Modified epoxy resin and preparation method thereof

Abstract

The invention provides modified epoxy resin and a preparation method thereof. The modified epoxy resin is prepared from epoxy resin and composite nanoparticles SiO2 coated PMMA (polymethyl methacrylate), the composite nanoparticles SiO2 (at) PMMA are uniformly distributed in the epoxy resin; in the modified epoxy resin, the mass ratio of the epoxy resin to the composite nanoparticle SiO2-coated PMMA is 0.1%-1%; according to the invention, the composite nanoparticle SiO2-coated PMMA is used as a flexibilizer, and the impact strength of the obtained modified epoxy resin reaches 15-25 kJ / m < 2 >; the bending strength is 135 to 145 MPa; compared with pure epoxy resin (the impact strength is 13.7 kJ / m < 2 >, the bending strength is 130.2 Mpa, and the tensile strength is 54.7 Mpa), the modified epoxy resin provided by the invention has the advantages that the bending strength, the tensile strength and other mechanical properties are improved, the fracture mode is converted into ductile fracture from brittle fracture, and the material toughness is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of thermosetting resins and modified thermosetting resins, and particularly relates to a modified epoxy resin and a preparation method thereof. Background Art

[0002] When an epoxy resin reacts with a curing agent, a three-dimensional network thermosetting resin can be formed. The cured epoxy resin has excellent properties such as adhesiveness, corrosion resistance, processability, and thermal stability, and is superior in terms of mechanical, thermal, electrical, and chemical resistance properties. With these excellent properties, it can be used as coatings, adhesives, and molding materials, and has been widely used in fields such as electronic device encapsulation, civil construction, and aerospace.

[0003] However, while the highly crosslinked three-dimensional network structure endows the epoxy resin with excellent properties, it also makes the resin brittle and poor in toughness, which limits the practical application of the epoxy resin. Therefore, it is necessary to modify the epoxy resin in terms of toughness. Summary of the Invention

[0004] In view of the above problems existing in the prior art, the present invention provides a modified epoxy resin and a preparation method thereof. The present invention uses polymethyl methacrylate-coated silica to form core-shell nanoparticles SiO2@PMMA as a reinforcing body to modify the epoxy resin. The mechanical properties such as the flexural strength and tensile strength of the obtained modified epoxy resin are improved, and the fracture mode is changed from brittle fracture to ductile fracture, and the toughness of the material is improved.

[0005] The specific content of the invention is as follows: In a first aspect, the present invention provides a modified epoxy resin, and the composition of the modified epoxy resin includes: an epoxy resin and composite nanoparticles SiO2@PMMA; the composite nanoparticles SiO2@PMMA are uniformly distributed in the epoxy resin; The mass ratio of the epoxy resin to the composite nanoparticles SiO2@PMMA is 0.1%-1%.

[0006] Optionally, the epoxy equivalent of the epoxy resin is 150-800 g / eq.

[0007] Optionally, the particle size of the composite nanoparticles SiO2@PMMA is 5-15 nm.

[0008] Optionally, the impact strength of the modified epoxy resin is 15-25 kJ / m 2 ; The flexural strength of the modified epoxy resin is 135-145 MPa; The tensile strength of the modified epoxy resin is 60-70 MPa.

[0009] Second aspect, the present invention provides a method for preparing a modified epoxy resin, and the preparation method includes the following steps: Stir a mixture of composite nanoparticles SiO2@PMMA and epoxy resin with a mass ratio of 1:100 - 1:1000. After the composite nanoparticles SiO2@PMMA are fully dispersed, add an appropriate amount of curing agent, continue stirring until evenly mixed, and then perform vacuum pumping to obtain a mixed system; Perform segmented temperature-controlled curing on the mixed system to obtain the modified epoxy resin.

[0010] Optionally, the mass ratio of the curing agent to the epoxy resin is 1:1.1 - 1.5; The curing agent is a mixture of methyltetrahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol.

[0011] Optionally, the segmented temperature-controlled curing includes: placing the mixed system at 90 - 100 °C and maintaining for 0.5 - 1 h; then raising the temperature to 110 - 120 °C and maintaining for 0.5 - 1 h; continuing to raise the temperature to 130 - 140 °C and maintaining for 2 - 3 h; continuing to raise the temperature to 150 - 160 °C and maintaining for 1 - 2 h.

[0012] Optionally, the composite nanoparticles SiO2@PMMA are obtained by the following method: Dissolve isobutyl cyanoacetate, azobisisobutyronitrile and methyl methacrylate in a tetrahydrofuran solution to form a first mixed solution; after the first mixed solution is subjected to 2 - 5 freeze-thaw deoxygenation treatments, transfer it to a nitrogen atmosphere and perform a first free radical polymerization reaction at 40 - 80 °C to obtain a macromolecular chain transfer agent; Dissolve the macromolecular chain transfer agent, 3-(triethoxysilyl)propyl methacrylate and azobisisobutyronitrile in a tetrahydrofuran solution to form a second mixed solution; after the second mixed solution is subjected to 2 - 5 freeze-thaw deoxygenation treatments, transfer it to a nitrogen atmosphere and perform a second free radical polymerization reaction at 40 - 80 °C to obtain a diblock copolymer; Fully dissolve the diblock copolymer in a tetrahydrofuran solution, then transfer it to a dryer and volatilize the solvent at room temperature to obtain a microphase-separated diblock copolymer; transfer the microphase-separated diblock copolymer to 100 - 200 °C and perform annealing treatment for 15 - 24 h to obtain a composite nanoparticle precursor; Place the composite nanoparticle precursor in an atmosphere containing gaseous HCl molecules and let it stand for 1 - 5 h to obtain the composite nanoparticles SiO2@PMMA.

