A topological polymer

Abstract

The application relates to a topological polymer, and the structure is shown in general formula I. A self-repairing elastomer is successfully prepared, and the contradiction between the processing performance and the mechanical performance is decoupled. A new dynamic amidine-urea bond and oxime-carbamate bond coupling locking unit is designed to construct an elastomer with high performance and good processing performance.

Description

Technical Field

[0001] This invention belongs to the field of polymers, and specifically relates to a polymer with a topological structure. Background Technology

[0002] Thermosetting plastics and thermoplastic plastics are two traditional classifications of polymers. Thermosetting materials are robust and stable, typically synthesized through covalent cross-linking of polymer chains, forming a network throughout the sample. However, this stability, a hallmark of thermosetting materials, comes at the cost of being unrecyclable through traditional methods such as direct mechanical reprocessing. With the increasing demand for sustainable materials, prioritizing polymers that combine the mechanical properties of thermosetting plastics with the processability and recyclability of thermoplastic plastics can effectively reduce the carbon footprint of the plastics industry.

[0003] Significant efforts have been made to develop reversible crosslinking in covalent adaptive networks (CANs), enabling the disruption and recombination of connections between polymer chains, thus blurring the lines between thermoset and thermoplastic plastics. Despite the widespread use of various dynamic covalent bonds in thermoset materials, achieving CANs with excellent processability and high mechanical strength remains a challenge in polymer science. This is due to the fundamental trade-off between sufficient chain mobility for dynamic exchange and a sufficiently stable structure for robust mechanical properties. Therefore, discovering innovative dynamic chemical strategies or topological network designs that effectively reconcile this dichotomy is a top priority for polymer researchers. Since Wudl's groundbreaking report in 2001 on thermally repairable networks utilizing the Diels-Alder reaction, many other reversible processes (such as urea bonds, boron-oxygen bonds, and disulfide bonds) have been explored to address the processing challenges associated with thermoset polymers. Yan's research group has been dedicated to designing sophisticated micro-topological networks to tune macroscopic material properties. Recently, in 2022, they proposed a polymer network inspired by interwoven fibers, successfully balancing dynamic behavior and robust stability using Cu(I) ion-coordinated crosslinking. While these dynamic responses and network designs endow dynamic polymers with adaptive and responsive properties, the inherent contradiction between the mechanical properties and processability of the materials remains. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a topological structure polymer, particularly a topological structure polymer with four-arm dynamic crosslinking points.

[0005] This invention provides a polymer represented by the following general formula I.

[0006]

[0007] Where x = 12 to 28; and the wavy line represents a repeating chain segment.

[0008] Preferably, the polymer is a topological network structure polymer with four arms of dynamic crosslinking points of adjacent dynamic bonds, having dynamic amidine-urea bonds and oxime-carbamate bonds coupled and locked units.

[0009] This invention provides a method for preparing the polymer, comprising:

[0010] An alcohol and a diisocyanate are mixed and reacted under a protective gas to obtain a prepolymer. Then, a tetrafunctional crosslinking agent and a solvent are added, and the reaction is carried out to obtain a polymer.

[0011] The alcohol is an alcohol that has undergone drying treatment.

[0012] Preferably, the alcohol is a diol; the diol is polytetrahydrofuran; the M of the diol... n =1000-2000gmol -1 The diisocyanate is isophorone diisocyanate (IPDI); the solvent is tetrahydrofuran or N,N-dimethylformamide.

[0013] Preferably, the tetrafunctional crosslinking agent contains two oximes and two amines.

[0014] More preferably, the tetrafunctional crosslinking agent is diaminoglyoxime (DAG).

[0015] Preferably, the reaction temperature under the protective gas is 80-110℃, and the reaction time is 2-4 hours; wherein the protective gas is at least one of nitrogen and argon.

[0016] Preferably, the addition of a tetrafunctional crosslinking agent and a solvent, followed by a reaction, is carried out at a temperature of 40-60°C for 24-48 hours.

