Preparation method of low-viscosity bio-based polyamide curing agent

Abstract

The invention relates to the technical field of high polymer materials, in particular to a preparation method of a low-viscosity bio-based polyamide curing agent, and the specific technical scheme is as follows: S1, synthesizing a polypeptide sequence with a coiled spiral structure, the polypeptide sequence comprises an amino acid sequence capable of forming a stable alpha-helix, amino acid containing a reactive group, a flexible chain segment and a functional group; s2, assembling the polypeptide sequence obtained in the step S1 into a coiled spiral structure in a solution; s3, adding a cross-linking agent to carry out cross-linking reaction by utilizing the reactive groups introduced in the step S1 to obtain a stable coiled spiral structure; s4, adjusting the viscosity of the polyamide material with the coiled spiral structure obtained in the step S3 by controlling the molecular weight; and S5, carrying out polymerization reaction on the low-viscosity curled spiral structure polyamide material obtained in the step S4 and other monomers to prepare the polyamide curing agent.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and particularly relates to a preparation method of a low-viscosity bio-based polyamide curing agent. Background Art

[0002] Polyamide curing agent is an important polymer material, which is widely used in fields such as coatings, adhesives, and composite materials. Traditional polyamide curing agents are mainly made from petroleum-based raw materials, which have problems such as non-renewable resources and environmental pollution. With the enhancement of environmental awareness, the development of bio-based polyamide curing agents using renewable resources as raw materials has become a research hotspot.

[0003] In recent years, researchers have developed various bio-based polyamide curing agents, such as vegetable oil-based polyamide curing agents and amino acid-based polyamide curing agents. However, these bio-based polyamide curing agents generally have problems such as high viscosity and poor processing performance, which limit their application scope.

[0004] To solve the above problems, researchers have tried to reduce the viscosity of bio-based polyamide curing agents through means such as molecular design and optimization of synthesis processes. For example, some studies have reported reducing the viscosity by introducing flexible segments into the polyamide molecular chain, but this method often leads to a decrease in the mechanical properties of the material. Summary of the Invention

[0005] The present invention aims to provide a preparation method of a low-viscosity bio-based polyamide curing agent to solve the technical problems of high viscosity, poor processing performance, and difficulty in balancing mechanical properties and viscosity existing in existing bio-based polyamide curing agents.

[0006] The above technical object of the present invention is achieved through the following technical solutions:

[0007] A preparation method of a low-viscosity bio-based polyamide curing agent provided by the present invention includes the following steps:

[0008] S1. Synthesize a polypeptide sequence with a coiled-coil structure, and the polypeptide sequence includes: an amino acid sequence capable of forming a stable α-helix, an amino acid containing a reactive group, a flexible segment, and a functional group;

[0009] S2. Assemble the polypeptide sequence obtained in step S1 into a coiled-coil structure in a solution;

[0010] S3. Utilize the reactive group introduced in step S1, add a cross-linking agent to carry out a cross-linking reaction to obtain a stable coiled-coil structure;

[0011] S4. Adjust the viscosity of the coiled-coil structure polyamide material obtained in step S3 by controlling the molecular weight;

[0012] S5. Polymerize the low-viscosity coiled-coil structured polyamide material obtained in step S4 with other monomers to prepare a polyamide curing agent.

[0013] Further, the amino acid sequence capable of forming a stable α-helix is one or more of polyalanine, polyleucine, polyglutamic acid, or polylysine.

[0014] Further, the amino acid containing a reactive group is one or more of cysteine, lysine, aspartic acid, or glutamic acid.

[0015] Further, the flexible segment is one or more of a polyethylene glycol segment, a polypropylene glycol segment, or a polycaprolactone segment.

[0016] Further, the functional group is one or more of a disulfide bond, a Diels-Alder reaction group, a pH-sensitive group, a temperature-sensitive group, or a light-sensitive group.

[0017] Further, the assembly conditions in step S1 are to adjust one or more of the solution pH value, ionic strength, or temperature.

[0018] Further, the crosslinking agent is one or more of bismaleimide, diisocyanate, or epoxy resin.

[0019] Further, the diluent is one or more of epoxy soybean oil, epoxy fatty acid methyl ester, or vegetable oil.

[0020] Further, the molecular weight in step S4 is controlled at 5000 - 20000 Da.

[0021] Further, the other monomers in step S1 are one or more of the following: lysine, glutamic acid, aspartic acid, itaconic acid, fumaric acid, or citric acid.

[0022] In summary, the present invention has the following beneficial effects:

[0023] The present invention utilizes the characteristics of the coiled-coil structure to endow the material with excellent mechanical properties and functional characteristics, making it outstanding in terms of strength, toughness, and functionality. Secondly, by precisely controlling the molecular weight and introducing flexible segments and other means, the viscosity of the material is effectively reduced, and its processing performance is significantly improved, making it easier to operate and apply. Detailed Description of the Invention

[0024] To further elaborate on the technical means and effects adopted by the present invention to achieve the intended invention purpose, a preparation method of a low-viscosity bio-based polyamide curing agent according to the present invention, its specific implementation manner, characteristics, and effects are described in detail as follows.

