Cylindrical nanocapsules from photo-cross-linkable core-shell bottlebrush copolymers

Organic nanotubes with controlled dimensions were prepared from photo-cross-linkable core-shell bottlebrush copolymer precursors composed of an inner degradable polylactide block and an outer block containing photoactive coumarin functionalities. Bottlebrush copolymer precursors with diblock copolymer branches were synthesized by a grafting-from method using reversible addition-fragmentation chain transfer (RAFT) to prepare a well-defined backbone first, followed by ring-opening and RAFT polymerizations to install side chains. Shell-cross-linked bottlebrush nanostructures were prepared by UV irradiation at 365 nm, which promoted [2 + 2] cyclodimerization of the peripheral coumarin functionalities. Subsequent degradation of the polylactide core provided hollow cylindrical nanoparticles held together by dimerized coumarin units in the shell layer. The length and the inner diameter of the nanotubes were consistent with the structural dimensions of the bottlebrush copolymer precursors.