Chain-folding and overall molecular conformation in a novel amphiphilic starlike macromolecule

The crystallization and self-assembly behavior of an amphiphilic starlike macromolecule (ASM) with a lipophilic core and four poly(ethylene oxide) (PEO) arms (M _n = 2000 g/mol) were characterized by synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction at different crystallization temperatures (T _c). The overall d-spacing of the alternating amorphous core and crystalline PEO lamellae almost doubled from 11. 4 nm for samples quenched into liquid nitrogen to 21.0 nm for T _c = 42°C, indicating gradual transitions from nearly once-folded to fractionally folded and finally to extended chain crystals with increasing the T _c. On the basis of SAXS, transmission electron microscopy, and computer simulation results, it was suggested that the lamellae contained an interdigitated, single-layered PEO crystal, and an amorphous layer consisted of a double-layered lipophilic core and amorphous PEO. A folded (four PEO arms at one side of the core) rather than an extended (two PEO arms on each side of the core) overall molecular conformation (OMC) of the ASM was deduced in the solid state. These results implied that chain-folding and OMC of the ASM closely depended on its star-block-like architecture.