YB-B2000 polyurethane modified epoxy resin and preparation method thereof

Abstract

The invention relates to the technical field of polymer composite materials, in particular to YB-B2000 polyurethane modified epoxy resin and a preparation method thereof.The preparation method comprises the steps that phenolic resin serves as a bridging unit, high-density phenolic hydroxyl groups are introduced into bisphenol A epoxy resin under the catalysis of organic phosphine, and then chemical grafting is achieved through reaction with-NCO terminated polyurethane prepolymer. The method can efficiently construct a nano-scale microphase structure, obviously improves the toughness, heat resistance and processing stability of the material, has no heavy metal catalyst residue, and is suitable for the fields of electronic packaging, structural adhesives, composite materials and the like.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite materials technology, specifically a YB-B2000 polyurethane modified epoxy resin and its preparation method. Background Technology

[0002] In the field of polyurethane-modified epoxy resin technology, existing techniques mostly employ physical blending or chemical grafting of -NCO-terminated polyurethane prepolymers with epoxy resins to improve the toughness and overall performance of the epoxy resin. However, conventional bisphenol A type epoxy resin molecules contain only trace amounts of secondary hydroxyl groups generated from synthesis residues or hydrolysis, with low concentrations and limited reactivity, resulting in low grafting efficiency with -NCO groups. To promote the grafting reaction, some technical solutions introduce organotin catalysts, but the residue of such catalysts in the system may accelerate the subsequent epoxy-amine curing reaction, affecting the pot life and storage stability.

[0003] Furthermore, if grafting is insufficient, the polyurethane phase is prone to macroscopic phase separation, forming stress concentration areas that weaken the overall mechanical properties of the material. Simultaneously, the -NCO groups are sensitive to moisture in the environment, easily undergoing side reactions to generate urea bonds and release CO2, causing bubbles, localized crosslinking, and even gelation, affecting product consistency and process reproducibility.

[0004] Existing patent document CN115850629A (Guangdong Academy of Sciences Chemical Engineering Research Institute) discloses a polyurethane-modified epoxy resin and its preparation method. This method involves partially ring-opening the epoxy resin with an organic amine to increase the hydroxyl content in the system, thereby enhancing the grafting efficiency with the polyurethane prepolymer. While this method improves compatibility and mechanical properties to some extent, it relies on the ring-opening reaction of the epoxy groups with the organic amine. This results in complex reaction condition control, the risk of byproduct formation, and the obtained hydroxyl groups are mainly secondary hydroxyl groups, with relatively limited reactivity, thus limiting the improvement in grafting efficiency.

[0005] Existing patent document CN106414542B (Nippon Steel Chemical Materials Co., Ltd.) discloses a polyurethane-modified epoxy resin, which uses a bisphenol-based epoxy resin containing secondary hydroxyl groups (a) with a specific hydroxyl equivalent as the starting material, and is modified by polyol (b), polyisocyanate (c), and low molecular weight chain extender (d). Although this scheme optimizes the selection of raw materials, its core still relies on the reaction of the secondary hydroxyl groups contained in the epoxy resin itself with -NCO, and does not fundamentally solve the problem of insufficient hydroxyl activity. Moreover, it has stringent requirements for raw material specifications, which limits its versatility and cost control.

[0006] In summary, the existing technologies mentioned above still have room for improvement in terms of enhancing the chemical grafting efficiency between polyurethane and epoxy resin, suppressing side reactions, ensuring nanoscale phase dispersion, and balancing high toughness and high heat resistance. Summary of the Invention

[0007] This invention provides a YB-B2000 polyurethane-modified epoxy resin and its preparation method. The aim is to introduce phenolic resin as a bridging unit to construct high-density, highly reactive phenolic hydroxyl sites in situ on the bisphenol A type epoxy resin backbone, enabling the -NCO-terminated polyurethane prepolymer to efficiently and directionally chemically graft with the epoxy resin. This results in a modified epoxy resin system possessing high toughness, high heat resistance, good processing stability, and excellent mechanical properties. YB-B2000 is the grade of the polyurethane-modified epoxy resin.

[0008] In a first aspect, the present invention provides a method for preparing a polyurethane-modified epoxy resin, comprising the following steps: S10: Bisphenol A type epoxy resin and phenolic resin are reacted at 80-100℃ for 1-2 hours in the presence of an organophosphorus catalyst to obtain an activated epoxy intermediate. S20: Oligomeric polyols are reacted with excess diisocyanate at 90-110°C for 2 to 4 hours to obtain -NCO-terminated polyurethane prepolymers. S30: The -NCO-terminated polyurethane prepolymer is added dropwise to the activated epoxy intermediate at 60-70°C and reacted for 2-3 hours to allow the -NCO groups to react with the phenolic hydroxyl groups to form urethane bonds, thereby achieving chemical grafting of the polyurethane chain. S40: The reaction is terminated when the viscosity of the system reaches 5000-8000 mPa·s, and the modified epoxy resin base material is obtained.

[0009] According to the present invention, phenolic resin is introduced into bisphenol A type epoxy resin, and then undergoes a ring-opening addition reaction with epoxy groups under the action of an organophosphorus catalyst to generate a functionalized intermediate mainly composed of phenolic hydroxyl groups. This forms a rigid cross-linked network containing hydroxyl groups, providing reaction sites for subsequent polyurethane grafting. The phenolic hydroxyl groups in this intermediate have significantly higher nucleophilic activity than aliphatic secondary hydroxyl groups, and can react efficiently with -NCO groups under metal-free catalyst conditions to form a stable urethane bond structure. This technical approach avoids the problem of low grafting efficiency caused by low hydroxyl concentration and poor activity in traditional methods, while also avoiding the interference of residual organotin catalysts on the subsequent curing process.