[0013] Optionally, the mass ratio of isobutyronitrile dithiobenzoate to methyl methacrylate is 0.1-1%; The mass ratio of azobisisobutyronitrile to methyl methacrylate is 0.01-1%.

[0014] Optionally, the molar ratio of the macromolecular chain transfer agent, 3-(triethoxysilyl)propyl methacrylate and azobisisobutyronitrile is 1:50:0.2.

[0015] Compared with the prior art, the present invention has the following advantages: A modified epoxy resin provided by the present invention, the composition of the modified epoxy resin includes: epoxy resin and composite nanoparticles SiO2@PMMA; the composite nanoparticles SiO2@PMMA are uniformly distributed in the epoxy resin; in the modified epoxy resin, the mass ratio of epoxy resin to composite nanoparticles SiO2@PMMA is 0.1%-1%; the present invention uses composite nanoparticles SiO2@PMMA as a toughening agent, and the impact strength of the obtained modified epoxy resin reaches 15-25 kJ / m 2 ; the flexural strength is 135-145 MPa; the tensile strength is 60-70 MPa. Compared with pure epoxy resin (impact strength is 13.7 kJ / m 2 , flexural strength is 130.2 Mpa, and tensile strength is 54.7 Mpa), the modified epoxy resin provided by the present invention has improved mechanical properties such as flexural strength and tensile strength, and the fracture mode has changed from brittle fracture to ductile fracture, improving the toughness of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0017] Figure 1 Shows the process flow chart of the preparation method of the modified epoxy resin provided by the embodiment of the present invention; Figure 2 Shows the process flow chart of the preparation method of the composite nanoparticles SiO2@PMMA in the embodiment of the present invention; Figure 3 Shows the transmission electron microscope image of the composite nanoparticles SiO2@PMMA provided by the embodiment of the present invention; Figure 4 Shows the scanning electron microscope image of the impact fracture surface of the modified epoxy resin provided by the embodiment and the comparative example of the present invention at a low magnification; Figure 5 The SEM images of the impact fracture surfaces of the modified epoxy resins provided by the embodiments and comparative examples of the present invention are shown at a high magnification; Figure 6 The test results of the impact strength of the modified epoxy resin provided by the embodiment of the present invention are shown; Figure 7 The test results of the flexural strength of the modified epoxy resin provided by the embodiment of the present invention are shown; Figure 8 The test results of the flexural strength of the modified epoxy resin provided by the embodiment of the present invention are shown. Detailed implementation manners

[0018] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. Based on the embodiments of the present invention, any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with those of other existing technologies falls within the protection scope of the present invention. And all other embodiments obtained by those of ordinary skill in the art without creative work also belong to the protection scope of the present invention.

[0019] If the specific experimental steps or conditions are not specified in the embodiments, the operations or conditions of the conventional experimental steps described in the existing technologies in the art can be followed. The reagents and other instruments not indicating the manufacturer can be obtained as conventional reagent products through commercial purchase. In addition, the drawings are only schematic diagrams of the embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings represent the same or similar parts, and thus their repeated description will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0020] For technologies, methods, and devices known to those of ordinary skill in the relevant fields, detailed discussions may not be made, but where appropriate, the said technologies, methods, and devices should be regarded as part of the specification of the present invention.

[0021] In the description of the present invention, it should be understood that using words such as "first" and "second" to limit the components is only for the convenience of distinguishing the corresponding components. Without further statement, the above words have no special meanings and thus cannot be construed as limiting the protection scope of the present invention.

[0022] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] Explanation of abbreviations and related terms: SiO2@PMMA: An ordered assembly structure at the nanoscale formed by coating SiO2 nanomaterials with PMMA nanomaterials through chemical bonds or other forces.

[0024] Freeze-thaw deoxygenation treatment: First, use liquid nitrogen to freeze the solution containing the reaction monomer, aiming to precipitate the oxygen dissolved in the solution. After that, evacuate the frozen solution to remove the precipitated oxygen. After removing the oxygen, place the reaction vessel containing the frozen solution in normal-temperature water to thaw the solid-state solution back to a liquid solution. Completing all the above processes means completing one freeze-thaw treatment. Chain transfer agent: A substance that can effectively cause the growth radicals to undergo radical transfer, used to adjust the relative molecular mass of the polymer. RAFT reaction: A radical polymerization reaction. In a conventional polymer chain growth reaction, it is irreversible and the molecular chain length is uncontrollable. By introducing a chain transfer agent, a degenerative transfer occurs between the growing radicals and the chain transfer agent, realizing a chemical reaction with controllable molecular chain length. Block copolymer: A special polymer prepared by connecting two or more polymer segments with different properties together. Microphase separation: When polymers with moderate compatibility are blended, since it is not a completely thermodynamically stable system, phase separation will occur. However, the two polymers have a certain degree of compatibility, so the size of this phase separation is microscopic or submicroscopic, and it appears uniform on the outside without macroscopic layering.

[0025] Generally speaking, traditional epoxy resins can be modified by adding toughening agents. With the development of technology, various toughening agents have emerged, such as rubber elastomers, thermoplastic resins, inorganic rigid particles, core-shell nanoparticles, etc. Among them, nanoparticles with a core-shell structure are considered ideal toughening agents that can significantly improve the strength, stiffness, and toughness of composite materials because the core-shell structure provides excellent interfacial compatibility and enhances the interaction between the epoxy resin matrix and the nano-fillers. However, in the research on using core-shell-structured nanoparticles for toughening epoxy resins, there are still the following problems: which type of core-shell nanoparticles has a significant improvement effect on toughening epoxy resins; and due to the complex structure of core-shell nanoparticles, the preparation cost is relatively higher than that of other types of nano-fillers; and how to obtain core-shell-structured nanoparticles with balanced particle sizes.