[0017] Preferably, the molar ratio of the alcohol to the diisocyanate is (1-5):(1-3); and the molar ratio of the prepolymer to the tetrafunctional crosslinking agent is (1-9):(1-6).

[0018] More preferably, the molar ratio of the prepolymer to the tetrafunctional crosslinking agent is 4:3 to 2:1.

[0019] This invention provides an application of the polymer in the field of remodelable processing.

[0020] This invention proposes a novel strategy for constructing polymer topological networks: dynamic crosslinking coupled locking units, rather than the usual independent dynamic covalent crosslinking or supramolecular crosslinking, to improve mechanical properties at ambient temperature while inducing a rare melting point reduction—a phenomenon seldom seen in previous polymer chemistry research. The key to the topological design is the tetrafunctional crosslinking agent diaminoglyoxime (DAG), where two oximes and two amines react with isocyanates to generate dynamic covalent oxime-carbamate bonds and hydrogen-rich dynamic covalent amine-urea bonds, thus constructing a crosslinked structure—a network with triple dynamic bonds. At room temperature, the dynamic bonds are in a frozen state, which is beneficial for significantly improving the mechanical properties of DAG-PU elastomers by increasing the crosslinking density. As the temperature increases, the density of integrated dynamic bonds at the crosslinking points becomes higher, making dissociation more likely and causing the network to rapidly disintegrate into a prepolymer, thus facilitating flow. Overall, the design with synergistically multiple dynamic covalent and non-covalent locking units eliminates the trade-off between polymer mechanical strength and reprocessing properties. Furthermore, compared to networks with lower crosslinking density, networks with higher crosslinking density exhibit significantly enhanced tensile strength and damping. Moreover, these networks demonstrate excellent toughness and resistance to deformation and creep under sustained loads before significant bond dissociation.

[0021] Beneficial effects

[0022] This invention successfully prepared a self-healing elastomer, resolving the contradiction between processing performance and mechanical properties. A novel dynamic amidine-urea bond and oxime-carbamate bond coupling locking unit was designed to construct a high-performance elastomer with good processing properties.

[0023] DAG concentrates triple dynamic bonds in a single locked unit, rather than forming typically independent covalent or non-covalent crosslinks, to avoid excessive crosslinking sites and ensure high polymer chain fluidity. Simultaneously, adjacent dynamic bonds induce a neighboring group effect, catalyzing the dynamic dissociation of oxime-carbamates. This unit exhibits high mechanical properties and reversibility. This novel molecular design with a locked unit topology coupling multiple bonds and multiple crosslinking sites effectively resolves the long-standing contradiction between high tensile strength and processability in materials. Therefore, this invention proposes a unique molecular design that couples multiple dynamic bonds into a single locked unit to simultaneously modulate the chemical and topological structure of the polymer, providing a powerful new principle for regulating material properties. Attached Figure Description

[0024] Figure 1Topological design for DAG-PU elastomers to decouple processability and mechanical properties; including chemical structures and cartoon representations of prepolymer monomer A and crosslinking agent monomer B, as well as hydrogen bonding units; schematic diagrams of dynamic oxime-carbamate bond and dynamic amine-urea bond mechanisms; schematic diagrams of robust mechanical properties of the polymer network at room temperature and dynamic properties at high temperature;

