Synthesis method of high-temperature-resistant bismaleimide resin

Abstract

The invention relates to synthesis of high-molecular compounds, in particular to a synthesis method of high-temperature-resistant bismaleimide resin, which comprises the following steps of: mixing a bismaleimide monomer with allyl phenyl ether, performing staged heating polymerization (pre-polymerization at the temperature of 100 DEG C and curing at the temperature of 160 DEG C), and regulating and controlling the reaction process in real time in combination with a kinetic model to obtain the high-temperature-resistant bismaleimide resin. And finally, curing at 200 DEG C to obtain a product. The method solves the problems of out-of-control reaction, high brittleness and high energy consumption in the traditional process, and the obtained resin has high heat resistance, low defect rate and excellent mechanical strength, and is suitable for the fields of aerospace and electronic packaging.

Description

Technical Field

[0001] This invention relates to the field of polymer synthesis technology, and in particular to a method for synthesizing a high-temperature resistant bismaleimide resin. Background Technology

[0002] Bismaleimide resin (BMI), as a high-performance thermosetting polymer, is widely used in aerospace (engine cowlings, radomes), electronic packaging (high-frequency circuit boards), and new energy vehicles (battery insulation layers). Its high-temperature resistance (long-term operating temperature > 250℃), excellent mechanical strength, and dielectric properties make it a preferred material to replace epoxy resin. For example, in the C919 passenger aircraft, BMI composite materials are used to manufacture cabin fireproof partitions, which must maintain structural integrity for more than 60 seconds under an 800℃ flame.

[0003] Traditional BMI synthesis employs a one-step high-temperature polymerization method (>200℃). While this traditional method can solve the problems of BMI production, it still has the following shortcomings in practical implementation:

[0004] 1. Traditional synthesis methods are prone to runaway reactions. Due to the problem of concentrated exothermic reactions, the source material is prone to local overheating, resulting in bubbles and pores.

[0005] 2. BMI synthesized by traditional methods is brittle, has uneven cross-linking density, is prone to microcracks, and has insufficient impact strength.

[0006] 3. Traditional synthesis methods have a narrow process window; temperature fluctuations of ±5℃ can lead to differences in curing degree and poor product consistency.

[0007] 4. Traditional synthesis methods are energy-intensive and require long curing times, typically more than 5 hours, which increases production costs.

[0008] Therefore, those skilled in the art need a controllable, low-energy gradient polymerization method for bismaleimide resins: Summary of the Invention

[0009] The purpose of this invention is to solve the above-mentioned problems by designing a method for synthesizing high-temperature resistant bismaleimide resin.

[0010] The technical solution of the present invention to achieve the above objectives is a method for synthesizing a high-temperature resistant bismaleimide resin, comprising the following steps:

[0011] Step 1: Monomer premixing. The bismaleimide monomer (BMI) and reactive diluent (such as allyl phenyl ether) are introduced into a container. Under the condition of 60-80℃, the stirring action of the stirrer in the container is adjusted and controlled according to the homogeneity mixing prediction model (stirring action mainly refers to the stirring time and speed) until the two are completely dissolved, thereby obtaining a uniformly dispersed mixture. The main purpose of this step is to achieve uniform dispersion of the monomer, reduce the viscosity of the system, and provide a homogeneous environment for subsequent reactions.

[0012] It should be noted that the reactive diluents include, but are not limited to: allyl phenyl ether, diallyl bisphenol A, allyl phenol and other allyl-containing compounds, or other reactive diluents that can undergo copolymerization with bismaleimide monomers.

[0013] Step 2: Staged heating polymerization. The step heating process is controlled by the step heating polymerization trigger conditions, allowing the mixture to react during the step heating process. At the same time, the degree of reaction (i.e., reaction conversion rate α) is monitored by kinetic control. The main function of this step is to control the reaction rate, avoid explosive polymerization, and ensure the orderly formation of the network structure.

[0014] Step 3: Post-curing treatment. The temperature is increased, and the reaction products are further treated at high temperatures to obtain the final product, further optimizing the crosslinking density. The main purpose of this step is to increase the glass transition temperature (Tg) of the resin. g ) and thermal stability.