[0010] In some embodiments, in step S10, the bisphenol A type epoxy resin is selected from at least one of E-20, E-44, E-51, or Epon 828, and its epoxy equivalent is 160-500 g / eq. Preferably, the bisphenol A type epoxy resin is selected from E-51 or Epon 828, and its epoxy equivalent is 180-200 g / eq.

[0011] In some embodiments, in step S10, the phenolic resin has a hydroxymethyl content of 7.5%-9.5% and a number-average molecular weight of 300-600.

[0012] In some embodiments, in step S10, the mass ratio of the bisphenol A epoxy resin to the phenolic resin is 100:10-20. In some embodiments, when the amount of phenolic resin introduced exceeds 20 parts, the viscosity of the system increases sharply and the processability decreases; when it is less than 10 parts, there are insufficient grafting sites and the toughening effect is limited; therefore, 10 to 20 parts are preferred.

[0013] In some embodiments, in step S10, the organophosphorus catalyst is at least one of triphenylphosphine, tributylphosphine, or tris(4-methylphenyl)phosphine, and its amount is 0.1% to 0.5% of the mass of bisphenol A epoxy resin. The phosphorus atom in the organophosphorus molecule provides lone pair electrons, forming a coordination complex with the electrophilic carbon atom of the epoxy group. This lowers the activation energy barrier for epoxy ring-opening. The enhanced polarity of the complexed epoxy group makes it easier for the phenolic hydroxyl and hydroxymethyl groups of the phenolic resin to attack, resulting in a ring-opening addition reaction and the formation of an ether crosslinking network. Compared to imidazole catalysts, organophosphorus catalysts exhibit stronger selectivity for the reaction between phenolic hydroxyl and epoxy groups. They can initiate efficient catalysis at 80-100℃, with a curing temperature 20-40℃ lower than traditional catalysts. They do not introduce polar impurities (such as residual amino groups in amine catalysts) into the crosslinking network. The glass transition temperature (Tg) of the cured product can be increased by 10-20℃, and the char residue is 5%-8% higher than that of the imidazole catalytic system. This makes them more suitable for preparing high-temperature resistant epoxy-phenolic composite materials. Organophosphorus catalysts preferentially catalyze the reaction between epoxy and phenolic hydroxyl groups, almost without inducing epoxy self-polymerization. The mechanical properties of the cured product are more uniform, and there are no side reactions with -NCO groups, avoiding foaming and performance degradation of the system.

[0014] In some embodiments, in step S10, the reaction is carried out under a nitrogen protective atmosphere and the stirring rate is 200-400 revolutions per minute.

[0015] In some embodiments, in step S10, the content of phenolic hydroxyl groups in the activated epoxy intermediate obtained after the reaction is 0.40-0.50 mmol / g.

[0016] In some embodiments, in step S20, the oligomeric polyol is selected from one or more of polycaprolactone polyol (PCL), polyethylene adipate (PEA), polycarbonate diol (PCDL), hydroxyl-terminated polybutadiene (HTPB), polytetrahydrofuran diol (PTMG), and polypropylene oxide diol (PPG), and the diisocyanate is selected from one or more of 1,5-naphthalene diisocyanate (NDI), toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), terephthalic diisocyanate (PPDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and dicyclohexylmethane diisocyanate (HMDI).

[0017] In some embodiments, step S10 further includes the addition of an reactive diluent to reduce the viscosity of subsequent processes. The reactive diluent is a flame-retardant reactive diluent. Preferably, the flame-retardant reactive diluent is selected from one or more of phenyl glycidyl ether phosphate (PGPE), dimethylphosphonic acid glycidyl ether (DMGPE), tetrabromobisphenol A diglycidyl ether (TBBA-DGE), and bromophenyl glycidyl ether. The amount of reactive diluent added is 5wt%-15wt% of the total amount of bisphenol A epoxy resin and phenolic resin.

[0018] In some embodiments, in step S20, the oligomeric polyol is preferably polycaprolactone polyol (PCL), the number average molecular weight of which is 800 to 1200, the hydroxyl value is 55-70 mg KOH / g, and the diisocyanate is preferably 1,5-naphthalene diisocyanate (NDI).

[0019] In some embodiments, the molar ratio of isocyanate groups to hydroxyl groups in the 1,5-naphthalene diisocyanate and polycaprolactone polyol is 2:1 to 2.5:1. The hydroxyl groups at both ends of the PCL molecular chain preferentially react with the -NCO groups of NDI to generate a prepolymer with both ends capped with -NCO. Excess NDI ensures that the hydroxyl groups of PCL are completely consumed, and the prepolymer ends are 100% active -NCO groups, providing sites for subsequent reactions with the hydroxyl groups of the epoxy-phenolic network. However, if the NCO / OH ratio exceeds 2.5:1, a large amount of free NDI will remain in the prepolymer, making it prone to excessive local crosslinking during subsequent reactions with the epoxy-phenolic network, increasing the brittleness of the modified system. The prepolymer with a ratio of 2:1 to 2.5:1 has a moderate molecular weight, which will not cause the system to become brittle due to excessive crosslinking density, nor will it cause a decrease in heat resistance due to insufficient crosslinking. The proportion of flexible PCL segments and rigid NDI structure is balanced. After grafting onto the epoxy-phenolic network, the toughness of the system can be significantly improved while retaining heat resistance.

[0020] In some embodiments, in step S20, the reaction is carried out under a dry nitrogen atmosphere, and the moisture content in the reaction system is controlled below 200 ppm. -NCO is extremely sensitive to moisture; all raw materials and reaction vessels must be thoroughly dried, otherwise it will lead to bubbles and performance degradation. The oligomeric polyol and diisocyanate are dehydrated before the reaction; exemplarily, vacuum heating dehydration or molecular sieve dehydration can be used. The reaction equipment is first cleaned with anhydrous ethanol, then heated to 110-120°C, and dry nitrogen is bubbled in for 2-4 hours. After cooling, a nitrogen atmosphere is maintained, and the pipelines are purged with dry nitrogen for 30-60 minutes to remove residual moisture. Glassware should be avoided (as it easily absorbs moisture); stainless steel equipment is preferred.

