Intrinsic fluorescent polyester elastomer and method for preparing the same

Abstract

This invention relates to an intrinsically fluorescent polyester elastomer and its preparation method. The elastomer is copolymerized from vanillin-based aldehyde monomers with small-molecule cyano monomers and cyano-terminated polyethers or polyester diols via a Knoevenagel polycondensation reaction. By adjusting the molar fraction of the soft segment, a continuous transition from rigid fluorescent plastics to highly elastic fluorescent polyester elastomers can be achieved. The resulting material exhibits both high fluorescence quantum yield and high elongation at break, and can be applied in fields such as melt spinning, fluorescent anti-counterfeiting, and flexible optoelectronic devices.

Description

Technical Field

[0001] This invention belongs to the field of fluorescent polymer materials technology, specifically relating to an intrinsically fluorescent polyester elastomer and its preparation method. In particular, this invention, through molecular structure design, introduces flexible soft segments into the conjugated backbone and precisely controls their proportion, obtaining a novel fluorescent polymer material that combines high fluorescence quantum yield with excellent mechanical elasticity. This solves key technical problems in traditional fluorescent elastomer materials, such as poor compatibility between the fluorescence source and the matrix, insufficient stability, and complex response mechanisms in mechanochromic materials. Background Technology

[0002] Fluorescent polymers have broad application prospects in organic light-emitting diodes (OLEDs), fluorescent sensors, anti-counterfeiting labels, and smart textiles. Currently, constructing polymer materials that combine good fluorescence properties with mechanical flexibility (especially elasticity) is one of the research hotspots in this field. The mainstream technical routes for obtaining fluorescent elastomers currently include the following: (1) Physical doping method: This involves dispersing organic small molecule fluorescent dyes or inorganic fluorescent nanoparticles in an elastomer matrix. However, this doping system generally suffers from problems such as poor compatibility between fluorescent molecules and polymer matrix, easy migration and phase separation after long-term use, and poor fluorescence stability. Furthermore, high doping content often degrades the mechanical properties of the matrix material.

[0003] (2) Covalent bonding strategy: Introducing fluorescent chromophores into the polymer network via covalent bonds fundamentally avoids the stability problems of physical doping. Based on different fluorescence mechanisms, this strategy can be further divided into the following two categories: (a) Mechanochromic materials: By covalently introducing specific mechanosensitive groups into the polymer network, chemical bonds break or conformational changes occur under mechanical force, resulting in changes in fluorescence signals. Although this type of material shows potential in stress sensing, its mechanism is usually quite complex, and often requires significant deformation to trigger a significant fluorescence response, so its sensitivity and universality need to be improved. (b) Non-conjugated clustered luminescent polyesters: In recent years, non-traditional intrinsic luminescent materials have attracted widespread attention because they can generate fluorescence without large π-conjugated structures. Studies have shown that non-conjugated polymers containing electron-rich groups such as ester, carbonyl, and cyano groups can form clustered luminescence through spatial interactions. For example, by introducing isosorbide into the polyester backbone or adjusting the ratio of terephthalic acid / isophthalic acid, a wide color gamut of fluorescence emission from blue to red light has been achieved in non-conjugated polyesters. However, the fluorescence of these non-conjugated polyesters originates from ester clusters, the fluorescence quantum yield is generally low, and the fluorescence efficiency is highly sensitive to the aggregation state, making it difficult to maintain high fluorescence brightness while also considering mechanical elasticity.

[0004] In summary, while existing technologies have addressed the stability issue of physical doping through covalent bonding strategies, they still suffer from the following shortcomings: the response mechanism of mechanochromic materials is complex and their sensitivity is limited; the fluorescence efficiency of non-conjugated clustered luminescent polyesters is relatively low. More importantly, although intrinsically linked conjugated fluorescent polymers possess high fluorescence quantum yields, their rigid backbone and severe inter-chain π-π stacking typically result in brittle materials lacking elastic deformation capabilities, severely limiting their applications in flexible electronics, stretchable sensors, and smart textiles.

