Abstract: The invention relates to a process for the preparation of a stable microdispersion of particles comprised of acrylic polymers in an organic solvent used as reaction medium in the presence of a stabilizing agent comprised of a block copolymer, characterized in that said acrylic polymer is obtained by radical polymerization of at least one acrylic monomer in the presence of a block copolymer based on polymethyl methacrylate (PMMA) and polytert-butyl acrylate (PtBuA). It also relates to microdispersions which may be obtained by said process as well as to microgels produced from said microdispersions and compositions, particularly cosmetic compositions such as nail varnish.

Abstract: Block copolymers denoted by AB from acrylic or methacrylic acid, the corresponding blocks being denoted by A, and from alkyl acrylate or methacrylate with the alkyl chain being C.sub.1 -C.sub.10, the corresponding blocks being denoted by B. Said copolymer blocks are used as wetting and/or dispersing agents for solid particles in an essentially organic medium consisting of a solvent or a mixture of solvents solubilizing the block B.The invention also concerns solid particle dispersions using the above-defined block copolymers.It also concerns compositions, in particular cosmetic compositions, containing said dispersions.