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Aug 24, 2023

Silicone-Modified Epoxy Resin: Enhancements through Chemical Copolymerization


In recent research, a series of epoxy resins modified with organosilicon compounds have been successfully synthesized utilizing polymethyltriethoxysilane (PTS) through two distinct methodologies: physical blending and chemical copolymerization. Notably, investigations have revealed that chemically modified epoxy resin products exhibit superior performance compared to those modified through physical blending. As a result, this article will delve into a comprehensive exploration of the study focusing on chemical copolymerization for organic silicon modification of epoxy resin.

Chemical Copolymerization Modification

Chemical copolymerization modification involves the chemical interaction between active groups such as amino, hydroxyl, and alkoxy groups present in polyorganosiloxane molecules, and the hydroxyl and epoxy groups within epoxy resin. This process aims to achieve chemical copolymerization, thereby effecting modification. Following the chemical modification of epoxy resin with organic silicon, the primary outcomes encompass organic silicon block formations or grafted epoxy resin copolymers. This modification enhances the compatibility between these materials. Additionally, the incorporation of flexible and stable Si-O chains into the cured resin's coating structure augments the epoxy resin's heat resistance and fracture toughness.

Functional Group Polysiloxane Modified Epoxy Resin/Coating

Through the integration of pliable polysiloxane segments characterized by strong bond energy into the epoxy resin system, an intricate network structure is established between the two constituents. This results in a substantial improvement in compatibility, leading to a reduction in phase separation and an increased flexibility within the epoxy resin coating. Consequently, this enhancement contributes to improved thermal stability, flame retardancy, and hydrophobicity of the coating. These attributes lay a solid foundation for potential applications within fields such as structural bonding, packaging, and aerospace technology. At present, noteworthy advancements have occurred in both domestic and international research related to silicone-modified epoxy resin.

One specific approach involves the reaction of γ-aminopropyltriethoxysilane (AP-TES) with 2,3-epoxypropyl-terminated polydimethylsiloxane (GPPMS), enabling the opening of the epoxy group at one end of GPPMS through the amino group. This synthesis results in a polysiloxane intermediate denoted as AGPMS. Subsequently, AGPMS is combined with bisphenol A epoxy resin (DGEBA) and cured to yield an epoxy resin coating modified with organosilicon. Experimental outcomes demonstrate varying degrees of enhancement in impact strength, fracture toughness, and thermal stability of the resulting silicone-modified epoxy resin coating. However, it is noted that when the quantity of AGPMS added is low, there is a slight reduction in the tensile strength of the epoxy resin.

A similar methodology has been employed to produce a novel class of epoxy resin bridged by fused phenyl oligosiloxane. This is accomplished through the condensation reaction between C-OH groups of bisphenol A epoxy resin and Si-OH groups within the intermediate of hexaphenyl fused cyclosiloxane disiloxane. Research has unveiled the feasibility of generating a transparent organic silicon-modified epoxy coating through the room-temperature curing of the modified resin with polyamide. At a polycyclic phenyl oligosiloxane content of 44.2%, the modified epoxy resin coating achieves a hardness of 6H and an initial decomposition temperature of 348.96°C. However, it's important to highlight that the glass transition temperature (Tg) of the modified coating experiences a decrease with the escalation of organic silicon modifier content. This chemical modification utilizing phenyl silicone resin significantly amplifies the heat resistance and impact strength of the modified epoxy resin.

Moreover, employing phosphoric acid as a catalyst, a reaction occurs between small molecule hydroxyl-terminated polydimethylsiloxane (HPDMS) and bisphenol A epoxy resin (DGEBA), involving the ring opening reaction between the silicone hydroxyl group on HPDMS and the epoxy group on DGEBA under acid catalysis. This process initially results in the preparation of singly ended polydimethylsiloxane modified epoxy resin (ESR), which subsequently serves as the precursor for the creation of a high gloss organic silicon-modified epoxy coating (ESR-PA), with polyamide (PA) as the curing agent. Research demonstrates the favorable compatibility between siloxane and epoxy resin, resulting in superior mechanical properties, heat resistance, and corrosion resistance for the ESR-PA coating compared to a pure DGEBA coating.

Lastly, the modification of epoxy resin using low molecular weight bis(glycidyl ether propyl) tetramethyldisiloxane or bis(3-aminopropyl) tetramethyldisiloxane, both comprising 15% of the mass fraction, has been investigated. Notably, both small molecule modifiers significantly reduce the glass transition temperature of epoxy resin coatings. The modified coatings exhibit diminished flexural strength, storage modulus, and flammability, accompanied by a minor increase in impact strength. Notably, the siloxane modifier exerts negligible influence on the Brinell hardness of the epoxy resin.

In conclusion, the chemical copolymerization approach to modifying epoxy resin with organosilicon compounds offers promising avenues for enhancing the performance and properties of epoxy resin coatings, with potential applications spanning various industries.

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