Branched active oligoester modifier as well as preparation method and application thereof

Abstract

The invention discloses a branched active oligoester modifier as well as a preparation method and application thereof, and belongs to the technical field of polymer materials. The method comprises the following steps: step 1, preparing carboxyl-terminated branched glyceride through condensation polymerization of dicarboxylic acid and glycerol; and step 2, preparing the epoxy-terminated reactive activity modifier by reacting carboxyl-terminated branched glyceride with aliphatic epoxy resin. The dicarboxylic acid is sebacic acid or azelaic acid, the purity is 99%, and the molar ratio of the glycerol to the dicarboxylic acid is (2.0-2.05): (3.2-3.4). The mass ratio of the carboxyl-terminated branched glyceride to the aliphatic epoxy resin is 20: (31-33). The modifier prepared by the invention can significantly improve the impact toughness, tensile strength and energy storage modulus of epoxy resin. When the mass fraction of the modifier is lower than 20%, the storage modulus of the modified epoxy resin is higher than that of pure epoxy resin; meanwhile, the thermal stability of the system is basically kept unchanged, and the glass transition temperature is maintained at the level of the original epoxy polymer.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a branched low-activity polyester modifier, its preparation method, and its application. Background Technology

[0002] Epoxy resins are widely used in composite materials, electronic packaging, coatings, and adhesives due to their excellent adhesion, corrosion resistance, electrical insulation, and mechanical strength. However, after curing, epoxy resins have a high crosslinking density and restricted molecular chain segment movement, resulting in brittleness and poor impact resistance, making it difficult to meet the application requirements of high-toughness structural components.

[0003] To improve the toughness of epoxy resins, existing technologies are mainly divided into three categories:

[0004] 1. Toughening with rubber elastomers: For example, carboxyl-terminated nitrile butadiene rubber (CTBN) can significantly toughen by inducing crazes and shear bands to dissipate energy. However, it has poor compatibility with epoxy resins, is prone to phase separation, and will significantly reduce the glass transition temperature (Tg) and modulus of the material, sacrificing rigidity.

[0005] 2. Toughening of thermoplastic plastics: such as polyethersulfone (PES), which reduces performance loss by forming an interpenetrating network, but requires high-temperature melting and processing, which is complex, energy-intensive, and excessive addition will lead to a sharp increase in the viscosity of the system, making processing difficult;

[0006] 3. Other modification technologies: such as core-shell particle toughening and hyperbranched polymer toughening. The former has a complex dispersion process, and the latter requires multiple catalysts for synthesis. Residual catalysts will reduce the thermal stability of the material and accelerate aging, making them unsuitable for high-precision scenarios such as electronic packaging.

[0007] In summary, existing technologies suffer from three major drawbacks: "performance at odds, catalyst residue, and environmentally unfriendly processes." There is an urgent need to develop an epoxy resin modification scheme that is highly efficient in toughening, has balanced performance, is prepared in a green manner, and is compatible with cold curing. Summary of the Invention

[0008] This invention aims to overcome the shortcomings of existing technologies and provide a branched, low-activity polyester modifier, its preparation method, and its application. The modifier has epoxy groups at the end and contains a tribranched structure. Its purpose is to improve the impact resistance of room-temperature cured epoxy polymers while maintaining or increasing their mechanical strength and glass transition temperature.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing a branched, low-activity polyester modifier, the method comprising:

[0011] Step 1: Terminally carboxyl-branched glycerol esters are prepared by polycondensation of dicarboxylic acids and glycerol; the synthetic route is shown in the following formula:

[0012] ;

[0013] Step 2: The terminal epoxy group reactive modifier is prepared by reacting terminal carboxyl branched glycerol esters with aliphatic epoxy resin. The synthetic route is shown in the following formula:

[0014]

[0015] The infrared characteristic peak of the terminal epoxy group modifier is 3465 cm⁻¹. -1 (OH stretching), 2932 / 2856cm -1 (CH2 telescopic), 1733cm -1 (C=O stretching), 1092cm -1 (CO expansion), 900cm -1 (Characteristic peaks of epoxy groups); In the 1H NMR spectrum, the characteristic peaks of epoxy methylene hydrogen are located at 2.50 / 2.70 ppm, and the characteristic peaks of epoxy methine hydrogen are located at 3.56 ppm.