[0025] A preparation method of a low-viscosity bio-based polyamide curing agent provided by this specific embodiment includes the following steps:

[0026] S1. Synthesize a polypeptide sequence with a coiled-coil structure, and the polypeptide sequence includes: an amino acid sequence capable of forming a stable α-helix, an amino acid containing a reactive group, a flexible segment, and a functional group;

[0027] S2. Assemble the polypeptide sequence obtained in step S1 into a coiled-coil structure in a solution;

[0028] S3. Utilize the reactive group introduced in step S1, add a cross-linking agent to carry out a cross-linking reaction to obtain a stable coiled-coil structure;

[0029] S4. Adjust the viscosity of the coiled-coil structure polyamide material obtained in step S3 by controlling the molecular weight;

[0030] S5. Polymerize the low-viscosity coiled-coil structure polyamide material obtained in step S4 with other monomers to prepare a polyamide curing agent.

[0031] It can be understood that through bionic design, the coiled-coil structure with excellent mechanical properties and functional characteristics in natural proteins is introduced into synthetic polymer materials, and combined with molecular weight control and functional modification, a low-viscosity and high-performance bio-based polyamide curing agent is prepared. Among them, the coiled-coil structure is a superhelical structure formed by the intertwining of two or more α-helices, and has excellent properties such as high strength and high toughness. Introducing it into the polyamide molecular chain can significantly improve the mechanical properties and functional characteristics of the material. By means of controlling the length of the polypeptide chain, using a chain transfer agent, enzymatic hydrolysis, etc., the molecular weight of the coiled-coil structure polyamide material is controlled, thereby adjusting its viscosity. Functional groups, such as self-healing groups and stimulus-responsive groups, are introduced into the polypeptide sequence to endow the material with functions such as self-healing and stimulus response.

[0032] Furthermore, the amino acid sequence capable of forming a stable α-helix is one or more of polyalanine, polyleucine, polyglutamic acid, or polylysine.

[0033] It can be understood that the α-helix is a protein secondary structure, and its stability mainly depends on the nature and arrangement of amino acid side chains. In this specific embodiment, the side chain of polyalanine is a methyl group, with small steric hindrance, which is conducive to forming a tight α-helix structure and improving the mechanical strength of the material; the side chain of polyleucine is an isobutyl group, with certain hydrophobicity, which can improve the water resistance of the material; the side chain of polyglutamic acid has a carboxyl group, which can endow the material with pH responsiveness and can be further modified through the carboxyl group; the side chain of polylysine has an amino group, which can endow the material with pH responsiveness and can be further modified through the amino group.

[0034] Further, the amino acid containing a reactive group is one or more of cysteine, lysine, aspartic acid or glutamic acid.

[0035] It can be understood that the side chains of cysteine, lysine, aspartic acid and glutamic acid contain reactive groups and can participate in various chemical reactions. Cysteine contains a mercapto group (-SH) and can participate in oxidation reactions, nucleophilic addition reactions, etc.; lysine contains an amino group (-NH2) and can participate in amidation reactions, condensation reactions, etc.; aspartic acid and glutamic acid contain a carboxyl group (-COOH) and can participate in esterification reactions, amidation reactions, etc.; these reactive groups can be used for cross-linking reactions and functional modifications. They can react with cross-linking agents through reactive groups to form a cross-linked network, improving the mechanical strength and stability of the material, or introduce functional groups, such as fluorescent groups, targeting groups, etc., through reactive groups to endow the material with specific functions.

[0036] Further, the flexible segment is one or more of a polyethylene glycol segment, a polypropylene glycol segment or a polycaprolactone segment.

[0037] It can be understood that introducing PEG, PPG or PCL flexible segments into the coiled-coil structure polyamide material can reduce the interaction between molecular chains, thereby reducing the viscosity of the material and improving the processing performance; the flexible segment can absorb impact energy and improve the toughness and impact resistance of the material.

[0038] Further, the functional group is one or more of a disulfide bond, a Diels - Alder reaction group, a pH - sensitive group, a temperature - sensitive group or a light - sensitive group.

[0039] It can be understood that introducing functional groups into the coiled - coil structure polyamide material can endow the material with specific functions. The disulfide bond can undergo reversible redox reactions, endowing the material with self - healing function; the Diels - Alder reaction group can undergo reversible Diels - Alder reactions, endowing the material with self - healing function and shape - memory function; pH - sensitive groups, such as carboxyl groups, amino groups, etc., can respond to changes in pH value, endowing the material with pH responsiveness; temperature - sensitive groups such as poly(N - isopropylacrylamide) (PNIPAAm), etc., can respond to changes in temperature, endowing the material with temperature responsiveness; light - sensitive groups such as azobenzene, etc., can respond to light stimuli, endowing the material with light responsiveness.

[0040] Further, the assembly conditions in step S1 are to adjust one or more of the solution pH value, ionic strength or temperature.

[0041] It can be understood that in step S1, by adjusting conditions such as the solution pH value, ionic strength, or temperature, the assembly behavior of the polypeptide sequence can be controlled, thereby obtaining a coiled-coil structured polyamide material with specific structures and properties. The following are the specific refinement of the technical solutions:

[0042] Adjusting the pH value, the side chain groups of certain amino acids in the polypeptide sequence (such as carboxyl groups, amino groups, etc.) will be protonated or deprotonated at different pH values, thereby changing the charge state and conformation of the polypeptide chain and affecting its assembly behavior; using a buffer solution to adjust the solution pH value, such as phosphate buffer solution, Tris-HCl buffer solution, etc. or according to the isoelectric point (pI) of the target polypeptide sequence, select an appropriate pH value range, such as pI±1.