[0026] Based on this, the first object of the present invention is to provide a modified epoxy resin, and the composition of the modified epoxy resin includes: epoxy resin and composite nanoparticles SiO2@PMMA; the composite nanoparticles SiO2@PMMA are uniformly distributed in the epoxy resin.

[0027] Specifically in implementation, the toughening agent used in the embodiments of the present invention is composite nanoparticles SiO2@PMMA, that is, taking SiO2 as the core structure and coating polymethyl methacrylate on the outside to form composite nanoparticles as the toughening agent to improve the performance of epoxy resin in terms of mechanical properties such as flexural strength and tensile strength, and to achieve the transformation of the fracture mode from brittle fracture to ductile fracture. The huge surface area of the composite nanoparticles SiO2@PMMA forms a large number of interfaces inside the epoxy resin, changing the toughness performance of the epoxy resin; in the modified epoxy resin, the addition amount of the composite nanoparticles SiO2@PMMA should be 0.1%-1% (the mass ratio of nanoparticles to epoxy resin), specifically it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%. The preferred mass ratio of nanoparticles to epoxy resin in the embodiments of the present invention is 0.5%.

[0028] It should be noted that the modification of epoxy resin toughness using composite nanoparticles SiO2@PMMA provided by the present invention is applicable to most commercially available epoxy resins, including but not limited to one or a combination of bisphenol A epoxy resin, bisphenol S epoxy resin, linear phenolic epoxy resin, resorcinol diglycidyl ether epoxy resin, aliphatic polyol glycidyl ether epoxy resin, glycidyl ester epoxy resin, glycidyl aromatic amine epoxy resin, silicone epoxy resin, linear aliphatic epoxy resin, and alicyclic epoxy resin. Or, represented by epoxy equivalent, it includes epoxy resins with an epoxy equivalent of 150-800 g / eq.

[0029] It should also be noted that the particle size range of the composite nanoparticles SiO2@PMMA used in the embodiments of the present invention is 5-15 nm. If the particle size is too small, it will cause difficulties in the dispersion of the composite nanoparticles SiO2@PMMA in the epoxy resin, ultimately affecting the toughness improvement effect of the modified epoxy resin; if the particle size is too large, there will also be problems of poor dispersion and easy agglomeration; at the same time, the binding force between the nanoparticles and the epoxy resin matrix decreases, and the strengthening effect is limited; in addition, too large a particle size makes the surface area of the nanoparticles decrease and the interfacial effect weaken, and the modification effect will also weaken accordingly.

[0030] The present invention uses composite nanoparticles SiO2@PMMA as the toughening agent, and the impact strength of the obtained modified epoxy resin reaches 15-25 kJ / m 2; flexural strength is 135-145 MPa; tensile strength is 60-70 MPa, compared with pure epoxy resin (impact strength is 13.7 kJ / m 2 , flexural strength of 130.2 Mpa, tensile strength of 54.7 Mpa) The modified epoxy resin provided by the present invention has improved mechanical properties such as flexural strength and tensile strength, the fracture mode is changed from brittle fracture to ductile fracture, and the toughness of the material is improved.

[0031] The second object of the present invention is to provide a method for preparing a modified epoxy resin. Figure 1 The flow chart of the preparation method of the modified epoxy resin provided in the embodiment of the present invention is shown as follows: Figure 1 As shown, the following steps are included: S1. Stirring a mixture of composite nanoparticles SiO2@PMMA and epoxy resin in a mass ratio of 1:100-1:1000 to fully disperse the composite nanoparticles SiO2@PMMA, adding a proper amount of curing agent, continuing to stir until the mixture is uniform, and then vacuuming to obtain a mixed system; In the embodiment of the present invention, a mixture of methyltetrahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol is selected as a curing agent, which is mixed with the composite nanoparticles SiO2@PMMA and epoxy resin, and after being fully stirred until the mixture is uniform, a thermosetting treatment is performed.

[0032] To ensure that the composite nanoparticles SiO2@PMMA are fully dispersed, ultrasonic stirring can be used for stirring, and it can be carried out under heating; for example, the mixture of composite nanoparticles SiO2@PMMA and epoxy resin is placed in a water bath at 60-70 °C and ultrasonically stirred for 1-3 h to fully disperse the composite nanoparticles SiO2@PMMA. Then, methyltetrahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol are added, and ultrasonic stirring is continued for 1-3 h. After stirring until fully mixed, the air mixed in the stirring process is removed by vacuuming. Furthermore, if the vacuumed mixed system needs to be cast into a mold pre-coated with a release agent for thermosetting treatment before thermosetting treatment, the mixed system needs to be vacuumed again after casting to remove the air mixed in the mixed system to avoid the appearance of bubbles in the finished product obtained by thermosetting treatment and affect the quality of the finished product.

[0033] S2, curing the mixed system in sections under controlled temperature to obtain the modified epoxy resin.

[0034] In specific implementation, the obtained mixed system can be cured by segmented temperature control, specifically including: placing the mixed system at 90 - 100 °C and maintaining for 0.5 - 1 h; then heating to 110 - 120 °C and maintaining for 0.5 - 1 h; continuously heating to 130 - 140 °C and maintaining for 2 - 3 h; continuously heating to 150 - 160 °C and maintaining for 1 - 2 h.

