The coil-to-globule transition of single-chain polymeric nanoparticles with a chiral internal secondary structure

The intramolecular folding of chiral single polymeric chains into single-chain polymeric nanoparticles (SCPNs) via π-stacking was investigated. To this end, hydrophilic polymers grafted with structuring, chiral 3,3′-bis(acylamino)-2,2′-bipyridine-substituted benzene-1,3,5-tricarboxamides (BiPy-BTAs) units were prepared via ring-opening metathesis polymerization (ROMP). A combination of spectroscopic and scattering techniques was employed to obtain a better understanding of the folding behavior and the chiral internal structure of these systems. Circular dichroism spectroscopy showed that the folding of the polymer is highly dependent on the solvent quality and temperature. The folding process in water was fine-tuned via the addition of a good cosolvent (tetrahydrofuran), resulting in an optimal balance between the conformational freedom of the polymer's backbone and the stability of the π-stacked units. Small-angle X-ray scattering (SAXS) experiments showed that the shape of the SCPNs is controlled by the formation of a chiral internal secondary structure.