Cholesterol side groups in Helical Poly(3-alkylesterfurans)

Poly(3-alkylesterfurans) fold into helical conformations due to a preference for adjacent furan repeat units in the polymer backbone to adopt a syn conformation in which the oxygen atoms of the furan rings are oriented in the same direction. In this contribution, a new chiral helical poly(3-alkylesterfuran) is reported in which a cholesterol group has been attached to the backbone to ensure excess single-handed helix chirality. This rigid side group promotes a folded conformation of the polymer in chloroform, as evidenced by 1 H NMR, absorption, and circular dichroism studies. This is unique among previously reported helical poly(3-alkylesterfurans) with S -3-octanol side chains, as those polymers are much more disordered in the same solvent. Circularly polarized luminescence studies also indicated how the chiroptical properties are impacted by intermolecular aggregation of these helical polymers. The study reveals the potential for tuning the properties of helical polyfurans via precise choice of the chiral side chain, which can be installed during monomer synthesis via a Steglich modification of 2-bromo-3-furoic acid. Suzuki-Miyaura cross-coupling polymerization produces the desired chiral helical polymers in reasonable yields with molecular weights above 10 kg/mol when the commercially available PEPPSI-IPent catalyst is used to catalyze cross-coupling.