A cyclic spirofused polyurethane polyrotaxane and a method for preparing the same

Abstract

The application discloses a kind of annular spirofuran type polyurethane polyrotaxane and its preparation method, with rigid conjugated structure annular spirofuran derivative as macrocyclic host, with linear polyurethane chain as through axis molecule, and introduce end-capping group in polyurethane chain both ends, greater than annular spirofuran cavity, to constitute quasi wheelane of stable structure.Its preparation method mainly includes: first, synthesis of functionalized annular spirofuran macrocycle with through site;Then it is with isocyanate end-capped polyurethane prepolymer in solution by host-guest interaction and is penetrated to obtain target polyrotaxane.The material combines the rigidity, conjugation of spirofuran unit and the sliding crosslinking effect of polyrotaxane, and shows excellent thermal stability, mechanical properties and stimulus response characteristics.The polyrotaxane provided by the application is suitable for high-performance elastomer, intelligent shape memory material, damping material and optoelectronic functional composite material and the like fields.

Description

Technical Field

[0001] This invention belongs to the field of supramolecular chemistry and polymer materials technology, specifically relating to a cyclic spirofluorene-type polyrotaxane and its preparation method. Background Technology

[0002] This invention belongs to the interdisciplinary field of supramolecular chemistry, topological polymers, and smart materials, specifically relating to a cyclic spirofluorene-type polyrotaxane with a mechanically interlocked structure, its preparation, and applications. Mechanically interlocked molecules, especially polyrotaxanes, have become an important platform for developing high-performance smart materials due to their unique sliding crosslinking topological networks. Currently, research and material construction in this field mainly rely on classic macrocyclic hosts such as cyclodextrins, crown ethers, and cucurbiturils. These macrocycles form quasi-rotaxane structures through host-guest assembly with flexible linear polymer chains such as polyethylene glycol and polypropylene glycol. The core advantage of this structure lies in the fact that the macrocyclic component can slide along the polymer axis. This dynamic characteristic theoretically can effectively dissipate energy, thereby significantly improving the material's toughness, damage tolerance, and responsiveness to external stimuli. Therefore, such materials show potential application value in high-end damping, repairable elastomers, and soft actuators.

[0003] However, with increasingly stringent requirements for the comprehensive performance of materials, the inherent limitations of the aforementioned polyrotaxane systems based on traditional macrocycles are becoming increasingly apparent when facing practical engineering applications, especially in highly reliable, multifunctional integrated intelligent systems. These limitations manifest in three main key bottlenecks: First, the intrinsic properties of the core structural unit—the macrocycle—are insufficient. Taking cyclodextrin, the most widely used macrocycle, as an example, its thermal decomposition temperature is typically below 300°C, and its molecular skeleton is highly flexible, resulting in a low glass transition temperature for materials constructed from it. Under high temperatures or long-term loads, it is prone to network creep, relaxation, and even thermal decomposition, severely limiting its operating temperature range. More importantly, these macrocycles themselves lack conjugated structures, exhibit electrical insulation, and inherently lack optical, electrical, and magnetic functional activities. Although functional groups can be introduced through complex chemical modifications, such modifications are often cumbersome, yield unstable results, and may disrupt the regularity of the macrocycle cavity, weakening its host-guest binding ability with the polymer axis. This "functional inertia" makes it difficult for the final material to intrinsically and efficiently integrate sensing, response, and execution capabilities, severely limiting its in-depth application in cutting-edge fields such as flexible electronics and adaptive sensing. Secondly, there is an inherent contradiction between the "dynamics" and "stability" of the material network, making synergistic optimization difficult. An ideal polyrotaxane material needs to simultaneously possess high toughness and self-healing capabilities brought about by the sliding mechanism, as well as high strength and dimensional stability guaranteed by topological constraints. Existing systems often compromise one aspect for the other: if weak host-guest pairs or flexible macrocycles are used, good sliding properties and energy dissipation can be achieved, but insufficient crosslink strength leads to low macromodulus, poor strength, and large permanent deformation. Conversely, if too many static covalent crosslinks are introduced to improve mechanical strength or rigid combinations with excessive resistance to movement are used, the sliding of the macrocycles will be substantially inhibited, causing the material to lose the core dynamic advantages of its mechanically interlocked structure and degenerate into an ordinary crosslinked network. How to precisely control the dynamic behavior of sliding crosslinking points at the molecular level to achieve an ideal balance between strength and toughness has been a long-standing challenge in this field. Furthermore, current technologies struggle to achieve a deep integration of material mechanical properties and intelligent response functions at the molecular scale. Current research largely focuses on improving mechanical behavior through sliding mechanisms, while neglecting the development of intrinsic, programmable multi-field (e.g., optical, electrical, thermal) response characteristics. Common approaches involve introducing functional fillers such as carbon nanotubes and conductive polymers into the matrix through physical blending, or post-modifying the material surface. These methods often lead to uneven distribution of functional components, weak interfacial bonding, and phase separation or functional failure during use, resulting in unstable response signals and poor durability. This "non-intrinsic" functionalization strategy fails to achieve sensitive, stable, and efficient bidirectional coupling between mechanical deformation and optical, electrical, and thermal signals, thus failing to meet the stringent requirements of next-generation intelligent systems (such as artificial muscles and adaptive optics devices) for integrated "sensing-response-execution" of materials.To address these challenges, researchers have explored various improvement pathways, such as replacing traditional macrocycles with more thermally stable cycloaromatics (e.g., columnar aromatics) or modifying cyclodextrins with complex functional groups. However, these alternatives often come with new problems: the synthesis and purification of cycloaromatics are complex and costly, and their host-guest interactions are sensitive to solvent environments, limiting their processing adaptability; while chemical modification of macrocycles can unpredictably alter their cavity size and electronic properties, affecting their assembly efficiency and stability with the polymer axis, ultimately leading to large fluctuations in material properties and poor reproducibility.

