Applicable to shellac, dry powder emulsion paint, diatomaceous mud, putty powder and other dry powder coatings, also used in plastics (such as PP/PE/EVA/PVC/PU) to add anti-mildew.
Hydrogen abstraction type photoinitiator
Hydrogen abstraction type photoinitiator is also called type Ⅱ photoinitiator, which is generally based on aromatic ketone structure, and also includes some fused ring aromatic hydrocarbons, which have certain light absorption properties, and the matching co-initiator, that is, hydrogen donor , It has no absorption in the range of commonly used long-wave ultraviolet light. The hydrogen abstraction type photoinitiator absorbs light energy, and has bimolecular interaction with the co-initiator in the excited state to generate active free radicals. Tertiary amines are commonly used as co-initiators to pair with oxygen-abstracting photoinitiators.
Benzophenone is excited by light and intersystem jumps to an excited triplet state, and contains. The tertiary amine of H forms an exciplex (exci plex), electron transfer occurs, and benzophenone obtains electrons to form ket yl radical (ket yl radical) and extremely active Amine positive ion. The carbonyl anion is relatively stable due to the conjugation of the two benzene rings. The latter loses protons quickly due to the increased acidity and becomes a very active amine alkyl radical. It has strong addition activity to vinyl monomers and is the main active species for initiating polymerization. The final destination of the benzyl alcohol radical is generally micronized polyolefin wax the disproportionation of two identical free radicals to form benzophenone and benzyl alcohol, or the double-radical coupling to form tetraphenylpinacol. It is also believed that part of the carbonyl group acts as a polymerization The terminator is combined with chain radicals.
Representative hydrogen abstraction photoinitiators include benzophenone, thioxanthone and its derivatives, anthraquinone, coumarone and camphorquinone, etc. The latter three can also be classified as visible light sensitive photoinitiators . Aromatic ketone photoinitiators have a greater chance of bimolecular reactions with compounds with active hydrogen due to their longer excited triplet lifetime. Although the direct hydrogen abstraction efficiency is very low, there are a large number of esters, alcohols, ethers and other structures in the resin formulation system, which can provide a large amount of active hydrogen. Therefore, the aromatic ketone photoinitiator is directly added to the acrylic resin and other systems. Photopolymerization may also occur slowly.
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