The unusual eutectic crystallization behavior in the poly(epsilon-caprolactone) (PCL) and 3-pentadecylphonel (PDP) binary blends was investigated by differential scanning calorimetry and Fourier transform infrared (FTIR) spectroscopy. A eutectic system was found with the eutectic composition at 60 wt % PDP and the eutectic melting temperature at 35 degrees C. The melting process of the blend at the eutectic composition was studied by in situ FTIR. The concurrence of the melting of PCL and PDP crystallites and the sequential formation of hydrogen bonding interaction between PDP molecules and PCL chains were traced. It was also found that a further increase in temperature above the eutectic melting temperature would impair the hydrogen bonding and increase the content of nonassociated phenol hydroxyl group. The semi-crystalline morphology of blends affected by the composition was also investigated. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1015-1023, 2009