Poly(vinyl ether)s (PVEs) are useful materials of different applications. In this work, we have developed a versatile and highly efficient initiation approach based on thienyl chloride derivatives with readily available starting materials for the living cationic polymerization of vinyl ethers. The resulting polymers exhibited precise chemical structures, predetermined molecular weights, and narrow molecular weight distributions at complete monomer conversions, allowing in situ chain extension to give diblock copolymers in several minutes. The synthetic advances of this method enable highly efficient connection of aryl, benzyl, and alkyl groups, as well as other functional substituents onto PVEs' terminals, and also facilitate the preparation of di-end-functional polymers. Furthermore, the high chain-end fidelity allows post-synthetic modifications through diverse pathways, such as RAFT polymerization, photocontrolled radical polymerization, Ni-catalyzed Negishi cross-couplings, and Pd-catalyzed Suzuki-Miyaura cross-couplings. While the incorporation of PVEs could bring macromolecules interesting properties, this method provides a new and simple pathway for materials engineering with such segments.