[0015] In step one, the molar ratio of bismaleimide monomer to reactive diluent is 1:0.5-1.2, preferably 1:0.8.

[0016] The mathematical expression for the uniformity mixing prediction model in step one is:

[0017]

[0018] in,

[0019]

[0020] In the formula, CU represents the mixing uniformity, expressed as a percentage. The closer the value is to 100%, the more uniform the mixing. It is the dependent variable for evaluating the mixing effect. σ represents the standard deviation of the sample concentration, characterizing the dispersion of the concentration values ​​at each sampling point from the average value. It is an intermediate variable in the calculation process. X represents the theoretical target concentration value, the expected concentration calculated based on the feed ratio, and is a known constant. N represents the number of sampling points, the total number of sampling points set at different locations in the mixing container (such as top, middle, bottom, edge, etc.), and is a pre-defined independent variable (experimental parameter). i represents the sampling point number. C iThe measured concentration at the i-th sampling point is obtained through analytical techniques such as online near-infrared spectroscopy or rapid liquid chromatography, and is an input variable of the model. This is the average of the measured concentrations at all sampling points. It is an intermediate variable in the calculation process.

[0021] The stepwise heating procedure in step two is as follows: first, heat to 100°C and hold for 1 hour, then heat to 160°C and hold for 2 hours. The first stage is to hold the mixture at 100°C for 1 hour to allow it to undergo a pre-polymerization reaction; the second stage is to hold the mixture at 160°C for 2 hours to allow it to complete the cross-linking and curing reaction.

[0022] The mathematical expression for the step-by-step heating polymerization triggering condition in step two is:

[0023]

[0024] In the formula, α(t) is the real-time reaction conversion rate, ranging from 0 (unreacted) to 1 (completely reacted), and is the core dependent variable of the model, its value being calculated by integration; t is the reaction time, which is the independent variable; τ is the integral variable, representing any time point from the start of the reaction to the current moment; k is the pre-exponential factor. The kinetic parameters obtained through thermal analysis experiments (such as DSC) are constants; n is the reaction order, a kinetic parameter obtained through thermal analysis experiments, and is a constant; E a τ is the apparent activation energy of the reaction, expressed in kJ / mol, and is a constant; R is the universal gas constant, with a value of 8.314 J / (mol·K), and is a constant; T(τ) is the temperature function that varies with time, which is the independent variable of the process control, i.e., the set temperature program.

[0025] The triggering criteria for the stepped heating polymerization in step two are as follows:

[0026] α(t)≥α critical

[0027] In the formula, α critical The critical conversion rate is a threshold constant (e.g., α) determined experimentally beforehand based on the material system. critical =0.65), which represents the optimal degree of reaction that needs to be achieved in the prepolymerization stage. At this point, the system has sufficient molecular weight but has not yet gelled, and will not cause explosive polymerization after heating. When the real-time conversion rate (α(t)) reaches the triggering standard, the step heating program is triggered from the first stage (prepolymerization, 100℃) to the second stage (curing, 160℃).

[0028] The mathematical expression for the dynamic control model in step two is:

[0029]

[0030] In the formula, α is the reaction conversion rate (dependent variable), t is the reaction time (independent variable), k is the pre-exponential factor, n is the reaction order, and E is the reaction coefficient. a R is the apparent activation energy of the reaction, R is the gas constant (8.314 J / mol·K), and T is the reaction temperature (independent variable).

[0031] The post-curing treatment in step three involves treating at 200°C for 1-3 hours.

[0032] A high-temperature resistant bismaleimide resin, said high-temperature resistant bismaleimide resin is prepared by the method of any one of claims 1-8.

[0033] The high-temperature resistant bismaleimide resin has a glass transition temperature ≥320℃ and a thermal decomposition temperature ≥450℃.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. This invention adopts a kinetic model coupled with the process, embedding the mathematical model into the temperature control system to achieve closed-loop feedback control of the reaction degree, thereby better regulating the reaction process and improving the efficiency and yield of product synthesis;

[0036] 2. This invention employs a diluent screening strategy, selecting composite diluents containing allyl and benzene rings to simultaneously reduce viscosity and toughen, while introducing flexible segment monomers (such as allyl compounds) to improve toughness;

[0037] 3. This invention adopts a step-heating reaction design, and balances the reaction rate and network structure through a three-step method of "low temperature prepolymerization - medium temperature curing - high temperature post-treatment". By using a staged temperature control program, the curing shrinkage rate is reduced to <2%, which fully guarantees product quality and performance and can also effectively shorten the production cycle, which can be controlled within 4 hours.

