Low-molecular-weight hydrogenated polybutadiene-b-poly(ethylene glycol) (HPBd-b-PEG) block copolymers with double crystallizable blocks were synthesized by the coupling of hydroxyl-end-group-containing hydrogenated polybutadiene and poly(ethylene glycol) with terephthaloyl chloride as a coupling reagent. The block structure was confirmed by H-1-NMR, and the molecular weights of the blocks were determined as well. Gel permeation chromatography showed that the HPBd-b-PEG block copolymers had narrow molecular weight distributions. The crystallization and superstructures of the HPBd-b-PEG block copolymers were studied with differential scanning calorimetry, wide-angle X-ray diffraction (WAXD), and polarized optical microscopy. The results revealed that the crystallization of both blocks was suppressed mutually, especially for the shorter block. WAXD patterns showed that the crystal structures remained unchanged for both blocks. (c) 2005 Wiley Periodicals, Inc.