Synthesis of Segmented Polylactide Molecular Brushes and Their Transformation to Open-End Nanotubes

Segmented polylactide (PLA) core-shell molecular brushes, where the shell layer was located only in the middle part of the bottlebrush, were synthesized and converted to organic nanotubes with controlled dimensions and open ends. Segmented bottlebrush copolymer precursors were prepared from a triblock copolymer backbone with orthogonally protected hydroxyl groups and consisted of a poly(solketal methacrylate) middle block and poly(2-(p-methoxybenzyloxy)ethyl methacrylate) end blocks. The use of two selective protecting groups allowed for the sequential grafting of the middle and end PLA brushes with different end-groups. The shell layer of poly(4-(3-butenyl)styrene) was added by RAFT polymerization from the middle PLA brushes. Nanotubes were obtained by cross-linking of the shell layer under dilute conditions and subsequent removal of the PLA core. Transmission electron microscopy characterization revealed the formation of nanotubes with uniform size and open pore structure. The cylindrical shape of the bottlebrush macromolecules was maintained by the inner PLA core, while the nanotube length was independently controlled by the width of the shell layer.