[0025] Figure 2 Basic performance characteristics of DAG-PU elastomers; (a) Fourier transform infrared absorption spectra of DAG-PU-1, DAG-PU-2, and DAG-PU-3; (b) Variable-temperature infrared spectroscopy to investigate the effect of temperature on the dynamic covalent bond dissociation in DAG-PU-3; (c) Swelling ratio curves of DAG-PU-1, DAG-PU-2, and DAG-PU-3 in THF; (d) Stress-strain curves of DAG-PU-1, DAG-PU-2, and DAG-PU-3 recorded at a deformation rate of 50 mm / min; (e) Calculation of the properties of DAG-PU-1, DAG-PU-2, and DAG-PU-3 based on the stress-strain curves. (f) Toughness and Young's modulus of DAG-PU-3; (g) Storage modulus and loss modulus of DAG-PU-1, DAG-PU-2 and DAG-PU-3 recorded by frequency scanning at 30°C; (h) Cyclic tensile test of DAG-PU-1, DAG-PU-2 and DAG-PU-3 with a maximum strain of 100%; (h) Calculation of dissipative toughness ratio of DAG-PU-1, DAG-PU-2 and DAG-PU-3 in five consecutive loading-unloading tensile tests; (i) Damping capacity of DAG-PU-1, DAG-PU-2 and DAG-PU-3 calculated based on cyclic tensile test;

[0026] Figure 3 Thermal properties of DAG-PU elastomers; (a) Tanδ curves of DAG-PU-1, DAG-PU-2, and DAG-PU-3 with temperature sweeps using rheological testing; solid-liquid transition occurs at temperatures of approximately 150 to 130 °C; (b) Summary of glass transition temperature and solid-liquid transition temperature data for DAG-PU-1, DAG-PU-2, and DAG-PU-3; (c) Viscosity-temperature curves for DAG-PU-1 and DAG-PU-3; (d) Comparison of mechanical and processing properties of DAG-PU-1, DAG-PU-2, and DAG-PU-3;

[0027] Figure 4 To gain a deeper understanding of the structure-property relationship of DAG-PU elastomers; (a) the conversion rate of compound b at equilibrium with or without amidine-urea bonds (conversion rate = ([b]0 - [b])). t ) / ([b]0-[b] eq ), [b]0: the initial concentration b, [b]t The concentration of b at time t, [b] eq (b) Equilibrium concentration of DAG-PU-1; (b) Normalized stress relaxation curves of DAG-PU-1, DAG-PU-2 and DAG-PU-3 measured at 60 °C; (c) Normalized stress relaxation curves of DAG-PU-1, DAG-PU-2 and DAG-PU-3 measured at 130 °C; (d) Relaxation time fitted to the Arrhenius equation; (e) Strain scan curves of DAG-PU-1, DAG-PU-2 and DAG-PU-3 at 130 °C; (f) Creep recovery curves of DAG-PU-1, DAG-PU-2 and DAG-PU-3 with the same stress level at 100 °C;

[0028] Figure 5 The molecular formula for DAG-PU is given, with x values ​​ranging from approximately 12 to 28.

[0029] Figure 6 (a) Schematic diagram of the DAG-PU reprocessing process and the mechanism of dynamic oxime-carbamate bonds and amidine-urea bonds. (b) FTIR spectra, (c) stress-strain curves, and (d) temperature scanning rheological analysis of the original and reprocessed DAG-PU-3 samples, showing that the chemical and mechanical integrity was preserved. Detailed Implementation

[0030] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0031] Unless otherwise stated, all tests were performed at room temperature. Nuclear magnetic resonance (NMR) spectra were recorded using a Bruker Avance 600 spectrophotometer, with deuterated solvents as locks and residual solvents or TMS as internal references.

[0032] FTIR spectra were recorded on a Nicolet 8700 spectrometer. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra were recorded on a Thermo Fisher Scientific Nicolet iS50 spectrometer with an ATR accessory.

[0033] The surface morphology of the samples was studied using a Dimension FastScan / lcon atomic force microscope (AFM) with an aluminum reflective coated silicon cantilever probe (HQ:NSC19 / Al BS).

[0034] The glass transition temperature was obtained by dynamic thermodynamic analysis on a DMA1 (Mettler-Toledo) analyzer. Rectangular samples (approximately 1 mm (T) × 5 mm (W) × 10 mm (L)) were tested at a frequency of 1 Hz and a strain of 0.1%. The temperature range was from -120 °C to 80 °C in 5 °C min increments. -1 The heating rate. Calculate T from the maximum value of tanδ. g value.