[0038] 4. The product synthesized by this invention has significantly improved performance, and the product's T... g It can reach 320℃ (40℃ higher than traditional methods), and the thermal decomposition temperature of the product must be greater than 450℃;

[0039] 5. The product synthesized by this invention can effectively reduce the defect rate, with a bubble rate of less than 3% and an impact strength of 18 kJ / m. 2 ;

[0040] 6. The synthesis method of the present invention can effectively optimize energy consumption, shorten the synthesis reaction time by 30%, reduce the energy consumption of the synthesis process by 25%, and achieve good product consistency, with the degree of curing difference between products in the same batch being less than 5%. Attached Figure Description

[0041] Figure 1 This is a flowchart of a method for synthesizing a high-temperature resistant bismaleimide resin according to the present invention;

[0042] Figure 2 This is the process parameter table of Embodiment 2 of the present invention;

[0043] Figure 3 This is the process parameter table of Embodiment 3 of the present invention;

[0044] Figure 4 This is the process parameter table of Embodiment 4 of the present invention;

[0045] Figure 5 This is the process parameter table of Embodiment 5 of the present invention;

[0046] Figure 6 This is the process parameter table of Embodiment 6 of the present invention;

[0047] Figure 7 This is a comparison table of the implementation effects of embodiments 2 to 6 of the present invention. Detailed Implementation

[0048] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings;

[0049] Example 1;

[0050] A method for synthesizing a high-temperature resistant bismaleimide resin, such as... Figure 1 As shown, the implementation process of this method is as follows:

[0051] First, monomer premixing is performed by introducing bismaleimide monomer (BMI) and reactive diluent (such as allyl phenyl ether) into a container. Under conditions of 60-80°C, the stirring action of the stirrer in the container (stirring action mainly refers to the stirring time and speed) is adjusted and controlled according to the homogeneity mixing prediction model until the two are completely dissolved, thereby obtaining a uniformly dispersed mixture. The main function of this step is to achieve uniform dispersion of the monomer, reduce the viscosity of the system, and provide a homogeneous environment for subsequent reactions.

[0052] It should be noted that the molar ratio of bismaleimide monomer to reactive diluent is 1:0.5, 1:1.2, or 1:0.8; and the mathematical expression for the homogeneity mixing prediction model is:

[0053]

[0054] in,

[0055]

[0056] In the formula, CU represents the mixing uniformity, expressed as a percentage. The closer the value is to 100%, the more uniform the mixing. It is the dependent variable for evaluating the mixing effect. σ represents the standard deviation of the sample concentration, characterizing the dispersion of the concentration values ​​at each sampling point from the average value. It is an intermediate variable in the calculation process. X represents the theoretical target concentration value, the expected concentration calculated based on the feed ratio, and is a known constant. N represents the number of sampling points, the total number of sampling points set at different locations in the mixing container (such as top, middle, bottom, edge, etc.), and is a pre-defined independent variable (experimental parameter). i represents the sampling point number. C i The measured concentration at the i-th sampling point is obtained through analytical techniques such as online near-infrared spectroscopy or rapid liquid chromatography, and is an input variable of the model. This is the average of the measured concentrations at all sampling points. It is an intermediate variable in the calculation process.

[0057] It is important to note that the primary function of the homogeneity mixing prediction model is to quantitatively assess the homogeneity of the mixing system in real-time or offline, determining whether the mixing process can be completed and proceed to the next stage. It is a monitoring and control model that ensures subsequent polymerization reactions occur under homogeneous conditions, reducing performance defects caused by uneven mixing from the outset. This model is built upon mathematical statistics principles. First, it determines the sampling strategy (number of sampling points N and their locations). Then, it measures the real-time concentration data at each point using analytical instruments. Finally, it calculates the standard deviation and compares it with the theoretical value, normalizing it into an intuitive homogeneity index. When CU ≥ 98%, the mixing is considered homogeneous, triggering the next step.

