Polyamide acid polycondensation stage kinetics monitoring method based on in-situ infrared detection

Abstract

The application discloses a polyamide acid polycondensation stage kinetics monitoring method based on in-situ infrared detection, and comprises the following steps: for the initial low-viscosity rapid oligomerization stage in PAA synthesis, selecting inherent isolated characteristic infrared absorption peaks of aromatic diamine monomers as quantitative probes, and using in-situ FTIR to monitor the intensity change in real time; then, after data normalization and differentiation, a second-order kinetics model containing a non-catalytic term and a self-catalytic term is used for fitting, so that the rate constant and of the intrinsic kinetics of stage I are obtained. By using the technical scheme, quantitative kinetics analysis of a high-activity diamine-dianhydride system in an initial stage without considering the influence of diffusion is realized, and the synergistic regulation law of temperature and dianhydride structure on the self-catalysis degree of the stage is revealed.

Description

Technical Field

[0001] This invention belongs to the field of polymer chemistry and polymer polymerization process monitoring technology, specifically involving a kinetic monitoring method for the polyamic acid polycondensation stage based on in-situ infrared detection. It is used to monitor and analyze the kinetic behavior of the initial rapid oligomerization stage (stage I) during the polycondensation of aromatic diamines and dianhydride monomers in polar aprotic solvents to form polyamic acid (PAA) in real time and quantitatively. Background Technology

[0002] Polyamic acid (PAA) is typically produced by the nucleophilic ring-opening addition of aromatic diamines and dianhydrides in polar aprotic solvents, following a stepwise polymerization mechanism. Macroscopically, the reaction typically exhibits the following characteristics: initially, the reaction is rapid at low viscosity and high functional group concentration, quickly forming oligomers (Stage I); as conversion increases and system viscosity rises, molecular diffusion becomes restricted, leading to a decrease in the apparent reaction rate, and the process enters a later stage dominated by chain segment coupling growth (Stage II).

[0003] Current kinetic studies of this polycondensation reaction almost entirely focus on stage II, employing techniques such as ¹H NMR, titration / viscosity analysis, pulsed field gradient NMR (PFG-NMR), or end-group analysis. These methods are primarily used to monitor the slow, diffusion-controlled stage II. However, for highly reactive monomer combinations, stage I is extremely rapid (typically exceeding 90% reaction rate within 180-300 seconds), accompanied by significant autocatalytic effects and exothermic reactions. Existing techniques, due to insufficient temporal resolution or the inability to perform in-situ real-time monitoring, struggle to accurately acquire rapid, realistic kinetic data under these low-viscosity, high-concentration conditions, resulting in gaps in our understanding of the initial critical stages of the polymerization process. This leads to kinetic models extrapolated from stage II data exhibiting deviations of up to 20-30% when simulating the behavior in the first few minutes of the reaction.

[0004] Therefore, in order to reduce the cost of high-end polyimide (PI) and accelerate its application in high-end fields, there is an urgent need for a method that can monitor and quantify the kinetics of PAA polymerization stage I (rapid oligomer formation stage) in real time and accurately, especially its intrinsic autocatalytic properties. In-situ Fourier transform infrared spectroscopy (FTIR) has the advantages of real-time (second-level), non-destructive, and continuous tracking of functional group changes, providing a potential approach to solving the above problems. However, to date, no quantitative analysis of the autocatalytic kinetics of PAA stage I in synthesis and numerical simulations have been reported. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a kinetic monitoring method for the polyamic acid polycondensation stage based on in-situ infrared detection. This method can monitor and analyze the kinetic behavior of aromatic diamines and dianhydrides in the early stage of polycondensation reaction (low viscosity rapid oligomerization stage, stage I) in real time and quantitatively, especially their autocatalytic kinetic characteristics. This invention reveals the synergistic influence of reaction temperature and monomer molecular structure on the reaction process of this stage, providing key data and theoretical guidance for precise control and optimization of the polyamic acid synthesis process from the source.