[0035] Thermogravimetric analysis (TGA) was used to study dynamic thermal stability using a thermogravimetric analyzer (Libra / 209F1). The analysis was conducted under a nitrogen atmosphere at 10 °C / min. -1 The heating rate was used to evaluate the synthesized copolymers at 600 °C.

[0036] Rheological experiments were conducted using an Anton Paar MCR702 stress-controlled rheometer with an 8 mm parallel plate attachment. Normalized stress relaxation experiments were performed in strain-controlled (10% strain) mode. The relaxation modulus (G) was normalized to its initial value (G0). a E represents the activation energy, τ0 represents the characteristic relaxation time at 1 / e, R is the gas constant, T is the temperature relaxation time, and τ(T) corresponds to the time it takes for the modulus to relax to 1 / e. a It can be calculated by multiplying the slope obtained by plotting ln(τ)-1000 / T by a constant R. The characteristic relaxation time (τ*) is defined as the time required for G / G0=1 / e, and has an exponentially decaying function: G(t)=G0 exp(-t / τ*).

[0037] The mechanical properties of the samples were evaluated using an MTS E42 tensile testing machine equipped with a 100N force sensor. The crosshead was adjusted to 50mm min. -1 Uniaxial tensile testing was performed. A rectangular tensile bar (1 mm (T) × 3 mm (W) × 20 mm (L)) cut from a large film was used. The deflection rate for uniaxial tensile measurement was 50 mm / min. At least three samples were tested for each specimen, and the average value was taken. If not specified, cyclic tensile testing was performed at 50 mm / min. -1 The stretching rate and 50mm min -1 The recovery rate is determined. Energy dissipation is calculated by the area enclosed by the integral cyclic stretching curve. Damping capacity is defined as the ratio of dissipated energy (the area enclosed by the loading and unloading curves) to the loaded energy (the area enclosed by the loading curve).

[0038] Example 1

[0039] Polytetrahydrofuran (M n=1000)(PTMEG, 24 g, 24 mmol) was added to a glass reactor equipped with a magnetic stirrer and dried under vacuum at 110 °C for 2 hours. After cooling to 70 °C, isophorone diisocyanate (IPDI, 10.68 g, 48 mmol) was added dropwise to the reactor and heated to 110 °C for 2 hours under a nitrogen atmosphere. After cooling to 60 °C, diaminoglyoxime (DAG, 1.42 g, 12 mmol) and THF (265 mL) were added and reacted for 24 hours, with a ratio of A:B = 2:1. The solution after the above reaction was completed was poured into a tetrafluoroethylene mold and dried to obtain DAG-PU-1.

[0040] The preparation method of DAG-PU-2 is the same as that of DAG-PU-1, except that the amount of isophorone diisocyanate added is 54 mmol, 12.00 g and the amount of diaminoglyoxime added is 15 mmol, 1.77 g, which corresponds to the ratio of A:B = 8:5.

[0041] The preparation method of DAG-PU-3 is the same as that of DAG-PU-1, except that the amount of isophorone diisocyanate added is 60 mmol, 13.34 g and the amount of diaminoglyoxime added is 18 mmol, 2.13 g, which corresponds to the ratio of A:B = 4:3.

[0042] Design, synthesis, structural characterization, and mechanical properties of DAG-PU.