[0058] Secondly, a phased heating polymerization is implemented, using the step heating polymerization trigger condition to control the step heating process, allowing the mixture to react during the step heating process, while using kinetic control to monitor the degree of reaction (i.e., reaction conversion rate α). The main function of this step is to control the reaction rate, avoid explosive polymerization, and ensure the orderly formation of the network structure.

[0059] It should be noted that the stepped heating program is as follows: first, the temperature is raised to 100℃ and held for 1 hour, then raised to 160℃ and held for 2 hours. The first stage involves holding the mixture at 100℃ for 1 hour to allow pre-polymerization; the second stage involves holding at 160℃ for 2 hours (the second stage is the pre-curing process) to allow the mixture to complete the cross-linking and curing reaction. The mathematical expression for the step-heating polymerization trigger condition is:

[0060]

[0061] In the formula, α(t) is the real-time reaction conversion rate, ranging from 0 (unreacted) to 1 (completely reacted), and is the core dependent variable of the model, its value being calculated by integration; t is the reaction time, which is the independent variable; τ is the integral variable, representing any time point from the start of the reaction to the current moment; k is the pre-exponential factor. The kinetic parameters obtained through thermal analysis experiments (such as DSC) are constants; n is the reaction order, a kinetic parameter obtained through thermal analysis experiments, and is a constant; E a τ is the apparent activation energy of the reaction, expressed in kJ / mol, and is a constant; R is the universal gas constant, with a value of 8.314 J / (mol·K), and is a constant; T(τ) is the temperature function that varies with time, which is the independent variable of the process control, i.e., the set temperature program.

[0062] It should be noted that the main function of the mathematical expression for the step-heating polymerization trigger condition is to calculate and predict the reaction process in real time. Its core function is to serve as the decision basis for intelligent temperature control, ensuring that the temperature conversion occurs at the most suitable chemical reaction node, thereby accurately controlling the formation of the network structure and avoiding problems such as internal stress, bubbles, or excessively wide molecular weight distribution caused by heating too early or too late.

[0063] In practical applications, the above-mentioned step-heating polymerization triggering conditions require the acquisition of kinetic parameters. Through a series of DSC experiments with different heating rates, the initial reaction data are fitted using methods such as Kissinger and Ozawa to calculate the activation energy Ea and pre-exponential factor k of the specific resin system. Then, the obtained Ea, k, n are substituted into the above differential equation and integrated over time at a known temperature program T(τ) to solve for α(t).

[0064] The threshold was determined by correlating rheological and DSC experiments to identify the conversion rate before the system viscosity abruptly changed (gel point), and this value was set as the safety threshold α. critical The step-heating polymerization triggering conditions are integrated into the PLC or DCS control system of the reactor to receive temperature signals in real time, calculate α(t), and ensure that α(t) ≥ α critical The heating command is executed automatically; that is, the triggering criteria for stepped heating polymerization are:

[0065] α(t)≥α critical

[0066] In the formula, α critical The critical conversion rate is a threshold constant (e.g., α) determined experimentally beforehand based on the material system. critical=0.65), which represents the optimal degree of reaction that needs to be achieved in the prepolymerization stage. At this point, the system has sufficient molecular weight but has not yet gelled, and will not cause explosive polymerization after heating. When the real-time conversion rate (α(t)) reaches the triggering standard, the step heating program is triggered from the first stage (prepolymerization, 100℃) to the second stage (curing, 160℃).

[0067] It should be noted that the mathematical expression of the dynamic control model is:

[0068]

[0069] In the formula, α is the reaction conversion rate (dependent variable), t is the reaction time (independent variable), k is the pre-exponential factor, n is the reaction order, and E is the reaction coefficient. a R is the apparent activation energy of the reaction, R is the gas constant (8.314 J / mol·K), and T is the reaction temperature (independent variable).

[0070] Finally, a post-curing treatment was performed, involving heat treatment at 200℃ for 3 hours to further optimize the crosslinking density; the main purpose of this step was to increase the glass transition temperature (Tg) of the resin. g ) and thermal stability.

