The preparation of a novel class of E-caprolactone (CL) monomers, modified at the beta-position of the ester function, is described. The efficient thia-Michael addition to cyclohex-2-en-1-one and subsequent Baeyer-Villiger oxidation provided the regioselectively modified CL monomers. To enable a sustainable Baeyer-Villiger oxidation, several reaction procedures were investigated. In order to test a controlled ring-opening polymerization of the prepared monomers, the kinetics were studied and the monomer to initiator ratios were varied in order to prepare poly(epsilon-caprolactone)s with different molecular weights and different side groups.