[0043] Polyurethane is widely used in the preparation of elastomer materials due to its mechanical properties. Therefore, this invention selected PU as the polymer component. A DAG-PU network was synthesized via one-pot condensation polymerization using commercially available polytetrahydrofuran (PTMEG), isophorone diisocyanate (IPDI), and diaminoglyoxime (DAG). PTMEG was chosen as the soft segment because its flexible chain facilitates chain movement, thus enabling better self-healing. IPDI was chosen as the hard segment because its large structure can inhibit crystallization and increase chain fluidity for better self-healing. Due to the spatial influence of the cyclohexyl ring, the IPDI-derived carbamate exhibits relatively high dynamism, which further promotes covalent network recombination. DAG is crucial in the design of DAG-PU; its two oxime groups can form reversible dynamic bonds with the isocyanate, while its two amino groups can form dynamic amidine-urea bonds, providing numerous hydrogen bonds that dissipate energy during mechanical deformation and result in high toughness. The simultaneous presence of multiple dynamic bonds imparts processability, while relatively strong chemical crosslinking ensures stable mechanical properties and structural stability (e.g., ...). Figure 1 (As shown).

[0044] The structure of the polymer network was first investigated using Fourier transform infrared spectroscopy (FTIR) in attenuated total reflectance (ATR) mode. Figure 2As shown in figure a, the 2275 cm⁻¹ corresponding to the -N=C=O group -1 The nearby peaks disappear completely within the polymer network, indicating that IPDI and the formed monomers with -N=C=O groups have reacted completely. (3329 cm⁻¹) -1 and 1717cm -1 The peaks at these locations were assigned to stretching vibrations of NH and C=O, respectively, consistent with the formation of urethane groups. Simultaneously, peaks at 1533 cm⁻¹ belonging to -C=N⁻ and NO were observed in the spectrum. -1 and 954cm -1 The peak indicates the presence of DAG in the polymer network. To elucidate the dynamic properties of DAG-PU, Fourier transform infrared (FTIR) spectroscopy was performed as a function of temperature. FTIR results at different temperatures revealed the integrity of the oxime-carbamate bonds in DAG-PU at room temperature. Furthermore, when the temperature was increased to 100°C, a small portion of free isocyanate (2275 cm⁻¹) was observed. -1 It will separate from the oxime-carbamate bond. Figure 2 b). Above 130°C, the oxime-carbamate bonds within the DAG-PU undergo significant dissociation. The formed network structure was then confirmed by swelling tests in THF. The results showed that the sample exhibited significant swelling behavior in THF. Figure 2 As shown in Figure c, the sample size increased significantly after soaking in THF for 30 minutes. In this case, the highly cross-linked network in DAG-PU-3 limits the network expansion, which explains its low swelling ratio. In contrast, DAG-PU-1 with a low cross-linking density exhibits a higher swelling ratio, which also demonstrates the design of this invention.

[0045] The mechanical properties of three polymers were investigated through tensile testing to reveal the differences resulting from increased crosslinking degree. For example... Figure 2 As shown in Figure d, the stress-strain curves of all samples exhibit typical rubber-like tensile behavior. DAG-PU-3 exhibits the highest modulus and strength due to its highest crosslinking agent content and highest hydrogen bond density. The Young's moduli of DAG-PU-1, DAG-PU-2, and DAG-PU-3 are 3.8±1.0, 12.3±2.0, and 29.7±0.9 MPa, respectively, and the maximum stresses are 19.5±1.6, 28.6±8.1, and 45.0±1.7 MPa, respectively. The tensile strength at break decreases with increasing crosslinking points, at 1039.7±32.8%, 717.3±23.3%, and 567.3±37.8%, respectively. Notably, due to its good strength and elongation, compared with DAG-PU-2 (94.9±15.6 MJ / m), DAG-PU-3 also shows high strength. 3 ) and DAG-PU-1 (51.7±18.2MJ / m 3Compared to other materials, DAG-PU-3 exhibits the highest toughness, at 105.5 ± 12.9 MJ / m. 3 ( Figure 2 e). These results indicate that the material exhibits higher toughness due to increased cross-linking. The frequency scanning results are consistent with the tensile test results. Figure 2 f). The storage modulus of DAG-PU-3 is higher than that of DAG-PU-1 and DAG-PU-2, indicating that the network with higher crosslinking density has a more robust characteristic.

