A block copolymer composition is disclosed herein. In some embodiments, a block copolymer composition includes a diblock copolymer and a triblock copolymer, each including a polyolefin-based block and a polystyrene-based block, wherein the polyolefin-based blocks are present between 45 wt % to 90 wt %, wherein the polystyrene-based blocks are present between 10 wt % to 55 wt %, wherein the difference (ΔT) between a thermal decomposition initiation temperature and a thermal decomposition termination temperature (ΔT) measured by Thermo-Gravimetric Analysis (TGA) is 55° C. or greater, and the diblock copolymer and the triblock copolymer do not have a residual unsaturated bond.