1、Siloxane

Herein, a rapid degradation, enhanced mechanical properties, and low dielectric constant epoxy vitrimer (EP-BOB) is proposed through a unique rigid-flexible structure bio-based curing agent (BOB). BOB is synthesized using siloxane as a flexible chain to bridge with vanillin in a one-pot process.

2、Bio

Herein, a selenium/Schiff base-containing, bio-based flame retardant (SNC) has been successfully synthesized and applied as a multifunctional co-curing agent in EP.

3、High

The fully bio-based Schiff base epoxy curing agents, VLYS and VLEV (scheme 1), were synthesized through a one-step reaction involving aldehyde-amine condensation, a process that is not only eco-friendly but also straightforward and well-suited for industrial-scale production.

Siloxane

Herein, a rapid degradation, enhanced mechanical properties, and low dielectric constant epoxy vitrimer (EP-BOB) is proposed through a unique rigid-flexible structure bio-based curing agent (BOB). BOB is synthesized using siloxane as a flexible chain to bridge with vanillin in a one-pot process.

Siloxane

Herein, a rapid degradation, enhanced mechanical properties, and low dielectric constant epoxy vitrimer (EP‐BOB) is proposed through a unique rigid‐flexible structure bio‐based curing agent...

A designer Schiff based motif offered dual dynamic exchangeable bonds

A fast-curing epoxy with improved mechanical properties, self-healing and re-processability was designed using a tailored Schiff based motif that offered dual covalent adaptable network (CAN) in epoxy.

High

The Schiff base structure is introduced into epoxy oligomers, enabling the self-curing of epoxy resins solely through heating, without the need for curing agents, catalysts, or active hydrogen, resulting in a novel functional class of self-curing epoxy resins.

Siloxane‐Mediated Schiff Base Bio‐Based Curing Agent: Achieving Epoxy

Herein, a rapid degradation, enhanced mechanical properties, and low dielectric constant epoxy vitrimer (EP‐BOB) is proposed through a unique rigid‐flexible structure bio‐based curing agent (BOB). BOB is synthesized using siloxane as a flexible chain to bridge with vanillin in a one‐pot process.

High

Both epoxy resins cured by these two hardeners, VLYS-E and VLEV-E, show high glass transition temperatures (Tg > 141°C) and superior mechanical properties (Young's modulus >1000 MPa and flexural modulus >2900 MPa), which are far better than the resin system based on a petroleum-based curing agent.

Siloxane

Herein, a rapid degradation, enhanced mechanical properties, and low dielectric constant epoxy vitrimer (EP-BOB) is proposed through a unique rigid-flexible structure bio-based curing agent (BOB). BOB is synthesized using siloxane as a flexible chain to bridge with vanillin in a one-pot process.

In the vast field of modern materials science and chemical engineering, Schiff base epoxy curing agents have become a research and application hotspot due to their unique chemical properties and broad application prospects. This article provides an in-depth exploration of the definition, classification, synthesis methods, and practical applications of Schiff base epoxy curing agents, aiming to offer readers a comprehensive understanding of the topic.

1. Definition and Classification

A Schiff base is a compound formed through a condensation reaction between an aldehyde group and an amine group, characterized by one or more covalent bonds in its molecular structure. Epoxy curing agents are chemicals that react with epoxy groups to promote the cross-linking and curing of liquid epoxy resins, forming a rigid, stable three-dimensional network structure. This imparts superior physical and chemical properties to the material.

Based on the nature of the Schiff base and the type of epoxy groups, Schiff base epoxy curing agents can be classified into the following categories:

1. Amine-based curing agents: Contain functional groups such as primary, secondary, or tertiary amines, which undergo ring-opening addition reactions with epoxy groups to form stable Schiff bases.
2. Phenolic curing agents: Contain phenolic hydroxyl groups that react with epoxy groups via esterification, producing stable Schiff bases.
3. Alcohol-based curing agents: Contain alcohol hydroxyl groups that react with epoxy groups through etherification, forming stable Schiff bases.
4. Thiol-based curing agents: Contain thiol groups that react with epoxy groups via sulfidation (thiol-epoxy reaction), generating stable Schiff bases.
5. Other types: Include amides, ketones, acid anhydrides, and other specialized curing agents that chemically interact with epoxy groups to form stable Schiff bases.

2. Synthesis Methods

The synthesis of Schiff base epoxy curing agents varies based on raw materials, reaction conditions, and target product requirements. Common methods include:

1. Condensation reaction: Aldehyde and amine groups condense to form a Schiff base, which then reacts with epoxy groups. This method is straightforward but requires strict control to avoid side reactions.
2. Esterification reaction: Phenolic hydroxyl groups react with epoxy groups to form Schiff bases, followed by reactions with amine or alcohol-based curing agents. This approach enhances selectivity and purity.
3. Etherification reaction: Alcohol hydroxyl groups react with epoxy groups to form Schiff bases, subsequently reacting with amine or phenolic curing agents. This method reduces costs and expands application fields.
4. Sulfidation reaction: Thiol groups react with epoxy groups to form Schiff bases, followed by reactions with amine or phenolic curing agents. This improves heat resistance and mechanical properties.

3. Practical Applications

Schiff base epoxy curing agents are widely used across industries due to their versatility:

1. Coatings industry: Used in polyurethane and acrylic coatings to enhance adhesion, wear resistance, and corrosion protection.
2. Electronic encapsulation: Employed to encapsulate chips and circuit boards, improving reliability and reducing thermal stress and electromigration issues.
3. Composite materials: Utilized in carbon fiber and glass fiber composites for aerospace and automotive applications, offering lightweight, high strength, and heat resistance.
4. Building coatings: Formulated into waterproof and fire-resistant coatings for interior/exterior walls and ceilings, combining functionality with decorative appeal.

As critical chemical intermediates, Schiff base epoxy curing agents hold significant potential in materials science and chemical engineering. With ongoing technological advancements and growing demands for new materials, research and applications of these agents are poised for further development. Future innovations may yield high-performance, eco-friendly, and cost-effective Schiff base epoxy curing agents, contributing to broader societal progress.