Triblock self-assembly toughened resin as well as synthesis method and application thereof

Abstract

The invention relates to the technical field of epoxy adhesives, in particular to a triblock self-assembly toughened resin and a synthesis method and application thereof.The toughened resin is synthesized from (50.0-70.0) eq. First monomer, (30.0-50.0) eq. Second monomer, 0.2 eq. Free radical initiator and (4.0-8.0) eq. RAFT reagent, the first monomer is a methacrylate soft monomer, the second monomer is a hard monomer, and the second monomer is an acrylic acid monomer. The free radical initiator is any one of a peroxide initiator and an azo initiator, and the RAFT reagent is dicarboxyl trithiocarbonate. The toughened resin disclosed by the invention can form a low-molecular-weight ABA type triblock copolymer, an aggregation state of the copolymer can be evolved into an elastomer taking a crystal phase domain as a physical crosslinking point through a spontaneous crystallization behavior between chains by a segment A, and two carboxyl groups at the tail ends of the chains and an epoxy group are subjected to a ring-opening reaction, so that an internal toughening effect is achieved; the shearing strength and the fracture toughness can be remarkably improved, and the epoxy structural adhesive has relatively high application value in the field of epoxy structural adhesives.

Description

Technical Field

[0001] The present invention relates to the technical field of epoxy adhesives, and in particular to a triblock self-assembly toughening resin, a synthesis method thereof, and applications thereof. Background Art

[0002] The high degree of crosslinking after curing epoxy resins results in insufficient toughness and susceptibility to fracture, limiting their application in structural bonding applications requiring high mechanical strength and impact toughness. Studies have shown that improving the fracture toughness of epoxy resin curing systems can improve their bonding performance. Therefore, improving the toughness of epoxy resins while minimizing the impact on their inherent properties is key to developing high-bonding epoxy structural adhesives.

[0003] Epoxy resin toughening approaches can be categorized into three main groups based on their microstructure: 1) Toughening by forming a phase-separated structure between the modifier and the matrix. These modifiers primarily include rubber elastomers, rigid nanoinorganic particles, thermotropic liquid crystals, block copolymers, thermoplastic resins, hyperbranched polymers, and core-shell polymers. The key to these approaches lies in the compatibility of the modifier with the epoxy resin and the control of the phase structure. 2) Toughening by forming two interlocking crosslinked networks. For example, long-chain polymers are co-cured with epoxy resin, where the long chains continuously penetrate the epoxy resin crosslinked network to form an interpenetrating / semi-interpenetrating network, achieving a toughening effect. The key to this strategy is controlling the size of the phase domains to achieve optimal interpenetration. 3) Modifying the chemical structure of the crosslinked network to improve toughness by introducing flexible segments or mixed crosslinking to enhance segment mobility. For example, flexible groups such as ether bonds, carbon-nitrogen bonds, and silicon-oxygen bonds can be introduced, or high-toughness epoxy resin segments can be introduced to reduce the rigidity of the epoxy resin. This strategy relies on the selection and introduction of flexible segments, and the final structure and properties can be adjusted by manipulating the ratio of different combined structures.

[0004] Polyacrylate copolymers containing a large amount of soft monomers have a certain degree of flexibility in their backbones, making them suitable for use as toughening agents for epoxy resins. Zhang Shixian et al. used RAFT polymerization to prepare copolymers containing isooctyl acrylate (EHA) and acrylic acid to toughen epoxy resins. However, this synthetic route requires polymerization within the epoxy resin, and the product contains a large amount of free epoxy resin, resulting in a low effective toughening component introduced into the epoxy resin structural adhesive system. Therefore, it is necessary to explore new molecular design approaches to synthesize polyacrylate copolymers that are well compatible with epoxy resins as toughening agents while maintaining high levels of adhesion. Achieving this goal is challenging and has industrial application value. Summary of the Invention

[0005] In order to solve the above-mentioned shortcomings and deficiencies of the existing toughening resins, the present invention provides a triblock self-assembly toughening resin having more significant effects in terms of dispersion uniformity and improved fracture toughness, as well as a synthesis method and application thereof.

[0006] The present invention adopts the following technical solutions to achieve the above-mentioned purpose: A triblock self-assembly toughening resin is mainly synthesized from (50.0-70.0) eq. of a first monomer, (30.0-50.0) eq. of a second monomer, 0.2 eq. of a free radical initiator, and (4.0-8.0) eq. of a RAFT agent.