[0035] Furthermore, the composite nanoparticles SiO2@PMMA used in the embodiments of the present invention are prepared by using isobutyronitrile dithiobenzoate as a chain transfer agent, azobisisobutyronitrile as an initiator, and methyl methacrylate as a monomer. First, a free radical polymerization reaction is carried out to form a macromolecular chain transfer agent, and then the macromolecular chain transfer agent further undergoes a free radical polymerization reaction with 3-(triethoxysilyl)propyl methacrylate to form a block copolymer of polymethyl methacrylate and poly-3-(triethoxysilyl)propyl methacrylate (a diblock copolymer). Under the action of tetrahydrofuran, the diblock copolymer undergoes microphase separation to obtain a spherical core-shell structure. The particle size of the composite nanoparticles SiO2@PMMA obtained by the above method can be well controlled within 5 - 15 nm, meeting the application requirements. Figure 2 The flow chart of the preparation method of the composite nanoparticles SiO2@PMMA in the embodiments of the present invention is shown, as Figure 2 shown, the preparation method includes: S11. Dissolve isobutyronitrile dithiobenzoate, azobisisobutyronitrile, and methyl methacrylate sufficiently in a tetrahydrofuran solution to form a first mixed solution; after the first mixed solution is subjected to 2 - 5 freeze-thaw deoxygenation treatments, it is transferred to a nitrogen atmosphere and undergoes a first free radical polymerization reaction at 40 - 80 °C to obtain a macromolecular chain transfer agent.

[0036] In the specific implementation of this step, isobutyronitrile dithiobenzoate (CPDB) is used as a chain transfer agent, azobisisobutyronitrile (AIBN) is used as an initiator, and methyl methacrylate (MMA) is used as a monomer to participate in the first free radical polymerization to prepare a polymethyl methacrylate macromolecular chain transfer agent (PMMA-CTA).

[0037] When preparing PMMA-CTA, the selection of the chain transfer agent plays an important role in the synthesis of the block copolymer and is the key to controlling the molecular weight of the PMMA-CTA block copolymer and the grafting position of the block; in this step, isobutyronitrile dithiobenzoate (CPDB) is selected as the chain transfer agent, and the dosage of the chain transfer agent CPDB is controlled to be in the ratio of 0.1 wt% to 1 wt% with respect to the dosage of the monomer MMA to ensure the uniformity of the molecular weight distribution and structure of the block copolymer generated in the free radical polymerization reaction. Preferably, the ratio of the chain transfer agent CPDB to the monomer MMA dosage is between 0.4 wt% and 0.5 wt%.

[0038] In this step, the dosage of initiator AIBN can be controlled such that the ratio of its dosage to that of monomer MMA ranges from 0.01 wt% to 0.1 wt%, so as to ensure that the rate and molecular weight of the free radical polymerization reaction meet the application requirements. Preferably, the ratio of the dosage of initiator AIBN to that of monomer MMA ranges from 0.06 wt% to 0.07 wt%.

[0039] It should be noted that the present invention does not limit the specific process for extracting PMMA-CTA from the product of the first free radical polymerization reaction; those skilled in the art can also choose the following process for extraction: Using methanol as a precipitant, under stirring at room temperature, the crude product is slowly added dropwise to methanol for precipitation, and the obtained precipitate is filtered by suction to obtain a primary purified product. The primary purified product is dissolved in an appropriate amount of THF. The above operation is repeated three times to remove the unreacted MMA monomer. The sample obtained by suction filtration is dried under vacuum for 24 h to remove methanol, and finally a pink PMMA-CTA solid is obtained and stored sealed at room temperature.

[0040] S12. The macromolecular chain transfer agent, 3-(triethoxysilyl)propyl methacrylate, and azobisisobutyronitrile are fully dissolved in a tetrahydrofuran solution to form a second mixed solution; after the second mixed solution is subjected to 2-5 freeze-thaw deoxygenation treatments, it is transferred to a nitrogen atmosphere, and a second free radical polymerization reaction is carried out at 40-80 °C to obtain a diblock copolymer; When this step is specifically implemented, the same means as in step S11 are adopted. The polymethyl methacrylate macromolecular chain transfer agent (PMMA-CTA) is further fully mixed with initiator AIBN and monomer 3-(triethoxysilyl)propyl methacrylate (TEPM), and after freeze-thaw deoxygenation, the synthesis of the diblock copolymer of polymethyl methacrylate and poly-3-(triethoxysilyl)propyl methacrylate (PMMA- b -PTEPM) is carried out.

[0041] In this step, by controlling the molar ratio of the macromolecular chain transfer agent PMMA-CTA, monomer TEPM, and initiator AIBN participating in the second free radical polymerization reaction to be 1:50:0.2, the molecular weight of the obtained diblock copolymer PMMA- b -PTEPM is constant, and further, after PMMA- b -PTEPM undergoes subsequent microphase separation by a tetrahydrofuran solvent and crosslinking treatment in an acidic atmosphere, the particle size of the formed composite nanoparticles SiO2@PMMA is maintained at 5-15 nm, and the average particle size is about 10 nm; this helps to achieve the controllability of the particle size of the composite nanoparticles SiO2@PMMA.

