Abstract: A copolymer comprising (a) units of a fluorine-containing acrylic monomer having a general formula ##STR1## wherein X is F or CF.sub.3, Y is H or CH.sub.3, n is an integer of 2 to 7, and (b) units of an ethylenically unsaturated monomer having a photosensitive group. The copolymer has an excellent photosensitivity and excellent water and oil repellent properties, and is useful for example as a photosensitive material for dry offset printing plate or resist and as a photo-curable, water and oil repelling coating material.

Abstract: A process for producing cobalt-modified iron oxide particles, which comprises the steps of:(1) adding to magnetic iron oxide particles(a) a cobalt compound,(b) an iron component which is either (b.sub.1) a ferric compound at an atomic ratio to the cobalt compound in the range of 0.68 to 2 or (b.sub.2) a combination of a ferrous compound and a ferric compound, and(c) an alkali at a concentration enough to cause the cobalt and iron to precipitate as hydroxides; and(2) heating the mixture at a temperature of at least 50.degree. C. and not higher than the reflux temperature thereof in a non-oxidizing atmosphere.