[0005] Therefore, developing an intrinsically fluorescent main-chain conjugated polyester elastomer—that is, embedding a highly fluorescent conjugated structure into the polymer backbone through covalent bonds, while simultaneously endowing the material with excellent mechanical elasticity through molecular design—has significant scientific and practical value. This invention is based on this idea, constructing a cyanostilbene main-chain conjugated structure through the Knoevenagel polycondensation reaction and introducing flexible soft segments to regulate the material's elasticity, thereby achieving a synergistic balance between high fluorescence efficiency and high mechanical elasticity. Summary of the Invention

[0006] The purpose of this invention is to provide a fluorescent elastomer based on the Knoevenagel polycondensation reaction and its preparation method. By introducing flexible soft segments and precisely controlling their ratio with rigid conjugated hard segments, the polymer can be continuously transformed from a rigid inelastic fluorescent material to a highly elastic fluorescent material while maintaining excellent fluorescence performance.

[0007] Technical solution An intrinsically fluorescent polyester elastomer, characterized in that the copolymer is copolymerized from rigid conjugated hard segments and flexible soft segments via a Knoevenagel polycondensation reaction; The rigid conjugated hard segment is formed by the reaction of vanillin-based aldehyde monomer and small molecule cyano monomer, and the main chain contains a cyano-substituted stilbene structure, which serves as the fluorescent chromophore and physical crosslinking point of the copolymer. The flexible segment is a cyano-terminated flexible segment, which is prepared by reacting polyethylene glycol, polytetramethylene ether glycol or polycaprolactone glycol with cyanoacetic acid with a number average molecular weight of 400~4000 g / mol. Its end group contains an active methylene group, which can participate in the Knoevenagel polycondensation reaction. The copolymer is characterized in that: by adjusting the molar fraction (20%~70%) of the flexible soft segment in the copolymer, the fluorescence properties and mechanical elasticity can be synergistically regulated; The method for preparing the fluorescent copolymer includes the following steps: (1) Preparation of cyano-terminated flexible soft segments (CN-soft): The flexible diol was dissolved in toluene, and then cyanoacetic acid and p-toluenesulfonic acid were added. After the reaction was completed by stirring, the toluene was evaporated, and the mixture was washed with saturated brine and saturated sodium bicarbonate. After vacuum drying, the cyano-double-terminated flexible segment was obtained.

[0008] In the above technical solution, in step (1), the molecular weight of the diol is 400-4000 g / mol; the molar ratio of flexible diol to cyanoacetic acid is 1:5-1:10.

[0009] (2) Preparation of bio-based elastomers: Knoevenagel polycondensation of fluorescent copolymers Vanillin-based aldehyde monomers, small-molecule cyano monomers, and cyano-terminated flexible segments are dissolved in an organic solvent in a certain proportion. An alkaline catalyst (selected from one or more of piperidine, pyridine, and triethylamine) is added, and the reaction is carried out at 60-120℃ for 12-48 h under nitrogen protection. After the reaction is completed, the reaction solution is added dropwise to a precipitant, filtered, washed, and dried to obtain the target fluorescent copolymer.

[0010] The second objective of this invention is to provide a high-performance intrinsically fluorescent polyester elastomer, which is prepared by the above-described preparation method.

[0011] Compared with existing technologies, it has the following characteristics: 1. The fluorescent elastomer prepared by this method is intrinsically fluorescent and has stable performance: the fluorescent chromophore is embedded in the main chain through covalent bonds, which fundamentally avoids the problems of dye migration and phase separation in physical doping systems.

[0012] 2. Overcoming the contradiction between rigidity and fluorescence: For the first time, a highly fluorescent cyano-substituted stilbene structure was introduced into the elastomer backbone through Knoevenagel polycondensation, successfully preparing an intrinsic fluorescent elastomer with both high fluorescence quantum yield and high elongation at break.

[0013] 3. High performance designability: By simply adjusting the soft segment ratio, the macroscopic mechanical properties (from rigid plastics to elastomers) and microscopic fluorescence properties of materials can be continuously controlled.

