News

Knowledge

Company News

Application Mind Map

Test Report

Technical Article

Industry News

Common classification methods for reactive diluents

Release time:

2024-08-28 23:03

Common classification methods for reactive diluents
Common classification methods for reactive diluents

An active diluent—also known as a monomer, functional monomer, or reactive solvent—is a specialized compound widely used in the chemical and coatings industries. Active diluents are primarily small organic molecules containing polymerizable functional groups, typically including epoxy groups, acrylate groups, and others. These functional groups can participate in curing reactions and become an integral part of the cured film’s network structure. They not only dissolve or disperse film-forming substances but also take part in the film-forming process during coating application, becoming non-volatile components that remain in the finished coating film. In addition to reducing system viscosity and improving application performance, active diluents can also participate in the curing reaction itself, thereby maintaining or enhancing the performance of the cured product.

Common types of reactive diluents can be classified primarily from the perspectives of functional group type, functionality, and curing mechanism.

I. Classification by Functional Group Type

1. Acrylate esters:

These types of reactive diluents primarily contain acrylate groups, such as methyl methacrylate-β-hydroxyethyl ester (HEMA), isodecyl acrylate (IDA), and triethylene glycol dimethacrylate (TEGDMA). They can participate in free-radical polymerization reactions and rapidly cure under the influence of light, heat, or initiators. They exhibit high reactivity, excellent diluting effects, and outstanding film-forming properties.

2. Epoxy-based:

Epoxy reactive diluents primarily contain epoxy groups, such as butyl glycidyl ether, phenyl glycidyl ether, and 1,4-butanediol diglycidyl ether. The epoxy groups can react with a variety of curing agents (such as amines and anhydrides) to form highly crosslinked cured products.

3. Vinyl ethers:

These reactive diluents contain vinyl ether groups (such as -OCH=CH2); they can participate in both free-radical polymerization and cationic polymerization, offering broad applicability. They cure relatively quickly and are well-suited for applications such as rapid prototyping and repair.

4. Other categories:

Active diluents such as mineral oil-based, alcohol-based, ketone-based, and benzene-based solvents are applied in specific fields according to their respective characteristics.

II. Classification by Functional Degree

1. Monofunctional reactive diluent:

Each molecule contains only one functional group capable of participating in the curing reaction, such as methyl methacrylate-β-hydroxyethyl ester (HEMA) and isodecyl acrylate (IDA). These monomers offer advantages including low volumetric shrinkage, high conversion rate, strong diluting ability, and low viscosity. However, because they have only a single reactive group, their UV curing rate is relatively slow, they exhibit higher volatility, and their crosslinking density is comparatively lower. They are ideally suited for applications that require low viscosity, excellent diluting performance, and a relatively low crosslinking density. In certain specific applications—such as those requiring controlled volumetric shrinkage or maintaining a high conversion rate—monofunctional active diluents also represent an ideal choice.

2. Bisfunctional active diluent:

Each molecule contains two functional groups capable of participating in the curing reaction, such as tripropylene glycol diacrylate (TPGDA), dipropylene glycol diacrylate (DPGDA), and 1,6-hexanediol diacrylate (HDDA). Compared to monofunctional active diluents, bifunctional active diluents exhibit faster UV curing rates, higher crosslinking densities, and superior physical-mechanical properties and thermal resistance in the cured products. They are widely used in fields such as UV-curable coatings, inks, and adhesives. They are particularly well-suited for applications requiring rapid curing, high crosslinking density, and excellent physical performance.

3. Polyfunctional active diluent:

Each molecule contains three or more functional groups capable of participating in the curing reaction. These diluents can impart higher crosslinking density and superior performance to the cured product; however, when using them, it is crucial to carefully control the addition amount to avoid problems caused by excessive crosslinking. They are particularly suitable for applications requiring extremely high crosslinking density and outstanding performance, such as high-performance coatings and composite materials. Due to their high reactivity, polyfunctional active diluents are also frequently employed in the preparation of rapidly curing, light-curable materials.

