Abstract: Three-dimensional polymeric material in the form of spherical particles of diameter .ltoreq.3 mm and containing up to 40% of free aldehyde groups which exhibits a measurable specific surface area is prepared by copolymerization of an aldehyde monomer R.sub.1 CH.dbd.C(CH.dbd.O)R.sub.2, where R.sub.1 is H, C.sub.1-5 alkyl, aryl or furyl and R.sub.2 is H, C.sub.1-5 alkyl, halogen, CN, phenyl or furyl, with a crosslinking agent in the aqueous dispersion phase. The dispersion contains 1 - 25% of a component reducing the monomer solubility in water, which is either an inorganic salt of alkali metal or alkaline earth metal or a water-soluble alcohol. The crosslinking agent used as comonomer is divinylbenzene, diester CH.sub.2 .dbd.C(R.sub.1)COOR.sub.2 OCOC(R.sub.1).dbd.CH.sub.2 (R.sub.1 .dbd. H, C.sub.1-10 alkyl or halogen; R.sub.2 .dbd. C.sub.1-10 alkylene or hydroxyalkylene), or diamide CH.sub.2 .dbd.C(R.sub.1)CONHR.sub.2 NHCOC(R.sub.1).dbd.CH.sub.2 (R.sub.1 .dbd. H, C.sub.1-10 alkyl or halogen; R.sub.2 .dbd. C.