Preparation method and application of degradable epoxy resin

Abstract

According to the preparation method and application of the degradable epoxy resin, a Schiff base epoxy monomer and an alkyl glycidyl ether grafted amine curing agent are designed, and step-by-step polymerization crosslinking is realized according to different reaction activities of primary amine and secondary amine on epoxy groups in the epoxy resin. A microphase separation structure formed by the flexible chain in a cross-linked network plays a role in blocking crack propagation; meanwhile, under the stretching action of external force, molecular chain slippage of aggregates in the microcosmic phase separation structure occurs due to orientation, so that the elongation at break is increased. Moreover, due to the existence of a Schiff base bond, the epoxy resin shows degradability in an acidic aqueous solution or m-xylylenediamine before and after modification, so that cyclic utilization can be realized. Meanwhile, due to the existence of a flexible chain in the epoxy resin, the contact area between an epoxy matrix and an interface is increased, the adhesion performance is also greatly improved, and meanwhile, the epoxy resin has degradability.

Description

Technical Field

[0001] The present invention belongs to the technical field of material synthesis, and specifically relates to a preparation method and application of a degradable epoxy resin. Specifically, it relates to an amine curing agent modified by grafting alkyl glycidyl ethers of different lengths and a Schiff base epoxy monomer to achieve adjustable stiffness and toughness through a polymerization-induced microphase separation method. And it can be applied to the field of high-performance degradable adhesives. Background Art

[0002] Epoxy resin is one of the most widely used thermosetting plastics. Its covalent cross-linked network structure provides good mechanical properties, thermal stability, dimensional stability and solubility resistance, and is widely used in composite materials, coatings, adhesives and other fields. Among them, due to the strong polar groups of epoxy resin itself, it can form a strong interface layer on most substrates, so it is widely used in the field of adhesives. However, the permanent cross-linked structure of epoxy resin makes the material unable to be recycled and reprocessed, resulting in resource waste and environmental damage. Although epoxy resin degradation and recycling can be achieved by direct pyrolysis, strong oxidant degradation, organometallic catalytic degradation and the introduction of dynamic covalent bonds, direct pyrolysis and strong oxidant degradation are not suitable for epoxy resins in the adhesive field because they will also damage the adhered substrate, and organometallic catalytic degradation is expensive. Therefore, the introduction of dynamic covalent bonds in the synthesis process of epoxy resin can not only quickly degrade the resin matrix under mild conditions, but also achieve closed-loop recycling and reuse. In addition, there are many types of dynamic covalent bonds, the most common of which are acetal bonds, borate bonds, disulfide bonds, Schiff base bonds (imine bonds) and Diels-Alder adducts, etc. In order to obtain a multi-pathway and closed-loop recycling chemical degradation method, the Schiff base bond has become the best choice because it can dissociate in acidic solutions or in fatty amines, thereby achieving the purpose of degrading epoxy resins containing Schiff bases.

[0003] CN 117567444 A discloses an epoxy resin monomer based on furan containing imine bonds, its preparation and application. It constructs a series of furan ring-containing epoxy monomers through reversible imine bonds, and the hydroxyl groups formed during the curing ring-opening process react with the oxygen atoms of the furan ring, so that a large number of hydrogen bonds exist in the cross-linked network, providing higher mechanical strength and impact strength. However, the elongation at break of the obtained epoxy resin is low, and it tends to be brittle fracture.

