Controlled synthesis of β-cyclodextrin-based starlike helical poly(phenyl isocyanide) and its application in chiral resolution

In an effort to expand the diversity of helical polymers exhibiting intricate structures, a strategy for the precise fabrication of β-cyclodextrin-based star polymers adorned with helical poly(phenyl isocyanide) (PPI) arms has been successfully realized through the integration of isocyanide polymerization and atom transfer radical polymerization (ATRP). An elegant β-cyclodextrin embellished with 7 Pd(II) complexes on one side and 14 bromine groups on the other side, denoted as ((Pd(II))7-CD-(Br)14), was initially synthesized. Subsequently, the (PPI)7-CD-(Br)14 was synthesized through the polymerization of the phenyl isocyanide monomer initiated with (Pd(II))7-CD-(Br)14. Finally, starlike PPI was obtained by ATRP of 1,2-diacrylyl ethane initiated via the macro-initiator of (PPI)7-CD-(Br)14. Circular dichroism measurement analysis indicated that the obtained starlike PPI exhibited a consistent helical conformation with a preferred handedness, and it was revealed that the helical structure of starlike PPI originated from the PPI backbone, rather than intermolecular aggregation in solutions. Furthermore, the starlike PPI demonstrated excellent efficacy in the chiral resolution of racemic compounds, achieving an enantiomeric excess (e.e.) of 92 % for threonine racemates when used as a chiral resolution agent.