A polyurethane sliding ring crosslinked network elastomeric material and a method of making the same

Abstract

This invention belongs to the interdisciplinary field of polymer materials and supramolecular chemistry, specifically relating to a polyurethane slip-ring crosslinked network elastic material with a slip-ring effect. The invention uses a macrocyclic molecule with oxetane-functionalized side groups as the cyclic component of a rotaxane. Through host-guest inclusion interactions, it forms a rotaxane polymer with the linear backbone, followed by a ring-opening crosslinking reaction of the oxetane groups, constructing an interpenetrating network structure that combines a three-dimensional covalent network with a supramolecular slip-ring effect. Under mechanical stimulation, this material dissipates energy through the relative slippage of the ring molecules along the backbone, exhibiting high resilience and wide-temperature-range stability. It can be applied in fields such as flexible electronics, wearable devices, and high-performance damping materials.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of polymer materials science and supramolecular chemistry, specifically relating to a polyurethane slip ring crosslinked network elastic material and its preparation method. Background Technology

[0002] Polymer cross-linked network materials are indispensable basic materials in modern manufacturing, electronics, new energy, and biomedicine. Their core structural feature is a continuous three-dimensional spatial framework formed by polymer segments connected by covalent or non-covalent bonds. Traditional thermosetting resins, vulcanized rubbers, and polyurethane elastomers rely on fixed covalent cross-linking points for structural stability, possessing advantages such as adjustable modulus, good chemical stability, and strong load-bearing capacity, occupying an irreplaceable position in industrial production and daily life. However, the inherent drawback of traditional covalent cross-linked networks lies in the fixed position of the cross-linking points and the limited conformational changes of the chain segments. Under external forces such as tension, compression, bending, or fatigue impact, stress rapidly concentrates at the cross-linking points and nearby chain segments, leading to problems such as brittle fracture, high springback hysteresis, large permanent deformation, and short fatigue life. Especially in scenarios with extremely high requirements for material deformation capacity and cyclic stability, such as flexible wearable devices, high-frequency vibration damping structures, dynamic seals, and soft robots, traditional fixed cross-linked network materials can no longer meet the needs of long-term reliable use. The bottleneck in mechanical performance is becoming increasingly prominent, becoming a key material problem restricting the development of high-end equipment and new electronic industries.

[0003] To address the intrinsic performance limitations imposed by fixed crosslinking points, academia and industry have successively proposed modification strategies such as dynamic covalent bonds, supramolecular interactions, and topological structure regulation. Among these, slip ring topological polymers based on mechanically interlocked structures such as rotaxanes and sesquicyclic compounds, with their unique "movable crosslinking point" design, have become one of the most promising technologies for industrialization. Rotaxane molecules consist of a linear axis molecule, a macrocyclic molecule inserted into the axis, and large-volume end-capping groups at both ends. There are no covalent bonds connecting the macrocyclic molecule and the axis; the mechanical interlocking state is maintained only by non-covalent interactions such as host-guest recognition, hydrophobic interactions, and van der Waals forces. When the rotaxane structure is introduced into the polymer network as a crosslinking unit, the macrocyclic molecule can slide freely along the linear axis, allowing the crosslinking points to adaptively move under external forces. This results in rapid release of local stress, uniform load distribution, and efficient energy dissipation—a characteristic known as the slip ring effect. The slip ring effect breaks through the motion limitations of traditional cross-linked networks at the molecular level, enabling materials to maintain structural integrity while possessing liquid-like chain segment movement capabilities and solid-like mechanical stability. It can simultaneously achieve high elongation at break, low springback hysteresis, excellent fatigue resistance, and high toughness, providing a new design logic for the next generation of high-performance dynamic mechanical materials.

[0004] Despite the significant advantages of slip ring topological polymers, existing technologies still face numerous intractable technical challenges that severely limit their practical applications. First, existing rotaxane molecules generally lack reactive groups capable of efficient covalent crosslinking. Most slip ring materials rely on physical entanglement or non-covalent interactions to form networks, resulting in low strength, poor solvent resistance, susceptibility to high-temperature creep, and insufficient structural stability, failing to meet engineering requirements. Second, some slip ring systems incorporating crosslinking groups suffer from conflicts between crosslinking sites and slip ring unit structures. For example, attaching crosslinking groups to a linear backbone can hinder macrocyclic molecule slippage during crosslinking, causing a significant attenuation or even disappearance of the slip ring effect. Furthermore, excessively high reactivity of the crosslinking groups can lead to localized over-crosslinking, network inhomogeneity, and severe phase separation, resulting in large dispersion and poor reproducibility of the material's mechanical properties. Furthermore, commonly used cyclic molecules such as cyclodextrins, simple crown ethers, and macrocyclic alkanes suffer from drawbacks such as difficulty in functional modification, poor controllability of inclusion forces with the main chain, and insufficient environmental stability. Under conditions of high temperature, high humidity, immersion in organic solvents, or long-term mechanical cycling, they are prone to macroring desorption, inclusion structure depolymerization, and overall network collapse. In addition, existing slip ring materials generally suffer from complex synthetic routes, high preparation costs, harsh reaction conditions, and difficulty in large-scale preparation, further restricting their transition from laboratory research to industrial applications.

