A new metallocene-based polymerization mechanism is elucidated in which a zirconium hydride center inserts α-methyl­styrene at the start of a polymer chain. The hydride is then regenerated by hydrogenation to release a polyolefin containing a single terminal α-methyl­styrenyl group. Through the use of the difunctional monomer 1,3-diiso­propenyl­benzene, this catalytic hydride insertion polymerization is applied to the production of linear polyethylene and ethylene–hexene copolymers containing an isopropenyl­benzene end group. Conducting simple radical polymerizations in the presence of this new type of macro­monomer leads to diblock copolymers containing a polyolefin attached to an acrylate, methacrylate, vinyl ester, or styrenic segments. The new materials are readily available and exhibit interfacial phenomena, including the mediation of the mixing of immiscible polymer blends.