[0006] To achieve the above objectives, the present invention provides the following solution: A kinetic monitoring method for the polyamic acid (PAA) polycondensation stage based on in-situ infrared detection is proposed. Targeting the initial low-viscosity, rapid oligomerization stage in PAA synthesis, the method selects the inherent isolated characteristic infrared absorption peaks of aromatic diamine monomers as quantitative probes and monitors their intensity changes in real time using in-situ FTIR. After data normalization and differentiation, a second-order kinetic model including non-catalytic and autocatalytic terms is used for fitting to obtain the rate constants characterizing the intrinsic kinetics of stage I. and .

[0007] This invention also provides a method for monitoring the kinetics of polyamic acid polycondensation stage based on in-situ infrared detection, comprising: S1. Dissolve the aromatic diamine monomer in a polar aprotic solvent and control the reaction system to the target temperature; S2. Add aromatic dianhydride monomer to the system of step S1 to initiate the polymerization reaction, and simultaneously use an in-situ Fourier transform infrared spectrometer to continuously monitor the reaction system. S3. From the continuously monitored infrared spectrum, select the characteristic infrared absorption peak that is inherent to the aromatic diamine monomer and has an isolated spectral peak as a quantitative probe, and obtain the spectral data of the intensity of the characteristic peak changing with time in real time; S4. Based on the characteristic peak intensity data, the normalized parameter m(t) reflecting the change in diamine concentration is calculated; S5. Differentiate the normalized parameter m(t) with respect to time t to obtain the reaction rate dm / dt, and construct the relationship curve between dm / dt and m; S6. The relationship curve is fitted using a second-order irreversible reaction kinetic model that includes non-catalytic and autocatalytic terms, thereby obtaining the rate constant K1 of the non-catalytic pathway and the rate constant K3 of the autocatalytic pathway characterizing the rapid oligomerization stage.

[0008] Preferably, in step S3, the characteristic infrared absorption peak must meet the following conditions: (a) it can be clearly identified in the infrared spectrum of the aromatic diamine monomer; (b) its intensity is linearly related to the diamine concentration; and (c) it is not affected by the overlap of other component peaks during the entire reaction process.

[0009] Preferably, the aromatic diamine is p-phenylenediamine (p-PDA), and the characteristic infrared absorption peak is the out-of-plane bending vibration peak of the hydrocarbons of the para-disubstituted benzene ring, located at 830°. Up to 850 Within the specified range; the aromatic diamine is 4,4'-diaminodiphenylmethane (MDA), and the characteristic infrared absorption peak is located at 818. Nearby; the aromatic diamine is 4,4'-diaminodiphenyl ether (ODA), and the characteristic infrared absorption peak is located at 1240. Up to 1260 Within the specified range; the aromatic diamine is 1,3-bis(4-aminophenoxy)benzene (APB), and the characteristic infrared absorption peak is located at 1240°C. Up to 1260 Within the specified range; the aromatic diamine is 2,2'-bis(trifluoromethyl)biphenyl-4,4'-diamine (TFMB), and the characteristic infrared absorption peak is located at 1150°C. Up to 1250 Within the range.

[0010] Preferably, the aromatic dianhydride is selected from at least one of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (α-BPDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA), pyromellitic dianhydride (PMDA), 4,4'-oxobisphthalic dianhydride (ODPA), and 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA).

[0011] Preferably, in step S6, the second-order irreversible reaction kinetic model is: in, By fitting the initial molar concentration of the aromatic diamine, two key parameters characterizing the intrinsic kinetics of stage I reaction can be directly obtained: K1 and K3. In this model, K1 is defined as the non-catalytic path rate constant, reflecting the rate of the reaction path not catalyzed by the product; K3 is defined as the autocatalytic path rate constant, reflecting the rate of the reaction path accelerated by the catalysis of the carboxylic acid product generated in the reaction. Through fitting, the K1 and K3 values ​​reflecting the characteristics of stage I reaction at a specific temperature T can be obtained.

[0012] As a preferred option, it also includes: S7. Repeat steps S1-S6 at different temperatures to obtain K1 and K3 at a series of temperatures; S8. According to the Arrhenius equation, K1 and K3 are fitted respectively to obtain the activation energy of the non-catalytic pathway in the rapid oligomerization stage. and activation energy of autocatalytic pathway .

