PURPOSE: To obtain the particles having a specified mean diameter, excellent in redispersibility, useful for delustering agents, chromatographic carriers, etc., by polymerization in an alcoholic medium between each specific polymer and monomer at specified proportions.

CONSTITUTION: The particles 1-20μm in mean diameter can be obtained by polymerizing 100 pts.wt. of styrene or its mixture with a monomer copolymerizable with styrene in an alcoholic solution containing 0.1-30 pts.wt. of a polymer S ≥10000 in weight-average molecular weight prepared by copolymerization between (A) 0.1-20 pts.wt. of a monomer A of formula I (R is 1-18C alkyl or phenyl) and (B) 50-99.9 pts.wt. of a second monomer B selected from monomers of formulas II to VI (R1 is H or methyl; Q is O or NH; R2 and R3 are each methyl or ethyl; n is 1-3; R4 is the same as R1; R5 is H, hydroxyethyl, etc.; R6 is the same as R1).