[0043] Adjusting the ionic strength, the ions in the solution can shield the electrostatic interaction between polypeptide chains, thereby affecting its assembly behavior; adding salts to adjust the solution ionic strength, such as NaCl, KCl, etc. or according to the charge distribution of the target polypeptide sequence, select an appropriate salt concentration range, such as 0.1M - 1M.

[0044] Adjusting the temperature, the temperature can affect the conformation and motility of the polypeptide chain, thereby affecting its assembly behavior; using a constant temperature water bath or a heating magnetic stirrer to control the solution temperature or according to the thermal stability of the target polypeptide sequence, select an appropriate temperature range, such as 40 - 60°C.

[0045] Furthermore, the crosslinking agent is one or more of bismaleimide, diisocyanate, or epoxy resin.

[0046] It can be understood that bismaleimide, diisocyanate, and epoxy resin can react with reactive groups (such as sulfhydryl groups, amino groups, carboxyl groups, etc.) in the polypeptide sequence to form a crosslinked network, thereby improving the mechanical strength and stability of the material; bismaleimide can undergo a Michael addition reaction with sulfhydryl groups to form stable thioether bonds, with a fast reaction rate, high crosslinking efficiency, and good stability of the formed thioether bonds; diisocyanate can react with amino groups or hydroxyl groups to form urea bonds or carbamate bonds, with high reaction activity, can react with a variety of groups, and the formed urea bonds and carbamate bonds have high strength; epoxy resin can react with amino groups or carboxyl groups to form ether bonds or ester bonds, with mild reaction conditions, can react with a variety of groups, and the formed ether bonds and ester bonds have good stability.

[0047] Furthermore, the diluent is one or more of epoxy soybean oil, epoxy fatty acid methyl ester, or vegetable oil.

[0048] It can be understood that using epoxidized soybean oil, epoxidized fatty acid methyl ester or vegetable oil as a diluent in the coiled-coil structure polyamide material can reduce the interaction between molecular chains, thereby reducing the viscosity of the material and improving its processing performance, such as facilitating spraying, casting, etc. At the same time, the diluent can act as a plasticizer to improve the toughness and impact resistance of the material.

[0049] Further, the molecular weight in step S4 is controlled to be 5000 - 20000 Da.

[0050] It can be understood that controlling the molecular weight of the coiled-coil structure polyamide material within the range of 5000 - 20000 Da can effectively balance the viscosity, mechanical properties and processing performance of the material, which is a key step in preparing a high-performance bio-based polyamide curing agent.

[0051] Preferably, the solid-phase synthesis method is used to synthesize a polypeptide chain with a target length of 50 amino acid residues, then thiol is used as a chain transfer agent to control the molecular weight distribution, and finally fractionation is carried out by gel filtration chromatography to obtain a polypeptide sample with a narrow molecular weight distribution.

[0052] More preferably, the liquid-phase synthesis method is used to synthesize a polypeptide chain with a target length of 100 amino acid residues, then trypsin is used for enzymatic hydrolysis to control the polypeptide chain length, and finally fractionation is carried out by ultrafiltration to obtain a polypeptide sample with the target molecular weight.

[0053] Further, the other monomers in step S1 are one or more of the following: lysine, glutamic acid, aspartic acid, itaconic acid, fumaric acid or citric acid.

[0054] It can be understood that lysine contains an amino group and can participate in cross-linking reactions or functionalization modifications, such as introducing fluorescent dyes, targeting molecules, etc.; glutamic acid and aspartic acid contain carboxyl groups and can participate in cross-linking reactions or functionalization modifications, such as introducing pH-sensitive groups, metal ion coordination groups, etc.; itaconic acid and fumaric acid contain double bonds and can participate in Diels-Alder reactions to endow the material with self-healing and shape memory functions; citric acid contains three carboxyl groups and can form a cross-linked network to improve the mechanical strength and stability of the material.

[0055] The following further illustrates the present invention with specific embodiments.

[0056] Example 1

[0057] This Example 1 provides a preparation method of a low-viscosity bio-based polyamide curing agent based on polyalanine and cysteine, including the following steps:

[0058] S1. Synthesize the polypeptide sequence

[0059] S101. Polypeptide sequence design: Design the polypeptide sequence as (PA)10C, where PA is polyalanine and C is cysteine.

[0060] S102. Solid-phase synthesis: Use the Fmoc solid-phase synthesis method to synthesize the target polypeptide sequence.

[0061] Among them, DMF is the solvent, HBTU / HOBt is the condensing agent, DIEA is the base, and each amino acid condensation reaction lasts for 1 hour.

[0062] S103. Deprotection: Use a 20% piperidine / DMF solution to remove the Fmoc protecting group, 10 minutes each time, and repeat twice.

[0063] S104. Cleavage and purification: Use a TFA / TIS / H2O (95:2.5:2.5) cleavage solution to cleave the polypeptide from the resin and precipitate it with cold ether. Purify the polypeptide using HPLC and collect the target peak.

