PURPOSE: To make it possible to impart properties such as corrosion resistance solvent resistance, chemical resistance, nonstickiness, low frictional property, stain resistance, water repellency and weathering resistance to the surface of a polymeric material, by mixing a polymeric material with a specified block copolymer.

CONSTITUTION: The surface properties of a polymeric material are modified by mixing the polymeric material with a block copolymer having a block (A) of a polymer resin having an affinity for the polymer as a principal constituent and a block (B) of a fluorinated polymer chain. This block copolymer is one formed by polymerizing either a monomer which forms block (A) or a monomer which forms block (B) in the presence of a radical polymerization initiator to form a polymer chain which corresponds to the block (A) or block (B) and is terminated with a free radical source comprising a free radical or a precursor thereof. This polymer chain is polymerized with another monomer through this free radical source.