Patent No. U.S. 7,648,715 B2
Ciba Specialty Chemicals Water Treatments Ltd. has received a patent for polymeric particles comprised of a polymeric matrix and colorant distributed throughout the matrix, wherein the polymeric matrix has been formed from a blend of monomers comprised of a first monomer which is an ethylenically unsaturated ionic monomer which is anionic, and the anionic monomer is (meth)acrylic acid and at least 60% weight of a second monomer which is an ethylenically unsaturated hydrophobic monomer which is capable of forming a homopolymer of glass transition temperature in excess of 80° C, wherein the second monomer is selected from the group consisting of styrene, methyl methacrylate, tertiary butyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate and isobornyl methacrylate, and in which the first monomer is a salt of ammonia or a volatile amine wherein the polymeric matrix is crosslinked, the polymeric matrix exhibits improved performance in regard to the impermeability of the colorant and the colourant is selected from the group consisting of pigments.