we have demonstrated the synthesis of a novel trinuclear Pd-diimine complex (2) and its enabled ethylene trifunctional “living” polymerization for “core-first” synthesis of star polyethylenes. Well-defined narrow-distributed threearm star polyethylenes of controllable arm lengths have been obtained by purifying the as-produced polymers. The arms of these star polymers contain a backbone of linear topology with short branching structures.