Free-radical photoinitiators

Free-radical photoinitiators are classified by their chemical nature as type I and type II however, there are a few systems with different chemistry, e.g., borate salt initiators that depend on inter-/intramolecular electron transfer,i that do not fit into either category. 

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Vinyl ethers can also be formulated with acryHc and unsaturated polyesters containing maleate or fumarate functionaHty. Because of their abiHty to form alternating copolymers by a free-radical polymeri2ation mechanism, such formulations can be cured using free-radical photoinitiators. With acryHc monomers and oligomers, a hybrid approach has been taken using both simultaneous cationic and free-radical initiation. A summary of these approaches can be found in Table 9. 

A new class of free radical photoinitiators such as 499 (Figure 33) <1998CM3555> have been developed based on pyrazolone azomethine dyes. 

Resins H11-H13 were UV-cured using a free radical photoinitiator (Iigacure 184 , 1-benzoylcyclohexanol) in a Mini-Cure equipped with medium-pressure mercury lamps (80 W/cm). The samples were postbaked at 100 °C for 20 minutes to obtain a similar thermal history for all samples. 

In addition to these examples, an electron-transfer free radical photoinitiator H-Nu 470 (5,7-diiodo-3-butoxy-6-fluorone) has been also successfully used for 3D microfabrication by near-IR two-photon induced polymerization... 

Figure 6.10 Two examples of free radical photoinitiation reactions dissociation of dioxolane and hydrogen atom abstraction of anthraquinone in tetrahydrofuran...

Polymer and copolymer. Polymer and copolymer were prepared in our laboratory for strict control of purity, branching content and molecular weight. All monomers and solvents were carefully purified. PVC samples were prepared as powders in bulk using free radical photoinitiation with either AIBN or uranyl nitrate as initiators. The AIBN/UV initiation was used for photopolymerization at temperatures of 50°, 25°, and 0°C. 

The free radical photoinitiator may be any compound that produces a free radical on exposure to radiation, such as ultraviolet or visible radiation, and thereby initiates a polymerization reaction. 

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