Quantitative characterization method for freezing transition temperature of covalent adaptive network topology

Abstract

The invention relates to a quantitative characterization method for topological freezing transition temperature of a dynamic adaptive network (CANs), and the method comprises the steps: fitting a dielectric modulus imaginary part of the CANs under variable temperature and variable frequency through a Havriliak-Negami equation, achieving the quantitative analysis of the dielectric relaxation process of the CANs, and obtaining the average dielectric relaxation time of the CANs at different temperatures. Dielectric relaxation is subjected to isothermal division, the dielectric relaxation time change rate (tau) of the CANs in an isothermal interval is calculated, tau reaches the maximum value at the Tv position, and obvious inflection point temperature appears on a change curve of the dielectric constant of the CANs along with the temperature, namely the Tv of the CANs. The effectiveness of the method disclosed by the invention is verified in ionic, free radical and synergistic CANs with Tv higher than Tg and silyl ether CAN with Tv lower than Tg, and a quantitative characterization strategy is provided for researching the CANs.

Description

Technical Field

[0001] This invention belongs to the field of covalent adaptive network materials technology, and specifically relates to a quantitative characterization method for the topology freezing transition temperature of covalent adaptive networks. Background Technology

[0002] Thermosetting plastics play a crucial role in modern industry, with a global annual production of approximately 65 million tons. The inherent properties of covalent crosslinking endow thermosetting materials with excellent structural stability, heat resistance, chemical resistance, and high mechanical properties. However, this often comes at the cost of their reprocessing and recycling capabilities, which significantly limits their applications and exacerbates the global plastic pollution burden. The emergence of covalent adaptive networks (CANs) offers a new approach to addressing this issue. CANs not only possess the excellent properties of thermosetting materials but also exhibit outstanding reprocessing and recycling performance due to the reversible dissociation and recombination of dynamic covalent bonds. Topological freezing transition temperature (T0) v The temperature at which CAN topology is rearranged is defined and is closely related to the processing and recycling temperatures, safe operating temperatures, and other performance and application characteristics of CANs. Therefore, T... v Quantitative and accurate measurement is crucial for the design and development of CANs, but certain challenges remain.

[0003] Based on different dynamic exchange mechanisms, CANs can be divided into associative and dissociative types. Researchers such as Leibler proposed the concept of Vitrimer and defined a viscosity of 10... 12 The temperature of Pa s is used as T v Reference temperature. Vitrimers are a typical class of associated CANs. There are reports of using rheometers or dynamic thermomechanical analysis to test the TV of CANs via stress relaxation extrapolation or thermal expansion methods. v However, during the test, the sample is susceptible to localized external forces such as shear force or pre-tension, which affect the breakage and rearrangement of the dynamic cross-linked network, and thus affect the measured T. v The accuracy of the test is questionable. In thermal expansion testing, samples are prone to irreversible deformation, destroying their original morphology. Some functional components, such as aggregate-induced luminescent groups, are used as fluorescent probes to detect the T-values ​​of CANs. v The breaking and recombination of dynamic bonds causes varying degrees of aggregation of fluorescent groups within the network, leading to significant changes in fluorescence intensity before and after network rearrangement. This method requires molecular chain motion and is typically applicable to T... v Higher than T g The CANs system. The introduction of functional fluorescent components may not reflect the true T of CANs. vIt is worth noting that the above methods have only been validated in associative CANs; their effectiveness in dissociative CANs has not yet been reported. In summary, there is currently no simple and universal characterization method to achieve accurate representation of the intrinsic T values ​​of CANs. v Non-destructive testing. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a quantitative characterization method for the topology freeze transition temperature of covalent adaptive networks. This method mainly utilizes dielectric analysis to achieve the T-value of CANs. v Quantitative and non-destructive testing without the need to introduce additional components or external forces.