[0013] As a preferred option, it also includes: optimizing the polyamic acid synthesis process, including: Determine the autocatalytic pathway rate constant K3 during the initial rapid oligomerization stage of the polycondensation reaction of a specific aromatic diamine with different aromatic dianhydrides at different temperatures; Compare the magnitude of K3 and its sensitivity to temperature; Based on the performance requirements of the target product and the controllability of the synthesis process, select the type of aromatic dianhydride and / or the reaction initiation temperature that can keep the exothermic rate of the rapid oligomerization stage in the early stage of the reaction within the desired range. When it is necessary to suppress the intense exothermic reaction during the rapid oligomerization phase at the beginning of the reaction, pairing with a specific diamine at the same temperature is appropriate. Aromatic dianhydrides with relatively low values, and / or lowering the reaction initiation temperature.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. For the first time, a quantitative kinetic analysis of the key initial oligomerization stage in PAA synthesis has been achieved: This invention creatively utilizes the isolated characteristic peaks of the diamine monomer as in-situ probes to successfully capture and quantify the rapid autocatalytic polycondensation process (stage I) that is difficult to observe under low viscosity conditions within minutes, which is difficult to observe by previous techniques. This fills the gap in the understanding of the kinetics of the key initial stage of this polymerization process.

[0015] 2. The key influencing factors and mechanisms of action in Stage I were revealed: Using the method of this invention, for the first time, the effects of reaction temperature and different dianhydride monomer structures on non-catalytic (catalytic) processes in Stage I, where diffusion effects are negligible, were quantitatively obtained. ) and autocatalysis ( The independent effects of the path rate constant were analyzed, and the corresponding intrinsic activation energies were calculated. The quantitative structure-activity relationship between the structural characteristics of several typical dianhydrides and their autocatalytic tendency in stage I was clarified.

[0016] 3. It provides direct evidence for precise control of the industrial synthesis process at its source: based on the method of this invention, it reflects the essential characteristics of stage I. , By understanding its relationship with temperature and monomer structure, production personnel can scientifically predict and evaluate the exothermic and accelerating behavior of different monomer combinations in the initial stage of the reaction. By selectively choosing monomers from a wide dianhydride library and / or setting the initial reaction temperature, the intensity of the initial reaction can be effectively controlled from the source, avoiding local overheating and side reactions, laying the foundation for the smooth progress of the subsequent stage II, thereby improving the safety, reproducibility, and product consistency of the entire PAA synthesis process.

[0017] 4. The method possesses high universality and reliability: This invention has constructed a complete verification system ranging from the simplest symmetric to complex functionalized compounds, covering various key diamines such as p-phenylenediamine (p-PDA), 4,4'-diaminodiphenylmethane (MDA), 4,4'-diaminodiphenyl ether (ODA), 1,3-bis(4-aminophenoxy)benzene (APB), and 2,2'-bis(trifluoromethyl)biphenyl-4,4'-diamine (TFMB), and has confirmed their corresponding isolated characteristic peaks. This systematically demonstrates that the core idea of ​​this invention—using the inherent isolated intrinsic characteristic infrared absorption peaks of the diamine monomer itself as a quantitative probe in stage I—has broad universality for the polycondensation systems of most aromatic diamines with identifiable functional groups in infrared spectra and the aforementioned dianhydrides, providing a universal and reliable solution to the common industry problem of rapid kinetic monitoring in the early stages of polymerization reactions. Attached Figure Description