[0004] Therefore, even though a series of recyclable and reprocessable epoxy resins with good adhesion properties can be produced through dynamic covalent bonds such as Schiff bases, it is known that epoxy resins based on dynamic covalent bonds have the disadvantage of being brittle and it is difficult to achieve a balance between rigidity and toughness. At the same time, the bonding joints formed by the brittle resin matrix will suddenly fail due to mechanical stress. How to regulate the rigidity and toughness of degradable epoxy resins while maintaining high adhesion properties has become an important research topic. Summary of the invention

[0005] In view of the problem that the rigidity and toughness of existing degradable epoxy resins are difficult to control, the purpose of the present invention is to improve the adjustable rigidity and toughness of Schiff base epoxy resins, and to provide a preparation method and application of a degradable epoxy resin, which is specifically achieved through the following technical solutions:

[0006] A method for preparing a degradable epoxy resin comprises the following steps:

[0007] 1) dissolving a phenolic aromatic aldehyde monomer and an aliphatic diamine in an alcohol solvent at a molar ratio of 2:1, respectively, and adding the alcohol solution of the aliphatic diamine dropwise into the alcohol solution of the phenolic aromatic aldehyde monomer at room temperature to carry out a chemical reaction until a large amount of yellow precipitate is generated in the reaction system. After the reaction is completed, filtering the suspension to obtain a yellow solid product, washing with an alcohol solvent and drying to obtain a precursor of an epoxy monomer;

[0008] 2) The precursor obtained in step 1) is mixed with epichlorohydrin, and 0.05 equivalent of tetrabutylammonium bromide (TBAB) of the precursor is added as a catalyst. Under nitrogen protection, the precursor is dissolved by stirring at 80° C., and then reacted for 3 hours to obtain a clear and transparent golden solution. The solution is then cooled to room temperature, and a methanol solution of sodium hydroxide of a certain concentration is prepared, and is added dropwise to the golden solution in an ice water bath. The reaction is then continued at room temperature for several hours, and a large amount of white precipitate is generated in the reaction system. The precipitate is filtered, the filtrate is washed, the filtrate is dried, and finally distilled under reduced pressure to obtain a Schiff base epoxy monomer, which is recorded as EVD;

[0009] 3) Using glycidyl ether C x As a grafting agent, m-xylylenediamine was used as an amine curing agent, and the molar ratio of the two was controlled to be consistent. m-xylylenediamine was weighed and placed in a single-necked flask and preheated. DMF was added as a solvent. Glycidyl ether C was reacted with the amine curing agent under nitrogen protection. x Add dropwise to m-phenylenediamine and continue to stir the reaction. After the addition is completed, continue the reaction for a period of time to obtain C x The single grafted product is denoted as MXDA-C x ;

[0010] 4) Take the EVD synthesized in step 2) and add DMF solvent, then add MXDA-C with the same active hydrogen concentration and epoxy group concentration. x , stirring and mixing, casting the stirred mixed solution into a dumbbell-shaped sample mold, keeping it horizontal, and curing in stages, the time is controlled at 60°C for 1-3h, 80°C for 2-4h, and 120°C for 3-6h, and finally weighing to confirm that most of the DMF has volatilized, obtaining a cured sample, and preparing a degradable epoxy resin, recorded as EVD / MXDA-C X .

[0011] Further, in step 1), the phenolic aromatic aldehyde monomer is any one of vanillin, syringaldehyde and p-hydroxybenzaldehyde; the aliphatic diamine is any one of 1,6-hexanediamine, isophoronediamine and meta-xylylenediamine; the alcohol solvent is any one of methanol, ethanol and isopropanol; the mass concentration of the phenolic aromatic aldehyde monomer in the alcohol solvent is 30wt%-60wt%, preferably 40wt%, the mass concentration of the aliphatic diamine in the alcohol solvent is 10wt%-30wt%, preferably 20wt%, the dropping time is controlled at 30-90min, preferably 60min, and the reaction time is controlled at 6-12h, preferably 8h.

[0012] Furthermore, in step 2), the molar ratio of the precursor to epichlorohydrin is 1:15, the concentration of the methanol solution of sodium hydroxide is 5wt%-20wt%, preferably 10wt%, the sodium hydroxide addition time is controlled at 30-90min, preferably 60min, and the subsequent reaction time is controlled at 2-6h, preferably 3h.

