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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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08

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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08

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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08

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.

07

2024

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08

What is a Type I photoinitiator for free radicals?

What is a Type I photoinitiator for free radicals?

Type-I photoinitiators, also known as radical-type photoinitiators, are characterized by the fact that after absorbing light energy, the chemical bonds within the photoinitiator molecule break, generating free radicals that play a crucial role in initiating monomer polymerization. These free radicals then participate in free-radical polymerization reactions, enabling monomer molecules to gradually add and polymerize into high-molecular-weight chains.

07

2024

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08

Classification of Cationic Photoinitiators

Classification of Cationic Photoinitiators

Cationic photoinitiators are an essential component of light-curing systems. They absorb light energy and convert it into chemical energy, thereby triggering a series of reactions that promote the polymerization of specific resins and compounds. When exposed to ultraviolet or visible light, cationic photoinitiators absorb the light energy and transition to an excited state. In this excited state, the photoinitiators undergo photolysis, generating substances with extremely high acidity—so-called superstrong proton acids or Lewis acids. These superstrong acids then serve as active centers, initiating cationic polymerization reactions in oligomers such as epoxy resins and vinyl ether resins, as well as in reactive diluents. Cationic photoinitiators are a class of highly important photoinitiating agents that play a crucial role in light-curing technologies. This group of photoinitiators primarily includes diazonium salts, diaryliodonium salts, triarylsulfonium salts, alkylsulfonium salts, iron-arene salts, sulfonyloxy ketones, and triarylsiloxides.

06

2024

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08

Classification of Free-Radical Polymerization Photoinitiators

Classification of Free-Radical Polymerization Photoinitiators

Free-radical photoinitiators are a class of compounds that, upon absorbing energy at specific wavelengths in the ultraviolet or visible light region, can generate free radicals. These free radicals subsequently initiate polymerization, crosslinking, and curing reactions of monomers, making them a crucial component of light-curing technologies. Under relatively mild conditions, these substances decompose or undergo chemical transformations to produce atoms or molecules containing unpaired electrons—namely, free radicals. Such free radicals exhibit high reactivity and can rapidly react with other molecules, thereby initiating or accelerating the entire chemical reaction process. Depending on different classification criteria, free-radical photoinitiators can be categorized in various ways. Based on their structural characteristics, free-radical photoinitiators can be broadly divided into carbonyl compound types, dye types, organometallic types, halogen-containing compounds, azo compounds, and peroxide compounds.

06

2024

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08

Polymerization technology for photochemical reactions

Polymerization technology for photochemical reactions

A photochemical reaction is a special type of chemical reaction in which photons interact with matter, leading to changes in the chemical properties of the substance. In this process, light energy—typically ultraviolet, visible, or infrared light—is absorbed by the substance, triggering the breaking or formation of chemical bonds and thereby generating new chemical species or altering the properties of the original substance. In a photochemical reaction, photons provide sufficient energy to overcome the activation energy barrier of the reactants, enabling reactions that would otherwise be thermodynamically unfavorable to proceed. This energy-transfer process usually involves several steps, including light absorption, electronic excitation, energy transfer, and chemical reaction.

05

2024

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08

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