[0046] Subsequently, cyclic stress-strain tests were conducted on three different samples with a maximum strain range from 100% to 500%. The quantitative analysis of energy dissipation was summarized in... Figure 2 In h, it is noteworthy that all three networks exhibit considerable hysteresis, with the amplitude of the hysteresis loop increasing with the degree of crosslinking. This improvement is primarily attributed to the dissociation of hydrogen bonds prevalent in the polyurethane segments. Damping capacity is defined as the ratio of energy dissipation to input energy, summarized from calculations based on cyclic tensile tests. Figure 2 The variation in damping capacity may be related to the effect of crosslinking on the energy dissipation mechanism. The results show that the damping capacity decreases with increasing strain levels applied to samples with different crosslinking densities. This may be due to the tendency of chemically crosslinked networks to primarily recover their original dimensions through elastic deformation under high strain.

[0047] DAG-PU's thermal properties, self-healing properties, and reprocessability

[0048] To date, the advantages of tetrafunctional crosslinking in ensuring the mechanical properties of materials have been confirmed. Further research has focused on enhancing their processing properties. DMA studies have shown that all DAG-PU-1–3 possess two distinct glass transition temperatures (T0). g The transformation observed in DAG-PU at approximately -60°C is attributed to the relaxation of the soft polytetrahydrofuran segments, independent of the content of rigid crosslinks in the network. Notably, DAG-PU-1–3 also exhibit a second T… g The measurement range is -15.2 to 33.8℃. g The value shows an upward trend because as more hard segments are added, the network becomes denser, making it more difficult for polymer segments to move. To better understand the temperature dependence of DAG-PU viscoelasticity, G' and G'' were investigated in an extended temperature scan. The temperature corresponding to the point where the loss factor tangent (tanδ) equals 1 represents the transition temperature (T) of the material from the rubbery state to the viscous state. f Generally, this temperature can be approximated as the lower limit of the material's reprocessing temperature range. When the viscous response dominates the viscoelastic behavior, T is observed. fThe values ​​recorded for DAG-PU-1, DAG-PU-2, and DAG-PU-3 showed a downward trend, with corresponding values ​​of 153.8℃, 147.7℃, and 131.3℃, respectively. Figure 3 a) indicates that relaxation accelerates with increasing dynamic bond concentration in the DAG-PU. At T f Below, the elastic plateau of DAG-PU-3 is not obvious, but the elastic plateau of DAG-PU-1 is very obvious, which means that DAG-PU-3 has a more dynamic network than the control group. In T f Above, G' and G” for all three samples decreased with increasing temperature, indicating eventual relaxation. The glass transition temperatures (T) of DAG-PU-1, DAG-PU-2, and DAG-PU-3 are shown in the table. g ) and solid-liquid transition temperature (T f The specific data has been summarized in Figure 3 b in. Figure 3 c clearly illustrates the alternating viscosity trends of DAG-PU-1 and DAG-PU-3. The significant transition in complex viscosity occurs near the solid-liquid transition point of the materials. DAG-PU-3 exhibits higher crosslinking density and complex viscosity at low temperatures. However, when heated to the dissociation temperature, the higher content of dynamic bonds in DAG-PU-3 causes the polymer network to rapidly collapse through dissociation, decomposing into easily mobile small molecular chains, resulting in a significant decrease in the complex viscosity of DAG-PU-3. This result provides intuitive evidence for the property of highly crosslinked materials being more easily processed.

[0049] Structure-property relationship of DAG-PU.