[0016] Further, in step one, the dicarboxylic acid is sebacic acid or azelaic acid with a purity of 99%, and the molar ratio of glycerol to dicarboxylic acid is 2.0~2.05:3.2~3.4.

[0017] Further, in step one, the reaction temperature is 135~145℃, the reaction time is 8~9h, nitrogen protection is applied (flow rate 50mL / min), the acid value is monitored in real time, the endpoint acid value is 135~160mgKOH / g, and the branching degree of the product is 46~48%. The product is dried under vacuum at 80℃ and 0.09MPa for 2h to obtain a pale yellow waxy solid (melting point 70℃).

[0018] Further, in step two, the mass ratio of the terminal carboxyl branched glycerol ester to the aliphatic epoxy resin (diethylene glycol diglycidyl ether (DEG-1, purity 99%)) is 20:31~33.

[0019] Further, in step two, the reaction temperature is 130-135℃, under nitrogen protection, and the reaction time is 5-7 hours. The endpoint acid value is ≤5 mgKOH / g, and the epoxy value is 6-9 mol / 100g (determined by the hydrochloric acid-acetone method). The product is dried under vacuum at 80℃ and 0.09 MPa for 2 hours to obtain a pale yellow liquid terminal epoxy group modifier. The terminal epoxy group modifier has a Mn of 2765-4713, a Mw of 12243-19541, and a polydispersity index of 4.14-4.43.

[0020] Furthermore, the specific steps of the method are as follows:

[0021] Step 1: Mix glycerol with dicarboxylic acid (sebacic acid or azelaic acid) at a molar ratio of 2.0~2.05:3.2~3.4, and perform non-catalytic melt polycondensation at 140~145℃ under nitrogen protection for 8~9 hours until the acid value is 135~160mgKOH / g. Dry under vacuum to obtain terminal carboxyl branched glycerol ester.

[0022] Step 2: Mix terminal carboxyl branched glycerol ester with diethylene glycol diglycidyl ether at a mass ratio of 20:31~33, and react without catalysis at 135℃ under nitrogen protection for 5~7 hours until the acid value is ≤5mgKOH / g. Vacuum drying yields the modifier containing reactive epoxy groups and branched segments.

[0023] Furthermore, glycerol is a byproduct of biodiesel production with a purity of ≥99%.

[0024] A modifier prepared by the above preparation method.

[0025] An application of the modifier prepared by the above method is characterized in that: the application involves curing an amine curing agent, epoxy resin, and the modifier at 15-25℃ for 3-7 days (cold curing, no external heating required); the epoxy resin is CYD128 type bisphenol A epoxy resin, and the amine curing agent is diethylenetriamine (DETA). With a 20wt% addition of the modifier, the tensile strength increases by ≥93%, the 5% thermogravimetric temperature decreases by ≤8℃, and there is no obvious phase separation (thermogravimetric analysis shows a single decomposition stage). Performance indicators: the modified epoxy resin exhibits a 93.0-113.9% increase in tensile strength, a 400% increase in impact strength, and higher low-temperature storage energy than pure epoxy resin, with a 5% thermogravimetric temperature (T... d5% The temperature will only decrease by ≤8℃.

[0026] Furthermore, the mass percentage of epoxy resin to modifier is 50%~100%: 0%~50%, and the amount of curing agent added is determined according to the epoxy value of epoxy resin and the epoxy value of modifier: m(curing agent) = EV(epoxy resin) × 0.112g + EV(modifier) ​​× 0.045g.

[0027] The advantages of this invention over the prior art are as follows:

[0028] (1) Green and environmentally friendly advantages: No catalysts or solvents are used throughout the process, energy consumption is reduced compared to traditional processes, and it is both environmentally friendly and safe. It also avoids the generation of residual pollutants and reduces the cost of waste treatment.