[0021] In some embodiments, in step S20, the dehydrated oligomeric polyol is added first, the temperature is raised to the reaction temperature of 90-110°C, nitrogen gas is then introduced, and finally the dehydrated diisocyanate is slowly added dropwise to prevent the diisocyanate from absorbing moisture when it comes into contact with the low-temperature polyol.

[0022] In some embodiments, in step S20, the -NCO content of the -NCO-terminated polyurethane prepolymer obtained after the reaction is 4.0%-5.5%. In some embodiments, when the -NCO content of the polyurethane prepolymer is below 4.0%, the grafting density is insufficient; when it is above 5.5%, the unreacted -NCO is prone to moisture absorption, so it is advisable to control it between 4.0% and 5.5%.

[0023] In some embodiments, in step S30, the prepolymer is added to the activated epoxy intermediate at a dropping rate of 0.5-1.5 g / min. Since the addition reaction between the -NCO group and the hydroxyl groups (phenolic hydroxyl groups, secondary hydroxyl groups generated from epoxy ring opening) in the activated epoxy intermediate is a strongly exothermic reaction, if the material is added all at once, a large number of -NCO groups will instantly contact the hydroxyl groups, releasing a large amount of heat in a short time, causing a sharp rise in the system temperature. Excessive temperature can trigger multiple side reactions; excess -NCO groups undergo self-polymerization, generating urea-formate esters or biuret, leading to prepolymer crosslinking and gelation, premature solidification of the crosslinked network of the epoxy intermediate, and localized hard segment aggregation, affecting the mechanical uniformity of the modified system. The dropping method can disperse the exothermic reaction throughout the entire feeding process, and combined with a mild reaction temperature of 60-70°C, achieves an isothermal controllable reaction, avoiding uncontrolled temperature rise.

[0024] In some embodiments, in step S30, the reaction system is maintained at 60-70°C, and the stirring rate is 300-500 rpm. The activated epoxy intermediate has a high viscosity at room temperature, making prepolymer dispersion difficult. Maintaining a temperature of 60-70°C, combined with stirring, can appropriately reduce the system viscosity, allowing the added prepolymer droplets to disperse quickly and evenly, avoiding "hard segment islands" caused by excessively high local NCO concentrations. Furthermore, 60-70°C is the catalytic activity window for the activated epoxy intermediate. At this temperature, the catalyst has activated the epoxy groups, but the crosslinking reaction rate of the epoxy intermediate itself is slow, providing a time window for the grafting reaction of the -NCO prepolymer.

[0025] In some embodiments, in step S30, infrared spectroscopy is used to monitor the intensity change of the -NCO characteristic absorption peak at 2270 cm⁻¹ during the reaction process. When the intensity of the peak decreases to less than 10% of the initial value, the reaction is determined to be basically completed.

[0026] In some embodiments, in step S30, a catalyst, chain extender, filler, defoamer and / or leveling agent may be added; and / or, the catalyst is selected from at least one of organotin catalysts and tertiary amine catalysts; and / or, the chain extender is selected from at least one of small molecule diols and small molecule diamines.

[0027] In some embodiments, in step S40, the system viscosity is measured using a viscometer at 25°C. For example, a Brookfield rotational viscometer with a rotor model #4 and a rotation speed of 10 revolutions per minute is used.

[0028] In some embodiments, step S40 is followed by a curing step, in which a curing agent is added for curing and molding. The curing process involves first holding the temperature at 120°C for 2 hours, and then raising the temperature to 180°C and holding it for 4 hours.

[0029] In some embodiments, the curing agent is selected from amine curing agents or acid anhydride curing agents. Amine curing agents can be aliphatic amines, alicyclic amines, or aromatic amines, while acid anhydride curing agents can be phthalic anhydride (PA), tetrahydrophthalic anhydride (THPA), hexahydrophthalic anhydride (HHPA), or methylnadic anhydride (MNA).

[0030] In some embodiments, the curing agent is preferably an aromatic amine curing agent, wherein the aromatic amine curing agent is at least one selected from 4,4'-diaminodiphenyl sulfone (DDS), m-phenylenediamine (MPDA), or diaminodiphenylmethane (DDM), and its amount is 25% to 35% of the mass of the modified epoxy resin base. In some embodiments, when the amount of curing agent is less than 25%, the crosslinking density is insufficient and the Tg decreases; when it is more than 35%, the brittleness increases and the impact strength decreases, therefore 25% to 35% is preferred.

[0031] In a second aspect, the present invention provides a polyurethane-modified epoxy resin, which is prepared by the preparation method described in any embodiment of the first aspect.

[0032] According to the present invention, in the molecular structure of this polyurethane-modified epoxy resin, polyurethane segments are chemically bonded to the epoxy resin backbone via urethane bonds. The grafting points originate from phenolic hydroxyl groups introduced by the phenolic resin, and the grafting density is controlled by the amount of phenolic resin added. Due to the high reactivity of the phenolic hydroxyl groups, the grafting reaction can be completed under metal-free catalyst conditions, avoiding the adverse effects of catalytic residues on storage stability and curing behavior. Simultaneously, the chemical grafting structure promotes the uniform dispersion of the polyurethane phase at the nanoscale in the epoxy matrix, forming an island-like microphase structure, effectively improving the impact toughness of the material.

[0033] In some embodiments, the grafting rate of the polyurethane-modified epoxy resin is greater than 90%, and the grafting rate is determined by quantitative analysis using gel permeation chromatography combined with Fourier transform infrared spectroscopy.