[0050] Tensile and thermal analyses demonstrated that increasing the degree of crosslinking significantly improves the mechanical and reprocessing thermal properties of DAG-PU. However, it remains interesting to understand how highly crosslinked polymers affect mechanical behavior and how they lower the heat treatment solid-liquid transition temperature while still improving the mechanical properties of DAG-PU. To address these questions, rheological experiments and... 1 HNMR spectroscopy analysis was used to comprehensively understand the structure-property relationship of DAG-PU. To investigate the reversibility of the DAG unit, a small molecule model containing amidine-urea and oxime-carbamate bonds was synthesized and mixed with benzyl isocyanate in deuterated DMSO-d6. The exchange reaction was monitored by NMR, and its equilibrium rate was calculated. Equilibrium was reached in approximately 36 hours at 25°C. Figure 4 a) The exchange reaction without the amino group only reached equilibrium after 50 hours. Therefore, it can be inferred that the neighboring group effect in the DAG group leads to a higher reversibility of the oxime-carbamate bond compared to the oxime without the amino group. This experiment clearly demonstrates the reversibility of the amidine-urea bond, thereby promoting the dynamic recombination of the DAG-PU chain.

[0051] Stress relaxation and creep experiments can also yield valuable structural information about the network. Bond dissociation in the CAN leads to significant stress relaxation, and the characteristic relaxation time (τ*) as a function of temperature is an important aspect describing its rheological behavior. Figure 4 As shown in b, the smallest relaxation was observed among the three sample groups. Notably, DAG-PU-3 showed no relaxation after 3000 seconds at 60°C, while DAG-PU-1 and DAG-PU-2 experienced slightly faster stress relaxation behavior. Subsequently, when the same stress was applied to all three samples at 130°C, significant changes were observed. Figure 4 c). The results show that DAG-PU-3 relaxes rapidly within 100 seconds, which is in stark contrast to the results obtained at 60 °C. Given the dependence of the relaxation behavior of polymer networks on their respective crosslinks, the results reinforce the view that DAG-PU-3 has a higher density of dynamic crosslinks compared to DAG-PU-1 and DAG-PU-2. As mentioned earlier, stress maintenance at 60 °C is commendable until bonds begin to dissociate extensively, and then stress relaxation accelerates with increasing temperature. It is assumed that dynamic crosslink activation occurs around 130 °C, but it is speculated that stress release is not complete even after extensive bond dissociation, which may be attributed to the presence of partial crosslinks. The conventional 1 / e method for stress relaxation experiments was first used to determine the time when τ is the normalized stress reduced to 36.8% (1 / e) of the initial value. ln(τ) shows a good linear relationship with 1000 / T. Figure 4 e) The apparent activation energies calculated from their slopes were 97.42 kJ / mol, 87.72 kJ / mol, and 76.98 kJ / mol (for DAG-PU-1, DAG-PU-2, and DAG-PU-3, respectively). Increasing the number of oxime carbamate bonds enhanced the temperature sensitivity of dynamic exchange. Similarly, increasing the number of crosslinking points decreased the temperature sensitivity of CAN. In this study, the number of dynamic bonds and crosslinks were increased simultaneously, combined with the catalytic effect of the neighboring group effect, indicating that the synergistic effect of these two factors led to a decrease in activation energy with increasing DAG. Since this activation energy is related to the dissociation of dynamic crosslinks in DAG-PU, the lower activation energy of DAG-PU-3 indicates that its dynamic crosslinks can be more easily broken with increasing temperature, thereby improving its processability. The viscoelastic behavior of the three samples was studied using strain scanning tests. The changes in G' and G” with increasing oscillation amplitude reflect the integrity of the network. Figure 4As shown in Figure e, under 5.25% oscillatory strain, G' and G” of DAG-PU-3 intersect first, indicating that the DAG-PU-3 network is damaged due to extensive dynamic bond dissociation. On the other hand, under the same strain conditions, G' and G” of DAG-PU-1 show smaller changes at larger oscillation amplitudes because its lower dynamic bond density allows it to maintain the network. Rheological experiments show that the network remains elastic even under large strains at temperatures below the point of extensive dissociation of dynamic crosslinks. Conversely, smaller strains easily damage the network once significant bond dissociation occurs. To verify the stability of the polymers before network dissociation, creep and recovery experiments were conducted on DAG-PU-1, DAG-PU-2, and DAG-PU-3 under external loads of 50℃ and 100℃, respectively, and 800 Pa. DAG-PU-3 also maintains its excellent creep resistance at 100℃, with a creep strain of only 0.15%. These creep strain values ​​are almost comparable to those exhibited by the static network. It has been noted that the oxime-carbamate and amidine-urea bonds in DAG-PU have been shown to undergo significant dissociation reactions at 100°C. Figure 4 f). Therefore, the dynamic chemistry of DAG-PU is expected to be active, but at a very low level during the 100°C creep test. This is also confirmed by the network's creep recovery behavior at 100°C, as the strain did not fully recover 300 seconds after stress relief. However, considering the negligible creep strain and low residual strain, the triple dynamic bond dissociation rate is considered sufficiently low to almost prevent creep at 100°C. This study compares the decoupling of the mechanical properties and thermal processing characteristics of dynamic polymer networks through topology design. The fundamental insights gained from this study are expected to guide the development of high-performance, easily processable elastomers through topology network design strategies.

