The present invention provides a method for producing a polymer by efficiently removing residue of metals such as titanium, aluminum and lithium from a polymer solution containing the residue of these metals to successfully obtain a purified polymer solution containing a smaller amount of the metal residue and having satisfactory color tone and transparency, a polymer solution and a polymer obtained by the production method.

The purpose of the present invention is to provide: a cross-copolymer in which a residual catalyst component remains in a reduced amount and which has improved transparency, applicability to medical materials and yellowish discoloration resistance; and a method for producing the cross-copolymer. According to the present invention, a cross-copolymer is provided, wherein the cross-copolymer is produced through a coordination polymerization step of carrying out copolymerization of an olefin monomer, an aromatic vinyl compound monomer and an aromatic polyene using a single-site coordination polymerization catalyst to synthesize an olefin-(aromatic vinyl compound)-(aromatic polyene) copolymer and a subsequent anionic polymerization step of carrying out polymerization in the co-presence of the olefin-(aromatic vinyl compound)-(aromatic polyene) copolymer and an aromatic vinyl compound monomer using an anionic polymerization initiator, the cross-copolymer being characterized in that the total mass of aluminum and lithium, which are residual catalyst components, contained in the cross-copolymer is 200 ppm or less.