The potential of cationic photopolymerization's long lived active centers

Photopolymerizations offer many advantages (such as temporal and spatial control of initiation, cost efficiency, and solvent-free systems) over traditional thermopolymerization. While they are now well-established as the preferred option for a variety of films and coating applications, they are limited from many applications due to problems such as oxygen inhibition, light attenuation, additive interference, or the creation of shadow regions and oxygen pockets due to complex shapes. These problems can be solved by using an underutilized form of photopolymerization--cationic photopolymerization.

Cationic photopolymerizations have unique active centers which are essentially non-terminating causing extremely long active center lifetimes. In this contribution, the unique characteristics of cationic active centers are explored for their ability to be used in many new applications where previous photopolymerization techniques failed. It was found that the long lifetimes of the active centers permitted them to be very mobile, allowing them to migrate into and polymerize regions that were never illuminated in a process termed shadow cure. The mobility of cationic active centers provides a very efficient means of photopolymerizing of thick and pigmented systems. The long lifetimes of the cationic active centers can be used in the creation of a sequential stage curable polymer system and in the development of novel methods to cure complex shapes, two applications previously unattainable by photopolymerization. The termination of the cationic active centers was found to be reversible and can be used as a technique for external temporal control of the photopolymerization after the illumination has ceased. These abilities have great potential and will allow cationic photopolymerization to be used in many new applications where previous photopolymerization techniques failed, expanding their influence and benefits.