The graft polymer poly(ethylene oxide)-g-poly(epsilon-caprolactone)(2) (PEO-g-PCL2) with modulated grafting sites was synthesized by the combination of ring-opening polymerization (ROP) mechanism, efficient Williamson reaction, with thiol-ene addition reaction. First, the precursor of PEO-Allyl-PEO with two terminal hydroxyl groups and one middle allyl group was prepared by ROP of EO monomers. Then, the macroinitiator [PEO-(OH)(2)-PEO](s) was synthesized by sequential Williamson reaction between terminal hydroxyl groups and thiol-ene addition reaction on pendant allyl groups. Finally, the graft polymer PEO-g-PCL2 was obtained by ROP of E-CL monomers using [PEO-(OH)(2)-PEO](s) as macroinitiator. The target graft polymer and all intermediates were well characterized by the measure-ments of gel permeation chromatography, H-1 NMR, and thermal gravimetric analysis. The crystallization behavior was investigated by the measurements of differential scanning calorimetry, wide-angle X-ray diffraction and polarized optical microscope. The results showed that when the PCL content of side chains reached 59.2%, the crystalline structure had been dominated by PCL part and the crystalline structure formed by PEO part can be almost neglected. (c) 2014 Wiley Periodicals, Inc.