Latex polymer particles containing fluorescent substance or contrast medium and process for producing the same

Hydrophobic core-hydrophilic shell type latex polymer particles which include, in their hydrophobic core domain, inorganic fluorescent substance or inorganic contrast medium, said latex polymer particles having an average particle size of 0.001 to 5 μm, and being formed by radical polymerization in an aqueous medium which comprises:

• (a) 0.5 to 99.5% by weight of one or more kinds of latex-forming monomer,
• (b) 0.5 to 99.5% by weight of macromer which has, on one terminal, a polymerizable ethylenic group and has, on the other terminal, a hydrophilic polymer segment which is not linked by a hydrophobic polymer segment [this macromer includes two kinds of macromers each of which has, on said the other terminal, a poly(ethyleneglycol) segment which carries a group selected from the group consisting of hydroxyl group, carboxyl group, aldehyde group, amino group, imino group, mercapto group, active ester-type protected hydroxyl group, active ester-type protected carboxyl group, acetal-type protected aldehyde group, organic sulfonyl-protected hydroxyl group, reactivity-protected amino group and C1-C4 alkoxyl group, recurring unit of said ethyleneglycol being 5 to 1200].