Role of Conformation in π-π Interactions and Polymer/Fullerene Miscibility

The origin of the miscibility between C-60 fullerene and a series of phenyl vinyl polymers has been investigated using a combination of wide-angle X-ray (WAXS) and neutron (WANS) scattering and density functional theory (DFT) computational modeling. The solubility limit of the C60 in the polymers was found to increase nonlinearly with increasing phenyl rings in the side groups from 1 wt % in polystyrene (PS) to 12 wt % in poly(9-vinylphenanthrene) (P9VPh). The DFT calculations showed that the polymer interacts with the fullerene preferentially via the phenyl groups in these vinyl polymers. However, due to the backbone these phenyl groups are unable to form the energetically favorable T-junction or planar pi-pi stacks with the fullerene and are randomly oriented to the cage. The nonlinear increase in solubility is believed to be associated with shape conformity of the three-ring phenanthrene to the curvature of the fullerene.