Method for preparing hyperbranched polysiloxane grafted modified imidazole epoxy resin and latent curing agent

Abstract

The application discloses a preparation method of hyperbranched polysiloxane grafted modified imidazole epoxy resin and latent curing agent, and belongs to the field of epoxy resin. The application aims at solving the problems that the existing imidazole modification method is difficult to balance the latency and curing activity, the traditional steric hindrance modification (such as alkylation) leads to a significant increase in the curing temperature (>180 DEG C), the microcapsule technology has a low coating rate, a core material leakage risk and the traditional imidazole curing epoxy resin system has a large water absorption rate. In the method, the terminal silicon hydrogen bond hyperbranched polysiloxane and allyl imidazole are dissolved in dry tetrahydrofuran, Karstedt catalyst is added, and the silicon hydrogen addition reaction is carried out until the Si-H characteristic peak disappears, namely, the preparation is completed. The application has the advantages of significantly enhanced latency, optimized curing characteristics, strengthened mechanical properties and enhanced moisture resistance.

Description

Technical Field

[0001] This invention belongs to the field of epoxy resins, specifically relating to a latent curing agent for hyperbranched polysiloxane-grafted modified imidazole epoxy resins and its preparation method; as well as a method for preparing hyperbranched polysiloxane-grafted modified imidazole epoxy resins. Background Technology

[0002] Imidazole and its derivatives (such as 2-ethyl-4-methylimidazole) are widely used as medium-temperature curing agents for epoxy resins due to their high reactivity, but direct use has problems such as short storage period and easy pre-curing at room temperature.

[0003] Existing modification methods include: forming adducts with isocyanates, liquefying imidazole salt ions, and microencapsulation; however, these methods either sacrifice reactivity or involve complex processes, and it is difficult to balance storage stability and curing efficiency.

[0004] On the other hand, traditional imidazole-cured epoxy systems have high moisture absorption, resulting in a wet-state decrease in glass transition temperature (Tg) of >30°C and an increase in dielectric loss in high-frequency electronic packaging applications.

[0005] Although hyperbranched polysiloxanes (HBPSi) have the characteristics of three-dimensional structure, strong end-modifiable properties, intramolecular cavities and hydrophobicity, and have been used for toughening epoxy resins, there are no reports of their application as steric hindrance regulators in curing agent modification. Summary of the Invention

[0006] This invention addresses the challenges of existing imidazole modification methods in balancing latency and curing activity, the significant increase in curing temperature (>180℃) caused by traditional steric hindrance modification (such as alkylation), the low encapsulation rate and core material leakage risk of microencapsulation technology, and the high water absorption of traditional imidazole-cured epoxy resin systems. It provides a method for preparing hyperbranched polysiloxane-grafted modified imidazole epoxy resins and a latent curing agent.

[0007] To address the aforementioned technical problems, the present invention adopts the following technical solution:

[0008] The purpose of this invention is to provide a latent curing agent for hyperbranched polysiloxane-grafted modified imidazole epoxy resins with the general formula: HBPSi-[O-Si(CH3)2-(CH2)3-Im]n, where Im represents an imidazole ring with a "core-shell" structure. The curing agent is obtained through a hydrosilylation reaction between the hyperbranched polysiloxane and allyl imidazole via silanol bonds.

[0009] Another objective of this invention is to provide a method for preparing the above-mentioned hyperbranched polysiloxane graft-modified imidazole epoxy resin latent curing agent, comprising the following steps: dissolving terminal silane-hydrogen bond hyperbranched polysiloxane and allyl imidazole in dry tetrahydrofuran, adding Karstedt catalyst, and performing a hydrosilylation reaction until the Si-H characteristic peak disappears, thus completing the process.

[0010] Further specifying, 8 g to 16 g of terminal silane-hydrogen bond hyperbranched polysiloxane and 2.8 g to 6 g of allyl imidazole are dissolved in 50 to 120 mL of dry tetrahydrofuran; 0.03 mL to 0.05 mL of Karstedt catalyst is added. Further specifying, the hyperbranched polysiloxane is a silane-hydrogen bond-terminated hyperbranched polysiloxane.

