Star-shaped homo- and copolymers were synthesized in a controlled fashion using two different initiating systems. Homopolymers of E-caprolactone, L-lactide, and 1,5-dioxepan-2-one were firstly polymerized using (I) a spirocyclic tin initiator and (II) stannous octoate (cocatalyst) together with pentaerythritol ethoxylate 15/4 EO/OH (coinitiator), to give polymers with identical core moieties. Our gained understanding of the versatile and controllable initiator systems kinetics, the transesterification reactions occurring, and the role which the reaction conditions play on the material outcome, made it possible to tailor the copolymer microstructure. Two strategies were used to successfully synthesize copolymers of different microstructures with the two initiator systems, i.e., a more multiblock- or a block-structure. The correct choice of the monomer addition order enabled two distinct blocks to be created for the copolymers of poly(DXO-co-LLA) and poly(CL-co-LLA). In the case of poly(CL-co-DXO), multiblock copolymers were created using both systems whereas longer blocks were created with the spirocyclic tin initiator. (C) 2008 Wiley Periodicals, Inc.