The crystallization kinetics and semicrystalline morphology of a polymer blend consisting of two crystalline components, poly(ethylene oxide) (PEO) and poly(ethylene succinate) (PES), have been investigated. PEO and PES were miscible in the melt. Slight dilution with PEO (w(PEO) less than or equal to 0.2) promoted the crystallization kinetics of PES because of enhanced segmental mobility upon blending. Further increase in PEO content reduced the PES crystallization rate owing to the dominant effect of depression in crystallization driving force. The semicrystalline morphology of PEO/PES blends was probed by small-angle X-ray scattering (SAXS). At temperatures between the melting point of PEO (T-m(PEO) approximate to 59 degrees C) and that of PES (T-m(PES) approximate to 101 degrees C), the blend was a crystalline/amorphous system. Both crystallizations via direct cooling to 70 degrees C (where only PES crystallized) and direct cooling to 40 degrees C (where two components crystallized simultaneously) followed by heating to 68 degrees C (to melt PEO crystals) created a high extent of interfibrillar segregation coupled with a minor extent of interlamellar incorporation of amorphous PEG. At temperatures below T-m(PEO), where the blend was a crystalline/crystalline system, direct cooling to 40 degrees C (one-step crystallization) generated two separate lamellar stack (LS) domains: one containing almost pure PES lamellae and the other consisting of mixed PEO and PES lamellae. Crystallization at 70 degrees C followed by cooling to room temperature (two-step crystallization) also yielded two separate LS domains, due to the crystallization of PEO within the interfibrillar regions. (C) 2000 Elsevier Science Ltd. All rights reserved.