Hairy cylinders based on a coil-comb-coil copolymer

Abstract

Self-assembled complex structures with finely controlled arrangements are universal in biological systems but the corresponding formation mechanism usually remains unknown. Herein we report an example using fully synthetic copolymers with complex molecular structure and fuzzy hydrophilic/hydrophobic boundary to mimic multiple levels of self-assembly. We report the formation and possible mechanism insight of a complex hairy cylinder that is self-assembled from linear cylinders which are formed from an amphiphilic coil-comb-coil copolymer, PTMA₄₂-b-[(St-PEG₁₆)-alt-(MI-PCL₂₁)]₄-S-S-[(St-PEG₁₆)-alt-(MI-PCL₂₁)]₄-b-PTMA₄₂ (see Schemes 1 and 2). The copolymer was synthesized by two-step reversible addition–fragmentation chain transfer (RAFT) polymerization. The “comb” is the H-shaped [(St-PEG₁₆)-alt-(MI-PCL₂₁)]₄-S-S-[(St-PEG₁₆)-alt-(MI-PCL₂₁)]₄ and the “coils” are linear PTMA₄₂. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) studies revealed the subtle nanostructure of hairy cylinders: a “head” made up of densely compacted linear cylinders and tens of surrounding “tentacles” (linear cylinders). The synergetic effect between the coil-comb-coil structure and the coils facilitates the formation of hairy cylinders. A control experiment where a coil-only copolymer without comb-like structure confirms that no hairy cylinders formed in this case. Compared with another coil (control), PTMA coils attached on two ends of the comb have stronger synergetic effect and then facilitate the formation of well-defined hairy cylinders. Finally, “embryo”, “baby”, “adult” and “ageing” hairy cylinders were observed by increasing the ratio of water to DMF during self-assembly. Overall, our study demonstrates a new insight for understanding the formation of hierarchical polymeric nanostructures and a new principle for designing complex polymeric nanoparticles.