III. Classification by Curing Mechanism

1. Free-radical-type reactive diluent:

These types of diluents primarily contain functional groups capable of participating in free-radical polymerization reactions, such as (meth)acrylate groups. Under the action of photoinitiators or thermal initiators, these groups can generate free radicals and initiate the polymerization reaction, thereby forming a polymeric network structure. Free-radical polymerization reactions typically exhibit fast reaction rates and high conversion yields. Free-radical active diluents are widely used in fields such as UV-curable coatings, inks, and adhesives. They can impart excellent hardness, abrasion resistance, chemical resistance, and gloss to the cured products.

2. Cationic active diluent:

These diluents primarily contain functional groups capable of participating in cationic polymerization reactions, such as epoxy groups. Cationic polymerization typically requires the presence of an acidic or basic catalyst and proceeds at a relatively slow rate but with good controllability. The cured products exhibit high cross-linking density as well as excellent thermal stability, chemical resistance, and mechanical properties. Cationically active diluents offer advantages in systems that demand high-temperature curing or special curing conditions. They are commonly used in the preparation of high-performance coatings, composite materials, and electronic encapsulating materials.

IV. Summary

Active diluents play a crucial role in industrial production and scientific research fields such as coatings, adhesives, and resins. What sets them apart is their multifunctional nature: not only do they reduce the viscosity of materials during processing, thereby improving application performance, but they also become an integral part of the final product during subsequent curing, thus enhancing the overall performance of the product.

When designing coating formulations, selecting the right active diluent is crucial. Several factors need to be considered, including performance requirements (such as viscosity, curing rate, and adhesion), the nature of the substrate, and application conditions. Typically, it is necessary to choose different types of active diluents based on the specific situation in order to achieve optimal performance.

Disclaimer: The above content is sourced from the internet and is for reference only. If any infringement occurs, please contact us, and we will remove it promptly. 

Share to:

Previous page

Monofunctional Acrylate-Based Active Diluent (I)

Polar ether-type non-reactive diluent

Next page

Related News

Polar ether-type non-reactive diluent

Polar ethers are ether compounds whose molecular structures contain polar bonds—particularly ether linkages (C-O-C) formed between oxygen and carbon atoms—and thus exhibit certain polar characteristics. Polar ethers are organic compounds formed by an oxygen atom connecting two hydrocarbon groups (which can be aliphatic or aromatic). The ether bond in their molecules imparts a degree of polarity to the entire molecule. Due to the high electronegativity of the oxygen atom, polar ethers display an uneven distribution of charge within their molecules, giving them a certain degree of polarity. However, compared with other polar solvents, ethers have relatively lower polarity. While they can dissolve some polar molecules, their ability to dissolve strongly polar substances is comparatively limited. Ether compounds possess relatively stable chemical properties and do not readily react with bases, oxidizing agents, or reducing agents.

Special Types of Inactive Diluents (II)

Propylene glycol monomethyl ether acetate (PMA/PGMEA), also known as propylene glycol monomethyl ether acetate, is primarily classified as a non-reactive diluent belonging to the ether ester family. Although its name includes both “ether” and “ester,” in practical applications it is often regarded as a distinct category due to its unique combined chemical properties—possessing both ether bonds and ester structures. Dimethylformamide (DMF) is an organic solvent with exceptional properties; under standard temperature and pressure conditions, it appears as a colorless, transparent liquid with a slight ammonia-like odor. DMF exhibits outstanding solvency, being completely miscible with water and most organic solvents. It demonstrates excellent dissolving power toward a wide range of organic and inorganic compounds, including fats, water, alcohols, ethers, esters, ketones, unsaturated hydrocarbons, and aromatic hydrocarbons. However, DMF is immiscible with saturated hydrocarbons such as gasoline, hexane, and cyclohexane.

Special Types of Inactive Diluents (I)

Non-reactive diluents based on aliphatic hydrocarbons consist primarily of linear or cyclic hydrocarbons. Common aliphatic hydrocarbon solvents include No. 200 solvent gasoline, kerosene, and diesel oil. These solvents have relatively simple molecular structures, composed mainly of carbon and hydrogen atoms, and do not contain other elements or functional groups such as oxygen, nitrogen, or sulfur. Non-reactive aliphatic hydrocarbon diluents are widely used in fields such as coatings, paints, and adhesives. They are primarily employed to reduce the viscosity of materials and improve their flowability, thereby facilitating easier application and construction.