Types of Photoinitiators

PowerCure photoinitiators are essential components in photopolymerization materials. They are substances that can absorb radiation energy and undergo chemical changes upon excitation, producing reactive intermediates, such as free radicals or cations, which initiate polymerization reactions.

According to the wavelength of light absorption, types of photoinitiators can be categorized into ultraviolet photoinitiators (wavelengths 250nm~400nm) and visible light photoinitiators (wavelengths 400nm~700nm). Based on the mechanism of photopolymerization, types of photoinitiators can be divided into free radical photoinitiators and cationic photoinitiators.

Free radical photoinitiators can further be differentiated based on their mechanism of generating free radicals into cleavage-type photoinitiators (also known as Type I initiators) and hydrogen abstraction-type photoinitiators (also known as Type II initiators).

Cleavage-Type Free Radical Photoinitiators

Cleavage-type free radical photoinitiators refer to photoinitiators whose molecules, upon absorbing light energy, transition to the excited singlet state and then intersystem cross to the excited triplet state. In these states, the molecular structure becomes unstable, causing the weak bonds to homolytically cleave, producing primary active free radicals that initiate the polymerization and crosslinking of oligomers and reactive diluents.

Cleavage-type free radical photoinitiators are mostly aromatic alkyl ketone compounds, including benzoin and its derivatives (benzoin ethers), benzil and its derivatives (such as PowerCure 651), acetophenone derivatives (such as PowerCure DEAP), α-hydroxy ketone derivatives (such as PowerCure 1173, PowerCure 184, PowerCure 2959), α-amino alkyl acetophenone (PowerCure 907, PowerCure 369), and acylphosphine oxide compounds (PowerCure TPO, PowerCure TPO-L, PowerCure 819).

Hydrogen Abstraction-Type Free Radical Photoinitiators

Hydrogen abstraction-type photoinitiators refer to those that, after absorbing light energy and getting excited, transition to the excited triplet state, where they undergo bimolecular interaction with a co-initiator—a hydrogen donor. Through electron transfer, they produce active free radicals that initiate the polymerization and crosslinking of oligomers and reactive diluents. Major examples include benzophenone and its derivatives, thioxanthone compounds (ITX, DETX), and anthraquinone compounds (2-EA).