[0007] As a preferred technical solution: the toughening resin is mainly synthesized from 60 eq. of a first monomer, 40 eq. of a second monomer, 0.2 eq. of a free radical initiator, and 6 eq. of a RAFT agent.

[0008] A further preferred technical solution: the first monomer is a methacrylate soft monomer, specifically any one of butyl acrylate, isooctyl acrylate, n-butyl methacrylate, methoxyethyl methacrylate, ethoxyethyl methacrylate, methoxyethyl acrylate, ethoxyethyl acrylate, lauryl methacrylate, 2-dodecyl acrylate, octadecyl acrylate, 2-ethylhexyl acrylate, n-octyl methacrylate, and n-octyl acrylate.

[0009] A further preferred technical solution: the second monomer is a hard monomer, specifically any one of acrylonitrile, methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, styrene, 4-acryloylmorpholine, acrylamide, cyclohexyl methacrylate, cyclohexyl acrylate, 2-phenoxyethyl methacrylate, isobornyl methacrylate, isobornyl acrylate, tetrahydrofurfuryl methacrylate, and tetrahydrofurfuryl acrylate.

[0010] A further preferred technical solution: the free radical initiator is any one of a peroxide initiator and an azo initiator, specifically any one of benzoyl peroxide, tert-butyl hydroperoxide, isopropylbenzene hydroperoxide, methyl ethyl ketone peroxide, diisopropylbenzene peroxide, azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, and azoisobutylcyanamide.

[0011] A further preferred technical solution: the RAFT agent is a dicarboxy trithiocarbonate, specifically 2,2'-[thiocarbonyl(thio)]bis[2-methylpropionic acid].

[0012] A method for synthesizing a triblock self-assembly toughening resin comprises the following steps: Step S1: Selecting raw materials: Select appropriate amounts of 0.2 eq. of a free radical initiator, 6.0 eq. of a RAFT agent, 60 eq. of a first monomer, and 40 eq. of a second monomer for standby use; Step S2: primary stirring: the raw materials of 0.2 eq. free radical initiator, 6.0 eq. RAFT agent, 60 eq. first monomer and polar organic solvent in step S1 are added into the reaction kettle in turn, and stirred at room temperature until the free radical initiator and the RAFT agent are fully dissolved; Step S3: secondary stirring: high-purity nitrogen is introduced into the mixture in step S2, and the mixture is stirred at 60-90 DEG C for 12-48 hours; Step S4: tertiary stirring: 40 eq. second monomer selected in step S1 is introduced into the mixture in step S3, and then high-purity nitrogen is continuously introduced and the mixture is continuously stirred at 60-90 DEG C for 12-48 hours; Step S5: reaction termination: the mixture in step S4 is quenched to terminate the reaction at a temperature lower than 30 DEG C, and a copolymer solution is obtained; Step S6: obtaining a resin finished product: the copolymer solution in step S5 is distilled under reduced pressure to remove residual monomers and solvents, and the toughening resin is obtained, which is then sealed and packaged for use.

[0013] The application of the triblock self-assembled toughening resin can make the adhesive made of the toughening resin, an epoxy resin, a polyamide curing agent 140 and a promoter DMP-30 maintain lap shear strength ≥21.18 MPa and fracture toughness ≥5.63 MPa·m 1 / 2 .

[0014] The beneficial effects of the present application compared with the prior art are that the synthesis route of the toughening resin is controlled free radical polymerization, which can form a low molecular weight ABA type triblock copolymer, the B section is a soft segment chain, the A section is a hard segment with crystallinity, and the A section can make the aggregate state of the copolymer evolve into an elastomer with the crystalline phase domain as the physical crosslinking point; The two chain ends of the toughening resin triblock copolymer are carboxyl groups, which can undergo ring-opening reaction with the epoxy groups in the epoxy resin, especially the aromatic epoxy groups, so that the toughening resin and the epoxy resin are linked by chemical bonds, achieving the effect of internal toughening, and the toughening resin has more significant effect on dispersion uniformity and fracture toughness than the physically blended MBS, powdered polyolefin rubber and other toughening resins. DETAILED DESCRIPTION

[0015] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0016] It should be noted that, in the specific embodiments of the present invention, terms such as "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the phrase "including one" or other defined elements that may appear does not exclude the presence of other identical elements in the process, method, article or device including the elements. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood based on specific circumstances.

