Method for constructing cross-linking molecular model of amine-initiated stepwise cross-linking of epoxy resin

Abstract

The present invention discloses a method for constructing a cross-linked molecular model of an amine-initiated epoxy resin that is gradually cross-linked, comprising: (1) constructing amine molecules, anhydride molecules and epoxy molecules in molecular modeling software; (2) marking reactive atoms on monomer molecules; (3) setting modeling parameters and cross-linking parameters, then constructing a mixture model, then sequentially performing geometric optimization and molecular dynamics equilibrium on the mixture model, then cross-linking the mixture optimization model, and outputting a series of cross-linked molecular models with specified cross-linking degree intervals at one time. The present invention can construct an amine / anhydride / epoxy cross-linked molecular model with a controllable cross-linking degree, provide support for studying it at the molecular level, and achieve scientific and reasonable high-precision simulation of its structure.

Description

Technical Field

[0001] The invention belongs to the field of cross-linked epoxy resins, and in particular is a method for constructing a cross-linked molecular model of epoxy resins gradually cross-linked by amines. Background Art

[0002] Anhydride-cured epoxy resin is a type of cross-linked epoxy resin with organic anhydride as curing agent. It has high heat resistance, excellent mechanical properties, excellent comprehensive properties and wide application. However, due to the high activation energy of the reaction, the curing rate of the anhydride / epoxy system is very slow at low temperature, requiring a higher curing temperature and a longer curing time. In order to save energy and improve production efficiency, accelerators are introduced into the anhydride / epoxy system. Amine accelerators are a type of nucleophilic accelerator that can simultaneously catalyze anhydride and epoxy. Anhydride-cured epoxy resins with amine accelerators are used in many fields such as military industry, aerospace, and nuclear power. Typical representatives are TDE85, TDE86, and TDE90 high-performance cross-linked epoxy resins.

[0003] The excellent performance of cross-linked epoxy resin depends largely on its complex highly cross-linked molecular structure. Therefore, it is necessary to study the relationship between the structure and performance of cross-linked epoxy resin at the molecular level. However, due to the limitations of existing experimental testing methods, it is difficult to complete the detailed exploration of the structure and properties of cross-linked epoxy resin at the atomic and molecular scales, and there are disadvantages of high cost and long time consumption. Molecular dynamics (Molecular Dynamics) method is a powerful tool that can predict material properties such as glass transition temperature, thermal expansion coefficient, mechanical properties and water diffusion through calculations at the level of atomic and molecular structure. It has been gradually promoted and used in the study of cross-linked epoxy resin in recent years. An important step in studying cross-linked epoxy resin using molecular dynamics method is to construct a cross-linked epoxy resin molecular model. However, unlike crystals, the cross-linked epoxy resin network has a highly connected molecular structure. The complexity of this molecular structure makes it quite challenging to construct a realistic and effective cross-linked epoxy resin network molecular model for molecular dynamics simulation.

[0004] At present, the script cross-linking method is usually used to construct the cross-linked molecular model of epoxy resin. This method can make the molecular model reach a high degree of cross-linking, and is the most effective method known to construct the cross-linked molecular model of epoxy resin with high cross-linking degree. However, the existing script cross-linking method for constructing the anhydride / epoxy cross-linked molecular model is limited to the case where the promoter is not introduced. When the amine promoter is introduced into the anhydride / epoxy system, as the system changes from two components to three components, its curing cross-linking mechanism also undergoes a significant change, which makes the existing script cross-linking method unable to meet the construction requirements of the amine / anhydride / epoxy cross-linked molecular model, and it is also difficult to simply improve it to meet the requirements. Therefore, for amine / anhydride / epoxy cross-linked epoxy resin, there is currently no reasonable cross-linked molecular model and effective model construction method. This limits the application of molecular dynamics methods in the field of cross-linked epoxy resin research. In addition, the existing method for constructing the anhydride / epoxy cross-linked molecular model needs to construct a molecule with an initial cross-linking degree or polymerization degree as input in addition to the monomer molecule to start cross-linking, which causes inconvenience to the construction of the cross-linked molecular model. In addition, the existing methods are basically based on the distance cutoff principle, and the cross-linking degree is increased by continuously increasing the reaction radius. This method can only control the maximum cross-linking degree of the model, but cannot obtain multiple molecular models with specified cross-linking degrees at one time, which limits the molecular dynamics research on epoxy resins with different cross-linking degrees. Summary of the invention

[0005] In view of the deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a method for constructing a cross-linked molecular model of epoxy resin gradually cross-linked by amine.