[0064] S2. Assemble the coiled-coil structure

[0065] S201. Dissolve the polypeptide: Dissolve the purified polypeptide in 10 mM PBS buffer (pH 7.4) at a concentration of 1 mg / mL.

[0066] S202. Assembly: Let the polypeptide solution stand at 25 °C for 24 hours to allow it to self-assemble into a coiled-coil structure.

[0067] S3. Cross-linking reaction

[0068] S301. Add the cross-linking agent: Add bismaleimide (BMI) to the assembled polypeptide solution. The molar ratio of BMI to cysteine is 1:1, and stir and react at 25 °C for 12 hours.

[0069] S302. Purification: Dialyze the reaction product using a dialysis bag (MWCO 3500) to remove the unreacted BMI.

[0070] S4. Control the molecular weight

[0071] S401. Enzymatic hydrolysis: Use trypsin to enzymatically hydrolyze the cross-linked polypeptide. The mass ratio of the enzyme to the polypeptide is 1:100, react at 37 °C for 2 hours, and add 1% TFA to terminate the reaction.

[0072] S402. Purification: Purify the enzymatic hydrolysis product using HPLC and collect the components with a molecular weight in the range of 5000 - 20000 Da.

[0073] S5: Polymerization reaction

[0074] S501, Dissolution: Dissolve the purified polypeptide in DMF at a concentration of 10 wt%.

[0075] S502, Addition of other monomers: Add itaconic acid (IA), and the molar ratio of IA to the polypeptide is 1:1. Stir and react at 80 °C for 24 hours.

[0076] S503, Purification: Dialyze the reaction product using a dialysis bag (MWCO 3500) to remove unreacted IA.

[0077] Example 2

[0078] This Example 2 provides a preparation method of a low-viscosity bio-based polyamide curing agent based on poly(leucine) and lysine, including the following steps:

[0079] S1, Synthesis of polypeptide sequence

[0080] S101, Polypeptide sequence design: Design the polypeptide sequence as (PL)10K, where PL is poly(leucine) and K is lysine.

[0081] S102, Solid-phase synthesis: Adopt the Fmoc solid-phase synthesis method to synthesize the target polypeptide sequence, using DMF as the solvent, HBTU / HOBt as the condensing agent, and DIEA as the base. Each amino acid condensation reaction lasts for 1 hour.

[0082] S103, Deprotection: Use a 20% piperidine / DMF solution to remove the Fmoc protecting group, 10 minutes each time, and repeat twice.

[0083] S104, Cleavage and purification: Use a cleavage solution of TFA / TIS / H2O (95:2.5:2.5) to cleave the polypeptide from the resin and precipitate it with cold ether. Purify the polypeptide using HPLC and collect the target peak.

[0084] S2, Assembly of coiled-coil structure

[0085] S201, Dissolution of polypeptide: Dissolve the purified polypeptide in 10 mM PBS buffer (pH 7.4) at a concentration of 1 mg / mL.

[0086] S202, Assembly: Let the polypeptide solution stand at 25 °C for 24 hours to self-assemble into a coiled-coil structure.

[0087] S3, Crosslinking reaction

[0088] S301, Addition of crosslinking agent: Add diisocyanate (HDI) to the assembled polypeptide solution, and the molar ratio of HDI to lysine is 1:1. React: Stir and react at 25 °C for 12 hours.

[0089] S302. Purification: Dialyze the reaction product using a dialysis bag (MWCO 3500) to remove unreacted HDI.

[0090] S4. Control the molecular weight

[0091] S401. Enzymatic hydrolysis: Hydrolyze the cross-linked polypeptide using trypsin, with the mass ratio of enzyme to polypeptide being 1:100. React: React at 37 °C for 2 hours, and add 1% TFA to terminate the reaction.

[0092] S402. Purification: Purify the enzymatic hydrolysis product using HPLC, and collect the fractions with a molecular weight in the range of 5000 - 20000 Da.

[0093] S5. Polymerization reaction

[0094] S501. Dissolution: Dissolve the purified polypeptide in DMF at a concentration of 10 wt%.

[0095] S502. Add other monomers: Add citric acid (CA), with the molar ratio of CA to polypeptide being 1:1, and stir and react at 80 °C for 24 hours.

[0096] S503. Purification: Dialyze the reaction product using a dialysis bag (MWCO 3500) to remove unreacted CA.

[0097] Example 3

[0098] This Example 3 provides a preparation method of a low-viscosity bio-based polyamide curing agent based on polyglutamic acid and aspartic acid, including the following steps:

[0099] Step S1. Synthesize the polypeptide sequence

[0100] S101. Polypeptide sequence design: Design the polypeptide sequence as (PE)10D, where PE is polyglutamic acid and D is aspartic acid.

[0101] S102. Solid-phase synthesis: Adopt the Fmoc solid-phase synthesis method to synthesize the target polypeptide sequence, using DMF as the solvent, HBTU / HOBt as the condensing agent, and DIEA as the base, with each amino acid condensation reaction lasting for 1 hour.

[0102] S103. Deprotection: Use a 20% piperidine / DMF solution to remove the Fmoc protecting group, 10 minutes each time, and repeat twice.

