Graft polymerization of vinyl monomers initiated by azo groups introduced onto organic pigment surface

Dispersing organic pigments uniformly into a polymer matrix or an organic solvent is hardly achieved, the dispersibility of an organic pigment is remarkably improved by grafting of polymers onto the surface. To modify the dispersibility of organic pigment, such as quinacridone, diketopyrrolopyrrole, and anthraquinone, the graft polymerization of vinyl monomers from the organic pigments initiated by azo groups introduced onto these surfaces was investigated. Organic pigments having azo groups were prepared by the following four methods: (1) the reaction of 4,4'-azobis(4-cyanopentanoic acid) with surface isocyanate groups, which were introduced by the treatment of surface amino groups with tolylene 2,4-diisocyanate, (2) the reaction of 2,2'-azobis(2-cyano-n-propanol) (ACP) with surface isocyanate groups, (3) the reaction of ACP with surface acyl chloride groups which were introduced by the treatment of surface amino groups with terephthaloyl dichloride, and (4) the reaction of 2,2'-azobis[2-(imidazolin-2-yl)-propane] with surface acyl chloride groups. It was found that the radical graft polymerization of vinyl monomers, such as styrene, methyl methacrylate, and 2-isocyanatoethyl methacrylate were successfully initiated by the azo groups introduced onto these organic pigment surfaces. During the polymerization, the corresponding polymers was effectively grafted onto the surface based on the propagation of the polymer from the surface radical formed on the surface by the decomposition of the azo groups. Polymer-grafted organic pigments gave a stable dispersion in good solvents for grafted polymers. (C) 1999 Elsevier Science S.A. All rights reserved.