[0042] It should be noted that the present invention does not limit the specific process for extracting the diblock copolymer PMMA- b -PTEPM from the product of the second free radical polymerization reaction; those skilled in the art can also choose the following process for extraction: using a composite solvent with a volume ratio of methanol / water of 7 / 3 as a precipitant, and precipitating the crude product under stirring at room temperature. The initially purified product is dissolved in an appropriate amount of THF. The above precipitation operation is repeated three times to remove the unreacted TEPM monomer. The sample obtained by suction filtration is dried under vacuum to remove the solvent, and the finally obtained light pink powder is sealed and stored at room temperature.

[0043] S13. Dissolve the diblock copolymer fully in a tetrahydrofuran solution, then transfer it to a dryer, and volatilize the solvent at room temperature to obtain a microphase-separated diblock copolymer; transfer the microphase-separated diblock copolymer to 100-200 °C and perform annealing treatment for 15-24 h to obtain a composite nanoparticle precursor.

[0044] In this step, the diblock copolymer is fully dissolved in a tetrahydrofuran solution. Since in the diblock copolymer PMMA- b -PTEPM, the solubility differences between the PMMA block and the PTEPM block in tetrahydrofuran (THF) are obvious. The PMMA block has a higher solubility in THF, while the PTEPM block has a lower solubility in THF; thus, the PMMA block tends to form hydrophobic microdomains, and the PTEPM block tends to form hydrophilic microdomains; during the process of volatilizing the solvent THF at room temperature, PMMA- b -PTEPM undergoes microphase separation under the action of THF, forming a microphase-separated structure with the PMMA block arranged outward and coating the PTEPM block.

[0045] At this time, the molecular chain structure formed by microphase separation is not stable and will undergo a phase structure transformation due to environmental changes; in order to maintain the stability of the microphase-separated structure, this step further uses annealing treatment to promote the crystallization process of the copolymer, enhance the phase interface between the PMMA and PTEPM blocks, thereby optimizing the molecular chain structure formed by microphase separation, obtaining a composite nanoparticle precursor with more uniform and stable phase separation and improved thermal stability of the material.

[0046] S14. Place the composite nanoparticle precursor in an atmosphere containing gaseous HCl molecules and let it stand for 1-5 h to obtain the composite nanoparticle SiO2@PMMA.

[0047] When this step is implemented, the HCl atmosphere acts on the composite nanoparticle precursor. The acidic atmosphere provided by HCl promotes the hydrolysis and cross-linking of PTEPM in the composite nanoparticle precursor, causing SiO2 to deposit and form a stable SiO2@PMMA spherical structure. The specific hydrolysis reaction formula is shown in the following formulas ① and ②:

[0048] The product formed by hydrolysis and cross-linking is placed in a THF solution and subjected to ultrasonic and mechanical stirring. The dispersion is centrifuged and the collected precipitate is placed in a freeze dryer to remove residual moisture, ultimately obtaining a fluffy and dry white powder, namely, composite nanoparticles SiO2@PMMA.

[0049] In order to enable those skilled in the art to more clearly understand the present invention, the modified epoxy resin and the preparation method of the present invention are now described in detail through the following examples.

[0050] Example 1 (1) Preparation of spherical composite nanoparticles SiO2@PMMA 1) Preparation of polymethyl methacrylate macromolecular chain transfer agent (PMMA-CTA) Isobutyronitrile dithiobenzoate (CPDB) (0.13 g, 0.599 mmol), azobisisobutyronitrile (AIBN) (19.3 mg, 0.118 mmol), methyl methacrylate (MMA) (30.01 g, 299.7 mmol) and a small amount of tetrahydrofuran (THF) were added to a 100 mL Schlenk reaction bottle in sequence, and the solution was stirred with a magnetic bar until the solution became transparent. After three freeze-thaw deoxygenation cycles, the solution was sealed under nitrogen and stirred in an oil bath at 60°C for 24 h before stopping the reaction to obtain PMMA-CTA.

[0051] Post-treatment of PMMA-CTA: Use methanol as a precipitant. Under stirring at room temperature, slowly add the crude product to methanol for precipitation. The precipitate is filtered to obtain the primary purified product. Dissolve the primary purified product with an appropriate amount of THF. Repeat the above operation three times to remove the unreacted MMA monomer. The sample obtained by filtration is vacuum dried for 24 hours to remove methanol, and finally a pink PMMA-CTA solid is obtained and sealed and stored at room temperature.

[0052] 2) Block copolymer of polymethyl methacrylate and poly 3-(triethoxysilyl)propyl methacrylate (PMMA- b Synthesis of 2-PTEPM Preparation of PMMA- b-PTEPM diblock copolymer, and the specific process is as follows: PMMA-CTA, 3-(triethoxysilyl)propyl methacrylate (TEPM) and AIBN were added to a 25 mL Schlenk reaction tube in a molar ratio of 1:50:0.2, and then 10 g of THF was added (Table 1 shows the actual feeding ratio of the block copolymer). The solution was stirred with a magnetic stirrer until it became transparent. After three "freeze-thaw" deoxygenation treatment cycles, it was sealed under nitrogen conditions and stirred in an oil bath at 60 °C for 24 h.

[0053] After the polymerization was completed, a composite solvent with a volume ratio of methanol / water of 7 / 3 was used as a precipitant, and the crude product was precipitated under stirring at room temperature. The initially purified product was dissolved in an appropriate amount of THF. The above precipitation operation was repeated three times to remove the unreacted TEPM monomer. The sample obtained by suction filtration was dried under vacuum to remove the solvent, and the finally obtained light pink powder was stored sealed at room temperature.

