Supramolecular ABA triblock copolymer with polyrotaxane as B block and its hierarchical self-assembly

A series of novel well-defined supramolecular ABA triblock copolymers of polyrotaxane are synthesized via atom transfer radical polymerization (ATRP) of 2-(dimethylamino)ethyl methacrylate (DMA) initiated by a polypseudorotaxane initiator of alpha-cyclodextrins (alpha-CDs) and PEG. The molecular structure of the ABA triblock copolymer with a polyrotaxane as B block, poly(2-(dimethylamino)ethyl methacrylate)-b-PEG[included by alpha-CDs]-b-poly(2-(dimethylamino)ethyl methacrylate) (DMA-b-PEGCD-b-DMA), was confirmed by two-dimensional rotating frame Overhauser effect spectroscopy (2D ROESY) and X-ray diffraction (XRD) analyses. Self-assembly behaviors of the copolymers in water solution were studied by dynamic light scattering (DLS), static light scattering (SLS), and transmission electron microscopy (TEM). Different from the model triblock copolymer without alpha-CDs and the polypseudorotaxanes composed of homo-PEG and alpha-CDs, the supramolecular triblock copolymers in water self-assembled into spheres with an amorphous core. Furthermore, the block copolymers at an acidic aqueous solution where the flanking chains were protonated generated the particles with a core of hexagonally packed polyrotaxanes. It is interesting to notice that the particles further aggregated into large disks induced by the solvent evaporation.