Spherulitic Characterization and Hierarchical Structural Evaluation of Azacalixarene‐Polyethylene Glycol Copolymers Containing s‐Triazine Rings

Abstract

This study investigates the solid‐state structure of a copolymer composed of polyethylene glycol (PEG) and azacalixarene, which has two s‐triazine rings and two phenyl rings alternately crosslinked by amino groups. Azacalixarene derivatives containing a low‐molecular‐weight linker moiety and exhibiting an amorphous structure have been synthesized in previous studies; however, in this study, they are crystallized by the substitution of the linker moiety with PEG. The spherulites formed by the corresponding copolymer possess the ability to form higher‐order structures, growing up to a diameter of 1.7 mm depending on the crystallization conditions. The azacalixarene‐PEG copolymer forms negative spherulites via homogeneous nucleation and exhibits a lamellar period at 13.8 nm. The lamellar crystalline part itself is 5.8 nm in thickness; bulky amorphous regions are also observed in the copolymer structure. Reciprocal lattice analysis results reveal that the crystal parts form a packing structure similar to the crystal lattice of PEG. The promotion of spherulite growth is predicted to reflect the characteristics of the corresponding copolymer, which crystallizes while universally containing many amorphous regions.

Formation of interfacial molecular film and metal‐trapping function of azacalixarene‐containing copolymers having spherulite‐forming ability

“…No in‐plane diffraction peaks are observed for the aliphatic linkers, indicating that they are amorphous. The derivative in this study is the first to exhibit crystallinity in the bulk state and has the ability to form spherulites 25 . High crystallinity is observed, with sharp diffraction peaks not only in the bulk state but also in the two‐dimensional film, because of the strategic molecular design that included crystalline polymer chains in repeating units.…”

“…Figure 3 shows the π‐A isotherm of the azacalixarene‐based copolymer with a PEG linker in a monolayer on the water surface. Previous studies have been conducted on derivatives with similar chemical structures, 20–25 but this is the first study in which a polymer chain is included in the repeating unit. In this case, as the repeating unit itself has a molecular weight distribution, the horizontal axis of the isotherm represents “trough area reduction (%),” which is the reduction rate of the relative film area on the trough owing to compression 35 .…”

“…One feature is that dot‐like domain shapes are observed on the surfaces of all the single‐layer films. In previous studies, 20–25 surface morphology was divided into two systems. As shown in Figure S1, an extremely homogeneous surface is formed on amorphous films with low‐molecular‐weight aliphatic chains as linkers.…”

“…The chemical structure and intermolecular interactions of the linker moiety attached to the azacalixarene ring affect the properties and metal‐trapping ability of the resultant interfacial film 24 . Recently, a copolymer that exhibits crystallinity in the bulk state and can form giant spherulites was created for the first time by changing the linker moiety attached to the azacalixarene ring to a polyethylene glycol (PEG) chain 25 . Evaluations of the arrangement and packing state of the two‐dimensional film formed by this compound at the air/water interface and whether two‐dimensional film of this compound has metal‐trapping ability will confirm whether this copolymer is suitable for practical and widespread use.…”