[0018] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart of the kinetic monitoring method for polyamic acid polycondensation stage based on in-situ infrared detection according to an embodiment of the present invention; Figure 2 This is a comparison of the Fourier transform infrared spectra of the monomer (MDA) and the product used in the embodiments of the present invention, used to illustrate the selection of the characteristic absorption peak (818) of the diamine. This serves as the basis for quantitative probes; Figure 3 In this embodiment of the invention, a scatter plot of the relationship between the instantaneous reaction rate (dm / dt) and the degree of reaction (m) in the initial stage of the reaction of MDA and α-BPDA at different reaction temperatures, calculated from experimental data, and a fitting curve based on a second-order autocatalytic kinetic model are shown. Figure 4This is a comparison chart of experimental monitoring data of MDA and three different dianhydrides (BTDA, α-BPDA, s-BPDA) at 25°C and theoretical curves fitted based on the method of this invention, in an embodiment of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] Example 1: like Figure 1 As shown, this invention provides a kinetic monitoring method for the polyamic acid polycondensation stage based on in-situ infrared detection, specifically for monitoring the rapid polymer chain growth stage under low viscosity conditions in the early stage of the polymerization reaction, including the following steps: S1. Dissolve the aromatic diamine monomer in a polar aprotic solvent and control the reaction system to the target temperature; S2. Add aromatic dianhydride monomer to the system of step S1 to initiate the polymerization reaction, and simultaneously use an in-situ Fourier transform infrared spectrometer to continuously monitor the reaction system. S3. From the continuously monitored infrared spectrum, select the characteristic infrared absorption peak that is inherent to the aromatic diamine monomer and has an isolated spectral peak as a quantitative probe, and obtain the spectral data of the intensity of the characteristic peak changing with time in real time; S4. Based on the characteristic peak intensity data, the normalized parameter m(t) reflecting the change in diamine concentration is calculated; S5. Differentiate the normalized parameter m(t) with respect to time t to obtain the reaction rate dm / dt, and construct the relationship curve between dm / dt and m; S6. The relationship curve is fitted using a second-order irreversible reaction kinetic model that includes non-catalytic and autocatalytic terms, thereby obtaining the rate constant K1 of the non-catalytic pathway and the rate constant K3 of the autocatalytic pathway characterizing the rapid oligomerization stage.

[0023] As one embodiment of the present invention, in step S3, the characteristic infrared absorption peak must meet the following conditions: (a) it can be clearly identified in the infrared spectrum of the aromatic diamine monomer; (b) its intensity is linearly related to the diamine concentration; and (c) it is not affected by the overlap of other component peaks during the entire reaction process.

[0024] As one embodiment of the present invention, the characteristic infrared absorption peak is a specific out-of-plane bending vibration peak or skeletal vibration peak of the carbon-hydrogen bond on the benzene ring of the aromatic diamine monomer, or a carbon-oxygen-carbon asymmetric stretching vibration peak of the ether bond in the molecule, or a stretching vibration peak of the carbon-fluorine bond in the trifluoromethyl group.

[0025] In one embodiment of the present invention, the aromatic diamine is p-phenylenediamine (p-PDA), and the characteristic infrared absorption peak is the out-of-plane bending vibration peak of the hydrocarbon ring in the para-disubstituted benzene ring, located at 830°. Up to 850 Within the specified range; the aromatic diamine is 4,4'-diaminodiphenylmethane (MDA), and the characteristic infrared absorption peak is located at 818. Nearby; the aromatic diamine is 4,4'-diaminodiphenyl ether (ODA), and the characteristic infrared absorption peak is located at 1240. Up to 1260 Within the specified range; the aromatic diamine is 1,3-bis(4-aminophenoxy)benzene (APB), and the characteristic infrared absorption peak is located at 1240°C. Up to 1260 Within the specified range; the aromatic diamine is 2,2'-bis(trifluoromethyl)biphenyl-4,4'-diamine (TFMB), and the characteristic infrared absorption peak is located at 1150°C. Up to 1250 Within the range.

[0026] As one embodiment of the present invention, the aromatic dianhydride is selected from at least one of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 2,3,3',4'-biphenyl tetracarboxylic dianhydride (α-BPDA), 3,3',4,4'-biphenyl tetracarboxylic dianhydride (s-BPDA), pyromellitic dianhydride (PMDA), 4,4'-oxobisphthalic dianhydride (ODPA), and 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA).

[0027] In one embodiment of the present invention, in step S6, the second-order irreversible reaction kinetic model is as follows: in, The initial molar concentration of the aromatic diamine is given.

[0028] As one embodiment of the present invention, it further includes: S7. Repeat steps S1-S6 at different temperatures to obtain K1 and K3 at a series of temperatures; S8. According to the Arrhenius equation, K1 and K3 are fitted respectively to obtain the activation energy of the non-catalytic pathway in the rapid oligomerization stage. and activation energy of autocatalytic pathway .

