Supramolecular Multiblock Copolymers Featuring Complex Secondary Structures

This contribution introduces main-chain supra­molecular ABC and ABB′A block copolymers sustained by orthogonal metal coordination and hydrogen bonding between telechelic polymers that feature distinct secondary structure motifs. Controlled polymerization techniques in combination with supra­molecular assembly are used to engineer hetero­telechelic π-sheets that undergo high-fidelity association with both helical and coil-forming synthetic polymers. Our design features multiple advances to achieve our targeted structures, in particular, those emulating sheet-like structural aspects using poly­(p-phenylene­vinylene)­s (PPVs). To engineer hetero­telechelic PPVs in a sheet-like design, we engineer an iterative one-pot cross metathesis–ring-opening metathesis polymerization (CM-ROMP) strategy that affords functionalized Grubbs-II initiators that subsequently polymerize a para­cyclophane­diene. Supramolecular assembly of two hetero­telechelic PPVs is used to realize a parallel π-sheet, wherein further orthogonal assembly with helical motifs is possible. We also construct an antiparallel π-sheet, wherein terminal PPV blocks are adjacent to a flexible coil-like poly­(norbornene) (PNB). The PNB is designed, through supramolecular chain collapse, to expose benzene and perfluoro­benzene motifs that promote a hairpin turn via charge-transfer-aided folding. We demonstrate that targeted helix–(π-sheet)–helix and helix–(π-sheet)–coil assemblies occur without compromising intrinsic helicity, while both parallel and antiparallel β-sheet-like structures are realized. Our main-chain orthogonal assembly approach allows the engineering of multi­block copolymer scaffolds featuring diverse secondary structures via the directional assembly of telechelic building blocks. The targeted assemblies, a mix of sequence-defined helix–sheet–coil and helix–sheet–helix architectures, are Nature-inspired synthetic mimics that expose α/β and α+β protein classes via de novo design and cooperative assembly strategies.