[0013] Furthermore, in step 2), the filtrate is washed with 5wt%-15wt% saline solution, the optimal concentration is 10wt%, and dried with anhydrous sodium sulfate for 6-24h, the optimal drying time is 12h, and the reduced pressure distillation temperature is controlled at 40-80°C, the optimal temperature is 60°C.

[0014] Further, in step 3), the glycidyl ether C x Choose butyl glycidyl ether (C4), C8-C 10 Alkyl glycidyl ether (C 8-10 ) and C 12 -C 14 Alkyl glycidyl ether (C 12-14 )

[0015] Further, in step 3), the amount of DMF used is m-phenylenediamine and glycidyl ether C x 50wt% to 150wt% of the total mass, preferably 100wt%, the preheating temperature of m-phenylenediamine is 60-100°C, preferably 80°C, glycidyl ether C xThe dropping time is 1-3 hours, preferably 2 hours, and the subsequent reaction time is 1-4 hours, preferably 2 hours.

[0016] Furthermore, in step 4), the epoxy value of EVD is measured in advance, and the epoxy value is measured using N,N'-dimethylformamide DMF instead of acetone to ensure the dissolution of the epoxy monomer.

[0017] The degradable epoxy resin prepared by the preparation method is used as a high-adhesion adhesive.

[0018] The present invention designs a Schiff base epoxy monomer and an amine curing agent grafted with an alkyl glycidyl ether, and realizes step-by-step polymerization and crosslinking according to the different reaction activities of primary amine and secondary amine to epoxy groups in epoxy resin. In addition, the microphase separation structure formed by the flexible chain in the crosslinked network plays a role in hindering crack propagation; at the same time, when subjected to external force stretching, the agglomerates in the microphase separation structure slip due to orientation, thereby increasing the elongation at break. Moreover, due to the presence of the Schiff base bond, the epoxy resin shows degradability in an acidic aqueous solution or meta-phenylenediamine before and after modification, so it can be recycled. At the same time, the presence of the flexible chain in the epoxy resin increases the contact area between the epoxy matrix and the interface, and greatly improves the adhesion performance. In summary, the epoxy resin obtained by curing the amine curing agent grafted with an alkyl glycidyl ether and the Schiff base epoxy monomer reported in the present invention not only has high toughness and high adhesion performance, but also has degradability.

[0019] The present invention has the following beneficial effects:

[0020] 1) The present invention achieves high toughness by inducing the formation of a microphase separation structure through polymerization of an amine curing agent grafted with an alkyl glycidyl ether and a Schiff base epoxy resin;

[0021] 2) Compared with the one-pot curing of Schiff base epoxy resin, alkyl glycidyl ether and amine curing agent, the alkyl glycidyl ether and amine curing agent are first grafted and then the Schiff base epoxy resin is cured. The reaction controllability is high, and the alkyl glycidyl ether will not precipitate from the cross-linked network to cause macroscopic phase separation;

[0022] 3) After the alkyl glycidyl ether grafted amine curing agent and Schiff base epoxy resin were mixed and cured, their degradation performance was not reduced, and they could also be hydrolyzed in acidic solution or aminolyzed in m-xylenediamine;

[0023] 4) After the alkyl glycidyl ether grafted amine curing agent is mixed and cured with the Schiff base epoxy monomer, its flexible side chain can increase the interaction force between the epoxy resin and the matrix, thereby improving the adhesion performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1is the structural formula of Schiff base epoxy monomer;

[0025] Figure 2 It is a schematic diagram of the structure of alkyl glycidyl ether grafted amine curing agent and Schiff base epoxy resin;

[0026] Figure 3 Schematic diagram of the cross-linked network after segmented polymerization of glycidyl ether grafted amine curing agent and Schiff base epoxy monomer. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with specific implementations to provide a better understanding of the technical solution.