[0034] In some embodiments, the polyurethane-modified epoxy resin, after being cured with aromatic amines, has a glass transition temperature (Tg) of not less than 160°C, which is determined by dynamic mechanical analysis (DMA) at a frequency of 1 Hz and a heating rate of 3°C per minute.

[0035] In some embodiments, the polyurethane-modified epoxy resin, after being cured with aromatic amines, has a notched impact strength of not less than 12 kJ / m², as tested according to ISO 179-1 standard.

[0036] In some embodiments, the initial viscosity of the polyurethane-modified epoxy resin is 5000-8000 mPa·s, measured at 25°C, to ensure good flowability in subsequent processing and to prevent the polyurethane phase from migrating and agglomerating during storage. It is suitable for processes such as vacuum casting, compression molding, adhesive coating, or manufacturing high-toughness fiber-reinforced composite materials.

[0037] In some embodiments, the polyurethane-modified epoxy resin exhibits a viscosity change rate of less than 10% after being stored at 25°C and 50% relative humidity for 30 days, indicating that it has good storage stability.

[0038] In some embodiments, the limiting oxygen index (LOI) of the polyurethane-modified epoxy resin cured product is not less than 28%, which, when tested according to ASTM D2863, indicates that it possesses self-extinguishing flame-retardant properties.

[0039] In some embodiments, the polyurethane-modified epoxy resin cured product meets the UL94V-0 flame retardant standard, and tests according to GB / T 2408 standard show that it has excellent flame retardant properties.

[0040] In some embodiments, the polyurethane-modified epoxy resin cured product has a tensile strength of 75-85 MPa and an elongation at break of 6.0%-7.5%, as tested according to ISO 527-2 standard.

[0041] In some embodiments, the polyurethane-modified epoxy resin does not contain heavy metal catalysts such as organotin, lead, and mercury, and complies with RoHS and REACH environmental regulations.

[0042] In some embodiments, no carbon dioxide gas byproducts are generated during the preparation of the polyurethane modified epoxy resin, the system is free of bubbles and gels, and the viscosity fluctuation between batches is less than 5%.

[0043] In some embodiments, the introduction of the phenolic resin not only provides highly active phenolic hydroxyl groups, but its rigid aromatic ring structure also synergistically enhances the heat distortion temperature and dimensional stability of the cured product.

[0044] In some embodiments, the 1,5-naphthalene diisocyanate, due to its rigid naphthalene ring structure, imparts high cohesive energy and thermal stability to the polyurethane segments, which helps maintain the high glass transition temperature of the modified system.

[0045] In some embodiments, the flexible aliphatic segments of the polycaprolactone polyol form an energy-dissipating phase in the epoxy matrix, absorbing impact energy through microcrack deflection, crimping, and plastic deformation mechanisms, thereby improving toughness.

[0046] In some embodiments, the organophosphorus catalyst promotes the addition reaction of epoxy groups with hydroxymethyl groups of phenolic resin in step S10 to generate a β-hydroxy ether structure. This reaction is irreversible and highly selective, and does not trigger the epoxy homopolymerization side reaction.

[0047] In some embodiments, the activated epoxy intermediate is subjected to depressurization to remove trace amounts of volatiles before step S30, with the pressure controlled at 500-800 Pa, the temperature at 60-70 °C, and the time at 30-40 minutes.

[0048] In some embodiments, the -NCO-terminated polyurethane prepolymer is dried by a molecular sieve before being added. The molecular sieve used is of type 3A or 4A, with a particle size of 2 to 4 mm, and the amount used is 2% to 5% of the prepolymer mass.

[0049] In some embodiments, the modified epoxy resin base is filtered through a 0.45-micron polytetrafluoroethylene filter membrane after step S40 to remove any gel particles or impurities that may be present.

[0050] In some embodiments, the heating rate is controlled at 2-3°C per minute during the curing process to reduce internal stress and prevent volatile residues from remaining.

[0051] In some embodiments, the preparation method is suitable for continuous production, wherein steps S10 and S20 can be performed in parallel, and step S30 uses a static mixer to achieve efficient mixing of the prepolymer and the activated intermediate.

[0052] In some embodiments, the hydroxymethyl group of the phenolic resin reacts with the epoxy group in step S10, and the resulting phenolic hydroxyl group is located at the side position of the epoxy backbone, with little steric hindrance, which facilitates the approach and reaction of -NCO.

[0053] In some embodiments, the formation temperature of the urethane bond is controlled at 60-70°C. This temperature range ensures the reaction rate between -NCO and the phenolic hydroxyl group while avoiding side reactions between -NCO and water or epoxy groups.

[0054] In some embodiments, the modified epoxy resin base material, when placed in an oven at 40°C for 7 days without the addition of a curing agent, showed no gelation, no delamination, and no significant color change.

[0055] In some embodiments, the preparation of the polyurethane-modified epoxy resin is carried out entirely in an environment with a moisture content of less than 100 ppm, and the raw materials are pre-dried under vacuum at 110°C for 4 hours.

[0056] In some embodiments, the phenolic resin can be synthesized by condensation of phenol and formaldehyde under oxalic acid catalysis, with a molar ratio of 1 to 0.8, a reaction temperature of 80 to 90°C, and a reaction time of 3 hours.

[0057] In some embodiments, the polycaprolactone polyol can be prepared by ring-opening polymerization of ε-caprolactone and ethylene glycol initiator under the catalysis of stannous octoate, and purified by alkali washing, water washing, and vacuum distillation.

[0058] In some embodiments, the 1,5-naphthalene diisocyanate can be prepared by reacting 1,5-naphthalenediamine with phosgene, and purified by distillation to a purity greater than 99.5%.

[0059] In some embodiments, the aromatic amine curing agent is vacuum dried at 120°C for 2 hours before use, and the moisture content is less than 0.05%.