[0005] This invention provides a quantitative characterization method for the topology freezing transition temperature of covalent adaptive networks, comprising the following steps:

[0006] (1) The dielectric properties of the CANs samples were measured at different temperatures and frequencies using a broadband dielectric spectrometer, and temperature-frequency domain dielectric spectrum curves were obtained. The dielectric constant as a function of temperature curve was obtained at the topological freezing transition temperature of the covalently cross-linked polymer network (T). v A step-like change occurred;

[0007] (2) The temperature-frequency domain dielectric spectrum curve is fitted with the Havriliak-Negami (HN) equation. If strong dielectric polarization occurs, the imaginary part of the dielectric constant is converted into the imaginary part of the dielectric modulus by the equation, and then the HN equation is used for fitting to obtain the fitted dielectric spectrum and dielectric relaxation time τ at different temperatures, so as to realize the quantitative analysis of the dielectric relaxation process of CANs.

[0008] (3) Dielectric relaxation process is divided into isothermal regions, and the rate of change of dielectric relaxation time in the isothermal gradient region is calculated by equation.

[0009] (4) The activation energy of first-order or second-order relaxation is calculated by fitting the reciprocal of τ with respect to temperature obtained in step (2) using the Arrhenius equation or the Vogel-Fulcher-Tammann equation. The results show that the fitted curve is in the range of T. v A turning point occurred at this point, validating the quantitative dielectric characterization of T. v The effectiveness;

[0010] Preferably, the CANs samples in step (1) include associative and dissociative types.

[0011] Preferably, the CANs samples in step (1) include ionic, radical, and co-occurring types.

[0012] Preferably, the dielectric constant curve in step (1) changes with temperature in a stepwise manner near the phase transition temperature, including the glass transition and topological freezing transition.

[0013] Preferably, the temperature range in step (1) is -160 to 400°C; the frequency range is 10. -6 Hz~10 9 Hz.

[0014] Preferably, the equation for transforming the imaginary part of the dielectric constant into the imaginary part of the dielectric modulus in step (2) is: Where M* is the dielectric modulus and M″ is the imaginary part of the dielectric modulus.

[0015] Preferably, the HN equation in step (2) is: and Where ε * The complex permittivity under the HN model; Δε=ε t -ε ∞ ;ε t ε ∞ τ is the dielectric constant of the sample before and after relaxation; ω is the angular frequency; τ HN f is the characteristic relaxation time; α and β are the symmetric and asymmetric broadenings of the loss peak, respectively; max This is the frequency corresponding to the maximum value of the dielectric loss ε″.

[0016] Preferably, the calculation equation in step (3) is: Where Δτ is the rate of change of τ over the relaxation time interval as temperature increases. ΔT is the temperature gradient, and τ... (T+ΔT) and τ (T) The relaxation times are (T+ΔT)(K) and T(K), respectively.

[0017] Preferably, the Arrhenius equation in step (4) is: Where E represents the activation energy E a τ is the relaxation time; τ0 is a constant; R is the molar gas constant; T is the temperature.

[0018] Preferably, the Vogel-Fulcher-Tammann equation in step (4) is: Where τ0 is a constant, E a It is a constant related to the activation energy of the relaxation process, and T0 is the Vogel-Fulcher temperature.

[0019] Beneficial effects

[0020] This invention mainly utilizes dielectric analysis to achieve T-strain analysis of covalent adaptive networks. v The method of this invention provides quantitative and non-destructive detection of s without the need for additional components or external forces. It is applicable to ionic, radical, and synergistic CANs, as well as T...v Below T g The results have been validated in silyl ether-based CANs, providing a powerful tool for the study of CANs and offering new perspectives for a deeper understanding of CANs and their wider application. Attached Figure Description

[0021] Figure 1 To characterize the T of CANs by dielectric relaxation v The schematic diagram shows the principle of the thermosetting resin network and the change of dielectric relaxation rate over time.

[0022] Figure 2 The following are the molecular structures and dielectric analysis results of transesterification CANs: a) Schematic diagram of the chemical structure and transesterification reaction mechanism of transesterification CANs; b) Activation energies of TBD-0, TBD-2.5, and TBD-5.0 calculated using the Arrhenius equation based on stress relaxation data; c) Dielectric loss ε″ of TBD-5.0 as a function of frequency at different temperatures; d) Dielectric modulus M″ (scatter plot) of TBD-0 and e) TBD-5.0 as a function of frequency at different temperatures, along with the corresponding HN fitting curves; f) Average relaxation time τ of TBD-0 and g) TBD-5.0 in different temperature ranges. max Rate of change; h) τ of TBD-0 and i) TBD-5.0 max The results of temperature variation and the corresponding Arrhenius fitting curves; j) the temperature variation curves of the dielectric constant ε′ of TBD-0, TBD-2.5 and TBD-5.0 at a frequency of 1 Hz.

