Block copolymer and method for producing same

Disclosed is a novel block copolymer which enables to significantly improve adhesion between a molded body composed of a nonpolar polymer such as polypropylene or polyethylene, and a coating composition or a molded body composed of a polar polymer. Also disclosed is a method for producing such a block copolymer. Specifically disclosed is a block copolymer composed of at least one aromatic vinyl polymer block having an weight average molecular weight of 1,000-500,000, and at least one block of a cyclization product of a conjugated diene polymer. Also disclosed are an oxygen absorbent and modifying agent for polymer molding materials respectively containing such a block copolymer as an active constituent.