A compound which undergoes a photoreaction on absorption of light by producing reactive species is known as photo initiators. Photo initiators are capable of initiating or catalyzing chemical reactions which results in significant changes in the solubility and also physical properties of suitable formulations as photo initiator is a compound which can transform the physical energy of light into suitable chemical energy which is in the form of reactive intermediates. The changes which take place are commonly achieved by polymerization or by poly condensation reaction. Thus the process which is set by a photo initiator and also by light is known as photo polymerization.
The types of photo initiators are radical photo initiators which have styrene based formulations which are widespread application due to which broad variety of radical photo initiators as most radiation curing is performed using near uv light but these initiators are extended into the visible which is up to the infrared range. The other type includes cationic photo initiators are those which produce lewis acid that are used as initiators for cationic ally polymerizing materials. In this type the use of the light is utilized to trigger the initiation process which is the key to the outstanding advantage of radiation.
Another type includes industrial photo initiators which are used for the uv curing process which shows remarkable possibilities in myriads applications and also highlights critical factors like reactivity, cure speed etc. Commercial photo initiators are known for their variations in their structure as the factors which determine photo initiators should be very properly chosen and different types are used. Photo initiators in the form of white powder are used for vinyl based polymers such as polyvinyl chloride which are also known as pvc as this produces nitrogen gas upon the decomposition and also is used as blowing agent to change the shape or texture of plastics.