[0029] Furthermore, it also includes: optimizing the polyamic acid synthesis process, including: Determine the autocatalytic pathway rate constant K3 during the initial rapid oligomerization stage of the polycondensation reaction of a specific aromatic diamine with different aromatic dianhydrides at different temperatures; Compare the magnitude of K3 and its sensitivity to temperature; Based on the performance requirements of the target product and the controllability of the synthesis process, select the type of aromatic dianhydride and / or the reaction initiation temperature that can keep the exothermic rate of the rapid oligomerization stage in the early stage of the reaction within the desired range. When it is necessary to suppress the intense exothermic reaction during the rapid oligomerization phase at the beginning of the reaction, pairing with a specific diamine at the same temperature is appropriate. Aromatic dianhydrides with relatively low values, and / or lowering the reaction initiation temperature.

[0030] Example 2: Monitoring methods and data analysis for the initial oligomerization stage (Stage I) of the reaction (taking MDA as an example) This embodiment uses 4,4'-diaminodiphenylmethane (MDA) and 2,3,3',4'-biphenyltetracarboxylic dianhydride (α-BPDA) as model systems to demonstrate the specific implementation process of this invention for the rapid oligomerization stage (Stage I) in the early stage of polycondensation reaction.

[0031] 1. Identification and confirmation of characteristic probe peaks: First, the infrared spectrum of pure MDA in N,N-dimethylacetamide (DMAc) solvent was obtained. For example... Figure 2 As shown, in the spectrum of MDA, a region located at 818 can be observed. A strong absorption peak nearby is attributed to the out-of-plane bending vibration of the CH group in the para-disubstituted benzene ring structure. The peak is sharp and extends across the entire spectrum of the reaction system (650-3000 nm). The peak did not overlap with the main characteristic peaks of the solvent, dianhydride monomer, and the generated PAA product, and its peak area showed a good linear relationship with MDA concentration within the experimental range. Therefore, this peak was selected as a quantitative probe for monitoring changes in MDA concentration during stage I.

[0032] 2. Monitoring and data analysis process for Phase I: a. Dissolve MDA in DMAc to prepare a solution of a certain concentration, and stabilize the temperature in the reactor at 5, 10, 15, 20, and 25°C respectively.

[0033] b. Add an equimolar amount of α-BPDA powder to initiate the reaction, while simultaneously acquiring infrared spectra every 15 seconds using a Mettler Toledo ReactIR 15 spectrometer (equipped with a DiComp probe of diamond ATR), focusing on monitoring the first few minutes after the reaction begins (e.g., 0-600 seconds).

[0034] c. Extracting 818 from the continuous spectrum Peak area A(t) is the area before the reaction begins. Based on the baseline, calculate the normalized concentration. .

[0035] d. Perform numerical differentiation on the m(t)-t data to obtain the instantaneous reaction rate dm / dt of stage I, and plot it as follows. Figure 3 The scatter plot shows the relationship between dm / dt and m.

[0036] e. Using formulas right Figure 3 Nonlinear least-squares fitting was performed on the dm / dt-m data to obtain K1 and K3 values ​​characterizing the kinetics of stage I at various temperatures. Taking the MDA and α-BPDA reaction system as an example, the non-catalytic path rate constant K1 at 25°C, 20°C, 15°C, 10°C, and 5°C were 0.210, 0.189, 0.143, 0.100, and 0.099 L·mol⁻¹, respectively. -1 ·s -1 The rate constants K3 for the autocatalytic pathway were 5.880, 5.000, 4.490, 4.310, and 3.420 L, respectively. 2 ·mol -2 ·s -1 Model fit determination coefficient R 2 All values ​​are above 0.948, indicating that the model can accurately describe the dynamic behavior at this stage.

[0037] f. Based on the above... and The value was further fitted using the Arrhenius equation to calculate the apparent activation energy E of the non-catalytic pathway in stage I of the reaction system. a1 It is 29.57 kJ·mol -1 Apparent activation energy E of autocatalytic pathway a3 It is 17.01 kJ·mol -1 E a3 Significantly lower than Ea1 This provides direct quantitative evidence that the carboxyl group (-COOH) generated during the reaction process catalyzes subsequent reactions through a proton transfer mechanism (i.e., autocatalysis).

