Free radical-photocurable system

The basic mechanism for any free-radical photocurable system is shown in Scheme II. 

In general, cationic photocure systems (4) are often deemed superior to free-radical photocuring processes since they are ... 

Photopolymer systems are photocurable resins incorporating reactive liquid monomers, photoinitiators, chemical modihers and hhers. Typically stereolithography utilizes UV radiation, so UV-curable systems are used. Free-radical-photopolymerizable acrylate systems were originally used however, newer cationic epoxy-resin and vinyl ether systems (based on iodinium- or sulfonium-salt cationic initiators) are now being utilized. 

The mfichanisms for free-radical type photocurable and cationic photocurable systems can be discussed individually. 

The choice to use one photocurable system over another is dictated by the particular requirements of the application and consideration should be given to both free radical and cationic photocurables. 

With the basic mechanism of free-radical and cationic photocuring presented in Schemes II and III, we turn to consideration of each of the individual components in UV curable systems. It is this aspect over which the formulator has control in producing a resin system which will cure in an appropriate environment (temperature, air, etc.) at reasonably fast rates to generate the type of film desired. 

Dual Free Radical/Cationic Photocurable Systems... 

Hybrid systems are understood to be photocurable compositions that cure by both ionic and free radical mechanisms. As can be seen in Chapter 2, section 2.3.4. photoinitiators were actually designed for use with systems that contain both type of monomers, or prepolymers, and both to cure by both mechanisms. One such example are combinations of phosphonium and sulfonium salts described in that chapter ... 

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