. . . . "In addition, as the block copolymer, there can be used those having a stellate (for example, [(AB)mX], wherein m is an integer of 2 or more, X is a residue of a coupling agent) molecular structure, obtained by using divinyl benzene, a tin compound, a silane compound or the like as a coupling agent. [0028] The individual block copolymers may comprise only a single kind of molecular structure." .