[0004] In summary, starting from the molecular design stage, creating a novel polyrotaxane system that combines excellent intrinsic thermal / chemical stability, independently controllable sliding dynamics, and intrinsic multifunctionality is a key breakthrough in overcoming the performance bottlenecks of existing materials and propelling them into harsh environments and high-end intelligent applications. This invention aims to solve this technical challenge. Summary of the Invention

[0005] The technical problem to be solved by this invention is to overcome the following defects of existing polyrotaxane materials: the macrocyclic host (such as cyclodextrin, crown ether, etc.) on which the existing technology relies has inherent defects of insufficient thermal and chemical stability, and its molecular skeleton lacks intrinsic photoelectric activity, resulting in a narrow operating temperature window, poor environmental tolerance, and single function, which makes it difficult to meet the requirements of high-end applications for multifunctional integration of materials; the traditional dynamic sliding crosslinking network construction strategy is difficult to achieve optimal synergy of macroscopic properties of materials, often resulting in an imbalance between high toughness, high energy dissipation and high strength, low creep, and failing to achieve both excellent mechanical strength and excellent dynamic response characteristics; existing methods are difficult to achieve stable and efficient intrinsic fusion of mechanical load-bearing skeleton and photoelectric and other functional units at the molecular scale, usually relying on physical blending or surface modification, which easily leads to problems such as functional inhomogeneity and interface failure, which seriously restricts the reliable application of materials in next-generation intelligent sensing and actuation devices.

[0006] To address the aforementioned technical problems, this invention provides a cyclic spirofluorene-type polyrotaxane. The polyrotaxane has a defined mechanically interlocked topology and comprises: Macrocyclic host: A cyclic spirofluorene derivative precisely prepared via organic synthesis. This macrocyclic host possesses a rigid three-dimensional spirocyclic framework and an extended π-conjugated system.

[0007] Through-axis molecules: linear polyurethane chains terminated with active functional groups (such as isocyanate groups). Their segment structure, molecular weight, and functional groups can be tuned to accommodate through-axis assembly.

[0008] End-capping group: This is an end-capping agent introduced through a covalent reaction, with steric hindrance significantly greater than the internal size of the cyclic spirofluorene, used to permanently confine the macrocyclic host to the polyurethane axis, forming a stable quasi-rotaxane structure.

[0009] The preparation of this material is based on a stepwise assembly strategy: first, functionalized cyclic spirofluorene macrocycles are synthesized; then, they are assembled with isocyanate-terminated polyurethane prepolymers in a suitable solvent; finally, the topology is locked through a capping reaction to obtain the target polyrotaxane.