[0028] Example 1: Preparation of Schiff base epoxy monomer

[0029] (1) Phenolic aromatic aldehyde monomer and aliphatic diamine are dissolved in an alcohol solvent at a molar ratio of 2:1, wherein the mass concentration of the phenolic aromatic aldehyde monomer in the alcohol is 40wt%, and the mass concentration of the diamine in the alcohol is 20wt%. At room temperature, the ethanol solution of the aliphatic diamine is added dropwise to the alcohol solution of the phenolic aromatic aldehyde monomer to carry out a chemical reaction, and the rate of the dropwise addition reaction is controlled, and the dropwise addition time is 60min. After the dropwise addition is completed, the reaction is continued for 8 hours until a large amount of yellow precipitate is generated in the reaction system, and the reaction is completed;

[0030] (2) filtering the suspension obtained in step (1) to obtain a yellow solid product, washing it with an alcohol and drying it to obtain a precursor of an epoxy monomer;

[0031] (3) The precursor obtained in step (2) is blended with epichlorohydrin at a molar ratio of 1:15, and 0.05 equivalent of tetrabutylammonium bromide (TBAB) is added to the precursor as a catalyst. Under nitrogen protection, the precursor is stirred at 80°C to dissolve, and then reacted for 3 hours to obtain a clear and transparent golden solution. The solution is then cooled to room temperature, and a 10 wt% methanol solution of sodium hydroxide is prepared and added dropwise to the golden solution in an ice water bath for 60 minutes, followed by reaction at room temperature for 3 hours. A large amount of white precipitate is produced in the reaction system, which is filtered, and the filtrate is washed with 10 wt% saline solution, and the filtrate is dried with anhydrous sodium sulfate for 12 hours. Finally, distillation under reduced pressure at 60°C is performed to obtain a Schiff base epoxy monomer, which is denoted as EVD. The structural formula of the obtained Schiff base epoxy monomer is as follows: Figure 1As shown, R1 and R2 are related to the type of phenolic aromatic aldehyde used. When vanillin is used, the substituent R1 is -OCH3 (methoxy) and R2 is -H (hydrogen atom). When syringaldehyde is used, the substituents R1 and R2 are both -OCH3 (methoxy). When p-hydroxybenzaldehyde is used, the substituents R1 and R2 are both -H (hydrogen atom). R' is related to the aliphatic diamine used, which has been marked in the figure, and from left to right are the structures of n-hexyl chain, isophorone diamine and m-phenylenediamine.

[0032] Example 2: Preparation of alkyl glycidyl ether grafted amine curing agent

[0033] Using glycidyl ether (C x ) as a grafting agent, and then meta-xylylenediamine (MXDA) as an amine curing agent, and the molar ratio of the two is controlled to be consistent. A certain amount of MXDA is weighed and placed in a single-necked flask and preheated to 80°C, and a certain amount of DMF is added as a solvent, wherein the amount of DMF is MXDA and C x 100wt% of the total mass, C x Add dropwise to MXDA for 2 hours and stir the reaction continuously. After the addition is completed, continue the reaction for 2 hours to obtain C x The single grafted product is denoted as MXDA-C x In addition, since the reaction is an addition reaction, no subsequent separation and purification is required, and DMF can be volatilized during the subsequent curing process.

[0034] Among them, C x Butyl glycidyl ether (C4), C8-C 10 Alkyl glycidyl ether (C 8-10 ) and C 12 -C 14 Alkyl glycidyl ether (C 12-14 ), C x Type C 12-14 The best tensile toughness can be obtained.

[0035] Example 3: Preparation of epoxy cured strips

[0036] (1) The epoxy value of the synthesized EVD reference standard GB / T 1677-2008 was measured in advance. The epoxy value was determined by using N,N'-dimethylformamide (DMF) instead of acetone to ensure the dissolution of the epoxy monomer. Then a certain mass of the epoxy monomer was weighed, a certain amount of DMF solvent was added, and finally MXDA-C with the same active hydrogen concentration and epoxy group concentration was added. x , and stir for some time.

