Multi-component molecular bottlebrushes: Tunable building blocks for nanomaterial fabrication
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Well-defined multi-component molecular bottlebrushes were synthesized using both “grafting-from” and “grafting-through” techniques. Resulting polymers were characterized by SEC and 1H NMR analyses. Novel nanostructures were prepared by single molecular templating or solution self-assembly of the synthesized bottlebrushes and further characterized with TEM or cryo-TEM. 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. 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. Polymeric nanotubes were prepared with controlled dimensions and inner surface chemistry, and their dynamic anisotropic organization into micron- sized tubular assemblies was investigated. Nanotube building blocks were produced by molecular templating of cylindrical bottlebrush copolymers featuring tri-component side chains. The produced nanostructures were composed of nonionic and bioinert polyethylene glycol (PEG) shells and stimuli-responsive poly(methacrylic acid) (PMA) chains grafted on the interior. PMA chains were then functionalized with ferrocene functionalities, and their electrochemical properties were investigated. Amphiphilic diblock and triblock bottlebrush copolymers containing polylactide (PLA) and poly(ethylene oxide) (PEO) were synthesized by grafting-through method, and their phase behaviors with varying structural parameters were explored in dilute aqueous solutions. The aggregate morphologies were manipulated by independent control over the backbone and the side-chain lengths of the bottlebrush copolymer precursors. Obtained nanostructures were characterized with DLS and cryo-TEM. The effect of molecular shape on the interfacial curvature was discussed. A series of photo-cross-linkable diblock bottlebrush amphiphiles containing coumarin functionalized polylactide (PLA) and poly(ethylene oxide) (PEO) were synthesized by grafting-from and grafting-through methods. Obtained bottlebrush copolymers with various architectures were self-assembled in dilute aqueous solutions, and their aggregate sizes were investigated by DLS and cryo-TEM. The potential of brush spherical micelles as drug delivery vehicles was explored by drug loading and in vitro release experiments. The effect of bottlebrush architecture on molecular packing was discussed based on core cross-linking efficiencies and paclitaxel loading capacities.