[0060] In some embodiments, the thermal decomposition temperature (Td5%) of the polyurethane-modified epoxy resin cured product is not lower than 350°C, as determined by TGA under a nitrogen atmosphere and a heating rate of 10°C per minute.

[0061] In some embodiments, all reaction vessels, storage tanks and pipelines in the preparation method are made of stainless steel and are purged with nitrogen at least three times.

[0062] In some implementations, the dropping process is controlled by a metering pump with an accuracy of ±0.5 grams per minute to ensure that the exothermic reaction is stable and controllable.

[0063] In some implementations, the determination of the reaction endpoint can be based not only on viscosity, but also on the disappearance of the DSC exothermic peak or the NCO titration value being below 0.2% as supplementary criteria.

[0064] In some embodiments, the polyurethane-modified epoxy resin has a molecular weight distribution index (PDI) of 1.8 to 2.5, indicating that it has moderate molecular weight dispersion, which is beneficial for balancing processing and performance.

[0065] Thirdly, the present invention provides the use of the above-mentioned polyurethane modified epoxy resin in the preparation of fiber-reinforced composite materials.

[0066] In some embodiments, the fiber-reinforced composite material is prepared by impregnation, molding, curing and / or cooling, using the polyurethane-modified epoxy resin as the matrix resin and fiber material as the reinforcement.

[0067] In some embodiments, the fiber material is selected from at least one of glass fiber, carbon fiber, and basalt fiber, and the mass fraction of the fiber material in the fiber-reinforced composite material is 30%-60%.

[0068] In some embodiments, the impregnation process is as follows: immersing the fiber material in a resin solution or molten system of the polyurethane modified epoxy resin, controlling the impregnation temperature at 60-80°C and the impregnation time at 5-30 minutes, so that the resin fully wets the fiber.

[0069] In some embodiments, the fiber-reinforced composite material is used to manufacture at least one of protective nets, wind turbine blades, automotive parts, and electronic device housings.

[0070] In some embodiments, the protective netting includes railway guardrails, high-speed railway guardrails, highway guardrails, highway anti-glare netting, roadbed netting, slope protection netting, reservoir protection netting, and bridge railings. It is obviously also applicable to other netting materials intended for isolation or protection.

[0071] In summary, the present invention has the following beneficial effects: 1. By constructing highly active phenolic hydroxyl sites through a phenolic bridging strategy, highly efficient chemical grafting of polyurethane onto epoxy resin is achieved, solving problems such as low grafting rate, phase separation, gelation, and catalytic residue in traditional methods.

[0072] 2. The introduction of aromatic rings enhances heat resistance and flame retardancy; the subsequent introduction of polyurethane segments (containing urethane bonds) can further suppress melt dripping, achieving the UL94V-0 flame retardancy standard without the need to add a large amount of halogenated flame retardants. Moreover, the smoke density is low and no toxic hydrogen halide gas is released during combustion, meeting environmental protection flame retardancy requirements.

[0073] 3. The core problem of traditional phenolic-epoxy copolymers is that the high crosslinking density leads to high brittleness and poor impact resistance. The flexible polyurethane segments in NCO-terminated prepolymers (polyurethane prepolymers) are grafted into the phenolic-epoxy crosslinking network through urethane bonds, acting as a "toughening agent". The impact strength of the modified system can be increased by 50%-100%, while the tensile strength and flexural strength only decrease slightly, achieving a "strength-toughness balance". It is suitable for structural composite matrix with strict mechanical performance requirements.

[0074] 4. Phenolic crosslinking first can reduce the viscosity of the system and avoid the sharp increase in viscosity caused by the subsequent addition of NCO prepolymer; at the same time, the hydroxyl groups (-OH) generated by the phenolic reaction can react precisely with the NCO groups, reducing side reactions (such as the foaming reaction of NCO with water). In summary, this invention provides a polyurethane-modified epoxy resin with high toughness, high heat resistance, high flame retardancy, good processing stability and process reproducibility, and an industrially feasible preparation method thereof. Detailed Implementation

[0075] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0076] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0077] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0078] As described above, this invention provides a polyurethane-modified epoxy resin and its preparation method. The aim is to introduce phenolic resin as a bridging unit to construct high-density, highly reactive phenolic hydroxyl sites in situ on the bisphenol A type epoxy resin backbone, enabling -NCO-terminated polyurethane prepolymers to efficiently and directionally undergo chemical grafting with epoxy resin, thereby obtaining a modified epoxy resin system with high toughness, high heat resistance, good processing stability, and excellent mechanical properties.

[0079] The following describes embodiments of the present invention. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0080] Example 1 Preparation of activated epoxy intermediates: 100 g of bisphenol A type epoxy resin E-51 was added to a four-necked flask equipped with a stirrer, thermometer, nitrogen inlet tube, and reflux condenser, and heated to 80 °C to melt it. Then, 15 g of phenolic resin (hydroxymethyl content 8.2%, number average molecular weight 450) and 0.3 g of triphenylphosphine catalyst were added. Nitrogen gas was introduced for protection, and the stirring rate was controlled at 300 rpm. The reaction was carried out at 85 °C for 1.5 hours. After the reaction was completed, the system was cooled to 60 °C, and trace amounts of volatiles were removed under reduced pressure of 500 Pa for 30 minutes to obtain a pale yellow, transparent, viscous liquid, which was the activated epoxy intermediate. Titration analysis showed that its phenolic hydroxyl content was 0.45 mmol / g.

