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Demonstrating the 81‑Helicity and Nanomechanical Function of Self-Organizable Dendronized Polymethacrylates and Polyacrylates

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journal contribution
posted on 11.07.2017, 19:06 by Katerina A. Andreopoulou, Mihai Peterca, Daniela A. Wilson, Benjamin E. Partridge, Paul A. Heiney, Virgil Percec
A library of six dendronized polymers synthesized via single-electron transfer living radical polymerization (SET-LRP) of self-assembling dendrons with a methacrylate or acrylate apex is reported. Structural and retrostructural analysis by X-ray diffraction, molecular modeling, reconstructed electron density maps, and circular dichroism demonstrated that dendronized polymethacrylates and polyacrylates adopt a chiral, 81-helix induced by self-organization of the dendritic side groups. The helical handedness is selected by the stereocenter of the ethylene glycol linker between the dendron and polymer. Upon heating, oriented fibers of polymers with this linker undergo a phase transition between two columnar hexagonal phases, accompanied by unidirectional macroscopic thermal expansion. Replacement of the flexible linker with a shorter, rigid linker eliminates this expansion. Polyacrylates exhibit substantially quicker phase transition dynamics than polymethacrylates. The relationship between the primary structure of the dendritic monomer and the macroscopic thermal response elucidated here is expected to guide the design of additional macromolecules with nanomechanical function.