Cationic Photoinitiators

Cationic photoinitiators can be classified into two main categories based on the type of cations they generate during the photoinitiation process:

• Onium Salts: These types of photoinitiators generate cations through the cleavage of onium salts. Onium salts contain elements like sulfur, phosphorus, or nitrogen and are known for their ability to generate strong cations. The main subcategories under onium salts include:
  

a. Iodonium Salts: These initiators release iodonium cations upon UV or visible light exposure. They are commonly used in UV-curing applications, including dental composites and coatings.

b. Sulfonium Salts: Sulfonium-based photoinitiators generate sulfonium cations. They find applications in various industries, such as adhesives, printing, and electronics.

c. Phosphonium Salts: Phosphonium initiators generate phosphonium cations and are used in UV curing for materials like coatings and inks.

• Metallocene Complexes: In this category, cationic photoinitiators generate cations through the cleavage of metallocene complexes. These initiators are typically used in specific applications, and some common subcategories include:
  

a. Titanocene Complexes: Titanocene-based photoinitiators release titanocene cations. They are used in specialty applications like 3D printing and semiconductor manufacturing.

b. Chromium Complexes: Chromium-based initiators release chromium cations and are used in unique applications where their properties are beneficial.