[0014] 4. Bio-based source: Vanillin is derived from biomass, which aligns with the concept of sustainable development. Attached Figure Description

[0015] Figure 1 ¹H NMR spectrum of the cyano-terminated flexible soft segment described in Example 1 of this invention Figure 2 The UV-Vis absorption spectrum of the representative fluorescent copolymer (P-20, soft segment content 20%) described in Example 1 of this invention. Figure 3Fluorescence photograph of the representative fluorescent copolymer (P-20) described in Example 1 of this invention. Figure 4 Fluorescence emission spectrum (PL) of the representative fluorescent copolymer (P-40) described in Example 2 of this invention. Figure 5 Stress-strain curves of the representative fluorescent copolymer (P-60) described in Example 3 of this invention Detailed Implementation The following describes in detail the specific embodiments of the technical solution of the present invention, but the present invention is not limited to the following description: The present invention will now be described in conjunction with specific embodiments: Example 1 Synthesis of cyano-double-terminated flexible soft segments Polytetramethylene ether glycol (PTMG), M n =1000 g / mol, 20.0 g, 0.02 mol), cyanoacetic acid (8.5 g, 0.10 mol), p-toluenesulfonic acid (0.19 g, 0.001 mol), and toluene (100 mL) were added to a reaction flask, and the mixture was refluxed at 110 °C for 12 h to remove water. After the reaction was completed, the mixture was washed with saturated sodium bicarbonate solution and saturated brine, dried over anhydrous magnesium sulfate, and toluene was removed by rotary evaporation to obtain the cyanoacetic acid ester-terminated polytetramethylene ether diol monomer.

[0016] Vanillin aldehyde monomer A (8.84 g, 20 mmol), small molecule cyano monomer B (6.46 g, 16 mmol), and cyanoacetate-terminated polytetramethylene ether glycol monomer (8.07 g, 4 mmol) were dissolved in anhydrous dimethyl sulfoxide (DMSO, 50 mL), and piperidine catalyst (0.05 mmol) was added. The reaction was carried out at 80 °C for 24 h under nitrogen protection. After the reaction was completed, the reaction solution was slowly added dropwise to excess methanol to precipitate the product. The precipitate was filtered, washed three times with methanol, and dried under vacuum to constant weight to obtain fluorescent copolymer P-20.

[0017] Figure 1 The image shows the ¹H NMR spectrum of the cyano-double-terminated flexible segment in Example 1 of this invention. A peak at 4.25 ppm, attributed to the methylene group adjacent to the ester bond, is observed. Furthermore, apart from the deuterated chloroform peak, no other impurity peaks are present, indicating the successful synthesis of the cyano-soft segment monomer.

[0018] Figure 2The image shows the UV-Vis absorption spectrum of the fluorescent copolymer P-20 in Example 1 of this invention. A distinct absorption peak is observed in the 325-375 nm range, which is attributed to the π→π* transition in the conjugated structure of the cyano-substituted stilbene backbone, confirming that the Knoevenagel polycondensation reaction successfully constructed the conjugated backbone.

[0019] Figure 3 This is a fluorescence photograph of the fluorescent copolymer P-20 in Example 1 of the present invention. The photograph clearly shows that the P-20 polymer emits a distinct blue light under 365 nm ultraviolet light.

[0020] Example 2 Synthesis of P-40 fluorescent copolymer According to Example 1, only the ratio of small molecule cyano monomer B to flexible soft-segment cyano monomer was changed. Vanillin aldehyde monomer A (8.84 g, 20 mmol), small molecule cyano monomer B (4.84 g, 12 mmol), and cyanoacetate-terminated polytetramethylene ether glycol monomer (16.14 g, 8 mmol) were dissolved in anhydrous dimethyl sulfoxide (DMSO, 50 mL), and piperidine catalyst (0.05 mmol) was added. The reaction was carried out at 80 °C for 24 h under nitrogen protection. After the reaction was completed, the reaction solution was slowly added dropwise to excess methanol to precipitate the product. The mixture was filtered, washed three times with methanol, and dried under vacuum to constant weight to obtain fluorescent copolymer P-40.

