Thermoplastic elastomers (TPE) can be easily molded, extruded, and reused like plastics and exhibit typical elastic properties like rubbers. They are widely used in the automotive sector and household appliances sector. The synthesis of thermoplastic polyolefin elastomers using only ethylene as feedstock in a single step is a fascinating concept. The synthesis of polyethylene thermoplastic elastomers through alpha-diimine nickel catalyzed ethylene polymerization has been successfully achieved in recent years. However, the utilization of alpha-diimine palladium catalysts for this purpose is much more challenging due to their greater chain-walking tendency versus the nickel counterpart, there by leading to the formation of highly branched polyolefins with poor mechanical properties. In this contribution, we report the direct synthesis of polyethylene thermoplastic elastomers through alpha-diimine palladium catalyzed ethylene polymerization. With exquisite catalyst design and polymerization regulation, polyethylene thermoplastic elastomers with great mechanical and elastic properties can be obtained. Most importantly, polar functionalized polyethylene thermoplastic elastomers bearing great elastic properties can be generated through copolymerization of ethylene with biomass-derived comonomers.