[0017] Example: A triblock self-assembling toughening resin is synthesized primarily from (50.0-70.0) eq. of a first monomer, (30.0-50.0) eq. of a second monomer, 0.2 eq. of a free radical initiator, and (4.0-8.0) eq. of a RAFT agent. "eq" is short for "equivalent," generally read as "equivalent," indicating the molar multiple of the added reagent relative to the substrate. For example, 2.4 eq. of a certain compound is added to the reaction, or it can be written before the substrate in the reaction equation.

[0018] As a preferred technical solution: the toughening resin is mainly synthesized from 60 eq. of a first monomer, 40 eq. of a second monomer, 0.2 eq. of a free radical initiator, and 6 eq. of a RAFT agent.

[0019] A further preferred technical solution: the first monomer is a methacrylate soft monomer, specifically any one of butyl acrylate, isooctyl acrylate, n-butyl methacrylate, methoxyethyl methacrylate, ethoxyethyl methacrylate, methoxyethyl acrylate, ethoxyethyl acrylate, lauryl methacrylate, 2-dodecyl acrylate, octadecyl acrylate, 2-ethylhexyl acrylate, n-octyl methacrylate, and n-octyl acrylate.

[0020] A further preferred technical solution: the second monomer is a hard monomer, specifically any one of acrylonitrile, methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, styrene, 4-acryloylmorpholine, acrylamide, cyclohexyl methacrylate, cyclohexyl acrylate, 2-phenoxyethyl methacrylate, isobornyl methacrylate, isobornyl acrylate, tetrahydrofurfuryl methacrylate, and tetrahydrofurfuryl acrylate.

[0021] A further preferred technical solution: the free radical initiator is any one of a peroxide initiator and an azo initiator, specifically any one of benzoyl peroxide (BPO), tert-butyl hydroperoxide (BHP), isopropylbenzene hydroperoxide (CHPO), methyl ethyl ketone peroxide (MEKP), diisopropylbenzene peroxide, azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN), dimethyl azobisisobutyrate (AIBME), and azoisobutylcyanamide.

[0022] A further preferred technical solution: the RAFT agent is a dicarboxy trithiocarbonate, specifically 2,2'-[thiocarbonyl(thio)]bis[2-methylpropionic acid].

[0023] A method for synthesizing a triblock self-assembly toughening resin comprises the following steps: Step S1: Selecting raw materials: Select appropriate amounts of 0.2 eq. of a free radical initiator, 6.0 eq. of a RAFT agent, 60 eq. of a first monomer, and 40 eq. of a second monomer for standby use; Step S2: Primary stirring: 0.2 eq. of the free radical initiator, 6.0 eq. of the RAFT agent, 60 eq. of the first monomer, and the polar organic solvent from Step S1 are sequentially added to the reactor and stirred at room temperature until the free radical initiator and the RAFT agent are fully dissolved. Step S3: Secondary stirring: high-purity nitrogen is introduced into the mixed solution in step S2, and the mixture is stirred at 60-90° C. for 12-48 hours; Step S4: Stir three times: Add 40 eq. of the second monomer selected in step S1 to the mixed solution in step S3; then continue to introduce high-purity nitrogen and continue stirring and reacting at 60-90° C. for 12-48 hours; Step S5: Termination of the reaction: quenching the mixed solution in step S4 at a temperature below 30° C. to terminate the reaction and obtain a copolymer solution; Step S6: Obtaining the finished resin product: The copolymer solution in step S5 is subjected to reduced pressure distillation to remove residual monomers and solvent to obtain the toughened resin, which is then sealed and packaged for later use.

[0024] A triblock self-assembly toughening resin is used. According to GB / T 7214-2008, the adhesive made of the toughening resin, epoxy resin, polyamide curing agent 140, and accelerator DMP-30 maintains a lap shear strength of ≥21.18 MPa and a fracture toughness of ≥5.63 MPa·m 1 / 2 .

[0025] Further analysis: The raw materials used in the experiments in the embodiments and comparative examples of the present invention are as follows, but are not limited to the following raw materials. The present invention only uses the following raw materials as specific examples to further illustrate the effect of the triblock self-assembly toughening resin described in the present invention.