[0103] S104. Cleavage and purification: Use a cleavage solution of TFA / TIS / H2O (95:2.5:2.5) to cleave the polypeptide from the resin, and precipitate it with cold ether. Purify the polypeptide using HPLC and collect the target peak.

[0104] S2. Assemble the coiled-coil structure

[0105] S201, Dissolve the polypeptide: Dissolve the purified polypeptide in 10 mM PBS buffer (pH 7.4) at a concentration of 1 mg / mL.

[0106] S202, Assembly: Let the polypeptide solution stand at 25 °C for 24 hours to self-assemble into a coiled-coil structure.

[0107] S3, Crosslinking reaction

[0108] S301, Add crosslinking agent: Add epoxy resin (EP) to the assembled polypeptide solution. The molar ratio of EP to aspartic acid is 1:1, and the reaction is stirred at 25 °C for 12 hours.

[0109] S302, Purification: Dialyze the reaction product using a dialysis bag (MWCO 3500) to remove the unreacted EP.

[0110] S4, Control the molecular weight

[0111] S401, Enzymatic hydrolysis: Use trypsin to enzymatically hydrolyze the crosslinked polypeptide. The mass ratio of the enzyme to the polypeptide is 1:100, and the reaction is carried out at 37 °C for 2 hours. Terminate the reaction: Add 1% TFA to terminate the reaction.

[0112] S402, Purification: Purify the enzymatic hydrolysis product using HPLC and collect the fractions with a molecular weight in the range of 5000 - 20000 Da.

[0113] S5, Polymerization reaction

[0114] S501, Dissolve: Dissolve the purified polypeptide in DMF at a concentration of 10 wt%.

[0115] S502, Add other monomers: Add fumaric acid (FA). The molar ratio of FA to the polypeptide is 1:1, and the reaction is stirred at 80 °C for 24 hours.

[0116] S503, Purification: Dialyze the reaction product using a dialysis bag (MWCO 3500) to remove the unreacted FA.

[0117] Comparative Example 1

[0118] This Comparative Example 1 provides a preparation method of a low-viscosity bio-based polyamide curing agent based on polyalanine and cysteine, including the following steps:

[0119] S1, Synthesize polypeptide sequence

[0120] S101, Polypeptide sequence design: Design the polypeptide sequence as (PA)10C, where PA is polyalanine and C is cysteine.

[0121] S102, Solid-phase synthesis: The target polypeptide sequence was synthesized using the Fmoc solid-phase synthesis method. Among them, DMF was used as the solvent, HBTU / HOBt was used as the condensing agent, and DIEA was used as the base. Each amino acid condensation reaction was carried out for 1 hour.

[0122] S103, Deprotection: The Fmoc protecting group was removed using a 20% piperidine / DMF solution, 10 minutes each time, and repeated twice.

[0123] S104, Cleavage and purification: The polypeptide was cleaved from the resin using a TFA / TIS / H2O (95:2.5:2.5) cleavage solution and precipitated with cold ether. The polypeptide was purified using HPLC, and the target peak was collected.

[0124] S2, Assemble the random coil structure

[0125] S201, Dissolve the polypeptide: The purified polypeptide was dissolved in 10 mM PBS buffer (pH 7.4) at a concentration of 1 mg / mL.

[0126] S202, Assembly: The polypeptide solution was allowed to stand at 25 °C for 24 hours to form a random coil structure.

[0127] S3, Crosslinking reaction

[0128] S301, Add the crosslinking agent: Bismaleimide (BMI) was added to the assembled polypeptide solution. The molar ratio of BMI to cysteine was 1:1, and the reaction was stirred at 25 °C for 12 hours.

[0129] S302, Purification: The reaction product was dialyzed using a dialysis bag (MWCO 3500) to remove the unreacted BMI.

[0130] S4, Control the molecular weight

[0131] S401, Enzymatic digestion: The crosslinked polypeptide was enzymatically digested using trypsin. The mass ratio of the enzyme to the polypeptide was 1:100, and the reaction was carried out at 37 °C for 2 hours. 1% TFA was added to terminate the reaction.

[0132] S402, Purification: The enzymatic digestion product was purified using HPLC, and the components with a molecular weight in the range of 5000 - 20000 Da were collected.

[0133] S5: Polymerization reaction

[0134] S501, Dissolution: The purified polypeptide was dissolved in DMF at a concentration of 10 wt%.

[0135] S502, Add other monomers: Itaconic acid (IA) was added. The molar ratio of IA to the polypeptide was 1:1, and the reaction was stirred at 80 °C for 24 hours.

[0136] S503, Purification: Dialyze the reaction product using a dialysis bag (MWCO 3500) to remove unreacted IA.

[0137] Comparative Example 2

[0138] This Comparative Example 2 provides a method for preparing a low-viscosity bio-based polyamide curing agent based on poly-L-leucine and lysine, including the following steps:

[0139] S1, Synthesis of polypeptide sequence

[0140] S101, Polypeptide sequence design: Design the polypeptide sequence as (PL)10K, where PL is poly-L-leucine and K is lysine.

[0141] S102, Solid-phase synthesis: Use the Fmoc solid-phase synthesis method to synthesize the target polypeptide sequence, with DMF as the solvent, HBTU / HOBt as the condensing agent, and DIEA as the base. Each amino acid condensation reaction takes 1 hour.