[0010] The beneficial effects of this invention are mainly reflected in the following aspects: 1. Revolutionary improvements in fundamental material properties. Due to the extremely high thermal stability (thermal decomposition temperature typically exceeds 500°C) and chemical inertness of cyclic spirofluorene units, the operating temperature range of material systems using them as crosslinking points is greatly broadened. The upper limit of long-term operating temperature is more than 200°C higher than that of cyclodextrin-based systems, enabling them to adapt to more demanding environments. Simultaneously, the inherent three-dimensional rigid structure of spirofluorene significantly enhances the effective strength of the crosslinking points. Combined with its sliding topological nature, the material of this invention successfully achieves a high-performance combination that was previously difficult to achieve: while maintaining high elastic modulus and excellent creep resistance, it exhibits extremely high fracture toughness, excellent fatigue resistance, and low hysteresis loss, thus solving the classic problem of the difficulty in synergistically balancing strength and toughness in dynamic networks.

[0011] 2. Intrinsic integration of mechanical framework and optoelectronic function is achieved. The cyclic spirofluorene in this invention is not only a mechanical crosslinking point but also an intrinsic optoelectronic active unit. Its large π-conjugated structure endows the material with tunable fluorescence emission characteristics, good carrier transport capability, and a certain degree of optical transparency. This "structure as function" design allows the material to possess stable optoelectronic performance without relying on external functional fillers or complex post-modification, fundamentally avoiding performance degradation problems caused by phase separation and poor interfacial compatibility, and laying the material foundation for the development of truly integrated mechanical-optoelectronic intelligent devices.

[0012] 3. This invention creates multi-dimensional, programmable intelligent response behavior. The material integrates multi-level, multi-mechanism stimulus responsiveness: the polyurethane soft segments provide thermally triggered shape memory and self-healing behavior based on microphase separation; the mechanically interlocked topology itself has unique dissipation, distribution, and memory functions for external forces; and the spirofluorene conjugated units can respond to light of specific wavelengths or applied electric fields. Through molecular engineering design of the macrocyclic structure, polyurethane segments, and end-capping groups, precise control can be achieved from single stimulus response to synergistic responses to multiple stimuli such as light-heat and force-electricity, thereby developing advanced intelligent materials with complex shape memory, adaptive deformation, and signal conversion functions, showing broad application prospects in the fields of flexible robotics, adaptive optics, and intelligent sensing.

[0013] In summary, this invention, by innovatively introducing rigid conjugated cyclic spirofluorene into a mechanical interlocking network, not only effectively solves the key bottlenecks in stability, mechanical balance, and functional integration of traditional polyrotaxane materials, but also successfully constructs a novel multifunctional material platform with extraordinary stability, excellent comprehensive mechanical properties, and rich intelligent response characteristics, demonstrating significant scientific innovation and broad application value. Attached Figure Description

[0014] Figure 1 This is the infrared spectrum of cyclic spirofluorene-type polyrotaxane; Figure 2 These are the GPC test results for cyclic spirofluorene polyrotaxane. Figure 3 Thermogravimetric analysis of cyclic spirofluorene polyurethane polyrotaxane; Figure 4 It is the stress-strain curve of cyclic spirofluorene polyurethane polyrotaxane; Figure 5 This is the ultraviolet spectrum of cyclic spirofluorene-type polyrotaxane. Detailed Implementation

[0015] The following examples, in conjunction with the appendix, illustrate the concepts. Figure 1-5 The present invention will be further described as follows: A cyclic spirofluorene-type polyurethane polyrotaxane and its preparation method are disclosed. The method uses a cyclic spirofluorene derivative with a rigid conjugated structure as the macrocyclic host, a linear polyurethane chain as the through-axis molecule, and introduces end-capping groups with a volume larger than the cyclic spirofluorene cavity at both ends of the polyurethane chain, thereby constructing a structurally stable quasi-rotaxane. The preparation method mainly includes: firstly, synthesizing a functionalized cyclic spirofluorene macrocycle with through-sites; then, assembling it with an isocyanate-terminated polyurethane prepolymer in solution through host-guest interactions to obtain the target polyrotaxane. This material combines the rigidity and conjugation of the spirofluorene unit with the unique sliding crosslinking effect of polyrotaxane, exhibiting excellent thermal stability, mechanical properties, and stimulus-response characteristics. The polyrotaxane provided by this invention is suitable for high-performance elastomers, smart shape memory materials, damping materials, and optoelectronic functional composite materials. S1. Synthesis of Alkyl Fluorenes Bisphenol fluorene (2.1 g, 1 mmol), 1,10-dibromodecane (30 g, 5 mmol), and anhydrous potassium carbonate (8.3 g, 3 mmol) were added to a 250 mL round-bottom flask. 100 mL of acetone was added as the reaction solvent. The mixture was refluxed at 65 °C for 24 h under nitrogen protection. After cooling, filtration, and vacuum distillation, the reaction solution was purified by column chromatography using petroleum ether / dichloromethane as the eluent, yielding 5.4 g of a white solid. Theoretical yield: 7.23 g, yield: 75%.

