PHOTOCHEMICAL CATALYST

Polymerization of resin requires initiation by a free radical.  Initiation starts propagation or continued joining of molecules at double bonds until termination is reached.  Early photochemical systems used were benzoin methyl ether which is sensitive to UV wavelengths at 365 nm.  UV systems had limited use as depth of cure was limited.  Visible light activation of diketones is the preferred photochemical systems.  Diketones activate by visible, blue light  to produce slow reactions.  Amines are added to accelerate curing time. 

Presently, different composites use different photochemical systems.  These systems are activated by different wavelengths of light.  In addition, different curing lights produce various ranges of wavelengths that might not match composite activation wavelengths.  This can result in no cure or partial cure.  Composite materials must be matched to curing lights.

Common photochemical initiators are:

Camphoroquinone

Acenaphthene quinone

Benzyl

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