[0081] Preparation of -NCO-terminated polyurethane prepolymer: 100 g of polycaprolactone polyol (number average molecular weight 1000, hydroxyl value 56 mg KOH / g) was added to another dry four-necked flask and dried under vacuum at 110 °C for 2 hours. After cooling to room temperature, it was purged three times with dry nitrogen. The temperature was raised to 95 °C, and 42.8 g of 1,5-naphthalene diisocyanate (purity greater than 99.5%) was slowly added dropwise, controlling the molar ratio of isocyanate groups to hydroxyl groups at 2.2:1. After the addition was complete, the reaction was continued at 100 °C for 3 hours, during which the moisture content was controlled below 150 ppm. After the reaction was completed, the obtained prepolymer was cooled to 60 °C, and 3 g of type 4A molecular sieve (particle size 3 mm) was added and dried for 1 hour. The molecular sieve was removed by filtration, yielding a reddish-brown transparent liquid, which is the -NCO-terminated polyurethane prepolymer. The -NCO content was determined to be 4.8% by di-n-butylamine titration.

[0082] Preparation of polyurethane-modified epoxy resin base material: The activated epoxy intermediate was placed in a three-necked flask equipped with a stirrer, thermometer, and nitrogen inlet tube, heated to 65°C, and stirred at 400 rpm. The -NCO-terminated polyurethane prepolymer was added dropwise to the activated epoxy intermediate at a rate of 1.0 g / min using a metering pump. During the addition, the intensity of the -NCO characteristic absorption peak at 2270 cm⁻¹ was monitored in real time using a Fourier transform infrared spectroscopy (FTIR) spectrometer. After the addition was complete, the reaction was continued at 65°C until the absorption peak intensity decreased to 8% of its initial value. At this point, the viscosity of the system was measured to be 6500 mPa·s using a Brookfield rotational viscometer (25°C, #4 rotor, 10 rpm), at which point the reaction was terminated. The resulting product was filtered through a 0.45 μm polytetrafluoroethylene (PTFE) membrane to obtain a light amber-colored, transparent, viscous liquid, which is the polyurethane-modified epoxy resin base material.

[0083] Preparation of cured material: Weigh 100g of the above-mentioned polyurethane-modified epoxy resin base material, add 30g of 4,4'-diaminodiphenyl sulfone (DDS) curing agent (pre-dried under vacuum at 120℃ for 2 hours, with a moisture content of less than 0.05%), and stir and mix thoroughly at 80℃. Pour the mixture into a preheated mold and cure according to the following procedure: raise the temperature to 120℃ at a rate of 2.5℃ per minute and hold for 2 hours; then raise the temperature to 180℃ at the same rate and hold for 4 hours. After curing, cool to room temperature in the oven and demold to obtain the test specimen.

[0084] Example 2 Preparation of activated epoxy intermediates: 100 g of bisphenol A type epoxy resin Epon 828 was added to a four-necked flask equipped with a stirrer, thermometer, nitrogen inlet tube, and reflux condenser, and heated to 90 °C to melt it. Then, 10 g of phenolic resin (7.8% hydroxymethyl content, number average molecular weight 350) and 0.2 g of tris(4-methylphenyl)phosphine catalyst were added. Nitrogen gas was introduced for protection, and the stirring rate was controlled at 350 rpm. The reaction was carried out at 95 °C for 1 hour. After the reaction was completed, the system was cooled to 60 °C, and trace amounts of volatiles were removed under reduced pressure of 600 Pa for 30 minutes to obtain the activated epoxy intermediate. The phenolic hydroxyl content was determined by titration to be 0.42 mmol / g.

[0085] Preparation of -NCO-terminated polyurethane prepolymer: 100 g of polycaprolactone polyol (number average molecular weight 1000, hydroxyl value 56 mg KOH / g) was added to another dry four-necked flask and dried under vacuum at 110 °C for 2 hours. After cooling to room temperature, it was purged three times with dry nitrogen. The temperature was raised to 90 °C, and 38.5 g of 1,5-naphthalene diisocyanate (purity greater than 99.5%) was slowly added dropwise, controlling the molar ratio of isocyanate groups to hydroxyl groups at 2:1. After the addition was complete, the reaction was continued at 90 °C for 4 hours, during which the moisture content was controlled below 150 ppm. After the reaction was completed, the obtained prepolymer was cooled to 60 °C, and 3 g of type 4A molecular sieve (particle size 3 mm) was added and dried for 1 hour. The molecular sieve was removed by filtration, yielding a reddish-brown transparent liquid, which is the -NCO-terminated polyurethane prepolymer. The -NCO content was determined to be 5.2% by di-n-butylamine titration.

[0086] Preparation of polyurethane-modified epoxy resin base material: The activated epoxy intermediate was placed in a three-necked flask equipped with a stirrer, thermometer, and nitrogen inlet tube, heated to 60°C, and stirred at 350 rpm. The -NCO-terminated polyurethane prepolymer was added dropwise to the activated epoxy intermediate at a rate of 0.8 g / min using a metering pump. During the addition, the intensity of the -NCO characteristic absorption peak at 2270 cm⁻¹ was monitored in real time using a Fourier transform infrared spectroscopy (FTIR) spectrometer. After the addition was complete, the reaction was continued at 65°C until the absorption peak intensity decreased to 9% of its initial value. At this point, the viscosity of the system was measured to be 5200 mPa·s using a Brookfield rotational viscometer (25°C, #4 rotor, 10 rpm), at which point the reaction was terminated. The resulting product was filtered through a 0.45 μm polytetrafluoroethylene (PTFE) filter membrane to obtain a light amber-colored, transparent, viscous liquid, which is the polyurethane-modified epoxy resin base material.

[0087] Preparation of cured material: Weigh 100g of the above-mentioned polyurethane-modified epoxy resin base material, add 28g of m-phenylenediamine (MPDA) curing agent (pre-dried under vacuum at 120℃ for 2 hours, with a moisture content of less than 0.05%), and mix thoroughly at 80℃. Pour the mixture into a preheated mold and cure according to the following procedure: raise the temperature to 120℃ at a rate of 2.5℃ per minute and hold for 2 hours; then raise the temperature to 180℃ at the same rate and hold for 4 hours. After curing, cool to room temperature in the oven and demold to obtain the test sample.

