Microscopic and Small-/Wide-Angle Microbeam X-ray Analyses on Dendritic Crystals in Poly(butylene succinate)

A unique composite dendritic spherulite is detected in a specific crystallization temperature range (T-c = 60-78 C), whose assembly is probed using microscopy techniques and dendritic spherulites composed of feather-like and fern-like branches in poly(butylene succinate) (PBSu) crystallized with poly(ethylene oxide) diluent are analyzed on top surface morphologies correlating with interior-dissected assembly, concurrently through polarized-light optical microscopy, scanning electron microscopy, and synchrotron-radiation X-ray microbeam analysis. The feather-like branch is composed of fully edge-on crystal plates, while the fern-like branch is composed of flat-on crystal plates. These branches originate from a common nucleus with different growth rates. For the first time, the dendritic PBSu spherulite serves as a convenient model for understanding the mechanisms how edge-on and flat-on crystal orientations can alternate not only in a serial mode to form ring bands but also in a parallel mode to form straight dendrites. Morphology evidence and detailed microbeam techniques collectively prove that these discontinuous lamellar plates discretely and gradually tilt and bend to transform from a vertical to a horizontal crystal plate with a corresponding alteration in birefringence.