[0026] Among them, the first monomer is isooctyl acrylate (EHA); the second monomer is methyl methacrylate (MMA); the free radical initiator is azobisisobutyronitrile (AIBN); and the RAFT agent is 2,2'-[thiocarbonyl(thio)]bis[2-methylpropionic acid].

[0027] Epoxy resin: Nan Ya 128, epoxy equivalent weight 190 g / mol; curing agent: polyamide curing agent 140, active hydrogen equivalent weight 97 g / mol; accelerator: DMP-30.

[0028] The present invention sets Examples 1-6 and Comparative Examples 1-2, and their formulas are shown in Table 1: Table 1 EHA / mol MMA / mol AIBN / mol RAFT / mol Example 1 7.0 3.0 0.02 0.4 Example 2 7.0 3.0 0.02 0.6 Example 3 7.0 3.0 0.02 0.8 Example 4 5.0 5.0 0.02 0.4 Example 5 5.0 5.0 0.02 0.6 Example 6 5.0 5.0 0.02 0.8 Comparative Example 1 7.0 3.0 0.02 Comparative Example 2 5.0 5.0 0.02 Examples 1-6 and Comparative Examples 1-2 were synthesized according to the following process: 0.2 mol of free radical initiator, corresponding moles of RAFT agent, corresponding moles of first monomer and polar organic solvent THF were added to a reaction kettle, stirred at room temperature to fully dissolve the initiator and RAFT agent, and high-purity nitrogen was introduced, and the reaction was stirred at 70°C for 24 hours; A corresponding number of moles of the second monomer was added, high-purity nitrogen was introduced, and the mixture was stirred and reacted at 70° C. for 12-48 hours. The reaction was terminated by quenching at below 30° C. to obtain a copolymer solution. The residual monomers and solvent were removed by vacuum distillation, and the solution was granulated or powdered to obtain the toughened resin. The products of Examples 1-6 were named Copolymers 1-6, and the products of Comparative Examples 1-2 were named Copolymers 7-8. The products were sealed and packaged for later use.

[0029] The products prepared in the examples and comparative examples of the present invention were mixed and sampled according to the formula in Table 2, and the curing condition was 80 degrees for 6 hours. The lap shear strength was evaluated with reference to the method specified in GB / T 7124-2008, and the fracture toughness K was evaluated with reference to the method specified in ASTM D4812. IC .

[0030] The sample preparation formulas of the products of Examples 1-6 and Comparative Examples 1-2 of the present invention are shown in Table 2: the unit of the feeding amount is g.

[0031] Table 2 Formula 1 Formula 2 Formula 3 Formula 4 Formula 5# Formula 6# Formula 7# Formula 8 South Asia 128 60 60 60 60 60 60 60 60 Copolymer 1 40 Copolymer 2 40 Copolymer 3 40 Copolymer 4 40 Copolymer 5 40 Copolymer 6 40 Copolymer 7 40 Copolymer 8 40 Curing agent 140 30 30 30 30 30 30 30 30 DMP-30 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 The performance evaluation results of the sample preparation formulas of the products of Examples 1-6 and Comparative Examples 1-2 of the present invention are shown in Table 3: Formula 1 Formula 2 Formula 3 Formula 4 Formula 5# Formula 6# Formula 7# Formula 8 Shear strength / MPa 24.3 25.9 27.2 21.18 23.13 25.25 15.3 13.7 Failure Mode 100% CF 100% CF 100% CF 80%CF 90%CF 100% CF AF AF <![CDATA[断裂韧性K IC / MPa·m 1 / 2 ]]> 6.83 7.13 7.52 5.63 6.24 6.97 3.17 2.86 From the test results of examples 1-6 and comparative examples 1-2, it can be seen that the ABA triblock resin synthesized by the RAFT agent can greatly improve the shear strength and fracture toughness, and the failure mode of the bonding surface can reach 80-100% cohesive failure. The product synthesized without introducing the RAFT agent is a random copolymer with large molecular weight, which is a solid powder at room temperature, can only be physically mixed with the epoxy resin, has poor dispersibility, and cannot chemically react with the epoxy resin. The fracture toughness and shear strength of comparative examples 1-2 are obviously lower than those of examples 1-6, and the failure mode is interfacial failure. With the increase of the amount of the RAFT agent, the molecular weight of the corresponding ABA block copolymer decreases, the resin can be obtained in liquid state, the compatibility with the epoxy resin is improved, the number of functional groups that can chemically react increases, and therefore the shear strength and fracture toughness show an increasing trend. The above results show that, by controlling the copolymerization monomer ratio and the amount of the RAFT agent within a reasonable range, the shear strength and fracture toughness can be effectively improved.