[0038] This embodiment demonstrates the effectiveness of the method of the present invention in capturing and quantitatively analyzing the kinetic behavior of aromatic diamine systems with isolated characteristic peaks in the low viscosity stage (stage I) of the initial polycondensation phase.

[0039] Example 3: Application of simple symmetrical diamines in Stage I (taking p-PDA as an example) This embodiment uses p-phenylenediamine (p-PDA) as an example to demonstrate the applicability of the method of the present invention to the kinetic monitoring of structurally simple and symmetrical diamines in stage I.

[0040] 1. Identification of characteristic probe peaks: The p-PDA molecule has a para-disubstituted benzene ring structure. In its infrared spectrum, a ring located at approximately 840 nm can be observed. A strong absorption peak nearby is attributed to the out-of-plane bending vibration of the CH group of the para-disubstituted benzene ring. This peak represents a vibration of the benzene ring skeleton and remains stable in the early stages of the polycondensation reaction. In the full spectrum of the reaction system, this peak is effectively separated from the main characteristic peaks of the solvent, dianhydride monomer, and PAA product, and its intensity shows a good linear relationship with the p-PDA concentration. Therefore, this benzene ring CH characteristic peak meets the "isolated characteristic infrared absorption peak" condition described in step S3 of this invention and can serve as a reliable probe for monitoring the concentration change of p-PDA in stage I.

[0041] 2. Explanation of method application: When p-PDA is selected as the diamine monomer, the general procedure of this invention is followed, using 840 Using the characteristic CH peak of the nearby benzene ring as a probe, in-situ real-time monitoring and kinetic analysis of stage I can be performed. This demonstrates that the method of this invention is applicable to the kinetic study of a wide range of diamine systems, from the simplest symmetrical to complex functionalized systems, in the early stages of the reaction.

[0042] Example 4: Applications of diamines containing ether bonds in Stage I (taking ODA and APB as examples) This embodiment uses 4,4'-diaminodiphenyl ether (ODA) and 1,3-bis(4-aminophenoxy)benzene (APB) as examples to illustrate the applicability of the present invention to the kinetic monitoring of diamines containing characteristic ether bonds in stage I.

[0043] 1. Identification of characteristic probe peaks (ODA and APB): Both ODA and APB molecules contain aromatic ether structures (COC). Their respective infrared spectra are located at approximately 1240-1260 nm. Within the range (e.g., 1245) A very strong absorption peak exists nearby, which is attributed to the COC asymmetric stretching vibration of the aromatic ether structure. This vibration peak is highly characteristic; in the full spectrum of the PAA synthesis system, it is completely separated from the carbonyl peaks of the solvent and dianhydride, as well as the characteristic peaks of the amide and carboxylic acids of PAA, without overlap or interference, and the peak intensity is linearly correlated with concentration. Therefore, this COC stretching vibration peak is an ideal isolated characteristic probe for monitoring the concentration of ODA or APB in Stage I.

[0044] 2. Explanation of method application: For ODA or APB systems, 1245 Using the nearby COC characteristic peak as a probe, and applying steps S1-S6 of this invention, kinetic monitoring and modeling of stage I can be successfully performed. This demonstrates that the method of this invention can fully utilize the characteristic functional groups (such as ether bonds) in monomer molecules to achieve accurate analysis in the initial stage of the reaction.

[0045] Example 5: Application of diamines with fluorine-containing characteristic groups in Stage I (taking TFMB as an example) This embodiment uses 2,2'-bis(trifluoromethyl)biphenyl-4,4'-diamine (TFMB) as an example to demonstrate the excellent applicability of the method of the present invention to the kinetic monitoring of aromatic diamines containing strong infrared characteristic functional groups in stage I.

[0046] 1. Identification of characteristic probe peaks: The two trifluoromethyl groups in the TFMB molecule ( ) is its most prominent infrared active group. In its infrared spectrum, it can be observed that it is located at approximately 1150-1250. Within the range (e.g., 1180) The extremely strong, sharp absorption peaks (nearby) belong to The stretching vibration of the CF bond in the group. This region of absorption is absolutely unique in the PAA synthesis system, unaffected by any other components, and is an ideal isolated characteristic probe peak that meets the requirements.