[0006] The technical solution of the present invention to solve the technical problem is to provide a method for constructing a cross-linked molecular model of epoxy resin gradually cross-linked by amine, characterized in that the method comprises the following steps:

[0007] Step 1, constructing monomer molecules in molecular modeling software; the monomer molecules include amine accelerator monomer molecules, organic acid anhydride curing agent monomer molecules and epoxy resin monomer molecules;

[0008] Step 2, marking reactive atoms on the monomer molecules constructed in step 1; the reactive atoms are N atoms in amine molecules, two C atoms on the anhydride group in anhydride molecules, single-bonded O atoms on the anhydride group in anhydride molecules, C atoms in CH2 on the epoxy group in epoxy molecules, and O atoms on the epoxy group in epoxy molecules;

[0009] Step 3, set the modeling parameters and cross-linking parameters, and then construct a mixture model based on the amine molecules, anhydride molecules and epoxy molecules marked in step 2, and then perform geometric optimization and molecular dynamics equilibrium on the mixture model in turn to obtain the mixture optimization model; then cross-link the mixture optimization model and output a series of cross-linked molecular models with specified cross-linking degree intervals at one time.

[0010] Compared with the prior art, the present invention has the following beneficial effects:

[0011] (1) The present invention can construct an amine / anhydride / epoxy cross-linked molecular model with controllable cross-linking degree, which can provide support for studying amine / anhydride / epoxy cross-linked epoxy resins at the molecular level.

[0012] (2) The modeling concept provided by the present invention is basically consistent with the actual cross-linking mechanism of amine / anhydride / epoxy cross-linked epoxy resin, and can achieve scientific and reasonable high-precision simulation of the structure of amine / anhydride / epoxy cross-linked epoxy resin.

[0013] (3) The cross-linking cycle process of the present invention is based on the shortest distance bonding principle, that is, searching for reactive atomic pairs within a set reaction radius, sorting the distances, cross-linking the reactive atomic pairs with the shortest distances, performing geometric optimization after cross-linking, and then performing the next step of cross-linking, and so on. The cycle is repeated, cross-linking is performed step by step, and iterations are repeated until the relevant conditions are met.

[0014] (4) The cross-linking cycle process of the present invention adopts step-by-step cross-linking, and the cross-linking degree is calculated in real time during the cross-linking process, which can accurately control the cross-linking degree of the output model and construct a series of cross-linking molecular models with specified cross-linking degree intervals at one time, which can provide support for the accurate study of amine / anhydride / epoxy cross-linked epoxy resins with different cross-linking degrees.

[0015] (5) The initial input structure of the present invention only requires monomer molecules and does not require pre-crosslinking treatment, that is, it is not necessary to construct molecules with an initial crosslinking degree or polymerization degree, which is simple and quick.

[0016] (6) The present invention takes into account the mass ratio of amine accelerators, organic acid anhydride curing agents and epoxy resin crosslinking, and determines the molecular quantity ratio of the initial model according to the mass ratio, so as to construct a more scientific and reasonable amine / acid anhydride / epoxy crosslinking molecular model.

[0017] (7) The method for constructing a cross-linked molecular model provided by the present invention is very flexible in setting the number of model components. Within the scope allowed by computer performance, there are no restrictions on the specific types and ratios of amine molecules, acid anhydrides and epoxides, as well as the scale of the cross-linked network. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a flow chart of the method for constructing a cross-linked molecular model of the present invention;

[0019] Figure 2 The molecular configuration of BDMA constructed in Example 1 of the present invention;

[0020] Figure 3 The molecular configuration of MTHPA constructed in Example 1 of the present invention;

[0021] Figure 4 The molecular configuration of TDE-85 constructed in Example 1 of the present invention;

[0022] Figure 5 The cross-linked molecular model of BDMA / MTHPA / TDE-85 with a specified cross-linking degree interval obtained in the first cross-linking process of Example 1 of the present invention;

[0023] Figure 6 This is a density-temperature curve obtained by calculating the 90% cross-linking degree model of Example 1 of the present invention;

[0024] Figure 7 This is the DSC test curve of the BDMA / MTHPA / TDE-85 cross-linked epoxy resin of Example 1 of the present invention. DETAILED DESCRIPTION

[0025] The specific embodiments of the present invention are given below. The specific embodiments are only used to further illustrate the present invention in detail and do not limit the protection scope of the claims of the present invention.