[0142] S103, Deprotection: Use a 20% piperidine / DMF solution to remove the Fmoc protecting group, 10 minutes each time, repeat twice.

[0143] S104, Cleavage and purification: Use a TFA / TIS / H2O (95:2.5:2.5) cleavage solution to cleave the polypeptide from the resin and precipitate it with cold ether. Purify the polypeptide using HPLC and collect the target peak.

[0144] S2, Assembly of coiled-coil structure

[0145] S201, Dissolve the polypeptide: Dissolve the purified polypeptide in 10 mM PBS buffer (pH 7.4) at a concentration of 1 mg / mL.

[0146] S202, Assembly: Let the polypeptide solution stand at 25 °C for 24 hours to allow self-assembly to form a coiled-coil structure.

[0147] S3, Crosslinking reaction

[0148] S301, Add crosslinking agent: Add diisocyanate (HDI) to the assembled polypeptide solution, with the molar ratio of HDI to polypeptide being 1:1. React: Stir and react at 25 °C for 12 hours.

[0149] S302, Purification: Dialyze the reaction product using a dialysis bag (MWCO 3500) to remove unreacted HDI.

[0150] S4, Control of molecular weight

[0151] S401. Enzymatic digestion: Trypsin is used to digest the cross-linked polypeptide. The mass ratio of the enzyme to the polypeptide is 1:100. The reaction is carried out at 37 °C for 2 hours, and 1% TFA is added to terminate the reaction.

[0152] S402. Purification: The enzymatic digestion product is purified by HPLC, and the components with a molecular weight in the range of 5000 - 20000 Da are collected.

[0153] S5. Polymerization reaction

[0154] S501. Dissolution: The purified polypeptide is dissolved in DMF at a concentration of 10 wt%.

[0155] S502. Adding other monomers: Citric acid (CA) is added. The molar ratio of CA to the polypeptide is 1:1. The reaction is stirred at 80 °C for 24 hours.

[0156] S503. Purification: The reaction product is dialyzed using a dialysis bag (MWCO 3500) to remove the unreacted CA.

[0157] Comparative Example 3

[0158] This Comparative Example 3 provides a preparation method of a low-viscosity bio-based polyamide curing agent based on polyglutamic acid and aspartic acid, including the following steps:

[0159] Step S1. Synthesizing polypeptide sequence

[0160] S101. Polypeptide sequence design: The designed polypeptide sequence is (PE)10D, where PE is polyglutamic acid and D is aspartic acid.

[0161] S102. Solid-phase synthesis: The target polypeptide sequence is synthesized by the Fmoc solid-phase synthesis method, using DMF as the solvent, HBTU / HOBt as the condensing agent, and DIEA as the base. Each amino acid condensation reaction takes 1 hour.

[0162] S103. Deprotection: The Fmoc protecting group is removed using a 20% piperidine / DMF solution, 10 minutes each time, and repeated twice.

[0163] S104. Cleavage and purification: The polypeptide is cleaved from the resin using a cleavage solution of TFA / TIS / H2O (95:2.5:2.5) and precipitated with cold ether. The polypeptide is purified by HPLC, and the target peak is collected.

[0164] S2. Assembling coiled-coil structure

[0165] S201. Dissolving polypeptide: The purified polypeptide is dissolved in 10 mM PBS buffer (pH 7.4) at a concentration of 1 mg / mL.

[0166] S202. Assembly: Let the polypeptide solution stand still at 25 °C for 24 hours to self-assemble into a coiled-coil structure.

[0167] S3. Crosslinking reaction

[0168] S301. Adding crosslinking agent: Add epoxy resin (EP) to the assembled polypeptide solution. The molar ratio of EP to aspartic acid is 1:1, and the reaction is stirred at 25 °C for 12 hours.

[0169] S302. Purification: Dialyze the reaction product using a dialysis bag (MWCO 3500) to remove the unreacted EP.

[0170] S4. Without controlling molecular weight

[0171] The crosslinked polypeptide is directly used for the subsequent polymerization reaction without controlling the molecular weight.

[0172] S5. Polymerization reaction

[0173] S501. Dissolution: Dissolve the purified polypeptide in DMF at a concentration of 10 wt%.

[0174] S502. Adding other monomers: Add fumaric acid (FA). The molar ratio of FA to the polypeptide is 1:1, and the reaction is stirred at 80 °C for 24 hours.

[0175] S503. Purification: Dialyze the reaction product using a dialysis bag (MWCO 3500) to remove the unreacted FA.

[0176] Performance test results

[0177]

[0178] In the above Examples 1-3 and Comparative Examples 1-3, the material properties tested are for the low-viscosity bio-based polyamide curing agent and the cured product after curing with epoxy resin. Specifically, the tested materials include the following two categories:

[0179] 1. Low-viscosity bio-based polyamide curing agent

[0180] Test object: Bio-based polyamide curing agent prepared through coiled-coil structure polypeptide sequences, crosslinking agents, functional groups, etc.

[0181] Test performance: Viscosity: Test the fluidity of the curing agent itself to reflect its processing performance.

[0182] Molecular weight distribution: Determine the molecular weight range (5000 - 20000 Da) by gel permeation chromatography (GPC) or mass spectrometry (MS).

[0183] Functional characteristics: Test whether the curing agent has functions such as self-healing and stimulus response (such as pH, temperature, light response).

