Thioxanthones: Their fate when used as photoinitiators

It has been shown that when thioxanthones are used in conjunction with an amine synergist they initiate the polymerization of lauryl acrylate. Gel permeation chromatography (g.p.c.) showed that the polymer which is formed contains thioxanthone residues. It is suggested that the thioxanthyl ketyl radical acts as a chain terminator, with reactions occurring at the 2-, 4-, 5-, 7-, and 9-positions. Reactions at positions other than 9- can lead to incorporation of thioxanthone residues. When the aromatic amine synergist, ethyl p-dimethylaminobenzoate, is used the aromatic amine is also incorporated into the polymer. (C) 1996 Elsevier Science Ltd.