[0023] Figure 3 The following are the molecular structure and dielectric analysis results of dissociated imidazole-based CANs: a) Schematic diagram of the chemical structure and dynamic dissociation reaction mechanism of imidazole-based CANs; b) Activation energies of BIMU-CPU and Cu-BIMU-CPU calculated using the Arrhenius equation based on stress relaxation data; c) Dielectric loss ε″ of BIMU-CPU as a function of frequency at different temperatures; d) Dielectric modulus M″ (scatter plot) of BIMU-CPU and e) Cu-BIMU-CPU as a function of frequency at different temperatures, along with the corresponding HN fitting curves; f) Average relaxation time τ of BIMU-CPU and g) Cu-BIMU-CPU in different temperature ranges. max Rate of change; h) BIMU-CPU and i) Cu-BIMU-CPU τ maxResults of temperature variation and corresponding Arrhenius fitting curves; j) Dielectric constant ε′ of BIMU-CPU and Cu-BIMU-CP as a function of temperature at a frequency of 1 Hz.

[0024] Figure 4 The following are the structural and dielectric analysis results of disulfide-based radical CANs: a) Chemical structure and dynamic mechanism of exchange reaction of disulfide-based CANs; b) Normalized stress relaxation curves of disulfide-based CANs at different temperatures; the inset shows the activation energy calculated from the stress relaxation data; c) Dielectric loss ε″ of disulfide-based CANs as a function of frequency at different temperatures; d) Dielectric modulus M″ (scatter plot) of disulfide-based CANs as a function of frequency at different temperatures and the fitting curve of the HN equation; e) Average relaxation time τ of disulfide-based CANs in different temperature ranges. max Rate of change; f) τ of disulfide CAN max Results of temperature variation and corresponding Arrhenius fitting curves; g) Disulfide-based CAN dielectric constant ε′ as a function of temperature at a frequency of 1 Hz.

[0025] Figure 5 The following are the structural and dielectric analysis results of the synergistic CAN containing the dynamic Diels-Alder (DA) reaction: a) Chemical structure and dynamic mechanism of the exchange reaction of DA-based CAN; b) Normalized stress relaxation curves of DA-based CAN at different temperatures; the inset shows the activation energy calculated from the stress relaxation data; c) Dielectric loss ε″ of DA-based CAN as a function of frequency at different temperatures; d) Dielectric modulus M″ (scattered points) of DA-based CAN as a function of frequency at different temperatures and the fitting curve of the HN equation; e) Average relaxation time τ of DA-based CAN in different temperature ranges. max Rate of change; f) τ of DA-based CAN max Results of temperature variation and corresponding Arrhenius fitting curves; g) Curve of dielectric constant ε′ of DA-based CAN varying with temperature at a frequency of 1 Hz.

[0026] Figure 6 The following are the structural and dielectric analysis results of associated CANs containing dynamic silyl ether bonds: a) Chemical structure and dynamic mechanism of exchange reaction of silyl ether-based CANs; b) Normalized stress relaxation curves of silyl ether-based CANs at different temperatures; the inset shows the activation energy calculated from the stress relaxation data; c) Dielectric loss ε″ (scatter plot) of silyl ether-based CANs at different temperatures as a function of frequency and the fitting curve of the HN equation; d) Dielectric modulus ε″ (scatter plot) of silyl ether-based CANs at 60℃ as a function of frequency and the peak fitting result of the HN equation; e) Average relaxation time τ of silyl ether-based CANs in different temperature ranges. max Rate of change; f) τ of silyl ether-based CANmax Results of temperature variation and corresponding Arrhenius fitting curves; g) Curve of dielectric constant ε′ of silyl ether-based CAN varying with temperature at a frequency of 1 Hz. Detailed Implementation

[0027] 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.