[0054] 3) Preparation of poly(methyl methacrylate) coated silica core-shell nanoparticles (SiO2@PMMA) by microphase separation The synthesized diblock copolymer was dissolved in THF to cause microphase separation of the block copolymer to obtain a spherical structure. The specific operation is as follows: First, the block copolymer obtained in 2) above and THF were added to a 200 mL beaker and stirred to obtain a transparent solution with a concentration of 60 mg / mL. Then, it was dropped into a pre-prepared polytetrafluoroethylene (PTFE) flat-bottomed boat with a dropper, and the boat was placed in a desiccator for the solvent to slowly volatilize. The dried block copolymer film was annealed in an oil bath at 150 °C for 17 h under a nitrogen atmosphere.

[0055] A 200 mL beaker was inverted in a 500 mL large beaker, 10 mL of concentrated hydrochloric acid was added and sealed with a plastic wrap to create a saturated acidic atmosphere. The annealed film was placed in the acidic atmosphere and left standing for 3 h, then taken out. After being broken up, the film was placed in a THF solution for ultrasonic and mechanical stirring, and finally a dispersion of SiO2@PMMA nanoparticles was obtained.

[0056] Since the SiO2@PMMA nanoparticles are insoluble in water, the SiO2@PMMA dispersion was dropped into deionized water for precipitation, and the precipitated suspension was centrifuged using a centrifuge. The solid precipitate after centrifugation was placed in a freeze dryer to remove the residual moisture. The fluffy and dry white powder obtained after freeze drying is the SiO2@PMMA nanoparticles.

[0057] Figure 3 The transmission electron microscope image of the composite nanoparticles SiO2@PMMA provided in the embodiment of the present invention is shown, as Figure 3As shown, the composite nanoparticles SiO2@PMMA are spherical nanoparticles with a uniform shape and an average particle size of about 10 nm.

[0058] 2. Preparation of modified epoxy resin Weigh 65 g of epoxy resin (E51) and mix it with spherical composite nanoparticles SiO2@PMMA with mass fractions of 0.1 wt%, 0.5 wt%, and 1 wt% respectively. Place the mixture in a water bath at 65 °C and stir it ultrasonically for 3 hours to fully disperse the particles. Then, weigh 52 g of methyltetrahydrophthalic anhydride (MeTHPA) and 0.65 g of (DMP-30) and mix them with the above mixture. The mixture is placed in a water bath at 65 °C again and stirred ultrasonically for 1 h. After the mixed product is placed in a vacuum oven at 70 °C and evacuated for 30 min, the epoxy resin is cast into a mold pre-coated with a release agent, and evacuated again for 20 min. Finally, cure it in segments according to the process of 90 °C / 0.5 h + 110 °C / 0.5 h + 130 °C / 2 h + 150 °C / 1 h to finally obtain 3 groups of epoxy resins modified with SiO2@PMMA nanoparticles.

[0059] Observed with the naked eye, the transparency of the epoxy resin decreases with the increase in the content of the nanoparticle reinforcement. This is because the specific surface area of the nanoparticles is large. As the content of the reinforcement increases, the probability of contact between particles increases, and the number of aggregates increases, resulting in a decrease in transparency.

[0060] Comparative Example 1 Weigh 65 g of epoxy resin (E51) and place it in a water bath at 65 °C and stir it ultrasonically for 3 hours. Then, weigh 52 g of methyltetrahydrophthalic anhydride (MeTHPA) and 0.65 g of (DMP-30) and mix them with the above mixture. The mixture is placed in a water bath at 65 °C again and stirred ultrasonically for 1 h. After the mixed product is placed in a vacuum oven at 70 °C and evacuated for 30 min, the epoxy resin is cast into a mold pre-coated with a release agent, and evacuated again for 20 min. Finally, cure it in segments according to the process of 90 °C / 0.5 h + 110 °C / 0.5 h + 130 °C / 2 h + 150 °C / 1 h to finally obtain pure epoxy resin.

[0061] Figure 4 The SEM images of the impact fracture surfaces of the modified epoxy resins provided in the examples and comparative examples of the present invention are shown at a low magnification. Among them, Figure 4 (a1) is the cross-sectional morphology diagram of the pure epoxy resin provided in Comparative Example 1, Figure 4 (a2), Figure 4 (a3), Figure 4(a4) are the cross-sectional morphology diagrams of the modified epoxy resins containing spherical composite nanoparticles SiO2@PMMA with mass fractions of 0.1 wt%, 0.5 wt% and 1 wt% provided in Example 1. It was found by observing under low magnification through scanning electron microscopy that the cross-section of pure epoxy resin ( Figure 4 (a1)) is relatively smooth and the crack distribution is relatively sparse, which is a typical brittle fracture surface. The cross-section of the epoxy resin modified by adding spherical nanoparticles ( Figure 4 (a2-a4)) has a larger roughness; moreover, there are many uneven gully structures, and the matrix has undergone plastic deformation, indicating that the modified epoxy resin has undergone ductile fracture.