[0037] (2) The stirred mixed solution was cast into a dumbbell-shaped sample mold, kept horizontal, and cured in stages. The time was controlled at 60°C for 1-3 hours, 80°C for 2-4 hours, and 120°C for 3-6 hours. Finally, it was weighed to confirm that most of the DMF had volatilized, and a cured sample was obtained, which was recorded as EVD / MXDA-C. x .

[0038] The schematic diagram of the structure of the alkyl glycidyl ether grafted amine curing agent and the Schiff base epoxy resin is as follows Figure 2 As shown, the structural formula of alkyl glycidyl ether grafted amine curing agent, wherein n=1, 3, 4, 5, 6.

[0039] The schematic diagram of the cross-linked network after the segmented polymerization of the alkyl glycidyl ether grafted amine curing agent and the Schiff base epoxy monomer of the present invention is as follows: Figure 3 shown.

[0040] Example 4: Application of the prepared Schiff base epoxy resin in a degradable high-adhesion adhesive

[0041] (1) Preparation of adhesion samples of Schiff base epoxy resin and rigid substrate: Schiff base epoxy resin and MXDA-C 12-14 The curing agent is dissolved in DMF solvent, then heated to 60-100°C, volatilized for 30-120 minutes, and vacuum degassed after cooling. The viscous epoxy prepolymer is applied to a specific area on the rigid substrate, and then bonded together to form a sample shape as shown in standard GB / T7124-2008.

[0042] (2) Thermal curing of the adhered sample: The Schiff base epoxy resin is pre-gelled at 50° C., and the gel time is controlled to be 2-5 hours. At this time, it can be ensured that the residual DMF will not volatilize and form bubbles; then, the preferred curing temperature of step (2) in Scheme 3 is used to perform high-temperature curing on the adhered sample.

[0043] (3) Degradation of the adhesion sample and recovery of the matrix: The adhesion sample is degraded in an acidic solution or an aliphatic diamine. In an acidic solution, the degradation recovery is carried out in a 0.5-2.0 mol / L HCl solution. The solvent used is a HCl / DMF mixed solution. The DMF content is controlled at 40wt%-80wt%. After degradation at 30-80°C for a certain period of time, the degradation is completed when the matrix can be separated from each other and there is no visible resin adhesion on the surface. In an aliphatic diamine solution, the degradation recovery is carried out in an aliphatic amine 10-20 times the mass of the epoxy resin. The aliphatic diamine used is meta-xylylenediamine. After degradation at 50-100°C for a certain period of time, the degradation is also completed when the matrix can be separated from each other and there is no visible resin adhesion on the surface. The degradation liquid and rigid matrix obtained by synthesis recovery can be reused.

[0044] The present invention, MXDA and C12-14 After the grafting reaction with a molar ratio of 1:1, it has the highest tensile toughness after curing with EVD, specifically 12.8MJ·m -3 , which is 5 times higher than EVD / MXDA. The highest tensile shear strength reaches 12MPa, which is better than bisphenol A diglycidyl ether and MXDA-C 12-14 of solidified material.