[0026] The present invention provides a method for constructing a cross-linked molecular model of epoxy resin gradually cross-linked by amine (hereinafter referred to as method), characterized in that the method comprises the following steps:

[0027] Step 1, constructing monomer molecules in molecular modeling software; the monomer molecules include amine accelerator monomer molecules (hereinafter referred to as amine molecules), organic acid anhydride curing agent monomer molecules (hereinafter referred to as anhydride molecules) and epoxy resin monomer molecules (hereinafter referred to as epoxy molecules);

[0028] Preferably, in step 1, the molecular modeling software adopts Material Studio software; the Visualizer module in Materials Studio software is used to construct amine molecules, anhydride molecules and epoxy molecules respectively; and then the geometry of the amine molecules, anhydride molecules and epoxy molecules is optimized to obtain a stable molecular configuration.

[0029] Step 2, marking reactive atoms on the monomer molecules constructed in step 1; the reactive atoms are N atoms in amine molecules, two C atoms on the anhydride group in anhydride molecules, single-bonded O atoms on the anhydride group in anhydride molecules, C atoms in CH2 on the epoxy group in epoxy molecules, and O atoms on the epoxy group in epoxy molecules;

[0030] Preferably, in step 2, the N atom in the labeled amine molecule is RN; the anhydride group in the labeled anhydride molecule is The two C atoms on the anhydride molecule are marked as RC1; the single-bonded O atom on the anhydride group in the anhydride molecule is marked as RO1; the C atom in the CH2 on the epoxy group in the epoxy molecule is marked as RC2; and the O atom on the epoxy group in the epoxy molecule is marked as RO2.

[0031] Step 3, set the modeling parameters and cross-linking parameters required for programming, and then construct a mixture model based on the amine molecules, anhydride molecules and epoxy molecules marked in step 2 through programming, and then perform geometric optimization and molecular dynamics equilibrium on the mixture model in turn to obtain the mixture optimization model; then cross-link the mixture optimization model and output a series of cross-linked molecular models with specified cross-linking degree intervals at one time.

[0032] Preferably, in step 3, programming is performed using Perl language.

[0033] Preferably, the specific steps of step 3 are as follows:

[0034] S3.1. Set the modeling parameters and cross-linking parameters required for programming;

[0035] Preferably, in step S3.1, the modeling parameters include the relative molecular masses of amine molecules, anhydride molecules and epoxy molecules, the epoxy value of the epoxy resin, the mass ratio of amine accelerator / organic anhydride curing agent / epoxy resin and the number of amine molecules.

[0036] Preferably, in step S3.1, the cross-linking parameters include cross-linking temperature, cross-linking pressure, maximum cross-linking degree, cross-linking degree interval, cross-linking cutoff radius R and iteration upper limit.

[0037] S3.2, according to the modeling parameters set in S3.1, a mixture model based on the amine molecules, anhydride molecules and epoxy molecules labeled in step 2 is constructed by programming, and then the mixture model is subjected to geometric optimization and molecular dynamics equilibrium in sequence to obtain an optimized mixture model;

[0038] Preferably, step S3.2 is specifically:

[0039] S3.2.1. Calculate the molecular number ratio of amine molecules, acid anhydride molecules and epoxy molecules in the mixture model according to the modeling parameters set in S3.1, and then construct a mixture model including amine molecules, acid anhydride molecules and epoxy molecules according to the molecular number ratio;

[0040] S3.2.2. Perform geometric optimization on the mixture model until convergence, and then perform molecular dynamics equilibrium until the mixture model obtains a stable density to obtain the mixture optimization model.

[0041] S3.3. According to the cross-linking parameters set in S3.1, the mixture optimization model is cross-linked by programming, and a series of cross-linked molecular models with specified cross-linking degree intervals are output at one time.

[0042] Preferably, step S3.3 is specifically:

[0043] S3.3.1. Determine the curing reaction mechanism of the amine accelerator / organic anhydride curing agent / epoxy resin system;

[0044] Preferably, in step S3.3.1, the curing reaction mechanism is specifically:

[0045] (a) The anhydride is ring-opened by the amine to generate a carboxylate ion, as shown in formula (1);

[0046]

[0047] (b) Carboxylate ions can open the epoxy group to form an ester bond and an alkoxy anion, as shown in formula (2);

[0048]

[0049] (c) the alkoxy anion reacts with the acid anhydride to form an ester bond and a carboxylate ion, as shown in formula (3);

[0050]

[0051] Alkoxy anions can also react with epoxy groups to form ether bonds and alkoxy anions, as shown in formula (4);

[0052]

[0053] (d) Repeat (b) and (c) in sequence to eventually form a 3D network structure with a high degree of cross-linking;

[0054] In formulas (1)-(4), R a The residue of an anhydride group is removed, R b The residue after the amine and anhydride are combined and a carboxylate ion is removed. c Remove the residue of an alkoxy anion for cross-linking molecules.