[0062] Figure 5 Show the scanning electron microscopy images of the impact cross-sections of the modified epoxy resins provided in the examples and comparative examples of the present invention at high magnification; among them, Figure 5 (a1), Figure 5 (a2) and Figure 5 (a3) respectively show the cross-sectional morphology diagrams of the modified epoxy resins containing spherical composite nanoparticles SiO2@PMMA with mass fractions of 0.1 wt%, 0.5 wt% and 1 wt% provided in Example 1; by observing under a high-magnification scanning electron microscope, it was found that the SiO2@PMMA nanoparticles act as non-penetrable obstacles in the matrix. When the crack propagates to the vicinity of the particles, the crack will be blocked and deflected. The deflection and detour of the crack will dissipate part of the impact energy. At the same time, the hindering effect of the particles can inhibit the formation of destructive cracks from microcracks. Therefore, the introduction of SiO2@PMMA can obtain a better toughening effect. As shown by Figure 5 (a2), when the filler addition amount increases to 0.5 wt%, the SiO2@PMMA particles still maintain a good dispersion state in the matrix. In addition to the presence of spherical particles shown by the red circles on the cross-section surface, spherical holes marked by blue circles were also found. Among them, the hole size is comparable to the spherical particle size. Therefore, it can be inferred that the holes are formed by the debonding of spherical nanoparticles. The presence of holes can cause crack tip blunting, reduce stress concentration and prevent fracture. When the filler content is less than 0.5 wt%, the SiO2@PMMA nanoparticles can maintain good dispersion in the epoxy resin. When the filler content continues to increase to 1 wt%, as shown by Figure 5 (a3), the dispersion of the SiO2@PMMA particles decreases at this time, and more aggregates appear in the epoxy resin matrix, resulting in an increase in stress concentration areas inside the epoxy resin and a decrease in the impact performance of the material.

[0063] Performance verification 1. Impact strength test of modified epoxy resin The impact strength tests were carried out on the 3 groups of modified epoxy resins provided in Example 1 and the pure epoxy resin provided in Comparative Example 1 by using a pendulum impact test. Figure 6 The test results of the impact strength of the modified epoxy resin provided in the embodiment of the present invention are shown as Figure 6 shown. The impact strength of the pure epoxy resin is 13.7 kJ / m 2 , and with the increase of the nanoparticle content, the impact strength shows a trend of increasing first and then decreasing. Among them, when the addition amount of the nanoparticles is 0.5 wt%, the impact strength can reach up to 22.0 kJ / m 2 , which is 61% higher than that of the pure epoxy resin. The toughening mechanism of the SiO2@PMMA nanoparticles is mainly crack passivation, crack pinning and debonding toughening. Since the interaction between the SiO2@PMMA nanoparticles and the epoxy resin matrix is physical, the interfacial interaction is relatively weak. When the interface transfers the load, some SiO2@PMMA nanoparticles dissipate the impact energy and debond, generating micropores. On the one hand, these pores can produce plastic expansion, and on the other hand, they can cooperate with the nanoparticles to induce local shear yield of the matrix between adjacent particles, thereby causing crack tip passivation, reducing stress concentration and preventing fracture. When the material is stressed, many microcracks will be generated near the nanoparticles and the original crack will turn to dissipate energy, thus achieving a toughening effect.

[0064] The fundamental reason for the increase and then decrease of the strengthening effect of the SiO2@PMMA nanoparticles lies in the dispersibility of the nanoparticles. When the nanoparticle content is 0.1 wt%, the SiO2@PMMA nanoparticles are well dispersed in the epoxy resin, which can passivate cracks, generate cavities and reduce stress concentration to play a certain toughening role, but due to the low content of the SiO2@PMMA nanoparticles, the toughening effect is limited. When the content of the SiO2@PMMA nanoparticles increases to 0.5 wt%, at this time, the SiO2@PMMA still has good dispersibility in the matrix, so the toughening effect is further improved. When the content of the SiO2@PMMA nanoparticles continues to increase to 1 wt%, some particles agglomerate, forming stress concentration points, resulting in a decrease in the toughening effect.

[0065] Therefore, it can be seen from the impact strength of the epoxy resin modified by different addition amounts of SiO2@PMMA nanoparticles that the optimal addition amount of the spherical core-shell nanoparticles in this method is 0.5 wt%, and the toughening effect is 61% higher than that of the pure epoxy resin.

[0066] 2. Flexural strength test of modified epoxy resin The flexural strength tests were carried out on the 3 groups of modified epoxy resins provided in Example 1 and the pure epoxy resin provided in Comparative Example 1 by using a high-pressure bending test. Figure 7 The test results of the flexural strength of the modified epoxy resin provided in the embodiment of the present invention are shown asFigure 7 As shown, the flexural strength of pure epoxy resin is 130.2 Mpa. With the increase of the content of SiO2@PMMA nanoparticles, the flexural strength first increases and then decreases. When the addition amount of SiO2@PMMA nanoparticles is 0.5 wt%, the flexural strength reaches the highest value of 145.2 MPa, which is 11.5% higher than that of pure epoxy resin. During the curing and crosslinking process of epoxy resin, internal stress will be generated due to volume shrinkage and different thermal expansion coefficients of different materials. These internal stresses will be distributed on the matrix and the interface between the matrix and the filler. When the internal stress is too large, a small external load can cause the epoxy resin in the stress concentration area to break. Since the PMMA shell of the SiO2@PMMA nanoparticles used in Example 1 has a certain compatibility with epoxy resin but is not completely compatible, when the material is subjected to an external load, the internal stress can be released through the relative slip and interface deformation between the matrix and the filler, thereby achieving the purpose of strengthening. Moreover, when the content of SiO2@PMMA nanoparticles is 0.5 wt%, the particle content is high and the dispersion is good. Therefore, more interfaces can be formed to release more internal stress, thereby achieving the best strengthening effect.