[0028] Example 1

[0029] This embodiment provides a quantitative characterization method for the topology freezing transition temperature of covalent adaptive networks, including the following steps:

[0030] (1) Test the stress relaxation data of CANs samples and calculate the activation energy of the samples using the Arrhenius equation;

[0031] (2) The dielectric properties of the sample were measured at different temperatures and frequencies using a broadband dielectric spectrometer, and temperature-frequency domain dielectric spectrum curves were obtained. The dielectric constant as a function of temperature curve was obtained at the topological freezing transition temperature of the covalently cross-linked polymer network (T). v Steps appear;

[0032] (3) The dielectric loss spectrum is fitted using the Havriliak-Negami (HN) equation. If strong dielectric polarization occurs, the imaginary part of the dielectric constant can be converted into the imaginary part of the dielectric modulus using the equation, and then the HN equation is used for fitting to obtain the fitted dielectric spectrum and dielectric relaxation time τ at different temperatures, thereby realizing the quantitative analysis of the dielectric relaxation process of CANs.

[0033] (4) Dielectric relaxation process is divided into isothermal regions, and the rate of change of dielectric relaxation time in the isothermal gradient region is calculated by equation.

[0034] (5) The activation energy of first-order or second-order relaxation is calculated by fitting the reciprocal of τ with respect to temperature obtained in step (2) using the Arrhenius equation or the Vogel-Fulcher-Tammann equation. The results show that the fitted curve is in the range of T. v A turning point occurred at this point, validating the quantitative dielectric characterization of T. v The effectiveness;

[0035] Preferably, the dielectric constant curve in step (1) changes with temperature in a stepwise manner near the phase transition temperature, including the glass transition and topological freezing transition.

[0036] Preferably, the temperature range in step (1) is -160 to 400°C; the frequency range is 10. -6 Hz~10 9 Hz.

[0037] Preferably, the equation for transforming the imaginary part of the dielectric constant into the imaginary part of the dielectric modulus in step (2) is: Where M* is the dielectric modulus and M″ is the imaginary part of the dielectric modulus.

[0038] Preferably, the HN equation in step (2) is: and Where ε * The complex permittivity under the HN model; Δε=ε t -ε ∞ ;ε t ε ∞ τ is the dielectric constant of the sample before and after relaxation; ω is the angular frequency; τ HN f is the characteristic relaxation time; α and β are the symmetric and asymmetric broadenings of the loss peak, respectively; max This is the frequency corresponding to the maximum value of the dielectric loss ε″.

[0039] Preferably, the calculation equation in step (3) is: Where Δτ is the rate of change of τ over the relaxation time interval as temperature increases. ΔT is the temperature gradient, and τ... (T+ΔT) and τ (T) The relaxation times are (T+ΔT)(K) and T(K), respectively.

[0040] Preferably, the Arrhenius equation in step (4) is: Where E represents the activation energy E a τ is the relaxation time; τ0 is a constant; R is the molar gas constant; T is the temperature.

[0041] Preferably, the Vogel-Fulcher-Tammann equation in step (4) is: Where τ0 is a constant, E a It is a constant related to the activation energy of the relaxation process, and T0 is the Vogel-Fulcher temperature.

[0042] Example 2

[0043] Synthesis of transesterification CANs: A certain amount of bisphenol A diglycidyl ether (10 g, 29.3 mmol) and sebacic acid (5.941 g, 29.3 mmol) were mixed and stirred at 125 °C for 2 h until homogeneous. Different contents (2.5 mmol% and 5.0 mmol% of carboxyl functional groups) of the transesterification catalyst 1,5,7-triazabicyclo[4.4.0]dec-5-ene were added to the above homogeneous mixture, and the reaction was further carried out at 180 °C for 5 h to obtain a series of transesterification CANs. Based on the different catalyst contents, these CANs were named TBD-0, TBD-2.5, and TBD-5.0, respectively.