[0071] Example 2;

[0072] A method for synthesizing a high-temperature resistant bismaleimide resin, the implementation process of which is as follows:

[0073] Monomer premixing: Bismaleimide (BMI) monomer and allyl phenyl ether (reactive diluent) are added to a mixing vessel at a molar ratio of 1:0.5 and heated to 60°C. Stirring is controlled according to a homogeneity mixing prediction model. When the calculated homogeneity (CU) value reaches 98.5%, stirring is stopped to obtain a homogeneous mixture.

[0074] Staged heating polymerization: The mixture is prepolymerized by heating it to 100℃ at a rate of 5℃ / min. The conversion rate (α) is calculated in real-time using a kinetic model based on online monitoring data. When the calculated α value reaches the preset critical conversion rate (α... critical When the temperature reaches 0.60, the next stage is automatically triggered, raising the system temperature to 160℃ and holding it at that temperature for 2 hours to complete the initial curing.

[0075] Post-curing treatment: The product is placed in an oven at 200°C for 3 hours and then naturally cooled to room temperature to obtain the final resin product.

[0076] The process parameters for Example 2 are as follows: Figure 2 As shown, everything else is the same as in Example 1.

[0077] Example 3;

[0078] A method for synthesizing a high-temperature resistant bismaleimide resin, the implementation process of which is as follows:

[0079] Monomer premixing: Mix BMI monomer and diluent at a molar ratio of 1:1.2 and stir at 70°C. Monitor the mixture using a uniformity model; when the CU value reaches 99.0%, it is considered uniformly mixed.

[0080] Staged heating polymerization: Prepolymerization is performed by heating to 100℃. A relatively high critical conversion rate (α) is set in this stage. critical =0.70), to ensure that the prepolymer has a higher molecular weight, after reaching the trigger condition, heat to 160℃ and hold for 2 hours; post-curing treatment: post-curing at 200℃ for 3 hours.

[0081] The process parameters for Example 3 are as follows: Figure 3 As shown, everything else is the same as in Example 1.

[0082] Example 4;

[0083] This embodiment aims to test the effect of milder prepolymerization conditions on product toughness, and the implementation process is as follows:

[0084] Monomer premixing: Using a preferred molar ratio of 1:0.8, mix at 75°C until the CU value is >98%;

[0085] Phased heating polymerization: First, prepolymerization is carried out at 90℃ (slightly lower than the claimed temperature), setting α... critical =0.55; After triggering, heat to 155℃ and hold for 2.5 hours (extend curing time).

[0086] Post-curing treatment: Standard post-curing conditions (200℃ / 3h).

[0087] The process parameters for Example 4 are as follows: Figure 4 As shown, everything else is the same as in Example 1.

[0088] Example 5;

[0089] This embodiment explores the possibility of shortening the total working time by using a higher prepolymerization temperature. The specific implementation process is as follows:

[0090] Monomer premixing: molar ratio 1:0.8, high-speed stirring at 80℃ (upper limit) to quickly reach CU 98%;

[0091] Staged heating polymerization: Prepolymerization is carried out directly at 110℃, and the α-polymerization is rapidly achieved through kinetic model monitoring. critical =0.65; then kept at 160°C for only 1.5 hours (shortening the curing time).

[0092] Post-curing treatment: still at 200℃, but the time is shortened to 2 hours.

[0093] The process parameters for Example 5 are as follows: Figure 5 As shown, everything else is the same as in Example 1.

[0094] Example 6 (Optimized Example);

[0095] Considering all optimization conditions, the optimal parameter combination is adopted for implementation, and the specific implementation process is as follows:

[0096] Monomer premixing: Using the optimal molar ratio of 1:0.8, mix at 75°C until the CU value reaches 99.5% (extremely high uniformity).

[0097] Staged temperature-increasing polymerization: prepolymerization at 100℃, using the standard critical conversion rate α. critical =0.65. After the trigger condition is met, the temperature is raised to 160℃ and held for 2 hours.

[0098] Post-curing treatment: Standard post-curing conditions (200℃ / 3h).

[0099] The process parameters for Example 6 are as follows: Figure 6 As shown, everything else is the same as in Example 1.

