Ring opening polymerization of epsilon-caprolactone was realized in the presence of monomethoxy poly(ethylene glycol) with M-n = 1000 and 2000, using Zn(La)(2) as catalyst. The resulting PCL-PEG diblock copolymers with CL/EO repeat unit molar ratios from 0.2 to 3.0 were characterized by using DSC, WAXD, SEC, and H-1 NMR. The crystal phase of PCL blocks exist in all polymers, and the crystallization ability of PCL blocks increases with CL/EO ratio. PEG blocks are able to crystallize for copolymers with CL/EO below 1.0 only. Melt crystallization results were analyzed with Avrami equation. The Averami exponent n is around 3.0 in most cases, in agreement with heterogeneous nucleation with three dimensional growth. The morphology of the crystals was observed by using POM. Rod-like crystals were found to grow in 1, 3 or 2, 4 quadrants for samples with low molecular weights. In the case of a copolymer with M-n,M-PEG = 2000 and M-n,M-PCL = 800, PEG blocks could crystallize and grow on PCL crystals after PCL finished to form rod-like crystals, leading to formation of poorly or well structured spherulites. The spherulite growth rate (G) was determined at different crystallization temperatures (T-c) ranging from 9 to 49 degrees C. All the copolymers present a steady G decrease with increasing crystallization temperature due to lower undercooling. On the other hand, increase of CL/EO ratio leads to increase of G in the same T-c range. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 286-293, 2010