[0044] Figure 2 The dielectric constant and dielectric modulus of ester-exchange-group CANs as a function of frequency at different temperatures are presented. Dielectric loss results show that TBD-0, TBD-2.5, and TBD-5.0 all exhibit outstanding dielectric polarization properties at different temperatures. Under dielectric polarization, the composite dielectric constant (ε*) can be transformed into a composite dielectric modulus (M* = 1 / ε*). The dielectric modulus is fitted using the HN equation and the Arrhenius equation to quantitatively analyze the dielectric relaxation process of CANs. Figure 2 As shown, the dielectric modulus of TBD-0 and TBD-5.0 exhibits frequency and temperature dependence. The dielectric modulus as a function of frequency spectrum shows one dielectric relaxation peak, while the dielectric modulus as a function of temperature spectrum shows two peaks, indicating that the dielectric relaxation of TBD-0 and TBD-5.0 is a synergistic effect of two relaxation modes. Figure 2 As shown in c and d, a peak appears at T values ​​for TBD-0 and TBD-5.0. g This corresponds to the relaxation caused by the glass transition motion of the molecular chains. Another peak appears in a higher temperature range, possibly due to dielectric relaxation behavior caused by the breaking of dynamic covalent bonds. The average relaxation time (τ) was obtained by fitting the dielectric modulus spectra of TBD-0 and TBD-5.0 at different temperatures using HN. max To further observe the changes in dielectric relaxation before and after dynamic bond breaking, τ max The rate of change over a certain time interval was calculated, and the result is as follows: Figure 2 As shown in a and 2b. The τ values ​​of TBD-0 and TBD-5.0 max The rate of change of each temperature reaches its maximum at 90℃, which is their respective T0. v Below T v At this time, since the dynamic covalent bonds have not broken and recombinated, the network is still in a cross-linked state, and chain relaxation is restricted by the cross-linked network, resulting in the corresponding τ. max The rate of change gradually increases with increasing temperature. When the temperature reaches T... v or T vIn the above situations, dynamic covalent bond breaking and chain relaxation are relatively easy to occur, and the corresponding τ max The rate of change is less than T v The following values ​​are given, and they gradually decrease with increasing temperature. Apply the Arrhenius equation to T... v The up and down τ max The corresponding activation energy (E) is obtained by fitting the values. a As shown in the figure, both are at T. v The following is about τ max E obtained from fitting a All are greater than T v The above values ​​may be due to T. v The presence of the following cross-linked networks restricts molecular chain movement, hindering both movement and relaxation of the molecular chains. And T v Due to the breaking of dynamic bonds, molecular chain movement and relaxation are relatively easy to occur. To further demonstrate the effectiveness of quantitative dielectric analysis of T... v To ensure accuracy, the frequency spectrum of the dielectric constant versus temperature was analyzed. The dielectric constants of the three polymers increased with increasing temperature, reaching a certain value at T0. g The dielectric constants of TBD-5.0 and TBD-2.5 increase with decreasing frequency. The higher dielectric constant of TBD-5.0 compared to TBD-0 and TBD-2.5 indicates that the addition of the catalyst helps to improve the dielectric constant of the transesterified polyester. This is because the introduction of the catalyst promotes the mobility of the molecular chains. At 1 Hz, the dielectric constant versus temperature curves of the three materials show two distinct inflection points. One of these inflection points corresponds to temperature T. g Another inflection point temperature is 90℃, corresponding to TBD-5.0's T... v Temperature. The first inflection point is caused by the thawing phase transition of the molecular chains. The dielectric constant of a polymer is mainly composed of the effective dipole moment and the defect dipole moment. The effective dipole moment is related to the molecular chain length and its mobility. As the temperature increases, the mobility of the molecular chains increases, and the effective dipole moment of the polymer increases. When the temperature rises to T... v In polymers, dynamic covalent bonds break, the effective dipole moment decreases, and the defect dipole moment increases. The competition between these two factors slows down the increase in dielectric constant at T. v A turning point appears at that point.

[0045] Example 3

[0046] Synthesis of imidazole-based CANs: Bisimilar-2-methane (BIM) (0.35 g, 2.4 mmol), dibutyltin dilaurate (DBTDL) (0.0163 g, 0.025 mmol), copper chloride (CuCl2) (16.1 mg), and anhydrous N,N-dimethylformamide (DMF) (4 mL) were sequentially added to a round-bottom flask and mixed to form a homogeneous solution. Following the above steps, isophorone diisocyanate (IPDI) (1.30 g, 5.88 mmol) was added to the mixture, and the reaction was carried out at 75 °C for 20 h under argon atmosphere. Subsequently, dissolved glycidyl ether (GLY) (0.0663 g, 0.72 mmol) was added, and the reaction was carried out again at 75 °C for 4 h under argon atmosphere. The mixture was then dried under vacuum in a 75 °C oven to obtain a solid sample (Cu-BIMU-CPU).

