Distribution of Polymorphic Crystals in the Ring-Banded Spherulites of Poly(butylene adipate) Studied Using High-Resolution Raman Imaging

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Abstract:Poly(butylene adipate) (PBA), an important biodegradable polymer, can crystallize into a particular type of ring-banded spherulite, in each of which two crystal forms, α and β, coexist. However, the distribution of the polymorphic crystals and the molecular chains orientation within the ring-banded PBA spherulites are still unclear. To determine these, in our present study, Raman spectroscopy and high spatial resolution Raman imaging were used. Characteristic Raman peaks were identified for both the α- and β-forms and for amorphous structures. Using these peaks, we investigated the polymorphic crystal distribution and molecular chain orientation within the spherulites through Raman imaging. The two crystal forms are found to be unevenly distributed in the center, ring-banded, and out-layer ringless region. The results of this study also suggested that the two crystal forms can nucleate and grow in the same temperature range (31-33 °C), but the relative content of the α-form in the ring-banded region becomes higher with the higher crystallization temperature. The image based on the Hermans orientation function for the ring-banded spherulite shows both bow-tie and ring-banded patterns, which means that the molecular chains in the ring-banded region orient not only about the radial direction of the spherulites but also about the substrate plane. Moreover, the molecular chain orientations also show periodically change along the radial direction of the ring-banded spherulite. The present study shows that Raman imaging is a very powerful technique in polymer crystal structure research. © 2017 American Chemical Society.

Volume:50

Issue:8

Translation or Not:no