Folded Well-Defined 3D Architecture from Synthetic Helical and Sheet-Like Polymers

The fabrication of truly hierarchically folded single-chain polymeric nanoparticles with primary, secondary, and defined 3D architecture is still an unfulfilled goal. In this contribution, a polymer is reported that folds into a well-defined 3D structure from a synthetic sheet-helix block copolymer. The sheet-like poly(p-phenylene vinylene) (PPV) block is synthesized via the ring-opening metathesis polymerization of a thymine-bearing dialkoxy-substituted [2.2]paracyclophane-1,9-diene. The PPV block is terminated with a Pd complex using a Pd-containing chain-terminating agent. The terminal Pd complex catalyzes the polymerization of isocyanide monomers with side-chains containing either a chiral menthol or an achiral diaminopyridine resulting in the formation of a helical poly(isocyanide) (PIC) random copolymer. The PIC side-chains are capable of engaging in complementary hydrogen-bonding with thymine units along the PPV block resulting in the folding of the two secondary structural domains into a well-defined 3D structure. The folding and unfolding of the polymer in both chloroform and THF are monitored using dynamic light scattering and NMR spectroscopy. This work is the first example of a hierarchically folded synthetic polymer featuring a defined 3D structure achieved by using two different polymer backbones with two distinct secondary structures.