The synthesis of star block co-polymers with polytetrahydrofuran (PTHF) core and poly(tert-butyl acrylate) (PtBA) shell was performed using a dual initiator, 4-hydroxy butyl bromoisobutyrate, by combination of cationic ring-opening polymerization (CROP) and atom transfer radical polymerization (ATRP). The in situ reaction of the hydroxyl groups originating from the dual initiator with trifluoromethane sulfonic anhydride provides a triflate ester initiating group for the CROP of THF PTHF star polymers having three arms with tertiary bromide end groups (PTHF)(3) have been prepared by reaction of living PTHF chains with tris(2-aminoethyl)amine (TAEA) in the presence of 2,2,6,6-tetramethylpiperidine (TMP) as a proton trap. Subsequently, the star polymers were used as macroinitiators for the ATRP of tBA using the CuBr/N,N,N',N",N"-pentamethyldiethylenetriamine (PMDETA) catalyst system to obtain the tri-armed star block copolymers (PTHF-b-PtBA)(3). The polymers were characterized with gel-permeation chromatography (GPC) and H-1-NMR. Both techniques demonstrated the formation of tri-armed star block copolymers.