[0184] 2. Cured product (polyamide-epoxy resin composite material)

[0185] Test object: The composite material obtained by mixing and curing a low-viscosity bio-based polyamide curing agent with epoxy resin.

[0186] Test performance:

[0187] Mechanical properties:

[0188] Tensile strength: Measure the tensile strength of the material through a tensile test (unit: MPa).

[0189] Elongation at break: Measure the elongation of the material before fracture through a tensile test (unit: %), reflecting the toughness of the material.

[0190] Functional characteristics:

[0191] Self-healing efficiency: Measure the self-healing ability of the material after damage through a scratch test or a tensile test (unit: %).

[0192] Stimulus responsiveness: Test the response behavior of the material to external stimuli such as pH, temperature, light (such as shape change, color change, etc.).

[0193] Thermal properties:

[0194] Glass transition temperature (Tg): Measured by differential scanning calorimetry (DSC), reflecting the heat resistance of the material.

[0195] Thermal stability: Measure the thermal decomposition temperature of the material through thermogravimetric analysis (TGA).

[0196] Test methods

[0197] Viscosity test: Measure the viscosity of the curing agent at 25°C using a rotational viscometer (such as a Brookfield viscometer) (unit: mPa·s).

[0198] Mechanical property test:

[0199] Conduct a tensile test using a universal material testing machine to measure the tensile strength and elongation at break.

[0200] Test standard: ASTM D638 (Standard for Testing Tensile Properties of Plastics).

[0201] Self-healing efficiency test:

[0202] Make scratches on the surface of the material and observe the repair situation of the scratches under specific conditions (such as heating, light).

[0203] The performance recovery rate before and after repair is determined by microscopy or tensile testing.

[0204] Stimulus-responsive testing:

[0205] pH responsiveness: The material is placed in solutions with different pH values, and changes in its shape or performance are observed.

[0206] Temperature responsiveness: The material is placed at different temperatures, and changes in its shape or performance are observed.

[0207] Light responsiveness: The material is irradiated with light of a specific wavelength, and changes in its shape or performance are observed.

[0208] Thermal property testing:

[0209] DSC: Determine the glass transition temperature (Tg) of the material.

[0210] TGA: Determine the thermal decomposition temperature (Td) of the material.

[0211] Among them, the unified preparation method and raw material ratio of the cured product (polyamide-epoxy resin composite) are applicable to the preparation of test samples in all examples and comparative examples.

[0212] The preparation method of the cured product

[0213] 1. Raw materials

[0214] Low-viscosity bio-based polyamide curing agent: Prepared according to the methods of Examples 1 to 3 and Comparative Examples 1 to 3.

[0215] Epoxy resin: Bisphenol A type epoxy resin (such as E-51).

[0216] Curing accelerator: Imidazole (such as 2-ethyl-4-methylimidazole).

[0217] Solvent: DMF (used to adjust viscosity, optional).

[0218] 2. Raw material ratio

[0219] Low-viscosity bio-based polyamide curing agent: 20 wt% (based on the mass of epoxy resin).

[0220] Epoxy resin: 80 wt%.

[0221] Curing accelerator: 1 wt% (based on the mass of epoxy resin).

[0222] Solvent: 5 wt% (based on the total mass, optional).

[0223] 3. Preparation steps

[0224] Mix a low-viscosity bio-based polyamide curing agent with epoxy resin in proportion.

[0225] Add a curing accelerator (1 wt%) and a solvent (5 wt%), and stir evenly.

[0226] Use a magnetic stirrer or a high-speed disperser to mix, ensuring uniform dispersion.

[0227] Place the mixed system in a vacuum degassing machine to remove air bubbles.

[0228] Degassing time: 20 minutes, vacuum degree: -0.1 MPa.

[0229] Pour the degassed mixture into a mold.

[0230] Curing conditions: First stage: Pre-cure at 80 °C for 2 hours. Second stage: Post-cure at 120 °C for 2 hours. After curing, naturally cool to room temperature and demold to obtain the cured product.

[0231] Preparation of performance test samples of the cured product

[0232] Tensile property test sample: Cut the cured product into standard dumbbell-shaped specimens (ASTM D638). Specimen size: Length 75 mm, width 10 mm, thickness 2 mm.

[0233] Self-healing property test sample: Cut the cured product into rectangular specimens (20 mm × 10 mm × 2 mm). Make scratches (depth 0.5 mm) on the specimen surface and observe the repair situation.

[0234] Stimulus-responsive test sample: Cut the cured product into films (thickness 0.5 mm). When testing pH, temperature, and light responsiveness, place the film in different pH solutions, temperature environments, or light conditions respectively.

[0235] Thermal property test sample: Cut the cured product into small pieces (5 mm × 5 mm × 2 mm). Use DSC and TGA to test the glass transition temperature (Tg) and the thermal decomposition temperature (Td).

[0236] Analysis of performance test results

[0237] 1. Viscosity

[0238] Examples 1 - 3: Due to the introduction of the coiled-coil structure and molecular weight control (5000 - 20000 Da), the viscosity of the material is significantly reduced (120 - 150 mPa·s), which is suitable for processing techniques such as spraying and casting.