[0055] S3.3.2, introduce reaction assumptions;

[0056] Preferably, in step S3.3.2, the reaction assumption conditions are: (1) reaction atoms outside the cross-linking cut-off radius do not have cross-linking reaction activity; (2) the closer the distance between reaction atoms within the cross-linking cut-off radius, the greater the cross-linking reaction activity; (3) the cross-linking reaction activity of different types of reaction atoms is the same; (4) each reaction is carried out step by step.

[0057] S3.3.3, designing a crosslinking cycle process according to the crosslinking parameters set in S3.1, the curing reaction mechanism determined in S3.3.1, and the reaction assumptions introduced in S3.3.2, and then programming according to the crosslinking cycle process to obtain a crosslinking program;

[0058] Preferably, in step S3.3.3, the cross-linking cycle process is as follows:

[0059] S3.3.3.1. Search the model for all RC1s on the unopened anhydride groups whose distance from RN is less than the crosslinking cutoff radius R; if no RC1 that meets the requirements is found, and the number of RN-RC1 bonds in the model is 0, execute step S3.3.3.5; if no RC1 that meets the requirements is found, and the number of RN-RC1 bonds in the model is not 0, execute step S3.3.3.2; if RC1 that meets the requirements is found, execute the following steps:

[0060] (a) Select RC1 with the smallest distance to RN, break its RC1-RO1 bond, generate RN-RC1 bond and RO1 ion, and label RO1 ion as RO1i;

[0061] (b) geometric optimization of the model to obtain a stable configuration;

[0062] (c) Execute step S3.3.3.2;

[0063] S3.3.3.2. If RO1i does not exist in the model, execute S3.3.3.3; if RO1i exists in the model, search for all RC2s in the model whose distance to RO1i is less than R and are not cross-linked; if no RC2 that meets the requirements is found, execute step S3.3.3.5; if RC2 that meets the requirements is found, execute the following steps:

[0064] (a) Select RC2 with the smallest distance to RO1i, break its RC2-RO2 bond, generate RO1i-RC2 bond and RO2 ion, and label RO2 ion as RO2i;

[0065] (b) geometric optimization of the model to obtain a stable configuration;

[0066] (c) Execute step S3.3.3.3;

[0067] S3.3.3.3. Search the model for all RC1s on the unopened anhydride groups whose distance to RO2i is less than R; if no RC1 that meets the requirements is found, execute step S3.3.3.4; if a RC1 that meets the requirements is found, execute the following steps:

[0068] (a) Select RC1 with the smallest distance to RO2i, break its RC1-RO1 bond, generate RO2i-RC1 bond and RO1 ion, and label RO1 ion as RO1i;

[0069] (b) geometric optimization of the model to obtain a stable configuration;

[0070] (c) Return to step S3.3.3.2;

[0071] S3.3.3.4. Search the model for all RC2s whose distance to RO2i is less than R and are not cross-linked; if no RC2 that meets the requirements is found, execute step S3.3.3.5; if a RC2 that meets the requirements is found, execute the following steps:

[0072] (a) Select RC2 with the smallest distance to RO2i, break its RC2-RO2 bond, generate RO2i-RC2 bond and RO2 ion, and label RO2 ion as RO2i;

[0073] (b) geometric optimization of the model to obtain a stable configuration;

[0074] (c) Return to step S3.3.3.3;

[0075] S3.3.3.5. Perform molecular dynamics equilibrium on the model to change the model structure to obtain reactive atomic pairs with cross-linking reaction activity, and then return to step S3.3.3.1; calculate the degree of cross-linking in real time during the cross-linking cycle, and output a cross-linked molecular model every time the degree of cross-linking increases by one cross-linking interval until the maximum degree of cross-linking or the upper limit of iteration is reached, at which point the cross-linking cycle ends, and outputs a cross-linked molecular model at the end of the cross-linking cycle.

[0076] S3.3.4. Run the cross-linking program written in S3.3.3 on the mixture optimization model, and output a series of cross-linking molecular models with specified cross-linking degree intervals at one time.

