Well-defined nonmigrating polymeric plasticizers, poly(vinyl chloride)-block-polycaprolactone (PVC-b-PCL), were synthesized by sequential reversible addition-fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP) with 2-hydroxyethyl 2-(ethoxycarbonothioylthio)propanoate (HECP) as RAFT agent and incipient initiator for ROP of ϵ-caprolactone (CL, oxepan-2-one). Kinetic experiments demonstrated that HECP provided good control in RAFT polymerization of vinyl chloride (VC) with dispersity (D) ∼ 1.2 for 3400 < M n < 11000. Chain extension experiments with VC and vinyl acetate proved the high end-group fidelity of the macroRAFT agent formed. The hydroxy end-group of the PVC macroRAFT agent allowed its use as a ROP initiator in forming a series of PVC-b-PCL with different PCL block lengths by RAFT-T-ROP. Characterization by wide-angle X-ray diffraction (WAXD), polarized light microscopy (PLM), and differential scanning calorimetry (DSC) indicates that there is enhanced chain entanglement for PVC-b-PCL block copolymers when compared to PCL homopolymers in PVC blends, which accounts for PVC-b-PCL being able to provide permanent plasticization. The PVC-b-PCL copolymers are also effective as polymeric compatibilizers in PVC/PCL blends where they suppress the migration of PCL. PVC blends plasticized with PVC-b-PCL show similar or better ductility than PVC containing the archetypical PVC plasticizer dioctyl phthalate (DOP) for the same level of plasticizer. Most importantly, the PVC-b-PCL polymeric plasticizers are nonleaching and do not migrate under conditions where DOP is readily extractable.