylactic acid oligomers with fluorescence effects can be calculated by using the integral area ratio of the proton peak connected to the terminal hydroxyl group to the corresponding non-terminal hydroxyl group connected proton peak. This indicates that within the required range of monomer type, gas atmosphere, catalyst type and amount, reaction temperature and time, the lactide ring-opening polymerization reaction used in this invention can proceed smoothly, thereby realizing the preparation of polylactic acid oligomers with fluorescence effects. By comparing the theoretically designed relative molecular mass and total degree of polymerization of the polylactic acid oligomers with fluorescence effects in Examples 1-17 with their corresponding NMR calculations, it can be found that the differences between the two sets of data for each example are small. This indicates that the preparation of polylactic acid oligomers with fluorescence effects based on the ring-opening polymerization of lactide has excellent controllability within the required molar ratio of organic fluorescent small molecules to lactide monomers.

[0123] Comparing Example 1 with Comparative Example 3, it can be found that when the molar ratio of the organic fluorescent small molecule to lactide monomer is lower than the lower limit of the range required by this invention, the theoretical design values ​​of the relative molecular mass and total degree of polymerization of the prepared polylactic acid oligomer with fluorescence effect differ greatly from the NMR calculation values. The relative molecular mass deviation rate can reach 74%, indicating that the randomness of chain growth in ring-opening polymerization increases sharply under this condition, resulting in poor controllability. This demonstrates the rationality and effectiveness of this invention in terms of the structural design, preparation scheme, and synthesis requirements of polylactic acid oligomers with fluorescence effect. Furthermore, the synthesis yield of Comparative Example 3 is extremely low, approximately 17%, significantly lower than the 93.2% synthesis yield in Example 1. After multiple dissolution-precipitation purifications following polymerization in Comparative Example 3, it was almost impossible to collect a quantity of product suitable for characterization. This reflects that an excessive number of amino groups in the organic fluorescent small molecule leads to a strong alkalinity in the polymerization system, affecting the controllable ring-opening polymerization of lactide. This further illustrates the scientific validity and rationality of the requirement for the number of amino groups in the organic fluorescent small molecule in this invention.

[0124] Table 2 Application Example 1 Data

[0125] As can be seen from the data in Table 2:

[0126] The fluorescence intensity of the fiber products obtained from the bio-based polymer materials with fluorescence effect and chemical recyclability prepared in Examples 1-17 was measured by a fluorescence spectrophotometer. This showed that the introduction of homogenized polylactic acid molecular chains into organic fluorescent small molecules via amino bonding did not affect the luminescence properties of the organic fluorescent small molecules. This reflects the scientific and rational nature of the strategy of preparing bio-based polymer materials with fluorescence effect and chemical recyclability by initiating the ring-opening polymerization of lactide in organic fluorescent small molecules.

[0127] Table 3 Application Example 2 Data

[0128] As can be seen from the data in Table 3:

[0129] The fluorescent and chemically cyclic bio-based polymer materials prepared in Examples 1-17, when spun by electrospinning, also maintain high fluorescence intensity. The fiber diameter of the electrospun products fluctuates around 800 nm, reflecting that the fluorescent and chemically cyclic bio-based polymer materials prepared in this invention have excellent spinnability and uniform electrospun fiber diameter.

[0130] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A polylactic acid oligomer exhibiting a fluorescent effect, characterized in that, It has the structure shown in equation (I): Formula (I) Where m is 1 or 2, n is 10~120, A is the electron acceptor, and π is the π bridge; Polylactic acid oligomers are prepared by the ring-opening polymerization of lactide. Structurally, they are composed of homogenized polylactic acid molecular chains composed of dehydrated lactic acid repeating structural units and organic fluorescent small molecules. The relative molecular mass of polylactic acid oligomers exhibiting fluorescence is greater than 800 g / mol and less than 8900 g / mol; The electron acceptor is one or more of -NH2, -COOR, -CN, -CH3, -COR, -NO2, and -C3H7, wherein R is an alkyl group.

2. A method for preparing the polylactic acid oligomer with fluorescence effect as described in claim 1, characterized in that, After the organic fluorescent small molecule and lactide are melt-mixed, a catalyst is added. Under the action of the catalyst, the active amino group in the organic fluorescent small molecule directly initiates the controlled ring-opening polymerization of lactide to generate polylactic acid oligomer with fluorescence effect. The organic fluorescent small molecule is a D-π-A type fluorescent molecule, which includes an electron acceptor, an electron donor and a π bridge. The electron donor is an amino group, and there is at least one amino group.

3. The method for preparing the polylactic acid oligomer with fluorescence effect according to claim 2, characterized in that, The organic fluorescent small molecule has the structure described in the following formula: Wherein, R1 is one of -H, -NH2, -COOR, -CN, -CH3, and -COR; R2 is one of -H, -COOR, and -CN; R3 is one of -H, -CN, -NO2, -COOR, and -C3H7; R4 is one of -H, -COOR, -NH2, and -CH3; R5 is one of -H, -NO2, -COOR, and -CN; R1, R2, R3, R4, and R5 cannot all be -H. If any one of R1, R2, R3, and R5 is -NH2, the others cannot all be -H.

4. The method for preparing polylactic acid oligomers with fluorescent effects according to claim 2, characterized in that, The chemical structural formula of the organic fluorescent small molecule is one of the following: ， ， ， ， ， ， ， ， ， ， ， ， ， ， ， ， 。 5. The method for preparing polylactic acid oligomers with fluorescent effects according to any one of claims 3-4, characterized in that, The preparation steps are as follows: Step (1): Add the selected organic fluorescent small molecule and lactide monomer to the reaction flask, and then heat to 110~120 ℃ under an inert atmosphere and stir continuously for 20~30 minutes. After the lactide is completely melted and mixed evenly with the organic fluorescent small molecule, cool the resulting organic fluorescent small molecule / lactide mixture to room temperature. The molar ratio of organic fluorescent small molecule to lactide monomer is 1:10~60. Step (2): Add the catalyst to the organic fluorescent small molecule / lactide mixture obtained in step (1), and then carry out the lactide ring-opening polymerization reaction under the protection of an inert atmosphere. Control the reaction temperature to be 120~130 ℃ and the reaction time to be 24~48 hours. The molar ratio of the amount of catalyst to the amount of lactide monomer added is 1.1~1.3:1000. Step (3): Cool the crude product obtained from step (2) to room temperature and add dichloromethane to dissolve it completely. Then add the resulting solution dropwise to ice-cold methanol to precipitate and separate by filtration. Repeat the dissolution-precipitation cycle several times. Dry the purified product under vacuum to constant weight to obtain polylactic acid oligomer with fluorescent effect.

6. The method for preparing polylactic acid oligomers with fluorescent effects according to claim 5, characterized in that, The catalyst is at least one of stannous octoate, stannous chloride, zinc lactate, zinc chloride, and zinc acetate.

7. The method for preparing polylactic acid oligomers with fluorescent effects according to claim 5, characterized in that, The lactide monomer is at least one of L-lactide, D-lactide, and meso-lactide.

8. A polylactic acid-based polymer material exhibiting fluorescence and capable of chemical recycling, characterized in that, The product includes the polylactic acid oligomer with fluorescence effect as described in claim 1 or the polylactic acid oligomer with fluorescence effect prepared by the method described in any one of claims 2-7, and polylactic acid, wherein the amount of the polylactic acid oligomer with fluorescence effect added is 5 wt.%-20 wt.% of the polylactic acid.

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