Sequence-defined main-chain photoswitching macromolecules with odd-even-effect-controlled properties

The installation of stimuli-responsive moieties into their main chain maximizes the stimuli response of polymers. Yet, facile and orthogonal synthesis of such complex macromolecules is a daunting challenge, especially for achieving absolute chain-end-group fidelity, monodispersity, and the formation of block copolymers (BCPs). We harness metal-free hydroxyl-yne click and deprotection chemistry to realize monodisperse, sequence-defined oligomers and BCPs featuring a-bisimines as main-chain photoswitches and orthogonally incorporate functional terminal groups (olefins, acrylates, and non-activated alkynes). We reveal the significant influence of the sequence on solution and solid-state material properties, which manifests as a strong odd-even effect on the hydrodynamic volume, glass transition temperature, and BCP domain spacing. The odd-even effect originates from the distinct symmetries of the sequences resulting from our precise synthetic strategy. Thus, our sequence-defined, orthogonal synthesis strategy with near absolute chain-end-group fidelity and wide functional group compatibility paves the way toward complex polymeric materials with precise properties, topology, composition, and main-chain functionalities.