[0047] To verify the effectiveness of dielectric analysis in dissociative CANs, two different dissociative CANs were synthesized: one without copper(II) (named BIMU-CPU) and the other containing copper(II) (named Cu-BIMU-CPU), as disclosed in CN116355172A. Previous studies have demonstrated the reversible dissociation mechanism of the imidazole-urea bond, and copper(II) can promote the dynamic reversibility of the imidazole-urea bond. Based on the Arrhenius equation and stress relaxation data, the activation energies of BIMU-CPU and Cu-BIMU-CPU were calculated to be 125.9 kJ mol⁻¹. -1 and 121.9 kJmol -1 (See Figure 3 b). Due to the significant dielectric polarization characteristics of BIMU-CPU and Cu-BIMU-CPU, their dielectric relaxation was quantitatively analyzed. Figure 3 c). The M″ of both BIMU-CPU and Cu-BIMU-CPU exhibits frequency and temperature dependence. The relaxation peaks appearing in their M″ versus frequency curves indicate the presence of a cooperative relaxation process in both BIMU-CPU and Cu-BIMU-CPU. Figure 3 d, e). Cooperatively relaxed τ max Extracted from the HN fitting results of M″. The rates of change of BIMU-CPU and Cu-BIMU-CPU reach their highest values ​​at 90℃. Figure 3 f, g). At temperatures below 90 °C, the synergistic relaxation activation energy of Cu-BIMU-CPU is Ea′ (81.6 kJ mol). -1 ) higher than BIMU-CPU (79.3 kJmol) -1 ()( Figure 3The introduction of Cu(II) promotes the rearrangement of molecular chains and networks, thereby increasing the Ea′ of Cu-BIMU-CPU, while also promoting the rearrangement of polarization units, accelerating the relaxation process, and shortening the corresponding relaxation time. When the temperature exceeds 90℃, Cu-BIMU-CPU (55.3 kJmol) -1 ) and BIMU-CPU (67.9kJmol) -1 Conversely, the Ea′ of Cu(II) shows that coordination with the imidazole-urea bond promotes the mobility of both segmental and long-range chains. Their ε′ curves as a function of temperature exhibit two distinct inflection points at a frequency of 1 Hz. One is observed at 65 °C, corresponding to their T... g Another one appears at 92℃, corresponding to their T... v Because no freezing or melting signal was observed in the loss tangent curve of dissociated imidazole-urea CANs in the -1℃ range.

[0048] Example 4

[0049] Synthesis of disulfide-based CAN: 1,4-Butanediol diglycidyl ether (5 g, 0.024 mmol) and 4-aminophenyl disulfide (3.07 g, 0.5 mmol) were mixed in a round-bottom flask and reacted at 80 °C for 2 h. Finally, the mixture was further crosslinked at 180 °C for 2 h to obtain a solid sample.

[0050] Synthesis of DA-based CAN: PTMEG (average Mn = ~1000) and 2,5-furandimethyl were purified before use. Briefly, PTMEG (5 g, 5 mmol) was heated in a round-bottom flask under vacuum at 100 °C for 2 h, then cooled to 65 °C. 2,5-furandimethyl was dried under vacuum at room temperature. Then, 2,5-furandimethyl (0.64 g, 5 mmol), IPDI (2.22 g, 10 mmol), and DBTDL (0.04 g, 0.5 wt%) dissolved in anhydrous tetrahydrofuran were mixed with PTMG. The mixture was reacted at 65 °C for 20 h under nitrogen atmosphere. Fourier transform infrared spectroscopy (FTIR) was used to monitor the reaction. The reaction stopped when the infrared absorption peak of -NCO in IPDI disappeared from the Fourier transform infrared spectrum. The mixture was then washed with petroleum ether to remove unreacted monomers and tetrahydrofuran, and then vacuum-treated at 60°C for 12 hours to obtain a solid linear prepolymer. The prepolymer (Mn = 11458, PDI = 1.37, 10 g, 0.8 mmol) was dissolved in chloroform to prepare a homogeneous solution, and then bismaleimide (BMI) (0.90 g, 0.04 mmol) was added. The resulting mixture was poured into a mold and reacted for 36 hours. After evaporating the solvent, the mixture was baked in an oven at 60°C for 24 hours to obtain a crosslinked CAN containing Diels-Alder bonds.

