Photoinitiators

Free radical photoinitiators, typically referred to simply as photoinitiators (PIs), induce polymerization through double bonds.  They are commonly used in acrylate, methacrylate, styrene, and many other systems.  PIs are classified into two categories, Norrish type I and Norrish type II.  Norrish type I PIs are unimolecular.  Upon irradiation, type I PIs undergo homolytic cleavage, generating radical species.  Norrish type II PIs are bimolecular.  Type II PIs require the presence of a coinitiator from which to abstract a hydrogen atom, to generate free radicals.

HABI photoinitiators operate in a unique situation, as a cross between type I and II.  Upon irradiation, they split into two radicals like a type I PI.  Although, those lophyl radicals are highly stable and have low reactivity.  As a result, HABIs require an external hydrogen donor or chain-transfer agent, similar to a coinitiator, to increase their reactivity and induce polymerization, like a type II PI.  Hampford Research experts can help you choose the ideal combination for your application.

Through careful modification of the substituents on the aryl groups, HRI has been able to significantly improve the performance of HABIs into the LED wavelength range.  These innovative compounds resist oxygen inhibition and their high molecular weights make them ideal for applications where low migration characteristics are paramount.