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

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 becom...