[0051] The dielectric modulus-frequency spectrum of disulfide-based CAN exhibits a characteristic peak, indicating at least one dielectric relaxation. The dielectric modulus-temperature spectrum shows two peaks, suggesting that this relaxation is a cooperative process, resulting from network rearrangement caused by glass transition and dynamic covalent bond breaking. The τ values ​​extracted by fitting the dielectric modulus using the HN equation further support this process. max The maximum rate of change occurs at 200℃, which is its T. v The Arrhenius equation is used to apply the equation to τ. max T is obtained by fitting the logarithm. v The activation energies at the top and bottom are 62.5 kJ / mol. -1 and 159.3 kJ mol -1 The reason is consistent with the previous analysis, T v The above-mentioned dynamic covalent bond breaking promotes the rearrangement ability of the cross-linked network, resulting in the network activation energy relative to T. v The activation energy is low. The dielectric constant versus temperature curve of disulfide-based CAN also shows two inflection points, one at T... g The other corresponds to T v Further evidence was provided regarding the T-disulfide-based CAN by dielectric analysis. v The accuracy.

[0052] The dielectric modulus-frequency relationship spectrum of DA-based CAN also shows a characteristic peak, and the dielectric modulus-temperature dielectric spectrum shows two peaks, indicating that at least one dielectric relaxation occurs, and this relaxation is a cooperative relaxation process caused by network rearrangement resulting from glass transition and dynamic covalent bond breaking. Its τ max The maximum rate of change occurs at 120℃, which is its T. v The Arrhenius equation is used to apply the equation to τ. max T is obtained by fitting the logarithm. v The activation energies at the top and bottom are 29.6 kJ / mol. -1 and 117.0 kJ mol -1 The dielectric constant of DA-based CAN versus temperature spectrum at T g and T v The two inflection point temperatures at the point of origin prove the T0 of the DA-based CAN based on dielectric analysis. v The accuracy.

[0053] Example 5

[0054] Synthesis of silyl ether-based CAN: Ethylene glycol (33.1 g, 0.53 mol) was added to a mixture of 4-vinylbenzyl (3.05 g, 0.02 mol), sodium hydroxide (0.02 mol), and deionized water (0.02 mol). The resulting mixture was heated at 70 °C for 24 hours with magnetic stirring. After extraction and vacuum drying, the crude product was obtained, and then subjected to column chromatography (SiO2, C6H). 12 The 2-(4-vinylbenzyloxy)-ethanol (yield: 3.06 g, 86%) was purified to give a yellow oily substance. LCMS: purity 99.6%. Styrene (10.0 mL, 87.0 mmol), 2-(4-vinylbenzyloxy)-ethanol (1.72 g, 9.67 mmol), and 2,2-azobis(2-methylpropionitrile) (47.6 mg, 0.290 mmol) were then dissolved in toluene (40 mL). The reaction mixture was cooled to 25 °C, and hexane (1000 mL) was slowly added with stirring to precipitate the copolymer. The resulting copolymer was filtered, dissolved in DCM, precipitated three times in MeOH, and then dried under vacuum at 80 °C for 24 h to give a white solid poly(styrene-costyrene-OH) (9.8 g, yield 72%).

[0055] For T v Greater than T g The CANs system, dielectric analysis characterizes its T v The principle is to use the HN equation to quantitatively analyze the principal-level cooperative relaxation process caused by glass transition and topological network rearrangement. And for T... v Less than T gIn the CAN system, the molecular chains or segments are frozen, and dielectric analysis, due to its wide detection frequency range and high sensitivity, can be used to analyze secondary relaxation processes caused by the migration of polar branches or side chains. When dynamic covalent bonds break, they easily affect the migration of polar terminal units; therefore, quantitative analysis of secondary relaxation may be suitable for quantitative analysis of T. v Less than T g The CAN system.