[0100] In the technical solution of this application, the data comparison and analysis of embodiments 2-6 in the specific implementation process are as follows: Figure 7 As shown in the figure. Based on the above data comparison and analysis, it can be seen that Example 6 (optimized parameters) has the best overall performance, significantly outperforming the comparative example in all key indicators, and fully achieving the purpose of "high performance, low defects, and high consistency" of this invention; Example 4 (mild prepolymerization) exhibits the best toughness (highest impact strength), indicating that product performance can be optimized in a targeted manner by adjusting the prepolymerization parameters; Example 5 (high temperature short time) successfully shortened the total production cycle to 3.5 hours, with an estimated energy consumption reduction of 30%. Although some performance indicators (such as Tg and impact strength) were slightly sacrificed, it provides a feasible solution for application scenarios with extremely high efficiency requirements; the defect rate of all examples is much lower than the 15% of the comparative example, proving the great advantages of the uniformity mixing prediction model and staged heating polymerization in controlling the reaction and avoiding local overheating and explosive polymerization; the curing degree difference of products in the same batch is less than 10% (less than 3% for Example 6), proving the effectiveness of the closed-loop control of the kinetic model in improving product consistency.

[0101] These embodiments fully demonstrate that the synthesis method provided by the present invention has high adjustability and superiority, and the process parameters can be flexibly adjusted according to different product performance focuses.

[0102] The above technical solutions only embody the preferred technical solutions of the present invention. Any modifications that may be made by those skilled in the art to certain parts thereof embody the principles of the present invention and fall within the protection scope of the present invention.

Claims

1. A method for synthesizing a high-temperature resistant bismaleimide resin, characterized in that, The method involves the following steps: Step 1: Monomer premixing. The bismaleimide monomer and reactive diluent are introduced into a container. Under the condition of 60-80℃, the stirring action is adjusted according to the homogeneity mixing prediction model to obtain a homogeneous mixture. Step 2: Staged heating polymerization. The step heating process is controlled by the step heating polymerization trigger conditions, allowing the mixture to react during the step heating process. At the same time, the degree of reaction is monitored by kinetic control to obtain the reaction products. Step 3: Post-curing treatment, increasing the temperature and continuing high-temperature treatment of the reaction products to obtain the final product.

2. The method according to claim 1, characterized in that, In step one, the molar ratio of bismaleimide monomer to reactive diluent is 1:0.5-1.

2.

3. The method according to claim 2, characterized in that, The mathematical expression for the uniformity mixing prediction model in step one is: in, In the formula, CU represents the mixing uniformity, σ represents the standard deviation of the sample concentration, X represents the theoretical target concentration value, N represents the number of sampling points, i represents the sampling point number, and C i Let be the measured concentration at the i-th sampling point. This represents the average concentration measured at all sampling points.

4. The method according to claim 1, characterized in that, The step-by-step heating process in step two is as follows: first, heat to 100°C and hold for 1 hour, then heat to 160°C and hold for 2 hours.

5. The method according to claim 4, characterized in that, The mathematical expression for the step-by-step heating polymerization triggering condition in step two is: In the formula, α(t) is the real-time reaction conversion rate, t is the reaction time, τ is the integral variable, k is the pre-exponential factor, n is the reaction order, and E a Let τ be the apparent activation energy of the reaction, R be the universal gas constant, and T(τ) be the temperature function that varies with time.

6. The method according to claim 5, characterized in that, The triggering criteria for the stepped heating polymerization in step two are as follows: α(t)≥α critical In the formula, α critical The critical conversion rate.

7. The method according to claim 6, characterized in that, The mathematical expression for the dynamic control model in step two is: In the formula, α is the reaction conversion rate, t is the reaction time, and T is the reaction temperature.

8. The method according to claim 1, characterized in that, In step three, the post-curing treatment involves raising the temperature to 200°C and processing for 1-3 hours.

9. A high-temperature resistant bismaleimide resin, characterized in that, The high-temperature resistant bismaleimide resin is prepared by the method described in any one of claims 1-8.

10. The resin according to claim 9, characterized in that, The high-temperature resistant bismaleimide resin has a glass transition temperature ≥320℃ and a thermal decomposition temperature ≥450℃.

Images