Claims

1. A method for preparing a degradable epoxy resin, characterized in that The following steps are involved: 1) Dissolve the phenolic aromatic aldehyde monomer and the aliphatic diamine in an alcohol solvent at a molar ratio of 2:1, and dropwise add the aliphatic diamine solution into the alcohol solution of the phenolic aromatic aldehyde monomer at room temperature to carry out a chemical reaction until a large amount of yellow precipitate is generated in the reaction system. After the reaction is completed, filter the suspension to obtain a yellow solid product, wash it with an alcohol solvent, and dry it to obtain a precursor of the epoxy monomer; 2) The precursor prepared in step 1) is mixed with epichlorohydrin, and 0.05 equivalent of tetrabutylammonium bromide (TBAB) of the precursor is added. Under nitrogen protection, the precursor is dissolved by reflux stirring at 80°C, and then reacted for 3 hours to obtain a clear and transparent golden solution. The solution is then cooled to room temperature, and a methanol solution of sodium hydroxide of a certain concentration is prepared, and added dropwise to the golden solution in an ice water bath. The reaction is then continued at room temperature for several hours, and a large amount of white precipitate is generated in the reaction system. The precipitate is filtered, the filtrate is washed, the filtrate is dried, and finally distilled under reduced pressure to obtain a Schiff base epoxy monomer, which is recorded as EVD; 3) Using glycidyl ether C x As a grafting agent, m-xylylenediamine was used as an amine curing agent, and the molar ratio of the two was controlled to be consistent. m-xylylenediamine was weighed and placed in a single-necked flask and preheated. DMF was added as a solvent. Glycidyl ether C was reacted with the amine curing agent under nitrogen protection. x Add dropwise to m-phenylenediamine and continue to stir the reaction. After the addition is completed, continue the reaction for a period of time to obtain C x The single grafted product is denoted as MXDA-C x ; 4) Take the EVD synthesized in step 2) and add a certain amount of solvent to dilute it, then add MXDA-C with the same active hydrogen concentration and epoxy group concentration x , stirring and mixing, casting the stirred mixed solution into a dumbbell-shaped sample mold, keeping it horizontal, and curing in stages, the time is controlled at 60 ° C for 1-3 h, 80 ° C for 2-4 h, and 120 ° C for 3-6 h, and finally weighing to confirm that most of the solvent has evaporated, obtaining a cured sample, and preparing a degradable epoxy resin, recorded as EVD / MXDA-C X .

2. The method for preparing a degradable epoxy resin according to claim 1, characterized in that In step 1), the phenolic aromatic aldehyde monomer is any one of vanillin, syringaldehyde and p-hydroxybenzaldehyde; the aliphatic diamine is any one of 1,6-hexanediamine, isophoronediamine and meta-xylylenediamine; the alcohol solvent is any one of methanol, ethanol and isopropanol; the mass concentration of the phenolic aromatic aldehyde monomer in the alcohol solvent is 30 wt%-60 wt%, the mass concentration of the aliphatic diamine in the alcohol solvent is 10 wt%-30 wt%, the dropping time is controlled at 30-90 min, and the reaction time is controlled at 6-12 h.

3. The method for preparing a degradable epoxy resin according to claim 1, characterized in that In step 2), the molar ratio of the precursor to epichlorohydrin is 1:15, the concentration of the methanol solution of sodium hydroxide is 5 wt%-20 wt%, the sodium hydroxide addition time is controlled at 30-90 min, and the subsequent reaction time is controlled at 2-6 h.

4. The method for preparing a degradable epoxy resin according to claim 1, characterized in that In step 2), the filtrate is washed with 5wt%-15wt% saline solution, dried with anhydrous sodium sulfate for 6-24 hours, and the vacuum distillation temperature is controlled at 40-80°C.

5. The method for preparing a degradable epoxy resin according to claim 1, characterized in that In step 3), glycidyl ether C x Choose butyl glycidyl ether (C4), C8-C 10 Alkyl glycidyl ether (C 8-10 ) and C 12 -C 14 Alkyl glycidyl ether (C 12-14 ) 6. The method for preparing a degradable epoxy resin according to claim 1, characterized in that In step 3), the amount of DMF used is m-phenylenediamine and glycidyl ether C x 50 wt% to 150 wt% of the total mass, the preheating temperature of m-phenylenediamine is 60-100°C, glycidyl ether C x The dropwise addition time is 1-3 h, and the subsequent reaction time is 1 to 4 h.

7. The method for preparing a degradable epoxy resin according to claim 1, characterized in that In step 4), the epoxy value of EVD is measured in advance, and N,N'-dimethylformamide DMF is used instead of acetone to ensure the dissolution of the epoxy monomer.

8. Use of the degradable epoxy resin prepared by the preparation method according to any one of claims 1 to 7 as a high-adhesion adhesive.

Images