POLYMER, RUBBER COMPOSITION CONTAINING POLYMER, CROSSLINKED RUBBER COMPOSITION OBTAINED BY CROSSLINKING RUBBER COMPOSITION, AND TIRE HAVING CROSSLINKED RUBBER COMPOSITION

Provided are: a polymer capable of providing a crosslinked rubber composition with improved durability (i.e., breaking resistance, abrasion resistance, and crack growth resistance) and a method for producing the same, a rubber composition containing the polymer, a crosslinked rubber composition obtained by crosslinking the rubber composition, and a tire having the crosslinked rubber composition. The polymer is either a synthesized polyisoprene or an isoprene copolymer, and contains a residual catalyst in an amount of 300 ppm or less.