[0047] 2. Explanation of method application: When TFMB is selected as the diamine monomer, in-situ monitoring of stage I using the CF characteristic peak as a probe can track the diamine concentration decay with the highest signal-to-noise ratio and accuracy. This proves that the method of this invention can perfectly adapt to and fully utilize the unique strong characteristic functional groups in the monomer molecule (such as... ), and perform kinetic analysis of the initial stage of the reaction.

[0048] Example 6: Comparative analysis, pattern summary, and process optimization guidance of different dianhydride monomers To verify the universality of the method of this invention and quantitatively reveal the influence of monomer structure on the initial reaction kinetics, a systematic comparative study was conducted on the kinetic behavior of MDA and three dianhydrides (BTDA, α-BPDA, s-BPDA) with different structures in stage I, based on the same method described in Example 2. Figure 4 As shown.

[0049] 1. Systematic comparison of kinetic parameters and structure-activity relationship: Kinetic analysis of different systems at 25°C showed that their autocatalytic pathway rate constants Following this order: MDA+BTDA system (K3 = 10.671 L) 2 ·mol -2 ·s -1 MDA+s-BPDA system ( MDA+ α-BPDA system ( This order is highly correlated with the molecular planarity of the dianhydride monomer and the electrophilicity of the linking group. Meanwhile, the K1 and K3 values ​​of each system decrease systematically with decreasing temperature within the temperature range of 5-25°C.

[0050] 2. The dominant mechanism revealed by the difference in activation energy: The activation energy parameters obtained through Arrhenius analysis further elucidated the underlying mechanism. For the MDA+BTDA and MDA+α-BPDA systems, the activation energy of their autocatalytic pathways was... (30.75 and 17.01 kJ respectively) The activation energies of these pathways are all significantly lower than their own non-catalytic pathway activation energies. (48.35 and 29.57 kJ respectively) This strongly confirms once again that the autocatalytic pathway dominates in the early stages of the reaction. The MDA+s-BPDA system, however, exhibits different activation energy characteristics.

[0051] 3. Quantitative basis for process optimization application: The above quantitative data provides a direct basis for precise control of the initial stage of PAA synthesis in industry. For example, if it is necessary to suppress the intense exothermic and autoacceleration in the early stage of the reaction, it is preferable to select a PAA that is paired with MDA under the same conditions. Lower values ​​of α-BPDA or s-BPDA, rather than The highest value for BTDA. Furthermore, lowering the reaction initiation temperature generally reduces [the BTDA value]. and The absolute value of the kinetic parameters is an effective means of controlling the initial reaction rate. Based on the kinetic parameters of specific monomer combinations obtained by the method of this invention, the initial reaction process can be predicted and actively "programmed," thereby improving the safety, reproducibility, and product consistency of the synthesis process.

[0052] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for monitoring the kinetics of polyamic acid polycondensation stage based on in-situ infrared detection, characterized in that, For the initial low-viscosity, rapid oligomerization stage in PAA synthesis, the isolated characteristic infrared absorption peaks inherent in aromatic diamine monomers were selected as quantitative probes, and their intensity changes were monitored in real time using in-situ FTIR. After data normalization and differentiation, a second-order kinetic model including non-catalytic and autocatalytic terms was used for fitting, obtaining the rate constants K1 and K3 characterizing the intrinsic kinetics of stage I. Specifically, this includes: S1. Dissolve the aromatic diamine monomer in a polar aprotic solvent and control the reaction system to the target temperature; S2. Add aromatic dianhydride monomer to the system of step S1 to initiate the polymerization reaction, and simultaneously use an in-situ Fourier transform infrared spectrometer to continuously monitor the reaction system. S3. From the continuously monitored infrared spectrum, select the characteristic infrared absorption peaks that are inherent to the aromatic diamine monomer and have isolated spectral peaks as quantitative probes, and obtain the spectral data of the intensity of the characteristic infrared absorption peaks changing with time in real time. S4. Based on the characteristic infrared absorption peak intensity data, the normalized parameter m(t) reflecting the change in diamine concentration is calculated; S5. Differentiate the normalized parameter m(t) with respect to time t to obtain the reaction rate dm / dt, and construct the relationship curve between dm / dt and m; S6. The relationship curve is fitted using a second-order irreversible reaction kinetic model that includes non-catalytic and autocatalytic terms, thereby obtaining the rate constant K1 and the rate constant K3 of the autocatalytic path characterizing the rapid oligomerization stage. In step S6, the second-order irreversible reaction kinetic model is as follows: in, By fitting the initial molar concentration of the aromatic diamine, two key parameters characterizing the intrinsic kinetics of stage I reaction can be directly obtained: K1 and K3. In this model, K1 is defined as the rate constant of the non-catalytic path, reflecting the rate of the reaction path not catalyzed by the product; K3 is defined as the rate constant of the autocatalytic path, reflecting the rate of the reaction path accelerated by the catalysis of the carboxylic acid product generated in the reaction. By fitting, the K1 and K3 values ​​reflecting the characteristics of stage I reaction at a specific temperature T can be obtained.