[0005] Oxycyclic butanes are a class of cationic curing reaction units with a four-membered ring ether structure. Due to their moderate ring strain, high ring-opening reactivity, mild crosslinking reaction, extremely low volume shrinkage, and stable ether bond structure of the cured product, they are widely used in photocurable coatings, electronic device packaging, adhesives, dental resins, and high-performance composite materials. Compared with traditional crosslinking groups such as epoxy groups, acrylates, and isocyanates, oxycyclic butane groups have unique advantages in the crosslinking process, including controllable reaction rates, fewer side reactions, less damage to supramolecular structures, and high network uniformity, making them very suitable as functional crosslinking units for rotaxane molecules. Covalently linking oxycyclic butane groups to rotaxane macrocycles in a suspended manner allows for efficient covalent crosslinking of three-dimensional networks without disrupting the host-guest inclusion structure, while also ensuring that the macrocycle molecule retains space to slide along the linear backbone after crosslinking. This achieves a synergistic effect between the slip ring effect and the structural stability of the covalent network. However, in currently available technologies, no technical solution has emerged that uses oxobutane functionalized macrocycles as rotaxane components to construct slip-ring polymer interpenetrating networks. Significant technological gaps exist in related molecular structure design, crosslinking mechanisms, network morphology control, and dynamic mechanical property regulation. Currently, with the rapid development of flexible electronics, artificial intelligence, new energy vehicles, and high-end equipment manufacturing industries, the market demand for dynamic mechanical materials possessing high elasticity, high toughness, low hysteresis, fatigue resistance, and environmental aging resistance is growing rapidly. Traditional fixed crosslinked materials are approaching their theoretical limits, while existing slip-ring materials, due to structural defects, uncontrollable crosslinking, and unstable slip-ring effects, cannot provide effective solutions. The industry urgently needs a novel rotaxane polymer interpenetrating network material with a well-defined molecular structure, clear crosslinking pathway, controllable network morphology, stable slip-ring effect, and excellent overall performance to fill the technological gap in the field of high-end functional materials.

[0006] Based on the aforementioned practical needs and technological shortcomings, this invention addresses the core problems of existing slip ring polymers, such as uncontrollable crosslinking, easy detachment of ring molecules, dynamic performance degradation, and poor network uniformity. It designs and constructs an interpenetrating network material with slip ring effect, using oxetane-functionalized macrocycles as ring components and linear polymers as axis molecules. Rotaxane polymers are formed through host-guest inclusion interactions, and then crosslinked with oxetane groups to construct the interpenetrating network material. This invention precisely positions the crosslinking sites on the macrocycle molecules, ensuring the complete preservation of the mechanical interlocking structure after network formation. The ring molecules can slide freely, achieving stress relaxation and energy dissipation, ultimately yielding a novel polymer material that combines covalent network stability with supramolecular dynamic properties. This invention effectively solves long-standing technical problems such as stress concentration, rebound hysteresis, and poor fatigue resistance in traditional crosslinked networks. Simultaneously, it improves the structural strength, solvent resistance, and environmental adaptability of slip ring materials, providing a new technical path and material basis for high-performance flexible functional materials, damping materials, sealing materials, and electronic packaging materials. It has significant scientific research value and broad industrial application prospects. Summary of the Invention

[0007] This invention aims to systematically address a series of key scientific problems and technological bottlenecks in the molecular design, network construction, and dynamic mechanical property synergy of existing rotaxane-type supramolecular polymer materials. Specifically, macrocyclic molecules (such as cyclodextrins and simple crown ethers) that serve as sliding units in traditional slip ring systems generally suffer from inherent defects such as insufficient structural rigidity, single reactive sites, and poor matching with the polymer backbone: their hollow structures and linear polymer chains cannot form stable and efficient host-guest inclusion interactions, resulting in low rotaxane assembly efficiency and easy dissociation of the structure; their molecular backbone lacks reactive groups that can be mildly crosslinked, making it impossible to construct a stable three-dimensional network without destroying the slip ring structure, leading to problems such as ring molecule shedding, hindered slip, and decreased mechanical properties during the stress process. Furthermore, most existing technologies struggle to achieve a compatible balance between cross-linked structures and slip ring effects. Uneven distribution of cross-linking sites and significant network structure defects make it difficult to achieve efficient stress dispersion and energy dissipation under external forces. In particular, under dynamic cyclic deformation, high resilience, low hysteresis loss, and excellent fatigue resistance are difficult to improve in synergy, which greatly restricts their practical application in high-end fields such as flexible electronics, precision damping, and dynamic sealing.

