Polymeric photo initiators have at least two advantages: (1) low migration rate due to their long polymer chain compared with small molecular counterparts; (2) higher cross linking efficiency since only one step reaction is needed to form bridges between two polymer chains, while small molecular initiators need two steps.
As shown in above Figure, a novel kind of photo initiators with low migration was synthesized by Johannes Kreutzer and colleagues through Schiff base reaction (reference). The polymeric photo initiator has two segments with thioxanthone aldehyde and amine functional poly(propylene oxide) (PPO). The Thioxanthone structure and Schiff base reaction are shown in the following picture.
A new class of hyperbranched polymeric photoinitiators have been developed by Yu Chen team, with built-in amine coinitiators , showing high functionality, low viscosity, good compatibility with the usual radiation curable formulations, high photoactivity and low extractability from the cured sample.