[0016] The reaction equation is:

[0017] S2. Synthesis of Spirofluorene Macrocycles The S1 product (1.47 g, 1.5 mmol) was dissolved in 100 ml toluene along with bisphenol fluorene (2.1 g, 1 mmol) and potassium carbonate (2.5 g, 3 mmol). The mixture was refluxed at 65 °C for 24 h under nitrogen protection and purified by column chromatography with petroleum ether / dichloromethane as eluent to give 2.4 g of white solid.

[0018] The reaction equation is:

[0019] S3. Synthesis of end-capping groups Under a nitrogen atmosphere, a mixture of triphenylamine (2 g, 8.16 mmol) and N-bromosuccinimide (NBS, 30 g, 168.5 mmol) in anhydrous tetrahydrofuran (60 ml) was stirred at room temperature for 24 hours. After the reaction was complete, the mixture was filtered to remove the succinimide byproduct. The filtrate was concentrated under reduced pressure. The crude residue was purified by silica gel column chromatography using a mixture of petroleum ether and dichloromethane as eluent to give a white solid tris(4-bromophenyl)amine (3.2 g, 80% yield).

[0020] Tris(4-bromophenyl)amine (1 g, 1.9 mmol), carbazole (0.6 g, 3.6 mmol), and anhydrous potassium carbonate (1.6 g, 11.6 mmol) were mixed and placed in a 250 mL pear-shaped flask. Cuprous chloride (0.07 g, 0.37 mmol) and 1,10-phenanthroline (0.06 g, 0.33 mmol) were added as a catalyst, and anhydrous DMF (60 mL) was added as a solvent under a nitrogen atmosphere. The reaction mixture was heated to 160 °C and refluxed for 24 hours. After cooling to room temperature, the mixture was filtered to remove inorganic salts. The filtrate was concentrated under reduced pressure. The crude product was purified by silica gel column chromatography using a mixture of petroleum ether and dichloromethane as eluent to give the title compound—a triphenylamine-terminated carbazole derivative—as a white solid.

[0021] 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboran-2-yl)phenol (1 g, 4.9 mmol), 4-bromo-1-butanol (1.0 g, 5.9 mmol), and anhydrous potassium carbonate (2.5 g, 18 mmol) were added to a 100 mL pear-shaped flask. Tetrabutylammonium bromide (TBAB, 0.05 g, 0.15 mmol) was added as a phase transfer catalyst to promote the reaction in the heterogeneous system. Anhydrous acetone (30 mL) was then added as a solvent. The reaction mixture was heated to 65 °C and stirred for 12 hours. After the reaction was complete, the mixture was cooled and concentrated under reduced pressure to obtain the crude product. Purification was performed by silica gel column chromatography using a mixture of petroleum ether and ethyl acetate as eluent to give the target borate ester derivative as a white solid.

[0022] 4-BrBuO-Ph-Bpin (0.11 g, 0.39 mmol), 2CZ-BrTPa (0.1 g, 0.13 mmol), and tetrakis(triphenylphosphine)palladium (0.01 g, 0.009 mmol) were mixed and placed in a 50 mL pear-shaped flask. Anhydrous potassium carbonate (0.05 g, 0.36 mmol) was dissolved in water (10 mL), followed by the addition of toluene (12 mL) and ethanol (6 mL) as solvents. The reaction mixture was heated to 80°C under a nitrogen atmosphere and stirred for 24 hours. After the reaction was complete, the mixture was cooled and concentrated under reduced pressure to give a crude product. Purification by silica gel column chromatography (using a mixture of petroleum ether and ethyl acetate as eluent) yielded the target product as a white solid.