[0008] To overcome the aforementioned limitations, this invention provides a polyurethane slip ring crosslinked network elastic material and its efficient construction method based on supramolecular topology engineering. The core innovation of this material lies in the precise introduction and stable locking of mechanically interlocked rotaxane structural units formed by the host-guest recognition between oxocyclic butane functionalized macrocycles and linear polymer backbones within a three-dimensional polymer network. This structural unit consists of three core parts: First, a precisely molecularly designed functional macrocyclic backbone with both rigidity and stability, featuring lateral covalently linked oxerocyclic butyl groups that provide specific and efficient reaction sites for subsequent crosslinking reactions without affecting the inclusion and slippage between the macrocycle and the main chain; second, a linear polymer backbone serving as the sliding axis, with macro-blocking end groups at both ends to effectively prevent ring molecule slippage and ensure the integrity and stability of the rotaxane structure during crosslinking and use; finally, using the ring-opening reaction of the oxerocyclic butyl groups as the crosslinking pathway, covalent bonding between macrocycles is achieved through mild and controllable cationic crosslinking, fixing the sliding rotaxane unit in situ within the three-dimensional network backbone, forming a slip-ring crosslinked network structure that combines covalent stability and supramolecular dynamics, achieving integrated and efficient preparation from molecular assembly to macroscopic material forming.

[0009] The beneficial effects of this invention are significant and multi-layered. At the structural construction level, through the molecular design of functionalized macrocycles of oxobutane and the synergistic strategy of "host-guest assembly-in-situ crosslinking locking," a high-density and high-stability rotaxane structure is achieved, ensuring a uniform crosslinked network structure with few defects and full utilization of the slip ring effect. At the macroscopic performance level, this unique topological structure endows the material with revolutionary dynamic mechanical behavior: when the material is subjected to external forces, the macrocyclic molecules can slide freely along the linear backbone, dispersing stress and dissipating energy in real time through molecular-scale movement. This fundamentally avoids problems such as stress concentration, chain segment breakage, and crosslinking point destruction in traditional fixed crosslinked networks, achieving a highly efficient synergy of high strength, high toughness, and high resilience. Specifically, while maintaining excellent structural stability and solvent resistance, the material possesses extremely low rebound hysteresis, minimal internal heat generation, extremely high fatigue life, and excellent dimensional stability, successfully solving the core contradiction in traditional crosslinked elastomers where it is difficult to simultaneously achieve "high modulus" and "high deformation," and "high resilience" and "low loss." In terms of material design and application expansion, this invention has strong controllability and scalability. By adjusting the macrocyclic structure, oxobutane substitution sites, linear main chain type and crosslinking degree, the network density, slip capability, glass transition temperature, mechanical loss and temperature stability can be finely controlled, which can meet the stringent requirements of various high-end application scenarios such as flexible electronic devices, wearable devices, high-frequency damping materials, dynamic seals and precision buffer structures.

[0010] In summary, this invention not only overcomes the key challenges of traditional slip-ring polymers in simultaneously achieving structural stability, crosslinking uniformity, and dynamic slip-ring effects from a molecular perspective, but also successfully develops a class of polyurethane slip-ring crosslinked network elastic material systems with well-defined structures, excellent performance, and strong designability through innovative molecular design and efficient network construction strategies. This provides new ideas and technical support for the development of next-generation high-performance supramolecular elastomers, intelligent dynamic materials, and high-end functional polymers, and has significant scientific value and broad industrialization prospects in fields such as advanced manufacturing, flexible electronics, precision instruments, and high-end equipment. (See attached figures.)