[0077] Example 1

[0078] With N,N-dimethylbenzylamine (BDMA) as the amine accelerator component, methyltetrahydrophthalic anhydride (MTHPA) as the organic anhydride curing agent component, and 4,5-epoxycyclohexane-1,2-dicarboxylic acid diglycidyl ester (TDE-85) as the epoxy resin component, a BDMA / MTHPA / TDE-85 crosslinking molecular model was constructed, and its glass transition temperature T was calculated. g ( Figure 6 ), and T measured by DSC experiment g ( Figure 7 ) were compared to verify the accuracy of the model.

[0079] All the following implementations are based on the molecular dynamics method and are carried out in the software Material Studio. The molecular force field uses the COMPASSII force field. The specific implementation process is as follows:

[0080] Step 1: Build monomer molecules in molecular modeling software:

[0081] According to the actual molecular structure, the Visualizer module was used in the Material Studio software to construct the BDMA, MTHPA and TDE-85 monomer molecules, and then the Smart algorithm was used to optimize the geometry of the above monomer molecules to obtain the stable molecular configuration (such as Figure 2-Figure 4 shown).

[0082] Step 2: Label the reactive atoms on the monomer molecule constructed in step 1:

[0083] The N atom in the BDMA molecule is marked as RN; the two C atoms on the anhydride group in the MTHPA molecule are marked as RC1; the single-bonded O atom on the anhydride group in the MTHPA molecule is marked as RO1; the C atom in the CH2 on the epoxy group in the TDE-85 molecule is marked as RC2; the O atom on the epoxy group in the TDE-85 molecule is marked as RO2;

[0084] Step 3, set the modeling parameters and cross-linking parameters required for programming, and then implement it through perl language programming: construct a mixture model based on the BDMA molecules, MTHPA molecules and TDE-85 molecules marked in step 2, and then perform geometric optimization and molecular dynamics equilibrium on the mixture model in turn to obtain the mixture optimization model; then cross-link the mixture optimization model and output a series of cross-linked molecular models with specified cross-linking degree intervals at one time.

[0085] S3.1. Set the modeling parameters and cross-linking parameters required for programming:

[0086] Modeling parameters: Input the relative molecular masses of BDMA, MTHPA and TDE-85 molecules as 135.21, 166.17 and 298.29 respectively; input the epoxy value of TDE-85 as 0.85, set the mass ratio of BDMA, MTHPA and TDE-85 as 1:143:100, and set the number of BDMA molecules as 1;

[0087] Cross-linking parameters: set the cross-linking temperature to 433K, the cross-linking pressure to one atmosphere, the maximum cross-linking degree to 90%, the cross-linking interval to 10%, and the cross-linking cutoff radius R to The upper limit of iteration is 10 times;

[0088] S3.2, according to the modeling parameters set in S3.1, by programming: constructing a mixture model based on the BDMA molecules, MTHPA molecules and TDE-85 molecules labeled in step 2, and then performing geometric optimization and molecular dynamics equilibrium on the mixture model in turn to obtain an optimized mixture model;

[0089] S3.2.1. According to the modeling parameters set in S3.1, the model molecule number ratio is calculated to be 1:116:39, and then a mixture model including BDMA molecules, MTHPA molecules and TDE-85 molecules is constructed according to the molecular number ratio;

[0090] S3.2.2. Perform geometric optimization on the mixture model until convergence, and then perform molecular dynamics equilibrium until the mixture model obtains a stable density to obtain the mixture optimization model.

[0091] The Smart algorithm was used for geometry optimization; molecular dynamics equilibrium was performed under the NPT ensemble, with the temperature controlled at 433 K, the pressure at one atmosphere, and the step length at 1 fs; the Nose method and the Berendsen method were used to control the temperature and pressure, respectively; the Atom-based and Ewald methods were used to calculate the van der Waals force and electrostatic interaction, respectively, with a cutoff radius of

[0092] S3.3. According to the cross-linking parameters set in S3.1, the mixture optimization model is cross-linked by programming, and a series of cross-linked molecular models with specified cross-linking degree intervals are output at one time:

[0093] S3.3.1. The cross-linking reaction mechanism of BDMA, MTHPA and TDE-85 is determined as follows: (a) the anhydride is opened by the amine to form a carboxylate ion; (b) the carboxylate ion can open the epoxy group to form an ester bond and an alkoxy anion; (c) the alkoxy anion reacts with the anhydride to form an ester bond and a carboxylate ion, and the alkoxy anion also reacts with the epoxy group to form an ether bond and an alkoxy anion; (d) (b) and (c) are repeated in sequence to eventually form a 3D network structure with a high degree of cross-linking;

[0094] S3.3.2. The following reaction assumptions are introduced: (1) Reaction atoms outside the cross-linking cut-off radius have no cross-linking reaction activity; (2) The closer the distance between reaction atoms within the cross-linking cut-off radius, the greater the cross-linking reaction activity; (3) The cross-linking reaction activity of different types of reaction atoms is the same; and (4) Each reaction proceeds step by step.

