Grafting polymerization of single-handed helical poly(phenyl isocyanide)s on graphene oxide and their application in enantioselective separation

We herein report a “grafting from” strategy to immobilize optically active helical poly(phenyl isocyanide)s onto graphene oxide (GO) nanosheets. After covalently bounding alkyne-Pd(II) initiator onto GO nanosheets, the designed GO/polymer composites P1@GO and P1-b-P2@GO featuring single-handed helical poly(phenyl isocyanide)s growing from GO nanosheets were prepared by sequential addition of the chiral and achiral isocyanide monomers. Post-synthetic hydrolysis rendered P1-b-P3@GO to improve the hydrophilicity. The successful covalent bonding of poly(phenyl isocyanide)s chains onto GO nanosheets was certified by several cross evidences including scan emission microscopy, atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. Circular dichroism spectra proved that the chiral information was introduced through the grafted single-handed helical polymer chains successfully. In addition, the resulting GO/polymer composites were explored as a chiral additive to induce enantioselective crystallization of racemic organic molecules. Preferential formation of rod-like L-alanine crystals was induced by composites bearing right-handed helical poly(phenyl isocyanide)s. The enantiomeric excess value of the induced crystals reached 76%, displaying the potential in future applications.