[0011] Figure 1 This is the infrared spectrum of a polyurethane slip ring cross-linked network elastic material;

[0012] Figure 2 This is the ultraviolet spectrum of a polyurethane slip ring crosslinked network elastic material;

[0013] Figure 3 Thermogravimetric analysis of polyurethane slip ring crosslinked network elastic material;

[0014] Figure 4 These are the GPC test results for polyurethane slip ring crosslinked network elastic materials;

[0015] Figure 5 It is the stress-strain curve of a polyurethane slip ring cross-linked network elastic material. Detailed Implementation

[0016] The following is in conjunction with the appendix Figure 1-5 The present invention will be further described as follows:

[0017] This invention belongs to the interdisciplinary field of polymer materials and supramolecular chemistry, specifically relating to a polyurethane slip-ring crosslinked network elastic material with a slip-ring effect. The invention uses a macrocyclic molecule with oxetane-functionalized side groups as the cyclic component of a rotaxane. Through host-guest inclusion interactions, it forms a rotaxane polymer with the linear backbone, followed by a ring-opening crosslinking reaction of the oxetane groups, constructing an interpenetrating network structure that combines a three-dimensional covalent network with a supramolecular slip-ring effect. Under mechanical stimulation, this material dissipates energy through the relative slippage of the ring molecules along the backbone, exhibiting high resilience and wide-temperature-range stability. It can be applied in fields such as flexible electronics, wearable devices, and high-performance damping materials.

[0018] S1. Synthesis of cyclic macromolecules

[0019] Pentafluorobenzonitrile (0.2 g, 1 mmol) was dissolved in 50 mL of tetrahydrofuran with carbazole-oxetane (0.3 g, 1 mmol) and NAH (0.1 g, 4 mmol). The mixture was reacted at room temperature under nitrogen protection for 24 h. The mixture was purified by column chromatography with petroleum ether / dichloromethane as the eluent to give 0.2 g of white solid.

[0020] The obtained product (0.2 g, 0.5 mmol), the S1 product (0.5 g, 0.5 mmol), and NAH (0.1 g, 4 mmol) were dissolved in 50 mL of tetrahydrofuran and reacted at room temperature for 24 h under nitrogen protection. The product was then purified by column chromatography using petroleum ether / dichloromethane as the eluent to give 0.4 g of a white solid.

[0021] The reaction equation is:

[0022]

[0023]

[0024] S2. Synthesis of end-capping groups

[0025] Under a nitrogen atmosphere, triphenylamine (2 g, 8.16 mmol) and N-bromosuccinimide (30 g, 168.5 mmol) were stirred at room temperature in anhydrous tetrahydrofuran (60 mL) for 24 hours. After filtering to remove the succinimide byproduct, the filtrate was concentrated. The crude product was purified by silica gel column chromatography (petroleum ether / dichloromethane) to obtain tris(4-bromophenyl)amine as a white solid (3.2 g, yield 80%). Subsequently, the obtained tris(4-bromophenyl)amine (1 g, 1.9 mmol), phenothiazine (0.6 g, 3.6 mmol), and anhydrous potassium carbonate (1.6 g, 11.6 mmol) were placed in a reaction flask, and cuprous chloride (0.07 g, 0.37 mmol) and 1,10-phenanthroline (0.06 g, 0.33 mmol) were added as a catalytic system. The mixture was refluxed in anhydrous DMF (60 mL) at 160°C for 24 hours. After cooling and filtration, the filtrate was concentrated and purified by column chromatography to obtain a white solid of triphenylamine-terminated carbazole derivative. Meanwhile, 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboronolan-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 stirred at 65°C for 12 hours in anhydrous acetone (30 mL) under the catalysis of tetrabutylammonium bromide (0.05 g, 0.15 mmol). After concentration, column chromatography (petroleum ether / ethyl acetate) was used to obtain a white solid borate ester derivative. Finally, the above borate ester (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 stirred at 80°C under a nitrogen atmosphere for 24 hours in the presence of potassium carbonate (0.05 g, 0.36 mmol) using toluene (12 mL) / ethanol (6 mL) / water (10 mL) as solvent. The reaction solution was concentrated and purified by column chromatography to obtain the target product as a white solid.

[0026] S3. Synthesis of Highly Elastic Polyrotaxane

[0027] The S2 product (5.9 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 4.7 g of grayish-white translucent elastomer.

[0028] The reaction equation is:

[0029]

[0030] S4. Synthesis of SRPU (Slip Ring Crosslinked Network Elastic Material)

[0031] The prepared rotaxane polymer was uniformly dissolved in THF to prepare a homogeneous solution of a certain concentration. The solution was then spin-coated or cast onto a clean substrate and placed under vacuum conditions to remove most of the solvent, thus obtaining a precursor film.

[0032] Based on the total mass of the above-mentioned rotaxane polymer, 3.0 wt% of the cationic initiator triphenylsulfonium hexafluorophosphate was added to the system, and the mixture was stirred thoroughly until the initiator was completely dissolved and uniformly dispersed. The above mixture was placed in a temperature-controlled reaction apparatus, and the crosslinking reaction temperature was strictly controlled at 50°C. The reaction was carried out at this temperature for 6 hours.

