Type II photoinitiators

Some examples of type I and type II photoinitiators are shown in Tables 4.1 and 4.2, respectively. 

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Type II photoinitiators undergo a bimolecular reaction where the excited state of the photoinitiator (acting as a photosensitizer)... 

Coumarin Derivatives Coumarins are known as an interesting class of laser dyes. Various structures are able to behave as type II photoinitiators (they work in their first excited singlet state) or to sensitize the photolysis of peresters or bis-aryl imidazoles [210] (see below). 

TABLE 13.1 Various In-Chain or Side-Chain Type II Photoinitiators for Graft Polymerization... 

Table 10.2 Chemical structures of typical type II photoinitiators.

II photoinitiators and react with the plastic surface through hydrogen abstraction from COC surfaces. It is shown that type I photoinitiators can simultaneously act as type II photoinitiators. The mechanism allows the use of a single initiator to functionalize the COC surfaces and to synthesize the organic monolith simultaneously. The only requirement is to have a polymerizing formulation containing a sufficient photoinitiator concentration. This simple approach is expected to facilitate in the development of organic monolith as a stationary phases inside thermoplastic microchannels. 

Yagci, Tnrro and coworkers also reported a mechanistic study of photoinitiation of free radical polymerization with thioxanthone thioacetic acid as a one-component, Type II, photoinitiator. 

TAS 07a] Tasdelen M.A., Demirel A.L., Yagci Y., Poly(propylene imine) dendrimers as hydrogen donor in Type II photoinitiated free radical polymerization , European Polymer Journal, vol. 43, pp. 4423-4430, 2007. 

Norrish type II photoinitiators are bimolecular initiators. Generally an aromatic ketone is used in combination with a tertiary amine. Both aliphatic and aromatic tertiary amines can be used. A well-known example of such an initiating system is benzophenone with dimethylaminoethanol. 

Those that undergo intermolecular H-abstraction from an H-donor, known as H-abstraction type or Type II photoinitiators (non-fragmentation type). Tertiary amines with abstractable a-H atoms have been shown to be particularly effective as synergists (H-donors). Type II photoinitiators include benzophenone, Michler s ketone. 

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