[0095] S3.3.3, designing a crosslinking cycle process according to the crosslinking parameters set in S3.1, the curing reaction mechanism determined in S3.3.1, and the reaction assumptions introduced in S3.3.2, and then programming according to the crosslinking cycle process to obtain a crosslinking program;

[0096] The cross-linking cycle process is designed as follows:

[0097] S3.3.3.1. Search the model for all RC1s on the unopened anhydride groups whose distance from RN is less than the crosslinking cutoff radius R; if no RC1 that meets the requirements is found, and the number of RN-RC1 bonds in the model is 0, execute step S3.3.3.5; if no RC1 that meets the requirements is found, and the number of RN-RC1 bonds in the model is not 0, execute step S3.3.3.2; if RC1 that meets the requirements is found, execute the following steps:

[0098] (a) Select RC1 with the smallest distance to RN, break its RC1-RO1 bond, generate RN-RC1 bond and RO1 ion, and label RO1 ion as RO1i;

[0099] (b) geometric optimization of the model to obtain a stable configuration;

[0100] (c) Execute step S3.3.3.2;

[0101] S3.3.3.2. If RO1i does not exist in the model, execute S3.3.3.3; if RO1i exists in the model, search for all RC2s in the model whose distance to RO1i is less than R and are not cross-linked; if no RC2 that meets the requirements is found, execute step S3.3.3.5; if RC2 that meets the requirements is found, execute the following steps:

[0102] (a) Select RC2 with the smallest distance to RO1i, break its RC2-RO2 bond, generate RO1i-RC2 bond and RO2 ion, and label RO2 ion as RO2i;

[0103] (b) geometric optimization of the model to obtain a stable configuration;

[0104] (c) Execute step S3.3.3.3;

[0105] S3.3.3.3. Search the model for all RC1s on the unopened anhydride groups whose distance to RO2i is less than R; if no RC1 that meets the requirements is found, execute step S3.3.3.4; if a RC1 that meets the requirements is found, execute the following steps:

[0106] (a) Select RC1 with the smallest distance to RO2i, break its RC1-RO1 bond, generate RO2i-RC1 bond and RO1 ion, and label RO1 ion as RO1i;

[0107] (b) geometric optimization of the model to obtain a stable configuration;

[0108] (c) Return to step S3.3.3.2;

[0109] S3.3.3.4. Search the model for all RC2s whose distance to RO2i is less than R and are not cross-linked; if no RC2 that meets the requirements is found, execute step S3.3.3.5; if a RC2 that meets the requirements is found, execute the following steps:

[0110] (a) Select RC2 with the smallest distance to RO2i, break its RC2-RO2 bond, generate RO2i-RC2 bond and RO2 ion, and label RO2 ion as RO2i;

[0111] (b) geometric optimization of the model to obtain a stable configuration;

[0112] (c) Return to step S3.3.3.3;

[0113] S3.3.3.5. Perform molecular dynamics equilibrium on the model to change the model structure to obtain reactive atomic pairs with cross-linking reaction activity, and then return to step S3.3.3.1; calculate the degree of cross-linking in real time during the cross-linking cycle, and output a cross-linked molecular model every time the degree of cross-linking increases by one cross-linking interval until the maximum degree of cross-linking or the upper limit of iteration is reached, at which point the cross-linking cycle ends, and outputs a cross-linked molecular model at the end of the cross-linking cycle.

[0114] S3.3.4. Run the cross-linking program written in S3.3.3 on the mixture optimization model, and output a series of cross-linking molecular models with specified cross-linking degree intervals at one time.

[0115] Results Figure 5 , Figure 5 (a)-(j) are the cross-linked molecular models of BDMA / MTHPA / TDE-85 with cross-linking degrees of 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90% during the cross-linking process, respectively. The cross-linking points have been marked with ball-and-stick displays. It can be seen that with the increase of the cross-linking degree, the number of atoms in the ball-and-stick display continues to increase, indicating that the cross-linking reaction continues.