[0023]

[0024] S3. Synthesis of Spirofluorene-Polyrotaxane SR-SPR The S3 product (4.7 g, 4 mmol) and sebacyl chloride (0.2 g, 1 mmol) were dissolved in 60 ml of anhydrous THF. The mixture was subjected to high-frequency ultrasonic vibration for 1 h to generate cavitation bubbles, which released energy instantaneously, forcibly disintegrating the linear molecular entanglement and pushing it into the cavity. After 1 h, NCO (0.042 g, 1 mmol) and PTMG (2 g, 1 mmol) were added to induce polymerization with sebacyl chloride. The reaction was heated to 65 °C and reacted for 6 h. After quenching, filtration, and vacuum distillation, the mixture was purified by column chromatography using anhydrous ethanol / dichloromethane as the eluent to obtain 3.2 g of grayish-white translucent elastomer.

[0025] The reaction equation is:

[0026]

[0027] Experimental testing of the present invention This invention systematically characterized the structure and properties of the synthesized cyclic spirofluorene polyurethane polyrotaxane (hereinafter referred to as SF-PU-PR). Through a series of mutually corroborating analyses and tests, the unique properties and comprehensive advantages of this material were fully revealed from multiple levels, including molecular structure, thermodynamic behavior, macroscopic mechanical response and realization of intelligent functions.

[0028] First, in terms of molecular structure confirmation and synthetic process monitoring, Fourier transform infrared spectroscopy (FT-IR) provides crucial information on the evolution of chemical functional groups. Figure 1 In the spectrum, significant urethane characteristic absorption bands appeared at 3320 cm⁻¹ (νN-H), 1720 cm⁻¹ (νC=O), and 1530 cm⁻¹ (δN-H coupled with νC-N). This change clearly confirms that the -NCO group has fully participated in the reaction and successfully transformed into a polyurethane structural unit. To further quantify the molecular parameters of the polymer, gel permeation chromatography (GPC) results showed ( Figure 2 The final product's number-average molecular weight (Mn = 6,502 g / mol) closely matches the theoretical design value, and the molecular weight distribution index (Đ) is controlled below 2. This data demonstrates a high degree of controllability throughout the assembly and end-capping reaction process, enabling the preparation of target polymers with well-defined structures and narrow molecular weight distributions, thus laying the foundation for the reproducibility and controllability of material properties.

[0029] Thermal stability is a core indicator of a material's suitability for high-temperature or harsh environmental applications. Thermogravimetric analysis (TGA) results show that ( Figure 3 SF-PU-PR exhibits superior thermal decomposition performance. Under a nitrogen atmosphere, its 5% weight loss temperature (Td, 5%) is more than 80°C higher than that of traditional cyclodextrin-based polyrotaxane and physical blend control samples, reaching a high level of over 350°C. Simultaneously, the peak temperature corresponding to its maximum thermal weight loss rate also shifts significantly into the high-temperature region. This leap in performance is directly attributed to the inherent high thermal stability of the rigid conjugated cyclic spirofluorene backbone and its strong constraint on the thermal motion of the polymer backbone as a topological crosslinking point, fundamentally overcoming the bottleneck of insufficient thermal stability in traditional flexible macrocyclic backbones.

[0030] In terms of macroscopic mechanical property characterization ( Figure 4Uniaxial static tensile testing quantifies the strength, ductility, and elastic behavior of the material. SF-PU-PR exhibits an excellent combination of high strength and high toughness, with a tensile strength of 20-30 MPa and an elongation at break exceeding 300%. Its stress-strain curve shows a continuous strain hardening phenomenon after yielding, which is direct evidence that the internal sliding crosslinking network gradually orients and effectively bears the load during the tensile process. Compared with the control sample without the introduction of a mechanical interlocking structure, the initial modulus of SF-PU-PR is significantly improved, confirming the reinforcing effect of the cyclic spirofluorene as a rigid crosslinking point on the network rigidity. More importantly, cyclic tensile testing shows that its hysteresis loop area is small, and after multiple loading-unloading cycles, the residual deformation rate is less than 10%. This precisely explains the core advantage of its sliding crosslinking mechanism: under the action of external force, the large ring slides along the axial direction, effectively dissipating energy through friction; after the external force is removed, the entropic elasticity of the network drives the chain segment retraction and the redistribution of the large ring, achieving near-complete shape recovery, thus synergistically achieving high damping, high resilience, and low permanent deformation at the molecular level.

