The spherulitic growth of poly(ethylene oxide) (PEO) was found to continue in the spherulites of poly(butylene adipate-co-butylene succinate) (PBAS) in the simultaneous spherulitic growth process of the two components in PBAS/PEO blends. This phenomenon, namely the formation of interpenetrating spherulites (IPS), was analyzed on the basis of birefringence observed by polarizing optical microscopy. The growth direction of PEO lamellae in the PBAS spherulites was found to be along the preexisting PBAS lamellae. PEO crystals also nucleated inside PBAS spherulites and showed spherulitic growth in them at relatively high crystallization temperatures. The conditions for realizing IPS were also discussed. Miscibility in these novel crystalline/crystalline polymer blends in the molten state was confirmed by differential scanning calorimetry and optical microscopy.

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Miscible blends of three crystalline polymers, namely poly(butylene succinate) (PBS), poly(ethylene succinate) (PES), and poly(oxyethylene) (POE), exhibited interpenetrating spherulites, where a spherulite of one component grows inside the spherulites of other components. PBS and PES were immiscible above the melting points, Tm, of these substances, while ternary blends with POE showed miscibility, which depended on the molecular weight of POE. PBS and PES exhibited the same spherulitic growth process as in a miscible binary blend when they were crystallized from a homogeneous ternary melt. Spherulites of PBS, which is the highest‐Tm component, filled the whole volume first when a miscible ternary blend was quenched below Tm of POE, the lowest‐Tm component. Then, the blends showed either two types of crystallization processes. One was successive nucleation and growth of PES and POE spherulites, that is, PES nucleated and developed spherulites inside the PBS spherulites and then POE spherulites grew inside the interlocked spherulites of PBS and PES. The other was simultaneous growth and the formation of interpenetrating spherulites of PES and POE inside the PBS spherulites. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 706–711, 2010

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