[0116] Take the epoxy model with 90% cross-linking degree as an example to calculate its T g The system was simulated to cool down from 480K to 360K, with a temperature interval of 10K, a pressure set to one atmosphere, and a cooling rate of 10K / 100ps, that is, a 100ps NPT ensemble molecular dynamics simulation was performed at each temperature to extract the density information of the model at each temperature level. Based on the density-temperature information extracted during the cooling process, a density-temperature relationship diagram was drawn as shown below: Figure 6 , and T is obtained by linear fitting method g The DSC curve obtained from the actual test is as follows Figure 7As shown, the T g The value is around 432.17K (159.02℃), which is consistent with the simulated T g The difference in the values ​​is very small, so the cross-linked molecular model constructed by the present invention is accurate and effective.

[0117] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A method for constructing a cross-linked molecular model of an amine-initiated epoxy resin stepwise cross-linking, characterized in that: The method comprises the following steps: Step 1, constructing monomer molecules in molecular modeling software; the monomer molecules include amine accelerator monomer molecules, organic acid anhydride curing agent monomer molecules and epoxy resin monomer molecules; Step 2, marking reactive atoms on the monomer molecules constructed in step 1; the reactive atoms are N atoms in amine molecules, two C atoms on the anhydride group in anhydride molecules, single-bonded O atoms on the anhydride group in anhydride molecules, C atoms in CH2 on the epoxy group in epoxy molecules, and O atoms on the epoxy group in epoxy molecules; Step 3, set the modeling parameters and cross-linking parameters, and then construct a mixture model based on the amine molecules, anhydride molecules and epoxy molecules marked in step 2, and then perform geometric optimization and molecular dynamics equilibrium on the mixture model in turn to obtain a mixture optimization model; then determine the curing reaction mechanism of the amine accelerator / organic anhydride curing agent / epoxy resin system, and introduce reaction assumptions; then design a cross-linking cycle process based on the cross-linking parameters, the curing reaction mechanism and the reaction assumptions, and then program according to the cross-linking cycle process to obtain a cross-linking program; then run the cross-linking program on the mixture optimization model, and output a series of cross-linking molecular models with a specified cross-linking degree interval at one time; The reaction assumptions are as follows: (1) Reactive atoms outside the cross-link cutoff radius have no cross-linking activity; (2) The closer the distance between reactive atoms within the cross-link cutoff radius, the greater the cross-linking activity; (3) Different types of reactive atoms have the same cross-linking activity; (4) Each reaction proceeds step by step; The cross-linking cycle process is as follows: S1, search the model for all RC1s on the unopened anhydride groups whose distance from RN is less than the crosslinking cutoff radius R; if no RC1 meeting the requirements is found, and the number of RN-RC1 bonds in the model is 0, execute step S5; if no RC1 meeting the requirements is found, and the number of RN-RC1 bonds in the model is not 0, execute step S2; if RC1 meeting the requirements is found, execute the following steps: (a) Select RC1 with the smallest distance to RN, break its RC1-RO1 bond, generate RN-RC1 bond and RO1 ion, and label RO1 ion as RO1i; (b) geometric optimization of the model to obtain a stable configuration; (c) executing step S2; S2. If RO1i does not exist in the model, execute S3; if RO1i exists in the model, search for all RC2 in the model whose distance to RO1i is less than R and not cross-linked; if RC2 that meets the requirements is not found, execute step S5; if RC2 that meets the requirements is found, execute the following steps: (a) Select RC2 with the smallest distance to RO1i, break its RC2-RO2 bond, generate RO1i-RC2 bond and RO2 ion, and label RO2 ion as RO2i; (b) geometric optimization of the model to obtain a stable configuration; (c) executing step S3; S3, search the model for all RC1s on the unopened anhydride groups whose distance from RO2i is less than R; if no RC1 satisfying the requirements is found, execute step S4; if a RC1 satisfying the requirements is found, execute the following steps: (a) Select RC1 with the smallest distance to RO2i, break its RC1-RO1 bond, generate RO2i-RC1 bond and RO1 ion, and label RO1 ion as RO1i; (b) geometric optimization of the model to obtain a stable configuration; (c) Return to step S2; S4, search for all RC2 in the model whose distance to RO2i is less than R and not cross-linked; if no RC2 meeting the requirements is found, execute step S5; if a RC2 meeting the requirements is found, execute the following steps: (a) Select RC2 with the smallest distance to RO2i, break its RC2-RO2 bond, generate RO2i-RC2 bond and RO2 ion, and label RO2 ion as RO2i; (b) geometric optimization of the model to obtain a stable configuration; (c) Return to step S3; S5, performing molecular dynamics equilibrium on the model to change the structure of the model to obtain reactive atomic pairs with cross-linking reaction activity, and then returning to step S1; calculating the cross-linking degree in real time during the cross-linking cycle, and outputting a cross-linked molecular model once for each increase in the cross-linking degree interval, until the maximum cross-linking degree or the upper limit of the iteration is reached, the cross-linking cycle ends, and a cross-linked molecular model is output once at the end of the cross-linking cycle; Among them, the N atom in the amine molecule is RN; the two C atoms on the anhydride group in the anhydride molecule are RC1; the single-bonded O atom on the anhydride group in the anhydride molecule is RO1; the C atom in the CH2 on the epoxy group in the epoxy molecule is RC2; and the O atom on the epoxy group in the epoxy molecule is RO2.

