Biodegradable poly(ε-caprolactone-co-L-lactide)-b-poly(ethylene glycol) (PCLA-b-PEG) copolymers were synthesized via solution polymerization by varying the feed composition of ε-caprolactone (ε-CL) and L-lactide (LLA) (ε-CL:LLA=10:0, 7:3, 5:5, 3:7, 0:10). The feed ratio based on weight is in accordance with the copolymer composition except for the case of ε-CL:LLA=3:7 (C3L7), which was verified by 1H-NMR. Two different approaches were used for the exceptional case, which is an extension of the reaction time or the sequential introduction of the monomer. A copolymer composition of ε-CL:LLA=3:7 could be obtained in either case. The chemical microstructure of PCLA-b-PEG was determined using the 13C-NMR spectra and the effect of the sequential structure on the thermal properties and crystallinity were examined. Despite the same composition ratio of the copolymer, the microstructure can differ according to the reaction conditions.