[0021] Figure 4 The fluorescence emission spectrum (PL) of P-40 in Example 2 of this invention is shown. Under 350 nm excitation, the polymer exhibits a strong fluorescence emission peak at 425 nm, demonstrating its good fluorescence properties.

[0022] Example 3 Synthesis of P-60 fluorescent copolymer Compared to Example 1, only the ratio of small molecule cyano monomer B to flexible soft-segment cyano monomer was changed. Vanillin aldehyde monomer A (8.84 g, 20 mmol), small molecule cyano monomer B (3.23 g, 8 mmol), and cyanoacetate-terminated polytetramethylene ether glycol monomer (24.21 g, 12 mmol) were dissolved in anhydrous dimethyl sulfoxide (DMSO, 50 mL), and piperidine catalyst (0.05 mmol) was added. The reaction was carried out at 80 °C for 24 h under nitrogen protection. After the reaction was completed, the reaction solution was slowly added dropwise to excess methanol to precipitate the product. The mixture was filtered, washed three times with methanol, and dried under vacuum to constant weight to obtain fluorescent copolymer P-60.

[0023] Figure 5This is the stress-strain curve of P-60 in Example 3 of the present invention. At a tensile rate of 50 mm / min, the fluorescent polymer exhibits a tensile strength of 4 MPa and an elongation at break of 250%, demonstrating good mechanical properties.

[0024] The above examples are merely illustrative of the technical concept and features of the present invention and should not be construed as limiting the scope of protection of the present invention. All equivalent transformations or modifications made in accordance with the essence of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an intrinsically type main-chain conjugated fluorescent polyester elastomer, characterized in that, Includes the following steps: (a) Preparation of cyano-double-terminated flexible soft segment: Flexible diol was dissolved in toluene, then cyanoacetic acid and p-toluenesulfonic acid were added. After the reaction was completed by stirring, the toluene was evaporated and dried. The segment was washed with saturated brine and saturated sodium bicarbonate and then dried under vacuum to obtain cyano-double-terminated flexible soft segment. (b) Dissolve vanillin-based aldehyde monomer A, small molecule cyano monomer B, and the cyano double-terminated flexible segment obtained in step (a) in an organic solvent in a certain proportion, add an alkaline catalyst, and carry out Knoevenagel polycondensation reaction at 60-120 °C for 12-48 h. (c) After the reaction is complete, the sample is precipitated, filtered, washed and dried to obtain the target fluorescent copolymer.

2. The method for preparing an intrinsic main-chain conjugated fluorescent polyester elastomer according to claim 1, characterized in that, The flexible diol mentioned in step (a) is one of polyethylene glycol, polytetramethylene ether glycol or polycaprolactone diol, with a number average molecular weight of 400-4000 g / mol; the molar ratio of the flexible diol to cyanoacetic acid is 1:5-1:

10.

3. The method for preparing an intrinsic main-chain conjugated fluorescent polyester elastomer according to claim 1, characterized in that, The alkaline catalyst in step (b) is selected from piperidine, pyridine, or triethylamine; the organic solvent is one of N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, or tetrahydrofuran.

4. The method for preparing an intrinsic main-chain conjugated fluorescent polyester elastomer according to claim 1, characterized in that, The structural formulas of monomers A and B mentioned in step (b) are as follows: 。 5. An intrinsically type main-chain conjugated fluorescent polyester elastomer, characterized in that, An intrinsic main-chain conjugated fluorescent polyester elastomer prepared by the method described in any one of claims 1 to 4.

6. The intrinsic main-chain conjugated fluorescent polyester elastomer according to claim 5, characterized in that, It consists of rigid conjugate hard segments and flexible soft segments.

7. The intrinsic main-chain conjugated fluorescent polyester elastomer according to claim 6, characterized in that, The rigid conjugated hard segment is formed by the reaction of vanillin-based aldehyde monomer A and small molecule cyano monomer B, while the flexible soft segment is a polyether or polyester segment with cyano double-terminated ends.

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