[0029] (2) Processing performance advantages: The product is a low-viscosity liquid at room temperature, has good compatibility with epoxy resin, and the fluidity of the system meets the requirements for field use at an addition amount of 5~20wt%. The product has both low viscosity (liquid at room temperature) and high reactivity, making it suitable for cold-curing epoxy systems.

[0030] (3) Mechanical performance advantages: Impact strength: When the addition amount is 20wt%, the EBOGSeb system is improved by 400% and the EBOGAze system is improved by 500%; Tensile strength: When the addition amount is 20wt%, the EBOGAze system is improved by 113.9%; Low temperature performance: The energy storage modulus at -100℃ is improved by 38.1%, which is suitable for low temperature scenarios;

[0031] (4) Thermal stability advantage: Adding 5%, 10%, and 20% modifier has no significant effect on the 5% mass loss (Td5%) during heating. By adding 20% ​​modifier by mass, Td5% is reduced by only < 8℃ while maintaining the inherent heat resistance of epoxy resin.

[0032] (5) Application scenario advantages: It is compatible with cold curing systems, requires no heating equipment, and can be used for outdoor on-site repair, low-temperature equipment bonding and other scenarios.

[0033] (6) As a modifier, it can significantly improve the impact toughness (≥400%), tensile strength (≥93%) and energy storage modulus (temperature range from -100℃ to about 75℃) of epoxy resin. When the mass fraction of the modifier is less than 20%, the storage modulus of the modified epoxy resin is higher than that of pure epoxy resin; at the same time, the thermal stability of the system remains basically unchanged, and the glass transition temperature is maintained at the level of the original epoxy polymer. Attached Figure Description

[0034] Figure 1 The infrared spectrum of terminal carboxyl-branched glycerol ester (BOGSeb / BOGAze) is shown at 3460 cm⁻¹. -1 (OH), 2932 / 2832cm -1 (CH2), 1726cm -1 (C=O), 1170cm -1 (COC) characteristic peak;

[0035] Figure 2 The infrared spectrum of the terminal epoxy group modifier (EBOGSeb / EBGAze) was updated to include a 900 cm⁻¹. -1 The characteristic peaks of epoxy groups, and the C=O peak shifted to 1733 cm⁻¹. -1 ;

[0036] Figure 3 The image shows the 1H NMR spectrum of terminal carboxyl branched glycerol ester (BOGSeb / BOGAze). The peaks are: 5.23 ppm for the central carbotriester of glycerol (characteristic peak of branching point), 4.29 ppm for the primary hydroxyl ester, and 2.31 ppm and 1.59 ppm for fatty acid chain hydrogens, confirming the branched ester structure.

[0037] Figure 4The NMR chromatogram of terminal carboxyl branched glycerol ester (BOGSeb / BOGAze) shows the terminal carboxyl carbon at 179.30 ppm, the ester carbonyl carbon at 173.45 ppm, and the fully esterified carbon of glycerol at 69.08 ppm (C2) and 62.23 ppm (C1 / C3), confirming the branched skeleton and terminal carboxyl group.

[0038] Figure 5 The image shows a partial extension of the ¹³C NMR spectrum (61.0–72.5 ppm) of terminal carboxyl-branched glycerol esters, used to resolve dendritic units (D), terminal units (T), and linear units (L), and to calculate the degree of branching.

[0039] Figure 6 The 1H NMR spectrum of the epoxy group-terminated modifier (EBOGSeb / EBOGAze) shows ethylene oxide hydrogen at 3.56 ppm, epoxy methylene hydrogen at 2.50 / 2.70 ppm, and glycerol central hydrocarbon at 5.20 ppm, which together verify the epoxy group-terminated structure.

[0040] Figure 7 The image shows the carbon NMR spectrum of the terminal epoxy group modifier (EBOGSeb / EBOGAze). The terminal methylene carbon (epoxy modification site) is at 71.0 ppm, the ester carbonyl carbon is at 173.1 ppm, and the glycerol skeleton carbon is at 69.0 / 61.9 ppm, confirming that the epoxy group is grafted to the end of the fatty acid chain.