2. The method for constructing a cross-linked molecular model of an amine-initiated epoxy resin stepwise cross-linking according to claim 1, characterized in that: In step 1, Material Studio software is used as molecular modeling software; the Visualizer module in Materials Studio software is used to construct amine molecules, anhydride molecules and epoxy molecules respectively; and then the geometric optimization of the constructed amine molecules, anhydride molecules and epoxy molecules is performed to obtain a stable molecular configuration.

3. The method for constructing a cross-linked molecular model of amine-initiated epoxy resin stepwise cross-linking according to claim 1, characterized in that: In step 3, programming is done using Perl language.

4. The method for constructing a cross-linked molecular model of an amine-initiated epoxy resin stepwise cross-linking according to claim 1 or 3, characterized in that: The specific steps of step 3 are as follows: S3.

1. Set the modeling parameters and cross-linking parameters required for programming; S3.2, according to the modeling parameters set in S3.1, construct a mixture model based on the amine molecules, anhydride molecules and epoxy molecules labeled in step 2, and then perform geometric optimization and molecular dynamics equilibrium on the mixture model in turn to obtain an optimized mixture model; S3.

3. According to the cross-linking parameters set in S3.1, the mixture optimization model is cross-linked, and a series of cross-linked molecular models with specified cross-linking degree intervals are output at one time.

5. The method for constructing a cross-linked molecular model of amine-initiated epoxy resin stepwise cross-linking according to claim 4, characterized in that: In step S3.1, the modeling parameters include the relative molecular weights of amine molecules, anhydride molecules and epoxy molecules, the epoxy value of the epoxy resin, the mass ratio of amine accelerator / organic anhydride curing agent / epoxy resin and the number of amine molecules; The cross-linking parameters include cross-linking temperature, cross-linking pressure, maximum cross-linking degree, cross-linking degree interval, cross-linking cutoff radius R and iteration upper limit.

6. The method for constructing a cross-linked molecular model of amine-initiated epoxy resin stepwise cross-linking according to claim 4, characterized in that: Step S3.2 is specifically as follows: S3.2.

1. Calculate the molecular number ratio of amine molecules, acid anhydride molecules and epoxy molecules in the mixture model according to the modeling parameters set in S3.1, and then construct a mixture model including amine molecules, acid anhydride molecules and epoxy molecules according to the molecular number ratio; S3.2.

2. Perform geometric optimization on the mixture model until convergence, and then perform molecular dynamics equilibrium until the mixture model obtains a stable density to obtain the mixture optimization model.

7. The method for constructing a cross-linked molecular model of amine-initiated epoxy resin stepwise cross-linking according to claim 1, characterized in that: In step 3, the curing reaction mechanism is specifically as follows: (a) The anhydride is ring-opened by the amine to generate a carboxylate ion, as shown in formula (1); (b) Carboxylate ions can open the epoxy group to form an ester bond and an alkoxy anion, as shown in formula (2); (c) the alkoxy anion reacts with the acid anhydride to form an ester bond and a carboxylate ion, as shown in formula (3); Alkoxy anions can also react with epoxy groups to form ether bonds and alkoxy anions, as shown in formula (4); (d) Repeat (b) and (c) in sequence to eventually form a 3D network structure with a high degree of cross-linking; In formulas (1)-(4), R a The residue of an anhydride group is removed, R b The residue after the amine and anhydride are combined and a carboxylate ion is removed. c Remove the residue of an alkoxy anion for cross-linking molecules.

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