[0052] Applications of DAG-PU in reshaping and processing

[0053] The processability of DAG-PU-3 was studied through cyclic remodeling experiments, demonstrating its practical performance in the field of recycled elastomers. Figure 6This paper describes the reprocessing process of DAG-PU-3 samples, highlighting the mechanism of heat-activated dynamic bonds. The original DAG-PU-3 samples were cut into small pieces and compressed at 110°C with a pressure of 5 MPa for 10 minutes to obtain reshaped samples. Unlike self-healing properties, processability places more stringent requirements on the dynamic properties of crosslinking. This process was repeated three times. As shown in the figure, the original and reshaped DAG-PU-3 samples exhibited almost identical FTIR spectra, indicating that chemical integrity was maintained even after three reprocessing cycles. Furthermore, tensile tests and rheological temperature scanning were performed on the reprocessed DAG-PU-3, demonstrating its excellent reprocessability in maintaining mechanical properties (including storage modulus and toughness). The good reprocessability of DAG-PU-3 implies that the tetrafunctional crosslinking agent possesses good dynamic properties, showing promising application prospects in the field of recyclable elastomers.

Claims

1. A polymer represented by general formula I, Where n = 12 - 28.

2. The polymer according to claim 1, characterized in that, The polymer is a topological network structure polymer with four arms of dynamic cross-linking points.

3. A method for preparing the polymer of claim 1, comprising: An alcohol and a diisocyanate are mixed and reacted under a protective gas to obtain a prepolymer. Then, a tetrafunctional crosslinking agent and a solvent are added, and the reaction is carried out to obtain a polymer.

4. The preparation method according to claim 3, characterized in that, The alcohol is a diol; the diol is polytetrahydrofuran; the M of the diol n =1000~2000g mol -1 The diisocyanate is isophorone diisocyanate (IPDI); the solvent is tetrahydrofuran or N,N-dimethylformamide.

5. The preparation method according to claim 3, characterized in that, The tetrafunctional crosslinking agent contains two oximes and two amines.

6. The preparation method according to claim 5, characterized in that, The tetrafunctional crosslinking agent is diaminoglyoxime (DAG).

7. The preparation method according to claim 3, characterized in that, The reaction is carried out at a temperature of 80–110°C for 2–4 hours under the protective gas; wherein the protective gas is at least one of argon and nitrogen.

8. The preparation method according to claim 3, characterized in that, The process involves adding a tetrafunctional crosslinking agent and a solvent, followed by a reaction at a temperature of 40-60°C for 24-48 hours.

9. The preparation method according to claim 3, characterized in that, The molar ratio of the alcohol to the diisocyanate is (1-5):(1-3); the molar ratio of the prepolymer to the tetrafunctional crosslinker is (1-9):(1-6).

10. The application of the polymer of claim 1 in the field of remolding processing.

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