[0067] 3. Tensile Strength Test of Modified Epoxy Resin The universal testing machine was used to test the tensile properties of the three groups of modified epoxy resins provided in Example 1 and the pure epoxy resin provided in Comparative Example 1. Figure 8 The test results of the flexural strength of the modified epoxy resin provided in the embodiment of the present invention are shown, as Figure 8 As shown, the tensile strength of pure epoxy resin is 54.7 Mpa. With the increase of the content of SiO2@PMMA nanoparticles, the tensile strength first increases and then decreases. When the addition amount of SiO2@PMMA nanoparticles is 0.5 wt%, the tensile strength reaches the highest value of 69.4 MPa, which is 27% higher than that of pure epoxy resin. The interfacial interaction between SiO2@PMMA nanoparticles and the epoxy resin matrix is a physical interaction. Therefore, when subjected to an external load, due to the weak interfacial interaction, relative slip occurs between SiO2@PMMA and the matrix, thereby consuming the internal stress generated during the curing process and resulting in an increase in the tensile strength of the material. When the addition amount of SiO2@PMMA nanoparticles is 0.5 wt%, more interfaces are formed by SiO2@PMMA in the matrix and good dispersion can be maintained. Therefore, more energy can be dissipated through interfacial slip when subjected to an external load, thereby achieving the best toughening effect.

[0068] The above performance test results show that compared with pure epoxy resin, the epoxy resin modified with SiO2@PMMA nanoparticles has better improvement effects in impact strength, flexural strength and tensile strength, indicating that this method plays a good role in modifying epoxy resin.

[0069] In the description of this specification, the descriptions referring to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples", etc., mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0070] For method embodiments, for the sake of simple description, they are all expressed as a series of combinations of actions. However, those skilled in the art should know that the present invention is not limited by the described order of actions, because according to the present invention, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and components involved are not necessarily essential to the present invention.

[0071] The above has introduced in detail a modified epoxy resin and a preparation method provided by the present invention. Specific examples are used herein to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A modified epoxy resin, characterized in that: The modified epoxy resin comprises: epoxy resin and composite nanoparticles SiO2@PMMA; the composite nanoparticles SiO2@PMMA are uniformly distributed in the epoxy resin; The mass ratio of the epoxy resin to the composite nanoparticle SiO2@PMMA is 0.1%-1%.

2. The modified epoxy resin according to claim 1, characterized in that: The epoxy equivalent of the epoxy resin is 150-800 g / eq.

3. The modified epoxy resin according to claim 1, characterized in that: The particle size of the composite nanoparticle SiO2@PMMA is 5-15 nm.

4. The modified epoxy resin according to claim 1, characterized in that: The impact strength of the modified epoxy resin is 15-25 kJ / m 2 ; The flexural strength of the modified epoxy resin is 135-145 MPa; The tensile strength of the modified epoxy resin is 60-70 MPa.

5. A method for preparing a modified epoxy resin, characterized in that: The preparation method comprises the following steps: A mixture of composite nanoparticles SiO2@PMMA and epoxy resin in a mass ratio of 1:100-1:1000 is stirred to fully disperse the composite nanoparticles SiO2@PMMA, and then a proper amount of curing agent is added, and the mixture is stirred until uniformly mixed, and then vacuumed to obtain a mixed system; The mixed system is cured by controlled temperature in sections to obtain the modified epoxy resin.

6. The method for preparing the modified epoxy resin according to claim 5, characterized in that: The mass ratio of the curing agent to the epoxy resin is 1:1.1-1.5; The curing agent is a mixture of methyltetrahydrophthalic anhydride and 2,4,6-tris(dimethylaminomethyl)phenol.

7. The method for preparing the modified epoxy resin according to claim 5, characterized in that: The segmented temperature-controlled curing includes: placing the mixed system at 90-100°C for 0.5-1 h; then heating to 110-120°C for 0.5-1 h; continuing to heat to 130-140°C for 2-3 h; continuing to heat to 150-160°C for 1-2 h.

8. The method for preparing the modified epoxy resin according to claim 5, characterized in that: The composite nanoparticle SiO2@PMMA is obtained by the following method: Fully dissolving isobutyronitrile dithiobenzoate, azobisisobutyronitrile and methyl methacrylate in a tetrahydrofuran solution to form a first mixed solution; after the first mixed solution is subjected to 2-5 freeze-thaw deoxygenation treatments, it is transferred to a nitrogen atmosphere and subjected to a first free radical polymerization reaction at 40-80° C. to obtain a macromolecular chain transfer agent; The macromolecular chain transfer agent, 3-(triethoxysilyl)propyl methacrylate and azobisisobutyronitrile are fully dissolved in a tetrahydrofuran solution to form a second mixed solution; the second mixed solution is subjected to 2-5 freeze-thaw deoxygenation treatments, and then transferred to a nitrogen atmosphere, and subjected to a second free radical polymerization reaction at 40-80° C. to obtain a diblock copolymer; The diblock copolymer is fully dissolved in a tetrahydrofuran solution, and then transferred to a dryer to volatilize the solvent at room temperature to obtain a microphase-separated diblock copolymer; the microphase-separated diblock copolymer is transferred to 100-200° C. and annealed for 15-24 h to obtain a composite nanoparticle precursor; The composite nanoparticle precursor is placed in an atmosphere containing gaseous HCl molecules and allowed to stand for 1-5 hours to obtain the composite nanoparticle SiO2@PMMA.

9. The method for preparing the modified epoxy resin according to claim 8, characterized in that: The mass ratio of the dithiobenzoic acid isobutyronitrile to the methyl methacrylate is 0.1-1%; The mass ratio of the azobisisobutyronitrile to the methyl methacrylate is 0.01-1%.

10. The method for preparing the modified epoxy resin according to claim 8, characterized in that: The molar ratio of the macromolecular chain transfer agent, 3-(triethoxysilyl)propyl methacrylate and azobisisobutyronitrile is 1:50:0.2.

Images