[0041] Figure 8 The dynamic thermomechanical analysis (DMA) storage modulus diagram of the modified epoxy resin shows that the storage modulus of the modified system is significantly higher than that of the pure epoxy resin in the range of -100℃ to 75℃.

[0042] Figure 9 SEM images of the impact fracture surfaces of modified epoxy resins are shown. (a) pure epoxy resin, (b) 10 wt% EBOGSeb, (c) 15 wt% EBOGSeb, (d) 20 wt% EBOGSeb, (e) 50 wt% EBOGSeb, (f) 10 wt% EBOGAze, (g) 15 wt% EBOGAze, (h) 20 wt% EBOGAze, and (i) 50 wt% EBOGAze. The rough tear surface confirms the shear yield energy dissipation mechanism.

[0043] Figure 10 The thermogravimetric curve of the modified epoxy resin shows that when the content of the modifier is less than 20%, it has little effect on the Td5% of the epoxy resin.

[0044] Figure 11 This is a schematic diagram of the epoxy resin flexural strength test when the modifier content is 50wt%. Detailed Implementation

[0045] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0046] This invention relates to a reactive low-polyester modifier with a tribranched structure for modifying epoxy resins. This modifier increases toughness while maintaining or improving the strength properties and glass transition temperature of cold-curing epoxy polymers. It also provides a green synthesis method under catalyst-free and solvent-free conditions. The products of this invention can be used to produce adhesives, sealants, and cold-curing coatings that are highly efficient over a wide temperature range, particularly in the low-temperature region.

[0047] This invention relates to the application of branched, low-reactivity polyester modifiers in epoxy resin modification, aiming to improve the impact toughness of epoxy resins while maintaining or increasing their strength properties and glass transition temperature. The invention comprises: a carboxyl-terminated branched glycerol ester prepared by polycondensation of a dicarboxylic acid with glycerol under catalyst-free and solvent-free conditions; a terminal epoxy-based reactive modifier prepared by reacting the carboxyl-terminated branched glycerol ester with an aliphatic epoxy resin under catalyst-free and solvent-free conditions; and curing the epoxy polymer using an amine curing agent at a temperature of 15-25°C.

[0048] This invention achieves the preparation and modification application of terminal epoxy group modifiers through "two-step non-catalytic reaction + cold curing application", and achieves technological breakthroughs through three major mechanisms: "molecular design, reaction regulation, and performance synergy": (1) branching topology control mechanism: based on Flory According to the BMNLP theory, by adjusting the molar ratio of glycerol to dicarboxylic acid (r>0.5), combined with the steric hindrance effect of the secondary hydroxyl group of glycerol (which has lower reactivity than the primary hydroxyl group), star-shaped branched structures are preferentially formed rather than cross-linked networks. The branching degree is precisely controlled to be 46%~48%. This branching degree can balance the flexibility (long-chain dicarboxylic acid) and rigidity (branched skeleton) of the molecular chain, which not only ensures the sufficiency of the epoxy end-capping reaction, but also lays the foundation for the subsequent formation of interpenetrating cross-linked networks; (2) Low-temperature non-catalytic reaction mechanism: The alkyl chain of the long-chain dicarboxylic acid (sebacic acid / azelic acid) reduces the viscosity of the system in the molten state and enhances the molecular mobility, so that the polycondensation reaction can be carried out at 140~145℃; In the epoxy end-capping stage, the carboxyl group has high nucleophilic attack activity on the epoxy group. Combined with the steric hindrance reduction effect of the diethylene glycol ether chain, the reaction can be carried out without a catalyst. Efficient end-group conversion is achieved at around 135℃, avoiding epoxy self-polymerization or hydroxyl side reactions at high temperatures; (3) Toughening synergistic effect mechanism: Chemical bonding interface strengthening: The epoxy group at the end of the modifier reacts with the amine curing agent and chemically bonds into the epoxy crosslinking network, avoiding phase separation (confirmed by TGA single thermal decomposition stage); Flexible chain segment energy consumption: The long-chain aliphatic structure and diethylene glycol ether bond undergo chain segment extension and rearrangement under stress, dissipating impact energy (confirmed by SEM impact fracture rough tear surface); Branching structure regulation: Glyceryl branching core reduces the crosslinking density of the epoxy network, increases the crosslinking point spacing, enhances the molecular chain mobility, and induces matrix shear yielding; Low temperature performance optimization: Branching structure inhibits molecular crystallization, enhances the chain segment flexibility at low temperatures, and makes the energy storage modulus at 100℃ significantly higher than that of pure epoxy resin (confirmed by DMA test).

