Janus polymerization combines cationic and anionic polymerizations into the two ends of a single growing chain and presents a novel pathway to produce topologically defined polymers. In this contribution, we report a one-step synthesis of 3-miktoarm star terpolymers of poly(ethylene glycol)-star-poly(epsilon-caprolactone)-star-poly(epsilon-caprolactone-cotetrahydrofuran ) ( PEG-star-PCL-star-P (CL-co-THF) ) via Janus polymerization using lutetium triflates (Lu(OTf) (3 )) and methoxypoly(ethylene glycol) epoxy (mPEG-EO) as catalyst and macroinitiator, respectively. Self-assembly of PEG-star-PCL-star-P(CL-co-THF) into vesicles in aqueous solution depends on the ratio of hydrophilic and hydrophobic block of the terpolymers. Coassembly of the terpolymer with a PCL homopolymer (MW = 3000), on the other hand, increases shell thickness and vesicle diameter. Furthermore, nanorods and needle-shaped aggregates featuring high aspect ratios are obtained upon self-assembly at an interface. This unique behavior can be attributed to crystallization of the PCL segments. Based on the biocompatible and biodegradable nature of the constituting segments, the herein described 3-miktoarm star terpolymers might be promising materials for drug/gene delivery or as bionanoreactors, especially as wall thickness and stiffness of the structures observed can be tuned. With that control over (nano)local permeability might be feasible.