[0011] Further specifying, allylimidazole is 1-allylimidazole.

[0012] Further specified, the hydrosilylation reaction is carried out at 80℃~90℃.

[0013] Further specifying, the platinum content of the Karstedt catalyst is 300 ppm to 3000 ppm.

[0014] This invention also provides a method for preparing hyperbranched polysiloxane-grafted modified imidazole epoxy resin, which is carried out according to the following steps: adding any of the curing agents described above or any of the curing agents prepared by the above methods to DGEBA epoxy resin at a concentration of 5 to 15 phr, and curing to obtain the epoxy resin.

[0015] Further specifying, the curing process involves first curing at 90°C for 1 hour, and then curing at 120°C for 4 hours.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. Significantly enhanced latency

[0018] The modified imidazole curing system of this invention exhibits a storage period at 40°C that is more than four times longer than that of the unmodified imidazole curing system. The steric hindrance groups introduced into the molecular structure of this invention effectively suppress low-temperature prepolymerization reactions, solving the problems of process interruption and material waste caused by poor storage stability of the curing agent in existing technologies. This makes it suitable for long-cycle, large-scale continuous production scenarios.

[0019] 2. Resistance to damp heat:

[0020] Water absorption (85℃ / 85%RH 48h): reduced to 1.7% (2.6% for unmodified system), water erosion resistance increased by 53%. Detailed Implementation

[0021] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, while not limiting the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0022] Example 1: In this example, the hyperbranched polysiloxane-grafted modified imidazole epoxy resin latent curing agent was prepared by the following steps:

[0023] Under nitrogen protection, 10 g of terminal silane-hydrogen bond hyperbranched polysiloxane and 3.2 g of 1-allyl imidazole were dissolved in 50 mL of dry tetrahydrofuran; 0.05 mL of Karstedt catalyst (platinum content 3000 ppm) was added, and the reaction was carried out at 85 °C; the reaction endpoint was determined by the disappearance of the Si-H characteristic peak in the 2120~2160 cm⁻¹ region by FT-IR monitoring, and a latent curing agent for hyperbranched polysiloxane grafted and modified imidazole epoxy resin was obtained.

[0024] The curing agent prepared by the above method was added to DGEBA epoxy resin at 5 phr, and cured according to the curing regime of 90℃ / 1h+120℃ / 4h to obtain hyperbranched polysiloxane grafted modified imidazole epoxy resin.

[0025] 1. Latency: The storage period at 40℃ is more than 4 times longer than that of the unmodified system.

[0026] 2. Resistance to damp heat: Water absorption rate (85℃ / 85%RH 48h): 1.7% (unmodified system: 2.6%).

[0027] The specific embodiments of the present invention have been described above. It should be noted that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a latent curing agent for hyperbranched polysiloxane-grafted modified imidazole epoxy resin, characterized in that, The process includes the following steps: dissolving 8g~16g of terminal silane-hydrogen bond hyperbranched polysiloxane and 2.8g~6g of allyl imidazole in 50mL~120mL of dry tetrahydrofuran, adding 0.03mL~0.05mL of Karstedt catalyst, and performing a hydrosilylation reaction until the Si-H characteristic peak disappears, which completes the process. The curing agent has a "core-shell" structure, and the allyl imidazole is 1-allyl imidazole.

2. The method according to claim 1, characterized in that, Hydrosilylation reaction at 80℃~90℃.

3. The method according to claim 1, characterized in that, Karstedt catalysts contain 300 ppm to 3000 ppm of platinum.

4. A curing agent prepared by the method according to any one of claims 1-3.

5. A method for preparing hyperbranched polysiloxane-grafted modified imidazole epoxy resin, characterized in that, The method includes the following steps: adding the curing agent prepared by the method according to any one of claims 1-3 to DGEBA epoxy resin at a rate of 5-15 phr, and curing to obtain the epoxy resin.

6. The method according to claim 5, characterized in that, The curing process involves first curing at 90°C for 1 hour, and then curing at 120°C for 4 hours.