Disclosed are block copolymers represented by the following general formula ##STR1##

wherein AI represents a hydroxyl group or an organic residue derived from an anionic polymerization initiator, R represents a hydrogen atom or an acyl group, NP represents a residue derived from a nucleophilic reagent, m is an integer of 2 to 20,000, and n is an integer of 1 to 20,000.