[0049] The present invention is described in detail below through examples. All raw materials used are industrial grade, and the testing methods comply with national standards. Each performance test is performed in parallel three times, and the average value of the results is taken.

[0050] Example 1: Preparation of an epoxy-terminated modifier based on sebacic acid (EBOGSeb)

[0051] 1. Synthesis of terminal carboxyl-branched glycerides (BOGSeb):

[0052] Add glycerol (2.05 mol) and sebacic acid (3.2 mol) to a 500 mL five-necked reaction flask, and install a mechanical stirrer, thermometer, water separator, and nitrogen gas delivery tube; introduce nitrogen gas (50 mL / min), raise the temperature to 140 °C and hold for 9 h, take a sample every 2 h to measure the acid value, and stop the reaction when the acid value stabilizes at 158.5 mg KOH / g; cool to 60 °C, transfer to a vacuum drying oven (80 °C, 0.09 MPa) and dry for 2 h to obtain BOGSeb (pale yellow waxy solid, melting point 70 °C).

[0053] Branching degree is

[0054]

[0055] 2. EBOGSeb Synthesis:

[0056] Add BOGSeb (100g) and DEG-1 (155g) to a 500mL five-necked reaction flask, heat to 135℃ under nitrogen protection and hold for 7h; take samples every 2h to measure the acid value, and stop the reaction when the acid value drops to 4.2 mgKOH / g; cool to room temperature and vacuum dry (80℃, 0.09MPa) for 2h to obtain EBOGSeb (pale yellow liquid, epoxy value 7.85%, Mn=2765, Mw=12243, PDI=4.43).

[0057] Example 2: Preparation of an epoxy-terminated modifier based on azelaic acid (EBGAze)

[0058] 1. Synthesis of terminal carboxyl branched glycerides (BOGAze):

[0059] Glycerol (70.95 g, 0.77 mol) and azelaic acid (217.52 g, 1.21 mol) were added to a 500 mL five-necked reaction flask. The mixture was heated to 145 °C and kept at that temperature for 8 h under nitrogen protection. The reaction was stopped when the acid value stabilized at 156.1 mg KOH / g. The mixture was dried under vacuum (80 °C, 0.09 MPa) for 2 h to obtain BOGAze (a yellow waxy solid with a melting point of 70 °C).

[0060] Branching degree is

[0061]

[0062] 2. EBGAze Synthesis:

[0063] Add BOGAze (100g) and DEG-1 (165g) to a 500mL five-necked reaction flask and keep the reaction at 135℃ for 5h. Stop the reaction when the acid value drops to 0mgKOH / g. After vacuum drying, EBGAze (yellow liquid, epoxy value 8.0%, Mn=4713, Mw=19541, PDI=4.14) is obtained.

[0064] Example 3: Performance Testing of Epoxy Resin with Terminal Epoxy Groups

[0065] Modified epoxy resins were prepared according to the proportions in Table 1. Tensile strength, impact strength, thermal stability, and low-temperature storage modulus were tested, and the results are shown in Tables 2-5.

[0066] Table 1 Modified epoxy resin formulation

[0067]

[0068] The selected CYD-128 epoxy resin has an epoxy value (EV) of 23.4%, and m (curing agent) = EV (epoxy resin) × 0.112g + EV (modifier) ​​× 0.045g.

