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What is a diluent?

What is a diluent?

A diluent is a liquid additive widely used in various industrial fields to reduce the viscosity or consistency of coatings, inks, adhesives, and other similar materials, thereby facilitating application and enhancing product performance. While diluents themselves do not possess adhesive properties or film-forming capabilities, they can mix readily with components such as resins or pigments in these materials, improving their flowability, lowering their viscosity, and making application smoother. Additionally, diluents help regulate key product characteristics, such as drying speed and gloss level.

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2024

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Photoinitiator System Based on Thioxanthone and Tertiary Amines

Photoinitiator System Based on Thioxanthone and Tertiary Amines

A prominent feature of hydrogen-abstraction-type photoinitiators is that they typically need to be used in conjunction with a hydrogen donor (co-initiator) in order to effectively initiate polymerization reactions. This mechanism is known as the "hydrogen-abstraction reaction," in which the photoinitiator, after absorbing light energy, becomes sufficiently reactive to abstract a hydrogen atom from another molecule (the hydrogen donor), thereby generating free radicals. The thioxanthone/tertiary amine photoinitiator system represents an important class of hydrogen-abstraction-type photoinitiators. After absorbing ultraviolet light, thioxanthone undergoes an electronic transition from its ground state to an excited state and becomes sufficiently reactive to abstract a hydrogen atom from a tertiary amine molecule.

10

2024

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Photoinitiator system of benzophenone and tertiary amine

Photoinitiator system of benzophenone and tertiary amine

Benzophenone is a common hydrogen-abstraction-type photoinitiator that appears as colorless or slightly yellowish crystals. When exposed to ultraviolet light, benzophenone molecules absorb energy from the ground state and transition into an excited state. However, due to the presence of two benzene rings in its molecule, which create a relatively large free volume, benzophenone experiences significant steric hindrance and thus cannot directly initiate polymerization. To trigger the polymerization reaction, benzophenone must abstract hydrogen atoms from a hydrogen donor (such as a tertiary amine), transferring the absorbed energy to the hydrogen donor, thereby generating free radicals and initiating polymerization.

10

2024

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Unique cationic photoinitiator: diaryl iodonium salts

Unique cationic photoinitiator: diaryl iodonium salts

Diphenyliodonium salts are among the most typical representatives of cationic photoinitiator iodonium salts. As a unique type of cationic photoinitiator, they undergo complex photolysis reactions upon exposure to ultraviolet or visible light, generating both superacids and active free radicals in the process. This dual capability allows them to initiate both cationic polymerization and radical polymerization. Such dual-initiation ability endows diphenyliodonium salts with broad application prospects in the field of polymer synthesis.

09

2024

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Typical representatives of hydrogen-abstraction photoinitiators

Typical representatives of hydrogen-abstraction photoinitiators

Hydrogen-abstraction photoinitiators, also known as Type II photoinitiators, operate primarily through the interaction between a photosensitizer and a hydrogen donor. These photoinitiators typically contain an aromatic ketone group. Aromatic ketones are a class of organic compounds characterized by the presence of a benzene ring and a carbonyl group; their structural features endow them with unique electronic properties. In addition to the aromatic ketone group, certain polycyclic aromatic hydrocarbons may also serve as components of hydrogen-abstraction photoinitiators. Polycyclic aromatic hydrocarbons are compounds in which two or more benzene rings are directly linked via shared carbon-carbon bonds.

09

2024

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A typical representative of cationic photoinitiators

A typical representative of cationic photoinitiators

Cationic photoinitiators are a class of photosensitive compounds that, under illumination, undergo photochemical reactions to generate species with cationic polymerization activity, thereby initiating cationic polymerization of specific monomers or oligomers. When exposed to light, cationic photoinitiators are activated, causing their molecules to transition from the ground state to an excited state. In the excited state, these molecules undergo a series of decomposition reactions, which may involve homolytic or heterolytic cleavage processes, ultimately yielding species with initiating activity. One of the outcomes of these decomposition reactions is the generation of superstrong proton acids or Lewis acids, which serve as active species for cationic polymerization. The superstrong acids or Lewis acids interact with the monomers or oligomers to be polymerized, triggering their cationic polymerization and leading to the formation of polymeric materials.

08

2024

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Typical representatives of photoinitiators of the cleavage type

Typical representatives of photoinitiators of the cleavage type

Type-I photoinitiators, also known as cleavage-type photoinitiators, function as follows: After absorbing light energy, these photoinitiators undergo an electronic transition from the ground state to the excited state, followed by homolytic cleavage of chemical bonds, thereby generating primary active free radicals. These free radicals are highly reactive and can rapidly initiate chain-growth polymerization reactions with monomer molecules, enabling rapid curing of the material.

08

2024

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What is a Type II photoinitiator for free radicals?

What is a Type II photoinitiator for free radicals?

Hydrogen-abstraction photoinitiators, also known as Type II photoinitiators, are a class of photoinitiators used in free-radical polymerization. The key feature of these photoinitiators is that, after absorbing ultraviolet light energy, they react with hydrogen donors in the system—such as tertiary amines or alcohols—to abstract hydrogen atoms, thereby generating active free radicals. These free radicals are highly reactive and can rapidly combine with monomer molecules, initiating and accelerating the growth of the polymerization chain and ultimately forming high-molecular-weight polymers. The advantage of hydrogen-abstraction photoinitiators lies in their ability to initiate polymerization reactions under relatively mild conditions, making them highly popular in many industrial applications. Moreover, since hydrogen-abstraction photoinitiators typically work in synergy with hydrogen donors, it is possible to optimize the conditions and rate of the polymerization reaction by adjusting the type and amount of co-initiators, thus obtaining polymeric materials with the desired properties.

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2024

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