Powdery hydrophilic fillers

Claim 1

A process for producing a powdered hydrophilic solid carboxylic-containing polymeric filler, which comprises providing a mixture of (a) at least one monomer comprising a mono- or poly-olefinically unsaturated mono- or poly-carboxylic acid, the anhydride thereof, or the acid chloride thereof and (b) at least 5% based on the weight of monomer (a) of a crosslinking monomer containing more than one vinyl group in an oxygen bearing organic solvent including (c) a free radical catalyst, polymerizing said monomer mixture for a time and at a temperature sufficient to form a particulate solid polymeric precipitate, said oxygen bearing organic solvent being a solvent for said monomers (a) and (b) but a non-solvent for said solid polymeric precipitate, the relative proportions of said monomer mixture and said oxygen bearing organic solvent being such that the particle size of said solid polymeric precipitate is less than 100 μm, directly treating said solid polymeric precipitate in the polymerization system with (d) a solution containing sodium, potassium or ammonium ions for a time sufficient to transform the solid polymeric precipitate into the corresponding solid polymeric salt, said solution being a non-solvent for said solid polymeric precipitate and its salt, and thereafter separating and drying said solid polymeric salt into a solid particulate powder.