Polymerization Using Photolabile Compounds as Initiators

Photoinitiation is limited to thin layers due to the low penetration of light, nevertheless it possesses several advantages compared to the common techniques. Thus, it is possible to control the rate and degree of polymerization and also the number and length of crosslinks, by the intensity of light. 

These advantages are commercially used in the so-called photolithography, a technique that allows the production of very tiny and accurate nanometer scale structures on the surface of semiconductors (e.g., silicon wafers). 

The principles of photolithography are as follows Onto the surface of a semiconductor is spread a thin film of a photosensitive composition that consists of several chemicals. This composition is called photoresist and it is characterized by the effect that it changes its solubility upon irradiation. Thus, when the thin film is irradiated through a mask, the structure of this mask is projected onto the film which changes its solubility at the exposed segments. If the photoresist con- 

The same principle is also applied in the manufacturing of printing plates for modern printing processes. Moreover, photopolymerization is used for coating of metals or wood and it finds also application in dentistry. 

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