[0056] When the temperature is higher than T g At that time, due to the presence of DC conductivity, the dielectric constant and dielectric loss are shielded. However, for T... v Less than T g For this system, the dielectric relaxation process can be quantitatively analyzed by directly fitting the dielectric loss using the HN equation. Figure 6 ). T g Below, the molecular chain of silyl ether-based CAN is frozen, and its dielectric constant changes little with frequency at different temperatures. Peak fitting of the dielectric loss using the HN equation reveals the existence of three relaxation processes: α, β, and γ. With a temperature range of 10℃, the τ... max The maximum rate of change is 40℃, which is its T. v Value. Apply the Arrhenius equation to τ. max Fitting was performed to obtain the silyl ether-based CAN at T v The activation energies before and after activation are 27.5 kJ / mol. -1 and 72.2 kJ mol -1 Because in T g The following molecular chain motion is frozen, and the dielectric constant of the silyl ether-based CAN remains almost constant with temperature. Near T... g At that time, network rearrangement dynamics are influenced by the controlled diffusion theory. v Below, the movement of end groups is restricted by the cross-linked network, and the activation energy required for the movement of end group charges is relatively high compared to T. v The above demonstrates that dielectric analysis is not only applicable to the quantitative analysis of T. v Greater than T g The CAN system can also quantitatively analyze T. v Less than T g The CAN system.

Claims

1. A quantitative characterization method for the topology freezing transition temperature of covalent adaptive networks, comprising the following steps: (1) The dielectric properties of the CANs samples were measured at different temperatures and frequencies using a broadband dielectric spectrometer, and temperature-frequency domain dielectric spectrum curves were obtained. The dielectric constant as a function of temperature curve was obtained at the topological freezing transition temperature T of the covalently cross-linked polymer network. v A step-like change occurred; (2) Fit the temperature-frequency domain dielectric spectrum curve with the HN equation. If strong dielectric polarization occurs, convert the imaginary part of the dielectric constant into the imaginary part of the dielectric modulus using the equation, and then fit it with the HN equation to obtain the fitted dielectric spectrum and dielectric relaxation time τ at different temperatures, so as to realize the quantitative analysis of the dielectric relaxation process of CANs. (3) Dielectric relaxation process is divided into isothermal regions, and the rate of change of dielectric relaxation time in the isothermal gradient region is calculated by equation. (4) The activation energy of first-order or second-order relaxation is calculated by fitting the reciprocal of τ with respect to temperature obtained in step (2) using the Arrhenius equation or the Vogel-Fulcher-Tammann equation. The results show that the fitted curve is in the range of T. v A turning point occurred at this point, validating the quantitative dielectric characterization of T. v The effectiveness.

2. The method according to claim 1, characterized in that: The CANs samples in step (1) include associative and dissociative types.

3. The method according to claim 1, characterized in that: The CANs samples in step (1) include ionic, radical, and co-occurring types.

4. The method according to claim 1, characterized in that: The dielectric constant curve in step (1) changes with temperature in a step-like manner near the phase transition temperatures, including the glass transition and topological freezing transition.

5. The method according to claim 1, characterized in that: The temperature range in step (1) is -160 to 400°C; the frequency range is 10. -6 Hz~10 9 Hz.

6. The method according to claim 1, characterized in that: The equation for transforming the imaginary part of the dielectric constant into the imaginary part of the dielectric modulus in step (2) is as follows: Where M* is the dielectric modulus and M″ is the imaginary part of the dielectric modulus.

7. The method according to claim 1, characterized in that: The HN equation in step (2) is: and Where ε * The complex permittivity under the HN model; Δε=ε t -ε ∞ ;ε t ε ∞ τ is the dielectric constant of the sample before and after relaxation; ω is the angular frequency; τ HN The characteristic relaxation time; α and β represent the symmetric and asymmetric broadening of the loss peak, respectively; f max This is the frequency corresponding to the maximum value of the dielectric loss ε″.

8. The method according to claim 1, characterized in that: The equation in step (3) is: Where Δτ is the rate of change of τ with increasing temperature over the relaxation time interval; ΔT is the temperature gradient, and τ (T+ΔT) and τ (T) The relaxation times are (T+ΔT)(K) and T(K), respectively.

9. The method according to claim 1, characterized in that: The Arrhenius equation in step (4) is: Where E represents the activation energy E a τ is the relaxation time; τ0 is a constant; R is the molar gas constant; T is the temperature; the Vogel-Fulcher-Tammann equation is: Where τ0 is a constant, E a It is a constant related to the activation energy of the relaxation process, and T0 is the Vogel-Fulcher temperature.

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