[0031] To visually verify the intelligent properties imparted to the material by this dynamic topological network, we designed a self-healing performance demonstration experiment. After cutting an SF-PU-PR film sample, the fresh fracture surfaces were brought into contact and heat-treated at a moderate temperature (e.g., 100°C) for several hours. The repaired sample not only visually reformed into a continuous whole, but its mechanical properties were also effectively restored. Tensile tests showed that the fracture location of the repaired sample occurred within the material itself rather than at the original cut, and it could withstand significant tensile deformation again. This phenomenon stems from the dynamic nature of the mechanically interlocked network: under thermal activation, the polymer chain segments at the fracture point exhibit enhanced mobility, allowing the large rings to cross the interface and re-interlock with new polymer axes, rebuilding an effective topological cross-linked network, thus achieving intrinsic self-healing. This characteristic is of great significance for extending the service life of materials in fields such as flexible electronics and smart coatings.

[0032] Finally, UV-Vis absorption spectroscopy confirmed the successful integration and retention of the functional building block. Figure 5 The SF-PU-PR film exhibits a distinct characteristic absorption band in the 300-350 nm wavelength range, which perfectly corresponds to the spectral characteristics of the cyclic spirofluorene model compound and is attributed to the π-π* electronic transitions of the spirofluorene aromatic conjugated system. This result conclusively demonstrates that the photoelectric active centers of the cyclic spirofluorene macrocycle, which serves as the crosslinking point of the mechanical network, are completely preserved during polymerization and molding and are uniformly distributed throughout the entire material system. This achieves a fundamental fusion of the mechanical framework and photoelectric functional units at the molecular scale, providing a key material foundation for developing a new generation of flexible smart devices that combine excellent mechanical properties with photoresponse and electroluminescence characteristics.

[0033] In summary, through progressive testing and analysis ranging from structural characterization (FT-IR, GPC), basic physical properties (TGA), core mechanics (static tensile testing), to advanced functions (self-healing demonstration, UV-Vis), this study comprehensively and deeply verifies the innovative value of cyclic spirofluorene-type polyrotaxane. This material not only synergistically enhances thermal stability and mechanical properties through ingenious topological design, but also achieves intelligent properties such as self-healing and photoelectric response thanks to its dynamic interlocking network and intrinsic functional units, demonstrating the enormous potential of an integrated, multifunctional advanced material.

[0034] The above descriptions are all preferred embodiments of the present invention. For those skilled in the art, any modifications to the present invention in various equivalent forms without departing from the principle of the present invention shall fall within the protection scope of the appended claims.

Claims

1. A cyclic spirofluorene type polyurethane polyrotaxane, characterized in that: The polymer is passed through the cavity of the spirofluorene macrocyclic molecule to form a polyrotaxane structure SR-SPR, with the following general structural formula: 。 2. The cyclic spirofluorene polyurethane polyrotaxane according to claim 1, characterized in that: Cyclic spirofluorene derivatives have a rigid conjugated macrocyclic structure composed of spirofluorene units.

3. The cyclic spirofluorene polyurethane polyrotaxane according to claim 1, characterized in that: The linear polyurethane axis molecules are composed of isocyanate-terminated polyurethane prepolymers.

4. A method for preparing cyclic spirofluorene-type polyurethane polyrotaxane as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1: Provides a polyurethane prepolymer linked to cyclic spirofluorene derivatives and isocyanates; S2: Cyclic spirofluorene derivatives and polyurethane prepolymers are subjected to a through-assembly reaction in a solvent to form a quasi-rotaxane intermediate; S3: Add an end-capping agent to the quasi-rotaxane intermediate to carry out an end-capping reaction, and obtain cyclic spirofluorene polyurethane polyrotaxane.

5. The preparation method according to claim 4, characterized in that, The cyclic spirofluorene derivative described in step S1 is prepared by cyclization reaction of a monomer having a spirofluorene structure; the through-assembly reaction described in step S2 is carried out under inert gas protection.

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