Molecular Architecture Induced Chain-Folding in Polymeric Amphiphilic Unimolecular Micelles*

An amphiphilic star-like macromolecule (ASM) with an aliphatic core and four poly(ethylene oxide) (PEO) arms was synthesized. Its crystallization and self-assembly behaviors at different crystallization temperatures ($T_{c}$s) were characterized by synchrotron small angle X-ray scattering (SAXS). The overall $d$-spacing of alternating amorphous and crystalline lamellae almost doubled from 11.4 nm for samples quenched into liquid nitrogen to 21.0 nm for $T_{c}$ = 42 \r{ }C. Due to an insufficient arm-to-core ratio in the ASM, chain-folding was forced to occur in the arm PEO crystals, while only extended chain crystals were observed for the PEO oligomer having a molecular weight of 2000 g/mol. In the ASM, gradual transitions from almost once-folded to non-integer folded, and finally to extended chain crystals were observed with increasing $T_{c}$ from -20 \r{ }C to 42 \r{ }C.