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 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.

Enhancing Chain Mobility of Ultrahigh Molecular Weight Polyethylene by Regulating Residence Time under a Consecutive Elongational Flow for Improved Processability

“…Herein, the Herman’s orientation function (ƒ) was used to examine the orientation behavior of the UHMWPE molecular chains, and can be defined as follows: where θ is the angle between the reference axis (based on the x -axis level) and the molecular chain axis, and γ is the angle between the transition dipole moment and the molecular chain axis. R is the dichroic ratio, which is defined as the ratio between parallel and perpendicular polarized intensities [ 16 , 17 ]. The 1130 cm −1 peak under an assumption of γ = 0° (parallel dichroism) was used for the calculation of ƒ.…”

Enzymatic Synthesis of Poly(alkylene succinate)s: Influence of Reaction Conditions

“…For PBA, two crystallographic structures have been reported, too. The monoclinic modification with a = 0.673 nm, b = 0.794 nm, c = 1.420 nm and  = 45.5° is often accompanied by the orthorhombic -modification with a = 0.506 nm, b = 0.735 nm and c = 1.467 nm [79][80][81][82][83][84]. The content of -phase depends strongly on the preparation conditions.…”

Phase Transition and Melt-Recrystallization Behavior of Poly(Butylene Adipate) Investigated by Simultaneous Measurements of Wide-Angle X-Ray Diffraction (WAXD) and Differential Scanning Calorimetry (DSC)

“…It has been reported that β form is crystallized below 29 • C, while above 31 • C α form is formed, and these two phases are crystallized simultaneously at 30 ± 1 • C, from the melt [17,18]. The β form crystal transforms into the α form spontaneously even by storing it at room temperature [19].…”