Conventional polyolefin-based thermoplastic elastomers have have a variety of merit. But the copolymers including block, graft and blend types have some limitations due to their low utility temperature. In this study, novel polyolefin-g-poly(t-butylstyrene) as one of the promising high utility temperature polyolefin-based thermoplastic elastomers was synthesized by the graft-from anionic living polymerization to form the poly(t-butylstyrene) hard grafts along the poly(ethylene-ter-1-hexane-ter-divinylbenzene) backbone as the soft block via the initiation of styrene moieties. Phase-seperation occurred in these polyolefin TPEs when the Mn of poly(t-butylstyrene) was more than 5,000g/mol, which was evidenced by the presence of two distinct Tgs(-20℃ of polyolefin soft block and 125℃ of poly(t-butylstyrene) hard block) observed in DSC and DMTA. These high utility temperature polyolefin TEPs exhibited distinct mechanical property with high modulus and toughness even at 125℃. And when the content of P(t-butylstyrene) more than 28wt%, excellent mechanical properties: high tensile strength (>21MPa) with high elongation (>1,100%) could be obtained. The multi-carboxyl functionalized polyolefin-g-poly(t-butylstyrene) could be synthesized by the incorporation of high vinyl oligo-isoprene at the end of poly(t-butylstyrene) hard block via sequential anionic polymerization followed by the thiol-ene click reaction with thioglycolic acid to incorporate multi-carboxyl groups at the pendant vinyl units. The contact angle of these result multi-carboxyl functionalized polyolefin (12 -COOH/molecule) was decreased to 58° from 95° of the non-functionalized one.