The influence of chain entanglements in shear-induced crystallization remains unclear. It is of particular interest the difference in entanglement species between cyclic and linear polymers. To clarify the role of entanglement species in the formation of shish-like fibril crystals, the shear-induced crystallization behaviors of cyclic polyethylene (C-PE), linear polyethylene (L-PE), and C-PE and L-PE blends were investigated using a hot stage equipped with a polarizing optical microscope. The shear-induced crystallization behavior of the C-PE(115k) and L-PE(65k) homopolymers, where the values in parentheses represent the molecular weights (M_w), indicated that the formation rate of the shish-like fibril crystals of the former was one order of magnitude smaller than that of the latter. This implies that it is more difficult for C-PE to form shish-like fibril crystals than L-PE due to the topological effect of C-PE; that is, C-PE chains are more difficult to elongate by shear than L-PE chains due to the lack of chain ends. The shear-induced crystallization behavior of the blended C-PE and L-PE samples provided further insight into the effect of entanglement species on the formation of shish-like fibril crystals. The addition of small amounts of L-PE to C-PE remarkably enhanced the formation rate and density of the shish-like fibril crystals. The influence of the novel entanglement formed by the penetration of the L-PE molecule into the C-PE ring on the formation of the oriented melt was speculated to be significant.

Hollow spheres of poly (1,4-phenylene-5-hydroxyisophthalamide) (PPHIA) which was an intractable aromatic polyamide were prepared by the reaction-induced phase separation during polymerization, and they are hopeful candidates as high-performance hollow spheres. In this study, porosity control of PPHIA hollow spheres was examined by optimizing polymerization conditions, focusing on polymerization temperature and time. Porosity became lower with smaller sphere size, and this tendency was more conspicuous at lower polymerization temperature. Skin layer gradually became thicker with polymerization owing to the accumulation of oligomers on both the outer surface and the inner surface of hollow spheres, resulting in the decrease in the porosity. The porosity of PPHIA hollow sphere could be controlled in the range from 4% to 16% by tuning polymerization temperature and time.

Since crazes have a porous structure in the order of tens of nanometers, if they could be generated periodically in polyacrylonitrile (PAN), which is a raw material for carbon fiber, we can create new porous carbon materials (e.g., carbon films with periodic porous layers). However, according to Wu, PAN is a polymer that predominant yield behavior than craze behavior. Therefore, in this study, to generate crazes in polymers with predominant yield behavior, such as PAN, we used a method that focuses on the entanglement of molecular chains on the film surface, which is the starting point of craze generation (solid coating), as well as a method that focuses on the interfacial free energy (liquid coating). The results clarified that crazes can be generated in even polymers with predominant yield behavior, such as PAN, by sufficiently lowering at least one of the following: the entanglement density of the film surface, which is the starting point of craze generation, or the interfacial free energy of the film surface. Additionally, it is concluded that Wu’s indexes (see the manuscript for details) should be applied to the surface rather than the bulk because the surface properties are crucial for craze generation. Moreover, it was confirmed that a craze can continue to grow in the direction of the film thickness once it has been generated, even if the inside of the film with predominant yield behavior according to Wu’s indexes and the interfacial free energy of the craze tip is about several tens of mJ/m².