2. The method for monitoring the kinetics of polyamic acid polycondensation stage based on in-situ infrared detection according to claim 1, characterized in that, In step S3, the characteristic infrared absorption peak must meet the following conditions: (a) it can be clearly identified in the infrared spectrum of the aromatic diamine monomer; (b) its intensity is linearly related to the concentration of the diamine; and (c) it is not affected by the overlap of peaks of other components during the entire reaction process.

3. The method for monitoring the kinetics of polyamic acid polycondensation stage based on in-situ infrared detection according to claim 2, characterized in that, The aromatic diamine is p-phenylenediamine (p-PDA), and the characteristic infrared absorption peak is the out-of-plane bending vibration peak of the p-disubstituted benzene ring, located at 830°. Up to 850 Within the specified range; the aromatic diamine is 4,4'-diaminodiphenylmethane (MDA), and the characteristic infrared absorption peak is located at 818. Nearby; the aromatic diamine is 4,4'-diaminodiphenyl ether (ODA), and the characteristic infrared absorption peak is located at 1240. Up to 1260 Within the specified range; the aromatic diamine is 1,3-bis(4-aminophenoxy)benzene (APB), and the characteristic infrared absorption peak is located at 1240°C. Up to 1260 Within the specified range; the aromatic diamine is 2,2'-bis(trifluoromethyl)biphenyl-4,4'-diamine (TFMB), and the characteristic infrared absorption peak is located at 1150°C. Up to 1250 Within the range.

4. The method for monitoring the kinetics of polyamic acid polycondensation stage based on in-situ infrared detection according to claim 3, characterized in that, The aromatic dianhydride is selected from at least one of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (α-BPDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA), pyromellitic dianhydride (PMDA), 4,4'-oxobisphthalic dianhydride (ODPA), and 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA).

5. The method for monitoring the kinetics of polyamic acid polycondensation stage based on in-situ infrared detection according to claim 4, characterized in that, Also includes: S7. Repeat steps S1-S6 at different temperatures to obtain K1 and K3 at a series of temperatures; S8. According to the Arrhenius equation, K1 and K3 are fitted respectively to obtain the activation energy E of the non-catalytic pathway in the rapid oligomerization stage. a1 and the activation energy E of the autocatalytic pathway a3 .

6. The method for monitoring the kinetics of polyamic acid polycondensation stage based on in-situ infrared detection according to claim 5, characterized in that, Also includes: Optimize the polyamic acid synthesis process, including: Determine the autocatalytic pathway rate constant K3 during the initial rapid oligomerization stage of the polycondensation reaction of a specific aromatic diamine with different aromatic dianhydrides at different temperatures; Compare the magnitude of K3 and its sensitivity to temperature; Based on the performance requirements of the target product and the controllability of the synthesis process, select the type of aromatic dianhydride and / or the reaction initiation temperature that can keep the exothermic rate of the rapid oligomerization stage in the early stage of the reaction within the desired range. When it is necessary to suppress the intense exothermic reaction during the rapid oligomerization phase at the beginning of the reaction, an aromatic dianhydride with a relatively low K3 value when paired with a specific diamine at the same temperature is selected, and / or the reaction initiation temperature is reduced.

Images