Photopolymerization amplification

Dry-Film Resists Based on Radical Photopolymerization. Photoinitiated polymerization (PIP) is widely practiced ia bulk systems, but special measures must be taken to apply the chemistry ia Hthographic appHcations. The attractive aspect of PIP is that each initiator species produced by photolysis launches a cascade of chemical events, effectively forming multiple chemical bonds for each photon absorbed. The gain that results constitutes a form of "chemical amplification" analogous to that observed ia silver hahde photography, and illustrates a path for achieving very high photosensitivities. 

This chapter includes diaryl iodonium salts and some related heteroaromatic and heterocyclic analogues other categories are discussed separately in Chapter 9. Arylation is the dominating reaction of diaryl iodonium salts. From the applied point of view, they are useful in photopolymerizations and for the chemical amplification in imaging systems. Also, they show interesting biological activity [1,2]. 

Photoinitiated polymerization uses the energy of light for the rapid conversion of monomeric liquids to solid polymeric products. The term photopolymerization implies that the initiation step of a radical, cationic, or anionic chain reaction producing a macromolecule requires the absorption of a photon. Since the absorption of one photon may start the reaction of up to 10 monomeric units, photoinitiated polymerization is, in practice, one of the most powerful chemical amplification techniques. 

Sulfonic (-SO3H) and Sulfinic (-SO2H) Acid-Based Nonsalt Photoinitiators Photosensitive tosylate esters of nitrobenzyl [65] and benzoin [73], sulfonyl ketones [67,68], and diphenyl disulfones [68] can be employed in cationic photopolymerization, especially in photolithography and chemical amplification processes. The advantages of these photoinitiators are the ease of synthesis, the absorption wavelengths suitable for deep-UV curing and the high yield of acid formation [65]. 

Chemical anq>lificatioii, the process by which a cascade of chemical reactions are triggered by absorption of a photon, represents a landmark concept in relied photochemistry. Ch cal amplification leads to the efiScient use of the available light and, therefore, enables imaging systems with high sensitivity. Photopolymerization and photoresists are two commercially in rtant applications of this concept In conventional vinyl photopolymerization,... 

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