[0033]

[0034] Experimental testing of the present invention

[0035] This invention provides a systematic and mutually corroborating structural and performance characterization of the synthesized polyurethane slip-ring crosslinked network elastic material (SRPU), fully revealing its unique properties and comprehensive advantages from molecular structure to macroscopic function. In-situ monitoring of the reaction process using Fourier transform infrared spectroscopy confirmed that the significant –NCO characteristic absorption band of the isocyanate-terminated prepolymer at approximately 2270 cm⁻¹ decreased to below the detection limit after pre-assembly with the cyclic molecules and in-situ polymerization. Simultaneously, polyurethane characteristic absorption peaks appeared and intensified at 3330 cm⁻¹ (N–H stretching vibration), 1725 cm⁻¹ (urethane C=O stretching vibration), and 1530 cm⁻¹. This change directly proves that the –NCO groups have completely reacted to form the polyurethane network, and the characteristic peaks of the cyclic molecules remain stable before and after the reaction, indicating that the mechanically interlocked precursor structure is completely preserved under polymerization conditions. Further UV-Vis absorption spectroscopy analysis revealed that the characteristic absorption peaks of the π-conjugated skeleton of the cyclic molecules constituting the slip ring in the 300-350 nm range were retained in the final material.

[0036] The thermal stability of the material was evaluated using thermogravimetric analysis (TGA). Its initial decomposition temperature under nitrogen atmosphere was typically above 300°C. The thermogravimetric curve morphology indicated that the introduction of the slip ring unit did not introduce a new weak decomposition pathway, demonstrating the good synergy between the high thermal stability of the cyclic molecules and the polyurethane matrix, thus significantly broadening the material's high-temperature application window. Gel permeation chromatography (GPC) was used to track molecular weight evolution. The prepolymer exhibited a narrow, single-peak distribution, and its number-average molecular weight was consistent with the design value. The final material formed through in-situ locking showed a significant increase in the high-molecular-weight tail and a shift in peak position in its soluble fraction GPC spectrum, confirming the successful formation of a higher molecular weight crosslinked network structure. Furthermore, the molecular weight distribution data indicated that the polymerization process was controllable, which is beneficial for obtaining a material with a uniform structure.

[0037] In terms of macroscopic mechanical properties, uniaxial tensile tests conducted according to ASTM D412 standards demonstrate that the material achieves an excellent synergy between high elasticity and high strength. Its typical stress-strain curve exhibits high toughness characteristics, with a tensile strength reaching 50 MPa and a maximum strain exceeding 700%. This performance improvement is attributed to the slip ring structure acting as a dynamic and movable physical cross-linking point, which effectively transfers loads and dissipates energy during deformation, thereby avoiding premature stress concentration and failure at traditional rigid cross-linking points. This fundamentally optimizes the material's energy dissipation mechanism and damage resistance.

[0038] 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 polyurethane slip ring crosslinked network elastic material SRPU, characterized in that: Flexible polyurethane chains are passed through the cavities of macrocyclic molecules to form a polyrotaxane structure, which is then cross-linked through oxobutane rings to create a rotaxane polymer interpenetrating cross-linked network with a slip ring effect. The general structural formula is as follows: 。 2. The polyurethane slip ring crosslinked network elastic material SRPU according to claim 1, characterized in that: The linear backbone of the rotaxane polymer is a polyurethane backbone, with sterically hindered end-capping groups at both ends to prevent ring molecules from slipping off the backbone.

3. The polyurethane slip ring crosslinked network elastic material SRPU according to claim 1, characterized in that: The cyclic molecule is a macrocycle with oxetane side groups, and the oxetane group is connected to the cyclic molecule backbone by a flexible alkyl chain.

4. The polyurethane slip ring crosslinked network elastic material SRPU according to claim 1, characterized in that: The interpenetrating network structure was prepared by a cationic ring-opening crosslinking reaction. Based on the mass of the rotaxane polymer, 3.0 wt% of triphenylsulfonium hexafluorophosphate was added as a cationic initiator, and crosslinking was carried out at 50 °C for 6 hours to open the oxocyclic butyl group and form a covalent crosslinked network.

5. A polyurethane slip ring crosslinked network elastic material and its preparation method according to claim 1 or 4, characterized in that: In the interpenetrating cross-linked network structure, the ring molecules are interconnected through the ring-opening cross-linking of the oxocyclic butyl group, while the ring molecules can still slip relative to each other along the main chain, exhibiting a slip ring effect.

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