[0032] The above merely describes preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A triblock self-assembly toughening resin, characterized in that: The toughening resin is mainly synthesized from (50.0-70.0) eq. of a first monomer, (30.0-50.0) eq. of a second monomer, 0.2 eq. of a free radical initiator, and (4.0-8.0) eq. of a RAFT agent.

2. A triblock self-assembly toughening resin according to claim 1, characterized in that: The toughening resin is mainly synthesized from 60 eq. of a first monomer, 40 eq. of a second monomer, 0.2 eq. of a free radical initiator, and 6 eq. of a RAFT agent.

3. A triblock self-assembly toughening resin according to claim 2, characterized in that: The first monomer is a methacrylate soft monomer, specifically any one of butyl acrylate, isooctyl acrylate, n-butyl methacrylate, methoxyethyl methacrylate, ethoxyethyl methacrylate, methoxyethyl acrylate, ethoxyethyl acrylate, lauryl methacrylate, 2-dodecyl acrylate, octadecyl acrylate, 2-ethylhexyl acrylate, n-octyl methacrylate, and n-octyl acrylate.

4. A triblock self-assembly toughening resin according to claim 3, characterized in that: The second monomer is a hard monomer, specifically any one of acrylonitrile, methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, styrene, 4-acryloylmorpholine, acrylamide, cyclohexyl methacrylate, cyclohexyl acrylate, 2-phenoxyethyl methacrylate, isobornyl methacrylate, isobornyl acrylate, tetrahydrofurfuryl methacrylate, and tetrahydrofurfuryl acrylate.

5. A triblock self-assembly toughening resin according to claim 4, characterized in that: The free radical initiator is any one of a peroxide initiator and an azo initiator, specifically any one of benzoyl peroxide, tert-butyl hydroperoxide, isopropylbenzene hydroperoxide, methyl ethyl ketone peroxide, diisopropylbenzene peroxide, azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, and azoisobutylcyanamide.

6. A triblock self-assembling toughening resin according to claim 5, characterized in that: The RAFT agent is a dicarboxy trithiocarbonate, specifically 2,2'-[thiocarbonyl(thio)]bis[2-methylpropionic acid].

7. A method for synthesizing a triblock self-assembly toughening resin according to any one of claims 1 to 6, characterized in that: The steps include: Step S1: Selecting raw materials: Select appropriate amounts of 0.2 eq. of a free radical initiator, 6.0 eq. of a RAFT agent, 60 eq. of a first monomer, and 40 eq. of a second monomer for standby use; Step S2: Primary stirring: 0.2 eq. of the free radical initiator, 6.0 eq. of the RAFT agent, 60 eq. of the first monomer, and the polar organic solvent from Step S1 are sequentially added to the reactor and stirred at room temperature until the free radical initiator and the RAFT agent are fully dissolved. Step S3: Secondary stirring: high-purity nitrogen is introduced into the mixed solution in step S2, and the mixture is stirred at 60-90° C. for 12-48 hours; Step S4: Stir three times: Add 40 eq. of the second monomer selected in step S1 to the mixed solution in step S3; then continue to introduce high-purity nitrogen and continue stirring and reacting at 60-90° C. for 12-48 hours; Step S5: Termination of the reaction: quenching the mixed solution in step S4 at a temperature below 30° C. to terminate the reaction and obtain a copolymer solution; Step S6: Obtaining the finished resin product: The copolymer solution in step S5 is subjected to reduced pressure distillation to remove residual monomers and solvent to obtain the toughened resin, which is then sealed and packaged for later use.

8. Use of a triblock self-assembling toughening resin according to any one of claims 1 to 6, characterized in that: The adhesive made of the toughening resin, epoxy resin, polyamide curing agent 140, and accelerator DMP-30 maintains a lap shear strength of ≥21.18 MPa and a fracture toughness of ≥5.63 MPa·m 1 / 2 .