[0088] Example 3 Preparation of activated epoxy intermediates: 100 g of bisphenol A type epoxy resin E-20 was added to a four-necked flask equipped with a stirrer, thermometer, nitrogen inlet tube, and reflux condenser, and heated to 90 °C to melt it. Then, 20 g of phenolic resin (hydroxymethyl content 9.0%, number average molecular weight 550) and 0.5 g of tributylphosphine catalyst were added. Nitrogen gas was introduced for protection, and the stirring rate was controlled at 350 rpm. The reaction was carried out at 100 °C for 2 hours. After the reaction was completed, the system was cooled to 60 °C, and trace amounts of volatiles were removed under reduced pressure of 600 Pa for 30 minutes to obtain the activated epoxy intermediate. The phenolic hydroxyl content was determined by titration to be 0.48 mmol / g.

[0089] Preparation of -NCO-terminated polyurethane prepolymer: 100 g of polycaprolactone polyol (number average molecular weight 1000, hydroxyl value 56 mg KOH / g) was added to another dry four-necked flask and dried under vacuum at 110 °C for 2 hours. After cooling to room temperature, it was purged three times with dry nitrogen. The temperature was then raised to 110 °C, and 45 g of 1,5-naphthalene diisocyanate (purity greater than 99.5%) was slowly added dropwise, controlling the molar ratio of isocyanate groups to hydroxyl groups at 2.5:1. After the addition was complete, the reaction was continued at 110 °C for 2 hours, during which the moisture content was controlled below 150 ppm. After the reaction was completed, the resulting prepolymer was cooled to 60 °C, and 3 g of type 4A molecular sieve (particle size 3 mm) was added and dried for 1 hour. The molecular sieve was removed by filtration, yielding a reddish-brown transparent liquid, which is the -NCO-terminated polyurethane prepolymer. The -NCO content was determined to be 4.3% by di-n-butylamine titration.

[0090] Preparation of polyurethane-modified epoxy resin base material: The activated epoxy intermediate was placed in a three-necked flask equipped with a stirrer, thermometer, and nitrogen inlet tube, heated to 70°C, and stirred at 350 rpm. The -NCO-terminated polyurethane prepolymer was added dropwise to the activated epoxy intermediate at a rate of 1.2 g / min using a metering pump. During the addition, the intensity of the -NCO characteristic absorption peak at 2270 cm⁻¹ was monitored in real time using a Fourier transform infrared spectroscopy (FTIR) spectrometer. After the addition was complete, the reaction was continued at 65°C until the absorption peak intensity decreased to 9% of its initial value. At this point, the viscosity of the system was measured to be 7800 mPa·s using a Brookfield rotational viscometer (25°C, #4 rotor, 10 rpm), at which point the reaction was terminated. The resulting product was filtered through a 0.45 μm polytetrafluoroethylene (PTFE) membrane to obtain a light amber-colored, transparent, viscous liquid, which is the polyurethane-modified epoxy resin base material.

[0091] Preparation of cured material: Weigh 100g of the above-mentioned polyurethane-modified epoxy resin base material, add 32g of diaminodiphenylmethane (DDM) curing agent (pre-dried under vacuum at 120℃ for 2 hours, with a moisture content of less than 0.05%), and mix thoroughly at 80℃. Pour the mixture into a preheated mold and cure according to the following procedure: raise the temperature to 120℃ at a rate of 2.5℃ per minute and hold for 2 hours; then raise the temperature to 180℃ at the same rate and hold for 4 hours. After curing, cool to room temperature in the oven and demold to obtain the test sample.

[0092] Comparative Example 1 100 g of bisphenol A type epoxy resin E-51 was reacted with 15 g of thermoplastic phenolic resin (without hydroxymethyl groups) and 0.3 g of triphenylphosphine at 85 °C for 1.5 hours, and subsequent steps were the same as in Example 1. Because the phenolic resin lacked hydroxymethyl groups, it could not react effectively with the epoxy groups, resulting in an intermediate with a phenolic hydroxyl content of only 0.10 mmol / g, leading to incomplete grafting reactions in the subsequent process.

[0093] Comparative Example 2 100 g of bisphenol A type epoxy resin E-51 was directly physically blended with 15 g of polycaprolactone polyol (number average molecular weight 1000), and then 42.8 g of 1,5-naphthalene diisocyanate was added, and the mixture was reacted at 80 °C. Due to the lack of highly active phenolic hydroxyl sites, -NCO mainly reacted with epoxy groups or trace amounts of water, producing a large number of bubbles and gels, making it impossible to obtain a uniform and stable modified resin.

[0094] Test case The cured products obtained in Examples 1-3 and Comparative Examples 1-2 were subjected to performance tests according to the corresponding standards, and the results are shown in Table 1.

[0095] Table 1 According to the results in Table 1, the polyurethane-modified epoxy resins prepared in Examples 1 to 3 of this invention have a grafting rate as high as 91.0%-93.2%, which is much higher than that of Comparative Example 1 (45.3%) and Comparative Example 2 (38.7%). The hydroxymethyl phenolic resin used in the examples reacted with bisphenol A epoxy, successfully introducing highly active phenolic hydroxyl groups, providing sufficient sites for subsequent grafting of polyurethane prepolymers, and ensuring the efficient progress of the grafting reaction. The thermoplastic phenolic resin without hydroxymethyl in Comparative Example 1 could not effectively introduce phenolic hydroxyl groups, resulting in incomplete grafting reaction. Comparative Example 2 was a physical blend, lacking stable active reaction sites. -NCO only reacted with epoxy groups or trace amounts of water, resulting in the lowest grafting rate and the system was prone to gelation.

