Free Radical Photoinitiators - Type I

Free radical photoinitiators react differently when exposed to UV light. Depending on their reactivity, they are classified as Norrish photoinitiator type 1 and 2.

Norish Type 1 photoinitiator are typically compounds containing a benzoyl group which, when exposed to UV light, cleaves to produce two highly reactive free radicals, at least one of which reacts with the monomer to initiate polymerization. Type i photoinitiator are irreversibly incorporated into the polymer matrix.

Norrish Type II photoinitiators require hydrogen donors to react when exposed to UV light, and the most common of these hydrogen donors are amines (amine synergists). Upon UV irradiation, the Type II photoinitiator abstracts a hydrogen atom from the synergist used to form two very reactive alkylamino radicals, which subsequently initiate polymerization. Type II photoinitiators are generally not incorporated during the reaction, but synergists are incorporated.

TINTOLL is one of the photoinitiator manufacturers, which is also one of the cornerstone businesses of TINTOLL. Our product portfolio covers free radical and cationic photoinitiators (photo-acid generators) including photoinitiator type 1 and 2, as well as amine synergists. UV-curable materials are widely used in graphic arts, industrial coatings, adhesives, printed circuit boards, and 3D printing. TINTOLL provides application support, product development and custom solutions, and collaborates with customers to develop next-generation photoinitiators.

What is a Type I Photoinitiator?
What is a Type I Photoinitiator?
The two most common types of photoinitiators are free radicals and cationic.

Type I photoinitiators are a type of photoinitiator that absorb light and split into two primary radicals.

These photoinitiators are aromatic carbonyl organic compounds that undergo a homolytic or heterolytic bond cleavage after light excitation. The radicals then initiate the polymerization.

Typical type I photoinitiators include: Alpha hydroxy ketones and phosphine oxides.

Type II photoinitiators, also known as photosensitizing photoinitiators or co-initiators, extract hydrogen from the co-initiator to generate secondary radicals.

Typical type II photoinitiators include: Benzophenones, Thioxanthones.