The II to I Phase Transition of Isotactic Poly(1-butene) Single Crystals at an Early Stage
Rui Xin, Yunpeng Li, Haoran Shen, Jian Hu, Shaojuan Wang, Hao Zhang, Shouke Yan
Abstract
Regular and dendritic (i.e., composed of multiple flat-on dendritic crystals with a fixed 90° branching angle) single crystals of isotactic poly(1-butene) (iPBu) in its form II were obtained by ultrathin film melt crystallization. Their II–I phase transition behavior was studied by atomic force microscopy (AFM) and electron diffraction techniques. Ex-situ electron diffraction studies on both the regular and dendritic single crystals reveal that the II–I phase transition leads generally to the formation of untwinned hexagonal form I iPBu crystals. In-situ AFM studies on the regular single crystal show that the II–I phase transition occurs easier at its edge facets than inside the crystal, analogous to the preferential form I nucleation at the edges of individual crystal sheet within the dendritic single crystals. It is also found that inside the regular single crystal rowlike nuclei form preferentially along [100]/[010] directions of the parent form II single crystal, which may be related to a larger shrinkage in these directions caused by densification during the II–I phase transition. These obtained results may shed more light on the II–I phase transition mechanism and kinetics of the iPBu.