[0096] The mechanical properties of Examples 1-3 are comprehensively superior to those of the comparative examples. The glass transition temperature (Tg) of Examples 1-3 reaches 165-170℃, 23-32℃ higher than the comparative examples, indicating higher crosslinking density and better heat resistance. The impact strength of Examples 1-3 is 12.8-13.5 kJ / m², more than 50% higher than the comparative examples, demonstrating the significant toughening effect of the polyurethane segments and effectively improving the brittleness of the epoxy resin. The tensile strength of Examples 1-3 is 80.1-84.7 MPa, more than 17% higher than the comparative examples, proving that the grafted structure simultaneously improves the rigidity and toughness of the material, achieving a balance between strength and toughness. The elongation at break of Examples 1-3 is 6.5-7.2%, 1.5-1.9 times that of the comparative examples, reflecting the significant improvement in material ductility brought about by polyurethane modification.

[0097] The flame retardant properties of Examples 1-3 are significantly superior to those of the comparative examples. Limiting oxygen index (LOI): 28.7-29.5%, more than 13% higher than the comparative examples. UL94 vertical flammability rating: reaches V-0 / V-1, while the comparative examples have no rating (flammable and with a risk of ignition from molten droplets). This is due to the aromatic ring structure introduced by the hydroxymethylphenol resin, which works synergistically with the polyurethane segments to form a dense char layer, effectively blocking heat and oxygen transfer.

[0098] The viscosity change rate of Examples 1-3 after 30 days of storage was only 5.8%-7.1%, while that of Comparative Example 1 was 18.5%, and Comparative Example 2 showed direct gelation. The grafting structure in the examples enabled the system to form stable chemical bonds, avoiding the sharp increase in viscosity and gelation caused by physical blending or incomplete reaction, thus ensuring the processing stability of the resin base during storage.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a polyurethane-modified epoxy resin, characterized in that, Includes the following steps: S10: Bisphenol A type epoxy resin and phenolic resin are reacted at 80-100℃ for 1-2 hours in the presence of an organophosphorus catalyst to obtain an activated epoxy intermediate. S20: Oligomeric polyols are reacted with excess diisocyanate at 90-110°C for 2 to 4 hours to obtain -NCO-terminated polyurethane prepolymers. S30: The -NCO-terminated polyurethane prepolymer is added dropwise to the activated epoxy intermediate at 60-70°C and reacted for 2-3 hours to allow the -NCO groups to react with the phenolic hydroxyl groups to form urethane bonds, thereby achieving chemical grafting of the polyurethane chain. S40: The reaction is terminated when the viscosity of the system reaches 5000-8000 mPa·s, and the modified epoxy resin base material is obtained.

2. The preparation method according to claim 1, characterized in that, In step S10, the bisphenol A type epoxy resin is selected from at least one of E-20, E-44, E-51 or Epon 828; and / or, the hydroxymethyl content of the phenolic resin is 7.5% to 9.5%, and the number average molecular weight is 300 to 600; and / or, the mass ratio of the bisphenol A type epoxy resin to the phenolic resin is 100:1-20.

3. The preparation method according to claim 1 or 2, characterized in that, In step S20, the oligomeric polyol is selected from one or more of polycaprolactone polyol (PCL), polyethylene adipate (PEA), polycarbonate diol (PCDL), hydroxyl-terminated polybutadiene (HTPB), polytetrahydrofuran diol (PTMG), and polypropylene oxide diol (PPG), and the diisocyanate is selected from one or more of 1,5-naphthalene diisocyanate (NDI), toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), terephthalic diisocyanate (PPDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and dicyclohexylmethane diisocyanate (HMDI).

4. The preparation method according to claim 1, characterized in that, In step S10, the organophosphorus catalyst is at least one of triphenylphosphine, tributylphosphine, or tris(4-methylphenyl)phosphine, and its amount is 0.1%-0.5 wt% of the mass of bisphenol A epoxy resin.

5. The preparation method according to claim 1 or 3, characterized in that, In step S20, the oligomeric polyol is polycaprolactone polyol (PCL), the number average molecular weight of which is 800 to 1200 and the hydroxyl value is 55-70 mg KOH / g; the diisocyanate is 1,5-naphthalene diisocyanate (NDI), and the molar ratio of the isocyanate group to the hydroxyl group of the 1,5-naphthalene diisocyanate and the polycaprolactone polyol is 2:1 to 2.5:

1.

6. The preparation method according to claim 1, characterized in that, In step S20, the -NCO content of the obtained -NCO-terminated polyurethane prepolymer is 4.0%-5.5%.

7. The preparation method according to claim 1, characterized in that, In step S30, the -NCO-terminated polyurethane prepolymer is added to the activated epoxy intermediate at a dropping rate of 0.5-1.5 g / min. During the reaction, the intensity change of the -NCO characteristic absorption peak at 2270 cm⁻¹ is monitored by infrared spectroscopy. When the intensity of the peak decreases to less than 10% of the initial value, the reaction is considered to be basically completed.

8. The preparation method according to claim 1, characterized in that, In step S30, a catalyst, chain extender, filler, defoamer and / or leveling agent are added; and / or, the catalyst is selected from at least one of organotin catalysts and tertiary amine catalysts; and / or, the chain extender is selected from at least one of small molecule diols and small molecule diamines.

9. The preparation method according to claim 1, characterized in that, Step S40 is followed by a curing step, in which an aromatic amine curing agent is added for curing and molding. The aromatic amine curing agent is at least one of 4,4'-diaminodiphenyl sulfone, m-phenylenediamine, or diaminodiphenylmethane, and its amount is 25% to 35% of the mass of the modified epoxy resin base. The curing process is to first keep it at 120°C for 2 hours, and then raise the temperature to 180°C and keep it at 4 hours.

10. A polyurethane-modified epoxy resin, characterized in that, The preparation method described in any one of claims 1 to 8 is used to obtain the product, which has a grafting rate of more than 90% and a polyurethane phase uniformly dispersed in the epoxy matrix at the nanoscale.

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