[0069] Table 2. Tensile property test results of modified epoxy resin

[0070]

[0071] Table 3 Impact strength test results of modified epoxy resin (kJ / m) 2 )

[0072]

[0073] Table 4. Flexural strength test results of modified epoxy resin (MPa)

[0074]

[0075] Table 5. Thermal stability test results of modified epoxy resin (T) d5% (℃)

[0076]

[0077] The core innovation of this invention lies in the combination of "catalytic-free green synthesis" and "cold curing high-efficiency toughening": (1) It is synthesized using glycerol, a byproduct of biodiesel production, and medium-chain dicarboxylic acids, which do not pose a threat to the environment and can be synthesized according to green chemistry requirements. (2) The preparation process is free of catalysts and solvents, avoiding the negative impact of residual pollutants on material performance, which is in line with the trend of green chemistry. (3) The product is compatible with cold curing systems, requiring no heating equipment, and can be used in on-site repair, low-temperature construction, and other scenarios, reducing application costs and energy consumption. (4) In terms of performance, it achieves "toughening without sacrificing rigidity and heat resistance", solving the problem of performance trade-offs in traditional modification technologies, and is highly practical.

Claims

1. A method for preparing a branched, low-activity polyester modifier, characterized in that: The method is as follows: Step 1: Terminal carboxyl branched glycerol esters are prepared by polycondensation reaction of dicarboxylic acids and glycerol; Step 2: The terminal epoxy group reactive modifier is prepared by reacting terminal carboxyl branched glycerol esters with aliphatic epoxy resin.

2. The preparation method according to claim 1, characterized in that: In step one, the dicarboxylic acid is sebacic acid or azelaic acid, and the molar ratio of glycerol to dicarboxylic acid is 2.0~2.05:3.2~3.

4.

3. The preparation method according to claim 1, characterized in that: In step one, the reaction temperature is 135~145℃, the reaction time is 8~9h, nitrogen protection is applied, and the product is dried under vacuum to obtain a pale yellow waxy solid.

4. The preparation method according to claim 1, characterized in that: In step two, the mass ratio of the terminal carboxyl branched glycerol ester to the aliphatic epoxy resin (diethylene glycol diglycidyl ether) is 20:31~33.

5. The preparation method according to claim 1, characterized in that: In step two, the reaction temperature is 130~135℃, nitrogen protection is applied, and the reaction time is 5~7h. The product is dried under vacuum to obtain a pale yellow liquid terminal epoxy modifier.

6. The preparation method according to claim 1, characterized in that: The specific steps of the method are as follows: Step 1: Mix glycerol with dicarboxylic acid (sebacic acid or azelaic acid) at a molar ratio of 2.0~2.05:3.2~3.4, and perform non-catalytic melt polycondensation at 140~145℃ under nitrogen protection for 8~9 hours until the acid value is 135~160mgKOH / g. Dry under vacuum to obtain terminal carboxyl branched glycerol ester. Step 2: Mix terminal carboxyl branched glycerol ester with diethylene glycol diglycidyl ether at a mass ratio of 20:31~33, and react without catalysis at 135℃ under nitrogen protection for 5~7 hours until the acid value is ≤5mgKOH / g. Vacuum drying yields the modifier containing reactive epoxy groups and branched segments.

7. The preparation method according to claim 2 or 6, characterized in that: Glycerin is a byproduct of biodiesel production with a purity of ≥99%.

8. A modifier prepared by the preparation method according to any one of claims 1 to 7.

9. The application of a modifier prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The application involves curing an amine curing agent, epoxy resin, and modifier at 15-25°C for 3-7 days (cold curing, no external heating required); the epoxy resin is CYD128 type bisphenol A epoxy resin, and the amine curing agent is diethylenetriamine (DETA).

10. The application according to claim 9, characterized in that: The mass percentage of epoxy resin to modifier is 50%~100%: 0%~50%. The amount of curing agent added is determined according to the epoxy value of epoxy resin and the epoxy value of modifier: m(curing agent) = EV(epoxy resin) × 0.112g + EV(modifier) ​​× 0.045g.

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