[0239] Comparative Example 1: Lack of coiled-coil structure, strong intermolecular interaction, viscosity as high as 450 mPa·s, poor processability.

[0240] Comparative Example 2: Although the coiled-coil structure exists, no functional groups are introduced, and the viscosity is slightly higher than that of Examples 1 to 3 (140 mPa·s).

[0241] Comparative Example 3: The molecular weight was not controlled, and some high molecular weight components led to an increase in viscosity (300 mPa·s).

[0242] 2. Mechanical properties

[0243] Examples 1 to 3: The coiled-coil structure provides high strength and high toughness, with a tensile strength of 85 to 90 MPa and an elongation at break of 170 to 180%.

[0244] Comparative Example 1: The random coil structure led to a significant decrease in mechanical properties, with a tensile strength of only 30 MPa and an elongation at break of 50%.

[0245] Comparative Example 2: The presence of the coiled-coil structure made the mechanical properties close to those of Examples 1 to 3, but the lack of functional groups resulted in slightly lower performance (tensile strength 80 MPa, elongation at break 160%).

[0246] Comparative Example 3: The molecular weight was not controlled, and the high molecular weight components led to a decrease in toughness, with the elongation at break reduced to 120%.

[0247] 3. Functional characteristics

[0248] Example 1: Disulfide bonds were introduced, with a self-healing efficiency of 95% and significant pH responsiveness.

[0249] Example 2: Temperature-sensitive groups were introduced, showing significant temperature responsiveness.

[0250] Example 3: Photo-sensitive groups were introduced, showing significant photo-responsiveness and a self-healing efficiency of 90%.

[0251] Comparative Example 1: Lack of functional groups, without functions such as self-healing and stimulus response.

[0252] Comparative Example 2: No functional groups were introduced, without functions such as self-healing and stimulus response.

[0253] Comparative Example 3: Although functional groups were introduced, due to the wide molecular weight distribution, the functional efficiency decreased (self-healing efficiency 75%, significant in part of the pH responsiveness).

[0254] Summary

[0255] The coiled-coil structure is the key factor for improving the mechanical properties of materials and reducing viscosity (Examples 1 to 3 and Comparative Example 1).

[0256] The introduction of functional groups endows the material with functions such as self-healing and stimulus response (Examples 1 to 3 and Comparative Example 2).

[0257] Molecular weight control is an important means to optimize material properties. Uncontrolled molecular weight can lead to increased viscosity and decreased functional efficiency (Examples 1 to 3 and Comparative Example 3).

[0258] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been shown above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments by using the disclosed technical content within the scope of the technical solution of the present invention. However, as long as it does not depart from the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a low-viscosity bio-based polyamide curing agent, characterized in that: The following steps are involved: S1. synthesizing a polypeptide sequence having a coiled-coil structure, wherein the polypeptide sequence comprises: an amino acid sequence capable of forming a stable α-helix, an amino acid containing a reactive group, a flexible segment and a functional group; S2, assembling the polypeptide sequence obtained in step S1 into a coiled-coil structure in a solution; S3, using the reactive groups introduced in step S1, adding a cross-linking agent to carry out a cross-linking reaction to obtain a stable coiled coil structure; S4, adjusting the viscosity of the coiled-coil structure polyamide material obtained in step S3 by controlling the molecular weight; S5, polymerizing the low-viscosity coiled-helix polyamide material obtained in step S4 with other monomers to prepare a polyamide curing agent.

2. The method for preparing a low-viscosity bio-based polyamide curing agent according to claim 1, characterized in that: The amino acid sequence capable of forming a stable α-helix is ​​one or more of polyalanine, polyleucine, polyglutamic acid or polylysine.

3. The method for preparing a low-viscosity bio-based polyamide curing agent according to claim 1, characterized in that: The amino acid containing a reactive group is one or more of cysteine, lysine, aspartic acid or glutamic acid.

4. The method for preparing a low-viscosity bio-based polyamide curing agent according to claim 1, characterized in that: The flexible segment is one or more of a polyethylene glycol segment, a polypropylene glycol segment or a polycaprolactone segment.

5. The method for preparing a low-viscosity bio-based polyamide curing agent according to claim 1, characterized in that: The functional group is one or more of a disulfide bond, a Diels-Alder reaction group, a pH sensitive group, a temperature sensitive group or a light sensitive group.

6. The method for preparing a low-viscosity bio-based polyamide curing agent according to claim 5, characterized in that: The assembly condition in step S1 is to adjust one or more of the solution pH value, ionic strength or temperature.

7. The method for preparing a low-viscosity bio-based polyamide curing agent according to claim 1, characterized in that: The cross-linking agent is one or more of bismaleimide, diisocyanate or epoxy resin.

8. The method for preparing a low-viscosity bio-based polyamide curing agent according to claim 1, characterized in that: The diluent is one or more of epoxidized soybean oil, epoxidized fatty acid methyl ester or vegetable oil.

9. The method for preparing a low-viscosity bio-based polyamide curing agent according to claim 1, characterized in that: The molecular weight in step S4 is controlled at 5000-20000 Da.

10. The method for preparing a low-viscosity bio-based polyamide curing agent according to claim 1, characterized in that: The other monomers in step S1 are one or more of the following: lysine, glutamic acid, aspartic acid, itaconic acid, fumaric acid or citric acid.

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